In this study, the Whole Human Genome 44K DNA microarray assay was used for the first time to obtain gene expression profiles in human peripheral blood lymphocytes 2 h after exposure (in suspension) to 6.78 MeV mean energy α particles from extracellular ²¹¹At. Lymphocytes were exposed to fluences of 0.3–9.6 × 10⁶ α particles/cm² [corresponding to mean absorbed α-particle doses (D_α) of 0.05–1.60 Gy] over 30 min. Significantly modulated expression was identified in 338 early-response genes. Up-regulated expression was evident in 183 early-response genes, while the remaining 155 were down-regulated. Over half of the up-regulated genes and 40% of the down-regulated genes had a known biological process related primarily to cell growth and maintenance and cell communication. Genes associated with cell death were found only in the up-regulated genes and those with development only in the down-regulated genes. Eight selected early-response genes that displayed a sustained up- or down-regulation (CD36, HSPA2, MS4A6A, NFIL3, IL1F9, IRX5, RASL11B and SULT1B1) were further validated in α-particle-irradiated lymphocytes of two human individuals using the TaqMan® RT-qPCR technique. The results confirmed the observed microarray gene expression patterns. The expression modulation profiles of IL1F9, IRX5, RASL11B and SULT1B1 genes demonstrated similar trends in the two individuals studied. However, no significant linear correlation between increasing relative gene expression and the α-particle dose was evident. The results suggest the possibility that a panel of genes that react to α-particle radiation does exist and that they merit further study in a greater number of individuals to determine their possible value regarding α-particle biodosimetry.

The detection of ⁴¹Ca atoms in tooth enamel using accelerator mass spectrometry is suggested as a method capable of reconstructing thermal neutron exposures from atomic bomb survivors in Hiroshima and Nagasaki. In general, ⁴¹Ca atoms are produced via thermal neutron capture by stable ⁴⁰Ca. Thus any ⁴¹Ca atoms present in the tooth enamel of the survivors would be due to neutron exposure from both natural sources and radiation from the bomb. Tooth samples from five survivors in a control group with negligible neutron exposure were used to investigate the natural ⁴¹Ca content in tooth enamel, and 16 tooth samples from 13 survivors were used to estimate bomb-related neutron exposure. The results showed that the mean ⁴¹Ca/Ca isotope ratio was (0.17 ± 0.05) × 10⁻¹⁴ in the control samples and increased to 2 × 10⁻¹⁴ for survivors who were proximally exposed to the bomb. The ⁴¹Ca/Ca ratios showed an inverse correlation with distance from the hypocenter at the time of the bombing, similar to values that have been derived from theoretical free-in-air thermal-neutron transport calculations. Given that γ-ray doses were determined earlier for the same tooth samples by means of electron spin resonance (ESR, or electron paramagnetic resonance, EPR), these results can serve to validate neutron exposures that were calculated individually for the survivors but that had to incorporate a number of assumptions (e.g. shielding conditions for the survivors).

⁴¹Ca is produced mainly by absorption of low-energy neutrons on stable ⁴⁰Ca. We used accelerator mass spectrometry (AMS) to measure ⁴¹Ca in enamel of 16 teeth from 13 atomic bomb survivors who were exposed to the bomb within 1.2 km from the hypocenter in Hiroshima. In our accompanying paper (Wallner et al., Radiat. Res. 174, 000–000, 2010), we reported that the background-corrected ⁴¹Ca/Ca ratio decreased from 19.5 × 10⁻¹⁵ to 2.8 × 10⁻¹⁵ with increasing distance from the hypocenter. Here we show that the measured ratios are in good correlation with γ-ray doses assessed by electron paramagnetic resonance (EPR) in the same enamel samples, and agree well with calculated ratios based on either the current Dosimetry System 2002 (DS02) or more customized dose estimates where the regression slope as obtained from an errors-in-variables linear model was about 0.85. The calculated DS02 neutron dose to the survivors was about 10 to 80 mGy. The low-energy neutrons responsible for ⁴¹Ca activation contributed variably to the total neutron dose depending on the shielding conditions. Namely, the contribution was smaller (10%) when shielding conditions were lighter (e.g., outside far away from a single house) and was larger (26%) when they were heavier (e.g., in or close to several houses) because of local moderation of neutrons by shielding materials. We conclude that AMS is useful for verifying calculated neutron doses under mixed exposure conditions with γ rays.

