Cytogenetic analysis in lymphocytes from workers occupationally exposed to low levels of ionizing radiation

Re-evaluation of CBMN test reference values of persons continuously occupationally exposed to low doses of ionizing radiation in Serbia

When established, cytokinesis-block micronucleus (CBMN) test reference values should be periodically evaluated according to the recommendations of reference documents. The biodosimetry cytogenetic laboratory of the Serbian Institute of Occupational Health established the CBMN test reference range for people occupationally exposed to ionizing radiation in 2016. Since then, new occupationally exposed persons have been subjected to micronucleus testing, resulting in the need for re-evaluation of existing CBMN test values. The examined population comprised 608 occupationally exposed subjects - 201 from the previous laboratory database and 407 newly examined. Comparison of groups based on gender, age and cigarette consumption did not show significant differences, although certain CBMN values differed significantly between the old and new groups. Duration of occupational exposure, gender, age and smoking habit influenced micronuclei frequency in all three analyzed groups, while no relation was found between type of work and micronucleus test parameters. Since the mean values of all tested parameters in the new group of examinees are within previously established reference ranges, existing values can be used in further research.

Mitotic index maximization with no effect on radiation-induced dicentric chromosome frequency

PURPOSE

The dicentric chromosome (Dic) assay, which is the gold standard for biological dose assessment in radiation emergency medicine, requires an analysis of at least 500 lymphocyte metaphases or 100 Dic aberrations. Therefore, peripheral blood culture conditions able to obtain a high frequency of metaphases for efficient dose evaluation should be optimized. However, the type of blood cultures [i.e. whole blood (WB) or isolated peripheral blood mononuclear cell (PBMC)-culture] and blood volume differ between biodosimetry laboratories. The purpose of this study is to investigate the blood volume at which a high mitotic index (MI) is obtained in peripheral WB-culture and isolated PBMC-culture, and to examine the possible effect of blood volume on radiation-induced Dic frequency.

MATERIALS AND METHODS

Peripheral blood was collected from three healthy donors with their informed consent. The complete and differential blood counts were performed using an automated hematology analyzer. After blood count, peripheral blood was irradiated with 0 or 2 Gy X-ray. Blood was cultured with phytohemagglutinin (180 μg/ml) and demecolcine　(0.05 μg/ml) for 48 h. The MI and Dic frequency were analyzed in 5, 10, 15, 20, 25, and 30% WB-cultures and 0.6, 1.2, 1.8, 2.4, 3.0, 3.6, and 4.2 ml WB-equivalent PBMC-cultures.

RESULTS

In WB-culture, MI showed the highest value (∼22%) in 5-15% WB-culture and then gradually decreased to ∼9% with 30% WB-culture. MI peaked at 36 and 31% in 1.8 and 2.4 ml-WB equivalent volumes for PMBC-cultures, respectively. MI progressively decreased as the amount of PBMCs increased. Although individual differences were observed in the MI values among the three subjects, all the subjects showed the same tendency and higher MI was seen in PBMC than WB-cultures. However, these factors had no significant impact on the yield of Dics. In all culture conditions, the estimated dose calculated based on the Dic frequency was equivalent to the absorbed dose of ex vivo X-ray-irradiated blood.

CONCLUSION

While MI was affected by the blood culture type and the volume of cultured blood, Dic yield did not differ significantly between these conditions. These results could be used by relevant laboratories to optimize MI in certain circumstances.

