Ethnic Differences in Genetic Polymorphisms of CYP2D6, CYP2C19, CYP3As and MDR1/ABCB1

Association of CYP2C19*2 and *3 genetic variants with essential hypertension in Koreans

PURPOSE

The cytochrome P450 2C19 (CYP2C19) metabolizes arachidonic acid to produce epoxyicosanoid acids, which are involved in vascular tone and regulation of blood pressure. Recent findings suggest that CYP2C19 gene might be considered as a novel candidate gene for treatment of cardiovascular disease. The aim of the present study was to evaluate the association between two variants, CYP2C19* 2 (681G>A) and CYP2C19*3 (636G>A) and the development of essential hypertension (EH) in Koreans.

MATERIALS AND METHODS

We carried out an association study in a total of 1190 individuals (527 hypertensive subjects and 663 unrelated healthy controls). The CYP2C19 polymorphisms were genotyped using the SNaPShot™ assay.

RESULTS

The distribution of alleles and genotypes of CYP2C19* 3 showed significant difference between hypertensive patients and normal controls (p=0.011 and p=0.013, respectively). Logistic regression analysis indicated that the CYP2C19*3 (636A) allele carriers were significantly associated with EH [odds ratio, 0.691; 95% confidence interval (CI), 0.512-0.932, p=0.016], in comparison to wild type homozygotes (CYP2C19*1/*1). Neither genotype nor allele distribution of CYP2C19*2 polymorphism showed significant differences between hypertensive and control groups (p>0.05).

CONCLUSION

Our present findings strengthen the evidence of an association between CYP2C19 gene polymorphism and EH prevalence. In particular, the CYP2C19*3 defective allele may contribute to reduced risk for the development of EH.

Pharmacokinetics and toxicity of antimuscarinic drugs for overactive bladder treatment in females

INTRODUCTION

Antimuscarinics (AMs) are the mainstay of pharmacological treatment of overactive bladder (OAB), a symptom complex defined by the presence of urinary urgency, usually associated with frequency and nocturia, with or without urgency urinary incontinence. The AMs used to treat OAB differ in their pharmacological profiles, which may affect their potential for causing adverse effects (AEs).

AREAS COVERED

The present article aims to review the literature about pharmacokinetics (PK) of the different AMs used in the treatment of OAB. Furthermore, the AEs related to the use of these drugs and their incidence are presented. This systematic review is based on material searched and obtained via Medline, Pubmed and EMBASE up to March 2012 using the search terms "adverse events, pharmacokinetics, tolerability" in combination with "darifenacin, fesoterodine, imidafenacin, oxybutynin, propiverine, solifenacin, tolterodine, and trospium."

EXPERT OPINION

Antimuscarinics are the first-line pharmacological treatment for OAB. Despite the development of new molecules that improve their efficacy/safety profile, there are some drugs that are pharmacokinetically more appropriate to be prescribed in specific populations such as patients with neurological disease or the elderly. Moreover, research should be encouraged in evaluating antimuscarinics in conjunction with other drugs such as estrogens or beta-agonists. The identification of prognostic criteria for pharmacological therapy would be helpful.

A rapid multiplex PCR assay that can reliably discriminate the cytochrome P450 2D6 whole-gene deletion allele from 2D6*10 alleles

BACKGROUND

Genetic polymorphisms of the human CYP2D6 gene can affect the metabolism of many drugs in clinical use. As a first step toward identifying poor drug metabolizers in the clinical setting, we developed a new multiplex PCR-based genotyping method to detect CYP2D6 whole-gene deletion.

METHODS

We validated the new method by analyzing 500 genomic DNA samples from a Japanese population with the conventional long-PCR method and the new multiplex PCR method. The long-PCR system used a forward primer for CYP2D7P (a pseudogene closely related to CYP2D6) and a common reverse primer for the untranslated region. The multiplex PCR system used the same two primers as the long PCR and an additional forward primer for CYP2D6.

RESULTS

With the long-PCR system, DNA samples identified as containing CYP2D6*5 (whole-gene deletion) formed 3.5-kb PCR products. With the multiplex PCR system, many samples yielded 4.7-kb PCR products (implying the existence of normal CYP2D6) and some DNA samples yielded 6.2-kb PCR products (probably indicating CYP2D6*10D). The long-PCR assay detected 64 CYP2D6*5 alleles among 1000 Japanese alleles; however, the new multiplex PCR system identified 5 of these 64 alleles as CYP2D6*10D.

CONCLUSIONS

The new multiplex PCR method is useful for detecting CYP2D6*5. This system could reliably discriminate CYP2D6*5 from homologous pseudogene CYP2D7P and functional CYP2D6*10D.

