Influence of CYP4F2 polymorphisms and plasma vitamin K levels on warfarin sensitivity in Japanese pediatric patients

Utility of Cytochrome P450 4F2 Genotyping to Assess Drug Interaction Risk for Brincidovovir, a Cytochrome P450 4F2 Substrate

Smallpox was eradicated in 1980 but remains a biothreat due to the potential release of variola virus into the general population. Brincidofovir, the second medicine approved by the US Food and Drug Administration to treat smallpox, is metabolized by oxidative and hydrolytic pathways. The oxidative pathway is initiated by cytochrome P450 4F2 (CYP4F2), an enzyme lacking clinical probes for drug interaction studies. The aim of this work was to assess the impact of reduced activity CYP4F2 variants (rs2108622, C/T and T/T) on brincidofovir pharmacokinetics as a surrogate for drug inhibition. Genotyping was performed on blood from healthy participants receiving oral (n = 261) and intravenous (IV, n = 49) brincidofovir across 6 phase 1 trials. Plasma concentrations were measured by validated liquid chromatography tandem mass spectrometry methods. After oral administration, subjects with the lowest activity CYP4F2 genotype (T/T) had up to 36% higher AUCinf and 29% higher Cmax while subjects with the moderate activity CYP4F2 genotype (C/T) had similar Cmax and AUCinf compared to those with the wild-type genotype. Little to no increase in brincidofovir exposure parameters was observed following IV administration. Based on the lack of significant increases in brincidofovir plasma concentrations in subjects with low activity CYP4F2, a clinically meaningful drug-drug interaction is not expected with CYP4F2 inhibitor and brincidofovir coadministration.

Exploring the complex relationship between vitamin K, gut microbiota, and warfarin variability in cardiac surgery patients

BACKGROUND AND OBJECTIVES

Due to the high individual variability of anticoagulant warfarin, this study aimed to investigate the effects of vitamin K concentration and gut microbiota on individual variability of warfarin in 246 cardiac surgery patients.

METHODS

The pharmacokinetics and pharmacodynamics (PKPD) model predicted international normalized ratio (INR) and warfarin concentration. Serum and fecal samples were collected to detect warfarin and vitamin K [VK1 and menaquinone-4 (MK4)] concentrations and gut microbiota diversity, respectively. In addition, the patient's medical records were reviewed for demographic characteristics, drug history, and CYP2C9, VKORC1, and CYP4F2 genotypes.

RESULTS

The PKPD model predicted ideal values of 62.7% for S-warfarin, 70.4% for R-warfarin, and 76.4% for INR. The normal VK1 level was 1.34±1.12 nmol/ml (95% CI: 0.33-4.08 nmol/ml), and the normal MK4 level was 0.22±0.18 nmol/ml (95% CI: 0.07-0.63 nmol/ml). The MK4 to total vitamin K ratio was 16.5±9.8% (95% CI: 4.3-41.5%). The S-warfarin concentration of producing 50% of maximum anticoagulation and the half-life of prothrombin complex activity tended to increase with vitamin K. Further, Prevotella and Eubacterium of gut microbiota identified as the main bacteria associated with individual variability of warfarin. The results suggest that an increase in vitamin K concentration can decrease anticoagulation, and gut microbiota may influence warfarin anticoagulation through vitamin K2 synthesis.

CONCLUSION

This study highlights the importance of considering vitamin K concentration and gut microbiota when prescribing warfarin. The findings may have significant implications for the personalized use of warfarin. Further research is needed to understand better the role of vitamin K and gut microbiota in warfarin anticoagulation.

