Murray M, Sefton R M, Martini R, Butler A M
Department of Medicine, University of Sydney, Westmead Hospital, NSW, Australia.
Toxicol Lett. 1997 Dec;93(2-3):195-203. doi: 10.1016/s0378-4274(97)00092-1.
Pyridine derivatives are widely used solvents and precursors for the synthesis of chemicals of industrial importance. Oxidized metabolites have been implicated in the observed toxicity of pyridines and are known to induce drug-metabolizing enzymes in rat liver. In this study the three isomeric picoline (methylpyridine) N-oxides, as major oxidized metabolites of 2-, 3- and 4-picoline, were evaluated as inducers of cytochrome P450 (CYP) enzymes in rat liver. After a single dose of 100 mg/kg 24 h before sacrifice the 3- and 4-isomers were effective inducers of microsomal substrate oxidations associated with the phenobarbital-inducible CYPs 2B; upregulation of CYP2B protein was confirmed by immunoblotting. In contrast, the 2-isomer did not increase CYP2B protein or activity in rat liver but CYP2E1 protein expression was upregulated by the isomers to 160-200% of control. The three chemicals increased aniline 4-hydroxylation activity in rat liver, which is consistent with induction of CYPs 2B or 2E1 and 4-nitrophenol 2-hydroxylation activity was increased in microsomal fractions from 3- and 4-picoline N-oxide-treated rats. The activities of several other CYPs were also determined and CYP1A-dependent 7-ethylresorufin O-deethylation was increased (to approximately 6- and 2-fold of control) by the 3- and 4-isomer, respectively, whereas the activity of CYP3A-mediated androstenedione 6beta-hydroxylation was decreased by the agents--most notably by the 2-isomer. During NADPH-supported oxidation of CCl4, lipid peroxidation was increased in microsomes from 3- and 4-picoline N-oxide-pretreated rats and was modulated in vitro by the CYP2B inhibitor orphenadrine, but not by the CYP2E1 inhibitor 4-methylpyrazole. These findings establish that particular isomers of picoline N-oxide rapidly upregulate CYP2B or, to a lesser extent, CYP2E1 and implicate CYP2B in the enhanced lipid peroxidation observed in microsomes from rats treated with 3- and 4-picoline N-oxides. Such induction process may contribute to the hepatotoxicity of pyridines by enhancing the capacity for microsomal lipid peroxidation.
吡啶衍生物是广泛使用的溶剂，也是合成具有工业重要性化学品的前体。氧化代谢物与吡啶所观察到的毒性有关，并且已知会诱导大鼠肝脏中的药物代谢酶。在本研究中，作为2-、3-和4-甲基吡啶的主要氧化代谢物，三种异构的甲基吡啶氮氧化物被评估为大鼠肝脏中细胞色素P450（CYP）酶的诱导剂。在处死前24小时给予100mg/kg的单次剂量后，3-和4-异构体是与苯巴比妥诱导的CYP2B相关的微粒体底物氧化的有效诱导剂；通过免疫印迹证实了CYP2B蛋白的上调。相比之下，2-异构体不会增加大鼠肝脏中CYP2B蛋白或活性，但异构体可将CYP2E1蛋白表达上调至对照的160%-200%。这三种化学物质增加了大鼠肝脏中苯胺4-羟化活性，这与CYP2B或CYP2E1的诱导一致，并且在3-和4-甲基吡啶氮氧化物处理的大鼠的微粒体组分中4-硝基苯酚2-羟化活性增加。还测定了其他几种CYP的活性，3-和4-异构体分别使CYP1A依赖性的7-乙基试卤灵O-脱乙基作用增加（至对照的约6倍和2倍），而CYP3A介导的雄烯二酮6β-羟化活性则被这些试剂降低——最显著的是被2-异构体降低。在四氯化碳的NADPH支持的氧化过程中，3-和4-甲基吡啶氮氧化物预处理的大鼠微粒体中的脂质过氧化增加，并且在体外被CYP2B抑制剂邻苯海拉明调节，但不被CYP2E1抑制剂4-甲基吡唑调节。这些发现表明，甲基吡啶氮氧化物的特定异构体可迅速上调CYP2B，或在较小程度上上调CYP2E1，并表明CYP2B与在用3-和4-甲基吡啶氮氧化物处理的大鼠微粒体中观察到的脂质过氧化增强有关。这种诱导过程可能通过增强微粒体脂质过氧化能力而导致吡啶的肝毒性。
