Photon absorption in the mitochondria: Potential immediate and early events associated with photobiomodulation

Abstract

Photobiomodulation (PBM) is a biological outcome of exposure to low-level light in the red and near-infrared (NIR) wavelengths. Current literature has attributed beneficial effects to PBM, to include improved wound healing, enhanced mitochondrial function, functional enhancements in patients suffering from stroke, and improved cognitive function in a murine model for traumatic brain injury. Cytochrome c oxidase, also named complex IV (C-IV) in the electron transport chain (ETC), is the expected primary chromophore for the red and NIR exposures. The direct evidence that PBM is a consequence of absorption by C-IV is incomplete. Recently, our lab has found metabolic perturbations in cells and isolated mitochondria from low-level exposures to blue and green light as well. To study the immediate and early events of PBM we used a combination of fluorescence microscopy, resonance Raman spectroscopy, Fourier transformed IR (FTIR) spectroscopy, and ultrafast transient absorption spectroscopy (TAS) on cells, isolated mitochondria, and purified ETC enzymes. In this paper, we show that FTIR spectroscopy is useful in determining substrate-dependent, steady-state rates of CO2 production by the tricarboxylic acid (TCA) cycle. The method allows for determinations of wavelength-specific changes in metabolic rate in real time with low-level light exposures. These data will help determine if any mitochondrial components have absorption spectra that correlate with the global PBM response in the literature.