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Long-Term Ozone Exposure Attenuates 1-Nitronaphthalene–Induced Cytotoxicity in Nasal Mucosa

Departments of ¹ Anatomy, Physiology, and Cell Biology, and ² Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, California; and ³ Division of Respiratory Medicine, Department of Medicine, Karolinska Institutet, Stockholm, Sweden

Correspondence and requests for reprints should be addressed to Åsa M. Wheelock, PhD, Lung Research Lab L4:01, Respiratory Medicine Unit, Department of Medicine, Karolinska Institutet, 171 76 Stockholm, Sweden. E-mail: asa{at}para-docs.org

1-Nitronaphthalene (1-NN) and ozone are cytotoxic air pollutants commonly found as components of photochemical smog. The mechanism of toxicity for 1-NN involves bioactivation by cytochrome P450s and subsequent adduction to proteins. Previous studies have shown that 1-NN toxicity in the lung is considerably higher in rats after long-term exposure to ozone compared with the corresponding filtered air–exposed control rats. The aim of the present study was to establish whether long-term exposure to ozone alters the susceptibility of nasal mucosa to the bioactivated toxicant, 1-NN. Adult male Sprague-Dawley rats were exposed to filtered air or 0.8 ppm ozone for 8 hours per day for 90 days, followed by a single treatment with 0, 12.5, or 50.0 mg/kg 1-NN by intraperitoneal injection. The results of the histopathologic analyses show that the nasal mucosa of rats is a target of systemic 1-NN, and that long-term ozone exposure markedly lessens the severity of injury, as well as the protein adduct formation by reactive 1-NN metabolites. The antagonistic effects were primarily seen in the nasal transitional epithelium, which corresponds to the main site of histologic changes attributed to ozone exposure (goblet cell metaplasia and hyperplasia). Long-term ozone exposure did not appear to alter susceptibility to 1-NN injury in other nasal regions. This study shows that long-term ozone exposure has a protective effect on the susceptibility of nasal transitional epithelium to subsequent 1-NN, a result that clearly contrasts with the synergistic toxicological effect observed in pulmonary airway epithelium in response to the same exposure regimen.

Key Words: goblet cell metaplasia • nasal transitional epithelium • 1-nitronaphthalene • ozone • protein adduct formation