Genetic contribution to variable human CYP3A-mediated metabolism

The potential implication of SCN1A and CYP3A5 genetic variants on antiepileptic drug resistance among Egyptian epileptic children

PURPOSE

Despite the advances in the pharmacological treatment of epilepsy, pharmacoresistance still remains challenging. Understanding of the pharmacogenetic causes is critical to predict drug response hence providing a basis for personalized medications. Genetic alteration in activity of drug target and drug metabolizing proteins could explain the development of pharmacoresistant epilepsy. So the aim of this study was to explore whether SCN1A c.3184 A/G (rs2298771) and CYP3A5*3 (rs776746) polymorphisms could serve as genetic based biomarkers to predict pharmacoresistance among Egyptian epileptic children.

METHODS

Genotyping of SCN1A c.3184 A/G and CYP3A5*3 polymorphisms using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was performed in 65 healthy control subjects and 130 patients with epilepsy, of whom 50 were drug resistant and 80 were drug responsive.

RESULTS

There was a significant higher frequency of the AG genotype (p=0.001) and G allele (p=0.006) of SCN1A polymorphism in epileptic patients than in controls. Also their frequency was significantly higher in drug resistant patients in comparison with drug responders (p=0.005 and 0.054 respectively). No significant association between CYP3A5*3 polymorphism and drug-resistance was found.

CONCLUSIONS

Overall, results confirmed the claimed role of SCN1A c.3184 A/G polymorphism in epilepsy and moreover in development of pharmacoresistance among Egyptian epileptic children. CYP3A5*3 variants have no contributing effect on pharmacoresistance among Egyptian epileptic children.

Cytochrome P450 3A4 and CYP3A5-Catalyzed Bioactivation of Lapatinib

Metabolic activation of the dual-tyrosine kinase inhibitor lapatinib by cytochromes CYP3A4 and CYP3A5 has been implicated in lapatinib-induced idiosyncratic hepatotoxicity; however, the relative enzyme contributions have not been established. The objective of this study was to examine the roles of CYP3A4 and CYP3A5 in lapatinib bioactivation leading to a reactive, potentially toxic quinoneimine. Reaction phenotyping experiments were performed using individual human recombinant P450 enzymes and P450-selective chemical inhibitors. Lapatinib metabolites and quinoneimine-glutathione (GSH) adducts were analyzed using liquid chromatography-tandem mass spectrometry. A screen of cDNA-expressed P450s confirmed that CYP3A4 and CYP3A5 are the primary enzymes responsible for quinoneimine-GSH adduct formation using lapatinib or O-dealkylated lapatinib as the substrate. The mean kinetic parameters (Km and kcat) of lapatinib O-dealkylation revealed that CYP3A4 was 5.2-fold more efficient than CYP3A5 at lapatinib O-dealkylation (CYP3A4 kcat/Km = 6.8 μM(-1) min(-1) versus CYP3A5 kcat/Km = 1.3 μM(-1) min(-1)). Kinetic analysis of GSH adduct formation indicated that CYP3A4 was also 4-fold more efficient at quinoneimine-GSH adduct formation as measured by kcat (maximum relative GSH adduct levels)/Km (CYP3A4 = 0.0082 vs. CYP3A5 = 0.0021). In human liver microsomal (HLM) incubations, CYP3A4-selective inhibitors SR-9186 and CYP3cide reduced formation of GSH adducts by 78% and 72%, respectively, compared with >90% inhibition by the pan-CYP3A inhibitor ketoconazole. The 16%-22% difference between CYP3A- and CYP3A4-selective inhibition indicates the involvement of remaining CYP3A5 activity in generating reactive metabolites from lapatinib in pooled HLMs. Collectively, these findings support the conclusion that both CYP3A4 and CYP3A5 are quantitatively important contributors to lapatinib bioactivation.

Pharmacogenetics of the Cytochrome P450 Enzyme System: Review of Current Knowledge and Clinical Significance

Genetic variation in drug metabolizing enzymes is an important contributor to interindividual variation in drug disposition and response and is associated with significant clinical consequences. Many commonly used drugs are dependent on the cytochrome P450 monooxygenase enzymes (CYP450) for their metabolism and elimination. At present, more than 57 active human CYP450 genes are known, and the majority of these genes are polymorphic. Despite the large number of CYP450 genes, only the CYP1, CYP2, and CYP3 families of enzymes have a major role in drug metabolism. Approximately 10 CYP450s are responsible for the metabolism of a large number of pharmacologic agents in human beings. The polymorphic forms of the CYP450s are responsible for the development of a significant number of adverse drug reactions and may also contribute to drug response. Genetic polymorphisms have now been identified in the genes encoding all the main CYP450s that contribute to drug and other xenobiotic metabolism, and there are marked interethnic differences in the distribution and frequency of variant alleles. A review of the progress in the pharmacogenetics of P450s that are important for drug metabolism is presented with particular emphasis on the clinical relevance of this research.

Liver Transplant Patient Carriers of Polymorphism Cyp3a5*1 Donors May Need More Doses of Tacrolimus From the First Month After Transplantation

BACKGROUND

The aim of this work was to evaluate the CYP3A5:CYP3A5*1/CYP3A5*3 (6986A>G) polymorphism related to the pharmacokinetic characteristics of tacrolimus during the first 3 months after transplantation, analyzing both donor and recipient genotype, in liver transplant patients.

METHODS

This retrospective, single-center, cohort study included patients who had been treated with tacrolimus monotherapy with or without corticoids (n = 67). Donors and recipients were genotyped for the CYP3A5*3 allele polymorphism (6986A>G) by use of a TaqMan polymerase chain reaction technique. The presence or absence of the *1 allele ("minor-allele") was analyzed for correlation with the tacrolimus dose-normalized ratio during the 3 months after transplantation.

RESULTS

The following observations were obtained in the population studied: (1) Frequency of the minor allele*1 was much lower both in recipients (11.9% versus 88.1%) and donors (19.4% versus 80.6%), with no statistically significant differences between both distributions. (2) Recipient genotype for CYP3A5*1/*3-polymorphism had no influence in tacrolimus pharmacokinetics, with no differences between carriers and non-carriers of the minor-allele*1. (3) However, from the first month after transplantation, patients with grafts from donor carriers of minor allele*1 had lower concentration-dose ratios compared with patients with grafts from donor non-carriers of that allele (71.1 versus 119.3 and 90.5 versus 126.3, for 30 and 90 days after transplantation, respectively; P < .05).

CONCLUSIONS

The presence of the CYP3A5-6986A>G-polymorphism in the donor affects tacrolimus pharmacokinetics in the recipient, although the difference was statistically significant only for the first month after transplantation. This means that in liver transplant patients receiving grafts from donors carrying the CYP3A5*1-polymorphism, a larger dose of tacrolimus from the first month after transplantation would be needed. The evidence provided in this study showed no effect of the recipient genotype.

Contribution of Estrone Sulfate to Cell Proliferation in Aromatase Inhibitor (AI) -Resistant, Hormone Receptor-Positive Breast Cancer

Aromatase inhibitors (AIs) effectively treat hormone receptor-positive postmenopausal breast cancer, but some patients do not respond to treatment or experience recurrence. Mechanisms of AI resistance include ligand-independent activation of the estrogen receptor (ER) and signaling via other growth factor receptors; however, these do not account for all forms of resistance. Here we present an alternative mechanism of AI resistance. We ectopically expressed aromatase in MCF-7 cells expressing green fluorescent protein as an index of ER activity. Aromatase-overexpressing MCF-7 cells were cultured in estrogen-depleted medium supplemented with testosterone and the AI, letrozole, to establish letrozole-resistant (LR) cell lines. Compared with parental cells, LR cells had higher mRNA levels of steroid sulfatase (STS), which converts estrone sulfate (E1S) to estrone, and the organic anion transporter peptides (OATPs), which mediate the uptake of E1S into cells. LR cells proliferated more in E1S-supplemented medium than did parental cells, and LR proliferation was effectively inhibited by an STS inhibitor in combination with letrozole and by ER-targeting drugs. Analysis of ER-positive primary breast cancer tissues showed a significant correlation between the increases in the mRNA levels of STS and the OATPs in the LR cell lines, which supports the validity of this AI-resistant model. This is the first study to demonstrate the contribution of STS and OATPs in E1S metabolism to the proliferation of AI-resistant breast cancer cells. We suggest that E1S metabolism represents a new target in AI-resistant breast cancer treatment.

