Platelets treated with ticlopidine are less reactive to unusually large von Willebrand factor multimers than are those treated with aspirin under high shear stress

Ratio of von Willebrand factor to ADAMTS13 is a useful predictor of esophagogastric varices progression after sustained virologic response in patients with hepatitis C virus-related liver cirrhosis

AIM

Esophagogastric varices (EGV) are a serious complication of hepatitis C virus (HCV)-related liver cirrhosis (HCV-LC). In most cases, portal hypertension improves after a sustained virologic response (SVR) is achieved with direct-acting antiviral (DAA) treatment; however, in some cases, EGV exacerbation occurs after HCV elimination. We investigated whether von Willebrand factor (VWF) and a disintegrin-like metalloproteinase with thrombospondin type-1 motif 13 (ADAMTS13) can predict EGV progression with HCV-LC after SVR achievement.

METHODS

This retrospective study enrolled 47 patients with HCV-LC who achieved an SVR after DAA treatment. Eighteen patients experienced EGV progression after the SVR was achieved (EGV progression group). Twenty-nine patients did not experience EGV progression after the SVR was achieved (non-EGV progression group). Plasma VWF antigen levels and ADAMTS13 activity were measured the day before DAA treatment.

RESULTS

The EGV progression group had significantly higher plasma VWF antigen levels (p = 0.00331) and VWF-to-ADAMTS13 ratios (p = 0.000249) than the non-EGV progression group. Multivariate logistic regression models found that a VWF-to-ADAMTS13 ratio >2.3 was the only risk factor for EGV progression after the SVR was achieved (hazard ratio [HR], 18.4; 95% confidence interval [CI], 3.08-109; p = 0.00138). During the observation period, patients with a VWF-to-ADAMTS13 ratio >2.3 had a significantly higher cumulative incidence of EGV progression after SVR achievement than patients with a VWF-to-ADAMTS13 ratio ≤2.3 (HR, 6.4; 95% CI, 1.78-22.96; p = 0.0044).

CONCLUSIONS

The VWF-to-ADAMTS13 ratio before DAA treatment for HCV could predict EGV progression after SVR achievement.

Mitral regurgitation is associated with similar loss of von Willebrand factor large multimers but lower frequency of anemia compared with aortic stenosis

Background

Various cardiovascular diseases cause acquired von Willebrand syndrome (AVWS), which is characterized by a decrease in high-molecular-weight (large) von Willebrand factor (VWF) multimers. Mitral regurgitation (MR) has been reported as a cause of AVWS. However, much remains unclear about AVWS associated with MR.

Objectives

To evaluate VWF multimers in MR patients and examine their impact on clinical characteristics.

Methods

Moderate or severe MR patients (n = 84) were enrolled. VWF parameters such as the VWF large multimer index (VWF-LMI), a quantitative value that represents the amount of VWF large multimers, and clinical data were prospectively analyzed.

Results

At baseline, the mean hemoglobin level was 12.9 ± 1.9 g/dL and 58 patients (69.0%) showed loss of VWF large multimers defined as VWF-LMI < 80%. VWF-LMI in patients with degenerative MR was lower than in those with functional MR. VWF-LMI appeared to be restored the day after mitral valve intervention, and the improvement was maintained 1 month after the intervention. Seven patients (8.3%) had a history of bleeding, 6 (7.1%) of whom had gastrointestinal bleeding. Gastrointestinal endoscopy was performed in 23 patients (27.4%) to investigate overt gastrointestinal bleeding, anemia, etc. Angiodysplasia was detected in 2 of the 23 patients (8.7%).

Conclusion

Moderate or severe MR is frequently associated with loss of VWF large multimers, and degenerative MR may cause more severe loss compared with functional MR. Mitral valve intervention corrects the loss of VWF large multimers. Gastrointestinal bleeding may be relatively less frequent and hemoglobin level remains stable in MR patients.

VWF/ADAMTS13 Ratio as a Potential Predictive Biomarker for Acute Kidney Injury Onset in Cirrhosis

AIM

We investigated the von Willebrand factor to ADAMTS13 ratio (von Willebrand factor [VWF]:Ag/ADAMTS13:AC) as a potential biomarker for the outcomes of acute kidney injury (AKI) in liver cirrhosis (LC).

METHODS

This retrospective cross-sectional study included patients with LC who developed AKI (AKI group: n = 91) and patients with LC who did not develop AKI [non-AKI (NAKI) group, n = 91] as a control group. Plasma levels of the von Willebrand factor antigen (Ag) and ADAMTS13 activity (AC) were measured in patients with AKI or NAKI. Moreover, risk factors for onset of AKI, AKI-associated 90-day mortality, and poor AKI treatment response were identified.

RESULTS

The AKI group had a significantly higher VWF:Ag/ADAMTS13:AC than the NAKI group. Values of VWF:Ag/ADAMTS13:AC ≥ 5.7 were identified as risk factors for AKI onset in patients with LC (odds ratio [OR] 2.56; 95% CI 1.26-4.99; p < 0.001). Among patients with AKI, values of VWF:Ag/ADAMTS13:AC ≥ 9.0 were identified as risk factors for 90-day mortality (OR 6.83; 95% CI 2.32-20.10; p < 0.001). Cumulative survival was significantly lower in those with high (≥ 9.0) than in those with low (< 9.0) VWF:Ag/ADAMTS13:AC. Furthermore, values of VWF:Ag/ADAMTS13:AC ≥ 7.4 were identified as risk factors for poor treatment response (OR 4.2; 95% CI 1.39-12.70; p < 0.001). The treatment response rates were significantly higher in those with low (< 7.4) VWF:Ag/ADAMTS13:AC than in those with high (≥ 7.4) VWF:Ag/ADAMTS13:AC.

CONCLUSION

VWF:Ag/ADAMTS13:AC potentially predicts the onset, prognosis, and treatment response of AKI in patients with LC.

von Willebrand factor Ristocetin co-factor activity to von Willebrand factor antigen level ratio for diagnosis of acquired von Willebrand syndrome caused by aortic stenosis

Background

Severe aortic stenosis (AS) causes acquired von Willebrand syndrome by the excessive shear stress-dependent cleavage of high molecular weight multimers of von Willebrand factor (VWF). While the current standard diagnostic method is so-called VWF multimer analysis that is western blotting under nonreducing conditions, it remains unclear whether a ratio of VWF Ristocetin co-factor activity (VWF:RCo) to VWF antigen levels (VWF:Ag) of <0.7, which can be measured with an automated coagulation analyzer in clinical laboratories and is used for the diagnosis of hereditary von Willebrand disease.

