Protected by nature? Effects of strenuous physical exercise on FVIII activity in moderate and mild haemophilia A patients: a pilot study.

Increase of factor VIII activity (FVIII) after physical exercise has been reported in healthy subjects and small-scale studies in patients with coagulopathies. The aim was to study whether moderate and mild haemophilia A patients are able to increase their endogenous FVIII activity levels by physical activity. We studied changes in FVIII activity levels after high-intensity exercise in 15 haemophilia A patients, 20-39 years, eight with moderate, seven with mild haemophilia. Patients cycled until volitional exhaustion, blood samples were drawn before and 10 min after the exercise test. FVIII activity increased 2.5 times (range 1.8-7.0 times), for both severities. Absolute increases were markedly different: median 7 IU dL(-1) (range 3-9 IU dL(-1) ) in patients with moderate, compared to 15 IU dL(-1) (range 6-62 IU dL(-1) ) in mild haemophilia patients. VWF and VWFpp increased independently of severity; median 50% (range 8-123%) and median 165% (range 48-350%), respectively, reflecting acute release of VWF. These observations may be used to promote high-intensity activities before participating in sports for moderate and mild haemophilia A patients, to reduce bleeding risk. Further studies are warranted to fully appreciate the clinical significance of exercise on different levels of intensity in patients with mild and moderate haemophilia A.

Genome scan of clot lysis time and its association with thrombosis in a protein C-deficient kindred.

BACKGROUND: Previously, we found increased clot-lysis time (CLT), as measured with a plasma-based assay, to increase the risk of venous thrombosis in two population-based case-control studies. The genes influencing CLT are as yet unknown. PATIENTS/METHODS: We tested CLT as risk factor for venous thrombosis in Kindred Vermont II (n = 346), a pedigree suffering from a high thrombosis risk, partially attributable to a type I protein C deficiency. Furthermore, we tested for quantitative trait loci (QTLs) for CLT, using variance component linkage analysis. RESULTS: Protein C-deficient family members had shorter CLTs than non-deficient members (median CLT 67 min vs. 75 min). One standard deviation increase in CLT increased the risk of venous thrombosis 2.4-fold in non-deficient family members. Protein C deficiency without elevated CLT increased the risk 6.9-fold. Combining both risk factors yielded a 27.8-fold increased risk. The heritability of CLT was 42-52%. We found suggestive evidence of linkage on chromosome 11 (62 cM), partly explained by the prothrombin 20210A mutation, and on chromosome 13 (52 cM). Thrombin-activatable fibrinolysis inhibitor genotypes did not explain the variation in CLT. CONCLUSION: Hypofibrinolysis appears to increase thrombosis risk in this family, especially in combination with protein C deficiency. Protein C deficiency is associated with short CLT. CLT is partly genetically regulated. Suggestive QTLs were found on chromosomes 11 and 13.

An international multicentre-laboratory evaluation of a new assay to detect specifically lupus anticoagulants dependent on the presence of anti-beta2-glycoprotein autoantibodies.

BACKGROUND: Antiphospholipid syndrome (APS) is diagnosed by the simultaneous presence of vascular thrombosis and/or pregnancy morbidity and detection of antiphospholipid antibodies in plasma. OBJECTIVES: We have shown that prolongation of clotting time by anti-beta2-glycoprotein I (beta2GPI) antibodies correlates better with thrombosis than a positive classic lupus anticoagulant (LAC) assay in a single center study. To confirm or falsify this finding we have conducted a multicenter study. METHODS AND RESULTS: In 325 LAC-positive samples, we found that the beta2GPI-dependent LAC correlated 2.0 times better with thrombosis than the classic LAC assay. Although significant, this was a minimal improvement compared with the 'classic' LAC. It was published that calcium influences the behavior of anti-beta2GPI antibodies in coagulation assays. To investigate whether calcium plays a role in the present study, we divided the patient population into two groups: (i) blood was collected in 0.109 m sodium citrate and (ii) blood was drawn in 0.129 m sodium citrate as anticoagulant. We found that a positive result with the beta2GPI-dependent LAC assay correlated better with thrombosis [odds ratio (OR): 3.3, 95% confidence interval (CI) 1.9-5.8] when 0.109 m sodium citrate was used compared with 0.129 m sodium citrate (OR: 0.4, 95% CI 0.1-1.1). CONCLUSION: We were able to confirm in an international multicenter study that a positive result in a beta2GPI-dependent LAC assay correlates better with thrombosis than the classic LAC assay, but that the assay needs further study as it is sensitive to external factors such as the sodium citrate concentration used as anticoagulant in the test sample.

The minor allele of GP6 T13254C is associated with decreased platelet activation and a reduced risk of recurrent cardiovascular events and mortality: results from the SMILE-Platelets project.