Genomics of Dementia: APOE- and CYP2D6-Related Pharmacogenetics

Dementia is a major problem of health in developed societies. Alzheimer's disease (AD), vascular dementia, and mixed dementia account for over 90% of the most prevalent forms of dementia. Both genetic and environmental factors are determinant for the phenotypic expression of dementia. AD is a complex disorder in which many different gene clusters may be involved. Most genes screened to date belong to different proteomic and metabolomic pathways potentially affecting AD pathogenesis. The ε4 variant of the APOE gene seems to be a major risk factor for both degenerative and vascular dementia. Metabolic factors, cerebrovascular disorders, and epigenetic phenomena also contribute to neurodegeneration. Five categories of genes are mainly involved in pharmacogenomics: genes associated with disease pathogenesis, genes associated with the mechanism of action of a particular drug, genes associated with phase I and phase II metabolic reactions, genes associated with transporters, and pleiotropic genes and/or genes associated with concomitant pathologies. The APOE and CYP2D6 genes have been extensively studied in AD. The therapeutic response to conventional drugs in patients with AD is genotype specific, with CYP2D6-PMs, CYP2D6-UMs, and APOE-4/4 carriers acting as the worst responders. APOE and CYP2D6 may cooperate, as pleiotropic genes, in the metabolism of drugs and hepatic function. The introduction of pharmacogenetic procedures into AD pharmacological treatment may help to optimize therapeutics.

Biotransformation of the antiretroviral drug etravirine: metabolite identification, reaction phenotyping, and characterization of autoinduction of cytochrome P450-dependent metabolism

Etravirine (ETR) is a second-generation non-nucleoside reverse transcriptase inhibitor prescribed for the treatment of HIV-1. By using human liver microsomes (HLMs), cDNA-expressed cytochromes P450 (P450s), and UDP-glucuronosyltransferases (UGTs), the routes of ETR metabolism were defined. Incubations with cDNA-expressed P450 isozymes and chemical inhibition studies using HLMs indicated that CYP2C19 is primarily responsible for the formation of both the major monohydroxylated and dihydroxylated metabolites of ETR. Tandem mass spectrometry suggested that these metabolites were produced via monomethylhydroxylation and dimethylhydroxylation of the dimethylbenzonitrile moiety. Formation of these monohydroxy and dihydroxy metabolites was decreased by 75 and 100%, respectively, in assays performed using HLMs that were genotyped as homozygous for the loss-of-function CYP2C19*2 allele compared with formation by HLMs genotyped as CYP2C19*1/*1. Two monohydroxylated metabolites of lower abundance were formed by CYP3A4, and interestingly, although CYP2C9 showed no activity toward the parent compound, this enzyme appeared to act in concert with CYP3A4 to form two minor dihydroxylated products of ETR. UGT1A3 and UGT1A8 were demonstrated to glucuronidate a CYP3A4-dependent monohydroxylated product. In addition, treatment of primary human hepatocytes with ETR resulted in 3.2-, 5.2-, 11.8-, and 17.9-fold increases in CYP3A4 mRNA levels 6, 12, 24, and 72 h after treatment. The presence of the pregnane X receptor antagonist sulforaphane blocked the ETR-mediated increase in CYP3A4 mRNA expression. Taken together, these data suggest that ETR and ETR metabolites are substrates of CYP2C19, CYP3A4, CYP2C9, UGT1A3, and UGT1A8 and that ETR is a PXR-dependent modulator of CYP3A4 mRNA levels.

Tamoxifen resistance and CYP2D6 copy numbers in breast cancer patients

BACKGROUND

Breast cancer accounts about one million from total annual ten million new diagnosed cases of neoplasia worldwide and is the main cause of death due to cancer in women. Tamoxifen is the most popular selective estrogen receptor modulator used in anti estrogen treatments. Tamoxifen must be converted into its metabolite endoxifen for biologic effects; this conversion process is catalysed by highly polymorphic cytochrome P450 2D6 (CYP2D6). This study surveyed copy number variation of the CYP2D6 gene and its possible correlation with Tamoxifen resistance in breast cancer patients.

METHODS

This case control study was performed on samples taken from 79 patients with breast cancer who used tamoxifen in Yazd and Tehran Cities, Iran. Real time reactions were conducted for 10 healthy samples using the comparative Ct (Cycles threshold) method, each pair of genes being compared and samples with ratios around 1 were taken as control samples. Proliferation reactions were done by Real-Time PCR ABI Prism 7500. All registered data were transformed into SPSS 15 program and analyzed.

RESULTS

Efficiency of PCR for both CYP2D6 and ALB genes was 100%. From all 23 drug resistant patients 21.7% had one copy, 47.8% two copies and 30.4% had three copies. Also from all 56 drug sensitive patients, 26.8% had one copy, 51.8% two copies and 21.4% had three copies. The percentage of patients with one and two copies was similar between two groups but patients with three copies were more likely to belong to the drug resistant group more. Odd ratios for one and two copies were 0.759 and 0.853 respectively, indicating possible protective effects while that for three copies was 1.604.

CONCLUSIONS

Based on our study there is no significant link between CYP2D6 gene copy numbers and tamoxifen resistance in women with breast cancer. But more studies considering other influencing factors appear warranted.

