bradykinin-(1-5) and Coronary-Thrombosis

Thrombostatins are a group of compounds based upon a breakdown product of bradykinin, RPPGF. They inhibit alpha-thrombin-induced platelet activation by binding to protease activated receptor 1 and, at a lower affinity, by interacting with thrombin's active site. After a single intravenous infusion of MAP4-RPPGF (11.58 mg/kg), its t1/2alpha was 4.5 min with a clearance of 2.0 ml/min. MAP4-RPPGF administration had a sustained antiplatelet effect, preventing gamma-thrombin-induced (12.5 nM) platelet activation for 4 h. Its antiplatelet effect summated with that of aspirin and/or clopidogrel. MAP4-RPPGF was compared with aspirin and clopidogrel in the Folts model of coronary artery thrombosis. Dogs were randomized to 3 treatment groups: aspirin 1.14 mg/kg i.v., clopidogrel 0.5 mg/kg i.v., or MAP4-RPPGF 0.77 mg/kg i.v. Cyclic flow variations (CFV) were recorded in 5 untreated dogs hourly for 3 successive hours and for 1 h before (all groups >11 CFV/h), and for 2 h after drug infusion in each of the 3 treatment groups. After 1 h drug treatment, all groups of animals had <6 CFV/h; after 2 h treatment, all had <1 CFV/h. All agents significantly reduced CFV from control at each hour, but none was significantly better than any other. Thrombostatin was as effective as aspirin or clopidogrel in inhibiting coronary artery thrombosis in this canine model.

Topics: Animals; Aspirin; Blood Coagulation Tests; Bradykinin; Clopidogrel; Coronary Stenosis; Coronary Thrombosis; Disease Models, Animal; Dogs; Drug Evaluation; Metabolic Clearance Rate; Peptide Fragments; Platelet Function Tests; Regional Blood Flow; Therapeutic Equivalency; Ticlopidine; Time Factors

Thrombostatin (RPPGF), an angiotensin converting enzyme metabolite of bradykinin, is an inhibitor of alpha-thrombin's ability to activate platelets. We examined the in vivo pharmacokinetics and pharmacodynamics of thrombostatin in rabbits and its ability to inhibit coronary thrombosis induced by electrolytic injury in dogs. Plasma half-life of thrombostatin had a t1/2alpha of 2.6 min and a t1/2beta of 24 min in rabbits. Ligating the renal arteries did not prolong clearance (t1/2alpha = 2.4 min; t1/2beta = 12 min). Thrombostatin produced a prolonged in vivo antiplatelet effect. At 30 min after a single intravenous administration in rabbits, thrombostatin's plasma concentration was <8.7 microM (5 microg/ml). However, ex vivo 20 and 40 nM gamma-thrombin-induced platelet aggregation of these rabbits' platelets was inhibited 40% for 2.75 and 1 h, respectively. In vitro, flow cytometry studies revealed that thrombostatin specifically bound to human platelets and washed human platelets treated with thrombostatin were less responsive to gamma-thrombin than control platelets. Using electrolytic injury to induce coronary artery thrombosis, dogs treated with thrombostatin, aspirin, or combined thrombostatin and aspirin occluded in 62+/-25 (mean +/- SD), 62+/-36, or 89+/-32 min versus untreated animals which occluded at 39+/-27 min, (p<0.01, p<0.01 and p<0.001, respectively). These studies show that thrombostatin binds to platelets and can delay coronary occlusion in vivo.

Topics: Amino Acid Sequence; Animals; Aspirin; Blood Platelets; Bradykinin; Coronary Thrombosis; Dogs; Humans; In Vitro Techniques; Molecular Sequence Data; Peptide Fragments; Peptides; Platelet Aggregation; Platelet Aggregation Inhibitors; Rabbits; Thrombin