Lipoic acid prevents liver metabolic changes induced by administration of a fructose-rich diet.

BACKGROUND: To evaluate whether co-administration of R/S-α-lipoic acid can prevent the development of oxidative stress and metabolic changes induced by a fructose-rich diet (F).
METHODS: We assessed glycemia in the fasting state and during an oral glucose tolerance test, triglyceridemia and insulinemia in rats fed with standard diet (control) and fructose without or with R/S-α-lipoic acid. Insulin resistance and hepatic insulin sensitivity were also calculated. In liver, we measured reduced glutathione, protein carbonyl groups, antioxidant capacity by ABTS assay, antioxidant enzymes (catalase and superoxide dismutase 1 and 2), uncoupling protein 2, PPARδ and PPARγ protein expressions, SREBP-1c, fatty acid synthase and glycerol-3-phosphate acyltransferase-1 gene expression, and glucokinase activity.
RESULTS: R/S-α-lipoic acid co-administration to F-fed rats a) prevented hyperinsulinemia, hypertriglyceridemia and insulin resistance, b) improved hepatic insulin sensitivity and glucose tolerance, c) decreased liver oxidative stress and increased antioxidant capacity and antioxidant enzymes expression, d) decreased uncoupling protein 2 and PPARδ protein expression and increased PPARγ levels, e) restored the basal gene expression of PPARδ, SREBP-1c and the lipogenic genes fatty acid synthase and glycerol-3-phosphate acyltransferase, and f) decreased the fructose-mediated enhancement of glucokinase activity.
CONCLUSIONS: Our results suggest that fructose-induced oxidative stress is an early phenomenon associated with compensatory hepatic metabolic mechanisms, and that treatment with an antioxidant prevented the development of such changes. GENERAL SIGNIFICANCE: This knowledge would help to better understand the mechanisms involved in liver adaptation to fructose-induced oxidative stress and to develop effective strategies to prevent and treat, at early stages, obesity and type 2 diabetes mellitus.