OBJECTIVE--To apply an electron spin resonance (ESR) spectroscopic technique as a means of determining the oxidising capacity of reactive oxygen species produced during hypoxia and reoxygenation of diseased human synovial tissue. METHODS--Twenty four specimens of fresh synovial tissue were obtained from patients undergoing primary total knee joint replacement and graded according to the degree of inflammation present. Tissue samples were subjected to an ex vivo hypoxia-reoxygenation cycle in the presence of the nitroso based spin trap, 3,5-dibromo-4-nitrosobenzene sulphonate. The degree of oxidation of the spin trap to a stable free radical was determined and followed with time. Control samples were subjected to hypoxia only. RESULTS--The results indicate that the oxidising capacity of reactive oxygen species produced by human synovial tissue varies with the degree of inflammation present. Only the more inflamed specimens, from both rheumatoid arthritis and osteoarthritis patients, demonstrated increased production of reactive oxygen species when subjected to a hypoxia-reoxygenation cycle. This change was reduced by both competitive and non-competitive inhibitors of the endothelial based enzyme xanthine oxidase. The relative concentration of reactive oxygen species generated by the synovial tissue samples correlated with the mean capillary density of the specimens. CONCLUSION--This study supports the hypothesis of movement induced hypoxicreperfusion injury of the chronically inflamed joint by demonstrating the generation of reactive oxygen species within inflamed human synovium following an ex vivo hypoxia-reoxygenation cycle. Evidence is presented that the microvascular endothelial based enzyme xanthine oxidase is the predominant source of ESR detectable oxidising species in inflamed synovial specimens exposed to hypoxia-reoxygenation.
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