No lengthening of life span in mice continuously exposed to gamma rays at very low dose rates

Late effects of continuous exposure to ionizing radiation are potential hazards to workers in radiation facilities as well as to the general public. Recently, low-dose-rate and low-dose effects have become a serious concern. Using a total of 4000 mice, we studied the late biological effects of chronic exposure to low-dose-rate radiation as assayed by life span. Two thousand male and 2000 female 8-week-old specific-pathogen-free (SPF) B6C3F1 mice were randomly divided into four groups (one nonirradiated control and three irradiated). Irradiation was carried out for approximately 400 days using (137)Cs gamma rays at dose rates of 21 mGy day(-1), 1.1 mGy day(-1) and 0.05 mGy day(-1) with total doses equivalent to 8000 mGy, 400 mGy and 20 mGy, respectively. All mice were kept under SPF conditions until they died spontaneously. Statistical analyses showed that the life spans of mice of both sexes irradiated with 21 mGy day(-1) (P < 0.0001) and of females irradiated with 1.1 mGy day(-1) (P < 0.05) were significantly shorter than those of the control group. Our results show no evidence of lengthened life span in mice continuously exposed to very low dose rates of gamma rays.     

Induction and persistence of micronuclei, sister-chromatid exchanges and chromosomal aberrations in splenocytes and bone-marrow cells of rats exposed to ethylene oxide

Studies on the induction and persistence of ethylene oxide (EO) induced chromosomal alterations in rat bone-marrow cells and splenocytes following in vivo exposure were carried out. Rats were exposed to ethylene oxide either chronically by inhalation (50-200ppm, 4 weeks, 5 days/week, 6h/day) or acutely by intraperitoneal injection (i.p.) at dose levels of 50-100ppm.Spontaneous- and induced-frequencies of micronuclei (MN), sister-chromatid exchanges (SCEs) and chromosomal aberrations were determined in rat bone-marrow cells, and in splenocytes following in vitro mitogen stimulation. Unstable chromosomal aberrations were studied in whole genome using standard Giemsa staining technique and fluorescence in situ hybridisation using probe for chromosome #2 was employed to detect chromosome translocations.Following chronic exposure, the cytogenetic analyses were carried out at days 5 and 21 in rat splenocytes, to study the induction and persistence of sister-chromatid exchanges. Following chronic exposure, ethylene oxide was effective in inducing SCEs, and markedly cells with high frequency SCEs were observed and they in-part persisted until day 21 post-exposure. However, no significant effect was observed in rat splenocytes for induction of MN and chromosomal aberrations. Following acute exposure, both SCEs and MN were increased significantly in rat bone-marrow cells as well as splenocytes.In conclusion, this study indicates that ethylene oxide at the concentrations employed by intraperitoneal injection or inhalation in adult rats is mutagenic and can induce both SCEs and MN.     

Gene expression profiles in mouse liver after long-term low-dose-rate irradiation with gamma rays

Changes in gene expression profiles in mouse liver induced by long-term low-dose-rate γ irradiation were examined by microarray analysis. Three groups of male C57BL/6J mice were exposed to whole-body radiation at dose rates of 17-20 mGy/day, 0.86-1.0 mGy/day or 0.042-0.050 mGy/day for 401-485 days with cumulative doses of approximately 8 Gy, 0.4 Gy or 0.02 Gy, respectively. The gene expression levels in the livers of six animals from each exposure group were compared individually with that of pooled sham-irradiated animals. Some genes revealed a large variation in expression levels among individuals within each group, and the number of genes showing common changes in individuals from each group was limited: 20 and 11 genes showed more than 1.5-fold modulation with 17-20 mGy/day and 0.86-1.0 mGy/day, respectively. Three genes showed more than 1.5-fold modulation even at the lowest dose-rate of 0.04-0.05 mGy/day. Most of these genes were down-regulated. RT-PCR analysis confirmed the expression profiles of the majority of these genes. The results indicate that a few genes are modulated in response to very low-dose-rate irradiation. The functional analysis suggests that these genes may influence many processes, including obesity and tumorigenesis.     

