Frequency of cytochrome P450 2C9 mutant alleles in a Korean population

Drug-induced cis-regulatory elements in human hepatocytes affect molecular phenotypes associated with adverse reactions

Genomic variation drives phenotypic diversity, including individual differences in drug response. While coding polymorphisms linked to drug efficacy and adverse reactions are well characterized, the contribution of noncoding regulatory elements remains underexplored. Using CAGE (Cap Analysis of Gene Expression), profiling transcription initiations of mRNAs and enhancer RNAs, we identify candidate cis-regulatory elements (CREs) and assessed their activities simultaneously in HepG2 cells expressing the drug-responsive transcription factor pregnane X receptor (PXR). Comparison with GWAS data reveals strong enrichment of the drug-induced CREs near variants associated with bilirubin and vitamin D levels. Among those bound by PXR in primary hepatocytes, we identify enhancers of UGT1A1, TSKU, and CYP24A1 and functional alleles that alter regulatory activities. We also find that TSKU influences expression of vitamin D-metabolizing enzymes. This study expands the landscape of PXR-mediated regulatory elements and uncovers noncoding variants impacting drug response, providing insights into the genomic basis of adverse drug reactions.

The frequency of major ABCG2, SLCO1B1 and CYP2C9 variants in Asian, Native Hawaiian and Pacific Islander women subgroups: implications for personalized statins dosing

Aim: The frequencies of SLCO1B1*5 and CYP2C9*2 and *3 in specific Asian, Native Hawaiian and Pacific Islander (NHPI) subgroups are unknown. Patients & methods: Repository DNA samples from 1064 women self-identifying as Filipino, Korean, Japanese, Native Hawaiian, Marshallese or Samoan and aged 18 years or older were used for targeted sequencing of three genetic variants (rs4149056, rs1799853 and rs1057910). Results: SLCO1B1*5 was significantly less frequent in NHPI women (0.5-6%) than in Europeans (16%). Except for Koreans, CYP2C9*2 (0-1.4%) and *3 (0.5-3%) were significantly less frequent in all subgroups than in Europeans (8 and 12.7%, respectively). Prior reports showed that Asian and NHPI individuals have significantly higher ABCG2 Q141K allele frequency (13-46%) than Europeans (9.4%). Combined phenotype rates for rosuvastatin and fluvastatin revealed that Filipinos and Koreans had the highest frequencies of statin-associated myopathy symptoms risk alleles. Conclusion: Differences in ABCG2, SLCO1B1 and CYP2C9 allele frequencies among different racial and ethnic subgroups highlight the need for increased diversity in pharmacogenetic research. Risk alleles for statin-associated myopathy symptoms are more prevalent in Filipinos, underscoring the importance of genotype-based statin dosing.

Polymorphisms of genes related to phase-I metabolic enzymes affecting the clinical efficacy and safety of clopidogrel treatment

Introduction: Clopidogrel is an antiplatelet medication described as a prodrug, which cannot exert the antiplatelet effect until being biotransformed to the active metabolite. It is commonly used to reduce the risk of blood coagulation in patients diagnosed with acute coronary syndrome, or ischemic stroke.Area covered: We reviewed published articles in PubMed and Google Scholar that focused on the mutations of CYP2C19, CYP3A4, CYP2C9, CYP2B6, and CYP1A2 genes related to clopidogrel clinical efficacy and safety.Expert opinion: Based on current pharmacogenetic studies, patients carrying CYP2C19*2, CYP2C19*3, CYP2C9*3, and CYP2B6*5 alleles may not respond to clopidogrel due to poor platelet inhibition efficacy revealed among them. In contrast, carriers of CYP2C19*17, CYP3A4*1G, and CYP1A2*1C alleles showed a more significant antiplatelet effect in clopidogrel users and expected to have a protective role as a genetic factor against cardiovascular events. Genotyping for either CYP2C19, CYP3A4, CYP2C9, CYP2B6, or CYP1A2 variants is not recommended when considering clopidogrel treatment for patients, as some trials showed specific non-genetic factors (e.g. age and diabetes) that could affect clopidogrel responsiveness. Instead, platelets inhibition tests could be used as predictors of the clinical efficacy of clopidogrel treatment. Other P2Y12 receptor inhibitors should be considered as alternative medications.

Metabolizer phenotype prediction in different Peruvian ethnic groups through CYP2C9 polymorphisms

OBJECTIVES

The CYP2C9 gene have three common alleles, CYP2C9*1, CYP2C9*2 and CYP2C9*3, associated with different homozygous (*1/*1, *2/*2 and *3/*3) and heterozygous (*1/*2 and *1/*3) genotypes, which in turn are related to extensive (gEM), intermediate (gIM) and poor (gPM) metabolizers. Likewise, the inter-ethnic variability was intimately associated with different drug metabolism. Therefore, the aim of the present study was predict the metabolizer phenotypes in different Peruvian ethnic groups from lowland (<2,500 m) and highland (>2,500 m).

METHODS

TaqMan genotyping assays were performed in a group of 174 healthy unrelated Peruvian individuals.

RESULTS

In this study, the allelic comparison between the three eco-regions showed that the CYP2C9*1 was the most common in Andean (96.32%); the *2 was the most frequent in Coast (7.45%, p<0.05). Regarding the *3 was the most common in Amazonian (6.25%, p<0.05). In a corroborative manner, the gEM was the most common in Andean (94.74%), the gIM in Coast (17.02%) and gPM in Amazonian (6.25%) populations.

CONCLUSIONS

Our study provides a valuable source of information about to metabolizer phenotype drugs in different Peruvian ethnic groups. In this way, it could be established suitable genetic-dosage medicaments for various common diseases in these heterogenetic populations.

Pharmacogenetics of tamoxifen therapy in Asian populations: from genetic polymorphism to clinical outcomes

BACKGROUND

Compared with western countries, Asian breast cancer patients have unique pathological and biological characteristics. Most of them are premenopausal women with HR positive. Tamoxifen as the first-line drug for premenopausal women with HR+ is involved in multiple enzymes and transporters during metabolizing and transporting process. Variants that cause decreased or inactive gene products leading to abnormal responses in tamoxifen therapy have well been studied in western countries, whereas such information is much less reported in Asian populations.

OBJECTIVE

In order to elucidate the relationship between genetic variants and tamoxifen-induced individual drug reactions in different Asian populations and further identify genotypes/phenotypes with potential therapeutic significance.

METHODS

We reviewed the frequencies of genetic variants in major enzymes and transporter genes involved in the metabolism and transport of tamoxifen across Asian populations as well as significant correlations between genotypes/metabolic phenotypes and metabolites concentrations or BC clinical outcomes.

RESULTS

Significant inter-ethnic differences in allele frequencies was found among Asian populations, such as CYP2D6*4, *10, *41, CYP2C9*2, ABCB1 C3435T and SLCO1B1*5, and CYP2D6*10/*10 is the most common genotype correlated with adverse clinical outcomes. Moreover, we summarized the barriers and controversies of implementing pharmacogenetics in tamoxifen therapy and concluded that more population-specific pharmacogenetic studies are needed in the future.

CONCLUSION

This review revealed more systematic pharmacogenomics of genes involved in the metabolism and transport besides CYP2D6, are required to optimize the genotyping strategies and guide the personalized tamoxifen therapy in Asian populations.

