Frequencies of CYP2D6 mutant alleles in a normal Japanese population and metabolic activity of dextromethorphan O-demethylation in different CYP2D6 genotypes

Population differences in major functional polymorphisms of pharmacokinetics/pharmacodynamics-related genes in Eastern Asians and Europeans: implications in the clinical trials for novel drug development

Drug lag, recently discussed extensively in Japan, can be divided into two phases: clinical development time and application review time. The former factor is still an important problem that might be improved by promoting multi-regional clinical trials and considering the results from other similar populations with Japanese, such as Koreans and Chinese. In this review, we compare the allelic or genotype frequencies of 30 relatively common functional alleles mainly between Eastern Asians and Europeans as well as among 3 major populations in Eastern Asian countries, Japan, Korea, and China, in 12 pharmacokinetics (PK)/pharmacodynamics (PD)-related genes; CYP2C9 (*2 and *3), CYP2C19 (*2, *3 and *17), 13 CYP2D6 haplotypes including *4, *5 and *10, CYP3A5 (*3), UGT1A1 (*28 and *6), NAT2 (*5, *6 and *7), GSTM1 and GSTT1 null genotypes, SLCO1B1 521T>C, ABCG2 421C>A, and HLA-A*31:01 and HLA-B*58:01. In this review, differences in allele frequencies (AFs) or genotype frequencies (GFs) less than 0.1 (in the cases of highest AF (GF) ≥0.1) or less than 0.05 (in the cases of lowest AF (GF) <0.1) were regarded as similar. Between Eastern Asians and Europeans, AFs (or GFs) are regarded as being different for many alleles such as CYP2C9 (*2), CYP2C19 (*2, *3 and *17), CYP2D6 (*4 and *10), CYP3A5 (*3), UGT1A1 (*28 and *6), NAT2 (*5*7), GSTT1 null and ABCG2 421C>A. Among the 3 Eastern Asian populations, however, only AFs of CYP2C19*3, CYP2D6*10, HLA-A*31:01 and HLA-B*58:01 are regarded as dissimilar. For CYP2C19*3, the total functional impact on CYP2C19 could be small if the frequencies of the two null alleles CYP2C19*2 and *3 are combined. Regarding CYP2D6*10, frequency difference over 0.1 is observed only between Japanese and Chinese (0.147). Although environmental factors should be considered for PK/PD differences, we could propose that among Japan, Korea, and China, genetic differences are very small for the analyzed common PK-related gene polymorphisms. On the other hand, AFs of the two HLA alleles important for cutaneous adverse drug reactions are diverse even among Eastern Asians and thus should be taken into account.

Frequencies of three CYP2D6 nonfunctional alleles (CYP2D6*3, *4, and *6) within an Iranian population (Mazandaran)

Although the frequencies of CYP2D6 nonfunctional alleles have been extensively studied in most populations worldwide, limited information is available for those of the Iranian population. The present study aimed to determine the frequency of three CYP2D6 nonfunctional alleles (CYP2D6*3, *4, and *6) in the Mazandarani ethnic group among the Iranian population. A total of 100 unrelated healthy subjects living in Mazandaran, a Caspian province in the north of Iran, were selected. Lymphocytic genomic DNA was genotyped by a polymerase chain reaction amplification method for detection of three nonfunctional alleles. Finally, the obtained data were used to determine the frequencies of the three alleles, and the results were compared with published data from other populations. The frequencies for CYP2D6 alleles *3, *4, and *6 were 0.5%, 9%, and 0.5%, respectively. Homozygous or compound heterozygous genotypes that predict poor metabolizer phenotype, that is, *4/*4 or *4/*6, were not found in this study. The result of the present study showed that CYP2D6*4 is the major nonfunctional allele found in Mazandarani subjects. In addition, the three inactive alleles of CYP2D6 accounted for 10% of CYP2D6 alleles in our sample versus 0.2%-25.2% reported in other populations. The frequencies of the studied alleles resulted in significant differences between our sample and East Asians, Black-Tanzanians, Saudi Arabians, and Caucasians.

Breast cancer: a neglected disease for the majority of affected women worldwide

Recent progress with declines in mortality in some high-income countries has obscured the fact that for the majority of women worldwide who are newly diagnosed, breast cancer is a neglected disease in the context of other numerically more frequent health problems. For this growing majority, it is also an orphan disease, in that detailed knowledge about tumor characteristics and relevant host biology necessary to provide even basic care is absent. With the possible exception of nutritional recommendations, current international cancer policy and planning initiatives are irrelevant to breast cancer. The progress that has occurred in high-income countries has come at extraordinary fiscal expense and patient toxicity, which of themselves suggest nonrelevance to women and healthcare practitioners in middle- and low-income countries. The implications of these circumstances appear clear: if the promise of the now 60-year-old Declaration of Human Rights that the fruits of medical science accrue to all mankind is to be realized with respect to breast cancer, a basic and translational global research initiative should be launched.

Copy number variants in pharmacogenetic genes

Variation in drug efficacy and toxicity remains an important clinical concern. Presently, single nucleotide polymorphisms (SNPs) only explain a portion of this problem, even in situations where the pharmacological trait is clearly heritable. The Human CNV Project identified copy number variations (CNVs) across approximately 12% of the human genome, and these CNVs were considered causes of diseases. Although the contribution of CNVs to the pathogenesis of many common diseases is questionable, CNVs play a clear role in drug-related genes by altering drug metabolizing and drug response. In this review, we provide a comprehensive evaluation of the clinical relevance of CNVs to drug efficacy, toxicity, and disease prevalence in world populations, and discuss the implication of using CNVs as a diagnostic tool in clinical intervention.

Genetics of tardive dyskinesia

Tardive dyskinesia (TD) is one of the most serious adverse side effects of antipsychotic drugs and is an important topic of pharmacogenetic studies. Since there is a genetic susceptibility for developing this adverse reaction, and given that it is hard to predict its development prior to or during the early period of medication, the genetic study of TD is a promising research topic that has a direct clinical application. Moreover, such studies would improve our understanding of the genetic mechanism(s) underlying abnormal dyskinetic movement. A substantial number of case-control association studies of TD have been performed, with numbers of studies focusing on the genes involved in antipsychotic drug metabolism, such as those for cytochrome P450 (CYP) and oxidative stress related genes as well as various neurotransmitter related genes. These studies have produced relatively consistent though controversial findings for certain polymorphisms such as CYP2D6*10, DRD2 Taq1A, DRD3 Ser9Gly, HTR2A T102C, and MnSOD Ala9Val. Moreover, the application of the genome-wide association study (GWAS) to the susceptibility of TD has revealed certain associated genes that previously were never considered to be associated with TD, such as the rs7669317 on 4q24, GLI2 gene, GABA pathway genes, and HSPG2 gene. Although a substantial number of genetic studies have investigated TD, many of the positive findings have not been replicated or are inconsistent, which could be due to differences in study design, sample size, and/or subject ethnicity. We expect that more refined research will be performed in the future to resolve these issues, which will then enable the genetic prediction of TD and clinical application thereof.

Metabolic capacity of CYP2D6 within an Iranian population (Mazandaran Province)

BACKGROUND

CYP2D6 is polymorphically expressed enzyme that show marked interindividual and interethnic variation. Phenotyping of CYP2D6 provides valuable information about real-time activity of this important drug-metabolizing enzymes through the use of specific probe drugs. The aim of this study was to identify the CYP2D6 oxidation phenotype with dextromethorphan (DEX) as a probe drug in Mazandarani ethnic group among Iranian population.

