The immunotoxicity of three nickel compounds following 13-week inhalation exposure in the mouse

A T-dependent antibody response evaluation in CD-1 mice after an acute whole-body inhalation exposure to nickel (II) chloride hexahydrate

Nickel (Ni) in ambient air may vary regionally with contributions from both natural processes and anthropogenic activities. Exposure to Ni compounds in ambient air above a certain level is associated with acute adverse effects, such as upper respiratory tract irritation, pneumonitis, and chronic adverse effects, such as respiratory cancer. Inhalation reference exposure standards are enacted in different jurisdictions to minimize exposures to ambient Ni above levels that can elicit adverse effects. This paper reports a guideline-/GLP-compliant study designed for setting inhalation exposure standards to protect from immunological effects associated with acute exposure to Ni. Female CD-1 mice were exposed via whole-body inhalation to aerosolized nickel chloride hexahydrate for 24-hr at nominal (vs. mean analyzed) concentrations of 20 (16), 50 (44) and 100 (81) µg Ni/m³. Host T-cell antibody immunological responses to intravenously-injected sheep red blood cells were then measured ex vivo in an Antibody-Forming Cell (AFC) assay. Exposure to the Ni substance significantly decreased spleen cell levels by 33%, but this was within biological variability for outbred mice. No concurrent decreases in spleen, thymus, or body weights were noted. No immunosuppression was observed with the Ni substance in the context of Total Spleen Activity [IgM AFC/spleen (× 10³)] and Specific Activity [IgM AFC/spleen cells (× 10⁶)]. Significant concentration-independent increases in Total Spleen Activity and Specific Activity seen with the nickel chloride hexahydrate were normal and within biological variability for outbred mice. In contrast, cyclophosphamide (positive control) significantly decreased spleen cell numbers, spleen and thymus weights, and abolished Specific Activity and Total Spleen Activity. Based on results here, an NOAEC of 81 µg Ni/m³ for immunosuppressive effects from inhaled nickel chloride hexahydrate was identified. It is hoped this value can be used to derive a reference standard for human exposure to ambient Ni.

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.

Role of hypoxia-inducible factor 1, α subunit and cAMP-response element binding protein 1 in synergistic release of interleukin 8 by prostaglandin E2 and nickel in lung fibroblasts

Numerous epidemiological studies have linked exposure to particulate matter (PM) air pollution with acute respiratory infection and chronic respiratory and cardiovascular diseases. We have previously shown that soluble nickel (Ni), a common component of PM, alters the release of CXC chemokines from cultured human lung fibroblasts (HLF) in response to microbial stimuli via a pathway dependent on disrupted prostaglandin (PG)E2 signaling. The current study sought to identify the molecular events underlying Ni-induced alterations in PGE2 signaling and its effects on IL-8 production. PGE2 synergistically enhances Ni-induced IL-8 release from HLF in a concentration-dependent manner. The effects of PGE2 were mimicked by butaprost and PGE1-alcohol and inhibited with antagonists AH6809 and L-161,982, indicating PGE2 signals via PGE2 receptors 2 and 4. PGE2 and forskolin stimulated cAMP, but it was only in the presence of Ni-induced hypoxia-inducible factor 1, α subunit (HIF1A) that these agents stimulated IL-8 release. The Ni-induced HIF1A DNA binding was enhanced by PGE2 and mediated, in part, by activation of p38 MAPK. Negation of cAMP-response element binding protein 1 or HIF1A using short interfering RNA blocked the synergistic interactions between Ni and PGE2. The results of the current study provide novel information on the ability of atmospheric hypoxia-mimetic metals to disrupt the release of immune-modulating chemokines by HLF in response to PGE2. Moreover, in the presence of HIF1A, cAMP-mediated signaling pathways may be altered to exacerbate inflammatory-like processes in lung tissue, imparting a susceptibility of PM-exposed populations to adverse respiratory health effects.