The Chernobyl fallout in Salzburg/Austria and its effect on blood chromosomes

The radioactive fallout of the Chernobyl accident caused an increase in radiation dose of 20 to 110 per cent over the normal environmental burden to the inhabitans of Salzburg City in Austria (in a distance of about 1300 km from the accident). The structural chromosome aberration in the lymphocytes of the peripheral blood of 15 test-persons have been investigated one year after the accident. From two of these we know also the aberration frequencies before the accident which were significantly lower. The results from all test persons were pooled according to their Cs137 and Cs134 content, measured by whole body counter. Their mean additional blood doses from the incorporated caesium plus the external fallout radiation were 0.23, 0.36 and 0.55 mGy/yr. The aberration frequencies increased with dose. The slope of the best straight-line through the points was 2.0 +/- 0.7 total chromosome type aberrations in 100 metaphases per mGy/yr. This result fits in well with former investigations of persons with individually calculated radiation burden from the environment. The sharp increase with dose at this low level is not compatible with values extrapolated from high doses. The usual dose assessment based on chromosome aberrations extrapolated from high to low doses is therefore not possible in the range considered in this investigation.     

The mouse splenocyte assay, an in vivo/in vitro system for biological monitoring: studies with X-rays, fission neutrons and bleomycin.

A modified mouse splenocyte culture system was standardized after testing different mitogens (i.e., phytohemagglutinin (PHA), concanavalin A (Con A)). The mitotic index was determined for comparison between different mitogens. Following selection of appropriate mitogen (PHA 16, Flow), a series of experiments were conducted to evaluate the application of a cytokinesis-block for scoring micronuclei and assays for chromosomal aberrations produced by treatment in G0 and G2 for the purposes of biological dosimetry following in vivo and/or in vitro exposure to X-rays, fission neutrons and bleomycin. In the X-irradiation studies, the frequencies of micronuclei and chromosomal aberrations (i.e., dicentrics and rings) increased in a dose-dependent manner. These data could be fitted to a linear-quadratic model. No difference was observed between irradiation in vivo and in vitro, suggesting that measurement of dicentrics and micronuclei in vitro after X-irradiation can be used as an in vivo dosimeter. Following in vivo irradiation with 1 MeV fission neutrons and in vitro culturing of mouse splenocytes, linear dose-response curves were obtained for induction of micronuclei and chromosomal aberrations. The lethal effects of neutrons were shown to be significantly greater than for a similar dose of X-rays. The relative biological effectiveness (RBE) was 6-8 in a dose range of 0.25-3 Gy for radiation-induced asymmetrical exchanges (dicentrics and rings), and about 8 for micronuclei in a dose range of 0.25-2 Gy. Furthermore, the induction of chromosomal aberrations by bleomycin was investigated in mouse G0 splenocytes (in vitro) and compared with X-ray data. Following bleomycin treatment (2 h) a similar pattern of dose-response curve was obtained as with X-rays. In this context a bleomycin rad equivalent of 20 micrograms/ml = 0.50 Gy was estimated.     

Cause of death and neoplasia in mice continuously exposed to very low dose rates of gamma rays

