Contrasting biological responses of gingival fibroblasts and keratinocyte to blue and violet light irradiation: implications for photobiomodulation use in the therapeutic management of periodontal disease.

Blue light is known to possess anti-microbial activity and has subsequently been proposed as a prophylactic treatment for the management of periodontal diseases. This study investigated the effect of blue light on cells from the soft gingival tissues within the oral cavity, with particular focus on its influence on the regulation of intracellular reactive oxygen species (ROS) production. Primary human gingival fibroblasts (pHGFs) and keratinocytes (pHGKs) were irradiated with either 457nm blue light or with 415nm violet light, with fluences 3-90 J/cm(2) and cell viability was assessed. The influence of blue light on ROS production was measured using 2',7'-dichlorodihydrofluorescein diacetate assay, in the presence and absence of ROS scavenger, N-acetylcysteine. Gene expression for a range of antioxidant genes was quantified and expression changes evaluated by western blot analysis. Following irradiation with blue light, pHGFs displayed minor reductions in cell viability across the fluence range, while pHGK proliferation and metabolic activity was enhanced following irradiation. Significant cytotoxic effects were seen in cells irradiated with violet light. Treatment of pHGFs with blue light induced significant ROS generation, which was inhibited by N-acetylcysteine. Only non-significant increases in antioxidant gene expression were identified for NQO1, GSR, GSS and KEAP1, in response to 36 and 60 J/cm2 doses. No corresponding changes in their corresponding protein levels were evident. Irradiation of gingival cells with 457 nm blue light produced negligible detrimental effects. Although ROS increased, this paper discusses how endogenous antioxidant defence mechanisms are sufficient to control any potential detrimental effects.