Photobiomodulation (PBM) is the term now used in place of what was once called low level laser therapy (LLLT). LLLT refers to a general invigoration of eukaryotic cells following exposure to low doses of red or near-infrared (NIR) electromagnetic radiation (“light”). It has been shown to reduce inflammation, prevent light-induced cell death, protect tissues against poisons, relieve pain and stimulate healing of tissues, stimulate nerve regeneration, and even ameliorate some cognitive decrements associated with traumatic brain injury. Many of the characteristic responses to low level light exposure involve cell proliferation but others (e.g., inflammation relief, nerve regeneration, and restoring cognitive function) do not, at least in principle. The physiological characteristics of PBM look very much like classical hormesis: only very low exposures create the effect, the response is biphasic, it invigorates cell metabolism, and can prevent cell death. Hormesis has been likened to a stress response, but it is unclear why cells respond to low level red light as if they are being stressed (unlike pharmaceutical approaches) as PBM has never been shown to have any deleterious side effects. Our research focuses on understanding the cellular physiology of this response in an effort to determine if this phenomenon can be exploited to improve protection and/or performance of military personnel.
We have shown that exposure to 2.88 J/cm2 of red light protects human retinal pigmented epithelium (hTERT-RPE) cells growing in vitro against the lethal effects of a pulse of 2 μm laser radiation. The increased resistance in hTERT-RPE cells correlates with changes in the expression of genes that control apoptosis, (Bax, Bcl-2, Bcl-xL, Hsp 70, caspase 8, caspase 9, FasL, and p53), growth factors (NF-κB, cyclin D, and VEGF-C), and increases oxygen soncumption rates, levels of nitric oxide (NO) and ATP. These changes are largely absent in a VEGF-C knockdown strain of these cells. An increase in the intracellular levels of nitric oxide (NO), an important signaling and regulatory molecule, following exposure to red light offers the best correlation between early events (i.e., while photons are being absorbed) and the "downstream" events already mentioned. One of the regulatory functions of NO is to stimulate soluble guanyl cyclase (sGC) to synthesize cGMP, a potent second messenger molecule. Using subcellular fractions we found that the NO increase in the cytosolic proteins is on par with the increase in the mitochondria fraction so it appears that red light can stimulate cellular nitric oxide synthase (NOS) enzymes (iNOS, eNOS, or nNOS), in addition to the long-postulated role of cytochrome c oxidase (Complex IV) in the electron transport chain of mitochondria. More recently, we found that mitochondria in whole cells can also synthesize NO, so mitochondria can be a significant NO source during red light exposure in these cells. The PBM effects are limited in both magnitude and time: the maximum effect is obtained at 2.88 J/cm2 and the response peaks at ~24 hr post-exposure then decays away. Since the response is biphasic, simply increasing the exposure is not effective. No response is seen in the cells after exposures of 1.44 or 5.76 J/cm2.
The goal of this research is to determine if it is possible to increase the magnitude (potentiate) and/or duration (prolong) of this effect. To do this we must understand the biochemical pathway from photon absorption to peak protein levels. Therefore, the effects of the absorption of light (600-900nm) on reduction/oxidation potentials in cells, the relative biological effectiveness (RBE) of different wavelengths (e.g. 637 vs. 810nm), effectiveness of pulsed versus. continuous wave expsures, DNA transcription, RNA translation, protein phosphorylation, cell cycle perturbations, oxidative phosphorylation, NO metabolism, cGMP, cAMP, reactive oxygen species (ROS), and the competing roles of apoptosis and necrosis are all of interest. The laboratory is located in a new building (completed spring 2011), offers extensive laser resources and support equipment, two tissue culture suites, flow cytometer, qRT-PCR, Luminex 200 system with xPONENT 3.1, Seahorse XF-24 extracellular flux analyzer, Tecan 200 Pro multiwell plate reader with gas control, Bio-Rad ChemiDoc with V3 Western Workflow System for Mini Gels, Stimulated Emission Depletion Confocal microscope, and a vivarium with full veterinary support.
da Silva JP, et al: Photomedicine and Laser Surgery 28(1): 17-21, 2010
Albarracin R, Eells J, Valter K: Investigative Ophthalmology & Vision Science 52: 3582-3592, 2011
Huang YY, et al: Dose-Response 9(4): 602-618, PMCID: PMC3315174, 2011
Hashmi JT, et al: Lasers in Surgery and Medicine 42(6): 450-466, doi:10.1002/lsm.20950, 2010
Wu Q, et al: Lasers in Surgery and Medicine 44(3): 218-226, doi:10.1002/lsm.22003, 2012
Sarti F, et al: Biochem Biophys Acta 1817(4): 610-9, doi:10.1016/j.bbabio.2011.09.002, 2012
Photobiomodulation; Low level red light; Apoptosis; Adaptive response; Retinal pigmented epithelium; Mitochondria; Nitric oxide; Reactive oxygen species; Cryptochromes;