Subacute effects of ozone exposure on cultivated human respiratory mucosa

This study was designed to investigate subacute effects of long-term exposure of both healthy and chronically inflamed human respiratory mucosa to ozone. Functional and metabolic effects on ciliary beat frequency (CBF), release of interleukin 8 (IL-8), interleukin 4 (IL-4), and gamma interferon (g-INF), as well as cellular viability and cytotoxicity, were monitored. Cell cultures of 60 specimens (healthy mucosa: n = 30, inflamed mucosa: n = 30) were exposed to synthetic air and to ozone-enriched synthetic air in different concentrations of 100, 500, and 1000 micrograms/m3. Continuous expositions were performed using an air/liquid interface cell culture technique for a period of 4 weeks. CBF was monitored using video-interference contrast microscopy and cytokine release was quantified by enzyme immunoassays. Cellular viability and cytotoxicity were controlled by measuring lactate dehydrogenase activity, cytosolic activity of esterases, and by staining of nuclear DNA. Synthetic air had no influence on CBF during the 4 weeks of exposure. IL-8 release was continuously diminished in unaffected and in chronically inflamed mucosa. Within the first week of continuous exposure with any ozone concentration neither CBF nor release of IL-8 were affected in healthy or in inflamed mucosa. During the second and the following weeks of exposure CBF and the release of IL-8 were reduced in both tissues. Release of IL-4 or g-INF were not detectable at any time during the 4 weeks of ozone exposure. At higher ozone concentrations of 500 and 1000 micrograms/m3 there was an increase of cytotoxicity which was greater in chronically inflamed than in healthy mucosa. In conclusion, ozone had no measurable effect on those parameters measured in human upper respiratory epithelium after one week of in vitro exposure to different concentrations, but did after longer periods of exposure. Chronically inflamed mucosa had a tendency toward a higher susceptibility to intermediate and high concentrations of ozone that did not reach a level of statistical significance under the conditions used in this study.