Von Willebrand Factor Activity Research Articles

Sec22b determines Weibel-Palade body length by controlling anterograde ER-Golgi transport.

Von Willebrand factor (VWF) is a multimeric hemostatic protein that is synthesized in endothelial cells, where it is stored for secretion in elongated secretory organelles called Weibel-Palade bodies (WPB). The hemostatic activity of VWF is strongly related to the length of these bodies, but how endothelial cells control the dimensions of their WPB is unclear. In this study, using a targeted short hairpin RNA screen, we identified longin-SNARE Sec22b as a novel determinant of WPB size and VWF trafficking. We found that Sec22b depletion resulted in loss of the typically elongated WPB morphology together with disintegration of the Golgi and dilation of rough endoplasmic reticulum cisternae. This was accompanied by reduced proteolytic processing of VWF, accumulation of VWF in the dilated rough endoplasmic reticulum and reduced basal and stimulated VWF secretion. Our data demonstrate that the elongation of WPB, and thus adhesive activity of their cargo VWF, is determined by the rate of anterograde transport between endoplasmic reticulum and Golgi, which depends on Sec22b-containing SNARE complexes.

Comparative assessment of von Willebrand factor multimers vs activity for von Willebrand disease using modern contemporary methodologies.

Diagnosis of von Willebrand disease (VWD) is challenging due to heterogeneity of VWD and test limitations. Many von Willebrand factor (VWF) assays are utilized, including antigen (Ag), activity and multimer analysis. Activity assays include ristocetin cofactor using platelets (VWF:RCo) or other particles incorporating recombinant glycoprotein I ('VWF:GPIbR'), or other GPI binding assays using gain-of-function mutations ('VWF:GPIbM'), or collagen binding (VWF:CB). To comparatively evaluate modern contemporary VWF activity assays vs VWF multimer analysis using modern contemporary methods. Several VWF activity assays (VWF:RCo, VWF:GPIbR, VWF:GPIbM, VWF:CB) assessed (typically as a ratio against VWF:Ag) against a new semi-automated procedure for different types of VWD (1, 3, 2A, 2B, 2M), plus control material (n=580). The evaluation also focussed on relative loss of high and very high molecular weight multimers (HMWM and VHMWM) by densitometric scanning. All evaluated VWF activity/Ag ratios showed high correlation to the presence/absence of HMWM and VHMWM, although VWF:CB/Ag and VWF:GPIbR/Ag ratios using an automated chemiluminescence method yielded highest correlation coefficients (r=.909 and .874, respectively, for HMWM). Use of the investigative procedure (VHMWM) identified fewer false positives for 'loss' in type 1 VWD. This comparative investigation identified that new automated chemiluminescence VWF activity assays best identified relative loss or presence of HMWM and VHMWM according to activity to Ag ratios and an alternative investigative method for identifying VHMWM in multimer testing for a new commercial multimer method may lead to fewer false identifications of HMW loss in type 1 VWD.

Autonomic dysfunction syndrome in pregnant women.

Available studies and information on the regulatory effect of the autonomic nervous system (ANS) in pregnancy are insufficient and contradictory due to a variety of research methods of ANS, the lack of a single standardized approach to the assessment of the functional tone of the ANS departments, and interpretation of the results. The aim of the study is investigation and predictive assessment of clinical and laboratory data in pregnant women with suprasegmental autonomic dysfunction with or without hypertension to determine the main directions of effective prevention of the nervous system damage. The material of the study included 206 pregnant women diagnosed with the syndrome of autonomic dysfunction in different variants. Age ranged from 17 to 47years. All pregnant women had the following laboratory tests: general clinical tests, biochemical blood tests, including prothrombin index, fibrinogen, von Willebrand factor activity. The clinical and laboratory data were analyzed in pregnant women with autonomic dysfunction with or without hypertension. According to the results, it was found that in all groups of pregnant women a sympathetic effect prevails. This study showed that in the group of normotensive pregnant women, the main symptom is venous dysfunction, which poses a risk of an adverse course of cerebrovascular disease.

