Department of Clinical Pharmacology, School of Medicine, Flinders University, Adelaide, Australia (N.C., D.J.E., B.C.L., K.B., P.I.M., J.O.M.); and School of Chemical and Physical Sciences, Flinders University, Adelaide, Australia (M.R.J.).
J Pharmacol Exp Ther. 2014 Apr;349(1):126-37. doi: 10.1124/jpet.113.212258. Epub 2014 Jan 23.
Morphine 3-β-D-glucuronide (M3G) and morphine 6-β-D-glucuronide (M6G) are the major metabolites of morphine in humans. More recently, morphine-3-β-d-glucoside (M-3-glucoside) was identified in the urine of patients treated with morphine. Kinetic and inhibition studies using human liver microsomes (HLM) and recombinant UGTs as enzyme sources along with molecular modeling were used here to characterize the relationship between morphine glucuronidation and glucosidation. The M3G to M6G intrinsic clearance (C(Lint)) ratio (∼5.5) from HLM supplemented with UDP-glucuronic acid (UDP-GlcUA) alone was consistent with the relative formation of these metabolites in humans. The mean C(Lint) values observed for M-3-glucoside by incubations of HLM with UDP-glucose (UDP-Glc) as cofactor were approximately twice those for M6G formation. However, although the M3G-to-M6G C(Lint) ratio remained close to 5.5 when human liver microsomal kinetic studies were performed in the presence of a 1:1 mixture of cofactors, the mean C(Lint) value for M-3-glucoside formation was less than that of M6G. Studies with UGT enzyme-selective inhibitors and recombinant UGT enzymes, along with effects of BSA on morphine glycosidation kinetics, were consistent with a major role of UGT2B7 in both morphine glucuronidation and glucosidation. Molecular modeling identified key amino acids involved in the binding of UDP-GlcUA and UDP-Glc to UGT2B7. Mutagenesis of these residues abolished morphine glucuronidation and glucosidation. Overall, the data indicate that morphine glucuronidation and glucosidation occur as complementary metabolic pathways catalyzed by a common enzyme (UGT2B7). Glucuronidation is the dominant metabolic pathway because the binding affinity of UDP-GlcUA to UGT2B7 is higher than that of UDP-Glc.
吗啡 3-β-D-葡糖苷酸（M3G）和吗啡 6-β-D-葡糖苷酸（M6G）是人体中吗啡的主要代谢物。最近，在接受吗啡治疗的患者的尿液中发现了吗啡-3-β-D-葡糖苷（M-3-葡糖苷）。本研究采用人肝微粒体（HLM）和重组 UGT 作为酶源的动力学和抑制研究，以及分子建模，来描述吗啡葡糖醛酸化和葡糖苷化之间的关系。单独用 UDP-葡糖醛酸（UDP-GlcUA）补充的 HLM 中 M3G 至 M6G 的固有清除率（C(Lint)）比值（~5.5）与这些代谢物在人体内的相对形成一致。用 UDP-葡萄糖（UDP-Glc）作为辅因子孵育 HLM 时观察到的 M-3-葡糖苷的平均 C(Lint)值约为 M6G 形成的两倍。然而，尽管在存在 1:1 混合辅因子的情况下进行人肝微粒体动力学研究时，M3G 至 M6G 的 C(Lint)比值仍接近 5.5，但 M-3-葡糖苷形成的平均 C(Lint)值小于 M6G。用 UGT 酶选择性抑制剂和重组 UGT 酶进行的研究，以及 BSA 对吗啡糖基化动力学的影响，都表明 UGT2B7 在吗啡葡糖醛酸化和葡糖苷化中都起着主要作用。分子建模确定了与 UDP-GlcUA 和 UDP-Glc 结合到 UGT2B7 相关的关键氨基酸。这些残基的突变使吗啡葡糖醛酸化和葡糖苷化完全失活。总的来说，数据表明吗啡葡糖醛酸化和葡糖苷化是由共同的酶（UGT2B7）催化的互补代谢途径。葡糖醛酸化是主要的代谢途径，因为 UDP-GlcUA 与 UGT2B7 的结合亲和力高于 UDP-Glc。
