Plasmin-induced Alterations to Platelet GPIIb/IIIa Receptors Impair Secondary Blood Clot Firmness

Background: Haemostasis involves the recruitment of platelets to the site of a vessel wall defect, the activation of plasmatic coagulation factors and the strengthening of the primary platelet plug by a network of emerging fibrin strands. About a quarter of severely injured patients present with an impairment of haemostasis, a phenomenon that has been termed trauma-induced coagulopathy (TIC). TIC is characterized by the depletion of functional coagulation factors, fibrinolytic activation and platelet dysfunction. Excessive release of tissue-plasminogen activator (t-PA) during fibrinolytic activation cannot only result in hyperfibrinolysis but can also affect platelet glycoprotein receptors. Here we investigated ex vivo, whether a global state of pro-coagulant and fibrinolytic activation can interfere with glycoprotein-mediated platelet-fibrinogen interaction and whether these conditions can affect secondary clot stability.

Methods: Whole blood of healthy donors was incubated with t-PA in the presence or absence of the antifibrinolytic tranexamic acid (TXA). Platelets were isolated, washed and transferred to a 1.5 or 3 mg/mL solution of fibrinogen in isotonic saline. Platelet-fibrin clots were formed by the addition of CaCl2 and thrombin to assess functional clot stability by thromboelastometry. Fluorescence Microscopy with fluorophore labeled fibrinogen and a monoclonal antibody against GPIIb/IIIa as well as flow cytometry (FC) were performed to assess platelet-fibrinogen interaction.

Results: Pre-incubation with t-PA resulted in a significant impairment of maximum clot firmness (MCF) and a fulminant breakdown of the platelet-fibrin clot in thromboelastometry. Both effects could be reversed by the prior co-incubation with TXA. When comparing the two fibrinogen concentrations in the t-PA group, differences in MCF and lysis onset time (LOT) were observed. Fibrinogen binding in FC and co-localization of platelet GPIIb/IIIa with fibrinogen in FM were diminished in the t-PA group. This was not the case in the group with TXA co-incubation.

Conclusions: Platelet activation in a fibrinolytic micro-environment can affect platelet GPIIb/IIIa receptors and impair their ability to contribute to a stable secondary clot. Our laboratory findings might have implications for the pathophysiology of hyperfibrinolysis, the efficacy of therapeutic fibrinogen supplementation and the significance of early tranexamic acid administration.

No conflict of interest has been declared by the author(s).