Reductive dominance and limited cytochrome P450 activity in neonicotinoid metabolism by elephant liver microsomes

Neonicotinoids (NNs) are commonly used insecticides; however, their biotransformation in wild mammals remains poorly understood. Asian elephants, which are declining in numbers, may be vulnerable to these chemicals. In this study, we examined the liver metabolism of four major NNs: acetamiprid, imidacloprid, thiamethoxam, and clothianidin, using elephant liver microsomes. Metabolite profiling and targeted analysis were conducted with liquid chromatography quadrupole time-of-flight mass spectrometry and liquid chromatography tandem mass spectrometer, respectively. Results indicated that elephants mainly metabolize these NNs via reductive pathways, suggesting the involvement of nitroreductase-like enzymes. Conversely, cytochrome P450-mediated oxidation may be limited; however, the roles of other enzymatic or microbial systems cannot be ruled out. These findings provide insights into xenobiotic metabolism in elephants, helping evaluate their toxicological vulnerability and supporting conservation efforts and risk assessments.