Incidence of and mortality from cardiovascular diseases have been studied in a cohort of 12,210 workers first employed at one of the main plants of the Mayak nuclear facility during 1948–1958 and followed up to 31 December 2000. Information on external γ-ray doses is available for virtually all of these workers (99.9%); the mean total γ-ray dose (±SD) was 0.91 ± 0.95 Gy (99% percentile 3.9 Gy) for men and 0.65 ± 0.75 Gy (99% percentile 2.99 Gy) for women. In contrast, plutonium body burden was measured for only 30.0% of workers; among those monitored, the mean cumulative liver dose from plutonium alpha exposure (± SD) was 0.40 ± 1.15 Gy (99% percentile 5.88 Gy) for men and 0.81 ± 4.60 Gy (99% percentile 15.95 Gy) for women. A total of 3751 cases of ischemic heart disease (IHD), including 683 cases of acute myocardial infarction (AMI), and 1495 IHD deaths, including 338 AMI deaths, were identified in the study cohort during the follow-up period. Having adjusted for non-radiation factors, there were statistically significant increasing trends with both total external γ-ray dose and internal liver dose in IHD incidence. The trend with internal dose was weaker and was not statistically significant after adjusting for external dose, whereas the external dose trend was little changed after adjusting for internal dose. The trend with external dose in IHD mortality was not statistically significantly greater than zero but was consistent with the corresponding trend in IHD incidence. The estimated trend in IHD mortality with internal dose was lower and was not statistically significant once adjustment was made for external dose. There was a statistically significantly increasing trend in AMI incidence but not AMI incidence with external dose. The risk estimates for IHD in relation to external radiation are generally compatible with those from other large occupational studies and the Japanese A-bomb survivors.

Recent reports suggest that mobile phone radiation may diminish male fertility. However, the effects of this radiation on human spermatozoa are largely unknown. The present study examined effects of the radiation on induction of apoptosis-related properties in human spermatozoa. Ejaculated, density-purified, highly motile human spermatozoa were exposed to mobile phone radiation at specific absorption rates (SARs) of 2.0 and 5.7 W/kg. At various times after exposure, flow cytometry was used to examine caspase 3 activity, externalization of phosphatidylserine (PS), induction of DNA strand breaks, and generation of reactive oxygen species. Mobile phone radiation had no statistically significant effect on any of the parameters studied. This suggests that the impairment of fertility reported in some studies was not caused by the induction of apoptosis in spermatozoa.

NFE2-related factor 2 (Nrf2), which belongs to the cap “n” collar family of basic region leucine zipper transcription factors, is a key protein in the coordinated transcriptional induction of expression of various antioxidant genes. The purpose of this study was to analyze the expression of Nrf2 target genes, such as heme oxygenase 1 (HO-1), ferritin heavy polypeptide 1 (FTH1), NAD(P)H dehydrogenase, quinone 1 (NQO1), glutamate-cysteine ligase catalytic subunit, glutamate-cysteine ligase modifier subunit, glutathione reductase (GSR) and thioredoxin reductase 1 (TXNRD1), after X irradiation of CD34 cells that were prepared from human placental/umbilical cord blood hematopoietic stem cells (HSCs). We evaluated the relationship between radiosensitivity and expression of Nrf2 target genes in HSCs. The number of colony-forming cells derived from 2-Gy-irradiated HSCs decreased to approximately 20% of the nonirradiated control. At the same time, the mRNA expression of HO-1, FTH1, NQO1, GSR and TXNRD1 was significantly increased after X irradiation. A statistically significant negative correlation was observed between the surviving fraction of HSCs and the intrinsic NQO1 mRNA expression, indicating that HSCs in which NQO1 mRNA levels are low may also be radioresistant. The present results suggest that the antioxidant system associated with Nrf2 is involved in the radiosensitivity of HSCs.

Recent studies have suggested that visualization of γ-H2AX nuclear foci can be used to estimate exposure to very low doses of ionizing radiation. Although this approach is widely used for various purposes, its suitability for individual human biodosimetry has not yet been assessed. We therefore conducted such an assessment with the help of available software for observing and automatically scoring γ-H2AX foci. The presence of γ-H2AX foci was evaluated in human peripheral blood lymphocytes exposed ex vivo to γ rays in a dose range of 0.02 to 2 Gy. We analyzed the response of γ-H2AX to ionizing radiation in relation to dose, time after exposure, and individual variability. We constructed dose–effect calibration curves at 0.5, 8 and 16 h after exposure and evaluated the threshold of detection of the technique. The results show the promise of automatic γ-H2AX scoring for a reliable assessment of radiation doses in a dose range of 0.6 Gy to 2 Gy up to 16 h after exposure. This γ-H2AX-based assay may be useful for biodosimetry, especially for triage to distinguish promptly among individuals the ones who have received negligible doses from those with significantly exposures who are in need of immediate medical attention. However, additional in vivo experiments are needed for validation.

