Abstract
Photobiomodulation, also known as low-level laser/light therapy (LLLT), refers to the use of red-to-near-infrared light to stimulate cellular functions for physiological or clinical benefits. The mechanism of LLLT is assumed to rely on photon absorption by cytochrome c oxidase (CCO), the terminal enzyme in the mitochondrial respiratory chain that catalyzes the reduction of oxygen for energy metabolism. In this study, we used broadband near-infrared spectroscopy (NIRS) to measure the LLLT-induced changes in CCO and hemoglobin concentrations in human forearms in vivo. Eleven healthy participants were administered with 1064-nm laser and placebo treatments on their right forearms. The spectroscopic data were analyzed and fitted with wavelength-dependent, modified Beer-Lambert Law. We found that LLLT induced significant increases of CCO concentration (Δ[CCO]) and oxygenated hemoglobin concentration (Δ[HbO]) on the treated site as the laser energy dose accumulated over time. A strong linear interplay between Δ[CCO] and Δ[HbO] was observed for the first time during LLLT, indicating a hemodynamic response of oxygen supply and blood volume closely coupled to the up-regulation of CCO induced by photobiomodulation. These results demonstrate the tremendous potential of broadband NIRS as a non-invasive, in vivo means to study mechanisms of photobiomodulation and perform treatment evaluations of LLLT.
Highlights
Optical imaging approach to observe level laser/light therapy (LLLT)-induced up-regulation of CCO and its relationship with hemoglobin oxygenation in human forearms for better understanding and validation of photobiomodulation in vivo effects
Near-infrared spectroscopy (NIRS)[20] is a non-invasive and portable technology that can be used to probe biological and physiological states of living tissues based on the level of absorption and scattering of near-infrared light
To the best of our knowledge, this is the first study to assess the CCO enzyme up-regulation effects of photobiomodulation in human tissues in vivo. These results demonstrate the great potential of broadband NIRS (bb-NIRS) as a non-invasive technology for mechanistic studies and treatment evaluations of LLLT
Summary
Optical imaging approach to observe LLLT-induced up-regulation of CCO and its relationship with hemoglobin oxygenation in human forearms for better understanding and validation of photobiomodulation in vivo effects. While the actual implementation of this approach started more than 20 years ago[30,31], it had uncertainty on the accuracy of the methodology[29,32,33] It is only in recent years when bb-NIRS has been reported by numerous publications to be a reliable means for computing both cerebral hemoglobin and CCO concentration changes during brain activations[34,35,36] and/or brain injury[37,38]. The current study applied LLLT on human forearms using a 1064-nm laser and interleaved the bb-NIRS data acquisition in vivo for simultaneous assessment of interplay between photoactivation/up-regulation of CCO and alteration of hemoglobin oxygenation of the treated tissue
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