Naringenin Inhibits TNF-α-induced Proliferation And Migration Of Vascular Smooth Muscle By Inducing HO-1 Production

Atherosclerosis (AS), which is a chronic inflammatory cardiovascular disease with the artery wall thickening as a result of build-up of fatty materials such as cholesterol, led to a catastrophe in global human health.According to the findings in cell biology, vascular smooth muscle cell (VSMC) proliferation and migration are critical events in the pathogenesis of AS. After the initial injury, various cell types, such as EC, platelets, and inflammatory cells are recruited and secrete growth factors and proinflammatory cytokines. Among which, tumor necrosis factor alpha (TNF-a) plays an essential role in increasing the expression of adhesion molecules and promoting the secretion of numerous chemokines, as well as recruiting monocytes to the site of injury and enhancing their adhesiveness to the endothelium. TNF-α also regulates the proliferative, migratory and synthetic behavior of VSMCs and induces the transition of VSMCs toward an osteoblast/chondrogenic phenotype, which causing calcium deposition in the arteries and increasing arterial stiffness. More importantly, inflammation mediated by cytokines including TNF-α causes oxidative stress since production of reactive oxygen species (ROS) is an inherent property of activated immune cells. A strategy aiming to inhibit TNF-α-induced VSMC growth and migration has a high value in the prevention and attenuation of AS.Naringenin, which is a flavonoid aglycone responsible for the bitter taste in grapefruits, demonstrates various promising pharmaceutical effects. Naringenin improves hyperlipidemia by increasing hepatic fatty acid oxidation and inhibiting sterol regulatory element binding protein-lc (SREBP-1c) mediated lipogenesis in both liver and muscle. Clinical investigations indicate that naringenin treatment reduce low density lipoprotein (LDL) levels in hypercholesterolemia patients and alleviate atheroslcerotic risks. Naringenin also performs its beneficial effects on cardiovascular system through inhibiting pathophysiological changes of VSMCs, including excess proliferation, matrix metalloproteinase-9(MMP-9) expression and Akt phosphorylation. The activation of large conductance Ca2+-activated K+channels in VSMCs by naringenin has also been reported. However, all these studies did not reveal the direct molecular target of naringenin, which limits the full understanding of mechanism through which naringenin exerts its diverse functions.Heme oxygenase-1(HO-1), belongs to the HO family, is an anti-inflammatory protein in response to various stimuli, such as ox-LDL, UV and hypoxia. Both HO-1over-expression and induction have been associated with anti-inflammatory events. Lung-specific HO-1transgenic mice showed resistance to the pulmonary inflammation. A human patient with HO-1deficiency exhibited a fatal severe phenotype of general inflammation, and similar observations were noted in HO-1null mice. In vascular cells, HO-1inhibits platelet aggregation in a platelet-VSMC co-incubation system and represses VSMC activation through generating carbon monoxide (CO). Based on these observations which suggest that HO-1is involved in the modulation of inflammation, we examined whether naringenin inhibits VSMC proliferation and migration during inflammation through HO-1gene induction.In this investigation, we found that naringenin induced HO-1mRNA and protein levels, as well as its activity in VSMCs. Naringenin inhibited TNF-α induced VSMC proliferation and migration in a dose-dependent manner. Mechanistic study demonstrated that naringenin prevented ERK/MAPK and Akt phosphorylation while left p38MAPK and JNK unchanged. Naringenin also blocked the increase of ROS generation induced by TNF-α, while HO-1inhibitor ZnPP IX or HO-1siRNA partially abolished the beneficial effects of naringenin on VSMCs.In conclusion, these results suggest that naringenin may serve as a novel drug in the treatment of cardiovascular diseases by inducing HO-1expression/activity and subsequently decreasing VSMC proliferation and migration. In addition, HO-1ranks one of the most promising drug targets for the treatment of cardiovascular diseases, due to its dynamically modulatory property.