Advantages in the use of carvedilol versus propranolol for the protection of cardiac mitochondrial function.

BACKGROUND Carvedilol is a neurohormonal antagonist of multiple action which is used in clinical practice for the treatment of congestive heart failure, mild to moderate hypertension and myocardial infarction. Previous results from our group have demonstrated that one of the main targets for the protective effect of carvedilol is the cardiac mitochondrial network. In-this work, we compare the effect of carvedilol with propranolol in different models of mitochondrial dysfunction and in the generation of transmembrane electric potential (EP). We further tested if carvedilol was able to inhibit the mitochondrial permeability transition (MPT) induced by doxorubicin and calcium-dependent cytochrome c release, a phenomenon frequently associated with apoptotic cell death. METHODS Cardiac mitochondria were isolated by differential centrifugation. Oxygen consumption and mitochondrial EP were determined using an oxygen electrode and a tetraphenylphosphonium-sensitive electrode, respectively. Changes in mitochondrial volume and the release of cytochrome c were measured with spectrophotometric techniques. RESULTS Propranolol, compared with carvedilol, had only a marginal effect, not only in protection against MPT induction, but also against oxygen consumption linked to the oxidation of external NADH, a process that is considered by several authors as key in the cardiotoxicity of doxorubicin. Regarding EP generation, propranolol had no effect, in contrast to carvedilol, which was confirmed to act as a protonophore. For the first time we also show that carvedilol inhibits the MPT induced by doxorubicin and calcium-dependent cytochrome c release. CONCLUSIONS With this work, we further support the notion that carvedilol is effective in several models of mitochondrial dysfunction, particularly those involving oxidative stress. The results demonstrate that for some pathological conditions, carvedilol and propranolol have different mechanisms of action at the sub-cellular level, as propranolol seems to lack effectiveness in the protection of cardiac mitochondria.