title: Flesh quality loss in response to dietary isoleucine deficiency and excess in fish: a link to impaired Nrf2-dependent antioxidant defense in muscle.
abstract: The present study explored the impact of dietary isoleucine (Ile) on fish growth and flesh quality and revealed a possible role of muscle antioxidant defense in flesh quality in relation to dietary Ile. Grass carp (weighing 256.8±3.5 g) were fed diets containing six graded levels of Ile (3.8, 6.6, 9.3, 12.5, 15.2 and 18.5 g/kg) for eight weeks. The results indicated that compared with Ile deficiency (3.8 g/kg diets) and excess (18.5 g/kg diets) groups, 9.3-15.2 g Ile/kg diet supplementations promoted fish growth and muscle fat deposition, whereas 6.6-15.2 g Ile/kg diets supplementation enhanced muscle nutrients (protein and total EAAs) deposition. Furthermore, muscle shear force, pH value, and hydroxyproline concentration were improved by 9.3-12.5, 9.3 and 9.3 g Ile/kg diet supplementations, respectively. However, muscle cooking loss, lactate content, and activities of cathepsin B and L were decreased by 6.6-15.2, 9.3-12.5, 9.3-12.5 and 9.3-15.2 g Ile/kg diet supplementations, respectively. Additionally, 6.6-15.2 and 6.6-12.5 g Ile/kg diet supplementations attenuated malondialdehyde and protein carbonyl contents, respectively. The activities of copper/zinc superoxide dismutase (Cu/Zn-SOD) and glutathione peroxidase (GPx), and glutathione content were enhanced by 6.6-9.3, 6.6-12.5 and 6.6-15.2 g Ile/kg diet supplementations, respectively. Moreover, the relative mRNA expressions of antioxidant enzymes, including Cu/Zn-SOD (6.6-12.5 g/kg diets) and GPx (12.5 g/kg diets), as well as antioxidant-related signaling molecules, including NF-E2-related factor 2 (Nrf2) (6.6-12.5 g/kg diets), target of rapamycin (6.6-12.5 g/kg diets), ribosomal S6 protein kinase 1 (9.3-12.5 g/kg diets) and casein kinase 2 (6.6-12.5 g/kg diets), were up-regulated when Ile diet supplementations were administered at these levels, respectively, whereas the relative mRNA expression of Kelch-like ECH-associated protein 1 was down-regulated with 9.3 g Ile/kg diet supplementations. Collectively, the present study indicated that optimum isoleucine improved flesh quality, partly due to the activation of antioxidant defense through the Nrf2 signaling pathway.
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Chengdu, Sichuan, China.
authors.forename: Lu
authors.initials: L
authors.lastname: Gan
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Chengdu, Sichuan, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Chengdu, Sichuan, China.
authors.forename: Wei-Dan
authors.initials: WD
authors.lastname: Jiang
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Chengdu, Sichuan, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Chengdu, Sichuan, China.
authors.forename: Pei
authors.initials: P
authors.lastname: Wu
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Chengdu, Sichuan, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Chengdu, Sichuan, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Chengdu, Sichuan, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Chengdu, Sichuan, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Jiang
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Chengdu, Sichuan, China.
authors.forename: Shu-Hong
authors.initials: SH
authors.lastname: Li
authors.affiliation: Animal Nutrition Institute, Sichuan Academy of Animal Science, Chengdu, Sichuan, China.
authors.forename: Ling
authors.initials: L
authors.lastname: Tang
authors.affiliation: Animal Nutrition Institute, Sichuan Academy of Animal Science, Chengdu, Sichuan, China.
authors.forename: Sheng-Yao
authors.initials: SY
authors.lastname: Kuang
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Chengdu, Sichuan, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Chengdu, Sichuan, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Feng
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Chengdu, Sichuan, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu, Sichuan, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Chengdu, Sichuan, China.
authors.forename: Xiao-Qiu
authors.initials: XQ
authors.lastname: Zhou
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D050218:Body Fat Distribution; D002347:Carps; D047390:Casein Kinase II / Q000378:metabolism; D004032:Diet; D019587:Dietary Supplements; D005786:Gene Expression Regulation; D005978:Glutathione / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000378:metabolism; D007532:Isoleucine / Q000494:pharmacology*; D008315:Malondialdehyde / Q000378:metabolism; D008460:Meat / Q000032:analysis*; D009132:Muscles / Q000378:metabolism*; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D009753:Nutritive Value / Q000187:drug effects*; D018384:Oxidative Stress / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D000975:Antioxidants; D051267:NF-E2-Related Factor 2; D012333:RNA, Messenger; D007532:Isoleucine; D008315:Malondialdehyde; D005979:Glutathione Peroxidase; D013482:Superoxide Dismutase; D047390:Casein Kinase II; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D005978:Glutathione