A vitamin K epoxide reductase-oxidase complex gene polymorphism (-1639G>A) and interindividual variability in the dose-effect of vitamin K antagonists

Farmacogenômica e Doença Cardiovascular: Onde Estamos e Para Onde Vamos

A farmacogenômica (FGx) investiga a interação entre genes e medicamentos. Através da análise de regiões específicas do DNA, informações sobre o perfil de metabolização do paciente para um determinado fármaco podem ser descritas, assim como o perfil esperado de resposta ao tratamento. Objetivamente, esse tipo de teste pode ter impacto no tratamento de pacientes que não estão respondendo adequadamente a um determinado medicamento, seja pela ausência dos efeitos esperados ou em virtude do aparecimento de efeitos adversos. Neste cenário, o objetivo desta revisão é o de informar o cardiologista clínico sobre esta importante área do conhecimento e atualizá-lo sobre o tema, procurando preencher as lacunas no que diz respeito à relação custo-benefício da aplicação da FGx nas doenças cardiovasculares, além de fornecer informações para a implementação da terapia guiada pela FGx na prática clínica.

Establishment of the Variation of Vitamin K Status According to Vkorc1 Point Mutations Using Rat Models

Vitamin K is crucial for many physiological processes such as coagulation, energy metabolism, and arterial calcification prevention due to its involvement in the activation of several vitamin K-dependent proteins. During this activation, vitamin K is converted into vitamin K epoxide, which must be re-reduced by the VKORC1 enzyme. Various VKORC1 mutations have been described in humans. While these mutations have been widely associated with anticoagulant resistance, their association with a modification of vitamin K status due to a modification of the enzyme efficiency has never been considered. Using animal models with different Vkorc1 mutations receiving a standard diet or a menadione-deficient diet, we investigated this association by measuring different markers of the vitamin K status. Each mutation dramatically affected vitamin K recycling efficiency. This decrease in recycling was associated with a significant alteration of the vitamin K status, even when animals were fed a menadione-enriched diet suggesting a loss of vitamin K from the cycle due to the presence of the Vkorc1 mutation. This change in vitamin K status resulted in clinical modifications in mutated rats only when animals receive a limited vitamin K intake totally consistent with the capacity of each strain to recycle vitamin K.

Impact of CYP2C9 and VKORC1 genetic polymorphisms upon warfarin dose requirements in Egyptian patients with acute coronary syndrome

Warfarin is the most widely prescribed anticoagulant drugs. Cytochrome P450-2C9 (CYP2C9) and vitamin K epoxide reductase-oxidaxe complex subunit 1 (VKORC1) contribute significantly to the variability of warfarin dose requirements among patients. We investigated the impact of CYP2C9 and VKORC1 polymorphisms on the variability of warfarin dosage requirements in Egyptian patients with acute coronary syndrome and their association with other nongenetic factors. Eighty participants with acute coronary syndrome were enrolled in this cross-sectional study. Associations between CYP2C9 and VKORC1 gene variants together with daily warfarin dose, demographic data, clinical status of patients and time to target international normalized ratio were assessed. Mean warfarin dose among patients with wild-type CYP2C91/1 genotype was significantly higher than heterozygous CYP2C91/2 and CYP2C91/3 variants (P ≤ 0.001). Patients with wild VKORC1 (G/G) genotype were treated with significantly higher daily warfarin dosages than homozygous (A/A) and heterozygous (G/A) genotypes. Patients carrying VKORC1 (G/G) genotype in combination with the CYP2C91/1 type alleles had the highest daily warfarin dosage, whereas the lowest daily warfarin dosage to achieve the required clinical effect was found among patients having CYP2C91/2 and CYP2C91/3 genotypes combined with VKORC1 (A/A) genotype (P ≤ 0.001). Regression analysis revealed that age, height, CYP2C9 and VKORC1 genotypes were significantly associated with warfarin dose. Genetic polymorphisms in VKORC1, CYP2C9 along with age and height are determinants of warfarin dose requirements in Egyptian population acute coronary syndrome. Higher warfarin loading dose is required for both wild CYP2C9 and VKORC1 gene variants which may contribute to warfarin-resistant cases.

