Spectrum of chromosomal aberrations in peripheral lymphocytes of hospital workers occupationally exposed to low doses of ionizing radiation

Chromosome aberrations frequency was estimated in peripheral lymphocytes from hospital workers occupationally exposed to low levels of ionizing radiation and controls. Chromosome aberrations yield was analyzed by considering the effects of dose equivalent of ionizing radiation over time, and of confounding factors, such as age, gender and smoking status. Frequencies of aberrant cells and chromosome breaks were higher in exposed workers than in controls (P = 0.007, and P = 0.001, respectively). Seven dicentric aberrations were detected in the exposed group and only three in controls, but the mean frequencies were not significantly different. The dose equivalent to whole body of ionizing radiation (Hwb) did appear to influence the spectrum of chromosomal aberrations when the exposed workers were subdivided by a cut off at 50 mSv. The frequencies of chromosome breaks in both subgroups of workers were significantly higher than in controls (< or =50 mSv, P = 0.041; >50 mSv, P = 0.018). On the other hand, the frequency of chromatid breaks observed in workers with Hwb >50 mSv was significantly higher than in controls (P = 0.015) or workers with Hwb < or =50 mSv (P = 0.046). Regarding the influence of confounding factors on genetic damage, smoking status and female gender seem to influence the increase in chromosome aberration frequencies in the study population. Overall, these results suggested that chromosome breaks might provide a good marker for assessing genetic damage in populations exposed to low levels of ionizing radiation.     

Cytogenetic monitoring of hospital workers exposed to low-level ionizing radiation

In the present study the cytogenetic effects in hospital workers exposed to low-level radiation were evaluated. Samples of peripheral blood were collected from 63 subjects working in radiodiagnostics and from 30 subjects, working in the same hospitals, who were used as controls. A higher number of cells with chromosome-type aberrations (CA) was observed in the exposed workers vs. the controls and the difference was statistically significant (p less than 0.05). No correlation was, on the contrary, found between CA and years of exposure. A significant difference was observed in the incidence of cells with CA between smokers and non-smokers, but in the control group only. In contrast, in the workers exposed to ionizing radiation, the frequency of cells with CA was very similar in smokers and non-smokers.     

Frequency of micronuclei in peripheral blood lymphocytes from subjects occupationally exposed to low levels of ionizing radiation

The aim of this study was to evaluate the genotoxic effect of low dose of occupational radiation exposure in Nuclear Medicine Department employees, by using cytokinesis-blocked micronucleus assay in peripheral blood lymphocytes. The study included 46 exposed individuals together with 27 from the same area without occupational exposure to radiation which served as controls. The results obtained were evaluated with respect to age, gender, smoking habits, pathological condition and the occupational exposure to radiation of the individuals. The frequency of micronuclei increased significantly with the age of the subjects (P = 0.007). However there were no significant differences in micronucleus frequency with gender, smoking habits and occupational exposure. The frequency of micronuclei was significantly higher in individuals with presence of pathological condition (P < 0.0001) in comparison to healthy population irrespective of their exposure status.     

Cytogenetic analysis of chromosomal aberrations of peripheral lymphocytes in workers occupationally exposed to nickel.

The authors carried out a cytogenetic examination of chromosomal aberrations of peripheral lymphocytes (100 cells evaluated in each sample) with simultaneous monitoring of the level of exposure by means of determination of nickel in the urine, serum and hair. The series included 21 workers occupationally exposed to nickel at two workshops producing NiO (6 persons) and NiSO4 (15 persons) in a chemical plant. At the same time a comparable control group, i.e., 19 workers of the same chemical plant but without any direct occupational nickel exposure (clerks, service men, etc.), were examined in the same way. In the exposed group chromosomal aberrations of peripheral lymphocytes were detected with an average value of 6.41 +/- 1.9% (range 2-14%); in the group producing NiO it was, on the average, 9.5 +/- 3.2% (range 7-14%) whereas in the NiSO4 production workers it was only 5.2 +/- 1.9% (range 2-10%). There was a dependence of chromosomal aberrations of peripheral lymphocytes on the exposure time and on the nickel content of the biological material. Significantly increased values (in contrast to the normal value of chromosomal aberrations of peripheral lymphocytes, up to 2%) were detected in the control group as well (average value of 4.05 +/- 2.27%, range 1-10%). The authors explain this fact by the nickel-polluted environment of the whole observed chemical plant.     

