title: Bystander effects induced by diffusing mediators after photodynamic stress.
abstract: The bystander effect, whereby cells that are not traversed by ionizing radiation exhibit various responses when in proximity to irradiated cells, is well documented in the field of radiation biology, Here we demonstrate that considerable bystander responses are also observed after photodynamic stress using the membrane-localizing dye deuteroporphyrin (DP). Using cells of a WTK1 human lymphoblastoid cell line in suspension and a transwell insert system that precludes contact between targeted and bystander cells, we have shown that the bystander signaling is mediated by diffusing species. The extranuclear localization of the photosensitizer used suggests that primary DNA damage is not the trigger for initiating these bystander responses, which include elevated oxidative stress, DNA damage (micronucleus formation), mutagenesis and decreased clonogenic survival. In addition, oxidative stress in the bystander population was reduced by the presence of the membrane antioxidant vitamin E in the targeted cells, suggesting that lipid peroxidation may play a key role in mediating these bystander effects. The fluence responses for these bystander effects are non-linear, with larger effects seen at lower fluences and toxicity to the target cell population. Hence, when considering outcomes of photodynamic action in cells and tissue, bystander effects may be significant, especially at sublethal fluences.
authors: Wellman Center for Photomedicine, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
authors: Asima
authors: A
authors: Chakraborty
authors: Kathryn D
authors: KD
authors: Held
authors: Kevin M
authors: KM
authors: Prise
authors: Howard L
authors: HL
authors: Liber
authors: Robert W
authors: RW
authors: Redmond
mesh_terms: D024201:Bystander Effect; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000528:radiation effects; D018920:Coculture Techniques; D004249:DNA Damage / Q000528:radiation effects; D003905:Deuteroporphyrins / Q000494:pharmacology*; D005453:Fluorescence; D006801:Humans; D008027:Light; D016296:Mutagenesis / Q000528:radiation effects*; D018384:Oxidative Stress / Q000187:drug effects / Q000528:radiation effects; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011837:Radiation-Protective Agents / Q000008:administration & dosage; D017382:Reactive Oxygen Species / Q000378:metabolism; D014810:Vitamin E / Q000008:administration & dosage
chemical_list: D003905:Deuteroporphyrins; D017319:Photosensitizing Agents; D011837:Radiation-Protective Agents; D017382:Reactive Oxygen Species; D014810:Vitamin E; C028839:deuteroporphyrin-IX