A peptide analogue of thrombin receptor-activating peptide inhibits thrombin and thrombin-receptor-activating peptide-induced vascular smooth muscle cell proliferation

The serine protease thrombin, in addition to its pivotal role in the coagul ation cascade, plays an important role in the development of atherosclerosi s and restenosis by inducing smooth cell proliferation. Thrombin exerts its cellular effects mainly by cleaving its own receptor, leaving a new NH2-te rminus that can act as a tethered ligand to activate the thrombin receptor. Peptides derived from the new NH2-terminus are able to fully activate thro mbin receptor acid mimic cellular effects of thrombin. Peptides with struct ural similarities to the tethered ligand have been tested for their ability to prevent thrombin- and tethered ligand-induced platelet aggregation and thrombus formation. We synthesized a peptide with multiple alanine substitu tions in both critical and noncritical residues of tethered ligand that spe cifically inhibited platelet aggregation induced by thrombin and thrombin r eceptor-activating peptide and prevented thrombus formation in a rabbit thr ombosis model. In the present study we demonstrate that this peptide inhibi ted only thrombin- and tethered ligand-induced human vascular smooth muscle cell proliferation as determined by (H-3)-thymidine incorporation and has no effect on platelet-derived growth factor and serum-induced smooth muscle cell proliferation. The inhibitory effect of this peptide is dependent on the concentration of the antagonist used and length of preincubation time, The possible mechanism by which this peptide exerts its inhibitory effect m ay by desensitizing the thrombin receptor. The results of the present study suggest that apart from being antithrombotic, tethered ligand antagonist p eptides can also act as antiatherosclerotic or antirestenotic agents.