Jane Skov

The influence of VKORC1 and CYP2C9 gene sequence variants on the stability of maintenance phase warfarin treatment.

INTRODUCTION A substantial part of the inter-individual variation in vitamin K-antagonist dose can be explained by certain sequence variants in the genes CYP2C9 (NG_008385.1:g.8633C>T or *1/*2, NG_008385.1:g.47639A>C or *1/*3) and VKORC1 (NG_011564.1:g.6399C>T). Patients possessing these variant alleles require lower doses and have increased risk of overanticoagulation. METHODS We investigated the influence of the above sequence variants on stability of maintenance phase warfarin therapy in a prospective study of 300 consecutive patients followed for one year at an anticoagulant clinic. RESULTS Patients having one VKORC1 variant allele (n=144) had a time in therapeutic range of INR (TTR) of 71.4%, significantly lower (p=0.02) than the 76.7% TTR of patients with none (n=96) or two (n=46) variant alleles. Patients carrying the CYP2C9 *3 allele (n=40) trended towards lower TTR than patients without this variant allele (69.8% vs. 74.7%, p=0.09). Six patients possessed two variant alleles of CYP2C9 (*2/*3 or *3/*3) and had significantly lower TTR (60.5% vs. 74.3%, p=0.012) and higher risk of an INR>4.5 (67% vs. 23%, p=0.03) compared with the remaining patients. CONCLUSIONS We observed modest effects of common gene sequence variants in CYP2C9 and VKORC1 on stability of maintenance phase warfarin therapy. Patients attending an anticoagulant clinic using computer-assisted dosage were safely monitored regardless of these sequence variants, but for the small subgroup of patients with the CYP2C9 genotype *2/*3 or *3/*3, treatment stability was reduced.

Multivariate analysis of the relation between diet and warfarin dose

PurposeThe vitamin K antagonist (VKA) warfarin is effective for the prevention of thromboembolisms. Maintenance doses differ greatly among patients and are known to be primarily determined by genetic polymorphisms. The relative impact of dietary vitamin K intake is still a matter of debate. We hypothesize that a multivariate model is more suitable for exploring the relation between dietary intake of vitamin K and warfarin dose than conventional uni- or bivariate analyses.MethodsIn a cross-sectional study, we interviewed 244 patients in the maintenance phase of warfarin therapy and detected polymorphisms in the VKORC1 and CYP2C9 genes. Dietary vitamin K intake was estimated from food frequency questionnaires.ResultsA univariate correlation analysis and the regression coefficient from the multivariate model showed a small but significant negative relation between vitamin K intake and warfarin dose. A loading plot of the partial least squares regression model illustrated this counter-intuitive observation, which might be explained by the latent structure between variables. The variation in warfarin dose could be divided into two significant latent variables, the so-called components. In component one, pharmacogenetics explained 52% of dose variation. Component two described health-related behavior (diet, physical activity and body weight) and explained 8% of dose variation. Here, vitamin K intake positively correlated with warfarin dose.DiscussionThis study highlights the importance of choosing a statistical method that reflects the complexity of data for interpretation of results from observational studies. The multivariate model appears to be well suited to describe the complex relationship between vitamin K intake and VKA dose.

Genetic, Clinical and Behavioural Determinants of Vitamin K-Antagonist Dose – Explored Through Multivariable Modelling and Visualization

Vitamin K antagonists (VKA) are highly effective anticoagulants but their use is hampered by multiple interactions with food and medicine and a narrow therapeutic range. The large variation in dose requirements has led to the development of several dosing algorithms based on pharmacogenetic and clinical variables. In contrast, evidence about the influence of behavioural (i.e. diet and exercise) and socio-psychological factors is sparse. To investigate the impact of pharmacogenetic, clinical, behavioural and socio-psychological factors on maintenance dose of VKA. In a cross-sectional study, we interviewed 250 consecutive patients from an anticoagulant clinic and subsequently measured pharmacogenetic and anthropometric variables. Statistical analyses were carried out using linear regression and multivariable models with visualization features. In both types of analyses, the strongest determinants of VKA dose were polymorphisms in the VKORC1 and CYP2C9 genes and age. Half of the variation in VKA dose could be explained by a linear regression model including four variables, while a multivariable model with 20 pharmacogenetic and clinical variables explained 60%. A multivariable model including 94 predictor variables was not notably better regarding predictive performance, but visualization of this model offered information about the correlation structure between predictor variables. The strongest determinants of VKA dose are well-known pharmacogenetic variables and age. The variables describing health-related behaviour and socio-psychological factors are strongly inter-correlated and not useful in dosing algorithms.

