Aberrant splicing caused by single nucleotide polymorphism c.516G>T [Q172H], a marker of CYP2B6*6, is responsible for decreased expression and activity of CYP2B6 in liver

Functional significance of CYP2B6 gene rare allelic variants identified in Japanese individuals

Cytochrome P450 2B6 (CYP2B6) catalyzes the metabolism of many drugs, including efavirenz and propofol. Genetic polymorphisms in CYP2B6 alter its enzymatic activity and substantially affect its pharmacokinetics. High-frequency variants, such as CYP2B6*6, are associated with the risk of developing side effects due to reduced CYP2B6 activity. However, the impact of rare alterations on enzyme function remains unknown, and some of these variants may significantly decrease the CYP2B6 activity. Therefore, in this study, we evaluated in vitro the functional alterations in 29 missense variants of the CYP2B6 gene identified in 8,380 Japanese individuals. Wild-type CYP2B6 and 29 rare CYP2B6 variants were transiently expressed in mammalian cells. The expression levels of variant CYP2B6 proteins in the microsomal fractions extracted from 293FT cells were assessed using western blotting and reduced-carbon monoxide difference spectroscopy, and a specific peak at 450 nm was detected in the wild-type and 19 variants. Furthermore, kinetic parameters were determined by assaying the reactions with efavirenz and propofol and quantifying the metabolite concentrations. We found that 12 variants had significantly lower or abolished enzymatic activity with both the substrates. In silico three-dimensional docking and molecular-dynamics simulations suggested that these functional changes were due to conformational changes in essential regions, such as the heme-binding site and ligand channels involved in transporting substrates to the active site. These findings have implications for predicting the plasma concentrations of CYP2B6 substrates and controlling their side effects.

Clinical Pharmacogenetics Implementation Consortium Guideline for CYP2B6 Genotype and Methadone Therapy

Methadone is a mu (μ) opioid receptor agonist used clinically in adults and children to manage opioid use disorder, neonatal abstinence syndrome, and acute and chronic pain. It is typically marketed as a racemic mixture of R- and S-enantiomers. R-methadone has 30-to 50-fold higher analgesic potency than S-methadone, and S-methadone has a greater adverse effect (prolongation) on the cardiac QTc interval. Methadone undergoes stereoselective metabolism. CYP2B6 is the primary enzyme responsible for catalyzing the metabolism of both enantiomers to the inactive metabolites, S- and R-2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (S- and R-EDDP). Genetic variation in the CYP2B6 gene has been investigated in the context of implications for methadone pharmacokinetics, dose, and clinical outcomes. Most CYP2B6 variants result in diminished or loss of CYP2B6 enzyme activity, which can lead to higher plasma methadone concentrations (affecting S- more than R-methadone). However, the data do not consistently indicate that CYP2B6-based metabolic variability has a clinically significant effect on methadone dose, efficacy, or QTc prolongation. Expert analysis of the published literature does not support a change from standard methadone prescribing based on CYP2B6 genotype (updates at www.cpicpgx.org).

Pharmacogenetic Influence on Stereoselective Steady-State Disposition of Bupropion

Bupropion is used for treating depression, obesity, and seasonal affective disorder, and for smoking cessation. Bupropion is commonly prescribed, but has complex pharmacokinetics and interindividual variability in metabolism and bioactivation may influence therapeutic response, tolerability, and safety. Bupropion is extensively and stereoselectively metabolized, the metabolites are pharmacologically active, and allelic variation in cytochrome P450 (CYP) 2B6 affects clinical hydroxylation of single-dose bupropion. Genetic effects on stereoselective disposition of steady-state bupropion are not known. In this preplanned secondary analysis of a prospective, randomized, double-blinded, crossover study which compared brand and generic bupropion XL 300 mg drug products, we measured steady-state enantiomeric plasma and urine parent bupropion and primary and secondary metabolite concentrations. This investigation evaluated the influence of genetic polymorphisms in CYP2B6, CYP2C19, and P450 oxidoreductase on the disposition of Valeant Pharmaceuticals Wellbutrin brand bupropion in 67 participants with major depressive disorder. We found that hydroxylation of both bupropion enantiomers was lower in carriers of the CYP2B6*6 allele and in carriers of the CYP2B6 516G>T variant, with correspondingly greater bupropion and lesser hydroxybupropion plasma concentrations. Hydroxylation was 25-50% lower in CYP2B6*6 carriers and one-third to one-half less in 516T carriers. Hydroxylation of the bupropion enantiomers was comparably affected by CYP2B6 variants. CYP2C19 polymorphisms did not influence bupropion plasma concentrations or hydroxybupropion formation but did influence the minor pathway of 4'-hydroxylation of bupropion and primary metabolites. P450 oxidoreductase variants did not influence bupropion disposition. Results show that CYP2B6 genetic variants affect steady-state metabolism and bioactivation of Valeant brand bupropion, which may influence therapeutic outcomes. SIGNIFICANCE STATEMENT: Bupropion, used for depression, obesity, and smoking cessation, undergoes metabolic bioactivation, with incompletely elucidated interindividual variability. We evaluated cytochrome P450 (CYP) 2B6, CYP2C19 and P450 oxidoreductase genetic variants and steady-state bupropion and metabolite enantiomers disposition. Both enantiomers hydroxylation was lower in CYP2B6*6 and CYP2B6 516G>T carriers, with greater bupropion and lesser hydroxybupropion plasma concentrations. CYP2C19 polymorphisms did not affect bupropion or hydroxybupropion but did influence minor 4'-hydroxylation of bupropion and primary metabolites. CYP2B6 variants affect steady-state bupropion bioactivation, which may influence therapeutic outcomes.

Genetic variants, haplotype determination, and function of novel alleles of CYP2B6 in a Han Chinese population

Amino acid variants in protein may result in deleterious effects on enzymatic activity. In this study we investigate the DNA variants on activity of CYP2B6 gene in a Chinese Han population for potential use in precision medicine. All exons in CYP2B6 gene from 1483 Chinese Han adults (Zhejiang province) were sequenced using Sanger sequencing. The effects of nonsynonymous variants on recombinant protein catalytic activity were investigated in vitro with Sf12 system. The haplotype of novel nonsynonymous variants with other single nucleotide variants in the same allele was determined using Nanopore sequencing. Of 38 alleles listed on the Pharmacogene Variation Consortium, we detected 7 previously reported alleles and 18 novel variants, of which 11 nonsynonymous variants showed lower catalytic activity (0.00-0.60) on bupropion compared to CYP2B6*1. Further, these 11 novel star-alleles (CYP2B6*39-49) were assigned by the Pharmacogene Variation Consortium, which may be valuable for pharmacogenetic research and personalized medicine.

Genetic polymorphisms of CYP2B6 is a risk of metabolic associated fatty liver disease in Chinese population

BACKGROUND

The expression and activity of cytochrome P450 2B6 (CYP2B6) may be related to the metabolic associated fat liver disease (MAFLD). Since constitutive androstane receptor (CAR) is a classic transcriptional regulator of CYP2B6, and the single nucleotide polymorphisms (SNPs) of CYP2B6 and CAR are both associated with adverse reactions of efavirenz, we hypothesized that genetic polymorphisms of CAR might also result in additional interindividual variability in CYP2B6. This study was devoted to explore the association between CYP2B6 and CAR SNPs and susceptibility to MAFLD.

MATERIALS AND METHODS

A total of 590 objects of study (118 with MAFLD and 472 healthy control) between December 2014 and April 2018 were retrospectively enrolled. Twenty-two selected SNPs in CYP2B6 and CAR were genotyped with a custom-designed 48-plex SNP Scan TM® Kit. The frequencies of the alleles, genotypes and genetic models of the variants were compared between the two groups. The odds ratios (ORs) and the corresponding 95% confidence intervals (CIs) were calculated.

RESULTS

The T allele of rs3745274 in CYP2B6 was associated with a decreased risk for MAFLD (OR 0.610; 95% CI: 0.451-0.825, p = 0.001) which was still statistically significant after adjusting with Bonferroni method(p = 0.014) The allele, genotype and genetic model frequencies were similar in the two groups for the other twenty-one SNPs (all P > 0.05). There were no multiplicative or additive interactions between the SNPs.

CONCLUSION

Our study revealed that rs3745274 variants in CYP2B6 is associated with susceptibility to MAFLD in the Han Chinese population.

Pharmacogenetic Variation in Neanderthals and Denisovans and Implications for Human Health and Response to Medications

Modern humans carry both Neanderthal and Denisovan (archaic) genome elements that are part of the human gene pool and affect the life and health of living individuals. The impact of archaic DNA may be particularly evident in pharmacogenes-genes responsible for the processing of exogenous substances such as food, pollutants, and medications-as these can relate to changing environmental effects, and beneficial variants may have been retained as modern humans encountered new environments. However, the health implications and contribution of archaic ancestry in pharmacogenes of modern humans remain understudied. Here, we explore 11 key cytochrome P450 genes (CYP450) involved in 75% of all drug metabolizing reactions in three Neanderthal and one Denisovan individuals and examine archaic introgression in modern human populations. We infer the metabolizing efficiency of these 11 CYP450 genes in archaic individuals and find important predicted phenotypic differences relative to modern human variants. We identify several single nucleotide variants shared between archaic and modern humans in each gene, including some potentially function-altering mutations in archaic CYP450 genes, which may result in altered metabolism in living people carrying these variants. We also identified several variants in the archaic CYP450 genes that are novel and unique to archaic humans as well as one gene, CYP2B6, that shows evidence for a gene duplication found only in Neanderthals and modern Africans. Finally, we highlight CYP2A6, CYP2C9, and CYP2J2, genes which show evidence for archaic introgression into modern humans and posit evolutionary hypotheses that explain their allele frequencies in modern populations.

