An Interethnic Comparison of Polymorphisms of the Genes Encoding Drug-Metabolizing Enzymes and Drug Transporters: Experience in Singapore

The influence of drug-induced metabolic enzyme activity inhibition and CYP3A4 gene polymorphism on aumolertinib metabolism

The purpose of this study is to clarify the drug interaction profile of aumolertinib, and the influence of CYP3A4 genetic polymorphism on aumolertinib metabolic characteristics. Through microsomal enzyme reactions, we screened 153 drugs and identified 15 that significantly inhibited the metabolism of aumolertinib. Among them, telmisartan and carvedilol exhibited potent inhibitory activities in rat liver microsomes (RLM) and human liver microsomes (HLM). In vivo, the pharmacokinetic parameters of aumolertinib, including AUC and Cmax, were significantly altered when co-administered with carvedilol, with a notable decrease in the clearance rate CLz/F. Interestingly, the pharmacokinetic parameters of the metabolite HAS-719 exhibited a similar trend as aumolertinib when co-administered. Mechanistically, both telmisartan and carvedilol exhibited a mixed-type inhibition on the metabolism of aumolertinib. Additionally, we used a baculovirus-insect cell expression system to prepare 24 recombinant CYP3A4 microsomes and obtained enzymatic kinetic parameters using aumolertinib as a substrate. Enzyme kinetic studies obtained the kinetic parameters of various CYP3A4 variant-mediated metabolism of aumolertinib. Based on the relative clearance rates, CYP3A4.4, 5, 7, 8, 9, 12, 13, 14, 17, 18, 19, 23, 24, 33, and 34 showed significantly lower clearance rates compared to the wild-type. Among the different CYP3A4 variants, the inhibitory potency of telmisartan and carvedilol on the metabolism of aumolertinib also varied. The IC50 values of telmisartan and carvedilol in CYP3A4.1 were 6.68 ± 1.76 μM and 0.60 ± 0.25 μM, respectively, whereas in CYP3A4.12, the IC50 exceeded 100 μM. Finally, we utilized adeno-associated virus to achieve liver-specific high expression of CYP3A4*1 and CYP3A4*12. In the group with high expression of the less active CYP3A4*12, the magnitude of the drug-drug interaction was significantly attenuated. In conclusion, CYP3A4 genetic polymorphism not only influences the pharmacokinetic characteristics of aumolertinib, but also the inhibitory potency of telmisartan and carvedilol on it.

Differential drug response in pulmonary arterial hypertension: The potential for precision medicine

Pulmonary arterial hypertension (PAH) is a rare, complex, and deadly cardiopulmonary disease. It is characterized by changes in endothelial cell function and smooth muscle cell proliferation in the pulmonary arteries, causing persistent vasoconstriction, resulting in right heart hypertrophy and failure. There are multiple drug classes specific to PAH treatment, but variation between patients may impact treatment response. A small subset of patients is responsive to pulmonary vasodilators and can be treated with calcium channel blockers, which would be deleterious if prescribed to a typical PAH patient. Little is known about the underlying cause of this important difference in vasoresponsive PAH patients. Sex, race/ethnicity, and pharmacogenomics may also factor into efficacy and safety of PAH-specific drugs. Research has indicated that endothelin receptor antagonists may be more effective in women and there have been some minor differences found in certain races and ethnicities, but these findings are muddled by the impact of socioeconomic factors and a lack of representation of non-White patients in clinical trials. Genetic variants in genes such as CYP3A5, CYP2C9, PTGIS, PTGIR, GNG2, CHST3, and CHST13 may influence the efficacy and safety of certain PAH-specific drugs. PAH research faces many challenges, but there is potential for new methodologies to glean new insights into PAH development and treatment.

Pharmacogenetics of Anticancer Drugs: Clinical Response and Toxicity

Cancer is the most challenging disease for medical professionals to treat. The factors underlying the complicated situation include anticancer drug-associated toxicity, non-specific response, low therapeutic window, variable treatment outcomes, development of drug resistance, treatment complications, and cancer recurrence. The remarkable advancement in biomedical sciences and genetics, over the past few decades, however, is changing the dire situation. The discovery of gene polymorphism, gene expression, biomarkers, particular molecular targets and pathways, and drug-metabolizing enzymes have paved the way for the development and provision of targeted and individualized anticancer treatment. Pharmacogenetics is the study of genetic factors having the potential to affect clinical responses and pharmacokinetic and pharmacodynamic behaviors of drugs. This chapter emphasizes pharmacogenetics of anticancer drugs and its applications in improving treatment outcomes, selectivity, toxicity of the drugs, and discovering and developing personalized anticancer drugs and genetic methods for prediction of drug response and toxicity.

A phase 1b study of OXIRI in pancreatic adenocarcinoma patients and its immunomodulatory effects

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal and debilitating disease with limited therapeutic options. The aim of this clinical study was to evaluate the safety, efficacy and pharmacokinetics of a novel regimen comprised of metronomic oxaliplatin (O), chronomodulated capecitabine (X) and UGT1A1 genotype-guided dosing of irinotecan (IRI) [OXIRI] as well as its immunomodulatory effects. Thirty-six patients were enrolled into either dose-escalation or expansion cohorts. In the dose escalation phase, capecitabine doses (2000, 2650, 3500 and 4500 mg/day) were administered at midnight on days 1 to 14 while oxaliplatin and irinotecan were intravenously infused at fixed doses of 50 and 75 mg/m2 respectively on days 1, 8 in a 21-day cycle. The maximum tolerated dose of capecitabine was 2650 mg/day and the most common grade 3 adverse events were neutropenia (30.6%) and diarrhea (13.9%). No grade 4 toxicity was observed. UGT1A1-genotype directed dosing resulted in similar exposure levels of irinotecan, SN-38 and SN-38G in all patients. Objective response rate was 22.2%. Median overall survival and progression-free survival were 8.1 and 5.2 months, respectively. Exploratory immunoprofiling by flow cytometry and quantitative spatial localization analysis of infiltrated immune cells performed on biopsy and plasma samples revealed significant declines in CCL22, CCL2 and TNFα levels at end of first cycle and an active host immune response. Our study showed that OXIRI was well-tolerated and exhibited good efficacy, with immunomodulatory effects. It may be considered as an alternative to FOLFIRINOX in patients intolerant to the latter.

Genetic Polymorphism of Drug Metabolic Gene CYPs, VKORC1, NAT2, DPYD and CHST3 of Five Ethnic Minorities in Heilongjiang Province, Northeast China

Introduction

Genetic variability in genes encoding drug-metabolizing enzymes may contribute to the heterogeneity of drug responses in different populations. Extensive research in pharmacogenomics in major populations around the world provides us with a great deal of information about drug-related genetic polymorphisms.

Objective

The purpose of this study was to detect the genetic variation of drug-metabolism-related genes in the five ethnic minorities Daur, Hezhen, Ewenki, Mongolian and Manchu in China, and to analyze the distribution differences among ethnic groups.

Methods

We genotyped 32 SNPs of drug metabolism genes in 882 healthy Chinese volunteers from five ethnic groups. The genotype frequency and allele frequency of the five ethnic groups were calculated, and the different variants among the five ethnic groups were compared by chi-square test. Genetic parameters were analyzed using Popgene software. The genetic structure of five ethnic minorities was analyzed by principal component analysis, and compared with 26 populations.

