Fibrin(ogen) represent an adhesive substrate for platelets in different pathological conditions. When coagulation becomes activated fibrinogen adhered to different surfaces can be converted into fibrin. The aim of this study was to explore how promotion of crosslinking of immobilized fibrin(ogen) by FXHIa influences the plasmin generation and the adhesion of platelets onto this substrates at static and dynamic conditions. Human fibrinogen coated to polystyrene microtitre wells orThermanox coverslips was treated with thrombin or thrombin and FXIII in the presence of Ca ions. In certain samples to obtain crosslinked fibrinogen after activation of FXIII thrombin was inhibited with hirudin. The effect of thrombin and FXIII on immobilized fibrinogen was tested by measuring the release of fibrinopeptide A and by SDS-PAGE analysis of surface bound proteins. Plasmin generation was measured with S2251 chromogenic substrate in the presence of plasminogen and tissue plasminogen activator. Adhesion of washed platelets in static conditions was measured in the microtitre wells. For dynamic adhesion Sakariassen type chambers were perfused with Fraxiparine amicoagulated blood at 100/s, 650/s and 2600/s wall shear rates for 5 min. Adhered fibrinogen could be converted into fibrin by thrombin and FXIIIa induced the formation of y-chain dimers and a-chain polymers. Plsmin generation on immobilized fibrinogen compared to fibrinogen in solution was 3-4 times faster and thrombin or FX1I1 treatment did not results in any further change. Adhesion of platelets to immobilized fibrinogen or non-crosslinked fibrin was similar. Crosslinking of fibrin or fibrinogen resulted in a significant reduction of platelet adhesion both in static and dynamic conditions. The relatively shear rate independent adhesion of platelets to immobilized fibrinogen and non-crosslinked fibrin shows that binding domains for platelet receptors remain intact during thrombin cleavage of fibrinogen and adhesion to these substrates might be mediated through the same mechanisms. Shear rate idependent reduction of platelet deposition onto crosslinked fibrin suggests that different domains involved in platelet adhesion and responsible for receptor binding become hidden in the process of fibrin chains corsslinking. This mechanism might have a role in the down-regulation of platelet adhesion to fibrin(ogen) surfaces. However, domains responsible for plasmin generation which become exposed during immobilization are not effected by thrombin cleavage or crosslinking.
|Number of pages||1|
|Journal||Fibrinolysis and Proteolysis|
|Issue number||SUPPL. 1|
|Publication status||Published - Dec 1 1998|
ASJC Scopus subject areas