Lower frequency of CYP2C9*2 in Mexican-Americans compared to Spaniards

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.

Interethnic Variability in CYP2D6, CYP2C9, and CYP2C19 Genes and Predicted Drug Metabolism Phenotypes Among 6060 Ibero- and Native Americans: RIBEF-CEIBA Consortium Report on Population Pharmacogenomics

Pharmacogenetic variation in Latin Americans is understudied, which sets a barrier for the goal of global precision medicine. The RIBEF-CEIBA Network Consortium was established to characterize interindividual and between population variations in CYP2D6, CYP2C9, and CYP2C19 drug metabolizing enzyme genotypes, which were subsequently utilized to catalog their "predicted drug metabolism phenotypes" across Native American and Ibero American populations. Importantly, we report in this study, a total of 6060 healthy individuals from Ibero-America who were classified according to their self-reported ancestry: 1395 Native Americans, 2571 Admixed Latin Americans, 96 Afro-Latin Americans, 287 white Latin Americans (from Cuba), 1537 Iberians, and 174 Argentinean Ashkenazi Jews. Moreover, Native Americans were grouped into North-, Central-, and South Amerindians (from Mexico, Costa Rica, and Peru, respectively). All subjects were studied for the most common and functional CYP2D6, CYP2C9, and CYP2C19 allelic variants, and grouped as genotype-predicted poor or ultrarapid metabolizer phenotypes (gPMs and gUMs, respectively). Native Americans showed differences from each ethnic group in at least two alleles of CYP2D6, CYP2C9, and CYP2C19. Native Americans had higher frequencies of wild-type alleles for all genes, and lower frequency of CYP2D6*41, CYP2C9*2, and CYP2C19*17 (p < 0.05). Native Americans also showed less CYP2C19 gUMs than the rest of the population sample. In addition, differences within Native Americans (mostly North vs. South) were also found. The interethnic differences described supports the need for population-specific personalized and precision medicine programs for Native Americans. To the best of our knowledge, this is the largest study carried out in Native Americans and other Ibero-American populations analyzing CYP2D6, CYP2C9, and CYP2C19 genetic polymorphisms. Population pharmacogenomics is a nascent field of global health and warrants further research and education.

Interethnic variability of pharmacogenetic biomarkers in Mexican healthy volunteers: a report from the RIBEF (Ibero-American Network of Pharmacogenetics and Pharmacogenomics)

Mexico presents a complex population diversity integrated by Mexican indigenous (MI) (7% of Mexico's population) and Mexican mestizos (MMs). This composition highlights the importance of pharmacogenetic studies in Mexican populations. The aims of this study were to analyze the reported frequencies of the most relevant pharmacogenetic biomarkers and metabolic phenotypes in healthy volunteers from Mexican populations and to assess its interethnic variability across MI and MM populations. After a literature search in PubMed, and according to previously defined inclusion criteria, 63 pharmacogenetic studies performed in Mexican healthy volunteers up to date were selected. These reports comprised 56,292 healthy volunteers (71.58% MM). Allele frequencies in 31 pharmacogenetic biomarkers, from 121 searched, are described. Nine of these biomarkers presented variation within MM and MI groups. The frequencies of CYP2D6*3, *4, *5, *10, *17, *35 and *41 alleles in the MM group were different from those reported in the MI group. CYP2C9*2 and *3 alleles were more frequent in MM than in MI populations (χ2 test, p<0.05). CYP2C19*3 allele was not found in the MM or MI populations reported. For UGT1A1*28, only one study was found. HLA-A*31:01 and HLA-B*15:02 were present in some MM and MI populations. Poor metabolizers for CYP2D6 and CYP2C9 were more frequent in MM than in MI groups (χ2 test, p<0.05). Only 26% of the relevant pharmacogenetic biomarkers searched have been studied in Mexican healthy volunteers; therefore, further studies are warranted. The frequency variation of biomarkers in MM and MI populations could be important for the clinical implementation of pharmacogenetics in Mexico.

