Hyaluronan
Encyclopedia
Hyaluronan is an anionic, nonsulfated
glycosaminoglycan
distributed widely throughout connective
, epithelial, and neural tissues. It is unique among glycosaminoglycans in that it is nonsulfated, forms in the plasma membrane instead of the Golgi
, and can be very large, with its molecular weight often reaching the millions.
One of the chief components of the extracellular matrix
, hyaluronan contributes significantly to cell proliferation and migration, and may also be involved in the progression of some malignant tumor
s.
The average 70 kg (154 lbs) person has roughly 15 grams of hyaluronan in the body, one-third of which is turned over (degraded and synthesized) every day. Hyaluronic acid is also a component of the group A streptococcal extracellular capsule, and is believed to play a role in virulence
.
the vitreous humor,” , hyaluronan was described as a "goo" molecule, a ubiquitous carbohydrate
polymer
that is part of the extracellular matrix. For example, hyaluronan is a major component of the synovial fluid
, and was found to increase the viscosity of the fluid. Along with lubricin, it is one of the fluid's main lubricating components.
What makes hyaluronan unique?
Hyaluronan is used in medical application for its unique physical/chemical properties. It is very hydrophilic; its viscous solutions have
most unusual rheological properties and are exceedingly lubricious.Hyaluronan is an important component of articular cartilage
, where it is present as a coat around each cell (chondrocyte
). When aggrecan
monomers bind to hyaluronan in the presence of link protein, large highly negatively-charged aggregates form. These aggregates imbibe water and are responsible for the resilience
of cartilage
(its resistance to compression). The molecular weight (size) of hyaluronan in cartilage
decreases with age, but the amount increases.
Hyaluronan is also a major component of skin
, where it is involved in tissue repair. When skin
is exposed to excessive UVB rays, it becomes inflamed (sunburn
) and the cells
in the dermis stop producing as much hyaluronan, and increase the rate of its degradation. Hyaluronan degradation products also accumulate in the skin after UV exposure.
While it is abundant in extracellular matrices, hyaluronan also contributes to tissue hydrodynamics, movement and proliferation of cells, and participates in a number of cell surface receptor interactions, notably those including its primary receptors, CD44
and RHAMM. Upregulation of CD44 itself is widely accepted as a marker of cell activation in lymphocytes. Hyaluronan's contribution to tumor growth may be due to its interaction with CD44. Receptor CD44 participates in cell adhesion interactions required by tumor cells.
Although hyaluronan binds to receptor CD44
, there is evidence hyaluronan degradation products transduce their inflammatory signal through toll-like receptor 2 (TLR2), TLR4 or both TLR2, and TLR4 in macrophages and dendritic cells. TLR and hyaluronan play a role in innate immunity.
High concentrations of hyaluronan in the brains of young rats, and reduced concentrations in the brains of adult rats suggest hyaluronan plays an important role in brain development.
Hyaluronan is a polymer
of disaccharide
s, themselves composed of D-glucuronic acid and D-N-acetylglucosamine, linked via alternating β-1,4 and β-1,3 glycosidic bond
s. Hyaluronan can be 25,000 disaccharide repeats in length. Polymers of hyaluronan can range in size from 5,000 to 20,000,000 Da
in vivo. The average molecular weight in human synovial fluid
is 3−4 million Da, and hyaluronan purified from human umbilical cord
is 3,140,000 Da.
Hyaluronan is energetically stable, in part because of the stereochemistry
of its component disaccharides. Bulky groups on each sugar molecule are in sterically favored positions, whereas the smaller hydrogens assume the less-favorable axial positions.
s called hyaluronan synthase
s, of which vertebrates have three types: HAS1, HAS2, and HAS3. These enzymes lengthen hyaluronan by repeatedly adding glucuronic acid
and N-acetylglucosamine
to the nascent polysaccharide as it is extruded via ABC-transporter through the cell membrane
into the extracellular space.
Hyaluronan synthesis (HAS) has been shown to be inhibited by 4-methylumbelliferone (hymecromone
, heparvit), a 7-hydroxy-4-methylcoumarin derivative.
This selective inhibition (without inhibiting other glycosaminoglycans) may prove useful in preventing metastasis
of malignant tumor cells.
Bacillus Subtilis
recently has been genetically modified (GMO) to culture a proprietary formula to yield hyaluronans, in a patented process producing human-grade product.
CD44 is widely distributed throughout the body, and the formal demonstration of HA-CD44 binding was proposed by Aruffo et al. in 1990. To date, it is recognized as the main cell surface receptor for HA. CD44 mediates cell interaction with HA and the binding of the two functions as an important part in various physiologic events, such as cell aggregation, migration, proliferation and activation; cell-cell and cell-substrate adhesion; endocytosis of HA, which leads to HA catabolism
in macrophages; and assembly of petircellular matrices from HA and proteoglycan
. Two significant roles of CD44 in skin were proposed by Kaya et al. The first is regulation of keratinocyte
proliferation in response to extracellular stimuli, and the second is the maintenance of local HA homeostasis.
ICAM-1 is known mainly as a metabolic cell surface receptor for HA, and this protein may be responsible mainly for the clearance of HA from lymph and blood plasma, which accounts for perhaps most of its whole-body turnover Ligand binding of this receptor, thus, triggers a highly coordinated cascade of events that includes the formation of an endocytotic vesicle, its fusion with primary lysosomes, enzymatic digestion to monosaccharides, active transmembrane transport of these sugars to cell sap, phosphorylation
of GlcNAc and enzymatic deacetylation
. Like its name, ICAM-1 may also serve as a cell adhesion molecule, and the binding of HA to ICAM-1 may contribute to the control of ICAM-1-mediated inflammatory activation.
s. In humans, there are at least seven types of hyaluronidase-like enzymes, several of which are tumor suppressors. The degradation products of hyaluronan, the oligosaccharides and very low-molecular-weight hyaluronan, exhibit pro-angiogenic properties . In addition, recent studies showed hyaluronan fragments, not the native high-molecular mass of hyaluronan, can induce inflammatory responses in macrophages and dendritic cells in tissue injury and in skin transplant rejection .
Inflammation
Many biological factors, such as growth factors, cytokines, eicosanoids etc., are generated in the inflammation process. These factors are necessary for the subsequent steps of wound healing due to their roles in promoting migration of inflammatory cells, fibroblasts, and endothelial cells into the wound site.
The wound tissue in the early inflammatory phase of wound repair is abundant in HA, probably a reflection of increased synthesis. HA acts as a promoter of early inflammation, which is crucial in the whole skin wound-healing process. In a murine air pouch model of carrageenan/IL-1-induced inflammation, HA was observed to enhance cellular infiltration. Kobayashi and colleagues showed a dose-dependent increase of the proinflammatory cytokines TNF-α and IL-8 production by human uterine
fibroblasts at HA concentrations of 10μg/ml to 1 mg/ml via a CD44-mediated mechanism. Endothelial cells, in response to inflammatory cytokines such as TNF-α, and bacterial lipopolysaccharide
, also synthesize HA, which has been shown to facilitate primary adhesion of cytokine-activated lymphocytes expressing the HA-binding variants of CD44 under laminar and static flow conditions. It is interesting to note that HA has contradictory dual functions in the inflammatory process. It not only can promote the inflammation, as stated above, but also can moderate the inflammatory response, which may contribute to the stabilization of granulation tissue matrix, as described in the following part.
Granulation and organization of the granulation tissue matrix
Granulation tissue
is the perfused
, fibrous connective tissue that replaces a fibrin
clot in healing wounds. It typically grows from the base of a wound and is able to fill wounds of almost any size it heals. HA is abundant in granulation tissue matrix. A variety of cell functions that are essential for tissue repair may attribute to this HA-rich network. These functions include facilitation of cell migration into the provisional wound matrix, cell proliferation and organization of the granulation tissue matrix. Absolutely, initiation of inflammation is extremely crucial for the formation of granulation tissue, therefore the pro-inflammatory role of HA as discussed above also contribute to this stage of wound healing.
HA and cell migration
Cell migration is essential for the formation of granulation tissue. The early stage of granulation tissue is dominated by a HA-rich extracellular matrix, which is regarded as a conducive environment for migration of cells into this temporary wound matrix. Contributions of HA to cell migration may attribute to its physicochemical properties as stated above, as well as its direct interactions with cells. For the former scenario, HA provides an open hydrated matrix that facilitates cell migration, whereas, in the latter scenario, directed migration and control of the cell locomotory mechanisms are mediated via the specific cell interaction between HA and cell surface HA receptors. As discussed before, the three principal cell surface receptors for HA are CD44, RHAMM, and ICAM-1. RHAMM is more related to cell migration. It forms links with several protein kinases associated with cell locomotion, for example, extracellular signal-regulated protein kinase (ERK), p125fak, and pp60c-src. During fetal development, the migration path through which neural crest cells migrate is rich in HA. HA is closely associated with the cell migration process in granulation tissue matrix, and studies show that cell movement can be inhibited, at least partially, by HA degradation or blocking HA receptor occupancy.
By providing the dynamic force to the cell, HA synthesis has also been shown to associate with cell migration. Basically, HA is synthesized at the plasma membrane and released directly into the extracellular environment. This may contribute to the hydrated microenvironment at sites of synthesis, and is essential for cell migration by facilitating cell detachment.
Role of HA in moderation of the inflammatory response
Although inflammation is an integral part of granulation tissue formation, for normal tissue repair to proceed, inflammation needs to be moderated. The initial granulation tissue formed is highly inflammatory with a high rate of tissue turnover mediated by matrix degrading enzymes and reactive oxygen metabolites that are products of inflammatory cells. Stabilization of granulation tissue matrix can be achieved by moderating inflammation. HA functions as an important moderator in this moderation process, which contradicts its role in inflammatory stimulation, as described above. HA can protect against free-radical damage to cells. This may attribute to its free-radical scavenging property, a physicochemical characteristic shared by large polyionic polymers. In a rat model of free-radical scavenging property investigated by Foschi D. and colleagues, HA has been shown to reduce damage to the granulation tissue.
In addition to the free-radical scavenging role, HA may also function in the negative feedback loop of inflammatory activation through its specific biological interactions with the biological constituents of inflammation. TNF-α, an important cytokine generated in inflammation, stimulates the expression of TSG-6 (TNF-stimulated gene 6) in fibroblasts and inflammatory cells. TSG-6, a HA-binding protein, also forms a stable complex with the serum proteinase inhibitor IαI (Inter-α-inhibitor) with a synergistic effect on the latter’s plasmin-inhibitory activity. Plasmin
is involved in activation of the proteolytic
cascade of matrix metalloproteinases and other proteinases leading to inflammatory tissue damage. Therefore, the action of TSG-6/ IαI complex, which may be additionally organized by binding to HA in the extracellular matrix, may serve as a potent negative feedback loop to moderate inflammation and stabilize the granulation tissue as healing progresses. In the murine air pouch model of carragenan/IL-1 (Interleukin-1β)-induced inflammation, where HA has been shown to have a proinflammatory property, reduction of inflammation can be achieved by administrating TSG-6, and the result is comparable with systemic dexamethasone treatment.
Reepithelization
HA plays an important role in the normal epidermis. HA also has crucial functions in the reepithelization process due to several of its properties. It serves as an integral part of the extracellular matrix of basal keratinocytes, which are major constituents of the epidermis; its free-radical scavenging function and its role in keratinocyte proliferation and migration.
In normal skin, HA is found in relative high concentrations in the basal layer of the epidermis where proliferating keratinocytes are found. CD44 is collocated with HA in the basal layer of epidermis where additionally it has been shown to be preferentially expressed on plasma membrane facing the HA-rich matrix pouches. Maintaining the extracellular space and providing an open, as well as hydrated, structure for the passage of nutrients are the main functions of HA in epidermis. Tammi R. and other colleagues found HA content increases at the presence of retinoic acid
(vitamin A). The proposed effects of retinoic acid against skin photo-damage and aging may be correlated, at least in part, with an increase of skin HA content, giving rise to increase of tissue hydration. It has been suggested the free-radical scavenging property of HA contributes to protection against solar radiation, supporting the role of CD44 acting as a HA receptor in the epidermis.
Epidermal HA also functions as a manipulator in the process of keratinocyte proliferation, which is essential in normal epidermal function, as well as during reepithelization in tissue repair. In the wound healing process, HA is expressed in the wound margin, in the connective tissue matrix, and collocating with CD44 expression in migrating keratinocytes. Kaya et al. found suppression of CD44 expression by an epidermis-specific antisense transgene
resulted in animals with defective HA accumulation in the superficial dermis, accompanied by distinct morphologic alterations of basal keratinocytes and defective keratinocyte proliferation in response to mitogen
and growth factors. Decrease in skin elasticity, impaired local inflammatory response, and impaired tissue repair were also observed. Their observations are strongly supportive of the important roles HA and CD44 have in skin physiology and tissue repair.
Fetal wound healing and scarring
Lack of fibrous scarring is the primary feature of fetal wound healing. Even for longer periods, HA content in fetal wounds is still higher than that in adult wounds, which suggests that HA may, at least in part, reduce collagen deposition and therefore lead to reduced scarring. This suggestion is in agreement with the research of West et al., who showed in adult and late gestation fetal wound healing, removal of HA results in fibrotic scarring. Though the exact role of HA in skin scarring is still under investigation, based on all the facts that have been observed, it must be a great contributor to the less fibrous scarring.
As shown in Figure 1, the various types of molecules that interact with hyaluronan can contribute to many of the stages of cancer metastasis.
Hyaluronan synthase
s (HAS) play roles in all of the stages of cancer metastasis. By producing anti-adhesive HA, HAS can allow tumor cells to release from the primary tumor mass, and if HA associates with receptors such as CD44, the activation of Rho GTPases can promote epithelial-mesenchymal transition (EMT) of the cancer cells. During the processes of intravasation or extravasation
, the interaction of HAS produced HA with receptors such as CD44 or RHAMM promote the cell changes that allow for the cancer cells to infiltrate the vascular
or lymphatic systems. While traveling in these systems, HA produced by HAS protects the cancer cell from physical damage. Finally, in the formation of a metastatic lesion, HAS produces HA to allow the cancer cell to interact with native cells at the secondary site and to produce a tumor for itself.
Hyaluronidases
(HAase or HYAL) also play many roles in cancer
metastasis
. By helping to degrade the ECM
surrounding the tumor, hyaluronidases help the cancer cell escape from the primary tumor mass and play a major role in intravasation
by allowing degradation of the basement membrane of the lymph or blood vessel. Hyaluronidases again play these roles in establishment of a metastatic lesion
by helping with extravasation and clearing the ECM of the secondary site. Finally, hyaluronidases play a key role in the process of angiogenesis
. HA fragments promote angiogenesis and hyaluronidases produce these fragments. Interestingly, hypoxia
also increases production of HA and activity of hyaluronidases.
The hyaluronan receptors, CD44 and RHAMM, are most thoroughly studied in terms of their roles in cancer metastasis. Increased clinical CD44 expression has been positively correlated to metastasis in a number of tumor types. In terms of mechanics, CD44 affects adhesion of cancer cells to each other and to endothelial cells, rearranges the cytoskeleton
through the Rho GTPases, and increases the activity of ECM degrading enzymes. Increased RHAMM expression has also been clinically correlated with cancer metastasis. In terms of mechanics, RHAMM promotes cancer cell motility through a number of pathways including focal adhesion kinase (FAK), Map kinase (MAPK), pp60(c-src), and the downstream targets of Rho kinase (ROK). RHAMM can also cooperate with CD44 to promote angiogenesis toward the metastatic lesion.
, and is approved for use in eye surgery
(i.e., corneal transplantation, cataract
surgery, glaucoma
surgery, and surgery to repair retinal detachment
). Other biomedical companies also produce brands of hyaluronan for opthalmic surgery.
Native hyaluronan has a relatively short half-life (shown in rabbits) so various manufacturing techniques have been deployed to extend the length of the chain and stabilise the molecule for its use in medical applications. The introduction of protein based cross-links, the introduction of free-radical scavenging molecules such as sorbitol
and minimal stabilisation of the HA chains through chemical agents e.g. NASHA stabilisation are all techniques that have been used.
In the late 1970s, intraocular lens implantation was often followed by severe corneal edema
, due to endothelial cell damage during the surgery. It was evident that a viscous, clear, physiologic lubricant to prevent such scraping of the endothelial cells was needed. Endre Balazs patented a process for purifying hyaluronic acid, a physiologic lubricant (which he called Healon) from rooster combs in the early 1970s. At first, Balazs saw Healon as a noninflammatory vitreous substitute. Claus Dohlman had used Balazs’ Healon in one case in which the anterior chamber flattened after a complicated corneal transplant. Although one might imagine the viscous hyaluronic acid would have caused a rise in IOP
, Dohlman reported no such rise in his case. Since that time, Balazs had licensed the synthesis process to Pharmacia, a Swedish drug company. Although Pharmacia saw no market for a vitreous substitute, when their scientists figured out a way to increase the viscosity of hyaluronic acid, they felt it might work as an injectable agent in the treatment of both human and equine arthritis
. The equine arthritis market proved to be small and the treatment of human osteoarthritis
produced only marginal improvement, so Pharmacia decided to abandon Healon. At this time, David Miller realized that Healon was the lubricant needed by the eye surgeon.
Balazs arranged to have Pharmacia send 20 sterile vials to Dr. David Miller for rabbit experiments. By 1976, Miller and colleagues published a study showing Healon worked well in protecting the rabbit corneal endothelium during IOL implantation. With a new possible use for Healon, Miller met with Pharmacia and performed a lens extraction and IOL implantation using Healon in a rabbit eye. The demonstration ignited a new enthusiasm for eye surgery with Healon. A small human pilot study at Boston’s Beth Israel Hospital by Miller confirmed Healon’s beneficial effects.
In a large, well-controlled clinical trial, Dr. Robert Stegmann, of Pretoria
, South Africa was able to quantify the advantages of Healon in IOL implantation by showing significantly higher postoperative corneal endothelial counts in the Healon eyes as opposed to the controls.
The U.S. Food and Drug Administration
quickly approved Healon as a surgical device in 1980, and Healon was successfully launched. By the year 2009, an estimated quarter of a billion patients had benefited from the useful properties of Healon in eye surgery.
In 1992, Miller and Stegmann received the Innovators Award by the American Society of Cataract and Refractive Surgery for developing the use of Healon in repairing injured eyes.
Hyaluronan is also used to treat osteoarthritis
of the knee. Such treatments, called viscosupplementation, are administered as a course of injections into the knee joint, and are believed to supplement the viscosity of the joint fluid, thereby lubricating the joint, cushioning the joint, and producing an analgesic effect. It has also been suggested that hyaluronan has positive biochemical effects on cartilage cells
. However, some placebo-controlled studies have cast doubt on the efficacy of hyaluronan injections, and hyaluronan is recommended primarily as a last alternative before surgery Oral use of hyaluronan has been lately suggested, although its effectiveness needs to be demonstrated. At present, there are some preliminary clinical studies that suggest oral administration of hyaluronan has a positive effect on osteoarthritis, but it remains to be seen if there is any real benefit from the treatment.
Dry, scaly skin (xerosis
) such as that caused by atopic dermatitis
(eczema
) may be treated with a prescription skin lotion containing sodium hyaluronate as its active ingredient.
Due to its high biocompatibility
and its common presence in the extracellular matrix
of tissues, hyaluronan is gaining popularity as a biomaterial
scaffold in tissue engineering
research.
Hyaluronan (also called hyaluronic acid or hyaluronate) is an anionic, nonsulfated
glycosaminoglycan
distributed widely throughout connective
, epithelial, and neural tissues. It is unique among glycosaminoglycans in that it is nonsulfated, forms in the plasma membrane instead of the Golgi
, and can be very large, with its molecular weight often reaching the millions.
One of the chief components of the extracellular matrix
, hyaluronan contributes significantly to cell proliferation and migration, and may also be involved in the progression of some malignant tumor
s.
