Alkaline single cell gel electrophoresis and human biomonitoring for genotoxicity: a study on subjects with residential exposure to radon

Domestic radon exposure and childhood cancer risk by site and sex in 727 counties in the United States, 2001-2018

BACKGROUND

Childhood cancer has few established risk factors and environmental influences are underexplored. This ecologic study investigated the association between domestic radon exposure and childhood cancer risk in a large sample of United States (U.S.) counties.

METHODS

Monthly ZIP code-level basement radon estimates from a geographic machine learning model were aggregated annually to counties, analyzed as continuous and dichotomized (cut point: 74 Bq/cubic meter (Bq/m3) or 2.0 picocuries/L (pCi/L)) versions, and lagged by one year. Annual county-level counts of sex- and site-specific (all, leukemia, brain and central nervous system [CNS], and other sites) incident cancer diagnoses among those 0-19 years from 2001 to 2018 were obtained from the National Cancer Institute's Surveillance, Epidemiology, and End Results Program database. Sex- and site-specific counts were modeled as zero-inflated Poisson distributions in a Bayesian spatiotemporal framework and sequentially adjusted for random and fixed confounder effects.

RESULTS

In 727 counties across 14 states, the average population aged 0-19 years was 41,599 people at baseline. Results from fully adjusted spatiotemporal statistical models indicated 1.05 (95% credible interval, CrI: 1.00, 1.09) times higher relative risks (RRs) of leukemia among both sexes and a RR of 1.06 (95%CrI: 1.00, 1.12) in males from a 50 Bq/m3 (1.35 pCi/L) increase in radon concentration the year prior. For radon exposures ≥74 Bq/m3 (2.00 pCi/L) the year prior, RRs were 1.08 (95%CrI: 1.02, 1.15) for both sexes and 1.12 (95%CrI: 1.04, 1.22) for females. No associations were found with other cancer sites or sexes from prior year radon exposures.

CONCLUSIONS

County-level childhood leukemia risk in both sexes were associated with average radon levels below U.S. Environmental Protection Agency guidelines recommending mitigation (148 Bq/m3 or 4.00 pCi/L). These findings warrant further investigation using population-based and individual-level study designs.

A comparative study of genotoxicity endpoints for women exposed to different levels of indoor radon concentrations

BACKGROUND AND PURPOSE

Radon and its radioactive progenies are the most important source of ionizing radiation of natural origin, being classified as a Group 1 carcinogen. The aim of this study is to investigate the genotoxic effects of a wide range of indoor radon concentrations, as well as the kinetics of the process of repairing DNA-induced lesions by a challenging dose of gamma irradiation.

MATERIAL AND METHODS

Female subjects residing in the Băiţa-Ştei radon priority area were selected as the exposed group. The reference group was comprised of women from the same county (Bihor), but located in an area with an average indoor radon concentration typical of the county from which they were taken. Radon concentration values of 300 Bq/m³ and 148 Bq/m³, respectively, were chosen as a threshold in order to capture the impact of radon exposure between the groups. The alkaline comet assay was used in order to measure the DNA damage, as well as the repair kinetics at 2 and 24 h after 2 Gy challenging doses of gamma irradiation using peripheral blood lymphocytes. From the serum of the subjects, the oxidative damage by 8-hydroxydeoxyguanosine as well as the PARP induction was evaluated. The chromosomal aberrations were evaluated using the Cytokinesis Block MicroNucleus Assay.

RESULTS

A statistically significant increase was observed in terms of DNA-induced lesions assessed by comet assay for the exposed group compared to the reference group. A positive correlation was obtained between DNA damage and the annual effective dose, respectively with the radon progenies concentrations. A statistically significant difference was also observed for the frequency of the micronuclei between the exposed - reference groups. Significantly faster repair kinetics of DNA-induced lesions was recorded for the first 2 h after gamma irradiation in the reference group compared to the exposed group. Using the threshold of 300 Bq/m³ for radon concentration, faster kinetics of DNA damage repair for people exposed to low radon concentrations, compared to those exposed to higher concentrations for the second phase of DNA repair kinetics was observed.

CONCLUSION

An increased radiosensitivity of lymphocytes, as well as slower repair kinetics, may be associated with exposure to higher indoor radon concentrations.

