295-LB: Metformin Biphasic Effect on Human Cardiac Mitochondria

Mechanisms by which metformin (Mtf) protects human heart in type 2 diabetes remain debated. We hypothesize that Mtf has a biphasic effect on mitochondria: it causes activation of respiration at low doses via AMPK signaling and inhibition at high doses by directly affecting the activity of complex I and reducing oxidative stress. Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) and mitochondria isolated from human cardiac tissue were exposed to different doses of Mtf (0-20 mM) for 24h and acutely. Oxygen consumption rate (OCR) was assessed in the cells and mitochondria energized by glutamate and malate (complex I substrates) using XF96 Extracellular Flux Analyzer. Superoxide production was measured by monitoring changes in fluorescence intensity of dihydroethidium (DHE). At low doses (0.1 - 1 mM), Mtf significantly increased OCR in hiPSC-CMs (Fig. 1A). The highest OCR was observed at 0.5 mM Mtf. This effect was abrogated by compound C, an inhibitor of AMP-kinase (Fig. 1A). Mtf did not increase OCR in isolated mitochondria (Fig. 1B). At higher doses (1-20 mM), it inhibited OCR both in the cells and isolated mitochondria. This was associated with reduction of superoxide production in the mitochondria (Fig. 1C). In the human heart, Mtf improves cardioprotection due to its biphasic effect on mitochondria. This can be a beneficial alternative to patients with impaired endogenous cardioprotective responses.

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