Studies on cytotoxic and genotoxic effects of cadmium nitrate and lead nitrate in Chinese hamster ovary cells

Cadmium nitrate and DNA methylation in gastropods: comparison between ovotestis and hepatopancreas

Dietary ingestion is the main route of exposure to hazardous contaminants in land animals. Cadmium, a high-profile toxic metal, affects living systems at different organismal levels, including major storage organs (liver, kidneys), key organs for species survival (gonads), and epigenetic networks regulating gene expression. 5-methylcytosine (5mC) is the most common and best-characterized epigenetic mark among different modified nucleosides in DNA. This important player in methylation-driven gene expression is impacted by cadmium in sentinel terrestrial vertebrates. However, limited information exists regarding its impact on macroinvertebrates, especially land snails commonly used as (eco)toxicological models. We first investigate the methylomic effects of dietary cadmium given as cadmium nitrate on terrestrial mollusks. Mature specimens of the common brown garden snail, Cornu aspersum, were continuously exposed for four weeks to environmentally-relevant cadmium levels. We determined global genomic DNA methylation in hepatopancreas and ovotestis, as well as changes in the methylation status of CG pairs at the 5' region close to the transcription site of gene encoding the Cd-selective metallothionein (Cd-MT). Weight gain/loss, hypometabolism tendency, and survival rates were also assessed. Although this exposure event did not adversely affect survival, gastropods exposed to the highest Cd dose revealed a significant reduction in body weight and a significant increase in hypometabolic behavior. The hepatopancreas, but not the ovotestis, displayed significant hypermethylation, but only for the aforementioned specimens. We also found that the 5' end of the Cd-MT gene was unmethylated in both organs and its methylation status was insensitive to cadmium exposure. Our results are important since they provide scientists, for the first time, with quantitative data on DNA methylation in gastropod ovotestis and refine our understanding of Cd epigenetic effects on terrestrial mollusks.

Differences in root surface adsorption, root uptake, subcellular distribution, and chemical forms of Cd between low- and high-Cd-accumulating wheat cultivars

The differences in the mechanism of cadmium (Cd) accumulation in the grains of different wheat (Triticum aestivum L.) cultivars remain unclear. Thus, we conducted a hydroponic experiment in a greenhouse to compare root surface adsorption, root uptake, subcellular distribution, and chemical forms of Cd between low- and high-Cd-accumulating wheat cultivars at seedling stage, to improve our understanding of the differences between cultivars. The results showed that Cd adsorbed on the root surface was mainly in a complexed form, and the total amount of Cd on the Yaomai16 (YM, high-Cd-accumulating genotypes) root surface was higher (p < 0.05) than that on Xinmai9817 (XM, low-Cd-accumulating genotypes). A large amount of Cd ions adsorbed on root surface would cause plant damage and inhibit growth. Comparing the root-to-shoot translocation factors of Cd, the transfer coefficients of YM were 1.017, 1.446, 1.464, and 1.030 times higher than those of XM under 5, 10, 50, and 100 μmol L^-1 Cd treatments, respectively. The subcellular distribution of Cd under Cd exposure is mainly in the cell wall and soluble fraction. The proportions of Cd in YM shoot soluble fraction were higher than those in XM, which was the main detoxification mechanism limiting the activity of Cd and may be responsible for low Cd accumulation in grains, while the effects of the chemical forms of Cd on migration and detoxification were not found to be related to Cd accumulation in the kernels.

Cellular pathologies and genotoxic effects arising secondary to heavy metal exposure: A review

Environmental pollution is significant and oftentimes hazardous in the areas, where mining, foundries and smelters and other metallurgical operations are located. Systematic research on the chronic effects of metals started during the past century; nevertheless, it is evident that even today, there are large gaps in knowledge regarding the assessment of the health effects caused by environmental and occupational exposures to these metals. Heavy metals induce the production of reactive oxygen species (ROS) causing oxidative stress, make several repair-inhibiting cellular changes and alter the DNA repair processes. They favour the ‘false’ repairing of double-strand breaks (DSBs), propagate DNA mutations and induce carcinogenesis. A detailed literature search was performed using the MedLine/PubMed database. Depending on the mechanism of action, arsenicals can act as genotoxins, non-genotoxic agents and carcinogens. Cadmium can bind to proteins, reduce DNA repair, activate protein degradation, up-regulate cytokines and proto-oncogenes (c-fos, c-jun and c-myc), induce the expression of metallothionein, haeme-oxygenases, glutathione transferases, heat-shock proteins, acute-phase reactants and DNA polymerase β at lower concentrations. Inorganic mercury damages oxidative phosphorylation and electron transport pathways at the ubiquinone–cytochrome b5 locus and thus induces ROS production. Abandoned mining areas generate environmentally persistent waste. These specific sites urgently require maximally efficient and cheap remediation. This bears the need for methodologies employing green and sustainable remediation. Phytoremediation is important in that it is a prevalent in situ remediation technique. Its advantages include the use of solar energy, cost-effectiveness, easy operation, reduction in secondary contaminants, the use of biomass for biofuel production and low-cost adsorbents.

