Activation of skeletal muscle glucose uptake by am [i.e. an] amino acid mixture and its impact on glucose tolerance and insulin resistance

Abstract

Recent research suggests that amino acids can significantly increase skeletal muscle glucose uptake. However, the mechanism(s) have not been fully elucidated and it is also not clear if the beneficial impact amino acids have on healthy tissue translates to insulin resistant skeletal muscle. Therefore, in this series of studies, the effects of an amino acid mixture on glucose tolerance and insulin resistance were investigated. Study 1 Experiment-1 (Exp-1) demonstrated that an amino acid mixture significantly reduced the blood glucose response to an oral glucose challenge in Sprague Dawley rats. In Study 1 Exp-2, it was found that the improved glucose tolerance was due to an increase in skeletal muscle glucose uptake. The enhanced amino acid induced muscle glucose uptake was associated with improved cellular signaling. In Study 1 we could not determine the combined and/or individual effects of insulin and amino acids on glucose uptake, so in Study 2, the hindlimb of Sprague Dawley rats were perfused with glucose with or without amino acids in the presence and absence of insulin. Study 2, confirmed our previous findings that an amino acid mixture increased skeletal muscle glucose uptake compared to a carbohydrate supplement in the presence of insulin. The enhanced amino acid-stimulated glucose uptake was not due to increased phosphatidylinositol 3-kinase (PI 3-kinase) activity, although it was related to an increase in Akt substrate of 160 kDa (AS160) phosphorylation and a greater number of glucose transporters at the plasma membrane. In the final experiment, Study 3 investigated whether amino acids could improve glucose tolerance in an insulin resistant model. Study 3 Exp-1, demonstrated that an amino acid mixture significantly lowered the blood glucose response to an oral glucose challenge in obese Zucker rats. Study 3 Exp-2 showed that the improved glucose tolerance was due to enhanced amino acid induced skeletal muscle glucose uptake. Taken together, the results of this research suggests that adding an amino acid mixture to a carbohydrate supplement improves the blood glucose response to an oral glucose challenge, acutely lowers insulin resistance and this appears due to increased skeletal muscle glucose clearance and enhanced cellular signaling.