The Relationship Among Intestinal Bacteria, Vitamin K and Response of Vitamin K Antagonist: A Review of Evidence and Potential Mechanism

The vitamin K antagonist is a commonly prescribed effective oral anticoagulant with a narrow therapeutic range, and the dose requirements for different patients varied greatly. In recent years, studies on human intestinal microbiome have provided many valuable insights into disease development and drug reactions. A lot of studies indicated the potential relationship between microbiome and the vitamin K antagonist. Vitamin K is absorbed by the gut, and the intestinal bacteria are a major source of vitamin K in human body. A combined use of the vitamin K antagonist and antibiotics may result in an increase in INR, thus elevating the risk of bleeding, while vitamin K supplementation can improve stability of anticoagulation for oral vitamin K antagonist treatment. Recently, how intestinal bacteria affect the response of the vitamin K antagonist remains unclear. In this review, we reviewed the research, focusing on the physiology of vitamin K in the anticoagulation treatment, and investigated the potential pathways of intestinal bacteria affecting the reaction of the vitamin K antagonist.

[Development of Stratified and Personalized Medicine Based on Pharmacogenomic and Pharmacokinetic Analyses]

To administer optimal and safe pharmacotherapy, development of stratified and personalized therapy is imperative. Pharmacogenomics (PGx) is useful in elucidating factors causing individual differences in drug efficacy and the emergence of adverse effects. It also helps design accurate drug administration methods by evaluating the effects of patient-related factors, such as genetic factors, that influence pharmacokinetics (PK) and pharmacodynamics (PD). In addition, selection of appropriate therapeutic agents requires the implementation of precision medicine allowing accurate disease diagnosis. To establish precision medicine, it is necessary to uncover the association of pathophysiological factors, which are represented as endotype or genotype, with the pathology of several phenotypes. This review describes two aspects related to realization of individualized medicine, namely the effectiveness of PK/PD/PGx studies and the stratification of pathological conditions. First, we conducted a PK/PD/PGx study with the aim to individualize warfarin treatment. In this study, we elucidated the effect of CYP4F2 polymorphisms associated with vitamin K metabolism by measuring the blood concentrations of warfarin and vitamin K. Then, to develop precision medicine for asthma and chronic obstructive pulmonary disease (COPD), we analyzed not only clinical symptoms but also pathological biomarkers and genes associated with inflammation. The findings may contribute toward better understanding of the pathological conditions of asthma, COPD, and asthma-COPD overlap.

Effects of Ketoconazole, a CYP4F2 Inhibitor, and CYP4F2*3 Genetic Polymorphism on Pharmacokinetics of Vitamin K1

The objective of this study was to evaluate whether cytochrome P450 (CYP)4F2 is involved in the exposure of vitamin K₁ through a drug interaction study with ketoconazole, a CYP4F2 inhibitor, and a pharmacogenetic study with CYP4F2*3. Twenty-one participants with different CYP4F2*3 polymorphisms were enrolled (8 for *1/*1, 7 for *1/*3, and 6 for *3/*3). All participants were treated twice daily for 5 days with 200 mg of ketoconazole or placebo. Finally, a single dose of 10 mg vitamin K₁ was administered, plasma levels of vitamin K₁ were measured, and its pharmacokinetics was assessed. Ketoconazole elevated the plasma levels of vitamin K₁ and increased the average area under the concentration-time curve (AUC_inf ) and peak concentration by 41% and 40%, respectively. CYP4F2*3 polymorphism also affected plasma levels of vitamin K₁ and its pharmacokinetics in a gene dose-dependent manner. The average AUC_inf value was 659.8 ng·h/mL for CYP4F2*1/*1, 878.1 ng·h/mL for CYP4F2*1/*3, and 1125.2 ng·h/mL for CYP4F2*3/*3 (P = .010). This study revealed that ketoconazole and CYP4F2*3 polymorphism substantially increased the exposure of vitamin K₁ in humans. These findings provide a plausible explanation for variations in warfarin dose requirements resulting from interindividual variations in vitamin K₁ exposure due to CYP4F2-related drug interactions and genetic polymorphisms.