Objectives

To evaluated whether the VWF:RCo/VWF:Ag is useful for the diagnosis of AS-induced acquired von Willebrand syndrome.

Methods

VWF:RCo and VWF:Ag were evaluated with the VWF large multimer index as a reference, which represents the percentage of a patient's VWF high molecular weight multimer ratio to that of standard plasma in the VWF multimer analysis.

Results

We analyzed 382 patients with AS having transaortic valve maximal pressure gradients of >30 mmHg, 27 patients with peripheral artery disease, and 46 control patients free of cardiovascular disease with osteoarthritis, diabetes, and so on. We assumed a large multimer index of <80% as loss of VWF large multimers since 59.0% of patients with severe AS had the indices of <80%, while no control patients or patients with peripheral artery disease, except for 2 patients, exhibited the indices of <80%. The VWF:RCo/VWF:Ag ratios, measured using an automated blood coagulation analyzer, were correlated with the indices (rs = 0.470, P < .001). When the ratio of <0.7 was used as a cut-off point, the sensitivity and specificity to VWF large multimer indices of <80% were 0.437 and 0.826, respectively.

Conclusion

VWF:RCo/VWF:Ag ratios of <0.7 may indicate loss of VWF large multimers with high specificity, but low sensitivity. VWF:RCo/VWF:Ag ratios in patients with AS having a ratio of <0.7 may be useful for monitoring the loss of VWF large multimers during their clinical courses.

Two pregnant women with immune-mediated thrombotic thrombocytopenic purpura: A case report

Thrombotic thrombocytopenic purpura (TTP) during pregnancy is life-threatening. We encountered two pregnant women with immune-mediated TTP (iTTP). A 40-year-old primigravida woman was referred at 19 gestational weeks (GWs) owing to iTTP. She received plasma exchange (PE) and steroid therapies and delivered a live infant at 27 GWs by cesarean delivery. A 29-year-old primigravida woman was referred owing to intrauterine fetal death and thrombocytopenia at 20 GWs. She was diagnosed with iTTP and received PE therapy. She required additional PE and steroid therapies owing to relapse. Before her second pregnancy, she received prednisolone and hydroxychloroquine according to the therapy for systemic lupus erythematosus (SLE). She had induced labor at 37 GWs owing to decrease plasma level of a disintegrin-like and metalloproteinase with thrombospondin type 1 motif 13 (ADAMTS13) activity. Close monitoring of plasma ADAMTS13 activity level and treatments for underlying SLE may prevent iTTP relapse and lead to a good prognosis.

The Ratio of von Willebrand Factor Antigen to ADAMTS13 Activity: Usefulness as a Prognostic Biomarker in Acute-on-Chronic Liver Failure

Acute-on-chronic liver failure (ACLF) has a high risk of short-term mortality. A disintegrin-like and metalloproteinase with thrombospondin type-1 motifs 13 (ADAMTS13) is a metalloproteinase that specifically cleaves multimeric von Willebrand factor (VWF). Imbalance between ADAMTS13 and VWF is associated with portal hypertension, which induces ACLF development. A previous study reported that ADAMTS13 activity (ADAMTS13:AC) and VWF antigen (VWF:Ag) are predictive biomarkers of ACLF development in patients with cirrhosis. This study investigated the changes in ADAMTS13:AC and VWF:Ag levels from before to after the development of ACLF to determine their usefulness as a prognostic biomarker in patients with ACLF. In total, 101 patients with cirrhosis were enrolled in this study. The level of ADAMTS13:AC and VWF:Ag was determined by an enzyme-linked immunosorbent assay. Cox proportional hazard regression analysis was conducted to determine independent prognostic factors for patients with liver cirrhosis in the post-ACLF group. ADAMTS13:AC levels gradually decreased in the order of non-ACLF group, pre-ACLF group, and finally post-ACLF group. VWF:Ag and the ratio of VWF:Ag to ADAMTS13:AC (VWF:Ag/ADAMTS13:AC) levels gradually increased in the order of non-ACLF group, pre-ACLF group, followed by post-ACLF group. VWF:Ag/ADAMTS13:AC and CLIF-C ACLF scores were associated with prognosis in the post-ACLF group in multivariate analysis. The cumulative survival of the post-ACLF group was significantly lower for patients with high VWF:Ag/ADAMTS13:AC (>9) compared with those with low VWF:Ag/ADAMTS13:AC (≤9) (HR: 10.72, 95% confidence interval: 1.39-82.78, p < 0.05). The VWF:Ag/ADAMTS13:AC increased according to the progression of ACLF in patients with cirrhosis and predicted prognosis in patients with cirrhosis with ACLF.

The efficacy and safety of caplacizumab in Japanese patients with immune-mediated thrombotic thrombocytopenic purpura: an open-label phase 2/3 study

Caplacizumab is an anti-von Willebrand factor humanized single-variable-domain immunoglobulin fragment whose efficacy and safety in immune-mediated thrombotic thrombocytopenia purpura (iTTP) have been demonstrated in international studies. This prospective, open-label phase 2/3 study evaluated caplacizumab 10 mg administered daily during plasma exchange and for 30 days afterward, in combination with immunosuppressive treatment, in Japanese adults with a clinical diagnosis of iTTP (new or recurrent). The primary endpoint was prevention of iTTP recurrence; key secondary endpoints included time to platelet count response, time to organ damage normalization, and safety. Among 21 treated patients, 1 of 15 (6.7%) evaluable patients developed iTTP recurrence. Median time to normalization was 2.79 days for platelet count and 2.65 days for organ damage markers (n = 15). Treatment-emergent adverse events (TEAEs) were mostly mild to moderate in severity; the most frequently reported caplacizumab-related TEAEs were increased alanine aminotransferase, epistaxis, and gastrointestinal hemorrhage (all in 9.5% of patients). At least one bleeding event was reported in 7 of 21 patients (33%). Caplacizumab was effective in Japanese patients with iTTP, with a low rate of iTTP recurrence, rapid normalization of platelet counts and organ damage markers, and no unexpected TEAEs. Trial registration: ClinicalTrials.gov identifier, NCT04074187.

