Hydrogen peroxide is the major oxidant product of xanthine oxidase

Xanthine oxidise (XO) is a critical source of reactive oxygen species (ROS) in inflammatory disease Focus, however. has centered almost exclusively on XO-derived superoxide (O-2(center dot-)), whereas direct H2O2 production from XO has been less well investigated Therefore, we examined the relative quantities of O-2(center dot-) and H2O2 produced by XO under a range (1-21%) of O-2 tensions At O-2 concentrations between 10 and 21%, H2O2 accounted for similar to 75% of ROS production As O-2 concentrations were lowered, there was a concentration-dependent increase in H2O2 formation, accounting for 90% of ROS production at 1% O-2. Alterations in pH between 5.5 and 7.4 did not affect the relative proportions of H2O2 and O-2(center dot-) formation. Immobilization of XO. by binding to heparin-Sepharose. further enhanced relative H2O2 production by similar to 30%, under both normoxic and hypoxic conditions Furthermore. XO bound to glycosaminoglycans on the apical surface of bovine aortic endothelial cells demonstrated a similar ROS production profile. These data establish H2O2 as the dominant (70-95%) reactive product produced by XO tinder clinically relevant conditions and emphasize the importance of H2O2 as a critical factor when examining the contributory roles of XO-catalyzed ROS in inflammatory processes as well as cellular signaling. Published by Elsevier Inc.