Micronuclei as Biomarkers of Carcinogen Exposure in Populations Exposed to Arsenic Through Drinking Water in West Bengal, India: A Comparative Study in Three Cell Types

Micronuclei and other nuclear anomalies in exfoliated urothelial cells and urinary 8-hydroxy-deoxyguanosine levels among Turkish hairdressers

Hairdressers are constantly occupationally exposed to many chemicals have the potential to cause allergies and carcinogenic effects, act as skin and eye irritants and induce oxidative stress and DNA damage. This study aimed to evaluate occupation-induced genotoxicity based on the presence of micronucleus (MN) and other nuclear anomalies in urothelial cells and measure oxidative DNA damage based on the 8-hydroxy-2'-deoxyguanosine level in the urine of Turkish hairdressers. Originality of this study comes from that there was no study on MN and other nuclear anomalies frequencies and oxidative DNA damage in urine samples of hairdressers in the literature. The mean±standard deviation frequency (‰) of micronucleated (MNed) cells was higher in the hairdresser group (n=56) (4.81±7.87, p<0.001) than in the control group (n=56) (0.93±1.85). Nuclear buds were not observed in either group. While the frequency of basal cells was higher in the control group (446.6±106.21) than in the hairdresser group (367.78±101.51, p<0.001), the frequency of binuclear, karyolytic, pycnotic and karyorrhectic cells were higher in the hairdresser group (0.41±0.80, p<0.001; 438.02±118.27, p<0.001; 0.43±0.76, p<0.001; and 47.27±28.40, p<0.001) than in the control group (0.04±0.27, 358.57±95.71, 0.05±0.23 and 24.41±14.50). Condensed chromatins were observed only in the hairdresser group. Specific gravity adjusted 8-hydroxy-2'-deoxyguanosine level was statistically lower in the hairdresser group (908.21±403.25 ng/mL-SG) compared to the control group (1003.09±327.09 ng/mL-SG) (p=0.024). No significant correlation was found between the 8-hydroxy-2'-deoxyguanosine level and the frequency MN. The amount of formaldehyde released during Brazilian keratin treatment was higher than the American Conference of Governmental Industrial Hygienists -Threshold Limit Value (ACGIH-TLV; 0.1 ppm). Similarly, the amount of ethyl acetate released in three salons was above the recommended limit (400 ppm). These findings suggest that hairdressers have an increased risk of genotoxicity and cytotoxicity owing to occupational exposure, regardless of age, working hours, smoking and alcohol consumption.

The probable reasons of arsenic susceptibility in a chronically exposed population of West Bengal

Arsenic is potent human carcinogen which affects millions of people across the globe. Arsenic induced pre-cancerous and cancerous skin lesions are hall marks of chronic arsenic toxicity. Even then, only 15%-20% of the population manifest arsenic-induced skin lesions but the rest do not, the reason for which in not very clear. Not only that, conjunctival irritations of the eyes, peripheral neuropathy and respiratory distress are the non-dermatological health effects which are often manifested in them in addition to the cancers of skin and other internal organs. In this work we have considered 233 arsenic exposed individuals with skin lesions and 205 arsenic exposed individuals without skin lesions from the highly arsenic affected Murshidabad district of West Bengal. We have compared arsenic exposure in the two groups through drinking water. Both the study groups have similar levels of arsenic exposure, drinking same arsenic laden water. Results show that higher amounts of arsenic were retained in the nails and hair of the skin lesion group compared to the no skin lesion group. Significant higher amounts of chromosomal aberration and micronucleus formation were found in the skin lesion group, than the no skin lesion group. Incidences of conjunctival irritations of the eyes, peripheral neuropathy and respiratory distress were much higher in the former group compared to the later. We, thus found that one group was more susceptible than the other, even with similar levels of arsenic exposure. We have tried to identify and discuss the probable reasons for this observation with reference to our previous works in the exposed population from West Bengal, India.

