Sagstuen, E., Sanderud, A. and Hole, E. O., The Solid-State Radiation Chemistry of Simple Amino Acids, Revisited. Radiat. Res. 162, 112–119 (2004).

The solid-state radiation-induced free radical formation in simple amino acids like α-glycine (gly) and l-α-alanine (ala) has been the subject of investigations by EPR spectroscopy since the late 1950s. The EPR spectra from crystals of gly and ala generally are very complex due to the simultaneous trapping of several free radicals regardless of irradiation and observation temperatures. Untangling these complex spectra is necessary for understanding the mechanisms for the solid-state radiation chemistry of amino acids. Recently, radical formation in gly and ala after room-temperature irradiation has been reinvestigated in our laboratories using X-, K- and Q-band EPR and ENDOR spectroscopy, combined with the ENDOR-induced EPR (EIE) techniques as well as single-crystal and powder EPR and ENDOR spectrum simulations. Several new radical products have been detected and characterized, most prominently the gly species H₂N − C^·H − COOH and the ala species H₃ N − C^·(CH₃) − COO⁻ and H₂N − C^·(CH₃) − COOH. A short description of these radicals is given, and an overview of the solid-state radiation chemistry of the simple amino acids is presented, based on a review of the literature combined with these recent experimental results.

Heyes, G. H. and Mill, A. J. The Neoplastic Transformation Potential of Mammography X Rays and Atomic Bomb Spectrum Radiation. Radiat. Res. 162, 120–127 (2004).

Considerable controversy currently exists regarding the biological effectiveness of 29 kVp X rays which are used for mammography screening. This issue must be resolved to enable proper evaluation of radiation risks from breast screening. Here a definitive assessment of the biological effectiveness of 29 kVp X rays compared to the quality of radiation to which the atomic bomb survivors were exposed is presented for the first time. The standard radiation sources used were (a) an atomic bomb simulation spectrum and (b) 2.2 MeV electrons from a strontium-90/yttrium-90 (⁹⁰Sr/⁹⁰Y) radioactive source. The biological end point used was neoplastic transformation in vitro in CGL1 (HeLa × human fibroblast hybrid) cells. No significant difference was observed for the biological effectiveness of the two high-energy sources for neoplastic transformation. A limiting relative biological effectiveness (RBE_M) of 4.42 ± 2.02 was observed for neoplastic transformation by 29 kVp X rays compared to these two sources. This compares with values of 4.67 ± 3.93 calculated from previously published data and 3.58 ± 1.77 when the reference radiation was 200 and 220 kVp X rays. This suggests that the risks associated with mammography screening may be approximately five times higher than previously assumed and that the risk–benefit relationship of mammography exposures may need to be re-examined.

Fletcher, L., Cerniglia, G. J., Nigg, E. A., Yen, T. J. and Muschel, R. J. Inhibition of Centrosome Separation after DNA Damage: A Role for Nek2. Radiat. Res. 162, 128–135 (2004).

DNA damage results in cell cycle arrest in G₂. Centrosomes also separate in G₂, raising the question of whether separation occurs during the DNA damage-induced G₂ arrest. Nek2, the mammalian homologue of NIMA, is a cell cycle-regulated serine/threonine protein kinase that regulates centrosome separation during G₂. Here we show that damaged cells fail to activate Nek2. Both Nek2 levels and activity are reduced after DNA damage. Radiation inhibits the premature centrosome splitting induced by overexpression of Nek2, indicating that Nek2 is involved in activation of the G₂ checkpoint and is not secondary to cell cycle arrest. We confirm using siRNA that centrosome separation and cell growth are impaired in the absence of Nek2. These studies define a previously unreported DNA damage response of inhibition of centrosome separation mechanistically linked to Nek2.

Latre, L., Genescà, A., Martín, M., Ribas, M., Egozcue, J., Blasco, M. A. and Tusell, L. Healing of DNA Broken Ends is Similar in Embryonic Fibroblasts with and without Telomerase. Radiat. Res. 162, 136–142 (2004).

