OZONOLYSIS PRODUCTS OF MEMBRANE FATTY-ACIDS ACTIVATE EICOSANOID METABOLISM IN HUMAN AIRWAY EPITHELIAL-CELLS

When inhaled, ozone reacts at the airway luminal surface with unsaturated fatty acids contained in the extracellular fluid and plasma membrane to form an aldehyde and hydroxyhydroperoxide. The resulting hydroxyhydroperoxide degrades in aqueous systems to yield a second aldehyde and hydrogen peroxide (H2O2). Previously, we demonstrated that ozone can augment eicosanoid metabolism in bovine airway epithelial cells. To examine structure-activity relationships of ozone-fatty acid degradation products on eicosanoid metabolism in human airway epithelial cells, 3-, 6-, and 9-carbon saturated aldehydes and hydroxyhydroperoxides were synthesized and purified. Eicosanoid metabolism was evaluated by determination of total H-3-activity release from confluent cells previously incubated with [H-3]arachidonic acid and by identification of specific metabolites with high performance liquid chromatography and radioimmunoassay. The major metabolites detected were prostaglandin E(2), prostaglandin F-2 alpha, and 15-hydroxy-eicosatetraenoic acid. The 9-carbon aldehyde, nonanal, in contrast to 3- or 6-carbon aldehydes, stimulated release at concentrations greater than or equal to 100 mu M, suggesting that the stimulatory effect increases with increasing chain length. When tested under identical conditions, the 3-, 6-, and 9-carbon hydroxyhydroperoxides were more potent than the corresponding aldehydes. Again, a greater effect was noted when the chain length was increased. One possible explanation for the increased potency of the hydroxyhydroperoxides over the aldehydes could be due to degradation of the hydroxyhydroperoxide into H2O2 and aldehyde. We consider this an unlikely explanation because responses varied with chain length (although each hydroxyhydroperoxide would produce an equivalent amount of H2O2) and because exposure to H2O2 alone or H2O2 plus hexanal produced a response dissimilar to 1-hydroxy-1-hexanehydroperoxide. Inasmuch as these compounds are ozonolysis products of unsaturated fatty acids of the membrane phospholipids, this study ascribes pathophysiologic significance to this chemical mechanism of ozone toxicity.