Dietary lipid levels in meagre (Argyrosomus regius): Effects on biochemical and molecular indicators of liver

The present study provides characterization of cellular and metabolic responses and examines the antioxidant defence in the liver of meagre (Argyrosomus regius) in relation to dietary lipid consumed (13%, 17% and 21%). Molecular responses were addressed through the levels of Hsp70 and Hsp90 and the phosphorylation of mitogen activated protein kinases (p38-MAPK, the extracellular signal-regulated kinases - ERKs and c-Jun N-terminal kinases - JNKs). Metabolic capacities were assessed by studying the activities of lactate dehydrogenase (L-LDH), malate dehydrogenase (MDH), citrate synthase (CS), lipase (LP) and 3-hydroxyacyl CoA dehydrogenase (HOAD). For the determination of the possible activation of antioxidant defence, the activities of the antioxidant enzymes catalase (CAT) and glutathione reductase (GR) and the levels of thiobarbituric acid reactive substances (TBARS) were studied. The results showed that the 17% and 21%-lipid diets induced Hsp70 and activated the phosphorylation of p38-MAPK, while an induction of Hsp90 was found only in fish fed the 17%-lipid diet. Phosphorylation ratio of both ERKs and JNKs were mostly observed at 17%-lipid diet. Moreover, an increase was also observed on CAT activity levels in fish of 17% diet, while both 17% and 21%-lipid diets led to elevated GR levels. The lowest activity of the metabolic enzymes MDH and HOAD was observed in fish fed with the 17%-lipid diet, while fish under the 21%-lipid diet increased their activity levels compared to 17% group. The lowest activity levels of LP were observed in fish fed with the 21%-lipid diet. L-LDH, CS and TBARS were not affected by the dietary lipid level. The obtained results can be used in order to evaluate the possible effects of the lipid diets on the hepatic physiology of this species.