Dioscorealide B suppresses LPS-induced nitric oxide production and inflammatory cytokine expression in RAW 264.7 macrophages: The inhibition of NF-kappaB 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-kappaB (NF-kappaB) 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 microM that was due to the significant suppression of LPS-induced iNOS mRNA expression as well as IL-1beta, IL-6, and IL-10 mRNA at a concentration of 6 microM. At the signal transduction level, DB significantly inhibited NF-kappaB binding activity, as determined using pNFkappaB-Luciferase reporter system, which action resulted from the prevention of IkappaBalpha degradation. In addition, DB in the range of 1.5-6 microM 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-1beta, IL-6, and IL-10 were due to the inhibition of the upstream kinases activation, which further alleviated the NF-kappaB and MAPK/ERK signaling pathway in LPS-induced RAW264.7 macrophage cells.