Carcinogen soil radon enrichment in a geothermal area: Case of Güzelçamlı-Davutlar district of Aydın city, western Turkey

Radon gas is noble gas formed from the normal radioactive decay series of 238U. Uranium is present in almost all rocks but enriched in silica-rich rocks like granites, gneisses, schists, volcanics, pegmatites, migmatites. The study area extends over metamorphic, volcanic, and clastic sedimentary rocks. Soil radon was measured in 34 measuring points and its concentrations reach 3700 Bq/m³. The mean values decrease due to seawater penetrations or to collections of atmospheric waters in a basin. Those water saturates the soil and prevents radon emanation and exhalation. The emanation of radon to the surface requires transporting agents. In geothermal fields, hot water or fluids take on this task. For that reason, geothermal fields can represent high soil radon. As radon was classified as a human carcinogen, our study area and whole Aydın province which has rich geothermal potential must be surveyed for public health.

Residential exposure to radon and levels of histone γH2AX and DNA damage in peripheral blood lymphocytes of residents of Kowary city regions (Poland)

INTRODUCTION

Radon-induced biological effects have been studied mainly through epidemiological investigations, and well-controlled in vitro and in vivo experiments. To provide data explaining radon exposure-induced harmful effects in natural environment, exposure assessment under these conditions is needed. The objective of the study was to examine the level of genetic damage assessed with biomarkers of DNA single- and double-strand breaks (SSBs and DSBs) in peripheral blood mononuclear cells obtained from individuals continuously exposed to Rn in homes. Naturally elevated Rn concentrations in homes can be found in the South of Poland, in Kowary city.

METHODS

Measurements of expression of phosphorylated histone γH2AX was used as a marker of DNA double strand breaks. To detect DNA single and double-strand breaks and alkali labile sites, the alkaline comet assay was used. Oxidative damage of DNA was evaluated by formamidopyrimidyne (FPG)-modified comet assay. The blood was collected from 94 volunteers living in Kowary. Subjects were grouped according to their status of living in radon concentration ≥100 Bq/m³ (n = 67), and <100 Bq/m³ (n = 27).

RESULTS

The statistically significant differences in levels of DNA damage in peripheral lymphocytes assessed with comet assay were found to be associated with levels of radon exposure in indoor air (p = 0.034). DNA damage in the comet assay was significantly correlated with DNA damage assessed with γH2AX staining.

CONCLUSIONS

Results of the present study indicate the suitability of alkaline comet assay for the detection of DNA damage in peripheral blood lymphocytes of people environmentally exposed to radon.

γ-H2AX/53BP1/pKAP-1 foci and their linear tracks induced by in vitro exposure to radon and its progeny in human peripheral blood lymphocytes

The biodosimetric information is critical for evaluating the human health hazards caused by radon and its progeny. Here, we demonstrated that the formation of phosphorylated histone variant H2AX (γ-H2AX), p53-binding protein 1 (53BP1) and phosphorylated KRAB-associated protein 1 (pKAP-1) foci and their linear tracks in human peripheral blood lymphocytes (HPBLs) in vitro exposed to radon and its progeny were dependent on the cumulative absorbed dose of radon exposure but was unrelated to the concentration of radon. Among them, γ-H2AX foci and its linear tracks were the most sensitive indicators with the lowest estimable cumulative absorbed dose of 1.74 mGy from their linear dose-response curves and sustained for 12 h after termination of radon exposure. In addition, three types of foci showed an overdispersed non-Poisson distribution in HPBLs. The ratios of pKAP-1/γ-H2AX foci co-localization, 53BP1/γ-H2AX foci co-localization and 53BP1/pKAP-1 foci co-localization were significantly increased in HPBLs exposed to radon while they were unrelated to the cumulative dose of radon exposure, suggesting that γ-H2AX, pKAP-1 and 53BP1 play an important role in the repair of heterochromatic double-strand breaks. Altogether, our findings provide an experimental basis for estimating the biological dose of internal α-particle irradiation from radon and its progeny exposure in humans.

Evaluation of DNA damage in lymphocytes of radiology personnel by comet assay

OBJECTIVES

The importance of X-rays as a diagnostic medical tool cannot be denied. However, continuous exposure to X-rays can cause DNA damage. This study aimed to use the comet assay technique to investigate the level of DNA damage in lymphocytes due to X-rays in occupationally exposed personnel.

METHODS

Blood samples were collected from 74 exposed and 70 control subjects for analysis. A total of 100 randomly captured cells from each slide were examined using an epifluorescent microscope. The comets were analyzed by a visual scoring method according to comet tail length.

RESULTS

The results indicated a significant increase (p<0.05) in DNA damage in X-rays technicians (129.8 ± 17.2) as compared with the control group (53.0 ± 25.0). A significant increase (p<0.02) in DNA damage was also observed with an increase in exposure duration of technicians because of their service length.

