Dietary histidine affects intestinal antioxidant enzyme activities, antioxidant gene expressions and inflammatory factors in juvenile blunt snout bream (Megalobrama amblycephala)

Six semipurified diets of graded histidine levels (from 4.1 to 14.2 g/kg) were fed to fish for 8 weeks. The results showed that the intestinal content of malondialdehyde (MDA), activities of total superoxide dismutase (T-SOD) and glutathione peroxidase (GPx) were noticeably lower in 8.0 g/kg diet compared to control group. While the lowest activities of copper-zinc superoxide dismutase (Cu/Zn-SOD) and manganese superoxide dismutase (Mn-SOD) were observed in 9.9 g/kg diet, the intestinal activities of total antioxidant capacity (T-AOC) and catalase (CAT) in 14.2 g/kg diet were noticeably higher than those in 8.0 and 9.9 g/kg diets. Plasma biochemical indexes were not significantly affected by dietary histidine levels. In the intestine, the Kelch-like ECH-associated protein 1 (Keap1) mRNA levels were increased in 8.0 g/kg diet, which suppressed the nuclear translocation of nuclear factor E2-related factor 2 (Nrf2), and subsequently decreased CAT, GPx1, Cu/Zn-SOD and Mn-SOD expression levels. The lowest mRNA levels of interleukin 8 (IL-8) and tumour necrosis factor-alpha (TNF-alpha) were observed in 8.0 g/kg diet, whereas the highest mRNA levels of transforming growth factor-beta (TGF-beta) and interleukin 10 (IL-10) were observed in 8.0 g/kg diet. These results indicated that dietary histidine plays a major role in maintaining intestinal health in juvenile blunt snout bream.