Genetic toxicology of a paradoxical human carcinogen, arsenic: a review

Arsenic is widely distributed in nature in air, water and soil in the form of either metalloids or chemical compounds. It is used commercially, as pesticide, wood preservative, in the manufacture of glass, paper and semiconductors. Epidemiological and clinical studies indicate that arsenic is a paradoxical human carcinogen that does not easily induce cancer in animal models. It is one of the toxic compounds known in the environment. Intermittent incidents of arsenic contamination in ground water have been reported from several parts of the world. Arsenic containing drinking water has been associated with a variety of skin and internal organ cancers. The wide human exposure to this compound through drinking water throughout the world causes great concern for human health. In the present review, we have attempted to evaluate and update the mutagenic and genotoxic effects of arsenic and its compounds based on available literature.

Comparative antimutagenic and anticlastogenic effects of green tea and black tea: a review

Tea is the most popular beverage next to water, consumed by over two-thirds of the world's population. It is processed in different ways in different parts of the world to give green, black or oolong tea. Experimental studies have demonstrated the significant antimutagenic and anticlastogenic effects of both green and black tea and its polyphenols in multiple mutational assays. In the present review, we have attempted to evaluate and update the comparative antimutagenic and anticlastogenic effects of green tea, black tea and their polyphenols in different test systems, based on available literature. Existing reports have suggested that the protective effects of black tea is as good as green tea, however, more studies on black tea and its polyphenols are needed before a final conclusion can be made.

Analysis of T-cell proliferation and cytokine secretion in the individuals exposed to arsenic

Over six million people in nine districts of West Bengal, India are exposed to very high levels of arsenic primarily through their drinking water. More than 300,000 people showed arsenic-induced skin lesions in these districts. This is regarded as the greatest arsenic calamity in the world. Chronic arsenicosis causes varied dermatological signs ranging from pigmentation changes, hyperkeratosis to non-melanocytic cancer of skin, and also malignancies in different internal organs. Higher incidences of opportunistic infections are found in the arsenic-exposed individuals, indicating that their immune systems may be impaired somehow. We have thus investigated the effect of arsenic on T-cell proliferation and cytokine secretion in 20 individuals with arsenic-induced skin lesions and compared the results with 18 arsenic-unexposed individuals. A marked dose-dependent suppression of Concanavalin A (Con A) induced T-cell proliferation was observed in the arsenic-exposed individuals compared with the unexposed ( P < 0.001) individuals. This correlated with a significant decrease in the levels of secreted cytokines by the T cells (TNF-α, IFN-γ, IL2, IL10, IL5, and IL4) in the exposed individuals ( P < 0.001). Thus it can be inferred that arsenic exposure can cause immunosuppression in humans.

Chromosomal aberrations and sister chromatid exchanges in individuals exposed to arsenic through drinking water in West Bengal, India

Arsenic contamination in groundwater has become a worldwide problem. Currently an unprecedented number of people in West Bengal, India and Bangladesh are exposed to the ubiquitous toxicant via drinking water in exposure levels far exceeding the maximum recommended limit laid down by WHO. This arsenic epidemic has devastated nine districts of West Bengal encompassing an area of 38,865 km(2) leading to various clinical manifestations of chronic arsenicosis. We conducted a human bio-monitoring study using chromosomal aberrations (CA) and sister chromatid exchanges (SCE) as end points to explore the cytogenetic effects of chronic arsenic toxicity in the population of North 24 Parganas, one of the arsenic affected districts in West Bengal. Study participants included 59 individuals residing in this district where the mean level (+/-S.E.) of arsenic in drinking water (microg/l) was 211.70+/-15.28. As age matched controls with similar socio-economic status we selected 36 healthy, asymptomatic individuals residing in two unaffected districts--Midnapur and Howrah where the mean arsenic content of water (microg/l) was 6.35+/-0.45. Exposure was assessed by standardized questionnaires and by detecting the levels of arsenic in drinking water, nails, hair and urine samples. In the exposed group the mean arsenic concentrations in nails (microg/g), hair (microg/g) and urine (microg/l) samples were 9.04+/-0.78, 5.63+/-0.38 and 140.52+/-8.82, respectively, which were significantly high (P<0.01) compared to the corresponding control values of 0.44+/-0.03, 0.30+/-0.02 and 5.91+/-0.49, respectively. Elevated mean values (P<0.01) of the percentage of aberrant cells (8.08%) and SCEs per cell (7.26) were also observed in the exposed individuals in comparison to controls (1.96% and 5.95, respectively). The enhanced rates of CAs and SCEs among the residents of North 24 Parganas are indicative of the cytogenetic damage due to long term exposure to arsenic through consumption of contaminated water.