Biodetection of potential genotoxic pollutants entering the human food chain through ashes used in livestock diets

Ash derived from energy generation is used as a source of minerals in livestock feeds. The microbial biosensor recApr-Luc2 was built to detect genotoxic hazard in recycled ash. Escherichia coli SOS gene (recA, lexA, dinI and umuC) expression in response to cisplatin-induced DNA damage led to the selection of the recA promoter. The biosensor required functional RecA expression to respond to genotoxic heavy metals (Cr>Cd≈Pb), and polluted ash induced a strong recApr-Luc2 response. In human liver and intestinal cells, heavy metals induced acute toxicity (Cr>Cd>Pb) at concentrations sufficient to activate recApr-Luc2. Cytostatic effects, including genotoxicity, were cell- and metal-dependent, apart from Cr. In agreement with the recApr-Luc2 bioassay, Cr had the strongest effect in all cells. In conclusion, recApr-Luc2 could be useful for evaluating the genotoxic risk of pollutants present in ash that might be concentrated in animal products and, thus, entering the human food chain.

Genotoxicity and cytotoxicity of chromium, copper, manganese and lead, and their mixture in WIL2-NS human B lymphoblastoid cells is enhanced by folate depletion

Heavy metal exposure or dietary deficiency is associated with increased genetic damage, cancer and age-related diseases. Folate (vitamin B9) required for DNA repair and synthesis may increase cellular susceptibility to metal induced genotoxicity. This study investigated the interactive effects of folic acid deficiency and sufficiency on genome instability and cytotoxicity induced by chromium (VI), copper (II), manganese (II), lead (IV), and their mixture (CCMP) in WIL2-NS human B lymphoblastoid cells. WIL2-NS cells were cultured in folic acid deficient (20 nM) and replete (2000 nM) RPMI 1640 medium treated with different concentrations (0.00-1000 μM) of the metals and CCMP for 48 h. Chromosomal damage and cytotoxicity were measured using the Cytokinesis-block Micronucleus Cytome assay. CCMP, Cr, Pb, Cu and Mn induced concentration dependent, increases in cells with chromosome damage (micronuclei, nucleoplasmic bridges, nuclear buds) and necrotic cells and decreased nuclear division index. The metals exhibited different cytotoxic and genotoxic potentials (CCMP>Cr>Pb>Cu>Mn) in both folate deficient and sufficient cells, with the cytogenotoxic effects being greater in folate deficient cells. Significant interaction between the metals and folic acid suggests that folic acid deficiency exacerbated cell proliferation inhibition and genome instability induced by metals. Folate deficiency, increasing metal concentration, and their interactions explained 3-11%, 74-92% and 4-12% of the variance of DNA damage biomarkers. In conclusion, exposure to the tested metals (0.01-1000 μM) increased chromosomal DNA damage in WIL2-NS cells and this was exacerbated by folate deficiency.

Heavy metal toxicity and the environment

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least five times greater than that of water. Their multiple industrial, domestic, agricultural, medical, and technological applications have led to their wide distribution in the environment, raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the US Environmental Protection Agency and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.

Mimosa (Mimosa caesalpiniifolia) prevents oxidative DNA damage induced by cadmium exposure in Wistar rats

The Mimosa (Mimosa caesalpiniifolia) is a plant native from South America; it is used in the traditional medicine systems for treating bacterial, fungal, parasitic and inflammatory conditions. The aim of this study was to evaluate the antigenotoxic and antioxidant activities induced by mimosa (M. caesalpiniifolia) in multiple rodent organs subjected to intoxication with cadmium chloride. A total of 40 Wistar rats (8 weeks old, 250 g) were distributed into eight groups (n = 5), as follows: Control group (non-treated group, CTRL); Cadmium exposed group (Cd); cadmium exposure and treated with extract at 62.5 mg/kg/day; cadmium exposure and treated with extract at 125 mg/kg/day; cadmium exposure and treated with extract at 250 mg/kg/day; cadmium exposure and treated with ethyl acetate fraction at 62.5 mg/kg/day. For evaluating the toxicogenetic potential of mimosa, two groups were included in the study being treated with extract at 250 mg/kg/day and acetate fraction of mimosa at 62 mg/kg/day, only. Extract of mimosa at concentrations of 62.5 and 125 mg decreased DNA damage in animals intoxicated with cadmium when compared to cadmium group. In a similar manner, treatment with ethyl acetate fraction of mimosa at 62.5 mg concentration in animals previously exposed to cadmium reduced genetic damage in peripheral blood cells. In a similar manner, the treatment with ethyl acetate fraction reduced DNA damage in liver cells. Oxidative DNA damage was reduced to animals exposed to cadmium and treated with 125 mg of extract as well as those intoxicated to cadmium and treated with 62.5 of acetate fraction of mimosa. Taken together, our results indicate that mimosa prevents genotoxicity induced by cadmium exposure in liver and peripheral blood cells of rats as a result of antioxidant activity.

