Substrate reduction therapy
Encyclopedia
Substrate reduction therapy offers an approach to treatment of certain metabolic disorders, especially glycogen storage diseases and lysosomal storage disorders. In a storage disorder, a critical failure in a metabolic pathway
prevents cellular breakdown and disposal of some large molecule. If residual breakdown through other pathways is insufficient to prevent harmful accumulation, the molecule accumulates in the cell and eventually interferes with normal biological processes. Examples of lysosomal storage disorders include Gaucher's disease
, Tay-Sachs disease
, and Sandhoff disease
.
In a metabolic or genetic pathway, enzymes catalyze a series of reactions. Each enzyme is regulated or mediated by one gene through its RNA and protein products. At each phase in the pathway, enzyme activity catalyzes a reaction in which a precursor molecule (the substrate
) is transformed into its next intermediate state. Failure of the metabolic pathway leads to accumulation of the substrate, with possible harmful effects. Substrate reduction therapy addresses this failure by reducing the level of the substrate to a point where residual degradative activity is sufficient to prevent substrate accumulation.
Metabolic pathway
In biochemistry, metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by a series of chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function...
prevents cellular breakdown and disposal of some large molecule. If residual breakdown through other pathways is insufficient to prevent harmful accumulation, the molecule accumulates in the cell and eventually interferes with normal biological processes. Examples of lysosomal storage disorders include Gaucher's disease
Gaucher's disease
Gaucher's disease is a genetic disease in which a fatty substance accumulates in cells and certain organs.Gaucher's disease is the most common of the lysosomal storage diseases. It is caused by a hereditary deficiency of the enzyme glucosylceramidase. The enzyme acts on the fatty acid...
, Tay-Sachs disease
Tay-Sachs disease
Tay–Sachs disease is an autosomal recessive genetic disorder...
, and Sandhoff disease
Sandhoff disease
Sandhoff disease, also known as Sandhoff-Jatzkewitz disease, variant 0 of GM2-Gangliosidosis or Hexosaminidase A and B deficiency, is a lysosomal genetic, lipid storage disorder caused by the inherited deficiency to create functional beta-hexosaminidases A and B...
.
In a metabolic or genetic pathway, enzymes catalyze a series of reactions. Each enzyme is regulated or mediated by one gene through its RNA and protein products. At each phase in the pathway, enzyme activity catalyzes a reaction in which a precursor molecule (the substrate
Substrate (biochemistry)
In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or...
) is transformed into its next intermediate state. Failure of the metabolic pathway leads to accumulation of the substrate, with possible harmful effects. Substrate reduction therapy addresses this failure by reducing the level of the substrate to a point where residual degradative activity is sufficient to prevent substrate accumulation.
Examples
- Tay-Sachs diseaseTay-Sachs diseaseTay–Sachs disease is an autosomal recessive genetic disorder...
. The disease occurs when harmful quantities of a fatty acidFatty acidIn chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
derivative called a gangliosideGangliosideGanglioside is a molecule composed of a glycosphingolipid with one or more sialic acids linked on the sugar chain. The 60+ known gangliosides differ mainly in the position and number of NANA residues.It is a component of the cell plasma membrane that modulates cell signal transduction events...
accumulate in the nerve cells of the brainBrainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. Gangliosides are lipids, components of cellular membranes, and the gangliosideGangliosideGanglioside is a molecule composed of a glycosphingolipid with one or more sialic acids linked on the sugar chain. The 60+ known gangliosides differ mainly in the position and number of NANA residues.It is a component of the cell plasma membrane that modulates cell signal transduction events...
GM2, implicated in Tay-Sachs diseaseTay-Sachs diseaseTay–Sachs disease is an autosomal recessive genetic disorder...
, is especially common in the nervous tissueNervous tissueNervous tissue is one of four major classes of vertebrate tissue.Nervous tissue is the main component of the nervous system - the brain, spinal cord, and nerves-which regulates and controls body functions...
of the brainBrainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. By manipulating the brain's metabolism of GM2 gangliosideGangliosideGanglioside is a molecule composed of a glycosphingolipid with one or more sialic acids linked on the sugar chain. The 60+ known gangliosides differ mainly in the position and number of NANA residues.It is a component of the cell plasma membrane that modulates cell signal transduction events...
s, an effective therapy could potentially be developed. One experiment has demonstrated that, by using the enzyme sialidaseSialidaseSialidases hydrolyse alpha--, alpha--, alpha--glycosidic linkages of terminal sialic residues in oligosaccharides, glycoproteins, glycolipids, colominic acid and synthetic substrates...
, the genetic defect can be effectively bypassed and GM2 gangliosideGangliosideGanglioside is a molecule composed of a glycosphingolipid with one or more sialic acids linked on the sugar chain. The 60+ known gangliosides differ mainly in the position and number of NANA residues.It is a component of the cell plasma membrane that modulates cell signal transduction events...
s can be metabolized so that they become almost inconsequential. If a safe pharmacological treatment can be developed, one that causes the increased expression of lysosomal sialidase in neurons, a new form of therapy, essentially curing the disease, could be on the horizon. Metabolic therapies under investigation for Late-Onset TSD include treatment with the drug OGT 918 (Zavesca).