METHODS

The study included 71 unrelated healthy volunteers. Dextromethorphan hydrobromide (30 mg) was given orally to healthy subjects and peripheral venous blood samples (10 ml) were taken at 3 hr post-dose. Dextromethorphan and the metabolite dextrorphan (DOR) were analyzed by the HPLC method. The log DEX/DOR metabolic ratio (MR) at 3 hr plasma sample was used as the index of CYP2D6 activity and a value of 0.3 was used as the antimode separating extensive metabolizers (EM) and poor metabolizers (PM) phenotypes.

RESULTS

A 560-fold interindividual variation in dextromethorphan MRs was observed in this study. Considering the antimode 0.3 in log scale, 7.04% (5/71) volunteers were identified as PMs. Conclusion : The result showed that the frequency of CYP2D6 PM phenotypes accounted for 7.04% of subjects in our samples. Despite these findings, we propose a further study in larger samples to provide a wider image and to get more valuable information upon pharmacogenetic basis for individual therapy and personalized medicine.

Effects of cigarette smoking and cytochrome P450 2D6 genotype on fluvoxamine concentration in plasma of Japanese patients

Fluvoxamine is a selective serotonin reuptake inhibitor widely used in the treatment of depression and other psychiatric diseases. The aim of this study was to assess the clinical impact of cigarette smoking on plasma fluvoxamine concentration in Japanese patients, and evaluate whether the cytochrome P450 (CYP) 1A2 and CYP2D6 genotypes have effects on that concentration. Thirty-two Japanese patients receiving fluvoxamine were enrolled. They were maintained on the same daily dose of fluvoxamine (mean + or - S.D., 109.4 + or - 66.2 mg/d) for at least 4 weeks to obtain the steady-state plasma concentration. The steady-state plasma concentration-to-dose (C/D) ratio of fluvoxamine in patients who smoked (n = 6, 11.8 + or - 6.5 ng/ml/dose) was significantly lower than that in non-smoker patients (n = 26, 22.8 + or - 11.2 ng/ml/dose). There was no significant difference for the C/D ratio of fluvoxamine in patients with CYP1A2 -3860G/G, -3860G/A, and -3860A/A between non-smokers and smokers. Among non-smoker patients, the C/D ratios of fluvoxamine in those with one and two mutated alleles of CYP2D6 were 1.6- and 1.4-fold higher, respectively, than those with no mutated alleles, though the differences among those three genotype groups were not significant. Furthermore, stepwise multiple regression analysis revealed that cigarette smoking and daily dose had significant positive correlations with the plasma concentration of fluvoxamine. Our findings suggest that cigarette smoking has a significant impact on the steady-state plasma concentration of fluvoxamine in Japanese patients.

Genetic polymorphisms of cytochrome P450 enzymes influence metabolism of the antidepressant escitalopram and treatment response

AIMS

The antidepressant escitalopram (S-CIT) is metabolized by the cytochrome-P450 (CYP) enzymes CYP 2D6, 2C19 and 3A4. This study evaluated the impact of CYP2D6, 2C19 and 3A4 genetic polymorphisms on plasma concentrations of S-CIT and patient treatment response.

MATERIALS & METHODS

A total of 100 patients diagnosed with major depressive disorder were recruited to the study and their depression symptoms were assessed using the Hamilton Depression Rating Scale. The genetic polymorphisms *4, *5 and *10 on CYP2D6, *2, *3 and *17 on CYP2C19, and *18 on CYP3A4 were selected based on their function and respective allele frequencies in Asian populations. Polymorphisms were analyzed using the SNPstream genotyping system, PCR and direct sequencing methods. The steady-state serum concentrations of S-CIT and its metabolites S-desmethylcitalopram and S-didesmethylcitalopram were analyzed by HPLC. According to semiquantitative gene dose (SGD) and gene dose (GD) models for allele combinations of these polymorphisms, CYP2D6 was clustered into intermediate (0.5, 1 and 1.5 SGD) and extensive (2 SGD) metabolizers, while CYP2C19 was clustered into poor (0 GD) and extensive (1 and 2 GDs) metabolizers.

RESULTS

The group of patients with intermediate CYP2D6 metabolism (0.5 SGD) had a significantly higher frequency of remitters from major depressive disorder during the 8-week treatment (p = 0.0001). Furthermore, CYP2C19 poor metabolizers had significantly higher S-CIT serum levels than did extensive metabolizers at weeks 2, 4 and 8 (p < 0.05). The allele frequencies in CYP3A4*18 and CYP2C19*17 were too low to permit further subgroup analyses.

CONCLUSION

Our results suggest that the genetic polymorphisms in CYP2C19 may be influencing S-CIT serum concentrations, and that specific CYP2D6 polymorphisms may be predicting patient treatment outcomes based on gene dosage analyses.

Pharmacokinetic and pharmacodynamic interactions between carbamazepine and aripiprazole in patients with schizophrenia

Pharmacokinetic and pharmacodynamic interactions between carbamazepine and aripiprazole were studied in 18 inpatients with schizophrenia being treated with aripiprazole. The daily dose of aripiprazole was 24 mg in 15 cases and 12 mg in 3 cases. Carbamazepine 400 mg/d was coadministered for 1 week, and blood samples were taken twice before the start of carbamazepine coadministration and then 1 week after completion. In addition, on these days, the severity of illness and side effects were evaluated using the Positive and Negative Syndrome Scale and the Udvalg for Kliniske Undersøgelser side effects rating scale, respectively. Plasma concentrations of aripiprazole and dehydroaripiprazole were measured using liquid chromatography with mass spectrometric detection. Carbamazepine significantly decreased both plasma concentrations of aripiprazole and dehydroaripiprazole by 64% and 68%, respectively (P < 0.001). Despite these decreases in plasma concentrations, the total and negative scores in Positive and Negative Syndrome Scale, together with the neurological score in Udvalg for Kliniske Undersøgelser, decreased slightly but significantly (P < 0.05) after carbamazepine coadministration. The present study implies that carbamazepine augmentation may be effective for patients with schizophrenia treated with aripiprazole, although carbamazepine dramatically decreases plasma concentrations of aripiprazole and dehydroaripiprazole, by inducing the metabolism of these compounds.

Frequency of five important CYP2D6 alleles within an Iranian population (Eastern Azerbaijan)

Polymorphisms in cytochrome P450 genes encoding enzymes of critical importance for drug metabolism have the highest genetic influence on interindividual variations in drug bioavailability. Human CYP2D6 enzyme is claimed to be polymorphically expressed among different ethnic groups. It has been suggested to account for a large part of the interindividual differences in drug metabolism and pharmacokinetics. In the current investigation, 100 healthy unrelated subjects living in Tabriz, Iran, were randomly selected. Genotyping was designed to determine the frequencies of five major and important alleles: CYP2D6*2, CYP2D6*4, CYP2D6*5, CYP2D6*10, and CYP2D6*17. After collecting venous blood samples, polymerase chain reaction-restriction fragment length polymorphism methodology was performed for detection of the alleles (except CYP2D6*5, which has been detected using an allele-specific polymerase chain reaction procedure). Finally, the obtained data were used to determine the allele frequencies. The frequencies for CYP2D6 alleles *2, *4, *5, and *10 were 32%, 12.5%, 3%, and 9%, respectively. CYP2D6*17 was completely absent in this study group. Poor metabolizer phenotype can be related to *4/*4 and *4/*5 genotypes with a total frequency of 4%. This is the first study of the CYP2D6 genetic polymorphism in an Iranian population. The frequencies of the studied alleles resulted in degrees of differences between this population and Orientals, Saudi Arabians, and Caucasians, while similarities to the reported results obtained from the studies among Mediterraneans and South Indians are noticeable.