Mechanism of erythrocyte death in human population exposed to arsenic through drinking water

Arsenic contamination in drinking water is one of the biggest natural calamities, which has become an imperative threat to human health throughout the world. Abbreviation of erythrocyte lifespan leading to the development of anemia is a common sequel in arsenic exposed population. This study was undertaken to explore the mechanism of cell death in human erythrocytes during chronic arsenic exposure. Results revealed transformation of smooth discoid red cells into evaginated echinocytic form in the exposed individuals. Further distortion converted reversible echinocytes to irreversible spheroechinocytes. Arsenic toxicity increased membrane microviscosity along with an elevation of cholesterol/phospholipid ratio, which hampered the flexibility of red cell membrane and made them less deformable. Significant increase in the binding of merocyanine 540 with erythrocyte membrane due to arsenic exposure indicated disruption of lipid packing in the outer leaflet of the cell membrane resulting from altered transbilayer phospholipid asymmetry. Arsenic induced eryptosis was characterized by cell shrinkage and exposure of phosphatidylserine at the cell surface. Furthermore, metabolic starvation with depletion of cellular ATP triggered apoptotic removal of erythrocytes from circulation. Significant decrease in reduced glutathione content indicating defective antioxidant capacity was coupled with enhancement of malondialdehyde and protein carbonyl levels, which pointed to oxidative damage to erythrocyte membrane. Arsenic toxicity intervened into red cell membrane integrity eventually leading to membrane destabilization and hemoglobin release. The study depicted the involvement of both erythrophagocytosis and hemolysis in the destruction of human erythrocytes during chronic arsenic exposure.

Enhanced frequency of micronuclei in individuals exposed to arsenic through drinking water in West Bengal, India

In West Bengal, India arsenic in ground water has been found to be above the maximum permissible limit in seven districts covering an area of 37,493km2. In the present study, evaluation of the micronuclei (MN) formation in oral mucosa cells, urothelial cells and peripheral blood lymphocytes was carried out in the symptomatic individuals exposed to arsenic through drinking water. Forty five individuals with cutaneous signs of arsenicism from four affected districts (368.11 microg/l of As in drinking water) were considered as the exposed group and 21 healthy individuals with no symptoms of arsenic poisoning and residing in two unaffected districts (5.49 microg/l of As) were considered as controls. The exposed and control groups had similar age distribution and socioeconomic status. Standardised questionnaires were utilised and medical examination was conducted to ascertain exposure history, sociodemographic characteristics, diet, health, medication, addiction and chief symptoms in the study participants. Arsenic exposure was confirmed by measuring the arsenic content in the drinking water, nails, hair and urine samples from the volunteers. Arsenic contents in the urine, nail and hair in the exposed group were 24.45 microg/l, 12.58 and 6.97 microg/g, respectively which were significantly high in comparison to corresponding control group values of 4.88 microg/l, 0.51 and 0.34 microg/g, respectively. Exposed individuals showed a statistically significant increase in the frequency of MN in oral mucosa, urothelial cells and lymphocytes (5.15, 5.74 and 6.39/1000 cells, respectively) when compared with the controls (0.77, 0.56 and 0.53/1000 cells, respectively). Thus, the above results indicate that the symptomatic individuals exposed to arsenic through drinking water in this region have significant cytogenetic damage.

Genetic toxicology of epichlorohydrin: a review

Epichlorohydrin (ECH) is one of the more commercially important aliphatic epoxides used extensively as an industrial intermediate, a laboratory reagent, and as an insecticide. It is a volatile, colourless liquid with an ethereal odour. It behaves as an alkylating agent. Reports have shown it to cause the respiratory and dermal toxicity in animals and humans. It has also been reported to be carcinogenic in experimental models. Thus, the wide-spread use of this aliphatic epoxide is of great concern in human health problem. The purpose of this paper is to critically review and update the mutagenic and clastogenic effects of ECH based on available literature.

