Nitric oxide (NO) has been shown to be a potent vasodilator. Inhaled NO is being used to treat diseases with increased pulmonary vascular resistance such as persistent pulmonary hypertension of the newborn. Despite NO's reported benefits, potential adverse effects and appropriate dosage have not been completely studied. This is especially true when NO is used in conjunction with oxygen (O2) as in most clinical settings. The combination of these two gases may be lethal to exposed lung epithelium. We compared cytotoxic profiles of isolated rat alveolar type II cells in four exposure groups: 20 ppm NO + 95% O2; 20 ppm NO + room air (RA); 95% O2; and RA alone. Primary alveolar type II cells were isolated by using elastase/DNAase and purified using differential adhesion (IgG) technique from lungs of adult rats (N = 8). Cells from each rat were suspended in a phenol free medium and studied in the four treatment groups. Each group was exposed to the respective gas for four hours. The cells were then stained with a live/dead fluorescent probe (Molecular Probe) and the percent of cell death from each group was calculated and compared. Student-Neuman-Keuls test demonstrated an increase in the percent of cell death in the NO + 95% O2 group (mean ± SEM, 43.9 ± 5.54) as compared to the groups exposed to NO + RA (24.1± 2.94, P ≤ 0.05); 95% O2 (24.7 ± 4.15, P ≤ 0.05); and RA (22.8 ± 3.28, P ≤ 0.05). We concluded that NO in combination with O2 leads to an increase of alveolar type II cell death by nearly 100%. The mechanism by which the combination of NO with O2 causes increased cell death is unknown but may be related to the formation of free radicals. Clinically, NO is delivered with increased concentrations of O2. The potential cytotoxic effect of this combination warrants further investigation prior to the routine use of inhaled NO. This study points to the urgent need for ongoing studies concerning the cytotoxic profile of NO when used with O2 since damage to alveolar epithelia may have important short-term (surfactant production) and long-term (regeneration of epithelial lining) consequences.
