The aptamer BT200 effectively inhibits von Willebrand factor (VWF) dependent platelet function after stimulated VWF release by desmopressin or endotoxin

Aptamer BT200 is protective against myocardial ischemia-reperfusion injury in mice

BACKGROUND

Myocardial ischemia-reperfusion (MI/R) injury tends to affect cardiac function and leads to poor patient prognosis, and there is still no effectively targeted drug to develop anti-von Willebrand factor (VWF) aptamer in acute coronary heart disease. However, the newly anti-VWF aptamer BT200 is applied not only for stroke and hemophilia but also for antithrombolism function in clinical development. The role of BT200 in acute myocardial injury during MI/R is still unknown.

OBJECTIVES

To investigate the cardioprotective effect of aptamer BT200 in a mouse model of MI/R.

METHODS

C57BL/6 mice were subjected to 30-minute ischemia and 24-hour reperfusion to establish MI/R model. Mice were treated with intravenous injection of cy3-labeled BT200 and were observed by an in vivo imaging system at different time points. Then, mice were sampled and evaluated by echocardiography, Evans triphenyltetrazolium chloride staining, histopathologic, western blotting, and real-time quantitative polymerase chain reaction assays to detect cardiac injury and inflammation response after 24-hour reperfusion.

RESULTS

BT200 aptamer can enter and infiltrate into the ischemic myocardium after 24-hour reperfusion. BT200 was shown to inhibit VWF A1 activity and prolong bleeding time in MI/R mice. Moreover, BT200-treated mice had a significant reduction in infarct size and an improvement in cardiac function post-MI/R. BT200 treatment can also alleviate MI/R-induced microvascular obstruction, inflammation response, and cardiomyocyte apoptosis.

CONCLUSION

Pharmacologic targeting of VWF with BT200 alleviates acute MI/R injury in a murine model and may be a novel therapy strategy for acute myocardial infarction.

Conformation-specific RNA aptamers for phenotypic distinction between normal von Willebrand factor and type 2B von Willebrand disease

The A1 domain in Von Willebrand Factor (VWF) initiates coagulation through binding to platelet glycoprotein GPIbα receptors. Von Willebrand Disease (VWD)-Mutations in A1 that either impair (type 2M) or enhance (type 2B) platelet adhesion to VWF can locally destabilize and even misfold the domain. We leveraged misfolding in the gain-of-function type 2B VWD phenotype as a target, distinct from the normal conformation. Two nuclease-resistant 2'-fluoropyrimidine RNA aptamers were selected to discriminate normal A1 domains from a type 2B V1314D A1 variant in a glycosylated A1A2A3 tri-domain VWF-fragment. Two aptamers, W9 and V1, were isolated that selectively recognize, bind, and inhibit the A1-GPIbα interaction with WT A1A2A3 and V1314D A1A2A3, respectively. These aptamers were tested against their respective recombinant targets, plasma VWF, VWF concentrates, and patient plasma with the heterozygous type 2B VWD R1306W variant using clinical assays, surface plasmon resonance and inhibition assays of platelet adhesion to recombinant A1 and A1A2A3 domains under shear stress. The specificity of W9 and V1 aptamers confirms that pathological conformations of VWD Type 2B proteins are different from normal VWF. The availability of aptamers that distinguish normal plasma-derived VWF from VWD suggests potential applicability in clinical diagnosis of severe gain-of-function phenotypes.

The aptamer BT200 blocks interaction of K1405-K1408 in the VWF-A1 domain with macrophage LRP1

