Dihydrocapsaicin Suppresses Proinflammatory Cytokines Expression By Enhancing Nuclear Factor IA In A NF-?B-dependent Manner

BackgroundAtherosclerosis is a systemic chronic disease that affects human health seriously.Its major clinical complications,stroke,myocardial infarction,and heart failure are on the rise in many regions of the world.Actually,inflammation has become recognized as a hallmark implicated in all stages of atherosclerotic development,ranging from onset of plaque to rupture.Although the underlying role of inflammation in atherosclerosis has been elucidated.current treatments of atherosclerosis predominantly are still center on targeting abnormal lipid levels in serum rather than combating the deleterious effects of acute and chronic inflammation.Increased research and applications have begun targeting various inflammatory mediators in atherosclerosis.Dihydrocapsaicin(DHC),as one of pungent ingredients derived from chili peppers,has been found to exert multiple pharmacological and physiological effects including the activities of analgesia,anticancer,anti-inflammation,antioxidant and anti-obesity.Our group has demonstrated that DHC can significantly attenuate atherosclerosis plaque formation through a PPARy/LXRa pathway in apoE-/-mice fed a high-fat/high-cholesterol diet.We also observed that plasma levels of IL-1?,IL-6 and TNF-? were markedly decreased by treatment with DHC of apoE-/-mice.Moreover,our group also found that DHC can down-regulate apoM expression throuph inhibiting Foxa2 expression and enhancing LXRa expression in HepG2 cells.By taking all of these results into consideration,it is a trend to suggest that DHC may have potential beneficial effects on the prevention of cardiovascular diseases,especially in atherosclerosis.Yet,little is known about the specific effect of DHC on inflammation,which plays an important role in all stages of atherosclerosis.The detailed mechanism of how DHC affects inflammatory cytokines expression remains ambiguous.Results1.DHC upregulated NFIA expression and suppressed NF-?B and inflammatory cytokines expressionWe found that DHC obviously increased NFIA expression and decreased NF-?B expression at both transcriptional level and translational level in a dose-dependent manner.Treatment with LPS increased the levels of proinflamatory cytokines,including TNF-?,IL-1? and IL-6.Up-regulation of the levels of these cytokines induced by LPS were markedly suppressed by DHC treatment.We next explored whether the expression of NFIA and NF-?B as well as proinflamatory cytokines could be affected by DHC in experimental mice.ApoE-/-mice were randomized into the control group or the DHC group,and were treated with either vehicle(cholesterol-free vegetable oil)or DHC(3.0 mg/kg body weight)daily by oral gavage for 12 weeks.Immunohistochemistry results demonstrated that treatment of apoE-/-mice with DHC led to a significant increase in NFIA expression whereas a decrease in NF-?B expression in the plaque area.Moreover,we assessed protein expression of TNF-?,IL-1? and IL-6 in plaque tissues.All of these cytokines were markedly downregulated compared with control group.2.NFIA suppressed NF-?B and proinflammatory cytokines expression.The protein level of NF-?B was obviously inhibited by treatment with lentivirus-mediated overexpression of NFIA in THP-1 macrophages.Treatment with LPS increased the levels of TNF-?,IL-1? and IL-6.The up-regulation of these cytokines induced by LPS were markedly suppressed by treatment with lentivirus-mediated overexpression of NFIA.Then we verified the roles of NFIA on NF-?B and proinflammatory cytokines expression levels in apoE-/-mice by immunohistochemistry and western blot respectively.The NFIA-treated(LV-NFIA)groups had significantly lower expression of NF-?B than their control groups(LV-Mock).Meanwhile,protein levels of TNF-?,IL-1? and IL-6 were also downregulated by treatment of LV-NFIA compared with control group.3.DHC suppressed inflammatory response by enhancing NFIA in a NF-?B-dependent manner.Treatment with DHC could decrease NF-?B expression.The down regulation of NF-?B expression via DHC treatment was markedly accentuated by lentivirus-mediated overexpression of NFIA.Treatment with DHC and lentivirus-mediated overexpression of NFIA respectively could upregulated I?B?which is the inhibitor of NF-?B expression.The upgulation of I?B? expression via DHC treatment was markedly enhanced by lentivirus-mediated overexpression of NFIA.Moreover,NF-?B activity was measured by ELISA.The down regulation of NF-?B activity via DHC treatment was markedly accentuated by lentivirus-mediated overexpression of NFIA.Similarly,the proinflammatory cytokines levels induced by LPS could be down-regulated by DHC and lentivirus-mediated overexpression of NFIA respectively.Suppression of these cytokines via DHC treatment was also accentuated by lentivirus-mediated overexpression of NFIA.Lentivirus-mediated overexpression of NFIA decreases the expression of TNF-?,IL-l? and IL-6.Treatment with siRNA targeting NF-?B accentuated the suppression of these proinflammatory cytokines by lentivirus-mediated overexpression of NFIA.These observations indicated that suppression of NF-?B may be a critical regulator in the downregulation effects of proinflammatory cytokines stimulated by NFIA overexpression in THP-1 macrophages.At last we verified the role of NFIA in DHC-mediated suppression of proinflammatory cytokines in vivo experiments by using a lentivirus overexpressing NFIA in apoE-/-.Treatment with lentivirus-mediated overexpression of NFIA downregulated proinflammatory cytokines expression induced by DHC even more obviously.These results suggest that the down-regulation of proinflammatory cytokines induced by DHC may be mediated by enhancing NFIA in a NF-KB-dependent manner.ConclusionThese observations demonstrated that DHC can significantly decrease proinflammatory cytokines through enhancing NFIA and inhibiting NF-?B expression and thus DHC may be a promising candidate as an anti-inflammatory drug for atherosclerosis as well as other disorders.