Toxicity and carcinogenicity of nickel compounds

Nickel-induced oxidative stress and effect of antioxidants in human lymphocytes

The purpose of this study was to evaluate the oxidative effect in human lymphocytes after acute nickel (Ni) treatment for 1 h; levels of intracellular reactive oxygen species (ROS), lipid peroxidation (LPO) and hydroxyl radicals ((*)OH) were examined in isolated lymphocytes. The potential effects of antioxidants were also examined. After acute treatment, NiCl(2) (0-10 mM) significantly decreased the viability of lymphocytes. NiCl(2) appear to increase the degree of dichlorofluorescein (DCF) fluorescence and the levels of thiobarbituric acid-reactive substances (TBARS) in human lymphocytes in vitro in a concentration-dependent manner. The level of (*)OH was quantified by two main hydroxylated derivates, 2,3- and 2,5-dihydroxybenzate (DHB). Levels of 2,3- and 2,5-DHB were significantly higher in the Ni-treated group than in controls. Catalase partially reduced the NiCl(2)-induced elevation of oxidants and TBARS, whereas superoxide dismutase (SOD) enhanced the level of oxidants and TBARS. Both NiCl(2)-induced fluorescence and LPO were prevented significantly by glutathione (GSH) and mannitol. NiCl(2)-induced increase in generation of (*)OH was prevented significantly by catalase, GSH and mannitol, but not by SOD. These results suggest that NiCl(2)-induced lymphocyte toxicity may be mediated by oxygen radical intermediates, for which the accelerated generation of (*)OH may plays an important role in Ni-induced oxidative damage of human lymphocytes. Catalase, GSH and mannitol each provides protection against the oxidative stress induced by Ni.

High nuclearity nickel compounds with three, four or five metal atoms showing antibacterial activity

The effect on DNA and the antibacterial activity of a series of high nuclearity nickel compounds with three, four and five metal atoms were examined. The compounds have a mixed ligand composition with salicylhydroxamic acid and di-2-pyridyl-ketonoxime as chelate agents. In the trinuclear compound Ni(3)(shi)(2)(Hpko)(2)(py)(2)(1), two metal ions show a square planar geometry while the third one is in an octahedral environment. The compounds with four and five nickel atoms construct metallacrown cores with two distinct connectivities. The tetranuclear vacant metallacrown [12-MC(Ni(II)N(Hshi)2(pko)2)-4](2+) shows the connectivity pattern [-O-Ni-O-N-Ni-N-](2), while the pentanuclear ([Ni(II)][12-MC(Ni(II)N(shi)2(pko)2)-4])(2+) follows the pattern [-Ni-O-N-](4). Two distinct arrangements of the chelates around the ring metal ions were observed; a 6-5-6-5-6-5-6-5 arrangement for the [12-MC(Ni(II)N(Hshi)2(pko)2)-4] core and a 6-6-5-5-6-6-5-5 arrangement for the [12-MC(Ni(II)N(shi)2(pko)2)-4] core. Magnetic variable temperature susceptibility study of the trinuclear compound revealed the presence of one paramagnetic nickel(II) ion with strong crystal field dependence, with D=5.0(4) cm(-1), g(xy)=2.7(3) and g(z)=2.3(3). The effect of the synthesized Ni(II) complexes on the integrity and electrophoretic mobility of nucleic acids was examined. Only compounds 2, 3 and 4 altered the mobility of pDNA, forming high molecular weight concatamers at low concentrations or precipitates at higher concentrations. Antibacterial activity screening of the above compounds suggests that nickel compounds 2, 3 and 4 were the most active and can act as potent antibacterial agents.

Nickel-induced plasma lipid peroxidation and effect of antioxidants in human blood: involvement hydroxyl radical formation and depletion of alpha-tocopherol

To provide evidence for the oxidative effect of nickel (Ni) treatment on blood, lipid peroxidation (LPO) and hydroxyl radical (*OH) generation were examined in human plasma. Nickel chloride induced LPO in plasma of human blood in vitro in a concentration-dependent (0-10 mM) and time-dependent (0-2 h) manner. The *OH production in plasma was quantified by measurement of conversion of salicylic acid (SA) into its hydroxylated products, 2,3- and 2,5-dihydroxybenzoate (DHB). The concentrations of 2,3- and 2,5-DHB in plasma increased in a concentration-dependent manner after Ni treatment for 1 h. Furthermore, a decreasing trend in alpha-tocopherol levels in plasma was observed after Ni treatment. Concurrent incubation with gluthathione (GSH), catechin (CTCH), and mannitol decreased lipid peroxidation and reduced *OH formation induced by Ni, but exacerbation of the decrease of alpha-tocopherol in plasma occurred with catechin.

Nickel essentiality, toxicity, and carcinogenicity

The increasing utilization of heavy metals in modern industries leads to an increase in the environmental burden. Nickel represents a good example of a metal whose use is widening in modern technologies. As the result of accelerated consumption of nickel-containing products nickel compounds are released to the environment at all stages of production and utilization. Their accumulation in the environment may represent a serious hazard to human health. Among the known health related effects of nickel are skin allergies, lung fibrosis, variable degrees of kidney and cardiovascular system poisoning and stimulation of neoplastic transformation. The mechanism of the latter effect is not known and is the subject of detailed investigation. This review provides an analysis of the current state in the field.

Localization of metallic ions with gingival fibroblast subcellular fractions

Nickel-based alloys have been in use since the 1930s; however, there are concerns regarding the release of metal ions (Be(+2), Cr(+6), Cr(+3), Ni(+2), Mo(+6)) from these alloys into surrounding tissues. Therefore, the objective of this study was to determine the cellular location and accumulation of ions using atomic absorption spectroscopy and correlate location with the cytotoxic, morphologic, and ultrastructural evaluations reported previously. Human gingival fibroblasts were exposed to the metal ions for 72 h. Controlled atomic absorption spectroscopy studies were used to determine the intracellular location of these ions reported as parts per million metal ions per milligram protein. Enzymatic markers were shown to correspond to the appropriate fraction indicating success in fractionation of the gingival fibroblasts. These results correspond with the cytotoxic, morphologic, and ultrastructural alterations reported previously for fibroblasts exposed to these ions. The highest concentration of beryllium ions occurred in the low-density molecule fraction, where lipofuscin granules were found, which has been shown to contain metal ions. The highest concentrations of hexavalent chromium ions occurred in the plasma membrane and nuclear fractions followed by the mitochondria fraction, which is supported by the ions' ability to oxidize to trivalent chromium accumulating at the membrane as well as the alterations in nuclear and mitochondrial function. For trivalent chromium, the highest concentrations occurred in the low-density molecule and the plasma membrane fractions, which correlates with the ions' inability to readily cross membranes. The highest concentration of molybdenum ions occurred in the plasma membrane fraction correlating with alterations in membrane morphology and increased numbers of myelin figures. The highest concentration of nickel ions was associated with the cytosol fraction where lipid droplets seen in the transmission electron micrographs were located. The current study demonstrates that a successful subcellular fractionation was obtained on gingival fibroblasts and that the location of metallic ions within the fractions correlated with cellular alterations reported previously.

Detection of DNA strand breaks, DNA-protein crosslinks, and telomerase activity in nickel-transformed BALB/c-3T3 cells

Although nickel compounds are known carcinogens, the underlying carcinogenic mechanisms are not fully understood. The objective of this research was to determine if the genotoxic lesions of DNA strand breaks and DNA-protein crosslinks are present in nickel-transformed BALB/c-3T3 cells, and to further elucidate the potential carcinogenesis of insoluble and soluble nickel compounds through telomerase activity in nickel-transformed BALB/c-3T3 cell lines. DNA strand breaks, DNA-protein crosslinks and telomerase activity were investigated by single cell gel electrophoresis (comet assay), (125)I-postlabelling techniques, and the TRAP-silver staining assay, respectively. Results showed that both DNA strand breaks and DNA-protein crosslinks were present in nickel-transformed BALB/c-3T3 cells. However, the highest levels of DNA strand breaks and DNA-protein crosslinks were found in insoluble crystalline NiS-transformed cells and high levels of DNA strand breaks and DNA-protein crosslinks were also found in the transformed cells induced by two water-soluble NiCl(2) and NiSO(4) at moderate concentrations of cytotoxicity. These data suggest that these two genetic endpoints are useful biomarkers and are associated with cell transformation and carcinogensis of insoluble and soluble nickel compounds. Also, we found that the crystalline NiS- and NiCl(2)-transformed cells possessed a high telomerase activity. A weak telomerase was found in NiSO(4)-transformed cells. The results seem to indicate that in addition to crystalline NiS, some water-soluble nickel compounds such as NiCl(2) are also highly carcinogenic. These results may partly explain the cell transformation and relative carcinogenic potency of insoluble crystalline NiS, soluble NiCl(2), and NiSO(4).

