Ogura, K., Magae, J., Kawakami, Y. and Koana, T. Reduction in Mutation Frequency by Very Low-Dose Gamma Irradiation of Drosophila melanogaster Germ Cells. Radiat. Res. 171, 1–8 (2009).

To determine whether the linear no-threshold (LNT) model for stochastic effects of ionizing radiation is applicable to very low-dose radiation at a low dose rate, we irradiated immature male germ cells of the fruit fly, Drosophila melanogaster, with several doses of ⁶⁰Co γ rays at a dose rate of 22.4 mGy/h. Thereafter, we performed the sex-linked recessive lethal mutation assay by mating the irradiated males with nonirradiated females. The mutation frequency in the group irradiated with 500 μGy was found to be significantly lower than that in the control group (P < 0.01), whereas in the group subjected to 10 Gy irradiation, the mutation frequency was significantly higher than that in the control group (P < 0.03). A J-shaped dose–response relationship was evident. Molecular experiments using DNA microarray and quantitative reverse transcription PCR indicated that several genes known to be expressed in response to heat or chemical stress and grim, a positive regulator of apoptosis, were up-regulated immediately after irradiation with 500 μGy. The involvement of an apoptosis function in the non-linear dose–response relationship was suggested.

Cao, N., Li, S., Wang, Z., Ahmed, K. M., Degnan, M. E., Fan, M., Dynlacht, J. R. and Li, J. J. NF-κB-Mediated HER2 Overexpression in Radiation-Adaptive Resistance. Radiat. Res. 171, 9–21 (2009).

The molecular mechanisms governing acquired tumor resistance during radiotherapy remain to be elucidated. In breast cancer patients, overexpression of HER2 (human epidermal growth factor receptor 2) is correlated with aggressive tumor growth and increased recurrence. In the present study, we demonstrate that HER2 expression can be induced by radiation in breast cancer cells with a low basal level of HER2. Furthermore, HER2-postive tumors occur at a much higher frequency in recurrent invasive breast cancer (59%) compared to the primary tumors (41%). Interestingly, NF-κB is required for radiation-induced HER2 transactivation. HER2 was found to be co-activated with basal and radiation-induced NF-κB activity in radioresistant but not radiosensitive breast cancer cell lines after long-term radiation exposure, indicating that NF-κB-mediated HER2 overexpression is involved in radiation-induced repopulation in heterogeneous tumors. Finally, we found that inhibition of HER2 resensitizes the resistant cell lines to radiation. Since HER2 is shown to activate NF-κB, our data suggest a loop-like HER2-NF-κB-HER2 pathway in radiation-induced adaptive resistance in breast cancer cells.

Edin, N. J., Sandvik, J. A., Olsen, D. R. and Pettersen, E. O. The Elimination of Low-Dose Hyper-radiosensitivity by Transfer of Irradiated-Cell Conditioned Medium Depends on Dose Rate. Radiat. Res. 171, 22–32 (2009).

Irradiation of T-47D cells with 0.3 Gy delivered by a ⁶⁰Co source at a low dose rate of 0.3 Gy/h abolished low-dose hyper-radiosensitivity (HRS) for at least 14 months (with continuous cell culturing), while the same dose administered acutely (40 Gy/h) eliminated HRS for less than 24 h. Medium transferred from the low-dose-rate primed cells (low-dose-rate ICCM) to unirradiated cells eliminated HRS in recipient cells even if the donor cells had been cultivated for 14 months after the priming dose. Thus low-dose-rate priming activates mechanisms that involve modification or induction of a factor in the medium. This factor affects unirradiated cells in such a way that HRS is eliminated in cells exposed to medium from the primed cells. However, only cells directly exposed to low-dose-rate radiation induce or modify the putative factor, since unirradiated cells that were exposed to low-dose-rate ICCM regained HRS within 2 weeks of cultivation in fresh medium. The ability of ICCM to eliminate HRS in recipient cells is dependent on dose rate. However, an increase in clonogenic survival was observed in cells receiving only medium transfer without subsequent irradiation that was independent of dose rate.

Roig, A. I., Hight, S. K. and Shay, J. W. Two- and Three-Dimensional Models for Risk Assessment of Radiation-Enhanced Colorectal Tumorigenesis. Radiat. Res. 171, 33–40 (2009).

