Dietary supplementation of β-glucan, inulin and emodin modulates antioxidant response and suppresses intestinal inflammation of grass carp (Ctenopharyngodon idellus)

Abstract Excessive use of plant protein can cause various diseases, and functional additives have been proven to improve the health of aquatic fish but its underlying mechanism is still unclear. A 60-day trial was conducted to explore the action mechanism of β-glucan (1 g/kg), inulin (1 g/kg) and emodin (0.1 g/kg) supplementation improving the health of grass carp (initial weight 27.19 ± 0.05 g) fed low fishmeal diet. Our results indicated that emodin exhibited a positive impact on the growth of grass carp. Diet with β-glucan, inulin and emodin displayed hepatoprotective effects through the suppression of activities of serum alanine aminotransferase, aspartate aminotransferase and γ‐glutamyl transaminase, and β-glucan and inulin exerted hypocholesterolemic effects simultaneously. High level of antioxidant parameters in serum and intestine tissue confirmed the antioxidant property of β-glucan, inulin and emodin on grass carp, companying by a notable reduction in malondialdehyde content. Modulation of antioxidant response by β-glucan, inulin and emodin supplementation was to activate Nrf2 signaling pathway and up-regulate the expression of antioxidant genes including catalase and copper/zinc superoxide dismutase. Additionally, TLR4 signaling pathway was notably inhibited by three additive diets, and the transcription level of pro-inflammatory cytokines like IL-1β, TNF-α, and/or IL-6 was dramatically suppressed in intestine tissue simultaneously. Afterward, an enhancement of intestinal barrier function was observed in fish fed β-glucan, inulin and emodin by inducing the overexpression of junction proteins such as Occludin, ZO3, ZO1, and/or ZO2. The above results documented that diet with β-glucan, inulin and emodin could exhibit beneficial impacts on the health of grass carp through the improvement in antioxidant capacity, suppression of inflammatory response, and enhancement of intestinal barrier function.