Type 2N von Willebrand disease: Characterization and diagnostic difficulties.

INTRODUCTION: An abnormal factor VIII (FVIII) binding capacity of von Willebrand factor (VWF) identifies type 2N von Willebrand disease (VWD). Type 2N VWD patients are identified by means of the VWF FVIII binding (VWF:FVIIIB) assay, and especially their VWF:FVIIIB/VWF:Ag ratio (VWF:FVIIIB ratio). AIM: We report on our 15-year experience of diagnosing type 2N VWD. METHODS: We have performed 2178 VWF:FVIIIB assays in bleeders and normal subjects. RESULTS: von Willebrand factor (VWF):FVIIIB was reduced in 682, but only 60 had low VWF:FVIIIB ratios (<0.74). Among nine patients who had a VWF:FVIIIB ratio below 0.3, four had normal VWF levels and were homozygotes for the p.R854Q mutation; the other five had low VWF levels due to a quantitative VWF mutation combined with p.R854Q. The VWF:FVIIIB ratio ranged between 0.3 and 0.73 in 51 subjects; 34 of them were heterozygotes for the p.R854Q mutation, while one carried the p.R760C. The heterozygotes for type 2N included subjects with or without bleeding symptoms, the former with significantly lower mean VWF levels than the latter. Among the 116 normal subjects tested, six were heterozygotes for the p.R854Q mutation (all asymptomatic). CONCLUSIONS: The prevalence of type 2N in our VWD cohort was 2.5%, and 5.2% of the general population in Northeast Italy was found heterozygous for the p.R854Q mutation. It might be difficult to reveal a type 2N defect using routine tests alone, especially when it is combined with a quantitative VWF mutation. Accordingly, we always recommend VWF:FVIIIB assay in the diagnostic workup of VWD.

Usefulness of the Total Thrombus-Formation Analysis System (T-TAS) in the diagnosis and characterization of von Willebrand disease.

INTRODUCTION: The heterogeneity of von Willebrand disease (VWD) makes its diagnosis a difficult task. METHODS: We report here on the usefulness of a microchip-based flow-chamber system, the total thrombus-formation analysis system (T-TAS), in the identification and characterization of VWD. Thirty VWD patients and 20 healthy subjects were studied with the T-TAS platelet (PL) and atherome (AR) microchips developed for the in vitro assessment of platelet thrombus formation and fibrin-rich platelet thrombus formation respectively. RESULTS: Samples from severe type 1 VWD, characterized by von Willebrand factor (VWF) levels below 10 U dL-1 , failed to occlude either the PL or the AR chip capillaries, while the occlusion times were normal in patients with mild type 1 VWD (VWF above 25 U dL-1 ). PL and/or AR chip occlusion occurred, but took longer than normal, for samples from type Vicenza and type 1 VWD patients, whose VWF levels ranged between 10 and 25 U dL-1 . No PL or AR chip capillary occlusion was seen for samples from patients with type 2A or 2B VWD featuring the absence of large VWF multimers, whereas no abnormalities emerged for type 2B patients with normal multimer patterns. CONCLUSION: The T-TAS appears to be sensitive mainly to plasma VWF concentration and the presence of large multimers. Failure of the PL and AR chips to become occluded points to a lack of large VWF multimers, or type 1 VWD with VWF levels below 10 U dL-1 . Although the T-TAS does not assure a precise VWD diagnosis, it does point us in the right direction, and thus seems a useful global preliminary test.

Venous thromboembolism in patients with Cushing's syndrome: need of a careful investigation of the prothrombotic risk profile.

A high incidence of venous thromboembolic (VTE) complications has been reported in Cushing's syndrome (CS), mostly post-operatively and attributable to hypercoagulability. The prevalence of symptomatic VTE was investigated retrospectively in 58 consecutive CS patients in relation to acquired and genetic thrombotic risk factors. Eight CS patients (14 %) developed VTE (group A), 3 of them related and 5 unrelated to surgery. These patients had higher urinary free cortisol (p = 0.01) and VWF levels (p = 0.02) than the 50 patients without VTE (group B), as well an increase in the hemostatically more efficient, high-molecular-weight VWF multimers (p = 0.002). Factor V Leiden and the prothrombin gene 20210A variants (the most common inherited thrombophilic defects) were more represented in group A than in group B, as was the genotype GCAG/GCAG of the VWF gene promoter, known to hyperinduce VWF upregulation under cortisol excess. All but one of the patients with VTE unrelated to surgery had at least four acquired and at least one inherited risk factor. Severe hypercortisolism and VWF levels with increased haemostatic activity are strongly associated with VTE in CS. VTE episodes unrelated to surgery are attributable to the synergistic action of acquired and inherited thrombotic risk factors. Based on these observations, we believe that severely affected CS patients should be screened for coagulation disorders and receive antithrombotic prophylaxis whenever they have concomitant prothrombotic risk factors.

