Interaction of low and high LET radiation in TK6 cells—mechanistic aspects and significance for radiation protection

Abstract

Most environmental, occupational and medical exposures to ionising radiation are associated with a simultaneous action of different radiation types. An open question remains whether radiations of different qualities interact with each other to yield effects stronger than expected based on the assumption of additivity. It is possible that DNA damage induced by high linear energy transfer (LET) radiation will lead to an opening of the chromatin structure making the DNA more susceptible to attack by reactive oxygen species (ROS) generated by the low LET radiation. In such case, the effect of mixed beams should be strongly expressed in cells that are sensitive to ROS. The present investigation was carried out to test if cells with an impaired capacity to handle oxidative stress are particularly sensitive to the effect of mixed beams of alpha particles and x-rays. Clonogenic cell survival curves and mutant frequencies were analysed in TK6 wild type (wt) cells and in TK6 cells with a knocked down hMYH glycosylase. The results showed a synergistic effect of mixed beams on clonogenic cell survival of TK6 but not TK6 cells. The frequencies of mutants showed a high degree of interexperimental variability without any indications for synergistic effects of mixed beams. TK6 cells were generally more tolerant to radiation exposure with respect to clonogenic cell survival but showed a strong increase in mutant frequency. The results demonstrate that exposure of wt cells to a mixed beam of alpha particles and x-rays leads to a detrimental effect which is stronger than expected based on the assumption of additivity. The role of oxidative stress in the reaction of cells to mixed beams remains unclear.

Simultaneous induction of dispersed and clustered DNA lesions compromises DNA damage response in human peripheral blood lymphocytes

“…As suggested earlier [ 24 ], the interaction of alpha particles and X-rays can occur via various mechanisms. Firstly, it is possible that the action of both radiation types will lead to an increase of LET and, consequently, of DNA damage complexity.…”

“…They suggest that, per unit dose, the biological effect of mixed radiation beam may be higher than expected based on a simple sum of single doses coming from radiations of various qualities, even if these are multiplied by appropriate radiation weighting factors [ 40 ]. The impact of the finding on transfer of cancer risk among cohorts exposed to different radiation types has been extensively discussed in [ 24 ]. Here a short discussion is given on why the results may also be important for the medical use of radiation in IMRT and proton therapy.…”

“…Our experience does not allow drawing a decisive conclusion about whether this is the case. We observed synergism in PBL with cytogenetic damage as the endpoint [ 21 , 22 ], human lymphoblastoid TK6 (clonogenic cell survival) [ 24 ] and human bone osteosarcoma epithelial (U2OS) cells [ 25 , 39 ] (DNA repair foci). In contrast, we registered additivity in human VH10 cells [ 23 ] (DNA repair foci) and in AA8 Chinese hamster ovary cells [ 20 ] (clonogenic cell survival).…”

Live Dynamics of 53BP1 Foci Following Simultaneous Induction of Clustered and Dispersed DNA Damage in U2OS Cells

“…Since several years, we study the cellular effects in cells exposed to a mixed beam of alpha particles and X-rays [ 34 ]. Using different endpoints, we could show that alpha particles and X-rays interact to produce more DNA damage than expected from an additive action of the two radiation types [ 35 , 36 , 37 ]. More recently, we used U2OS cells which are stably transfected with a plasmid coding for the DNA repair gene 53BP1 coupled to a gene coding for the green fluorescent protein (GFP) [ 12 ] to analyse the induction and decay of 53BP1 foci [ 24 ].…”

Molecular Analysis of Carbon Ion-Induced Mutations in DNA Repair-Deficient Strains of Saccharomyces cerevisiae

“…In contrast, gamma ray-induced mutations were located uniformly throughout the marker gene. The damage induced by high-LET radiation opens the chromatin structure, making the DNA more susceptible to attack by Reactive Oxygen Ppecies (ROS) generated by low-LET radiation [30]. It was hypothesized that the non-uniform distribution of carbon-ion-induced mutations in the URA3 gene might be related to the nucleosome structure.…”