title: Dietary phenylalanine-improved intestinal barrier health in young grass carp (Ctenopharyngodon idella) is associated with increased immune status and regulated gene expression of cytokines, tight junction proteins, antioxidant enzymes and related signalling molecules.
abstract: The present work evaluated the effects of dietary phenylalanine (Phe) on the intestinal immune response, tight junction proteins transcript abundance, and the gene expression of immune- and antioxidant-related signalling molecules in the intestine. In addition, the dietary Phe (and Phe + Tyr) requirement of young grass carp (Ctenopharyngodon idella) was also estimated. Fish were fed fish meal-casein-gelatin based diets (302.3 g crude protein kg(-1)) containing 3.4 (basal diet), 6.1, 9.1, 11.5, 14.0 and 16.8 g Phe kg(-1) with a fixed amount of 10.7 g tyrosine kg(-1) for 8 weeks. The results showed that Phe deficiency or excess Phe reduced the lysozyme and acid phosphatase activities and complement C 3 content in the intestine (P < 0.05). Moreover, zonula occludens-1 (ZO-1), occludin and claudin c mRNA levels were highest in the fish fed the diet containing 11.5 g Phe kg(-1) (P < 0.05). However, claudin 12 and claudin b mRNA levels were not significantly affected by dietary Phe (P > 0.05). Gene expression of interleukin-10 (IL-10), transforming growth factor-β1 (TGF-β1), target of rapamycin (TOR) and inhibitor of nuclear factor κBα (IκBα) in proximal intestine (PI), mid intestine (MI) and distal intestine (DI) increased as dietary Phe increased up to 6.1, 9.1, 11.5 and 14.0 g kg(-1), respectively (P < 0.05). However, interleukin-8 (IL-8), tumour necrosis factor-α (TNF-α) and nuclear factor-κB p65 (NF-κB p65) mRNA levels showed opposite tendencies. In addition, the mRNA level of superoxide dismutase (SOD) was significantly lower in the intestinal tissue of the group fed a diet with Phe levels of 16.8 g kg(-1) than in those of other groups (P < 0.05). The expression of NF-E2-related factor 2 (Nrf2) gene was increased as dietary Phe increased up to 9.1 g kg(-1) (P < 0.05). In conclusion, Phe improved intestinal immune status, and regulated gene expression of cytokines, tight junction proteins, antioxidant enzymes, NF-κB p65, IκBα, TOR, and Nrf2 in the fish intestine. Based on the quadratic regression analysis of lysozyme activity at a 95% maximum, the dietary Phe requirement of young grass carp (256-629 g) was estimated to be 8.31 g kg(-1), corresponding to 2.75 g 100 g(-1) protein.
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Feng
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China.
authors.forename: Wen
authors.initials: W
authors.lastname: Li
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China.
authors.forename: Wei-Dan
authors.initials: WD
authors.lastname: Jiang
authors.affiliation: Animal Nutrition Institute, Sichuan Academy of Animal Science, Chengdu, 610066, China.
authors.forename: Sheng-Yao
authors.initials: SY
authors.lastname: Kuang
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Jiang
authors.affiliation: Animal Nutrition Institute, Sichuan Academy of Animal Science, Chengdu, 610066, China.
authors.forename: Ling
authors.initials: L
authors.lastname: Tang
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China.
authors.forename: Pei
authors.initials: P
authors.lastname: Wu
authors.affiliation: Animal Nutrition Institute, Sichuan Academy of Animal Science, Chengdu, 610066, China.
authors.forename: Wu-Neng
authors.initials: WN
authors.lastname: Tang
authors.affiliation: Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China.
authors.forename: Yong-An
authors.initials: YA
authors.lastname: Zhang
authors.affiliation: Animal Nutrition Institute, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Fish Nutrition and Safety Production University Key Laboratory of Sichuan Province, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China; Key Laboratory for Animal Disease-Resistance Nutrition of China Ministry of Education, Sichuan Agricultural University, Sichuan, Chengdu, 611130, China. Electronic address: xqzhouqq@tom.com.
authors.forename: Xiao-Qiu
authors.initials: XQ
authors.lastname: Zhou
mesh_terms: D000818:Animals; D002347:Carps / Q000276:immunology*; D002374:Catalase / Q000235:genetics; D057167:Claudins / Q000235:genetics; D016207:Cytokines / Q000235:genetics; D004032:Diet; D029941:Fish Proteins / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects; D005979:Glutathione Peroxidase / Q000235:genetics; D020672:I-kappa B Proteins / Q000235:genetics; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000187:drug effects* / Q000276:immunology; D051267:NF-E2-Related Factor 2 / Q000235:genetics; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000235:genetics; D010649:Phenylalanine / Q000494:pharmacology*; D015398:Signal Transduction; D013482:Superoxide Dismutase / Q000235:genetics; D000072105:Superoxide Dismutase-1; D058570:TOR Serine-Threonine Kinases / Q000235:genetics; D062826:Zonula Occludens-1 Protein / Q000235:genetics
chemical_list: D057167:Claudins; D016207:Cytokines; D029941:Fish Proteins; D020672:I-kappa B Proteins; D051267:NF-E2-Related Factor 2; D016328:NF-kappa B; D062826:Zonula Occludens-1 Protein; D000072000:NF-KappaB Inhibitor alpha; D010649:Phenylalanine; D002374:Catalase; D005979:Glutathione Peroxidase; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D058570:TOR Serine-Threonine Kinases
keywords: Cytokines; Immune status; Nrf; Phenylalanine; TOR; Tight junction proteins