Similarities and differences between US and Japan as to pharmacogenomic biomarker information in drug labels

Pharmacogenomics (PGx) has been utilized as a tool to improve a drug's benefit/risk ratio and the efficiency of drug developments. In order to examine what factors are involved to determine the level of contexts (contents and descriptions) of drug-PGx biomarker information, we graded sections of Japanese package inserts and US drug labels into six levels according to the importance of cautions in regards to clinical practice and compared similarities and differences of the contexts between the two countries. Out of 54 contexts identified, 33 (61%) were graded differently between Japan and the US. The different contexts were mainly related to metabolizing enzymes used in terms of safety, therapeutic areas other than oncology, outcome before 1993, Japan-based companies having marketing authorization and no PGx data on the Japanese population. We describe the potential reasons that could lead to the differences between the two countries such as genetic differences and quantitative evidence in the Japanese population, and also discuss future perspectives to improve PGx utilization in clinical practices in Japan.

Genomics and pharmacogenomics of dementia

Dementia is a major problem of health in developed countries, and a prototypical paradigm of chronic disability, high cost, and social-family burden. Approximately, 10-20% of direct costs in this kind of neuropathology are related to pharmacological treatment, with a moderate responder rate below 30% and questionable cost-effectiveness. Over 200 different genes have been associated with the pathogenesis of dementia. Studies on structural and functional genomics, transcriptomics, proteomics and metabolomics have revealed the paramount importance of these novel technologies for the understanding of pathogenic cascades and the prediction of therapeutic outcomes in dementia. About 10-30% of Western populations are defective in genes of the CYP superfamily. The most frequent CYP2D6 variants in the Iberian peninsula are the *1/*1 (57.84%), *1/*4 (22.78%), *1×N/*1 (6.10%), *4/*4 (2.56%), and *1/*3 (2.01%) genotypes, accounting for more than 80% of the population. The frequency of extensive (EMs), intermediate (IMs), poor (PMs), and ultra-rapid metabolizers (UMs) is about 59.51%, 29,78%, 4.46%, and 6.23%, respectively, in the general population, and 57.76, 31.05%, 5.27%, and 5.90%, respectively, in AD cases. The construction of a genetic map integrating the most prevalent CYP2D6+CYP2C19+CYP2C9 polymorphic variants in a trigenic cluster yields 82 different haplotype-like profiles, with *1*1-*1*1-*1*1 (25.70%), *1*1-*1*2-*1*2 (10.66%), *1*1-*1*1-*1*1 (10.45%), *1*4-*1*1-*1*1 (8.09%), *1*4-*1*2-*1*1 (4.91%), *1*4-*1*1-*1*2 (4.65%), and *1*1-*1*3-*1*3 (4.33%), as the most frequent genotypes. Only 26.51% of AD patients show a pure 3EM phenotype, 15.29% are 2EM1IM, 2.04% are pure 3IM, 0% are pure 3PM, and 0% are 1UM2PM. EMs and IMs are the best responders, and PMs and UMs are the worst responders to a combination therapy with cholinesterase inhibitors, neuroprotectants, and vasoactive substances. The pharmacogenetic response in AD appears to be dependent upon the networking activity of genes involved in drug metabolism and genes involved in AD pathogenesis (e.g., APOE). AD patients harboring the APOE-4/4 genotypes are the worst responders to conventional antidementia drugs. To achieve a mature discipline of pharmacogenomics in CNS disorders and dementia it would be convenient to accelerate the following processes: (i) to educate physicians and the public on the use of genetic/genomic screening in daily clinical practice; (ii) to standardize genetic testing for major categories of drugs; (iii) to validate pharmacogenomic information according to drug category and pathology; (iv) to regulate ethical, social, and economic issues; and (v) to incorporate pharmacogenomic procedures both to drugs in development and drugs on the market in order to optimize therapeutics.

Genomics and pharmacogenomics of schizophrenia

Schizophrenia (SCZ) is among the most disabling of mental disorders. Several neurobiological hypotheses have been postulated as responsible for SCZ pathogenesis: polygenic/multifactorial genomic defects, intrauterine and perinatal environment-genome interactions, neurodevelopmental defects, dopaminergic, cholinergic, serotonergic, gamma-aminobutiric acid (GABAergic), neuropeptidergic and glutamatergic/N-Methyl-D-Aspartate (NMDA) dysfunctions, seasonal infection, neuroimmune dysfunction, and epigenetic dysregulation. SCZ has a heritability estimated at 60-90%. Genetic studies in SCZ have revealed the presence of chromosome anomalies, copy number variants, multiple single-nucleotide polymorphisms of susceptibility distributed across the human genome, aberrant single nucleotide polymorphisms (SNPs) in microRNA genes, mitochondrial DNA mutations, and epigenetic phenomena. Pharmacogenetic studies of psychotropic drug response have focused on determining the relationship between variation in specific candidate genes and the positive and adverse effects of drug treatment. Approximately, 18% of neuroleptics are major substrates of CYP1A2 enzymes, 40% of CYP2D6, and 23% of CYP3A4; 24% of antidepressants are major substrates of CYP1A2 enzymes, 5% of CYP2B6, 38% of CYP2C19, 85% of CYP2D6, and 38% of CYP3A4; 7% of benzodiazepines are major substrates of CYP2C19 enzymes, 20% of CYP2D6, and 95% of CYP3A4. About 10-20% of Western populations are defective in genes of the CYP superfamily. Only 26% of Southern Europeans are pure extensive metabolizers for the trigenic cluster integrated by the CYP2D6+CYP2C19+CYP2C9 genes. The pharmacogenomic response of SCZ patients to conventional psychotropic drugs also depends on genetic variants associated with SCZ-related genes. Consequently, the incorporation of pharmacogenomic procedures both to drugs in development and drugs on the market would help to optimize therapeutics in SCZ and other central nervous system (CNS) disorders.