Increased von Willebrand factor levels in polycythemia vera and phenotypic differences with essential thrombocythemia

BackgroundAcquired von Willebrand factor (VWF) deficiency was described in Philadelphia‐negative myeloproliferative neoplasms, especially in essential thrombocythemia (ET). VWF phenotype in contemporary patients with polycythemia vera (PV) remains less explored. ObjectivesTo characterize the VWF phenotype in PV and to compare VWF phenotype in PV with matched healthy subjects and ET patients. Patients/MethodsWe studied 48 PV patients, treated according to current recommendations (hematocrit ≤ 45%, on low‐dose aspirin prophylaxis); 48 healthy and 41 subjects with ET, all sex, age, and blood group matched. We measured VWF antigen, activity, multimeric pattern, ADAMTS‐13, and factor VIII (FVIII) antigen. ResultsIn patients with PV, VWF antigen and activity were significantly higher than in healthy subjects (antigen: 119[96‐137] vs 93[79‐107] IU/dL; activity: 114[95‐128] vs 90[79‐107] IU/dL, respectively, medians and interquartile, P < 0.01), with normal multimeric distribution. ADAMTS‐13 levels were similar between patients with PV and healthy subjects. FVIII levels were higher in PV than in healthy subjects (141[119‐169] versus 98[88‐123] IU/dL, respectively, P < 0.01). By multivariable analysis, JAK2‐p.V617F allelic burden, erythrocyte count, and male sex significantly predicted VWF antigen and activity levels. As compared to patients with ET, patients with PV showed similar VWF antigen levels but approximately 40% higher activity (79[49‐104] vs 112[93‐125] IU/dL, respectively, P < 0.01). ConclusionsPatients with PV show increased VWF and FVIII levels, predicted by JAK2‐p.V617F burden and erythrocyte count. At variance with ET, acquired VWF defect was not observed in PV. High VWF/FVIII levels may sustain the thrombotic diathesis of PV and may be investigated as biomarkers for risk stratification.

Low Response to Clopidogrel in Coronary Artery Disease.

In patients with coronary artery disease, cardiovascular mortality and other acute events showed a clear correlation with risk factors and biomarkers including platelet activation. Which was the incidence of low response to clopidogrel and its correlation with risk factors and biomarkers in coronary artery disease? Four hundred patients (pts) with coronary artery disease-stable angina (SA) and acute coronary syndrome-were divided into 8 groups of study, consistent with low response to clopidogrel and the type of coronary artery disease. Low response to clopidogrel-defined as adenosine diphosphate test-ADP-test of >46 U by multiple electrode platelet aggregometry was evaluated in correlation with cardiovascular risk factors and biomarkers of oxidative stress, endothelial dysfunction, hypercoagulability, high platelet reactivity. In coronary artery disease, low response to clopidogrel significantly correlated with older than 65 years, smoking, hypertension, diabetes mellitus, body mass index of >25, previous aspirin treatment (P < 0.05), high value of total and low-density lipoprotein cholesterol, low value of high-density lipoprotein cholesterol, low response to aspirin, high mean platelets volume and von Willebrand factor activity, low flow-mediated vasodilatation, total antioxidant status (P < 0.01) and only in patients with SA of male gender (P < 0.01). The incidence of other hypercoagulability biomarkers, such as reduced values of S protein, C protein, antithrombin III, and V Factor Leiden resistance to activated protein C, was very low and not correlated with low response to clopidogrel. In coronary artery disease, low response to clopidogrel significantly correlated with the most of old cardiovascular risk factors, with previous aspirin treatment, low response to aspirin, higher mean platelets volume, higher von Willebrand factor activity, lower flow-mediated vasodilatation, and lower total antioxidant status values and only in patients with SA of male gender.

