Soluble nickel interferes with cellular iron homeostasis

Association of exposure to multiple metals with hemoglobin levels in Chinese children and adolescents

BACKGROUND

Previous studies have linked single metal to hemoglobin levels in children and adolescents; however, studies with regards to metal mixtures are still limited.

OBJECTIVE

We aimed to investigate the associations of single metal and metal mixtures with hemoglobin levels in children and adolescents.

METHODS

We conducted a cross-sectional study of 2064 children and adolescents aged 6 to 19 years in Liuzhou, China in 2018. The concentrations of 15 metals in urine were determined by inductively coupled plasma mass spectrometry. Generalized linear regression and weighted quantile sum (WQS) regression were used to estimate the associations of single metal and metal mixtures with hemoglobin levels, respectively.

RESULTS

The multivariable-adjusted β-values for the highest versus the first quartiles of urinary metal concentrations were - 1.57 (95 % confidence interval [CI]: -3.01, -0.13) for chromium, -2.47 (95 % CI: -3.90, -1.05) for nickel and 1.88 (95 % CI: 0.49, 3.28) for copper. In addition, we found a significant negative association between the WQS index and hemoglobin levels (adjusted β = -0.93, 95 % CI: -1.69, -0.19), with nickel contributing the most to the WQS index at 59.0 %. Subgroup analyses showed that exposure to urinary nickel or metal mixtures were associated with decreased hemoglobin levels in adolescents, but not in children (all Pinteration < 0.001).

CONCLUSION

Among children and adolescents, urinary chromium and nickel concentrations were associated with decreased hemoglobin levels, while copper showed a positive relationship. Moreover, a negative association was observed between exposure to metal mixtures and hemoglobin levels. These findings need to be further validated in prospective studies.

Iron Metabolism, Calcium, Magnesium and Trace Elements: A Review

Iron (Fe) is fundamental to life on earth. In the human body, it is both essential and harmful if above threshold. A similar balance applies to other elements: calcium (Ca), magnesium (Mg), and trace elements including copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), mercury (Hg), and nickel (Ni). These elements share some proteins involved in the absorption and transport of Fe. Cu and Cd can inhibit Fe absorption, while excess of Fe may antagonize Cu metabolism and reduce ceruloplasmin (Cp). Excessive Fe can hinder Zn absorption and transferrin (Trf) can bind to both Zn and Ni. Ca is able to inhibit the divalent metal transporter 1 (DMT1) in a dose-dependent manner to reduce Fe absorption and low Mg concentrations can exacerbate Fe deficiency. Pb competitively inhibits Fe distribution and elevated Cd absorption reduces Fe uptake. Exposure to Hg is associated with higher ferritin concentrations and Ni alters intracellular Fe metabolism. Fe removal by phlebotomy in hemochromatosis patients has shown to increase the levels of Cd and Pb and alter the concentrations of trace elements in some types of anemia. Yet, the effects of chronic exposure of most trace elements remain poorly understood.

Single is not combined: The role of Co and Ni bioavailability on toxicity mechanisms in liver and brain cells

The two trace elements cobalt (Co) and nickel (Ni) are widely distributed in the environment due to the increasing industrial application, for example in lithium-ion batteries. Both metals are known to cause detrimental health impacts to humans when overexposed and both are supposed to be a risk factor for various diseases. The individual toxicity of Co and Ni has been partially investigated, however the underlying mechanisms, as well as the interactions of both remain unknown. In this study, we focused on the treatment of liver carcinoma (HepG2) and astrocytoma (CCF-STTG1) cells as a model for the target sites of these two metals. We investigated their effects in single and combined exposure on cell survival, cell death mechanisms, bioavailability, and the induction of oxidative stress. The combination of CoCl2 and NiCl2 resulted in higher Co levels with subsequent decreased amount of Ni compared to the individual treatment. Only CoCl2 and the combination of both metals led to RONS induction and increased GSSG formation, while apoptosis and necrosis seem to be involved in the cell death mechanisms of both CoCl2 and NiCl2. Collectively, this study demonstrates cell-type specific toxicity, with HepG2 representing the more sensitive cell line. Importantly, combined exposure to CoCl2 and NiCl2 is more toxic than single exposure, which may originate partly from the respective cellular Co and Ni content. Our data imply that the major mechanism of joint toxicity is associated with oxidative stress. More studies are needed to assess toxicity after combined exposure to elements such as Co and Ni to advance an improved hazard prediction for less artificial and more real-life exposure scenarios.

Evaluating the role of protective creams on the cutaneous penetration of Ni nanoparticles

There is an increase of application of Nickel in the form of nanoparticles (NiNPs) in several fields including modern metallurgy, bioengineering, and medicine. Such growth of the areas of application is actually accompanied with an increase of exposure to Nickel, thus an intensification of the negative effects, the most frequent being the allergic contact dermatitis. Indeed, due to their smaller size, and therefore their higher surface area, NiNPs can release more Ni ions compared to bulk material, that can penetrate and permeate through the skin. To reduce the Ni cutaneous penetration, barrier creams (BC) are applied on the skin surface. There is little information, however, on the efficiency of such commercial protective creams on decreasing Ni cutaneous penetration. For this reason, the objective of the current study was to investigate the protective role of one commercially available formulation for Ni (Nik-L-Block™ containing a chelating agent) and one moisturizing cream (Ceramol 311 basic cream without chelating agent), following exposure to NiNPs, using in vitro Franz cells, as well as the cytotoxicity of NiNPs in primary human dermal fibroblasts was studied. Our results demonstrated that although both tested formulations can decrease Ni accumulation in the skin (4.13 ± 1.74 μg/cm² for Nik-L-Block™ and 7.14 ± 1.46 μg/cm² for Ceramol 311 basic cream); there are significant differences between the two creams (p = 0.004). Based on the experimental evidence, we therefore conclude that the composition of such formulations has an imperative role for dermal uptake of Ni. Finally, NiNPs showed no cytotoxic effect on cultured human dermal fibroblasts after 24 and 72 h.

Low-dose and repeated exposure to nickel leads to bioaccumulation and cellular and metabolic alterations in quails

Nickel (Ni) is a widespread environmental pollutant commonly released into effluent due to industrial activities, the use of fuels, or wastewater disposal. Many studies confirm the toxic effects of this heavy metal. However, there is a lack of knowledge and data on bioaccumulation patterns in tissues as well as cellular and molecular responses following the exposure of living organisms to Ni. In this study, Japanese quails were exposed to low (10 μg/L) and high (2000 μg/L) Ni concentrations in the form of nickel(II) chloride via drinking water. Sub-chronic exposure lasted 30 days while nominal concentrations represented average Ni content in drinking water (low dose) and average Ni levels in highly polluted aquatic environments (high dose). It was revealed that a high dose of Ni was correlated with increased water intake and decreased body weight. Overall, Ni exposure induced the development of microcytic anemia and alterations in measured blood indices. Moreover, Ni exposure impaired immunological activation as seen through the increased number of the white blood cells, increased heterophile/lymphocyte (H/L) ratio, and pronounced thrombocytosis. Ni elicited changes in the albumin, glucose, cholesterol, and triglyceride serum levels in a concentration-dependent manner. Alterations of plasma protein fractions suggested liver functional impairment while high levels of urea and creatinine indicated potential kidney injury. Granulation of heterophiles and an increase in erythroblasts in the bone marrow showed that the hematopoietic tissue was also impacted by Ni toxicity. On average each quail bioaccumulated 5.87 μg of Ni per gram of tissue. Moreover, the distribution and bioaccumulation of Ni in terms of relative concentration were as follows: feathers > kidneys > heart > liver > pectoral muscles. Assessed bioaccumulation levels and associated cellular and metabolic alterations have revealed new multilayer toxicological data that will help in the extrapolation of Ni toxicity in other vertebrates, including humans.

Renal hypoxia-HIF-PHD-EPO signaling in transition metal nephrotoxicity: friend or foe?

