Echinacea species and alkamides inhibit prostaglandin E₂ production in RAW264.7 mouse macrophage cells

Inhibition of prostaglandin E₂ (PGE₂) 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 μg/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 μM, by Bauer alkamides 8, 12A analogue, and 14, Chen alkamide 2, and Chen alkamide 2 analogue at 25 μM and by Bauer alkamide 14 at 10 μM. 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 μM in the extracts from the six Echinacea species (15 μg/mL crude extract). Because active extracts contained <2.8 μM of specific alkamide and the results showed that synthetic alkamides must have a minimum concentration of 10 μM to inhibit PGE₂, it is likely that alkamides may contribute toward the anti-inflammatory activity of Echinacea in a synergistic or additive manner.