Association between Genetic Polymorphism of Multidrug Resistance 1 Gene and Sasang Constitutions

Multidrug resistance 1 (MDR1) is a gene that expresses P-glycoprotein (P-gp), a drug transporter protein. Genetic polymorphisms of MDR1 can be associated with Sasang constitutions because Sasang constitutional medicine (SCM) prescribes different drugs according to different constitutions. A Questionnaire for Sasang Constitution Classification II (QSCC II) was used to diagnose Sasang constitutions. Two hundred and seven healthy people whose Sasang constitutions had been identified were tested. Genotype analyses, restriction fragment length polymorphism (RFLP) and pyrosequencing were used in MDR1 C1236T, and in MDR1 G2677T/A and C3435T, respectively. Significant differences in MDR1 C1236T genotypes were found between So-yangin and So-eumin. MDR1 G2677T/A genotype also showed significant differences in allele distribution between So-yangin and Tae-eumin. So-yangin and So-eumin showed significant differences in the distribution of both 1236C-2677G-3435C and 1236T-2677G-3435T, haplotypes of MDR1. The genetic polymorphism of the MDR1 gene was thus shown to be an indicator that could distinguish So-yangin from other constitutions.

The relationship between clinical pharmacokinetics of aripiprazole and CYP2D6 genetic polymorphism: effects of CYP enzyme inhibition by coadministration of paroxetine or fluvoxamine

Purpose

To investigate the effects of coadministration of paroxetine or fluvoxamine on the pharmacokinetics of aripiprazole in healthy adult Japanese with different CYP2D6 genotypes.

Methods

Fourteen CYP2D6 extensive metabolizer (EM) and 14 CYP2D6 intermediate metabolizer (IM) subjects were coadministered a single oral dose of aripiprazole 3 mg after steady-state plasma concentrations of the SSRIs paroxetine (20 mg/day) or fluvoxamine (100 mg/day) were reached by repeated oral doses for 6–7 days. The pharmacokinetics of aripiprazole with and without coadministration of SSRIs were compared according to CYP2D6 genotypes.

Results

Coadministration of paroxetine, a potent CYP2D6 inhibitor, decreased systemic clearance (CL/F) of aripiprazole by 58 and 23% in CYP2D6 EMs and IMs, respectively, demonstrating that the percentage inhibition of CYP2D6 activity by coadministration of paroxetine was apparently greater in CYP2D6 EMs than in IMs. Coadministration of fluvoxamine, a less potent CYP3A4 inhibitor, decreased the CL/F of aripiprazole by 39% in CYP2D6 EMs and 40% in IMs, indicating the same inhibitory effect on CYP enzymes, regardless of the CYP2D6 genotype. Percent contribution of CYP2D6 to total CL/F (CYP2D6 plus CYP3A4) of aripiprazole estimated as a reduced percentage of CL/F by CYP enzyme inhibition was 62% for CYP2D6 EMs and 24% for IMs in paroxetine coadministration, and 40% for CYP2D6 EMs and 18% for IMs in fluvoxamine coadministration.

Conclusions

There were marked differences in the degree of influence of paroxetine coadministration on the pharmacokinetics of aripiprazole between CYP2D6 EMs and IMs, but no apparent differences were found between two CYP2D6 genotypes in fluvoxamine coadministration. Aripiprazole can be used safely in combination with SSRIs that have a CYP enzyme-inhibitory action.

Pharmacogenomics of antipsychotics efficacy for schizophrenia

Central nervous system disorders are the third greatest health problem in developed countries, and schizophrenia represents some of the most disabling ailments in young individuals. There is an abuse and/or misuse of antipsychotics, and recent advances in pharmacogenomics pose new challenges for the clinical management of this complex disorder. Schizophrenia is a multi-factorial/polygenic complex disorder in which hundreds of different genes are potentially involved, leading to the phenotypic expression of the disease in conjunction with epigenetic and environmental phenomena. Consequently, structural and functional genomic changes induce proteomic and metabolomic defects associated with the disease phenotype. Disease-related genomic profiles and genetic variants in genes involved in drug metabolism are responsible for drug efficacy and safety. About 20% of Caucasians are defective in CYP2D6 enzymes, which participate in the metabolism of 25-30% of central nervous system drugs. Approximately 40% of antipsychotics are substrates of CYP2D6 enzymes, 23% are substrates of CYP3A4, and 18% are substrates of CYP1A2. In order to achieve a mature discipline of pharmacogenomics of schizophrenia it would be effective to accelerate: (i) the education of physicians and the public in the use of genomic screening in daily clinical practice; (ii) the standardization of genetic testing for major categories of drugs; (iii) the validation of pharmacogenomic procedures according to drug category and pathology; (iv) the regulation of ethical, social, and economic issues; and (v) the incorporation of pharmacogenomic procedures of drugs in development and drugs on the market in order to optimize therapeutics.