A framework for the optimal design of a minimum set of clinical trials to characterize von Willebrand disease.

BACKGROUND AND OBJECTIVE: Von Willebrand disease (VWD) is one of the most severe inherited bleeding disorder in humans, and it is associated with a qualitative and/or quantitative deficiency of von Willebrand factor, a multimeric glycoprotein fundamental in the coagulation process. At present, the diagnosis of VWD is extremely challenging and mostly based on clinical experience. Kinetic models have been recently proposed and applied to help in the diagnosis and characterization of VWD, but the complexity of these models is such that they requires long and stressful clinical tests, such as the desmopressin response test (DDAVP), to achieve a satisfactory estimation of the individual haemostatic parameters. The goal of this paper is to design a minimal set of clinical tests for the identification of akinetic model to decrease the required time and effort for the characterization and diagnosis of VWD. METHODS: A model proposed in the literature is used as a building block to develop a new model, where response surface methodologies have been applied to determine a set of explicit correlations linkingkinetic model parameters to basal clinical trials data. Model-based design of experiments techniques are then used to devise optimally informative tests for model validation which are shorter and easier to implement. RESULTS: Results show an excellent agreement between the original model for VWD and the new proposed model on representing healthy and VWD subjects. The application of experimental design techniques for model validation shows the possibility to drastically reduce the duration of DDAVP tests from 24 h-3 h by exploiting complementary information from basal clinical tests. CONCLUSIONS: Basal clinical tests can be used alongside a time-reduced DDAVP test to validate pharmacokinetic models for a quantitative characterisation of subjects affected by VWD and for a quicker and easier diagnosis of the disease.

Von Willebrand factor propeptide makes it easy to identify the shorter Von Willebrand factor survival in patients with type 1 and type Vicenza von Willebrand disease.

Reduced von Willebrand factor (VWF) half-life has been suggested as a new pathogenic mechanism in von Willebrand disease (VWD). The usefulness of VWF propeptide (VWFpp) in exploring VWF half-life was assessed in 22 type 1 and 14 type Vicenza VWD patients, and in 30 normal subjects, by comparing the findings on post-Desmopressin (DDAVP) VWF t(1/2) elimination (t(1/2el)). The VWFpp/VWF antigen ratio (VWFpp ratio) was dramatically increased in type Vicenza VWD (13.02 +/- 0.49) when compared to normal subjects (1.45 +/- 0.06), whereas it appeared to be normal in all type 1 VWD patients (1.56 +/- 0.7), except for the four carrying the C1130F mutation (4.69 +/- 0.67). A very short VWF t(1/2el) was found in type Vicenza VWD (1.3 +/- 0.2 h), while all type 1 VWD patients had a t(1/2el) similar to that of the controls (11.6 +/- 1.4 and 15.4 +/- 2.5 h respectively), except for the four patients carrying the C1130F mutation, who had a significantly shorter VWF survival (4.1 +/- 0.2 h). A significant inverse correlation emerged between VWFpp ratio and VWF t(1/2el) in both VWD patients and normal subjects. The VWFpp ratio thus seemed very useful for distinguishing between type 1 VWD cases with a normal and a reduced VWF survival, as well as for identifying type Vicenza VWD.

Distinct abnormalities in the interaction of purified types IIA and IIB von Willebrand factor with the two platelet binding sites, glycoprotein complexes Ib-IX and IIb-IIIa.

