A Monomeric von Willebrand Factor Fragment, Leu-504-Ser-728, Inhibits von Willebrand Factor Interaction with Glycoprotein Ib-IX

von Willebrand factor interaction with glycoprotein Ibα(GPIbα) plays a critical role in the initial phase of platelet adhesion at high shear rates, and it may also play a role in platelet thrombus formation in partially occluded arteries. Previous studies have indicated that two peptides, Cys-474-Pro-488 (peptide 153) and Ser-692-Pro-708 (peptide 154), inhibit von Willebrand factor-GPIbαinteraction. We have expressed a recombinant fragment of von Willebrand factor, Leu-504-Ser-728, with a single intrachain disulfide bond linking residues Cys-509-Cys-695 and examined its ability to inhibit von Willebrand factor-GPIbαinteractions and platelet adhesion at high shear forces. This recombinant fragment, named VCL, inhibits ristocetin-induced, botrocetin-induced, and asialo-von Willebrand factor-induced platelet aggregation and binding to platelets at an IC50= 0.011-0.260 μM, significantly lower than the IC50of peptide 153 or 154, IC50= 86-700 μM. Peptides 153 and 154 did not result in any inhibition of platelet adhesion (IC50> 500 μM). In contrast, VCL inhibited 50% of platelet adhesion at 0.94 μM and at 7.6 μM inhibited >80% of platelet adhesion to human umbilical artery subendothelium at high shear forces. VCL inhibited the contact and spreading of platelets and also caused a marked decrease in thrombus formation. These studies indicate that VCL may be an effective antithrombotic agent in preventing arterial thrombus formation in areas of high shear force.