Yin H, Anders M W, Jones J P
Department of Pharmacology, University of Rochester, New York 14642, USA.
Chem Res Toxicol. 1996 Jan-Feb;9(1):50-7. doi: 10.1021/tx950086n.
1,2-Dichloro-1-fluoroethane (HCFC-141) and 1,1,2-trichloro-2-fluoroethane (HCFC-131) were chosen as models to study the regioselectivity of halogenated alkane metabolism. Metabolites in the urine of rats given HCFC-131 ip were the following: inorganic fluoride, chlorofluoroacetic acid, dichloroacetic acid, N-(2-hydroxyethyl)chlorofluoroacetamide, and three unidentified minor metabolites. In vitro incubation of HCFC-131 with either rat liver microsomes from pyridine-treated rats or expressed human cytochrome P450 2E1 isozyme in the presence of NADPH gave fluoride, chlorofluoroacetic acid, and dichloroacetic acid as metabolites. HCFC-141 was biotransformed in rats to inorganic fluoride, chlorofluoroacetic acid, 2-chloro-2-fluoroethanol, and 2-chloro-2-fluoroethyl glucuronide, which were detected in urine. Incubation of HCFC-141 with NADPH-fortified liver microsomes from pyridine-induced rats or expressed human cytochrome P450 2E1 afforded fluoride, chlorofluoroacetaldehyde hydrate, and chloroacetic acid as products. The metabolites identified were consistent with a cytochrome P450-dependent oxidation mechanism. The data also indicated that phosphatidylethanolamine may be a cellular target for chlorofluoroacetyl chloride, a reactive intermediate generated from HCFC-131 by cytochrome P450-dependent oxidation. Chlorofluoroacetic acid given to rats ip was largely recovered in the rat urine, although the formation of inorganic fluoride as a metabolite was observed. The mechanism of defluorination of chlorofluoroacetic acid is not clear. Regioselective oxidation by cytochrome P450 was observed between the two potential oxidizable sites in HCFC-141 and in HCFC-131. Comparison of the observed ratio of oxidation at different sites in in vitro experiments with the calculated activation energies for hydrogen-atom abstraction from these sites indicated that electronic factors are the primary determinant of regioselectivity. In vivo regioselectivity could not be compared with theory since this ratio does not reflect the true regioselectivity due to differences in excretion, reabsorption, secondary metabolism (e.g., fluoride generation from chlorofluoroacetic acid), other routes of fluoride formation, and limitation of the method of detection.
选择1,2 - 二氯 - 1 - 氟乙烷（HCFC - 141）和1,1,2 - 三氯 - 2 - 氟乙烷（HCFC - 131）作为模型来研究卤代烷烃代谢的区域选择性。经腹腔注射给予HCFC - 131的大鼠尿液中的代谢产物如下：无机氟化物、氯氟乙酸、二氯乙酸、N -（2 - 羟乙基）氯氟乙酰胺以及三种未鉴定的次要代谢产物。在存在NADPH的情况下，将HCFC - 131与来自用吡啶处理过的大鼠的肝微粒体或表达的人细胞色素P450 2E1同工酶进行体外孵育，得到氟化物、氯氟乙酸和二氯乙酸作为代谢产物。HCFC - 141在大鼠体内被生物转化为无机氟化物、氯氟乙酸、2 - 氯 - 2 - 氟乙醇和2 - 氯 - 2 - 氟乙基葡萄糖醛酸苷，这些在尿液中被检测到。将HCFC - 141与来自吡啶诱导的大鼠的用NADPH强化的肝微粒体或表达的人细胞色素P450 2E1一起孵育，得到氟化物、氯氟乙醛水合物和氯乙酸作为产物。鉴定出的代谢产物与细胞色素P450依赖性氧化机制一致。数据还表明，磷脂酰乙醇胺可能是氯氟乙酰氯的细胞靶点，氯氟乙酰氯是由细胞色素P450依赖性氧化的HCFC - 131产生的一种反应性中间体。经腹腔注射给予大鼠氯氟乙酸后，尽管观察到有作为代谢产物的无机氟化物形成，但大部分氯氟乙酸仍在大鼠尿液中回收。氯氟乙酸的脱氟机制尚不清楚。在HCFC - 141和HCFC - 131的两个潜在可氧化位点之间观察到了细胞色素P450的区域选择性氧化。将体外实验中不同位点的氧化观察比例与从这些位点夺取氢原子的计算活化能进行比较，表明电子因素是区域选择性的主要决定因素。由于排泄、重吸收、次级代谢（例如氯氟乙酸产生氟化物）、氟化物形成的其他途径以及检测方法的局限性导致该比例不能反映真正的区域选择性，所以无法将体内区域选择性与理论进行比较。