Heavy metal toxicity and the environment

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least five times greater than that of water. Their multiple industrial, domestic, agricultural, medical, and technological applications have led to their wide distribution in the environment, raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the US Environmental Protection Agency and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.

Mechanisms of cadmium induced genomic instability

Cadmium is an ubiquitous environmental contaminant that represents hazard to humans and wildlife. It is found in the air, soil and water and, due to its extremely long half-life, accumulates in plants and animals. The main source of cadmium exposure for non-smoking human population is food. Cadmium is primarily toxic to the kidney, but has been also classified as carcinogenic to humans by several regulatory agencies. Current evidence suggests that exposure to cadmium induces genomic instability through complex and multifactorial mechanisms. Cadmium dose not induce direct DNA damage, however it induces increase in reactive oxygen species (ROS) formation, which in turn induce DNA damage and can also interfere with cell signalling. More important seems to be cadmium interaction with DNA repair mechanisms, cell cycle checkpoints and apoptosis as well as with epigenetic mechanisms of gene expression control. Cadmium mediated inhibition of DNA repair mechanisms and apoptosis leads to accumulation of cells with unrepaired DNA damage, which in turn increases the mutation rate and thus genomic instability. This increases the probability of developing not only cancer but also other diseases associated with genomic instability. In the in vitro experiments cadmium induced effects leading to genomic instability have been observed at low concentrations that were comparable to those observed in target organs and tissues of humans that were non-occupationally exposed to cadmium. Therefore, further studies aiming to clarify the relevance of these observations for human health risks due to cadmium exposure are needed.

Evaluation of differential representative values between Chinese hamster cells and human lymphocytes in mitomycin C-induced cytogenetic assays and caspase-3 activity

Chinese hamster ovary (CHO) cells, its lung fibroblasts (V79), and human lymphocytes are routinely used in in vitro cytogenetic assays, which include micronuclei (MN), sister chromatid exchange (SCE), and chromosome aberration (CA) assays. Mitomycin C (MMC), a DNA cross-link alkylating agent, is both an anticancer medicine and a carcinogen. To study the differential representative values of cell types in MMC-treated cytogenetic assays and its upstream factor, cysteine aspartic acid-specific protease (caspase)-3. Among the chosen cell types, lymphocytes expressed the highest sensitivity in all three MMC-induced assays, whereas CHO and V79 showed varied sensitivity in different assays. In MN assay, the sensitivity of CHO is higher than or equal to V79; in SCE assay, the sensitivity of CHO is the same as V79; and in CA assay, the sensitivity of CHO is higher than V79. In-depth analysis of CA revealed that in chromatid breaks and dicentrics formation, lymphocyte was the most sensitive of all and CHO was more sensitive than V79; and in acentrics and interchanges formation, lymphocyte was much more sensitive than the others. Furthermore, we found caspase-3 activity plays an important role in MMC-induced cytogenetic assays, with MMC-induced caspase-3 activity resulting in more sensitivity in lymphocytes than in CHO and V79. Based on these findings, lymphocyte will make a suitable predictive or representative control reference in cytogenetic assays and caspase-3 activity with its high specificity, positive predictive value, and sensitivity.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Genotoxic effects of lead: an updated review

Lead is a ubiquitous toxic heavy metal with unique physical and chemical properties that make it suitable for a great variety of applications. Because of its high persistence in the environment and its use since ancient times for many industrial activities, lead is a common environmental and occupational contaminant widely distributed around the world. Even though the toxic effects of lead and its compounds have been investigated for many years in a variety of systems, the data existing with regard to its mutagenic, clastogenic and carcinogenic properties are still contradictory. The International Agency for Research on Cancer has classified lead as possible human carcinogen (group 2B) and its inorganic compounds as probable human carcinogens (group 2A). Furthermore, although the biochemical and molecular mechanisms of action of lead remain still unclear, there are some studies that point out indirect mechanisms of genotoxicity such as inhibition of DNA repair or production of free radicals. This article reviews the works listed in the literature that use different parameters to evaluate the genotoxic effects of lead in vitro, in vivo and in epidemiological studies.

