Risk to preimplantation mouse embryos of combinations of heavy metals and radiation

The influence of arsenic, cadmium, lead or mercury on radiation risk to preimplantation mouse embryos in vitro was studied under various conditions. Morphological development, cell proliferation, and formation of micronuclei were used for assessment of risk after combined exposure to these metals and X-rays. No conditions were found under which arsenic altered radiation risk; the effects were merely additive. Cadmium acted similarly, though a few results indicated that morphological development might be impaired more strongly after combined exposure than expected from the addition of the single effects. Lead enhanced radiation risk with regard to micronucleus formation, but had an additive effect only in the case of morphological development and cell proliferation. Of all four metals, mercury had the greatest potential for enhancement of radiation risk, when morphological development and cell proliferation were studied. The observed combination effects exceeded even those effects which were calculated by taking into account the shape of the dose-effect curves (isobologram analysis, envelope of additivity). Mercury neither induced micronuclei nor enhanced their formation in combination experiments.     

Melanoma and ionizing radiation: is there a causal relationship?

This review was initiated in response to concerns that ionizing radiation could be a cause of melanoma. Studies presenting the relative risks for melanoma after external ionizing radiation exposure were in seven categories: (1) The Canadian Radiation Dose Registry, (2) nuclear industry workers, (3) subjects near nuclear test blasts, (4) survivors of the atomic bombings of Japan, (5) airline pilots and cabin attendants, (6) recipients of medical radiation, and (7) radiological technicians. Relative risks for leukemia in each of the studies were used to confirm the likelihood of exposure to ionizing radiation. When studies within a category were compatible, meta-analytic methods were used to obtain combined estimates of the relative risk, and a meta-regression analysis of melanoma relative risk compared to leukemia relative risk was used to examine consistency across exposure categories. Generally, exposure categories with elevated relative risks of leukemia had proportionately elevated relative risks of melanoma. This suggests that people exposed to ionizing radiation may be at increased risk of developing melanoma, although alternative explanations are possible. Future epidemiological studies of ionizing radiation effects should include melanoma as an outcome of interest.     

Sensitivity of germ cells and embryos to ionizing radiation

Experiments performed in laboratory animals suggest that ionizing radiation can induce DNA damage in the germ cells of exposed individuals and lead to various deleterious effects in their progeny, including miscarriage, low birth weight, congenital abnormalities and perhaps cancer. However, no clear evidence for such effects has been found in epidemiological studies of people exposed to radiation. The predicted risks of hereditary effects of any kinds resulting from parental exposure to relatively low doses of ionizing radiation remain very low, compared to the spontaneous risks in the absence of irradiation. Irradiation of the mouse embryo can lead to various effects (lethality, growth retardation, congenital abnormalities), depending on the period of gestation at which irradiation occurs. In humans, prenatal irradiation has only been exceptionally associated with congenital abnormalities, but irradiation between weeks 8-25 has been shown to be able to induce severe mental retardation. Although being not proven, the risk of developing a childhood cancer following prenatal irradiation may also not be excluded. Like for genetic effects, the risk of adverse effects following exposure of the embryo to relatively low doses remains quite low compared to the natural risks.     

X-ray and UV-radiation sensitivity of circulating lymphocytes in multiple epidermal cancer in relation to previous radiation exposure

The cellular sensitivity to X rays (200 kV, 16 mA) and UV radiation (254 nm) was examined in lymphocytes from three groups of patients with multiple epidermal malignant tumors, selected by their clinical history of carcinogenesis. Eight patients previously exposed to low energy ionizing radiation (less than or equal to 12 kV) had an increased cellular sensitivity to UV radiation as well as X rays compared with 24 age and sex matched controls. This indicates the existence of a cellular cross-sensitivity to UV radiation and ionizing radiation not previously established for human cells. In contrast six patients previously exposed to high energy ionizing radiation (between 25 and 170 kV) had normal cellular response to both UV radiation and X rays, indicating a different biologic effect of low and high energy ionizing radiation. In the third group of patients, previously exposed to therapeutic UV radiation/excess sunlight, the lymphocytes had a normal response to X rays, but an increased sensitivity to UV radiation. The possibility of evaluating the individual risk at radiation exposure is suggested.     

