Copper Enhances Isoproterenol Toxicity in Isolated Rat Cardiomyocytes: Effects on Oxidative Stress

Sustained high levels of circulating catecholamines may result in cardiotoxicity. Although cardiotoxicity could occur primarily via adrenoceptor activation, there is increasing evidence that it may also occur through oxidative mechanisms. In fact, catecholamines can be converted into aminochromes by auto-oxidation, enzymatically or metal catalyzed, with the concomitant production of reactive intermediates and free radicals. Nevertheless, there is only scarce information concerning the effects of the catecholamine oxidation process on isolated cardiomyocytes. The aim of this work was to evaluate the cardiotoxic effects of isoproterenol (ISO) and its oxidation process in freshly isolated adult rat cardiomyocytes by assessing the cell shape, lactate dehydrogenase leakage, reduced and oxidized glutathione content, and glutathione reductase, peroxidase, and transferase activities. ISO was incubated at concentrations of 0.1, 0.5, and 1 mM in cardiomyocyte suspensions at subphysiological and physiological Ca2+ concentrations for 4 h. The same study was repeated in the presence of 20 microM of Cu2+. The levels of ISO in the incubation medium were monitored throughout the assays. Isoproterenol (1 mM) induced both glutathione oxidation and conjugation, but this effect decreased at subphysiological Ca2+ concentrations. The concomitant incubation with Cu2+ increased ISO oxidation and increased the glutathione oxidation but decreased the extent of glutathione conjugation. Although only a partial ISO oxidation was observed for all studied ISO concentrations in the presence of copper, the underlying oxidative process or its oxidation products, or both, were sufficient to induce a loss of cardiomyocyte viability and a decrease in the glutathione reductase, peroxidase, and transferase activities. Thus, the results suggest that the oxidation of catecholamines could be a major mechanism for catecholamine-induced cardiotoxicity.