Comparative effects of Cd and Pb on biochemical response and DNA damage in the earthworm Eisenia fetida (Annelida, Oligochaeta)

There are rising concerns about the hazardous effects of cadmium (Cd) and lead (Pb) on the environment in China. Biochemical and comet assays were conducted on the earthworm Eisenia fetida, a suitable bio-indicator organism for evaluating soil pollution after exposure to two heavy metals, Cd and Pb. Protein content increased at low Cd concentrations (p<0.05) and decreased at the highest concentration of 10 mg kg(-1), compared to control (p<0.05). Pb showed an inhibitory effect on protein content at low concentrations but demonstrated no significant effect at higher concentrations. There were no significant differences between control and treated groups at the doses of 1 and 10 mg kg(-1) Cd while at a dose of 0.1 mg kg(-1) Cd the cellulase activity was significantly increased compared to control. Cellulase activities of Pb-treated E. fetida increased in a dose dependent fashion. Results of the comet assay indicated toxicant induced DNA damage. Cd exposure caused significant differences between control and treatment groups (ANOVA, p< 0.05, p< 0.01) and a positive dose-response profile. As for Pb treatment, there were no significant differences between the groups treated with 50 and 500 mg kg(-1) of Pb and the control. Results showed that DNA damage from Cd was more serious than that from Pb. And this indicated that the earthworm was more sensitive to the effects of Cd.

Molecular mechanisms of cadmium induced mutagenicity

Cadmium is a human carcinogen of worldwide concern because it accumulates in the environment due to its extremely long half-life. Its compounds are classified as human carcinogens by several regulatory agencies. Cadmium affects cell proliferation, differentiation, apoptosis and other cellular activities and can cause numerous molecular lesions that would be relevant to carcinogenesis. For a long time cadmium has been considered as a non-genotoxic carcinogen, as it is only weakly mutagenic in bacterial and mammalian cell test systems. Recently, we presented evidence that when assayed in a test system, in which both intragenic and multilocus mutations can be detected, cadmium acts as a strong mutagen which induces predominantly multilocus deletions. In this review, we discuss two mechanisms that play an important role in cadmium mutagenicity: (i) induction of reactive oxygen species (ROS); and (ii) inhibition of DNA repair. Experimental evidence suggests that cadmium at low, for environmental exposure relevant concentrations, induces mutations by inducing oxidative DNA damage and that it decreases genetic stability by inhibiting the repair of endogenous and exogenous DNA lesions, which in turn increase the probability of mutations and consequently cancer initiation by this metal.

Cadmium Down-regulates Human OGG1 through Suppression of Sp1 Activity

Cadmium is a well known human and animal carcinogen and is a ubiquitous contaminant in the environment. Although the carcinogenic mechanism of cadmium is a multifactorial process, oxidative DNA damage is believed to be of prime importance. In particular, cadmium suppresses the capacity of cells to repair oxidative DNA damage. In this study, cadmium treatment led to a significant increase in gamma-ray-induced 8-oxoguanine (8-oxoG) formation. Western blotting and semiquantitative reverse transcription-PCR revealed that cadmium treatment caused a decrease in the expression level of human OGG1 (8-oxoguanine-DNA glycosylase-1; hOGG1) in human fibroblast GM00637 and HeLa S3 cells. In addition, the cadmium-mediated decrease in hOGG1 transcription was the result of decreased binding of the transcription factor Sp1 to the hOGG1 promoter. Finally, we show that an increase in the functional hOGG1 expression level could inhibit the cadmium-mediated increase in gamma-ray-induced 8-oxoG accumulation as well as in gamma-radiation-induced mutation frequency at the HPRT (hypoxanthine-guanine phosphoribosyltransferase) gene locus. These results suggest that cadmium attenuates removal of gamma-ray-induced 8-oxoG adducts, which in turn increases the mutation frequency, and that this effect might, at least in part, result from suppression of hOGG1 transcription via inactivation of Sp1 as a result of cadmium treatment.

Genotoxicity of inorganic lead salts and disturbance of microtubule function

Lead compounds are known genotoxicants, principally affecting the integrity of chromosomes. Lead chloride and lead acetate induced concentration-dependent increases in micronucleus frequency in V79 cells, starting at 1.1 microM lead chloride and 0.05 microM lead acetate. The difference between the lead salts, which was expected based on their relative abilities to form complex acetato-cations, was confirmed in an independent experiment. CREST analyses of the micronuclei verified that lead chloride and acetate were predominantly aneugenic (CREST-positive response), which was consistent with the morphology of the micronuclei (larger micronuclei, compared with micronuclei induced by a clastogenic mechanism). The effects of high concentrations of lead salts on the microtubule network of V79 cells were also examined using immunofluorescence staining. The dose effects of these responses were consistent with the cytotoxicity of lead(II), as visualized in the neutral-red uptake assay. In a cell-free system, 20-60 microM lead salts inhibited tubulin assembly dose-dependently. The no-observed-effect concentration of lead(II) in this assay was 10 microM. This inhibitory effect was interpreted as a shift of the assembly/disassembly steady-state toward disassembly, e.g., by reducing the concentration of assembly-competent tubulin dimers. The effects of lead salts on microtubule-associated motor-protein functions were studied using a kinesin-gliding assay that mimics intracellular transport processes in vitro by quantifying the movement of paclitaxel-stabilized microtubules across a kinesin-coated glass surface. There was a dose-dependent effect of lead nitrate on microtubule motility. Lead nitrate affected the gliding velocities of microtubules starting at concentrations above 10 microM and reached half-maximal inhibition of motility at about 50 microM. The processes reported here point to relevant interactions of lead with tubulin and kinesin at low dose levels.

