Biphasic effect of metformin on human cardiac energetics.
Level 5 - mechanism / opinion, no new human data
In vitro laboratory study using human iPSC-derived cardiomyocytes and isolated human cardiac mitochondria
PubMed 33045408 · doi:10.1016/j.trsl.2020.10.002
What was done
Investigators evaluated the cellular and mitochondrial effects of metformin using human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and mitochondria isolated from human cardiac tissue. They assessed oxygen consumption rate (OCR), the role of AMPK using the inhibitor compound C, electron-transport chain complex I activity, superoxide production, and calcium-induced mitochondrial permeability transition pore (mPTP) opening across varying metformin concentrations.
What was found
In hiPSC-CMs, metformin concentrations ≤2.5 mM significantly increased OCR through AMPK-dependent signaling and enhanced mitochondrial biogenesis, an effect abrogated by compound C. Concentrations >5 mM inhibited OCR and triggered metabolic reprogramming toward glycolysis and glutaminolysis. In isolated cardiac mitochondria, metformin did not increase OCR at any level but inhibited OCR starting at 1 mM via direct complex I inhibition, which correlated with reduced superoxide production and delayed mPTP opening. Specific numerical values and effect sizes were not provided in the abstract.
Why it matters
The study outlines a biphasic mechanism for metformin in human cardiac tissue: lower concentrations promote respiration and mitochondrial biogenesis, while higher concentrations inhibit complex I and reduce oxidative stress and pore opening.
Limits
The study is purely in vitro using stem cell-derived models and isolated mitochondria, which cannot replicate whole-organism physiology. The concentrations evaluated (1 to >5 mM) are substantially higher than typical clinical therapeutic plasma concentrations. Sample sizes (number of biological replicates or donors) were not reported in the abstract.
Cited by
- supports Metformin stimulates mitochondrial biogenesis.