And Metalloprotease With ThromboSpondin Type 1 Repeats Research Articles

ADAMTS13-Mediated Proteolytic Cleavage of Unusually Large von Willebrand Factor Polymers on Endothelial Cells in the Absence of Fluid Shear Stress

To investigate the molecular mechanism of proteolytic cleavage of unusually large von Willebrand Factor(ULVWF) on endothelial cells by ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats-13) in the absence of fluid shear stress, so as to provide a theoretical basis for the pathogenesis of thrombotic thrombocytopenic purpura (TTP) and other thrombotic disorders. The ADAMTS13-mediated proteolysis of ULVWF on the surface of endothelial cells in the absence of fluid shear stress was observed through immunofluorescence microscopy. The variation in VWF antigen levels in the conditioned media were determined by ELISA assay. The levels of VWF and the proteolytic fragments released into the conditioned media were determined by ELISA assay and Western blot in the absence and presence of fluid shear stress or FVIII. The effect of ADAMTS13-mediated ULVWF cleavage on the normal distribution of plasma VWF multimers was evaluated by multimer analysis. Histamine stimulated human umbilical vein endothelial cells (HUVECs) were incubated with ADAMTS13 and various N- and C-terminally truncated mutants. Then the ULVWF that maintained binding to the cells were observed through immunofluorescence microscopy and the soluble ULVWF released from endothelial cells was determined by ELISA, so as to demonstrate the domains of ADAMTS13 required for proteolysis of ULVWF on endothelial cells. The ULVWF strings on the endothelial cell surface were rapidly proteolyzed by recombinant and plasma ADAMTS13 in the absence of fluid shear stress. This proteolytic processing of ULVWF depended on incubation time and ADAMTS13 concentration, but not shear stress and FVIII. The distribution of VWF releaseded by ADAMTS13-mediated proteolysis was quite similar to that secreted by endothelial cells under histamine stimulation, suggesting the ULVWF cleavage occured at the cell surface. The proteolysis of the ULVWF on endothelial cells required the Cys-rich(CysR) and spacer domains, but not the TSP1 2-8 and CUB domains of ADAMTS13. The ULVWF polymers on endothelial cells are sensitive to ADAMTS13-mediated cleavage even in the absence of fluid shear stress. The findings provide novel insight into the molecular mechanism of ADAMTS13-mediated ULVWF cleavage at the cellular level and may contribute to understanding of the pathogenesis of TTP and other thrombotic disorders.

Biological Function of CysR Domain of ADAMTS13

To investigate the biological function of Cysteine rich (CysR) domain of a disintegrin and metalloprotease with thrombospondin type 1 repeats-13 (ADAMTS13) on cleavage of von Willebrand factor (vWF) and provide experimental evidence for exploring the pathogenesis of thrombotic thrombocytopenic purpura (TTP). The six amino acids (EDGTLS) in ADAMTS13 CysR domain were point mutated one by one, and the mutant ADAMTS13 proteins were expressed and purified. The cleavage products of vWF polymer by wild-type or mutant ADAMTS13 under denaturing condition or shear stress were separated by 1% SeaKem HGT agarose gel and detected by Western blot. The mutant ADAMTS13 plasmids (M1: Glu515Ala; M2: Asp516Ala; M3: Gly517Ala; M4: Thr518Ala; M5: Leu519Ala; M6: Ser520Ala) were successfully constructed and the proteins of wild-type and mutant ADAMTS13 were purified. Wild-type ADAMTS13 almost completely cleaved the vWF polymer under denaturing condition, while the cleavage activity of M1 mutant was significantly reduced in the same condition (P<0.01). The cleavage activity of M1 mutant of ADAMTS13 was also significantly reduced compared with that of the wild-type under shear stress (P<0.01). The activity of M1 mutant to cleave the FRETS-vWF73 was dramatically reduced compared with that of wild-type ADAMTS13. However, the binding ability of M1 mutant to vWF was similar with that of wild-type ADAMTS13. The CysR domain of ADAMTS13 plays an important role in the digestion of vWF under denaturing condition and shear stress. The Glu515 amino acid residue might be an important site for substrate recognition.

Unresponsive Thrombotic Thrombocytopenic Purpura (TTP): Challenges and Solutions.

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy secondary to a severely decreased A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats 13 (ADAMTS13) activity, resulting in the formation of widespread von Willebrand factor - and platelet-rich microthrombi. ADAMTS13 deficiency is mainly acquired through anti-ADAMTS13 autoantibodies in adults. With modern standards of care, unresponsive TTP has become rarer with a frequency of refractory/relapsing forms dropping from >40% to <10%. As patients with unresponsive TTP are at increased risk of mortality, prompt recognition and early therapeutic intensification are mandatory. Therapeutic options at the disposal of clinicians caring for patients with refractory TTP consist of increased ADAMTS13 supplementation, increased immunosuppression, and inhibition of von Willebrand factor adhesion to platelets. In this work, we focus on possible therapies for the management of patients with unresponsive TTP, and propose an algorithm for the management of these difficult cases.