ABSTRACT

Rondaptivon pegol (previously BT200) is a pegylated RNA aptamer that binds to the A1 domain of von Willebrand factor (VWF). Recent clinical trials demonstrated that BT200 significantly increased plasma VWF-factor VIII levels by attenuating VWF clearance. The biological mechanism(s) through which BT200 attenuates in vivo clearance of VWF has not been defined. We hypothesized that BT200 interaction with the VWF-A1 domain may increase plasma VWF levels by attenuating macrophage-mediated clearance. We observed that full-length and VWF-A1A2A3 binding to macrophages and VWF-A1 domain binding to lipoprotein receptor-related protein 1 (LRP1) cluster II and cluster IV were concentration-dependently inhibited by BT200. Additionally, full-length VWF binding to LRP1 expressed on HEK293T (HEK-LRP1) cells was also inhibited by BT200. Importantly, BT200 interacts with the VWF-A1 domain in proximity to a conserved cluster of 4 lysine residues (K1405, K1406, K1407, and K1408). Alanine mutagenesis of this K1405-K1408 cluster (VWF-4A) significantly (P < .001) attenuated binding of VWF to both LRP1 clusters II and IV. Furthermore, in vivo clearance of VWF-4A was significantly (P < .001) reduced than that of wild-type VWF. BT200 did not significantly inhibit binding of VWF-4A to LRP1 cluster IV or HEK-LRP1 cells. Finally, BT200 interaction with the VWF-A1 domain also inhibited binding to macrophage galactose lectin and the SR-AI scavenger receptor. Collectively, our findings demonstrate that BT200 prolongs VWF half-life by attenuating macrophage-mediated clearance and specifically the interaction of K1405-K1408 in the VWF-A1 domain with macrophage LRP1. These data support the concept that targeted inhibition of VWF clearance pathways represents a novel therapeutic approach for von Willebrand disease and hemophilia A.

Kinetic Modeling for BT200 to Predict the Level of Plasma-Derived Coagulation Factor VIII in Humans

Lack of Factor VIII (FVIII) concentrates is one of limiting factors for Hemophilia A prophylaxis in resource-limited countries. Rondaptivon pegol (BT200) is a pegylated aptamer and has been shown to elevate the level of von Willebrand Factor (VWF) and FVIII in previous studies. A population pharmacokinetic model for BT200 was built and linked to the kinetic models of VWF and FVIII based on reasonable assumptions. The developed PK/PD model for BT200 described the observed kinetic of BT200, VWF, and FVIII in healthy volunteers and patients with mild-to-moderate hemophilia A from two clinical trials. The developed model was evaluated using an external dataset in patients with severe hemophilia A taking recombinant FVIII products. The developed and evaluated PK/PD model was able to describe and predict concentration-time profiles of BT200, VWF, and FVIII in healthy volunteers and patients with hemophilia A. Concentration-time profiles of FVIII were then predicted following coadministration of plasma-derived FVIII concentrate and BT200 under various dosing scenarios in virtual patients with severe hemophilia A. Plasma-derived products, that contain VWF, are more accessible in low-resource countries as compared to their recombinant counterparts. The predicted time above 1 and 3 IU/dL FVIII in one week was compared between scenarios in the absence and presence of BT200. A combination dose of 6 mg BT200 once weekly plus 10 IU/kg plasma-derived FVIII twice weekly maintained similar coverage to a 30 IU/kg FVIII thrice weekly dose in absence of BT200, representing only 22% of the FVIII dose per week.