Results

We found that SNPs of genes related to drug metabolism existed diversity in different populations. Among them, rs8192766 and rs9419082 in CYP2E1 showed statistical differences between Daur and Manchu, and NAT2 rs1801280 showed statistical differences between Hezhen and Mongolian. In addition, the five populations we studied had the smallest differences with EAS populations. There was haplotype diversity in CHST3, VKORC1, CYP1A2 and CYP2E1 genes in the five ethnic minorities, and these haplotype polymorphisms were related to the use of corresponding drug doses. Cluster analysis shows that the five ethnic minorities in Heilongjiang Province are clustered together with the EAS populations.

Conclusion

These results suggest that understanding the diversity of drug-related genetic markers is critical for individualized drug gene therapy programs in ethnic minorities in China as well as in populations highly mixed with these ethnic groups.

Beneficial effects of Wuzhi Capsule on tacrolimus blood concentrations in liver transplant patients with different donor-recipient CYP3A5 genotypes

WHAT IS KNOWN AND OBJECTIVE

Tacrolimus (Tac) is an immunosuppressant that is widely used to prevent allograft rejection in patients after liver transplantation. Its metabolism mainly depends on the cytochrome P450 3A5 (CYP3A5), which has genetic polymorphisms. Recently, a Chinese herbal medicine known as Wuzhi Capsule (WZC) was shown to increase Tac blood concentrations by inhibiting the activity of CYP3A in animal studies in rats. To date, it remains unexplored whether WZC can be efficiently used to enhance the blood concentration of Tac in liver transplant patients with different donor-recipient CYP3A5 genotypes.

METHODS

A total of 185 liver transplant patients were enrolled and two-way ANOVA was carried out, then they were divided into four groups according to the combinations of donor-recipient CYP3A5 phenotypes. WZC was given to patients when the dose of Tac was ≥4 mg, and the dose-adjusted C₀ (C₀ /D) of Tac measured twice in succession was ≤1 ng/ml/mg. The blood trough concentration of Tac (C₀ ), C₀ /D, and dose- and body weight-adjusted C₀ (C₀ /D/W) was analysed on days 7 and 14 after liver transplantation.

RESULTS

The genotypes of donor and recipient or WZC had significant effects on C0, C0/D and C0/D/W. There were significant differences in the Tac blood concentrations between the groups. The recipient expression (*1)/donor expression (*1) (R+/D+) group had the lowest C₀ , C₀ /D and C₀ /D/W among the four groups. Furthermore, a larger proportion of patients in the CYP3A5 expression groups required Tac dose adjustment to achieve a therapeutic effect and were given Tac with WZC. Notably, the use of WZC significantly increased the blood concentrations of Tac in the CYP3A5 expression groups and greater increases in the C₀ /D and C₀ /D/W were significantly associated with higher doses of WZC in the CYP3A5 expression groups. What is more, WZC reduced the hospitalization cost of patients to a certain extent.

WHAT IS NEW AND CONCLUSION

WZC significantly increased the C₀ , C₀ /D and C₀ /D/W in the CYP3A5 expression groups and reduced the hospitalization expenses of patients to a certain extent. What is more, greater increases in the C₀ /D and C₀ /D/W were significantly associated with higher doses of WZC.

Analysis of Very Important Pharmacogenomics Variants in the Chinese Lahu Population

Background

Genetic polymorphism, obviously, has a potential clinical role in determining differences in drug efficacy; however, there are no reports about the pharmacogenomic information of the Lahu population. Therefore, our research aimed to screen the genotypic frequencies of the very important pharmacogenomics (VIP) mutations and determined the differences between Lahu and the other 11 populations.

Methods

Agena MassARRAY (AgenaMassARRAY) single nucleotide polymorphism (SNP) genotyping technique was used to detect 81 VIP mutations of pharmacogenomics genes in Lahu, and their genotypic frequencies were compared with the other major 11 populations. Chi-square tests were used to identify different loci among these populations. Finally, the genetic structure and pairwise Fst values of Lahu and the other 11 populations were analyzed.

Results

We found that the distribution of allele frequencies within different pharmacogenes in Lahu showed significantly different with other populations. Additionally, the pairwise F-statistics (Fst) values and genetic structure revealed the variants in the Lahu population as well were mostly related to the Han Chinese in Beijing, China (CHB) and the Japanese population in Tokyo, Japan (JPT) genetically.

Conclusion

This study will provide a theoretical basis for safe drug use and help to establish the appropriate individualized treatment strategies in the Lahu population.

CYP2D6 Allele Frequency in Five Malaria Vivax Endemic Areas From Brazilian Amazon Region

Genetic variability was linked with individual responses to treatment and susceptibility to malaria by Plasmodium vivax. Polymorphisms in the CYP2D6 gene may modulate enzyme level and activity, thereby affecting individual responses to pharmacological treatment. The aim of the study was to investigate whether or not CYP2D6 single nucleotide polymorphisms rs1065852, rs38920-97, rs16947 and rs28371725 are unequally distributed in malaria by Plasmodium vivax individuals from the Brazilian Amazon region. The blood samples were collected from 220 unrelated Plasmodium vivax patients from five different endemic areas. Genotyping was performed using SNaPshot^® and real-time polymerase chain reaction methods. In all five areas, the rs1065852 (CYP2D6*10, C.100C > T), rs3892097 (CYP2D6*4, 1846C > T) and rs16947 (CYP2D6*2, C.2850G > A), as a homozygous genotype, showed the lowest frequencies. The rs28371725 (CYP2D6*41, 2988G > A) homozygous genotype was not detected, while the allele A was found in a single patient from Macapá region. No deviations from Hardy-Weinberg equilibrium were found, although a borderline p-value was observed (p = 0.048) for the SNP rs3892097 in Goianésia do Pará, Pará state. No significant associations were detected in these frequencies among the five studied areas. For the SNP rs3892097, a higher frequency was observed for the C/T heterozygous genotype in the Plácido de Castro and Macapá, Acre and Amapá states, respectively. The distribution of the CYP2D6 alleles investigated in the different areas of the Brazilian Amazon is not homogeneous. Further investigations are necessary in order to determine which alleles might be informative to assure optimal drug dosing recommendations based on experimental pharmacogenetics.

Pharmacogenetics of common SNP affecting drug metabolizing enzymes: comparison of allele frequencies between European and Malaysian/Singaporean

Compared to Europe, data on genetic variation in genes transcribing drug metabolizing enzymes among Asian is limited due to ethnic diversity. Here we compare frequencies for clinically relevant single nucleotide polymorphism (SNP) commonly observed in drug metabolizing enzymes between European and Malaysian/Singaporean. Minor allele frequencies (MAF) for the indicated SNPs for European, South Asian and East Asian populations were obtained from the NCBI website (https://www.ncbi.nlm.nih.gov/snp). The SNP prevalence among Malaysian/Singaporean was characterized from gene association studies. Generally, some SNPs in CYP2D6 and CYP2C19 do not show good agreement between the two populations as to the MAF value obtained. CYP2D6*4 tends to be more common among European, whereas CYP2D6*10 is more common in Malays and Chinese among Singaporean. Regardless of different phenotype, MAF of CYP2D6*4 for Indians is similar to that seen by the European. Singaporeans show smaller MAF for CYP2C19*17 but higher CYP2C19*2 frequencies as opposed to European ones. Following growing attention to the contribution of CYP3A4/5, N-acetyltransferases (NAT2), thiopurine methyltransferase (TPMT) and uridine diphosphate glucuronosyltransferases (UGT)2B7 in predicting drug response across Europe, there are limited pharmacogenetics (PGx) studies examining the gene-drug interaction among Malaysian/Singaporean. To better understand the heterogeneity of the drug response, PGx studies for the abovementioned enzymes between ethnics in Malaysian/Singaporean should be identified.