Genetic variability of CYP2C9*2 and CYP2C9*3 in seven indigenous groups from Mexico

Aim: CYP2C9 is one of the major drug metabolizing enzymes, however, little is known about polymorphisms in CYP2C9 gene and pharmacological implications in Mexican indigenous populations. Thus, frequencies of CYP2C9*2 and CYP2C9*3 alleles were evaluated in indigenous groups located in northwest (Cora), center (Mazahua and Teenek), south (Chatino and Mixteco) and southeast (Chontal and Maya) regions Mexico. Materials & methods: Allelic discrimination was performed by real-time PCR. Results: CYP2C9*2 allele was found only in Chontal and Maya groups, despite the low contribution of Caucasian component in these populations. CYP2C9*3 allele was present in all populations except in Mazahua, showing a wide genetic variability in the studied populations. Interestingly, we found significant differences between indigenous groups in CYP2C9*3 allele, even in groups located at the same region and belonging to the same linguistic family. Conclusion: These results contribute to laying the pharmacogenetic bases in Mexico, in addition to improving treatment, taking into account the genetic interethnic differences.

Pharmacogenetics of drug-metabolizing enzymes in US Hispanics

Although the Hispanic population is continuously growing in the United States, they are underrepresented in pharmacogenetic studies. This review addresses the need for compiling available pharmacogenetic data in US Hispanics, discussing the prevalence of clinically relevant polymorphisms in pharmacogenes encoding for drug-metabolizing enzymes. CYP3A5*3 (0.245-0.867) showed the largest frequency in a US Hispanic population. A higher prevalence of CYP2C9*3, CYP2C19*4, and UGT2B7 IVS1+985 A>G was observed in US Hispanic vs. non-Hispanic populations. We found interethnic and intraethnic variability in frequencies of genetic polymorphisms for metabolizing enzymes, which highlights the need to define the ancestries of participants in pharmacogenetic studies. New approaches should be integrated in experimental designs to gain knowledge about the clinical relevance of the unique combination of genetic variants occurring in this admixed population. Ethnic subgroups in the US Hispanic population may harbor variants that might be part of multiple causative loci or in linkage-disequilibrium with functional variants. Pharmacogenetic studies in Hispanics should not be limited to ascertain commonly studied polymorphisms that were originally identified in their parental populations. The success of the Personalized Medicine paradigm will depend on recognizing genetic diversity between and within US Hispanics and the uniqueness of their genetic backgrounds.

Pharmacogenomic assessment of Mexican and Peruvian populations

BACKGROUND

Clinically relevant polymorphisms often demonstrate population-specific allele frequencies. Central and South America remain largely uncategorized in the context of pharmacogenomics.

MATERIALS & METHODS

We assessed 15 polymorphisms from 12 genes (ABCB1 3435C>T, ABCG2 Q141K, CYP1B1*3, CYP2C19*2, CYP3A4*1B, CYP3A5*3C, ERCC1 N118N, ERCC2 K751Q, GSTP1 I105V, TPMT 238G>C, TPMT 460G>A, TPMT 719A>G, TYMS TSER, UGT1A1*28 and UGT1A1 -3156G>A) in 81 Peruvian and 95 Mexican individuals.

RESULTS

Six polymorphism frequencies differed significantly between the two populations: ABCB1 3435C>T, CYP1B1*3, GSTP1 I105V, TPMT 460G>A, UGT1A1*28 and UGT1A1 -3156G>A. The pattern of observed allele frequencies for all polymorphisms could not be accurately estimated from any single previously studied population.

CONCLUSION

This highlights the need to expand the scope of geographic data for use in pharmacogenomics studies.

Genetic polymorphism analysis of the drug-metabolizing enzyme CYP2C9 in a Chinese Tibetan population

OBJECTIVES

The enzymatic activity of CYP2C9 results in broad inter-individual variability in response to certain pharmacotherapies. The present study aimed to screen Tibetan volunteers for CYP2C9 genetic polymorphisms. Previous research has focused on Han Chinese patients, while little is known about the genetic variation of CYP2C9 in Tibetan populations.

METHODS

We used DNA sequencing to investigate the promoter, exons and surrounding introns, and 3'-untranslated region of the CYP2C9 gene in 96 unrelated healthy Tibetan individuals.

RESULTS

We identified 26 different CYP2C9 polymorphisms in the Tibetan population, including two novel variants detected in exon 9 (50193G>A and 50197G>C). In addition, we determined the allele frequencies of CYP2C9*1 and *3 were 93.75% and 5.73%, respectively. The rare CYP2C9*55 allele was also found in 0.52% of the study population.

