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Castaman G.,San Bortolo Hospital | Tosetto A.,San Bortolo Hospital | Goodeve A.,University of Sheffield | Federici A.B.,Foundation IRCCS Maggiore Policlinico Hospital | And 13 more authors.
British Journal of Haematology | Year: 2010

The relationships between the Platelet Function Analyzer (PFA)-100 and von Willebrand factor (VWF) levels and bleeding score (BS) were evaluated within a multicentre project on Molecular and Clinical Markers for the Diagnosis and Management of type 1 von Willebrand disease (MCMDM- 1VWD). PFA-100 closure time, either with epinephrine (EPI) or adenosine diphosphate (ADP)-cartridges, was measured in 107 index cases, 105 affected and 71 unaffected family members, and 79 healthy controls. By regression analysis VWF levels were strongly related to both closure times, with a nonlinear progression. In a multiple stepwise regression model, age- and sexadjusted PFA-100 ADP and VWF ristocetin cofactor activity (VWF:RCo) were independently associated with BS. Most of the variation of BS was predicted by PFA-100 ADP and VWF:RCo alone. In the subgroup of patients with subtle abnormalities of the multimeric pattern, VWF was invariably reduced and closure time prolonged in almost all of them. Neither PFA-100 ADP nor EPI closure times appeared to significantly improve the diagnostic capability of VWF antigen (VWF:Ag) measurement. Thus, in an unselected population a normal PFA-100 would be useful to exclude VWD, but whether it could replace the more specific VWF assay in patients with significant mucocutaneous bleeding symptoms remains to be investigated prospectively. © 2010 Blackwell Publishing Ltd.


Abdo A.A.,King Saud University | Sanai F.M.,Riyadh Military Hospital | Azzam N.,King Saud University | Al Sawat K.,King Saud University | And 4 more authors.
Blood Coagulation and Fibrinolysis | Year: 2010

Protein S (PS), protein C (PC), and antithrombin (AT) are produced by the liver, and their levels were previously shown to be reduced in chronic as well as acute liver disease. The aim of this study was to determine whether measurement of PS, PC, and AT levels in patients would be as good as the commonly used clinical and histological parameters of liver disease in discriminating early and advanced hepatocyte dysfunction. A total of 154 patients were recruited and categorized into five groups: hepatitis B inactive carriers in group 1 (n = 29), nonalcoholic steatohepatitis patients in group 2 (n = 30), chronic hepatitis B patients with elevated liver enzymes in group 3 (n = 29), chronic hepatitis C patients with elevated liver enzymes in group 4 (n = 30), liver cirrhosis patients in group 5 (n = 36). There were significant differences between groups in the levels of PC (P = 0.0001), total PS (P = 0.0001), and free PS (P = 0.0001) and AT (P = 0.0001). These parameters were least affected in the control group, then groups 1 and 2, followed by groups 3 and 4, and most affected in group 5. No differences in these tests were detected between groups 1 and 2 and between groups 3 and 4. Univariate and multivariate analyses showed that free PS was the only predictor of significant inflammation (P = 0.0001), and AT (P = 0.001) and PC (P = 0.003) were the most important factors associated with advanced fibrosis. Both PS and PC are sensitive markers of liver disease, but PS is a sensitive marker of liver inflammation, whereas PC may be a more sensitive marker for liver fibrosis. © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins.


Haberichter S.L.,Medical College of Wisconsin | Budde U.,Coagulation Laboratory | Obser T.,University of Hamburg | Schneppenheim S.,Coagulation Laboratory | And 2 more authors.
Blood | Year: 2010