Relating nickel-induced tissue inflammation to nickel release in vivo

Nickel has a number of adverse biological effects that have made the use of nickel in biomedical implants controversial. Yet information about the distribution of nickel in tissues around nickel-containing implants is scarce. The purpose of the current study was to use a laser ablation technique, combined with inductively coupled mass spectroscopy, to assess the spatial distribution of nickel around nickel-containing implants in vivo. Polyethylene, pure nickel wire, or a nickel-containing alloy (Ni-Cr) were implanted subcutaneously into rats for 7 days. The tissues were analyzed for Ni content and inflammation at 1-mm intervals up to 5 mm away from the implants. The sham surgery sites and the polyethylene caused mild to moderate inflammation 1-2 mm from the implant site with no detectable nickel in the tissue. The nickel wire caused severe inflammation up to 5 mm away from the implant site with necrosis for 1 mm around the implant. Nickel concentrations reached 48 microg/g near the implants, falling exponentially to undetectable levels at 3-4 mm from the implants. The Ni-Cr wire caused inflammation equivalent to polyethylene, with less than 4 microg/g of nickel present in the tissue for 1-2 mm around the implants. The current study showed that the laser-ablation technique was well suited for the analysis of soft tissues for metal-ion content, and that the nickel distribution in tissues correlated well with overt tissue inflammation.

Nickel requires hypoxia-inducible factor-1 alpha, not redox signaling, to induce plasminogen activator inhibitor-1

Human epidemiological and animal studies have associated inhalation of nickel dusts with an increased incidence of pulmonary fibrosis. At the cellular level, particulate nickel subsulfide inhibits fibrinolysis by transcriptionally inducing expression of plasminogen activator inhibitor (PAI)-1, an inhibitor of the urokinase-type plasminogen activator. Because nickel is known to mimic hypoxia, the present study examined whether nickel transcriptionally activates PAI-1 through the hypoxia-inducible factor (HIF)-1 alpha signaling pathway. The involvement of the NADPH oxidase complex, reactive oxygen species, and kinases in mediating nickel-induced HIF-1 alpha signaling was also investigated. Addition of nickel to BEAS-2B human airway epithelial cells increased HIF-1 alpha protein levels and elevated PAI-1 mRNA levels. Pretreatment of cells with the extracellular signal-regulated kinase inhibitor U-0126 partially blocked HIF-1 alpha protein and PAI-1 mRNA levels induced by nickel, whereas antioxidants and NADPH oxidase inhibitors had no effect. Pretreating cells with antisense, but not sense, oligonucleotides to HIF-1 alpha mRNA abolished nickel-stimulated increases in PAI-1 mRNA. These data indicate that signaling through extracellular signal-regulated kinase and HIF-1 alpha is required for nickel-induced transcriptional activation of PAI-1.

Specific amino acids moderate the effects on Ni2+ on the testosterone production of mouse leydig cells in vitro

The purpose of this investigation was to study the effectiveness of two nickel-binding amino acids, histidine (His) and cysteine (Cys), to prevent the inhibitory action of Ni2+ on testosterone (T) production by mouse primary Leydig cell culture. The maximal human chorionic gonadotropin (hCG)-stimulated T response was measured by radioimmunoassay (RIA) in the culture media. Three types of experiments were performed. In a concentration-response study, Ni2+ (62.5 to 1,000 microM) was added to the cells simultaneously with equimolar or twice the equimolar concentrations of His or Cys and the cultures were maintained for 48 h. Nickel-induced reduction in T production was completely prevented by equimolar concentrations of His at Ni2+ concentrations of 125, 250, and 500 microM; equimolar or twice the equimolar concentrations of His were only partially effective at 1,000 microM Ni2+. Protective action of Cys was complete only at the lowest concentration of Ni2+ (125 microM). In a second series, the cells were incubated for various times (0.5 to 48 h) with 1,000 microM Ni2+ in the presence of 2,000 microM His or Cys. Increasing the time of incubation, the protective effect of both amino acids against Ni2+ was reduced. In a third series, attempts were made to reverse the action of 1,000 microM Ni2+ after incubation with cells for various times (0.5 to 24 h), followed by exposure to 2,000 microM His or Cys. Cell cultures were maintained for 48 h. A partial recovery of hCG-stimulated T production could be observed only if the amino acid was added not later than 4 h after the metal. This time was also required to elicit the T depression produced by Ni2+. Administration of either His or Cys at later times had no effect. Our results show that both His and Cys are able to moderate the effects of Ni2+ on Leydig cell T production, depending on the concentration of this metal ion, as well as on amino acid. However, at higher Ni2+ concentrations the complete protection by His or Cys is only temporary. Administration of these amino acids after the Ni2+-produced decrease in T production was not able to reverse the process.

DNA-protein crosslinks induced by nickel compounds in isolated rat lymphocytes: role of reactive oxygen species and specific amino acids

Isolated rat lymphocytes in salts-glucose medium (pH 7.2) were incubated with nickel chloride, nickel acetate, nickel sulfate, and a soluble form of nickel subsulfide (0-2 mM) at 37 degrees C for 2 h. The soluble form of nickel subsulfide induced a significant increase in DNA-protein crosslinks (DPXLs) (111%) beginning at 0.5 mM and a maximum increase of 700% from that of the control value was reached at a 2 mM concentration, whereas nickel sulfate produced only a 65% increase of such crosslinks at the 2 mM concentration only. No significant reduction in viability of rat lymphocytes (as measured by trypan blue exclusion) due to these nickel compounds was observed at any concentration used. Time-course studies of DPXLs and cellular viability due to 2 mM nickel subsulfide indicate that DPXL formation may not be due in part to cellular necrosis. Coincubation of nickel subsulfide (2 mM) with l-histidine (16 mM), l-cysteine (4 or 8 mM), or l-aspartic acid (24 mM) significantly reduced the DPXLs induced by 2 mM nickel subsulfide. But Mg(2+) even at 24 mM failed to antagonize nickel subsulfide-induced increase in DPXLs. High concentrations of these amino acids significantly decreased the accumulation of Ni(2+) from nickel subsulfide in lymphocytes, suggesting that such reduction of cellular uptake of Ni(2+) by these amino acids is partly responsible for the potent protective effects of these amino acids against such genotoxicity of nickel subsulfide. In vitro exposure of lymphocytes to nickel subsulfide (0-2 mM) increased the formation of reactive oxygen species (ROS) in a concentration-dependent manner. Furthermore, coincubation of 2 mM nickel subsulfide with catalase, dimethylthiourea, mannitol, or vitamin C at 37 degrees C for 2 h resulted in a significant decrease of nickel subsulfide-induced formation of DPXLs, suggesting that nickel subsulfide-induced DPXLs formation in isolated rat lymphocytes is caused by the formation of ROS. The amino acid treatment also abrogated Ni(3)S(2)-induced generation of ROS. Deferoxamine (a highly specific iron chelator) treatment prevented nickel subsulfide-induced DNA-protein crosslink formation, suggesting that Ni(2+)-induced DPXL formation in rat lymphocytes is caused by the induction of Fenton/Haber-Weiss reaction, generating hydroxyl radicals. The potent protective effects of these specific amino acids against nickel subsulfide-induced DPXL formation in isolated rat lymphocytes may be due in part to impaired cellular uptake of Ni(2+), inhibition of the binding of Ni(2+) to deproteinized DNA, and a reduction in reactive oxygen species.

The effects of sulfhydryl blockers and metal ions on nickel accumulation by rat primary hepatocyte cultures

Previously, we found that nickel (Ni) accumulation by rat hepatocytes involves Ca channel transport processes. However, other mechanisms responsible for Ni accumulation are still unclear. Therefore, in the present study we examined the effects of sulfhydryl (SH) blockers on Ni accumulation by hepatocytes. Hepatocytes were exposed to various concentrations of N-ethylmaleimide (NEM) (0.5, 1 or 2 mM) or monoiodoacetic acid (MIA) (0.1, 0.25 or 0.5 mM), potent blockers of SH ligands, for 30 min and subsequently exposed to 10 microM NiCl(2) for an additional 60 min. Pretreatment with NEM and MIA enhanced the Ni accumulation by hepatocytes to maximum of 156 and 73%, respectively. The effects of essential and nonessential metal ions on Ni accumulation were also investigated. Pretreatment with 10 microM of Cu, Zn, Co, Cd and Mn, decreased Ni accumulation by 46, 30, 20, 18 and 11%, respectively. In contrast, pretreatment with Hg (10 and 20 microM) enhanced the Ni accumulation by almost 81 and 140%, respectively. Furthermore, significant decrease in SH concentration in the hepatocyte membrane was observed by the treatment with NEM, MIA and Hg, but not with Cu, Zn and Cd. These results suggest that Ni accumulation by hepatocytes does not appear to be dependent on the SH carrier-mediated transport processes, and that to block the SH ligands in the plasma membrane may facilitate the Ni crossing of the cell membrane.

