Genetic analysis of the interethnic difference between Chinese and Caucasians in the polymorphic metabolism of debrisoquine and codeine

Summary The Far Eastern and Caucasian populations are strikingly different with respect to the debrisoquine/sparteine hydroxylation polymorphism. The number of poor metabolizers, as defined for Caucasians, is very low among Chinese and Japanese. We investigated the molecular basis for this difference by analysis of the CYP2D6 gene in 115 Chinese subjects, combined with phenotypic classification of codeine and debrisoquine metabolism.A correlation between the rates of metabolism of these two drugs and genotype, as analyzed by RFLP using XbaI, was observed among the Chinese. A high frequency (37%) of alleles indicative of gene insertions (reflected by Xba I 44kb fragments) was recorded in the Chinese, but was not associated with the poor metabolizer phenotype, as it is in Caucasians. PCR amplification of part of the CYP2D6 gene with mutation specific primers for CYP2D6A (29A) and CYP2D6B (29B) allelic variants revealed that the XbaI 44kb fragment in Chinese apparently contains a functional CYP2D6 gene, in contrast to the situation among Caucasians.The results provide a molecular explanation of the interethnic difference in the metabolism of drugs affected by the debrisoquine hydroxylation polymorphism.     

Recent developments and future directions for the use of pharmacogenomics in cardiovascular disease treatments

Introduction: Cardiovascular disease is still the leading cause of death worldwide. There are many environmental and genetic factors that play a role in the development of cardiovascular disease. The treatment of cardiovascular disease is beginning to move in the direction of personalized medicine by using biomarkers from the patient’s genome to design more effective treatment plans. Pharmacogenomics have already uncovered many links between genetic variation and response of many different drugs.

Areas covered: This article will focus on the main polymorphisms that impact the risk of adverse effects and response efficacy of statins, clopidogrel, aspirin, β-blockers, warfarin dalcetrapib and vitamin E. The genes discussed include SLCO1B1, ABCB1, CYP3A4, CYP3A5, CYP2C19, PTGS1, PTGS2, ADRB1, ADCY9, CYP2C19, PON1, CES1, PEAR1, GPIIIa, CYP2D6, CKORC1, CYP2C9 and Hp.

Expert opinion: Although there are some convincing results that have already been incorporated in the labelling treatment guidelines, most gene-drug relationships have been inconsistent. A better understanding of the relationships between genetic factors and drug response will provide more opportunities for personalized diagnosis and treatment of cardiovascular disease.     

Metoclopramide is metabolized by CYP2D6 and is a reversible inhibitor,but not inactivator,of CYP2D6

Abstract

1. Metoclopramide is a widely used clinical drug in a variety of medical settings with rare acute dystonic events reported. The aim of this study was to assess a previous report of inactivation of CYP2D6 by metoclopramide, to determine the contribution of various CYPs to metoclopramide metabolism, and to identify the mono-oxygenated products of metoclopramide metabolism.

2. Metoclopramide interacted with CYP2D6 with Type I binding and a K_s value of 9.56?±?1.09?µM. CYP2D6 was the major metabolizer of metoclopramide and the two major products were N-deethylation of the diethyl amine and N-hydroxylation on the phenyl ring amine. CYPs 1A2, 2C9, 2C19, and 3A4 also metabolized metoclopramide.

3. While reversible inhibition of CYP2D6 was noted, CYP2D6 inactivation by metoclopramide was not observed under conditions of varying concentration or varying time using Supersomes^TM or pooled human liver microsomes.

4. The major metabolites of metoclopramide were N-hydroxylation and N-deethylation formed most efficiently by CYP2D6 but also formed by all CYPs examined. Also, while metoclopramide is metabolized primarily by CYP2D6, it is not a mechanism-based inactivator of CYP2D6 in vitro.     

