Mitochondrial hydrogen peroxide generation and activities of glutathione peroxidase and superoxide dismutase following global ischemia

We used isolated,buffer-perfused rabbit hearts to evaluate whether global, normothermic ischemia altered mitochondrial hydrogen peroxide (H 2O 2) generation and mitochondrial activities of the major enzymes responsible for degrading H 2O 2 and superoxide anion (O 2 .−): glutathione peroxidase (GPD) and superoxide dismutase (SOD), respectively. This preparation lacks exogenous neutrophils and endogenous xanthine oxidase, which are other potential sources of oxygen metabolites. Ischemia depressed mitochondrial oxidative phosphorylation parameters, State 4 succinate-supported H 2O 2 generation rates, and the relative flux of State 4 oxygen consumption that was diverted to H 2O 2 formation. The production of H 2O 2 was not abolished. Ischemia and reperfusion significantly reduced the activities of SOD (by 43%) and GPD (by 39%) in the mitochondrial fraction. Cytosolic GPD activity was also depressed. The results suggest that the myocardial cell's ability to enzymatically degrade H 2O 2 and O 2 .− is compromised,particularly in the mitochondrion. Although mitochondrial H 2O 2 production is decreased, the mitochondria may persist as a source of this oxygen metabolite following ischemia. Collectively, the data may help explain why mitochondria are vulnerable targets of free radical-mediated damage due to ischemia.