The association of arsenic exposure with mortality due to cancer, diabetes, Alzheimer's and congenital anomalies using Poisson regression

The present study aims to determine the relationship between the concentration of arsenic in the groundwater of Hamadan province and the mortality rate due to various types of malignancies, congenital anomalies, diabetes mellitus and Alzheimer's. Mortality data due to various causes of death in Hamadan province were collected for five years (2016-2020). Sampling of drinking water was determined in the reference laboratory using polarography method. Poisson regression was used to investigate the relationship between arsenic level and the death rate due to various types of disease, at a significant level (p value < 0.05). According to the results of Poisson regression, among the various causes of death (N = 8042), Alzheimer's 5.94 (3.67-9.61), diabetes mellitus 4.05 (3.5-5.37), congenital malformations 2.98 (1.88-4.72), breast cancer 2.72 (1.56-4.71), leukemia 1.90 (1.24-2.92), stomach cancer 1.64 (1.28-2.10), Liver cancer 1.58 (1.58-2.30), other digestive organs 5.86 (3.38-10.16), meninges and brain cancer 1.57 (1.02-2.41) showed the highest relationship with arsenic contamination. The results of this study could be evidence for a positive and significant relationship between arsenic concentrations and mortality rates due to cancers, diabetes mellitus, Alzheimer disease, and congenital malformations. Therefore, it's necessary to use appropriate water treatment methods to remove arsenic at the source in contaminated areas.

Arsenic and cancer: Evidence and mechanisms

Arsenic is a potent carcinogen and poses a significant health concern worldwide. Exposure occurs through ingestion of drinking water and contaminated foods and through inhalation due to pollution. Epidemiological evidence shows arsenic induces cancers of the skin, lung, liver, and bladder among other tissues. While studies in animal and cell culture models support arsenic as a carcinogen, the mechanisms of arsenic carcinogenesis are not fully understood. Arsenic carcinogenesis is a complex process due its ability to be metabolized and because of the many cellular pathways it targets in the cell. Arsenic metabolism and the multiple forms of arsenic play distinct roles in its toxicity and contribute differently to carcinogenic endpoints, and thus must be considered. Arsenic generates reactive oxygen species increasing oxidative stress and damaging DNA and other macromolecules. Concurrently, arsenic inhibits DNA repair, modifies epigenetic regulation of gene expression, and targets protein function due its ability to replace zinc in select proteins. While these mechanisms contribute to arsenic carcinogenesis, there remain significant gaps in understanding the complex nature of arsenic cancers. In the future improving models available for arsenic cancer research and the use of arsenic induced human tumors will bridge some of these gaps in understanding arsenic driven cancers.

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.

Substantial Evidences Indicate That Inorganic Arsenic Is a Genotoxic Carcinogen: a Review

Arsenic is one of the most toxic environmental toxicants. More than 150 million people worldwide are exposed to arsenic through ground water contamination. It is an exclusive human carcinogen. Although the hallmarks of arsenic toxicity are skin lesions and skin cancers, arsenic can also induce cancers in the lung, liver, kidney, urinary bladder, and other internal organs. Arsenic is a non-mutagenic compound but can induce significant cytogenetic damage as measured by chromosomal aberrations, sister chromatid exchanges, and micronuclei formation in human systems. These genotoxic end points are extensively used to predict genotoxic potentials of different environmental chemicals, drugs, pesticides, and insecticides. These cytogenetic end points are also used for evaluating cancer risk. Here, by critically reviewing and analyzing the existing literature, we conclude that inorganic arsenic is a genotoxic carcinogen.

Urinary Arsenic in Human Samples from Areas Characterized by Natural or Anthropogenic Pollution in Italy

Arsenic is ubiquitous and has a potentially adverse impact on human health. We compared the distribution of concentrations of urinary inorganic arsenic plus methylated forms (uc(iAs+MMA+DMA)) in four Italian areas with other international studies, and we assessed the relationship between uc(iAs+MMA+DMA) and various exposure factors. We conducted a human biomonitoring study on 271 subjects (132 men) aged 20-44, randomly sampled and stratified by area, gender, and age. Data on environmental and occupational exposure and dietary habits were collected through a questionnaire. Arsenic was speciated using chromatographic separation and inductively coupled mass spectrometry. Associations between uc(iAs+MMA+DMA) and exposure factors were evaluated using the geometric mean ratio (GMR) with a 90% confidence interval by stepwise multiple regression analysis. The 95th percentile value of uc(iAs+MMA+DMA) for the whole sample (86.28 µg/L) was higher than other national studies worldwide. A statistical significant correlation was found between uc(iAs+MMA+DMA) and occupational exposure (GMR: 2.68 [1.79-4.00]), GSTT gene (GMR: 0.68 [0.52-0.80]), consumption of tap water (GMR: 1.35 [1.02-1.77]), seafood (GMR: 1.44 [1.11-1.88]), whole milk (GMR: 1.34 [1.04-1.73]), and fruit/vegetables (GMR: 1.37 [1.03-1.82]). This study demonstrated the utility of uc(iAs+MMA+DMA) as a biomarker to assess environmental exposure. In a public health context, this information could be used to support remedial action, to prevent individuals from being further exposed to environmental arsenic sources.

