Bystander effects induced by diffusing mediators after photodynamic stress.

Area of Science:

• Cell Biology
• Radiation Biology
• Photodynamic Therapy

Background:

• The bystander effect is a known phenomenon in radiation biology, where cells near irradiated cells show adverse responses.
• This effect, previously documented for ionizing radiation, has not been extensively studied for other cellular stresses like photodynamic stress.

Purpose of the Study:

• To investigate whether photodynamic stress can induce bystander responses in cells.
• To elucidate the signaling mechanisms and key mediators involved in photodynamic-induced bystander effects.

Main Methods:

• Utilized a transwell insert system with WTK1 human lymphoblastoid cells to separate targeted and bystander cells, preventing direct contact.
• Applied photodynamic stress using deuteroporphyrin (DP) as a membrane-localizing photosensitizer.
• Assessed bystander responses including oxidative stress, DNA damage (micronucleus formation), mutagenesis, and clonogenic survival.

Main Results:

• Photodynamic stress induced significant bystander responses, including elevated oxidative stress, DNA damage, mutagenesis, and decreased clonogenic survival.
• Bystander signaling was mediated by diffusing species, and the extranuclear localization of the photosensitizer suggested primary DNA damage was not the trigger.
• Oxidative stress in bystander cells was mitigated by vitamin E in targeted cells, implicating lipid peroxidation in the bystander effect.

Conclusions:

• Photodynamic stress, like ionizing radiation, triggers significant bystander effects mediated by diffusing factors and potentially lipid peroxidation.
• These findings underscore the importance of considering bystander effects in the context of photodynamic actions, particularly at sublethal fluences.
• The non-linear fluence response suggests that lower doses may disproportionately activate these intercellular communication pathways.