CONCLUSIONS

Our results provide information on CYP2C9 polymorphisms in Tibetan individuals, which may help to optimize pharmacotherapy effectiveness by providing personalized medicine to this ethnic group.

Pharmacogenetics of adverse reactions to antiepileptic drugs

INTRODUCTION

Adverse drug reactions (ADRs) are a major public health concern and a leading cause of morbidity and mortality in the world. In the case of antiepileptic drugs (AEDs), ADRs constitute a barrier to successful treatment since they decrease treatment adherence and impact patients' quality of life of patients. Pharmacogenetics aims to identify genetic polymorphisms associated with drug safety. This article presents a review of genes coding for drug metabolising enzymes and drug transporters, and HLA system genes that have been linked to AED-induced ADRs.

DEVELOPMENT

To date, several genetic variations associated with drug safety have been reported: CYP2C9*2 and *3 alleles, which code for enzymes with decreased activity, have been linked to phenytoin (PHT)-induced neurotoxicity; GSTM1 null alleles with hepatotoxicity induced by carbamazepine (CBZ) and valproic acid (VPA); EPHX1 polymorphisms with teratogenesis; ABCC2 genetic variations with CBZ- and VPA-induced neurological ADRs; and HLA alleles (e.g. HLA-B*15:02, -A*31:01, -B*15:11, -C*08:01) with cutaneous ADRs.

CONCLUSIONS

Published findings show that there are ADRs with a pharmacogenetic basis and a high interethnic variability, which indicates a need for future studies in different populations to gather more useful results for larger number of patients. The search for biomarkers that would allow predicting ADRs to AEDs could improve pharmacotherapy for epilepsy.

Present status and perspective of pharmacogenetics in Mexico

Drug costs account for up to 24% of the country's health expenditure and there are 13,000 registered drugs being prescribed. Diabetes is the main cause of death in the country, with over 85% of diabetic patients currently under drug treatment. The importance of knowing interindividual variability in drug metabolism on Mexican populations is thus evident. The purpose of this article is to provide an overlook of the current situation of pharmacogenetic research in Mexico, focusing on drug-metabolizing enzymes, and the possibility of developing a phenotyping cocktail for Mexican populations. So far, 21 pharmacogenetic studies on Mexican population samples (Mestizos and Amerindian) have been published. These have reported interindividual variability through phenotyping and/or genotyping cytochromes: CYP2D6, 2C19, 2C9, 2E1, and phase II enzymes UGT and NAT2. Some cytochromes with important clinical implications have not yet been phenotyped in Mexican populations. The development of a cocktail adapted to them could be a significant contribution to a larger knowledge on drug response variability at a lower price and shorter time. There are validated phenotyping cocktails that present several practical advantages, being valuable, safe, and inexpensive tools in drug metabolism characterization, which require only a single experiment to provide information on several cytochrome activities.

Cytochrome P450 genetic polymorphisms of Mexican indigenous populations

This review focuses on the genetic polymorphisms of the cytochrome P450 (CYP) genes in Mexican indigenous populations, who are a part of the wide ethnic diversity of this country. These native groups have a particular historical trajectory that is different from the Mexican Mestizos. This variability may be reflected in the frequency distribution of polymorphisms in the CYP genes that encode enzymes involved in the metabolism of drugs and other xenobiotics. Therefore, these polymorphisms may affect drug efficacy and safety in indigenous populations in Mexico. The present study aimed to analyze the prevalence of CYP polymorphisms in indigenous Mexicans and to compare the results with studies in Mexican Mestizos. Because the extrapolation of pharmacogenetic data from Mestizos is not applicable to the majority of indigenous groups, pharmacogenetic studies directed at indigenous populations need to be developed. The Amerindians analyzed in this study showed a low phenotypic (CYP2D6) and genotypic (CYP2D6, CYP2C9) diversity, unlike Mexican Mestizos. The frequency of polymorphisms in the CYP1A1, CYP2C19, CYP2E1, and CYP3A4 genes was more similar among the Amerindians and Mexican Mestizos, with the exception of the CYP1A2 gene, whose *1F variant frequency in Mexican Amerindians was the highest described to date.

