Comparative inhalation toxicity of nickel sulfate to F344/N rats and B6C3F1 mice exposed for twelve days

Immunotoxicity of nickel: Pathological and toxicological effects

Nickel (Ni) is a widely distributed metal in the environment and an important pollutant because of its many industrial applications. With increasing incidences of Ni contamination, Ni toxicity has become a global public health concern and recent evidence suggests that Ni adversely affects the immune system. Hence, this paper reviews the literature on immune-related effects of Ni exposure, the immunotoxicological effects of Ni, and the underlying mechanism of Ni immunotoxicity. The main focus was on the effect of Ni on the development of organs of immune system, lymphocyte subpopulations, cytokines, immunoglobulins, natural killer (NK) cells, and macrophages. Moreover, Ni toxicity also induces inflammation and several studies demonstrated that Ni could induce immunotoxicity. Excessive Ni exposure can inhibit the development of immune organs by excessively inducing apoptosis and inhibiting proliferation. Furthermore, Ni can decrease T and B lymphocytes, the specific mechanism of which requires further research. The effects of Ni on immunoglobulin A (IgA), IgG, and IgM remain unknown and while Ni inhibited IgA, IgG, and IgM levels in an animal experiment, the opposite result was found in research on humans. Ni inhibits the production of cytokines in non-inflammatory responses. Cytokine levels increased in Ni-induced inflammation responses, and Ni activates inflammation through toll like (TL)4-mediated nuclear factor-κB (NF-κB) and signal transduction cascades mitogen-activated protein kinase (MAPK) pathways. Ni has been indicated to inactivate NK cells and macrophages both in vitro and in vivo. Identifying the mechanisms underlying the Ni-induced immunotoxicity may help to explain the growing risk of infections and cancers in human populations that have been exposed to Ni for a long time. Such knowledge may also help to prevent and treat Ni-related carcinogenicity and toxicology.

Short-term exposure to nickel alters the adult rat brain antioxidant status and the activities of crucial membrane-bound enzymes: neuroprotection by L-cysteine

Nickel (Ni) is an environmental pollutant towards which human exposure can be both occupational (mainly through inhalation) and dietary (through water and food chain-induced bioaccumulation). The aim of this study was to investigate the effects of short-term Ni-administration (as NiCl(2), 13 mg/kg) on the adult rat whole brain total antioxidant status (TAS) and the activities of acetylcholinesterase (AChE), Na(+),K(+)-ATPase, and Mg(2+)-ATPase; in addition, the potential effect of the co-administration of the antioxidant L-cysteine (Cys, 7 mg/kg) on the above parameters was studied. Twenty-eight male Wistar rats were divided into four groups: A (saline-treated control), B (Ni), C (Cys), and D (Ni and Cys). All rats were treated once daily with intraperitoneal injections of the tested compounds, for 1-week. Rats were sacrificed by decapitation and the above-mentioned parameters were measured spectrophotometrically. Rats treated with Ni exhibited a significant reduction in brain TAS (-47%, p < 0.001, BvsA) that was efficiently limited by the co-administration of Cys (-4%, p > 0.05, DvsA; +83%, p < 0.001, DvsB), while Cys (group C) had no effect on TAS. The rat brain AChE activity was found significantly increased by both Ni (+30%, p < 0.001, BvsA) and Cys (+62%, p < 0.001, CvsA), while it tended to adjust to control levels by the co-administration of Ni and Cys (+13%, p < 0.001, DvsA; -13%, p < 0.001, DvsB). The activity of rat brain Na(+),K(+)-ATPase was significantly decreased by Ni-administration (-49%, p < 0.001, BvsA), while Cys supplementation could not reverse this decrease (-44%, p < 0.001, DvsA). The activity of Mg(2+)-ATPase was not affected by Ni-administration (-3%, p > 0.05, BvsA), but was significantly reduced when combined with Cys administration (-17%, p < 0.001, DvsA). The above findings suggest that Ni short-term in vivo administration causes a statistically significant decrease in the rat brain TAS and an increase in AChE activity. Both effects can be, partially or totally, reversed to control levels by Cys co-administration; Cys could thus be considered (for future applications) as a potential neuroprotective agent against chronic exposure to Ni. The activity of Na(+),K(+)-ATPase that was inhibited by Ni, could not be reversed by Cys co-administration. The matter requires further investigation in order to fully elucidate the spectrum of the neurotoxic effects of Ni.

