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Purpose: Modifications of gene expression following ionizing radiation (IR) exposure of cells in vitro and in vivo are well documented. However, little is known about the dose-responses of transcriptionally responsive genes, especially at low doses. In this study, we investigated these dose-responses and assessed inter-individual variability. Materials and methods: High dose (0.5-4 Gy) and low dose (5-100 mGy) gene expression responses at 2 h and 24 h using 13 biomarkers transcriptionally regulated through the DNA damage response by the tumor suppressor p53 were investigated. Inter-individual variation was also examined. Results: High dose-response curves were best constructed using a polynomial fit while the low dose-response curves used a linear fit with linear R2 values of 0.841-0.985. Individual variation was evident in the high and low dose ranges. The FDXR, DDB2 high dose gene combination produced a mean dose estimate of 0.7 Gy for 1 Gy irradiated 'unknown' samples (95% CIs of 0.3-1.1 Gy) and 1.4 Gy for 2 Gy exposure (95% CIs of 0.6-2.1 Gy). The FDXR, DDB2, CCNG1 low dose gene combination estimated 98 mGy (95% CIs of 27-169 mGy) for 100 mGy exposure. Conclusions: These findings identify genes that fulfill some of the requirements of a good exposure biomarker even at low doses, such as sensitivity, reproducibility and simple proportionality with dose. [ABSTRACT FROM AUTHOR]

Purpose: To compare the development of intestinal adenomas following neutron and X-ray exposure of ApcMin/++ mice ( Apc -- adenomatous polyposis coli; Min -- multiple intestinal neoplasia). Materials and methods: Adult mice were exposed to acute doses of X-rays or fission neutrons. Tumour counting was undertaken 200 days later and samples were taken for Loss of Heterozygosity (LOH) analysis. Results: Tumour numbers (adenomas and microadenomas) increased by 1.4-fold, 1.7-fold, 2.7-fold and 9-fold, after 0.5, 1, 2 and 5 Gy X-rays, respectively, and by 2.4-fold and 5.7-fold, after 0.5 and 1 Gy fission neutrons, respectively. LOH analysis of tumours from neutron-exposed mice showed that 63%% had lost Apc and 90%% (cf. 53%% in controls) had lost D18mit84, a marker for Epb4.1l4a/NBL4 (erythrocyte protein band 4.1-like 4a/novel band 4.1-like 4), known to be involved in the Wnt (ingless-related mouse mammary tumour virus egration site) pathway. Some tumours from neutron-exposed mice appeared to have homozygous loss of some chromosomal markers. Conclusions: X-ray or fission neutron irradiation results in strongly enhanced tumour multiplicities. Comparison of tumour yields indicated a low Relative Biological Effectiveness of around 2--8 for fission neutrons compared with X-rays. LOH in intestinal tumours from neutron-exposed mice appeared to be more complex than previously reported for tumours from X-irradiated mice. [ABSTRACT FROM AUTHOR]

Purpose: To establish a panel of highly radiation responsive genes suitable for biological dosimetry and to explore inter-individual variation in response to ionising radiation exposure. Materials and methods: Analysis of gene expression in response to radiation was carried out using three independent techniques (Microarray, Multiplex Quantitative Real-Time Polymerase Chain Reaction (MQRT- PCR) and nCounter®® Analysis System) in human dividing lymphocytes in culture and peripheral blood leukocytes exposed ex vivo from the same donors. Results: Variations in transcriptional response to exposure to ionising radiation analysed by microarray allowed the identification of genes which can be measured accurately using MQRT PCR and another technique allowing direct count of mRNA copies. We have identified genes which are consistently up-regulated following exposure to 2 or 4 Gy of X-rays at different time points, for all individuals in blood and cultured lymphocytes. Down-regulated genes including cyclins, centromeric and mitotic checkpoint genes, particularly those associated with chromosome instability and cancer could be detected in dividing lymphocytes only. Conclusions: The data provide evidence that there are a number of genes which seem suitable for biological dosimetry using peripheral blood, including sestrin 1 (SESN1), growth arrest and DNA damage inducible 45 alpha (GADD45A), cyclin-dependent kinase inhibitor 1A (CDKN1A), cyclin G1 (CCNG1), ferredoxin reductase (FDXR), p53 up-regulated mediator of apoptosis (BBC3) and Mdm2 p53 binding protein homolog (MDM2). These biomarkers could potentially be used for triage after large-scale radiological incidents and for monitoring radiation exposure during radiotherapy. [ABSTRACT FROM AUTHOR]

