Tamoxifen induces resistance to activated protein C

Introduction

The estrogen antagonist tamoxifen (TAM) increases the thrombotic risk similar to estrogen containing oral contraceptives (OC). In OC users this risk is attributed to alterations of hemostasis resulting in acquired resistance to activated protein C (APC). TAM-induced APC resistance has not been reported yet.

Materials and Methods

Blood samples were collected prospectively from women with breast cancer before (n = 25) and monthly after start of adjuvant TAM treatment (n = 75). APC resistance was evaluated on basis of the effect of APC on the endogenous thrombin generation potential. To detect increased in vivo APC generation APC plasma levels were measured using a highly sensitive oligonucleotide-based enzyme capture assay. Routine hemostasis parameters were measured additionally.

Results

APC sensitivity decreased by 41% (p = 0.001) compared to baseline after one month of TAM application and remained significantly decreased during the study period. Free protein S increased (p = 0.008) while other analyzed procoagulant factors, inhibitors, and activation markers of coagulation decreased or did not change significantly. In five patients the APC concentration increased to non-physiological levels but an overall significant increase of APC was not observed.

Conclusions

This is the first study showing acquired APC resistance under TAM therapy. Acquired APC resistance might explain the increased thrombotic risk during TAM treatment. Observed changes of hemostasis parameters suggest different determinants of TAM-induced APC resistance than in OC-induced APC resistance. The presence of acquired APC resistance in TAM patients warrants further evaluation if these patients may benefit from antithrombotic prophylaxis in the presence of additional thrombotic risk factors.     

Superficial vein thrombosis,thrombin generation and activated protein C resistance as predictors of thromboembolic events in lupus and antiphospholipid patients. A prospective cohort study

Introduction

Predicting thrombosis in patients with systemic lupus erythematosus (SLE) and/or antiphospholipid antibodies (aPL) is still challenging. Our objective was to determine risk factors for thrombotic events including activated protein C (APC) resistance proven by a thrombin generation (TG) assay in patients with SLE and/or aPL.

Materials and methods

We performed a prospective cohort study in a French University Hospital and tertiary care center. Ninety-two consecutive patients with SLE and/or aPL without ongoing anticoagulant treatment were enrolled. The outcome was time to thrombotic event. We evaluated clinical and laboratory variables including APC sensitivity ratio (APCsr) determined by TG. An APCsr > 90th percentile of a control population indicated APC resistance.

Results

Patients were followed-up for a median duration of 35 months (inter-quartile range: 26 to 62; 320 patient-years). Thrombosis during follow-up occurred in 18 patients. In univariate analysis, together with history of hypertension, superficial vein thrombosis (SVT) and arterial thrombosis, patients with both aPL and APC resistance had an increased risk for incident thromboembolic events (HR, 3.67[95% confidence interval, 1.31 to 10.31]). In multivariate analysis, only history of hypertension (HR, 10.77 [95% confidence interval, 3.15 to 36.83]), SVT (HR, 7.45 [95% confidence interval, 2.25 to 24.66]) and arterial thrombosis (HR, 3.31 [95% confidence interval, 1.14 to 9.55]) remained independent risk factors.

Conclusions

History of thrombosis including seemingly benign SVT have a higher predictive value for incident thrombotic events in SLE or aPL patients than APC resistance proven by TG.     

Hereditary protein C deficiency caused by the Ala267Thr mutation in the protein C gene is associated with symptomatic and asymptomatic venous thrombosis

Introduction

Protein C (PC) is a key anticoagulant that regulates hemostasis, and inherited deficiency of PC is an established risk factor for venous thrombosis (VT). The factor V Leiden mutation causing activated PC (APC) resistance is an additional risk factor for VT. Reduced PC levels in the circulation and/or APC resistance do not necessarily lead to thrombotic disease. In the present study we describe and characterize an ethnic Lebanese family in which individuals with reduced PC levels and APC resistance have various clinical symptoms.