Arsenic in groundwater of West Bengal, India: A review of human health risks and assessment of possible intervention options

This paper reviews how active research in West Bengal has unmasked the endemic arsenism that has detrimental effects on the health of millions of people and their offspring. It documents how the pathways of exposure to this toxin/poison have been greatly expanded through intensive application of groundwater in agriculture in the region within the Green Revolution framework. A goal of this paper is to compare and contrast the similarities and differences in arsenic occurrence in West Bengal with those of other parts of the world and assess the unique socio-cultural factors that determine the risks of exposure to arsenic in local groundwater. Successful intervention options are also critically reviewed with emphasis on integrative strategies that ensure safe water to the population, proper nutrition, and effective ways to reduce the transfer of arsenic from soil to crops. While no universal model may be suited for the vast areas of the world affected with by natural contamination of groundwater with arsenic, we have emphasized community-specific sustainable options that can be adapted. Disseminating scientifically correct information among the population coupled with increased community level participation and education are recognized as necessary adjuncts for an engineering intervention to be successful and sustainable.

Does smoking habit increase the micronuclei frequency in the oral mucosa of adults compared to non-smokers? A systematic review and meta-analysis

OBJECTIVES

A systematic review of clinical studies to evaluate the frequency of micronuclei in the oral mucosa of smokers and non-smokers in adult patients was performed.

MATERIALS AND METHODS

A comprehensive search was carried out on MEDLINE via PubMeb, Scopus, Web of Science, LILACS, BBO, and Cochrane Library and SIGLE without restrictions. Dissertations and thesis were searched using the ProQuest Dissertations and Periodicos Capes Thesis Databases. We included only cross-sectional clinical trials that compared the frequency of micronuclei in the oral mucosa of smokers and non-smokers in adult patients.

DATA

After the removal of duplicates, 1338 articles were identified. After title and abstract screening, 35 studies remained. Eighteen studies were further excluded, whereas 17 studies remained for qualitative analysis and 16 for the meta-analysis of the primary and secondary outcomes. A significant difference in the frequency of micronuclei in smokers when compared to non-smokers was observed in the present study.

CONCLUSIONS

Despite the high variation in the methodology of the assessed studies, this study showed a higher frequency of micronuclei in exfoliated cells of smokers compared to non-smokers.

CLINICAL SIGNIFICANCE

The use of tobacco is associated with cytotoxic and genotoxic effects because a higher frequency of micronuclei in exfoliated cells of smokers was observed.

Inorganic arsenic: A non-genotoxic carcinogen

Inorganic arsenic induces a variety of toxicities including cancer. The mode of action for cancer and non-cancer effects involves the metabolic generation of trivalent arsenicals and their reaction with sulfhydryl groups within critical proteins in various cell types which leads to the biological response. In epithelial cells, the response is cell death with consequent regenerative proliferation. If this continues for a long period of time, it can result in an increased risk of cancer. Arsenicals do not react with DNA. There is evidence for indirect genotoxicity in various in vitro and in vivo systems, but these involve exposures at cytotoxic concentrations and are not the basis for cancer development. The resulting markers of genotoxicity could readily be due to the cytotoxicity rather than an effect on the DNA itself. Evidence for genotoxicity in humans has involved detection of chromosomal aberrations, sister chromatid exchanges in lymphocytes and micronucleus formation in lymphocytes, buccal mucosal cells, and exfoliated urothelial cells in the urine. Numerous difficulties have been identified in the interpretation of such results, including inadequate assessment of exposure to arsenic, measurement of micronuclei, and potential confounding factors such as tobacco exposure, folate deficiency, and others. Overall, the data strongly supports a non-linear dose response for the effects of inorganic arsenic. In various in vitro and in vivo models and in human epidemiology studies there appears to be a threshold for biological responses, including cancer.

Plasma-aminothiols status and inverse correlation of total homocysteine with B-vitamins in arsenic exposed population of West Bengal, India

