Long-term effects of polymer-based, slow-release, sirolimus-eluting stents in a porcine coronary model

Background: Stent-based delivery of sirolimus (SRL) has shown reduction in neointimal hyperplasia and restenosis. The purpose of this study was to evaluate the chronic vascular response and the expression of cell cycle regulators after SRL-eluting stent implantation in a porcine coronary model. Methods: Forty-nine pigs underwent placement of 109 oversized stents (control, n =54, SRL (140 μg/cm2), n =55) in the coronary arteries with histologic analysis and Western blot (PCNA, p27kip1, CD45, MCP-1, IL-2, IL-6, TNF-β) at 3, 30, 90 or 180 days. Results: At 3 days, the mean thrombus area was similar for control (0.38±0.19 mm2) and SRL (0.29±0.09 mm2) stents. After 30 days, the mean neointimal area was significantly less for the SRL (1.40±0.35 mm2) versus the control stents (2.94±1.28 mm2, p <0.001). At 90 and 180 days, the mean neointimal area was similar for the SRL (3.03±0.92 and 3.34±0.99 mm2) as compared with control stents (3.45±1.09 and 3.65±1.23 mm2). Western blot analysis demonstrated an increased expression of p27kip1 in the vessel wall at 90 days for the SRL versus control stents ( p =0.05) but with increased levels of PCNA in the SRL as compared with control stents ( p =0.003). Conclusion: SRL-eluting stents favorably modulate neointimal formation for 30 days in the porcine coronary model. Long-term inhibition of neointimal hyperplasia is not sustained presumably due to delayed cellular proliferation despite increased levels of the cyclin-dependent kinase p27kip1 in the vessel wall.