Variations in the frequencies of polymorphisms in the CYP2C9 gene in six major ethnicities of Pakistan

Genetic variation in cytochrome P450 (CYP) 2C9 is known to cause significant inter-individual differences in drug response and adverse effects. The frequencies of CYP2C9*2 and CYP2C9*3, both of which are responsible for the low activity of the enzyme, are not known in the Pakistani population. Therefore, we screened various ethnic groups residing in Pakistan for these polymorphisms. A total of 467 healthy human volunteers were recruited from six major ethnicities of Pakistan after written informed consent. Our results indicate that about 20% of the Pakistani population has a genotype containing at least one low activity allele. Ethnic Punjabi and Pathan populations had the highest frequencies of wild type genotypes while Urdu, Seraiki, and Sindhi populations showed higher rates of both low activity genotypes. The Baloch population showed the highest rates of low activity genotypes with less than 50% of the samples showing wild type genotypes, suggesting that more than half of the Baloch population possesses low activity genotypes. The frequencies found in various ethnic groups in Pakistan were comparable with ethnicities in the South Asian region except for the Baloch population. These results suggest that pharmacogenetics screening for low activity genotypes may be a helpful tool for clinicians while prescribing medications metabolized by CYP2C9.

Physiologically Based Pharmacokinetic/Pharmacodynamic Modeling to Predict the Impact of CYP2C9 Genetic Polymorphisms, Co-Medication and Formulation on the Pharmacokinetics and Pharmacodynamics of Flurbiprofen

Physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) models can serve as a powerful framework for predicting the influence as well as the interaction of formulation, genetic polymorphism and co-medication on the pharmacokinetics and pharmacodynamics of drug substances. In this study, flurbiprofen, a potent non-steroid anti-inflammatory drug, was chosen as a model drug. Flurbiprofen has absolute bioavailability of ~95% and linear pharmacokinetics in the dose range of 50–300 mg. Its absorption is considered variable and complex, often associated with double peak phenomena, and its pharmacokinetics are characterized by high inter-subject variability, mainly due to its metabolism by the polymorphic CYP2C9 (fmCYP2C9 ≥ 0.71). In this study, by leveraging in vitro, in silico and in vivo data, an integrated PBPK/PD model with mechanistic absorption was developed and evaluated against clinical data from PK, PD, drug-drug and gene-drug interaction studies. The PBPK model successfully predicted (within 2-fold) 36 out of 38 observed concentration-time profiles of flurbiprofen as well as the CYP2C9 genetic effects after administration of different intravenous and oral dosage forms over a dose range of 40–300 mg in both Caucasian and Chinese healthy volunteers. All model predictions for C_max, AUC_inf and CL/F were within two-fold of their respective mean or geometric mean values, while 90% of the predictions of C_max, 81% of the predictions of AUC_inf and 74% of the predictions of Cl/F were within 1.25 fold. In addition, the drug-drug and drug-gene interactions were predicted within 1.5-fold of the observed interaction ratios (AUC, C_max ratios). The validated PBPK model was further expanded by linking it to an inhibitory E_max model describing the analgesic efficacy of flurbiprofen and applying it to explore the effect of formulation and genetic polymorphisms on the onset and duration of pain relief. This comprehensive PBPK/PD analysis, along with a detailed translational biopharmaceutic framework including appropriately designed biorelevant in vitro experiments and in vitro-in vivo extrapolation, provided mechanistic insight on the impact of formulation and genetic variations, two major determinants of the population variability, on the PK/PD of flurbiprofen. Clinically relevant specifications and potential dose adjustments were also proposed. Overall, the present work highlights the value of a translational PBPK/PD approach, tailored to target populations and genotypes, as an approach towards achieving personalized medicine.

Single nucleotide polymorphisms on CYP2C9 gene among Filipinos and its association with post-operative pain relief via COX-2 inhibitors

CYP2C9 gene encodes an enzyme involved in the metabolism of a wide variety of drugs which include celecoxib. This study investigated the frequencies of the alleles and genotypes of CYP2C9*1, CYP2C9*2, and CYP2C9*3 among Filipinos who underwent surgery, and to determine the association of CYP2C9 polymorphisms with post-operative pain relief via COX-2 inhibitors. Response to celecoxib was determined using the numerical rating scale (0-10) on the 24th and 48th hour of surgery. The CYP2C9 alleles were detected by real-time PCR. For CYP2C9*1 and CYP2C9*3, the allele frequencies among Filipinos were 99% and 1% respectively, which is similar with other East Asians. CYP2C9*2 alleles were not detected. The frequencies of CYP2C9*1/*1 and CYP2C9*1/*3 genotypes were 98% and 2% respectively. At 24 hours post-surgery, the average pain score was 2.57 ± 1.03, while on 48 hours post-surgery, the average pain score was 0.67 ± 0.61 among those who have the wild-type CYP2C9*1 allele. The average pain score on the 24th and 48th hour post-operatively was observed to be 2.5 ± 0.71 and 0.5 ± 0.71 respectively among two patients classified as intermediate metabolizer carrying the CYP2C9*1/*3 genotype. Low frequencies of CYP2C9 polymorphisms were observed in the present study, this pattern was similar with other Asians except Indians, and considerably lower than Caucasians. Our results suggest that CYP2C9 genotyping is not routinely needed for Filipinos but must be considered among mixed races. Consequently, a more personalized therapeutic strategy was derived from these data, resulting in good clinical outcomes and less adverse drug effects.

Brazilian cohort and genes encoding for drug-metabolizing enzymes and drug transporters

Background & aim: Genetic variability in drug absorption, distribution, metabolism and excretion (ADME) genes contributes to the high heterogeneity of drug responses. The present study investigated polymorphisms of ADME genes frequencies and compared the findings with populations from other continents, available in the 1000 Genome Project (1 KGP) and the Exome Aggregation Consortium (ExAC) databases. Methodology & results: We conducted a study of 100 patients in Brazil and a total of 2003 SNPs were evaluated by targeted next-generation sequencing in 148 genes, including Phase I enzymes (n = 50), Phase II enzymes (n = 38) and drug transporters (n = 60). Overall, the distribution of minor allele frequency (MAF) suggests that the distribution of 2003 SNPs is similar between Brazilian cohort, 1 KGP and ExAC; however, we found moderate SNP allele-frequency divergence between Brazilian cohort and both 1000 KGP and ExAC. These differences were observed in several relevant genes including CYP3A4, NAT2 and SLCO1B1. Conclusion: We concluded that the Brazilian population needs clinical assessment of drug treatment based on individual genotype rather than ethnicity.

Effects of Celecoxib on the QTc Interval: A Thorough QT/QTc Study

PURPOSE

Celecoxib is a selective cyclooxygenase-2 inhibitor widely used in patients with osteoarthritis and rheumatoid arthritis. Recently, nonclinical data on the inhibition of human ether-à-go-go-related gene potassium channels by celecoxib were reported, but there is no compelling evidence for this finding in humans. The aim of this study was to assess the potential effects of celecoxib on cardiac repolarization by conducting a thorough QT study, which was designed in compliance with the related guidelines.

METHODS

This randomized, open-label, positive- and negative-controlled, crossover clinical study was conducted in healthy male and female subjects. Each subject received, in 1 of 4 randomly assigned sequences, all of the following 3 interventions: celecoxib 400 mg once daily for 6 days; a single dose of moxifloxacin 400 mg, which served as a positive control to assess the assay sensitivity; and water without any drug, which served as a negative control. Serial 12-lead ECG and blood samples for pharmacokinetic analysis were collected periodically over 24 h. Individually RR-corrected QT intervals (QTcI) and Fridericia method-corrected QT intervals (QTcF) were calculated and evaluated.