Effects of CYP3A5 polymorphism on the pharmacokinetics of a once-daily modified-release tacrolimus formulation and acute kidney injury in hematopoietic stem cell transplantation

Background

Tacrolimus is metabolized by cytochrome P450 (CYP) 3A4 and 3A5. We investigated the influence of CYP3A5 polymorphism and concurrent use of azole antifungal agents (AZ) on the pharmacokinetics of a once-daily modified-release tacrolimus formulation (Tac-QD) in patients after hematopoietic stem cell transplantation (HSCT).

Design and methods

Twenty-four patients receiving allogeneic HSCT were enrolled. Genotyping for CYP3A5*3 was done by a PCR-restriction fragment length polymorphism method. Trough blood concentrations (C₀) of tacrolimus were measured by chemiluminescence magnetic microparticle immunoassay. Continuous infusion of tacrolimus was administered from the day before transplantation and was switched to Tac-QD after adequate oral intake.

Results

Thirteen patients had a CYP3A5*3/*3 genotype, and 11 patients had a CYP3A5*1/*1 or *1/*3 genotype. No significant difference was observed in daily dosages and the C₀ of tacrolimus between the two genotype groups without AZ. However, in patients who were co-administered AZ, the C₀ values of tacrolimus were higher in patients with the CYP3A5*3/*3 allele than with the CYP3A5*1 allele (P = 0.034), although daily doses of Tac-QD in patients with CYP3A5*3/*3 were significantly lower than those with the CYP3A5*1 allele (P = 0.041). The cumulative incidence of acute kidney injury was higher in patients with the CYP3A5*3/*3 than with the CYP3A5*1 allele when AZ was co-administered. The decrement for daily dosage of Tac-QD was significantly greater in patients expressing the CYP3A5*3/*3 than the CYP3A5*1 allele.

Conclusions

CYP3A5 genotyping may be useful for safe and effective immunosuppressive therapy with Tac-QD in HSCT patients in whom the use of AZ is anticipated.

Electronic supplementary material

The online version of this article (doi:10.1007/s00280-016-3060-4) contains supplementary material, which is available to authorized users.

Regulation of cytochrome P450 3A4 by small vault RNAb derived from the non-coding vault RNA1 of multidrug resistance-linked vault particle

Cytochrome P450 3A4 (CYP3A4) is the most abundant cytochrome P450 enzyme in human liver and intestine, contributing to the metabolism of >60% of all pharmaceuticals. The expression levels of hepatic CYP3A4 show great inter‑individual variation. However, the detailed regulatory mechanism of CYP3A4 expression has remained largely elusive. It has been reported that the non‑coding RNA small vault (sv)RNAb targets the 3' untranslated region (3'UTR) of CYP3A4 in MCF7 cells. However, to date, the role of svRNAb has not been examined in human liver tissue and hepatic cell lines such as HepG2, which was the aim of the present study. Polymerase chain reaction analysis indicated that the expression of CYP3A4 was significantly different within a study cohort (n=19). In addition, a significant negative correlation was observed between svRNAb and CYP3A4 expression in human liver tissue samples. Furthermore, a luciferase assay on HepG2 cells verified that svRNAb directly targets CYP3A4 and regulates the expression of CYP3A4 by interacting with the validated binding sites of the CYP3A4 3'UTR. The results provided insight into the variation of the expression of CYP3A4 among individuals and provided a novel method for the adjustment of personalized drug treatment. Furthermore, the present study provided a mechanism of the regulatory role of svRNAb in multidrug‑resistant cells.

Association of Polymorphisms of Cytochrome P450 2D6 With Blood Hydroxychloroquine Levels in Patients With Systemic Lupus Erythematosus

OBJECTIVE

To evaluate associations of genetic polymorphisms in cytochrome P450 (CYP) isoforms 2D6, 3A5, and 3A4 with blood concentrations of hydroxychloroquine (HCQ) and its metabolite, N-desethyl HCQ (DHCQ), in patients with systemic lupus erythematosus (SLE).

METHODS

SLE patients taking HCQ for >3 months were recruited and were genotyped for 4 single-nucleotide polymorphisms in CYP2D6*10, CYP3A5*3, and CYP3A4*18B. Blood HCQ and DHCQ concentrations ([HCQ] and [DHCQ]) were measured and their association with corresponding genotypes was investigated.

RESULTS

A total of 194 patients were included in the analysis. CYP2D6*10 polymorphisms (rs1065852 and rs1135840) were significantly associated with the [DHCQ]:[HCQ] ratio after adjustment for age, sex, dose per weight per day, and SLE Disease Activity Index score (P = 0.03 and P < 0.01, respectively). In adjusted models, the [DHCQ]:[HCQ] ratio was highest in patients with the G/G genotype of the CYP2D6*10 (rs1065852) polymorphism and lowest in those with the A/A genotype (P = 0.03). Similarly, the [DHCQ]:[HCQ] ratio was highest in patients with the C/C genotype of the CYP2D6*10 (rs1135840) polymorphism and lowest in those with the G/G genotype (P < 0.01). The CYP2D6*10 (rs1065852) polymorphism was significantly related to the [DHCQ] (P = 0.01). However, the polymorphisms of CYP3A5*3 and CYP3A4*18B did not show any significant association with the [HCQ], [DHCQ], or [DHCQ]:[HCQ] ratio.

CONCLUSION

Our study showed that the [DHCQ]:[HCQ] ratio was related to CYP2D6 polymorphisms in Korean lupus patients taking oral HCQ. CYP polymorphisms may explain why there is wide variation in blood HCQ concentrations. The role of an individual's CYP polymorphisms should be considered when prescribing oral HCQ.

Potential utility of precision medicine for older adults with polypharmacy: a case series study

Pharmacogenomic (PGx) testing has been increasingly used to optimize drug regimens; however, its potential in older adults with polypharmacy has not been systematically studied. In this hypothesis-generating study, we employed a case series design to explore potential utility of PGx testing in older adults with polypharmacy and to highlight barriers in implementing this methodology in routine clinical practice. Three patients with concurrent chronic heart and lung disease aged 74, 78, and 83 years and whose medication regimen comprised 26, 17, and 18 drugs, correspondingly, served as cases for this study. PGx testing identified major genetic polymorphisms in the first two cases. The first case was identified as "CYP3A4/CYP3A5 poor metabolizer", which affected metabolism of eleven prescribed drugs. The second case had "CYP2D6 rapid metabolizer" status affecting three prescribed medications, two of which were key drugs for managing this patient's chronic conditions. Both these patients also had VKORC1 allele *A, resulting in higher sensitivity to warfarin. All cases demonstrated a significant number of potential drug-drug interactions. Both patients with significant drug-gene interactions had a history of frequent hospitalizations (six and 23, respectively), whereas the person without impaired cytochrome P450 enzyme activity had only two acute episodes in the last 5 years, although he was older and had multiple comorbidities. Since all patients received guideline-concordant therapy from the same providers and were adherent to their drug regimen, we hypothesized that genetic polymorphism may represent an additional risk factor for higher hospitalization rates in older adults with polypharmacy. However, evidence to support or reject this hypothesis is yet to be established. Studies evaluating clinical impact of PGx testing in older adults with polypharmacy are warranted. For practical implementation of pharmacogenomics in routine clinical care, besides providing convincing evidence of its clinical effectiveness, multiple barriers must be addressed. Introduction of intelligent clinical decision support in electronic medical record systems is required to address complexities of simultaneous drug-gene and drug-drug interactions in older adults with polypharmacy. Physician training, clear clinical pathways, evidence-based guidelines, and patient education materials are necessary for unlocking full potential of pharmacogenomics into routine clinical care of older adults.

