DNA damage in leukocytes of workers occupationally exposed to arsenic in copper smelters

The Comet Assay as a Tool in Human Biomonitoring Studies of Environmental and Occupational Exposure to Chemicals-A Systematic Scoping Review

Biomonitoring of human populations exposed to chemical substances that can act as potential mutagens or carcinogens, may enable the detection of damage and early disease prevention. In recent years, the comet assay has become an important tool for assessing DNA damage, both in environmental and occupational exposure contexts. To evidence the role of the comet assay in human biomonitoring, we have analysed original research studies of environmental or occupational exposure that used the comet assay in their assessments, following the PRISMA-ScR method (preferred reporting items for systematic reviews and meta-analyses extension for scoping reviews). Groups of chemicals were designated according to a broad classification, and the results obtained from over 300 original studies (n = 123 on air pollutants, n = 14 on anaesthetics, n = 18 on antineoplastic drugs, n = 57 on heavy metals, n = 59 on pesticides, and n = 49 on solvents) showed overall higher values of DNA strand breaks in the exposed subjects in comparison with the unexposed. In summary, our systematic scoping review strengthens the relevance of the use of the comet assay in assessing DNA damage in human biomonitoring studies.

Use of the alkaline comet assay for monitoring genotoxic effects of arsenic in human populations

The alkaline comet assay has been widely used to determine genotoxicity in human populations exposed to arsenic. The sample sizes of earlier studies were usually small, and inconsistent results were found. Meta-analyses can merge the results of multiple studies of the same type and increase the credibility of the conclusion by increasing the sample size. Thus, to investigate the monitoring effect of alkaline comet assay on genotoxicity for arsenic exposed population, meta-analyses were performed. Thirteen studies were found to meet the inclusion criteria and were included in this study; of them, twelve articles were of medium quality (15-20 points), only one study was of high quality (21-27 points). Meta-analyses showed that the overall estimates of Mean Ratio (MR, defined as the mean value of the response in the exposed group divided by that in the reference group) were 2.81(95 % confidence interval (CI) 1.93-4.10); 2.37(95 % CI, 1.73-3.26), and 1.69(95 %CI, 1.29-2.20) for comet tail length, % tail DNA, and tail moment, respectively. This shows that the level of DNA damage in arsenic exposed population is significantly higher than that in control populations. A meta-analysis of the correlation coefficients showed that the overall estimate was 0.52 (95 %CI, 0.48∼0.56, P<0.05) with all correlation coefficients included, but it changed to 0.24 (95 %CI, 0.17∼0.28, P<0.05) when two abnormal correlation coefficients were excluded, suggesting there was a positive correlation between arsenic load in vivo and DNA damage, but the overall estimate value of coefficients was unstable. Therefore, we conclude that the alkaline comet assay can be used as an effective genotoxic biomonitoring tool for arsenic-exposed populations. However, more and higher-quality studies are still needed to verify its actual application value.

Risk assessment of low arsenic exposure using biomarkers of oxidative and genotoxic stress in a piscine model

The high level exposure to arsenic induces marked oxidative and genotoxic stress. However, information on the potential of low level arsenic exposure in this context is still scanty. In the present study, the extent of oxidative stress and genetic toxicity induced by low arsenic exposure was explored in freshwater fish Channa punctatus. Fish were exposed to low levels of arsenic (10 and 50 µg L^-1) as well as to its high level (500 µg L^-1) using sodium arsenite in aquaria water for 14 consecutive days. The TBARS assay for lipid peroxidation exhibited the increased occurrence of oxidative damage in the erythrocytes of fish at both the lower and higher levels of arsenic exposure. The level of reduced glutathione was also elevated in all the three arsenic exposed groups of fish compared to control. In contrast, significant decline was observed in the levels of three major antioxidant enzymes namely, superoxide dismutase, catalase and glutathione peroxidase, upon exposure to higher as well as lower levels of arsenic. Significant increases in micronucleus induction were found in the erythrocytes of fish even at the low levels of arsenic exposure. The study further revealed the occurrence of DNA fragmentation in the erythrocytes of fish at low arsenic exposures as well. The low level exposure to arsenic (using sodium arsenite), therefore, appeared to be capable of inducing noticeable oxidative stress as well as potential genotoxic effect in Channa punctatus. Moreover, the ability of arsenic to induce oxidative stress invariably appeared correlated with its genotoxic potential.

