Increased chromatid-type chromosomal aberrations in mouse m5S cells exposed to power-line frequency magnetic fields

Purpose : To investigate the induction of chromosomal aberrations in mouse m5S cells after exposure to power-line frequency magnetic fields (extremely low frequency magnetic fields; ELFMF) at high-flux densities. Material and methods : m5S cells were either untreated or pretreated during the G1 phase with mitomycin C (MMC, 1 μ M) for 1 h or 3Gy X-rays, and then exposed to ELFMF at three different flux densities (5 and 50mT at 60 Hz, 400 mT at 50 Hz) for 40 h. Unexposed control cells were incubated for the same period in a conventional CO 2 incubator. Chromosomal aberrations were analysed in the first post-treatment metaphases. Cell kinetics were assessed by DNA flow cytometry and the mitotic index. Results and conclusions : ELFMF enhanced the formation of spontaneous and MMC- or X-ray-induced chromosomal aberrations, in a flux-density-dependent manner. Statistically significant increases in the frequency of chromosomal aberrations were observed in cells exposed to 400mT ELFMF with respect to unexposed controls. The aberrations induced by ELFMF were mostly chromatid-type, not chromosome-type. The cells exposed to 400mT ELFMF exhibited a three-fold higher level of chromatid-type aberrations than did the unexposed cells. Flow cytometric and mitotic index analyses revealed that the S or G2 arrest following MMC or X-irradiation was more profound in ELFMF-exposed cells than in unexposed cells. Our results suggest that ELFMF can interfere with post-replication repair, resulting in increased levels of chromatid-type chromosomal aberrations induced spontaneously and by DNA damaging agents.     

Telomere shortening in mouse strains with constitutional chromosomal aberrations

PURPOSE: To compare telomere length in mouse strains with constitutional chromosomal aberrations generated either by exposure of parents to ionizing radiation, a chemical mutagen or arising spontaneously with that of the karyotypically normal mouse from the same genetic background. MATERIALS AND METHODS: Telomere length was assessed in five independently derived strains of mouse with constitutional chromosomal aberrations and in the karyotypically normal control mouse using quantitative fluorescence in situ hybridization (Q-FISH). Bone marrow cells obtained directly from the animals were used for the analysis. RESULTS: Chromosomal aberrations, one in each mouse strain, included three reciprocal translocations induced by ionizing radiation, one insertion induced by a chemical mutagen and one spontaneous Robertsonian translocation. There was no cytogenetically detectable loss of material in any of the strains and most mice were phenotypically normal. Telomeres were significantly shorter in all mouse strains with constitutional chromosomal aberrations in comparison with those originating from the karyatypically normal mouse from the same genetic background. Telomeres were significantly shorter at p-arms than at q-arms in all animals. The telomere length in individual chromosomes was variable and there was no single chromosome with consistently short telomeres in all animals. CONCLUSIONS: The presence of stable chromosomal aberrations, such as translocations or insertions, in the mouse genome may generate telomere shortening. This might have implications for understanding biological consequences or radiation-induced stable chromosomal aberrations.     

Telomere shortening in mouse strains with constitutional chromosomal aberrations

Purpose : To compare telomere length in mouse strains with constitutional chromosomal aberrations generated either by exposure of parents to ionizing radiation, a chemical mutagen or arising spontaneously with that of the karyotypically normal mouse from the same genetic background. Materials and methods : Telomere length was assessed in five independently derived strains of mouse with constitutional chromosomal aberrations and in the karyotypically normal control mouse using quantitative fluorescence in situ hybridization (Q-FISH). Bone marrow cells obtained directly from the animals were used for the analysis. Results : Chromosomal aberrations, one in each mouse strain, included three reciprocal translocations induced by ionizing radiation, one insertion induced by a chemical mutagen and one spontaneous Robertsonian translocation. There was no cytogenetically detectable loss of material in any of the strains and most mice were phenotypically normal. Telomeres were significantly shorter in all mouse strains with constitutional chromosomal aberrations in comparison with those originating from the karyotypically normal mouse from the same genetic background. Telomeres were significantly shorter at p-arms than at q-arms in all animals. The telomere length in individual chromosomes was variable and there was no single chromosome with consistently short telomeres in all animals. Conclusions : The presence of stable chromosomal aberrations, such as translocations or insertions, in the mouse genome may generate telomere shortening. This might have implications for understanding biological consequences or radiation-induced stable chromosomal aberrations.     

