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

Blood concentrations of lead, cadmium, mercury and their association with biomarkers of DNA oxidative damage in preschool children living in an e-waste recycling area

Reactive oxygen species (ROS)-induced DNA damage occurs in heavy metal exposure, but the simultaneous effect on DNA repair is unknown. We investigated the influence of co-exposure of lead (Pb), cadmium (Cd), and mercury (Hg) on 8-hydroxydeoxyguanosine (8-OHdG) and human repair enzyme 8-oxoguanine DNA glycosylase (hOGG1) mRNA levels in exposed children to evaluate the imbalance of DNA damage and repair. Children within the age range of 3-6 years from a primitive electronic waste (e-waste) recycling town were chosen as participants to represent a heavy metal-exposed population. 8-OHdG in the children's urine was assessed for heavy metal-induced oxidative effects, and the hOGG1 mRNA level in their blood represented the DNA repair ability of the children. Among the children surveyed, 88.14% (104/118) had a blood Pb level >5 μg/dL, 22.03% (26/118) had a blood Cd level >1 μg/dL, and 62.11% (59/95) had a blood Hg level >10 μg/dL. Having an e-waste workshop near the house was a risk factor contributing to high blood Pb (r _s  = 0.273, p < 0.01), while Cd and Hg exposure could have come from other contaminant sources. Preschool children of fathers who had a college or university education had significantly lower 8-OHdG levels (median 242.76 ng/g creatinine, range 154.62-407.79 ng/g creatinine) than did children of fathers who had less education (p = 0.035). However, we did not observe a significant difference in the mRNA expression levels of hOGG1 between the different variables. Compared with children having low lead exposure (quartile 1), the children with high Pb exposure (quartiles 2, 3, and 4) had significantly higher 8-OHdG levels (β _Q2 = 0.362, 95% CI 0.111-0.542; β _Q3 = 0.347, 95% CI 0.103-0.531; β _Q4 = 0.314, 95% CI 0.087-0.557). Associations between blood Hg levels and 8-OHdG were less apparent. Compared with low levels of blood Hg (quartile 1), elevated blood Hg levels (quartile 2) were associated with higher 8-OHdG levels (β _Q2 = 0.236, 95% CI 0.039-0.406). Compared with children having low lead exposure (quartile 1), the children with high Pb exposure (quartiles 2, 3, and 4) had significantly higher 8-OHdG levels.

Oxidative DNA damage and oxidative stress in lead-exposed workers

There are many discrepancies among the results of studies on the genotoxicity of lead. The aim of the study was to explore lead-induced DNA damage, including oxidative damage, in relation to oxidative stress intensity parameters and the antioxidant defense system in human leukocytes. The study population consisted of 100 male workers exposed to lead. According to the blood lead (PbB) levels, they were divided into the following three subgroups: a group with PbB of 20-35 μg/dL (low exposure to lead (LE) group), a group with a PbB of 35-50 µg/dL (medium exposure to lead (ME) group), and a group with a PbB of >50 μg/dL (high exposure to lead (HE) group). The control group consisted of 42 healthy males environmentally exposed to lead (PbB < 10 μg/dL). A comet assay was used to measure the DNA damage in leukocytes. We measured the activity of superoxide dismutase (SOD), catalase, glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD), and glutathione-S-transferase (GST) as well as the concentration of malondialdehyde (MDA), and the value of the total antioxidant capacity. The level of PbB was significantly higher in the examined subgroups than in the control group. The percentage of DNA in the tail was significantly higher in the LE, ME, and HE subgroups than in the control group by 10% ( p = 0.001), 15% ( p < 0.001), and 20% ( p < 0.001), respectively. The activity of GR was significantly lower in the LE and ME subgroups than in the control group by 25% ( p = 0.007) and 17% ( p = 0.028), respectively. The activity of G6PD was significantly lower in the ME subgroup by 25% ( p = 0.022), whereas the activity of GST was significantly higher in the HE subgroup by 101% ( p = 0.001) than in the control group. Similarly, the activity of SOD was significantly higher in the LE and ME subgroups by 48% ( p = 0.026) and 34% ( p = 0.002), respectively. The concentration of MDA was significantly higher in the LE, ME, and HE subgroups than in the control group by 43% ( p = 0.016), 57% ( p < 0.001), and 108% ( p < 0.001), respectively. Occupational lead exposure induces DNA damage, including oxidative damage, in human leukocytes. The increase in DNA damage was accompanied by an elevated intensity of oxidative stress.

