Glutamine alleviates β-conglycinin-induced enteritis in juvenile hybrid groupers Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂ by suppressing the MyD88/NF-κB pathway

Abstract

Soybean is a potential alternative protein source for fish feeds; however, it contains a number of allergens, of which β-conglycinin (7S) is a major component. 7S is known to cause intestinal inflammation and decrease the immunity of several cultured fish species, including hybrid groupers (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂). Glutamine supplementation has been used to promote immunity and intestinal morphology in fish. This study investigated the mitigative effects of glutamine on the growth suppression and intestinal inflammation induced by 7S in juvenile hybrid groupers. Four isonitrogenous (48% crude protein) and isolipidic (11% crude lipid) trial diets were formulated: a fishmeal-based diet (FM), a diet containing 7% 7S, and 7S diets supplemented with 1% or 2% alanine-glutamine (1% and 2% Ala-Gln). Compared with Group 7S, fish fed the 2% Ala-Gln diet had increased weight gain and specific growth rates; enhanced intestinal muscular layer thickness, plica height, and plica width; increased intestinal lysozyme and acid phosphatase activities as well as complement (C3 and C4) and immunoglobulin M contents; reduced expression levels of myd88, ikkβ, nf-κb p65, tnf-α, il-1β, ifn-α and hsp70 genes; enhanced relative abundances of potentially beneficial bacterial genera Akkermansia, Allobaculum, Ileibacterium, Bifidobacterium, Blautia, Lactobacillus and Sharpea. These results demonstrate that dietary glutamine probably enhances the intestinal immune defence to alleviate enteritis by inhibiting the MyD88/NF-κB pathway, and also alters the microbiome, ultimately increasing grouper growth. Thus, when the content of 7S in grouper feed exceeds 7%, supplementation with 2% Ala-Gln is recommended.