CONCLUSIONS

The present study suggests that the exposed radiology personnel should carefully comply with radiation protection procedures such as wearing of lead apron during diagnostic procedures and minimize radiation exposure where possible to avoid potential genotoxic effects due to X-rays.

Can the use of medical muds cause genotoxicity in eukaryotic cells? A trial using comet assay

Despite the lack of knowledge of their exact effects, peloids (natural muds) are widely applied in clinical treatment and prevention of different diseases, especially in rheumatic and gynecological disorders or skin diseases. Primarily we have information on their inorganic components, but only limited data are available on the organic components and nothing on their mechanism of chemical action. The objective of the present study was to detect the DNA-damaging effects (possible genotoxic effect) of peloid samples using the single-cell comet assay on Long Evans rat lymphocytes, human lymphocytes, and Eisenia fetida coelomocytes. Rat and human lymphocytes were exposed to the in toto peloid samples, in vitro. The Eisenia cells were extracted from the coelom of animals kept in the intact peloid sample. An indicator derived from the DNA fluorescence intensity was used in the statistical evaluation. The predominantly organic (Hévíz) sample showed a significant alteration from the negative control in several cases, while the inorganic (Kolop) applied did not. A higher quantity of organic compounds may have an important role in the emergence of DNA damage. The results revealed that medical muds have not only positive health effects but can also contain substances with potential human toxicity risk. Our research provides essential steps towards the creation of a toxicity profile and the possible safe use of peloids as medicinal therapy.

Environmental radon exposure and childhood leukemia

Despite the fact that animal and human epidemiological studies confirmed a link between radon exposure in homes and increased risk of lung cancer in general population, other types of cancers induced by radon, such as leukemia, have not been consistently demonstrated. The aim of this review was to summarize data published thus far from ecological and case-control studies in exposed populations, taking into account radon dose estimation and evidence of radon-induced genotoxicity, in an effort to clarify the correlation between home radon exposure and incidence of childhood leukemia. Among 12 ecological studies, 11 reported a positive association between radon levels and elevated frequency of childhood leukemia, with 8 being significant. In conjunction with ecological studies, several case-control studies on indoor radon exposure and childhood leukemia were examined, and most investigations indicated a weak association with only a few showing significance. A major source of uncertainty in radon risk assessment is radon dose estimate. Methods for radon exposure measurement in homes of children are one of the factors that affect the risk estimates in a case-control study. The effects of radon-induced genetic damage were studied both in vitro and in vivo using genetic endpoints including chromosomal aberration (CA), micronuclei (MN) formation, gene mutation, and deletions and insertions. By applying a meta-analysis, an increased risk of childhood leukemia induced by indoor radon exposure was noted for overall leukemia and for acute lymphoblastic leukemia (ALL). Data thus indicated an association between environmental radon exposure and elevated leukemia incidence, but more evidence is required in both human investigations and animal mechanistic research before this assumption may be confirmed with certainty.

Antineoplastic Drugs as a Potential Risk Factor in Occupational Settings: Mechanisms of Action at the Cell Level, Genotoxic Effects, and Their Detection Using Different Biomarkers

U članku je prikazana osnovna podjela antineoplastičnih lijekova prema mehanizmima djelovanja na razini stanice. Objašnjeni su mehanizmi genotoksičnosti najvažnijih vrsta lijekova koji se primjenjuju u okviru uobičajenih protokola za liječenje zloćudnih novotvorina. Navedena je važeća klasifikacija antineoplastika prema kancerogenom potencijalu, podaci o mutagenom potencijalu te je prikazana njihova podjela u skladu s anatomsko-terapijsko-kemijskim sustavom klasifikacije. Sustavno su prikazani najvažniji rezultati svjetskih i hrvatskih istraživanja na populacijama radnika izloženih antineoplasticima, provedenih u razdoblju 1980.-2009. s pomoću četiri najčešće primjenjivane metode: analize izmjena sestrinskih kromatida, analize kromosomskih aberacija, mikronukleus-testa i komet-testa. Objašnjena su osnovna načela navedenih metoda te raspravljene njihove prednosti i nedostaci. Biološki pokazatelji daju važne podatke o individualnoj osjetljivosti profesionalno izloženih ispitanika koji mogu poslužiti unaprjeđenju postojećih uvjeta rada i upravljanju rizicima pri izloženosti genotoksičnim agensima. Na osnovi prednosti i nedostataka citogenetičkih metoda zaključeno je da je mikronukleus-test, koji podjednako uspješno dokazuje klastogene i aneugene učinke, jedna od najboljih metoda dostupnih za otkrivanje štetnih djelovanja antineoplastičnih lijekova koji su u aktivnoj primjeni.

