Degradation of hyaluronic acid, poly- and monosaccharides, and model compounds by hypochlorite: evidence for radical intermediates and fragmentation.
Degradation of hyaluronic acid by oxidants such as HO. and HOCl/CIO- is believed to be important in the progression of rheumatoid arthritis. While reaction of hyaluronic acid with HO. has been investigated extensively, reaction with HOCl/ClO- is less well defined. Thus, little is known about the site(s) of HOCl/ClO- attack, the intermediates formed, or the mechanism(s) of polymer degradation. In this study reaction of HOCl/ClO- with amides, sugars, polysaccharides, and hyaluronic acid has been monitored by UV-visible (220-340 nm) and EPR spectroscopy. UV-visible experiments have shown that HOCl/ClO- reacts preferentially with N-acetyl groups. This reaction is believed to give rise to transient chloramide (R-NCl-C(O)-R') species, which decompose rapidly to give radicals via either homolysis (to produce N. and Cl.) or heterolysis (one-electron reduction, to give N. and Cl.) of the N--C bond. The nature of the radicals formed has been investigated by EPR spin trapping. Reaction of HOCl/ClO- with hyaluronic acid, chondroitin sulphates A and C, N-acetyl sugars, and amides gave novel, carbon-centered, spin adducts, the formation of which is consistent with selective initial attack at the N-acetyl group. Thus, reaction with hyaluronic acid and chondroitin sulphate A, appears to be localized at the N-acetylglucosamine sugar rings. These carbon-centered radicals are suggested to arise from rapid rearrangement of initial nitrogen-centered radicals, formed from the N-acetyl chloramide, by reactions analogous to those observed with alkoxyl radicals. The detection of increasing yields of low-molecular-weight radical adducts from hyaluronic acid and chondroitin sulphate A with increasing HOCl/ClO-concentrations suggests that formation of the initial nitrogen-centered species on the N-acetylglucosamine rings, and the carbon-centered radicals derived from them, brings about polymer fragmentation.
Hawkins
C L
CL
EPR Group, The Heart Research Institute, Camperdown, Sydney, NSW, Australia.
Davies
M J
MJ
D000081:Acetamides / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005296:Ferrous Compounds / Q000737:chemistry; D005609:Free Radicals / Q000378:metabolism; D006820:Hyaluronic Acid / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry; D006997:Hypochlorous Acid / Q000737:chemistry*; D009005:Monosaccharides / Q000737:chemistry*; D010084:Oxidation-Reduction; D011134:Polysaccharides / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D019097:Spin Trapping
D000081:Acetamides; D005296:Ferrous Compounds; D005609:Free Radicals; D009005:Monosaccharides; D011134:Polysaccharides; D017665:Hydroxyl Radical; D006997:Hypochlorous Acid; D006820:Hyaluronic Acid