Structural and functional impairment of surfactant protein A after exposure to nitrogen dioxide in rats.

The major surfactant protein A (SP-A) determines the dynamics of surfactant metabolism and function. We now for the first time studied the in vivo exposure of the SP-A to nitrogen dioxide (NO2) and compared it to in vitro exposure effects. Several properties that are believed to possess physiological functions were investigated. Exposure of rat SP-A to NO2 showed 1) a higher alveolar pool size after in vivo exposure, 2) a slightly decreased mannose binding capacity for the in vivo exposed form but a highly decreased binding after in vitro exposure, 3) an affected protein-lipid aggregation that was impaired most by the in vitro exposed protein, 4) a low inhibition for the secretion of phosphatidylcholine in isolated type II pneumocytes, and 5) no difference in apparent molecular weight and immunological reactivity of the differently exposed SP-A. The NO2-induced alterations of the SP-A may contribute to the pulmonary toxicity of this oxidant. It is clear from this study that the extend of the effects from in vivo and in vitro exposure are different. Therefore both forms of exposure are necessary to assess the biological significance of NO2 exposure.