Micronuclei in peripheral blood lymphocytes of workers exposed to lead

Lead plays an important role in many industrial processes. Although highly useful to man, lead has various types of toxic effects. There is constantly growing evidence of a relationship between the induction of chromosome breaks and an increased risk of onset of cancer. However, available data about the possible genotoxic and carcinogenic action of lead are conflicting. In this report we present the results of studies on lead concentrations in blood and the respective micronucleus frequencies in peripheral blood lymphocytes from workers employed in the recycling of automotive batteries in the surroundings of Porto Alegre, Brazil. We observed that in the occupationally exposed group, both lead concentration in peripheral blood and micronucleus frequency in lymphocytes were significantly higher compared to control (Z=6.35, P<0.0001 and Z=4.47, P<0.0001). The nuclear division index (NDI) values were significantly higher in the control group than in the exposed group (Z=2.13, P=0.0330), indicating a possible effect of Pb on nuclear proliferation. We also detected a negative correlation between micronuclei and progression of nuclear division (tau=-0.312, P=0.0129). There were no changes in micronucleus frequency between smoking and non-smoking workers exposed to lead (Z=0.03, P=0.9790). The only difference found between the groups of smokers and non-smokers was with respect to NDI, whose values were significantly higher among non-smokers (Z=1.98, P=0.0481).

Lead-induced cytotoxicity and transcriptional activation of stress genes in human liver carcinoma (HepG2) cells

Lead is a non-essential element that exhibits a high degree of toxicity, especially in children. Most research on lead has focused on its effects on organ systems such as the nervous system, the red blood cells, and the kidneys which are considered to be the primary targets of lead toxicity. However, the molecular mechanisms by which it induces toxicity, and carcinogenesis remain to be elucidated. In this research, we performed the MTT assay to assess the cytotoxicity, and the CAT-Tox assay to assess the transcriptional responses associated with lead exposure to thirteen different recombinant cell lines generated from human liver carcinoma cells (HepG2), by creating stable transfectants of mammalian promoter chloramphenicol (CAT) gene fusions. Study results indicated that lead nitrate is cytotoxic to HepG2 cells, showing LD50 values of 49.0 +/- 18.0 microg/mL, 37.5 +/- 9.2 microg/mL, and 3.5 +/- 0.7 microg/mL for cell mortality upon 24, 48 and 72 h of exposure, respectively; indicating a dose- and time-dependent response with regard to the cytotoxic effect of lead nitrate. A dose-response relationship was also recorded with respect to the induction of stress genes in HepG2 cells exposed to lead nitrate. Overall, six out of the thirteen recombinant cell lines tested showed inductions to statistically significant levels (p < 0.05). At 50 microg/mL of lead nitrate, the average fold inductions were: 2.1 +/- 1.0, 5.4 +/- 0.4, 12.1 +/- 6.2, 5.0 +/- 1.7, 2.5 +/- 1.3, and 4.8 +/- 4.5 for XRE, HSP70, CRE, GADD153, and GRP78, respectively. These results indicate the potential for lead nitrate to undergo biotransformation in the liver (XRE), to cause cell proliferation (c-fos), protein damage (HSP70, GRP78), metabolic perturbation (CRE), and growth arrest and DNA damage (GADD153). Marginal but not significant inductions were also obtained with the GSTYa (1.5 +/- 0.8), and GADD45 (5.7 +/- 8.1) promoters, and the NF-KB (2.0 +/- 1.7) response element, indicating the potential for oxidative stress. No significant inductions (p > 0.05) were recorded for CYP1A1, HMTIIA, p53RE, and RARE.

Biomonitoring results and cytogenetic markers among harbour workers with potential exposure to river silt aerosols

BACKGROUND

Workers on dredgers and lighters on rivers are potentially exposed to a variety of substances.

AIMS

To determine the internal load of heavy metals and arsenic as well as levels of cytogenetic markers in workers exposed to river silt aerosols.

METHODS

One hundred exposed workers were examined up to eight times within three years. Additionally, 100 control workers were studied once. Blood samples were analysed for lead, mercury, and cadmium. Additionally, micronuclei frequency and sister chromatid exchange (SCE) rates were determined. Urinary samples were analysed for cadmium, mercury, nickel, chromium, and arsenic. Information on potential confounders, such as smoking habits and consumption of fish were assessed.

