Genetic findings and functional studies of human CYP3A5 single nucleotide polymorphisms in different ethnic groups

Evaluation of Published Population Pharmacokinetic Models to Inform Tacrolimus Therapy in Adult Lung Transplant Recipients

BACKGROUND

The applicability of currently available tacrolimus population pharmacokinetic models in guiding dosing for lung transplant recipients is unclear. In this study, the predictive performance of relevant tacrolimus population pharmacokinetic models was evaluated for adult lung transplant recipients.

METHODS

Data from 43 lung transplant recipients (1021 tacrolimus concentrations) administered an immediate-release oral formulation of tacrolimus were used to evaluate the predictive performance of 17 published population pharmacokinetic models for tacrolimus. Data were collected from immediately after transplantation up to 90 days after transplantation. Model performance was evaluated using (1) prediction-based assessments (bias and imprecision) of individual predicted tacrolimus concentrations at the fourth dosing based on 1 to 3 previous dosings and (2) simulation-based assessment (prediction-corrected visual predictive check; pcVPC). Both assessments were stratified based on concomitant azole antifungal use. Model performance was clinically acceptable if the bias was within ±20%, imprecision was ≤20%, and the 95% confidence interval of bias crossed zero.

RESULTS

In the presence of concomitant antifungal therapy, no model showed acceptable performance in predicting tacrolimus concentrations at the fourth dosing (n = 33), and pcVPC plots displayed poor model fit to the data set. However, this fit slightly improved in the absence of azole antifungal use, where 4 models showed acceptable performance in predicting tacrolimus concentrations at the fourth dosing (n = 33).

CONCLUSIONS

Although none of the evaluated models were appropriate in guiding tacrolimus dosing in lung transplant recipients receiving concomitant azole antifungal therapy, 4 of these models displayed potential applicability in guiding dosing in recipients not receiving concomitant azole antifungal therapy. However, further model refinement is required before the widespread implementation of such models in clinical practice.

Effects of CYP3A5 Genotype on Tacrolimus Pharmacokinetics and Graft-versus-Host Disease Incidence in Allogeneic Hematopoietic Stem Cell Transplantation

Tacrolimus (Tac) is pivotal in preventing acute graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (alloHSCT). It has been reported that genetic factors, including CYP3A5*3 and CYP3A4*22 polymorphisms, have an impact on Tac metabolism, dose requirement, and response to Tac. There is limited information regarding this topic in alloHSCT. The CYP3A5 genotype and a low Tac trough concentration/dose ratio (Tac C0/D ratio) can be used to identify fast metabolizers and predict the required Tac dose to achieve target concentrations earlier. We examined 62 Caucasian alloHSCT recipients with a fast metabolizer phenotype (C0/dose ratio ≤ 1.5 ng/mL/mg), assessing CYP3A5 genotypes and acute GVHD incidence. Forty-nine patients (79%) were poor metabolizers (2 copies of the variant *3 allele) and 13 (21%) were CYP3A5 expressers (CYP3A5*1/*1 or CYP3A5*1/*3 genotypes). CYP3A5 expressers had lower C0 at 48 h (3.7 vs. 6.2 ng/mL, p = 0.03) and at 7 days (8.6 vs. 11.4 ng/mL, p = 0.04) after Tac initiation, tended to take longer to reach Tac therapeutic range (11.8 vs. 8.9 days, p = 0.16), and had higher incidence of both global (92.3% vs. 38.8%, p < 0.001) and grade II-IV acute GVHD (61.5% vs. 24.5%, p = 0.008). These results support the adoption of preemptive pharmacogenetic testing to better predict individual Tac initial dose, helping to achieve the therapeutic range and reducing the risk of acute GVHD earlier.

When the same treatment has different response: The role of pharmacogenomics in statin therapy

Statins, also known as HMG-CoA reductase inhibitors, are one of the most potently prescribed and thoroughly researched medications, predominantly utilized for managing cardiovascular diseases by modulating serum cholesterol levels. Despite the well-documented efficacy of statins in reducing overall mortality via attenuating the risk of cardiovascular diseases, notable interindividual variability in therapeutic responses persists as such variability could compromise the lipid-lowering efficacy of the drug, potentially increasing susceptibility to adverse effects or attenuating therapeutic outcomes.This phenomenon has catalysed a growing interest in the scientific community to explore common genetic polymorphisms within genes that encode for pivotal enzymes within the pharmacokinetic pathways of statins. In our review, we focus to provide insight into potentially clinically relevant polymorphisms associated with statins' pharmacokinetic participants and assess their consequent implications on modulating the therapeutic outcomes of statins among distinct genetic carrier.

Interethnic differences in drug response: projected impact of genetic variations in the Saudi population

Ethnicity is known to have an impact on drug responses. This is particularly important for drugs that have a narrow therapeutic window, nonlinearity in pharmacokinetics and are metabolized by enzymes that demonstrate genetic polymorphisms. However, most clinical trials are conducted among Caucasians, which might limit the usefulness of the findings of such studies for other ethnicities. The representation of participants from Saudi Arabia in global clinical trials is low. Therefore, there is a paucity of evidence to assess the impact of ethnic variability in the Saudi population on drug response. In this article, the authors assess the projected impact of genetic polymorphisms in drug-metabolizing enzymes and drug targets on drug response in the Saudi population.

PharmVar GeneFocus: CYP3A5

The Pharmacogene Variation Consortium (PharmVar) catalogs star (*) allele nomenclature for the polymorphic human CYP3A5 gene. Genetic variation within the CYP3A5 gene locus impacts the metabolism of several clinically important drugs, including the immunosuppressants tacrolimus, sirolimus, cyclosporine, and the benzodiazepine midazolam. Variable CYP3A5 activity is of clinical importance regarding tacrolimus metabolism. This GeneFocus provides a CYP3A5 gene summary with a focus on aspects regarding standardized nomenclature. In addition, this review also summarizes recent changes and updates, including the retirement of several allelic variants and provides an overview of how PharmVar CYP3A5 star allele nomenclature is utilized by the Pharmacogenomics Knowledgebase (PharmGKB) and the Clinical Pharmacogenetics Implementation Consortium (CPIC).

Impact of CYP3A5 Status on the Clinical and Financial Outcomes Among African American Kidney Transplant Recipients

Pharmacogenetic profiling of transplant recipients demonstrates that the marked variation in the metabolism of immunosuppressive medications, particularly tacrolimus, is related to genetic variants. Patients of African ancestry are less likely to carry loss-of-function (LoF) variants in the CYP3A5 gene and therefore retain a rapid metabolism phenotype and higher clearance of tacrolimus. Patients with this rapid metabolism typically require higher dosing to achieve therapeutic trough concentrations. This study aims to further characterize the impact of CYP3A5 genotype on clinical outcomes and financial expenditure.

Quantitative Proteomics in Translational Absorption, Distribution, Metabolism, and Excretion and Precision Medicine

A reliable translation of in vitro and preclinical data on drug absorption, distribution, metabolism, and excretion (ADME) to humans is important for safe and effective drug development. Precision medicine that is expected to provide the right clinical dose for the right patient at the right time requires a comprehensive understanding of population factors affecting drug disposition and response. Characterization of drug-metabolizing enzymes and transporters for the protein abundance and their interindividual as well as differential tissue and cross-species variabilities is important for translational ADME and precision medicine. This review first provides a brief overview of quantitative proteomics principles including liquid chromatography-tandem mass spectrometry tools, data acquisition approaches, proteomics sample preparation techniques, and quality controls for ensuring rigor and reproducibility in protein quantification data. Then, potential applications of quantitative proteomics in the translation of in vitro and preclinical data as well as prediction of interindividual variability are discussed in detail with tabulated examples. The applications of quantitative proteomics data in physiologically based pharmacokinetic modeling for ADME prediction are discussed with representative case examples. Finally, various considerations for reliable quantitative proteomics analysis for translational ADME and precision medicine and the future directions are discussed. SIGNIFICANCE STATEMENT: Quantitative proteomics analysis of drug-metabolizing enzymes and transporters in humans and preclinical species provides key physiological information that assists in the translation of in vitro and preclinical data to humans. This review provides the principles and applications of quantitative proteomics in characterizing in vitro, ex vivo, and preclinical models for translational research and interindividual variability prediction. Integration of these data into physiologically based pharmacokinetic modeling is proving to be critical for safe, effective, timely, and cost-effective drug development.

