Low-dose Radioactive Palmaz-Schatz Stents Prevent Smooth Muscle Cell Proliferation and Neointimal Hyperplasi in Rabbits

The long-term consequences of ionizing irradiation of arteries with doses of more than 10 Gray (Gy) are vascular stenosis. To evaluate anti-proliferative effects of much lower irradiation doses, we implanted radioactive Palmaz-Schatz stents (RS) emitting doses of 0.002 Gy/h in rabbit arteries (n = 20). The radiation dose absorbed in the arteries after 100 days is lower than human chest dose after single cardiac catheterization. Arterial smooth muscle cell (SMC) proliferation and neointimal hyperplasi were compared 1 and 12 weeks after RS and non-radioactive stent (NRS) implantation. SMC proliferation was assessed by immunostaining with antibodies to proliferating cell nuclear antigen (PCNA) and SMC-α-actin and by computer-assisted counting of neointimal cells (NIC)/0.1 mm2 neointima. Quantitative morphometry of arterial cross-sections was applied to compare the neointimal areas after implantation of RS and NRS. After 1 week, 30% neointimal SMCs were positive for PCN in NRS, whereas 0.5% SMCs were PCNA-positive in NRS (p < 0.01). After 12 weeks, 850 ± 50 NIC (mean ± SD) were found in arteries with NRS compared to 237 ± 26 NIC in arteries with RS (p < 0.01). The neointimal are was 0.8 ± 0.2 mm2 12 weeks following implantation of NRS versus 0.4 ± 0.2 mm2 following RS implantation (p < 0.01). Conclusion: low-dose endovascular irradiation vi radioactive stents prevents smooth muscle cell proliferation and stenotic neointimal thickening after angioplasty. The results do not confirm previous reports of vascular stenosis after ionizing irradiation.