Some Effects of Hypothermia and Hypoxia on the Sensitivity of HeLa Cells to X-rays

Summary

In vivo studies on the alterations in radio-sensitivity produced in hypothermic mammals do not enable a distinction to be drawn between the effects of hypothermia per se and the concomitant hypoxia.

The present experiments on the radio-sensitivity of mammalian (HeLa) cells in vitro have permitted observations to be made on the separate effects of hypoxia and hypothermia.

It is concluded that, whereas hypoxia produces a decrease in radio-sensitivity, hypothermia produces no detectable change.     

A role for p53 in the response of bystander cells to receipt of medium borne signals from irradiated cells

Abstract

Purpose: A number of contradictory studies have reported a role or not for p53 (protein 53) in the production of radiation-induced bystander effects. Most of these studies looked at a range of cell lines with normal or compromised p53 function.

Methods: In this study, Human Colon Tumour line 116 (HCT 116) cells with confirmed wild type p53 function and a corresponding p53 null HCT 116 line were used to test for bystander signal production and response to bystander signals in a mix/match protocol using the medium transfer technique.

Results: The results showed that both the null cells and the wild type cells produced bystander signals. However, only the p53 wild type cells responded to signals from either cell line. The Human Papilloma Virus transfected keratinocyte line G (HPV-G) reporter cell line used routinely in our laboratory was used to confirm that the null cells were producing signals.

Conclusions: We conclude that in this system the p53 pathway is involved in response of cells to bystander signals but that signals can be produced by cells which do not have functional p53. If these results apply in vivo, they could be important in radiotherapy where tumours may have compromised p53 function but surrounding (and distant) normal tissue may have wild type functional p53.     

Chemical Steps Involved in the Production of Mutations and Chromosome Aberrations by X-irradiation in Drosophila

Summary

Post-treatment with hydrocyanic acid results in a significant increase of the mutation frequency in spermatids, if x-radiation is delivered at a high dose-rate, but not after irradiation at a low dose-rate. A greater overall genetic effect of intensity per se has not been observed.

Following radiation at both low and high intensities, post-treatment with cyanide increases the frequency of translocations in spermatids. Consequently, it has been inferred that cyanide causes a prolonged opening of chromosome breaks in spermatids and thus favours the formation of translocations.

Both this finding and the fact that cyanide post-treatment also raises the mutation rate in a ring-shaped chromosome suggest that the increase in lethal frequency due to post-treatment refers not only to position-effect lethals but also to gene mutations and possibly small deletions.

Data relating differential sensitivity in successive broods to oxygen tension are presented. Post-treatment with cyanide is equally effective in raising the mutation rate if high-intensity radiation is given in pure N₂, as in O₂.

It is assumed that cyanide inhibits a mechanism responsible for repair of the initial radiation damage. Recovery from changes leading to lethal gene mutations then seems a metabolic process, possibly connected with respiratory energy. Injury to this repair system is independent of oxygen tension, and the reparable fraction of the initial damage after radiation in N₂ is equal to that after radiation in O₂.     

The effect of genetic background and dose on non-targeted effects of radiation

Abstract

Purpose: This work investigates the hypothesis that genetic background plays a significant role in the signalling mechanisms underlying induction and perpetuation of genomic instability following radiation exposure.

Materials and methods: Bone marrow from two strains of mice (CBA and C57) were exposed to a range of X-ray doses (0, 0.01, 0.1, 1 and 3 Gy). Different cellular signalling endpoints: Apoptosis, cytokine levels and calcium flux, were evaluated at 2 h, 24 h and 7 d post-irradiation to assess immediate and delayed effects.

Results: In CBA (radiosensitive) elevated apoptosis levels were observed at 24 h post X-irradiation, and transforming growth factor-β (TGF-β) levels which increased with time and dose. C57 showed a higher background level of apoptosis, and sustained apoptotic levels 7 days after radiation exposure. Levels of tumor necrosis factor-α (TNF-α were increased in C57 at day 7 for higher X-ray doses. TGF-β levels were higher in CBA, whilst C57 exhibited a greater TNF-α response. Calcium flux was induced in reporter cells on exposure to conditioned media from both strains.

Conclusions: These results show genetic and dose specific differences in radiation-induced signalling in the initiation and perpetuation of the instability process, which have potential implications on evaluation of non-targeted effects in radiation risk assessment.     

