High Dose Metformin Treatment to Inhibit Complex I during Early Reperfusion Protects the Aged Mouse Heart via Decreased MPTP Opening

Acute, high-dose metformin (MET, 2 mM) results in partial complex I inhibition in ischemia (ISC)-modified mitochondria. Mitochondrial permeability transition pore (MPTP) opening increases cardiac injury during ISC-reperfusion (REP). We evaluated whether MET (2 mM) can decrease MPTP opening in aged hearts during REP. Sestrin2 (Sesn2) regulates metabolism through activation of AMP-dependent protein kinase. Sesn2 decreases in aged hearts. The knockout (KO) of Sesn2 mimics the aging phenotype. Inactivation of glycogen synthase kinase-3 β (GSK-3β) via serine-9 phosphorylation decreases MPTP opening. We assessed if 2 mM MET given during early REP can decrease cardiac injury by partial blockade of complex I with decreased MPTP opening and if the protection depends on Sesn2-mediated GSK-3β phosphorylation. C57BL/6BJ male mice (22-24 months) and adult Sesn2 KO mice were evaluated. MET dose-dependently inhibited NADH oxidase activity in permeabilized mitochondria in both aged and Sesn2 KO greater after 25 minutes of ISC. MET (2 mM) given during REP decreased infarct size in aged hearts. MET improved calcium retention capacity in both aged wild-type and adult Sesn2 KO mice. MET treatment only increased phosphorylation of GSK-3β in aged heart mitochondria but not in Sesn2 KO hearts. Thus, high-dose MET at REP partially inhibits complex I and decreases MPTP opening. The decreased MPTP susceptibility downstream of complex I inhibition is not fully dependent on GSK-3β inhibition. Complex I downregulation with acute, high-dose MET has translational potential to protect the aged heart. SIGNIFICANCE STATEMENT: This study explores the efficacy and mechanism of acute high-dose metformin treatment in reducing mitochondrial-driven cardiac injury during reperfusion after stop-flow ischemia in the high-risk aged heart. Metformin dose-dependently inhibits complex I (NADH oxidation) in ischemia-altered mitochondria. Metformin given during early reperfusion mitigated MPTP opening as the mechanism of decreased reperfusion injury. Thus, modulation of complex I via metformin at reperfusion has potential translational application to mitigate injury during ST-elevation myocardial infarction in the high-risk aged heart.