Quercetin dietary supplementation protects against difenoconazole-induced carp spleen inflammatory damage via regulating ROS/NF-κB/NLRP3 inflammasome axis

As a widely used fungicide at present, difenoconazole can enter the aquatic ecosystem and cause adverse effects on freshwater carp culture. The spleen, an important immune organ of carp, is vulnerable to damage by environmental toxins. Studies have shown that the inflammatory response is an important mechanism of immunotoxicity of difenoconazole. Whereas quercetin has anti-inflammatory pharmacological activity, the role and mechanism of quercetin in difenoconazole-induced inflammatory damage in the spleen of carp is unknown. In this study, we developed a model for carp with quercetin added to the diet and exposed to environmentally relevant concentrations of difenoconazole. We found that quercetin protects against inflammatory damage in the splenic tissue of carp through histopathological observations. We found that quercetin alleviated ROS enrichment and disruption of redox homeostasis (dynamic balance of GSH, T-AOC, CAT, and MDA) in the spleen tissue of carp by fluorescence assay and biochemical assay. We found that quercetin was able to inhibit the activation of the NF-kappa B signaling pathway (elevated p-NF-kappa B p65 expression level) and NLRP3 inflammasome pathway (NLRP3/ASC/caspase-1) in carp spleen tissue induced by difenoconazole by immunohistochemistry and qPCR analysis. In conclusion, this study confirms that the addition of quercetin as a supplement to the diets of freshwater cultured carp is effective against the spleen toxicity induced by difenoconazole. Mechanistically, quercetin may alleviate the difenoconazole-induced splenic inflammatory injury in carp by suppressing the excessive activation of ROS/NF-kappa B/NLRP3 inflammasome axis, providing new insights into the mechanism of quercetin alleviation of splenic inflammatory injury in carp.