The present study explored the possible preventive effects of dietary
glutamate (Glu) on LPS-induced oxidative damage,
mRNA expression changes of tight junction (TJ) and
defensin proteins, inflammatory and apoptosis response signaling molecules in fish intestine. Young Jian carp were fed five diets supplemental graded levels of Glu (0, 4, 8, 16 and 32 g kg-1 diet) for 63 days. The results indicated that Glu supplementation depressed LPS induced the production of
reactive oxygen species (ROS) and severe oxidative damage (lipid peroxidation and
protein oxidation) in fish intestine, which was partially due to the increased
glutathione (GSH) content and
antioxidant enzyme activities including
superoxide dismutase (SOD),
glutathione peroxidase (GPX),
glutathione-S-transferase (GST), and
glutathione reductase (GR) (P < 0.05). Further investigations indicated that Glu supplementation caused elevation of those
antioxidant enzyme activities are related to the up-regulation of corresponding
antioxidant enzymes and the related signaling factor Nrf2
mRNA levels (P < 0.05). Meanwhile, Glu pre-treatment significantly suppressed LPS-induced COX-2 and inflammatory
cytokines mRNA expression and down-regulated NF-κB p65 and
MAPK p38 transcription. Furthermore, pre-treatment with Glu prevented LPS induced apoptosis-related gene expression (
caspase 3 and 9, P < 0.05). Lastly, Glu supplementation also attenuated LPS induced intestinal barrier function-related gene TJ
proteins (ZO-1, occludin1, claudin2, 3, and 7), β-defensin1 and 3 mRNA expressions decreasing (P < 0.05). Taken together, the present results showed Glu could attenuate LPS induced the oxidative damage by Nrf2 signal pathway and depress LPS induced
inflammation response (
cytokines, COX-2, NF-κB p65, and
MAPK p38), apoptosis (caspase3 and 9), and barrier function (ZO-1, occludin1, claudin2, 3 and 7, and β-
defensin 1 and 3)-related gene expression changes of fish intestine.