Losartan hydroxylation phenotype in an Ecuadorian population: influence of CYP2C9 genetic polymorphism, habits and gender

AIM

To describe for the first time CYP2C9 hydroxylation phenotype with CYP2C9 genotypes in a Hispanic (Ecuadorian) population using losartan; and the relevance of gender, tobacco, ethanol and caffeine consumption on the enzyme hydroxylation capacity.

METHODS

Ecuadorian healthy volunteers (n = 194) received a single oral dose of 25 mg losartan. Losartan metabolic ratio was defined as losartan:E3174 concentration. CYP2C9 alleles *2, *3, *4, *5 and *6 were analyzed.

RESULTS

No phenotypically poor metabolizers were found. The metabolic ratio (mean ± standard deviation) was higher (p < 0.05) in CYP2C9*1/*3 carriers (12.4 ± 13.8; n = 6) versus CYP2C9*1/*1 (4.9 ± 7.0; n = 167), as well as in females versus males (6.72 ± 9.72 and 3.76 ± 4.48, respectively; p < 0.05). Only the following genotypes, CYP2C9*1/*1, CYP2C9*1/*2 and CYP2C9*1/*3, were found with a frequency of 86.1%, 10.8% and 3.1%, respectively.

CONCLUSION

Despite the mean metabolic ratio being higher in this population than in others previously studied across genotypes, no poor metabolizers, either phenotypically or genotypically, were found.

Allele frequency distribution of CYP2C9 2 and CYP2C9 3 polymorphisms in six Mexican populations

Allele frequency differences of functional CYP2C9 polymorphisms are responsible for some of the variation in drug response observed in human populations. The most relevant CYP2C9 functional variants are CYP2C9*2 (rs1799853) and CYP2C9 3 (rs1057910). These polymorphisms show variation in allele frequencies among different population groups. The present study aimed to analyze these polymorphisms in 947 Mexican-Mestizo from Mexico City and 483 individuals from five indigenous Mexican populations: Nahua, Teenek, Tarahumara, Purepecha and Huichol. The CYP2C9*2 allele frequencies in the Mestizo, Nahua and Teenek populations were 0.051, 0.007 and 0.005, respectively. As for CYP2C9 3, the allelic frequencies in the Mestizo, Nahua and Teenek populations were 0.04, 0.005 and 0.005, respectively. The CYP2C9 2 and CYP2C9 3 alleles were not observed in the Tarahumara, Purepecha and Huichol populations. These findings are in agreement with previous studies reporting very low allele frequencies for these polymorphisms in American Indigenous populations.

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.

Pharmacogenetics of the antiepileptic drugs phenytoin and lamotrigine

Patients treated with antiepileptic drugs can exhibit large interindividual variability in clinical efficacy or adverse effects. This could be partially due to genetic variants in genes coding for proteins that function as drug metabolizing enzymes, drug transporters or drug targets. The purpose of this article is to provide an overview of the current knowledge on the pharmacogenetics of two commonly prescribed antiepileptic drugs with similar mechanisms of action; phenytoin (PHT) and lamotrigine (LTG). These two drugs have been selected in order to model the pharmacogenetics of Phase I and Phase II metabolism for PHT and LTG, respectively. In light of the present evidence, patients treated with PHT could benefit from CYP2C9 and CYP2C19 genotyping/phenotyping. For those under treatment with LTG, UGT1A4 and UGT2B7 genotyping might be of clinical use and could contribute to the interindividual variability in LTG concentration to dose ratio in epileptic patients.

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.

Prediction of warfarin dose reductions in Puerto Rican patients, based on combinatorial CYP2C9 and VKORC1 genotypes

BACKGROUND

The influence of CYP2C9 and VKORC1 polymorphisms on warfarin dose has been investigated in white, Asian, and African American populations but not in Puerto Rican Hispanic patients.

OBJECTIVE

To test the associations between genotypes, international normalized ratio (INR) measurements, and warfarin dosing and gauge the impact of these polymorphisms on warfarin dose, using a published algorithm.

