analysis-amyloid-induced-abnormalities-on-fibrin-clot-structure

Analysis of &#946;-Amyloid-induced Abnormalities on Fibrin Clot Structure by Spectroscopy and Scanning Electron Microscopy

This article presents methods for generating in vitro fibrin clots and analyzing the effect of beta-amyloid (A&#946;) protein on clot formation and ...

Rockefeller University

The majority of patients with Alzheimer disease (AD) suffer from impaired cerebral circulation. Accumulating evidence suggests that fibrinogen, the main protein component of blood clots, plays an important role in this circulatory dysfunction in AD. Fibrinogen interacts with β-amyloid (Aβ), forming plasmin-resistant abnormal blood clots, and increased fibrin deposition is found in the brains of AD patients and mouse models. In this study, we investigated the biochemical and structural details of the Aβ-fibrinogen interaction. We identified the central region of Aβ42 as the most critical region for the interaction, which can be inhibited by specific antibodies against the central region of Aβ and by naturally occurring p3 peptides, Aβ17-40 and Aβ17-42. X-ray crystallographic analysis revealed that Aβ42 binding to fragment D of fibrinogen induced a structural change in the C-terminal region of the fibrinogen β-chain (β384-393). Furthermore, we identified an additional Aβ-binding site within the αC region of fibrinogen. Aβ binding to this αC region blocked plasmin-mediated fibrin cleavage at this site, resulting in the generation of increased levels of a plasmin-resistant fibrin degradation fragment. Overall, our study elucidates the Aβ-fibrinogen interaction and clarifies the mechanism by which Aβ-fibrinogen binding delays fibrinolysis by plasmin. These results may facilitate the development of effective therapeutics against the Aβ-fibrinogen interaction to treat cerebrovascular abnormalities in AD.

Biochemical and structural analysis of the interaction between β-amyloid and fibrinogen.

Accumulating evidence suggests that fibrinogen, a key protein in the coagulation cascade, plays an important role in circulatory dysfunction in Alzheimer's disease (AD). Previous work has shown that the interaction between fibrinogen and β-amyloid (Aβ), a hallmark pathological protein in AD, induces plasmin-resistant abnormal blood clots, delays fibrinolysis, increases inflammation, and aggravates cognitive function in mouse models of AD. Since Aβ oligomers have a much stronger affinity for fibrinogen than Aβ monomers, we tested whether amyloid aggregation inhibitors could block the Aβ-fibrinogen interaction and found that some Aβ aggregation inhibitors showed moderate inhibitory efficacy against this interaction. We then modified a hit compound so that it not only showed a strong inhibitory efficacy toward the Aβ-fibrinogen interaction but also retained its potency toward the Aβ42 aggregation inhibition process. Furthermore, our best hit compound, TDI-2760, modulated Aβ42-induced contact system activation, a pathological condition observed in some AD patients, in addition to inhibiting the Aβ-fibrinogen interaction and Aβ aggregation. Thus, TDI-2760 has the potential to lessen vascular abnormalities as well as Aβ aggregation-driven pathology in AD.

Aminopyrimidine Class Aggregation Inhibitor Effectively Blocks Aβ-Fibrinogen Interaction and Aβ-Induced Contact System Activation.

Alzheimer disease (AD) is a neurodegenerative disorder characterized by extracellular β-amyloid (Aβ) deposition. Although peripheral inflammation and cerebrovascular pathology are reported in AD, there is a lack of plasma biomarkers in this field. Because the contact system is triggered in patient plasma, we hypothesized that the hemostasis profile could be a novel biomarker in AD. Here, we assessed the clotting profile in plasma from AD patients and age-matched controls. Utilizing clinically relevant assays, thromboelastography and activated partial thromboplastin time, we found impaired clot initiation and formation rate in AD patient plasma. These coagulation end points correlated with cerebrospinal fluid neurofilament-light levels and cognition and were more profound in younger AD patients. Ex vivo intrinsic clotting of plasma from AD mice expressing human amyloid precursor protein (APP) was also delayed in an age-dependent manner, suggesting that this phenotype is related to APP, the parent protein of Aβ. Further analysis of coagulation factors in human plasma indicated that endogenous inhibitor(s) of factors XII and XI in AD plasma contribute to this delayed clotting. Together, these data suggest that delayed clotting in young AD patients is a novel biomarker and that therapies aimed to correct this phenotype might be beneficial in this patient population. Follow-up studies in additional AD patient cohorts are warranted to further evaluate these findings.

Article	Year
Biochemical and structural analysis of the interaction between β-amyloid and fibrinogen. Blood\| PubMed ID: 27389717	2016
Aminopyrimidine Class Aggregation Inhibitor Effectively Blocks Aβ-Fibrinogen Interaction and Aβ-Induced Contact System Activation. Biochemistry\| PubMed ID: 29394041	2018
Abnormal clotting of the intrinsic/contact pathway in Alzheimer disease patients is related to cognitive ability. Blood advances\| PubMed ID: 29700007	2018

Pradeep K. Singh

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