Four thousand 8-week-old SPF B6C3F1 mice (2000 of each sex) were divided into four groups, one nonirradiated (control) and three irradiated. The irradiated groups were exposed to (137)Cs gamma rays at dose rates of 21, 1.1 and 0.05 mGy day(-1) for approximately 400 days with total doses equivalent to 8000, 400 and 20 mGy, respectively. All mice were kept until natural death, and pathological examination was performed to determine the cause of death. Neoplasms accounted for >86.7% of all deaths. Compared to the nonirradiated controls, the frequency of myeloid leukemia in males, soft tissue neoplasms and malignant granulosa cell tumors in females, and hemangiosarcoma in both sexes exposed to 21 mGy day(-1) were significantly increased. The number of multiple primary neoplasms per mouse was significantly increased in mice irradiated at 21 mGy day(-1). Significant increases in body weights were observed from 32 to 60 weeks of age in males and females exposed to 1.1 mGy day(-1) and 21 mGy day(-1), respectively. Our results suggest that life shortening (Tanaka et al., Radiat. Res. 160, 376-379, 2003) in mice continuously exposed to low-dose-rate gamma rays is due to early death from a variety of neoplasms and not from increased incidence of specific neoplasms.     

DNA repair defect in AT cells and their hypersensitivity to low-dose-rate radiation

Ataxia telangiectasia (AT) and normal cells immortalized with the human telomerase gene were irradiated in non-proliferative conditions with high- (2 Gy/min) or low-dose-rate (0.3 mGy/min) radiation. While normal cells showed a higher resistance after irradiation at a low dose rate than a high dose rate, AT cells showed virtually the same survival after low- and high-dose-rate irradiation. Although the frequency of micronuclei induced by low-dose-rate radiation was greatly reduced in normal cells, it was not reduced significantly in AT cells. The number of gamma-H2AX foci increased in proportion to the dose in both AT and normal cells after high-dose-rate irradiation. Although few gamma-H2AX foci were observed after low-dose-rate irradiation in normal cells, significant and dose-dependent numbers of gamma-H2AX foci were observed in AT cells even after low-dose-rate irradiation, indicating that DNA damage was not completely repaired during low-dose-rate irradiation. Significant phosphorylation of ATM proteins was detected in normal cells after low-dose-rate irradiation, suggesting that the activation of ATM plays an important role in the repair of DNA damage during low-dose-rate irradiation. In conclusion, AT cells may not be able to repair some fraction of DNA damage and are severely affected by low-dose-rate radiation.     

Low doses of very low-dose-rate low-LET radiation suppress radiation-induced neoplastic transformation in vitro and induce an adaptive response

The purpose of this study was to determine whether adaptation against neoplastic transformation could be induced by exposure to very low-dose-rate low-LET radiation. HeLa x skin fibroblast human hybrid cells were irradiated with approximately 30 kVp photons from an array of (125)I seeds. The initial dose rate was 4 mGy/day. Cell samples were taken at four intervals at various times over a period of 88 days and assayed for neoplastic transformation and the presence of reactive oxygen species (ROS). The dose rate at the end of this treatment period was 1.4 mGy/day. Transformation frequencies and ROS levels were compared to those of parallel unirradiated controls. At the end of 3 months and an accumulated dose of 216 mGy, cells treated with very low-dose-rate radiation were exposed to a high-dose-rate 3-Gy challenge dose of (137)Cs gamma rays, and the effects compared with the effect of 3 Gy on a parallel culture of previously unirradiated cells. Cells exposed to very low-dose-rate radiation exhibited a trend toward a reduction in neoplastic transformation frequency compared to the unirradiated controls. This reduction seemed to diminish with time, indicating that the dose rate, rather than accumulated dose, may be the more important factor in eliciting an adaptive response. This pattern was in general paralleled by a reduction of ROS present in the irradiated cultures compared to controls. The very low-dose-rate-treated cells were less sensitive to the high challenge dose than unirradiated controls, suggesting the induction of an adaptive response. Since there was a suggestion of a dose-rate threshold for induction suppression, a second experiment was run with a fresh batch of cells at an initial dose rate of 1 mGy/day. These cells were allowed to accumulate 40 mGy over 46 days (average dose rate=0.87 mGy/day), and there was no evidence for suppression of transformation frequency compared to parallel unirradiated controls. It is concluded that doses of less than 100 mGy delivered at very low dose rates in the range 1 to 4 mGy/day can induce an adaptive response against neoplastic transformation in vitro. When the dose rate drops below approximately 1 mGy/day, this suppression is apparently lost, suggesting a possible dose-rate-dependent threshold for this process.     

