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“Our data show that at lower doses of ionizing radiation, DNA repair mechanisms work much better than at higher doses,” says Mina Bissell, a world-renowned breast cancer researcher with Berkeley Lab’s Life Sciences Division. “This non-linear DNA damage response casts doubt on the general assumption that any amount of ionizing radiation is harmful and additive.”
Bissell was part of a study led by Sylvain Costes, a biophysicist also with Berkeley Lab’s Life Sciences Division, in which DNA damage response to low dose radiation was characterized simultaneously across both time and dose levels. This was done by measuring the number of RIF, for “radiation induced foci,” which are aggregations of proteins that repair double strand breaks, meaning the DNA double helix is completely severed.
“We hypothesize that contrary to what has long been thought, double strand breaks are not static entities but will rapidly cluster into preferred regions of the nucleus we call DNA repair centers as radiation exposure increases,” says Costes. “As a result of this clustering, a single RIF may reflect a center where multiple double strand breaks are rejoined. Such multiple repair activity increases the risks of broken DNA strands being incorrectly rejoined and that can lead to cancer.”
Costes and Bissell have published the results of their study in the Proceedings of the National Academy of Sciences in a paper titled “Evidence for formation of DNA repair centers and dose-response nonlinearity in human cells.” Also co-authoring the paper were Teresa Neumaier, Joel Swenson, Christopher Pham, Aris Polyzos, Alvin Lo, PoAn Yang, Jane Dyball, Aroumougame Asaithamby, David Chen and Stefan Thalhammer.
is the term for generally favorable biological responses to low exposures to toxins and other stressors.
... hormesis is a dose response phenomenon characterized by a low dose stimulation, high dose inhibition, resulting in either a J-shaped or an inverted U-shaped dose response. Such environmental factors that would seem to produce positive responses have also been termed “eustress”.