FINDINGS

Twenty-eight subjects were allocated to 1 of the 4 intervention sequences. The largest time-matched mean effects of celecoxib on the QTcI and QTcF were <5 ms, and the upper bounds of the 1-sided 95% CIs of those values did not exceed 10 ms. Moreover, none of the subjects had an absolute QTcI value of >450 ms or a change from baseline in QTcI of >60 ms after multiple administrations of celecoxib. The QTcI did not show a positive correlation with celecoxib concentrations in the range up to ~2700 μg/L. The overall effects of moxifloxacin on the QTcI and QTcF were enough to establish assay sensitivity. No serious adverse events were reported, with a total of 11 AEs reported in 8 subjects.

IMPLICATIONS

Celecoxib caused no clinically relevant increase in the QT/QTc interval at the maximum dose level used in current practice settings. ClinicalTrials.gov identifier: NCT03822520.

A Rare Combination of CYP2C9*3/*3 and VKORC1 1639AA in a Patient Who Had Myxoma and Thromboembolism

We report a case of intolerance to warfarin. A 20-year-old woman with toe pain was diagnosed with myxoma with multiple systemic embolisms. She was prescribed warfarin for remaining embolic pain after myxoma excision and mitral annuloplasty. Even on 1 mg of warfarin, the international normalized ratio was much increased. The patient was found to have cytochrome P450 2C9 (CYP2C9)*3/*3 and vitamin K epoxide reductase complex subunit 1 (VKORC1) 1639AA genotype, which is extremely rare in Koreans. Based on this result, we assessed the potential risks and benefits of warfarin and decided to switch to aspirin because the risk of bleeding was considered to be too high.

CYP2C9 polymorphisms in epilepsy: influence on phenytoin treatment

Phenytoin (PHT) is an antiepileptic drug widely used in the treatment of focal epilepsy and status epilepticus, and effective in controlling focal seizures with and without tonic-clonic generalization and status epilepticus. The metabolization of PHT is carried out by two oxidative cytochrome P450 enzymes CYP2C9 and CYP2C19; 90% of this metabolization is done by CYP2C9 and the remaining 10% by CYP2C19. Genetic polymorphism of CYP2C9 may reduce the metabolism of PHT by 25-50% in patients with variants *2 and *3 compared to those with wild-type variant *1. The frequency distribution of CYP2C9 polymorphism alleles in patients with epilepsy around the world ranges from 4.5 to 13.6%, being less frequent in African-Americans and Asians. PHT has a narrow therapeutic range and a nonlinear pharmacokinetic profile; hence, its poor metabolization has significant clinical implications as it causes more frequent and more serious adverse effects requiring discontinuation of treatment, even if it had been effective. There is evidence that polymorphisms of CYP2C9 and the use of PHT are associated with an increase in the frequency of some side effects, such as cerebellar atrophy, gingival hypertrophy or acute cutaneous reactions. The presence of HLA-B*15:02 and CYP2C9 *2 or *3 in the same patient increases the risk of Stevens-Johnson syndrome and toxic epidermal necrolysis; hence, PHT should not be prescribed in these patients. In patients with CYP2C9 *1/*2 or *1/*3 alleles (intermediate metabolizers), the usual PHT maintenance dose (5-10 mg/kg/day) must be reduced by 25%, and in those with CYP2C9 *2/*2, *2/*3 or *3/*3 alleles (poor metabolizers), the dose must be reduced by 50%. It is controversial whether CYP2C9 genotyping should be done before starting PHT treatment. In this paper, we aim to review the influence of CYP2C9 polymorphism on the metabolization of PHT and the clinical implications of poor metabolization in the treatment of epilepsies.

Distribution of CYP2C8 and CYP2C9 amino acid substitution alleles in South Indian diabetes patients: A genotypic and computational protein phenotype study

The CYP2C8 and CYP2C9 are two major isoforms of the cytochrome P450 enzyme family, which is involved in drug response, detoxification, and disease development. This study describes the differential distribution of amino acid substitution variants of CYP2C8 (*2-I269F & *3-R139K) and CYP2C9 (*2-C144R & *3-L359A) genes in 234 type 2 diabetes mellitus (T2DM) patients and 218 healthy controls from Andhra Pradesh, South India. Single locus genotype analysis has revealed that homozygous recessive genotypes of 2C8*2-TT (P ≤ .03), 2C9*2-TT (P ≤ .02), and heterozygous 2C9*3-AC (P ≤ .006) are seen to be increasingly present in the case group, indicating a significant level of their association with diabetes in Andhra population. The statistical significance of these recessive genotypes has persisted even under their corresponding allelic forms (P ≤ .01). Genotype association results were further examined by computational protein structure and stability analysis to assess the deleteriousness of the amino acid changes. The mutant CYP 2C8 and 2C9 (both *2 and *3) proteins showed structural drifts at both amino acid residue (range 0.43Å-0.77Å), and polypeptide chain levels (range 0.68Å-1.81Å) compared to their wild-type counterparts. Furthermore, the free energy value differences (range -0.915 to -1.38 Kcal/mol) between mutant and native protein structures suggests the deleterious and destabilizing potential of amino acid substitution polymorphisms of CYP genes. The present study confirms the variable distribution of CYP2C8 (*2 and *3) and CYP2C9 (*2 and *3) allelic polymorphisms among South Indian diabetic populations and further warrants the serious attention of CYP gene family, as a putative locus for disease risk assessment and therapy.

The allele frequency of CYP2C9 and VKORC1 in the Southern Khorasan population

The genetic factors are determinants in required dosage changes of warfarin among which are polymorphisms of CYP2C9 and VKORC1 genes. The present study aimed to determine the allele and genotype frequency of CYP2C9 and VKORC1 genes in Birjand population. This study was conducted on 120 individuals who referred to Imam Reza and Vali-Asr hospitals for PT/INR test. After extracting the genomic DNA, the considered sequences were amplified by PCR, and restriction fragment length polymorphism analysis was done by AvaII and KpnI enzymes to determine allele polymorphisms. Moreover, related sequences of VKORC1, after amplification, were sequenced for determining the genotype. Allelic and genotypic frequencies as well as Hardy-Weinberg equilibrium, observed heterozygosity, expected heterozygosity, and polymorphism information content were calculated by PowerMarker V 3.25 software. Amongst 120 individuals in this study with the mean age of 58.12 ± 12.7 years, 80.8%, 9.1%, and 10% exhibited the alleles of 1, 2, and 3 CYP2C9 gene, respectively. The genotype frequencies of 1/1, 1/2, 2/2, 3/1, 3/2, and 3/3 of this gene were found to be 64.1, 15.8, 0, 17.5, 2.5, and 0 %, respectively. In -1639 G>A region, VKORC1 had normal homozygote genotype (GG) and in 1173 C>T region, heterozygote (CT) with the frequency of 48.7% and 45.9% had the most prevalence. Compared with other populations, there is a considerable difference between the allele frequency of CYP2C9 and VKORC1 genetic variance. Since 35.8% of the selected populations carry an abnormal allele causing sensitivity to warfarin, the specialists at medical centers must be informed about the genotypes of patients before prescribing warfarin.

Pharmacogenomic Effect of Cytochrome P450 2C9 Polymorphisms in Different Populations

Presently, warfarin sodium or coumadin is the therapeutic drug of choice for maintenance anticoagualtion therapy. One of several factors underlying the variability in warfarin dose response in the patients receiving this oral anticoagulant is a genetic predisposition, especially the CYP2C9 polymorphisms. The pharmacogenomic effect of CYP2C9 polymorphisms is assessed in different racial populations. A retrospective review was performed with an electronic search engine on this topic to get the data for further meta-analysis. A significant correlation between population ethnicity and gene frequencies was detected in this study. A significant low frequency of CYP2C9 variants among the Asian can be demonstrated. The clinical correlation between CYP2C9 polymorphism and warfarin metabolism was also assessed. Four available case-control reports were selected for this meta-analysis. CYP2C9 variants are strongly associated with low-dose warfarin requirement. In summary, the CYP2C9 variants strongly affect the warfarin dose requirement. This phenomenon is ethnically dependent. Due to the high variant frequency among whites in the West, the investigation for CYP2C9 might be useful for this population, not the Asians, whose variant frequency is very low.

