Alteration of epithelial integrity, alkaline phosphatase activity, and fibronectin expression in lungs of rats exposed to ozone.

The deleterious effects of ozone (O3), an oxidant air pollutant, in the lung are dependent on dose and exposure duration and generally evolve with time postexposure. This study characterized the time sequence of epithelial injury and fibronectin expression in the lungs of rats exposed to O3. Bronchoalveolar lavage (BAL) fluid was analyzed for alkaline phosphatase and total protein as markers of epithelial injury and increased permeability, and fibronectin for its role in inflammation and lung injury. The results revealed a time-related increase in total protein in the BAL fluid following a 3-h exposure of rats to 1 ppm O3. The increased protein concentrations peaked at 12 h and then declined, but remained significantly higher than control at 24 h postexposure. A similar time-related significant increase also occurred for BAL fibronectin and alkaline phosphatase activity. However, the return of alkaline phosphatase levels to baseline prior to a comparable reduction in protein levels suggests repair of injured cells, but a delay in the formation of epithelial junctions that limit the transfer of serum proteins to air spaces. By cytochemistry, alkaline phosphatase activity was detected in association with lung type II epithelial cells and in BAL polymorphonuclear leukocytes (PMNs), but not in macrophages. While a significant increase in cytochemically detectable alkaline phosphatase resulted from the increase in PMN number following O3 exposure, mononuclear cells constituted the primary cell type responsible for fibronectin mRNA upregulation. While the cytochemical observations support the role of inflammatory cells in the injury process, the comparability of temporal changes in BAL protein, fibronectin, and alkaline phosphatase suggests a mechanistic role for fibronectin in lung injury.