A simple, sensitive, and high-throughput LC-APCI-MS/MS method for simultaneous determination of vitamin K1, vitamin K1 2,3-epoxide in human plasma and its application to a clinical pharmacodynamic study of warfarin

Warfarin exerts its anticoagulation activity by blocking the vitamin K-epoxide cycle. A quantitative understanding of how warfarin and related genes interact with the vitamin K-epoxide cycle and the associated change of coagulation activity in the human body may help study the pharmacodynamics of warfarin. The plasma concentration of vitamin K₁ (VK₁) and vitamin K₁ 2,3-epoxide (VK₁O) could reflect the status of vitamin K-epoxide cycle. However, their determination is a challenging task due to their extremely low concentrations in human plasma and the severe interferences caused by co-extracted lipids. In this study, we developed an LC-APCI-MS/MS method for the simultaneous determination of VK₁ and VK₁O in human plasma using stable deuterium-labeled vitamin K₁ (vitamin K₁-d7) as the internal standard (IS). Plasma samples were prepared through protein denaturation followed by one-step liquid extraction with cyclohexane. Chromatographic separation of analytes from isobaric interferences and endogenous ion suppressor was performed on a Synergi Hydro-RP column (150 mm × 4.6 mm, 4 μm) under the reversed-phase condition with isocratic elution. The selective reaction monitoring (SRM) transitions were chosen as m/z = 451.5→187.3 for VK₁, m/z = 467.5→161.2 for VK₁O, and m/z = 458.6→194.3 for IS in APCI positive mode. The assay was linear in the range of 100-10,000 pg/mL for the two analytes and achieved considerable extraction recoveries (87.8-93.3%, 91.0-96.9%, and 92.0% for VK₁, VK₁O, and IS, respectively), negligible matrix effects (93.6-96.0%, 96.3-100.1%, and 95.5%), and high selectivity with a small sample volume requirement (0.2 mL) and short run time (15 min). The validated method was successfully applied in a clinical pharmacodynamic study of warfarin, and the clotting activity was found to be negatively correlated with the plasma concentration ratio of VK₁O to VK₁.

Anticoagulant prophylaxis and therapy in children: current challenges and emerging issues

This review is aimed at describing the unique challenges of anticoagulant prophylaxis and treatment in children, and highlighting areas for research for improving clinical outcomes of children with thromboembolic disease. The evidence presented demonstrates the challenges of advancing the evidence base informing optimal management of thromboembolic disease in children. Recent observational studies have identified risk factors for venous thromboembolism in children, but there are few interventional studies assessing the benefit-risk balance of using thromboprophylaxis in risk-stratified clinical subgroups. A risk level-based framework is proposed for administering mechanical and pharmacological thromboprophylaxis. More research is required to refine the assignment of risk levels. The anticoagulants currently used predominantly in children are unfractionated heparin, low molecular weight heparin, and vitamin K antagonists. There is a paucity of robust evidence on the age-specific pharmacology of these agents, and their efficacy and safety for prevention and treatment of thrombosis in children. The available literature is heterogeneous, reflecting age-specific differences, and the various clinical settings for anticoagulation in children. Monitoring assays and target ranges are not well established. Nevertheless, weight-based dosing appears to achieve acceptable outcomes in most indications. Given the limitations of the classical anticoagulants for children, there is great interest in the direct oral anticoagulants (DOACs), whose properties appear to be particularly suitable for children. All DOACs currently approved for adults have Pediatric Investigation Plans ongoing or planned. These are generating age-specific formulations and systematic dosing information. The ongoing pediatric studies still have to establish whether DOACs have a positive benefit-risk balance in the various pediatric indications and age groups.

Effect of VKORC1, CYP2C9, CFP4F2, and GGCX Gene Polymorphisms on Warfarin Dose in Japanese Pediatric Patients

BACKGROUND

Warfarin dosage requirements show considerable inter-individual variability. There are some reports of warfarin dose regimens correlating with single nucleotide polymorphisms (SNP) for CYP2C9, VKORC1 and other genes in adults. In children, however, reports are scarcer than in adults and the number of genes examined is more limited. We explored the effects of genetic variation on warfarin dose requirement in Japanese pediatric patients.