Chronic arsenic toxicity is a serious environmental health problem across the world. Bangladesh and India (particularly the state of West Bengal) are the worst affected countries with such problem. The present study reports plasma-aminothiols (p-aminothiols) like L-cysteine (L-Cys), cysteinyl glycine (Cys-gly), total homocysteine (t-Hcy) and glutathione (GSH) status, and the inverse relationship of t-Hcy with B-vitamins (B1, B6, B9 and B12) in arsenic exposed population of West Bengal, India. Reverse phase HPLC was used to measure p-aminothiols and serum B-vitamins in different arsenic exposed population. Arsenic in drinking water and urine were measured by flow injection analysis system - Atomic Absorption Spectrometry (FIAS-AAS) and Transversely heated graphite atomizer (THGA-AAS) techniques, respectively. Water arsenic exposure was >50 µg/L in 50% population, of which majority (33.58%) belong to the range of >50-500 µg/L and more than 8% were even >1000 µg/L. Urine arsenic (µg/g creatinine) levels increased with arsenic exposure. The variability among p-aminothiols was also observed with higher exposure to arsenic in drinking water. A significant difference between exposed and control population was noticed for plasma L-Cys. The difference of B-vitamins between the population exposed to <50 and >50 µg/L arsenic in drinking water was also found to be significant. B9 and B12 deficiency with increased consumption of arsenic in water corroborates the anemic conditions commonly observed among arsenic exposed population. The aminothiol status indicated oxidative stress in exposed population. This study demonstrated progressive increase in plasma t-Hcy as well as inverse relationships of serum B-vitamins with increased water arsenic concentration.

Arsenic transformations and biomarkers in meadow voles (Microtus pennsylvanicus) living on an abandoned gold mine site in Montague, Nova Scotia, Canada

Arsenic is one of the most widely encountered environmental contaminants because of a number of anthropogenic sources; in Canada the main anthropogenic release of arsenic is from mine tailings ponds. The present study is part of a series of studies to measure chemical and biological effects of exposure for meadow voles (Microtus pennsylvanicus) living on arsenic contaminated sites. Two additional objectives were addressed in the present study: the effect of higher arsenic concentrations compared with previous studies, and the comparison of chemical speciation and biological effects. To obtain the higher environmental concentrations, specimens were collected from a former gold mining site in Montague, NS that contains highly elevated concentrations of arsenic in soils and plants. Meadow voles were collected and their tissues were analyzed for total arsenic to measure uptake, and arsenic speciation to examine the chemical effects of the high arsenic exposure. In addition to the arsenic analysis, a biomonitoring study was undertaken to examine the sub-cellular effects in meadow voles resulting from the elevated arsenic exposure. Meadow voles living on the contaminated site had substantially higher concentrations of total arsenic than animals from the background (reference) location. The extractable arsenic in internal tissues was present mainly as monomethylarsonic acid (up to 14% of total arsenic). A statistically significant relationship was observed between the reduction of glutathione in vole livers and the increase in liver arsenic concentrations, and micronucleated monochromatic red blood cells were also significantly elevated in voles from the arsenic contaminated site. This is one of the few field studies where sub-cellular effects were observed, and the first to show a co-existence of such effects with relatively high proportions of monomethylarsonic acid in voles living near mine tailings.

Arsenate and dimethylarsinic acid in drinking water did not affect DNA damage repair in urinary bladder transitional cells or micronuclei in bone marrow

Arsenic is a human skin, lung, and urinary bladder carcinogen, and may act as a cocarcinogen in the skin and urinary bladder. Possible modes of action of arsenic carcinogenesis/cocarcinogenesis include oxidative stress induction and inhibition of DNA damage repair. We investigated the effects of arsenic in drinking water on DNA damage repair in urinary bladder transitional cells and on micronucleus formation in bone marrow. F344 rats were given 100 ppm arsenate [As(V)] or dimethylarsinic acid [DMA(V)] in drinking water for 1 week. The in vivo repair of cyclophosphamide (CP)-induced DNA damage resulting from a single oral gavage of CP, and the in vitro repair of hydrogen peroxide (H(2)O(2))- or formaldehyde-induced DNA damage, resulting from adding H(2)O(2) or formaldehyde into cell medium, were measured by the Comet assay. DMA(V) effects were not observed on either CP-induced DNA damage induction or on DNA repair. Neither DMA(V) nor As(V) increased the H(2)O(2)- or formaldehyde-induced DNA damage, and neither inhibited the repair of H(2)O(2)-induced DNA damage. Neither DMA(V) nor As(V) increased the micronucleus frequency, nor did they elevate micronucleus frequency resulting from CP treatment above the level observed by the treatment with CP alone. These results suggest that arsenic carcinogenesis/cocarcinogenesis in the urinary bladder may not be via DNA damage repair inhibition. To our knowledge this is the first report of arsenic effects on DNA damage repair in the urinary bladder.