Alteration of plasma von Willebrand factor in the treatment of retinal vein occlusion with cystoid macular edema

Retinal vein occlusion (RVO) is a major retinal disease caused by venous thrombosis. Although several studies have proposed an association between venous thrombosis and von Willebrand factor (VWF), the association between RVO and VWF remains unclear. We aimed to investigate the association between RVO and VWF and the alteration of VWF levels under anti-vascular endothelial growth factor (VEGF) treatment. We enrolled 55 patients with RVO involved cystoid macular edema. They received intravitreal injection of anti-VEGF drugs, either ranibizumab or aflibercept. We examined the clinical data and measured plasma VWF antigen and a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) activity to identify variabilities during treatment. At baseline, there was no significant difference between the RVO group and age-matched controls in both VWF antigen and ADAMTS13 activity levels, but ADAMTS13 activity was significantly lower in central RVO than in branch RVO (P = 0.015). In branch RVO, VWF antigen was negatively correlated with central choroidal thickness (r = −0.51, P < 0.001). In branch RVO after anti-VEGF treatment, VWF antigen levels decreased significantly from 134% at baseline to 109% at 1 day (P = 0.002) and 107% at 1 month (P = 0.030) after treatment. In contrast, ADAMTS13 activity showed no significant difference during this period. In branch RVO at 1 month after treatment, VWF antigen was negatively correlated with central choroidal thickness (r = −0.47, P = 0.001). Our findings suggest an association between VWF and central choroidal thickness in patients with branch RVO, thus the measurement of VWF may be useful for evaluating disease activity and prognosis.

Ratio of von Willebrand factor antigen to ADAMTS13 activity is a useful biomarker for acute-on-chronic liver failure development and prognosis in patients with liver cirrhosis

AIM

Acute-on-chronic liver failure (ACLF) is associated with a high risk of short-term mortality after progression to multiple organ failure. A disintegrin-like and metalloproteinase with thrombospondin type-1 motifs 13 (ADAMTS13) is a metalloproteinase that specifically cleaves multimeric von Willebrand factor (VWF). An imbalance between ADAMTS13 enzyme and VWF substrate is associated with liver cirrhosis progression that induces ACLF. This study examined the relationship between ADAMTS13 and VWF and ACLF development to determine whether ADAMTS13 and VWF are useful predictive biomarkers for ACLF development and prognosis of patients with liver cirrhosis.

METHODS

The study enrolled 67 patients with Child-Pugh class A and B liver cirrhosis. ADAMTS13 activity (ADAMTS13:AC) and VWF antigen (VWF:Ag) were measured using enzyme-linked immunosorbent assays. The ratio of VWF:Ag to ADAMTS13:AC (VWF:Ag/ADAMTS13:AC) was used to divide patients into two groups according to the classification and regression tree based on Gray model survival analysis.

RESULTS

Compared with patients with Child-Pugh class A liver cirrhosis, class B patients had a higher VWF:Ag/ADAMTS13:AC and a higher risk of ACLF development. Cumulative incidence of ACLF was significantly higher in patients with high (>7.9) versus low (≤7.9) VWF:Ag/ADAMTS13:AC (hazard ratio [HR], 6.50; 95% CI, 2.31-18.29; p < 0.001). Cumulative survival was significantly lower in cirrhotic patients with high versus low VWF:Ag/ADAMTS13:AC (HR 5.11; 95% CI, 1.85-14.14; p = 0.002).

CONCLUSIONS

For patients with liver cirrhosis, VWF:Ag/ADAMTS13:AC is associated with functional liver reserve and predicts the development of ACLF and the prognosis.

ADAMTS13, VWF, and Endotoxin Are Interrelated and Associated with the Severity of Liver Cirrhosis via Hypercoagulability

ADAMTS13 specifically cleaves the multimeric von Willebrand factor (VWF), and an imbalance between ADAMTS13 activity (ADAMTS13:AC) and VWF antigen (VWF:Ag) levels is associated with the severity of liver cirrhosis (LC). However, the reason for this imbalance in patients with LC is unknown. This study investigated the relationship among ADAMTS13:AC, VWF:Ag, and endotoxin (Et) levels in patients with LC. ADAMTS13:AC and VWF:Ag levels were determined using ELISA, whereas Et levels were estimated using a chromogenic substrate assay. The levels of ADAMTS13 inhibitor (ADAMTS13:INH) were evaluated by measuring the extent that heat-inactivated patient’s plasma reduces the ADAMTS13:AC of the control. The status (degraded, normal, or unusually large [UL]) of the VWF multimer (VWFM) was determined through vertical agarose gel electrophoresis. ADAMTS13:AC, VWF:Ag, and Et levels decreased, increased, and increased, respectively, with the severity of LC. Patients with cirrhosis with high Et levels had lower and higher ADAMTS13:AC and VWF:Ag levels, respectively, than those with low Et levels. Patients with cirrhosis with detectable ADAMTS13:INH had higher Et levels than those with undetectable ADAMTS13:INH. Patients whose VWFM was either normal or UL had higher Et levels than those with degraded VWFM. In conclusion, ADAMTS13, VWF, and Et may be interrelated and associated with the severity of LC via hypercoagulability.

Analysis focusing on plasma von Willebrand factor in pachychoroid neovasculopathy and age-related macular degeneration

Pachychoroid neovasculopathy (PNV) is a new concept of macular disorder. Some cases diagnosed as age-related macular degeneration (AMD) have been re-diagnosed as PNV. However, the biological features of PNV are still uncertain. The purpose of this study was to compare PNV and AMD by analyses focusing on von Willebrand factor (VWF) and complement factor H (CFH). Ninety-seven patients who were previously diagnosed with treatment naïve AMD were enrolled in this study. They were re-classified as either PNV or AMD based on the clinical criteria and 33 patients were classified as PNV and 64 patients as AMD. We examined the clinical data, analyzed VWF multimer and two genetic polymorphisms (I62V and Y402H) in the CFH. PNV group was significantly younger than AMD group (P = 0.001). In both I62V and Y402H, there were no significant differences between PNV and AMD while the recessive homozygous (AA) was found only in PNV group in I62V. The presence of unusually large VWF multimers (UL-VWFMs) and subretinal hemorrhages were significantly higher in PNV than in AMD (P = 0.045, P = 0.020, respectively). Thus, the residual UL-VWFMs may result in platelet thrombosis and hemorrhages in the choriocapillaris of PNV. In conclusion, our results suggest the biological differences between PNV and AMD.

