Hyperoxia upregulates the NO pathway in alveolar macrophages in vitro: role of AP-1 and NF-kappa B

The inducible nitric oxide (NO) synthase gene in alveolar macrophages (AMs) is a stress response gene that may contribute to tissue injury in the lung after respiration with high O-2 concentrations through extensive productio n of NO. In this study, we investigated the influence of hyperoxia on the N O pathway in rat AMs in vitro, its regulation by the transcription factors nuclear factor (NF)-kappaB and activator protein (AP)-1, and the role of re active oxygen species (ROS). AMs were treated with lipopolysaccharide (LPS) and/or interferon (IFN)-gamma and incubated under 21 or 85% O-2. Stimulati on with LPS and IFN-gamma led to induction of the NO pathway that was furth er upregulated by hyperoxia. The binding activity of NF-kappaB, in contrast to that of AP-1, was activated on stimulation with LPS and IFN-gamma, and both were further increased under hyperoxia. The antioxidants pyrrolidine d ithiocarbamate and N-acetyl-L-cysteine inhibited intracellular ROS producti on and the NO pathway under both normoxic and hyperoxic conditions but had diverse effects on the transcription factors. The results presented here in dicate that hyperoxia can upregulate the NO pathway in stimulated AMs throu gh increased production of intracellular ROS and activation of NF-kappaB an d AP-1.