An Updated Overview of the Role of CYP450 during Xenobiotic Metabolization in Regulating the Acute Myeloid Leukemia Microenvironment

Oxidative stress is associated with several acute and chronic disorders, including hematological malignancies such as acute myeloid leukemia, the most prevalent acute leukemia in adults. Xenobiotics are usually harmless compounds that may be detrimental, such as pharmaceuticals, environmental pollutants, cosmetics, and even food additives. The storage of xenobiotics can serve as a defense mechanism or a means of bioaccumulation, leading to adverse effects. During the absorption, metabolism, and cellular excretion of xenobiotics, three steps may be distinguished: (i) inflow by transporter enzymes, (ii) phases I and II, and (iii) phase III. Phase I enzymes, such as those in the cytochrome P450 superfamily, catalyze the conversion of xenobiotics into more polar compounds, contributing to an elevated acute myeloid leukemia risk. Furthermore, genetic polymorphism influences the variability and susceptibility of related myeloid neoplasms, infant leukemias associated with mixed-lineage leukemia (MLL) gene rearrangements, and a subset of de novo acute myeloid leukemia. Recent research has shown a sustained interest in determining the regulators of cytochrome P450, family 2, subfamily E, member 1 (CYP2E1) expression and activity as an emerging field that requires further investigation in acute myeloid leukemia evolution. Therefore, this review suggests that CYP2E1 and its mutations can be a therapeutic or diagnostic target in acute myeloid leukemia.

Multidisciplinary Insights into the Structure-Function Relationship of the CYP2B6 Active Site

Cytochrome P450 2B6 (CYP2B6) is a highly polymorphic human enzyme involved in the metabolism of many clinically relevant drugs, environmental toxins, and endogenous molecules with disparate structures. Over the last 20-plus years, in silico and in vitro studies of CYP2B6 using various ligands have provided foundational information regarding the substrate specificity and structure-function relationship of this enzyme. Approaches such as homology modeling, X-ray crystallography, molecular docking, and kinetic activity assays coupled with CYP2B6 mutagenesis have done much to characterize this originally neglected monooxygenase. However, a complete understanding of the structural details that make new chemical entities substrates of CYP2B6 is still lacking. Surprisingly little in vitro data has been obtained about the structure-function relationship of amino acids identified to be in the CYP2B6 active site. Since much attention has already been devoted to elucidating the function of CYP2B6 allelic variants, here we review the salient findings of in silico and in vitro studies of the CYP2B6 structure-function relationship with a deliberate focus on the active site. In addition to summarizing these complementary approaches to studying structure-function relationships, we note gaps/challenges in existing data such as the need for more CYP2B6 crystal structures, molecular docking results with various ligands, and data coupling CYP2B6 active site mutagenesis with kinetic parameter measurement under standard expression conditions. Harnessing in silico and in vitro techniques in tandem to understand the CYP2B6 structure-function relationship will likely offer further insights into CYP2B6-mediated metabolism. SIGNIFICANCE STATEMENT: The apparent importance of cytochrome P450 2B6 (CYP2B6) in the metabolism of various xenobiotics and endogenous molecules has grown since its discovery with many in silico and in vitro studies offering a partial description of its structure-function relationship. Determining the structure-function relationship of CYP2B6 is difficult but may be aided by thorough biochemical investigations of the CYP2B6 active site that provide a more complete pharmacological understanding of this important enzyme.

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.

Quantitative Prediction of Drug Interactions Caused by Cytochrome P450 2B6 Inhibition or Induction

BACKGROUND

Numerous drugs have the potential to be affected by cytochrome P450 (CYP) 2B6-mediated drug-drug interactions (DDIs).

OBJECTIVES

In this work, we extend a static approach to the prediction of the extent of pharmacokinetics DDIs between substrates and inhibitors or inducers of CYP2B6.

METHODS

This approach is based on the calculation of two parameters (the contribution ratio [CR], representing the fraction of dose of the substrate metabolized via this pathway and the inhibitory or inducing potency of the perpetrator [IR or IC, respectively]) calculated from the area under the concentration-time curve (AUC) ratios obtained in in-vivo DDI studies.

RESULTS

Forty-eight studies involving 5 substrates, 11 inhibitors and 18 inducers of CYP2B6 (overall 15 inhibition and 33 induction studies) were divided into test and validation sets and considered for estimation of the parameters. The proposed approach demonstrated a fair accuracy for predicting the extent of DDI related to CYP2B6 inhibition and induction, all predictions related to the validation test (N = 18) being 50-200% of the observed ratios.

CONCLUSIONS

This methodology can be used for proposing initial dose adaptations to be adopted, for example in clinical use or for designing DDI studies involving this enzyme.

The Effects of Cumulative Dose and Polymorphisms in CYP2B6 on the Mitotane Plasma Trough Concentrations in Chinese Patients With Advanced Adrenocortical Carcinoma

Mitotane is the only drug approved to treat adrenocortical carcinoma (ACC), and a relationship of pharmacokinetic/pharmacodynamic has been characterized. However, limited evidence concerning affecting factors in large interindividual variability of the pharmacokinetics of mitotane is available. To address this question, a retrospective analysis was performed on ACC Chinese patients treated with mitotane for more than 3 months. Mitotane plasma trough concentrations were detected at the steady state, and CYP2B6, CYP3A4, and pregnane X receptor (PXR) polymorphisms were genotyped. After examining homogeneous pharmacologic data, we restricted the analyses to 36 patients that received mitotane for a median (interquartile range, IQR) of 9 months (5.00–22.50) with a median dose of 2 g/day (2.00–2.50). As a result, drug exposure was significantly influenced by the cumulative dose of mitotane, and CYP2B6 516GG and CYP2B6 26570CC were at high risk to be below the therapeutic range of mitotane. No association was found between mitotane concentrations with CYP3A4 or PXR polymorphism. Our data firstly indicated that the cumulative dose of mitotane and polymorphisms of CYP2B6 516 and CYP2B6 26570 might significantly affect mitotane plasma trough concentrations in Chinese ACC patients.

Effects of cytochrome P450 2B6 and constitutive androstane receptor genetic variation on Efavirenz plasma concentrations among HIV patients in Kenya

The effects of genetic variation of cytochrome P450 2B6 (CYP2B6) and constitutive androstane receptor (CAR) on efavirenz (EFV) plasma concentration was evaluated among 312 HIV patients in Nairobi Kenya. The EFV plasma concentration at steady-state were determined using ultra-high-performance liquid chromatography with a tandem quadruple mass spectrometer (LC-MS/MS). Thirteen CYP2B6 (329G>T, 341T>C, 444 G>T/C, 15582C>T, 516G>T, 548T>G, 637T>C, 785A>G, 18492C>T, 835G>C, 1459C>T and 21563C>T) and one CAR (540C>T) single nucleotide polymorphisms (SNPs) were genotyped using real-time polymerase chain reaction. HIV drug resistance mutations were detected using an in-house genotypic assay. The EFV concentration of patients ranged from 4 ng/mL to 332697 ng/mL (median 2739.5 ng/mL, IQR 1878-4891.5 ng/mL). Overall, 22% patients had EFV concentrations beyond therapeutic range of 1000-4000 ng/mL (4.5%% < 1000 ng/mL and 31.7% > 4000 ng/mL). Five SNPs (15582C>T, 516G>T, 785A>G, 983T>C and 21563C>T) were associated with higher EFV plasma concentration while 18492C>T with lower EFV plasma concentration (p<0.05). Strong linkage disequilibrium (LD) was observed for 15582C>T, 516G>T, 785A>G, 18492C>T, 983T>C, 21563C>T, 1459C>T and CAR 540C>T. Sixteen haplotypes were observed and CTGCTTCC, CTGCTTCT, TTGCTTCT and CGACCCCT were associated with high EFV plasma concentration. In multivariate analysis, factors significantly associated with EFV plasma concentration included; the presence of skin rash (β = 1379, 95% confidence interval (CI) = 3216.9-3416.3; p < 0.039), T allele of CYP2B6 516G>T (β = 1868.9, 95% CI 3216.9-3416.3; p < 0.018), the C allele of CYP2B6 983T>C (β = 2638.3, 95% CI = 1348-3929; p < 0.0001), T allele of CYP2B6 21563C>T (β = 1737, 95% CI = 972.2-2681.9; p < 0.0001) and the presence of 5 to 7 numbers of SNPs per patient (β = 570, 95% CI = 362-778; p < 0.0001) and HIV viral load ≤1000 cells/mL (β = -4199.3, 95% CI = -7914.9 --483.6; p = 0.027). About 36.2% of the patients had EFV plasma concentrations beyond therapeutic window, posing high risk of treatment failure or toxicity. The SNPs of CYP2B6 516G>T, CYP2B6 983T>C, 21563C>T, presence of higher numbers of SNPs per patient and haplotypes CTGCTTCC, CTGCTTCT, TTGCTTCT and CGACCCCT could efficiently serves as genetic markers for EFV plasma concentration and could guide personalization of EFV based ART treatment in Kenya.

