Genetic Polymorphism of Drug Metabolizing Enzymes: New Mutations in CYP2D6 and CYP2A6 Genes in Japanese

Genetic polymorphism of drug metabolizing enzymes, particularly cytochrome P450 (CYP), is an important cause of adverse drug reactions. Multiple gene mutations in CYP have been shown to be phenotype. The occurrence of genetic polymorphism has been seen in genes for CYP1A1, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A5. This review discusses the molecular mechanism of two genetic polymorphisms, debrisoquine/sparteine (CYP2D6) coumarin (CYP2A6) polymorphisms. In addition, elucidation of gene mutations of CYP2D6 and CYP2A6 in Japanese will be discussed.     

CYP2A6多态性对尼古丁代谢及烟草依赖行为的影响

细胞色素P450(cytochrome P450,CYP)超基因家族是人体内最重要的药物代谢酶,其中的一些亚型所具有的基因多态性表现出人体对药物和/或环境化合物毒性、敏感性存在差异,CYP2A6为其一例。     

The influence of CYP2A6 polymorphisms and cadmium on nicotine metabolism in Thai population

We investigated the influence of genetic, cadmium exposure and smoking status, on cytochrome P450-mediated nicotine metabolism (CYP2A6) in 182 Thai subjects after receiving 2 mg of nicotine gum chewing for 30 min. The urinary excretion of cotinine was normally distributed over a 2 h period (logarithmically transformed). Individuals with urinary cotinine levels in the ranges of 0.01–0.21, and 0.52–94.99 μg/2 h were categorized as poor metabolizes (PMs: 6.5%), and extensive metabolizers (EMs: 93.5%), respectively. The majority of EMs (45%) carried homozygous wild-type genotypes (CYP2A6*1A/*1A, CYP2A6*1A/*1B and CYP2A6*1B/*1B), whereas only 1% of PMs carried these genotypes. Markedly higher frequencies of EMs were also observed in all heterozygous defective genotypes including the null genotype (*4C/*4C; 1 subject).A weak but significant positive correlation was observed between total amounts of urinary cadmium excretion and total cotinine excretion over 2 h. Our study shows generally good agreement between CYP2A6 genotypes and phenotypes. Smokers accumulated about 3–4-fold higher mean total amounts of 2-h urinary cadmium excretion (127.5 ± 218.2 ng/2 h) than that of non-smokers (40.5 ± 78.4 ng/2 h). Among the smokers (n = 16), homologous wild-type genotype *1/*1 was significantly the predominant genotype (6/16) compared with other defective allele including *4C/*4C. In addition, 2 h urinary excretion of cotinine in smokers of all genotypes was significantly higher than non-smokers. The proportion of smokers who smoked more than 5 cigarettes/day was significantly higher in EMs in all CYP2A6 genotypes (n = 14) than in PMs (n = 0).     

CYP2A6 polymorphisms in Malays,Chinese and Indians

The genetically polymorphic cytochrome P450 (CYP) 2A6 is the major nicotine-oxidase in humans that may contribute to nicotine dependence and cancer susceptibility. The authors investigated the types and frequencies of CYP2A6 alleles in the three major ethnic groups in Malaysia and CYP2A6*1A, CYP2A6*1B, CYP2A6*1x2, CYP2A6*2, CYP2A6*3, CYP2A6*4, CYP2A6*5, CYP2A6*7, CYP2A6*8 and CYP2A6*10 were determined by allele-specific polymerase chain reaction (PCR) in 270 Malays, 172 Chinese and 174 Indians. Except for CYP2A6*2 and *3 that were not detected in the Malays and Chinese, all the other alleles were detected. Frequencies for the CYP2A6*4 allele were 7, 5 and 2%, respectively, in Malays, Chinese and Indians. A statistically significant high frequency of the duplicated CYP2A6*1x2 allele occurred among Chinese. Among Malays and Chinese, the most common allele was CYP2A6*1B, but it was CYP2A6*1A among Indians. These ethnic difference in frequencies suggested that further studies are required to investigate the implications on diseases such as cancer and smoking behaviour among these major ethnic groups in Malaysia.     