Analysis of CYP2C9 polymorphisms (*2 and *3) in warfarin therapy patients in Pakistan. Association of CYP2C9 polymorphisms (*2 and*3) with warfarin dose, age, PT and INR

Warfarin is a widely used anticoagulant characterized by having a narrow therapeutic index and exhibiting a wide range of inter-individual and inter-ethnic variation. Single nucleotide polymorphisms in hepatic VKORC1 and CYP2C9 genes causes decreased and increased metabolism of warfarin respectively. The objective of this study was to evaluate the allele frequency of CYP2C9 polymorphic variants *2 and *3 and the association of these allelic variants with PT/INR and daily/weekly dose of warfarin. Seventy-four patients with heart valve replacement were selected. Patients taking low warfarin dose (4.90-17.50 mg weekly) for at least last 3 months and had a stable INR in the range of 2-3 were included in this study. CYP2C9 polymorphism was analyzed by polymerase chain reaction followed by restriction fragment length polymorphism (PCR-RFLP) technique. Among 74 patients, 9 (12.1 %) showed to have *2 allele, whereas 11 (14.1 %) had *3 allele. Genotype frequencies of wild and variant alleles were, 54.1, 17.6, 21.6 and 6.8 % for *1/*1, *1/*2, *1/*3 and *2/*3 respectively. None of the patient was homozygous for *2 and *3. Statistical analysis showed that low warfarin dose (weekly) is significantly associated with *1/*2 and *1/*3 genotypes (p value ≥ 0.001), whereas PT/INR showed no significant association with the any genotypes of CYP2C9. Our study suggest that polymorphic variants of CYP2C9 (*2 and *3) might influence warfarin dose requirements and associated with the low dose of warfarin in patients.

The effect of CYP2C9 and VKORC1 genetic polymorphisms on warfarin dose requirements in a pediatric population

OBJECTIVE

The aim was to investigate the frequency of genetic polymorphisms of cytochrome P4502C9 (CYP2C9) and vitamin K epoxide reductase complex subunit1 (VKORC1) and determine the effect of these polymorphisms on warfarin dose requirements in pediatric patients.

METHODS

Fifty-eight pediatric patients with cardiac disease, thrombophilia, or other conditions, taking a stable warfarin dose, aged 0.2-18 years, and with international normalized ratio (INR) between 2 and 3 and 149 healthy children as a control group were included in this prospective, observational study. Patients receiving drugs that interact with warfarin, having chronic liver or renal disease, obesity, or thyroid dysfunctions were excluded. Polymerase chain reaction (real time and restriction fragment length polymorphism) was used to analyze the CYP2C9*2, CYP2C9*3, and VKORC1 polymorphisms. The ideal warfarin dose was calculated according to the patient's age, height, and the presence of CYP2C9*2, CYP2C9*3, and VKORC1 genetic polymorphisms. The mean daily administered doses and ideal doses were compared. Analysis of variance, Student's t-test, logistic regression analysis, and Pearson's correlation analysis were used for statistical analyses.

RESULTS

The frequency of the CYP2C9 and VKORC1 genetic polymorphisms was determined as CYP2C9*1/*1 (54.6%), *1/*2 (16.4%), *1/*3 (24.2%), *2/*3 (2.9%), *3/*3 (1.9%), wild-type VKORC1 (26.6%), heterozygote alleles (52.7%), and mutant alleles (20.8%). Patients with allelic variants were found to require lower warfarin doses, and a 64.5% correlation was found between the calculated ideal doses and the administered warfarin doses.

CONCLUSION

Considering CYP2C9 and VKORC1 genetic polymorphisms prior to commencing warfarin treatment will make it easier to reach target INRs and reduce the rate of complications.

Cytochrome P450 2C9 (CYP2C9) polymorphisms in Chinese Li population

BACKGROUND

The frequencies of Cytochrome P450 2C9 (CYP2C9) genotypes were various between populations. The aim of this study was to investigate the frequencies of the major variants of the CYP2C9 in Chinese Li minority populations.

METHODS

The promoter, exons and surrounding introns, and 3'-untranslated region of the CYP2C9 gene was detected by DNA sequencing to investigate in 100 unrelated healthy Chinese Li subjects. The protein function prediction was used the online tools: Sorting Intolerant From Tolerant (SIFT) and Phenotyping Version 2 (PolyPhen-2). The comparison of CYP2C9 allele frequencies in different populations were analyzed by Chi-square (χ(2)) test. Linkage disequilibrium (LD) analysis was performed using Haploview software.

RESULTS

We identified 17 different CYP2C9 single nucleotide polymorphisms (SNPs) in the Li population, including two missense mutations (3549 G > A and 42614 A > C) and two silent mutations (3514 T > Cand 50298A > T). The protein function prediction revealed the two missense mutations result in protein damaging. In addition, we detected the allele frequencies of CYP2C9*1, CYP2C9*3 and CYP2C9*42 were 98%, 1%, and 1%, respectively. Finally, we compared three major allelic frequency (CYP2C9*1, CYP2C9*2, and CYP2C9*3) between Li and other populations. We found that our results were similar to East Asians and Africans.

Stereoselective metabolism of donepezil and steady-state plasma concentrations of S-donepezil based on CYP2D6 polymorphisms in the therapeutic responses of Han Chinese patients with Alzheimer's disease

The therapeutic response rates of patients to donepezil vary from 20% to 60%, one of the reasons is their genetic differences in donepezil-metabolizing enzymes, which directly influence liver metabolism. However, the mechanism of donepezil metabolism and that of its enantiomers is unknown. This study evaluated CYP2D6 polymorphisms to elucidate the stereoselective metabolism of donepezil and to confirm the association between the steady-state plasma concentrations of the pharmaco-effective S-donepezil and the therapeutic responses of Han Chinese patients with Alzheimer's disease. The in vitro study of the stereoselective metabolism demonstrated that CYP2D6 is the predominant P450 enzyme that metabolizes donepezil and that different CYP2D6 alleles differentially affect donepezil enantiomers metabolism. A total of 77 Han Chinese patients with Alzheimer's disease were recruited to confirm these results, by measuring their steady-state plasma concentrations of S-donepezil. The related CYP2D6 genes were genotyped. Plasma concentrations of S-donepezil (based on CYP2D6 polymorphisms) were significantly associated with therapeutic responses. This finding suggests that plasma concentrations of S-donepezil influence therapeutic outcomes following treatment with donepezil in Han Chinese patients with Alzheimer's disease. Therefore, determining a patient's steady-state plasma concentration of S-donepezil in combination with their CYP2D6 genotype might be useful for clinically monitoring the therapeutic efficacy of donepezil.

Genetic Polymorphism of Cytochrome p450 (2C9) Enzyme in Iranian Baluch Ethnic Group

The aim of the present study is to assess and compare the frequencies of the cytochrome P450 CYP2C9 variations in the Baluch ethnic group (n=110) with other ethnic groups. The allele frequencies of CYP2C9*1, CYP2C9*2 and CYP2C9*3 were 80.90%, 11.82% and 7.27%, respectively. 70.90%, 11.82%, 8.18%, 4.55%, 2.73% and 1.82% of subjects were with CYP2C9*1/*1, CYP2C9*1/*2, CYP2C9*1/*3, CYP2C9*2/*2, CYP2C9*2/*3 and CYP2C9*3/*3 genotypes, respectively. Different mutants may effect on prediction of drug dose requirements in different ethnic groups. Thus, CYP2C9 variants to be determined for findings high risk groups use optimal dosage of drugs metabolized by this polymorphic enzyme.

