Revisiting the Photon/Cell Interaction Mechanism in Low-Level Light Therapy

Area of Science:

• Biophysics
• Cellular Biology
• Photomedicine

Background:

• Current low-level light therapy (LLLT) research often cites cytochrome c oxidase (CCO) as the primary absorber of red-to-near-infrared (R-NIR) light.
• This hypothesis suggests CCO's absorption of R-NIR photons drives mitochondrial adenosine triphosphate (ATP) upregulation and explains the therapeutic superiority of pulsed R-NIR light over continuous wave (CW) modes.

Purpose of the Study:

• To critically evaluate the existing evidence supporting CCO as the primary R-NIR light absorber in cells.
• To investigate the validity of the CCO hypothesis in explaining the enhanced therapeutic effects of pulsed R-NIR light in LLLT.
• To propose an alternative, conflict-free model for R-NIR light's biological effects.

Main Methods:

• Comprehensive literature review and rigorous analysis of published data on R-NIR light absorption by CCO.
• Systematic analysis of theoretical models linking CCO absorption to ATP upregulation and pulsed vs. CW light effects.
• Comparison of existing data with a newly proposed biophysical model.

Main Results:

• Significant inconsistencies were found in the literature supporting CCO as the primary R-NIR light absorber.
• The CCO-based hypothesis fails to coherently explain the superiority of pulsed R-NIR irradiation.
• A new, simpler model aligns with recent experimental findings and explains both ATP upregulation and pulsed light efficacy.

Conclusions:

• Cytochrome c oxidase is not the primary acceptor of R-NIR photons in cellular processes.
• The prevailing CCO hypothesis for LLLT mechanisms is not generally valid.
• A revised model offers a more consistent explanation for R-NIR light's biological impacts in LLLT.