Degradation of hyaluronic acid, poly- and monosaccharides, and model compounds by hypochlorite: evidence for radical intermediates and fragmentation

TY - JOUR

T1 - Degradation of hyaluronic acid, poly- and monosaccharides, and model compounds by hypochlorite

T2 - evidence for radical intermediates and fragmentation

AU - Hawkins, C L

AU - Davies, Michael Jonathan

PY - 1998/6

Y1 - 1998/6

N2 - 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.

AB - 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.

KW - Acetamides

KW - Electron Spin Resonance Spectroscopy

KW - Ferrous Compounds

KW - Free Radicals

KW - Hyaluronic Acid

KW - Hydroxyl Radical

KW - Hypochlorous Acid

KW - Monosaccharides

KW - Oxidation-Reduction

KW - Polysaccharides

KW - Spectrophotometry, Ultraviolet

KW - Spin Trapping

M3 - Journal article

C2 - 9641257

SN - 0891-5849

VL - 24

SP - 1396

EP - 1410

JO - Free Radical Biology & Medicine

JF - Free Radical Biology & Medicine

IS - 9

ER -