Alveolar lining fluid S-nitrosoglutathione may contribute as a source of airway gaseous nitric oxide

Nitric oxide (NO) has normal physiologic functions in the lung serving both as a bronchodilator and vasodilatator. Glutathione (GSH), found in abundance in the alveolar epithelial lining fluid (ELF), has been studied as an extracellular antioxidant and may also react with NO in the ELF to form a S-nitrosothiol, S-Nitrosoglutathione (GSNO). In vitro, GSNO also demonstrates bronchodilatory and vasodilatory activities. We hypothesized that GSNO in ELF may serve as a source of exhaled NO in the alveolar air by the breakdown to GSH and NO followed by the partition of NO between liquid to gas phase. To test this, we measured the presence of NO in the head space gas from various solution containing known concentration of GSNO or Sodium Nitrate (NaNO₃). These solutions (either with Phosphate Buffered Saline (PBS, pH7.4) or cell culture media [containing HEPES Buffer, DME-S12, Non-essential amino acid, Bovine Serum Albumin, and L-glutamine]) were placed in sealed glass chambers (10 mL solution, 125 mL chambers). NO gas was measured utilizing a chemilucent reaction detected by a NO analyzer (Seivers 280). At one hour, NO gas (2.5 ±0.1ppm, mean± SEM) was present in the head space of a 10mL solution containing GSNO [100μM] in PBS. We found that the presence of NO gas was substantially higher from PBS solution containing GSNO than PBS solution containing equimolar concentration of NaNO3 (p <0.002, at 1 hour). Gas phase partial pressure of NO increased both as a function of the concentration of GSNO and time (p<0.00001, p < 0.016 respectively). The release of NO from GSNO in cell culture media was significantly increased in comparison to GSNO in PBS alone (p < 0.002). We conclude that GSNO in solution is able to release nitric oxide. In addition, this release may be further enhanced in biological fluids. Thus, in ELF, the presence of GSNO may serve as an important source of airway gaseous nitric oxide in both the normal lung function and may have a role for therapeutic intervention.