Oral anticoagulants: Pharmacogenetics

Effect of MEF2A and SLC22A3-LPAL2-LPA gene polymorphisms on warfarin sensitivity and responsiveness in Jordanian cardiovascular patients

AIMS

This study aims to investigate the influence of MEF2A and SLC22A3-LPAL2-LPA polymorphisms on cardiovascular disease susceptibility and responsiveness to warfarin medication in Jordanian patients, during the initiation and maintenance phases of treatment.

BACKGROUNDS

Several candidate genes have been reported to be involved in warfarin metabolism and studying such genes may help in finding an accurate way to determine the needed warfarin dose to lower the risk of adverse drug effects, resulting in more safe anticoagulant therapy.

METHODS

The study population included 212 cardiovascular patients and 213 healthy controls. Genotyping of MEF2A and SLC22A3-LPAL2-LPA polymorphisms was conducted to examine their effects on warfarin efficiency and cardiovascular disease susceptibility using PCR-based methods.

RESULTS

One SNP (SLC22A3-LPAL2-LPA rs10455872) has been associated with cardiovascular disease in the Jordanian population, whereas the other SNPs in the MEF2A gene and SLC22A3-LPAL2-LPA gene cluster did not have any significant differences between cardiovascular patients and healthy individuals. Moreover, SLC22A3-LPAL2-LPA rs10455872 was correlated with moderate warfarin sensitivity, the other SNPs examined in the current study have not shown any significant associations with warfarin sensitivity and responsiveness.

CONCLUSION

Our data refer to a lack of correlation between the MEF2A polymorphism and the efficacy of warfarin treatment in both phases of treatment, the initiation, and maintenance phases. However, only rs10455872 SNP was associated with sensitivity to warfarin during the initiation phase. Furthermore, rs3125050 has been found to be associated with the international normalized number treatment outcomes in the maintenance phase.

Influence of CYP4F2, ApoE, and CYP2A6 gene polymorphisms on the variability of Warfarin dosage requirements and susceptibility to cardiovascular disease in Jordan

Cardiovascular diseases are among the leading causes of death worldwide. Many of those diseases require treatment with warfarin, an anticoagulant that has a large high inter and intra-variability in the required doses. The aim of this study is to find if there are any associations between rs2108622 of CYP4F2, rs7412 and rs405509 of ApoE, and rs1801272 of CYP2A6, and CVD and warfarin dose variability. The selected genes and their polymorphisms are involved in many GWAS associated with cardiovascular disease and variability in warfarin treatment. The study sample consisted of 212 Jordanian Cardiovascular patients and 213 healthy controls. DNA was extracted and the Mass ARRAY™ system was used to genotype four selected SNPs within three genes (CYP4F2, ApoE, and CYP2A6). Only one out of the four selected SNPs (ApoE rs7412 SNP) was found to be associated with the risk of cardiovascular disease. Also, this SNP showed significant differences in warfarin initial doses. CYP2A6 rs1801272 SNP was found to be associated with warfarin sensitivity during the initiation phase of therapy and with warfarin responsiveness and INR measurement during the stabilization phase of therapy. This study improves the current understanding of the high inter and intra-variabilities in response to warfarin, including the variety of dosing requirements and the susceptibility to cardiovascular disease in the Jordanian Arab population. Further study on a larger sample and in different ethnic groups could help in improving our understanding of warfarin's pharmacogenetics and its application in personalized medicine.

Effects of coagulation factor VII polymorphisms on warfarin sensitivity and responsiveness in Jordanian cardiovascular patients during the initiation and maintenance phases of warfarin therapy

Purpose

This study aims to investigate the relationships between genetic polymorphisms of the coagulation factor VII (FVII) gene and warfarin responsiveness and sensitivity.

Patients and methods

The study population consisted of 417 subjects (207 Jordanian cardiovascular patients and 210 healthy individuals). Cardiovascular patients were classified into two groups: those sensitive to warfarin dosage (sensitive, moderate, and resistant) and those responsive to warfarin based on International Normalized Ratios (INRs; poor, good, and extensive responders). The HVR4 polymorphism of the FVII gene was genotyped.