Glucose homeostasis in rats exposed to magnetic fields.

The development of diagnostic and therapeutic applications of magnetic fields, especially with regard to magnetic resonance imaging (MRI), draws attention to accompanying possible adverse effects. Recent investigations revealing an increase in insulin release in diabetic rats, increase in glycogen, and decrease in glucose level in rats exposed to magnetic fields, have provided the stimulus for the current studies. Rats were exposed to uniform constant magnetic fields of 10(-3) T and 10(-2) T, 1 hour each day, for a period of ten days. Blood glucose slightly increased, the release of insulin decreased, and the glucagon content increased when compared with controls. The efficiency of the hypophysis-hypothalamic system changed, as indicated by an increase in the level of growth hormone and thyroid-stimulating hormone. The content of the thyroid hormones, triiodothyronine and thyroxine, was higher between the third and seventh day of exposure. An increase in the cortisol level was also observed. The results might implicate a temporarily diabetic-like response in rats exposed to the magnetic field.     

辐射诱发小鼠生殖细胞染色体畸变研究

本文对小鼠受0～4Gyx射线照后60天的分化型精原千细胞染色体易位和初级精母细胞终变期一中期I的多价体进行了分析。两项指标的畸变量与剂量符合二次多项式模型。由于二者都是精原干细胞发育的不同阶段, 故彼此呈直线相关(Y=-0.24+2.25X).因乡价体在第一次减数分裂时, 有1/4的几率把易位传递给子代, 所以用本实验条件照射后, 在子代中易位携带者的危险度预计为2.13×10^-5/配子·cGy, 以各剂量点的预期值作剂量效应分析, 其子代易位再现率为Y=-0.19+0.35D, 与Generoso(1984)所观察的子代易位率Y=0.16+0.31D基本一致。     

镉诱导小鼠胚胎细胞抗辐射的适应性反应及时间效应

目的对镉（ＣｄＣｌ）诱导小鼠胚胎细胞１．５Ｇｙ６０Ｃｏγ射线的交叉适应性反应及时间效应进行了研究。方法小鼠于孕９天给予氯化镉（ｉｖ）后，分不同时间间隔给１．５Ｇｙ６０Ｃｏγ射线照射，孕１０天时进行胚胎细胞染色体制备。结果０．２５～２．０ｍｇ／ｋｇ剂量的镉能诱导胚胎细胞抗辐射的交叉适应性反应，而且与给镉后照射的时间间隔有密切关系，４小时已显示明显适应性反应，８小时达最高，１２，２４小时则产生协同作用。结论氯化镉可引起交叉适应性反应并与给镉后照射时间相关。     

Evaluation of the frequencies of chromosomal aberrations in a population exposed to prolonged low dose-rate 60Co gamma-irradiation