New insights into the structural characteristics and functional relevance of the human cytochrome P450 2D6 enzyme

To date, the crystal structures of at least 12 human CYPs (1A2, 2A6, 2A13, 2C8, 2C9, 2D6, 2E1, 2R1, 3A4, 7A1, 8A1, and 46A1) have been determined. CYP2D6 accounts for only a small percentage of all hepatic CYPs (< 2%), but it metabolizes approximately 25% of clinically used drugs with significant polymorphisms. CYP2D6 also metabolizes procarcinogens and neurotoxins, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1,2,3,4-tetrahydroquinoline, and indolealkylamines. Moreover, the enzyme utilizes hydroxytryptamines and neurosteroids as endogenous substrates. Typical CYP2D6 substrates are usually lipophilic bases with an aromatic ring and a nitrogen atom, which can be protonated at physiological pH. Substrate binding is generally followed by oxidation (5-7 A) from the proposed nitrogen-Asp301 interaction. A number of homology models have been constructed to explore the structural features of CYP2D6, while antibody studies also provide useful structural information. Site-directed mutagenesis studies have demonstrated that Glu216, Asp301, Phe120, Phe481, and Phe483 play important roles in determining the binding of ligands to CYP2D6. The structure of human CYP2D6 has been recently determined and shows the characteristic CYP fold observed for other members of the CYP superfamily. The lengths and orientations of the individual secondary structural elements in the CYP2D6 structure are similar to those seen in other human CYP2 members, such as CYP2C9 and 2C8. The 2D6 structure has a well-defined active-site cavity located above the heme group with a volume of approximately 540 A(3), which is larger than equivalent cavities in CYP2A6 (260 A(3)), 1A2 (375 A(3)), and 2E1 (190 A(3)), but smaller than those in CYP3A4 (1385 A(3)) and 2C8 (1438 A(3)). Further studies are required to delineate the molecular mechanisms involved in CYP2D6 ligand interactions and their implications for drug development and clinical practice.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Opioid rotation: the science and the limitations of the equianalgesic dose table

Opioid rotation refers to a switch from one opioid to another in an effort to improve the response to analgesic therapy or reduce adverse effects. It is a common method to address the problem of poor opioid responsiveness despite optimal dose titration. Guidelines for opioid rotation are empirical and begin with the selection of a safe and reasonably effective starting dose for the new opioid, followed by dose adjustment to optimize the balance between analgesia and side effects. The selection of a starting dose must be based on an estimate of the relative potency between the existing opioid and the new one. Potency, which is defined as the dose required to produce a given effect, differs widely among opioids, and among individuals under varying conditions. To effectively rotate from one opioid to another, the new opioid must be started at a dose that will cause neither toxicity nor abstinence, and will be sufficiently efficacious in that pain is no worse than before the change. The estimate of relative potency used in calculating this starting dose has been codified on "equianalgesic dose tables," which historically have been based on the best science available and have been used with little modification for more than 40 years. These tables, and the clinical protocols used to apply them to opioid rotation, may need revision, however, as the science underlying relative potency evolves. Review of these issues informs the use of opioid rotation in the clinical setting and defines key areas for future research.

Effect of smoking and CYP2D6 polymorphisms on the extent of fluvoxamine-alprazolam interaction in patients with psychosomatic disease

PURPOSE

Fluvoxamine (FVX) is metabolized by cytochrome P450 (CYP) 2D6 and CYP1A2 and inhibits CYP3A4. The aim of this study was to investigate the factors responsible for interindividual variability in the extent of interaction between FVX and alprazolam (ALP).

METHODS

Blood samples were taken from 49 depressive patients to determine plasma concentration of FVX, ALP or both. Twenty-four samples were taken during the FVX-alone period, 21 samples during the ALP-alone period and 30 samples during the FVX-ALP period. Subjects were also genotyped for CYP2D6.

RESULTS

The concentration-to-dose (C/D) ratio of ALP during the FVX-treatment period was significantly higher than that during the ALP-alone period. The CYP2D6 genotype affected neither the C/D ratios of FVX nor the extent of interaction. The mean C/D ratio of FVX in smokers was reduced by more than 30% in comparison with that in non-smokers. The mean C/D ratio of ALP in non-smokers was increased by FVX, while that in smokers was unchanged.

CONCLUSIONS

The extent of interaction between FVX and ALP may be affected by smoking, which alters the C/D ratio of FVX. Therefore, when FVX and ALP are concomitantly administered, it should be noted that non-smokers may exhibit greater drug interaction than smokers.

Impact of CYP2D6 polymorphisms in tamoxifen adjuvant breast cancer treatment

The aim of this study is to evaluate the impact of CYP2D6 genotyping in predicting disease-free survival and toxicity in breast cancer patients treated with adjuvant tamoxifen. DNA from 91 patients was genotyped using the AmpliChip CYP450 GeneChip, Roche that facilitates the classification of individuals by testing 27 alleles. When patients were grouped into group 1 (*4/*4, *4/*41, *1/*5 and *2/*5) and group 2 (the remaining genotypes), a significant difference in disease-free survival (DFS) was observed between groups (P = 0.016). The mean DFS in group 1 was 95 months in contrast with 119 months in group 2. No significant relationship was found between the CYP2D6 genotype classification and severe, mild or no toxicity (P = 0.2). Nevertheless, severe, and mild toxicity was more frequent among poor metabolizer patients than in patients with a normal metabolizer pattern (18.8 and 43.8% vs. 10.7 and 36%, respectively). In breast cancer, patients treated with adjuvant tamoxifen, non-functional and severely impaired CYP2D6 variants are associated with a worse DFS and with a higher frequency of severe and mild toxicities. Larger studies of the CYP2D6 genotype-clinical outcomes association are needed to complement initial results.

Genetic polymorphism in cytochrome P450 2D6 (CYP2D6): Population distribution of CYP2D6 activity

Cytochrome P-450 2D6 (CYP2D6) is involved in the metabolism of many therapeutic drugs even though the enzyme represents a small proportion of the total CYP content of human liver. In vivo phenotyping with probe drug substrates such as debrisoquine and dextromethorphan showed a clear separation between poor metabolizers (PM) and extensive metabolizers (EM). This polymorphism may affect susceptibility to environmental disease, as suggested by molecular epidemiologic studies that found an association between CYP2D6 metabolizer phenotype and cancer risk; however, this association is not consistent. There are only a few examples of CYP2D6 involvement in toxicant mechanism of action, but this has not been extensively studied. Gene probe studies documented a number of genetic polymorphisms that underlie CYP2D6 metabolizer phenotypes. The EM group carries the wild-type (*1) or active (*2) variant alleles, while the PM group carries the *3, *4, *5, or *6 alleles, all of which code for a protein that has lower or null CYP2D6 activity. The current analysis characterizes (a) influence of genotype on phenotype based upon in vivo metabolism studies of probe drugs and (b) frequency of the major genotypes in different population groups is also characterized. These data were then incorporated into Monte Carlo modeling to simulate population distributions of CYP2D6 activity. This analysis reproduced the bimodal distributions commonly seen in phenotyping studies of Caucasians and found extensive population variability in enzyme activity, as indicated by the 9- to 56-fold difference between the PM modal median and the total population median CYP2D6 activity. This substantial degree of interindividual variability in CYP function indicates that assessments involving CYP2D6 substrates need to consider the full distribution of enzyme activity in refining estimates of internal dose in health assessments of xenobiotics.

