Chromosome changes in human lymphocytes after separate and combined treatment with divalent salts of lead, cadmium, and zinc

Safety Assessment of Zinc Salts as Used in Cosmetics

The Expert Panel for Cosmetic Ingredient Safety (Panel) assessed the safety of 27 inorganic and organometallic zinc salts as used in cosmetic formulations; these salts are specifically of the 2+ (II) oxidation state cation of zinc. These ingredients included in this report have various reported functions in cosmetics, including hair conditioning agents, skin conditioning agents, cosmetic astringents, cosmetic biocides, preservatives, oral care agents, buffering agents, bulking agents, chelating agents, and viscosity increasing agents. The Panel reviewed the relevant data for these ingredients, and concluded that these 27 ingredients are safe in cosmetics in the present practices of use and concentration described in this safety assessment when formulated to be non-irritating.

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.

Assessment of abnormal DNA repair responses and genotoxic effects in lead exposed workers

BACKGROUND

One of the main sources of occupational exposure to lead (Pb) in Turkey is in workers of battery industries. Genotoxic studies in human populations exposed to this metal have had conflicting results.

METHODS

Genotoxic effects of Pb were studied in blood cell samples from workers of battery manufactures exposed to Pb compounds by chromosomal aberration (CA) assay and X-ray induced challenge (XRC) assay to assess DNA damage and interference with DNA repair processes after an in vitro exposure of X-ray (1 Gy). The battery manufacturers (n=23) and 23 people who were not occupationally exposed to lead compounds were selected as a control group and classified into categories according to their blood lead levels.

RESULTS

The CA frequencies in the exposed and control group were not significantly different (P>0.05) by conventional CA (CCA) assay, however, the XRC assay demonstrated significantly elevated CAs (P<0.05). Statistically non-significant but reduced DNA repair responses have also been observed in lead exposed workers.

CONCLUSION

The results of this study showed significant increases in the CAs by XRC assay in Pb exposed workers compared to CCA assay. Our data suggests that Pb exposure may cause reduction in DNA repair capacity and these individuals will be more prone to DNA damage. Therefore, preventive measures should be improved against genotoxic risk in workplaces.

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.

Induction of micronuclei in eel (Anguilla anguilla L.) by heavy metals

Micronucleus test was performed in situ on eels (Anguilla anguilla) from river sites with different levels of heavy metal pollution (cadmium and mercury). Cadmium content in eel liver but not micronuclei averages in kidney were associated with cadmium content in sediments. Mercury content in liver was not significantly associated with mercury content in sediments. Both cadmium and mercury induced micronuclei expression in eels when injected, the concentration tested being 1.7 mg metal/kg body weight and the micronuclei induction being 2.64 and 2.35 micronuclei per 1000 cells for cadmium and mercury respectively. It was concluded that these heavy metals are genotoxic for European eel, that eel liver metal content is a sensitive indicator for environmental monitoring of cadmium pollution, and that the micronuclei scores in eels are not a sensitive method to detect heavy metals pollution in freshwater ecosytems.

The genetic effects of environmental lead

This article reviews the effects of lead on genetic systems in the context of lead's various other toxic effects and its abundance and distribution in the environment. Lead is perhaps the longest used and best recognized toxic environmental chemical, yet it continued be used recklessly until only very recently. Lead is thus a lesson in the limitations and strengths of science, human conscience and common sense. Lead has been tested and found to be capable of eliciting a positive response in an extraordinarily wide range of biological and biochemical tests; among them tests for enzyme inhibition, fidelity of DNA synthesis, mutation, chromosome aberrations, cancer and birth defects. It reacts or complexes with many biomolecules and adversely affects the reproductive, nervous, gastrointestinal, immune, renal, cardiovascular, skeletal, muscular and hematopoietic systems as well as developmental processes. It is likely that lead is a selective agent that continues to act on and influence the genetic structure and future evolution of exposed plant and animal populations.

