Objectives: We examined whether amlodipine, a calcium channel antagonist with potent antioxidant activity, inhibits doxorubicin-induced apoptosis in cultured neonatal rat cardiac myocytes.
Background: Recent studies have shown that doxorubicin induces apoptosis as well as necrosis in myocytes through generation of reactive oxygen species.
Methods: The effects of amlodipine and several other antioxidants on doxorubicin-induced oxidative stress and mitochondria-mediated apoptosis were examined.
Results: Treatment of myocytes with doxorubicin (10(-6) mol/l) for 14 h increased the number of cells with elevated peroxides, as histochemically estimated by 2',7'-dichlorofluorescin (DCF) diacetate, and the percentage of apoptotic myocytes, as estimated by Hoechst 33258 nuclear staining, compared with control myocytes (25.0 +/- 1.6% vs. 5.2 +/- 1.2%). Moreover, doxorubicin-induced myocyte apoptosis was also confirmed by annexin V-fluorescein isothiocyanate binding assay. Doxorubicin induced a reduction in myocyte adenosine 5'-triphosphate content, a loss of mitochondrial membrane potential, cytochrome c release from the mitochondria into the cytosol, and caspase-3 activation to 1.9-fold of control. Amlodipine significantly attenuated increased DCF fluorescence, inhibited the mitochondria-mediated apoptotic responses described earlier, and decreased apoptosis in the doxorubicin-treated myocytes in a dose-dependent fashion. Amlodipine at 10(-6) mol/l significantly decreased apoptosis to 15.4 +/- 0.7%, and this antiapoptotic action was more effective than that seen with other antioxidants, including probucol, ascorbic acid, and alpha-tocopherol. In contrast, the calcium channel antagonist nifedipine (10(-6) mol/l) did not inhibit apoptosis. Catalase, glutathione, and N-acetylcysteine, but not mannitol or superoxide dismutase, significantly decreased DCF fluorescence and attenuated myocyte apoptosis induced by doxorubicin to 18.7 +/- 1.2%, 19.1 +/- 1.7%, and 18.7 +/- 0.6%, respectively.
Conclusions: Amlodipine significantly inhibits doxorubicin-induced myocyte apoptosis by suppressing the mitochondrial apoptotic pathway. This effect is attributed to the antioxidant properties of amlodipine, affecting mainly hydrogen peroxide.