Chromosome translocations are a well-recognized biological marker of radiation exposure and cancer risk. However, there is uncertainty about the lowest dose at which excess translocations can be detected, and whether there is temporal decay of induced translocations in radiation-exposed populations. Dosimetric uncertainties can substantially alter the shape of dose-response relationships; although regression-calibration methods have been used in some datasets, these have not been applied in radio-occupational studies, where there are also complex patterns of shared and unshared errors that these methods do not account for. In this article we evaluated the relationship between estimated occupational ionizing radiation doses and chromosome translocation rates using fluorescent in situ hybridization in 238 U.S. radiologic technologists selected from a large cohort. Estimated cumulative red bone marrow doses (mean 29.3 mGy, range 0–135.7 mGy) were based on available badge–dose measurement data and on questionnaire-reported work history factors. Dosimetric assessment uncertainties were evaluated using regression calibration, Bayesian and Monte Carlo maximum likelihood methods, taking account of shared and unshared error and adjusted for overdispersion. There was a significant dose response for estimated occupational radiation exposure, adjusted for questionnaire-based personal diagnostic radiation, age, sex and study group (5.7 translocations per 100 whole genome cell equivalents per Gy, 95% CI 0.2, 11.3, P = 0.0440). A significant increasing trend with dose continued to be observed for individuals with estimated doses <100 mGy. For combined estimated occupational and personal-diagnostic-medical radiation exposures, there was a borderline-significant modifying effect of age (P = 0.0704), but little evidence (P > 0.5) of temporal decay of induced translocations. The three methods of analysis to adjust for dose uncertainty gave similar results. In summary, chromosome translocation dose-response slopes were detectable down to <100 mGy and were compatible with those observed in other radiation-exposed populations. However, there are substantial uncertainties in both occupational and other (personal-diagnostic-medical) doses that may be imperfectly taken into account in our analysis.

Space missions beyond the protection of Earth's magnetosphere expose astronauts to an environment that contains ionizing proton radiation. The hazards that proton radiation pose to normal tissues, such as the central nervous system (CNS), are not fully understood, although it has been shown that proton radiation affects the neurogenic environment, killing neural precursors and altering behavior. To determine the time and dose-response characteristics of the CNS to whole-body proton irradiation, C57BL/6J mice were exposed to 1 GeV/n proton radiation at doses of 0–200 cGy and behavioral, physiological and immunohistochemical end points were analyzed over a range of time points (48 h–12 months) postirradiation. These experiments revealed that proton radiation exposure leads to: 1. an acute decrease in cell division within the dentate gyrus of the hippocampus, with significant differences detected at doses as low as 10 cGy; 2. a persistent effect on proliferation in the subgranular zone, at 1 month postirradiation; 3. a decrease in neurogenesis at doses as low as 50 cGy, at 3 months postirradiation; and 4. a decrease in hippocampal ICAM-1 immunoreactivity at doses as low as 10 cGy, at 1 month postirradiation. The data presented contribute to our understanding of biological responses to whole-body proton radiation and may help reduce uncertainty in the assessment of health risks to astronauts. These findings may also be relevant to clinical proton beam therapy.

The altered DNA damage response pathway in patients with Fanconi anemia (FA) may increase the toxicity of clinical radiotherapy. We quantitated oral cavity mucositis in irradiated Fanconi anemia Fancd2^–/– mice, comparing this to Fancd2 ^/– and Fancd2 ^/ mice, and we measured distant bone marrow suppression and quantitated the effect of the intraoral radioprotector GS-nitroxide, JP4-039 in F15 emulsion. We found that FA mice were more susceptible to radiation injury and that protection from radiation injury by JP4-039/F15 was observed at all radiation doses. Adult 10–12-week-old mice, of FVB/N background Fancd2^–/–, Fancd2 ^/– and Fancd2 ^/ were head and neck irradiated with 24, 26, 28 or 30 Gy (large fraction sizes typical of stereotactic radiosurgery treatments) and subgroups received intraoral JP4-039 (0.4 mg/mouse in 100 μL F15 liposome emulsion) preirradiation. On day 2 or 5 postirradiation, mice were sacrificed, tongue tissue and femur marrow were excised for quantitation of radiation-induced stress response, inflammatory and antioxidant gene transcripts, histopathology and assay for femur marrow colony-forming hematopoietic progenitor cells. Fancd2^–/– mice had a significantly higher percentage of oral mucosal ulceration at day 5 after 26 Gy irradiation (59.4 ± 8.2%) compared to control Fancd2 ^/ mice (21.7 ± 2.9%, P = 0.0063). After 24 Gy irradiation, Fancd2^–/– mice had a higher oral cavity percentage of tongue ulceration compared to Fancd2 ^/ mice irradiated with higher doses of 26 Gy (P = 0.0123). Baseline and postirradiation oral cavity gene transcripts were altered in Fancd2^–/– mice compared to Fancd2 ^/ controls. Fancd2^–/– mice had decreased baseline femur marrow CFU-GM, BFUe and CFU-GEMM, which further decreased after 24 or 26 Gy head and neck irradiation. These changes were not seen in head- and neck-irradiated Fancd2 ^/ mice. In radiosensitive Fancd2^–/– mice, biomarkers of both local oral cavity and distant marrow radiation toxicity were ameliorated by intraoral JP4-039/F15. We propose that Fancd2^–/– mice are a valuable radiosensitive animal model system, which can be used to evaluate potential radioprotective agents.