Intra-laboratory Comet Assay Sample Scoring Exercise for Determination of Formamidopyrimidine DNA Glycosylase Sites in Human Mononuclear Blood Cell DNA

Oxidative DNA damage detected by the comet assay as formamidopyrimidine DNA glycosylase (FPG) sensitive sites, almost as a rule is reported as comet assay score rather than numerical sites in the genome, probably because the latter requires X-ray calibration. We compared the ability of five experienced and five inexperienced comet assay investigators to detect a dose-response relationship in irradiated A549 lung epithelial cell culture samples (0, 10 Gy and three samples of 5 Gy), based on an arbitrary five class scoring system. The samples were scored on three different occasions, thus allowing determination of the variation in sample scoring. All investigators qualitatively distinguished between samples in a dose-dependent manner, albeit with large variation in the slope and intercept of dose-response curves. There was a tendency that investigators with experience in scoring A549 cells had more consistent results than experienced investigators who had only scored lymphocytes or inexperienced investigators. The inexperienced investigators improved their scoring ability during the three sessions. Subsequently we showed that the variation in baseline level of FPG modifications in mononuclear blood cells of five healthy humans was lower when investigators used their individual X-ray calibration curve as compared to a common calibration curve. In conclusion, this study showed that comet assay investigators score differently when using a five class scoring system, which indicates that more consistent estimations of FPG sites in the genome are obtained by use of investigators' individual X-ray calibrations.

Adverse effects attributed to long-term radon inhalation in rats

The aim of this study was to investigate the adverse effect of long-term radon exposure on lung and blood cells in rats exposed to different radiation doses. Sprague-Dawley rats were exposed to radon for cumulative doses up to 66, 111, and 174 WLM (work level month). Total number and differential cells counts were determined in the bronchoalveolar lavage fluid (BALF) and the peripheral blood, as well as the activity of lactate dehydrogenase (LDH) and levels of glutathione (GSH) and total protein. DNA damage and interleukin (IL)-6 mRNA expression in BALF cells and peripheral blood mononuclear cells (PBMC) were detected by single cell gel electrophoresis (SCGE) and reverse-transcription polymerase chain reaction (RT-PCR), respectively. The results showed that radon-exposed lymphocytes were significantly lower and granulocytes higher in BALF compared to blood in exposed groups. The distance of DNA migration in the BALF and PBMC increased in a dose-dependent manner. A positive correlation between the PBMC and BALF cells in terms of DNA damage was noted. These findings suggested that PBMC might be used as a surrogate for BALF cells and thus the easier non-invasive ability to obtain PBMC may be useful in detection of lung DNA damage induced by radon.

[Increased DNA damage of lymphocytes in Korean male smokers]

OBJECTIVE

The purpose of this study was to evaluate the levels of DNA damage in human lymphocytes caused by smoking and other lifestyle factors.

METHODS

The study population consisted of 173 normal healthy male adults from 21 to 59 years old. The demographic and lifestyle variables were obtained from administered questionnaires. The level of lymphocytic DNA damage in the peripheral blood was evaluated by the Comet assay. Statistical analyses were done by general linear model analysis and Dunnett's multiple comparison.

RESULTS

The difference in DNA damage between smokers and non-smokers was statistically significant. The means for the Tail%DNA were found to be 10.48 in the current smokers and 9.60 in the non-smokers (p < 0.05). The tail moment means were 1.58 and 1.45 (p < 0.05) for the current smokers and non-smokers, respectively. The number of cigarettes smoked per day did not result in a significant difference in the level of DNA damage among the smokers. Other lifestyle factors such as age, and drinking and exercise habits were not related to DNA damage.

CONCLUSIONS

The DNA damage in the lymphocytes of smokers was found to be significantly higher than that for non-smokers. However, the number of cigarettes smoked per day was not related to DNA damage. Further study is needed to evaluate the relationship between the amount of smoking and level of damage to DNA. In addition, the status of DNA repair activities should be assessed.

