Alpha-Lipoic Acid Inhibits Glycogen Synthesis and Modifies Glucose Metabolism and Signaling Pathways in Soleus Muscles from Healthy Rats

Abstract

Alpha-lipoic acid is a known hypoglycemic agent that may be useful in the treatment of diabetes. The objective of this study was to investigate the fate of glucose in isolated muscles incubated with lipoic acid by determining its direct effects on specific metabolic, signaling pathways. Soleus muscles from healthy rats were incubated with lipoic acid in the absence or presence of insulin. Glucose transport, glycogen synthesis, glucose oxidation, lipid synthesis were determined, affects on major pathways associated with insulin signaling were evaluated. Glucose transport was not significantly altered by the addition of lipoic acid to the incubation medium. However, lipoic acid decreased glycogen synthesis in comparison to controls. Glucose oxidation was moderately increased while de-novo lipid synthesis from glucose was inhibited. Wortmannin repressed insulin stimulation of glucose incorporation into glycogen, an effect that was augmented by the combined treatment of wortmannin, lipoic acid. Basal, insulin-stimulated serine phosphorylation of Akt was not changed by the addition of lipoic acid to the incubation medium. These data show that in this in vitro model, lipoic acid did not significantly affect glucose uptake but dramatically modified pathways of glucose metabolism within muscle tissue.