Platelet activation by sustained exposure to low-dose plasmin

Area of Science:

• Hematology
• Biochemistry
• Thrombosis Research

Background:

• Plasmin's effect on platelet function is dose- and temperature-dependent.
• Previous studies indicate plasmin can both activate and inhibit platelets.

Purpose of the Study:

• To investigate fibrinogen-dependent platelet aggregation induced by prolonged exposure to very low plasmin doses.
• To characterize the nature and mechanisms of plasmin-induced platelet activation at different temperatures.

Main Methods:

• Platelet aggregation assays following 60-minute exposure to low-dose plasmin (0.05 CU/ml) at 22°C and 37°C.
• Microscopic evaluation of platelet aggregates, assessment of procoagulant activity, and analysis of dense/alpha-granule secretion.
• Investigation of inhibitory effects of ADP antagonists, aspirin, metabolic inhibitors, PGE1, PI3K, and PKC inhibitors on plasmin-induced aggregation.

Main Results:

• Maximum platelet aggregation occurred at 22°C, with significant aggregation also observed at 37°C.
• Plasmin-induced aggregates were larger, less reversible, and exhibited higher procoagulant activity compared to ADP-induced aggregates.
• Aggregation was fibrinogen-dependent but showed reduced fibrinogen binding and clot retraction compared to ADP-induced aggregation.
• Dense/alpha-granule secretion was not observed; aggregation was unaffected by ADP antagonists or aspirin but partially inhibited by metabolic inhibitors and specific kinase inhibitors.

Conclusions:

• Sustained exposure to very low plasmin doses induces platelet activation.
• This activation is characterized by fibrinogen-dependent aggregation and enhanced procoagulant activity.
• Plasmin-induced platelet activation may play a role in thrombotic complications.