Methods

PC activity and antigen levels and APC resistance in the family members were quantified with commercial kits. Sequencing of PC DNA and mRNA was performed with BigDye Terminator Cycle Sequencing kit on the ABI 3730 Genetic Analyzer.

Results

PC antigen and anticoagulant activity in the plasma of the proband and family members ranged from 9% to 69% and 3% to 63%, respectively, compared to levels measured in pooled normal plasma. Sequencing analysis of the PC gene of family members revealed that they were either homozygous or heterozygous for the Ala267Thr mutation. In addition, three of them exhibited APC resistance. None of the family members, except the proband, have had a history of VT despite that two of them have two genetic risk factors for thrombosis.     

Self-reported family history in estimating the risk of hormone,surgery and cast related VTE in women

Background

Combined hormonal contraceptives, menopause hormone treatment and surgery/cast in orthopedic patients are important risk factors for venous thromboembolism (VTE) in women.

Objectives

To evaluate whether self-reported family history can be used for risk assessment concerning hormone and surgery /cast related VTE in women.

Patients/methods

1288 women 18–64 years with a first event of VTE and 1327 age-matched controls were included in a nation-wide population-based case–control study in Sweden. Odds ratios were calculated by comparing occurrence of VTE in women with and without a positive family history in combination with hormones or surgery/cast.

Results

The risk of hormone-associated VTE was doubled in women with a family history of VTE as compared to women with hormones and negative family history. The risk was more than tripled in women with surgery/cast and a positive family history, as compared to surgery/cast patients with negative family history. Women with a positive family history and combined hormonal contraceptive or menopause hormone treatment had an OR of 15.3 (95% CI 6.1–38) and 5.9 (95% CI 3.3–11) respectively compared to women without hormones or family history. The corresponding OR in women with surgery/cast and a positive family history was 67 (95% CI 21–213) compared to women without surgery/cast treatment and a negative family history.

Conclusion

Self-reported family history is associated with increased odds of developing VTE on combined hormonal contraceptives, menopause hormone treatment and in connection with surgery or plaster. We believe that assessing family history of VTE can be helpful in identifying high risk patients.     

Changes in haemostatic parameters during the menstrual cycle and subsequent use of drospirenone-containing oral contraceptives

Introduction

Oral contraceptives (OC) increase the risk of venous thromboembolism that depends on the OC formulation and could at least partially be explained by impaired function of the protein C-system (APC resistance) and the tissue factor pathway inhibitor (TFPI)-system. There is limited information available on the effects of OC, containing a newer progestogen- drospirenone (DRSP-OC) on these two major anticoagulant pathways, thrombin generation, reflecting the overall state of coagulation, and other coagulation parameters.

Methods

In a study population consisting of 14 healthy women (age 21–33 years) we investigated the effect of the menstrual cycle and subsequent use of DRSP-OC on APC resistance, the function of the TFPI-system, thrombin generation and on their major determinants, i.e. prothrombin, antithrombin, FV, FX, FVIII, protein C, protein S_{(total and free)} and TFPI_{(full-length and free)}.

Results

All studied parameters remained unchanged during the menstrual cycle. During DRSP-OC use we observed a significant increase in APC resistance (~ 2.4-fold), thrombin generation measured at low (~ 2.2-fold) and high tissue factor concentrations (~ 1.4-fold), plasma concentrations of prothrombin (19%), FX (31%), FVIII (17%) and protein C (43%). DRSP-OC use impaired the function of the TFPI-system and decreased plasma levels of antithrombin (− 6%), FV (− 22%), protein S_total (− 21%), protein S_free (− 20%), TFPI_full-length (− 36%) and TFPI_free (− 46%).

Conclusions

DRSP-OC caused procoagulant changes in all studied haemostatic parameters. The impairment of the protein C- and TFPI-systems was more pronounced than the impairment of the coagulation pathways and can at least partially account for the increased risk of venous thromboembolism in users of DRSP-OC.     

