Nickel chloride inhibits the DNA repair of UV-treated but not methyl methanesulfonate-treated Chinese hamster ovary cells

Nickel Carcinogenesis Mechanism: DNA Damage

Nickel (Ni) is known to be a major carcinogenic heavy metal. Occupational and environmental exposure to Ni has been implicated in human lung and nasal cancers. Currently, the molecular mechanisms of Ni carcinogenicity remain unclear, but studies have shown that Ni-caused DNA damage is an important carcinogenic mechanism. Therefore, we conducted a literature search of DNA damage associated with Ni exposure and summarized known Ni-caused DNA damage effects. In vitro and vivo studies demonstrated that Ni can induce DNA damage through direct DNA binding and reactive oxygen species (ROS) stimulation. Ni can also repress the DNA damage repair systems, including direct reversal, nucleotide repair (NER), base excision repair (BER), mismatch repair (MMR), homologous-recombination repair (HR), and nonhomologous end-joining (NHEJ) repair pathways. The repression of DNA repair is through direct enzyme inhibition and the downregulation of DNA repair molecule expression. Up to now, the exact mechanisms of DNA damage caused by Ni and Ni compounds remain unclear. Revealing the mechanisms of DNA damage from Ni exposure may contribute to the development of preventive strategies in Ni carcinogenicity.

Toxic effect of NiCl2 on development of the bursa of Fabricius in broiler chickens

This study was conducted with objective of evaluating the toxic effects of nickel chloride (NiCl₂) on development of bursa of Fabricius in broilers fed on diets supplemented with 0, 300, 600 and 900 mg/kg of NiCl₂ for 42 days by using the methods of experimental pathology, flow cytometry (FCM), and quantitative real-time polymerase chain reaction (qRT-PCR). The results showed that dietary NiCl₂ in 300 mg/kg and over induced toxic suppression in the bursal development, which was characterized by decreasing lymphocytes histopathologically and relative weight, increasing G₀/G₁ phase (a prolonged nondividing state), reducing S phase (DNA replication) and proliferating index, and increasing percentages of apoptotic cells. Concurrently, the mRNA expression levels of bax, cytochrome c (cyt c), apoptotic peptidase activating factor 1 (Apaf-1), caspase-3, caspase-6, caspase-7 and caspase-9 were increased and the bcl-2 mRNA expression levels were decreased. The toxic suppression of bursal development finally impaired humoral immunity duo to the reduction of B lymphocyte population and B lymphocyte activity in the broiler chicken. This study provides new evidences for further studying the effect mechanism of Ni and Ni compoundson B-cell or bursa of Fabricius.

The association between splenocyte apoptosis and alterations of Bax, Bcl-2 and caspase-3 mRNA expression, and oxidative stress induced by dietary nickel chloride in broilers

Two hundred and forty avian broilers were equally divided into four groups, and raised with a corn-soybean basal diet or the same diet supplemented with 300, 600, 900 mg/kg NiCl₂ for 42 days. Numbers or percentages of apoptotic splenocytes by flow cytometry (FCM) and TUNEL were higher (p < 0.05 or p < 0.01) in the 300, 600 and 900 mg/kg groups than those in the control group. Results measured by qRT-PCR and ELISA showed that mRNA expression and contents were significantly higher (p < 0.05 or p < 0.01) in Bax and Caspase-3, and were significantly lower (p < 0.05 or p < 0.01) in Bcl-2 of the 300, 600 and 900 mg/kg groups. Also, the SOD, CAT and GSH-Px activities, and the ability to inhibit hydroxyl radical, and GSH contents were significantly decreased (p < 0.05 or p < 0.01), and MDA contents were increased (p < 0.05 or p < 0.01) in all groups. In conclusion, dietary NiCl₂ in excess of 300 mg/kg caused apoptosis, altered Bax, Bcl-2 and Caspase-3 mRNA expression levels and contents, and induced oxidative stress in the spleen. Also, splenocyte apoptosis was closely related to the alternations of Bax, Bcl-2 and Caspase-3 mRNA expression, and oxidative damage. The splenic immunity and blood filtration functions were impaired in broilers.