METHODS

A total of 45 patients who were prescribed warfarin at the Yokohama City University Hospital were included in this study. The influence of genetic polymorphisms on stable warfarin dosage requirement was investigated by genotyping SNPs of the VKORC1, CYP2C9, CYP4F2, and GGCX genes (rs9923231, rs1057910, rs2108622, and rs699664, respectively) in each patient.

RESULTS

Patients with the TT genotype in rs9923231 in VKORC1 required significantly lower maintenance dosages than those with the TC genotype (p = 0.001). Multiple regression analysis showed that, while VKORC1 status and patient height account for 78.2 % of the variability in maintenance warfarin dosage, genetic polymorphisms in VKORC1 account for 27 %, although polymorphisms in CYP4F2 and GGCX had no effect on dosage and the effect of CYP2C9 could not be evaluated.

CONCLUSIONS

Polymorphisms in VKORC1 partially affected daily warfarin dosage requirements. VKORC1 genotype and height are the primary determinants influencing warfarin dosage in Japanese pediatric patients. Further studies with larger sample sizes are needed to confirm our results.

Theory-based pharmacokinetics and pharmacodynamics of S- and R-warfarin and effects on international normalized ratio: influence of body size, composition and genotype in cardiac surgery patients

AIMS

The aims of this study are to apply a theory-based mechanistic model to describe the pharmacokinetics (PK) and pharmacodynamics (PD) of S- and R-warfarin.

METHODS

Clinical data were obtained from 264 patients. Total concentrations for S- and R-warfarin were measured by ultra-high performance liquid tandem mass spectrometry. Genotypes were measured using pyrosequencing. A sequential population PK parameter with data method was used to describe the international normalized ratio (INR) time course. Data were analyzed with NONMEM. Model evaluation was based on parameter plausibility and prediction-corrected visual predictive checks.

RESULTS

Warfarin PK was described using a one-compartment model. CYP2C9 *1/*3 genotype had reduced clearance for S-warfarin, but increased clearance for R-warfarin. The in vitro parameters for the relationship between prothrombin complex activity (PCA) and INR were markedly different (A = 0.560, B = 0.386) from the theory-based values (A = 1, B = 0). There was a small difference between healthy subjects and patients. A sigmoid E_max PD model inhibiting PCA synthesis as a function of S-warfarin concentration predicted INR. Small R-warfarin effects was described by competitive antagonism of S-warfarin inhibition. Patients with VKORC1 AA and CYP4F2 CC or CT genotypes had lower C50 for S-warfarin.

CONCLUSION

A theory-based PKPD model describes warfarin concentrations and clinical response. Expected PK and PD genotype effects were confirmed. The role of predicted fat free mass with theory-based allometric scaling of PK parameters was identified. R-warfarin had a minor effect compared with S-warfarin on PCA synthesis. INR is predictable from 1/PCA in vivo.

Pharmacogenetic-guided Warfarin Dosing Algorithm in African-Americans

We aim to develop warfarin dosing algorithm for African-Americans. We explored demographic, clinical, and genetic data from a previously collected cohort of 163 African-American patients with a stable warfarin dose. We explored 2 approaches to develop the algorithm: multiple linear regression and artificial neural network (ANN). The clinical significance of the 2 dosing algorithms was evaluated by calculating the percentage of patients whose predicted dose of warfarin was within 20% of the actual dose. Linear regression model and ANN model predicted the ideal dose in 52% and 48% of the patients, respectively. The mean absolute error using linear regression model was estimated to be 10.8 mg compared with 10.9 mg using ANN. Linear regression and ANN models identified several predictors of warfarin dose including age, weight, CYP2C9 genotype *1/*1, VKORC1 genotype, rs12777823 genotype, rs2108622 genotype, congestive heart failure, and amiodarone use. In conclusion, we developed a warfarin dosing algorithm for African-Americans. The proposed dosing algorithm has the potential to recommend warfarin doses that are close to the appropriate doses. The use of more sophisticated ANN approach did not result in improved predictive performance of the dosing algorithm except for patients of a dose of ≥49 mg/wk.

