Modulation of Electron Transport by Metformin in Cardiac Protection: Role of Complex I

Abstract

RationaleModulation of mitochondrial complex I during reperfusion reduces cardiac injury following ischemia. Complex I exists in two structural states: active (A) and deactive (D) with transition from A→D during ischemia. Reperfusion reactivates D→A with reactive oxygen species (ROS) production. Metformin treatment may preserve the D form.ObjectiveWe hypothesize that maintenance of deactivation of complex I during early reperfusion will protect cardiomyocytes. The goal is to evaluate the potential of acute, high dose Metformin treatment to modulate complex I at the onset of reperfusion/reoxygenation and decrease subsequent cellular injury.MethodsH9c2 cells underwent 6 hr. simulated ischemia and 24 hr. reoxygenation with or without metformin treatment (1 mM) at the onset of reoxygenation. Cell death, ROS and thiol modification were studied. Additional experiments were performed with or without siRNA knockdown of AMPKa2 catalytic subunit.ResultsMetformin selectively inhibited complex I oxidative phosphorylation measured at reoxygenation (Metformin: 0.34±0.1 vs control: 0.59±0.05 nmolO2/min/106cells; ±SE; n=5–10; p<0.05) with decreased total cell death following simulated ischemia and reoxygenation (Metformin: 8.3±0.2 vs. control: 14.4±0.6%; n=3–6; p<0.05). Complex II driven oxidative phosphorylation was not reduced by metformin, supporting selectively to complex I. Apoptosis assessed by annexin‐V labeling and flow cytometry was also decreased by metformin treatment. The “burst” of ROS at reoxygenation was decreased and free thiol group content was preserved by metformin treatment at reoxygenation. Metformin decreased cell death in AMPK knockdown cells.ConclusionMetformin blockade of complex I at the onset of reoxygenation reduces cell injury. Metformin specifically inhibited complex I at reoxygenation with less oxidative injury, in line with protection against D→A reactivation of complex I. Metformin protection was AMPK independent, supporting a complex I mechanism of protection. Acute, high dose Metformin is a potentially safe translational complex I inhibitor to treat ischemia‐reperfusion injury.Support or Funding InformationThis work was supported by the Office of Research and Development, Medical Research Service Merit Review Award (2IO1BX001355‐01A2) and Department of Veterans Affairs; National Institutes of Health NIH R21AG054975‐01This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.