ANTAGONISM OF VWF INHIBITS BOTH INJURY-INDUCED ARTERIAL AND VENOUS THROMBOSIS IN THE HAMSTER

von Willebrand factor (vWF) is instrumental in arterial but has also b een implicated in venous thrombogenesis. To address its role in venous thrombosis. experimental thrombosis was induced in the carotid artery and the femoral vein of hamsters, following which thrombus pre ventio n by two different antagonists of VWF was studied. The first antagonis t was the anti-human vWF monoclonal antibody AJvW-2, which inhibits th e botrocetin and ristocetin induced aggregation of human blood platele ts. AJvW-2 reacts with an epitope present in the Al domain of VWF in v ery different species (human, pig, rabbit, dog, Guinea pig and rat). T his epitope was found to be conformational and overlapping with VWF bi nding sites for aurin tricarboxylic acid (ATA), but not for botrocetin and heparin. AJvW-2 has affinities for vWF in the absence (K-d = 0.5 +/- 0.03 nmol/l in solution) and in the presence of shear stress (K-d = 3.3 +/- 0.6 nmol/l during perfusion at 1,300 s(-1) over subendotheli al matrix associated vWF) sufficiently elevated to neutralize vWF. Dur ing perfusion of subendothelial matrix with anticoagulated human blood , the surface covered by adhering platelets was reduced by AJvW-2, wit h IC,,s equal to 6.6 +/- 0.34 mu g/ml at 1,300 s(-1) and to 1 +/- 0.01 mu g/ml at 2,700 s(-1). As a second antagonist, molecular size gel fi ltered ATA was selected. Fractionated ATA inhibited platelet adhesion to matrix with IC,,s equal to 0.27 +/- 0.09 mmol/l at 1,300 s(-1) and 0.16 +/- 0.008 mmol/l at 2,700 s(-1). When administered to hamsters, A JvW-2 prevented thrombosis in the injured carotid artery dose-dependen tly (ED50 = 0.15 +/- 0.01 mg/kg). Thrombosis in the similarly injured femoral vein was however also inhibited (ED50 = 0.37 +/- 0.06 mg/kg). Likewise, fractionated ATA completely inhibited carotid artery thrombo sis (ED50 = 0.42 +/- 0.13 mg/kg), but also interfered with femoral vei n thrombosis (apparent ED50 between 2 and 3 mg/kg). We conclude that a ntagonizing the VWF Al domain by AJvW-2 and to a lesser extent also by fractionated ATA, inhibits thrombosis not only in the arterial but al so in the venous circulation. Since venous thrombi were prevented at o nly 3-5-fold higher doses of antagonist, vWF participates in injury in duced venous thrombosis.