title: GPIIb-IIIa antagonist-induced reduction in platelet surface factor V/Va binding and phosphatidylserine expression in whole blood.
abstract: In addition to inhibition of platelet aggregation, GPIIb-IIIa antagonists may reduce thrombotic events via other mechanisms. In a novel whole blood flow cytometric system, we investigated the effects of GPIIb-IIIa antagonists, in the presence or absence of thrombin inhibitors, on platelet surface-bound factor V/Va and platelet surface phospholipids. Diluted venous blood was incubated with either buffer or a GPIIb-IIIa antagonist (abciximab, tirofiban, or eptifibatide). Some samples were pre-incubated with clinically relevant concentrations of unfractionated heparin (UFH), a low molecular weight heparin, a direct thrombin inhibitor, or buffer only. Platelets were then activated and labeled with mAb V237 (factor V/Va-specific) or annexin V (binds phosphatidylserine), fixed, and analyzed by flow cytometry. In the absence of thrombin inhibitors, GPIIb-IIIa antagonists (especially abciximab) significantly reduced agonist-induced platelet procoagulant activity, as determined by reduced binding of V237 and annexin V. At high pharmacologic concentrations, unfractionated heparin and enoxaparin, but not hirudin, further reduced factor V/Va binding to the surface of activated platelets in the presence of GPIIb-IIa antagonists. Agonist-induced platelet procoagulant activity was reduced in a patient with Glanzmann's thrombasthenia. We conclude that GPIIb-IIIa antagonists reduce platelet procoagulant activity in whole blood and heparin and enoxaparin augment this reduction. Fibrinogen binding to GPIIb-IIIa is important in the generation of platelet procoagulant activity.
authors.affiliation: Center for Platelet Function Studies, University of Massachusetts Medical School, Worcester, PA 01655, USA. Furman@platelets.org
authors.forename: M I
authors.initials: MI
authors.lastname: Furman
authors.forename: L A
authors.initials: LA
authors.lastname: Krueger
authors.forename: A L
authors.initials: AL
authors.lastname: Frelinger
authors.forename: M R
authors.initials: MR
authors.lastname: Barnard
authors.forename: M A
authors.initials: MA
authors.lastname: Mascelli
authors.forename: M T
authors.initials: MT
authors.lastname: Nakada
authors.forename: A D
authors.initials: AD
authors.lastname: Michelson
mesh_terms: D000077284:Abciximab; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism; D003094:Collagen / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D000077542:Eptifibatide; D005165:Factor V / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D007231:Infant, Newborn; D008565:Membrane Proteins / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D010718:Phosphatidylserines / Q000097:blood*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors*; D011485:Protein Binding; D013915:Thrombasthenia / Q000097:blood; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000077466:Tirofiban; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000911:Antibodies, Monoclonal; D007140:Immunoglobulin Fab Fragments; D008565:Membrane Proteins; D010455:Peptides; D010718:Phosphatidylserines; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D014443:Tyrosine; D005165:Factor V; D003094:Collagen; D013917:Thrombin; D000077466:Tirofiban; D000077542:Eptifibatide; D000077284:Abciximab