The discovery of dabigatran etexilate

Factor XI and XII inhibitors-Dawn of a new era

The history of coagulation cascade dates back to 17th century. The extrinsic and intrinsic pathways were proposed in 1998. Extrinsic pathway includes the tissue factor and stable factor which activates factor X and with help of factor V, this converts prothrombin to thrombin which is stabilised by factor XIII. This helps to seal the bleeding vessel and is a physiological process as there is only "limited" production of thrombin which doe not expand beyond the damaged site due to absence of tissue factor. On the other hand intrinsic pathway is activated by polyanions, neutrophilic extracellular traps which are present during infection and inflammation. These activate factor XI which activates factor X with the help of factor IX and VIII and then the common pathway ensues. But newer discoveries have shown that this is a very simplified way of explaining the coagulation system. The researches propose that haemostasis is divided into initiation, amplification and propagation phase. Also, the factor VII-tissue factor complex formed activates factor IX and leads to sustained thrombin production as the amount of thrombin produced by extrinsic pathway alone is not sufficient to form a haemostatic plug. Thrombin also activates factor XI and lead to self perpetuation of intrinsic pathway. All the anticoagulants have an inherent property of bleeding. So the newer factor XI and XII inhibitors focus to inhibit the excessive thrombin production without hampering the physiological haemostasis process. This is supported by the fact that congenital factor XI and XII deficiency does not cause excessive bleeding but increased levels did make patients more vulnerable to thromboembolism. This review shall focus on the various factor XI and XII inhibitors which are in the pipeline.

Pericytes in Alzheimer's disease: Key players and therapeutic targets

Alzheimer's disease (AD) is a devastating neurodegenerative disorder that leads to progressive cognitive decline and neuropathological changes. Pericytes, which are vessel mural cells on the basement membrane of capillaries, play a crucial role in regulating cerebrovascular functions and maintaining neurovascular unit integrity. Emerging research substantiates the involvement of pericytes in AD. This review provides a comprehensive overview of pericytes, including their structure, origin, and markers and various functions within the central nervous system. Emphatically, the review explores the intricate mechanisms through which pericytes contribute to AD, including their interactions with amyloid beta and apolipoprotein E, as well as various signaling pathways. The review also highlights potential for targeted pericyte therapy for AD, with a focus on stem cell therapy and drug treatments. Future research directions include the classification of pericyte subtypes, studies related to aging, and the role of pericytes in exosome-related mechanisms in AD pathology. In conclusion, this review consolidates current knowledge on the pivotal roles of pericytes in AD and their potential as therapeutic targets, providing valuable insights for future research and clinical interventions aimed at addressing the impact of AD on patients' lives.

Distinct pleiotropic effects of direct oral anticoagulants on cultured endothelial cells: a comprehensive review

Direct Oral Anticoagulants (DOACs) have simplified the treatment of thromboembolic disease. In addition to their established anticoagulant effects, there are indications from clinical and preclinical studies that DOACs exhibit also non-anticoagulant actions, such as anti-inflammatory and anti-oxidant actions, advocating overall cardiovascular protection. In the present study, we provide a comprehensive overview of the existing knowledge on the pleiotropic effects of DOACs on endothelial cells (ECs) in vitro and their underlying mechanisms, while also identifying potential differences among DOACs. DOACs exhibit pleiotropic actions on ECs, such as anti-inflammatory, anti-atherosclerotic, and anti-fibrotic effects, as well as preservation of endothelial integrity. These effects appear to be mediated through inhibition of the proteinase-activated receptor signaling pathway. Furthermore, we discuss the potential differences among the four drugs in this class. Further research is needed to fully understand the pleiotropic effects of DOACs on ECs, their underlying mechanisms, as well as the heterogeneity between various DOACs. Such studies can pave the way for identifying biomarkers that can help personalize pharmacotherapy with this valuable class of drugs.

New insight into the traditional model of the coagulation cascade and its regulation: illustrated review of a three-dimensional view

The coagulation process relies on an intricate network of three-dimensional structural interactions and subtle biological regulations. In the present review, we illustrate the state of the art of the structural biology of the coagulation cascade by surveying the Protein Data Bank and the EBI AlphaFold databases. Investigations performed in the last decade have provided structural information on essentially all players involved in the process. Indeed, the initial characterization of specific and rather canonical domains has been progressively extended to complicated multidomain proteins. Recently, the application of cryogenic electron microscopy techniques has unraveled the structural features of highly complex coagulation factors, which has led to enhanced understanding. This review initially focuses on the structure of the individual factors as a function of their involvement in intrinsic, extrinsic, and common pathways. A specific emphasis is given to what is known or unknown on the structural basis of each step of the cascade. Available data providing clues on the structural recognition of the factors involved in the functional partnerships of the pathways are illustrated. Recent structures of important complexes formed by these proteins with regulators are described, focusing on the drugs used as anticoagulants and on their reversal agents. Finally, we highlight the different roles that innovative biomolecules such as aptamers may have in the regulation of the cascade.

Preclinical testing of dabigatran in trypsin-dependent pancreatitis

Pancreatitis, the inflammatory disorder of the pancreas, has no specific therapy. Genetic, biochemical, and animal model studies revealed that trypsin plays a central role in the onset and progression of pancreatitis. Here, we performed biochemical and preclinical mouse experiments to offer proof of concept that orally administered dabigatran etexilate can inhibit pancreatic trypsins and shows therapeutic efficacy in trypsin-dependent pancreatitis. We found that dabigatran competitively inhibited all human and mouse trypsin isoforms (Ki range 10-79 nM) and dabigatran plasma concentrations in mice given oral dabigatran etexilate well exceeded the Ki of trypsin inhibition. In the T7K24R trypsinogen mutant mouse model, a single oral gavage of dabigatran etexilate was effective against cerulein-induced progressive pancreatitis, with a high degree of histological normalization. In contrast, spontaneous pancreatitis in T7D23A mice, which carry a more aggressive trypsinogen mutation, was not ameliorated by dabigatran etexilate, given either as daily gavages or by mixing it with solid chow. Taken together, our observations showed that benzamidine derivatives such as dabigatran are potent trypsin inhibitors and show therapeutic activity against trypsin-dependent pancreatitis in T7K24R mice. Lack of efficacy in T7D23A mice is probably related to the more severe pathology and insufficient drug concentrations in the pancreas.