Purpose: To examine the hypothesis that lymphocyte telomere length may be predictive of both breast cancer susceptibility and severity of acute reactions to radiotherapy. Materials and methods: Peripheral blood lymphocyte cultures from breast cancer patients (with normal or severe skin reactions to radiotherapy) and normal individuals were assessed for in vitro radiosensitivity as measured by apoptosis, cell cycle delay and cytotoxicity. Telomere lengths were determined by a flow cytometric fluorescence in situ hybridization assay (FLOW-FISH). Results: Female breast cancer cases (n = 24) had reduced lymphocyte telomere lengths by comparison with healthy controls (n = 20, p < 0.04). However, the average age of healthy controls was less (45.4) than cases (53). When the control group was modified to give a better age match (51.5, n = 13) the reduced telomere length in cases was not significantly different from controls. Lymphocytes from breast cancer cases also showed reduced cell cycle delay (p < 0.001) and increased apoptosis (p < 0.01) following irradiation in vitro at 3 and 5 Gy respectively, compared to healthy controls. Statistical significance was maintained with the improved age matching of groups. Comparison of lymphocytes from breast cancer patients with normal (n = 11) and severe (n = 13) skin reactions to radiotherapy failed to identify differences in telomere length or cellular radiosensitivity in this limited sample. Conclusions: This study adds to the evidence suggesting a correlation between altered cellular radiosensitivity and breast cancer. However, in the cases investigated, telomere length does not appear to be predictive of acute skin reactions to radiotherapy. [ABSTRACT FROM AUTHOR]

Here we analyze the functional interaction between Ku86 and telomerase at the mammalian telomere by studying mice deficient for both proteins. We show that absence of Ku86 prevents the end-to-end chromosomal fusions that result from critical telomere shortening in telomerase-deficient mice. In addition, Ku86 deficiency rescues the mate early germ cell apoptosis triggered by short telomeres in these mice. Together, these findings define a rote for Ku86 in mediating chromosomal instability and apoptosis triggered by short telomeres. In addition, we show here that Ku86 deficiency results in telomerase-dependent telomere elongation and in the fusion of random pairs of chromosomes in telomerase-proficient cells, suggesting a model in which Ku86 keeps normal- length telomeres less accessible to telomerase-mediated telomere lengthening and to DNA repair activities. [ABSTRACT FROM AUTHOR]

X-irradiation of two mouse myeloid leukaemia cell lines was found to lead to increased telomerase activities. Maximal increases in activity at 24 h post-irradiation were approximately three times control unirradiated cell levels. These maxima were reached at between 3–5 Gy depending upon cell line. Peak activity was reached at 8h, remained elevated to 24 h and returned to control levels by 48 h. In contrast, X-irradiation did not activate telomerase in a telomerase-negative human fibroblast line, while in cultured normal mouse bone marrow cells irradiation appeared to reduce activities. No simple relationship between radiation-induced increases in telomerase activity in the myeloid leukaemia lines and the proportions of cells in the S or M phases of the cell cycle was apparent. Radiation-induced increases in activity were significantly reduced by inhibitors of transcription (actinomycin D, α-amanatin) and protein synthesis (cycloheximide). These data are consistent with two possibilities: (i) X-irradiation leads to increased transcription and/or translation of a component of telomerase, thus increasing activities; or (ii) X-irradiation induces the transcription of a positive regulator of telomerase activity. Northern blot analysis did not indicate that transcription of mTert, the catalytic subunit of telomerase, or mTerc, the RNA component, was elevated after irradiation. Similarly, no significant changes in the expression of Myc or Tnks, the tankyrase gene, two suspected telomerase regulators, were detected. These data are therefore consistent with the induction by X-irradiation of a positive regulator of telomerase activity other than Tnks or Myc or the core protein and RNA components of the enzyme. [ABSTRACT FROM PUBLISHER]

A letter to the editor is presented in response to the article "Footnote to Radiation-induced cataracts: the Health Protection Agency's response to the ICRP statement on tissue reactions and recommendation on the dose limit for the eye lens" in the December 2012 issue.