Tacrolimus Therapy in Adult Heart Transplant Recipients: Evaluation of a Bayesian Forecasting Software

BACKGROUND

Therapeutic drug monitoring is recommended to guide tacrolimus dosing because of its narrow therapeutic window and considerable pharmacokinetic variability. This study assessed tacrolimus dosing and monitoring practices in heart transplant recipients and evaluated the predictive performance of a Bayesian forecasting software using a renal transplant-derived tacrolimus model to predict tacrolimus concentrations.

METHODS

A retrospective audit of heart transplant recipients (n = 87) treated with tacrolimus was performed. Relevant data were collected from the time of transplant to discharge. The concordance of tacrolimus dosing and monitoring according to hospital guidelines was assessed. The observed and software-predicted tacrolimus concentrations (n = 931) were compared for the first 3 weeks of oral immediate-release tacrolimus (Prograf) therapy, and the predictive performance (bias and imprecision) of the software was evaluated.

RESULTS

The majority (96%) of initial oral tacrolimus doses were guideline concordant. Most initial intravenous doses (93%) were lower than the guideline recommendations. Overall, 36% of initial tacrolimus doses were administered to transplant recipients with an estimated glomerular filtration rate of <60 mL/min/1.73 m despite recommendations to delay the commencement of therapy. Of the tacrolimus concentrations collected during oral therapy (n = 1498), 25% were trough concentrations obtained at steady-state. The software displayed acceptable predictions of tacrolimus concentration from day 12 (bias: -6%; 95%confidence interval, -11.8 to 2.5; imprecision: 16%; 95% confidence interval, 8.7-24.3) of therapy.

CONCLUSIONS

Tacrolimus dosing and monitoring were discordant with the guidelines. The Bayesian forecasting software was suitable for guiding tacrolimus dosing after 11 days of therapy in heart transplant recipients. Understanding the factors contributing to the variability in tacrolimus pharmacokinetics immediately after transplant may help improve software predictions.

Precision Dosing for Tacrolimus Using Genotypes and Clinical Factors in Kidney Transplant Recipients of European Ancestry

Genetic variation in the CYP3A4 and CYP3A5 (CYP3A4/5) genes, which encode the key enzymes in tacrolimus metabolism, is associated with tacrolimus clearance and dose requirements. Tacrolimus has a narrow therapeutic index with high intra- and intersubject variability, in part because of genetic variation. High tacrolimus clearance and low trough concentration are associated with a greater risk for rejection, whereas high troughs are associated with calcineurin-induced toxicity. The objective of this study was to develop a model of tacrolimus clearance with a dosing equation accounting for genotypes and clinical factors in adult kidney transplant recipients of European ancestry that could preemptively guide dosing. Recipients receiving immediate-release tacrolimus for maintenance immunosuppression from 2 multicenter studies were included. Participants in the GEN03 study were used for tacrolimus model development (n = 608 recipients) and was validated by prediction performance in the DeKAF Genomics study (n = 1361 recipients). Nonlinear mixed-effects modeling was used to develop the apparent oral tacrolimus clearance (CL/F) model. CYP3A4/5 genotypes and clinical covariates were tested for their influence on CL/F. The predictive performance of the model was determined by assessing the bias (median prediction error [ME] and median percentage error [MPE]) and the precision (root median squared error [RMSE]) of the model. CYP3A5*3, CYP3A4*22, corticosteroids, calcium channel blocker and antiviral drug use, age, and diabetes significantly contributed to the interindividual variability of oral tacrolimus apparent clearance. The bias (ME, MPE) and precision (RMSE) of the final model was good, 0.49 ng/mL, 6.5%, and 3.09 ng/mL, respectively. Prospective testing of this equation is warranted.

Single Nucleotide Polymorphism Induces Divergent Dynamic Patterns in CYP3A5: A Microsecond Scale Biomolecular Simulation of Variants Identified in Sub-Saharan African Populations

Pharmacogenomics aims to reveal variants associated with drug response phenotypes. Genes whose roles involve the absorption, distribution, metabolism, and excretion of drugs, are highly polymorphic between populations. High coverage whole genome sequencing showed that a large proportion of the variants for these genes are rare in African populations. This study investigated the impact of such variants on protein structure to assess their functional importance. We used genetic data of CYP3A5 from 458 individuals from sub-Saharan Africa to conduct a structural bioinformatics analysis. Five missense variants were modeled and microsecond scale molecular dynamics simulations were conducted for each, as well as for the CYP3A5 wildtype and the Y53C variant, which has a known deleterious impact on enzyme activity. The binding of ritonavir and artemether to CYP3A5 variant structures was also evaluated. Our results showed different conformational characteristics between all the variants. No significant structural changes were noticed. However, the genetic variability seemed to act on the plasticity of the protein. The impact on drug binding might be drug dependant. We concluded that rare variants hold relevance in determining the pharmacogenomics properties of populations. This could have a significant impact on precision medicine applications in sub-Saharan Africa.

Antiplatelet regimens for Asian patients with ischemic stroke or transient ischemic attack: a systematic review and network meta-analysis

Background

The optimal antiplatelet treatment for the secondary prevention of non-cardioembolic stroke or transient ischemic attack (TIA) remains uncertain in Asians.

Methods

We searched for eligible randomized control trials in Medline, Embase, and the Cochrane Library. A Bayesian network meta-analysis (NMA) was performed to assess the efficacy and safety of antiplatelet regimens with placebo as the control. Each therapy was compared using relative risk ratios (RR) and 95% credible intervals (CrI), and ranked according to the value of the surface under the cumulative ranking curve.

Results

A total of 84,103 patients from 32 studies were included: patients in used aspirin (n=26,834); cilostazol (n=3,303); clopidogrel (n=12,406); prasugrel (n=1,885); sarpogrelate (n=752); ticagrelor (n=1,933); ticlopidine (n=1,644); triflusal (n=391); aspirin plus cilostazol (n=1,120), aspirin plus clopidogrel (n=4,623); aspirin plus dipyridamole (n=10,853); aspirin plus ticagrelor (n=5,859); aspirin plus ticlopidine (n=132). Patients who used aspirin plus clopidogrel and cilostazol had a lower risk of recurrent stroke than those who used placebo. Patients administered with aspirin plus ticagrelor, aspirin plus clopidogrel, and cilostazol had a lower risk of composite vascular events than those administered placebo. Patients administered aspirin plus ticagrelor had a higher risk of major bleeding than those administered placebo. Clustered three-dimensional rank plots of recurrent stroke, major bleeding, and composite vascular events demonstrated that cilostazol had higher values of the surface under the cumulative ranking curve than other treatments.

Conclusions

Of the antiplatelet regimens, cilostazol showed the best net clinical benefits than other antiplatelet regimens in Asians with non-cardioembolic stroke or TIA.