等位基因特异扩增法研究中国人CYP2D6中速代谢的相关基因

目的　建立CYP2D6*10B的等位基因特异扩增法(ASA-PCR),以探讨中国人CYP2D6中速代谢的基因分型。方法　采用两步扩增法得到CYP2D6*10B等位基因特异片段,分析健康中国汉族人CYP2D6*10B等位基因,并探讨基因分型结果与右美沙芬表型分型结果的相关性。结果　35名表型为极快代谢受试者(VEMs)中,CYP2D6*10B以杂合子(wt/m)为主占57%;29名中速代谢受试者(IMs)以突变型纯合子(m/m)为主占69%;慢代谢受试者(PM)基因型为m/m。CYP2D6*10Bm/m组的MR明显大于wt/m组和野生型组(wt/wt)。结论　ASA-PCR法有快速、准确的优点,可用于CYP2D6中速代谢的检测与研究。     

Ilaprazole for the treatment of gastro-esophageal reflux

Introduction: Despite the undoubted benefit of proton pump inhibitors (PPIs), they have several shortcomings, such as a slow onset of action and a remarkable inter-individual variability, that limit the complete success of these drugs. Recently, a new PPI, ilaprazole, has been developed and used in GERD patients.

Areas covered: The present review provides an update on the following points: current knowledge of GERD mechanisms; limitations of actual therapies; pharmacokinetic profile and metabolism of ilaprazole; initial studies on the therapeutic efficacy of ilaprazole in GERD.

Expert opinion: Compared with all other approved PPIs, ilaprazole has shown an extended plasma half-life, a metabolism not significantly influenced by CYP2C19 genetic polymorphism and similar safety. This characteristics account for a low inter-individual variability, particularly in Asian populations, a higher suppression of gastric acid secretion, a more rapid acid control and consequent quicker symptom relief and a better effect on nocturnal acidity. However, clinical investigations assessing the efficacy of ilaprazole in the management of GERD are lacking and therefore the potential improvements achievable with ilaprazole in the current standard of care for acid-suppressing treatment must be confirmed in large and randomly controlled clinical trials enrolling patients with both erosive and non-erosive reflux disease.     

Polymorphisms in CYP2D6 duplication-negative individuals with the ultrarapid metabolizer phenotype: a role for the CYP2D6*35 allele in ultrarapid metabolism?

Ultrarapid drug metabolism mediated by CYP2D6 is associated with inheritance of alleles with duplicated or amplified functional CYP2D6 genes. However, genotyping for duplicated CYP2D6 alleles only explains a fraction (10-30%) of the ultrarapid metabolizer phenotypes observed in Caucasian populations. Using a sample of CYP2D6 duplication-negative ultrarapid metabolizer subjects and selected control subjects with extensive metabolism, we examined parts of the CYP2D7 pseudogene, and the promoter region and 5'-coding sequence of CYP2D6 for polymorphisms possibly associated with the ultrarapid metabolizer phenotype. In an initial screening of 17 subjects (13 ultrarapid metabolizers and four extensive metabolizers), we identified three DNA variants in the 5'-end of the CYP2D7 pseudogene and 29 variants in the 5'-end of the CYP2D6 gene. Five variants were then selected for examination in a larger sample of subjects having the ultrarapid metabolizer (n = 27) or extensive metabolizer phenotype (n = 77). Subsequent statistical analyses of allele, genotype and estimated haplotype distributions showed that the 31A allele of the 31G > A (Val(II)Met) polymorphism was significantly more frequent in ultrarapid metabolizer subjects than in extensive metabolizer subjects (P = 0.04). Also, estimation of haplotype frequencies suggested that one of the haplotypes with the 31A variant was significantly more frequent among the ultrarapid metabolizers compared with the extensive metabolizers (P = 0.03). The average metabolic ratio was significantly lower in subjects possessing the 31A allele compared with subjects homozygous for the 31G allele (P = 0.02). We also observed a nonsignificant over-representation of the G-allele of a - 1584 C > G promoter polymorphism in the ultrarapid metabolizer group. Since our results are based on a relatively low number of subjects, further studies on larger samples and functional analyses of the polymorphisms detected are necessary to determine the role of the 31G > A and - 1584C > 6 variants in CYP2D6 duplication-negative ultrarapid metabolizer subjects.     

