The potential for irradiated cells to induce biological effects in their unirradiated neighbors (known as the bystander effect) has been observed repeatedly in vitro. However, whether bystander effects occur in vivo under the specific conditions relevant to low-dose radiation protection is still unclear. To test this, the fate of bystander cells in the mouse spleen was examined using an adoptive transfer method designed to replicate the rare, irradiated cells in an organ that might be expected after a low-dose-rate, low-LET radiation exposure. Splenic lymphocytes radiolabeled with low activities of ³H-thymidine were introduced into the spleens of unirradiated recipient mice. In this study, the apoptotic and proliferative response of the neighboring bystander spleen cells was compared to the response of spleen cells in parallel control recipients that received sham-irradiated cells. Neither the local area surrounding lodged radiolabeled cells nor the spleen as a whole showed a change in apoptosis or proliferation either 1 or 3 days after adoptive transfer. Increasing the irradiated cell numbers, increasing the mean ³H-thymidine activity per cell, or exposing cells ex vivo to an acute X-ray dose also had no effect. Possible reasons for the absence of a bystander effect in the spleen under these conditions are discussed.

The effect of dose rate on radiation-induced mutations in two somatic tissues, the spleen and liver, was examined in transgenic gpt delta mice. These mice can be used for the detection of deletion-type mutations, and these are the major type of mutation induced by radiation. The dose rates examined were 920 mGy/min, 1 mGy/min and 12.5 µGy/min. In both tissues, the number of mutations increased with increasing dose at each of the three dose rates examined. The mutation induction rate was dependent on the dose rate. The mutation induction rate was higher in the spleen than in the liver at the medium dose rate but was similar in the two tissues at the high and low dose rates. The mutation induction rate in the liver did not show much change between the medium and low dose rates. Analysis of the molecular nature of the mutations indicated that 2- to 1,000-bp deletion mutations were specifically induced by radiation in both tissues after high- and low-dose-rate irradiation. The occurrence of deletion mutation without any sequence homology at the break point was elevated in spleen after high-dose-rate irradiation. The results indicate that the mutagenic effects of radiation in somatic tissues are dependent on dose rate and that there is some variability between tissues.

CD4 CD25 regulatory T cells (Treg cells) are an important subset of T cells for keeping proper immune responses and tolerance. However, the effects of γ radiation on CD4 CD25^high Foxp3 Treg cells have not been examined previously. In the present study, we compared the sensitivity of mouse CD4 CD25^high Foxp3 Treg cells and CD4 CD25⁻ T cells to γ radiation in vitro and in vivo. After C57BL/6 mice received a whole-body dose of 5 Gy γ rays, the numbers of lymphocyte subsets in blood, lymph nodes, spleens and thymuses clearly decreased. However, γ radiation significantly enhanced the ratios of CD4 CD25^high Treg cells and CD4 CD25^high Foxp3 Treg cells to CD4 T cells in the blood, lymph nodes, spleens and thymuses of mice. More dead cells were observed in CD4 CD25⁻ T cells than in CD4 CD25^high Treg cells or CD4 CD25^high Foxp3 Treg cells when the cells were irradiated in vitro, indicating that CD4 CD25^high Foxp3 Treg cells are more resistant to γ radiation than other T cells. Moreover, a higher expression of Bcl-2 in CD4 CD25^high Treg cells was detected compared with that in CD4 CD25⁻ T cells. CD4 CD25 Treg cells from irradiated mice were functional, though their immunosuppressive ability was somewhat impaired compared to those from nonirradiated mice as determined by an in vitro assay. These results indicate that mouse CD4 CD25 Treg cells and CD4 CD25⁻ T effector cells have different sensitivities to γ radiation in mice.