Recent Advances in the Understanding of Thrombosis.

Recent Advances in the Understanding of Thrombosis.

The Importance of the Knee Joint Meniscal Fibrocartilages as Stabilizing Weight Bearing Structures Providing Global Protection to Human Knee-Joint Tissues.

The aim of this study was to review aspects of the pathobiology of the meniscus in health and disease and show how degeneration of the meniscus can contribute to deleterious changes in other knee joint components. The menisci, distinctive semilunar weight bearing fibrocartilages, provide knee joint stability, co-ordinating functional contributions from articular cartilage, ligaments/tendons, synovium, subchondral bone and infra-patellar fat pad during knee joint articulation. The meniscus contains metabolically active cell populations responsive to growth factors, chemokines and inflammatory cytokines such as interleukin-1 and tumour necrosis factor-alpha, resulting in the synthesis of matrix metalloproteases and A Disintegrin and Metalloprotease with ThromboSpondin type 1 repeats (ADAMTS)-4 and 5 which can degrade structural glycoproteins and proteoglycans leading to function-limiting changes in meniscal and other knee joint tissues. Such degradative changes are hall-marks of osteoarthritis (OA). No drugs are currently approved that change the natural course of OA and translate to long-term, clinically relevant benefits. For any pharmaceutical therapeutic intervention in OA to be effective, disease modifying drugs will have to be developed which actively modulate the many different cell types present in the knee to provide a global therapeutic. Many individual and combinatorial approaches are being developed to treat or replace degenerate menisci using 3D printing, bioscaffolds and hydrogel delivery systems for therapeutic drugs, growth factors and replacement progenitor cell populations recognising the central role the menisci play in knee joint health.

Correction to: Transfusion of Platelets Loaded With Recombinant ADAMTS13 (A Disintegrin and Metalloprotease With Thrombospondin Type 1 Repeats-13) Is Efficacious for Inhibiting Arterial Thrombosis Associated With Thrombotic Thrombocytopenic Purpura.

HomeArteriosclerosis, Thrombosis, and Vascular BiologyVol. 39, No. 1Correction to: Transfusion of Platelets Loaded With Recombinant ADAMTS13 (A Disintegrin and Metalloprotease With Thrombospondin Type 1 Repeats-13) Is Efficacious for Inhibiting Arterial Thrombosis Associated With Thrombotic Thrombocytopenic Purpura Free AccessCorrectionPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessCorrectionPDF/EPUBCorrection to: Transfusion of Platelets Loaded With Recombinant ADAMTS13 (A Disintegrin and Metalloprotease With Thrombospondin Type 1 Repeats-13) Is Efficacious for Inhibiting Arterial Thrombosis Associated With Thrombotic Thrombocytopenic Purpura Originally published26 Dec 2018https://doi.org/10.1161/ATV.0000000000000074Arteriosclerosis, Thrombosis, and Vascular Biology. 2019;39:e29This article corrects the followingTransfusion of Platelets Loaded With Recombinant ADAMTS13 (A Disintegrin and Metalloprotease With Thrombospondin Type 1 Repeats-13) Is Efficacious for Inhibiting Arterial Thrombosis Associated With Thrombotic Thrombocytopenic PurpuraIn the article by Abdelgawwad et al, “Transfusion of Platelets Loaded With Recombinant ADAMTS13 (A Disintegrin and Metalloprotease With Thrombospondin Type 1 Repeats-13) Is Efficacious for Inhibiting Arterial Thrombosis Associated With Thrombotic Thrombocytopenic Purpura,” which published in the November 2018 issue of the journal (Arterioscler Thromb Vasc Biol. 2018;38:2731–2743. DOI: 10.1161/ATVBAHA.118.311407), a correction was needed.In Figure 2, panels G, H, and I, the “WP” labeling is not correct. The panels should have been labeled with “αG,” which indicates platelet α-granules.The authors apologize for the error.This correction has been made to the current online version of the article, which is available at http://atvb.ahajournals.org/content/38/11/2731. Previous Back to top Next FiguresReferencesRelatedDetailsRelated articlesTransfusion of Platelets Loaded With Recombinant ADAMTS13 (A Disintegrin and Metalloprotease With Thrombospondin Type 1 Repeats-13) Is Efficacious for Inhibiting Arterial Thrombosis Associated With Thrombotic Thrombocytopenic PurpuraMohammad S. Abdelgawwad, et al. Arteriosclerosis, Thrombosis, and Vascular Biology. 2018;38:2731-2743 January 2019Vol 39, Issue 1 Advertisement Article InformationMetrics © 2018 American Heart Association, Inc.https://doi.org/10.1161/ATV.0000000000000074PMID: 30586332 Originally publishedDecember 26, 2018 PDF download Advertisement

Transfusion of Platelets Loaded With Recombinant ADAMTS13 (A Disintegrin and Metalloprotease With Thrombospondin Type 1 Repeats-13) Is Efficacious for Inhibiting Arterial Thrombosis Associated With Thrombotic Thrombocytopenic Purpura.

