Yacoub, A., McKinstry, R., Hinman, D., Chung, T., Dent, P. and Hagan, M. P. Epidermal Growth Factor and Ionizing Radiation Up-regulate the DNA Repair Genes XRCC1 and ERCC1 in DU145 and LNCaP Prostate Carcinoma through MAPK Signaling. Radiat. Res. 159, 439–452 (2003).

This work examined the importance of radiation-induced and ligand-induced EGFR-ERK signaling for the regulation of DNA repair proteins XRCC1 and ERCC1 in prostate carcinoma cells, DU145 (TP53^mut), displaying EGFR-TGFA-dependent autocrine growth and high MAPK (ERK1/2) activity, and LNCaP (TP53^wt) cells expressing low constitutive levels of ERK1/2 activity. Using quantitative RT-PCR and Western analyses, we determined that ionizing radiation activated the DNA repair genes XRCC1 and ERCC1 in an ERK1/2-dependent fashion for each cell line. After irradiation, a rapid increase followed by a decrease in ERK1/2 activity preceded the increase in XRCC1/ERCC1 expression in DU145 cells, while only the rapid decrease in ERK1/2 preceded the increase in XRCC1/ERCC1 expression in LNCaP cells. Administration of EGF, however, markedly increased the up-regulation of phospho-ERK, ERCC1 and XRCC1 in both cell lines. Although the EGFR inhibitor tyrphostin (AG-1478) and the MEK inhibitor PD90859 both attenuated EGF-induced levels of the ERCC1 and XRCC1 protein, PD98059 blocked the induction of ERCC1 and XRCC1 by radiation more effectively in both cell lines. Inhibition of ERK at a level that reduced the up-regulation of DNA repair led to the persistence of apurinic/apyrimidinic (AP) sites of DNA damage and increased cell killing. Taken together, these data imply a complex control of DNA repair activation that may be more generally dependent on MAPK (ERK1/2) signaling than was previously noted. These data provide novel insights into the capacity of the EGFR-ERK signaling to modulate DNA repair in cancer cells and into the functional significance of this signaling.

Varadkar, P. A., Krishna, M. and Verma, N. C. Dose-Dependent Differential Expression of Protein Kinase C Isozymes in Mouse Lymphocytes after Gamma Irradiation In Vivo and Ex Vivo. Radiat. Res. 159, 453–457 (2003).

Protein kinase C (PKC, now known as Prkc) plays an important role in the response of cells to radiation, but little is known about the specific response of each isozyme in the radiation-induced response of cells in whole animals. However, most studies are based on single cells. There is a paucity of data on signaling after whole-body irradiation. In this study, a comparison has been made between the expression of Prkc isozymes after in vivo and ex vivo irradiation. There was a significant difference in the dose response of the isozymes. In animals in which lymphocytes were irradiated ex vivo, the expression of the Prkca isozyme was found to be maximum at 3 Gy, while in vivo irradiation did not increase the expression beyond that of 1 Gy. Prkcd was marginally activated after 0.1 Gy ex vivo irradiation, whereas there was significant activation of expression after in vivo irradiation with 3 Gy. The response of Prkcz was found to be similar to that of Prkcd. Prkc is a crucial enzyme that is being used to manipulate the response of tumors to radiotherapy. Conventional radiotherapy is delivered at low doses, and hence only those isozymes that are activated at these doses should be taken into consideration. Moreover, the differences between the response of a single cell and that of the whole animal must be considered.

Wickliffe, J. K., Rodgers, B. E., Chesser, R. K., Phillips, C. J., Gaschak, S. P. and Baker, R. J. Mitochondrial DNA Heteroplasmy in Laboratory Mice Experimentally Enclosed in the Radioactive Chernobyl Environment. Radiat. Res. 159, 458–464 (2003).

