作者:Sanna Kaivosaari、Päivi Toivonen、Leah M. Hesse、Mikko Koskinen、Michael H. Court、Moshe Finel
DOI:10.1124/mol.107.037093
日期:2007.9
Nicotine biotransformation affects the smoking habits of addicted individuals and therefore their health risk. Using an improved analytical method, we have discovered that the human UDP-glucuronosyltransferase (UGT) 2B10, a liver enzyme previously unknown to conjugate nicotine or exhibit considerable activity toward any compound, plays a major role in nicotine inactivation by direct conjugation with glucuronic acid at the aromatic nitrogen atom. The K m value of recombinant UGT2B10 for nicotine (0.29 mM) was similar to that determined for human liver microsomes (0.33 mM), whereas the K m value of UGT1A4 for nicotine was almost 10-fold greater (2.4 mM). UGT2B10 was also more active than UGT1A4 in N -glucuronidation of cotinine (oxidative nicotine metabolite), whereas UGT2B7 exhibited only low nicotine glucuronidation activity and was essentially inactive toward cotinine. UGT1A9 did not glucuronidate nicotine or cotinine. Quantitative reverse transcription-polymerase chain reaction showed that UGT2B10 mRNA was exclusively expressed in human liver, whereas UGTs 1A4 and 2B7 were expressed at comparable, although somewhat lower, levels in liver and several other extrahepatic tissues, including kidney and intestine. These findings for UGT2B10 (but not for UGT1A4 and UGT2B7) were mirrored by human tissue activities because nicotine and cotinine glucuronidation rates in intestine microsomes were less than 0.1% that of human liver microsomes. These novel findings solve two seemingly separate questions: which UGT is primarily responsible for nicotine glucuronidation in human liver, and what conjugation reactions are catalyzed by UGT2B10.
尼古丁生物转化会影响成瘾者的吸烟习惯,从而影响他们的健康风险。使用改进的分析方法,我们发现人 UDP-葡萄糖醛酸基转移酶 (UGT) 2B10 是一种以前未知的肝酶,可与尼古丁结合或对任何化合物表现出相当大的活性,通过与葡萄糖醛酸直接结合,在尼古丁失活中发挥着重要作用。芳香族氮原子。重组 UGT2B10 对尼古丁的 K m 值 (0.29 mM) 与人肝微粒体测定的 K m 值 (0.33 mM) 相似,而 UGT1A4 对尼古丁的 K m 值几乎高出 10 倍 (2.4 mM)。 UGT2B10 在可替宁(氧化尼古丁代谢物)的 N-葡萄糖醛酸化中也比 UGT1A4 更活跃,而 UGT2B7 仅表现出较低的尼古丁葡萄糖醛酸化活性,并且对可替宁基本上没有活性。 UGT1A9 不使尼古丁或可替宁葡萄糖醛酸化。定量逆转录聚合酶链反应表明,UGT2B10 mRNA 仅在人肝脏中表达,而 UGT 1A4 和 2B7 在肝脏和其他几种肝外组织(包括肾和肠)中的表达水平相当,尽管略低。 UGT2B10(但不包括 UGT1A4 和 UGT2B7)的这些发现与人体组织活动相一致,因为肠微粒体中的尼古丁和可替宁葡萄糖醛酸化率低于人肝微粒体中的 0.1%。这些新发现解决了两个看似独立的问题:哪种 UGT 主要负责人肝脏中的尼古丁葡萄糖醛酸化,以及 UGT2B10 催化哪些结合反应。