Dietary high β-conglycinin reduces the growth through enhancing hepatic lipid peroxidation and impairing intestinal barrier function of orange-spotted grouper (Epinephelus coioides)

Abstract

β-conglycinin is one of the major soy antigen proteins in soybean meal (SBM) and exhibits growth inhibition and intestinal health damage in grouper, but the underlying mechanisms are still poorly understood. In this study, orange-spotted grouper (Epinephelus coioides) was used to investigate whether the poor growth performance induced by dietary β-conglycinin levels is associated with intestinal structural integrity disruption, the intestinal apoptosis and intestinal microbiota. The basal diet (FM diet) was formulated to contained 48% protein and 12% fat without SBM supplementation. Fish meal protein in the FM diet was replaced by SBM to prepare a high SBM diet (SBM diet). β-conglycinin at 3% and 7% were added into FM diets to prepare two diets (B-3 and B-7). Triplicate groups of fish (20 fish/tank) were fed one of the experimental diets twice daily in a feeding period of 8 weeks. Compared with FM diet, fish fed diets SBM and B-7 had decreased the growth rate, hepatosomatic index, whole-body lipid and ash contents, and increased whole-body moisture content. However, the maximum growth was observed for diet B-3 and was not different from that of FM diet. The liver total antioxidant capacity and glutathione peroxidase activity, the muscle layer thickness of middle and distal intestine, and the mucosal fold length of distal intestine were lower, while liver malondialdehyde content, intestinal diamine oxidase activity, d-lactic acid and endotoxin contents, and the number of intestinal apoptosis were higher in SBM and B-7 groups than that in FM and/or B-3 groups. SBM and B-7 diets down-regulated the intestinal expression of tight junction genes (occludin, claudin-3 and ZO-1), apoptosis genes (bcl-2 and bcl-xL) and anti-inflammatory factor genes (IκBα, TGF-β1 and IL-10), but up-regulated the intestinal expression of apoptosis genes (caspase-3, caspase-8 and caspase-9) and pro-inflammatory factor genes (NF-κB1, RelA, TAK1, IKK, MyD88, TNF-α, IL-1β, and IL-8) vs FM and/or B-3 diets. The richness and diversity indexes of OTUs, Chao1, ACE, Shannon and Simpson were not affected by dietary treatments. The relative abundances of intestinal bacteria (phylum Proteobacteria and genus Vibrio) were generally higher, and relative abundance of phylum Tenericutes was lower in SBM and/or B-7 groups than that in B-3 group. The above results indicate that high dietary β-conglycinin level, rather than intermediate level could decrease liver antioxidant capacity, reshape the intestinal microbiota, and impair the intestinal normal morphology through disrupting the intestinal tight junction structure, increasing intestinal mucosal permeability, and promoting intestinal apoptosis, which in turn triggers intestinal inflammatory responses and the occurrence of enteritis, and ultimately leads to poor growth performance in fish.