## 4 Discussion  
Atherosclerosis is an inflammatory disease with a progressive, long-term pathology, and it places heavy economic burdens on human beings. Vascular inflammation was thought to be the first incident responsible for atherosclerosis development. In previous studies, we uncovered that treatment by platonin can reduce VSMC proliferation and attenuate macrophage activation [30]. The present study further demonstrates that platonin, a cyanine photosensitizing dye, suppresses inflammatory responses in VSMCs induced by various mediators. The inhibitory property of platonin in inflammatory VSMCs may be another advantage for the treatment of atherosclerosis. Indeed, platonin was reported to reduce mortality and lung injury and to preserve blood-brain barrier integrity in septic rats [31]. The protective effect of platonin against vascular inflammation thus may also be involved in the mechanisms underlying sepsis. Vascular inflammation is crucial in the pathogenesis of atherosclerosis and other inflammatory diseases [32]. In this study, platonin suppressed LPS/IFN-\(\gamma\) or ox-LDL-induced inflammation in VSMCs at 0.5-2 \(\upmu\)M/mL. The results suggest that platonin could be a potential agent for treating VSMC inflammation-associated diseases. Vascular injury follows inflammatory processes such as the recruiting of immune cells and the releasing of cytokines/chemokines, which are crucial in atherosclerosis [33]. The recruitment of circulating monocyte-derived cells occurs in lesions of atherosclerosis [34], where they differentiate into macrophages. These macrophages yield lipid-laden foam cells by actively ingesting and accumulating lipoprotein in atherosclerotic lesions [34; 35; 36]. The accumulation of foam cells results in lipid storage and atherosclerotic plaque growth [34]. MCP-1, a member of chemotactic cytokine family, is a potent monocyte activator induced by oxidized lipids [37]. It is also a proinflammatory factor playing key roles in foam cell formation [38]. Ox-LDL is known to induce robust expression of MCP-1 in the lesions of atherosclerosis. This indicates that MCP-1 should be a crucial factor in the recruitment of monocytes or macrophages in the early stage of atherosclerosis [37]. Platonin has been reported to be a potent antioxidant and to suppress macrophage activation and associated inflammatory responses [20]. In the present study, platonin inhibited ox-LDL-induced MCP-1 production in VSMCs. These results indicate that platonin could also be a potential agent for treating vascular inflammatory diseases through its dual inhibition on macrophages and VSMCs. IkBa protein degradation is a critical step in the NF-kB signaling pathway; the binding of IkBa protein modulates the entry of cytosolic NF-kB into nuclei. The dissociation of IkBa from the NF-kB subunits is modulated by the phosphorylation of IkB kinase complex and is ubiquitinated then rapidly degraded by the proteasome [39]. In the present study, the administration of platonin led to significant inhibition of NF-kB activation; however, IkBa degradation was unaffected by treatment with platonin in LPS/IFN-\(\gamma\)-stimulated VSMCs. Previous studies reported that the phosphorylation of crucial serine residues in p65 can regulate its dimerization, nuclear translocation, and DNA binding activity [23]. An individual phosphorylation site may be modulated by a single or multiple kinases [40]. The phosphorylation of Ser536 after LPS or TNF stimulation can increase transcriptional activity of NF-kB [41]. We, thus, examined whether the phosphorylation of p65 contributes to the inhibitory mechanism of platonin in NF-kB activation. Pretreatment by platonin indeed attenuated p65 ur536 phosphorylation in VSMCs stimulated by LPS/IFN-\(\gamma\). It is imaginable that platonin may directly dephosphorylate Ser536 through activating a protein phosphatase, then lead to the downregulation of NF-kB and iNOS. The previous study indicated that PP2A-modulated p65 phosphorylation regulated NF-kB activation in an IkBa-independent pathway [24].