Association between ADAMTS13 activity–VWF antigen imbalance and the therapeutic effect of HAIC in patients with hepatocellular carcinoma

BACKGROUND

Prediction of HAIC treatment response is important for improving the prognosis in patients with hepatocellular carcinoma (HCC). The progression of HCC is related to hypercoagulability and angiogenesis. It is known that ADAMTS13 and von Willebrand factor (VWF) are related to hypercoagulability. In addition, previous study reported that the association between ADAMTS13 and VWF, and angiogenesis via vascular endothelial growth factor (VEGF). Recently, ADAMTS13 and VWF have been associated with the prognosis in patients with various kinds of cancer undergoing chemotherapy.

AIM

To investigate whether ADAMTS13 and VWF become useful biomarkers of treatment response in HCC patients before the initiation of HAIC treatment.

METHODS

Seventy-two patients were enrolled in this study. ADAMTS13 activity (ADAMTS13:AC), VWF antigen (VWF:Ag) and VEGF levels were determined via enzyme-linked immunosorbent assay. Univariable and multivariable analyses were performed to determine the predictive factors of treatment response in patients with HCC undergoing HAIC treatment.

RESULTS

ADAMTS13:AC levels in HCC patients with stable disease (SD) + partial response (PR) of HAIC treatment were significantly higher than those with progressive disease (PD) (P < 0.05). In contrast, VWF:Ag/ADAMTS13:AC ratio and VEGF levels in HCC patients with SD + PR were significantly lower than those with PD (both P < 0.05). Patients with high VWF:Ag/ADAMTS13:AC ratio (> 2.7) had higher VEGF levels than those with low ratio (≤ 2.7). Multivariable analysis revealed that VWF:Ag/ADAMTS13:AC ratio was a predictive factor of HAIC treatment response.

CONCLUSION

VWF:Ag/ADAMTS13:AC ratio may become a useful biomarker of treatment response in HCC patients before the initiation of HAIC treatment.

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

BACKGROUND AND PURPOSE

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.

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

VWF/ADAMTS13 ratio as a potential biomarker for early detection of hepatocellular carcinoma

Background

To investigate the von Willebrand factor to ADAMTS13 ratio as a potential biomarker for early detection of hepatocellular carcinoma (HCC) in cirrhosis.

Methods

Serum levels of alpha-fetoprotein, des-γ-carboxy prothrombin, Lens culinaris agglutinin-reactive fraction of alpha-fetoprotein (alpha-fetoprotein-L3%), vascular endothelial growth factor, and vascular endothelial growth factor receptor-2, as well as the plasma levels of von Willebrand factor antigen (von Willebrand factor: Ag) and ADAMTS13 activity (ADAMTS13:AC), were evaluated in 41 cirrhotic patients with HCC undergoing radiofrequency ablation and in 20 cirrhotic patients without HCC. The diagnostic accuracy of each biomarker was evaluated using the receiver operating characteristic curve analysis.

Results

The von Willebrand factor: Ag and von Willebrand factor: Ag/ADAMTS13:AC ratios were significantly higher in cirrhotic patients with HCC than in those without HCC (p < 0.05 and p < 0.01, respectively), whereas ADAMTS13:AC was significantly lower in those with HCC than those without HCC (p < 0.05). However, no relationship was observed between the von Willebrand factor: Ag/ADAMTS13:AC ratio and serum tumor markers such as alpha-fetoprotein, des-γ-carboxy prothrombin, and alpha-fetoprotein-L3%. Multivariate regression analysis identified von Willebrand factor: Ag/ADAMTS13:AC ratio and alpha-fetoprotein-L3% as significant factors of HCC development. Receiver operating characteristic analysis showed that the von Willebrand factor: Ag/ADAMTS13:AC ratio and alpha-fetoprotein-L3% had a better performance than alpha-fetoprotein, des-γ-carboxy prothrombin, alpha-fetoprotein-L3%, vascular endothelial growth factor, and vascular endothelial growth factor receptor-2, von Willebrand factor: Ag, and ADAMTS13:AC. The von Willebrand factor: Ag/ADAMTS13:AC ratio was exclusively correlated with tumor volume and stage as well as serum vascular endothelial growth factor levels.

Conclusions

The von Willebrand factor: Ag/ADAMTS13:AC ratio can potentially serve as a novel biomarker for early diagnosis of HCC in cirrhotic patients.

Ischaemia-reperfusion injury with Pringle's maneuver induces unusually large von Willebrand factor multimers after hepatectomy

INTRODUCTION

von Willebrand factor (VWF) is synthesised in vascular endothelial cells and released into the plasma as unusually large VWF multimers (UL-VWFMs). Sinusoidal endothelial cells are a major target of ischaemia-reperfusion injury due to liver surgery. This study aimed to clarify the effect of hepatectomy on UL-VWFMs.

MATERIALS AND METHODS

Thirty-five patients who underwent hepatectomy were eligible for the study. Plasma ADAMTS13 activity and VWF antigen levels were measured by enzyme-linked immunosorbent assay and multimer analysis of plasma VWF was performed according to Ruggeri and Zimmerman's method. For analyses, patients were categorised according to UL-VWFM positivity after hepatectomy.

RESULTS

Plasma ADAMTS13 activity significantly decreased from 61.0% (27.7%-126.2%) before operation to 37.4% (20.2%-71.4%) on postoperative day 7 (p < 0.001). Plasma VWF antigen levels significantly increased from 172.1% (80.5%-412.8%) before operation to 361.0% (154.7%-745.8%) on postoperative day 2, which remained high until postoperative day 7 (p < 0.001). Seven patients remained UL-VWFMs-negative and 22 patients became UL-VWFMs-positive after operation. Pringle's maneuver duration was significantly longer and blood loss volume was significantly higher in the UL-VWFMs-positive group (p = 0.001 and p = 0.003, respectively). By multivariable analysis, Pringle's maneuver duration [odds ratio 1.049, 95% confidence interval (CI) 1.001-1.098; p = 0.043] was significantly associated with increased UL-VWFMs level after hepatectomy. UL-VWFMs index was significantly correlated with Pringle's maneuver duration (r = 0.444, p = 0.017).

CONCLUSIONS

Plasma UL-VWFMs levels increased after hepatectomy due to ischaemia-reperfusion injury with Pringle's maneuver.

