title: Platelet-associated tissue factor enhances platelet reactivity and thrombin generation in experimental studies in vitro.
abstract: BACKGROUND
  The thrombogenic potential of tissue factor (TF) associated to platelets is controversial. We have investigated the in vitro contribution of platelet-associated TF to thrombus formation.
  
  
  METHODS
  Platelets suspensions were exposed to human TF-rich microvesicles (TF-MV) from placental or recombinant origin. Platelet-associated TF was quantified through coagulometric assays. Adhesive and cohesive properties of platelets containing TF were assessed in perfusion models using two thrombogenic surfaces: 1) type-I collagen, or 2) damaged vascular segments. Perfusion studies were performed with heparinized blood enriched with a 30% of washed platelets exposed to TF-MV vs. washed control platelets. Thrombin generation and thromboelastometric properties of clots were also assessed using a fluorometric assay and ROTEM analysis, respectively. Inhibitory strategies with an antibody to TF were performed in some cases.
  
  
  RESULTS
  The addition of 30% of platelets containing TF to blood perfusates resulted in a statistically significant increase in the platelet coverage (%CS) vs. non-exposed platelets on collagen surfaces (%CS: 19.7 ± 0.6 and 23.9 ± 0.7 respectively, vs.14.5 ± 1.4; p<0.01) and on the vascular subendothelium (%CS: 54.0 ± 1.5 and 47.2 ± 6.8 respectively vs. 38.0 ± 3.5, p<0.05), with a statistically significant increase in the size of large platelet aggregates (p<0.05) vs. control platelets. These effects on collagen surfaces were almost totally prevented by an antibody to TF. Platelet-associated TF significantly accelerated thrombin generation and clot formation (p<0.05), effects that were partially prevented by a neutralizing anti-TF.
  
  
  CONCLUSIONS
  Platelet-associated TF potentiated adhesive and aggregating properties in in vitro studies with flowing blood and accelerated thrombin generation and clot formation time under steady conditions.
authors.affiliation: Servicio de Hemoterapia y Hemostasia, Hospital Clinic, Centro de Diagnostico Biomedico, Instituto de Investigaciones Biomedicas August Pi i Sunyer, Universidad de Barcelona, Spain.
authors.forename: Irene
authors.initials: I
authors.lastname: Lopez-Vilchez
authors.forename: Ana Maria
authors.initials: AM
authors.lastname: Galan
authors.forename: Maria Rosa
authors.initials: MR
authors.lastname: Hernandez
authors.forename: Carolina
authors.initials: C
authors.lastname: Caballo
authors.forename: Merce
authors.initials: M
authors.lastname: Roque
authors.forename: Maribel
authors.initials: M
authors.lastname: Diaz-Ricart
authors.forename: James G
authors.initials: JG
authors.lastname: White
authors.forename: Gines
authors.initials: G
authors.lastname: Escolar
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects*; D005260:Female; D006801:Humans; D010973:Platelet Adhesiveness / Q000187:drug effects; D011817:Rabbits; D012307:Risk Factors; D013917:Thrombin / Q000096:biosynthesis*; D013925:Thromboplastin / Q000008:administration & dosage*
chemical_list: D013925:Thromboplastin; D013917:Thrombin