Von Willebrand Factor Activity Levels Research Articles

Early Online.

Long-haul flights have been associated with a two- to four-fold increased risk of aviation-related thrombosis (ART). Several studies have investigated the extent to which hypoxic hypobaric exposure, dehydration and prolonged immobilisation during air travel induce changes in haemostasis. To investigate the role of high altitude as a risk factor for ART. Healthy volunteers aged ≥18 years (N=40), without risk factors for venous thromboembolism, were exposed to an exacerbated altitude of 18 000 feet (5 486 m) for 1 hour. During the flight, the oxygen (O2) levels of the participants, who received supplemental O2, were measured by pulse oximetry and maintained at >92%. Venous blood and urine samples were collected prior to departure and immediately after flying in an unpressurised twin-engine airplane. D-dimer levels, thromboelastography (TEG) parameters, von Willebrand factor (VWF) activity and urine osmolality were measured. The participants were 19 men and 21 women, with a mean (standard deviation) age of 46 (14) years. A significant difference in D-dimer levels, VWF activity, urine osmolality and TEG parameters (reaction (R) time, kinetic (K) time and maximum amplitude (MA)) before and after the 1-hour flight was observed (p<0.001). Urine osmolality correlated positively with VWF activity levels (r=0.469; p<0.002). Air travel at high altitude induced a hypercoagulable state in healthy volunteers. Future research should focus on whether thromboprophylaxis can significantly obviate the activation of coagulation in response to high altitude.

Efficacy of a 1:1 ratio VWF/FVIII concentrate in patients with von Willebrand disease.

Patients with von Willebrand disease (VWD) require administration of von Willebrand factor (VWF) concentrates peri-operatively. Concerns about FVIII accumulation after repetitive injections of a 1:1 ratio VWF/FVIII clotting factor concentrate (CFC) led this study to explore the recovery and FVIII accumulation over time. This monocentre study examined patients with VWD receiving perioperative 1:1 ratio CFC infusions. CFC dosing was based on body weight and endogenous VWF/FVIII activity. FVIII and VWF activity was monitored at T0 (baseline), T1 (15 min postinfusion), and trough levels at T2-T6 (24-120h). We included 125 patients, undergoing 125 procedures (63 major surgeries, 62 minor), with a median of two CFC infusions (IQR 1-3). With a mean administered dose of 35.7IU/kg CFC, recovery rates of FVIII and VWF were 2.6IU/dL per IU/kg and 2.4IU/dL per IU/kg, respectively. Mean FVIII levels at T0 were 62 (SD 51.9), T1: 164 (SD 80.4), T2: 155 (SD 62.8), T3: 162 (SD 59.8), T4: 124 (SD 78.4), and T5: 120 (SD 65.3) IU/dL. Mean VWF activity levels at T0 were 29 (SD 25.0), T1: 133 (SD 43.7), T2: 92 (SD 37.2), and T3: 86 (SD 37.5) IU/dL. Subgroup analysis in 47 patients with more than three infusions, showed no accumulation of mean FVIII levels. This perioperative study demonstrated excellent FVIII and VWF recovery of a 1:1 ratio VWF product in patients with VWD. Stable FVIII and VWF activity levels were observed after repeated infusions, without accumulation. Most major surgeries required only three CFC infusions.

A comparative study of anti–ADAMTS-13 antibody dynamics in immune-mediated thrombotic thrombocytopenic purpura

BackgroundThrombotic thrombocytopenic purpura, particularly its immune-mediated variant (iTTP), necessitates accurate diagnostic approaches for effective management. ObjectivesTo compare a chemiluminescence immunoassay (CLIA) and an enzyme-linked immunosorbent assay (ELISA) for testing ADAMTS-13 activity and detecting anti–ADAMTS-13 autoantibodies (AAbs) in patients with iTTP. MethodsThis study involved 31 paired samples from 12 iTTP patients. ADAMTS-13 activity was measured using the HemosIL AcuStar (IL, CLIA) and Technozym (Technoclone) activity assay (ELISA). The presence of AAbs was assessed using Technozym ADAMTS-13-INH assay (ELISA) and HemosIL AcuStar activity (CLIA) within a Bethesda assay following mixing with normal pool plasma. von Willebrand factor (VWF) multimers were analyzed using the HYDRASYS-2 SCAN system and the HYDRAGEL 5- or 11-VW Multimer kits (Sebia). VWF activity levels were measured with the HemosIL AcuStar VWF:GPIbR on the ACL AcuStar Analyzer (IL). ResultsFor ADAMTS-13 activity, a strong linear relationship and no bias between CLIA and ELISA were confirmed (slope = 1.01 [0.91, 1.11], intercept = 0.00 [−0.47, 0]). However, significant discrepancies were found in AAb detection during remission phases with ADAMTS-13 activity between 10% and 50%, with CLIA and ELISA showing significant divergence (P < .001, Cohen’s g = 0.34). Consistently, VWF multimers and activity levels exhibited significantly different values between remission samples with ADAMTS-13 activity below 50% and above 50%. In longitudinal analysis of patients with multiple iTTP relapses, positivity to CLIA appears to precede ELISA in predicting exacerbations. ConclusionWhile CLIA and ELISA might be interchangeable for assessing ADAMTS-13 activity, they are not equivalent for detecting AAbs, particularly in patients in clinical remission with ADAMTS-13 activity between 10% and 50%.