Telomeres cap the ends of chromosomes, preventing end-to-end fusions and subsequent chromosome instability. Here we used a telomerase knockout model to investigate whether telomerase participates in the processes of DNA break repair by de novo synthesis of telomere repeats at broken chromosome ends (chromosome healing). Chromosome healing giving rise to new detectable telomeric signals has not been observed in embryonic fibroblasts of telomerase-proficient mice exposed to ionizing radiation. Since the synthesis of telomeric sequences to broken DNA ends would make them refractory to rejoining events, the efficiency of rejoining of broken chromosomes in cell environments with and without telomerase has also been investigated. We conclude that the efficiency of rejoining broken chromosomes is not significantly different in the two cell environments. All together, our results indicate that there is no significant involvement of telomerase in the healing of broken DNA ends by synthesizing new telomeres in mouse embryo fibroblasts after exposure to ionizing radiation.

Yoshioka, Y., Yamazaki, H., Yoshida, K., Ozeki, S., Inoue, T., Yoneda, M. and Inoue, T. Impact of Mitochondrial DNA on Radiation Sensitivity of Transformed Human Fibroblast Cells: Clonogenic Survival, Micronucleus Formation and Cellular ATP Level. Radiat. Res. 162, 143–147 (2004).

The purpose of this study was to evaluate the impact of mitochondrial DNA (mtDNA) on the radiation sensitivity of transformed human fibroblast cells. The ρ and ρ⁰ human fibroblast cell lines were used, which carry wild-type mtDNA and no mtDNA, respectively. Clonogenic radiosensitivity was evaluated by colony formation assay and micronucleus (MN) formation assay. The ATP assay was then used to address the discrepancy between the results of the former two assays. Despite the lack of a significant difference in survival in the colony formation assay, ρ and ρ⁰ cells exhibited high and low radiosensitivities, respectively, in the MN formation assay (P < 0.003). This difference in MN formation correlated with high and low levels of cellular ATP content in ρ and ρ⁰ cells (P = 0.004). The addition of antimycin A suppressed differences in both MN formation and cellular ATP content. In the transformed human fibroblast cells we used, mtDNA played an important role in radiation-induced MN formation that was correlated with the levels of cellular ATP content. These results may imply the presence of an MN expression pathway that is dependent on the intrinsic ATP level and that may be compensated and lead to an equivalent level of clonogenic survival.

Pecaut, M. J., Haerich, P., Zuccarelli Miller, C. N., Smith, A. L., Zendejas, E. D. and Nelson, G. A. The Effects of Low-Dose, High-LET Radiation Exposure on Three Models of Behavior in C57BL/6 Mice. Radiat. Res. 162, 148–156 (2004).

To investigate the behavioral consequences of exposure to whole-body irradiation such as might occur for astronauts during space flight, female C57BL/6 mice were exposed to 0, 0.1, 0.5 or 2 Gy accelerated iron ions (⁵⁶Fe, Z = 26, β = 0.9, LET = 148.2 keV/μm) of 1 GeV per nucleon using the Alternating Gradient Synchrotron at the Brookhaven National Laboratory. Animal testing began 2 weeks after exposure and continued for 8 weeks. Under these conditions, there were few significant effects of radiation on open-field, rotorod or acoustic startle activities at any of the times examined. The lack of radiation effects in these behavioral models appears to offer reassurance to NASA mission designers. These results suggest that there may be negligible effects of HZE radiation on many behaviors during a 2–8-week period immediately after radiation.

Hao, J., Sun, L., Huang, H., Xiong, G., Liu, X., Qiu, L., Chen, G., Dong, B., Li, Y., Chen, W., Buechler, Y., Sun, J., Shen, C. and Luo, Q. Effects of Recombinant Human Interleukin 11 on Thrombocytopenia and Neutropenia in Irradiated Rhesus Monkeys. Radiat. Res. 162, 157–163 (2004).