Mitochondrial DNA heteroplasmy using the protein-coding cytochrome b (Mtcyb) gene was assessed in laboratory mice (C57BL/6 and BALB/c) exposed to the Chernobyl environment. Subacute to subchronic (30–40 days) exposure resulted in a cumulative radiation dose of 1.2–1.6 Gy (∼0.04 Gy/day). Mice were sampled prior to introduction into the enclosures and again after removal from the enclosures. Nucleotide variation (site heteroplasmy) in 306 pre-exposure Mtcyb gene copies (122,400 base pairs) was compared to variation in 354 postexposure gene copies (141,600 base pairs). Five mutant copies, each characterized by a single nucleotide substitution, were observed (four in the pre-exposure samples, one in a postexposure sample). The frequencies of mutant gene copies and nucleotide substitutions in pre-exposure and postexposure samples were not significantly different. This suggests that this type of exposure (i.e. low dose rate) does not pose a significant mutation risk to the Mtcyb gene in digit tissue. Furthermore, no significant radiation risk to analogous human tissues may exist when occupational exposures involve low dose rates such as these. Finally, linear, cumulative models of genetic risk currently used to estimate radiation-induced effects are likely to be inappropriate for low-dose-rate exposures and need to be re-evaluated critically.

Takeda, I., Kizu, Y., Okamoto, Y., Saito, I. and Yamane, G. Possible Role of Nitric Oxide in Radiation-Induced Salivary Gland Dysfunction. Radiat. Res. 159, 465–470 (2002).

In this study, we developed a murine model of xerostomia to elucidate the mechanism of radiation-induced salivary gland dysfunction and determined the levels of nitric oxide (NO) in the salivary glands to assess its involvement in the salivary dysfunction induced by radiation. In addition, an inhibitor of NO synthesis was administered to the model in vivo, and its effect on saliva secretion was investigated. Salivary gland irradiation at a dose of 15 Gy caused a significant decrease in secretion compared to unirradiated salivary glands. There were no marked differences between the irradiated mice and unirradiated mice in water or food consumption or in body weight changes. The NO levels in the cultured salivary gland epithelial cells were increased by treatment with a combination of interferon γ (Ifng), interleukin β (Il1b), and tumor necrosis factor α (Tnfa). Irradiation increased the NO level in the salivary gland tissue. The presence of N^G-monomethyl-l-arginine acetate (l-NMMA), an inhibitor of NO synthesis, caused a decrease in the NO level in cultured salivary gland tissues after irradiation. Administration of l-NMMA to irradiated mice improved saliva secretion. These results suggest that excessive production of NO induced by radiation is involved in the formation of radiation-induced xerostomia. The finding that administration of an inhibitor of NO synthesis ameliorated the dysfunction of irradiated salivary glands indicates that NO plays a role as a mediator of the dry mouth symptoms that occur after irradiation.

Benderitter, M., Vincent-Genod, L., Pouget, J. P. and Voisin, P. The Cell Membrane as a Biosensor of Oxidative Stress Induced by Radiation Exposure: A Multiparameter Investigation. Radiat. Res. 159, 471–483 (2003).

The role of biological membranes as a target in biological radiation damage remains unclear. The present study investigates how the biochemical and biophysical properties of a simple biological model, i.e. human erythrocyte membranes, are altered after exposure to relatively low doses of ⁶⁰Co γ rays. Lipid peroxidation increased in the hours after radiation exposure, based on measurements of MDA and on the lipid peroxidation index after parinaric acid incorporation. Protein carbonyl content also increased rapidly after radiation exposure. An imbalance between the radiation-mediated oxidative damages and the antioxidant capacity of the erythrocytes was observed in the hours after radiation exposure. Antioxidant enzyme activities, mainly catalase and glutathione peroxidase, were found to decrease after irradiation. The development of a radiation-induced oxidative stress probably explains the reorganization of the fatty acid pattern 72 h after radiation exposure. The phosphatidylethanolamine (PE) fatty acids of the (n-3) and (n-6) series decreased, while the PE saturated fatty acid content increased. All these modifications may be involved in the variation of the biophysical properties of the membranes that we noted after radiation exposure. Specifically, we observed that the lipid compartment of the membrane became more fluid while the lipid–protein membrane interface became more rigid. Taken together, these findings reinforce our understanding that the cell membrane is a significant biological target of radiation. Thus the role of the biological membrane in the expression and course of cell damage after radiation exposure must be considered.