Effect of Environmental Exposure and Pharmacogenomics on Drug Metabolism

BACKGROUND

Pesticides are major xenobiotic compounds and environmental pollutants, which are able to alter drug-metabolizing enzyme as well as pharmacokinetics of drugs. Subsequent to the release of the human genome project, genetic variations (polymorphism) become an integral part of drug development due to their influence on disease susceptibility/ progression of the disease and their impact on drug absorption, distribution, metabolism of active metabolites and finally excretion of the drug. Genetic polymorphisms crucially regulate pharmacokinetics and pharmacodynamics of drugs under the influence of physiological condition, lifestyle, as well as pathological conditions collectively.

OBJECTIVE

To review all the evidence concerning the effect of environmental exposure on drug metabolism with reference to pharmacogenomics.

METHODS

Scientific data search and review of basic, epidemiological, pharmacogenomics and pharmacokinetics studies were undertaken to evaluate the influence of environmental contaminants on drug metabolism.

RESULTS

Various environmental contaminants like pesticides effectively alter drug metabolism at various levels under the influence of pharmacogenomics, which interferes with pharmacokinetics of drug metabolism. Genetic polymorphism of phase I and phase II xenobiotic-metabolizing enzymes remarkably alters disease susceptibility as well as the progression of disease under the influence of various environmental contaminants at various levels.

CONCLUSION

Individual specific drug response may be attributed to a large variety of factors alone or in combination ranging from genetic variations (SNP, insertion, deletion, duplication etc.) to physiological setting (gender, age, body size, and ethnicity), environmental or lifestyle factors (radiation exposure, smoking, alcohol, nutrition, exposure to toxins, etc.); and pathological conditions (obesity, diabetes, liver and renal function).

Pharmacogenetic relevant polymorphisms of CYP2C9, CYP2C19, CYP2D6, and CYP3A5 in Bhutanese population

Background Marked differences among genotype frequencies (Caucasians, Asians, and Africans) have been observed in cytochrome P450 (CYP) genes. Data on the frequency of pharmacogenetic relevant polymorphisms in Bhutanese population is absent. This study aimed to investigate the frequencies of pharmacogenetic relevant polymorphisms of CYP2C9 (*2 and *3), CYP2C19 (*2 and *3), CYP2D6 (*10), and CYP3A5 (*3) in Bhutanese population. Methods Genotyping was performed in 443 DNA samples using polymerase chain reaction-restriction fragment length polymorphism. Results For CYP2C9, allele frequencies of *2 and *3 variants were 0.339% and 0%, respectively. For CYP2C19, frequencies of *2 and *3 variants were 30.135% and 15.689%, respectively. Allele frequencies of CYP2D6*10 and CYP3A5*3 were 21.332% and 77.314%, respectively. Allele frequencies of CYP2C9*2 are similar to most Asians while CYP2C9*3 was absent. CYP2C19*2 showed a close resemblance to Japanese and Burmese, while CYP2C19*3 is near to Japanese and Korean. CYP2D6*10 is noticeably lower than other Asians. CYP3A5*3 is similar to East Asians (Chinese, Japanese, and Korean). Conclusions The Bhutanese population is polymorphic for these CYP genes, except for CYP2C9*3. Similar to other populations, genetic testing for these genes may, therefore, be helpful to obtain the benefit from pharmacological treatments and prevent adverse drug reactions.

Melding Pharmacogenomic Effect of MDR1 and CYP3A5 Gene Polymorphism on Tacrolimus Dosing in Renal Transplant Recipients in Northern India

Introduction

Tacrolimus (TAC) is the mainstay immunosuppressant for renal transplantation. A narrow therapeutic index, multiple drug interactions, and interindividual variability in pharmacokinetics make it obligatory to monitor therapeutic drug levels. The Multidrug resistance gene 1 (MDR1) and CYP3A5 gene polymorphism may blend to achieve the optimal level. The optimal dose as per body weight is difficult to single out in the early posttransplantation period. In this study, we aimed to analyze the melding effect of both gene polymorphisms and to elicit the dose depending on the combination of genetic single nucleotide polymorphisms (SNPs) in northern Indian transplant recipients, for whom data are limited.

Methods

The daily TAC dose, weight-adjusted doses (mg/kg per day), TAC trough blood concentration (average of at least 3 levels), dose normalized with a corresponding dose using TAC concentration/weight-adjusted dose ratio (ng/ml per mg/kg per day) of 248 patients were recorded. All recipients were genotyped for the SNPs of CYP3A5 at intron 3 A6986G (the *3 or *1 allele), MDR1 at exons 12 (C1236T), 21 (G2677A/T), and 26 (C3435T). We analyzed the blending effect of mutant SNPs of the MDR gene and CYP3A5 for optimized TAC levels.

Results

Among CYP3A5 genotypic variants, the dose-adjusted TAC level was significantly lower, and the TAC dose required to achieve the target level was significantly higher, in CYP3A5*1*1 (expressor) than that of CYP3A5*1*3 and CYP3A5*3*3. Of the MDR1 gene SNPs, only the G2677T/A homozygous mutant was significantly associated with TAC level, and it was strongly correlated with P-gp expression.The daily TAC dose requirement was highest with a combination of CYP3A5*1*1 and homozygous mutant TT+AA genotype of G2677T/A, and was lowest with CYP3A5*3*3 and wild-type GG of the G2677T/A genotype.

Conclusion

Both CYP gene and MDR1 gene polymorphism affect TAC dose requirements, and there is a need to look for both in an individual to achieve the target trough concentration.

Effectiveness of Measuring Genetic Polymorphisms in Metabolizing Enzymes of Tacrolimus within One Medical Facility

OBJECTIVES

Because genetic polymorphisms cause diverse activity in drug metabolizing enzymes, drug concentrations in the blood may be variable among patients. We analyzed the genotypes of CYP3A5 and MDR1, and investigated their relationship with whole blood drug concentrations.

METHODS

Eight patients were administered an oral dose of tacrolimus for one week or longer prior to enrollment in this study. Whole blood concentrations for tacrolimus were measured 12 hours post oral administration, on the same day as genotyping, within our hospital using a fully automated gene analyzer. The procedures became so rapid that collection of blood samples could be completed within the same day (approximately one hour).

RESULTS

The genotype frequency of CYP3A5 was ^*3/^*3 in five patients, ^*1/^*3 in two patients, and ^*1/^*1 in one patient. All five patients with ^*3/^*3 showed favorable increases in tacrolimus blood concentrations. In the two patients with ^*1/^*3, an increase in tacrolimus blood concentration was not readily achieved in one patient, but increased favorably in the other patient. In the patient with ^*1/^*1, tacrolimus was not detectable in the patient's blood. A favorable treatment effect was obtained by changing tacrolimus to cyclosporine. It is notable that genotypes in patients where tacrolimus was not detected in the blood were wild types: 2677G/G and 3435C/C in MDR1.

CONCLUSIONS

The measurement of genetic polymorphisms in metabolizing enzymes of tacrolimus, within one medical facility, is applicable for the selection of immunosuppressants and individual dosing for the treatment of autoimmune disease.

