Nicotine metabolism and CYP2A6 allele frequencies in Koreans.

CYP2A6 is a major catalyst of nicotine metabolism to cotinine. Previously, we demonstrated that the interindividual difference in nicotine metabolism is related to a genetic polymorphism of the CYP2A6 gene in Japanese. To clarify the ethnic differences in nicotine metabolism and frequencies of CYP2A6 alleles, we studied nicotine metabolism and the CYP2A6 genotype in 209 Koreans. The cotinine/nicotine ratio of the plasma concentration 2 h after chewing one piece of nicotine gum was calculated as an index of nicotine metabolism. The genotypes of CYP2A6 gene (CYP2A6*1A, CYP2A6*1B, CYP2A6*2, CYP2A6*3, CYP2A6*4 and CYP2A6*5) were determined by polymerase chain reaction (PCR)-restriction fragment length polymorphism or allele specific (AS)-PCR. There were ethnic differences in the allele frequencies of CYP2A6*1A, CYP2A6*1B, CYP2A6*4 and CYP2A6*5 between Koreans (45.7%, 42.8%, 11.0% and 0.5%, respectively) and Japanese (42.4%, 37.5%, 20.1% and 0%, respectively, our previous data). Similar to the Japanese, no CYP2A6*2 and CYP2A6*3 alleles were found in Koreans. The homozygotes of the CYP2A6*4 allele (four subjects) were completely deficient in cotinine formation, being consistent with the data among Japanese. The heterozygotes of CYP2A6*4 tended to possess a lower metabolic ratio (CYP2A6*1A/CYP2A6*4, 4.79 +/- 3.17; CYP2A6*1B/CYP2A6*4, 7.43 +/- 4.97) than that in subjects without the allele (CYP2A6*1A/CYP2A6*1A, 7.42 +/- 6.56; CYP2A6*1A/CYP2A6*1B, 9.85 +/- 16.12; CYP2A6*1B/CYP2A6*1B, 11.33 +/- 9.33). The subjects who possess the CYP2A6*1B allele appeared to show higher capabilities of cotinine formation. It was confirmed that the interindividual difference in nicotine metabolism was closely related to the genetic polymorphism of CYP2A6. The probit plot of the metabolic ratios in Koreans (8.73 +/- 11.88) was shifted to a higher ratio than that in the Japanese (3.78 +/- 3.09). In each genotype group, the Korean subjects revealed significantly higher metabolic ratios than the Japanese subjects. The ethnic difference in cotinine formation might be due to environmental and/or diet factors as well as genetic factors.     

多索茶碱对大鼠肝CYP2D6酶的影响

目的:通过体内、体外实验观察多索茶碱对大鼠肝CYP2D6酶的影响。方法:取16只大鼠随机均分为对照Ⅰ组和实验组,分别灌胃给予生理盐水1mL和多索茶碱50mg·kg-1·d-1,连续1周,第8天时均灌胃给予探针药物右美沙芬(6mg·kg-1),收集8h尿液后处死大鼠,测定大鼠尿样及肝微粒体中右美沙芬浓度并计算其代谢率;实验组肝微粒体再分为对照Ⅱ组、多索茶碱组和CYP2D6特异性抑制剂西咪替丁组,分别加入相应药物孵育后测定并计算右美沙芬的代谢率;将体内、体外实验得到的右美沙芬的代谢率进行相关性分析。结果:以右美沙芬的代谢率为指标,体内实验中2组比较无明显差别(P>0.05);体外试验中,与对照Ⅱ组比较,多索茶碱组未见明显降低(P>0.05),西咪替丁组明显降低(P<0.01);体内和体外实验数据具有很好的相关性(r=0.9537)。结论:多索茶碱对大鼠肝CYP2D6酶无诱导或抑制作用。     

CYP2C19 activity comparison between Swedes and Koreans: effect of genotype, sex, oral contraceptive use, and smoking

Objectives  

To compare CYP2C19 enzyme activity between Swedes and Koreans controlling for the effect of CYP2C19 genotype, sex, oral contraceptive use, and smoking habits.     

