Metformin improves atypical protein kinase C activation by insulin and phosphatidylinositol-3,4,5-(PO4)3 in muscle of diabetic subjects

Aims/hypothesis Metformin is widely used for treating type 2 diabetes mellitus, but its actions are poorly understood. In addition to diminishing hepatic glucose output, metformin, in muscle, activates 5′-AMP-activated protein kinase (AMPK), which alone increases glucose uptake and glycolysis, diminishes lipid synthesis, and increases oxidation of fatty acids. Moreover, such lipid effects may improve insulin sensitivity and insulin-stimulated glucose uptake. Nevertheless, the effects of metformin on insulin-sensitive signalling factors in human muscle have only been partly characterised to date. Interestingly, other substances that activate AMPK, e.g., aminoimidazole-4-carboxamide-1-β-d-riboside (AICAR), simultaneously activate atypical protein kinase C (aPKC), which appears to be required for the glucose transport effects of AICAR and insulin.