Laboratory of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
Drug Metab Dispos. 2011 Dec;39(12):2290-7. doi: 10.1124/dmd.111.040469. Epub 2011 Sep 13.
Null mutation of glutathione transferase (GST) M1 and GSTT1 was reported to correlate statistically with an abnormal increase in the plasma levels of alanine aminotransferase or aspartate aminotransferase caused by troglitazone in diabetic patients (Clin Pharmacol Ther, 73:435-455, 2003). This clinical evidence leads to the hypothesis that GSH conjugation catalyzed by GSTT1 and GSTM1 has a role in the elimination of reactive metabolites of troglitazone. However, the contribution of GST isoforms expressed in human liver to the detoxification of reactive metabolites of troglitazone has not yet been clarified. We investigated the involvement of human GST isoforms in the GSH conjugation of reactive metabolites of troglitazone using recombinant GST enzymes. Five reported GSH conjugates of reactive metabolites were produced from troglitazone after incubation with liver microsomes, NADPH, and GSH in a GSH concentration-dependent manner. Addition of human recombinant GSTA1, GSTA2, GSTM1, or GSTP1 protein to the incubation mixture further increased the GSH conjugates. However, the addition of GSTT1 did not show any catalytic effect. It is of interest that one of the reactive metabolites with a quinone structure was predominantly conjugated with GSH by GSTM1. Thus, we demonstrated that the GST isoforms contributed differently to the GSH conjugation of individual reactive metabolites of troglitazone, and GSTM1 is the most important GST isoform in the GSH conjugation of a specific reactive metabolite produced from the cytotoxic, quinone-form metabolite of troglitazone.
谷胱甘肽转移酶（GST）M1 和 GSTT1 的无效突变与曲格列酮引起的糖尿病患者血浆丙氨酸氨基转移酶或天冬氨酸氨基转移酶水平异常升高有统计学相关性（Clin Pharmacol Ther，73：435-455，2003）。这一临床证据提出了假设，即 GSTT1 和 GSTM1 催化的 GSH 缀合在曲格列酮的反应性代谢物的消除中起作用。然而，尚未阐明人肝中 GST 同工酶对曲格列酮反应性代谢物的解毒作用。我们使用重组 GST 酶研究了人 GST 同工酶在曲格列酮反应性代谢物的 GSH 缀合中的作用。在 GSH 浓度依赖性方式下，用肝微粒体、NADPH 和 GSH 孵育曲格列酮后，生成了 5 种报道的反应性代谢物的 GSH 缀合物。向孵育混合物中添加人重组 GSTA1、GSTA2、GSTM1 或 GSTP1 蛋白会进一步增加 GSH 缀合物。然而，添加 GSTT1 没有显示出任何催化作用。有趣的是，一种具有醌结构的反应性代谢物主要与 GSTM1 缀合。因此，我们证明了 GST 同工酶对曲格列酮的各个反应性代谢物的 GSH 缀合作用不同，并且 GSTM1 是曲格列酮细胞毒性醌代谢物产生的特定反应性代谢物的 GSH 缀合中最重要的 GST 同工酶。
