Wormhoudt L W, Commandeur J N, Ploemen J H, Abdoelgafoer R S, Makansi A, Van Bladeren P J, Vermeulen N P
Leiden Amsterdam Center for Drug Research, Department of Pharmacochemistry, Vrije Universiteit, The Netherlands.
Drug Metab Dispos. 1997 Apr;25(4):508-15.
1,2-Dibromoethane (1,2-DBE) is a carcinogenic compound that is metabolized both by cytochrome P450 (P450) and glutathione S-transferase (GST) enzymes, and that has been used by us as a model compound to study interindividual variability in biotransformation reactions. In this study, the excretion of thiodiacetic acid (TDA) and S-(2-hydroxyethyl)-N-acetyl-l-cysteine (2-HEMA) were measured in the urine of rats dosed with 1,2-DBE, and experiments were performed to investigate to what extent P450 and GST enzymes contribute to the formation of TDA. To this end, CYP2E1, the main P450 isoenzyme catalyzing the oxidation of 1,2-DBE, was inhibited using disulfiram and diallylsulfide. Significant inhibition of CYP2E1, as confirmed by inhibition of the hydroxylation of chlorzoxazone, as well as inhibition of the formation of TDA from 1,2-DBE, was observed upon pretreatment of rats with these inhibitors, indicating that the P450-catalyzed oxidation of 1,2-DBE plays the major role in the TDA formation. No significant excretion of TDA was observed after administration of intermediate products of the GST pathway [i.e. S-(2-hydroxyethyl)glutathione and 2-HEMA], indicating that the GST-catalyzed metabolism of 1,2-DBE does not contribute to a significant extent to the formation of TDA. The results of this study show that TDA is specifically formed by P450 metabolites of 1,2-DBE, whereas the conjugation of 1,2-DBE to glutathione by GST enzymes does not contribute to the formation of TDA. TDA, excreted in urine, may thus be used as a biomarker of exposure to 1,2-DBE selectively reflecting the P450-catalyzed oxidation. In addition to 2-HEMA and S-[2-(N7-guanyl)ethyl]-N-acetyl-l-cysteine, TDA may be a valuable tool for biomonitoring and mechanistic studies into the metabolism and toxicity of 1,2-DBE.
1,2 - 二溴乙烷（1,2 - DBE）是一种致癌化合物，可通过细胞色素P450（P450）和谷胱甘肽S - 转移酶（GST）酶进行代谢，我们已将其用作模型化合物来研究生物转化反应中的个体差异。在本研究中，测定了给予1,2 - DBE的大鼠尿液中硫代二乙酸（TDA）和S -（2 - 羟乙基）- N - 乙酰 - L - 半胱氨酸（2 - HEMA）的排泄情况，并进行实验以研究P450和GST酶在TDA形成中所起作用的程度。为此，使用双硫仑和二烯丙基硫醚抑制催化1,2 - DBE氧化的主要P450同工酶CYP2E1。在用这些抑制剂预处理大鼠后，观察到CYP2E1受到显著抑制，这通过氯唑沙宗羟基化的抑制以及1,2 - DBE生成TDA的抑制得以证实，表明P450催化的1,2 - DBE氧化在TDA形成中起主要作用。给予GST途径的中间产物[即S -（2 - 羟乙基）谷胱甘肽和2 - HEMA]后，未观察到TDA有显著排泄，这表明GST催化的1,2 - DBE代谢对TDA的形成贡献不大。本研究结果表明，TDA是由1,2 - DBE的P450代谢产物特异性形成的，而GST酶催化的1,2 - DBE与谷胱甘肽的结合对TDA的形成没有贡献。因此，尿液中排泄的TDA可作为暴露于1,2 - DBE的生物标志物，选择性反映P450催化的氧化作用。除了2 - HEMA和S - [2 -（N7 - 鸟嘌呤基）乙基] - N - 乙酰 - L - 半胱氨酸外，TDA可能是用于1,2 - DBE代谢和毒性生物监测及机制研究的有价值工具。
