Carnosol Increases Skeletal Muscle Cell Glucose Uptake via AMPK-Dependent GLUT4 Glucose Transporter Translocation

Skeletal muscle is a major insulin-target tissue and plays an important role in glucose homeostasis. Insulin action in muscle activates the phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway causing the translocation of intracellularly stored GLUT4 glucose transporters to the plasma membrane and increased glucose uptake. Impaired insulin action in muscle results in insulin resistance and type 2 diabetes mellitus (T2DM). Activation of the energy sensor AMP-activated kinase (AMPK) increases muscle glucose uptake and the use of AMPK activators is viewed as an effective strategy to combat insulin resistance. Rosemary extract (RE) has been shown to stimulate muscle AMPK and glucose uptake, but the exact components responsible for these effects are unknown. In the current study, we investigated the effect of carnosol, a RE polyphenol, in L6 rat muscle cells. Carnosol stimulated glucose uptake in L6 myotubes in a dose- and time-dependent manner, did not affect Akt, increased AMPK phosphorylation and plasma membrane GLUT4 levels. The carnosol-stimulated glucose uptake and GLUT4 translocation was significantly reduced by the AMPK inhibitor compound C (CC). Our study is the first to show an AMPK-dependent increase in muscle glucose uptake by carnosol. Carnosol has potential as a glucose homeostasis regulating agent and deserves further study.