The genetic toxicology of metal compounds: II. Enhancement of ultraviolet light-induced mutagenesis in Escherichia coli WP2

Pulmonary toxicity of silver vapours, nanoparticles and fine dusts: A review

Silver is used in a wide range of products, and during their production and use, humans may be exposed through inhalation. Therefore, it is critical to know the concentration levels at which adverse effects may occur. In rodents, inhalation of silver nanoparticles has resulted in increased silver in the lungs, lymph nodes, liver, kidney, spleen, ovaries, and testes. Reported excretion pathways of pulmonary silver are urinary and faecal excretion. Acute effects in humans of the inhalation of silver include lung failure that involved increased heart rate and decreased arterial blood oxygen pressure. Argyria-a blue-grey discoloration of skin due to deposited silver-was observed after pulmonary exposure in 3 individuals; however, the presence of silver in the discolorations was not tested. Argyria after inhalation seems to be less likely than after oral or dermal exposure. Repeated inhalation findings in rodents have shown effects on lung function, pulmonary inflammation, bile duct hyperplasia, and genotoxicity. In our evaluation, the range of NOAEC values was 0.11-0.75 mg/m³. Silver in the ionic form is likely more toxic than in the nanoparticle form but that difference could reflect their different biokinetics. However, silver nanoparticles and ions have a similar pattern of toxicity, probably reflecting that the effect of silver nanoparticles is primarily mediated by released ions. Concerning genotoxicity studies, we evaluated silver to be positive based on studies in mammalian cells in vitro and in vivo when considering various exposure routes. Carcinogenicity data are absent; therefore, no conclusion can be provided on this endpoint.

Proteomic analysis of beryllium-induced genotoxicity in anEscherichia coli mutant model system

Beryllium is the second lightest metal, has a high melting point and high strength-to-weight ratio, and is chemically stable. These unique chemical characteristics make beryllium metal an ideal choice as a component material for a wide variety of applications in aerospace, defense, nuclear weapons, and industry. However, inhalation of beryllium dust or fumes induces significant health effects, including chronic beryllium disease and lung cancer. In this study, the mutagenicity of beryllium sulfate (BeSO(4)) and the comutagenicity of beryllium with a known mutagen 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) were evaluated using a forward mutant detection system developed in Escherichia coli. In this system, BeSO(4) was shown to be weakly mutagenic alone and significantly enhanced the mutagenicity of MNNG up to 3.5-fold over MNNG alone. Based on these results a proteomic study was conducted to identify the proteins regulated by BeSO(4). Using the techniques of 2-DE and oMALDI-TOF MS, we successfully identified 32 proteins being differentially regulated by beryllium and/or MNNG in the E. coli test system. This is the first study to describe the proteins regulated by beryllium in vitro, and the results suggest several potential pathways for the focus of further research into the mechanisms underlying beryllium-induced genotoxicity.

Current aspects in metal genotoxicity

While carcinogenic metal ions are mostly non-mutagenic in bacteria, different types of cellular damage have been observed in mammalian cells, which may account for their carcinogenic potential. Two modes of action seem to be predominant: the induction of oxidative DNA damage, best established for chromium compounds, and the interaction with DNA repair processes, leading to an enhancement of genotoxicity in combination with a variety of DNA damaging agents. In the case of Cd(II), Ni(II), Co(II), Pb(II) and As(III), DNA repair processes are disturbed at low, non-cytotoxic concentrations of the respective metal compounds. Even though different steps in DNA repair are affected by the diverse metals, one common mechanism might be the competition with essential metal ions.

Effects on enzymes and the genetic apparatus of sheep after administration of samples from industrial emissions

In the present work the influence of the administration of industrial emissions from a zinc and copper plant on aspartate aminotransferase (AST), alanine aminotransferase, gammaglutamyl transferase, creatine phosphokinase (CK), total bilirubin, serum zinc levels and the genetic apparatus was studied on seven ewes. Each animal was given a dose of 31.99 g of emissions per day. The first and the last animals died of zinc intoxication on days 42 and 58, respectively. Significantly increased zincemia could be observed from day 8 of the experiment (P < 0.01). In the enzymes under investigation, the most pronounced effects of the emission were seen in AST and CK activities. In comparison with the starting levels, AST values revealed significant differences on days 37 and 58 (P < 0.05 and P < 0.01, respectively), and CK on day 58 (P < 0.01). Significantly increased bilirubinemia (P < 0.01) could be observed from day 8 of the experiment. In the period prior to the first gavage of emission and day 30 of administration no significant increase of chromosome breaks per cell was observed in the experimental sheep. The genotoxic effect of the emission was also stated on the basis of recombination frequency visualized by means of the sister chromatid exchange test; on day 30, the increase of these disturbances revealed statistical significance (P < 0.01).