细胞色素P450的基因多态性与药物代谢

细胞色素P450（cytochrome P450，CYP）是重要的药物代谢酶，参与催化多种内源和外源化合物，特别是多种临床药物的生物转化。CYP存在广泛的基因多态性和表型多态性，使其对于各种化合物的代谢存在统计学个体差异。核受体是配体依赖性转录因子超家族，与药物代谢过程中的基因表达调控密切相关，被外源物质活化后诱导或抑制CYP基因的表达。现综述CYP与药物代谢、CYP的基因多态性、CYP表达的诱导机制、核受体及其配体诱导CYP表达及近年研究CYP450的各种实验方法。     

中国汉族和回族药物代谢酶细胞色素P450(CYP)3A4、CYP2C9、CYP2C19及CYP2D6基因多态性分析

目的对中国汉族、回族健康人群细胞色素P450(CYP)3A4、CYP2C9、CYP2C19及CYP2D6进行基因多态性分析,比较汉族和回族健康人群基因表型和基因频率分布。方法多聚酶链反应-限制性片段长度多态性(PCR-RFLP)法,对300名志愿者的几种基因进行分型。结果汉族、回族CYP3A4*5等位基因频率均为0,CYP3A4*18等位基因频率分别为0.18,0.19;汉族、回族CYP2C9*2等位基因频率分别为0.01,0.05;CYP2C9*13等位基因频率均为0;汉族、回族CYP2C19*2等位基因频率分别为0.39,0.50;CYP2C19*3等位基因频率分别为0.05,0.05;汉族、回族CYP2D6*10等位基因频率分别为0.57,0.39。结论汉族、回族健康人群的CYP3A4*18、CYP2C9*2、CYP2C19*2、CYP2C19*3均没有显著性差异;在汉族、回族健康人群中未发现CYP3A4*5和CYP2C9*13突变;汉族、回族CYP2D6*10等位基因频率有显著性差异(P<0.01);回族人群CYP2D6中速代谢型(*10/*10)频率为13.4%,明显低于汉族的33.1%(P<0.01)。     

CYP2A6 Genotype and Smoking Behavior in Current Smokers Screened for Lung Cancer

Functional CYP2A6 genetic variation partially determines nicotine metabolism. In 2005, we examined functional CYP2A6 variants associated with reduced metabolism (CYP2A6*2, CYP2A6*9, CYP2A6*4), smoking history, and change in smoking in 878 adult smokers undergoing lung cancer screening in an urban setting. At one year, 216 quit smoking for more than 30 days while 662 continued smoking. Compared to subjects who smoked 30 cigarettes per day at baseline, the odds of a reduced metabolism genotype was 52% higher in subjects smoking 20–29 cigarettes per day and 86% higher in subjects smoking less than 20 cigarettes per day (p-trend = 0.016). Reduced metabolism genotypes appeared unrelated to quitting. Though related to smoking dose, CYP2A6 may not influence cessation.     

安徽省汉族人群CYP2C19基因多态性的调查研究

目的探讨CYP2C19基因型检测方法及其在安徽省汉族人群中基因多态性的分布。方法在110名汉族健康人的外周血中,应用聚合酶链反应(PCR)-限制性片段长度多态性分析(RFLP)技术,进行CYP2C19等位基因分型研究。结果应用PCR-RFLP技术可准确区分CYP2C19基因型。在110名检测标本中,CYP2C19纯合子强代谢型、杂合子强代谢型和弱代谢型的发生率分别40%、49%和11%。结论PCR-RFLP方法检测CYP2C19基因型特异性高,成熟,稳定;中国安徽汉族人群存在CYP2C19的基因多态性,其弱代谢型的发生率与中国总体发生率基本一致。     

细胞色素P-450 CYP2D6基因分型与表型的吻合率

目的:研究细胞色素P-450 2D6基因分型测定方法及其与表型的吻合率。方法:利用等位基因特异扩增法基本原理,对CYP2D6酶缺陷等位基因CYP2D6*3,*4,*6和*7进行测定。结果:通过168例基因分型,并将结果与表型对照,发现同时测定CYP2D6*3,*4,*6和*7等位基因时,125例快代谢者和43例慢代谢者的基因分型结果与表型结果的吻合率为100％。快代谢者至少有一个野生型CYP2D6等位基因,基因型为*1/*1,*1/*3和*1/*4。发现慢代谢者是CYP2D6突变型纯合子,基因型为*3/*4,*4/*4,*3/*6,*4/*7,*4/*6和*6/*6。结论:对CYP2D6*3,*4,*6和*7等位基因的测定能够准确预测其表型。     

CYP2A13 genetic polymorphism in French Caucasian,Gabonese and Tunisian populations