The kidney is the main organ that senses changes in systemic oxygen tension, but it is also the key detoxification, transit and excretion site of transition metals (TMs). Pivotal to oxygen sensing are prolyl-hydroxylases (PHDs), which hydroxylate specific residues in hypoxia-inducible factors (HIFs), key transcription factors that orchestrate responses to hypoxia, such as induction of erythropoietin (EPO). The essential TM ion Fe is a key component and regulator of the hypoxia–PHD–HIF–EPO (HPHE) signaling axis, which governs erythropoiesis, angiogenesis, anaerobic metabolism, adaptation, survival and proliferation, and hence cell and body homeostasis. However, inadequate concentrations of essential TMs or entry of non-essential TMs in organisms cause toxicity and disrupt health. Non-essential TMs are toxic because they enter cells and displace essential TMs by ionic and molecular mimicry, e. g. in metalloproteins. Here, we review the molecular mechanisms of HPHE interactions with TMs (Fe, Co, Ni, Cd, Cr, and Pt) as well as their implications in renal physiology, pathophysiology and toxicology. Some TMs, such as Fe and Co, may activate renal HPHE signaling, which may be beneficial under some circumstances, for example, by mitigating renal injuries from other causes, but may also promote pathologies, such as renal cancer development and metastasis. Yet some other TMs appear to disrupt renal HPHE signaling, contributing to the complex picture of TM (nephro-)toxicity. Strikingly, despite a wealth of literature on the topic, current knowledge lacks a deeper molecular understanding of TM interaction with HPHE signaling, in particular in the kidney. This precludes rationale preventive and therapeutic approaches to TM nephrotoxicity, although recently activators of HPHE signaling have become available for therapy.

Effect of nickel on red blood cell parameters and on serum vitamin B12, folate and homocysteine concentrations during pregnancy with and without anemia

BACKGROUND

Research to date suggests that nickel affects not only the metabolism of vitamin B12 but also folates and thus may affect hematopoiesis processes.

OBJECTIVE

The aim of the study was to examine the relationship of nickel (Ni) status to red blood cell (RBC) parameters and serum vitamin B12, folate and homocysteine concentrations in the course of normal pregnancy and in pregnant women with anemia.

METHODS

The study included fifty-three pregnant women recruited to the study from the Lower Silesia region of Poland, 17 % of whom developed anemia. Nickel concentration was determined in urine, whole blood and food samples by atomic absorption spectrometry. At the same time as the food and urine samples were taken, blood was also collected for the determination of RBC parameters and serum vitamin B12, homocysteine and folate concentrations.

RESULTS

The median reported Ni intake, and the urinary and whole blood nickel contents for the studied pregnant women for the first trimester were respectively - 162.46 μg/day, 3.98 μg/L and 3.32 μg/L; for the second trimester - 110.48 μg/day, 6.86 μg/L and 1.04 μg/L; and for the third trimester - 132.20 μg/day, 3.41 μg/L and 0.70 μg/L. With regard to Ni concentration in whole blood (p = 0.0204) and in urine (p = 0.0003), the differences in the values for individual trimesters were statistically significant. The whole blood Ni level was significantly higher (9.28 vs 3.62 μg/L, p = 0.0114), while the concentration of homosysteine was significantly lower (4.09 vs 5.04 μmol/L, p = 0.0165) in pregnant women with anemia compared to those without anemia. The whole blood Ni concentration was negatively correlated with almost all RBC parameters in non-anemic pregnant women.

CONCLUSIONS

Ni status changes with the development of normal pregnancy, and in the case of anemia, an increase in Ni concentration in whole blood is observed. The demonstrated correlations between the Ni status in pregnant women and RBC parameters as well as serum vitamin B12 and folate concentrations suggest that nickel is associated with the methionine-folate cycle, iron homeostasis and bacterial synthesis of vitamin B12 in humans.

Epithelial-mesenchymal transition: Insights into nickel-induced lung diseases

Nickel compounds are environmental toxicants, prevalent in the atmosphere due to their widespread use in several industrial processes, extensive consumption of nickel containing products, as well as burning of fossil fuels. Exposure to nickel is associated with a multitude of chronic inflammatory lung diseases including asthma, chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis. In addition, nickel exposure is implicated in the development of nasal and lung cancers. Interestingly, a common pathogenic mechanism underlying the development of diseases associated with nickel exposure is epithelial-mesenchymal transition (EMT). EMT is a process by which the epithelial cells lose their junctions and polarity and acquire mesenchymal traits, including increased ability to migrate and invade. EMT is a normal and essential physiological process involved in differentiation, development and wound healing. However, EMT also contributes to a number of pathological conditions, including fibrosis, cancer and metastasis. Growing evidence suggest that EMT induction could be an important outcome of nickel exposure. In this review, we discuss the role of EMT in nickel-induced lung diseases and the mechanisms associated with EMT induction by nickel exposure.

Intracellular nickel accumulation induces apoptosis and cell cycle arrest in human astrocytic cells

Nickel, a heavy metal found in electronic wastes and fume from electronic cigarettes, induces neuronal cell death and is associated with neurocognitive impairment. Astrocytes are the first line of defense against nickel after entering the brain; however, the effects of nickel on astrocytes remain unknown. Herein, we investigated the effect of nickel exposure on cell survival and proliferation and the underlying mechanisms in U-87 MG human astrocytoma cells and primary human astrocytes. Intracellular nickel levels were elevated in U-87 MG cells in a dose- and time-dependent manner after exposure to nickel chloride. The median toxic concentrations of nickel in astrocytoma cells and primary human astrocytes were 600.60 and >1000 µM at 48 h post-exposure, respectively. Nickel exposure triggered apoptosis in concomitant with the decreased expression of anti-apoptotic B-cell lymphoma protein (Bcl-2) and increased caspase-3/7 activity. Nickel induced reactive oxygen species formation. Additionally, nickel suppressed astrocyte proliferation in a dose- and time-dependent manner by delaying G2 to M phase transition through the upregulation of cyclin B1 and p27 protein expression. These results indicate that nickel-induced cytotoxicity of astrocytes is mediated by the activation of apoptotic pathway and disruption of cell cycle regulation.

Update of the risk assessment of nickel in food and drinking water

The European Commission asked EFSA to update its previous Opinion on nickel in food and drinking water, taking into account new occurrence data, the updated benchmark dose (BMD) Guidance and newly available scientific information. More than 47,000 analytical results on the occurrence of nickel were used for calculating chronic and acute dietary exposure. An increased incidence of post-implantation loss in rats was identified as the critical effect for the risk characterisation of chronic oral exposure and a BMDL 10 of 1.3 mg Ni/kg body weight (bw) per day was selected as the reference point for the establishment of a tolerable daily intake (TDI) of 13 μg/kg bw. Eczematous flare-up reactions in the skin elicited in nickel-sensitised humans, a condition known as systemic contact dermatitis, was identified as the critical effect for the risk characterisation of acute oral exposure. A BMDL could not be derived, and therefore, the lowest-observed-adverse-effect-level of 4.3 μg Ni/kg bw was selected as the reference point. The margin of exposure (MOE) approach was applied and an MOE of 30 or higher was considered as being indicative of a low health concern. The mean lower bound (LB)/upper bound (UB) chronic dietary exposure was below or at the level of the TDI. The 95th percentile LB/UB chronic dietary exposure was below the TDI in adolescents and in all adult age groups, but generally exceeded the TDI in toddlers and in other children, as well as in infants in some surveys. This may raise a health concern in these young age groups. The MOE values for the mean UB acute dietary exposure and for the 95th percentile UB raises a health concern for nickel-sensitised individuals. The MOE values for an acute scenario regarding consumption of a glass of water on an empty stomach do not raise a health concern.