Effects of 36.6 GHz and static magnetic field on degree of endoreduplication in Drosophila melanogaster polytene chromosomes

Purpose To study the effect of microwave (MW) irradiation and consistent action of microwaves and static magnetic field (MF) on the giant chromosomes endoreduplication in Drosophila melanogaster Meig.

Materials and methods Experiments were carried out on inbred wild type Canton-S strain. Exposure to microwaves (frequency – 36.64 GHz, power density – 1 W/m², exposure time – 30 sec) and static magnetic field (intensity – 25 mT, exposure time – 5 min) applied at the egg stage after a 2-h oviposition. Giant chromosomes were investigated in squashed preparations of the salivary glands stained by acetoorcein by the cytomorphometric method. Preparations were obtained from Drosophila larvae at the 0 h prepupae stage.

Results Exposure to microwaves increased the degree of polyteny in chromosomes (DPC) by 7.5%, and the statistical power of the impact was: h²?=?35.3%. A similar effect occurred after the sequential action of microwaves and static magnetic field: The polyteny level of chromosomes increased by 7.4%, statistical power was: h²?=?30.6%.

Conclusions Exposure to microwaves on the stage of embryogenesis has a stimulating effect on endoreduplication in Drosophila development. The effect of microwaves was not modified by the action of the static magnetic field.     

The Effect of Cysteamine on the Radiosensitivity of the Haemopoietic System of Severely Hypoxic Mice

In an attempt to determine whether the thiols alter the radiosensitivity of mammalian cells over and above that produced by the oxygen-effect, the radioprotection afforded by cysteamine to the haemopoietic tissues of severely hypoxic mice has been studied.

The mice were maintained in a state of profound hypoxia during irradiation by keeping them at body temperatures of 0 to 1°c.

Damage was assessed five days after irradiation on total leucocyte counts and histological examination of the spleen and femoral bone marrow.

On comparison with other experimental results, the difference between the protection given by the combination of severe hypoxia and cysteamine and by severe hypoxia alone, was of doubtful significance. It was concluded that cysteamine acts mainly through oxygen-dependent pathways.     

Alpha-tocopherol succinate-mobilized progenitors improve intestinal integrity after whole body irradiation

Abstract

Purpose: The objective of this study was to elucidate the action of α-tocopherol succinate (TS)- and AMD3100-mobilized progenitors in mitigating radiation-induced injuries.

Material and methods: CD2F1 mice were exposed to a high dose of radiation and then transfused intravenously with 5 million peripheral blood mononuclear cells (PBMC) from TS- and AMD3100-injected mice after irradiation. Intestinal and splenic tissues were harvested after irradiation and cells of those tissues were analyzed for markers of apoptosis and mitosis. Bacterial translocation from gut to heart, spleen, and liver in TS-treated and irradiated mice was evaluated by bacterial culture.

Results: We observed that the infusion of PBMC from TS- and AMD3100-injected mice significantly inhibited apoptosis, increased cell proliferation in the analyzed tissues of recipient mice, and inhibited bacterial translocation to various organs compared to mice receiving cells from vehicle-mobilized cells. This study further supports our contention that the infusion of TS-mobilized progenitor-containing PBMC acts as a bridging therapy by inhibiting radiation-induced apoptosis, enhancing cell proliferation, and inhibiting bacterial translocation in irradiated mice.

Conclusions: We suggest that this novel bridging therapeutic approach that involves the infusion of TS-mobilized hematopoietic progenitors following acute radiation injury might be applicable to humans as well.     

Induction of lethal bystander effects in human breast cancer cell cultures by DNA-incorporated Iodine-125 depends on phenotype

Abstract

Purpose: This study uses a three-dimensional cell culture model to investigate lethal bystander effects in human breast cancer cell cultures (MCF-7, MDA-MB-231) treated with ¹²⁵I-labeled 5-iodo-2 -deoxyuridine (¹²⁵IdU). These breast cancer cell lines respectively form metastatic xenografts in nude mice in an estrogen-dependent and independent manner.

