Evaluation of laser-photobiomodulation different irradiation parameters on macrophages (RAW 264.7) inflammatory mediators' production.

Purpose: Macrophages are pivotal cells in the inflammatory process, and their functions can be modulated by laser irradiation. However, there is no consensus in the literature about Laser-photobiomodulation (L-PBM) parameters that are more suited to stimulate or inhibit them. The goal of this research is to contribute to the understanding of the effects of different L-PBM protocols on inflammatory mediators' production/inhibition and cell viability of macrophage cells in vitro.

Materials and methods: The macrophages cells (RAW 264.7) were divided into two groups: LPS-stimulated (Lipopolysaccharide from Escherichia coli) and non-LPS-stimulated. Each group was subdivided into non-irradiated and irradiated groups. The irradiated group was further divided into: 660 nm, 1 J, 10s; 660 nm, 2 J, 20s; 660, 3 J, 30s; 808 nm 1 J, 10s; 808 nm, 2 J, 20s; 808, 3 J, 30s groups. To all groups and subgroups, a negative (non-irradiated) group was added. All groups and subgroups were evaluated for cell viability, Nitric oxide (NO), interleukin-6 (IL-6) and Tumor Necrosis Factor- α (TNF-α) production.

Results: The results indicated that macrophages irradiated at 660 nm and 808 nm, operating in 1 J, 10s; 2 J, 20s and 3 J, 30s did not change NO, TNF-α and IL-6 production nor cell Viability in non-LPS groups. However, in LPS-stimulated macrophages, a significant stimulatory effect on NO production was observed after laser-irradiation with 660 nm for 2 J, 20s. This NO-stimulatory effect was not observed in the 880 nm irradiated group. LPS-activated macrophages and L-PBM irradiation at 660 nm and 808 nm also resulted in significant inhibitory effects on TNF-α and IL-6 production after 2 J, 20s irradiation. However, TNF-α and IL-6 inhibition using 1 J, 10s was achieved only in 660 nm group.

Conclusion: Our findings suggested that, if other parameters are fixed, time and related fluence/energy delivery are important dimensions to consider in L-PBM-production/inhibition on the inflammatory mediators tested. The NO synthesis was more prone to be modulated by a specific wavelength (660 nm) and a broader time-range inhibition of TNF-α and IL-6 was observed in 660 nm groups. Cell viability was not changed in any parameter tested.