Warfarin Metabolites in Patients Following Cardiac Valve Implantation: A Contribution of Clinical and Genetic Factors

INTRODUCTION

Warfarin, a racemic mixture of S- and R-enantiomers, is the cornerstone of therapy in patients following cardiac valve replacement. S-warfarin is metabolized to 7-S-hydroxywarfarin by the cytochrome P450 isoform 2C9 encoded by CYP2C9 gene. R-warfarin is metabolized by multiple cytochromes P450. We sought to assess the impact of clinical and genetic factors on circulating warfarin metabolites following valve implantation.

MATERIAL AND METHODS

Venous blood was collected from 120 patients after 3 months since elective mitral and/or aortic valve replacement. Plasma S-warfarin, R-warfarin, S-7-hydroxywarfarin, and R-7-hydroxywarfarin were determined using high-performance liquid chromatography. The S-7-hydroxywarfarin/S-warfarin and S-warfarin/R-warfarin (S/R) ratios, along with warfarin sensitivity index (WSI), defined as INR/S-warfarin ratio, were calculated. Vitamin K epoxide reductase complex subunit 1 (VKORC1) c.-1639A, CYP2C9*3 and CYP2C9*2 alleles were determined using real-time polymerase chain reaction.

RESULTS

The S-warfarin was higher in former smokers (p = 0.047) and the VKORC1 c.-1639A allele carriers (p < 0.0001). The S-7-hydroxywarfarin was lower in carriers of the VKORC1 c.-1639A allele (p = 0.0005) and CYP2C9*3 (p = 0.047). The S-7-hydroxywarfarin/S-warfarin ratio was lower in the carriers of CYP2C9*3 (p = 0.008), but not in those with VKORC1 -c.1639A allele. The S/R ratio was higher in patients with hypertension (p = 0.01). The independent predictors of elevated S/R ratio defined as the upper quartile were diabetes (p = 0.045), CYP2C9*3 (p < 0.0001) and CYP2C9*2 (p = 0.0002). The independent predictors of elevated WSI were current smoking (p = 0.049), implantation of mechanical valve (p = 0.006) and VKORC1c.-1639A allele (p = 0.007).

CONCLUSION

We conclude that not only genetic, but also several clinical factors affect warfarin metabolites in patients following cardiac valve implantation.

Genetic determinants of acenocoumarol and warfarin maintenance dose requirements in Slavic population: a potential role of CYP4F2 and GGCX polymorphisms

INTRODUCTION

VKORC1 and cytochrome CYP2C9 genetic variants contribute largely to inter-individual variations in vitamin K antagonists (VKAs) dose requirements. Cytochrome P450 4F2 isoform (CYP4F2), gamma-glutamyl carboxylase (GGCX) and apolipoprotein E (APOE) polymorphisms have been suggested to be of minor significance.

MATERIALS AND METHODS

We sought to assess the impact of those polymorphisms on dose requirements in Central-Eastern European cohort of 479 patients receiving acenocoumarol (n=260) or warfarin (n=219).