In vitro genotoxicity assays to evaluate the role of vitamin A on arsenic in human lymphocytes

Ground water contamination of arsenic in drinking water is a burning problem worldwide; especially in West Bengal (India) and Bangladesh. The main endeavor in this study was to assess the role of vitamin A (2.72 microM/7 ml culture), a naturally occurring antioxidant upon arsenic-induced genotoxicity; with respect to chromosomal aberrations (structural and numerical) and micronuclei. Whole blood cultures set for 72 h were exposed to test chemicals for a period of 24 h ahead of harvesting. Arsenic concentrations tested in the present study are 0.36, 0.72 and 1.4 microM/7 ml culture. Mitomycin C (MMC), the direct acting mutagen was used as positive control. Our data indicates that at concentrations tested, arsenic-induced increase in the mean frequencies of these genotoxic indices were diminished by vitamin A, indicating its protective role towards cells from arsenic exerted injury.

Genetic variants associated with arsenic susceptibility: study of purine nucleoside phosphorylase, arsenic (+3) methyltransferase, and glutathione S-transferase omega genes

BACKGROUND

Individual variability in arsenic metabolism may underlie individual susceptibility toward arsenic-induced skin lesions and skin cancer. Metabolism of arsenic proceeds through sequential reduction and oxidative methylation being mediated by the following genes: purine nucleoside phosphorylase (PNP), arsenic (+3) methyltransferase (As3MT), glutathione S-transferase omega 1 (GSTO1), and omega 2 (GSTO2). PNP functions as arsenate reductase; As3MT methylates inorganic arsenic and its metabolites; and both GSTO1 and GSTO2 reduce the metabolites. Alteration in functions of these gene products may lead to arsenic-specific disease manifestations.

OBJECTIVES

To find any probable association between arsenicism and the exonic single nucleotide polymorphisms (SNPs) of the above-mentioned arsenic-metabolizing genes, we screened all the exons in those genes in an arsenic-exposed population.

METHODS

Using polymerase chain reaction restriction fragment length polymorphism analysis, we screened the exons in 25 cases (individuals with arsenic-induced skin lesions) and 25 controls (individuals without arsenic-induced skin lesions), both groups drinking similar arsenic-contaminated water. The exonic SNPs identified were further genotyped in a total of 428 genetically unrelated individuals (229 cases and 199 controls) for association study.

RESULTS

Among four candidate genes, PNP, As3MT, GSTO1, and GSTO2, we found that distribution of three exonic polymorphisms, His20His, Gly51Ser, and Pro57Pro of PNP, was associated with arsenicism. Genotypes having the minor alleles were significantly overrepresented in the case group: odds ratio (OR) = 1.69 [95% confidence interval (CI), 1.08-2.66] for His20His; OR = 1.66 [95% CI, 1.04-2.64] for Gly51Ser; and OR = 1.67 [95% CI, 1.05-2.66] for Pro57Pro.

CONCLUSIONS

The results indicate that the three PNP variants render individuals susceptible toward developing arsenic-induced skin lesions.

Comparison of health effects between individuals with and without skin lesions in the population exposed to arsenic through drinking water in West Bengal, India

A study was conducted to explore the effect of arsenic causing conjunctivitis, neuropathy and respiratory illness in individuals, with or without skin lesions, as a result of exposure through drinking water, contaminated with arsenic to similar extent. Exposed study population belongs to the districts of North 24 Parganas and Nadia, West Bengal, India. A total of 725 exposed (373 with skin lesions and 352 without skin lesions) and 389 unexposed individuals were recruited as study participants. Participants were clinically examined and interviewed. Arsenic content in drinking water, urine, nail and hair was estimated. Individuals with skin lesion showed significant retention of arsenic in nail and hair and lower amount of urinary arsenic compared to the group without any skin lesion. Individuals with skin lesion also showed higher risk for conjunctivitis ((odd's ratio) OR: 7.33, 95% CI: 5.05-10.59), peripheral neuropathy (OR: 3.95, 95% CI: 2.61-5.93) and respiratory illness (OR: 4.86, 95% CI: 3.16-7.48) compared to the group without any skin lesion. The trend test for OR of the three diseases in three groups was found to be statistically significant. Again, individuals without skin lesion in the exposed group showed higher risk for conjunctivitis (OR: 4.66, 95% CI: 2.45-8.85), neuropathy (OR: 3.99, 95% CI: 1.95-8.09), and respiratory illness (OR: 3.21, 95% CI: 1.65-6.26) when compared to arsenic unexposed individuals. Although individuals with skin lesions were more susceptible to arsenic-induced toxicity, individuals without skin lesions were also subclinically affected and are also susceptible to arsenic-induced toxicity and carcinogenicity when compared to individuals not exposed to arsenic.

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.