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

There is evidence that some lung responses to ozone (O-3) exposure are mediated through the altered metabolism of arachidonic acid (AA). Inc reased concentrations of some AA metabolites such as prostaglandin E-2 (PGE(2)) and prostaglandin F-2 alpha (PGF(2 alpha)) are observed in t he bronchoalveolar lavage fluid recovered from human subjects exposed to O-3. Airway epithelial cells may contribute to this increase in eic osanoid formation. Previous reports have shown increased PGE(2) and PG F(2 alpha) production by O-3-exposed airway epithelial cells, believed to be mediated at least in part by increased phospholipase activity. We examined other potential biochemical mechanisms for the increased f ormation of these two prostaglandins by O-3-exposed epithelial cells. Cultured normal human bronchial epithelial (NHBE) cells, prelabeled wi th H-3-AA, were exposed to air or to 0.1 ppm or 1.0 ppm O-3 for 60 min in a Transwell cell culture system. NHBE cells produced increased amo unts of H-3-PGE(2) and H-3-PGF(2 alpha) in response to 0.1 ppm O-3 exp osure but not with 1.0 ppm exposure as measured in the conditioned med ia by high-performance liquid chromatography. Other H-3-AA products, i ncluding [H-3]-15-hydroxyeicosatetraenoic acid, [H-3]-12-heptadecatrie noic, and [H-3]aldehydic substances derived from the ozonation of H-3- AA, also were observed in increased amounts. Pulsing of cells with 15 nM H-3-AA after 0.1 ppm and 1.0 ppm O-3 exposure revealed a decrease i n H-3-AA esterification into cellular phospholipids, resulting in an i ncrease in free H-3-AA available for metabolism to prostaglandins. No O-3-induced alteration in NHBE cell cyclooxygenase activity was observ ed with the 0.1 ppm exposures. Impaired esterification of free AA into cellular phospholipids appears to be a very sensitive target for O-3- induced effects on AA metabolism, and may play a role in the increased prostaglandin production observed upon O-3 inhalation in vivo.