Results

Our results showed that there are significant differences between patients and controls according to both genotypic and allelic frequencies (P<0.0001) in the genetic susceptibility study. Moreover, the pharmacogenetics study reported that HVR4 had no association with warfarin sensitivity or responsiveness during the initiation and maintenance phases of therapy, the only significant differences were in the INR outcome measured during the maintenance phase of therapy (P=0.012).

Conclusion

Our data suggests lacking of association between the HVR4 polymorphism in the FVII gene and warfarin sensitivity and responsiveness during the initiation and maintenance phases of therapy. It is possible that these patients carry additional mutations in genes involved in the coagulation pathway.

Influence of genetic and non-genetic factors on acenocoumarol maintenance dose requirement in a Tunisian population

PURPOSE

We aimed to study potential variables involved in interindividual variability to acenocoumarol (AC) response in order to establish a pharmacogenetic algorithm (PA) that includes clinical and genetic factors to predict adequate AC dose to stabilize anticoagulation in a cohort of Tunisian patients.

METHODS

Genotyping of the CYP2C9, VKORC1, CYP4F2, and CALU polymorphisms was conducted on 246 patients using PCR-RFLP technique. AC normalized maintenance dose (NMD): ((mean maintenance dose/international normalized ratio (INR)) equilibrium) was calculated. The statistical study was carried out with SPSS V20.

RESULTS

A significant correlation was found between age, BMI, and daily AC dose (r = - 0.397; p < 0.001 and r = 0.215; p = 0.001, respectively). The carriers of mutated alleles CYP2C9*2 or CYP2C9*3 or VKORC1 haplotypes (H1 and H7) were associated with AC hyper-sensibility. After adjustment to potential covariates, these patients presented supra-therapeutic INR during treatment period and needed low AC dose (ORs* = 0.28 [0.06-0.60], p = 0.004; ORs* = 0.12 [0.04-0.05], p < 0.001; ORs* = 0.45 [0.24-0.84], p = 0.01; and ORs* = 0.28 [0.06-0.98], p = 0.049, respectively). However, carriers of VKORC1 haplotypes (H3 and H12) or mutated alleles CYP4F2 (rs2108622) or CALU (rs1043550) tend to resist to treatment, hence long period of therapy initiation, and must be treated with high AC dose (ORs* = 2.67 [81.12-5.91], p = 0.013; ORs* = 8.76 [1.07-76.26], p = 0.019; ORs* = 3.12 [1.01-9.63], p = 0.047; and ORs* = 3.96 [1.41-11.09], p = 0.009, respectively). A final multivariate regression model explained 48.1% of the global interindividual variability in AC dose requirement.

CONCLUSION

The PA demonstrated that VKORC1 and CYP2C9 polymorphisms contribution was more important than clinical factors. Applying the PA would allow dose adjustment to treat patients in a personalized manner.

Factors influencing warfarin control in Australia and Singapore

INTRODUCTION

Warfarin is widely used for patients with non-valvular atrial fibrillation (NVAF). Variations in warfarin control, as measured by time in therapeutic range (TTR), have been reported across different regions and ethnicities, particularly between Western and Asian countries. However, there is limited data on comparative factors influencing warfarin control in Caucasian and Asian patients. Therefore, the aim of this study was to determine warfarin control and potential factors influencing this in patients with NVAF in Australia and Singapore.

METHODS

Retrospective data was collected for patients receiving warfarin for January to June 2014 in Australia and Singapore. TTR was calculated for individuals with mean patient TTR used for analysis. Possible influential factors on TTR were analysed including age, gender, concurrent co-morbidities, and concurrent medication.

RESULTS

The mean TTR was significantly higher in Australia (82%) than Singapore (58%). At both sites, chronic kidney disease significantly lowered this TTR. Further factors influencing control were anaemia and age<60years in Australia, and vascular disease, CHA₂DS₂-VASc score of 6, and concurrent platelet inhibitor therapy in Singapore.