Relative efficacy of short-term tests in detecting genotoxic effects of cadmium chloride in mice in vivo

The ability of intraperitoneally administered cadmium chloride (0.42-6.75 mg/kg) to induce genotoxic damage in somatic and germ cells of mice was evaluated using chromosomal aberrations, sister-chromatid exchanges (SCE), micronuclei and sperm-head abnormalities as end-points. A significant increase in the frequency of chromosomal aberrations and SCEs was observed in almost all treated series when compared to the negative control. Micronucleus formation in polychromatic erythrocytes was not affected significantly except at the highest concentration used (6.75 mg/kg). Significant differences were observed in the frequency of sperm with abnormal head morphology at all concentrations tested except the lowest one. The clastogenic effects of cadmium chloride in both somatic and germinal cells are found to depend directly on the concentrations used.

Comparative mutagenic and genotoxic effects of three antimalarial drugs, chloroquine, primaquine and amodiaquine

Comparative mutagenic and genotoxic effects of three antimalarial drugs, chloroquine, primaquine and amodiaquine, were assessed in the Ames mutagenicity assay (in strains TA97a, TA100, TA102 and TA104) and in vivo sister chromatid exchange (SCE) and chromosome aberration (CA) assays in bone marrow cells of mice. These are the most commonly used antimalarial drugs available at present throughout the world. The results of the bacterial mutagenicity assays showed a very weak mutagenic effect of all three drugs in Salmonella strains TA97a and TA100 both with and without S9 mix and in TA104 only with S9 mix. The results of the in vivo SCE and CA assays indicate that these three drugs are genotoxic in bone marrow cells of mice.

Inhibition of benzo[a]pyrene induced mutagenicity and genotoxicity by black tea polyphenols theaflavins and thearubigins in multiple test systems

This study investigated the antimutagenic and anticlastogenic effects of black tea polyphenols, theaflavins (TF) and thearubigins (TR) in Salmonella assay in vitro and in vivo in bone marrow cells of mice as measured by chromosomal aberrations (CA) and sister chromatid exchange (SCE) against a known carcinogen, benzo[a]pyrene (B[a]P). A significant decrease in mutagenicity in Salmonella assay and both CA and SCE were observed in all the different concentrations of TF and TR plus B[a]P treated series when compared with B[a]P treated group alone. These results indicate that both TF and TR have significant antimutagenic and anticlastogenic effects.

Genetic damage and the inhibition of 7,12-dimethylbenz[a]anthracene-induced genetic damage by the phytoestrogens, genistein and daidzein, in female ICR mice

Populations consuming soybeans have reduced rates of breast, colon and prostate cancer possibly due, in part, to the presence in soybeans of two estrogenic isoflavones, genistein and daidzein. This study investigated the genotoxicity of these soya isoflavones and their interactions with 7,12-dimethylbenz[a]anthracene (DMBA)-induced sister chromatid exchanges (SCE) in bone marrow cells and DNA adduct formations in liver and mammary glands of mice. Groups of female ICR mice were pretreated i.p. with daidzein and/or genistein (10-20 mg/kg per day for 6 days or 50 mg/kg per 12 h for 3 days) or with the solvent, dimethylsulfoxide (DMSO). The mice were implanted with bromodeoxyuridine (BrdU) tablets s.c., and treated with DMBA (50 mg/kg) i.p. and colchicine (4 mg/kg) i.p. 24, 23, and 2 h before sacrifice, respectively. In bone marrow cells. DMBA alone induced 11.73 +/- 1.42 SCE/cell compared to 4.35 +/- 0.83 SCE/cell in the DMSO treated controls (P = 0.001). DMBA induced 20% fewer SCE (P < 0.05) in mice pretreated with daidzein, genistein or a combination of genistein and daidzein (6 x 20 mg/kg per day for 6 days) when compared to mice that received no pretreatments. Genistein at 50 mg/kg per 12 h for 3 days also inhibited DMBA-induced SCE by 20%. However, treatment for 3 days with 50 mg/kg per 12 h of genistein or daidzein alone, or a combination of daidzein plus genistein (without DMBA treatment) also induced more SCE than treatment with only the solvent (DMSO, P < 0.05). Pretreatment with both the low and the high doses of daidzein plus genistein or the high dose of genistein reduced the replication index of bone marrow cells when compared to pretreatment with DMSO (P < 0.05). Pretreatment with genistein reduced DMBA-induced DNA adduct formation by 34%, but this was only marginally significant (P = 0.08) due to the large inter-individual variability in adduct levels. These results show that genistein and daidzein suppress SCE and possibly DNA adduct formation induced by the known carcinogen, DMBA. This response to a low dose isoflavone exposure may be partly responsible for the protective effect against endocrine cancers of soya consumption.