We have studied the interaction of the congenitally abnormal type IIA and IIB von Willebrand factor (vWF) molecules, both lacking the larger multimeric forms, with the two vWF binding sites on platelets, the glycoprotein (GP) Ib-IX and GP IIb-IIIa complexes. Variant as well as normal (N) vWF were purified from plasma. Estimates for binding of subunit molecules per platelet at saturation (Bmax) and dissociation constant in moles/liter (Kd), respectively, were obtained from binding isotherms of 125I-labeled vWF, with the following results. In the presence of ristocetin (binding to GP Ib-IX): N, 25,693 and 0.5 x 10(-8); IIA, both parameters not measurable; IIB, 17,708 and 0.87 x 10(-8). After thrombin stimulation (binding to GP IIb-IIIa): N, 17,059 and 1.12 x 10(-8); IIA, 23,751 and 4.87 x 10(-8); IIB, 19,890 and 2.52 x 10(-8). Distinct experiments based on measuring the ability of the variant species (from the same patients and one additional IIB patient) to inhibit the binding of normal 125I-vWF to platelets gave results in agreement with those reported above. Other studies showed that only IIB vWF bound to platelets in the absence of any mediating substance (Kd = 5.21 x 10(-8) mol/liter and Bmax = 9,599 subunits per platelet) and induced aggregation at a concentration of 10 micrograms/ml (3.6 x 10(-8) M). Thus, IIB vWF binds to GP Ib-IX with high affinity and induces platelet aggregation, whether with or without ristocetin, in spite of the absence of larger multimers. In contrast, the binding of IIA vWF to GP Ib-IX occurs with very decreased affinity, and this defective function may result from specific structural abnormalities rather than just being a reflection of the absence of larger multimeric forms. Both IIA and IIB vWF exhibit decreased affinity for GP IIb-IIIa. In this case, the extent of the defect correlates with the absence of larger multimers.

Identifying carriers of type 2N von Willebrand disease: procedures and significance.

The defective FVIII carrier function of von Willebrand factor (VWF) identifies type 2N von Willebrand disease (VWD), a variant with a pattern resembling hemophilia A. Type 2N characterization is based on the evaluation of the capacity of VWF to bind exogenous FVIII (VWF:FVIIIB). Here we report on a retrospective evaluation of hemostatic laboratory parameters most useful in detecting type 2N carriers. The diagnostic capacity of aPTT, FVIII, VWF:Ag, FVIII/VWF:Ag ratio, VWF:FVIIIB and VWF:FVIIIB/VWF:Ag ratio was evaluated in 21 type 2N VWD carriers. Twenty subjects were heterozygous for the R854Q mutation, one was heterozygous for the R760C missense mutation, which interferes with cleavage of the VWF propeptide. We found that prolongation of aPTT and decrease in FVIII and FVIII/VWF:Ag ratio were not frequent findings in type 2N carriers. The same was true for VWF:FVIIIB which was not always abnormal. On the contrary, VWF:FVIIIB/VWF:Ag ratio was always defective and its values were not related with FVIII and FVIII/VWF:Ag ratio or influenced by plasma VWF concentration. Given these results, we attribute the greatest significance to VWF:FVIIIB/VWF:Ag ratio in the diagnosis of type 2N defects, and only search for type 2N mutations, to validate the diagnosis, if the ratio proves abnormal.

Diagnosis and follow-up of thrombotic thrombocytopenic purpura by means of von Willebrand factor collagen binding assay.

Thrombotic thrombocytopenic purpura (TTP) is characterized by intravascular thrombosis leading to consumption of large or unusually large von Willebrand factor (VWF) multimers. The usefulness of VWF collagen binding (VWF:CB) assay was assessed in detecting the decrease/absence of large VWF multimers or the presence of abnormally large forms in patients with TTP. Nine patients with TTP were studied during the acute phase of the disorder and the absence of large VWF multimers was demonstrated by means of the VWF:CB assay. These findings were confirmed by VWF multimer pattern analysis; VWF:CB deficiency appeared to correlate with abnormalities in large VWF multimers. The diagnostic potency of VWF:CB was especially evident when the values were expressed as VWF:CB/VWF:Ag ratio. VWF:CB was also used during the follow-up of the disorder to document improvement or restoration of large VWF multimers. VWF:CB was able to detect the absence or decrease of large VWF multimers better than VWF ristocetin cofactor (VWF:RCo); in fact, VWF:CB was defective when large VWF multimers persisted to be decreased, in contrast with what observed with VWF:RCo. In conclusion, VWF:CB is a simple test that appears to be useful, together with clinical symptoms and reduced platelet count, for the diagnosis and follow-up of TTP.

Severe, recessive type 1 is a discrete form of von Willebrand disease: the lesson learned from the c.1534-3C>A von Willebrand factor mutation.

