作者:Shannon Kozlovich、Gang Chen、Philip Lazarus
DOI:10.1021/acs.chemrestox.5b00278
日期:2015.11.16
Among the most potent carcinogens in tobacco are the tobacco-specific nitrosamines (TSNAs), with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) being the most potent as well as one of the most abundant. NNK is extensively metabolized to the equally carcinogenic 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL). Of the two NNAL enantiomers, (S)-NNAL not only appears to be preferentially glucuronidated and excreted in humans but also exhibits higher stereoselective tissue retention in mice and humans and has been shown to be more carcinogenic in mice than its (R) counterpart. Due to the differential carcinogenic potential of the NNAL enantiomers, it is increasingly important to know which UGT enzyme targets the specific NNAL enantiomers for glucuronidation. To examine this, a chiral separation method was developed to isolate enantiomerically pure (S)- and (R)-NNAL. Comparison of NNAL glucuronides (NNAL-Glucs) formed in reactions of UGT2B7-, UGT2B17-, UGT1A9-, and UGT2B10-overexpressing cell microsomes with pure NNAL enantiomers showed large differences in kinetics for (S)- versus (R)-NNAL, indicating varying levels of enantiomeric preference for each enzyme. UGT2B17 preferentially formed (R)-NNAL-O-Gluc, and UGT2B7 preferentially formed (S)-NNAL-O-Gluc. When human liver microsomes (HLM) were independently incubated with each NNAL enantiomer, the ratio of (R)-NNAL-O-Gluc to (S)-NNAL-O-Gluc formation in HLM from subjects exhibiting the homozygous deletion UGT2B17 (*2/*2) genotype was significantly lower (p = 0.012) than that with HLM from wild-type (*1/*1) subjects. There was a significant trend (p = 0.015) toward a decreased (R)-NNAL-O-Gluc/(S)-NNAL-O-Gluc ratio as the copy number of the UGT2B17*2 deletion allele increased. These data demonstrate that variations in the expression or activity of specific UGTs may affect the clearance of specific NNAL enantiomers known to induce tobacco-related cancers.
烟草中最有效的致癌物质是烟草特异性亚硝胺(TSNAs),其中 4-(甲基亚硝基氨基)-1-(3-吡啶基)-1-丁酮(NNK)是最有效的致癌物质,也是含量最高的致癌物质之一。NNK 会被广泛代谢为同样具有致癌性的 4-(甲基亚硝基氨基)-1-(3-吡啶基)-1-丁醇(NNAL)。在 NNAL 的两种对映体中,(S)-NNAL 似乎不仅在人体内优先被葡萄糖醛酸化和排泄,而且在小鼠和人体内表现出更高的立体选择性组织滞留,并已证明在小鼠体内比其 (R) 对映体更具致癌性。由于 NNAL 对映体的致癌潜力不同,了解哪种 UGT 酶针对特定的 NNAL 对映体进行葡萄糖醛酸化变得越来越重要。为了研究这一点,我们开发了一种手性分离方法来分离对映体纯的(S)-和(R)-NNAL。在 UGT2B7-、UGT2B17-、UGT1A9- 和 UGT2B10-过表达细胞微粒体与纯 NNAL 对映体反应中形成的 NNAL 葡萄糖醛酸(NNAL-Glucs)的比较显示,(S)- 与 (R)-NNAL 的动力学差异很大,表明每种酶对映体的偏好程度不同。UGT2B17 更倾向于形成 (R)-NNAL-O-Gluc,而 UGT2B7 更倾向于形成 (S)-NNAL-O-Gluc。将人肝脏微粒体(HLM)与每种 NNAL 对映体分别独立培养,在同源染色体缺失 UGT2B17(*2/*2)基因型受试者的 HLM 中,(R)-NNAL-O-Gluc 与 (S)-NNAL-O-Gluc 的形成比例明显低于野生型(*1/*1)受试者的 HLM(p = 0.012)。随着 UGT2B17*2 缺失等位基因拷贝数的增加,(R)-NNAL-O-Gluc/(S)-NNAL-O-Gluc 比率呈明显下降趋势(p = 0.015)。这些数据表明,特定 UGTs 的表达或活性变化可能会影响已知会诱发烟草相关癌症的特定 NNAL 对映体的清除。