DISCUSSION

Warfarin control was significantly higher in Australia compared to Singapore, however chronic kidney disease reduced control at both sites. The different levels of control in these two countries, together with patient factors further reducing control may impact on anticoagulant choice in these countries with better outcomes from warfarin in Australia compared to Singapore.

VKORC1 polymorphisms and warfarin maintenance dose in population of Sakha (Yakuts)

BACKGROUND

Vitamin K antagonists are effective in the prevention and treatment of thromboembolic disorders. Warfarin is one of the most widely prescribed vitamin K antagonists in the world [1, 2]. It has a narrow therapeutic range and a given dose may result in a large inter-individual variation of response. Insufficient dose may fail to prevent thromboembolism, while an overdose increases the risk of bleeding. Patient-specific factors (e.g., age, body size, race, concurrent diseases, and medications) explain some of the variability in warfarin dosage, but genetic factors influencing warfarin response explain a significantly higher proportion of this variability [3]. Molecular analysis of the gene that encodes the target enzyme vitamin K epoxide reductase complex 1 (VKORC1) strongly suggests that its genetic variations greatly affect the individual response to oral anticoagulants [4-7].

OBJECTIVE

To evaluate effects of VKORC1 polymorphisms on warfarin dose excess anticoagulation (INR >4.0) in the population of Sakha (S) patients.

METHODS

53 patients (29-women, 24-men) with atrial fibrillation (68%), congestive heart failure (60%), hypertension (49%) and cardiac valve replacement (26%) were recruited. The age range was 26-80 years, with a mean age of 62.87 ± 12.57 years.International normalized ratio and plasma warfarin concentrations were determined. Genotyping was carried out by RT-PCR (real-time PCR). The three genetic polymorphisms of the gene VKORC1 G3673A (rs9923231) were studied: normal (GG), heterozygous (GA) and homozygous (AA). Fisher exact probability test and chi-square test (with Yates correction) were applied to compare data among the AA and GG + GA groups; also Mann-Whitney test was used.

RESULTS

The median maintenance daily dose of warfarin among AA carriers was 3.0 mg/day [1.25-7.5 mg], while in GG and GA patients it was 3.13 mg/day [1.88-7.92 mg]. The mean daily warfarin dosage was higher in GG and GA genotype carriers 4.05 mg/day (SD ± 1.7) than in patients with AA genotype 3.13 (SD ± 1.5). Differences are of borderline significance (p = 0.054). Of the 41 patients who required warfarin doses of less than 5 mg, 28 (63%) were found to be AA carriers and 14 (37%) were GG, GA carriers. Differences were not quite significant (p = 0.072). Among 31 homozygous polymorphism carriers 2 (4%) patients developed overanticoagulation (INR >4.0), while among 22 normal and heterozygous polymorphisms carriers only 3 (6%) patients developed overanticoagulation (INR >4.0). Differences were not statistically significant (p = 0.36).

CONCLUSIONS

No significant association between VKORC1 polymorphisms and the frequency of excess anticoagulation (INR >4.0) was found. This may be explained by the number of cases included. AA polymorphisms compared to other polymorphisms shows borderline difference in the warfarin dose. The results can be used for the development of a pharmacogenetic-guided warfarin dosing algorithm.

Is there a role for MDR1, EPHX1 and protein Z gene variants in modulation of warfarin dosage? a study on a cohort of the Egyptian population

BACKGROUND

There is considerable inter-individual variability in warfarin dosages necessary to achieve target therapeutic anticoagulation. Polymorphisms in genes, which master warfarin pharmacokinetics and pharmacodynamics, might influence warfarin dose variation. Genes encoding drug transporters, such as human multidrug resistance (MDR1), as well as epoxide hydrolase 1 (EPHX1), which is a putative subunit of the vitamin K epoxide reductase, and Protein Z (PZ), which is a vitamin K-dependent plasma glycoprotein, are among those candidate genes.

OBJECTIVE

The purpose of this study was to investigate the contribution of MDR1 C3435T, EPHX1 H139R and PZ A-13G gene polymorphisms in warfarin dose variation in a cohort of the Egyptian population.

