Tonge R P, Kelly E J, Bruschi S A, Kalhorn T, Eaton D L, Nebert D W, Nelson S D
Department of Medicinal Chemistry, University of Washington, Seattle 98195-7631, USA.
Toxicol Appl Pharmacol. 1998 Nov;153(1):102-8. doi: 10.1006/taap.1998.8543.
Acetaminophen (APAP) is known to cause centrilobular hepatic necrosis under overdose conditions. This is thought to be mediated via the P450-generated reactive intermediate N-acetyl-p-benzoquinone imine (NAPQI). Initially, NAPQI is detoxified by conjugation with glutathione (GSH), but once GSH is depleted, NAPQI reacts more extensively with hepatic proteins leading to hepatocellular damage. The P450 isoforms thought to be responsible for APAP hepatotoxicity in humans are CYP2E1, CYP1A2, and CYP3A4, and thus, we have investigated the effect of murine Cyp1a2 on APAP hepatotoxicity using Cyp1a2 knockout mice (Liang et al., Proc. Natl. Acad. Sci. USA 93, 1671-1676, 1996). Doses of 250 mg/kg were markedly hepatotoxic in these mice, and surprisingly, deaths only occurred in the knock-out and heterozygote mice over a 24-h period after dosing. Furthermore, there were no significant differences among survivors of any genotype in serum ALT concentrations, a well correlated indicator of APAP hepatotoxicity in mice. Finally, no differences were observed in the urinary metabolites excreted ove the 24-h period, including those derived from GSH conjugation of the major reactive metabolite NAPQI. Consistent with the effects on hepatotoxicity and metabolism, 2 h after hepatotoxic doses (500 mg/kg, i.p.) of APAP no significant differences were observed in total whole liver homogenate nonprotein thiol concentrations among the three genotypes even though hepatic thiols were decreased compared to control animals (> 90%). In addition, when the liver cytosol and microsome samples were examined by immunoblotting for the presence of APAP-protein adducts using a specific antiserum, there were no observable differences in either the intensity of staining or in the spectrum of adducts formed between APAP-dosed mice of any genotype. The cumulative data suggest that Cyp1a2 doses not play a significant role in APAP hepatotoxicity in these mice.
已知对乙酰氨基酚（APAP）在过量情况下会导致小叶中心性肝坏死。这被认为是通过细胞色素P450产生的反应性中间体N - 乙酰 - 对苯醌亚胺（NAPQI）介导的。最初，NAPQI通过与谷胱甘肽（GSH）结合而解毒，但一旦GSH耗尽，NAPQI会更广泛地与肝脏蛋白质反应，导致肝细胞损伤。被认为与人类APAP肝毒性有关的细胞色素P450同工酶是CYP2E1、CYP1A2和CYP3A4，因此，我们使用Cyp1a2基因敲除小鼠研究了小鼠Cyp1a2对APAP肝毒性的影响（Liang等人，《美国国家科学院院刊》93，1671 - 1676，1996）。250 mg/kg的剂量在这些小鼠中具有明显的肝毒性，令人惊讶的是，仅在给药后24小时内，基因敲除小鼠和杂合子小鼠出现死亡。此外，血清谷丙转氨酶（ALT）浓度是小鼠APAP肝毒性的良好相关指标，在任何基因型的存活小鼠中，其ALT浓度均无显著差异。最后，在24小时内排泄的尿液代谢产物中未观察到差异，包括主要反应性代谢产物NAPQI与GSH结合产生的代谢产物。与对肝毒性和代谢的影响一致，在给予肝毒性剂量（500 mg/kg，腹腔注射）的APAP 2小时后，即使与对照动物相比肝脏硫醇减少（> 90%），三种基因型的全肝匀浆总非蛋白硫醇浓度也未观察到显著差异。此外，当使用特异性抗血清通过免疫印迹法检测肝细胞质和微粒体样品中APAP - 蛋白质加合物的存在时，在任何基因型的APAP给药小鼠之间，染色强度或形成的加合物谱均未观察到差异。累积数据表明，Cyp1a2在这些小鼠的APAP肝毒性中不发挥重要作用。