Type 1 von Willebrand disease (VWD) is transmitted mainly as a dominant trait - especially in forms involving von Willebrand factor (VWF) levels below 20 U/dL - and less frequently as a recessive trait. In the latter case, mutations at heterozygous level may be associated with type 3 carrier status, while mutations at homozygous or compound heterozygous level often coincide with type 3 VWD. Here we present a recessive, severe type 1 form as a distinct type of VWD. Eight patients with severe type 1 VWD belonging to 7 unrelated families were studied. They had VWF levels below 10 U/dL, FVIII higher than 10 U/dL, and a significantly lower than normal platelet VWF content. All patients were homozygous or compound heterozygous for the c.1534-3C>A VWF mutation, that simultaneously induces the skipping of exon 14, the activation of a cryptic splice site, and a normal VWF gene transcription. This means that one of the three different mRNA generated assures the synthesis of normal VWF. The probands' relatives who were heterozygous for the c.1534-3C>A mutation always had low platelet VWF levels, sometimes with circulating VWF levels within normal range. This finding confirms the utility of measuring platelet VWF content to identify an abnormal VWF synthesis. Because the c.1534-3C>A mutation impairs, but does not abolish normal mRNA processing, it may never cause type 3 VWD. We propose a model of severe recessive type 1 VWF defect associated with mutations that sporadically go undetected by the cells' molecular machinery, as the c.1534-3C>A VWF mutation. BULLET POINTS: What is known about this topic? - Type 1 VWD is transmitted mainly as a dominant trait. - Recessive type 1 mutations at homozygous or compound heterozygous level are often associated with type 3 VWD, and at heterozygous level with type 3 VWD carrier status. What does this paper add? - There are quantitative VWF mutations, such as c.1534-3C>A, that impair, but do not abolish normal mRNA processing. - The c.1534-3C>A VWF mutation simultaneously induces the skipping of exon 14, the activation of a cryptic splice site, and a normal VWF gene transcription. - The c.1534-3C>A mutation is the archetype of mutations that cause severe recessive type 1 VWD, but never type 3 VWD. - Recessive, severe type 1 appears to be a distinct form of VWD.

Impairment of fibrinolytic potential in long-term steroid treatment after heart transplantation.

Thrombotic complications constitute an important risk in transplant recipients, in whom a hypercoagulable state and hypofibrinolysis have been associated with immunosuppressive treatment, especially with cyclosporine. In no case have clotting and fibrinolytic abnormalities been correlated with steroid immunosuppression, even though steroids were always administered. Previous studies found a relationship between hypercorticism and hypofibrinolysis both in Cushing's disease and after renal transplantation. The aim of this investigation was to compare fibrinolytic potential using the venous occlusion test in two similar groups of heart transplant patients treated with or without steroids. Euglobulin lysis time, tissue-type plasminogen activator and plasminogen activator inhibitor-1 (PAI-1) activities, and antigens were determined before and after the venous occlusion test. A reduced fibrinolytic potential (significant prolongation of lysis time) due to a significant increase in PAI-1 activity and antigen levels was found in heart transplant patients treated with steroids, as compared with patients without steroid treatment and control subjects. The prevalence of reduced fibrinolytic potential was 69.2% (18 cases) in the steroid-treated group and 34.8% (8 cases) in the non-steroid-treated group. In every case, the impaired fibrinolytic potential was due to high basal PAI-1 levels. Our results are compatible with the presence of a hypofibrinolytic state secondary to long-term steroid treatment. In heart transplant recipients, steroid-induced hypofibrinolysis may constitute a further risk factor for thrombotic disease.

Platelet aggregation induced by plasma from type IIB von Willebrand's disease patients is associated with an increase in cytosolic Ca2+ concentration.

The effect of type IIB von Willebrand's factor (vWF) on platelet cytosolic Ca2+ ion concentration, measured by means of the probe fura 2, was investigated. Seven patients with type IIB von Willebrand disease (vWD) were studied. Addition of type IIB vWD plasma to platelet suspensions induced a cytosolic calcium increase accompanied by platelet aggregation. Both processes were completely abolished by addition of the calcium-chelating agent EGTA, indomethacin, peptide RGDS, and monoclonal antibodies blocking the vWF binding site on GPIb-IX (LJIB1) or the cytoadhesive receptor on GPIIb-IIIa (LJCP8). The ADP-scavenger apyrase and the protein kinase C-inhibitor staurosporine partially inhibited the rate of the cytosolic calcium increase. No direct correlation between the extent of Ca2+ rise and the phenotypic expression of IIB vWD, such as the degree of spontaneous platelet aggregation or thrombocytopenia was apparent. It is suggested that aggregation and cytosolic Ca2+ increase in platelets exposed to plasma from type IIB vWD patients is mediated by a self-potentiating mechanism involving both GPIb and GPIIb-IIIa receptors as well as the thromboxane biosynthetic pathway.