Disappearance of Angiodysplasia Following Transcatheter Aortic Valve Implantation in a Patient with Heyde's Syndrome: A Case Report and Review of the Literature

An 83-year-old woman with severe aortic stenosis was admitted to our hospital due to heart failure with refractory anemia requiring blood transfusions. She had repetitive bleeding episodes from endoscopically proven angiodysplasia in the stomach. Moreover, she repeatedly underwent endoscopic argon plasma coagulation for hemostasis. Importantly, she had a deficiency of the high-molecular-weight (HMW) multimers of von Willebrand factor (VWF), and she was diagnosed with Heyde's syndrome.After she underwent transcatheter aortic valve implantation (TAVI), aortic valve area and mean left ventricular aorta pressure gradient improved. Notably, endoscopy showed cessation of bleeding at 10 days after TAVI and the disappearance of angiodysplasia at 4 months after TAVI. Even at 2 years after TAVI, follow-up endoscopy showed remaining free of angiodysplasia in the stomach. She experienced no episodes of anemia since TAVI procedure. Additionally, analysis of HMW multimers demonstrated immediate and lasting recovery after TAVI.Recovery of HMW multimers of VWF with cessation of gastrointestinal bleeding following aortic valve replacement has been previously reported in a patient diagnosed with Heyde's syndrome. To the best our knowledge, this is the first case to demonstrate that angiodysplasia disappears after TAVI for a long term with endoscopic images in a patient with Heyde's syndrome. Here, we summarized case reports of patients with Heyde's syndrome that required aortic valve intervention. Cessation of gastrointestinal bleeding and anemia after aortic valve intervention for severe aortic stenosis may be attributed not only to recovery of HMW multimers of VWF but also to the disappearance of angiodysplasia.

Association between the severity of acquired von Willebrand syndrome and gastrointestinal bleeding after continuous-flow left ventricular assist device implantation

OBJECTIVES

Acquired von Willebrand syndrome, characterized by the reduction in von Willebrand factor (vWF) large multimers, has recently been considered as one of the causes of gastrointestinal bleeding (GIB). It remains unclear whether its haematological severity is linked with susceptibility to bleeding because the definition of the haematological severity of acquired von Willebrand syndrome has not been precisely determined. This study sought to establish a quantitative methodology to assess the haematological severity of acquired von Willebrand syndrome and to define the threshold for occurrence of GIB in patients implanted with left ventricular assist devices (LVADs).

METHODS

In total, 41 patients treated with continuous-flow LVAD implanted between 2011 and 2017 at Tohoku University Hospital were investigated. vWF large multimers were quantitatively evaluated using the 'vWF large multimer index' defined as the ratio of a large multimer proportion in total vWF derived from a patient to that from a normal control. Using this index, the amount of vWF large multimers was expressed as a percentage of its normal control value obtained with a simultaneous analysis of each time measurement.

RESULTS

Twelve (29%) patients developed GIB events during follow-up periods (median 591 days) after an LVAD implantation. The vWF large multimer index in patients with GIB was significantly lower than that in those without GIB (25.0 ± 10.3% vs 37.5 ± 17.8%, P = 0.008). Most importantly, all patients experiencing GIB exhibited a vWF large multimer index below 40%.

CONCLUSIONS

Patients with GIB exhibited a more severe loss of vWF large multimers. The vWF large multimer index may dictate the risk of GIB after an LVAD implantation.

Clinical trial registration number

UMIN000018135.

Blood group antigen A on von Willebrand factor is more protective against ADAMTS13 cleavage than antigens B and H

BACKGROUND

ADAMTS13 specifically cleaves the peptide bond between Y1605 and M1606 within the VWF-A2 domain.

OBJECTIVE

The VWF contains ABO(H) blood group antigens, which may influence the susceptibility of VWF to ADAMTS13.

METHODS

Using a unique monoclonal antibody recognizing the Y1605 residue, we have developed a sandwich ELISA to analyze the generation of a VWF-DP by ADAMTS13 quantitatively.

RESULTS

Production of VWF-DP after exposure to four different degrees of high shear stress was validated in comparison to the reduction in high-molecular-weight multimers using VWF multimer analysis. In analysis of plasma from 259 healthy individuals, plasma levels of VWF antigen (VWF:Ag) were significantly lower in blood group O than in the other groups and were significantly correlated with plasma VWF-DP levels. The ratio between VWF-DP and VWF:Ag was significantly higher in blood group O than in blood groups A and AB. The ratio in blood group B was also significantly higher than those in A and AB, but did not differ from blood group O. Finally, to examine whether ABO(H) blood group antigens contributed to VWF cleavage, 82 plasma samples were exposed to high shear stress using a cone-plate shear stress inducer. The difference in the VWF-DP/VWF:Ag ratio before and after high shear stress in blood group O was significantly greater than those in groups A and AB.

CONCLUSION

These results indicate that blood group antigen A on VWF was more protective against ADAMTS13 cleavage than antigens B and H.

ADAMTS13 and von Willebrand factor are useful biomarkers for sorafenib treatment efficiency in patients with hepatocellular carcinoma

BACKGROUND

Many advanced hepatocellular carcinoma (HCC) patients are receiving sorafenib treatment. Sorafenib reportedly improves overall survival (OS) significantly in patients with HCC. Prediction of sorafenib response and prognosis in patients with HCC receiving sorafenib treatment are important due to the potentially serious side effects of sorafenib. A disintegrin-like and metalloproteinase with thrombospondin type-1 motifs 13 (ADAMTS13) and von Willebrand factor (VWF) are associated with the pathophysiology of liver cirrhosis and HCC through their roles in hypercoagulability; they are also associated with angiogenesis via vascular endothelial growth factor (VEGF). The imbalance between ADAMTS13 and VWF was associated with prognosis of various cancers in patients undergoing chemotherapy.

AIM

To investigate ADAMTS13 and VWF as potential biomarkers for sorafenib response and prognosis in patients with HCC receiving sorafenib treatment.

METHODS

Forty-one patients with HCC receiving sorafenib treatment were included in this study. The initial daily sorafenib dose was 400 mg in all patients. ADAMTS13 activity (ADAMTS13:AC), VWF antigen (VWF:Ag), VEGF levels were determined by enzyme-linked immunosorbent assay. Univariate and multivariate analyses were used to determine predictive factors for sorafenib response and prognosis in patients with HCC receiving sorafenib treatment.