Nanobody activator improves sensitivity of the von Willebrand factor activity assay to multimer size

BackgroundThe activity of von Willebrand factor (VWF) in facilitating platelet adhesion and aggregation correlates with its multimer size. Traditional ristocetin-dependent functional assays lack sensitivity to multimer sizes. Recently, nanobodies targeting the autoinhibitory module and activating VWF were identified. ObjectivesTo develop an assay that can differentiate the platelet-binding activity of VWF multimers. MethodsA novel enzyme-linked immunosorbent assay (nanobody-triggered glycoprotein Ib binding assay [VWF:GPIbNab]) utilizing a VWF-activating nanobody was developed. Recombinant VWF, plasma-derived VWF (pdVWF), and selected gel-filtrated fractions of pdVWF were evaluated for VWF antigen and activity levels. A linear regression model was developed to estimate the specific activity of VWF multimers. ResultsOf the 3 activating nanobodies tested, 6C11 with the lowest activation effect exhibited the highest sensitivity for high-molecular-weight multimers (HMWMs) of VWF. VWF:GPIbNab utilizing 6C11 (VWF:GPIbNab6C11) produced significantly higher activity/antigen ratios for recombinant VWF (>2.0) and HMWM-enriched pdVWF fractions (>2.0) than for pdVWF (∼1.0) or fractions enriched with shorter multimers (<1.0). The differences were much larger than those produced by VWF:GPIbNab utilizing other nanobodies, VWF:GPIbM, VWF:GPIbR, or VWF:CB assays. Linear regression analysis of 5 pdVWF fractions of various multimer sizes produced an estimated specific activity of 2.7 for HMWMs. The analysis attributed >90% of the VWF activity measured by VWF:GPIbNab6C11 to that of HMWMs, which is significantly higher than all other activity assays tested. ConclusionThe VWF:GPIbNab6C11 assay exhibits higher sensitivity to HMWMs than ristocetin-based and collagen-binding assays. Future studies examining the application of this assay in clinical settings and any associated therapeutic benefit of doing so are warranted.

Monitoring of Hemostatic Status and Treatment Response in Von Willebrand Disease Using a Microchip Flow Chamber Assay

Introduction: Von Willebrand factor (VWF) carries out its hemostatic roles by interacting with both platelets and FVIII, and its appropriate active multimeric conformation is strongly affected by blood flow shear. Our aim was to assess the hemostatic status and the response to treatments in VW disease (VWD) using a flow chamber-based thrombus formation analysis system (T-TAS ®, Zacros) that allows evaluation of both primary and secondary hemostasis in a scenario closer to in vivo conditions. Methods: Blood samples from patients diagnosed with VWD type 1 (n=3), type 2A (n=2), type 2B (n=1) and type 3 (n=8, two of them with inhibitory antibodies) were collected before and after in vivo administration of the prescribed treatment with desmopressin (DDAVP ®) or plasma-derived (pd)VWF/FVIII concentrates (Table-1). The effect of ex vivo administration of 100, 150 and 300 IU/dL of pdVWF/FVIII (Fanhdi ®, Grifols) was also evaluated. Thrombus formation analysis was performed according to the manufacturer's standardized protocols: Blood samples collected in tubes containing BAPA (inhibitor of FXa and thrombin) were loaded onto type-1 collagen-coated platelet (PL)-chips to assess platelet-dependent thrombus formation. Citrated blood samples were recalcified in presence of CTI and loaded onto collagen/tissue factor-coated atherome (AR)-chips to assess thrombus formation mediated by both platelet and coagulation activation. An optimized flow rate is automatically adjusted for each chip. Area under the flow-pressure curve (AUC) values were collected. Platelet count, fibrinogen levels, prothrombin time (PT), activated partial thromboplastin time (aPTT), aPTT ratio, antigenic VWF (VWF:Ag), VWF activity by recombinant GPIb binding assay (VWF:GPIbR) and FVIII activity (FVIII:C) were also analyzed. Results: All VWD patient samples tested, including type-1 patients, showed a deficient platelet function (PL_AUC) and a reduced coagulation-dependent thrombus formation (AR_AUC) prior to treatment (Table-1). VWD type-1 responded to desmopressin with a high increase of FVIII activity (FVIII:C &amp;gt;200%) and normalization of VWF activity (VWF:GPIbR &amp;gt;100%) and AUC levels. Treatment with pdVWF/FVIII increased VWF:GPIbR levels (&amp;gt;60% after treatment) in all cases, but failed to completely normalize the AUC values, which showed a slight increase (Table-1). A high correlation (r&amp;gt;0.8) was observed between plasma levels of VWF or FVIII activity and AUC values obtained both before and after treatment Ex vivo administration of pdVWF/FVIIIa resulted in a concentration-dependent increased of PL_ and AR_AUC, with values within the normal range at the highest dose tested (300 IU/dL, equivalent to 150 IU/kg) in all cases, except for VWD type-3 samples with inhibitor and for VWD type-2B sample with PL-chip assay (Figure-1). Conclusions: Monitoring treatment efficacy in VWD using a flow chamber-based thrombus formation analysis system could be a reliable and standardized method to assess the response to desmopressin and pdVWF/FVIII concentrates in patients with VWD, allowing an optimal personalized therapeutic dosing and a better prevention of bleeding episodes in these patients. Funding: Grifols; Zacros; Fundación Rodríguez Pascual; Instituto de Salud Carlos III (ISCIII) (PI22/01461), co-funded by the European Union.

