Synergistic inhibition of platelet aggregation by fibrinogen-related peptides

We have evaluated the ability of the fibrinogen-related peptides Gly-Arg-Gly-Asp-Ser (GRGDS), Gly-Gln-Gln-His-His-Leu-Gly-Gly-Ala-Lys-Gln-Ala-Gly-Asp-Val (gamma-chain peptide), and Gly-Pro-Arg-Pro (GPRP) to inhibit platelet aggregation in platelet-rich plasma individually and in combination. When used alone, GRGDS totally inhibited ADP-induced aggregation of human platelets in platelet-rich plasma; however, the maximum inhibitory effect of the other peptides was less than 80%. The concentrations necessary to inhibit platelet aggregation in plasma by 50% were 100 mumols/l and 1 and 3.2 mmol/l for GRGDS, gamma-chain peptide, and GPRP, respectively. When evaluating the effect of peptide mixtures, we discovered that the combination GPRP + GRGDS worked together synergistically (p less than 0.001, analysis by surface response methodology), whereas GPRP + gamma-chain peptide did not. For example, our analysis indicated that a mixture of 50 mumols/l GRGDS plus 180 mumols/l GPRP would produce 50% inhibition of platelet aggregation. This is an effect twofold greater than that produced by 50 mumols/l GRGDS alone, and one that would require an 18-fold greater concentration of GPRP if used alone. These data indicate that the combination GPRP + GRGDS inhibited platelet aggregation in plasma in a synergistic fashion and suggest the potential value of their combined use in antithrombotic therapy.