Perivascular Delivery of Rapamycin in Pluronic Gel Inhibits Neointimal Hyperplasia in a Rat Carotid Artery Injury Model, and the Complementary Role of Carotid Arteriography

BACKGROUND AND OBJECTIVES: Rapamycin has been shown to inhibit the vascular smooth muscle cell migration and proliferation that contributes to neointimal formation. We investigated whether the perivascular delivery of rapamycin in Pluronic gel could inhibit neointimal hyperplasia in a rat carotid artery model, and we tested the usefulness of carotid arteriography. MATERIALS AND METHODS: To assess the kinetics of rapamycin's release from Pluronic gel, a [3H] thymidine incorporation assay was performed with using the media exposed to rapamycin in Pluronic gel for 10, 20, 60 and 120 min. We applied 100 microgram of rapamycin in Pluronic gel to the perivascular space of the carotid artery after the balloon injury (n=9), whereas only gel was applied in a control group (n=9). We performed the carotid arteriography and the morphometric analysis 14 days after injury. RESULTS: The [3H] thymidine incorporation assay showed a reduction of uptake in a time-dependent manner (86%, 48%, 45% and 40% of the control, respectively, at 10, 20, 60 and 120 minutes). The inhibiting effect of rapamycin on neointimal hyperplasia was identified on the carotid arteriography (mean luminal diameter; 0.75+/-0.11 vs. 0.60+/-0.12 arbitrary units, respectively, p< 0.05) and on the morphometric analysis (neointima area: 0.09+/-0.03 vs. 0.17+/-0.06 mm(2), respectively, p< 0.05). CONCLUSION: This study demonstrated that perivascular delivery of rapamycin in Pluronic gel inhibits neointimal hyperplasia in a rat carotid injury model. This animal model combined with arteriography can be used for developing new drugs to treat restenosis. In addition, this technique might be useful for vascular surgery such as coronary artery bypass grafting, arteriovenous fistula formation and peripheral vascular bypass graft insertion.

A Slight Variation in the Age of Rats Commonly used as a Carotid Artery Injury Model Results in a Large Difference in Neointima Formation

BACKGROUND AND OBJECTIVES: The degree of neointima formation after infliction of a carotid artery balloon injury in rats varies greatly depending on the sex, age, species and operational method. Strong variation is common, even within only a single control. This study attempted to find if there was any significant difference in neointima formation following a carotid artery balloon injury in 6 to 12 week old rats; the age commonly used in these types of experiments. MATERIALS AND METHODS: A balloon injury was inflicted on the carotid arteries of male SpragueDawley rats at 6 (n=9, 250-270 g), 8 (n=8, 280-300 g) and 11 weeks (n=10, 320-340 g) of age. Two weeks postoperation, a histomorphometric analysis was carried out. The vascular smooth muscle cell proliferation was measured in situ via BrdU incorporation 2 days after injury infliction. RESULTS: The neointima areas of the 6 week (0.22+/-0.04 mm2) and 8 week old groups (0.17+/-0.08 mm2) were 3.1 and 2.4 times larger than that of the 11 week old group (0.07+/-0.03 mm2). The mitotic index was significantly reduced in 11 week old group (n=4, 9.22+/-1.51%) compared to those of the 6 (n=4, 25.03+/-3.92%) and 8 week old (n=4, 21.66+/-3.66%) groups. CONCLUSION: Special care should be taken when interpreting neointima formation, as even a slight variation in the age and weight in 6 to 12 week old (250-340 g) rats; the age commonly used in these types of experiments, results in an unexpectedly large difference.