Anti-inflammatory activity of aucubin by inhibition of tumor necrosis factor-α production in RAW 264.7 cells

To elucidate a possible mechanism for the anti-inflammatory action of iridoid glycosides, the effects of both aucubin (AU) and its hydrolyzed product (H-AU) by beta-glucosidase treatment were studied on the production of TNF-alpha in RAW 264.7 cells. H-AU suppressed the production of both mRNA for TNF-alpha and subsequent TNF-alpha protein in the culture, but AU did not. The production of TNF-alpha protein was inhibited in a dose-dependent manner with an IC50 of 9.2 muM. In addition, treatment with H-AU blocked both the I-kappaBalpha degradation and the translocation of NF-kappaB from the cytosol fraction to the nuclear fraction (55 % inhibition) in the culture. However, treatment with H-AU did not affect the intracellular level of cAMP formed by forskolin treatment in human monocytes U937 culture, implying that there is no influence on the cAMP level in other cell systems. The present study indicates a possible justification for those medicinal plants containing iridoid glycoside that have been used for the treatment of inflammation.