4-Methylesculetin improves the growth performance of grass carp (Ctenopharyngodon idella) by enhancing the proliferation and structural integrity of the intestinal epithelium

Animal intestines are extremely susceptible to the adverse effects of feed and external conditions within intensive production systems. 4-Methylesculetin (4-ME) is a natural coumarin with a catechol structure and has potent antioxidant and anti-inflammatory properties. This study was investigating the effects of 4-ME as a functional substance added to the diet on the growth performance, intestine growth, and intestinal integrity of juvenile grass carp (<i>Ctenopharyngodon idella</i>). A total of 1080 healthy grass carp (11.40 ± 0.01 g) were randomly assigned to 18 net cages. The experiment was divided into 6 treatment groups with 3 replicates in each group and 60 fish in each replicate. Different levels of 4-ME (0.00, 2.46, 5.14, 10.14, 19.88, and 39.86 mg/kg) were added to the basal diet. The experimental period of 60 days. Dietary supplementation with 10.14 mg/kg 4-ME increased specific growth rate (SGR), feed efficiency (FE), and whole body composition (crude protein and crude fat) (<i>P</i> < 0.05), but there is no significant effect on crude ash (<i>P</i> > 0.05). Dietary supplementation with 10.14 mg/kg 4-ME increased the content of UDP-glycosyltransferase (UGT) enzymes in hepatopancreas (<i>P</i> < 0.001), and digestive and absorptive enzyme activity in the intestine (<i>P</i> < 0.05). Dietary supplementation with 10.14 mg/kg 4-ME promoted intestine somatic index and fold height by increasing intestinal proliferation in intestine (<i>P</i> < 0.05), possibly through the WNT/β-catenin pathway. Dietary supplementation with 10.14 mg/kg 4-ME improved the structural integrity of intestinal apical junctional complex (AJC), including mRNA expression levels of <i>zo-2b,</i> claudin (-b, c, f, 3c, 11, 12) and increased the protein expression levels of ZO-1, occludin and β-catenin (<i>P</i> < 0.05). Dietary supplementation with 10.14 mg/kg 4-ME were decreased mRNA expression levels of claudin-15a, claudin-15b, <i>ROCK, RhoA, MLCK</i> and the protein expression levels of MLCK and ROCK1 (<i>P</i> < 0.05), and its mechanism may have been mediated through the RhoA/ROCK pathway. In addition, according to SGR, diamine oxidase (DAO) and UGT, the appropriate addition of 4-ME in juvenile grass carp were determined to be 9.62, 9.25, and 10.65 mg/kg, respectively. In this experiment, 4-ME was incorporated into the diet as a functional substance to investigate its effects on the growth performance and intestinal health of fish, indicating that 4-ME has potential for development as a functional feed additive in aquaculture production.