To determine the chemical constituents responsible for pharmacological effects of Inula britannica-F,three specific sesquiterpene lactones in Inula britannica were isolated from chloroform extract and identified, including britannilactone (BL), 1-O-acetylbritannilactone (ABLO), and 1,6-O,O-diacetylbritannilactone (ABLOO). Electrophoretic mobility shift assay (EMSA) was performed to detect the nuclear translocation of nuclear factor-kappa B (NF-kappa B) p65. The expressions of I kappa B alpha, pI kappa B alpha, inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), I kappa B kinase alpha/beta (IKK alpha/beta) and NF-kappa B kinase (NIK) were detected by Western blot and RT-PCR. We found that acetyl side groups enhanced the inhibitory action of the agents on LPS/IFN-gamma-induced iNOS and COX-2 expression. Their inhibiting activity was positive correlation with the acetyl side group number. The effects of LPS/IFN-gamma were reversed by ABLOO, and BL without acetyl side groups showed only a weak inhibitory action. Further study indicated that ABLOO markedly inhibited the phosphorylation of IKK beta down to based level, but not IKK alpha, corresponding with decreased in I kappa B alpha degradation and phosphorylation induced by LPS/IFN-gamma, resulting in the suppression of NF-kappa B nuclear translocation and activity. These results suggest that the acetyl moieties add to the lipophilicity, and consequently enhance cellular penetration, so that ABLOO possess the most anti-inflammatory effect and may be a potent lead structure for the development of therapeutic and cytokine-suppressing remedies valuable for the treatment of various inflammatory diseases. (C) 2008 Elsevier GmbH. All rights reserved.