RESULTS

ADAMTS13:AC was significantly higher in patients with stable disease (SD), partial response (PR), and complete response (CR) than in those with progressive disease (PD) (P < 0.05). In contrast, VWF:Ag and the VWF:Ag/ADAMTS13:AC ratio were significantly lower in patients with SD, PR, and CR than in those with PD (P < 0.05 for both). Multivariate analysis showed that the VWF:Ag/ADAMTS13:AC ratio was the only predictive factor for sorafenib response and ADAMTS13:AC was the only prognostic factor in patients with HCC receiving sorafenib treatment. The patients with a low ADAMTS13:AC (< 78.0) had significantly higher VEGF levels than those with a high ADAMTS13:AC (≥ 78.0) (P < 0.05).

CONCLUSION

The VWF:Ag/ADAMTS13:AC ratio and ADAMTS13:AC are potentially useful biomarkers for sorafenib response and prognosis, respectively, in patients with HCC receiving sorafenib treatment.

Involvement of the ADAMTS13-VWF axis in acute Kawasaki disease and effects of intravenous immunoglobulin

INTRODUCTION

ADAMTS13 modulates shear-dependent platelet thrombus formation (PTF) by limited proteolysis of von Willebrand factor (VWF). A high-plasma-ratio of VWF antigen to ADAMTS13 activity (VWF:Ag/ADAMTS13:AC) promotes PTF and aggravates shear-induced inflammation mediated by VWF. A role of ADAMTS13 in Kawasaki disease (KD) remains unknown, however. We investigated the involvement of ADAMTS13-VWF axis in the acute-phase of KD (acute-KD).

METHODS

VWF:Ag and ADAMTS13:AC in 77 KD infants were measured at three time-points; immediately before (Pre), one-week (1 W) and one-month (1 M) after intravenous-immunoglobulin (IVIG) treatment. VWF multimer (VWFM) distribution and ADAMTS13-isoelectrofocusing (IEF) patterns were compared between the responders and non-responders to IVIG.

RESULTS

A high VWF:Ag (195.7 ± 85.6%, p < 0.05), low ADAMTS13:AC (60.3 ± 23.8%, p < 0.05) and high VWF:Ag/ADAMTS13:AC ratio (3.70 ± 2.12, p < 0.05) at Pre were seen compared to control plasmas. These parameters returned to normal levels time-dependently after IVIG treatment. Non-responders to IVIG demonstrated high VWF:Ag and low ADAMTS13:AC at Pre, and high VWF:Ag/ADAMTS13:AC ratio at 1 W compared to responders, but there were no significant differences in VWFM distribution between both groups. IEF analyses revealed the decreased free form of ADAMTS13 and increased complex form with ADAMTS13 and high-molecular-weight-VWFM at Pre in non-responders. A high VWF:Ag/ADAMTS13:AC ratio was associated with increased white blood cell counts, together with decreased serum albumin and sodium at Pre and 1 W.

CONCLUSIONS

A high VWF:Ag/ADAMTS13:AC ratio in acute-KD persisted after primary treatment in non-responders, and unbalanced substrate-to-enzyme ratio appeared to associate with vascular endothelial damage. Analysis of existing mode of ADAMTS13 may help to clarify pathogenesis of IVIG resistance in acute-KD.

Acquired von Willebrand Syndrome Associated with Cardiovascular Diseases

The blood glycoprotein von Willebrand factor (VWF) plays an important role in hemostasis and thrombosis. VWF is produced and secreted as large multimers by endothelial cells and megakaryocytes. It is then cleaved in a sheer-stress dependent manner by a specific protease, ADAMTS13, into multimers consisting of 2–80 subunits. Among VWF multimers, high molecular weight (HMW) multimers play important roles in platelet aggregation. Therefore, their loss induces a hemostatic disorder known as von Willebrand disease (VWD) type 2A. Various cardiovascular diseases, such as aortic stenosis, hypertrophic obstructive cardiomyopathy (HOCM), and several congenital structural diseases, as well as mechanical circulatory support systems, generate excessive high shear stress in the bloodstream. These cause excessive cleavage of VWF multimers resulting in a loss of HMW multimers, known as acquired von Willebrand syndrome (AVWS), a hemostatic disorder similar to VWD type 2A. Bleeding often occurs in the gastrointestinal tract since a fragile angiodysplasia develops associated with these diseases. Radical treatment for AVWS is to remove the pathological high shear causing AVWS.

Effects of plasma glycosyltransferase on the ABO(H) blood group antigens of human von Willebrand factor

Von Willebrand factor (VWF) is one of the plasma protein carrying ABO(H) blood group antigens, but the combining process of these antigens is not clear. In the present study, we examined whether plasma glycosyltransferase affects the blood group antigens on VWF. VWF expressing H-antigen (H-VWF) from blood group O and bovine serum albumin conjugated with H-antigen (H-BSA) were incubated with recombinant α1-3-N-acetylgalactosaminyltransferase (rA-transferase) and A-plasma with or without an additional UDP-GalNAc. Transformed antigens were detected by western blotting and ELISA, using an anti-A antibody. Both H-VWF and H-BSA acquired the A-antigen after incubation with rA-transferase and UDP-GalNAc. Incubation with A-plasma very weakly converted the H-antigen on BSA and VWF to A-antigen only in the presence of supplemented UDP-GalNAc. This conversion was enhanced on desialylation of H-VWF. These results indicate that sugar chains of plasma VWF can be modified by the external glycosyltransferase, but that plasma glycosyltransferase has no effect on the blood group antigens of VWF due to its low activity and the lack of donor sugars. Further, sialic acid residues of VWF may exert a protective effect against post-translational glycosylation. Our results clearly exclude the possibility that blood group antigens of VWF are constructed extracellularly in plasma.