DNA damage and decreased DNA repair in peripheral blood mononuclear cells in individuals exposed to arsenic and lead in a mining site

The aim of this study was to evaluate DNA damage and the capacity for DNA repair in children exposed to arsenic and lead. During 2006, we studied a total of 85 healthy children (aged 4-11 years) who were residents of Villa de la Paz (community A), Matehuala (community B), and Soledad de Graciano Sanchez (community C) in San Luis Potosi, Mexico. The quantification of arsenic in urine (AsU) and lead in blood (PbB) was performed by atomic absorption spectrophotometry. The alkaline comet assay was used to evaluate DNA damage and DNA repair. The highest levels of AsU and PbB in children were found in community A (44.5 μg/g creatinine for arsenic and 11.4 μg/dL for lead), followed by community B (16.8 μg/g creatinine for arsenic and 7.3 μg/dL for lead) and finally by children living in community C (12.8 μg/g creatinine for arsenic and 5.3 μg/dL for lead). When DNA damage was assessed, children living in community A had the highest DNA damage. Analysis of these same cells 1 h after a challenge with H(2)O(2) 10 μM showed a dramatic increase in DNA damage in the cells of children living in community B and community C, but not in the cells of children living in community A. Moreover, significantly higher levels of DNA damage were observed 3 h after the challenge ended (repair period) in cells from individuals living in community A. Our results show that children exposed to metals might be more susceptible to DNA alterations.

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.

Genotoxicity evaluation in workers occupationally exposed to lead

Lead (Pb) is a widely used heavy metal with a broad industrial usage. Nevertheless, Pb is a serious public health issue as it is one of the most widespread environmental and industrial toxins. The aim of this investigation was to assess the genotoxicity of Pb using the comet assay, micronucleus (MN) and chromosomal aberrations (CA) test. Blood and urinary Pb content, levels of delta-aminolevulinic acid dehydratase in the erythrocytes (E-ALAD) and delta-aminolevulinic acid in urine (U-ALA) were determined. The exposure associated oxidative stress was also studied. The study group comprised of 90 male Pb recovery unit workers and 90 matched controls. The results indicated that the exposed workers had a significantly higher mean comet tail length than that of controls (P<0.05). Analysis of micronuclei in buccal epithelial cells (BEC's) and peripheral blood lymphocytes (PBL) revealed that there was a significant increase in frequency of MN in exposed subjects than controls. The frequency of aberrant metaphases was also found to be significantly elevated in the Pb exposed workers. The levels of antioxidant enzymes were relatively reduced (P>0.05) while the rate of lipid peroxidation was higher in the exposed subjects. Blood and urinary Pb concentrations were found to be higher in exposed workers than in controls. E-ALAD levels were reduced and U-ALA levels were elevated in the exposed subjects in comparison to controls. Results of analysis, taking the confounding factors into consideration provide evidence for the association of Pb exposure and genotoxicity, and predict the increased risk of cancer to the exposed workers. In view of the observed results, it can be strongly concluded that the workers comprise the risk group and adequate safety, precautionary and preventive measures could only minimize exposure and the related health hazards.

Intersex in Littorina littorea and DNA damage in Mytilus edulis as indicators of harbour pollution

Intersex in snails (Littorina littorea) and DNA damage in blue mussels (Mytilus edulis) were analysed to assess how these bio-indicators reflected the level of chemical contamination at two sites in a highly contaminated harbour in Denmark. The comet assay using mussel gill cells was an indicator of exposure to genotoxic chemicals, and the intersex index (ISI) observed in snails was an indicator of exposure to butyltin (BT) compounds. Biota and sediments were analysed for heavy metals (Cd, Cu, Pb and Zn), butyltin compounds (TBT, DBT and MBT), nine PCB congeners and 19 PAH compounds. The biological effects were found to reflect the levels of the chemicals, and it was concluded that intersex in L. littorea and DNA damage in M. edulis can be used as bio-indicators of harbour pollution.

