Goeptar A R, Te Koppele J M, Neve E P, Vermeulen N P
Department of Pharmacochemistry, Free University, Amsterdam, The Netherlands.
Chem Biol Interact. 1992 Aug 28;83(3):249-69. doi: 10.1016/0009-2797(92)90101-p.
The main objective of the present study was to investigate the proposed role of cytochrome P450 in the reductive metabolism of quinones as well as in the formation of reduced oxygen species in liver microsomes from phenobarbital (PB-microsomes) and beta-naphthoflavone (beta NF-microsomes) pretreated rats. In the present study, 2,3,5,6-tetramethylbenzoquinone (TMQ) was chosen as a model quinone. Anaerobic one-electron reduction of TMQ by PB-microsomes showed relatively strong electron spin resonance (ESR) signals of the oxygen-centered semiquinone free radical (TMSQ), whereas these signals were hardly detectable with beta NF-microsomes. Under aerobic conditions TMSQ formation was diminished and concomitant reduction of molecular oxygen occurred in PB-microsomes. Interestingly, TMQ-induced superoxide anion radicals, measured by ESR (using the spin trap 5,5'-dimethyl-1-pyrroline-N-oxide), and hydrogen peroxide generation was found to occur with beta NF-microsomes as well. Furthermore, SK&F 525-A (a type I ligand inhibitor of cytochrome P450) inhibited TMQ-induced hydrogen peroxide formation in both PB- and beta NF-microsomes. However, metyrapone and imidazole (type II ligand inhibitors of cytochrome P450) inhibited molecular oxygen reduction in beta NF-microsomes and not in PB-microsomes. The present study indicates that cytochrome P450-mediated one-electron reduction of TMQ to TMSQ and subsequent redox cycling of TMSQ with molecular oxygen constitutes the major source for superoxide anion radical and hydrogen peroxide generation in PB-microsomes (i.e. from the reductase activity of cytochrome P450). However, most of the superoxide anion radical formed upon aerobic incubation of TMQ with beta NF-microsomes originates directly from the dioxyanion-ferri-cytochrome P450 complex (i.e. from the oxidase activity of cytochrome P450). In conclusion, both the one-electron reduction of TMQ and molecular oxygen were found to be cytochrome P450 dependent. Apparently, both the reductase and oxidase activities of cytochrome P450 may be involved in the reductive cytotoxicity of chemotherapeutic agents containing the quinoid moiety.
本研究的主要目的是探究细胞色素P450在醌类化合物的还原代谢以及在苯巴比妥（PB微粒体）和β-萘黄酮（βNF微粒体）预处理大鼠肝脏微粒体中活性氧生成过程中所起的作用。在本研究中，选用2,3,5,6-四甲基苯醌（TMQ）作为醌类模型。PB微粒体对TMQ进行厌氧单电子还原时，显示出以氧为中心的半醌自由基（TMSQ）相对较强的电子自旋共振（ESR）信号，而βNF微粒体几乎检测不到这些信号。在有氧条件下，PB微粒体中TMSQ的形成减少，同时发生分子氧的还原。有趣的是，通过ESR（使用自旋捕获剂5,5'-二甲基-1-吡咯啉-N-氧化物）测定发现，βNF微粒体也会产生TMQ诱导的超氧阴离子自由基和过氧化氢。此外，SK&F 525-A（细胞色素P450的I型配体抑制剂）抑制PB微粒体和βNF微粒体中TMQ诱导的过氧化氢形成。然而，甲吡酮和咪唑（细胞色素P450的II型配体抑制剂）抑制βNF微粒体中的分子氧还原，而不抑制PB微粒体中的分子氧还原。本研究表明，细胞色素P450介导的TMQ单电子还原为TMSQ以及随后TMSQ与分子氧的氧化还原循环是PB微粒体中超氧阴离子自由基和过氧化氢生成的主要来源（即源于细胞色素P450的还原酶活性）。然而，TMQ与βNF微粒体在有氧孵育时形成的大部分超氧阴离子自由基直接来源于双氧阴离子-高铁细胞色素P450复合物（即源于细胞色素P450的氧化酶活性）。总之，发现TMQ的单电子还原和分子氧都依赖于细胞色素P450。显然，细胞色素P450的还原酶和氧化酶活性都可能参与含醌类部分的化疗药物的还原细胞毒性作用。
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