Intravitreal injection of aflibercept, an anti-VEGF antagonist, down-regulates plasma von Willebrand factor in patients with age-related macular degeneration

We investigated the association between von Willebrand factor (VWF) and exudative age-related macular degeneration (AMD) in 114 Japanese patients. Intravitreal injection of vascular endothelial growth factor (VEGF) inhibitor is the most effective therapy for AMD. Therefore, we analyzed changes of VWF antigen (VWF:Ag) and VWF multimers (VWFMs) after intravitreal injection of aflibercept, an anti-VEGF antagonist. The relationship between polymorphisms in complement factor H (p.Y402H and p.I62V) and AMD was previously reported. In our patients, p.I62V, but not p.Y402H, was significantly associated with an increased risk of AMD. Pre-treatment plasma levels of VWF:Ag in patients with AMD were significantly higher than those in controls. Unusually large VWFMs (UL-VWFMs) were detected in the majority of AMD patients with concurrent vitreous or subretinal hemorrhage. After intravitreal injection of aflibercept, plasma levels of VWF:Ag and VEGF-A were significantly decreased. UL-VWFMs disappeared after aflibercept injection in three cases, but persisted even 1 month after injection in the other five cases. In conclusion, plasma VWF:Ag levels were significantly elevated in patients with AMD, and decreased after intravitreal aflibercept injection. VWF may play an important role in the pathophysiology of AMD, and aflibercept might improve AMD by reducing plasma levels of VWF in addition to VEGF-A.

Rapid Restoration of Thrombus Formation and High-Molecular-Weight von Willebrand Factor Multimers in Patients with Severe Aortic Stenosis After Valve Replacement

AIM

Patients with severe aortic stenosis (AS) may have bleeding episodes due to the loss of high-molecular-weight (HMW) von Willebrand factor multimers (VWFMs). The absence of HMW-VWFMs and bleeding tendency are usually corrected after aortic valve replacement (AVR). To investigate the process of VWFM recovery and symptoms in patients with severe AS, we analyzed changes in VWF antigen (VWF:Ag), ADAMTS13 activity (ADAMTS13:AC), and platelet thrombus formation under high shear stress conditions.

METHODS

Nine patients with severe AS undergoing AVR were analyzed.

RESULTS

Evident deficiency of HMW-VWFMs was observed in six patients before surgery, which was rapidly restored within 8 days after AVR. Median levels of VWF:Ag before surgery, on postoperative days (PODs) 1, 8, 15, and 22, and one year after AVR were 78.1%, 130%, 224%, 155%, 134%, and 142%, respectively. In contrast, ADAMTS13:AC was 50.5%, 35.5%, 25.5%, 25.1%, 30.3%, and 84.6%, respectively. Preoperative thrombus formation but not surface coverage was significantly lower than that on POD 22, which was considered as normal level in each patient. Compared with preoperative levels, thrombus volume was significantly lower on POD 1, but rapidly increased by POD 8.

CONCLUSION

Bleeding tendency and loss of HMW-VWFMs observed in patients with severe AS before surgery was rapidly corrected after AVR. Instead, patients were in a VWF-predominant state between POD 8 and 22.

von Willebrand Factor-Rich Platelet Thrombi in the Liver Cause Sinusoidal Obstruction Syndrome following Oxaliplatin-Based Chemotherapy

Oxaliplatin-based chemotherapy is widely used to treat advanced colorectal cancer (CRC). Sinusoidal obstruction syndrome (SOS) due to oxaliplatin is a serious type of chemotherapy-associated liver injury (CALI) in CRC patients. SOS is thought to be caused by the sinusoidal endothelial cell damage, which results in the release of unusually-large von Willebrand factor multimers (UL-VWFMs) from endothelial cells. To investigate the pathophysiology of CALI after oxaliplatin-based chemotherapy, we analyzed plasma concentration of von Willebrand factor (VWF) and the distribution of VWFMs in CRC patients. Twenty-three patients with advanced CRC who received oxaliplatin-based chemotherapy with (n = 6) and without (n = 17) bevacizumab were analyzed. CALI (n = 6) and splenomegaly (n = 9) were found only in patients who did not treated with bevacizumab. Plasma VWF antigen (VWF:Ag) and serum aspartate aminotransferase (AST) levels increased after chemotherapy only in patients without bevacizumab. VWFM analysis in patients who did not receive bevacizumab showed the presence of UL-VWFMs and absence of high molecular weight VWFMs during chemotherapy, especially in those with CALI. In addition, plasma VWF:Ag and AST levels increased after chemotherapy in patients with splenomegaly (n = 9), but not in patients without splenomegaly (n = 14). Histological findings in the liver tissue of patients who did not receive bevacizumab included sinusoidal dilatation and microthrombi in the sinusoids. Many microthrombi were positive for both anti-IIb/IIIa and anti-VWF antibodies. Plasma UL-VWFM levels might be increased by damage to endothelial cells as a result of oxaliplatin-based chemotherapy. Bevacizumab could prevent CALI and splenomegaly through inhibition of VWF-rich platelet thrombus formation.

How do we prevent the vulnerable atherosclerotic plaque from rupturing? Insights from in vivo assessments of plaque, vascular remodeling, and local endothelial shear stress

Coronary atherosclerosis progresses both as slow, gradual enlargement of focal plaque and also as a more dynamic process with periodic abrupt changes in plaque geometry, size, and morphology. Systemic vasculoprotective therapies such as statins, angiotensin-converting enzyme inhibitors, and antiplatelet agents are the cornerstone of prevention of plaque rupture and new adverse clinical outcomes, but such systemic therapies are insufficient to prevent the majority of new cardiac events. Invasive imaging methods have been able to identify both the anatomic features of high-risk plaque and the ongoing pathobiological stimuli responsible for progressive plaque inflammation and instability and may provide sufficient information to formulate preventive local mechanical strategies (eg, preemptive percutaneous coronary interventions) to avert cardiac events. Local endothelial shear stress (ESS) triggers vascular phenomena that synergistically exacerbate atherosclerosis toward an unstable phenotype. Specifically, low ESS augments lipid uptake and catabolism, induces plaque inflammation and oxidation, downregulates the production, upregulates the degradation of extracellular matrix, and increases cellular apoptosis ultimately leading to thin-cap fibroatheromas and/or endothelial erosions. Increases in blood thrombogenicity that result from either high or low ESS also contribute to plaque destabilization. An understanding of the actively evolving vascular phenomena, as well as the development of in vivo imaging methodologies to identify the presence and severity of the different processes, may enable early identification of a coronary plaque destined to acquire a high-risk state and allow for highly selective, focal preventive interventions to avert the adverse natural history of that particular plaque. In this review, we focus on the role of ESS in the pathobiologic processes responsible for plaque destabilization, leading either to accelerated plaque growth or to acute coronary events, and emphasize the potential to utilize in vivo risk stratification of individual coronary plaques to optimize prevention strategies to preclude new cardiac events.

