The development of intimal hyperplasia is recognized as a major impediment to graft patency. D-Limonenes are monoterpenes with a recognized cytostatic effect on cell proliferation by inhibiting post-translational isoprenylation of p21ras and other small G-proteins. This study examines the effect of perillyl alcohol, an oral hydroxylated D-limonene, on the development of intimal hyperplasia and its associated smooth muscle cell physiological responses in an experimental model of vein bypass grafting. Twenty New Zealand white rabbits had a right carotid interposition bypass graft using the ipsilateral external jugular vein. Ten animals received chronic oral therapy with a perillyl alcohol (200 mg/kg/day; begun 5 days before surgery and continued until harvest) and 10 control animals received vehicle only. All animals were sacrificed on the 28th postoperative day. Vein grafts were harvested either for morphology/videomorphometry (n = 6 per group) or for in vitro isometric tension studies (n = 4; four 5-mm rings per graft). The cell proliferation and incorporation of [3H]thymidine into the cellular DNA of serum-stimulated rabbit aortic smooth muscle cells was also assessed in the presence of increasing concentrations of perillyl alcohol (10-9-10-4 M). Perillyl alcohol treated vein grafts showed a 22% reduction in overall mean intimal thickness (54 ± 4 μm vs 69 ± 3 μm; P = 0.006) but a 25% increase in overall mean medial thickness (86 ± 4 μm vs 61 ± 3μm). The intimal ratio of the perillyl alcohol treated vein grafts decreased by 27% compared to controls. Perillyl alcohol induced norepinephrine and serotonin hypersensitivity in vein grafts compared to controls. The IC50 for perillyl alcohol was 176 nM with maximal inhibition at 5 μM. Incubation of smooth muscle cell cultures with increasing concentrations of perillyl alcohol showed a dose-dependent decrease in in vitro cellular proliferation, maximal at 1 μM. Therapy with perillyl alcohol alters the early development of intimal hyperplasia reducing the intimal response but increasing the medial response without significant changes in the physiological responses of the smooth muscle cells. Modulating G-proteins will affect the intimal hyperplastic response in vein grafts.
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