Cadmium chloride induces dose-dependent increases in the frequency of micronuclei in mouse bone marrow

The frequency of micronucleated polychromatic erythrocytes (MPCE) and normochromatic erythrocytes (MNCE) was studied in Swiss albino mice treated with 0, 0.025, 0.05, 0.1, 0.25, 0.5, 1 and 2 mg/kg body weight of cadmium chloride. It was observed that cadmium chloride induced a dose-dependent increase in the frequency of MPCE and MNCE. However, this increase was significant only after treatment with 0.05 mg/kg of CdCl2 (MPCE). The polychromatic and normochromatic erythrocyte ratio (PCE/NCE ratio) declined with the increase in CdCl2 dose and this depletion was dose-dependent. A significant decline was observed only after 0.25 mg/kg CdCl2. The dose-response relationship for all three parameters was linear-quadratic.

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

Cadmium nitrate decreased the viability of Chinese hamster ovary (CHO) cells in a concentration-dependent manner; 50% inhibition (IC50) was achieved at 0.015 mM. In contrast, lead nitrate appeared to be less toxic. Neither cadmium nitrate nor lead nitrate significantly increased frequencies of binucleated CHO cells with micronuclei (MN). However, both cadmium nitrate and lead nitrate could augment sister chromatid exchanges (SCEs). Cadmium nitrate induced SCEs with a potency approximately equal to that of mitomycin C and more than 10 times higher than lead nitrate. Cadmium nitrate also increased chromosome aberrations (CAs), which included breaks, acentrics, interchanges, and dicentrics of chromosomes. In addition, cadmium nitrate induced a decrease in the mitotic index (MI), but lead nitrate increased it. In summary, it appears that both of these two heavy metal salts have cytogenetic toxicities with different degrees of effects on the cytotoxicity, MN, CAs, and SCEs in CHO cells. However, SCE was the most sensitive endpoint for indicating mutagenetic effects of cadmium and lead in the present study.

The genotoxicity of lead

Lead has been tested for genotoxic potential in a range of mutagenicity assays. Such studies report varying effects, and the results are equivocal. The reasons for this may be related to problems of the solubility of many lead compounds, their inability to dissolve in biological fluids, chemical interferences resulting in conflicting observations, the nonspecificity of the assays used, the delivery of toxic doses to specific genetic processes or the mediation of genotoxicity through indirect mechanisms. Occupational and environmental exposures to lead have also been associated with increases in chromosomal damage in humans at moderate to high exposures, although this evidence is contradictory. Where positive findings have been reported, many are related to exposure. The possibility that lead is genotoxic is by no means clear, but evidence is still accumulating.

Synergistic and antagonistic effects on genotoxicity of chemicals commonly found in hazardous waste sites

Synergistic and antagonistic effects on genotoxicity of mixtures of four chemicals; i.e., lead tetraacetate (LTA), arsenic trioxide (ATO), dieldrin (DED), and tetrachloroethylene (TCE), were evaluated by the Tradescantia-micronucleus (Trad-MCN) assay. The chemicals were mixed in ratios of 1:1, 1:2 and 2:1 for mixtures of two chemicals and 1:1:1 each for three chemicals. The concentration of stock solution of these chemicals was around the minimum effective dose (MED) or below the MED for these chemicals as reported by Sandhu et al. (1989). Treatments were applied to plant cuttings by hydroponic uptake of the mixed solutions through the stems of the plant for 30 h followed by fixation of the flower buds in aceto-alcohol (1:3 ratio) without a recovery period. Microslides were prepared for scoring MCN frequencies. Results of two series of repeated experiments indicated that all mixtures of LTA/ATO exhibited antagonistic effects. On the other hand, all mixtures of TCE and DED exhibited synergistic effect. These data indicate that for evaluating biological hazards at chemical waste sites, it is prudent to evaluate the genotoxicity of complex chemical mixtures as these exist in nature because the biological effects based on evaluating individual chemicals may not be true predictors of the interactive effects of the pollutants.

