Metabolism of oxidized linoleic acid: characterization of 13-hydroxyoctadecadienoic acid dehydrogenase activity from rat colonic tissue.

An oxidized derivative of linoleic acid, 13-hydroxyoctadecadienoic acid (13-HODE), is dehydrogenated by an NAD+ dependent dehydrogenase present in rat colon mucosa. The product of the reaction is the 2,4-dienone, 13-oxooctadecadienoic acid. Enzyme activity was determined by HPLC analysis of incubation mixtures as well as by measuring the increase in absorbance at 285 nm, which represents formation of the 2,4-dienone chromophore. Characteristics of the reaction with respect to protein concentration, time of incubation and substrate dependence were investigated. Several inhibitors of known dehydrogenases had no effect on the 13-HODE dehydrogenase. These include, ethanol, indomethacin, 6-methyl-17-hydroxyprogesterone acetate, 4-(diethylamino)-benzaldehyde, and aspirin. The enzyme was mildly inhibited by pyrazole, 4-methylpyrazole and ibuprofen. Disulfiram was found to be a potent inhibitor of enzyme activity with an IC50 of 200 microM. Inhibitor specificity, and other characteristics of the reaction suggest the enzyme is neither alcohol dehydrogenase, diol dehydrogenase, nor a prostaglandin dehydrogenase. It is possible this enzyme plays an important role in the response of the colonic mucosa to the mitogenic effect of oxidized fatty acids.