PURPOSE: Chromosomal aberration analysis in peripheral blood lymphocytes was performed to evaluate late cytogenetic effects of long-term low dose-rate gamma-irradiation exposure among students and residents exposed in radiocontaminated buildings. MATERIALS AND METHODS: Blood samples were taken from 1913 subjects (age 17.8+/-13.6, mean+/-SD) 5-8 years after their relocation from radioactive environments as well as from 176 non-exposed subjects (age 29.6+/-11.9) from the local community. Their lymphocytes were cultured for 48 h and metaphase spreads were prepared. A total of 208 900 metaphases were analysed for different types of chromosomal aberrations. RESULTS: Relatively higher frequencies of translocations (2.1 x 10(-3)), rings (0.6 x 10(-3)) and dicentrics (0.6 x 10(-3)) were noted in the exposed population as compared with the nonexposed reference populations. Moreover, 356 (78.6%) of the 453 inversions were found on 14q11.2q32 in the exposed population. Among 392 well-demonstrated translocations, 167 (42.6%) and 175 (44.6%) occurred in chromosomes 7 and 14, respectively, while 139 (35.5%) occurred as t(7;14). In particular, the aberrations t(7;14)(p13;q11.2), t(7;14)(p15;q11.2) and t(7;14)(q36;q11.2) were the most prevalent, occurring with frequencies of 19 (13.7%), 20 (14.4%) and 27 (19.4%), respectively. In these, 3205 breakpoints were documented, with chromosomes 7, 9 and 14 shown to carry significantly higher frequencies of breakpoints than expected (chi(2)-test, p<0.0001). A further six hotspots were identified on 7p15 (57, 1.8%), 7q36 (42, 1.3%), 9q12 (244, 7.6%), 9q13 (86, 2.7%), 14q11.2 (509, 15.9%) and 14q32 (387, 12.1%) in the exposed population. CONCLUSION: In comparison with the unexposed population, we observed increased frequencies of various chromosomal aberrations in this human population with previous exposure to prolonged low dose-rate gamma-radiation. Moreover, several hotspot breakpoints and inversions and translocations were observed on chromosomes 7 and 14.     

Brain DNA damage and 70-kDa heat shock protein expression in CD1 mice exposed to extremely low frequency magnetic fields

Purpose:?The question of whether exposure to extremely low frequency magnetic fields (ELF-MF), may contribute to cerebral cancer and neurodegeneration is of current interest. In this study we investigated whether exposure to ELF-MF (50 Hz-1 mT) harms cerebral DNA and induces expression of 70-kDa heat shock protein (hsp70).

Materials and methods:?CD1 mice were exposed to a MF (50 Hz-1 mT) for 1 or 7 days (15 h/day) and sacrificed either at the end of exposure or after 24?h. Unexposed and sham-exposed mice were used as controls. Mouse brains were dissected into cerebral cortex-striatum, hippocampus and cerebellum to evaluate primary DNA damage and hsp70 gene expression. Food intake, weight gain, and motor activity were also evaluated.

Results:?An increase in primary DNA damage was detected in all cerebral areas of the exposed mice sacrificed at the end of exposure, as compared to controls. DNA damage, as can be evaluated by the comet assay, appeared to be repaired in mice sacrificed 24?h after a 7-day exposure. Neither a short (15?h) nor long (7 days) MF-exposure induced hsp70 expression, metabolic and behavioural changes.

Conclusions:?These results indicate that in?vivo ELF-MF induce reversible brain DNA damage while they do not elicit the stress response.     

Domestic radon exposure and the frequency of stable or unstable chromosomal aberrations in lymphocytes

Purpose: To clarify the relationship between domestic radon exposure and the occurrence of chromosomal aberrations, stable translocations especially, in peripheral blood lymphocytes. Materials and methods: The study comprised a total of 84 nonsmoking individuals, divided into three groups according to radon concentration measurements performed in their homes: low radon concentration (< 100Bq/m3, mean 67Bq/m3), medium (200-400Bq/m3, mean 293Bq/m3) or high (> 800Bq/m3, mean 1737Bq/m3). Minimum residence in the present low-rise house was 10 years. The groups were matched with regard to age, gender and medical exposure. Fluorescence in-situ hybridization (FISH) was performed using chromosome paints for chromosomes 1, 2 and 4; 1500 metaphases were scored from each individual. Results: Equal frequencies of translocations and also other aberrations, e.g. dicentrics and complex rearrangements, were obtained in each group. Significant correlation of translocations with age was observed, and due to the high mean age (50 years) the genome-corrected frequency of translocations was high: about one translocation in 100 metaphases. Conclusions: Chronic exposure to high concentrations of domestic radon did not increase the rate of stable or unstable chromosomal aberrations in peripheral blood lymphocytes detected by FISH chromosome painting. A strong age effect was observed.     

