Ergolide, sesquiterpene lactone from Inula britannica, inhibits inducible nitric oxide synthase and cyclo-oxygenase-2 expression in RAW 264.7 macrophages through the inactivation of NF-κB

Abstract

1. We investigated the mechanism of suppression of inducible nitric oxide synthase (iNOS) and cyclo-oxygenase-2 (COX-2) by ergolide, sesquiterpene lactone from Inula britannica. 2. iNOS activity in cell-free extract of LPS/IFN-γ-stimulated RAW 264.7 macrophages was markedly attenuated by the treatment with ergolide. Its inhibitory effect on iNOS was paralleled by decrease in nitrite accumulation in culture medium of LPS/IFN-γ-stimulated RAW 264.7 macrophages in a concentration-dependent manner. However, its inhibitory effect does not result from direct inhibition of the catalytic activity of NOS. 3. Ergolide markedly decreased the production of prostaglandin E2 (PGE2) in cell-free extract of LPS/IFN-γ-stimulated RAW 264.7 macrophages in a concentration-dependent manner, without alteration of the catalytic activity of COX-2 itself. 4. Ergolide decreased the level of iNOS and COX-2 protein, and iNOS mRNA caused by stimulation of LPS/IFN-γ in a concentration-dependent manner, as measured by Western blot and Northern blot analysis, respectively. 5. Ergolide inhibited nuclear factor-κB (NF-κB) activation, a transcription factor necessary for iNOS and COX-2 expression in response to LPS/IFN-γ. This effect was accompanied by the parallel reduction of nuclear translocation of subunit p65 of NF-κB as well as IκB-α degradation. In addition, these effects were completely blocked by treatment of cysteine, indicating that this inhibitory effect of ergolide could be mediated by alkylation of NF-κB itself or an upstream molecule of NF-κB. 6. Ergolide also directly inhibited the DNA-binding activity of active NF-κB in LPS/IFN-γ-pretreated RAW 264.7 macrophages. 7. These results demonstrate that the suppression of NF-κB activation by ergolide might be attributed to the inhibition of nuclear translocation of NF-κB resulted from blockade of the degradation of IκB and the direct modification of active NF-κB, leading to the suppression of the expression of iNOS and COX-2, which play important roles in inflammatory signalling pathway.