Haplotype structure and allele frequencies of CYP2B6 in Spaniards and Central Americans

Frequency of CYP2B6 Alleles in Major Iranian Ethnicities, Affecting Response to Efavirenz

Introduction

Efavirenz is an antihuman immunodeficiency virus (HIV) drug metabolized by cytochrome P450 2B6 (CYP2B6) enzyme. Cytochrome P450 2B6 is an enzyme that in humans is encoded by the CYP2B6 gene. Polymorphisms of this gene play a crucial role in the metabolism of drugs such as Efavirenz. This study aims to evaluate the frequency of three clinically significant CYP2B6 polymorphisms (CYP2B6^∗6 (516G > T), CYP2B6^∗4 (785A > G), and CYP2B6^∗5 (1459C > T)) in three major Iranian ethnicities.

Methods

One hundred forty-seven participants from three main Iranian ethnicities were included in this study. After DNA extraction, CYP2B6^∗6 (516G > T), CYP2B6^∗4 (785A > G), and CYP2B6^∗5 (1459C > T) were genotyped using tetra-primer amplification refractory mutation system polymerase chain reaction (ARMS-PCR).

Results

The frequency of the mutated allele in the Iranian population for CYP2B6^∗6 (516G > T) was 41.50 (95% CI: 35.81, 47.36), which was significantly lower than in Kurds (59.62, 95% CI: 45.10, 72.99). Similarly, Kurds had a higher frequency of mutated allele of CYP2B6^∗5 (1459C > T) (46.15%, 95% CI: 32.23, 60.53) than in Iranians (24.49%, 95% CI: 19.68, 29.82). The frequency of A and G alleles of CYP2B6^∗4 (785A > G) was 62.59% (95% CI: 56.78, 68.13) and 37.41 (95% CI: 31.87, 43.22), respectively.

Conclusion

Kurds are at higher risk of adverse drug reactions (ADRs) and insufficient anti-HIV response compared to other Iranians.

Association between CYP2B6 polymorphism and acute leukemia in a Han population of Northwest China

Background

The aim of this study was to investigate potential associations between CYP2B6 c.516G>T polymorphism and the occurrence and prognosis of acute leukemias (AL) in the Han population of Northwest China.

Methods

The CYP2B6 gene polymorphism was analyzed by PCR‐RFLP and Sanger DNA sequencing in 126 patients with AL and 161 healthy controls.

Results

Compared with controls, there were significantly higher frequencies of GT and TT genotypes and T alleles in AL patients (p < .05), particularly in fusion gene‐positive AL patients. There was no significant difference in CYP2B6 polymorphic genotypes and T alleles between AL patients with complete remission after the first course of chemotherapy and controls (p > .05), while the frequencies in AL patients with partial remission and no remission were significantly higher. The CYP2B6 allele frequency in Han Chinese in Northwest China was significantly different to that reported in Han Chinese and other ethnic minorities in southern China, Uygur Chinese, Vietnamese, African, German, British, Spanish, Turkish, and Argentinian populations; however, there was no significant difference compared with allele frequencies reported in Tibetan and Mongolian Chinese, Japanese, Korean, and American populations.

Conclusion

Our findings show a strong correlation of the CYP2B6 c.516G>T polymorphism in the Han population of Northwest China with AL, especially fusion gene‐positive AL, and indicate a poor prognosis after the first course of chemotherapy. Our findings also implicate the T allele in AL susceptibility and indicate the existence of racial and geographical differences in allele frequencies of CYP2B6 c.516G>T polymorphism.

Human cytochrome P450 2B6 genetic variability in Botswana: a case of haplotype diversity and convergent phenotypes

Identification of inter-individual variability for drug metabolism through cytochrome P450 2B6 (CYP2B6) enzyme is important for understanding the differences in clinical responses to malaria and HIV. This study evaluates the distribution of CYP2B6 alleles, haplotypes and inferred metabolic phenotypes among subjects with different ethnicity in Botswana. A total of 570 subjects were analyzed for CYP2B6 polymorphisms at position 516 G > T (rs3745274), 785 A > G (rs2279343) and 983 T > C (rs28399499). Samples were collected in three districts of Botswana where the population belongs to Bantu (Serowe/Palapye and Chobe) and San-related (Ghanzi) ethnicity. The three districts showed different haplotype composition according to the ethnic background but similar metabolic inferred phenotypes, with 59.12%, 34.56%, 2.10% and 4.21% of the subjects having, respectively, an extensive, intermediate, slow and rapid metabolic profile. The results hint at the possibility of a convergent adaptation of detoxifying metabolic phenotypes despite a different haplotype structure due to the different genetic background. The main implication is that, while there is substantial homogeneity of metabolic inferred phenotypes among the country, the response to drugs metabolized via CYP2B6 could be individually associated to an increased risk of treatment failure and toxicity. These are important facts since Botswana is facing malaria elimination and a very high HIV prevalence.

