Plasma concentration of von Willebrand factor in acute myocardial infarction

Recent investigations have revealed the crucial role of von Willebrand factor (vWF) in platelet thrombus formation under flow conditions. The plasma concentrations of vWF were measured together with various hemodynamic and hemostatic parameters in 51 cases of acute myocardial infarction. In 10 randomly selected cases, the plasma concentrations and distribution of multimers vWF were serially determined after reperfusion therapy by percutaneous transluminal coronary angioplasty (PTCA). The vWF concentration at the onset of the acute myocardial infarction was significantly higher than in an age-matched control group (vWF AG: 18.7 +/- 1.2 microg/ml vs. 10.3 +/- 0.5 microg/ml, p = 8.43 x 10-(12), mean +/- SE). Simultaneous determination of hemodynamic and hemostatic parameters revealed that the only two parameters that were significantly correlated with the patients' plasma vWF concentrations were their pulmonary capillary wedge pressure (PCWP) and heart rate, suggesting a relationship between hemodynamic changes induced by the onset of myocardial infarction and the vWF plasma concentrations. Serial determinations revealed that the vWF concentrations had not changed 1 h after reperfusion therapy, but that they significantly increased by 24 to 72 h. The distribution of the larger multimers of vWF also increased in the acute and subacute phase. The vWF concentration and multimer distribution normalized 14 days after the onset of the myocardial infarction. Our findings suggest that the vWF concentration increased in acute myocardial infarction patients, possibly in association with the hemodynamic deterioration that occurs in acute myocardial infarction.     

Enhanced shear-induced von Willebrand factor binding to platelets in acute myocardial infarction

Recent investigations have suggested that von Willebrand factor (vWF) plays a crucial role in platelet thrombosis under flow conditions. The effects of plasma obtained from 15 patients with acute myocardial infarction and 10 patients with the chest pain syndrome as controls, on shear-induced vWF binding to platelets and subsequent platelet activation, as evidenced by microparticle release, were investigated by quantitative flow cytometry. Platelet-rich plasma was obtained from a 38-year-old healthy male volunteer with blood type O. Stored plasma from either the acute myocardial infarction or control patients was then added to the freshly prepared platelet-rich plasma in equal volumes. The mixtures were then exposed to specific shear rates in an optically modified cone-plate viscometer. The number of vWF molecules bound to the platelet surface and the number of microparticles released from the platelets were then measured by quantitative flow cytometry using an FITC-conjugated anti-vWF monoclonal antibody. The shear-induced increase in vWF binding to the platelet surface was enhanced in the presence of plasma from patients with acute myocardial infarction (acute myocardial infarction plasma). The shear-induced release of microparticles from platelets was enhanced from 889+/-134 in the presence of control plasma to 1045+/-222 in the presence of the acute myocardial infarction plasma (p<0.05). Acute myocardial infarction plasma also reduced the shear rate threshold required to induce measurable shear-induced vWF binding from 10800 s(-1) to 9000 s(-1). We conclude that the plasma of acute myocardial infarction patients contains factors that enhance shear-induced vWF binding and vWF-mediated platelet activation, which may contribute to thrombotic re-occlusions of the coronary arteries in patients who have received reperfusion treatments.     

Platelet von Willebrand factor: Comparison with plasma von Willebrand factor

Platelet von Willebrand factor (vWf) was compared to its plasma counterpart. The platelet vWf was different from plasma vWf in that 1) the multimeric organization was different, 2) larger multimers were present, and 3) the ratio of vWf activity to antigen was higher. Platelet and plasma vWf were similar in their antigenic reactivity in the electroimmunoassay and by liquid phase radioimmunoassay. The amount of vWf activity in large platelets was significantly higher than in normal platelets while the antigen content, although somewhat higher, was not significant. These studies show differences between normal platelet and plasma vWf, and also suggest that platelet size must be considered when platelet vWf is measured in disease states.     

Platelet-type von Willebrand disease platelet aggregating factor: a novel functional assay of von Willebrand factor

Blood platelets from patients with platelet-type von Willebrand disease (vWD) aggregate upon the addition of human von Willebrand factor (vWf) in the absence of ristocetin or other stimulating factors. We measured quantitatively the ability of vWf to induce directly aggregation of platelet-type vWD platelets (platelet-type vWD platelet aggregating factor [PT-PAF]). Cryoprecipitate and factor VIII concentrates were used as a source of vWf of various multimeric composition. The PT-PAF activity was dependent on the multimer size of vWf, like in the case of ristocetin cofactor (RCof) activity. However, PT-PAF activity was not equivalent to RCof activity and the relative PT-PAF/RCof ratio ranged from 1.00 to 0.18 in the materials studied. The preparations containing the higher-molecular-weight multimers had higher PT-PAF/RCof ratio. These findings suggest that PT-PAF activity is a functional expression of more highly polymerized multimers of vWf as compared with RCof activity. Measurement of PT-PAF would serve as a novel functional assay of vWf.     