Pharmacogenomics in Pediatric Patients: Towards Personalized Medicine

It is well known that drug responses differ among patients with regard to dose requirements, efficacy, and adverse drug reactions (ADRs). The differences in drug responses are partially explained by genetic variation. This paper highlights some examples of areas in which the different responses (dose, efficacy, and ADRs) are studied in children, including cancer (cisplatin), thrombosis (vitamin K antagonists), and asthma (long-acting β2 agonists). For childhood cancer, the replication of data is challenging due to a high heterogeneity in study populations, which is mostly due to all the different treatment protocols. For example, the replication cohorts of the association of variants in TPMT and COMT with cisplatin-induced ototoxicity gave conflicting results, possibly as a result of this heterogeneity. For the vitamin K antagonists, the evidence of the association between variants in VKORC1 and CYP2C9 and the dose is clear. Genetic dosing models have been developed, but the implementation is held back by the impossibility of conducting a randomized controlled trial with such a small and diverse population. For the long-acting β2 agonists, there is enough evidence for the association between variant ADRB2 Arg16 and treatment response to start clinical trials to assess clinical value and cost effectiveness of genotyping. However, further research is still needed to define the different asthma phenotypes to study associations in comparable cohorts. These examples show the challenges which are encountered in pediatric pharmacogenomic studies. They also display the importance of collaborations to obtain good quality evidence for the implementation of genetic testing in clinical practice to optimize and personalize treatment.

Effect of CYP2C9, VKORC1, and CYP4F2 polymorphisms on warfarin maintenance dose in children aged less than 18 years: a protocol for systematic review and meta-analysis

BACKGROUND

Despite its shortcomings, warfarin is still the most commonly prescribed anticoagulant to prevent thromboembolism in children. In adults, numerous studies confirmed the robust relationship between warfarin maintenance doses and single nucleotide polymorphisms of cytochrome P450 2C9 (CYP2C9), vitamin K epoxide reductase (VKORC1), and cytochrome P450 4F2 (CYP4F2). However, their effect in children still remains to be determined. The primary objective of the present systematic review and meta-analysis is to assess the effect of genotypes of CYP2C9, VKORC1, and CYP4F2 on warfarin maintenance dose in children.

METHODS/DESIGN

A comprehensive literature review search using the OVID platform will be conducted by a specialized librarian, without language restrictions (i.e., MEDLINE/EMBASE/Cochrane Central Register of Controlled Trials), and all abstracts will be reviewed by two authors. Data abstraction from each eligible study will be extracted individually by two authors (MT and TK), and disagreements will be resolved through discussion with a third person (SI). Critical appraisal of the included analysis of the primary objective will follow the Newcastle-Ottawa Scale, in addition to the Strengthening the Reporting of Genetic Association study (STREGA) statement, and data reporting will follow the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. For the meta-analysis, the presence vs. absence of each genetic polymorphism will be pursued, respectively, using a random effect model with effect size expressed as a mean difference plus 95 % confidence interval.

DISCUSSION

Our study will provide a comprehensive systematic review and meta-analysis on the potential effects of CYP2C9, VKORC1, or CYP4F2 on the warfarin maintenance dose in children, exploring the feasibility of the development of pharmacogenetic-guided warfarin dosing algorithm for children on oral vitamin K antagonists.

SYSTEMATIC REVIEW REGISTRATION

The review has been registered with PROSPERO (registration number CRD42015016172 ).

