Far red and near infrared (NIR) light promotes wound healing, but the mechanism is poorly understood. Our previous studies using 670 nm light-emitting diode (LED) arrays suggest that cytochrome c oxidase, a photoacceptor in the NIR range, plays an important role in therapeutic photobiomodulation. If this is true, then an irreversible inhibitor of cytochrome c oxidase, potassium cyanide (KCN), should compete with LED and reduce its beneficial effects. This hypothesis was tested on primary cultured neurons. LED treatment partially restored enzyme activity blocked by 10 -100 M KCN. It significantly reduced neuronal cell death induced by 300 M KCN from 83.6 to 43.5%. However, at 1-100 mM KCN, the protective effects of LED decreased, and neuronal deaths increased. LED significantly restored neuronal ATP content only at 10 M KCN but not at higher concentrations of KCN tested. Pretreatment with LED enhanced efficacy of LED during exposure to 10 or 100 M KCN but did not restore enzyme activity to control levels. In contrast, LED was able to completely reverse the detrimental effect of tetrodotoxin, which only indirectly down-regulated enzyme levels. Among the wavelengths tested (670, 728, 770, 830, and 880 nm), the most effective ones (830 nm, 670 nm) paralleled the NIR absorption spectrum of oxidized cytochrome c oxidase, whereas the least effective wavelength, 728 nm, did not. The results are consistent with our hypothesis that the mechanism of photobiomodulation involves the up-regulation of cytochrome c oxidase, leading to increased energy metabolism in neurons functionally inactivated by toxins. Near infrared (NIR)1 light has been used in therapeutic devices for the treatment of a variety of injuries, especially infected, ischemic, and hypoxic wounds (1-4). NIR light penetrates more deeply than UV or visible light and is benign to living tissue. This presents clear clinical advantages to treatment within a tissue transparency window of 650 -1000 nm. Most of the devices utilize lasers as the light source. Recently, however, light-emitting diodes (LEDs) have been found to be more beneficial than lasers in several respects (3, 5). LEDs can be constructed to form relatively large arrays to treat wounds that commonly involve areas much larger than the size of a laser beam. Unlike lasers, there is virtually no heat generated by the LED array and therefore no potential thermal injury to individuals being treated. LED is well tolerated by biological tissues and has no known detrimental effect. As a therapeutic device, LED has achieved FDA non-significant risk status. Moreover, LED units are more compact, portable, and affordable than lasers.The cellular mechanisms of action of NIR in wound healing are not well understood. The basic premise is that long wavelength lights stimulate cellular energy metabolism and energy production. Three major photoacceptor molecules in mammalian tissues are known to absorb light in the NIR range: hemoglobin, myoglobin, and cytochrome c oxidase. Of the three, only cytochrome c oxidase (EC 1.9...

Objective: The purpose of this study was to assess the effects of hyperbaric oxygen (HBO) and near-infrared light therapy on wound healing. Background Data: Light-emitting diodes (LED), originally developed for NASA plant growth experiments in space show promise for delivering light deep into tissues of the body to promote wound healing and human tissue growth. In this paper, we review and present our new data of LED treatment on cells grown in culture, on ischemic and diabetic wounds in rat models, and on acute and chronic wounds in humans. Materials and Methods: In vitro and in vivo (animal and human) studies utilized a variety of LED wavelength, power intensity, and energy density parameters to begin to identify conditions for each biological tissue that are optimal for biostimulation. Results: LED produced in vitro increases of cell growth of 140-200% in mouse-derived fibroblasts, rat-derived osteoblasts, and rat-derived skeletal muscle cells, and increases in growth of 155-171% of normal human epithelial cells. Wound size decreased up to 36% in conjunction with HBO in ischemic rat models. LED produced improvement of greater than 40% in musculoskeletal training injuries in Navy SEAL team members, and decreased wound healing time in crew members aboard a U.S. Naval submarine. LED produced a 47% reduction in pain of children suffering from oral mucositis. Conclusion: We believe that the use of NASA LED for light therapy alone, and in conjunction with hyperbaric oxygen, will greatly enhance the natural wound healing process, and more quickly return the patient to a preinjury/illness level of activity. This work is supported and managed through the NASA Marshall Space Flight Center-SBIR Program. 305