Prevalence of genetic variants associated with cardiovascular disease risk and drug response in the Southern Indian population of Kerala

BACKGROUND AND AIM:

This study reports the prevalence of five clinically significant variants associated with increased risk of cardiovascular disorders, and variable responses of individuals to commonly prescribed cardiovascular drugs in a South Indian population from the state of Kerala.

MATERIALS AND METHODS:

Genomic DNA isolated from 100 out-patient samples from Kerala were sequenced to examine the frequency of clinically relevant polymorphisms in the genes MYBPC3 (cardiomyopathy), SLCO1B1 (statin-induced myopathy), CYP2C9, VKORC1 (response to warfarin) and CYP2C19 (response to clopidogrel).

RESULTS:

Our analyses revealed the frequency of a 25 bp deletion variant of MYBPC3 associated with risk of cardiomyopathy was 7%, and the SLCO1B1 “C” allele associated with risk for statin-induced myopathy was 15% in this sample group. Among the other variants associated with dose-induced toxicity of warfarin, VKORC1 (c.1639G>A), was detected at 22%, while CYP2C9*3 and CYP2C9*2 alleles were present at a frequency of 15% and 3% respectively. Significantly, the tested sample population showed high prevalence (66%) of CYP2C19*2 variant, which determines response to clopidogrel therapy.

CONCLUSIONS:

We have identified that certain variants associated with cardiovascular disease and related drug response in the five genes, especially those in VKORC1, CYP2C19 and MYBPC3, are highly prevalent in the Kerala population, with almost 2 times higher prevalence of CYP2C19*2 variant compared with other regions in the country. Since the variants chosen in this study have relevance in disease phenotype and/or drug response, and are detected at a higher frequency, this study is likely to encourage clinicians to perform genetic testing before prescribing therapy.

Genetic epidemiology of pharmacogenetic variations in CYP2C9, CYP4F2 and VKORC1 genes associated with warfarin dosage in the Indian population

Aim: Warfarin, a widely used anticoagulant, exhibits large interindividual variability in dose requirements. CYP2C9 and VKORC1 polymorphisms in various ethnic groups have been extensively studied as genetic markers associated with variable drug response. However, allele frequencies of these variants have not been assessed in major ethnic groups in the Indian population. Materials & methods: To study the functional variants known to affect warfarin dosing, we reanalyzed genotype microarray datasets generated as a part of genome-wide association studies as well as data from the Indian Genome Variation database. We examined data from 2680 individuals across 24 ethnically diverse Indian subpopulations. Results: Allelic distribution of VKORC1 (-1639G>A) showed a greater degree of variation across Indian subpopulations, with frequencies as low as 6.5% in an out-group subpopulation to >70% in Tibeto–Burmans. Risk allele frequency of CYP4F2*3 (V433M) was higher in north Indians (0.30–0.44), as compared with other world populations, such as African–American (0.12), Caucasian (0.34) and Hispanic (0.23). TheVKORC1 variant (-1639A) was shown to be prevalent amongst Tibeto–Burmans, whereas CYP2C9 (R144C, I359L) and CYP4F2 (V433M) variants were observed in considerable variability amongst Indo–Europeans. The frequency of CYP2C9*3 (I359L) in north Indians was found to be higher than in most Asian populations. Furthermore, geographical distribution patterns of these variants in north India showed an increased trend of warfarin extensive metabolizers from the Himalayan to Gangetic region. Combined allele frequency (CYP2C9*3 and CYP4F2*3) data suggest that poor metabolizers varied in the range of 0.38–1.85% in Indo–Europeans. Conclusion: Based on genotypic distribution, the majority of the Indian subpopulation might require higher doses for stable anticoagulation, whereas careful assessment is required for Tibeto–Burmans who are expected to have intermediate dose requirement. This is the largest global genetic epidemiological study examining variants associated with warfarin that could potentially be valuable to clinicians in optimizing dosage strategies.

Original submitted 4 April 2014; Revision submitted 23 May 2014

Analysis of CYP2C9*2, CYP2C9*3 and VKORC1 -1639 G>A polymorphisms in a population from South-Eastern Europe

The CYP2C9 enzyme metabolizes a wide range of relevant drugs, among which are oral anticoagulants. VKORC1 is the pharmacodynamic target of the oral anticoagulants. The genetic polymorphisms CYP2C9*2, CYP2C9*3 and VKORC1 -1639 G>A are the major determinants of the inter-individual variability in the dosage requirements of oral anticoagulants. This study provides a first evaluation of these 3 polymorphisms in a Romanian population. A total of 332 Romanian individuals were genotyped for the CYP2C9*2, CYP2C9*3 and VKORC1 -1639 G>A polymorphisms using the PCR-RFLP technique. Sixty-two individuals (18.7%) were heterozygous for CYP2C9*2, whereas 47 individuals (14.1%) were heterozygous for CYP2C9*3. Fourteen individuals (4.2%) had a CYP2C9*2 homozygous, CYP2C9*3 homozygous or CYP2C9*2/CYP2C9*3 compound heterozygous genotype. These individuals are predicted to have the lowest CYP2C9 enzymatic activity. The allele frequencies of the CYP2C9*2 and CYP2C9*3 polymorphisms were 11.3% and 9.3% respectively. For the VKORC1 -1639 G>A polymorphism, there were 170 heterozygotes (51.2%) and 55 (16.6%) homozygotes for the A allele. The frequency of the A allele was 42.2%. Overall, the distribution of the CYP2C9*2, CYP2C9*3 and VKORC1 -1639 G>A polymorphisms observed in our cohort is in accordance with other Caucasian populations. A large number of Romanians are expected to harbour at least one CYP2C9 variant allele and/or one VKORC1 -1639 G>A allele. This frequency has major implications in the pharmacogenomics of oral anticoagulants in Romanians.

Genetic polymorphisms of CYP2C8, CYP2C9 and CYP2C19 in Ecuadorian Mestizo and Spaniard populations: a comparative study

This study was designed to investigate the potential differences between Spaniards and Ecuadorian Mestizo people regarding CYP2C8, CYP2C9, and CYP2C19 genetic polymorphisms. DNA from 282 Spaniard and 297 Ecuadorian subjects were analyzed by either a previously reported pyrosequencing method (CY2C8*3, CYP2C9*2, CYP2C9*3, CYP2C19*2 and CYP2C19*3) or a nested PCR technique (CYP2C19*17). Whereas CYP2C19*17 allele distribution was higher in Ecuadorians than in Spaniards (P < 0.001) and the frequency of CYP2C19*3 was similar in these two populations (P > 0.05), the other allelic variants were detected at significantly lower frequencies in Ecuadorians than in Spaniards (P < 0.05). According to the diplotype distributions, the prevalence of the presumed CYP2C9 and CYP2C8 extensive metabolizers was higher in Ecuadorians than in Spaniards (P < 0.05). Individuals genotyped CYP2C19*1/*17 and *17/*17 who were considered as ultrarapid metabolizers were overrepresented in Ecuadorians in relation to Spaniards (P < 0.001). By contrast, among Ecuadorians no poor metabolizers (PMs) of either CYP2C8 or CYP2C9 were found and only two individuals were CYP2C19 PMs. These data are compatible with a higher CYP2C8, CYP2C9, and CYP2C19 activity in Mestizo Ecuadorians as opposed to Spaniards, which could imply differences in dosage requirements for drugs metabolized by these cytochromes and should also be considered in allele-disease association studies.