Inhibition and induction of SOS responses in Escherichia coli by cobaltous chloride

Mutagenesis induced by several genotoxic agents has been reported to be inhibited by cobaltous chloride. In order to study the effects of this metal in some SOS functions we evaluated mutagenesis, lysogenic induction and phage reactivation in Escherichia coli cells treated with CoCl2. We detected that cobaltous chloride, when present in the plating medium, was able to block mutagenesis and lysogenic induction promoted by UV irradiation. We also found that CoCl2 blocked protein synthesis, so we propose that this effect can be responsible for the antimutagenic and antilysogenic effects of this metal. On the other hand, if the cells were treated for a short period of time with CoCl2, in the absence of Mg, we observed that cobaltous chloride per se was able to promote lysogenic induction as well as to enhance the phage reactivation induced by UV irradiation. We conclude that depending on experimental conditions, cobaltous chloride may act either as an inhibitor or as an inducer of the SOS functions.

The genetic toxicology of cobalt

Genetic and related effects of cobalt compounds are reviewed and discussed with respect to mechanisms. In prokaryotic assays, Co(II) salts generally are nonmutagenic. In Saccharomyces cerevisiae, CoCl2 is mutagenic to mitochondrial genes and weakly mutagenic or nonmutagenic to chromosomal genes. In plants, Co(II) salts induced gene mutations and chromosomal aberrations. In mammalian cells in vitro, Co(II) compounds caused DNA strand breaks, sister-chromatid exchanges and aneuploidy, but not chromosomal aberrations. In two cell lines, CoCl2 was weakly mutagenic. Interestingly, the poorly soluble compound CoS caused DNA strand breaks and morphological transformation of mammalian cell lines. In contrast to its weak clastogenic and mutagenic properties, cobalt(II) exerts pronounced antimutagenicity in bacteria and mostly comutagenic effects in mammalian cells. In Escherichia coli CoCl2 lowered the frequency of mutations induced by MNNG, uv or X rays. In Chinese hamster V79 cells, CoCl2 enhanced the mutagenicity and clastogenicity of uv light but not of gamma rays. Regarding direct genotoxic mechanisms, Co(II) induces the formation of reactive oxygen species when combined with hydrogen peroxide in cell-free systems. At high (i.e., millimolar) concentrations, Co(II) also decreases the fidelity of DNA synthesis. Regarding anti- and co-mutagenic mechanisms, evidence for the interference of Co(II) with DNA repair processes is discussed. These mechanisms are regarded as relevant for the risk assessment of human exposure to cobalt in combination with other agents.

Mutagenicity, carcinogenicity and teratogenicity of cobalt metal and cobalt compounds

Cobalt metal and cobalt compounds are extensively used for the production of high-temperature alloys, diamond tools, cemented carbides and hard metals, for the production of various salts used in electroplating and as catalysts, drying agents in paints, additives in animal feeds and pigments. Cobalt oxides are used not only in the enameling industry and for pigments, but also in catalytic applications. There is no indication that cobalt metal and cobalt compounds constitute a health risk for the general population. Allergic reactions (asthma, contact dermatitis) can be induced by certain cobalt compounds. Interstitial fibrosis has also been observed in workers exposed to high concentrations of dust containing cobalt, tungsten, iron, etc., mainly in the cemented carbides and the diamond-polishing industries. Several experiments have demonstrated that single or repeated injections of cobalt metal powder or some forms of cobalt salt and cobalt oxide may give rise to injection site sarcoma in rats and in rabbits but the human health significance of such data is questionable. Intratracheal administration of a high dose of one type of cobalt oxide induces lung tumors in rats but not in hamsters. In the latter long-term inhalation of cobalt oxide (10 mg/m3) did not increase the incidence of lung cancer. The human data are too limited to assess the potential carcinogenic risk for workers. Co2+ interacts with protein and nucleic acid synthesis and displays only weak mutagenic activity in microorganisms. Some cobalt salts have been reported to enhance morphological transformation of Syrian hamster embryo cells. Cobalt chloride displays some limited mutagenic activity in yeast and some cobalt compounds are able to produce numerical and structural chromosome aberrations in plant cells. Cobalt and its salts appear to be devoid of mutagenic and clastogenic activity in mammalian cells. Cobaltous acetate and cobaltous chloride have not been found to be teratogenic in hamsters and rats respectively.

