Human risks from chronic exposures to both low- and high-LET radiation are of intensive research interest in recent years. In the present study, human epithelial cells were exposed in vitro to gamma-rays at a dose rate of 17mGy/h or secondary neutrons of 25mGy/h. The secondary neutrons have a broad energy spectrum that simulates the Earth's atmosphere at high altitude, as well as the environment inside spacecrafts like the Russian MIR station and the International Space Station (ISS). Chromosome aberrations in the exposed cells were analyzed using the multicolor banding in situ hybridization (mBAND) technique with chromosome 3 painted in 23 colored bands that allows identification of both inter- and intrachromosome exchanges including inversions. Comparison of present dose responses between gamma-rays and neutron irradiations for the fraction of cells with damaged chromosome 3 yielded a relative biological effectiveness (RBE) value of 26+/-4 for the secondary neutrons. Our results also revealed that secondary neutrons of low dose rate induced a higher fraction of intrachromosome exchanges than gamma-rays, but the fractions of inversions observed between these two radiation types were indistinguishable. Similar to the previous findings after acute radiation exposures, most of the inversions observed in the present study were accompanied by other aberrations. The fractions of complex type aberrations and of unrejoined chromosomal breakages were also found to be higher in the neutron-exposed cells than after gamma-rays. We further analyzed the location of the breaks involved in chromosome aberrations along chromosome 3, and observed hot spots after gamma-ray, but not neutron, exposures.

<p>Recently a high-throughput version of the comet assay was developed using a special 96-well multichamber plate (MCP) [1]. In this version, the electrophoresis is performed directly on the MCP, which makes transferring of cells to microscope slides unnecessary. In order to facilitate the scoring procedure we adapted an automated slide-scanning system (Metafer MetaCyte with CometScan) to enable unattended analysis of comets on the MCP. The results of the system were compared with the data obtained with two interactive comet-assay analysis systems. For induction of DNA damage in human fibroblasts methylmethane sulfonate (MMS) or H(2)O(2) was used. The three systems revealed similar, concentration-dependent results for all parameters tested: tail moment (tm), % DNA-in-tail and olive tail moment. Near the detection limit of 5-6% DNA-in-tail a significant difference with the untreated control was obtained by use of four parallel samples (p=0.01). With the newly developed automated analysis system, the evaluation of either 50 or 100 comets yielded similar standard errors for either treatment with MMS or H(2)O(2), thus showing that the method is suitable to reveal the crucial low-dose effects with high precision. The results also show that the time needed for automated evaluation of comets on the MCP was reduced by a factor of 10 when compared with the time required for interactive evaluation. In summary, the high-throughput version of the comet assay combined with the automated evaluating system increased the output by a factor up to 180 compared with the standard method.</p>

Dental resin composites and their reactive monomers/co-monomers have been shown to elicit cytotoxic responses in human gingival fibroblasts (HGF), and their metabolic radical intermediates have the potential to attack the DNA backbone, which may induce DNA double-strand breaks (DSBs). In this study we have tested the cytotoxicity and induction of DSBs by the most common composite resin monomers/co-monomers: BisGMA, HEMA, TEGDMA, and UDMA in gingival fibroblasts using the sensitive gamma-H2AX DNA repair focus assay. Our results show increasing monomer cytotoxicities in the order of BisGMA>UDMA>TEGDMA>HEMA, an order that was also observed for their capacity to induce DSBs. BisGMA at the EC50 concentration of 0.09 mm evoked the highest rate of gamma-H2AX foci-formation that was 11-fold higher DNA DSBs as compared to the negative controls that ranged between 0.25 and 0.5gamma-H2AX foci/HGF cell. Our results for the first time show that exposure to dental resin monomers can induce DSBs in primary human oral cavity cells, which underscores their genotoxic capacity.