Polymorphic cytochrome P450 2D6: humanized mouse model and endogenous substrates

Cytochrome P450 2D6 (CYP2D6) is the first well-characterized polymorphic phase I drug-metabolizing enzyme, and more than 80 allelic variants have been identified for the CYP2D6 gene, located on human chromosome 22q13.1. Human debrisoquine and sparteine metabolism is subdivided into two principal phenotypes--extensive metabolizer and poor metabolizer--that arise from variant CYP2D6 genotypes. It has been estimated that CYP2D6 is involved in the metabolism and disposition of more than 20% of prescribed drugs, and most of them act in the central nervous system or on the heart. These drug substrates are characterized as organic bases containing one nitrogen atom with a distance about 5, 7, or 10 A from the oxidation site. Aspartic acid 301 and glutamic acid 216 were determined as the key acidic residues for substrate-enzyme binding through electrostatic interactions. CYP2D6 transgenic mice, generated using a lambda phage clone containing the complete wild-type CYP2D6 gene, exhibits enhanced metabolism and disposition of debrisoquine. This transgenic mouse line and its wild-type control are models for human extensive metabolizers and poor metabolizers, respectively, and would have broad application in the study of CYP2D6 polymorphism in drug discovery and development, and in clinical practice toward individualized drug therapy. Endogenous 5-methoxyindole- thylamines derived from 5-hydroxytryptamine were identified as high-affinity substrates of CYP2D6 that catalyzes their O-demethylations with high enzymatic capacity and specificity. Thus, polymorphic CYP2D6 may play an important role in the interconversions of these psychoactive tryptamines, including a crucial step in a serotonin-melatonin cycle.     

A systematic review and combined analysis of therapeutic drug monitoring studies for long-acting risperidone

Introduction: This systematic review of therapeutic drug monitoring (TDM) identifies three long-acting injectable (LAI) risperidone formulations.

Areas covered: Limited data is available on two formulations (RBP-7000 and in Situ Microparticle), but 20 TDM articles on the microsphere formulation were found. Risperidone TDM includes the serum concentrations of risperidone and its active metabolite, 9-hydroxyrisperidone, used for calculating: 1) the risperidone/9-hydroxyrisperidone (R/9-OH-R) ratio (a measure of CYP2D6; values >1 are indicative of a CYP2D6 poor metabolizer) and 2) the total risperidone concentration-to-dose (C/D) ratio (a measure of risperidone clearance with a normal value around 7 in oral risperidone). The weighted mean R/9-OH-R ratio was 0.48 (approximately twice that of oral risperidone TDM) in a combined analysis from 329 patients in 6 risperidone LAI studies without major confounders. The total C/D ratios from 297 patients in 6 risperidone LAI studies ranged from 7.4 to 9.7 ng/ml/mg/day with a weighted mean of 8.8 ng/ml/mg/day.

Expert commentary: Clinicians using TDM for risperidone LAI microsphere formulation need to: 1) consider steady state to be reached ≥ 6 weeks after the first injection, 2) pay attention to a) co-medications with inducers/inhibitors, b) severe inflammations/infections, and c) hepatic/renal impairment, and 3) use Castberg’s recommendation to calculate risperidone dosing.     

肺移植患者术后使用他克莫司1年CYP3A5、CYP3A4、ABCB1、POR~*28基因多态性与他克莫司个体化用药的关系研究

目的:研究肺移植患者术后使用他克莫司1年CYP3A5、CYP3A4、ABCB1、POR*28基因多态性与他克莫司给药剂量(D)和稳态血药浓度/给药剂量比值(c0/D)的关系。方法:采用回顾性分析方法,选取2017年5月-2018年5月期间在中日友好医院接受肺移植术的46例受试者为研究对象,统计受试者术后使用他克莫司1年后他克莫司的c0和D,并计算c0/D。收集受试者CYP3A5(rs776746)、CYP3A4(rs2242480、rs28371759)、ABCB1(rs1045642、rs2032582、rs1128503)和POR*28(rs1057868)位点的基因型,对基因多态性与D、c0/D的关系进行统计学分析。结果:本研究中涉及位点的基因型频率均符合Hardy-Weinberg平衡(P>0.05)。维持他克莫司c0在治疗窗范围内的条件下,受试者的CYP3A5(rs776746)和CYP3A4(rs2242480)基因型多态性对他克莫司的D、c0/D有显著影响(P<0.05);其他位点各基因型之间的D、c0/D差异均无统计学意义(P>0.05)。联合CYP3A5(rs776746)和CYP3A4(rs2242480)两个位点分析受试者CYP3A代谢型发现,同时携带CYP3A5(rs776746)*1和CYP3A4(rs2242480)*1G等位基因的快代谢型受试者与只携带CYP3A5(rs776746)*1或CYP3A4(rs2242480)*1G等位基因的正常代谢型受试者和不携带CYP3A5(rs776746)*1和CYP3A4(rs2242480)*1G等位基因的慢代谢受试者比较,D、c0/D差异具有统计学意义(P<0.05),其中快代谢型受试者的他克莫司D最高,慢代谢型受试者的他克莫司D最低。结论:检测CYP3A5(rs776746)和CYP3A4(rs2242480)基因多态性对肺移植患者术后使用他克莫司1年后他克莫司的个体化给药具有指导意义。     