GSH-dependent iNOS and HO-1 mediated apoptosis of human Jurkat cells induced by nickel(II)

The molecular mechanisms by which nickel compounds cause immune cytotoxicity are far from understood. Our preliminary data suggested that nickel(II) induced apoptosis in Jurkat cells by mitochondrial pathway, specifically via mitochondrial membrane potential dissipation and antiapoptotic gene bcl-2 down-regulation. The main goal of this study was to further investigate the toxicity of nickel, especially the induction of reactive oxygen species (ROS) on immune cells, which finally induced apoptosis. Nickel was found to induce glutathione (GSH) depletion in a dose- and time-dependent manner. When Jurkat cells were preincubated with antioxidant N-acetylcysteine (NAC), apoptosis was inhibited distinctly, which suggested that ROS played an initial role in nickel immune toxicity. Heme oxygenase-1 (HO-1) and Nitric oxide (NO) which may play an important role in regulatory and protective processes in cells were assayed upon nickel treatment. A significant increase in HO-1 mRNA levels was detected in nickel treated cells. We confirmed that reduction of Nitrate levels in Jurkat cells was due to down-regulation of inducible nitric oxide synthase (iNOS), not endothelial nitric oxide synthase (eNOS). Expression changes of HO-1 and iNOS were markedly blocked when Jurkat cells were preincubated with NAC, suggesting that ROS resulted in HO-1 and iNOS dysfunction in Jurkat cells. We supposed that the immune toxicity of nickel(II) was mainly due to GSH depletion and finally led to apoptosis, probably via changing the expression levels of HO-1 and iNOS in human T lymphocytes.

Effect of nickel exposure on peripheral tissues: role of oxidative stress in toxicity and possible protection by ascorbic acid

The vast industrial use of nickel has led to environmental pollution by the metal and its by-products during production, recycling, and disposal. Nickel is a known hematotoxic, immunotoxic, hepatotoxic, pulmotoxic, and nephrotoxic agent. Allergic skin reactions are common in individuals who are sensitive to nickel. This article presents a selective review on nickel and its effect on certain metabolically active peripheral tissues of human and animals. The subtopics include nickel sources and uses, exposure pathways, transport, excretion, general health effects, and specific acute and chronic nickel toxicities in peripheral tissues like liver, lungs, and kidneys. The review particularly addresses the nickel-induced generation of reactive oxygen species and increased lipid peroxidation in various metabolically active tissues in humans and animals, and the possible role of vitamin c as a protective antioxidant.

Sensitization to nickel: etiology, epidemiology, immune reactions, prevention, and therapy

Nickel is a contact allergen causing Type I and Type IV hypersensitivity, mediated by reagins and allergen-specific T lymphocytes, expressing in a wide range of cutaneous eruptions following dermal or systemic exposure. As such, nickel is the most frequent cause of hypersensitivity, occupational as well as among the general population. In synoptic form, the many effects that nickel has on the organism are presented to provide a comprehensive picture of the aspects of that metal with many biologically noxious, but metallurgically indispensable characteristics. This paper reviews the epidemiology, the prognosis for occupational and non-occupational nickel allergic hypersensitivity, the types of exposure and resulting immune responses, the rate of diffusion through the skin, and immunotoxicity. Alternatives toward prevention and remediation, topical and systemic, for this pervasive and increasing form of morbidity are discussed. The merits and limitations of preventive measures in industry and private life are considered, as well as the effectiveness of topical and systemic therapy in treating nickel allergic hypersensitivity.

Involvement of histone hypoacetylation in Ni2+-induced bcl- 2 down-regulation and human hepatoma cell apoptosis

Although induction of cell apoptosis is known to be involved in the cytotoxicity of Ni(2+), little research has been aimed at the mechanism of Ni(2+)-induced apoptosis. Recent studies showed that Ni(2+) induces histone hypoacetylation in different cell lines. Since histone hypoacetylation plays important roles in the control of cell cycle progress and apoptosis, we hypothesized that histone hypoacetylation may be an unrevealed pathway in Ni(2+)-induced apoptosis. To address this, effects of Ni(2+) on cell apoptosis, bcl- 2 gene expression and histone acetylation were examined in human hepatoma Hep3B cells. We found that Ni(2+) treatment resulted in cell proliferation arrest, the appearance of detached cells, condensed chromatin, apoptotic bodies and specific DNA fragmentation, indicating the occurrence of cell apoptosis. At the same time, Ni(2+) induced a significant decrease in bcl- 2 expression and histone acetylation; the decrease of histone H4 acetylation in nucleosomes associated with the bcl- 2 promoter region was also proven by a chromatin immunoprecipitation assay, indicating the involvement of histone hypoacetylation in Ni(2+)-induced bcl- 2 down-regulation. Further studies showed that increasing histone acetylation by either 100 nM of trichostatin A or over-expressing histone acetyltranferase p300 in Hep3B cells obviously attenuated the bcl- 2 down-regulation and cell apoptosis caused by Ni(2+). Considering the importance of bcl- 2 in determining cell survival and apoptosis, the data presented here suggest that histone hypoacetylation may represent one unrevealed pathway in Ni(2+)-induced cell apoptosis, where bcl- 2 is one of its targets.