Prothrombotic alterations in plasma fibrin clot properties in thyroid disorders and their post-treatment modifications

Introduction

Available data on fibrin clot properties and fibrinolysis in hyperthyroidism and hypothyroidism are inconsistent. Our objective was to assess the impact of effective treatment of hyper- and hypothyroidism on fibrin clot characteristics.

Material and Methods

In a case-control study, ex vivo plasma fibrin clot permeability (K_s) and efficiency of fibrinolysis were assessed in 35 consecutive hyperthyroid and 35 hypothyroid subjects versus 30 controls. All measurements were performed before and after 3 months of thyroid function normalizing therapy.

Results

At baseline, hyperthyroid, but not hypothyroid, patients had lower K_s than controls (p < 0.0001). Hyperthyroid and hypothyroid groups compared with controls had prolonged clot lysis time (CLT), and lower rate of D-dimer release from clots (D-D_rate) (all p < 0.05). The regression analysis adjusted for fibrinogen showed that in hyperthyroid patients, pre-treatment thyroid stimulating hormone (TSH) independently predicted K_s, while thrombin activatable fibrinolysis inhibitor (TAFI) antigen predicted CLT. In hypothyroid individuals a similar regression model showed that TSH independently predicts CLT. After 3 months of thyroid function normalizing therapy, 32 (91.4%) hyperthyroid and 30 (85.7%) hypothyroid subjects achieved euthyroidism and had improved fibrin clot properties (all p < 0.05), with normalization of K_s in hyperthyroid and lysability in hypothyroid patients.

Conclusions

Both hyper- and mild-to-moderate hypothyroidism are associated with prothrombotic plasma fibrin clot phenotype and restoration of euthyroidism improves clot phenotype. Abnormal fibrin clot phenotype might contribute to thromboembolic risk in thyroid disease.     

Selective tissue factor/factor VIIa Inhibitor,ER-410660, and its prodrug,E5539, have anti-venous and anti-arterial thrombotic effects with a low risk of bleeding

Introduction

Many anticoagulant drugs target factors common to both the intrinsic and extrinsic coagulation pathways, which may lead to bleeding complications. Since the tissue factor (TF)/factor VIIa complex is associated with thrombosis onset and specifically activates the extrinsic coagulation pathway, compounds that inhibit this complex may provide therapeutic and/or prophylactic benefits with a decreased risk of bleeding.

Materials and Methods

The in vitro enzyme profile and anticoagulation selectivity of the TF/VIIa complex inhibitor, ER-410660, and its prodrug E5539 were assessed using enzyme inhibitory and plasma clotting assays. In vivo effects of ER-410660 and E5539 were determined using a TF-induced, thrombin generation rhesus monkey model; a stasis-induced, venous thrombosis rat model; a photochemically induced, arterial thrombosis rat model; and a rat tail-cut bleeding model.

Results

ER-410660 selectively prolonged prothrombin time, but had a less potent anticoagulant effect on the intrinsic pathway. It also exhibited a dose-dependent inhibitory effect on thrombin generation caused by TF-injection in the rhesus monkey model. ER-410660 also reduced venous thrombus weights in the TF-administered, stasis-induced, venous thrombosis rat model and prolonged the occlusion time induced by arterial thrombus formation after vascular injury. The compound was capable of doubling the total bleeding time in the rat tail-cut model, albeit with a considerably higher dose compared to the effective dose in the venous and arterial thrombosis models. Moreover, E5539, an orally available ER-410660 prodrug, reduced the thrombin-anti-thrombin complex levels, induced by TF-injection, in a dose-dependent manner.

Conclusion

Selective TF/VIIa inhibitors have potential as novel anticoagulants with a lower propensity for enhancing bleeding.     

Sensitivity to activated protein C during the menstrual cycle in women with and without factor VLeiden

Introduction

Activated protein C (APC) resistance is associated with an increased risk of venous thrombosis. High levels of estradiol and progesterone, e.g. during ovarian stimulation and pregnancy, as well as exogenously administered estrogens and progestagens during oral contraceptive use, induce an acquired form of APC resistance. Several coagulation factors display a cyclic pattern during the menstrual cycle due to the fluctuation of estradiol and progesterone. The aim of the study was to evaluate whether varying levels of estradiol and progesterone during the menstrual cycle are associated with differences in sensitivity to APC.