Distribution of genetic polymorphisms of genes encoding drug metabolizing enzymes & drug transporters - a review with Indian perspective

Phase I and II drug metabolizing enzymes (DME) and drug transporters are involved in the absorption, distribution, metabolism as well as elimination of many therapeutic agents, toxins and various pollutants. Presence of genetic polymorphisms in genes encoding these proteins has been associated with marked inter-individual variability in their activity that could result in variation in drug response, toxicity as well as in disease predisposition. The emergent field pharmacogenetics and pharmacogenomics (PGx) is a promising discipline, as it predicts disease risk, selection of proper medication with regard to response and toxicity, and appropriate drug dosage guidance based on an individual's genetic make-up. Consequently, genetic variations are essential to understand the ethnic differences in disease occurrence, development, prognosis, therapeutic response and toxicity. For that reason, it is necessary to establish the normative frequency of these genes in a particular population before unraveling the genotype-phenotype associations. Although a fair amount of allele frequency data are available in Indian populations, the existing pharmacogenetic data have not been compiled into a database. This review was intended to compile the normative frequency distribution of the variants of genes encoding DMEs (CYP450s, TPMT, GSTs, COMT, SULT1A1, NAT2 and UGTs) and transporter proteins (MDR1, OCT1 and SLCO1B1) with Indian perspective.

Genotyping of CYP2C9 and VKORC1 in the Arabic population of Al-Ahsa, Saudi Arabia

Polymorphisms in the genes encoding CYP2C9 enzyme and VKORC1 reductase significantly influence the dose variability of coumarinic oral anticoagulants (COAs). Substantial inter- and intraethnic variability exists in the frequencies of CYP2C9*2 and *3 and VKORC1 -1639A alleles. However, the prevalence of CYP2C9 and VKORC1 genetic variants is less characterized in Arab populations. A total of 131 healthy adult subjects from the Al-Ahsa region of Saudi Arabia were genotyped for the CYP2C9 *2 and *3 and VKORC1 -1639G>A polymorphisms by PCR-RFLP method. The frequencies of the CYP2C9 *2 and *3 and VKORC1 -1639A alleles were 13.3%, 2.3%, and 42.4%, respectively, with no subjects carrying 2 defective alleles. The frequencies of the CYP2C9 *3 and VKORC1 -1639A alleles were significantly lower than those reported in different Arabian populations. None of the subjects with the VKORC1 -1639AA genotype were carriers of CYP2C9 *1/*3 genotypes that lead to sensitivity to COAs therapy. The low frequency of the CYP2C9 *3 allele combined with the absence of subjects carrying 2 defective CYP2C9 alleles suggests that, in this specific population, pharmacogenetic COAs dosing may mostly rely upon VKORC1 genotyping.

Genotype-phenotype correlation of cytochrome P450 2C9 polymorphism in Indian National Capital Region

Identification of polymorphism of cytochrome P450 2C9 (CYP2C9) enzymes in different ethnic populations is important to understand the differences in clinical responses to drugs. This study determines the CYP2C9 genetic polymorphism in Indian National Capital Region and correlates the phenotype-genotype. Losartan (25 mg) was administered to 107 volunteers to assess CYP2C9 activity, and, on the basis of results, volunteers were categorized as rapid and poor metabolizers. Molecular typing of CYP2C9*1 (wild type), CYP2C9*2, and CYP2C9*3 (the most common variant) was carried out by single-base primer extension technology for 37 subjects, of which 9 were poor metabolizers, and 28 were rapid metabolizers. 14.28 % of the studied population was identified as poor metabolizer for the category of drugs metabolized by CYP2C9. Significant difference was observed between the mean ratio (drug/metabolite) of poor (11.38 ± 5.88) and rapid (1.18 ± 1.11) drug metabolizers. The study suggests that phenotyping of CYP2C9 is desirable before enrollment of subjects for clinical trials or for deciding drug dose regimen as 14.28 % of study population was found to be poor metabolizer for the category of drugs metabolized by CYP2C9. This study establishes phenotype-genotype correlation, and proposes to use genotyping or phenotyping to evaluate the status of drug metabolizing capacity of CYP2C9 as a primary screening procedure before enrolling subjects in clinical trials or in clinical practice.

Interethnic and Intraethnic Variability of CYP2C8 and CYP2C9 Polymorphisms in Healthy Individuals

Cytochrome P450 (CYP) superfamily members CYP2C8 and CYP2C9 are polymorphically expressed enzymes that are involved in the metabolic inactivation of several drugs, including, among others, antiepileptics, NSAIDs, oral hypoglycemics, and anticoagulants. Many of these drugs have a narrow therapeutic index, and growing evidence indicates a prominent role of CYP2C8 and CYP2C9 polymorphisms in the therapeutic efficacy and in the development of adverse effects among patients treated with drugs that are CYP2C8 or CYP2C9 substrates. In this review, we summarize present knowledge on human variability in the frequency of variant CYP2C8 and CYP2C9 alleles. Besides an expected interethnic variability in allele frequencies, a large intraethnic variability exists. Among Asian subjects, for example, statistically significant differences (p < 0.0001) in CYP2C9*3 allele frequencies between Chinese and Japanese individuals have been reported. In addition, individuals from East Asia present different allele frequencies for CYP2C9*2 and CYP2C9*3 compared with South Asian subjects (p < 0.0001). Among Caucasian Europeans, statistically significant differences for the frequency of CYP2C8*3, CYP2C9*2, and CYP2C9*3 exist (p < 0.0001). This indicates that Asian individuals or Caucasian European individuals cannot be considered as homogeneous groups regarding CYP2C8 or CYP2C9 allele frequencies. Caucasian American subjects also show a large variability in allele frequencies, which is likely to be related to ethnic ancestry. A higher frequency of variant CYP2C8 and CYP2C9 alleles is expected among Caucasian Americans with South European ancestry than in individuals with North European ancestry. The findings summarized in this review suggest that among individuals with Asian or European ancestry, intraethnic differences in the risk of developing adverse effects with drugs that are CYP2C8 or CYP2C9 substrates are to be expected. In addition, the observed intraethnic variability reinforces the need for proper selection of control subjects and points against the use of surrogate control groups for studies involving association of CYP2C8 or CYP2C9 alleles with adverse drug reactions or spontaneous diseases.

Frequency of VKORC1 (C1173T) and CYP2C9 genetic polymorphisms in Egyptians and their influence on warfarin maintenance dose: proposal for a new dosing regimen

INTRODUCTION

Warfarin is one of the most widely used anticoagulants, yet interindividual differences in drug response, a narrow therapeutic range and a high risk of bleeding or stroke complicate its use. We aimed to determine the allele and genotype frequency of VKORC1 1173 C>T, CYP2C9*2 and CYP2C9*3 variant polymorphisms in the Egyptian population and to evaluate their influence on the interindividual differences in warfarin dosage.

METHODS

A total of 154 unrelated healthy adult patients and 46 warfarin-treated patients were included. SYBR Green-based real-time polymerase chain reaction (PCR) assay was used for studying VKORC1 (C1173T) and CYP2C9*3 polymorphisms. Mutagenically separated PCR assay was used to detect the CYP2C9*2 allele.

