Variability In Drug Metabolism Research Articles

Ontogeny of Pediatric Pharmacogenetics: Celebrating the Past and Vision for the Future.

Ontogeny of Pediatric Pharmacogenetics: Celebrating the Past and Vision for the Future.

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

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

Pharmacogene Variation Consortium: A Global Resource and Repository for Pharmacogene Variation.

The Pharmacogene Variation Consortium (PharmVar) was founded in 2017 to provide the clinical and research communities a repository and standardized nomenclature of genes contributing to variability in drug metabolism and response. Over the past four years, PharmVar has provided the research and clinical pharmacogenetics/genomics communities with essential information for flagship pharmacogenes with well-established drug-gene relationships and published clinical guidelines such as CYP2C9, CYP2C19 and CYP2D6. In this perspective we highlight recent milestones and standardization efforts.

Genomic Risk Factors Driving Immune-Mediated Delayed Drug Hypersensitivity Reactions.

Adverse drug reactions (ADRs) remain associated with significant mortality. Delayed hypersensitivity reactions (DHRs) that occur greater than 6 h following drug administration are T-cell mediated with many severe DHRs now associated with human leukocyte antigen (HLA) risk alleles, opening pathways for clinical prediction and prevention. However, incomplete negative predictive value (NPV), low positive predictive value (PPV), and a large number needed to test (NNT) to prevent one case have practically prevented large-scale and cost-effective screening implementation. Additional factors outside of HLA contributing to risk of severe T-cell-mediated DHRs include variation in drug metabolism, T-cell receptor (TCR) specificity, and, most recently, HLA-presented immunopeptidome-processing efficiencies via endoplasmic reticulum aminopeptidase (ERAP). Active research continues toward identification of other highly polymorphic factors likely to impose risk. These include those previously associated with T-cell-mediated HLA-associated infectious or auto-immune disease such as Killer cell immunoglobulin-like receptors (KIR), epistatically linked with HLA class I to regulate NK- and T-cell-mediated cytotoxic degranulation, and co-inhibitory signaling pathways for which therapeutic blockade in cancer immunotherapy is now associated with an increased incidence of DHRs. As such, the field now recognizes that susceptibility is not simply a static product of genetics but that individuals may experience dynamic risk, skewed toward immune activation through therapeutic interventions and epigenetic modifications driven by ecological exposures. This review provides an updated overview of current and proposed genetic factors thought to predispose risk for severe T-cell-mediated DHRs.

Pharmacokinetics of the CYP3A4 and CYP2B6 Inducer Carbamazepine and Its Drug-Drug Interaction Potential: A Physiologically Based Pharmacokinetic Modeling Approach.

The anticonvulsant carbamazepine is frequently used in the long-term therapy of epilepsy and is a known substrate and inducer of cytochrome P450 (CYP) 3A4 and CYP2B6. Carbamazepine induces the metabolism of various drugs (including its own); on the other hand, its metabolism can be affected by various CYP inhibitors and inducers. The aim of this work was to develop a physiologically based pharmacokinetic (PBPK) parent−metabolite model of carbamazepine and its metabolite carbamazepine-10,11-epoxide, including carbamazepine autoinduction, to be applied for drug–drug interaction (DDI) prediction. The model was developed in PK-Sim, using a total of 92 plasma concentration−time profiles (dosing range 50–800 mg), as well as fractions excreted unchanged in urine measurements. The carbamazepine model applies metabolism by CYP3A4 and CYP2C8 to produce carbamazepine-10,11-epoxide, metabolism by CYP2B6 and UDP-glucuronosyltransferase (UGT) 2B7 and glomerular filtration. The carbamazepine-10,11-epoxide model applies metabolism by epoxide hydroxylase 1 (EPHX1) and glomerular filtration. Good DDI performance was demonstrated by the prediction of carbamazepine DDIs with alprazolam, bupropion, erythromycin, efavirenz and simvastatin, where 14/15 DDI AUClast ratios and 11/15 DDI Cmax ratios were within the prediction success limits proposed by Guest et al. The thoroughly evaluated model will be freely available in the Open Systems Pharmacology model repository.

For better drugs, diversify clinical trials.

