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Metformin is a first-line drug for the treatment of individuals with type 2 diabetes, yet its precise mechanism of action remains unclear. Metformin exerts its antihyperglycemic action primarily through lowering hepatic glucose production (HGP). This suppression is thought to be mediated through inhibition of mitochondrial respiratory complex I, and thus elevation of 5'-adenosine monophosphate (AMP) levels and the activation of AMP-activated protein kinase (AMPK), though this proposition has been challenged given results in mice lacking hepatic AMPK. Here we report that the AMP-inhibited enzyme fructose-1,6-bisphosphatase-1 (FBP1), a rate-controlling enzyme in gluconeogenesis, functions as a major contributor to the therapeutic action of metformin. We identified a point mutation in FBP1 that renders it insensitive to AMP while sparing regulation by fructose-2,6-bisphosphate (F-2,6-P 2 ), and knock-in (KI) of this mutant in mice significantly reduces their response to metformin treatment. We observe this during a metformin tolerance test and in a metformin-euglycemic clamp that we have developed. The antihyperglycemic effect of metformin in high-fat diet-fed diabetic FBP1-KI mice was also significantly blunted compared to wild-type controls. Collectively, we show a new mechanism of action for metformin and provide further evidence that molecular targeting of FBP1 can have antihyperglycemic effects.

Aims: To test the hypothesis that brown adipose tissue (BAT) is a metformin target tissue by investigating in vivo uptake of [ 11 C]-metformin tracer in mice and studying in vitro effects of metformin on cultured human brown adipocytes., Materials and Methods: Tissue-specific uptake of metformin was assessed in mice by PET/CT imaging after injection of [ 11 C]-metformin. Human brown adipose tissue was obtained from elective neck surgery and metformin transporter expression levels in human and murine BAT were determined by qPCR. Oxygen consumption in metformin-treated human brown adipocyte cell models was assessed by Seahorse XF technology., Results: Injected [ 11 C]-metformin showed avid uptake in the murine interscapular BAT depot. Metformin exposure in BAT was similar to hepatic exposure. Non-specific inhibition of the organic cation transporter (OCT) protein by cimetidine administration eliminated BAT exposure to metformin, demonstrating OCT-mediated uptake. Gene expression profiles of OCTs in BAT revealed ample OCT3 expression in both human and mouse BAT. Incubation of a human brown adipocyte cell models with metformin reduced cellular oxygen consumption in a dose-dependent manner., Conclusion: These results support BAT as a putative metformin target., (© 2018 John Wiley & Sons Ltd.)

Metformin is the most widely prescribed oral antiglycemic drug, with few adverse effects. However, surprisingly little is known about its human biodistribution and target tissue metabolism. In animal experiments, we have shown that metformin can be labeled by 11 C and that 11 C-metformin PET can be used to measure renal function. Here, we extend these preclinical findings by a first-in-human 11 C-metformin PET dosimetry, biodistribution, and tissue kinetics study., Methods: Nine subjects (3 women and 6 men) participated in 2 studies: in the first study, human radiation dosimetry and biodistribution of 11 C-metformin were estimated in 4 subjects (2 women and 2 men) by whole-body PET. In the second study, 11 C-metformin tissue kinetics were measured in response to both intravenous and oral radiotracer administration. A dynamic PET scan with a field of view covering target tissues of metformin (liver, kidneys, intestines, and skeletal muscle) was obtained for 90 (intravenous) and 120 (oral) min., Results: Radiation dosimetry was acceptable, with effective doses of 9.5 μSv/MBq (intravenous administration) and 18.1 μSv/MBq (oral administration). Whole-body PET revealed that 11 C-metformin was primarily taken up by the kidneys, urinary bladder, and liver but also to a lesser extent in salivary glands, skeletal muscle, and intestines. Reversible 2-tissue-compartment kinetics was observed in the liver, and volume of distribution was calculated to be 2.45 mL/mL (arterial input) or 2.66 mL/mL (portal and arterial input). In the kidneys, compartmental models did not adequately fit the experimental data, and volume of distribution was therefore estimated by a linear approach to be 6.83 mL/mL. Skeletal muscle and intestinal tissue kinetics were best described by 2-tissue-compartment kinetics and showed only discrete tracer uptake. Liver 11 C-metformin uptake was pronounced after oral administration of the tracer, with tissue-to-blood ratio double what was observed after intravenous administration. Only slow accumulation of 11 C-metformin was observed in muscle. There was no elimination of 11 C-metformin through the bile both during the intravenous and during the oral part of the study., Conclusion: 11 C-metformin is suitable for imaging metformin uptake in target tissues and may prove a valuable tool to assess the impact of metformin treatment in patients with varying metformin transport capacity., (© 2016 by the Society of Nuclear Medicine and Molecular Imaging, Inc.)