Genomics in CKD: Is This the Path Forward?

Recent advances in genomics and sequencing technology have led to a better understanding of genetic risk in CKD. Genetics could account in part for racial differences in treatment response for medications including antihypertensives and immunosuppressive medications due to its correlation with ancestry. However, there is still a substantial lag between generation of this knowledge and its adoption in routine clinical care. This review summarizes the recent advances in genomics and CKD, discusses potential reasons for its underutilization, and highlights potential avenues for application of genomic information to improve clinical care and outcomes in this particularly vulnerable population.

Interindividual Variability in Cytochrome P450-Mediated Drug Metabolism

The cytochrome P450 (P450) enzymes are the predominant enzyme system involved in human drug metabolism. Alterations in the expression and/or activity of these enzymes result in changes in pharmacokinetics (and consequently the pharmacodynamics) of drugs that are metabolized by this set of enzymes. Apart from changes in activity as a result of drug-drug interactions (by P450 induction or inhibition), the P450 enzymes can exhibit substantial interindividual variation in basal expression and/or activity, leading to differences in the rates of drug elimination and response. This interindividual variation can result from a myriad of factors, including genetic variation in the promoter or coding regions, variation in transcriptional regulators, alterations in microRNA that affect P450 expression, and ontogenic changes due to exposure to xenobiotics during the developmental and early postnatal periods. Other than administering a probe drug or cocktail of drugs to obtain the phenotype or conducting a genetic analysis to determine genotype, methods to determine interindividual variation are limited. Phenotyping via a probe drug requires exposure to a xenobiotic, and genotyping is not always well correlated with phenotype, making both methodologies less than ideal. This article describes recent work evaluating the effect of some of these factors on interindividual variation in human P450-mediated metabolism and the potential utility of endogenous probe compounds to assess rates of drug metabolism among individuals.

The impact of genetic factors on response to glucocorticoids therapy in IBD

Glucocorticosteroids (GCs) are used for many years as first-line drugs for the achievement of remission in exacerbations of inflammatory bowel disease (IBD). However, close to 20% of patients are resistant to GCs, and 40% of patients become dependent on GCs. The challenge of today's personalized medicine is the anticipation of the steroid therapy effects even before the initiation of treatment. As several studies show, individually variable response to GCs in population has a genetic background and may depend on gene variability encoding proteins involved in the function and metabolism of GCs. To those genes belong: NR3C1--responsible for the synthesis of GC receptor (GR); Hsp90, HSP70, STIP1, FKB5--genes of GR protein complex; ABCB1 and IPO13 coding glycoprotein p170; and importin 13--involved in GCs transport; IL1A, IL1B, IL2, IL4, IL8, IL10, TNF, and MIF--genes of the epithelial pro-inflammatory factors synthesis, which excessive activation causes steroid resistance as well as CYP3A4 and CYP3A5--encoding GCs biotransformation enzymes. This work systematizes and sums up the state of current knowledge in the field of pharmacogenetics as well as expectations for the future in the realm of individualized medicine in IBD patients treated with GC drugs.

In vitro evaluation of hepatotoxic drugs in human hepatocytes from multiple donors: Identification of P450 activity as a potential risk factor for drug-induced liver injuries

A possible risk factor for drug-induced hepatotoxicity is drug metabolizing enzyme activity, which is known to vary among individuals due to genetic (genetic polymorphism) and environmental factors (environmental pollutants, foods, and medications that are inhibitors or inducers of drug metabolizing enzymes). We hypothesize that hepatic cytochrome P450-dependent monooxygenase (CYP) activity is one of the key risk factors for drug induced liver injuries (DILI) in the human population, especially for drugs that are metabolically activated to cytotoxic/reactive metabolites. Human hepatocytes from 19 donors were evaluated for the activities of 8 major P450 isoforms: CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4. Extensive individual variations were observed, consistent with what is known to be in the human population. As CYP3A4 is known to be one of the most important P450 isoforms for drug metabolism, studies were performed to evaluate the relationship between the in vitro cytotoxicity of hepatotoxic drugs and CYP3A4 activity. In a proof of concept study, hepatocytes from six donors (lots) representing the observed range of CYP3A4 activities were chosen for the evaluation of in vitro hepatotoxicity of four drugs known to be associated with acute liver failure: acetaminophen, cyclophosphamide, ketoconazole, and tamoxifen. The hepatocytes were cultured in collagen-coated plates and treated with the hepatotoxicants for approximately 24 h, followed by viability determination based on cellular adenosine triphosphate (ATP) contents. HH1023, the lot of hepatocytes with the highest CYP3A4 activity, was found to be the most sensitive to the cytotoxicity of all 4 hepatotoxic drugs, thereby suggesting that high CYP3A4 activity may be a risk factor. To further validate the relationship, a second study was performed with hepatocytes from 16 donors. In this study, the hepatocytes were quantified for CYP3A4 activity at the time of treatment. Results of the second study show confirm the correlation between with high CYP3A4 activity and sensitivity to hepatotoxic drugs. Our results with primary cultured hepatocytes from multiple donors support the hypothesis that elevated P450 activity may be a risk factor for drug-induced liver injuries.

No effect of CYP3A4 intron 6 C>T polymorphism (CYP3A4*22) on lipid-lowering response to statins in Greek patients with primary hypercholesterolemia

BACKGROUND

Interindividual variability exists in statin lipid-lowering response, partially attributed to genetic factors. CYP3A4 intron 6 C>T polymorphism (CYP3A4*22 allele, rs35599367) has been recently identified and was associated with reduced CYP3A4 expression. We analyzed the association of CYP3A4*22 allele with response to atorvastatin and simvastatin.

METHODS

A total of 416 statin-treated (207 atorvastatin- and 209 simvastatin-treated) adults with primary hypercholesterolemia were included in the study. Total cholesterol and low-density lipoprotein cholesterol were measured at baseline and on 6 months of treatment. CYP3A4*22 allele was analyzed with TaqMan assay.

RESULTS

In the entire cohort population, 41 individuals carried CYP3A4*22 allele (18 in atorvastatin and 23 in simvastatin treatment). CYP3A4*22 allele was not associated with lipid-lowering response to atorvastatin or simvastatin. No sex-gene or statin dose-gene interaction was observed in either statin-treated patient cohort.

CONCLUSIONS

The effect of CYP3A4*22 allele on lipid-lowering response to CYP3A metabolized statins, if present, can potentially be masked by relevant confounding or uncontrolled factors; therefore, further population-driven studies are required.

Impact of fraction unbound, CYP3A, and CYP2D6 in vivo activities, and other potential covariates to the clearance of tramadol enantiomers in patients with neuropathic pain

The pharmacokinetics of tramadol is characterized by a large interindividual variability, which is partially attributed to polymorphic CYP2D6 metabolism. The contribution of CYP3A, CYP2B6, fraction unbound, and other potential covariates remains unknown. This study aimed to investigate the contribution of in vivo activities of cytochrome P450 (CYP) 2D6 and 3A as well as other potential covariates (CYP2B6 genotype to the SNP g.15631G>T, fraction unbound, age, body weight, creatinine clearance) to the enantioselective pharmacokinetics of tramadol. Thirty patients with neuropathic pain and phenotyped as CYP2D6 extensive metabolizers were treated with a single oral dose of 100 mg tramadol. Multiple linear regressions were performed to determine the contribution of CYP activities and other potential covariates to the clearance of tramadol enantiomers. The apparent total clearances were 44.9 (19.1-102-2) L/h and 55.2 (14.8-126.0) L/h for (+)- and (-)-tramadol, respectively [data presented as median (minimum-maximum)]. Between 79 and 83% of the overall variation in apparent clearance of tramadol enantiomers was explained by fraction unbound, CYP2D6, and CYP3A in vivo activities and body weight. Fraction unbound explained 47 and 41% of the variation in clearance of (+)-tramadol and (-)-tramadol, respectively. Individually, CYP2D6 and CYP3A activities were shown to have moderate contribution on clearance of tramadol enantiomers (11-16% and 11-18%, respectively). In conclusion, factors affecting fraction unbound of drugs (such as hyperglycemia or co-administration of drugs highly bound to plasma proteins) should be monitored, because this parameter dominates the elimination of tramadol enantiomers.