Pancreatic cancer is relatively radioresistant, however, radiotherapy has been shown to provide efficacy in the treatment of local disease. To increase the effectiveness of radiotherapy in pancreatic cancer, radiosensitizing drugs are under development. In this study, we investigated the radiosensitizing activity of the anti-diabetic drug metformin on pancreatic cancer cells in vitro. We demonstrated that metformin radiosensitized MiaPaCa-2 and Panc1 cells with radiation enhancement ratios (ER) ranging from 1.33–1.45 with metformin concentrations of 30–100 μM, and in addition, we showed that metformin sensitized cells to gemcitabine alone or in combination with radiation treatment. In addition, we found that pancreatic cancer stem cell-like cells showed enhanced radiosensitization in a tumorsphere assay with a REF of 1.66. At these radiosensitizing doses, metformin alone had low toxicity (as shown by >75% clonogenic survival) and did not affect cell cycle. The combination of metformin and radiation yielded greater numbers of γ-H2AX foci after 1 h compared to radiation alone, suggesting increased DNA damage signaling. Examination of the AMPK pathway showed that pharmacological inhibition of AMPK signaling or RNAi of AMPKα1 reversed metformin-mediated radiosensitization. These studies show that metformin radiosensitization of pancreatic cancer cells at micromolar concentration acts through AMPK and may affect DNA damage signaling. The data indicate that metformin may increase the efficacy of radiation therapy for pancreatic cancer.

Patients treated with whole-brain irradiation often develop cognitive deficits that are presumed to result from normal tissue injury. Age is a risk factor for these side effects. We compared the cognitive effects of fractionated whole-brain irradiation (300 kV X rays) in rats irradiated either as young adults or in middle age. A deficit in object memory was apparent at 3 months in rats irradiated as young adults, however, no comparable deficit was apparent in rats irradiated in middle age. In addition, the deficit in object memory in young adults was no longer apparent at 6 and 12 months after fractionated whole-brain irradiation and no radiation-induced deficit was detectable in a spatial memory task at any time, regardless of age at time of irradiation. Thus, clinically relevant fractionated whole-brain irradiation in adult rats resulted in early-delayed cognitive changes that were heterogeneous, transient and age-dependent. The results of the current and previous studies of radiation-induced cognitive changes support the continued investigation and validation of rodent models of radiation-induced brain injury, which are critical for developing and testing new therapies for treatment-induced cognitive dysfunction in cancer survivors.

Relationships based on the microdosimetric-kinetic model are presented that calculate the average number of lethal lesions, and the associated cell survival, produced in mammalian cells by exposure to protracted continuous irradiation by temporary and permanent implantation of radioactive sources. The influence of cell parameters of linear-quadratic survival, repair function and proliferation rate, as well as the influence of dose rate, isotopic decay rate and linear energy transfer (LET) quality on cell killing are displayed and discussed. An expression for biologic effective dose (BED) is presented that facilitates comparison of the effects of protracted low-dose-rate irradiation and with a course of multiple instantaneously administered radiation treatments (fractions).

In a previous study, we established an image-guided small-animal micro-irradiation system mimicking clinical stereotactic body radiotherapy (SBRT). The goal of this study was to develop a rodent model of acute phase lung injury after ablative irradiation. A radiation dose of 90 Gy was focally delivered to the left lung of C57BL/6 mice using a small animal stereotactic irradiator. At days 1, 3, 5, 7, 9, 11 and 14 after irradiation, the lungs were perfused with formalin for fixation and paraffin sections were stained with hematoxylin and eosin (H&E) and Masson's trichrome. At days 7 and 14 after irradiation, micro-computed tomography (CT) images of the lung were taken and lung functional measurements were performed with a flexiVent™ system. Gross morphological injury was evident 9 days after irradiation of normal lung tissues and dynamic sequential events occurring during the acute phase were validated by histopathological analysis. CT images of the mouse lungs indicated partial obstruction located in the peripheral area of the left lung. Significant alteration in inspiratory capacity and tissue damping were detected on day 14 after irradiation. An animal model of radiation-induced lung injury (RILI) in the acute phase reflecting clinical stereotactic body radiotherapy was established and validated with histopathological and functional analysis. This model enhances our understanding of the dynamic sequential events occurring in the acute phase of radiation-induced lung injury induced by ablative dose focal volume irradiation.