Methodologies for predicting the expected combined stochastic radiobiological effects of different ionizing radiations and some applications

A methodology for predicting the expected combined stochastic radiobiological effects of sequential exposure to different ionizing radiations is used to arrive at a methodology for predicting the radiobiological effects of simultaneous exposure. Both methodologies require developing additive-damage dose-effect models. Additive-damage dose-effect models are derived assuming (a) each radiation comprised by the combined exposure produces initial damage called critical damage that could lead to the radiobiological effect of interest; (b) doses of different radiations that lead to the same level of radiobiological effect (or risk) can be viewed as producing the same amount of critical damage and being indistinguishable as far as the effects of subsequently administered radiation. Derived dose-effect functions that describe the risk per individual, conditional on radiation dose, are called risk functions. The methodologies allow the use of known radiation-specific risk functions to derive risk functions for combined effects of different radiations. The risk functions for combined exposure to different radiations are called global risk functions. For sequential exposures to different ionizing radiations, the global risk functions derived depend on how individual radiation doses are ordered. Global risk functions can also differ for sequential and simultaneous exposure. The methodologies are used to account for some previously unexplained radiobiological effects of combined exposure to high and low linear-energy-transfer radiations.     

Differential genetic responses to ionizing irradiation in individual families of Japanese medaka, Oryzias latipes

Although no statistically significant hereditary effects have yet been detected in the children of survivors from the atomic bombings in Hiroshima and Nagasaki, recent animal studies have found that exposure to ionizing radiation can cause genomic and epigenomic instability in the exposed individuals, as well as their offspring, and therefore, may have much larger genetic effects than predicted by earlier studies. When individuals are exposed to various environmental insults, including radiation, individual sensitivity to the insults often varies. Variance in germ-line response to radiation among individuals has been widely recognized, but it is difficult to address due to the use of inbred strains and the limited number of offspring that can be produced by a pair of mice, the common model used to study genetic effects of radiation. Herein is the first study to examine individual family responses to ionizing radiation using a parent-pedigree approach in an outbred strain of a vertebrate model, the Japanese medaka fish. Changes in frequencies of radiation-induced germline mutations at nine microsatellite loci were examined in the same families before and after exposure to one of four acute doses of ionizing radiation (0.1, 0.5, 2.5, 5Gy, plus sham-exposed controls). Families varied significantly in pre-exposure mutation frequencies and responses to irradiation, but germline mutations were elevated in at least one family after 0.1, 0.5, and 5Gy exposures. Variance among individuals in sensitivity to radiation is well documented for many endpoints, and our work now extends these endpoints to include germ-line mutations. Further studies are needed to elucidate dose response, effects at varying stages of spermatogenesis, and the mechanisms underlying the variance in these individual responses to radiation.     

Synergistic effects of ionizing radiation and 60 Hz magnetic fields

Experiments designed to evaluate the synergistic production of clastogenic effects by ionizing radiation and 60 Hz magnetic fields were performed using human lymphocytes from peripheral blood. Following exposure to ionizing radiation, cells were cultured in 60 Hz magnetic fields having field strengths up to 1.4 mT. Cells exposed to both ionizing radiation and 60 Hz magnetic fields demonstrated an enhanced frequency of near tetraploid chromosome complements, a feature not observed following exposure to only ionizing radiation. The results are discussed in the context of a multiple-stage model of cellular transformation, employing both initiating and promoting agents. © 1993 Wiley-Liss. Inc.     

The biological effects of diagnostic cardiac imaging on chronically exposed physicians: the importance of being non-ionizing

Ultrasounds and ionizing radiation are extensively used for diagnostic applications in the cardiology clinical practice. This paper reviewed the available information on occupational risk of the cardiologists who perform, every day, cardiac imaging procedures. At the moment, there are no consistent evidence that exposure to medical ultrasound is capable of inducing genetic effects, and representing a serious health hazard for clinical staff. In contrast, exposure to ionizing radiation may result in adverse health effect on clinical cardiologists. Although the current risk estimates are clouded by approximations and extrapolations, most data from cytogenetic studies have reported a detrimental effect on somatic DNA of professionally exposed personnel to chronic low doses of ionizing radiation. Since interventional cardiologists and electro-physiologists have the highest radiation exposure among health professionals, a major awareness is crucial for improving occupational protection. Furthermore, the use of a biological dosimeter could be a reliable tool for the risk quantification on an individual basis.     

