Ozone exposure and the production of reactive oxygen species by bronchoalveolar cells in humans

Exposure to ozone injures respiratory epithelium, and the mechanisms may involve the generation of reactive oxygen species (ROS). This study tested the hypothesis that ozone exposure increases the airway burden of ROS to a greater degree in smokers than nonsmokers, and that this effect is independent of ozone-induced changes in spirometry. Healthy subjects were selected as either responders (decrement in FEV₁ > 15%) or non-responders (decrement in FEV₁ < 5%) to ozone; each underwent 2 exposures to ozone and 1 to air, with bronchoalveolar lavage (BAL) performed 30 min (early) and 18 h (late) after exposure. Release of superoxide anion (O₂^-) was used as a measure of ROS release by all BAL cells, and flow cytometry was used to detect ROS production in alveolar macrophages (AM) only. Recovery of AM was approximately threefold greater in smokers than nonsmokers. Unstimulated, but not stimulated, cells obtained by BAL from smokers released approximately twofold greater amounts of O₂^- than cells from nonsmokers, both early and late after ozone exposure (p = .012 and p = .046, respectively). Stimulated, but not unstimulated, ROS generation by AM from smokers increased following ozone exposure, but the ozone effect was not significant. ROS production by AM decreased in nonsmokers (air vs. ozone late, p = .014). Total protein, albumin, and immunoglobulin M (IgM) increased in BAL fluid, consistent with an increase in epithelial permeability. In addition, the concentration of α₂-macroglobulin increased approximately threefold 18 h after exposure in nonsmokers (p < .001). No relationship was found between measures of ROS production and lung function responsiveness to ozone. These studies suggest the airways of smokers experience a greater burden of ROS than those of nonsmokers following ozone exposure.