Patients with aortic stenosis have von Willebrand factor abnormalities and increased proliferation of endothelial colony forming cells

BackgroundPatients with aortic stenosis (AS) can experience bleeding complications including gastrointestinal bleeding from angiodysplastic lesions due to acquired von Willebrand syndrome. Studies have pointed to a role for von Willebrand factor (VWF) in angiogenesis. ObjectiveThe objective of this study was to assess VWF defects in AS patients over time and the impact on angiogenesis using patient‐derived endothelial colony‐forming cells (ECFCs). Patients/MethodsPlasma sample collection and ECFC isolations were performed before valve replacement surgery, 3 to 5 days after, and 6 months after surgery. Plasma VWF antigen, activity, propeptide, collagen binding, multimers, factor VIII coagulant activity, and ADAMTS13 activity (a disintegrin‐like and metalloprotease with thrombospondin type 1 motifs 13) were determined. ECFCs were assessed for VWF and angiopoietin‐2 (Ang‐2) storage and secretion, cell proliferation, and tubule formation in Matrigel. Results and ConclusionsAortic stenosis patients exhibited quantitative and qualitative abnormalities of VWF including significantly increased VWF antigen, activity, and propeptide levels following surgery (P < .01). Increased high molecular weight VWF multimers were observed at all time points and in particular 3 to 5 days after surgery (mean = 14% ± 6%) relative to before (mean = 10% ± 4%), suggesting increased proteolysis by ADAMTS13 pre‐operatively in a shear‐dependent manner. ECFCs from patients with aortic stenosis were more proliferative than controls (P < .05) and had increased retention of Ang‐2 (P < .05) suggesting epigenetic modification of the cells. Overall, there are hemostatic changes in AS patients that are present before valve replacement surgery and these persist long after surgery has occurred. These findings have implications for the current clinical management of AS patients.

Evaluation of a fully automated von Willebrand factor assay panel for the diagnosis of von Willebrand disease.

von Willebrand disease (VWD) diagnosis starts with first level tests: factor VIII coagulant activity, VWF antigen (VWF:Ag) and platelet-dependent VWF activity (VWF:RCo, VWF:Ab, VWF:GPIbR or VWF:GPIbM). The VWF collagen binding (VWF:CB) assay measures the binding capacity of von Willebrand factor (VWF) to collagen. To assess, in previously diagnosed VWD patients, the performance of a fully automated chemiluminescent test panel including VWF:Ag, VWF:GPIbR and VWF:CB assays. The patients, historically evaluated using in-house VWF:Ag and VWF:CB assays and an automated latex enhanced immunoassay VWF:GPIbR method, were re-evaluated using the VWF test panel HemosIL AcuStar. The VWF:GPIbR/VWF:Ag and VWF:CB/VWF:Ag obtained by means of AcuStar showed an overall good concordance with the corresponding data obtained at the time of the historical diagnosis. When discrepancies occurred, these were generally due to the lower VWF:CB/VWF:Ag obtained with AcuStar as compared with that obtained with the historical methods and this affected particularly the diagnosis of VWD type 2M. Together, the AcuStar VWF:GPIbR/VWF:Ag and VWF:CB/VWF:Ag were able to distinguish type 1 from types 2A, 2B and 2M, whereas no distinction was possible between type 2A and 2B. The AcuStar panel offers a good performance in the differential diagnosis between VWD type 1 and 2A/2B patients. A high rate of coincidence with historical diagnosis was obtained for VWD types 3, 2A/2B and 1. Even though in some cases more tests (eg, RIPA/multimeric analysis) are needed to complete an accurate VWD classification, the AcuStar panel is considered a sensitive, rapid and reliable tool to diagnose VWD patients.

Discovery of Type 3 von Willebrand Disease in a Cohort of Patients with Suspected Hemophilia A in Côte d'Ivoire.

