In vitro toxicity of pirimiphos-methyl in Atlantic salmon hepatocytes

Recent screening of Atlantic salmon feeds has uncovered residues of several pesticides, including pirimiphos-methyl. Pirimiphos-methyl is an organophosphate (OP) insecticide, causing inhibition of acetylcholinesterase in target organisms. The aim of this study was to examine pirimiphos-methyl non-targeted mode of action toxicity in Atlantic salmon using in vitro exposure. Hepatocyte cells were exposed to pirimiphos-methyl (control-0.1-1.0-10-100-1000μM) for 48h. Transcriptomics (RNA-seq) and non-targeted metabolomics were used to screen for effects of the pesticide. The results showed that the compound acts cytotoxic and impacts accumulation of lipids (steatosis) at 1000μM. Metabolomics screening revealed effects on lipid metabolism (diHOME fatty acids, Cholesterol and lysophospholipids), glutathione (depletion), glycolysis and tryptophan metabolism, as well as on several Vitamins. At 1000μM, vitamin E levels increased, while folate and thiamine derivate levels decreased. Surprisingly few transcripts were affected by the treatment, with only 64 differentially expressed genes (DEGs) showing a clear dose-dependent response. Several DEGs encoding proteins in Cholesterol biosynthesis showed negative correlations with pirimiphos-methyl exposure. Other affected DEGs indicate an estrogenic effect, and points to mitochondrial dysfunction at the highest dose. The finding suggests that glutathione and glycine conjugation reactions are involved in the detoxification process. In conclusion, this study shows that pirimiphos-methyl is a relatively potent toxicant in Atlantic salmon hepatocytes affecting lipid and vitamin metabolism as well as glutathione turn-over.