Enhancement of 2'-deoxyguanosine hydroxylation and DNA damage by coal and oil fly ash in relation to particulate metal content and availability

Epidemiologic studies have shown causal relationships between air pollution particles and adverse health effects in susceptible subpopulations. Fly ash particles (containing water-soluble and insoluble metals) are a component of ambient air particulate pollution and may contribute to particulate-induced health effects. Some of the pathological effects after inhalation of the particles may be due to reactive oxygen species (ROS) produced by metal-catalyzed reactions. In this investigation, we analyzed emission source particulates oil fly ash (OFA) and coal fly ash (CFA) for metal content and solubility in relation to their ability to induce 2'-deoxyguanosine (dG) hydroxylation and DNA damage as measured by 8-oxo-dG formation by HPLC/UV-electrochemical detection (ECD). Water-soluble vanadium and nickel were present at the highest concentrations, and iron was present in trace amounts in OFA (5.1% V, 1.0% Ni, and 0.4% Fe by weight). In contrast, CFA comprised mostly of water-insoluble aluminosilicates and iron (9.2% Al, 12.2% Si, and 2.8% Fe by weight). As a first approach to gain insight into the mode of action of these particulates, we examined metal species-catalyzed kinetics of dG hydroxylation. Metal species at a concentration of 0.1 mM in the incubation mixture containing 0.1 mM dG under ambient air at room temperature catalyzed maximum 8-oxo-dG formation at 15 min with yields ranging from 0.05 to 0.17%, decreasing in the following order: vanadium(IV) > iron(II) > vanadium(V) > iron(III) > or = nickel(II). Insoluble Fe(III) oxide (Fe(2)O(3)) under similar conditions had no effect. Consistent with these results, OFA rich in vanadium and nickel concentrations showed a dose-dependent increase in the level of dG hydroxylation to 8-oxo-dG formation at particulate concentrations of 0.1-1 mg/mL (p < 0.05). In contrast, CFA with high concentrations of aluminosilicates and iron did not result in a significant increase in the level of 8-oxo-dG over that of the control, i.e., dG (p > 0.05). DMSO, a (*)OH scavenger, inhibited OFA-induced 8-oxo-dG formation, and metal ion chelators, deferoxamine (DFX), DTPA, and ferrozine blocked OFA-induced 8-oxo-dG formation. OFA and CFA induced 8-oxo-dG formation in a pattern similar to that observed for dG hydroxylation when calf thymus DNA was used as a substrate. Treatment of OFA particles with DFX before reacting with DNA or addition of a catalase in the incubation mixture significantly suppressed 8-oxo-dG formation (p < 0.05). These results suggest that metal availability, but not the concentration of metals present in CFA and OFA, is critical in mediating molecular oxygen-dependent dG hydroxylation and DNA base damage.

An investigation of fibroblast mitochondria enzyme activity and respiration in response to metallic ions released from dental alloys

Most cellular functions evaluated for biocompatibility are high-energy processes such as proliferation and therefore are not usually affected before a decrease in energy production is observed. Several studies have shown that metabolic functions are altered at much lower concentrations than several normally used biocompatibility tests such as viability. Therefore, the purpose of this study was to provide an in-depth evaluation of metallic ion effects on mitochondria function and thereby biocompatibility. These studies evaluated the mitochondrial function of human gingival fibroblasts exposed to the salt solutions of ions released from nickel-based dental alloys, particularly beryllium (Be(2+)), chromium (Cr(6+) and Cr(3+)), nickel (Ni(2+)), and molybdenum (Mo(6+)). Mitochondrial function was examined by NADH:CoQ reductase activity, succinate dehydrogenase activity, and oxygen consumption.

Hazard identification and dose response of inhaled nickel-soluble salts

A substantial body of occupational epidemiology data has shown that exposure to mixed soluble and insoluble nickel causes the development of lung and nasal cancer. However, due to coexposure of these populations to soluble and insoluble forms of nickel, and limitations in exposure measurements, the contribution of soluble nickel is difficult to determine. Soluble nickel was negative in an NTP inhalation bioassay, while there was some evidence for tumorigenicity in rats for less soluble nickel oxide, and there was clear evidence for tumorigenicity of insoluble nickel subsulfide in rats. Results of parenteral assays follow a similar pattern, but provide evidence of weak carcinogenicity of soluble nickel. Kinetic factors also indicate that exposure to soluble nickel alone has a low carcinogenic potential. Overall, we conclude that the carcinogenic activity of insoluble nickel compounds should not be used to predict the carcinogenic potential of water-soluble nickel salts. The overall data suggest a nonlinear dose-response relationship for carcinogenicity, but the data are insufficient to determine the doses at which such nonlinearities occur. Under the U.S. EPA's 1996 proposed "Guidelines for Carcinogen Risk Assessment," inhaled soluble nickel compounds would be classified as "cannot be determined," because the existing evidence is composed of conflicting data. A reference concentration of 2 x 10(-4) mg Ni/cu x m was calculated, based on lung fibrosis in male rats observed in the NTP study.

Molecular models in nickel carcinogenesis

Nickel compounds are known human carcinogens, but the exact molecular mechanisms of nickel carcinogenesis are not known. Due to their abundance, histones are likely targets for Ni(II) ions among nuclear macromolecules. This paper reviews our recent studies of peptide and protein models of Ni(II) binding to histones. The results allowed us to propose several mechanisms of Ni(II)-inflicted damage, including nucleobase oxidation and sequence-specific histone hydrolysis. Quantitative estimations of Ni(II) speciation, based on these studies, support the likelihood of Ni(II) binding to histones in vivo, and the protective role of high levels of glutathione. These calculations indicate the importance of histidine in the intracellular Ni(II) speciation.

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.

Role of oxidative stress in nickel chloride-induced cell injury in rat renal cortical slices

Nickel chloride (NiCl2) induced lactate dehydrogenase (LDH) release and lipid peroxidation (LPO) in rat renal cortical slices in vitro in a concentration- (0-2 mM) and time- (0-4 hr) dependent manner, with initial significant LDH release occurring as early as 1 hr, whereas significant increase in LPO started 3 hr after exposure, suggesting that LPO results from renal cell injury. Both NiCl2-induced LDH release and LPO were prevented significantly by glutathione and dithiothreitol, suggesting that NiCl2-induced renal cell injury is dependent on thiols. However, such injury is not dependent solely on thiols, because (a) these thiols failed to inhibit completely the uptake of Ni2+ by the renal cortex, and (b) diethylmaleate pretreatment failed to increase NiCl2-induced cell injury further. Superoxide dismutase partially reduced the NiCl2-induced LDH release without affecting LPO and glutathione, whereas catalase did not affect such LDH release and LPO. Dimethylthiourea and DMSO completely prevented NiCl2-induced LPO, but only partially reduced LDH release. Deferoxamine prevented NiCl2-induced renal cell injury without affecting LPO and without significantly reducing Ni2+ uptake by the renal cortex, suggesting that nickel chelation is not important in such prevention of injury. NiCl2-induced inhibition of para-aminohippurate uptake was prevented significantly by thiols, deferoxamine, and dimethylthiourea. NiCl2-induced loss of cellular glutathione content was prevented significantly by thiols and deferoxamine, but not by superoxide dismutase and dimethylthiourea. These results suggest that LPO was not related to NiCl2-induced lethal renal cell injury, whereas such injury may be caused by the induction of the Fenton reaction, generating hydroxyl radicals.

