Neomycin
Overview
Neomycin is an aminoglycoside
Aminoglycoside
An aminoglycoside is a molecule or a portion of a molecule composed of amino-modifiedsugars.Several aminoglycosides function as antibiotics that are effective against certain types of bacteria...

 antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...

 that is found in many topical medications such as creams, ointments, and eyedrops. The discovery of Neomycin dates back to 1949. It was discovered in the lab of Selman Waksman, who was later awarded the Nobel Prize in Physiology and medicine in 1951. Neomycin, belongs to aminoglycoside class of antibiotics which contain two or more aminosugars connected by glycosidic bonds.
Encyclopedia
Neomycin is an aminoglycoside
Aminoglycoside
An aminoglycoside is a molecule or a portion of a molecule composed of amino-modifiedsugars.Several aminoglycosides function as antibiotics that are effective against certain types of bacteria...

 antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...

 that is found in many topical medications such as creams, ointments, and eyedrops. The discovery of Neomycin dates back to 1949. It was discovered in the lab of Selman Waksman, who was later awarded the Nobel Prize in Physiology and medicine in 1951. Neomycin, belongs to aminoglycoside class of antibiotics which contain two or more aminosugars connected by glycosidic bonds. Neamine (two rings), Ribostamycin (three rings), Paromomycin (four rings) and Lividomycin (five rings) are some other examples of aminoglycosides. They have shown tremendous potential as antibacterials. One of them, Gentamicin
Gentamicin
Gentamicin is an aminoglycoside antibiotic, used to treat many types of bacterial infections, particularly those caused by Gram-negative organisms. However, gentamicin is not used for Neisseria gonorrhoeae, Neisseria meningitidis or Legionella pneumophila...

 has been used extensively in clinical practice. Due to the inherent oto and nephrotoxicity of these substances, systemic use has declined as safer alternatives have become available.

Uses

Neomycin is overwhelmingly used as a topical
Topical
In medicine, a topical medication is applied to body surfaces such as the skin or mucous membranes such as the vagina, anus, throat, eyes and ears.Many topical medications are epicutaneous, meaning that they are applied directly to the skin...

 preparation, such as Neosporin
Neosporin
Neosporin is the product branding & formulas now owned by Johnson & Johnson of an antibiotic over-the-counter topical created under Warner-Lambert Consumer Healthcare, now a part of Pfizer...

. It can also be given orally, where it is usually combined with other antibiotics. Neomycin is not absorbed from the gastrointestinal tract and has been used as a preventive measure for hepatic encephalopathy
Hepatic encephalopathy
Hepatic encephalopathy is the occurrence of confusion, altered level of consciousness and coma as a result of liver failure. In the advanced stages it is called hepatic coma or coma hepaticum...

 and hypercholesterolemia
Hypercholesterolemia
Hypercholesterolemia is the presence of high levels of cholesterol in the blood. It is not a disease but a metabolic derangement that can be caused by many diseases, notably cardiovascular disease...

. By killing bacteria in the intestinal tract, it keeps ammonia levels low and prevents hepatic encephalopathy, especially prior to GI surgery. It has also been used to treat small intestinal bacterial overgrowth. It is not given intravenously, as neomycin is extremely nephrotoxic (causes kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

 damage), especially compared to other aminoglycoside
Aminoglycoside
An aminoglycoside is a molecule or a portion of a molecule composed of amino-modifiedsugars.Several aminoglycosides function as antibiotics that are effective against certain types of bacteria...

s. The exception is when neomycin is included, in very small quantities, as a preservative in some vaccines - typically 0.025 mg per dose.

Molecular biology

Neomycin resistance is conferred by either one of two aminoglycoside phosphotransferase genes. A neo gene is commonly included in DNA plasmid
Plasmid
In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...

s used by molecular biologists to establish stable mammalian cell lines expressing cloned proteins in culture; many commercially available protein expression plasmids contain neo as a selectable marker
Selectable marker
A selectable marker is a gene introduced into a cell, especially a bacterium or to cells in culture, that confers a trait suitable for artificial selection. They are a type of reporter gene used in laboratory microbiology, molecular biology, and genetic engineering to indicate the success of a...

. Non-transfected cells will eventually die off when the culture is treated with neomycin or similar antibiotic. Neomycin or kanamycin
Kanamycin
Kanamycin sulfate is an aminoglycoside antibiotic, available in oral, intravenous, and intramuscular forms, and used to treat a wide variety of infections. Kanamycin is isolated from Streptomyces kanamyceticus.-Mechanism:...

 can be used for prokaryotes, but geneticin (G418) is, in general, needed for eukaryotes.

Spectrum

Similar to other aminoglycosides, neomycin has excellent activity against Gram-negative bacteria, and has partial activity against Gram-positive bacteria. It is relatively toxic to humans, and many people have allergic reactions to it. See: Hypersensitivity
Hypersensitivity
Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...

. Physicians sometimes recommend using antibiotic ointments without neomycin, such as Polysporin
Polysporin
Polysporin is a line of antibiotic ointments produced by Johnson & Johnson used in the prevention of infection and speeding the healing of wounds. The original formulation contains bacitracin and polymyxin B....

.

History

Neomycin was discovered in 1949 by the microbiologist Selman Waksman
Selman Waksman
Selman Abraham Waksman was an American biochemist and microbiologist whose research into organic substances—largely into organisms that live in soil—and their decomposition promoted the discovery of Streptomycin, and several other antibiotics...

 and his student Hubert Lechevalier at Rutgers University. It is produced naturally by the bacterium Streptomyces fradiae
Streptomyces fradiae
Streptomyces fradiae is a species of actinobacteria. It produces the antibiotics neomycin, tylosin and fosfomycin ....

.

Neomycin as a DNA binder

Neomycin belongs to the family of aminoglycosides. This family includes many other medicinally important drugs: streptomycin
Streptomycin
Streptomycin is an antibiotic drug, the first of a class of drugs called aminoglycosides to be discovered, and was the first antibiotic remedy for tuberculosis. It is derived from the actinobacterium Streptomyces griseus. Streptomycin is a bactericidal antibiotic. Streptomycin cannot be given...

, paromomycin
Paromomycin sulfate
Paromomycin is an aminoglycoside antibiotic, first isolated from Streptomyces krestomuceticus in the 1950s. It is also called monomycin and aminosidine;-Uses:...

 and kanamycin
Kanamycin
Kanamycin sulfate is an aminoglycoside antibiotic, available in oral, intravenous, and intramuscular forms, and used to treat a wide variety of infections. Kanamycin is isolated from Streptomyces kanamyceticus.-Mechanism:...

. Aminoglycosides are known for their ability to bind to duplex RNA with high affinity. A study done by Daniel Pilch, Associate Professor Dept. of Pharmacology at Rutgers University, and his coworkers determined the association constant for neomycin with A-site RNA was found to be in the ~109 range. However, more than 50 years after its discovery, its DNA-binding properties were still unknown. In 2000, Dev P. Arya, currently Director of the Laboratory of Medicinal Chemistry at Clemson University, and his coworkers discovered that neomycin induces enormous thermal stabilization of triplex DNA while having little or almost no effect on the DNA duplex stabilization. They also showed that neomycin binds to structures that adopt A-form structure, triplex DNA being one of them. They later went on to show that neomycin even induces DNA:RNA hybrid triplex formation.
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