Gamma-H2AX foci in cells exposed to a mixed beam of X-rays and alpha particles

Abstract

BackgroundLittle is known about the cellular effects of exposure to mixed beams of high and low linear energy transfer radiation. So far, the effects of combined exposures have mainly been assessed with clonogenic survival or cytogenetic methods, and the results are contradictory. The gamma-H2AX assay has up to now not been applied in this context, and it is a promising tool for investigating the early cellular response to mixed beam irradiation.PurposeTo determine the dose response and repair kinetics of gamma-H2AX ionizing radiation-induced foci in VH10 human fibroblasts exposed to mixed beams of 241Am alpha particles and X-rays.ResultsVH10 human fibroblasts were irradiated with each radiation type individually or both in combination at 37°C. Foci were scored for repair kinetics 0.5, 1, 3 and 24 h after irradiation (one dose per irradiation type), and for dose response at the 1 h time point. The dose response effect of mixed beam was additive, and the relative biological effectiveness for alpha particles (as compared to X-rays) was of 0.76 ± 0.52 for the total number of foci, and 2.54 ± 1.11 for large foci. The repair kinetics for total number of foci in cells exposed to mixed beam irradiation was intermediate to that of cells exposed to alpha particles and X-rays. However, for mixed beam-irradiated cells the frequency and area of large foci were initially lower than predicted and increased during the first 3 hours of repair (while the predicted number and area did not).ConclusionsThe repair kinetics of large foci after mixed beam exposure was significantly different from predicted based on the effect of the single dose components. The formation of large foci was delayed and they did not reach their maximum area until 1 h after irradiation. We hypothesize that the presence of low X-ray-induced damage engages the DNA repair machinery leading to a delayed DNA damage response to the more complex DNA damage induced by alpha particles.

Measurement of complex DNA damage induction and repair in human cellular systems after exposure to ionizing radiations of varying linear energy transfer (LET)

“…The existence of more than one DSB under a focus can be an issue for underestimation and the correct assignment of focus size can improve this situation but up to a point. The yields we found for low-LET (Figure 2) are compatible with previous findings of 10-20 DSB foci/Gy/cell [37,42,43] and the same stands also for a-particles [35,44,45] and Ar ions [46], although in the specific study 40 Ar ions of a much lower LET (125 keV/lm) were used. Previous studies using cold lysis PFGE protocols in order to minimize conversion of heat-labile sites to DSBs suggest relatively increased numbers of $25 DSBs/Gy/cell for normal human skin fibroblasts (GM5758) for low-LET radiations [47].…”

Impact of ATM and DNA-PK Inhibition on Gene Expression and Individual Response of Human Lymphocytes to Mixed Beams of Alpha Particles and X-Rays

“…Synergy was also detected at the level of 53BP1 foci and the activation of DNA repair proteins using human U2OS osteosarcoma cells [20] and as the hindered mobility of foci in mixed-beam-exposed cells as demonstrated by live cell imaging [21]. However, in certain cases, we observed the additivity of both radiation types: at the level of clonogenic cell survival in AA8 Chinese hamster ovary cells [25] and at the level of gamma-H2AX foci in human VH10 cells [26]. Several studies from other laboratories have also analysed the effect of mixed low-and high-LET radiation beams, some detecting synergism and other additivity (summarised in [13]), yet the reason for this variance is unclear.…”

The effects of chronic radiation of gamma ray on protein expression and oxidative stress inBrachypodium distachyon

“…Cells can be irradiated with sparsely ionizing X-rays and gamma rays (low-linear energy transfer [LET] radiation) or with densely ionizing alpha particles and heavy ions (referred to as high-LET radiation) (Staaf et al 2012). Ionizing radiation typically aff ects plant growth, development, and diff erentiation.…”