Nitrogen dioxide depletes uric acid and ascorbic acid but not glutathione from lung lining fluid

The aim of this study was to determine the kinetics of the reactions between the gaseous free-radical pollutant, nitrogen dioxide (NO2), and the water-soluble antioxidants present in respiratory tract lining fluid (RTLF). Samples of RTLF, recovered from 12 subjects (mean age 54.1 +/- 16.3 years; eight male, four female) as bronchoalveolar lavage (BAL) fluid were exposed ex vivo to NO2 [50-1000 parts per billion (ppb)] for 4 h. For comparison, similar exposures were carried out with single and composite solutions with relevant RTLF antioxidant concentrations. Ascorbic acid (AA), uric acid (UA), GSH depletion, and GSSG and malondialdehyde (MDA) formation were determined with time. In the three models, UA and AA were consumed in a time- and NO2-concentration-related fashion. In addition, their rate of depletion correlated positively with their initial concentration (UA, r = 0.92, P < 0.05; AA, r = 0.94, P < 0.05). Little difference was found between the rate of loss of AA (2.2 +/- 0.2; 1.9 +/- 0.5; 1.4 +/- 0.3 nmol.l(-1).h(-1).ppb(-1)), and that of UA (2.4 +/- 0.2; 2.1 +/- 0.6; 1.3 +/- 0.2 nmol.l(-1).h(-1).ppb(-1)) in the three RTLF models examined (single, composite, BAL fluid respectively). GSH loss from BAL fluid (0.2 +/- 0.1) was significantly less than that seen in either single (1.4 +/- 0.3) or composite (1.2 +/- 0.5 nmol.l(-1).h(-1).ppb(-1)) antioxidant solutions. In all cases, GSH consumption was significantly less than AA or UA. As model complexity increased, the rate of individual antioxidant loss decreased, such that in BAL fluid, AA, UA and GSH consumption rates were significantly less (P < 0.05) than in the pure or composite antioxidant mixtures. In BAL fluid, little GSSG production was observed at any NO2 concentration. MDA concentration, determined as a measure of lipid peroxidation, did not change following exposure to 50, 150 or 400 ppb NO2, but increased MDA was seen in BAL fluid from 8/12 subjects following exposure to 1000 ppb NO2 for 1 h or more. In conclusion, NO2, at environmentally relevant concentrations, depletes BAL fluid of the antioxidant defences, UA and AA, but not GSH.