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Dietary leucine improves flesh quality and alters mRNA expressions of Nrf2-mediated antioxidant enzymes in the muscle of grass carp (Ctenopharyngodon idella)

Deng, Yu-Ping, Jiang, Wei-Dan, Liu, Yang, Qu, Biao, Jiang, Jun, Kuang, Sheng-Yao, Tang, Ling, Tang, Wu-Neng, Wu, Pei, Zhang, Yong-An, Zhou, Xiao-Qiu, Feng, Lin
Aquaculture 2016 v.452 pp. 380-387
Ctenopharyngodon idella, antioxidant activity, antioxidants, catalase, cathepsin L, cooking quality, copper, dietary protein, enzyme activity, essential amino acids, gene expression, gene expression regulation, glutathione, glutathione peroxidase, hydroxyproline, leucine, lipid content, malondialdehyde, meat quality, messenger RNA, muscle protein, muscles, superoxide dismutase, zinc
The objective of the study was to assess the influence of dietary leucine on flesh quality and the mRNA level of Nrf2-mediated antioxidant enzymes in the muscle of grass carp (Ctenopharyngodon idella). A total of 540 grass carp (295.85±2.07g) were fed six diets with graded levels of leucine (7.1, 8.9, 11.0, 13.3, 15.2 and 17.1gkg−1 diet) for eight weeks. The result indicated that muscle protein, lipid content, muscle EAA (essential amino acid) levels, shear force, and hydroxyproline concentration were significantly improved by 11.0–17.1, 8.9–17.1, 8.9–17.1, 11.0–13.3, 8.9–13.3gleucinekg−1 diet supplementations, respectively. On the other hand, cooking loss, activities of cathepsin L, malondialdehyde and protein carbonyl contents exhibited an opposite tendency. Moreover, the results indicated that compared with leucine unsupplemented group (7.1gleucinekg−1 diet), 8.9–17.1, 11.0–17.1, 11.0–15.2 and 8.9–15.2gkg−1 leucine supplementations significantly enhanced the activities of copper/zinc superoxide dismutase (SOD1), catalase (CAT) and glutathione peroxidase (GPx), and glutathione content, respectively. Furthermore, the changes in the relative mRNA expressions of SOD1, CAT, GPx, nuclear factor erythroid 2-related factor 2 (Nrf2), target of rapamycin (TOR), and ribosomal protein S6 kinase beta-1 (S6K1) induced by leucine were similar to those noted in their enzyme activities. Conversely, the mRNA levels of Kelch-like ECH-associated protein 1 (Keap1) were significantly down-regulated by leucine supplementation. In conclusion, optimum leucine improved flesh quality, partly due to the enhancement of antioxidant capacity through regulating antioxidant-related signaling molecule. Based on muscle MDA, the optimum dietary leucine requirements of young grass carp (296–690g) for flesh quality were estimated to be 12.8gkg−1 diet, corresponding to 39.3gkg−1 of dietary protein.