CYP2A6 genetic polymorphisms and liver microsomal coumarin and nicotine oxidation activities in Japanese and Caucasians

Genotypes of CYP2A6, namely CYP2A6(*)1 (wild-type), CYP2A6(*)2, and CYP2A6(*)3, were examined in liver DNA of 39 Japanese and 43 Caucasians using two-step polymerase chain reaction (PCR) methods. We first amplified a DNA fragment (1725 bp) located between near middle of exon 1 and end of exon 4 of the CYP2A6 gene and further amplified using a forward primer 't' or 'mut' (middle of exon 3) and a reverse primer 'E3R' (middle of intron 3) for the detection of CYP2A6(*)2-genetic polymorphism. The 1725 bp fragment was also used for the amplification between exon 3 and near middle of intron 3 of the CYP2A6 gene and the fragment thus obtained digested with XcmI or DdeI to detect and confirm the CYP2A6(*)2- and CYP2A6(*)3-types, respectively. Only one DNA sample from a Japanese origin (J18) was not amplified by CYP2A6-specific primers; liver microsomes from this individual had very low activity of coumarin 7-hydroxylation and were devoid of protein(s) immunoreactive to anti-CYP2A6 antibody. Thus, this individual was suggested to be due to the gene deletion in CYP2A6. By analyzing the remaining 38 Japanese and 43 Caucasians, we found that there were no cases of CYP2A6(*)3-type polymorphism in the samples examined in this study, and no cases of CYP2A6(*)2-type polymorphism in the Japanese samples. Of Caucasians studied two individuals were classified into heterozygous CYP2A6(*)1/(*)2-type. Liver microsomal coumarin 7-hydroxylation activities in these two Caucasians were found to be lower than those of the other 41 Caucasians. Kinetic analysis showed that two CYP2A6(*)1/(*)2 individuals had a very low ratio of V(max) to K(m) for nicotine C-oxidation as well as coumarin 7-hydroxylation in liver microsomes, compared with those of homozygous CYP2A6(*)1-type. These results suggest that among 39 Japanese and 43 Caucasians examined one Japanese is classified to be CYP2A6 gene deletion and two Caucasians are heterozygous CYP2A6(*)1/(*)2-genotype. Thus the race-related differences in the occurrence of CYP2A6 genetic polymorphisms were supported.     

Low frequency of CYP2A6 gene polymorphism as revealed by a one-step polymerase chain reaction method.

Human cytochrome P450 2A6 (CYP2A6) has been shown to metabolically activate carcinogens and mutagens. Genetic polymorphisms for CYP2A6 have been reported previously in different ethnic groups using a two-step polymerase chain reaction (PCR) method to identify CYP2A6*1, CYP2A6*2 and CYP2A6*3. Moreover, a new truncated allele has been recently identified in a Japanese population. We report here a one-step PCR amplification of the CYP2A6 gene from human genomic DNA and the detection of intact CYP2A6 alleles by restriction enzyme digestion. The diagnostic exon (exon 3) of the CYP2A6 gene was amplified from human genomic DNA with a primer pair. The forward primer is unique to the CYP2A6 gene, which eliminates previous problems in amplifying two highly homologous CYP2A genes, CYP2A7 and CYP2A13, in humans. The resulting PCR products (214 bp) were digested with XcmI or DdeI to detect the presence of CYP2A6*2 or CYP2A6*3 alleles, respectively. The allelic frequencies for CYP2A6*2 were 2.3% (n = 320) in the Caucasian and 0.7% (n = 71) in the Chinese populations, respectively. CYP2A6*3 allelic frequency in the Chinese population was 0.7%; while no CYP2A6*3 allele was detected in the Caucasian population. The allelic frequencies are relatively low and the reason for this discrepancy between different methods is discussed.     