Mitochondrial DNA mutations in individuals occupationally exposed to ionizing radiation

Mutations in a 443-bp amplicon of the hypervariable region HVR1 of the D-loop of mitochondrial DNA (mtDNA) were quantified in DNA extracted from peripheral blood samples of 10 retired radiation workers who had accumulated external radiation doses of >0.9 Sv over the course of their working life and were compared to the levels of mutations in 10 control individuals matched for age and smoking status. The mutation rate in the 10 exposed individuals was 9.92 x 10(-5) mutations/ nucleotide, and for the controls it was 8.65 x 10(-5) mutations/ nucleotide, with a procedural error rate of 2.65 x 10(-5) mutations/nucleotide. No increase in mtDNA mutations due to radiation exposure was detectable (P = 0.640). In contrast, chromosomal translocation frequencies, a validated radiobiological technique for retrospective dosimetric purposes, were significantly elevated in the exposed individuals. This suggests that mutations identified through sequencing of mtDNA in peripheral blood lymphocytes do not represent a promising genetic marker of DNA damage after low-dose or low-dose-rate exposures to ionizing radiation. There was an increase in singleton mutations above that attributable to procedural error in both exposed and control groups that is likely to reflect age-related somatic mutation.     

Redox status in workers occupationally exposed to long-term low levels of ionizing radiation: A pilot study

Objectives: Reactive oxygen species (ROS), including superoxide (O₂^??), play an important role in the biological effects of ionizing radiation. The human body has developed different antioxidant systems to defend against excessive levels of ROS. The aim of the present study is to investigate the redox status changes in the blood of radiologic technologists and compare these changes to control individuals.

Methods: We enrolled 60 medical workers: 20 occupationally exposed to ionizing radiation (all radiologic technologists), divided in three subgroups: conventional radiography (CR), computerized tomography (CT), and interventional radiography (IR) and 40 age- and gender-matched unexposed controls. Levels of O₂^?? and malondialdehyde (MDA) in blood were measured as an index of redox status, as were the activities of antioxidant enzymes superoxide dismutase (SOD) and catalase. Redox status was also assessed by measuring levels of reduced and oxidized glutathione (GSH, GSSG, respectively).

Results: Levels of O₂^?? and MDA, and SOD activity in the blood of IR and CT-exposed subjects were significantly higher than both the CR-exposed subjects and control individuals. However, there were no statistically significant differences in the levels of catalase, GSH and ratio of GSH/GSSG between exposed workers and control individuals.

Discussion: This study suggests that healthcare workers in CT and IR occupationally exposed to radiation have an elevated circulating redox status as compared to unexposed individuals.     

DNA damage in cells exposed to ionizing radiation

Ionizing radiation induces variety of structural lesions in DNA of irradiated organisms. Their formation depends largely on the degree of cell oxygenation, the level of endogenous antioxidants, on DNA-protein complexes and compactization of DNA in the chromatin and activity of DNA repair systems. All ionizing radiation-induced DNA lesions can arbitrarily be divided into two groups. Group 1 includes singly damaged sites (single-sites): base modification, single-strand breaks, alkaline-labile sites (including a basic sites). Group 2 contains: locally multiply damaged sites (clustered lesions), double-strand breaks, intermolecular cross-links. The yields of lesions of group 2 increases with high linear energy transfer of radiation and these lesions play a dominant role in the radiation death, formation of chromosome and gene mutations, cell transformation.     

Absence of chromosomal damage in human lymphocytes exposed to microwave radiation with hyperthermia

Specimens of human blood were exposed to 0, 4, 40, 100, and 200 Wkg-1 of 2.45 GHz microwave radiation for 20 minutes. The blood temperature was carefully controlled so that it rose from 37 to 40 degrees C. Cultured lymphocytes were examined for induced chromosomal damage but no effect in excess of background was observed.     

Cytogenetic analysis in lymphocytes from radiation workers exposed to low level of ionizing radiation in radiotherapy,CT-scan and angiocardiography units

Ionizing radiation is known as a classical mutagen capable of inducing various kinds of stable and unstable chromosomal aberrations. The percentage of cells with chromosomal aberrations was analyzed in peripheral blood lymphocytes of occupationally exposed workers in radiotherapy, CT-scan, angiography and healthy controls. The incidence of all types of aberrations (gap, acentric fragment, dicentric and ring) in exposed subjects were higher than those observed in healthy controls (P = 0.0001). However, the frequency of aberrant cells with dicentric and ring chromosome in exposed subjects were not significantly different from those in controls. To see whether there is a significant difference in the incidence of chromosomal aberrations among three groups, they were compared for all types of observed aberrations. No significant difference was found between radiotherapy and CT-scan groups (P = 0.838). The percentage of aberrant cells observed, for angiography groups were significantly higher than radiotherapy (P = 0.0001) and CT-scan (P = 0.0001) group. Taken together these data suggest that the cumulative effects of low level chronic exposure to ionizing radiation is higher for those who occupationally exposed in angiography.     

