Understanding Photobiomodulation and Red Light Therapy.

Red Light therapy is a modality of Low Level Light therapy (also known as photobiomodulation), which can be defined as the therapeutic use of red or near-infrared light to generate more energy, induce faster recovery and optimal performance. 

 A more in depth explanation would be:

Photobiomodulation (PBM), also known as Low-Level Light Therapy can be described as the use of non-ionizing electromagnetic energy (low-level photonic emissions typically within a specific wavelength range ~300-1000 nm) to trigger photochemical changes within cellular structures receptive to photons; the so-called photon-acceptors or photon-sensitive structures; which lead to stimulation or inhibition of cellular and biological processes. 

More specifically, PBM is a low risk, inexpensive treatment carried out with either low-level LASER (light amplification by stimulated emission of radiation) or light-emitting diodes (LEDs), that modulate cellular functions, such as proliferation and migration, resulting in tissue regeneration (Yu et al., 2019), wound healing, reduction of pain and inflammation (Cidral-Filho et al., 2013; Cidral-Filho et al., 2014, Martins et al., 2016), as well as a gamut of neurological indications (Caldieraro & Cassano, 2019). 

PBM has proven its efficiency in general medicine for more than 40 years, and is widely used in different medical settings ranging from dermatology, physiotherapy, and neurology to dentistry (Robijns et al., 2017), as well as to improve sports performance and reduce muscular fatigue (Vanin et al., 2018).

As for the mechanism (how does it work?)

When irradiated on the skin, the light beam undergoes two processes: 

Part of it is reflected and part of it penetrates into the tissue. 

Penetration depth is directly proportional to the wavelength, the nature of the tissue surface and the angle of incidence. The portion of light radiation that is not reflected, in turn, can undergo absorption or scattering. 

Scattering comprises any change in the direction of light beam propagation and depends on the wavelength of the incident beam and the characteristics of the receiving tissue. 

The remaining portion of light radiation is absorbed by photoreceptor or photoreceptor molecules that are excited or even change mechanical configuration through interaction with photons, due to their electronic or atomic configurations (NUSSBAUM & BAXTER , 2003).

Among the molecules capable of reacting with photons are amino acids, nucleic acids and chromophores. Amino acids and nucleic acids show significant absorption in the ultraviolet spectrum; chromophores, in turn, absorb light in the visible spectrum, the most common being hemoglobin and melanin (BAXTER, 2003), in addition to some components of the respiratory chain, especially cytochrome c-oxidase (complex IV of the mitochondrial respiratory chain) , which absorbs both visible and infrared radiation (Hamblim et al., 2018).

The interaction between the photo-acceptor molecule and the light beam results in the acceleration of electron transfer in the respiratory chain through a change in the oxidation-reduction properties of the transporters. A fraction of the excitation energy is converted into heat, with an increase in the local temperature of the chromophores. Such increment, in turn, can cause structural alterations in the photoreceptors and, thus, trigger biochemical reactions (NIEMZ, 2007).

Furthermore, certain photoreceptor molecules, such as porphyrins and flavoproteins, can be reversibly converted into photosensitized structures, with the generation of molecular oxygen (O2), which can play a mediating role in the biological effects of irradiation. Finally, there is the release of free radicals, such as superoxide (O2-) and hydrogen peroxide (H2O2), due to the reduction of oxygen in water at the end of the respiratory chain. 

Although mitochondria has a reabsorption mechanism for such radicals, these substances can trigger multiple secondary responses, as they constitute a source of electrons for ADP phosphorylation (KARU, 1989; KARU, 1999, Hanblim, 2018).

These main mechanisms that occur during exposure to light are followed by dark reactions (secondary mechanisms), which occur when the effective radiation is turned off. Thus, a complex cascade of cell signaling or photonic signal transduction and amplification begins, associated, for example, with changes in cell homeostasis, changes in ATP or cAMP levels, modulation of DNA and RNA synthesis, changes in membrane permeability , alkalinization of the cytoplasm and depolarization of the cell membrane (REDDY, 2004).

In summary, the effects triggered by the LIGHT-TISSUE interaction result in a series of essential physiological biochemical (mitochondrial) effects among which (Kim & Calderhead, 2011):

  • Increased ATP production - Increased Release of nitric oxide (NO) - Increased Very low levels of reactive oxygen species (ROS)
  • Increased Fibroblast proliferation and Collagen & elastin synthesis
  • Increased Mast cell degranulation: cytokine, chemokine and trophic factor release
  • Increased Macrophage activity (chemotaxis & internalization) leading to increased release of FGF
  • Increased Keratinocyte activity cytokine release in epidermis and dermis
  • Increased Opiate and non-opiate pain control (endorphins, dynorphins and enkephalins)
  • Increased RNA/DNA synthesis
  • Increased Enzyme production
  • Increased production of Superoxide dismutase (SOD) production

Bioelectric effects:

  • Increased Electromotive action on membrane bound ion transport mechanisms
  • Increased Intracellular extra-cellular ion gradient changes
  • Increased Depolarization of synaptic cleft and closure of synaptic gate
  • Increased Activation of the dorsal horn gate control mechanism with pain transmission slowed, and pain control increased

Bioenergetic effects:

  • Increased Rotational & vibrational changes to membrane molecule electrons
  • Increased Stimulation of acupuncture meridian points
  • Increased Increased biophotonic activity