Genotoxicity of chromium compounds. A review

This article reviews approximately 700 results reported in the literature with 32 chromium compounds assayed in 130 short-term tests, using different targets and/or genetic end-points. The large majority of the results obtained with Cr(VI) compounds were positive, as a function of Cr(VI) solubility and bioavailability to target cells. On the other hand, Cr(III) compounds, although even more reactive than Cr(VI) with purified nucleic acids, did not induce genotoxic effects in the majority of studies using intact cells. Coupled with the findings of metabolic studies, the large data-base generated in short-term test systems provides useful information for predicting and interpreting the peculiar patterns of Cr(VI) carcinogenicity.

Mutagenesis and micronutrients relationship

Several micronutrients have been reported to be mutagenic or co-mutagenic in certain in vitro testing systems. However, micronutrients have not been shown to be mutagenic or co-mutagenic in vivo, or at physiological concentrations in vitro. Most of the mutagenic or co-mutagenic effects of micronutrients observed in vitro can be attributed to their involvement in the generation of oxygen radicals. Many micronutrients have been shown to possess anti-mutagenic or co-antimutagenic activity in vitro and in vivo. This property of micronutrients appears to be linked to their specific and interrelated biochemical functions.

On the mechanism of the comutagenic effect of Cu(II) with ultraviolet light

Although CuCl2 alone is not mutagenic in E. coli or in Chinese hamster cells, exposure of E. coli to CuCl2 during UV-irradiation causes enhancement of UV-mutagenesis. The mechanism for this comutagenic effect appears to be owing to increased DNA damage by the combined treatment of UV and Cu(II) compared with UV or Cu(II) alone. Using a sequencing gel approach, UV alone is found to cause a particular pattern of alkali-labile sites, whereas CuCl2 alone caused few such sites. The combined action of UV + CuCl2 greatly increased the amount of sites over that of UV alone, and caused a change in their pattern. In the presence of high NaCl concentrations, however, Cu(II) is able to induce DNA damage. This latter effect is most likely owing to the formation of hypochlorite ion. The hypothesis that the comutagenic effect of Cu(II) plus UV might be owing to hydroxyl radical formed via a Fenton reaction involving Cu(II) and UV-generated H2O2 was not supported, since no H2O2 is detectable in aqueous medium after UV irradiation, and catalase did not block the DNA damage. These results favor the hypothesis that UV-irradiation of Cu(II) causes a photoactivation, enabling it to generate free radicals, perhaps by reacting with dissolved oxygen.

Comutagenicity and inhibition of DNA repair by metal ions in mammalian cells

Mutagenic and/or carcinogenic metal compounds may act directly by interaction with DNA and/or indirectly by interference with genetic control and repair mechanisms. In a previous report, we investigated the mutagenicity and comutagenicity of nickel(II) in the V79 Chinese hamster HGPRT-assay. Our present findings demonstrate that like nickel(II), chromium(VI) and cadmium(II) are also comutagenic with UV. Furthermore, there is only a weak concordance with comutagenic effects observed in bacterial test systems. In the case of nickel(II), there is a good correlation between comutagenicity and inhibition of DNA repair, as determined by using the nucleoid sedimentation technique with HeLa cells. This inhibition may occur via replacement of other divalent ions essential in repair enzymes.

Cancer risk from inorganics

Inorganic metals and minerals for which there is evidence of carcinogenicity are identified. The risk of cancer from contact with them in the work place, the general environment, and under conditions of clinical (medical) exposure is discussed. The evidence indicates that minerals and metals most often influence cancer development through their action as cocarcinogens. The relationship between the physical form of mineral fibers, smoking and carcinogenic risk is emphasized. Metals are categorized as established (As, Be, Cr, Ni), suspected (Cd, Pb) and possible carcinogens (Table 6), based on the existing in vitro, animal experimental and human epidemiological data. Cancer risk and possible modes of action of elements in each class are discussed. Views on mechanisms that may be responsible for the carcinogenicity of metals are updated and analysed. Some specific examples of cancer risks associated with the clinical use of potentially carcinogenic metals and from radioactive pharmaceuticals used in therapy and diagnosis are presented. Questions are raised as to the effectiveness of conventional dosimetry in accurately measuring risk from radiopharmaceuticals.