细胞色素P4502D6基因多态性和药物相互作用

细胞色素P4502D6（CYP2D6）是一种重要的P450系氧化代谢酶,参与多种重要药物的代谢.CYP2D6具有基因多态性,对药物的代谢呈现明显的个体差异.而且CYP2D6能被多种药物竞争性抑制和诱导,药物联用时易产生相互作用.本文从CYP2D6的基因多态性与代谢表型、底物竞争作用、代谢酶的诱导和抑制等方面,探讨CYP2D6基因多态性与药物相互作用的关系.     

Potential role of CYP2D6 in the central nervous system

Abstract

1. Cytochrome P450 2D6 (CYP2D6) is a pivotal enzyme responsible for a major drug oxidation polymorphism in human populations. Distribution of CYP2D6 in brain and its role in serotonin metabolism suggest that CYP2D6 may have a function in the central nervous system.

2. To establish an efficient and accurate platform for the study of CYP2D6 in vivo, a human CYP2D6 (Tg-2D6) model was generated by transgenesis in wild-type (WT) C57BL/6 mice using a P1 phage artificial chromosome clone containing the complete human CYP2D locus, including the CYP2D6 gene and 5′- and 3′-flanking sequences.

3. Human CYP2D6 was expressed not only in the liver but also in the brain. The abundance of serotonin and 5-hydroxyindoleacetic acid in brain of Tg-2D6 is higher than in WT mice, either basal levels or after harmaline induction. Metabolomics of brain homogenate and cerebrospinal fluid revealed a significant up-regulation of L-carnitine, acetyl-L-carnitine, pantothenic acid, 2′-deoxycytidine diphosphate (dCDP), anandamide, N-acetylglucosaminylamine and a down-regulation of stearoyl-L-carnitine in Tg-2D6 mice compared with WT mice. Anxiety tests indicate Tg-2D6 mice have a higher capability to adapt to anxiety.

4. Overall, these findings indicate that the Tg-2D6 mouse model may serve as a valuable in vivo tool to determine CYP2D6-involved neurophysiological metabolism and function.     

A short-term high fat diet increases exposure to midazolam and omeprazole in healthy subjects

Objectives: Knowledge of factors contributing to variation in drug metabolism is of vital importance to optimize drug treatment. This study assesses the effects of a short-term hypercaloric high fat diet on metabolism of five oral drugs, which are each specific for a single P450 isoform: midazolam (CYP3A4), omeprazole (CYP2C19), metoprolol (CYP2D6), S-warfarin (CYP2C9) and caffeine (CYP1A2).

Methods: In 9 healthy volunteers, pharmacokinetics of the five drugs were assessed after an overnight fast at two separate occasions: after a regular diet and after 3 days of a hypercaloric high fat diet (i.e. regular diet supplemented with 500 mL cream [1715 kcal, 35% fat]). Pharmacokinetic parameters (mean [SEM]) were estimated by non-compartmental analysis.

Results: The high fat diet increased exposure to midazolam by 19% from 24.7 (2.6) to 29.5 (3.6) ng ml-1h-1 (p=0.04) and exposure to omeprazole by 31% from 726 (104) to 951 (168) ng ml-1h-1 (p=0.05). Exposure to metoprolol, caffeine and S-warfarin was not affected by the high fat diet.

Conclusion: A short-term hypercaloric high fat diet increases exposure to midazolam and omeprazole, possibly reflecting modulation of CYP3A4 and CYP2C19.     