Genetic variation in drug metabolism can affect drug outcomes

Fatal poisoning case involving drug interaction due to the inhibition of cytochrome P450

Introduction. Cytochrome P450 (CYP) enzymes are responsible for the metabolism of various drugs and chemicals. The forensic pathologist should consider not only pharmacodynamic interactions by multiple drugs but also the pharmacokinetic drug interactions of each drug in the case of multiple drug ingestion. Case report. A female in her forties, receiving therapy for alcohol dependence, was found dead in her house. The medicolegal autopsy revealed no findings suggestive of natural cause of death. Quantitative toxicological analysis showed that levomepromazine, promethazine, dextromethorphan, estazolam, clomipramine, risperidone, and flunitrazepam concentrations in femoral blood were 0.750 ?g/mL, 0.701 ?g/mL, 0.332 ?g/mL, 0.390 ?g/mL, 0.216 ?g/mL, 0.031 ?g/mL, and 0.002 ?g/mL, respectively, along with a blood ethanol level of 377 mg/dL. Conclusion. We concluded that the cause of death was the interaction between ethanol and multiple psychotropic drugs. Pharmacokinetic drug interactions due to the CYPs inhibition should be considered in the evaluation of toxicity in poisoning cases involving multiple drugs.

In vitro study on the effect of peucedanol on the activity of cytochrome P450 enzymes

Context Peucedanol is a major extract of Peucedanum japonicum Thunb. (Apiaceae) roots, which is a commonly used herb in paediatrics. Its interaction with cytochrome P450 enzymes (CYP450s) would lead to adverse effects or even failure of therapy. Objective The interaction between peucedanol and CYP450s was investigated. Materials and methods Peucedanol (0, 2.5, 5, 10, 25, 50, and 100 μM) was incubated with eight human liver CYP isoforms (CYP1A2, 2A6, 3A4, 2C8, 2C9, 2C19, 2D6, and 2E1), in pooled human liver microsomes (HLMs) for 30 min with specific inhibitors as positive controls and untreated HLMs as negative controls. The enzyme kinetics and time-dependent study (0, 5, 10, 15, and 30 min) were performed to obtain corresponding parameters in vitro. Results Peucedanol significantly inhibited the activity of CYP1A2, 2D6, and 3A4 in a dose-dependent manner with IC50 values of 6.03, 13.57, and 7.58 μM, respectively. Peucedanol served as a non-competitive inhibitor of CYP3A4 with a Ki value of 4.07 μM and a competitive inhibitor of CYP1A2 and 2D6 with a Ki values of 3.39 and 6.77 μM, respectively. Moreover, the inhibition of CYP3A4 was time-dependent with the Ki /Kinact value of 5.44/0.046 min/μM. Discussion and conclusions In vitro inhibitory effect of peucedanol on the activity of CYP1A2, 2A6, and 3A4 was reported in this study. As these CYPs are involved in the metabolism of various drugs, these results implied potential drug-drug interactions between peucedanol and drugs metabolized by CYP1A2, 2D6, and 3A4, which needs further in vivo validation.

Crystal Structures of Drug-Metabolizing CYPs.

The complex enzyme kinetics displayed by drug-metabolizing cytochrome P450 enzymes (CYPs) (see Chapter 9 ) can, in part, be explained by an examination of their crystallographic protein structures. Fortunately, despite low sequence similarity between different families of drug-metabolizing CYPs, there exists a high degree of structural homology within the superfamily. This similarity in the protein fold allows for a direct comparison of the structural features of CYPs that contribute toward differences in substrate binding, heterotropic and homotropic cooperativity, and genetic variability in drug metabolism. In this chapter, we first provide an overview of the nomenclature and the role of structural features that are common in all CYPs. We then apply these definitions to understand the different substrate specificities and functions in the CYP3A, CYP2C, and CYP2D families of enzymes.

Analysis of Live Single Cells by Confocal Microscopy and High-Resolution Mass Spectrometry to Study Drug Uptake, Metabolism, and Drug-Induced Phospholipidosis.