CYP2C19 and ABCB1 gene polymorphisms are differently distributed according to ethnicity in the Brazilian general population

Background

Recent studies have reported the clinical importance of CYP2C19 and ABCB1 polymorphisms in an individualized approach to clopidogrel treatment. The aims of this study were to evaluate the frequencies of CYP2C19 and ABCB1 polymorphisms and to identify the clopidogrel-predicted metabolic phenotypes according to ethnic groups in a sample of individuals representative of a highly admixtured population.

Methods

One hundred and eighty-three Amerindians and 1,029 subjects of the general population of 4 regions of the country were included. Genotypes for the ABCB1c.C3435T (rs1045642), CYP2C19*2 (rs4244285), CYP2C19*3 (rs4986893), CYP2C19*4 (rs28399504), CYP2C19*5 (rs56337013), and CYP2C19*17 (rs12248560) polymorphisms were detected by polymerase chain reaction followed by high resolution melting analysis. The CYP2C19*3, CYP2C19*4 and CYP2C19*5 variants were genotyped in a subsample of subjects (300 samples randomly selected).

Results

The CYP2C19*3 and CYP2C19*5 variant alleles were not detected and the CYP2C19*4 variant allele presented a frequency of 0.3%. The allelic frequencies for the ABCB1c.C3435T, CYP2C19*2 and CYP2C19*17 polymorphisms were differently distributed according to ethnicity: Amerindian (51.4%, 10.4%, 15.8%); Caucasian descent (43.2%, 16.9%, 18.0%); Mulatto (35.9%, 16.5%, 21.3%); and African descent (32.8%, 20.2%, 26.3%) individuals, respectively. As a result, self-referred ethnicity was able to predict significantly different clopidogrel-predicted metabolic phenotypes prevalence even for a highly admixtured population.

Conclusion

Our findings indicate the existence of inter-ethnic differences in the ABCB1 and CYP2C19 variant allele frequencies in the Brazilian general population plus Amerindians. This information could help in stratifying individuals from this population regarding clopidogrel-predicted metabolic phenotypes and design more cost-effective programs towards individualization of clopidogrel therapy.

Future Trends in the Pharmacogenomics of Brain Disorders and Dementia: Influence of APOE and CYP2D6 Variants

About 80% of functional genes in the human genome are expressed in the brain and over 1,200 different genes have been associated with the pathogenesis of CNS disorders and dementia. Pharmacogenetic studies of psychotropic drug response have focused on determining the relationship between variations in specific candidate genes and the positive and adverse effects of drug treatment. Approximately, 18% of neuroleptics are substrates of CYP1A2 enzymes, 40% of CYP2D6, and 23% of CYP3A4; 24% of antidepressants are substrates of CYP1A2 enzymes, 5% of CYP2B6, 38% of CYP2C19, 85% of CYP2D6, and 38% of CYP3A4; 7% of benzodiazepines are substrates of CYP2C19 enzymes, 20% of CYP2D6, and 95% of CYP3A4. 10-20% of Western populations are defective in genes of the CYP superfamily; and the pharmacogenomic response of psychotropic drugs also depends on genetic variants associated with dementia. Prospective studies with anti-dementia drugs or with multifactorial strategies have revealed that the therapeutic response to conventional drugs in Alzheimer’s disease is genotype-specific. The disease-modifying effects (cognitive performance, biomarker modification) of therapeutic intervention are APOE-dependent, with APOE-4 carriers acting as the worst responders (APOE-3/3 > APOE-3/4 > APOE-4/4). APOE-CYP2D6 interactions also influence the therapeutic outcome in patients with dementia.

Pharmacogenetics and forensic toxicology

Large inter-individual variability in drug response and toxicity, as well as in drug concentrations after application of the same dosage, can be of genetic, physiological, pathophysiological, or environmental origin. Absorption, distribution and metabolism of a drug and interactions with its target often are determined by genetic differences. Pharmacokinetic and pharmacodynamic variations can appear at the level of drug metabolizing enzymes (e.g., the cytochrome P450 system), drug transporters, drug targets or other biomarker genes. Pharmacogenetics or toxicogenetics can therefore be relevant in forensic toxicology. This review presents relevant aspects together with some examples from daily routines.

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.

Comparative description of haplotype structure and genetic diversity of MDR1 (ABCB1) in HIV-positive and HIV-negative populations