Comparisons of <Emphasis Type="Italic">CYP1A2</Emphasis> genetic polymorphisms,enzyme activity and the genotype-phenotype relationship in Swedes and Koreans

Objectives To investigate the CYP1A2 genotype-phenotype relationship and to compare CYP1A2 genetic polymorphisms and enzyme activity in terms of the effect of smoking and oral contraceptive (OC) use in Swedes and Koreans. Methods CYP1A2 enzyme activity was determined in 194 and 150 healthy Swedish and Korean subjects, respectively, on the basis of the 4-h plasma paraxanthine/caffeine (17X/137X) ratio determined using high-performance liquid chromatography. Genotyping for the −3860G>A, −2467delT, −739 T>G, −729 C>T, −163C>A and −3113A>G polymorphisms was performed by PCR-restriction fragment length polymorphism analysis. Results The mean 17X/137X ratio was 1.54-fold higher in Swedes than in Koreans (mean difference: 0.16; 95% CI of the mean difference: 0.12, 0.20; p < 0.0001). Smokers had a significantly higher 17X/137X ratio (higher CYP1A2 activity) than non-smokers, while Swedish OC users had a significantly lower 17X/137X ratio than non-users (mean difference: 0.31, 95% CI of the mean difference: 0.23, 0.39; p < 0.0001). No effect of gender differences on enzyme activity was observed. Four known (CYP1A2*1A, *1D, *1F, and *1L) and two novel haplotypes (CYP1A2*1V and CYP1A2*1W) were found. CYP1A2*1K was rare in Swedes and absent in Koreans. No significant genotype-phenotype relationship was observed, with the exception of CYP1A2*1F in Swedish smokers, where it was associated with higher enzyme inducibility (p = 0.02). Koreans displayed a significantly lower mean 17X/137X ratio than Swedes having the same CYP1A2 genotype, smoking habit and OC use. Conclusions We found significant differences in CYP1A2 enzyme activity between Swedes and Koreans that could not be explained by environmental factors or the CYP1A2 haplotypes examined, despite differences in allele frequencies. None of the investigated CYP1A2 haplotypes are critical in inducing variations in enzyme activity, with the exception of CYP1A2*1F.     

Metabolism of citalopram enantiomers in CYP2C19/CYP2D6 phenotyped panels of healthy Swedes

AIMS: To investigate pharmacokinetics of the enantiomers of citalopram (CT) and its metabolites desmethylcitalopram (DCT) and didesmethylcitalopram (DDCT) in Swedish healthy volunteers in relation to CYP2C19 and CYP2D6 geno- and phenotypes. METHODS: Racemic CT was given for seven days to panels with different genotypes and the following mephenytoin (Me) and debrisoquine (De) hydroxylation phenotypes: EMDe/EMMe, PMDe/EMMe, EMDe/PMMe (n = 6 in all groups), and one PMDe/PMMe subject. Blood sampling was carried out during day 7, and all urine was collected for 12 h after the last dose of CT. RESULTS: The AUC of S-CT was significantly higher in the EMDe/PMMe panel compared to the EMDe/EMMe and PMDe/EMMe panels (P < 0.05), whereas the AUC of R-CT did not differ between the panels. Similar differences, although they did not reach statistical significance, were noted for S-DCT and R-DCT. The enantiomers of DDCT were not quantifiable in PMDe, and there was no difference in DDCT enantiomer concentrations between the other two panels. A PMDe/PMMe subject stopped taking CT after five days due to severe adverse effects. Based on two time points, this subject had a very long CT half-life of 95 h. The value of 1.0 for the S/R ratio of the CT trough in this subject was similar to the mean S/R CT trough ratio of the EMDe/PMMe panel, but higher than the S/R CT ratio of the EMDe/EMMe panel (0.56; 95% CI 0.49-0.63) and the PMDe/EMMe panel (0.44; 95% CI 0.31-0.57). Thus the latter two phenotypes eliminated S-CT more rapidly via CYP2C19. An adverse effect described as an 'alcohol hangover' feeling was reported by one subject from each of the three panels. These individuals had the highest concentrations of both CT enantiomers. CONCLUSIONS: The AUC of S-, but not R-(CT) was found to be significantly higher in PM of mephenytoin compared to EMs, PMs may need a lower dosage of CT.     

