Division of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland.
Drug Metab Dispos. 2010 Mar;38(3):386-95. doi: 10.1124/dmd.109.031138. Epub 2009 Dec 10.
We have examined the glucuronidation of psilocin, a hallucinogenic indole alkaloid, by the 19 recombinant human UDP-glucuronosyltransferases (UGTs) of subfamilies 1A, 2A, and 2B. The glucuronidation of 4-hydroxyindole, a related indole that lacks the N,N-dimethylaminoethyl side chain, was studied as well. UGT1A10 exhibited the highest psilocin glucuronidation activity, whereas the activities of UGTs 1A9, 1A8, 1A7, and 1A6 were significantly lower. On the other hand, UGT1A6 was by far the most active enzyme mediating 4-hydroxyindole glucuronidation, whereas the activities of UGTs 1A7-1A10 toward 4-hydroxyindole resembled their respective psilocin glucuronidation rates. Psilocin glucuronidation by UGT1A10 followed Michaelis-Menten kinetics in which psilocin is a low-affinity high-turnover substrate (K(m) = 3.8 mM; V(max) = 2.5 nmol/min/mg). The kinetics of psilocin glucuronidation by UGT1A9 was more complex and may be best described by biphasic kinetics with both intermediate (K(m1) = 1.0 mM) and very low affinity components. The glucuronidation of 4-hydroxyindole by UGT1A6 exhibited higher affinity (K(m) = 178 microM) and strong substrate inhibition. Experiments with human liver and intestinal microsomes (HLM and HIM, respectively) revealed similar psilocin glucuronidation activity in both samples, but a much higher 4-hydroxyindole glucuronidation rate was found in HLM versus HIM. The expression levels of UGTs 1A6-1A10 in different tissues were studied by quantitative real-time-PCR, and the results, together with the activity assays findings, suggest that whereas psilocin may be subjected to extensive glucuronidation by UGT1A10 in the small intestine, UGT1A9 is likely the main contributor to its glucuronidation once it has been absorbed into the circulation.
我们研究了 19 种重组人 UDP-葡糖醛酸基转移酶（UGT）亚家族 1A、2A 和 2B 对迷幻吲哚生物碱裸头草碱的葡糖醛酸化作用，同时也研究了相关的缺乏 N,N-二甲基氨基乙基侧链的 4-羟基吲哚的葡糖醛酸化作用。UGT1A10 对裸头草碱的葡糖醛酸化活性最高，而 UGTs1A9、1A8、1A7 和 1A6 的活性则明显较低。另一方面，UGT1A6 是介导 4-羟基吲哚葡糖醛酸化的最活跃的酶，而 UGTs1A7-1A10 对 4-羟基吲哚的活性类似于它们各自的裸头草碱葡糖醛酸化率。UGT1A10 介导的裸头草碱葡糖醛酸化遵循米氏动力学，其中裸头草碱是一种低亲和力高周转率的底物（K(m)=3.8 mM；V(max)=2.5 nmol/min/mg）。UGT1A9 介导的裸头草碱葡糖醛酸化动力学更为复杂，可能最好用两相动力学来描述，其中包括中间（K(m1)=1.0 mM）和极低亲和力成分。UGT1A6 介导的 4-羟基吲哚葡糖醛酸化具有更高的亲和力（K(m)=178 microM）和强烈的底物抑制。用人肝和肠微粒体（HLM 和 HIM，分别）进行的实验表明，这两种样品中均具有相似的裸头草碱葡糖醛酸化活性，但 HLM 中的 4-羟基吲哚葡糖醛酸化率远高于 HIM。通过实时定量 PCR 研究了不同组织中 UGTs1A6-1A10 的表达水平，结合活性测定结果，提示在小肠中，裸头草碱可能被 UGT1A10 广泛葡糖醛酸化，一旦被吸收到循环中，UGT1A9 可能是其葡糖醛酸化的主要贡献者。
