Immuno-biochemical findings in groups of individuals occupationally and non-occupationally exposed to emissions containing nickel and cobalt

Immune reactions elicited in the sera of individuals exposed to nickel and cobalt were assessed by changes in the concentration of serum immunoglobulins IgG, IgA and IgM and serum proteins alpha 2 macroglobulin (A2M), transferrin (TRF), alpha 1-antitrypsin (A1AT), ceruloplasmin (CPL) and lysozyme (LYS). Examinations were carried out in workers occupationally exposed to Ni (38 individuals) or Co (35 individuals) and in groups of non-occupationally exposed children living in areas with a different degree of air pollution from a nearby source of Ni and Co emissions (one group was made up of 54 exposed children, the other one of 64 "less exposed" children of the same age). Groups of non-exposed controls were represented by a group of 42 male adults matched by age and by a group of 48 children from a non-polluted area. Significantly increased average values were obtained for IgG, IgA and IgM in group of workers exposed to Ni, for IgA in workers exposed to Co and for A1AT, A2M, CPL and LYS in both groups of occupationally exposed adults (p less than 0.001 - p less than 0.005). Among non-occupationally exposed children the group of the most exposed had significantly elevated average values for A2M and A1AT which were higher than those recorded in groups of "less exposed" and control children (p less than 0.02 and p less than 0.05, respectively). The biomedical importance of these findings is discussed in detail.     

Mechanisms of nickel toxicity in microorganisms

Nickel has long been known to be an important human toxicant, including having the ability to form carcinomas, but until recently nickel was believed to be an issue only to microorganisms living in nickel-rich serpentine soils or areas contaminated by industrial pollution. This assumption was overturned by the discovery of a nickel defense system (RcnR/RcnA) found in microorganisms that live in a wide range of environmental niches, suggesting that nickel homeostasis is a general biological concern. To date, the mechanisms of nickel toxicity in microorganisms and higher eukaryotes are poorly understood. In this review, we summarize nickel homeostasis processes used by microorganisms and highlight in vivo and in vitro effects of exposure to elevated concentrations of nickel. On the basis of this evidence we propose four mechanisms of nickel toxicity: (1) nickel replaces the essential metal of metalloproteins, (2) nickel binds to catalytic residues of non-metalloenzymes; (3) nickel binds outside the catalytic site of an enzyme to inhibit allosterically and (4) nickel indirectly causes oxidative stress.     

Urinary mutagenicity tests in lead-exposed workers

Urinary mutagenic activity detected by the bacterial fluctuation assay, using Salmonella typhimurium TA98 and Escherichia coli WP2 uvrA with and without metabolic activation (S9 mix), was studied in a group of 21 workers exposed to inorganic lead and a control group of 22 non-occupationally exposed subjects. Occupational exposure to inorganic lead had no effect on urinary mutagenicity in the strains considered, with or without metabolic activation. In smokers (exposed and non-exposed), urinary mutagenic activity appeared to increase compared to non-smokers (exposed and non-exposed), only with Salmonella typhimurium TA98 in the presence of S9 mix.     

Cytogenetic monitoring of industrial populations potentially exposed to genotoxic chemicals and of control populations

Currently the most applied technique for monitoring biological effects of exposure to genotoxic chemicals in industrial workers is the measurement of chromosome aberrations in peripheral blood lymphocytes. In the Shell petrochemical complex in The Netherlands cytogenetic monitoring studies have been carried out from 1976 till 1981 inclusive, in workers potentially exposed to a variety of genotoxic chemicals, i.e. vinyl chloride, ethylene oxide, benzene, epichlorohydrin, epoxy resins. Average exposure levels to these chemicals were well below the occupational exposure limits. Results of these studies indicate that no biologically significant increase in the frequencies of chromosome aberrations in the exposed populations occurred compared with control populations. Our experience with this methodology has shown that the results of chromosome analyses are difficult to interpret, due to the variable and high background levels of chromosome aberrations in control populations and in individuals. It is concluded that the method is not sufficiently sensitive for routine monitoring of cytogenetic effects in workers exposed to the low levels of genotoxic compounds.     

