Nitric oxide (NO) is recognized as a mediator and regulator of inflammatory responses. Rengyolone, a cyclohexylethanoid isolated from the fruits of Forsythia koreana, exhibits anti-inflammatory activity with unknown mechanism. In this study, we found that rengyolone has a strong inhibitory effect on the production of nitric oxide (NO) and tumor necrosis factor-α (TNF-α). Rengyolone also inhibited inducible nitric oxide synthase (iNOS) gene expression and cyclooxygenase 2 (COX-2) by lipopolysaccharide (LPS). In order to explore the mechanism responsible for the inhibition of iNOS gene expression by rengyolone, we investigated its effect on LPS-induced nuclear factor-κB (NF-κB) activation. The LPS-induced DNA binding activity of NF-κB was significantly inhibited by rengyolone, and this effect was mediated through inhibition of the degradation of inhibitory factor-κBα and phosphorylation of p38 MAP kinase. Furthermore, rengyolone suppressed the expression of ICE protein in IL-1β-treated D10S cells. Taken together, these results suggest that rengyolone attenuates the inflammation through inhibition of NO production and iNOS expression by blockade of NF-κB and p38 MAPK activation in LPS-stimulated RAW 264.7 cells.
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