The role of thrombin activatable fibrinolysis inhibitor and factor XI in platelet-mediated fibrinolysis resistance: a thromboelastographic study in whole blood.
BACKGROUND
The resistance of platelet-rich thrombi to fibrinolysis is generally attributed to clot retraction and platelet PAI-1 release. The role of TAFI in platelet-mediated resistance to lysis is unclear.


OBJECTIVE
We investigated the contribution of TAFI to the antifibrinolytic effect of platelets in whole blood by thromboelastography.


METHODS
Platelet-poor (PP-WB, < 40 × 10(3) μL(-1) ) and platelet-rich (PR-WB, > 400 × 10(3) μL(-1) ) blood samples were obtained from normal human blood (N-WB, 150-220 × 10(3) μL(-1) ). Clot lysis time was measured by thromboelastography in recalcified blood supplemented with t-PA (100 ng mL(-1) ) and tissue factor (1:1000 Recombiplastin).


RESULTS
t-PA-induced lysis time increased in parallel with platelet concentration (up to 3-fold). Neutralization of TAFI, but not of PAI-1, shortened the lysis time by ∼ 50% in PR-WB and by < 10% in PP-WB. Accordingly, prothrombin F1+2 and TAFIa accumulation was greater in PR-WB than in PP-WB. A similar TAFI-dependent inhibition of fibrinolysis was observed when clot retraction was prevented by cytochalasin D or abciximab, or when platelet membranes were tested. Moreover, in blood with an intact contact system, platelet-mediated fibrinolysis resistance was attenuated by an anti-FXI but not by an anti F-XII antibody. Finally, platelets made the clots resistant to the profibrinolytic effect of heparin concentrations displaying a strong anticoagulant activity.


CONCLUSIONS
Our data indicate that TAFI activation is one major mechanism whereby platelets make clots resistant to fibrinolysis and underscore the importance of TAFI inhibitors as new antithrombotic agents.
Department of Biomedical Sciences and Human Oncology, Section of General and Experimental Pathology, Aldo Moro University, Bari, Italy.
C
C
Carrieri
R
R
Galasso
F
F
Semeraro
C T
CT
Ammollo
N
N
Semeraro
M
M
Colucci
D000077284:Abciximab; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000925:Anticoagulants / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D025901:Carboxypeptidase B2 / Q000097:blood*; D015638:Cytochalasin D / Q000494:pharmacology; D005172:Factor XI / Q000378:metabolism*; D005342:Fibrinolysis / Q000187:drug effects; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D010446:Peptide Fragments / Q000097:blood; D017395:Plasminogen Activator Inhibitor 1 / Q000097:blood; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011516:Prothrombin; D013916:Thrombelastography; D013925:Thromboplastin / Q000378:metabolism; D013997:Time Factors; D010959:Tissue Plasminogen Activator / Q000097:blood
D000911:Antibodies, Monoclonal; D000925:Anticoagulants; D007140:Immunoglobulin Fab Fragments; D010446:Peptide Fragments; D017395:Plasminogen Activator Inhibitor 1; D010975:Platelet Aggregation Inhibitors; C051321:SERPINE1 protein, human; C045879:prothrombin fragment 1.2; D015638:Cytochalasin D; D011516:Prothrombin; D006493:Heparin; D005172:Factor XI; D013925:Thromboplastin; D025901:Carboxypeptidase B2; D010959:Tissue Plasminogen Activator; D000077284:Abciximab