EFFECTS OF ANTISENSE OLIGONUCLEOTIDES ON MYOINTIMAL HYPERPLASIA IN A MODEL OF ABDOMINAL AORTIC TRAUMA IN THE RAT

Restenosis at a rate > 30% at 6 months is the major complication of bo th coronary and peripheral arterial angioplasty. Restenosis is mainly due to proliferation of smooth muscle cells, extracellular matrix and collagen which form a neointima. The proto-oncogen c-myb is a gene wit h an immediate response which has been implicated in the proliferation and alteration of the phenotype of smooth muscle cells. The antisense s are molecules of single-helix DNA the sequence of which is inverse t o that of messenger RNA of the target proto-oncogen. They therefore ha ve the possibility of forming a double helix with the messenger RNA an d of preventing its translation. The antisenses of c-myb have already been successfully tested in in vitro and in vivo models of neointimal proliferation. The aim of this study was to demonstrate the efficacy o f c-myb antisenses on the proliferation of smooth muscle cells in a mo del of abdominal aortic injury in the rat. Thirty-five male Wistar rat s with an average weight of 350 grammes were operated. Smooth muscle c ell proliferation was obtained by desendothelialisation of the abdomin al aorta from the level of the left renal vein to the aortic bifurcati on. Using a randomised, double-blind protocol, 17 rats were given 500 microlitres of pluronic gel (control group), 9 a sense oligonucleotide of c-myb in 500 microlitres of pluronic gel (sense group) and 9 a c-m yb antisense oligonucleide in 500 microlitres of pluronic gel (antisen segroup). Two rats were given fluorescinlabelled antisenses; one was s acrified 4 hours and the other 24 hours later. All these solutions wer e applied around the adventitiae of the abdominal aortas. After 21 day s, the rats were sacrificed and the aortas sent for histomorphometric analysis. The average thickness and surface of the neointima (MNT and MNS) the ratio (R) of mean neointimal thickness/mean (neointima + medi a) thickness and the mean thickness of neointimal proliferation (MTNP) were calculated. The MTNP only takes the regions of smooth muscle cel lular proliferation into the consideration. All results were considere d to be significant when p < 0.05. The two aortas treated with labelle d antisense were frozen then sectioned for examination with a confocal microscope. The MNT, MNS and R were significantly smaller in the anti sense group than in controls (p < 0.03, p < 0.02 and p < 0.02 respecti vely). The MTNP of the antisense group was significantly less than in the control and sense groups with p < 0.03 and p < 0.05 respectively. The thickness of the neointimal of the antisense group was on average 35% less than that of the control group (in all calculations). The two antisense-labelled aortas showed penetration of the antisense into th e cells which in creased with time. The authors conclude that c-myb an tisense seems to be a valuable therapy for the prevention of posttraum a myointimal proliferation in their model. Other studies on larger ani mals with intraluminal administration of the produce should be carried out to better assimilate the clinical situation.