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.

Physicochemical characteristics and toxicity of nickel oxide particles calcined at different temperatures

The physicochemical characteristics and cytotoxicity of two types of commercial nickel oxide particles (black and green nickel oxide) and five types of nickel oxide particles prepared by calcination of the black nickel oxide at 600-1000 degrees C were studied. Thermal analysis with mass spectroscopy showed that the black nickel oxide particles contained approximately 1.4% impurity, which seemed to be basic nickel carbonate. The calcination treatment at 600 degrees C increased the nickel content and decreased the oxygen content, but these remained constant in the particles treated at higher temperatures (700-1000 degrees C) and in the green nickel oxide particles. The water solubility of black nickel oxide particles was markedly greater than that of the other particles, especially in the first 24 h after mixing with water. The solubility of the calcined particles decreased with increasing calcination temperature. The cytotoxicity of these particles was evaluated by the viability of rat alveolar macrophages and by the inhibition of cell proliferation in Chinese hamster ovary cells. The black nickel oxide was the most cytotoxic of the particles examined, and this may be attributable, at least in part, to a rapid dissolution of nickel from the contained impurity. The toxicity of the calcined particles decreased with increasing calcination temperature. These results indicate that water solubility, which depends on calcination temperature, modulates the acute cytotoxicity of nickel oxide particles.

Antibody forming cell response to nickel and nickel-coated fly ash in rats

The potential of nickel as nickel chloride, native fly ash and Ni-coated fly ash to alter pulmonary and systemic immune response was evaluated upon intratracheal (I/T) exposure of rats. The animals were sensitised with sheep red blood cells (SRBC) through I/T and intraperitoneal (I/P) routes. Nickel exposure resulted in a decrease in the number of antibody forming cells (AFC) in lung associated lymph nodes (LALN) and spleen. In rats exposed to native fly ash there was a reduction in the number of AFC in LALN but not in spleen. The results did not demonstrate any significant difference in the immunosuppression of fly ash and Ni-coated fly ash exposed rats. The decrease in AFC formation in Ni-coated fly ash exposed animals was of a lesser magnitude than in rats exposed to Ni-alone.

Immunologic specificity of lymphocyte cell lines from dogs exposed to beryllium oxide

We have reported that dogs exposed twice to aerosols of beryllium oxide (BeO) developed Be-specific immune responses within the lung, along with granulomatous and fibrotic lung lesions. To evaluate the specificity of the immune response, lymphocytes from lungs and blood of BeO-exposed dogs were co-cultured over an irradiated blood monocyte layer, alternately with interleukin 2 and BeSO4. Resultant cell lines were then tested for their response to different metal cations, common canine recall antigens, and BeSO4 in an in vitro cell proliferation assay. The cell lines responded to BeSO4 in a dose-dependent fashion, with mean stimulation indices of 7, 58, 119, and 112 at concentrations of 0.01, 1.0, 10, and 100 microM BeSO4 respectively. Cells not proliferate when incubated with ZnSO4 or NiSO4, or with canine distemper, leptospira, adenovirus 2, parvovirus, or parainfluenza antigens. Lymphocytes from normal vaccinated dogs proliferated markedly when cultured with these antigens. Cells from the cultured cell lines (91%) stained with Thy-1 (a pan T-cell marker) and 96% stained with DT2 (a helper T-cell marker). Furthermore, the Be-induced proliferative response was restricted by major histocompatibility (MHC) class II antigens. These data reinforce the premise that inhalation exposure of dogs to BeO produces lung lesions and MHC class II restricted immunologic responses mediated by Be-specific, helper T-Cells. These data further confirm the hypothesis that antigen localized to the lung results in the recruitment of T-cells to the lung, followed by localized antigen-specific, cell-mediated immune responses.