Clomipramine, fluoxetine and CYP2D6 metabolic capacity in depressed patients

Cytochrome P450-2D6 may be involved in the metabolism of many drugs such as psychotropic drugs and its genetic polymorphism is responsible for inter-individual differences in the therapeutic effect and toxicity of these drugs. Moreover with the same genetic basis, CYP2D6 metabolic capacity variations are observed. Different factors of variation may be involved, among them the prescribed drugs. The aim of this study was to compare the influence of two types of antidepressants, tricyclic (clomipramine) and serotonergic specific recapture inhibitor (SSRI) (fluoxetine), on the CYP2D6 metabolic capacity of depressed inpatients. The CYP2D6 phenotype (dextromethorphan test) was determined in 56 genotyped (PCR-SSCP) depressed caucasian inpatients with a heterozygous genotype. Forty-five subjects were treated with clomipramine and eleven received fluoxetine. The dextromethorphan metabolic ratio (MR) median was significantly higher in the fluoxetine group (0.255) than in the clomipramine group (0.083, p < 0.014). In this study, fluoxetine involved a greater decrease of CYP2D6 metabolic capacity than clomipramine. Clinical implications and the possible connection between a decreased CYP2D6 activity and adverse drug effects were discussed. Caution should be taken when drugs with a low therapeutic index must be coprescribed in such patients.     

Evaluation of dextromethorphan metabolism using hepatocytes from CYP2D6 poor and extensive metabolizers

It is important to estimate the defective metabolism caused by genetic polymorphism of drug metabolizing enzymes before the clinical stage. We evaluated the utility of cryopreserved human hepatocytes of CYP2D6 poor metabolizer (PM) for the estimation of the metabolism in PM using dextromethorphan (DEX) as the probe drug for CYP2D6 substrate. The results of low formations of dextrorphan (DXO) and 3-hydroxymorphinan (3-HM) in CYP2D6 PM hepatocytes incubated with dextromethorphan reflected the clinical data. Formation of 3-methoxymorphinan (3-MEM) normalized by CYP3A4/5 activity in the PM hepatocytes reached about 2.8-fold higher than that in CYP2D6 extensive metabolizer (EM) hepatocytes, which clearly showed the compensatory metabolic pathway of O-demethylation catalyzed by CYP2D6 as seen in clinical study. On the contrary, in the condition of the EM hepatocytes with CYP2D6 inhibitors, the enhancement of 3-MEM formation was not observed. In phase II reaction, the glucuronide formation rate of DXO in the PM hepatocytes was lower than that in the EM hepatocytes, which was consistent with clinical data of DXO-glucuronide (DXO-glu) concentration. These results would suggest that CYP2D6 PM hepatocytes could be a good in vitro tool for estimating CYP2D6 PM pharmacokinetics.     

Significance of genetic polymorphism of CYP2D6 in the pathogenesis of systemic sclerosis

BackgroundSystemic sclerosis (SSc) belongs to the group of systemic diseases of the connective tissue, which are characterized by a chronic autoimmune inflammatory process. The studies on etiopathogenesis of autoimmune diseases focus on the impact the genetically conditioned impairment of xenobiotic metabolism may exert. The genetically polymorphic CYP2D6 is one of the most important phase I drug metabolizing enzymes. The knowledge of oxidation polymorphism in the course of SSc may be helpful in choosing more efficient and safer therapy, particularly in the case of a disease involving various organs and treated with drugs belonging to diverse therapeutic groups. The aim of the study was to evaluate the CYP2D6 polymorphism in the SSc patients and to investigate a possible correlation with disease susceptibility.MethodsThe study was carried out in 77 patients with SSc and 129 healthy volunteers. The CYP2D6 genotypes were analyzed by polymerase chain reaction fragment length polymorphism (PCR-RFLP) method.ResultsRisk of SSc development for particular genotype carriers expressed by the odds ratio (OR) was statistically significantly higher for subjects with CYP2D6*1/CYP2D6*4 (OR = 3.2; p = 0.001). A statistically significant correlation between the CYP2D6*4 allele prevalence and the risk for developing SSc was found (OR = 1.6; p = 0.029).ConclusionsThe obtained results may suggest the influence of CYP2D6*4 gene mutated alleles on increased incidence of systemic sclerosis.     