The analysis of large numbers of cells from a population results in information that does not reflect differences in cell phenotypes. Individual variations in cellular drug uptake, metabolism, and response to drug treatment may have profound effects on cellular survival and lead to the development of certain disease states, drug persistence, and resistance. Herein, we present a method that combines live cell confocal microscopy imaging with high-resolution mass spectrometry to achieve absolute cell quantification of the drug amiodarone (AMIO) and its major metabolite, N-desethylamiodarone (NDEA), in single liver cells (HepG2 and HepaRG cells). The method uses a prototype system that integrates a confocal microscope with an XYZ stage robot to image and automatically sample selected cells from a sample compartment, which is kept under growth conditions, with nanospray tips. Besides obtaining the distributions of AMIO and NDEA cell concentrations across a population of individual cells, as well as variabilities in drug metabolism, the effect of these on phospholipidosis and cell morphology was studied. The method was suited to identify subpopulations of cells that metabolized less drug and to correlate cell drug concentrations with cell phospholipid content, cell volume, sphericity, and other cell phenotypic features. Using principal component analysis (PCA), the treated cells could be clearly distinguished from vehicle control cells (0 μM AMIO) and HepaRG cells from HepG2 cells. The potential of using multidimensional and multimodal information collected from single cells to build predictive models for cell classification is demonstrated.

Transcriptional and post-transcriptional regulation of the pregnane X receptor: a rationale for interindividual variability in drug metabolism.

The pregnane X receptor (PXR, encoded by the NR1I2 gene) is a ligand-regulated transcription factor originally described as a master regulator of xenobiotic detoxification. Later, however, PXR was also shown to interact with endogenous metabolism and to be further associated with various pathological states. This review focuses predominantly on such aspects, currently less covered in literature, as the control of PXR expression per se in the context of inter-individual differences in drug metabolism. There is growing evidence that non-coding RNAs post-transcriptionally regulate PXR. Effects on PXR have especially been reported for microRNAs (miRNAs), which include miR-148a, miR-18a-5p, miR-140-3p, miR-30c-1-3p and miR-877-5p. Likewise, miRNAs control the expression of both transcription factors involved in PXR expression and regulators of PXR function. The impact of NR1I2 genetic polymorphisms on miRNA-mediated PXR regulation is also discussed. As revealed recently, long non-coding RNAs (lncRNAs) appear to interfere with PXR expression. Reciprocally, PXR activation regulates non-coding RNA expression, thus comprising another level of PXR action in addition to the direct transactivation of protein-coding genes. PXR expression is further controlled by several transcription factors (cross-regulation) giving rise to different PXR transcript variants. Controversies remain regarding the suggested role of feedback regulation (auto-regulation) of PXR expression. In this review, we comprehensively summarize the miRNA-mediated, lncRNA-mediated and transcriptional regulation of PXR expression, and we propose that deciphering the precise mechanisms of PXR expression may bridge our knowledge gap in inter-individual differences in drug metabolism and toxicity.

DPYD and UGT1A1 Pharmacogenetic Testing in Patients with Gastrointestinal Malignancies: An Overview of the Evidence and Considerations for Clinical Implementation.

Gastrointestinal (GI) malignancies are among the most commonly diagnosed cancers worldwide. Despite the introduction of targeted and immunotherapy agents in the treatment landscape, cytotoxic agents, such as fluoropyrimidines and irinotecan, remain as the cornerstone of chemotherapy for many of these tumors. Pharmacogenetics (PGx) is a rapidly evolving field that accounts for interpatient variability in drug metabolism to predict therapeutic response and toxicity. Given the significant incidence of severe treatment-related adverse events associated with cytotoxic agents, utilizing PGx can allow clinicians to better anticipate drug tolerability while minimizing treatment interruptions or delays. In this review, the PGx profiles of drug-gene pairs with potential impact in GI malignancy therapy - DPYD-5-fluorouracil/capecitabine and UGT1A1-irinotecan - and the available clinical evidence of their roles in reducing severe adverse events are discussed. Considerations for clinical implementation, such as optimal laboratory workflows, electronic health record integration, and stakeholder engagement, as well as provider education, are addressed. Last, exploratory PGx markers in GI malignancy treatment are described. As the PGx knowledge base rapidly evolves, pharmacists will be vital in leveraging their pharmacology knowledge and clinical skills to implement PGx testing in the clinic.

Pharmacogenomics of Antiretroviral Drug Metabolism and Transport.

