Reactive oxygen species-independent apoptosis in doxorubicin-treated H9c2 cardiomyocytes: Role for heme oxygenase-1 down-modulation

Increased oxidative stress and apoptosis have been implicated in the cardiotoxicity that limits the clinical use of doxorubicin (DOX) as an anti-tumoral drug, but the mechanism of DOX-mediated apoptosis remains unclear. We examined the interplay between oxidative stress and cell death in cardiac-derived H9c2 myocytes exposed to DOX doses in the range of the plasma levels found in patients undergoing chemotherapy. A low DOX concentration (0.25 mu M) induced apoptosis, whereas the cells treated with the high dose of 2 mu M also showed necrosis. The production of reactive oxygen species (ROS) and induction of oxidative stress markets was increased in the cells treated with 2 mu M DOX but not in those treated with the low dose. Surprisingly, heme oxygenase (HO-1) expression was clown-modulated in the cells exposed to 0.25 mu M DOX, and its Bach I transcriptional repressor was induced. In line with the role of HO-1 as an anti-apoptotic protein, inhibiting HO-1 activity with SnPPIX was sufficient to induce apoptosis and increased DOX-mediated apoptosis, whereas hemin-induced HO-1 activation prevented DOX-mediated apoptotic cell death. In brief, our findings do not Support the hypothesis that oxidative stress plays a role in the apoptotic cell death occurring in cardiomyocytes exposed to low concentrations of DOX. but suggest that DOX may facilitate the apoptosis of cardiomyocytes by inhibiting the anti-apoptotic HO-1. (C) 2008 Elsevier Ireland Ltd. All rights reserved.