Yoshida Ryoko, Nakajima Miki, Nishimura Kiyoko, Tokudome Shogo, Kwon Jun-Tack, Yokoi Tsuyoshi
Division of Drug Metabolism, Faculty of Pharmaceutical Sciences, Kanazawa University, Japan.
Clin Pharmacol Ther. 2003 Jul;74(1):69-76. doi: 10.1016/S0009-9236(03)00090-0.
Cytochrome P450 (CYP) 2A6 catalyzes nicotine C-oxidation, leading to cotinine formation, a major metabolic pathway of nicotine in humans. There are genetic polymorphisms in the human CYP2A6 gene. Previously, we demonstrated that in vivo nicotine metabolism is impaired with the CYP2A64, CYP2A67, and CYP2A610 alleles in Japanese subjects and Korean subjects. An allele possessing a point mutation in the TATA box termed CYP2A69 (T-48G) has been reported to decrease the transcriptional activity in vitro as assessed by luciferase assay. In this study we investigated the effects of the CYP2A69 allele on in vivo enzymatic activity by evaluating nicotine metabolism. The mutation of T-48G was found only on the CYP2A61A allele but not on the CYP2A61B allele. Allele frequencies of CYP2A69 in Japanese subjects (n = 92) and Korean subjects (n = 209) were 21.3% and 22.3%, respectively. In Korean subjects the cotinine/nicotine ratios as an index of nicotine metabolism in the subjects with CYP2A69/CYP2A69 (4.3 +/- 2.4) were significantly lower than those in the subjects with CYP2A61A/CYP2A69 (7.7 +/- 5.6) and CYP2A61A/CYP2A61A (10.4 +/- 9.2) (P <.05 and P <.005, respectively). In Japanese subjects a similar result was observed, although it was not significant. Thus it is suggested that the mutation in the TATA box (CYP2A69 allele) caused the decreased in vivo enzymatic activity. With an in vitro study, it was shown that the expression levels of CYP2A6 messenger ribonucleic acid and coumarin 7-hydroxylase activity in human livers genotyped as CYP2A61/CYP2A69 and CYP2A69/CYP2A69 tended to be lower than those in human livers genotyped as CYP2A61/CYP2A61, although there was no significant difference because of the small number of samples. These in vitro data supported the in vivo data demonstrating that the CYP2A69 allele caused the decreased expression level and enzymatic activity of CYP2A6.
细胞色素P450（CYP）2A6催化尼古丁的C-氧化反应，导致可替宁的形成，这是尼古丁在人体内的主要代谢途径。人类CYP2A6基因存在基因多态性。此前，我们证明在日本人和韩国人中，携带CYP2A64、CYP2A67和CYP2A610等位基因会损害体内尼古丁代谢。据报道，一种在TATA框中存在点突变的等位基因CYP2A69（T-48G），通过荧光素酶测定评估，其在体外会降低转录活性。在本研究中，我们通过评估尼古丁代谢来研究CYP2A69等位基因对体内酶活性的影响。发现T-48G突变仅存在于CYP2A61A等位基因上，而不存在于CYP2A61B等位基因上。日本受试者（n = 92）和韩国受试者（n = 209）中CYP2A69的等位基因频率分别为21.3%和22.3%。在韩国受试者中，以可替宁/尼古丁比值作为尼古丁代谢指标，CYP2A69/CYP2A69受试者（4.3±2.4）显著低于CYP2A61A/CYP2A69受试者（7.7±5.6）和CYP2A61A/CYP2A61A受试者（10.4±9.2）（分别为P <.05和P <.005）。在日本受试者中观察到类似结果，尽管不显著。因此，提示TATA框中的突变（CYP2A69等位基因）导致体内酶活性降低。通过体外研究表明，基因型为CYP2A61/CYP2A69和CYP2A69/CYP2A69的人肝脏中CYP2A6信使核糖核酸的表达水平和香豆素7-羟化酶活性倾向于低于基因型为CYP2A61/CYP2A61的人肝脏，不过由于样本数量少，差异无统计学意义。这些体外数据支持了体内数据，表明CYP2A69等位基因导致CYP2A6的表达水平和酶活性降低。
