Inhaled NO is being used to treat a variety of clinical conditions, often in conjunction with high concentrations of inspired oxygen. We have previously shown that 95% oxygen and 2 mM SNAP (an NO donor) are synergistically toxic to cultured airway epithelial cells (A549). To explore the combined cytotoxicity of NO and HYP further, A549 cells were grown in either 2 mM SNAP + 50% oxygen or 2 mM SNAP + 75% oxygen. Additional cell lines, small airway epithelial cells and human lung microvascular endothelial cells - grown in 2 mM SNAP + 95% oxygen - were also studied. Cells from each group were also grown in room air as additional controls. Live cells were counted and media and gases were refreshed daily for 6 d. Cytotoxicity was seen in the A549 cells even when the oxygen concentration was reduced to 75 or 50%. These cells began to die on day 2 and continued to die rapidly thereafter (the rate of cell death was proportional to the oxygen concentration). Small airway epithelial cells grown in SNAP and NO began to die almost immediately and died even more rapidly than the A549 cells. However, the endothelial cells were much more resistant to the effects of NO and HYP. Live cell counts were relatively unchanged for the first 5 days and then decreased on day 6. Data indicate that human lung endothelial cells are more resistant to the toxic effects of NO and HYP compared to pulmonary epithelial cells. In view of previous reports of in vivo toxicity from NO and HYP, these data suggest that the primary target of such toxicity is the pulmonary epithelial cell.

Funded by NIH-K08HL02791 and a grant by the American Lung Association.