中国服用氯吡格雷冠心病患者CYP2C19基因多态性与血小板聚集抑制率相关性研究的系统评价

目的 系统评价服用氯吡格雷的中国冠心病患者其CYP2C19基因多态性与血栓弹力图（thromboelastography，TEG）检测的血小板聚集抑制率之间的相关性。方法 检索英文数据库PubMed、Embase、Cochrane图书馆和中文数据库中国知网（CNKI）、维普期刊资源整合服务平台（CQVIP）、万方数据知识服务平台、中国生物医学文献库（CBM），获得服用氯吡格雷且同时行CYP2C19基因多态性和TEG检测的中国冠心病患者资料。采用RevMan 5.3软件对患者CYP2C19基因多态性和TEG检测的血小板聚集抑制率及氯吡格雷抵抗率进行meta分析。结果 最终纳入25篇文献共计4 967例患者。Meta分析显示，快代谢型患者的血小板聚集抑制率显著高于中间代谢型[MD=9.17，95% CI（3.68，14.65），P=0.001]和弱代谢型[MD=20.63，95% CI（11.32，29.94），P<0.000 1]，且中间代谢型显著高于弱代谢型[MD=11.63，95% CI（5.60，17.67），P=0.000 2]。与此同时，快代谢型患者氯吡格雷抵抗的发生风险显著低于中间代谢型[RR=0.60，95% CI（0.53，0.67），P<0.000 01]和弱代谢型[RR=0.36，95% CI（0.28，0.47），P<0.000 01]，且中间代谢型显著低于弱代谢型[RR=0.59，95% CI（0.48，0.73），P<0.000 01]。结论 服用氯吡格雷的中国冠心病患者其CYP2C19基因多态性与TEG检测的血小板聚集抑制率之间存在明显的相关性，但临床在制定决策时仍应结合患者具体病情对其CYP2C19基因型和（或）血小板聚集抑制率做出正确解读。     

Genetic polymorphism of debrisoquine (CYP2D6) and proguanil (CYP2C19) in South Pacific Polynesian populations

Objective: Genetic oxidation polymorphisms of debrisoquine (CYP2D6) and proguanil (CYP2C19) were studied in unrelated healthy South Pacific Polynesian volunteers recruited in the South Island of New Zealand. Methods: Phenotyping for CYP2D6 and CYP2C19 activities was determined using debrisoquine and proguanil, respectively, as probe drugs by measuring the urinary metabolic ratio of parent drug and its␣metabolite. Results: Of 100 Polynesian subjects phenotyped, the metabolic ratio of debrisoquine ranged from 0.01 to 9.94. Therefore, all South Pacific Polynesians were classified as extensive metabolizers of debrisoquine according to previously established criteria of the antimode. The prevalence of poor metabolizers of debrisoquine (CYP2D6) in this Polynesian population is 0% (95% confidence interval of 0–3.6%). Oxidation polymorphism of CYP2C19 using proguanil as a probe was also studied in 59 Polynesian volunteers. The frequency distribution of the proguanil/cycloguanil ratio was bimodal. The proguanil/cycloguanil ratios for these subjects ranged from 0.09 to 34.4. Using a recommended proguanil/cycloguanil ratio cut-off point of 10 established in Caucasian populations, eight Polynesian subjects were identified as poor metabolizers of proguanil (CYP2C19), which corresponds to a poor metabolizer phenotype frequency of 13.6% (a 95% confidence interval of 5.9–24.6%). Conclusion: The incidence of poor metabolizer phenotypes for debrisoquine (CYP2D6) in South Pacific Polynesians appears to lower than in Caucasian populations, while the prevalence of poor metabolizers for proguanil (CYP2C19) in this ethnic population is higher. The frequencies of the poor metabolizer phenotype for debrisoquine and also for proguanil in South Pacific Polynesians are similar to those reported in Asian populations. Received: 18 December 1997 / Accepted in revised form: 30 April 1998     

Phenotype and genotype analysis of debrisoquine hydroxylase (CYP2D6) in a black Zimbabwean population Reduced enzyme activity and evaluation of metabolic correlation of CYP2D6 probe drugs

