INHIBITION OF ARACHIDONIC ACID ESTERIFICATION IN HUMAN AIRWAY EPITHELIAL CELLS EXPOSED TO OZONE IN VITRO

Abstract

There is evidence that some lung responses to ozone (O3) exposure are mediated through the altered metabolism of arachidonic acid (AA). Increased concentrations of some AA metabolites such as prostaglandin E2 (PGE2) and prostaglandin F2 (PGF2) are observed in the bronchoalveolar lavage fluid recovered from human subjects exposed to O3. Airway epithelial cells may contribute to this increase in eicosanoid formation. Previous reports have shown increased PGE2 and PGF2 production by O3-exposed air way epithelial cells, believed to be mediated at least in part by increased phospholipase activity. We examined other potential biochemical mechanisms for the increased formation of these two prostaglandins by O3-exposed epithelial cells. Cultured normal human bronchial epithelial (NHBE) cells, prelabeled with 3H-AA, were exposed to air or to 0.1 ppm or1.0 ppm O3 for 60 min in a Transwell cell culture system. NHBE cells produced increased amounts of 3H-PGE2 and 3H-PGF2 in response to 0.1 ppm O3 exposure but not with 1.0 ppm exposure as measured in the conditioned media by high-performance liquidchromatography. Other 3H-AA products, including [3H]-15-hydroxyeicosatetraenoic acid, [3H]-12-heptadecatrienoic, and [3H]aldehydic substances derived from the ozonation of 3H-AA, also were observed in increased amounts. Pulsing of cells with 15 n 3H-AA after 0.1 ppm and 1.0 ppm O3 exposure revealed a decrease in 3H-AA esterification into cellular phospholipids, resulting in an increase in free 3H-AA available for metabolism to prostaglandins. No O3-induced alteration in NHBE cell cyclooxyge nase activity was observed with the 0.1 ppm exposures. Impaired esterification of free AA into cellular phospholipids appears to be a very sensitive target for O3-induced effects on AA metabolism, and may play a role in the increased prostaglandin production observed upon O3 inhalation in vivo.