Kinetics of protein depletion in rat bronchoalveolar lavage fluid following in vitro exposure to nitrogen dioxide

Upon inhalation, nitrogen dioxide (NO2), a strong oxidizing agent, first co mes into contact and reacts with the fluids lining the airways of the respi ratory tract. These respiratory tract lining fluids (RTLF) form a barrier b etween the inhaled toxic pollutant and the epithelium which protects the un derlying tissue from inflammation. Proteins, mainly albumin, and antioxidan ts are the major components of the RTLF. Many studies have utilized human b lood plasma to study the interaction of an extracellular fluid with ozone. In this study, we used bronchoalveolar lavage fluids (BALF) as a more speci fic surrogate for rat RTLF, and we utilized the native fluorescence as a ma rker to investigate the depletion kinetics of naturally-occurring protein f ollowing exposure to NO2 in a controlled flow reactor system. We also studi ed the depletion kinetics of albumin in a buffered salt solution. The resul ts indicated that: (1) the decay in fluorescence was linearly dependent on the concentration of NO2, indicating that protein oxidation was first order with respect to NO2 concentration in both BALF and in buffered albumin sol ution; (2) the depletion kinetics of protein in BALF was non-linear with re spect to substrate concentration; (3) the rate of protein depletion was muc h slower in BALF than in a buffered solution of albumin, suggesting that th e presence of antioxidants in BALF protected proteins from being oxidized b y NO2; and (4) whereas the addition of ascorbic acid to buffered albumin so lution significantly attenuated albumin depletion, the addition of glutathi one had no effect. This suggested that the reaction rate constant of ascorb ic acid was considerably higher than that of glutathione. (C) 1998 Elsevier Science B.V. All rights reserved.