PRODUCTION OF UNSATURATED CARBONYL-COMPOUNDS DURING METABOLISM OF HYDROPEROXY FATTY-ACIDS BY COLONIC HOMOGENATES

Recent evidence has suggested that unsaturated carbonyl compounds may be the ultimate mitogens produced from the primary auto-oxidation products of unsaturated fatty acids. The present study has investigated the metabolism of 13-hydroperoxyoctadecadienoic acid (13-ROOH) by rat colon homogenates. This hydroperoxide is one of the primary products formed from the oxygenation of linoleic acid, the most abundant dietary polyunsaturated fatty acid. Incubation mixtures contained [1-14C]13-ROOH and colonic homogenates prepared from male Sprague-Dawley rats. After 30 min of incubation the reaction was quenched and the products extracted for analysis by HPLC. The identity of the eluted products were verified by UV, MS and NMR spectroscopy. The major products include a mixture of isomers of 2,4-dienone C18 fatty acids and 13-hydroxyoctadecadienoic acid. Direct comparison of homogenate metabolism to the hematin-catalyzed, alkoxyl radical-mediated decomposition of 13-ROOH shows some significant differences. In particular, no epoxy products are detected in the presence of tissue homogenates whereas these are the major products observed during the decomposition of 13-ROOH by hematin and a number of other agents. These experiments demonstrate the production of relatively large amounts of unsaturated carbonyl-containing fatty acids during the metabolism of hydroperoxy fatty acids by colonic tissue. The major product, 13-oxo-9Z,11E-octadecadienoic acid, when instilled intrarectally stimulates the incorporation of [3H]deoxythymidine into colonic mucosal DNA, and induces colonic mucosal ornithine decarboxylase activity in vivo. These findings have important implications for the mechanism by which dietary fat promotes colon tumorigenesis as the formation of relatively reactive 2,4-dienones may be a key to the in vivo mitogenic activity of oxidized fatty acids. © 1990 Oxford University Press.