Cellular lesions (e.g. DSBs) are induced into DNA upon exposure to radiation, with DSB complexity increasing with radiation ionization density. Using M059K and M059J human glioblastoma cells (proficient and deficient in DNA-PKcs activity, respectively), we investigated the repair of DNA damage, including DSBs, induced by high- and low-LET radiation [γ rays, α particles and high-charge and energy (HZE) ions]. In the absence of DNA-PKcs activity, less DSB repair and increased recruitment of RAD51 was seen at 24 h. After exposure to ⁵⁶Fe heavy ions, the number of cells with RAD51 tracks was less than the number of cells with γ-H2AX at 24 h with both cell lines. Using α particles, comparable numbers of cells with visible γ-H2AX and RAD51 were seen at 24 h in both cell lines. M059J cells irradiated with α particles accumulated in S phase, with a greater number of cyclin A and RAD51 co-stained cells seen at 24 h compared with M059K cells, where an S-phase block is absent. It is proposed that DNA-PKcs plays a role in the repair of some frank DSBs, which are longer-lived in NHEJ-deficient cells, and some non-DSB clustered damage sites that are converted into DSBs at replication as the cell cycles through to S phase.

Chromosomal amplifications and deletions are thought to be important events in spontaneous and radiation-induced carcinogenesis. To clarify how ionizing radiation induces mammary carcinogenesis, we characterized genomic copy number aberrations for γ-ray-induced rat mammary carcinomas using microarray-based comparative genomic hybridization. We examined 14 carcinomas induced by γ radiation (2 Gy) and found 26 aberrations, including trisomies of chromosomes 4 and 10 for three and one carcinomas, respectively, an amplification of the chromosomal region 1q12 in two carcinomas, and deletions of the chromosomal regions 3q35q36, 5q32 and 7q11 in two, two and four carcinomas, respectively. These aberrations were not observed in seven spontaneous mammary carcinomas. The expression of p16Ink4a and p19Arf, which are located in the chromosomal region 5q32, was always up-regulated except for a carcinoma with a homozygous deletion of region 5q32. The up-regulation was not accounted for by gene mutations or promoter hypomethylation. However, the amounts of Rb and its mRNA were down-regulated in these carcinomas, indicating a disruption of the p16Ink4a/Rb pathway. This is the first report of array CGH analysis for radiation-induced mammary tumors, which reveals that they show distinct DNA copy number aberration patterns that are different from those of spontaneous tumors and those reported previously for chemically induced tumors.

The study of radiation-induced bystander effects in normal human cells maintained in three-dimensional (3D) architecture provides more in vivo-like conditions and is relevant to human risk assessment. Linear energy transfer, dose and dose rate have been considered as critical factors in propagating radiation-induced effects. This investigation uses an in vitro 3D tissue culture model in which normal AG1522 human fibroblasts are grown in a carbon scaffold to investigate induction of a G₁ arrest in bystander cells that neighbor radiolabeled cells. Cell cultures were co-pulse-labeled with [³H]deoxycytidine (³HdC) to selectively irradiate a minor fraction of cells with 1–5 keV/µm β particles and bromodeoxyuridine (BrdU) to identify the radiolabeled cells using immunofluorescence. The induction of a G₁ arrest was measured specifically in unlabeled cells (i.e. bystander cells) using a flow cytometry-based version of the cumulative labeling index assay. To investigate the relationship between bystander effects and adaptive responses, cells were challenged with an acute 4 Gy γ-radiation dose after they had been kept under the bystander conditions described above for several hours, and the regulation of the radiation-induced G₁ arrest was measured selectively in bystander cells. When the average dose rate in ³HdC-labeled cells (<16% of population) was 0.04–0.37 Gy/h (average accumulated dose 0.14–10 Gy), no statistically significant stressful bystander effects or adaptive bystander effects were observed as measured by magnitude of the G₁ arrest, micronucleus formation, or changes in mitochondrial membrane potential. Higher dose rates and/or higher LET may be required to observe stressful bystander effects in this experimental system, whereas lower dose rates and challenge doses may be required to detect adaptive bystander responses.

