Hyaluronidase as a vitreous liquefactant

Abstract

Hyaluronan (HA) is a member of the glycosaminoglycan (GAG) family of polysaccharides, which are composed of repeating disaccharide units, each consisting of hexosamine (usually N-acetylglucosamine or N-acetylgalactosamine) glycosidically linked to either uronic (glucuronic or iduronic) acid or galactose. The nature of the predominant repeating unit is characteristic for each GAG, and the relative amount, molecular size, and type of GAG are said to be tissue specific. GAGs do not normally occur in vivo as free polymers but are covalently linked to a protein core, the ensemble called a proteoglycan [see chapter I.F. Vitreous biochemistry and artificial vitreous]. HA is a GAG that plays an important role as a structural macromolecule in the vitreous. HA is a long, unbranched polymer of the repeating disaccharide glucuronic acid beta 1,3 N-acetylglucosamine, linked by beta l,4 bonds. Its interactions with collagen and other molecular components of the vitreous account for the gel state of the transparent extracellular matrix that is the vitreous [see chapter I.F. Vitreous biochemistry and artificial vitreous], although HA does not likely play a role in mediating vitreoretinal adhesion [see chapter II.E. Vitreo-retinal interface and ILM].