BIOTRANSFORMATION AND PHARMACOKINETICS OF PYRETHROID INSECTICIDES

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。农药的水解和氧化代谢有助于其解毒和从暴露的生物体排泄。为了开发基于生理的药代动力学（PBPK）模型来预测农药在人体内的处置，每种生物转化途径对农药清除的相对贡献需要定量表征。本项目的中心假设是羧基酯酶（CES）和细胞色素P450 （CYP）单加氧酶对拟除虫菊酯类杀虫剂的生物转化在很大程度上影响了这些杀虫剂的药代动力学。本研究将探讨啮齿动物和人类的CES和CYP酶在氯菊酯和氨菊酯（I型拟除虫菊酯）以及溴氰菊酯和氯菊酯（II型拟除虫菊酯）体外代谢中的作用，这些酶在人体代谢方面尚未进行研究。在人类肝脏中发现了两种主要的羧酸酯酶异构体，称为hCE-1和hCE-2。具体目标#1将涉及研究杆状病毒表达的hCE-1和hCE-2对拟除虫菊酯化合物的底物特异性。拟除虫菊酯的水解产物将通过LC-MS方法进行检测和定量。描述含酯拟除虫菊酯裂解速率的动力学参数（Km, kcat）将对每个同工酶进行估计，以确定哪些化合物被最有效地水解。特异性目标#2将使用重组人CYP同工酶，并确定其对拟除虫菊酯化合物的底物特异性和动力学参数。将直接比较人类CYP酶和CES酶的催化效率，从而确定每种酶对拟除虫菊酯生物转化的相对贡献。本提案中描述的体外毒性动力学研究将补充和支持拟除虫菊酯PBPK模型的体内研究。了解农药在酯酶和氧化代谢方面的构效关系对于预测农药在人体内的代谢和药代动力学至关重要。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Hydrolytic and oxidative metabolism of pesticides contribute to their detoxification and excretion from exposed organisms. To enable development of physiologically based pharmacokinetic (PBPK) models that predict the disposition of pesticides in humans, the relative contribution of each biotransformation pathway to pesticide clearance requires quantitative characterization. The central hypothesis to be addressed in this project is that biotransformation of pyrethroid insecticides by carboxylesterases (CES) and cytochrome P450 (CYP) monooxygenases largely influence the pharmacokinetics of these pesticides. This study will investigate the role of rodent and human CES and CYP enzymes in the in vitro metabolism of permethrin and resmethrin (type I pyrethroids) and deltamethrin and cypermethrin (type II pyrethroids), which have not been investigated with respect to their human metabolism. Two major carboxylesterase isoforms have been identified in human liver and are termed hCE-1 and hCE-2. Specific aim #1 will involve investigating the substrate specificity of baculovirus-expressed hCE-1 and hCE-2 toward the pyrethroid compounds. Hydrolysis products of the pyrethroids will be detected and quantified by LC-MS methods. The kinetic parameters (Km, kcat) that describe the rates of cleavage of the ester-containing pyrethroids will be estimated for each isozyme to determine which compounds are most effectively hydrolyzed. Specific aim #2 will use recombinant human CYP isozymes and determine their substrate specificity and kinetic parameters toward the pyrethroid compounds. The catalytic efficiencies of the human CYP and CES enzymes will be directly compared so that the relative contribution of each enzyme to pyrethroid biotransformation can be determined. The in vitro toxicokinetic studies described in this proposal will complement and support in vivo studies in the development of PBPK models of pyrethroids. The knowledge of pesticide structure-activity relationships with respect to esterase and oxidative metabolism will be critical for predicting the metabolism and pharmacokinetics of pesticides in humans.