Stevia chlorogenic acid strengthens intestinal mucosal barrier function and alleviates soybean meal-induced enteritis in turbot (Scophthalmus maximus).

A 10-week feeding trial was performed to assess the potential benefits of stevia chlorogenic acid (SCGA) on intestinal health in turbot receiving high plant-protein feeds. Juvenile turbot (13.52 ± 0.03 g) were randomly assigned to four isonitrogenous and isolipidic dietary treatments: a fish meal-based control diet (PC), a soybean meal (SBM) replacement diet (HP, replacing 25% of fish meal protein with SBM), and two HP-based diets supplemented with 200 (HP200) or 400 mg/kg (HP400) SCGA. Results indicated that the HP200 group exhibited a significantly higher FI, while the HP400 group showed significantly improved FBW, WGR, and SGR compared to the HP group. And the HP group exhibited significantly decreased serum immune parameters (LZM, ALP, ACP) and intestinal digestive and antioxidant enzyme activities (trypsin, α-amylase; CAT, SOD, T-AOC), alongside significantly increased metabolic indices (TG and GLU) and D-LA and intestinal MDA levels. Concurrently, the HP group exhibited impaired intestinal morphology, significantly up-regulated expression of genes related to TLR signaling (TLR2, TLR3, MyD88, JNK), pro-inflammatory (IL-8, INF-γ,TNF-α), apoptosis (Caspase-3, -7, -9), while the expression of genes associated with tight junctions (Claudin-3, -7, ZO-1), anti-inflammatory (IL-10, TGF-β1), the Bcl-2/Bax ratio, and antioxidant (CAT, SOD, GSH-Px, GST zeta1, Nrf2, HO-1) was significantly down-regulated. The inclusion of SCGA at either 200 or 400 mg/kg in the diet effectively alleviated these adverse effects. Specifically, SCGA effectively enhanced serum biochemical parameters as well as digestive and antioxidant enzyme activities. It also improved intestinal morphology and normalized the dysregulated expression of the aforementioned genes. In conclusion, SCGA improves the growth performance of turbot and ameliorates SBM-induced intestinal damage by promoting intestinal homeostasis through multi-dimensional mechanisms, including barrier repair, inflammation alleviation, enhanced antioxidant capacity, and optimized digestion and absorption. The TLR/MAPK/NF-κB and Keap1/Nrf2 signaling pathways may serve as key targets underlying these beneficial effects.