| A total of 540 young grass carp(Ctenopharyngodon idella) (280±1.1 g) were fed graded levels of histidine (2.0,3.7,5.9,7.9,9.8 and 12.2 g/kg diet) for 8 weeks to investigate the effects of dietary histidine on growth performance and flesh quality of young grass carp. At the end of the feeding trail,30 fish with similar weight from each treatment were exposed to 0.7 mg copper/L of water for 4 days to investigate the protective effects of histidine on intestinal damage of young grass carp.The results indicated that dietary histidine significantly increased the percentage weight gain (PWG), feed intake (FI), feed efficiency (FE) and protein efficiency ratio (PER), as well as decreased plasma ammonia concentration (PAC) (P<0.05). Additionally, optimum histidine significantly increased muscle protein, lipid and hydroxyproline concentration, enhanced shear force value (SFV) and pH, as well as decreased cooking loss, cathepsins B and L activities and lactic acid content (P<0.05). Optimum histidine significantly decreased MDA and PC contents, and enhanced copper, zinc-superoxide dismutase (SOD1), glutathione peroxidase (GPx) and catalase (CAT) activities as well as glutathione (GSH) content in muscle (P<0.05). Moreover, histidine significantly up-regulated SOD1, GPx, CAT, and NF-E2-related factor-2 (Nrf2), TOR and S6K1, down-regulated Kelch-like-ECH-associated protein 1 (Keapl) mRNA levels in muscle (P<0.05). In addition, Cu exposure significantly down-regulated claudin-c, claudin-3, claudin-15, occludin and ZO-1 mRNA levels in the intestine, histidine could significantly up-regulate these mRNA levels. Histidine significantly down-regulated tumour necrosis factor α (TNF-α) and interleukin 8 (IL-8), up-regulated interleukin 10 (IL-10) and transforming growth factor β (TGF-β) mRNA levels to inhibit Cu-induced intestinal inflammation. Cu exposure significantly decreased GSH content as well as SOD1 and GPx activities and mRNA levels in the intestine. Moreover, Cu exposure significantly down-regulated signaling molecules NF-κB inhibitor protein (IκB) and Nrf2, as well as up-regulated nuclear factor kappa B (NF-κB) and Keapl mRNA levels in the intestine, and these changes were completely blocked by histidine supplementation (P< 0.05). Based on the quadratic regression analysis for PWG, GPx and SFA, the requirement of histidine for young grass carp (279.1-685.4 g) were estimated to be 7.53, 8.31 and 8.62 g/kg, or 24.43,26.96 and 27.97 g/kg CP, respectively.In conclusion, the present study results indicated that dietary histidine improved growth performance. Meanwhile, histidine could improve flesh quality party via enhancing non-enzyme antioxidant (GSH) and antioxidant enzyme activities in muscle. The enhancement of antioxidant enzyme activities were closely related to the mRNA levels of antioxidant enzyme and Nrf2 signaling molecule。Additionally, histidine could efficiency protect intestinal damage, which are associated with keeping integrity of barrier function and structure. Histidine maintained the function of intestinal barrier partly via regulating cytokines and NF-κB signaling molecule. Histidine could keep the integrity of intestine partly via decreasing lipid peroxidation and protein oxidation, as well as enhancing non-enzyme antioxidant (GSH), antioxidant enzyme activities and mRNA levels and up-regulating Nrf2 signaling molecule. |
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