PURPOSE: In case of a large-scale radiation accident when hundreds of people may be exposed, it is important to distinguish the severely exposed individuals (> or =1 gray), who require early medical treatment, from those less exposed. The aim of our study was to develop a quick population triage method based on automated micronucleus (MN) scoring. MATERIALS AND METHODS: Using the MN software module developed by MetaSystems specifically for the Metafer4 platform, about 60 blood samples can be scored in one day. Standard dose response curves were determined for manual and automated MN scoring. RESULTS: The automated MN assay results were closely correlated with MN yields obtained with the manual procedure. A dose of 1 Gy can be estimated with an uncertainty of 0.2 Gy. Corrections for false positives and false negatives by visual inspection of the image gallery did not result in an improved accuracy or reproducibility. To test the automated MN assay in a multicenter setting, an inter-laboratory comparison was performed whereby irradiated blood samples were processed in Ghent University (Belgium) and BfS (Bundesamt fuer Strahlenschutz; Germany). Both laboratories obtained comparable results. CONCLUSIONS: These results confirm the efficacy of the automated MN assay for fast population triage in a multicenter setting, in the case of large radiation accidents.

Digital object identifier (DOI): 10.3109/09553000903264481

BACKGROUND AND PURPOSE: To investigate the cytogenetic damage in blood lymphocytes of patients treated for prostate cancer with different radiation qualities and target volumes. MATERIALS AND METHODS: Twenty patients receiving carbon-ion boost irradiation followed by IMRT or IMRT alone for the treatment of prostate cancer entered the study. Cytogenetic damage induced in peripheral blood lymphocytes of these patients was investigated at different times during the radiotherapy course using Giemsa staining and mFISH. A blood sample from each patient was taken before initiation of radiation therapy and irradiated in vitro to test for individual radiosensitivity. In addition, in vitro dose-effect curves for the induction of chromosomal exchanges by X-rays and carbon ions of different energies were measured. RESULTS: The yield of chromosome aberrations increased during the therapy course, and the frequency was lower in patients irradiated with carbon ions as compared to patients treated with IMRT with similar target volumes. A higher frequency of aberrations was measured by increasing the target volume. In vitro, high-LET carbon ions were more effective than X-rays in inducing aberrations and yielded a higher fraction of complex exchanges. The yield of complex aberrations observed in vivo was very low. CONCLUSION: The investigation showed no higher aberration yield induced by treatment with a carbon-ion boost. In contrast, the reduced integral dose to the normal tissue is reflected in a lower chromosomal aberration yield when a carbon-ion boost is used instead of IMRT alone. No cytogenetic #signature# of exposure to densely ionizing carbon ions could be detected in vivo.

<p>A better understanding of the underlying mechanisms of DNA repair after exposure to ionizing radiation represents a research priority aimed at improving the outcome of clinical radiotherapy. Because of the close association with DNA double strand break (DSB) repair, phosphorylation of the histone H2AX protein (gamma-H2AX), quantified by immunodetection, has recently been used as a method to study DSB induction and repair at low and clinically relevant radiation doses. However, the lack of consistency in literature points to the need to further validate the role of H2AX phosphorylation in DSB repair and the use of this technique to determine intrinsic radiosensitivity. In the present study we used human mammary epithelial MCF10A cells, characterized by a radiosensitive phenotype due to reduced levels of the Ku70 and Ku80 repair proteins, and investigated whether this repair-deficient cell line displays differences in the phosphorylation pattern of H2AX protein compared to repair-proficient MCF10A cells. This was established by measuring formation and disappearance of gamma-H2AX foci after irradiating synchronized cell populations with (60)Co alpha-rays. Our results show statistically significant differences in the number of gamma-H2AX foci between the repair-deficient and -proficient cell line, with a higher amount of gamma-H2AX foci present at early times post-irradiation in the Ku-deficient cell line. However, the disappearance of those differences at later post-irradiation times questions the use of this assay to determine intrinsic radiosensitivity, especially in a clinical setting.</p>