A model analysis for dose-response relationship of warfarin in Japanese children: An introduction of the SIZE parameter

The objective of the present study was to develop an optimal equation for the pediatric dose-response relationship of warfarin using a size parameter with an exponent of body weight (SIZE) which has been proposed for scaling drug clearance. Twenty patients with stable anticoagulation by warfarin were enrolled in the present study. During a mean follow-up period of 7.36 years, 857 data points were obtained. The average patient age and body weight were 8.49 years and 24.5 kg, respectively. The relative response index to warfarin with PT-INR values normalized by daily-dose per SIZE showed fewer systematic changes than those per body weight. The anticoagulant effect of warfarin in patients with the VKORC1 1173CT or 1173CC genotype was 47.3% of that with the 1173TT genotype. Concomitant use of bosentan attenuated the anticoagulant effect of warfarin to 84.1%. In conclusion, the SIZE parameter appeared to be an effective way to describe the pediatric dose-response relationship of warfarin, and consequently, a longitudinal follow-up study design with multiple measurements was useful to detect changes within individual subjects.

Pharmacogenetic Markers of Drug Efficacy and Toxicity

The action of a drug is dictated by its pharmacokinetic and pharmacodynamics properties, both of which can vary in different individuals because of environmental and genetic factors. Pharmacogenetics, the study of genetic factors determining drug response, has the potential to improve clinical outcomes through targeting therapies, individualizing dosing, preventing adverse drug reactions, and potentially rescuing previously failed therapies. Although there have been significant advances in pharmacogenetics over the last decade, only a few have been translated into clinical practice. However, with new rapid genotyping technologies, regulatory modernization, novel clinical trial designs, systems approaches, and integration of pharmacogenetic data into decision support systems, there is hope that pharmacogenetics, as an important component of the overall drive towards personalized medicine, will advance more quickly in the future. There will continue to be a need for collaboration between centers all over the world, and multisector working, capitalizing on the current data revolution.

The impact of age and CYP2C9 and VKORC1 variants on stable warfarin dose in the paediatric population

The influence of genetic variation on warfarin dose requirement is limited for paediatric patients. We performed a retrospective, cross-sectional study to examine the effect of variant CYP2C9 and VKORC1 genotypes on warfarin dose in 100 children. Those with VKORC1 genotype AA required 48% of the dose of homozygous wild-type (GG, P < 0·0001). Patients with any variant CYP2C9 allele required 71% of the dose for wild-type (P = 0·001). The effect of variant VKORC1 alleles tended to vary with age, suggesting developmental ontogeny may influence warfarin sensitivity. Age, CYP2C9 genotype, VKORC1 genotype and age:VKORC1 interaction accounted for 53% of warfarin dose variability.

Pharmacogenetics in clinical pediatrics: challenges and strategies

The use of genetic information to guide medication decisions holds great promise to improve therapeutic outcomes through increased efficacy and reduced adverse events. As in many areas of medicine, pediatric research and clinical implementation in pharmacogenetics lag behind corresponding adult discovery and clinical applications. In adults, genotype-guided clinical decision support for medications such as clopidogrel, warfarin and simvastatin are in use in some medical centers. However, research conducted in pediatric populations demonstrates that the models and practices developed in adults may be inaccurate in children, and some applications lack any pediatric research to guide clinical decisions. To account for additional factors introduced by developmental considerations in pediatric populations and provide pediatric patients with maximal benefit from genotype-guided therapy, the field will need to develop and employ creative solutions. In this article, we detail some concerns about research and clinical implementation of pharmacogenetics in pediatrics, and present potential mechanisms for addressing them.

Pharmacogenetics in clinical pediatrics: challenges and strategies

The use of genetic information to guide medication decisions holds great promise to improve therapeutic outcomes through increased efficacy and reduced adverse events. As in many areas of medicine, pediatric research and clinical implementation in pharmacogenetics lag behind corresponding adult discovery and clinical applications. In adults, genotype-guided clinical decision support for medications such as clopidogrel, warfarin and simvastatin are in use in some medical centers. However, research conducted in pediatric populations demonstrates that the models and practices developed in adults may be inaccurate in children, and some applications lack any pediatric research to guide clinical decisions. To account for additional factors introduced by developmental considerations in pediatric populations and provide pediatric patients with maximal benefit from genotype-guided therapy, the field will need to develop and employ creative solutions. In this article, we detail some concerns about research and clinical implementation of pharmacogenetics in pediatrics, and present potential mechanisms for addressing them.