Radioadaptive response revisited |
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Authors: | Soile Tapio Vesna Jacob |
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Institution: | (1) Department of Radiation Protection and Health, Federal Office for Radiation Protection, Ingolstaedter Landstrasse 1, 85764 Neuherberg, Germany;(2) GSF National Research Center for Environment and Health, Institute for Radiation Protection, Ingolstaedter Landstrasse 1, 85764 Neuherberg, Germany;(3) Present address: Klinikum rechts der Isar, TU München, Ismaninger Str. 22, 81675 München, Germany |
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Abstract: | Radiation-induced adaptive response belongs to the group of non-targeted effects that do not require direct exposure of the
cell nucleus by radiation. It is described as the reduced damaging effect of a challenging radiation dose when induced by
a previous low priming dose. Adaptive responses have been observed in vitro and in vivo using various indicators of cellular
damage, such as cell lethality, chromosomal aberrations, mutation induction, radiosensitivity, and DNA repair. Adaptive response
can be divided into three successive biological phenomena, the intracellular response, the extracellular signal, and the maintenance.
The intracellular response leading to adaptation of a single cell is a complex biological process including induction or suppression
of gene groups. An extracellular signal, the nature of which is unknown, may be sent by the affected cell to neighbouring
cells causing them to adapt as well. This occurs either by a release of diffusible signalling molecules or by gap-junction
intercellular communication. Adaptive response can be maintained for periods ranging from of a few hours to several months.
Constantly increased levels of reactive oxygen species (ROS) or nitric oxide (NO) have been observed in adapted cells and
both factors may play a role in the maintenance process. Although adaptive response seems to function by an on/off principle,
it is a phenomenon showing a high degree of inter- and intraindividual variability. It remains to be seen to what extent adaptive
response is functional in humans at relevant dose and dose-rate exposures. A better understanding of adaptive response and
other non-targeted effects is needed before they can be confirmed as risk estimate factors for the human population at low
levels of ionising radiation. |
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