Assessment of arsenic-induced DNA damage in goldfish by a polymerase chain reaction-based technique using random amplified polymorphic DNA markers

Arsenic is a groundwater contaminant of global concern. It is a potent human carcinogen, and its marked genotoxic effects have been reported in several human and animal studies. The present work investigates the applicability of the random amplified polymorphic DNA (RAPD) assay to study the DNA-damaging effects of arsenic at low-level exposure in goldfish Carassius auratus. Four experimental groups of fish, A, B, C and D, were exposed to 0, 10, 50, and 1,000 µg L(-1) of arsenic, respectively, in aquaria water for 15 consecutive days. Genomic DNA extraction was followed by RAPD-polymerase chain reaction amplification for each fish separately. One arbitrary decamer primer (PUZ-19) of 33 primers used appeared as the most informative and was capable of exhibiting marked alterations in RAPD profiles between arsenic-exposed and unexposed (control) samples. Different sets of 11 loci were amplified in various experimental groups with four clear polymorphic bands by the primer PUZ-19. The X and XIII amplification loci, which were prominent in the unexposed group, failed to appear in the arsenic-exposed groups. In contrast, the I and XI RAPD bands appeared as new amplification loci in all of the exposed groups. Such alterations in genomic DNA, however, did not exhibit a clear dose-dependent tendency. The RAPD assay, because of its efficacy to unmask alterations in genomic DNA induced by arsenic at low exposure level of 10 µg L(-1), appears to be a sensitive and potential tool for detecting arsenic genotoxicity.

Mouse micronucleus assay as a surrogate to assess genotoxic potential of arsenic at its human reference dose

Exposure to high contents of arsenic (a genotoxic carcinogen) in humans through drinking water is one of the most serious concerns in many parts of the world including India. The United States Environmental Protection Agency (USEPA) has recommended a permissible limit of daily exposure in humans to arsenic as its reference dose (0.3 μg kg(-1) d(-1)) with almost no likelihood of any adverse effect. The present work was a quantitative assessment of the genotoxic potential of arsenic at the exposure level of its human reference dose through micronucleus (MN) assay in mice. The animals were exposed to various doses of arsenic through oral gavaging for 15 consecutive days. Significant increases in the frequency of micronucleated erythrocytes were observed in mice upon exposure to arsenic which occurred even at its human reference dose and in a dose-dependent manner. The study of the genotoxic potential of arsenic in humans at lower exposure levels (including its human reference dose) is, therefore, highly desirable for risk assessment and hazard identification.

What is the best biomarker to assess arsenic exposure via drinking water?

Arsenic (As) is a ubiquitous element. The current WHO guideline for As in drinking water is 10 μg/L. Furthermore, about 130 million people have only access to drinking water containing more than 10 g As/L. Although numerous studies have shown the related adverse effects of As, sensitive appropriate biomarkers are still required for studies of environmental epidemiology. A review of the literature has shown that various biomarkers are used for such research. Their limits and advantages are highlighted in this paper: (i) the detection of As or its derivatives in the blood is an indication of the dose ingested but it is not evidence of chronic intoxication. (ii) The detection of As in urine is an indispensible procedure because it is a good marker for internal dose. It has been demonstrated to correlate well for a number of chronic effects related to As levels in drinking water. However confounding factors must be taken into account to avoid misinterpretation and this may require As speciation. (iii) As in the hair and nails reflects the level of long term exposure but it is difficult to relate the level with the dose ingested. (iv) Some studies showed a correlation between urinary As and urinary and blood porphyrins. However, it is difficult to use only porphyrins as a biomarker in a population survey carried out without doing further studies. (v) Genotoxic effects are based on the characterization of these potential effects. Most studies have detected increases in DNA damage, sister chromatid exchange, micronuclei or chromosomal aberrations in populations exposed to As in drinking water. Micronuclei assay is the technique of choice to follow these populations, because it is sensitive and easy to use. To conclude, whatever epidemiological studies are, the urinary and toenail biomarkers are useful to provide indications of internal dose. Moreover, micronuclei assay can be complementary use as biomarker of early effects.