CYP2B6 allelic variants and non-genetic factors influence CYP2B6 enzyme function

Human CYP2B6 enzyme although constitutes relatively low proportion (1–4%) of hepatic cytochrome P450 content, it is the major catalyst of metabolism of several clinically important drugs (efavirenz, cyclophosphamide, bupropion, methadone). High interindividual variability in CYP2B6 function, contributing to impaired drug-response and/or adverse reactions, is partly elucidated by genetic polymorphisms, whereas non-genetic factors can significantly modify the CYP2B6 phenotype. The influence of genetic and phenoconverting non-genetic factors on CYP2B6-selective activity and CYP2B6 expression was investigated in liver tissues from Caucasian subjects (N = 119). Strong association was observed between hepatic S-mephenytoin N-demethylase activity and CYP2B6 mRNA expression (P < 0.0001). In less than one third of the tissue donors, the CYP2B6 phenotype characterized by S-mephenytoin N-demethylase activity and/or CYP2B6 expression was concordant with CYP2B6 genotype, whereas in more than 35% of the subjects, an altered CYP2B6 phenotype was attributed to phenoconverting non-genetic factors (to CYP2B6-specific inhibitors and inducers, non-specific amoxicillin + clavulanic acid treatment and chronic alcohol consumption, but not to the gender). Furthermore, CYP2B6 genotype–phenotype mismatch still existed in one third of tissue donors. In conclusion, identifying potential sources of CYP2B6 variability and considering both genetic variations and non-genetic factors is a pressing requirement for appropriate elucidation of CYP2B6 genotype–phenotype mismatch.

Investigation of the genetic effect of 56 tobacco-smoking susceptibility genes on DNA methylation and RNA expression in human brain

Although various susceptibility genes have been revealed to influence tobacco smoking, the underlying regulatory mechanisms between genetic variants and smoking are poorly understood. In this study, we investigated cis-expression quantitative trait loci (cis-eQTLs) and methylation quantitative trait loci (mQTLs) for 56 candidate smoking-linked genes using the BrainCloud cohort samples. An eQTL was revealed to significantly affect EGLN2 expression in the European sample and two mQTLs were respectively detected in CpG sites in NRXN1 and CYP2A7. Interestingly, we found for the first time that the minor allele of the single nucleotide polymorphism (SNP) rs3745277 located in CYP2A7P1 (downstream of CYP2B6) significantly decreased methylation at the CpG site for CYP2A7 (cg25427638; P = 5.31 × 10^-7), reduced expression of CYP2B6 (P = 0.03), and lowered the percentage of smokers (8.8% vs. 42.3%; Odds Ratio (OR) = 0.14, 95% Confidence Interval (CI): 0.02-0.62; P = 4.47 × 10^-3) in a dominant way for the same cohort sample. Taken together, our findings resulted from analyzing genetic variation, DNA methylation, mRNA expression, and smoking status together using the same participants revealed a regulatory mechanism linking mQTLs to the smoking phenotype. Moreover, we demonstrated the presence of different regulatory effects of low-frequency and common variants on mRNA expression and DNA methylation.

Frequencies of CYP2B6∗4,∗5, and ∗6 Alleles within an Iranian Population (Mazandaran)

Background

The human CYP2B subfamily consists of one functional gene (CYP2B6) and one pseudogene (CYP2B7P). Cytochrome P450 2B6 (CYP2B6) is a highly polymorphic enzyme that shows marked interindividual and interethnic variations. Currently, 38 alleles have been described, and some of the allelic variants have been associated with low enzyme activity. The aim of this study was to investigate the frequencies of CYP2B6^∗4, CYP2B6^∗5, and CYP2B6^∗6 alleles in the Mazani ethnic group among Iranian Population.

Methods

The study was conducted in 289 unrelated healthy volunteers. DNA was extracted from peripheral blood and analyzed by the PCR-RFLP protocol. The PCR product was digested with restriction enzymes and then separated using agarose gel electrophoresis.

Results

The frequency of CYP2B6^∗4, CYP2B6^∗5, and CYP2B6^∗6 in this study was 34.60%, 7.26%, and 34.54%, respectively.

Conclusion

The frequency of the CYP2B6^∗4 allele in the Mazani ethnic group was much higher (34.60%) than other population. The frequency of CYP2B6^∗6 (34.54%) also was higher than its frequency in other previously reported population. But the frequency of CYP2B6^∗5 in this study was lower than expected. These results will be useful in understanding the ethnic diversity in Iranian population and offer a preliminary basis for more rational use of drugs that are substrates for CYP2B6 in this population.

Effect of albumin and CYP2B6 polymorphisms on exposure of efavirenz: A population pharmacokinetic analysis in Chinese HIV-infected adults

BACKGROUND

Efavirenz is a vital component used to treat HIV-1 infection. Nevertheless, it shows large between-subject variability, which affects both its therapeutic response and adverse effects.

OBJECTIVE

To investigate the impact of gene polymorphisms and non-genetic factors on the variability of efavirenz pharmacokinetics and to propose the optimal dose regimens.

METHODS

A total of 769 plasma samples from 376 HIV-infected Han Chinese outpatients were collected to develop a population pharmacokinetic model using NONMEM software. The impact of patient demographics, laboratory tests, concomitant medication, and genetic polymorphisms of CYP2B6 and ABCB1 on efavirenz pharmacokinetics were explored. According to the final model, the model-informed dose optimization was conducted.

RESULTS

The pharmacokinetics of efavirenz was characterized by a one-compartment model with first-order absorption and elimination. The typical values of the estimated apparent oral clearance, volume of distribution, and absorption rate constant in the final model were 9.44 L/h, 200 L, and 0.727 h ^- 1, respectively. Efavirenz clearance was significantly influenced by CYP2B6 variants, including rs2099361, rs3745274, and rs2279343, along with albumin and weight. The volume of distribution was affected by albumin and weight. Based on the CYP2B6 polymorphisms of patients, the recommended daily doses of efavirenz were 100 mg for CYP2B6 slow metabolizers, 400 or 600 mg for intermediate metabolizers, and 800 or 1000 mg for extensive metabolizers.

CONCLUSIONS

Polymorphisms of CYP2B6, along with albumin and weight, resulted as the predictors of efavirenz pharmacokinetic variability, which could be used in prescribing optimal efavirenz doses.

Association of CYP2B6 genetic polymorphisms with bupropion and hydroxybupropion exposure: A systematic review and meta-analysis

INTRODUCTION

Bupropion is metabolized to its active metabolite, hydroxybupropion (HB), by the genetically polymorphic cytochrome P450 2B6 (CYP2B6) enzyme. Despite its significant role in bupropion metabolism, the magnitude of the impact of CYP2B6 genotype on the exposure of bupropion has not been quantified.

OBJECTIVES

A systematic review and meta-analysis was conducted to quantify the association of bupropion and HB exposure with CYP2B6 variant alleles and genotype-defined metabolizer phenotypes.

METHODS

MEDLINE, EMBASE, Web of Science, Scifinder, PsycINFO, and CENTRAL were screened to identify studies that met the following inclusion criteria (search updated on February 2021): (1) area under the plasma drug concentration-time curve (AUC) of bupropion and/or HB in relation to CYP2B6 genotypes was studied, and (2) study participants were genotyped for common CYP2B6 variant alleles including at least CYP2B6*6. The Newcastle Ottawa Scale was used to assess risk of bias in each included study. The ratio of means (RoM) between CYP2B6 genotype or genotype-defined phenotype groups for bupropion exposure was calculated for each study and combined in a meta-analysis.

RESULTS

Eleven studies met the inclusion criteria for this systematic review, and 10 (including N = 413 participants) were included in the meta-analysis. All 10 studies involved healthy adult volunteers, where other medications were not allowed. The AUCs of HB and the active moiety (bupropion + HB) were significantly reduced in CYP2B6*6 carriers compared with the non-carriers (HB: RoM 0.77, 95% CI 0.71-0.83; active moiety: RoM 0.81, 95% CI 0.75-0.88). Both CYP2B6 poor and intermediate metabolizers had significantly decreased exposures to HB and the active moiety than normal metabolizers.

CONCLUSION

The CYP2B6*6 allele and genotype-determined CYP2B6 poor and intermediate metabolizer phenotypes are associated with significantly lower exposures to HB and the total active moiety. The findings of this study suggest opportunities to further study precision dosing strategies for bupropion therapy based on CYP2B6 genotype.