The effects of recombinant human interleukin 11 (rhIL11) on thrombocytopenia and neutropenia in irradiated rhesus monkeys were evaluated after administration different doses at different times. Twenty-three rhesus monkeys were exposed to a total-body irradiation (TBI) with a single dose of 3 Gy ⁶⁰Co γ rays. Either placebo, rhIL11 at a dose of 30, 60 or 120 μg/kg day⁻¹ on days 0–13, or rhIL11 at a dose of 60 μg/kg day⁻¹ on days 13–26 after TBI was administered to the animals. The results showed that the immediate treatment with rhIL11 but not treatment on days 13–26 resulted in much higher platelet nadirs than in the placebo-treated group. The accelerated recovery of platelets to normal levels after TBI was demonstrated in all groups treated with rhIL11, but the effects of rhIL11 were independent of dose. However, rhIL11 treatment could also accelerate the recovery of leukocytes to normal levels. The numbers of colony-forming bone marrow cells (CFU-E, CFU-Mix, CFU-MK and CFU-GM) in all groups treated with rhIL11 were increased 4- to 14-fold relative to those of the placebo group on day 30. We conclude that rhIL11 may directly promote megakaryocyte development and ameliorate myelosuppression in irradiated monkeys.

Lindholm, C., Murphy, B. P., Bigbee, W. L., Bersimbaev, R. I., Hultén, M. A., Dubrova, Y. E. and Salomaa, S. Glycophorin A Somatic Cell Mutations in a Population Living in the Proximity of the Semipalatinsk Nuclear Test Site. Radiat. Res. 162, 164–170 (2004).

The glycophorin A (GPA) somatic mutation assay was performed to evaluate the magnitude of exposure to ionizing radiation among the human population living in the vicinity of the Semipalatinsk nuclear test site in Kazakhstan. All together, 113 blood samples were analyzed from three generations of people living in villages that were under the trail of the radioactive cloud from the first Soviet surface nuclear test performed in August 1949 and from later tests. The oldest generation (P₀) lived in the area at the time of testing, whereas the younger generations (F₁, F₂) were exposed to smaller doses from the residual fallout and later tests. The GPA assay did not reveal significant differences in the variant cell frequencies for all subjects selected from the Semipalatinsk area compared with 74 matched controls living in a noncontaminated area. However, a significant increase (P < 0.05) in the mean allele-loss ØN variant frequency was observed among the exposed P₀ generation (12 × 10⁻⁶) in comparison to controls (7 × 10⁻⁶). Considering the sensitivity of the GPA assay, the results suggest that the mean dose to the P₀ generation of the affected villages was relatively low, a finding which is in accordance to the conclusions obtained from other biological assays performed on the same population.

Bijwaard, H., Brugmans, M. J. P. and Leenhouts, H. P. Two-Mutation Models for Bone Cancer due to Radium, Strontium and Plutonium. Radiat. Res. 162, 171–184 (2004).

Data from beagle experiments and radium dial painters were used to derive two-mutation carcinogenesis models for bone cancer induced by the bone-seeking radionuclides radium, strontium and plutonium. For all data, the model fits indicate that at low doses both mutation rates depend linearly and equally strongly on dose rate. For the high-LET α-particle emitters, a cell killing term reduces the second mutation rate at high dose rates. In all cases, the combined effect of both mutation rates is a linear-quadratic dose–effect relationship for cancer at low doses. This behavior may lead to experimental data that could be mistaken as showing a threshold below which no cancers are induced. Derived parameters such as toxicity ratios and tumor growth times compare well with values reported in the literature. Furthermore, results for plutonium indicate that rapid burial of the nuclide in the growing bones of juvenile beagles leads to a significant reduction of its toxicity, as was suggested previously. The results for radium in beagles compare well with those for humans and suggest that the models derived for strontium and plutonium in beagles may be translated to humans. The significant model parameters for the accurate animal data could then also be used to fit human epidemiological data.

Maxim, P. G., Carson, J. J. L., Ning, S., Knox, S. J., Boyer, A. L., Hsu, C. P., Benaron, D. A. and Walleczek, J. Enhanced Effectiveness of Radiochemotherapy with Tirapazamine by Local Application of Electric Pulses to Tumors. Radiat. Res. 162, 185–193 (2004).

