Abstract

This investigation used the same growth trial as the previous study, which showed that folic acid deficiency retarded growth in young grass carp (the percent weight gain of Groups 1-6 were 102.32±3.41%, 137.25±10.48%, 179.78±3.95%, 164.33±3.21%, 143.35±8.12% and 115.28±2.66%) [1]. In the present study, we investigated the effects of dietary folic acid on the immune response, antioxidant status and tight junctions in the intestine of young grass carp (Ctenopharyngodon idella). A total of 540 young grass carp were fed diets containing graded levels of folic acid at 0.10, 0.47, 1.03, 1.48, 1.88 and 3.12mgkg(-1) diet for 8 weeks. The results indicated that acid phosphatase and lysozyme activities, and the complement component 3 content in the proximal intestine (PI), mid intestine (MI) and distal intestine (DI) were decreased with folic acid deficiency (0.1mgkg(-1))(P<0.05). Folic acid deficiency (0.1mgkg(-1)) up-regulated interleukin 1β, interleukin 8, tumor necrosis factor α, nuclear factor κB p65 (NF-κB p65), IκB kinase α (IKK-α), IKK-β and IKK-γ gene expression, meanwhile down-regulated interleukin 10, transforming growth factor β, IκB and target of rapamycin gene expression in the PI, MI and DI (P<0.05). These data suggested that folic acid deficiency decreased fish intestinal innate immune function may be partly contributed to the regulation of NF-κB p65 pathway. Moreover, the activities and corresponding gene expression of glutathione content, Cu/Zn superoxide dismutase, catalase, glutathione peroxidase, glutathione s-transferases and glutathione reductase in fish intestine were depressed by deficient folic acid diet (0.1mgkg(-1))(P<0.05). Furthermore, folic acid deficiency (0.1mgkg(-1)) down-regulated NF-E2-related factor 2 (Nrf2) gene expression, up-regulated Kelch-like-ECH-associated protein 1a (Keap1a) and Keap1b gene expression in fish intestine (P<0.05). These data indicated that deficient folic acid diet damaged fish intestinal antioxidant capacity partly by regulating Nrf2/Keap1 pathway. Additionally, folic acid deficiency (0.1mgkg(-1)) down-regulated claudin-b, claudin-c, claudin-3, occludin and zonula occludens 1 gene expression; whereas folic acid deficiency (0.1mgkg(-1)) up-regulated claudin-12, claudin-15, myosin light chain kinase (MLCK) and p38 mitogen activated protein kinase (p38 MAPK) gene expression in the PI, MI and DI (P<0.05), suggesting that folic acid deficiency may damage fish intestinal tight junctions associated with the mediation of MLCK and p38 MAPK gene expression. In conclusion, folic acid deficiency (0.1mgkg(-1)) impaired fish intestinal immunity, antioxidant capacity and tight junctions.

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