Anti-inflammatory effect of austroinulin and 6-O-acetyl-austroinulin from Stevia rebaudiana in lipopolysaccharide-stimulated RAW264.7 macrophages

Austroinulin (AI) and 6-O-acetyl-austroinulin (6-OAAI) are natural diterpenoids isolated from Stevia rebaudiana with anti-inflammatory activity. However, the mechanisms underlying their anti-inflammatory effects are not well understood. The purpose of this study was to investigate the effect of AI and 6-OAAI on nitric oxide (NO) production and their molecular mechanism in LPS-stimulated RAW264.7 macrophages. We found that AI and 6-OAAI inhibit the production of NO, iNOS, and pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, and MCP-1) in LPS-stimulated RAW264.7 macrophages. In these same cells, AI and 6-OAAI also suppressed the phosphorylation of STAT1 and the production of interferon-beta (IFN-β). Moreover, treatment with AI and 6-OAAI inhibited the activation of interferon regulatory factor-3 (IRF3) and NF-κB. Taken together, our results suggest that AI and 6-OAAI inhibit NO production and iNOS expression by blocking the activation of STAT1, IRF3, and NF-κB in LPS-stimulated RAW264.7 macrophages.