The aim of this study was to assess the effects of dietary
pyridoxine (PN) deficiency on intestinal
antioxidant capacity, cell apoptosis and intercellular tight junction in young grass carp (Ctenopharyngodon idella). A total of 540 young grass carp (231.85 ± 0.63 g) were fed six diets containing graded levels of PN (0.12-7.48 mg/kg diet) for 10 weeks. At the end of the feeding trial, the fish were challenged with Aeromonas hydrophila for 2 weeks. The results showed that compared with the optimal PN level, PN deficiency (1) increased the contents of
reactive oxygen species (ROS),
malondialdehyde (MDA) and
protein carbonyl (PC), decreased the activities and
mRNA levels of
antioxidant enzymes such as
copper,
zinc superoxide dismutase (CuZnSOD),
catalase (CAT),
glutathione peroxidase (GPx),
glutathione-S-transferase (GST) and
glutathione reductase (GR) (P < .05); (2) up-regulated the
mRNA levels of cysteinyl aspartic acid-protease-3 (caspase-3),
caspase-7,
caspase-8,
caspase-9, Bcl-2 associated X
protein (Bax), apoptotic
protease activating factor-1 (Apaf-1) and
Fas ligand (FasL), and down-regulated the
mRNA levels of
inhibitor of apoptosis proteins (IAP),
B-cell lymphoma protein-2 (Bcl-2) and myeloid cell leukaemia-1 (Mcl-1) (P < .05); (3) down-regulated the
mRNA levels of ZO-1,
occludin [only in middle intestine (MI)],
claudin-b,
claudin-c,
claudin-f, claudin-3c, claudin-7a, claudin-7b and claudin-11, and up-regulated the
mRNA levels of claudin-12 and claudin-15a (P < .05), which might be partly linked to Kelch-like-ECH-associated
protein 1a (Keap1a)/
NF-E2-related factor 2 (Nrf2),
p38 mitogen-activated protein kinase (p38MAPK) and
myosin light chain kinase (MLCK) signalling in the intestines of fish. However, the activities and
mRNA levels of MnSOD, the
mRNA levels of Keap1b, c-Jun N-terminal
protein kinase (JNK) and claudin-15b in three intestinal segments, and the
mRNA levels of
occludin in the proximal intestine (PI) and distal intestine (DI) were not affected by graded levels of PN. These data indicate that PN deficiency could disturb the intestinal physical barrier function of fish. Additionally, based on the quadratic regression analysis for MDA content and GST activity, the dietary PN requirements for young grass carp were estimated as 4.85 and 5.02 mg/kg diet, respectively.