title: Tirofiban blocks platelet adhesion to fibrin with minimal perturbation of GpIIb/IIIa structure.
abstract: A biophysical approach tested the hypothesis that tirofiban, like eptifibatide, perturbs GpIIb/IIIa structure. Tirofiban bound tightly to platelet GpIIb/IIIa (EC50 approximately 24 nmol/L) and effectively inhibited platelet aggregation (IC50 approximately 37 nmol/L) but blocked platelet adhesion to clotted fibrin only at much higher doses (IC50 approximately 580 nmol/L). Electrophoretic analyses demonstrated that tirofiban protected GpIIb/IIIa from SDS-induced subunit dissociation. However, saturating tirofiban concentrations had little or no effect on GpIIb/IIIa secondary or tertiary structure, as determined by circular dichroic spectroscopy, dynamic light scattering, and sedimentation velocity measurements performed with purified receptors in octyl glucoside. Moderate dose-dependent effects on GpIIb/IIIa quaternary structure were detected by sedimentation equilibrium. Transmission electron microscopy showed minimal tirofiban-induced receptor activation or oligomerization. Thus, even at the increased concentrations needed to block platelet:fibrin adhesive interactions, tirofiban exhibited only limited effects on GpIIb/IIIa conformation and clustering. Our results provide new insights into the mechanisms and potential prothrombotic complications of integrin antagonists.
authors.affiliation: Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, NC 27157-1019, USA. rhantgan@wfubmc.edu
authors.forename: Roy R
authors.initials: RR
authors.lastname: Hantgan
authors.forename: Mary C
authors.initials: MC
authors.lastname: Stahle
authors.forename: W Gray
authors.initials: WG
authors.lastname: Jerome
authors.forename: Chandrasekaran
authors.initials: C
authors.lastname: Nagaswami
authors.forename: John W
authors.initials: JW
authors.lastname: Weisel
mesh_terms: D000328:Adult; D002942:Circular Dichroism; D004305:Dose-Response Relationship, Drug; D005337:Fibrin / Q000378:metabolism; D006801:Humans; D008854:Microscopy, Electron; D009391:Nephelometry and Turbidimetry; D010973:Platelet Adhesiveness / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry / Q000187:drug effects* / Q000648:ultrastructure; D011487:Protein Conformation / Q000187:drug effects; D025941:Protein Interaction Mapping; D017433:Protein Structure, Secondary / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000187:drug effects; D021122:Protein Subunits; D011940:Receptor Aggregation / Q000187:drug effects; D000077466:Tirofiban; D014443:Tyrosine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D021122:Protein Subunits; D014443:Tyrosine; D005337:Fibrin; D000077466:Tirofiban