Long-Term Dabigatran Treatment Delays Alzheimer's Disease Pathogenesis in the TgCRND8 Mouse Model.
ABSTRACT: 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.
Project description:Blood-brain barrier (BBB) defects and cerebrovascular dysfunction contribute to amyloid-? (A?) brain accumulation and drive Alzheimer disease (AD) pathology. By regulating vascular functions and inflammation in the microvasculature, a disintegrin and metalloprotease with thrombospondin type I motif, member 13 (ADAMTS13) plays a significant protective effect in atherosclerosis and stroke. However, whether ADAMTS13 influences AD pathogenesis remains unclear. Using in vivo multiphoton microscopy, histological, behavioral, and biological methods, we determined BBB integrity, cerebrovascular dysfunction, amyloid accumulation, and cognitive impairment in APPPS1 mice lacking ADAMTS13. We also tested the impact of viral-mediated expression of ADAMTS13 on cerebrovascular function and AD-like pathology in APPPS1 mice. We show that ADAMTS13 deficiency led to an early and progressive BBB breakdown as well as reductions in vessel density, capillary perfusion, and cerebral blood flow in APPPS1 mice. We found that deficiency of ADAMTS13 increased brain plaque load and A? levels and accelerated cerebral amyloid angiopathy (CAA) by impeding BBB-mediated clearance of brain A?, resulting in worse cognitive decline in APPPS1 mice. Virus-mediated expression of ADAMTS13 attenuated BBB disruption and increased microvessels, capillary perfusion, and cerebral blood flow in APPPS1 mice already showing BBB damage and plaque deposition. These beneficial vascular effects were reflected by increase in clearance of cerebral A?, reductions in A? brain accumulation, and improvements in cognitive performance. Our results show that ADAMTS13 deficiency contributes to AD cerebrovascular dysfunction and the resulting pathogenesis and cognitive deficits and suggest that ADAMTS13 may offer novel therapeutic opportunities for AD.
Project description:Proteins that regulate the coagulation cascade, including thrombin, are elevated in the brains of Alzheimer's disease (AD) patients. While studies using amyloid-based AD transgenic mouse models have implicated thrombin as a protein of interest, the role of thrombin in tau-based animal models has not been explored. The current study aims to determine how inhibiting thrombin could alter oxidative stress, inflammation, and AD-related proteins in a tau-based mouse model, the Tg4510. Aged Tg4510 mice were treated with the direct thrombin inhibitor dabigatran or vehicle for 7 days, brains collected, and western blot and data-independent proteomics using mass spectrometry with SWATH-MS acquisition performed to evaluate proteins related to oxidative stress, intracellular signaling, inflammation, and AD pathology. Dabigatran reduced iNOS, NOX4, and phosphorylation of tau (S396, S416). Additionally, dabigatran treatment increased expression of several signaling proteins related to cell survival and synaptic function. Increasing evidence supports a chronic procoagulant state in AD, highlighting a possible pathogenic role for thrombin. Our data demonstrate that inhibiting thrombin produces alterations in the expression of proteins involved in oxidative stress, inflammation, and AD-related pathology, suggesting that thrombin-mediated signaling affects multiple AD-related pathways providing a potential future therapeutic target.
Project description:Fibrotic lung disease, most notably idiopathic pulmonary fibrosis (IPF), is thought to result from aberrant wound-healing responses to repetitive lung injury. Increased vascular permeability is a cardinal response to tissue injury, but whether it is mechanistically linked to lung fibrosis is unknown. We previously described a model in which exaggeration of vascular leak after lung injury shifts the outcome of wound-healing responses from normal repair to pathological fibrosis. Here we report that the fibrosis produced in this model is highly dependent on thrombin activity and its downstream signaling pathways. Direct thrombin inhibition with dabigatran significantly inhibited protease-activated receptor-1 (PAR1) activation, integrin ?v?6 induction, TGF-? activation, and the development of pulmonary fibrosis in this vascular leak-dependent model. We used a potentially novel imaging method - ultashort echo time (UTE) lung magnetic resonance imaging (MRI) with the gadolinium-based, fibrin-specific probe EP-2104R - to directly visualize fibrin accumulation in injured mouse lungs, and to correlate the antifibrotic effects of dabigatran with attenuation of fibrin deposition. We found that inhibition of the profibrotic effects of thrombin can be uncoupled from inhibition of hemostasis, as therapeutic anticoagulation with warfarin failed to downregulate the PAR1/?v?6/TGF-? axis or significantly protect against fibrosis. These findings have direct and important clinical implications, given recent findings that warfarin treatment is not beneficial in IPF, and the clinical availability of direct thrombin inhibitors that our data suggest could benefit these patients.
