title: The role of reactive oxygen species in the antibacterial photodynamic treatment: photoinactivation vs proliferation.
abstract: Low-level light/low concentration of reactive oxygen species (ROS) may trigger some biochemical pathways that lead to cell proliferation. Thus, there is a risk of stimulation of bacterial cell proliferation during photodynamic therapy (PDT). In this study, PDT with different doses of 809-nm laser and indocyanine green (ICG) was investigated in vitro for safe bactericidal application. The combined effect of laser doses with ICG concentrations were examined on Pseudomonas aeruginosa in vitro. Data showed that low energy dose and ICG concentration caused bacterial cell proliferation. When these parameters were increased high enough, photoinactivation of the bacteria was achieved. Energy dose and photosensitizer concentration ranges at which proliferation, cell death or neither observed were determined. Furthermore, l-histidine was used as a scavenger of ROS to block the mechanism of biostimulation and cell killing. It inhibited proliferation when laser dose and ICG concentrations were low. It also inhibited cell killing when dose and concentration were high. Data showed that mechanisms of proliferation and cell killing depend on the amount of ROS and antibacterial photodynamic treatment have serious biostimulative risk. Effective range might need to be determined before any therapeutic usage. The risk seems to exist specifically at lower energy doses and photosensitizer concentrations.
  
  
  CONCLUSIONS
  The main purpose in antibacterial photodynamic therapy (PDT) is to kill the micro-organisms that cannot be destroyed by conventional methods. Low-level light and/or low concentration of reactive oxygen species may trigger some biochemical pathways that lead to cell proliferation. Thus, there is a risk of bacterial cell proliferation during PDT. In this study we report that PDT with ICG application can induce biostimulation when laser dose and photosensitizer concentration are not optimized properly. Therefore, optimum dosimetry in PDT possesses great importance in the treatment of wounds infected by antibiotic-resistant bacteria.
authors.affiliation: Institute of Biomedical Engineering, Bogazici University, Istanbul, Turkey.
authors.forename: N
authors.identifier: http://orcid.org/0000-0001-7001-8327
authors.initials: N
authors.lastname: Topaloglu
authors.affiliation: Institute of Biomedical Engineering, Bogazici University, Istanbul, Turkey.|Department of Biomedical Engineering, Istanbul Medeniyet University, Istanbul, Turkey.
authors.forename: M
authors.initials: M
authors.lastname: Guney
authors.affiliation: Institute of Biomedical Engineering, Bogazici University, Istanbul, Turkey.
authors.forename: N
authors.initials: N
authors.lastname: Aysan
authors.affiliation: Institute of Biomedical Engineering, Bogazici University, Istanbul, Turkey.
authors.forename: M
authors.initials: M
authors.lastname: Gulsoy
authors.affiliation: Molecular Biology and Genetics Department, Bogazici University, Istanbul, Turkey.
authors.forename: S
authors.initials: S
authors.lastname: Yuksel
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D049109:Cell Proliferation / Q000187:drug effects; D006639:Histidine / Q000494:pharmacology; D007208:Indocyanine Green / Q000494:pharmacology; D008027:Light; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D017319:Photosensitizing Agents; D017382:Reactive Oxygen Species; D006639:Histidine; D007208:Indocyanine Green
keywords: 809-nm diode laser; Gram-negative bacteria; antibacterial treatment; indocyanine green; photoinactivation; proliferation