The capillary thrombometer and von Willebrand factor

A modified capillary thrombometer was constructed to study the rate of thrombus formation using heparinized whole blood (2 U/ml) from 4 different groups of pigs: normal, heterozygous von Willebrand's disease (vWD), homozygous vWD, and platelet storage pool disease (SPD). The median thrombosis times for the 4 groups of pigs were: 5.3 min (range = 3.0-14), 31 min (range = 4.0-47), 55 min (range = 41-60), and 60 min (range = 15-60), respectively. Significant differences were demonstrated between all pig groups (p less than .01 - p less than .001), except between the homozygous vWD pigs and the SPD pigs (p = 0.8), both of which are clinical bleeders. Cryoprecipitate was infused into 3 pigs with homozygous vWD. Partial correction of the capillary thrombometer thrombosis time and the in vivo ear bleeding time was observed. Murine monoclonal antibodies to porcine von Willebrand factor were added to normal pig whole blood samples in the capillary thrombometer. Four of six antibodies prolonged the thrombosis time and had similar effects on the ear bleeding time. Using these monoclonal antibodies, an immunoperoxidase stain demonstrated plasmatic and platelet associated von Willebrand factor in sections of thrombi from the capillary thrombometer. These experiments confirm that von Willebrand factor is important to thrombus formation in the capillary thrombometer and that measurements by this instrument may relate to in vivo hemostasis as measured by the ear bleeding time.     

Changes in plasma von Willebrand factor-cleaving protease (ADAMTS13) levels in patients with unstable angina

INTRODUCTION: Increased plasma levels of von Willebrand factor (VWF) have been reported in acute myocardial infarction (AMI). Recently, we showed reduced activity of a VWF-cleaving protease (ADAMTS13) in AMI patients. However, there is no information as to whether ADAMTS13 affects the pathogenesis of unstable angina (UA). Thus, the purpose of this study was to examine changes in plasma VWF and ADAMTS13 levels in UA patients. MATERIALS AND METHODS: Plasma VWF and ADAMTS13 levels (mU/ml) were measured in 45 patients with UA, 55 with stable exertional angina (SEA) and 47 with chest pain syndrome (CPS) at the time of coronary angiography. Levels were also measured in 15 UA patients after 6 months of follow-up. RESULTS: VWF antigen levels (mU/ml) increased significantly in UA patients compared with SEA or CPS (2129.3+/-739.5, 1571.8+/-494.2 and 1569.5+/-487.0, respectively; P<0.0001 in UA vs. SEA or CPS). ADAMTS13 antigen levels (mU/ml) were significantly lower in UA patients than SEA or CPS (737.3+/-149.5, 875.3+/-229.0 and 867.7+/-195.5, respectively; P<0.01 in UA vs. SEA or CPS). Furthermore, there was a significant inverse correlation between VWF and ADAMTS13 antigen levels (r=-0.302, P=0.0002). The antigen levels at 6 months of follow-up were not different compared to the acute phase in the 15 UA patients that had repeated blood sampling. CONCLUSIONS: These findings suggest that there is prolonged thrombogenicity in UA patients represented as an imbalance between VWF and ADAMTS13 activity.     

The factor VIII/von Willebrand factor ratio discriminates between reduced synthesis and increased clearance of von Willebrand factor

It is often stated that a decrease in Von Willebrand factor (VWF), the carrier protein of factor VIII, results in a concordant change in factor VIII. Clinical data suggest that this is not always the case and we hypothesized that the ratio between factor VIII and VWF depends on the genetic defect that causes the VWF deficiency. We have analyzed the ratio between plasma factor VIII and VWF in several subtypes of Von Willebrand Disease and we show that the ratio is increased when VWF synthesis is reduced, but that the ratio remains one when VWF clearance is increased. These observations could be of clinical importance as an increased factor VIII/VWF ratio in combination with a borderline VWF level may indicate the presence of a true genetic defect, possibly a VWF null allele.     

