Inhibited autophagy may contribute to heme toxicity in cardiomyoblast cells

Several groups have demonstrated that induction of heme-oxygenase-1 (HO-1) could protect the myocardium against ischemic events; however, heme accumulation could lead to toxicity. The aim of the present study was to investigate the role of autophagy in heme toxicity. H9c2 cardiomyoblast cells were treated with different dose of hemin or cobalt-protoporphyrin IX (CoPP_IX) or vehicle. Cell viability was measured by MTT assay. DCF and MitoSOX staining was employed to detect reactive oxygen species. Western blot analysis was performed to analyse the levels of HO-1, certain autophagy related proteins and pro-caspase-3 as an apoptosis marker. To study the autophagic flux, CytoID staining was carried out and cells were analyzed by fluorescence microscope and flow cytometry. Decreased cell viability was detected at high dose of hemin and CoPP_IX treated H9c2 cells in a dose-dependent manner. Furthermore, at concentration of the inducers used in the present study a significantly enhanced level of ROS were detected. As it was expected both treatments induced a robust elevation of HO-1 level. In addition, the Beclin-1- independent autophagy was significantly increased, but caused a defective autophagic flux with triggered activation of caspase-3. In conclusion, these results suggest that overexpression of HO-1 by high dose of hemin and CoPP_IX can induce cell toxicity in H9c2 cells via enhanced ROS level and impaired autophagy.