Biomarkers of Genotoxicity in Medical Workers Exposed to Low-Dose Ionizing Radiation: Systematic Review and Meta-Analyses

Medical staff represent the largest group of workers occupationally exposed to ionizing radiation (IR). Chronic exposure to low-dose IR may result in DNA damage and genotoxicity associated with increased risk of cancer. This review aims to identify the genotoxicity biomarkers that are the most elevated in IR-exposed vs. unexposed health workers. A systematic review of the literature was performed to retrieve relevant studies with various biomarkers of genotoxicity. Subsequent meta-analyses produced a pooled effect size for several endpoints. The search procedure yielded 65 studies. Chromosome aberrations (CA) and micronuclei (MN) frequencies were significantly different between IR-exposed and unexposed workers (θ_pooled = 3.19, 95% CI 1.46–4.93; and θ_pooled = 1.41, 95% CI 0.97–1.86, for total aberrant cells and MN frequencies, respectively), which was not the case for ring chromosomes and nucleoplasmic bridges. Although less frequently used, stable translocations, sister chromatid exchanges (SCE) and comet assay endpoints were also statistically different between IR-exposed and unexposed workers. This review confirms the relevance of CA and MN as genotoxicity biomarkers that are consistently elevated in IR-exposed vs. unexposed workers. Other endpoints are strong candidates but require further studies to validate their usefulness. The integration of the identified biomarkers in future prospective epidemiological studies is encouraged.

Antioxidant status and cytogenetic damage in hospital workers occupationally exposed to low dose ionizing radiation

The aim of the present study was to assess the oxidative stress level and chromosomal damage induced by occupational exposure to low dose ionizing radiation (LDIR). Two hundred and eighteen hospital workers occupationally exposed to LDIR were included in this study, along with 118 healthy age- and gender-comparable controls. Occupational dosimetry records were collected over the last year and revealed that the accumulated annual dose for each hospital worker was below the permissible limit of the International Commission on Radiological Protection (ICRP). The individuals' oxidative and antioxidative status were determined by measuring the activities of copper zinc-superoxide dismutase (CuZn-SOD), glutathione peroxidase (GSH-Px), catalase (CAT) enzymes, and the levels of malondialdehyde (MDA) in erythrocytes. The effect of radiation on chromosomal integrity was measured by the frequency of micronuclei (MN) formation using the cytokinesis block technique. Our results showed that the activities of CuZn-SOD and CAT enzymes and MDA levels observed in the hospital workers were higher than those in the controls (p < 0.05). We did not find significant difference in GSH-Px enzyme activity between the two groups (p = 0.247). A higher frequency of MN was found in exposed groups than in the controls [3(1-5) ‰ versus 2(0.75-4) ‰; p<0.001]. The difference was significant for males (p = 0.012), but not females (p = 0.14). Multiple linear regression analysis showed differences in the oxidant activities and MN frequency between hospital workers and controls adjusted for age, gender, smoking status and drinking status. Correlation analysis indicated that the frequency of MN was positively associated with MDA levels (p < 0.05). Altogether, these results support the detrimental effects of chronic low dose radiation in humans, which involves the induction of oxidative stress and chromosomal damage.

Exposure Assessment and Biomonitoring of Workers in Magnetic Resonance Environment: An Exploratory Study

Magnetic resonance imaging (MRI) has evolved rapidly over the past few decades as one of the most flexible tools in medical research and diagnostic imaging. MRI facilities are important sources of multiple exposure to electromagnetic fields for both patients and health-care staff, due to the presence of electromagnetic fields of multiple frequency ranges, different temporal variations, and field strengths. Due to the increasing use and technological advancements of MRI systems, clearer insights into exposure assessment and a better understanding of possible harmful effects due to long-term exposures are highly needed. In the present exploratory study, exposure assessment and biomonitoring of MRI workers at the Radio-diagnostics Unit of the National Cancer Institute of Naples "Pascale Foundation" (Naples, Italy) have been carried out. In particular, exposure to the MRI static magnetic field (SMF) has been evaluated by means of personal monitoring, while an application tool has been developed to provide an estimate of motion-induced, time-varying electric fields. Measurement results have highlighted a high day-to-day and worker-to-worker variability of the exposure to the SMF, which strongly depends on the characteristics of the environment and on personal behaviors, and the developed application tool can be adopted as an easy-to-use tool for rapid and qualitative evaluation of motion-induced, time-varying electric field exposure. Regarding biomonitoring, the 24 workers of the Radio-diagnostics Unit were enrolled to evaluate both spontaneous and mitomycin C-induced chromosomal fragility in human peripheral blood lymphocytes, by means of the cytokinesis-block micronucleus assay. The study subjects were 12 MRI workers, representative of different professional categories, as the exposed group, and 12 workers with no MRI exposure history, as the reference group. The results show a high worker-to-worker variability for both field exposure assessment and biomonitoring, as well as several critical issues and practicalities to be faced with in this type of investigations. The procedures for risk assessment and biomonitoring proposed here can be used to inform future research in this field, which will require a refinement of exposure assessment methods and an enlargement of the number of subjects enrolled in the biomonitoring study to gain robust statistics and reliable results.

