Photolysis of solid-state S-nitrosoglutathione: Mechanism and kinetics of nitric oxide release

S-Nitrosoglutathione (GSNO) is an endogenous nitric oxide (NO) donor molecule. Photolysis of solid GSNO may be utilized effectively as an NO source for inhaled nitric oxide (iNO) therapy. In this work, solid GSNO was photolyzed using narrow-band LED lights as a function of wavelength and intensity of incident light. The photolytic NO release efficiency, the presence of any decomposition products, as well as the morphology and the photolytic pathways for GSNO photo-decomposition were examined using NMR, UV, FTIR, ESR, TGA, DSC, SEM and UPLC-MS. The initial photochemical yield for NO release was 0.37 ± 0.03%, 0.10 ± 0.01%, and 0.02 ± 0.01% (n = 3 independent experiments) respectively using 340 nm, 385 nm, and 470 nm of LED light sources. The photolyzed solid GSNO reacted with oxygen in ambient air and immediately produced an oxygenated glutathione-derived species with m/z ratio (∼354) suggesting the possible formation of sulfonyl peroxyl radical GS(O)₂O^• without a measurable stable thiyl radical formation. However, the photolyzed product did not recombine with NO to reform the GSNO, strongly suggesting that the photolysis of GSNO is irreversible under our conditions. Based on PXRD and SEM analysis, after photolysis and NO generation the GSNO lost its crystallinity. Hence, these data may prove useful for development of GSNO as a solid-phase NO source for iNO therapy.