Clastogenicity evaluation of seven chemicals commonly found at hazardous industrial waste sites

7 chemicals commonly found at the industrial waste sites were tested with the Tradescantia-Micronucleus (Trad-MCN) assay to evaluate their clastogenic potential. Chemicals selected from the US EPA Superfund Priority 1 list were: aldrin, arsenic trioxide, 1,2-benz[a, h]anthracene, dieldrin, heptachlor, lead tetraacetate and tetrachloroethylene. Results of repeated tests for clastogenicity yielded the minimum effective dose (MED) for clastogenicity of 0.44 ppm for lead tetraacetate, 1.88 ppm for heptaclor, 3.81 ppm for dieldrin and arsenic trioxide and 1,2-benz[a, h]anthracene yielded positive responses at the MED of 3.96 ppm and 12.50 ppm respectively. Aldrin and tetrachloroethylene were considered to be immiscible with water, and the tests yielded negative responses. Tetrachloroethylene in gaseous state was also used to treat the flower buds. Results of tetrachloroethylene vapor phase treatment yielded a positive response at the MED of 30 ppm/min after a 2-h exposure. 5 chemicals determined to be clastogens by this test were ranked according to their MED in the descending order of potency as follows: lead tetraacetate, heptachlor, dieldrin, arsenic trioxide and 1,2-benz[a, h]anthracene. Results of this study indicate that the Trad-MCN bioassay could be effectively utilized for assessing the potential clastogenicity of the chemicals commonly found at the industrial hazardous waste sites.

Genotoxicity of zinc in 4 short-term mutagenicity assays

The genotoxicity of zinc was examined in 4 short-term mutagenicity assays. Zinc acetate produced dose-related positive responses in the L5178Y mouse lymphoma assay and an in vitro cytogenetic assay with Chinese hamster ovary cells, but was negative in the Salmonella mutation assay and did not induce unscheduled DNA synthesis in primary cultures of rat hepatocytes. Zinc-2,4-pentanedione produced frameshift mutations in Salmonella tester strains TA1538 and TA98, but did not induce unscheduled DNA synthesis in primary cultures of rat hepatocytes. The effect of ligand binding of zinc in the in vitro test systems is discussed.

Embryotoxicity and in vivo cytogenetic changes following maternal exposure to cadmium chloride in mice

Cadmium is a well-known teratogen in laboratory animals and a widespread environmental pollutant. The frequencies of sister chromatid exchanges (SCEs), nucleolar organizing regions (NORs) and chromosomal aberrations were analysed in maternal bone marrow and fetal liver and/or lung cells of mice, following maternal treatment with cadmium chloride, on gestational days 8 through 10. The embryotoxic effects and morphological changes on day 18 fetuses were also studied. Cadmium chloride is readily transferred across the placenta and significant levels were detected in both the placenta and fetus. No significant changes in the frequencies of SCEs or NORs in maternal and fetal cells were observed following exposure to cadmium chloride. Fetal tissues showed mitotic inhibition at the highest dose levels (8.4 and 11.4 mg/kg, b.w.). Maternal treatment with cadmium chloride increased embryonic resorptions and fetal lethality, as well as reduced placental weight; however, it did not produce significant chromosomal changes except at the highest dose level (11.4 mg/kg).

Relationship of embryotoxicity to genotoxicity of lead nitrate in mice

Frequency of sister chromatid exchanges (SCEs), nucleolar organizing regions (NORs) and chromosomal aberrations were analysed, in maternal bone marrow and fetal liver and/or lung cells of ICR Swiss Webster mice, following maternal exposure to lead nitrate on gestational day 9. The number of implantations and morphological changes in day 18 fetuses, following the treatment, were also noted. Chemical analysis of lead in maternal and fetal tissues showed that it is readily transferred across the placenta. Lead caused a moderate, but statistically significant, increase in the frequency of SCEs in maternal bone marrow cells and significant reduction in NORs at the 2 highest dose levels (150 and 200 mg/kg b.w.). Lead treated animals showed several specific chromosomal aberrations, mostly deletions in maternal bone marrow and fetal cells. Aneuploidy was found to be frequently associated with the lowest dose levels of lead nitrate (100 mg/kg). Maternal treatment with lead nitrate also significantly increased embryonic resorptions and reduced placental weights. The results suggest that the embryotoxic effects of lead might be associated with the chromosomal changes.

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.