Factor VIII: A Dynamic Modulator of Hemostasis and Thrombosis in Trauma

A trace amount of thrombin cleaves factor VIII (FVIII) into an active form (FVIIIa), which catalyzes FIXa-mediated activation of FX on the activated platelet surface. FVIII rapidly binds to von Willebrand factor (VWF) after secretion and becomes highly concentrated via VWF-platelet interaction at a site of endothelial inflammation or injury. Circulating levels of FVIII and VWF are influenced by age, blood type (nontype O > type O), and metabolic syndromes. In the latter, hypercoagulability is associated with chronic inflammation (known as thrombo-inflammation). In acute stress including trauma, releasable pools of FVIII/VWF are secreted from the Weibel-Palade bodies in the endothelium and then augment local platelet accumulation, thrombin generation, and leukocyte recruitment. Early systemic increases of FVIII/VWF (>200% of normal) levels in trauma result in a lower sensitivity of contact-activated clotting time (activated partial thromboplastin time [aPTT] or viscoelastic coagulation test [VCT]). However, in severely injured patients, multiple serine proteases (FXa plasmin and activated protein C [APC]) are locally activated and may be systemically released. Severity of traumatic injury correlates with prolonged aPTT and elevated activation markers of FXa, plasmin, and APC, culminating in a poor prognosis. In a subset of acute trauma patients, cryoprecipitate that contains fibrinogen, FVIII/VWF, and FXIII is theoretically advantageous over purified fibrinogen concentrate to promote stable clot formation, but comparative efficacy data are lacking. In chronic inflammation or subacute phase of trauma, elevated FVIII/VWF contributes to the pathogenesis of venous thrombosis by enhancing not only thrombin generation but also augmenting inflammatory functions. Future developments in coagulation monitoring specific to trauma patients, and targeted to enhancement or inhibition of FVIII/VWF, are likely to help clinicians gain better control of hemostasis and thromboprophylaxis. The main goal of this narrative is to review the physiological functions and regulations of FVIII and implications of FVIII in coagulation monitoring and thromboembolic complications in major trauma patients.

Aptamers Regulating the Hemostasis System

The hemostasis system is a complex structure that includes the fibrinolysis system, and Yes this is correct coagulation and anticoagulation parts. Due to the multicomponent nature, it becomes relevant to study the key changes in the functioning of signaling pathways, and develop new diagnostic methods and modern drugs with high selectivity. One of the ways to solve this problem is the development of molecular recognition elements capable of blocking one of the hemostasis systems and/or activating another. Aptamers can serve as ligands for targeting specific clinical needs, promising anticoagulants with minor side effects and significant biological activity. Aptamers with several clotting factors and platelet proteins are used for the treatment of thrombosis. This review is focused on the aptamers used for the correction of the hemostasis system, and their structural and functional features. G-rich nucleic acid aptamers, mostly versatile G-quadruplexes, recognize different components of the hemostasis system and are capable of correcting the functioning.

Von Willebrand factor in diagnostics and treatment of cardiovascular disease: Recent advances and prospects

Von Willebrand factor (VWF) is a large multimeric glycoprotein involved in hemostasis. It is essential for platelet adhesion to the subendothelium of the damaged endothelial layer at high shear rates. Such shear rates occur in small-diameter arteries, especially at stenotic sites. Moreover, VWF carries coagulation factor VIII and protects it from proteolysis in the bloodstream. Deficiency or dysfunction of VWF predisposes to bleeding. In contrast, an increase in the concentration of high molecular weight multimers (HMWM) of VWF is closely associated with arterial thrombotic events. Severe aortic stenosis (AS) or hypertrophic obstructive cardiomyopathy (HOCM) can deplete HMWM of VWF and lead to cryptogenic, gastrointestinal, subcutaneous, and mucosal bleeding. Considering that VWF facilitates primary hemostasis and a local inflammatory response at high shear rates, its dysfunction may contribute to the development of coronary artery disease (CAD) and its complications. However, current diagnostic methods do not allow for an in-depth analysis of this contribution. The development of novel diagnostic techniques, primarily microfluidic, is underway. Such methods can provide physiologically relevant assessments of VWF function at high shear rates; however, they have not been introduced into clinical practice. The development and use of agents targeting VWF interaction with the vessel wall and/or platelets may be reasonable in prevention of CAD and its complications, given the prominent role of VWF in arterial thrombosis.

Factors Associated with Platelet Activation-Recent Pharmaceutical Approaches

Platelets are at the forefront of human health and disease following the advances in their research presented in past decades. Platelet activation, their most crucial function, although beneficial in the case of vascular injury, may represent the initial step for thrombotic complications characterizing various pathologic states, primarily atherosclerotic cardiovascular diseases. In this review, we initially summarize the structural and functional characteristics of platelets. Next, we focus on the process of platelet activation and its associated factors, indicating the potential molecular mechanisms involving inflammation, endothelial dysfunction, and miRs. Finally, an overview of the available antiplatelet agents is being portrayed, together with agents possessing off-set platelet-inhibitory actions, while an extensive presentation of drugs under investigation is being given.