Antiretroviral therapy has markedly reduced morbidity and mortality for persons living with human immunodeficiency virus (HIV). Individual tailoring of antiretroviral regimens has the potential to further improve the long-term management of HIV through the mitigation of treatment failure and drug-induced toxicities. While the mechanisms underlying anti-HIV drug adverse outcomes are multifactorial, the application of drug-specific pharmacogenomic knowledge is required in order to move toward the personalization of HIV therapy. Thus, detailed understanding of the metabolism and transport of antiretrovirals and the influence of genetics on these pathways is important. To this end, this review provides an up-to-date overview of the metabolism of anti-HIV therapeutics and the impact of genetic variation in drug metabolism and transport on the treatment of HIV. Future perspectives on and current challenges in pursuing personalized HIV treatment are also discussed.

Transcriptomic analysis across liver diseases reveals disease-modulating activation of constitutive androstane receptor in cholestasis.

Background & AimsLiver diseases are caused by many factors, such as genetics, nutrition, and viruses. Therefore, it is important to delineate transcriptomic changes that occur in various liver diseases.MethodsWe performed high-throughput sequencing of mouse livers with diverse types of injuries, including cholestasis, diet-induced steatosis, and partial hepatectomy. Comparative analysis of liver transcriptome from mice and human samples of viral infections (HBV and HCV), alcoholic hepatitis (AH), non-alcoholic steatohepatitis (NASH), and biliary atresia revealed distinct and overlapping gene profiles associated with liver diseases. We hypothesised that discrete molecular signatures could be utilised to assess therapeutic outcomes. We focused on cholestasis to test and validate the hypothesis using pharmacological approaches.ResultsHere, we report significant overlap in the expression of inflammatory and proliferation-related genes across liver diseases. However, cholestatic livers were unique and displayed robust induction of genes involved in drug metabolism. Consistently, we found that constitutive androstane receptor (CAR) activation is crucial for the induction of the drug metabolic gene programme in cholestasis. When challenged, cholestatic mice were protected against zoxazolamine-induced paralysis and acetaminophen-induced hepatotoxicity. These protective effects were diminished upon inhibition of CAR activity. Further, drug metabolic genes were also induced in the livers from a subset of biliary atresia patients, but not in HBV and HCV infections, AH, or NASH. We also found a higher expression of CYP2B6, a CAR target, in the livers of biliary atresia patients, underscoring the clinical importance of our findings.ConclusionsComparative transcriptome analysis of different liver disorders revealed specific induction of phase I and II metabolic genes in cholestasis. Our results demonstrate that CAR activation may lead to variations in drug metabolism and clinical outcomes in biliary atresia.Lay summaryTranscriptomic analysis of diverse liver diseases revealed alterations in common and distinct pathways. Specifically, in cholestasis, we found that detoxification genes and their activity are increased. Thus, cholestatic patients may have an unintended consequence on drug metabolism and not only have a beneficial effect against liver toxicity, but also may require adjustments to their therapeutic dosage.

Safety of Janus Kinase Inhibitors in Older Patients: A Focus on the Thromboembolic Risk.

The Janus kinase (JAK)–signal transducer and activator of transcription (STAT) pathway is a membrane-to-nucleus signaling cascade that effects activation of gene transcription. JAK inhibitors have demonstrated effectiveness in autoimmune diseases such as rheumatoid arthritis. An increased risk of infection, mainly varicella-zoster reactivation, with these new agents is of concern. Comorbid conditions, along with pharmacokinetic variations in drug metabolism in the older population, further increase the risk of adverse outcomes. Newly raised concerns for potential adverse effects such as deep vein thrombosis and pulmonary embolism are essential considerations for clinicians. Older patients are at increased risk because of multiple comorbid conditions and pharmacokinetic changes related to drug metabolism and excretion. Both the US FDA and the European Medicines Agency have issued warnings regarding this risk. These warnings highlight individuals aged > 50 years with concomitant cardiovascular risk factors. Furthermore, the FDA released a black box warning for increased thromboembolic risk associated with JAK inhibitors. As the use of these drugs increases, a solid understanding of adverse effects and risks is critical to those treating older adults.

Nrf2 Antioxidative System is Involved in Cytochrome P450 Gene Expression and Activity: A Delay in Pentobarbital Metabolism in Nrf2-Deficient Mice.

