THE ANTITHROMBOTIC EFFECT OF AURIN TRICARBOXYLIC-ACID IN THE GUINEA-PIG IS NOT SOLELY DUE TO ITS INTERACTION WITH THE VON-WILLEBRAND FACTOR-GPIB AXIS

Commercial aurin tricarboxylic acid (ATA) has been reported to interfe re specifically with von Willebrand factor-glycoprotein Ib (vWF-GPIb) axis. This study was designed to explore the antithrombotic effects of ATA by examining its effects on guinea pig platelet function in vitro , in vivo and ex vivo. In vitro, addition of various concentrations of ATA to platelet-rich guinea pig plasma totally inhibited ristocetin-i nduced platelet aggregation, as expected. Unexpectedly, however, ATA s imilarly inhibited the aggregation induced by ADP, PAF, collagen, I-BO P (a thromboxane A(2)/prostaglandin H-2 analogue) and arachidonic acid . In vivo, the antithrombotic action of ATA was assessed in a model of acute platelet-dependent guinea pig mesenteric artery thrombosis trig gered by laser-induced intimal injury. As the thrombotic response of a rteries to such injury is a spontaneous cyclic recurrent process, 5 ar teries in each animal were consecutively studied for 15 min each after i.v. bolus injection of 5, 7.5 or 10 mg/kg of ATA, which reduced the number of recurrent thrombi per artery in a dose-dependent manner. The highest dose of 10 mg/kg induced maximal inhibition of thrombus forma tion (72%, p <0.001) 5 min after injection. Ex vivo, platelet aggregat ion was assessed in blood samples taken before and after i.v. bolus in jection of 10 or 15 mg/kg ATA. Ten mg/kg significantly inhibited colla gen-induced aggregation, and 15 mg/kg, the aggregation induced by rist ocetin, ADP, PAF, collagen, I-BOP and arachidonic acid. The results of the in vivo studies confirmed that ATA is an effective antithrombotic agent. In the in vitro and ex vivo studies, ristocetin-induced platel et aggregation confirmed that ATA interacts with the vWF-GPIb axis, an d suggests that the final common pathway of the aggregation induced by other agents tested consists of fibrinogen binding to the platelet GP IIb/IIIa receptor. We conclude that ATA interferes with VWF binding to GPIb, that it may interact with fibrinogen binding to GPIIb/IIIa, and that it might possess potent antithrombotic properties in platelet-me diated thrombosis.