Materials and methods

Normalized APC sensitivity ratios (nAPCsr) were determined with the thrombin generation-based APC-resistance test at six different time points during the menstrual cycle in thirteen wildtype women and six women with factor V_Leiden.

Results

Mean nAPCsr varied slightly during the menstrual cycle. Women without factor V_Leiden were more likely to have lower nAPCsr at the beginning of the cycle than later on in the cycle (1.34 versus 1.54 and 1.58, Friedman ranking test p = 0.009).

Conclusions

The sensitivity to APC differs between the different phases of the menstrual cycle. This cyclic variability could be useful in improving studies on APC resistance in women.     

Molecular basis and thrombotic manifestations of antithrombin deficiency in 15 unrelated Chinese patients

Introduction

Antithrombin (AT) deficiency is associated with an increasing risk of thrombosis.

Materials and methods

15 unrelated patients with AT deficiency defined by thrombophilic assays were recruited and detailed clinical information about patients, focusing on the personal and family history of thromboembolism (TE), were recorded. Mutation analysis was performed by direct sequencing of an AT gene (SERPINC1) in the patients and their family members.

Results

A total of 15 heterozygous causative mutations, each being identified in one family, were identified. Five mutations (33.3%) were reported here for the first time, including three null mutations (Ser36X, Lys70X and Try307X) and two missense mutations (Phe123Cys and Leu340Phe) probably impairing the structural integrity and stability of protein based on the AT structural analysis. Of the 15 patients, 33.3% (5/15) had additional risk factors and only one patient presented with additional genetic alteration causing an early onset of thrombosis. Fourteen patients (93.9%) suffered from multisite recurrent thrombotic episodes after a first episode of thrombosis. 93.3% of the patients experienced deep vein thrombosis (DVT) and 40.0% presented with mesenteric venous thrombosis (MVT). In addition, both venous and arterial thrombosis was present in two unrelated patients. 51.0% subjects with AT deficiency in the 15 unrelated pedigrees experienced TE events.

Conclusions

Prophylactic anticoagulation may be suggested in AT-deficient patients to avoid the recurrent and multisite thrombosis. The association of primary MVT and AT deficiency is highlighted.     

Plasma haemostatic potential of haemodialysis patients assessed by thrombin generation assay: Hypercoagulability in patients with vascular access thrombosis

Introduction

Patients with end-stage renal disease (ESRD) on maintenance haemodialysis are predisposed to bleeding and thrombotic events. Recently thrombin generation assay (TGA) has been introduced as a laboratory assessment of global haemostatic potential. We investigated the global haemostatic potential assessed by TGA in ESRD patients on haemodialysis and patients who developed vascular access thrombosis.

Materials and Methods

A total of 69 ESRD patients who underwent haemodialysis (58 stable patients and 11 vascular access thrombosis patients) were included and 33 healthy controls were included. TGA was performed on the calibrated automated thrombogram using tissue factor with/without addition of thrombomodulin or activated protein C, producing three parameters including lag time, endogenous thrombin potential (ETP) and peak thrombin.

Results

Haemodialysis patients showed low ETP values measured by thrombin generation assay compared with the healthy controls. Interestingly, patients with vascular access thrombosis exhibited short PT and aPTT and increased resistance of coagulation inhibition to APC anticoagulant protein, reflecting hyper-coagulability. Haemodialysis patients who are taking anti-platelet agents showed decreased thrombin inhibition rate, representing antithrombotic effect of anti-platelet agents.

Conclusion

Whereas the haemodialysis patients showed hypo-coagulability, the patients with vascular access thrombosis exhibited hyper-coagulability. Further study is required to investigate how this haemostatic potential may be utilized to guide the physician to more effective management of haemostatic complication.     