METHODS

A retrospective warfarin pharmacogenetic association study in 106 Puerto Rican patients was performed. DNA samples from patients were assayed for 12 variants in both CYP2C9 and VKORC1 loci by HILOmet PhyzioType assay. Demographic and clinical nongenetic data were retrospectively collected from medical records. Allele and genotype frequencies were determined and Hardy-Weinberg equilibrium (HWE) was tested.

RESULTS

Sixty-nine percent of patients were carriers of at least one polymorphism in either the CYP2C9 or the VKORC1 gene. Double, triple, and quadruple carriers accounted for 22%, 5%, and 1%, respectively. No significant departure from HWE was found. Among patients with a given CYP2C9 genotype, warfarin dose requirements declined from GG to AA haplotypes; whereas, within each VKORC1 haplotype, the dose decreased as the number of CYP2C9 variants increased. The presence of these loss-of-function alleles was associated with more out-of-range INR measurements (OR = 1.38) but not with significant INR >4 during the initiation phase. Analyses based on a published pharmacogenetic algorithm predicted dose reductions of up to 4.9 mg/day in carriers and provided better dose prediction in an extreme subgroup of highly sensitive patients, but also suggested the need to improve predictability by developing a customized model for use in Puerto Rican patients.

CONCLUSIONS

This study laid important groundwork for supporting a prospective pharmacogenetic trial in Puerto Ricans to detect the benefits of incorporating relevant genomic information into a customized DNA-guided warfarin dosing algorithm.

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.

Drug interactions with antiretrovirals and warfarin

IMPORTANCE OF THE FIELD

Antiretroviral therapy exhibits significant potential to alter the metabolism of other medications. Warfarin is widely used for the management of clotting disorders and is prone to drug-drug interactions that can result in subtherapeutic anticoagulation or over-anticoagulation.

AREAS COVERED IN THIS REVIEW

The mechanism and clinical significance of drug-drug interactions between warfarin and individual antiretrovirals are discussed. Literature searches were conducted in August of 2009 using multiple databases including Medline (1950 - 2009), EMBASE (1980 - 2009), International Pharmaceutical Abstracts (1970 - 2009) and the Cochrane Database of Systematic Reviews. The following search terms were utilized: warfarin, HIV, antiretroviral, drug interaction, protease inhibitor (PI), non-nucleoside reverse-transcriptase inhibitor (NNRTI), cytochrome P450 (CYP450), CYP2C9 and individual antiretrovirals by name. The manufacturers of PIs and NNRTIs were also contacted regarding unpublished data.

WHAT THE READER WILL GAIN

Clinicians will gain an understanding of the antiretrovirals that are prone to alter warfarin metabolism and the implications for warfarin dose modification.

TAKE HOME MESSAGE

Metabolic interaction between warfarin and antiretrovirals is likely, particularly if NNRTIs or PIs are included in the antiretroviral regimen. Titration of warfarin dose should be conducted on the basis of close monitoring of the international normalized ratio. Empiric warfarin dose modifications should be considered for individual antiretrovirals.

CYP2C9 allele frequency differences between populations of Mexican-Mestizo, Mexican-Tepehuano, and Spaniards

Earlier we had found that the CYP2C9*2 allelic frequency was lower in Mexican-Americans living in California than in Spaniards (SP). This was assumed to be related to the low CYP2C9*2 and *3 allele frequencies in Orientals. This study was therefore aimed at analyzing whether there were also differences in CYP2C9 allele frequencies between Mexican-Tepehuanos (MT) and Mexican-Mestizos (MM) living in northwestern Mexico and SP. The CYP2C9*2 frequency was expected to be lower in the indigenous MT than in the two other groups, and lower in MM than in SP as in our earlier study. CYP2C9 genotypes and allele frequencies of two populations of healthy volunteers, MT (n=99) and MM (n=102), were compared with a population of SP (n=327). The data were also compared with our previously published population of Mestizo-Mexican-Americans (MA). The CYP2C9 genotypes among the studied populations were in equilibrium. The frequencies of CYP2C9*2 were 0.01, 0.07, 0.08, and 0.16 for MT, MM, MA, and SP subjects, respectively. In agreement with our hypothesis, CYP2C9*2 was significantly lower in the Mexican populations than in the SP (P<0.05), and among Mexicans in the MT than in the MM and MA groups (P<0.05), which presented similar frequencies. Moreover, the frequency of CYP2C9*3 was found to be lower (P<0.05) in MM (0.015) and MT (0.015) than in MA (0.06) and SP (0.08). Finally, the CYP2C9*6 allele was present just in one MM subject, and CYP2C9*4 and *5 were not found in the studied populations. Therefore, these findings add further evidence about CYP2C9 genetic diversity within Hispanic populations with regard to their ancestry. Considering that CYP2C9*2 and CYP2C9*3 alleles have altered catalytic activities relative to CYP2C9*1, the present data suggest the need for pharmacogenetic studies to optimize drug dosages in different populations.