Gene-gene interactions between CYP2B6 and CYP2A6 in nicotine metabolism

OBJECTIVES: CYP2A6 is the major enzyme involved in nicotine metabolism, yet large interindividual variations in the rate of nicotine metabolism exist within groups of individuals having the same CYP2A6 genotype. We investigated the influence of genetic variation in another potential nicotine-metabolizing enzyme, CYP2B6, and its interaction with CYP2A6, on the metabolism of nicotine. METHODS: Two hundred and twelve healthy Caucasian adult twin volunteers underwent an intravenous infusion of stable isotope-labeled nicotine and its major metabolite, cotinine, for characterization of pharmacokinetic and metabolism phenotypes. Five CYP2B6 genetic polymorphisms causing amino acid substitutions (R22C, Q172 H, S259R, K262R, and R487C) were analyzed. RESULTS: We observed that the CYP2B6*6 haplotype (defined as having both Q172 H and K262R variants) was associated with faster nicotine and cotinine clearance, and that such associations were more prominent among individuals having decreased-activity CYP2A6 genotypes. Statistically significant interactions between CYP2B6 and CYP2A6 genotypes were observed (P<0.003 for nicotine clearance and P<0.002 for cotinine clearance). CONCLUSIONS: Our results indicate that CYP2B6 genetic variation is associated with the metabolism of nicotine and cotinine among individuals with decreased CYP2A6 activity. Further investigation of the roles of CYP2B6 and the interaction between CYP2B6 and CYP2A6 genotypes in mediating nicotine dependence and tobacco-related diseases is merited.     

Genotype and allele frequency of CYP2D6 in Tamilian population

Objective To assess the frequency of CYP2D6 *3, *4, *5 and *10 allelic variants in a South Indian population and compare the frequencies with other major populations.Methods Polymerase chain reaction (PCR) or PCR-restriction fragment length polymorphism (RFLP)-based methods were used to identify the CYP2D6 genotypes of 106 healthy unrelated male and female volunteers of Tamilian origin. The allele and genotype frequencies observed were compared with other major populations.Results The *10 allele was the most frequent mutant allele in Tamilians (20.3%). The *5 allele occurred at 0.9% and the *3 allele was not detected. The most frequent allele causing enzyme inactivation was *4 allele in Tamilians (6.6%), which is significantly higher than that reported in Japanese (0%).Conclusions The *10 allele is the most common mutant allele in Tamilians. The CYP2D6*4 and CYP2D6*5 alleles are distributed in a significantly different way in the Tamil population relative to Oriental populations.     

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.     

