RECOMBINANT LEECH ANTIPLATELET PROTEIN SPECIFICALLY BLOCKS PLATELET DEPOSITION ON COLLAGEN SURFACES UNDER FLOW CONDITIONS

Salivary glands of the leech Haementeria officinalis contain a protein , leech antiplatelet protein (LAPP). This protein was cloned and expre ssed in yeast and blocks collagen-mediated platelet aggregation and th e adhesion of platelets to collagen-coated plates under static conditi ons. In the current study we investigated the effect of rLAPP on plate let deposition to collagen and collagen-rich surfaces under flow condi tions. rLAPP completely inhibited platelet adhesion on collagen types I, III, and IV with IC50 values of 70, 600, and 90 nmol/L, respectivel y (shear rate=1600 s(-1)). Approximately 10-fold more rLAPP was requir ed to obtain a similar inhibition at a low shear rate of 375 s(-1). rL APP caused a concentration-dependent inhibition of binding of I-125-vo n Willebrand factor (VWF) to collagen type III and was able to displac e prebound VWF even after 24 hours. Since platelet adhesion at low she ar rate is less dependent on VWF than at high shear rate, this propert y of rLAPP may explain why less rLAPP is needed at high shear rate tha n at low shear rate to produce the same effect. Platelet adhesion to c ollagen type VI was only partially inhibited by rLAPP (maximal 44% wit h 3 mu mol/L rLAPP). rLAPP also caused a pronounced inhibition of plat elet deposition to cross sections of human atherosclerotic coronary ar teries but had no effect on matrices of cultured human umbilical vein endothelial cells. rLAPP is a potent platelet adhesion inhibitor at hi gh shear rate, which binds to collagen and works by inhibiting binding of vWF to collagen.