AIMS/HYPOTHESIS:
Metformin has been shown to increase
fatty acid oxidation, an effect mediated by AMP activated
protein kinase (
AMPK). We hypothesised that
metformin could prevent both caspase-3
activation and
apoptosis when induced by
palmitic acid. MATERIALS AND METHODS:
Cardiomyocytes were incubated with 1 mmol/l
palmitic acid, in the absence or presence of
metformin (1-5 mmol/l). Following 1 to 16 h,
cell damage was evaluated by measuring
lactate dehydrogenase released into the incubation medium, and Hoechst
staining. To investigate the mechanism of metformin's effect on
cardiomyocytes,
substrate utilisation and
phosphorylation of
AMPK and
acetyl-CoA carboxylase were measured.
Intracellular mediators of
apoptosis were also evaluated. RESULTS: Incubation of
myocytes with
palmitic acid for 16 h increased
apoptosis, an effect that was partly blunted by 1 and 2 mmol/l
metformin. This beneficial effect of
metformin was associated with increased
AMPK phosphorylation,
palmitic acid oxidation and suppression of high-fat-induced increases in (1)
long chain base
biosynthesis protein 1 levels, (2)
ceramide levels, and (3) caspase-3 activity. Unexpectedly, 5 mmol/l
metformin dramatically increased
apoptosis in
myocytes incubated with high fat. This effect was associated with a robust increase in
glycolysis,
lactate accumulation, and a significant drop of pH in the
myocyte incubation medium. CONCLUSIONS/INTERPRETATION: Our study demonstrates that
metformin reduces high-fat-induced
cardiac cell death, probably through inhibition of
ceramide synthesis. However, at high concentrations,
metformin causes proton and
lactate accumulation, leading to
cell damage that is independent of caspase-3.