Occupational genotoxicity among copper smelters

Occupational exposure in a copper smelting industry may produce various adverse health effects including cancer. Despite a number of well-documented studies reporting an increased risk of cancer among copper smelter workers, the data on genotoxic effects in this industry are scarce. In view of the above, an assessment of DNA damage in peripheral blood leukocytes by Comet assay from copper smelter workers was undertaken. Additionally, the proton-induced X-ray emission (PIXE) analysis was assessed to determine the metal content of samples. The study was conducted with all workers from a copper smelter (males; n = 11), and a control group ( n = 11) was recruited. The results of our study showed a significant increase ( p < 0.001; Mann-Whitney test) in DNA damage in peripheral blood lymphocytes of smelter workers, compared to the controls ( p < 0.001; Mann-Whitney test). No correlation between DNA damage or metal concentration and age mean or time of exposure was found under study. Our findings indicate that copper smelter workers have increased levels of DNA damage in somatic cells, suggesting a potential health risk for the workers. PIXE results show the presence of copper, iron, and other metals.

Geno- and immunotoxic effects on populations living near a mine: a case study of Panasqueira mine in Portugal

Mining industry is a vital economic sector for many countries but it is also one of the most hazardous activities, both occupationally and environmentally. Existing studies point to several adverse effects on communities' health living near mines, effects such as mesothelioma and respiratory illnesses. Results achieved in a geochemical sampling campaign undertaken in the vicinity of São Francisco de Assis village showed an anomalous distribution of some heavy metals in soils and waters. To evaluate the effects of mining activities on human health produced by these conditions, a group of 28 individuals from São Francisco de Assis village was examined for some biological endpoints. A nonexposed group (30 individuals) with the same demographic characteristics without exposure to genotoxic compounds was also studied and data obtained from both groups compared. Results of the T-cell receptor mutation assay and micronucleus (MN) test showed significant increases in the frequencies of both mutations and MN in exposed subjects compared to controls. Data obtained in the analysis of the different lymphocyte subsets demonstrated significant decreases in percentages of CD3+ and CD4+ cells, and a significant increase in percentage of CD16/56+ cells, in exposed individuals. The results of the present study indicate an elevated risk of human environmental contamination resulting from mining activities, emphasizing the need to implement preventive measures, remediation, and rehabilitation plans. This would lead to a reduction in cancer risk not only for this particular population but for all populations exposed under similar conditions.

Biomarkers of oxidative stress and damage in human populations exposed to arsenic

Arsenic (As) is an ubiquitous element in the environment for which the main route of human exposure is through consumption of drinking water. Reactive oxygen species generation (ROS) associated with As exposure is known to play a fundamental role in the induction of adverse health effects and disease (cancer, diabetes, hypertension, and cardiovascular and neurological diseases). However, the precise mechanisms of oxidative stress and damage from As exposure are not fully understood and moreover the use of non-invasive methods of measuring ROS generation and oxidative damage footprints in humans is no easy task. Although As induces adverse health effects not all exposed individuals develop degenerative chronic diseases or even manifest adverse effects or symptoms, suggesting that genetic susceptibility is an important factor involved in the human response to As exposure. This mini-review summarizes the literature describing the molecular mechanisms affected by As, as well as the most used biomarkers of oxidative stress and damage in human populations. The most reported biomarkers of oxidative DNA damage are the urinary excretion of 8-OHdG and the comet assay in lymphocytes, and more recently DNA repair mechanism markers from the base and nuclear excision repair pathways (BER and NER). Genetic heterogeneity in the oxidative stress pathways involved in As metabolism are important causative factors of disease. Thus further refinement of human exposure assessment is needed to reinforce study design to evaluate exposure-response relationships and study gene-environment interactions. The use of microarray-based gene expression analysis can provide better insights of the underlying mechanisms involved in As-induced diseases and could help to identify target genes that can be modulated to prevent disease.