Clastogenicity and aneuploidy in newborn and adult mice exposed to 50 Hz magnetic fields

PURPOSE: To detect possible clastogenic and aneugenic properties of a 50 Hz, 650 muT magnetic field. MATERIALS AND METHODS: The micronucleus test with CREST (Calcinosis, Raynaud's phenomenon, Esophageal dismotility, Sclerodactility, Telangectasia) antibody staining was performed on liver and peripheral blood sampled from newborn mice exposed to an ELF (Extremely Low Frequency) magnetic field during the whole intra-uterine life (21 days), and on bone marrow and peripheral blood sampled from adult mice exposed to the same magnetic field for the same period. RESULTS: Data obtained in newborn mice show a significant increase in micronuclei frequencies. In absolute terms, most of the induced micronuclei were CREST-negative (i.e., formed by a chromosome fragment). However, in relative terms, ELF exposure caused a two-fold increase in CREST-negative micronuclei and a four-fold increase in CREST-positive micronuclei (i.e., formed by a whole chromosome). No significant effect was recorded on exposed adults. CONCLUSIONS: These findings suggest the need for investigation of aneugenic properties of ELF magnetic fields in order to establish a possible relationship to carcinogenesis.     

Domestic radon exposure and the frequency of stable or unstable chromosomal aberrations in lymphocytes.

PURPOSE: To clarify the relationship between domestic radon exposure and the occurrence of chromosomal aberrations, stable translocations especially, in peripheral blood lymphocytes. MATERIALS AND METHODS: The study comprised a total of 84 nonsmoking individuals, divided into three groups according to radon concentration measurements performed in their homes: low radon concentration (<100Bq/m3, mean 67Bq/m3), medium (200-400Bq/m3, mean 293Bq/m3) or high (>800Bq/m3, mean 1737Bq/m3). Minimum residence in the present low-rise house was 10 years. The groups were matched with regard to age, gender and medical exposure. Fluorescence in-situ hybridization (FISH) was performed using chromosome paints for chromosomes 1, 2 and 4; 1500 metaphases were scored from each individual. RESULTS: Equal frequencies of translocations and also other aberrations, e.g. dicentrics and complex rearrangements, were obtained in each group. Significant correlation of translocations with age was observed, and due to the high mean age (50 years) the genome-corrected frequency of translocations was high: about one translocation in 100 metaphases. CONCLUSIONS: Chronic exposure to high concentrations of domestic radon did not increase the rate of stable or unstable chromosomal aberrations in peripheral blood lymphocytes detected by FISH chromosome painting. A strong age effect was observed.     

Clastogenicity and aneuploidy in newborn and adult mice exposed to 50 Hz magnetic fields

Purpose:?To detect possible clastogenic and aneugenic properties of a 50 Hz, 650 μT magnetic field.

Materials and methods:?The micronucleus test with CREST (Calcinosis, Raynaud's phenomenon, Esophageal dismotility, Sclerodactility, Telangectasia) antibody staining was performed on liver and peripheral blood sampled from newborn mice exposed to an ELF (Extremely Low Frequency) magnetic field during the whole intra-uterine life (21 days), and on bone marrow and peripheral blood sampled from adult mice exposed to the same magnetic field for the same period.

Results:?Data obtained in newborn mice show a significant increase in micronuclei frequencies. In absolute terms, most of the induced micronuclei were CREST-negative (i.e., formed by a chromosome fragment). However, in relative terms, ELF exposure caused a two-fold increase in CREST-negative micronuclei and a four-fold increase in CREST-positive micronuclei (i.e., formed by a whole chromosome). No significant effect was recorded on exposed adults.

Conclusions:?These findings suggest the need for investigation of aneugenic properties of ELF magnetic fields in order to establish a possible relationship to carcinogenesis.     