Implementing genotype-guided antithrombotic therapy

Genotyping has the potential to improve the efficacy and safety of major antithrombotic drugs. For warfarin, the stable maintenance dose varies from 1-10 mg/day. The VKORC1 -1639G>A allele and the CYP2C9*2 and *3 alleles (cumulative frequency: 90% in Asians, 65% in Europeans and 20% in Africans), explain 45% of response variability in European and 30% in African populations. The large clinical trials COAG and EU-PACT will define the extent to which pharmacogenetic dosing affects the safety and efficacy of warfarin and coumarin derivatives. The platelet inhibitor clopidogrel requires activation by the CYP2C19 enzyme. CYP2C19*2 and *3 alleles (cumulative frequency: 20-50%) produce null enzyme activity, and their presence attenuates platelet inhibition and increases cardiovascular events. The US FDA-mandated drug labeling recognizes the relevance of genotyping in the selection and dosing of both warfarin and clopidogrel.

Polymorphisms of human cytochrome P450 2C9 and the functional relevance

Human cytochrome P450 2C9 (CYP2C9) accounts for ∼20% of hepatic total CYP content and metabolizes ~15% clinical drugs such as phenytoin, S-warfarin, tolbutamide, losartan, and many nonsteroidal anti-inflammatory agents (NSAIDs). CYP2C9 is highly polymorphic, with at least 33 variants of CYP2C9 (*1B through *34) being identified so far. CYP2C9*2 is frequent among Caucasians with ~1% of the population being homozygous carriers and 22% are heterozygous. The corresponding figures for the CYP2C9*3 allele are 0.4% and 15%, respectively. There are a number of clinical studies addressing the impact of CYP2C9 polymorphisms on the clearance and/or therapeutic response of therapeutic drugs. These studies have highlighted the importance of the CYP2C9*2 and *3 alleles as a determining factor for drug clearance and drug response. The CYP2C9 polymorphisms are relevant for the efficacy and adverse effects of numerous NSAIDs, sulfonylurea antidiabetic drugs and, most critically, oral anticoagulants belonging to the class of vitamin K epoxide reductase inhibitors. Warfarin has served as a practical example of how pharmacogenetics can be utilized to achieve maximum efficacy and minimum toxicity. For many of these drugs, a clear gene-dose and gene-effect relationship has been observed in patients. In this regard, CYP2C9 alleles can be considered as a useful biomarker in monitoring drug response and adverse effects. Genetic testing of CYP2C9 is expected to play a role in predicting drug clearance and conducting individualized pharmacotherapy. However, prospective clinical studies with large samples are warranted to establish gene-dose and gene-effect relationships for CYP2C9 and its substrate drugs.

Prevalence of CYP2C9 polymorphisms in the south of Europe

CYP2C9 is a major liver enzyme responsible of the metabolism of many clinically important drugs. The presence of CYP2C9 genetic polymorphisms has been associated with marked interindividual variability in its catalytic activity that could result in drug toxicity. Here we present frequencies of the most common CYP2C9 coding variants CYP2C9*2 (C430T) and CYP2C9*3 (A1075C) in representative samples of four regions from Spain (Basque Country, n=358; Catalonia, n=240; Central Spain, n=190 and Galicia, n=288) and one northern Italian region, (Verona, n=164), which range between 0.125 and 0.165 in the case of CYP2C9*2 and between 0.071 and 0.085 for CYP2C9*3. No significant differences between CYP2C9 allele frequencies were found comparing all the sampled populations. A more extensive comparative analysis using allele frequency data of populations widely spread over Europe was performed, showing significant differences in the CYP2C9*2 allele frequencies distribution between some of the regions, being quite homogeneous in the case of CYP2C9*3 variant. The results obtained show that above 40% of our samples carry a mutate allele, which can result in a poor metabolization of low therapeutic index drugs as oral anticoagulants (warfarin, acenocoumarol), oral antidiabetic drugs and some non-steroidal anti-inflammatory drugs. Our study constitutes both a large (n=1240) and robust allele frequency database on CYP2C9 polymorphisms, which represents one of the most numerous CYP2C9*2 and *3 database existing to date.

