Lipoic acid acutely induces hypoglycemia in fasting nondiabetic and diabetic rats

Lipoic acid (LA) is a unique antioxidant that increases peripheral glucose utilization in diabetic patients. This study was conducted to investigate w hether the inhibition of glucose production could be an additional mechanis m for the action of LA. Intravenous (IV) LA injection (100 or 60 mg/kg body weight) to fasting nondiabetic or streptozotocin (STZ)-induced diabetic ra ts caused a rapid reduction in blood glucose with no effect on circulating insulin levels. In vivo conversion of fructose to glucose was not inhibited by LA, whereas the gluconeogenesis flux from alanine was completely preven ted. Reduced liver pyruvate carboxylase (PC) activity in vivo is suggested by the finding that LA induced a decrease in liver coenzyme A (CoA) content (44% and 28% reduction in nondiabetic and diabetic rats, respectively, com pared with vehicle-treated animals) and liver acetyl CoA content (80% and 6 7% reduction in nondiabetic and diabetic rats, respectively). A reduction i n plasma free carnitine (42% and 22% in nondiabetic and diabetic rats, resp ectively) was observed in LA-treated animals, and acylcarnitine revels were increased twofold. This could be attributed to elevated levels of C16 and C18 acylcarnitine, without a detectable accumulation of lipoylcarnitine, Un der such conditions, a significant increase in the plasma free fatty acid ( FFA) concentration (204% in nondiabetic and 151% in diabetic animals) with no elevation in beta-hydroxybutyrate levels was noted. In conclusion, this study suggests that short-term administration of LA at high dosage to norma l and diabetic rats causes an inhibition of gluconeogenesis secondary to an interference with hepatic fatty acid oxidation, This may render LA an anti hyperglycemic agent for the treatment of diabetic subjects, who display glu cose overproduction as a major metabolic abnormality, Copyright (C) 1999 by W.B. Saunders Company.