RESULTS

VKORC1 genotype frequencies were 11%, 24% and 65% for CC, CT and TT, respectively. The prevalence of CYP2C9 haplotypes was 81% (*1\*1), 3.3% (*1\*2), 9.7% (*1\*3), 4.5% (*2\*2) and 0.65% (2\*3 and *3\*3). VKORC1 TT and CYP2C9*2\*2 were associated with a significantly lower warfarin dose. VKORC1 and CYP2C9 accounted for 31.7% and 15.6% of warfarin dose variability, respectively, and together with clinical factors explained 61.3% of total variability.

CONCLUSION

VKORC1-TT and CYP2C9 *1/*1 are the most prevalent genotypes among Egyptians. Patients with VKORC1-TT genotype required a lower warfarin dose.

Allele and genotype frequencies of CYP2C9 within an Iranian population (Mazandaran)

Cytochrome P450 2C9 (CYP2C9) is a polymorphic enzyme responsible for the metabolism of different drugs, some with low therapeutic index. The frequency of functionally important mutations and alleles of the gene coding for CYP2C9 shows wide ethnic variations. The present study aimed to determine the prevalence of the most common allelic variants of the CYP2C9 enzyme and to predict the genotype frequency in the Mazandarani ethnic group among the Iranian population. Genotyping of CYP2C9 allelic variants was carried out in 103 unrelated subjects by polymerase chain reaction and restriction fragment length pattern analysis. The frequencies for CYP2C9 alleles *1, *2, and *3 were 78%, 12%, and 10%, respectively. No subjects were found carrying the CYP2C19*11 allele. The frequencies of CYP2C9 genotypes *1/*1, *1/*2, *1/*3, *2/*2, *2/*3, and *3/*3 were 61%, 19%, 16%, 1.5%, 2.5%, and 0.0%, respectively. The result of the present study showed that the two inactive alleles of CYP2C9 accounted for 22% of CYP2C9 alleles in our sample versus 1.5%-29% reported in other populations. The frequencies of the studied alleles resulted in significant differences between our sample and African and Eastern Asian populations.

CYP2C9 polymorphism in patients with epilepsy: genotypic frequency analyzes and phenytoin adverse reactions correlation

OBJECTIVE

CYP2C9 is a major enzyme in human drug metabolism and the polymorphism observed in the corresponding gene may affect therapeutic outcome during treatment. The distribution of variant CYP2C9 alleles and prevalence of phenytoin adverse reactions were hereby investigated in a population of patients diagnosed with epilepsy.

METHOD

Allele-specific PCR analysis was carried out in order to determine frequencies of the two most common variant alleles, CYP2C9*2 and CYP2C9*3 in genomic DNA isolated from 100 epileptic patients. We also analyzed the frequency of phenytoin adverse reactions among those different genotypes groups. The data was presented as mean±standard deviation.

RESULTS

The mean age at enrollment was 39.6±10.3 years (range, 17-72 years) and duration of epilepsy was 26.5±11.9 years (range 3-48 years). The mean age at epilepsy onset was 13.1±12.4 years (range, 1 month-62 years). Frequencies of CYP2C9*1 (84%), CYP2C9*2 (9%) and CYP2C9*3 (7%) were similar to other published reports. Phenytoin adverse reactions were usually mild and occurred in 15% patients, without correlation with the CYP2C9 polymorphism (p=0.34).

CONCLUSION

Our findings indicate an overall similar distribution of the CYP2C9 alleles in a population of patients diagnosed with epilepsy in the South of Brazil, compared to other samples. This sample of phenytoin users showed no drug related adverse reactions and CYP2C9 allele type correlation. The role of CYP2C9 polymorphism influence on phenytoin adverse reaction remains to be determined since some literature evidence and our data found negative results.

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.

Frequency of CYP2C9 alleles in Koreans and their effects on losartan pharmacokinetics

AIM

CYP2C9 enzyme metabolizes numerous clinically important drugs. The aim of this study is to investigate the frequencies of CYP2C9 genotypes and the effects of selected alleles on losartan pharmacokinetics in a large sample of the Korean population.

METHODS

The CYP2C9 gene was genotyped in 1796 healthy Korean subjects. CYP2C9 alleles (CYP2C9*1, *2, *3 and *13 alleles) were measured using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay and direct sequencing assay. The enzymatic activity of each CYP2C9 genotype was evaluated using losartan as the substrate.

RESULTS

The frequencies of CYP2C9*1, *3 and *13 allele were 0.952 (95% confidence interval 0.945-0.959), 0.044 (95% CI 0.037-0.051) and 0.005 (95% CI 0.003-0.007), respectively. The frequencies of the CYP2C9*1/*1, *1/*3, *1/*13 and *3/*3 genotypes were 0.904 (95% CI 0.890-0.918), 0.085 (95% CI 0.072-0.098), 0.009 (95% CI 0.005-0.013) and 0.001 (95% CI 0.000-0.002), respectively. In the pharmacokinetics studies, the AUC(0-∞) of losartan in CYP2C9*3/*3 subjects was 1.42-fold larger than that in CYP2C9*1/*1 subjects, and the AUC(0-∞) of E-3174, a more active metabolite of losartan, in CYP2C9*3/*3 subjects was only 12% of that in CYP2C9*1/*1 subjects.

CONCLUSION

The results confirmed the frequencies of CYP2C9 genotypes in a large cohort of Koreans, and detected the CYP2C9*3/*3 genotype. CYP2C9*3/*3 subjects metabolized much less losartan into E-3174 than CYP2C9*1/*1 subjects.

Population pharmacokinetic analysis of glimepiride with CYP2C9 genetic polymorphism in healthy Korean subjects

PURPOSE

The purpose of this study was to develop a population pharmacokinetic (PPK) model of glimepiride and to investigate the influence of genetic polymorphisms in CYP2C9 on the PPK of glimepiride in healthy Korean subjects.

METHODS

Serum data after a single oral dose of 2 mg of glimepiride in 177 healthy male Korean subjects (CYP2C9*1*1: 163 subjects, *1/*3: 14 subjects) were used. We estimated the PPK of glimepiride using a nonlinear mixed effects modeling (NONMEM) method and explored the possible influence of genetic polymorphisms in CYP2C9 on the PPK of glimepiride.

RESULTS

The disposition of glimepiride was best described with a two-compartment model with a Weibull-type absorption and first-order elimination. The visual predictive check indicated that the pharmacokinetic profile of glimepiride was adequately described by the proposed PPK model. The CYP2C9 genotypes as covariate significantly (P < 0.001) influenced the apparent oral clearance (CL/F) of glimepiride. The estimated CL/F of glimepiride was higher (1.60-fold) in CYP2C9*1/*1 subjects than in CYP2C9*1/*3 subjects.

CONCLUSIONS

This study indicates that genetic polymorphisms of CYP2C9 influence the substantial interindividual variability in the disposition of glimepiride, and these polymorphisms may affect the clinical response to glimepiride therapy.

Distribution of the major cytochrome P450 (CYP) 2C9 genetic variants in a Saudi population

Cytochrome P450 (CYP) 2C9 is responsible for the metabolism of a number of widely used drugs such as oral anticoagulants, oral antidiabetics and non-steroidal anti-inflammatory drugs. The CYP2C9 is a genetically polymorphic enzyme. The most common allele is CYP2C9*1, while CYP2C9*2 and CYP2C9*3 are the less-frequent variants. The activity of the enzyme encoded by either CYP2C9 *2 or *3 variant is lower compared with that of the CYP2C9*1. The metabolism of most of the CYP2C9 substrates decreases in varying degrees in subjects carrying the CYP2C9 *2 or *3 allele. The aim of this study was to investigate the frequencies of the major variants of the CYP2C9 in Saudi Arabians.