Increasing the copper sensitivity of microorganisms by restricting iron supply, a strategy for bio-management practices

Pollution by copper (Cu2+ ) extensively used as antimicrobial in agriculture and farming represents a threat to the environment and human health. Finding ways to make microorganisms sensitive to lower metal concentrations could help decreasing the use of Cu2 + in agriculture. In this respect, we showed that limiting iron (Fe) uptake makes bacteria much more susceptible to Cu2 + or Cd2+ poisoning. Using efflux mutants of the purple bacterium Rubrivivax gelatinosus, we showed that Cu+ and Cd2+ resistance relies on the expression of the Fur-regulated FbpABC and Ftr iron transporters. To support this conclusion, inactivation of these Fe-importers in the Cu+ or Cd2+ -ATPase efflux mutants gave rise to hypersensitivity towards these ions. Moreover, in metal overloaded cells the expression of FbpA, the periplasmic iron-binding component of the ferric ion transport FbpABC system was induced, suggesting that cells perceived an 'iron-starvation' situation and responded to it by inducing Fe-importers. In this context, the Fe-Sod activity increased in response to Fe homoeostasis dysregulation. Similar results were obtained for Vibrio cholerae and Escherichia coli, suggesting that perturbation of Fe-homoeostasis by metal excess appeared as an adaptive response commonly used by a variety of bacteria. The presented data support a model in which metal excess induces Fe-uptake to support [4Fe-4S] synthesis and thereby induce ROS detoxification system.

Nickel-induced transcriptional changes persist post exposure through epigenetic reprogramming

Background

Nickel is an occupational and environmental toxicant associated with a number of diseases in humans including pulmonary fibrosis, bronchitis and lung and nasal cancers. Our earlier studies showed that the nickel-exposure-induced genome-wide transcriptional changes, which persist even after the termination of exposure may underlie nickel pathogenesis. However, the mechanisms that drive nickel-induced persistent changes to the transcriptome remain elusive.

Results

To elucidate the mechanisms that underlie nickel-induced long-term transcriptional changes, in this study, we examined the transcriptome and the epigenome of human lung epithelial cells during nickel exposure and after the termination of exposure. We identified two categories of persistently differentially expressed genes: (i) the genes that were differentially expressed during nickel exposure; and (ii) the genes that were differentially expressed only after the termination of exposure. Interestingly, > 85% of the nickel-induced gene expression changes occurred only after the termination of exposure. We also found extensive genome-wide alterations to the activating histone modification, H3K4me3, after the termination of nickel exposure, which coincided with the post-exposure gene expression changes. In addition, we found significant post-exposure alterations to the repressive histone modification, H3K27me3.

Conclusion

Our results suggest that while modest first wave of transcriptional changes occurred during nickel exposure, extensive transcriptional changes occurred during a second wave of transcription for which removal of nickel ions was essential. By uncovering a new category of transcriptional and epigenetic changes, which occur only after the termination of exposure, this study provides a novel understanding of the long-term deleterious consequences of nickel exposure on human health.

A direct comparison of divalent metal-ion transporter (DMT1) and hinokitiol, a potential small molecule replacement

Hinokitiol, a natural lipophilic chelator, appears capable of replacing several iron transporters after they have been genetically ablated. Divalent metal-ion transporter (DMT1) is the major iron importer in enterocytes and erythroblasts. We have compared DMT1 and hinokitiol in multiple fashions to learn if the smaller molecule is a suitable substitute using two HEK293 cell lines engineered to overexpress different isoforms of DMT1. Both the macromolecule and the lipophilic chelator enable import of ferrous ions into HEK293 cells. Hinokitiol also mediates ferric ion import but DMT1 cannot do so. While DMT1 can also import Mn²⁺ ions, hinokitiol lacks this ability. The Michaelis–Menten analysis for kinetics of macromolecular catalysis is also suitable for hinokitiol-supported iron import. To compare hinokitiol to DMT1 relative to other metal ions that DMT1 can transport, we employed an organic extraction procedure with which we initially matched the results obtained for Fe²⁺, Fe³⁺ and Mn²⁺, and then showed that multiple other cations were unlikely to enter via hinokitiol. The small chelator thus shares some functional properties with DMT1, but distinct difference were also noted.

The Role of Non-Coding RNAs Involved in Nickel-Induced Lung Carcinogenic Mechanisms

Nickel is a naturally occurring element found in the Earth’s crust and an International Agency for Research on Cancer (IARC)-classified human carcinogen. While low levels found in the natural environment pose a minor concern, the extensive use of nickel in industrial settings such as in the production of stainless steel and various alloys complicate human exposure and health effects. Notably, interactions with nickel macromolecules, primarily through inhalation, have been demonstrated to promote lung cancer. Mechanisms of nickel-carcinogenesis range from oxidative stress, DNA damage, and hypoxia-inducible pathways to epigenetic mechanisms. Recently, non-coding RNAs have drawn increased attention in cancer mechanistic studies. Specifically, nickel has been found to disrupt expression and functions of micro-RNAs and long-non-coding RNAs, resulting in subsequent changes in target gene expression levels, some of which include key cancer genes such as p53, MDM2, c-myc, and AP-1. Non-coding RNAs are also involved in well-studied mechanisms of nickel-induced lung carcinogenesis, such as the hypoxia-inducible factor (HIF) pathway, oxidative stress, DNA damage and repair, DNA hypermethylation, and alterations in tumor suppressors and oncogenes. This review provides a summary of the currently known epigenetic mechanisms involved in nickel-induced lung carcinogenesis, with a particular focus on non-coding RNAs.

The third pillar of metal homeostasis inCupriavidus metalliduransCH34: preferences are controlled by extracytoplasmic function sigma factors

InC. metallidurans, a network of 11 extracytoplasmic function sigma factors forms the third pillar of metal homeostasis acting in addition to the metal transportome and metal repositories as the first and second pillar.

Transition Metal Homeostasis

This chapter focuses on transition metals. All transition metal cations are toxic-those that are essential for Escherichia coli and belong to the first transition period of the periodic system of the element and also the "toxic-only" metals with higher atomic numbers. Common themes are visible in the metabolism of these ions. First, there is transport. High-rate but low-affinity uptake systems provide a variety of cations and anions to the cells. Control of the respective systems seems to be mainly through regulation of transport activity (flux control), with control of gene expression playing only a minor role. If these systems do not provide sufficient amounts of a needed ion to the cell, genes for ATP-hydrolyzing high-affinity but low-rate uptake systems are induced, e.g., ABC transport systems or P-type ATPases. On the other hand, if the amount of an ion is in surplus, genes for efflux systems are induced. By combining different kinds of uptake and efflux systems with regulation at the levels of gene expression and transport activity, the concentration of a single ion in the cytoplasm and the composition of the cellular ion "bouquet" can be rapidly adjusted and carefully controlled. The toxicity threshold of an ion is defined by its ability to produce radicals (copper, iron, chromate), to bind to sulfide and thiol groups (copper, zinc, all cations of the second and third transition period), or to interfere with the metabolism of other ions. Iron poses an exceptional metabolic problem due its metabolic importance and the low solubility of Fe(III) compounds, combined with the ability to cause dangerous Fenton reactions. This dilemma for the cells led to the evolution of sophisticated multi-channel iron uptake and storage pathways to prevent the occurrence of unbound iron in the cytoplasm. Toxic metals like Cd2+ bind to thiols and sulfide, preventing assembly of iron complexes and releasing the metal from iron-sulfur clusters. In the unique case of mercury, the cation can be reduced to the volatile metallic form. Interference of nickel and cobalt with iron is prevented by the low abundance of these metals in the cytoplasm and their sequestration by metal chaperones, in the case of nickel, or by B12 and its derivatives, in the case of cobalt. The most dangerous metal, copper, catalyzes Fenton-like reactions, binds to thiol groups, and interferes with iron metabolism. E. coli solves this problem probably by preventing copper uptake, combined with rapid efflux if the metal happens to enter the cytoplasm.

Selective Tumor Cell Inhibition Effect of Ni-Ti Layered Double Hydroxides Thin Films Driven by the Reversed pH Gradients of Tumor Cells

Nitinol is widely fabricated as stents for the palliation treatment of many kinds of cancers. It is of great importance to develop nitinol stents with selective tumor cell inhibition effects. In this work, a series of pH sensitive films composed of Ni(OH)2 and Ni-Ti layered double hydroxide (Ni-Ti LDH) with different Ni/Ti ratios were prepared on the surface of nitinol via hydrothermal treatment. The films with specific Ni/Ti ratios would release a large amount of nickel ions under acidic environments but were relatively stable in neutral or weak alkaline medium. Cell viability tests showed that the films can effectively inhibit the growth of cancer cells but have little adverse effects to normal cells. Besides, extraordinarily high intracellular nickel content and reactive oxygen species (ROS) level were found in cancer cells, indicating the death of cancer cells may be induced by the excessive intake of nickel ions. Such selective cancer cell inhibition effect of the films is supposed to relate with the reversed pH gradients of tumor cells.