1-Desamino-8-D-arginine vasopressin (DDAVP) infusion in type IIB von Willebrand's disease: shortening of bleeding time and induction of a variable pseudothrombocytopenia.

We have investigated the effects of 1-desamino-8-D-arginine vasopressin (DDAVP) infusion on platelet count and bleeding time in 4 patients with type IIB von Willebrand's disease (vWd). Three of four patients showed a normalization of the bleeding time within 1 h after the infusion, while bleeding time was not modified in the fourth. In accordance with the literature, thrombocytopenia was observed after DDAVP infusion, but this thrombocytopenia was due to the anticoagulants used for blood collection. In two patients (F.I., G.F.) no thrombocytopenia was observed when platelets were counted by fingerstick method but there was a 20% platelet decrease in blood samples collected in sodium citrate and a 50% decrease in samples collected in EDTA. Dramatic falls in platelet counts (70-95%) were observed in the additional two patients (C.A., D.Z.) after DDAVP infusion, when both sodium citrate or EDTA were used as anticoagulants. In the latter two patients there was also a 50% decrease in platelet count when the fingerstick method was used. The decrease in the patient's platelet count in EDTA samples after DDAVP infusion could be prevented, in part, by the previous additions of an anti GPIb monoclonal antibody and an anti GPIIb-IIIa monoclonal antibody. Thus, the thrombocytopenia observed in the four IIB vWd patients studied after DDAVP infusion seems to be, at least partially, a pseudothrombocytopenia depending on the calcium concentration in the blood samples and the availability of GPIb and GPIIb-IIIa receptors. These findings and the normalization of the bleeding time observed in three of the four patients has led us to reconsider the possible use of DDAVP in the treatment of our IIB vwd patients.

Inhibitory effect of prostacyclin and nitroprusside on type IIB von Willebrand factor-promoted platelet activation.

Von Willebrand disease (vWD) of type IIB is a hereditary haemorrhagic disorder characterised by an excessive interaction of von Willebrand factor (vWF) with the platelet receptor GPIb which promotes platelet activation and aggregation through a phospholipase A2-mediated release of arachidonic acid. The present report shows that prostacyclin and nitroprusside, vasodilator-compounds that enhance the cAMP and cGMP concentration respectively, cause a drastic inhibition of the type IIB vWF-induced platelet responses including increase of cytosolic Ca2+ concentration, phosphorylation of pleckstrin (47 kDa) and myosin light chain (20 kDa), secretion of ATP and serotonin, and aggregation parallel to a decrease of arachidonic acid release. Type IIB vWF also elicits tyrosine phosphorylation of proteins with apparent molecular mass of 60, 74, 82 and 130 kDa. Prostacyclin, which induces per se tyrosine-phosphorylation of proteins of about 38 and 45 kDa, inhibits drastically the type IIB vWF-promoted tyrosine-phosphorylation of the 74 kDa protein while inhibits slightly that of 60 kDa band. The protein tyrosine-kinase inhibitor genistein causes a little decrease in the type IIB vWF-induced release of arachidonic acid. It is concluded that the inhibition exerted by prostacyclin and nitroprusside on type IIB vWF-elicited platelet activation seems to be largely ascribable to prevention of the phospholipase A2 activation with the ensuing decrease of the subsequent protein tyrosine phosphorylation.

Post-DDAVP thrombocytopenia in type 2B von Willebrand disease is not associated with platelet consumption: failure to demonstrate glycocalicin increase or platelet activation.