Kinetics of chromatid aberrations in G2 ataxia-telangiectasia cells exposed to X-rays and ara A

The cytogenetic effects of X-rays alone or in combination with 9-beta-D-arabinofuranosyladenine (ara A) were studied in an immortalized fibroblastic line of ataxia-telangiectasia (A-T) cells. The average length of G2 in this line was determined by autoradiographic labelling (labelled mitoses) to be approximately 5 h. Samples of A-T cells treated with or without ara A, 4 h prior to fixation were irradiated at 1/2-hourly intervals, from 1.5 h to 3.5 h before fixation and then examined for the presence of metaphase chromatid aberrations. It is postulated that the kinetics of disappearance (rejoining) of chromatid deletions with postirradiation incubation time reflects the underlying repair of dsb. This rejoining was found to be inhibited by ara A. Thus the frequency of deletions in the presence of ara A should represent the frequency of deletions in the absence of dsb repair. The rejoining kinetics for deletions in A-T was similar to that found in a previous study of normal human fibroblasts (Mozdarani and Bryant 1987). The number of deletions in X-irradiated A-T cells at 1.5 h before fixation was found to be higher by a factor of approximately 2 than that found previously in normals, indicating that in A-T a higher rate of conversion of dsb into chromatid deletions occurs. The frequency of exchanges induced in G2 A-T cells was similarly enhanced but, unlike the situation in normal cells, ara A was found to cause only a slight increase in this frequency.     

Cell survival and chromosomal aberrations in CHO-K1 cells irradiated by carbon ions

Chinese hamster ovary CHO-K1 cells were exposed to high LET ¹²C-beam (LET: 830 keV/μm) in the dose range of 0–6 Gy and to ⁶⁰Co irradiation and the RBE value was obtained. Effects of ¹²C-beam exposure on cell survival and chromosomal aberrations were calculated. The chromosomal aberration data were fitted with linear equation. The distribution of aberration in cells was examined with a standard u-test and used to evaluate the data according to Poisson probabilities. The variance to the mean ratio σ²/Y and the dispersion index (u) were determined. Overdispersion was significant (p<0.05) when the value of u exceeded 1.96.     

Labeling of mixed leukocytes with (99m)Tc-HMPAO causes severe chromosomal aberrations in lymphocytes.

99mTc-d,1-hexamethylpropyleneamine oxime (HMPAO) is widely used as a labeling agent for leukocytes in the diagnosis of inflammatory or infectious foci. Cytotoxicity studies have indicated that intracellular labeling of leukocytes with (111)In compounds may have severe detrimental effects on the cells. METHODS: In this study, the radiotoxic effects on mixed lymphocytes after labeling with (99m)Tc-HMPAO was investigated using the cytokinesis-blocked micronucleus assay and chromosomal aberration assay. RESULTS: Whereas negligible numbers of chromosome abnormalities were noted in unlabeled lymphocytes, the labeled lymphocytes showed multiple aberrations of various types, including dicentric, tricentric, and fivecentric chromosomes; centric rings; chromosome and chromatid type breaks; and acentric fragments. CONCLUSION: Heavily aberrant lymphocytes are seen in (99m)Tc-HMPAO-labeled mixed leukocytes after routine clinical procedures. It is unlikely, however, that this would cause detrimental effects, such as lymphoid malignancy, as these cells would normally be eliminated through apoptosis or phagocytosis.     

Increased uptake of99mTc-HL91 in tumor cells exposed to X-ray radiation

99mTc-HL91, a hypoxic marker, may be a predictor of tumor response to radiotherapy and an indicator of tumor oxygenation in the course of treatment. In this study, serial changes in 99mTc-HL91 uptake were observed in the normoxic condition in a human bladder cancer cell line exposed to a single dose or a fractionated dose of 10 Gy with an x-ray beam. The uptake per cell increased during cell growth retardation induced by the irradiation. This finding indicates that 99mTc-HL91 uptake is affected by injury to cells due to radiation; it may therefore be difficult to correctly assess the tissue oxygenation status during radiotherapy with 99mTc-HL91.     