BackgroundType 3 von Willebrand disease (VWD) is the most severe form of VWD, characterized by a near-total absence of von Willebrand factor (vWF), leading to a massive deficiency in plasmatic factor VIII (FVIII). VWD may be confused with hemophilia A, sometimes leading to misdiagnosis. The purpose of this work was to finalize the biological diagnosis of patients with FVIII activity deficiency in Abidjan in order to guide the best type of management.MethodsWe conducted a cross-sectional descriptive study from June 2018 to April 2019. Forty-nine patients, all of whom had lower FVIII levels or had been referred for a bleeding disorder, were monitored in the clinical hematology service. The pro-coagulant activity of coagulation factors was performed in Abidjan. The assays for von Willebrand antigen and activity were performed at Nîmes University Hospital in France.ResultsThe mean age of patients was 13.8 years (1 – 65) and 86% were Ivorian. FVIII deficiency was discovered during a biological checkup, circumcision or post-traumatic bleeding, in 33%, 31% and 29% respectively. The FVIII deficiency of patients was classified as severe (89.8%), moderate (8.2%) and mild (2%). Only one patient had a quantitative deficiency of von Willebrand factor (vWF: Ag <3%) with undetectable von Willebrand factor activity (vWF: Ac) and an FVIII level <1%.ConclusionsNot all of the congenital deficiency of FVIII are represented by hemophilia A. It was crucial to assess the Willebrand factor of these patients followed in Côte d’Ivoire for whom hemophilia A had been suspected.

Significant decrease of von Willebrand factor and plasminogen activator inhibitor-1 by providing supplementation with selenium and coenzyme Q10 to an elderly population with a low selenium status

PurposeEndothelial dysfunction and inflammation are conditions which fuel atherosclerosis and ischaemic heart disease. We have previously reported reduced cardiovascular (CV) mortality following supplementation with selenium and coenzyme Q10 to 443 elderly individuals with low selenium status (mean 67 μg/L) for 4 years. Here, we wanted to evaluate a possible association between the supplementation and the plasma concentrations of the von Willebrand factor (vWf), and the plasminogen activator inhibitor-1 (PAI-1), as they, besides other functions, are also strongly associated with endothelial function.MethodsIn this sub-study, 308 individuals (active substance: 157, placebo: 151) were included. Blood samples were drawn after 6 and 36 months and vWf and PAI-1 were determined in plasma by ELISA. Changes in concentrations of the biomarkers were evaluated by the use of T tests, repeated measures of variance, and ANCOVA analyses.ResultsThe active treatment group presented a lower level of vWf after 36 months compared with the placebo group (1.08 U/mL vs. 5.10 U/mL; p = 0.0007). The results were validated through the repeated measures of variance evaluation. The PAI-1 levels showed an equally significant decrease in the active group (26.2 ng/mL vs. 49.2 ng/mL; p = 0.0002) and were also validated through repeated measures of variance evaluation.ConclusionIn this sub-study on elderly receiving selenium and coenzyme Q10, or placebo we found significantly lower levels of vWf and PAI-1 in the active treatment group as compared to the placebo group. We interpret this as a better endothelial function because of the intervention, which accords with a previous finding of reduced CV mortality.

ADAMTS-13 and Von Willebrand Factor Levels and Activities in Children With Cirrhosis and/or Portal Hypertension

ADAMTS-13 and Von Willebrand Factor Levels and Activities in Children With Cirrhosis and/or Portal Hypertension

Efficacy of fibrinogen concentrate in major abdominal surgery – A prospective, randomized, controlled study in cytoreductive surgery for pseudomyxoma peritonei

BackgroundCytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy for pseudomyxoma peritonei (PMP) is associated with excessive bleeding and acquired fibrinogen deficiency. Maintaining plasma fibrinogen may support hemostasis. ObjectivesTo compare hemostatic efficacy and safety of human fibrinogen concentrate (HFC) vs cryoprecipitate as fibrinogen sources for bleeding patients with acquired fibrinogen deficiency undergoing PMP CRS. MethodsFORMA‐05 was an off‐label single‐center, prospective, randomized, controlled phase 2 study. Patients undergoing PMP surgery with predicted intraoperative blood loss ≥2 L received human fibrinogen concentrate (HFC; 4 g) or cryoprecipitate (two pools of 5 units, containing approximately 4.0‐4.6 g fibrinogen), repeated as needed. The primary endpoint was a composite of intraoperative and postoperative efficacy, graded using objective 4‐point scales and adjudicated by an independent committee. ResultsOne hundred percent of patients receiving HFC (95% confidence interval: 83.9‐100.0, n = 21) or cryoprecipitate (84.6‐100.0, n = 22) achieved hemostatic success. HFC demonstrated noninferior efficacy (P = .0095; post hoc) and arrived in the operating room 46 minutes faster. There were significantly greater mean increases with HFC vs cryoprecipitate in plasma fibrinogen (0.78 vs 0.35 g/L; P < .0001) and FIBTEM A20 (3.33 vs 0.93 mm; P = .003). Factor XIII, factor VIII, and von Willebrand factor activity were maintained throughout surgery. Only red blood cells were transfused intraoperatively (median units: HFC group, 1.0; cryoprecipitate group, 0.5). Thromboembolic events were detected with cryoprecipitate only. Safety was otherwise comparable between groups. ConclusionsHuman fibrinogen concentrate was hemostatically efficacious in patients undergoing major abdominal PMP surgery, with a favorable safety profile. These results are relevant to other surgical settings where bleeding and acquired fibrinogen deficiency occur.

Abstract WP97: The Aptamer BT200 Blocks Von Willebrand Factor and Platelet Function in Blood of Stroke Patients

Background: The effect of conventional anti-platelet agents is limited in secondary stroke prevention, and their effects are further blunted under conditions of high shear stress in the presence of increased levels of circulating VWF. VWF mediates platelet adhesion to collagen under high shear stress and is thereby critically involved in thrombus formation at sites of stenotic extracranial intracranial arteries (reviewed by Buchtele et al. 2018). We have created a novel anti-VWF aptamer (BT200) which could be useful for secondary stroke prevention, because the anti-VWF aptamer ARC1779 effectively reduced cerebral embolization after carotid endarterectomy (Markus et al. 2011). Aims: To characterize the effects of BT200 in blood of patients with large artery atherosclerosis stroke. Methods: Blood samples were obtained from 30 patients with acute stroke Inhibition of VWF activity by BT200 was quantified by REAADS ELISA and VWF ristocetin cofactor activity (VWF:RCo), platelet function under high shear rates with the PFA-100, and ristocetin-induced platelet aggregation in whole blood. Results: The majority of stroke patients had elevated VWF:RCo levels (mean: 198%; range 55-330%). Of 15 patients receiving clopidogrel with or without aspirin, only two had a prolonged collagen adenosine diphosphate closure time (CADP-CT) &gt;123s, and only one patient had a ristocetin induced aggregation of &lt;20U. BT200 concentration dependently inhibited VWF activity to &lt;3% and VWF dependent platelet function (p&lt;0.001): BT200 invariably prolonged CADP-CT to target levels of &gt;300s, and decreased aggregation to &lt;20U in blood samples from all patients. Conclusions: BT200 effectively inhibits VWF activity and VWF-dependent platelet function in blood from patients with acute stroke. Results from this study proved useful for planning of the ongoing phase I and planned phase II trial.

One piece of the puzzle: Population pharmacokinetics of FVIII during perioperative Haemate P®/Humate P® treatment in von Willebrand disease patients

IntroductionMany patients with von Willebrand disease (VWD) are treated on demand with von Willebrand factor and factor VIII (FVIII) containing concentrates present with VWF and/or FVIII plasma levels outside set target levels. This carries a risk for bleeding and potentially for thrombosis. Development of a population pharmacokinetic (PK) model based on FVIII levels is a first step to more accurate on‐demand perioperative dosing of this concentrate. MethodsPatients with VWD undergoing surgery in Academic Haemophilia Treatment Centers in the Netherlands between 2000 and 2018 treated with a FVIII/VWF plasma‐derived concentrate (Haemate® P/Humate P®) were included in this study. Population PK modeling was based on measured FVIII levels using nonlinear mixed‐effects modeling (NONMEM). ResultsThe population PK model was developed using 684 plasma FVIII measurements of 97 VWD patients undergoing 141 surgeries. Subsequently, the model was externally validated and reestimated with independent clinical data from 20 additional patients undergoing 31 surgeries and 208 plasma measurements of FVIII. The observed PK profiles were best described using a one‐compartment model. Typical values for volume of distribution and clearance were 3.28 L/70 kg and 0.037 L/h/70 kg. Increased VWF activity, decreased physical status according to American Society of Anesthesiologists (ASA) classification (ASA class >2), and increased duration of surgery were associated with decreased FVIII clearance. ConclusionThis population PK model derived from real world data adequately describes FVIII levels following perioperative administration of the FVIII/VWF plasma‐derived concentrate (Haemate® P/Humate P®) and will help to facilitate future dosing in VWD patients.