Interaction of nickel with mutagens in the induction of sister chromatid exchanges in human lymphocytes

In this study, individual treatments of human lymphocytes with Ni(II) [0.5–25 μM], Cr(VI) [0.65–1.30 μM], UV-light or X-rays induced SCEs in a dose-dependent fashion, and combined treatments of Ni(II) with Cr(VI), UV-light or X-rays interacted antagonistically. Nickel, at environmentaly relevant exposure levels, cna have the effect in complex mixtures of reducing an otherwise positive SCE response and could lead to underestimating human exposures to certain classes of chemicals or radiation. Furthermore, our data indicate that antagonism may occure when human lymphocytes are exposed simultaneously to Ni(II) and Cr(VI), suggesting an explanation for epidemiological studies reporting conflicting results for cytogenetic effects in lymphocytes of workers exposed to chromium and nickel.     

Health effects of static magnetic fields--a review of the epidemiological evidence

Potential health effects of static magnetic fields have received far less attention than, for example, power frequency or radiofrequency fields. Static fields are found in certain occupational settings, e.g. in the aluminium and chloralkali industries, in arc-welding processes, and certain railways systems. Magnetic resonance imaging (MRI) for medical diagnosis is another source. This paper summarizes the epidemiological evidence of static magnetic field exposure and long-term health effects. There are only a few epidemiological studies available, and the majority of these have focused on cancer risks. There are some reports on reproductive outcomes, and sporadic studies of other outcomes. Overall, few occupational studies have focused specifically on effects of static magnetic field exposure, and exposure assessment have consequently been poor or non-existent. Results from studies that have estimated static magnetic field exposure have not indicated any increased cancer risks, but they are generally based on small numbers of cases and crude exposure assessment. Control of confounding has been limited, and it is likely that the “healthy worker” effect have influenced the results. A few studies have reported results on reproductive outcomes among aluminium workers and MRI operators, but limitations in study designs prevent conclusions. A problem in epidemiological studies of static magnetic fields is that workers in exposed occupations are also exposed to a wide variety of other potentially harmful agents, including some known carcinogens. In conclusion, the available evidence from epidemiological studies is not sufficient to draw any conclusions about potential health effects of static magnetic field exposure.     

Novel nickel transport mechanism across the bacterial outer membrane energized by the TonB/ExbB/ExbD machinery

Nickel is a cofactor for various microbial enzymes, yet as a trace element, its scavenging is challenging. In the case of the pathogen Helicobacter pylori, nickel is essential for the survival in the human stomach, because it is the cofactor of the important virulence factor urease. While nickel transport across the cytoplasmic membrane is accomplished by the nickel permease NixA, the mechanism by which nickel traverses the outer membrane (OM) of this Gram-negative bacterium is unknown. Import of iron-siderophores and cobalamin through the bacterial OM is carried out by specific receptors energized by the TonB/ExbB/ExbD machinery. In this study, we show for the first time that H. pylori utilizes TonB/ExbB/ExbD for nickel uptake in addition to iron acquisition. We have identified the nickel-regulated protein FrpB4, homologous to TonB-dependent proteins, as an OM receptor involved in nickel uptake. We demonstrate that ExbB/ExbD/TonB and FrpB4 deficient bacteria are unable to efficiently scavenge nickel at low pH. This condition mimics those encountered by H. pylori during stomach colonization, under which nickel supply and full urease activity are essential to combat acidity. We anticipate that this nickel scavenging system is not restricted to H. pylori, but will be represented more largely among Gram-negative bacteria.     