BALB/c mice are sensitive to radiation-induced lymphomagenesis, while STS mice are resistant. Using 219 [(BALB/c × STS)F₁ × BALB/c] (N2C) and 197 [(BALB/c × STS)F₁ × STS] (N2S) animals, we performed a genome-wide search for loci controlling susceptibility to lymphomagenesis induced by radiation. Association of markers with the survival of animals was analyzed by the log rank test. For N2C mice, a significant correlation was detected, with four markers on the proximal to mid portion of chromosome 4: D4Mit302 and D4Mit255, P  =  0.0075; D4Mit17, P  =  0.034; and D4Mit86, P  =  0.048. On the other hand, no significant linkage was detected in N2S mice. We analyzed BALB/c mice congenic for the STS allele in different regions of chromosome 4 and identified a locus with a conspicuous effect on survival located within a 7-Mb region between D4Mit302 and D4Mit144, where BALB/c mice harbor hypomorphic variant alleles of the tumor suppressor gene Cdkn2a, which encodes the cyclin-dependent kinase inhibitor protein p16INK4a. Using pooled F₂ intercrosses between the BALB/c and congenic lines carrying the STS allele near D4Mit17, but not in the range from D4Mit302 to D4Mit144, we assigned the second locus to an 11.4-Mb region in the vicinity of D4Mit17. Although Cdkn2a is a likely candidate for the locus controlling susceptibility to lymphomagenesis on chromosome 4, a novel tumor susceptibility gene different from Cdkn2a exists near the primary locus.

To investigate the relationship of HIF1α signaling to oxidative stress, tissue hypoxia, angiogenesis and inflammation, female Fischer 344 rats were irradiated to the right hemithorax with a fractionated dose of 40 Gy (8 Gy × 5 days). The lung tissues were harvested before and at 4, 6, 10, 14, 18, 22 and 26 weeks after irradiation for serial studies of biological markers, including markers for hypoxia (HIF1α, pimonidazole and CA IX), oxidative stress (8-OHdG), and angiogenesis/capillary proliferation (VEGF/CD 105), as well as macrophage activation (ED-1) and cell signaling/fibrosis (NFκB, TGFβ1), using immunohistochemistry and Western blot analysis. HIF1α staining could be observed as early as 4 weeks postirradiation and was significantly increased with time after irradiation. Importantly, HIF1α levels paralleled oxidative stress (8-OHdG), tissue hypoxia (pimonidazole and CA IX), and macrophage accumulation consistent with inflammatory response. Moreover, changes in HIF1α expression identified by immunohistochemistry assay parallel the changes in TGFβ1, VEGF, NFκB and CD 105 levels in irradiated lungs. These results support the notion that oxidative stress and tissue hypoxia might serve as triggering signals for HIF1α activity in irradiated lungs, relating to radiation-induced inflammation, angiogenesis and fibrosis.

Repair of DNA damage through homologous recombination (HR) pathways plays a crucial role in maintaining genome stability. However, overstimulation of HR pathways in response to genotoxic stress may abnormally elevate recombination frequencies, leading to increased mutation rates and delayed genomic instability. Radiation-induced genomic instability has been detected after exposure to both low- and high-linear energy transfer (LET) radiations, but the mechanisms responsible for initiating or propagating genomic instability are not known. We have demonstrated that WR-1065, the active metabolite of amifostine, protects against radiation-induced cell killing and delayed genomic instability. We hypothesize that hyperstimulation of HR pathways plays a mechanistic role in radiation-induced genomic instability and that, in part, WR-1065 exerts it radioprotective effect through suppression of the HR pathway. Results of this study demonstrate that WR-1065 treatment selectively protected against radiation-induced cell killing in HR-proficient cell lines compared to an HR-deficient cell line. Further, WR-1065 treatment decreases HR in response to DNA damage using two different mammalian cell systems. This suppression of hyper-recombination is a previously unrecognized mechanism by which WR-1065 effects radioprotection in mammalian cells.