Tumor hypoxia is associated with resistance to radiotherapy and anticancer chemotherapy. However, it can be exploited to therapeutic advantage by concomitantly using hypoxic cytotoxins, such as tirapazamine (TPZ). Tumor electroporation offers the means to further increase tumor hypoxia by temporarily reducing tumor blood flow and therefore increase the cytotoxicity of TPZ. The primary objective of this work was to determine whether electric pulses combined with TPZ and radiotherapy (electroradiochemotherapy) was more efficacious than radiochemotherapy (TPZ radiation). In these studies using the SCCVII tumor model in C3H mice, electroradiochemotherapy produced up to sixfold more tumor growth delay (TGD) than TPZ radiation. In these studies, (1) large tumors (280 ± 15 mm³) responded better to electroradiochemotherapy than small tumors (110 ± 10 mm³), (2) TGD correlated linearly with tumor volume at the time of electroradiochemotherapy, (3) electric pulses induced a rapid but reversible reduction in O₂ saturation, and (4) the electric field was highest near the periphery of the tumor in a 3D computer model. The findings suggested that electroradiochemotherapy gained its therapeutic advantage over TPZ radiation by enhancing the cytotoxic action of TPZ through reduced tumor oxygenation. The greater antitumor effect achieved in large tumors may be related to tumor morphology and the electric-field distribution. These results suggest that electro-pulsation of large solid tumors may be of benefit to patients treated with radiation in combination with agents that kill hypoxic cells.

Sommer, A. M. and Lerchl, A. The Risk of Lymphoma in AKR/J Mice does not Rise with Chronic Exposure to 50 Hz Magnetic Fields (1 μT and 100 μT). Radiat. Res. 162, 194– 200 (2004).

Some epidemiological studies suggest that exposure to 50 or 60 Hz magnetic fields might increase the risk of leukemia, especially in children with a comparable high residential exposure. To investigate this possibility experimentally, the influence of 50 Hz magnetic-field exposure on lymphoma induction was determined in a mouse strain that is genetically predisposed to this disease. The AKR/J mouse genome carries the AK virus, which leads within 1 year to spontaneous development of thymic lymphoblastic lymphoma. Beginning at an age of 4–5 weeks, groups of 160 female mice were sham-exposed or exposed to 50 Hz magnetic fields at 1 or 100 μT for 24 h per day, 7 days per week, for 38 weeks. Animals were checked visually daily and were weighed and palpated weekly. There was no effect of magnetic-field exposure on body weight gain or survival rate, and lymphoma incidence did not differ between exposed and sham-exposed animals. Therefore, these data do not support the hypothesis that chronic exposure to 50 Hz magnetic fields is a significant risk factor for developing hematopoietic malignancy.

Anderson, L. E., Sheen, D. M., Wilson, B. W., Grumbein, S. L., Creim, J. A. and Sasser, L. B. Two-Year Chronic Bioassay Study of Rats Exposed to a 1.6 GHz Radiofrequency Signal. Radiat. Res. 162, 201–210 (2004).

The purpose of this study was to determine whether long-term exposure to a 1.6 GHz radiofrequency (RF) field would affect the incidence of cancer in Fischer 344 rats. Thirty-six timed-pregnant rats were randomly assigned to each of three treatment groups: two groups exposed to a far-field RF Iridium signal and a third group that was sham exposed. Exposures were chosen such that the brain SAR in the fetuses was 0.16 W/kg. Whole-body far-field exposures were initiated at 19 days of gestation and continued at 2 h/day, 7 days/week for dams and pups after parturition until weaning (∼23 days old). The offspring (700) of these dams were selected, 90 males and 90 females for each near-field treatment group, with SAR levels in the brain calculated to be as follows: (1) 1.6 W/kg, (2) 0.16 W/kg and (3) near-field sham controls, with an additional 80 males and 80 females as shelf controls. Confining, head-first, near-field exposures of 2 h/day, 5 days/week were initiated when the offspring were 36 ± 1 days old and continued until the rats were 2 years old. No statistically significant differences were observed among treatment groups for number of live pups/litter, survival index, and weaning weights, nor were there differences in clinical signs or neoplastic lesions among the treatment groups. The percentages of animals surviving at the end of the near-field exposure were not different among the male groups. In females a significant decrease in survival time was observed for the cage control group.