Structure-Based Cyclic Glycoprotein Ibα-Derived Peptides Interfering with von Willebrand Factor-Binding, Affecting Platelet Aggregation under Shear

The plasmatic von Willebrand factor (VWF) circulates in a compact form unable to bind platelets. Upon shear stress, the VWF A1 domain is exposed, allowing VWF-binding to platelet glycoprotein Ib-V-IX (GPIbα chain). For a better understanding of the role of this interaction in cardiovascular disease, molecules are needed to specifically interfere with the opened VWF A1 domain interaction with GPIbα. Therefore, we in silico designed and chemically synthetized stable cyclic peptides interfering with the platelet-binding of the VWF A1 domain per se or complexed with botrocetin. Selected peptides (26–34 amino acids) with the lowest-binding free energy were: the monocyclic mono- vOn Willebrand factoR-GPIbα InTerference (ORbIT) peptide and bicyclic bi-ORbIT peptide. Interference of the peptides in the binding of VWF to GPIb-V-IX interaction was retained by flow cytometry in comparison with the blocking of anti-VWF A1 domain antibody CLB-RAg35. In collagen and VWF-dependent whole-blood thrombus formation at a high shear rate, CLB-RAg35 suppressed stable platelet adhesion as well as the formation of multilayered thrombi. Both peptides phenotypically mimicked these changes, although they were less potent than CLB-RAg35. The second-round generation of an improved peptide, namely opt-mono-ORbIT (28 amino acids), showed an increased inhibitory activity under flow. Accordingly, our structure-based design of peptides resulted in physiologically effective peptide-based inhibitors, even for convoluted complexes such as GPIbα-VWF A1.

Oligonucleotide aptamers: Recent advances in their screening, molecular conformation and therapeutic applications

Aptamers are single stranded oligonucleotides with specific recognition and binding ability to target molecules, which can be obtained by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Aptamers have the advantages of low molecular weight, low immunogenicity, easy modification and high stability. They play promising role in promoting food safety, monitoring the environment and basic research, especially in clinical diagnosis and therapeutic drugs. To date, great achievements regarding the selection, modifications and application of aptamers have been made. However, since it is still a challenge to obtain aptamers with high affinity in a more effective way, few aptamer-based products have already successfully entered into clinical use. This review aims to provide a thorough overview of the latest advances in this rapidly developing field, focusing on aptamer screening methods for different targets, the structure of the interaction between aptamers and target substances, and the challenges and potential of current therapeutic aptamers.

Inflammatory Mediators of Platelet Activation: Focus on Atherosclerosis and COVID-19

Background: Atherosclerotic cardiovascular diseases are characterized by a dysregulated inflammatory and thrombotic state, leading to devastating complications with increased morbidity and mortality rates. Summary: In this review article, we present the available evidence regarding the impact of inflammation on platelet activation in atherosclerosis. Key messages: In the context of a dysfunctional vascular endothelium, structural alterations by means of endothelial glycocalyx thinning or functional modifications through impaired NO bioavailability and increased levels of von Willebrand factor result in platelet activation. Moreover, neutrophil-derived mediators, as well as neutrophil extracellular traps formation, have been implicated in the process of platelet activation and platelet-leukocyte aggregation. The role of pro-inflammatory cytokines is also critical since their receptors are also situated in platelets while TNF-α has also been found to induce inflammatory, metabolic, and bone marrow changes. Additionally, important progress has been made towards novel concepts of the interaction between inflammation and platelet activation, such as the toll-like receptors, myeloperoxidase, and platelet factor-4. The accumulating evidence is especially important in the era of the coronavirus disease-19 pandemic, characterized by an excessive inflammatory burden leading to thrombotic complications, partially mediated by platelet activation. Lastly, recent advances in anti-inflammatory therapies point towards an anti-thrombotic effect secondary to diminished platelet activation.

