Regulation of von Willebrand factor by ADAMTS13 ameliorates lipopolysaccharide-induced lung injury in mice.

The relationship between von Willebrand factor (VWF) and inflammation has attracted considerable attention in recent years. VWF, which is stored in the Weibel-Palade bodies (WPBs) of endothelial cells (ECs), is released from WPBs in response to inflammatory stimuli and is thought to contribute to inflammation by promoting leukocyte extravasation. In this study, lung injury model mice were produced by intratracheal injection with lipopolysaccharides. The severity of lung inflammation was evaluated in mice with different genotypes (wild-type, Vwf-/-, Adamts13-/-) and mice treated with drugs that inhibit VWF function. Lung inflammation was significantly ameliorated in Vwf-/- mice compared with wild-type mice. Furthermore, inflammation was significantly suppressed in wild-type mice treated with anti-VWF A1 antibody or recombinant human ADAMTS13 compared with the untreated control group. The underlying mechanism appears to be an increased VWF/ADAMTS13 ratio at the site of inflammation and the interaction between blood cell components, such as leukocytes and platelets, and the VWF A1 domain, which promotes leukocyte infiltration into the lung. This study suggested that ADAMTS13 protein and other VWF-targeting agents may be a novel therapeutic option for treatment of pulmonary inflammatory diseases.

Development of alternative gene transfer techniques for ex vivo and in vivo gene therapy in a canine model.

INTRODUCTION: Gene therapy have recently attracted much attention as a curative therapeutic option for inherited single gene disorders such as hemophilia. Hemophilia is a hereditary bleeding disorder caused by the deficiency of clotting activity of factor VIII (FVIII) or factor IX (FIX), and gene therapy for hemophilia using viral vector have been vigorously investigated worldwide. Toward further advancement of gene therapy for hemophilia, we have previously developed and validated the efficacy of novel two types of gene transfer technologies using a mouse model of hemophilia A. Here we investigated the efficacy and safety of the technologies in canine model. Especially, validations of technical procedures of the gene transfers for dogs were focused. METHODS: Green fluorescence protein (GFP) gene were transduced into normal beagle dogs by ex vivo and in vivo gene transfer techniques. For ex vivo gene transfer, blood outgrowth endothelial cells (BOECs) derived from peripheral blood of normal dogs were transduced with GFP gene using lentivirus vector, propagated, fabricated as cell sheets, then implanted onto the omentum of the same dogs. For in vivo gene transfer, normal dogs were subjected to GFP gene transduction with non-viral piggyBac vector by liver-targeted hydrodynamic injections. RESULTS: No major adverse events were observed during the gene transfers in both gene transfer systems. As for ex vivo gene transfer, histological findings from the omental biopsy performed 4 weeks after implantation revealed the tube formation by implanted GFP-positive BOECs in the sub-adipose tissue layer without any inflammatory findings, and the detected GFP signals were maintained over 6 months. Regarding in vivo gene transfer, analyses of liver biopsy samples revealed more than 90% of liver cells were positive for GFP signals in the injected liver lobes 1 week after gene transfers, then the signals gradually declined overtime. CONCLUSIONS: Two types of gene transfer techniques were successfully applied to a canine model, and the transduced gene expressions persisted for a long term. Toward clinical application for hemophilia patients, practical assessments of therapeutic efficacy of these techniques will need to be performed using a dog model of hemophilia and FVIII (or FIX) gene.

Functional regulation of von Willebrand factor ameliorates acute ischemia-reperfusion kidney injury in mice.

Acute kidney injury (AKI), an abrupt loss of renal function, is often seen in clinical settings and may become fatal. In addition to its hemostatic functions, von Willebrand factor (VWF) is known to play a role in cross-talk between inflammation and thrombosis. We hypothesized that VWF may be involved in the pathophysiology of AKI, major causes of which include insufficient renal circulation or inflammatory cell infiltration in the kidney. To test this hypothesis, we studied the role of VWF in AKI using a mouse model of acute ischemia-reperfusion (I/R) kidney injury. We analyzed renal function and blood flow in VWF-gene deleted (knock-out; KO) mice. The functional regulation of VWF by ADAMTS13 or a function-blocking anti-VWF antibody was also evaluated in this pathological condition. Greater renal blood flow and lower serum creatinine were observed after reperfusion in VWF-KO mice compared with wild-type (WT) mice. Histological analysis also revealed a significantly lower degree of tubular damage and neutrophil infiltration in kidney tissues of VWF-KO mice. Both human recombinant ADAMTS13 and a function-blocking anti-VWF antibody significantly improved renal blood flow, renal function and histological findings in WT mice. Our results indicate that VWF plays a role in the pathogenesis of AKI. Proper functional regulation of VWF may improve the microcirculation and vessel function in the kidney, suggesting a novel therapeutic option against AKI.