To characterize the differences in the radiosensitivity of individual populations of human hematopoietic stem/progenitor cells (HSPCs), we examined the relationship among cell surface antigens, clonogenic potential and radiation survival. The expressions of CD34, CD38, CD45RA, CD110 and Tie-2, early differentiation pathway-related antigens in hematopoiesis, were analyzed on the surface of HSPCs enriched for CD34 antigen expression in 20 samples prepared from human placental/umbilical cord blood. A significantly positive relationship was observed between CD38 antigen and CD45RA and between CD110 and Tie-2. No significant relationship was observed in most cases among the antigens and the number of colony-forming cells (CFCs); however, the number of megakaryocytic progenitor cells correlated negatively with the percentage of Tie-2 cells. The percentage Tie-2 cells correlated significantly with the surviving fraction of CFCs irradiated with 2 Gy of X rays, suggesting that the radiosensitivity of individual CFC populations is related to the percentage of Tie-2-expressing cells. In addition, the number of progenitor cells closely correlated with the surviving fraction after 2 Gy of X rays. These results suggest that the radiosensitivity of individual HSPC populations is related to the number of progenitor cells in the population especially dependent on the presence of immature HSPCs such as Tie-2 cells.

Planning for long-duration manned lunar and interplanetary missions requires an understanding of radiation-induced cataractogenesis. Previously, it was demonstrated that low-linear energy transfer (LET) irradiation with 10 Gy of ⁶⁰Co γ rays resulted in an increased incidence of cataracts in male rats compared to female rats. This gender difference was not due to differences in estrogen, since male rats treated with the major secreted estrogen 17-β-estradiol (E2) showed an identical increase compared to untreated males. We now compare the incidence and rate of progression of cataracts induced by high-LET radiation in male and female Sprague-Dawley rats. Rats received a single dose of 1 Gy of 600 MeV ⁵⁶Fe ions. Lens opacification was measured at 2–4-week intervals with a slit lamp. The incidence and rate of progression of radiation-induced cataracts was significantly increased in the animals in which estrogen was available from endogenous or exogenous sources. Male rats with E2 capsules implanted had significantly higher rates of progression compared to male rats with empty capsules implanted (P  =  0.025) but not compared to the intact female rats. These results contrast with data obtained after low-LET irradiation and suggest the possibility that the different types of damage caused by high- and low-LET radiation may be influenced differentially by steroid sex hormones.

The objective of this study was to assess lenticular changes in a young population years after exposure to protracted long-term low-dose-rate γ radiation in Taiwan. A total of 41 males and 32 females who lived for several years in ⁶⁰Co-contaminated buildings and were less than 20 years old at their first ophthalmological examination in 1998 had a similar examination 4.7 ± 0.5 years later. Lens opacities were examined by slit-lamp biomicroscopy and were scored by the Lens Opacities Classification System III (LOCS III) and a modified subclinical minor focal lens defect (FLD) system. The FLD scores for both eyes were significantly higher than those in the 1998 examinations. Increases in FLD scores compared to those for unexposed subjects occurred particularly in the anterior lens cortex. Increases in FLD scores were also significantly associated with the amount of previous protracted radiation exposure. An exposure-dependent increase in lens opacities was noted years after individuals relocated from the radiocontaminated environment, suggesting that late lenticular changes persisted and progressed in individuals with previous protracted radiation exposure.

To evaluate the genetic effects of A-bomb radiation, we examined mutations at 40 microsatellite loci in exposed families (father-mother-offspring, mostly uni-parental exposures), which consisted of 66 offspring having a mean paternal dose of 1.87 Gy and a mean maternal dose of 1.27 Gy. The control families consisted of 63 offspring whose parents either were exposed to low doses of radiation (< 0.01 Gy) or were not in the cities of Hiroshima or Nagasaki at the time of the bombs. We found seven mutations in the exposed alleles (7/2,789; mutation rate 0.25 × 10⁻²/locus/generation) and 26 in the unexposed alleles (26/7,465; 0.35 × 10⁻²/locus/generation), which does not indicate an effect from parental exposure to radiation. Although we could not assign the parental origins of four mutations, the conclusion may hold since even if we assume that these four mutations had occurred in the exposed alleles, the estimated mean mutation rate would be 0.39 × 10⁻² in the exposed group [(7 4)/2,789)], which is slightly higher than 0.35 × 10⁻² in the control group, but the difference is not statistically significant.

