OZONE ENHANCES THE UPTAKE OF MINERAL PARTICLES BY TRACHEOBRONCHIAL EPITHELIAL-CELLS IN ORGAN-CULTURE

We have previously shown that the basal uptake of mineral particles by tracheobronchial epithelial cells in organ culture is mediated in pa rt by active oxygen species (AOS) and can be greatly augmented by expo sure to cigarette smoke, a concentrated source of AOS, and other radic als. We hypothesized that ozone, another generator of AOS in tissues, might have the same effect. To test this hypothesis, tracheal explants were exposed to room air (control) or ozone in varying concentrations from 0.01 to 1.0 ppm for 10 min, and subsequently to a suspension of either amosite asbestos or titanium dioxide (rutile) for 1 h. Explants were then transferred to an air/CO2 incubator for 1 wk to allow parti cle uptake to occur, and uptake was determined by morphometry. We foun d that ozone exposure increased the uptake of both asbestos and titani um dioxide in a dose-response fashion; this effect appeared at lower e xposure levels and was more marked with titanium dioxide than with amo site. The ozone effect could be prevented by addition of catalase but not superoxide dismutase to the particle suspension, or by preincubati on of the particles with deferoxamine. These observations indicate tha t ozone can directly increase uptake of mineral particles by tracheobr onchial epithelial cells; this effect occurs with brief exposures at v ery low ozone levels and appears to be mediated by hydrogen peroxide a nd possibly by hydroxyl radical. These findings support the general hy pothesis that AOS are important mediators of epithelial particle uptak e in many different settings. Enhanced uptake may be one of the mechan isms by which ozone impairs particle clearance from the lung and may p lay a role in the increased morbidity seen in populations with exposur e to high levels of both ozone and atmospheric particulates.