Enhanced Exposure Risk of Penthiopyrad S-Enantiomer: Insights into the Roles of Intestinal Absorption and CYP3A4-Mediated Metabolism

Penthiopyrad, a chiral fungicide with a riskier S-enantiomer, exhibited poorly understood stereoselective behaviors in mammals. This study investigated the enantioselective accumulation and metabolism of penthiopyrad enantiomers in mammals using in vivo, in vitro, and in silico approaches. Penthiopyrad accumulated in the liver and kidneys at concentrations over 10-fold higher than those in the blood. S-penthiopyrad showed preferential absorption with 1.6-fold higher bioavailability than the R-enantiomer. Twenty-three metabolites (12 novel) were identified, with CYP-mediated N-demethylation as the dominant pathway. S-penthiopyrad was preferentially metabolized in mouse liver microsomes with a 1.5-fold shorter half-life, while human liver microsomes favored the R-enantiomer. CYP2E1, CYP2C (mouse), and CYP3A4 (human) mediated stereoselective metabolism, with the preferential metabolism of the R-enantiomer by human CYP3A4 attributed to its low binding energy and favorable conformation. This study comprehensively clarified the stereoselective behavior and metabolic pathway of penthiopyrad in mammals, providing valuable metabolic insights for further toxicological evaluation of penthiopyrad.