Biaglow, J. E., Ayene, I. S., Koch, C. J., Donahue, J., Stamato, T. D., Mieyal, J. J. and Tuttle, S. W. Radiation Response of Cells during Altered Protein Thiol Redox. Radiat. Res. 159, 484–494 (2003).

The major focus of this work was to investigate how altered protein thiol redox homeostasis affects radiation-induced cell death. We used the cells of wild-type CHO cell line K1, the CHO cell line E89, which is null for G6PD activity, and a radiation-sensitive CHO cell line, XRS5. The protein-thiol redox status of cells was altered with cell-permeable disulfides, hydroxyethyldisulfide (HEDS) or lipoate. HEDS is primarily reduced by thioltransferase (glutaredoxin), with GSH as the electron donor. In contrast, lipoate is reduced by thioredoxin reductase. HEDS was reduced at a greater rate than lipoate by G6PD-containing K1 (wild-type) cells. Reduction of disulfides by G6PD-deficient cells was significantly slower with HEDS as substrate and was nearly absent with lipoate. The rate of reduction of HEDS by E89 cells decelerated to near zero by 30 min, whereas the reduction continued at nearly the same rate during the entire measurement period for K1 cells. HEDS treatment decreased the GSH and protein thiol (PSH) content more in G6PD-deficient cells than in G6PD-containing cells. On the other hand, lipoate did not significantly alter the protein thiol, but it increased the GSH in K1 cells. Acute depletion of GSH by l-buthionine-sulfoximine (l-BSO) in combination with dimethylfumarate significantly decreased the rate of reduction of HEDS by K1 cells close to that of G6PD-deficient cells. Prior GSH depletion by l-BSO alone significantly decreased the PSH in glucose-depleted E89 cells exposed to HEDS, but this did not occur with K1 cells. The radiation response of G6PD-deficient cells was significantly sensitized by HEDS, but HEDS did not have this effect on K1 cells. The DNA repair-deficient XRS5 CHO cells displayed the same capacity as K1 cells for HEDS reduction, and like K1 cells the XRS5 cells were not sensitized to radiation by HEDS treatment. Deprivation of glucose, which provides the substrate for G6PD in the oxidative pentose phosphate cycle, decreased the rate of bioreduction of HEDS and lipoate in G6PD-containing cells to the level in G6PD-deficient cells. In the absence of glucose, HEDS treatment diminished non-protein thiol and protein thiol to the same level as those in G6PD-deficient cells and sensitized the K1 cells to HEDS treatment. However, depletion of glucose did not alter the sensitivity of XRS5 cells in either the presence or absence of HEDS. Overall the results suggest a major role for pentose cycle control of protein redox state coupled to the activities of the thioltransferase and thioredoxin systems. The results also show that protein thiol status is a critical factor in cell survival after irradiation.

Cedervall, B., Edgren, M. R. and Lewensohn, R. X-Ray-Induced DNA Double-Strand Breaks in Mouse L1210 Cells: A New Computational Method for Analyzing Neutral Filter Elution Data. Radiat. Res. 159, 495–501 (2003).