Age-Associated Increase in Thrombogenicity and Its Correlation with von Willebrand Factor

Endothelial cells that cover the lumen of all blood vessels have the inherent capacity to express both pro and anticoagulant molecules. However, under normal physiological condition, they generally function to maintain a non-thrombogenic surface for unobstructed blood flow. In response to injury, certain stimuli, or as a result of dysfunction, endothelial cells release a highly adhesive procoagulant protein, von Willebrand factor (VWF), which plays a central role in formation of platelet aggregates and thrombus generation. Since VWF expression is highly restricted to endothelial cells, regulation of its levels is among the most important functions of endothelial cells for maintaining hemostasis. However, with aging, there is a significant increase in VWF levels, which is concomitant with a significant rise in thrombotic events. It is not yet clear why and how aging results in increased VWF levels. In this review, we have aimed to discuss the age-related increase in VWF, its potential mechanisms, and associated coagulopathies as probable consequences.

The Intriguing Relationships of von Willebrand Factor, ADAMTS13 and Cardiac Disease

von Willebrand factor (VWF) is an adhesive protein involved in primary hemostasis and facilitates platelet adhesion to sites of vascular injury, thereby promoting thrombus formation. VWF exists in plasma as multimers of increasing size, with the largest (high molecular weight; HMW) expressing the greatest functional activity. A deficiency of VWF is associated with a bleeding disorder called von Willebrand disease (VWD), whereas an excess of VWF, in particular the HMW forms, is associated with thrombosis. ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif-13), also known as VWF-cleaving protease, functions to moderate the activity of VWF by cleaving multimers of VWF and limiting the expression of the largest multimers of VWF. A deficiency of ADAMTS13 is therefore associated with an excess of (HMW forms of) VWF, and thus thrombosis. Indeed, any disturbance of the VWF/ADAMTS13 ratio or ‘axis’ may be associated with pathophysiological processes, including prothrombotic tendency. However, both thrombosis or bleeding may be associated with such disturbances, depending on the presenting events. This review evaluates the relationship of VWF and ADAMTS13 with cardiac disease, including cardiac failure, and associated pathophysiology.

The Use of Fluorescently Labeled ARC1779 Aptamer for Assessing the Effect of H2O2 on von Willebrand Factor Exocytosis

Here, we propose a new approach for quantitative estimation of von Willebrand factor (vWF) exposed on the surface of endothelial cells (ECs) using the ARC1779 aptamer that interacts with the vWF A1 domain. To visualize complex formation between vWF and the aptamer, the latter was conjugated with the Cy5 fluorescent label. Cultured human umbilical vein endothelial cells (HUVEC) were stained with the ARC1779-Cy5 conjugate and imaged with a fluorescence microscope. The images were analyzed with the CellProfiler software. vWF released from the Weibel-Palade bodies was observed as bright dot-like structures of round and irregular shape, the number of which increased several times after HUVEC exposure to histamine or thrombin. Staining with ARC1779-Cy5 also revealed long filamentous vWF structures on the surface of activated HUVEC. vWF secretion by ECs is activated by the second messengers cAMP and Ca2+. There is evidence that hydrogen peroxide also acts as a second messenger in ECs. In addition, exogenous H2O2 formed in leukocytes can enter ECs. The aim of our study was to determine the effect of H2O2 on the vWF exposure at the surface of HUVEC using the proposed method. It was shown that hydrogen peroxide at concentration 100 µM, which is lower than the cytotoxicity threshold of H2O2 for cultured HUVEC, increased several times the number of dot-like structures and total amount of vWF exposed on plasma membrane of HUVEC, which suggest that H2O2 acts as a mediator that activates exocytosis of Weibel-Palade bodies and vWF secretion in the vascular endothelium during inflammation and upon elevated generation of endogenous reactive oxygen species in ECs.