Materials and methods: In the present study, these cells were cultured in loosely-packed three-dimensional architecture in a Cytomatrix? carbon scaffold. Cultures were pulse-labeled for 3 h with ¹²⁵IdU to selectively irradiate a minor fraction of cells, and simultaneously co-pulse-labeled with 0.04 mM 5-ethynyl-2′-deoxyuridine (EdU) to identify the radiolabeled cells using Click-iT^® EdU and flow cytometry. The cultures were then washed and incubated for 48 h. The cells were then harvested, serially diluted, and seeded for colony formation. Aliquots of cells were subjected to flow cytometry to determine the percentage of cells labeled with ¹²⁵IdU/EdU. Additional aliquots were used to determine the mean ¹²⁵I activity per labeled cell. The percentage of labeled cells was about 15% and 10% for MCF-7 and MDA cells, respectively. This created irradiation conditions wherein the cross-dose to unlabeled cells was small relative to the self-dose to labeled cells. The surviving fraction relative to EdU-treated controls was measured.

Results: Survival curves indicated significant lethal bystander effect in MCF-7 cells, however, no significant lethal bystander effect was observed in MDA-MB-231 cells.

Conclusions: These studies demonstrate the capacity of ¹²⁵IdU to induce lethal bystander effects in human breast cancer cells and suggest that the response depends on phenotype.     

A laboratory inter-comparison of the importance of serum serotonin levels in the measurement of a range of radiation-induced bystander effects: Overview of study and results presentation

Abstract

Purpose: Recent research has suggested that serotonin may play an important role in the expression of radiation-induced bystander effects. Serotonin levels in serum were reported to range from 6–22 μM and to correlate inversely with the magnitude of cellular colony-forming ability in medium transfer bystander assays. That is, high serotonin concentration correlated with a low cloning efficiency in cultures receiving medium derived from irradiated cells.

Methods: Because of the potential importance of this observation, the European Union's Non-targeted Effects Integrated Project (NOTE) performed an inter-comparison exercise where serum samples with high and low serotonin levels were distributed to seven laboratories which then performed their own assay to determine the magnitude of the bystander effect.

Results: The results provided some support for a role for serotonin in four of the laboratories. Two saw no difference between the samples and one gave inconclusive results. In this summary paper, full data sets are presented from laboratories whose data was inconclusive or insufficient for a full paper. Other data are published in full in the special issue.

Conclusion: The data suggest that there may be multiple bystander effects and that the underlying mechanisms may be modulated by both the culture conditions and the intrinsic properties of the cells used in the assay.     

On the structure of thorium and americium adenosine triphosphate complexes

Abstract

Purpose: The actinides are chemical poisons and radiological hazards. One challenge to better appraise their toxicity and develop countermeasures in case of exposure of living organisms is to better assess pathways of contamination. Because of the high chemical affinity of those actinide elements for phosphate groups and the ubiquity of such chemical functions in biochemistry, nucleotides and in particular adenosine triphosphate nucleotide (ATP) may be considered critical target building blocks for actinides.

Materials and methods: Combinations of spectroscopic techniques (Fourier transformed Infra Red [FTIR], Electrospray Ionization Mass Spectrometry [ESI-MS], and Extended X-ray Absorption Fine Structure [EXAFS]) with quantum chemical calculations have been implemented in order to assess the actinides coordination arrangement with ATP.

Results: We describe and compare herein the interaction of ATP with thorium and americium; thorium(IV) as a representative of actinide(IV) like plutonium(IV) and americium(III) as a representative of all heavier actinides. In the case of thorium, an insoluble complex is readily formed. In the case of americium, a behavior identical to that described previously for lutetium has been observed with insoluble and soluble complexes.

Conclusions: The comparative study of ATP complexation with Th(IV) and Am(III) shows their ability to form insoluble complexes for which a structural model has been proposed by analogy with previously described Lu(III) complexes.     

Models of the radiation-induced bystander effect

Abstract

Purpose: To implement quantitative models of the Radiation-Induced Bystander Effects (RIBE) based on cellular excitation at a rate proportional to the concentration of signal molecules (called signals here) released by irradiated cells. Clonogenic cell survival and transformation frequency as a function of rescue time and dose were considered.

Materials and methods: Our first stochastic model was based on the hypothesis that chemical signals are released into the extracellular medium by irradiated cells. These signals act on unirradiated cells switching them from the healthy to the dead state at rate R(t). We extended this model including a non-lethal transformed state in order to describe clonogenic cell survival and transformation frequency as a function of the number of alpha particles.

Results: The first stochastic model was applied to an experiment on human keratinocyte (HaCat) cells yielding the half-life of at least one signal among the ensemble of possible candidates to trigger cell death in this cell culture. The second model yielded good fits to the data on clonogenic cell survival and transformation frequency in microbeam experiments with mouse embryo (C3H10T_1/2) cells (Sawant et al. 2001a, 2001b).

