Gardner I, Wakazono H, Bergin P, de Waziers I, Beaune P, Kenna J G, Caldwell J
Pharmacology and Toxicology, Imperial College School of Medicine at St. Mary's, Norfolk Place, London, UK.
Carcinogenesis. 1997 Sep;18(9):1775-83. doi: 10.1093/carcin/18.9.1775.
Cytochrome P450 mediated metabolism of methyleugenol to the proximate carcinogen 1'-hydroxymethyleugenol has been investigated in vitro. Kinetic studies undertaken in liver microsomes from control male Fischer 344 rats revealed that this reaction is catalyzed by high affinity (Km of 74.9 +/- 9.0 microM, Vmax of 1.42 +/- 0.17 nmol/min/nmol P450) and low affinity (apparent Km several mM) enzymic components. Studies undertaken at low substrate concentration (20 microM) with microsomes from livers of rats treated with the enzyme inducers phenobarbital, dexamethasone, isosafrole and isoniazid indicated that a number of cytochrome P450 isozymes can catalyze the high affinity component. In control rat liver microsomes, 1'-hydroxylation of methyleugenol (assayed at 20 microM substrate) was inhibited significantly (P < 0.05) by diallylsulfide (40%), p-nitrophenol (55%), tolbutamide (30%) and alpha-naphthoflavone (25%) but not by troleandomycin, furafylline, quinine or cimetidine. These results suggested that the reaction is catalyzed by CYP 2E1 and by another as yet unidentified isozyme(s) (most probably CYP 2C6), but not by CYP 3A, CYP 1A2, CYP 2D1 or CYP 2C11. Administration of methyleugenol (0-300 mg/kg/day for 5 days) to rats in vivo caused dose-dependent auto-induction of 1'-hydroxylation of methyleugenol in vitro which could be attributed to induction of various cytochrome P450 isozymes, including CYP 2B and CYP 1A2. Consequently, high dose rodent carcinogenicity studies are likely to over-estimate the risk to human health posed by methyleugenol. The rate of 1'-hydroxylation of methyleugenol in vitro in 13 human liver samples varied markedly (by 37-fold), with the highest activities being similar to the activity evident in control rat liver microsomes. This suggests that the risk posed by dietary ingestion of methyleugenol could vary markedly in the human population.
细胞色素P450介导的甲基丁香酚代谢生成近致癌物1'-羟基甲基丁香酚的过程已在体外进行了研究。在对照雄性Fischer 344大鼠的肝微粒体中进行的动力学研究表明，该反应由高亲和力（Km为74.9±9.0微摩尔，Vmax为1.42±0.17纳摩尔/分钟/纳摩尔P450）和低亲和力（表观Km为几毫摩尔）的酶组分催化。在用酶诱导剂苯巴比妥、地塞米松、异黄樟素和异烟肼处理的大鼠肝脏微粒体中，在低底物浓度（20微摩尔）下进行的研究表明，多种细胞色素P450同工酶可催化高亲和力组分。在对照大鼠肝微粒体中，二烯丙基硫醚（40%）、对硝基苯酚（55%）、甲苯磺丁脲（30%）和α-萘黄酮（25%）可显著抑制甲基丁香酚的1'-羟基化（在20微摩尔底物下测定）（P<0.05），但不能被三乙酰竹桃霉素、呋拉茶碱、奎宁或西咪替丁抑制。这些结果表明，该反应由CYP 2E1和另一种尚未鉴定的同工酶（很可能是CYP 2C6）催化，但不由CYP 3A、CYP 1A2、CYP 2D1或CYP 2C11催化。在体内给大鼠施用甲基丁香酚（0 - 300毫克/千克/天，共5天）会导致体外甲基丁香酚1'-羟基化的剂量依赖性自身诱导，这可归因于包括CYP 2B和CYP 1A2在内的多种细胞色素P450同工酶的诱导。因此，高剂量啮齿动物致癌性研究可能会高估甲基丁香酚对人类健康造成的风险。在13个人类肝脏样本中，体外甲基丁香酚1'-羟基化的速率差异显著（达37倍），最高活性与对照大鼠肝微粒体中明显的活性相似。这表明，饮食摄入甲基丁香酚对人类群体造成的风险可能有显著差异。