NF-E2-related factor 2 (Nrf2) is a transcriptional regulator of biologic defense proteins, such as antioxidant proteins and phase II detoxification enzymes. Cytochrome P450 (P450) enzymes have been shown to regulate phase I metabolism of various drugs and are partially regulated by Nrf2; however, the influence of Nrf2 on drug pharmacokinetics is not known. Here, we showed that Nrf2 depletion prolonged the effect of pentobarbital, a sleep-promoting drug. Pretreatment with phenobarbital, a P450 inducer, shortens the sleeping time associated with pentobarbital-induced sedation in wild-type (WT) mice; however, this effect was not observed in Nrf2-/- mice. Furthermore, the blood pentobarbital concentration was higher in Nrf2-/- mice than in WT mice at 30-60 minutes, and the phenobarbital-induced enhancement of its clearance was attenuated in Nrf2-/- mice compared with WT mice. Total P450 content was decreased in Nrf2-/- mouse livers, and the phenobarbital-induced increase in P450 content was lower in Nrf2-/- mice than WT mice. Cyp1a2, Cyp2a5, Cyp2c29, and Cyp2e1 gene expression levels under physiologic conditions and Cyp1a2, Cyp2a5, and Cyp2b10 gene expression levels under phenobarbital-treated conditions were lower in Nrf2-/- mice compared with WT mice. Additionally, pentobarbital metabolism in liver microsomes was attenuated by Nrf2 depletion. Taken together, these findings suggested that Nrf2 influenced pentobarbital pharmacokinetics through the regulation of drug metabolism and P450 gene expression. Thus, Nrf2-mediated regulation of P450 may contribute to the biologic defense against increased reactive oxygen species production. SIGNIFICANCE STATEMENT: NF-E2-related factor 2 (Nrf2) plays a critical role in the cellular defense against oxidative stress. Nrf2-/- mice with reduced ability to eliminate reactive oxygen species (ROS) showed a significant delay in emergence from pentobarbital-induced sleep, which was associated with decreased P450 activities and gene expression. Our findings provide that Nrf2 dysfunction or ROS that exceed a threshold level of the eliminating ability of the Nrf2 system may reduce P450 activity.

Study of CYP3A5 genetic polymorphism in Vietnamese Kinh ethnic group

Cytochrome P450 3A5 (CYP) belongs to the CYP3A cluster, which encode for several enzymes involved in metabolism of various drugs, endogenous substrates as well as exogenous compounds. Among the four genes of CY3A cluster, CYP3A5 plays an important role in pharmacogenetics since this enzyme metabolizes over 30% of the clinically prescribed drugs. The inter-individual variability in clearance of CYP3A substrates mainly depends on the genetic factors. In the present study, after collecting peripheral bloods samples from 100 unrelated healthy Kinh ethnic group in Vietnam, Sanger sequencing was used in order to determine the CYP3A5 variants responsible for enzyme activity alteration (*3, *6, *8 and *9). It was shown that CYP3A5*3 is the most prevalent variant with 67.5%, in which a haft of individuals carrying *3 were homozygous for this allele. In contrast, the variants *6, *8 and *9 were not found the study subjects. The data observed in current study would support dosing of drugs that metabolized by CYP3A5 and thereby increase treatment outcome.

Impact of host and environmental factors on β-glucuronidase enzymatic activity: implications for gastrointestinal serotonin.

The gastrointestinal tract houses a reservoir of bacterial-derived enzymes that can directly catalyze the metabolism of drugs, dietary elements and endogenous molecules. Both host and environmental factors may influence this enzymatic activity, with the potential to dictate the availability of the biologically-active form of endogenous molecules in the gut and influence inter-individual variation in drug metabolism. We aimed to investigate the influence of the microbiota, and the modulation of its composition, on fecal enzymatic activity. Intrinsic factors related to the host, including age, sex and genetic background, were also explored. Fecalase, a cell-free extract of feces, was prepared and used in a colorimetric-based assay to quantify enzymatic activity. To demonstrate the functional effects of fecal enzymatic activity, we examined β-glucuronidase-mediated cleavage of serotonin β-d-glucuronide (5-HT-GLU) and the resultant production of free 5-HT by HPLC. As expected, β-glucuronidase and β-glucosidase activity were absent in germ-free mice. Enzymatic activity was significantly influenced by mouse strain and animal species. Sex and age significantly altered metabolic activity with implications for free 5-HT. β-Glucuronidase and β-glucosidase activity remained at reduced levels for nearly two weeks after cessation of antibiotic administration. This effect on fecalase corresponded to significantly lower 5-HT levels as compared with incubation with pre-antibiotic fecalase from the same mice. Dietary targeting of the microbiota using prebiotics did not alter β-glucuronidase or β-glucosidase activity. Our data demonstrate that multiple factors influence the activity of bacterial-derived enzymes which may have potential clinical implications for drug metabolism and the deconjugation of host-produced glucuronides in the gut.NEW & NOTEWORTHY This article explores a comprehensive range of host and environmental factors that introduce variability in the expression of bacterial-derived metabolic enzymes. Our results demonstrate that altered β-glucuronidase activity has implications for the bioavailability of luminal serotonin. The experimental approach employed, fecalase, provides a mechanistic basis and translational platform to further delineate the functional outputs of altered metabolic activity, and the associated physiological effects of microbiota-targeted interventions on host response to drugs and host-produced glucuronides.