DNA damage in leukocytes of workers occupationally exposed to 1-bromopropane

1-bromopropane (1-BP; n-propyl bromide) (CAS No. 106-94-5) is an alternative to ozone-depleting chlorofluorocarbons that has a variety of potential applications as a degreasing agent for metals and electronics, and as a solvent vehicle for spray adhesives. Its isomer, 2-brompropane (2-BP; isopropyl bromide) (CAS No. 75-26-3) impairs antioxidant cellular defenses, enhances lipid peroxidation, and causes DNA damage in vitro. The present study had two aims. The first was to assess DNA damage in human leukocytes exposed in vitro to 1- or 2-BP. DNA damage was also assessed in peripheral leukocytes from workers with occupational exposure to 1-BP. In the latter assessment, start-of- and end-of-work week blood and urine samples were collected from 41 and 22 workers at two facilities where 1-BP was used as a solvent for spray adhesives in foam cushion fabrication. Exposure to 1-BP was assessed from personal-breathing zone samples collected for 1-3 days up to 8h per day for calculation of 8h time weighted average (TWA) 1-BP concentrations. Bromide (Br) was measured in blood and urine as a biomarker of exposure. Overall, 1-BP TWA concentrations ranged from 0.2 to 271 parts per million (ppm) at facility A, and from 4 to 27 ppm at facility B. The highest exposures were to workers classified as sprayers. 1-BP TWA concentrations were statistically significantly correlated with blood and urine Br concentrations. The comet assay was used to estimate DNA damage. In vitro, 1- or 2-BP induced a statistically significant increase in DNA damage at 1mM. In 1-BP exposed workers, start-of- and end-of-workweek comet endpoints were stratified based on job classification. There were no significant differences in DNA damage in leukocytes between workers classified as sprayers (high 1-BP exposure) and those classified as non-sprayers (low 1-BP exposure). At the facility with the high exposures, comparison of end-of-week values with start-of-week values using paired analysis revealed non-sprayers had significantly increased comet tail moments, and sprayers had significantly increased comet tail moment dispersion coefficients. A multivariate analysis included combining the data sets from both facilities, log transformation of 1-BP exposure indices, and the use of multiple linear regression models for each combination of DNA damage and exposure indices including exposure quartiles. The covariates were gender, age, smoking status, facility, and glutathione S-transferase M1 and T1 (GSTM1, GSTT1) polymorphisms. In the regression models, start-of-week comet tail moment in leukocytes was significantly associated with serum Br quartiles. End-of-week comet tail moment was significantly associated with 1-BP TWA quartiles, and serum Br quartiles. Gender, facility, and GSTM1 had a significant effect in one or more models. Additional associations were not identified from assessment of dispersion coefficients. In vitro and in vivo results provide limited evidence that 1-BP exposure may pose a small risk for increasing DNA damage.     

Age associated alteration in DNA damage and repair capacity in Turbatrix aceti exposed to ionizing radiation

Excision repair capacity was measured in young and old Turbatrix aceti (phylum Nematoda) following exposure to ionizing radiation. Both repair synthesis and removal of 5,6-dihydroxydihydrothymine type (glycol) base damage were quantitated. At least two-fold higher glycol levels were produced in the DNA of young than of old nematodes for the same radiation dose. Young worms also excised glycol damage more rapidly and completely than old worms. Both peak repair synthesis activity and completion of repair synthesis occurred at earlier times during post-irradiation incubation in young nematodes. The data indicate there is a significant age-associated difference in both the incidence and removal of ionizing radiation damage in T. aceti which is used as a model of the ageing process.     

mFISH analysis of chromosome aberrations in workers occupationally exposed to mixed radiation

We performed a study on the presence of chromosome aberrations in a cohort of plutonium workers of the Mayak production association (PA) with a mean age of 73.3 ± 7.2 years to see whether by multi-color fluorescence in situ hybridization (mFISH) translocation analysis can discriminate individuals who underwent occupational exposure with internal and/or external exposure to ionizing radiation 40 years ago. All Mayak PA workers were occupationally exposed to chronic internal alpha-radiation due to incorporated plutonium-239 and/or to external gamma-rays. First, we obtained the translocation yield in control individuals by mFISH to chromosome spreads of age-matched individuals and obtained background values that are similar to previously published values of an international study (Sigurdson et al. in Mutat Res 652:112–121, 2008). Workers who had absorbed a total dose of >0.5 Gy external gamma-rays to the red bone marrow (RBM) displayed a significantly higher frequency of stable chromosome aberrations relative to a group of workers exposed to <0.5 Gy gamma-rays total absorbed RBM dose. Thus, the translocation frequency may be considered to be a biological marker of external radiation exposure even years after the exposure. In a group of workers who were internally exposed and had incorporated plutonium-239 at a body burden >1.48 kBq, mFISH revealed a considerable number of cells with complex chromosomal rearrangements. Linear associations were observed for translocation yield with the absorbed RBM dose from external gamma-rays as well as for complex chromosomal rearrangements with the plutonium-239 body burden.     