Validity of standard gamble estimated quality of life in acute venous thrombosis

Introduction

The standard gamble is considered the ‘gold standard’ technique for measuring quality of life. We recently used the standard gamble to estimate quality of life in acute venous thrombosis, and found unexpected variability in the responses. The current study aimed to explore the reasons for variability by comparing the standard gamble technique in patients with acute venous thrombosis to other quality of life measurement tools.

Materials and Methods

Thrombosis clinic patients treated for venous thrombosis were eligible to participate. Patients evaluated their current health state by performing a standard gamble interview, reporting on a visual analogue scale, completing the SF-36 and disease specific questionnaires (PEmb-Qol and VEINES-QOL/Sym). Validity was assessed by correlating the standard gamble utilities with the other methods. Test-retest reliability, responsiveness and acceptability were also assessed.

Results

Forty-four patients were interviewed, with 16 attending for a repeat interview. The median standard gamble utility was 0.97 (0.84-1.0), SF-6D 0.64 (0.59 - 0.80) and visual analogue score 70 (60 - 80). Participants with pulmonary embolism had lower standard gamble estimates than those with deep vein thrombosis. There was good discriminant validity in that the standard gamble estimates were not associated with risk taking behavior, negative outlook, sex or education. Test-retest reliability with the standard gamble was moderate and there was evidence of a ceiling effect.

Conclusions

Standard gamble utilities are higher than other methods of measuring quality of life in venous thrombosis. The choice of utility values adopted in studies will impact on future economic studies.     

Who are at risk for thromboembolism after arthroplasty? A systematic review and meta-analysis

Background

Thromboembolism, including deep venous thrombosis and pulmonary embolism, is a grave threat to patients undergoing total joint replacement. Using a systematic review and meta-analysis we asked whether gene mutations or polymorphisms could be risk factors for thrombosis after arthroplasty.

Methods

We performed a comprehensive search of Medline, PubMed, Embase, Cochrane databases, China National Knowledge Infrastructure (CNKI), and Google Scholar, and identified 19 studies detailing genetic investigations of patients with thromboembolism following joint replacement.

Results

Our meta-analyses included 5149 patients who underwent arthroplasty surgery. Significant associations with venous thromboembolism were identified for factor G1691A (odds ratio (OR) 1.41, 95% confidence interval (CI) 1.03 - 1.94, p = 0.03), prothrombin G20210A (OR 2.16, 95% CI, 1.27- 3.69, p = 0.005), and MTHFR/C677T/TT (OR 2.36, 95% CI 1.03 - 5.42, p = 0.04) in Caucasian populations. No significant gene mutation was identified in Asian populations.

Conclusion

This study suggests a way to identify patients scheduled for arthroplasty who are at higher risk of thrombosis, enabling individualized treatment.     

Rapid relapse in depression following initialization of oral contraception with ethinyl estradiol and chlormadinone acetate

Objective

Female sexual hormones (estrogens and gestagens) may affect neurocognitive functioning and mood. Thus, the use of oral hormonal contraceptives (OHC) bears the risk of psychiatric adverse drug reactions such as depression and psychosis. However, the available empiric evidence regarding this connection is conflicting, and, moreover, female sex hormones seem to feature also mood-stabilizing and antidepressive effects. Hence, individual susceptibility factors and preparation-specific pharmacologic properties might play a pivotal role in the development of mood disturbances related to OHC. Single case reports provide empiric data for further systematic approaches.

Methods

A clinical case is presented and discussed.

Results

A 36-year-old female patient with recurrent major depressive disorder developed rapid relapse in depression after initialization of OHC with ethinyl estradiol 30 μg/chlormadinone acetate 2 mg. This OHC combination was described to particularly feature positive effects on depressive mood.

Conclusions

OHC may induce serious mood disturbances and should be administered with care, particularly in patients with affective disorders.     