Genetic polymorphisms of human cytochrome P450 CYP1A1 in an Egyptian population and tobacco-induced lung cancer

Background

Cytochrome P450 CYP1A1 helps detoxify the potential carcinogens in tobacco smoke, it was reported that polymorphisms in the coding gene result in variation in the expression and activity levels which alter metabolism and clearance of carcinogens and therefore modify cancer risk. In this work, we aimed to identify CYP1A1 gene polymorphisms associated with lung cancer in Egyptian population and to examine the interaction effect with Tobacco smoking in modulating disease risk.

Methods

A case–control study was conducted on 150 unrelated lung cancer patients and 150 unrelated control subjects. Genomic DNA was extracted and sequencing analysis of CYP1A1 gene was performed on ABI PRISM 3100 genetic analyzer.

Results

Three variants in CYP1A1 gene were identified in heterozygous forms in lung cancer patients I462V, T461N and I286T. A combined variant T461N/ I462V associated with lung cancer and those who carried this variant were 2-times more likely to develop lung cancer (OR = 2.03, 95% CI = 1.81-2.29, P = 0.04), specially the non-small cell type (NSCLC) (OR = 2.20, 95% CI = 1.93–2.50, P = 0.02). Wild type was more frequent among smoker controls (83.3%) compared to smoker lung cancer patients (54.8%), P = 0.03. Association studies to examine the interaction effect of identified variants with Tobacco smoking in modulating disease risk showed no significant associations. Identified polymorphisms showed no significant implication on the stage or the prognosis of the disease.

Conclusion

Our findings support that CYP1A1 polymorphisms play a role in the pathogenesis of lung cancer. In Egyptian population, CYP1A1 I462V, T461N and I286T variants were identified among lung cancer patients and combined T461N/ I462V was a risk variant for NSCLC in non smokers.

Comparative persistence of antiepileptic drugs in patients with epilepsy: A STROBE-compliant retrospective cohort study

We compared persistence of antiepileptic drugs (AEDs) including carbamazepine, oxcarbazepine, gabapentin, lamotrigine, topiramate, valproic acid, and phenytoin in an Asian population with epilepsy.A retrospective cohort study was conducted by analyzing Taiwan's National Health Insurance Research Database (NHIRD). Adult epilepsy patients newly prescribed with AEDs between 2005 and 2009 were included. The primary outcome was persistence, defined as the treatment duration from the date of AED initiation to the date of AED discontinuation, switching, hospitalization due to seizure or disenrollment from databases, whichever came first. Cox proportional hazard models were used to estimate the risk of non-persistence with AEDs.Among the 13,061 new users of AED monotherapy (mean age: 58 years; 60% men), the persistence ranged from 218.8 (gabapentin) to 275.9 (oxcarbazepine) days in the first treatment year. The risks of non-persistence in patients receiving oxcarbazepine (adjusted hazard ratio [HR], 0.78; 95% CI, 0.74-0.83), valproic acid (0.88; 0.85-0.92), lamotrigine (0.72; 0.65-0.81), and topiramate (0.90; 0.82-0.98) were significantly lower than in the carbamazepine group. Compared with carbamazepine users, the non-persistence risk was higher in phenytoin users (1.10; 1.06-1.13), while gabapentin users (1.03; 0.98-1.09) had similar risk. For risk of hospitalization due to seizure and in comparison with carbamazepine users, oxcarbazepine (0.66; 0.58-0.74) and lamotrigine (0.46; 0.35-0.62) users had lower risk, while phenytoin (1.35; 1.26-1.44) users had higher risk. The results remained consistent throughout series of sensitivity and stratification analyses.The persistence varied among AEDs and was better for oxcarbazepine, valproic acid, lamotrigine, and topiramate, but worse for phenytoin when compared with carbamazepine.

Ethnic sensitivity assessment of fluticasone furoate/vilanterol in East Asian asthma patients from randomized double-blind multicentre Phase IIb/III trials

Background

Fluticasone furoate (FF)/vilanterol (VI) is a once daily (OD) inhaled corticosteroid/long-acting β₂-agonist combination asthma therapy approved in Japan and the EU. FF/VI efficacy and safety data from asthma studies including patients in East Asia were evaluated to assess ethnic sensitivity.

Methods

Randomized, double-blind, multicenter Phase IIb/III trials were assessed. Change from baseline relative to placebo or twice-daily fluticasone propionate 500 μg in trough FEV₁ was compared between patients from Japan (N = 148) and Not-Japan (N = 3,066; three studies). Adverse events (AEs), laboratory results, and electrocardiograms were compared between patients from Japan + Korea (N = 188) and Not-Japan + Korea (N = 3,840; five studies).

Results

For trough FEV₁, improvements from baseline (least-squares mean difference [95 % confidence interval]) were reported for FF/VI 100/25 μg OD versus placebo at Week 12 (Japan: 0.323 L [0.104–0.542]; Not-Japan: 0.168 L [0.095–0.241]). Improvements from baseline (least-squares mean change [standard error]) were reported with FF/VI 200/25 μg OD at Week 24 (Japan: 0.355 L [0.1152]; Not-Japan: 0.396 L [0.0313]). A greater proportion of patients from Japan + Korea versus Not-Japan + Korea reported AEs in all treatment arms including placebo (FF/VI 100/25 μg: 79 % versus 57 %; FF/VI 200/25 μg: 64 % versus 45 %; placebo: 41 % versus 23 %). There were no notable differences in treatment-related or class-related AEs. No clinically significant changes in electrocardiogram assessments or statistically significant differences in 24 h urinary cortisol excretion were observed between the Japan + Korea and Not-Japan + Korea cohorts.

Conclusions

Good efficacy and an acceptable safety profile were observed for FF/VI 100/25 μg and 200/25 μg OD in East Asian asthma patients; these globally recommended doses are appropriate for asthma patients in Japan.

Trial registration

Clinicaltrials.gov registration numbers: NCT01165138, NCT01134042, NCT01086384, NCT00603278, NCT00603382.

Electronic supplementary material

The online version of this article (doi:10.1186/s12890-015-0159-z) contains supplementary material, which is available to authorized users.

Interethnic differences in pharmacokinetics of antibacterials

BACKGROUND

Optimal antibacterial dosing is imperative for maximising clinical outcome. Many factors can contribute to changes in the pharmacokinetics of antibacterials to the extent where dose adjustment may be needed. In acute illness, substantial changes in important pharmacokinetic parameters such as volume of distribution and clearance can occur for certain antibacterials. The possibility of interethnic pharmacokinetic differences can further complicate attempts to design an appropriate dosing regimen. Factors of ethnicity, such as genetics, body size and fat distribution, contribute to differences in absorption, distribution, metabolism and elimination of drugs. Despite extensive previous work on the altered pharmacokinetics of antibacterials in some patient groups such as the critically ill, knowledge of interethnic pharmacokinetic differences for antibacterials is limited.

OBJECTIVES

This systematic review aims to describe any pharmacokinetic differences in antibacterials between different ethnic groups, and discuss their probable mechanisms as well as any clinical implications.

METHODS

We performed a structured literature review to identify and describe available data of the interethnic differences in the pharmacokinetics of antibacterials.