Pharmacogenetic research activity in Central America and the Caribbean: a systematic review

AIM

The present review was aimed at analyzing the pharmacogenetic scientific activity in Central America and the Caribbean.

MATERIALS & METHODS

A literature search for pharmacogenetic studies in each country of the region was conducted on three databases using a list of the most relevant pharmacogenetic biomarkers including 'phenotyping probe drugs' for major drug metabolizing enzymes. The review included 132 papers involving 47 biomarkers and 35,079 subjects (11,129 healthy volunteers and 23,950 patients).

RESULTS

The country with the most intensive pharmacogenetic research was Costa Rica. The most studied medical therapeutic area was oncology, and the most investigated biomarkers were CYP2D6 and HLA-A/B. Conclusion: Research activity on pharmacogenetics in Central American and the Caribbean populations is limited or absent. Therefore, strategies to promote effective collaborations, and foster interregional initiatives and research efforts among countries from the region could help for the rational clinical implementation of pharmacogenetics and personalized medicine.

CYP2B6 rs2279343 polymorphism is associated with smoking cessation success in bupropion therapy

BACKGROUND

Previous studies suggested that polymorphisms in the CYP2B6 gene (which encodes an isoenzyme that metabolizes bupropion) and in the ANKK1 gene (which is located in the ANKK1/DRD2 gene cluster) might influence response to therapy. Thus, the aim of the present study was to evaluate whether the CYP2B6 and ANKK1 polymorphisms are associated with the response to smoking cessation therapies in patients from a smoking cessation assistance program.

METHODS

The cohort study enrolled 478 smokers who received behavioral counseling and drug therapy (bupropion, nicotine replacement therapy, and/or varenicline). Smoking cessation success was considered for patients who completed 6 months of continuous abstinence. Fagerström test for nicotine dependence (FTND) and Issa situational smoking scores were analyzed for nicotine dependence (ND). The ANKK1 rs1800497, CYP2B6*4 (rs2279343), CYP2B6*5 (rs3211371), and CYP2B6*9 (rs3745274) polymorphisms were genotyped by high resolution melting analysis or by restriction fragment length polymorphism.

RESULTS

Patients with CYP2B6 rs2279343 wild-type AA genotype had higher success rate (48.0 %) compared with patients carrying AG or GG genotypes (CYP2B6*4 variant) (35.5 %) on bupropion therapy. The AA genotype was associated with higher OR for success during bupropion therapy (OR = 1.92, 95 % CI = 1.08-3.42, p = 0.03) in a multivariate model. We did not observe significant differences in the FTND and Issa scores according to the studied polymorphisms.

CONCLUSION

We showed that patients with CYP2B6*4 (rs2279343) variant had lower success rate with bupropion. Likely, the CYP2B6*4 variant, which leads to a rapid predicted metabolic phenotype for the isoenzyme, influences the pharmacological activity of bupropion. Our finding suggests that CYP2B6*4 may be an important genetic marker for individualized bupropion pharmacotherapy.

Effect of CYP2B6 Gene Polymorphisms on Efavirenz Plasma Concentrations in Chinese Patients with HIV Infection

Objectives

The main aim of this study was to investigate the effect of CYP2B6 gene polymorphisms on efavirenz (EFV) plasma concentrations in Han Chinese patients with human immunodeficiency virus (HIV) infection.

Methods

In total, 322 patients were recruited for study. EFV plasma concentrations at steady-state were determined using high-performance liquid chromatography. Genotyping for seven single nucleotide polymorphisms (SNPs), including 171+967C>A, 171+3212C>T, 171+4335T>C, 516G>T, 785A>G, 1295-913G>A, and *1355A>G of CYP2B6, was performed using ligase detection reaction (LDR). SPSS 18.0 and Haploview 4.2 were applied for statistical analyses.

Results

The average EFV concentration of patients was 2.35±2.09 μg/mL. Overall, 22% patients displayed EFV concentrations out of the therapeutic range of 1–4 μg/mL (13.1% < 1 μg/mL, 9.3% > 4 μg/mL). We observed significant association of 171+967C>A, 171+4335T>C, 516G>T, 785A>G and *1355A>G with high plasma EFV levels (p<.01). The predictive accuracy values of 171+4335CC, 516TT and 785GG for EFV concentrations > 4 μg/mL were 56.7%, 56.7% and 60%, respectively. We observed strong linkage disequilibrium for 171+967C>A, 171+4335T>C, 516G>T and 785A>G, resulting in five haplotypes. The frequencies of the five haplotypes (high to low) were as follows: CCTG (0.328), ACTG (0.280), ACCT (0.189), ATTG (0.186) and ACCG (0.017). The frequency of CCTG (0.524) in patients with EFV plasma concentrations < 1 μg/mL was significantly higher than that in other patient groups, while that of ACCT (0.733) was significantly higher in patients with EFV concentrations > 4 μg/mL, relative to other patient groups. Average EFV concentrations of patients carrying ACTG (1.78 μg/mL), ACCT (7.50 μg/mL), and ATTG (1.92 μg/mL) haplotypes were markedly higher than those of patients carrying the CCTG haplotype. The predictive accuracy of ACCT for EFV > 4 μg/mL was 81%.