Clinical significance of slightly reduced von Willebrand factor activity.

Von Willebrand disease (VWD) is the most common congenital bleeding disorder, with a clinical presentation of mucocutaneous and surgical bleeding varying from mild to severe. It is inherited in an autosomal dominant or autosomal recessive manner. The disease is caused by quantitative or qualitative deficiency of the von Willebrand factor (VWF) and is classified as type 1, 2 (2A, 2B, 2M, 2N), and 3. Although type 1 VWD is the most common form of VWD, the f ormal cutoff for diagnosis remains a subject of debate. In our paper, we present results of studies regarding the clinical and laboratory importance of a new type of bleeding disorder called low VWF. The new guidelines for VWD diagnosis and management suggested that patients with historically type 1 VWD should be divided into 2 subsets: type 1 VWD with a VWF antigen level (VWF:Ag) of less than 30 IU/dl or less than 40 IU/dl, in which about 80% of patients exhibited VWF gene mutations, and low VWF with a VWF:Ag level of 30 to 50 IU/dl or 40 to 50 IU/dl, in which the causative mutation is detected in merely 40% of patients and in most families, inheritance is not dependent on the locus of VWF on chromosome 12. Previously, moderately reduced VWF levels (30-50 IU/dl) were considered a risk factor for bleeding, but not a true bleeding disorder, and this condition was named low VWF. Recently, it was documented in a large group of patients with type 1 VWD and low VWF that bleeding score does not correlate with VWF:Ag and bleeding symptoms in type 1 VWD (<30 IU/dl) and low VWF can change from infrequent and moderate to severe bleeds. Because the plasma concentration of VWF depends on many physiological and pathological factors that may mask the diagnosis of VWD, separation of the group of patients with low VWF (30-50 IU/dl) from those with type 1 VWD may delay or prevent them from receiving appropriate treatment. Diagnosis of VWD in each case, particularly those with a slight decrease in VWF (30-50 IU/dl), should be based primarily on the clinical manifestations and family history of hemorrhagic diathesis.

Low VWF levels in children and lack of association with bleeding in children undergoing tonsillectomy

Abstractvon Willebrand disease is a common bleeding disorder, but diagnosis can be difficult in young children who have not had bleeding challenges. We sought to evaluate the correlation between bleeding and von Willebrand factor (VWF) levels in children undergoing surgical challenge with tonsillectomy. Children ages 0 to 18 undergoing tonsillectomy without a personal or family history of bleeding were enrolled prospectively following informed consent and institutional review board approval. VWF levels were obtained at the time of surgery. VWF antigen (VWF:Ag) and VWF activity (VWF:GPIbM) were tested via enzyme-linked immunosorbent assay. Bleeding score was calculated using the International Society of Hematology bleeding assessment tool (BAT). Surgical and postoperative bleeding were determined using questionnaires filled out by the surgeon and patient/family. A total of 1399 subjects were enrolled with evaluable data, with a median age of 5 years. The median VWF:Ag was 85 IU/dL and the median VWF:GPIbM was 100 U/dL. Median BAT for the entire population was 0, including those with postoperative bleeding. There was no difference in VWF level between those who experienced postoperative bleeding and those who did not, with median VWF:Ag 85 vs 85 (P = .89) and mean VWF:GPIbM 98 vs 100 (P = .5). Interestingly, there was a difference in VWF levels with age, with median VWF:Ag 81 for those younger than 3 years, 82 for those 3 to 6 years, 90 for those 7 to 10 years, and 100 for those 11 to 18 years. A similar trend was noted for VWF:GPIbM. Of the 2 to 6 year olds, 5% had VWF:Ag <50, which would meet criteria for low VWF, but only 1.8% had an abnormal BAT at study entry and only 2.5% bled after surgery. Only 1 subject with low VWF had an elevated postoperative BAT >2. These data suggest that low VWF levels do not correlate with bleeding in children undergoing tonsillectomy. In addition, VWF levels outside the adult normal range in young children may be more common than previously thought and do not necessarily predict surgical bleeding.