Direct Oral Anticoagulants (DOACs) for Therapeutic Targeting of Thrombin, a Key Mediator of Cerebrovascular and Neuronal Dysfunction in Alzheimer's Disease

Although preclinical research and observer studies on patients with atrial fibrillation concluded that direct oral anticoagulants (DOACs) can protect against dementia like Alzheimer's disease (AD), clinical investigation towards therapeutical approval is still pending. DOACs target pathological thrombin, which is, like toxic tau and amyloid-ß proteins (Aß), an early hallmark of AD. Especially in hippocampal and neocortical areas, the release of parenchymal Aß into the blood induces thrombin and proinflammatory bradykinin synthesis by activating factor XII of the contact system. Thrombin promotes platelet aggregation and catalyzes conversion of fibrinogen to fibrin, leading to degradation-resistant, Aß-containing fibrin clots. Together with oligomeric Aß, these clots trigger vessel constriction and cerebral amyloid angiopathy (CAA) with vessel occlusion and hemorrhages, leading to vascular and blood-brain barrier (BBB) dysfunction. As consequences, brain blood flow, perfusion, and supply with oxygen (hypoxia) and nutrients decrease. In parenchymal tissue, hypoxia stimulates Aß synthesis, leading to Aß accumulation, which is further enhanced by BBB-impaired perivascular Aß clearance. Aß trigger neuronal damage and promote tau pathologies. BBB dysfunction enables thrombin and fibrin(ogen) to migrate into parenchymal tissue and to activate glial cells. Inflammation and continued Aß production are the results. Synapses and neurons die, and cognitive abilities are lost. DOACs block thrombin by inhibiting its activity (dabigatran) or production (FXa-inhibitors, e.g., apixaban, rivaroxaban). Therefore, DOAC use could preserve vascular integrity and brain perfusion and, thereby, could counteract vascular-driven neuronal and cognitive decline in AD. A conception for clinical investigation is presented, focused on DOAC treatment of patients with diagnosed AD in early-stage and low risk of major bleeding.

Effects of intermittent hypoxia with thrombin in an in vitro model of human brain endothelial cells and their impact on PAR-1/PAR-3 cleavage

Patients with obstructive sleep apnea/hypopnea (OSA) are at high risk of cerebrovascular diseases leading to cognitive impairment. The oxidative stress generated by intermittent hypoxia (IH) could lead to an increase in blood-brain barrier (BBB) permeability, an essential interface for the protection of the brain. Moreover, in patients with OSA, blood coagulation could be increased leading to cardiovascular complications. Thrombin is a factor found increased in these populations that exerts various cellular effects through activation of protease activated receptors (PARs). Thus, we have evaluated in an in vitro BBB model the association of IH with thrombin at two concentrations. We measured the apparent BBB permeability, expression of tight junctions, ROS production, HIF-1α expression, and cleavage of PAR-1/PAR-3. Pre-treatment with dabigatran was performed. IH and higher thrombin concentrations altered BBB permeability: high levels of HIF-1α expression, ROS and PAR-1 activation compared to PAR-3 in such conditions. Conversely, lower concentration of thrombin associated with IH appear to have a protective effect on BBB with a significant cleavage of PAR-3. Dabigatran reversed the deleterious effect of thrombin at high concentrations but also suppressed the beneficial effect of low dose thrombin. Therefore, thrombin and PARs represent novel attractive targets to prevent BBB opening in OSA.

The value and limitations of new oral anticoagulant plasma level assessments

The class of new oral anticoagulants (NOACs) has been developed to provide reliable oral anticoagulation without the need for therapeutic drug monitoring. Based on phase I and II trials and pharmacokinetic and pharmacodynamic modeling, fixed drug doses have been selected for large phase III clinical trials for each currently available NOAC. In these trials, the use of the fixed dose without plasma level assessments was shown to be at least as effective and at least as safe as vitamin K antagonists with continuous therapeutic drug monitoring. Real world evidence reaffirms that the use of a fixed NOAC dose without plasma level assessment is safe and effective in a large variety of patients. Nevertheless, measurement of NOAC plasma levels can add information that may be useful in some clinical scenarios. This review discusses the possible use cases, the limitations, and the practical implementation of measuring NOAC plasma concentrations.

Highly sensitive and selective lateral flow aptasensor for anti-coagulant dabigatran etexilate determination in blood

Dabigatran etexilate (DBG) is a new anticoagulant drug (commercially sold under the names Pradaxa® and Pradax™) that replaces Warfarin, the landmark agent for anticoagulation therapy. Inadequate administration of DBG or in the cases of massive bleeding that occurs after renal impairment, DBG therapy can carry a substantial life-threatening risks. One of the major limitations of DBG treatment is the lack of a simple and quick tool for measuring its level in blood in the case of massive bleedings or emergency operations. In this work, we have incorporated a previously isolated aptamer for DBG to develop a simple competitive lateral flow aptasensor (LFA) for the determination of DBG in buffer and blood samples. A full-length 60-mer aptamer as well as a truncated 38-mer aptamer were conjugated to gold nanoparticles (AuNPs) via thiol-Au coupling chemistry. After appropriate AuNP surface passivation steps, the aptamer's core region was hybridized with 8-mer biotinylated sequences. The conjugated particles could be capture on the test line by the interaction of the biotin molecules with a previously deposited streptavidin. Incubation of the conjugated particles with DBG causes the aptamer to undergo a conformational change that releases the 8-mer biotinylated sequences and result in the disappearance of the test line. Lysozyme protein was used to construct the control line that non-specifically interacts with the conjugated particles whether or not the target compound is present. The developed LFA achieves 20 nM detection level in buffer and blood samples, operates within the nanomolar range, and shows excellent selectivity against potential interfering molecules. The developed sensor could help assessing the levels of DBG in medical conditions that require rapid interventions.