Static electric fields interfere in the viability of cells exposed to ionising radiation

Purpose: The interference of electric fields (EF) with biological processes is an issue of considerable interest. No studies have as yet been reported on the combined effect of EF plus ionising radiation. Here we report studies on this combined effect using the prokaryote Microcystis panniformis, the eukaryote Candida albicans and human cells.

Materials and methods: Cultures of Microcystis panniformis (Cyanobacteria) in glass tubes were irradiated with doses in the interval 0.5–5 kGy, using a ⁶⁰Co gamma source facility. Samples irradiated with 3 kGy were exposed for 2 h to a 20 V · cm^?1 static electric field and viable cells were enumerated. Cultures of Candida albicans were incubated at 36°C for 20 h, gamma-irradiated with doses from 1–4 kGy, and submitted to an electric field of 180 V · cm^?1. Samples were examined under a fluorescence microscope and the number of unviable (red) and viable (apple green fluorescence) cells was determined. For crossing-check purposes, MRC5 strain of lung cells were irradiated with 2 Gy, exposed to an electric field of 1250 V/cm, incubated overnight with the anti-body anti-phospho-histone H2AX and examined under a fluorescence microscope to quantify nuclei with γ-H2AX foci.

Results: In cells exposed to EF, death increased substantially compared to irradiation alone. In C. albicans we observed suppression of the DNA repair shoulder. The effect of EF in growth of M. panniformis was substantial; the number of surviving cells on day-2 after irradiation was 12 times greater than when an EF was applied. By the action of a static electric field on the irradiated MRC5 cells the number of nuclei with γ-H2AX foci increased 40%, approximately.

Conclusions: Application of an EF following irradiation greatly increases cell death. The observation that the DNA repair shoulder in the survival curve of C. albicans is suppressed when cells are exposed to irradiation + EF suggests that EF likely inactivate cellular recovering processes. The result for the number of nuclei with γ-H2AX foci in MRC5 cells indicates that an EF interferes mostly in the DNA repair mechanisms. A molecular ad-hoc model is proposed.     

Stable chromosomal aberrations in haemopoietic stem cells in the blood of radiation accident victims

Purpose : The detection of long-term persistent chromosome aberrations in circulating haemopoietic stem cells after accidental radiation exposure. Materialand methods : Peripheral blood samples fromhighly exposed persons were collected 7-25 years after the radiation accidents in Moscow (1971), Kazan (1975) and Chernobyl (1996). Haemopoietic blood stem cells were analysed when investigating individual colonies derived from haemopoietic progenitor cells: burst-forming units-erythroid (BFU-E), granulocytemacrophage-colony-forming cells (GM-CFC) and multipotent granulocyte-erythrocyte-macrophage-megakaryocyte-colonyforming cells (GEMM-CFC). Colony formation was obtained in methylcellulose cultures. Chromosome preparations in single colonies were performed using a microtechnique. Results : Nine patients were investigated at 1 to 4 follow-up time points after radiation exposure. Three hundred and thirty-four single colonies were analyzed resulting in 1375 mitoses. It was found that colonies showed chromosome aberrations (ChA) up to 25 years after radiation exposure by classical cytogenetics and by fluorescence in situ hybridization (FISH). Stable aberrations were detected in 21% of colonies. They were clonal in 19% of colonies, i.e. the same abnormality was found in all cells derived from a single colony. In 2% of colonies ChA were stable but non-clonal; unstable ChA were not observed. Conclusions : The results indicate that blood-derived haemopoietic stem cells may serve as a biological indicator to detect radiation-induced ChA. Since they are considered to be in dynamic and functional exchange with stem cells in the medullary sites of blood cell formation such as bone marrow, the use of blood stem cells as a marker of radiation effects should be explored to assess the repair status of the stem cell pool as such.