Von Willebrand Factor Aggravates Hepatic Ischemia-Reperfusion Injury by Promoting Neutrophil Recruitment in Mice.

Hepatic ischaemia-reperfusion (I/R) injury is a serious liver damage that critically influences the clinical outcome of liver surgery or transplantation. Since recent studies indicated the critical involvement of von Willebrand factor (VWF) in reperfusion injuries of brain and myocardium, we hypothesized that VWF-dependent thrombotic or inflammatory responses also play a role in hepatic I/R injury. Using a mouse model of hepatic I/R injury, we explored the functional relevance of the VWF-ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) axis in this pathologic condition. Time-course studies during hepatic I/R revealed significantly lower alanine aminotransferase (ALT) values, as well as greater hepatic blood flow, in VWF gene-deleted (KO) mice in comparison with wild-type (WT) mice. Histological analysis revealed a significantly lesser extent of neutrophil infiltration and hepatocellular necrosis in liver tissues of VWF-KO mice. Human recombinant ADAMTS13 significantly improved the impairment in ALT values and hepatic blood flow and decreased neutrophil infiltration within the liver tissue of WT mice. Real-time intravital imaging successfully visualized significantly reduced leukocyte-vessel wall interactions in I/R liver of VWF-KO mice. Taken together, our results indicate that VWF promotes neutrophil recruitment in ischaemic mouse liver, critically aggravating reperfusion injury, and suggest that functional regulation of VWF by ADAMTS13 represents a promising therapeutic option for hepatic I/R injury.

Highly elevated plasma level of von Willebrand factor accelerates the formation of platelet thrombus under high shear stress in plasma with deficient ADAMTS13 activity.

Upshaw-Schulman syndrome (USS) is a thrombo-hemorrhagic disease caused by congenital deficiency of ADAMTS13 due to ADAMTS13 gene mutations. USS is characterized by repeated episodes of thrombocytopenia and microangiopathic hemolytic anemia that respond dramatically to infusions of fresh frozen plasma. There are two phenotypic expressions of USS: one is the early-onset type and the other, the late-onset type, is asymptomatic during childhood with the first bout of thrombotic thrombocytopenic purpura (TTP) developing after adolescence or during adulthood. We found that gravida with the latter phenotype developed thrombocytopenia and hemolytic anemia during the second or third trimesters, often followed by thrombotic microangiopathies (TMAs). These phenomena suggest that elevated plasma von Willebrand Factor (VWF) might be crucial because plasma levels of VWF antigen usually increase by 200-500% during this period of gestation. Here, we performed platelet function assays using a mixture of anti-coagulated blood from normal volunteers, human VWF, anti-ADAMTS13 monoclonal antibody A10, and purified plasma-derived ADAMTS13 to investigate the effect of plasma VWF levels on platelet thrombus formation in the context of deficient ADAMTS13. In vitro studies showed that mural thrombus formation and platelet aggregation under high shear stress were markedly augmented by increasing the amounts of exogenously added VWF when ADAMTS13 activity was deficient, as may be the case in the in vivo circulation of gravida with USS. These results suggest that highly elevated plasma VWF might accelerate platelet thrombus formation not only in the circulation but also on the surface of vascular endothelial cells in the setting of ADAMTS13 deficiency in USS.

Functional characterization of tissue factor in von Willebrand factor-dependent thrombus formation under whole blood flow conditions.

