Studies on the metabolism of troglitazone to reactive intermediates in vitro and in vivo. Evidence for novel biotransformation pathways involving quinone methide formation and thiazolidinedione ring scission
Studies on the metabolism of troglitazone to reactive intermediates in vitro and in vivo. Evidence for novel biotransformation pathways involving quinone methide formation and thiazolidinedione ring scission
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DOI：
10.1021/tx000180q
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发表时间：
2001-01-01
影响因子：
4.1
通讯作者：
Baillie, TA
中科院分区：
文献类型：
--
作者：
Kassahun, K;Pearson, PG;Baillie, TA
口服降糖药曲格列酮（Rezulin）治疗与严重肝毒性和药物性肝衰竭的发生率相关，这导致该产品最近从美国市场撤回。虽然这种毒性的机制尚不清楚，但药物的化学反应性代谢物可能起了致病作用。为了解决这一可能性，本研究旨在确定曲格列酮是否在人肝微粒体制剂中代谢为亲电中间体。在谷胱甘肽（GSH）存在的情况下，将曲格列酮与人肝微粒体和cdna表达的细胞色素P450同型体孵育，共检测到5种谷胱甘肽偶联物（M1-M5），并通过LC-MS/MS分析初步鉴定。在两种情况下（M1和M5），加合物的结构通过核磁共振波谱和/或与合成的真实标准物进行比较得到证实。GSH偶联物M1-M5的形成揭示了曲格列酮的两种不同的代谢激活途径，其中一种途径是将取代的铬烷环系统氧化为反应性的邻醌甲基衍生物，而另一种途径是对噻唑烷二酮（TZD）环进行新的氧化裂解，可能产生高度亲电的α -酮异氰酸酯和磺酸中间体。当给大鼠口服曲格列酮时，发现胆汁样品中含有谷胱甘肽缀合物，这反映了体内这些相同代谢途径的运作。鉴于最近有报道称曲格列酮是人肝细胞中该异构体的诱导剂，该发现具有重要意义，即曲格列酮的TZD环的代谢被P450 3A酶选择性地催化。这些结果的含义在曲格列酮共价修饰肝蛋白和通过氧化还原循环过程引起氧化应激的可能性的背景下进行了讨论，这两种情况都可能在药物性肝损伤中发挥作用。
Therapy with the oral antidiabetic agent troglitazone (Rezulin) has been associated with eases of severe hepatotoxicity and drug-induced liver failure, which led to the recent withdrawal of the product from the U.S. market. While the mechanism of this toxicity remains unknown, it is possible that chemically reactive metabolites of the drug play a causative role. In an effort to address this possibility, this study was undertaken to determine whether troglitazone undergoes metabolism in human liver microsomal preparations to electrophilic intermediates. Following incubation of troglitazone with human liver microsomes and with cDNA-expressed cytochrome P450 isoforms in the presence of glutathione (GSH), a total of five GSH conjugates (M1-M5) were detected and identified tentatively by LC-MS/MS analysis. In two cases (M1 and M5), the structures of the adducts were confirmed by NMR spectroscopy and/or by comparison with an authentic standard prepared by synthesis. The formation of GSH conjugates M1-M5 revealed the operation of two distinct metabolic activation pathways for troglitazone, one of which involves oxidation of the substituted chromane ring system to a reactive o-quinone methide derivative, while the second involves a novel oxidative cleavage of the thiazolidinedione (TZD) ring, potentially generating highly electrophilic alpha -ketoisocyanate and sulfenic acid intermediates. When troglitazone was administered orally to a rat, samples of bile were found to contain GSH conjugates which reflected the operation of these same metabolic pathways in vivo. The finding that metabolism of the TZD ring of troglitazone was catalyzed selectively by P450 3A enzymes is significant in Light of the recent report that troglitazone is an inducer of this isoform in human hepatocytes. The implications of these results are discussed in the context of the potential for troglitazone to covalently modify hepatic proteins and to cause oxidative stress through redox cycling processes, either of which may play a role in drug-induced liver injury.