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 expressed in yeast and blocks collagen-mediated platelet aggregation and the adhesion of platelets to collagen-coated plates under static conditions. In the current study we investigated the effect of rLAPP on platelet deposition to collagen and collagen-rich surfaces under flow conditions. rLAPP completely inhibited platelet adhesion on collagen types I, III, and IV with IC50 values of 70, 600, and 90 nmol/L, respectively (shear rate = 1600 s-1). Approximately 10-fold more rLAPP was required to obtain a similar inhibition at a low shear rate of 375 s-1. rLAPP caused a concentration-dependent inhibition of binding of 125I-von Willebrand factor (vWF) to collagen type III and was able to displace prebound vWF even after 24 hours. Since platelet adhesion at low shear rate is less dependent on vWF than at high shear rate, this property of rLAPP may explain why less rLAPP is needed at high shear rate than at low shear rate to produce the same effect. Platelet adhesion to collagen type VI was only partially inhibited by rLAPP (maximal 44% with 3 mumol/L rLAPP). rLAPP also caused a pronounced inhibition of platelet deposition to cross sections of human atherosclerotic coronary arteries but had no effect on matrices of cultured human umbilical vein endothelial cells. rLAPP is a potent platelet adhesion inhibitor at high shear rate, which binds to collagen and works by inhibiting binding of vWF to collagen.