Von Willebrand factor (VWF) plays an important role in mediating platelet adhesion and aggregation under high shear rate conditions. Such platelet aggregates are strengthened by fibrin-network formation triggered by tissue factor (TF). However, little is known about the role of TF in VWF-dependent thrombus formation under blood flow conditions. We evaluated TF in thrombus formation on immobilized VWF under whole blood flow conditions in an in vitro perfusion chamber system. Surface-immobilized TF amplified intra-thrombus fibrin generation significantly under both low and high shear flow conditions, while TF in sample blood showed no appreciable effects. Furthermore, immobilized TF enhanced VWF-dependent platelet adhesion and aggregation significantly under high shear rates. Neutrophil cathepsin G and elastase increased significantly intra-thrombus fibrin deposition on immobilized VWF-TF complex, suggesting the involvement of leukocyte inflammatory responses in VWF/TF-dependent mural thrombogenesis under these flow conditions. These results reveal a functional link between VWF and TF under whole blood flow conditions, in which surface-immobilized TF and VWF mutually contribute to mural thrombus formation, which is essential for normal hemostasis. By contrast, TF circulating in blood may be involved in systemic hypercoagulability, as seen in sepsis caused by severe microbial infection, in which neutrophil inflammatory responses may be active.

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.

Exsanguinating bleeding following tooth extraction in a 12-year-old girl: a rare case of acquired haemophilia A.

Acquired haemophilia A (AHA) is a life-threatening haemorrhagic disorder that occurs with various underlying conditions such as autoimmune disease, drug reactions, lymphoproliferative diseases, solid tumours and pregnancy/postpartum status. However, in half of all reported cases, the underlying disease is unknown. Most AHA cases develop in adults; paediatric/adolescent cases are extremely rare. The main clinical symptom is bleeding into the skin, muscles, soft tissues and/or mucous membranes. Here, we report the case of an otherwise healthy 12-year-old girl who presented with prolonged bleeding postexodontia. After being diagnosed with AHA, she was successfully treated with recombinant activated factor VII infusion and oral prednisolone. To avoid such unanticipated bleeding when performing dental extraction, preoperative haemostatic screening tests are recommended.

Delivery of full-length factor VIII using a piggyBac transposon vector to correct a mouse model of hemophilia A.

Viral vectors have been used for hemophilia A gene therapy. However, due to its large size, full-length Factor VIII (FVIII) cDNA has not been successfully delivered using conventional viral vectors. Moreover, viral vectors may pose safety risks, e.g., adverse immunological reactions or virus-mediated cytotoxicity. Here, we took advantages of the non-viral vector gene delivery system based on piggyBac DNA transposon to transfer the full-length FVIII cDNA, for the purpose of treating hemophilia A. We tested the efficiency of this new vector system in human 293T cells and iPS cells, and confirmed the expression of the full-length FVIII in culture media using activity-sensitive coagulation assays. Hydrodynamic injection of the piggyBac vectors into hemophilia A mice temporally treated with an immunosuppressant resulted in stable production of circulating FVIII for over 300 days without development of anti-FVIII antibodies. Furthermore, tail-clip assay revealed significant improvement of blood coagulation time in the treated mice. piggyBac transposon vectors can facilitate the long-term expression of therapeutic transgenes in vitro and in vivo. This novel gene transfer strategy should provide safe and efficient delivery of FVIII.

A novel cell-sheet technology that achieves durable factor VIII delivery in a mouse model of hemophilia A.

Gene- or cell-based therapies aimed at creating delivery systems for coagulation factor VIII (FVIII) protein have emerged as promising options for hemophilia A treatment. However, several issues remain to be addressed regarding the efficacies and adverse events of these new classes of therapies. To improve an existing cell-based therapy involving the subcutaneous transplantation of FVIII-transduced blood outgrowth endothelial cells (BOECs), we employed a novel cell-sheet technology that allows individual dispersed cells to form a thin and contiguous monolayer without traditional bioabsorbable scaffold matrices. Compared to the traditional methodology, our cell-sheet approach resulted in longer-term and 3-5-fold higher expression of FVIII (up to 11% of normal) in recipient hemophilia A mice that lacked a FVIII humoral immune response due to transient immunosuppression with cyclophosphamide. Histological studies revealed that the transplanted BOEC sheets were structured as flat clusters, supporting the long-term expression of therapeutic FVIII in plasma from an ectopic subcutaneous space. Our novel tissue-engineering approach using genetically modified BOEC sheets could aid in development of cell-based therapy that will allow safe and effective in vivo delivery of functional FVIII protein in patients with hemophilia A.

Coagulation potential of immobilised factor VIII in flow-dependent fibrin generation on platelet surfaces.