Bloodletting therapy in hemochromatosis: Does it affect trace element homeostasis?

Hemochromatosis is the most common hereditary disorder in the Nordic population, if left untreated it can result in severe parenchymal iron accumulation. Bloodletting is mainstay treatment. Iron and trace elements partially share cellular uptake and transport mechanisms, and the aim of the present study was to see if bloodletting for hemochromatosis affects trace elements homeostasis. We recruited patients referred for diagnosis and treatment of hemochromatosis, four women and 22 men 23-68 years of age. Thirteen were C282Y homozygote, one was C282Y heterozygote, three were H63D homozygote, seven were compound heterozygote and two had none of the mutations above. Iron and liver function tests were performed; serum levels of trace elements were measured using inductively coupled plasma mass spectrometry. Results before the start of treatment and after normalization of iron parameters were compared. On completion of the bloodlettings the following average serum concentrations increased: Co from 5.6 to 11.5 nmol/L, serum Cu 16.2-17.6 μmol/L, Ni increased from 50.0 to 52.6 nmol/L and Sb from 13.2 to 16.3 nmol/L. Average serum Mn concentration declined from 30.2 to 28.3 nmol/L. All changes were statistically significant (by paired t-test). B, Ba, Cs, Mo, Se, Sr and Zn were not significantly changed. We conclude that bloodlettings in hemochromatosis lead to changes in trace element metabolism, including increased absorption of potentially toxic elements.

Toxicogenomic effect of nickel and beyond

Nickel is widely applied in industrial settings and Ni(II) compounds have been classified as group one human carcinogens. The molecular basis of Ni(II) carcinogenicity has proved complex, for many stress response pathways are activated and yield unexpected Ni(II)-specific toxicology profile. Ni(II)-induced toxicogenomic change has been associated with altered activity of HIF, p53, c-MYC, NFκB and iron and 2-oxoglutarate-dependent dioxygenases. Advancing high-throughput technology has indicated the toxicogenome of Ni(II) involves crosstalk between HIF, p53, c-MYC, NFκB and dioxygenases. This paper is intended to review the network of Ni(II)-induced common transcription-factor-governed pathways by discussing transcriptome alteration, its governing transcription factors and the underlying mechanism. Finally, we propose a putative target network of Ni(II) as a human carcinogen.

MiRNA-210 modulates a nickel-induced cellular energy metabolism shift by repressing the iron-sulfur cluster assembly proteins ISCU1/2 in Neuro-2a cells

The cellular energy metabolism shift, characterized by the inhibition of oxidative phosphorylation (OXPHOS) and enhancement of glycolysis, is involved in nickel-induced neurotoxicity. MicroRNA-210 (miR-210) is regulated by hypoxia-inducible transcription factor-1α (HIF-1α) under hypoxic conditions and controls mitochondrial energy metabolism by repressing the iron-sulfur cluster assembly protein (ISCU1/2). ISCU1/2 facilitates the assembly of iron-sulfur clusters (ISCs), the prosthetic groups that are critical for mitochondrial oxidation-reduction reactions. This study aimed to investigate whether miR-210 modulates alterations in energy metabolism after nickel exposure through suppressing ISCU1/2 and inactivating ISCs-containing metabolic enzymes. We determined that NiCl2 exposure leads to a significant accumulation of HIF-1α, rather than HIF-1β, in Neuro-2a cells. The miR-210 overexpression and ISCU1/2 downregulation was observed in a dose- and time-dependent manner. The gain-of-function and loss-of-dysfunction assays revealed that miR-210 mediated the ISCU1/2 suppression, energy metabolism alterations, and ISC-containing metabolic enzyme inactivation after nickel exposure. In addition, the impact of miR-210 on ISC-containing metabolic enzymes was independent from cellular iron regulation. Overall, these data suggest that repression of miR-210 on ISCU1/2 may contribute to HIF-1α-triggered alterations in energy metabolism after nickel exposure. A better understanding of how nickel impacts cellular energy metabolism may facilitate the elucidation of the mechanisms by which nickel affects the human health.

How does exposure to nickel and cadmium affect the transcriptome of yellow perch (Perca flavescens)--results from a 1000 candidate-gene microarray

The molecular mechanisms underlying nickel (Ni) and cadmium (Cd) toxicity and their specific effects on fish are poorly understood. Documenting gene transcription profiles offers a powerful approach toward identifying the molecular mechanisms affected by these metals and to discover biomarkers of their toxicity. However, confounding environmental factors can complicate the interpretation of the results and the detection of biomarkers for fish captured in their natural environment. In the present study, a 1000 candidate-gene microarray, developed from a previous RNA-seq study on a subset of individual fish from contrasting level of metal contamination, was used to investigate the transcriptional response to metal (Ni and Cd) and non metal (temperature, oxygen, and diet) stressors in yellow perch (Perca flavescens). Specifically, we aimed at (1) identifying transcriptional signatures specific to Ni and Cd exposure, (2) investigating the mechanisms of their toxicity, and (3) developing a predictive tool to identify the sublethal effects of Ni and Cd contaminants in fish sampled from natural environments. A total of 475 genes displayed significantly different transcription levels when temperature varied while 287 and 176 genes were differentially transcribed at different concentrations of Ni and Cd, respectively. These metals were found to mainly affect the transcription level of genes involved in iron metabolism, transcriptional and translational processes, vitamin metabolism, blood coagulation, and calcium transport. In addition, a linear discriminant analysis (LDA) made using gene transcription levels yielded 94% correctly reassigned samples regarding their level of metal contamination, which indicates the potential of the microarray to detect perch response to Cd or Ni effects.

Anti-apoptotic proteins and catalase-dependent apoptosis resistance in nickel chloride-transformed human lung epithelial cells

Chronic exposure to nickel compounds is associated with increased incidence of certain types of human cancer, including lung and nasal cancers. Despite intensive investigation, the oncogenic processes remain poorly understood. Apoptosis resistance is a key feature for tumor cells to escape physiological surveillance and acquire growth advantage over normal cells. Although NiCl₂ exposure induces transformation of human lung epithelial cells, little information is available with regard to its molecular mechanisms, it is also not clear if the transformed cells are apoptosis resistant and tumorigenic. We explored the apoptosis resistance properties of nickel chloride-transformed human lung epithelial cells and the underlying mechanisms. The results showed that transformed BEAS-2B human lung epithelial cells are resistant to NiCl₂-induced apoptosis. They have increased Bcl-2, Bcl-xL and catalase protein levels over the passage matched non-transformed counterparts. The mechanisms of apoptosis resistance are mitochondria-mediated and caspase-dependent. Forced overexpression of Bcl-2, Bcl-xL and catalase proteins reduced NiCl₂-induced cell death; siRNA-mediated knockdown of their expression sensitized the cells to nickel-induced apoptosis, suggesting that Bcl-2, Bcl-xl and catalase protein expression plays a critical role in apoptosis resistance. Akt also participates in this process, as its overexpression increases Bcl-xL protein expression levels and attenuates NiCl₂-induced apoptosis. Furthermore, transformed cells are tumorigenic in a xenograft model. Together, these results demonstrate that nickel-transformed cells are apoptosis-resistant and tumorigenic. Increased expression of Bcl-2, Bcl-xL and catalase proteins are important mechanisms contributing to transformed cell oncogenic properties.