Radiobiological effects of a low-energy ion beam on wheat

The radiobiological effects of a low-energy nitrogen ion (N⁺) beam on wheat were studied, particularly with regard to the induction of chromosome aberrations. The results demonstrated that the three test varieties showed different sensitivities to ion implantation, and a higher dose of ion implantation had a marked effect on the germination and survival rate of the seeds exposed. The germination rate and survival rate curve basically followed a similar trend in the same variety. Cytological analysis indicated that ion beams were effective in producing chromosome aberrations. The frequencies of mitotic or meiotic cells with chromosome aberrations increased linearly with increasing doses. The aberration types included, for example, acentric fragments, chromosome deletions, lagging chromosomes, chromosome bridges and micronuclei. In the root tip cells, aberrations chiefly consisted of acentric fragments and deletions. Chromosome bridges and lagging chromosomes were the main aberration phenomena observed in the pollen mother cells. The highest frequencies of root tip cells and pollen mother cells with chromosome aberrations were 15.2% and 39.8%, respectively. Changes in morphology and mutant were also observed in the plants derived from exposed seeds. Received: 10 April 2000 / Accepted: 10 October 2000     

Frequency of spontaneous chromosome aberrations in mice: effects of age

In this paper, we present data on chromosome aberration frequencies in mice which served as unexposed controls in a variety of radiation and chemical toxicology experiments conducted in our laboratory in recent years. All chromosome aberration data were obtained by chromosome painting. In peripheral blood lymphocytes from 102 animals, the frequencies of translocations and insertions increased significantly with age. No increase with age was seen for dicentrics or acentric fragments. When the data were analyzed by strain, the age-related increase in translocation frequencies was observed only in the 71 homozygous C57BL/6 mice and not in any of the three heterozygous strains. Very few aberrations of any type were observed in 62 bone marrow samples, and no effect of age was seen for any aberration type in this tissue. These results are similar to those observed in unexposed humans, and suggest that the increase in translocations is not the result of accumulated damage from chronic 'background' environmental exposures but instead may be due to biological processes associated with aging.     

Measurement of micronuclei by cytokinesis-block method in cultured Chinese hamster cells: comparison with types and rates of chromosome aberrations

The cytokinesis-block method of Fenech and Morley (1985) has been tested for the enumeration and characterization of micronuclei in exponentially growing Chinese hamster cells in culture. The consistent dose-response relations were obtained in cultures treated with mitomycin C, caffeine and colcemid. Comparison with the chromosome aberration frequencies indicated that approximately 30% of the acentric chromosomes are expressed as micronuclei in the mitomycin C and caffeine treated cells. The size distribution of the micronuclei suggested that the base-line frequency of micronuclei is mainly a reflection of mitotic dysfunctions rather than chromosome structural aberrations.     

Cytogenetic alterations in field workers routinely exposed to pesticides in Bogota flowers farms

Frequency of cytogenetic alterations (micronuclei and chromosome aberrations), DNA repair deficiencies and acetylcholinesterase activity was determined for field workers in Bogotá, Colombia. These workers were regularly exposed to organophosphate and carbamate insecticides while employed on farms for flower growing. Interviews were conducted with 31 workers associated with occupational risk of pesticides exposure and 30 without exposure. A standard cytogenetic assay was used to determine chromosome aberrations and micronuclei frequencies. In addition, a challenge assay assessed response to gamma-rays as an indication of DNA repair deficiencies--cells were exposed to gamma-rays in vitro and the frequencies of chromosome aberrations in post-irradiation metaphase cells were quantified. The data were evaluated for percentage of aberrant cells, cells with chromosome aberrations and frequencies of chromatid breaks per 100 metaphase cells in each worker. The exposed group had a significantly higher frequency of cells with chromosome aberrations and micronuclei as compared with the non-exposed group (p = 0.02). However, the challenge assay did not indicate a significant difference (p > 0.1). These findings require confirmation by further analytical studies involving larger sample. Cytogenetic and toxicological studies, in conjunction with thorough clinical examination are recommended.     