Nickel induced structural and functional alterations in mouse Leydig cells in vitro

The present study was aimed at investigating effects of nickel (NiCl(2)) on secretion of testosterone (T), cell viability, ultrastructure and apoptosis in mouse Leydig cells. Testosterone release was measured after 48h of culture with 15.67, 31.25, 62.5, 125, 250, 500 and 1000μmol/L NiCl(2) or without NiCl(2) using radioimmunoassay. Cell viability was assessed by a MTT (metabolic activity assay). Quantification of apoptotic cells was performed using TUNEL assay and the ultrastructural changes were analyzed using transmission electron microscopy. The viability was decreased after addition of ≥250μmol/L NiCl(2). A concentration-dependent depression of T production was observed. The percentage of apoptotic cells was significantly increased only after addition of 125, 250 and 1000μmol/L NiCl(2). After addition of ≥250μmol/L NiCl(2) higher incidence of euchromatin was observed. Lipid droplets and vacuoles in cytoplasm were increased after addition of ≥125μmol/L NiCl(2). NiCl(2) induced decrease in numbers of mitochondria and smooth endoplasmic reticulum after treatment with ≥500μmol/L NiCl(2). Our findings suggest a negative effect of NiCl(2) on steroidogenesis, viability, apoptosis and ultrastructure of mouse Leydig cells.

Genetic susceptibility to nickel-induced acute lung injury

Human exposure to insoluble and soluble nickel compounds is extensive. Besides wide usage in many industries, nickel compounds are contained in cigarette smoke and, in low levels, in ambient particulate matter. Soluble nickel particulate, especially nickel sulfate (NiSO(4)), has been associated with acute lung injury. To begin identifying genes controlling susceptibility to NiSO(4), mean survival times (MSTs) of eight inbred mouse strains were determined after aerosol exposure. Whereas A/J (A) mice were sensitive, C57BL/6J (B6) mice survived nearly twice as long (resistant). Their offspring were similarly resistant, demonstrating heritability as a dominant trait. Quantitative trait locus (QTL) analysis of backcross mice generated from these strains identified a region on chromosome 6 significantly linked to survival time. Regions on chromosomes 1 and 12 were suggestive of linkage and regions on chromosomes 8, 9, and 16 contributed to the response. Haplotype analysis demonstrated that QTLs on chromosomes 6, 9, 12, and 16 could explain the MST difference between the parental strains. To complement QTL analysis results, cDNA microarray analysis was assessed following NiSO(4) exposure of A and B6 mice. Significant expression changes were identified in one or both strains for >100 known genes. Closer evaluation of these changes revealed a temporal pattern of increased cell proliferation, extracellular matrix repair, hypoxia, and oxidative stress, followed by diminished surfactant proteins. Certain expressed sequence tags clustered with known genes, suggesting possible co-regulation and novel roles in pulmonary injury. Together, results from QTL and microarray analyses of nickel-induced acute lung injury survival allowed us to generate a short list of candidate genes.

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.

Genetic susceptibility to irritant-induced acute lung injury in mice

Recent studies suggest that genetic variability can influence irritant-induced lung injury and inflammation. To begin identifying genes controlling susceptibility to inhaled irritants, seven inbred mouse strains were continuously exposed to nickel sulfate (NiSO(4)), polytetrafluoroethylene, or ozone (O(3)), and survival time was recorded. The A/J (A) mouse strain was sensitive, the C3H/He (C3) strain was intermediate, and the C57BL/6 (B6) strain was resistant to NiSO(4)-induced acute lung injury. The B6AF(1) offspring were also resistant. The strain sensitivity pattern for NiSO(4) exposure was similar to that of polytetrafluoroethylene or ozone (O(3)). Pulmonary pathology was comparable for A and B6 mice. In the A strain, 15 microg/m(3) of NiSO(4) produced 20% mortality. The strain sensitivity patterns for lavage fluid proteins (B6 > C3 > A) and neutrophils (A >/= B6 > C3) differed from those for acute lung injury. This phenotype discordance suggests that these traits are not causally linked (i.e., controlled by independent arrays of genes). As in acute lung injury, B6C3F(1) offspring exhibited phenotypes (lavage fluid proteins and neutrophils) resembling those of the resistant parental strain. Agreement of acute lung injury strain sensitivity patterns among irritants suggested a common mechanism, possibly oxidative stress, and offspring resistance suggested that sensitivity is inherited as a recessive trait.