Induction of CYP1A2 by heavy coffee consumption in Serbs and Swedes

Objectives To investigate the influence of coffee consumption on CYP1A2 enzyme activity controlling for the effects of smoking and oral contraceptive (OC) use among Serbs and Swedes and to compare CYP1A2 activity between the two populations. Methods Data on oral contraceptive use, habitual coffee consumption and smoking habits were obtained from 100 Serbian and 149 Swedish healthy volunteers using a detailed questionnaire. CYP1A2 activity was estimated by plasma paraxanthine/caffeine (17X/137X) ratio analysed by reversed-phase HPLC after oral administration of 100 mg caffeine. Results Daily consumption of at least three cups of coffee significantly increased CYP1A2 enzyme activity in both Serbs (P = 0.0002) and Swedes (P < 0.0001). Among non-smokers and non-OC users, heavy coffee consumption significantly increased CYP1A2 activity in Serbs (mean difference 0.11; 95% CI of the mean difference 0.04, 0.18; P = 0.003) and Swedes (mean difference 0.07; 95% CI of the mean difference 0.01, 0.12; P = 0.02). Significantly higher 17X/137X ratio was detected in Serbian smokers compared to non-smokers. There was no significant gender difference in CYP1A2 activity in Serbs. Controlling for the effect of smoking, heavy coffee consumption habit and oral contraceptive use, significantly lower 17X/137X ratio was observed in Serbs than in Swedes (P = 0.0003). Conclusions Habitual heavy coffee consumption increases CYP1A2 activity. Polycyclic aromatic hydrocarbons formed during roasting of coffee beans might partly be responsible for this effect. The reason for the observed lower CYP1A2 activity in Serbs as compared to Swedes remains to be investigated.     

4Beta-hydroxycholesterol is a new endogenous CYP3A marker: relationship to CYP3A5 genotype, quinine 3-hydroxylation and sex in Koreans, Swedes and Tanzanians

OBJECTIVES: To study the potential endogenous marker of CYP3A activity, 4beta-hydroxycholesterol, and its relation to sex and the CYP3A5 geno/haplotypes and compare with CYP3A4/5 catalyzed 3-hydroxylation of quinine in the three major races. METHODS: The plasma concentration of 4beta-hydroxycholesterol was measured in healthy Tanzanians (n=138), Swedes (n=161) and Koreans (n=149) by gas chromatography-mass spectrometry. The metabolic ratio of quinine/3-hydroxyquinine in plasma 16-h post dose was determined by high performance liquid chromatography, previously reported in Tanzanians and Swedes, and now also in Koreans. The participants were genotyped for relevant alleles of CYP3A5. RESULTS: The mean plasma concentrations of 4beta-hydroxycholesterol in Koreans, Swedes and Tanzanians were 29.3, 26.8 and 21.9 ng/ml, respectively (P<0.01 between all three populations). Within all three populations there were significant differences in 4beta-hydroxycholesterol levels between the CYP3A5 genotypes. Women had higher concentrations than men, but the difference was only significant in Tanzanians (P<0.001) and Koreans (P<0.00001). The quinine/3-hydroxyquinine metabolic ratio was significantly different in all three populations with the highest CYP3A activity in Koreans and the lowest in Tanzanians. Korean women had a lower metabolic ratio than men (P<0.00001). Significant correlations between 4beta-hydroxycholesterol and quinine 3-hydroxylation were found in Tanzanians and Koreans. CONCLUSION: Clear differences in the activity of both CYP3A4 and CYP3A5 were shown in the three major human races. Both 4beta-hydroxycholesterol and quinine/3-hydroxyquinine metabolic ratio showed a higher CYP3A activity in women than in men. The results give strong evidence that the plasma concentration of 4beta-hydroxycholesterol may be used as an endogenous marker of CYP3A activity (CYP3A4+5).     

Pharmacogenomics of CYP2A6, CYP2B6, CYP2C19, CYP2D6, CYP3A4, CYP3A5 and MDR1 in Vietnam