The characterization and transmissibility of chromosome aberrations induced in peripheral blood lymphocytes by in vitro alpha-particle radiation

Peripheral blood lymphocytes were irradiated in vitro with (213)Bi alpha particles at doses of 0, 10, 20, 50, 100, 200 and 500 mGy. Chromosome analysis was performed on 47-h cultures using single-color fluorescence in situ hybridization (FISH) to paint chromosomes 1, 3 and 5. The whole genome was analyzed for unstable aberrations to derive aberration frequencies and determine cell stability. The dose response for dicentrics was 33.60 +/- 0.47 x 10(-2) per Gy. A more detailed analysis revealed that the majority of aberrations scored as dicentrics were part of complex/multiple aberrations, with the proportion of cells containing complexes increasing with dose. Cells containing aberrations involving painted chromosomes (FISH aberrations) were further classified according to cell stability and complexity. The majority of cells with FISH aberrations were unstable. The proportion of aberrant FISH cells with complex/multiple aberrations ranged from 56% at 10 mGy to 89% at 500 mGy. A linear dose response for genomic frequencies of translocations in stable cells fitted the data from 0 to 200 mGy with a dose response of 7.90 +/- 0.98 x 10(-2) per Gy, thus indicating that they are likely to be observed in peripheral blood lymphocytes from individuals with past or chronic exposure to high-LET radiation. Comparisons with the dose response for low-LET radiation suggest an RBE of 13.6 for dicentrics in all cells and 3.2 for translocations in stable cells. Since stochastic effects of radiation are attributable to genetic changes in viable cells, translocations in stable cells may be a better measure when considering the comparative risks of different qualities of radiation.     

Chromosome aberration frequencies produced by a 70-MeV proton beam

The effectiveness of a 70-MeV proton beam in the induction of chromosome aberrations was studied. We employed peripheral lymphocytes and analyzed the frequencies of dicentrics and rings after irradiation at doses ranging from 0.1 to 8.0 Gy at various depths within a Lucite phantom. The frequency of chromosome aberrations after irradiation with an unmodulated proton beam at 5 mm showed a dose-response relationship similar to that of 60Co gamma rays. However, irradiation at greater depths with the spread-out Bragg peak induced higher aberration frequencies at doses lower than those with gamma rays. Furthermore, the distribution curve of chromosome aberration frequencies as a function of depth was found to be slightly different from the physically measured depth-dose curve. With the spread-out Bragg peak the biological effects were more marked at greater depths, resulting in a distribution of relative biological effectiveness values. The results obtained from chromosome aberration analysis may not be related directly to those for the relationship between dose and cell killing. Slight differences in values for relative biological effectiveness due to the change of dose and site of proton beam irradiation may not be important for practical proton beam therapy, but may be important in the prevention of late radiation injuries.     

Optimal conditions of LDR to protect the kidney from diabetes: Exposure to 12.5 mGy X-rays for 8 weeks efficiently protects the kidney from diabetes

Aims

We reported the attenuation of diabetes-induced renal dysfunction by exposure to multiple low-dose radiation (LDR) at 25 mGy every other day by suppressing renal oxidative damage. We here explored the optimal conditions of LDR to protect the kidney from diabetes.

Main methods

Male C57BL/6J mice with type 1 diabetes were induced with multiple injections of low-dose streptozotocin. Diabetic mice received whole body X-irradiation at a dose of 12.5, 25 or 50 mGy every other day for either 4 or 8 weeks. Age-matched normal mice were similarly irradiated at the dose of 25 mGy for 4 or 8 weeks. The renal function and histopathological changes were examined at the 4th and 8th weeks of the study.