Astronauts may be at an increased risk for developing colorectal cancer after a prolonged interplanetary mission given the potential for greater carcinogenic effects of radiation to the colon. In addition, with an increase in age, there is a greater incidence of premalignant colon adenomas with age. In the present study, we have compared the effects of radiation on human colon epithelial cells in two-dimensional (2D) monolayer culture, in three-dimensional (3D) culture, and in intact human colon tissue biopsies. Immortalized colon epithelial cells were irradiated at the NASA Space Radiation Laboratory (NSRL) with either 1 Gy 1 GeV/nucleon ⁵⁶Fe particles or 1 Gy 1 GeV/nucleon protons and were stained at various times to assess DNA damage and repair responses. The results show more persisting damage at 24 h with iron-particle radiation compared to protons. Similar results were seen in 3D colon epithelial cell cultures in which ⁵⁶Fe-particle-irradiated specimens show more persisting damage at 24 h than those irradiated with low-LET γ rays. We compared these results to those obtained from human colon tissue biopsies irradiated with 1 Gy γ rays or 1 Gy 1 GeV ⁵⁶Fe particles. Observations of radiation-induced DNA damage and repair in γ-irradiated specimens revealed more pronounced early DNA damage responses in the epithelial cell compartment compared to the stromal cell compartment. After low-LET irradiation, the damage foci mostly disappeared at 24 h. Antibodies to more than one type of DNA repair factor display this pattern of DNA damage, and staining of nonirradiated cells with nonphosphorylated DNA-PKcs shows a predominance of epithelial staining over stromal cells. Biopsy specimens irradiated with high-LET radiations also show a pattern of predominance of the DNA damage response in the highly proliferative epithelial cell compartment. Persistent unrepaired DNA damage in colon epithelial cells and the differing repair responses between the epithelial and mesenchymal compartments in tissues may enhance tumorigenesis by both stem cell transformation and alterations in the radiation-induced permissive tissue microenvironment that may potentiate cancer progression.

Sanchez, M. C., Benitez, A., Ortloff, L. and Green, L. M. Alterations in Glutamate Uptake in NT2-Derived Neurons and Astrocytes after Exposure to Gamma Radiation. Radiat. Res. 171, 41–52 (2009).

Currently, the cellular and molecular mechanisms that underlie radiation-induced damage in the CNS are unclear. The present study began investigations of the underlying mechanism(s) for radiation-induced neurotoxicity by characterizing glutamate transport expression and function in neurons and astrocytes after exposure to γ rays. NTera2-derived neurons and astrocytes, isolated as pure cultures, were exposed to doses of 10 cGy, 50 cGy and 2 Gy γ rays, and transporter expression and function were assessed 3 h, 2 days and 7 days after exposure. In neurons, at 7 days after exposure, a significant increase was detected in EAAT3 after 50 cGy (P < 0.05) and a dose-dependent increase in GLT-1 expression was seen between doses of 10 and 50 cGy (P < 0.05). Functional assays of glutamate uptake revealed that neurons and astrocytes respond in a reciprocal manner after irradiation. Neurons responded to radiation exposure by increased glutamate uptake, an effect still evident at our last time (7 days) after exposure (P < 0.05). The astrocyte response to γ radiation was an initial decrease in uptake followed by recovery to baseline levels at 2 days after exposure (P < 0.05). The observations made in this study demonstrate that neurons and astrocytes, while part of the same multifunctional unit, have distinct functional and reciprocal responses. The response in neurons appears to indicate a protracted response with potential long-term effects after irradiation.

Lowe, X. R., Bhattacharya, S., Marchetti, F. and Wyrobek, A. J. Early Brain Response to Low-Dose Radiation Exposure Involves Molecular Networks and Pathways Associated with Cognitive Functions, Advanced Aging and Alzheimer's Disease. Radiat. Res. 171, 53–65 (2009).

