Environmental particulate-mediated cytokine production in lung epithelial cells (A549): role of preexisting inflammation and oxidant stress.

Epidemiologic data show that air pollution particulates cause adverse pulmonary health effects, especially in individuals with preexisting lung disease. We sought to model in vitro preexisting lung inflammation in order to investigate the hypothesis that "primed" lung epithelial cells will exhibit enhanced phlogistic responses [e.g., interleukin-8 (IL-8) production] to particulate air pollution. Exposure of tumor necrosis factor alpha (TNF-alpha) primed or control A549 cells to the air pollution particulates, residual oil fly ash (ROFA), and the known pathogenic dust alpha-quartz, but not inert TiO2, caused increased IL-8 production in primed cells compared to normal cells in a concentration-dependent manner (particle concentration range 0-200 microg/ml). We hypothesized that oxidant mechanisms may be involved in the cellular response to particulates. Addition of the antioxidant N-acetylcysteine (NAC, 1.0 mM) decreased ROFA and alpha-quartz-mediated IL-8 production by approximately 50% in normal and TNF-alpha-primed A549 cells. In addition, exposure of A549 cells to ROFA caused a substantial (and NAC inhibitable) increase in oxidant levels as measured by fluorometry (DCFH oxidation). These data suggest that (1) lung epithelial cells primed by inflammatory mediators can show enhanced cytokine production after exposure to air pollution particulates, and (2) oxidant stress is a key mechanism for this response.