Human P-glycoprotein (P-gp), encoded by MDR1 (ABCB1), is an efflux transporter with a wide specificity for substrates/drugs, including HIV protease inhibitors which are commonly used in HIV/AIDS treatment. Three single nucleotide polymorphisms (SNPs) in MDR1 have been shown to affect P-gp expression and function, and may affect HIV/AIDS treatment outcome: 1236C>T [G412G, exon-12], 2677G>T/A [A893S/T, exon-21] and 3435C>T [I1145I, exon-26]. In the present study, our aims were (i) to compare the 3-SNP MDR1 haplotype structure and genetic diversity between North American HIV-positive and HIV-negative individuals belonging to four major ethnic groups and (ii) to determine whether the haplotype structure and genetic diversity observed in these ethnically admixed populations differ from that in ethnically non-admixed populations. For these aims, we analyzed a cohort of 447 HIV/AIDS patients (White [n=193], Black [n=235], Hispanic [n=17], and Asian [n=2]). Results obtained for these patients were compared with the results for (i) HIV-negative individuals (n=356) and (ii) various HapMap and Environmental Genome Project populations. We observed that the genetic characteristics of MDR1 were largely consistent between HIV-positive and HIV-negative populations, but there were striking interethnic differences in the genetic characteristics of MDR1 in both populations. Although it appeared that the genetic characteristics of MDR1 were largely consistent between ethnically admixed and non-admixed populations, genetic characterization of the admixed populations remains to be done. Thus, our results provide useful comparative insights about the genetic characteristics of MDR1 that could be extrapolated across population groups worldwide. For a meaningful interpretation of these results regarding HIV/AIDS treatment outcome, MDR1 haplotype/diplotype structure data, genetic characterization of population admixture, and polymorphisms in other relevant drug transporter and/or metabolizing enzyme genes should be considered in future clinical studies.

Aripiprazole in the treatment of early-onset schizophrenia spectrum disorder: A case series in Korean children and adolescents

OBJECTIVE

The aim of this case series was to assess the effectiveness and tol-erability of aripiprazole in Korean children and adolescents with early-onset schizophrenia spectrum (EOSS) disorder.

METHODS

The medical records of aripiprazole-treated patients with EOSS were retrospectively reviewed. Changes in illness severity were measured using the Clinical Global Impression-Severity of Illness (CGI-S) and Clinical Global Impression-Improvement (CGI-I) scales.

RESULTS

Data from 22 children and adolescents were included (12 girls, 10 boys; mean [SD] age, 14.0 [2.4] years). The mean (SD) dosage of aripiprazole was 19.8 (9.4) mg/d (median, 18.7 mg/d; mode, 15, 30 mg/d), and the range of treatment duration was 21 to 838 days. Mean (SD) CGI-S score improved significantly from baseline to end point (from 5.7 [0.7] to 4.3 [1.4]; P < 0.001). Based on changes in chart-extracted CGI-I scores, significantly greater improvement was associated with negative symptoms compared with positive symptoms (U = 25.5; P = 0.028; r = -0.47). Aripiprazole was discontinued due to insufficient effect in 5 patients (22.7%) and treatment-emergent adverse events in 3 patients (13.6%).

CONCLUSION

The results from this small study suggest that aripiprazole was moderately effective in reducing psychotic symptoms in these Korean children and adolescents with EOSS.

Associations between common variants in the MDR1 (ABCB1) gene and ulcerative colitis among North Indians

OBJECTIVES

There are suggestions that the MDR1 (ABCB1) gene is associated with ulcerative colitis (UC) in Caucasians. We investigated whether common MDR1 variants were associated with UC in the genetically heterogeneous North Indian population.

METHODS

Confirmed cases of UC and healthy controls frequency matched for age (+/-10 years) and geographic region were studied. Three exonic (C1236T, G2677T/A, and C3435T) and one promoter (C129T) single nucleotide polymorphism (SNP) in the gene were assessed. Allelic, genotypic, and haplotypic associations were evaluated.

RESULTS

A total of 270 patients and 274 controls were studied. The mean age at diagnosis (+/-SD) of the patients was 38.6 (+/-12.4) years. Most patients had left-sided disease (63.3%) and steroids were administered to them (78%). All SNPs were in Hardy-Weinberg equilibrium in the controls. SNP C129T was monomorphic in the population. SNP C1236T was significantly (P=0.05) overrepresented in the UC patients. Borderline nonsignificant associations were also evident with SNP G2677A/T. Three-marker (C1236T, G2677T/A, C3435T) and two-marker (C1236T, G2677T/A) haplotype analysis revealed significant associations with UC (TTT, P=0.04; TGT, P=0.01; TT, P=0.01; CT, P=0.03). There were indications that SNPs C1236T and G2677T/A were significantly associated with earlier age of onset (<29 years) of UC and left-sided disease. Specific haplotypes comprising the three SNPs were associated with steroid response.

CONCLUSION

Our findings indicate that common SNPs in the MDR1 gene are associated with an overall susceptibility for UC and specific disease phenotypes in North Indians. Larger studies to replicate these findings are required.

Mini-series: II. clinical aspects. clinically relevant CYP450-mediated drug interactions in the ICU

BACKGROUND

In the critically ill, multiple drug therapies for acute and chronic conditions are often used at the same time and adverse drug events occur frequently. Many pharmacological and disease-related factors, e.g. altered renal and hepatic function, catecholamine-related circulatory changes, altered drug volume of distribution, enteral versus parenteral feeding and morbid obesity, along with concomitant multiple drug regimens may account for the wide inter-individual variability in drug exposure and response in critically ill patients and for the high risk for drug-drug interactions to occur. The practicing intensivist must remain aware of the major mechanisms for drug-drug interactions, among which the drug-metabolizing enzyme inhibitory or induction potential of associated chemical entities are paramount. Metabolism-based drug-drug interactions are largely due to changes in levels of drug-metabolizing enzymes caused by one drug, leading to changes in the systemic exposure clearance of another. Among the numerous drug-metabolizing enzymes identified to date, the activity of cytochrome P450s (CYP450) is a critical determinant of drug clearance and appears to be involved in the mechanism of numerous clinically relevant drug-drug interactions observed in critically ill patients.