Abstract: Background and purpose: Identification of mechanisms of late normal tissue responses to curative radiotherapy that discriminate individuals with marked or mild responses would aid response prediction. This study aimed to identify differences in gene expression, apoptosis, residual DNA double strand breaks and chromosomal damage after in vitro irradiation of lymphocytes in a series of patients with marked (31 cases) or mild (28 controls) late adverse reaction to adjuvant breast radiotherapy. Materials and methods: Gene expression arrays, residual γH2AX, apoptosis, G2 chromosomal radiosensitivity and G0 micronucleus assay were used to compare case and control lymphocyte radiation responses. Results: Five hundred and thirty genes were up-regulated and 819 down-regulated by ionising radiation. Irradiated samples were identified with an overall cross-validated error rate of 3.4%. Prediction analyses to classify cases and controls using unirradiated (0Gy), irradiated (4Gy) or radiation response (4–0Gy) expression profiles correctly identified samples with, respectively, 25%, 22% or 18.5% error rates. Significant inter-sample variation was observed for all cellular endpoints but cases and controls could not be distinguished. Conclusions: Variation in lymphocyte radiosensitivity does not necessarily correlate with normal tissue response to radiotherapy. Gene expression analysis can predict of radiation exposure and may in the future help prediction of normal tissue radiosensitivity. [Copyright &y& Elsevier]

Introduction: Lynch syndrome patients have an inherited predisposition to cancer due to a deficiency in DNA mismatch repair (MMR) genes which could lead to a higher risk of developing cancer if exposed to ionizing radiation. This pilot study aims to reveal the association between MMR deficiency and radiosensitivity at both a CT relevant low dose (20 mGy) and a therapeutic higher dose (2 Gy)., Methods: Human colorectal cancer cell lines with (dMMR) or without MMR deficiency (pMMR) were analyzed before and after exposure to radiation using cellular and cytogenetic analyses i.e., clonogenic assay to determine cell reproductive death; sister chromatid exchange (SCE) assay to detect the exchange of DNA between sister chromatids; γH2AX assay to analyze DNA damage repair; and apoptosis analysis to compare cell death response. The advantages and limitations of these assays were assessed in vitro , and their applicability and feasibility investigated for their potential to be used for further studies using clinical samples., Results: Results from the clonogenic assay indicated that the pMMR cell line (HT29) was significantly more radio-resistant than the dMMR cell lines (HCT116, SW48, and LoVo) after 2 Gy X-irradiation. Both cell type and radiation dose had a significant effect on the yield of SCEs/chromosome. When the yield of SCEs/chromosome for the irradiated samples (2 Gy) was normalized against the controls, no significant difference was observed between the cell lines. For the γH2AX assay, 0, 20 mGy and 2 Gy were examined at post-exposure time points of 30 min (min), 4 and 24 h (h). Statistical analysis revealed that HT29 was only significantly more radio-resistant than the MLH1 -deficient cells lines, but not the MSH2 -deficient cell line. Apoptosis analysis (4 Gy) revealed that HT29 was significantly more radio-resistant than HCT116 albeit with very few apoptotic cells observed., Discussion: Overall, this study showed radio-resistance of the MMR proficient cell line in some assays, but not in the others. All methods used within this study have been validated; however, due to the limitations associated with cancer cell lines, the next step will be to use these assays in clinical samples in an effort to understand the biological and mechanistic effects of radiation in Lynch patients as well as the health implications., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Sun, Moquet, Barnard, Mancey, Burling, Baldwin-Cleland, Monahan, Latchford, Lloyd, Bouffler, Badie, Anyamene and Ainsbury.)

