Chemoattractant and Leukotriene B4 Production from Rat Alveolar Macrophages Exposed to Nitrogen Dioxide

Abstract

The present study examined the hypothesis that exposure of alveolar macrophages to nitrogen dioxide (NO2) resulted in enhanced production of a lipophilic chemotactic agent for neutrophils, possibly leukotriene B4 (LTB4). Neutrophil migration was significantly increased in response to the reconstituted ethyl acetate extract of the medium surrounding macrophages exposed for 1 h to 5 or 20 ppm NO2. Compared with air-treated macrophages, production of LTB4 was found to be significantly increased by exposure to 5 ppm NO2, but unchanged by exposure to 20 ppm NO2. Treatment of macrophages with the calcium ionophore A23187 at a concentration of 2 microM for 15 min following a 1-h exposure to 5 ppm NO2 led to a significant increase in the production of LTB4 compared with A23187-treated air controls; however, LTB4 production in response to the calcium ionophore was unchanged following exposure to 20 ppm NO2. Thus, while increased neutrophil migration in response to products from macrophages exposed to 5 ppm NO2 correlated with the increased production of LTB4, increased migration in response to products from macrophages exposed to 20 ppm NO2 suggested the presence of another chemotactic lipid. Lipid peroxidation processes induced by NO2 at 5 ppm may lead to the formation of hydroperoxides that enhance the formation of LTB4; yet at 20 ppm, significantly higher concentrations of hydroperoxides may be responsible for impaired LTB4 formation. Phorbol ester-stimulated macrophage superoxide production was significantly inhibited in a dose-dependent manner following exposure to NO2 concentrations of 1, 5, or 20 ppm.