Ozone inactivates cyclooxygenase in human tracheal epithelial cells without altering PGHS-2 mRNA or protein
Alpert, S.E.; Walenga, R.W.; Jaspers, I.; Qu, Q.; Chen, L.C.
American Journal of Physiology 272(5 Pt 1): L879-L887
1997
ISSN/ISBN: 0002-9513 PMID: 9176252 Document Number: 474336
Exposure of human tracheal epithelial (TE) cells to ozone (0.1-0.5 ppm) leads to a transient increase followed by decreased production of prostaglandin (PG) E-2 concomitant with dose-dependent loss and delayed recovery of cyclooxygenase (CO) activity (S. E. Alpert and R. W. Walenga. Am. J. Physiol. 269 (Lung Cell. Mol. Physiol. 13): L734-L743, 1995). Formation of reactive oxygen species (ROS) in cultured tracheobronchial epithelial cells during ozone exposure was recently demonstrated (L. C. Chen and Q. Qu. Toxicol. Appl. Pharmacol. 143: 96-101, 1997). In 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-dependent ROS generation, assessed by fluorescence of dihydrorhodamine 123, 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. Ozone-induced ROS formation, the transient increase and decline in PGE-2, and CO inactivation were attenuated by an intracellular hydroxyl radical scavenger, 1,3-dimethyl-2-thiourea. Ibuprofen, a reversible CO inhibitor, prevented PGE-2 release during ozone exposure (and hence autocatalytic CO inactivation) but not loss of CO activity. Although CO activity remained depressed for hours after ozone exposure, compared with air-exposed cultures, no differences were detected in mRNA and protein 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 PGHS-2 synthesis. Our findings suggest that ozone-induced PGE-2 production and CO inactivation are primarily the result of formation of intracellular oxidant molecules and that delayed recovery of CO activity in human TE cells after short-term ozone exposure is due to persistent inactivation of PGHS-2, rather than to interference with its synthesis.