Conclusions

Chinese patients administered standard doses of EFV require therapeutic drug monitoring or personalized medication management. Based on the current findings, we propose that 171+4335T>C, 516G>T, 785A>G and haplotype ACCT may be effectively used as genomic markers for EFV, which should aid in improving the efficacy of EFV-containing treatments and reduce the incidence of adverse reactions.

Allele and genotype frequencies of CYP2B6 in a Turkish population

Increasing interest in cytochrome P450 2B6 (CYP2B6) genetic polymorphism was stimulated by revelations of a specific CYP2B6 genotype significantly affecting the metabolism of various drugs in common clinical use in terms of increasing drug efficacy and avoiding adverse drug reactions. The present study aimed to determine the frequencies of CYP2B6*4 CYP2B6*5, CYP2B6*6, CYP2B6*7 and CYP2B6*9 alleles in healthy Turkish individuals (n = 172). Frequencies of three single nucleotide polymorphisms were 516G>T (28%), 785A>G (33%), and 1459C>T (12%). The frequencies of CYP2B6*1, *4, *5, *6, *7, and *9 alleles were 54.3 (95% CI 49.04-59.56), 6.4% (95% CI 3.81-8.99), 11% (95% CI 7.69-14.31), 25.3% (95% CI 20.71-29.89), 0.87% (95% CI -0.11-1.85) and 2.0% (95% CI 0.52-3.48), respectively. Allele *6 was more frequent (25.3%) than the other variant alleles in Turkish subjects. The frequencies of CYP2B6*4, *5, *6, *7, and *9 alleles were similar to European populations but significantly different from that reported for Asian populations. This is the first study to document the frequencies of the CYP2B6*4, *5, *6, *7, *9 alleles in the healthy Turkish individuals and our results could provide clinically useful information on drug metabolism by CYP2B6 in Turkish population.

Worldwide variation in human drug-metabolism enzyme genes CYP2B6 and UGT2B7: implications for HIV/AIDS treatment

AIM

Hepatic enzymes, CYP2B6 and UGT2B7 play a major role in the metabolism of the widely used antiretroviral drugs efavirenz, nevirapine and zidovudine. In the present study, we provide a view of UGT2B7 haplotype structure, and quantify the genetic diversity and differentiation at both CYP2B6 and UGT2B7 genes on a worldwide scale.

MATERIALS & METHODS

We genotyped one intronic and three promoter SNPs, and together with three nonsynonymous SNPs, inferred UGT2B7 alleles in north American (n = 326), west African (n = 133) and Papua New Guinean (n = 142) populations. We also included genotype data for five CYP2B6 and six UGT2B7 SNPs from an additional 12 worldwide populations (n = 629) analyzed in the 1000 Genomes Project.

RESULTS

We observed significant differences in certain SNP and allele frequencies of CYP2B6 and UGT2B7 among worldwide populations. Diversity values were higher for UGT2B7 than for CYP2B6, although there was more diversity between populations for CYP2B6. For both genes, most of the genetic variation was observed among individuals within populations, with the Papua New Guinean population showing the highest pairwise differentiation values for CYP2B6, and the Asian and European populations showing higher pairwise differentiation values for UGT2B7.

CONCLUSION

These new genetic distinctions provide additional insights for investigating differences in antiretroviral pharmacokinetics and therapy outcomes among ethnically and geographically diverse populations.

Contribution of cytochrome P450 and ABCB1 genetic variability on methadone pharmacokinetics, dose requirements, and response

Although the efficacy of methadone maintenance treatment (MMT) in opioid dependence disorder has been well established, the influence of methadone pharmacokinetics in dose requirement and clinical outcome remains controversial. The aim of this study is to analyze methadone dosage in responder and nonresponder patients considering pharmacogenetic and pharmacokinetic factors that may contribute to dosage adequacy. Opioid dependence patients (meeting Diagnostic and Statistical Manual of Mental Disorders, [4(th) Edition] criteria) from a MMT community program were recruited. Patients were clinically assessed and blood samples were obtained to determine plasma concentrations of (R,S)-, (R) and (S)-methadone and to study allelic variants of genes encoding CYP3A5, CYP2D6, CYP2B6, CYP2C9, CYP2C19, and P-glycoprotein. Responders and nonresponders were defined by illicit opioid consumption detected in random urinalysis. The final sample consisted in 105 opioid dependent patients of Caucasian origin. Responder patients received higher doses of methadone and have been included into treatment for a longer period. No differences were found in terms of genotype frequencies between groups. Only CYP2D6 metabolizing phenotype differences were found in outcome status, methadone dose requirements, and plasma concentrations, being higher in the ultrarapid metabolizers. No other differences were found between phenotype and responder status, methadone dose requirements, neither in methadone plasma concentrations. Pharmacokinetic factors could explain some but not all differences in MMT outcome and methadone dose requirements.