Lead contamination results in late and slowly repairable DNA double-strand breaks and impacts upon the ATM-dependent signaling pathways

Despite a considerable amount of data, evaluation of the potential genotoxicity and cancer proneness of lead compounds remains unclear, probably due to the plethora of experimental procedures, biological endpoints and cellular models used. In parallel, the understanding in DNA damage formation, repair and signaling has considerably progressed all along these last years, notably for DNA double-strand breaks (DSBs). Here, were examined DNA damage formation and repair in human cells exposed to lead nitrate (Pb(NO(3))(2)) and their consequences upon the ATM-dependent stress signaling, cell cycle progression and cell death. As observed with anti-pH2AX immunofluorescence, exposure to Pb(NO(3))(2) results in formation of late DSBs, that would not originate from conversion of nucleotide damage but likely by a direct production of single-strand breaks. Lead contamination inhibits non-homologous end-joining repair process by preventing the DNA-PK kinase activity whereas the MRE11-dependent repair pathway is exacerbated. Lead contamination triggers successive synchronization of cells in G2/M phase in which the RAD51-dependent homologous recombination was found to be activated. Altogether, our findings support that lead contamination generates late unrepairable DSBs that impact upon the ATM-dependent stress signaling pathway by favoring propagation of errors. Such findings should help to consider more carefully the biological action of lead compounds in the frame of public and occupational exposures.

Lead promotes abasic site accumulation and co-mutagenesis in mammalian cells by inhibiting the major abasic endonuclease Ape1

Lead is a widespread environmental toxin, found in contaminated water sources, household paints, and certain occupational settings. Classified as a probable carcinogen by the International Agency for Research on Cancer (IARC), lead promotes mutagenesis when combined with alkylating and oxidizing DNA-damaging agents. We previously reported that lead inhibits the in vitro repair activity of Ape1, the major endonuclease for repairing mutagenic and cytotoxic abasic sites in DNA. We investigated here whether lead targets Ape1 in cultured mammalian cells. We report a concentration-dependent inhibition of apurinic/apyrimidinic (AP) site incision activity of Chinese hamster ovary (CHO) AA8 whole cell extracts by lead. In addition, lead exposure results in a concentration-dependent accumulation of AP sites in the genomic DNA of AA8 cells. An increase in the oxidative base lesion 8-oxoguanine was observed only at high lead levels (500 microM), suggesting that non-specific oxidation plays little role in the production of lead-related AP lesions at physiological metal concentrations--a conclusion corroborated by "thiobarbituric acid reactive substances" assays. Notably, Ape1 overexpression in AA8 (hApe1-3 cell line) abrogated the lead-dependent increase in AP site steady-state levels. Moreover, lead functioned cooperatively to promote a further increase in abasic sites with agents known to generate AP sites in DNA (i.e., methyl methansulfonate (MMS) and hydrogen peroxide (H2O2), but not the DNA crosslinking agent mitomycin C. Hypoxanthine guanine phosphoribosyltransferase (hprt) mutation analysis revealed that, whereas lead alone had no effect on mutation frequencies, mutagenesis increased in MMS treated, and to a greater extent lead/MMS treated, AA8 cells. With the hApe1-3 cell line, the number of mutant colonies in all treatment groups was found to be equal to that of the background level, indicating that Ape1 overexpression reverses MMS- and lead-associated hprt mutagenesis. Our studies in total indicate that Ape1 is a member of an emerging group of DNA surveillance proteins that are inhibited by environmental heavy metals, and suggest an underlying mechanism by which lead promotes co-carcinogenesis.

Lead-induced genotoxicity in lymphocytes from peripheral blood samples of humans: in vitro studies

Lead is a known toxicant that has been implicated in encephalopathy in children and may affect the gastrointestinal and hematopoietic and other systems in adults. In fact, lead has been shown to compete with calcium for entry into the synaptosome and induce toxic effects. The aim of the current study was to evaluate the cytotoxic and genotoxic effects of lead by using lymphocytes from human peripheral blood in vitro. The LC50 for lead nitrate as determined by Trypan blue dye exclusion technique was found to be 3.14 mM. Chromosomal aberration frequency at sublethal doses (1/10 of LC50) as determined by examining the metaphase chromosomes (karyotyping) did not show significant aberrations except for some aneuploidy and about 2-4% gaps, breaks (3-4%), and about 5% satellite associations. However, significant DNA damage was determined by SCGE (Comet assay). The comet tail length proportionately increased with increasing lead nitrate concentration. Thus, Pb can induce single-strand DNA breaks, possibly by competing with metal binding sites.