Metabolism of Long-Acting Rilpivirine After Intramuscular Injection: HIV Prevention Trials Network Study 076 (HPTN 076)

A long-acting injectable formulation of rilpivirine (RPV), a non-nucleoside reverse transcriptase inhibitor, is currently under investigation for use in human immunodeficiency virus (HIV) maintenance therapy. We previously characterized RPV metabolism after oral dosing and identified seven metabolites: four metabolites resulting from mono- or dioxygenation of the 2,6-dimethylphenyl ring itself or either of the two methyl groups located on that ring, one N-linked RPV glucuronide conjugate, and two O-linked RPV glucuronides produced via glucuronidation of mono- and dihydroxymethyl metabolites. However, as is true for most drugs, the metabolism of RPV after injection has yet to be reported. The phase II clinical trial HPTN 076 enrolled 136 HIV-uninfected women and investigated the safety and acceptability of long-acting injectable RPV for use in HIV pre-exposure prophylaxis. Through the analysis of plasma samples from 80 of these participants in the active product arm of the study, we were able to detect 2 metabolites after intramuscular injection of long-acting RPV, 2-hydroxymethyl-RPV, and RPV N-glucuronide. Of the total of 80 individuals, 72 participants exhibited detectable levels of 2-hydroxymethyl-RPV in plasma samples whereas RPV N-glucuronide was detectable in plasma samples of 78 participants. In addition, RPV N-glucuronide was detectable in rectal fluid, cervicovaginal fluid, and vaginal tissue. To investigate potential genetic variation in genes encoding enzymes relevant to RPV metabolism, we isolated genomic DNA and performed next-generation sequencing of CYP3A4, CYP3A5, UGT1A1 and UGT1A4. From these analyses, four missense variants were detected for CYP3A4 whereas one missense variant and one frameshift variant were detected for CYP3A5. A total of eight missense variants of UGT1A4 were detected, whereas two variants were detected for UGT1A1; however, these variants did not appear to account for the observed interindividual variability in metabolite levels. These findings provide insight into the metabolism of long-acting RPV and contribute to an overall understanding of metabolism after oral dosing versus injection. ClinicalTrials.gov Identifier: NCT02165202.

CYP2C9 inhibits the invasion and migration of esophageal squamous cell carcinoma via downregulation of HDAC

Cytochrome P450 2C9 (CYP2C9) is involved in the metabolism of cancer drugs and exogenous carcinogens. In our study, CYP2C9 was downregulated in multiple cohorts of human esophageal squamous cell carcinoma (ESCC). Until now, its role and epigenetic regulation of CYP2C9 repression in ESCC remain poorly understood. CYP2C9 repression in collected ESCC patient tumor tissues was demonstrated by RT-qPCR and Western blot. The histone acetylation level was carried out by the treatment of histone deacetylase inhibitor TSA and RNA interference. Epigenetic analysis revealed that the increased expression of CYP2C9 in KYSE-150 and TE1 cells was characterized by inhibition of HDAC8 and HDAC1, respectively. TSA decreased the levels of HDAC occupancy around CYP2C9 promoter region greatly. Overexpression of CYP2C9 reduced the invasion and migration of ESCC cells.

Temporary decrease in tacrolimus clearance in cytochrome P450 3A5 non-expressors early after living donor kidney transplantation: Effect of interleukin 6-induced suppression of the cytochrome P450 3A gene

Tacrolimus is important for immunosuppression in kidney transplantation. In this historical cohort and in vitro study, we evaluated the changes in tacrolimus pharmacokinetics early after living donor kidney transplantation and the effects of interleukin (IL)-6 on cytochrome P450 3A4 (CYP3A4) and cytochrome P450 3A5 (CYP3A5) expression. In the historical cohort study, 22 patients who met the inclusion criteria were classified into CYP3A5 expressors and non-expressors (n = 16 and 6, respectively). The blood tacrolimus concentration per dose ratio (C/D) temporarily increased post-kidney transplantation on days 3-4 only in CYP3A5 non-expressors. The effects of IL-6 on CYP3A4 and CYP3A5 expression were also investigated in vitro using HepG2 and Caco-2 cells. IL-6 induced a significant concentration- and time-dependent decrease in CYP3A4 and CYP3A5 expression in both cells. The mean CYP3A4 expression level at 12 hours after IL-6 exposure (% of 0 hour) was 44.0 and 62.6 in HepG2 and Caco-2 cells, respectively, whereas the CYP3A5 expression level was 30.7 and 52.4, respectively. We hypothesize that CYP3A5 non-expressors might exhibit a temporary decrease in the oral clearance of tacrolimus via an increase in serum IL-6 concentrations early after kidney transplantation. These results may help develop strategies to improve kidney transplant outcome.

Using a pharmacogenetic clinical decision support system to improve psychopharmacotherapy dosing in patients with affective disorders

Objectives Although pharmacogenetic tests provide the information on a genotype and the predicted phenotype, these tests do not themselves provide the interpretation of data for a physician. Currently, there are approximately two dozen pharmacogenomic clinical decision support systems (CDSSs) used in psychiatry. Implementation of the CDSSs forming the recommendations on drug and dose selection according to the results of pharmacogenetic testing is an urgent task. Fulfillment of this task will allow increasing the efficacy of therapy and decreasing the risk of undesirable side effects. Methods The study included 118 male patients (48 in the main group and 70 in the control group) with affective disorders and comorbid alcohol use disorder. To evaluate the efficacy and safety of therapy, several international psychometric scales and rating scales to measure side effects were used. Genotyping was performed using the real-time polymerase chain reaction with allele-specific hybridization. Pharmacogenetic testing results were interpreted using free software PGX2 (LLE Medicine, Russian Federation, Biomedical Cluster of Skolkovo, Moscow Innovative Cluster; www.pgx2.com). Results The statistically significant differences across the scores on psychometric scales were revealed. For instance, the total score on the Hamilton Rating Scale for Depression by day 9 was 9.0 [8.0; 10.0] for the main group and 11.0 [10.0; 12.0] (p<0.001) for the control group and by day 16 it was 4.0 [2.0; 6.0] for the main group and 14.0 [13.0; 14.0] (p<0.001) for the control group. The UKU Side-Effect Rating Scale (UKU) also revealed a statistically significant difference. The total score on the UKU scale by day 9 was 4.0 [4.0; 5.0] for the main group and 5.0 [5.0; 6.0] (p<0.001) for the control group and by day 16 this difference grew significantly: 3.0 [0.0; 4.2] for the main group and 9.0 [7.0; 11.0] (p<0.001) for the control group. Conclusions Pharmacogenetic-guided personalization of the drug dose in patients with affective disorders and comorbid alcohol use disorder can reduce the risk of undesirable side effects and pharmacoresistance. It allows recommending the use of pharmacogenetic CDSSs for optimizing drug dosage.

Effect of the Most Relevant CYP3A4 and CYP3A5 Polymorphisms on the Pharmacokinetic Parameters of 10 CYP3A Substrates

Several cytochrome P450 (CYP) CYP3A polymorphisms were associated with reduced enzyme function. We aimed to evaluate the influence of these alleles on the pharmacokinetic parameters (PK) of several CYP3A substrates. We included 251 healthy volunteers who received a single dose of ambrisentan, atorvastatin, imatinib, aripiprazole, fentanyl, amlodipine, donepezil, olanzapine, fesoterodine, or quetiapine. The volunteers were genotyped for CYP3A4 and CYP3A5 polymorphisms by qPCR. To compare the PK across studies, measurements were corrected by the mean of each parameter for every drug and were logarithmically transformed. Neither CYP3A phenotype nor individual CYP3A4 or CYP3A5 polymorphisms were significantly associated with differences in PK. However, regarding the substrates that are exclusively metabolized by CYP3A, we observed a higher normalized AUC (p = 0.099) and a tendency of lower normalized Cl (p = 0.069) in CYP3A4 mutated allele carriers what was associated with diminished drug metabolism capacity. CYP3A4 polymorphisms did not show a pronounced influence on PK of the analysed drugs. If so, their impact could be detectable in a very small percentage of subjects. Although there are few subjects carrying CYP3A4 double mutations, the effect in those might be relevant, especially due to the majority of subjects lacking the CYP3A5 enzyme. In heterozygous subjects, the consequence might be less noticeable due to the high inducible potential of the CYP3A4 enzyme.