Effects of nickel sulfate on pulmonary natural immunity in Wistar rats

This study was designed to investigate the in vivo effect of nickel sulfate on the pulmonary non-specific immune defences. Groups of four male Wistar rats were treated with a single intratracheal instillation of NiSO(4) at different doses: 1, 2, 4 and 8 micromol of NiSO(4) per rat. Control rats received a corresponding instillation of the saline vehicle. The effect of NiSO(4) on the cytotoxic activity of the pulmonary natural killer (NK) cells and alveolar macrophages (AM), as well as the pulmonary production of cytokines such as alpha-tumor necrosis factor (TNF-alpha) and gamma-interferon (IFN-gamma), were examined 1, 2 and 7 days later. Spontaneous NK-cytotoxicity towards mouse-derived tumor cell line, Yac-1 was suppressed 1 day after treatment at doses of 2 micromol/rat and above with only one result significant (P<0.05); 2 days after treatment the suppression was increased with all results significant at the same doses; 1 week after treatment NK activity restoration was observed except for the highest dose, 8 micromol/rat. AM-mediated cytotoxicity towards mouse-derived tumor cell line, 3T12, did not show any significant difference in treated and untreated animals. In contrast, whereas moderate levels of TNF-alpha were detected in the broncho-alveolar lavage (BAL) fluid supernatants of controls, the NiSO(4) treatment highly suppressed TNF-alpha production with a maximum observed after 2 days. TNF-alpha suppression was found to be transient, at least with the lowest NiSO(4) dose, with levels returning to normal after 7 days. A non-significant increase in IFN-gamma was observed in the BAL fluids of treated animals at each time of examination. Taken together, these results indicate that NK cell activity and TNF-alpha secretion are sensitive targets for instilled NiSO(4) in Wistar rats.

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.

Uptake of nickel into the brain via olfactory neurons in rats

Intranasal instillation of nickel ([63]Ni2+) in rats resulted in an uptake of the metal in the olfactory epithelium and a migration along primary olfactory neurons to the glomeruli of the olfactory bulb. The metal was then seen to pass to the interior of the bulb and further to the olfactory peduncle, the olfactory tubercle and the rostral parts of the prepiriform, frontal and cingulate corticis. These results indicate that (63)Ni2+ slowly passes to secondary and tertiary olfactory neurons. Intraperitoneal injection of (63)Ni2+ resulted in a low uptake in the brain, without preferential labelling of the olfactory pathways. Inhalation of nickel compounds can impair the olfactory system. An uptake of nickel in the olfactory neurons may underly these lesions.

Parental occupational exposure and the risk of testicular cancer in Ontario

The incidence of germ cell testicular cancer is increasing, but its etiology remains largely unknown. Initiation may occur in a parental germ cell. In a case-control study in Ontario, jobs and industries of mothers (before and during pregnancy) and fathers (before pregnancy) of 343 case subjects and 524 control subjects were analyzed. Significantly increased risk was associated with fathers who were wood processors (odds ratio [OR] = 10.46; 95% confidence interval [CI], 1.20 to 91.14), metalworkers (OR = 3.28; 95% CI, 1.03 to 10.52), stationary engineers (OR = 1.05; 95% CI, 1.05 to 11.87), or employees of the food products (OR = 2.79; 95% CI, 1.34 to 5.79), metal products (OR = 5.77, 95% CI, 1.53 to 21.77), or food and beverage services (OR = 4.36; 95% CI, 1.50 to 12.63) industries. There was little evidence of risk associated with maternal employment. Paternal employment before conception in jobs related particularly to metal or food and beverages may be related to testicular cancer risk in sons.