Perceived stress predicts the stability of vitamin K-antagonist treatment of anticoagulant clinic patients

Perceived stress predicts the stability of vitamin K-antagonist treatment of anticoagulant clinic patients -

Lysability of fibrin clots is a potential new determinant of stroke risk in atrial fibrillation

INTRODUCTION Atrial fibrillation increases the risk of ischemic stroke, but the risk depends on other factors as well. Present risk stratification schemes use age and co-morbidities, but not biochemical markers. We investigated the hypothesis that the formation, structure and lysability of fibrin clots are potential determinants of stroke risk in patients with atrial fibrillation. MATERIALS AND METHODS A total of 179 patients with atrial fibrillation in stable anticoagulant treatment were included. Thirty-two had a previous ischemic stroke. We measured thrombin generation, plasma concentrations of fibrinogen and C-reactive protein and analysed fibrin structure and lysability by turbidity. Fibrinolytic capacity was measured using the euglobulin fraction of plasma expressed in terms of t-PA equivalents (IU/ml). RESULTS The patients with previous stroke had a slightly higher burden of co-morbidities compared with the remaining patients as indicated by the CHA2DS2-VASc score, but no significant differences were found regarding age, fibrinogen concentration, C-reactive protein, thrombin generation or fibrinolytic capacity. Furthermore, the patients with previous stroke had a higher mass/length ratio of fibrin fibers (5.5 vs. 5.1 x10(12) Da/cm, p=0.044) and an increased lysability (79.3 vs. 55.3%, p<0.01). CONCLUSION The higher lysability of fibrin clots in atrial fibrillation patients with previous stroke is most likely a result of a difference in fibrin fiber properties. An increased lysability may increase the risk of embolization of clots formed in the atria, and therefore fibrin clot structure seems to be a determinant of stroke risk in atrial fibrillation.

Difference in fibrinolytic capacity in young patients with venous thrombosis or ischaemic stroke.

Many recent studies focus on the common pathophysiological mechanisms and risk factors for arterial and venous thrombosis. We investigated the hypothesis that fibrinolytic capacity is similar in patients with ischaemic stroke and venous thromboembolism. Retrospective study of 604 consecutive patients (age <50 years) referred to systematic thrombophilia testing at a single regional centre. The thrombophilia test included clinical variables, genetic polymorphisms, biomarkers of coagulation and a global assay of fibrinolysis that tested the patients blood fibrinolytic capacity by application of the euglobulin fraction of plasma to a preformed clot of plasminogen-rich bovine fibrin. The patients with venous thromboembolism (n = 284) were slightly younger (32.3 vs. 33.9 years; <0.01) than those with ischaemic stroke (n = 320), had a significantly higher prevalence of obesity (28 vs. 18%; P < 0.01), higher plasminogen activator inhibitor 1 (PAI-1) activity (12.3 vs. 11.1 IU/ml; P = 0.049) and a significantly lower fibrinolytic capacity (3.4 vs. 3.9 IU/ml; P < 0.01). The lower fibrinolytic capacity in patients with venous thromboembolism was also observed in the subgroup of patients with PAI-1 activity within the normal range (n = 430, 3.7 vs. 4.1IU/ml; P < 0.01). After adjustment for age, BMI, fibrinogen concentration, PAI-1 activity and tissue plasminogen activator activity, fibrinolytic capacity still differed significantly between the two groups. Our results indicate that the capacity for fibrinolysis is lower in young patients with venous thromboembolism than ischaemic stroke, suggesting a different mechanistic role of fibrinolysis in arterial and venous thromboembolism.

Impact of point-of-care international normalized ratio monitoring on quality of treatment with vitamin K antagonists in non-self-monitoring patients: a cohort study.

Essentials It is unclear if point‐of‐care (POC) monitoring is safe in non‐self‐monitoring (NSM) patients. We compared time in therapeutic range (TTR) and outcome during laboratory and POC monitoring. Median TTR was lower during POC monitoring (77.9 vs. 81.0%), but adverse event rates were similar. POC monitoring is a safe and effective alternative to laboratory monitoring in NSM patients.

