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 comes into contact and reacts with the fluids lining the airways of the respiratory tract. These respiratory tract lining fluids (RTLF) form a barrier between the inhaled toxic pollutant and the epithelium which protects the underlying tissue from inflammation. Proteins, mainly albumin, and antioxidants are the major components of the RTLF. Many studies have utilized human blood plasma to study the interaction of an extracellular fluid with ozone. In this study, we used bronchoalveolar lavage fluids (BALF) as a more specific surrogate for rat RTLF, and we utilized the native fluorescence as a marker to investigate the depletion kinetics of naturally-occurring protein following exposure to NO2 in a controlled flow reactor system. We also studied the depletion kinetics of albumin in a buffered salt solution. The results 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 solution; (2) the depletion kinetics of protein in BALF was non-linear with respect to substrate concentration; (3) the rate of protein depletion was much slower in BALF than in a buffered solution of albumin, suggesting that the presence of antioxidants in BALF protected proteins from being oxidized by NO2; and (4) whereas the addition of ascorbic acid to buffered albumin solution significantly attenuated albumin depletion, the addition of glutathione had no effect. This suggested that the reaction rate constant of ascorbic acid was considerably higher than that of glutathione. (C) 1998 Elsevier Science B.V. All rights reserved.