Conclusions: The fit of the first stochastic model to HaCat cell survival yielded a half-life of the order of minutes for possible signal candidates. This model also furnished the variance of the fraction of surviving cells.     

Role of Nrf2-antioxidant in radioprotection by root extract of Inula racemosa

Abstract

Purpose: Inula racemosa, a Trans-Himalayan plant is an important medicinal herb. In this study, the radio-modulatory efficacy of aqueous root extract of I. racemosa was investigated.

Materials and methods: Normal Kidney Epithelium cells were treated with extract (50–200?μg/ml) and exposed to 3?Gy of γ-radiation, while C57BL/6 mice were administered with extract (300–600?mg/kg BW) intraperitoneally prior to exposure to 7.5?Gy of γ-radiation to assess radiation modulatory efficacy.

Results: The administration of extract (30?min and 1?h) prior to radiation exposure improved the survival of NKE cells (as measured by proliferation), restored MMP and ROS levels as compared to radiation-exposed alone cells. These cells showed up-regulated Nrf2 protein levels at 7?h and increased expression of HO-1 and NOQ1 protein at 24?h In mice, the 30 days whole body survival study demonstrated that extract pre-treatment increases survival or delays the onset of radiation-induced mortality as against 70% mortality of 7.5?Gy of γ-radiation.

Conclusions: The aqueous extract of roots of I. racemosa enhanced the survival of irradiated NKE cells and rescued C57BL/6 mice against WBI-induced mortality. The radiation modulation efficacy was mediated through cumulative activation of HO-1 and NQO1 downstream of Nrf2 translocation in NKE cells.

Abbreviations:

ARE: Antioxidant Response Element; FITC: Fluorescein isothiocyanate; GCS: Glutamylcysteine synthase; HO-1: Heme oxygenase-1; LPS: Lipopolysacharide; MRP: Multidrug Resistance-Associated Proteins; NQO1: NAD(P)H Quinone Dehydrogenase 1; NRH: Quinone Oxidoreductase 2 (NQO2); PBS: Phosphate Buffer Saline; PKA: Protein Kinase A; PKC: Protein Kinase C; PI3-kinase: Phosphatidylinositol 3-Kinase; SRB: Sulforhodamine B; UV: Ultra-Violet radiation     

The role of serotonin and p53 status in the radiation-induced bystander effect

Abstract

Purpose: The aim of this study was to investigate the role of serotonin and protein 53 (p53) status of the cells in the radiation-induced bystander effects (RIBE).

Materials and methods: The radiation-induced bystander response was investigated in human MCF-7 breast cancer cells and human HCT116 colorectal cancer cells employing medium-transfer experiments and micronuclei (MN) induction as an end-point. Irradiated cell conditioned medium (ICCM) from cells exposed to α-particle or γ-radiation was filtered and transferred to unirradiated cells 2 h following irradiation. MCF-7 cells were irradiated with 0.5 Gy α-particles, while HCT116 p53^+/+ and HCT116 p53^?/? cells were irradiated with 0.5 Gy γ-radiation.

Results: Bystander MCF-7 cells, recipient of ICCM from 0.5 Gy α-particle irradiated MCF-7 cells grown in high serotonin conditions showed a modest but significant increase in MN, while MCF-7 cells receiving ICCM with low serotonin levels did not show any bystander effect. Added serotonin (100 ng/ml) led to a bystander effectin HCT116 p53^?/? cells recipient of ICCM from 0.5 Gy γ-irradiated HCT116 p53^+/+ cells, but had no effect when the ICCM was from γ-irradiated HCT116 P53^?/? cells.

Conclusion: The results indicate that serotonin levels in the medium play a role in the RIBE and that there may be an interaction between the role of serotonin and the p53 status of the irradiated cells.     

Protection of Tissue-culture Cells against Ionizing Radiation

Summary

1. Using a plating technique of tissue-culture cells, as developed by Puck, an investigation was done to discover whether the radioprotective action of cysteamine could be explained by means of a hypoxia caused by its autoxidation, or whether another protective mechanism at the cellular level was involved.

2. The protective activity of a 4 and a 16 mM cysteamine solution and of anoxia is expressed by dose-reduction factors (DRF) of 1·9, 3·3 and 2·6, respectively. Under anoxic conditions the application of 4 and 16 mM cysteamine solutions resulted in a protection characterized by DRF's of 3 and 3·95. Since a high concentration of cysteamine provided a better protection than anoxia, and cysteamine gave an additional protection under anoxic conditions, it was concluded that the protective action of cysteamine cannot be explained by a hypoxia caused by its autoxidation.