Clinical and Laboratory Presentation and Underlying Mechanism in Patients with Low VWF.

Low von Willebrand factor (VWF) refers to subjects with plasma levels of 30 to 50 IU/dL. The mechanism of low VWF is poorly understood. We chose to determine the clinical presentation, laboratory phenotype, and underlying mechanisms of low VWF. We included 250 patients characterized with low VWF. The International Society on Thrombosis and Haemostasis Bleeding Assessment Tool (ISTH-BAT) was used to assess clinical symptoms. To determine the underlying mechanisms of low VWF, we used as markers the VWF propeptide (VWFpp) assay and FVIII:C/VWF:Ag ratio for VWF synthesis and the VWFpp/VWF:Ag ratio for VWF clearance. Results were compared with those of 120 healthy controls. Cases with abnormal screening tests were further evaluated for coagulation factor levels and platelet disorders. The median age of the cohort was 35 years (range 3-85), 21% were children (n = 53), 34% were adult males (n = 85), and 45% (n = 112) were adult females. According to the ISTH-BAT, abnormal bleeding was found in 35% of children, 47% of males, and 49% of females. No association was found between VWF activity levels and ISTH-BAT. Patients showed an overall decreased VWF synthesis/secretion and an enhanced VWF clearance was identified in 33% of them. In 89 patients (36%), there were other hemostasis-related defects, but there was no difference in the ISTH-BAT between the two groups. Our findings indicate that reduced VWF synthesis/secretion and enhanced VWF clearance are major mechanisms of low VWF levels. Patients with low VWF have significant bleeding manifestations. While other hemostasis defects occurred together with low VWF, this combination did not exacerbate clinical symptoms.

Effect of Factor VIII and Von Willebrand Factor Activities on Number of Bleeding Events in Previously Treated Patients with Von Willebrand Disease on Regular Prophylaxis with a Plasma-Derived Von Willebrand Factor/Factor VIII Concentrate

Background: von Willebrand disease (VWD) is characterized by a deficiency or reduction of activity in von Willebrand factor (VWF). As VWF has a role in stabilizing coagulation factor VIII (FVIII), VWD patients often suffer from secondary FVIII deficiency. Current guidelines recommend that VWD patients with a history of severe and frequent bleeds should use long-term prophylaxis with factor replacement therapy. The WIL-31 study demonstrated the efficacy of prophylaxis with a plasma-derived VWF/factor VIII concentrate containing VWF and FVIII in a 1:1 activity ratio (pdVWF/FVIII; wilate ®) in adults and children with VWD. The primary endpoint was met, showing a decrease of 84% in the mean total annualized bleeding rate (ABR). As elevated levels of FVIII are associated with an increased risk for thrombosis, it is important to determine whether repeated dosing with pdVWF/FVIII leads to accumulation of FVIII over time. Aims: To investigate the activity levels of VWF and FVIII in patients with VWD receiving regular prophylaxis with pdVWF/FVIII. Methods: WIL-31 (NCT04052698) was a prospective, non-controlled, international, multicenter phase 3 trial that enrolled male/female patients, aged ≥6 years old with VWD type 1 (VWF:RCo &amp;lt;30 IU/dL), type 2 (except 2N) or type 3. Prior to entering the WIL-31 study, all patients had received on-demand treatment with a pdVWF/FVIII concentrate during a 6-month, prospective, observational, run-in study (WIL-29). Patients in WIL-31 received regular pdVWF/FVIII prophylaxis 2-3 times per week at a dose of 20-40 IU/kg for 12 months. VWF activity (VWF:RCo) and FVIII activity (measured by the chromogenic [Chr] and one-stage [OS] assays) were performed at baseline and throughout the study. Full pharmacokinetic (PK) analyses were performed in all patients aged 6-16 years, a single dose of 60 ± 10 IU/kg pdVWF/FVIII was administered. Samples were collected at up to 1 hour prior to injection and then at multiple time points post-injection (1-72 hours). Safety, including the occurrence of thrombotic events, was monitored throughout the study. Results: The overall study population included 33 patients, with a median age of 18 years consisting of 9 (27.3%) patients aged 6-11 years, 6 (18.2%) patients aged 12-16 years, and 18 (54.5%) patients aged ≥17 years. Six (18.2%) patients had severe type 1 VWD, 5 (15.2%) patients had type 2, and 22 (66.7%) patients had type 3. Baseline FVIII and VWF activities in WIL-31 were similar regardless of age group, and as expected were lower in patients with type 3 VWD compared with severe type 1 and type 2 (Figure 1). There was a negative correlation of baseline FVIII and VWF activity with the number of spontaneous bleeding episodes (BEs) during prophylaxis. Patients who had no spontaneous BEs during prophylaxis had higher baseline FVIII and VWF levels compared with those who had spontaneous BEs. Mean peak and trough FVIII and VWF activity levels remained consistent during the study and there was no accumulation of either factor over the 12-month prophylaxis period (Figure 2). Full PK assessments were performed according to protocol in 13 patients aged 6-16 years. The mean ± standard deviation in vivo half-life was 16.1±6.7, 16.2±7.7, and 9.8±7.7 hours, for FVIII Chr, FVIII OS, and VWF:RCo, respectively. No thrombotic events were observed. Conclusion: No accumulation of FVIII or VWF in the plasma was reported in 33 patients who received regular prophylaxis with pdVWF/FVIII for 12 months, regardless of VWD type and age.