Understanding the cognitive and behavioral consequences of brain exposures to low-dose ionizing radiation has broad relevance for health risks from medical radiation diagnostic procedures, radiotherapy and environmental nuclear contamination as well as for Earth-orbit and space missions. Analyses of transcriptome profiles of mouse brain tissue after whole-body irradiation showed that low-dose exposures (10 cGy) induced genes not affected by high-dose radiation (2 Gy) and that low-dose genes were associated with unique pathways and functions. The low-dose response had two major components: pathways that are consistently seen across tissues and pathways that were specific for brain tissue. Low-dose genes clustered into a saturated network (P < 10⁻⁵³) containing mostly down-regulated genes involving ion channels, long-term potentiation and depression, vascular damage, etc. We identified nine neural signaling pathways that showed a high degree of concordance in their transcriptional response in mouse brain tissue after low-dose irradiation, in the aging human brain (unirradiated), and in brain tissue from patients with Alzheimer's disease. Mice exposed to high-dose radiation did not show these effects and associations. Our findings indicate that the molecular response of the mouse brain within a few hours after low-dose irradiation involves the down-regulation of neural pathways associated with cognitive dysfunctions that are also down-regulated in normal human aging and Alzheimer's disease.

Kalm, M., Fukuda, A., Fukuda, H., Öhrfelt, A., Lannering, B., Björk-Eriksson, T., Blennow, K., Márky, I. and Blomgren, K. Transient Inflammation in Neurogenic Regions after Irradiation of the Developing Brain. Radiat. Res. 171, 66–76 (2009).

We characterized the inflammatory response after a single dose of 8 Gy to the brains of postnatal day 9 rats. Affymetrix gene chips revealed activation of multiple inflammatory mechanisms in the acute phase, 6 h after irradiation. In the subacute phase, 7 days after irradiation, genes related to neurogenesis and cell cycle were down-regulated, but glial fibrillary acidic protein (GFAP) was up-regulated. The concentrations of 14 different cytokines and chemokines were measured using a microsphere-based xMAP™ technology. CCL2, Gro/KC and IL-1α were the most strongly up-regulated 6 h after irradiation. CCL2 was expressed in astrocytes and microglia in the dentate gyrus and the subventricular zone (SVZ). Hypertrophy, but not hyperplasia, of astrocytes was demonstrated 7 days after irradiation. In summary, we found transient activation of multiple inflammatory mechanisms in the acute phase (6 h) after irradiation and activation of astrocytes in the subacute phase (7 days) after irradiation. It remains to be elucidated whether these transient changes are involved in the persistent effects of radiation observed on neurogenesis and cognition in rodents.

Sigurdson, A. J., Land, C. E., Bhatti, P., Pineda, M., Brenner, A., Carr, Z., Gusev, B. I., Zhumadilov, Z., Simon, S. L., Bouville, A., Rutter, J. L., Ron, E. and Struewing, J. P. Thyroid Nodules, Polymorphic Variants in DNA Repair and RET-Related Genes, and Interaction with Ionizing Radiation Exposure from Nuclear Tests in Kazakhstan. Radiat. Res. 171, 77–88 (2009).

Risk factors for thyroid cancer remain largely unknown except for ionizing radiation exposure during childhood and a history of benign thyroid nodules. Because thyroid nodules are more common than thyroid cancers and are associated with thyroid cancer risk, we evaluated several polymorphisms potentially relevant to thyroid tumors and assessed interaction with ionizing radiation exposure to the thyroid gland. Thyroid nodules were detected in 1998 by ultrasound screening of 2997 persons who lived near the Semipalatinsk nuclear test site in Kazakhstan when they were children (1949–1962). Cases with thyroid nodules (n = 907) were frequency matched (1:1) to those without nodules by ethnicity (Kazakh or Russian), gender and age at screening. Thyroid gland radiation doses were estimated from fallout deposition patterns, residence history and diet. We analyzed 23 polymorphisms in 13 genes and assessed interaction with ionizing radiation exposure using likelihood ratio tests (LRT). Elevated thyroid nodule risks were associated with the minor alleles of RET S836S (rs1800862, P = 0.03) and GFRA1 −193C>G (rs not assigned, P = 0.05) and decreased risk with XRCC1 R194W (rs1799782, P trend = 0.03) and TGFB1 T263I (rs1800472, P = 0.009). Similar patterns of association were observed for a small number of papillary thyroid cancers (n = 25). Ionizing radiation exposure to the thyroid gland was associated with significantly increased risk of thyroid nodules (age and gender adjusted excess odds ratio/Gy = 0.30, 95% CI 0.05–0.56), with evidence for interaction by genotype found for XRCC1 R194W (LRT P value = 0.02). Polymorphisms in RET signaling, DNA repair and proliferation genes may be related to risk of thyroid nodules, consistent with some previous reports on thyroid cancer. Borderline support for gene-radiation interaction was found for a variant in XRCC1, a key base excision repair protein. Other pathways such as genes in double-strand break repair, apoptosis and genes related to proliferation should also be pursued.