The aim of this article is to present a method for studying the shape of the dose and repair responses for X-ray-induced double-strand breaks (DSBs) as measured by neutral filter elution (NFE). The approach is closely related to a method we developed for the use of specific molecular size markers and used for determination of the absolute number of randomly distributed radiation-induced DSBs by pulsed-field gel electrophoresis (PFGE). Mouse leukemia L1210 cells were X-irradiated with 0–50 Gy. Samples were then evaluated both with PFGE and with NFE. Assuming that with both migration (PFGE) and elution (NFE), a heterogeneous population of double-stranded DNA fragments will start with the smallest fragments and proceed with increasingly larger fragments, it is possible to match the migration behavior of fractions of fragments smaller than a certain size to the fraction eluted at a specific time. This assumption does not exclude the possibility of DNA being sheared in the NFE filter. The yield, as determined by the size markers in PFGE, was used to find the corresponding elution times in the NFE experiment. These experimentally used elution times could then reversely be interpreted as size markers which finally were used to calculate DSBs/Mbp as a function of X-ray dose. The resulting lines were almost straight. The data were also plotted as relative elution and showed that, as expected, the dose response then appears with a more pronounced sigmoid shape.

Stenerlöw, B., Karlsson, K. H., Cooper, B. and Rydberg, B. Measurement of Prompt DNA Double-Strand Breaks in Mammalian Cells without Including Heat-Labile Sites: Results for Cells Deficient in Nonhomologous End Joining. Radiat. Res. 159, 502–510 (2003).

Ionizing radiation induces prompt single-strand breaks and double-strand breaks in DNA. In addition, labile sites are induced that can be converted to breaks by heat or mild alkali. When such labile lesions are present within multiply damaged sites, additional double-strand breaks can form. Current protocols for measurement of DNA double-strand breaks involve a lysis step at an elevated temperature, and consequently breaks from heat-labile sites will be generated during lysis and will be included in the measurement. However, such sites may not develop into breaks within the cell and therefore may not need DNA double-strand break repair processes for elimination. We present here a new lysis and pulsed-field gel electrophoresis protocol that is carried out entirely at 0–4°C and thus avoids inclusion of heat-labile sites in the measurement. The new recommended lysis procedure involves two steps: The first step includes proteinase K, which has sufficient activity at 0°C to support lysis, and the second step includes a high-salt buffer to further free the DNA from proteins and other cellular structures. Using various tests, we conclude that lysis is sufficient with this procedure to allow accurate determination of double-strand breaks by pulsed-field gel electrophoresis. Using the new protocol, it was found that heat-labile sites account for 30% of the initial number of double-strand breaks measured by conventional protocols after exposure to low-LET radiation. In addition, we show that heat-labile sites that can be converted to double-strand breaks are repaired with fast kinetics and are almost completely eliminated after 1 h at 37°C. A study of cells deficient in nonhomologous end joining reveals that the residual fast repair response typically seen in such cells is solely due to repair at heat-labile sites and is not due to repair of prompt DSBs.

Pierce, D. A., Sharp, G. B. and Mabuchi, K. Joint Effects of Radiation and Smoking on Lung Cancer Risk among Atomic Bomb Survivors. Radiat. Res. 159, 511–520 (2003).

Results are given on the joint effect of radiation exposure and cigarette smoking on lung cancer risks among A-bomb survivors, based on 592 cases through 1994. Information on smoking was derived from mail surveys and clinical interviews of 45,113 persons in the Radiation Effects Research Foundation cohort. Radiation and smoking effects on lung cancer are found to be significantly sub-multiplicative and quite consistent with additivity. The smoking relative risk, previously very low in studies of this cohort, is now similar to that found in Western populations. This increase is likely to be related to the scarcity of cigarettes during and after the war. The smoking relative risk depends little on sex. After adjusting for smoking, the radiation-related risks relative to background rates for nonsmokers are similar to those for other solid cancers: a sex-averaged ERR/Sv of about 0.9 with a female:male sex ratio of about 1.6. Adjusting for smoking removes a spuriously large female:male ratio in radiation relative risk due to confounding between sex and smoking level. The adjustment also removes an artifactual age-at-exposure effect in the radiation relative risk, opposite in direction to other cancers, which is due to birth cohort variation in lung cancer rates.

dos Santos Silva, I., Malveiro, F., Jones, M. E. and Swerdlow, A. J. Mortality after Radiological Investigation with Radioactive Thorotrast: A Follow-up Study of up to Fifty Years in Portugal. Radiat. Res. 159, 521–534 (2003).