The international radiation biodosimetry community has recently been engaged in activities focused on establishing cooperative networks for biodosimetric triage for radiation emergency scenarios involving mass casualties. To this end, there have been several recent publications in the literature regarding the potential for shared scoring in such an accident or incident. We present details from a medical irradiation case where two independently validated laboratories found very different yields of dicentric chromosome aberrations. The potential reasons for this disparity are discussed, and the actual reason is identified as being the partial-body nature of the radiation exposure combined with differing criteria for metaphase selection. In the context of the recent networking activity, this report is intended to highlight the fact that shared scoring may produce inconsistencies and that further validation of the scoring protocols and experimental techniques may be required before the networks are prepared to deal satisfactorily with a radiological or nuclear emergency. Also, the findings presented here clearly demonstrate the limitations of the dicentric assay for estimating radiation doses after partial-body exposures and bring into question the usefulness of rapid #triage##mode# scoring in such exposure scenarios.

To characterise the radiation response of human hematopoietic stem and progenitor cells (HSPC) with respect to X and carbon ion irradiation.HSPC from peripheral blood of healthy donors treated with granulocyte-colony stimulating factor (G-CSF) were enriched for the transmembrane glycoprotein CD34 (cluster of differentiation) and irradiated with X rays or carbon ions (29 keV/microm monoenergetic beam and 60-85 keV/microm spread-out Bragg peak), mimicking radiotherapy conditions. Apoptotic cell death, cell cycle progression and the frequency of chromosomal aberrations were determined.After radiation exposure no inhibition in the progression of the cell cycle was detected. However, an enhanced frequency of apoptotic cells and an increase in aberrant cells were observed, both effects being more pronounced for carbon ions than X rays, resulting in a relative biological effectiveness (RBE) of 1.4-1.7. The fraction of complex-type aberrations was higher following carbon ion exposure.RBE values of carbon ions are low, as expected for radiosensitive cells. The observed frequencies of apoptotic cells and chromosome aberrations in HSPC are similar to those reported for human peripheral blood lymphocytes suggesting that at least with respect to apoptosis and chromosomal aberrations mature lymphocytes reflect the respective radiation responses of their proliferating progenitors.

DNA double-strand breaks (DSBs) are a serious threat to genome stability and cell viability. Although biological effects of low levels of radiation are not clear, the risks of low-dose radiation are of societal importance. Here, we directly monitored induction and repair of single DSBs and quantitatively analyzed the dynamics of interaction of DNA repair proteins at individual DSB sites in living cells using 53BP1 fused to yellow fluorescent protein (YFP-53BP1) as a surrogate marker. The number of DSBs formed was linear with dose from 5 mGy to 1 Gy. The DSBs induced by very low radiation doses (5 mGy) were repaired with efficiency similar to repair of DSBs induced at higher doses. The YFP-53BP1 foci are dynamic structures: 53BP1 rapidly and reversibly interacted at these DSB sites. The time frame of recruitment and affinity of 53BP1 for DSB sites were indistinguishable between low and high doses, providing mechanistic evidence for the similar DSB repair after low- and high-dose radiation. These findings have important implications for estimating the risk associated with low-dose radiation exposure on human health.

Both occupational exposure to the leukemogen benzene and in vitro exposure to its metabolite hydroquinone (HQ) lead to the induction of numerical and structural chromosome changes. Several studies have shown that HQ can form DNA adducts, disrupt microtubule assembly and inhibit DNA topoisomerase II (topo II) activity. As these are potential mechanisms underlying endoreduplication (END), a phenomenon that involves DNA amplification without corresponding cell division, we hypothesized that HQ could cause END. We measured END in the human lymphoblastoid cell line, TK6, treated with HQ (0-20 microM) and etoposide (0-0.2 microM) for 48 h. Etoposide was used as a positive control as it is a topo II poison and established human leukemogen that has previously been shown to induce END in Chinese hamster ovary cells. Both HQ and etoposide significantly induced END in a dose-dependent manner (P(trend) s.