Identifying of Anti-Thrombin Active Components From Curcumae Rhizoma by Affinity-Ultrafiltration Coupled With UPLC-Q-Exactive Orbitrap/MS

Recent studies concerning products that originate from natural plants have sought to clarify active ingredients, which both explains the mechanisms of the function and aids in quality control during production. As a traditional functional plant, Curcumae Rhizoma (CR) has been proven to be effective in promoting blood circulation and removing blood stasis. However, the components that play a role in its huge compound library are still unclear. The present study aimed to develop a high-throughput screening method to identify thrombin inhibitors in CR and validate them by in vitro and in vivo experiments. The effect of CR on thrombin in HUVECs cells was determined by ELISA, then an affinity-ultrafiltration-UPLC-Q-Exactive Orbitrap/MS approach was applied. Agatroban and adenosine were used as positive and negative drugs respectively to verify the reliability of the established method. The in vitro activity of the compounds was determined by specific substrate S-2238. The in vivo effect of the active ingredients was determined using zebrafish. Molecular docking was used to understand the internal interactions between compounds and enzymes. ELISA results showed that CR had an inhibitory effect on thrombin. The screening method established in this paper is reliable, by which a total of 15 active compounds were successfully identified. This study is the first to report that C7, 8, and 11 have in vitro thrombin-inhibitory activity and significantly inhibit thrombosis in zebrafish models at a safe dose. Molecular docking studies were employed to analyze the possible active binding sites, with the results suggesting that compound 16 is likely a better thrombin inhibitor compared with the other compounds. Based on the affinity-ultrafiltration-UPLC-Q-Exactive Orbitrap/MS approach, a precisely targeted therapy method using bio-active compounds from CR might be successfully established, which also provides a valuable reference for targeted therapy, mechanism exploration, and the quality control of traditional herbal medicine.

Thrombin Signaling Contributes to High Glucose-Induced Injury of Human Brain Microvascular Endothelial Cells

BACKGROUND

Diabetes is one of the strongest disease-related risk factors for Alzheimer's disease (AD). In diabetics, hyperglycemia-induced microvascular complications are the major cause of end-organ injury, contributing to morbidity and mortality. Microvascular pathology is also an important and early feature of AD. The cerebral microvasculature may be a point of convergence of both diseases. Several lines of evidence also implicate thrombin in AD as well as in diabetes.

OBJECTIVE

Our objective was to investigate the role of thrombin in glucose-induced brain microvascular endothelial injury.

METHODS

Cultured Human brain microvascular endothelial cells (HBMVECs) were treated with 30 mM glucose±100 nM thrombin and±250 nM Dabigatran or inhibitors of PAR1, p38MAPK, MMP2, or MMP9. Cytotoxicity and thrombin activity assays on supernatants and western blotting for protein expression in lysates were performed.

RESULTS

reatment of HBMVECs with 30 mM glucose increased thrombin activity and expression of inflammatory proteins TNFα, IL-6, and MMPs 2 and 9; this elevation was reduced by the thrombin inhibitor dabigatran. Direct treatment of brain endothelial cells with thrombin upregulated p38MAPK and CREB, and induced TNFα, IL6, MMP2, and MMP9 as well as oxidative stress proteins NOX4 and iNOS. Inhibition of thrombin, thrombin receptor PAR1 or p38MAPK decrease expression of inflammatory and oxidative stress proteins, implying that thrombin may play a central role in glucose-induced endothelial injury.

CONCLUSION

Since preventing brain endothelial injury would preserve blood-brain barrier integrity, prevent neuroinflammation, and retain intact functioning of the neurovascular unit, inhibiting thrombin, or its downstream signaling effectors, could be a therapeutic strategy for mitigating diabetes-induced dementia.

Improved efficacy/safety profile of factor XIa inhibitor BMS-724296 versus factor Xa inhibitor apixaban and thrombin inhibitor dabigatran in cynomolgus monkeys

Background

Inhibition of activated factor XI (FXIa) is a promising antithrombotic drug target. BMS-724296 is a selective, reversible, small-molecule inhibitor of human FXIa (K_i 0.3 nM).

Objectives

This study assessed effects of BMS-724296 versus standard-of-care oral anticoagulants apixaban (activated factor X inhibitor) and dabigatran (thrombin inhibitor) on arterial thrombosis, kidney bleeding time (KBT), and clotting time (CT) in nonhuman primate (NHP) cynomolgus monkey models.

Methods

Carotid artery thrombosis was produced by electrical stimulation in anesthetized NHPs. Hemostasis was assessed with a provoked KBT model. Thrombosis, KBT, and CT were monitored. Vehicle and various doses of BMS-724296, apixaban, and dabigatran were administered as bolus (intravenous [i.v.]) followed by infusion starting 30 minutes before initiation of thrombosis and continued until the experiment's end (n = 3-8/group). Primary end points included thrombus weight reduction (TWR), KBT, and CT (activated partial thromboplastin time [aPTT], prothrombin time [PT], and thrombin time [TT]).

Results

BMS-724296 at 0.025 + 0.05, 0.05 + 0.1, 0.102 + 0.2, and 0.4 + 0.8 mg/kg+mg/kg/h i.v. (bolus + infusion) reduced thrombus weight by 0 ± 0, 35 ± 7*, 72 ± 4*, and 86 ± 4%*, respectively (*P < .05 vs vehicle; n = 5-6/group). BMS-724296 at the highest dose (0.4 + 0.8 mg/kg+mg/kg/h) did not increase KBT compared to vehicle (109 ± 6 vs 113 ± 20 seconds, respectively) and increased ex vivo aPTT by 2.9 ± 0.1-fold without changing PT and TT. In companion NHP studies, high doses of apixaban and dabigatran produced similar TWR as BMS-724296, but increased KBT 4.3 ± 0.5-fold and 5.8 ± 0.5-fold, respectively (n = 3-4/group).