Pharmacoeconomic analysis of sertraline treatment of depression in patients with unstable angina or a recent myocardial infarction

BACKGROUND: The prevalence of major depressive disorder in patients with acute coronary syndromes (ACSs) is high and associated with worse cardiovascular outcomes and higher health care costs. Sertraline is the only treatment for major depressive disorder studied in a placebo-controlled trial of patients with ACS and found to be safe and effective. The cost implications of providing antidepressant treatment in this population have not yet been examined. The objective was to evaluate from a payer perspective the potential reduction in costs and psychiatric and cardiovascular events and procedures following sertraline versus placebo treatment of major depressive disorder in patients hospitalized for ACS. METHOD: Data were analyzed from a randomized, double-blind, placebo-controlled 24-week trial (Sertraline Antidepressant Heart Attack Randomized Trial) of sertraline treatment for major depressive disorder in patients hospitalized for ACS. Main outcome measures included frequency and costs (derived from Medicare diagnosis-related group fee schedules) of psychiatric and cardiovascular events occurring during the treatment period. RESULTS: There was a trend toward significantly fewer psychiatric or cardiovascular hospitalizations in the sertraline compared with the placebo group (55/186 vs. 76/183; p = .054). The mean per patient cost associated with psychiatric and medical events over the course of treatment was 2733 US dollars for sertraline and 3326 US dollars for placebo, but the difference was not statistically significant (p = .32). After including the costs of the sertra-line (360 US dollars over 24 weeks), there was no increase in treatment costs for sertraline compared with placebo. CONCLUSION: Sertraline treatment of major depressive disorder following hospitalization for a recent myocardial infarction or unstable angina appears to be a cost-effective strategy.     

Cerebral venous thrombosis and plasma concentrations of factor VIII and von Willebrand factor: a case control study

Background

High plasma concentrations of factor VIII (FVIII) and von Willebrand factor (VWF) have been recently associated with a moderately increased risk of venous thrombosis, but their roles in cerebral sinus and venous thrombosis (CSVT) have not been addressed. To determine whether elevation of FVIII and VWF is more frequent in CSVT, we analysed plasma levels of FVIII and VWF in a case control study.

Methods

The study population consisted of 25 consecutive patients (of whom nine were excluded) admitted for CSVT to the Department of Neurology, Amiens University Hospital, France, from January 1997 to December 2002, for a general screening for thrombophilia. Sixty‐four healthy subjects matched for age and sex formed the group control.

Results

Mean FVIII (CSVT: 167.3 (SD 48.8) IU/dl; control group: 117.9 (39.8) IU/dl; p = 0.001) and VWF levels (CSVT: 165.4 (76.5)%; control group: 108.5 (27.8)%; p = 0.01) were significantly higher in the CSVT group. Using the 95th percentile of the control group as the cut off value, elevated FVIII (>190 IU/dl) occurred in 25% (4/16) (p = 0.005) and elevated VWF (>168%) in 37.5% (6/16) of patients with CSVT (p<0.001). Using previously reported cut off values (>150 IU/dl or >150%) showed the same results (FVIII: p = 0.005; VWF: p = 0.009).

Conclusion

Our study suggests that elevation of plasma factor VIII levels is the most common prothrombotic risk factor for CSVT. Elevation of VWF is also associated with an increased risk of CSVT but its effect seems to be partly mediated through FVIII.Cerebral sinus and vein thrombosis (CSVT) is a rare localisation of venous thromboembolic disease. It generally occurs in young or middle‐aged adults and accounts for approximately 1% of strokes.¹ Many coagulation disorders have been associated with CSVT.^2,3,4Several prospective studies showed that high concentrations of factor VIII (FVIII) are associated with a moderately increased risk of venous thromboembolism (VTE).^5,6 The role of increased levels of von Willebrand Factor (VWF) in VTE remains unclear.^5,7 Recent studies suggest that the effect of VWF is fully explained by FVIII concentrations.⁵ Indeed, the ABO blood group, which regulates plasma concentrations of both FVIII and VWF, may also play a role in susceptibility to thrombosis.^8,9,10The increased risk of VTE with elevated levels of FVIII or VWF has been observed in previous studies.^5,6,7,11 However, they did not specifically include patients with CSVT^7,9 or they were incomplete.¹²The aim of our study was to assess plasma levels of FVIII, VWF and other thrombophilic factors in patients with CSVT in a case control study.     