SUR1基因多态性与2型糖尿病的相关性研究

目的：探讨2型糖尿病（T2DM）与磺脲类药物受体1（SUR1）基因多态性的关系。方法：随机抽取正常人136例（正常组）及2型DM患者173例（T2DM组）外周血白细胞基因组DNA，PCR扩增SUR1基因31号外显子多态性位点的区域．用限制性酶切片段长度多态性分析其基因型，并用测序证实不同酶切图形基因型的准确性。结果：T2DM组和正常组SUR1基因31号外显子基因型及等位基因分布差别有统计学意义（P〈0．05）。结论：SUR1基因可能是中国天津地区2型糖尿病发生的易感基因。     

膀胱移行细胞癌组织中PTEN基因第5、8外显子的突变分析

目的：了解膀胱移行细胞癌（TCC）组织中PTEN基因第5外显子（Exon5）和第8外显子（Exon8）的突变情况及其与膀胱癌生物学行为的关系。方法：选择突变率较高的PTEN基因Exon5和Exon8，应用银染PCR—SSCP并结合基因测序方法分析46例TCC患者的PTEN突变情况。结果：PTEN的Exon5扩增产物为379bp，所有肿瘤组织均表现为3条迁移带（2条单链和1条双链），没有发现额外迁移带。Exon8扩增产物为550bp，经酶切为两个片段。所有肿瘤组织均表现为6条迁移带（4条单链和2条双链），没有发现额外迁移带。结论：TCC患者的肿瘤组织中PTEN基因Exon5和Exon8的突变不是一个常见事件，PTEN是否还存在其他灭活方式还需要进一步研究。     

一个Rett综合征家系MECP2基因突变分析及X染色体失活研究

目的:研究Rett综合征(RTT)患者的MECP2基因突变,探讨X染色体失活在RTT致病机制中的作用.寻找临床基因诊断Rett综合征的实验方法.方法:首先采集Rett综合征先证者及家系成员的外周血提取基因组DNA,聚合酶链式反应扩增RTT致病基因MECP2的3个外显子和3′UTR(3′端非翻译区),琼脂糖凝胶电泳和非变性聚丙烯酰胺凝胶电泳分离目的片段,PCR产物经纯化后直接测序.应用甲基化PCR(methylation specific PCR,MSP)进行X染色体失活分析.结果:发现患儿MECP2基因的Exon3发生1个点突变C473T(T158M),该突变为新生突变.患儿与患儿母亲表现为非随机X染色体失活.结论: X染色体非随机失活在RTT的致病机制中发挥某种作用,C473T(T158M)点突变可作为典型Rett患者基因诊断的位点之一.     

颅骨锁骨发育不全家系基因多态性与表型关系的研究

目的研究家族性颅锁骨发育不全家系基因型与临床表型的关系。方法提取临床收集的一个先天性颅锁骨发育不全家系中患者和健康成员外周血基因组DNA,PCR扩增RUNX2/CBFA1基因7个编码外显子及其侧翼内含子序列,分别进行正反向测序,对发现的突变位点行酶切分析验证。结果家系中两位患者（先证者及其父亲）显示cDNA 346T→A的杂合突变,使编码的色氨酸变成精氨酸（W 116R）,属错义突变。酶切结果进一步证实了该错义突变。测序还发现先证者父亲cDNA 198G→A的杂合突变,致第66位氨基酸的密码子GCG被GCA取代,但二者均编码丙氨酸,属同义突变。先证者及家系健康成员中未见此改变。结论 RUNX2/CBFA1基因346T→A杂合突变是该家系发病的分子基础。     

Expression of CYP2E1 in Human Lung and Kidney during Development and in Full-Term Placenta: A Differential Methylation of the Gene is Involved in the Regulation Process

Abstract: Methylation of dinucleotide CG residues located in the 5′end of the CYP2E1 gene has been demonstrated to play a role in the control of gene expression in the human developing liver. This study was undertaken to examine the CYP2E1 RNA content of human lung, kidney and full-term placenta and to determine whether the expression of CYP2E1 was controlled by its methylation status in these tissues. CYP2E1 was expressed at a very low level in the lung and kidney at whatever age, and at a variable level in full-term placentas. The restriction profile of genomic DNA was identical in lung and kidney and corresponded to a heavy methylation of Hpall/Mspl sites located within the promoter, the first exon and first intron of the CYP2E1 gene. A different pattern of methylation was obtained in full-term placentas, indicating that CpG residues located in the 5′end of the gene were predominantly but not fully demethylated. However, the variable level of CYP2E1 RNA in full-term placentas suggests the involvement of other elements in the regulation process of CYP2E1 in this tissue.     