Our previous studies demonstrated distant/abscopal bystander effects in A. thaliana seeds and embryos; the postembryonic development of bystander tissues, such as root hair differentiation, primary root elongation, lateral root initiation and survival, were inhibited significantly by localized irradiation with microbeam protons and low-energy ions. In the present study, we further investigated radiation-induced bystander mutagenic effects in vivo in A. thaliana plants using homologous recombination (HR) and the expression level of the HR-related AtRAD54 gene as mutagenic end points. We found that α-particle irradiation of distal primary roots of young seedlings resulted in a significant increase in the frequency of HR in the aerial plants; the increased induction of HR occurred in every true leaf over the course of rosette development. Moreover, we also found that localized α-particle irradiation of roots induced a short-term up-regulated expression of the HR-related AtRAD54 gene in the nonirradiated aerial plants. These results suggested the existence of bystander mutagenic effects in vivo in plants. Treatment with the ROS scavenger DMSO dramatically reduced the effects of localized root irradiation on the induction of HR and expression of the AtRAD54 gene in bystander tissues, suggesting that ROS play a critical role in mediating the bystander mutagenic effects in plants.

To determine the linear energy transfer (LET) dependence of the biological effects of densely ionizing radiation in relation to changes in the ionization density along the track, we measured the yields and spectrum of clustered DNA damages induced by charged particles of different atomic number but similar kinetic energy per nucleon in different DNA microenvironments. Yeast DNA embedded in agarose in solutions of different free radical scavenging capacity was irradiated with 1 GeV protons, 1 GeV/nucleon oxygen ions, 980 MeV/nucleon titanium ions or 968 MeV/nucleon iron ions. The frequencies of double-strand breaks (DSBs), abasic sites and oxypurine clusters were quantified. The total DNA damage yields per absorbed dose induced in non-radioquenching solution decreased with LET, with minor variations in radioquenching conditions being detected. However, the total damage yields per particle fluence increased with LET in both conditions, indicating a higher efficiency per particle to induce clustered DNA damages. The yields of DSBs and non-DSB clusters as well as the damage spectra varied with LET and DNA milieu, suggesting the involvement of more than one mechanism in the formation of the different types of clustered damages.

Radical formation in polycrystalline lithium formate monohydrate after irradiation with γ rays, protons and nitrogen ions at room temperature was studied by continuous-wave electron paramagnetic resonance (EPR) spectroscopy. The linear energy transfer (LET) of the various radiation beams was 0.2, 0.7–3.9 and 110–164 keV/µm for γ rays, protons and nitrogen ions, respectively. Doses between 5 and 20 Gy were given. The EPR reading (the area under the EPR absorption resonance) increased linearly with dose for all types of radiation. As the LET increased, the relative effectiveness (the EPR reading per dose relative to that for γ rays) decreased, while the EPR line width increased. Track structure theory and modeling of detector effectiveness predicted the dosimeter response observed after proton and nitrogen-ion irradiation. A semi-empirical line broadening model including dipolar spin-spin interactions was developed that explained the dependence of the line width on LET. The findings indicate that the local radical density in lithium formate is increased after high-LET irradiation.

Pulmonary tissue is sensitive and often treatment-limiting in patients exposed to total-body irradiation (TBI) in preparation for hematopoietic stem cell transplantation. Many rodent strains, however, exhibit a relatively high resistance to radiation lung damage that often requires extra radiation doses to be delivered locally to the thorax to generate significant levels of pulmonary injury. The present study compared the effects of TBI and bone marrow transplantation (BMT) on two mouse strains that are known to differ in lung radiosensitivity after whole-thorax irradiation, namely the relatively resistant CBA mice and the sensitive C57L mice. Evaluation by survival, microcomputerized tomography (micro-CT), lung tissue weights and histopathology showed that the C57L mice responded with severe lethal radiation pneumonitis at 4 months after 12.5 Gy while CBA mice showed only minimal sublethal damage at this dose. C57L mice receiving 10 Gy TBI also had focal fibrotic lesions in the lungs out to 8 months. The manifestation of both pneumonitis and focal fibrosis in the lungs of C57L mice at relatively low radiation doses points to the merits of using this strain in further studies aimed at exploring and ameliorating the high susceptibility of the lung as encountered in clinical TBI.