RESULTS

Apart from some increased concentrations of mercury in blood (maximum 14.6 microg/l) and arsenic in urine (maximum 356.5 microg/l) all measurements were within reference values. None of the exposure and effect markers were found to be significantly increased in exposed workers compared to non-exposed controls. In multiple linear regression models, mercury levels in blood as well as the concentration of arsenic in urine were strongly related to fish consumption. Cadmium levels in blood as well as urinary cadmium concentrations were strongly related to smoking habits. After adjusting for smoking habits, SCE rates were associated with cadmium levels in blood.

CONCLUSION

Increased exposure levels or enhanced levels of cytogenetic markers were not found in workers exposed to river silt aerosols. However, cadmium exposure in blood was related to SCE frequency.

Influence of delta-aminolevulinic acid dehydratase (ALAD) polymorphism on the frequency of sister chromatid exchange (SCE) and the number of high-frequency cells (HFCs) in lymphocytes from lead-exposed workers

In this study, the cytogenetic response to lead exposure in storage battery manufacturing workers carrying different alleles of delta-aminolevulinic acid dehydratase (ALAD 1 and ALAD 2) was evaluated. The cytogenetic response was measured by analysis of the frequency of sister chromatid exchange (SCE) and the number of high-frequency cells (HFCs) in peripheral blood lymphocytes from workers occupationally exposed to lead. A total of 71 voluntary male workers were enrolled in the study. According to our genotype analysis, 50 workers had the ALAD 1-1 genotype and 21 workers had the ALAD 1-2 genotype. In spite of the statistically insignificant difference in mean values of SCE per cell between ALAD 1-1 and ALAD 1-2 workers, the percentage of HFC (HFC (%)) was statistically (chi2-test, P<0.05) higher in ALAD 1-1 workers. The control group was selected among voluntary male office workers (n = 20) and genotyping was also performed for this group in order to rule out the possibility that ALAD 1-1 subjects had a higher HFC (%) than ALAD 1-2 carriers, independent of the exposure to lead. Accordingly, 11 control workers had the ALAD 1-1 genotoype and 9 workers had ALAD 1-2. The differences in mean values of SCE per cell and HFC (%) were not statistically significant when the two genotypes in the control group were compared. On the basis of this result we suggest that ALAD 1-1 subjects might be more susceptible to cytogenetic effects of lead exposure than ALAD 1-2 subjects. There were no ALAD 2-2 subjects in the exposed and control groups.

Cadmium inhibits repair of UV-, methyl methanesulfonate- and N-methyl-N-nitrosourea-induced DNA damage in Chinese hamster ovary cells

The co-genotoxic effects of cadmium are well recognized and it is assumed that most of these effects are due to the inhibition of DNA repair. We used the comet assay to analyze the effect of low, non-toxic concentrations of CdCl2 on DNA damage and repair-induced in Chinese hamster ovary (CHO) cells by UV-radiation, by methyl methanesulfonate (MMS) and by N-methyl-N-nitrosourea (MNU). The UV-induced DNA lesions revealed by the comet assay are single-strand breaks which are the intermediates formed during nucleotide excision repair (NER). In cells exposed to UV-irradiation alone the formation of DNA strand breaks was rapid, followed by a fast rejoining phase during the first 60 min after irradiation. In UV-irradiated cells pre-exposed to CdCl2, the formation of DNA strand breaks was significantly slower, indicating that cadmium inhibited DNA damage recognition and/or excision. Methyl methanesulfonate and N-methyl-N-nitrosourea directly alkylate nitrogen and oxygen atoms of DNA bases. The lesions revealed by the comet assay are mainly breaks at apurinic/apyrimidinic (AP) sites and breaks formed as intermediates during base excision repair (BER). In MMS treated cells the initial level of DNA strand breaks did not change during the first hour of recovery; thereafter repair was detected. In cells pre-exposed to CdCl2 the MMS-induced DNA strand breaks accumulated during the first 2h of recovery, indicating that AP sites and/or DNA strand breaks were formed but that further steps of BER were blocked. In MNU treated cells the maximal level of DNA strand breaks was detected immediately after the treatment and the breaks were repaired rapidly. In CdCl2 pre-treated cells the formation of MNU-induced DNA single-strand breaks was not affected, while the repair was slower, indicating inhibition of polymerization and/or the ligation step of BER. Cadmium thus affects the repair of UV-, MMS- and MNU-induced DNA damage, providing further evidence, that inhibition of DNA repair is an important mechanism of cadmium induced mutagenicity and carcinogenicity.