Aim  The aim of this study was to obtain pharmacogenetic data in a Vietnamese population on genes coding for proteins involved in the elimination of drugs currently used for the treatment of malaria and human immunodeficiency virus/acquired immunodeficiency syndrome. Method  The main polymorphisms on the cytochrome P450 (CYP) genes, CYP2A6, CYP2B6, CYP2C19, CYP2D6, CYP3A4 and CYP3A5, and the multi-drug resistance 1 gene (MDR1) were genotyped in 78 healthy Vietnamese subjects. Pharmacokinetic metrics were available for CYP2A6 (coumarin), CYP2C19 (mephenytoin), CYP2D6 (metoprolol) and CYP3As (midazolam), allowing correlations with the determined genotype. Results  In the CYP2 family, we detected alleles CYP2A6*4 (12%) and *5 (15%); CYP2B6*4 (8%), *6 (27%); CYP2C19*2 (31%) and *3 (6%); CYP2D6*4, *5, *10 (1, 8 and 44%, respectively). In the CYP3A family, CYP3A4*1B was detected at a low frequency (2%), whereas CYP3A5 *3 was detected at a frequency of 67%. The MDR1 3435T allele was present with a prevalence of 40%. Allele proportions in our cohort were compared with those reported for other Asian populations. CYP2C19 genotypes were associated to the S-4′-OH-mephenytoin/S-mephenytoin ratio quantified in plasma 4 h after intake of 100 mg mephenytoin. While CYP2D6 genotypes were partially reflected by the α-OH-metroprolol/metoprolol ratio in plasma 4 h after dosing, no correlation existed between midazolam plasma concentrations 4 h post-dose and CYP3A genotypes. Conclusions  The Vietnamese subjects of our study cohort presented allele prevalences in drug-metabolising enzymes that were generally comparable with those reported in other Asian populations. Deviations were found for CYP2A6*4 compared to a Chinese population (12 vs. 5%, respectively; P = 0.023), CYP2A6*5 compared with a Korean population (15 vs. <1%, respectively; P < 0.0001), a Malaysian population (1%; P < 0.0001) and a Chinese population (1%; P < 0.0001); CYP2B6*6 compared with a Korean population (27 vs. 12%; P = 0.002) and a Japanese population (16%; P = 0.021). Pharmacokinetic metrics versus genotype analysis reinforces the view that the predictive value of certain globally common variants (e.g. CYP2D6 single nucleotide polymorphisms) should be evaluated in a population-specific manner.     

Comparisons of CYP2C19 genetic polymorphisms between Korean and Vietnamese populations

It is well known that CYP2C19 is an enzyme showing genetic polymorphism that may cause marked interindividual and interethnic variation in the metabolism and disposition of its substrates. This study compared the frequency distribution of CYP2C19*1, *2, and *3 alleles in Korean and Vietnamese populations, representing Far Eastern and Southwestern Asian populations, respectively. The presence of the CYP2C19 variant alleles was analyzed in 377 Korean and 165 Vietnamese healthy subjects using a new pyrosequencing method. The respective allele frequencies of CYP2C19*1, *2, and *3 were 64%, 28%, and 8% in Koreans and 69%, 24%, and 5% in Vietnamese. The frequency of poor metabolizer genotype (*2/*2, *2/*3, *3/*3) in Korean (12.5%, 95% confidence interval 11.4-13.6) was not significantly different from that of Vietnamese population (7.2%, 95% confidence interval 6.2-8.2) (P = 0.074). These results obtained from a large number of subjects can be used in comparative studies with other ethnic groups in future clinical research.     

奥拉西坦对肝微粒体酶CYP2C9活性的影响研究

目的:考察奥拉西坦对肝微粒体酶CYP2C9活性的影响。方法:将大鼠随机分为对照组和实验组,每组18只,对照组每天灌胃蒸馏水,实验组每天灌胃奥拉西坦80 mg/kg,每日2次,连续8 d。第8天灌胃后两组大鼠均立即灌胃给予CYP2C9的探针药物甲苯磺丁脲50 mg/kg,并于给予甲苯磺丁脲后0.25、0.5、0.75、1、1.5、2、3、4、6、10、12、24 h内眼内眦取血。采用高效液相色谱法测定血药浓度,拟合药动学参数,并对两组药动学参数进行比较。结果:对照组与实验组主要药动学参数t1/2分别为(5.45±1.98)、(6.54±1.45)h,cmax分别为(169.12±58.14)、(146.19±49.44)mg/L,AUC0-24 h分别为(1 113.01±264.32)、(1 120.14±208.91)mg·h/L,Vd分别为(0.77±0.32)、(0.91±0.40)L/kg,CL分别为(0.08±0.03)、(0.08±0.02)L/(h·kg),两组间比较差异无统计学意义(P>0.05)。结论:奥拉西坦对甲苯磺丁脲在大鼠体内的药动学未见明显影响,初步认为奥拉西坦对经CYP2C9代谢的药物的药动学无明显影响。     