Association of ABO blood group with bleeding severity in patients with bleeding of unknown cause

Blood group O has been associated with an increased bleeding tendency due to lower von Willebrand factor (VWF) and factor VIII (FVIII) levels. We explored whether blood group O is independently associated with bleeding severity in patients with mild-to-moderate bleeding of unknown cause (BUC) in the Vienna Bleeding Biobank cohort. Bleeding severity was recorded with the Vicenza bleeding score (BS). Blood group O was overrepresented in 422 patients with BUC compared with its presence in 23 145 healthy blood donors (47.2% vs 37.6%; odds ratio, 1.48; 95% confidence interval [CI], 1.22-1.79). The BS and the number of bleeding symptoms were significantly higher in patients with blood group O than in patients with non-O after adjustment for VWF and FVIII levels and sex (least-square [LS] means of BSs: 6.2; 95% CI, 5.8-6.6 vs 5.3; 4.9-5.7; and of number of symptoms: LS, 3.5; 95% CI, 3.2-3.7 vs 3.0; 2.8-3.2, respectively). Oral mucosal bleeding was more frequent in those with blood group O than in those with other blood types (group non-O; 26.1% vs 14.3%), independent of sex and VWF and FVIII levels, whereas other bleeding symptoms did not differ. Patients with blood group O had increased clot density in comparison with those with blood group non-O, as determined by rotational thromboelastometry and turbidimetric measurement of plasma clot formation. There were no differences in thrombin generation, clot lysis, or platelet function. Our data indicate that blood group O is a risk factor for increased bleeding and bleeding severity in patients with BUC, independent of VWF and FVIII levels.

The aptamer BT200 blocks von Willebrand factor and platelet function in blood of stroke patients

The effect of conventional anti-platelet agents is limited in secondary stroke prevention, and their effects are blunted under high shear stress in the presence of increased levels of circulating von Willebrand factor (VWF). VWF is critically involved in thrombus formation at sites of stenotic extracranial/intracranial arteries. A third generation anti-VWF aptamer (BT200) has been generated which could be useful for secondary stroke prevention. To characterize the effects of BT200 in blood of patients with large artery atherosclerosis stroke (LAA). Blood samples were obtained from 33 patients with acute stroke or transient ischemic attack to measure inhibition of VWF activity and VWF-dependent platelet function. Patients who received clopidogrel or dual antiplatelet therapy did not differ in VWF dependent platelet function tests from aspirin treated patients. Of 18 patients receiving clopidogrel with or without aspirin, only 3 had a prolonged collagen adenosine diphosphate closure time, and none of the patients had ristocetin induced aggregation in the target range. BT200 concentration-dependently reduced median VWF activity from 178 to < 3%, ristocetin induced platelet aggregation from 40U to < 10U and prolonged collagen adenosine diphosphate closure times from 93 s to > 300 s. Baseline VWF activity correlated (r = 0.86, p < 0.001) with concentrations needed to reduce VWF activity to < 20% of normal, indicating that BT200 acts in a target concentration-dependent manner. Together with a long half-life supporting once weekly administration, the safety and tolerability observed in an ongoing phase I trial, and the existence of a reversal agent, BT200 is an interesting drug candidate.

Shear Stress-Induced Activation of von Willebrand Factor and Cardiovascular Pathology

The von Willebrand factor (vWF) is a plasma protein that mediates platelet adhesion and leukocyte recruitment to vascular injury sites and carries coagulation factor VIII, a building block of the intrinsic pathway of coagulation. The presence of ultra-large multimers of vWF in the bloodstream is associated with spontaneous thrombosis, whereas its deficiency leads to bleeding. In cardiovascular pathology, the progression of the heart valve disease results in vWF deficiency and cryptogenic gastrointestinal bleeding. The association between higher plasma levels of vWF and thrombotic complications of coronary artery disease was described. Of note, it is not the plasma levels that are crucial for vWF hemostatic activity, but vWF activation, triggered by a rise in shear rates. vWF becomes highly reactive with platelets upon unfolding into a stretched conformation, at shear rates above the critical value (more than 5000 s⁻¹), which might occur at sites of arterial stenosis and injury. The activation of vWF and its counterbalance by ADAMTS-13, the vWF-cleaving protease, might contribute to complications of cardiovascular diseases. In this review, we discuss vWF involvement in complications of cardiovascular diseases and possible diagnostic and treatment approaches.