CYP2B6 Functional Variability in Drug Metabolism and Exposure Across Populations-Implication for Drug Safety, Dosing, and Individualized Therapy

Adverse drug reactions (ADRs) are one of the major causes of morbidity and mortality worldwide. It is well-known that individual genetic make-up is one of the causative factors of ADRs. Approximately 14 million single nucleotide polymorphisms (SNPs) are distributed throughout the entire human genome and every patient has a distinct genetic make-up which influences their response to drug therapy. Cytochrome P450 2B6 (CYP2B6) is involved in the metabolism of antiretroviral, antimalarial, anticancer, and antidepressant drugs. These drug classes are commonly in use worldwide and face specific population variability in side effects and dosing. Parts of this variability may be caused by single nucleotide polymorphisms (SNPs) in the CYP2B6 gene that are associated with altered protein expression and catalytic function. Population variability in the CYP2B6 gene leads to changes in drug metabolism which may result in adverse drug reactions or therapeutic failure. So far more than 30 non-synonymous variants in CYP2B6 gene have been reported. The occurrence of these variants show intra and interpopulation variability, thus affecting drug efficacy at individual and population level. Differences in disease conditions and affordability of drug therapy further explain why some individuals or populations are more exposed to CYP2B6 pharmacogenomics associated ADRs than others. Variabilities in drug efficacy associated with the pharmacogenomics of CYP2B6 have been reported in various populations. The aim of this review is to highlight reports from various ethnicities that emphasize on the relationship between CYP2B6 pharmacogenomics variability and the occurrence of adverse drug reactions. In vitro and in vivo studies evaluating the catalytic activity of CYP2B6 variants using various substrates will also be discussed. While implementation of pharmacogenomic testing for personalized drug therapy has made big progress, less data on pharmacogenetics of drug safety has been gained in terms of CYP2B6 substrates. Therefore, reviewing the existing evidence on population variability in CYP2B6 and ADR risk profiles suggests that, in addition to other factors, the knowledge on pharmacogenomics of CYP2B6 in patient treatment may be useful for the development of personalized medicine with regards to genotype-based prescription.

Pharmacogenetic Associations Between Atazanavir/UGT1A1*28 and Efavirenz/rs3745274 (CYP2B6) Account for Specific Adverse Reactions in Chilean Patients Undergoing Antiretroviral Therapy

Background: Efavirenz (EFV), a non-nucleoside reverse transcriptase inhibitor, and atazanavir (ATV), a protease inhibitor, are drugs widely used in antiretroviral therapy (ART) for people living with HIV. These drugs have shown high interindividual variability in adverse drug reactions (ADRs). UGT1A1*28 and CYP2B6 c.516G>T have been proposed to be related with higher toxicity by ATV and EFV, respectively. Objective: To study the association between genetic polymorphisms and ADRs related to EFV or ATV in patients living with HIV treated at a public hospital in Chile. Methods: Epidemiologic, case-control, retrospective, observational study in 67 adult patients under EFV or ATV treatment was conducted, in the San Juan de Dios Hospital. Data were obtained from patients' medical records. Genotype analyses were performed using rtPCR for rs887829 (indirect identification of UGT1A1*28 allele) and rs3745274 (CYP2B6 c.516G>T), with TaqMan® probes. The association analyses were performed with univariate logistic regression between genetic variants using three inheritance models (codominant, recessive, and dominant). Results: In ATV-treated patients, hyperbilirubinemia (total bilirubin >1.2 mg/dl) had the main incidence (61.11%), and moderate and severe hyperbilirubinemia (total bilirubin >1.9 mg/dl) were statistically associated with UGT1A1*28 in recessive and codominant inheritance models (OR = 16.33, p = 0.028 and OR = 10.82, p = 0.036, respectively). On the other hand, in EFV-treated patients adverse reactions associated with CNS toxicity reached 34.21%. In this respect, nightmares showed significant association with CYP2B6 c.516G>T, in codominant and recessive inheritance models (OR = 12.00, p = 0.031 and OR = 7.14, p = 0.042, respectively). Grouped CNS ADRs (nightmares, insomnia, anxiety, and suicide attempt) also showed a statistically significant association with CYP2B6 c.516G > T in the codominant and recessive models (OR = 30.00, p = 0.011 and OR = 14.99, p = 0.021, respectively). Conclusion: Our findings suggest that after treatment with ATV or EFV, UGT1A1*28 and CYP2B6 c.516G>T influence the appearance of moderate-to-severe hyperbilirubinemia and CNS toxicity, respectively. However, larger prospective studies will be necessary to validate these associations in our population. Without a doubt, improving adherence in patients living with HIV is a critical issue to the success of therapy. Hence, validating and applying international pharmacogenetic recommendations in Latin American countries would improve the precision of ART: a fundamental aspect to achieve the 95-95-95 treatment target proposed by UNAIDS.

Impact of Cytochromes P450 3A4 and 2B6 gene polymorphisms on predisposition and prognosis of acute myeloid leukemia: an Egyptian case-control study

Background

It has been postulated that the interaction between environmental risk factors and genetic susceptibility is a possible cause for the development of acute myeloid leukemia (AML). Cytochrome P450 (CYP) detoxification enzymes are responsible for the elimination of oxidative stress. Genetic polymorphisms in these enzymes may cause AML due to enhanced accumulation of reactive oxygen species. To study the association between CYP3A4 (A290G) and CYP2B6 (G516T) gene polymorphisms and the predisposition and prognosis of AML, 50 upfront AML patients and 50 healthy individuals were genotyped for CYP2B6 (G516T) and CYP3A4 (A290G) single-nucleotide polymorphisms (SNPs) using polymerase chain reaction (PCR)-based restriction fragment length polymorphism (RFLP) technique. The polymorphisms were evaluated in relation to the response to chemotherapy and survival.

Results

CYP2B6 gene mutation carries a threefold risk of developing AML (odds ratio [OR], 3.0; 95% confidence interval [CI], 1.3–6.9), whereas CYP3A4 gene mutation carries approximately fourfold risk (OR, 3.8; 95% CI, 1.4–10.1). The presence of combined gene mutation conferred about 15-fold increased risk of developing AML compared with the presence of a single gene mutation (OR, 14.8; 95% CI, 1.8–124.2). CYP3A4 gene mutation is associated with worse overall survival (P = 0.030).

Conclusion

CYP enzyme gene polymorphisms are associated with the development of AML. Elimination of oxidative stress in genetically susceptible individuals may decrease the risk of AML and may improve survival.

PharmVar GeneFocus: CYP2B6

The Pharmacogene Variation Consortium (PharmVar) catalogs star (*) allele nomenclature for the polymorphic human CYP2B6 gene. Genetic variation within the CYP2B6 gene locus impacts the metabolism or bioactivation of clinically important drugs. Of particular importance are efficacy and safety concerns regarding: efavirenz, which is used for the treatment of HIV type-1 infection; methadone, a mainstay in the treatment of opioid use disorder and as an analgesic; ketamine, used as an antidepressant and analgesic; and bupropion, which is prescribed to treat depression and for smoking cessation. This GeneFocus provides a comprehensive overview and summary of CYP2B6 and describes how haplotype information catalogued by PharmVar is utilized by the Pharmacogenomics Knowledgebase (PharmGKB) and the Clinical Pharmacogenetics Implementation Consortium (CPIC).

Identification of miRNAs that regulate human CYP2B6 expression

Human hepatic cytochrome P450 2B6 (CYP2B6) expressed is responsible for the metabolism of many drugs, such as cyclophosphamide, ifosfamid, and efavirenz. In the present study, the correlation between CYP2B6 mRNA and protein levels in human liver samples was found to be moderate, indicating a contribution of posttranscriptional regulation of CYP2B6. Thus, we examined the role of microRNAs (miRNAs) in the regulation of CYP2B6. We established two kinds of HEK293 cell lines stably expressing CYP2B6, including or excluding the full-length 3'-untranslated region (3'-UTR) (HEK/2B6+UTR and HEK/2B6 cells, respectively). We tested 14 miRNAs that were predicted to bind to the 3'-UTR of CYP2B6 and found that the overexpression of miR-145, miR-194, miR-222, and miR-378 decreased the CYP2B6 protein level and activity in HEK/2B6+UTR but not in HEK/2B6 cells. These results suggested that miR-145, miR-194, miR-222, and miR-378 negatively regulate CYP2B6 expression by binding to the 3'-UTR. A negative correlation was not observed between the translational efficiency of CYP2B6 and the expression level of miR-145, miR-194, miR-222, or miR-378. This is due to the contribution of multiple miRNAs to CYP2B6 regulation. In conclusion, this study demonstrated that human CYP2B6 is posttranscriptionally regulated by miR-145, miR-194, miR-222, and miR-378.

Whole-Exome Sequencing in Patients Affected by Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis Reveals New Variants Potentially Contributing to the Phenotype

Background

Adverse drug reactions (ADRs) are frequent occurring events that can essentially be defined as harmful or unpleasant symptoms secondary to the use of a medicinal product. ADRs involve a wide spectrum of clinical manifestations ranging from minor itching and rash to life-threatening reactions. Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are rare ADRs. SJS-TEN may be considered a polygenic pathology due to additive/epistatic effects caused by sequence variants in numerous genes. Next-generation sequencing (NGS) represents a potentially interesting exploration tool in such scenario as it facilitates the simultaneous analysis of large genomic regions and genes at affordable cost.

Methods

The present study has involved using whole-exome sequencing (WES) for the first time on SJS-TEN patients. It involved robust and innovative multistep bioinformatics analysis focusing on 313 candidate genes potentially participating in the disease’s aetiology, specific drugs’ metabolism and gene regulation.

