Modulation of leukotriene formation by various acetylenic acids.

A series of acetylenic acids varying in chain length as well as in number and position of triple bonds were tested for their effect on arachidonic acid metabolism via cyclo-oxygenase and 5-lipoxygenase in homogenates of RBL-l cells. A number of trends which differentiate 5-lipoxygenase from cyclo-oxygenase were observed: (a) In general, the potency of the acetylenic acids to inhibit 5-lipoxygenase increased with the carbon chain length up to carbons. (b) A minimum of three triple bonds is necessary for the inhibitory action. (c) With the 20-carbon delta 8 and delta 6 acetylenic acids, activity decreased when the number of triple bonds increased from three to four. These structure activity relationships were not observed with cyclo-oxygenase. The delta 4 acetylenic acids proved to be an interesting group of compounds. They did not inhibit cyclo-oxygenase or 5-lipoxygenase but were good inhibitors of SRS synthesis. The potency of the delta 4 acetylenic acids increased with chain length, and 21:4 (4a, 7a, 10a, 13a) was the most potent compound inhibiting SRS formation. The delta 4 acetylenic acids are therefore useful tools for investigating the function and action of LTC4 and LTD4.