Vicinal-thiol-containing molecules enhance but mono-thiol-containing molecules reduce nickel-induced DNA strand breaks

Several thiol-containing molecules (TCM) are currently used as antidotes for nickel, and vicinal TCM seem to be more effective in mobilizing tissue nickel than are mono TCM. Using single cell alkaline electrophoresis, we have shown that the vicinal TCM, meso-2, 3-dimercaptosuccinic acid (DMSA), 2,3-dimercaptopropane-1-sulfonate, and 2,3-dimercaptopropanol markedly enhanced, whereas the mono TCM, D-penicillamide, glutathione, beta-mercaptoethanol, and diethyl dithiocarbomate, reduced nickel chloride (Ni)-induced DNA breaks in a human leukemia cell line, NB4 cells. Ni or TCM alone did not induce plasmid DNA breaks in test tubes and neither did Ni plus mono TCM; however, Ni plus vicinal TCM did. Vicinal TCM did, but mono TCM did not generate H(2)O(2) in solution. H(2)O(2) alone did not, but H(2)O(2) plus Ni induced plasmid DNA breaks. Although Ni plus glutathione did not break DNA, Ni plus glutathione plus H(2)O(2) did. The Ni-DMSA-induced DNA breaks in NB4 cells, as well as in plasmids, were completely prevented by d-mannitol or partially prevented by several antioxidants. Therefore, the DNA breaks induced by Ni plus vicinal TCM seem to be due to the complex of Ni with TCM in concert with the H(2)O(2) produced by the vicinal TCM. The results that DMSA at a concentration as low as 5 microM enhanced the Ni-induced DNA breaks suggest a further evaluation of the TCM as nickel chelators is needed.

Effects of metallic ion toxicity on human gingival fibroblasts morphology

Alloys used as implant materials release metal ions to surrounding tissues. Cytotoxic substances attack at the molecular level, and these effects are reflected in the structure of the cells and organelles. The objective of this study was to evaluate the cellular morphology and ultrastructural changes of cultured human gingival fibroblasts to salt solutions of ions (beryllium (Be+2), chromium (Cr+6 and Cr+3), nickel (Ni+2), molybdenum (Mo+6)) which may be released from nickel-chromium dental alloys. The concentrations chosen were based on previously conducted cell culture studies. Fibroblasts were exposed to the different ion concentrations for 24 or 72 h. Cellular morphology and ultrastructural features were examined using scanning electron microscopy and transmission electron microscopy. Ultrastructural alterations observed included irregular shaped nuclei for cells exposed to hexavalent chromium and nickel, pseudopodia for cells exposed to beryllium and molybdenum, and lipid droplet formation in cells exposed to nickel.

DNA fingerprint analysis reveals differences in mutational patterns in experimentally induced rat peritoneal tumors, depending on the type of environmental mutagen

We performed tumor DNA fingerprint analysis using the synthetic minisatellite probe S3315x2 based on the 33.15-repeat unit. The aim of the study was to investigate fingerprinting patterns of peritoneal tumors induced experimentally in Wistar rats by two carcinogens with unknown mechanism of action (crocidolite asbestos and nickel powder) and, as a positive control, benzo[a]pyrene. The carcinogens were administered intraperitoneally into rats. The banding patterns obtained with DNA from 71 peritoneal tumors were compared to the corresponding normal tissues. DNA derived from peritoneal tumors induced by the three carcinogens differed with respect to mutation frequencies and mutation patterns. The mutation frequencies in these tumors, revealed by DNA fingerprinting, were 18.2% for benzo[a]pyrene, 14.8% for crocidolite asbestos, and 40.9% for nickel powder. The alterations detected in the banding pattern of benzo[a]pyrene-induced peritoneal tumors were exclusively additional bands. On the contrary, in the DNA from asbestos-induced peritoneal tumors, only deletions of bands were observed on the autoradiographs. In the DNA from nickel-induced peritoneal tumors, both types of mutations occurred. The different mutation frequencies and mutation patterns appear to discriminate between benzo[a]pyrene, crocidolite asbestos, and nickel powder, and may be related to the mechanisms of action of these compounds.

Nickel enhances telomeric silencing in Saccharomyces cerevisiae

Certain nickel compounds including crystalline nickel sulfide (NiS) and subsulfide (Ni3S2) are potent human and animal carcinogens. In Chinese hamster embryo cells, an X-linked senescence gene was inactivated following nickel-induced DNA methylation. Nickel also induced the inactivation of the gpt reporter gene by chromatin condensation and a DNA methylation process in a transgenic gpt+ Chinese hamster cell line (G12), which is located near a heterochromatic region. To determine if nickel can cause gene silencing independently of DNA methylation, based only on the induction of changes in chromatin structure, we measured its effect on gene silencing in Saccharomyces cerevisiae. Growth of yeast in the presence of nickel chloride repressed a telomeric marker gene (URA3) and resulted in a stable epigenetic switch. This phenomenon was dependent on the number of cell doubling prior to selection and also on the distance of the marker gene from the end of the chromosome. The level of TPE (telomeric position effect) increased linearly with elevations of nickel concentration. Addition of magnesium inhibited this effect, but magnesium did not silence the reporter gene by itself. The level of silencing was also assessed following treatment with other transition metals: cobalt, copper and cadmium. In the sublethal range, cobalt induced similar effects as nickel, while copper and cadmium did not change the basal level of gene expression. Silencing by copper and cadmium were evident only at concentrations of those metals where the viability was very low.

DNA-Protein crosslinks induced by nickel compounds in isolated rat renal cortical cells and its antagonism by specific amino acids and magnesium ion

Suspensions of isolated renal cortical cells in modified Krebs-Henseleit buffer (pH 7.4) were incubated with nickel chloride, nickel acetate, nickel sulfate, and nickel subsulfide (0-2 mM) at 37 degreesC for 2 h. A significant increase (63%) in DNA-protein crosslinks was observed at 2 mM nickel sulfate, whereas nickel subsulfide induced a significant increase in such crosslinks beginning at 0.5 mM concentration and a maximum increase of 200% of the control value reached at 2 mM concentration. No significant reduction in viability of renal cortical cells (as measured by trypan blue exclusion) was observed due to these nickel compounds at any concentration used. In the second series of experiments, coincubation of nickel subsulfide (2 mM) with l-histidine (8 or 16 mM), l-cysteine (4 or 8 mM), or l-aspartic acid (8 or 24 mM) significantly reduced the DNA-protein crosslinks induced by 2 mM nickel subsulfide. Similarly Mg2+ (24 mM), but not Ca2+ (24 mM), was able to antagonize nickel subsulfide-induced increase in DNA-protein crosslinks. High extracellular levels of Mg2+ and these amino acids significantly decreased the accumulation of Ni2+ from nickel subsulfide in renal cortical cells. Furthermore, these amino acids at high concentrations significantly inhibited the binding of Ni2+ from nickel subsulfide to deproteinized DNA from renal cortical cells, whereas such inhibition due to Mg2+ was close to significant (0.1 > p > 0.05). In vitro exposures of renal cortical cells to nickel subsulfide (0-2 mM) increased the formation of reactive oxygen species in concentration-dependent manner. Furthermore, coincubation of 2 mM nickel subsulfide with either catalase, dimethylthiourea, mannitol, or vitamin C at 37 degreesC for 2 h resulted in a significant decrease of nickel subsulfide-induced formation of DNA-protein crosslinks, suggesting that nickel subsulfide-induced DNA-protein crosslink formation in isolated rat renal cortical cells is caused by the formation of reactive oxygen species. The potent protective effects of these specific amino acids and Mg2+ against nickel subsulfide-induced DNA-protein crosslink formation in isolated renal cortical cells are due to reduction of cellular uptake of Ni2+ and inhibition of the binding of Ni2+ to deproteinized DNA.

Evaluations of metabolic activities as biocompatibility tools: a study of individual ions' effects on fibroblasts

OBJECTIVES

Nickel-based dental alloys have been in use since 1930. However, there are concerns regarding the release of metal ions from these alloys to surrounding tissues. Cell culture evaluations can be used to address these concerns and to develop a biocompatibility model by providing a more basic understanding of the metabolic response to individual ions released from dental alloys. This study evaluates the metabolic as well as the morphological response of cultured human gingival fibroblasts to salt solutions of ions which may be released from these alloys; beryllium (Be2+), chromium (Cr6+ and Cr3+), nickel (Ni2+), molybdenum (Mo6+).

METHODS

These evaluations include viability, lysosomal activity, oxygen consumption, membrane integrity, DNA synthesis, RNA synthesis, protein synthesis, intracellular ATP levels, and glucose-6-phosphate dehydrogenase activity. The results of all cell culture evaluations are reported as the concentration (ppm) required to cause a significant change from the controls, as determined by Duncan's multiple comparison test at 0.05 significance level.