Key findings

Diabetes induced renal dysfunction is shown by the decreased creatinine and increased microalbumin in the urine. Renal oxidative damage, detected by protein nitration and lipid oxidation, and remodeling, reflected by increased expression of connective tissue growth factor, collagen IV and fibronectin, were significantly increased in diabetic mice. All these renal pathological and function changes in diabetic mice were significantly attenuated by exposure to LDR at all regimens, among which, however, exposure to LDR at 12.5 mGy for 8 weeks provided the best protective effect on the kidney of diabetic mice.

Significance

Our results suggest that whole-body LDR at 12.5 mGy every other day for 8 weeks is the optimal condition of LDR to protect the kidney from diabetes.     

Relative effectiveness of HZE iron-56 particles for the induction of cytogenetic damage in vivo

One of the risks of prolonged manned space flight is the exposure of astronauts to radiation from galactic cosmic rays, which contain heavy ions such as (56)Fe. To study the effects of such exposures, experiments were conducted at the Brookhaven National Laboratory by exposing Wistar rats to high-mass, high-Z, high-energy (HZE) particles using the Alternating Gradient Synchrotron (AGS). The biological effectiveness of (56)Fe ions (1000 MeV/nucleon) relative to low-LET gamma rays and high-LET alpha particles for the induction of chromosome damage and micronuclei was determined. The mitotic index and the frequency of chromosome aberrations were evaluated in bone marrow cells, and the frequency of micronuclei was measured in cells isolated from the trachea and the deep lung. A marked delay in the entry of cells into mitosis was induced in the bone marrow cells that decreased as a function of time after the exposure. The frequencies of chromatid aberrations and micronuclei increased as linear functions of dose. The frequency of chromosome aberrations induced by HZE particles was about 3.2 times higher than that observed after exposure to (60)Co gamma rays. The frequency of micronuclei in rat lung fibroblasts, lung epithelial cells, and tracheal epithelial cells increased linearly, with slopes of 7 x 10(-4), 12 x 10(-4), and 11 x 10(-4) micronuclei/binucleated cell cGy(-1), respectively. When genetic damage induced by radiation from (56)Fe ions was compared to that from exposure to (60)Co gamma rays, (56)Fe-ion radiation was between 0.9 and 3.3 times more effective than (60)Co gamma rays. However, the HZE-particle exposures were only 10-20% as effective as radon in producing micronuclei in either deep lung or tracheal epithelial cells. Using microdosimetric techniques, we estimated that 32 cells were hit by delta rays for each cell that was traversed by the primary HZE (56)Fe particle. These calculations and the observed low relative effectiveness of the exposure to HZE particles suggest that at least part of the cytogenetic damage measured was caused by the delta rays. Much of the energy deposited by the primary HZE particles may result in cell killing and may therefore be "wasted" as far as production of detectable micronuclei is concerned. The role of wasted energy in studies of cancer induction may be important in risk estimates for exposure to HZE particles.     

Cytogenetic effects of microwave irradiation on male germ cells of the mouse

Hybrid male mice were exposed to 2.45 GHz microwaves for 30 min/day, 6 days a week for two consecutive weeks at power densities of 1.0, 100 or 400 W m-2, with sham-exposed controls. Rectal temperatures before and after exposure were measured on days 1, 6 and 12. Measurements made on day 1 were treated with caution because of heterogeneity in rectal temperatures taken before exposure between the groups of mice given different treatments. On days 6 and 12, rectal temperatures rose by approximately 1 degree C in mice sham exposed, or exposed to 1 W m-2 or 100 W m-2. Only in the group of mice exposed to 400 W m-2 was the mean rise in rectal temperature during exposure (about 3 degrees C) significantly increased above the sham value. In groups killed 2-3 days after treatment (mainly meiotic exposure) frequencies of chromosome aberrations in spermatocytes showed no significant heterogeneity although the highest frequency of 1.5 per cent was at the highest (400 W m-2) power density. Another group killed 30 days after 100 W m-2 exposures (spermatogonial sampling) showed no significant increase over controls in chromosome aberration frequency. There was a small but significant increase in sperm count with increasing power density in mice killed 12-13 days after exposure, but a non-significant one in those exposed as spermatogonia (killed 41 days later). Thus effects were markedly less severe than those reported previously by Manikowska-Czerska et al. (1985) with a very similar radiation regime and were probably caused by the temperature enhancement.     