Effects of nickel oxide on the production of tumor necrosis factor by alveolar macrophages of rats

To evaluate the effect of green nickel oxide (NiO) on the production of tumor necrosis factor (TNF) by alveolar macrophages, alveolar macrophages were exposed to NiO in vitro and in vivo. For the in vitro study, rats alveolar macrophages were incubated with NiO on a microplate for 24 h. TNF activity in the culture supernatant was determined by the L929 bioassay. Rats alveolar macrophages cultured with 100 and 200 micrograms/mL of NiO in vitro induced the production of TNF, however, it was not statistically significant compared with the control that was free from NiO exposure. For exposure in vivo, rats were divided into two groups. Five were exposed to a daily concentration of 11.7 +/- 2.0 mg/m3 of NiO for an 8-hr/d, 5 d/wk, for 4 wk, and five rats (control) were kept in a cage and not exposed to NiO. Bronchoalveolar lavage was performed and the recovered alveolar macrophages were incubated on a microplate for 24 h. TNF production by exposed alveolar macrophages was significantly higher than that of controls.

The Effect of Nickel Compounds on Mitogen Dependent Human Lymphocyte Stimulation

The effect of metal salts, three nickel and one non-nickel (manganese chloride), was examined on the ability to influence mitogen stimulated normal human blood lymphocytes by means of short term in vitro culture and a tritiated thymidine incorporation test. Purified lymphocytes were incubated for one hour with tissue culture medium containing either one of the nickel salts tested (nickel subsulfide, nickel sulfate or nickel acetate) or manganese chloride. Separate portions of cells were incubated in the metal salt mixtures containing both, nickel and manganese salts. All metal salts were used in predetermined subtoxic concentrations. Two mitogens, phytohemagglutinin (PHA) and concanavalin A (Con A), were used as lymphocyte stimulatory agents. Cells were cultured for 72 hrs.

It was found that following incubation with nickel salts, mitogen dependent lymphocyte stimulation was inhibited proportionally to the metal salt concentration. This blocking effect on tritiated thymidine incorporation was stronger for readily soluble nickel salts i.e. sulfate and acetate than for almost insoluble nickel subsulfide with either mitogen used. Manganese chloride used as a single salt resulted in a dose-dependent increase of lymphocyte stimulation as compared to the mitogen stimulated cells without preincubation with either metal (control samples). Cells preincubated with nickel salt-manganese chloride mixtures exhibited an increase of thymidine incorporation but below values for control cells.

Human immune toxicity

This review examines xenobiotic toxicity to the immune system, stressing in particular those aspects of most relevance to humans. Immunotoxicity is examined especially from three points of view: by what immunological component is affected, by classes of foreign agents that adversely affect the human immune system and by critical evaluation of human case reports and epidemics. Mechanisms by which xenobiotics interrupt cytokine networks are emphasized. The concept that microbial agents, both environmental as well as infectious, may act as immunotoxicants, either alone or in synergism with conventional agents is introduced. Instances of human immunotoxicology are critically evaluated in terms of clinical relevance, i.e. whether increased susceptibility to opportunistic infections or tumor emergence takes place in the affected individuals.

In vivo exposure to ultraviolet radiation enhances pathogenic effects of murine leukemia virus, LP-BM5, in murine acquired immunodeficiency syndrome

LP-BM5 murine leukemia virus (MuLV) induces an immunodeficiency syndrome (MAIDS) in C57BL/6 mice which resembles immunological abnormalities observed in early stages of human AIDS. In our study, MAIDS virus-infected mice were exposed to low doses of ultraviolet radiation (UVR) before and after virus inoculation and compared with MAIDS-infected but not UVR-exposed mice. In all tested parameters (blood IgM levels; mitogenic responses to PHA, ConA, LPS and anti-mu; MLR; antigenic response to SRBC; enlargement and histopathologic changes of the spleen) we observed the same trend: changes due to MAIDS infection were more pronounced in the UVR-exposed group than in the unexposed group. Statistically significant differences between these two groups were seen for mitogenic responses at two different time points after virus inoculation. These results demonstrate that in vivo UVR exposure enhances the immunosuppressive effects of a retroviral infection. UVR exposure may affect the progression of AIDS in a similar manner.