The alkaline comet assay: towards validation in biomonitoring of DNA damaging exposures

Generation of DNA damage is considered to be an important initial event in carcinogenesis. The single cell gel electrophoresis (comet) assay is a technically simple and fast method that detects genotoxicity in virtually any mammalian cell type without requirement for cell culture. This review discusses the strength of the comet assay in biomonitoring at its present state of validation. The simple version of the alkaline comet assay detects DNA migration caused by strand breaks, alkaline labile sites, and transient repair sites. By incubation with bacterial glycosylase/endonuclease enzymes, broad classes of oxidative DNA damage, alkylations, and ultraviolet light-induced photoproducts are detected as additional DNA migration. The most widely measured enzyme sensitive sites have been those detected by formamidopyrimidine DNA glycosylase (FPG) and endonuclease III (ENDOIII). Reports from biomonitoring studies show that the basal level of DNA damage in leukocytes is influenced be a variety of lifestyle and environmental exposures, including exercise, air pollution, sunlight, and diet. Although not all types of carcinogenic exposures should be expected to damage DNA in leukocytes, the comet assay is a valuable method for detection of genotoxic exposure in humans. However, the predictive value of the comet assay is unknown because it has not been investigated in prospective cohort studies. Also, it is important that the performance of the assay is investigated in multi-laboratory validation trials. As a tool in risk assessment the comet assay can be used in characterization of hazards.

Aberrant Promoter Methylation of p16 INK4a and O 6 ‐Methylguanine‐DNA Methyltransferase Genes in Workers at a Chinese Uranium Mine

To find the possible association of gene methylation of p16(INK4a) and O(6)-Methylguanine-DNA Methyltransferase (O(6)-MGMT) with occupational exposure to radon, 91 male miners from a uranium mine in China were divided into 4 groups according to the cumulative doses of radon exposure from 2 to 425 WLM (working-level months), and aberrant promoter methylation of p16(INK4a) and O(6)-MGMT genes in sputum samples was determined by a specific PCR assay. The results revealed that the methylated rates of 16(INK4a) gene (z=2.844, P=0.005) and O(6)-MGMT gene (z=3.034, P=0.002), and the total methylated rate of these two genes (z=3.859, P=0.0001) increased significantly with the cumulative doses of radon among the miners. This methylation could be applied as a potential marker for the detection of early DNA damage induced by occupational radon exposure.

A biological evaluation of DNA damage detected by comet assay in healthy populations residing in areas that differ in lung cancer incidence

The comet assay was performed to evaluate the effect of environmental exposure between human populations residing in two areas that differ in lung cancer incidence, Saraphi (n = 91) and Chom Thong (n = 94). Three parameters, the tail length, tail intensity, and tail moment, were used to detect DNA damage in peripheral blood and stimulated lymphocytes with and without the DNA repair inhibitor, aphidicolin. Internal standards, cryopreserved isolated lymphocytes, and isolated lymphocytes irradiated with 2 Gy gamma rays, were used to correct the interexperimental variability. Results revealed a significant difference between two populations only when the tail length was used to measure DNA damage. The evaluation of various potential confounding factors, such as gender, pesticide exposure, smoking, alcohol drinking, and fermented tea leaf or betel nut chewing, indicated no significant influence in DNA damage. In conclusion, significant difference in DNA damage, detected only by tail length between the two populations residing in the areas with different incidence of lung cancer, may reflect a nonhazardous level of exposure to toxic substances.

Assessment of DNA damage in nuclear medicine personnel--comparative study with the alkaline comet assay and the chromosome aberration test

Despite much research over the last few decades, there still remains considerable uncertainty as to the genetic impact of ionizing radiation on human populations, particularly at low levels. The aim of the present study was to provide data on the genetic hazards due to occupational exposure of low doses of ionizing radiation in nuclear medicine departments. The assessment of primary DNA damage in peripheral blood leukocytes of medical staff was performed using the alkaline comet assay and the data obtained were compared with the results of conventional cytogenetic biodosimetry using the chromosome aberration (CA) test. Altogether 120 subjects (60 exposed and 60 controls) participated in the study. Statistically significant increases in primary DNA damage and increased frequencies of CAs compared to controls were observed. Within the exposed population, significant inter-individual differences in DNA damage were found, indicating differences in genome sensitivity. Age and gender were not confounding factors, while smoking enhanced the levels of primary DNA damage only in control subjects, as revealed by both biomarkers studied. The present study suggests that genotoxic damage results from exposure to chronic low doses of ionizing radiation in nuclear medicine departments. Therefore, the exposed medical personnel should carefully comply with the radiation protection procedures and should minimize radiation exposure where possible to avoid potential genotoxic effects. The results obtained in this study point to the significance of biological indicators providing information on the actual risk to the radiation exposed individuals. According to our results, the alkaline comet assay and CA test are sensitive biomarkers that can be used as additional complements to physical dosimetry for assessing exposure to radiation in nuclear medicine personnel.