Results

We identified combinations of frequently occurring and rare variants that may contribute to the disease’s pathogenesis. Depending on the specific drug being taken, different variants (and alleles) in NAT2, CYP2D8, CYP2B6, ABCC2, UGT2B7 and TCF3 were identified as coherent candidates representing potential future markers for SJS-TEN.

Conclusion

The present study proposed and has described (for the first time) a large-scale genomic analysis of patients affected by SJS-TEN. The genes and variants identified represent relevant candidates potentially participating in the disease’s pathogenesis. Corroborating that proposed by others, we found that complex combinations of frequently occurring and rare variants participating in particular drug metabolism molecular cascades could be associated with the phenotype. TCF3 TF may be considered a coherent candidate for SJS-TEN that should be analysed in new cohorts of patients having ADRs.

Allelic and genotype frequencies of major CYP2B6 polymorphisms in the Pakistani population

BACKGROUND

Cytochrome P450 (CYP2B6) is an important enzyme that metabolizes about 3.0% of therapeutic drugs. Drugs metabolized mainly by CYP2B6 include artemisinin, bupropion, cyclophosphamide, efavirenz, ketamine, and methadone. The genetic polymorphisms in the CYP2B6 gene have earlier been studied in many populations, but the data are lacking for the Pakistani population. This research study aimed to determine the frequencies of the three of the most important variant alleles and genotypes of the CYP2B6 gene in the Pakistani population.

METHODS

Blood was withdrawn from healthy volunteers after taking informed consent. DNA was extracted using commercial kits, and allelic and genotype frequencies were determined after PCR amplification followed by restriction fragment length polymorphism (RFLP) and gel electrophoresis.

RESULTS

Our results show a minor allele frequency of 33.8% for CYP2B6*6, 25.8% for CYP2B6*4, 6.5% for CYP2B6*3, whereas wild-type genotype frequency was 48.57% for CYP2B6*6, 59.79% for CYP2B6*4, and 90.20% for CYP2B6*3. A significant interethnic variation was also observed.

CONCLUSIONS

Our results suggest that the frequency of poor metabolizers of CYP2B6, especially *6 variant, is significant enough in the Pakistani population to be given an important consideration when drugs metabolized by this enzyme are prescribed.

Sources of Interindividual Variability

The efficacy, safety, and tolerability of drugs are dependent on numerous factors that influence their disposition. A dose that is efficacious and safe for one individual may result in sub-therapeutic or toxic blood concentrations in others. A significant source of this variability in drug response is drug metabolism, where differences in presystemic and systemic biotransformation efficiency result in variable degrees of systemic exposure (e.g., AUC, C_max, and/or C_min) following administration of a fixed dose.Interindividual differences in drug biotransformation have been studied extensively. It is recognized that both intrinsic factors (e.g., genetics, age, sex, and disease states) and extrinsic factors (e.g., diet , chemical exposures from the environment, and the microbiome) play a significant role. For drug-metabolizing enzymes, genetic variation can result in the complete absence or enhanced expression of a functional enzyme. In addition, upregulation and downregulation of gene expression, in response to an altered cellular environment, can achieve the same range of metabolic function (phenotype), but often in a less predictable and time-dependent manner. Understanding the mechanistic basis for variability in drug disposition and response is essential if we are to move beyond the era of empirical, trial-and-error dose selection and into an age of personalized medicine that will improve outcomes in maintaining health and treating disease.

How Can Drug Metabolism and Transporter Genetics Inform Psychotropic Prescribing?

Many genetic variants in drug metabolizing enzymes and transporters have been shown to be relevant for treating psychiatric disorders. Associations are strong enough to feature on drug labels and for prescribing guidelines based on such data. A range of commercial tests are available; however, there is variability in included genetic variants, methodology, and interpretation. We herein provide relevant background for understanding clinical associations with specific variants, other factors that are relevant to consider when interpreting such data (such as age, gender, drug-drug interactions), and summarize the data relevant to clinical utility of pharmacogenetic testing in psychiatry and the available prescribing guidelines. We also highlight areas for future research focus in this field.

Effects of CYP2B6 polymorphisms on plasma nevirapine concentrations: a systematic review and meta-analysis

Cytochrome P450 (CYP) is involved in the metabolism of nevirapine (NVP); especially, CYP2B6 has been known to be one of the main enzymes involved in NVP metabolism. The objective of this study was to investigate the effects of CYP2B6 variants on plasma concentrations of NVP by a systematic review and meta-analysis. A search for qualifying studies published until April 2020 was conducted using the EMBASE, PubMed, and Web of Science databases. The mean difference (MD) and 95% confidence intervals (CIs) were calculated. Data analysis was performed using R Studio (version 3.6) and Review Manager (version 5.3). In total, data from six studies involving 634 patients were analyzed in the systematic review and five studies in the meta-analysis. We found that carriers of the CYP2B6 516TT genotype had a 2.18 µg/mL higher NVP concentration than did the GG or GT (95% CI 1.28-3.08). In the respective comparisons of the three genotypes, it was found that the MD was 1.87 µg/mL between the TT and GT groups, 2.53 µg/mL between TT and GG, and 0.60 µg/mL between GT and GG. This meta-analysis confirmed that CYP2B6 polymorphisms was associated with plasma NVP concentrations. Therefore, CYP2B6 genotyping may be useful to predict the responses to NVP.

Circulating miRNAs as Biomarkers for CYP2B6 Enzyme Activity

The CYP2B6 gene is highly polymorphic and its activity shows wide interindividual variability. However, substantial variability in CYP2B6 activity remains unexplained by the known CYP2B6 genetic variations. Circulating, cell-free micro RNAs (miRNAs) may serve as biomarkers of hepatic enzyme activity. CYP2B6 activity in 72 healthy volunteers was determined using the disposition of efavirenz as a probe drug. Circulating miRNA expression was quantified from baseline plasma samples. A linear model consisting of the effects of miRNA expression, genotype-determined metabolizer status, and demographic information was developed to predict CYP2B6 activity. Expression of 2,510 miRNAs were quantified out of which 7 miRNAs, together with the CYP2B6-genotypic metabolizer status and demographics, was shown to be predictive markers for CYP2B6 activity. The reproducibility of the model was evaluated by cross-validation. The average Pearson's correlation (R) between the predicted and observed maximum plasma concentration (C_max ) ratios of efavirenz and its metabolite-8-OH efavirenz using the linear model with all features (7 miRNA + metabolizer status + age + sex + race) was 0.6702. Similar results were also observed using area under the curve (AUC) ratios (Pearson correlation's R = 0.6035). Thus, at least 36% (R² ) of the variability of in vivo CYP2B6 activity was explained using this model. This is a significant improvement over the models using only the genotype-based metabolizer status or the demographic information, which explained only 6% or less of the variability of in vivo CYP2B6 activity. Our results, therefore, demonstrate that circulating plasma miRNAs can be valuable biomarkers for in vivo CYP2B6 activity.

Meta-analysis of the effect of CYP2B6, CYP2A6, UGT2B7 and CAR polymorphisms on efavirenz plasma concentrations

BACKGROUND

Efavirenz primary metabolism is catalysed by CYP2B6 with minor involvement of CYP2A6. Subsequently, phase I metabolites are conjugated by UGT2B7, and constitutive androstane receptor (CAR) has been shown to transcriptionally regulate many relevant enzymes and transporters. Several polymorphisms occurring in the genes coding for these proteins have been shown to impact efavirenz pharmacokinetics in some but not all studies.

OBJECTIVES

A meta-analysis was performed to assess the overall effect of CYP2B6 rs3745274, CYP2A6 (rs28399454, rs8192726 and rs28399433), UGT2B7 (rs28365062 and rs7439366) and NR1I3 (rs2307424 and rs3003596) polymorphisms on mid-dose efavirenz plasma concentrations.

METHODS

Following a literature review, pharmacokinetic parameters were compiled and a meta-analysis for these variants was performed using Review Manager and OpenMetaAnalyst. A total of 28 studies were included.

RESULTS

Unsurprisingly, the analysis confirmed that individuals homozygous for the T allele for CYP2B6 rs3745274 had significantly higher efavirenz concentrations than those homozygous for the G allele [weighted standard mean difference (WSMD) = 2.98; 95% CI 2.19-3.76; P < 0.00001]. A subgroup analysis confirmed ethnic differences in frequency but with a similar effect size in each ethnic group (P = 0.96). Associations with CYP2A6 and UGT2B7 variants were not statistically significant, but T homozygosity for CAR rs2307424 was associated with significantly lower efavirenz concentrations than in C homozygotes (WSMD = -0.32; 95% CI -0.59 to -0.06; P = 0.02).

CONCLUSIONS

This meta-analysis provides the overall effect size for the impact of CYP2B6 rs3745274 and NR1I3 rs2307424 on efavirenz pharmacokinetics. The analysis also indicates that some previous associations were not significant when interrogated across studies.

Effect of patient genetics on etonogestrel pharmacokinetics when combined with efavirenz or nevirapine ART

BACKGROUND

We previously demonstrated that etonogestrel concentrations were 82% lower in women using etonogestrel contraceptive implants plus efavirenz-based ART compared with women not receiving ART.