Association between cytochrome CYP17A1, CYP3A4, and CYP3A43 polymorphisms and prostate cancer risk and aggressiveness in a Korean study population

In this study, we evaluated genetic variants of the androgen metabolism genes CYP17A1, CYP3A4, and CYP3A43 to determine whether they play a role in the development of prostate cancer (PCa) in Korean men. The study population included 240 pathologically diagnosed cases of PCa and 223 age-matched controls. Among the 789 single-nucleotide polymorphism (SNP) database variants detected, 129 were reported in two Asian groups (Han Chinese and Japanese) in the HapMap database. Only 21 polymorphisms of CYP17A1, CYP3A4, and CYP3A43 were selected based on linkage disequilibrium in Asians (r² = 1), locations (SNPs in exons were preferred), and amino acid changes and were assessed. In addition, we performed haplotype analysis for the 21 SNPs in CYP17A1, CYP3A4, and CYP3A43 genes. To determine the association between genotype and haplotype distributions of patients and controls, logistic analyses were carried out, controlling for age. Twelve sequence variants and five major haplotypes were identified in CYP17A1. Five sequence variants and two major haplotypes were identified in CYP3A4. Four sequence variants and four major haplotypes were observed in CYP3A43. CYP17A1 haplotype-2 (Ht-2) (odds ratio [OR], 1.51; 95% confidence interval [CI], 1.04–2.18) was associated with PCa susceptibility. CYP3A4 Ht-2 (OR: 1.87; 95% CI: 1.02–3.43) was associated with PCa metastatic potential according to tumor stage. rs17115149 (OR: 1.96; 95% CI: 1.04–3.68) and CYP17A1 Ht-4 (OR: 2.01; 95% CI: 1.07–4.11) showed a significant association with histologic aggressiveness according to Gleason score. Genetic variants of CYP17A1 and CYP3A4 may play a role in the development of PCa in Korean men.

Combined effects of CYP3A5*1, POR*28, and CYP3A4*22 single nucleotide polymorphisms on early concentration-controlled tacrolimus exposure in de-novo renal recipients

AIM

In a cohort of 298 de-novo renal recipients treated with a standard tacrolimus loading dose of 0.2 mg/kg, the combined effects of the CYP3A5*1, POR*28, and CYP3A4*22 genotypes on early tacrolimus exposure (C0), dose requirements, and achievement of the therapeutic target, C0, were examined. The incidence of clinical events (e.g. acute rejection, diabetes mellitus) was compared between genotypes.

RESULTS

Fast metabolizers (CYP3A5*1/POR*28T carriers) had two-fold to three-fold higher tacrolimus dose requirements compared with slow metabolizers (CYP3A5*3/*3/CYP3A4*22 carriers) and needed significantly more time to achieve the target tacrolimus C0 of a minimum 10 ng/ml (3.3±1.7 vs. 1.34±0.75 days; P<0.0001). No differences in acute rejection incidence and time to first rejection were observed. Slow metabolizers more frequently had tacrolimus C0 above the target range early after transplantation (70 vs. 13% on day 3); however, this did not translate into a higher incidence of post-transplantation diabetes mellitus or graft dysfunction. Multivariate analyses identified the CYP3A5*1/POR*28/CYP3A4*22 genotype combination as the single strongest determinant of tacrolimus dose requirements throughout the first year, explaining between 24-40% of its variability, whereas recipient age, hematocrit, and delayed graft function were additional nongenetic determinants of tacrolimus dose.

CONCLUSION

Combining the CYP3A5*1, POR*28 and CYP3A4*22 genotypes allows partial differentiation of early tacrolimus dose requirements and the time to reach therapeutic target concentrations after transplantation, but without obvious clinical implications. Larger prospective studies need to address the clinical relevance of early combined genotype-based tacrolimus dosing in de-novo renal recipients.

Polymorphisms of pesticide-metabolizing genes in children living in intensive farming communities

Polymorphisms in genes encoding xenobiotic-metabolizing enzymes (XME) are important parameters accounting for the wide inter-individual variability to environmental exposures. Paraoxonase-1 (PON1), butyrylcholinesterase (BChE) and Cytochrome-P450 constitute major classes of XME involved in the detoxification of pesticide chemicals, in particular organophosphates. This study explored the allelic frequency, linkage disequilibrium and haplotype analysis of ten common polymorphic variants of seven key genes involved in organophosphate metabolism (BCHE-K, BCHE-A, PON1 Q192R, PON1 L55M, PON1 -108C/T, CYP2C19 G681A, CYP2D6 G1846A, CYP3AP1 -44G/A, GSTM1∗0 and GSTT1∗0) in a children population living near an intensive agriculture area in Spain. It was hypothesized that individuals with unfavorable combinations of gene variants will be more susceptible to adverse effects from organophosphate exposure. Genomic DNA from 496 healthy children was isolated and amplified by PCR. Hydrolysis probes were used for the detection of eight specific SNPs and two copy number variants (CNVs) by using TaqMan® Assay-based real-time PCR. Frequencies of SNPs and CNVs in the target genes were in Hardy-Weinberg equilibrium and broadly consistent with European populations. Linkage disequilibrium was found between the three PON1 genetic polymorphisms studied and between BCHE-K and BCHE-A. The adverse genotype combination (unusual BCHE variants, PON1 55MM/-108TT and null genotype for both GSTM1 and GSTT1) potentially conferring a greater genetic risk from exposure to organophosphates was observed in 0.2% of our study population. This information allows broadening our knowledge about differential susceptibility toward environmental toxicants and may be helpful for further research to understand the inter-individual toxicokinetic variability in response to organophosphate pesticides exposure.

Development of HepG2-derived cells expressing cytochrome P450s for assessing metabolism-associated drug-induced liver toxicity

The generation of reactive metabolites from therapeutic agents is one of the major mechanisms of drug-induced liver injury (DILI). In order to evaluate metabolism-related toxicity and improve drug efficacy and safety, we generated a battery of HepG2-derived cell lines that express 14 cytochrome P450s (CYPs) (1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4, 3A5 and 3A7) individually using a lentiviral expression system. The expression/production of a specific CYP in each cell line was confirmed by an increased abundance of the CYP at both mRNA and protein levels. Moreover, the enzymatic activities of representative CYPs in the corresponding cell lines were also measured. Using our CYP-expressed HepG2 cells, the toxicity of three drugs that could induce DILI (amiodarone, chlorpromazine and primaquine) was assessed, and all of them showed altered (increased or decreased) toxicity compared to the toxicity in drug-treated wild-type HepG2 cells. CYP-mediated drug toxicity examined in our cell system is consistent with previous reports, demonstrating the potential of these cells for assessing metabolism-related drug toxicity. This cell system provides a practical in vitro approach for drug metabolism screening and for early detection of drug toxicity. It is also a surrogate enzyme source for the enzymatic characterization of a particular CYP that contributes to drug-induced liver toxicity.

