Evaluation of light and concentration dose on cell viability at photodynamic therapy in vitro

Photodyanmic Therapy is a promising and safe antmicrobial treatment that includes in a chemical agent, called a photosensitizer, which is activated by appropriate light energy and it results in production of reactive oxygen species (ROS) which have an important role in destroying the target cells. PDT dosimetry (light dose, photosensitizer dose and concentration of produced ROS) is very critical in the photoactivation process. Low concentration of oxygen radicals or low level light may cause cell proliferation with some biochemical pathways instead of the killing effect of antibacterial PDT. For this reason, there is a biostimulation risk during antibacterial PDT and optimization of PDT dose properly is very important to overcome the multidrug resistant bacteria problem on wounds. The main purpose of this study was to investigate the PDT safe region for bactericidal application and to demonstrate the importance of PDT dosimetry. In this study, PDT with different concentrations of indocyanine green (ICG) (20, 50, 100, 125, 150, 200 and 250μg/ml) and different doses of 809-nm diode laser (84, 168 and 252J/cm2) was investigated on Pseudomonas aeruginosa ATCC 27853 in vitro for PDT safe region. In this study, the cell proliferation of P. aeruginosa strain was observed instead of the PDT killing effect, when 84 J/cm2 of energy dose (809-nm diode laser) was applied with 20, 50, 100, 125 and 150 μg/ml of ICG concentrations. When we increase the energy doses with the same concentrations, at optimum higher concentrations, the PDT killing effect was significantly observed (150 μg/ml ICG with 168J/cm2 and 125 μg/ml ICG with 252 J/cm2). The results of experiments show that there could be biostimulation on pathogens if PDT dosimetry is not optimized properly.