DISCUSSION

This manuscript will cover a practical overview of clinically relevant CYP450-mediated drug-drug interactions. Medications frequently used in the intensive care unit such as benzodiazepines, immunosuppressive agents, opioid analgesics, certain anticonvulsants, the azoles and macrolides have the potential to interact with CYP450-mediated metabolism and may lead to toxicity or therapeutic failure.

ABCB1 and ABCC1 expression in peripheral mononuclear cells is influenced by gene polymorphisms and atorvastatin treatment

This study investigated the effects of atorvastatin on ABCB1 and ABCC1 mRNA expression on peripheral blood mononuclear cells (PBMC) and their relationship with gene polymorphisms and lowering-cholesterol response. One hundred and thirty-six individuals with hypercholesterolemia were selected and treated with atorvastatin (10 mg/day/4 weeks). Blood samples were collected for serum lipids and apolipoproteins measurements and DNA and RNA extraction. ABCB1 (C3435T and G2677T/A) and ABCC1 (G2012T) gene polymorphisms were identified by polymerase chain reaction-restriction (PCR)-RFLP and mRNA expression was measured in peripheral blood mononuclear cells by singleplex real-time PCR. ABCB1 polymorphisms were associated with risk for coronary artery disease (CAD) (p<0.05). After atorvastatin treatment, both ABCB1 and ABCC1 genes showed 50% reduction of the mRNA expression (p<0.05). Reduction of ABCB1 expression was associated with ABCB1 G2677T/A polymorphism (p=0.039). Basal ABCB1 mRNA in the lower quartile (<0.024) was associated with lower reduction rate of serum low-density lipoprotein (LDL) cholesterol (33.4+/-12.4%) and apolipoprotein B (apoB) (17.0+/-31.3%) when compared with the higher quartile (>0.085: LDL-c=40.3+/-14.3%; apoB=32.5+/-10.7%; p<0.05). ABCB1 substrates or inhibitors did not affect the baseline expression, while ABCB1 inhibitors reversed the effects of atorvastatin on both ABCB1 and ABCC1 transporters. In conclusion, ABCB1 and ABCC1 mRNA levels in PBMC are modulated by atorvastatin and ABCB1 G2677T/A polymorphism and ABCB1 baseline expression is related to differences in serum LDL cholesterol and apoB in response to atorvastatin.

Genetic polymorphism analysis of CYP2C19 in Chinese Han populations from different geographic areas of mainland China

Aims: Although many studies have been performed on CYP2C19, most of them have mainly examined the effects of the defective alleles CYP2C19*2 and CYP2C19*3. A comprehensive search for genetic polymorphisms of the CYP2C19 gene in the Chinese Han population has rarely been conducted. The present study was designed to determine the genetic basis of CYP2C19 polymorphisms. Materials & Methods: We investigated the 5´-regulatory region, all the exons and their surrounding introns of the CYP2C19 gene in 400 unrelated healthy Chinese Han volunteers from four different geographical locations, namely Shanghai, Shantou, Shenyang and Xi’an, with a sample of 100 subjects in each population, using direct sequencing. Results: A total of 14 different CYP2C19 polymorphisms, including one novel variant (-2306G>A) in the enhancer region and a novel nonsynonymous one (905C>G, T302R) were identified. In addition, CYP2C19*1, *2, *3, *15 and *17 alleles showed frequencies of 69.7%, 24.7%, 3.3%, 1.2% and 1.2%, respectively, and CYP2C19*15 was the first detected in an Asian population. The frequencies of the prevalent defective alleles CYP2C19*2 and CYP2C19*3 in Chinese Han populations are similar to those in other Asians, and much higher than those reported in American European and other Caucasian populations. Haplotype analysis demonstrated CATCGG was the dominating haplotype with a frequency of 38.6% in the Chinese Han population. Furthermore, homology modeling analysis for CYP2C19 indicates that Thr302Arg could cause the displacement of heme. Conclusion: This is the first study that systematically screened the polymorphisms of the whole CYP2C19 gene in a large Chinese Han population. The results suggest that a few low frequent variants show significant differences among the four populations, while the prevalent polymorphisms show no differences. Therefore, our database provides important information on CYP2C19 polymorphisms in the Chinese population, and could be helpful for future personalized medicine studies in Asian populations generally.

Role of CYP3A5 in Abnormal Clearance of Methadone

Objective:

To report a case of unusually low concentrations of methadone in a polydrug abuser during maintenance treatment with methadone.