OBJECTIVES

To investigate the genetic contribution to this previously observed drug-drug interaction through studying SNPs in genes known to be involved in efavirenz, nevirapine or etonogestrel metabolism in the same group of women.

PATIENTS AND METHODS

Here, we present a secondary analysis evaluating SNPs involved in efavirenz, nevirapine and etonogestrel metabolism and associated etonogestrel pharmacokinetics among 57 women, 19 not receiving ART (control group), 19 receiving efavirenz- (600 mg daily) based ART and 19 receiving nevirapine- (200 mg twice daily) based ART. Associations between patient genotype and etonogestrel pharmacokinetic parameters were determined through univariate and multivariate linear regression. This study was registered at clinicaltrials.gov (NCT02082652).

RESULTS

Within the control group, CYP2B6 983 T>C was associated with 27% higher etonogestrel Cmax and 28% higher AUC0-24weeks. In the efavirenz group CYP2B6 516 G>T was associated with 43% lower etonogestrel Cmin and 34% lower AUC0-24weeks. For participants receiving nevirapine, NR1I2 63396 C>T was associated with 39% lower etonogestrel Cmin and 37% lower AUC0-24weeks.

CONCLUSIONS

This study demonstrates the influence of pharmacogenetics on the extent of drug-drug interactions between etonogestrel and efavirenz- or nevirapine-based ART. Efavirenz plus the etonogestrel contraceptive implant results in a detrimental drug-drug interaction irrespective of patient genetics, which is worsened in women possessing variant alleles for these CYP2B6 SNPs.

Five genetic polymorphisms of cytochrome P450 enzymes in the Czech non-Roma and Czech Roma population samples

Objectives Cytochromes P450 play a role in human drugs metabolic pathways and their genes are among the most variable in humans. The aim of this study was to analyze genotype frequencies of five common polymorphisms of cytochromes P450 in Roma/Gypsy and Czech (non-Roma) population samples with Czech origin. Methods Roma/Gypsy (n=302) and Czech subjects (n=298) were genotyped for CYP1A2 (rs762551), CYP2A6 (rs4105144), CYP2B6 (rs3745274) and CYP2D6 (rs3892097; rs1065852) polymorphisms using PCR-RFLP or Taqman assay. Results We found significant allelic/genotype differences between ethnics in three genes. For rs3745274 polymorphism, there was increased frequency of T allele carriers in Roma in comparison with Czech population (53.1 vs. 43.7%; p=0.02). For rs4105144 (CYP2A6) there was higher frequency of T allele carriers in Roma in comparison with Czech population (68.7 vs. 49.8%; p<0.0001). For rs3892097 (CYP2D6) there was more carriers of the A allele between Roma in comparison with Czech population (39.2 vs. 38.2%; p=0.048). Genotype/allelic frequencies of CYP2D6 (rs1065852) and CYP1A2 (rs762551) variants did not significantly differ between the ethnics. Conclusions There were significant differences in allelic/genotype frequencies of some, but not all cytochromes P450 polymorphisms between the Czech Roma/Gypsies and Czech non-Roma subjects.

Five genetic polymorphisms of cytochrome P450 enzymes in the Czech non-Roma and Czech Roma population samples

Objectives Cytochromes P450 play a role in human drugs metabolic pathways and their genes are among the most variable in humans. The aim of this study was to analyze genotype frequencies of five common polymorphisms of cytochromes P450 in Roma/Gypsy and Czech (non-Roma) population samples with Czech origin. Methods Roma/Gypsy (n=302) and Czech subjects (n=298) were genotyped for CYP1A2 (rs762551), CYP2A6 (rs4105144), CYP2B6 (rs3745274) and CYP2D6 (rs3892097; rs1065852) polymorphisms using PCR-RFLP or Taqman assay. Results We found significant allelic/genotype differences between ethnics in three genes. For rs3745274 polymorphism, there was increased frequency of T allele carriers in Roma in comparison with Czech population (53.1 vs. 43.7%; p=0.02). For rs4105144 (CYP2A6) there was higher frequency of T allele carriers in Roma in comparison with Czech population (68.7 vs. 49.8%; p<0.0001). For rs3892097 (CYP2D6) there was more carriers of the A allele between Roma in comparison with Czech population (39.2 vs. 38.2%; p=0.048). Genotype/allelic frequencies of CYP2D6 (rs1065852) and CYP1A2 (rs762551) variants did not significantly differ between the ethnics. Conclusions There were significant differences in allelic/genotype frequencies of some, but not all cytochromes P450 polymorphisms between the Czech Roma/Gypsies and Czech non-Roma subjects.

Involvement of CYP2D6 and CYP2B6 on tramadol pharmacokinetics

This study included 24 healthy volunteers who received a single 37.5 mg oral dose of tramadol. We analyzed 18 polymorphisms within CYP2D6, CYP2B6, CYP3A, COMT, ABCB1, SLC22A1 and OPRM1 genes by quantitative PCR, to study whether these polymorphisms affect its pharmacokinetics, pharmacodynamics and safety. CYP2D6 intermediate metabolizers (n = 6) showed higher tramadol plasma concentrations and lower clearance compared with normal and ultrarapid metabolizers. CYP2B6 G516T T/T (n = 2) genotype was also associated to higher tramadol plasma levels. No other polymorphism affected tramadol pharmacokinetics. Three volunteers experienced a prolonged QTc not associated with the genetic variants studied or altered phamacokinetic parameters. The correlation of CYP2B6 genotype with higher tramadol concentrations is remarkable since its influence on its elimination is also relevant and has been less studied to date. However, given our small sample size, it is important to interpret our results with caution.

Analysis of CYP450 gene allelic variants can predict ifosfamide toxicity in Mexican paediatric patients

Context: Ifosfamide (IFA) is an effective antineoplastic for solid tumours in children, although it is associated with high levels of systemic toxicity and causes death in some cases. Objective: The aim of this study was to determine whether the presence of certain allelic variants of genes CYP2B6, CYP2C9, CYP3A4 and CYP3A5 increases the risk of toxicity in children with solid tumours treated with ifosfamide.Materials and methods: A total of 131 DNA samples were genotyped by real-time polymerase chain reaction (RT-PCR) using TaqMan probes. Toxicity was assessed using WHO criteria, and survival analysis was performed using Kaplan-Meier curves.Results: The rs3745274 allelic variant in CYP2B6 was associated with haematological toxicity, affecting neutrophils; CYP3A4 variant rs2740574 was also associated with toxicity, affecting both leukocytes and neutrophils. Additionally, the CYP3A5 gene variant rs776746 was found to affect haemoglobin.Conclusions: Our results show that allelic variants rs3745274 (CYP2B6), rs2740574 (CYP34) and rs776746 (CYP3A5) increase the risk for high haematological toxicity.Clinical trial registration: 068/2013.

CYP2B6 Polymorphisms Are Associated with Ischemic Stroke Risk in a Chinese Han Population

Genetic factors have been demonstrated to play an important role in the pathology of ischemic stroke (IS). This study was conducted to explore the association between CYP2B6 polymorphisms and IS risk in a Chinese Han population. Four single-nucleotide polymorphisms (SNPs) in CYP2B6 from 477 cases and 495 controls were genotyped using the Agena MassARRAY. The odds ratio (OR) and 95% confidence interval (CI) were calculated under genetic models and haplotype analysis to assess the association between SNPs and IS risk. We found that rs2099361 was associated with an increased IS risk (CC vs. AA: overall: OR = 1.85, 95% CI: 1.16-2.93, P = 0.010; age ≤ 60: OR = 1.94, 95% CI: 1.02-3.70, P = 0.045; male: OR = 2.17, 95% CI: 1.22-3.86, P = 0.009). The GT genotype of rs4803420 was associated with a reduced IS risk (OR = 0.74, 95% CI: 0.57-0.98, P = 0.036); the GG genotype was associated with an increased IS risk in women (OR = 2.31, 95% CI: 1.00-5.31, P = 0.049). The rs1038376 polymorphism was associated with reduced IS risk for age ≤ 60 years (AT vs. TT: OR = 0.63, 95% CI: 0.40-0.99, P = 0.046). Interestingly, there were significant differences in some clinical indicator levels between case and control groups, and genotypes of SNPs. Our results indicated that CYP2B6 polymorphisms (rs2099361, rs4803420, and rs1038376) were associated with the risk of IS. Further studies are still needed to validate our findings with larger sample sizes.