Frequency of CYP2C9 variant alleles, including CYP2C9*13 in a Korean population and effect on glimepiride pharmacokinetics

WHAT IS KNOWN AND OBJECTIVE

Cytochrome P450 (CYP) 2C9 is a clinically important enzyme involved in the metabolism of many drugs commonly used in humans. Of several allelic variants known to affect the catalytic activity of the CYP2C9 enzyme, the frequencies of the CYP2C9*3 and CYP2C9*13 alleles in the Korean population have been reported as 1·1% and 0·6%, respectively. Our objective was to re-evaluate the frequencies of CYP2C9 allelic variants in the Korean population, including the CYP2C9*13 allele by pyrosequencing, and to investigate the pharmacokinetics of glimepiride in relation to CYP2C9 genotypes, including CYP2C9*3/*3.

METHODS

295 subjects were genotyped for CYP2C9*2 and CYP2C9*3 using the TaqMan procedure, and for CYP2C9*13 using pyrosequencing. These data were combined with our previously reported data to assess the CYP2C9 allele and genotype frequencies in 869 Korean subjects. Data from 24 of the 295 genotyped subjects (22 CYP2C9*1/*1 homozygotes, one CYP2C9*1/*3 heterozygote and one CYP2C9*3/*3 homozygote) who had participated in a bioequivalence study were analysed retrospectively to examine the effects of CYP2C9 genotype on glimepiride pharmacokinetics.

RESULTS

The frequencies of the CYP2C9*1/*3, *3/*3, and *1/*13 genotypes in the study population (n = 295) were 0·081 (n = 24), 0·010 (n = 3) and 0·003 (n = 1), respectively. In the 869 subjects from the combined studies, allele frequencies for CYP2C9*3 and CYP2C9*13 were 0·025 (95% CI: 0·018, 0·033) and 0·002 (95% CI: 0·000, 0·010), respectively. Relative to CYP2C9*1 homozygotes, the one CYP2C9*3 homozygous subject was found to have a higher AUC(0-∞) value (490% of the reference value) and a lower oral clearance rate (18% of the reference).

WHAT IS NEW AND CONCLUSION

This study is the first examination of CYP2C9*3 homozygotes in the Korean population. Our data on the one subject with this genotype suggest that CYP2C9*3/*3 momozygotes have lower clearance of glimepiride and are exposed to higher levels of the drug than wild-type homozygotes. Although we identified a subject with the CYP2C9*13 allele using a new pyrosequencing assay, we were unfortunately unable to investigate its effects on glimepiride pharmacokinetics.

A haplotype of CYP2C9 associated with warfarin sensitivity in mechanical heart valve replacement patients

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT * CYP2C9 single nucleotide polymorphisms (SNPs) are important in safe and effective oral anticoagulation with warfarin use. * Although CYP2C9*2 and *3 are important genetic factors for the warfarin dose, one of the CYP2C9 SNPs, IVS-65G>C, has been suggested to be associated with warfarin sensitivity. However, as of yet, there has been no explanation about the possible mechanism and linkage analysis. WHAT THIS PAPER ADDS * New information on CYP2C9 SNPs and their occurrences in common haplotype structures in healthy unrelated Koreans and in individuals who require low warfarin dose after mechanical heart valve replacements (MHVRs) were studied. * Additional evidence showed that an Asian dominant haplotype consisting of -1565C>T, -1188T>C, IVS3+197G>A, IVS3-334C>T, IVS3-65G>C, IVS4-115A>G and IVS5-73A>G could be associated with a low warfarin maintenance dose in mechanical heart valve replacement (MHVR) patients. AIMS The objectives of this study were to determine the distribution of CYP2C9 variants in Koreans and investigate their association with warfarin dose requirements in patients who received MHVRs. METHODS All nine exons, intron-exon junction, and promoter region of CYP2C9 were amplified and directly sequenced in 50 healthy normal Koreans. Additional direct DNA sequencing of the CYP2C9 gene was conducted in 36 of the 267 MHVR patients who required low maintenance warfarin doses without carrying CYP2C9*3 and VKORC1 1173T mutations. The effects of CYP2C9 genetics on warfarin maintenance dose were assessed in 267 MHVR patients. RESULTS Thirty-nine single nucleotide polymorphisms (SNPs) including seven previously unidentified SNPs were identified in 50 Koreans by direct DNA sequencing. One of the CYP2C9 haplotypes exhibited an association with warfarin low dose requirement. The adjusted odds ratio for the haplotype between the low dose group and the normal subjects was 2.5 (95% confidence interval 1.05, 6.16). This haplotype consisting of -1565C>T, -1188T>C, IVS3+197G>A, IVS3-334C>T, IVS3-65G>C, IVS4-115A>G, and IVS5-73A>G was found in 15% of 36 MHVR patients who required low warfarin doses, while 4% of 50 normal healthy subjects exhibited this haplotype. One of the SNPs comprising this haplotype, -1565C>T, apparently changed a protein binding pattern as observed in electrophoretic mobility shift assay. CONCLUSION The haplotype including -1565C>T, -1188T>C, IVS3+197G>A, IVS3-334C>T, IVS3-65G>C, IVS4-115A>G, and IVS5-73A>G seems to be associated with low warfarin dose requirement and this haplotype could be considered in the development of a warfarin dose prediction model for Asian populations.

VKORC1 pharmacogenetics and pharmacoproteomics in patients on warfarin anticoagulant therapy: transthyretin precursor as a potential biomarker

Background

Recognizing specific protein changes in response to drug administration in humans has the potential for the development of personalized medicine. Such changes can be identified by pharmacoproteomics approach based on proteomic technologies. It can also be helpful in matching a particular target-based therapy to a particular marker in a subgroup of patients, in addition to the profile of genetic polymorphism. Warfarin is a commonly prescribed oral anticoagulant in patients with prosthetic valve disease, venous thromboembolism and stroke.

Methods and Finding

We used a combined pharmacogenetics and iTRAQ-coupled LC-MS/MS pharmacoproteomics approach to analyze plasma protein profiles of 53 patients, and identified significantly upregulated level of transthyretin precursor in patients receiving low dose of warfarin but not in those on high dose of warfarin. In addition, real-time RT-PCR, western blotting, human IL-6 ELISA assay were done for the results validation.

Conclusion

This combined pharmacogenomics and pharmacoproteomics approach may be applied for other target-based therapies, in matching a particular marker in a subgroup of patients, in addition to the profile of genetic polymorphism.

Influence of CYP4F2 rs2108622 (V433M) on warfarin dose requirement in Asian patients

Warfarin exhibits wide interpatient variability in dosing requirements. Recent studies have shown a novel polymorphism (rs2108622, V433M) in the CYP4F2 gene to be associated with variability in warfarin requirements in Caucasians. The purpose of this study was to evaluate the impact of rs2108622 on warfarin dose requirements in the Asian population. The mean warfarin dose was found to be significantly lower in patients carrying homozygous wild-type allele CC when compared with patients carrying variant alleles CT and TT (CC vs CT+TT: 3.0 mg/day vs 3.75 mg/day, p = 0.033). In patients harboring VKORC1 diplotypes associated with low warfarin requirements, a linear regression model which included age, weight, CYP2C9 and CYP4F2 variants accounted for 38% of the variability in warfarin dose. Approximately 11% of the dose variation was explained by CYP4F2 rs2108622 (p = 0.004). The influence of rs2108622 in patients harboring VKORC1 diplotypes associated with high warfarin requirements was not significant. This study suggests that CYP4F2 rs2108622 may significantly affect warfarin dose requirements in carriers of VKORC1 low-dose-associated diplotypes.