RESULTS

While Ni2+ ion solutions altered metabolic functions at 3-30 ppm and Cr3+ and Mo6+ both at 10 and 100 ppm, Cr6+ and Be2+ were the most toxic causing cellular alterations at 0.04-12 ppm.

SIGNIFICANCE

These studies indicated that monitoring metabolic activities may be better than the normally used morphology and viability assays for evaluating biocompatibility.

Multivariate analysis of metal concentration profiles in mushrooms

The present work is an overview of the levels of contamination of 92 macromycetes by 15 metals. Data were collected around Paris (France) in 1989 and 1990. A progressive approach involving the use of univariate followed by multivariate statistical analyses allowed to fully exploit the resulting data matrix. Thus, conclusions regarding the origin of the metals, the toxicological implications and the possible use of mushrooms as environmental markers of pollutions are drawn.

Update on metal content profiles in mushrooms--toxicological implications and tentative approach to the mechanisms of bioaccumulation

Fifteen metals (macroelements, heavy metals and trace elements) have been investigated using inductively coupled plasma-atomic emission spectrometry (ICP-AES) on 92 specimens of mushrooms collected in France, in the Paris region. Their levels and distributions are given. Taking in account the respective contents and bioaccumulation abilities, the data reveal that different mechanisms are involved depending on fungi species and genera besides physicochemical influences. Moreover, they suggest that the different elements might accumulate through various ways that are successively mentioned. Metabolic, toxicological and environmental significances are discussed.

Association between oxidative stress and cytokine production in nickel-treated rats

The aim of this study was to evaluate a possible relationship between lipid peroxidation, cytokine production, such as interleukin-1 (IL-1), tumor necrosis factor alpha (TNF-alpha), and transforming growth factor beta (TGF-beta), and hepatotoxicity of rats after nickel chloride (NiCl2) acute poisoning. Administration of NiCl2 significantly elevated the levels of malondialdehyde (MDA), IL-1, TNF-alpha, and TGF-beta in the serum of rats. The dose-effect relationship for the increase of serum MDA, as observed in the present study, corresponds closely to the increase of IL-1, TNF-alpha, and TGF-beta in serum. Treatment with ascorbic acid (Vit C) significantly lowered the levels of lipid peroxidation, cytokine production, and the activities of alanine transaminase and aspartate transaminase in the serum of the rats given NiCl2. The hepatic toxicity was increased in a dose-dependent manner and corresponds to the increase of serum IL-1, TNF-alpha, and TGF-beta. There was an association between lipid peroxidation and the levels of cytokines in serum of rats after NiCl2 administration. Reactive oxygen species may serve as a mediator of lipid peroxidation and production of cytokines in NiCl2 injection.

Effects of nickel on DNA methyltransferase activity and genomic DNA methylation levels

Methylation of DNA plays an important role in organizing the genome into transcriptionally active and inactive zones. Nickel compounds cause chromatin condensation and DNA methylation in the transgenic gpt+ Chinese hamster cell line (G12). Here we show that nickel is an inhibitor of cytosine 5-methyltransferase activity in vivo and in vitro. In living cells, this inhibition is transient and following a recovery period after nickel treatment, Mtase activity slightly rebounds. Genomic DNA methylation levels are also somewhat decreased following nickel treatment, but with time, there is an elevation of total DNA methylation above basal levels and before any rebound of methyltransferase activity. These results suggest that nickel exposure can elevate total genomic DNA methylation levels even when DNA methyltransferase activity is depressed. These findings may explain the hypermethylation of senescence and tumor suppressor genes found during nickel carcinogenesis and support the model of a direct effect of Ni2+ on chromatin leading to de novo DNA methylation.

Lipid peroxidation in liver of mice administrated with nickel chloride: with special reference to trace elements and antioxidants

The relationship between Ni-induced hepatic lipid peroxidation (LPO) and the concentrations of Ni and trace elements was investigated in male ICR mice. The protective effects of antioxidants were also examined. Hepatic LPO and the concentrations of Ni, Fe, Cu, and Zn in the liver were enhanced after an ip injection of nickel chloride (NiCl2). Dose-response studies were conducted on male mice with different groups being injected with 50, 85, and 170 micromol Ni/kg. LPO increased significantly in a dose-dependent manner. In time-course studies, mice were administrated NiCl2 (170 micromol Ni/kg) and killed at intervals of 6, 12, 24, and 48 h after injection. Both LPO and the accumulation of Ni, Fe, Cu, and Zn in the liver showed a significantly positive time-course relationship after NiCl2 injection. At 1 h and 24 h after a single ip injection of 170 micromol Ni/kg, the mice were given an ip injection of ascorbic acid (vit C), glutathione (GSH), and selenium (Se). Vit C and GSH significantly decreased both the level of hepatic LPO and the concentration of Ni in the liver, but did not decrease the accumulation of Fe, Cu, and Zn. However, LPO in the experimental group of mice was different significantly from that in the control group. In conclusion, the results suggest that Ni-induced hepatic LPO may result from increasing the amounts of Ni, Fe, and Cu, since these elements are involved in the generation of hydroxyl radical by inducing the Fenton reaction, thus instigating the Ni-mediated hepatic LPO. The protective effects of vit C and GSH in hepatic LPO result not only from removing the oxygen reactive species, but also from decreasing the Ni concentration.

Effect of Ni ions on expression of intercellular adhesion molecule 1 by endothelial cells

Previous studies have shown that Ni-based alloys implanted into soft tissues cause an infiltration of inflammatory cells around the implant. This phenomenon is potentially important to dental alloys which are adjacent to oral tissues. To help define the mechanisms by which Ni causes an infiltration of inflammatory cells, we exposed endothelial cells in vitro to Ni ions and measured the expression of intercellular adhesion molecule 1 (ICAM-1). ICAM-1 is known to be involved in the recruitment of inflammatory cells from the bloodstream. We also exposed macrophages to Ni ions to test the hypothesis that Ni might alter cytokine secretion and subsequently cause expression of ICAM-1 on endothelial cells. The results showed that Ni ions could promote the expression of ICAM-1 on endothelial cells, but only at concentrations which were high enough (850 mumol/L for 24 h) to suppress cell metabolic activity. Although we had previous evidence that Ni could cause macrophages to secrete cytokines such as interleukin 1 beta, Ni-exposed macrophage supernatants did not induce expression of ICAM-1 on endothelial cells at concentrations subtoxic to the macrophages (85 mumol/L). At subtoxic concentrations, Ni ions were able to suppress ICAM-1 expression on endothelial cells which were stimulated with lipopolysaccharide. Thus, Ni ions either promoted or suppressed the expression of ICAM-1 depending on their concentration. This dual action of Ni ions may be important in vivo where a gradient of concentrations of released ions is likely to exist around the implanted biomaterial. Further studies are necessary to determine the effect of time of exposure and the molecular mechanisms of increased ICAM-1 expression.

DNA strand breaks and poly (ADP-ribose) polymerase activation induced by crystalline nickel subsulfide in MRC-5 lung fibroblast cells

Nickel compounds are potent carcinogens. Their carcinogenicity is believed to be associated with their solubility and cellular uptake. In the present study, we assessed the in vitro genotoxic effect of a water-insoluble nickel compound, crystalline nickel subsulfide (alpha-Ni3S2) on human embryo lung fibroblast cell line (MRC-5 cells). DNA strand breaks was evaluated using single cell gel electrophoresis, or comet assay. The alpha-Ni3S2 induction of poly (ADP-ribose) polymerase (PADPRP), a nuclear enzyme associated with DNA damage and repair was also studied. Hydrogen peroxide (H2O2) was used as a reference compound. A dose-response relationship was found between alpha-Ni2S2 concentrations (2.5 micrograms/cm2 to 20 micrograms/cm2) and the comet tail length. The increase of PADPRP activity of alpha-Ni2S2 treated MRC-5 cells was also significant and dose-dependent within the concentration range of 2.5 micrograms/ cm2 to 10 micrograms/cm2. Close associations have been found between the comet length and PADPRP level for H2O2 (r = 0.98) and alpha-Ni3S2 (r = 0.97). These results clearly suggest that alpha-Ni3S2 is a potent agent in inducing DNA strand breaks, which may be closely related to its carcinogenic effects. Data from the present study also suggest that both comet assay and PADPRP determination are sensitive techniques for quantitative evaluation of DNA damage induced by nickel compounds.