Lack of Influence by CYP3A4 and CYP3A5 Genotypes on Pain Relief by Hydrocodone in Postoperative Cesarean Section Pain Management

Background

Genetic polymorphisms of cytochrome P450 are contributors to variability in individual response to drugs. Within the P450 family, CYP2D6 is responsible for metabolizing hydrocodone, a widely prescribed opioid for pain management. Alternatively, CYP3A4 and CYP3A5 can form norhydrocodone and dihydrocodeine. We have previously found that in a postcesarean section cohort, the rate of hydromorphone formation was dependent on the genotype of CYP2D6 and that plasma hydromorphone, not hydrocodone, was predictive of pain relief.

Method

Blood was obtained from a postcesarean cohort that were surveyed for pain response and common side effects. Plasma samples were genotyped for CYP3A4/5, and their hydrocodone concentrations were measured by LC-MS. R statistical software was used to check for differences in the outcomes due to CYP3A4/5 and CYP2D6, and a multivariate regression model was fit to determine factors associated with pain score.

Results

Two-way ANOVA between CYP3A4/A5 and CYP2D6 phenotypes revealed that the former variants did not have a statistical significance on the outcomes, and only CYP2D6 phenotypes had a significant effect on total dosage (P = 0.041). Furthermore, a 3-way ANOVA analysis showed that CYP2D6 (P = 0.036) had a predictive effect on plasma hydromorphone concentrations, and CYP3A4/A5 did not have any effect on the measured outcomes.

Conclusions

With respect to total dosages in a cesarean section population, these results confirm that CYP2D6 phenotypes are predictors for plasma hydromorphone concentration and pain relief, but CYP3A4/A5 phenotypes have no influence on pain relief or on side effects.

Tacrolimus exposure early after lung transplantation and exploratory associations with acute cellular rejection

AIMS

To (i) describe tacrolimus (TAC) pre-dose concentrations (C₀), (ii) calculate apparent oral TAC clearance (CL/F_HCT) adjusted for measured haematocrit (HCTi) and standardised to a HCT of 45%, across three observation time points and (iii) explore if low TAC C₀ or high mean CL/F_HCT are associated with an increased risk of rejection episodes early after lung transplantation.

METHODS

TAC whole blood concentration-time profiles and transbronchial biopsies were performed prospectively at weeks 3, 6 and 12 after lung transplantation. The TAC pre-dose concentration (C₀) was measured, and CL/F_HCT was determined using non-compartmental analysis. The associations between TAC C₀ and CL/F_HCT and rejection status were explored using repeated measures logistic regression.

RESULTS

Eighteen patients provided 377 TAC whole blood concentrations. Considerable variability around the median (IQR) CL/F_HCT 6.8 (4.2-15.9) L h^-1, and the median C₀ 12.7 (9.9-16.6) μg L^-1 was noted. Despite adjustment for haematocrit, a significant decrease was observed in CL/F_HCT in all patients over time: CL/F_HCT 14 (5.4-23) at week 3, CL/F_HCT 7.7 (4.5-12) at week 6 and CL/F_HCT 3.9 (2.4-11) L h^-1 at week 12 (p < 0.01). Seven (38.9%) patients experienced a single grade 2 rejection, whilst 11 (61.1%) patients experienced no rejection. Higher TAC C₀ were associated with a reduced risk of rejection OR 0.68 (95% CI 0.51-0.91, p = 0.02), and greater mean CL/F_HCT was associated with an increased risk of rejection OR 1.34 (95% CI 1.01-1.81 p = 0.04).

CONCLUSION

Monitoring TAC C₀, HCT and CL/F_HCT in patients after lung transplantation may assist clinicians in detecting patients at risk of acute rejection and may guide future research into TAC and HCT monitoring after lung transplantation.

Pharmacogenetic landscape of Metabolic Syndrome components drug response in Tunisia and comparison with worldwide populations

Genetic variation is an important determinant affecting either drug response or susceptibility to adverse drug reactions. Several studies have highlighted the importance of ethnicity in influencing drug response variability that should be considered during drug development. Our objective is to characterize the genetic variability of some pharmacogenes involved in the response to drugs used for the treatment of Metabolic Syndrome (MetS) in Tunisia and to compare our results to the worldwide populations. A set of 135 Tunisians was genotyped using the Affymetrix Chip 6.0 genotyping array. Variants located in 24 Very Important Pharmacogenes (VIP) involved in MetS drug response were extracted from the genotyping data. Analysis of variant distribution in Tunisian population compared to 20 worldwide populations publicly available was performed using R software packages. Common variants between Tunisians and the 20 investigated populations were extracted from genotyping data. Multidimensional screening showed that Tunisian population is clustered with North African and European populations. The greatest divergence was observed with the African and Asian population. In addition, we performed Inter-ethnic comparison based on the genotype frequencies of five VIP biomarkers. The genotype frequencies of the biomarkers rs3846662, rs1045642, rs7294 and rs12255372 located respectively in HMGCR, ABCB1, VKORC1 and TCF7L2 are similar between Tunisian, Tuscan (TSI) and European (CEU). The genotype frequency of the variant rs776746 located in CYP3A5 gene is similar between Tunisian and African populations and different from CEU and TSI. The present study shows that the genetic make up of the Tunisian population is relatively complex in regard to pharmacogenes and reflects previous historical events. It is important to consider this ethnic difference in drug prescription in order to optimize drug response to avoid serious adverse drug reactions. Taking into account similarities with other neighboring populations, our study has an impact not only on the Tunisian population but also on North African population which are underrepresented in pharmacogenomic studies.

The role of hepatic cytochrome P450s in the cytotoxicity of dronedarone

Dronedarone is used to treat patients with cardiac arrhythmias and has been reported to be associated with liver injury. Our previous mechanistic work demonstrated that DNA damage-induced apoptosis contributes to the cytotoxicity of dronedarone. In this study, we examined further the underlying mechanisms and found that after a 24-h treatment of HepG2 cells, dronedarone caused cytotoxicity, G1-phase cell cycle arrest, suppression of topoisomerase II, and DNA damage in a concentration-dependent manner. We also investigated the role of cytochrome P450s (CYPs)-mediated metabolism in the dronedarone-induced toxicity using our previously established HepG2 cell lines expressing individually 14 human CYPs (1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4, 3A5, and 3A7). We demonstrated that CYP3A4, 3A5, and 2D6 were the major enzymes that metabolize dronedarone, and that CYP3A7, 2E1, 2C19, 2C18, 1A1, and 2B6 also metabolize dronedarone, but to a lesser extent. Our data showed that the cytotoxicity of dronedarone was decreased in CYP3A4-, 3A5-, or 2D6-overexpressing cells compared to the control HepG2 cells, indicating that the parent dronedarone has higher potency than the metabolites to induce cytotoxicity in these cells. In contrast, cytotoxicity was increased in CYP1A1-overexpressing cells, demonstrating that CYP1A1 exerts an opposite effect in dronedarone's toxicity, comparing to CYP3A4, 3A5, or 2D6. We also studied the involvement of topoisomerase II in dronedarone-induced toxicity, and demonstrated that the overexpression of topoisomerase II caused an increase in cell viability and a decrease in γ-H2A.X induction, suggesting that suppression of topoisomerase II may be one of the mechanisms involved in dronedarone-induced liver toxicity.