Low doses of ionizing radiation and circulatory diseases: a systematic review of the published epidemiological evidence

Recent analyses of mortality among atomic bomb survivors have suggested a linear dose-response relationship between ionizing radiation and diseases of the circulatory system for exposures in the range 0-4 Sv. If confirmed, this has substantial implications. We have therefore reviewed the published literature to see if other epidemiological data support this finding. Other studies allowing a comparison of the rates of circulatory disease in individuals drawn from the same population but exposed to ionizing radiation at different levels within the range 0-5 Gy or 0-5 Sv were identified through systematic literature searches. Twenty-six studies were identified. In some, disease rates among those exposed at different levels may have differed for reasons unrelated to radiation exposure, while many had low power to detect effects of the relevant magnitude. Among the remainder, one study found appreciable evidence that exposure to low-dose radiation was associated with circulatory diseases, but five others, all with appreciable power, did not. We conclude that the other epidemiological data do not at present provide clear evidence of a risk of circulatory diseases at doses of ionizing radiation in the range 0-4 Sv, as suggested by the atomic bomb survivors. Further evidence is needed to characterize the possible risk.     

Childhood exposure to ionizing radiation to the head and risk of schizophrenia

While the association between exposure to ionizing radiation and cancer is well established, its association with schizophrenia is unclear. The aim of our study was to assess risk of schizophrenia after childhood exposure to ionizing radiation to the head (mean dose: 1.5 Gy). The study population included an exposed group of 10,834 individuals irradiated during childhood for treatment of tinea capitis in the 1950s and two unexposed comparison groups of 5392 siblings and 10,834 subjects derived from the National Population Registry individually matched to the exposed group by age, sex (when possible), country of birth, and year of immigration to Israel. These groups were followed for a median 46 years for diagnosis of schizophrenia updated to December 2002. The Cox proportional hazards model stratified by matched sets was used to compare the risk of schizophrenia between the groups. Based on 1,217,531 person-years of follow-up, 451 cases were identified. No statistically significant association was found between radiation exposure and schizophrenia for the total group (hazard ratio per 1 Gy to the brain: 1.05, 95% confidence interval: 0.93-1.18) or within subgroups of sex, dose categories or latent period. When comparing a subgroup of subjects irradiated under 5 years of age with the matched unexposed group, the estimated hazard ratio reached 1.18 (95% confidence interval: 0.96-1.44; P = 0.1). The results of our analysis do not support an association between exposure to ionizing radiation and risk of schizophrenia. More research on possible effects of early exposure to ionizing radiation on schizophrenia specifically and brain tissue in general is needed.     

The evaluation of protective effect of lycopene against genotoxic influence of X-irradiation in human blood lymphocytes

Many studies suggest that exogenous antioxidants may protect cells against DNA damage caused with ionizing radiation. One of the most powerful antioxidants is lycopene (LYC), a carotenoid derived from tomatoes. The aim of this study was to investigate, using the comet assay, whether LYC can act as protectors/modifiers and prevent DNA damage induced in human blood lymphocytes, as well as to mitigate the effects of radiation exposure. In this project, LYC, dissolved in DMSO at a concentration of 10, 20 or 40 μM/ml of cell suspension, was added to the isolated lymphocytes from human blood at appropriate intervals before or after the X-irradiation at doses of 0.5, 1 and 2 Gy. Cell viability in all groups was maintained at above 70%. The results showed the decrease of DNA damage in cells treated with various concentrations of LYC directly and 1 h before exposure to X-rays compared to the control group exposed to irradiation alone. Contrary results were observed in cells exposed to LYC immediately after exposure to ionizing radiation. The studies confirmed the protective effect of LYC against DNA damage induced by ionizing radiation, but after irradiation the carotenoid did not stimulate of DNA repair and cannot act as modifier. However, supplementation with LYC, especially at lower doses, may be useful in protection from radiation-induced oxidative damage.     

