Response to: Can Transdermal Photobiomodulation Help Us at the Time of COVID-19?

To the Editor,

It was with great interest that I read the letter to the editor entitled “Can Transdermal Photobiomodulation Help Us at the Time of COVID-19?” written by Domínguez et al.¹ I would like to congratulate Photobiomodulation, Photomedicine, and Laser Surgery and the authors for bringing up this subject at this time of great concern about human health.

Nevertheless, I feel it necessary to raise some points for consideration, relative to the references cited in the article.

Domínguez et al. cited some parts of a chapter from the book by Thais-Meneguzzo et al.² This is a chapter from the Handbook of Low-Level Laser Therapy edited by Michael R. Hamblin, Marcelo Victor Pires de Sousa, and Tanupriya Agrawal. The chapter entitled “Intravascular Laser Irradiation of Blood” (ILIB) does not intend to present research results produced by the authors, but made a great review about the theme. Thais-Meneguzzo and her collaborators listed a wide range of conclusions about wrist skin laser irradiation, also called modified ILIB (MILIB), but in some lines they wrote that, “these effects, however, have not been published yet.” The chapter was published in 2017 and up until 2020 no scientific article has been published with the scientifically proven benefits listed such as “improvement in sleep quality and emotional state, increased performance in sports, and enhanced physical and mental disposition in general.”

In the work of Szymczyszyn et al.,³ they used a 50 mW laser, 808 nm wavelength, and 20 J energy once a day for 3 consecutive days. Although the authors did not explain this in the article, this protocol may result in 6 min and 40 sec of laser application. Domínguez et al. recommended transdermal Photobiomodulation (PBM with a 30-min application per day for 3–5 days, using either visible or invisible diode laser. The authors did not explain other important parameters such as power (mW), energy (J), and specific wavelengths (nm). Moreover, the parameters differed completely from those in the listed reference.

Domínguez et al. reported that Szymczyszyn et al.³ concluded that the protocol used had a beneficial effect on the endothelium and blood flow. But Szymczyszyn et al.³ also concluded that ILIB produced no significant differences in levels of the vascular endothelial growth factor, fibroblast growth factor, symmetric dimethylarginine, and asymmetric dimethylarginine. They also found no significant differences in levels of the nitric oxide pathway metabolites within 24 h after the laser irradiation.

Domínguez et al. used Kut'ko et al.⁴ and Inoue et al.⁵ to claim that PBM used in the MILIB process improved the immune system. The article by Kut'ko et al.⁴ is published in Russian with an abstract in English. As I am not a Russian speaker, I could only read the abstract, in which they did not explain the parameters of the laser used in the study. Inoue et al.⁵ refer to a great research work presented by Japanese scientists. They concluded that the results indicated that local irradiation with a low-power laser has systemic inhibitory effects on delayed hypersensitivity reactions to tuberculin. The research was conducted with Guinea pigs, and is an animal study, the results of which cannot be directly transferred to a conclusion for a human protocol. Fujimaki et al.⁶ refer to an article also published by Japanese researchers. This research was conducted with isolated neutrophils and the authors concluded that attenuation of reactive oxygen species production by neutrophils may play a role in the effects of LLLT in the treatment of inflammatory tissues.⁶ They also suggested the possible use of LLLT to improve wound healing and recovery from surgery in cigarette smokers. In my opinion, those are weak references^4,5 to show that MILIB improves the immune system.

The other references were used to describe the mechanisms related to the increment in superoxide dismutase synthesis, as a result of this therapy, and to evaluate whether transdermal PBM could control the cytokine storm that may occur in patients with COVID-19. But none of these references are related to the use of PBM.^7–11

Although the COVID-19 pandemic has posed new challenges and new treatments should be developed to mitigate the consequences of this new disease, it is premature to indicate the use of ILIB in these cases. No one can deny that there is an urgent need for effective treatment of COVID-19, but many studies must be conducted to enable us to conclude that we can produce systemic effects using PBM in the MILIB technique. It has taken decades of demanding research to enable humanity to understand the local effects of PBM, and yet, we still do not know all the pathways involved in this marvelous technology.

The ILIB and MILIB need to be better studied and researched. Further investigations on the specific doses, wavelengths, and rate of light absorption by the irradiated blood vessels should be made.