RESULTS

We found 50 articles that met our inclusion criteria and only six of these compared antibacterial pharmacokinetics between different ethnicities within the same study. Overall, there was limited evidence available. We found that interethnic pharmacokinetic differences are negligible for carbapenems, most β-lactams, aminoglycosides, glycopeptides, most fluoroquinolones, linezolid and daptomycin, whereas significant difference is likely for ciprofloxacin, macrolides, clindamycin, tinidazole and some cephalosporins. In general, subjects of Asian ethnicity achieve drug exposures up to two to threefold greater than Caucasian counterparts for these antibacterials. This difference is caused by a comparatively lower volume of distribution and/or drug clearance.

CONCLUSION

Interethnic pharmacokinetic differences of antibacterials are likely; however, the clinical relevance of these differences is unknown and warrants further research.

Role of SLCO1B1, ABCB1, and CHRNA1 gene polymorphisms on the efficacy of rocuronium in Chinese patients

This study explored the role of SLCO1B1, ABCB1, and CHRNA1 gene polymorphisms on the efficacy and duration of action of rocuronium in Chinese patients. Two hundred seven unrelated Chinese patients scheduled for elective surgery were recruited, and 200 completed the study. Their ABCB1, SLCO1B1, and CHRNA1 genotypes were determined. Demographic and clinical non-genetic data also were collected. The SLCO1B1, ABCB1, and CHRNA1 variants did not affect the onset time of rocuronium. Clinical duration and recovery time of rocuronium were prolonged in patients with the ABCB1 rs1128503TT and SLCO1B1 rs2306283 AG and GG genotypes. We demonstrate that the SLCO1B1 and ABCB1 gene variants could affect the pharmacodynamics of rocuronium. The ABCB1 rs1128503 C>T genotype was the most important factor on the efficacy of rocuronium.

Genotype, allele and haplotype frequencies of four TCL1A gene polymorphisms associated with musculoskeletal toxicity in the South Indian descent

INTRODUCTION

Decline in circulating estrogen levels causes lessening of bone mass accompanied with musculoskeletal pain, which is the primary cause of treatment discontinuation in patients taking aromatase inhibitors. Evidence from recent genome-wide association studies (GWAS) suggests that the genetic variability underlying TCL1A gene increases the risk of aromatase inhibitors (AIs) - induced musculoskeletal toxicity. Currently, no data is available on the frequency distribution of TCL1A gene polymorphisms in Indians.

METHODS

In this pilot study, we used TaqMan fluorescent probes to assess the genotypes of four TCL1A gene polymorphisms associated with musculoskeletal toxicity in 247 healthy homogenous South Indian subjects on real time thermocycler. Haplotype estimation and pairwise linkage disequilibrium (LD) analysis were executed by Haploview.

RESULTS

The incidence of polymorphic variant allele (G) frequencies of rs7158782, rs7159713, rs2369049 and rs11849538 were 22.1%, 23.5%, 18.2% and 22.9% in the study population, respectively. The polymorphisms were found to be in complete LD with each other. Four different haplotypes, each of which having a frequency of above 1% were inferred in South Indians using an expectation-maximization algorithm. Notably, three haplotypes were found to be population specific viz H4 A-A-A-G (1.2%) for South India, H5 G-G-A-C (1.3%) for JPT and H6 G-G-G-C (40.4%) for YRI. Further, H3 G-G-A-G (2.3-16.3%) haplotype occurs primarily in Asians and is virtually absent in Africans. Overall, the genetic variability and haplotype profile of South Indian population revealed significant inter-racial variability compared with HapMap data.

CONCLUSION

This documentation contributes for further investigations on the pharmacogenetics of AIs in South Indians.

The real-life perception of efficacy, attitude, satisfaction and safety of vardenafil therapy (REPEAT): a prospective, non-interventional, observational study

This study assessed the improvement in relationship quality, effectiveness and safety associated with vardenafil for the treatment of erectile dysfunction (ED). The study was conducted in 1433 centres across 21 countries and comprised a baseline patient visit and up to four follow-up visits during an observational period of 1 year. Relationship quality, happiness, satisfaction with vardenafil treatment, and safety and tolerability were assessed by physician interviews and patient and partner questionnaires. Overall, 7496 patients were enrolled in the study, of which 7430 were included in the safety analyses and 6470 in the effectiveness analyses. Relationship quality, assessed by a relationship questionnaire (partnerschaftsfragebogen [PFB]), was improved at last observation carried forward, compared with baseline, in both patients and partners and satisfaction with the effectiveness of vardenafil treatment was high. Vardenafil was well tolerated and adverse events were consistent with the known safety profile of phosphodiesterase type 5 inhibitors. These results confirm the well-established effectiveness and safety profiles of vardenafil. This study is the first to demonstrate improvements in relationship quality following vardenafil therapy, in both patients and partners, using the PFB questionnaire.

Genetic polymorphisms of metabolic enzymes and the pharmacokinetics of indapamide in Taiwanese subjects

To understand the genetic makeup and impact on pharmacokinetics (PK) in the Taiwanese population, we analyzed the pharmacogenetic (PG) profile and demonstrated its effects on enzyme metabolism using indapamide as an example. A multiplex mass spectrometry method was used to examine the single nucleotide polymorphism (SNP) profile of eight major phases I and II metabolic enzymes in 1,038 Taiwanese subjects. A PG/PK study was conducted in 24 healthy subjects to investigate the possible effects of 28 SNPs on drug biotransformation. Among the genetic profile analyzed, eight SNPs from CYP2A6, CYP2C19, CYP2D6, CYP2E1, CYP3A5, and UGT2B7 showed higher variant frequencies than those previously reported in Caucasians or Africans. For instance, we observed 14.7% frequency of the SNP rs5031016 (I471T) from CYP2A6 in Taiwanese, whereas 0% variation was reported in Caucasians and Africans. The PG/PK study of indapamide demonstrated that the polymorphic SNPs CYP2C9 rs4918758 and CYP2C19 rs4244285 appeared to confer lowered enzyme activity, as indicated by increased C max (25% ∼ 64%), increased area under the plasma level-time curves (30~76%), increased area under the time infinity (43% ∼ 80%), and lower apparent clearance values than PK for wild-type indapamide. Our results reinforce the biochemical support of CYP2C19 in indapamide metabolism and identify a possible new participating enzyme CYP2C9. The PG/PK approach contributed toward understanding the genetic makeup of different ethnic groups and associations of enzymes in drug metabolism. It could be used to identify two genetic markers that enable to differentiate subjects with varied PK outcomes of indapamide.

Top Three Pharmacogenomics and Personalized Medicine Applications at the Nexus of Renal Pathophysiology and Cardiovascular Medicine

Pharmacogenomics is a field with origins in the study of monogenic variations in drug metabolism in the 1950s. Perhaps because of these historical underpinnings, there has been an intensive investigation of 'hepatic pharmacogenes' such as CYP450s and liver drug metabolism using pharmacogenomics approaches over the past five decades. Surprisingly, kidney pathophysiology, attendant diseases and treatment outcomes have been vastly under-studied and under-theorized despite their central importance in maintenance of health, susceptibility to disease and rational personalized therapeutics. Indeed, chronic kidney disease (CKD) represents an increasing public health burden worldwide, both in developed and developing countries. Patients with CKD suffer from high cardiovascular morbidity and mortality, which is mainly attributable to cardiovascular events before reaching end-stage renal disease. In this paper, we focus our analyses on renal function before end-stage renal disease, as seen through the lens of pharmacogenomics and human genomic variation. We herein synthesize the recent evidence linking selected Very Important Pharmacogenes (VIP) to renal function, blood pressure and salt-sensitivity in humans, and ways in which these insights might inform rational personalized therapeutics. Notably, we highlight and present the rationale for three applications that we consider as important and actionable therapeutic and preventive focus areas in renal pharmacogenomics: 1) ACE inhibitors, as a confirmed application, 2) VDR agonists, as a promising application, and 3) moderate dietary salt intake, as a suggested novel application. Additionally, we emphasize the putative contributions of gene-environment interactions, discuss the implications of these findings to treat and prevent hypertension and CKD. Finally, we conclude with a strategic agenda and vision required to accelerate advances in this under-studied field of renal pharmacogenomics with vast significance for global public health.