Maraviroc: a review of its use in HIV infection and beyond

The human immunodeficiency virus-1 (HIV-1) enters target cells by binding its envelope glycoprotein gp120 to the CD4 receptor and/or coreceptors such as C-C chemokine receptor type 5 (CCR5; R5) and C-X-C chemokine receptor type 4 (CXCR4; X4), and R5-tropic viruses predominate during the early stages of infection. CCR5 antagonists bind to CCR5 to prevent viral entry. Maraviroc (MVC) is the only CCR5 antagonist currently approved by the United States Food and Drug Administration, the European Commission, Health Canada, and several other countries for the treatment of patients infected with R5-tropic HIV-1. MVC has been shown to be effective at inhibiting HIV-1 entry into cells and is well tolerated. With expanding MVC use by HIV-1-infected humans, different clinical outcomes post-approval have been observed with MVC monotherapy or combination therapy with other antiretroviral drugs, with MVC use in humans infected with dual-R5- and X4-tropic HIV-1, infected with different HIV-1 genotype or infected with HIV-2. This review discuss the role of CCR5 in HIV-1 infection, the development of the CCR5 antagonist MVC, its pharmacokinetics, pharmacodynamics, drug–drug interactions, and the implications of these interactions on treatment outcomes, including viral mutations and drug resistance, and the mechanisms associated with the development of resistance to MVC. This review also discusses available studies investigating the use of MVC in the treatment of other diseases such as cancer, graft-versus-host disease, and inflammatory diseases.

Pharmacogenetics may Influence Tacrolimus Daily Dose, but not Urinary Tubular Damage Markers in the Long-Term Period after Renal Transplantation

Background

The primary goal of this study was to evaluate the influence of cytochrome P450 (CYP) 3A5 (6986A>G) and ABCB1 (3435C>T) polymorphisms on tacrolimus (TAC) dosage regimen and exposure. Second, we evaluated the influence of TAC dosage regimen and the tested polymorphisms on renal oxidative injury, as well as the urinary activities of tubular ectoenzymes in a long-term period after transplantation. Also, we aimed to determine the association between renal oxidative stress and tubular damage markers in the renal transplant patients.

Methods

The study included 72 patients who were on TAC based immunosuppression. Allele-specific PCR was used for polymorphism determination. We measured the urinary thiobarbituric acid reactive substances (TBARS) and reactive carbonyl derivates (RCD) in order to evaluate oxidative injury, as well as the urinary activities of ectoenzymes (N-acetyl-β-D-glucosaminidase, aminopeptidase N and dipeptidyl peptidase IV) to evaluate tubular damage.

Results

The carriers of CYP 3A5*1 allele required statistically higher daily doses of TAC than CYP *3/*3 carriers, as well as the carriers of C allele of ABCB1 gene compared to those with TT genotype. Also, there were no differences in TBARS, RCD and the activities of ectoenzymes between the patients’ genotypes. Our results showed significant correlations between urinary TBARS and RCD and the ectoenzymes’ activities.

Conclusions

Our findings suggest that CYP 3A5 and ABCB1 3435 polymorphism may affect TAC daily doses, but not the drug’s tubular toxicity. Furthermore, tubular damage may be associated with increased renal oxidative stress.

Analysis of DNA methylation landscape reveals the roles of DNA methylation in the regulation of drug metabolizing enzymes

Background

Drug metabolizing enzymes (DMEs) exhibit dramatic inter- and intra-individual variability in expression and activity. However, the mechanisms determining this variability have not been fully elucidated. The aim of this study was to evaluate the biological significance of DNA methylation in the regulation of DME genes by genome-wide integrative analysis.

Results

DNA methylation and mRNA expression profiles of human tissues and hepatoma cells were examined by microarrays. The data were combined with GEO datasets of liver tissues, and integrative analysis was performed on selected DME genes. Detailed DNA methylation statuses at individual CpG sites were evaluated by DNA methylation mapping. From analysis of 20 liver tissues, highly variable DNA methylation was observed in 37 DME genes, 7 of which showed significant inverse correlations between DNA methylation and mRNA expression. In hepatoma cells, treatment with a demethylating agent resulted in upregulation of 5 DME genes, which could be explained by DNA methylation status. Interestingly, some DMEs were suggested to act as tumor-suppressor or housekeeper based on their unique DNA methylation features. Moreover, tissue-specific and age-dependent expression of UDP-glucuronosyltransferase 1A splicing variants was associated with DNA methylation status of individual first exons.

Conclusions

Some DME genes were regulated by DNA methylation, potentially resulting in inter- and intra-individual differences in drug metabolism. Analysis of DNA methylation landscape facilitated elucidation of the role of DNA methylation in the regulation of DME genes, such as mediator of inter-individual variability, guide for correct alternative splicing, and potential tumor-suppressor or housekeeper.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-015-0136-7) contains supplementary material, which is available to authorized users.

Influence of Absorption, Distribution, Metabolism, and Excretion Genomic Variants on Tacrolimus/Sirolimus Blood Levels and Graft-versus-Host Disease after Allogeneic Hematopoietic Cell Transplantation

Allelic variants of genes implicated in drug absorption, distribution, metabolism, and excretion (ADME) determine the pharmacokinetic variability of many medications and are increasingly recognized as important factors determining the success or failure of medical treatments. Both tacrolimus and sirolimus have narrow therapeutic ranges maintained by therapeutic drug monitoring (TDM). Using an ADME panel that covers >99% of the PharmaADME working group core list (188 single nucleotide polymorphism [SNP] and 12 copy number variant [CNV] assays in 36 pharmacogenetically relevant genes), we studied 177 patients who underwent allogeneic hematopoietic cell transplantation (HCT) using tacrolimus/sirolimus-based graft-versus-host disease (GVHD) prophylaxis. We tested for possible associations between ADME variants and tacrolimus/sirolimus drug levels, concentration/dose (C/D) ratio, and clinical endpoints, including acute GVHD. A total of 62 SNP and 6 CNV assays were evaluable after removing the variants, which were homozygous in (nearly) all samples. For sirolimus, rs2032582 (ABCB1) T-carriers versus non-T-carriers were associated with higher blood levels (P = .01), with similar results for C/D ratio. Generalized estimating equation analysis supported these findings. For tacrolimus, rs776746 CYP3A5*3/*3 and CYP3A5*3/*1 were associated with higher blood levels than CYP3A5*1/*1 (P = .002). By multivariable analysis, rs776746 CYP3A5*3/*3 and CYP3A5*3/*1 were independently associated with decreased acute GVHD compared with CYP3A5*1/*1, after adjustment for conditioning, donor type, race/ethnicity, and age. We demonstrated association of specific ADME genetic polymorphisms with blood levels of tacrolimus/sirolimus, and incidence of acute GVHD after HCT, in spite of TDM and dose adjustment. A larger ongoing study will determine whether these associations have clinical utility beyond TDM.

Population pharmacokinetic analysis of isoniazid, acetylisoniazid, and isonicotinic acid in healthy volunteers

In this study, we aimed to quantify the effects of the N-acetyltransferase 2 (NAT2) phenotype on isoniazid (INH) metabolism in vivo and identify other sources of pharmacokinetic variability following single-dose administration in healthy Asian adults. The concentrations of INH and its metabolites acetylisoniazid (AcINH) and isonicotinic acid (INA) in plasma were evaluated in 33 healthy Asians who were also given efavirenz and rifampin. The pharmacokinetics of INH, AcINH, and INA were analyzed using nonlinear mixed-effects modeling (NONMEM) to estimate the population pharmacokinetic parameters and evaluate the relationships between the parameters and the elimination status (fast, intermediate, and slow acetylators), demographic status, and measures of renal and hepatic function. A two-compartment model with first-order absorption best described the INH pharmacokinetics. AcINH and INA data were best described by a two- and a one-compartment model, respectively, linked to the INH model. In the final model for INH, the derived metabolic phenotypes for NAT2 were identified as a significant covariate in the INH clearance, reducing its interindividual variability from 86% to 14%. The INH clearance in fast eliminators was 1.9- and 7.7-fold higher than in intermediate and slow eliminators, respectively (65 versus 35 and 8 liters/h). Creatinine clearance was confirmed as a significant covariate for AcINH clearance. Simulations suggested that the current dosing guidelines (200 mg for 30 to 45 kg and 300 mg for >45 kg) may be suboptimal (3 mg/liter ≤ Cmax ≤ 6 mg/liter) irrespective of the acetylator class. The analysis established a model that adequately characterizes INH, AcINH, and INA pharmacokinetics in healthy Asians. Our results refine the NAT2 phenotype-based predictions of the pharmacokinetics for INH.

