Belyakov, O.V., Hall, E.J., Marino, S.A., Randers-Pehrson, G., Brenner, D.J. Columbia University, Irvington, NY.

According to the target theory of radiation-induced effects (1), a central tenet of radiation biology, DNA damage occurs during or very shortly after irradiation of the nuclei in targeted cells, and the potential for biological consequences can be expressed within one or two cell generations. A range of evidence has now emerged that challenges the classical effects resulting from targeted damage to DNA. These effects have also been termed “non-targeted” (2) and include radiation-induced bystander effects (3), genomic instability (4), adaptive response (5), low dose hyper-radiosensitivity (HRS) (6), delayed reproductive death (7) and induction of genes by radiation (8). An essential feature of “non-targeted” effects is that they do not require a direct nuclear exposure by irradiation to be expressed, and they are particularly significant at low doses. This evidence suggests a new paradigm for radiation biology that challenges the universality of target theory. The radiation-induced bystander effect is the phenomenon whereby cellular effects such as sister chromatid exchanges, chromosome aberrations, apoptosis, micronucleation, transformation, mutations, differentiation and changes of gene expression are expressed in unirradiated neighboring cells near to an irradiated cell or cells (9). The bystander effect cannot be comprehensively explained on the basis of a single cell reaction. It is well known that an organism is composed of different cell types that interact as functional units in a way to maintain normal tissue function. Radiation effects at the tissue level under normal conditions prove that individual cells cannot be considered as an isolated functional unit within most tissues of a multicellular organism (10). Experimental models, which maintain tissue-like intercellular cell signaling and 3-D structure, are essential for proper understanding of the bystander effect. Only a few papers have been published on bystander effects in multicellular system (11-15). With the exception of abscopal effects (16) and clastogenic factors in the blood plasma of patients undergoing radiation therapy (17), little evidence of a bystander effect under in-vivo conditions is available. The only experimental work which deals with the bystander effect under in-vivo conditions is from Watson and coauthors (18), who utilized a bone marrow transplantation protocol to demonstrate that genomic instability could be induced in bystander cells; a mixture of irradiated and non-irradiated cells, distinguished by a cytogenetic marker, was transplanted into CBA/H mice, and genomic instability was demonstrated in the progeny of the non-irradiated cells. Our rationale for the current project is that the bystander effect is likely to be a natural phenomenon, which should be studied in an in-vivo-like multicellular system with preserved 3-D tissue microarchitecture. This necessitates moving from purely in-vitro cell culture systems to a tissue based system for in situ microbeam irradiation, allowing us to study bystander effects in samples with preserved 3-D microarchitecture and an intact tissue microenvironment.


3-D tissue microarchitecture, Abscopal effects, Adaptive response, Apoptosis, Bystander cells, Bystander effects, Chromosome aberrations, Clastogenic factors, DNA damage, Delayed reproductive death, EpiAirway, EpiDerm, EpiOcular, Gene expression, Genomic instability, HRS, Hyper-radiosensitivity, Induction of genes by radiation, Ionizing, Irradiation, Microbeam, Microbeam irradiation, Micronucleation, Radiation biology, Radiation therapy, Radiation-induced bystander effect, Radiation-induced effects, Sister chromatid exchanges, Target theory, Tissue based system, Tissue microenvironment, Tissue-like intercellular cell signaling, Transformation

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