Nickel carcinogenesis: epigenetics and hypoxia signaling

Both water soluble and insoluble nickel compounds have been implicated in the etiology of human lung and nasal cancers. Water insoluble nickel compounds have been shown to enter cells by phagocytosis and are contained in cytoplasmic vacuoles, which are acidified thus accelerating the dissolution of soluble nickel from the particles. Using Newport Green, a dye that fluoresces when ionic nickel is bound, we have shown that following exposure (48-72 h) of human lung (A549) cells to NiS particles, most of the nickel is contained in the nucleus, while cells exposed to soluble NiCl2 exhibit most of the ions localized in the cytoplasm. This effect is consistent with previously published reports showing that short-term exposure of cells to crystalline nickel particles (1-3 days) is able to epigenetically silence target genes placed near heterochromatin, while similar short-term exposure to soluble nickel compounds are not able to induce silencing of genes placed near heterochromatin. However, a 3 week exposure of cells to soluble NiCl2 is also able to induce gene silencing. A similar effect was found in yeast cells where nickel was able to silence the URA-3 gene placed near (1.3 kb) a telomere silencing element, but not when the gene was placed farther away from the silencing element (2.0 kb). In addition to epigenetic effects, nickel compounds activate hypoxia signaling pathways. The mechanism of this effect involves the ability of either soluble or insoluble nickel compounds to block iron uptake leading to cellular iron depletion, directly affect iron containing enzymes, or both. This results in the inhibition of a variety of iron-dependent enzymes, such as aconitase and the HIF proline hydroxylases (PHD1-3). The inhibition of the HIF proline hydroxylases stabilizes the HIF protein and activates hypoxic signaling. Additional studies have shown that nickel and hypoxia decrease histone acetylation and increase the methylation of H3 lysine 9. These events are involved in gene silencing and hypoxia can also cause these effects in human cells. It is hypothesised that the state of hypoxia either by low oxygen tension or as a result of agents that signal hypoxia under normal oxygen tension (iron chelation, nickel and cobalt) results in low levels of acetyl CoA, which is a substrate for histone and other protein acetylation. This effect may in part be responsible for the gene silencing following nickel exposure and during hypoxia.     

Biological half time of deposited nickel oxide aerosol in rat lung by inhalation

Wistar male rats were exposed to nickel oxide (NiO) aerosols (mass median aerodynamic diameter, 1.2 and 4.0 μm). The average exposure concentration was controlled from a low level of 0.6 mg/m³ to a high level of 70 mg/m³ and total exposure time was 140 h. Some rats were sacrificed just after the exposure, whereas others were exposed for 1 mo and kept for 12 and 20 mo clearance periods before sacrifice. There were no differences in body weight gain between NiO exposure groups and controls. Nickel concentrations in lungs of exposure groups were much higher than those of controls and decreased with the passing of the clearance time. No apparent deposition of nickel was observed in the liver, kidney, spleen, and blood immediately after the exposure, but in the case of the high exposure groups, the nickel concentration in the liver, spleen, and blood slightly increased with the increasing time of clearance. The biological half time of NiO deposited in the lungs was estimated by the assumption that the amount of the clearance is proportional to the amount of the NiO deposited. This resulted in a biological half time of 11.5 and 21 mo for 1.2 and 4.0 μm, respectively.     

10th NTES Conference: Nickel and arsenic compounds alter the epigenome of peripheral blood mononuclear cells

The mechanisms that underlie metal carcinogenesis are the subject of intense investigation; however, data from in vitro and in vivo studies are starting to piece together a story that implicates epigenetics as a key player. Data from our lab has shown that nickel compounds inhibit dioxygenase enzymes by displacing iron in the active site. Arsenic is hypothesized to inhibit these enzymes by diminishing ascorbate levels – an important co-factor for dioxygenases. Inhibition of histone demethylase dioxygenases can increase histone methylation levels, which also may affect gene expression. Recently, our lab conducted a series of investigations in human subjects exposed to high levels of nickel or arsenic compounds. Global levels of histone modifications in peripheral blood mononuclear cells (PBMCs) from exposed subjects were compared to low environmentally exposed controls. Results showed that nickel increased H3K4me3 and decreased H3K9me2 globally. Arsenic increased H3K9me2 and decreased H3K9ac globally. Other histone modifications affected by arsenic were sex-dependent. Nickel affected the expression of 2756 genes in human PBMCs and many of the genes were involved in immune and carcinogenic pathways. This review will describe data from our lab that demonstrates for the first time that nickel and arsenic compounds affect global levels of histone modifications and gene expression in exposed human populations.     