Identification of novel CYP4F2 genetic variants exhibiting decreased catalytic activity in the conversion of arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE)

CYP4F2 is an enzyme involved in the formation of 20-hydroxyeicosatetraenoic acid (20-HETE) from arachidonic acid and metabolizes vitamin K into an inactive form. Our objectives were to identify new CYP4F2 genetic variants and to characterize the functional consequences of the conversion of arachidonic acid into 20-HETE. We used direct DNA sequencing to identify a total of 20 single-nucleotide polymorphisms (SNPs) including four coding variants, A27V, R47C, P85A, and V433M, in 50 randomly selected subjects. Of these, A27V and P85A were new. Recombinant variant proteins were prepared using an Escherichia coli expression system, purified, and quantified via CO-difference spectral analysis. The conversion of arachidonic acid to 20-HETE by the coding variants was compared to that of the wild-type protein. Wild-type CYP4F2 exhibited the highest intrinsic clearance, followed by P85A, A27V, V433M, and R47C (40-65% of the wild-type value). The locations of the mutated residues in the three-dimensional protein structure were predicted by structural modeling, and the possible effects on 20-HETE synthesis discussed. In summary, we describe the allele frequency, haplotype distribution, and linkage disequilibrium of CYP4F2 and functionally analyze the CYP4F2 coding variants. Our findings suggest that individuals having the low-activity alleles of CYP4F2 may inefficiently convert arachidonic acid into 20-HETE. This may aid in our understanding of 20-HETE-related blood pressure problems and cardiovascular diseases when genotype-phenotype association studies are performed in the future.

Impact of CYP3A5 genomic variances on clinical outcomes among African American kidney transplant recipients

Little is known about the impact of CYP3A5 polymorphisms on transplantation outcomes among African American (AA) kidney transplant recipients (KTRs). To assess this issue, clinical outcomes were compared between AA CYP3A5*1 expressers and nonexpressers. This retrospective cohort study analyzed AA KTRs. Biopsy-proven acute rejection (BPAR), delayed graft function (DGF), glomerular filtration rate (GFR), infections, and tacrolimus dosing requirements were examined in 106 immunologically high-risk AA kidney transplant patients over a 2-year follow-up period. In CYP3A5*1 expressers compared to nonexpressers, the incidence of BPAR was significantly higher in the first 6 months (13% vs 0%; P = .016) compared to 24 months (13% vs 7%; P = .521). Tacrolimus total daily dose at first therapeutic level was significantly higher in CYP3A5*1 expressers (12 mg/day) compared to nonexpressers (8 mg/day; P < .001). Compared to CYP3A5*1 nonexpressers, DGF incidence was significantly higher among CYP3A5*1 expressers (27.6% vs 6.7%; P = .006). By contrast, median GFR was significantly higher in CYP3A5*1 expressers compared to nonexpressers (54.5 mL/min vs 50.0 mL/min; P = .003) at 24 months. The findings from this retrospective study suggest that AAs with CYP3A5*1 expression require 50% more tacrolimus and have an increased incidence of DGF and acute rejection.

Digging Deeper into CYP3A Testosterone Metabolism: Kinetic, Regioselectivity, and Stereoselectivity Differences between CYP3A4/5 and CYP3A7

The metabolism of testosterone to 6β-hydroxytestosterone (6β-OH-T) is a commonly used assay to evaluate human CYP3A enzyme activities. However, previous reports have indicated that CYP3A7 also produces 2α-hydroxytestosterone (2α-OH-T) and that a 2α-OH-T/6β-OH-T ratio may be a unique endogenous biomarker of the activity of the enzyme. Until now, the full metabolite and kinetic profile for testosterone hydroxylation by CYP3A7 has not been fully examined. To this end, we performed a complete kinetic analysis of the 6β-OH-T, 2α-OH-T, and 2β-hydroxytestosterone metabolites for recombinant Supersome CYP3A4, CYP3A5, and CYP3A7 enzymes and monitored metabolism in fetal and adult human liver microsomes for comparison. In general, a decrease in the velocity of the reaction was observed between CYP3A4 and the two other enzymes, with CYP3A7 showing the lowest metabolic capacity. Interestingly, we found that the 2α-OH-T/6β-OH-T ratio varied with substrate concentration when testosterone was incubated with CYP3A7, suggesting that this ratio would likely not function well as a biomarker for CYP3A7 activity. In silico docking studies revealed at least two different binding modes for testosterone between CYP3A4 and CYP3A7. In CYP3A4, the most energetically favorable docking mode places testosterone in a position with the methyl groups directed toward the heme iron, which is more favorable for oxidation at C6β, whereas for CYP3A7 the testosterone methyl groups are positioned away from the heme, which is more favorable for an oxidation event at C2α In conclusion, our data indicate an alternative binding mode for testosterone in CYP3A7 that favors the 2α-hydroxylation, suggesting significant structural differences in its active site compared with CYP3A4/5.

Differential Regulation of CYP3A4 and CYP3A5 and its Implication in Drug Discovery

BACKGROUND

Cancer cells use several mechanisms to resist the cytotoxic effects of drugs, resulting in tumor progression and invasion. One such mechanism capitalizes on the body's natural defense against xenobiotics by increasing the rate of xenobiotic efflux and metabolic inactivation. Xenobiotic metabolism typically involves conversion of parent molecules to more soluble and easily excreted derivatives in reactions catalyzed by Phase I and Phase II drug metabolizing enzymes.

METHODS

We performed a structured search of peer-reviewed literature on P450 (CYP) 3A, with a focus on CYP3A4 and CYP3A5.

RESULTS

Recent reports indicate that components of the xenobiotic response system are upregulated in some diseases, including many cancers. Such components include the pregnane X receptor (PXR), CYP3A4 and CYP3A5 enzymes. The CYP3A enzymes are a subset of the numerous enzymes that are transcriptionally activated following the interaction of PXR and many ligands.

CONCLUSION

Intense research is ongoing to understand the functional ramifications of aberrant expression of these components in diseased states with the goal of designing novel drugs that can selectively target them.

Physiological Content and Intrinsic Activities of 10 Cytochrome P450 Isoforms in Human Normal Liver Microsomes

Due to a lack of physiologic cytochrome P450 (P450) isoform content, P450 activity is typically only determined at the microsomal level (per milligram of microsomal protein) and not at the isoform level (per picomole of P450 isoform), which could result in the misunderstanding of variations in P450 activity between individuals and further hinder development of personalized medicine. We found that there were large variations in protein content, mRNA levels, and intrinsic activities of the 10 P450s in 100 human liver samples, in which CYP2E1 and CYP2C9 showed the highest expression levels. P450 gene polymorphisms had different effects on activity at two levels: CYP3A5*3 and CYP2A6*9 alleles conferred increased activity at the isoform level but decreased activity at the microsomal level; CYP2C9*3 had no effect at the isoform level but decreased activity at the microsomal level. The different effects at each level stem from the different effects of each polymorphism on the resulting P450 protein. Individuals with CYP2A6*1/*4, CYP2A6*1/*9, CYP2C9*1/*3, CYP2D6 100C>T TT, CYP2E1 7632T>A AA, CYP3A5*1*3, and CYP3A5*3*3 genotypes had significantly lower protein content, whereas CYP2D6 1661G>C mutants had a higher protein content. In conclusion, we first offered the physiologic data of 10 P450 isoform contents and found that some single nucleotide polymorphisms had obvious effects on P450 expression in human normal livers. The effects of gene polymorphisms on intrinsic P450 activity at the isoform level were quite different from those at the microsomal level, which might be due to changes in P450 protein content.

