Allopurinol attenuates oxidative injury in rat hearts suffered ischemia/reperfusion via suppressing the xanthine oxidase/vascular peroxidase 1 pathway

Allopurinol, a xanthine oxidase (XO) inhibitor, is reported to alleviate myocardial ischemia/reperfusion (I/R) injury by reducing the production of reactive oxygen species (ROS). As an XO-derived product, H2O2 can act as a substrate of vascular peroxidase 1 (VPO1) to induce the generation of hypochlorous acid (HOCl), a potent oxidant. This study aims to explore whether the XO/VPO1 pathway is involved in the anti-oxidative effects of allopurinol on the myocardial I/R injury. In a rat heart model of I/R, allopurinol alleviated I/R oxidative injury accompanied by decreased XO activity, XO-derived products (H2O2 and uric acid), and VPO1 expression (mRNA and protein). In a cardiac cell model of hypoxia/reoxygenation (H/R), allopurinol or XO siRNA reduced H/R injury concomitant with decreased XO activity, VPO1 expression as well as the XO and VPO1-derived products (H2O2, uric acid, and HOCl). Although knockdown of VPO1 could also exert a beneficial effect on H/R injury, it did not affect XO activity, XO expression, and XO-derived products. Based on these observations, we conclude that the novel pathway of XO/VPO1 is responsible for, at least partly, myocardial I/R-induced oxidative injury, and allopurinol exerted the cardioprotective effects on myocardial I/R injury via inhibiting the XO/VPO1 pathway.