Comparison of catheter-related large vein thrombosis in centrally inserted versus peripherally inserted central venous lines in the neurological intensive care unit

Objective

To compare cumulative complication rates of peripherally (PICC) and centrally (CICVC) inserted central venous catheters, including catheter-related large vein thrombosis (CRLVT), central line-associated bloodstream infection (CLABSI), and line insertion-related complications in neurological intensive care patients.

Methods

Retrospective cohort study and detailed chart review for 431 consecutive PICCs and 141 CICVCs placed in patients under neurological intensive care from March 2008 through February 2010. Cumulative incidence of CRLVT, CLABSI, and line insertion-related complications were compared between PICC and CICVC groups. Risk factors for CRLVT including mannitol therapy during dwell time, previous history of venous thromboembolism, surgery longer than 1 h during dwell time, and line placement in a paretic arm were also compared between groups.

Results

During the study period, 431 unique PICCs were placed with cumulative incidence of symptomatic thrombosis of 8.4%, CLABSI 2.8%, and line insertion-related complications 0.0%. During the same period, 141 unique CICVCs were placed with cumulative incidence of symptomatic thrombosis of 1.4%, CLABSI 1.4%, and line insertion-related complications 0.7%. There was a statistically significant difference in CRLVT with no difference in CLABSI or line insertion-related complications.

Conclusions

In neurological critical care patients, CICVCs appear to have a better risk profile compared to PICCs, with a decreased risk of CRLVT. As use of PICCs in critical care patients increases, a prospective randomized trial comparing PICCs and CICVCs in neurological critical care patients is necessary to assist in choosing the appropriate catheter and to minimize risks of morbidity and mortality associated with central venous access.     

Anti-thrombosis effect of LRRFIP1 shRNA lentivirus in a mouse model of deep vein thrombosis

Introduction

Deep vein thrombosis (DVT) is one of the common complications of orthopedic surgery. Low molecular weight heparin (LMWH) is a usually used agent for DVT, but it would increase the risk of bleeding. LRRFIP1 has been shown to play an important role in the formation of thrombosis. Therefore, we investigated the effect of LRRFIP1 shRNA lentivirus on DVT in mice.

Materials and Methods

Lentiviral Vectors carrying LRRFIP1 shRNA were constructed and transfected into cultured mouse bone marrow cells (BMCs). Male ICR mice were irradiated with a single dose of 9.5 Gy and then were injected with different agents through the tail vein. Stasis venous thrombosis was induced by inferior vena cava (IVC) ligation. Mice were sacrificed on the 1st, 3rd and 7th day post operation and the thrombi were removed, blotted the excess blood on it with filter paper and immediately weighed. P-selectin and d-Dimer were determined by enzyme-linked immunosorbent assay (ELISA).

Results

LRRFIP1 shRNA significantly suppressed the expression of LRRFIP1 in the thrombi. In contrast, low molecular weight heparin (LMWH) and negative shRNA exhibited little effect on the expression of LRRFIP1. LRRFIP1 shRNA, LMWH and negative shRNA inhibited the thrombus formation in vivo significantly. The plasma P-selectin and d-Dimer levels were significantly increased after IVC ligation. LRRFIP1 shRNA significantly decreased the plasma P-selectin and d-Dimer levels. However, LMWH and negative shRNA showed little effects on the levels of plasma P-selectin and d-Dimer.

Conclusion

LRRFIP1 shRNA might represent a promising prevention strategy for DVT.     

A case series of LMWH use in pregnancy: Should trough anti-Xa levels guide dosing?

Introduction

Pregnancy is a thrombogenic state, increasing the risk for venous thromboembolism (VTE), and the risk of valve thrombosis amongst women with mechanical heart valves (MHV). While low molecular weight heparins (LMWH) are generally dosed based on weight (i.e., enoxaparin 1 mg/kg every 12 hours), data in pregnant women have shown that weight-based dosing does not consistently achieve target anti-Xa levels. In women with MHV, our practice includes titrating LMWH doses to target both trough and peak anti-Xa levels, while for those with VTE peak anti-Xa levels guide dosing.