Conclusions

BMS-724296 produced similar antithrombotic efficacy as apixaban and dabigatran but with no increase in KBT in NHPs. These findings suggest that FXIa inhibitors may provide safe and effective antithrombotic therapy.

Alzheimer's Disease-Rationales for Potential Treatment with the Thrombin Inhibitor Dabigatran

Alzheimer's disease (AD) is caused by neurodegenerative, but also vascular and hemostatic changes in the brain. The oral thrombin inhibitor dabigatran, which has been used for over a decade in preventing thromboembolism and has a well-known pharmacokinetic, safety and antidote profile, can be an option to treat vascular dysfunction in early AD, a condition known as cerebral amyloid angiopathy (CAA). Recent results have revealed that amyloid-β proteins (Aβ), thrombin and fibrin play a crucial role in triggering vascular and parenchymal brain abnormalities in CAA. Dabigatran blocks soluble thrombin, thrombin-mediated formation of fibrin and Aβ-containing fibrin clots. These clots are deposited in brain parenchyma and blood vessels in areas of CAA. Fibrin-Aβ deposition causes microvascular constriction, occlusion and hemorrhage, leading to vascular and blood-brain barrier dysfunction. As a result, blood flow, perfusion and oxygen and nutrient supply are chronically reduced, mainly in hippocampal and neocortical brain areas. Dabigatran has the potential to preserve perfusion and oxygen delivery to the brain, and to prevent parenchymal Aβ-, thrombin- and fibrin-triggered inflammatory and neurodegenerative processes, leading to synapse and neuron death, and cognitive decline. Beneficial effects of dabigatran on CAA and AD have recently been shown in preclinical studies and in retrospective observer studies on patients. Therefore, clinical studies are warranted, in order to possibly expand dabigatran approval for repositioning for AD treatment.

The Impact of Dabigatran Treatment on Sinusoidal Protection Against Hepatic Ischemia/Reperfusion Injury in Mice

Thrombin is a key player in the coagulation cascade, and it is attracting much attention as a promotor of cellular injured signaling. In ischemia/reperfusion injury (IRI), which is a severe complication of liver transplantation, thrombin may also promote tissue damage. The aim of this study is to reveal whether dabigatran, a direct thrombin inhibitor, can attenuate hepatic IRI with focusing on a protection of sinusoidal endothelial cells (SECs). Both clinical patients who underwent hepatectomy and in vivo mice model of 60-minute hepatic partial-warm IRII, thrombin generation was evaluated before and after IRI. In next study, IRI mice were treated with or without dabigatran. In addition, hepatic SECs and hepatocytes pretreated with or without dabigatran were incubated in hypoxia/reoxygenation (H-R) environment in vitro. Thrombin generation evaluated by thrombin-antithrombin complex (TAT) was significantly enhanced after IRI in the clinical study and in vivo study. Thrombin exacerbated lactate dehydrogenase cytotoxicity levels in a dose-dependent manner in vitro. In an IRI model of mice, dabigatran treatment significantly improved liver histological damage, induced sinusoidal protection, and provided both antiapoptotic and anti-inflammatory effects. Furthermore, dabigatran not only enhanced endogenous thrombomodulin (TM) but also reduced excessive serum high-mobility group box-1 (HMGB-1). In H-R models of SECs, not hepatocytes, pretreatment with dabigatran markedly attenuated H-R damage, enhanced TM expression in cell lysate, and decreased extracellular HMGB-1. The supernatant of SECs pretreated with dabigatran protected hepatocytes from H-R damage and cellular death. Thrombin exacerbated hepatic IRI, and excessive extracellular HMGB-1 caused severe inflammation-induced and apoptosis-induced liver damage. In this situation, dabigatran treatment improved vascular integrity via sinusoidal protection and degraded HMGB-1 by endogenous TM enhancement on SECs, greatly ameliorating hepatic IRI.

Dabigatran reduces thrombin-induced neuroinflammation and AD markers in vitro: Therapeutic relevance for Alzheimer's disease

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Thrombin treatment induced proteins linked to neuroinflammation in SH-SY5Y cells.

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Thrombin exposure elevated the expression/ levels of proteins of AD pathway.

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EMSA showed dabigatran reduced activation of NFκB in SH-SY5Y cells.

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Dabigatran reduced thrombin-driven neuroinflammation and downstream AD pathology.

Background

Vascular risk factors such as atherosclerosis, diabetes, and elevated homocysteine levels are strongly correlated with onset of Alzheimer's disease (AD). Emerging evidence indicates that blood coagulation protein thrombin is associated with vascular and non-vascular risk factors of AD. Here, we examined the effect of thrombin and its direct inhibitor dabigatran on key mediators of neuro-inflammation and AD pathology in the retinoic acid (RA)-differentiated human neuroblastoma cell line SH-SY5Y.

Methods

SH-SY5Y cells exposed to thrombin concentrations (10–100 nM) +/- 250 nM dabigatran for 24 h were analyzed for protein and gene expression. Electrophoretic mobility shift assay (EMSA) was used to determine DNA binding of NFkB. Western blotting, qRT-PCR and ELISA were used to measure the protein, mRNA, and activity levels of known AD hallmarks and signaling molecules.

Results

Dabigatran treatment attenuated thrombin-induced increase in DNA binding of NFκB by 175% at 50 nM and by 77% at 100 nM thrombin concentration. Thrombin also augmented accumulation of Aβ protein expression and phosphorylation of p38 MAPK, a downstream molecule in the signaling cascade, expression of pro-apoptotic mediator caspase 3, APP, tTau and pTau. Additionally, thrombin increased BACE1 activity, GSK3β expression, and APP, BACE1, Tau and GSK3β mRNA levels. Co-incubation with dabigatran attenuated thrombin-induced increases in the protein, mRNA, and activities of the aforesaid molecules to various extents (between −31% and −283%).

Conclusion

Our data demonstrates that thrombin promotes AD-related pathological changes in neuronal cultures and suggests that use of direct oral anticoagulants may provide a therapeutic benefit against thrombin-driven neuroinflammation and downstream pathology in AD.

