Inhibition of gluconeogenesis in rat liver by lipoic acid. Evidence for more than one site of action

Hepatocytes obtained from starved rats were incubated in oxygenated Krebs bicarbonate buffer containing 2% defatted bovine serum albumin. DL-alpha-Lipoic (dithio-octanoic) acid (1.0 mM) caused striking reductions in hepatic glucose output in the presence of each of the following substrates: pyruvate, lactate, alanine, dihydroxyacetone, glycerol, and fructose. With lactate as substrate, 0.1-1.0 mM-lipoate caused a concentration-dependent inhibition of gluconeogenesis. With the same substrate, e.g. lactate, 0.25-2.0 mM-octanoate abolished the effect of lipoate in a dose-dependent manner. Additional experimental data are presented which support the concept that the antigluconeogenic effects of lipoic acid in liver can be attributed largely, if not entirely, to sequestration of intramitochondrial coenzyme. A, presumably as lipoyl-CoA, bisnorlipoyl-CoA, or tetranorlipoyl-CoA.