Bioactivation of 4-methylphenol (p-cresol) via cytochrome p450-mediated aromatic oxidation in human liver microsomes
Bioactivation of 4-methylphenol (p-cresol) via cytochrome p450-mediated aromatic oxidation in human liver microsomes
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DOI：
10.1124/dmd.105.006387
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发表时间：
2005-12-01
影响因子：
3.9
通讯作者：
Huebert, N
中科院分区：
文献类型：
--
作者：
Yan, ZY;Zhong, HM;Huebert, N
以前有人提出，4-甲基苯酚（对甲酚）是通过甲基氧化形成活性醌的代谢激活的。本研究揭示了人肝微粒体的一种新的代谢途径。芳香族环氧化生成4-甲基-邻苯二酚，再进一步氧化生成活性中间体4-甲基-邻苯二酚。这种生物激活途径得到了以下观察结果的充分支持：1)在存在谷胱甘肽的对甲酚微粒体培养中检测到一种主要和两种次要谷胱甘肽（GSH）加合物；2)在微粒体培养中，对甲酚的主要代谢产物为4-甲基-邻对苯二酚；3)在4-甲基-邻对苯二酚微粒体培养中检测到相同的谷胱甘肽加合物；4)通过氧化4-甲基-邻对苯二酚，再加入谷胱甘肽，化学合成了相同的谷胱甘肽加合物，并通过液相色谱-串联质谱和核磁共振鉴定了主要缀合物为3-（谷胱甘肽- s -基）-5-甲基-邻对苯二酚。此外，还发现肝脏微粒体中甲基氧化产生的主要代谢物4-羟基苯基醇进一步转化为4-羟基苯甲醛。体外研究还发现，对甲酚的生物活性是由多种细胞色素P450介导的，但CYP2D6、2E1和1A2分别是合成甲醌、4-甲基-邻苯醌和4-羟基苯甲醛最活跃的酶。新发现的反应性代谢物在对甲酚诱导的毒性中的意义有待进一步研究。
It has previously been proposed that 4-methylphenol (p-cresol) is metabolically activated by oxidation of the methyl group to form a reactive quinone methide. In the present study a new metabolism pathway is elucidated in human liver microsomes. Oxidation of the aromatic ring leads to formation of 4-methyl-ortho-hydroquinone, which is further oxidized to a reactive intermediate, 4-methyl-ortho-benzoquinone. This bioactivation pathway is fully supported by the following observations: 1) one major and two minor glutathione (GSH) adducts were detected in microsomal incubations of p-cresol in the presence of glutathione; 2) a major metabolite of p-cresol was identified as 4-methyl-ortho-hydroquinone in microsomal incubations; 3) the same GSH adducts were detected in microsomal incubations of 4-methyl-ortho-hydroquinone; and 4) the same GSH adducts were chemically synthesized by oxidizing 4-methyl-ortho-hydroquinone followed by the addition of GSH, and the major conjugate was identified by liquid chromatography-tandem mass spectrometry and NMR as 3-( glutathione-S-yl)-5-methylortho-hydroquinone. In addition, it was found that 4-hydroxybenzylalcohol, a major metabolite derived from oxidation of the methyl group in liver microsomes, was further converted to 4-hydroxybenzaldehyde. In vitro studies also revealed that bioactivation of p-cresol was mediated by multiple cytochromes P450, but CYP2D6, 2E1, and 1A2 are the most active enzymes for formation of quinone methide, 4-methyl-ortho-benzoquinone, and 4-hydroxybenzaldehyde, respectively. Implications of the newly identified reactive metabolite in p-cresol-induced toxicity remain to be investigated in the future.