title: Reversibility versus persistence of GPIIb/IIIa blocker-induced conformational change of GPIIb/IIIa (alphaIIbbeta3, CD41/CD61).
abstract: Clinically used GPIIb/IIIa blockers are ligand mimetics, and thereby their binding can induce conformational changes of the platelet integrin GPIIb/IIIa. Since the reversibility of these conformational changes may be an important determinant of potential adverse effects of GPIIb/IIIa blockers, we produced a new monoclonal antibody (anti-LIBS-mAb), and by using its binding properties, we investigated the conformational changes of GPIIb/IIIa during the binding and especially the dissociation of GPIIb/IIIa blockers. Production of monoclonal antibody (mAb) clones was performed using purified GPIIb/IIIa in a high affinity conformation and using activated platelets. Clone anti-LIBS-145-mAb was chosen, since it allowed the sensitive probing of eptifibatide-induced conformational changes of GPIIb/IIIa. On resting and activated platelets and on GPIIb/IIIa-expressing Chinese hamster ovary cells, anti-LIBS-145-mAb binding returned to background binding after dissociation of eptifibatide, indicating a complete reversibility of the eptifibatide-induced conformational change. Furthermore, with the mixing of eptifibatide-preincubated and nonincubated cells, a fast reversibility could be demonstrated. However, when fibrinogen was present in a physiological concentration, the GPIIb/IIIa blocker-induced conformation was partially retained after the dissociation of eptifibatide and to the same extent binding of fibrinogen and the activation-specific mAb Pac-1 was induced. In conclusion, a fast reversibility of the conformational change of GPIIb/IIIa after dissociation of GPIIb/IIIa blockers could be demonstrated as an intrinsic property of the GPIIb/IIIa receptor. This mechanism prevents general platelet aggregation after dissociation of ligand mimetic GPIIb/IIIa blockers. Nevertheless, in the presence of fibrinogen this reversibility is not complete, which may explain some of the side effects of GPIIb/IIIa blockers, especially those of the oral GPIIb/IIIa blockers.
authors: Department of Internal Medicine III, University of Freiburg, Germany.
authors: Meike
authors: M
authors: Schwarz
authors: Yasuhiro
authors: Y
authors: Katagiri
authors: Masaharu
authors: M
authors: Kotani
authors: Nicole
authors: N
authors: Bassler
authors: Christoph
authors: C
authors: Loeffler
authors: Christoph
authors: C
authors: Bode
authors: Karlheinz
authors: K
authors: Peter
mesh_terms: D000818:Animals; D001665:Binding Sites; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D006224:Cricetinae; D000077542:Eptifibatide; D005260:Female; D005340:Fibrinogen / Q000494:pharmacology; D006801:Humans; D010455:Peptides / Q000494:pharmacology; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000276:immunology; D011487:Protein Conformation / Q000187:drug effects
chemical_list: D010455:Peptides; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D005340:Fibrinogen; D000077542:Eptifibatide