Anti-inflammatory effect of Etlingera pavieana (Pierre ex Gagnep.) R.M.Sm. rhizomal extract and its phenolic compounds in lipopolysaccharide-stimulated macrophages

Background: In our continuing search for anti-inflammatory agents from Thai herbs, Etlingera pavieana (Pierre ex Gagnep.) R.M.Sm. showed potent inhibition on nitric oxide (NO) production in lipopolysaccharide (LPS)-induced macrophages. However, the mechanism behind its inhibitory effect has not been yet explored, and little is known regarding its bioactive compounds responsible for the anti-inflammatory effect. Objective: In the present study, anti-inflammatory effect of hexane, ethyl acetate, and water fractions of rhizomal ethanol extracts of E. pavieana was evaluated for their inhibition on NO production and mechanism in LPS-stimulated macrophages. Active compounds responsible for such anti-inflammatory activity were identified. Materials and Methods: Inhibitory activities on NO production were performed in LPS-stimulated RAW264.7 macrophage. Cytotoxicity of plant extracts was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, mRNA and protein expressions by reverse transcription-polymerase chain reaction and Western blotting analysis, respectively. Anti-inflammatory compounds were isolated by activity-guided isolation technique using column chromatography. Results: Ethyl acetate fraction of E. pavieana (EPE) showed the most potent inhibitory effect on NO production in macrophages. EPE significantly decreased NO production and inhibited inducible nitric oxide synthase (iNOS) protein and mRNA expression in a dose-dependent manner. Furthermore, the level of nuclear factor-kappa B p65 subunit was markedly reduced in activated cells treated with EPE. Four phenolic compounds, 4-methoxycinnamyl alcohol (1), trans-4-methoxycinnamaldehyde (2), 4-methoxycinnamyl p-coumarate (3), and p-coumaric acid (4), were obtained from bioactivity-guided isolation technique. Conclusions: The anti-inflammatory property contained in E. pavieana rhizome extract and conferred through inhibition of iNOS expression, and NO formation provides scientific evidence and support for the development of new anti-inflammatory agents based on extracts from this plant.