Observations on clot properties in atrial fibrillation: Relation to renal function and choice of anticoagulant

INTRODUCTION

Atrial fibrillation (AF) is associated with increased risk of stroke and thromboembolism. Patients with AF have a higher incidence of renal impairment, which may influence the risks of systemic thromboembolism or bleeding. We determined how different oral anticoagulants affect plasma clot properties and whether progressive renal dysfunction affects plasma clot properties in patients on warfarin.

MATERIALS AND METHODS

We studied 257 patients with AF receiving oral anticoagulants. Furthermore, we recruited 192 separate patients with AF on warfarin and divided them in 4 groups based on estimated glomerular filtration rate (eGFR). Platelet poor plasma was prepared and clot formation and fibrinolysis was monitored kinetically up to 1 h.

RESULTS

Rate of clot formation was significantly slower with dabigatran and rivaroxaban. Time between 50% clotting and 50% lysis was prolonged in patients receiving warfarin compared to NOACs. Time to 50% lysis from maximum absorbance was significantly shorter in patients receiving rivaroxaban. Time between 50% clotting and 50% lysis became significantly prolonged with worsening eGFR. Time to 50% lysis from maximum absorbance was prolonged as renal function worsened.

CONCLUSIONS

Compared to warfarin, NOACs differently modulate coagulation and fibrinolysis under ex vivo conditions. Worsening renal function in AF patients on warfarin prolongs fibrinolysis, potentially increasing the risk of thrombosis.

Long-Term Dabigatran Treatment Delays Alzheimer's Disease Pathogenesis in the TgCRND8 Mouse Model

BACKGROUND

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder with important vascular and hemostatic alterations that should be taken into account during diagnosis and treatment.

OBJECTIVES

This study evaluates whether anticoagulation with dabigatran, a clinically approved oral direct thrombin inhibitor with a low risk of intracerebral hemorrhage, ameliorates AD pathogenesis in a transgenic mouse model of AD.

METHODS

TgCRND8 AD mice and their wild-type littermates were treated for 1 year with dabigatran etexilate or placebo. Cognition was evaluated using the Barnes maze, and cerebral perfusion was examined by arterial spin labeling. At the molecular level, Western blot and histochemical analyses were performed to analyze fibrin content, amyloid burden, neuroinflammatory activity, and blood-brain barrier (BBB) integrity.

RESULTS

Anticoagulation with dabigatran prevented memory decline, cerebral hypoperfusion, and toxic fibrin deposition in the AD mouse brain. In addition, long-term dabigatran treatment significantly reduced the extent of amyloid plaques, oligomers, phagocytic microglia, and infiltrated T cells by 23.7%, 51.8%, 31.3%, and 32.2%, respectively. Dabigatran anticoagulation also prevented AD-related astrogliosis and pericyte alterations, and maintained expression of the water channel aquaporin-4 at astrocytic perivascular endfeet of the BBB.

CONCLUSIONS

Long-term anticoagulation with dabigatran inhibited thrombin and the formation of occlusive thrombi in AD; preserved cognition, cerebral perfusion, and BBB function; and ameliorated neuroinflammation and amyloid deposition in AD mice. Our results open a field for future investigation on whether the use of direct oral anticoagulants might be of therapeutic value in AD.

Mapping the binding region of aptamer targeting small molecule: Dabigatran etexilate, an anti-coagulant

Aptamers are single-stranded DNA or RNA, which have attracted considerable scientific interest due to their characteristic of specific and selective binding to target molecules. They are evolved from the in vitro process known as systematic evolution of ligands by exponential enrichment (SELEX). This paper reports a simple experimental approach to elucidate the binding region of small targets binding aptamers. A previously isolated 60-mer aptamer for the anti-coagulant dabigatran etexilate (DBG) was used for this investigation. Complimentary sequences labelled with a fluorophore and a quencher were used for testing the binding region by change in the fluorescence signal. The full-length aptamer was truncated to multiple shorter copies including a 38 nucleotides sequence that showed 47 fold high affinity compared to the original aptamer. Circular dichroism spectroscopy (CD) measurements indicate that the 38-mer is remarkably more sensitive than the parent aptamer. The truncated 38-mer sequence was used to construct a turn-on fluorescence sensor with the detection limit of 1 nM. The performance of the sensor was examined in blood serum samples and showed excellent recovery percentages exceeding 98%. The reported screening protocol could be applied to the growing small targets aptasensors that require efficient binding aptamer sequences coupled with optimum signal transduction methods.

Atrial fibrillation in patients with end-stage renal disease on hemodialysis: Magnitude of the problem and new approach to oral anticoagulation

Atrial fibrillation (AF) is a frequent comorbid condition in patients with end-stage renal disease on hemodialysis (HD) with a prevalence of up to 27%. The incidence rate of stroke in AF patients on HD is approximately 5%. The AF-associated risk of stroke is a major clinical challenge because current evidence for anticoagulation in HD patients with AF is based on observational data. Results from these observational studies is largely contradictory because they do not show a clear benefit of vitamin K antagonists over no treatment in terms of stroke prevention, and they show an increased risk of hemorrhage associated with anticoagulation treatment in HD patients. HD patients were not included in randomized trials of the direct oral anticoagulants (DOACs), and therefore there is no evidence to support efficacy and safety of DOACs compared to vitamin K antagonists in HD patients. The pharmacological characteristics of DOACs are of particular interest in the HD setting. The factor Xa inhibitors rivaroxaban, apixaban, and edoxaban are not predominantly eliminated via the kidneys. The thrombin inhibitor dabigatran is 80% eliminated via the kidneys but is dialyzable due to its low protein binding. In this narrative review, we examine the current state of evidence regarding the prevalence of AF in patients on HD, the associated risk of stroke, and the efficacy and safety of anticoagulation for stroke prevention in the HD setting. Further, based on the pharmacokinetic properties of DOACs, we discuss their potential use in patients on HD and ongoing randomized trials.