Biochemical and clinical aspects of nickel toxicity

Nickel is an important metal in the automobile industry, in electronics, as a catalyst in chemical processes, in nickel-cadmium batteries and accumulators, in many household products, and in cheap jewelry. Almost everyone in the industrially developed countries may be in daily contact with nickel. Cutaneous nickel allergy (contact dermatitis) is very common, as typically 15% to 20% of the population have positive results in epicutaneous testing. Nickel sensitization may be avoided by restricting contact with objects that release nickel ions through sweat on skin. Because nickel is also carcinogenic to man, causing upper respiratory tract and lung malignancies, advanced control of exposure at workplaces is necessary. Control can be accomplished either by measuring the exposure in the occupational environment or through urinary nickel analysis by applying so-called biological monitoring. As covalent nickel adducts have not been found in DNA, the carcinogenic effect of nickel is probably related to its lipid-peroxidation properties, which induce DNA-strand gaps and breaks and DNA-protein crosslinks. The negative effect of nickel ions on glycoprotein metabolism may explain the nephrotoxic effects of excessive exposure.

The detection of pollutant impact in marine environments: condition index, oxidative DNA damage, and their associations with metal bioaccumulation in the Sydney rock oyster Saccostrea commercialis

Specimens of the Sydney rock oyster Saccostrea commercialis were deployed for a 3-month period at control and sewage disturbed marine locations in the Hunter Region, New South Wales, Australia. The DNA damage product,8-hydroxyguanine, was measured by GC/MS-SIM from chromatin extracts of the gill tissues of oysters to assess oxidative damage. The levels ranged from 11.5 to 18.8 modified bases per 10(7) guanine bases. Although the condition indices were significantly different between the Redhead control site (178.3+/-3. 6) and the Burwood sewage disturbed location (140.4+/-4.4), no significant differences in 8-hydroxyguanine concentrations were detected between the sites, and the concentration of 8-hydroxyguanine was not correlated to condition index. However, levels of the DNA base modification were correlated with the concentrations of bioaccumulated lead (r=0.84, P=0.036). This association provides in vivo evidence that the bioaccumulation of lead results in oxidative damage to DNA. An additional control and sewage disturbed site were included to investigate the relationship between heavy metal bioaccumulation and the condition index of deployed oysters. After the 3-month deployment period, the condition index was negatively correlated to concentrations of bioaccumulated mercury (r=-0.80, P<0.001), cobalt (r=-0.65, P<0.01), and nickel (r=-0.69, P<0.01), suggesting a strong negative influence of these metals at relatively low concentrations on the physiological condition of the oysters.

Interlaboratory validation of a new assay for DNA-protein crosslinks

In 1992, a simple and sensitive assay for detecting DNA-protein crosslinks was developed [1]. In an effort to facilitate the greater use of the assay, a number of studies were conducted to evaluate its reliability and reproducibility. During this work, the assay was used to assess whether various metals and other compounds could induce crosslinks in cultured human lymphocytes (Epstein-Barr virus-transformed Burkitt's Lymphoma cell line). Potassium permanganate, mercury chloride, lead nitrate, magnesium perchlorate, aluminum chloride, and cadmium chloride did not induce DNA-protein crosslinks at either cytotoxic or non-cytotoxic levels. Copper sulfate, arsenic trioxide, and potassium chromate induced DNA-protein crosslinks only at cytotoxic concentrations. Acute lethality of the cells was assessed immediately after exposure to metals by trypan blue exclusion while long-term lethality was assessed by cell proliferation and trypan blue exclusion following an incubation period of 5 days after exposure to the metal compound. All metals exhibited more toxicity in the long-term lethality assay compared to the short-term assay. The cultured human lymphocytes treated with various doses of lead acetate, cadmium chloride, arsenic trioxide and copper sulfate, as well as cis-platinum and chromate, were sent to four different laboratories to compare the reliability and reproducibility of the DNA-protein crosslink assay. Depending on the chemical studied, there were quantitative differences in the results observed among the various laboratories using the assay. However, all laboratories generally showed that cis-platinum, chromate, arsenic trioxide and copper sulfate induced DNA-protein crosslinks at levels that produced acute cytotoxicity, whereas cadmium chloride and lead acetate did not.

In vitro biocompatibility, mechanical properties, and corrosion resistance of Ti-Zr-Nb-Ta-Pd and Ti-Sn-Nb-Ta-Pd alloys

There is much discussion about the toxic effect of vanadium and aluminum contained in Ti-6Al-4V alloy for prosthetic implants. The goal of the present investigation was to develop new titanium alloys with sufficient mechanical properties using more biocompatible alloying elements: zirconium, tin, niobium, tantalum, and palladium. The relative growth rates of L929 and MC3T3-E1 cells were significantly higher when cultured with the extraction of Ti-10Zr-8Nb-2Ta-0.2Pd or Ti-15Zr-4Nb-2Ta-0.2Pd alloys than when cultured with the extraction of Ti-6Al-4AV ELI alloy. The tensile strength, elongation, and reduction of area for Ti-15Sn-4Nb-2Ta-0.2Pd alloy were 989 MPa, 14.4%, and 49.3%, respectively, surpassing Ti-6Al-4V ELI alloy. (ASTM F138-84); those for Ti-15Zr-4Nb-2Ta-0.2Pd alloy were 725 MPa, 23.6% and 54.9%, respectively. More than 15% addition of tin as well as zirconium deteriorated the tensile properties. Titanium release into a 5% hydrochloric acid solution from the new titanium alloys was 20-50 micrograms/cm2 per day, though that from Ti-6Al-4V ELI alloy was 1300 micrograms/cm2 per day. The optimum alloy compositions are Ti-15Zr-4Nb-2Ta-0.2Pd and Ti-15Sn-4Nb-2Ta-0.2Pd, judging from cytocompatibility, corrosion resistance, and mechanical properties. The former is characterized by its higher level cytocompatibility and corrosion resistance, while the latter is characterized by mechanical properties.

Study on DNA-protein crosslinks induced by chromate and nickel compounds in vivo with 125I-postlabelling assay

In an attempt to develop biomarkers of chromate and nickel exposure, we have used a rapid, simple and sensitive 125I-postlabelling assay to detect the formation of DNA-protein crosslinks (DPCs) in different tissues from male Sprague-Dawley rats exposed i.p. to potassium chromate (K2CrO4) and nickel chloride (NiCl2). The results demonstrated that 20 h after rats were injected i.p. with these agents, DPCs were observed in WBC, liver and kidney of rats treated with K2CrO4 in doses ranging from 10 to 40 mg/kg body wt. There was a dose-dependent relationship between chromate exposure and DPCs in WBC and liver, but no DPC increase was shown in lung. In the same way, DPCs were found in WBC and lung of rats treated with NiCl2 in doses ranging from 10 to 30 mg/kg in a dose-dependent manner. The formation of DPCs in different tissues was also observed following repeated exposure of rats to K2CrO4 and NiCl2 (10 mg/kg, i.p.) for 3 weeks. These results were similar with the single dose. It is indicated that chromate and nickel compounds possibly cause DNA or protein damage to form DPCs, suggesting DPCs might be useful as a biomarker for quantitative K2CrO4 and NiCl2 exposure and genotoxic lesions. In addition, WBC were shown to be more sensitive to chromate(VI) and nickel(II) induced DPCs than other targets. There were significant correlations between DPCs induced by K2CrO4 in WBC and liver, and by NiCl2 generated DPCs in WBC and lung, indicating that DPCs in WBC may be a good surrogate for some internal organs of humans exposed to chromate(VI) and nickel(II) compounds.

HPLC investigation on Ni(II)-mediated DNA damage in the presence of t-butyl hydroperoxide and glutathione

By use of HPLC with UV and electrochemical detection, the present study demonstrates that reaction of Ni2+ with t-butyl hydroperoxide in the presence of glutathioine (GSH) generates 8-hydroxy-2'-deoxyguanosine (8-OH-dG) from 2'-deoxyguanosine (dG) and from dG residues in calf thymus DNA at physiological pH. No significant amount of 8-OH-dG was generated in the absence of GSH, indicating an important role of GSH in enhancing the reactivity of Ni2+ toward lipid hydroperoxide to oxidize dG or dG residues in DNA. The rate of dG conversion to 8-OH-dG depends on the concentration of the reagents. During a two hour incubation of 0.75 mM dG, 10 mM t-butyl hydroperoxide, 1 mM Ni2+, and 2 mM GSH at room temperature under ambient air, dG was converted to 8-OH-dG with a yield of about 0.2%. For dG residues in DNA, 24 hour incubation at 37 degrees C yielded 0.1% 8-OH-dG. The 8-OH-dG generation from both dG and dG residues in DNA was inhibited by superoxide dismutase, catalase, and ethanol (hydroxyl radical scavenger), implying the involvement of oxygen free radicals in the 8-OH-dG generation process. The metal ion chelators, deferoxamine and EDTA, efficiently inhibited the 8-OH-dG formation. Similar results were obtained for the conversion of dG residues in calf thymus DNA to 8-OH-dG. Electrophoretic assays of DNA strand breaks showed that Ni2+ caused DNA double-strand breaks in the presence of t-butyl hydroperoxide and GSH. Because GSH is ubiquitously present in cellular systems at relatively high concentration, and the exposure of cells to Ni2+ results in the generation of lipid hydroperoxides, the 8-OH-dG generation and DNA double-strand breaks caused by the reaction of Ni2+ with lipid hydroperoxides in the presence of GSH may be an important mechanism in Ni(2+)-induced carcinogenesis. The inhibitory effect of chelators suggests a possible prevention strategy against Ni(2+)-induced toxicity and carcinogenesis.