Sommer, A. M., Grote, K., Reinhardt, T., Streckert, J., Hansen, V. and Lerchl, A. Effects of Radiofrequency Electromagnetic Fields (UMTS) on Reproduction and Development of Mice: A Multi-generation Study. Radiat. Res. 171, 89–95 (2009).

Male and female mice (C57BL) were chronically exposed (life-long, 24 h/day) to mobile phone communication electromagnetic fields at approximately 1966 MHz (UMTS). Their development and fertility were monitored over four generations by investigating histological, physiological, reproductive and behavioral functions. The mean whole-body SARs, calculated for adult animals at the time of mating, were 0 (sham), 0.08, 0.4 and 1.3 W/kg. Power densities were kept constant for each group (0, 1.35, 6.8 and 22 W/m²), resulting in varying SARs due to the different numbers of adults and pups over the course of the experiment. The experiment was done in a blind fashion. The results show no harmful effects of exposure on the fertility and development of the animals. The number and the development of pups were not affected by exposure. Some data, albeit without a clear dose–response relationship, indicate effects of exposure on food consumption that is in accordance with some data published previously. In summary, the results of this study do not indicate harmful effects of long-term exposure of mice to UMTS over several generations.

Szőke, I., Farkas, Á., Balásházy, I. and Hofmann, W. Stochastic Aspects of Primary Cellular Consequences of Radon Inhalation. Radiat. Res. 171, 96–106 (2009).

In this study, a composite, biophysical mechanism-based microdosimetric model was developed for the assessment of the primary cellular consequences of radon inhalation. Based on the concentration of radio-aerosols in the inhaled air and the duration of exposure, this mathematical approach allows the computation of the distribution of cellular burdens and the resulting distribution of cellular inactivation and oncogenic transformation probabilities within the epithelium of the human central airways. The composite model is composed of three major parts. The first part is a lung-particle interaction model applying computational fluid and particle dynamics (CFPD) methods. The second part is a lung dosimetry model that quantifies the cellular distribution of radiation exposure within the bronchial epithelium. The third part of the composite model is the unit-track-length model, which allows the prediction of the biological outcome of the exposure at the cellular level. Computations were made for different exposure durations for a miner working in a New Mexico uranium mine. The spatial pattern of the exposed cell nuclei along the epithelium, the distributions of single and multiple α-particle hits, the distributions of cell nucleus doses, and cell inactivation and cell transformation probabilities as a function of the number of inhalations (length of exposure) were investigated and compared for up to 500 inhalations.

Sato, T., Kase, Y., Watanabe, R., Niita, K. and Sihver, L. Biological Dose Estimation for Charged Particle Therapy Using an Improved PHITS Code Coupled with a Microdosimetric Kinetic Model. Radiat. Res. 171, 107–117 (2009).

Microdosimetric quantities such as lineal energy, y, are better indexes for expressing the RBE of HZE particles in comparison to LET. However, the use of microdosimetric quantities in computational dosimetry is severely limited because of the difficulty in calculating their probability densities in macroscopic matter. We therefore improved the particle transport simulation code PHITS, providing it with the capability of estimating the microdosimetric probability densities in a macroscopic framework by incorporating a mathematical function that can instantaneously calculate the probability densities around the trajectory of HZE particles with a precision equivalent to that of a microscopic track-structure simulation. A new method for estimating biological dose, the product of physical dose and RBE, from charged-particle therapy was established using the improved PHITS coupled with a microdosimetric kinetic model. The accuracy of the biological dose estimated by this method was tested by comparing the calculated physical doses and RBE values with the corresponding data measured in a slab phantom irradiated with several kinds of HZE particles. The simulation technique established in this study will help to optimize the treatment planning of charged-particle therapy, thereby maximizing the therapeutic effect on tumors while minimizing unintended harmful effects on surrounding normal tissues.