The measurement of micronuclei (MN) in human peripheral blood lymphocytes is frequently used in molecular epidemiology as one of the preferred methods for assessing chromosomal damage resulting from environmental mutagen exposure. In the present study, we evaluated the effect of exposure to carcinogenic polycyclic aromatic hydrocarbons (c-PAHs), volatile organic compounds (VOC) and smoking on the frequency of MN in a group of 56 city policemen living and working in Prague. The average age of the participants was 34+/-6 years. The study was conducted on the same subjects in February and May 2007. The concentrations of air pollutants were obtained from personal and stationary monitoring. A statistically significant decrease in the levels of pollutants was observed in May when compared with February, with the exception of toluene levels measured by stationary monitoring. The frequency of MN was determined by the automatic image scoring (MetaSystems Metafer 4, version 3.2.1) of DAPI-stained slides. The results of the image analysis indicated a significant difference in the frequency of MN (mean levels 7.32+/-3.42 and 4.67+/-2.92, for February and May, respectively). Our study suggests that automatic image analysis of MN is a highly sensitive method for evaluating the effect of c-PAHs and confirms that there are no differences between smokers and nonsmokers. These results demonstrate the ability of c-PAHs to increase MN frequency, even if the exposure to c-PAHs occurred up to 60 days before the collection of biological material. Our work is the first human biomonitoring study focused on the measurement of MN by automated image analysis for assessing chromosomal damage as a result of environmental mutagen exposure.

The cytokinesis-block micronucleus assay in peripheral blood lymphocytes is a standardised and validated technique for biodosimetry. Automated scoring of micronuclei allows large scale applications as in population triage in case of radiation accidents or malevolent use of radioactive sources. The dose detection limit (95% confidence) of the micronucleus assay for individual dose assessment is restricted to 0.2 Gy but can be decreased to 0.1 Gy by scoring centromeres in micronuclei using fluorescence in situ hybridization (FISH). In the past the micronucleus assay was applied for a number of large scale biomonitoring studies of nuclear power plant workers and hospital workers. Baseline micronucleus frequencies depend strongly on age and gender. The assay was also already used for biodosimetry of radiation accidents. In a multiple endpoint biodosimetry study for dose assessment of a worker exposed accidentally in 2003 to X-rays, a good agreement was obtained between dose estimates resulting from the micronucleus assay, the scoring of dicentrics and translocations. Automated scoring of micronuclei in combination with centromere signals, allowing systematic biodosimetry of exposed populations, remains a challenge for the future.

<p>After large-scale accidental overexposure to ionizing radiation, a rapid triage of the exposed population can be performed by scoring dicentrics and ring chromosomes among 50 metaphases. This is rapid but is not accurate because the sensitivity is around 0.5 Gy. After the triage step, dose can be estimated by scoring 500 metaphases. This is lengthy but very accurate because the sensitivity is between 0.1 and 0.2 Gy. To improve the methodology, we propose the use of software for automatic dicentric scoring that was tested on victims of an accident in Dakar. Manual scoring of 50 metaphases was carried out, then manual scoring of 500 metaphases, and automatic scoring. Comparison between the dose classifications obtained with manual scoring on 50 metaphases and 500 metaphases showed 50% misclassification with the manual scoring on 50 metaphases. Comparison between the dose classifications obtained with the automatic scoring and manual scoring on 500 metaphases showed only 4.35% misclassification with the automatic scoring. The automatic scoring method is more accurate than the manual scoring on 50 metaphases and can therefore be used for triage, and in place of the manual scoring on 500 metaphases method for individual dose estimation, because it is as accurate and much faster.</p>

