Photobiomodulation Response From 660 nm is Different and More Durable Than That From 980 nm.

BACKGROUND AND OBJECTIVES: Photobiomodulation (PBM) therapy uses light at various wavelengths to stimulate wound healing, grow hair, relieve pain, and more-but there is no consensus about optimal wavelengths or dosimetry. PBM therapy works through putative, wavelength-dependent mechanisms including direct stimulation of mitochondrial respiration, and/or activation of transmembrane signaling channels by changes in water activity. A common wavelength used in the visible red spectrum is ~660 nm, whereas recently ~980 nm is being explored and both have been proposed to work via different mechanisms. We aimed to gain more insight into identifying treatment parameters and the putative mechanisms involved. STUDY DESIGN/MATERIALS AND METHODS: Fluence-response curves were measured in cultured keratinocytes and fibroblasts exposed to 660 or 980 nm from LED sources. Metabolic activity was assessed using the MTT assay for reductases. ATP production, a major event triggered by PBM therapy, was assessed using a luminescence assay. To measure the role of mitochondria, we used an ELISA to measure COX-1 and SDH-A protein levels. The respective contributions of cytochrome c oxidase and ATP synthase to the PBM effects were gauged using specific inhibitors. RESULTS: Keratinocytes and fibroblasts responded differently to exposures at 660 nm (red) and 980 nm (NIR). Although 980 nm required much lower fluence for cell stimulation, the resulting increase in ATP levels was short-term, whereas 660 nm stimulation elevated ATP levels for at least 24 hours. COX-1 protein levels were increased following 660 nm treatment but were unaffected by 980 nm. In fibroblasts, SDH-A levels were affected by both wavelengths, whereas in keratinocytes only 660 nm light impacted SDH-A levels. Inhibition of ATP synthase nearly completely abolished the effects of both wavelengths on ATP synthesis. Interestingly, inhibiting cytochrome c oxidase did not prevent the rise in ATP levels in response to PBM treatment. CONCLUSION: To the best of our knowledge, this is the first demonstration of differing kinetics in response to PBM therapy at red versus NIR wavelength. We also found cell-type-specific differences in PBM therapy response to the two wavelengths studied. These findings confirm that different response pathways are involved after 660 and 980 nm exposures and suggest that 660 nm causes a more durable response. © 2021 Wiley Periodicals LLC.

Pulmonary Phototherapy to Treat Carbon Monoxide Poisoning in Rats.

BACKGROUND: Carbon monoxide (CO) poisoning is a common cause of poison-related mortality. CO binds to hemoglobin in the blood to form carboxyhemoglobin (COHb), impairing oxygen delivery to peripheral tissues. Current treatment of CO-poisoned patients involves oxygen administration to rapidly remove CO and restore oxygen delivery. Light dissociates CO from COHb with high efficiency. Exposure of murine lungs to visible laser-generated light improved the CO elimination rate in vivo. The aims of this study were to apply pulmonary phototherapy to a larger animal model of CO poisoning, to test novel approaches to light delivery, and to examine the effect of chemiluminescence-generated light on the CO elimination rate. METHODS: Anesthetized and mechanically ventilated rats were poisoned with CO and subsequently treated with air or oxygen combined with or without pulmonary phototherapy delivered directly to the lungs of animals at thoracotomy, via intrapleural optical fibers or generated by a chemiluminescent reaction. RESULTS: Direct pulmonary phototherapy dissociated CO from COHb reducing COHb half-life by 38%. Early treatment with phototherapy in critically CO poisoned rats improved lactate clearance. Light delivered to the lungs of rats via intrapleural optical fibers increased the rate of CO elimination without requiring a thoracotomy, as demonstrated by a 16% reduction in COHb half-life. Light generated in the pleural spaces by a chemiluminescent reaction increased the rate of CO elimination in rats breathing oxygen, reducing the COHb half-life by 12%. CONCLUSIONS: Successful application of pulmonary phototherapy in larger animals and humans may represent a significant advance in the treatment of CO-poisoned patients.