As genome-wide association studies of breast cancer are replicating findings and refinement studies are narrowing the signal location, additional efforts are necessary to elucidate the underlying functional relationships. One approach is to evaluate variation in risk by genotype based on known breast carcinogens, such as ionizing radiation. Given the public health concerns associated with recent increases in medical radiation exposure, this approach may also identify potentially susceptible subpopulations. We examined interaction between 27 newly identified breast cancer risk alleles (identified within the NCI Cancer Genetic Markers of Susceptibility and the Breast Cancer Association Consortium genome-wide association studies) and occupational and medical diagnostic radiation exposure among 859 cases and 1083 controls nested within the United States Radiologic Technologists cohort. We did not find significant variation in the radiation-related breast cancer risk for the variant in RAD51L1 (rs10483813) on 14q24.1 as we had hypothesized. In exploratory analyses, we found that the radiation-associated breast cancer risk varied significantly by linked markers in 5p12 (rs930395, rs10941679, rs2067980 and rs4415084) in the mitochondrial ribosomal protein S30 (MRPS30) gene (P_interaction  =  0.04). Chance, however, may explain these findings, and as such, these results need to be confirmed in other populations with low to moderate levels of radiation exposure. Even though a complete understanding of the way(s) in which these variants may increase breast cancer risk remains elusive, this approach may yield clues for further investigation.

The scientific literature contains an ever-growing number of reports of applications of vibrational spectroscopy as a multivariate non-invasive tool for analysis of biological effects at the molecular level. Recently, Fourier transform infrared microspectroscopy (FTIRM) has been demonstrated to be sensitive to molecular events occurring in cells and tissue after exposure to ionizing radiation. In this work the application of FTIRM in the examination of dose-dependent molecular effects occurring in skin cells after exposure to ionizing radiation with the use of partial least-squares regression (PLSR) and generalized regression neural networks (GRNN) was studied. The methodology is shown to be sensitive to molecular events occurring with radiation dose and time after exposure. The variation in molecular species with dose and time after irradiation is shown to be non-linear by virtue of the higher modeling efficiency yielded from the non-linear algorithms. Dose prediction efficiencies of approximately ±10 mGy were achieved at 96 h after irradiation, highlighting the potential applications of the methodology in radiobiological dosimetry.

We calculated how the radiation environment in a habitat on the surface of the Moon would have depended on the thickness of the habitat in the 1977 galactic cosmic-ray environment. The Geant4 Monte Carlo transport code was used, and a hemispherical dome made of lunar regolith was used to simulate the lunar habitat. We investigated the effective dose from primary and secondary particles including nuclei from protons up to nickel, neutrons, charged pions, photons, electrons and positrons. The total effective dose showed a strong decrease with the thickness of the habitat dome. However, the effective dose values from secondary neutrons, charged pions, photons, electrons and positrons all showed a strong increase followed by a gradual decrease with the habitat thickness. The fraction of the summed effective dose from these secondary particles in the total effective dose increased with the habitat thickness, from ∼5% for the no-habitat case to about 47% for the habitat with an areal thickness of 100 g/cm².

Radiation exposures from accidents, nuclear detonations or terrorist incidents are unlikely to be homogeneous; however, current biodosimetric approaches are developed and validated primarily in whole-body irradiation models. A workshop was held at the Armed Forces Radiobiology Research Institute in May 2008 to draw attention to the need for partial-body biodosimetry, to discuss current knowledge, and to identify the gaps to be filled. A panel of international experts and the workshop attendees discussed the requirements and concepts for a path forward. This report addresses eight key areas identified by the Workshop Program Committee for future focus: (1) improved cytogenetics, (2) clinical signs and symptoms, (3) cutaneous bioindicators, (4) organ-specific biomarkers, (5) biophysical markers of dose, (6) integrated diagnostic approaches, (7) confounding factors, and (8) requirements for post-event medical follow-up. For each area, the status, advantages and limitations of existing approaches and suggestions for new directions are presented.