Effects of photobiomodulation on the redox state of healthy and cancer cells

Photobiomodulation (PBM) uses light to stimulate cells. The molecular basis of the effects of PBM is being unveiled, but it is stated that the cytochrome-c oxidase enzyme in mitochondria, a photon acceptor of PBM, contributes to an increase in ATP production and modulates the reduction and oxidation of electron carriers NADH and FAD. As it can stimulate cells, PBM is not used on tumors. Thus, it is interesting to investigate if its effects correlate to mitochondrial metabolism and if so, how it could be linked to the optical redox ratio (ORR). To that end, fibroblasts and oral cancer cells were irradiated with a light source of 780 nm and a total dose of 5 J/cm 2 , and imaged by optical microscopy. PBM down-regulated the SCC-25 ORR by 10%. Furthermore, PBM led to an increase in ROS and ATP production in cancer cells after 4 h, while fibroblasts only had a modest ATP increase 6 h after irradiation. Cell lines did not show distinct cell cycle profiles, as both had an increase in G2/M cells. This study indicates that PBM shifts the redox state of oral cancer cells towards glycolysis and affects normal and tumor cells through distinct pathways. To our knowledge, this is the first study that investigated the effects of PBM on mitochondrial metabolism from the initiation of the cascade to DNA replication. This is an essential step in the investigation of the mechanism of action of PBM in an effort to avoid misinterpretations of a variety of combined protocols.