RESULTS

There were no differences between the acenocoumarol and warfarin groups with regard to the gender, age, body mass index and international normalized ratio. The VKORC1 c.-1639A allele carriers required a lower dose of acenocoumarol and warfarin than the non-carriers (28.0 [21.0-35.0] vs. 42.0 [28.0-56.0] mg/week, p<0.0001; 35.0 [28.0-52.0] vs. 52.0 [35.0-70.0] mg/week, p=0.0001, respectively). Carriers of 2 and/or 3 variant alleles for CYP2C9 also required a lower dose of warfarin as compared with 1 1 carriers (35.0 [31.5-52.5] vs. 43.8 [35.0-60.2] mg/week, p=0.02; 35.0 [23.5-35.0] vs. 43.8 [35.0-60.2] mg/week, p<0.0001, respectively). Similarly, possession of G allele of GGCX c.2084+45 polymorphism was associated with lower warfarin dose (35.0 [26.3-39.2] vs. 45.5 [35.0-65.1] mg/week, p=0.03). No effect of CYP2C9*2,-*3 and GGCX c.2084+45G>C polymorphisms on acenocoumarol dosage was observed. Interestingly, carriers of CYP4F2 c.1297A variant required a higher dose of acenocoumarol and warfarin than non-carriers (43.8 [35.0-60.2] vs. 35.0 [35.0-52.5] mg/week, p=0.01; 35.0 [28.0-52.5] vs. 28.0 [28.0-42.0] mg/week, p=0.05).

CONCLUSIONS

We have shown for the first time, that besides VKORC1 and CYP2C9 genetic variants, the CYP4F2 c.1297A and GGCX c.2084+45G have a moderate effect on VKAs dose requirements in Slavic population from Central-Eastern Europe.

VKORC1 and CYP2C9 genotypes in Egyptian patients with warfarin resistance

Warfarin is the most commonly prescribed anticoagulant drug; however, a narrow therapeutic range and a high risk of bleeding or stroke complicate its clinical use. Warfarin resistance was defined as prolonged warfarin requirements of more than 15 mg/day to achieve therapeutic anticoagulation or failure to achieve therapeutic anticoagulation with more than 20 mg/day. The resistance is associated with polymorphisms of the vitamin K epoxide reductase-oxidase complex (VKORC1) and cytochrome P450-2C9 (CYP2C9) genes, which affect warfarin pharmacodynamics and pharmacokinetics, respectively. Identification of the VKORC1 -1639 (A/G) and CYP2C9 (*1/*2/*3) allelic variants was performed using the PGX-Thrombo Strip in 41 patients with warfarin resistance compared with 30 patients with normal warfarin response out of 352 diagnosed cases of deep vein thrombosis. In warfarin-resistant patients, the VKORC1-1639 genotype frequencies were GG 0.756, GA 0.244 and AA 0.0, whereas in warfarin responder patients, they were: GG 0.333, GA 0.400 and AA 0.276 with P ≤ 0.001. The CYP2C9 genotype frequencies showed nonsignificant difference in both group of patients (P = 0.31). Our results suggest that the VKORC1-1639 GG and the wild type CYP2C9*1*1genotypes are associated with the high-dose requirement for warfarin therapy, and that VKORC1-1639 GG is responsible for warfarin resistance and failure in Egyptian patients.

Association of functional VKORC1 promoter polymorphism with occurrence and clinical aspects of ischemic stroke in a Greek population

Genetic factors are considered to play an important role in determining the susceptibility to the occurrence, clinical course, and functional outcome of an acute ischemic stroke (IS). Undercarboxylation of specific vitamin K-dependent proteins, due to genetic polymorphisms of VKORC1, can affect both vascular calcification and thrombogenicity. We sought to determine the association of VKORC1 −1639G > A polymorphism with IS incidence, age of onset, severity of disease, and functional outcome after an acute IS. VKORC1 −1639G > A polymorphism was determined in 145 consecutive patients with first ever IS and 145 age- and sex-matched control subjects of Greek Caucasian origin using PCR-RFLP. Stroke severity and functional outcome were assessed on admission and at one month after stroke, respectively. Frequency of VKORC1 −1639G > A genotypes did not differ between IS patients and controls (OR = 1.12, P = 0.51). Moreover, carriage of the A allele was not associated with age of stroke onset, severity of disease (Scandinavian stroke scale score 32.2 versus 32.9, resp., P = 0.96), or poor outcome at 1 month post-stroke (52.9 versus 64.4%, resp., P = 0.31). In conclusion, VKORC1 −1639G > A polymorphism is not a genetic determinant of IS occurrence, age of onset, severity, or functional outcome of disease in a Greek population.