DNA microarray technology in the clinical environment: the AmpliChip CYP450 test for CYP2D6 and CYP2C19 genotyping

INTRODUCTION

An important technological advance in genetic testing is the DNA microarray, which allows for the simultaneous testing of thousands of DNA sequences. The AmpliChip CYP450 Test employs this microarray technology for cytochrome P450 (CYP) 2D6 and CYP2C19 genotyping. Isoenzymes encoded by these genes are responsible for the metabolism of many widely prescribed drugs. The objectives of this study were to identify CYP2D6 and CYP2C19 alleles and phenotypes in a psychiatric patient population in Kentucky, and to describe practical issues associated with DNA microarray technology.

METHODS

A total of 4,532 psychiatric patients were recruited from three state hospitals in Kentucky. Whole blood, buccal swabs, or saliva samples were genotyped with the AmpliChip CYP450 Test to derive a predicted phenotype.

RESULTS

In this cohort, the overall prevalence of CYP2D6 poor metabolizers was 7.6% (95% CI 7%, 8.3%), 8.2% in the Caucasians (95% CI 7.4%, 9.%) and 1.8% in the African Americans (95% CI 0.9%, 3.5%). The overall prevalence of CYP2D6 ultrarapid metabolizers was 1.5% (95% CI 1.2%, 1.9%), 1.5% in the Caucasians (95% CI 1.1%, 1.9%) and 2.0% in the African Americans (95% CI 1.1%, 3.7%). The overall prevalence of CYP2C19 poor metabolizers was 2.0% (95% CI 1.8%, 2.7%), 2.2% in Caucasians (95% CI 1.6%, 2.5%) and 4.0% in African Americans (95% CI 2.6%, 6.1%).

CONCLUSION

We also propose a numeric system for expression of CYP2D6 and CYP2C19 enzyme activity to aid clinicians in determining treatment strategy for patients receiving therapeutics that are metabolized by the CYP2D6 or CYP2C19 gene products.

Novel CYP2C9 promoter variants and assessment of their impact on gene expression

There are a considerable number of reports identifying and characterizing genetic variants within the CYP2C9 coding region. Much less is known about polymorphic promoter sequences that also might contribute to interindividual differences in CYP2C9 expression. To address this problem, approximately 10,000 base pairs of CYP2C9 upstream information were resequenced using 24 DNA samples from the Coriell Polymorphism Discovery Resource. Thirty-one single-nucleotide polymorphisms (SNPs) were identified; nine SNPs were novel, whereas 22 were reported previously. Using both sequencing and multiplex single-base extension, individual SNP frequencies were determined in 193 DNA samples obtained from unrelated, self-reported Hispanic Americans of Mexican descent, and they were compared with similar data obtained from a non-Latino white cohort. Significant interethnic differences were observed in several SNP frequencies, some of which seemed unique to the Hispanic population. Analysis using PHASE 2.1 inferred nine common (>1%) variant haplotypes, two of which included the g.3608C>T (R144C) CYP2C9(*)2 and two the g.42614A>C (I359L) CYP2C9(*)3 SNPs. Haplotype variants were introduced into a CYP2C9/luciferase reporter plasmid using site-directed mutagenesis, and the impact of the variants on promoter activity assessed by transient expression in HepG2 cells. Both constitutive and pregnane X receptor-mediated inducible activities were measured. Haplotypes 1B, 3A, and 3B each exhibited a 65% decrease in constitutive promoter activity relative to the reference haplotype. Haplotypes 1D and 3B exhibited a 50% decrease and a 40% increase in induced promoter activity, respectively. These data suggest that genetic variation within CYP2C9 regulatory sequences is likely to contribute to differences in CYP2C9 phenotype both within and among different populations.