METHODS

Eighty-four patients whose international normalized ratio (INR) was in the range of 2-3, 41 males and 43 females, with a mean (±SD) age of 40.9 (13.3) years were recruited into this study. MDR1 C3435T, EPHX1 H139R and PZ A-13G gene polymorphisms were detected by polymerase chain reaction-restriction fragment length polymorphism. Primarily, linear regression analysis, including the variables age, gender, MDR1 C3435T, EPHX1 H139R and combined MDR1 C3435T, EPHX1 H139R and PZ A-13G genotypes, was used to assess the effective factors for warfarin maintenance dose. Secondly, the previously examined cytochrome P450 (CYP) 2C9 A1075C and vitamin K epoxide reductase complex subunit 1 (VKORC1) C1173T were added to the regression analysis.

RESULTS

Warfarin dose/week was not influenced by each of the MDR1 C3435T, EPHX1 H139R, and PZ A-13G gene polymorphisms when examined separately. However, when these single nucleotide polymorphisms (SNPs) were combined, MDR1 TT/EPHX1 RH,RR/PZ AA subjects showed statistically significant increase in warfarin dose/week when compared with MDR1 CC/EPHX1 RH,RR/PZ AA subjects [median (25th-75th percentiles): 49.0 (42.0-59.5) vs. 35.0 (24.5-42.0) mg/week, respectively] (p = 0.014). In contrast, in the presence of wild-type EPHX1 HH, there was a decrease in warfarin dose/week in MDR1 TT subjects when compared with CT and CC subjects [median (25th-75th percentiles): 22.0 (17.5-30.6), 42.0 (35.0-49.0) and 42.0 (28.0-54.3) mg/week, respectively] (p = 0.005 and 0.030, respectively). Age had a significant contribution (p = 0.048) to the overall variability in warfarin dose. Calculated weekly dose = 52.928 - (0.289 × age) + (9.709 × combined genotype). The multivariate linear regression equation of warfarin maintenance dose accounted for about 8 % of variation in dose (R (2) = 0.079), age accounted for 5 % of variation, while combined genotypes added the extra 3 %. However, the new regression equation accounted for 20.9 % of variation in dose. Age accounted for 5 %, while VKORC1 C1173T accounted for an extra 13 % of variation and MDR1 C3435T accounted for the remaining 3 % of variation. Calculated dose = 64.909 - (0.282 × age) - (13.390 × VKORC1) - (7.164 × MDR1). Correlation analysis showed a close and significant relationship between the calculated and actual warfarin dose (r = 0.457; p < 0.0005).

CONCLUSION

Warfarin dose/week was significantly influenced by the combined MDR1 C3435T and EPHX1 H139R gene polymorphism since no polymorphism of PZ A-13G SNP was detected in our studied Egyptian population. Future studies with larger sample size will be needed to confirm our findings before definitive conclusions can be made.

The VKORC1 Asp36Tyr variant and VKORC1 haplotype diversity in Ashkenazi and Ethiopian populations

The vitamin K epoxide reductase (VKORC1) is a key enzyme in the vitamin K cycle impacting various biological processes. VKORC1 genetic variability has been extensively studied in the context of warfarin pharmacogenetics revealing different distributions of VKORC1 haplotypes in various populations. We previously identified the VKORC1 Asp36Tyr mutation that was associated with warfarin resistance and with distinctive ethnic distribution. In this study, we performed haplotype analysis using Asp36Tyr and seven other VKORC1 markers in Ashkenazi and Ethiopian-Jewish and non-Jewish individuals. The VKORC1 variability was represented by nine haplotypes (V1-V9) that could be grouped into two distinct clusters (V1-V3 and V4-V9) with intra-cluster difference limited to two nucleotide changes. Phylogeny analysis suggested that these haplotypes could have developed from an ancestral variant, the common V8 haplotype (40 % in all population samples), after ten single mutation events. Asp36Tyr was exclusive to the V5 haplotype of the second cluster. Two haplotypes V5 and V4, distinguished only by Asp36Tyr, were prevalent in both Ethiopian population samples. The V2 haplotype, belonging to the first cluster, was the second most prevalent haplotype in the Ashkenazi population sample (15.8 %) but relatively uncommon in the Ethiopian origin (4.5-4.7 %). We discuss the genetic diversity among studied populations and its potential impact on warfarin-dose management in certain populations of African and European origin.

