RESUMO
The heavy metal poisoning in humans and fish represents a significant global problem. Copper (Cu), as an essential micronutrient in human and animal metabolism, often accumulates excessively in aquatic environment. The microbial floc is rich in a variety of probiotics and bioactive compounds, which has been documented to have the functions of antioxidant and immunoenhancement. A 64-day experiment was conducted to investigate the protective effects and potential mechanisms of dietary supplementation of microbial floc and Cu exposure on inflammatory response, oxidative stress, intestinal apoptosis and barrier dysfunction in Rhynchocypris lagowski Dybowski. A total of four hundred fifty R. lagowski were fed five experimental diets containing graded levels of microbial floc from 0% to 16% (referred to as B0, B4, B8, B12 and B16, respectively) in the first 60 days, and 96 h of acute copper exposure test was carried out in the last four days. The results showed that microbial floc exerted significant alleviative effects by preventing alterations in the levels of bioaccumulation, caspase3, caspase8, caspase9, malondialdehyde and interleukin-6, improving the activities of lysozyme, complement C3, complement C4, immunoglobulin M, alkaline phosphatase, heat shock protein 70, heat shock protein 90 and glutathione peroxidase, catalase, superoxide dismutase, total antioxidant capacity. In addition, microbial floc assisted in regulating the expression of NF-κB/Nrf2 signaling molecule genes, including NF-κB, TNF-α, IL-1ß, IL-8, IL-10, TGF-ß, Keap1, Nrf2, Maf, HO-1, CAT, CuZn-SOD, GCLC and GPX. Overall, our results suggest that dietary supplementation with of microbial floc can alleviate copper-induced inflammation, oxidative stress, intestinal apoptosis and barrier dysfunction in R. lagowski. A suitable supplementation level of approximately 12% microbial floc is recommended in the present study.