Metformin is the most commonly prescribed oral antidiabetic drug, with well-documented beneficial preventive effects on diabetic complications. Despite being in clinical use for almost 60 years, the underlying mechanisms for metformin action remain elusive. Organic cation transporters (OCT), including multidrug and toxin extrusion proteins (MATE), are essential for transport of metformin across membranes, but tissue-specific activity of these transporters in vivo is incompletely understood. Here, we use dynamic positron emission tomography with [(11)C]-labeled metformin ([(11)C]-metformin) in mice to investigate the role of OCT and MATE in a well-established target tissue, the liver, and a putative target of metformin, the small intestine. Ablation of OCT1 and OCT2 significantly reduced the distribution of metformin in the liver and small intestine. In contrast, inhibition of MATE1 with pyrimethamine caused accumulation of metformin in the liver but did not affect distribution in the small intestine. The demonstration of OCT-mediated transport into the small intestine provides evidence of direct effects of metformin in this tissue. OCT and MATE have important but separate roles in uptake and elimination of metformin in the liver, but this is not due to changes in biliary secretion. [(11)C]-Metformin holds great potential as a tool to determine the pharmacokinetic properties of metformin in clinical studies., (© 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

Non-alcoholic fatty liver disease and non-alcoholic steatohepatitis (NASH) are increasing clinical problems for which effective treatments are required. The polyphenol resveratrol prevents the development of fatty liver disease in a number of experimental studies. We hypothesized that it could revert steatohepatitis, including hepatic inflammation and fibrosis, in an experimental NASH model. To induce hepatic steatohepatitis, a 65% fat, 2% cholesterol and 0.5% cholate (HFC) diet was fed to rats for 1 or 16 weeks, prior to treatment. Subsequently, the diet was supplemented with resveratrol (approx. 100mg/rat/day) to three intervention groups; week 2-4, 2-7 or 17-22. Treated animals were sacrificed at the end of each intervention period with appropriate control and HFC diet controls. Blood and liver were harvested for analysis. When commenced early, resveratrol treatment partially mitigated transaminase elevations, hepatic enlargement and TNFα induced protein-3 protein expression, but generally resveratrol treatment had no effect on elevated hepatic triglyceride levels, histological steatohepatitis or fibrosis. We observed a slight reduction in Collagen1α1 mRNA expression and no reduction in the mRNA expression of other markers of fibrosis, inflammation or steatosis (TGFβ, TNFα, α2-MG, or SREBP-1c). Resveratrol metabolites were detected in serum, including trans-resveratrol-3-O-sulphate/trans-resveratrol-4'-O-sulphate (mean concentration 7.9 μg/ml). Contrary to the findings in experimental steatosis, resveratrol treatment had no consistent therapeutic effect in alleviating manifest experimental steatohepatitis., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Regular physical exercise has undisputed health benefits in the prevention and the treatment of many diseases. Understanding the mechanisms that regulate adaptations to exercise training therefore has obvious clinical perspectives. Several lines of evidence suggest that the AMP-activated protein kinase (AMPK) has a central role as a master metabolic regulator in skeletal muscle. Exercise is a potent activator of AMPK, and AMPK signaling can play a key part in regulating protein turnover during and after exercise training., (Copyright © 2014 Elsevier Ltd. All rights reserved.)