Capri, M., Scarcella, E., Fumelli, C., Bianchi, E., Salvioli, S., Mesirca, P., Agostini, C., Antolini, A., Schiavoni, A., Castellani, G., Bersani, F. and Franceschi, C. In Vitro Exposure of Human Lymphocytes to 900 MHz CW and GSM Modulated Radiofrequency: Studies of Proliferation, Apoptosis and Mitochondrial Membrane Potential. Radiat. Res. 162, 211–218 (2004).

The aim of this study was to investigate the nonthermal effects of radiofrequency (RF) fields on human immune cells exposed to a Global System for Mobile Communication (GSM) signal generated by a commercial cellular phone and by a sinusoidal non-modulated signal. To assess whether mobile phone RF-field exposure affects human immune cell functions, peripheral blood mononuclear cells (PBMCs) from healthy donors were exposed in vitro to a 900 MHz GSM or continuous-wave (CW) RF field 1 h/day for 3 days in a transverse electromagnetic mode (TEM) cell system (70–76 mW/kg average specific absorption rate, SAR). The cells were cultured for 48 or 72 h, and the following end points were studied: (1) mitogen-induced proliferation; (2) cell cycle progression; (3) spontaneous and 2-deoxy-d-ribose (dRib)-induced apoptosis; (4) mitochondrial membrane potential modifications during spontaneous and dRib-induced-apoptosis. Data obtained from cells exposed to a GSM-modulated RF field showed a slight decrease in cell proliferation when PBMCs were stimulated with the lowest mitogen concentration and a slight increase in the number of cells with altered distribution of phosphatidylserine across the membrane. On the other hand, cell cycle phases, mitochondrial membrane potential and susceptibility to apoptosis were found to be unaffected by the RF field. When cells were exposed to a CW RF field, no significant modifications were observed in comparison with sham-exposed cells for all the end points investigated.

Foster, K. R. and Repacholi, M. H. Biological Effects of Radiofrequency Fields: Does Modulation Matter? Radiat. Res. 162, 219–225 (2004).

This commentary considers modulation as a factor of potential biological importance in assessment of risk of radiofrequency (RF) energy emitted by communications systems and other technologies. Modulation introduces a spread of frequencies into a carrier waveform, but in nearly all cases this spread is small compared to the frequency of the carrier. Consequently, any nonthermal (field-dependent) biological effects related to modulation must result from interaction mechanisms that are fast enough to produce a response at radiofrequencies. Despite considerable speculation, no such mechanisms have been established. While a variety of modulation-dependent biological effects of RF energy have been reported, few such effects have been independently confirmed. Some widely discussed effects, for example a reported modulation-dependent effect of RF fields on the efflux of calcium from brain tissue, remain controversial with no established biological significance. The lack of understanding of the mechanisms underlying such effects prevents any assessment of their significance for communications signals with complex modulation characteristics. Future research should be directed at confirmation and mechanistic understanding of reported biological effects related to modulation. While modulation should be considered in the design of risk studies involving communications-type signals, it should not compromise other aspects of good study design, such as maintaining adequate statistical power and identifying dose–response relationships.

Lyng, F. M., Lyons-Alcantara, M., Olwell, P., Ní Shuilleabháin, S., Seymour, C., Cottell, D. C. and Mothersill, C. Ionizing Radiation Induces a Stress Response in Primary Cultures of Rainbow Trout Skin. Radiat. Res. 162, 226–232 (2004).

Fish skin is very vulnerable to damage from physical and chemical pollutants because it is in direct contact with the aquatic environment. In this study, the effect of γ radiation on primary cultures of rainbow trout skin was investigated. Primary cultures containing two cell types, epidermal cells and goblet mucous cells, were exposed to doses ranging from 0.5–15 Gy ⁶⁰Co γ radiation. Expression of PCNA, c-myc and BCL2 was investigated as well as growth and levels of apoptosis and necrosis. Morphological and functional changes were also studied. The irradiated cultures showed evidence of a dose-dependent increase in necrosis and enhanced proliferation as well as morphological damage. In addition, mucous cell area was found to decrease significantly after irradiation. The study shows the value of these primary cultures as in vitro models for studying radiation effects. They provide an effective alternative to whole-animal exposures for radiation risk assessment.