The anti-von Willebrand factor aptamer ARC1779 increases von Willebrand factor levels and platelet counts in patients with type 2B von Willebrand disease

Blockade of hyperactive von Willebrand factor (VWF) by ARC1779 blunted the platelet drop induced by desmopressin in patients with type 2B von Willebrand disease (VWD). Thus, we hypothesised that ARC1779 may increase VWF levels and correct thrombocytopenia. Three thrombocytopenic patients suffering from type 2B VWD received a loading dose of 0.23 mg/kg ARC1779 followed by 4 μg/kg/min intravenously for 72 hours in a prospective clinical trial. ARC1779 was well tolerated and safe. Plasma concentrations of ARC1779 increased to 76 μg/ml (59-130) leading to an immediate decrease of free VWF A1 domains. VWF/FVIII levels increased as early as 12 h after start of infusion, peaked near the end of infusion, and returned to baseline at follow-up. VWF ristocetin cofactor activity (VWF:RCo) showed a median 10-fold increase 8 hours after end of infusion, while the median VWF-antigen and FVIII increase was less (5-fold and 4-fold, respectively). Most importantly inhibition of hyperactive VWF rapidly increased platelet counts from 40 x 10(9)/l (38-58 x 10(9)//l) to a maximum of 146 x 10(9)//l (107-248 x 10(9)//l). In conclusion, ARC1779 markedly increases VWF/FVIII levels and most importantly improves or even corrects thrombocytopenia in VWD type 2B patients. This underscores the in vivo potency of ARC1779.     

Increased von Willebrand factor in migraine

The authors determined von Willebrand factor (vWF) in 63 persons with migraine, 11 persons with migraine and prior stroke, and 35 frequency-matched controls. Additional studies were done in a subset with migraine without aura who were headache free for >7 days. Migraineurs with prior stroke had significantly higher vWF antigen (170% versus 106%) and activity (162% versus 108%) than the control group. vWF antigen (126%) and activity (130%) were also significantly higher in migraineurs without stroke. Multimers and protease activity were normal in the interictal subset.     

von Willebrand factor antigen in urine

Human urine was analyzed using a sensitive enzyme linked immunosorbent assay (ELISA) for von Willebrand factor (VWF) antigen. Urine of healthy persons contained VWF immunoreactivity. In the urine of a patient with severe von Willebrand disease, the VWF antigen was not detectable before but after intravenous infusion of von Willebrand factor-Factor VIII (VWF-FVIII) concentrate. The VWF antigen in normal urine was analyzed by gel permeation high performance liquid chromatography (HPLC). Three immunoreactive components of Mr 350 KDa, 60 KDa, and 20 KDa, respectively, were observed. Chromatography on concanavalin A-Sepharose revealed heterogeneity of the major 60 KDa component since only part of the material had affinity for the matrix. The 350 KDa material displayed affinity for Con A-Sepharose but not the 20 KDa. Gel electrophoresis combined with immunoblotting of normal urine gave similar results to those obtained by HPLC analysis. Immunoreactive components with apparent molecular weights similar to the largest urinary antigens were also observed in normal plasma but they were, nevertheless, not identical to the urinary antigens.     

The role of von Willebrand factor in thrombus formation

Von Willebrand factor (VWF) is a large multimeric glycoprotein produced in endothelial cells and megakaryocytes and present in subendothelial matrix, blood plasma and platelets. VWF mediates adhesion and aggregation of platelets at sites of vascular injury, processes that are critical for both haemostasis and thrombosis. Thrombus formation involves complex events that are influenced by different environmental conditions. Progress in understanding the structure and function of VWF and the mechanisms that underlie its interactions with platelets has led to important insight into the differentiation between normal haemostasis and pathological arterial thrombosis. The conventional view of signalling-induced platelet aggregation has recently been extended to include activation-independent aggregation. A novel mechanism has been demonstrated for initiating thrombus formation under high haemodynamic forces that involves alpha(IIb)beta(3)-independent platelet aggregation at the interface between immobilised and soluble VWF. This VWF-mediated process may be a key determinant of platelet accumulation in stenotic arteries leading to acute thrombotic occlusion.     

The role of von Willebrand factor in pre-eclampsia.

