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

Nickel tolerance is channeled through C-4 methyl sterol oxidase Erg25 in the sterol biosynthesis pathway

Nickel (Ni) is an abundant element on Earth and it can be toxic to all forms of life. Unlike our knowledge of other metals, little is known about the biochemical response to Ni overload. Previous studies in mammals have shown that Ni induces various physiological changes including redox stress, hypoxic responses, as well as cancer progression pathways. However, the primary cellular targets of nickel toxicity are unknown. Here, we used the environmental fungus Cryptococcus neoformans as a model organism to elucidate the cellular response to exogenous Ni. We discovered that Ni causes alterations in ergosterol (the fungal equivalent of mammalian cholesterol) and lipid biosynthesis, and that the Sterol Regulatory Element-Binding transcription factor Sre1 is required for Ni tolerance. Interestingly, overexpression of the C-4 methyl sterol oxidase gene ERG25, but not other genes in the ergosterol biosynthesis pathway tested, increases Ni tolerance in both the wild type and the sre1Δ mutant. Overexpression of ERG25 with mutations in the predicted binding pocket to a metal cation cofactor sensitizes Cryptococcus to nickel and abolishes its ability to rescue the Ni-induced growth defect of sre1Δ. As overexpression of a known nickel-binding protein Ure7 or Erg3 with a metal binding pocket similar to Erg25 does not impact on nickel tolerance, Erg25 does not appear to simply act as a nickel sink. Furthermore, nickel induces more profound and specific transcriptome changes in ergosterol biosynthetic genes compared to hypoxia. We conclude that Ni targets the sterol biosynthesis pathway primarily through Erg25 in fungi. Similar to the observation in C. neoformans, Ni exposure reduces sterols in human A549 lung epithelial cells, indicating that nickel toxicity on sterol biosynthesis is conserved.

Rare-earth element yttrium enhances the tolerance of curly-leaf pondweed (Potamogeton crispus) to acute nickel toxicity

Nickel is a ubiquitous heavy-metal pollutant in lakes and severely affects aquatic organisms. Aquatic plants are often initially linked to having heavy metal contents and further are proposed as phytoremediation agent to remove heavy metal from water. Although the toxic effects of nickel on aquatic plants are thoroughly explored, the effective investigation to increase Ni tolerance is still in its infancy. The role of rare-earth elements (REEs) in plant resisting heavy-metal pollution has recently received considerable interest. To explore the physiological effects of REEs on Potamogeton crispus under Ni stress, we explored whether or not the additive exposure to low-dose yttrium (Y; 2.5 μM) promotes the polyamine metabolism, antioxidation, and photosynthesis performance of P. crispus under Ni stress values of 0, 50, 100, 150, and 200 μM. Results showed that Y exposure did not influence Ni bioaccumulation in P. crispus. Furthermore, Y exposure alleviated the adverse effects of Ni stress to convergent degrees because Y positively converts putrescine into spermidine and spermine, inhibits oxidative stress, increases the total chlorophyll content, and maximum/potential quantum efficiency of photosystem II. We concluded that low-dose Y can positively regulate polyamine transformation, inhibit oxidative stress, stimulate photosynthesis, and finally promote the resist ability of P. crispus to nickel stress. Thus, REEs have potential to be applied in regulating submerged plant tolerance to aquatic heavy-metal pollution.

Biochemical and physiological effects of nickel in the euryhaline crab Neohelice granulata (Dana, 1851) acclimated to different salinities

The estuarine crab Neohelice granulata was maintained under control condition or exposed to sublethal concentrations of dissolved Ni (measured: 128 and 1010μg/L) for 96h at different salinities (2 and 30ppt). After metal exposure, whole-body oxygen consumption was measured and tissue (hemolymph, gills, hepatopancreas and muscle) samples were collected. Control crabs acclimated to 2ppt salinity showed lower hemolymph concentrations of Na⁺ (33%), Mg²⁺ (19%) and K⁺ (30%), as well as increased LPO levels in anterior gills (379%), posterior gills (457%) and hepatopancreas (35%) with respect to those acclimated to 30ppt salinity. In crabs acclimated to 2ppt salinity, Ni exposure increased whole-body oxygen consumption (75%), hemolymph K⁺ concentration (52%), hemolymph (135%) and hepatopancreas (62%) LDH activity. Also, it reduced hemolymph Cl^- concentration (16%) and muscle LDH activity (33%). In crabs acclimated to 30ppt salinity, Ni exposure increased LDH activity in hemolymph (195%), hepatopancreas (126%) and muscle (53%), as well as hemolymph osmolality (10%), Cl^- (26%) and Ca²⁺ (20%) concentration. It also reduced hepatopancreas lipid peroxidation (20%) and hemolymph Mg²⁺ (29%) and K⁺ (31%) concentration. These findings indicate that N. granulata is hyper-osmoregulating in 2ppt salinity and hypo-regulating in 30ppt salinity, showing adjustments of hemolymph ionic composition and metabolic rates, with consequent higher oxidative damage to lipids in low salinity (2ppt). Ni effects are associated with metabolic (aerobic and anaerobic) disturbances in crabs acclimated to 2ppt salinity, while osmotic and ionoregulatory disturbances were more evident in crabs acclimated to 30ppt salinity.

