Physiologically based kinetic modelling-facilitated reverse dosimetry to predict in vivo red blood cell acetylcholinesterase inhibition following exposure to chlorpyrifos in the Caucasian and Chinese population

: Organophosphates (OPs) have a long history of use as insecticides over the world. The aim of the present study was to investigate the interethnic differences in kinetics, biomarker formation and in vivo red blood cell (RBC) acetylcholinesterase (AChE) inhibition of chlorpyrifos (CPF) in the Chinese and the Caucasian population. To this purpose, PBK models for CPF in both the Chinese and Caucasian population were developed, and used to study time- and dose-dependent interethnic variation in urinary biomarkers and to convert concentration-response curves for RBC AChE inhibition to in vivo dose-response curves in these two populations by reverse dosimetry. The results obtained revealed a marked interethnic difference in toxicokinetics of CPF, with lower urinary biomarker levels at similar dose levels and slower CPF bioactivation and faster CPO detoxification in the Chinese compared with the Caucasian population, resulting in 5- to 6-fold higher CPF sensitivity of the Caucasian than the Chinese population. These differences might be related to variation in the frequency of single-nucleotide polymorphisms (SNPs) for the major biotransformation enzymes involved. To conclude, the interethnic variation in kinetics of CPF may affect both its biomarker-based exposure assessment as well as its toxicity and risk assessment and that PBK modelling facilitates the characterisation and quantification of these interethnic variations.