Citric acid could strengthen the intestinal tight junction barrier and improve intestinal immune function in vivo and vitro experiments of hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂)

In this experiment, the primary intestinal epithelial cells (IECs) inflammation model was constructed to investigate the intestinal injury mechanism under high level addition of plant-derived proteins in hybrid grouper ( Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂ ), and citric acid (CA) addition was used to investigate the protective effect in the primary IECs inflammation model. The vitro experiment was fed 30 fishes to three replicates of each group for 8 weeks. In the inflammation model of IECs, the addition of CA (1 mM) remarkably enhanced cell survival, and significantly reduced the secretion of inflammatory cytokines TNF-α and IL-1β ( P < 0.05). CA activated phosphorylation of S6K and 4EBP-1 in the mTOR pathway and promoted the protein expression of tight junction proteins (ZO-1, E-cadherin, occludin and claudin-1) ( P < 0.05). The supplementation of CA in the diet also could improve the expression of tight junction in intestine of hybrid grouper ( P < 0.05). CA attenuated the protein expression of inflammatory cytokines (IL-1β, IL-6 and TNF-α) in inflammation models by regulating ERK and NF-κB pathways ( P < 0.05). These findings suggest that citric acid enhances cell survival, strengthens the intestinal tight junction barrier and enhances intestinal immune function in the LPS-stimulated inflammatory model of IECs. Citric acid could serve as an effective means to counteract growth inhibition and reduced digestibility caused by high proportions of plant protein in fish feed. • In the inflammation model of IECs, CA (1 mM) remarkably enhanced cell survival, and significantly reduced the secretion of inflammatory cytokines TNF-α and 1L-1β ( P < 0.05). • CA(1 mM) activated phosphorylation of S6K and 4EBP-1 in the mTOR pathway and promoted the protein expression of tight junction proteins (ZO-1, E-cadherin, occludin1 and claudin-1). The supplementation of CA in the diet also could improve the expression of tight junction in intestine of hybrid grouper. • CA attenuated the protein expression of inflammatory cytokines (1L-1β, 1L-6 and TNF-α) in inflammation models by regulating ERK and NF-κB pathways.