Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China (X.H., J.Z., S.Y., L.Z., Y.Z., D.Z., X.C.); and University of Chinese Academy of Sciences, Beijing, China (X.H., D.Z., X.C.).
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China (X.H., J.Z., S.Y., L.Z., Y.Z., D.Z., X.C.); and University of Chinese Academy of Sciences, Beijing, China (X.H., D.Z., X.C.)
Drug Metab Dispos. 2018 Sep;46(9):1320-1328. doi: 10.1124/dmd.118.081182. Epub 2018 Jul 6.
Imrecoxib is a typical cyclooxygenase-2 inhibitor and the benzylic carbon motif is its major site of oxidative metabolism, producing a hydroxymethyl metabolite (M1) and a carboxylic acid metabolite (M2). The plasma exposure of M2 is four times higher than those of both M0 and M1 in humans. However, this metabolite is rarely formed in in vitro experiments. Therefore, this study aims to investigate the formation mechanism of M2 and to further elucidate the reason for the discrepancy between in vitro and in vivo metabolic data. By employing human hepatocytes, human liver microsomes (HLMs), human liver cytosols (HLCs), recombinant enzymes, and selective enzyme inhibitors, the metabolic map of imrecoxib was elaborated as follows: the parent drug was initially hydroxylated to form M1 in HLMs, mainly mediated by CYP3A4 and CYP2D6, and to subsequently form aldehyde imrecoxib (M-CHO) in HLMs and HLCs. The latter process is the rate-limiting step in generating the end-product M2. In further M-CHO metabolism, two opposite reactions (namely, rapid oxidation catalyzed by CYP3A4, CYP2D6, and cytosolic aldehyde oxidase to form M2 versus reduction to regenerate M1 mediated by NADPH-dependent reductases in HLMs and HLCs, such as cytochrome P450 reductase) led to marked underestimation of the M2 amount in static in vitro incubations. The findings provided a possible explanation for the difference between in vitro and in vivo metabolism of imrecoxib, suggesting that the effect of competitive reduction on the static oxidation metabolism in in vitro metabolic experiments should be considered.
依托考昔是一种典型的环氧化酶-2 抑制剂，其苄基碳结构是其主要的氧化代谢部位，产生羟甲基代谢物（M1）和羧酸代谢物（M2）。在人体中，M2 的血浆暴露量是 M0 和 M1 的四倍。然而，这种代谢物在体外实验中很少形成。因此，本研究旨在探讨 M2 的形成机制，并进一步阐明体外和体内代谢数据之间的差异原因。本研究采用人肝细胞、人肝微粒体（HLMs）、人肝胞质（HLCs）、重组酶和选择性酶抑制剂，阐述了依托考昔的代谢图谱如下：母体药物首先在 HLMs 中羟化形成 M1，主要由 CYP3A4 和 CYP2D6 介导，随后在 HLMs 和 HLCs 中形成醛依托考昔（M-CHO）。这个过程是生成终产物 M2 的限速步骤。在进一步的 M-CHO 代谢中，两个相反的反应（即由 CYP3A4、CYP2D6 和胞质醛氧化酶快速氧化形成 M2，以及由 HLMs 和 HLCs 中的 NADPH 依赖性还原酶介导的还原反应以再生 M1）导致在静态体外孵育中对 M2 量的明显低估。这些发现为依托考昔体外和体内代谢之间的差异提供了可能的解释，表明在体外代谢实验中，竞争还原对静态氧化代谢的影响应予以考虑。
