Metformin inhibits mitochondrial permeability transition and cell death: a pharmacological in vitro study

Abstract

Metformin, a drug widely used in the treatment of Type II diabetes, has recently received attention owing to new findings regarding its mitochondrial and cellular effects. In the present study, the effects of metformin on respiration, complex 1 activity, mitochondrial permeability transition, cytochrome c release and cell death were investigated in cultured cells from a human carcinoma-derived cell line (KB cells). Metformin significantly decreased respiration both in intact cells and after permeabilization. This was due to a mild and specific inhibition of the respiratory chain complex 1. In addition, metformin prevented to a significant extent mitochondrial permeability transition both in permeabilized cells, as induced by calcium, and in intact cells, as induced by the glutathione-oxidizing agent t-butyl hydroperoxide. This effect was equivalent to that of cyclosporin A, the reference inhibitor. Finally, metformin impaired the t-butyl hydroperoxide-induced cell death, as judged by Trypan Blue exclusion, propidium iodide staining and cytochrome c release. We propose that metformin prevents the permeability transition-related commitment to cell death in relation to its mild inhibitory effect on complex 1, which is responsible for a decreased probability of mitochondrial permeability transition.

Metformin induced expression of Hsp60 in human THP-1 monocyte cells

“…6). These results are comparable to earlier observations which documented the inhibition of 53% of respiration in human carcinoma-derived KB cells after exposure to 10 mM metformin (Guigas et al 2004).…”

“…The LDH data suggest that the increase in expression of Hsp60 observed at both mRNA and protein levels were not due to cellular lysis and that the growth inhibitory effects of 500 μM metformin was not due to cell death but possibly due to metformin having an inhibitory effect on mitochondrial bionenergetic functions. Interestingly, metformin has been documented to prevent cell death by modulation of the mitochondrial permeability transition pore opening induced by a glutathione-oxidising agent t-butyl hydroperoxide (Guigas et al 2004) and also due to high glucose-induced cell death in a human dermal microvascular endothelial cell line, HMEC-1 (Detaille et al 2005). However, reports of metformin treatment resulting in an increase in H 2 O 2 production in rat liver mitochondria (Carvalho et al 2008), a short-term trial involving 15 type 2 diabetes mellitus patients treated with metformin showing an elevation in oxidative stress, indicated by elevated malidialdehyde levels (Škrha et al 2007) and metformin causing mitochondrial depolarization and oxidative stressdependent apoptosis in cultured glioma cells (Isakovic et al 2007), suggest that the role of mitochondria in metformininduced cytotoxicity remains to be of defined.…”

“…Interestingly, there is also accumulating data in support of mitochondria being metformin's primary site of action. Metformin has been shown to affect complex I of the mitochondrial respiratory chain (Brunmair et al 2004;Guigas et al 2004;Owen et al 2000). Mitochondrial complex I is also one of the main sites at which reactive oxygen species can be generated (Brownlee 2001;Nishikawa et al 2000).…”

Genes involved in oxidative phosphorylation are coordinately upregulated with fasting hyperglycaemia in livers of patients with type 2 diabetes

“…The upregulation of genes involved in OXPHOS may contribute to hyperglycaemia through the supply of ATP for gluconeogenic enzymes. The glucose-lowering drug metformin is reported to restrain hepatic gluconeogenesis through inhibition of the respiratory chain 1 [30,31]. Our analysis is compatible with these reports on the pharmacological effect of metformin.…”

Global gene expression analysis in liver of obese diabetic db/db mice treated with metformin

“…Based on data from a variety of experimental conditions, metformin has been shown to activate AMPactivated protein kinase [10] and inhibit mitochondrial respiratory complex I [11,12], mitochondrial permeability transition [13] and tyrosine phosphatase activity [14]. Additionally, metformin has been reported to influence hepatic gene expression in cultured hepatocytes, with noted alterations in the expression of particular genes, such as glucose-6-phosphatase (G6pc), glucokinase, and 3-hydroxy-3-methylglutaryl-Coenzyme A synthase 2 (Hmgcs2).…”