Cancer has been suggested to result from interactions between genetic and environmental factors, and certain subgroups in the general population may be at increased risk because of their relatively higher susceptibility to environmental carcinogens. The current study, part of a large biomonitoring study conducted in Flanders from 2002 to 2006 (The Flanders Environment and Health Survey), aims to determine these susceptible subpopulations based on multiple genotypic differences between individuals. A random selection of 429 adolescents and 361 adults was genotyped for 36 polymorphisms in 23 genes selected because of their known role in carcinogen metabolism, DNA repair, and oxidative stress. In both age groups, relationships between endogenous exposure to organochloride substances (polychlorinated biphenyl, hexachlorobenzene, dichlorodiphenyl dichloroethane), metals (cadmium, lead), and urinary metabolites (1-hydroxypyrene, trans-trans muconic acid) versus genotoxic effects (Comet assay and micronuclei in lymphocytes, and urinary 8-hydroxydeoxyguanosine) were investigated. In addition, in the study among adults, the relationship of these exposures with several tumor markers (prostate-specific antigen, carcinoembryonic antigen, and p53) was tested. The impact of the genotype on established exposure-effect relationships was evaluated. Eight exposure-effect relationships were found, including three novel associations, with an impact of various genotypes, predominantly affecting biotransformation and oxidative stress response. This study shows that at least part of the interindividual differences in relationships between carcinogen exposure and genotoxic effect can be explained by genotypic differences, enabling the identification of more susceptible subgroups for environmental cancer risks. This may be of relevance for environmental health policy setting.

Mazor, R., Korenstein-Ilan, A., Barbul, A., Eshet, Y., Shahadi, A., Jerby, E. and Korenstein, R. Increased Levels of Numerical Chromosome Aberrations after In Vitro Exposure of Human Peripheral Blood Lymphocytes to Radiofrequency Electromagnetic Fields for 72 Hours. Radiat. Res. 169, 28-37 (2008). We investigated the effects of 72 h in vitro exposure of 10 human lymphocyte samples to radiofrequency electromagnetic fields (800 MHz, continuous wave) on genomic instability. The lymphyocytes were exposed in a specially designed waveguide resonator at specific absorption rates (SARs) of 2.9 and 4.1 W/kg in a temperature range of 36-37 degrees C. The induced aneuploidy of chromosomes 1, 10, 11 and 17 was determined by interphase FISH using semi-automated image analysis. We observed increased levels of aneuploidy depending on the chromosome studied as well as on the level of exposure. In chromosomes 1 and 10, there was increased aneuploidy at the higher SAR, while for chromosomes 11 and 17, the increases were observed only for the lower SAR. Multisomy (chromosomal gains) appeared to be the primary contributor to the increased aneuploidy. The effect of temperature on the level of aneuploidy was examined over the range of 33.5-40 degrees C for 72 h with no statistically significant difference in the level of aneuploidy compared to 37 degrees C. These findings suggest the possible existence of an athermal effect of RF radiation that causes increased levels of aneuploidy. These results contribute to the assessment of potential health risks after continuous chronic exposure to RF radiation at SARs close to the current levels set by ICNIRP guidelines.

Nonsynonymous SNPs (nsSNPs) in DNA repair genes may be important determinants of DNA damage and cancer risk. We applied a set of screening criteria to a large number of nsSNPs and selected a subset of SNPs that were likely candidates for phenotypic effects on DNA double-strand break repair (DSBR). In order to induce and follow DSBR, we exposed panels of cell lines to gamma irradiation and followed the formation and disappearance of gammaH2A.X foci over time. All panels of cell lines showed significant increases in number, intensity, and area of foci at both the 1-hour and 3-hour time points. Twenty four hours following exposure, the number of foci returned to preexposure levels in all cell lines, whereas the size and intensity of foci remained significantly elevated. We saw no significant difference in gammaH2A.X foci between controls and any of the panels of cell lines representing the different nsSNPs.