An update on ethnic differences in drug metabolism and toxicity from anti-cancer drugs

INTRODUCTION

Based on recent emerging evidence of inter-ethnic differences in drug response and toxicity, ethnic diversity in pharmacokinetics, pharmacogenomics and clinical outcomes are being increasingly investigated. Ultimately, this will promote improved understanding of inter-individual differences in the pharmacokinetics and tolerance of cytotoxic drugs.

AREAS COVERED

This article reviews potential explanations for the observed ethnic differences in treatment outcomes and provides clinical data to support this concept. A literature search was implemented on PubMed and PharmGKB to investigate the areas of ethnic differences in pharmacogenomics, pharmacogenetics and clinical outcomes of cancer therapies.

EXPERT OPINION

There has been a relative paucity of clinical evidence linking genetic polymorphisms of genes encoding drug-metabolizing enzymes to the pharmacokinetics, pharmacodynamics and tolerance of anti-cancer drugs. Future research should focus on studies using large sample sizes, in the hope that they will provide results of high clinical significance. Due to the potential for ethnic differences to impact on both toxicities and benefits of systemic cancer therapies, the development of new therapeutic agents should include patients from diverse geographical ancestries in each phase of drug development.

Prevalence of topoisomerase I genetic mutations and UGT1A1 polymorphisms associated with irinotecan in individuals of Asian descent

Topoisomerase I (TOP-I) mutations have been shown to be correlated to irinotecan resistance in vitro. However, the prevalence of TOP-I germline mutations has yet to be systematically elucidated. On the other hand, polymorphisms of UGT1A1 have been shown to be associated with CPT-11 toxicity in clinical situations. The primary aim of this study was to investigate the prevalence of mutations in the TOP-I exons associated with CPT-11 resistance, including untreated cancer tissue. A secondary aim was to confirm the less frequent UGT1A1*28 and more frequent UGT1A1*6 in individuals of Asian descent compared to Caucasians and individuals of African descent. The prevalence of 5 reported TOP-I mutations in exons was investigated in volunteers (n=236) using DNA sequencing of the PCR products. The prevalence of TOP-I mutations in untreated lung cancer tissues (n=16) was also investigated. Additionally, 3 UGT1A1 polymorphisms, UGT1A1*6, *27 and *28, were investigated in volunteers (n=126). There were no mutations of TOP-I in any of the 236 subjects or in the untreated lung tissues. Among 128 subjects, the distribution of homozygous polymorphisms of UGT1A1 was: UGT1A1*28 in 3 (2.4%) and UGT1A1*6 in 4 (3.2%) subjects, and co-occurrence of heterozygous polymorphisms for both UGT1A1*6 and UGT1A1*28 in 4 (3.2%) subjects, and for UGT1A1*27 and UGT1A1*28 in 1 subject (0.8%). The Hardy-Weinberg deviation test showed there was no significant deviation from the equilibrium, and the association analysis indicated no significant linkage between UGT1A1*6 and UGT1A1*28. In conclusion, TOP-I genetic mutations correlated to CPT-11 resistance were not detected in any of the subjects and untreated lung cancer tissues. Less frequent UGT1A1*28 and more frequent UGT1A1*6 were confirmed in East Asian individuals compared to Caucasians and individuals of African descent. Linkage disequilibrium was not detected between UGT1A1*6 and UGT1A1*28.

Analysis of CYP3A4 genetic polymorphisms in Han Chinese

Our study aimed to comprehensively investigate the genetic polymorphisms of CYP3A4 in Han Chinese. We sequenced the gene regions of CYP3A4, including its promoter, exons, surrounding introns and 3' untranslated region (3'UTR), from 100 unrelated-healthy Han Chinese individuals. We detected 11 SNPs, three of which are novel. According to in silico functional prediction of novel variants, 20148 A>G in exon 10, resulting in substitution of Tyr319 with Cys (CYP3A4*21), may induce dramatic alteration of protein conformation, and 26908 G>A in 3'UTR may disrupt post-transcriptional regulation. We identified five alleles in Han Chinese, the allele frequencies of CYP3A4*1, *5, *6, *18 and *21 are 97, 0.5, 1, 1 and 0.5%, respectively. Haplotype inference revealed 14 haplotypes, of which the major haplotype CYP3A4*1A constitutes 59% of the total chromosomes. We also examined the possible role of natural selection in shaping the variation of CYP3A4 and confirmed a trend, consistent with the action of positive selection. We systematically screened the genetic polymorphisms of CYP3A4 in Han Chinese, highlighted possible functional impairment of the novel allele and summarized the distinct allele and haplotype frequency distribution, with an emphasis on detecting the footprint of recent positive selection on the CYP3A4 gene in Han Chinese.

Efflux transporters- and cytochrome P-450-mediated interactions between drugs of abuse and antiretrovirals

Multidrug regimens and corresponding drug interactions cause many adverse reactions and treatment failures. Drug efflux transporters: P-gp, MRP, BCRP in conjunction with metabolizing enzymes (CYPs) are major factors in such interactions. Most effective combination antiretrovirals (ARV) therapy includes a PI or a NNRTI or two NRTI. Coadministration of such ARV may induce efflux transporters and/or CYP3A4 resulting in sub-therapeutic blood levels and therapeutic failure due to reduced absorption and/or increased metabolism. A similar prognosis is true for ARV-compounds and drugs of abuse combinations. Morphine and nicotine enhance CYP3A4 and MDR1 expression in vitro. A 2.5 fold rise of cortisol metabolite was evident in smokers relative to nonsmokers. Altered functions of efflux transporters and CYPs in response to ARV and drugs of abuse may result in altered drug absorption and metabolism. Appropriate in vitro models can be employed to predict such interactions. Influence of genetic polymorphism, SNP and inter-individual variation in drug response has been discussed. Complexity underlying the relationship between efflux transporters and CYP makes it difficult to predict the outcome of HAART as such, particularly when HIV patients taking drugs of abuse do not adhere to HAART regimens. HIV(+) pregnant women on HAART medications, indulging in drugs of abuse, may develop higher viral load due to such interactions and lead to increase in mother to child transmission of HIV. A multidisciplinary approach with clear understanding of mechanism of interactions may allow proper selection of regimens so that desired therapeutic outcome of HAART can be reached without any side effects.

