Doxorubicin-derived metabolites induce release of cytochrome C and inhibition of respiration on cardiac isolated mitochondria.

The generation of doxorubicin metabolites other than semiquinone free radicals and mitochondrial dysfunction have been implicated in doxorubicin (DOX)-induced cardiotoxicity. This study examines pro-apoptotic mechanisms in isolated rat cardiac mitochondria exposed to DOX-derived cardiac metabolites i.e. doxorubicinol, doxorubicin aglycone and doxorubicinol aglycone.Freshly isolated mitochondria were incubated in the presence of doxorubicin and its derivatives and the released cytochrome c was detected by Western blotting analysis. Oxygen consumption was measured with a Clark-type oxygen electrode and mitochondrial transmembrane potential (delta psi) was measured in a fluorometer in the presence of a fluorescent probe.The data obtained show that exposure of isolated mitochondria to the drugs determines a significant release of cytochrome c and a slight decrease in the mitochondrial transmembrane potential (delta psi). These effects are more evident when the experiments are performed in the presence of the aglycone derivatives. Moreover, an inhibition of the respiratory chain at the level of complex I is evidenced in the drug-treated mitochondria.The data obtained are consistent with the proposal that doxorubicin-induced cardiotoxicity may be partially exerted by the induction of programmed cell death, both directly and even more through its derived metabolites.