Effects of xanthine: xanthine oxidase on membrane function: an in vitro model of endothelial damage

Endothelial damage caused by the oxidative species from activated granulocytes has been studied in vitro using the cell-free oxygen radical generating system, xanthine: xanthine oxidase and cultured porcine aortic endothelium. Increasing concentrations of xanthine oxidase caused dose dependent effects on the following functions, 86Rb efflux, prostaglandin production, release of 3H from adenine nucleotides, adenine uptake, 51chromium release and cell morphology. The threshold concentration of xanthine oxidase required for these effects varied by approximately 30 fold, 86Rb+ efflux being affected first at 0.003 units/ml of enzyme. Xanthine oxidase alone had a dose-dependent effect on 86Rb+ efflux which was heat labile and potentiated by xanthine. Neither superoxide dismutase (SOD) nor catalase (CAT) affected the response to xanthine: xanthine oxidase but a mixture of SOD and CAT reduced it by approximately 50% to the response to enzyme alone. Therefore the effect of xanthine: xanthine oxidase has at least two components, one due to enzyme alone and one due to the oxidation of xanthine, probably resulting from an interaction of oxygen radicals and hydrogen peroxide.