An unequal cross-over event within the CYP2D gene cluster generates a chimeric CYP2D7/CYP2D6 gene which is associated with the poor metabolizer phenotype.

1. The study of the CYP2D genotype and phenotype of a Caucasian family revealed that a XbaI-9 kb allele was associated with the poor metabolizer phenotype. 2. A Polymerase Chain Reaction (PCR)-based assay showed that the previously described mutations D6A and D6B are not associated with the XbaI-9 kb allele. 3. To explore the molecular basis of the poor metabolizer phenotype associated with the XbaI-9 kb allele, complete sequencing of the nine exons and intron-exon boundaries of the CYP2D6 gene was undertaken after amplification by PCR. 4. All the exons were successfully amplified using CYP2D6 gene-specific primers except exon 1 which required a combination of CYP2D7 gene-specific 5' primer and a CYP2D6 gene-specific 3' primer. 5. Sequence data derived from this amplified product revealed that the XbaI-9 kb allele corresponds to a novel rearrangement of the locus. This involved a deletion of an approximately 20 kilobase (kb) DNA segment generating a hybrid 5' CYP2D7/CYP2D6 3' gene. 6. The chimeric gene is non-functional presumably due to an insertion in exon 1 (characteristic of the exon 1 of the CYP2D7 gene) which causes a shift in the reading frame with premature termination of translation.     

CYP2C19基因多态性真核表达载体的构建及稳定转染细胞系的建立

目的:构建细胞色素P450CYP2C19*1、*2、*3真核表达载体,并分别转染人肝癌细胞(HepG2),建立高表达目的基因的稳定转染细胞系。方法:应用化学合成法合成CYP2C19*1(野生型)序列,再以此为模板,体外定点突变PCR法构建*2、*3(突变型)。DNA重组技术将其定向插入到真核表达载体pcDNA3.l(-),经菌落PCR、酶切以及测序鉴定后,脂质体转染法转染HepG2细胞,通过G418选择培养,建立稳定转染细胞系,RT-PCR、Western Blot分别检测CYP2C19*1、*2、*3 mRNA以及蛋白的表达。结果:成功构建了pcDNA3.1(-)-CYP2C19*1、*2、*3表达质粒,并建立了相应稳定转染细胞系。进一步的RT-PCR和Western Blot检测结果表明,目的基因均得到了稳定的表达。结论:人CYP2C19*1、*2、*3稳定表达细胞系为研究创新药物或新药先导化合物临床前代谢性质的筛选和预测以及为临床潜在药物相互作用提供了有效实验平台。     

载脂蛋白E基因多态性青年冠心病关系的研究

目的 研究载脂蛋白E(apo E)基因多态性与青年冠心痛的相关关系。方法 采用聚舍酶链反应及限制性酶切技术来分析鉴别apo E基因第四外显子中含多态位点的DNA片断。结果 青年冠心病组E3/4基因型及E4等位基因频率明显高于对照组。结论apo E的E3/4基因型及E4等位基因与青年冠心病有关。     

检测CYP2A6基因多态性的PCR技术的基因型方法

综述检测CYP2A6基因多态性的PCR技术的基因型方法。CYP2A6基因多态性存在于白种人、东方人及非洲裔美国人群中 ,包括CYP2A6 1至CYP2A6 12 ,总共 12个变异等位基因。本文列举了检测CYP2A6基因型的不同的DNA来源、引物和限制性内切酶。已开发PCR技术结合诊断性限制性内切酶分析 (RFLP)如两步PCR和一步PCR RFLP方法检测CYP2A6基因型。此外 ,尚有PCR SSCP +RFLP及直接DNA测序方法。     

Metabolic cytochrome P450 genotypes and assessment of individual susceptibility to lung cancer.