Computed tomographies and cancer risk in children: a literature overview of CT practices,risk estimations and an epidemiologic cohort study proposal

Radiation protection is a topic of great public concern and of many scientific investigations, because ionizing radiation is an established risk factor for leukaemia and many solid tumours. Exposure of the public to ionizing radiation includes exposure to background radiation, as well as medical and occupational exposures. A large fraction of the exposure from diagnostic procedures comes from medical imaging. Computed tomography (CT) is the major single contributor of diagnostic radiation exposure. An increase in the use of CTs has been reported over the last decades in many countries. Children have smaller bodies and lower shielding capacities, factors that affect the individual organ doses due to medical imaging. Several risk models have been applied to estimate the cancer burden caused by ionizing radiation from CT. All models predict higher risks for cancer among children exposed to CT as compared to adults. However, the cancer risk associated with CT has not been assessed directly in epidemiological studies. Here, plans are described to conduct an historical cohort study to investigate the cancer incidence in paediatric patients exposed to CT before the age of 15 in Germany. Patients will be recruited from radiology departments of several hospitals. Their individual exposure will be recorded, and time-dependent cumulative organ doses will be calculated. Follow-up for cancer incidence via the German Childhood Cancer Registry will allow computation of standardized incidence ratios using population-based incidence rates for childhood cancer. Dose–response modelling and analyses for subgroups of children based on the indication for and the result of the CT will be performed.     

Increased frequency of spontaneous neoplastic transformation in progeny of bystander cells from cultures exposed to densely ionizing radiation

An increased risk of carcinogenesis caused by exposure to space radiation during prolonged space travel is a limiting factor for human space exploration. Typically, astronauts are exposed to low fluences of ionizing particles that target only a few cells in a tissue at any one time. The propagation of stressful effects from irradiated to neighboring bystander cells and their transmission to progeny cells would be of importance in estimates of the health risks of exposure to space radiation. With relevance to the risk of carcinogenesis, we investigated, in model C3H 10T½ mouse embryo fibroblasts (MEFs), modulation of the spontaneous frequency of neoplastic transformation in the progeny of bystander MEFs that had been in co-culture 10 population doublings earlier with MEFs exposed to moderate doses of densely ionizing iron ions (1 GeV/nucleon) or sparsely ionizing protons (1 GeV). An increase (P<0.05) in neoplastic transformation frequency, likely mediated by intercellular communication through gap junctions, was observed in the progeny of bystander cells that had been in co-culture with cells irradiated with iron ions, but not with protons.     

Cardiac endothelial cells isolated from mouse heart - a novel model for radiobiology

Cardiovascular disease is recognized as an important clinical problem in radiotherapy and radiation protection. However, only few radiobiological models relevant for assessment of cardiotoxic effects of ionizing radiation are available. Here we describe the isolation of mouse primary cardiac endothelial cells, a possible target for cardiotoxic effects of radiation. Cells isolated from hearts of juvenile mice were cultured and irradiated in vitro. In addition, cells isolated from hearts of locally irradiated adult animals (up to 6 days after irradiation) were tested. A dose-dependent formation of histone γH2A.X foci was observed after in vitro irradiation of cultured cells. However, such cells were resistant to radiation-induced apoptosis. Increased levels of actin stress fibres were observed in the cytoplasm of cardiac endothelial cells irradiated in vitro or isolated from irradiated animals. A high dose of 16 Gy did not increase permeability to Dextran in monolayers formed by endothelial cells. Up-regulated expression of Vcam1, Sele and Hsp70i genes was detected after irradiation in vitro and in cells isolated few days after irradiation in vivo. The increased level of actin stress fibres and enhanced expression of stress-response genes in irradiated endothelial cells are potentially involved in cardiotoxic effects of ionizing radiation.     

