In Vivo Inhibition of Acute Platelet-Dependent Thrombosis in a Baboon Model by BAY U3405, a Thromboxane A2-Receptor Antagonist

Abstract

SummaryBay U3405 is a thromboxane A2 (TxA2)-receptor antagonist that inhibits the binding of TxA2 to its target cells. The aim of this study was to determine if Bay U3405 could be used to inhibit arterial thrombosis. A thrombogenic de vice, consisting of uncrimped Dacron vascular graft material (0.5 cm2) built into the wall of silicone rubber tubing with 4 mm inside diameter, was exposed to native flowing blood under arterial blood flow conditions (100-140 ml/min) by interposing the devices as extension segments into permanent femoral arteriovenous shunts implanted in baboons. Thrombus formation was quantified in vivo by measuring the deposition of 111In-labelled platelets onto the graft material with a scintillation camera. In six baboons, a bolus injection of Bay U3405, calculated to attain an initial plasma concentration of 300 ng/ml, reduced the maximum thrombus formation measured over a 2 h study period. Platelet deposition was reduced by 33 ± 14% (SD) at 2 h as compared to control studies done in the same baboons. The accumulation of additional platelets onto a thrombus that was allowed to form for 1 h, was reduced by 58 ± 28% at 2 h. Ex vivo platelet aggregation in response to ADP, activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT) were not affected by the treatment. Ex vivo platelet aggregation in response to collagen was markedly inhibited for 2 h after treatment. The results demonstrated that selective blocking of the TxA2-receptor on platelets reduced platelet-dependent thrombus formation and the accumulation of additional platelets in a freshly formed thrombus. This may provide a viable approach for preventing excessive thrombus formation in patients undergoing arterial reconstructive surgery.

Antithrombotic Effect of Platelet Glycoprotein Ib–Blocking Monoclonal Antibody Fab Fragments in Nonhuman Primates

“…In similar studies, only Ϸ0.7ϫ10 9 platelets accumulated in 30 minutes on Dacron vascular graft material (0.9 cm 2 ). 31 It is therefore also not surprising that a number of control thrombogenic devices became occluded before 30 minutes of exposure to flowing blood. Treatment of baboons with 6B4 Fab fragments inhibited platelet deposition on the thrombogenic devices by 43% to 65%.…”

“…The plasma volume was calculated by assuming a blood volume of 65 mL/kg body mass and correcting for the hematocrit. 31 Platelet-dependent arterial thrombus formation was induced by using bovine pericardium (0.6 cm 2 fixed in buffered glutaraldehyde). 32 The pericardium was built into the wall of Silastic tubing (3-mm inside diameter).…”

“…32 The pericardium was built into the wall of Silastic tubing (3-mm inside diameter). The method of preparation of the thrombogenic device has been described in detail, 31 except that fixed bovine pericardium was used instead of Dacron vascular graft material. In each experiment, a thrombogenic device prefilled with saline to avoid a blood-air interface was incorporated as an extension segment into the permanent arteriovenous shunt by means of Teflon connectors.…”

“…30,31 In brief, image acquisition of the grafts, including proximal and distal Silastic segments, was done with a large-field-of-view scintillation camera fitted with a high-resolution collimator. The images were stored on and analyzed with a Medical Data Systems A 3 computer (Medtronic) interfaced with the scintillation camera.…”

Determination of the Dosage of Recombinant Hirudin to Inhibit Arterial Thrombosis in Baboons

“…The method of preparation of the thrombogenic device is described in detail. 17 In each experiment, a thrombogenic device, prefilled with saline to avoid a blood-air interface, was incorporated as an extension segment into the permanent AV shunt by means of Teflon connectors. 14,15 In six baboons, control studies were done in which the devices were placed for 120 min.…”