Chronic heart failure in Japan: implications of the CHART studies

The prognosis of patients with chronic heart failure (CHF) still remains poor, despite the recent advances in medical and surgical treatment. Furthermore, CHF is a major public health problem in most industrialized countries where the elderly population is rapidly increasing. Although the prevalence and mortality of CHF used to be relatively low in Japan, the disorder has been markedly increasing due to the rapid aging of the society and the Westernization of lifestyle that facilitates the development of coronary artery disease. The Chronic Heart Failure Analysis and Registry in the Tohoku District (CHART)-1 study was one of the largest cohorts in Japan. The study has clarified the characteristics and prognosis of Japanese patients with CHF, demonstrating that their prognosis was similarly poor compared with those in Western countries. However, we still need evidence for the prevention and treatment of CHF based on the large cohort studies or randomized treatment trials in the Japanese population. Since the strategy for CHF management is now changing from treatment to prevention, a larger-size prospective cohort, called the CHART-2 study, has been initiated to evaluate the risk factors of CHF in Japan. This review summarizes the current status of CHF studies in Japan and discusses their future perspectives.

Systematic polymorphism analysis of the CYP2D6 gene in four different geographical Han populations in mainland China

In this study, we systematically screened the polymorphisms of the whole CYP2D6 gene in the populations of four different geographical locations in China, namely, Shanghai, Shantou, Shenyang, and Xi'an, using a sample of 100 subjects from each population. Forty-eight different polymorphisms were detected as well as 12 novel ones. One novel nonsynonymous SNP was detected, and one novel intronic SNP was revealed that might inactivate a cryptic donor site 392 nucleotides downstream of the exon 6 natural donor site. In addition, the frequencies of some polymorphisms and alleles demonstrated significant differences among the four populations. Linkage disequilibrium analysis and tag SNP selection were performed separately for each population. Haplotypes were analyzed within the selected tag SNPs. Tag SNP selection and haplotype distributions showed differences across the four populations. This is the first large-scale study to analyze polymorphisms systematically across the whole CYP2D6 gene in the Chinese Han population.

Impact of CYP2D6*10 on recurrence-free survival in breast cancer patients receiving adjuvant tamoxifen therapy

The clinical outcomes of breast cancer patients treated with tamoxifen may be influenced by the activity of cytochrome P450 2D6 (CYP2D6) enzyme because tamixifen is metabolized by CYP2D6 to its active forms of antiestrogenic metabolite, 4-hydroxytamoxifen and endoxifen. We investigated the predictive value of the CYP2D6*10 allele, which decreased CYP2D6 activity, for clinical outcomes of patients that received adjuvant tamoxifen monotherapy after surgical operation on breast cancer. Among 67 patients examined, those homozygous for the CYP2D6*10 alleles revealed a significantly higher incidence of recurrence within 10 years after the operation (P = 0.0057; odds ratio, 16.63; 95% confidence interval, 1.75-158.12), compared with those homozygous for the wild-type CYP2D6*1 alleles. The elevated risk of recurrence seemed to be dependent on the number of CYP2D6*10 alleles (P = 0.0031 for trend). Cox proportional hazard analysis demonstrated that the CYP2D6 genotype and tumor size were independent factors affecting recurrence-free survival. Patients with the CYP2D6*10/*10 genotype showed a significantly shorter recurrence-free survival period (P = 0.036; adjusted hazard ratio, 10.04; 95% confidence interval, 1.17-86.27) compared to patients with CYP2D6*1/*1 after adjustment of other prognosis factors. The present study suggests that the CYP2D6 genotype should be considered when selecting adjuvant hormonal therapy for breast cancer patients.

Reduced CYP2D6 activity is a negative risk factor for methamphetamine dependence

Because methamphetamine (METH) is metabolized by CYP2D6 at the first step of hydroxylation and demethylation, it is possible that functional variants of CYP2D6 alter susceptibility to methamphetamine-induced dependence. We genotyped CYP2D6*1, *4, *5, *10, and *14 for 202 patients with METH dependence and 337 controls in a Japanese population and found a significant association of the CYP2D6 gene with METH dependence (p=0.0299). The patients had fewer *10 and *14 alleles, which are hypofunction alleles, than the controls. CYP2D6 genotypes were divided into three phenotypes: extensive metabolizers, intermediate metabolizers, and poor metabolizers. There was no poor metabolizer among our Japanese subjects, and intermediate metabolizers of CYP2D6 were significantly fewer in methamphetamine-dependent subjects than in controls (p=0.0212), with an odds ratio of 0.62 (95% confidence interval: 0.51-0.76). The present study demonstrated that reduced CYP2D6 activity was a negative risk factor for methamphetamine dependence.

Effectiveness of in silico tagSNP selection methods: virtual analysis of the genotypes of pharmacogenetic genes

INTRODUCTION

SNP tagging has been recently introduced, and the use of this strategy reduces the dimension of disease association studies and eventually saves on genotyping costs. There is no single set of tagging SNPs (tagSNPs) that will satisfy every association study design; thus, many different methods have been introduced. We evaluated various tagSNP selection methods using known haplotype data of pharmacogenetic genes. We also compared the selected tagSNPs among different ethnic groups.

METHODS

We collected genotype data for the NAT2 and CYP2D6 genes from the previously published literature where the linkage phase was resolved directly through molecular haplotyping. Three computational tagSNP selection methods (ldSelect, Tagger and TagIT software) were evaluated with these data sets.

RESULTS

Tagging effectiveness and efficiency were variable in all three tagSNP selection methods. No tagSNP sets were identical among the different ethnic groups. The haplotype r(2)-based method was more effective in determining genotype-phenotype correlation than the other methods employed.

CONCLUSION

All of the three computational tagSNP selection methods showed acceptable efficiency and effectiveness. The selected tagSNPs were different from each other among the different ethnic groups.

Effects of CYP2D6 polymorphisms on neuroleptic malignant syndrome

OBJECTIVE

Neuroleptic malignant syndrome (NMS) is one of the most serious adverse reactions to antipsychotic medications. We accumulated data on Japanese NMS patients and, in a study designed to examine the effects of drug metabolism on the occurrence of NMS, tested the possibility of association between NMS and CYP2D6 polymorphisms.

METHODS

We studied 53 patients who had experienced NMS and 112 healthy individuals. We determined what drugs the patients with NMS had been given and retrospectively identified candidates for drugs causing NMS. We screened the prevalence of CYP2D6 genotypes using polymerase chain reaction and restriction fragment length polymorphism analyses.