Abacavir use is associated with increased prothrombin conversion.

There is ongoing debate as to whether abacavir (ABC) increases the risk for cardiovascular disease(CVD) in people living with HIV (PLHIV) and the mechanisms underlying this possible association. We recently showed that the use of an ABC-containing regimen was independently associated with increased thrombin generation (TG). In the present study, we aim to explore these findings further, by studying the mechanistical processes that underly the global thrombin generation test via thrombin dynamics analysis. Thrombin dynamics analysis can pinpoint the cause of increased thrombin generation associated with ABC-use either to the procoagulant prothrombin conversion pathway or the anticoagulant thrombin inactivation pathway. In this cross-sectional study, 208 virally suppressed PLHIV were included, of whom 94 were on a ABC-containing regimen, 92 on a tenofovir disoproxil fumarate (TDF)-containing regimen, and the remainder on other regimens. We used Calibrated Automated Thrombinography to measure thrombin generation and perform thrombin dynamics analysis. The total amount of prothrombin conversion, as well as the maximum rate of prothrombin conversion were significantly increased in PLHIV on an ABC containing regimen compared to other treatment regimens. The levels of pro- and anticoagulant factors were comparable, indicating that the ABC-induced changes affect the kinetics of prothrombin conversion rather than procoagulant factor levels. Moreover, Von Willebrand Factor (VWF), active VWF and VWF pro-peptide levels were significantly higher in PLHIV than controls without HIV. However, they did not differ between ABC and non-ABC treated participants.

Von Willebrand factor: from figurant to main character in the scene of inflammation

von Willebrand factor: from figurant to main character in the scene of inflammation

Analysis of thrombogenicity under flow reveals new insights into the prothrombotic state of patients with post-COVID syndrome

BackgroundPost-COVID syndrome (PCS) affects millions of people worldwide, causing a multitude of symptoms and impairing quality of life months or even years after acute COVID-19. A prothrombotic state has been suggested; however, underlying mechanisms remain to be elucidated. ObjectivesTo investigate thrombogenicity in PCS using a microfluidic assay, linking microthrombi, thrombin generation, and the von Willebrand factor (VWF):a Disintegrin and Metalloproteinase with a Thrombospondin Type 1 motif, member 13 (ADAMTS13) axis. MethodsCitrated blood was perfused through microfluidic channels coated with collagen or an antibody against the VWF A3 domain, and thrombogenicity was monitored in real time. Thrombin generation assays were performed and α(2)-antiplasmin, VWF, and ADAMTS13 activity levels were also measured. ResultsWe investigated thrombogenicity in a cohort of 21 patients with PCS with a median time following symptoms onset of 23 months using a dynamic microfluidic assay. Our data show a significant increase in platelet binding on both collagen and anti-VWF A3 in patients with PCS compared with that in controls, which positively correlated with VWF antigen (Ag) levels, the VWF(Ag):ADAMTS13 ratio (on anti-VWF A3), and inversely correlated with ADAMTS13 activity (on collagen). Thrombi forming on collagen presented different geometries in patients with PCS vs controls, with significantly increased thrombi area mainly attributable to thrombi length in the patient group. Thrombi length positively correlated with VWF(Ag):ADAMTS13 ratio and thrombin generation assay results, which were increased in 55.5% of patients. α(2)-Antiplasmin levels were normal in 89.5% of patients. ConclusionTogether, these data present a dynamic assay to investigate the prothrombotic state in PCS, which may help unravel the mechanisms involved and/or establish new therapeutic strategies for this condition.

Repeated Testing Unfolds the Challenge of Diagnosing Von Willebrand Disease: Longitudinal Data from the Vienna Bleeding Biobank