Coagulation factor VIII (FVIII) plays an essential role in haemostasis. To date, physiologic activity of FVIII circulating in the bloodstream (S-FVIII) is evaluated by classic coagulation assays. However, the functional relevance of FVIII (-von Willebrand factor complex) immobilised on thrombogenic surfaces (I-FVIII) remains unclear. We used an in vitro perfusion chamber system to evaluate the function of I-FVIII in the process of mural thrombus formation under whole blood flow conditions. In perfusion of either control or synthetic haemophilic blood, the intra-thrombus fibrin generation on platelet surfaces significantly increased as a function of I-FVIII, independent of S-FVIII, under high shear rate conditions. This I-FVIII effect was unvarying regardless of anti-FVIII inhibitor levels in synthetic haemophilic blood. Thus, our results illustrate coagulation potentials of immobilised clotting factors, distinct from those in the bloodstream, under physiologic flow conditions and may give a clue for novel therapeutic approaches for haemophilic patients with anti-FVIII inhibitors.

Ratio of von Willebrand factor propeptide to ADAMTS13 is associated with severity of sepsis.

Von Willebrand factor (VWF)-cleaving protease (ADAMTS13) cleaves ultralarge VWF (ULVWF) secreted from endothelium and by which is regulating its physiologic function. An imbalance between ULVWF secretion and ADAMTS13 level occurs in sepsis and may cause multiple organ dysfunction. We evaluated the association between the VWF-propeptide (VWF-pp)/ADAMTS13 ratio and disease severity in patients with severe sepsis or septic shock. In 27 patients with severe sepsis or septic shock and platelet count less than 120,000/µL, we measured plasma VWF, VWF-pp, and ADAMTS13 levels on hospital days 1, 3, 5, and 7. The VWF-pp/ADAMTS13 ratio was increased greater than 12-fold in patients with severe sepsis or septic shock on day 1 and remained markedly high on days 3, 5, and 7 compared with normal control subjects. The VWF-pp/ADAMTS13 ratio significantly correlated with Acute Physiology and Chronic Health Evaluation II score on days 1 and 5; Sepsis-related Organ Failure Assessment score on days 1, 3, and 5; maximum Sepsis-related Organ Failure Assessment score and tumor necrosis factor α level on days 1, 3, 5, and 7; and creatinine level on days 1, 5, and 7. Patients with greater than stage 1 acute kidney injury had significantly higher VWF-pp/ADAMTS13 ratio than patients without acute kidney injury. In summary, the VWF-pp/ADAMTS13 ratio was associated with disease severity in patients with severe sepsis or septic shock and may help identify patients at risk for multiple organ dysfunction by detecting severe imbalance between ULVWF secretion and ADAMTS13 level.

Cilostazol down-regulates the height of mural platelet thrombi formed under a high-shear rate flow in the absence of ADAMTS13 activity.

Cilostazol is an anti-platelet drug that reversibly inhibits phosphodiesterase III (PDE-III), which is ubiquitously expressed in platelets and various tissues. PDE-III converts cyclic adenosine monophosphate (cAMP) to 5'-AMP and up-regulates the intracellular concentration of cAMP, a potent inhibitor of platelet aggregation. Unlike other anti-platelet drugs, cilostazol is unique because patients receiving this drug do not have a significantly prolonged bleeding time, but the reasons for this difference are still unknown. In this study, we have examined how cilostazol inhibits platelet thrombus formation using anti-coagulated normal whole blood in which the platelets were labeled with a fluorescent dye in comparison with the anti-GPIIb/IIIa agent, tirofiban. We used an in vitro assay to examine mural platelet thrombus growth on a collagen surface under a high-shear rate flow in the absence of ADAMTS13 activity. These experimental conditions mimic the blood flow in patients with thrombotic thrombocytopenic purpura. Using this model, we clearly determined that cilostazol down-regulates the height of mural platelet thrombi formed on a collagen surface in a dose-dependent manner, without affecting the surface coverage. The concentration of cilostazol used in this study was relatively high (60-120 µM) compared to clinically relevant concentrations (1-3 µM), which may be due to the in vivo synergistic effects of PDE-III present in other tissues aside from platelets. Cilostazol does not affect the initial formation of platelet thrombi, but does inhibit the height of thrombi. These results showed a sharp contrast to tirofiban, and address why cilostazol does not significantly prolong bleeding time, despite its strong anti-platelet activity.

Antithrombotic properties of pravastatin reducing intra-thrombus fibrin deposition under high shear blood flow conditions.