Mitochondrial Ca2+ uptake from plasma membrane Cav3.2 protein channels contributes to ischemic toxicity in PC12 cells

T-type Ca(2+) channel inhibitors protect hippocampal CA1 neurons from delayed death after global ischemia in rats, suggesting that Cav3.1, Cav3.2, or Cav3.3 channels generate cytotoxic Ca(2+) elevations during anoxia. To test this hypothesis, we measured the Ca(2+) concentration changes evoked by oxygen and glucose deprivation (OGD) in the cytosol and in the mitochondria of PC12 cells. OGD evoked long-lasting cytosolic Ca(2+) elevations that were reduced by Cav3.2 inhibition (50 μm Ni(2+)) and Cav3.1/Cav3.2 silencing and potentiated by Cav3.2 overexpression. The kinetics of the sustained cytosolic Ca(2+) elevations occurring during OGD directly correlated to the extent of cell death measured 20 h after reoxygenation, which was decreased by Ni(2+) and Cav3.1/Cav3.2 silencing and increased by Cav3.2 overexpression. Ni(2+) and Cav3.1/Cav3.2 silencing delayed the decline of cellular ATP during OGD, consistent with a reduction in the Ca(2+) load actively extruded by plasma membrane Ca(2+) pumps. The cytosolic Ca(2+) elevations were paralleled by mitochondrial Ca(2+) elevations that were also increased by Cav3.2 overexpression and decreased by Ni(2+) but not by Cav3.1/Cav3.2 silencing. Overexpression and silencing of the mitochondrial Ca(2+) uniporter, the major mitochondrial Ca(2+) uptake protein, revealed that the cytotoxicity was correlated to the amplitude of the mitochondrial, rather than the cytosolic, Ca(2+) elevations. Selective activation of T-type Ca(2+) channels evoked both cytosolic and mitochondrial Ca(2+) elevations, but only the mitochondrial responses were reduced by Cav3.1/Cav3.2 silencing. We conclude that the opening of Cav3.2 channels during ischemia contribute to the entry of Ca(2+) ions that are transmitted to mitochondria, resulting in a deleterious mitochondrial Ca(2+) overload.

Antioxidant system efficiently protects goldfish gills from Ni(2+)-induced oxidative stress

Fish gills are target organs for waterborne metal ions and this work aimed to investigate the effects of waterborne Ni(2+) (10, 25 and 50 mg L(-1)) on goldfish gills. A special focus was on the relationship between Ni uptake and the homeostasis of reactive oxygen species (ROS) in the gills, the tissue, in direct contact with the metal pollutant. Ni-accumulation in the gills occurred as a function of exposure concentration (R(2)=0.98). The main indices of oxidative stress, namely carbonyl proteins (CP) and lipid peroxides (LOOH), decreased by 21-33% and 21-24%, as well as the activities of principal antioxidant enzymes superoxide dismutase and glutathione-dependent peroxidase, by 29-47% and 41-46%, respectively, in gills of Ni-exposed fish. One of the main players in the antioxidant defense of gills seems to be catalase, which increased by 23-53% in Ni-treated fish, and low molecular mass thiol-containing compounds (L-SH), exceeding untreated controls by 73-105% after fish exposure to 10-50 mg L(-1) of Ni(2+). The increased level of L-SH, mainly represented by reduced glutathione, was supported by enhanced activities of glutathione reductase (by 27-38%), glutathione-S-transferase (56-141%) and glucose-6-phosphate dehydrogenase (by 96-117%) and demonstrates the ability of the antioxidant system of gills to resist Ni-induced oxidative stress.

The control of histone methylation and gene expression by oxidative stress, hypoxia, and metals

The harmful consequences of carcinogenic metals, such as nickel, arsenic, and chromium, are thought to be in part due to their ability to induce oxidative stress. The ubiquity of oxidative stress in biological systems has made it a fairly obvious culprit in causing cellular damage and/or development of disease. However, the full extent of oxidative stress-induced damage is not limited to its direct effects on cellular components, such as lipids, proteins, and DNA, but may extend to its ability to alter gene expression. Gene expression regulation is an important component of cellular and/or tissue homeostasis, and its alteration can have detrimental consequences. Therefore, a growing amount of interest is being paid to understanding how oxidative stress can influence gene expression. Oxidative stress-induced epigenetic dysregulation in the form of posttranslational histone modifications, in particular, is a popular topic of research. This review will therefore primarily focus on discussing the role of oxidative stress and hypoxia on histone methylation and/or gene expression alterations. The sources of oxidative stress discussed here are carcinogenic metals, such as, nickel, arsenic, and chromium.

Substrate profile and metal-ion selectivity of human divalent metal-ion transporter-1

Divalent metal-ion transporter-1 (DMT1) is a H(+)-coupled metal-ion transporter that plays essential roles in iron homeostasis. DMT1 exhibits reactivity (based on evoked currents) with a broad range of metal ions; however, direct measurement of transport is lacking for many of its potential substrates. We performed a comprehensive substrate-profile analysis for human DMT1 expressed in RNA-injected Xenopus oocytes by using radiotracer assays and the continuous measurement of transport by fluorescence with the metal-sensitive PhenGreen SK fluorophore. We provide validation for the use of PhenGreen SK fluorescence quenching as a reporter of cellular metal-ion uptake. We determined metal-ion selectivity under fixed conditions using the voltage clamp. Radiotracer and continuous measurement of transport by fluorescence assays revealed that DMT1 mediates the transport of several metal ions that were ranked in selectivity by using the ratio I(max)/K(0.5) (determined from evoked currents at -70 mV): Cd(2+) > Fe(2+) > Co(2+), Mn(2+) ≫ Zn(2+), Ni(2+), VO(2+). DMT1 expression did not stimulate the transport of Cr(2+), Cr(3+), Cu(+), Cu(2+), Fe(3+), Ga(3+), Hg(2+), or VO(+). (55)Fe(2+) transport was competitively inhibited by Co(2+) and Mn(2+). Zn(2+) only weakly inhibited (55)Fe(2+) transport. Our data reveal that DMT1 selects Fe(2+) over its other physiological substrates and provides a basis for predicting the contribution of DMT1 to intestinal, nasal, and pulmonary absorption of metal ions and their cellular uptake in other tissues. Whereas DMT1 is a likely route of entry for the toxic heavy metal cadmium, and may serve the metabolism of cobalt, manganese, and vanadium, we predict that DMT1 should contribute little if at all to the absorption or uptake of zinc. The conclusion in previous reports that copper is a substrate of DMT1 is not supported.

Carcinogenic metals and the epigenome: understanding the effect of nickel, arsenic, and chromium

Carcinogenic metals, such as nickel, arsenic, and chromium, are widespread environmental and occupational pollutants. Chronic exposure to these metals has been connected with increased risks of numerous cancers and as well as non-carcinogenic health outcomes, including cardiovascular disease, neurologic deficits, neuro-developmental deficits in childhood, and hypertension. However, currently the specific molecular targets for metal toxicity and carcinogenicity are not fully understood. Here, we propose that the iron- and 2-oxoglutarate-dependent dioxygenase family enzymes, as well as, other histone modifying enzymes are important intracellular targets that mediate the toxicity and carcinogenicity of nickel, and maybe potential targets in chromium and arsenic induced carcinogenesis. Our data demonstrate that all three metals are capable of inducing post-translational histone modifications and affecting the enzymes that modulate them (i.e. the iron- and 2-oxoglutarate-dependent dioxygenase family, including HIF-prolyl hydroxylase PHD2, histone demethylase JHDM2A/JMJD1A, and DNA repair enzymes ABH3 and ABH2, and histone methyltransferases, G9a). Given the effects that these metals can exert on the epigenome, future studies of their involvement in histone modifying enzymes dynamics would deepen our understanding on their respective toxicities and carcinogenicities.

Nickel-induced epithelial-mesenchymal transition by reactive oxygen species generation and E-cadherin promoter hypermethylation

Epithelial-mesenchymal transition (EMT) is considered a critical event in the pathogenesis of lung fibrosis and tumor metastasis. During EMT, the expression of differentiation markers switches from cell-cell junction proteins such as E-cadherin to mesenchymal markers such as fibronectin. Although nickel-containing compounds have been shown to be associated with lung carcinogenesis, the role of nickel in the EMT process in bronchial epithelial cells is not clear. The aim of this study was to examine whether nickel contributes to EMT in human bronchial epithelial cells. We also attempted to clarify the mechanisms involved in NiCl(2)-induced EMT. Our results showed that NiCl(2) induced EMT phenotype marker alterations such as up-regulation of fibronectin and down-regulation of E-cadherin. In addition, the potent antioxidant N-acetylcysteine blocked EMT and expression of HIF-1α induced by NiCl(2), whereas the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine restored the down-regulation of E-cadherin induced by NiCl(2). Promoter hypermethylation of E-cadherin, determined by quantitative real time methyl-specific PCR and bisulfate sequencing, was also induced by NiCl(2). These results shed new light on the contribution of NiCl(2) to carcinogenesis. Specifically, NiCl(2) induces down-regulation of E-cadherin by reactive oxygen species generation and promoter hypermethylation. This study demonstrates for the first time that nickel induces EMT in bronchial epithelial cells.