People are more often exposed to low as opposed to high doses of ionising radiation (IR). Knowledge on the health risks associated with exposures to ionising radiation above 100 mGy is quite well established, while lower dose risks are inferred from higher level exposure information (ICRP). The health risk assessments are mainly based on epidemiological data derived from the atomic bombing of Hiroshima and Nagasaki, medical exposure studies and follow-up studies after nuclear accidents. For the estimation of long-term stochastic radiation health effects (such as cancer) and radiation protection purposes, a linear non-threshold (LNT) model is applied. However, the general validity of the LNT hypothesis for extrapolations from effects of high to low doses (<100 mGy) and low dose-rates (<6 mGy/h) has been questioned as epidemiological studies are statistically limited at low doses and unable to evaluate low dose and low dose-rate health risks (UNSCEAR). Thus, uncertainties on health risks need to be clarified with the help of mechanistic studies. The European Network of Excellence DoReMi (2010-2016) was designed to address some of the existing uncertainties and to identify research lines that are likely to be most informative for low dose risk assessment. The present review reports the results obtained from studies addressing the induction of cancer and non-cancer effects by low dose IR as well as on individual radiation sensitivity. It is shown that low dose and low dose-rate effects are the result of complex network responses including genetic, epigenetic, metabolic and immunological regulation. Evidence is provided for the existence of nonlinear biological responses in the low and medium dose range as well as effects other than the classical DNA damage. Such effects may have a bearing on the quantitative and qualitative judgements on health effects induced by low dose radiations., (Copyright © 2018. Published by Elsevier B.V.)

Leukaemia is the prevailing neoplastic disorder of the hematopoietic system. Epidemiological analyses of the survivors of the Japanese atomic bombings show that exposure to ionising radiation (IR) can cause leukaemia. Although a clear association between radiation exposure and leukaemia development is acknowledged, the underlying mechanisms remain incompletely understood. A hemizygous deletion on mouse chromosome 2 (del2) is a common feature in several mouse strains susceptible to radiation-induced acute myeloid leukaemia (rAML). The deletion is an early event detectable 24h after exposure in bone marrow cells. Ultimately, 15-25% of exposed animals develop AML with 80-90% of cases carrying del2. Molecular mapping of leukaemic cell genomes identified a minimal deleted region (MDR) on chromosome 2 (chr2) in which a tumour suppressor gene, Sfpi1 is located, encoding the transcription factor PU.1, essential in haematopoiesis. The remaining copy of Sfpi1 has a point mutation in the coding sequence for the DNA-binding domain of the protein in 70% of rAML, which alters a single CpG sequence in the codon for arginine residue R235. In order to identify chr2 deletions and Sfpi.1/PU.1 loss, we performed array comparative genomic hybridization (aCGH) on a unique panel of 79rAMLs. Using a custom made CGH array specifically designed for mouse chr2, we analysed at unprecedentedly high resolution (1.4M array- 148bp resolution) the size of the MDR in low LET and high-LET induced rAMLs (32 X-ray- and 47 neutron-induced). Sequencing of Sfpi1/PU.1DNA binding domain identified the presence of R235 point mutations, showing no influence of radiation quality on R235 type or frequency. We identified for the first time rAML cases with complex del2 in a subset of neutron-induced AMLs. This study allowed us to re-define the MDR to a much smaller 5.5Mb region (still including Sfpi1/PU.1), identical regardless of radiation quality., (Crown Copyright © 2015. Published by Elsevier B.V. All rights reserved.)

Purpose: To compare the development of intestinal adenomas following neutron and X-ray exposure of Apc(Min/+) mice (Apc - adenomatous polyposis coli; Min - multiple intestinal neoplasia)., Materials and Methods: Adult mice were exposed to acute doses of X-rays or fission neutrons. Tumour counting was undertaken 200 days later and samples were taken for Loss of Heterozygosity (LOH) analysis., Results: Tumour numbers (adenomas and microadenomas) increased by 1.4-fold, 1.7-fold, 2.7-fold and 9-fold, after 0.5, 1, 2 and 5 Gy X-rays, respectively, and by 2.4-fold and 5.7-fold, after 0.5 and 1 Gy fission neutrons, respectively. LOH analysis of tumours from neutron-exposed mice showed that 63% had lost Apc and 90% (cf. 53% in controls) had lost D18mit84, a marker for Epb4.1l4a/NBL4 (erythrocyte protein band 4.1-like 4a/novel band 4.1-like 4), known to be involved in the Wnt (wingless-related mouse mammary tumour virus integration site) pathway. Some tumours from neutron-exposed mice appeared to have homozygous loss of some chromosomal markers., Conclusions: X-ray or fission neutron irradiation results in strongly enhanced tumour multiplicities. Comparison of tumour yields indicated a low Relative Biological Effectiveness of around 2-8 for fission neutrons compared with X-rays. LOH in intestinal tumours from neutron-exposed mice appeared to be more complex than previously reported for tumours from X-irradiated mice.