Mutagenic and genotoxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin, a review

2,3,7,8-Tetrachlorodibenzo-p-dioxin is one of the most toxic and highly stable compounds known in the environment. Due to uncontrolled exothermic reactions during manufacture of 2,4,5-T and other chlorophenoxy compounds, TCDD is released in the environment. The importance of determining the hazards to human health from dioxin became apparent because of its severe adverse health effects. 'Agent Orange' which is a mixture of 2,4,5-T and 2,4-D has been extensively used during the late Vietnam War. In this review an attempt has been made to evaluate the mutagenic and genotoxic effects of 2,3,7,8-TCDD as known at present.

Genetic toxicology of vinyl chloride--a review

Vinyl chloride (VC) is a colorless gas with a mild, sweet odor. It is extensively used in the production of vinyl chloride polymer, copolymer resin, packaging materials, wire and cable coatings as well as in industrial and laboratory intermediates. It is toxic and also carcinogenic in experimental animals. The wide human exposure to this compound in different industries throughout the world causes great concern for human health. In the present review an attempt has been made to evaluate and update the genotoxic effects of vinyl chloride based on the available literature.

Comparative antimutagenic effects of D- and L-centchroman and their comparison with tamoxifen in Salmonella assay

Centchroman (CC)--a contraceptive and a candidate drug for breast cancer has been developed by the Central Drug Research Institute. It has been successfully marketed as a contraceptive for last several years. CC has also been reported to exhibit partial to complete remission of lesions in 40.5% breast cancer patients. Recently, we have reported the antimutagenic effects of CC in Ames Salmonella assay and in vivo and in vitro mammalian cells in multiple mutational assay. The potent antimutagenic activity of CC and its anti-breast cancer activity prompted us to evaluate the antimutagenic effects of its enantiomers, i.e., D-centchroman (DC) and L-centchroman (LC) in the Ames Salmonella strains TA97a, TA98, TA100 and TA102 against known bacterial mutagens. Attempts have also been made to compare the results of antimutagenicity assays of CC and its enantiomers with the known breast cancer drug tamoxifen (TM). The main objective was to identify the best suitable form of CC having antimutagenic effects with anticancer profile similar to TM, would replace the latter for toxicity reasons. When mutagenicity assays were carried out with these compounds as expected like CC, none of these enantiomers or TM showed any mutagenic effects in these Salmonella strains. In the antimutagenicity assay a significantly reduced number of bacterial histidine revertant colonies were observed when positive compounds were co-incubated with certain concentrations of LC compared with bacterial plates treated with respective positive compound. This was observed in some concentrations in all the four strains in both plate incorporation and preincubation tests. The protective effects of LC in preincubation tests were slightly more than in plate incorporation tests. Both the DC and TM showed protective effects only in certain concentrations in some strains in either plate or preincubation tests. Thus the above results indicate that LC showed more protective effects in Salmonella strains TA97a, TA98, TA100 and TA102 than either DC or TM.

Comparative genotoxicity of six salicylic acid derivatives in bone marrow cells of mice

In vivo sister chromatid exchange (SCE) and chromosome aberrations (CA) were carried out for six salicylic acid derivatives in bone marrow cells of mice. Six salicylic acid derivatives, namely acetyl salicylic acid (aspirin), salicylic acid, salicylamide, sodium salicylate, diflunisal and niclosamide, were used for these experiments. Drugs were administered both intraperitoneally (i.p.) and orally by gavage. Out of these six salicylic acid derivatives tested, only diflunisal and niclosamide showed genotoxicity as measured by both SCE and CA assays. Acetyl salicylic acid and sodium salicylate showed weak genotoxicity as measured by SCE and CA, respectively, only at the highest dose tested.