Elucidating the mechanisms of nickel compound uptake: a review of particulate and nano-nickel endocytosis and toxicity

Nickel (Ni) is a worldwide pollutant and contaminant that humans are exposed to through various avenues resulting in multiple toxic responses - most alarming is its clear carcinogenic nature. A variety of particulate Ni compounds persist in the environment and can be distinguished by characteristics such as solubility, structure, and surface charge. These characteristics influence cellular uptake and toxicity. Some particulate forms of Ni are carcinogenic and are directly and rapidly endocytized by cells. A series of studies conducted in the 1980s observed this process, and we have reanalyzed the results of these studies to help elucidate the molecular mechanism of particulate Ni uptake. Originally the process of uptake observed was described as phagocytosis, however in the context of recent research we hypothesize that the process is macropinocytosis and/or clathrin mediated endocytosis. Primary considerations in determining the route of uptake here include calcium dependence, particle size, and inhibition through temperature and pharmacological approaches. Particle characteristics that influenced uptake include size, charge, surface characteristics, and structure. This discussion is relevant in the context of nanoparticle studies and the emerging interest in nano-nickel (nano-Ni), where toxicity assessments require a clear understanding of the parameters of particulate uptake and where establishment of such parameters is often obscured through inconsistencies across experimental systems. In this regard, this review aims to carefully document one system (particulate nickel compound uptake) and characterize its properties.

Bioavailability, intracellular mobilization of nickel, and HIF-1α activation in human lung epithelial cells exposed to metallic nickel and nickel oxide nanoparticles

Micron-sized particles of poorly soluble nickel compounds, but not metallic nickel, are established human and rodent carcinogens. In contrast, little is known about the toxic effects of a growing number of Ni-containing materials in the nano-sized range. Here, we performed physicochemical characterization of NiO and metallic Ni nanoparticles and examined their metal ion bioavailability and toxicological properties in human lung epithelial cells. Cellular uptake of metallic Ni and NiO nanoparticles, but not metallic Ni microparticles, was associated with the release of Ni(II) ions after 24-48 h as determined by Newport Green fluorescence. Similar to soluble NiCl₂, NiO nanoparticles induced stabilization and nuclear translocation of hypoxia-inducible factor 1α (HIF-1α) transcription factor followed by upregulation of its target NRDG1 (Cap43). In contrast to no response to metallic Ni microparticles, nickel nanoparticles caused a rapid and prolonged activation of the HIF-1α pathway that was stronger than that induced by soluble Ni(II). Soluble NiCl₂ and NiO nanoparticles were equally toxic to H460 human lung epithelial cells and primary human bronchial epithelial cells; metallic Ni nanoparticles showed lower toxicity and Ni microparticles were nontoxic. Cytotoxicity induced by all forms of Ni occurred concomitant with activation of an apoptotic response, as determined by dose- and time-dependent cleavage of caspases and poly (ADP-ribose) polymerase. Our results show that metallic Ni nanoparticles, in contrast to micron-sized Ni particles, activate a toxicity pathway characteristic of carcinogenic Ni compounds. Moderate cytotoxicity and sustained activation of the HIF-1α pathway by metallic Ni nanoparticles could promote cell transformation and tumor progression.

Competitive binding of Fe3+, Cr3+, and Ni2+ to transferrin

Competitive binding of Fe(3+), Cr(3+), and Ni(2+) to transferrin (Tf) was investigated at various physiological iron to Tf concentration ratios. Loading percentages for these metal ions are based on a two M(n+) to one Tf (i.e., 100% loading) stoichiometry and were determined using a particle beam/hollow cathode-optical emission spectroscopy (PB/HC-OES) method. Serum iron concentrations typically found in normal, iron-deficient, iron-deficient from chronic disease, iron-deficient from inflammation, and iron-overload conditions were used to determine the effects of iron concentration on iron loading into Tf. The PB/HC-OES method allows the monitoring of metal ions in competition with Fe(3+) for Tf binding. Iron-overload concentrations impeded the ability of chromium (15.0 μM) or nickel (10.3 μM) to load completely into Tf. Low Fe(3+) uptake by Tf under iron-deficient or chronic disease iron concentrations limited Ni(2+) loading into Tf. Competitive binding kinetic studies were performed with Fe(3+), Cr(3+), and Ni(2+) to determine percentages of metal ion uptake into Tf as a function of time. The initial rates of Fe(3+) loading increased in the presence of nickel or chromium, with maximal Fe(3+) loading into Tf in all cases reaching approximately 24%. Addition of Cr(3+) to 50% preloaded Fe(3+)-Tf showed that excess chromium (15.0 μM) displaced roughly 13% of Fe(3+) from Tf, resulting in 7.6 ± 1.3% Cr(3+) loading of Tf. The PB/HC-OES method provides the ability to monitor multiple metal ions competing for Tf binding and will help to understand metal competition for Tf binding.

Comparative pulmonary toxicity of inhaled nickel nanoparticles; role of deposited dose and solubility

In this pilot study, we investigated which physicochemical properties of nickel hydroxide nanoparticles (nano-NH) were mainly responsible in inducing pulmonary toxicity. First, we studied the role of nickel ions solubilized from nano-NH by comparing the toxic effects of nano-NH to those of readily soluble nickel sulfate nanoparticles (nano-NS). Additionally, to test whether there was a non-specific stress response due to particle morphology, we compared the toxicity of nano-NH with that of carbon nanoparticles (nano-C) and titanium dioxide nanoparticles (nano-Ti), both of which had similar physical properties such as particle size and shape, to nano-NH. We exposed mice to each type of nanoparticles for 4?h via a whole-body inhalation system and examined oxidative stress and inflammatory responses in the lung. We also determined the lung burden and clearance of Ni following nano-NH and nano-NS exposures. The results showed that lung deposition of nano-NH was significantly greater than that of nano-NS and nano-NH appeared to have stronger inflammogenic potential than nano-NS even when lung Ni burden taken into consideration. This suggests that the toxicity of nano-NH is not driven solely by released Ni ions from deposited nano-NH particles. However, it is unlikely that the greater toxic potential of nano-NH is attributable to a generic stress response from any nanoparticle exposure, since nano-C and nano-Ti did not elicit toxic responses similar to those of nano-NH. These results indicate that the observed pulmonary toxicity by inhaled nano-NH were chemical-specific and deposited dose and solubility are key factors to understand toxicity induced by nano-NH.

Nickel ions inhibit histone demethylase JMJD1A and DNA repair enzyme ABH2 by replacing the ferrous iron in the catalytic centers

Iron- and 2-oxoglutarate-dependent dioxygenases are a diverse family of non-heme iron enzymes that catalyze various important oxidations in cells. A key structural motif of these dioxygenases is a facial triad of 2-histidines-1-carboxylate that coordinates the Fe(II) at the catalytic site. Using histone demethylase JMJD1A and DNA repair enzyme ABH2 as examples, we show that this family of dioxygenases is highly sensitive to inhibition by carcinogenic nickel ions. We find that, with iron, the 50% inhibitory concentrations of nickel (IC(50) [Ni(II)]) are 25 microm for JMJD1A and 7.5 microm for ABH2. Without iron, JMJD1A is 10 times more sensitive to nickel inhibition with an IC(50) [Ni(II)] of 2.5 microm, and approximately one molecule of Ni(II) inhibits one molecule of JMJD1A, suggesting that nickel causes inhibition by replacing the iron. Furthermore, nickel-bound JMJD1A is not reactivated by excessive iron even up to a 2 mm concentration. Using x-ray absorption spectroscopy, we demonstrate that nickel binds to the same site in ABH2 as iron, and replacement of the iron by nickel does not prevent the binding of the cofactor 2-oxoglutarate. Finally, we show that nickel ions target and inhibit JMJD1A in intact cells, and disruption of the iron-binding site decreases binding of nickel ions to ABH2 in intact cells. Together, our results reveal that the members of this dioxygenase family are specific targets for nickel ions in cells. Inhibition of these dioxygenases by nickel is likely to have widespread impacts on cells (e.g. impaired epigenetic programs and DNA repair) and may eventually lead to cancer development.