A cytogenetic biomonitoring of industrial radiographers occupationally exposed to low levels of ionizing radiation by using cbmn assay

Industrial radiography is the process of using either gamma-emitting radionuclide sources or X-ray machines to examine the safety of industrial materials. The average annual effective dose in industrial radiography is one of the highest among radiation workers. The aim of this study was to investigate the cytogenetic effects of ionizing radiation in the peripheral blood lymphocytes of 60 industrial radiographers and 40 non-exposed individuals as the control group by using cytokinesis-block micronucleus (CBMN) assay. Totally, the frequencies of micronuclei (MN), nucleoplasmic bridges (NPBs) and nuclear buds (NBUDs) were significantly higher in the industrial radiographers than in the controls (p = 0.000). The mean MN frequency per 1000 binucleated cells in the industrial radiographers with last 5-y radiation dose of >100 mSv was significantly higher than those with ≤100 mSv (34.81 ± 12.7‰ vs. 26.33 ± 7.94‰, p = 0.024). The effect of age was observed in the control group and subjects with the age of >30 y showed significantly higher MN frequency compared with the subjects with the age of ≤30 y (9.45 ± 3.71‰ vs. 6.81 ± 3.05‰, p = 0.02). No obvious trend of increased MN as a function of either duration of employment or age or smoking status was observed in the industrial radiographers. The results show the increased levels of cytogenetic damages in the industrial radiographers. Even the workers exposed to the permissible doses are subjected to elevated frequencies of DNA damages. These findings confirm the importance of cytogenetic biomonitoring program beside physical dosimetry, surveying radiation safety of equipment and periodic training of workers for improvement of safety and radiation protection.

A semi‑automated FISH‑based micronucleus‑centromere assay for biomonitoring of hospital workers exposed to low doses of ionizing radiation

The aim of the present study was to perform cytogenetic analysis by means of a semi‑automated micronucleus‑centromere assay in lymphocytes from medical radiation workers. Two groups of workers receiving the highest occupational doses were selected: 10 nuclear medicine technicians and 10 interventional radiologists/cardiologists. Centromere‑negative micronucleus (MNCM‑) data, obtained from these two groups of medical radiation workers were compared with those obtained in matched controls. The blood samples of the matched controls were additionally used to construct a 'low‑dose' (0‑100 mGy) MNCM‑ dose‑response curve to evaluate the sensitivity and suitability of the micronucleus‑centromere assay as an 'effect' biomarker in medical surveillance programs. The physical dosimetry data of the 3 years preceding the blood sampling, based on single or double dosimetry practices, were collected for the interpretation of the micronucleus data. The in vitro radiation results showed that for small sized groups, semi‑automated scoring of MNCM‑ enables the detection of a dose of 50 mGy. The comparison of MNCM‑ yields in medical radiation workers and control individuals showed enhanced MNCM‑ scores in the medical radiation workers group (P=0.15). The highest MNCM‑ scores were obtained in the interventional radiologists/cardiologists group, and these scores were significantly higher compared with those obtained from the matched control group (P=0.05). The higher MNCM‑ scores observed in interventional radiologists/cardiologists compared with nuclear medicine technicians were not in agreement with the personal dosimetry records in both groups, which may point to the limitation of 'double dosimetry' procedures used in interventional radiology/cardiology. In conclusion, the data obtained in the present study supports the importance of cytogenetic analysis, in addition to physical dosimetry, as a routine biomonitoring method in medical radiation workers receiving the highest occupational radiation burdens.

