Atherosclerosis manifests as plaque build-up in arteries, and its multifactorial etiology has been shown to involve the activities of inflammatory cells, vascular smooth muscle cells (VSMCs), and intracellular and extracellular lipids [1][2][3][4].The arterial wall is composed of three layers; the tunica intima, media, and adventitia. VSMCs of coronary arteries reside in the middle layer, and provide structural integrity to vessel walls and control vascular tone and blood pressure [5]. VSMCs also exhibit a contractile phenotype and low proliferative rates [6]. However, endothelial dysfunction and vessel wall injury during atherosclerosis result in the activation and dedifferentiation of arterial smooth muscle cells (SMCs) [5,7], and resultant intimal thickening provides the basis for the build-up of atherosclerotic plaque [8]. These processes are triggered by various cytokines and growth factors, including interleukin 1 beta (IL-1β), Abstract : Gambogic acid (GA) has powerful apoptotic actions. The authors investigated whether GA has apoptotic effects on aortic smooth muscle cells, and compared its potency with that of simvastatin.Smooth muscle cells were isolated from the aortas of Sprague-Dawley rats (4-6 week). Cell purities were confirmed by IF staining using α-smooth muscle actin antibody. The IC 50 values for cell death by GA and simvastatin were determined using a MTT assay, and the apoptotic effects of 1 μM GA or 30 μM simvastatin (concentrations correspond to IC 50 values) were determined after 24 h of treatment using live cell images and by FITC annexin-V and propidium iodide double-staining. In addition, western blotting was used to evaluate apoptosis by quantifying reductions in the expression levels of the PARP and procaspase-3 as well as cleavages of PARP and procaspase-3 after treatment with 1 μM GA or 30 μM simvastatin. The IC 50 of GA (1 μM) was lower than that of simvastatin (30 μM). Cell numbers were markedly reduced by both drugs in live cell images. GA (1 μM) produced a higher level of apoptosis than 30 μM simvastatin (26.4±2.37% vs. 8.3±1.54%, respectively; P⁄0.05, n= =3) by FITC annexin-V & PI double-staining. In addition, 1 μM GA reduced the expressions of PARP, procaspase-3, and Mcl-1 in cells, whereas 30 μM simvastatin did not. Pretreatment with z-VAD-fmk attenuated GA-induced apoptosis and the cleavages of PARP and procaspase-3. The decreased level of Mcl-1 protein induced by GA treatment was recovered by z-VAD-fmk.These results indicate that GA-induced apoptosis was mediated by a caspase-dependent pathway. Original Article interleukin 6 (IL-6), transforming growth factor beta 1 (TGF-β1), tumor necrosis factor alpha (TNF-α), thrombin, fibroblast growth factor (FGF), insulin-like growth factor 1 (IGF-1), platelet-derived growth factor (PDGF), urokinase plasminogen activator, angiotensin II, and vascular endothelial growth factor (VEGF), which are all expressionally upregulated in atherosclerotic lesions [9][10][11][12]. In the diseased state, VSMCs re-enter the cell cycle, proliferate, ...