RESULTS

The prevalence of *5 alleles in the group of all patients with NMS was higher than that in the controls, though this difference was not statistically significant (10.4% vs. 5.4%; P = 0.107; odds ratio (OR) 2.05; 95% confidence interval (CI) 0.87-4.80). No association was found between the frequency of *10 alleles and the occurrence of NMS. We found *4 and duplicated alleles in only one patient each among the patients with NMS. A total of 29 patients appeared to have developed NMS as a result of having taking CYP2D6 substrates. The prevalence of *5 alleles in these 29 patient was significantly higher than that in the controls (15.5% vs. 5.4%; P = 0.020; OR 3.25; 95% CI 1.30-8.13).

CONCLUSION

Our findings suggest that the CYP2D6*5 allele is likely to affect vulnerability to development of NMS.

The effect of Shoseiryuto, a traditional Japanese medicine, on cytochrome P450s, N-acetyltransferase 2 and xanthine oxidase, in extensive or intermediate metabolizers of CYP2D6

OBJECTIVE

Shoseiryuto (TJ-19) contains eight herbal components, including Ephedra sinica, and has been used for treating asthma and allergic rhinitis in Asian countries for several centuries. In this study, we investigated the potential herb-drug interaction of TJ-19 in healthy volunteers and attempted to ascertain whether or not the interaction might be affected by the cytochrome P450 (CYP) 2D6 genotype.

METHODS

We assessed the effect of TJ-19 on the activities of CYP1A2, CYP2D6, CYP3A, xanthine oxidase (XO), and N-acetyltransferase 2 (NAT2) in 37 healthy subjects. The subject pool consisted of 19 extensive metabolizers (EMs) with CYP2D6*Wild/*Wild, and 18 intermediate metabolizers (IMs) with CYP2D6*10/*10. The baseline activities of five enzymes were ascertained by their respective urinary metabolic ratios from an 8-h urine sample, after an oral 150-mg and 30-mg dose of caffeine and dextromethorphan were administrated, respectively. Thereafter, the subjects received 4.5 g of TJ-19 twice daily for 7 days, and underwent the same phenotyping test on postdose day 7.

RESULTS

The activities of all enzymes examined did not differ before or after the 7-day administration of TJ-19. Consequently, the influence of the CYP2D6 genotype on the herb-drug interaction remained unsolved.

CONCLUSION

Our results indicate that TJ-19 at the generally recommended dosage is unlikely to cause pharmacokinetic interaction with co-administered medications primarily dependent on the CYP1A2, CYP2D6, CYP3A, XO, and NAT2 pathways for elimination.

Frequency of CYP2D6*10 and *14 alleles and their influence on the metabolic activity of CYP2D6 in a healthy Chinese population

To study the frequency of CYP2D6(*)10 and (*)14 alleles in a healthy Chinese population, and the influence of these two alleles on the metabolic activity of CYP2D6. CYP2D6(*)10 and (*)14 genotypes of 295 healthy Chinese subjects were determined using a tetra-primer method and allele-specific amplification. CYP2D6 phenotypes of 131 subjects were determined using dextramethorphan as probe drug. There were 10 subjects with a (*)14 allele, including one homozygous for (*)14. The gene frequency of (*)10 and (*)14 alleles were 55.8 and 1.8%, respectively. The metabolic ratio (MR) of dextramethorphan in 131 subjects was 0.032+/-0.106. The MR of (*)1/(*)1, (*)1/(*)10, (*)10/(*)10, (*)1/(*)14, (*)10/(*)14, and (*)14/(*)14 groups were 0.007+/-0.012, 0.009+/-0.010, 0.042+/-0.029, 0.093, 0.11, and 1.186, respectively. The MR of subjects with (*)14 allele was higher than those of (*)1/(*)1, (*)1/(*)10, or (*)10/(*)10 groups (P<0.001). The CYP2D6(*)10 and (*)14 alleles have substantial impact on the metabolic activity of CYP2D6, and the CYP2D6(*)14 allele may be the cause of the poor metabolizer phenotype in Chinese subjects.

Identifying drugs needing pharmacogenetic monitoring in a Korean hospital

PURPOSE

A decision matrix for identifying drugs for which pharmacogenetic drug monitoring (PDM) provides the greatest benefit in a Korean setting is described.

SUMMARY

We developed a decision matrix including the ethnic frequency of clinically relevant polymorphic cytochrome P-450 (CYP) enzymes, and the metabolic profiles and adverse drug reactions of drugs. Using the developed decision matrix based on the population allele frequencies of CYP enzymes, we identified potential candidates for PDM among the most commonly used drugs at Seoul National University Hospital (SNUH). Collectively, 17 of these drugs were largely metabolized by at least one polymorphic CYP enzyme. Pharmacogenetic information was used to identify CYP2C9, CYP2C19, and CYP2D6 as the major CYP enzymes of clinical importance for pharmacologic effect and safety in Koreans. The frequencies of poor and intermediate metabolizers among Koreans were 0% and 2.3-12% for CYP2C9, 12% and 42% for CYP2C19, and 0.44% and 28% for CYP2D6, respectively. The frequency of ultrarapid metabolizers of CYP2D6 was 2.28%. The decision matrix and pharmacogenetic information were used to identify seven drugs for PDM: warfarin, glimepiride, diazepam, amitriptyline, nortriptyline, codeine, and oxycodone. This approach can be applied to other institutional hospitals or other ethnic populations and would be helpful for advancing pharmacy practice. Further work is required to assess the practical and potential clinical relevance of pharmacogenetic variations on drugs of interest before the implementation of PDM.

CONCLUSION

A decision matrix helped identify drugs for which PDM provides the greatest potential benefit at one Korean hospital.

Impact of CYP2D6*10 on H1-antihistamine-induced hypersomnia

OBJECTIVE

This study investigated the relevance of the cytochrome P450 (CYP) 2D6 genotype to the adverse drug reactions (ADRs) of H1-antihistamines and the level of sedation.

METHODS

Japanese participants in a health screening program were asked to describe any past history of ADRs. Any subjects reporting ADRs induced by H1-antihistamines were then individually interviewed and defined as cases. Excessive daytime sleepiness, which had occurred in the cases as an H1-antihistamine-induced ADR, was assessed by the Epworth sleepiness scale (ESS), and an ESS score >or=12 was considered hypersomnia. CYP2D6*4, *5, *14, and *10 were genotyped by a panel of polymerase chain reaction techniques.

RESULTS

Out of 2,074 participants, 100 cases (M:F = 37:63, mean age 51.9 +/- 9.2 years) were eligible for analysis. The most common etiological drug was chlorpheniramine, which is the most frequently used H1-antihistamine in Japan. CYP2D6*10 allele and genotypes were more frequently found in the cases than in the healthy Japanese population in a large study (P < 0.005 and P = 0.039, respectively), but no difference was observed in the null alleles and genotypes. The ESS scores in 75 cases (M:F=25:50) who had experienced excessive daytime sleepiness were 9.5 +/- 5.5 in men and 12.9 +/- 6.1 in women (P < 0.001, cases vs. 34 subjects without symptoms; P = 0.001 men vs. women). The occurrence of hypersomnia increased as the number of CYP2D6 mutant alleles increased (P = 0.045).

CONCLUSION

The results suggest that the presence of the CYP2D6*10 allele is a risk factor for development of H1-antihistamine-induced ADRs in Japanese.

