The Role of Autophagy and Death Pathways in Dose-dependent Isoproterenolinduced Cardiotoxicity.

Background Isoproterenol (ISO) is a non-selective β-adrenergic agonist. Our aims were to investigate the autophagy and cell death pathways including apoptosis and necrosis in ISO-induced cardiac injury in a dosedependent manner. Methods Male Sprague-Dawley rats were treated for 24 hours with I. vehicle (saline); II. 0.005 mg/kg ISO; III. 0.05 mg/kg ISO; IV. 0.5 mg/kg ISO; V. 5 mg/kg ISO; VI. 50 mg/kg ISO, respectively. Hearts were isolated and infarct size was measured. Serum levels of Troponin T (TrT), lactate dehydrogenase (LDH), creatine kinase isoenzyme MB (CK-MB) were measured. TUNEL assay was carried out to monitor apoptotic cell death and Western blot was performed to evaluate the level of autophagic and apoptotic markers. Results Survival rate of animals was dose-dependently decreased by ISO. Serum markers and infarct size revealed the development of cardiac toxicity. Level of Caspase-3, and results of TUNEL assay, demonstrated that the level of apoptosis was dose-dependently increased. They reached the highest level in ISO 5 and it decreased slightly in ISO 50 group. Focusing on autophagic proteins, we found that level of Beclin-1 was increased in a dose-dependent manner, but significantly increased in ISO 50 treated group. Level of LC3B-II and p62 showed the same manner, but the elevated level of p62 indicated that autophagy was impaired in both ISO 5 and ISO 50 groups. Conclusion Taken together these results suggest that at smaller dose of ISO autophagy may cope with the toxic effect of ISO; however, at higher dose apoptosis is initiated and at the highest dose substantial necrosis occurs.