Cancer pharmacogenomics: implications on ethnic diversity and drug response

The goal of pharmacogenomic research is to discover and validate genetic variants that are predictive of drug response, for eventual implementation into clinical practice. Cancer pharmacogenomics provides the opportunity to analyze two sets of DNA, that of the tumor (somatic) and that of the host (germline). Germline variants are inherited variations and are often associated with the pharmacokinetic behavior of a drug, including drug disposition and ultimately drug efficacy and/or toxicity, whereas somatic mutations are often useful in predicting the pharmacodynamic response to drugs. Pharmacoethnicity, or ethnic diversity in drug response or toxicity, is an increasingly recognized factor accounting for interindividual variations in anticancer drug response. Pharmacoethnicity is often determined by germline pharmacogenomic factors and the distribution of single nucleotide polymorphisms across various populations, but it may also be influenced by nongenetic factors, such as environmental factors. This review aims to elucidate the importance of pharmacoethnicity in cancer pharmacogenomic research and implementation, focusing solely on germline variants.

Genotype-guided tacrolimus dosing in African-American kidney transplant recipients

Tacrolimus is dependent on CYP3A5 enzyme for metabolism. Expression of the CYP3A5 enzyme is controlled by several alleles including CYP3A5*1, CYP3A5*3, CYP3A5*6 and CYP3A5*7. African Americans (AAs) have on average higher tacrolimus dose requirements than Caucasians; however, some have requirements similar to Caucasians. Studies in AAs have primarily evaluated the CYP3A5*3 variant; however, there are other common nonfunctional variants in AAs (CYP3A5*6 and CYP3A5*7) that do not occur in Caucasians. These variants are associated with lower dose requirements and may explain why some AAs are metabolically similar to Caucasians. We created a tacrolimus clearance model in 354 AAs using a development and validation cohort. Time after transplant, steroid and antiviral use, age and CYP3A5*1, *3, *6 and *7 alleles were significant toward clearance. This study is the first to develop an AA-specific genotype-guided tacrolimus dosing model to personalize therapy.

Kidney transplant recipients carrying the CYP3A4*22 allelic variant have reduced tacrolimus clearance and often reach supratherapeutic tacrolimus concentrations

CYP3A4*22 is an allelic variant of the cytochrome P450 3A4 associated with a decreased activity. Carriers of this polymorphism may require reduced tacrolimus (Tac) doses to reach the target residual concentrations (Co). We tested this hypothesis in a population of kidney transplant recipients extracted from a multicenter, prospective and randomized study. Among the 186 kidney transplant recipients included, 9.3% (18 patients) were heterozygous for the CYP3A4*22 genotype and none were homozygous (allele frequency of 4.8%). Ten days after transplantation (3 days after starting treatment with Tac), 11% of the CYP3A4*22 carriers were within the target range of Tac Co (10-15 ng/mL), whereas among the CYP3A4*1/*1 carriers, 40% were within the target range (p = 0.02, OR = 0.19 [0.03; 0.69]). The mean Tac Co at day 10 in the CYP3A4*1/*22 group was 23.5 ng/mL (16.6-30.9) compared with 15.1 ng/mL (14-16.3) in the CYP3A4*1/*1 group, p < 0.001. The Tac Co/dose significantly depended on the CYP3A4 genotype during the follow-up (random effects model, p < 0.001) with the corresponding equivalent dose for patients heterozygous for CYP3A4*22 being 0.67 [0.54; 0.84] times the dose for CYP3A4*1/*1 carriers. In conclusion, the CYP3A4*22 allelic variant is associated with a significantly altered Tac metabolism and carriers of this polymorphism often reach supratherapeutic concentrations.

CYP3A5 Functions as a Tumor Suppressor in Hepatocellular Carcinoma by Regulating mTORC2/Akt Signaling

CYP3A5 is a cytochrome P450 protein that functions in the liver metabolism of many carcinogens and cancer drugs. However, it has not been thought to directly affect cancer progression. In this study, we challenge this perspective by demonstrating that CYP3A5 is downregulated in many hepatocellular carcinomas (HCC), where it has an important role as a tumor suppressor that antagonizes the malignant phenotype. CYP3A5 was downregulated in multiple cohorts of human HCC examined. Lower CYP3A5 levels were associated with more aggressive vascular invasion, poor differentiation, shorter time to disease recurrence after treatment, and worse overall patient survival. Mechanistic investigations showed that CYP3A5 overexpression limited MMP2/9 function and suppressed HCC migration and invasion in vitro and in vivo by inhibiting AKT signaling. Notably, AKT phosphorylation at Ser473 was inhibited in CYP3A5-overexpressing HCC cells, an event requiring mTORC2 but not Rictor/mTOR complex formation. CYP3A5-induced ROS accumulation was found to be a critical upstream regulator of mTORC2 activity, consistent with evidence of reduced GSH redox activity in most clinical HCC specimens with reduced metastatic capacity. Taken together, our results defined CYP3A5 as a suppressor of HCC pathogenesis and metastasis with potential utility a prognostic biomarker.

Analysis of genetic polymorphism and biochemical characterization of a functionally decreased variant in prostacyclin synthase gene (CYP8A1) in humans

Prostacyclin synthase (CYP8A1) is an enzyme responsible for the biosynthesis of prostacyclin (PGI2) which inhibits platelet activation and exhibits anti-inflammatory effect. The objectives of this study were to identify CYP8A1 genetic variants and characterize functional consequences of CYP8A1 variants. In total, 27 variants including four previously unidentified single-nucleotide polymorphisms (SNPs) were identified by direct DNA sequencing in Koreans (n=48). Among them, CYP8A1 A447T and E314Stop were newly assigned as CYP8A1(∗)5 and CYP8A1(∗)6 by the Human Cytochrome P450 Allele Nomenclature Committee, respectively. CYP8A1(∗)5 was found in the heme binding area in three individuals as a heterozygous mutation. To investigate the functional change of CYP8A1(∗)5, CYP8A1(∗)5 and wild-type CYP8A1 protein were overexpressed in an Escherichia coli expression system and purified. Metabolism of PGH2 by the CYP8A1(∗)5 protein exhibited significantly decreased activity, resulting in a 45% decrease in Vmax and a 1.8-fold decrease in intrinsic clearance compared to the wild-type. Based on the predicted crystal structure of CYP8A1(∗)5 using the Molecular Operating Environment platform, the distance from CYP8A1 Cys441 to the heme was altered with a significantly changed binding free energy for the mutant protein. Further studies would be needed to determine the effect of CYP8A1(∗)5 on PGI2 levels in humans.

Lower variability in 24-hour exposure during once-daily compared to twice-daily tacrolimus formulation in kidney transplantation

INTRODUCTION

Tacrolimus has originally been registered as a twice-daily formulation (Prograf, Tac BID), although a once-daily formulation (Advagraf, Tac QD) is also available. A reduced intrapatient variability of Tac Cmin, a surrogate marker for 24-hour drug exposure (AUC0-24), has been suggested. The variability of AUC0-24 has never been studied prospectively yet. The purpose of this study was to investigate the change in intrapatient variability of Tac AUC0-24 after converting from Tac BID to Tac QD.

METHODS

Forty renal transplant patients on Tac BID were converted on a 1:1 (mg/mg) basis to Tac QD in an investigator-driven comparative pharmacokinetic (PK) study. AUC0-24 was determined five times before and after conversion. Duplicate samples were collected by the patients themselves using the dried blood spot method. The main outcome measure is the change in intrapatient variability of AUC0-24 expressed as coefficient of variation (CV). Moreover, the influence of Cyp3A5 genotype polymorphism on the change in CV was studied.

RESULTS

In total, 400 AUC0-24 profiles were available for analysis. Conversion to Tac QD resulted in a significant improvement in intra-patient CV from 14.1% to 10.9% (P=0.012). Patients with the Cyp3A5*1/*3 genotype (n=11) had a numerically larger improvement in CV than patients with the CYP3A5*3/*3 genotype.