Role of DNA polymerase beta in the genotoxicity of arsenic

Arsenic, an important hazard in the environment, is associated with human cancer and other degenerative diseases. However, the mechanisms underlying arsenic hazardous effects remain unclear. It has been reported arsenic exposure can result in increased cellular reactive oxygen species and oxidative DNA damage. This suggests DNA base excision repair (BER), the major pathway for repairing oxidative DNA damage, may be involved in combating arsenic hazardous effects. As a critical repair enzyme in BER, DNA polymerase beta (Pol β) might play an essential role in reducing arsenic toxicity. To test this hypothesis, we evaluated arsenic-induced cytotoxic and genotoxic effects under Pol β deficiency. Our results demonstrated that the viability of Pol β-deficient mouse embryonic fibroblasts was much lower than that of Pol β wild-type cells after treatment with arsenite (As(3+) ). An increased level of DNA damage and significantly delayed arsenite-induced DNA damage repair in Pol β-deficient cells indicated reduced repair of DNA lesions under Pol β deficiency. This was consistent with the increase in the frequency of micronuclei (MN), an indicator of chromosomal breakage, which was also observed in Pol β-deficient cells treated with arsenite. In contrast, cells harboring overexpressed Pol β resulted in a lower level of DNA damage and MN than Pol β wild-type cells, indicating overexpression of the enzyme can combat arsenic-induced genotoxic effects. In conclusion, our results indicate an important role for Pol β in repairing arsenite-induced DNA damage and maintaining chromosomal integrity and further suggest deficiency of BER may be involved in arsenic genotoxicity and carcinogenicity.

Can human mesenchymal stem cells survive on a NiTi implant material subjected to cyclic loading?

Nickel-titanium shape memory alloys (NiTi-SMAs) exhibit mechanical and chemical properties which make them attractive candidate materials for various types of biomedical applications. However, the high nickel content of NiTi-SMAs may result in adverse tissue reactions, especially when they are considered for load-bearing implants. It is generally assumed that a protective titanium oxide layer separates the metallic alloy from its environment and that this explains the good biocompatibility of NiTi. Cyclic loading may result in failure of the protective oxide layer. The scientific objective of this work was to find out whether cyclic dynamic strain, in a range relevant for orthopedic implants, diminishes the biocompatibility of NiTi-SMAs. In order to analyze the biocompatibility of NiTi-SMA surfaces subjected to cyclic loading, NiTi-SMA tensile specimens were preloaded with mesenchymal stem cells, transferred to a sterile cell culture system and fixed to the pull rods of a tensile testing machine. Eighty-six thousand and four hundred strain cycles at 2% pseudoelastic strain were performed for a period of 24 h or 7 days. Cytokines (IL-6, IL-8 and VEGF) and nickel ion release were determined within the cell culture medium. Adherent cells on the tensile specimens were stained with calcein-AM and propidium iodide to determine cell viability. Dynamic loading of the tensile specimens did not influence the viability of adherent human mesenchymal stem cells (hMSCs) after 24 h or 7 days compared with the non-strained control. Dynamic cycles of loading and unloading did not affect nickel ion release from the tensile specimens. The release of IL-6 from hMSCs cultured under dynamic conditions was significantly higher after mechanical load (873 pg ml(-1)) compared with static conditions (323 pg ml(-1)). The present work demonstrates that a new type of mechanical in vitro cell culture experiment can provide information which previously could only be obtained in large animal experiments.

Nickel-induced apoptosis and relevant signal transduction pathways in Caenorhabditis elegans

Many investigations have shown that nickel exposure can induce micronuclei generation, inhibit DNA repair and induce cell apoptosis, both in cells and tissues. However, there is a lack of appropriate in vivo animal models to study the underlying mechanisms of nickel-induced apoptosis. The model organism, Caenorhabditis elegans, has been shown to be a good model for investigating many biological processes. In the present study, we detected 0.01 mM nickel induced significantly germline cell apoptosis after treatment for 12 hours, which demonstrated that C. elegans could be a mammalian in vivo substitute model to study the mechanisms of apoptosis. Then gene knockout C. elegans strains were utilized to investigate the relationship between nickel-induced apoptosis and relevant signal pathways, which were involved in DNA damage and repair, apoptosis regulation and damage signal transduction. The results presented here demonstrated that nickel-induced apoptosis was independent of the DNA damage response gene, such as hus-1, p53/cep-1 and egl-1. The loss-of-function of the genes that related to Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinases (MAPK) signaling cascades suppressed nickel-induced germline apoptosis, while ERK signaling cascades have no effects on the nickel-induced germline apoptosis.