Suppression of Cytochrome P450 3A4 Function by UDP-Glucuronosyltransferase 2B7 through a Protein-Protein Interaction: Cooperative Roles of the Cytosolic Carboxyl-Terminal Domain and the Luminal Anchoring Region

There is a large discrepancy between the interindividual difference in the hepatic expression level of cytochrome P450 3A4 (CYP3A4) and that of drug clearance mediated by this enzyme. However, the reason for this discrepancy remains largely unknown. Because CYP3A4 interacts with UDP-glucuronosyltransferase 2B7 (UGT2B7) to alter its function, the reverse regulation is expected to modulate CYP3A4-catalyzed activity. To address this issue, we investigated whether protein-protein interaction between CYP3A4 and UGT2B7 modulates CYP3A4 function. For this purpose, we coexpressed CYP3A4, NADPH-cytochrome P450 reductase, and UGT2B7 using a baculovirus-insect cell system. The activity of CYP3A4 was significantly suppressed by coexpressing UGT2B7, and this suppressive effect was lost when UGT2B7 was replaced with calnexin (CNX). These results strongly suggest that UGT2B7 negatively regulates CYP3A4 activity through a protein-protein interaction. To identify the UGT2B7 domain associated with CYP3A4 suppression we generated 12 mutants including chimeras with CNX. Mutations introduced into the UGT2B7 carboxyl-terminal transmembrane helix caused a loss of the suppressive effect on CYP3A4. Thus, this hydrophobic region is necessary for the suppression of CYP3A4 activity. Replacement of the hydrophilic end of UGT2B7 with that of CNX produced a similar suppressive effect as the native enzyme. The data using chimeric protein demonstrated that the internal membrane-anchoring region of UGT2B7 is also needed for the association with CYP3A4. These data suggest that 1) UGT2B7 suppresses CYP3A4 function, and 2) both hydrophobic domains located near the C terminus and within UGT2B7 are needed for interaction with CYP3A4.

Single nucleotide polymorphism of CYP3A4 intron 2 and its influence on CYP3A4 mRNA expression and liver enzymatic activity in human liver

In adult liver, CYP3A4 plays an important role in the metabolism of a wide range of endogenous and exogenous compounds. To investigate whether there is a single nucleotide polymorphism (SNP) of CYP3A4 intron 2 in the liver and its effects on the mRNA expression and enzymatic activity of CYP3A4, genomic DNA was extracted from 96 liver tissue samples obtained from patients who had undergone liver surgery. An SNP of CYP3A4 intron 2 was identified by polymerase chain reaction (PCR)-single-strand confirmation polymorphism and DNA sequencing. The mRNA expression of CYP3A4 was determined by the fluorescence quantitative PCR technique. The enzymatic activity of CYP3A4 was measured using erythromycin and testosterone as probe substrates. Twelve patients were found to have the SNP/T4127G CYP3A4 within intron 2. The mRNA levels of CYP3A4 in wild-type and SNP/T4127G samples were 2.62±1.09 and 2.79±1.63, respectively (P>0.05). Erythromycin N-demethylase activity in wild-type and SNP/T4127G samples were 121.2±32.8 and 124.7±61.6 nmol·mg(-1)·min(-1), respectively (P>0.05). The activity of testosterone 6β-hydroxylase was significantly different between wild-type (648±173 pmol·mg(-1)·min(-1)) and SNP/T4127G samples (540±196 pmol·mg(-1)·min(-1); P<0.05). In conclusion, the SNP/T4127G of CYP3A4 intron 2 exists in the liver. This SNP does not affect the mRNA expression of CYP3A4 but significantly decreases the hepatic microsomal testosterone 6β-hydroxylase activity of CYP3A4. Furthermore, this study indicates that the appropriate selection of probe substrates is very important in studying the relationship between the genotype and phenotype of CYP3A4.

Hsa-miR-27a is involved in the regulation of CYP3A4 expression in human livers from Chinese Han population

Aim: The huge interindividual difference of CYP3A4 expression may contribute to the variability of drug response. Post-transcriptional regulation of CYP3A4 remains elusive although transcriptional regulation has been studied much more clearly. microRNAs (miRNAs) were reported to be one of factors to regulate the expression of CYP3A4 previously. Materials & methods: Based on the in silico prediction of 3′-UTR-bindind site of microRNA-27a (miR-27a), the transcriptional and post-transcriptional regulation of miR-27a were investigated through luciferase reporter assay, real-time PCR and immunoblot. Results: The significantly decrease of CYP3A4 3′-UTR-luciferase activity in human embryonic kidney 293 and Hep3B cells was detected after transfected with plasmid that expressed miRNA-27a in luciferase reporter assay. Correlation study was conducted in human livers (n = 26) and significant correlation has been discovered between miRNA-27a and CYP3A4 mRNA and protein level. Conclusion: Together, these findings suggest that miR-27a might be involved in the regulation of CYP3A4 gene expression.

Gene-environment interactions in esophageal cancer

Esophageal cancer (EC) is one of the most common malignancies in low- and medium-income countries and represents a disease of public health importance because of its poor prognosis and high mortality rate in these regions. The striking variation in the prevalence of EC among different ethnic groups suggests a significant contribution of population-specific environmental and dietary factors to susceptibility to the disease. Although individuals within a demarcated geographical area are exposed to the same environment and share similar dietary habits, not all of them will develop the disease; thus genetic susceptibility to environmental risk factors may play a key role in the development of EC. A wide range of xenobiotic-metabolizing enzymes are responsible for the metabolism of carcinogens introduced via the diet or inhaled from the environment. Such dietary or environmental carcinogens can bind to DNA, resulting in mutations that may lead to carcinogenesis. Genes involved in the biosynthesis of these enzymes are all subject to genetic polymorphisms that can lead to altered expression or activity of the encoded proteins. Genetic polymorphisms may, therefore, act as molecular biomarkers that can provide important predictive information about carcinogenesis. The aim of this review is to discuss our current knowledge on the genetic risk factors associated with the development of EC in different populations; it addresses mainly the topics of genetic polymorphisms, gene-environment interactions, and carcinogenesis. We have reviewed the published data on genetic polymorphisms of enzymes involved in the metabolism of xenobiotics and discuss some of the potential gene-environment interactions underlying esophageal carcinogenesis. The main enzymes discussed in this review are the glutathione S-transferases (GSTs), N-acetyltransferases (NATs), cytochrome P450s (CYPs), sulfotransferases (SULTs), UDP-glucuronosyltransferases (UGTs), and epoxide hydrolases (EHs), all of which have key roles in the detoxification of environmental and dietary carcinogens. Finally, we discuss recent advances in the study of genetic polymorphisms associated with EC risk, specifically with regard to genome-wide association studies, and examine possible challenges of case-control studies that need to be addressed to better understand the interaction between genetic and environmental factors in esophageal carcinogenesis.