Occupation and risk of germ cell testicular cancer by histologic type in Ontario

Incidence of both major histologic subgroups of germ cell testicular cancer, seminoma and nonseminoma, is increasing, but the etiology is largely unknown. Occupational clusters have been observed. In a case-control study in Ontario with 495 incident cases and 974 population control subjects, jobs and industries were coded and analyzed. There is little evidence of occupational risk for all cases or for seminoma. Significantly increased risk of nonseminoma was associated with: miners (odds ratio [OR] = 12.39; 95% confidence interval [CI], 2.22 to 69.27), food and beverage processors (OR = 3.20; 95% CI, 1.39 to 7.35), utilities employees (OR = 3.15; 95% CI, 1.15 to 8.61), and other service workers (OR = 1.05; 95% CI, 1.05 to 4.56). Leather-industry employees had elevated risk of nonseminoma (OR = 4.60; 95% CI, 0.75 to 28.28) consistent with a leather tannery cluster. Increased risk of nonseminoma among some workers can be explained if an additional event is required for converting seminoma to nonseminoma.

A rapid digestion method for analysis of nickel compounds in tissue by electrothermal atomic absorption spectrometry

Quantification of nickel in animal soft tissue is of toxicological interest. A digestion method applying the use of microwave ovens for irradiating samples in Teflon digesters was developed. An acid mixture containing nitric acid (16 M, 1.0 ml g-1 tissue), hydrochloric acid (6 M, 0.5 ml g-1 tissue) and H2O2 (30%, 1.0 ml g-1 tissue) and irradiation at 600 W for 5 min were required for complete dissolution of tissue matrices and nickel compounds. Analyses of Ni in National Bureau of Standards Reference Material 1566 oyster tissue gave 0.87 +/- 0.24 micrograms g 1(mean +/- SD, n = 5), which was in agreement with the NBS certified value of 1.03 +/- 0.19 micrograms g-1. Recoveries of 1-300 micrograms Ni added as nickel sulfate (highly soluble), nickel subsulfide (moderately soluble in biological fluids and acid) or nickel oxide (green high-temperature oxide, low solubility in biological fluids and acid) to lung, liver, lymph node and kidney were quantitative, except in the case of nickel sulfate added to kidney, where recovery was less than quantitative for 1-10 micrograms Ni. The method appears effective for digestion of a variety of tissues requiring Ni analyses.

Biochemical responses of rat and mouse lung to inhaled nickel compounds

Nickel subsulfide (Ni3S2), nickel sulfate (NiSO4), and nickel oxide (NiO) are encountered occupationally in the nickel refining and electroplating industries, with inhalation being a common route of exposure. The purposes of this study were to evaluate the biochemical responses of lungs of rats and mice exposed for 13 weeks to occupationally relevant aerosol concentrations of Ni3S2, NiSO4, and NiO, to correlate biochemical responses with histopathologic changes, and to rank the compounds by toxicity. Biochemical responses were measured in bronchoalveolar lavage fluid (BALF) recovered from lungs of exposed animals. Parameters evaluated in BALF were lactate dehydrogenase (LDH), beta-glucuronidase (BG), and total protein (TP). Total and differential cell counts were performed on cells recovered in BALF. All compounds produced an increase in LDH, BG, TP, and total nucleated cells, and an influx of neutrophils, indicating the presence of a cytotoxic and inflammatory response in the lungs of exposed rats and mice. Increases in BG were greater than increases in LDH and TP for both rats and mice. Chronic active inflammation, macrophage hyperplasia, and interstitial phagocytic cell infiltrates were observed histologically in rats and mice exposed to all compounds. Statistically significant increases in BG, TP, neutrophils, and macrophages correlated well with the degree of chronic active inflammation. Results indicated a toxicity ranking of NiSO4 greater than Ni3S2 greater than NiO, based on toxicities of the compounds at equivalent mg Ni/m3 exposure concentrations.