Objective- ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats-13) cleaves VWF (von Willebrand factor). This process is essential for hemostasis. Severe deficiency of plasma ADAMTS13 activity, most commonly resulting from autoantibodies against ADAMTS13, causes thrombotic thrombocytopenic purpura. Therapeutic plasma exchange is the standard of care to date, which removes autoantibodies and replenishes ADAMTS13. However, such a therapy is often ineffective to raise plasma ADAMTS13 activity, and in-hospital mortality rate remains as high as 20%. Approach and Results- To overcome the inhibition by autoantibodies, we developed a novel approach by delivering rADAMTS13 (recombinant ADAMTS13 ) using platelets as vehicles. We show that both human and murine platelets can uptake rADAMTS13 ex vivo. The endocytosed rADAMTS13 within platelets remains intact, active, and is stored in α-granules. Under arterial shear (100 dyne/cm2), the rADAMTS13 in platelets is released and effectively inhibits platelet adhesion and aggregation on a collagen-coated surface in a concentration-dependent manner. Transfusion of rADAMTS13-loaded platelets into Adamts13-/- mice dramatically reduces the rate of thrombus formation in the mesenteric arterioles after FeCl3 injury. An ex vivo transfusion of rADAMTS13-loaded platelets to a reconstituted whole blood containing plasma from a patient with immune-mediated thrombotic thrombocytopenic purpura and the cellular components (eg, erythrocytes and leukocytes) from a healthy individual, as well as a fresh whole blood obtained from a patient with congenital or immune-mediated thrombotic thrombocytopenic purpura also dramatically reduces the rate of thrombus formation under arterial flow. Conclusions- Our results demonstrate that transfusion of rADAMTS13-loaded platelets may be a novel and potentially effective therapeutic approach for arterial thrombosis, associated with congenital and immune-mediated thrombotic thrombocytopenic purpura.

Relative Deficiency of Plasma A Disintegrin and Metalloprotease with Thrombospondin Type 1 Repeats 13 Activity and Elevation of Human Neutrophil Peptides in Patients with Traumatic Brain Injury.

Traumatic microvascular injury (tMVI) is a universal endophenotype of traumatic brain injury (TBI) that is responsible for significant neurological morbidity and mortality. The mechanism underlying tMVI is not fully understood. The present study aims to determine plasma levels of von Willebrand factor (VWF), a disintegrin and metalloprotease with thrombospondin type 1 repeats (ADAMTS) 13 activity, and human neutrophil peptides (HNP) 1-3 and to correlate these biomarkers with functional outcomes after moderate-severe TBI. Thirty-one consecutive TBI patients (Glasgow Coma Scale [GCS] range, 3-12) were enrolled into the study between February 2010 and November 2014. Blood samples were collected on 0, 1, 2, 3, and 5 days after admission and analyzed for plasma levels of VWF antigen (VWFAg), collagen-binding activity (VWFAc), ADAMTS13 activity, and HNP1-3 proteins. Mean values of plasma VWFAg, VWFAc, and HNP1-3 were significantly increased in TBI patients compared to those in healthy controls (n = 30). Conversely, mean plasma values of ADAMTS13 activity in TBI patients were significantly decreased during the first 2 days after admission. This resulted in a dramatic reduction in the ratio of ADAMTS13 activity to VWFAg or ADAMTS13 to VWFAc in all 5 post-TBI days. Cluster analysis demonstrated that high median plasma levels of VWFAg and HNP1-3 were observed in the cluster with a high mortality rate. These results demonstrate that a relative deficiency of plasma ADAMTS13 activity, resulting from activation of neutrophils and endothelium, may contribute to the formation of microvascular thrombosis and mortality after moderate-severe TBI.

Hypercoagulability progresses to hypocoagulability during evolution of acetaminophen-induced acute liver injury in pigs

Increases in prothrombin time (PT) and international normalised ratio (INR) characterise acute liver injury (ALI) and failure (ALF), yet a wide heterogeneity in clotting abnormalities exists. This study defines evolution of coagulopathy in 10 pigs with acetaminophen (APAP)-induced ALI compared to 3 Controls. APAP administration began at 0 h and continued to ‘ALF’, defined as INR >3. In APAP pigs, INR was 1.05 ± 0.02 at 0 h, 2.15 ± 0.43 at 16 h and > 3 at 18 ± 1 h. At 12 h thromboelastography (TEG) demonstrated increased clot formation rate, associated with portal vein platelet aggregates and reductions in protein C, protein S, antithrombin and A Disintegrin and Metalloprotease with Thrombospondin type 1 repeats–13 (ADAMTS-13) to 60%, 24%, 47% and 32% normal respectively. At 18 ± 1 h, INR > 3 was associated with: hypocoagulable TEG profile with heparin-like effect; falls in thrombin generation, Factor V and Factor VIII to 52%, 19% and 17% normal respectively; further decline in anticoagulants; thrombocytopenia; neutrophilia and endotoxemia. Multivariate analysis, found that ADAMTS-13 was an independent predictor of a hypercoagulable TEG profile and platelet count, endotoxin, Protein C and fibrinogen were independent predictors of a hypocoagulable TEG profile. INR remained normal in Controls. Dynamic changes in coagulation occur with progression of ALI: a pro-thrombotic state progresses to hypocoagulability.