Methanol intoxication produces toxic injury to the retina and optic nerve, resulting in blindness. The toxic metabolite in methanol intoxication is formic acid, a mitochondrial toxin known to inhibit the essential mitochondrial enzyme, cytochrome oxidase. Photobiomodulation by red to near-IR radiation has been demonstrated to enhance mitochondrial activity and promote cell survival in vitro by stimulation of cytochrome oxidase activity. The present studies were undertaken to test the hypothesis that exposure to monochromatic red radiation from light-emitting diode (LED) arrays would protect the retina against the toxic actions of methanolderived formic acid in a rodent model of methanol toxicity. Using the electroretinogram as a sensitive indicator of retinal function, we demonstrated that three brief (2 min, 24 s) 670-nm LED treatments (4 J͞cm 2 ), delivered at 5, 25, and 50 h of methanol intoxication, attenuated the retinotoxic effects of methanolderived formate. Our studies document a significant recovery of rod-and cone-mediated function in LED-treated, methanol-intoxicated rats. We further show that LED treatment protected the retina from the histopathologic changes induced by methanolderived formate. These findings provide a link between the actions of monochromatic red to near-IR light on mitochondrial oxidative metabolism in vitro and retinoprotection in vivo. They also suggest that photobiomodulation may enhance recovery from retinal injury and other ocular diseases in which mitochondrial dysfunction is postulated to play a role. D ecrements in mitochondrial function have been postulated to be involved in the pathogenesis of numerous retinal and optic nerve diseases, including age-related macular degeneration, diabetic retinopathy, and Leber's hereditary optic neuropathy (1-3). Decrements in mitochondrial function have also been postulated to be involved in the pathogenesis in methanol intoxication (4-7). Methanol intoxication produces toxic injury to the retina and optic nerve, frequently resulting in blindness. A toxic exposure to methanol typically results in the development of formic acidemia, metabolic acidosis, visual toxicity, coma, and, in extreme cases, death (8, 9). Visual disturbances generally develop between 18 and 48 h after methanol ingestion and range from misty or blurred vision to complete blindness. Both acute and chronic methanol exposure have been shown to produce retinal dysfunction and optic nerve damage clinically (8-10) and in experimental animal models (11)(12)(13)(14).Formic acid is the toxic metabolite responsible for the retinal and optic nerve toxicity produced in methanol intoxication (4-7, 15). Formic acid is a mitochondrial toxin that inhibits cytochrome c oxidase, the terminal enzyme of the mitochondrial electron transport chain of all eukaryotes (16,17). Cytochrome oxidase is an important energy-generating enzyme critical for the proper functioning of almost all cells, especially those of highly oxidative organs, including the retina and brain (18). Previous studies in...

This review presents current research on the use of far-red to near-infrared (NIR) light treatment in variousin vitro and in vivo models. Low-intensity light therapy, commonly referred to as "photobiomodulation," uses light in the far-red to near-infrared region of the spectrum (630-1000 nm) and modulates numerous cellular functions. Positive effects of NIR-light-emitting diode (LED) light treatment include acceleration of wound healing, improved recovery from ischemic injury of the heart, and attenuated degeneration of injured optic nerves by improving mitochondrial energy metabolism and production. Various in vitro and in vivo models of mitochondrial dysfunction were treated with a variety of wavelengths of NIR-LED light. These studies were performed to determine the effect of NIR-LED light treatment on physiologic and pathologic processes. NIR-LED light treatment stimulates the photoacceptor cytochrome c oxidase, resulting in increased energy metabolism and production. NIR-LED light treatment accelerates wound healing in ischemic rat and murine diabetic wound healing models, attenuates the retinotoxic effects of methanol-derived formic acid in rat models, and attenuates the developmental toxicity of dioxin in chicken embryos. Furthermore, NIR-LED light treatment prevents the development of oral mucositis in pediatric bone marrow transplant patients. The experimental results demonstrate that NIR-LED light treatment stimulates mitochondrial oxidative metabolism in vitro, and accelerates cell and tissue repair in vivo. NIR-LED light represents a novel, noninvasive, therapeutic intervention for the treatment of numerous diseases linked to mitochondrial dysfunction.