Three polymorphic cytochrome P450 genes that have attracted interest for their potential role in human pulmonary carcinogenesis, i.e. CYP1A1, CYP2D6 and CYP2E1, were studied in a population consisting of 106 lung cancer patients and 122 healthy controls. Polymorphism of the CYP2D6 gene encoding for debrisoquine hydroxylase was determined using XbaI restriction fragment length polymorphism (RFLP) analysis together with a PCR based method. All of the three most common presently known defective alleles of CYP2D6 were detected by this application. Subjects having genotypes either homozygous or heterozygous for the CYP2D6 wild type alleles were classified as extensive metabolizers (EMs) of debrisoquine whereas poor metabolizers (PMs) had two defective alleles. The PM individuals are thought to be less prone to develop lung cancer. The CYP1A1 and CYP2E1 genes were studied by RFLP analyses using Msp I and Dra I restriction enzymes, respectively, giving rise to two different sized hybridizable fragments in Southern blot analyses. In these RFPL analyses genotypes homozygous to the mutated allele have been presented as potent determinants of individual lung cancer risk. In the present study no association between polymorphic CYP1A1 and CYP2E1 genotypes and susceptibility to lung cancer was found. However, CYP2D6 polymorphism studies of the 122 healthy controls revealed seven poor metabolizer genotypes (5.7%), which compares well with the previously observed phenotypic distribution in the Finnish population, whereas only one PM genotype (1/106) was found among the lung cancer patients. These results agree with the previous suggestions that PMs of debrisoquine are less susceptible to lung cancer than EMs.     

Genetic polymorphisms of cytochrome P450 CYP1A1 (*2A) and microsomal epoxide hydrolase gene,interactions with tobacco-users,and susceptibility to bladder cancer: a study from North India

The role of low penetrance genes and environmental factors in the etiology of bladder cancer (CaB) is unclear, but may involve genetic and environmental factors. Most environmental pro-carcinogens require metabolic activation by phase I enzymes (CYP450s), However, phase II enzyme (i.e., microsomal epoxide hydrolase: mEH) is mainly involved in the detoxification of wide variety of endogenous or exogenous carcinogens. Genetic differences in CYP1A1 gene and the mEH gene polymorphisms have been reported to be associated with susceptibility to various cancers. In our case-control study, we assess whether Msp1 polymorphism of CYP1A1 (CYP1A1*2A), and His(113) in exon 3 and Arg(139) in exon 4 of the mEH susceptibility genotypes, tobacco-use and age factors contribute to bladder cancer risk among Indians. A case-control study was conducted in 106 bladder cancer (CaB) patients and 160 age matched controls from similar ethnic background. The CYP1A1*2A and mEH genotypes were determined by polymerase chain reaction/restriction fragment length polymorphism method from DNA extracted from peripheral blood samples. Binary logistic regression model was used for assessing differences in genotype prevalence between patients and the controls. The Arlequin software package was used to compute haplotype frequencies. We observed non-significant association in T/C polymorphism of the CYP1A1 gene (CYP1A1*2A); however, the exon 3 His genotype of the mEH gene polymorphism alone (odds ratio = 2.67, P = 0.001) or in combination with tobacco-users were significantly associated with the risk of bladder cancer. No associations were observed with stage or grade of bladder tumor with these genotypes. In conclusion, our study demonstrated that exon 3 His genotype of the mEH are more prone to the risk of sporadic bladder cancer in North India.     

宫颈癌p53外显子7突变与p53蛋白高表达的关系

目的　探讨宫颈癌 p5 3外显子 7突变与 p5 3蛋白高表达的关系。方法　采用免疫组织化学、聚合酶链反应 ( PCR)、限制性酶解片段长度多态性 ( RFL P)分析等方法对 49例宫颈癌组织石蜡包埋标本中 p5 3外显子 7的突变与 p5 3蛋白表达进行了检测。结果　 p5 3外显子 7的突变率 8.2 % ( 4/ 49)显著低于 p5 3蛋白阳性率49.0 % ( 2 4/ 49) (χ2 =18.0 5 ,P<0 .0 0 1) ;p5 3外显子 7突变不一定 p5 3蛋白阳性。结论　 p5 3外显子 7突变可能是部分宫颈癌变的一个重要因素 ;大部分宫颈癌可能主要由于高危人乳头状瘤病毒 ( HPV)感染后 ,通过 E6 / p5 3蛋白复合物的形成使 p5 3蛋白失活所致     