Materials/Methods

This retrospective case series included pregnant women requiring LMWH treatment doses with at least 3 peak (+/− trough) anti-Xa levels. Our primary objective was to describe the actual LMWH dose required to achieve targeted anti-Xa levels relative to weight-based dosing in patients with MHV. Secondarily, we compared the same for VTE patients; compared actual dosing between those with MHV and VTE; and examined maternal and fetal outcomes.

Results/Conclusion

Women with MHV (N = 4) required greater than weight-based dosing of enoxaparin (1.35 mg/kg Q12H) to achieve targeted anti-Xa levels. Importantly, achieving target peak anti-Xa levels did not always ensure maintenance of minimum trough levels. VTE patients (N = 12) did not require more enoxaparin (0.96 mg/kg Q12H) than weight based dosing. MHV patients received more enoxaparin compared to VTE patients (P < 0.001). No bleeding or clotting complications were associated with LMWH administration. In pregnant women with MHV at high risk of thromboembolism, LMWH dosing guided by trough and peak anti-Xa levels should be considered.     

Evaluation of the prevalence of severe hyperhomocysteinemia in adult patients with thrombosis who underwent screening for thrombophilia

Introduction

Treatment with B-vitamins and betaine reduces the high risk of thrombosis in patients with homocystinuria, a metabolic syndrome that is characterized by severe hyperhomocysteinemia (HHcy). In contrast, there is no clear demonstration that B-vitamins reduce the risk of thrombosis in patients with mild HHcy: for this reason, many question the clinical utility of measuring total Hcy (tHcy) in patients with thrombosis. However, thrombosis may be the first clinical manifestation of homocystinuria in patients reaching adulthood without signs and symptoms of the syndrome.

Aim

1) to measure the prevalence of severe, previously undiagnosed, HHcy among patients with thrombosis 2) to profile these patients on the basis of their characteristics.

Methods

Six Italian Thrombosis Centers completed a first questionnaire, reporting tHcy levels in patients with thrombosis who underwent thrombophilia screening, and a second questionnaire, reporting the characteristics of patients with severe HHcy (tHcy > 100 μmol/L).

Results

Of 19,678 cross-sectionally collected patients with thrombosis who underwent thrombophilia screening in the last 12.5 years (median value, range 6-17), 38 had severe HHcy (0.2%). Their median age at diagnosis was 47 years (range 19-83) and the median level of tHcy was 130 μmol/L (range 101-262). Venous thromboembolism (71%) was more frequent than arterial thromboembolism (26%); recurrent thrombosis occurred in 42% of cases.

Conclusions

Measurement of tHcy in adult patients with thrombosis may reveal the presence of severe HHcy. Since treatment of patients with severe HHcy decreases the risk of thrombosis, measurement of tHcy in patients with thrombosis may prove clinically useful.     

Dose escalation of low molecular weight heparin in patients with recurrent cancer-associated thrombosis

Introduction

Patients with cancer-associated thrombosis are at a high risk of developing recurrent events despite anticoagulant therapy. Escalation of the dose of low molecular weight heparin (LMWH) has been suggested as a potential treatment option to manage these patients. We sought to confirm the benefit and risk of this management strategy in patients with recurrent cancer-associated thrombosis.

Material and Methods

A retrospective cohort study of consecutive cancer outpatients seen for management of a symptomatic recurrent cancer-associated thrombosis while on anticoagulation was undertaken. Objectively confirmed episodes of recurrent thrombosis were treated with either dose escalation of LMWH or initiation of therapeutic dose of LMWH in patients already anticoagulated with LMWH or vitamin K antagonist (VKA) respectively. Included patients were followed for a minimum of 3 months after the index recurrent event.

Results

Fifty-five cancer patients with a recurrent venous thromboembolism (VTE) despite anticoagulation were included. At the time of the recurrence, 89% of patients were on LMWH. The median time between the initial cancer-associated thrombosis to the index recurrent event was 2.3 months (range 0.1 to 30.4 months). Four patients (7.3%; 95% CI: 2.0 to 17.6%) had a second recurrent VTE during the 3-month follow-up period. Three patients (5.5%; 95% CI 1.1 to 15.1%) had major bleeding complications after dose escalation of LMWH. There were no recurrent fatal VTE or major bleeding episodes.

