Red/near infrared light stimulates release of an endothelium dependent vasodilator and rescues vascular dysfunction in a diabetes model

Abstract

Peripheral artery disease (PAD) is a morbid condition whereby ischemic peripheral muscle causes pain and tissue breakdown. Interestingly, PAD risk factors, e.g. diabetes mellitus, cause endothelial dysfunction secondary to decreased nitric oxide (NO) levels, which could explain treatment failures. Previously, we demonstrated 670nm light (R/NIR) increased NO from nitrosyl-heme stores, therefore we hypothesized R/NIR can stimulate vasodilation in healthy and diabetic blood vessels. Vasodilation was tested by ex vivo pressure myography in wild type C57Bl/6, endothelial nitric oxide synthase (eNOS) knockout, and db/db mice (10 mW/cm2 for 5min with 10 min dark period). NOS inhibition with N-Nitroarginine methyl ester (L-NAME) or the NO scavenger Carboxy-PTIO (c-PTIO) tested the specificity of NO production. 4,5-Diaminofluorescein diacetate (DAF-2) measured NO in human dermal microvascular endothelial cells (HMVEC-d). R/NIR significantly increased vasodilation in wild type and NOS inhibited groups, however R/NIR dilation was totally abolished with c-PTIO and blood vessel denudation. Interestingly, the bath solution from intact R/NIR stimulated vessels could dilate light naïve vessels in a NO dependent manner. Characterization of the bath identified a NO generating substance suggestive of S-nitrosothiols or non heme iron nitrosyl complexes. Consistent with the finding of an endothelial source of NO, intracellular NO increased with R/NIR in HMVEC-d treated with and without L-NAME (1mM), yet c-PTIO (100μm) reduced NO production. R/NIR significantly dilated db/db blood vessels. In conclusion, R/NIR stimulates vasodilation by release of NO bound substances from the endothelium. In a diabetes model of endothelial dysfunction, R/NIR restores vasodilation, which lends the potential for new treatments for diabetic vascular disease.

Ascorbate attenuates red light mediated vasodilation: Potential role of S-nitrosothiols

“…We recently established that red light irradiation time-dependently increases dilation of pre-constricted murine facial artery in an NO-dependent, but eNOS-independent manner. Incubation of vessels with the NOS inhibitor L-NAME did not significantly affect vasodilation, however, the NO scavenger cPTIO abolished the effect [22] . These data suggest that red light-stimulated an NO-dependent vasodilation that was largely NOS-independent.…”

“…In our previous study [22] we showed that irradiation of vessels at 670 nm generates a relatively stable transferable NO-dependent mediator which is released from the endothelium and could dilate a naïve vessel in the dark. We examined if ascorbate pre-treatment would prevent the release of this mediator.…”

“…We previously demonstrated that red light (670 nm) is able to dilate pre-constricted facialis arterial preparations by an eNOS-independent but nitric-oxide dependent mechanism [22] . We have rigorously controlled for heating effects and have concluded that any slight temperature increase resulting from the irradiation procedure has negligible effects on vasodilation [32] .…”

“…Our recent work suggest that red light may have a dual action in accessing this material, acting directly on the material but also allowing release to the extracellular space ( Fig. 6 ) [22] , [32] . The potential transport of released vasodilator into the blood stream could extend the reach of red light to clinically relevant tissue beds more distal and deeper than the surface.…”

“…We have recently demonstrated that irradiation of isolated vessels with 670 nm light results in the release a substance from the vascular endothelium with vasodilatory activity and suggested that this substance was a small NO-containing molecule [22] . In this study we have further investigated the nature of this intermediate and conclude that it has characteristics closely aligned with RSNO, although a contribution from DNIC, cannot be ruled out.…”