We characterized a consanguineous Turkish family suffering from von Willebrand disease (VWD) with significant mucocutaneous and joint bleeding. The relative reduction of large plasma von Willebrand factor (VWF) multimers and the absent VWF triplet structure was consistent with type 2A (phenotype IIC) VWD. Surprisingly, platelet VWF was completely deficient of multimers beyond the VWF protomer, suggesting defective α-granular storage of larger multimers. Patients were nearly unresponsive to desmopressin acetate, consistent with a lack of regulated VWF release from endothelial cell Weibel-Palade bodies, suggesting defective storage also in endothelial cells. We identified an N528S homozygous mutation in the VWF propeptide D2 domain, predicting the introduction of an additional N-glycosylation site at amino acid 526 in close vicinity to a "CGLC" disulphide isomerase consensus sequence. Expression studies in mammalian cells demonstrated that N528S-VWF was neither normally multimerized nor trafficked to storage granules. However, propeptide containing the N528S mutation trafficked normally to storage granules. Our data indicate that the patients' phenotype is the result of defective multimerization, storage, and secretion. In addition, we have identified a potentially novel pathogenic mechanism of VWD, namely a transportation and storage defect of mature VWF due to defective interaction with its transporter, the mutant propeptide. © 2010 by The American Society of Hematology.


Giordano P.,University of Bari | Tesse R.,University of Bari | Lassandro G.,University of Bari | Fracchiolla D.,University of Bari | And 4 more authors.
Blood Transfusion | Year: 2012

Background. It is difficult to estimate the actual prevalence of antiphospholipid syndrome (APS) in the paediatric population since there are no standardised criteria. We aimed to assess clinical and laboratory characteristics of a cohort of children positive for antiphospholipid antibodies (aPL) to contribute to the understanding of the heterogeneous aPL-related features in childhood. Materials and methods. Forty-four patients with prolonged activated partial thromboplastin time were enrolled and assigned to group I ("transiently positive") or group II ("persistently positive"), based on the detection of elevated aPL plasma levels [lupus anticoagulant (LA), anticardiolipin (aCL), and anti-β2-glycoprotein I (anti-β2GPI) antibodies] on, respectively, one or more occasions, at least 12 weeks apart, by standard procedures. The clinical history and symptoms of all patients were recorded. Results. Thirty-three (75%) patients were assigned to group I, while the other 11 (25%) formed group II. Major associated diseases in group I were urticarial vasculitis (21%), acute infections (18%) and thalassaemia (12%). Five subjects (15%) were asymptomatic. Four out of the 11 subjects (36%) in group II had thrombotic events; they were all persistently aPL-positive and two of them had concomitant systemic lupus erythematosus. The rate of detection of LA-positivity was not signifi cantly different between the two groups (76% vs 91%, p>0.05), whereas the percentage of patients positive for overall aCL was higher in group II than in group I (54% vs 42%, respectively; p<0.05). Specifi cally, aCL IgG and anti-β2GPI IgM subtypes were signifi cantly more represented in group II than in group I (100% vs 62% and 75% vs 33%, respectively; p<0.05). Discussion. Our study shows that aPL-positive children have different features that should be taken into account in the classifi cation of criteria for paediatric APS. © SIMTI Servizi Srl.


Lippok S.,Ludwig Maximilians University of Munich | Radtke M.,Free University of Berlin | Obser T.,University of Hamburg | Kleemeier L.,Ludwig Maximilians University of Munich | And 4 more authors.
Biophysical Journal | Year: 2016

Proteolysis of the multimeric blood coagulation protein von Willebrand Factor (VWF) by ADAMTS13 is crucial for prevention of microvascular thrombosis. ADAMTS13 cleaves VWF within the mechanosensitive A2 domain, which is believed to open under shear flow. In this study, we combine fluorescence correlation spectroscopy (FCS) and a microfluidic shear cell to monitor real-time kinetics of full-length VWF proteolysis as a function of shear stress. For comparison, we also measure the Michaelis-Menten kinetics of ADAMTS13 cleavage of wild-type VWF in the absence of shear but partially denaturing conditions. Under shear, ADAMTS13 activity on full-length VWF arises without denaturing agent as evidenced by FCS and gel-based multimer analysis. In agreement with Brownian hydrodynamics simulations, we find a sigmoidal increase of the enzymatic rate as a function of shear at a threshold shear rate γË™1/2 = 5522/s. The same flow-rate dependence of ADAMTS13 activity we also observe in blood plasma, which is relevant to predict hemostatic dysfunction. © 2016 Biophysical Society.