3. Experiments were devised to obtain an intensive contact between air and a thin layer of a cysteamine solution to exclude the possibility of hypoxia. Chemical measurements indicated that cysteamine under this condition is oxidized rather quickly. The protective action of cysteamine in these experiments had a value that might be expected to be produced by the residual concentration of cysteamine present during irradiation.

4. Two hypotheses providing an explanation for the protective action of cysteamine at the cellular level are discussed.     

Cell inactivation by combined low dose-rate irradiation and intermittent hypoxia

Abstract

Purpose: To investigate in detail the earlier observed combined effect of low dose-rate β-irradiation delivered at a dose-rate of 15 mGy/h and continued intermittent hypoxia that leads to extensive cell death after approximately 3–6 weeks.

Material and methods: Continuous low dose-rate β-irradiation at a dose rate of 15, 1.5 or 0.6 mGy/h was given by incorporation of [³H]-labelled valine into cellular protein. The cells were cultivated in an atmosphere with 4% O₂ using an INVIVO₂ hypoxia glove box. Clonogenic capacity, cell-cycle distribution and cellular respiration were monitored throughout the experiments.

Results: After 3–6 weeks most cells died in response to the combined treatment, giving a surviving fraction of only 1–2%. However, on continued cultivation a few cells survived and restarted proliferation as the cellular oxygen supply increased with the reduced cell number. Irradiating the T-47D cells grown in an atmosphere with 4% O₂ at dose-rates 10 and 25 times lower than 15 mGy/h did not have a pronounced effect on the clonogenic capacity with surviving fractions of 60–80%.

Conclusions: Treatment of T-47D cells with low dose-rate β-irradiation leads to a specific effect on intermittent hypoxic cells, inactivating more than 98% of the cells in the population. Given improved oxygen conditions, the few surviving cells can restart their proliferation.     

Disruption of Hif-1α enhances cytotoxic effects of metformin in murine squamous cell carcinoma

Purpose: In the present study, we investigated whether the disruption of the Hif-1α gene affects the sensitivity of SCC VII cells to metformin and also if metformin functions as a radiosensitizer using murine squamous cell carcinoma (SCC VII) cells.

Materials and methods: Cultured SCC VII and SCC VII Hif-1α-deficient cells were incubated with metformin under glucose-free and/or hypoxia-mimetic conditions and cell viabilities were measured. Tumor-bearing mice were continuously given 5-bromo-2’-deoxyuridine (BrdU) to label all proliferating cells. Tumor-bearing mice were then subjected to γ-ray irradiation after the metformin treatment. Immediately after irradiation, cells were isolated from some tumors and incubated with a cytokinesis blocker. The responses of quiescent and total (=?proliferating?+?quiescent) cell populations were assessed based on the frequency of micronuclei using immunofluorescence staining for BrdU.

Results: The disruption of Hif-1α increased the sensitivity of SCC VII cells to metformin in glucose-free medium. Metformin-induced decreases in the percentage of dead cells in the presence of CoCl₂ were partially reduced when Hif-1α was disrupted. In vivo, metformin increased the radiosensitivity of SCC VII Hif-1α-deficient cells.

Conclusion: The combination of disruption of Hif-1α and metformin effectively enhanced the radiosensitivity of SCC VII cells.     

Track structure calculations on intracellular targets responsible for signal release in bystander experiments with transfer of irradiated cell-conditioned medium

Abstract

Purpose: To investigate alternative scenarios for the dose-dependent emission of bystander signals by irradiated cells in medium transfer experiments.

Methods: Energy deposition patterns to hypothetical intracellular targets whose hit by radiation initiates the emission of bystander signals have been simulated by Monte Carlo code PARTRAC, evaluating the effects of target size, multiplicity and threshold energy for activation. Scenarios in which individual irradiated cells release signals independently as well as those with signal amplification by neighbour cells have been analyzed. The non-linear response of unirradiated cells to signals in the transferred medium has been considered.

Results: The experimentally observed dose dependence of bystander effects is consistent with cell-autonomous signal release with a wide distribution of characteristic doses, covering the range of 3 mGy to 3 Gy. Alternatively, the data can be explained by assuming that only cells receiving a high specific energy (3 Gy to 0.5 μm targets) release primary signals, which are then amplified by secondary signalling by neighbour cells within about a millimetre distance.