CYP2D6 genetic polymorphism in South Indian populations

This study aimed to determine the prevalence of genetic polymorphism in the CYP2D6 gene, which codes for the polymorphically expressed CYP2D6 drug-metabolizing enzyme. The common variants CYP2D6 *2, *3, *4, *5, *10, *14, and *17 were studied in the populations (n=447) of the four South Indian states namely Tamilnadu (TN), Kerala (Ker), Karnataka (Kar) and Andhra Pradesh (AP). Genetic polymorphisms were identified using polymerase chain reaction (PCR) and PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) based methods. Differences in frequencies of CYP2D6 polymorphism between each South Indian state were statistically compared, and also the frequency of South Indian population as a whole in relation to other major populations. The CYP2D6*2 allele was the most frequent variant (34.8%), followed by the *10 allele (10.2%). The *4 and *5 alleles occurred at 7.3% and 1.9% respectively. The *3, *14 and *17 alleles were not detected in the study. The *1/*2, *1/*1 and *2/*2 genotypes were the most common CYP2D6 genotypes, representing 32.7%, 19.4% and 11.8% of the South Indian population. Genotypes that predict poor metabolizer phenotype i.e. *4/*4 and *4/*5 were found at 0.6% in South Indian population. The genetic composition at the CYP2D6 locus in South Indians is distinct from Caucasian, African and even other Asian (Chinese and Japanese) populations.

The high prevalence of the poor and ultrarapid metabolite alleles of CYP2D6, CYP2C9, CYP2C19, CYP3A4, and CYP3A5 in Taiwanese population

Genetic polymorphisms of drug metabolizing enzymes, such as cytochromes P450 (CYPs), play major roles in the variations of drug responsiveness in human. The aim of this study is to identify the high prevalence (minor allele frequencies >1%) of the abnormal metabolite alleles of CYP2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A5 in the Taiwanese population. The genotyping of the functional single nucleotide polymorphisms (SNPs) of CYPs were conducted by direct exon sequencing in 180 Taiwanese volunteers. Twenty-one unique SNPs including three newly identified SNPs were detected in the Taiwanese population. Six of the 21 SNPs in five genes showed frequencies more than 1%. The results indicated that it could be very useful and important in developing an inexpensive, convenient, and precise genotyping method for the high prevalence of CYPs metabolizing abnormal alleles in the Taiwanese population.

Allergy medication in Japanese volunteers: treatment effect of single doses on nocturnal sleep architecture and next day residual effects

OBJECTIVES

To evaluate the acute effects of two histamine H(1)-receptor antagonists on nocturnal sleep architecture and on next day cognitive function and psychomotor performance.

METHODS

This was a single-site, randomized, double-blind, 3-way crossover study, comparing the effects of a single dose of chlorpheniramine (6 mg), fexofenadine (120 mg) and placebo in 18 healthy (male and female) Japanese volunteers aged 20-55 years. Volunteers were resident for 3 days and each period was separated by a minimum 5-day washout period. The three treatments were administered at 23.00 h. Overnight sleep was measured from 23.00 h to 07.00 h using polysomnography. Residual effects were studied at 07.00 h and 9.00 h the next morning, with the latency to sleep (sleep latency test) measured at 09.30 h.

RESULTS

Compared with placebo, chlorpheniramine increased the latencies to sleep onset and rapid eye movement (REM) sleep (p < or = 0.05 for both), and reduced the duration of REM sleep (p <or= 0.01), but this was not observed with fexofenadine. As far as residual effects the next morning were concerned there were decrements in performance with chlorpheniramine, but not with fexofenadine. Chlorpheniramine 6 mg impaired divided attention (p < 0.001), vigilance (p < 0.05), working memory (p < 0.0001) and sensori-motor performance (p < 0.01), and the latency to daytime sleep was reduced (p < 0.0001). Six adverse events possibly related to study medication were reported during the study, three of which were related to placebo, two to fexofenadine and one to chlorpheniramine.

CONCLUSION

These findings suggest that a single nocturnal dose of fexofenadine has advantages over the first-generation antihistamine chlorpheniramine, being free of disruption of night-time sleep and detrimental effects on cognitive performance the next day. It is likely that this advantage will remain with chronic ingestion, but this would need to be confirmed.

Combined effects of itraconazole and CYP2D6*10 genetic polymorphism on the pharmacokinetics and pharmacodynamics of haloperidol in healthy subjects

This study was to evaluate the combined effects of the CYP3A4 inhibitor itraconazole and the CYP2D6*10 genotype on the pharmacokinetics and pharmacodynamics of haloperidol, a substrate of both CYP2D6 and CYP3A4, in healthy subjects. Nineteen healthy volunteers whose CYP2D6 genotypes were predetermined were enrolled (9 for CYP2D6*1/*1 and 10 for CYP2D6*10/*10). Four subjects (1 for CYP2D6*1/*1 and 3 for CYP2D6*10/*10) did not complete the study because of adverse events. The pharmacokinetics of haloperidol and its pharmacodynamic effects measured for QTc prolongation and neurologic side effects were evaluated after a single dose of 5 mg haloperidol following a pretreatment of placebo or itraconazole at 200 mg/d for 10 days in a randomized crossover manner. Itraconazole pretreatment increased the mean area under the time-concentration curves (AUCs) of haloperidol by 55% compared to placebo pretreatment (21.7 +/- 11.3 vs 33.5 +/- 29.3 ng h/mL). The subjects with CYP2D6*10/*10 genotype showed 81% higher AUC compared to that of subjects with CYP2D6*1/*1 genotype (27.6 +/- 22.2 vs 50.2 +/- 47.1 ng h/mL). In the presence of itraconazole, subjects with CYP2D6*10/*10 showed 3-fold higher AUC of haloperidol compared to that of placebo pretreated subjects with CYP2D6*1/*1 genotype (21.7 +/- 11.3 vs 66.7 +/- 62.1 ng h/mL; P < 0.05). The CYP2D6*10 genotype and itraconazole pretreatment decreased the oral clearance of haloperidol by 24% and 25%, respectively, but without a statistical significance. In the subjects with both CYP2D6*10 genotype and itraconazole pretreatment, however, the oral clearance was significantly decreased to 42% of subjects with wild genotype in the placebo pretreatment (4.7 +/- 3.6 vs 2.0 +/- 1.9 L/h/kg; P < 0.05). Barnes Akathisia Rating Scale (BARS) of subjects with CYP2D6*10/*10 in the presence of itraconazole pretreatment was significantly higher than that of subjects with CYP2D6*1/*1 genotype in the period of placebo pretreatment. Except for this, all other pharmacodynamic estimations did not reach to statistical significance although each CYP2D6*10 genotype and itraconazole pretreatment caused higher value of UKU side effect and BARS scores. The moderate effect of CYP2D6*10 genotype on the pharmacokinetics and pharmacodynamics of haloperidol seems to be augmented by the presence of itraconazole pretreatment.