The average 70 kg (154 lbs) person has roughly 15 grams of hyaluronan in the body, one-third of which is turned over (degraded and synthesized) every day. Hyaluronic acid is also a component of the group A streptococcal extracellular capsule, and is believed to play a role in virulence
.
the vitreous humor,” , hyaluronan was described as a "goo" molecule, a ubiquitous carbohydrate
polymer
that is part of the extracellular matrix. For example, hyaluronan is a major component of the synovial fluid
, and was found to increase the viscosity of the fluid. Along with lubricin, it is one of the fluid's main lubricating components.
What makes hyaluronan unique?
Hyaluronan is used in medical application for its unique physical/chemical properties. It is very hydrophilic; its viscous solutions have
most unusual rheological properties and are exceedingly lubricious.Hyaluronan is an important component of articular cartilage
, where it is present as a coat around each cell (chondrocyte
). When aggrecan
monomers bind to hyaluronan in the presence of link protein, large highly negatively-charged aggregates form. These aggregates imbibe water and are responsible for the resilience
of cartilage
(its resistance to compression). The molecular weight (size) of hyaluronan in cartilage
decreases with age, but the amount increases.
Hyaluronan is also a major component of skin
, where it is involved in tissue repair. When skin
is exposed to excessive UVB rays, it becomes inflamed (sunburn
) and the cells
in the dermis stop producing as much hyaluronan, and increase the rate of its degradation. Hyaluronan degradation products also accumulate in the skin after UV exposure.
While it is abundant in extracellular matrices, hyaluronan also contributes to tissue hydrodynamics, movement and proliferation of cells, and participates in a number of cell surface receptor interactions, notably those including its primary receptors, CD44
and RHAMM. Upregulation of CD44 itself is widely accepted as a marker of cell activation in lymphocytes. Hyaluronan's contribution to tumor growth may be due to its interaction with CD44. Receptor CD44 participates in cell adhesion interactions required by tumor cells.
Although hyaluronan binds to receptor CD44
, there is evidence hyaluronan degradation products transduce their inflammatory signal through toll-like receptor 2 (TLR2), TLR4 or both TLR2, and TLR4 in macrophages and dendritic cells. TLR and hyaluronan play a role in innate immunity.
High concentrations of hyaluronan in the brains of young rats, and reduced concentrations in the brains of adult rats suggest hyaluronan plays an important role in brain development.
Hyaluronan is a polymer
of disaccharide
s, themselves composed of D-glucuronic acid and D-N-acetylglucosamine, linked via alternating β-1,4 and β-1,3 glycosidic bond
s. Hyaluronan can be 25,000 disaccharide repeats in length. Polymers of hyaluronan can range in size from 5,000 to 20,000,000 Da
in vivo. The average molecular weight in human synovial fluid
is 3−4 million Da, and hyaluronan purified from human umbilical cord
is 3,140,000 Da.
Hyaluronan is energetically stable, in part because of the stereochemistry
of its component disaccharides. Bulky groups on each sugar molecule are in sterically favored positions, whereas the smaller hydrogens assume the less-favorable axial positions.
s called hyaluronan synthase
s, of which vertebrates have three types: HAS1, HAS2, and HAS3. These enzymes lengthen hyaluronan by repeatedly adding glucuronic acid
and N-acetylglucosamine
to the nascent polysaccharide as it is extruded via ABC-transporter through the cell membrane
into the extracellular space.
Hyaluronan synthesis (HAS) has been shown to be inhibited by 4-methylumbelliferone (hymecromone
, heparvit), a 7-hydroxy-4-methylcoumarin derivative.
This selective inhibition (without inhibiting other glycosaminoglycans) may prove useful in preventing metastasis
of malignant tumor cells.
Bacillus Subtilis
recently has been genetically modified (GMO) to culture a proprietary formula to yield hyaluronans, in a patented process producing human-grade product.
CD44 is widely distributed throughout the body, and the formal demonstration of HA-CD44 binding was proposed by Aruffo et al. in 1990. To date, it is recognized as the main cell surface receptor for HA. CD44 mediates cell interaction with HA and the binding of the two functions as an important part in various physiologic events, such as cell aggregation, migration, proliferation and activation; cell-cell and cell-substrate adhesion; endocytosis of HA, which leads to HA catabolism
in macrophages; and assembly of petircellular matrices from HA and proteoglycan
. Two significant roles of CD44 in skin were proposed by Kaya et al. The first is regulation of keratinocyte
proliferation in response to extracellular stimuli, and the second is the maintenance of local HA homeostasis.
ICAM-1 is known mainly as a metabolic cell surface receptor for HA, and this protein may be responsible mainly for the clearance of HA from lymph and blood plasma, which accounts for perhaps most of its whole-body turnover Ligand binding of this receptor, thus, triggers a highly coordinated cascade of events that includes the formation of an endocytotic vesicle, its fusion with primary lysosomes, enzymatic digestion to monosaccharides, active transmembrane transport of these sugars to cell sap, phosphorylation
of GlcNAc and enzymatic deacetylation
. Like its name, ICAM-1 may also serve as a cell adhesion molecule, and the binding of HA to ICAM-1 may contribute to the control of ICAM-1-mediated inflammatory activation.
s. In humans, there are at least seven types of hyaluronidase-like enzymes, several of which are tumor suppressors. The degradation products of hyaluronan, the oligosaccharides and very low-molecular-weight hyaluronan, exhibit pro-angiogenic properties . In addition, recent studies showed hyaluronan fragments, not the native high-molecular mass of hyaluronan, can induce inflammatory responses in macrophages and dendritic cells in tissue injury and in skin transplant rejection .
Inflammation
Many biological factors, such as growth factors, cytokines, eicosanoids etc., are generated in the inflammation process. These factors are necessary for the subsequent steps of wound healing due to their roles in promoting migration of inflammatory cells, fibroblasts, and endothelial cells into the wound site.
The wound tissue in the early inflammatory phase of wound repair is abundant in HA, probably a reflection of increased synthesis. HA acts as a promoter of early inflammation, which is crucial in the whole skin wound-healing process. In a murine air pouch model of carrageenan/IL-1-induced inflammation, HA was observed to enhance cellular infiltration. Kobayashi and colleagues showed a dose-dependent increase of the proinflammatory cytokines TNF-α and IL-8 production by human uterine
fibroblasts at HA concentrations of 10μg/ml to 1 mg/ml via a CD44-mediated mechanism. Endothelial cells, in response to inflammatory cytokines such as TNF-α, and bacterial lipopolysaccharide
, also synthesize HA, which has been shown to facilitate primary adhesion of cytokine-activated lymphocytes expressing the HA-binding variants of CD44 under laminar and static flow conditions. It is interesting to note that HA has contradictory dual functions in the inflammatory process. It not only can promote the inflammation, as stated above, but also can moderate the inflammatory response, which may contribute to the stabilization of granulation tissue matrix, as described in the following part.
Granulation and organization of the granulation tissue matrix
Granulation tissue
is the perfused
, fibrous connective tissue that replaces a fibrin
clot in healing wounds. It typically grows from the base of a wound and is able to fill wounds of almost any size it heals. HA is abundant in granulation tissue matrix. A variety of cell functions that are essential for tissue repair may attribute to this HA-rich network. These functions include facilitation of cell migration into the provisional wound matrix, cell proliferation and organization of the granulation tissue matrix. Absolutely, initiation of inflammation is extremely crucial for the formation of granulation tissue, therefore the pro-inflammatory role of HA as discussed above also contribute to this stage of wound healing.
HA and cell migration
Cell migration is essential for the formation of granulation tissue. The early stage of granulation tissue is dominated by a HA-rich extracellular matrix, which is regarded as a conducive environment for migration of cells into this temporary wound matrix. Contributions of HA to cell migration may attribute to its physicochemical properties as stated above, as well as its direct interactions with cells. For the former scenario, HA provides an open hydrated matrix that facilitates cell migration, whereas, in the latter scenario, directed migration and control of the cell locomotory mechanisms are mediated via the specific cell interaction between HA and cell surface HA receptors. As discussed before, the three principal cell surface receptors for HA are CD44, RHAMM, and ICAM-1. RHAMM is more related to cell migration. It forms links with several protein kinases associated with cell locomotion, for example, extracellular signal-regulated protein kinase (ERK), p125fak, and pp60c-src. During fetal development, the migration path through which neural crest cells migrate is rich in HA. HA is closely associated with the cell migration process in granulation tissue matrix, and studies show that cell movement can be inhibited, at least partially, by HA degradation or blocking HA receptor occupancy.
By providing the dynamic force to the cell, HA synthesis has also been shown to associate with cell migration. Basically, HA is synthesized at the plasma membrane and released directly into the extracellular environment. This may contribute to the hydrated microenvironment at sites of synthesis, and is essential for cell migration by facilitating cell detachment.
Role of HA in moderation of the inflammatory response
Although inflammation is an integral part of granulation tissue formation, for normal tissue repair to proceed, inflammation needs to be moderated. The initial granulation tissue formed is highly inflammatory with a high rate of tissue turnover mediated by matrix degrading enzymes and reactive oxygen metabolites that are products of inflammatory cells. Stabilization of granulation tissue matrix can be achieved by moderating inflammation. HA functions as an important moderator in this moderation process, which contradicts its role in inflammatory stimulation, as described above. HA can protect against free-radical damage to cells. This may attribute to its free-radical scavenging property, a physicochemical characteristic shared by large polyionic polymers. In a rat model of free-radical scavenging property investigated by Foschi D. and colleagues, HA has been shown to reduce damage to the granulation tissue.
In addition to the free-radical scavenging role, HA may also function in the negative feedback loop of inflammatory activation through its specific biological interactions with the biological constituents of inflammation. TNF-α, an important cytokine generated in inflammation, stimulates the expression of TSG-6 (TNF-stimulated gene 6) in fibroblasts and inflammatory cells. TSG-6, a HA-binding protein, also forms a stable complex with the serum proteinase inhibitor IαI (Inter-α-inhibitor) with a synergistic effect on the latter’s plasmin-inhibitory activity. Plasmin
is involved in activation of the proteolytic
cascade of matrix metalloproteinases and other proteinases leading to inflammatory tissue damage. Therefore, the action of TSG-6/ IαI complex, which may be additionally organized by binding to HA in the extracellular matrix, may serve as a potent negative feedback loop to moderate inflammation and stabilize the granulation tissue as healing progresses. In the murine air pouch model of carragenan/IL-1 (Interleukin-1β)-induced inflammation, where HA has been shown to have a proinflammatory property, reduction of inflammation can be achieved by administrating TSG-6, and the result is comparable with systemic dexamethasone treatment.
Reepithelization
HA plays an important role in the normal epidermis. HA also has crucial functions in the reepithelization process due to several of its properties. It serves as an integral part of the extracellular matrix of basal keratinocytes, which are major constituents of the epidermis; its free-radical scavenging function and its role in keratinocyte proliferation and migration.
In normal skin, HA is found in relative high concentrations in the basal layer of the epidermis where proliferating keratinocytes are found. CD44 is collocated with HA in the basal layer of epidermis where additionally it has been shown to be preferentially expressed on plasma membrane facing the HA-rich matrix pouches. Maintaining the extracellular space and providing an open, as well as hydrated, structure for the passage of nutrients are the main functions of HA in epidermis. Tammi R. and other colleagues found HA content increases at the presence of retinoic acid
(vitamin A). The proposed effects of retinoic acid against skin photo-damage and aging may be correlated, at least in part, with an increase of skin HA content, giving rise to increase of tissue hydration. It has been suggested the free-radical scavenging property of HA contributes to protection against solar radiation, supporting the role of CD44 acting as a HA receptor in the epidermis.
Epidermal HA also functions as a manipulator in the process of keratinocyte proliferation, which is essential in normal epidermal function, as well as during reepithelization in tissue repair. In the wound healing process, HA is expressed in the wound margin, in the connective tissue matrix, and collocating with CD44 expression in migrating keratinocytes. Kaya et al. found suppression of CD44 expression by an epidermis-specific antisense transgene
resulted in animals with defective HA accumulation in the superficial dermis, accompanied by distinct morphologic alterations of basal keratinocytes and defective keratinocyte proliferation in response to mitogen
and growth factors. Decrease in skin elasticity, impaired local inflammatory response, and impaired tissue repair were also observed. Their observations are strongly supportive of the important roles HA and CD44 have in skin physiology and tissue repair.
Fetal wound healing and scarring
Lack of fibrous scarring is the primary feature of fetal wound healing. Even for longer periods, HA content in fetal wounds is still higher than that in adult wounds, which suggests that HA may, at least in part, reduce collagen deposition and therefore lead to reduced scarring. This suggestion is in agreement with the research of West et al., who showed in adult and late gestation fetal wound healing, removal of HA results in fibrotic scarring. Though the exact role of HA in skin scarring is still under investigation, based on all the facts that have been observed, it must be a great contributor to the less fibrous scarring.
As shown in Figure 1, the various types of molecules that interact with hyaluronan can contribute to many of the stages of cancer metastasis.
Hyaluronan synthase
s (HAS) play roles in all of the stages of cancer metastasis. By producing anti-adhesive HA, HAS can allow tumor cells to release from the primary tumor mass, and if HA associates with receptors such as CD44, the activation of Rho GTPases can promote epithelial-mesenchymal transition (EMT) of the cancer cells. During the processes of intravasation or extravasation
, the interaction of HAS produced HA with receptors such as CD44 or RHAMM promote the cell changes that allow for the cancer cells to infiltrate the vascular
or lymphatic systems. While traveling in these systems, HA produced by HAS protects the cancer cell from physical damage. Finally, in the formation of a metastatic lesion, HAS produces HA to allow the cancer cell to interact with native cells at the secondary site and to produce a tumor for itself.
Hyaluronidases
(HAase or HYAL) also play many roles in cancer
metastasis
. By helping to degrade the ECM
surrounding the tumor, hyaluronidases help the cancer cell escape from the primary tumor mass and play a major role in intravasation
by allowing degradation of the basement membrane of the lymph or blood vessel. Hyaluronidases again play these roles in establishment of a metastatic lesion
by helping with extravasation and clearing the ECM of the secondary site. Finally, hyaluronidases play a key role in the process of angiogenesis
. HA fragments promote angiogenesis and hyaluronidases produce these fragments. Interestingly, hypoxia
also increases production of HA and activity of hyaluronidases.
The hyaluronan receptors, CD44 and RHAMM, are most thoroughly studied in terms of their roles in cancer metastasis. Increased clinical CD44 expression has been positively correlated to metastasis in a number of tumor types. In terms of mechanics, CD44 affects adhesion of cancer cells to each other and to endothelial cells, rearranges the cytoskeleton
through the Rho GTPases, and increases the activity of ECM degrading enzymes. Increased RHAMM expression has also been clinically correlated with cancer metastasis. In terms of mechanics, RHAMM promotes cancer cell motility through a number of pathways including focal adhesion kinase (FAK), Map kinase (MAPK), pp60(c-src), and the downstream targets of Rho kinase (ROK). RHAMM can also cooperate with CD44 to promote angiogenesis toward the metastatic lesion.
, and is approved for use in eye surgery
(i.e., corneal transplantation, cataract
surgery, glaucoma
surgery, and surgery to repair retinal detachment
). Other biomedical companies also produce brands of hyaluronan for opthalmic surgery.
Native hyaluronan has a relatively short half-life (shown in rabbits) so various manufacturing techniques have been deployed to extend the length of the chain and stabilise the molecule for its use in medical applications. The introduction of protein based cross-links, the introduction of free-radical scavenging molecules such as sorbitol
and minimal stabilisation of the HA chains through chemical agents e.g. NASHA stabilisation are all techniques that have been used.
In the late 1970s, intraocular lens implantation was often followed by severe corneal edema
, due to endothelial cell damage during the surgery. It was evident that a viscous, clear, physiologic lubricant to prevent such scraping of the endothelial cells was needed. Endre Balazs patented a process for purifying hyaluronic acid, a physiologic lubricant (which he called Healon) from rooster combs in the early 1970s. At first, Balazs saw Healon as a noninflammatory vitreous substitute. Claus Dohlman had used Balazs’ Healon in one case in which the anterior chamber flattened after a complicated corneal transplant. Although one might imagine the viscous hyaluronic acid would have caused a rise in IOP
, Dohlman reported no such rise in his case. Since that time, Balazs had licensed the synthesis process to Pharmacia, a Swedish drug company. Although Pharmacia saw no market for a vitreous substitute, when their scientists figured out a way to increase the viscosity of hyaluronic acid, they felt it might work as an injectable agent in the treatment of both human and equine arthritis
. The equine arthritis market proved to be small and the treatment of human osteoarthritis
produced only marginal improvement, so Pharmacia decided to abandon Healon. At this time, David Miller realized that Healon was the lubricant needed by the eye surgeon.
Balazs arranged to have Pharmacia send 20 sterile vials to Dr. David Miller for rabbit experiments. By 1976, Miller and colleagues published a study showing Healon worked well in protecting the rabbit corneal endothelium during IOL implantation. With a new possible use for Healon, Miller met with Pharmacia and performed a lens extraction and IOL implantation using Healon in a rabbit eye. The demonstration ignited a new enthusiasm for eye surgery with Healon. A small human pilot study at Boston’s Beth Israel Hospital by Miller confirmed Healon’s beneficial effects.
In a large, well-controlled clinical trial, Dr. Robert Stegmann, of Pretoria
, South Africa was able to quantify the advantages of Healon in IOL implantation by showing significantly higher postoperative corneal endothelial counts in the Healon eyes as opposed to the controls.
The U.S. Food and Drug Administration
quickly approved Healon as a surgical device in 1980, and Healon was successfully launched. By the year 2009, an estimated quarter of a billion patients had benefited from the useful properties of Healon in eye surgery.
In 1992, Miller and Stegmann received the Innovators Award by the American Society of Cataract and Refractive Surgery for developing the use of Healon in repairing injured eyes.
Hyaluronan is also used to treat osteoarthritis
of the knee. Such treatments, called viscosupplementation, are administered as a course of injections into the knee joint, and are believed to supplement the viscosity of the joint fluid, thereby lubricating the joint, cushioning the joint, and producing an analgesic effect. It has also been suggested that hyaluronan has positive biochemical effects on cartilage cells
. However, some placebo-controlled studies have cast doubt on the efficacy of hyaluronan injections, and hyaluronan is recommended primarily as a last alternative before surgery Oral use of hyaluronan has been lately suggested, although its effectiveness needs to be demonstrated. At present, there are some preliminary clinical studies that suggest oral administration of hyaluronan has a positive effect on osteoarthritis, but it remains to be seen if there is any real benefit from the treatment.
Dry, scaly skin (xerosis
) such as that caused by atopic dermatitis
(eczema
) may be treated with a prescription skin lotion containing sodium hyaluronate as its active ingredient.
Due to its high biocompatibility
and its common presence in the extracellular matrix
of tissues, hyaluronan is gaining popularity as a biomaterial
scaffold in tissue engineering
research.
Hyaluronan (also called hyaluronic acid or hyaluronate) is an anionic, nonsulfated
glycosaminoglycan
distributed widely throughout connective
, epithelial, and neural tissues. It is unique among glycosaminoglycans in that it is nonsulfated, forms in the plasma membrane instead of the Golgi
, and can be very large, with its molecular weight often reaching the millions.
One of the chief components of the extracellular matrix
, hyaluronan contributes significantly to cell proliferation and migration, and may also be involved in the progression of some malignant tumor
s.
The average 70 kg (154 lbs) person has roughly 15 grams of hyaluronan in the body, one-third of which is turned over (degraded and synthesized) every day. Hyaluronic acid is also a component of the group A streptococcal extracellular capsule, and is believed to play a role in virulence
.
the vitreous humor,” , hyaluronan was described as a "goo" molecule, a ubiquitous carbohydrate
polymer
that is part of the extracellular matrix. For example, hyaluronan is a major component of the synovial fluid
, and was found to increase the viscosity of the fluid. Along with lubricin, it is one of the fluid's main lubricating components.
What makes hyaluronan unique?