Morphological characterisation of BGM (Buffalo Green Monkey) cell line exposed to low doses of cadmium chloride

Morphological changes in the Buffalo Green Monkey (BGM) cell line after exposure to a subcytotoxic dose (0.062 mM, equivalent to EC(10)-effective concentration 10%) of cadmium chloride have been evaluated. Cells were exposed for 24 h and the effects observed at the ultrastructural level by transmission and scanning microscopy. Using transmission electron microscopy, the most notable findings in treated cells were the presence of intranuclear inclusion bodies and thin intracytoplasmic granules associated to myelin figures and the presence of apoptotic bodies. Other morphological alterations included cell vacuolisation and a reduced cytoplasm volume, condensation of the mitochondria and a decreased number of cytoplasmic organelles, except lysosomes and autophagic vacuoles, which increased in number. Scanning electron microscopy pointed to a cell with a disrupted perinuclear region and a decrease in the number of surface microvilli. We conclude that the BGM cell line may be considered an useful tool for toxicological studies involving cadmium.

DNA damage in workers exposed to lead using comet assay

Lead (Pb) is a ubiquitous and toxic metal. Secondary Pb recovery unit workers are prone to possible occupational Pb exposure. Hence, this investigation was conducted to assess the genotoxic effect of Pb exposure in these workers. In the study, 45 workers were monitored for DNA damage in blood leucocytes. Simultaneously 36 subjects were used as control group in this study. All the subjects were estimated for Pb content in whole blood by ICP-MS. The alkali single cell gel electrophoresis assay (comet assay) was adopted for detecting the DNA damage. The air inside the premises of the unit had Pb concentrations of 4.2 microg/m(3). The level of DNA damage was determined as the percentage of cells with comets. The mean Pb content was found to be significantly higher in the study group (248.3 microg/l) when compared with the controls (27.49 microg/l). Significantly more cells with DNA damage (44.58%) were observed in the study group than in the control persons (21.14%). Smoking had a significant effect on DNA damage in the control group whereas an insignificant effect was noticed in the exposed workers. Study as well as the control group failed to show a significant effect on DNA damage with age (P>0.05). Pb content and years of exposure significantly correlated with DNA damage in the study group (r=0.602, r=0.690; P<0.01). The increased levels of DNA damage observed in the exposed workers, justifies the use of the comet assay for the evaluation of genotoxic effects in humans exposed to Pb.

Effect of fetal calf serum on the cadmium clastogenicity

Inconsistent results among reports on cadmium genotoxicity revealed that certain confounding factors might significantly influence the outcomes of assessment. In Chinese hamster ovary (CHO-W8) cells, chromosome aberration induced by six different cadmium compounds was found positively associated with intracellular cadmium concentration. A parallel association was also observed among different CHO strains treated with same cadmium compound, the cadmium acetate. Both the cadmium-induced chromosome aberration and cadmium uptake were influenced by the presence of fetal calf serum (FCS). The presence of 10% FCS during the 2h treatment period greatly retarded the cellular cadmium uptake, and concurrently reduced the chromosome aberration induction. Other factors such as specific cadmium anion involved and the duration of cadmium treatment period in the investigation also influenced the assessment results of cadmium-induced chromosome aberration. In the protocol with a 2h pulse treatment, cadmium acetate, chloride and sulfate induced more chromosome aberration than cadmium nitrate, carbonate and oxide. When cadmium was present in the culture of the entire treatment period for 18 h, the results went the opposite way. Cadmium nitrate, carbonate and oxide induced significant chromosome aberration, while other three cadmium compounds gave negative results. Cadmium compounds did not induce significant SCE at the same dose level that yielded significant chromosome aberration induction, either in the protocol with the short pulse or long treatment period.

Genotoxic effect of lead nitrate on mice using SCGE (comet assay)

Single stranded DNA breakage induced by lead nitrate in mice has been studied in vivo using alkaline single cell gel electrophoresis (comet assay). Mice were administered orally 0.7, 1.4, 2.8, 5.6, 11. 2, 22.4, 44.8 and 89.6 mg/kg body weight of lead nitrate and the assay was performed on whole blood at 24, 48, 72 h, 1st and 2nd week. Significant increase in mean tail-length of DNA was observed at all time intervals after treatment with lead nitrate when compared to controls. The mean tail-length did not show a dose-related increase and the elevation in the mean tail-length was of a fluctuating type. Increase in mean tail-lengths clearly gives evidence that lead nitrate causes DNA damage effectively. The study indicates that the alkaline comet assay is a sensitive and rapid method to detect DNA damage caused by heavy metals.