The cytokinesis-blocked micronucleus assay: dose-response calibration curve, background frequency in the population and dose estimation

An in vitro study of the dose responses of human peripheral blood lymphocytes was conducted with the aim of creating calibrated dose-response curves for biodosimetry measuring up to 4 Gy (0.25-4 Gy) of gamma radiation. The cytokinesis-blocked micronucleus (CBMN) assay was employed to obtain the frequencies of micronuclei (MN) per binucleated cell in blood samples from 16 healthy donors (eight males and eight females) in two age ranges of 20-34 and 35-50 years. The data were used to construct the calibration curves for men and women in two age groups, separately. An increase in micronuclei yield with the dose in a linear-quadratic way was observed in all groups. To verify the applicability of the constructed calibration curve, MN yields were measured in peripheral blood lymphocytes of two real overexposed subjects and three irradiated samples with unknown dose, and the results were compared with dose values obtained from measuring dicentric chromosomes. The comparison of the results obtained by the two techniques indicated a good agreement between dose estimates. The average baseline frequency of MN for the 130 healthy non-exposed donors (77 men and 55 women, 20-60 years old divided into four age groups) ranged from 6 to 21 micronuclei per 1000 binucleated cells. Baseline MN frequencies were higher for women and for the older age group. The results presented in this study point out that the CBMN assay is a reliable, easier and valuable alternative method for biological dosimetry.

Effects of ionising radiation on micronucleus formation and chromosomal aberrations in Chinese radiation workers

This study is aimed to investigate the effects of ionising radiation (IR) on micronuclei (MN) formation and chromosome aberrations (CAs) in Chinese radiation workers. The study was conducted using peripheral blood lymphocytes from 1392 radiation workers from Public Hospitals of the city of Tangshan (the exposed group), and 143 healthy individuals as the control group. Fluorescence in situ hybridisation (FISH) was used to detect the unstable and stable nuclear CAs on metaphase. The MN assay was performed using the cytochalasin B method for cytokinesis-block. The MN and CA frequencies were significantly higher in the exposed group than in healthy controls (both p < 0.001). Examination of the incidence rates of MN and CA showed an increasing trend among workers in some occupations compared with the others (all p < 0.05). There were also significant differences in MN and CA rates among workers with different exposure times (all p < 0.05). Stable CA rates demonstrated an increased trend among workers with different exposure times (all p < 0.05), while no significance of unstable CA rates was found among workers with different exposure times (all p < 0.05). Importantly, the frequencies of CA and MN increased among different cumulative radiation dose groups (all p < 0.05). Correlation analysis showed that the frequencies of MN and CA were positively associated with the cumulative radiation dose. Long-term exposure to IR may have harmful effects on the health of radiation workers. The data obtained here show an increased risk of genetic instability that correlated with occupation, exposure time and equivalent dose among Chinese radiation workers.

Increased frequency of chromosomal aberrations and sister chromatid exchanges in peripheral lymphocytes of radiology technicians chronically exposed to low levels of ionizing radiations

Chromosome aberrations (CAs) and sister chromatid exchanges (SCEs) frequencies were estimated in peripheral lymphocytes from 21 radiology technicians, and from 21 non-exposed control subjects. We exclusively considered individuals who neither smoke nor consume drugs or alcohol for a period of at least two years prior to the analysis. Significant differences were found between exposed and controls in terms of SCEs and CAs frequencies. Technicians showed a significant higher number of high-frequency individuals (HFIs) with respect to the control group. Nevertheless, the mean frequency of SCEs observed among technician HFIs did not significantly differ with respect to that observed among control HFIs. Vice versa, the non-HFIs belonging to technicians group showed a statistically higher difference in the SCEs/NSM value with respect to the non-HFIs belonging to control group. Since the differences in the SCEs frequencies between the two groups are due to non-HFIs, our results seem to indicate a general genotoxic effect of the IR, not affected by HFIs. Among technicians, the level of chromosome damage correlated neither with years of radiation exposure nor with the age of the subjects. Vice versa, in the control group, a positive correlation was found between the number of SCEs and age. In both samples the gender status did not influence the frequencies of CAs and SCEs. Our results suggest that chronic long-term exposure to low doses of ionizing radiation could increase the CAs and SCEs frequencies. This study reinforces the relevance of the biomonitoring of hospital workers chronically exposed to ionizing radiation.