The prevalence of VKORC1 1639 G>A and CYP2C9*2*3 genotypes in patients that requiring anticoagulant therapy in Turkish population

The aim was to investigate the prevalence of VKORC1 and CYP2C9 genotypes in patients requiring anticoagulant therapy in two different region's populations of Turkey. The recent cohort included 292 patients that needed anticoagulant therapy, and who had a history of deep vein thrombosis and/or pulmonary artery thromboembolism. Genomic DNA was isolated from peripheral blood samples and the StripAssay reverse hybridization or Real Time PCR technique was used for genotype analysis. Genotypes for CYP2C9 were detected as follows: 165 (56.5 %) for CYP2C9*1/*1, 67 (23.0 %) for CYP2C9*1/*2, 25 (8.6 %) for CYP2C9*1/*3, 9 (3.0 %) for CYP2C9*2/*2, 21 (7.2 %) for CYP2C9*2/*3, 5(1.7 %) for CYP2C9*3/*3 for CYP2C9 and the allele frequencies were: 0.723 for allele*1, 0.182 for allele*2 and 0.095 for allele*3 respectively. Genotypes for VKORC1 were detected as follows: 64 (21.9 %) for GG, 220 (75.4 %) for GA and 8 (2.7 %) for AA alleles. The G allele frequency was detected as 0.596, and the A allele frequency was 0.404. The VKORC1 1639 G>A and CYP2C9 mutation prevalence and allele frequency of the current results from two different populations (Sivas and Canakkale) showed similarly very variable profiles when compared to the other results from the Turkish population.

Gene-drug interaction in stroke

Stroke is the third cause of mortality and one of most frequent causes of long-term neurological disability, as well as a complex disease that results from the interaction of environmental and genetic factors. The focus on genetics has produced a large number of studies with the objective of revealing the genetic basis of cerebrovascular diseases. Furthermore, pharmacogenetic research has investigated the relation between genetic variability and drug effectiveness/toxicity. This review will examine the implications of pharmacogenetics of stroke; data on antihypertensives, statins, antiplatelets, anticoagulants, and recombinant tissue plasminogen activator will be illustrated. Several polymorphisms have been studied and some have been associated with positive drug-gene interaction on stroke, but the superiority of the genotype-guided approach over the clinical approach has not been proved yet; for this reason, it is not routinely recommended.

Association of VKORC1 -1639 G>A polymorphism with carotid intima-media thickness in type 2 diabetes mellitus

AIMS

Media calcification is a predictor of cardiovascular mortality in type 2 diabetes mellitus (T2DM). Undercarboxylation of some vitamin K-dependent proteins, due to genetic polymorphisms of VKORC1, can lead to calcification. We examined a potential association between VKORC1 -1639 G>A polymorphism and T2DM and, also, the association of this polymorphism with carotid intima-media thickness (cIMT).

METHODS

VKORC1 -1639 G>A polymorphism was determined in 299 T2DM patients and 328 controls of Caucasian origin using PCR-RFLP. cIMT was measured in a subgroup of 118 T2DM patients.

RESULTS

The frequency of VKORC1 genotypes between diabetic and nondiabetic subjects differed significantly (p=0.01). VKORC1 genotype was associated with T2DM in an adjusted model (OR 1.36, p=0.009). A statistically significant difference was observed in the maximum value of cIMT among different genotypes. VKORC1 -1639 G>A polymorphism was an independent predictor of cIMT (p=0.029) after adjusting for established risk factors.

CONCLUSIONS

The association between VKORC1 -1639 G>A polymorphism and risk of T2DM could be due to the higher prevalence of calcification in T2DM patients. This is supported by the independent association between VKORC1 -1639 G>A polymorphism and maximum cIMT in T2DM patients which is likely due to atherosclerosis characterized by increased calcification.