Functionally Significant Coumarin-Related Variant Alleles and Time to Therapeutic Range in Chilean Cardiovascular Patients.

Despite the development of new oral agents over the last decade, vitamin K antagonists (VKAs) remain the most widely used anticoagulants for treating and preventing thromboembolism worldwide. In Chile, the Ministry of Health indicates that acenocoumarol should be used in preference to any other coumarin. Complications of inappropriate dosing are among the most frequently reported adverse events associated with this medication. It is well known that polymorphisms in pharmacokinetic and pharmacodynamic proteins related to coumarins (especially warfarin) influence response to these drugs. This work analyzed the impact of CYP2C19*2 (rs4244285), CYP1A2*1F (rs762551), GGCx (rs11676382), CYP2C9*2 (rs1799853), CYP2C9*3 (rs1057910), CYP4F2 (rs2108622), VKORC1 (rs9923231), VKORC1 (rs7294), CYP3A4*1B (rs2740574), and ABCB1 (rs1045642) polymorphisms on time to therapeutic range for oral anticoagulants in 304 Chilean patients. CYP2C9*3 polymorphisms were associated with time to therapeutic range for acenocoumarol in Chilean patients, and the CYP4F2 TT genotype, MDR1 A allele, CYP1A2 A allele, and CYP3A4T allele are promising variants that merit further analysis. The presence of polymorphisms explained only 4.1% of time to therapeutic range for acenocoumarol in a multivariate linear model. These results improve our understanding of the basis of ethnic variations in drug metabolism and response to oral anticoagulant therapy. We hope that these findings will contribute to developing an algorithm for VKA dose adjustment in the Chilean population in the near future, decreasing the frequency of stroke, systemic embolism, and bleeding-related adverse events.

Functional impact of cytochrome P450 3A (CYP3A) missense variants in cattle

Cytochrome P450 3A is the most important CYP subfamily in humans, and CYP3A4/CYP3A5 genetic variants contribute to inter-individual variability in drug metabolism. However, no information is available for bovine CYP3A (bCYP3A). Here we described bCYP3A missense single nucleotide variants (SNVs) and evaluated their functional effects. CYP3A28, CYP3A38 and CYP3A48 missense SNVs were identified in 300 bulls of Piedmontese breed through targeted sequencing. Wild-type and mutant bCYP3A cDNAs were cloned and expressed in V79 cells. CYP3A-dependent oxidative metabolism of testosterone (TST) and nifedipine (NIF) was assessed by LC-MS/MS. Finally, SNVs functional impact on TST hydroxylation was measured ex vivo in liver microsomes from individually genotyped animals. Thirteen missense SNVs were identified and validated. Five variants showed differences in CYP3A catalytic activity: three CYP3A28 SNVs reduced TST 6β-hydroxylation; one CYP3A38 variant increased TST 16β-hydroxylation, while a CYP3A48 SNV showed enhanced NIF oxidation. Individuals homozygous for rs384467435 SNV showed a reduced TST 6β-hydroxylation. Molecular modelling showed that most of SNVs were distal to CYP3A active site, suggesting indirect effects on the catalytic activity. Collectively, these findings demonstrate the importance of pharmacogenetics studies in veterinary species and suggest bCYP3A genotype variation might affect the fate of xenobiotics in food-producing species such as cattle.