Inhibitory effect of hexapeptide (RGRHGD) on platelet aggregation

The B chain of beta-bungarotoxin 1-6 sequence, RGRHGD, presents the highest local average hydrophilicity measured by Kyte and Doolittle modeling analy sis. The RGRHGD holds parts of both RGD and KGD peptides, which have been r eported as having high binding affinity to GPIIb-IIIa. The present study ev aluates whether the synthesized hexapeptide, RGRHGD, has an antiplatelet ef fect and further elucidates the possible mechanisms of action. RGRHGD dose- dependently inhibited rabbit platelet aggregation and adenosine triphosphat e release induced by arachidonic acid, collagen, platelet-activating factor , thrombin, or U46619 with the IC50 range of 82.7 to 510 mu g/mL. The plate let thromboxane B-2 formation induced by collagen or thrombin was also sign ificantly decreased by RGRHGD, but there was no effect on arachidonic acid- induced thromboxane B-2 formation. In addition, RGRHGD also inhibited the r ise of intracellular calcium level stimulated by arachidonic acid, collagen , or thrombin in Fura 2-AM-loaded platelets. The adenosine 3',5'-cyclic mon ophosphate level of washed platelets was not affected by RGRHGD. In conclus ion, these data indicate that the inhibitory effect of RGRHGD on platelet a ggregation may be due to the attenuation of thromboxane A(2) formation and intracellular calcium mobilization. In addition, this study may provide a u seful method of finding potential therapeutic agents by using molecular mod eling analysis. (C) 2000 Elsevier Science Ltd. All rights reserved.