In Vitro Selection of Specific DNA Aptamers Against the Anti-Coagulant Dabigatran Etexilate

Dabigatran Etexilate (PRADAXA) is a new oral anticoagulant increasingly used for a number of blood thrombosis conditions, prevention of strokes and systemic emboli among patients with atrial fibrillation. It provides safe and adequate anticoagulation for prevention and treatment of thrombus in several clinical settings. However, anticoagulation therapy can be associated with an increased risk of bleeding. There is a lack of specific laboratory tests to determine the level of this drug in blood. This is considered the most important obstacles of using this medication, particularly for patients with trauma, drug toxicity, in urgent need for surgical interventions or uncontrolled bleeding. In this work, we performed Systematic evolution of ligands by exponential enrichment (SELEX) to select specific DNA aptamers against dabigatran etexilate. Following multiple rounds of selection and enrichment with a randomized 60-mer DNA library, specific DNA aptamers for dabigatran were selected. We investigated the affinity and specificity of generated aptamers to the drug showing dissociation constants (Kd) ranging from 46.8-208 nM. The most sensitive aptamer sequence was selected and applied in an electrochemical biosensor to successfully achieve 0. 01 ng/ml level of detection of the target drug. With further improvement of the assay and optimization, these aptamers would replace conventional antibodies for developing detection assays in the near future.

Direct thrombin inhibition with dabigatran attenuates pressure overload-induced cardiac fibrosis and dysfunction in mice

INTRODUCTION

The multifunctional serine protease thrombin exerts proinflammatory and profibrotic cellular effects that may contribute to cardiac remodeling. This study was designed to investigate whether direct thrombin inhibition with dabigatran attenuates myocardial injury in the setting of pressure overload-induced heart failure.

MATERIAL AND METHODS

Transverse aortic constriction (TAC) surgery was performed on C57Bl/6J male mice to elicit cardiac hypertrophy. TAC, or sham, mice were randomly assigned to receive chow supplemented with the oral anticoagulant, dabigatran etexilate, or placebo.

RESULTS

Dabigatran did not affect cardiac hypertrophy, as measured by heart weight-to-body weight or the heart weight-to-tibia length, although a non-significant reduction in myocardial hypertrophic markers (ANP, BNP and MHC) occurred. Dabigatran reduced perivascular fibrosis by 25%, interstitial fibrosis by 54%, and the expression of myocardial fibrosis markers collagen I & III, MMP9, SMA, and PAR-1. These changes were associated with significant improvement in both coronary flow reserve and global left ventricular function. In cultured cardiac fibroblasts, dabigatran decreased thrombin and PAR-1-mediated collagen deposition by 30% and 37%, respectively.

CONCLUSIONS

Dabigatran attenuates cardiac fibrosis in the setting of pressure overload and improves coronary flow reserve and global cardiac function possibly by inhibiting thrombin activity and down-regulating PAR-1 expression in the absence of an effect on cardiomyocyte hypertrophy.

Thrombocytopenia induced by dabigatran: two case reports

Background

Vitamin K inhibitors (e.g. warfarin) and indirect thrombin inhibitors (e.g. heparin) are widely used to prevent thromboembolic disorders (e.g. myocardial infarction, venous thromboembolism, and stroke). These agents have been mainstays of anticoagulation for people older than 60 years. However, their administration is associated with a risk of bleeding and requires careful monitoring of patients. Novel oral anticoagulants (NOACs), such as dabigatran, are significantly safer in preventing thromboembolism than warfarin and heparin (sporadically causes thrombocytopenia) and are more specific for their target protein, thrombin. The major advantage of dabigatran, a direct thrombin inhibitor, is that it reversibly inhibits both free and clot-bound thrombin by tight binding affinity and the predictable pharmacodynamic effect. A few studies, however, reported that dabigatran can cause thrombocytopenia, although the underlying mechanism remains unclear. Thus, an antidote for dabigatran was developed to prevent thrombocytopenia.

Case presentation

In this report, we discuss two cases of thrombocytopenia and purpura after dabigatran treatment. A 73-year-old man showed hemorrhagic necrotic skin lesions on his neck and right hand. He was administered dabigatran (220 mg/day) for cerebral infarction for three days and his platelet count decreased abruptly (6000/μL). This suggested that dabigatran had caused thrombocytopenia and purpura; therefore, dabigatran administration was discontinued. The results of a blood test, performed 14 days after stopping dabigatran treatment, showed that the platelet count had recovered to the normal range of more than 150,000/μL. A 75-year-old woman had taken warfarin continuously for 8 years. However, she had a new cerebral infarction. Therefore, warfarin treatment was replaced with dabigatran (300 mg/day). Her platelet count decreased (41,000/μL) significantly and dabigatran treatment was discontinued. The blood test results show that platelet counts gradually recovered to the normal range.

Conclusions

Dabigatran application may cause bleeding; therefore, careful monitoring during dabigatran treatment is required to prevent thrombocytopenia. An explanation is that the interaction of dabigatran with thrombin, because of its strong binding affinity, may cause the observed thrombocytopenia.

The Reversal of Direct Oral Anticoagulants in Animal Models

Several direct oral anticoagulants (DOACs), including direct thrombin and factor Xa inhibitors, have been approved as alternatives to vitamin K antagonist anticoagulants. As with any anticoagulant, DOAC use carries a risk of bleeding. In patients with major bleeding or needing urgent surgery, reversal of DOAC anticoagulation may be required, presenting a clinical challenge. The optimal strategy for DOAC reversal is being refined, and may include use of hemostatic agents such as prothrombin complex concentrates (PCCs; a source of concentrated clotting factors), or DOAC-specific antidotes (which bind their target DOAC to abrogate its activity). Though promising, most specific antidotes are still in development.Preclinical animal research is the key to establishing the efficacy and safety of potential reversal agents. Here, we summarize published preclinical animal studies on reversal of DOAC anticoagulation. These studies (n = 26) were identified via a PubMed search, and used rodent, rabbit, pig, and non-human primate models. The larger of these animals have the advantages of similar blood volume/hemodynamics to humans, and can be used to model polytrauma. We find that in addition to varied species being used, there is variability in the models and assays used between studies; we suggest that blood loss (bleeding volume) is the most clinically relevant measure of DOAC anticoagulation-related bleeding and its reversal.The studies covered indicate that both PCCs and specific reversal agents have the potential to be used as part of a clinical strategy for DOAC reversal. For the future, we advocate the development and use of standardized, clinically, and pharmacologically relevant animal models to study novel DOAC reversal strategies.