Preservation of platelet function in patients with cirrhosis and thrombocytopenia undergoing esophageal variceal ligation

BackgroundThrombocytopenia is a possible risk factor for bleeding after band ligation of esophageal varices. However, elevated von Willebrand factor (VWF) in cirrhosis improves platelet function and could decrease this risk. Our objective was to assess platelet function in patients with cirrhosis undergoing esophageal variceal ligation (EVL). MethodsThe assessment consisted of platelet count, antigen and activity of VWF and VWF-cleaving protease ADAMTS-13 activity, and a platelet adhesion and aggregation test simulating vascular flow in vivo (Impact-RⓇ) prior to EVL. ResultsTotally 111 patients were divided into three groups according to platelet count: (1) < 50 × 109/L (n = 38, 34.2%); (2) 50 × 109/L to 100 × 109/L (n = 47, 42.3%); and (3) > 100 × 109/L (n = 26, 23.4%). No statistically significant difference was found in the aggregate size of platelets [group 1: 41.0 (31.8–67.3) µm2; group 2: 47.0 (33.8–71.3) µm2; and group 3: 47.0 (34.0–66.0) µm2; P = 0.60] and no significant correlation was found between aggregate size and platelet count (Spearman r = 0.07; P = 0.47). Surface coverage was 4.1% (2.8%–6.7%), 8.5% (4.0%–10.0%), and 9.0% (7.1%–12.0%) (P < 0.001) in groups 1, 2 and 3, respectively and correlated with platelet count (Spearman r = 0.39; P < 0.0001). There was no significant difference between groups in VWF or ADAMTS-13. Post-EVL bleeding occurred in six (5.4%) patients (n = 2 in group 1, n = 1 in group 2, and n = 3 in group 3; P = 0.32). Patients with bleeding had higher MELD scores [15.0 (11.3–20.3) versus 12.0 (10.0–15.0); P = 0.025], but no difference was demonstrated for platelet function parameters. ConclusionPlatelet function is preserved even in the presence of thrombocytopenia, including in the patients with post-EVL bleeding.

Reduced Activity of von Willebrand Factor after Flow-Diverting Stent Implantation for Intracranial Aneurysms: A Link to Acquired von Willebrand Disease?

Vascular devices generating high shear stress can cause type 2A acquired von Willebrand disease, which is characterized by low von Willebrand factor activity accompanied by hemorrhagic complications. The braided mesh structure of flow-diverting stents with a relatively small strut size can create abnormally high shear stress while arterial blood flows through the stent struts into the aneurysm, and flow-diverting stent may be associated with reduced von Willebrand factor activity. Aneurysmal morphologic parameters and patient data were examined retrospectively among patients who had an unruptured intracranial aneurysm treated with a flow-diverting stent. The RISTOtest (test for whole blood ristocetin-induced platelet aggregation) for von Willebrand factor activity, as well as tests for aspirin and clopidogrel/prasugrel effectiveness, were performed immediately before the endovascular procedure and 24 hours later by multiple electrode aggregometry. A total of 39 patients with 56 aneurysms were recruited, and statistical analyses were performed in 32 patents with 49 aneurysms. Compared with the baseline values, von Willebrand factor activity was reduced in 16 patients but increased in 23 patients. Aneurysmal variables (eg, neck area, volume, volume-to-neck area ratio, size ratio, and morphologic index) clearly distinguished patients with reduced von Willebrand factor activity from those with nonreduced von Willebrand factor activity. The receiver operating characteristic curve showed that the morphologic index and volume had the highest discriminative power, with an area under the curve of 0.99. In high-volume/large-neck aneurysms, flow-diverting stent implantation can cause reduced von Willebrand factor activity, which may be linked causally to acquired von Willebrand disease.