CONCLUSION

Intrapatient CV of Tac AUC0-24 improved after converting from Tac BID to Tac QD in stable renal transplant patients, especially in patients with the CYP3A5*1/3 genotype. Given the very strict protocol of this PK study, this improvement is most likely due to the different intrinsic PK properties of Tac QD and Tac BID.

Pharmacokinetics of pediatric lopinavir/ritonavir tablets in children when administered twice daily according to FDA weight bands

BACKGROUND

Lopinavir/ritonavir (LPV/r) pediatric tablets (100/25 mg) are approved by the United States Food and Drug Administration (FDA) and European Medicines Agency (EMA) as part of combination antiretroviral therapy. Dosing is based on body weight bands or body surface area under FDA approval and only body surface area by the EMA. This can lead to a different recommended dose. In addition, weight band-based dosing has not been formally studied in the target population. We evaluated the pharmacokinetics (PK) of LPV/r in children, administered twice daily according to the FDA weight bands, using pediatric tablets.

METHODS

Fifty-three HIV-infected children were included in the PK substudy of the Paediatric European Network for the Treatment of AIDS 18 trial (KONCERT). In this study, children were randomized to receive LPV/r twice or once daily, according to FDA weight bands. A PK assessment was performed in 17, 16 and 20 children in the 15-25 kg, ≥ 25-35 kg and >35 kg weight band, respectively, while children took the tablets twice daily. Rich sampling was performed, and PK parameters were calculated by noncompartmental analysis. Given the high percentage of Asian children, it was also tested whether there was a difference in PK parameters between Asian and non-Asian children.

RESULTS

For the total group, LPV geometric mean AUC0-12, Cmax and C12 were 106.9 h × mg/L, 12.0 mg/L and 4.9 mg/L, respectively. There were no significant differences in LPV PK parameters between the weight bands. In addition, weight was not found to be associated with variability in Cmax, C12 or AUC0-12 for the LPV PK parameters.

CONCLUSIONS

FDA weight band-based dosing recommendations provide adequate exposure to LPV when using LPV/r pediatric tablets.

African variation at Cytochrome P450 genes: Evolutionary aspects and the implications for the treatment of infectious diseases

The genomics revolution has provided a plethora of data from many previously uncharacterized populations. The increase in the amount of genetic data has improved our understanding of why individuals and populations differ in their susceptibility to multiple diseases. It has also enabled researchers to identify how genomic variation, including at the Cytochrome P450 (CYP450) super-family, affects the safety and efficacy of therapeutic drugs. CYP450 metabolize ∼90% of clinically administered drugs. Variability in CYP450 expression is known to affect the safety and efficacy of therapeutic drugs, including many used in the treatment and control of infectious diseases. There are inter-ethnic differences in the frequencies of clinically relevant CYP450 variants which affect CYP450 expression. Comparative studies of African populations have identified population structuring at CYP450 genes. This is associated with intra-African differences in the success of drug therapies used in the treatment of infectious diseases. Therapeutic drugs dominate control strategies for infectious diseases and are widely administered through mass drug administration campaigns. However, resistance to chemotherapy is spreading across endemic regions. The most common response has been to increase chemotherapeutic dosages, and administer combination therapies. However, there are few pharmacovigilance data examining how these changes influence adverse drug reactions. This review provides an overview of current knowledge of intra-Africa CYP450 variation, and the known associations with sub-optimal clinical outcomes in the treatment of infectious diseases. In addition, the potential for evolutionary approaches in the study of CYP450 variation is discussed to examine their potential in preventative medicine and intervention strategies within Africa.

Molecular diversity and population structure at the Cytochrome P450 3A5 gene in Africa

Background

Cytochrome P450 3A5 (CYP3A5) is an enzyme involved in the metabolism of many therapeutic drugs. CYP3A5 expression levels vary between individuals and populations, and this contributes to adverse clinical outcomes. Variable expression is largely attributed to four alleles, CYP3A5*1 (expresser allele); CYP3A5*3 (rs776746), CYP3A5*6 (rs10264272) and CYP3A5*7 (rs41303343) (low/non-expresser alleles). Little is known about CYP3A5 variability in Africa, a region with considerable genetic diversity. Here we used a multi-disciplinary approach to characterize CYP3A5 variation in geographically and ethnically diverse populations from in and around Africa, and infer the evolutionary processes that have shaped patterns of diversity in this gene. We genotyped 2538 individuals from 36 diverse populations in and around Africa for common low/non-expresser CYP3A5 alleles, and re-sequenced the CYP3A5 gene in five Ethiopian ethnic groups. We estimated the ages of low/non-expresser CYP3A5 alleles using a linked microsatellite and assuming a step-wise mutation model of evolution. Finally, we examined a hypothesis that CYP3A5 is important in salt retention adaptation by performing correlations with ecological data relating to aridity for the present day, 10,000 and 50,000 years ago.

Results

We estimate that ~43% of individuals within our African dataset express CYP3A5, which is lower than previous independent estimates for the region. We found significant intra-African variability in CYP3A5 expression phenotypes. Within Africa the highest frequencies of high-activity alleles were observed in equatorial and Niger-Congo speaking populations. Ethiopian allele frequencies were intermediate between those of other sub-Saharan African and non-African groups. Re-sequencing of CYP3A5 identified few additional variants likely to affect CYP3A5 expression. We estimate the ages of CYP3A5*3 as ~76,400 years and CYP3A5*6 as ~218,400 years. Finally we report that global CYP3A5 expression levels correlated significantly with aridity measures for 10,000 [Spearmann’s Rho= −0.465, p=0.004] and 50,000 years ago [Spearmann’s Rho= −0.379, p=0.02].

Conclusions

Significant intra-African diversity at the CYP3A5 gene is likely to contribute to multiple pharmacogenetic profiles across the continent. Significant correlations between CYP3A5 expression phenotypes and aridity data are consistent with a hypothesis that the enzyme is important in salt-retention adaptation.

Higher frequency of genetic variants conferring increased risk for ADRs for commonly used drugs treating cancer, AIDS and tuberculosis in persons of African descent

There is established clinical evidence for differences in drug response, cure rates and survival outcomes between different ethnic populations, but the causes are poorly understood. Differences in frequencies of functional genetic variants in key drug response and metabolism genes may significantly influence drug response differences in different populations. To assess this, we genotyped 1330 individuals of African (n=372) and European (n=958) descent for 4535 single-nucleotide polymorphisms in 350 key drug absorption, distribution, metabolism, elimination and toxicity genes. Important and remarkable differences in the distribution of genetic variants were observed between Africans and Europeans and among the African populations. These could translate into significant differences in drug efficacy and safety profiles, and also in the required dose to achieve the desired therapeutic effect in different populations. Our data points to the need for population-specific genetic variation in personalizing medicine and care.

Nifedipine pharmacokinetics are influenced by CYP3A5 genotype when used as a preterm labor tocolytic

OBJECTIVE

To characterize the pharmacokinetics and pharmacogenetics of nifedipine in pregnancy.

STUDY DESIGN

Pregnant women receiving oral nifedipine underwent steady-state pharmacokinetic testing over one dosing interval. DNA was obtained and genotyped for cytochrome P450 (CYP) 3A5 and CYP3A4*1B. Nifedipine and oxidized nifedipine concentrations were measured in plasma, and pharmacokinetic parameters were compared between those women who expressed a CYP3A5*1 allele and those who expressed only variant CYP3A5 alleles (*3,*6, or *7).

RESULTS

Fourteen women had complete data to analyze. Four women (29%) expressed variant CYP3A5; three of these women were also CYP3A4*1B allele carriers. The mean half-life of nifedipine was 1.68 ± 1.56 hours. The area under the curve from 0 to 6 hours for the women receiving nifedipine every 6 hours was 207 ± 138 µg·h /L. Oral clearance was different between high expressers and low expressers (232.0 ± 37.8 µg/mL versus 85.6 ± 45.0 µg/mL, respectively; p = 0.007).

