Axworthy D B, Hoffmann K J, Streeter A J, Calleman C J, Pascoe G A, Baillie T A
Department of Medicinal Chemistry, School of Pharmacy, University of Washington, Seattle 98195.
Chem Biol Interact. 1988;68(1-2):99-116. doi: 10.1016/0009-2797(88)90009-9.
When hepatotoxic doses of [ring-U-14C]acetaminophen ([ring-U-14C]APAP) were administered to mice, radioactivity became bound irreversibly to hemoglobin as well as to proteins in the liver and kidney. The covalent binding to hemoglobin was dose-dependent, and in phenobarbital-pretreated mice occurred to the extent of approximately 8% of the corresponding binding to liver proteins. Degradation of the modified globin by acid hydrolysis yielded 3-cystein-S-yl-4-hydroxyacetanilide as the major radioactive product, accounting for approximately 70% of protein-bound drug residues. This finding is consistent with the view that the majority of covalent binding of APAP to proteins is mediated by N-acetyl-p-benzoquinone imine (NAPQI), a reactive metabolite which preferentially arylates cysteinyl thiol residues. However, after administration of [acetyl-3H]APAP to mice, it was found that approximately 20% of the drug bound to hemoglobin had lost the N-acetyl side-chain, indicating the existence of a second type of APAP-protein adduct. One minor component of the globin hydrolysate was identified as S-(2,5-dihydroxyphenyl)-cysteine, which most likely arises from binding to hemoglobin of p-benzoquinone, a hydrolysis product of NAPQI. The two adducts reported represent the first identified examples of arylating drugs binding to hemoglobin. Experiments on the influence of different cytochrome P-450 inducing agents on the ratio of drug bound to hemoglobin versus hepatic proteins suggested that the reactive metabolites of APAP are formed in the liver and migrate to the erythrocyte, rather than being produced by hemoglobin-catalyzed oxidation of APAP. These findings imply that the reactive metabolites of APAP escape from hepatocytes in some latent forms, which then participate in the arylation of protein thiols in red blood cells and, possibly, at other remote sites.
当给小鼠施用肝毒性剂量的[环-U-¹⁴C]对乙酰氨基酚（[环-U-¹⁴C]APAP）时，放射性物质会不可逆地与血红蛋白以及肝脏和肾脏中的蛋白质结合。与血红蛋白的共价结合呈剂量依赖性，在苯巴比妥预处理的小鼠中，其发生程度约为与肝脏蛋白质相应结合量的8%。经酸水解后，修饰珠蛋白的降解产生3-半胱氨酸-S-基-4-羟基乙酰苯胺作为主要放射性产物，约占与蛋白质结合的药物残留量的70%。这一发现与以下观点一致，即APAP与蛋白质的大多数共价结合是由N-乙酰-p-苯醌亚胺（NAPQI）介导的，NAPQI是一种活性代谢物，优先使半胱氨酰硫醇残基芳基化。然而，给小鼠施用[乙酰-³H]APAP后，发现与血红蛋白结合的药物中约20%失去了N-乙酰侧链，这表明存在第二种类型的APAP-蛋白质加合物。珠蛋白水解产物的一种次要成分被鉴定为S-(2,5-二羟基苯基)-半胱氨酸，它很可能源于NAPQI的水解产物对苯醌与血红蛋白的结合。报道的这两种加合物代表了芳基化药物与血红蛋白结合的首批已鉴定实例。关于不同细胞色素P-450诱导剂对药物与血红蛋白结合量与肝脏蛋白质结合量之比影响的实验表明，APAP的活性代谢物在肝脏中形成并迁移至红细胞，而不是由血红蛋白催化的APAP氧化产生。这些发现意味着APAP的活性代谢物以某种潜在形式从肝细胞中逸出，然后参与红细胞以及可能在其他远处部位的蛋白质硫醇的芳基化反应。
