Inhibition of lipoxygenase and prostaglandin endoperoxide synthase by anacardic acids

C22:1 ω5-anacardic acid was found to be a good inhibitor of both potato lipoxygenase and ovine prostaglandin endoperoxide synthase with approximate IC₅₀'s of 6 and 27 μM, respectively. Very similar inhibition was seen with the crude exudate, rich in ω5-anacardic acids, from glandular trichomes of an arthropod-resistant strain of geranium, Pelargonium xhortorum. The saturated anacardic acid (C22:0 sat), abundant in the trichome exudate of susceptible strains, was nearly as inhibitory toward both prostaglandin endoperoxide synthase and lipoxygenase as the ω5-unsaturated compound. However, the dimethyl derivative of C22:1 ω5-anacardic acid was a poor inhibitor of prostaglandin endoperoxide synthase and caused only moderate (32%) inhibition of lipoxygenase even at 135 μM. The possible role of prostaglandin endoperoxide synthase and lipoxygenase inhibition in the enhanced pest resistance of geraniums which produce the ω5-AnAs is discussed.