The von Willebrand factor (vWF) has gained considerable interest in recent years as a marker of endothelial cell activation or insult and by virtue of its interactions with platelets and vessel walls. Altered patterns of vWF multimers were found to occur frequently in patients with thrombotic thrombocytopenic purpura in the acute and chronic stages. This disorder shares some clinical and laboratory findings with pre-eclampsia, including thrombocytopenia. Recent studies have also suggested that abnormalities of endothelial cell metabolism play a central role in the pathophysiology of pre-eclampsia. In order to determine if vWF could be instrumental in the disease process and the thrombocytopenia of pre-eclampsia we analyzed the ante- and postpartum structural and functional distribution of vWF. This data was correlated with hematological parameters such as platelet counts and the clinical severity of the disease. We found no consistent changes of vWF in association with thrombocytopenia or clinical severity. However, functional vWF was lower in postpartum samples of severely affected pre-eclamptics as compared to normal controls. This finding may reflect endothelial cell exhaustion after stimulation or cellular injury. Elevated titers of fibrin split products and thrombocytopenia were evident in severe pre-eclampsia, as seen in DIC, despite factor VIII coagulant levels within the normal range. Our data is consistent with the hypothesis of endothelial cell dysfunction in pre-eclampsia. However, the mechanism of thrombocytopenia in this disorder does not appear to be related to alterations in the structure or biological function of vWF.     

What a polyclonal antibody sees in von Willebrand factor

INTRODUCTION: Von Willebrand factor (VWF) plays a critical role in hemostasis by carrying factor VIII (FVIII) and binding to specific ligands on the surface of blood platelets and within the blood vessel wall. MATERIALS AND METHODS: We constructed a gene-specific phage display library containing small, random VWF fragments. Using this library, we mapped the repertoire of immune epitopes recognized by a commonly used commercial rabbit antihuman VWF polyclonal antibody. RESULTS: A total of eight discrete epitopes within the VWF protein were identified, including two dominant epitopes that account for 74% of immuno selected VWF fragments. Comparison with previously mapped epitopes for mouse monoclonal antibodies reveals four overlapping regions that may identify common antigenic determinants. The distribution of these epitopes was not readily predicted from primary amino acid sequence divergence among these mammalian species or standard algorithms for the prediction of antigenicity, hydrophobicity, or surface probability. CONCLUSION: Taken together with previous monoclonal antibody epitope mapping studies, our results suggest that a limited number of exposed domains on the surface of the human VWF protein may be the primary determinants of immunogenicity.     

The dynamic inter-relationship between factor VIII and von Willebrand factor.

A monospecific heterologous antibody which specifically inhibited von Willebrand factor (W.F.) but had no factor VIII procoagulant (VIIIc) neutralising properties was insolubilised by attachement to sepharose beads. When fresh normal plasma was mixed with such beads, VIIIc, W.F. and factor VIII related antigen (VIIIAg) were removed in equal proportions, with the VIIIc lost from the plasma being detectable attached to the sepharose. This VIIIc was removed from the sepharose and largely recovered in the eluate after treatment with 0.2M calcium chloride. Subsequent addition of plasma resulted in a high transfer of VIIIc from the plasma onto the sepharose beads without accompanying W.F. and VIIIAg. Similar experiments, with initial treatment of antibody attached sepharose beads with serum, resulted in no independent segregation of VIIIc on subsequent addition of plasma. It is suggested that VIIIc and W.F. exist in plasma as separate, but attached molecules in a dynamic equilibrium. In serum, W.F. loses its ability to attach VIIIc.     

Platelet reactivity in acute coronary syndromes: evidence for differences in platelet behaviour between unstable angina and myocardial infarction.

Previous work has shown that P-selectin and mean platelet volume, two markers associated with platelet reactivity, are elevated in acute coronary syndromes. This study investigated the possibility that these markers may define unstable angina (UA) and acute myocardial infarction (MI) as two separate conditions based on platelet behaviour. Mean platelet volume (MPV) was higher in UA patients (n = 15) than in those diagnosed with MI (n = 15) (10.7 +/- 0.25 fL, vs. 9.8 +/- 0.27 fL, P = 0.005). Platelet count was lower in UA than in MI (215 +/- 13 x 10(9)/L vs. 271 +/- 20 x 10(9)/L, P = 0.03). The percentage of platelets expressing P-selectin was higher in MI than in UA (9.1 +/- 1.9% vs. 4.2 +/- 0.85%, P = 0.03). This parameter was positively correlated with MPV in UA (r = 0.5, P = 0.04) but negatively correlated in MI (r = -0.6, P = 0.01), with no correlation for ACS as a whole (r = -0.32, P = 0.1). Our results suggest that in MI there is an acute process of generalised platelet activation that is unrelated to changes in MPV, whereas in UA there is an ongoing process of platelet consumption that leads to an increase in platelet size to compensate for a persistent decrease in platelet count. This study suggests that there is a fundamental difference in platelet biology between these two diseases.