Hyaluronan is used in medical application for its unique physical/chemical properties. It is very hydrophilic; its viscous solutions have
most unusual rheological properties and are exceedingly lubricious.Hyaluronan is an important component of articular cartilage
, where it is present as a coat around each cell (chondrocyte
). When aggrecan
monomers bind to hyaluronan in the presence of link protein, large highly negatively-charged aggregates form. These aggregates imbibe water and are responsible for the resilience
of cartilage
(its resistance to compression). The molecular weight (size) of hyaluronan in cartilage
decreases with age, but the amount increases.
Hyaluronan is also a major component of skin
, where it is involved in tissue repair. When skin
is exposed to excessive UVB rays, it becomes inflamed (sunburn
) and the cells
in the dermis stop producing as much hyaluronan, and increase the rate of its degradation. Hyaluronan degradation products also accumulate in the skin after UV exposure.
While it is abundant in extracellular matrices, hyaluronan also contributes to tissue hydrodynamics, movement and proliferation of cells, and participates in a number of cell surface receptor interactions, notably those including its primary receptors, CD44
and RHAMM. Upregulation of CD44 itself is widely accepted as a marker of cell activation in lymphocytes. Hyaluronan's contribution to tumor growth may be due to its interaction with CD44. Receptor CD44 participates in cell adhesion interactions required by tumor cells.
Although hyaluronan binds to receptor CD44
, there is evidence hyaluronan degradation products transduce their inflammatory signal through toll-like receptor 2 (TLR2), TLR4 or both TLR2, and TLR4 in macrophages and dendritic cells. TLR and hyaluronan play a role in innate immunity.
High concentrations of hyaluronan in the brains of young rats, and reduced concentrations in the brains of adult rats suggest hyaluronan plays an important role in brain development.
Hyaluronan is a polymer
of disaccharide
s, themselves composed of D-glucuronic acid and D-N-acetylglucosamine, linked via alternating β-1,4 and β-1,3 glycosidic bond
s. Hyaluronan can be 25,000 disaccharide repeats in length. Polymers of hyaluronan can range in size from 5,000 to 20,000,000 Da
in vivo. The average molecular weight in human synovial fluid
is 3−4 million Da, and hyaluronan purified from human umbilical cord
is 3,140,000 Da.
Hyaluronan is energetically stable, in part because of the stereochemistry
of its component disaccharides. Bulky groups on each sugar molecule are in sterically favored positions, whereas the smaller hydrogens assume the less-favorable axial positions.
s called hyaluronan synthase
s, of which vertebrates have three types: HAS1, HAS2, and HAS3. These enzymes lengthen hyaluronan by repeatedly adding glucuronic acid
and N-acetylglucosamine
to the nascent polysaccharide as it is extruded via ABC-transporter through the cell membrane
into the extracellular space.
Hyaluronan synthesis (HAS) has been shown to be inhibited by 4-methylumbelliferone (hymecromone
, heparvit), a 7-hydroxy-4-methylcoumarin derivative.
This selective inhibition (without inhibiting other glycosaminoglycans) may prove useful in preventing metastasis
of malignant tumor cells.
Bacillus Subtilis
recently has been genetically modified (GMO) to culture a proprietary formula to yield hyaluronans, in a patented process producing human-grade product.
CD44 is widely distributed throughout the body, and the formal demonstration of HA-CD44 binding was proposed by Aruffo et al. in 1990. To date, it is recognized as the main cell surface receptor for HA. CD44 mediates cell interaction with HA and the binding of the two functions as an important part in various physiologic events, such as cell aggregation, migration, proliferation and activation; cell-cell and cell-substrate adhesion; endocytosis of HA, which leads to HA catabolism
in macrophages; and assembly of petircellular matrices from HA and proteoglycan
. Two significant roles of CD44 in skin were proposed by Kaya et al. The first is regulation of keratinocyte
proliferation in response to extracellular stimuli, and the second is the maintenance of local HA homeostasis.
ICAM-1 is known mainly as a metabolic cell surface receptor for HA, and this protein may be responsible mainly for the clearance of HA from lymph and blood plasma, which accounts for perhaps most of its whole-body turnover Ligand binding of this receptor, thus, triggers a highly coordinated cascade of events that includes the formation of an endocytotic vesicle, its fusion with primary lysosomes, enzymatic digestion to monosaccharides, active transmembrane transport of these sugars to cell sap, phosphorylation
of GlcNAc and enzymatic deacetylation
. Like its name, ICAM-1 may also serve as a cell adhesion molecule, and the binding of HA to ICAM-1 may contribute to the control of ICAM-1-mediated inflammatory activation.
s. In humans, there are at least seven types of hyaluronidase-like enzymes, several of which are tumor suppressors. The degradation products of hyaluronan, the oligosaccharides and very low-molecular-weight hyaluronan, exhibit pro-angiogenic properties . In addition, recent studies showed hyaluronan fragments, not the native high-molecular mass of hyaluronan, can induce inflammatory responses in macrophages and dendritic cells in tissue injury and in skin transplant rejection .
Inflammation
Many biological factors, such as growth factors, cytokines, eicosanoids etc., are generated in the inflammation process. These factors are necessary for the subsequent steps of wound healing due to their roles in promoting migration of inflammatory cells, fibroblasts, and endothelial cells into the wound site.
The wound tissue in the early inflammatory phase of wound repair is abundant in HA, probably a reflection of increased synthesis. HA acts as a promoter of early inflammation, which is crucial in the whole skin wound-healing process. In a murine air pouch model of carrageenan/IL-1-induced inflammation, HA was observed to enhance cellular infiltration. Kobayashi and colleagues showed a dose-dependent increase of the proinflammatory cytokines TNF-α and IL-8 production by human uterine
fibroblasts at HA concentrations of 10μg/ml to 1 mg/ml via a CD44-mediated mechanism. Endothelial cells, in response to inflammatory cytokines such as TNF-α, and bacterial lipopolysaccharide
, also synthesize HA, which has been shown to facilitate primary adhesion of cytokine-activated lymphocytes expressing the HA-binding variants of CD44 under laminar and static flow conditions. It is interesting to note that HA has contradictory dual functions in the inflammatory process. It not only can promote the inflammation, as stated above, but also can moderate the inflammatory response, which may contribute to the stabilization of granulation tissue matrix, as described in the following part.
Granulation and organization of the granulation tissue matrix
Granulation tissue
is the perfused
, fibrous connective tissue that replaces a fibrin
clot in healing wounds. It typically grows from the base of a wound and is able to fill wounds of almost any size it heals. HA is abundant in granulation tissue matrix. A variety of cell functions that are essential for tissue repair may attribute to this HA-rich network. These functions include facilitation of cell migration into the provisional wound matrix, cell proliferation and organization of the granulation tissue matrix. Absolutely, initiation of inflammation is extremely crucial for the formation of granulation tissue, therefore the pro-inflammatory role of HA as discussed above also contribute to this stage of wound healing.
HA and cell migration
Cell migration is essential for the formation of granulation tissue. The early stage of granulation tissue is dominated by a HA-rich extracellular matrix, which is regarded as a conducive environment for migration of cells into this temporary wound matrix. Contributions of HA to cell migration may attribute to its physicochemical properties as stated above, as well as its direct interactions with cells. For the former scenario, HA provides an open hydrated matrix that facilitates cell migration, whereas, in the latter scenario, directed migration and control of the cell locomotory mechanisms are mediated via the specific cell interaction between HA and cell surface HA receptors. As discussed before, the three principal cell surface receptors for HA are CD44, RHAMM, and ICAM-1. RHAMM is more related to cell migration. It forms links with several protein kinases associated with cell locomotion, for example, extracellular signal-regulated protein kinase (ERK), p125fak, and pp60c-src. During fetal development, the migration path through which neural crest cells migrate is rich in HA. HA is closely associated with the cell migration process in granulation tissue matrix, and studies show that cell movement can be inhibited, at least partially, by HA degradation or blocking HA receptor occupancy.
By providing the dynamic force to the cell, HA synthesis has also been shown to associate with cell migration. Basically, HA is synthesized at the plasma membrane and released directly into the extracellular environment. This may contribute to the hydrated microenvironment at sites of synthesis, and is essential for cell migration by facilitating cell detachment.
Role of HA in moderation of the inflammatory response
Although inflammation is an integral part of granulation tissue formation, for normal tissue repair to proceed, inflammation needs to be moderated. The initial granulation tissue formed is highly inflammatory with a high rate of tissue turnover mediated by matrix degrading enzymes and reactive oxygen metabolites that are products of inflammatory cells. Stabilization of granulation tissue matrix can be achieved by moderating inflammation. HA functions as an important moderator in this moderation process, which contradicts its role in inflammatory stimulation, as described above. HA can protect against free-radical damage to cells. This may attribute to its free-radical scavenging property, a physicochemical characteristic shared by large polyionic polymers. In a rat model of free-radical scavenging property investigated by Foschi D. and colleagues, HA has been shown to reduce damage to the granulation tissue.
In addition to the free-radical scavenging role, HA may also function in the negative feedback loop of inflammatory activation through its specific biological interactions with the biological constituents of inflammation. TNF-α, an important cytokine generated in inflammation, stimulates the expression of TSG-6 (TNF-stimulated gene 6) in fibroblasts and inflammatory cells. TSG-6, a HA-binding protein, also forms a stable complex with the serum proteinase inhibitor IαI (Inter-α-inhibitor) with a synergistic effect on the latter’s plasmin-inhibitory activity. Plasmin
is involved in activation of the proteolytic
cascade of matrix metalloproteinases and other proteinases leading to inflammatory tissue damage. Therefore, the action of TSG-6/ IαI complex, which may be additionally organized by binding to HA in the extracellular matrix, may serve as a potent negative feedback loop to moderate inflammation and stabilize the granulation tissue as healing progresses. In the murine air pouch model of carragenan/IL-1 (Interleukin-1β)-induced inflammation, where HA has been shown to have a proinflammatory property, reduction of inflammation can be achieved by administrating TSG-6, and the result is comparable with systemic dexamethasone treatment.
Reepithelization
HA plays an important role in the normal epidermis. HA also has crucial functions in the reepithelization process due to several of its properties. It serves as an integral part of the extracellular matrix of basal keratinocytes, which are major constituents of the epidermis; its free-radical scavenging function and its role in keratinocyte proliferation and migration.
In normal skin, HA is found in relative high concentrations in the basal layer of the epidermis where proliferating keratinocytes are found. CD44 is collocated with HA in the basal layer of epidermis where additionally it has been shown to be preferentially expressed on plasma membrane facing the HA-rich matrix pouches. Maintaining the extracellular space and providing an open, as well as hydrated, structure for the passage of nutrients are the main functions of HA in epidermis. Tammi R. and other colleagues found HA content increases at the presence of retinoic acid
(vitamin A). The proposed effects of retinoic acid against skin photo-damage and aging may be correlated, at least in part, with an increase of skin HA content, giving rise to increase of tissue hydration. It has been suggested the free-radical scavenging property of HA contributes to protection against solar radiation, supporting the role of CD44 acting as a HA receptor in the epidermis.
Epidermal HA also functions as a manipulator in the process of keratinocyte proliferation, which is essential in normal epidermal function, as well as during reepithelization in tissue repair. In the wound healing process, HA is expressed in the wound margin, in the connective tissue matrix, and collocating with CD44 expression in migrating keratinocytes. Kaya et al. found suppression of CD44 expression by an epidermis-specific antisense transgene
resulted in animals with defective HA accumulation in the superficial dermis, accompanied by distinct morphologic alterations of basal keratinocytes and defective keratinocyte proliferation in response to mitogen
and growth factors. Decrease in skin elasticity, impaired local inflammatory response, and impaired tissue repair were also observed. Their observations are strongly supportive of the important roles HA and CD44 have in skin physiology and tissue repair.
Fetal wound healing and scarring
Lack of fibrous scarring is the primary feature of fetal wound healing. Even for longer periods, HA content in fetal wounds is still higher than that in adult wounds, which suggests that HA may, at least in part, reduce collagen deposition and therefore lead to reduced scarring. This suggestion is in agreement with the research of West et al., who showed in adult and late gestation fetal wound healing, removal of HA results in fibrotic scarring. Though the exact role of HA in skin scarring is still under investigation, based on all the facts that have been observed, it must be a great contributor to the less fibrous scarring.
As shown in Figure 1, the various types of molecules that interact with hyaluronan can contribute to many of the stages of cancer metastasis.
Hyaluronan synthase
s (HAS) play roles in all of the stages of cancer metastasis. By producing anti-adhesive HA, HAS can allow tumor cells to release from the primary tumor mass, and if HA associates with receptors such as CD44, the activation of Rho GTPases can promote epithelial-mesenchymal transition (EMT) of the cancer cells. During the processes of intravasation or extravasation
, the interaction of HAS produced HA with receptors such as CD44 or RHAMM promote the cell changes that allow for the cancer cells to infiltrate the vascular
or lymphatic systems. While traveling in these systems, HA produced by HAS protects the cancer cell from physical damage. Finally, in the formation of a metastatic lesion, HAS produces HA to allow the cancer cell to interact with native cells at the secondary site and to produce a tumor for itself.
Hyaluronidases
(HAase or HYAL) also play many roles in cancer
metastasis
. By helping to degrade the ECM
surrounding the tumor, hyaluronidases help the cancer cell escape from the primary tumor mass and play a major role in intravasation
by allowing degradation of the basement membrane of the lymph or blood vessel. Hyaluronidases again play these roles in establishment of a metastatic lesion
by helping with extravasation and clearing the ECM of the secondary site. Finally, hyaluronidases play a key role in the process of angiogenesis
. HA fragments promote angiogenesis and hyaluronidases produce these fragments. Interestingly, hypoxia
also increases production of HA and activity of hyaluronidases.
The hyaluronan receptors, CD44 and RHAMM, are most thoroughly studied in terms of their roles in cancer metastasis. Increased clinical CD44 expression has been positively correlated to metastasis in a number of tumor types. In terms of mechanics, CD44 affects adhesion of cancer cells to each other and to endothelial cells, rearranges the cytoskeleton
through the Rho GTPases, and increases the activity of ECM degrading enzymes. Increased RHAMM expression has also been clinically correlated with cancer metastasis. In terms of mechanics, RHAMM promotes cancer cell motility through a number of pathways including focal adhesion kinase (FAK), Map kinase (MAPK), pp60(c-src), and the downstream targets of Rho kinase (ROK). RHAMM can also cooperate with CD44 to promote angiogenesis toward the metastatic lesion.
, and is approved for use in eye surgery
(i.e., corneal transplantation, cataract
surgery, glaucoma
surgery, and surgery to repair retinal detachment
). Other biomedical companies also produce brands of hyaluronan for opthalmic surgery.
Native hyaluronan has a relatively short half-life (shown in rabbits) so various manufacturing techniques have been deployed to extend the length of the chain and stabilise the molecule for its use in medical applications. The introduction of protein based cross-links, the introduction of free-radical scavenging molecules such as sorbitol
and minimal stabilisation of the HA chains through chemical agents e.g. NASHA stabilisation are all techniques that have been used.
In the late 1970s, intraocular lens implantation was often followed by severe corneal edema
, due to endothelial cell damage during the surgery. It was evident that a viscous, clear, physiologic lubricant to prevent such scraping of the endothelial cells was needed. Endre Balazs patented a process for purifying hyaluronic acid, a physiologic lubricant (which he called Healon) from rooster combs in the early 1970s. At first, Balazs saw Healon as a noninflammatory vitreous substitute. Claus Dohlman had used Balazs’ Healon in one case in which the anterior chamber flattened after a complicated corneal transplant. Although one might imagine the viscous hyaluronic acid would have caused a rise in IOP
, Dohlman reported no such rise in his case. Since that time, Balazs had licensed the synthesis process to Pharmacia, a Swedish drug company. Although Pharmacia saw no market for a vitreous substitute, when their scientists figured out a way to increase the viscosity of hyaluronic acid, they felt it might work as an injectable agent in the treatment of both human and equine arthritis
. The equine arthritis market proved to be small and the treatment of human osteoarthritis
produced only marginal improvement, so Pharmacia decided to abandon Healon. At this time, David Miller realized that Healon was the lubricant needed by the eye surgeon.
Balazs arranged to have Pharmacia send 20 sterile vials to Dr. David Miller for rabbit experiments. By 1976, Miller and colleagues published a study showing Healon worked well in protecting the rabbit corneal endothelium during IOL implantation. With a new possible use for Healon, Miller met with Pharmacia and performed a lens extraction and IOL implantation using Healon in a rabbit eye. The demonstration ignited a new enthusiasm for eye surgery with Healon. A small human pilot study at Boston’s Beth Israel Hospital by Miller confirmed Healon’s beneficial effects.
In a large, well-controlled clinical trial, Dr. Robert Stegmann, of Pretoria
, South Africa was able to quantify the advantages of Healon in IOL implantation by showing significantly higher postoperative corneal endothelial counts in the Healon eyes as opposed to the controls.
The U.S. Food and Drug Administration
quickly approved Healon as a surgical device in 1980, and Healon was successfully launched. By the year 2009, an estimated quarter of a billion patients had benefited from the useful properties of Healon in eye surgery.
In 1992, Miller and Stegmann received the Innovators Award by the American Society of Cataract and Refractive Surgery for developing the use of Healon in repairing injured eyes.
Hyaluronan is also used to treat osteoarthritis
of the knee. Such treatments, called viscosupplementation, are administered as a course of injections into the knee joint, and are believed to supplement the viscosity of the joint fluid, thereby lubricating the joint, cushioning the joint, and producing an analgesic effect. It has also been suggested that hyaluronan has positive biochemical effects on cartilage cells
. However, some placebo-controlled studies have cast doubt on the efficacy of hyaluronan injections, and hyaluronan is recommended primarily as a last alternative before surgery Oral use of hyaluronan has been lately suggested, although its effectiveness needs to be demonstrated. At present, there are some preliminary clinical studies that suggest oral administration of hyaluronan has a positive effect on osteoarthritis, but it remains to be seen if there is any real benefit from the treatment.
Dry, scaly skin (xerosis
) such as that caused by atopic dermatitis
(eczema
) may be treated with a prescription skin lotion containing sodium hyaluronate as its active ingredient.
Due to its high biocompatibility
and its common presence in the extracellular matrix
of tissues, hyaluronan is gaining popularity as a biomaterial
scaffold in tissue engineering
research. In particular, a number of research groups have found hyaluronan's properties for tissue engineering
and regenerative medicine
are significantly improved with crosslinking, producing a hydrogel. This added feature allows a researcher to form a desired shape, as well as to deliver therapeutic molecules, into a host. Hyaluronan can be crosslinked by attaching thiol
s (trade names: Extracel, HyStem), methacrylate
s, and tyramine
s (trade name: Corgel). Hyaluronan can also be crosslinked directly with formaldehyde
(trade name: Hylan-A) or with divinylsulfone
(trade name: Hylan-B).
In some cancers, hyaluronan levels correlate well with malignancy and poor prognosis. Hyaluronan is, thus, often used as a tumor marker
for prostate
and breast cancer
. It may also be used to monitor the progression of the disease.
Hyaluronan may also be used postoperatively to induce tissue healing, notably after cataract
surgery. Current models of wound healing propose the larger polymers of hyaluronic acid appear in the early stages of healing to physically make room for white blood cells, which mediate the immune response.
Hyaluronan has also been used in the synthesis of biological scaffolds for wound-healing applications. These scaffolds typically have proteins such as fibronectin
attached to the hyaluronan to facilitate cell migration into the wound
. This is particularly important for individuals with diabetes suffering from chronic wound
s.
In 2007, the EMA
extended its approval of Hylan GF-20 as a treatment for ankle and shoulder osteoarthritis pain.
Hyaluronan is also used in anti-adhesive products such as Hyalobarrier
, widely used in pelvic and abdominal surgery to prevent postoperative adhesions.
In May, 2011, Dr Endre Balazs was awarded the Helen Keller
Award for Vision Research for his work in championing the development of hyaluronan and Healon. The award was presented by the Helen Keller Foundation for Research and education.
In 2003, the FDA approved hyaluronan injections for filling soft tissue defects such as facial wrinkles. Restylane
is a common trade name for the product. Hyaluronan injections temporarily smooth wrinkles by adding volume under the skin, with effects typically lasting for six months.
