HYDROXYL RADICAL FORMATION IN CHONDROCYTES AND CARTILAGE AS DETECTED BY ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY USING SPIN-TRAPPING REAGENTS

Chondrocytes have been shown to produce superoxide and hydrogen peroxi de, suggesting possible formation of hydroxyl radical in these cells, in this study, we used electron spin resonance/spin trapping technique to detect hydroxyl radicals in chondrocytes. We found that hydroxyl r adicals could be detected as a-hydroxyethyl spin trapped adduct of 4-p yridyl 1-oxide N-tert-butylnitrone (4-POBN) in chondrocytes stimulated with phorbol 12-myristate 13-acetate in the presence of ferrous ion. The formation of hydroxyl radical appears to be mediated by the transi tion metal-catalyzed Haber-Weiss reaction since no hydroxyl radical wa s detected in the absence of exogenous iron. The hydroxyl radical form ation was inhibited by catalase but not by superoxide dismutase, sugge sting that the hydrogen peroxide is the precursor. Cytokines, IL-1 and TNF enhanced the hydroxyl radical formation in phorbol 12-myristate 1 3-acetate treated chondrocytes. Interestingly, hydroxyl radical could be detected in unstimulated fresh human and rabbit cartilage tissue pi eces in the presence of iron. These results suggest that the formation of hydroxyl radical in cartilage could play a role in cartilage matri x degradation.