Ionizing radiation bystander effect

Radiation-induced genomic instability and bystander effects are now well-established consequences of exposure of living cells to ionizing radiation. Cells not directly traversed by radiation may still exhibit radiation effects. This phenomenon, known as bystander effect, has become a major activity in radiation biology and in some cases has challenged the conventional wisdom. An example is the currently accepted models used for low-dose extrapolation of radiation risks. The currently used models assume that cells in an irradiated population respond individually rather than collectively. If bystander effects have implications for health risks estimates from exposure to ionizing radiation, then the question of whether this is a general phenomenon or solely a characteristic of a particular type of cell and the radiation under test becomes an important issue. 

It is seen from this table that, at the LD50 level, the nucleus has received about the same dose, irrespective of whether X-rays, 3H-dThd or 125I-concanavalin are used as the source of ionizing radiation, while the membrane has received an immense dose with 125I-concanavalin and very little with 3H-dThd. As expected, the cytoplasm lies in between these two extremes. Yet, irradiation of the cytoplasm (single-ion-beam experiments) is not without an effect. It may cause mutations (Wu et al. 1999) and the formation of products that induce apoptosis in nearby (unirradiated) cells (bystander effect Shao et al. 2004). 

Greene-Schloesser, D., Robbins, M.E., 2012. Radiation-induced cognitive impair-ment-from bench to bedside. Neuro Oncol. 14 (Suppl. 4), iv37-iv44. Hamada, N., Maeda, M., Otsuka, K., et al., 2011. Signaling pathways underpinning the manifestations of ionizing radiation-induced bystander effects. Curr. Mol. Pharmacol. 2, 79-95. 

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