Lippok S.,Ludwig Maximilians University of Munich | Obser T.,University of Hamburg | Muller J.P.,Ludwig Maximilians University of Munich | Stierle V.K.,Ludwig Maximilians University of Munich | And 4 more authors.
Biophysical Journal | Year: 2013

Von Willebrand Factor (VWF) is a multimeric protein crucial for hemostasis. Under shear flow, it acts as a mechanosensor responding with a size-dependent globule-stretch transition to increasing shear rates. Here, we quantify for the first time, to our knowledge, the size distribution of recombinant VWF and VWF-eGFP using a multilateral approach that involves quantitative gel analysis, fluorescence correlation spectroscopy, and total internal reflection fluorescence microscopy. We find an exponentially decaying size distribution of multimers for recombinant VWF as well as for VWF derived from blood samples in accordance with the notion of a step-growth polymerization process during VWF biosynthesis. The distribution is solely described by the extent of polymerization, which was found to be reduced in the case of the pathologically relevant mutant VWF-IIC. The VWF-specific protease ADAMTS13 systematically shifts the VWF size distribution toward smaller sizes. This dynamic evolution is monitored using fluorescence correlation spectroscopy and compared to a computer simulation of a random cleavage process relating ADAMTS13 concentration to the degree of VWF breakdown. Quantitative assessment of VWF size distribution in terms of an exponential might prove to be useful both as a valuable biophysical characterization and as a possible disease indicator for clinical applications. © 2013 Biophysical Society.


PubMed | Ludwig Maximilians University of Munich, Free University of Berlin, Coagulation Laboratory and University of Hamburg
Type: Journal Article | Journal: Biophysical journal | Year: 2016

Proteolysis of the multimeric blood coagulation protein von Willebrand Factor (VWF) by ADAMTS13 is crucial for prevention of microvascular thrombosis. ADAMTS13 cleaves VWF within the mechanosensitive A2 domain, which is believed to open under shear flow. In this study, we combine fluorescence correlation spectroscopy (FCS) and a microfluidic shear cell to monitor real-time kinetics of full-length VWF proteolysis as a function of shear stress. For comparison, we also measure the Michaelis-Menten kinetics of ADAMTS13 cleavage of wild-type VWF in the absence of shear but partially denaturing conditions. Under shear, ADAMTS13 activity on full-length VWF arises without denaturing agent as evidenced by FCS and gel-based multimer analysis. In agreement with Brownian hydrodynamics simulations, we find a sigmoidal increase of the enzymatic rate as a function of shear at a threshold shear rate 1/2= 5522/s. The same flow-rate dependence of ADAMTS13 activity we also observe in blood plasma, which is relevant to predict hemostatic dysfunction.


Feys H.B.,Catholic University of Leuven | Roodt J.,University of the Free State | Roodt J.,Universitas Hospital | Vandeputte N.,Catholic University of Leuven | And 10 more authors.
Blood | Year: 2010

Thrombotic thrombocytopenic purpura (TTP) is the prototypical microangiopathy characterized by disseminated microthromboses, hemolytic anemia, and ultimately organ dysfunction. A link with deficiency of the von Willebrand factor - cleaving protease (ADAMTS13) has been demonstrated, but additional genetic and/or environmental triggers are thought to be required to incite acute illness. Here we report that 4 days of ADAMTS13 functional inhibition is sufficient to induce TTP in the baboon (Papio ursinus), in the absence of inciting triggers because injections with an inhibitory monoclonal antibody (mAb) consistently (n = 6) induced severe thrombocytopenia (< 12 × 109/L), microangiopathic hemolytic anemia, and a rapid rise in serum lactate dehydrogenase. Immunohistochemical staining revealed the characteristic disseminated platelet- and von Willebrand factor - rich thrombi in kidney, heart, brain, and spleen but not lungs. Prolonged inhibition (14 days, n = 1) caused myocardial ischemic damage and asplenia but not death. Control animals (n = 5) receiving equal doses of a noninhibitory anti-ADAMTS13 mAb remained unaffected. Our results provide evidence for a direct link between TTP and ADAMTS13 inhibition and for a mild disease onset. Furthermore, we present a reliable animal model of this disease as an opportunity for the development and validation of novel treatment strategies. © 2010 by The American Society of Hematology.

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