Effects of Germline CYP2W1*6 and CYP2B6*6 Single Nucleotide Polymorphisms on Mitotane Treatment in Adrenocortical Carcinoma: A Multicenter ENSAT Study

Mitotane is the only approved drug for advanced adrenocortical carcinoma (ACC) and no biomarkers are available to predict attainment of therapeutic plasma concentrations and clinical response. Aim of the study was to evaluate the suitability of cytochrome P450(CYP)2W1 and CYP2B6 single nucleotide polymorphisms (SNPs) as biomarkers. A multicenter cohort study including 182 ACC patients (F/M = 121/61) treated with mitotane monotherapy after radical resection (group A, n = 103) or in not completely resectable, recurrent or advanced disease (group B, n = 79) was performed. CYP2W1*2, CYP2W1*6, CYP2B6*6 and CYP2B6 rs4803419 were genotyped in germline DNA. Mitotane blood levels were measured regularly. Response to therapy was evaluated as time to progression (TTP) and disease control rate (DCR). Among investigated SNPs, CYP2W1*6 and CYP2B6*6 correlated with mitotane treatment only in group B. Patients with CYP2W1*6 (n = 21) achieved less frequently therapeutic mitotane levels (>14 mg/L) than those with wild type (WT) allele (76.2% vs 51.7%, p = 0.051) and experienced shorter TTP (HR = 2.10, p = 0.019) and lower DCR (chi-square = 6.948, p = 0.008). By contrast, 55% of patients with CYP2B6*6 vs. 28.2% WT (p = 0.016) achieved therapeutic range. Combined, a higher rate of patients with CYP2W1*6WT+CYP2B6*6 (60.6%) achieved mitotane therapeutic range (p = 0.034). In not completely resectable, recurrent or advanced ACC, CYP2W1*6 SNP was associated with a reduced probability to reach mitotane therapeutic range and lower response rates, whereas CYP2B6*6 correlated with higher mitotane levels. The association of these SNPs may predict individual response to mitotane.

Impact of cytochrome P450 variation on meperidine N-demethylation to the neurotoxic metabolite normeperidine

1. Meperidine is an opioid analgesic that undergoes N-demethylation to form the neurotoxic metabolite normeperidine. Previous studies indicate that meperidine N-demethylation is catalyzed by cytochrome P450 2B6 (CYP2B6), CYP3A4, and CYP2C19.2. The purpose of this study was to examine the relative P450 contributions to meperidine N-demethylation and to evaluate the effect of CYP2C19 polymorphism on normeperidine generation. Experiments were performed using recombinant P450 enzymes, selective chemical inhibitors, enzyme kinetic assays, and correlation analysis with individual CYP2C19-genotyped human liver microsomes.3. The catalytic efficiency (k_cat/K_m) for meperidine N-demethylation was similar between recombinant CYP2B6 and CYP2C19, but markedly lower by CYP3A4.4. In CYP2C19-genotyped human liver microsomes, normeperidine formation was significantly correlated with CYP2C19 activity (S-mephenytoin 4´-hydroxylation).5. CYP2C19 inhibitor (+)-N-3-benzylnirvanol and CYP3A inhibitor ketoconazole significantly reduced microsomal normeperidine generation by an individual donor with high CYP2C19 activity, whereas donors with lower CYP2C19 activity were sensitive to inhibition by ketoconazole but not benzylnirvanol.6. These findings demonstrate that the relative CYP3A4, CYP2B6, and CYP2C19 involvement in meperidine N-demethylation depends on the enzyme activities in individual human liver microsomal samples. CYP2C19 is likely an important contributor to normeperidine generation in individuals with high CYP2C19 activity, but additional factors influence inter-individual metabolite accumulation.

The Effect of UGT1A9, CYP2B6 and CYP2C9 Genes Polymorphism on Propofol Pharmacokinetics in Children

Purpose

This study was conducted to determine the effect of UGT1A9 98T>C, CYP2B6 516G>T and CYP2C9 430C>T genetic polymorphisms on the pharmacokinetics of propofol in children of different sexes and ages who undergone total intravenous anesthesia (ТIVA) and deep sedation during diagnostic and therapeutic procedures.

Patients and Methods

The prospective study included 94 children, ASA I-II status, 1 to 17 years of age, who undergone standard anesthetic protocol for TIVA, which implied the continuous use of propofol. Before the administration of propofol, venous blood was sampled to determine the presence of genetic variations in UGT1A9, CYP2B6 and CYP2C9 gene using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). From each patient included in the study blood samples were taken: 10 mins after the induction of anesthesia, immediately before the discontinuation of the propofol infusion, 10 mins after discontinuation of the propofol infusion and 20 mins after discontinuation of the propofol infusion to determine the pharmacokinetics of the drug in the plasma of the subjects The plasma propofol concentration was determined by HPLC analytical technique.

Results

UGT1A9 genotype is an independent predictor of the propofol concentration in children immediately after the end of the continuous infusion and 10 mins afterwards. In the carriers of the polymorphic UGT1A9 C allele, the propofol distribution constant was higher. The carriers of the polymorphic CYP2B6 T allele received a significantly lower overall and initial dose of propofol. Unlike polymorphism of the UGT1A9 gene, the tested CYP2C9 and CYP2B6 gene polymorphisms are not independent predictors of the pharmacokinetics of propofol.

Conclusion

Further investigations of UGT1A9, CYP2B6 and CYP2C9 and other genes that participate in propofol metabolism as well as detailed analyses of the general conditions, administered therapies and associated diseases could explain the large interindividual variability of propofol metabolism in children.

Repurposing of Diagnostic Whole Exome Sequencing Data of 1,583 Individuals for Clinical Pharmacogenetics

For ~ 80 drugs, widely recognized pharmacogenetics dosing guidelines are available. However, the use of these guidelines in clinical practice remains limited as only a fraction of patients is subjected to pharmacogenetic screening. We investigated the feasibility of repurposing whole exome sequencing (WES) data for a panel of 42 variants in 11 pharmacogenes to provide a pharmacogenomic profile. Existing diagnostic WES‐data from child‐parent trios totaling 1,583 individuals were used. Results were successfully extracted for 39 variants. No information could be extracted for three variants, located in CYP2C19, UGT1A1, and CYP3A5, and for CYP2D6 copy number. At least one actionable phenotype was present in 86% of the individuals. Haplotype phasing proved relevant for CYP2B6 assignments as 1.5% of the phenotypes were corrected after phasing. In conclusion, repurposing WES‐data can yield meaningful pharmacogenetic profiles for 7 of 11 important pharmacogenes, which can be used to guide drug treatment.

Circulating DNA as prognostic biomarker in patients with advanced hepatocellular carcinoma: a translational exploratory study from the SORAMIC trial

BACKGROUND

Liquid biopsy based on cell-free DNA circulating in plasma has shown solid results as a non-invasive biomarker. In the present study we evaluated the utility of circulating free DNA (cfDNA) and the sub-type tumor DNA (ctDNA) in hepatocellular cancer (HCC) patients to assess therapy response and clinical outcome.

METHODS

A cohort of 13 patients recruited in the context of the SORAMIC trial with unresectable, advanced HCC and different etiological and clinicopathological characteristics was included in this exploratory study. Plasma samples were collected between liver micro-intervention and beginning of sorafenib-based systemic therapy and then in correspondence of three additional follow-ups. DNA was isolated from plasma and next generation sequencing (NGS) was performed on a panel of 597 selected cancer-relevant genes.

RESULTS

cfDNA levels showed a significant correlation with the presence of metastases and survival. In addition cfDNA kinetic over time revealed a trend with the clinical history of the patients, supporting its use as a biomarker to monitor therapy. NGS-based analysis on ctDNA identified 28 variants, detectable in different combinations at the different time points. Among the variants, HNF1A, BAX and CYP2B6 genes showed the highest mutation frequency and a significant association with the patients' clinicopathological characteristics, suggesting a possible role as driver genes in this specific clinical setting.

CONCLUSIONS

Taken together, the results support the prognostic value of cfDNA/ctDNA in advanced HCC patients with the potential to predict therapy response. These findings support the clinical utility of liquid biopsy in advanced HCC improving individualized therapy and possible earlier identification of treatment responders.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2B6 and Efavirenz-Containing Antiretroviral Therapy

The HIV type-1 nonnucleoside reverse transcriptase inhibitor, efavirenz, is widely used to treat HIV type-1 infection. Efavirenz is predominantly metabolized into inactive metabolites by cytochrome P450 (CYP)2B6, and patients with certain CYP2B6 genetic variants may be at increased risk for adverse effects, particularly central nervous system toxicity and treatment discontinuation. We summarize the evidence from the literature and provide therapeutic recommendations for efavirenz prescribing based on CYP2B6 genotypes.

Human Genetic Variation and HIV/AIDS in Papua New Guinea: Time to Connect the Dots

PURPOSE OF REVIEW

Human genetic polymorphisms known to influence HIV acquisition and disease progression occur in Papua New Guinea (PNG). However, no genetic association study has been reported so far. In this article, we review research findings, with a view to stimulate genotype-to-phenotype research.

RECENT FINDINGS

PNG, a country in Oceania, has a high prevalence of HIV and many sexually transmitted infections. While limited data is available from this country regarding the distribution of human genetic polymorphisms known to influence clinical outcomes of HIV/AIDS, genetic association studies are lacking. Our studies, in the past decade, have revealed that polymorphisms in chemokine receptor-ligand (CCR2-CCR5, CXCL12), innate immune (Toll-like receptor, β-defensin), and antiretroviral drug-metabolism enzyme (CYP2B6, UGT2B7) genes are prevalent in PNG. Although our results need to be validated in further studies, it is urgent to pursue large-scale, comprehensive genetic association studies that include these as well as additional genetic polymorphisms.