Comet assay: a reliable tool for the assessment of DNA damage in different models

New chemicals are being added each year to the existing burden of toxic substances in the environment. This has led to increased pollution of ecosystems as well as deterioration of the air, water, and soil quality. Excessive agricultural and industrial activities adversely affect biodiversity, threatening the survival of species in a particular habitat as well as posing disease risks to humans. Some of the chemicals, e.g., pesticides and heavy metals, may be genotoxic to the sentinel species and/or to non-target species, causing deleterious effects in somatic or germ cells. Test systems which help in hazard prediction and risk assessment are important to assess the genotoxic potential of chemicals before their release into the environment or commercial use as well as DNA damage in flora and fauna affected by contaminated/polluted habitats. The Comet assay has been widely accepted as a simple, sensitive, and rapid tool for assessing DNA damage and repair in individual eukaryotic as well as some prokaryotic cells, and has increasingly found application in diverse fields ranging from genetic toxicology to human epidemiology. This review is an attempt to comprehensively encase the use of Comet assay in different models from bacteria to man, employing diverse cell types to assess the DNA-damaging potential of chemicals and/or environmental conditions. Sentinel species are the first to be affected by adverse changes in their environment. Determination of DNA damage using the Comet assay in these indicator organisms would thus provide information about the genotoxic potential of their habitat at an early stage. This would allow for intervention strategies to be implemented for prevention or reduction of deleterious health effects in the sentinel species as well as in humans.

Evaluation of micronucleus frequencies in blood lymphocytes from smelting plant workers exposed to arsenic

Arsenic is a world health problem due to the seriousness of its effects, mainly related with the increase of cancer. In Chile, the geological characteristics of the northern region, associated with the development of the copper mining and smelting activities, have contributed to increase the environmental levels of arsenic. This study has been conducted to investigate the relationship between arsenic occupational exposure and genotoxic effects in smelting plant workers. To determine the genotoxic risk related to the increase of cancer among the chronically exposed population, the frequency of micronuclei in blood (BNMN) has been evaluated. The study was carried out in a total of 207 men, divided into three groups: an exposed group of 105 individuals working in a smelting plant, an internal reference group with 52 employees at the same mine but in the administrative area, and an external reference group of 50 workers from another copper mine where no significant levels of arsenic were detected. As expected, differences between arsenic levels in urine have been detected between groups, with the exposed group being the one with a higher level of total arsenic in urine, followed by the internal reference group. Despite that, no significant differences in micronuclei frequencies in lymphocytes were detected among these groups.

Oxidative metabolism of lung macrophages exposed to sodium arsenite

Arsenic pollution has become increasingly severe. It occurs as the result of geological processes and different human activities. Arsenic toxicity at the respiratory level occurs mainly by inhalation of products of coal combustion. The aim of this study was to evaluate sodium arsenite (As(3+)) toxicity in murine alveolar macrophages (AMs) in vitro and its association with the alterations in cell metabolism. No changes in viability, apoptosis or cell area were detected in AMs treated with As(3+) concentrations up to 2 microM for 24-96 h. A marked decrease in these end-points was observed for As(3+) concentrations ranging from 2.5 microM to 10 microM. Regarding the dynamics of the endo-exocytic process triggered by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell incorporation, no variations were detected for As(3+) concentrations lower than 2 microM while higher concentrations markedly modified this response. MTT specific activity, as a measure of cell metabolic activity, was not modified irrespective of the As(3+) concentration assayed. However, nitroblue tetrazolium (NBT) specific activity, as a measure of superoxide anion generation, is responsive but only to low As(3+) doses. Although this study focuses on lung macrophages, the effects of As(3+) described herein may also apply to the response of macrophages residing in other organs. Arsenite modifies the metabolic and the oxidative status of AMs in vitro. When macrophages are in an As(3+) rich medium, they exhibit a reduction in respiratory burst levels and lose their intrinsic capacity to respond to toxicants.