Effect of bosutinib on the absorption of dabigatran etexilate mesylate, a P-glycoprotein substrate, in healthy subjects

PURPOSE

Bosutinib, a dual Src and Abl tyrosine kinase inhibitor for the treatment of chronic myeloid leukemia, demonstrated concentration-dependent inhibitory effects on P-glycoprotein (P-gp)-mediated digoxin efflux in vitro, suggesting that bosutinib may inhibit P-gp substrates. The effect of bosutinib on dabigatran etexilate mesylate (EM) absorption, a P-gp substrate, was evaluated.

METHODS

In this open-label, randomized, single-dose, one-cohort, two-sequence, two-period crossover study, healthy, fed subjects received dabigatran EM (150 mg × 1 orally) alone or 1 h after receiving bosutinib tablets (100 mg × 5 orally).

RESULTS

Dabigatran EM monotherapy and concurrent administration of dabigatran EM with bosutinib resulted in similar values for concentration time curves from time zero extrapolated to infinity (AUC_inf), but slightly lower maximum plasma concentration (C _max) values (AUC_inf, 1182 and 1186 ng·h/mL, respectively; C _max, 129.8 and 114.1 ng/mL). The time to maximum concentration for dabigatran was 2.99 and 3.99 h for combination therapy. The ratio of the adjusted geometric means (test/reference) of dabigatran AUC_inf and C _max (90 % confidence interval) were 101.4 % (89.6-114.9 %) and 89.7 % (77.8-103.4 %), respectively, following administration of dabigatran EM with bosutinib (test) relative to dabigatran EM administered alone (reference). Six subjects receiving combination treatment reported a total of seven adverse events (AEs) versus none for subjects receiving monotherapy alone. All AEs were mild to moderate and considered treatment related.

CONCLUSION

These data demonstrate that single doses of bosutinib do not affect dabigatran exposure, suggesting that bosutinib is not a clinical inhibitor of P-gp.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02102633. https://clinicaltrials.gov/ct2/show/NCT02102633?term=NCT02102633&rank=1.

An update on laboratory measurements of Dabigatran: Smart specific and calibrated dedicated assays for measuring anti-IIa activity in plasma

Use of Direct Oral Anticoagulants (DOACs) is continuously increasing for clinical application. The first product released was Dabigatran, which was proposed for many preventive and curative applications, especially for prevention of stroke in patients with non-valvular atrial fibrillation. Although measurement of Dabigatran Anti-IIa activity in plasma is not requested on a routine basis, in some situations its measurement is clinically useful. Especially, before an emergency surgery in treated patients, where its presence at high concentrations, which will expose the patient at an increased bleeding risk, has to be excluded. Hence, smart, specific, rapid and accurate quantitative assays are warranted as an essential required. Hemoclot™ Thrombin Inhibitors and Biophen® DTI were specifically designed for these applications, and can be used on all automated instruments with a standard range protocol for measuring concentrations at peak, or with a low range protocol for testing residual concentrations. Both functional assays have a good correlation with the reference LC-MS/MS method, and concentrations measured are similar. Performances of these assays and interferences of various substances or drugs are discussed. Some differences in variations of clotting times are observed between mechanical or optical clot detection instruments, which could be explained by the fibrin clot structure, altered by direct Factor Xa inhibitors, and more especially Rivaroxaban. Both clotting and chromogenic assays offer a safe and accurate quantitative measurement of Dabigatran in plasma in all situations where this determination is requested. In short this manuscript provides an in depth update on current opinions on laboratory aspects of measuring Dabigatran concentrations in plasma, when required.

Enhanced elimination of dabigatran through extracorporeal methods

Several pharmacokinetic studies have suggested that dabigatran possesses a number of ideal properties for expedited removal via extracorporeal methods. However, this practice has not been prospectively evaluated in patients with life-threatening bleeding or requiring emergency surgery secondary to dabigatran-associated coagulopathy. The purpose of this literature review is to evaluate the published evidence surrounding extracorporeal removal of dabigatran in the setting of emergency surgery or life-threatening bleeding. A query of MEDLINE, Web of Science, International Pharmaceutical Abstracts, and Google Scholar using the terms dabigatran, dabigatran etexilate, hemodialysis, renal replacement therapy, hemorrhage, and atrial fibrillation was used to retrieve relevant literature. Furthermore, a manual search of the references of the identified literature was performed to capture additional data. Current evidence suggests that extracorporeal removal of dabigatran may play a role in the setting of life-threatening bleeding and emergent surgery. Conflicting evidence exists with regard to the potential for redistribution based on serum dabigatran concentrations. In addition, a number of practicalities must be considered before incorporating this technique in the clinical setting. Extracorporeal removal of dabigatran may be a treatment modality in selected patients who require emergency reversal.

Update on Edoxaban for the Prevention and Treatment of Thromboembolism: Clinical Applications Based on Current Evidence

Vitamin K antagonists (VKA) and heparins have been utilized for the prevention and treatment of thromboembolism (arterial and venous) for decades. Targeting and inhibiting specific coagulation factors have led to new discoveries in the pharmacotherapy of thromboembolism management. These targeted anticoagulants are known as direct oral anticoagulants (DOACs). Two pharmacologically distinct classes of targeted agents are dabigatran etexilate (Direct Thrombin Inhibitor (DTI)) and rivaroxaban, apixaban, and edoxaban (direct oral factor Xa inhibitors (OFXaIs)). Emerging evidence from the clinical trials has shown that DOACs are noninferior to VKA or low-molecular-weight heparins in the prevention and treatment of thromboembolism. This review examines the role of edoxaban, a recently approved OFXaI, in the prevention and treatment of thromboembolism based on the available published literature. The management of edoxaban in the perioperative setting, reversibility in bleeding cases, its role in cancer patients, the relevance of drug-drug interactions, patient satisfaction, financial impacts, and patient education will be discussed.

