Biphasic Dose Response in Low Level Light Therapy

Abstract

ᮀ The use of low levels of visible or near infrared light for reducing pain, inflammation and edema, promoting healing of wounds, deeper tissues and nerves, and preventing cell death and tissue damage has been known for over forty years since the invention of lasers. Despite many reports of positive findings from experiments conducted in vitro, in animal models and in randomized controlled clinical trials, LLLT remains controversial in mainstream medicine. The biochemical mechanisms underlying the positive effects are incompletely understood, and the complexity of rationally choosing amongst a large number of illumination parameters such as wavelength, fluence, power density, pulse structure and treatment timing has led to the publication of a number of negative studies as well as many positive ones. A biphasic dose response has been frequently observed where low levels of light have a much better effect on stimulating and repairing tissues than higher levels of light. The so-called Arndt-Schulz curve is frequently used to describe this biphasic dose response. This review will cover the molecular and cellular mechanisms in LLLT, and describe some of our recent results in vitro and in vivo that provide scientific explanations for this biphasic dose response.

Red LED Photobiomodulates the Metabolic Activity of Odontoblast-Like Cells

“…Therefore, since the dose-response effect varies according to the set of irradiation parameters (21), it may be suggested that a higher frequency of exposure of MDPC-23 cells to LED exceeded the threshold of biological tolerance of these cells, leading to a reduction in their metabolism. Previous studies that evaluated the bio-stimulatory effects of light sources have observed such biphasic effect (1,15,20). These studies have shown that the effect of light is not linear, being dependent on the frequency of application and energy doses.…”

“…It has been reported that the power density has a direct influence on the effect of light by the generation of a two-stage dose-response effect, in which inhibition of stimulatory effects is achieved when the threshold of energy received by the cell is exceeded (15,20). Therefore, since the dose-response effect varies according to the set of irradiation parameters (21), it may be suggested that a higher frequency of exposure of MDPC-23 cells to LED exceeded the threshold of biological tolerance of these cells, leading to a reduction in their metabolism.…”

“…The energy doses were selected by pilot studies, the chosen power densities were those most frequently found in the literature (15). The time needed to deliver 2 J/cm 2 using 20 mW/cm 2 power density was 1 min and 40 s, while the time using 40 mW/cm 2 was 50 s. The evaluated exposure frequencies were 1 or 3 consecutive irradiations, with an interval of 1 min between each.…”

The influence of low-level laser irradiation on spinal cord injuries following ischemia- reperfusion in rats

“…The therapeutic effects of LLLT have been reported, being associated with production of anti-apoptotic, pro-proliferative, antioxidant, and angiogenic factors [31][32][33] . LLLT also known as photobiomodulation, is an emerging therapeutic approach in which cells or tissues are exposed to low-levels of red and near-IR light.…”

Of diamond surfaces, red light photobiomodulation and fertility: lessons from the laboratory

“…Light at this wavelength is known to be absorbed by cytochrome C oxidase and other molecules, stimulating ATP synthesis and affecting ROS production, among numerous other activities at the cellular, tissue and whole organism level (16). The caveat however is that the light dose and dose rate are important and that all cell and tissues are not equally responsive to photoradiation (16)(17)(18)(19)(20)(21)(22).…”