A single stranded DNA binding protein isolated from HeLa cells facilitates Ni2+ activation of DNA polymerases in vitro

The divalent nickel ion (Ni2+) is one of several metal ions that can substitute for Mg2+ in the activation of DNA polymerases in vitro, but usually with very low efficiency. We have purified and partially characterized a Ni(2+)-binding protein (p40) from HeLa cell extracts that can specifically enhance the polymerase activity of DNA polymerase alpha (pol alpha) and other DNA polymerases in response to Ni2+. This protein, with a molecular mass of 40 kDa, is a single stranded DNA binding protein that binds to a M13 DNA template-primer with an optimum stoichiometry of approximately 90 equiv of protein per equiv of DNA template and enhances the affinity of pol alpha for the primer-template. In the presence of Ni2+, p40 exhibits an increased affinity for DNA. The p40 increased by 3- to 6-fold the rates at which pol alpha and the Klenow fragment of Escherichia coli DNA polymerase I (KF) replicate different DNA templates in response to Ni2+. The low processivity of Ni(2+)-activated pol on primed M13 ssDNA was also enhanced by the presence of p40. The rates of Ni(2+)-dependent replication by inherently more processive enzymes, DNA polymerase delta and T4 DNA polymerase, were not significantly increased by p40 when M13 ssDNA was used as a template; however, p40 did increase the activity of T4 polymerase on an activated calf thymus DNA template. The protein did not stimulate Mg(2+)-activated DNA replication.

Elevated serum nickel concentration in psoriasis vulgaris

BACKGROUND

Psoriasis vulgaris is a common skin disease afflicting 1-3% of the American population. Its pathogenesis remains unknown despite concerted research efforts. Our purpose was to study baseline serum nickel concentrations in psoriasis vulgaris subjects and in healthy control subjects.

METHODS

Sixteen psoriasis vulgaris subjects with active disease (in 14 of moderate to marked severity), and 11 age- and sex-matched healthy control subjects were studied. Serum nickel determinations were performed using electrothermal atomic absorption spectrophotometry (ETAAS).

RESULTS

Despite the relatively small sample size, significant elevation of mean serum nickel concentration was found in the psoriasis group compared to the control group (P = 0.019).

CONCLUSIONS

Recognition of abnormal nickel homeostasis could point the way to greater understanding of the primary biochemical defect in the psoriatic process. Alternatively, this finding may mark an association without pathogenic significance. Further investigation is needed.

Effect of nickel(II) and tetraglycine on hydroxylation of the guanine moiety in 2'-deoxyguanosine, DNA, and nucleohistone by hydrogen peroxide

The purpose of this study was to determine whether the Ni(II)-tetraglycine complex system (NiG4) that is known to disproportionate H2O2 at pH > or = 8 can catalyze oxidation of the guanine residues in 2'-deoxyguanosine (dG), calf thymus DNA, and calf thymus nucleohistone (NH) by H2O2 at physiological pH. Incubation of dG with H2O2 in the presence of NiG4 at 37 degrees C, produced two effects: (a) formation of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) and (b) decomposition of dG to 2,6-diamino-4-hydroxy-5-formamidopyrimidine and several low molecular weight unidentified products. The magnitude of both effects depended on incubation time (1-48 h), H2O2 concentration (7.5-40 mM), NiG4 concentration (0.1 or 1 mM), and pH (6.0-8.0). The effects were not detected below pH 6 and above pH 8.0. For 0.1 mM NiG4 and 7.5 mM H2O2, production of 8-OH-dG from dG (0.75 mM) during 24 h at 37 degrees C was significantly lower than from NH (1 mg/ml) or DNA (0.5 mg/ml), indicating possible specific effects that might be related to the strength of interaction of NiG4 with dG, NH, or DNA. The results indicate production of hydroxyl radical or other oxidizing species in the reaction of H2O2 with NiG4 at pH 7-8. Reactions like this may be relevant to the mechanisms of Ni(II)-mediated oxidative damage, observed in vitro and in vivo, which may contribute to the toxic and carcinogenic effects of this metal.

Molecular mechanisms of nickel carcinogenesis

Nickel treatment of intact cultured cells oxidized dichlorofluorescin to a fluorescent product indicating that nickel elevated the level of oxidants in cells. Nickel also caused an increase in crosslinking of amino acids to DNA and these complexes did not appear to involve the direct participation of Ni2+. Histidine, cysteine and tyrosine were prominent among the amino acids crosslinked to DNA. Nickel selectively damaged heterochromatin and this resulted in deletions of heterochromatic regions during nickel carcinogenesis. Thrombospondin was one of the genes expressed in normal cells that was not expressed in nickel-transformed cells. Other aspects of the molecular mechanism of nickel carcinogenesis are discussed.

Interactions of alpha Ni3S2 with guinea pig alveolar macrophages and liberation of inflammatory mediators

Our previous investigation presented evidence of interaction between alpha Ni3S2 and membranous and cellular lipids of lung cells, resulting in significant increases in linoleic, linolenic and arachidonic acids. The present work was designed to follow the metabolic fate of arachidonic acid in alpha Ni3S2-exposed guinea pig alveolar macrophages (GPAM) in culture (50 microM alpha Ni3S2 for 3 days). The metabolites of arachidonic acid were assessed by HPLC coupled with UV or electrochemical detection. The concentrations of malondialdehyde (MDA), hydroxyeicosatetraenoic acid (HETE), leukotrienes (LT) and reduced glutathione (GSH) were measured. In exposed cells a significant increase of MDA, a breakdown product of lipid peroxidation, was observed. In addition, the enzymatic reduction of 5-hydroperoxyeicosatetraenoic acid (5-HPETE) by the associated oxidation of GSH to GSSG increased 5-HETE in GPAM cells and decreased GSH. 5-Hydroperoxyeicosatetraenoic acid was furthermore converted to epoxides, such as leukotriene A4, and we also quantified in exposed cells a significant increase of its subsequent catabolites LTB4, LTC4 and LTE4. Direct measurements of MDA and other metabolites of arachidonic acid clearly show that exposure of GPAM cells to alpha Ni3S2 enhances lipid peroxidation. This lipid peroxidation is an autocatalytic free-radical process and could be responsible for DNA damage. Furthermore, alpha Ni3S2 intoxication induces the release of proinflammatory products, such as leukotrienes, and the decrease of glutathione.

In vitro effects of metal ions on cellular metabolism and the correlation between these effects and the uptake of the ions

The effects of Ag+1, Au+3, Cd+2, Cu+2, Ga+3, In+3, Ni+2, Pd+2, and Zn+2 on DNA synthesis, protein synthesis, succinic dehydrogenase activity, and total cellular protein of mammalian fibroblasts were measured for exposures less than 12 h. The rates at which these cellular functions responded to metal ion exposure were compared and related to the uptake rate of the ions into the cells. These rates of response were significantly different: DNA synthesis decreased the fastest, followed by protein synthesis, succinic dehydrogenase activity, and total protein. This order of response was similar for most metal ions. At 4 h, the rate of uptake of the metal ions correlated most closely with depression of succinic dehydrogenase activity, whereas at 8 h, the uptake correlated most closely with depression of protein synthesis. The similar response of cells to all metal ions may imply that these ions act on cells by similar mechanisms. The rates of uptake of Ag+1, Cu+2, and Zn+2 were sufficiently fast that in vivo exposures of tissues to these metals for periods less than 12 h would be capable of disrupting cellular metabolism.

