Involvement of Intrinsically Generated Reactive Oxygen Species in Reoxygenation- and Reperfusion-Mediated Cardiac Injury (Superoxide Dismutase, Catalase, Allopurinol, Ischemia, Free Radicals).

Abstract

The administration of a hydrogen peroxide-metabolizing enzyme, catalase; an inhibitor of xanthine oxidase, allopurinol; or a chelator of ferric iron, deferoxamine, reduced myocardial cell injury reflected as creatine phosphokinase release from isolated buffer-perfused rabbit hearts in a model of global hypoxia and reperfusion. Reduced creatine phosphokinase leakage was not accompanied by parallel preservation of ventricular function or coronary vascular resistance. Administration of catalase during hypoxia was superior to administering it during reoxygenation; no additional protection was provided by administration during both hypoxia and reoxygenation. Catalase likewise enhanced the efficacy of a hypothermic crystalloid cardioplegic solution to preserve the functional integrity of globally ischemic and reperfused hearts as assessed by myocardial contractility, compliance, dP/dt, heart rate and coronary flow. Partial protection against ischemic injury in this model was afforded by allopurinol. Deferoxamine prevented ischemia-induced increases of coronary vascular resistance. In contrast, an enzymatic catalyst for the conversion of superoxide anion to hydrogen peroxide, superoxide dismutase, conferred no protection in either model. Thus, protective effects in two models of oxygen-associated cardiac damage were obtained with interventions which suppressed hydrogen peroxide formation, facilitated its degradation, or interfered with its ability to react with iron salts to form hydroxyl radical. Following two hours of global normothermic ischemia and reperfusion, activities of endogenous glutathione peroxidase, a hydrogen peroxide-metabolizing enzyme, and endogenous superoxide dismutase were reduced by 39 (+OR-) 6%, and 43 (+OR-) 14% (mean (+OR-) SEM), respectively, in mitochondrial fractions of heart homogenate. While superoxide dismutase activities were unchanged in crude homogenate, nuclear and cytosolic fractions of ischemic myocardium, postischemic glutathione peroxidase activities were diminished in all fractions. The diffuse cellular reduction of glutathione peroxidase activity and mitochondrial losses of glutathione peroxidase and superoxide dismutase activities found to accompany ischemic insult indicate that cellular hydrogen peroxide metabolism in general, and mitochondrial antioxidative defenses in particular, are impaired under such conditions. These results, obtained in asanguineous models of oxygen deprivation and repletion, collectively suggest that a significant component of reoxygenation- or reperfusion-induced cardiac cell damage is dependent on endogenously generated hydrogen peroxide, and may involve the formation of hydroxyl radical. Interception of cardiac ischemic injury mediated by such cytotoxic oxygen metabolities may have clinical application with regard to the intraoperative practice of elective cardiac arrest and resuscitation.