Neointimal Formation After Balloon-Induced Vascular Injury in Yucatan Minipigs is Reduced by Oral Rapamycin

Rapamycin, a macrolide antibiotic known to prevent allograft rejection, is a potent inhibitor of cell proliferation. Therefore we studied the effects of orally administered rapamycin in a pig model of balloon injury in an attempt to reduce the cellular proliferation and neointimal formation thought to play a role in restenosis. Twenty Yucatan minipigs, divided into groups of 10 animals each, were subjected to balloon inflation of the carotid arteries. One group received the methylcellulose vehicle for rapamycin, whereas the second group was treated for a total of 31 days with 2.0 mg/kg of rapamycin administered daily by oral gavage. This dose and treatment regimen produced significant (p < 0.05) reductions in neointimal area (59%) and in the maximal thickness of the neointima (59%) when comparisons were made with vehicle-treated animals. These effects were accompanied by a significant increase in the lumen area in animals that received rapamycin (33%). Medial area was decreased by 18% in these animals. Blood samples from rapamycin-treated pigs indicated peak concentrations of 1.87 +/- 0.45 and 1.70 +/- 0.24 ng/ml at 2 and 4 weeks after balloon angioplasty, respectively. Significant increases in blood pressure of 21 mm Hg and decreases in heart rate of 25 beats/min also were observed in rapamycin-treated animals relative to those that received vehicle. These results indicate that the antiproliferative effect of rapamycin can be demonstrated after oral dosing in a pig vascular injury model, suggesting a possible therapeutic utility for rapamycin or its analogs in patients undergoing balloon angioplasty.