Transport rather than diffusion-dependent route for nitric oxide gas activity in alveolar epithelium

Abstract

The pathway by which inhaled NO gas enters pulmonary alveolar epithelial cells has not been directly tested. Although the expected mechanism is diffusion, another route is the formation of Snitroso-L-cysteine, which then enters the cell through the L-type amino acid transporter(LAT). To determine if NO gas also enters alveolar epithelium this way, we exposed alveolar epithelial-rat type I, type II, L2, R3/1, and human A549-cells to NO gas at air liquid interface in the presence of L-and D-cysteine ± LAT competitors. NO gas exposure concentration-dependently increased intracellular NO and S-nitrosothiol levels in the presence of L-but not D-cysteine, which was inhibited by LAT competitors, and was inversely proportional to diffusion distance. The effect of L-cysteine on NO uptake was also concentration dependent. Without pre-incubation with Lcysteine, NO uptake was significantly reduced. We found similar effects using ethyl nitrite gas in place of NO. Exposure to either gas induced activation of soluble guanylyl cylase in a parallel manner, consistent with LAT-dependence. We conclude that NO gas uptake by alveolar epithelium achieves NO-based signaling predominantly by forming extracellular S-nitroso-Lcysteine that is taken up through LAT, rather than by diffusion. Augmenting extracellular Snitroso-L-cysteine formation may augment pharmacological actions of inhaled NO gas.

Nitric oxide suppresses NLRP3 inflammasome activation and protects against LPS-induced septic shock

“…We found that both SNAP and GSNO dramatically inhibited IL-1β secretion in a dose-dependent manner (Figure 1A and Supplementary information, Figure S1A). As L-cysteine facilitates the generation of NO from SNAP or GSNO 24 , the inhibitory effects of these NO donors on IL-1β secretion were greatly enhanced in the presence of L-cysteine. In contrast, the secretion of IL-6 or TNF-α, which depends on Toll-like receptor (TLR) signaling only, was not affected by the presence of these NO donors (Figure 1A and Supplementary information, Figure S1A).…”

Differential regulation of metabolism by nitric oxide andS-nitrosothiols in endothelial cells

“…Moreover, the biological activity of NO and S-nitrosothiols is not limited to only protection against ischemia-reperfusion injury. S-nitrosothiol formation after inhaled NO administration has recently been proposed as a mechanism of NO delivery to the alveolar epithelium (3), and others have suggested that NO metabolites such as S-nitrosothiols, rather than free NO, mediate some of the beneficial vascular effects of inhaled NO (15).…”

Diagnosis and treatment of pulmonary hypertension in infancy

“…However, it is now understood that NO is a free radical that can be inactivated through interaction with reactive oxygen species found in the alveolar space or alveolar lining. Others propose that NO gas gains entry into alveolar epithelium in part by forming a nitrosothiol derivative of cysteine that enters via an amino acid transporter [76]. Once in the blood stream, NO binds avidly to hemoglobin, which is subsequently reduced by methemoglobin reductase.…”