This study evaluated the effect of
dietary sodium butyrate (SB) supplementation on the intestinal physical barrier function of young grass carp (Ctenopharyngodon idella). The fish were fed one powdery
sodium butyrate (PSB) diet (1000.0 mg kg-1 diet) and five graded levels of microencapsulated
sodium butyrate (MSB) diets: 0.0 (control), 500.0, 1000.0, 1500.0 and 2000.0 mg kg-1 diet for 60 days. Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila to explore the effect of SB supplementation on intestinal physical barrier function and the potential mechanisms in fish. The results showed that optimal SB supplementation: (1) down-regulated the
cysteine-aspartic protease-2 (caspase-2),
caspase-3 (rather than PI),
caspase-7,
caspase-8 (rather than PI),
caspase-9,
fatty acid synthetase ligand (FasL), apoptotic
protease activating factor-1 (Apaf-1),
B-cell lymphoma 2 associated X
protein (Bax) and c-Jun Nterminal
protein kinase (JNK)
mRNA levels, up-regulated the
B-cell lymphoma protein-2 (Bcl-2) (rather than PI),
inhibitor of apoptosis proteins (IAP) and myeloid cell leukemia-1 (Mcl-1)
mRNA levels in the intestine (P < 0.05), inhibited the intestinal cell apoptosis, maintained the intestine cell structure integrity; (2) increased
NF-E2-related factor 2 (Nrf2)
mRNA levels and nucleus
protein levels, and down-regulated kelch-like-ECH-associated
protein (Keap1b) (rather than Keap1a)
mRNA levels in the intestine, up-regulated
copper/
zinc superoxide dismutase (CuZnSOD),
manganese superoxide dismutase (MnSOD),
catalase (CAT),
glutathione peroxidase 1a (GPx1a), GPx1b, GPx4a, GPx4b,
glutathione S-
transferases R (GSTR), GSTP1, GSTP2, GSTO1, GSTO2 and
glutathione reductase (GR)
mRNA levels in the intestine, increased the corresponding
antioxidant enzymes activity (P < 0.05), thus enhancing the ability of scavenging
free radicals and decreasing the
reactive oxygen species (ROS) content, decreasing the
lipid and
protein peroxidation, as well as alleviating oxidative damage; (3) down-regulated the molecule
myosin light-chain kinase (MLCK)
mRNA levels in the intestine, and up-regulated the
occludin, zonula occludens-1 (ZO-1), ZO-2,
claudin-b,
claudin-c,
claudin-f, claudin-3c (rather than PI), claudin-7a, claudin-7b and claudin-11
mRNA levels, down-regulated claudin-12, claudin-15a and claudin-15b
mRNA levels (P < 0.05), thus maintaining the structural integrity between cells. This study suggests that SB supplementation could improve fish intestinal physical barrier function. Furthermore, according to the positive effect, MSB was superior to PSB on improving intestinal physical barrier function of fish. Finally, based on
protein carbonyl content in the PI, the optimal SB supplementation (MSB as SB source) for young grass carp was estimated to be 338.8 mg kg-1 diet.