Comparative mutagenic and genotoxic effects of three propionic acid derivatives ibuprofen, ketoprofen and naproxen

The mutagenicity of three propionic acid derivatives, namely ibuprofen, ketoprofen and naproxen, was tested in the Ames mutagenicity assay (in strains TA97a, TA100 and TA102) and in vivo genotoxicity was tested by sister chromatid exchange (SCE) in bone marrow cells of mice. These are the anti-inflammatory drugs frequently used in different parts of the world. Mutagenicity results showed no mutagenic effects in strains TA97a, TA100 and TA102 for all three drugs. Results of in vivo SCE assays indicate that these three drugs are weakly genoxic in bone marrow cells of mice. This is the first report of the Ames mutagenicity assay for ketoprofen and in vivo SCE assay for three drugs.

Chromosomal aberrations in arsenic-exposed human populations: a review with special reference to a comprehensive study in West Bengal, India

For centuries arsenic has played an important role in science, technology, and medicine. Arsenic for its environmental pervasiveness has gained unexpected entrance to the human body through food, water and air, thereby posing a great threat to public health due to its toxic effect and carcinogenicity. Thus, in modern scenario arsenic is synonymous with "toxic" and is documented as a paradoxical human carcinogen, although its mechanism of induction of neoplasia remains elusive. To assess the risk from environmental and occupational exposure of arsenic, in vivo cytogenetic assays have been conducted in arseniasis-endemic areas of the world using chromosomal aberrations (CA) and sister chromatid exchanges (SCE) as biomarkers in peripheral blood lymphocytes. The primary aim of this report is to critically review and update the existing in vivo cytogenetic studies performed on arsenic-exposed populations around the world and compare the results on CA and SCE from our own study, conducted in arsenic-endemic villages of North 24 Parganas (district) of West Bengal, India from 1999 to 2003. Based on a structured questionnaire, 165 symptomatic (having arsenic induced skin lesions) subjects were selected as the exposed cases consuming water having a mean arsenic content of 214.96 microg/l. For comparison 155 age-sex matched control subjects from an unaffected district (Midnapur) of West Bengal were recruited. Similar to other arsenic exposed populations our population also showed a significant difference (P < 0.01) in the frequencies of CA and SCE between the cases and control group. Presence of substantial chromosome damage in lymphocytes in the exposed population predicts an increased future carcinogenic risk by this metalloid.

Sister chromatid exchanges and micronuclei formations induced by sorbic acid and sorbic acid-nitrite in vivo in mice

The in vivo induction of sister chromatid exchanges and micronuclei formations by acute treatment with different concentrations of sorbic acid and by nitrite, individually and in combination, was studied in bone marrow cells of mice. A significant increase in the frequency of sister chromatid exchanges was only observed with the three higher concentrations of sorbic acid when compared to a distilled water control. Sodium nitrite produced a significant increase at all doses tested. A combination of half the concentration of sorbic acid and of sodium nitrite gave an additive effect over that of sorbic acid or sodium nitrite alone. In the micronucleus assay, the highest dose of sorbic acid (150 mg/kg body weight) produced a significant increase in micronuclei formations compared to the distilled water control. Sodium nitrite alone induced significant numbers of micronuclei at all concentrations tested when compared to the negative control. However, a combination of half the concentration of sorbic acid and of sodium nitrite gave synergistic effects which could possibly be ascribed to the formation of certain genotoxic compounds in vivo.

Anticlastogenic effects of black tea polyphenols theaflavins and thearubigins in human lymphocytes in vitro

Black tea accounts for nearly 80% of total World tea production. It contains dimeric flavanols and polymeric polyphenols known as theaflavins (TF) and thearubigins (TR). TR is exclusively present in black tea. On the basis of our previous potent antimutagenic and anticlastogenic effects of TF and TR in vitro in bacterial system and in vivo in mouse bone marrow cells, we have decided to extend our study in human cells in vitro. This study investigated the anticlastogenic effects of black tea polyphenols TF and TR as measured by chromosomal aberrations (CA) and micronuclei formation (MN) against two known mutagens/carcinogens i.e. benzo[a]pyerne (B[a]P) and aflatoxin B1(AFB1) with S9 activation. A significant decrease in both CA and MN were observed in the human lymphocyte cultures treated with either TF or TR pretreated with either B[a]P or AFB1 (250, 500, 1000 microg/ml) when compared with B[a]P or AFB1 treated cultures alone. TF shows more protective effects than TR in this in vitro system. These results indicate that both TF and TR have significant anticlastogenic effects in vitro in human lymphocytes.