Characterization of thrombin-bound dabigatran effects on protease-activated receptor-1 expression and signaling in vitro

Thrombin, the key effector protease of the coagulation cascade, drives fibrin deposition and activates human platelets through protease-activated receptor-1 (PAR1). These processes are critical to the progression of thrombotic diseases. Thrombin is the main target of anticoagulant therapy, and major efforts have led to the discovery of new oral direct inhibitors of thrombin. Dabigatran is the first oral anticoagulant licensed for the prevention of thromboembolisms associated with orthopedic surgery and stroke prevention in atrial fibrillation. Dabigatran is a direct thrombin inhibitor that effectively blocks thrombin's catalytic activity but does not preclude thrombin's exosites and binding to fibrinogen. Thus, we hypothesized that catalytically inactive thrombin retains the capacity to bind to PAR1 through exosite-I and may modulate its function independent of receptor cleavage and activation. Here, we report that dabigatran at clinically relevant concentrations is an effective and acute inhibitor of thrombin-induced PAR1 cleavage, activation, internalization, and β-arrestin recruitment in vitro. Interestingly, prolonged exposure to catalytic inactive thrombin incubated with dabigatran at 20-fold higher therapeutic concentration resulted in increased PAR1 cell-surface expression, which correlated with higher detectable levels of ubiquitinated receptor. These findings are consistent with ubiquitin function as a negative regulator of PAR1 constitutive internalization. Increased PAR1 expression also enhanced agonist-induced phosphoinositide hydrolysis and endothelial barrier permeability. Thus, catalytically inactive thrombin appears to modulate PAR1 function in vitro by stabilizing receptor cell-surface expression; but given the high clearance rate of thrombin, the high concentration of dabigatran required to achieve this effect the in vivo physiologic relevance is unknown.

A proposal for dose-adjustment of dabigatran etexilate in atrial fibrillation guided by thrombin time

Dabigatran is an oral anticoagulant that is increasingly used for atrial fibrillation (AF). Presently, many authorities state that routine laboratory coagulation monitoring is not required. However, data have recently been published demonstrating that higher trough plasma dabigatran concentrations are associated with lower thromboembolic and higher haemorrhagic event rates. Using these data, we simulate a range of AF patients with varying risks for these events and derive a target range of trough plasma dabigatran concentrations (30-130 μg l(-1) ). Finally, we propose that a conventional screening coagulation assay, the thrombin time (TT), can be used to discern whether or not patients are within this range of dabigatran concentrations.

Prothrombin complex concentrates and a specific antidote to dabigatran are effective ex-vivo in reversing the effects of dabigatran in an anticoagulation/liver trauma experimental model

Introduction

New oral anticoagulants are effective alternatives to warfarin. However, no specific reversal agents are available for life-threatening bleeding or emergency surgery. Using a porcine model of trauma, this study assessed the ability of prothrombin complex concentrate (PCC), activated PCC (aPCC), recombinant FVIIa (rFVIIa) and a specific antidote to dabigatran (aDabi-Fab) to reverse the anticoagulant effects of dabigatran.

Methods

Dabigatran etexilate (DE) was given orally for 3 days (30 mg/kg bid) and intravenously on day 4 to achieve consistent, supratherapeutic concentrations of dabigatran. Blood samples were collected at baseline, after oral DE, after intravenous dabigatran, and 60 minutes post-injury. PCC (30 and 60 U/kg), aPCC (30 and 60 U/kg), rFVIIa (90 and 180 μg/kg) and antidote (60 and 120 mg/kg) were added to blood samples ex-vivo. Coagulation was assessed by thromboelastometry, global coagulation assays and diluted thrombin time.

Results

Plasma concentrations of dabigatran were 380 ± 106 ng/ml and 1423 ± 432 ng/ml after oral and intravenous administration, respectively, and all coagulation parameters were affected by dabigatran. Both PCCs and aDabi-Fab, but not rFVIIa, reversed the effects of dabigatran on thromboelastometry parameters and prothrombin time. In contrast, aPTT was only normalised by aDabi-Fab. Plasma concentration (activity) of dabigatran remained elevated after PCC and rFVIIa therapy, but was not measureable after aDabi-Fab.

Conclusion

In conclusion, PCC and aPCC were effective in reducing the anticoagulant effects of dabigatran under different conditions, while aDabi-Fab fully corrected all coagulation measures and decreased the plasma concentration of dabigatran below the limit of detection. No significant effects were observed with rFVIIa.

Differential contribution of FXa and thrombin to vascular inflammation in a mouse model of sickle cell disease

Activation of coagulation and vascular inflammation are prominent features of sickle cell disease (SCD). Previously, we have shown that inhibition of tissue factor (TF) attenuates activation of coagulation and vascular inflammation in mouse models of SCD. In this study, we examined the mechanism by which coagulation proteases enhance vascular inflammation in sickle BERK mice. To specifically investigate the contribution of FXa and thrombin, mice were fed chow containing either rivaroxaban or dabigatran, respectively. In addition, we used bone marrow transplantation to generate sickle mice deficient in either protease activated receptor-1 (PAR-1) or protease activated receptor-2 (PAR-2) on nonhematopoietic cells. FXa inhibition and PAR-2 deficiency in nonhematopoietic cells attenuated systemic inflammation, measured by plasma levels of interleukin-6 (IL-6). In contrast, neither thrombin inhibition nor PAR-1 deficiency in nonhematopoietic cells affected plasma levels of IL-6 in sickle mice. However, thrombin did contribute to neutrophil infiltration in the lung, independently of PAR-1 expressed by nonhematopoietic cells. Furthermore, the TF-dependent increase in plasma levels of soluble vascular cell adhesion molecule-1 in sickle mice was not mediated by FXa or thrombin. Our data indicate that TF, FXa, and thrombin differentially contribute to vascular inflammation in a mouse model of SCD.