Influence of lipoic acid supplementation on antioxidant and oxidative stress responses in common carp Cyprinus carpio (Teleostei, Cyprinidae)
Although the effects of lipoic acid have been tested in several aquatic organisms, studies evaluating antioxidant responses over time are scarce and need to be addressed. In addition, antioxidant responses caused by supplementation with lipoic acid in the intestine of fish have not yet been studied. In this study, the antioxidant and oxidative stress responses over time in the intestine, liver and muscle were evaluated in juveniles of Cyprinus carpio carp. Two experimental groups (treated or control) were fed respectively with a diet supplemented with lipoic acid (1 g/kg) or not. The experiment was conducted for four weeks. Weekly, nine fish from each group were selected and the organs were dissected to determine the activity of the enzyme glutathione-S-transferase (GST),reduced glutathione concentration (GSH), total antioxidant capacity against peroxiradicals (CAPR) and lipid peroxidation (TBARS). The results indicated that glutathione-S-transferase (GST) activity was significantly higher in the intestine of the treated group after two weeks of supplementation (p <0.05). In the liver and muscle, GST activity did not differ between groups (p> 0.05). The concentration of reduced glutathione GSH was significantly higher (p <0.05) in the intestine of the treated group after two weeks of supplementation. The liver showed peaks of response in the concentration of GSH after two and four weeks of supplementation with lipoic acid (p <0.05). The concentration of glutathione (GSH) in the muscle of the treated group was significantly higher after three weeks (p <0.05).After four weeks, the total antioxidant capacity against peroxiradicals in the muscle of supplemented animals was significantly higher (p <0.05). The levels of lipid peroxidation were not reduced by supplementation with lipoic acid in the evaluated organs (p> 0.05). However, the level of malondialdehyde was influenced by time. The level of lipid peroxidation in the intestines of both groups was significantly higher in the fourth week (p <0.05). In the liver, the level of lipid peroxidation showed a tendency to decrease after three weeks in both groups (p <0.05). These results suggest that lipoic acid induces differentiated antioxidant responses in a specific way in juveniles of C. carpio. The specific organ response can be explained by the particular metabolic differences of each organ,that can induce a particular redox state for each of them. In conclusion, supplementation with lipoic acid (1 g/kg) is an effective and safe dose to induce antioxidant responses and improve the antioxidant status in juvenile common carp organs. A minimum of two weeks of supplementation is required to influence antioxidant responses in the intestine and liver, and three weeks in muscle.