BACKGROUND Butaselen is an ebselen analog that is under clinical trials for treating hepatic and pulmonary fibrosis. Our previous studies showed that butaselen is mainly present in human plasma in the form of M2, a free Se-methylated metabolite. OBJECTIVE This study aimed to investigate the metabolic mechanisms of butaselen. METHODS AND RESULTS Butaselen was incubated with human plasma. Butaselen immediately disappeared, and the butaselen-HSA (human serum albumin) adduct was detected by HPLC-HRMS, showing that butaselen covalently binds to HSA. The butaselen-HSA adduct was precipitated using acetonitrile and then incubated with PBS, Cys, and GSH for 1 hour. The product was M1, a reduced form of butaselen. The results indicated that HSA, Cys, and GSH can reduce the butaselen-HSA covalent bond. The binding site for butaselen could be the cysteine-34 residue of HSA through pronase and trypsin hydrolysis. Incubating butaselen with cysteine, butaselen-Cys, butaselen-2Cys, and M1 were generated, indicating the covalent binding and reduction of butaselen by cysteine. We incubated liver microsomes and cytosol with butaselen, 6.22 and 246 nM M2 were generated, respectively. The results demonstrated that cytosolic enzymes are mainly involved in M2 production. The amount of M2 in the liver cytosol decreased from 246 nM to 2.21 nM when 10 mM m-anisic acid (a specific TPMT enzyme inhibitor) was added, showing that TPMT is responsible for M2 formation. CONCLUSION Butaselen was covalently bound to HSA, and the binding site was the cysteine-34 residue of HSA. The butaselen-HSA adduct was reduced by free thiol compounds to generate M1. M1 was further metabolized to M2 by cytosolic TPMT. This study provides a basis for studying the pharmacokinetics of selenium-containing drugs.

中文翻译：

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研究 Butaselen 的代谢机制，一种 Ebselen 类似物。

背景布塔硒啉是一种依布硒啉类似物，正在进行用于治疗肝纤维化和肺纤维化的临床试验。我们之前的研究表明，丁硒硒主要以 M2 的形式存在于人体血浆中，M2 是一种游离的硒甲基化代谢物。目的本研究旨在探讨丁硒硒的代谢机制。方法和结果 布塔硒啉与人血浆一起孵育。Butaselen 立即消失，HPLC-HRMS 检测到 butaselen-HSA（人血清白蛋白）加合物，表明 butaselen 与 HSA 共价结合。使用乙腈沉淀 butaselen-HSA 加合物，然后与 PBS、Cys 和 GSH 孵育 1 小时。产品是 M1，一种还原型丁硒硒。结果表明，HSA、Cys 和 GSH 可以减少 butaselen-HSA 共价键。通过链霉蛋白酶和胰蛋白酶水解，丁二烯硒的结合位点可能是 HSA 的半胱氨酸 34 残基。将丁二烯硒与半胱氨酸孵育，生成丁二烯硒-Cys、丁二烯硒-2Cys 和 M1，表明半胱氨酸共价结合和还原丁二烯硒。我们将肝微粒体和胞质溶胶与丁硒硒一起孵育，分别产生了 6.22 和 246 nM M2。结果表明，胞质酶主要参与 M2 的产生。当添加 10 mM 间茴香酸（一种特定的 TPMT 酶抑制剂）时，肝细胞溶质中 M2 的量从 246 nM 减少到 2.21 nM，表明 TPMT 负责 M2 的形成。结论 Butaselen与HSA共价结合，结合位点为HSA的34位半胱氨酸残基。butaselen-HSA 加合物被游离硫醇化合物还原生成 M1。M1 通过胞质 TPMT 进一步代谢为 M2。本研究为研究含硒药物的药代动力学提供了依据。