CONCLUSION

CYP3A5 genotype influences the oral clearance of nifedipine in pregnant women.

Influence of CYP3A5 6986A > G and ABCB1 3435C > T Polymorphisms on Adverse Events Associated With Tacrolimus in Jordanian Pediatric Renal Transplant Patients

The aim of the study is to investigate the influence of ABCB1(3435) and CYP3A5(6986) polymorphisms, tacrolimus troughs and clinical factors on the time of adverse events associated with tacrolimus in pediatric kidney transplant patients. Clinical data, adverse events, tacrolimus troughs, corresponding doses, ABCB1 3435C > T and CYP3A5 6986A > G genotypes were collected from 38 pediatric kidney transplant patients in a retrospective study for over 2 years post-transplant. We used a marginal Cox proportional hazard model to evaluate the influence of clinical factors and single nucleotide polymorphisms (SNPs) on tacrolimus-associated adverse events. CYP3A5 genotype, the Bayesian predicted tacrolimus concentrations, hematocrit and mean corpuscular volume are significant risk factors of adverse events over a 2-year-period. CYP3A5*1 genotype was associated with 36% relative risk of CYP3A5*3/*3 genotype. In the 9-month period, the additional factor, ABCB1 3435TT genotype, was shown to be associated with 38% relative risk of the CC and CT genotypes. For graft loss, acute and chronic rejection, only tacrolimus concentration and hematocrit, but not CYP3A5 or ABCB1 polymorphisms, are important factors influencing their occurrences.

Genetic and genomic approaches to the detection of heart transplant rejection

Since Christiaan Barnard performed the first heart transplant in 1967, over 100,000 heart transplants have been performed worldwide. As was true then, rejection remains the major threat to the function and survival of the allograft. The development of the endomyocardial biopsy as a means to monitor for rejection has allowed heart transplantation to thrive as a therapy for patients with end-stage heart disease. The need for a noninvasive method of rejection surveillance led to the development of the first genetic test for allograft rejection, the AlloMap^®. In this article, after presenting the pathological and clinical features of cardiac allograft rejection, the authors discuss the development and application of gene-expression testing for the detection of cardiac allograft rejection. We then explore emerging 'omic' approaches that will be the rejection detection methods of the future.

Pharmacogenetic Screening for Polymorphisms in Drug-Metabolizing Enzymes and Drug Transporters in a Dutch Population

BACKGROUND

A possible explanation for the wide interindividual variability in toxicity and efficacy of drug therapy is variation in genes encoding drug-metabolizing enzymes and drug transporters. The allelic frequency of these genetic variants, linkage disequilibrium (LD), and haplotype of these polymorphisms are important parameters in determining the genetic differences between patients. The aim of this study was to explore the frequencies of polymorphisms in drug-metabolizing enzymes (CYP1A1, CYP2C9, CYP2C19, CYP3A4, CYP2D6, CYP3A5, DPYD, UGT1A1, GSTM1, GSTP1, GSTT1) and drug transporters (ABCB1[MDR1] and ABCC2[MRP2]), and to investigate the LD and perform haplotype analysis of these polymorphisms in a Dutch population.

METHODS

Blood samples were obtained from 100 healthy volunteers and genomic DNA was isolated and amplified by PCR. The amplification products were sequenced and analyzed for the presence of polymorphisms by sequence alignment.

RESULTS

In the study population, we identified 13 new single nucleotide polymorphisms (SNPs) in Caucasians and three new SNPs in non-Caucasians, in addition to previously recognized SNPs. Three of the new SNPs were found within exons, of which two resulted in amino acid changes (A428T in CYP2C9 resulting in the amino acid substitution D143V; and C4461T in ABCC2 in a non-Caucasian producing the amino acid change T1476M). Several LDs and haplotypes were found in the Caucasian individuals.

CONCLUSION

In this Dutch population, the frequencies of 16 new SNPs and those of previously recognized SNPs were determined in genes coding for drug-metabolizing enzymes and drug transporters. Several LDs and haplotypes were also inferred. These data are important for further research to help explain the interindividual pharmacokinetic and pharmacodynamic variability in response to drug therapy.

Dimovski A. Frequency of the most common CYP3A5 polymorphisms in the healthy population of the Republic of Macedonia

The genetic polymorphism affecting the CYP3A5 enzyme is responsible for inter-individual and interethnic variability in the metabolism of CYP3A5 substrates. The aim of this study was to analyze the distribution of the most common CYP3A5*3 allelic variants in the healthy population of R. Macedonia and to investigate if the allelic frequency falls within the assumed range for European Caucasians. The total of 174 healthy volunteers from the general population were included. The genotyping of the CYP3A5*3 variant alleles, *3A (rs15524) and *3E (rs28365095), was performed with Real-Time PCR based on the allelic discrimination method using a TaqMan SNP genotyping assay according to the manufacturer’s instructions. The CYP3A5*3 allele is abundantly present displaying an allelic frequency of 0.922. We estimate that 0.82 of the Macedonian population are homozygotes for the variant and do not have a CYP3A5 enzymatic activity. Our study demonstrated a high prevalence of CYP3A5*3 allele in the Macedonian population. The distribution of CYP3A5 alleles was similar to that found in other European Caucasians. As the goals of personalized medicine are beginning to be realized, this provides basic information on the CYP3A5 allele frequency for the future pharmacogenetic research in R. Macedonia.

Effect of cytochrome P450 3A5 genotype on atorvastatin pharmacokinetics and its interaction with clarithromycin

Abstract Study Objective. To assess the effects of the cytochrome P450 (CYP) 3A genotype, CYP3A5, on atorvastatin pharmacokinetics and its interaction with clarithromycin. Design. Prospective, two-phase, randomized-sequence, open-label pharmacokinetic study. Setting. Clinical research center at a teaching hospital. Subjects. Twenty-three healthy volunteers who were screened for genotype: 10 subjects carried the CYP3A5*1 allele (expressors) and 13 subjects did not (nonexpressors). Intervention. In one phase, subjects received a single oral dose of atorvastatin 20 mg. In the other phase, subjects received clarithromycin 500 mg twice/day for 5 days; on day 4 after the morning dose, subjects also received a single oral dose of atorvastatin 20 mg. All subjects participated in both phases of the study, which were separated by at least 14 days. Measurements and Main Results. Pharmacokinetic parameters of both forms of atorvastatin-atorvastatin acid and atorvastatin lactone-were compared between CYP3A5 expressors and nonexpressors, both in the absence and presence of clarithromycin, a strong CYP3A inhibitor. The acid form is pharmacologically active, and the lactone form has been associated with the atorvastatin's muscle-related adverse effects. Atorvastatin acid exposure did not differ significantly between CYP3A5 genotype groups. When subjects had not received clarithromycin pretreatment, the area under the concentration-time curve from time zero extrapolated to infinity (AUC(0-∞)) of atorvastatin lactone was 36% higher in nonexpressors than in expressors (median 47.6 ng•hr/ml [interquartile range (IQR) 37.8-64.3 ng•hr/ml] vs 34.9 ng•hr/ml [IQR 21.6-42.2 ng•hr/ml], p=0.038). After clarithromycin pretreatment, changes in the pharmacokinetic parameters of atorvastatin acid and lactone were not significantly different between the nonexpressors versus the expressors; however, the increase in the AUC(0-∞) of atorvastatin lactone was 37% greater in expressors than in nonexpressors (geometric mean ± SD 3.59 ± 0.57 vs 2.62 ± 0.35, p=0.049). Conclusion. Our data suggest that the CYP3A5 genotype has minimal effects on the pharmacokinetic parameters of atorvastatin and its interaction with clarithromycin; these effects are unlikely to be clinically significant.