Mutations in Coagulation Factor VIII Are Associated with More Favorable Outcome in Patients with Cutaneous Melanoma.

Coagulation factor VIII (FVIII), von Willebrand factor (VWF), and ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats 13) play an important role in the regulation of normal hemostasis. However, little is known about their roles in patients with malignancy, particularly with cutaneous melanoma. Whole genome sequencing data are available for 25,719 cases in 126 cancer genomic studies for analysis. All sequencing data and corresponding pathology findings were obtained from The Cancer Genome Atlas. The cBioPortal bioinformatics tools were used for the data analysis. Our results demonstrated that mutations in genes encoding FVIII , VWF , and ADAMTS13 were reported in 92 of 126 cancer genomic studies, and high mutation rates in these three genes were observed in patients with cutaneous melanoma from three independent studies. Moreover, high mutation rates in FVIII , VWF , and ADAMTS13 were also found in patients with diffuse large B cell lymphoma (22.9%), lung small cell carcinoma (20.7%), and colon adenocarcinoma (19.4%). Among 366 melanoma cases from TCGA provisional, the somatic mutation rates of FVIII , VWF , and ADAMTS13 in tumor cells were 15, 14, and 5%, respectively. There was a strong tendency for coexisting mutations of FVIII , VWF , and ADAMTS13 . Kaplan–Meier survival analysis demonstrated that melanoma patients with FVIII mutations had a more favorable overall survival rate than those without FVIII mutations ( p = 0.02). These findings suggest, for the first time, that the FVIII mutation burden may have a prognostic value for patients with cutaneous melanoma. Further studies are warranted to delineate the molecular mechanisms underlying the favorable prognosis associated with FVIII mutations.

Change in plasma a disintegrin and metalloprotease with thrombospondin type-1 repeats-13 and von Willebrand factor levels in venous thromboembolic patients

Objectives: Venous thromboembolism (VTE) is an important cause of morbidity and mortality. A disintegrin and metalloprotease with thrombospondin type-1 repeats-13 (ADAMTS-13) is a metalloprotease that cleaves plasma von Willebrand factor (VWF) multimers. The presence of large VWF multimers in the plasma due to ADAMTS-13 deficiency is the main factor in the pathogenesis of thrombotic thrombocytopenic purpura. The present study aimed to investigate the relation of plasma levels of ADAMTS-13 and VWF antigen with VTE.Methods: The present study included 30 patients with VTE and age- and gender-matched 30 healthy subjects. Patients with any condition (diabetes, icterus, hyperlipidemia, physical, or surgical trauma, acute coronary syndrome, pregnancy, renal insufficiency, liver disease, malignancy, collagen tissue disease, chronic or acute inflammation, drug use affecting thrombocyte function) that could affect plasma VWF antigen or ADAMTS-13 levels were excluded. Plasma ADAMTS-13 and VWF antigen levels in the VTE and control groups were quantitatively determined by enzyme-linked immunosorbent assay method.Results: The median ADAMTS-13 level was 280 ng/ml (minimum–maximum, 70–1120 ng/ml) in the VTE group and 665 ng/ml (minimum–maximum, 350–2500 ng/ml) in the control group; the difference between the groups was significant (P < 0.0001). The mean VWF antigen level was 1750 ± 616 mU/ml in the patient group, which was significantly higher than that of the control group (950 ± 496 mU/ml) (P < 0.0001).Conclusion: Significantly lower ADAMTS-13 levels and significantly higher VWF antigen levels were concluded to be the result of a pathological process rather than an etiological factor for VTE.

Neutrophil Recruitment Is Regulated By Adamts-13 in a Murine Model of Invasive Aspergillosis

