title: Glycoprotein IIb/IIIa inhibitors increase COAT-platelet production in vitro.
abstract: Platelets activated simultaneously with thrombin and collagen reveal a subpopulation of cells that express on their surfaces high levels of several alpha-granule proteins, including factor V and fibrinogen; these COAT platelets (collagen and thrombin-activated platelets) represent roughly 30% of the total population. Evidence of enhanced stability of proteins on the COAT-platelet surface was provided by the observation that PAC-1, a mAB recognizing the activated form of glycoprotein (GP) IIb/IIIa, did not inhibit fibrinogen binding to COAT-platelets. We therefore undertook a systematic evaluation of the effects of other GP IIb/IIIa inhibitors on the production of COAT platelets. Not only did GP IIb/IIIa antagonists fail to inhibit the retention of fibrinogen on COAT-platelets, but several actually increased the absolute percentage of COAT platelets produced. The increases over control values in the presence of eptifibatide, tirofiban, and DMP-802 were 1.36-, 1.20-, and 1.05-fold, respectively (P <.01 for each comparison). COAT-platelet production in the presence of abciximab was not significantly affected. However, platelet activation with thrombin plus ALB6, an Fc-receptor agonist, produces a product, referred to as FcRT platelets, that is indistinguishable from COAT platelets; all 4 GP IIb/IIIa antagonists tested potentiated formation of FcRT platelets. These findings indicate that fibrinogen binding to COAT platelets and FcRT platelets is not affected by available GP IIb/IIIa inhibitors. More importantly, our study demonstrates a potentiation of COAT-platelet production by some GP IIb/IIIa antagonists that may be relevant to the observation that long-term administration of orally available GP IIb/IIIa inhibitors not only failed to protect patients but actually increased the frequency of acute coronary events.
authors.affiliation: College of Pharmacy, Department of Medicine, W.K. Warren Medical Research Institute, University of Oklahoma Health Sciences Center, Oklahoma City 73190, USA.
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Hamilton
authors.forename: Matt W
authors.initials: MW
authors.lastname: Miller
authors.forename: Cris A
authors.initials: CA
authors.lastname: Thompson
authors.forename: George L
authors.initials: GL
authors.lastname: Dale
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D003094:Collagen / Q000494:pharmacology; D000077542:Eptifibatide; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D007555:Isoxazoles / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors*; D013449:Sulfonamides / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D000077466:Tirofiban; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000911:Antibodies, Monoclonal; C114713:DMP 802; D007555:Isoxazoles; D010455:Peptides; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D013449:Sulfonamides; D014443:Tyrosine; D005340:Fibrinogen; D003094:Collagen; D013917:Thrombin; D000077466:Tirofiban; D000077542:Eptifibatide