Suppression of inducible nitric oxide synthase and cyclooxygenase-2 expression in raw 264.7 macrophages by sesquiterpene lactones

The molecular mechanism underlying the suppression of lipopolysaccharide (LPS)/interferon-γ (IFN-γ)-induced nitric oxide (NO) and prostaglandin (PG) E₂ production was investigated in RAW 264.7 macrophages treated with sesquiterpene lactones, zaluzanin-C and estafiatone, isolated from Ainsliaea. Zaluzanin-C and estafiatone decreased NO production in LPS/IFN-γ-stimulated RAW 264.7 macrophages with an IC50 of about 6.61 μM and 3.80 μM, respectively. In addition, these compounds inhibited the synthesis of PGE₂ in LPS/IFN-γ-treated RAW 264.7 macrophages. Furthermore, treatment with zaluzanin-C and estafiatone resulted in a decrease in inducible No Synthase (iNOS) and Cyclooxygenase-2 (COX-2) protein and mRNA expression levels. Zaluzanin-C and estafiatone 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 parallel reduction of phosphorylation and degradation of inhibitor of κB (IκB). In addition, these effects were completely blocked by treatment with cysteine, indicating that the inhibitory effect of zaluzanin-C and estafiatone might be mediated by alkylation of either NF-κB itself or an upstream molecule of NF-κB. These results demonstrate that the suppression of NF-κB activation by zaluzanin-C and estafiatone might be attributed to inhibition of nuclear translocation of NF-κB resulting from blockade of the degradation of IκB, leading to suppression of the expression of iNOS and COX-2, which play important roles in inflammatory signaling pathways. Copyright