Association of GGCX gene polymorphism with warfarin dose in atrial fibrillation population in Xinjiang

Objective

To study the effects of γ-glutamyl carboxylase (GGCX) rs2592551 polymorphism on warfarin dose in atrial fibrillation patients in Xinjiang region.

Methods

Polymerase chain reaction - restriction fragment length polymorphism and direct sequencing methods were used to detect the rs2592551 genotype in 269 atrial fibrillation patients with warfarin administration. The effects of different genotypes on warfarin dose were statistically analyzed.

Results

The rs2592551 polymorphism detection results were 136 cases of wild-type homozygous CC genotype (50.56%), 115 cases of heterozygous CT genotype (42.75%), 18 cases of homozygous TT genotype (6.69%). The allele frequency C was 71.93%, T was 28.07%. The stable warfarin dose average was 2.86 ± 0.61 mg/d in patients with CC genotype, 3.59 ± 0.93 mg/d in patients with CT genotype and 4.06 ± 0.88 mg/d in patients with TT genotype. The warfarin dose in different genotypes were compared, there was statistically significant difference between CC and TT, CC and CT (P <0. 05), but the TT and CT showed no significant difference (P > 0.05).

Conclusion

In atrial fibrillation population in Xinjiang, patients with CT and TT genotypes in GGCX gene rs259251 loci required for significantly higher warfarin dose than those with CC genotype. Therefore, rs2592551 polymorphism may one of the factors affecting the warfarin dose in patients with atrial fibrillation.

Positive selection in the chromosome 16 VKORC1 genomic region has contributed to the variability of anticoagulant response in humans

VKORC1 (vitamin K epoxide reductase complex subunit 1, 16p11.2) is the main genetic determinant of human response to oral anticoagulants of antivitamin K type (AVK). This gene was recently suggested to be a putative target of positive selection in East Asian populations. In this study, we genotyped the HGDP-CEPH Panel for six VKORC1 SNPs and downloaded chromosome 16 genotypes from the HGDP-CEPH database in order to characterize the geographic distribution of footprints of positive selection within and around this locus. A unique VKORC1 haplotype carrying the promoter mutation associated with AVK sensitivity showed especially high frequencies in all the 17 HGDP-CEPH East Asian population samples. VKORC1 and 24 neighboring genes were found to lie in a 505 kb region of strong linkage disequilibrium in these populations. Patterns of allele frequency differentiation and haplotype structure suggest that this genomic region has been submitted to a near complete selective sweep in all East Asian populations and only in this geographic area. The most extreme scores of the different selection tests are found within a smaller 45 kb region that contains VKORC1 and three other genes (BCKDK, MYST1 (KAT8), and PRSS8) with different functions. Because of the strong linkage disequilibrium, it is not possible to determine if VKORC1 or one of the three other genes is the target of this strong positive selection that could explain present-day differences among human populations in AVK dose requirement. Our results show that the extended region surrounding a presumable single target of positive selection should be analyzed for genetic variation in a wide range of genetically diverse populations in order to account for other neighboring and confounding selective events and the hitchhiking effect.

Vitamin K-antagonists accelerate atherosclerotic calcification and induce a vulnerable plaque phenotype

BACKGROUND

Vitamin K-antagonists (VKA) are treatment of choice and standard care for patients with venous thrombosis and thromboembolic risk. In experimental animal models as well as humans, VKA have been shown to promote medial elastocalcinosis. As vascular calcification is considered an independent risk factor for plaque instability, we here investigated the effect of VKA on coronary calcification in patients and on calcification of atherosclerotic plaques in the ApoE(-/-) model of atherosclerosis.

