Obovatol from Magnolia obovata inhibits vascular smooth muscle cell proliferation and intimal hyperplasia by inducing p21Cip1

Aims: Obovatol is isolated from Magnolia obovata leaves and this active component has various pharmacological properties such as anti-oxidant, anti-platelet, anti-fungal and anti-inflammatory activities. In the present study, we investigated the inhibitory effects of obovatol on in vitro vascular smooth muscle cell (VSMC) proliferation and in vivo neointimal formation in a rat carotid artery injury model. Methods and results: Obovatol (1-5 mu M) exerted concentration-dependent inhibition on platelet-derived growth factor (PDGF)-BB-induced rat VSMC proliferation, without exhibiting any cellular toxicity or apoptosis, as determined by cell count, [H-3] thymidine incorporation and Annexin-V-binding analyses. Treatment with obovatol blocked the cell cycle in G(1) phase by down-regulating the expression of cyclins and CDKs, and selectively up-regulating the expression of p21(Cip1), a well-known CDK inhibitor. Effects of perivascular delivery of obovatol were assessed 14 days after injury. The angiographic mean luminal diameters of the obovatol-treated groups (100 mu g and 1 mg: 0.78 +/- 0.06 and 0.77 +/- 0.07 AU, respectively) were significantly larger than that of the control group (0.58 +/- 0.07 AU). The obovatol-treated groups (100 mu g and 1 mg: 0.14 +/- 0.04 and 0.09 +/- 0.03mm(2), respectively) showed significant reduction in neointimal formation versus the control group (0.17 +/- 0.02mm(2)). Immunohistochemical staining demonstrated strong expression of p21(Cip1) in the neointima of the obovatol-treated groups. Conclusions: These data suggest that obovatol inhibits VSMC proliferation by perturbing cell cycle progression, possibly due to activation of p21(Cip1) pathway. These results also show that obovatol may have potential as an anti-proliferative agent for the treatment of restenosis and atherosclerosis. (C) 2009 Elsevier Ireland Ltd. All rights reserved.