l-Arginine improves multiple physiological parameters in mice exposed to diet-induced metabolic disturbances

l-Arginine (l-Arg) is a conditionally essential amino acid and a natural constituent of dietary proteins. Studies in obese rats and type 2 diabetic humans have indicated that dietary supplementation with l-Arg can diminish gain in white adipose tissue (WAT) and improve insulin sensitivity. However, the effects of l-Arg on glucose homeostasis, body composition and energy metabolism remain unclear. In addition, no studies have, to our knowledge, examined whether l-Arg has beneficial effects as a dietary supplement in the mouse model. In the present study, we investigated the effects of l-Arg supplementation to male C57BL/6 mice on an array of physiological parameters. l-Arg supplemented mice were maintained on a low-protein diet and body composition, appetite regulation, glucose tolerance, insulin sensitivity and energy expenditure were evaluated. A significant reduction in epididymal WAT was observed in l-Arg supplemented mice compared with mice fed an isocaloric control diet. Surprisingly, the l-Arg supplemented animals were hyperphagic corresponding to a highly significant decrease in feed efficiency, as body weight developed in a similar pattern in both experimental groups. Glucose homeostasis experiments revealed a major effect of l-Arg supplementation on glucose tolerance and insulin sensitivity, interestingly, independent of a parallel regulation in whole-body adiposity. Increased l-Arg ingestion also raised energy expenditure; however, no concurrent effect on locomotor activity, substrate metabolism or expression of uncoupling proteins (UCP1 and UCP2) in adipose tissues was displayed. In conclusion, dietary l-Arg supplementation substantially affects an array of metabolic-associated parameters including a reduction in WAT, hyperphagia, improved insulin sensitivity and increased energy expenditure in mice fed a low-protein diet.