Bioactivation of tetrachloroethylene. Role of glutathione S-transferase-catalyzed conjugation versus cytochrome P-450-dependent phospholipid alkylation.
Bioactivation of tetrachloroethylene. Role of glutathione S-transferase-catalyzed conjugation versus cytochrome P-450-dependent phospholipid alkylation.
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四氯乙烯的生物活化。
DOI：
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发表时间：
1987
影响因子：
3.9
通讯作者：
D. Henschler
中科院分区：
文献类型：
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作者：
W. Dekant;G. Martens;S. Vamvakas;M. Metzler;D. Henschler
采用体外系统研究了[14 C]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，以证实Tetra的体内代谢途径。在存在NADPH的情况下，大鼠肝微粒体组分将Tetra代谢为可溶性代谢物，通过气相色谱/质谱法鉴定为三氯乙酸和草酸，以及主要与微粒体大分子结合的代谢物。大多数的烷基化大分子被确定为N-三氯乙酰化磷脂的高效液相色谱法和GC/MS。当Tetra与肝微粒体和细胞溶质中存在的10 mM谷胱甘肽，但在没有NADPH的情况下，孵育，形成的极性代谢物以外的三氯乙酸和草酸观察。水解为相应的半胱氨酸结合物后，该代谢产物被鉴别为S-（1，2，2-三氯乙烯基）-谷胱甘肽（TCVG）。微粒体GSH S-转移酶比胞质GSH S-转移酶更有效地催化TCVG的形成;竞争性底物1-氯-2，4-二硝基苯抑制TCVG的形成。在NADPH和GSH的存在下，微粒体中TCVG的形成减少，表明Tetra的氧化代谢和GSH结合是竞争性反应。四代谢产物TCVC被细菌半胱氨酸缀合物b-裂解酶裂解为二氯乙酸和丙酮酸。所获得的结果证实了Tetra生物转化的假设途径，并表明在肝脏Tetra代谢中发生氧化和共轭反应。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形成、肾代谢为TCVC以及b-裂解酶在形成致突变中间体的情况下裂解TCVC可能导致Tetra的肾致癌作用。
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.