CYP2B6 genetic polymorphisms influence chronic obstructive pulmonary disease susceptibility in the Hainan population

Introduction

Chronic obstructive pulmonary disease (COPD) is a lung disease closely related to exposure to exogenous substances. CYP2B6 can activate many exogenous substances, which in turn affect lung cells. The aim of this study was to assess the association of single-nucleotide polymorphisms (SNPs) in CYP2B6 with COPD risk in a Chinese Han population.

Materials and methods

Genotypes of the five candidate SNPs in CYP2B6 were identified among 318 cases and 508 healthy controls with an Agena MassARRAY method. The association between CYP2B6 polymorphisms and COPD risk was evaluated using genetic models and haplotype analyses.

Results

In allele model, we observed that rs4803420 G and rs1038376 A were related to COPD risk. And rs4803420 G/T and G/T-T/T were related to a decreased COPD risk compared to GG genotype in the co-dominant and dominant models, respectively. When comparing with the AA genotype, rs1038376 A/T and A/T-T/T were associated with an increased COPD risk in the co-dominant and dominant models, respectively. Further gender stratification co-dominant and dominant models analysis showed that genotype G/T and G/T-T/T of rs4803420, and genotype A/T and A/T-T/T of rs1038376 were significantly associated with COPD risk compared to the wide type in males and females, while allele C of rs12979270 was only associated with COPD risk in females. Smoking status stratification analysis showed that rs12979270 C was significantly associated with an increased COPD risk under the allele model compared with allele A in the smoking subgroup. Haplotype analysis showed that haplotype GTA and TAA were related to COPD risk.

Conclusion

Our data is the first to demonstrate that CYP2B6 polymorphisms may exert effects on COPD susceptibility in the Chinese Han population.

The importance of both CYP2C19 and CYP2B6 germline variations in cyclophosphamide pharmacokinetics and clinical outcomes

Cyclophosphamide is an alkylating agent used in the treatment of solid and haematological malignancies and as an immunosuppressive agent. As a prodrug, it is dependent on bioactivation to the active phosphoramide mustard metabolite to elicit its therapeutic effect. This focused review will highlight the evidence for the role of germline pharmacogenetic variation in both plasma pharmacokinetics and clinical outcomes. There is a substantial indication from 13 pharmacokinetic and 17 therapeutic outcome studies, in contexts as diverse as haematological malignancy, breast cancer, systemic lupus erythematosus and myeloablation, that pharmacogenetic variation in both CYP2C19 and CYP2B6 influence the bioactivation of cyclophosphamide. An additional role for pharmacogenetic variation in ALDH1A1 has also been reported. Future studies should comprehensively assess these 3 pharmacogenes and undertake appropriate statistical analysis of gene-gene interactions to confirm these findings and may allow personalised treatment regimens.

Pharmacogenomic considerations for medications in the perioperative setting

Several high-profile examples of adverse outcomes from medications used in the perioperative setting are well known (e.g., malignant hyperthermia, prolonged apnea, respiratory depression, inadequate analgesia), leading to an increased understanding of genetic susceptibilities underlying these risks. Pharmacogenomic information is increasingly being utilized in certain areas of medicine. Despite this, routine preoperative genetic screening to inform medication risk is not yet standard practice. In this review, we assess the current readiness of pharmacogenomic information for clinical consideration for several common perioperative medications, including description of key pharmacogenes, pharmacokinetic implications and potential clinical outcomes. The goal is to highlight medications for which emerging or considerable pharmacogenomic information exists and identify areas for future potential research.

Inter-Individual Variability in Xenobiotic-Metabolizing Enzymes: Implications for Human Aging and Longevity

Xenobiotic-metabolizing enzymes (XME) mediate the body’s response to potentially harmful compounds of exogenous/endogenous origin to which individuals are exposed during their lifetime. Aging adversely affects such responses, making the elderly more susceptible to toxics. Of note, XME genetic variability was found to impact the ability to cope with xenobiotics and, consequently, disease predisposition. We hypothesized that the variability of these genes influencing the interaction with the exposome could affect the individual chance of becoming long-lived. We tested this hypothesis by screening a cohort of 1112 individuals aged 20–108 years for 35 variants in 23 XME genes. Four variants in different genes (CYP2B6/rs3745274-G/T, CYP3A5/rs776746-G/A, COMT/rs4680-G/A and ABCC2/rs2273697-G/A) differently impacted the longevity phenotype. In particular, the highest impact was observed in the age group 65–89 years, known to have the highest incidence of age-related diseases. In fact, genetic variability of these genes we found to account for 7.7% of the chance to survive beyond the age of 89 years. Results presented herein confirm that XME genes, by mediating the dynamic and the complex gene–environment interactions, can affect the possibility to reach advanced ages, pointing to them as novel genes for future studies on genetic determinants for age-related traits.

Pharmacokinetics and pharmacodynamics of cytochrome P450 inhibitors for HIV treatment

INTRODUCTION

Drugs used in HIV treatment; all protease inhibitors, some non-nucleoside reverse transcriptase inhibitors, and pharmacoenhancers ritonavir and cobicistat can inhibit cytochrome P450 (CYP) enzymes. CYP inhibition can cause clinically significant drug-drug interactions (DDI), leading to increased drug exposure and potential toxicity. Areas covered: A complete understanding of pharmacodynamics and CYP-mediated DDI is crucial to prevent adverse side effects and to achieve optimal efficacy. We summarized the pharmacodynamics of all the CYP inhibitors used for HIV treatment, followed by a discussion of drug interactions between these CYP inhibitors and other drugs, and a discussion on the effect of CYP polymorphisms. We also discussed the potential advancements in improving the pharmacodynamics of these CYP inhibitors by using nanotechnology strategy. Expert opinion: The drug-interactions in HIV patients receiving ARV drugs are complicated, especially when patients are on CYP inhibitors-based ART regimens. Therefore, evaluation of CYP-mediated drug interactions is necessary prior to prescribing ARV drugs to HIV subjects. To improve the treatment efficacy and minimize DDI, novel approaches such as nanotechnology may be the potential alternative approach. However, further studies with large cohort need to be conducted to provide strong evidence for the use of nano-formulated ARVs to effectively treat HIV patients.

Pharmacogenomics in Papua New Guineans: unique profiles and implications for enhancing drug efficacy while improving drug safety

Papua New Guinea (PNG) can be roughly divided into highland, coastal and island peoples with significant mitochondrial DNA differentiation reflecting early and recent distinct migrations from Africa and East Asia, respectively. Infectious diseases such as tuberculosis, malaria and HIV severely impact on the health of its peoples for which drug therapy is the major treatment and pharmacogenetics has clinical relevance for many of these drugs. Although there is generally little information about known single nucleotide polymorphisms in the population, in some instances, their frequencies have been shown to be higher than anywhere worldwide. For example, CYP2B6*6 is over 50%, and CYP2C19*2 and *3 are over 40 and 25%, respectively. Conversely, CYP2A6*9, 2B6*2, *3, *4 and *18, and 2C8*3 appear to be much lower than in Whites. CYP2D6 known variants are unclear, and for phase II enzymes, only UGT2B7 and UGT1A9 data are available, with variant frequencies either slightly lower than or similar to Whites. Although almost all PNG people tested are rapid acetylators, but which variant(s) define this phenotype is not known. For HLA-B*13:01, HLA-B*35:05 and HLA-C*04:01, the frequencies show some regioselectivity, but the clinical implications with respect to adverse drug reactions are not known. There are minimal phenotype data for the CYPs and nothing is known about drug transporter or receptor genetics. Determination of genetic variants that are rare in Whites or Asians but common in PNG people is a topic of both scientific and clinical importance, and further research needs to be carried out. Optimizing the safety and efficacy of infectious disease drug therapy through pharmacogenetic studies that have translation potential is a priority.

Nicotine oxidation by genetic variants of CYP2B6 and in human brain microsomes

Common variation in the CYP2B6 gene, encoding the cytochrome P450 2B6 enzyme, is associated with substrate-specific altered clearance of multiple drugs. CYP2B6 is a minor contributor to hepatic nicotine metabolism, but the enzyme has been proposed as relevant to nicotine-related behaviors because of reported CYP2B6 mRNA expression in human brain tissue. Therefore, we hypothesized that CYP2B6 variants would be associated with altered nicotine oxidation, and that nicotine metabolism by CYP2B6 would be detected in human brain microsomes. We generated recombinant enzymes in insect cells corresponding to nine common CYP2B6 haplotypes and demonstrate genetically determined differences in nicotine oxidation to nicotine iminium ion and nornicotine for both (S) and (R)-nicotine. Notably, the CYP2B6.6 and CYP2B6.9 variants demonstrated lower intrinsic clearance relative to the reference enzyme, CYP2B6.1. In the presence of human brain microsomes, along with nicotine-N-oxidation, we also detect nicotine oxidation to nicotine iminium ion. However, unlike N-oxidation, this activity is NADPH independent, does not follow Michaelis-Menten kinetics, and is not inhibited by NADP or carbon monoxide. Furthermore, metabolism of common CYP2B6 probe substrates, methadone and ketamine, is not detected in the presence of brain microsomes. We conclude that CYP2B6 metabolizes nicotine stereoselectively and common CYP2B6 variants differ in nicotine metabolism activity, but did not find evidence of CYP2B6 activity in human brain.