Phosphatidylserine positive microparticles improve hemostasis in in-vitro hemophilia A plasma models

Area of Science:

• Hemostasis and Thrombosis
• Biochemistry
• Cell Biology

Background:

• Circulating microparticles (MPs) possess procoagulant properties due to surface phosphatidylserine (PS).
• Hemophilia A (HA) is a bleeding disorder characterized by impaired coagulation, primarily due to Factor VIII (FVIII) deficiency.
• Understanding how MPs influence hemostasis in HA is crucial for developing novel therapeutic strategies.

Purpose of the Study:

• To investigate the potential of circulating MPs to improve hemostasis in various hemophilia A plasma models.
• To elucidate the mechanisms by which MPs exert their procoagulant effects in the context of FVIII deficiency.

Main Methods:

• Isolation of MPs from pooled normal human plasma.
• Preparation of severe, moderate, and mild HA plasma models with varying FVIII levels (0%, 2.5%, 20%).
• Assessment of hemostasis using calibrated automated thrombogram (CAT) and overall hemostasis potential (OHP) assays.
• Microscopic analysis of fibrin structure using confocal, STED, and SEM.

Main Results:

• MPs partially restored thrombin generation and fibrin formation across all tested HA plasma models.
• The procoagulant effect of MPs was primarily dependent on PS exposure and, to a lesser extent, contact pathway activation.
• MPs did not require tissue factor exposure or in vitro stimulation to exert their procoagulant effects.
• MPs partially normalized fibrin structure, with direct attachment to fibrin strands visualized via STED microscopy.

Conclusions:

• PS-positive MPs demonstrate a capacity to improve hemostasis in hemophilia A plasma models.
• These findings suggest that MPs could serve as a potential therapeutic agent for enhancing blood clotting in HA.
• The procoagulant activity of MPs is linked to PS exposure and contact pathway activation, independent of tissue factor.