Since human CYP2A13 is expressed in the respiratory tract and is involved in the activation of tobacco-specific nitrosamines, some of the previously reported sequence variations may contribute to inter-individual and inter-ethnic differences in the susceptibility of tobacco-related tumorigenesis. The aim was to compare the frequencies of the 578C?>?T (Arg¹⁰¹Stop), 3375C?>?T (Arg²⁵⁷Cys) and 7520C?>?G (3′-untranslated region) mutations in several populations. The frequencies of the 578C?>?T polymorphism were 3.8, 0 and 1.0% in French Caucasians, Gabonese and Tunisians, respectively. In the same populations, the frequencies of the 3375C?>?T mutation were 0, 15.3 and 4.2%, respectively, whereas the frequencies of the 7520C?>?G mutation were 1.0, 20.8 and 7.3%, respectively. Marked inter-ethnic variations in CYP2A13 were identified and confirmed. These findings provide data for further studies that associate CYP2A13 haplotypes with an incidence of smoking-related tumours in respect of ethnicity.     

细胞色素P450 2D6等位基因CYP2D6C的特异扩增法测定

细胞色素Ｐ４５０２Ｄ６（ＣＹＰ２Ｄ６）第２７０３－５位ＡＡＧ缺失造成表达产物第２８１位赖氨酸缺失的等位基因称为ＣＹＰ２Ｄ６Ｃ．利用等位基因特异扩增法（ＡＳＡ）原理,建立了ＡＳＡ－ＰＣＲ测定ＣＹＰ２Ｄ６的方法．经３９６例测定,说明本法快捷,污染少．测定结果显示ＣＹＰ２Ｄ６Ｃ不属于ＣＹＰ２Ｄ６酶缺陷等位基因,表型仍为快代谢．     

中国独龙族人群中CYP 2C19基因多态性的分布

目的:研究细胞色素P450 2C19(CYP 2C19)基因在中国云南独龙族人群中的基因型及突变频率.方法:采用聚合酶链式反应(PCR)与限制性内切酶片段长度多态性技术,分析205例独龙族人的基因型.结果:84例为CYP 2C19野生型纯合子(wt/wt);98例为CYP 2C19m1杂合子(wt/m1);23例为CYP 2C19m1突变型纯合子(m1/m1),CYP 2C19m1突变频率为0.351.结论:中国云南独龙族人群P450 2C19存在突变,突变频率与国内各种族相比具有一定的可比性.     

肝移植患者他克莫司血药浓度与细胞色素P450 3A5 1*3基因多态性的关系

目的研究细胞色素P450 3A5 1*3基因多态性对肝移植患者他克莫司(免疫抑制剂)血药浓度的影响,探讨他克莫司在不同个体间吸收、代谢差异的基因背景。方法观察150例肝移植术后常规使用他克莫司 吗替麦考酚酯胶囊 醋酸泼尼松三联免疫抑制治疗的成年患者,分别测定术后1、3、6个月和12月的他克莫司全血药浓度,采用等位基因特异PCR测定细胞色素P450 3A5 1*3基因多态性,比较不同基因型之间他克莫司的浓度/剂量比的差异。结果在口服相同剂量的他克莫司时,1个月内CYP3A5 1*1、CYP3A5 1*3和CYP3A5 3*3三种基因型的浓度/剂量比,差异不显著;但3个月后,差异显著;6个月和12个月的浓度/剂量比,差异非常显著。结论CYP3A5 1*3多态性与肝移植患者他克莫司血药浓度具有非常显著的相关性,携带等位基因1*1和1*3患者的血药浓度明显低于3*3纯合子患者。     

中国人群中CYP1A2基因G-2964A和C734A多态性分布

目的:研究中国人群中CYPlA2基因G-2964A和C734A多态性分布.方法:应用聚合酶链反应-限制片长多态性技术对163名启东人和78名长沙人进行基因型分析.结果:等位基因A-2964在启东和长沙人中的发生率分别是0.25和0.22.A734的发生率在启东人中为0.68,而在长沙人中为0.66.一个受试者的两条等位基因中至多含有两个底活性位点.结论:G-2964A和C734A基因多态性在中国人和日本人中的分布没有显著性差异,C734A基因多态性在中国人中的分布也类似于白种人.     