Catalytic roles of CYP2D6.10 and CYP2D6.36 enzymes in mexiletine metabolism: In vitro functional analysis of recombinant proteins expressed in Saccharomyces cerevisiae

Cytochrome P450 2D6 (CYP2D6) metabolizes approximately one-third of the medicines in current clinical use and exhibits genetic polymorphism with interindividual differences in metabolic activity. To precisely investigate the effect of CYP2D6*10B and CYP2D6*36 frequently found in Oriental populations on mexiletine metabolism in vitro, CYP2D6 proteins of wild-type (CYP2D6.1) and variants (CYP2D6.10 and CYP2D6.36) were heterologously expressed in yeast cells and their mexiletine p- and 2-methyl hydroxylation activities were determined. Both variant CYP2D6 enzymes showed a drastic reduction of CYP2D6 holo- and apoproteins compared with those of CYP2D6.1. Mexiletine p- and 2-methyl hydroxylation activities on the basis of the microsomal protein level at the single substrate concentration (100 microM) of variant CYP2D6s were less than 6% for CYP2D6.10 and 1% for CYP2D6.36 of those of CYP2D6.1. Kinetic analysis for mexiletine hydroxylation revealed that the affinity toward mexiletine of CYP2D6.10 and CYP2D6.36 was reduced by amino acid substitutions. The Vmax and Vmax/Km values of CYP2D6.10 on the basis of the microsomal protein level were reduced to less than 10% of those of CYP2D6.1, whereas the values on the basis of functional CYP2D6 level were comparable to those of CYP2D6.1. Although it was impossible to estimate the kinetic parameters for the mexiletine hydroxylation of CYP2D6.36, the metabolic ability toward mexiletine was considered to be poorer not only than that of CYP2D6.1 but also than that of CYP2D6.10. The same tendency was also observed in kinetic analysis for bufuralol 1''-hydroxylation as a representative CYP2D6 probe. These findings suggest that CYP2D6*36 has a more drastic impact on mexiletine metabolism than CYP2D6*10.

Data-Mining Methods as Useful Tools for Predicting Individual Drug Response: Application to CYP2D6 Data

OBJECTIVES

Selecting a maximally informative subset of polymorphisms to predict a clinical outcome, such as drug response, requires appropriate search methods due to the increased dimensionality associated with looking at multiple genotypes. In this study, we investigated the ability of several pattern recognition methods to identify the most informative markers in the CYP2D6 gene for the prediction of CYP2D6 metabolizer status.

METHODS

Four data-mining tools were explored: decision trees, random forests, artificial neural networks, and the multifactor dimensionality reduction (MDR) method. Marker selection was performed separately in eight population samples of different ethnic origin to evaluate to what extent the most informative markers differ across ethnic groups.

RESULTS

Our results show that the number of polymorphisms required to predict CYP2D6 metabolic phenotype with a high accuracy can be dramatically reduced owing to the strong haplotype block structure observed at CYP2D6. MDR and neural networks provided nearly identical results and performed the best.

CONCLUSION

Data-mining methods, such as MDR and neural networks, appear as promising tools to improve the efficiency of genotyping tests in pharmacogenetics with the ultimate goal of pre-screening patients for individual therapy selection with minimum genotyping effort.

Dose-dependent interaction of paroxetine with risperidone in schizophrenic patients

Augmentation with paroxetine (10-40 mg/d) for antipsychotic treatment may improve the negative symptoms in schizophrenic patients but involves a risk of drug-drug interaction. We studied the effects of paroxetine on plasma concentrations of risperidone and 9-hydroxyrisperidone and their clinical symptoms in risperidone-treated patients. Twelve schizophrenic inpatients with prevailingly negative symptoms receiving risperidone 4 mg/d were, in addition, treated with incremental doses of paroxetine for 12 weeks (10, 20, and 40 mg/d for 4 weeks each). Plasma concentrations of risperidone and 9-hydroxyrisperidone were quantified with liquid chromatography-mass spectrometry mass-mass spectrometry together with clinical assessments before and after each phase of the 3 paroxetine doses. Risperidone concentrations during coadministration of paroxetine 10, 20, and 40 mg/d were 3.8-fold (95% confidence interval, 3.2-5.8, P < 0.01), 7.1-fold (95% confidence interval, 5.3-16.5, P < 0.01), and 9.7-fold (95% confidence interval, 7.8-22.5, P < 0.01) higher than that before paroxetine coadministration, respectively. Active moiety (risperidone plus 9-hydroxyrisperidone) concentration was not increased during the paroxetine 10 mg/d (1.3-fold, not significant) or 20 mg/d (1.6-fold, not significant), but were significantly increased by 1.8-fold (95% confidence interval, 1.4-2.7, P < 0.05) during the paroxetine 40 mg/d. Significant improvement in negative symptoms was observed from 10 to 40 mg/d of paroxetine, whereas scores in extrapyramidal side effects during 20 and 40 mg/d of paroxetine were significantly higher than baseline score. This study indicates that paroxetine increases plasma risperidone concentration and active moiety concentration in a dose-dependent manner. Low-dose coadministration of paroxetine with risperidone may be safe and effective in the treatment of schizophrenic patients with negative symptoms.

High-throughput detection of multiple genetic polymorphisms influencing drug metabolism with mismatch primers in allele-specific polymerase chain reaction

Because of genetic polymorphisms of drug-metabolizing enzyme genes, the activities of the enzymes in humans vary widely and alter the metabolism of commonly used clinical agents. Severe adverse effects or resistance to therapy may result. We have developed a rapid and high-throughput genotyping method for detecting polymorphisms of the drug-metabolizing enzyme genes CYP2C9*3, CYP2C19*2, *3, CYP2D6*2, *4, *10, *14, *21, NAT2*5, *6, *7, and TPMT*3 using allele-specific polymerase chain reaction (PCR) with mismatch primers (ASPCR-MP) and CYP2D6*5, *36, and CYP2D6xN using stepdown PCR with detection by SYBR Green I. We analyzed genomic DNA from 139 Japanese volunteers. Identical genotyping results were obtained by using ASPCR-MP, stepdown PCR, and conventional PCR. We found that the methods clearly differentiate three specific profiles with no overlap in the signals. Moreover, both ASPCR-MP and stepdown PCR for genotyping took less than 3-4h. To our knowledge, this is the first report of successful simultaneous detection of multiple genetic polymorphisms with point mutations using ASPCR-MP or multiple genetic polymorphisms with large structural alterations using stepdown PCR. In conclusion, ASPCR-MP and stepdown PCR appear to be suitable for large clinical and epidemiological studies as methods that enable highly sensitive genotyping and yield a high-throughput.

Identification and characterization of novel sequence variations in the cytochrome P4502D6 (CYP2D6) gene in African Americans

Cytochrome P4502D6 (CYP2D6) genotyping reliably predicts poor metabolizer phenotype in Caucasians, but is less accurate in African Americans. To evaluate discordance we have observed in phenotype to genotype correlation studies, select African American subjects were chosen for complete resequencing of the CYP2D6 gene including 4.2 kb of the CYP2D7-2D6 intergenic region. Comparisons were made to a CYP2D6(*)1 reference sequence revealing novel SNPs in the upstream, coding and intervening sequences. These sequence variations, defining four functional alleles (CYP2D6(*)41B, (*)45A and B and (*)46), were characterized for their ability to influence splice site strength, transcription level or catalytic protein activity. Furthermore, their frequency was determined in a population of 251 African Americans. A -692(TGTG) deletion (CYP2D6(*)45B) did not significantly decrease gene expression, nor could any other upstream SNP explain a genotype-discordant case. CYP2D6(*)45 and (*)46 have a combined frequency of 4% and can be identified by a common SNP. Carriers are predicted to exhibit an extensive or intermediate CYP2D6 phenotype.

Genetic polymorphisms of cytochrome P450 in patients with hepatitis C virus-associated hepatocellular carcinoma

BACKGROUND

The carcinogenic process can be modulated by exposure to endogenous or environmental substance(s) acting as carcinogens or protocarcinogens. Polymorphic enzymes of cytochrome P450 (CYP) that play a role in detoxication/toxication of such substances via metabolization may account for the interpatient variability of clinical course in cancers such as hepatocellular carcinoma (HCC). Many CYP genetic polymorphisms, which may change enzyme activity, are known to exist in Japanese. The aim of the present study was to compare the frequencies of CYP polymorphisms between hepatitis C virus (HCV)-related HCC patients and healthy subjects.