Pulmonary response after exposure to inhaled nickel hydroxide nanoparticles: short and long-term studies in mice

Short and long-term pulmonary response to inhaled nickel hydroxide nanoparticles (nano-Ni(OH)(2), CMD = 40 nm) in C57BL/6 mice was assessed using a whole body exposure system. For short-term studies mice were exposed for 4 h to nominal concentrations of 100, 500, and 1000 mg/m(3). For long-term studies mice were exposed for 5 h/d, 5 d/w, for up to 5 months (m) to a nominal concentration of 100 mg/m(3). Particle morphology, size distribution, chemical composition, solubility, and intrinsic oxidative capacity were determined. Markers of lung injury and inflammation in bronchoalveolar lavage fluid (BALF); histopathology; and lung tissue elemental nickel content and mRNA changes in macrophage inflammatory protein-2 (Mip-2), chemokine ligand 2 (Ccl2), interleukin 1-alpha (Il-1α), and tumor necrosis factor-alpha (Tnf-α) were assessed. Dose-related changes in BALF analyses were observed 24 h after short-term studies while significant changes were noted after 3 m and/or 5 m of exposure (24 h). Nickel content was detected in lung tissue, Ccl2 was most pronouncedly expressed, and histological changes were noted after 5 m of exposure. Collectively, data illustrates nano-Ni(OH)(2) can induce inflammatory responses in C57BL/6 mice.

Chemically induced pheochromocytomas in rats: mechanisms and relevance for human risk assessment

Pheochromocytomas are tumors originating from chromaffin cells of the adrenal medulla, which have been observed in numerous carcinogenicity studies. The authors have evaluated pheochromocytoma concurrence with other effects and the possible mechanisms, in order to assess the relevance of such data for the classification of carcinogenic effects and their relevance to humans. The evaluation revealed that pheochromocytomas occur with relatively higher frequency in male rats, especially when the following conditions are involved: hypoxia, uncoupling of oxidative phosphorylation, disturbance in calcium homeostasis, and disturbance of the hypothalamic endocrine axis. The underlying biochemical mechanisms suggest that other substances that interfere with these biochemical endpoints also produce pheochromocytomas. Such endpoints include enzymes involved in catecholamine synthesis, receptor tyrosine kinase (RET), hypoxia-inducible factor (HIF), succinate dehydrogenase, fumarate hydratase, and pyruvate dehydrogenase. To date, there is no indication that the substances inducing pheochromocytomas in animal experiments also induce corresponding tumors in humans. Because the mechanisms of action identified in rats are to be expected in humans, pheochromocytomas may be induced after exposure conditions similar to those used in the animal studies. Whether hereditary mutations represent a risk factor in humans is not clear. Pheochromocytomas that occur in animal experiments currently appear to have little relevance for conditions at the work place. When sufficiently documented and evaluated, such secondary pheochromocytomas are not relevant for classification and human risk assessment.

The interactions of iron with other divalent metals in the intestinal tract of a freshwater teleost, rainbow trout (Oncorhynchusmykiss)

This study examined the concentration-dependent interactive effects of four essential (Cu(2+), Zn(2+), Ni(2+), Co(2+)) and two non-essential (Pb(2+) and Cd(2+)) divalent metals on intestinal iron (Fe(2+)) absorption in freshwater rainbow trout (Oncorhynchusmykiss) using an invitro gut sac technique. All of the divalent metals except cobalt inhibited the intestinal Fe(2+) absorption in fish, and the magnitude of inhibition followed the order of: Ni(2+)~Pb(2+)>Cd(2+)~Cu(2+)>Zn(2+). The mucosal epithelium of the intestine was found to be the most sensitive to inhibition relative to the mucus or blood compartment, suggesting that these interactions likely occur via the divalent metal transporter-1 (DMT1). In addition, the reciprocal effects of Fe(2+) on intestinal accumulation of lead and cadmium were investigated. Elevated Fe(2+) did not affect lead accumulation in the intestine, indicating a greater affinity of Pb(2+) to the Fe(2+) transport pathway and/or the existence of additional pathways for lead absorption. In contrast, the accumulation of cadmium in the intestine decreased considerably in the presence of excess Fe(2+), indicating the importance of the Fe(2+) absorption pathway in dietary cadmium accumulation in fish. Overall, our study provides important insights into the mechanisms of dietary uptake of several divalent metals in freshwater fish.

Simultaneous multiple element detection by particle beam/hollow cathode-optical emission spectroscopy as a tool for metallomic studies: determinations of metal binding with apo-transferrin

Particle beam/hollow cathode-optical emission spectroscopy (PB/HC-OES) is presented as a tool for the determination of metal ion loading in transferrin (Tf). The elemental specificity of optical emission spectroscopy provides a means of assessing metal ion concentrations as well as the relative amounts of metal per unit protein concentration (up to 2 moles of Fe per mole of protein). The PB/HC-OES method allows for the simultaneous detection of metal content (Fe (I) 371.99, Ni (I) 341.41 nm, Zn (I) 213.86 nm, and Ag (I) 338.28 nm in this case), as well as elemental carbon and sulfur (C (I) 156.14 nm and S (I) 180.73 nm) that are reflective of the protein composition and concentration. Quantification for the metal species is based on calibration functions derived from aqueous solutions, with limits of detection for the entire suite being less than 1.0 μM. Determinations in this manner eliminate much of the ambiguity inherent in UV-VIS absorbance determinations of Tf metal binding. Validation of this method is obtained by analyzing loading response of Fe(3+) into Tf using the PB/HC-OES method and comparing the results with those of the standard UV-VIS absorbance method. Maximum Fe(3+) loading of Tf (based on the number of available binding sites) was determined to be 71.2 ± 4.7% by the PB/HC-OES method and 67.5 ± 2.5% for the UV-VIS absorbance method. Element emission ratios between the dopant metals and the carbon and sulfur protein constituents allow for concentration independent determinations of metal binding into Tf. Loading percentages were determined for Ni(2+), Zn(2+), and Ag(+) into Tf with maximum loading values of 19.5 ± 0.4%, 41.0 ± 4.4%, and 141.2 ± 4.3%, respectively. While of no apparent biological significance, Ag(+) presents an interesting case as a surrogate for Pt(2+), whose binding with Tf has shown to be quite different from the other metals. A different mode from the others is indeed observed, and is consistent with conjecture on the Pt(2+) mechanisms. Competitive binding studies not easily performed using absorbance spectroscopy are easily performed by simultaneous, multielement analysis, reflective of the metals and the protein content. In this work, there is clear competition between and Fe(3+) and Zn(2+) for binding in the C-terminus lobe of Tf, while Ni(2+) binds within the N-terminus lobe. Addition of Ag(+) to this mixture does not affect the other metals' distributions, but reflects binding at other protein sites.

Iron- and 2-oxoglutarate-dependent dioxygenases: an emerging group of molecular targets for nickel toxicity and carcinogenicity

Nickel compounds are important occupational and environmental pollutants. Chronic exposure to these pollutants has been connected with increased risks of respiratory cancers and cardiovascular diseases. However, it is still not clear what are the specific molecular targets for nickel toxicity and carcinogenicity. Here, we propose that the iron- and 2-oxoglutarate-dependent dioxygenase family enzymes are important intracellular targets that mediate the toxicity and carcinogenicity of nickel. In support of this hypothesis, our data show that three different classes of enzymes in this iron- and 2-oxoglutarate-dependent dioxygenase family, including HIF-prolyl hydroxylase PHD2, histone demethylase JHDM2A/JMJD1A, and DNA repair enzyme ABH3, are all highly sensitive to nickel inhibition. Inactivation of these enzymes accounts for a number of deleterious effects caused by nickel in cells, namely hypoxia-mimic stress and aberrant epigenetic changes. Future studies on nickel's effects on these iron- and 2-oxoglutarate-dependent dioxygenases would deepen our understanding on nickel toxicity and carcinogenicity.

