Dioscorealide B Suppresses LPS-Induced Nitric Oxide Production and Inflammatory Cytokine Expression in RAW 264.7 Macrophages: The Inhibition of NF-κB and ERK1/2 Activation

Dioscorealide B (DB), a naphthofuranoxepin has been purified from an ethanolic extract of the rhizome of Dioscorea membranacea Pierre ex Prain & Burkill which has been used to treat inflammation and cancer in Thai Traditional Medicine. Previously, DB has been reported to have anti-inflammatory activities through reducing nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) production in lipopolysaccharides (LPS)-induced RAW 264.7 macrophage cells. In this study, the mechanisms of DB on LPS-induced NO production and cytokine expression through the activation of nuclear factor-kappa B (NF-kappa B) and ERK1/2 are demonstrated in RAW 264.7 cells. Through measurement with Griess's reagent, DB reduced NO level with an IC(50) value of 2.85 +/- 0.62 mu M that was due to the significant suppression of LPS-induced iNOS mRNA expression as well as IL-1 beta, IL-6, and IL-10 mRNA at a concentration of 6 mu M. At the signal transduction level, DB significantly inhibited NF-kappa B binding activity, as determined using pNF kappa B-Luciferase reporter system, which action resulted from the prevention of I kappa B alpha degradation. In addition, DB in the range of 1.5-6 mu M significantly suppressed the activation of the ERK1/2 protein. In conclusion, the molecular mechanisms of DB on the inhibition of NO production and mRNA expression of iNOS, IL-1 beta, IL-6, and IL-10 were due to the inhibition of the upstream kinases activation, which further alleviated the NF-kappa B and MAPK/ERK signaling pathway in LPS-induced RAW264.7 macrophage cells. J. Cell. Biochem. 109: 1057-1063, 2010. (C) 2010 Wiley-Liss, Inc.