International Commission for Protection Against Environmental Mutagens and Carcinogens. ICPEMC Working Paper 7/1/2. Shared risk factors for cancer and atherosclerosis--a review of the epidemiological evidence

This paper reviews the epidemiological literature of relevance for the hypothesis that somatic mutation is involved in the formation of the atherosclerotic plaque. Assuming that somatic mutations are involved in atherogenesis, one would expect at least some of the risk factors for cancer and for atherosclerosis to be identical. Therefore, the review covers the correlated occurrence of cancer and atherosclerotic disease. Special interest is given to populations at high risk of cancer, including subpopulations with certain genetic diseases, and populations exposed to certain carcinogenic environmental agents including ionizing radiation, vinyl chloride monomer (VCM), arsenic, tobacco, and various industrial combustion effluents containing polycyclic aromatic hydrocarbons (PAHs). Exposure to combustion effluents from burning of tobacco or fuel is associated with an increased risk of cancer and atherosclerotic disease. Combustion effluents constitute a complex mixture of potentially hazardous agents, however, and the observed correlation of cancer and atherosclerosis among exposed persons cannot be unambiguously interpreted as evidence of a common etiology of the two groups of diseases. For ionizing radiation, arsenic, and VCM there is suggestive evidence that these agents possess an atherogenic effect beside their well-known carcinogenic properties. Both arsenic and VCM seem to have a specific affinity to the vascular bed causing various lesions including angiosarcomas and atherosclerotic plaques. Regarding ionizing radiation, the atherogenic effects seem to be localized to heavily irradiated fields. Beside the carcinogenic and atherogenic effects, exposure to arsenic, VCM, and ionizing radiation brings about an increase in the incidence of mutations and chromosomal aberrations. A theory involving somatic mutation in the pathogenesis of the atherosclerotic plaque could be consistent with the observed biological effects of ionizing radiation, arsenic, and VCM. The scant data from families with certain inherited diseases may also be consistent with an involvement of the genome in the pathogenesis of atherosclerosis. In conclusion, there is strong epidemiological evidence that several factors associated with an increased risk of cancer are also associated with an increased risk of atherosclerosis.     

Radiation-induced signaling results in mitochondrial impairment in mouse heart at 4 weeks after exposure to X-rays

BACKROUND: Radiation therapy treatment of breast cancer, Hodgkin's disease or childhood cancers expose the heart to high local radiation doses, causing an increased risk of cardiovascular disease in the survivors decades after the treatment. The mechanisms that underlie the radiation damage remain poorly understood so far. Previous data show that impairment of mitochondrial oxidative metabolism is directly linked to the development of cardiovascular disease. METHODOLOGY/PRINCIPAL FINDINGS: In this study, the radiation-induced in vivo effects on cardiac mitochondrial proteome and function were investigated. C57BL/6N mice were exposed to local irradiation of the heart with doses of 0.2 Gy or 2 Gy (X-ray, 200 kV) at the age of eight weeks, the control mice were sham-irradiated. After four weeks the cardiac mitochondria were isolated and tested for proteomic and functional alterations. Two complementary proteomics approaches using both peptide and protein quantification strategies showed radiation-induced deregulation of 25 proteins in total. Three main biological categories were affected: the oxidative phophorylation, the pyruvate metabolism, and the cytoskeletal structure. The mitochondria exposed to high-dose irradiation showed functional impairment reflected as partial deactivation of Complex I (32%) and Complex III (11%), decreased succinate-driven respiratory capacity (13%), increased level of reactive oxygen species and enhanced oxidation of mitochondrial proteins. The changes in the pyruvate metabolism and structural proteins were seen with both low and high radiation doses. CONCLUSION/SIGNIFICANCE: This is the first study showing the biological alterations in the murine heart mitochondria several weeks after the exposure to low- and high-dose of ionizing radiation. Our results show that doses, equivalent to a single dose in radiotherapy, cause long-lasting changes in mitochondrial oxidative metabolism and mitochondria-associated cytoskeleton. This prompts us to propose that these first pathological changes lead to an increased risk of cardiovascular disease after radiation exposure.     