Urinary porphyrins as biomarkers for arsenic exposure among susceptible populations in Guizhou province, China

Coal is widely used in PR China. Unfortunately, coal from some areas in Guizhou Province contains elevated levels of arsenic. This has caused arsenicosis in individuals who use arsenic-contaminated coal for the purposes of heating, cooking and drying of food in poorly ventilated dwellings. The population at risk has been estimated to be approximately 200,000 people. Clinical symptoms of arsenicosis may include changes of skin pigmentation, hyperkeratosis of hand and feet, skin cancers, liver damage, persistent cough and chronic bronchitis. We analyzed the porphyrin excretion profile using a HPLC method in urine samples collected from 113 villagers who lived in Xing Ren district, a coal-borne arsenicosis endemic area and from 30 villagers from Xing Yi where arsenicosis is not prevalent. Urinary porphyrins were higher in the arsenic exposed group than those in the control group. The correlation between urinary arsenic and porphyrin concentrations demonstrated the effect of arsenic on heme biosynthesis resulting in increased porphyrin excretion. Both uroporphyrin and coproporphyrin III showed significant increases in the excretion profile of the younger age (<20 years) arsenic-exposed group, suggesting that porphyrins could be used as early warning biomarkers of chronic arsenic exposure in humans. Greater increases of urinary arsenic and porphyrins in women, children and older age groups who spend much of their time indoors suggest that they might be at a higher risk. Whether elevated porphyrins could predict adverse health effects associated with both cancer and non-cancer end-points in chronically arsenic-exposed populations need further investigation.

Arsenite induces delayed mutagenesis and transformation in human osteosarcoma cells at extremely low concentrations

Arsenite is a human multisite carcinogen, but its mechanism of action is not known. We recently found that extremely low concentrations (</=0.1 microM) of arsenite transform human osteosarcoma TE85 (HOS) cells to anchorage-independence. In contrast to other carcinogens which transform these cells within days of exposure, almost 8 weeks of arsenite exposure are required for transformation. We decided to reexamine the question of arsenite mutagenicity using chronic exposure in a spontaneous mutagenesis assay we previously developed. Arsenite was able to cause a delayed increase in mutagenesis at extremely low concentrations (</=0.1 microM) in a dose-dependent manner. The increase in mutant frequency occurred after almost 20 generations of growth in arsenite. Transformation required more than 30 generations of continuous exposure. We also found that arsenite induced gene amplification of the dihydrofolate reductase (DHFR) gene in a dose-dependent manner. Since HOS cells are able to methylate arsenite at a very low rate, it was possible that active metabolites such as monomethylarsonous acid (MMA(III)) contributed to the delayed mutagenesis and transformation in these cells. However, when the assay was repeated with MMA(III), we found no significant increase in mutagenesis or transformation, suggesting that arsenite-induced delayed mutagenesis and transformation are not caused by arsenite's metabolites, but by arsenite itself. Our results suggest that long-term exposure to low concentrations of arsenite may affect signaling pathways that result in a progressive genomic instability.

Interactions by carcinogenic metal compounds with DNA repair processes: toxicological implications

Even though compounds of nickel, arsenic, cobalt and cadmium are carcinogenic, their mutagenic potentials are rather weak. In contrast, they exert pronounced comutagenic effects, which may be explained by disturbances of different DNA repair systems. Thus, cobalt, arsenic, nickel and cadmium interfere with base and nucleotide excision repair, even though they affect different steps of the respective repair systems and act by different, not yet completely understood mechanisms. Potential target molecules for some metal ions are so-called zinc finger structures in DNA repair proteins, but each zinc finger protein exerts its own sensitivity towards toxic metal ions. Possible consequences of repair inhibitions are discussed in more detail for soluble and particulate nickel compounds, which have recently been shown to interfere with the repair of stable DNA adducts induced by benzo[a]pyrene (B[a]P). Since nickel compounds and polycyclic aromatic hydrocarbons such as B[a]P are frequently associated in the ambient air, in cigarette smoke and at many workplaces, an impaired removal of B[a]P-derived DNA adducts will lead to persistent DNA damage and thus increase the risk of mutations and tumor formation.

Recent advances in arsenic carcinogenesis: modes of action, animal model systems, and methylated arsenic metabolites