Singlet oxygen is the major species participating in the induction of DNA strand breakage and 8-hydroxydeoxyguanosine adduct by lead acetate

To investigate DNA damage induced by Pb2+ and its prevention by scavengers, we determined DNA strand breakage and the formation of 8-hydroxydeoxyguanosine (8-OHdG) in DNA using plasmid relaxation assay and HPLC with electrochemical detection, respectively. Lead acetate induced DNA strand breakage in 10 mM of Hepes buffer, pH 6.8, in a time- and dose-dependent manner. Compared with lead, zinc acetate did not significantly induce DNA breakage. The singlet oxygen scavengers NaN3 and 2,2,6,6-tetramethyl-4-piperidone (TEMP) inhibited lead-induced DNA breakage more efficiently than the hydroxyl radical scavengers mannitol and DMPO. Deuterium oxide (D2O), a singlet oxygen enhancer, potentiated lead-induced DNA breakage. At low ratios to Pb2+, NADPH, glutathione, and 2-mercaptoethanol enhanced lead-induced DNA breakage, whereas high ratios of these agents protected it. Catalase and superoxide dismutase (SOD) did not protect DNA breaks induced by Pb2+. Lead-induced DNA breakage was markedly enhanced by H2O2, and this induction was inhibited by NaN3, TEMP, EDTA, catalase, BSA, and glutathione. In contrast, mannitol and SOD potentiated Pb2+/H2O2-induced DNA breaks. The results indicate that singlet oxygen, lead, and H2O2 are all involved in the reaction system, whereas hydroxyl radical and superoxide did not. Lead could cause a small amount of 8-OHdG formation in calf thymus DNA and dose-dependently induced the formation of this adduct in the presence of H2O2. Singlet oxygen scavengers were more effective than hydroxyl radical scavengers in protection from lead/H2O2-induced 8-OHdG adducts. Taken together, these results suggest that lead may induce DNA damage through a Fenton-like reaction and that singlet oxygen is the principal species involved.

Effect of various concentrations of lead nitrate on the induction of micronuclei in mouse bone marrow

The frequency of micronuclei was evaluated in the bone marrow of mice of either sex administered with 0, 0.625, 1.25, 2.5, 5, 10, 20, 40 and 80 mg/kg b.wt of lead nitrate at 12, 24 and 36 h post-treatment. The frequency of micronucleated polychromatic erythrocytes (MPCE) and micronucleated normochromatic erythrocytes (MNCE) increased significantly at 12, 24 and 36 h after treatment with lead nitrate compared to non-drug treated controls. The frequency of micronuclei did not show a dose related increase and the elevation in the frequency of micronuclei was fluctuating type. One important observation which emerged from this study was that the male mice were more sensitive to the induction of micronuclei compared to female mice. This was evidenced by higher frequencies of MPCE in males than females at all the doses for all the post-treatment time periods. The lead nitrate treatment resulted in a spurt in the erythropoiesis as is evidenced by a significant increase in the ratios of polychromatic to normochromatic erythrocytes (P/N ratio) compared to non-drug treated controls at 12, 24 and 36 h post-treatment. The P/N ratio was significantly higher in females than males at 12 and 24 h post-treatment.

Increased sister chromatid exchanges in workers exposed to occupational lead and zinc

Sister chromatid exchange (SCE) in blood lymphocytes was determined in 32 male workers occupationally exposed to lead (Pb) and zinc (Zn) and in 20 controls matched for age and smoking habits. Exposed workers have higher SCE mean values than control workers (p < 0.01). In exposed persons, blood Pb concentrations were also significantly higher than controls (p < 0.0001), but the difference between Zn levels in the blood of these groups was not found to be significant (p > 0.05). Our results indicate that Pb may be genotoxic and harmful to human health.

Lead acetate mutagenicity and mutational spectrum in the hypoxanthine guanine phosphoribosyltransferase gene of Chinese hamster ovary K1 cells

The molecular nature of lead-induced mutations was examined in this study to more thoroughly understand lead mutagenesis. Chinese hamster ovary K1 cells were exposed to 0.5-3 mM lead acetate for 24 h. The median lethal dose (LD50) value was 1.5 mM, and the hypoxanthine guanine phosphoribosyltransferase (HPRT) mutant frequency increased linearly as lead concentrations were raised from 0.5 to 1.5 mM. We also amplified the HPRT cDNAs of 56 independent lead-induced mutants by reverse transcriptase-polymerase chain reaction (PCR). Forty-two mutant cDNAs were successfully amplified: 36 mutants had transcripts of normal or slightly smaller than normal size, and six mutants had large deletions. The other 14 mutants whose HPRT cDNA could not be amplified were subjected to genomic-DNA PCR analysis. All of those mutants had one or more exons missing from their genomic HPRT DNA. DNA sequencing of mutant cDNAs showed that 22 had single-base substitutions, four had small alterations, 10 had single-exon deletions, and six were missing two or three exons. Furthermore, DNA sequencing of the HPRT intron-exon boundaries in eight splice mutants revealed that all of them had single-base substitutions in their genomic DNA. G.C base substitutions occurred 3.3-fold more frequently than A.T base substitutions. Similar frequencies were observed for G.C-->A.T, G.C-->T.A, and G.C-->C.G mutations. These results suggest that G.C base pairs may be the primary target sites for lead mutagenesis.