CALIN FROM HIRUDO-MEDICINALIS, AN INHIBITOR OF VON-WILLEBRAND-FACTOR BINDING TO COLLAGEN UNDER STATIC AND FLOW CONDITIONS

Calin from the saliva of the medicinal leech, Hirudo medicinalis, is a potent inhibitor of collagen mediated platelet adhesion and activatio n. In addition to inhibition of the direct platelet-collagen interacti on, we presently demonstrate that binding of von Willebrand to coated collagen can be prevented by Calin, both under static and flow conditi ons in agreement with the occurrence of binding of Calin to collagen, confirmed by Biospecific Interaction Analysis. To define whether Calin acted by inhibiting the platelet-collagen or the platelet-von Willebr and factor (vWF)-collagen-mediated thrombus formation, platelet adhesi on to different types of collagens was studied in a parallel-plate flo w chamber perfused with whole blood at different shear rates. Calin do se-dependently prevented platelet adhesion to the different collagens tested both at high- and low-shear stress. The concentration of Calin needed to cause 50% inhibition of platelet adhesion at high-shear stre ss was some fivefold lower than that needed for inhibition of vWF-bind ing under similar conditions, implying that at high-sheat stress, the effect of Calin on the direct platelet-collagen interactions, suffices to prevent thrombus formation. Platelet adhesion to extracellular mat rix (ECM) of cultured human umbilical vein endothelial cells was only partially prevented by Calin, and even less so at a high-shear rather than a low-shear rate, whereas the platelet binding to coated vWF and fibrinogen were minimally affected at both shear rates. Thus, Calin in terferes with both the direct platelet-collagen interaction and the vW F-collagen binding. Both effects may contribute to the inhibition of p latelet adhesion in flowing conditions, although the former seems to p redominate. (C) 1995 by The American Society of Hematology.