Ozone exposure of human tracheal epithelial cells inactivates cyclooxygenase and increases 15-HETE production

We assessed the immediate and prolonged effects of ozone on arachidonic acid (AA) metabolism by primary cultured human tracheal epithelial (TE) cells. TE monolayers were exposed at a gas-fluid interface to air or 0.1, 0.25, or 0.5 ppm ozone (15 min air, then 45 min air/ozone), and serially collected effluents were analyzed by thin-layer chromatography (TLC) and/or high-performance liquid chromatography. Release of prostaglandin E(2) (PGE(2)) and AA, but not 15-hydroxyeicosatetraenoic acid (15-HETE) or its metabolites, was detected from cultures prelabeled with [C-14]AA. PGE(2) production, measured by immunoassay, was nearly constant during air exposure. In contrast, PGE(2) increased two- to threefold during the first 15-min exposure to all concentrations of ozone, but then progressively declined to 78 +/- 17, 57 +/- 12 (P less than or equal to 0.05), and 45 +/- 15% (P less than or equal to 0.05) of air controls after exposure to 0.1, 0.25, and 0.5 ppm ozone. Ozone did not induce a new spectrum of AA metabolites; only PGE(2), lesser amounts of PGF(2 alpha), and 15-HETE were present in media and cell extracts of air- or ozone-exposed cultures provided with 30 mu M exogenous AA. However, cyclooxygenase (GO) activity (PGE(2) produced from 30 mu M AA) decreased to 82 +/- 9, 53 +/- 8 (P less than or equal to 0.05), and 28 +/- 6% (P less than or equal to 0.05) vs. controls after 0.1, 0.25, and 0.5 ppm ozone, whereas 15-HETE production was unimpaired. When cells exposed to 0.5 ppm ozone were maintained for up to 6 h in 5% CO2-air, spontaneous PGE(2) production remained decreased and recovery of CO activity was extremely slow. TLC analysis of lipid extracts from [C-14]AA-labeled cells revealed a nearly twofold increase in free intracellular 15-HETE, and hydrolysis of phospholipids demonstrated increased esterified 15-HETE. Exposure of human TE cells to ozone leads to a transient increase followed by prolonged decrease in PGE(2) production and increased intracellular retention of 15-HETE. Loss of the bronchodilator and anti-inflammatory properties of epithelial PGE(2), with or without increased 15-HETE, might contribute to ozone-induced airway dysfunction.