Juvéderm
is a bacterial hyaluronic acid injectable filler, similar to Restylane, but differing slightly in terms of effect and longevity. It is used for lip augmentation, reduction of folds and wrinkles, and removal of scars. The effects of Juvéderm treatments are also temporary, and costs are similar to those of Restylane.
The presence of hyaluronic acid in epithelial tissue has been shown to promote keratinocyte proliferation and increase the presence of retinoic acid, effecting skin hydration. Hyaluronic acid's interaction with CD44
drives collagen synthesis and normal skin function. Present in the extracellular matrix of basal keratinocytes, hyaluronic acid is critical to the structural integrity of the dermal collagen matrix. These benefits make hyaluronic acid a very effective topical humectant
; however, results may only be sustained as part of an ongoing treatment program.
joint dysfunctions, but not when joint sepsis
or fracture are suspected. It is especially used for synovitis
associated with equine osteoarthritis
. It can be injected directly into an affected joint, or intravenously for less localized disorders. It may cause mild heating of the joint if directly injected, but this does not affect the clinical outcome. Intra-articularly administered medicine is fully metabolized in less than a week.
Note that, according to Canadian regulation, hyaluronan in HY-50 preparation should not be administered to animals to be slaughtered for horse meat
. In Europe, however, the same preparation is not considered to have any such effect, and edibility of the horse meat
is not affected.
because it was first isolated from the vitreous humour
and possesses a high uronic acid content.
The term hyaluronate refers to the conjugate base
of hyaluronic acid. Because the molecule typically exists in vivo in its polyanionic form, it is most commonly referred to as hyaluronan.
Sulfation
Sulfation in biochemistry is the enzyme-catalyzed addition of sulfate to another molecule. It often refers to a phase II enzyme reaction. This biotransformation process uses its cosubstrate 3'-phosphoadenosine-5'-phosphosulfate to transfer sulfate to a xenobiotic...
glycosaminoglycan
Glycosaminoglycan
Glycosaminoglycans or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit. The repeating unit consists of a hexose or a hexuronic acid, linked to a hexosamine .-Production:Protein cores made in the rough endoplasmic reticulum are posttranslationally...
distributed widely throughout connective
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
, epithelial, and neural tissues. It is unique among glycosaminoglycans in that it is nonsulfated, forms in the plasma membrane instead of the Golgi
Golgi apparatus
The Golgi apparatus is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi, after whom the Golgi apparatus is named....
, and can be very large, with its molecular weight often reaching the millions.
One of the chief components of the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
, hyaluronan contributes significantly to cell proliferation and migration, and may also be involved in the progression of some malignant tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
s.
The average 70 kg (154 lbs) person has roughly 15 grams of hyaluronan in the body, one-third of which is turned over (degraded and synthesized) every day. Hyaluronic acid is also a component of the group A streptococcal extracellular capsule, and is believed to play a role in virulence
Virulence
Virulence is by MeSH definition the degree of pathogenicity within a group or species of parasites as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenicity of an organism - its ability to cause disease - is determined by its...
.
Functions
It was first isolated from the vitreous body of the eye by Karl Meyer who called it hyaluronic acid, in 1934.The term hyaluronan was proposed by Dr. Endre A. Balazs in the 1980’s to encompass the different forms the molecule can take, e.g., the acid form, hyaluronic acid, and the salts, such as sodium hyaluronate, which form at physiological pH. Until the late 1970's, “The polysaccharide ofthe vitreous humor,” , hyaluronan was described as a "goo" molecule, a ubiquitous carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
that is part of the extracellular matrix. For example, hyaluronan is a major component of the synovial fluid
Synovial fluid
Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...
, and was found to increase the viscosity of the fluid. Along with lubricin, it is one of the fluid's main lubricating components.
What makes hyaluronan unique?
Hyaluronan is used in medical application for its unique physical/chemical properties. It is very hydrophilic; its viscous solutions have
most unusual rheological properties and are exceedingly lubricious.Hyaluronan is an important component of articular cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
, where it is present as a coat around each cell (chondrocyte
Chondrocyte
Chondrocytes are the only cells found in cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans...
). When aggrecan
Aggrecan
Aggrecan also known as cartilage-specific proteoglycan core protein or chondroitin sulfate proteoglycan 1 is a protein that in humans is encoded by the ACAN gene. This gene is a member of the aggrecan/versican proteoglycan family...
monomers bind to hyaluronan in the presence of link protein, large highly negatively-charged aggregates form. These aggregates imbibe water and are responsible for the resilience
Resilience
Resilience is the property of a material to absorb energy when it is deformed elastically and then, upon unloading to have this energy recovered. In other words, it is the maximum energy per unit volume that can be elastically stored...
of cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
(its resistance to compression). The molecular weight (size) of hyaluronan in cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
decreases with age, but the amount increases.
Hyaluronan is also a major component of skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, where it is involved in tissue repair. When skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
is exposed to excessive UVB rays, it becomes inflamed (sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...
) and the cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
in the dermis stop producing as much hyaluronan, and increase the rate of its degradation. Hyaluronan degradation products also accumulate in the skin after UV exposure.
While it is abundant in extracellular matrices, hyaluronan also contributes to tissue hydrodynamics, movement and proliferation of cells, and participates in a number of cell surface receptor interactions, notably those including its primary receptors, CD44
CD44
The CD44 antigen is a cell-surface glycoprotein involved in cell–cell interactions, cell adhesion and migration. In humans, the CD44 antigen is encoded by the CD44 gene.- Tissue distribution and isoforms :...
and RHAMM. Upregulation of CD44 itself is widely accepted as a marker of cell activation in lymphocytes. Hyaluronan's contribution to tumor growth may be due to its interaction with CD44. Receptor CD44 participates in cell adhesion interactions required by tumor cells.
Although hyaluronan binds to receptor CD44
CD44
The CD44 antigen is a cell-surface glycoprotein involved in cell–cell interactions, cell adhesion and migration. In humans, the CD44 antigen is encoded by the CD44 gene.- Tissue distribution and isoforms :...
, there is evidence hyaluronan degradation products transduce their inflammatory signal through toll-like receptor 2 (TLR2), TLR4 or both TLR2, and TLR4 in macrophages and dendritic cells. TLR and hyaluronan play a role in innate immunity.
High concentrations of hyaluronan in the brains of young rats, and reduced concentrations in the brains of adult rats suggest hyaluronan plays an important role in brain development.
Structure
Properties of hyaluronan were first determined in the 1930s in the laboratory of Karl Meyer.Hyaluronan is a polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
of disaccharide
Disaccharide
A disaccharide or biose is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only. Like monosaccharides, disaccharides form an aqueous solution when dissolved in water...
s, themselves composed of D-glucuronic acid and D-N-acetylglucosamine, linked via alternating β-1,4 and β-1,3 glycosidic bond
Glycosidic bond
In chemistry, a glycosidic bond is a type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate....
s. Hyaluronan can be 25,000 disaccharide repeats in length. Polymers of hyaluronan can range in size from 5,000 to 20,000,000 Da
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
in vivo. The average molecular weight in human synovial fluid
Synovial fluid
Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...
is 3−4 million Da, and hyaluronan purified from human umbilical cord
Umbilical cord
In placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta...
is 3,140,000 Da.
Hyaluronan is energetically stable, in part because of the stereochemistry
Stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms within molecules. An important branch of stereochemistry is the study of chiral molecules....
of its component disaccharides. Bulky groups on each sugar molecule are in sterically favored positions, whereas the smaller hydrogens assume the less-favorable axial positions.
Biological synthesis
Hyaluronan is synthesized by a class of integral membrane proteinIntegral membrane protein
An integral membrane protein is a protein molecule that is permanently attached to the biological membrane. Proteins that cross the membrane are surrounded by "annular" lipids, which are defined as lipids that are in direct contact with a membrane protein...
s called hyaluronan synthase
Hyaluronan synthase
Hyaluronan synthases are membrane-bound enzymes which use UDP-α-N-acetyl-D-glucosamine and UDP-α-D-glucuronate as substrates to produce the glycosaminoglycan hyaluronan at the cell surface and extrude it through the membrane into the extracellular space....
s, of which vertebrates have three types: HAS1, HAS2, and HAS3. These enzymes lengthen hyaluronan by repeatedly adding glucuronic acid
Glucuronic acid
Glucuronic acid is a carboxylic acid. Its structure is similar to that of glucose. However, glucuronic acid's sixth carbon is oxidized to a carboxylic acid...
and N-acetylglucosamine
N-Acetylglucosamine
N-Acetylglucosamine is a monosaccharide derivative of glucose. It is an amide between glucosamine and acetic acid...
to the nascent polysaccharide as it is extruded via ABC-transporter through the cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
into the extracellular space.
Hyaluronan synthesis (HAS) has been shown to be inhibited by 4-methylumbelliferone (hymecromone
Hymecromone
Hymecromone is a drug used in bile therapy. It is used as choleretic and antispasmodic drugs and as a standard for the fluorometric determination of enzyme activity....
, heparvit), a 7-hydroxy-4-methylcoumarin derivative.
This selective inhibition (without inhibiting other glycosaminoglycans) may prove useful in preventing metastasis
Metastasis
Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
of malignant tumor cells.
Bacillus Subtilis
Bacillus subtilis
Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...
recently has been genetically modified (GMO) to culture a proprietary formula to yield hyaluronans, in a patented process producing human-grade product.
Cell receptors for hyaluronan
So far, cell receptors that have been identified for HA fall into three main groups: CD44, Receptor for HA-mediated motility (RHAMM) and intracellular adhesion molecule-1 (ICAM-1). CD44 and ICAM-1 were already known as cell adhesion molecules with other recognized ligands before their HA binding was discovered.CD44 is widely distributed throughout the body, and the formal demonstration of HA-CD44 binding was proposed by Aruffo et al. in 1990. To date, it is recognized as the main cell surface receptor for HA. CD44 mediates cell interaction with HA and the binding of the two functions as an important part in various physiologic events, such as cell aggregation, migration, proliferation and activation; cell-cell and cell-substrate adhesion; endocytosis of HA, which leads to HA catabolism
Catabolism
Catabolism is the set of metabolic pathways that break down molecules into smaller units and release energy. In catabolism, large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides, and amino...
in macrophages; and assembly of petircellular matrices from HA and proteoglycan
Proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...
. Two significant roles of CD44 in skin were proposed by Kaya et al. The first is regulation of keratinocyte
Keratinocyte
Keratinocytes are the predominant cell type in the epidermis, the outermost layer of the human skin, constituting 95% of the cells found there. Those keratinocytes found in the basal layer of the skin are sometimes referred to as "basal cells" or "basal keratinocytes"...
proliferation in response to extracellular stimuli, and the second is the maintenance of local HA homeostasis.
ICAM-1 is known mainly as a metabolic cell surface receptor for HA, and this protein may be responsible mainly for the clearance of HA from lymph and blood plasma, which accounts for perhaps most of its whole-body turnover Ligand binding of this receptor, thus, triggers a highly coordinated cascade of events that includes the formation of an endocytotic vesicle, its fusion with primary lysosomes, enzymatic digestion to monosaccharides, active transmembrane transport of these sugars to cell sap, phosphorylation
Phosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....
of GlcNAc and enzymatic deacetylation
Acetylation
Acetylation describes a reaction that introduces an acetyl functional group into a chemical compound...
. Like its name, ICAM-1 may also serve as a cell adhesion molecule, and the binding of HA to ICAM-1 may contribute to the control of ICAM-1-mediated inflammatory activation.
Degradation
Hyaluronan is degraded by a family of enzymes called hyaluronidaseHyaluronidase
The hyaluronidases are a family of enzymes that degrade hyaluronic acid.In humans, there are six associated genes, including HYAL1, HYAL2, HYAL3, and PH-20/SPAM1.-Use as a drug:...
s. In humans, there are at least seven types of hyaluronidase-like enzymes, several of which are tumor suppressors. The degradation products of hyaluronan, the oligosaccharides and very low-molecular-weight hyaluronan, exhibit pro-angiogenic properties . In addition, recent studies showed hyaluronan fragments, not the native high-molecular mass of hyaluronan, can induce inflammatory responses in macrophages and dendritic cells in tissue injury and in skin transplant rejection .
Role of hyaluronan on wound repair process
Skin provides a mechanical barrier to the external environment and acts to prevent the ingress of infectious agents. Once injured, the tissues beneath are exposed to infection; therefore, rapid and effective healing is of crucial significance to reconstruct a barrier function. Skin wound healing is a complex process, and includes many interacting processes initiated by haemostasis and the release of platelet-derived factors. The following stages are inflammation, granulation tissue formation, reepithelization and remodeling. HA is likely to play a multifaceted role in mediation of these cellular and matrix events. The proposed roles of HA in this sequence of skin wound healing events are elucidated in details below.Inflammation
Many biological factors, such as growth factors, cytokines, eicosanoids etc., are generated in the inflammation process. These factors are necessary for the subsequent steps of wound healing due to their roles in promoting migration of inflammatory cells, fibroblasts, and endothelial cells into the wound site.
The wound tissue in the early inflammatory phase of wound repair is abundant in HA, probably a reflection of increased synthesis. HA acts as a promoter of early inflammation, which is crucial in the whole skin wound-healing process. In a murine air pouch model of carrageenan/IL-1-induced inflammation, HA was observed to enhance cellular infiltration. Kobayashi and colleagues showed a dose-dependent increase of the proinflammatory cytokines TNF-α and IL-8 production by human uterine
Uterine
The word uterine can refer to different meanings:* relating to or near the uterus or womb* having the same mother, but different fathers, see matrilineality...
fibroblasts at HA concentrations of 10μg/ml to 1 mg/ml via a CD44-mediated mechanism. Endothelial cells, in response to inflammatory cytokines such as TNF-α, and bacterial lipopolysaccharide
Lipopolysaccharide
Lipopolysaccharides , also known as lipoglycans, are large molecules consisting of a lipid and a polysaccharide joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, act as endotoxins and elicit strong immune responses in animals.-Functions:LPS is the major...
, also synthesize HA, which has been shown to facilitate primary adhesion of cytokine-activated lymphocytes expressing the HA-binding variants of CD44 under laminar and static flow conditions. It is interesting to note that HA has contradictory dual functions in the inflammatory process. It not only can promote the inflammation, as stated above, but also can moderate the inflammatory response, which may contribute to the stabilization of granulation tissue matrix, as described in the following part.
Granulation and organization of the granulation tissue matrix
Granulation tissue
Granulation tissue
Granulation tissue is the perfused, fibrous connective tissue that replaces a fibrin clot in healing wounds. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any size it heals...
is the perfused
Perfusion
In physiology, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue. The word is derived from the French verb "perfuser" meaning to "pour over or through."...
, fibrous connective tissue that replaces a fibrin
Fibrin
Fibrin is a fibrous, non-globular protein involved in the clotting of blood. It is a fibrillar protein that is polymerised to form a "mesh" that forms a hemostatic plug or clot over a wound site....
clot in healing wounds. It typically grows from the base of a wound and is able to fill wounds of almost any size it heals. HA is abundant in granulation tissue matrix. A variety of cell functions that are essential for tissue repair may attribute to this HA-rich network. These functions include facilitation of cell migration into the provisional wound matrix, cell proliferation and organization of the granulation tissue matrix. Absolutely, initiation of inflammation is extremely crucial for the formation of granulation tissue, therefore the pro-inflammatory role of HA as discussed above also contribute to this stage of wound healing.
HA and cell migration
Cell migration is essential for the formation of granulation tissue. The early stage of granulation tissue is dominated by a HA-rich extracellular matrix, which is regarded as a conducive environment for migration of cells into this temporary wound matrix. Contributions of HA to cell migration may attribute to its physicochemical properties as stated above, as well as its direct interactions with cells. For the former scenario, HA provides an open hydrated matrix that facilitates cell migration, whereas, in the latter scenario, directed migration and control of the cell locomotory mechanisms are mediated via the specific cell interaction between HA and cell surface HA receptors. As discussed before, the three principal cell surface receptors for HA are CD44, RHAMM, and ICAM-1. RHAMM is more related to cell migration. It forms links with several protein kinases associated with cell locomotion, for example, extracellular signal-regulated protein kinase (ERK), p125fak, and pp60c-src. During fetal development, the migration path through which neural crest cells migrate is rich in HA. HA is closely associated with the cell migration process in granulation tissue matrix, and studies show that cell movement can be inhibited, at least partially, by HA degradation or blocking HA receptor occupancy.
By providing the dynamic force to the cell, HA synthesis has also been shown to associate with cell migration. Basically, HA is synthesized at the plasma membrane and released directly into the extracellular environment. This may contribute to the hydrated microenvironment at sites of synthesis, and is essential for cell migration by facilitating cell detachment.
Role of HA in moderation of the inflammatory response
Although inflammation is an integral part of granulation tissue formation, for normal tissue repair to proceed, inflammation needs to be moderated. The initial granulation tissue formed is highly inflammatory with a high rate of tissue turnover mediated by matrix degrading enzymes and reactive oxygen metabolites that are products of inflammatory cells. Stabilization of granulation tissue matrix can be achieved by moderating inflammation. HA functions as an important moderator in this moderation process, which contradicts its role in inflammatory stimulation, as described above. HA can protect against free-radical damage to cells. This may attribute to its free-radical scavenging property, a physicochemical characteristic shared by large polyionic polymers. In a rat model of free-radical scavenging property investigated by Foschi D. and colleagues, HA has been shown to reduce damage to the granulation tissue.
In addition to the free-radical scavenging role, HA may also function in the negative feedback loop of inflammatory activation through its specific biological interactions with the biological constituents of inflammation. TNF-α, an important cytokine generated in inflammation, stimulates the expression of TSG-6 (TNF-stimulated gene 6) in fibroblasts and inflammatory cells. TSG-6, a HA-binding protein, also forms a stable complex with the serum proteinase inhibitor IαI (Inter-α-inhibitor) with a synergistic effect on the latter’s plasmin-inhibitory activity. Plasmin
Plasmin
Plasmin is an important enzyme present in blood that degrades many blood plasma proteins, most notably, fibrin clots. The degradation of fibrin is termed fibrinolysis. In humans, the plasmin protein is encoded by the PLG gene.- Function :...
is involved in activation of the proteolytic
Proteolysis
Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...
cascade of matrix metalloproteinases and other proteinases leading to inflammatory tissue damage. Therefore, the action of TSG-6/ IαI complex, which may be additionally organized by binding to HA in the extracellular matrix, may serve as a potent negative feedback loop to moderate inflammation and stabilize the granulation tissue as healing progresses. In the murine air pouch model of carragenan/IL-1 (Interleukin-1β)-induced inflammation, where HA has been shown to have a proinflammatory property, reduction of inflammation can be achieved by administrating TSG-6, and the result is comparable with systemic dexamethasone treatment.
Reepithelization
HA plays an important role in the normal epidermis. HA also has crucial functions in the reepithelization process due to several of its properties. It serves as an integral part of the extracellular matrix of basal keratinocytes, which are major constituents of the epidermis; its free-radical scavenging function and its role in keratinocyte proliferation and migration.
In normal skin, HA is found in relative high concentrations in the basal layer of the epidermis where proliferating keratinocytes are found. CD44 is collocated with HA in the basal layer of epidermis where additionally it has been shown to be preferentially expressed on plasma membrane facing the HA-rich matrix pouches. Maintaining the extracellular space and providing an open, as well as hydrated, structure for the passage of nutrients are the main functions of HA in epidermis. Tammi R. and other colleagues found HA content increases at the presence of retinoic acid
Retinoic acid
Retinoic acid is a metabolite of vitamin A that mediates the functions of vitamin A required for growth and development. Retinoic acid is required in chordate animals which includes all higher animals from fishes to humans...
(vitamin A). The proposed effects of retinoic acid against skin photo-damage and aging may be correlated, at least in part, with an increase of skin HA content, giving rise to increase of tissue hydration. It has been suggested the free-radical scavenging property of HA contributes to protection against solar radiation, supporting the role of CD44 acting as a HA receptor in the epidermis.