Gender Differences in Fibrin Polymerization and Lysability of Fibrin in Patients with Atrial Fibrillation

BACKGROUND Atrial fibrillation (AF) is the most common cardiac arrhythmia for both men and women. The embolic cardiovascular events represent serious complications of AF, and apparently women are affected more seriously than men. Little is known about prothrombotic factors and possible gender differences. The present study aimed to characterize fibrin polymerization, fibrinolysis, and fibrin fiber properties in men and in women with AF. MATERIALS AND METHODS Forty-six female and 101 male patients with AF and without previous stroke were included. Polymerization kinetics, lysis of preformed clot, and fibrin fiber properties were determined by turbidimetric methods. RESULTS Women were slightly older than men (P < .01), and the male group had a higher systolic blood pressure (P < .01) and a higher incidence of peripheral arterial disease (P < .01) than the female group. Compared with men, women had a higher Vmax during fibrin polymerization (P < .04) and a lower lysability of fibrin, when recombinant tissue plasminogen activator (rt-PA) was added during clot formation (P < .01), while external lysis (rt-PA added after clot formation), plasma fibrinolytic activity, d-dimer, and fibrin fiber properties did not differ between men and women. A significantly higher number of men received acetylsalicylic acid (ASA) compared with women (P < .004). Subgroup analyses on subjects not receiving ASA demonstrated that women still had higher Vmax (P < .04) and a lower rt-PA-induced fibrinolysis (P < .03). CONCLUSION Women with AF have a higher velocity of lateral aggregation of fibrin fiber protofibrils and a lower lysis of fibrin clots than men.

Biomarkers of coagulation, fibrinolysis, endothelial function, and inflammation in arterialized venous blood.

Effects of venous blood arterialization on cardiovascular risk markers are still unknown. We evaluated biomarkers of inflammation, coagulation, fibrinolysis, and endothelial function in arterialized compared with regular venous blood. Cubital venipunctures were obtained from 10 healthy volunteers. Arterialization was generated by 10 min heating of the contralateral hand. Concentrations of albumin, C-reactive protein (CRP), tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor type 1 (PAI-1), and von Willebrand factor (vWF) were measured by validated assays. Concentrations of albumin, CRP, and vWF were significantly lower in arterialized than in venous blood (albumin: 43.8 g/l and 44.8 g/l, P = 0.02). Differences in CRP and vWF became insignificant after adjusting for albumin. The endogenous thrombin potential (ETP) was significantly higher in arterialized than in venous blood (1929 nmol/l*min vs. 1872 nmol/l*min, P = 0.02). Addition of the FXIIa inhibitor Corn Trypsin Inhibitor (CTI) prior to the thrombin generation test eliminated the ETP difference suggesting that hand heating activates the FXII-dependent coagulation pathway.

Endurance exercise per se reduces the cardiovascular risk marker t-PA antigen in healthy, younger, overweight men

INTRODUCTION The cardiovascular risk marker tissue plasminogen activator antigen (t-PA:Ag) can be reduced by long-term exercise interventions, but it is unknown, whether this is due to the weight loss induced by physical activity or due to the physical activity per se. MATERIALS AND METHODS This was tested in 60 healthy, younger (20-40years), overweight (BMI: 25-30kg/m2) men randomly assigned to 12weeks of intervention in one of four groups: training (T); energy-reduced diet (D); training and increased diet (T-iD); sedentary lifestyle and unchanged diet (controls, C). Fasting blood samples were obtained before and after 12weeks of intervention and analyzed for plasma t-PA:Ag. RESULTS Body weight was reduced in groups T and D. We observed a decrease in t-PA:Ag from baseline to 12weeks in all three exercise and diet intervention groups, and no change in the control group. A between-group difference in t-PA:Ag was observed at 12weeks (p=0.001), and this was due to lower values in T (p=0.0005), D (p=0.005) and T-iD (p=0.009) compared with the control group. Total body fat mass was reduced in all three exercise groups, and we observed a positive correlation between changes in t-PA:Ag and changes in intra-abdominal and subcutaneous adipose tissue volume. CONCLUSIONS Our results demonstrate that t-PA:Ag was reduced in all three intervention groups. This suggests that 12weeks of endurance training per se, irrespective of concomitant weight loss, beneficially affects cardiovascular risk in healthy, younger, overweight men.