High Frequency of CYP2D6 Ultrarapid Metabolizer Genotype in the Finnish Population

CYP2D6 participates in the biotransformation of many commonly used drugs. Large genetic variability in CYP2D6 results in a wide interindividual variability in the response to CYP2D6 substrate drugs. Previous studies have assessed the phenotype and genotype distributions of CYP2D6 in relatively small Finnish population samples. The aim of our study was to investigate the frequencies of CYP2D6 genotypes in a larger Finnish population cohort of 857 healthy volunteers. The volunteers were genotyped for 10 CYP2D6 genetic variants (*2, *3, *4, *5, *6, *9, *10, *17, *39, *41) and copy number variation performed with TaqMan genotyping assays and copy number assay targeting exon 9. CYP2D6 phenotypes were inferred from the genotype data with the classical and activity score methods. According to the classical method, a large majority of the study cases were extensive metabolizers (EM; 87.3%; 95% confidence interval 84.9–89.3) and the second largest group was ultrarapid metabolizers (UM; 7.2%; 5.7–9.2%). Intermediate (IM) and poor metabolizers (PM) were in clear minority (3.0%; 2.1–4.4% and 2.3%; 1.5–3.6%, respectively). The activity score method yielded similar phenotype predictions. These results show that the frequency of UM genotype is higher and that of PM and IM genotype is lower in the Finnish population than in other North European populations. Accordingly, CYP2D6 genetic profile of the Finnish population differs from its geographically close neighbours, which has implications for the effective and safe use of drugs metabolized by CYP2D6.     

CYP2A13-catalysed coumarin metabolism: comparison with CYP2A5 and CYP2A6

1. We investigated the total metabolism of coumarin by baculovirus (BV)-expressed CYP2A13 and compared it with metabolism by BV-expressed CYP2A6. The major coumarin metabolite formed by CYP2A13 was 7-hydroxycoumarin, which accounted for 43% of the total metabolism. The product of 3,4-epoxidation, o-hydroxyphenylacetaldehyde (o-HPA), accounted for 30% of the total metabolites. 2. The K(m) and V(max) for CYP2A13-mediated coumarin 7-hydroxylation were 0.48+/-0.07 micro m and 0.15+/-0.006 nmol min(-1) nmol(-1) CYP, respectively. The V(max) of coumarin 7-hydroxylation by CYP2A13 was about 16-fold lower than that of CYP2A6, whereas the K(m) was 10-fold lower. 3. In the mouse, there were two orthologues for CYP2A6: CYP2A4 and CYP2A5, which differed by only 11 amino acids. However, CYP2A5 is an efficient coumarin 7-hydroxylase, where as CYP2A4 is not. We report here that BV-expressed CYP2A4 metabolizes coumarin by 3,4-epoxidation. Two products of the 3,4-epoxidation pathway, o-HPA and o-hydroxyphenylacetic acid (o-HPAA), were detected by radioflow HPLC. 4. The K(m) and V(max) for the coumarin 3,4-epoxidation by CYP2A4 were 8.7+/-3.6 micro m and 0.20+/-0.04 nmol min(-1) nmol(-1) CYP, respectively. Coumarin 7-hydroxylation by CYP2A5 was more than 200 times more efficient than 3,4 epoxidation by CYP2A4.     