Genetic polymorphism of CYP2C19 and lansoprazole pharmacokinetics in Japanese subjects

Objective: We investigated whether interindividual differences in the pharmacokinetic disposition of lansoprazole are attributed to the genetic polymorphism of CYP2C19 which occurred by two mutations, CYP2C19m1 and CYP2C19m2, in 20 Japanese subjects. Methods: Polymerase chain reaction (PCR) restriction fragment length polymorphism procedures were used to detect the CYP2C19m1 mutation in exon 5 and the CYP2C19m2 mutation in exon 4 using SmaI and BamHI, respectively. Results: Ten subjects were homozygous (wt/wt subjects) for the wt allele in both exon 5 and exon 4, four subjects were heterozygous (wt/m1) for the CYP2C19m1 mutation, and two subjects were heterozygous (wt/m2) for the CYP2C19m2. The remaining four subjects had both mutated alleles in CYP2C19 genes, i.e., two were homozygous (m1/m1) for the defect in exon 5 and two were heterozygous (m1/m2) for the two defects in exons 5 and 4. The subjects in group 1 (wt/wt, wt/m1 and wt/m2) were the extensive metabolizers (EMs) for 5-hydroxylation of lansoprazole and were in the range of hydroxylation indexes from 3.83 to 19.8, whereas the subjects in group 2 (m1/m1 and m1/m2) were the poor metabolizers (PMs) and the indexes were in the range of 38.5 to 47.6. In group 2, AUC, t_1/2 and CL/f of lansoprazole were significantly greater, longer, and lower, respectively, than those in group 1. Conclusion: The hydroxylation of lansoprazole to 5-hydroxylansoprazole was apparently impaired in the subjects with the genetic defects of CYP2C19 (m1/m1 or m1/m2). Received: 12 November 1996 / Accepted in revised form: 18 February 1997     

Rapid detection of CYP2C18 genotypes by real-time fluorescence polymerase chain reaction

In man, CYP2C19, a liver enzyme, plays an important role in the metabolism of several drugs. Mutation of the CYP2C19 gene results in a poor metaboliser phenotype. S-Mephenytoin hydroxylation genetic polymorphism is due to two mutations of the CYP2C19 gene, namely CYP2C19*2, located in exon 5, and CYP2C19*3, located in exon 4. CYP2C18 is also polymorphically expressed. The mutant alleles of this enzyme are CYP2C18m1, located in exon 2 and CYP2C18m2, located in the 5'-flanking region. We have developed an allele-specific TaqMan polymerase chain reaction (PCR) assay with which to detect CYP2C18 mutant alleles. This assay combines hybridization of the TaqMan probe and allele-specific amplification primers to the target DNA. The TaqMan probe is labelled with 6-carboxyfluorescein at the 5' end and 6-carboxytetramethylrhodamine together with a phosphate at the 3' end. Genotypes are separated according to the different threshold cycles of the wild type and mutant primers. We applied this procedure to DNA extracted from the blood or saliva of 144 healthy Japanese volunteers. The wt/wt, wt/m1, wt/m2, m1/m1, m1/m2 and m2/m2 genotypes of the CYP2C18 alleles detected by the assay were consistent with the results obtained from restriction enzyme cleavage. In accordance with a previous report, the genotypes of CYP2C18m1 and CYP2C18m2 coincided with those of CYP2C19*3 and CYP2C19*2, respectively. Therefore, detection of CYP2C18 mutant alleles also allows that of CYP2C19 mutant alleles. Among 19 poor metabolisers, eight showed the homozygous CYP2C19*2/CYP2C19*2, two the homozygous CYP2C19*3/CYP2C19*3 and nine the compound heterozygous CYP2C19*2/CYP2C19*3 genotype. We found the allele-specific TaqMan PCR assay rapid, simple and cost-effective, as well as suitable for high-throughput applications in a routine laboratory. This assay allows the fast and reliable detection of inherited disorders that might influence diagnosis and treatment.     

