Changes in Cytochrome C Oxidase Redox State and Hemoglobin Concentration in Rat Brain During 810 nm Irradiation Measured by Broadband Near-Infrared Spectroscopy

Abstract

Objective: The effects of 810 nm light-emitting diode (LED) photobiomodulation (PBM) on cerebral metabolism and cerebral hemodynamic were investigated by using a broadband near-infrared spectroscopy (bb-NIRS) under anesthesia conditions with isoflurane. Background data: PBM was supposed to increase cerebral hemodynamic and cerebral metabolism. There has been no study about the effect of 810 nm LED stimulation on cerebral hemodynamic and cerebral metabolism in vivo by using bb-NIRS measurement. Methods: PBM was applied to seven Sprague-Dawley rats at 50 mW/cm² power density. The changes in hemoglobin concentration ($\Delta \left(Hb{O}_2\right)$ and $\Delta \left(HHb\right)$) and oxidized cytochrome c oxidase (CCO) concentration ($\Delta \left(oxCCO\right)$) were measured using a bb-NIRS. The total hemoglobin and the difference in hemoglobin concentration changes were calculated by summation and difference of $\Delta \left(Hb{O}_2\right)$ and $\Delta \left(HHb\right)$, respectively. Results: PBM evoked the gradual increases of $\Delta \left(Hb{O}_2\right)$ (+7.7 μM vs. baseline, p = 0.008), $\Delta \left(HbT\right)$ (+9.5 μM vs. baseline, p = 0.0044), and $\Delta \left(HbD\right)$ (+5.9 μM vs. baseline, p > 0.05) during light stimulation. Meanwhile, $\Delta \left(oxCCO\right)$ (-3.5 μM vs. baseline, p = 0.0019) was significantly decreased right after the onset of stimulation. Conclusions: PBM with 810 nm LED (50 mW/cm²) increased cerebral oxygenation and blood volume as expected. However, oxidized CCO concentration was decreased, which was contrary to most previous studies. The two pathways of PBM effects on mitochondria and the inhibition of complex I by isoflurane were suggested to explain the decreased $\Delta \left(oxCCO\right)$ during PBM, but further study is required for the verification.

Keywords: 810 nm LED; bb-NIRS; cerebral hemodynamic; cerebral metabolism; photobiomodulation.