BACKGROUND: Contradictory results have been published on the effects of T13254C (rs1613662), which distinguishes the two major isoforms of GP6, the gene encoding the platelet receptor glycoprotein VI, on platelet function and the risk of cardiovascular disease. METHODS: We performed a population-based case-control study, the Study of Myocardial Infarctions in Leiden, among 547 male patients with a first myocardial infarction (MI) and 646 control subjects, as well as a prospective cohort study in which the same MI patients were followed for recurrent events (fatal and non-fatal MI and unstable angina) and mortality (median follow-up of 12 years). P-selectin expression by platelets induced by crosslinked collagen-related peptide (CRP-XL) was measured by whole blood flow cytometry in 274 MI patients. RESULTS: T13254C was not associated with a first MI, but seemed to be associated with a reduced incidence of recurrent events [per-allele hazard ratio 0.77, 95% confidence interval (CI) 0.56-1.06] and mortality (hazard ratio 0.57, 95% CI 0.37-0.89). Pooling with the Heart and Estrogen/Progestin Replacement Study revealed hazard ratios of 0.81 (95% CI 0.66-0.99) and 0.73 (95% CI 0.55-0.96). The minor C-allele was also strongly associated with a reduced percentage of P-selectin-expressing platelets. The reduction per C-allele was 23% (95% CI 18-28%). In an independent study of 219 healthy volunteers, the per-allele reduction of CRP-XL-induced aggregation was 10% (95% CI 2-18%). CONCLUSION: The minor allele of GP6 T13254C that reduced platelet activation and aggregation also seemed to be associated with a reduced incidence of recurrent cardiovascular events and mortality, but was not associated with first MI.

The active conformation of von Willebrand factor in patients with thrombotic thrombocytopenic purpura in remission.

BACKGROUND: Functional deficiency of ADAMTS13 in thrombotic thrombocytopenic purpura (TTP) patients is associated with circulating ultralarge von Willebrand factor (VWF) molecules that display spontaneous platelet-binding capacities. Upon remission, however, ADAMTS13 activity does not always return to baseline. OBJECTIVE: To study ADAMTS13 and VWF-related features in TTP patients in remission. METHODS: ADAMTS13 activity, anti-ADAMTS13 antibodies, VWF antigen, ultralarge VWF and levels of VWF that circulate in a glycoprotein Ibalpha-binding conformation were determined in plasma samples of 22 acquired TTP patients in remission between 1 month and 6 years after achieving remission. The composition of active multimers was investigated with a novel immunoprecipitation assay based on monoclonal antibody AU/VWF-a12, which specifically recognizes the active conformation of VWF. RESULTS: ADAMTS13 activity was undetectable in 23% of the patients, even years after they had achieved remission, and lack of ADAMTS13 activity was associated with increased active VWF levels and the presence of ultralarge VWF multimers. Active VWF levels and ultralarge VWF were also associated with blood groups. Results from immunoprecipitation experiments revealed the full range of multimers to be present. CONCLUSION: ADAMTS13 deficiency and the concurrent presence of ultralarge VWF and increased active VWF levels can be detected in TTP patients for years after they have achieved remission. Immunoprecipitation results suggest that the active conformation of VWF may be present in the lower molecular weight multimers, but future studies are necessary to confirm our findings.

Role of adipose tissue in haemostasis, coagulation and fibrinolysis.

Obesity is associated with an increased incidence of insulin resistance (IR), type 2 diabetes mellitus and cardiovascular diseases. The increased risk for cardiovascular diseases could partly be caused by a prothrombotic state that exists because of abdominal obesity. Adipose tissue induces thrombocyte activation by the production of adipose tissue-derived hormones, often called adipokines, of which some such as leptin and adiponectin have been shown to directly interfere with platelet function. Increased adipose tissue mass induces IR and systemic low-grade inflammation, also affecting platelet function. It has been demonstrated that adipose tissue directly impairs fibrinolysis by the production of plasminogen activator inhibitor-1 and possibly thrombin-activatable fibrinolysis inhibitor. Adipose tissue may contribute to enhanced coagulation by direct tissue factor production, but hypercoagulability is likely to be primarily caused by affecting hepatic synthesis of the coagulation factors fibrinogen, factor VII, factor VIII and tissue factor, by releasing free fatty acids and pro-inflammatory cytokines (tumour necrosis factor-alpha, interleukin-1beta and interleukin-6) into the portal circulation and by inducing hepatic IR. Adipose tissue dysfunction could thus play a causal role in the prothrombotic state observed in obesity, by directly and indirectly affecting haemostasis, coagulation and fibrinolysis.

The obstetric antiphospholipid syndrome.

The association of persistent presence of circulating antiphospholipid antibodies and thromboembolic events, (recurrent) pregnancy loss or both is termed antiphospholipid syndrome. Pregnancies in women with the syndrome should be regarded as at high-risk for complications. Optimal management consisting of close follow-up and pharmacological treatment can result in about 70-80% live births. Apart from the laboratory diagnosis of the syndrome and pathophysiology, this review will focus on treatment during pregnancy.