Recent advances in our knowledge of arsenic carcinogenesis include the development of rat or mouse models for all human organs in which inorganic arsenic is known to cause cancer-skin, lung, urinary bladder, liver, and kidney. Tumors can be produced from either promotion of carcinogenesis protocols (mouse skin and lungs, rat bladder, kidney, liver, and thyroid) or from complete carcinogenesis protocols (rat bladder and mouse lung). Experiments with p53(+/-) and K6/ODC transgenic mice administered dimethylarsinic acid or arsenite have shown some degree of carcinogenic, cocarcinogenic, or promotional activity in skin or bladder. At present, with the possible exception of skin, the arsenic carcinogenesis models in wild-type animals are more highly developed than in transgenic mice. Recent advances in arsenic metabolism have suggested that methylation of inorganic arsenic may be a toxification, rather than a detoxification, pathway and that trivalent methylated arsenic metabolites, particularly monomethylarsonous acid and dimethylarsinous acid, have a great deal of biological activity. Accumulating evidence indicates that these trivalent, methylated, and relatively less ionizable arsenic metabolites may be unusually capable of interacting with cellular targets such as proteins and even DNA. In risk assessment of environmental arsenic, it is important to know and to utilize both the mode of carcinogenic action and the shape of the dose-response curve at low environmental arsenic concentrations. Although much progress has been recently made in the area of arsenic's possible mode(s) of carcinogenic action, a scientific concensus has not yet been reached. In this review, nine different possible modes of action of arsenic carcinogenesis are presented and discussed-induced chromosomal abnormalities, oxidative stress, altered DNA repair, altered DNA methylation patterns, altered growth factors, enhanced cell proliferation, promotion/progression, gene amplification, and suppression of p53.

Inhibition of repair of radiation-induced DNA double-strand breaks by nickel and arsenite

The effect of arsenite or nickel on the repair of DNA double-strand breaks (DSBs) was studied in gamma-irradiated Chinese hamster ovary cells using pulsed-field gel electrophoresis. After treatment with nickel chloride or arsenite for 2 h, cells were irradiated with gamma rays at a dose of 40 Gy, and the numbers of DNA DSBs were measured immediately after irradiation as well as at 30 min postirradiation. Both arsenite and nickel(II) inhibited repair of DNA DSBs in a concentration-dependent manner; 0.08 mM arsenite significantly inhibited the rejoining of DSBs, while 76 mM nickel was necessary to observe a clear inhibition. The mean lethal concentrations for the arsenite and nickel(II) treatments were approximately 0.12 and 13 mM, respectively. This indicates that the inhibition of repair by arsenite occurred at a concentration at which appreciable cell survival occurred, but that nickel(II) inhibited repair only at cytotoxic concentrations at which the cells lost their proliferative ability. These novel observations provide insight into the mechanisms underlying the effects of combined exposure to arsenite and ionizing radiation in our environment.

Interaction between NiCl2, and nucleobases, nucleosides and nucleotides

The interaction between NiCl, and nucleobases, nucleosides and nucleotides has been studied by UV-Vis difference spectrophotometry, graphite furnace atomic absorption spectrophotometry, IR spectroscopy and high pressure liquid chromatography using the technique of continuous variation. The proposed structures of the complexes formed were optimised and their electronic and vibrational spectra generated using the molecular modelling program HyperChem 5. Ni2+ reacts with guanine, 2'-dGMP, GMP, adenine and AMP to form 1:1 complexes Ni(Guanine)(H2O)5, Ni(2'-dGMP)(H2O)5, Ni(GMP)(H2O)5, Ni(Adenine)(H2O)5, and Ni(AMP)(H2O)5 respectively. In these complexes, Ni2+ is believed to be bonded to the N7 atom of adenine and guanine.

Nickel subsulfide is similar to potassium dichromate in protecting normal human fibroblasts from the mutagenic effects of benzo[a]pyrene diolepoxide

The cellular response to multiple carcinogen treatment has not been extensively studied, even though the effect of individual carcinogens is, in many cases, well known. We have previously shown that potassium dichromate can protect normal human fibroblasts from the mutagenic effects of benzo[a]pyrene diolepoxide (BPDE), and that this effect may be via an oxidative stress mechanism [Tesfai et al. (1998) Mutat Res 416:159-168]. Here, we extend our previous work by showing that nickel subsulfide can produce the some effect. Normal human fibroblasts, preincubated with nickel subsulfide for 46 hr followed by a coincubation of nickel subsulfide and BPDE for 2 hr, showed a dramatic reduction in the mutant frequency of the hypoxanthine (guanine)phosphoribosyl-transferase (HPRT) gene when compared to cells treated only with BPDE. The preincubation period with nickel subsulfide was necessary to see the antagonistic effect, since it was not observed if the cells were simply incubated with both carcinogens for 2 hr. The extent of the antagonistic effect was nickel subsulfide dose-dependent and also appeared to be species-specific, since the effect was not observed when Chinese hamster fibroblasts were tested. Finally, the antagonistic effect of the nickel subsulfide was eliminated by vitamin E, suggesting that production of reactive oxygen species by the nickel may be required. This data, along with our previous work, suggest that the antagonistic effect we observe is not chromium-specific, and that it could be species-specific.