Evaluating the genotoxic effects of workers exposed to lead using micronucleus assay, comet assay and TCR gene mutation test

To evaluate the genotoxic effects of lead (Pb) exposure, 25 workers in a workplace producing storage battery were monitored for three genetic end-points using micronucleus (MN) assay, comet assay and TCR gene mutation test. Twenty-five controls were matched with workers according to age, gender and smoking. The air Pb concentration in the workplace was 1.26 mg/m(3). All subjects were measured for Pb concentration of blood by atom absorption spectrophotometry. The mean Pb concentration of blood in workers (0.32 mg/l) was significantly higher than that in controls (0.02 mg/l). The results of MN test showed that the mean micronuclei rate (MNR) and mean micronucleated cells rate (MCR) in workers were 9.04+/-1.51 per thousand and 7.76+/-1.23 per thousand, respectively, which were significantly higher than those (2.36+/-0.42 per thousand and 1.92+/-0.31 per thousand) in controls (P<0.01). It was found in the comet assay that the mean tail length (MTL) of 25 workers and 25 controls were 2.42+/-0.09 and 1.02+/-0.08 microm, respectively, there was significant difference between workers and controls for MTL (P<0.01), also the difference of the mean tail moment (MTM) between workers (0.85+/-0.05) and controls (0.30+/-0.09) was very significant (P<0.01). However, in TCR gene mutation assay Mfs-TCR of workers and controls were 1.69+/-0.15 x 10(-4) and 1.74+/-0.17 x 10(-4), respectively, there was no significant difference between workers and controls (P>0.05). The results of our study indicated that the genetic damage was detectable in 25 workers occupationally exposed to lead.

DNA damaging effects of carbofuran and its main metabolites on mice by micronucleus test and single cell gel electrophoresis

The DNA damaging effects of the carbamate pesticide carbofuran and its four metabolites (carbofuranphenol, 3-ketocarbofuran, 3-hydrocarbofuran and nitrosocarbofuran) on mice were evaluated by single cell gel electrophoresis (SCGE) assay and micronucleus test. KM mice were exposed to test compounds with different doses of 0.1, 0.2 and 0.4 mg/kg through intraperitoneal injection two times with an internal of 24 h, and then killed by cervical dislocation 6 h after the second injection. In SCGE assay, isolated mice peripheral blood lymphocytes were employed to determine DNA damaging degree after a 1 h treatment by test compounds and a following electrophoresis. Carbofuran and carbofuranphenol showed negative results in both test and had no obvious toxicity. 3-Hydrocarbofuran and nitrosocarbofuran were positive. 3-Ketocarbofuran could not induce micronucleus formation but caused significant DNA migration in SCGE test. These tests revealed that 3-ketocarbofuran, 3-hydrocarbofuran and nitrosocarbofuran are potential mutagesis and further research is needed.

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).

In vivo genotoxic effect of nickel chloride in mice leukocytes using comet assay

DNA damage induced by nickel chloride (NiCl2) in leucocytes of Swiss albino mice has been studied in vivo. The comet assay or the alkaline single cell gel electrophoresis (SCGE) assay was used to measure the DNA damage. The mice were administered orally with acute doses of 3.4, 6.8, 13.6, 27.2, 54.4 and 108.8 mg/kg body weight (b.wt.) NiCl2. Samples of whole blood were collected at 24, 48 and 72 h, first week and second week post-treatment for alkaline SCGE assay to study single/double strand breaks in DNA. A significant increase in mean comet tail length indicating DNA damage was observed with NiCl2 at 24, 48 and 72 h post-treatment (P<0.05). A gradual decrease in the mean tail length was observed at 72 h post-treatment indicating repair of the damaged DNA. The mean tail length showed a dose-related increase and time dependent decrease after treatment with NiCl2 when compared to controls. The study also confirms that the comet assay is a sensitive and rapid method to detect DNA damage caused by heavy metals like nickel (Ni).

