Low Level Laser Therapy Reduces the Development of Lung Inflammation Induced by Formaldehyde Exposure

Abstract

Lung diseases constitute an important public health problem and its growing level of concern has led to efforts for the development of new therapies, particularly for the control of lung inflammation. Low Level Laser Therapy (LLLT) has been highlighted as a non-invasive therapy with few side effects, but its mechanisms need to be better understood and explored. Considering that pollution causes several harmful effects on human health, including lung inflammation, in this study, we have used formaldehyde (FA), an environmental and occupational pollutant, for the induction of neutrophilic lung inflammation. Our objective was to investigate the local and systemic effects of LLLT after FA exposure. Male Wistar rats were exposed to FA (1%) or vehicle (distillated water) during 3 consecutive days and treated or not with LLLT (1 and 5 hours after each FA exposure). Non-manipulated rats were used as control. 24 h after the last FA exposure, we analyzed the local and systemic effects of LLLT. The treatment with LLLT reduced the development of neutrophilic lung inflammation induced by FA, as observed by the reduced number of leukocytes, mast cells degranulated, and a decreased myeloperoxidase activity in the lung. Moreover, LLLT also reduced the microvascular lung permeability in the parenchyma and the intrapulmonary bronchi. Alterations on the profile of inflammatory cytokines were evidenced by the reduced levels of IL-6 and TNF-α and the elevated levels of IL-10 in the lung. Together, our results showed that LLLT abolishes FA-induced neutrophilic lung inflammation by a reduction of the inflammatory cytokines and mast cell degranulation. This study may provide important information about the mechanisms of LLLT in lung inflammation induced by a pollutant.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1. Treatment with LLLT reduces cell recruitment in the blood (A) but did not alter the number of cells in the bone marrow after FA exposure.

Group of rats was exposed or not to FA inhalation (1%, 90 min/day, 3 days) and treated or not with LLLT (30mW, 1,8 J, 60s/point, total 540s, 1 and 5h post each FA inhalation). Non-manipulated rats were used to obtain basal parameters. The number of cells in the blood (panel A) and in the bone marrow (Panel B) was determined 24 h after the last FA inhalation. Data mean ± SD of 6 animals per group. *PθP<0.05 in relation to FA group.

Fig 2. Treatment with LLLT reduces neutrophilic lung inflammation after FA exposure.

Group of rats was exposed or not to FA inhalation (1%, 90 min/day, 3 days) and treated or not with LLLT (30mW, 1.8 J, 60s/point, total 540s, 1 and 5h post each FA inhalation). Non-manipulated rats were used to obtain basal parameters. The number of cells in the bronchoalveolar lavage (BAL) (panel A) and myeloperoxidase activity in the lung tissue (MPO) (Panel B) were determined 24 h after the last FA inhalation. Data mean ± SD of 6 animals per group. *PθP<0.05 in relation to FA group.

Fig 3. Treatment with LLLT reduces lung vascular permeability after FA exposure.

Group of rats was exposed or not to FA inhalation (1%, 90 min/day, 3 days) and treated or not with LLLT (30mW, 1.8 J, 60s/point, total 540s, 1 and 5h post each FA inhalation). Non-manipulated rats were used to obtain basal parameters. The lung vascular permeability in the parenchyma (A), trachea (B) and intrapulmonary bronchi (C) was assessed immediately after the last FA inhalation. Data are mean ± SD of 6 animals per group. *PθP<0.05 in relation to FA group.

Fig 4. Treatment with LLLT reduces TNF-alpha and IL-6 while increases IL-10 levels in the BAL fluid after FA exposure.

Group of rats was exposed or not to FA inhalation (1%, 90 min/day, 3 days) and treated or not with LLLT (30mW, 1.8 J, 60s/point, total 540s, 1 and 5h post each FA inhalation). Non-manipulated rats were used to obtain basal parameters. The evaluation of inflammatory cytokines TNF-alpha (A) and IL-6 (B) as well as anti-inflammatory IL-10 (C) in the supernatant of BAL fluid were determined 24 h after the last FA exposure. Data are mean ± SD of 6 animals per group. *PθP<0.05 in relation to FA group.

Fig 5. Treatment with LLLT increases IL-10 gene expression and did not alter IL-6 gene expression in the lung tissue after FA exposure.

Group of rats was exposed or not to FA inhalation (1%, 90 min/day, 3 days) and treated or not with LLLT (30mW, 1.8 J, 60s/point, total 540s, 1 and 5h post each FA inhalation). Non-manipulated rats were used to obtain basal parameters. The evaluation of gene expression of inflammatory cytokine IL-6 (A) and anti-inflammatory IL-10 (B) in the lung were determined 24 h after the last FA exposure. Data are mean ± SD of 6 animals per group. *PθP<0.05 in relation to FA group (Panel B).

Fig 6. Treatment with LLLT reduces leukocytes infiltration and mast cell degranulation in the lung tissue after FA exposure.

The airway inflammation induced by FA inhalation caused an intense cellular infiltration in the perivascular and peribrochiolar and mast cell activation in the lung parenchyma and pleura (arrows) (Panels C and D), whereas in the basal group, only resident leukocytes were observed and the mast cells were intact (arrowhead) (Panels A and B). Although, after the LLLT treatment, both cellular infiltration and mast cell activation were significantly reduced (Panels E and F).