Effect of Ni(II) on tissue hydrogen peroxide content in mice as inferred from glutathione and glutathione disulfide measurements

Studies on Ni(II)-induced carcinogenesis have suggested that oxidative damage caused by Ni(II) may in part be due to increased tissue H2O2 formation. However, there is lack of evidence in vivo. Because of limitations of available methods for direct measurement of the in vivo rate of H2O2 formation in animals, Ni(II)-induced production of H2O2 was estimated from changes in the rate of glutathione disulfide (GSSG) formation. Male B6C3F1 mice (6-8 wk old) were injected i.p. with 170 mumol NiAc2/kg. Biliary efflux and liver, kidney, and lung levels of glutathione (GSH and GSSG) were determined 0-2 h after treatment. In spite of slight increases in tissue GSSG levels by Ni(II), there was no significant change in the biliary efflux of GSSG. Pretreatment with 50 mg/kg (i.p.) of bis-chloroethyl-nitrosourea (BCNU), an inhibitor of GSSG reductase, did not augment the effects of Ni(II) on GSSG formation significantly. Based on these observations, it was apparent that Ni(II) did not change the concentration of H2O2 significantly in vivo.

Transformation of rat tracheal epithelial cells to immortal growth variants by particulate and soluble nickel compounds

The cytotoxicity and transforming activity of nickel subsulfide, nickel oxide and nickel sulfate was studied by assays of colony-forming efficiency and of transformation of rat tracheal epithelial (RTE) cells to enhanced growth variants (EGVs) and immortal growth variants (IGVs). Nickel subsulfide caused dose-dependent cytotoxicity between 1 and 5 micrograms/ml, whereas the cytotoxic range of nickel oxide and nickel sulfate was 50-200 micrograms/ml and 60-130 micrograms/ml, respectively. At lower concentrations, nickel sulfate caused modest (up to 126%) growth stimulation. During the initial 24-h treatment period, internalized nickel subsulfide particles were observed in phagocytic vesicles in cells near the periphery of all RTE cell colonies, whereas nickel oxide particles were not internalized but had adhered to both the cells and the tissue culture dish. After 7-10 days of the transformation assay, nickel subsulfide particles were no longer visible, but nickel oxide particles remained on the dish for the duration of the 5 week assay. During weeks 3-5 of the transformation assay, internalized nickel oxide particles were observed in non-vacuolated cells at the periphery of the colonies. All 3 nickel compounds significantly (p < 0.05) increased the transformation frequency of RTE cells to EGVs at moderately cytotoxic concentrations; the order of potency was Ni3S2 > NiO = NiSO4. MNNG, the positive control, was twice as active as nickel subsulfide at 1/3 the concentration and 1/6 the duration of treatment. EGVs induced by MNNG, nickel subsulfide and nickel sulfate were cloned and converted to IGVs at frequencies of 44, 24 and 43%, respectively. In contrast, EGVs transformed by nickel oxide rarely converted to IGVs (13%). All nickel-induced IGVs were immunohistochemically epithelial, mitotically active, aneuploid and exhibited high plating efficiencies. Our results suggest that respiratory epithelial cells are targets for the transforming capabilities of several nickel compounds but that the potency and mechanism of transformation by various forms of nickel may be different according to the physico-chemical properties of each compound.

Generation of free radicals in reactions of Ni(II)-thiol complexes with molecular oxygen and model lipid hydroperoxides

The generation of free radicals from reactions of nickel(II)-thiol complexes with molecular oxygen and model lipid hydroperoxides was investigated by electron spin resonance (ESR) utilizing 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap. Incubation of nickel(II) [Ni(II)] with cysteine in an aerobic environment generated hydroxyl (.OH) radical, which then reacted with cysteine to generate a carbon-centered alkyl (.R) radical. Radical generation was inhibited under a nitrogen atmosphere. Model lipid hydroperoxides, cumene hydroperoxide, and t-butyl hydroperoxide enhanced the yield of these radicals and also generated an alkoxyl (.OR) radical. Radical yield decreased by approximately half under a nitrogen atmosphere. Although histidine did not cause radical formation in the reaction between Ni(II) and cumene hydroperoxide under aerobic conditions, the addition of histidine to a mixture containing Ni(II), cysteine, and cumene hydroperoxide under the same experimental conditions increased the yield of .R radical but lowered the yield of .OR and .OH radical adducts. It thus appears that histidine caused the .OH attack to be more site-specific. Similar results were obtained utilizing t-butyl hydroperoxide. Penicillamine or N-acetylcysteine yielded similar results except that under aerobic conditions, reaction between Ni(II) and N-acetylcysteine without hydroperoxide did not generate a significant concentration of free radicals. Under the same experimental conditions, cystine did not generate any detectable free radicals, suggesting an important role of the -SH group in Ni(II)-mediated free radical generation. The results indicate that free radical generation from the reaction of Ni(II)-thiol complexes and molecular oxygen, and/or lipid hydroperoxides, may play an important role in the mechanism(s) of Ni(II) toxicity and carcinogenesis.

Bulky DNA-adduct formation induced by Ni(II) in vitro and in vivo as assayed by 32P-postlabeling

Various small oxidation products (e.g. 8-hydroxydeoxyguanosine) can be induced in DNA by nickel compounds. In this study, the 32P-postlabeling assay was applied to determine whether Ni(II) compounds are able to induce bulky DNA-adduct formation in vitro and in vivo. In vitro studies detected two major and several minor adducts in DNA incubated with NiCl2 and H2O2 at 37 degrees C for 1 h. Formation of the two major adducts increased with incubation time (0-24 h) and NiCl2 concentration (0-800 microM). Adduct levels were greatly reduced by hydroxyl free-radical scavengers, i.e. 0.4 M sodium formate or 0.05 M p-nitrosodimethylaniline, and by a singlet oxygen scavenger, 0.05 M sodium azide. The in vitro effects of NiCl2 on DNA were significantly enhanced by (1) addition of 3 mM ascorbic acid, (2) replacement of H2O with D2O in the reaction, and (3) prior denaturation of DNA. Adduct formation presumably involved a Fenton-type reaction, in which DNA crosslinks may arise by reaction with hydroxyl free radicals and singlet oxygen. For in vivo studies, male 6-8 wk old B6C3F1 mice were used. In untreated mice, several I-compounds (putative indigenous DNA modifications that increase with age) were detected in liver, kidney, and lung. Two of these (spots 1 and 2) were chromatographically identical to the two major spots induced by Ni(II) in vitro. The intensities of spots 1 and 2 in kidney and of some other spots in liver and lung were increased 1 and 2 h after i.p. injection with a single dose of 170 mumols/kg NiAc2. The effects of NiAc2 were reduced or undetectable in the three tissues 24 h after treatment. These observations indicate the capacity of Ni(II) to induce and modulate bulky DNA modifications both in vitro and in vivo.

Responses of hepatic xenobiotic metabolizing enzymes of mouse, rat and guinea-pig to nickel

The effects of nickel (Ni) on hepatic monooxygenase activities (aniline 4-hydroxylase, AH; ethylmorphine N-demethylase, EMND; aminopyrine N-demethylase, AMND), cytochrome P-450, cytochrome b5, microsomal haem and reduced glutathione (GSH) levels, and glutathione S-transferase (GST) activities toward several substrates (1, chloro-2-4-dinitrobenzene, CDNB; 1,2 dichloro-4-nitrobenzene, DCNB; ethacrynic acid, EAA) in mice, rats and guinea-pigs were studied. Ni (59.50 mg NiCl2.6H2O/kg, subcutaneously) was administered to the animals 16 hr prior to sacrifice. Ni significantly inhibited AH, EMND, AMND activities, and decreased cytochrome P-450, cytochrome b5 (except in the livers of rats), and microsomal haem levels in the livers of all the animal species examined. However, the depressions were more profound in livers of mice than in those of the other two species. The hepatic GSH level was significantly inhibited in mice whereas no alteration was observed in rats. In guinea-pigs, the hepatic GSH level was significantly increased by Ni. The hepatic GST activity toward the substrate CDNB was significantly depressed in mice, unaltered in rats and significantly increased in guinea-pigs by Ni. The hepatic GST activity toward DCNB was significantly inhibited in mice whereas no significant alteration was observed in rats. In guinea-pigs, Ni caused significant increase in hepatic GST activity for DCNB. However, hepatic GST activity toward EAA was significantly inhibited in mice whereas significantly increased in rats and guinea-pigs. These results seem to indicate that i) there exists quantitative, but not qualitative, differences among the hepatic monooxygenases of rodents in response to Ni, mice being more sensitive than rats and guinea-pigs, ii) the influence of Ni on hepatic GSH level varies depending on the animal species and iii) the hepatic GSTs of rodents are differentially regulated by Ni.