Metformin does not compromise energy status in human skeletal muscle at rest or during acute exercise: A randomised, crossover trial.

5´AMP-activated protein kinase (AMPK) is a mediator of a healthy metabolic phenotype in skeletal muscle. Metformin may exacerbate the energy disturbances observed during exercise leading to enhanced AMPK activation, and these disturbances may provoke early muscular fatigue. We studied acute (1 day) and short-term (4 days) effects of metformin treatment on AMPK and its downstream signaling network, in healthy human skeletal muscle and adipose tissue at rest and during exercise, by applying a randomized blinded crossover study design in 10 lean men. Muscle and fat biopsies were obtained before and after the treatment period at rest and after a single bout of exercise. Metformin treat ment elicited peak plasma and muscle metformin concentrations of 31 µM and 11 µM, respectively. Neither of the treatments affected AMPK activity in skeletal muscle and adipose at rest or during exercise. In contrast, whole-body stress during exercise was elevated as indicated by increased plasma lactate and adrenaline concentrations as well as increased heart rate and rate of perceived exertion. Also whole-body insulin sensitivity was enhanced by 4 days metformin treatment, that is reduced fasting plasma insulin and HOMA-IR. In conclusion, acute and short-term metformin treatment does not affect energy homeostasis and AMPK activation at rest or during exercise in skeletal muscle and adipose tissue of healthy subjects. However, metformin treatment is accompanied by slightly enhanced perceived exertion and whole-body stress which may provoke a lesser desire for physical activity in the metformin-treated patients.

Deletion of skeletal muscle SOCS3 prevents insulin resistance in obesity.

Obesity is associated with chronic low-grade inflammation that contributes to defects in energy metabolism and insulin resistance. Suppressor of cytokine signaling (SOCS)-3 expression is increased in skeletal muscle of obese humans. SOCS3 inhibits leptin signaling in the hypothalamus and insulin signal transduction in adipose tissue and the liver. Skeletal muscle is an important tissue for controlling energy expenditure and whole-body insulin sensitivity; however, the physiological importance of SOCS3 in this tissue has not been examined. Therefore, we generated mice that had SOCS3 specifically deleted in skeletal muscle (SOCS MKO). The SOCS3 MKO mice had normal muscle development, body mass, adiposity, appetite, and energy expenditure compared with wild-type (WT) littermates. Despite similar degrees of obesity when fed a high-fat diet, SOCS3 MKO mice were protected against the development of hyperinsulinemia and insulin resistance because of enhanced skeletal muscle insulin receptor substrate 1 (IRS1) and Akt phosphorylation that resulted in increased skeletal muscle glucose uptake. These data indicate that skeletal muscle SOCS3 does not play a critical role in regulating muscle development or energy expenditure, but it is an important contributing factor for inhibiting insulin sensitivity in obesity. Therapies aimed at inhibiting SOCS3 in skeletal muscle may be effective in reversing obesity-related glucose intolerance and insulin resistance.

Binding properties of antagonists to cannabinoid receptors in intact cells.

The implication of the cannabinoid receptor 1 (CB(1) receptor) in several pathophysiological states has sparked the development of selective antagonists. Here we compare binding of the antagonists [(3) H]-AZ12491187, [(3) H]-taranabant and [(3) H]-rimonabant to intact human embryonic kidney cells stably expressing recombinant human CB(1) receptors (CB1r cells). Unlabelled ligands decreased the total binding of the three radioligands with closely the same order of potency: i.e. AZ12288553∼AZ12491187∼taranabant>rimonabant. Nondisplaceable (i.e. nonspecific) binding to the CB1r cells was the same as total binding to the wells containing untransfected cells and it was more pronounced for [(3) H]-AZ12491187 and [(3) H]-rimonabant than for [(3) H]-taranabant. [(3) H]-Rimonabant and (to a lesser extent) [(3) H]-AZ12491187 were also prone to bind nonspecifically to the walls of the wells. Compared to the other radioligands, [(3) H]-rimonabant displayed lower potency for the CB(1) receptors in saturation binding studies and faster association and dissociation in kinetic experiments. When dissociated, the three radioligands also showed prominent rebinding to the cells in medium only. This could be relieved by the presence of excess of unlabelled ligand and of bovine serum albumin (BSA) but a combination thereof was most efficient. The long 'residence time' of AZ12491187 at the CB(1) receptor (because of slow dissociation and prominent rebinding) and its pronounced incorporation into the membranes of the cells could contribute to long-lasting in vivo CB(1) receptor blockade.