Thrombocytopenia is frequently reported in type 2B von Willebrand disease (vWD), and thought to be related to the abnormally high affinity of 2B von Willebrand factor (vWF) for platelet GPIb-IX. To gain an insight into the nature of this thrombocytopenia, we measured plasma glycocalicin (GC) levels (as a marker of platelet turnover), and platelet surface expression of the alpha granule protein P-selectin (as a marker of platelet activation) in 9 patients with type 2B vWD before, and in 4 patients also following the infusion of 1-desamino-8-d-arginine vasopressin (DDAVP). Three patients presented a persistent decrease of platelet counts in the resting condition. GC levels were within the normal range, regardless of the platelet counts, in all but one patient who presented, on the other hand, a normal platelet count. Moreover, platelets expressed normal amounts of P-selectin on their surface, regardless of platelet counts. These findings suggest that the thrombocytopenia observed in type 2B vWD is not due to platelet activation and subsequent consumption in circulation. Despite a significant, albeit transient, decrease in platelet count, DDAVP did not induce an increase in plasma GC levels, nor enhance P-selectin expression. These observations indicate that the acute post-DDAVP thrombocytopenia in type 2B vWD is not related to platelet activation and consumption. We advance that the post-DDAVP 2B vWF is hemostatically more active, and able to induce agglutination but not aggregation of circulating platelets. This would explain both the prompt recovery of basal platelet counts after the post-DDAVP decrease, and the lack of reported thrombotic complications in this disorder. Therefore, even though 2B vWF is characterized by an enhanced affinity for the platelet surface, its binding to platelet GPIb-IX in the soluble phase is not able to induce true platelet aggregation: vWF thus appears to be mainly an adhesive protein, rather than an aggregating agent.

The evaluation of factor VIII antigen by means of a simple slide test.

Factor VIII von Willebrand may be detected by a Ristocetin-dependent platelet agglutination reaction. The authors have measured plasma levels of Factor VIII-related Ristocetin cofactor (VIIIR:RCoF) using formalin-fixed platelets tested by an aggregometric method or by a new, commercially available glass slide test. Plasmas were obtained from patients with von Willebrand's disease and Cushing's syndrome, and from normal controls. Von Willebrand factor (vWf) levels varied between 0-500% of the normal. A good correlation (r = 0.95) was found comparing the results obtained by the two methods over the entire range. If all patients were considered, a satisfactory correlation was obtained between VIIIR:RCoF and VIII-related antigen (VIIIR:Ag), both by the aggregometric method (r = 0.79) and by the glass slide method (r = 0.88). On the contrary, if values below 25% of the normal are taken into account, only a mild correlation was found between VIIIR: RCoF (aggregometric method) and VIIIR:Ag and no correlation between VIIIR:RCoF (glass slide method) and VIIIR:Ag. No correlation, regardless of the method used, was found between VIIIR:RCoF and VIIIR:Ag for values above 120%.

The evaluation of factor VIII binding activity of von Willebrand factor by means of an ELISA method: significance and practical implications.

One of the functions of von Willebrand factor (vWF) is to serve as a carrier of clotting factor VIII (FVIII). Deficiency of this function results in the von Willebrand disease (vWD) variant type 2N, which resembles hemophilia A. We describe a new sandwich enzyme-linked immunosorbent assay (ELISA) to study the ability of vWF to bind exogenous recombinant FVIII (rFVIII), in which anti-vWF-coated plates are incubated with plasma vWF, followed by exogenous FVIII and a peroxidase-coupled anti-FVIII antibody. Dose-response curves obtained using normal plasma vWF and purified normal vWF revealed a hyperbolic relationship between the optical density and the vWF concentration. The assay allows the quantification of FVIII binding with values expressed in U/dL; 100 U/dL was the amount present in normal plasma. The sensitivity and specificity of the method are demonstrated by its ability to measure binding levels as low as 1 to 2 U/dL and the fact that no FVIII binding was observed using plasma known to contain less than 1 U/dL vWF. To verify the accuracy of the assay, three patients with type 2N vWD with characterized vWF gene mutations were studied using an existing chromogenic assay and our ELISA. A patient who was homozygous for the R53W mutation and had no FVIII binding capacity according to the chromogenic method showed undetectable FVIII binding by ELISA. The remaining two patients, one who was homozygous for the R91Q mutation and one with compound heterozygosity for the R91Q and R53W mutations, showed markedly decreased FVIII binding by the chromogenic method and yielded ELISA values ranging from 4 to 8 U/dL. Therefore, although the two methods produce qualitatively similar results, the ELISA method offers the advantage of allowing quantification of the FVIII binding function. FVIII binding was also analyzed in 20 patients with type 1 vWD; we found a decrease of FVIII binding that was proportionate to the decrease in vWF levels, showing a normal FVIII binding activity/vWF molecule ratio. We define the binding activity measured by this assay as vWF:FVIII binding activity and propose its use in the functional analysis of vWF.