CYP3A5 polymorphism and sensitivity of blood pressure to dietary salt in Japanese men

The cytochrome P-450 3A5 (CYP3A5) gene has recently been implicated in renal sodium reabsorption and blood pressure regulation. The genetic effect of CYP3A5*1 (expressor) and *3 (reduced-expressor) variants on blood pressure has been studied in African Americans and Caucasians, but not yet in the Asian population. In this cross-sectional study, 238 Japanese male workers were examined to determine whether CYP3A5 *1*3 affects the blood pressure level, taking daily salt intake into account as a potential gene-environment interaction. The A6986G polymorphism was determined by melting curve analysis, and the salt intake level was inferred from spot urine specimen by calculating 24-h urinary sodium excretion. CYP3A5 *1*3 per se had no association with systolic blood pressure (SBP) and only a weak association was detected for diastolic blood pressure (DBP) (*1/*1 vs *3/*3, P=0.038), which was strengthened after adjustment with age and body mass index (*1/*1 vs*3/*3, P=0.007; *1/*1 vs*1/*3, P=0.045). Significant interactions between the genotype and salt intake were observed in both SBP (P=0.046) and DBP (P=0.003). SBP and DBP were significantly associated with the level of salt intake in*3/*3 (P<0.001) but not in *1 carriers. *1carrier had higher blood pressure than *3/*3, but only in those with low salt intake. These results suggest that CYP3A5 variants may be a determinant of salt sensitivity of blood pressure in Japanese men.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

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

Ethnic differences in the distribution ofCYP3A5gene polymorphisms

The genetic polymorphism affecting the CYP3A5 enzyme is responsible for interindividual and interethnic variability in the metabolism of CYP3A5 substrates. The full extent of the CYP3A5 genetic polymorphism was analysed in French Caucasian, Gabonese and Tunisian populations using a polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) strategy. In the three populations, eight, 17 and ten single nucleotide polymorphisms (SNPs), respectively, were identified, among which nine correspond to rare new mutations. Also identified were 16 alleles including eight new allelic variants. Significant differences were observed in the distribution of these alleles. Particularly, the frequency of the CYP3A5*3C null allele in French Caucasians (81.3%) and in Tunisians (80.0%) is higher than in the Gabonese population (12.5%) (p < 0.001). Considering the CYP3A5 genotypes of the tested individuals, only 10.4% of French Caucasians and 30.0% of Tunisians were identified as CYP3A5 expressors. In contrast, 90.0% of Gabonese subjects appear to express the CYP3A5 protein.

CYP3A5 and ABCB1 genes and hypertension

Hypertension is the first single modifiable cause of disease burden worldwide. Genes encoding proteins that are involved in the metabolism (CYP3A5) and transport (ABCB1) of drugs and hormones might contribute to blood pressure control in humans. Indeed, recent data have suggested that CYP3A5 and ABCB1 gene polymorphisms are associated with blood pressure in the rat as well as in humans. Interestingly, the effects of these genes on blood pressure appear to be modified by dietary salt intake. This review summarizes what is known regarding the relationships of the ABCB1 and CYP3A5 genes with blood pressure, and discusses the potential underlying mechanisms of the association. If the role of these genes in blood pressure control is confirmed in other populations and other ethnic groups, these findings would point toward a new pathway for blood pressure control in humans.

Cigarette smoking, N-acetyltransferase 2 polymorphisms and systemic lupus erythematosus in a Japanese population

Cigarette smoking may be associated with an increased risk of systemic lupus erythematosus (SLE), but the underlying mechanism of this association remains unclear. N-acetyltransferase 2 (NAT2) is highly variable and detoxifies aromatic amines, an important class of carcinogens in tobacco smoke. Individuals who possess homozygous polymorphic alleles have a slower rate of metabolic detoxification of aromatic amines. We investigated the relationship of the NAT2 polymorphism to the risk of SLE with special reference to the interaction with cigarette smoking among 152 SLE cases and 427 controls in a female Japanese population. NAT2*4, NAT2*5B, NAT2*6A and NAT2*7B alleles were detected with polymerase chain reaction–restriction fragment length polymorphism. Individuals carrying the *4/*4 genotype are rapid acetylators, whereas those with homozygous non-*4 genotypes have a slow acetylator phenotype. Cigarette smoking was associated with an increased risk of SLE (odds ratio [OR] = 2.26; 95% confidence interval [CI] = 1.46–3.50). The slow acetylator genotype of NAT2 was significantly associated with an increased risk of SLE (OR = 2.34, 95% CI = 1.21–4.52) compared with the rapid acetylator genotype. A gene-environment interaction was suggested, with a combination of the NAT2 slow acetylator genotype and smoking conferring significantly higher risk (OR = 6.44, 95% CI = 3.07–13.52; attributable proportion due to interaction = 0.50, 95% CI = 0.12–0.88), compared with the NAT2 rapid acetylator genotype and no history of smoking. This study suggests that, in this Japanese population, the NAT2 slow acetylator status may be a determinant in susceptibility to SLE.

The environmental genome project: reference polymorphisms for drug metabolism genes and genome-wide association studies

The Environmental Genome Project (EGP) has generated a comprehensive resource of commonly occurring single nucleotide polymorphisms (SNPs) in more than six hundred environmental response genes, including a number of drug metabolism genes. The gene-oriented sequence variation discovery carried out by the EGP is complementary to the HapMap and enables genome-wide association studies (GWAS) that survey a large portion of the known common variation. For GWAS focused on drug metabolism genes and phenotypes, it is important to know the proportion of common SNPs covered by the commercially available high-throughput genotyping chips. Herein, we review a subset of Phase I cytochrome P450 genes studied by the EGP, approaches to GWAS, and the sensitivity of available genotyping platforms to capture common sequence variation in this subset of drug metabolism genes.

CYP3A5*3 and CYP3A4*1B allele distribution and genotype combinations: differences between Spaniards and Central Americans

The aim of this study was to detect genotypic differences between three populations of healthy volunteers from Northern Spain (204 subjects), Nicaragua (120 subjects), and El Salvador (112 subjects) regarding CYP3A4*1B and CYP3A5*3 polymorphisms. No significant differences were found by comparing allelic frequencies between the two Central American populations. The CYP3A5*3 allele frequency was significantly different (P < 0.01) between Central Americans (76%) and Spaniards (91%). By contrast, CYP3A4*1B allele was more prevalent among Central Americans (12.5%) than among North Spaniards (4%) (P < 0.01). Analysis of CYP3A4-3A5 genotype combinations revealed that individuals carrying CYP3A4*1B/CYP3A5*1 were more represented in Central Americans (16.9%) than in Spaniards (5.4%), suggesting a marked linkage disequilibrium. These data are compatible with a higher CYP3A enzyme activity in Central Americans as opposed to Spaniards and other white groups, which could imply differences in dose requirements for drugs metabolized by CYP3A and should be considered in allele-disease association studies.

Recent development in pharmacogenomics: from candidate genes to genome-wide association studies

Genetic diversity, most notably through single nucleotide polymorphisms and copy-number variation, together with specific environmental exposures, contributes to both disease susceptibility and drug response variability. It has proved difficult to isolate disease genes that confer susceptibility to complex disorders, and as a consequence, even fewer genetic variants that influence clinical drug responsiveness have been uncovered. As such, the candidate gene approach has largely failed to deliver and, although the family-based linkage approach has certain theoretical advantages in dealing with common/complex disorders, progress has been slower than was hoped. More recently, genome-wide association studies have gained increasing popularity, as they enable scientists to robustly associate specific variants with the predisposition for complex disease, such as age-related macular degeneration, Type 2 diabetes, inflammatory bowel disease, obesity, autism and leukemia. This relatively new methodology has stirred new hope for the mapping of genes that regulate drug response related to these conditions. Collectively, these studies support the notion that modern high-throughput single nucleotide polymorphism genotyping technologies, when applied to large and comprehensively phenotyped patient cohorts, will readily reveal the most clinically relevant disease-modifying and drug response genes. This review addresses both recent advances in the genotyping field and highlights from genome-wide association studies, which have conclusively uncovered variants that underlie disease susceptibility and/or variability in drug response in common disorders.