CYP2C8 polymorphisms in Caucasians and their relationship with paclitaxel 6alpha-hydroxylase activity in human liver microsomes

Published cDNA sequences suggest the existence of non-synonymous single nucleotide polymorphisms in the cytochrome P450 CYP2C8. To determine whether these polymorphisms could be confirmed in a Caucasian population and to investigate whether additional polymorphisms occur in the coding and upstream regions of this gene, we screened for previously described and for novel polymorphisms using PCR-RFLP and SSCP analysis. We confirmed the existence of two of the previously detected polymorphisms which give rise to the amino acid substitutions I264M and K399R, respectively, but failed to detect three others in our population. We also confirmed that a recently identified polymorphism (R139K) is linked to K399R (CYP2C8*3) in our study population. The allele frequencies for the I264M (CYP2C8*4 allele) and the CYP2C8*3 allele were 0.075 and 0.15, respectively. Three novel polymorphisms (T-370G, C-271A and T1196C/L390S) were also detected with the upstream polymorphisms showing allele frequencies of 0.061 and 0.196, respectively, but the L390S polymorphism detected only in a single subject. An additional single subject was heterozygous for a polymorphism recently described in African-Americans (A805T; CYP2C8*2 allele). The functional significance of the two upstream polymorphisms and the CYP2C8*3 and CYP2C8*4 alleles was investigated in human liver microsomes. Samples heterozygous for CYP2C8*3 showed significantly lower paclitaxel 6alpha-hydroxylase activity compared with wild-type samples. Median activity associated with CYP2C8*4 also appeared lower than the wild-type but the difference was not significant. There was no evidence that either upstream polymorphism gave rise to altered CYP2C8 expression.     

Identification of a novel splice-site mutation in the CYP1A2 gene

AIMS: To identify the molecular basis for a low CYP1A2 metabolic status, as determined by a caffeine phenotyping test, in a 71-year-old, nonsmoking, Caucasian woman who presented with very high clozapine concentrations despite being administered a standard dose of the drug. METHODS: The nucleotide sequence of the 7 exons, exon-intron boundaries and 5'-flanking region of the CYP1A2 gene was analysed by direct sequencing. RESULTS: Only one heterozygous point mutation was identified in the donor splice site of intron 6 (3534G > A) of CYP1A2. This mutation could cause abnormal RNA splicing and therefore lead to a truncated nonfunctional enzyme. No other carrier of this mutation was identified in a population of 100 unrelated healthy Caucasians. CONCLUSIONS: This is the first report of a splice-site mutation affecting the CYP1A2 gene. This polymorphism is a likely explanation for the low CYP1A2 activity associated with high clozapine concentrations in this patient.     

Genetic polymorphisms analysis of drug-metabolizing enzyme CYP2C9 in the Uyghur population

1. Genetic variations in cytochrome P450 2C9 are known to contribute to interindividual and interethnic variability in response to clinical drugs, but little is known about the genetic variation of CYP2C9 in the Uyghur population.

2. We directly sequenced the whole CYP2C9 gene in 96 unrelated, healthy Uyghur from Xinjiang Uygur Autonomous Region of China and screened for genetic variants in the promoter, exons, introns and 3′-UTR.

3. Thirty five previously reported alleles and six genotypes were detected in this study. The allele frequencies of CYP2C9*1, *2, *11, *12, *29 and *33 were 89.58, 7.81, 0.52, 0.52, 1.04 and 0.52%, respectively. We detected one non-synonymous novel variant at position 329 from Arg to Cys and this mutation is predicted to be intolerant by SIFT.

4. Our results provide basic information about CYP2C9 alleles in Uyghur, which may help to optimize pharmacotherapy effectiveness by providing personalized medicine to this ethnic group.

     

Inhibitory effects and oxidation of 6-methylcoumarin, 7-methylcoumarin and 7-formylcoumarin via human CYP2A6 and its mouse and pig orthologous enzymes

1.?Information about the metabolism of compounds is essential in drug discovery and development, risk assessment of chemicals and further development of predictive methods.

2.?In vitro and in silico methods were applied to evaluate the metabolic and inhibitory properties of 6-methylcoumarin, 7-methylcoumarin and 7-formylcoumarin with human CYP2A6, mouse CYP2A5 and pig CYP2A19.

