Platelet aggregation by fibrinogen polymers crosslinked across the E domain

Area of Science:

• Biochemistry
• Hematology
• Biomaterials Science

Background:

• Platelet interaction with artificial surfaces involves adsorbed plasma proteins like fibrinogen.
• High concentrations of adsorbed fibrinogen may trigger platelet adhesion and activation through multiple receptor interactions.

Purpose of the Study:

• To test the hypothesis that multiple fibrinogen binding sites are sufficient for platelet activation.
• To create a soluble model of fibrinogen-mediated platelet activation.

Main Methods:

• Preparation of soluble fibrinogen polymers (Fg-Fab'2(E)) by reacting fibrinogen with antibody fragments.
• Induction of platelet aggregation, serotonin release, and cytoplasmic Ca2+ elevation in gel-filtered platelets.
• Inhibition studies using monoclonal antibodies (anti-GPIIb/IIIa), Fab fragments, metabolic inhibitors, ADP pathway modulators (CP/CPK, FSBA), and aspirin.

Main Results:

• Fg-Fab'2(E) induced platelet aggregation, serotonin release, and Ca2+ increase, blocked by anti-GPIIb/IIIa and metabolic inhibitors.
• Aggregation was partially inhibited by ADP pathway modulators, suggesting a role for ADP but not solely.
• Crosslinked fibrinogen complexes lacking accessible D domains did not activate platelets, highlighting the importance of specific fibrinogen regions.

Conclusions:

• Soluble fibrinogen polymers with multiple available binding sites can activate platelets, supporting the hypothesis.
• This model provides insights into platelet adhesion and activation on artificial surfaces mediated by adsorbed fibrinogen.
• Specific domains of fibrinogen are critical for effective platelet receptor engagement and subsequent activation.