Distribution of the UGT1A1*28 polymorphism in Caucasian and Asian populations in the US: a genomic analysis of 138 healthy individuals

The hepatic isoform 1A1 of uridine diphosphate glucuronosyltransferase is responsible for glucuronidation and detoxification of SN-38, the active metabolite of irinotecan. The presence of an additional TA repeat in the TATA sequence of the UGT1A1 promoter leads to a significant decrease in SN-38 glucuronidation. Patients with the UGT1A1 (TA)7 allele are more likely to experience severe neutropenia and diarrhea following irinotecan chemotherapy. We assessed the distribution of the UGT1A1 (TA)n polymorphism in healthy male and female US residents of European and Asian descent. We used a fluorescent polymerase chain reaction-based assay to detect UGT1A1 (TA)n polymorphisms in 138 healthy volunteers (56 Caucasians, 37 Chinese, 37 Filipino and eight Japanese) between the ages of 18 and 65 years. The chi-test was used to assess between-group differences in the distribution of UGT1A1 (TA)n genotypes. The UGT1A1 (TA)6/6 genotype was significantly more common in Asians than in Caucasians (76 vs. 46%), whereas the (TA)6/7 (39 vs. 20%) and (TA)7/7 (13 vs. 5%) genotypes were more common in Caucasians than in Asians. Genotype distributions did not differ significantly between men and women in either group. The UGT1A1 (TA)5/5 genotype was detected in one Caucasian woman. In conclusion, consistent with previous reports, the UGT1A1 (TA)7/7 genotype was significantly more common in Caucasians than in Asians. UGT1A1 (TA)n/n genotype distribution did not vary with sex in individuals of European or Asian descent.

A brain-derived neurotrophic factor (BDNF) haplotype is associated with antidepressant treatment outcome in mood disorders

Brain-derived neurotrophic factor (BDNF) has been studied extensively in relation to the susceptibility to mood disorders (MD), although it remains to be clarified whether BDNF is a susceptibility locus for MD phenotypes, including therapeutic response to antidepressants. We have performed a single-marker and haplotype association study of eight TagSNPs polymorphisms in the genomic region containing the BDNF gene in 342 control subjects and 374 patients with MD, and have tested the association with antidepressant treatment outcome. None of the eight single nucleotide polymorphisms (TagSNPs) was significantly associated with MD phenotype after Bonferroni correction. In the single-marker analysis, a SNP was found to be associated with the patient's state of 'remitter' after adequate trial with a single antidepressant phenotype (odds ratio (OR)=2.95; P=0.0025). We also identified a haplotype associated with this phenotype. This study supports the implication of BDNF in antidepressant treatment outcome in MD, with specific association with 5' upstream region of BDNF gene.

CYP3A5 and ABCB1 genes influence blood pressure and response to treatment, and their effect is modified by salt

The permeability-glycoprotein efflux-transporter encoded by the multidrug resistance 1 (ABCB1) gene and the cytochromes P450 3A4/5 encoded by the CYP3A4/5 genes are known to interact in the transport and metabolism of many drugs. Recent data have shown that the CYP3A5 genotypes influence blood pressure and that permeability-glycoprotein activity might influence the activity of the renin-angiotensin system. Hence, these 2 genes may contribute to blood pressure regulation in humans. We analyzed the association of variants of the ABCB1 and CYP3A5 genes with ambulatory blood pressure, plasma renin activity, plasma aldosterone, endogenous lithium clearance, and blood pressure response to treatment in 72 families (373 individuals; 55% women; mean age: 46 years) of East African descent. The ABCB1 and CYP3A5 genes interact with urinary sodium excretion in their effect on ambulatory blood pressure (daytime systolic: P=0.05; nighttime systolic and diastolic: P<0.01), suggesting a gene-gene-environment interaction. The combined action of these genes is also associated with postproximal tubular sodium reabsorption, plasma renin activity, plasma aldosterone, and with an altered blood pressure response to the angiotensin-converting enzyme inhibitor lisinopril (P<0.05). This is the first reported association of the ABCB1 gene with blood pressure in humans and demonstration that genes encoding for proteins metabolizing and transporting drugs and endogenous substrates contribute to blood pressure regulation.

Genotyping of eight polymorphic genes encoding drug-metabolizing enzymes and transporters using a customized oligonucleotide array

Polymorphisms in drug-metabolizing genes may lead to the production of dysfunctional proteins and consequently affect therapeutic efficacy and toxicity of drugs. Different frequencies of polymorphic alleles among the races have been postulated to account for the observed ethnic variations in drug responses. In the current study, we aimed to estimate the frequencies of 14 polymorphisms in eight genes (TPMT, NQO1, MTHFR, GSTP1, CYP1A1, CYP2D6, ABCB1, and SLC19A1) in the Singapore multiracial populations by screening 371 cord blood samples from healthy newborns. To improve genotyping efficacy, we designed an oligonucleotide array based on the principle of allele-specific primer extension (AsPEX) that was capable of detecting the 14 polymorphisms simultaneously. Cross-validation using conventional polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) assays demonstrated 99% concordant results. Measurements on the fluorescent intensity displayed clear distinctions among different genotypes. Statistical analyses showed significantly different allele distributions in several genes among the three races, namely Chinese, Malays, and Indians. Comparing the allelic frequencies in Chinese with previous studies in Caucasian populations, NQO1 609C>T and SLC19A1 80G>A were distinctly different, whereas close similarity was observed for MTHFR 677C>T. We have demonstrated an array-based methodology for rapid multiplex detection of genetic polymorphisms. The allelic frequencies reported in this study may have important therapeutic and prognostic implications in the clinical use of relevant drugs.

Glutathione-S-transferase M1 polymorphisms on the susceptibility to esophageal cancer among three Chinese minorities: Kazakh, Tajik and Uygur

AIM: To investigate the glutathione-S-transferase M1 (GSTM1) polymorphisms in three Chinese minorities, Kazakh, Uygur, and Tajik; and the pathological significance of GSTM1 polymorphisms in esophageal carcinogenesis in Kazakh.

METHODS: A total of 1121 blood samples (442 males and 679 females) were obtained from healthy Kazakh (654), Uygur (412) and Tajik (55). Primary esophageal squamous cell cancer (ESCC) tissues from Kazakh were obtained from 116 patients who underwent surgery. GSTM1 polymorphisms were analyzed by a combined approach of PCR and electrophoresis techniques.

RESULTS: GSTM1 null genotype was found in 62.63% Uygur, 50.91% Tajik and 47.40% Kazakh. A significantly higher frequency of GSTM1 null genotype in Uygur was observed compared with Kazakh (OR: 1.859, 95% CI: 1.445 -2.391, χ² = 23.71, P = 0.000). In addition, GSTM1 null genotype was found in 23.53% of well-differentiated ESCC in Kazakh, in 49.23% of poorly differentiated ESCC, with a significant difference (OR: 3.152, 95% CI: 1.403-7.080, χ² = 8.018, P = 0.007).

CONCLUSION: There is a marked difference in the frequency of common GSTM1 null genotype between Uygur and Kazakh. GSTM1 null genotype is associated with differentiation of ESCC in Kazakh.