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。     

Structural characterization of a new variant of the CYP2A6 gene (CYP2A6*1B) apparently diagnosed as heterozygotes of CYP2A6*1A and CYP2A6*4C

During the course of investigating the frequency of a CYP2A6 whole deletion-type polymorphism (CYP2A6*4C) in Japanese, an unexpectedly large population of heterozygotes for CYP2A6*4C and the wild-type (CYP2A6*1A) was found. Cloning of a cDNA encoding CYP2A6 from the liver of individuals judged as heterozygotes for CYP2A6*4C and the CYP2A6*1A was carried out to identify the causal allele(s) responsible for a possible overestimation. A clone isolated from the liver cDNA library possessed 58 bp sequences in the 3'-untranslated region, which was replaced with the corresponding region of the CYP2A7 gene. The same gene conversion existed in the genomic DNA, indicating that the replacement was not a cloning artifact. Based on the gene structure of the allele (CYP2A6*1B), this variant was thought to be one of the causal alleles responsible for overestimation of heterozygotes for CYP2A6*4C and CYP2A6* A. To investigate this further, we developed a genotyping method which could distinguish the CYP2A6*A, CYP2A6*1B and CYP2A6*4C alleles from each other. The results clearly showed that CYP2A6*1B was the sole allele responsible for the overestimation. We conclude that the new genotyping method allows determination of six genotypes of the CYP2A6 gene, simultaneously and precisely, in both Oriental and Caucasian populations.     

Characterization of novel CYP2A6 polymorphic alleles (CYP2A6*18 and CYP2A6*19) that affect enzymatic activity.

Genetic polymorphisms of CYP2A6 gene are known as a causal factor of the interindividual differences in nicotine metabolism. We found three novel CYP2A6 alleles. The CYP2A6(*)18A allele has a single nucleotide polymorphism (SNP) of A5668T (A1175T, Y392F) in exon 8. The CYP2A6(*)18B allele has synonymous SNPs of G51A (G51A), T5684C (T1191C), and T5702C (T1209C) in addition to A5668T (A1175T, Y392F). The CYP2A6(*)19 allele has the SNPs of A5668T (A1175T, Y392F), T6354C (intron 8), and T6558C (T1412C, I471T) as well as the conversion with the CYP2A7 sequence in the 3'-untranslated region, in which the latter two changes correspond to CYP2A6(*)7. Ethnic differences in the frequencies of these alleles were observed between whites, African-Americans, Japanese, and Koreans. Wild or variant CYP2A6 (CYP2A6(*)18, CYP2A6(*)19, and CYP2A6(*)7) were expressed in Escherichia coli. For coumarin 7-hydroxylation and 5-fluorouracil formation from tegafur, the K(m) values were increased, and V(max) values were decreased in CYP2A6.18 compared with those in CYP2A6.1, resulting in decreased clearance to 50 and 35% of that of the wild type, respectively. The K(m) and V(max) values for nicotine C-oxidation were both increased, resulting in no change of clearance. In CYP2A6.19, the effects on the coumarin 7-hydroxylation and 5-fluorouracil formation (increased K(m) and decreased V(max)) were prominent, resulting in decreased clearance to 8% of those of the wild type. For nicotine C-oxidation, the K(m) and V(max) values were both decreased, resulting in decreased clearance to 30% of that of the wild type. The changes of the kinetics in CYP2A6.19 were similar to those in CYP2A6.7. In vivo nicotine metabolism was evaluated in whites (n = 56) and Koreans (n = 40). Although the CYP2A6(*)18 and CYP2A6(*)19 alleles were found only heterozygously, a subject with CYP2A6(*)7/CYP2A6(*)19 showed a lower cotinine/nicotine ratio of the plasma concentration compared with homozygotes of the CYP2A6(*)1A, supporting the in vitro results that the CYP2A6(*)19 allele leads to decreased enzymatic activity.     

细胞色素P—450 CYP2D6基因分型与表型的吻合率

研究细胞色素Ｐ４５０－２Ｄ６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％。