Adriamycin-induced oxidative stress, activation of MAP kinases and apoptosis in isolated cardiomyocytes

Background: Adriamycin (ADR) induced heart failure is associated with an increase in oxidative stress and apoptosis. Changes due to ADR in mitogen-activated protein kinases (ERK1/2 and p38 MAPKs), pro- and anti-apoptotic proteins (Bax and Bcl-xl) and apoptosis were examined in isolated adult rat cardiomyocytes. Methods: Isolated adult rat cardiomyocytes were exposed to different concentrations of ADR (0.1, 1 and 10 μmol/L) and analyzed at different post-treatment durations. Antioxidant, trolox (20 μmol/L) was used to determine involvement of oxidative stress on these changes. Results: Total ERK1/2 and p38 did not show any significant change. However, phosphorylated ERK1/2 showed a rapid increase (497%) after 5 min of ADR treatment, peaking (610%) at 10 min followed by a decline to submaximal levels at 30 min (280%) and 60 min (247%). Phosphorylated p38 showed no changes until after 30 min, peaking (284%) at 1 h, followed by a small decline at 2 h. These changes were found to be dose-dependent (0.1, 1 and 10 μmol/L of ADR). Adriamycin induced apoptosis was confirmed by Hoechst staining. The ratio of Bax/Bcl-xl increased in a dose-dependent manner. At 10 μmol/L, this ratio increased to a maximum at 1 h, remained steady at the level for up to 12 h, followed by a decline below the base line at 24 h. Antioxidant, trolox modulated the ADR-induced increase in phosphorylation of ERK1/2 and p38 MAPKs as well as in the ratio of Bax/Bcl-xl. Conclusion: It is suggested that ADR activates MAP kinases, followed by an activation of pro-apoptotic protein Bax which results in cardiomyocyte apoptosis and these effects appear to be mediated by ADR-induced oxidative stress.