Echinacea species and alkamides inhibit prostaglandin E(2) production in RAW264.7 mouse macrophage cells

Inhibition of prostaglandin E(2) (PGE(2)) production in lipopolysaccharide-stimulated RAW264.7 mouse macrophage cells was assessed with an enzyme immunoassay following treatments with Echinacea extracts or synthesized alkamides. Results indicated that ethanol extracts diluted in media to a concentration of 15 microg/mL from E. angustifolia, E. pallida, E. simulata, and E. sanguinea significantly inhibited PGE2 production. In further studies, PGE2 production was significantly reduced by all synthesized alkamides assayed at 50 microM, by Bauer alkamides 8, 12A analogue, and 14, Chen alkamide 2, and Chen alkamide 2 analogue at 25 microM and by Bauer alkamide 14 at 10 microM. Cytotoxicity did not play a role in the noted reduction of PGE2 production in either the Echinacea extracts or synthesized alkamides. High-performance liquid chromatography analysis identified individual alkamides present at concentrations below 2.8 microM in the extracts from the six Echinacea species (15 microg/mL crude extract). Because active extracts contained <2.8 microM of specific alkamide and the results showed that synthetic alkamides must have a minimum concentration of 10 microM to inhibit PGE2, it is likely that alkamides may contribute toward the anti-inflammatory activity of Echinacea in a synergistic or additive manner.