Objective: Debrisoquine hydroxylase (CYP2D6) is responsible for the oxidative metabolism of many clinically used drugs. Since this enzyme has been poorly studied in the southern part of Africa, we examined the CYP2D6 phenotypes and genotypes in 103 unrelated black Zimbabweans. Methods: Phenotyping for CYP2D6 activity was done using debrisoquine and metoprolol as probe drugs by measuring the urinary metabolic ratio (MR) of parent drug to metabolite concentration ratios. Genotyping was done using polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP), single-strand conformation polymorphism (SSCP) and sequencing analyses with respect to CYP2D6 variants of interest. Results and conclusion: Phenotyping with debrisoquine revealed two poor metabolisers (PMs), whereas 5 subjects out of 94 were PMs using metoprolol as probe drug. Genotypes predictive of the poor metaboliser status were observed for the two subjects who were PMs with both probe drugs, whereas no mutations could explain the PM phenotype for metoprolol among the three remaining subjects, a fact possibly explained by lack of compliance in metoprolol intake. There was a moderate correlation of 0.67 between the debrisoquine and metoprolol metabolic ratios in the 89 subjects who were extensive metabolisers for both probe drugs. The median values for the metabolic ratios for debrisoquine and metoprolol as probe drugs were 1.00 and 1.35, respectively, which are higher than those observed in Caucasian populations. This is indicative of a decreased capacity for metabolism of CYP2D6 substrates by Zimbabweans compared to Caucasians. Evaluation of the DNA samples for the known allelic variants CYP2D6A, CYP2D6B, CYP2D6C,CYP2D6D or CYP2D6Ch ₁ yielded no explanation for these results. Received: 4 February 1995/Accepted in revised form: 27 March 1996     

Impact of the <Emphasis Type="Italic">CYP2D6</Emphasis> polymorphism on steady-state plasma concentrations and clinical outcome of donepezil in Alzheimer’s disease patients

Objective The aims of this study were to evaluate the impact of the CYP2D6 polymorphism on both the steady-state plasma concentrations (Cp) and the clinical outcome of donepezil, a selective acetylcholinesterase inhibitor used in the treatment of Alzheimer’s disease (AD).Methods Forty-two patients of Caucasian ethnicity affected by probable AD were included in the study. All had been receiving therapy with donepezil for at least 3 months: 31 patients with 5 mg/day and 11 patients with 10 mg/day. The CYP2D6 genotype was analysed, and donepezil Cp was measured by using high-performance liquid chromatography.Results On the basis of their CYP2D6 genotype, 30 patients could be classified as homozygous extensive metabolizers (EM), 10 as heterozygous EM and 2 as ultrarapid metabolizers (UM). No poor metabolizer was found. The dose and body weight-corrected median donepezil Cp were slightly, though not significantly, lower in homozygous than in heterozygous EM (0.33 vs. 0.41 ng/ml/mg/kg, respectively). The latter group consistently showed a better clinical response to treatment, as measured by change in Mini-Mental State Examination score (median: 1.40 vs. −1.30, respectively). UM patients had lower Cp than EM patients and showed no clinical improvement.Conclusions Our preliminary data suggest that the CYP2D6 polymorphism influences both donepezil metabolism and therapeutic outcome and that a knowledge of a patient’s CYP2D6 genotype together with donepezil concentration measurements might be useful in the context of improving the clinical efficacy of donepezil therapy.     

文拉法辛与细胞色素P450酶的相关性研究进展

文拉法辛是具有5-HT和NE双重再摄取抑制作用的新型抗抑郁药,与文拉法辛代谢密切相关的2种酶是CYP3A4和CYP2D6。CYP2D6将其生物转化为主要的活性代谢产物——O-去甲基文拉法辛（ODV）,同时CYP3A4将文拉法辛转化为非活性代谢产物N-去甲基文拉法辛（NDV）。在常规治疗剂量下文拉法辛对于CYP3A4缺乏明显的诱导或抑制作用。而CYP2D6的活性直接影响文拉法辛和ODV的代谢和浓度,由于CYP2D6存在着基因遗传多态性,不同表型有着不同的文拉法辛代谢能力,而慢代谢者更易发生不良反应。研究证实文拉法辛与ODV的浓度比log（VENL／ODV）可作为异常代谢的指标,较简便地发现大多数异常基因型患者。