No threshold for the induction of chromosomal damage at clinically relevant low doses of X rays

The recent steep increase in population dose from radiation-based medical diagnostics, such as computed tomography (CT) scans, requires insight into human health risks, especially in terms of cancer development. Since the induction of genetic damage is considered a prominent cause underlying the carcinogenic potential of ionizing radiation, we quantified the induction of micronuclei and loss of heterozygosity events in human cells after exposure to clinically relevant low doses of X rays. A linear dose-response relationship for induction of micronuclei was observed in human fibroblasts with significantly increased frequencies at doses as low as 20 mGy. Strikingly, cells exposed during S-phase displayed the highest induction, whereas non S-phase cells showed no significant induction below 100 mGy. Similarly, the induction of loss of heterozygosity in human lymphoblastoid cells quantified at HLA loci, was linear with dose and reached significance at 50 mGy. Together the findings favor a linear-no-threshold model for genetic damage induced by acute exposure to ionizing radiation. We speculate that the higher radiosensitivity of S-phase cells might relate to the excessive cancer risk observed in highly proliferative tissues in radiation exposed organisms.

Genotoxic damage in hospital workers exposed to ionizing radiation and metabolic gene polymorphisms

Of all workers exposed globally to synthetic sources of radiation, medical personnel represent the largest group, but receive relatively low doses. Accidental or therapeutic acute radiation exposure of humans was observed to induce various forms of cytogenetic damage, including the possibility of increasing the incidence of micronuclei (MN) and chromosomal aberrations (CA). The aim of this study was to assess occupationally induced chromosomal damage in a large population of hospital workers exposed to low doses of ionizing radiation (IR). The cytokinesis-block MN and comet assays were used to examine peripheral blood lymphocytes (PBL) of 31 exposed workers to IR and 33 control subjects corresponding in gender, age, and smoking. Glutathione S-transferases (GSTM1, GSTT1, and GSTP1) are postulated to be involved in the detoxification of endogenous and exogenous genotoxicants. The association between these biomarkers and polymorphic genes of xenobiotic metabolizing enzymes was thus also assessed. MN frequency was significantly higher in the exposed subjects compared controls. Comet assay results showed a significant increase of tail length in workers exposed to IR. Data obtained suggest that GSTM1, GSTT1, and GSTP1 polymorphism do not modify significantly the genotoxic potential of IR. Therefore, the exposed medical personnel need to carefully apply radiation protection procedures and minimize, as low as possible, IR exposure to avoid possible genotoxic effects.

The micronucleus assay as a biological dosimeter of in vivo ionising radiation exposure

Biological dosimetry, based on the analysis of micronuclei (MN) in the cytokinesis-block micronucleus (CBMN) assay can be used as an alternative method for scoring dicentric chromosomes in the field of radiation protection. Biological dosimetry or Biodosimetry, is mainly performed, in addition to physical dosimetry, with the aim of individual dose assessment. Many studies have shown that the number of radiation-induced MN is strongly correlated with dose and quality of radiation. The CBMN assay has become, in the last years, a thoroughly validated and standardised technique to evaluate in vivo radiation exposure of occupational, medical and accidentally exposed individuals. Compared to the gold standard, the dicentric assay, the CBMN assay has the important advantage of allowing economical, easy and quick analysis. The main disadvantage of the CBMN assay is related to the variable micronucleus (MN) background frequency, by which only in vivo exposures in excess of 0.2-0.3 Gy X-rays can be detected. In the last years, several improvements have been achieved, with the ultimate goals (i) of further increasing the sensitivity of the CBMN assay for low-dose detection by combining the assay with a fluorescence in situ hybridisation centromere staining technique, (ii) of increasing the specificity of the test for radiation by scoring nucleoplasmic bridges in binucleated cells and (iii) of making the assay optimally suitable for rapid automated analysis of a large number of samples, viz. in case of a large-scale radiation accident. The development of a combined automated MN-centromere scoring procedure remains a challenge for the future, as it will allow systematic biomonitoring of radiation workers exposed to low-dose radiation.

