INTERACTION OF THROMBIN-ACTIVATED PLATELETS WITH EXTRACELLULAR MATRICES (FIBRONECTIN AND VITRONECTIN) - COMPARISON OF THE ACTIVITY OF ARG-GLY-ASP-CONTAINING VENOM PEPTIDES AND MONOCLONAL-ANTIBODIES AGAINST GLYCOPROTEIN IIB IIIA COMPLEX/

Platelets adhere to fibronectin and vitronectin substrates following a ctivation with physiological concentrations of thrombin. Adhesion of a ctivated-platelets to either substrate is dependent upon the amount of fibronectin and vitronectin, and the duration of the adhesion assay. In this study, we showed that the Arg-Gly-Asp-containing peptides (inc luding naturally occurring polypeptides, triflavin, trigramin and rhod ostomin, synthetic peptides GRGDS, GRGDSPK, GRGDF, and GRGD and monocl onal antibodies, 7E3, 10E5 and AP2, raised against glycoprotein IIb/II Ia complex, inhibited the adhesion of activated-platelets to fibronect in and vitronectin-coated plates in a dose-dependent manner. In fibron ectin-coated plates, GRGDF was shown to be much more efficient than GR GDS, GRGDSPK and GRGD at inhibiting the adhesion of activated-platelet s to immobilized fibronectin. On the other hand, there were no marked differences in the abilities of these three peptides (GRGDF, GRGDS and GRGDSPK) to inhibit platelet adhesion to immobilized vitronectin. Fur thermore, the RGD-containing venom peptide, triflavin was more effecti ve than rhodostomin and trigramin at inhibiting the adhesion of activa ted-platelets to either substrates. The monoclonal antibodies raised a gainst glycoprotein IIb/IIIa complex (i.e., 7E3, 10E5 and AP2) inhibit ed platelet adhesion to fibronectin and vitronectin in a similar dose- dependent manner. Interestingly, we found that 7E3 was more efficient than 10E5 and AP2 in this reaction. These studies suggest that the gly coprotein IIb/IIIa complex, present on activated-platelets, may intera ct with fibronectin and vitronectin substrates through the Arg-Gly-Asp -dependent mechanism. Since fibronectin and vitronectin are present in the subendothelial matrix, they may be involved in platelet-vessel wa ll interaction. The Arg-Gly-Asp containing peptide, especially triflav in, is an ideal therapeutic agent for inhibiting thrombus formation by interrupting platelet-platelet and platelet-subendothelium interactio ns.