Epidermal HA also functions as a manipulator in the process of keratinocyte proliferation, which is essential in normal epidermal function, as well as during reepithelization in tissue repair. In the wound healing process, HA is expressed in the wound margin, in the connective tissue matrix, and collocating with CD44 expression in migrating keratinocytes. Kaya et al. found suppression of CD44 expression by an epidermis-specific antisense transgene
Transgene
A transgene is a gene or genetic material that has been transferred naturally or by any of a number of genetic engineering techniques from one organism to another....
resulted in animals with defective HA accumulation in the superficial dermis, accompanied by distinct morphologic alterations of basal keratinocytes and defective keratinocyte proliferation in response to mitogen
Mitogen
A mitogen is a chemical substance that encourages a cell to commence cell division, triggering mitosis. A mitogen is usually some form of a protein.Mitogenesis is the induction of mitosis, typically via a mitogen....
and growth factors. Decrease in skin elasticity, impaired local inflammatory response, and impaired tissue repair were also observed. Their observations are strongly supportive of the important roles HA and CD44 have in skin physiology and tissue repair.
Fetal wound healing and scarring
Lack of fibrous scarring is the primary feature of fetal wound healing. Even for longer periods, HA content in fetal wounds is still higher than that in adult wounds, which suggests that HA may, at least in part, reduce collagen deposition and therefore lead to reduced scarring. This suggestion is in agreement with the research of West et al., who showed in adult and late gestation fetal wound healing, removal of HA results in fibrotic scarring. Though the exact role of HA in skin scarring is still under investigation, based on all the facts that have been observed, it must be a great contributor to the less fibrous scarring.
Role of hyaluronan in cancer metastasis
Hyaluronan synthase
Synthase
In biochemistry, a synthase is an enzyme that catalyses a synthesis process.Following the EC number classification, they belong to the group of ligases, with lyases catalysing the reverse reaction....
s (HAS) play roles in all of the stages of cancer metastasis. By producing anti-adhesive HA, HAS can allow tumor cells to release from the primary tumor mass, and if HA associates with receptors such as CD44, the activation of Rho GTPases can promote epithelial-mesenchymal transition (EMT) of the cancer cells. During the processes of intravasation or extravasation
Extravasation
Extravasation is the accidental administration of intravenously infused medicinal drugs into the surrounding tissue, either by leakage , or direct exposure...
, the interaction of HAS produced HA with receptors such as CD44 or RHAMM promote the cell changes that allow for the cancer cells to infiltrate the vascular
Vascular
Vascular in zoology and medicine means "related to blood vessels", which are part of the circulatory system. An organ or tissue that is vascularized is heavily endowed with blood vessels and thus richly supplied with blood....
or lymphatic systems. While traveling in these systems, HA produced by HAS protects the cancer cell from physical damage. Finally, in the formation of a metastatic lesion, HAS produces HA to allow the cancer cell to interact with native cells at the secondary site and to produce a tumor for itself.
Hyaluronidases
HYAL1
Hyaluronidase-1 is an enzyme that in humans is encoded by the HYAL1 gene.- Further reading :...
(HAase or HYAL) also play many roles in cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
metastasis
Metastasis
Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
. By helping to degrade the ECM
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
surrounding the tumor, hyaluronidases help the cancer cell escape from the primary tumor mass and play a major role in intravasation
Intravasation
As a part of the process of metastasis, intravasation refers to the invasion of a cancer through the basal membrane and into blood vessels.In radiology, intravasation is used to describe penetration of radiographic contrast into the soft tissue lymphatics and veins of a hollow organ as a result of...
by allowing degradation of the basement membrane of the lymph or blood vessel. Hyaluronidases again play these roles in establishment of a metastatic lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
by helping with extravasation and clearing the ECM of the secondary site. Finally, hyaluronidases play a key role in the process of angiogenesis
Angiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...
. HA fragments promote angiogenesis and hyaluronidases produce these fragments. Interestingly, hypoxia
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
also increases production of HA and activity of hyaluronidases.
The hyaluronan receptors, CD44 and RHAMM, are most thoroughly studied in terms of their roles in cancer metastasis. Increased clinical CD44 expression has been positively correlated to metastasis in a number of tumor types. In terms of mechanics, CD44 affects adhesion of cancer cells to each other and to endothelial cells, rearranges the cytoskeleton
Cytoskeleton
The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within a cell's cytoplasm and is made out of protein. The cytoskeleton is present in all cells; it was once thought to be unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton...
through the Rho GTPases, and increases the activity of ECM degrading enzymes. Increased RHAMM expression has also been clinically correlated with cancer metastasis. In terms of mechanics, RHAMM promotes cancer cell motility through a number of pathways including focal adhesion kinase (FAK), Map kinase (MAPK), pp60(c-src), and the downstream targets of Rho kinase (ROK). RHAMM can also cooperate with CD44 to promote angiogenesis toward the metastatic lesion.
Medical applications
Hyaluronan is found in many tissues of the body, such as skin, cartilage, and the vitreous humour. Therefore, it is well suited to biomedical applications targeting these tissues. The first hyaluronan biomedical product, Healon, was developed in the 1970s and 1980s by PharmaciaPharmacia
Pharmacia was a pharmaceutical and biotechnological company in Sweden.-History:Pharmacia was founded in 1911 in Stockholm, Sweden by pharmacist Gustav Felix Grönfeldt at the Elgen Pharmacy. The company is named after the Greek word φαρμακεία, transliterated pharmakeia, which means 'sorcery'...
, and is approved for use in eye surgery
Eye surgery
Eye surgery, also known as orogolomistician surgery or ocular surgery, is surgery performed on the eye or its adnexa, typically by an ophthalmologist.-Preparation and precautions:...
(i.e., corneal transplantation, cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
surgery, glaucoma
Glaucoma
Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...
surgery, and surgery to repair retinal detachment
Retinal detachment
Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blindness. It is a medical emergency.The retina is a...
). Other biomedical companies also produce brands of hyaluronan for opthalmic surgery.
Native hyaluronan has a relatively short half-life (shown in rabbits) so various manufacturing techniques have been deployed to extend the length of the chain and stabilise the molecule for its use in medical applications. The introduction of protein based cross-links, the introduction of free-radical scavenging molecules such as sorbitol
Sorbitol
Sorbitol, also known as glucitol, Sorbogem® and Sorbo®, is a sugar alcohol that the human body metabolizes slowly. It can be obtained by reduction of glucose, changing the aldehyde group to a hydroxyl group. Sorbitol is found in apples, pears, peaches, and prunes...
and minimal stabilisation of the HA chains through chemical agents e.g. NASHA stabilisation are all techniques that have been used.
In the late 1970s, intraocular lens implantation was often followed by severe corneal edema
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
, due to endothelial cell damage during the surgery. It was evident that a viscous, clear, physiologic lubricant to prevent such scraping of the endothelial cells was needed. Endre Balazs patented a process for purifying hyaluronic acid, a physiologic lubricant (which he called Healon) from rooster combs in the early 1970s. At first, Balazs saw Healon as a noninflammatory vitreous substitute. Claus Dohlman had used Balazs’ Healon in one case in which the anterior chamber flattened after a complicated corneal transplant. Although one might imagine the viscous hyaluronic acid would have caused a rise in IOP
Intraocular pressure
Intraocular pressure is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk from glaucoma...
, Dohlman reported no such rise in his case. Since that time, Balazs had licensed the synthesis process to Pharmacia, a Swedish drug company. Although Pharmacia saw no market for a vitreous substitute, when their scientists figured out a way to increase the viscosity of hyaluronic acid, they felt it might work as an injectable agent in the treatment of both human and equine arthritis
Arthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
. The equine arthritis market proved to be small and the treatment of human osteoarthritis
Osteoarthritis
Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...
produced only marginal improvement, so Pharmacia decided to abandon Healon. At this time, David Miller realized that Healon was the lubricant needed by the eye surgeon.
Balazs arranged to have Pharmacia send 20 sterile vials to Dr. David Miller for rabbit experiments. By 1976, Miller and colleagues published a study showing Healon worked well in protecting the rabbit corneal endothelium during IOL implantation. With a new possible use for Healon, Miller met with Pharmacia and performed a lens extraction and IOL implantation using Healon in a rabbit eye. The demonstration ignited a new enthusiasm for eye surgery with Healon. A small human pilot study at Boston’s Beth Israel Hospital by Miller confirmed Healon’s beneficial effects.
In a large, well-controlled clinical trial, Dr. Robert Stegmann, of Pretoria
Pretoria
Pretoria is a city located in the northern part of Gauteng Province, South Africa. It is one of the country's three capital cities, serving as the executive and de facto national capital; the others are Cape Town, the legislative capital, and Bloemfontein, the judicial capital.Pretoria is...
, South Africa was able to quantify the advantages of Healon in IOL implantation by showing significantly higher postoperative corneal endothelial counts in the Healon eyes as opposed to the controls.
The U.S. Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
quickly approved Healon as a surgical device in 1980, and Healon was successfully launched. By the year 2009, an estimated quarter of a billion patients had benefited from the useful properties of Healon in eye surgery.
In 1992, Miller and Stegmann received the Innovators Award by the American Society of Cataract and Refractive Surgery for developing the use of Healon in repairing injured eyes.
Hyaluronan is also used to treat osteoarthritis
Osteoarthritis
Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...
of the knee. Such treatments, called viscosupplementation, are administered as a course of injections into the knee joint, and are believed to supplement the viscosity of the joint fluid, thereby lubricating the joint, cushioning the joint, and producing an analgesic effect. It has also been suggested that hyaluronan has positive biochemical effects on cartilage cells
Chondrocyte
Chondrocytes are the only cells found in cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans...
. However, some placebo-controlled studies have cast doubt on the efficacy of hyaluronan injections, and hyaluronan is recommended primarily as a last alternative before surgery Oral use of hyaluronan has been lately suggested, although its effectiveness needs to be demonstrated. At present, there are some preliminary clinical studies that suggest oral administration of hyaluronan has a positive effect on osteoarthritis, but it remains to be seen if there is any real benefit from the treatment.
Dry, scaly skin (xerosis
Xerosis
Xerosis cutis is the medical term for dry skin.It can have many different causes, including general dehydration, atopic dermatitis, Vitamin A deficiency, and maybe diabetes. Treatment is primarily symptomatic. "Xero", meaning dry or dehydrated, "osis" usually referring to a medical disease or...
) such as that caused by atopic dermatitis
Atopic dermatitis
Atopic dermatitis is an inflammatory, chronically relapsing, non-contagious and pruritic skin disorder...
(eczema
Eczema
Eczema is a form of dermatitis, or inflammation of the epidermis . In England, an estimated 5.7 million or about one in every nine people have been diagnosed with the disease by a clinician at some point in their lives.The term eczema is broadly applied to a range of persistent skin conditions...
) may be treated with a prescription skin lotion containing sodium hyaluronate as its active ingredient.
Due to its high biocompatibility
Biocompatibility
Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is used , or to more empirical clinical success of a whole device in...
and its common presence in the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
of tissues, hyaluronan is gaining popularity as a biomaterial
Biomaterial
A biomaterial is any matter, surface, or construct that interacts with biological systems. The development of biomaterials, as a science, is about fifty years old. The study of biomaterials is called biomaterials science. It has experienced steady and strong growth over its history, with many...
scaffold in tissue engineering
Tissue engineering
Tissue engineering is the use of a combination of cells, engineering and materials methods, and suitable biochemical and physio-chemical factors to improve or replace biological functions...
research.
Hyaluronan (also called hyaluronic acid or hyaluronate) is an anionic, nonsulfated
Sulfation
Sulfation in biochemistry is the enzyme-catalyzed addition of sulfate to another molecule. It often refers to a phase II enzyme reaction. This biotransformation process uses its cosubstrate 3'-phosphoadenosine-5'-phosphosulfate to transfer sulfate to a xenobiotic...
glycosaminoglycan
Glycosaminoglycan
Glycosaminoglycans or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit. The repeating unit consists of a hexose or a hexuronic acid, linked to a hexosamine .-Production:Protein cores made in the rough endoplasmic reticulum are posttranslationally...
distributed widely throughout connective
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
, epithelial, and neural tissues. It is unique among glycosaminoglycans in that it is nonsulfated, forms in the plasma membrane instead of the Golgi
Golgi apparatus
The Golgi apparatus is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi, after whom the Golgi apparatus is named....
, and can be very large, with its molecular weight often reaching the millions.
One of the chief components of the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
, hyaluronan contributes significantly to cell proliferation and migration, and may also be involved in the progression of some malignant tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
s.
The average 70 kg (154 lbs) person has roughly 15 grams of hyaluronan in the body, one-third of which is turned over (degraded and synthesized) every day. Hyaluronic acid is also a component of the group A streptococcal extracellular capsule, and is believed to play a role in virulence
Virulence
Virulence is by MeSH definition the degree of pathogenicity within a group or species of parasites as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenicity of an organism - its ability to cause disease - is determined by its...
.
Functions
It was first isolated from the vitreous body of the eye by Karl Meyer who called it hyaluronic acid, in 1934.The term hyaluronan was proposed by Dr. Endre A. Balazs in the 1980’s to encompass the different forms the molecule can take, e.g., the acid form, hyaluronic acid, and the salts, such as sodium hyaluronate, which form at physiological pH. Until the late 1970's, “The polysaccharide ofthe vitreous humor,” , hyaluronan was described as a "goo" molecule, a ubiquitous carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
that is part of the extracellular matrix. For example, hyaluronan is a major component of the synovial fluid
Synovial fluid
Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...
, and was found to increase the viscosity of the fluid. Along with lubricin, it is one of the fluid's main lubricating components.
What makes hyaluronan unique?
Hyaluronan is used in medical application for its unique physical/chemical properties. It is very hydrophilic; its viscous solutions have
most unusual rheological properties and are exceedingly lubricious.Hyaluronan is an important component of articular cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
, where it is present as a coat around each cell (chondrocyte
Chondrocyte
Chondrocytes are the only cells found in cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans...
). When aggrecan
Aggrecan
Aggrecan also known as cartilage-specific proteoglycan core protein or chondroitin sulfate proteoglycan 1 is a protein that in humans is encoded by the ACAN gene. This gene is a member of the aggrecan/versican proteoglycan family...
monomers bind to hyaluronan in the presence of link protein, large highly negatively-charged aggregates form. These aggregates imbibe water and are responsible for the resilience
Resilience
Resilience is the property of a material to absorb energy when it is deformed elastically and then, upon unloading to have this energy recovered. In other words, it is the maximum energy per unit volume that can be elastically stored...
of cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
(its resistance to compression). The molecular weight (size) of hyaluronan in cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
decreases with age, but the amount increases.
Hyaluronan is also a major component of skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, where it is involved in tissue repair. When skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
is exposed to excessive UVB rays, it becomes inflamed (sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...
) and the cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
in the dermis stop producing as much hyaluronan, and increase the rate of its degradation. Hyaluronan degradation products also accumulate in the skin after UV exposure.
While it is abundant in extracellular matrices, hyaluronan also contributes to tissue hydrodynamics, movement and proliferation of cells, and participates in a number of cell surface receptor interactions, notably those including its primary receptors, CD44
CD44
The CD44 antigen is a cell-surface glycoprotein involved in cell–cell interactions, cell adhesion and migration. In humans, the CD44 antigen is encoded by the CD44 gene.- Tissue distribution and isoforms :...
and RHAMM. Upregulation of CD44 itself is widely accepted as a marker of cell activation in lymphocytes. Hyaluronan's contribution to tumor growth may be due to its interaction with CD44. Receptor CD44 participates in cell adhesion interactions required by tumor cells.
Although hyaluronan binds to receptor CD44
CD44
The CD44 antigen is a cell-surface glycoprotein involved in cell–cell interactions, cell adhesion and migration. In humans, the CD44 antigen is encoded by the CD44 gene.- Tissue distribution and isoforms :...
, there is evidence hyaluronan degradation products transduce their inflammatory signal through toll-like receptor 2 (TLR2), TLR4 or both TLR2, and TLR4 in macrophages and dendritic cells. TLR and hyaluronan play a role in innate immunity.
High concentrations of hyaluronan in the brains of young rats, and reduced concentrations in the brains of adult rats suggest hyaluronan plays an important role in brain development.
Structure
Properties of hyaluronan were first determined in the 1930s in the laboratory of Karl Meyer.Hyaluronan is a polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
of disaccharide
Disaccharide
A disaccharide or biose is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only. Like monosaccharides, disaccharides form an aqueous solution when dissolved in water...
s, themselves composed of D-glucuronic acid and D-N-acetylglucosamine, linked via alternating β-1,4 and β-1,3 glycosidic bond
Glycosidic bond
In chemistry, a glycosidic bond is a type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate....
s. Hyaluronan can be 25,000 disaccharide repeats in length. Polymers of hyaluronan can range in size from 5,000 to 20,000,000 Da
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
in vivo. The average molecular weight in human synovial fluid
Synovial fluid
Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...
is 3−4 million Da, and hyaluronan purified from human umbilical cord
Umbilical cord
In placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta...
is 3,140,000 Da.
Hyaluronan is energetically stable, in part because of the stereochemistry
Stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms within molecules. An important branch of stereochemistry is the study of chiral molecules....
of its component disaccharides. Bulky groups on each sugar molecule are in sterically favored positions, whereas the smaller hydrogens assume the less-favorable axial positions.
Biological synthesis
Hyaluronan is synthesized by a class of integral membrane proteinIntegral membrane protein
An integral membrane protein is a protein molecule that is permanently attached to the biological membrane. Proteins that cross the membrane are surrounded by "annular" lipids, which are defined as lipids that are in direct contact with a membrane protein...
s called hyaluronan synthase
Hyaluronan synthase
Hyaluronan synthases are membrane-bound enzymes which use UDP-α-N-acetyl-D-glucosamine and UDP-α-D-glucuronate as substrates to produce the glycosaminoglycan hyaluronan at the cell surface and extrude it through the membrane into the extracellular space....
s, of which vertebrates have three types: HAS1, HAS2, and HAS3. These enzymes lengthen hyaluronan by repeatedly adding glucuronic acid
Glucuronic acid
Glucuronic acid is a carboxylic acid. Its structure is similar to that of glucose. However, glucuronic acid's sixth carbon is oxidized to a carboxylic acid...
and N-acetylglucosamine
N-Acetylglucosamine
N-Acetylglucosamine is a monosaccharide derivative of glucose. It is an amide between glucosamine and acetic acid...
to the nascent polysaccharide as it is extruded via ABC-transporter through the cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
into the extracellular space.
Hyaluronan synthesis (HAS) has been shown to be inhibited by 4-methylumbelliferone (hymecromone
Hymecromone
Hymecromone is a drug used in bile therapy. It is used as choleretic and antispasmodic drugs and as a standard for the fluorometric determination of enzyme activity....
, heparvit), a 7-hydroxy-4-methylcoumarin derivative.
This selective inhibition (without inhibiting other glycosaminoglycans) may prove useful in preventing metastasis
Metastasis
Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
of malignant tumor cells.
Bacillus Subtilis
Bacillus subtilis
Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...
recently has been genetically modified (GMO) to culture a proprietary formula to yield hyaluronans, in a patented process producing human-grade product.
Cell receptors for hyaluronan
So far, cell receptors that have been identified for HA fall into three main groups: CD44, Receptor for HA-mediated motility (RHAMM) and intracellular adhesion molecule-1 (ICAM-1). CD44 and ICAM-1 were already known as cell adhesion molecules with other recognized ligands before their HA binding was discovered.CD44 is widely distributed throughout the body, and the formal demonstration of HA-CD44 binding was proposed by Aruffo et al. in 1990. To date, it is recognized as the main cell surface receptor for HA. CD44 mediates cell interaction with HA and the binding of the two functions as an important part in various physiologic events, such as cell aggregation, migration, proliferation and activation; cell-cell and cell-substrate adhesion; endocytosis of HA, which leads to HA catabolism
Catabolism
Catabolism is the set of metabolic pathways that break down molecules into smaller units and release energy. In catabolism, large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides, and amino...
in macrophages; and assembly of petircellular matrices from HA and proteoglycan
Proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...