METHODOLOGY/PRINCIPAL FINDINGS

A total of 266 patients (133 VKA users and 133 gender and Framingham Risk Score matched non-VKA users) underwent 64-slice MDCT to assess the degree of coronary artery disease (CAD). VKA-users developed significantly more calcified coronary plaques as compared to non-VKA users. ApoE(-/-) mice (10 weeks) received a Western type diet (WTD) for 12 weeks, after which mice were fed a WTD supplemented with vitamin K(1) (VK(1), 1.5 mg/g) or vitamin K(1) and warfarin (VK(1)&W; 1.5 mg/g & 3.0 mg/g) for 1 or 4 weeks, after which mice were sacrificed. Warfarin significantly increased frequency and extent of vascular calcification. Also, plaque calcification comprised microcalcification of the intimal layer. Furthermore, warfarin treatment decreased plaque expression of calcification regulatory protein carboxylated matrix Gla-protein, increased apoptosis and, surprisingly outward plaque remodeling, without affecting overall plaque burden.

CONCLUSIONS/SIGNIFICANCE

VKA use is associated with coronary artery plaque calcification in patients with suspected CAD and causes changes in plaque morphology with features of plaque vulnerability in ApoE(-/-) mice. Our findings underscore the need for alternative anticoagulants that do not interfere with the vitamin K cycle.

Frequency of VKORC1 (C1173T) and CYP2C9 genetic polymorphisms in Egyptians and their influence on warfarin maintenance dose: proposal for a new dosing regimen

INTRODUCTION

Warfarin is one of the most widely used anticoagulants, yet interindividual differences in drug response, a narrow therapeutic range and a high risk of bleeding or stroke complicate its use. We aimed to determine the allele and genotype frequency of VKORC1 1173 C>T, CYP2C9*2 and CYP2C9*3 variant polymorphisms in the Egyptian population and to evaluate their influence on the interindividual differences in warfarin dosage.

METHODS

A total of 154 unrelated healthy adult patients and 46 warfarin-treated patients were included. SYBR Green-based real-time polymerase chain reaction (PCR) assay was used for studying VKORC1 (C1173T) and CYP2C9*3 polymorphisms. Mutagenically separated PCR assay was used to detect the CYP2C9*2 allele.

RESULTS

VKORC1 genotype frequencies were 11%, 24% and 65% for CC, CT and TT, respectively. The prevalence of CYP2C9 haplotypes was 81% (*1\*1), 3.3% (*1\*2), 9.7% (*1\*3), 4.5% (*2\*2) and 0.65% (2\*3 and *3\*3). VKORC1 TT and CYP2C9*2\*2 were associated with a significantly lower warfarin dose. VKORC1 and CYP2C9 accounted for 31.7% and 15.6% of warfarin dose variability, respectively, and together with clinical factors explained 61.3% of total variability.

CONCLUSION

VKORC1-TT and CYP2C9 *1/*1 are the most prevalent genotypes among Egyptians. Patients with VKORC1-TT genotype required a lower warfarin dose.

"The end of good luck''--long-term survival without anticoagulation: a case report and review of the literature

Long-term anticoagulation in patients with metallic prosthetic valve disease is required according to current guidelines. We describe a patient with a functioning mitral mechanical valve without anticoagulation for 27 years. A 46-year-old man admitted to the emergency department with complains of palpitation. The patient had a mitral valve replacement because of severe mitral stenosis. He discontinued warfarin treatment 1 month after surgery because of the unavailability of this drug in Turkey. Transthoracic echocardiography revealed functioning metalic mitral valve with a mean gradient of 9 mm Hg. Fluoroscopy showed normal excursions of the mechanical mitral valve. Transesophageal echocardiography was performed and revealed fresh thrombus formation in the left atrial appendix. Admission international normalized ration (INR) level was 1.79. Due to the higher INR level and long-term survival, genetic analysis of warfarin polymorphism was performed. There was a homozygous mutation in the vitamin K epoxide reductase complex 1 (VKORC1) 1173C>T and 1639G>A genotypes. The possible explanations of long-term survival and baseline higher INR level were linked to the mutation in warfarin metabolism. We also briefly review the literature.