Genome Instability and Bleomycin Sensitivity Test

Procjena individualne osjetljivosti na mutagene često je dio istraživanja u epidemiološkim studijama koje prate pojavnost zloćudnih bolesti u populacijama. Posljedica djelovanja mutagena u genomu izloženih osoba jest nastanak osoba jest nastanak određene, manje ili veće, količine oštećenja, uvjetovane individualnim razlikama u osjetljivosti. Viša razina takve genomske nestabilnosti znači opasnost (rizik) od razvoja zloćudnih bolesti. Interindividualne razlike u odgovoru na mutagene obično se povezuju i s promijenjenom (većinom smanjenom) sposobnosti (kapacitetom) za popravak DNA. Citogenetičke studije su pokazale da je genom tumorskih stanica nestabilniji od normalnih, a time i skloniji akumuliranju oštećenja, bilo da je nestabilnost uzrokovana nasljeđem, izloženošću ili kombinacijom tih dvaju učinaka. U oboljelih ispitanika utvrđena je povećana učestalost kromatidnih i kromosomskih aberacija naspram normalne populacije te sklonost razvoju određenih vrsta neoplazija. U praćenju povezanosti promijenjenog odgovora i pojavnosti tumora služe nam različiti biomarkeri. Kao indirektni pokazatelji uspješnosti popravka DNA često se rabe testovi osjetljivosti na mutagene u kulturama limfocita periferne krvi. Jedan od takvih testova je i bleomicinski test. Radiomimetik i citostatik, a po strukturi glikopeptid, bleomicin se u stanici prevodi u aktivni oblik sposoban cijepati molekulu DNA što uzrokuje brojne jednolančane i dvolančane lomove. Kao jednostavna i jeftina metoda, zasniva se na utvrđivanju ukupnog broja jednolančanih lomova u kromosomima limfocita uzgajanih u staničnoj kulturi koji su u uvjetima in vitro tijekom kasne G2-faze staničnog ciklusa bili izloženi bleomicinu. Ovaj revijalni rad daje pregled utjecaja raznih faktora na rezultate samog testa i pokazuje njegovu široku primjenu u proučavanju genomske nestabilnosti koju najčešće uzrokuje kombinacija raznih faktora.

A cytogenetic approach to the effects of low levels of ionizing radiations on occupationally exposed individuals

The aim of the present study was to assess occupationally induced chromosomal damage in hospital workers exposed to low levels of ionizing radiation. Thirty-two interventional cardiologists, 36 nuclear medicine physicians and 33 conventional radiologists were included in this study, along with 35 healthy age- and sex-matched individuals as the control group. We used conventional metaphase chromosome aberration (CA) analysis, cytokinesis-block micronucleus (MN) assay as important biological indicators of ionizing radiation exposure. Occupational dosimetry records were collected over the last year (ranged from 0.25 to 48mSv) and their whole life exposure (ranged from 1.5 to 147mSv). The results showed significantly higher frequencies of dicentric and acentric CAs (p<0.001) and MN (p<0.01) in all exposed groups than in the controls. Taking all the confounding factors into account, no obvious trend of increased chromosomal damages as a function of either duration of employment, exposed dose, sex or age was observed. Interventional cardiologists had the highest rates of CA and MN frequencies between the worker groups, though the differences were not significant. These results indicate that long term exposure to low dose ionizing radiation could result in DNA damage. Hence, the personnel who work in the hospitals should carefully apply the radiation protection procedures.