New perspectives on the mechanism of curcumin in the gill mucosal immune barrier damaged by ochratoxin A in juvenile grass carp (Ctenopharyngodon idella)

Ochratoxin A (OTA) is a prevalent contaminant in fish feed, posing a threat to aquatic health. Curcumin (Cur), a widely used feed additive renowned for its antioxidant and anti-inflammatory functions, has emerged as a potential solution. Gills are one of the mucosal immune organs in fish. Adding a natural product to feed is one of the most popular strategies to alleviate mycotoxin. At present, it is unknown whether dietary Cur can alleviate the damage to the fish gill barrier caused by ochratoxin A in the diet. Here, we explored the mitigation effects of Cur on the physical, chemical, and immune barriers of gills in grass carp damaged by OTA. This study employed 720 juvenile grass carp (initial average body weight: 11.06 ± 0.05 g) were randomly assigned into 4 groups: the control group (devoid of OTA and Cur), the 1.2 mg/kg OTA group, the 400 mg/kg Cur group, with three replicates per treatment (180 fish) over a 60-day period. Results demonstrated that Cur supplementation could significantly counter OTA-induced damage to the gill barrier through distinct mechanisms: (1) Inhibition of OTA absorption while promoting efflux transporters mRNA expression, thereby diminishing OTA residuals. (2) Enhancement of the physical barrier by fortifying antioxidant defenses, reducing apoptosis, and strengthening tight junctions. (3) Improvement of the chemical barrier by elevating goblet cells, immune components, and antimicrobial peptides. (4) Enhanced the immune barrier by suppressing toll-like receptor 4 and nuclear factor-κB signaling pathways, leading to reduced expression of pro-inflammatory factors and increased T cell differentiation-related genes. In conclusion, Cur emerges as an effective agent in alleviating OTA-induced gill immune function, enhancing physical, chemical, and immune barriers. This study provides a valuable theoretical foundation and practical significance for employing Cur to mitigate the mucosal immune toxicity of OTA in fish.