Project description: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.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/?L). 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/?L. 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/?L) significantly and dabigatran treatment was discontinued. The blood test results show that platelet counts gradually recovered to the normal range.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.
Project description:The majority of Alzheimer’s disease patients and 20–40% of non-demented elderly experience amyloid deposits along their cerebral vasculature, a condition known as cerebral amyloid angiopathy (CAA). CAA impairs the function of the blood-brain barrier (BBB) leading to ischemia, hemorrhages, and accelerated cognitive dysfunction. The APOE4 allele is the strongest known genetic risk factor for CAA and sporadic AD, however the pathogenic mechanisms underlying this predisposition are unknown. Here, we recreate the human BBB in vitro by co-culturing the three cellular components of the BBB, endothelial cells, pericytes, and astrocytes in 3D scaffolding to construct a tractable model that recapitulates key anatomical and physiological properties of the BBB. Similar to the in vivo BBB, we find amyloid accumulates on our in vitro BBB (iBBB) and both APOE4 homozygous and heterozygous iBBBs exhibit significantly more amyloid accumulation than APOE3/3 iBBBs. Combinatorial experiments revealed that pericytes have a causal role in the development of CAA. We found that APOE expression is markedly up-regulated in APOE4 pericytes, but not in astrocytes or endothelial cells. Transcriptional profiling revealed that calcineurin/NFAT signaling is dysregulated in APOE4 pericytes. Pharmacologically inhibiting calcineurin led to downregulation of APOE and subsequently reduced amyloid deposition on the iBBB. These results demonstrate an unexpected role of pericytes in cerebral amyloid deposition and advocate for inhibiting calcineurin/NFAT-signaling as a therapeutic strategy to mitigate APOE4 predisposition to CAA and potentially AD. Overall design: RNA-Seq of iPSC-derived pericytes
Project description:BACKGROUND:Cerebral thromboembolism is a rare but feared complication of transcatheter ablation in patients with atrial fibrillation (AF). Here, we aimed to test which pre-procedural anticoagulation strategy results in less intracardiac activation of hemostasis during ablation. PATIENTS AND METHODS:In this observational study, 54 paroxysmal/persistent AF patients undergoing cryoballoon ablation were grouped according to their periprocedural anticoagulation strategy: no anticoagulation (oral anticoagulation (OAC) free; n = 24), uninterrupted vitamin K antagonists (VKA) (n = 11), uninterrupted dabigatran (n = 17). Blood was drawn from the left atrium before and immediately after the ablation procedure. Cryoablations were performed according to standard protocols, during which heparin was administered. Heparin-insensitive markers of hemostasis and endothelial damage were tested from intracardiac samples: D-dimer, quantitative fibrin monomer (FM), plasmin-antiplasmin complex (PAP), von Willebrand factor (VWF) antigen, chromogenic factor VIII (FVIII) activity. RESULTS:D-dimer increased significantly in all groups post-ablation, with lowest levels in the dabigatran group (median [interquartile range]: 0.27 [0.36] vs. 1.09 [1.30] and 0.74 [0.26] mg/L in OAC free and uninterrupted VKA groups, respectively, p < 0.001). PAP levels were parallel to this observation. Post-ablation FM levels were elevated in OAC free (26.34 [30.04] mg/L) and VKA groups (10.12 [16.01] mg/L), but remained below cut-off in all patients on dabigatran (3.98 [2.0] mg/L; p < 0.001). VWF antigen and FVIII activity increased similarly post-ablation in all groups, suggesting comparable procedure-related endothelial damage. CONCLUSION:Dabigatran provides greater inhibition against intracardiac activation of hemostasis as compared to VKAs during cryoballoon catheter ablation.
Project description:Alzheimer's disease (AD) is a neurodegenerative disorder in which vascular pathology plays an important role. Since the beta-amyloid peptide (Abeta) is a critical factor in this disease, we examined its relationship to fibrin clot formation in AD. In vitro and in vivo experiments showed that fibrin clots formed in the presence of Abeta are structurally abnormal and resistant to degradation. Fibrin(ogen) was observed in blood vessels positive for amyloid in mouse and human AD samples, and intravital brain imaging of clot formation and dissolution revealed abnormal thrombosis and fibrinolysis in AD mice. Moreover, depletion of fibrinogen lessened cerebral amyloid angiopathy pathology and reduced cognitive impairment in AD mice. These experiments suggest that one important contribution of Abeta to AD is via its effects on fibrin clots, implicating fibrin(ogen) as a potential critical factor in this disease.