. Two significant roles of CD44 in skin were proposed by Kaya et al. The first is regulation of keratinocyte
Keratinocyte
Keratinocytes are the predominant cell type in the epidermis, the outermost layer of the human skin, constituting 95% of the cells found there. Those keratinocytes found in the basal layer of the skin are sometimes referred to as "basal cells" or "basal keratinocytes"...
proliferation in response to extracellular stimuli, and the second is the maintenance of local HA homeostasis.
ICAM-1 is known mainly as a metabolic cell surface receptor for HA, and this protein may be responsible mainly for the clearance of HA from lymph and blood plasma, which accounts for perhaps most of its whole-body turnover Ligand binding of this receptor, thus, triggers a highly coordinated cascade of events that includes the formation of an endocytotic vesicle, its fusion with primary lysosomes, enzymatic digestion to monosaccharides, active transmembrane transport of these sugars to cell sap, phosphorylation
Phosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....
of GlcNAc and enzymatic deacetylation
Acetylation
Acetylation describes a reaction that introduces an acetyl functional group into a chemical compound...
. Like its name, ICAM-1 may also serve as a cell adhesion molecule, and the binding of HA to ICAM-1 may contribute to the control of ICAM-1-mediated inflammatory activation.
Degradation
Hyaluronan is degraded by a family of enzymes called hyaluronidaseHyaluronidase
The hyaluronidases are a family of enzymes that degrade hyaluronic acid.In humans, there are six associated genes, including HYAL1, HYAL2, HYAL3, and PH-20/SPAM1.-Use as a drug:...
s. In humans, there are at least seven types of hyaluronidase-like enzymes, several of which are tumor suppressors. The degradation products of hyaluronan, the oligosaccharides and very low-molecular-weight hyaluronan, exhibit pro-angiogenic properties . In addition, recent studies showed hyaluronan fragments, not the native high-molecular mass of hyaluronan, can induce inflammatory responses in macrophages and dendritic cells in tissue injury and in skin transplant rejection .
Role of hyaluronan on wound repair process
Skin provides a mechanical barrier to the external environment and acts to prevent the ingress of infectious agents. Once injured, the tissues beneath are exposed to infection; therefore, rapid and effective healing is of crucial significance to reconstruct a barrier function. Skin wound healing is a complex process, and includes many interacting processes initiated by haemostasis and the release of platelet-derived factors. The following stages are inflammation, granulation tissue formation, reepithelization and remodeling. HA is likely to play a multifaceted role in mediation of these cellular and matrix events. The proposed roles of HA in this sequence of skin wound healing events are elucidated in details below.Inflammation
Many biological factors, such as growth factors, cytokines, eicosanoids etc., are generated in the inflammation process. These factors are necessary for the subsequent steps of wound healing due to their roles in promoting migration of inflammatory cells, fibroblasts, and endothelial cells into the wound site.
The wound tissue in the early inflammatory phase of wound repair is abundant in HA, probably a reflection of increased synthesis. HA acts as a promoter of early inflammation, which is crucial in the whole skin wound-healing process. In a murine air pouch model of carrageenan/IL-1-induced inflammation, HA was observed to enhance cellular infiltration. Kobayashi and colleagues showed a dose-dependent increase of the proinflammatory cytokines TNF-α and IL-8 production by human uterine
Uterine
The word uterine can refer to different meanings:* relating to or near the uterus or womb* having the same mother, but different fathers, see matrilineality...
fibroblasts at HA concentrations of 10μg/ml to 1 mg/ml via a CD44-mediated mechanism. Endothelial cells, in response to inflammatory cytokines such as TNF-α, and bacterial lipopolysaccharide
Lipopolysaccharide
Lipopolysaccharides , also known as lipoglycans, are large molecules consisting of a lipid and a polysaccharide joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, act as endotoxins and elicit strong immune responses in animals.-Functions:LPS is the major...
, also synthesize HA, which has been shown to facilitate primary adhesion of cytokine-activated lymphocytes expressing the HA-binding variants of CD44 under laminar and static flow conditions. It is interesting to note that HA has contradictory dual functions in the inflammatory process. It not only can promote the inflammation, as stated above, but also can moderate the inflammatory response, which may contribute to the stabilization of granulation tissue matrix, as described in the following part.
Granulation and organization of the granulation tissue matrix
Granulation tissue
Granulation tissue
Granulation tissue is the perfused, fibrous connective tissue that replaces a fibrin clot in healing wounds. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any size it heals...
is the perfused
Perfusion
In physiology, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue. The word is derived from the French verb "perfuser" meaning to "pour over or through."...
, fibrous connective tissue that replaces a fibrin
Fibrin
Fibrin is a fibrous, non-globular protein involved in the clotting of blood. It is a fibrillar protein that is polymerised to form a "mesh" that forms a hemostatic plug or clot over a wound site....
clot in healing wounds. It typically grows from the base of a wound and is able to fill wounds of almost any size it heals. HA is abundant in granulation tissue matrix. A variety of cell functions that are essential for tissue repair may attribute to this HA-rich network. These functions include facilitation of cell migration into the provisional wound matrix, cell proliferation and organization of the granulation tissue matrix. Absolutely, initiation of inflammation is extremely crucial for the formation of granulation tissue, therefore the pro-inflammatory role of HA as discussed above also contribute to this stage of wound healing.
HA and cell migration
Cell migration is essential for the formation of granulation tissue. The early stage of granulation tissue is dominated by a HA-rich extracellular matrix, which is regarded as a conducive environment for migration of cells into this temporary wound matrix. Contributions of HA to cell migration may attribute to its physicochemical properties as stated above, as well as its direct interactions with cells. For the former scenario, HA provides an open hydrated matrix that facilitates cell migration, whereas, in the latter scenario, directed migration and control of the cell locomotory mechanisms are mediated via the specific cell interaction between HA and cell surface HA receptors. As discussed before, the three principal cell surface receptors for HA are CD44, RHAMM, and ICAM-1. RHAMM is more related to cell migration. It forms links with several protein kinases associated with cell locomotion, for example, extracellular signal-regulated protein kinase (ERK), p125fak, and pp60c-src. During fetal development, the migration path through which neural crest cells migrate is rich in HA. HA is closely associated with the cell migration process in granulation tissue matrix, and studies show that cell movement can be inhibited, at least partially, by HA degradation or blocking HA receptor occupancy.
By providing the dynamic force to the cell, HA synthesis has also been shown to associate with cell migration. Basically, HA is synthesized at the plasma membrane and released directly into the extracellular environment. This may contribute to the hydrated microenvironment at sites of synthesis, and is essential for cell migration by facilitating cell detachment.
Role of HA in moderation of the inflammatory response
Although inflammation is an integral part of granulation tissue formation, for normal tissue repair to proceed, inflammation needs to be moderated. The initial granulation tissue formed is highly inflammatory with a high rate of tissue turnover mediated by matrix degrading enzymes and reactive oxygen metabolites that are products of inflammatory cells. Stabilization of granulation tissue matrix can be achieved by moderating inflammation. HA functions as an important moderator in this moderation process, which contradicts its role in inflammatory stimulation, as described above. HA can protect against free-radical damage to cells. This may attribute to its free-radical scavenging property, a physicochemical characteristic shared by large polyionic polymers. In a rat model of free-radical scavenging property investigated by Foschi D. and colleagues, HA has been shown to reduce damage to the granulation tissue.
In addition to the free-radical scavenging role, HA may also function in the negative feedback loop of inflammatory activation through its specific biological interactions with the biological constituents of inflammation. TNF-α, an important cytokine generated in inflammation, stimulates the expression of TSG-6 (TNF-stimulated gene 6) in fibroblasts and inflammatory cells. TSG-6, a HA-binding protein, also forms a stable complex with the serum proteinase inhibitor IαI (Inter-α-inhibitor) with a synergistic effect on the latter’s plasmin-inhibitory activity. Plasmin
Plasmin
Plasmin is an important enzyme present in blood that degrades many blood plasma proteins, most notably, fibrin clots. The degradation of fibrin is termed fibrinolysis. In humans, the plasmin protein is encoded by the PLG gene.- Function :...
is involved in activation of the proteolytic
Proteolysis
Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...
cascade of matrix metalloproteinases and other proteinases leading to inflammatory tissue damage. Therefore, the action of TSG-6/ IαI complex, which may be additionally organized by binding to HA in the extracellular matrix, may serve as a potent negative feedback loop to moderate inflammation and stabilize the granulation tissue as healing progresses. In the murine air pouch model of carragenan/IL-1 (Interleukin-1β)-induced inflammation, where HA has been shown to have a proinflammatory property, reduction of inflammation can be achieved by administrating TSG-6, and the result is comparable with systemic dexamethasone treatment.
Reepithelization
HA plays an important role in the normal epidermis. HA also has crucial functions in the reepithelization process due to several of its properties. It serves as an integral part of the extracellular matrix of basal keratinocytes, which are major constituents of the epidermis; its free-radical scavenging function and its role in keratinocyte proliferation and migration.
In normal skin, HA is found in relative high concentrations in the basal layer of the epidermis where proliferating keratinocytes are found. CD44 is collocated with HA in the basal layer of epidermis where additionally it has been shown to be preferentially expressed on plasma membrane facing the HA-rich matrix pouches. Maintaining the extracellular space and providing an open, as well as hydrated, structure for the passage of nutrients are the main functions of HA in epidermis. Tammi R. and other colleagues found HA content increases at the presence of retinoic acid
Retinoic acid
Retinoic acid is a metabolite of vitamin A that mediates the functions of vitamin A required for growth and development. Retinoic acid is required in chordate animals which includes all higher animals from fishes to humans...
(vitamin A). The proposed effects of retinoic acid against skin photo-damage and aging may be correlated, at least in part, with an increase of skin HA content, giving rise to increase of tissue hydration. It has been suggested the free-radical scavenging property of HA contributes to protection against solar radiation, supporting the role of CD44 acting as a HA receptor in the epidermis.
Epidermal HA also functions as a manipulator in the process of keratinocyte proliferation, which is essential in normal epidermal function, as well as during reepithelization in tissue repair. In the wound healing process, HA is expressed in the wound margin, in the connective tissue matrix, and collocating with CD44 expression in migrating keratinocytes. Kaya et al. found suppression of CD44 expression by an epidermis-specific antisense transgene
Transgene
A transgene is a gene or genetic material that has been transferred naturally or by any of a number of genetic engineering techniques from one organism to another....
resulted in animals with defective HA accumulation in the superficial dermis, accompanied by distinct morphologic alterations of basal keratinocytes and defective keratinocyte proliferation in response to mitogen
Mitogen
A mitogen is a chemical substance that encourages a cell to commence cell division, triggering mitosis. A mitogen is usually some form of a protein.Mitogenesis is the induction of mitosis, typically via a mitogen....
and growth factors. Decrease in skin elasticity, impaired local inflammatory response, and impaired tissue repair were also observed. Their observations are strongly supportive of the important roles HA and CD44 have in skin physiology and tissue repair.
Fetal wound healing and scarring
Lack of fibrous scarring is the primary feature of fetal wound healing. Even for longer periods, HA content in fetal wounds is still higher than that in adult wounds, which suggests that HA may, at least in part, reduce collagen deposition and therefore lead to reduced scarring. This suggestion is in agreement with the research of West et al., who showed in adult and late gestation fetal wound healing, removal of HA results in fibrotic scarring. Though the exact role of HA in skin scarring is still under investigation, based on all the facts that have been observed, it must be a great contributor to the less fibrous scarring.
Role of hyaluronan in cancer metastasis
Hyaluronan synthase
Synthase
In biochemistry, a synthase is an enzyme that catalyses a synthesis process.Following the EC number classification, they belong to the group of ligases, with lyases catalysing the reverse reaction....
s (HAS) play roles in all of the stages of cancer metastasis. By producing anti-adhesive HA, HAS can allow tumor cells to release from the primary tumor mass, and if HA associates with receptors such as CD44, the activation of Rho GTPases can promote epithelial-mesenchymal transition (EMT) of the cancer cells. During the processes of intravasation or extravasation
Extravasation
Extravasation is the accidental administration of intravenously infused medicinal drugs into the surrounding tissue, either by leakage , or direct exposure...
, the interaction of HAS produced HA with receptors such as CD44 or RHAMM promote the cell changes that allow for the cancer cells to infiltrate the vascular
Vascular
Vascular in zoology and medicine means "related to blood vessels", which are part of the circulatory system. An organ or tissue that is vascularized is heavily endowed with blood vessels and thus richly supplied with blood....
or lymphatic systems. While traveling in these systems, HA produced by HAS protects the cancer cell from physical damage. Finally, in the formation of a metastatic lesion, HAS produces HA to allow the cancer cell to interact with native cells at the secondary site and to produce a tumor for itself.
Hyaluronidases
HYAL1
Hyaluronidase-1 is an enzyme that in humans is encoded by the HYAL1 gene.- Further reading :...
(HAase or HYAL) also play many roles in cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
metastasis
Metastasis
Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
. By helping to degrade the ECM
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
surrounding the tumor, hyaluronidases help the cancer cell escape from the primary tumor mass and play a major role in intravasation
Intravasation
As a part of the process of metastasis, intravasation refers to the invasion of a cancer through the basal membrane and into blood vessels.In radiology, intravasation is used to describe penetration of radiographic contrast into the soft tissue lymphatics and veins of a hollow organ as a result of...
by allowing degradation of the basement membrane of the lymph or blood vessel. Hyaluronidases again play these roles in establishment of a metastatic lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
by helping with extravasation and clearing the ECM of the secondary site. Finally, hyaluronidases play a key role in the process of angiogenesis
Angiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...
. HA fragments promote angiogenesis and hyaluronidases produce these fragments. Interestingly, hypoxia
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
also increases production of HA and activity of hyaluronidases.
The hyaluronan receptors, CD44 and RHAMM, are most thoroughly studied in terms of their roles in cancer metastasis. Increased clinical CD44 expression has been positively correlated to metastasis in a number of tumor types. In terms of mechanics, CD44 affects adhesion of cancer cells to each other and to endothelial cells, rearranges the cytoskeleton
Cytoskeleton
The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within a cell's cytoplasm and is made out of protein. The cytoskeleton is present in all cells; it was once thought to be unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton...
through the Rho GTPases, and increases the activity of ECM degrading enzymes. Increased RHAMM expression has also been clinically correlated with cancer metastasis. In terms of mechanics, RHAMM promotes cancer cell motility through a number of pathways including focal adhesion kinase (FAK), Map kinase (MAPK), pp60(c-src), and the downstream targets of Rho kinase (ROK). RHAMM can also cooperate with CD44 to promote angiogenesis toward the metastatic lesion.
Medical applications
Hyaluronan is found in many tissues of the body, such as skin, cartilage, and the vitreous humour. Therefore, it is well suited to biomedical applications targeting these tissues. The first hyaluronan biomedical product, Healon, was developed in the 1970s and 1980s by PharmaciaPharmacia
Pharmacia was a pharmaceutical and biotechnological company in Sweden.-History:Pharmacia was founded in 1911 in Stockholm, Sweden by pharmacist Gustav Felix Grönfeldt at the Elgen Pharmacy. The company is named after the Greek word φαρμακεία, transliterated pharmakeia, which means 'sorcery'...
, and is approved for use in eye surgery
Eye surgery
Eye surgery, also known as orogolomistician surgery or ocular surgery, is surgery performed on the eye or its adnexa, typically by an ophthalmologist.-Preparation and precautions:...
(i.e., corneal transplantation, cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
surgery, glaucoma
Glaucoma
Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...
surgery, and surgery to repair retinal detachment
Retinal detachment
Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blindness. It is a medical emergency.The retina is a...
). Other biomedical companies also produce brands of hyaluronan for opthalmic surgery.
Native hyaluronan has a relatively short half-life (shown in rabbits) so various manufacturing techniques have been deployed to extend the length of the chain and stabilise the molecule for its use in medical applications. The introduction of protein based cross-links, the introduction of free-radical scavenging molecules such as sorbitol
Sorbitol
Sorbitol, also known as glucitol, Sorbogem® and Sorbo®, is a sugar alcohol that the human body metabolizes slowly. It can be obtained by reduction of glucose, changing the aldehyde group to a hydroxyl group. Sorbitol is found in apples, pears, peaches, and prunes...
and minimal stabilisation of the HA chains through chemical agents e.g. NASHA stabilisation are all techniques that have been used.
In the late 1970s, intraocular lens implantation was often followed by severe corneal edema
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
, due to endothelial cell damage during the surgery. It was evident that a viscous, clear, physiologic lubricant to prevent such scraping of the endothelial cells was needed. Endre Balazs patented a process for purifying hyaluronic acid, a physiologic lubricant (which he called Healon) from rooster combs in the early 1970s. At first, Balazs saw Healon as a noninflammatory vitreous substitute. Claus Dohlman had used Balazs’ Healon in one case in which the anterior chamber flattened after a complicated corneal transplant. Although one might imagine the viscous hyaluronic acid would have caused a rise in IOP
Intraocular pressure
Intraocular pressure is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk from glaucoma...
, Dohlman reported no such rise in his case. Since that time, Balazs had licensed the synthesis process to Pharmacia, a Swedish drug company. Although Pharmacia saw no market for a vitreous substitute, when their scientists figured out a way to increase the viscosity of hyaluronic acid, they felt it might work as an injectable agent in the treatment of both human and equine arthritis
Arthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
. The equine arthritis market proved to be small and the treatment of human osteoarthritis
Osteoarthritis
Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...
produced only marginal improvement, so Pharmacia decided to abandon Healon. At this time, David Miller realized that Healon was the lubricant needed by the eye surgeon.
Balazs arranged to have Pharmacia send 20 sterile vials to Dr. David Miller for rabbit experiments. By 1976, Miller and colleagues published a study showing Healon worked well in protecting the rabbit corneal endothelium during IOL implantation. With a new possible use for Healon, Miller met with Pharmacia and performed a lens extraction and IOL implantation using Healon in a rabbit eye. The demonstration ignited a new enthusiasm for eye surgery with Healon. A small human pilot study at Boston’s Beth Israel Hospital by Miller confirmed Healon’s beneficial effects.
In a large, well-controlled clinical trial, Dr. Robert Stegmann, of Pretoria
Pretoria
Pretoria is a city located in the northern part of Gauteng Province, South Africa. It is one of the country's three capital cities, serving as the executive and de facto national capital; the others are Cape Town, the legislative capital, and Bloemfontein, the judicial capital.Pretoria is...
, South Africa was able to quantify the advantages of Healon in IOL implantation by showing significantly higher postoperative corneal endothelial counts in the Healon eyes as opposed to the controls.
The U.S. Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
quickly approved Healon as a surgical device in 1980, and Healon was successfully launched. By the year 2009, an estimated quarter of a billion patients had benefited from the useful properties of Healon in eye surgery.
In 1992, Miller and Stegmann received the Innovators Award by the American Society of Cataract and Refractive Surgery for developing the use of Healon in repairing injured eyes.
Hyaluronan is also used to treat osteoarthritis
Osteoarthritis
Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...
of the knee. Such treatments, called viscosupplementation, are administered as a course of injections into the knee joint, and are believed to supplement the viscosity of the joint fluid, thereby lubricating the joint, cushioning the joint, and producing an analgesic effect. It has also been suggested that hyaluronan has positive biochemical effects on cartilage cells
Chondrocyte
Chondrocytes are the only cells found in cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans...
. However, some placebo-controlled studies have cast doubt on the efficacy of hyaluronan injections, and hyaluronan is recommended primarily as a last alternative before surgery Oral use of hyaluronan has been lately suggested, although its effectiveness needs to be demonstrated. At present, there are some preliminary clinical studies that suggest oral administration of hyaluronan has a positive effect on osteoarthritis, but it remains to be seen if there is any real benefit from the treatment.
Dry, scaly skin (xerosis
Xerosis
Xerosis cutis is the medical term for dry skin.It can have many different causes, including general dehydration, atopic dermatitis, Vitamin A deficiency, and maybe diabetes. Treatment is primarily symptomatic. "Xero", meaning dry or dehydrated, "osis" usually referring to a medical disease or...
) such as that caused by atopic dermatitis
Atopic dermatitis
Atopic dermatitis is an inflammatory, chronically relapsing, non-contagious and pruritic skin disorder...