Background: Diagnosis of von Willebrand disease (VWD) in patients with a mild to moderate bleeding tendency (mild bleeding disorders, MBD) bears special challenges, as von Willebrand factor (VWF) levels are influenced by several factors, such as age, acute phase reaction and blood group, and might be unstable. Unstable VWF levels might lead to under- or over-diagnosis of VWD in MBD patients, and repeated measurements to identify VWD patients might be required. Aims: We aimed to identify clinical and epidemiological factors associated with unstable VWF levels, leading to change of the diagnosis based on the recommended diagnostic cut-off levels. Furthermore, we wanted to investigate cut-off of baseline VWF levels with a low probability to decrease below the diagnostic cut-off and, thus, not require subsequent VWF measurements. Methods: All patients enrolled into the Vienna bleeding biobank (VIBB, EC no. 603/2009) before October 2021 with at least two separate assessments of VWF levels, in particular VWF antigen (VWF:Ag) and activity (VWF:GPIbM and/or ristocetin-cofactor activity [VWF:RCo]), were included in this analysis. Detailed inclusion and exclusion criteria of the VIBB, a single-center cohort study on patients with MBD, have been published previously (Gebhart et al. Haemophilia.2018). For this analysis, pathological VWF levels were defined as any measurement of VWF:Ag, VWF:GPIbM or VWF:RCo ≤50 IU/dL, according to current guidelines (James et al. Blood Adv. 2021). We defined 3 subgroups of patients according to lowest VWF (VWF:Ag or VWF:GPIbM or VWF:RCo) at baseline and at each measurement: patients with steadily pathological measurements ≤50 IU/dL ("steady pathological"), patients with repeatedly normal measurements >50 IU/dL ("steady normal") and patients crossing the 50 IU/dL threshold between study visits ("changing"). Measurements were excluded from the analysis if an evident VWF influence such as pregnancy, infection, surgery or acute phase reaction was identified. Results: In total, 281 of 691 patients (40.7 %) from the VIBB study who had records of at least two VWF measurements of VWF antigen and activity levels were included in this analysis. Patients had a median number of 2 VWF measurements (Q1-Q3, 2-2) over a median follow-up time of 781 days (Q1-Q3, 105-1679) for a total of 660 measurements. 212 patients had 2 measurement of VWF antigen and activity, followed by 3 (n=47), 4 (n=11), 5 (n=5) and 6 (n=1) measurements. Of all analyzed patients, 217 patients (77.2 %) had VWF levels consistently above the cut-off of 50 IU/dL ( "steady normal"), 28 patients (10.0%) had repeatedly values ≤50 IU/dL ("steady pathological"), while 36 patients (12.8%) had changing results with values both below and above the cut-off of 50 IU/dL ( "changing"; Figure 1). The clinical and laboratory characteristics of each subgroup are summarized in Table 1. Patients in the "steady pathological” and "changing” groups compared to the "steady normal” group were younger and more commonly had blood group O. The values of VWF activity (VWF:RCo or VWF:GPIbM) at inclusion appeared to be more unstable than the VWF:Ag values (Figure 1). Seventeen (47.2%) patients in the changing group had pathological VWF activity values but VWF:Ag values above the cut-off of 50 IU/dL at study inclusion. VWF antigen and activity values at baseline within the changing group ranged from 36 IU/dL to 101 IU/dL and 28 IU/dL to 86 IU/dL, respectively. In a logistic regression model, modeling changing status as a binary outcome and lowest VWF at baseline using linear splines with a knot set at 50 IU/dL, the probability of changing was 37.2% (95%CI, 25.7-50.3), 18.6% (95%CI, 12.2-27.4) and 1.1% (95%CI, 0.2-4.8) at 40, 60 and 80 IU/dL, respectively (Figure 2). The added value of the clinical predictors age, sex, the Vicenza score and blood type O beyond lowest VWF at baseline, however, was only weak (χ2 5.0, p = 0.290). Conclusion: Based on our data, the reproducibility of VWF measurements is poor in patients with MBD. Re-evaluation of suspected patients for VWD who do not clearly fulfill the diagnostic criteria should be considered, especially if VWF levels are close to the cut-off level, as targeted treatment before surgical interventions might be warranted. Further studies are needed to better understand the reproducibility of VWF measurements and improve the diagnosis of VWD in patients with MBD. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Type 2M VWD Laboratory Defects More Consistent Than Bleeding Symptoms across Family Members

Background Von Willebrand disease (VWD) is an inherited bleeding disorder characterized by a defect or decrease of von Willebrand factor (VWF). Type 2 VWD results from qualitative defects in VWF. Type 2M VWD is defined by defective platelet binding to GPIb and/or collagen. While the inheritance of type 2M VWD is autosomal dominant, the extent of symptoms across family members has not been well characterized. Methods Subjects included index cases with type 2M VWD and all enrolled family members from a large US study of VWD (Zimmerman Program). Index cases were enrolled due to a prior diagnosis of VWD. All available family members were enrolled if willing. VWF testing performed included VWF antigen (VWF:Ag), VWF platelet binding by either VWF ristocetin cofactor activity (VWF:RCo) or VWF:GPIbM, collagen binding with types I, III or IV collagen (VWF:CB1, VWF:CB3, VWF:CB4) and VWF multimer distribution. Bleeding scores were calculated using the ISTH bleeding assessment tool (BAT). DNA sequencing was performed for the full length VWF gene. Statistics were calculated using GraphPad Prism with a p value of <0.05 considered significant. Family members were defined as affected if they had VWF activity levels consistent with type 2M VWD and presence of genetic variant if identified. Results 24 index cases, 51 affected family members and 40 unaffected family members were available for analysis. The mean VWF:RCo/VWF:Ag ratio for index cases was 0.5 and the mean VWF:CB/VWF:Ag ratio was 1.05. The VWF:RCo/VWF:Ag ratio was similar in affected family members (0.44, p=NS) but higher as expected in unaffected members (0.89, p<0.001 for index case vs. unaffected, p<0.001 for affected vs. unaffected). In contrast, there was no difference in VWF:CB/VWF:Ag ratios between index cases and affected family members (0.94, p=NS). Data for VWF:GPIbM, collagens I and IV were available only on index cases, and showed low VWF:GPIbM/VWF:Ag (mean 0.79), higher VWF:CBI/VWF:Ag (mean 1.31) and lower VWF:CBIV/VWF:Ag (mean 0.85). There was a negative correlation between VWF:GPIbM and VWF:CBIV, with subjects having either low VWF:GPIbM and normal VWF:CBIV or low VWF:CBIV and normal VWF:GPIbM. Similar results were seen for VWF:CB1 although only 1 subject was diagnosed with type 2M VWD and low VWF:CB1. Median bleeding scores were highest in index cases (7.5), intermediate in affected family members (3) and normal in unaffected family members (1). There was a significant difference between index cases and affected family members (<0.015), and between index cases and unaffected family members (p<0.001). One subject had a genetic variant in the VWF A3 domain, one in the VWF D3 domain and the remainder of index cases had a defect in the VWF A1 domain. Conclusions These findings suggest that decreases in platelet and collagen binding activity increase bleeding risk in families with type 2M VWD. Index cases had higher bleeding scores as compared to affected family members, suggesting that diagnosis of family members may require more attention. Precise understanding of these defects may assist in better diagnosis and treatment of von Willebrand disease.