Biosorption of arsenic (III) from aqueous solution by living cells of Bacillus cereus

In this work, removal of arsenic (III) from aqueous solution by living cells (Bacillus cereus), biosorption mechanism, and characterization studies have been reported. B. cereus cell surface was characterized using SEM-EDX and FTIR. Dependence of biosorption on pH of the solution, biosorbent dose, initial arsenic (III) concentration, contact time, and temperature had been studied to achieve optimum condition. The maximum biosorption capacity of living cells of B. cereus for arsenic (III) was found to be 32.42 mg/g at pH 7.5, at optimum conditions of contact time of 30 min, biomass dosage of 6 g/L, and temperature of 30 ± 2 °C. Biosorption data of arsenic (III) are fitted to linearly transformed Langmuir isotherm with R (2) (correlation coefficient) >0.99. The pseudo-second-order model description of the kinetics of arsenic (III) is successfully applied to predict the rate constant of biosorption. Thermodynamic parameters reveal the endothermic, spontaneous, and feasible nature of sorption process of arsenic (III) onto B. cereus biomass. The arsenic (III) ions are desorbed from B. cereus using both 1 M HCl and 1 M HNO(3).

Effects of certain food dyes on chromosomes of Allium cepa

The effects of 4 permitted food dyes, i.e., fast green FCF, indigo carmine, orange G and tartrazine, and the non-permitted dye metanil yellow on chromosomes of Allium cepa are reported. A significant increase in polyploid cells was observed in all cases. High doses of these dyes induced chromosome breaks and micronucleus formation. Although all dyes produced mitotic aberrations, metanil yellow and fast green FCF showed comparatively stronger clastogenic activity.

Antimutagenic effects of black tea (World Blend) and its two active polyphenols theaflavins and thearubigins in Salmonella assays

Almost two thirds of the world population consume tea everyday. Tea is processed differently in different parts of the world to give green (20%), black (78%) or oolong tea (2%). The antimutagenic and anticarcinogenic activities of green tea were extensively investigated compared with those of black tea. Considering the potent antimutagenic effects of green tea we recognized the need to evaluate the antimutagenic effects of black tea (World Blend Tea, Southern Tea Co., Marietta, GA) in Salmonella strains TA97a, TA98, TA100 and TA102 in preincubation tests, both with and without S9 activation. Attempts have also been made to compare the results of the tea extracts with their two active polyphenols theaflavins and thearubigins. Antimutagenicity assays were carried out in bacterial plates treated with different concentrations (1%, 2.5%, 5%, 10% and 20%) of tea extracts against known bacterial mutagens sodium azide, 4-nitro-o-phenylenediamine, cumine hydroperoxide, 2-aminofluorene and danthron. A significant decrease in the number of revertant colonies was observed in the plates treated with 1% to 20% of tea extract plus positive mutagen when compared with positive mutagen only. Both the active polyphenols theaflavins and thearubigins extracted from the black tea (World blend) also showed significant antimutagenic effects against known positive compounds in these strains. In the experiments with S9 activation, the antimutagenic effects were significantly higher. These results indicate that black tea and its two polyphenols have significant antimutagenic effects in Ames Salmonella assays.

In vivo cytogenetic studies on mice exposed to Orange G, a food colourant

Orange G, a monoazo dye, used as a food colourant, was evaluated with in vivo cytogenetic assays to determine its genotoxicity. Swiss albino male mice were exposed to Orange G through intraperitoneal injections. Bone marrow cells isolated from femora were analyzed for sister chromatid exchanges (SCE) and chromosome aberrations. The results showed that the incidence of SCEs and chromosome aberrations were significantly higher than controls at certain concentrations. 25 mg/kg of Orange G was found to be the minimum effective dose for the induction of both SCEs and chromosome aberrations. Orange G is thus found to be clastogenic and genotoxic in vivo in mice.