ELECTRON-SPIN-RESONANCE SPECTROSCOPIC DEMONSTRATION OF THE GENERATIONOF REACTIVE OXYGEN SPECIES BY DISEASED HUMAN SYNOVIAL TISSUE FOLLOWING EX-VIVO HYPOXIA-REOXYGENATION

Objective-To apply an electron spin resonance (ESR) spectroscopic tech nique as a means of determining the oxidising capacity of reactive oxy gen species produced during hypoxia and reoxygenation of diseased huma n synovial tissue. Methods-Twenty four specimens of fresh synovial tis sue were obtained from patients undergoing primary total knee joint re placement and graded according to the degree of inflammation present. Tissue samples were subjected to an ex vivo hypoxia-reoxygenation cycl e in the presence of the nitroso based spin trap, 3,5-dibromo-4-nitros obenzene sulphonate. The degree of oxidation of the spin trap to a sta ble free radical was determined and followed with time. Control sample s were subjected to hypoxia only. Results-The results indicate that th e oxidising capacity of reactive oxygen species produced by human syno vial tissue varies with the degree of inflammation present. Only the m ore inflamed specimens, from both rheumatoid arthritis and osteoarthri tis patients, demonstrated increased production of reactive oxygen spe cies when subjected to a hypoxia-reoxygenation cycle. This change was reduced by both competitive and non-competitive inhibitors of the endo thelial based enzyme xanthine oxidase. The relative concentration of r eactive oxygen species generated by the synovial tissue samples correl ated with the mean capillary density of the specimens. Conclusion-This study supports the hypothesis of movement induced hypoxic-reperfusion injury of the chronically inflamed joint by demonstrating the generat ion of reactive oxygen species within inflamed human synovium followin g an ex vivo hypoxia-reoxygenation cycle. Evidence is presented that t he microvascular endothelial based enzyme xanthine oxidase is the pred ominant source of ESR detectable oxidising species in inflamed synovia l specimens exposed to hypoxia-reoxygenation.