We measured residual cytogenetic damage in the progeny of human peripheral blood lymphocytes exposed to 1 GeV/ nucleon iron ions or gamma rays. Arm-specific DNA probes for chromosome 1 were used to detect aberrations as a function of dose in cells harvested 144 h after exposure. In addition, arm-specific mFISH was applied to samples exposed to a single dose of 2 Gy. These methods allowed the detection of interarm intrachanges (pericentric inversions) in addition to interchanges. The ratio of these types of aberrations (F ratio) has been proposed as a fingerprint of exposure to densely ionizing radiation. The fractions of aberrant cells in the progeny of cells exposed to iron ions were similar to those in the population exposed to gamma rays, possibly because many rearrangements induced by heavy ions ultimately lead to cell death. Simple inter- and intrachanges were also similar, but more complex rearrangements were found in cells that survived after exposure to iron ions. We did not find a significant difference in the ratio of simple interchanges to simple intrachanges for the two radiation types. However, iron ions induced a much higher frequency of events involving both inter- and intrachanges. We conclude that these complex rearrangements represent a hallmark of exposure to heavy ions and may be responsible of the decrease of the F ratio with increasing LET reported in the literature in some in vitro and in vivo experiments.

Food irradiation is the process of exposing food to ionising radiation in order to disinfect, sanitise, sterilise and preserve food or to provide insect disinfestation. Irradiated food should be adequately labelled according to international and national guidelines. In many countries, there are furthermore restrictions to the product-specific maximal dose that can be administered. Therefore, there is a need for methods that allow detection of irradiated food, as well as for methods that provide a reliable dose estimate. In recent years, the comet assay was proposed as a simple, rapid and inexpensive method to fulfil these goals, but further research is required to explore the full potential of this method. In this paper we describe the use of an automated image analysing system to measure DNA comets which allow the discrimination between irradiated and non-irradiated food as well as the set-up of standard dose-response curves, and hence a sufficiently accurate dose estimation.

In 1957/58 the British Government conducted a series of nuclear tests in the mid-Pacific codenamed Operation Grapple, which involved several naval vessels from Britain and New Zealand. Two New Zealand frigates with 551 personnel onboard were stationed at various distances between 20 and 150 nautical miles from ground zero. In the present study we applied the cytomolecular technique mFISH (multicolour fluorescent in situ hybridisation) to investigate a potential link between chromosome abnormalities and possible past radiation exposure in New Zealand nuclear test veterans who participated in Operation Grapple. Compared to age matched controls, the veterans showed significantly higher (P < 0.0001) frequencies of chromosomal abnormalities (275 translocations and 12 dicentrics in 9,360 cells vs. 96 translocations and 1 dicentric in 9,548 cells in the controls), in addition to a significant excess of CCRs (complex chromosomal rearrangements) in the veterans. A Kolmogorov-Smirnoff test showed that the distributions of translocations for the two groups were significantly different.

All cells have intricately coupled sensing and signaling mechanisms that regulate the cellular outcome following exposure to genotoxic agents such as ionizing radiation (IR). In the IR-induced signaling pathway, specific protein events, such as ataxia-telangiectasia mutated protein (ATM) activation and histone H2AX phosphorylation (gamma-H2AX), are mechanistically well characterized. How these mechanisms can be altered, especially by clinically relevant agents, is not clear. Here we show that hyperthermia, an effective radiosensitizer, can induce several steps associated with IR signaling in cells. Hyperthermia induces gamma-H2AX foci formation similar to foci formed in response to IR exposure, and heat-induced gamma-H2AX foci formation is dependent on ATM but independent of heat shock protein 70 expression. Hyperthermia also enhanced ATM kinase activity and increased cellular ATM autophosphorylation. The hyperthermia-induced increase in ATM phosphorylation was independent of Mre11 function. Similar to IR, hyperthermia also induced MDC1 foci formation; however, it did not induce all of the characteristic signals associated with irradiation because formation of 53BP1 and SMC1 foci was not observed in heated cells but occurred in irradiated cells. Additionally, induction of chromosomal DNA strand breaks was observed in IR-exposed but not in heated cells. These results indicate that hyperthermia activates signaling pathways that overlap with those activated by IR-induced DNA damage. Moreover, prior activation of ATM or other components of the IR-induced signaling pathway by heat may interfere with the normal IR-induced signaling required for chromosomal DNA double-strand break repair, thus resulting in increased cellular radiosensitivity.