VKORC1, CYP2C9 and CYP4F2 genetic-based algorithm for warfarin dosing: an Italian retrospective study

Aim: A total of 371 patients under stable warfarin therapy were retrospectively selected to develop a pharmacogenetic algorithm to identify the individual maintenance dose. Materials & methods: The variables that were entered into the algorithm were: VKORC1, CYP2C9 and CYP4F2 polymorphisms, body surface area and age. Results: The percentage of cases whose predicted mean weekly warfarin dose was within 20% of the actual maintenance dose was 51.8% considering patients overall, and were 36.2, 66.2 and 55.4%, respectively, taking into account patients requiring low (≤25 mg/week), intermediate (25–45 mg/week) and high (≥45 mg/week) doses. The algorithm could correctly assign 73.8 and 63.2% of patients to the low- and high-dose regimens, respectively. We developed and validated a pharmacogenetic algorithm in a series of Italian patients, we then tested, in the same series of italian patients, the formulas of three published algorithms. These three algorithms were developed and validated by their authors in a series of patients different from our own. The performance of our algorithm in our patients series was slightly higher than that achieved when using the three other algorithms in our patients series. Conclusion: The high predictive accuracy of low and high warfarin requirements of our algorithm warrants its application in prospective studies for clinical validation.

Role of warfarin pharmacogenetic testing in clinical practice

Chronic oral anticoagulation with warfarin is difficult to maintain within the therapeutic range and requires frequent monitoring and dose adjustments. Variations in two genes, VKORC1 and CYP2C9, have been associated with variation in warfarin metabolism among individuals. Patients with CYP2C9*2 and *3 variants have longer times to dose stabilization and are at higher risk of serious and life-threatening bleeding. VKORC1 polymorphisms significantly influence time to first therapeutic warfarin range, and variants in this gene determine low-, intermediate- and high-warfarin dose requirements. The prevalence of CYP2C9 and VKORC1 polymorphisms vary among different ethnic groups, and can account for over 30% of variance in warfarin dose. Recent studies suggest that the pharmacogenomics-guided dosing algorithm can accurately predict warfarin dosage and might reduce adverse events. We aim to review the pharmacogenetics of warfarin metabolism and the clinical role of genetic testing for warfarin therapy.

Use of human hepatocytes to investigate blood coagulation factor

Coagulation is the complex process by which activation of plasmatic haemostasis proteins ends up with the generation of fibrin. Most of the plasma coagulation proteins are synthesized in hepatocytes. The aim of this chapter is to describe experimental procedures allowing to measure the secretion by primary human hepatocytes and functional activity (including production of fibrillar material from extracellular medium) of haemostasis proteins including factors II, V, VII, VIII, PIVKA-II (protein induced by vitK 1 absence or antagonist II), antithrombin and protein S. In addition, we show how treatments of hepatocyte cultures with vitamin K and/or warfarin affect the secretion of haemostasis proteins. The results demonstrate that primary cultures of human hepatocytes constitute an invaluable model for investigating haemostasis protein expression and activity and therapeutic strategies targeting these proteins.

Vitamin K epoxide reductase complex 1 (VKORC1) haplotypes in healthy Hungarian and Roma population samples

The aim of this work was to determine the VKORC1 haplotype profile in healthy Hungarian and Roma population samples, and to compare our data with other selected populations. Using haplotype tagging SNPs (G-1639A, G9041A and C6009T), we characterized Hungarian (n = 510) and Roma (n = 451) population samples with regard to VKORC1*1, *2, *3 and *4 haplotypes. In the Hungarian samples, the VKORC1*1, *2, *3 and *4 haplotypes accounted for 3, 39, 37 and 21%, respectively and by contrast, in the Roma population samples the VKORC1 variants were 5, 30, 46 and 19%, respectively. Comparing the genotypes of Roma and Hungarian populations, difference was found in the *2/*2 (6.87 vs 13.5%), *2/*4 (13.9 vs 19.2%) and *3*3 (21.9 vs 13.7%) VKORC1 haplotype combinations. Comparing each group with the others, and our data with findings published previously by other groups, the VKORC1 genetic profile in Hungarians was more similar to European Caucasians and Americans with European descent than to Roma samples. Clear differences could be detected between Roma versus Hungarians and European or American Caucasians; the Roma population had only minor similarities with data from India.

