Changes induced by a fructose-rich diet on hepatic metabolism and the antioxidant system

The effect of a three-week fructose-rich diet (FRD) upon gene expression, protein and activity levels of liver antioxidant system and carbohydrate metabolism was studied.

Serum glucose (fasting and after a glucose load), triglyceride and insulin levels of normal male Wistar rats were measured. In liver, we measured gene/protein expression and enzyme activity of catalase (CAT), copper-zinc-superoxide dismutase (CuZnSOD) and glutathione peroxidase (GSHPx); reduced glutathione (GSH); protein carbonyl content; thiobarbituric acid reactive substances (TBARS) content and microsomal membrane susceptibility to lipid peroxidation; glucokinase (GK), glucose-6-phosphatase (G-6-Pase) and glucose-6-phosphate dehydrogenase (G-6-PDH) activity; and glycogen, pyruvate, lactate and triglyceride content.

Similar body weights and caloric intake were recorded in both groups. FRD rats had higher serum glucose, insulin and triglyceride levels, molar insulin:glucose ratio, HOMA-IR values and impaired glucose tolerance, whereas CAT, CuZnSOD and GSHPx relative gene expression levels were significantly lower. CAT and CuZnSOD protein expression, CAT activity and GSH content were also lower, while protein carbonyl content was higher. No differences were recorded in CuZnSOD, MnSOD and GSHPx activity, TBARS content and membrane susceptibility to lipid peroxidation. Glycogen, lactate and triglyceride content and GK, G-6-Pase and G-6-PDH activity were significantly higher in FRD rats.

In the presence of oxidative stress, the liver exhibits changes in the carbohydrate and lipid metabolic pathways that would decrease reactive oxygen species production and their deleterious effect, thus inducing little impact on specific antioxidant mechanisms. This knowledge could facilitate the design and implementation of strategies to prevent oxidative stress-induced liver damage.