Wavelength-dependence of vasodilation and NO release from S-nitrosothiols and dinitrosyl iron complexes by far red/near infrared light

Far red/near infrared (R/NIR) energy is a novel therapy, but its mechanism of action is poorly characterized. Cytochrome c oxidase (Cco) of the mitochondrial electron transport chain is considered the primary photoacceptor for R/NIR to photolyze a putative heme nitrosyl in Cco to liberate free nitric oxide (NO). We previously observed R/NIR light directly liberates NO from nitrosylated hemoglobin and myoglobin, and recently suggested S-nitrosothiols (RSNO) and dinitrosyl iron complexes (DNIC) may be primary sources of R/NIR-mediated NO. Here we indicate R/NIR light exposure induces wavelength dependent dilation of murine facial artery, with longer wavelengths (740, and 830 nm) exhibiting reduced potency when compared to 670 nm. R/NIR also stimulated NO release from pure solutions of low molecular weight RSNO (GSNO and SNAP) and glutathione dinitrosyl iron complex (GSH-DNIC) in a power- and wavelength-dependent manner, with the greatest effect at 670 nm. NO release from SNAP using 670 was nearly ten-fold more than GSNO or GSH-DNIC, with no substantial difference in NO production at 740 nm and 830 nm. Thermal effects of irradiation on vasodilation or NO release from S-nitrosothiols and DNIC was minimal. Our results suggest 670 nm is the optimal wavelength for R/NIR treatment of certain vascular-related diseases.