Two persistent organic pollutants which act through different xenosensors (alpha-endosulfan and 2,3,7,8 tetrachlorodibenzo-p-dioxin) interact in a mixture and downregulate multiple genes involved in human hepatocyte lipid and glucose metabolism

Individuals, typically, are exposed to mixtures of environmental xenobiotics affecting multiple organs and acting through different xenosensors and pathways in species and cell-type specific manners. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and α-endosulfan are Persistent Organic Pollutants (POPs) and endocrine disruptors which act through different xenosensors and accumulate in the liver. Our objective in this HEALS study was to investigate the effects of the mixture of these POPs on gene expression in a human-derived hepatocyte cell line, HepaRG. We found that, in spite of having largely uncorrelated effects, TCDD and α-endosulfan, when mixed, alter the expression of genes. The combined effects of the mixture of the POPs significantly altered the expression of 100 genes (42 up- and 58 down-regulated) whereas the same concentration of either POP alone did not alter significantly the expression of these genes. For 32 other genes, selective inhibitory crosstalk between TCDD and α-endosulfan was observed. One of the POPs inhibited the effect, on gene expression, of the other in the mixture although, when used alone, that POP did not affect expression. The expression of another 82 genes was significantly altered (up- or down-regulated) by a single POP. The addition of the second POP either increased, in the same direction, the effect on gene expression or had no further effect. At low concentrations (0.2 nM TCDD and 1 μM α-endosulfan), the POPs still had significant effects and the levels of expression of the corresponding proteins were found to be affected for some genes. Particularly striking was the 80-90% inhibition, by the mixture, of the expression of a number of genes of several hepatic intermediary metabolic pathways (glycerolipid metabolism, FXR/RXR activation, glycolysis/gluconeogenesis, retinoid and bile acid biosynthesis), whereas each pollutant alone had only a moderate effect.

Investigation of CYP 3A5 and ABCB1 gene polymorphisms in the long-term following renal transplantation: Effects on tacrolimus exposure and kidney function

The clinical use of tacrolimus (Tac) is complicated by the large inter-individual variability in its pharmacokinetics as well as by chronic adverse effects on renal function. The main goal of this study was to evaluate the potential influence of cytochrome P450 3A5 (CYP 3A5) and ATP-binding cassette transporter B1 (ABCB1) gene polymorphisms on Tac dose requirements and dose-adjusted concentrations in different long-term periods following renal transplantation. Another aim was to investigate whether these polymorphisms affect renal function in late post-transplant period. A total of 91 renal transplant recipients were enrolled for genotyping analysis, and 53 of these entered into a pharmacokinetic-pharmacogenetic study. Allele-specific polymerase chain reaction was used for CYP 3A5 and ABCB1 polymorphism determination. Pharmacokinetic data (dose, trough concentration and dose-adjusted concentration of Tac) and renal function parameters [creatinine (Cre) clearance and serum Cre level] were analyzed in relation to patient genotype at 6, 12 and 24 months after transplantation. Also, linear regression analysis was performed to evaluate the effect of CYP 3A5 and ABCB1 genotypes on Tac exposure and renal function up to 24 months post-transplant. Individuals carrying the CYP 3A5*1/*3 genotype had higher Tac dose requirements than CYP 3A5*3/*3 carriers at 6, 12 and 24 months after renal transplantation. The results revealed that ABCB1 polymorphism did not influence Tac dose requirements independently. Regression analysis showed that CYP 3A5 influenced the Tac dose-adjusted concentration as well as renal function up to 24 months post-transplant. These findings confirmed that CYP 3A5 polymorphism represents the most important determinant of Tac dose and exposure in the late period following renal transplantation. Furthermore, the obtained results indicate that the decline in renal function may be more pronounced in patients with CYP 3A5*1 in the long-term period after renal transplantation.

Determination of a Degradation Constant for CYP3A4 by Direct Suppression of mRNA in a Novel Human Hepatocyte Model, HepatoPac

Accurate determination of rates of de novo synthesis and degradation of cytochrome P450s (P450s) has been challenging. There is a high degree of variability in the multiple published values of turnover for specific P450s that is likely exacerbated by differences in methodologies. For CYP3A4, reported half-life values range from 10 to 140 hours. An accurate value for kdeg has been identified as a major limitation for prediction of drug interactions involving mechanism-based inhibition and/or induction. Estimation of P450 half-life from in vitro test systems, such as human hepatocytes, is complicated by differential decreased enzyme function over culture time, attenuation of the impact of enzyme loss through inclusion of glucocorticoids in media, and viability limitations over long-term culture times. HepatoPac overcomes some of these challenges by providing extended stability of enzymes (2.5 weeks in our hands). As such it is a unique tool for studying rates of enzyme degradation achieved through modulation of enzyme levels. CYP3A4 mRNA levels were rapidly depleted by >90% using either small interfering RNA or addition of interleukin-6, which allowed an estimation of the degradation rate constant for CYP3A protein over an incubation time of 96 hours. The degradation rate constant of 0.0240 ± 0.005 hour(-1) was reproducible in hepatocytes from five different human donors. These donors also reflected the overall population with respect to CYP3A5 genotype. This methodology can be applied to additional enzymes and may provide a more accurate in vitro derived kdeg value for predicting clinical drug-drug interaction outcomes.

Fatal methadone toxicity: potential role of CYP3A4 genetic polymorphism

Methadone is difficult to administer as a therapeutic agent because of a wide range of interindividual pharmacokinetics, likely due to genetic variability of the CYP450 enzymes responsible for metabolism to its principal metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP). CYP3A4 is one of the primary CYP450 isoforms responsible for the metabolism of methadone to EDDP in humans. The purpose of this study was to evaluate the role of CYP3A4 genetic polymorphisms in accidental methadone fatalities. A study cohort consisting of 136 methadone-only and 92 combined methadone/benzodiazepine fatalities was selected from cases investigated at the West Virginia and Kentucky Offices of the Chief Medical Examiner. Seven single nucleotide polymorphisms (SNPs) were genotyped within the CYP3A4 gene. Observed allelic and genotypic frequencies were compared with expected frequencies obtained from The National Center for Biotechnology Information dbSNP database. SNPs rs2242480 and rs2740574 demonstrated an apparent enrichment within the methadone-only overdose fatalities compared with the control group and the general population. This enrichment was not apparent in the methadone/benzodiazepine cases for these two SNPs. Our findings indicate that there may be two or more SNPs on the CYP3A4 gene that cause or contribute to the methadone poor metabolizer phenotype.

The Influence of the CYP3A4*22 Polymorphism and CYP2D6 Polymorphisms on Serum Concentrations of Aripiprazole, Haloperidol, Pimozide, and Risperidone in Psychiatric Patients

INTRODUCTION

Cytochrome P450 3A4 (CYP3A4) is involved in the metabolism of greater than 50% of the prescribed drugs. Recently, the CYP3A4*22 allele was reported to be associated with lower CYP3A4 expression and activity. Quetiapine, an antipsychotic metabolized by only CYP3A4, displayed higher serum levels in CYP3A4*22 carriers. Aripiprazole, haloperidol, pimozide, and risperidone are antipsychotics that are metabolized by CYP3A4 and CYP2D6. We investigated to which degree the CYP3A4*22 single-nucleotide polymorphism affects serum concentrations of patients receiving these drugs and compared this with the influence of CYP2D6 polymorphisms.

METHODS

Eight hundred thirty-four adult patients were included in this study, of whom 130 used aripiprazole, 312 used haloperidol, 86 used pimozide, and 396 used risperidone. Serum levels of the drug and, if available, their active metabolites were collected as well as information on dose. Patients were genotyped for CYP3A4*22 using restriction fragment length polymorphism analysis. Genotyping for CYP2D6 was done with allele-specific polymerase chain reaction.

RESULTS

No differences were found in serum (dose-corrected) concentrations of the antipsychotics between CYP3A4*22 wild-type and carrier groups. In contrast, CYP2D6 genotype did affect dose-corrected concentrations of the antipsychotics: for example, median dose-corrected concentrations were 56%, 86%, and 400% higher in predicted poor metabolizers versus extensive metabolizers for aripiprazole (P = 0.004), haloperidol (P > 0.001), and risperidone (P < 0.001), respectively, although a multiple regression analysis showed that only 4% to 17% of the variation in these concentrations could be explained by CYP2D6 status.