Conclusion

Escalating the dose of LMWH seems effective and safe for managing patients with recurrent cancer-associated thrombosis despite anticoagulant therapy.     

Comparison of antithrombotic and hemorrhagic effects of edoxaban,a novel factor Xa inhibitor,with unfractionated heparin,dalteparin, lepirudin and warfarin in rats

Background

Edoxaban is a novel, potent and orally active direct Factor Xa (FXa) inhibitor under development for prophylaxis and treatment of thromboembolic diseases. Properties of dose response and margin of safety of anticoagulants are the key factors for a positive risk/benefit of novel oral anticoagulants.

Objectives

To compare the dose response of antithrombotic effect and margin of safety between antithrombotic and hemorrhagic effects of edoxaban with conventional anticoagulants, unfractionated heparin (UFH), dalteparin (low molecular weight heparin), lepirudin, and warfarin in rat models of thrombosis and hemorrhage.

Methods

Rats were treated with edoxaban, UFH, dalteparin, and lepirudin by continuous intravenous (iv) infusion, or with oral warfarin for 4 days before inducing thrombosis or bleeding. Thrombosis was induced by inserting a platinum wire into the inferior vena cava for 60 minutes. Tail template bleeding time was measured after making an incision on the tail.

Results

In rats, iv infusion of edoxaban inhibited venous thrombosis in a dose-dependent manner. The other anticoagulants also exerted dose-dependent antithrombotic effects. The slopes of the dose–response curves of edoxaban were significantly shallower than the slopes of UFH, dalteparin, and warfarin. At supratherapeutic doses, edoxaban prolonged bleeding time in a rat tail bleeding model. To determine bleeding risk, the margins between antithrombotic and bleeding-time prolongation were compared. The margins of safety of edoxaban were wider than those of UFH, dalteparin, lepirudin, and warfarin.

Conclusions

These results suggest that edoxaban may be more easily controlled and has the potential for a more positive risk/benefit ratio compared to conventional anticoagulants.     

Antithrombin-resistant prothrombin Yukuhashi mutation also causes thrombomodulin resistance in fibrinogen clotting but not in protein C activation

Introduction

Prothrombin Yukuhashi (p.Arg596Leu) mutation can result in thrombophilia associated with antithrombin (AT) resistance. Mutant thrombin, an active form of prothrombin Yukuhashi, demonstrated moderately lower clotting activity than the wild-type but substantially impaired the formation of the complex with AT. However, the effects of the mutation on the thrombomodulin (TM)–protein C (PC) anticoagulant system have not been previously elucidated.

Materials and Methods

We prepared recombinant wild-type and mutant prothrombins, converted to thrombins using Oxyuranus scutellatus venom, and performed fibrinogen-clotting assays with or without recombinant soluble TM (rTM). We also evaluated activated PC (APC) generation activity of recombinant thrombins by measuring APC activity after incubation with human PC in the presence or absence of rTM.

Result and Conclusions

rTM treatment reduced the relative fibrinogen-clotting activity of the wild-type down to 8.4% in a concentration-dependent manner, whereas the activity of the mutant was only decreased to 44%. In the absence of rTM, APC generation activity (?A/min at 405 nm) was fairly low (0.0089 for the wild-type and 0.0039 for the mutant). In the presence of rTM, however, APC generation activity was enhanced to 0.0907 (10.2-fold) for the wild-type and to 0.0492 (12.6-fold) for the mutant, and the relative activity of the mutant with rTM was 54% of that of the wild-type. These data suggested that the prothrombin Yukuhashi mutation may cause TM resistance in terms of inhibition of fibrinogen clotting; this may contribute to susceptibility to thrombosis, although the enhancing effect of APC generation can be maintained.