Activated charcoal supplementation in cottonseed meal-based feed improved growth performance and antioxidant capacity through enhancing intestinal barrier function in grass carp juveniles (Ctenopharyngodon idellus)

To evaluate the efficiency of activated charcoal (AC) in cottonseed meal-based feed (CSM; 38.46 % CSM, 1275 mg/kg free gossypol), experimental diets supplemented with 0 % AC, 1.5 % AC and 3.0 % AC were prepared and used to feed grass carp juveniles (Ctenopharyngodon idellus, initial weight of 5.0±0.5 g) for 8 weeks. The results showed that the 1.5 % AC group significantly increased final body weight (FBW), weight growth rate (WGR), specific growth rate (SGR), and activated the expressions of intestinal barrier-associated genes zonula occludens-1 (zo-1), zo-2 and claudin-c compared with 0 % AC group (P < 0.05). Additionally, the 1.5 % AC and the 3.0 % AC groups significantly promoted the expression of claudin-12 (P < 0.05). Compared with the 0 % AC group, the 1.5 % AC group had significantly higher total protein (TP) concentration and significantly lower glucose (GLU) concentration and aspartate aminotransferase (AST) activity (P < 0.05). Liver antioxidant results showed that supplementation with 1.5 % AC and 3.0 % AC groups significantly reduced malondialdehyde (MDA) content and increased glutathione reductase (GR) activity (P < 0.05). Total-superoxide dismutase (T-SOD) and glutathione-S-transferase (GST) activities were significantly higher in the 1.5 % AC group than those in the other groups (P < 0.05). The antioxidant gene results showed that gr and GST omega 1 (gsto1) levels were significantly higher in the 3.0 % AC group than in the 0 % AC group (P < 0.05). The 1.5 % AC group significantly promoted nuclear factor erythroid 2-related factor 2 (nrf2) expression, and the 1.5 % AC and 3.0 % AC groups significantly inhibited the expressions of kelch-like ECH-associated protein 1 (keap1a) and keap1b (P < 0.05). Liver apoptotic and inflammatory genes showed that the expressions of caspase 9 (casp9), BCL2 associated X a (baxa), nuclear factor-kappa B (nfκb) and inhibitor of kappa B (iκb) were significantly lower in the 1.5 % AC group than those in the other groups (P < 0.05). The expression of casp8 in the 1.5 % AC group was significantly lower than in the 0 % AC group (P < 0.05). Additionally, the expressions of p38 mitogen-activated protein kinase (p38MAPK) and iκb kinase-beta (ikkβ) were significantly suppressed in the 1.5 % AC group and 3.0 % AC group (P < 0.05). In summary, 1.5 % AC supplementation in CSM-based feed can enhance intestinal barrier function, alleviate CSM-based feed-induced apoptosis, improve liver antioxidant, and thus promote grass carp weight growth rate.