Активность фактора Виллебранда у крыс после кратковременной ишемии головного мозга

The von Willebrand factor (vWF) is a recognized marker of endothelial dysfunction associated with an imbalance in endothelial production of substances with procoagulant activity. vWF activity and hematocrit index in Wistar rats after 12 min occlusion of both carotid arteries with simultaneous controlled hypotension to 45±3 mm Hg, was investigated. Post-ischemic changes were evaluated in 5 groups of rats: 1 hour and 3, 7, 14 and 21 days after ischemia. An increase in the activity of vWF was manifested as early as 1 hour after ischemia. By the 3rd day of the post-ischemic time, the concentration of vWF in the blood plasma decreased as a result of hemodilution, as evidenced by hematocrit decrease. After 7 days there was a sharp increase in the activity of the marker. In the future, the activity of vWF decreased and by 21 days after ischemia, the values of the vWF activity reached values in control rats. It was established that cerebral ischemia led to the development of vascular endothelial dysfunction associated with an imbalance of endothelial production of substances with procoagulant activity, which persists for 14 days after ischemia.

Endothelial dysfunction contributes to COVID-19-associated vascular inflammation and coagulopathy

Great attention has been paid to endothelial dysfunction (ED) in coronavirus disease 2019 (COVID-19). There is growing evidence to suggest that the angiotensin converting enzyme 2 receptor (ACE2 receptor) is expressed on endothelial cells (ECs) in the lung, heart, kidney, and intestine, particularly in systemic vessels (small and large arteries, veins, venules, and capillaries). Upon viral infection of ECs by severe acute respiratory syndrome coronarvirus 2 (SARS-CoV-2), ECs become activated and dysfunctional. As a result of endothelial activation and ED, the levels of pro-inflammatory cytokines (interleukin -1, interleukin-6 (IL-6), and tumor necrosis factor-α), chemokines (monocyte chemoattractant protein-1), von Willebrand factor (vWF) antigen, vWF activity, and factor VIII are elevated. Higher levels of acute phase reactants (IL-6, C-reactive protein, and D-dimer) are also associated with SARS-CoV-2 infection. Therefore, it is reasonable to assume that ED contributes to COVID-19-associated vascular inflammation, particularly endotheliitis, in the lung, heart, and kidney, as well as COVID-19-associated coagulopathy, particularly pulmonary fibrinous microthrombi in the alveolar capillaries. Here we present an update on ED-relevant vasculopathy in COVID-19. Further research for ED in COVID-19 patients is warranted to understand therapeutic opportunities.

Elevated Plasma von Willebrand Factor Antigen and Activity Levels Are Associated With the Severity of Coronary Stenosis.

von Willebrand factor (VWF) acts as a bridge between platelets and the subendothelial matrix following vessel damage and plays a vital role in coronary artery disease (CAD). The aim of this study was to investigate the association between VWF and the severity of coronary stenosis quantified by the Gensini score in acute myocardial infarction (AMI), the most dangerous complication of CAD. Plasma VWF antigen (VWF: Ag) and VWF-collagen binding (VWF: CB) in normal controls (n = 123) and in patients with AMI (n = 205) were tested, and then the patients were divided based on Gensini scores. The levels of VWF: Ag and VWF: CB in patients with AMI were significantly higher than those in the control group (P < .001). Plasma levels of VWF: Ag and VWF: CB were positively correlated with both Gensini score and the number of affected vessels. Both VWF: Ag and VWF: CB were independent factors for coronary stenosis, adjusting confounding factors. Thus, the levels of VWF: Ag and VWF: CB were positively correlated with the severity of coronary stenosis. Screening of VWF at time of AMI may have prognostic value in terms of the severity of coronary stenosis.