应用DHPLC筛查先天性巨结肠RET基因突变研究

目的：应用DHPLC方法筛查先天性巨结肠RET基因突变。方法：提取32例先天性巨结肠患者的全血DNA，聚合酶链反应后应用DHPLC方法分析11、13、15号外显子的基因表达情况。结果：DHPLC技术分析有13例出现双峰，经测序后有1例突变为Gln849Lys，在15号外显子上；有3例患者有基因多态性：1例为Ser667Ser，在11号外显子上；2例为Leu746Leu，在13号外显子上。结论：DHPLC是一种快速有效的基因突变筛查方法，RET基因的突变和基因多态性与先天性巨结肠的发生密切相关。     

Polymorphisms of drug-metabolizing enzymes CYP2C9, CYP2C19, CYP2D6, CYP1A1, NAT2 and of P-glycoprotein in a Russian population

Objective The frequency of functionally important mutations and alleles of genes coding for xenobiotic metabolizing enzymes shows a wide ethnic variation. However, little is known of the frequency distribution of the major allelic variants in the Russian population.Methods Using polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) genotyping assays and the real-time PCR with fluorescent probes, the frequencies of functionally important variants of the cytochromes P₄₅₀ (CYP) 2C9, 2C19, 2D6, 1A1 as well as arylamine N-acetyltransferase 2 (NAT2) and P-glycoprotein (MDR1) were determined in a sample of 290 Russian volunteers derived from Voronezh area.Results CYP2C9*2 and *3 alleles were found with allelic frequencies of 10.5% and 6.7%, respectively. The novel intron-2 T>C mutation at exon 2 +73 bp occurred in 24.8% of alleles. CYP2C19*2 and *3 alleles occurred in 11.4% and 0.3%, respectively. Six persons (2.1%) carried two of these CYP2C19 alleles responsible for poor metabolizing activity. Of all subjects, 5.9% were CYP2D6 poor metabolizers, whereas 3.4% were addressed to ultra-rapid metabolizers (CYP2D6*1×2/*1). The CYP1A1*2A allele was found in 4.7%, *2B in 5.0%, *4 in 2.6%, and the 5-mutations –3219C>T, –3229G>A, and the novel –4335G>A in 6.0%, 2.9% and 26.0% of alleles, respectively. Genotyping of eight different single nucleotide polymorphisms in the NAT2 gene provided in 58.0% a genotype associated with slow acetylation. The MDR1 triple variants G2677T and G2677A in exon 21 had an allelic frequency of 41.9% and 3.3%, respectively, and the variant C3435T in exon 26 one of 54.3%. Frequencies of functionally important haplotypes were calculated.Conclusion The overview of allele distribution of important xenobiotic-metabolizing enzymes among a Russian population shows similarity to other Caucasians. The data will be useful for clinical pharmacokinetic investigations and for drug dosage recommendations in the Russian population.     

High frequency of CYP1A1 mutations in a Turkish population

The frequency distribution of four cytochrome P4501A1 (CYP1A1) gene mutations was investigated in 271 Turks from southeast Anatolia by polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) assay. Allelic linkage of those mutations was proven by peptide nucleic acid-mediated PCR clamping. Mutation m1 (T6235C) forming an MspI restriction site in the 3′-flanking region occurred with 18.1% frequency (95% confidence interval 14.9–21.6%), m2 (A4889G) leading to an Ile/Val exchange in exon 7 had a frequency of 8.9% (6.6–11.6%), and m4 (C4887A; Thr/Asn-exchange also in exon 7) occurred with 5.7% (3.9–8.0%). T5639C (m3) in the 3′-flanking region was not detected. m2 was exclusively found linked with m1 forming allele CYP1A1*2B. The frequency of this allele supposedly at-risk for lung cancer was significantly higher than in Middle European populations, but lower than in the Far East. Received: 11 September 1997 / Accepted: 10 October 1997