Effect of nickel on oxygen free radical metabolism

The effect of nickel on superoxide dismutase activity (SOD), as well as on rate of hydroxydopamine oxidation, was studied in vitro since lipid peroxidation has been implicated in cell damage by nickel, whose toxicity and carcinogenicity are well established. Nickel strongly inhibits SOD activity. The degree of inhibition is directly proportion to the nickel concentration (tested range 0.066 to 0.33 microgram/mL in the reaction mixture); to the substrate concentration (tested range 0.4 x 10 4M to 1.1 x 10 4M 6-hydroxydopamine); and to reaction mixture. Autoxidation of 6-hydroxydopamine was increased by nickel concentrations higher than 15 micrograms/mL. The combination of excessive oxygen free radical production and inhibition of their elimination by inhibition of SOD activity may contribute to the nickel toxicity that has been reported in industrial accidents, as well as to the high incidence of cancer occurring in nickel workers. It may also contribute to many complications in uremic patients, in whom increased serum nickel levels were reported to be in a similar range to those inhibiting SOD.     

Essential trace metals and specific organ weights in diet-restricted and ad lib-fed rats

Wistar male rats were exposed to nickel oxide (NiO) aerosols (mass median aerodynamic diameter, 1.2 μm). The average exposure concentration was controlled from low level (0.6 mg/m³) to high level (8.0 mg/m³) and total exposure time ranged from 140 to 216 h. Some rats were sacrificed just after the exposure, whereas others were exposed for 1 mo and kept for a 1-yr clearance period before sacrifice. There were no differences in body weight gain between NiO exposure groups and controls. Nickel concentrations in lungs of exposure groups were much higher than those of controls. No apparent deposition of nickel was observed in liver, kidney, spleen, heart, brain, and blood, but lung burdens of up to about 2.35 mg of NiO were found. The apparent deposition fractions were 19.8 and 14.5% after the exposure to average concentrations of 1.4 and 6.5–7.0 mg/m³, respectively. The clearance rate of NiO deposited in lungs may be small.     

Micronuclei in humans induced by exposure to low level of ionizing radiation: influence of polymorphisms in DNA repair genes

Understanding the risks deriving from protracted exposure to low doses of ionizing radiation has remarkable societal importance in view of the large number of work settings in which sources of IR are encountered. To address this question, we studied the frequency of micronuclei (MN), which is an indicator of DNA damage, in a population exposed to low levels of ionizing radiation and in matched controls. In both exposed population and controls, the possible influence of single nucleotide polymorphisms in XRCC1, XRCC3 and XPD genes on the frequency of micronuclei was also evaluated. We also considered the effects of confounding factors, like smoking status, age and gender. The results indicated that MN frequency was significantly higher in the exposed workers than in the controls [8.62+/-2.80 versus 6.86+/-2.65; P=0.019]. Radiological workers with variant alleles for XRCC1 or XRCC3 polymorphisms or wild-type alleles for XPD exon 23 or 10 polymorphisms showed a significantly higher MN frequency than controls with the same genotypes. Smoking status did not affect micronuclei frequency either in exposed workers or controls, while age was associated with increased MN frequency in the exposed only. In the combined population, gender but not age exerted an influence on the yield of MN, being higher in females than in males. Even though there is a limitation in this study due to the small number of subjects, these results suggest that even exposures to low level of ionizing radiation could have genotoxic effects and that XRCC3, XRCC1 and XPD polymorphisms might contribute to the increased genetic damage in susceptible individuals occupationally exposed to chronic low levels of ionizing radiation. For a clear conclusion on the induction of DNA damage caused by protracted exposure to low doses of ionizing radiation and the possible influence of genetic polymorphism in DNA repair genes larger studies are needed.     

Nickel toxicology with reference to male molecular reproductive physiology

The toxicity of metals is a known phenomenon. Nickel toxicity is very common since nickel is used extensively both industrially and in items of personal use such as utensils and jewellery. Here we discuss human exposure to nickel and its toxicity in the light of the available scientific evidence to understand its underlying pathophysiology. The ability of Ni⁺² to get oxidized to Ni⁺³ renders it’s potential of generating reactive oxygen species (ROS) in the system leading to oxidative stress. Carcinogenesis, apoptosis induction, contact dermatitis, epigenetic changes, and alteration in gene regulation are a result of overexposure of nickel. Our focus is on how nickel affects the male reproductive physiology. Nickel primarily drives ROS mediated perturbations in the male reproductive system. It influences zinc metabolism, which is critical for sperm stability and affects the structure of DNA binding proteins, including protamines, thereby affecting sperm function.     