Von Willebrand Disease-Specific Aspects in Women.

Von Willebrand disease (VWD) is the most common inherited bleeding disorder, which results from a deficiency or dysfunction of von Willebrand factor (VWF). The major symptoms of patients affected by VWD include mucocutaneous and gastrointestinal bleeding, easy bruising, and prolonged provoked bleeding due to injury or surgery. Although women and men are equally likely to be affected by VWD, women continue to be disproportionately affected by the bleeding challenges. Women with VWD suffer from sex-specific symptoms, such as menorrhagia, and are at higher risk of reproductive problems and recurrent miscarriage. Furthermore, pregnant women with VWD are more likely at higher risk of suffering from primary and secondary peripartal hemorrhage and anemia and the need for transfusions. Despite being affected by gynecologic and obstetrical bleeding, women face multiple barriers in obtaining an accurate diagnosis. This constitutes a problem that needs to be addressed, and early appropriate medical care should be ensured. There are several effective treatment options for women with VWD that can significantly improve their quality of life, including desmopressin, VWF concentrates, hormonal therapy, and antifibrinolytic therapy. During pregnancy, the monitoring of VWF activity levels is essential. The peripartal management depends on the type of VWD and on the measured levels of VWF levels and activity prior to delivery.

Von Willebrand factor activity levels are influenced by driver mutation status in polycythemia vera and essential thrombocythemia patients with well-controlled platelet counts.

von Willebrand factor ristocetin cofactor (vWF activity) and platelet count (PLT) are negatively correlated in patients with polycythemia vera (PV) and essential thrombocythemia (ET). However, vWF activity does not always normalize upon controlling PLT in those patients. To address this issue, we investigated the correlation between vWF activity and PLT in PV and ET patients. The negative correlation between vWF activity and PLT was stronger in calreticulin mutation-positive (CALR+) ET than in Janus kinase 2 mutation-positive (JAK2+) PV or ET groups. When PLT were maintained at a certain level (<600 × 109 /L), low vWF activity (<50%) was more frequently observed in JAK2+ PV patients than in JAK2+ ET (p=.013) or CALR+ ET (p=.013) groups, and in PV and ET patients with ≥50% JAK2+ allele burden than in those with allele burden <50% (p=.015). High vWF activity (>150%) was more frequent in the JAK2+ ET group than in the CALR+ ET group (p=.005), and often associated with vasomotor symptoms (p=.002). This study suggests that some patients with JAK2+ PV or ET have vWF activity outside the standard range even with well-controlled PLT, and that the measurement of vWF activity is useful for assessing the risk of thrombosis and hemorrhage.

Population-wide persistent hemostatic changes after vaccination with ChAdOx1-S.

Various vaccines were developed to reduce the spread of the Severe Acute Respiratory Syndrome Cov-2 (SARS-CoV-2) virus. Quickly after the start of vaccination, reports emerged that anti-SARS-CoV-2 vaccines, including ChAdOx1-S, could be associated with an increased risk of thrombosis. We investigated the hemostatic changes after ChAdOx1-S vaccination in 631 health care workers. Blood samples were collected 32 days on average after the second ChAdOx1-S vaccination, to evaluate hemostatic markers such as D-dimer, fibrinogen, α2-macroglobulin, FVIII and thrombin generation. Endothelial function was assessed by measuring Von Willebrand Factor (VWF) and active VWF. IL-6 and IL-10 were measured to study the activation of the immune system. Additionally, SARS-CoV-2 anti-nucleoside and anti-spike protein antibody titers were determined. Prothrombin and fibrinogen levels were significantly reduced after vaccination (−7.5% and −16.9%, p < 0.0001). Significantly more vaccinated subjects were outside the normal range compared to controls for prothrombin (42.1% vs. 26.4%, p = 0.026) and antithrombin (23.9% vs. 3.6%, p = 0.0010). Thrombin generation indicated a more procoagulant profile, characterized by a significantly shortened lag time (−11.3%, p < 0.0001) and time-to-peak (−13.0% and p < 0.0001) and an increased peak height (32.6%, p = 0.0015) in vaccinated subjects compared to unvaccinated controls. Increased VWF (+39.5%, p < 0.0001) and active VWF levels (+24.1 %, p < 0.0001) pointed toward endothelial activation, and IL-10 levels were significantly increased (9.29 pg/mL vs. 2.43 pg/mL, p = 0.032). The persistent increase of IL-10 indicates that the immune system remains active after ChAdOx1-S vaccination. This could trigger a pathophysiological mechanism causing an increased thrombin generation profile and vascular endothelial activation, which could subsequently result in and increased risk of thrombotic events.

