Abstract Context: 23-Hydroxybetulinic acid (23-HBA), a major active constituent of Pulsatilla chinensis (Bunge) Regel (Ranunculaceae), exhibits potential antitumor activity. Its metabolism, however, has not yet been studied. Objective: This study focuses on the metabolism of 23-HBA in vitro by human liver microsomes. Materials and methods: The metabolic kinetics of 23-HBA (0.5–100 µM) and the effects of selective CYP450 (CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4) inhibitors on metabolism of 23-HBA were evaluated in human liver microsomes incubation system and then determined by LC-MS method. The Michaelis–Menten parameters Km and Vmax were initially estimated by analysing Lineweaver–Burk plot. The clearance (CLint) was also calculated. Results: The Vmax, Km, and CLint of 23-HBA were 256.41 ± 11.20 pmol/min/mg, 11.10 ± 1.07 μM, and 23.10 ± 1.32 μL/min/mg, respectively. The metabolism of 23-HBA was significantly inhibited by furafylline (0.05 μM, p < 0.01) and ketoconazole (0.02 μM, p < 0.05). Ticlopidine (1.3 μM, p < 0.05) could inhibit the metabolism of 23-HBA, while the other inhibitors (sulfaphenazole and quinidine) showed nonsignificant inhibition on the metabolism of 23-HBA. Discussion and conclusions: This is the first investigation of the metabolism of 23-HBA in human liver microsomes. The in vitro study indicates that CYP1A2 and CYP3A4 are mainly involved in the metabolism of 23-HBA. Special attention should be given to the pharmacokinetic and clinical outcomes when 23-HBA was co-administrated with other compounds mainly undergoing CYP1A2/CYP3A4-mediated metabolism. Further studies are needed to evaluate the significance of this interaction and strengthen the understanding of traditional Chinese medicine.

中文翻译：

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人肝微粒体中参与23-羟基桦木酸代谢的细胞色素P450同工酶的鉴定

摘要背景：23-羟基桦木酸 (23-HBA) 是白头翁 (Pulsatilla chinensis (Bunge) Regel (毛茛科)) 的主要活性成分，具有潜在的抗肿瘤活性。然而，尚未对其代谢进行研究。目的：本研究的重点是人肝微粒体对 23-HBA 的体外代谢。材料和方法：在人肝微粒体孵育系统中评估 23-HBA (0.5–100 µM) 的代谢动力学和选择性 CYP450（CYP1A2、CYP2C9、CYP2C19、CYP2D6 和 CYP3A4）抑制剂对 23-HBA 代谢的影响然后用LC-MS法测定。Michaelis-Menten 参数 Km 和 Vmax 最初是通过分析 Lineweaver-Burk 图来估计的。还计算了清除率 (CLint)。结果：23-HBA 的 Vmax、Km 和 CLint 分别为 256.41 ± 11.20 pmol/min/mg、11.10 ± 1.07 μM 和 23.10 ± 1。分别为 32 μL/min/mg。呋喃茶碱 (0.05 μM, p < 0.01) 和酮康唑 (0.02 μM, p < 0.05) 显着抑制 23-HBA 的代谢。噻氯匹定 (1.3 μM, p < 0.05) 可以抑制 23-HBA 的代谢，而其他抑制剂（磺胺吩唑和奎尼丁）对 23-HBA 的代谢没有显着抑制作用。讨论和结论：这是对23-HBA在人肝微粒体中代谢的首次研究。体外研究表明CYP1A2和CYP3A4主要参与23-HBA的代谢。当 23-HBA 与其他主要进行 CYP1A2/CYP3A4 介导代谢的化合物共同给药时，应特别注意药代动力学和临床结果。