Glycosaminoglycans (inci)

Glycosaminoglycans (GAGs) are a group of high-molecular substances made up of repeating, linear disaccharide units. The disaccharide repeating units consist of esters of a uronic acid, which are linked together 1-4-glycosidically. This is usually glucuronic acid, more rarely iduronic acid. The disaccharide units are linked 1-3-glycosidically with an amino sugar (e.g. N-acetylglucosamine). Glycosaminoglycans are often further esterified with sulphuric acid or acetic acid.

Due to the numerous hydroxyl, carboxy or sulphate group side chains, the glycosminoglycan molecules are negatively charged. Glycosaminoglycans form glycoproteins and proteoglycans with proteins.

Biological significance and composition of the various glycosaminoglycan subgroups Subgroups of glycosaminoglycans:

Hyaluronic acid (HA) - is the only glycosaminoglycan not bound to a protein central filament. Occurrence: Synovial fluid, vitreous humor, umbilical cord

Heparin/heparan sulphate - consisting of D-glucuronic acid, which is linked to the amino sugar glucosamine. The amino group of glucosamine can carry both an acetyl group and a sulphate group - glucosamine sulphate (GS)

Chondroitin-4-sulphate/dermatan sulphate, constituents: chondroitin sulphate A, glucuronic acid, N-acetylgalactosamine with a sulphate group at C4. Occurrence: cartilage, large vessels

Chondroitin-6-sulfate, components: glucuronic acid, N-acetylgalactosamine with a sulfate group at C6. Occurrence: Heart valves

Keratan sulphate (KS), constituents: galactose, N-acetylglucosamine with sulphate groups on galactose and N-acetylglucosamine. Occurrence: Cornea, nucleus pulposus, cartilage.

Medical: Diseases associated with disorders of the metabolism of glycosaminoglycans (lysosomal storage diseases):

M. Pfaundler-Hurler: In the autosomal recessive inherited mutations of the α-iduronidase gene (gene locus: 4p16.3) M. Pfaundler-Hurler) of lysosomal storage disease (mucopolysaccharidosis type I), the glycosaminoglycans dermatan sulfate and heparan sulfate are deposited lysosomally in the skin and internal organs.

M. Hunter: In Hunter's disease, a mutation-related misexpression of the lysosomal iduronate-2-sulfatase (gene locus Xq27.3-28), there is also impaired degradation of the glycosaminoglycans dermatan sulfate and heparan sulfate. This results in progressive organ damage, especially to the kidneys, liver, lungs and skeletal system.

Other diseases associated with disorders of the metabolism of glycosaminoglycans:

• Sanfilippo's disease (MPS III)
• Morquio's disease (MPS IV)
• Maroteaux-Lamy disease (MPS VI)
• Sly's disease (MPS VII)

The role of glycosaminoglycans in Alzheimer's disease has not yet been definitively clarified.

Cosmetics. Glycosaminoglycans are used in cosmetic formulations. They act as emollients (make the skin supple and smooth it), film formers (they form a film on the skin, hair or nails when applied) and skin care products.

1. Zhou X et al. (2016) The Structure-Activity Relationship of Glycosaminoglycans and Their Analogues with β-Amyloid Peptide. Protein Pept Lett 23:358-364.