Modeling the interactions of ozone with pulmonary epithelial lining fluid antioxidants.

Water soluble antioxidant--ascorbate (AA), urate (UA), and reduced glutathione (GSH)--consumption by ozone (O3) was investigated in a range of pulmonary epithelial lining fluid (ELF) models. Antioxidants were exposed individually and as a composite mixture, with and without human albumin to a range of ambient O3 concentrations: 0-1500 ppb using a continually mixed, interfacial exposure setup. We observed the following: (1) UA constituted the most o3-reactive substrate in each of the models examined. Reactivity hierarchies in each were as follows: UA > AA >> GSH (individual antioxidant), UA > AA > GSH (composite antioxidant), and UA >> AA approximately equal to GSH (composite antioxidant + albumin). Consumption of GSH as a pure antioxidant solution was associated with a 2:1 stoichiometric conversion of GSH to GSSG. This simplistic relationship was lost in the more complex models. (3) Consumption of antioxidants by O3 occurred without alteration of sample pH. (4) Protein carbonyl formation was observed when albumin alone was exposed to O3. However, in the presence of the composite antioxidant solution no evidence of this oxidative modification was apparent. These data indicate that GSH does not represent an important substrate for O3. In contrast, UA displays high reactivity consistent with its acting as a sacrificial substrate in the ELF. As UA concentrations are highest in the ELF of the proximal airways, its localization, allied to its reactivity, suggesting that it plays important roles, both in conferring protection locally and also by "scrubbing" O3, from inhaled air, limiting its penetration to the more sensitive distal lung.