Cytogenetic analysis of peripheral blood lymphocytes of workers occupationally exposed to styrene

The genetic risk run by workers occupationally exposed to styrene vapors was assessed in two different plants A and B, using the cytogenetic analysis of peripheral blood lymphocytes. In plant A engaged in the manufacture of polystyrene vessels the mean styrene exposure level was found to range between 70 and 150 mg . m-3, in plant B manufacturing sports boats, plastic slides for children and plastic guard-stones it reached the level of about 200 mg . m-3. The rate of aberrant cells (AB.C.) found in plant A workers (N = 36) at the time of first sampling was 1.38% and the value of break/cell (B/C) ratio was 0.015; at the second sampling the rate of AB.C. was 1.41% and the B/C ratio was 0.014. The group of matched controls (N = 19) was found to have 1.26% of AB.C. and 0.014 breaks per cell. Plant B workers (N = 22) exhibited at the first sampling 1.72% of AB.C. and their value of B/C ratio was 0.018, the group of matched controls (N = 22) had 1.36% of AB.C and the B/C ratio 0.015; the respective values at the time of second sampling were 2.81% for AB.C. rate and 0.029 for B/C ratio in the exposed and 1.89% for AB.C. rate and 0.021 for B/C ratio in the control group. It is concluded that styrene exposure levels below 100 mg . m-3 do not pose any serious genetic risk for the exposed population groups. The variations found in the degree of chromosome injury by smoking habits, drug intake pattern, or sex were not statistically significant.     

Cytogenetic analyses by fluorescence in situ hybridization (FISH) in hospital workers occupationally exposed to low levels of ionizing radiation

An occupationally exposed population has been studied to evaluate the suitability of FISH painting techniques to detect chronic exposures to very low doses of ionizing radiation by the analysis of translocations. Whole-chromosome painting probes for chromosomes 1, 4 and 11 in combination with a pancentromeric probe have been employed. For comparison, a matched control population has also been studied. The mean genomic frequencies per 100 cells of total translocations in the control and exposed populations were 0.90 +/- 0.12 and 1.04 +/- 0.11, respectively. In the occupationally exposed population, no correlation between the frequencies of translocations and the doses received was found. When the two populations were compared, no significant differences were observed for the frequencies of the different chromosomal abnormalities examined. The absence of differences between control and exposed populations could be attributed to the very low-dose exposures recorded in the occupationally exposed population and to the wide range of individual frequencies of translocations observed.     

G2 chromatid damage and repair kinetics in normal human fibroblast cells exposed to low- or high-LET radiation

Radiation-induced chromosome damage can be measured in interphase using the Premature Chromosome Condensation (PCC) technique. With the introduction of a new PCC technique using the potent phosphatase inhibitor calyculin-A, chromosomes can be condensed within five minutes, and it is now possible to examine the early damage induced by radiation. Using this method, it has been shown that high-LET radiation induces a higher frequency of chromatid breaks and a much higher frequency of isochromatid breaks than low-LET radiation. The kinetics of chromatid break rejoining consists of two exponential components representing a rapid and a slow time constant, which appears to be similar for low- and high-LET radiations. However, after high-LET radiation exposures, the rejoining process for isochromatid breaks influences the repair kinetics of chromatid-type breaks, and this plays an important role in the assessment of chromatid break rejoining in the G2 phase of the cell cycle.     

Study of reparative DNA synthesis in lymphocytes of persons occupationally exposed to radiation

The UDS efficiency in lymphocytes of professionals chronically exposed to gamma/neutron radiation, as well as for a control cohort was estimated. A credible reduction of UV-induced UDS (KUV) index as compared to the control was demonstrated. This shows an invalid repair state of blood cells in professionals. As for the control cohort, the decreasing tendency of UDS index with age was found. The correlative analysis of UDS index dependence upon an absorbed dose (based on physical dosimetry data) revealed the trend towards repair index reduction along with a higher total absorbed doze, that is followed by UDS index coming onto a plateau. It was also demonstrated that after a sharp and/or accidental irradiation UDS index reduces as compared to permanent portioned irradiation. It was not observed the influence of smoking upon UDS efficiency in blood lymphocytes neither for control, nor for experimental group. The analysis of vitamin therapy of the both cohorts showed that such therapy raises UDS index of the control (i.e., non-professional) group. Besides, it was found out an additional positive effect of vitamin therapy, i.e. doze leveling in long-term perspective after irradiation. The most expressed KUV/doze correlation was characteristic for professionals, who do not take vitamins and do not smoke. This proves that in blood cells of professionals it is preserved a dependence of repair system invalidity upon the absorbed doze without similar external factors.