Differential induction of micronuclei in peripheral lymphocytes and exfoliated urothelial cells of workers exposed to 4,4'-methylenebis-(2-chloroaniline) (MOCA) and bitumen fumes

Cytogenetic end-points used to estimate risk of genotoxic events in workers include the measurement of micronuclei (MN) in exfoliated cells, lymphocytes, and other tissues. Micronuclei are chromatin-containing bodies outside the cell nucleus resulting from contaminant-induced DNA damage. A review of 71 reports of human genotoxic responses to chemical or physical agents published between 1999 and 2001 revealed that 14% of such studies measured genotoxicity endpoints in specific target tissues relevant to the site of disease for the agent examined; 18% used endpoints in surrogate or non-target tissues but considered the relations between endpoints in surrogate and disease target tissues, and 68% measured genotoxicity endpoints in accessible tissues without reference to specific targets for disease. Methylenebis-(2-chloroaniline) (MOCA), used in polyurethane manufacture, is a suspected bladder carcinogen. Bitumen, used in road surfacing, contains skin and lung carcinogens. In this study, we aimed to compare genotoxicity in urothelial cells and in lymphocytes of workers exposed to these materials. Twelve men employed in polyurethane manufacture, twelve bitumen road layers, and eighteen hospital stores personnel (controls) were recruited and all provided blood and urine samples on the same day. Blood cultures were prepared using a cytochalasin B-block method. Exfoliated urothelial cells were collected from urine and stained for light microscopy. The number of MN in urothelial cells was higher in MOCA-exposed (14.27 +/- 0.56 MN/1000, 9.69 +/- 0.32 MN cells/1000) than in bitumen exposed workers (11.99 +/- 0.65 MN/1000, 8.66 +/- 0.46 MN cells/1000) or in control subjects (6.88 +/- 0.18 MN/1000, 5.17 +/- 0.11 MN cells/1000). Conversely, in lymphocytes, MN were higher in bitumen-exposed (16.24 +/- 0.63 MN/1000, 10.65 +/- 0.24 MN cells/1000) than in MOCA-exposed workers (13.25 +/- 0.48 MN/1000, 8.54 +/- 0.14 MN cells/1000) or in control subjects (9.24 +/- 0.29 MN/ 1000, 5.93 +/- 0.13 MN cells/1000). The results of this study suggest that genotoxins can cause different rates of micronuclei formation in different tissues. Thus, the sensitivity and relevance to cancer risk may be greater if the tissues selected for genotoxicity studies reflect the target tissue for the chemicals concerned.

DNA damage evaluated by the comet assay in lymphocytes of children with 137Cs internal contamination caused by the Chernobyl accident

The comet assay is one of the most versatile and popular tools for evaluating DNA damage. Its sensitivity to low dose radiation has been tested in vitro, but there are limited data showing its application and sensitivity in chronic exposure situations. The influence of the internal contamination caused by the Chernobyl accident on the level of DNA damage was evaluated by the comet assay on lymphocytes of 56 Ukrainian children. The study was performed during 2003 on children with demonstrable 137Cs internal contamination caused by food consumption. The children were selected for the study immediately after a 137Cs whole body counter measurement of internal contamination. The minimal detectable amount of 137Cs was 75 Bq. The control group included 29 children without detectable internal contamination, while in the exposed group 27 children with measured activity between 80 and 4037 Bq and committed effective dose between 54 and 3155 microSv were included. Blood samples were taken by a finger prick. The alkaline version of the comet assay was used, in combination with silver stained comets and arbitrary units (AU), for comet measurement. Factors such as disease, medical treatment, surface contamination of children's living location, etc., were considered in the study. Non-significant differences (p > 0.05) in DNA damage in control (9.0 +/- 5.7 AU) versus exposed (8.5 +/- 4.8 AU) groups were found. These results suggest that low doses of 137Cs internal contamination are not able to produce detectable DNA damage under the conditions used for the comet assay in this study. Further studies considering effects of high exposure should be performed on chronically exposed people using this assay.