Toward individualized treatment: prediction of anticancer drug disposition and toxicity with pharmacogenetics

A great deal of effort has been spent in defining the pharmacokinetics and pharmacodynamics of investigational and registered anticancer agents. Often, there is a marked variability in drug handling between individual patients, which contributes to variability in the pharmacodynamic effects of a given dose of a drug. A combination of physiological variables, genetic characteristics (pharmacogenetics) and environmental factors is known to alter the relationship between the absolute dose and the concentration-time profile in plasma. A variety of strategies are now being evaluated in patients with cancer to improve the therapeutic index of anticancer drugs by implementation of pharmacogenetic imprinting through genotyping or phenotyping individual patients. The efforts have mainly focused on variants in genes encoding the drug-metabolizing enzymes thiopurine S-methyltransferase, dihydropyrimidine dehydrogenase, members of the cytochrome P450 family, including the CYP2B, 2C, 2D and 3A subfamilies, members of the UDP glucuronosyltransferase family, as well as the ATP-binding cassette transporters ABCB1 (P-glycoprotein) and ABCG2 (breast cancer resistance protein). Several of these genotyping strategies have been shown to have substantial impact on therapeutic outcome and should eventually lead to improved anticancer chemotherapy.

Simultaneous genotyping of CYP2C9*2, *3, and 5′ flanking region (C-1189T) polymorphisms in a Spanish population through a new minisequencing multiplex single-base extension analysis

OBJECTIVE

To conduct a descriptive study on the prevalence of relevant cytochrome P450 2C9 (CYP2C9) polymorphisms--the *2, *3, and 5' flanking region (C-1189T)--in a Spanish population using a new minisequencing fluorescent method through a multiplex single base extension (SBE) analysis.

METHOD

The method simultaneously and accurately genotypes the CYP2C9 polymorphisms studied and is available as a commercial protocol (SNaPshot). Various strategies, including restriction fragment length polymorphism (RFLP) and Taqman, were used to validate the methodology.

RESULTS

The frequencies of alleles CYP2C9*2 (12%) and *3 (6.2%) were similar to those described for other Caucasian populations. The frequency of allele t at the 5' flanking region was 62%, which is close to the percentage reported in Japanese and French populations. The four haplotypes inferred in our samples and their frequencies were consistent with those reported in other studies.

CONCLUSION

Our results confirm previously reported Caucasian frequencies for the CYP2C9*2 and *3 alleles and, for the first time, provide data on the frequency of the CYP2C9 5' flanking region (C-1189T), a recently described polymorphism, in a Spanish population. The SBE technique detects unequivocally the three polymorphisms in a single reaction, which makes it suitable for the analysis of CYP2C9 in the many therapeutic situations in which it is involved.

Genetic diversity and new therapeutic concepts

The differences in medicinal drug responses among individuals had been known for quite some time. Some patients exhibit a life-threatening adverse reaction while others fail to show an expected therapeutic effect. Intermediate responses between the above two extreme cases are also known. In fact, it has been recently reported that approximately 100,000 deaths and more than 2 million hospitalizations annually in the United States are due to properly prescribed medications. This interindividual variability could be due in part to genetically determined characteristics of target genes or drug metabolizing enzymes. This has now been substantiated by a variety of studies. We know that "one size fits all" is not correct. Therefore, the application of pharmacogenetic concepts to clinical practice is an excellent goal in the postgenomic era. The successful completion of the human genome project provided necessary molecular tools, such as high-throughput SNP genotyping, HapMap, and microarray, that can be applied to develop proper therapeutic options for individuals. Recently, there have been considerable scientific, corporate, and policy interest in pharmacotherapy. However, identification of causal variations in a target gene is only a starting point, and the progress in this rapidly developing field is slower than expected. One major drawback could be due to the multigene determinant of drug response that requires a genome-wide screening. Additionally, application of pharmacogenetic knowledge into clinical practice requires a high level of accuracy, precision (risk/benefit ratio), and strict regulations. This is because the pharmacogenetic approach raises several ethical, moral, and legal questions. It is also necessary that both health professionals and the general public must be urgently educated. Despite these limitations, translation of pharmacogenomic data into clinical practice would certainly provide better opportunities to increase the safety and efficacy of medicine in the future.