Zaher H, Buters J T, Ward J M, Bruno M K, Lucas A M, Stern S T, Cohen S D, Gonzalez F J
Division of Basic Sciences, National Cancer Institute, Bethesda, Maryland 20892, USA.
Toxicol Appl Pharmacol. 1998 Sep;152(1):193-9. doi: 10.1006/taap.1998.8501.
Acetaminophen (APAP) hepatotoxicity is due to its biotransformation to a reactive metabolite, N-acetyl-p-benzoquinone imine (NAPQI), that is capable of binding to cellular macromolecules. At least two forms of cytochrome P450, CYP2E1 and CYP1A2, have been implicated in this reaction in mice. To test the combined roles of CYP1A2 and CYP2E1 in an intact animal model, a double-null mouse line lacking functional expression of CYP1A2 and CYP2E1 was produced by cross-breeding Cyp1a2-/- mice with Cyp2e1-/- mice. Animals deficient in the expression of both P450s developed normally and exhibited no obvious phenotypic abnormalities. Comparison of the dose-response to APAP (200-1200 mg/kg) indicated that double-null animals were highly resistant to APAP-induced toxicity whereas the wild-type animals were sensitive. Administration of 600 to 800 mg/kg of this drug to male wild-type animals resulted in increased plasma concentrations of liver enzymes (alanine aminotransferase, sorbitol dehydrogenase), lipidosis, hepatic necrosis, and renal tubular necrosis. In contrast, when APAP of equivalent or higher dose was administered to the double-null mice, plasma levels of liver enzymes and liver histopathology were normal. However, administration of 1200 mg of APAP/kg to the double-null mice resulted in infrequent liver lipidosis and mild kidney lesions. Consistent with the protection from hepatotoxicity, the expected depletion of hepatic glutathione (GSH) content was significantly retarded and APAP covalent binding to hepatic cytosolic proteins was not detectable in the double-null mice. Likewise, in vitro activation of APAP by liver microsomes from the double-null mice was approximately one tenth of that in microsomes from wild-type mice. Thus, the protection against APAP toxicity afforded by deletion of both CYP2E1 and CYP1A2 likely reflects greatly diminished production of the toxic electrophile, NAPQI.
对乙酰氨基酚（APAP）肝毒性是由于其生物转化为一种反应性代谢产物N - 乙酰 - 对苯醌亚胺（NAPQI），该代谢产物能够与细胞大分子结合。在小鼠中，至少有两种细胞色素P450形式，即CYP2E1和CYP1A2参与了此反应。为了在完整动物模型中测试CYP1A2和CYP2E1的联合作用，通过将Cyp1a2 - / - 小鼠与Cyp2e1 - / - 小鼠杂交，培育出了缺乏CYP1A2和CYP2E1功能性表达的双敲除小鼠品系。缺乏这两种P450表达的动物发育正常，未表现出明显的表型异常。对APAP（200 - 1200 mg/kg）的剂量反应比较表明，双敲除动物对APAP诱导的毒性具有高度抗性，而野生型动物则敏感。给雄性野生型动物施用600至800 mg/kg的这种药物会导致肝酶（丙氨酸转氨酶、山梨醇脱氢酶）血浆浓度升高、脂肪变性、肝坏死和肾小管坏死。相比之下，当给双敲除小鼠施用等量或更高剂量的APAP时，肝酶血浆水平和肝脏组织病理学均正常。然而，给双敲除小鼠施用1200 mg/kg的APAP会导致偶尔出现肝脂肪变性和轻度肾脏病变。与对肝毒性的保护作用一致，双敲除小鼠肝脏中谷胱甘肽（GSH）含量的预期消耗显著延迟，且未检测到APAP与肝脏胞质蛋白的共价结合。同样，双敲除小鼠肝脏微粒体对APAP的体外激活作用约为野生型小鼠微粒体的十分之一。因此，同时缺失CYP2E1和CYP1A2对APAP毒性的保护作用可能反映了有毒亲电试剂NAPQI的产生大幅减少。