There is an increasing need to better understand the long-term health effects of high-linear energy transfer (LET) radiation due to exposure during space missions, as well as its increasing use in clinical treatments. Previous studies have indicated that exposure to ⁵⁶Fe heavy ions increases the incidence of acute myeloid leukemia (AML) in mice but the underlying molecular mechanisms remain elusive. Epigenetic alterations play a role in radiation-induced genomic instability and the initiation and progression of AML. In this study, we assessed the effects of low-dose ⁵⁶Fe-ion irradiation on epigenetic alterations in bone marrow mononuclear cells (BM-MNCs) and hematopoietic progenitor and stem cells (HPSCs). Exposure to ⁵⁶Fe ions (600 MeV, 0.1, 0.2 and 0.4 Gy) resulted in significant epigenetic alterations involving methylation of DNA, the DNA methylation machinery and expression of repetitive elements. Four weeks after irradiation, these changes were primarily confined to HPSCs and were exhibited as dose-dependent hypermethylation of LINE1 and SINE B1 repetitive elements [4.2-fold increase in LINE1 (P < 0.001) and 7.6-fold increase in SINE B1 (P < 0.01) after exposure to 0.4 Gy; n = 5]. Epigenetic alterations were persistent and detectable for at least 22 weeks after exposure, when significant loss of global DNA hypomethylation (1.9-fold, P < 0.05), decreased expression of Dnmt1 (1.9-fold, P < 0.01), and increased expression of LINE1 and SINE B1 repetitive elements (2.8-fold, P < 0.001 for LINE1 and 1.9-fold, P < 0.05 for SINE B1; n = 5) were observed after exposure to 0.4 Gy. In contrast, exposure to ⁵⁶Fe ions did not result in accumulation of increased production of reactive oxygen species (ROS) and DNA damage, exhibited as DNA strand breaks. Furthermore, no significant alterations in cellular senescence and apoptosis were detected in HPSCs after exposure to ⁵⁶Fe-ion radiation. These findings suggest that epigenetic reprogramming is possibly involved in the development of radiation-induced genomic instability and thus, may have a causative role in the development of AML.

Secoisolariciresinol diglucoside (SDG) is the major lignan in wholegrain flaxseed. However, extraction methods are complex and are associated with low yield and high costs. Using a novel synthetic pathway, our group succeeded in chemically synthesizing SDG (S,S and R,R enantiomers), which faithfully recapitulates the properties of their natural counterparts, possessing strong antioxidant and free radical scavenging properties. This study further extends initial findings by now investigating the DNA-radioprotective properties of the synthetic SDG enantiomers compared to the commercial SDG. DNA radioprotection was assessed by cell-free systems such as: (a) plasmid relaxation assay to determine the extent of the supercoiled (SC) converted to open-circular (OC) plasmid DNA (pBR322) after exposure of the plasmid to gamma radiation; and (b) determining the extent of genomic DNA fragmentation. Exposure of plasmid DNA to 25 Gy of γ radiation resulted in decreased supercoiled form and increased open-circular form, indicating radiation-induced DNA damage. Synthetic SDG (S,S) and SDG (R,R), and commercial SDG at concentrations of 25–250 μM significantly and equipotently reduced the radiation-induced supercoiled to open-circular plasmid DNA in a dose-dependent conversion. In addition, exposure of calf thymus DNA to 50 Gy of gamma radiation resulted in DNA fragments of low-molecular weight (<6,000 bps), which was prevented in a dose-dependence manner by all synthetic and natural SDG enantomers, at concentrations as low as 0.5 μM. These novel results demonstrated that synthetic SDG (S,S) and SDG (R,R) isomers and commercial SDG possess DNA-radioprotective properties. Such properties along with their antioxidant and free radical scavenging activity, reported earlier, suggest that SDGs are promising candidates for radioprotection for normal tissue damage as a result of accidental exposure during radiation therapy for cancer treatment.

Radiation-induced bystander effects are a well-known phenomenon that are observed when treating cancer and other diseases after radiotherapy, and even after occupational exposure to radiation. However, little is known about the crosstalk between irradiated macrophages and endothelial cells that line the circulatory system, which may play a role in the development of atherosclerosis. In the current study, we found that the expression of inducible nitric oxide synthase (iNOS) and the intracellular level of nitric oxide (NO) in gamma-irradiated U937 macrophage cells were significantly increased. When human umbilical vein endothelial cells (HUVECs) were co-cultured with gamma-irradiated U937 cells, additional micronuclei (MN) and apoptosis were induced so that the plating efficiency of the bystander HUVECs decreased and P38 was overexpressed in the bystander HUVECs cells. In addition, the contents of vascular cell adhesion molecule 1 (VCAM-1) and the activities of matrix metalloproteinase-9 (MMP-9) in the culture medium of bystander HUVECs were increased. Furthermore, during cell co-culture the adhesive ability of irradiated U937 cells to the bystander HUVECs increased. When U937 cells were treated with 500 μM S-methylisothiourea sulfate (SMT) (iNOS inhibitor) before irradiation, and HUVECs were treated with 10 μM SB203580 (p38 inhibitor) before cell co-culture or treated with 20 μM c-PTIO (NO scavenger) in the co-culture medium, the bystander micronuclei and the amounts of VCAM-1 and MMP-9 in the medium of bystander HUVECs were diminished, and the ability of irradiated U937 cells adhering to HUVECs was also reduced, while the plating efficiency of bystander HUVECs partially recovered. These results demonstrated that irradiated U937 cells appear to release nitric oxide and thereby further trigger apoptosis and inflammatory responses in the bystander HUVECs through a p38-dependent pathway.