(eczema
Eczema
Eczema is a form of dermatitis, or inflammation of the epidermis . In England, an estimated 5.7 million or about one in every nine people have been diagnosed with the disease by a clinician at some point in their lives.The term eczema is broadly applied to a range of persistent skin conditions...
) may be treated with a prescription skin lotion containing sodium hyaluronate as its active ingredient.
Due to its high biocompatibility
Biocompatibility
Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is used , or to more empirical clinical success of a whole device in...
and its common presence in the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
of tissues, hyaluronan is gaining popularity as a biomaterial
Biomaterial
A biomaterial is any matter, surface, or construct that interacts with biological systems. The development of biomaterials, as a science, is about fifty years old. The study of biomaterials is called biomaterials science. It has experienced steady and strong growth over its history, with many...
scaffold in tissue engineering
Tissue engineering
Tissue engineering is the use of a combination of cells, engineering and materials methods, and suitable biochemical and physio-chemical factors to improve or replace biological functions...
research.
Hyaluronan (also called hyaluronic acid or hyaluronate) is an anionic, nonsulfated
Sulfation
Sulfation in biochemistry is the enzyme-catalyzed addition of sulfate to another molecule. It often refers to a phase II enzyme reaction. This biotransformation process uses its cosubstrate 3'-phosphoadenosine-5'-phosphosulfate to transfer sulfate to a xenobiotic...
glycosaminoglycan
Glycosaminoglycan
Glycosaminoglycans or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit. The repeating unit consists of a hexose or a hexuronic acid, linked to a hexosamine .-Production:Protein cores made in the rough endoplasmic reticulum are posttranslationally...
distributed widely throughout connective
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
, epithelial, and neural tissues. It is unique among glycosaminoglycans in that it is nonsulfated, forms in the plasma membrane instead of the Golgi
Golgi apparatus
The Golgi apparatus is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi, after whom the Golgi apparatus is named....
, and can be very large, with its molecular weight often reaching the millions.
One of the chief components of the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
, hyaluronan contributes significantly to cell proliferation and migration, and may also be involved in the progression of some malignant tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
s.
The average 70 kg (154 lbs) person has roughly 15 grams of hyaluronan in the body, one-third of which is turned over (degraded and synthesized) every day. Hyaluronic acid is also a component of the group A streptococcal extracellular capsule, and is believed to play a role in virulence
Virulence
Virulence is by MeSH definition the degree of pathogenicity within a group or species of parasites as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenicity of an organism - its ability to cause disease - is determined by its...
.
Functions
It was first isolated from the vitreous body of the eye by Karl Meyer who called it hyaluronic acid, in 1934.The term hyaluronan was proposed by Dr. Endre A. Balazs in the 1980’s to encompass the different forms the molecule can take, e.g., the acid form, hyaluronic acid, and the salts, such as sodium hyaluronate, which form at physiological pH. Until the late 1970's, “The polysaccharide ofthe vitreous humor,” , hyaluronan was described as a "goo" molecule, a ubiquitous carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
that is part of the extracellular matrix. For example, hyaluronan is a major component of the synovial fluid
Synovial fluid
Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...
, and was found to increase the viscosity of the fluid. Along with lubricin, it is one of the fluid's main lubricating components.
What makes hyaluronan unique?
Hyaluronan is used in medical application for its unique physical/chemical properties. It is very hydrophilic; its viscous solutions have
most unusual rheological properties and are exceedingly lubricious.Hyaluronan is an important component of articular cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
, where it is present as a coat around each cell (chondrocyte
Chondrocyte
Chondrocytes are the only cells found in cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans...
). When aggrecan
Aggrecan
Aggrecan also known as cartilage-specific proteoglycan core protein or chondroitin sulfate proteoglycan 1 is a protein that in humans is encoded by the ACAN gene. This gene is a member of the aggrecan/versican proteoglycan family...
monomers bind to hyaluronan in the presence of link protein, large highly negatively-charged aggregates form. These aggregates imbibe water and are responsible for the resilience
Resilience
Resilience is the property of a material to absorb energy when it is deformed elastically and then, upon unloading to have this energy recovered. In other words, it is the maximum energy per unit volume that can be elastically stored...
of cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
(its resistance to compression). The molecular weight (size) of hyaluronan in cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
decreases with age, but the amount increases.
Hyaluronan is also a major component of skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, where it is involved in tissue repair. When skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
is exposed to excessive UVB rays, it becomes inflamed (sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...
) and the cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
in the dermis stop producing as much hyaluronan, and increase the rate of its degradation. Hyaluronan degradation products also accumulate in the skin after UV exposure.
While it is abundant in extracellular matrices, hyaluronan also contributes to tissue hydrodynamics, movement and proliferation of cells, and participates in a number of cell surface receptor interactions, notably those including its primary receptors, CD44
CD44
The CD44 antigen is a cell-surface glycoprotein involved in cell–cell interactions, cell adhesion and migration. In humans, the CD44 antigen is encoded by the CD44 gene.- Tissue distribution and isoforms :...
and RHAMM. Upregulation of CD44 itself is widely accepted as a marker of cell activation in lymphocytes. Hyaluronan's contribution to tumor growth may be due to its interaction with CD44. Receptor CD44 participates in cell adhesion interactions required by tumor cells.
Although hyaluronan binds to receptor CD44
CD44
The CD44 antigen is a cell-surface glycoprotein involved in cell–cell interactions, cell adhesion and migration. In humans, the CD44 antigen is encoded by the CD44 gene.- Tissue distribution and isoforms :...
, there is evidence hyaluronan degradation products transduce their inflammatory signal through toll-like receptor 2 (TLR2), TLR4 or both TLR2, and TLR4 in macrophages and dendritic cells. TLR and hyaluronan play a role in innate immunity.
High concentrations of hyaluronan in the brains of young rats, and reduced concentrations in the brains of adult rats suggest hyaluronan plays an important role in brain development.
Structure
Properties of hyaluronan were first determined in the 1930s in the laboratory of Karl Meyer.Hyaluronan is a polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
of disaccharide
Disaccharide
A disaccharide or biose is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only. Like monosaccharides, disaccharides form an aqueous solution when dissolved in water...
s, themselves composed of D-glucuronic acid and D-N-acetylglucosamine, linked via alternating β-1,4 and β-1,3 glycosidic bond
Glycosidic bond
In chemistry, a glycosidic bond is a type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate....
s. Hyaluronan can be 25,000 disaccharide repeats in length. Polymers of hyaluronan can range in size from 5,000 to 20,000,000 Da
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
in vivo. The average molecular weight in human synovial fluid
Synovial fluid
Synovial fluid is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its yolk-like consistency , the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement.-Overview:The inner membrane of synovial joints...
is 3−4 million Da, and hyaluronan purified from human umbilical cord
Umbilical cord
In placental mammals, the umbilical cord is the connecting cord from the developing embryo or fetus to the placenta...
is 3,140,000 Da.
Hyaluronan is energetically stable, in part because of the stereochemistry
Stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms within molecules. An important branch of stereochemistry is the study of chiral molecules....
of its component disaccharides. Bulky groups on each sugar molecule are in sterically favored positions, whereas the smaller hydrogens assume the less-favorable axial positions.
Biological synthesis
Hyaluronan is synthesized by a class of integral membrane proteinIntegral membrane protein
An integral membrane protein is a protein molecule that is permanently attached to the biological membrane. Proteins that cross the membrane are surrounded by "annular" lipids, which are defined as lipids that are in direct contact with a membrane protein...
s called hyaluronan synthase
Hyaluronan synthase
Hyaluronan synthases are membrane-bound enzymes which use UDP-α-N-acetyl-D-glucosamine and UDP-α-D-glucuronate as substrates to produce the glycosaminoglycan hyaluronan at the cell surface and extrude it through the membrane into the extracellular space....
s, of which vertebrates have three types: HAS1, HAS2, and HAS3. These enzymes lengthen hyaluronan by repeatedly adding glucuronic acid
Glucuronic acid
Glucuronic acid is a carboxylic acid. Its structure is similar to that of glucose. However, glucuronic acid's sixth carbon is oxidized to a carboxylic acid...
and N-acetylglucosamine
N-Acetylglucosamine
N-Acetylglucosamine is a monosaccharide derivative of glucose. It is an amide between glucosamine and acetic acid...
to the nascent polysaccharide as it is extruded via ABC-transporter through the cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
into the extracellular space.
Hyaluronan synthesis (HAS) has been shown to be inhibited by 4-methylumbelliferone (hymecromone
Hymecromone
Hymecromone is a drug used in bile therapy. It is used as choleretic and antispasmodic drugs and as a standard for the fluorometric determination of enzyme activity....
, heparvit), a 7-hydroxy-4-methylcoumarin derivative.
This selective inhibition (without inhibiting other glycosaminoglycans) may prove useful in preventing metastasis
Metastasis
Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
of malignant tumor cells.
Bacillus Subtilis
Bacillus subtilis
Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...
recently has been genetically modified (GMO) to culture a proprietary formula to yield hyaluronans, in a patented process producing human-grade product.
Cell receptors for hyaluronan
So far, cell receptors that have been identified for HA fall into three main groups: CD44, Receptor for HA-mediated motility (RHAMM) and intracellular adhesion molecule-1 (ICAM-1). CD44 and ICAM-1 were already known as cell adhesion molecules with other recognized ligands before their HA binding was discovered.CD44 is widely distributed throughout the body, and the formal demonstration of HA-CD44 binding was proposed by Aruffo et al. in 1990. To date, it is recognized as the main cell surface receptor for HA. CD44 mediates cell interaction with HA and the binding of the two functions as an important part in various physiologic events, such as cell aggregation, migration, proliferation and activation; cell-cell and cell-substrate adhesion; endocytosis of HA, which leads to HA catabolism
Catabolism
Catabolism is the set of metabolic pathways that break down molecules into smaller units and release energy. In catabolism, large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides, and amino...
in macrophages; and assembly of petircellular matrices from HA and proteoglycan
Proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...
. Two significant roles of CD44 in skin were proposed by Kaya et al. The first is regulation of keratinocyte
Keratinocyte
Keratinocytes are the predominant cell type in the epidermis, the outermost layer of the human skin, constituting 95% of the cells found there. Those keratinocytes found in the basal layer of the skin are sometimes referred to as "basal cells" or "basal keratinocytes"...
proliferation in response to extracellular stimuli, and the second is the maintenance of local HA homeostasis.
ICAM-1 is known mainly as a metabolic cell surface receptor for HA, and this protein may be responsible mainly for the clearance of HA from lymph and blood plasma, which accounts for perhaps most of its whole-body turnover Ligand binding of this receptor, thus, triggers a highly coordinated cascade of events that includes the formation of an endocytotic vesicle, its fusion with primary lysosomes, enzymatic digestion to monosaccharides, active transmembrane transport of these sugars to cell sap, phosphorylation
Phosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....
of GlcNAc and enzymatic deacetylation
Acetylation
Acetylation describes a reaction that introduces an acetyl functional group into a chemical compound...
. Like its name, ICAM-1 may also serve as a cell adhesion molecule, and the binding of HA to ICAM-1 may contribute to the control of ICAM-1-mediated inflammatory activation.
Degradation
Hyaluronan is degraded by a family of enzymes called hyaluronidaseHyaluronidase
The hyaluronidases are a family of enzymes that degrade hyaluronic acid.In humans, there are six associated genes, including HYAL1, HYAL2, HYAL3, and PH-20/SPAM1.-Use as a drug:...
s. In humans, there are at least seven types of hyaluronidase-like enzymes, several of which are tumor suppressors. The degradation products of hyaluronan, the oligosaccharides and very low-molecular-weight hyaluronan, exhibit pro-angiogenic properties . In addition, recent studies showed hyaluronan fragments, not the native high-molecular mass of hyaluronan, can induce inflammatory responses in macrophages and dendritic cells in tissue injury and in skin transplant rejection .
Role of hyaluronan on wound repair process
Skin provides a mechanical barrier to the external environment and acts to prevent the ingress of infectious agents. Once injured, the tissues beneath are exposed to infection; therefore, rapid and effective healing is of crucial significance to reconstruct a barrier function. Skin wound healing is a complex process, and includes many interacting processes initiated by haemostasis and the release of platelet-derived factors. The following stages are inflammation, granulation tissue formation, reepithelization and remodeling. HA is likely to play a multifaceted role in mediation of these cellular and matrix events. The proposed roles of HA in this sequence of skin wound healing events are elucidated in details below.Inflammation
Many biological factors, such as growth factors, cytokines, eicosanoids etc., are generated in the inflammation process. These factors are necessary for the subsequent steps of wound healing due to their roles in promoting migration of inflammatory cells, fibroblasts, and endothelial cells into the wound site.
The wound tissue in the early inflammatory phase of wound repair is abundant in HA, probably a reflection of increased synthesis. HA acts as a promoter of early inflammation, which is crucial in the whole skin wound-healing process. In a murine air pouch model of carrageenan/IL-1-induced inflammation, HA was observed to enhance cellular infiltration. Kobayashi and colleagues showed a dose-dependent increase of the proinflammatory cytokines TNF-α and IL-8 production by human uterine
Uterine
The word uterine can refer to different meanings:* relating to or near the uterus or womb* having the same mother, but different fathers, see matrilineality...
fibroblasts at HA concentrations of 10μg/ml to 1 mg/ml via a CD44-mediated mechanism. Endothelial cells, in response to inflammatory cytokines such as TNF-α, and bacterial lipopolysaccharide
Lipopolysaccharide
Lipopolysaccharides , also known as lipoglycans, are large molecules consisting of a lipid and a polysaccharide joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, act as endotoxins and elicit strong immune responses in animals.-Functions:LPS is the major...
, also synthesize HA, which has been shown to facilitate primary adhesion of cytokine-activated lymphocytes expressing the HA-binding variants of CD44 under laminar and static flow conditions. It is interesting to note that HA has contradictory dual functions in the inflammatory process. It not only can promote the inflammation, as stated above, but also can moderate the inflammatory response, which may contribute to the stabilization of granulation tissue matrix, as described in the following part.
Granulation and organization of the granulation tissue matrix
Granulation tissue
Granulation tissue
Granulation tissue is the perfused, fibrous connective tissue that replaces a fibrin clot in healing wounds. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any size it heals...
is the perfused
Perfusion
In physiology, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue. The word is derived from the French verb "perfuser" meaning to "pour over or through."...
, fibrous connective tissue that replaces a fibrin
Fibrin
Fibrin is a fibrous, non-globular protein involved in the clotting of blood. It is a fibrillar protein that is polymerised to form a "mesh" that forms a hemostatic plug or clot over a wound site....
clot in healing wounds. It typically grows from the base of a wound and is able to fill wounds of almost any size it heals. HA is abundant in granulation tissue matrix. A variety of cell functions that are essential for tissue repair may attribute to this HA-rich network. These functions include facilitation of cell migration into the provisional wound matrix, cell proliferation and organization of the granulation tissue matrix. Absolutely, initiation of inflammation is extremely crucial for the formation of granulation tissue, therefore the pro-inflammatory role of HA as discussed above also contribute to this stage of wound healing.
HA and cell migration
Cell migration is essential for the formation of granulation tissue. The early stage of granulation tissue is dominated by a HA-rich extracellular matrix, which is regarded as a conducive environment for migration of cells into this temporary wound matrix. Contributions of HA to cell migration may attribute to its physicochemical properties as stated above, as well as its direct interactions with cells. For the former scenario, HA provides an open hydrated matrix that facilitates cell migration, whereas, in the latter scenario, directed migration and control of the cell locomotory mechanisms are mediated via the specific cell interaction between HA and cell surface HA receptors. As discussed before, the three principal cell surface receptors for HA are CD44, RHAMM, and ICAM-1. RHAMM is more related to cell migration. It forms links with several protein kinases associated with cell locomotion, for example, extracellular signal-regulated protein kinase (ERK), p125fak, and pp60c-src. During fetal development, the migration path through which neural crest cells migrate is rich in HA. HA is closely associated with the cell migration process in granulation tissue matrix, and studies show that cell movement can be inhibited, at least partially, by HA degradation or blocking HA receptor occupancy.
By providing the dynamic force to the cell, HA synthesis has also been shown to associate with cell migration. Basically, HA is synthesized at the plasma membrane and released directly into the extracellular environment. This may contribute to the hydrated microenvironment at sites of synthesis, and is essential for cell migration by facilitating cell detachment.
Role of HA in moderation of the inflammatory response
Although inflammation is an integral part of granulation tissue formation, for normal tissue repair to proceed, inflammation needs to be moderated. The initial granulation tissue formed is highly inflammatory with a high rate of tissue turnover mediated by matrix degrading enzymes and reactive oxygen metabolites that are products of inflammatory cells. Stabilization of granulation tissue matrix can be achieved by moderating inflammation. HA functions as an important moderator in this moderation process, which contradicts its role in inflammatory stimulation, as described above. HA can protect against free-radical damage to cells. This may attribute to its free-radical scavenging property, a physicochemical characteristic shared by large polyionic polymers. In a rat model of free-radical scavenging property investigated by Foschi D. and colleagues, HA has been shown to reduce damage to the granulation tissue.
In addition to the free-radical scavenging role, HA may also function in the negative feedback loop of inflammatory activation through its specific biological interactions with the biological constituents of inflammation. TNF-α, an important cytokine generated in inflammation, stimulates the expression of TSG-6 (TNF-stimulated gene 6) in fibroblasts and inflammatory cells. TSG-6, a HA-binding protein, also forms a stable complex with the serum proteinase inhibitor IαI (Inter-α-inhibitor) with a synergistic effect on the latter’s plasmin-inhibitory activity. Plasmin
Plasmin
Plasmin is an important enzyme present in blood that degrades many blood plasma proteins, most notably, fibrin clots. The degradation of fibrin is termed fibrinolysis. In humans, the plasmin protein is encoded by the PLG gene.- Function :...
is involved in activation of the proteolytic
Proteolysis
Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...
cascade of matrix metalloproteinases and other proteinases leading to inflammatory tissue damage. Therefore, the action of TSG-6/ IαI complex, which may be additionally organized by binding to HA in the extracellular matrix, may serve as a potent negative feedback loop to moderate inflammation and stabilize the granulation tissue as healing progresses. In the murine air pouch model of carragenan/IL-1 (Interleukin-1β)-induced inflammation, where HA has been shown to have a proinflammatory property, reduction of inflammation can be achieved by administrating TSG-6, and the result is comparable with systemic dexamethasone treatment.
Reepithelization
HA plays an important role in the normal epidermis. HA also has crucial functions in the reepithelization process due to several of its properties. It serves as an integral part of the extracellular matrix of basal keratinocytes, which are major constituents of the epidermis; its free-radical scavenging function and its role in keratinocyte proliferation and migration.
In normal skin, HA is found in relative high concentrations in the basal layer of the epidermis where proliferating keratinocytes are found. CD44 is collocated with HA in the basal layer of epidermis where additionally it has been shown to be preferentially expressed on plasma membrane facing the HA-rich matrix pouches. Maintaining the extracellular space and providing an open, as well as hydrated, structure for the passage of nutrients are the main functions of HA in epidermis. Tammi R. and other colleagues found HA content increases at the presence of retinoic acid
Retinoic acid
Retinoic acid is a metabolite of vitamin A that mediates the functions of vitamin A required for growth and development. Retinoic acid is required in chordate animals which includes all higher animals from fishes to humans...
(vitamin A). The proposed effects of retinoic acid against skin photo-damage and aging may be correlated, at least in part, with an increase of skin HA content, giving rise to increase of tissue hydration. It has been suggested the free-radical scavenging property of HA contributes to protection against solar radiation, supporting the role of CD44 acting as a HA receptor in the epidermis.
