Alveolar macrophage cytotoxicity for normal lung fibroblasts is mediated by nitric oxide release

Nitric oxide (NO) released by activated alveolar macrophages (AM) can mediate effects on target cells and can also react with superoxide anion (O2-) to form peroxynitrite (PN), a highly cytotoxic product. The role of NO and PN in AM cytotoxicity for normal lung cells was investigated using co-cultures of rat lung fibroblasts (FB) and rat AM treated with lipopolysaccharide + interferon-gamma (LI). AM and FB, alone and in co-culture, were treated with LI for 5 days and cell viability measured. The culture media was analyzed for NO, TNF-alpha, O2-, and IL-1beta. A decreased FB viability was correlated with increased NO release by LI-activated AM. Pretreatment of co-cultures with the inducible NOS inhibitor L-NAME caused dose-related decreases in NO release by AM and increases in FB viability. Although TNF-alpha release was increased in co-cultures treated with LI, the viability of FB was not affected when cultures were treated with similar concentrations of TNF-alpha in the absence of AM. O2- could not be detected in the media and addition of superoxide dismutase (SOD) did not protect FB. These data suggest that neither O2- nor PN contributed to the loss of cell viability. Activated AM may kill normal rat lung FB through a NO-mediated pathway that does not involve PN.