Metal ions-stimulated iron oxidation in hydroxylases facilitates stabilization of HIF-1 alpha protein

The exposure of cells to several metal ions stabilizes HIF-1 alpha protein. However, the molecular mechanisms are not completely understood. They may involve inhibition of hydroxylation by either substitution of iron by metal ions or by iron oxidation in the hydroxylases. Here we provide evidence supporting the latter mechanism. We show that HIF-1 alpha stabilization in human lung epithelial cells occurred following exposure to various metal and metalloid ions, including those that cannot substitute for iron in the hydroxylases. In each case addition of the reducing agent ascorbic acid (AA)* abolished HIF-1 alpha protein stabilization. To better understand the role of iron oxidation in hydroxylase inhibition and to define the role of AA in the enzyme recovery we applied molecular modeling techniques. Our results indicate that the energy required for iron substitution by Ni(II) in the enzyme is high and unlikely to be achieved in a biological system. Additionally, computer modeling allowed us to identify a tridentate coordination of AA with the enzyme-bound iron, which explains the specific demand for AA as the iron reductant. Thus, the stabilization of HIF-1 alpha by numerous metal ions that cannot substitute for iron in the enzyme, the alleviation of this effect by AA, and our computer modeling data support the hypothesis of iron oxidation in the hydroxylases following exposure to metal ions.

Nickel and the microbial toxin, MALP-2, stimulate proangiogenic mediators from human lung fibroblasts via a HIF-1alpha and COX-2-mediated pathway

Hypoxia-inducible factor (HIF-1alpha) and cyclooxygenase-2 (COX-2) have been implicated in the regulation of inflammatory-like processes that lead to angiogenesis and fibrotic disorders. Here we demonstrate that in human lung fibroblasts (HLFs) treated with mixed exposures to chemical and microbial stimuli, HIF-1alpha stabilization plays a pivotal role in the induction of COX-2 mRNA and protein, driving the release of vascular endothelial growth factor (VEGF) and proangiogenic and profibrotic chemokines. Upon costimulation with Ni and the mycoplasma-derived lipopeptide macrophage-activating lipopeptide-2 (MALP-2), there was a synergistic induction of CXCL1 and CXCL5 mRNA and protein release from HLF, as well as an enhanced response in VEGF compared to either stimulus alone. Consistent with our previous findings that Ni and MALP-2 stimulates the induction of CXCL8 via a COX-2-mediated pathway, CXCL1, CXCL5, and VEGF release were also regulated by COX-2. Ni induced the stabilization of HIF-1alpha protein in HLF, which was further enhanced in the presence of MALP-2. Depletion of HIF-1alpha using siRNA blocked COX-2 induction by Ni and MALP-2 along with the release of VEGF, CXCL1, CXCL5, and CXCL8. Our results indicate that Ni and MALP-2 interact to promote an angiogenic profibrotic phenotype in HLF. Moreover, these findings reveal a potential role for HIF-1alpha in mediating chemical-induced alterations in cellular response to microbial stimuli, modulating pulmonary inflammation and its consequences such as fibrosis and angiogenesis.

Relationship between serum nickel and homocysteine concentration in hemodialysis patients

Severe hyperhomocysteinemia (HHC) is associated with atherosclerosis. In hemodialysis (HD) patients, one of the main causes of death is cardiovascular disease. In animals, trace elements such as cobalt, copper, iron, and nickel ameliorated vitamin B(12) deficiency-induced HHC. However, correlations between plasma total homocysteine (tHcy) and trace elements in HD patients have not been investigated. Therefore, tHcy, folate, vitamin B(12), trace elements (cobalt, copper, iron, and nickel), and some laboratory parameters such as serum total protein, albumin, transferrin, ferritin, C-reactive protein (CRP), and interleukin-6 concentrations were determined in 122 hemodialysis patients. When patients were divided into groups according to their tHcy, we found no significant differences in concentrations of cobalt, copper, and total protein, while nickel was higher, and folate, vitamin B(12), and iron were lower in patients with lower than higher tHcy. In univariate regression analysis, tHcy negatively correlated with concentrations of folate (r = -0.302, p < 0.006), vitamin B(12) (r = -0.347, p < 0.0001), nickel (r = -0.289, p < 0.006), and CRP (r = -0.230, p < 0.02) and positively with serum albumin (r = 0.316, p < 0.0004) and hemoglobin (r = 0.329, p < 0.0001) values. No relationship between tHcy and serum concentrations of cobalt, copper, iron, or other laboratory parameters was found in HD patients. The effect of cobalt and nickel on homocysteine production was assessed in human peripheral mononuclear cells (PBMCs). Nickel but not cobalt at concentrations found in HD patients significantly inhibited homocysteine, cysteine, and S-adenosylhomocysteine production in human PBMCs. These results suggest that nickel might also be involved in the regulation of the methionine-folate cycle in humans, as was demonstrated in animal experiments.

Polo-like kinase 3 functions as a tumor suppressor and is a negative regulator of hypoxia-inducible factor-1 alpha under hypoxic conditions

Polo-like kinase 3 (Plk3) is an important mediator of the cellular responses to genotoxic stresses. In this study, we examined the physiologic function of Plk3 by generating Plk3-deficient mice. Plk3(-/-) mice displayed an increase in weight and developed tumors in various organs at advanced age. Many tumors in Plk3(-/-) mice were large in size, exhibiting enhanced angiogenesis. Plk3(-/-) mouse embryonic fibroblasts were hypersensitive to the induction of hypoxia-inducible factor-1 alpha (HIF-1 alpha) under hypoxic conditions or by nickel and cobalt ion treatments. Ectopic expression of the Plk3-kinase domain (Plk3-KD), but not its Polo-box domain or a Plk3-KD mutant, suppressed the nuclear accumulation of HIF-1 alpha induced by nickel or cobalt ions. Moreover, hypoxia-induced HIF-1 alpha expression was tightly associated with a significant down-regulation of Plk3 expression in HeLa cells. Given the importance of HIF-1 alpha in mediating the activation of the "survival machinery" in cancer cells, these studies strongly suggest that enhanced tumorigenesis in Plk3-null mice is at least partially mediated by a deregulated HIF-1 pathway.

Membrane transporters and protein traffic networks differentially affecting metal tolerance: a genomic phenotyping study in yeast

Genomic phenotyping was used to assess the role of all non-essential S. cerevisiae proteins in modulating cell viability after exposure to cadmium, nickel and other metals.

Background

The cellular mechanisms that underlie metal toxicity and detoxification are rather variegated and incompletely understood. Genomic phenotyping was used to assess the roles played by all nonessential Saccharomyces cerevisiae proteins in modulating cell viability after exposure to cadmium, nickel, and other metals.

Results

A number of novel genes and pathways that affect multimetal as well as metal-specific tolerance were discovered. Although the vacuole emerged as a major hot spot for metal detoxification, we also identified a number of pathways that play a more general, less direct role in promoting cell survival under stress conditions (for example, mRNA decay, nucleocytoplasmic transport, and iron acquisition) as well as proteins that are more proximally related to metal damage prevention or repair. Most prominent among the latter are various nutrient transporters previously not associated with metal toxicity. A strikingly differential effect was observed for a large set of deletions, the majority of which centered on the ESCRT (endosomal sorting complexes required for transport) and retromer complexes, which - by affecting transporter downregulation and intracellular protein traffic - cause cadmium sensitivity but nickel resistance.

Conclusion

The data show that a previously underestimated variety of pathways are involved in cadmium and nickel tolerance in eukaryotic cells. As revealed by comparison with five additional metals, there is a good correlation between the chemical properties and the cellular toxicity signatures of various metals. However, many conserved pathways centered on membrane transporters and protein traffic affect cell viability with a surprisingly high degree of metal specificity.