Dimethylbiguanide inhibits cell respiration via an indirect effect targeted on the respiratory chain complex I.
Level 5 - mechanism / opinion, no new human data
Preclinical in vitro and ex vivo laboratory study on rat hepatocytes and mitochondria
PubMed 10617608 · doi:10.1074/jbc.275.1.223
What was done
Researchers evaluated the cellular and mitochondrial effects of dimethylbiguanide (metformin) using isolated rat hepatocytes, permeabilized hepatocytes, and isolated liver mitochondria, as well as mitochondria harvested from pretreated rat livers and animals. They assessed oxygen consumption, mitochondrial membrane potential, and substrate-specific respiratory chain complex activities (complex I, II, and IV substrates), along with temperature dependence and the impact of various signaling pathway inhibitors (insulin signaling, nitric oxide, oxygen radical scavengers, ceramide synthesis inhibitors, and calcium chelators).
What was found
Direct addition of dimethylbiguanide decreased oxygen consumption and mitochondrial membrane potential in intact cells, but had no effect when added directly to permeabilized hepatocytes or isolated mitochondria. Permeabilized hepatocytes pre-exposed to dimethylbiguanide and mitochondria from pretreated livers or animals showed specific inhibition of oxygen consumption with complex I substrates (glutamate/malate), with no effect on complex II (succinate) or complex IV (TMPD/ascorbate) substrates. The inhibitory effect was temperature-dependent, reducing oxygen consumption by 50% at 37 °C, 20% at 25 °C, and 0% at 15 °C. The inhibition persisted in functionally isolated complex I and was unaffected by insulin signaling blockers, nitric oxide modulators, radical scavengers, ceramide inhibitors, or calcium chelation.
Why it matters
This study identifies respiratory chain complex I as the target of biguanide-mediated respiratory inhibition and demonstrates that the effect requires intact cellular architecture rather than direct mitochondrial interaction alone.
Limits
The study was conducted exclusively in rodent in vitro and ex vivo models, and sample sizes were not reported in the abstract. The exact upstream cell-signaling pathway mediating the persistent complex I inhibition was not identified.
Cited by
- context Metformin causes mitochondrial stress by inhibiting complex I or complex II of the electron transport chain.