L-carnitine prevents doxorubicin-induced apoptosis of cardiac myocytes:: role of inhibition of ceramide generation

Besides the well-documented effect of the chemotherapeutic drug doxorubicin on free radical generation, the exact signaling mechanisms by which it causes cardiac damage remain largely unknown and are of fundamental importance in understanding anthracycline cardiotoxicity In this study, we describe that a 1 h treatment of isolated adult rat cardiac myocytes with doxorubicin (0.5 mu M) induced DNA fragmentation associated with the classical morphological features of apoptosis observed after 7 days of culture, The doxorubicin toxicity was preceded by an increase in intracellular ceramide levels with a concurrent decrease in sphingomyelin, Anthracycline-induced ceramide accumulation resulted from the activation of a sphingomyelinase assayed under acidic conditions, an effect related to an increase in V-max. Pretreatment of cardiac myocytes with L-carnitine (200 mu g/ml), a compound known for its protective effect on cardiac metabolic injuries, was found to dose-dependently inhibit the doxorubicin-induced sphingomyelin hydrolysis and ceramide generation as well as subsequent cell death. However, L-carnitine did not protect cardiac myocytes from apoptosis induced by exogenous cell-permeant ceramide, L-carnitine pretreatment did not affect the sphingomyelinase basal activity but abolished the doxorubicin-induced increase in V-max. Moreover, in vitro studies conducted on cell extracts or with purified acid sphingomyelinase demonstrated that L-carnitine exerted a dose-dependent, sphingomyelinase inhibitory effect (through V-max reduction). Taken together, these findings show that by inhibiting a (perhaps novel) drug-activated acid sphingomyelinase and ceramide generation, L-carnitine can prevent doxorubicin-induced apoptosis of cardiac myocytes.