3.?6-Methylcoumarin was oxidized to fluorescent 7-hydroxy-6-methylcoumarin by CYP2A6 (K_m: 0.64–0.91?µM; V_max: 0.81–0.89?min^?1) and by CYP2A5 and CYP2A19. The reaction was almost completely inhibited at 10?µM 7-methylcoumarin in liver microsomes of human and mouse, but in pig only 40% inhibition was obtained with the anti-CYP2A5 antibody or with methoxsalen and pilocarpine. 7-Methylcoumarin was a mechanism-based inhibitor for CYP2A6, but not for the mouse and pig enzymes. 7-Formylcoumarin was a mechanism-based inhibitor for CYP2As of all species.

4.?Docking and molecular dynamics simulations of 6-methylcoumarin and 7-methylcoumarin in the active sites of CYP2A6 and CYP2A5 demonstrated a favorable orientation of the 7-position of 6-methylcoumarin towards the heme moiety. Several orientations of 7-methylcoumarin were possible in CYP2A6 and CYP2A5.

5.?These results indicate that the active site of CYP2A6 has unique interaction properties for ligands and differs in this respect from CYP2A5 and CYP2A19.     

Overview of enzymes of drug metabolism

Most pharmacologically active molecules are lipophilic and remain un-ionized or only partially ionized at physiological pH. Biotransformation means that a lipid-soluble xenobiotic or endobiotic compound is enzymatically transformed into polar, water-soluble, and excretable metabolites. The major organ for drug biotransformation is the liver. The metabolic products often are less active than the parent drug or inactive. However, some biotransformation products (metabolites) may have enhanced activity or toxic effects. Thus biotransformation may include both “detoxication” and “toxication” processes. One of the major enzyme systems that determines the organism's capability of dealing with drugs and chemicals is represented by the cytochrome P450 monooxygenases. Studies in the last 15 years have provided evidence that cytochrome P450 occurs in many different forms or “isozymes” which differ in spectral, chemical, and immunological properties and have different substrate affinities. These isozymes also differ in their regulation and tissue distribution. Recombinant DNA studies indicate that between 40 and 60 structural genes code for different cytochrome P450 isozymes in a single organism. Other enzyme systems include dehydrogenases, oxidases, esterases, reductases, and a number of conjugating enzyme systems including glucuronosyltransferases, sulfotransferases, glutathione S-transferases, etc. Environmental and genetic factors cause interindividual and intraindividual differences in drug metabolism and may alter the balance between toxification and detoxification reactions. Genetic polymorphisms lead to subpopulations of patients with decreased, absent, or even increased activities of certain reactions (e.g., CYP2D6, CYP2C19, N-acetyltransferase polymorphism). Environmental factors such as other drugs, steroids, dietary factors, alcohol, and cigarette smoke can induce or inhibit drug-metabolizing enzymes and cause intraindividual variation.     

CYP2D6 polymorphism in systemic lupus erythematosus patients

Objectives: To determine whether patients with idiopathic systemic lupus erythematosus (SLE) are associated with impaired CYP2D6 activity and to gain insight into whether there is an association between particular CYP2D6 genotypes and susceptibility to SLE, and whether CYP2D6 polymorphism is linked to any specific clinical features of SLE. Methods: Debrisoquine sulfate (10 mg p.o.) was given to 159 healthy volunteers and 39 idiopathic SLE patients. Genotypic assay was carried out in 80 healthy volunteers and 32 patients. A 10-ml blood sample was drawn for genotypic assay. Debrisoquine and 4-hydroxydebrisoquine were determined in 8-h urine samples. Blood samples were analysed for the presence of mutations in the CYP2D6 gene, by using polymerase chain reaction (PCR) specific for CYP2D6*3 and CYP2D6*4 alleles. Results: The metabolic ratio of debrisoquine to 4-hydroxydebrisoquine ranged from 0.01 to 86.98 in healthy subjects and from 0.02 to 96 in SLE patients. We observed the poor metabolizer(PM) debrisoquine phenotype in three of 39 patients with idiopathic SLE (7.6%) and five of 159 healthy subjects (3.1%). There was no significant difference in the frequency of PM phenotypes between idiopathic SLE and healthy subjects (Fisher's exact test, P = 0.19). No significant difference in the distribution of overall genotypes and allele frequencies were observed between the two groups. No significant relationships were found between specific clinical features and the overall genotype. Conclusion: The results of this study confirm that CYP2D6 activity is not impaired in SLE and that there is no association between SLE and phenotypic CYP2D6 status. The results also showed that there was no difference in the frequency of CYP2D6A and CYP2D6B alleles between controls and patients with SLE. Received: 14 May 1998 / Accepted in revised form: 19 October 1998