Epidermal HA also functions as a manipulator in the process of keratinocyte proliferation, which is essential in normal epidermal function, as well as during reepithelization in tissue repair. In the wound healing process, HA is expressed in the wound margin, in the connective tissue matrix, and collocating with CD44 expression in migrating keratinocytes. Kaya et al. found suppression of CD44 expression by an epidermis-specific antisense transgene
Transgene
A transgene is a gene or genetic material that has been transferred naturally or by any of a number of genetic engineering techniques from one organism to another....
resulted in animals with defective HA accumulation in the superficial dermis, accompanied by distinct morphologic alterations of basal keratinocytes and defective keratinocyte proliferation in response to mitogen
Mitogen
A mitogen is a chemical substance that encourages a cell to commence cell division, triggering mitosis. A mitogen is usually some form of a protein.Mitogenesis is the induction of mitosis, typically via a mitogen....
and growth factors. Decrease in skin elasticity, impaired local inflammatory response, and impaired tissue repair were also observed. Their observations are strongly supportive of the important roles HA and CD44 have in skin physiology and tissue repair.
Fetal wound healing and scarring
Lack of fibrous scarring is the primary feature of fetal wound healing. Even for longer periods, HA content in fetal wounds is still higher than that in adult wounds, which suggests that HA may, at least in part, reduce collagen deposition and therefore lead to reduced scarring. This suggestion is in agreement with the research of West et al., who showed in adult and late gestation fetal wound healing, removal of HA results in fibrotic scarring. Though the exact role of HA in skin scarring is still under investigation, based on all the facts that have been observed, it must be a great contributor to the less fibrous scarring.
Role of hyaluronan in cancer metastasis
Hyaluronan synthase
Synthase
In biochemistry, a synthase is an enzyme that catalyses a synthesis process.Following the EC number classification, they belong to the group of ligases, with lyases catalysing the reverse reaction....
s (HAS) play roles in all of the stages of cancer metastasis. By producing anti-adhesive HA, HAS can allow tumor cells to release from the primary tumor mass, and if HA associates with receptors such as CD44, the activation of Rho GTPases can promote epithelial-mesenchymal transition (EMT) of the cancer cells. During the processes of intravasation or extravasation
Extravasation
Extravasation is the accidental administration of intravenously infused medicinal drugs into the surrounding tissue, either by leakage , or direct exposure...
, the interaction of HAS produced HA with receptors such as CD44 or RHAMM promote the cell changes that allow for the cancer cells to infiltrate the vascular
Vascular
Vascular in zoology and medicine means "related to blood vessels", which are part of the circulatory system. An organ or tissue that is vascularized is heavily endowed with blood vessels and thus richly supplied with blood....
or lymphatic systems. While traveling in these systems, HA produced by HAS protects the cancer cell from physical damage. Finally, in the formation of a metastatic lesion, HAS produces HA to allow the cancer cell to interact with native cells at the secondary site and to produce a tumor for itself.
Hyaluronidases
HYAL1
Hyaluronidase-1 is an enzyme that in humans is encoded by the HYAL1 gene.- Further reading :...
(HAase or HYAL) also play many roles in cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
metastasis
Metastasis
Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
. By helping to degrade the ECM
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
surrounding the tumor, hyaluronidases help the cancer cell escape from the primary tumor mass and play a major role in intravasation
Intravasation
As a part of the process of metastasis, intravasation refers to the invasion of a cancer through the basal membrane and into blood vessels.In radiology, intravasation is used to describe penetration of radiographic contrast into the soft tissue lymphatics and veins of a hollow organ as a result of...
by allowing degradation of the basement membrane of the lymph or blood vessel. Hyaluronidases again play these roles in establishment of a metastatic lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
by helping with extravasation and clearing the ECM of the secondary site. Finally, hyaluronidases play a key role in the process of angiogenesis
Angiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...
. HA fragments promote angiogenesis and hyaluronidases produce these fragments. Interestingly, hypoxia
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
also increases production of HA and activity of hyaluronidases.
The hyaluronan receptors, CD44 and RHAMM, are most thoroughly studied in terms of their roles in cancer metastasis. Increased clinical CD44 expression has been positively correlated to metastasis in a number of tumor types. In terms of mechanics, CD44 affects adhesion of cancer cells to each other and to endothelial cells, rearranges the cytoskeleton
Cytoskeleton
The cytoskeleton is a cellular "scaffolding" or "skeleton" contained within a cell's cytoplasm and is made out of protein. The cytoskeleton is present in all cells; it was once thought to be unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton...
through the Rho GTPases, and increases the activity of ECM degrading enzymes. Increased RHAMM expression has also been clinically correlated with cancer metastasis. In terms of mechanics, RHAMM promotes cancer cell motility through a number of pathways including focal adhesion kinase (FAK), Map kinase (MAPK), pp60(c-src), and the downstream targets of Rho kinase (ROK). RHAMM can also cooperate with CD44 to promote angiogenesis toward the metastatic lesion.
Medical applications
Hyaluronan is found in many tissues of the body, such as skin, cartilage, and the vitreous humour. Therefore, it is well suited to biomedical applications targeting these tissues. The first hyaluronan biomedical product, Healon, was developed in the 1970s and 1980s by PharmaciaPharmacia
Pharmacia was a pharmaceutical and biotechnological company in Sweden.-History:Pharmacia was founded in 1911 in Stockholm, Sweden by pharmacist Gustav Felix Grönfeldt at the Elgen Pharmacy. The company is named after the Greek word φαρμακεία, transliterated pharmakeia, which means 'sorcery'...
, and is approved for use in eye surgery
Eye surgery
Eye surgery, also known as orogolomistician surgery or ocular surgery, is surgery performed on the eye or its adnexa, typically by an ophthalmologist.-Preparation and precautions:...
(i.e., corneal transplantation, cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
surgery, glaucoma
Glaucoma
Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...
surgery, and surgery to repair retinal detachment
Retinal detachment
Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blindness. It is a medical emergency.The retina is a...
). Other biomedical companies also produce brands of hyaluronan for opthalmic surgery.
Native hyaluronan has a relatively short half-life (shown in rabbits) so various manufacturing techniques have been deployed to extend the length of the chain and stabilise the molecule for its use in medical applications. The introduction of protein based cross-links, the introduction of free-radical scavenging molecules such as sorbitol
Sorbitol
Sorbitol, also known as glucitol, Sorbogem® and Sorbo®, is a sugar alcohol that the human body metabolizes slowly. It can be obtained by reduction of glucose, changing the aldehyde group to a hydroxyl group. Sorbitol is found in apples, pears, peaches, and prunes...
and minimal stabilisation of the HA chains through chemical agents e.g. NASHA stabilisation are all techniques that have been used.
In the late 1970s, intraocular lens implantation was often followed by severe corneal edema
Edema
Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
, due to endothelial cell damage during the surgery. It was evident that a viscous, clear, physiologic lubricant to prevent such scraping of the endothelial cells was needed. Endre Balazs patented a process for purifying hyaluronic acid, a physiologic lubricant (which he called Healon) from rooster combs in the early 1970s. At first, Balazs saw Healon as a noninflammatory vitreous substitute. Claus Dohlman had used Balazs’ Healon in one case in which the anterior chamber flattened after a complicated corneal transplant. Although one might imagine the viscous hyaluronic acid would have caused a rise in IOP
Intraocular pressure
Intraocular pressure is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk from glaucoma...
, Dohlman reported no such rise in his case. Since that time, Balazs had licensed the synthesis process to Pharmacia, a Swedish drug company. Although Pharmacia saw no market for a vitreous substitute, when their scientists figured out a way to increase the viscosity of hyaluronic acid, they felt it might work as an injectable agent in the treatment of both human and equine arthritis
Arthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
. The equine arthritis market proved to be small and the treatment of human osteoarthritis
Osteoarthritis
Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...
produced only marginal improvement, so Pharmacia decided to abandon Healon. At this time, David Miller realized that Healon was the lubricant needed by the eye surgeon.
Balazs arranged to have Pharmacia send 20 sterile vials to Dr. David Miller for rabbit experiments. By 1976, Miller and colleagues published a study showing Healon worked well in protecting the rabbit corneal endothelium during IOL implantation. With a new possible use for Healon, Miller met with Pharmacia and performed a lens extraction and IOL implantation using Healon in a rabbit eye. The demonstration ignited a new enthusiasm for eye surgery with Healon. A small human pilot study at Boston’s Beth Israel Hospital by Miller confirmed Healon’s beneficial effects.
In a large, well-controlled clinical trial, Dr. Robert Stegmann, of Pretoria
Pretoria
Pretoria is a city located in the northern part of Gauteng Province, South Africa. It is one of the country's three capital cities, serving as the executive and de facto national capital; the others are Cape Town, the legislative capital, and Bloemfontein, the judicial capital.Pretoria is...
, South Africa was able to quantify the advantages of Healon in IOL implantation by showing significantly higher postoperative corneal endothelial counts in the Healon eyes as opposed to the controls.
The U.S. Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
quickly approved Healon as a surgical device in 1980, and Healon was successfully launched. By the year 2009, an estimated quarter of a billion patients had benefited from the useful properties of Healon in eye surgery.
In 1992, Miller and Stegmann received the Innovators Award by the American Society of Cataract and Refractive Surgery for developing the use of Healon in repairing injured eyes.
Hyaluronan is also used to treat osteoarthritis
Osteoarthritis
Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...
of the knee. Such treatments, called viscosupplementation, are administered as a course of injections into the knee joint, and are believed to supplement the viscosity of the joint fluid, thereby lubricating the joint, cushioning the joint, and producing an analgesic effect. It has also been suggested that hyaluronan has positive biochemical effects on cartilage cells
Chondrocyte
Chondrocytes are the only cells found in cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans...
. However, some placebo-controlled studies have cast doubt on the efficacy of hyaluronan injections, and hyaluronan is recommended primarily as a last alternative before surgery Oral use of hyaluronan has been lately suggested, although its effectiveness needs to be demonstrated. At present, there are some preliminary clinical studies that suggest oral administration of hyaluronan has a positive effect on osteoarthritis, but it remains to be seen if there is any real benefit from the treatment.
Dry, scaly skin (xerosis
Xerosis
Xerosis cutis is the medical term for dry skin.It can have many different causes, including general dehydration, atopic dermatitis, Vitamin A deficiency, and maybe diabetes. Treatment is primarily symptomatic. "Xero", meaning dry or dehydrated, "osis" usually referring to a medical disease or...
) such as that caused by atopic dermatitis
Atopic dermatitis
Atopic dermatitis is an inflammatory, chronically relapsing, non-contagious and pruritic skin disorder...
(eczema
Eczema
Eczema is a form of dermatitis, or inflammation of the epidermis . In England, an estimated 5.7 million or about one in every nine people have been diagnosed with the disease by a clinician at some point in their lives.The term eczema is broadly applied to a range of persistent skin conditions...
) may be treated with a prescription skin lotion containing sodium hyaluronate as its active ingredient.
Due to its high biocompatibility
Biocompatibility
Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is used , or to more empirical clinical success of a whole device in...
and its common presence in the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
of tissues, hyaluronan is gaining popularity as a biomaterial
Biomaterial
A biomaterial is any matter, surface, or construct that interacts with biological systems. The development of biomaterials, as a science, is about fifty years old. The study of biomaterials is called biomaterials science. It has experienced steady and strong growth over its history, with many...
scaffold in tissue engineering
Tissue engineering
Tissue engineering is the use of a combination of cells, engineering and materials methods, and suitable biochemical and physio-chemical factors to improve or replace biological functions...
research. In particular, a number of research groups have found hyaluronan's properties for tissue engineering
Tissue engineering
Tissue engineering is the use of a combination of cells, engineering and materials methods, and suitable biochemical and physio-chemical factors to improve or replace biological functions...
and regenerative medicine
Regenerative medicine
Regenerative medicine is the "process of replacing or regenerating human cells, tissues or organs to restore orestablish normal function". This field holds the promise of regenerating damaged tissues and organs in the body by replacing damaged tissue and/or by stimulating the body's own repair...
are significantly improved with crosslinking, producing a hydrogel. This added feature allows a researcher to form a desired shape, as well as to deliver therapeutic molecules, into a host. Hyaluronan can be crosslinked by attaching thiol
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...
s (trade names: Extracel, HyStem), methacrylate
Methacrylate
Methacrylates are the salts or esters of methacrylic acid.Methacrylates contain methyl-vinyl groups, that is, two carbon atoms double bonded to each other, directly attached to the carbonyl carbon, and wherein the vinyl group is substituted with a non-terminal methyl group.Methacrylates are common...
s, and tyramine
Tyramine
Tyramine is a naturally occurring monoamine compound and trace amine derived from the amino acid tyrosine. Tyramine acts as a catecholamine releasing agent...
s (trade name: Corgel). Hyaluronan can also be crosslinked directly with formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...
(trade name: Hylan-A) or with divinylsulfone
Sulfone
A sulfone is a chemical compound containing a sulfonyl functional group attached to two carbon atoms. The central hexavalent sulfur atom is double bonded to each of two oxygen atoms and has a single bond to each of two carbon atoms, usually in two separate hydrocarbon substituents.-IUPAC name and...
(trade name: Hylan-B).
In some cancers, hyaluronan levels correlate well with malignancy and poor prognosis. Hyaluronan is, thus, often used as a tumor marker
Tumor marker
A tumor marker is a substance found in the blood, urine, or body tissues that can be elevated in cancer, among other tissue types. There are many different tumor markers, each indicative of a particular disease process, and they are used in oncology to help detect the presence of cancer...
for prostate
Prostate cancer
Prostate cancer is a form of cancer that develops in the prostate, a gland in the male reproductive system. Most prostate cancers are slow growing; however, there are cases of aggressive prostate cancers. The cancer cells may metastasize from the prostate to other parts of the body, particularly...
and breast cancer
Breast cancer
Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...
. It may also be used to monitor the progression of the disease.
Hyaluronan may also be used postoperatively to induce tissue healing, notably after cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
surgery. Current models of wound healing propose the larger polymers of hyaluronic acid appear in the early stages of healing to physically make room for white blood cells, which mediate the immune response.
Hyaluronan has also been used in the synthesis of biological scaffolds for wound-healing applications. These scaffolds typically have proteins such as fibronectin
Fibronectin
Fibronectin is a high-molecular weight glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins. In addition to integrins, fibronectin also binds extracellular matrix components such as collagen, fibrin and heparan sulfate proteoglycans...
attached to the hyaluronan to facilitate cell migration into the wound
Wound healing
Wound healing, or cicatrisation, is an intricate process in which the skin repairs itself after injury. In normal skin, the epidermis and dermis exists in a steady-state equilibrium, forming a protective barrier against the external environment...
. This is particularly important for individuals with diabetes suffering from chronic wound
Chronic wound
A chronic wound is a wound that does not heal in an orderly set of stages and in a predictable amount of time the way most wounds do; wounds that do not heal within three months are often considered chronic....
s.
In 2007, the EMA
European Medicines Agency
The European Medicines Agency is a European agency for the evaluation of medicinal products. From 1995 to 2004, the European Medicines Agency was known as European Agency for the Evaluation of Medicinal Products.Roughly parallel to the U.S...
extended its approval of Hylan GF-20 as a treatment for ankle and shoulder osteoarthritis pain.
Hyaluronan is also used in anti-adhesive products such as Hyalobarrier
Hyalobarrier
Hyalobarrier is a substance to keep tissue apart post surgery and therefore prevent adhesions. It contains autocross-linked hyaluronan. Highly viscous due to condensation. Hyaluronan is present in cartilage and skin hence there is a natural metabolic pathway for it...
, widely used in pelvic and abdominal surgery to prevent postoperative adhesions.
In May, 2011, Dr Endre Balazs was awarded the Helen Keller
Helen Keller
Helen Adams Keller was an American author, political activist, and lecturer. She was the first deafblind person to earn a Bachelor of Arts degree....
Award for Vision Research for his work in championing the development of hyaluronan and Healon. The award was presented by the Helen Keller Foundation for Research and education.
Cosmetic applications
Hyaluronan is a common ingredient in skin-care products.In 2003, the FDA approved hyaluronan injections for filling soft tissue defects such as facial wrinkles. Restylane
Restylane
Restylane is the trade name for a range of injectable fillers with a specific formulation of non-animal sourced hyaluronic acid . Restylane was the first stabilized hyaluronic acid filler on the market and reportedly has been used in over 11 million treatments worldwide .In the United States,...
is a common trade name for the product. Hyaluronan injections temporarily smooth wrinkles by adding volume under the skin, with effects typically lasting for six months.
Juvéderm
Juvéderm
Juvéderm , one of the newest of the so-called “injectable fillers,” is used by cosmetic, dermatological and plastic surgeons to soften deep folds and reduce wrinkles in the faces of patients. The substance is largely hyaluronic acid, a substance normally found in the skin, muscles, and tendons of...
is a bacterial hyaluronic acid injectable filler, similar to Restylane, but differing slightly in terms of effect and longevity. It is used for lip augmentation, reduction of folds and wrinkles, and removal of scars. The effects of Juvéderm treatments are also temporary, and costs are similar to those of Restylane.
The presence of hyaluronic acid in epithelial tissue has been shown to promote keratinocyte proliferation and increase the presence of retinoic acid, effecting skin hydration. Hyaluronic acid's interaction with CD44
CD44
The CD44 antigen is a cell-surface glycoprotein involved in cell–cell interactions, cell adhesion and migration. In humans, the CD44 antigen is encoded by the CD44 gene.- Tissue distribution and isoforms :...
drives collagen synthesis and normal skin function. Present in the extracellular matrix of basal keratinocytes, hyaluronic acid is critical to the structural integrity of the dermal collagen matrix. These benefits make hyaluronic acid a very effective topical humectant
Humectant
A humectant is a hygroscopic substance. It is often a molecule with several hydrophilic groups, most often hydroxyl groups, but amines and carboxyl groups, sometimes esterified, can be encountered as well; the affinity to form hydrogen bonds with molecules of water is crucial here.Since...
; however, results may only be sustained as part of an ongoing treatment program.
Equine applications
Hyaluronan is used in treatment of articular disorders in horses, in particular those in competition or heavy work. It is indicated for carpal and fetlockFetlock
Fetlock is the common name for the metacarpophalangeal and metatarsophalangeal joints of horses, large animals, and sometimes dogs. It is formed by the junction of the third metacarpal or metatarsal bones proximad and the proximal phalanx distad...
joint dysfunctions, but not when joint sepsis
Sepsis
Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...
or fracture are suspected. It is especially used for synovitis
Synovitis
Synovitis is the medical term for inflammation of the synovial membrane. This membrane lines joints which possess cavities, known as synovial joints. The condition is usually painful, particularly when the joint is moved. The joint usually swells due to synovial fluid collection.Synovitis may...
associated with equine osteoarthritis
Osteoarthritis
Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...
. It can be injected directly into an affected joint, or intravenously for less localized disorders. It may cause mild heating of the joint if directly injected, but this does not affect the clinical outcome. Intra-articularly administered medicine is fully metabolized in less than a week.
Note that, according to Canadian regulation, hyaluronan in HY-50 preparation should not be administered to animals to be slaughtered for horse meat
Horse meat
Horse meat is the culinary name for meat cut from a horse. It is a major meat in only a few countries, notably in Central Asia, but it forms a significant part of the culinary traditions of many others, from Europe to South America to Asia. The top eight countries consume about 4.7 million horses...
. In Europe, however, the same preparation is not considered to have any such effect, and edibility of the horse meat
Horse meat
Horse meat is the culinary name for meat cut from a horse. It is a major meat in only a few countries, notably in Central Asia, but it forms a significant part of the culinary traditions of many others, from Europe to South America to Asia. The top eight countries consume about 4.7 million horses...
is not affected.
Etymology
Hyaluronic acid is derived from hyalos (Greek for vitreous) and uronic acidUronic acid
thumb|300px|The [[Fischer projection]]s of [[glucose]] and [[glucuronic acid]]. Glucose's terminal carbon's hydroxyl group has been oxidized to a [[carboxylic acid]]....
because it was first isolated from the vitreous humour
Vitreous humour
The vitreous humour or vitreous humor is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates...
and possesses a high uronic acid content.
The term hyaluronate refers to the conjugate base
Conjugate acid
Within the Brønsted–Lowry acid-base theory , a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. A conjugate acid can also be seen as the chemical substance that releases, or donates, a proton in the forward chemical...
of hyaluronic acid. Because the molecule typically exists in vivo in its polyanionic form, it is most commonly referred to as hyaluronan.
External links
- ATC codes: , , ,