Conclusion: Alternative signal emission scenarios are consistent with the observed dose dependence of bystander effects in medium transfer experiments. Thus, further experimental research is needed to identify the actual mechanism of bystander signal emission.     

Cell death pathways in directly irradiated cells and cells exposed to medium from irradiated cells

Abstract

Purpose: The aim of this study was to compare levels of apoptosis, necrosis, mitotic cell death and senescence after treatment with both direct radiation and irradiated cell conditioned medium.

Materials and methods: Human keratinocytes (HaCaT cell line) were irradiated (0.005, 0.05 and 0.5 Gy) using a cobalt 60 teletherapy unit. For bystander experiments, the medium was harvested from donor HaCaT cells 1 hour after irradiation and transferred to recipient HaCaT cells. Clonogenic assay, apoptosis, necrosis, mitotic cell death, senescence and cell cycle analysis were measured in both directly irradiated cells and bystander cells

Results: A reduction in cell survival was observed for both directly irradiated cells and irradiated cell conditioned medium (ICCM)-treated cells. Early apoptosis and necrosis was observed predominantly after direct irradiation. An increase in the number of cells in G2/M phase was observed at 6 and 12 h which led to mitotic cell death after 72 h following direct irradiation and ICCM treatment. No senescence was observed in the HaCaT cell line following either direct irradiation or treatment with ICCM.

Conclusion: This study has shown that directly irradiated cells undergo apoptosis, necrosis and mitotic cell death whereas ICCM-treated cells predominantly undergo mitotic cell death.     

The importance of serum serotonin levels in the measurement of radiation-induced bystander cell death in HaCaT cells

Abstract

Purpose: The aim of this study was to investigate the importance of serum serotonin levels in the measurement of bystander cell death. The study was undertaken as part of an intercomparison exercise involving seven European laboratories funded under the European Union Sixth Framework Programme (FP6) Non-Targeted Effects (NOTE) integrated project.

Materials and methods: Three batches of foetal bovine serum were tested; serum with high and low serotonin content from the intercomparison exercise as well as serum from the home laboratory. Three sets of human keratinocytes (HaCaT cell line) were cultured in DMEM:F12 medium supplemented with serum with high or low serotonin content or serum from the home laboratory and both donor and recipient HaCaT cells were plated. The donor HaCaT cells were irradiated (0.5 Gy) using a cobalt 60 teletherapy unit, the medium was harvested 1 hour post irradiation and transferred to the recipient HaCaT cells. Bystander induced cell death was measured by the clonogenic survival assay and the Alamar blue viability assay.

Results: A significant reduction in cell survival, as measured by the clonogenic assay, and in cell viability, as measured by the Alamar blue assay, was observed in the recipient HaCaT cells treated with medium from irradiated cells compared to the cells treated with medium from unirradiated cells. No significant difference was found between the three batches of serum.

Conclusions: The data suggest that in our cell system and with our endpoints (clonogenic assay and Alamar blue assay), serum serotonin levels do not play a role in bystander-induced cell death.     

Ionizing radiation does not impair the mechanisms controlling genetic stability during T cell receptor gene rearrangement in mice

Purpose: To determine whether low dose/low dose rate radiation-induced genetic instability may result from radiation-induced inactivation of mechanisms induced by the ATM-dependent DNA damage response checkpoint. To this end, we analysed the faithfulness of T cell receptor (TR) gene rearrangement by V(D)J recombination in DNA from mice exposed to a single dose of X-ray or chronically exposed to low dose rate γ radiation.

Materials and methods: Genomic DNA obtained from the blood or the thymus of wild type or Ogg1-deficient mice exposed to low (0.1) or intermediate/high (0.2–1?Gy) doses of radiation either by acute X-rays exposure or protracted exposure to low dose-rate γ-radiation was used to analyse by PCR the presence of illegitimate TR gene rearrangements.

Results: Radiation exposure does not increase the onset of TR gene trans-rearrangements in irradiated mice. In mice where it happens, trans-rearrangements remain sporadic events in developing T lymphocytes.

Conclusion: We concluded that low dose/low dose rate ionizing radiation (IR) exposure does not lead to widespread inactivation of ATM-dependent mechanisms, and therefore that the mechanisms enforcing genetic stability are not impaired by IR in developing lymphocytes and lymphocyte progenitors, including BM-derived hematopoietic stem cells, in low dose/low dose rate exposed mice.