Population Differences in Postural Response Strategy Associated with Exposure to a Novel Continuous Perturbation Stimuli: Would Dancers Have Better Balance on a Boat?

Central or postural set theory suggests that the central nervous system uses short term, trial to trial adaptation associated with repeated exposure to a perturbation in order to improve postural responses and stability. It is not known if longer-term prior experiences requiring challenging balance control carryover as long-term adaptations that influence ability to react in response to novel stimuli. The purpose of this study was to determine if individuals who had long-term exposure to balance instability, such as those who train on specific skills that demand balance control, will have improved ability to adapt to complex continuous multidirectional perturbations. Healthy adults from three groups: 1) experienced maritime workers (n = 14), 2) novice individuals with no experience working in maritime environments (n = 12) and 3) individuals with training in dance (n = 13) participated in the study. All participants performed a stationary standing task while being exposed to five 6 degree of freedom motions designed to mimic the motions of a ship at sea. The balance reactions (change-in-support (CS) event occurrences and characteristics) were compared between groups. Results indicate dancers demonstrated significantly fewer CS events than novices during the first trial, but did not perform as well as those with offshore experience. Linear trend analyses revealed that short-term adaptation across all five trials was dependent on the nature of participant experience, with dancers achieving postural stability earlier than novices, but later than those with offshore experience. These results suggest that long term previous experiences also have a significant influence on the neural control of posture and balance in the development of compensatory responses.     

Chromosomal aberrations and sister-chromatid exchanges in Lithuanian populations: effects of occupational and environmental exposures

Cytogenetic analysis of chromosomal aberrations (CA) in 175,229 cells from 1113 individuals, both unexposed and occupationally or environmentally exposed to heavy metals (mercury and lead), organic (styrene, formaldehyde, phenol and benzo(a)pyrene) and inorganic (sulfur and nitrogen oxides, hydrogen and ammonium fluorides) volatile substances and/or ionizing radiation was performed. In addition, 11,250 cells from 225 individuals were scored for the frequency of sister-chromatid exchanges (SCE). Increased frequencies of CA were found in all occupationally exposed groups. A principal difference between the exposure to heavy metals and organic substances was found: increase in the CA frequency was dependent on duration of exposure to mercury but not dependent on duration of exposure to styrene, formaldehyde and phenol. A higher CA incidence was found in lymphocytes of children living in the vicinity of a plant manufacturing phosphate fertilizers. This indicates that children are a sensitive study group for the assessment of environmental exposure. However, the results of SCE analysis in these children were inconclusive. Exposure to ionizing radiation was found to cause chromosome breaks and chromatid exchanges in Chernobyl clean-up workers and chromatid breaks, chromatid exchanges, dicentric chromosomes and chromosome translocations in workers from the Ignalina Nuclear Power Plant. The increased frequency of chromatid exchanges in individuals exposed to ionizing radiation was quite unexpected. This may be attributed to the action of some unrecognized life-style or occupational factors, or to be a result of radiation-induced genomic instability. Also an increased SCE frequency was found in lymphocytes of Chernobyl clean-up workers.     

Respiratory disease in industry due to B. subtilis enzyme preparations

Detergent industry workers are known to become sensitized to enzyme preparations added to the products. In a Canadian plant about 25% of 644 employees exposed to airborne commercial B. subtilis enzyme preparations became sensitized. Skin tests with a number of antigens, including purified enzyme preparations, illustrated differences from person to person in the components to which there was sensitization. The presence of respiratory symptoms related to the industrial exposure was reported much more commonly among sensitized workers. Among employees obliged to miss work, FEV₁ values after 24 months were considerably higher than those obtained during the time of initial difficulties. Blood eosinophilia was observed in sensitized workers. Serum IgG antibodies to the enzyme preparations were demonstrable in most sensitized individuals but did not provide a reliable index of sensitization or of the symptomatic state.