Subchronic exposure to the neonicotinoid pesticide clothianidin disrupts gut microbiota composition in rats

Neonicotinoid pesticides (NNs) are widely used for their selective toxicity to insects via an agonistic action on nicotinic acetylcholine receptors. However, growing evidence suggests that NNs may have adverse health effects in mammals. In parallel, recent studies have shown that trace environmental chemicals such as antibiotics, endocrine disruptors, and pesticide residues can alter the gut microbiota, a key regulator of host health. Thus, NNs may also disrupt gut microbial homeostasis and impact host physiology. In this study, we investigated the effect of the neonicotinoid pesticide clothianidin (CLO) on the rat gut microbiota. Male rats were orally administered CLO at 0, 30, and 300 mg/kg/day (designated as the CLO-0, 30, and 300 groups) for 28 days; doses were selected based on the no-observed-adverse-effect level (NOAEL; 27.9 mg/kg/day). Cecal contents were collected after euthanasia and subjected to 16S rRNA sequencing. Our results showed that even at approximately the NOAEL dose, CLO exposure altered gut microbiota composition and tended to reduce microbial diversity, especially in the CLO-300 group. Notably, several CLO-affected taxa are known producers of short-chain fatty acids, and changes were particularly prominent in two individuals from the high-dose group. Moreover, CLO exposure resulted in distinct alterations in butyrate-producing bacteria, with increases observed in the CLO-30 group and decreases in the CLO-300 group. These results suggest that CLO has various effects on the gut microbiota and that even exposure at the NOAEL may affect host health.