Acute activation of the endothelium results in increased levels of active von Willebrand factor in hemolysis, elevated liver enzymes and low platelets (HELLP) syndrome.

BACKGROUND: HELLP (hemolysis, elevated liver enzymes and low platelets) syndrome is a severe complication of pre-eclampsia in pregnancy, characterized by microvascular platelet thrombi. Activation of the endothelium is thought to play a key role in pre-eclampsia and HELLP syndrome. Activation of endothelial cells may lead to release of von Willebrand factor (VWF) multimers, which are highly reactive with platelets. Normally, newly released multimers are cleaved by ADAMTS13, resulting in less reactive derivatives. OBJECTIVE: We hypothesized that HELLP syndrome is characterized by increased amounts of active VWF compared with healthy pregnancy and pre-eclampsia, due to acute activation of endothelial cells. This might contribute to thrombocytopenia and thrombotic microangiopathy. METHODS: Active VWF and ADAMTS13 activity were measured in healthy pregnant volunteers (n = 9), patients with pre-eclampsia (n = 6) and patients with HELLP syndrome (n = 14) at similar gestational ages. To study the role of endothelial cell activation, the propeptide/mature VWF ratio was determined, and VWF released by cultured endothelial cells was analyzed. RESULTS: Active VWF levels were increased 2.1-fold in HELLP syndrome compared with healthy pregnant volunteers (P < 0.001) and 1.6-fold compared with patients with pre-eclampsia (P = 0.001). ADAMTS13 activity was moderately decreased in patients with HELLP syndrome compared with healthy pregnant volunteers (P < 0.004), but not compared with patients with pre-eclampsia. The propeptide/mature VWF ratio was increased 1.7-fold compared with healthy pregnant volunteers (P < 0.001) and 1.5-fold compared with patients with pre-eclampsia (P < 0.05). A significant correlation was found between this ratio and the activation factor of VWF (r = 0.68, P < 0.001). The amount of active VWF was increased 1.4-fold in medium of stimulated endothelial cells when compared with non-stimulated cells (P < 0.05). CONCLUSION: Acute endothelial cell activation in HELLP syndrome and decreased ADAMTS13 activity result in increased amounts of active VWF. This might explain the consumptive thrombocytopenia and thrombotic microangiopathy associated with HELLP syndrome. Inhibition of circulating active VWF could be a potential new approach in the treatment of patients with HELLP syndrome.

Improving small-diameter vascular grafts: from the application of an endothelial cell lining to the construction of a tissue-engineered blood vessel.

One of the main reasons why vascular reconstruction with synthetic small-diameter grafts has limited success is the absence of endothelial cells. To improve the outcome of nonvenous vascular bypass surgery, cell seeding of vascular grafts and other tissue-engineering techniques were developed. In this article, an overview is given of the artificial blood vessel as an alternative for venous vascular bypass surgery.

[Activity loss of Von Willebrand factor cleaving protein (ADAMTS-13) is diagnostic for primary and pregnancy-related thrombotic thrombocytopenic purpura]. / Afwezige activiteit van Von Willebrand-factorsplitsend eiwit (ADAMTS-13) diagnostisch voor primaire en zwangerschapsgerelateerde trombotische trombocytopenische purpura.

OBJECTIVE: To determine whether the measurement of the Von Willebrand factor cleaving protease ADAMTS-13, such as is carried out at the University Medical Centre of Utrecht, The Netherlands, contributes towards the diagnosis and treatment of patients with thrombotic thrombocytopenic purpura (TTP). DESIGN: Descriptive. METHOD: In a group of 98 patients from 21 hospitals, with a Coombs-negative haemolytic anaemia and thrombocytopenia, the ADAMTS-13 activity was measured. Treatment was given irrespective of ADAMTS-13 activity. RESULTS: ADAMTS-13 activity was absent in 27 of 29 patients diagnosed with primary TTP and in all 5 pregnancy-TTP patients. In patients suffering from TTP after bone marrow transplantation (post-BMT) and in all other patients included in this study, ADAMTS-13 activity was normal. Of the 32 patients with absent ADAMTS-13 activity, 28 underwent plasmapheresis. This treatment proved effective as all 28 patients responded well. 17 patients with normal ADAMTS-13 activity also underwent plasmapheresis; 5 (30%) responded well to treatment. In 2 cases a final diagnosis of primary TTP was made, in a further 2, haemolytic uraemic syndrome and in 1 case sepsis was diagnosed. CONCLUSION: In this study, the absence of ADAMTS-13 activity predicted primary TTP and TTP of pregnancy with a sensitivity of 93% and a specificity of 100%. Absence of ADAMTS-13 activity is a strong indication for plasma exchange.