Metformin enhances mitochondrial biogenesis and thermogenesis in brown adipocytes of mice

Aims: We studied the effect of metformin on the brown adipose tissue (BAT) in a fructose-rich-fed model, focusing on BAT proliferation, differentiation, and thermogenic markers. Main methods: C57Bl/6 mice received isoenergetic diets for ten weeks: control (C) or high-fructose (F). For additional eight weeks, animals received metformin hydrochloride (M, 250 mg/kg/day) or saline. After sacrifice, BAT and white fat pads were prepared for light microscopy and molecular analyses. Key findings: Body mass gain, white fat pads, and adiposity index were not different among the groups. There was a reduction in energy intake in the F group and energy expenditure in the F and FM groups. Metformin led to a more massive BAT in both groups CM and FM, associated with a higher adipocyte proliferation (beta 1-adrenergic receptor, proliferating cell nuclear antigen, and vascular endothelial growth factor), and differentiation (PR domain containing 16, bone morphogenetic protein 7), in part by activating 5' adenosine monophosphate-activated protein kinase. Metformin also enhanced thermogenic markers in the BAT (uncoupling protein type 1, peroxisome proliferator-activated receptor gamma coactivator-1 alpha) through adrenergic stimuli and fibro-blast growth factor 21. Metformin might improve mitochondrial biogenesis in the BAT (nuclear respiratory factor 1, mitochondrial transcription factor A), lipolysis (perilipin, adipose triglyceride lipase, hormone-sensitive lipase), and fatty acid uptake (lipoprotein lipase, cluster of differentiation 36, adipocyte protein 2). Significance: Metformin effects are not linked to body mass changes, but affect BAT thermogenesis, mitochondrial biogenesis, and fatty acid uptake. Therefore, BAT may be a metformin adjuvant target for the treatment of metabolic disorders.