Inhibition of Inflammatory Cytokine Production and Lymphocyte Proliferation by Structurally Different Sesquiterpene Lactones Correlates with Their Effect on Activation of NF-κB 1 1abbreviations: Con A, Concanavalin A; HBSS, Hanks’ Balanced Salt Solution; IL, Interleukin; Inos, Inducible Nitric Oxide Synthase; LPS, Lipopolysaccharide; NF-κB, Nuclear Factor Kappab; NO, Nitric Oxide; PEC, Mouse Peritoneal Exsudate Cell; TNF-α, Tumor Necrosis Factor Α; and Sl(s), Sesquiterpene Lactone(s).

Many sesquiterpene lactones (Sls) are known to possess anti-inflammatory activities. To gain further insight into their structure-activity relationships and the molecular mechanism of action, four germacranolide sesquiterpene lactones which differ in the skeleton and the number of reactive centers (4β,15-epoxy-miller-9E-enolide (1), 15-acetoxy-eremantholide B (2), a mixture of 15-(isovaleroyl)/15-(2-methyl-butyryl)-2α-acetoxy-miguanin (3), and 15-(2-hydroxy)-isobutyryloxy-micrantholide (4)) were investigated for their effect on production of proinflammatory cytokines (interleukin-1β [IL-1β], IL-6, and tumor necrosis factor-α [TNF-α]) as well as proliferation of concanavalin A (Con A) and lipopolysaccharide (LPS)-stimulated mouse lymphocytes. Compounds 1 and 3 which possess an α-methylene-γ-lactone function and a conjugated carbonyl group induced a half-maximal inhibition of cytokine synthesis in adherent mouse peritoneal exsudate cells at micromolar concentrations (ic50 0.69–1.70 μM), while compound 4 which contains only an α-methylene-γ-lactone residue was less active (ic50 ≥ 8.38 μM). Interestingly, compound 2, which carries only a conjugated keto group, displayed a potency similar to those of the bifunctional compounds 1 and 3. All four Sls suppressed proliferation of murine lymphocyte at ic50 concentrations between 0.22 and 5.03 μM. The rank order of potency was 1 = 2 > 3 > 4. Generally, the growth of LPS-stimulated cells was more strongly influenced than those of Con A-activated lymphocytes. This effect was particularly pronounced with 4. Inhibitory concentrations correlated well with those necessary for inhibition of the transcription factor nuclear factor κB (NF-κB) observed in a previous investigation. Therefore, it can be assumed that NF-κB may be involved in the suppressive effect of Sls on cytokine production and lymphocyte proliferation.