INTIMAL HYPERPLASIA FOLLOWING VASCULAR INJURY IS NOT INHIBITED BY AN ANTISENSE THROMBIN RECEPTOR OLIGODEOXYNUCLEOTIDE

Thrombin is a multifunctional serine protease with central functions i n hemostasis, but demonstration of its role in the initiation and main tenance of cell proliferation which occurs following vascular injury i s still lacking. To determine the role played by thrombin and its rece ptor in neointimal accumulation of smooth muscle cells in a rabbit car otid artery model, we have used an 18 mer antisense phosphorothioate o ligonucleotide (ODN) directed against the translation initiation regio n of the human thrombin receptor gene. The antisense ODN inhibited in a dose-dependent manner thrombin- or thrombin receptor activating pept ide-induced human aortic smooth muscle cell proliferation. The growth- inhibitory effect of thrombin receptor antisense ODN was preventable b y an excess of sense oligomer and specific for thrombin. The suppressi on of growth was accompanied by a marked decrease of the level of thro mbin receptor expression as evidenced by [I-125]-thrombin binding to s mooth muscle cells. Under the same experimental conditions, the corres ponding sense ODN was inactive. The effect of the antisense ODN on int imal smooth muscle hyperplasia in rabbit carotid arteries subjected to endothelial injury was then investigated. The topical application of the antisense (500 mu g/artery) but not the sense ODN dissolved in F12 7 pluronic gel around the injured artery resulted, 2 weeks after the a pplication, in a dramatic reduction of the expression of the thrombin receptor mRNA and protein levels as determined by in situ hybridizatio n and immunohistochemistry. However, intimal smooth muscle cell accumu lation as estimated by an intimal to medial cross-sectional area ratio was reduced only by 2.7% (vs. 10.3% for the sense ODN), whereas r-hir udin (200 mu g/kg/day, sc), a potent direct thrombin inhibitor signifi cantly reduced the formation of neointima in denuded carotid arteries (35.4% inhibition, P = 0.03). (C) 1997 Wiley-Liss, Inc.