Radiation induced bystander effects

Full text: In recent years, radiation induced bystander effects have been reported in cells which were not themselves irradiated but were either in the vicinity of irradiated cells or exposed to medium from irradiated cells. The effects have been clearly shown to occur both in vivo and in vitro. This work has led to a paradigm shift in radiobiology over the last 5-10 years. The target theory of radiation induced effects is now being challenged because of an increasing number of studies which demonstrate non (DNA)-targeted effects. These effects appear to be particularly important at low doses. Considerable evidence now exists relating to radiation induced bystander effects but the mechanisms involved in the transduction of the signal are still unclear. Cell-cell communication through gap junctions and/or secretion of a cytotoxic factor into the medium are thought to be important in both mechanisms. Signalling pathways leading to apoptosis, such as calcium, MAP kinase, mitochondrial and reactive oxygen species (ROS) signaling are shown. The importance of oxidative metabolism and calcium signaling in bystander responses are demonstrated. Further investigations of these signalling pathways may aid in the identification of novel therapeutic targets