Changes in plasma von Willebrand factor and ADAMTS13 levels associated with left atrial remodeling in atrial fibrillation

INTRODUCTION

Previous studies have shown raised plasma von Willebrand factor (VWF) levels in patients with atrial fibrillation (AF). However, little is known about changes of VWF associated with VWF-cleaving protease (ADAMTS13) in AF. The aim of this study was to examine the relationship between changes in plasma VWF and ADAMTS13 levels, and left atrial remodeling in AF patients.

MATERIALS AND METHODS

We measured plasma VWF and ADAMTS13 antigen levels in 70 paroxysmal AF (PAF) patients, 56 chronic AF (CAF) patients, and 55 control subjects.

RESULTS

Plasma VWF levels (mU/ml) were significantly higher in CAF and PAF patients compared with the controls (2103 +/- 743, 1930 +/- 676, 1532 +/- 555, respectively, P < 0.0001 in CAF vs. controls, P = 0.001 in PAF vs. control), while ADAMTS13 levels (mU/ml) were significantly lower in CAF and PAF patients compared with the controls (795 +/- 169, 860 +/- 221, 932 +/- 173, respectively, P = 0.0002 in CAF vs. controls, P = 0.04 in PAF vs. control). The VWF/ADAMTS13 ratio was significantly higher in patients with CAF than PAF or controls (2.81 +/- 1.30, 2.34 +/- 0.92, 1.73 +/- 0.83, respectively; P = 0.01 in CAF vs. PAF, P < 0.0001 in CAF vs. controls). There was a significant correlation between the VWF/ADAMTS13 ratio and left atrial diameter (positive correlation; r = 0.275, P = 0.0002) and left atrial appendage flow velocity (negative correlation; r = -0.345, P = 0.0018).

CONCLUSIONS

These findings suggest that the imbalance between plasma VWF and ADAMTS13 levels caused by left atrial remodeling might be closely associated with intra-atrial thrombus formation in AF patients.

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

INTRODUCTION

Increased plasma levels of von Willebrand factor (VWF) have been reported in acute myocardial infarction (AMI). Recently, we showed reduced activity of a VWF-cleaving protease (ADAMTS13) in AMI patients. However, there is no information as to whether ADAMTS13 affects the pathogenesis of unstable angina (UA). Thus, the purpose of this study was to examine changes in plasma VWF and ADAMTS13 levels in UA patients.

MATERIALS AND METHODS

Plasma VWF and ADAMTS13 levels (mU/ml) were measured in 45 patients with UA, 55 with stable exertional angina (SEA) and 47 with chest pain syndrome (CPS) at the time of coronary angiography. Levels were also measured in 15 UA patients after 6 months of follow-up.

RESULTS

VWF antigen levels (mU/ml) increased significantly in UA patients compared with SEA or CPS (2129.3+/-739.5, 1571.8+/-494.2 and 1569.5+/-487.0, respectively; P < 0.0001 in UA vs. SEA or CPS). ADAMTS13 antigen levels (mU/ml) were significantly lower in UA patients than SEA or CPS (737.3+/-149.5, 875.3+/-229.0 and 867.7+/-195.5, respectively; P < 0.01 in UA vs. SEA or CPS). Furthermore, there was a significant inverse correlation between VWF and ADAMTS13 antigen levels (r = -0.302, P = 0.0002). The antigen levels at 6 months of follow-up were not different compared to the acute phase in the 15 UA patients that had repeated blood sampling.

CONCLUSIONS

These findings suggest that there is prolonged thrombogenicity in UA patients represented as an imbalance between VWF and ADAMTS13 activity.

Prophylactic fresh frozen plasma may prevent development of hepatic VOD after stem cell transplantation via ADAMTS13-mediated restoration of von Willebrand factor plasma levels

We initially conducted a multicenter, randomized trial (n=43), and subsequently a questionnaire study (n=209) of participating hospitals, to evaluate whether infused fresh frozen plasma (FFP) could prevent the occurrence of hepatic veno-occlusive disease (VOD) after stem cell transplantation (SCT). Forty-three patients were divided into two groups: 23 receiving FFP infusions and 20 not receiving it. VOD developed in three patients not receiving FFP. Plasma von Willebrand factor (VWF) antigen levels were lower at days 0, 7 and 28 after SCT in patients receiving FFP than in those not receiving it, whereas plasma ADAMTS13 activity (ADAMTS13:AC) did not differ between them. Plasma VWF multimer (VWFM) was demonstrated to be defective in the high approximately intermediate VWFM during the early post-SCT phase, but there was a significant increase in high VWFM just before VOD onset. This suggests that a relative enzyme-to-substrate (ADAMTS13/high-VWFM) imbalance is involved in the pathogenesis of VOD. To strengthen this hypothesis, the incidence of VOD was apparently lower in patients receiving FFP infusions than in those not receiving it (0/23 vs 3/20) in the randomized trial. Further, the results combined with the subsequent questionnaire study (0/36 vs 11/173) clearly showed the incidence to be statistically significant (0/59 vs 14/193, P=0.033).

Structural and functional correlation of ADAMTS13

PURPOSE OF REVIEW

ADAMTS13 represents a landmark in a journey that began over 80 years ago with a single clinical case. Thrombotic thrombocytopenic purpura exemplifies how von Willebrand factor can be responsible for life-threatening thrombosis. This review summarizes recent progress on ADAMTS13, which prevents this deadly event.

RECENT FINDINGS

Recent advances are summarized in four main areas. First, the core ADAMTS13-binding site is contained in a short sequence in the A2 domain, but other domains affect this interaction. Mutations from thrombotic thrombocytopenic purpura and von Willebrand disease provide clues for the structural prerequisites and regulation of von Willebrand factor cleavage. Second, studies are unraveling the reasons why urea, BaCl2, and low ionic strength are required to cleave von Willebrand factor under static conditions. Third, studies on thrombotic thrombocytopenic purpura and ADAMTS13-knockout mice suggest that ADAMTS13 deficiency alone may not be sufficient to cause thrombotic thrombocytopenic purpura. Finally, ADAMTS13 could be an antithrombotic agent for thrombotic thrombocytopenic purpura and other thrombotic conditions.

SUMMARY

Study of ADAMTS13 has exploded since this metalloprotease was characterized. This knowledge reveals the nature of ADAMTS13's interaction with von Willebrand factor and the pathogenesis of clinical thrombotic thrombocytopenic purpura, especially in relation to ADAMTS13.