A comparative analysis of data on the clastogenicity of 951 chemical substances tested in mammalian cell cultures

A literature review was conducted using original papers published during 1964-1985 on the in vitro clastogenicity of chemical substances. Results of tests on 951 chemical substances were abstracted from over 240 reports to form the database. The evaluation of these data relied on each author's original conclusion on a positive or negative outcome. Of these 951 substances, 447 (47%) were consistently positive either with or without activation; 417 (44%) were negative in the direct test but not tested with metabolic activation systems; 4 were negative but tested only with activation; and 30 (3%) were clearly negative both with and without activation. The remaining 53 substances gave variable results when tested under different experimental protocols or in different cell types, but were positive in at least one test. Although discrepant results were found associated with some cell types, the addition of metabolic activation systems tended to eliminate such variability. No one cell appeared to be superior in response to all clastogens. For screening purposes, the choice of cell may thus depend more on the general usefulness and reliability of a cell type than on a strong response to a particular chemical. However, the use of a suitable metabolic activation system does appear to be of critical importance. The concentration at which clastogenic effects were detected varied extensively for different test substances, ranging from a minimum of 4.3 X 10(-8) to 6.9 X 10(2) mM. Possible mechanisms of action for substances active at only high levels are discussed, but no satisfactory explanation is available at this time. The relevance of tests conducted at concentrations high enough to alter significantly the osmolarity and other culture conditions is considered, and caution urged in the interpretation of test results obtained under physiologically stressful conditions. The clastogenic potential was compared quantitatively using an index of effective concentration (D20) and one which estimates the number of cells with exchange aberrations expected per mg/ml (TR) for data obtained by using a uniform protocol and cultures of Chinese hamster lung (CHL) cells. Both values were distributed over a wide range, demonstrating the variety of genotoxic potential in chemicals. In general, a substance which was active at only high concentrations produced fewer exchange-type aberrations. In vivo activity, as measured by tumourigenic effect and formation of micronuclei in bone marrow, tended to be greater for substances with a D20 below 10(-2) mg/ml and a TR value over 10(3).(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of metals on chromosomes of higher organisms

An analysis of the available data on the clastogenic effects of metals and their compounds on higher organisms indicates some general trends. Following chronic exposure to subtoxic doses, a decrease in mitotic frequency and an increase in the number of chromosomal abnormalities are observed. These effects are usually directly proportional to the dose applied and the duration of treatment within the threshold limits. Recovery after acute treatment is inversely related to the dosage. The ultimate expression of the effects depends on certain factors, including the mode and vehicle of administration; the form administered; the test system used; the rate of detoxification, distribution, and retention in the different tissues; and interaction with foreign and endogenous substances as well as the mode of action with the biological macromolecules. In mammals, the clastogenic activity of the metals within each vertical group of the periodic table is directly proportional to the increase in atomic weight, electropositivity, and solubility of the metallic cations in water and lipids, except for Li and Ba. This pattern of inherent cytotoxicity increases with successive periods in the horizontal level. It is enhanced by the formation of covalent and coordinate covalent complexes by heavy metals with the biological macromolecules. In plants, the solubility of the metals in water is of much greater importance. The degree of dissociation of metallic salts and the rate of absorption affect significantly the frequency of chromosomal aberrations. In assessing the effects of environmental metal pollution, the presence of other metals and toxic chemicals and the level of nutrition should be taken into account, since in nature, metals occur in combination and these factors modify the cytotoxic effects to a significant extent.

Transformation of prostatic epithelial cells and fibroblasts with cadmium chloride in vitro

Primary cultures of fibroblasts and epithelial cells were established from rat ventral prostate (RVP), canine (CP), baboon (BP), and human (HP) prostates, and were used in an assay system to evaluate cadmium chloride (CdCl2) cytotoxicity in vitro. Fibroblasts were always more susceptible to CdCl2 cytotoxicity than the epithelial cells of the same species. There was a distinct species variability to CdCl2 cytotoxicity, with RVP cells being greater than 200 times more susceptible than HP. Primary cultures treated with CdCl2 were subcultivated to establish cell lines. Only RVP fibroblast and epithelial cells resulted in permanent cell lines. Two fibroblast and two epithelial cell lines were derived from CdCl2-treated RVP cell cultures. The epithelial cell lines possessed tonofilaments, desmosomes and keratin. All four cell lines were resistant to CdCl2, had different karyotypes and an excess of chromosome 13. These results demonstrate the transforming potential of cadmium on prostate cells. The role of metallothionein and the significance of extra chromosomes 13 are discussed as possible factors of cadmium resistance.