Objective: The aim of this study was to evaluate the effects of 940-nm diode laser irradiation on proinflammatory cytokine secretions [interleukin (IL)-6 and IL-8] by human gingival fibroblasts in vitro. Background: Photobiomodulation has been routinely used in many dental procedures; however, the exact biological action mechanism of photobiomodulation and its therapeutic benefits have not been established. Methods: Cells derived from systemically healthy individuals were treated with three different laser parameters-6 J for 20 sec [0.84 J/cm2 (0.04 W/cm2)], 10 J for 20 sec [1.4 J/cm2 (0.07 W/cm2)], and 14 J for 20 sec [1.97 J/cm2 (0.09 W/cm2)]-in the presence and absence of 1 μg/mL lipopolysaccharide (LPS) stimulation. Laser irradiations were carried out by a 940-nm diode laser device in continuous pain therapy mode with a deep tissue handpiece. Changes in cell viability, cytokine secretions, and mitogen-activated protein kinase pathway expressions were investigated, and results were compared with negative (medium) and positive control (1 μg/mL LPS) groups. The data obtained were statistically analyzed by the Mann-Whitney U test for pairwise comparisons among groups at the 0.05 level of significance. Results: Laser therapy with 0.84-1.4 J/cm2 amplified IL-6 and IL-8 secretions, whereas 1.97 J/cm2 suppressed IL-6 and IL-8 release in LPS-stimulated cells. Cell viability did not show a variation with photobiomodulation. Conclusions: These results demonstrate that photobiomodulation can alter IL-6 and IL-8 release, with cytokine suppression potency at a relatively high dose, as demonstrated previously. However, in contrast, we found that a low level of stimulation (6 J) in the presence of inflammation (LPS stimulation) may further enhance IL-6 and IL-8 release. We also found that p38 and ERK1/2 pathways are activated by LPS as well as by photobiomodulation.
Keywords: cell culture; cytokines; dentistry; diode; lasers.