Save
Coagulation Activation Induced by Platelet-Derived Microvesicles is Mediated by Kallikrein-Dependent Activation of Factor IX
ISTH Academy. Key N. Jul 10, 2019; 273908; OC 71.2
Prof. Nigel Key
Prof. Nigel Key
Access to Reserved content is available to attendees of the Congress until the end of the year and always available for full ISTH members.

Click here to join ISTH or renew your membership.

Abstract
Discussion Forum (0)
Rate & Comment (0)

OC 71.2

Coagulation Activation Induced by Platelet-Derived Microvesicles is Mediated by Kallikrein-Dependent Activation of Factor IX

D. Noubouossie1, M. Piegore1, M. Henderson1, A. Ilich1, P. Ellsworth1, M. Mooberry1, R. Pawlinski1, I. Welsby2, M. Hoffman3, D.M. Monroe1, N.S. Key1
1University of North Carolina, Medicine, Chapell Hill, United States, 2Duke University, Anesthesiology, Durham, United States, 3Duke University, Blood Bank and Pathology, Durham, United States

Main Topic: Coagulation and Anticoagulation
Category: Contact Pathway

Background: Platelet transfusion may be associated with thrombosis, inflammation and increased mortality. The mechanisms underlying these adverse outcomes are unclear.
Aims: To elucidate how microvesicles(MVs) isolated from platelet concentrates(PLTC-MVs) activate coagulation.
Methods: PLTC-MVs were isolated from discarded platelet apheresis units by double centrifugation(2500g;15 minutes). PLTC-MVs were visualized, sized and counted using electron microscopy and nanoparticle tracking analysis. Phosphatidylserine exposure was also measured. To assess their ability to initiate thrombin generation(TG), PLTC-MVs were re-suspended in re-calcified MV-free normal pooled plasma(MVfNPP), or in MV-free plasmas deficient in factor XII(MVfDef-XII), XI(MVfDef-XI), IX(MVfDef-IX) or VII(MVfDef-VII). Antibodies against tissue factor(antiTF-Ab), corn trypsin inhibitor(CTI) or soybean trypsin inhibitor(STI) were used to block TF, FXIIa or kallikrein, respectively. FXII, prekallikrein (+high molecular weight kininogen(HK)) or FXI(+HK) activation was detected in buffer using fluorogenic substrate sensitive to FXIIa, FXIa or kallikrein. FIX activation in buffer was assessed using an ELISA that detects FIXa-antithrombin complexes(FIXa-AT).
Results: The mean concentration of PLTC-MVs was 9.66 x 1012 particles/ml; mean diameter was 73.7nm with 90% of particles ≤100nm(Fig1B); mean phosphatidylserine activity was 428 nM(Fig1C). PLTC-MVs triggered TG in MVfNPP despite the presence of inhibitory antiTF-Abs, and in MVfDef-VII(Fig1D). No TF activity was detected on PLTC-MVs(Fig1E). PLTC-MV-induced TG was unchanged in MVfDef-XII and MVfDef-XI, but was abolished in MVfDefIX(Fig1F). PLTC-MVs directly activated FXII(Fig1G) and PK(Fig1H), but not FXI(Fig1I) in buffer. PLTC-MVs activated FIX in buffer in a PK(+HK)-dependent manner(Fig2A). Purified kallikrein similarly activated FIX in buffer(Fig2B) and in plasma(Fig2C). In contrast to kaolin(Fig2D-F), PLTC-MV-induced(Fig2G-I) TG was insensitive to CTI, FXII or FXI deficiency, but was abolished by STI.
Conclusions: PLTC-MVs activate the contact system leading to TG via a noncanonical kallikrein-FIX pathway. These results should be confirmed by using molecules that block kallikrein more specifically than STI. Our findings support that PLTC-MVs may support hemostasis, but also promote thrombotic and inflammatory reactions to platelet transfusion.


[Fig.1]




[Fig.2]

Code of conduct/disclaimer available in General Terms & Conditions
Anonymous User Privacy Preferences

Strictly Necessary Cookies (Always Active)

MULTILEARNING platforms and tools hereinafter referred as “MLG SOFTWARE” are provided to you as pure educational platforms/services requiring cookies to operate. In the case of the MLG SOFTWARE, cookies are essential for the Platform to function properly for the provision of education. If these cookies are disabled, a large subset of the functionality provided by the Platform will either be unavailable or cease to work as expected. The MLG SOFTWARE do not capture non-essential activities such as menu items and listings you click on or pages viewed.


Performance Cookies

Performance cookies are used to analyse how visitors use a website in order to provide a better user experience.



Google Analytics is used for user behavior tracking/reporting. Google Analytics works in parallel and independently from MLG’s features. Google Analytics relies on cookies and these cookies can be used by Google to track users across different platforms/services.


Save Settings