Cerebral angiography using a radioactive radiological contrast medium, Thorotrast, was pioneered by Moniz in Portugal in the 1920s. Thorotrast is retained by the reticuloendothelial system, with a biological half-life of several hundred years, so that such patients suffer lifetime exposure to internal radiation. We studied mortality in Portuguese patients who were administered Thorotrast during the period 1928–1959 and in a comparison group of patients who received nonradioactive contrast agents. There were 1096 systemically exposed, 1014 unexposed, and, unique to the Portuguese study, 240 locally exposed Thorotrast patients who were successfully traced and followed up to the end of 1996. Mortality was significantly raised among systemically exposed Thorotrast patients relative to those unexposed for all causes [relative risk (RR) = 2.63], all neoplasms (RR = 6.72), liver cancer (RR = 42.4), chronic liver disease (RR = 5.12), other non-neoplastic diseases of the digestive system (RR = 4.87), neoplastic (RR = 21.9) and non-neoplastic hematological disorders (RR = 6.00), and non-neoplastic diseases of the respiratory system (RR = 4.31). Risks for most of these conditions increased significantly with time since first administration of the contrast medium and with cumulative α-particle radiation dose. Mortality was also significantly raised for non-neoplastic disorders of the nervous system (RR = 12.7) and ill-defined conditions (RR = 3.74), but these associations are likely to reflect the initial diagnosis, not Thorotrast exposure, because risks declined significantly with time and/or dose. There were no significant excess deaths from oropharyngeal or nasal cancers, or from any other cause, among patients exposed to Thorotrast locally for visualization of the perinasal sinuses, and no clear trend in risk with time since exposure. This study shows an association between systemic, but not local, exposure to Thorotrast and mortality from liver cancer, chronic liver disease, and neoplastic and non-neoplastic hematological disorders, with risks for these conditions remaining high for over 40 years after administration. Liver conditions, but not hematological disorders, showed a strong and consistent gradient with cumulative α-particle radiation dose.

Endo, A. and Yamaguchi, Y. Analysis of Dose Distribution for Heavily Exposed Workers in the First Criticality Accident in Japan. Radiat. Res. 159, 535–542 (2003).

The first criticality accident in Japan occurred in a uranium processing plant in Tokai-mura on September 30, 1999. The accident, which occurred while a large amount of enriched uranyl nitrate solution was being loaded into a tank, led to a chain reaction that continued for 20 h. Two workers who were pouring the uranium solution into the tank at the time were heterogeneously exposed to neutrons and γ rays produced by nuclear fission. Analysis of dose distributions was essential for the understanding of the clinical course observed in the skin and organs of these workers. We developed a numerical simulation system, which consists of mathematical human models and Monte Carlo radiation transport programs, for analyzing dose distributions in various postures and applied the system to the dose analysis for the two workers. This analysis revealed the extreme heterogeneity of the doses from neutrons and γ rays in the skin and body, which depended on the positions and postures of the workers. The detailed dose analysis presented here using color maps is indispensable for an understanding of the biological effects of high-dose exposure to a mixed field of neutrons and γ rays as well as for the development of emergency treatments for victims of radiation exposure.

