den Besten C, Smink M C, de Vries E J, van Bladeren P J
Department of Toxicology, Agricultural University, Wageningen, The Netherlands.
Toxicol Appl Pharmacol. 1991 Apr;108(2):223-33. doi: 10.1016/0041-008x(91)90113-s.
Microsomal metabolism of 1,2,4-[14C]trichlorobenzene (1,2,4-TrCB) and [14C]pentachlorobenzene (PeCB) was studied with special emphasis on the conversion-dependent covalent binding to protein and DNA. 1,2,4-TrCB was metabolized to 2,3,6- and 2,4,5-trichlorophenol, and to a lesser extent to 2,4,6- and 2,3,5-trichlorophenol, and trichlorohydroquinone. About 10% of all metabolites became covalently bound to protein in a rather nonselective way. For 1,2,4-TrCB and PeCB a strong correlation between secondary metabolism to hydroquinones and covalent binding was established. Protein binding was completely inhibited by the addition of ascorbic acid, indicating quinone metabolites as the sole reactive species formed. Both 1,2,4-TrCB and PeCB alkylated DNA, although to a much lesser extent than protein (0.5 and 0.3% of all metabolites, respectively). Nonquinone intermediates, presumably epoxides, were responsible for a minor portion of the observed DNA binding, since complete inhibition by ascorbic acid was not reached. The differential role of cytochrome P450 both in primary and in secondary metabolism was demonstrated by the use of microsomes from rats pretreated with different inducers. Dexamethasone (DEX) microsomes (cytochrome P450IIIA1) showed the highest activity toward these chlorinated benzenes (14 nmol/mg/5 min for 1,2,4-TrCB and 36 nmol/mg/10 min for PeCB, both with regard to the formation of phenols and to the formation of protein-bound metabolites. In addition, DEX microsomes preferentially formed 2,3,6-trichlorophenol, whereas other microsomal suspensions formed 2,4,5-trichlorophenol as the major isomer. The present study clearly demonstrates the high alkylating potency of secondary quinone metabolites derived from chlorinated benzenes and poses a need for reevaluation of the role of epoxides in the observed toxicity of these compounds.
研究了微粒体对1,2,4-[¹⁴C]三氯苯（1,2,4-TrCB）和[¹⁴C]五氯苯（PeCB）的代谢，特别关注了与转化相关的与蛋白质和DNA的共价结合。1,2,4-TrCB代谢生成2,3,6-和2,4,5-三氯苯酚，在较小程度上生成2,4,6-和2,3,5-三氯苯酚以及三氯对苯二酚。所有代谢产物中约10%以相当非选择性的方式与蛋白质共价结合。对于1,2,4-TrCB和PeCB，建立了对苯二酚的二次代谢与共价结合之间的强相关性。加入抗坏血酸可完全抑制蛋白质结合，表明醌类代谢产物是形成的唯一反应性物种。1,2,4-TrCB和PeCB均使DNA烷基化，尽管程度远低于蛋白质（分别占所有代谢产物的0.5%和0.3%）。非醌中间体（可能是环氧化物）导致了观察到的DNA结合的一小部分，因为抗坏血酸未达到完全抑制作用。通过使用用不同诱导剂预处理的大鼠的微粒体，证明了细胞色素P450在一次代谢和二次代谢中的不同作用。地塞米松（DEX）微粒体（细胞色素P450IIIA1）对这些氯苯显示出最高活性（对于1,2,4-TrCB为14 nmol/mg/5 min，对于PeCB为36 nmol/mg/10 min，无论是就酚的形成还是就蛋白质结合代谢产物的形成而言）。此外，DEX微粒体优先形成2,3,6-三氯苯酚，而其他微粒体悬浮液则形成2,4,5-三氯苯酚作为主要异构体。本研究清楚地证明了源自氯苯的二次醌类代谢产物的高烷基化能力，并提出需要重新评估环氧化物在这些化合物所观察到的毒性中的作用。
