Butler M A, Lang N P, Young J F, Caporaso N E, Vineis P, Hayes R B, Teitel C H, Massengill J P, Lawsen M F, Kadlubar F F
Office of Research (HFT-100), National Center for Toxicological Research, Jefferson, AR 72079.
Pharmacogenetics. 1992 Jun;2(3):116-27. doi: 10.1097/00008571-199206000-00003.
The wide variations in urinary bladder and colo-rectal cancer incidence in humans have been attributed in part to metabolic factors associated with exposure to carcinogenic aromatic and heterocyclic amines. Cytochrome P-4501A2 (CYP1A2), which catalyses N-oxidation, and acetyltransferase (NAT2) which catalyses N- and O-acetylation, both appear to be polymorphically distributed in human populations; and slow and rapid NAT2 phenotypes have been implicated as risk factors for these cancers. Caffeine has also been shown to undergo 3-demethylation by CYP1A2, and it is further acetylated to 5-acetylamino-6-formylamino-3-methyluracil (AFMU) by the polymorphic NAT2. In this report, we describe a metabolic phenotyping procedure that can be used to determine concomitantly the hepatic CYP1A2 and NAT2 phenotypes. For the NAT2 phenotype, we confirm the valid use of the urinary molar ratio of AFMU/1-methylxanthine, even in alkaline urines. For the CYP1A2 phenotype, the urinary molar ratio of [1,7-dimethylxanthine + 1,7-dimethyluric acid]/caffeine, taken at 4-5 h after caffeine ingestion, was identified from pharmacokinetic analyses of 12 subjects as being better correlated (r = 0.73; p = 0.007) with the rate constant for caffeine 3-demethylation than other previously suggested ratios. This procedure was then used to determine the CYP1A2 phenotype in subjects from Arkansas (n = 101), Italy (n = 95), and China (n = 78). Statistical and probit analyses of nonsmokers indicated that the CYP1A2 activity was not normally distributed and appeared trimodal. This trimodality allowed arbitrary designation of slow, intermediate, and rapid phenotypes, which ranged from 12-13% slow, 51-67% intermediate, and 20-37% rapid, in the different populations. A reproducibility study of 13 subjects over a 5 day or 5 week period showed that, with one exception, intraindividual variability did not alter this CYP1A2 phenotypic classification. Induction of CYP1A2 by cigarette smoking was also confirmed by the increased caffeine metabolite ratios observed in the Arkansas and Italian smokers (blonde tobacco). However, Italian smokers of black tobacco and Chinese smokers did not appear to be induced. Furthermore, probit analyses of Arkansas and Italian blonde tobacco smokers could not discriminate between phenotypes, apparently as a consequence of enzyme induction.
人类膀胱癌和结直肠癌发病率的广泛差异部分归因于与接触致癌性芳香胺和杂环胺相关的代谢因素。催化N-氧化的细胞色素P-4501A2（CYP1A2）和催化N-和O-乙酰化的乙酰转移酶（NAT2）在人群中似乎均呈多态性分布；NAT2的慢代谢和快代谢表型被认为是这些癌症的危险因素。咖啡因也已被证明可被CYP1A2进行3-去甲基化，并且它会被多态性的NAT2进一步乙酰化为5-乙酰氨基-6-甲酰氨基-3-甲基尿嘧啶（AFMU）。在本报告中，我们描述了一种代谢表型分析方法，可用于同时测定肝脏CYP1A2和NAT2表型。对于NAT2表型，我们证实即使在碱性尿液中，尿中AFMU/1-甲基黄嘌呤的摩尔比也可有效用于评估。对于CYP1A2表型，在12名受试者的药代动力学分析中发现，咖啡因摄入后4-5小时测得的尿中[1,7-二甲基黄嘌呤+1,7-二甲基尿酸]/咖啡因的摩尔比与咖啡因3-去甲基化的速率常数相关性更好（r = 0.73；p = 0.007），优于其他先前提出的比值。然后使用该方法测定了来自阿肯色州（n = 101）、意大利（n = 95）和中国（n = 78）的受试者的CYP1A2表型。对非吸烟者的统计和概率分析表明，CYP1A2活性呈非正态分布且呈现三峰模式。这种三峰模式允许任意指定慢、中、快表型，在不同人群中，慢表型占12 - 13%，中间表型占51 - 67%，快表型占20 - 37%。一项对13名受试者进行的为期5天或5周的重复性研究表明，除了一个例外，个体内变异性并未改变这种CYP1A2表型分类。在阿肯色州和意大利吸烟者（浅色烟草）中观察到的咖啡因代谢物比值增加也证实了吸烟对CYP1A2的诱导作用。然而，意大利深色烟草吸烟者和中国吸烟者似乎未被诱导。此外，对阿肯色州和意大利浅色烟草吸烟者的概率分析无法区分表型，这显然是酶诱导的结果。
