Role of magnolol in the proliferation of vascular smooth muscle cells

Background. Proliferation of vascular smooth muscle cells (VSMCs) contributes to the development of vascular remodeling. Recently, magnolol has been reported to have a potential role in regulating tumor necrosis factor a-induced proliferation of VSMCs. However, the role of magnolol in platelet-derived growth factor (PDGF)-induced proliferation of VSMCs remains unknown. Aims. Our purpose was to elucidate the effect of magnolol on the proliferation of VSMCs induced by PDGF-BB and to investigate the underlying molecular mechanisms. Methods and results. Our data demonstrated that magnolol inhibited rat VSMC proliferation and DNA synthesis stimulated by 20 ng/ml PDGF-BB without causing cell cytotoxicity. Flow cytometric analysis showed that magnolol inhibited S-phase entry of VSMCs. We also demonstrated that magnolol caused this effect by inhibiting the mRNA and protein expression of cyclin D1, cyclin E, and cyclin-dependent kinases 2 and 4 in PDGF-BB-stimulated VSMCs. Further analysis showed that the inhibitory effect of magnolol on the proliferation of VSMCs was associated with the inhibition of the PDGF-BB-stimulated production of intracellular reactive oxygen species (ROS) and Ras, MEK, and ERK1/2 activation. Conclusion. These results demonstrate that magnolol can block the proliferation of VSMCs through inhibition of intracellular ROS production and Ras-MEK-ERK1/2 pathways. Magnolol, therefore, has a potential application in preventing atherosclerosis and restenosis.