VKORC1 polymorphisms in Amerindian populations of Brazil

Noncoding polymorphisms in the VKORC1 gene associate with variation of interindividual dosing requirements of warfarin and other coumarin anticoagulants. The frequency of VKORC1 polymorphisms displays distinct interpopulation differences. Here, we report the distribution of the VKORC1 3673G>A, 5808T>G, 6853G>C and 9041G>A SNPs in three endogamous Amerindian (Native American) populations, namely, Guarani-Kaiowá, Guarani-Ñandeva and Kaingang. Individual DNA from 180 healthy adults was genotyped for the VKORC1 polymorphisms using TaqMan® Detection System assays. The ARLEQUIN 3.1 software package was used to estimate haplotype frequency and linkage disequilibrium. The VKORC1 3673G>A, 5808T>G, 6853G>C and 9041G>A polymorphisms were in Hardy–Weinberg equilibrium in each population. The 5808G allele was absent or rare (<3%), whereas 3673A, 6853C and 9041A were frequent (34–63%) in the three Amerindian populations. No difference was detected in allele or genotype frequency bewteen the two Guarani populations, whereas significant differences were observed between Kaingang and Guarani. Polymorphisms 3673G>A, 6853G>C and 9041G>A were in significant linkage disequilibrium in both Guarani and Kaingang (pairwise r2 values: 0.77–1.0). Haplotypes ATCG and GTGA accounted for more than 94% of the haplotypes in both populations, ATCG being the most common in Guarani (49.5%) and GTGA in Kaingang (54%). These data disclose the uniqueness of the frequency distribution of the VKORC1 SNPs in the Amerindians, compared with Asian, African and European populations. In view of the vast interpopulational diversity among Amerindians, the present data should not be interpreted as representative of other extant Amerindian peoples. Our estimates that 40% of Kaingang and 60% of Guarani have haplotypes including the variant 3673A allele suggest that these two Amerindian populations comprise high proportions of individuals requiring reduced warfarin doses.

VKORC1 and CYP2C9 allelic variants influence acenocoumarol dose requirements in Greek patients

Aim: To identify the frequencies of the polymorphisms CYP2C9*2, CYP2C9*3 and VKORC1-1639 G>A in the Greek population and investigate whether these polymorphisms and patient demographics (age, sex and comedication) could explain the interindividual variability of acenocoumarol dose requirements for efficient anticoagulation. Materials & methods: CYP2C9*2 (Arg144Cys), CYP2C9*3 (Ile359Leu) and VKORC1–1639G>A allelic variants were analyzed in 98 patients treated with acenocoumarol. Results: Allelic frequencies of CYP2C9*2, CYP2C9*3 and VKORC1A were found to be 0.155, 0.075 and 0.485, respectively. Carriership of at least one CYP2C9*3 allele led to the most pronounced reduction in the required mean dose (p < 0.0001). In contrast, the CYP2C9*2 allele played a minor role (p = 0.3). VKORC1 A/A patients needed approximately a third of the dose required by wild-type patients to achieve the target INR (p < 0.0001). Age was the only demographical factor significantly affecting acenocoumarol dose (p < 0.0001). In a multivariable regression model, CYP2C9, VKORC1 genotypes and age explained 55% of acenocoumarol dosing variability. Conclusion: VKORC1-1639G>A, CYP2C9*2 and CYP2C9*3 polymorphisms were found to predispose to acenocoumarol sensitivity in Greeks. Other hereditary and nongenetic parameters must be incorporated in an individualized dosing algorithm to achieve a safer anticoagulant effect.