Adriamycin Induced Apoptosis of H9c2 Cardiomyocytes via a Caspase-Independent Pathway

ABSTRACT

BACKGROUND: The cardiotoxicity of adriamycin limits its clinical usefulness as a powerful drug for solid tumors and malignant hematological disease. Although the exact mechanism by which it causes cardiac damage is not yet known, several reports have suggested apoptosis to be the principal process in adriamycin-induced cardiomyopathy, which exhibits DNA fragmentation, cytochrome C release, and caspase activation. However, no direct evidence has linked the critical involvement of caspase-3 in adriamycin-induced apoptosis. METHODS: To determine the requirements for the activation of caspase-3 in adriamycin-treated cardiac cells, we examined the effect of caspase inhibitor on the cell survival and apoptotic changes, using MTT assay, microscopy and Western blotting. RESULTS: Exposure of H9c2 cells to adriamycin resulted in time- and dose-dependent cell death and cleavage of pro-caspase-3 and the nuclear protein poly (ADP-ribose) polymerase (PARP). However, neither the reduction of cell viability nor the characteristic morphological changes induced by adriamycin was prevented by pretreatment with the general caspase inhibitor z-VAD.FMK. In contrast, caspase inhibition effectively blocked the apoptosis induced by H2O2 in H9c2 cells, but was not essential for adriamycin-induced apoptosis in H9c2 cells. We also observed that p53 expression was increased by adriamycin, and this increase was not affected by the inhibition of caspase activity, suggesting a role for p53 in adriamycin-induced caspase-independent apoptosis in cardiac toxicity. CONCLUSION: Our results demonstrate that adriamycin specifically activates an apoptotic pathway that is not dependent upon the activation of caspase.