Relevance of radiation-induced bystander effects for environmental risk assessment.

A novel mechanism involving a medium borne signalling factor has been identified following irradiation of populations of cells to doses ranging from 5 mGy-5 Gy gamma-rays or to as little as 1 alpha particle traversal in a culture containing hundreds of cells. The factor can be released into culture medium and can induce responses in unexposed cultures. It has been called a "radiation-induced bystander factor". The effect is obviously relevant to risk assessment as it happens at very low doses. It could also offer new avenues for development of drugs aimed not at cell destruction but at restoring the tissues own control and coordination of response following DNA damage. The effect is clearly induced by radiation and probably by other substances. While these effects are now accepted to happen both in vitro and in vivo, their relevance and function is unknown. The investigation and modelling of the mechanism and the variation in level and type of effect in relation to genetic background and clinical history are key questions which need to be addressed in the field. The key driving hypothesis of the work being done by our laboratory is that radiation-induced bystander effects (RIBE) reflect emergent control in complex tissues and communicating cell systems, which can be harnessed for therapeutic gain.