Saikosaponin a inhibits LPS-induced inflammatory response by inducing liver X receptor alpha activation in primary mouse macrophages.

The aim of this study was to investigate the effects of SSa on LPS-induced endotoxemia in mice and clarify the possible mechanism. An LPS-induced endotoxemia mouse model was used to confirm the anti-inflammatory activity of SSa in vivo. The primary mouse macrophages were used to investigate the molecular mechanism and targets of SSa in vitro. In vivo, the results showed that SSa improved survival during lethal endotoxemia. In vitro, our results showed that SSa dose-dependently inhibited the expression of TNF-alpha, IL-6, IL-1 beta, IFN-beta-and RANTES in LPS-stimulated primary mouse macrophages. Western blot analysis showed that SSa suppressed LPS-induced NF-kappa B and IRF3 activation. Furthermore, SSa disrupted the formation of lipid rafts by depleting cholesterol and inhibited TLR4 translocation into lipid rafts. Moreover, SSa activated LXR alpha, ABCA1 and ABCG1. Silencing LXR alpha abrogated the effect of SSa. In conclusion, the anti-inflammatory effects of SSa is associated with activating LXR alpha dependent cholesterol efflux pathway which result in disrupting lipid rafts by depleting cholesterol and reducing translocation of TLR4 to lipid rafts, thereby attenuating LPS mediated inflammatory response.