Razskazovskiy, Y. Radiation-Activated Nuclease Activity of o,o′-Diphenyleneiodonium Cations (DPI): A Reductively Initiated Chain Reaction Involving the C1′ Chemistry. Radiat. Res. 159, 543–549 (2003).

o,o′-Diphenyleneiodonium cations (DPI) convert relatively harmless radiation-produced electrons into efficient DNA cleaving agents. The cleavage products are unaltered DNA bases, 5-methylenefuranone (5-MF), and a complete set of 3′ and 5′-phosphorylated DNA fragments. The production of alkali-labile sites is a minor factor in the process. Based on the production of 5-MF, it is concluded that DNA cleavage by DPI cations involves (but may not be limited to) the C1′ chemistry. The loss of 3-aminoDPI (ADPI) cations bound to highly polymerized calf thymus DNA appears to be due to a short-chain reaction with an apparent length of up to 2.1 ADPI cations consumed for each radiation-produced electron. The suggested chain reaction mechanism includes the one-electron oxidation of DNA radicals (including the C1′ sugar radical) by ADPI cations bound to the same duplex. The yields of DNA loss in complexes formed by ADPI with short synthetic duplexes indicate that there is more than a 60% probability of DNA damage after one-electron reduction of ADPI.

Bit-Babik, G., Chou, C. K., Faraone, A., Gessner, A., Kanda, M. and Balzano, Q. Estimation of the SAR in the Human Head and Body due to Radiofrequency Radiation Exposure from Handheld Mobile Phones with Hands-Free Accessories. Radiat. Res. 159, 550–557 (2003).

It was reported by others that hands-free accessories increase the absorption of RF energy in a human head compared to a handset alone. The results of this study show that the opposite is observed when proper dosimetric methods are employed. It is pointed out that for correct estimation of the exposure level it is necessary to use appropriate physical and experimental models and measurement instrumentation, following internationally recommended standards. The human phantoms used for measurements involving the hands-free accessories should include the torso; i.e., measurements should not be performed on the head phantom alone. This has a significant impact on the results because the RF energy coupled into the leads of hands-free accessories is strongly attenuated by the body. Numerical simulations using the Finite-Difference Time-Domain (FDTD) method and experimental measurements with a miniature electric-field probe are in good agreement and show a decrease, not an increase, in RF energy exposure in the human head from hands-free accessories.

Vijayalaxmi, Sasser, L. B., Morris, J. E., Wilson, B. W. and Anderson, L. E. Genotoxic Potential of 1.6 GHz Wireless Communication Signal: In Vivo Two-Year Bioassay. Radiat. Res. 159, 558–564 (2003).

Timed-pregnant Fischer 344 rats (from nineteenth day of gestation) and their nursing offspring (until weaning) were exposed to a far-field 1.6 GHz Iridium wireless communication signal for 2 h/day, 7 days/week. Far-field whole-body exposures were conducted with a field intensity of 0.43 mW/cm² and whole-body average specific absorption rate (SAR) of 0.036 to 0.077 W/kg (0.10 to 0.22 W/kg in the brain). This was followed by chronic, head-only exposures of male and female offspring to a near-field 1.6 GHz signal for 2 h/day, 5 days/week, over 2 years. Near-field exposures were conducted at an SAR of 0.16 or 1.6 W/kg in the brain. Concurrent sham-exposed and cage control rats were also included in the study. At the end of 2 years, all rats were necropsied. Bone marrow smears were examined for the extent of genotoxicity, assessed from the presence of micronuclei in polychromatic erythrocytes. The results indicated that the incidence of micronuclei/2000 polychromatic erythrocytes were not significantly different between 1.6 GHz-exposed, sham-exposed and cage control rats. The group mean frequencies were 5.6 ± 1.8 (130 rats exposed to 1.6 GHz at 0.16 W/kg SAR), 5.4 ± 1.5 (135 rats exposed to 1.6 GHz at 1.6 W/kg SAR), 5.6 ± 1.7 (119 sham-exposed rats), and 5.8 ± 1.8 (100 cage control rats). In contrast, positive control rats treated with mitomycin C exhibited significantly elevated incidence of micronuclei/2000 polychromatic erythrocytes in bone marrow cells; the mean frequency was 38.2 ± 7.0 (five rats). Thus there was no evidence for excess genotoxicity in rats that were chronically exposed to 1.6 GHz compared to sham-exposed and cage controls.