Toxicity and carcinogenicity of nickel compounds

The toxicity and carcinogenicity of nickel compounds are considered in three broad categories: (1) systemic toxicology, (2) molecular toxicology, and (3) carcinogenicity. The systemic toxicity of nickel compounds is examined based upon human and animal studies. The major organs affected are discussed in three categories: (1) kidney, (2) immune system, and (3) other organs. The second area of concentration is molecular toxicology, which will include a discussion of the chemistry of nickel, its binding to small and large molecular weight ligands, and, finally, its cellular effects. The third major area involves a discussion of the carcinogenicity and genotoxicity of nickel compounds. This section focuses on mechanisms, using studies conducted in vivo and in vitro. It also includes a discussion of the assessment of the carcinogenicity of nickel compounds.

Evaluation of tissue disposition, myelopoietic, and immunologic responses in mice after long-term exposure to nickel sulfate in the drinking water

Female B6C3F1 mice were exposed to graded doses of nickel sulfate to determine a threshold response for myelotoxicity and immunotoxicity, and to identify which of the populations of lymphoreticular cells were most sensitive to the toxic effects of nickel. Animals were given free access to the chemical in the drinking water at 0, 1, 5, or 10 g/l for 180 d. Water consumption, blood and tissue nickel concentrations, body and organ weights, histopathology, immune responses, bone marrow cellularity and proliferation, and cellular enzyme activities were evaluated. There was no mortality. Mice in the 5-g/l and 10-g/l dose groups drank less water than controls; the responses measured in the 10-g/l group may have been due to a combination of dehydration and chemical toxicity. Decreases in body and organ weights were confined to mice in the 10-g/l dose group, except for the dose-related reductions in thymus weights. Blood nickel was measured at 4, 8, 16, and 23 wk of exposure. The mean blood nickel values showed increases between 4 and 8 wk that were proportional to time and dose; thereafter there was no substantial increase in blood nickel in any of the dose groups, except for an increase in the mean blood concentration in the 10-g/l group at 23 wk. The kidney was the major organ of nickel accumulation. The primary toxic effects of nickel sulfate were expressed in the myeloid system. There were dose-related decreases in bone marrow cellularity, and in granulocyte-macrophage and pluripotent stem-cell proliferative responses. In unfractionated bone marrow cells glucose-6-phosphate dehydrogenase enzyme activity from the hexose monophosphate shunt was more sensitive to nickel sulfate than were representative glycolytic or Krebs cycle enzymes, with 25-35% maximum inhibition at 5 g/l and 10 g/l. Aliquots of bone marrow cells were separated into enriched bands of lymphocytes, granulocyte-macrophages, and erythrocytes; enzyme inhibition that occurred in unfractionated bone marrow cell aliquots was only expressed after cell separation in the enriched granulocyte-macrophage cell population, suggesting that these committed stem cells were a primary target of nickel sulfate toxicity. There was one example of systemic immunotoxicity, reduction in the lymphoproliferative response to lipopolysaccharide, and it was regarded as secondary to the primary effect of nickel sulfate on the myeloid system, since this was the only significant change among a panel of seven immune parameters that were evaluated.

Comparative in vitro cytotoxicity of nickel oxides and nickel-copper oxides to rat, mouse, and dog pulmonary alveolar macrophages

Metal oxides containing either Ni alone (NiO's) or both Ni and Cu (Ni-CuO's) are encountered during Ni refining. Six NiO compounds calcined at temperatures ranging from less than 650 to 1045 degrees and four Ni-CuO's containing from 6.9 to 28% Cu and 44 to 69% Ni were screened for their in vitro cytotoxicity to alveolar macrophages (AM). NiO's were less toxic to rat AM than were the Ni-CuO compounds. The toxicity of the Ni-CuO compounds increased with increasing Cu content and decreasing Ni content of the molecules, indicating that the toxicity was due to the Cu content of the molecules. AM obtained from beagle dogs, F344/N rats, and B6C3F1 mice displayed the following species sensitivities: dog greater than rat = mouse, with dog AM being most sensitive. The observed differences in species sensitivities correlated with differences in the phagocytic abilities of dog, rat, and mouse AM, with the ranking of phagocytic abilities of the AM in decreasing order of ability being dog greater than rat greater than mouse.