The present study aimed to evaluate the interaction between wavelength of light in the range of ultra violet A-visible and concentration of H2O2 in the reaction of photolysis of H2O2 from the point of view of hydroxyl radical (·OH) generation and the bactericidal activity. Light emitting diodes (LEDs) emitting the light at wavelengths of 365, 385, 400 and 465 nm were used at an irradiance of 1000 mW/cm(2). H2O2 was used at the final concentrations of 0, 250, 500, and 1000 mM. Quantitative analysis of ·OH generated by the LED irradiation of H2O2 were performed using an electron spin resonance-spin trapping technique. In a bactericidal assay, a bacterial suspension of Staphylococcus aureus prepared in sterile physiological saline was irradiated with the LEDs. The bactericidal activity of each test condition was evaluated by viable counts. When H2O2 was irradiated with the LEDs, ·OH was generated and bacteria were killed dependently on the concentration of H2O2 and the wavelength of LED. The two-way analysis of variance revealed that the wavelength, the H2O2 concentration and their interaction significantly affected the yield of ·OH and the bactericidal activity of the photolysis of H2O2. Therefore, it is suggested that bactericidal activity of photolysis of H2O2 could be enhanced by controlling the wavelength and the concentration of H2O2, which may contributes to shortening the treatment time and/or to reducing the concentration of H2O2.

Our previous study showed that exposing mouse fibroblasts to proanthocyanidin (PA) for only 1 min accelerated cell proliferation in a concentration-dependent manner. In this study, exposing human gingival fibroblasts (HGFs) to PA for 1 min similarly accelerated the proliferative response of the cells. Besides the accelerated proliferative response, PA showed a cytoprotective effect on HGFs exposed to harsh environmental conditions; short-term exposure of HGFs in the mitotic phase to pure water or physiological saline resulted in a lower recovery of viable cells. Pretreatment and concomitant treatment with PA improved the low recovery of cells exposed to pure water or physiological saline. In addition, HGFs exposed to PA for 1 min proliferated well even after being cultured in serum-free medium. In 100% confluent HGFs, being cultured in serum-free medium resulted in a high intracellular reactive oxygen species (ROS) level, but pretreatment with PA prevented the cells from increasing intracellular ROS. Thus, the results suggest that a short-term PA treatment exerts cytoprotective effects on HGFs exposed to harsh environmental conditions by improving the intracellular oxidative stress response.