Case Summary:

A 25-year-old man (weight 55 kg, height 165 cm) with a 12-year history of polydrug abuse was admitted to an opiates withdrawal methadone program. At the time of our observation, he was using both cannabinoids and heroin; no other medical conditions were discovered. Within the opiates withdrawal methadone program, under medical supervision, the patient started methadone therapy (20 mg/day). Two weeks later, an Abuscreen assay for methadone screening in the urine was negative and, to prevent the development of withdrawal symptoms, the dose of methadone was increased to 60 mg/day. One day later, the patient was asked to collect another urine sample in the presence of a nurse. The Abuscreen for methadone in urine remained negative. Evaluation of urinary samples collected over 24 hours documented low concentrations of methadone and high levels of 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (the primary metabolite of methadone). Evaluation for the presence of the most common polymorphisms in the cytochrome P450 and P-glycoprotein genes showed that the patient was heterozygous for the CYP3A531 allele and for 2 single nucleotide polymorphisms in the P-glycoprotein gene (1236C/T and 3435C/T).

Discussion:

In this patient, poor methadone adherence was ruled out because of the presence of physicians and nurses during both methadone maintenance treatment and Abuscreen screening. Moreover, because the patient reported only heroin and cannabis at the time of evaluation, drug interactions were ruled out as possible causes for the rapid clearance of methadone.

Conclusions:

In this case, CYP3A5 polymorphism may have played a role in the rapid methadone metabolism.

Integrating pharmacogenomics into oncology clinical practice

Oncology pharmacogenomics has seen a great deal of progress in the past 10 years. The release of the Human Genome Project data and the availability of fast, affordable genotyping platforms has allowed the field to expand and has provided invaluable data for pharmacogenomics research. The introduction of US FDA-approved targeted therapy (trastuzumab), package insert changes (irinotecan and tamoxifen) and the initiation of a genotype-guided clinical trial for cancer therapy (TYMS TSER in rectal cancer), along with panels of DNA and expression markers (Roche AmpliChip(®) and Oncotype Dx™ panel) are paving the way towards the integration of pharmacogenomics into clinical practice.

Genetic polymorphism of cytochrome P450s and P-glycoprotein in the Finnish population

The objective of this study was to investigate the genetic polymorphism of selected cytochrome P450 (CYP) enzymes and ABCB1 (encoding P-glycoprotein) of central importance with regard to the disposition of clinically used drugs in the Finnish population and to compare the results to pre-existing data from Caucasian populations. A random sample of 449 Finns was studied. Single nucleotide polymorphisms (SNPs) were genotyped using blood-derived genomic DNA and 5'-nuclease assays. We found that the allele frequencies of CYP1A2 SNP g.-163C>A, CYP2C8*3, CYP2C9*2, CYP2C9*3 and CYP2C19*2 were similar to those seen in other Caucasian populations. However, the allelic frequency of the variant ABCB1 SNP c.3435C>T allele was lower than previously reported. The frequency of the homozygous CYP3A5*1 expression was significantly higher than expected based on Hardy-Weinberg calculations (observed n = 8 vs. expected n = 3, P = 0.01). Other genotype frequencies corresponded to the expected values. The strong linkage between the CYP2C8*3 and the CYP2C9*2 alleles was confirmed in this study and the number of individuals with the rare haplotype CYP2C8*3*3/CYP2C9*2*2 was higher than expected. We conclude that the frequency of mutated CYP alleles in Finns were in agreement with earlier findings in Caucasian populations, but a lower frequency of the ABCB1 variant allele 3435T corresponding to that reported in Asian populations was found. The higher than expected frequency of the CYP3A5*1*1 genotype and the CYP2C8*3*3/CYP2C9*2*2 haplotype may influence the response to treatment with drugs metabolized by these enzymes.

Quantitative Structure−Activity Relationship Analysis and Molecular Dynamics Simulation To Functionally Validate Nonsynonymous Polymorphisms of Human ABC Transporter ABCB1 (P-Glycoprotein/MDR1)

Several preclinical and clinical studies suggest the importance of naturally occurring polymorphisms of drug transporters in the individual difference of drug response. To functionally validate the nonsynonymous polymorphisms of ABCB1 (P-glycoprotein/MDR1) in vitro, we generated SNP variant forms (i.e., S400N, R492C, R669C, I849M, A893P, A893S, A893T, M986V, A999T, P1051A, and G1063A) and expressed them in Sf9 cells. The kinetic properties (Km and Vmax) of those variants were analyzed by measuring the ATPase activity to obtain the ATPase profile for each variant toward structurally unrelated substrates. On the basis of the experimental data, we determined the substrate specificity of ABCB1 WT and its variants by the quantitative structure-activity relationship (QSAR) analysis method. While several SNP variants appeared to influence the substrate specificity of ABCB1, the nonsynonymous polymorphisms of 2677G > T, A, or C at amino acid position 893 (Ala > Ser, Thr, or Pro) have great impacts on both the activity and the substrate specificity of ABCB1. The A893P variant (2677G > C), a rare mutation, exhibited markedly high activity of ATPase toward different test compounds. Molecular dynamics (MD) simulation based on a three-dimensional structural model of human ABCB1 revealed that multiple kinks are formed in the intracellular loop between transmembrane domains 10 and 11 of the A893P variant (2677G > C) protein. The polymorphisms of 2677G, 2677T, and 2677A exhibit wide ethnic differences in the allele frequency, and these nonsynonymous polymorphisms are suggested to be clinically important because of their altered ATPase activity and substrate specificity toward different drugs.