Micronucleus frequency in peripheral blood lymphocytes and buccal mucosa cells of copper smelter workers, with special regard to arsenic exposure

Occupational exposure in copper smelters may produce various adverse health effects including cancer which, according to available epidemiologic data, is associated mainly with exposure to arsenic. Despite a number of well-documented studies reporting an increased risk of cancer among copper smelters workers, the data on genotoxic effects in this industry are scarce. In view of the above, an assessment of micronuclei (MN) frequency in peripheral blood lymphocytes and buccal epithelial cells from copper smelter workers was undertaken. Additionally, the clastogenic/aneugenic effect in lymphocytes was assessed with the fluorescence in situ hybridization (FISH). The study was conducted in three copper smelters in southwestern Poland. The subjects (n = 72) were enrolled among male workers at departments where As concentration in the air was up to at 80 microg/m(3). Exposure was assessed by measurement of arsenic concentration in urine and toenail samples. The control group (n = 83) was recruited from healthy male individuals living in central Poland who did not report any exposure to known genotoxins. The results of our study showed a significant increase in MN frequency in peripheral blood lymphocytes and in buccal epithelial cells of smelter workers, compared to the controls (7.96 +/- 4.28 vs. 3.47 +/- 1.70 and 0.98 +/- 0.76 vs. 0.50 +/- 0.52, respectively). The FISH technique revealed the presence of clastogenic and aneugenic effects in peripheral blood lymphocytes in both groups. The clastogenic effect was slightly more pronounced in the smelter workers; however, the difference was not statistically significant. The mean arsenic concentrations in urine (total arsenic species) and in toenail samples in the exposed group were 54.04 +/- 42.26 microg/l and 7.63 +/- 7.24 microg/g, respectively, being significantly different from control group 11.01 +/- 10.84 microg/l and 0.51 +/- 0.05 microg/g. No correlation between As content in urine or toenail samples and the genotoxic effect was found under study.

Evaluation of micronucleus frequencies and DNA damage in glass workers exposed to arsenic

Arsenic (As) is a known human carcinogen; however, very little is known about the health consequences of occupational exposure to As. In the present study, we assessed the genotoxic damage in the blood cells and in the buccal cells of south Indian glass factory workers who are occupationally exposed to As. The As content in the whole blood of 200 workers and 165 controls was evaluated with inductively coupled plasma mass spectrometry. Blood leukocytes from the subjects were monitored for the level of DNA damage using the Comet assay (mean comet tail length); buccal cells were used to determine the frequency of micronuclei (MN). The mean As concentration was significantly higher in the workers (56.76 microg/L) than in the controls (11.74 microg/L) (P < 0.001). The workers also had increased frequencies of MN in the buccal cells and increased levels of DNA damage in leukocytes compared to the controls (P < 0.001). There were significant correlations between the genotoxicity endpoints that were evaluated and blood As concentration, smoking, age, and the duration of working in the factory. Also, a significant correlation was observed between the frequency of MN and comet tail-length for the worker samples. Our findings indicate that chronic occupational exposure to As is genotoxic and that the Comet assay and micronucleus test are useful assays for evaluating genotoxicity in humans occupationally exposed to As.

Sister chromatid exchange analysis in smelting plant workers exposed to arsenic

There are many studies documenting the genotoxic effects of environmental exposure to arsenic. Nevertheless, few data are available on the genotoxic risks of occupational arsenic exposure. In the present study, we have evaluated whether or not occupational exposure to arsenic in a copper smelting plant results in a significant increase in the frequency of sister chromatid exchange (SCE). SCE frequencies, proliferation rate index (PRI), and high frequency cells (HFCs) were evaluated in peripheral blood lymphocytes from a group of 105 arsenic-exposed workers from a Chilean smelting plant (exposed group). Similar assays were conducted on a group of 55 workers employed at the same mine but involved in administrative jobs (internal control), and on 48 workers of another mine, with no significant levels of arsenic (external control). Small but significant increases in SCE frequency were observed in the arsenic-exposed workers compared with the external control group (6.28+/-0.09 vs. 5.84+/-0.14 SCE/cell; P<0.01). Also, significantly higher frequencies of HFCs were observed in the exposed group (2.21%+/-0.20%) than in either the external control group (1.20+/-0.23; P=0.002) or the internal control group (1.30+/-0.24; P=0.008). However, there was no relationship between arsenic levels in the urine of the subjects and SCE or HFC frequency. The results of the study indicate that copper smelting results in slightly increased levels of DNA damage. However, our data were not consistent with arsenic exposure being the cause of the increase.