▪Introduction: During inflammation von Willebrand factor (VWF) multimers are secreted as an acute phase protein whereupon the size and the prothrombotic activity play an essential role. The size of VWF multimers is regulated by the specific proteolytic activity of ADAMTS-13 (a disintegrin and metalloprotease with ThromboSpondin type 1 repeats-13) which is diminished under several pathological conditions. Employing a murine model of invasive pulmonary aspergillosis (IPA) we aimed to determine the relevance of this regulatory pathway for innate inflammatory responses and polymorphonuclear neutrophil (PMN) recruitment which is crucial for fungal clearance and survival.Methods: IPA was induced by intratracheal application of Aspergillus fumigatus (A. fumigatus) conidia in wildtype (129/Sv/Pas) or Adamts13 deficient (Adamts13-/-) mice. 24 h after infection some mice were sacrificed for analysis of fungal load and histology. To assess fungal load as CFU lung homogenates were plated and cultured on Sabourough agar plates. Paraffin sections of the lungs were prepared and stained with mouse complement component C3d antibody for histological analysis. In addition, degranulation, oxidative burst activity and CD62L shedding were assessed in PMN of wildtype and Adamts13-/- mice. Chemotactic properties of A. fumigatus -activated and control serum from wildtype and knock-out mice was evaluated by migration of purified human PMN, isolated by dextran sedimentation and Histopaque® centrifugation, in a transwell assay (Corning® HTS Transwell®-96 well permeable support; 3µm).Results: Adamts13 deficiency in mice was accompanied by a worse outcome of IPA infections compared to wildtype controls. Adamts13-/- mice displayed more severe signs of disease and a lethal course was observed in about 24% of animals. Compared to Adamts13-/- mice all neutropenic mice developed lethal IPA after infection, but all wild-type mice survived the disease. Besides, examination of the lungs revealed a higher fungal burden along with increased signs of acute lung injury, complement deposition and levels of pro-inflammatory cytokines in Adamts13-/- mice. Furthermore a more pronounced perivascular leukocyte infiltration was observed in histological sections indicating a dysregulated inflammatory response in Adamts13-/- mice. Importantly, the activation of neutrophil effector functions in response to TLR agonist or in PMN-mediated fungal killing of conidia or hyphae revealed no general defect in vitro. Despite enhanced complement deposition in the lungs in Adamts13-/- mice, PMN migration towards complement-activated serum revealed unaltered chemotactic properties comparing A. fumigatus -activated serum of wildtype and knock-out mice.Conclusion: In acute inflammatory processes such as fungal pneumonia the proteolytic regulation of VWF by ADAMTS-13 is an important mechanism to control PMN recruitment and outcome of infections. DisclosuresNo relevant conflicts of interest to declare.

Current status in diagnosis and treatment of hereditary thrombotic thrombocytopenic purpura.

Thrombotic Thrombocytopenic Purpura (TTP) is an acute and potentially fatal hematologic disorder. It is characterized by systemic platelet clumping in the microvasculature and small arterioles, resulting in thrombocytopenia and microangiopathic hemolytic anemia [1]. Some patients may present signs and symptoms that are consistent with end organ dysfunction [2]. The pathology of this disorder derives from the deficiency of plasma metalloenzyme ADAMTS13 (A Disintegrin and Metalloprotease with Thrombo Spondin type-1 repeats, 13) [3,4]. Under physiological conditions, ADAMTS13 cleaves ultra-large VWF (UL-VWF) that is released from endothelial cells upon activation or vascular injury [5-7]. This proteolytic cleavage of UL-VWF by ADAMTS13 in plasma is essential to remove UL-VWF from endothelial surface and to subsequently reduce the size of VWF multimers in circulation (Figure 1).

Increased Von Willebrand Factor and High Circulating Placental Growth Factor Correlate with Inflammation and Iron Overload in Patients with Compound Heterozygous Sickle Cell and Beta-Thalassemia