Functional changes in hemostasis during asexual and sexual parasitemia in a controlled human malaria infection.

Decreased platelet count is an early phenomenon in asexual Plasmodium falciparum parasitemia, but its association with acute or long-term functional changes in platelets and coagulation is unknown. Moreover, the impact of gametocytemia on platelets and coagulation remains unclear. We investigated the changes in platelet number and function during early asexual parasitemia, gametocytemia and convalescence in 16 individuals participating in a controlled human malaria infection study, and studied its relationship with changes in total and active von Willebrand factor levels (VWF) and the coagulation system. Platelet activation and reactivity were determined by flow cytometry, and the coagulation system was assessed using different representative assays including antigen assays, activity assays and global functional assays. Platelet count was decreased during asexual blood stage infection but normalized during gametocytemia. Platelet P-selectin expression was slightly increased during asexual parasitemia, gametocytemia and at day 64. In contrast, platelet reactivity to different agonists remained unchanged, except a marked decrease in reactivity to low dose collagen-related peptide-XL. Thrombin generation and antigen assays did not show a clear activation of the coagulation during asexual parasitemia, whereas total and active VWF levels were markedly increased. During gametocytemia and on day 64, the endogenous thrombin potential, thrombin peak and velocity index were increased and prothrombin conversion and plasma prothrombin levels were decreased. We conclude that the decreased platelet count during asexual parasitemia is associated with increased active VWF levels (i.e. endothelial activation), but not platelet hyperreactivity or hypercoagulability, and that the increased platelet clearance in asexual parasitemia could cause spontaneous VWF-platelet complexes formation.

Platelet thrombus formation in patients with end-stage renal disease before and after hemodialysis as measured by the total thrombus-formation analysis system

BackgroundPatients with end-stage renal disease (ESRD) receiving hemodialysis (HD) often experience bleeding. However, mechanisms behind this bleeding tendency are incompletely understood but may involve platelet dysfunction. We, therefore, studied platelet-dependent thrombus formation in flowing whole blood inside a microchip coated with collagen, and its association with circulating von Willebrand factor (VWF).MethodsBlood samples were obtained in 22 patients before and after HD. The area under the 10 min flow pressure curve in a microchip (AUC10) reflecting total platelet thrombogenicity was measured, using the Total Thrombus-formation Analysis System (T-TAS01). AUC10 < 260 indicates platelet dysfunction. VWF activity and antigen in plasma were also assayed.ResultsVWF levels were moderately elevated and increased further after HD (P < 0.01 or lower). In contrast, AUC10 before and after HD was < 260 in 17/22 patients and < 130 in 15/22 patients, with no statistically significant difference in pre- vs post-HD measurements, indicating reduced platelet thrombogenicity, but with some variability as 5/22 patients showed normal platelet responsiveness. AUC10 and VWF activity or antigen levels in plasma were not correlated, either before or after HD.ConclusionsMost ESRD patients display moderate-to-severe platelet dysfunction as assessed by shear-induced platelet-dependent thrombus formation with T-TAS01. HD does not influence platelet function despite HD-induced elevations in VWF. T-TAS01 should be further evaluated as a tool in the assessment of bleeding risk in patients on HD.Graphical abstract

Low ADAMTS13 Activity Correlates with Increased Mortality in COVID-19 Patients

Systemic inflammation and coagulopathy are characteristic hallmarks of COVID19. “COVID coagulopathy” manifests mainly as a prothrombotic state affecting both large and small blood vessels, and presenting as arterial, venous, and microangiopathic thrombotic events with von Willebrand factor (VWF) and soluble thrombomodulin increased in hospitalized patients. The causes of coagulopathy are poorly understood. Aim: To investigate the relationship between von Willebrand factor (VWF) biomarkers, intravascular hemolysis, coagulation, and organ damage in COVID19 patients and to study their association with disease severity and mortality. Methods: 181 hospitalized adult COVID19 patients were randomly selected with a balanced distribution of survivors and non-survivors during the period of March 26th 2020 to May 5th 2020. The medical records and laboratory values were reviewed. Statistical analysis was performed using R studio V.3.6.2. Results: Patients who died (n=90) had significantly lower ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity, elevated lactate dehydrogenase levels, increased schistocyte/RBC fragment counts, and elevated VWF antigen and activity levels compared to patients discharged alive (n=91). In 31 patients, we measured several of these biomarkers on two or more occasions. The trending of ADAMTS13 activity illustrated that it is not steady throughout the hospitalization course. ADAMTS13 activity levels tended to improve and/or reach normal levels in patients that survived, yet ADAMTS13 activity levels worsened in most patients that died. Likewise, the VWF antigen and activity levels tended to decrease in patients that survived whereas tended to increase well above the normal range (2-3 folds) in patients that died. D-Dimer levels trended downwards in survivors, sometimes to levels less than 1 µg/ml, yet tended to increase in patients who died. Given the relationship between ADAMTS13 activity and mortality, we wanted to determine a cut-point of initial ADAMTS13 activity (within 72 hours from admission) to predict mortality. 102 patients in our cohort had an ADAMTS13 activity measurement within this timeframe. We determined that this optimal cut-point of initial ADAMTS13 activity was 43% using Youden’s J statistic. Only 30% of patients who had an ADAMTS13 activity level of less than 43% on admission survived, yet 60% of patients survived who had an ADAMTS13 activity level of greater than 43% on admission. Conclusions: COVID-19 may present with low ADAMTS13 activity in a subset of hospitalized patients. Presence of schistocytes/RBC fragment and elevated D-dimer levels on admission may warrant a work-up for ADAMTS13 activity and VWF antigen and activity levels. These findings indicate the need for future investigation to study the relationship between endothelial and coagulation activation and the efficacy of treatments aimed at prevention and/or amelioration of microangiopathy in COVID-19.