Marchetti, A. A., McAninch, J. E., Rugel, G., Rühm, W., Korschinek, G., Martinelli, R. E., Faestermann, T., Knie, K., Egbert, S. D., Wallner, A., Wallner, C., Tanaka, K., Endo, S., Hoshi, M., Shizuma, K., Fujita, S., Hasai, H., Imanaka, T. and Straume, T. Fast Neutrons Measured in Copper from the Hiroshima Atomic Bomb Dome. Radiat. Res. 171, 118–122 (2009).

The first measurements of ⁶³Ni produced by A-bomb fast neutrons (above ∼1 MeV) in copper samples from Hiroshima encompassed distances from ∼380 to 5062 m from the hypocenter (the point on the ground directly under the bomb). They included the region of interest to survivor studies (∼900 to 1500 m) and provided the first direct validation of fast neutrons in that range. However, a significant measurement gap remained between the hypocenter and 380 m. Measurements close to the hypocenter are important as a high-value anchor for the slope of the curve for neutron activation as a function of distance. Here we report measurements of ⁶³Ni in copper samples from the historic Hiroshima Atomic Bomb Dome, which is located ∼150 m from the hypocenter. These measurements extend the range of our previously published data for ⁶³Ni providing a more comprehensive and consistent A-bomb activation curve. The results are also in good agreement with calculations based on the current dosimetry system (DS02) and give further experimental support to the accuracy of this system that forms the basis for radiation risk estimates worldwide.

Taylor, M. L., Franich, R. D., Trapp, J. V. and Johnston, P. N. Electron Interaction with Gel Dosimeters: Effective Atomic Numbers for Collisional, Radiative and Total Interaction Processes. Radiat. Res. 171, 123–126 (2009).

The effective atomic number is widely employed in radiation studies, particularly for the characterization of interaction processes in dosimeters, biological tissues and substitute materials. Gel dosimeters are unique in that they comprise both the phantom and dosimeter material. In this work, effective atomic numbers for total and partial electron interaction processes have been calculated for the first time for a Fricke gel dosimeter, five hypoxic and nine normally oxygenated polymer gel dosimeters. A range of biological materials are also presented for comparison. The spectrum of energies studied spans 10 keV to 100 MeV, over which the effective atomic number varies by 30%. The effective atomic numbers of gels match those of soft tissue closely over the full energy range studied; greater disparities exist at higher energies but are typically within 4%.

Blakely, W. F., Carr, Z., Chu, M. C-M., Dayal-Drager, R., Fujimoto, K., Hopmeir, M., Kulka, U., Lillis-Hearne, P., Livingston, G. K., Lloyd, D. C., Maznyk, N., Perez, M. D. R., Romm, H., Takashima, Y., Voisin, P., Wilkins, R. C. and Yoshida, M. A. WHO 1st Consultation on the Development of a Global Biodosimetry Laboratories Network for Radiation Emergencies (BioDoseNet). Radiat. Res. 171, 127–139 (2009).

The World Health Organization (WHO) held a consultation meeting at WHO Headquarters, Geneva, Switzerland, December 17–18, 2007, to develop the framework for a global biodosimetry network. The WHO network is envisioned to enable dose assessment using multiple methods [cytogenetics, electron paramagnetic resonance (EPR), radionuclide bioassays, etc.]; however, the initial discussion focused on the cytogenetic bioassay (i.e., metaphase-spread dicentric assay). Few regional cytogenetic biodosimetry networks have been established so far. The roles and resources available from United Nations (UN) agencies that provide international cooperation in biological dosimetry after radiological emergencies were reviewed. In addition, extensive reliance on the use of the relevant International Standards Organization (ISO) standards was emphasized. The results of a WHO survey of global cytogenetic biological dosimetry capability were reported, and while the survey indicates robust global capability, there was also a clear lack of global leadership and coordination. The expert group, which had a concentrated focus on cytogenetic biodosimetry, formulated the general scope and concept of operations for the development of a WHO global biodosimetry laboratory network for radiation emergencies (BioDoseNet). Follow-on meetings are planned to further develop technical details for this network.