Dekant W, Martens G, Vamvakas S, Metzler M, Henschler D
Institute of Toxicology, University of Wuerzburg, Federal Republic of Germany.
Drug Metab Dispos. 1987 Sep-Oct;15(5):702-9.
The metabolism of [14C]tetrachloroethylene (Tetra) and its metabolite S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC) was investigated with in vitro systems to substantiate metabolic pathways of Tetra deduced from in vivo experiments. In the presence of NADPH, rat hepatic microsomal fractions metabolized Tetra to soluble metabolites, which were identified as trichloroacetic acid and oxalic acid by gas chromatography/mass spectroscopy and a metabolite largely bound to microsomal macromolecules. The majority of the alkylated macromolecules were identified as N-trichloroacetylated phospholipids by high performance liquid chromatography and GC/MS. When Tetra was incubated with hepatic microsomes and cytosol in the presence of 10 mM glutathione, but in the absence of NADPH, the formation of a polar metabolite other than trichloroacetic acid and oxalic acid was observed. This metabolite was identified, after hydrolysis to the corresponding cysteine conjugate, as S-(1,2,2-trichlorovinyl)-glutathione (TCVG). Microsomal GSH S-transferases catalyzed TCVG formation more efficiently than cytosolic GSH S-transferases; the competitive substrate 1-chloro-2,4-dinitrobenzene inhibited TCVG formation. In the presence of both NADPH and GSH, TCVG formation in microsomes was decreased, indicating that oxidative metabolism and GSH conjugation of Tetra are competitive reactions. The Tetra metabolite TCVC was cleaved by bacterial cysteine conjugate b-lyase to dichloroacetic acid and pyruvate. The obtained results substantiate the postulated pathways of Tetra biotransformation and demonstrate that both oxidative and conjugative reactions occur in hepatic Tetra metabolism. Phospholipid alkylation, which occurs during oxidative metabolism, may be a deactivation reaction, whereas TCVG formation, renal metabolism to TCVC, and cleavage of TCVC by b-lyase under formation of mutagenic intermediates may contribute to the nephrocarcinogenic effect of Tetra.
利用体外系统研究了[14C]四氯乙烯（Tetra）及其代谢产物S-(1,2,2-三氯乙烯基)-L-半胱氨酸（TCVC）的代谢情况，以证实从体内实验推导得出的Tetra代谢途径。在NADPH存在的情况下，大鼠肝微粒体部分将Tetra代谢为可溶性代谢产物，通过气相色谱/质谱法鉴定为三氯乙酸和草酸，以及一种主要与微粒体大分子结合的代谢产物。通过高效液相色谱和气相色谱/质谱法，大部分烷基化大分子被鉴定为N-三氯乙酰化磷脂。当在10 mM谷胱甘肽存在但无NADPH的情况下，将Tetra与肝微粒体和胞液一起孵育时，观察到除三氯乙酸和草酸外的一种极性代谢产物的形成。该代谢产物在水解为相应的半胱氨酸共轭物后，被鉴定为S-(1,2,2-三氯乙烯基)谷胱甘肽（TCVG）。微粒体谷胱甘肽S-转移酶催化TCVG形成的效率高于胞液谷胱甘肽S-转移酶；竞争性底物1-氯-2,4-二硝基苯抑制TCVG形成。在NADPH和谷胱甘肽都存在的情况下，微粒体中TCVG的形成减少，表明Tetra的氧化代谢和谷胱甘肽共轭是竞争性反应。Tetra代谢产物TCVC被细菌半胱氨酸共轭β-裂解酶裂解为二氯乙酸和丙酮酸。所得结果证实了Tetra生物转化的假定途径，并表明氧化反应和共轭反应均发生在肝脏Tetra代谢过程中。氧化代谢过程中发生的磷脂烷基化可能是一种失活反应，而TCVG的形成、肾脏代谢为TCVC以及β-裂解酶在诱变中间体形成下对TCVC的裂解可能导致Tetra的肾致癌作用。
