den Besten C, Ellenbroek M, van der Ree M A, Rietjens I M, van Bladeren P J
Department of Toxicology, Agricultural University, Wageningen, The Netherlands.
Chem Biol Interact. 1992 Nov 16;84(3):259-75. doi: 10.1016/0009-2797(92)90128-8.
The microsomal oxidation of 1,2-[14C]- and 1,4-[14C]dichlorobenzene (DICB) was investigated with special attention for possible differences in biotransformation that might contribute to the isomer-specific hepatotoxicity. Major metabolites of both isomers were dichlorophenols (2,5-DICP for 1,4-DICB and 2,3- and 3,4-DICP for 1,2-DICB, respectively) and dichlorohydroquinones. The formation of polar dihydrodiols appeared to be a major route for 1,2-DICB but not 1,4-DICB. Both the hepatotoxic 1,2-DICB and the non-hepatotoxic 1,4-DICB were oxidized to metabolites that covalently interacted with protein and only to a small extent with DNA. Protein binding could be inhibited by the addition of the reducing agent ascorbic acid with a concomitant increase in the formation of hydroquinones and catechols, indicating the involvement of reactive benzoquinone metabolites in protein binding. However, in the presence of ascorbic acid, a substantial amount of protein-bound metabolites of 1,2-DICB was still observed, in contrast to 1,4-DICB where binding was nearly completely inhibited. This latter effect was ascribed to the direct formation of reactive benzoquinone metabolites in a single P450-mediated oxidation of para-substituted dichlorophenols (such as 3,4-DICP) in the case of 1,2-DICB. In contrast, the major phenol isomer derived from 1,4-DICB (i.e. 2,5-DICP) is oxidized to its hydroquinone derivative, which needs prior oxidation in order to generate the reactive benzoquinone species. Residual protein binding in the presence of ascorbic acid could also indicate the involvement of reactive arene oxides in the protein binding of 1,2-DICB, but not of 1,4-DICB. However, MO computer calculations did not provide indications for differences in chemical reactivity and/or stability of the various arene oxide/oxepin tautomers that can be formed from either 1,2-DICB or 1,4-DICB. In conclusion, reactive intermediates in the secondary metabolism of 1,2-DICB lead to more covalent binding than those derived from 1,4-DICB, which correlates very well with their reported hepatotoxic potency.
研究了1,2-[¹⁴C]-和1,4-[¹⁴C] -二氯苯（DICB）的微粒体氧化过程，特别关注可能导致异构体特异性肝毒性的生物转化差异。两种异构体的主要代谢产物均为二氯酚（1,4-DICB的2,5-DICP和1,2-DICB的2,3-和3,4-DICP）和二氯对苯二酚。极性二醇的形成似乎是1,2-DICB的主要代谢途径，但不是1,4-DICB的主要代谢途径。具有肝毒性的1,2-DICB和无肝毒性的1,4-DICB均被氧化为与蛋白质发生共价相互作用的代谢产物，与DNA的相互作用程度较小。添加还原剂抗坏血酸可抑制蛋白质结合，同时对苯二酚和邻苯二酚的生成量增加，这表明活性苯醌代谢产物参与了蛋白质结合。然而，在抗坏血酸存在的情况下，仍观察到大量1,2-DICB的蛋白质结合代谢产物，而1,4-DICB的结合几乎被完全抑制。后一种效应归因于在1,2-DICB的情况下，对位取代的二氯酚（如3,4-DICP）在单一细胞色素P450介导的氧化过程中直接形成活性苯醌代谢产物。相比之下，1,4-DICB衍生的主要酚异构体（即2,5-DICP）被氧化为其对苯二酚衍生物，该衍生物需要先氧化才能生成活性苯醌物种。抗坏血酸存在下的残留蛋白质结合也可能表明活性芳烃氧化物参与了1,2-DICB的蛋白质结合，但不参与1,4-DICB的蛋白质结合。然而，分子轨道（MO）计算机计算并未显示由1,2-DICB或1,4-DICB形成的各种芳烃氧化物/氧杂环庚三烯互变异构体在化学反应性和/或稳定性方面存在差异。总之，1,2-DICB次级代谢中的活性中间体比1,4-DICB衍生的中间体导致更多的共价结合，这与其报道的肝毒性效力非常相关。