DNA damage in blood cells from children exposed to arsenic and lead in a mining area

In this work, we studied the frequency of DNA damage in children living in Villa de la Paz, Mexico, a mining site contaminated with arsenic and lead. DNA damage in blood cells was assessed using the Comet assay, and the results were compared to those found in children living in a less exposed town (Matehuala). In Villa de la Paz, high concentrations of arsenic and lead in surface soil and household dust were found. All of the soil samples had concentrations above 100 mg/kg of arsenic, and 58% of the samples were higher than 400 mg/kg of lead (these concentrations are used as intervention guidelines by the United States Environmental Protection Agency). In agreement with the environmental results, urinary arsenic in children living in Villa de la Paz (geometric mean 136 microg/g creatinine) was significantly higher than that found in children living in Matehuala (34 microg/g creatinine). Blood lead levels were also significantly higher in children from Villa de la Paz (11.6 microg/dL) than in children from Matehuala (8.3 microg/dL). The results of the Comet assay showed that the tail length and the tail moment in children living in Villa de la Paz were higher than those observed for children in Matehuala (P<0.05). Taking all the data into account, our study has shown increased DNA damage in children exposed to arsenic and lead in the mining site of Villa de la Paz.

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.

In vitro genotoxicity of lead acetate: induction of single and double DNA strand breaks and DNA-protein cross-links

Lead is present in the natural and occupational environment and is reported to interact with DNA, but the mechanism of this interaction is not fully understood. Using the alkaline comet assay we showed that lead acetate at 1-100 microM induced DNA damage in isolated human lymphocytes measured the change in the comet tail length. At 1 and 10 microM we observed an increase in the tail length, whereas at 100 microM a decrease was seen. The former effect could follow from the induction of DNA strand breaks and/or alkali-labile sites (ALS), the latter from the formation of DNA-DNA and/or DNA-protein cross-links. No difference was observed between tail length for the alkaline and pH 12.1 versions of the assay, which indicates that strand breaks and not ALS are responsible for the tail length increase induced by lead. The neutral version of the test revealed that lead acetate induced DNA double-strand breaks at all concentrations tested. The presence of spin traps, 5,5-dimethyl-pyrroline N-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN) did not influence the level of DNA damage induced by lead. Post-treatment of the lead-damaged DNA (at 100 microM treatment concentration) by endonuclease III (Endo III) and formamidopyrimidine-DNA glycosylase (Fpg), enzymes recognizing oxidized DNA bases, as well as 3-methyladenine-DNA glycosylase II, an enzyme recognizing alkylated bases, gave rise to a significant increase in the extent of DNA damage. Proteinase K caused an increase in comet tail length, suggesting that lead acetate might cross-link DNA with nuclear proteins. Vitamin A, E, C, calcium chloride and zinc chloride acted synergistically on DNA damage evoked by lead. The results obtained suggest that lead acetate may induce single-strand breaks (SSB) and double-strand breaks (DSB) in DNA as well as DNA-protein cross-links. The participation of free radicals in DNA-damaging potential of lead is not important and it concerns other reactive species than could be trapped by DMPO or PBN.

In vivo genotoxic effect of potassium dichromate in mice leukocytes using comet assay

Hexavalent chromium is a well-known mutagen and carcinogen. In the present investigation, single-/double-stranded DNA breaks by potassium dichromate (K2Cr2O7) in mice, a sensitive model for genotoxic effects, have been studied in vivo using alkaline single-cell gel electrophoresis (SCGE)/comet assay. Mice were administered orally with a range of doses starting from 0.59 to 76.0 mg/kg body weight of K2Cr2O7 and samples of whole blood were collected at 24, 48, 72, 96 h, week 1 and week 2 post-treatment for alkaline SCGE assay to study DNA damage. The rationale for using leukocytes was to reflect biomarker analysis in humans. Significant increase in mean comet tail length (5.7-24.25 microM) indicating DNA damage was observed at all the doses with K2Cr2O7 when compared with controls (3.26 microM). Maximum increase in mean comet tail length was observed at 9.5 mg/kg body weight at 48 h post-treatment (24.25 microM). The mean comet tail length showed a clear dose-dependent increase from 0.59 to 9.5 mg/kg body weight and a dose-dependent decrease in higher doses (19.0-76.0 mg/kg body weight). A gradual decrease in the tail lengths from 72 h post-treatment was observed by the second week, and values had returned to control levels at all doses, indicating repair of the damaged DNA and/or loss of heavily damaged cells. The study also reveals that comet assay is a sensitive and rapid method for detecting DNA damage caused by heavy metals such as chromium (Cr).