title: Mechanisms and biological importance of photon-induced bystander responses: do they have an impact on low-dose radiation responses.
abstract: Elucidating the biological effect of low linear energy transfer (LET), low-dose and/or low-dose-rate ionizing radiation is essential in ensuring radiation safety. Over the past two decades, non-targeted effects, which are not only a direct consequence of radiation-induced initial lesions produced in cellular DNA but also of intra- and inter-cellular communications involving both targeted and non-targeted cells, have been reported and are currently defining a new paradigm in radiation biology. These effects include radiation-induced adaptive response, low-dose hypersensitivity, genomic instability, and radiation-induced bystander response (RIBR). RIBR is generally defined as a cellular response that is induced in non-irradiated cells that receive bystander signals from directly irradiated cells. RIBR could thus play an important biological role in low-dose irradiation conditions. However, this suggestion was mainly based on findings obtained using high-LET charged-particle radiations. The human population (especially the Japanese, who are exposed to lower doses of radon than the world average) is more frequently exposed to low-LET photons (X-rays or γ-rays) than to high-LET charged-particle radiation on a daily basis. There are currently a growing number of reports describing a distinguishing feature between photon-induced bystander response and high-LET RIBR. In particular, photon-induced bystander response is strongly influenced by irradiation dose, the irradiated region of the targeted cells, and p53 status. The present review focuses on the photon-induced bystander response, and discusses its impact on the low-dose radiation effect.
authors.affiliation: Radiation Safety Research Center, Central Research Institute of Electric Power Industry, 2-11-1 Iwado Kita, Komae, Tokyo 201-8511, Japan mstomita@criepi.denken.or.jp.
authors.forename: Masanori
authors.initials: M
authors.lastname: Tomita
authors.affiliation: Radiation Safety Research Center, Central Research Institute of Electric Power Industry, 2-11-1 Iwado Kita, Komae, Tokyo 201-8511, Japan Proton Medical Research Group, Research and Development Department, The Wakasa Wan Energy Research Center, 64-52-1 Nagatani, Tsuruga-shi, Fukui 914-0192, Japan.
authors.forename: Munetoshi
authors.initials: M
authors.lastname: Maeda
mesh_terms: D000818:Animals; D024201:Bystander Effect / Q000502:physiology* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D018499:Linear Energy Transfer / Q000502:physiology* / Q000528:radiation effects; D008954:Models, Biological; D017785:Photons; D011829:Radiation Dosage; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D016159:Tumor Suppressor Protein p53
keywords: X-rays; bystander response; low-dose radiation; microbeam; non-targeted effect