The use of the alkaline comet assay with lymphocytes in human biomonitoring studies

We reviewed the data of 45 alkaline comet assay studies with lymphocytes published during the last three years with the objective of monitoring human exposure to genotoxic agents as a result of occupation, drug treatment, diseases or environmental pollution. The strengths of the studies were that: (i) a lot of data could be obtained within a relatively short period of time in a cost-effective manner, (ii) lymphocytes could be easily collected in a non-invasive way and proved to be good surrogate cells in that they picked up effects caused by agents with different cancer target organs and (iii) a remarkable concordance between comet assay and cytogenetic assay data was proved. However, our analysis revealed some shortcomings of the studies such as: (i) the inclusion of low number of study participants and bias in the number and gender of subjects between control and exposed groups, (ii) lack of qualitative and quantitative exposure data, (iii) lack of consideration of differences in physical activity and diet between control and exposed groups, (iv) difficulty in comparison of the studies due to lack of uniformity in the comet assay procedures such as duration of alkali unwinding and electrophoresis, slide scoring method and the metrics used to assess the extent of DNA damage and (v) controversy in the sensitivity of comet assay since it picked up DNA damage caused by agents such as wood dust, pesticides and hormone preparations which were found to be weak genotoxins or non-genotoxins in other tests, but gave inconsistent results with known mutagens/carcinogens such as tobacco smoke. We feel that for the alkaline comet assay to be an important tool in human biomonitoring studies, serious consideration should be given to the flaws in the design and performance of the assay.

Toxic vents and DNA damage: first evidence from a naturally contaminated deep-sea environment

Levels of DNA strand breakage were measured, using the comet assay, in cells from vent mussels, Bathymodiolus azoricus, from three contrasting vent fields on the mid Atlantic Ridge. Different levels of DNA damage were recorded in untreated mussels, shortly after collection, and it was animals from the shallowest, and less active, Menez Gwen vent field (840-m depth), which showed the greatest amount of damage. In contrast to animals from two deeper and putatively more toxic sites, Menez Gwen animals went on to repair this damage and were able to survive under laboratory conditions at 1 bar pressure for several months. Animals from the two deeper sites showed both higher levels of initial mortality and a much reduced capacity for survival at 1 bar. The differences in DNA damage levels at the time of collection were interpreted as an expression of differences in cell viability/enzyme activity rather than a reflection of any differences in their natural environmental conditions. Small B. azoricus showed a capacity to repair DNA damage, whereas this ability appeared to be lacking in large individuals. By reproducing at a relatively early age, the deep-sea vent fauna may be able to resist the toxic effects of its environment by exploiting this natural, stage specific capacity to repair damaged DNA.

Comet assay on gill cells and hemocytes from the blue mussel Mytilus edulis

Gill cells and hemocytes from the blue mussel Mytilus edulis were examined for DNA damage using the comet assay after laboratory exposure in vitro and in vivo to methyl methansulfonate (MMS). Hydrogen peroxide and UV radiation were used as positive control. Comet assay was also carried out on hemocytes from blue mussels sampled at polluted and unpolluted coastal areas. After 60 min in vitro exposure of gill cells to MMS, the highest response, a tail moment of 6.70+/-4.25, was obtained at 1.0mg/L. At higher doses the response decreased. After 2 days in vivo exposure a dose response was seen at concentrations between 1.0 and 33.0mg/L MMS for both gill cells and hemocytes. However, after 4 days in vivo exposure using the same concentrations of MMS, a maximum effect was seen at a 10 times lower concentration of 3.3mg/L. At the higher doses, the effect decreased. Hemocytes from blue mussels sampled at four polluted sites in Køge Bay had a great variation in tail moments with the highest value of 5.38+/-4.39. The average of all samples from Køge Bay had tail moments of 2.75+/-1.00(n=19), which was significantly higher (P<0.05) than the average, 1.72+/-1.16(n=10), of samples from unpolluted coastal waters.

Differential rates of cytokine production and apoptosis in venipuncture and finger-stab derived blood cultures

The collection of finger-stab (FS) blood is a convenient and non-invasive method of rapidly acquiring human blood and is becoming increasingly popular for use in human biomonitoring studies. This study compared whole blood (WB) and peripheral blood mononuclear cell (PBMC) cultures derived from venipuncture (VP) and FS blood, to determine whether they respond similarly under culture conditions. The rates of spontaneous- and radiation-induced apoptosis and pro-inflammatory cytokine production were monitored over 72 h in each of four culture conditions. In non-irradiated WB cultures, the spontaneous rate of apoptosis was significantly lower in cultures from FS-derived blood than from VP-derived blood. However, FS- and VP-derived cultures responded similarly to radiation-induced apoptosis. PBMC cultures, regardless of the source, were the most responsive to radiation. When the levels of pro-inflammatory cytokines were measured, a significant time-dependent increase in TNF-alpha, IL-6 and IL-1beta production was observed in FS-derived cultures, but not in VP-derived cultures. While VP and FS blood cultures were found to respond similarly to radiation-induced apoptosis, there was a significant difference in the rate of spontaneous apoptosis in non-irradiated WB cultures and in the in situ production of pro-inflammatory cytokines between VP- and FS-derived blood cultures.