Sickle cell disease (SCD) is an inherited hemoglobinopathy characterized by pathological polymerization of hemoglobin, increased red cell rigidity, poor microvascular blood flow, with consequent tissue ischemia and infarction. Thus, hemolytic anemia, vaso-occlusion and vasculopathy are the hallmarks of its clinical presentation. Several other factors contribute to the clinical variability, which is present in SCD, including leukocyte dysfunction, platelet interactions with endothelial cells, pro-inflammatory cytokines, oxidative stress, reduced nitric oxide (NO) availability and hemostatic activation. Placental growth factor (PlGF) is a member of the vascular endothelial growth factor superfamily, which plays an important role in both inflammation and neoangiogenesis. Recently it has been reported that markers of iron overload are associated with high plasma level of PlGF and early mortality [Wang et al, Blood 2014]. Furthermore, in SCD patients, hemolysis can lead to a prothrombotic state by increasing the activity of von Willebrand factor (vWF), a multimeric plasma glycoprotein secreted by the endothelium [Chen et al, Blood 2011]. ADAMTS-13 is a member of the ADAMTS (A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats) family that cleaves vWF. Recent observations suggest that SCD patients suffer from an acquired ADAMTS-13 deficiency primarily because Hb competitively binds and blocks the proteolysis of vWF, leading to the accumulation of ultra-large VWF multimers in circulation and on endothelium.The aim of this study was to evaluate inflammation, endothelial dysfunction and angiogenesis in patients with compound heterozygous SCD and beta-thalassemia (HbS/βthal) and explore possible association with iron overload and other disease features.Eighty-nine adult caucasian patients with HbS/bthal were included in the study, while 20 apparently healthy individuals served as controls. Patients with HbS/βthal divided in two groups: group A included 49 patients under hydroxycarbamide (HC+) treatment and group B included 40 patients without hydroxycarbamide (HC-) treatment. Along with hematology and blood chemistry parameters determination, measurements of circulating high-sensitivity C-reactive protein (hs-CRP), vWF, D-Dimers, ADAMTS-13, hs-Troponin-T (hs-TnT) and PlGF were measured in patients with HbS/βthal and controls using immunoenzymatic techniques.Levels of hs-CRP, vWF and PlGF were elevated in patients with HbS/βthal compared to controls (6.9±5.3 vs. 0.4±0.4 mg/L, 170.1±78.3 vs. 85.3±22.1 IU/dL and 20.2±7.6 vs, 15.3±2.4 pg/mL, respectively, p<0.001), while ADAMTS-13 levels were decreased in patients with HbS/βthal compared to controls (965.2±244.0 vs. 1144.2±187.0 pg/mL, p<0.001). No significant differences were found for the above parameters between patients of groups A and B (p=0.211, p=0.710, p=0.589 and p=0.384, respectively. Hs-CRP correlated positively with vWF, PlGF and ADAMTS-13 (r=0.360, p<0.001; r=0.300, p=0.005 and r=0.382, p=0.002, respectively). PlGF levels in patients with HbS/βthal correlated positively with markers of hemolysis such as reticulocyte counts, LDH and with uric acid levels (r=0.674, p<0.001; r=0.425, p<0.001 and r=0.357, p<0.001, respectively). Ferritin levels correlated positively with hs-CRP, vWF, PlGF and D-Dimers (r=0.360, p<0.001; r=0.317, p=0.004; r=0.354, p<0.001; and r=0.344, p=0.002, respectively) as well as with markers of hemolysis (p<0.001). Furthermore, only 6 patients had slightly increased hs-TnT levels and almost all patients had pathologic D-Dimers levels.Our findings demonstrate that patients with HbS/βthal have a significant degree of endothelial dysfunction as assessed by increased vWF. The increased levels of the D-Dimers in almost all patients indicate the activation of coagulation and fibrinolytic systems even in the steady state of the disease. Iron overload and inflammation along with reduced circulating ADAMTS-13 contribute, at least partially, to the increased levels of vWF. Similarly, inflammation and iron overload enhance the production of angiogenesis markers, such as PlGF suggesting a possible pathogenetic role for iron load in SCD biology. Further studies will reveal if iron chelation is able to restore some of the above phenomena and improve endothelial dysfunction and inflammation in this entity. DisclosuresNo relevant conflicts of interest to declare.

A non-invasive laboratory panel as a diagnostic and prognostic biomarker for thrombotic microangiopathy: development and application in a Chinese cohort study.

BackgroundThrombotic microangiopathy (TMA) in the kidney is a histopathologic lesion that occurs in a number of clinical settings and is often associated with poor renal prognosis. The standard test for the diagnosis of TMA is the renal biopsy; noninvasive parameters such as potential biomarkers have not been developed.MethodsWe analyzed routine parameters in a cohort of 220 patients with suspected TMA and developed a diagnostic laboratory panel by logistic regression. The levels of candidate markers were validated using an independent cohort (n = 46), a cohort of systemic lupus erythematosus (SLE) (n = 157) and an expanded cohort (n = 113), as well as 9 patients with repeat biopsies.ResultsOf the 220 patients in the derivation cohort, 51 patients with biopsy-proven TMA presented with a worse renal prognosis than those with no TMA (P = 0.002). Platelet and L-lactate dehydrogenase (LDH) levels showed an acceptable diagnostic value of TMA (AUC = 0.739 and 0.756, respectively). A panel of 4 variables - creatinine, platelets, ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats 13) activity and LDH - can effectively discriminate patients with TMA (AUC = 0.800). In the validation cohort, the platelet and LDH levels and the 4-variable panel signature robustly distinguished patients with TMA. The discrimination effects of these three markers were confirmed in patients with SLE. Moreover, LDH levels and the 4-variable panel signature also showed discrimination values in an expanded set. Among patients undergoing repeat biopsy, increased LDH levels and panel signatures were associated with TMA status when paired evaluations were performed. Importantly, only the 4-variable panel was an independent prognostic marker for renal outcome (hazard ratio = 3.549; P<0.001).ConclusionsThe noninvasive laboratory diagnostic panel is better for the early detection and prognosis of TMA compared with a single parameter, and may provide a promising biomarker for clinical application.

