Effects of dietary protein levels on free amino acid and glutathione contents in the tissues of rainbow trout

Starvation and re-feeding affect Hsp expression, MAPK activation and antioxidant enzymes activity of European sea bass (Dicentrarchus labrax)

In the context of food deprivation in fish (wild and farmed), understanding of cellular responses is necessary in order to develop strategies to minimize stress caused by starvation in the aquaculture section. The present study evaluates the effects of long term starvation (1F-3S: one-month feeding-three-month starvation) and starvation/re-feeding (2S-2F: two-month starvation-two-month re-feeding) compared to the control group (4F-0S: four-month feeding-zero month starvation) on cellular stress response and antioxidant defense in organs, like the intestine, the liver, the red and white muscle of European sea bass Dicentrarchus labrax. Molecular responses were addressed through the expression of Hsp70 and Hsp90, the phosphorylation of stress-activated protein kinases and particularly p38 mitogen-activated protein kinase (p38 MAPK) and the extracellular signal-regulated kinases (ERK-1/2). For the determination of the effect of the oxidative stress caused by food deprivation and/or re-feeding, the (maximum) activities of antioxidant enzymes such as glutathione peroxidise (GPx), catalase (CAT) and superoxide dismutase (SOD) as well as the determination of thiobarbituric acid reactive substances (TBARS) were studied. The experimental feeding trials caused a tissue distinct and differential response on the cellular and antioxidant capacity of sea bass not only during the stressful process of starvation but also in re-feeding. Specifically, the intestine phosphorylation of ERKs and antioxidant enzymatic activities increased in the 2S-2F fish group, while in the 1F-3S group an increase was detected in the levels of the same proteins except for GPx. In the liver and the red muscle of 2S-2F fish, decreased Hsp70 and phosphorylated p38 MAPK levels and increased Hsp90 levels were observed. Additionally, SOD activity decreased in the red muscle of 2S-2F and 1F-3S groups. In the liver and red muscle of 1F-3S group Hsp70 levels increased, while the activation of p38 MAPK in the liver decreased. In the white muscle, Hsp90 levels decreased and the phosphorylation of p38 MAPK increased in both feeding regimes compared to control. In the same tissue, GPx and catalase levels were decreased in 2S-2F regime, while SOD levels were decreased in 1F-3S regime.