Project description:Neprilysin (NEP) is an endogenous protease that degrades a wide range of peptides including amyloid beta (A?), the main pathological component of Alzheimer's disease (AD). We have engineered NEP as a potential therapeutic for AD but found in pre-clinical safety testing that this variant increased prothrombin time (PT) and activated partial thromboplastin time (APTT). The objective of the current study was to investigate the effect of wild type NEP and the engineered variant on coagulation and define the mechanism by which this effect is mediated. PT and APTT were measured in cynomolgus monkeys and rats dosed with a human serum albumin fusion with an engineered variant of NEP (HSA-NEPv) as well as in control plasma spiked with wild type or variant enzyme. The coagulation factor targeted by NEP was determined using in vitro prothrombinase, calibrated automated thrombogram (CAT) and fibrin formation assays as well as N-terminal sequencing of fibrinogen treated with the enzyme. We demonstrate that HSA-NEP wild type and HSA-NEPv unexpectedly impaired coagulation, increasing PT and APTT in plasma samples and abolishing fibrin formation from fibrinogen. This effect was mediated through cleavage of the N-termini of the A?- and B?-chains of fibrinogen thereby significantly impairing initiation of fibrin formation by thrombin. Fibrinogen has therefore been identified for the first time as a substrate for NEP wild type suggesting that the enzyme may have a role in regulating fibrin formation. Reductions in NEP levels observed in AD and cerebral amyloid angiopathy may contribute to neurovascular degeneration observed in these conditions.
Project description:Essentials How the Alzheimer's disease (AD) peptide ?-amyloid (A?) disrupts neuronal function in the disease is unclear. Factor (F) XII initiates blood clotting via FXI, and thrombosis has been implicated in AD. A? triggers FXII-dependent FXI and thrombin activation, evidence of which is seen in AD plasma. A?-triggered clotting could contribute to neuronal dysfunction in AD and be a novel therapeutic target.Background ?-Amyloid (A?) is a key pathologic element in Alzheimer's disease (AD), but the mechanisms by which it disrupts neuronal function in vivo are not completely understood. AD is characterized by a prothrombotic state, which could contribute to neuronal dysfunction by affecting cerebral blood flow and inducing inflammation. The plasma protein factor XII triggers clot formation via the intrinsic coagulation cascade, and has been implicated in thrombosis. Objectives To investigate the potential for A? to contribute to a prothrombotic state. Methods and results We show that A? activates FXII, resulting in FXI activation and thrombin generation in human plasma, thereby establishing A? as a possible driver of prothrombotic states. We provide evidence for this process in AD by demonstrating decreased levels of FXI and its inhibitor C1 esterase inhibitor in AD patient plasma, suggesting chronic activation, inhibition and clearance of FXI in AD. Activation of the intrinsic coagulation pathway in AD is further supported by elevated fibrin levels in AD patient plasma. Conclusions The ability of A? to promote coagulation via the FXII-driven contact system identifies new mechanisms by which it could contribute to neuronal dysfunction and suggests potential new therapeutic targets in AD.
Project description:Activation of innate immunity and deposition of blood-derived fibrin in the central nervous system (CNS) occur in autoimmune and neurodegenerative diseases, including multiple sclerosis (MS) and Alzheimer’s disease (AD). However, mechanisms linking blood-brain barrier (BBB) disruption with neurodegeneration are poorly understood, and exploration of fibrin as a therapeutic target has been limited by its beneficial clotting functions. Here we report the generation of monoclonal antibody 5B8 targeted against the cryptic fibrin epitope γ377-395 to selectively inhibit fibrin-induced inflammation. 5B8 suppressed fibrin-induced proinflammatory gene expression, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation, and oxidative stress. In animal models of MS and AD, 5B8 entered the CNS and bound to parenchymal fibrin, and its therapeutic administration reduced innate immune activation and neurodegeneration without interfering with clotting. Thus, fibrin-targeting immunotherapy inhibits autoimmune- and amyloid-driven neurotoxicity and may have clinical benefit without globally suppressing innate immunity or interfering with coagulation in diverse neurological diseases. Overall design: Mouse macrophages were stimulated for 6 hr with fibrin in the presence of 5B8 or isotype control IgG2b and subjected for RNA extraction and hybridization on Affymatrix microarrays. Data are from three independent biological replicates.