title: Effects of monoclonal antibodies against the platelet glycoprotein IIb/IIIa complex on thrombosis and hemostasis in the baboon.
abstract: To assess the hemostatic consequences and antithrombotic effectiveness of blocking the platelet glycoprotein (GP) IIb/IIIa receptor for fibrinogen and other adhesive glycoproteins in vivo, well characterized murine monoclonal antibodies against the platelet GP IIb/IIIa complex, AP-2 and LJ-CP8, were infused intravenously into baboons. Four animals each received doses of 0.2, 0.4, and 1.0 mg/kg of purified AP-2 IgG, and three animals were given 1.0 mg/kg of the F(ab)2 fragment of AP-2. Five additional animals were given 10 mg/kg LJ-CP8 IgG. At the highest dose, radiolabeled AP-2 IgG bound to an average of 33,000 sites on the circulating platelets. Serial measurements included platelet count, bleeding time, platelet aggregation (induced by ADP, collagen, and gamma-thrombin), and 111In-platelet deposition onto Dacron vascular grafts. Bleeding times were markedly prolonged after injection of 1.0 mg/kg AP-2 IgG (19.2 +/- 3.4 min), 1.0 mg/kg AP-2 F(ab)2 (16.5 +/- 1.8 min), and 10 mg/kg LJ-CP8 (greater than 30 min) vs. control studies (4.6 +/- 0.2 min), and remained prolonged for 48 h. With each antibody platelet aggregation was initially reduced or absent, with partial recovery over 48 h in a manner that was inversely related to dose. AP-2, both whole IgG and F(ab)2 fragment, but not LJ-CP8, caused a dose-dependent reduction (20-46%) in the circulating platelet count over 24 h. Neither AP-2 nor LJ-CP8 caused a reduction in intraplatelet platelet factor 4, beta-thromboglobulin, or [14C]serotonin. Graft-associated platelet thrombus formation was reduced by 73% (1.0 mg/kg AP-2 IgG and 10 mg/kg LJ-CP8) and 53% (1.0 mg/kg AP-2 F(ab)2) relative to control values. In contrast, neither heparin (100 U/kg) nor aspirin (32.5 mg/kg twice a day) showed antithrombotic efficacy in this model. Thus, antibodies that functionally alter the platelet GP IIb/IIIa complex may produce immediate, potent, and transient, antihemostatic, and antithrombotic effects.
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000032:analysis / Q000502:physiology*; D001760:Bleeding Time; D001792:Blood Platelets / Q000502:physiology; D001807:Blood Vessel Prosthesis / Q000009:adverse effects; D002470:Cell Survival; D003594:Cytoplasmic Granules / Q000502:physiology; D005343:Fibrinolytic Agents / Q000502:physiology*; D006487:Hemostasis; D007074:Immunoglobulin G / Q000378:metabolism; D007262:Infusions, Intravenous; D008297:Male; D010215:Papio; D010974:Platelet Aggregation; D010976:Platelet Count; D010980:Platelet Membrane Glycoproteins / Q000276:immunology*; D011093:Polyethylene Terephthalates; D013927:Thrombosis / Q000097:blood* / Q000276:immunology / Q000628:therapy
chemical_list: D000911:Antibodies, Monoclonal; D005343:Fibrinolytic Agents; D007074:Immunoglobulin G; D010980:Platelet Membrane Glycoproteins; D011093:Polyethylene Terephthalates