title: Recombinant P-selectin glycoprotein-ligand-1 delays thrombin-induced platelet aggregation: a new role for P-selectin in early aggregation.
abstract: 1. P-selectin is involved, with P-selectin glycoprotein (GP)-ligand-1 (PSGL-1), in platelet/leukocyte interactions during thrombo-inflammatory reactions; it also stabilizes platelet aggregates. Its antagonism accelerates thrombolysis and enhances the anti-aggregatory effects of GPIIb-IIIa inhibitors. This study was designed to investigate the mechanisms of P-selectin-mediated platelet aggregation. 2. In freshly isolated human platelets, P-selectin translocation after thrombin stimulation increased rapidly to 48, 72, and 86% positive platelets after 60, 120, and 300 s, respectively. Platelet aggregation at 60 s post-stimulation averaged 46.7 +/- 1.9% and its extent followed closely the kinetics of P-selectin translocation. 3. Pre-treatment of platelets with P-selectin antagonists, a recombinant PSGL-1 (rPSGL-Ig) or a blocking monoclonal antibody, significantly delayed platelet aggregation in a dose-dependent manner. At 100 microg ml(-1) of rPSGL-Ig, platelet aggregation was completely inhibited up to 60 s post-stimulation and increased thereafter to reach maximal aggregation at 5 min. The second phase of platelet aggregation, in the presence of rPSGL-Ig, was completely prevented by the addition of a GPIIb-IIIa antagonist (Reopro) at 60 s, whereas its addition in the absence of rPSGL-Ig was without any significant effect. 4. Combination of rPSGL-Ig with Reopro or with an inhibitor of Pi3K (LY294002), which reduces GPIIb-IIIa activation, showed to be more effective in inhibiting platelet aggregation, in comparison to the effects observed individually. 5. rPSGL-Ig blocks P-selectin, whereas Reopro and LY294002 block GPIIb-IIIa and its activation, respectively, without a major effect on the percentage of platelets expressing P-selectin. 6. In summary, platelet P-selectin participates with GPIIb-IIIa in the initiation of platelet aggregation. Its inhibition, with rPSGL-Ig, delays the aggregation process and increases the anti-aggregatory potency of Reopro. Thus, combination of P-selectin and GPIIb-IIIa antagonism may constitute a promising therapeutic option in the management of thrombotic disorders.
authors.affiliation: Laboratory of Experimental Pathology, Research Centre, Montreal Heart Institute and University of Montreal, 5000 Belanger Street, Montreal, Quebec, Canada H1T 1C8.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Théorêt
authors.forename: Wissam
authors.initials: W
authors.lastname: Chahrour
authors.forename: Daniel
authors.initials: D
authors.lastname: Yacoub
authors.forename: Yahye
authors.initials: Y
authors.lastname: Merhi
mesh_terms: D001792:Blood Platelets / Q000166:cytology / Q000502:physiology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D019007:P-Selectin / Q000502:physiology*; D010974:Platelet Aggregation / Q000187:drug effects*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors / Q000502:physiology; D011994:Recombinant Proteins; D013917:Thrombin / Q000494:pharmacology*
chemical_list: D008562:Membrane Glycoproteins; D019007:P-Selectin; C084882:P-selectin ligand protein; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011994:Recombinant Proteins; D013917:Thrombin