Total antioxidant levels, gender, and age as risk factors for DNA damage in lymphocytes of the elderly

During past years, the association of oxidative stress with DNA damage and its possible clinical translation into chronic degenerative illnesses, such as atherosclerosis, cancer, diabetes mellitus and Alzheimer's disease, has been demonstrated. In addition, it has been pointed out that age and gender are factors that influence the generation of DNA damage; however, this is still controversial. We have previously reported the results of a study of 88 subjects older than 60 years of age in whom DNA damage is related with serum levels of total antioxidants. The results of this study demonstrate a greater frequency of DNA damage in elderly persons with normal levels of antioxidants, in addition to males, and in the younger group of subjects, i.e., 60-69 years. In this work, we enlarged our study sample to 160 elderly subjects; in this way, we were able to evaluate the consistency of the influence of total antioxidants, age, and gender on the magnitude and grade of DNA damage in lymphocytes of the elderly. The results demonstrated that 45% of the subjects showed DNA damage, measured by an alkaline unicellular electrophoresis technique (comet assay). Similarly, 62% of the subjects presented low levels of total antioxidant levels measured by a colorimetric method (Randox Kit). A greater percentage of DNA damage was observed in subjects with normal levels of antioxidants (48%) compared with subjects with low levels (43%), although the difference was not statistically significant. The group of subjects 70 years of age or older showed a greater percentage of DNA damage (50%) than the group of subjects of 60-69 years of age (41%). However, the difference was again not statistically significant (P>0.05). With respect to gender, 64% of males and 38% of females had DNA damage with an odds ratio (OR) of 2.86 and a 95% confidence interval (CI) of 1.31-6.32 (P<0.05). In the logistic regression analysis, the interaction of the male sex variables with low antioxidants had an OR of 2.5 (CI 95%, 1.33-4.68; P<0.01). We conclude that the interaction of male sex factors-low levels of antioxidants would justify the indication of antioxidant dietetic supplements.

Endpoints and surrogates for use in population studies in toxicology

Risk characterisation of human exposure to chemicals requires information on the intrinsic toxic (hazardous) properties of the chemical, dose response of effects for the critical endpoints and exposure of the population. Information on hazardous properties, including data on mechanism and toxicokinetics, is necessary to define the critical endpoints and the relevant parameters to assess internal exposure and its relation to external exposure. Consequently the design of population studies to evaluate toxic effects or to monitor exposed cohorts must consider the critical endpoints of toxic effects and exposure. External exposure is determined by chemical analysis of the chemicals in food, water or air. The more relevant internal exposure is assessed by analysis of the chemical or its metabolites in body fluids and, if appropriate, by protein- or DNA-adducts. Effects are monitored by determining the relevant organ-specific parameters. In the case of genotoxic agents, effect biomonitoring parameters, like cytogenetic effects in peripheral blood cells or DNA strand breaks, are applied. Genotyping to detect deficiencies in the expression of enzymes, e.g. those involved in metabolic activation or inactivation, may explain interindividual differences in susceptibility. Overall prospective population studies allow exposure monitoring and risk assessment of human exposure only when such parameters are included.

Evaluation of DNA damage in workers occupationally exposed to pesticides using single-cell gel electrophoresis (SCGE) assay. Pesticide genotoxicity revealed by comet assay

The comet assay, also called the single-cell gel electrophoresis (SCGE) assay, is a rapid and sensitive method for the detection of DNA damage (strand breaks and alkali-labile sites) in individual cells. The assay is based on the embedding of cells in agarose, their lysis in alkaline buffer and finally subjection to an electric current. In the present study, alkaline SCGE was used to evaluate the extent of primary DNA damage and DNA repair in peripheral blood lymphocytes of workers employed in pesticide production. After the period of high pesticide exposure, lymphocytes of the occupationally exposed workers manifested increased tail length and tail moment compared to the control group. After the workers spent 6 months out of the pesticide exposure zone, both endpoints were still above that of the control but significantly decreased as compared to the results of the first analysis.