OZONE INACTIVATES CYCLOOXYGENASE IN HUMAN TRACHEAL EPITHELIAL-CELLS WITHOUT ALTERING PGHS-2 MESSENGER-RNA OR PROTEIN

Exposure of human tracheal epithelial (TE) cells to ozone (0.1-0.5 ppm ) leads to a transient increase followed by decreased production of pr ostaglandin (PG) E-2 concomitant with dose-dependent loss and delayed recovery of cyclooxygenase (GO) activity [S. E. Alpert and R. W. Walen ga. Am. J. Physiol. 269 (Lung Cell. Mel. Physiol. 13): L734-L743, 1995 ]. Formation of reactive oxygen species (ROS) in cultured tracheobronc hial epithelial cells during ozone exposure was recently demonstrated (L. C. Chen and Q. Qu. Toxicol. Appl. Pharmacol. 143: 96-101, 1997). I n the present study, we investigated if ROS generated by ozone-exposed human TE cells contribute to PGE(2) production and/or CO inactivation and whether the delay in recovery of CO activity after ozone reflects impaired gene transcription and/or protein synthesis. Rapid, dose-dep endent ROS generation, assessed by fluorescence of dihydrorhodamine 12 3, was detected in human TE monolayers exposed to 0.21-0.63 ppm ozone. In a different system, TE cells were exposed to air or 0.5 ppm ozone for 1 h by serial renewal/collection of an adherent film of media. Ozo ne-induced ROS formation, the transient increase and decline in PGE(2) , and CO inactivation were attenuated by an intracellular hydroxyl rad ical scavenger, 1,3-dimethyl-2-thiourea. Ibuprofen, a reversible CO in hibitor, prevented PGE(2) release during ozone exposure (and hence aut ocatalytic CO inactivation) but not loss of CO activity. Although CO a ctivity remained depressed for hours after ozone exposure, compared wi th air-exposed cultures, no differences were detected in mRNA and prot ein levels of prostaglandin endoperoxide G/H synthase 2 (PGHS-2), the only CO isoform present in human TE cells, or in the rate of de novo P GHS-2 synthesis. Our findings suggest that ozone-induced PCE2 producti on and CO inactivation are primarily the result of formation of intrac ellular oxidant molecules and that delayed recovery of CO activity in human TE cells after short-term ozone exposure is due to persistent in activation of PGHS-2, rather than to interference with its synthesis.