Magnesium reduces nickel inhibition of DNA polymerization

The activities of DNA polymerization and DNA ligation in extract of Chinese hamster ovary cells were both stimulated by MgCl2. DNA polymerization was stimulated by MgCl2 above 0.25 mM, whereas, MgCl2 above 2 mM was required to stimulate DNA ligation. The activity of DNA polymerization maintained a plateau at MgCl2 1-12 mM, whereas DNA ligation reached a maximal activity at MgCl2 6 mM and decreased thereafter. NiCl2 0.1-0.2 mM also had a stimulatory effect on DNA polymerization, but was much less potent than MgCl2. However, nickel ion (Ni2+) had no detectable stimulating effect on the activity of DNA ligation. In the presence of MgCl2, the activities of DNA polymerization and DNA ligation decreased with increasing concentration of NiCl2. Ni2+ inhibition of DNA polymerization was reduced by increasing the concentration of MgCl2, but increasing the concentration of MgCl2 did not reduce Ni2+ inhibition of DNA ligation. Preincubating cell extract with MgCl2 decreased the Ni2+ inhibition of DNA polymerization but not DNA ligation. These results suggest that Ni2+ may compete with magnesium ion (Mg2+) to reduce DNA polymerization, but this mechanism seems not applicable to Ni2+ inhibition of DNA ligation.

Possible role of oxidative damage in metal-induced carcinogenesis

This review presents and evaluates evidence relevant to the mechanisms of metal carcinogenicity with special emphasis on the emerging hypothesis of the oxidative nature of metals' effect on DNA. The carcinogenic transition metals are capable of in vivo binding with the cell nucleus and causing promutagenic damage that includes DNA base modifications, inter- and intramolecular crosslinking of DNA and proteins, DNA strand breaks, rearrangements, and depurination. The chemistry of that damage and the resulting mutations observed in vitro and in metal-induced tumors are both characteristic for oxidative attack on DNA. The underlying mechanism involves various kinds of active oxygen and other radical species arising from metal-catalyzed redox reactions of O2, H2O2, lipid peroxides, and others, with certain amino acids, peptides, and proteins. Other metal-mediated pathogenic effects, such as enhancement of lipid peroxidation, stimulation of inflammation, inhibition of cellular antioxidant defenses, and inhibition of DNA repair, may also contribute to that mechanism. Thus far, published data revealing the oxidative character of metal-induced promutagenic DNA alterations are particularly strong for two of the most powerful human metal carcinogens, chromium and nickel. However, without excluding contribution of other effects, the promotion of oxidative damage tends to take the leading role in explaining mechanisms of carcinogenicity and acute toxicity of certain other metals as well.

Mechanisms in nickel genotoxicity: the significance of interactions with DNA repair

Even though nickel compounds are strong carcinogens, the underlying mechanism is still unclear. In contrast to their weak mutagenic potential, they enhance the cytotoxicity and genotoxicity of UV light, X-rays and cytostatic agents like cis-platinum, trans-platinum and mitomycin C. Studies in combination with UV light indicate an inhibition of DNA repair, presumably at the incision step of nucleotide excision repair. Possible reasons for repair inhibition are structural changes of the DNA or direct interactions with repair enzymes or proteins, possibly by competition with essential metal ions.

Differential effects of luminol, nickel, and arsenite on the rejoining of ultraviolet light and alkylation-induced DNA breaks

When Chinese hamster ovary cells were treated with ultraviolet (UV) light or methyl methanesulfonate (MMS), a large number of DNA strand breaks could be detected by alkaline elution. These strand breaks gradually disappeared if the treated cells were allowed to recover in a drug-free medium. The presence of nickel or arsenite during the recovery incubation retarded the disappearance of UV-induced strand breaks, whereas the disappearance of MMS-induced strand breaks was retarded by the presence of arsenite or of luminol, a new inhibitor for poly(ADP-ribose) synthetase. Luminol, however, had no apparent effect on the repair of UV-induced DNA strand breaks, and nickel had no effect on the repair of MMS-induced DNA strand breaks. When UV- or MMS-treated cells were incubated in cytosine arabinofuranoside (AraC) plus hydroxyurea (HU), a large amount of low molecular weight DNA was detected by alkaline sucrose sedimentation. The molecular weight of these DNAs increased if the cells were further incubated in a drug-free medium. This rejoining of breaks in cells pretreated with UV plus AraC and HU was inhibited by nickel and by arsenite, but not by luminol. The rejoining of breaks in cells pretreated with MMS plus AraC and HU was inhibited by luminol and by arsenite, but not by nickel. These results suggest that different enzymes may be used in DNA resynthesis and/or ligation during the repairing of UV- and MMS-induced DNA strand breaks, and that nickel, luminol, and arsenite may have differential inhibitory effects on these enzymes.