In addition to lowering cholesterol, the 3-hydroxyl-3-methylglutaryl coenzyme A reductase inhibitors (statins) have a range of pleiotropic effects that help reduce the risk of adverse cardiovascular events. We sought to understand the molecular mechanisms by which statins could exert anti-platelet actions under physiologic whole blood flow conditions. Using an in vitro perfusion chamber system, we examined the anti-platelet effects of pravastatin under whole blood flow conditions with high or low shear rates. We determined that pravastatin significantly suppressed platelet activation-dependent procoagulant activity, decreasing P-selectin membrane expression, tissue factor accumulation, and thrombin binding within platelet thrombi generated on a von Willebrand factor-surface under high shear rate conditions. These effects resulted in reductions of intra-thrombus fibrin deposition. These antithrombotic properties of pravastatin, which were comparable to those of atorvastatin, could be abrogated by mevalonate. Our experimental approach revealed a novel mechanism mediating the anti-platelet action of statins. Shear rate-dependent antithrombotic activity may explain the favourable effect of pravastatin on the reduction in cardiovascular events that typically occur in vivo under whole blood flow conditions with high shear rates.

ADAMTS13 gene deletion aggravates ischemic brain damage: a possible neuroprotective role of ADAMTS13 by ameliorating postischemic hypoperfusion.

Reperfusion after brain ischemia causes thrombus formation and microcirculatory disturbances, which are dependent on the platelet glycoprotein Ib-von Willebrand factor (VWF) axis. Because ADAMTS13 cleaves VWF and limits platelet-dependent thrombus growth, ADAMTS13 may ameliorate ischemic brain damage in acute stroke. We investigated the effects of ADAMTS13 on ischemia-reperfusion injury using a 30-minute middle cerebral artery occlusion model in Adamts13(-/-) and wild-type mice. After reperfusion for 0.5 hours, the regional cerebral blood flow in the ischemic cortex was decreased markedly in Adamts13(-/-) mice compared with wild-type mice (P < .05), which also resulted in a larger infarct volume after 24 hours for Adamts13(-/-) compared with wild-type mice (P < .01). Thus, Adamts13 gene deletion aggravated ischemic brain damage, suggesting that ADAMTS13 may protect the brain from ischemia by regulating VWF-platelet interactions after reperfusion. These results indicate that ADAMTS13 may be a useful therapeutic agent for stroke.

Functional imaging of shear-dependent activity of ADAMTS13 in regulating mural thrombus growth under whole blood flow conditions.

The metalloprotease ADAMTS13 is assumed to regulate the functional levels of von Willebrand factor (VWF) appropriate for normal hemostasis in vivo by reducing VWF multimer size, which directly represents the thrombogenic activity of this factor. Using an in vitro perfusion chamber system, we studied the mechanisms of ADAMTS13 action during platelet thrombus formation on a collagen surface under whole blood flow conditions. Inhibition studies with a function-blocking anti-ADAMTS13 antibody, combined with immunostaining of thrombi with an anti-VWF monoclonal antibody that specifically reflects the VWF-cleaving activity of ADAMTS13, provided visual evidence for a shear rate-dependent action of ADAMTS13 that limits thrombus growth directly at the site of the ongoing thrombus generation process. Our results identify an exquisitely specific regulatory mechanism that prevents arterial occlusion under high shear rate conditions during mural thrombogenesis.

Visual evaluation of blood coagulation during mural thrombogenesis under high shear blood flow.

Mural thrombus generation at sites of damaged vessel walls is essential for both physiological haemostasis and pathological intravascular thrombosis. While thrombi are established by the concerted action of platelet aggregation and blood coagulation, most previous in vitro coagulation assays have evaluated fibrin clot formation in a closed stirring situation that lacks blood cells including platelets. We describe here a modified flow chamber system, established originally for platelet functional studies, that enables real-time observation of intra-thrombus fibrin accumulation during platelet thrombogenesis under flow conditions. Analysis by confocal laser scanning microscopy during perfusion of whole blood anticoagulated to various extents revealed that the size and shape of mural thrombi can depend on the intra-thrombus fibrin development under high shear rate conditions. These observations were confirmed by perfusion of heparinized blood or blood from haemophilia patients with or without addition of activated factor VII. Thus, our experimental system provides visual evidence supporting the concept of "cell-based coagulation under whole blood flow", which might be the most physiologically relevant model of comprehensive thrombogenicity in vivo to date. This system promises to help formulate strategies for haemostatic management of congenital coagulation disorders as well as for antithrombotic therapy targeting fatal arterial thrombosis.