METHODS

Seven mutant alleles and related genotypes of CYP in 44 HCV-positive HCC patients were chosen as follows: *1C heterozygous, *1C homozygous and *1F homozygous for CYP1A2, *4A homozygous for CYP2A6, *2A or *3 heterozygous, *2A or *3 homozygous and *2A and *3 heterozygous for CYP2C19, and *10/*5 homozygous for CYP2D6. These mutant alleles have been reported to change the CYP enzyme activity in Japanese. The frequencies of the mutant alleles and genotypes were then compared with those reported in healthy Japanese.

RESULTS AND CONCLUSION

There is no statistically significant difference in genetic mutant alleles between the two groups, except for the genotype of CYP2A6*4A homozygous. The frequency of this genotype in the HCC patients (0.144) is significantly higher than that in healthy Japanese (0.034; P < 0.05; odds ratio 3.36). The clinical significance related to HCC is unknown. Further evaluation of CYP2A6*4A (deletion type) in HCV-related HCC patients is required.

MagSNiPer: A new single nucleotide polymorphism typing method based on single base extension, magnetic separation, and chemiluminescence

We have developed a new method for typing single nucleotide polymorphisms (SNPs), MagSNiPer, based on single base extension, magnetic separation, and chemiluminescence. Single base nucleotide extension reaction is performed with a biotinylated primer whose 3' terminus is contiguous to the SNP site with a tag-labeled ddNTP. Then the primers are captured by magnetic-coated beads with streptavidin, and unincorporated labeled ddNTP is removed by magnetic separation. The magnetic beads are incubated with anti-tag antibody conjugated with alkaline phosphatase. After the removal of excess conjugates by magnetic separation, SNP typing is performed by measuring chemiluminescence. The incorporation of labeled ddNTP is monitored by chemiluminescence induced by alkaline phosphatase. MagSNiPer is a simple and robust SNP typing method with a wide dynamic range and high sensitivity. Using MagSNiPer, we could perform SNP typing with as little as 10(-17) mol of template DNA.

Differences in drug pharmacokinetics between East Asians and Caucasians and the role of genetic polymorphisms

Interethnic variability in pharmacokinetics can cause unexpected outcomes such as therapeutic failure, adverse effects, and toxicity in subjects of different ethnic origin undergoing medical treatment. It is important to realize that both genetic and environmental factors can lead to these differences among ethnic groups. The International Conference on Harmonization (ICH) published a guidance to facilitate the registration of drugs among ICH regions (European Union, Japan, the United States) by recommending a framework for evaluating the impact of ethnic factors on a drug's effect, as well as its efficacy and safety at a particular dosage and dosage regimen. This review focuses on the pharmacokinetic differences between East Asians and Caucasians. Differences in metabolism between East Asians and Caucasians are common, especially in the activity of several phase I enzymes such as CYP2D6 and the CYP2C subfamily. Before drug therapy, identification of either the genotype and/or the phenotype for these enzymes may be of therapeutic value, particularly for drugs with a narrow therapeutic index. Furthermore, these differences are relevant for international drug approval when regulatory agencies must decide if they accept results from clinical trials performed in other parts of the world.

Two Novel Single Nucleotide Polymorphisms (SNPs) of the CYP2D6 Gene in Japanese Individuals

We analyzed all the exons and exon-intron junctions of the CYP2D6 gene from 286 Japanese individuals. We detected two novel single nucleotide polymorphisms (SNPs) 2556C>T in exon 5 (Thr261Ile) and 3835A>C in exon 8 (Lys404Gln). Both these SNPs showed a frequency of 0.002.

Lack of Interaction of Milnacipran with the Cytochrome P450 Isoenzymes Frequently Involved in the Metabolism of Antidepressants

OBJECTIVE

To compare the pharmacokinetics of milnacipran in extensive metabolisers (EMs) and poor metabolisers (PMs) of sparteine and mephenytoin, and to assess the influence of multiple administrations of milnacipran on the activity of cytochrome P450 (CYP) isoenzymes through its own metabolism and through various probes, namely CYP2D6 (sparteine/dextromethorphan), CYP2C19 (mephenytoin), CYP1A2 (caffeine) and CYP3A4 (endogenous 6-beta-hydroxy-cortisol excretion).

METHODS

Twenty-five healthy subjects, 12 EMs for both sparteine/dextromethorphan and mephenytoin, nine EMs for mephenytoin and PMs for sparteine/dextromethorphan (PM(2D6)) and four PMs for mephenytoin and EMs for sparteine/dextromethorphan (PM(2C19)) were administered milnacipran as a single 50 mg capsule on day 1 followed by a 50 mg capsule twice daily for 7 days. The pharmacokinetics of milnacipran and its oxidative metabolites were assessed after the first dose (day 1) and after multiple administration (day 8), and were compared for differences between CYP2D6 and CYP2C19 PMs and EMs. Metabolic tests were performed before (day -2), during (days 1 and 8) and after (day 20) milnacipran administration.

RESULTS

Milnacipran steady state was rapidly achieved. Metabolism was limited: approximately 50% unchanged drug, 30% as glucuronide and 20% as oxidative metabolite (mainly F2800 the N-dealkyl metabolite). Milnacipran administration to PM2D6 and PM2C19 subjects did not increase parent drug exposure or decrease metabolite exposure. Milnacipran oxidative metabolism is not mediated through CYP2D6 or CYP2C19 polymorphic pathways nor does it significantly interact with CYP1A2, CYP2C19, CYP2D6 or CYP3A4 activities.

CONCLUSION

Limited reciprocal pharmacokinetic interaction between milnacipran and CYP isoenzymes would confer flexibility in the therapeutic use of the drug when combined with antidepressants. Drug-drug interaction risk would be low, even if the combined treatments were likely to inhibit CYP2D6 and CYP2C19 isoenzyme activities.

Pharmacokinetic Characteristics of Amiodarone in Long-Term Oral Therapy in Japanese Population

To evaluate the pharmacokinetic properties and an optimum dose schedule of amiodarone in long-term oral therapy, serum concentrations of amiodarone and its metabolite, desethylamiodarone, were monitored from 345 Japanese inpatients who received amiodarone therapy for a variety of cardiac arrhythmias. Serum amiodarone and desethylamiodarone concentrations were determined by high performance liquid chromatography system. It was observed that the amiodarone and desethylamiodarone concentrations gradually increased with time. The frequency distribution in the amiodarone clearance of 245 subjects, who received fixed maintenance amiodarone therapy for at least 6 months, was nearly a unimodal one. The variation in the ratio of desetylamiodarone to amiodarone concentration in serum was very small. Although no differences in age, dose, dose duration, amiodarone or desethyamiodarone concentration or ratio were observed between men and women: however, the mean amiodarone clearance of women was significantly higer than that of men. The laboratory data were mostly within normal values and no significant relations were observed between serum amiodarone concentration and clinical laboratory data. These results suggest that the individual variation in pharmacokinetics of amiodarone is comparatively small, which might be sufficient to decide that the maintenance dose was the same one (200 mg/d) in long-term oral amiodarone therapy.