Hyperoxia amplifies LPS- and IFN-gamma-induced NO production in alveolar macrophages

Background: Oxygen therapy may lead to hyperoxic lung injury. Reactive oxyg en and nitroger, species are suggested to play a critical role. Alveolar ma crophages (AM) are a major source of inducible nitric oxide synthase (iNOS) -mediated nitric oxide (NO) production. Therefore, we asked whether hyperox ic conditions affect iNOS expression and. NO production by rat AM in vitro. Methods: AM were obtained by bronchoalveolar lavage from SD rats. Cells wer e cultured in the absence or presence of 100 ng/ml LPS and/or 100 U/ml IFN- gamma under normoxic (21% O-2) or hyperoxic (85% O-2) conditions for 24 hou rs. NO release was measured as nitrite with the Griess reaction. Expression of iNOS mRNA was detected by RT-PCR. Results: Under normoxic conditions, stimulation of AM with LPS/IFN-gamma in duced a significant NO release (28.7 +/- 1.1 nmol/10(6) cells) compared to unstimulated cells (<0.3 nmol/10(6) cells). Incubation of AM under hyperoxi c conditions amplified the LPS/IFN-gamma-induced NO formation significantly by 60% (46.8 +/- 2.4 nmol/ 10(6) cells). In line with these findings, incr eased iNOS mRNA levels were found in LPS/IFN-gamma-stimulated AM after hype roxic exposure. Conclusion: Taken together, our data indicate that hyperoxia amplifies LPS/ IFN-gamma-induced iNOS expression and NO formation by AM in vitro. We sugge st that hyperoxia-induced NO formation by AM participates in the pathogenes is of pulmonary oxygen toxicity.