Usmani Khawja A, Karoly Edward D, Hodgson Ernest, Rose Randy L
Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh, North Carolina 27695, USA.
Drug Metab Dispos. 2004 Mar;32(3):333-9. doi: 10.1124/dmd.32.3.333.
Cytochrome P450 (P450) and flavin-containing monooxygenase (FMO) enzymes are major catalysts involved in the metabolism of xenobiotics. The sulfoxidation of the thioether pesticides, phorate, disulfoton, sulprofos, and methiocarb, was investigated. Using pooled human liver microsomes (HLMs), thioether compounds displayed similar affinities; however, phorate and disulfoton displayed higher intrinsic clearance rates than either sulprofos or methiocarb. The sulfoxidation of thioethers by HLMs was found to be predominantly P450-driven (85-90%) compared with FMO (10-15%). Among 16 cDNA-expressed human P450 isoforms and 3 human FMO isoforms examined, the following isoforms and their polymorphisms had the highest rates for sulfoxidation, as follows: phorate, CYP1A2, 3A4, 2B6, 2C91, 2C18, 2C19, 2D61, and FMO1; disulfoton, CYP1A2, 3A4, 2B6, 2C91, 2C92, 2C18, 2C19, 2D61, and FMO1; sulprofos, CYP1A1, 1A2, 3A4, 2C91, 2C92, 2C93, 2C18, 2C19, 2D61, and FMO1; methiocarb, CYP1A1, 1A2, 3A4, 2B6, 2C91, 2C19, 2D6*1, and FMO1. Among these isoforms, members of the CYP2C subfamily often had the highest affinities and clearance rates. Moreover, sulfaphenazole, a CYP2C9 competitive inhibitor, inhibited disulfoton sulfoxidation by CYP2C9 (IC50 0.84 microM) as well as in HLMs. Ticlopidine, a CYP2C19 mechanism-based inhibitor, inhibited disulfoton sulfoxidation by CYP2C19 (IC50 after coincubation, 43.5 microM; IC50 after preincubation, 4.3 microM) and also in HLMs. Our results indicate that current models of the substrate binding site of the CYP2C subfamily would not effectively predict thioether pesticide metabolism. Thus, the substrate specificity of CYP2Cs is more extensive than is currently believed, and some reevaluation of structure-activity relationships may be required.
细胞色素P450（P450）和含黄素单加氧酶（FMO）是参与外源性物质代谢的主要催化剂。对硫醚类农药甲拌磷、乙拌磷、硫丙磷和灭扑威的亚砜化反应进行了研究。使用混合人肝微粒体（HLM）时，硫醚化合物表现出相似的亲和力；然而，甲拌磷和乙拌磷的内在清除率高于硫丙磷或灭扑威。发现HLM对硫醚的亚砜化反应主要由P450驱动（85 - 90%），而FMO的作用占比为10 - 15%。在所检测的16种cDNA表达的人P450同工型和3种人FMO同工型中，以下同工型及其多态性具有最高的亚砜化速率，具体如下：甲拌磷，CYP1A2、3A4、2B6、2C91、2C18、2C19、2D61和FMO1；乙拌磷，CYP1A2、3A4、2B6、2C91、2C92、2C18、2C19、2D61和FMO1；硫丙磷，CYP1A1、1A2、3A4、2C91、2C92、2C93、2C18、2C19、2D61和FMO1；灭扑威，CYP1A1、1A2、3A4、2B6、2C91、2C19、2D6*1和FMO1。在这些同工型中，CYP2C亚家族成员通常具有最高的亲和力和清除率。此外，CYP2C9竞争性抑制剂磺胺苯吡唑抑制了CYP2C9介导的乙拌磷亚砜化反应（IC50为0.84微摩尔）以及在HLM中的反应。噻氯匹定是一种基于CYP2C19作用机制的抑制剂，它抑制了CYP2C19介导的乙拌磷亚砜化反应（共孵育后的IC50为43.5微摩尔；预孵育后的IC50为4.3微摩尔）以及在HLM中的反应。我们的结果表明，目前关于CYP2C亚家族底物结合位点的模型无法有效预测硫醚类农药的代谢。因此，CYP2C的底物特异性比目前认为的更为广泛，可能需要对构效关系进行一些重新评估。
