Integration of histopathology, transcriptomics and non-targeted metabolomics reveals toxic effects of thiamethoxam under acute stress in mirror carp (Cyprinus carpio var. Longke-11 mirror)

In recent years, the increasing application of thiamethoxam (THM), coupled with its high leaching and solubility in water, has led to growing concerns regarding THM residues in aquatic environments, which may pose toxic effects on aquatic organisms, particularly fish. However, the toxicological mechanisms of THM in freshwater fish remain unclear. In this study, using histopathology, transcriptomics, and non-targeted metabolomics, the toxic effects of different concentrations of THM under acute stress (96 h) were investigated in mirror carp (Cyprinus carpio var. Longke-11 mirror). The results showed that under acute THM stress, liver tissues of the mirror carp exhibited vacuolation, cellular degeneration, and enhanced cytoplasmic eosinophilia, while gill tissues displayed epithelial structure loss, epithelial cell detachment, degeneration, and vacuolation, with the severity of lesions increasing with exposure concentration. Transcriptomic analysis revealed that the number of differentially expressed genes (DEGs) increased with the concentration of THM. Genes related to immune response and antioxidant stress were mostly downregulated, while genes related to inflammation and apoptosis were predominantly upregulated. The downregulation of common DEGs (SLC7A11, ITLN, CDH17) further confirmed these results. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed significant enrichment in pathways related to inflammation and oxidative stress, with the NF-kappa B signaling pathway identified as the key pathway affected. Metabolomic analysis showed that differentially expressed metabolites (SCMs) associated with amino acid and lipid metabolism were significantly downregulated. The downregulation of SCM acetylcysteine further affected the antioxidant capacity of mirror carp. Moreover, different concentrations of THM affected phenylalanine metabolism, cysteine and methionine metabolism, and biosynthesis of unsaturated fatty acids in the liver of mirror carp. Integrated analysis of apoptosis-related factors (TP53INP1, PRF1, Sphingosine) upregulation and anti-apoptotic factors (Bcl2l1) downregulation suggested that THM induces apoptosis in mirror carp cells. These results indicate that THM stress affects the immune system, amino acid, and lipid metabolism in mirror carp, leading to inflammation, oxidative stress, and apoptosis. This study provides preliminary insights into the toxic mechanisms of THM in fish and can serve as a scientific basis for THM risk assessment and environmental protection.