Abstract Body (Do not enter title and authors here): Introduction: Metformin (MET), a first-line diabetes therapy, exhibits cardioprotective effects during acute ischemia and reperfusion (I/R). Cardiac injury is enhanced in the aging heart in murine and humans. Acute, high dose MET treatment at the onset of reperfusion (R) markedly reduced infarct size (MI) in the high risk aged heart via modulation of mitochondrial complex I. However, the effect of subsequent chronic, standard dose MET to consolidate and possibly enhance cardioprotection and survival following I/R in the aged heart remains unknown.
Hypothesis: Administration of chronic standard dose of MET will ameliorate mortality and morbidity following MI through rescuing an impaired adaptive metabolic remodeling.
Methods: Aged (22-24 month) C57BL6/J mice were subjected to sham operations or 45 min of ischemia by LAD ligation followed by R. All mice received acute, high dose MET (2 mM, i.v.) at the onset of R followed by randomization to chronic MET (300 mg/kg/day) in drinking water versus vehicle (VEH) administered for 14 days. Cardiac function was determined by echocardiography weekly. IonOptix Myocyte Calcium and Contractility System measured the contractile functions and transient calcium signaling of isolated cardiomyocytes.
Results: The Kaplan-Meier survival analysis showed that chronic MET treatment following acute treatment at the onset of R significantly reduced mortality compared to VEH group. Although chronic MET treatment did not further reduce MI size, echo and histology showed that chronic MET preserved diastolic function, prevented left ventricular hypertrophy and reduced collagen deposition following I/R in aging. Moreover, isolated cardiomyocytes from MET treated hearts showed improvements in contractile function, transit calcium signaling, and the coupling between contractility and calcium levels as compared to the cardiomyocytes from VEH group hearts. Immunoblotting results showed that Sens2/AMPK metabolic signaling was significantly upregulated by chronic MET post-MI, indicating the metabolic homeostasis modulated by MET is a critical factor involved in the beneficial effects of chronic MET on limiting I/R-induced myocardial damage that leads to deleterious remodeling in aging.
Conclusions: The mortality and morbidity of MI in the high risk aged heart is attenuated with acute, high dose of MET treatment followed by chronic standard dose MET treatment to consolidate protection via rescuing the impaired adaptive metabolic response in aging.