Chromosome aberrations in workers of nuclear-power plants

The frequencies of chromosome aberrations in 135 workers from nuclear-power plants were compared with those in 135 age-matched controls. A total of 135,000 cells was scored. The frequencies of dicentric chromosome were 1.67 × 10⁻³ in the exposed group and 0.49 × 10⁻³ in the control group and those of chromosome-type deletion were 3.33 × 10⁻³ and 1.10 × 10⁻³, respectively. The frequencies of all types of chromosome aberrations in the exposed subjects were higher than those in the control group, but no significant trend of dose-dependent increase was observed when only the exposed group were considered. Poisson regression analysis, with both exposed and control included, showed that there was a significant association of chromosome aberration with radiation dose and the duration of work, but not with age, smoking habit and alcohol intake. It was also found that recent exposure to radiation, within the last 5 years, had contributed more to the observed chromosome aberration than earlier exposure.     

Radioprotective effects of Dragon's blood and its extract against gamma irradiation in mouse bone marrow cells

PurposeThe radioprotective effects of Dragon's blood (DB) and its extracts (DBE) were investigated using the chromosomal aberrant test, micronucleus and oxidative stress assay for anti-clastogenic and anti-oxidative activity.Materials and methodsAdult BALB/C mice were exposed to the whole body irradiation with 4 Gy ⁶⁰Co γ-rays. DB and DBE were administered orally once a day from 5 days prior to irradiation treatment to 1 day after irradiation. The mice were sacrificed on 24 h after irradiation. The cells of bone marrow were measured by counting different types of chromosomal aberrations and the frequency of micronuclei. Oxidative stress response was carried out by analysis of serum from blood.ResultsDB and DBE significantly decreased the number of bone marrow cells with chromosome aberrations after irradiation with respect to irradiated alone group. The administration of DB and DBE also significantly reduced the frequencies of micronucleated polychromatic erythrocytes (MPCE) and micronucleated normochromatic erythrocytes (MNCE). In addition, DB and DBE markedly increased the activity of antioxidant enzymes and the level of antioxidant molecular. Malondialdehyde (MDA) and nitric oxide (NO) levels in serum were significantly reduced by DB and DBE treatment.ConclusionsOur data suggested that DB and DBE have potential radioprotective properties in mouse bone marrow after ⁶⁰Co γ-ray exposure, which support their candidature as a potential radioprotective agent.     

The correlation between the frequency of micronuclei and specific chromosome aberrations in human lymphocytes exposed to microwave radiation in vitro.

Human whole-blood samples were exposed to continuous microwave radiation, frequency 7.7 GHz, power density 0.5, 10 and 30 mW/cm2 for 10, 30 and 60 min. A correlation between specific chromosomal aberrations and the incidence of micronuclei after in vitro exposure was observed. In all experimental conditions, the frequency of all types of chromosomal aberrations was significantly higher than in the control samples. In the irradiated samples the presence of dicentric and ring chromosomes was established. The incidence of micronuclei was also higher in the exposed samples. The results of the structural chromosome aberration test and of the micronucleus test were comparatively analyzed. The values obtained showed a positive correlation between micronuclei and specific chromosomal aberrations (acentric fragments and dicentric chromosomes). The results of the study indicate that microwave radiation causes changes in the genome of somatic human cells and that the applied tests are equally sensitive for the detection of the genotoxicity of microwaves.