EDTA dependent pseudothrombocytopenia caused by antibodies against the cytoadhesive receptor of platelet gpIIB-IIIA.

AIMS: To clarify the mechanisms involved in the development of EDTA dependent pseudothrombocytopenia, particularly the platelet receptors. METHODS: Platelets were measured in 33 patients with pseudothrombocytopenia, using different anticoagulants to collect blood samples (direct test). The results were compared with the counts obtained by adding patients' serum or immunoglobulins to normal blood samples (indirect test). The role of platelet function was explored using ASA, PGE1, and apyrase as platelet inhibitors. The contribution of platelet receptor/s was investigated using antigens to gpIb-IX and gpIIb-IIIa monoclonal antibodies. Immunoglobulin class was estimated by the ability of IgG, IgA, and IgM antibodies to prevent platelet clumping. RESULTS: Agglutinating antibodies were IgA in 40%, IgG in 30%, and IgM in 10% of patients studied. Both patients' serum and immunoglobulins induced platelet clumping in normal samples anticoagulated with EDTA (indirect test). This was prevented by incubation of blood samples at 37 degrees C and almost completely inhibited by the platelet inhibitors ASA, PGE1, and apyrase. Pseudothrombocytopenia was also entirely prevented by an antigen to gpIIb-IIIa monoclonal antibody that recognises fibrinogen and the von Willebrand factor binding site. Pseudothrombocytopenia was almost completely abolished after the addition of RGD peptide, the recognition sequence of cytoadhesive proteins. CONCLUSIONS: These findings suggest that EDTA dependent pseudothrombocytopenia is caused by agglutinating antibodies that recognise cytoadhesive receptors on platelet gpIIb-IIIa and that an efficient platelet metabolism is required.

Adrenaline potentiates type 2B von Willebrand factor-induced activation of human platelets by enhancing both the formation and action of thromboxanes.

Von Willebrand factor (vWF) is a large plasma glycoprotein that mediates platelet adhesion at sites of vascular injury. We have previously reported that the pathological type 2B (formerly named type IIB) variant of vWF promotes platelet activation through phospholipase A(2)-mediated release of arachidonic acid. The present report shows that adrenaline (1 microM) potentiates type 2B vWF-induced platelet aggregation, serotonin secretion, rise in cytosolic Ca(2+) concentration, and pleckstrin phosphorylation, as well as thromboxane B(2) production. The hormone also increases the partially inhibited release of serotonin observed in platelets pretreated with the anti-GPIIb-IIIa antibody LJCP8 but does remove the total inhibition on the secretion caused by the anti-GPIb antibody LJIB1. Adrenaline also increases type 2B vWF-elicited tyrosine phosphorylation of proteins with apparent molecular masses of 60 and 80 kDa. Furthermore, adrenaline potentiates the rise in cytosolic Ca(2+) and the release of thromboxane B(2) in platelets stimulated with arachidonic acid (2 microM) as well as the increase in Ca(2+) induced by the thromboxane mimetic U46619 (0.3 microM). Platelet pretreatment with yohimbine or 13-azaprostanoic acid, which are antagonists of the alpha(2)-adrenergic and thromboxane receptors, respectively, or with acetylsalicylate and indomethacin, both of which act as inhibitors of thromboxane formation, abolishes the potentiating effect of adrenaline. These observations lead to the conclusion that the potentiating action of adrenaline on type 2B vWF-promoted platelet responses is due to an increase in both the formation and activating action of thromboxanes.

Urokinase-type plasminogen activator release after DDAVP in von Willebrand disease: different behaviour of plasminogen activators according to the synthesis of von Willebrand factor.

Nine healthy volunteers and 23 patients with various types of von Willebrand disease were studied before and after DDAVP infusion. We investigated the behaviour of factor VIII/von Willebrand factor measurements, and of tissue plasminogen activator and urokinase-type plasminogen activator. In mild von Willebrand disease the increase of both plasminogen activators was similar to that seen in normal controls. A different fibrinolytic behaviour was found in the type I platelet low and in the type III von Willebrand disease patients. An impaired and absent fibrinolytic response to DDAVP was seen in the former and in the latter von Willebrand disease, respectively. A close relation between either u-PA and t-PA or von Willebrand factor was observed. The possibility of a linkage among these three proteins was discussed.