CONCLUSIONS

Heterozygous presence of CYP3A4*22 does not increase serum levels of antipsychotics metabolized by both CYP3A4 and CYP2D6, whereas CYP2D6 polymorphisms do affect serum levels to a limited extent.

Gender-Dimorphic Impact of PXR Genotype and Haplotype on Hepatotoxicity During Antituberculosis Treatment

Women have a higher risk of drug-induced hepatotoxicity during antituberculosis treatment (HATT) than men. We hypothesized that single nucleotide polymorphism (SNP) genotype and derived haplotype of pregnane X receptor (PXR) gene, which could regulate the expression of phase I enzyme cytochrome P450 (CYP) 3A4, had a sex-specific influence on the risk of HATT. Six SNPs of the PXR gene were sequenced. Genotypes and haplotypes of the PXR SNPs, and other potential risk factors for HATT were compared between pulmonary TB patients with and those without HATT. HATT was defined as an increase in serum transaminase level >3 times the upper limit of normal (ULN) with symptoms, or >5 times ULN without symptoms. We performed the study in a derivation and a validation cohort. Among the 355 patients with pulmonary TB in the derivation cohort, 70 (19.7%) developed HATT. Logistic regression analysis revealed the risk of HATT increased in female genotype AA at rs2461823 (OR: 6.87 [2.55-18.52]) and decreased in female genotype AA at rs7643645 (OR: 0.14 [0.02-1.02]) of PXR gene. Haplotype analysis showed that female h001101 (OR: 2.30 [1.22-4.32]) and female h000110 (OR: 2.25 [1.08-4.69]) haplotype were associated with increased HATT risk. The identified predictors were also significantly associated with female HATT risk among the 182 patients in the validation cohort. Two PXR SNP genotypes and 2 haplotypes influenced the risk of HATT only in females. The PXR SNP showed a sex-specific impact that contributed to an increased HATT risk in females.

Effect of CYP2C19 and CYP3A4 gene polymorphisms on the efficacy of bortezomib-based regimens in patients with multiple myeloma

Bortezomib is used to treat patients with multiple myeloma. It is primarily metabolized by the enzyme cytochrome P450 (CYP). Variations in the capacity of bortezomib metabolism affect the treatment outcomes and the side-effects experienced by patients. In the present study, polymorphisms in the CYP3A4 and CYP2C19 genes were analyzed by polymerase chain reaction in 56 newly-diagnosed patients with multiple myeloma. The polymorphisms analyzed included the c.681G>A, c.636G>A and c.-806C>T polymorphisms of CYP2C19. The CYP3A4 gene was sequenced after amplification and was classified into normal and mutant types. Associations between the metabolizer genotypes of CYP3A4 and CYP2C19, the therapeutic efficacy of bortezomib-based regimens, and the occurrence of peripheral neuropathy were studied. The results identified no significant differences in gender, serum β2 microglobulin, creatinine, blood albumin, isotypes, and the Durie-Salmon and International Staging System stages between the CYP2C19 poor + intermediate metabolizer types and the extensive + ultrarapid metabolizer types. In addition, it was revealed that the CYP2C19 and CYP3A4 phenotypes did not affect the efficacy of bortezomib-based regimens, nor were they correlated with peripheral neuropathy. Additional large-scale studies are required in order to evaluate the role of CYP enzymes in bortezomib treatments for patients with multiple myeloma.

Exploring the relationship between lifestyles, diets and genetic adaptations in humans

Background

One of the most important dietary shifts underwent by human populations began to occur in the Neolithic, during which new modes of subsistence emerged and new nutrients were introduced in diets. This change might have worked as a selective pressure over the metabolic pathways involved in the breakdown of substances extracted from food. Here we applied a candidate gene approach to investigate whether in populations with different modes of subsistence, diet-related genetic adaptations could be identified in the genes AGXT, PLRP2, MTRR, NAT2 and CYP3A5.

Results

At CYP3A5, strong signatures of positive selection were detected, though not connected to any dietary variable, but instead to an environmental factor associated with the Tropic of Cancer. Suggestive signals of adaptions that could indeed be connected with differences in dietary habits of populations were only found for PLRP2 and NAT2. Contrarily, the demographic history of human populations seemed enough to explain patterns of diversity at AGXT and MTRR, once both conformed the evolutionary expectations under selective neutrality.

Conclusions

Accumulated evidence indicates that CYP3A5 has been under adaptive evolution during the history of human populations. PLRP2 and NAT2 also appear to have been modelled by some selective constrains, although clear support for that did not resist to a genome wide perspective. It is still necessary to clarify which were the biological mechanisms and the environmental factors involved as well as their interactions, to understand the nature and strength of the selective pressures that contributed to shape current patterns of genetic diversity at those loci.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0212-1) contains supplementary material, which is available to authorized users.

Confounding factors and genetic polymorphism in the evaluation of individual steroid profiling

In the fight against doping, steroid profiling is a powerful tool to detect drug misuse with endogenous anabolic androgenic steroids. To establish sensitive and reliable models, the factors influencing profiling should be recognised. We performed an extensive literature review of the multiple factors that could influence the quantitative levels and ratios of endogenous steroids in urine matrix. For a comprehensive and scientific evaluation of the urinary steroid profile, it is necessary to define the target analytes as well as testosterone metabolism. The two main confounding factors, that is, endogenous and exogenous factors, are detailed to show the complex process of quantifying the steroid profile within WADA-accredited laboratories. Technical aspects are also discussed as they could have a significant impact on the steroid profile, and thus the steroid module of the athlete biological passport (ABP). The different factors impacting the major components of the steroid profile must be understood to ensure scientifically sound interpretation through the Bayesian model of the ABP. Not only should the statistical data be considered but also the experts in the field must be consulted for successful implementation of the steroidal module.

CHRNA3 and CYP3A5*3 genotype, lung function and chronic obstructive pulmonary disease in the general population

OBJECTIVE

Genetic variations are most likely an additional risk factor besides tobacco smoking per se for the risk of chronic obstructive pulmonary disease (COPD). In this study, we compared genetic variants influencing the effect of smoking on COPD, that is, the effect of the well-known splicing defect polymorphism, CYP3A5*3 (rs776746), identified before genome-wide association studies, with the genome-wide association studies identified CHRNA3 (rs1051730) polymorphism on the risk of decreased lung function and COPD.

MATERIALS AND METHODS

In all, 10 605 participants from the general population were genotyped. Information on spirometry, hospital admissions and smoking behaviour was recorded. Endpoints were lung function and COPD.

RESULTS

For CHRNA3, the percentage of forced expiratory volume in 1 s (FEV1%) predicted was 89.3, 90.6 and 92.4% in homozygous, heterozygous and noncarrier ever-smokers (P-trend<0.001). The corresponding values for forced vital capacity percentage (FVC%) predicted were 94.5, 95.2 and 96.7% (P-trend<0.001), and for FEV1/FVC ratio, the values were 0.753, 0.760 and 0.764 (P-trend=0.008). The odds ratio for COPD in homozygous versus noncarrier ever-smokers was 1.5 [95% confidence interval (CI) 1.3-1.9] for COPD hospitalization, 1.3 (95% CI 1.1-1.6) for COPD defined as FEV1/FVC less than lower limit of normal, 1.3 (95% CI 1.0-1.5) for the Global Initiative for Chronic Obstructive Lung Disease category 1-4 (GOLD 1-4), 1.2 (95% CI 1.0-1.5) for GOLD 2-4 and 1.5 (95% CI 1.1-2.2) for GOLD 3-4. This association could not be found in never-smokers. No association was found for CYP3A5*3.

CONCLUSION

The CHRNA3 genotype is associated with decreased lung function and risk of COPD among ever-smokers, whereas this was not the case for CYP3A5*3.