Unexpected Role of Adenosine-Monophosphate Activated Protein Kinase in Doxorubicin Cardiotoxicity and Metformin-Mediated Cardioprotection

Abstract

Doxorubicin (DOX), a commonly used antineoplastic drug, raises clinical concern due to its irreversible cardiotoxicity. Metformin (MET), a drug used for the treatment of type 2 diabetes mellitus, has been suggested as a cardioprotective agent against DOX-induced cardiotoxicity. However, the underlying mechanisms are not fully understood. Recent studies have suggested that Adenosine-monophosphate activated protein kinase (AMPK) may be responsible for the ability of MET to decrease DOX-induced cardiomyocyte death in culture. In the present study, we determined the role of AMPK pathway in DOX cardiotoxicity and in MET-induced cardioprotection using AMPK knockout mice. Wild type (WT) and AMPK knockout (AKO) mice were distributed into four groups (control, MET, DOX, DOX + MET). Mice were administered with MET (200 mg/kg/d, oral) every day for 6 consecutive days and DOX once only on day 3 (20 mg/kg, i.p.). Echocardiography confirmed that MET was sufficient to reverse DOX-impaired cardiac function in WT mice as shown by fractional shortening (DOX 27.8±0.96%, DOX+MET 34.9±1.79%, and Con 40.0±1.28%, n of 7 to 11). Surprisingly, DOX-induced-impairment of cardiac function was not further increased in AMPK knockout mice. Instead, there was a tendency towards reduced cardiac damage in AMPK knockout mice, suggesting that AMPK may contribute to DOX cardiotoxicity, in contrast to our initial hypothesis. As a result, MET did not provide further protection (DOX 33.0±1.23%, DOX+MET 35.7±1.15%, and Con 42.3±1.55%, n of 10 to12). These results were supported by serum levels of lactate dehydrogenase (LDH) and cardiac Troponin I as well as by in vitro studies using cultured cardiomyocytes. In summary, our results supported the concurrent use of MET and DOX to provide cardiac protection for patients that receive antitumor treatment. However, the true role of AMPK in DOX cardiotoxicity needs to be re-evaluated by further studies. Also, the cardioprotective effects of MET may be mediated through signaling pathways unrelated to AMPK.