Stevia chlorogenic acid attenuates oxidized fish oil-induced intestinal injury and lipid metabolism disorder in turbot (Scophthalmus maximus L.) through TLR/NF-KB signaling pathway and gut microbiota

The present study investigated the effects of stevia chlorogenic acid (SCGA) on oxidized fish oil-induced intestinal damage, lipid metabolism disorder, and gut microbiota imbalance in turbot (Scophthalmus maximus L.). Four isonitrogenous and isolipidic experimental diets were formulated: PC (5% fresh fish oil), OFO (5% oxidized fish oil), OFO200 (5% oxidized fish oil + 200 mg/kg SCGA), and OFO400 (5% oxidized fish oil + 400 mg/kg SCGA). Each feed set was randomly fed to triplicate groups of 40 fish (mean weight: 16.99 +/- 0.01 g), and the experiment was conducted for ten weeks. The results showed that long-term feeding with the OFO diet reduced the growth performance of turbot, decreased serum immune parameters and antioxidant enzyme activities, and inhibited the intestinal antioxidant enzyme activities and the expression of antioxidant-related genes. Furthermore, the OFO diet impaired intestinal barrier function by downregulating the mRNA expression of tight junctions proteins and upregulating pro-inflammatory cytokines and apoptosis-related genes expression. It also disrupted the expression of lipid metabolism-related genes, leading to liver lipid deposition, and altered the composition and distribution of the gut microbiota, resulting in gut microbiota imbalance. The addition of SCGA significantly enhances the growth performance of turbot and mitigates the adverse effects of oxidized fish oil on turbot. SCGA improves the intestinal antioxidant capacity and alleviates inflammation responses by modulating the Keap-1/Nrf2 and TLR/NF-KB signaling pathways. It also reduces liver lipid deposition by regulating pathways related to lipid metabolism. Moreover, SCGA modulates the gut microbiota to establish a "gut-liver" axis, thereby enhancing intestinal barrier function and improving hepatic lipid metabolism. In conclusion, SCGA effectively promotes the growth performance of turbot, mitigates intestinal oxidative stress and dysbiosis induced by oxidized fish oil, and regulates lipid metabolism to reduce hepatic lipid deposition.