Von Willebrand factor exerts hepatoprotective effects in acute but not chronic cholestatic liver injury in mice

Acute and chronic liver disease are associated with substantial alterations in the hemostatic system, including elevated levels of the platelet-adhesive protein von Willebrand factor (VWF). Carbon tetrachloride-induced liver fibrosis is reduced in VWF-deficient mice, but it is unclear if VWF plays a pathologic role in all settings of liver fibrosis. Indeed, several studies suggest an anti-fibrotic role for components of the hemostatic system, including platelets, in experimental settings of bile duct fibrosis. However, the role of VWF in this specific pathology has not been examined. We tested the hypothesis that VWF exerts hepatoprotective effects in experimental bile duct injury. Wild-type and VWF-deficient (VWF−/−) mice were challenged with the bile duct toxicant alpha-naphthylisothiocyanate (ANIT) and the impact of VWF deficiency on acute cholestatic liver injury and chronic liver fibrosis was determined. Acute ANIT (60 mg/kg, po)-induced cholestatic liver injury was associated with increased VWF plasma antigen and activity levels. VWF deficiency enhanced ANIT-induced hepatocellular injury, evidenced by increased plasma ALT activity and area of hepatocellular necrosis. Surprisingly, platelet accumulation within necrotic areas was increased in ANIT-challenged VWF−/− mice compared to wild-type mice. Compared to acute ANIT challenge, hepatic platelet accumulation was modest and appeared to be VWF-dependent in mice exposed to ANIT diet (0.05 %) for 6 weeks. However, contrasting the role of VWF after acute ANIT challenge, VWF deficiency did not impact biliary fibrosis induced by chronic ANIT exposure. The results suggest that VWF plays dichotomous roles in experimental acute and chronic ANIT-induced cholestatic liver injury.

ПОКАЗАТЕЛИ КОАГУЛЯЦИОННОГО РАВНОВЕСИЯ И АГРЕГАЦИИ ТРОМБОЦИТОВ У ПАЦИЕНТОВ С ИНФЕКЦИЕЙ COVID-19

Objective. To determine changes in coagulation balance and platelet aggregation in patient during the treatment of COVID-19 infection. Methods. A pilot non-randomized prospective clinical study of coagulation balance and platelet aggregation in patients admitted to the intensive care unit with acute respiratory distress syndrome and the diagnosis of COVID-19 (n=50) was performed. Out of 50 patients, 19 patients died, 31 patients were transferred to the therapeutic department. The study of indicators of coagulation balance and platelet aggregation was carried out once in 1-3 days starting from the patient’s admission to the hospital using coagulation analyzer ACL 10000 (Instrumentation Laboratory, USA) and platelet aggregation analyzer AP 2110 (ZAO “SOLAR”, Republic of Belarus). Results. In 45 (90%) patients with COVID-19, there is a significant increase of von Willebrand factor activity 350 (244.5; 480) %. There were no statistically significant differences in the level of von Willebrand factor activity among the deceased and surviving patients: 450.0 (338.8; 530.5) % in deceased patients and 342.0 (188.8; 480.0) % in survivors. At von Willebrand factor activity level of up to 250%, the mortality rate was 8.3%, at a level of 250-400% - 31.3%, at a level of more than 400% - 59.1%. Significantly above the normal range in most patients were fibrinogen (above normal in 68% of patients, 4.63 (3.49; 5.87) g/L) and D-dimers (above normal in 88% of patients, 0.73 (0,31; 1.4) μg/ml). Antithrombin III was below normal in 56% of patients (82 (67.1; 97.2) %). The degree of platelet aggregation has a strong direct correlation with the von Willebrand factor level: with an ADP inducer 0.3 μg/ml (R=0.71, р=0.003); ADP 0.6 μg/ml (R=0.74, р=0.0001); ADP 1.25 μg/ml (R=0.53, р=0.01). Conclusion. Analysis and evaluation of coagulation balance and platelet aggregation should be an integral part in the treatment of patients with COVID-19 infection. What this paper adds For the first time, the indicators of coagulation balance and platelet aggregation have been assessed in the treatment of COVID-19 infection. It has been found that 90% of patients had the increasedlevels ofvon Willebrand factor(VWF) - 350 (244.5; 480)%. In addition to an increase of von Willebrand factor activity, 56% of patients show a reduction of antithrombin III levels, and 88% and 68% of patients have an increasing D-dimers and fibrinogen, respectively. Analysis and assessment of coagulation balance and platelet aggregation indicators should be integral components of the treatment of patients with COVID-19 infection.