Carboxyl Terminus of ADAMTS13 Directly Inhibits Platelet Aggregation and Ultra Large von Willebrand Factor String Formation Under Flow in a Free-Thiol–Dependent Manner

ADAMTS13 (A Disintegrin And Metalloprotease with Thrombospondin type 1 repeats, 13) cleaves von Willebrand factor (VWF), thereby inhibiting thrombus formation. Proteolytic cleavage relies on the amino-terminal (MDTCS) domains, but the role of the more distal carboxyl-terminal domains of ADAMTS13 is not fully understood. A previous study demonstrated the presence of multiple surface-exposed free sulfhydryls on ADAMTS13 that seemed to interact with those on VWF under shear. Here, we determined the physiological relevance of such an interaction in antithrombotic responses under flow. A microfluidic assay demonstrated that a carboxyl-terminal fragment of ADAMTS13, comprising either 2 to 8 thrombospondin type 1 (TSP1) repeats and CUB domains (T2C) or 5 to 8 Thrombospondin type 1 (TSP1) repeats and CUB domains (T5C), directly inhibited platelet adhesion/aggregation on a collagen surface under arterial shear. In addition, an intravital microscopic imaging analysis showed that the carboxyl-terminal fragment of ADAMTS13 (T2C or T5C) was capable of inhibiting the formation and elongation of platelet-decorated ultra large (UL) VWF strings and the adhesion of platelets/leukocytes on endothelium in mesenteric venules after oxidative injury. The inhibitory activity of T2C and T5C on platelet aggregation and ULVWF string formation were dependent on the presence of their surface free thiols; pretreatment of T2C and T5C or full-length ADAMTS13 with N-ethylmaleimide that reacts with free sulfhydryls abolished or significantly reduced its antithrombotic activity. Our results demonstrate for the first time that the carboxyl terminus of ADAMTS13 has direct antithrombotic activity in a free-thiol-dependent manner. The free thiols in the carboxyl-terminal domains of ADAMTS13 may also contribute to the overall antithrombotic function of ADAMTS13 under pathophysiological conditions.

Predictive Value Of Markers Of Fibrinolysis and Endothelial Dysfunction In The Post Thrombotic Syndrome: A Systematic Review

IntroductionThe post thrombotic syndrome (PTS) is a chronic condition that develops in 20–40% of deep vein thrombosis (DVT) patients. While risk factors that predispose to the development of venous thromboembolism are widely known, factors that influence the development of PTS after DVT have not been well elucidated. Identification of factors to facilitate individualized risk assessment for PTS and thereby the need for prophylactic intervention is desirable. ObjectivesWe conducted a systematic review to determine whether biomarkers of fibrinolysis and endothelial dysfunction can predict the risk of developing PTS among patients diagnosed with DVT. MethodsStudies were identified by searching the electronic databases PubMed, EMBASE, Scopus and Web of science. Studies published between January 1990 and January 2013 which measured biomarker levels in blood of adult patients with DVT, and reported rates of PTS development in these patients were included. Extracted data included source and baseline characteristics of study subjects, potential confounders that could influence the result of measured marker (e.g. malignancy, use of anticoagulants), type of biomarker, time point(s) and method of measurement, criteria for PTS diagnosis, and measure of association including adjustment variables. Risk of bias was assessed using Newcastle-Ottawa Scale, with some additional quality items specific to this literature added. ResultsOut of 2376 records included in our primary screen of titles and abstracts, 84 articles were assessed for eligibility. Fourteen studies were included in this systematic review: 11 investigated the association between D-Dimer and PTS, three examined fibrinogen level, two measured Von Willebrand factor (VWF) antigen and activity, one study measured plasminogen activator inhibitor (PAI)-1, one assessed A Disintegrin and Metalloprotease with Thrombospondin type 1 repeats (ADAMTS)-13 antigen and activity and one study measured Factor XIII (FXIII) activity.Studies varied with regards to inclusion and exclusion criteria (e.g. first DVT, malignancy, current anticoagulant use), use of validated scales to diagnose PTS (e.g. Villalta scale or clinical, etiological, anatomical and pathological [CEAP] classification), timing of PTS assessment, time point of biomarker measurement after DVT, measurement method, and cut off value used for analysis of association between marker and outcome.Figure 1 summarizes results from 10 studies that reported on the association between D-Dimer and PTS. We used crude Odds Ratios (OR) as the summary measure, as adjusted ORs were available for only a few studies, and adjustment variables differed between studies. Furthermore, as some studies restricted their population on certain clinical characteristics, crude ORs may already reflect a certain degree of control for confounding. In general, adjusted ORs (where available) tended to attenuate the association. Studies were grouped according to the time point of D-Dimer measurement after DVT. Even after such subgrouping, we were still unable to combine the results within subgroups due to marked clinical heterogeneity. [Display omitted] Three studies measured fibrinogen levels, two on the day of DVT diagnosis and one a median of 28 months after DVT. None found a significant association between fibrinogen level and the development of PTS. Similarly, no association with PTS was found in the studies examining ADAMTS-13 antigen level and activity, VWF antigen and activity, or PAI-1.The one available study that measured FXIII activity found it to be significantly lower in patients with PTS. ConclusionsWe systematically reviewed the literature on the association between markers of fibrinolysis and endothelial dysfunction and the development of PTS in patients after acute DVT. An elevated D-dimer level may be an intrinsic marker of residual thrombus and/or persistent activation of clotting or inflammatory pathways that could increase the propensity to develop PTS. Similarly, impaired fibrinolysis and endothelial dysfunction are pathophysiological components of PTS. Whether these markers might be useful to predict the development of PTS after DVT is still unclear. Larger prospective studies using validated scores to diagnose PTS, strict inclusion and exclusion criteria, and accounting for confounders in the design and analysis are needed. Disclosures:No relevant conflicts of interest to declare.