Diagnosis of Partial Body Radiation Exposure in Mice Using Peripheral Blood Gene Expression Profiles

In the event of a terrorist-mediated attack in the United States using radiological or improvised nuclear weapons, it is expected that hundreds of thousands of people could be exposed to life-threatening levels of ionizing radiation. We have recently shown that genome-wide expression analysis of the peripheral blood (PB) can generate gene expression profiles that can predict radiation exposure and distinguish the dose level of exposure following total body irradiation (TBI). However, in the event a radiation-mass casualty scenario, many victims will have heterogeneous exposure due to partial shielding and it is unknown whether PB gene expression profiles would be useful in predicting the status of partially irradiated individuals. Here, we identified gene expression profiles in the PB that were characteristic of anterior hemibody-, posterior hemibody- and single limb-irradiation at 0.5 Gy, 2 Gy and 10 Gy in C57Bl6 mice. These PB signatures predicted the radiation status of partially irradiated mice with a high level of accuracy (range 79–100%) compared to non-irradiated mice. Interestingly, PB signatures of partial body irradiation were poorly predictive of radiation status by site of injury (range 16–43%), suggesting that the PB molecular response to partial body irradiation was anatomic site specific. Importantly, PB gene signatures generated from TBI-treated mice failed completely to predict the radiation status of partially irradiated animals or non-irradiated controls. These data demonstrate that partial body irradiation, even to a single limb, generates a characteristic PB signature of radiation injury and thus may necessitate the use of multiple signatures, both partial body and total body, to accurately assess the status of an individual exposed to radiation.     

Enhancement of radiation cytotoxicity by UCN-01 in non-small cell lung carcinoma cells

Thoracic ionizing radiation is a standard component of combined-modality therapy for locally advanced non-small cell lung cancer. To improve low 5-year survival rates (5- 15%), new strategies for enhancing the effectiveness of ionizing radiation are needed. The kinase inhibitor UCN-01 has multiple cell cycle effects, including abrogation of DNA damage-induced S- and G(2)-phase arrest, which may limit DNA repair prior to mitosis. To test the hypothesis that therapy-induced cell cycle effects would have an impact on the efficacy of a combination of UCN-01 plus ionizing radiation, the cell cycle responses of the non-small cell lung cancer cell lines Calu1 (TP53-null) and A549 (wild-type TP53) to 2 Gy ionizing radiation were correlated with clonogenic survival after irradiation plus UCN-01. Irradiated cells were exposed to UCN-01 simultaneously and at 3-h increments after irradiation. In Calu1 cells but not A549 cells, sequence-dependent potentiation of radiation by UCN-01 was observed, with maximal interaction occurring when UCN-01 was administered 6 h after irradiation. This coincided with the postirradiation time with the greatest depletion of cells from G(1). Abrogation of G(2) arrest was observed regardless of TP53 status. The role of TP53 was investigated using siRNA to achieve gene silencing. These studies demonstrated that radiation plus UCN-01 was more effective in cells with diminished TP53 activity, associated with a reduced G(1) checkpoint arrest. These studies indicate that simultaneous elimination of multiple DNA damage-induced checkpoints in G(1), S and G(2) may enhance the effects of radiation and that drug scheduling may have an impact on clinical efficacy.     

The micronucleus assay as a biological dosimeter in hospital workers exposed to low doses of ionizing radiation

The health risk associated with low levels of ionizing radiation is still a matter of debate. A number of factors, such as non-target effects, adaptive responses and low-dose hypersensitivity, affect the long-term outcome of low-dose exposures. Cytogenetic bio-dosimetry provides a measure of the absorbed dose, taking into account the individual radiation sensitivity. The aim of the present study is to evaluate the value of the micronucleus (MN) test as a bio-dosimeter in hospital workers exposed to low doses of ionizing radiation. Blood samples were obtained from 30 subjects selected among workers exposed to X- and gamma-radiation, and 30 controls matched for sex, age and smoking from the same hospital. Micronucleus frequencies were analyzed by use of the cytokinesis-block method. The MN frequency was compared among the groups considering the confounding factors and the length of employment. No increase in the number of bi-nucleated cells with MN (BNMN), but a significant increase in the number of mono-nucleated cells with micronuclei (MOMN) was observed in exposed subjects compared with the controls. The relationship between MN frequency and accumulated dose (mSv) was evaluated. The length of employment did not affect the extent of MN frequency, but an increase of BNMN and MOMN cells was observed based on the accumulated radiation dose. Our study shows the sensitivity of the MN test in the detection of cytogenetic effects of cumulative exposure levels, suggesting the potential usefulness of this assay in providing a biological index in medical surveillance programs.