PROTEOLYTIC PROCESSING OF VON WILLEBRAND FACTOR BY ADAMTS13 AND LEUKOCYTE PROTEASES

ADAMTS13 is a 190 kDa zinc protease encoded by a gene located on chromosome 9q34. This protease specifically hydrolyzes von Willebrand factor (VWF) multimers, thus causing VWF size reduction. ADAMTS13 belongs to the A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats (ADAMTS) family, involved in proteolytic processing of many matrix proteins. ADAMTS13 consists of numerous domains including a metalloprotease domain, a disintegrin domain, several thrombospondin type 1 (TSP1) repeats, a cysteine-rich domain, a spacer domain and 2 CUB (Complement c1r/c1s, sea Urchin epidermal growth factor, and Bone morphogenetic protein) domains. ADAMTS13 cleaves a single peptide bond (Tyr1605-Met1606) in the central A2 domain of the VWF molecule. This proteolytic cleavage is essential to reduce the size of ultra-large VWF polymers, which, when exposed to high shear stress in the microcirculation, are prone to form with platelets clumps, which cause severe syndromes called thrombotic microangiopathies (TMAs). In this review, we a) discuss the current knowledge of structure-function aspects of ADAMTS13 and its involvement in the pathogenesis of TMAs, b) address the recent findings concerning proteolytic processing of VWF multimers by different proteases, such as the leukocyte-derived serine and metallo-proteases and c) indicate the direction of future investigations.

Identification of a Novel Exosite (Glu634-Arg639) in the Spacer Domain of ADAMTS13 Required for Recognition of Von Willebrand Factor.

Abstract 2214Exosite binding plays a key role in cleavage of VWF by ADAMTS13 (A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats, 13). Two exosites that are evolutionarily conserved from zebra fish to mammals have been identified in the spacer domain by sequence alignment. Previous studies have shown that exosite 3 in the spacer domain plays a critical role for substrate recognition (Blood 115:2300–10, 2010), and modification of this exosite generates ADAMTS13 variants with improved specific activity but reduced autoantibody binding (Blood 119:3836–43, 2012). In the present study, using a site-directed mutagenesis approach, we identified a novel exosite near exosite 3 in the spacer domain, termed exosite 4, a region between residues Glu634 and Arg639. A partial (ΔEx4a:deletion of Leu632-Asp635 or ΔEx4b:deletion of Arg636-Arg639) or complete deletion of the exosite (ΔEx4) significantly impaired proteolytic activity towards peptidyl VWF73 and multimeric VWF. Moreover, substitution of all surface exposed residues in Ex4A (LTED/AAAA) or Ex4b (RLPR/AAAA) with alanine had a similarly detrimental effect on proteolytic activity. Further studies demonstrated that the residues Asp635 and Arg636 in exosite 4 play a critical role for substrate recognition. We conclude that the region between residues Glu634 and Arg639 is a novel exosite necessary for recognition and cleavage of VWF. Disclosures:No relevant conflicts of interest to declare.

Genetic Ablation of Adamts13 Gene Dramatically Accelerates the Formation of Early Atherosclerosis in a Murine Model

ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats-13) cleaves von Willebrand factor, thereby modulating thrombosis and inflammation. Low plasma ADAMTS13 activity is associated with cardiovascular events, including myocardial and cerebral infarction. Here, we investigated the role of ADAMTS13 in the development of early atherosclerosis in a murine model. Apolipoprotein E-null (ApoE(-/-)) and Adamts13-null (Adamts13(-/-)) ApoE(-/-) mice were fed with a high-fat Western diet for 12 weeks. Atherosclerotic lesions in the aorta and aortic roots were quantified after staining. Leukocyte rolling and adhesion onto cremaster venules after oxidative injury were determined by intravital microscopy. Although plasma cholesterol levels were largely similar in both groups, the extent of atherosclerotic lesions in the aorta en face and in the aortic roots in the Adamts13(-/-)ApoE(-/-) mice increased ≈ 5.5-fold (P=0.0017) and ≈ 6.1-fold (P=0.0037), respectively. In addition, the ratio of plasma high- to low-molecular-weight von Willebrand factor multimers increased ≈ 3-fold. The leukocyte rolling velocities were significantly reduced (P<0.001), with an increased number of leukocyte rolling (P=0.0026) and macrophage infiltration into the atherosclerotic lesions in the Adamts13(-/-)ApoE(-/-) mice. Our results suggest that ADAMTS13 plays a critical role in modulating the development of early atherosclerosis, likely through the proteolytic cleavage of ultra-large von Willebrand factor multimers, thereby inhibiting platelet deposition and inflammation.