Long-term exposure of the isopod Porcellionides pruinosus to nickel: Costs in the energy budget and detoxification enzymes

Terrestrial isopods from the species Porcellionides pruinosus were exposed to the maximum allowed nickel concentration in the Canadian framework guideline (50 mg Ni/kg soil) and to 5× this concentration (250 mg Ni/kg soil). The exposure lasted for 28 days and was followed by a recovery period of 14 days where organisms were changed to clean soil. Organisms were sampled after 24 h, 48 h, 96 h, 7 days, 14 days, 21 days, and 28 days of exposure, and at days 35 and 42 during the recovery period. For each sampling time the acetylcholinesterase (AChE), glutathione-S-transferases (GST), catalase (CAT), lactate dehydrogenase (LDH) activities were determined as well as lipid peroxidation rate (LPO) along with lipids, carbohydrates, proteins content, energy available (Ea), energy consumption (Ec) and cellular energy allocation (CEA). The integrated biomarker response (IBR) was calculated for each sampling time as well as for each one of the above parameters. In addition, mortality was also recorded throughout the assay. The results obtained showed that nickel induced oxidative stress, evidenced by results on GST, GPx, CAT or LPO, but also on changes in the energy reserves content of these organisms. In addition, this study showed that these organisms possess a specific strategy to handle nickel toxicity. In this case, biomarkers were associated with costs in the energy budget, and the increase of energy reserves has a compensation for that cost.

A review of metal-catalyzed molecular damage: protection by melatonin

Metal exposure is associated with several toxic effects; herein, we review the toxicity mechanisms of cadmium, mercury, arsenic, lead, aluminum, chromium, iron, copper, nickel, cobalt, vanadium, and molybdenum as these processes relate to free radical generation. Free radicals can be generated in cells due to a wide variety of exogenous and endogenous processes, causing modifications in DNA bases, enhancing lipid peroxidation, and altering calcium and sulfhydryl homeostasis. Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms. Also, melatonin has a chelating property which may contribute in reducing metal-induced toxicity as we postulate here. The aim of this review was to highlight the protective role of melatonin in counteracting metal-induced free radical generation. Understanding the physicochemical insights of melatonin related to the free radical scavenging activity and the stimulation of antioxidative enzymes is of critical importance for the development of novel therapeutic strategies against the toxic action of these metals.

Molecular and genomic approach for understanding the gene-environment interaction between Nrf2 deficiency and carcinogenic nickel-induced DNA damage

Nickel (II) is a toxic and carcinogenic metal which induces a redox imbalance following oxidative stress. Nuclear factor erythroid-2 related factor 2 (Nrf2) is a redox factor that regulates oxidation/reduction status and consequently mediates cytoprotective responses against exposure to environmental toxicants. In this study, we investigated the protective roles of the Nrf2 gene against oxidative stress and DNA damage induced by nickel at sub-lethal doses. Under nickel exposure conditions, we detected significantly increased intracellular ROS generation, in addition to higher amounts of DNA damage using comet assay and γ-H2AX immunofluorescence staining in Nrf2 lacking cells, as compared to Nrf2 wild-type cells. In addition, we attempted to identify potential nickel and Nrf2-responsive targets and the relevant pathway. The genomic expression data were analyzed using microarray for the selection of synergistic effect-related genes by Nrf2 knockdown under nickel treatment. In particular, altered expressions of 6 upregulated genes (CAV1, FOSL2, MICA, PIM2, RUNX1 and SLC7A6) and 4 downregulated genes (APLP1, CLSPN, PCAF and PRAME) were confirmed by qRT-PCR. Additionally, using bioinformatics tool, we found that these genes functioned principally in a variety of molecular processes, including oxidative stress response, necrosis, DNA repair and cell survival. Thus, we describe the potential biomarkers regarded as molecular candidates for Nrf2-related cellular protection against nickel exposure. In conclusion, these findings indicate that Nrf2 is an important factor with a protective role in the suppression of mutagenicity and carcinogenicity by environmental nickel exposure in terms of gene-environment interaction.

Hepatoprotective role of naringin on nickel-induced toxicity in male Wistar rats

Aim of the present study was planned to determine the protective role of naringin in attenuating the toxicity induced by nickel sulfate in rat liver. In this investigation nickel sulfate (20mg/kg body weight) was administered intraperitoneally for 20days to induce toxicity. Naringin was administered orally (20, 40 and 80mg/kg body weight) for 20days with intraperitoneal administration of nickel sulfate. Liver injury was measured by the increased activities of serum hepatic enzymes namely aspartate transaminase, alanine transaminase, alkaline phosphatase, gamma glutamyl transferase, lactate dehydrogenase and total bilirubin along with increased elevation of lipid peroxidation markers, thiobarbituric reactive acid substances, lipid hydroperoxides, protein carbonyl content and conjugated dienes. The toxic effect of nickel was also indicated by significantly decreased activities of enzymatic antioxidants like superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase, glutathione reductase and glucose-6-phosphate dehydrogenase and non-enzymatic antioxidants like reduced glutathione, total sulfhydryl groups, vitamin C and vitamin E levels were significantly decreased. Naringin administered at a dose of 80mg/kg body weight significantly reversed the activities of hepatic marker enzymes, decreasing lipid peroxidative markers, increasing the antioxidant cascade and decreasing the nickel concentration in the liver. The effect at a dose of 80mg/kg body weight was more pronounced than that of other two doses (20 and 40mg/kg body weight). All these changes were supported by histopathological observations. These results clearly demonstrate that naringin has the potential in alleviating the toxic effects of nickel in rat liver.

The influence of natural stressors on the toxicity of nickel to Daphnia magna

Global warming has become a source of awareness regarding the potential deleterious effects of extreme abiotic factors (e.g., temperature, dissolved oxygen (DO) levels) and also their influence on chemicals toxicity. In this work, we studied the combined effects of nickel and temperature (low and high levels) and nickel and low levels of DO to Daphnia magna, and concentration addition and independent action concepts as well as their deviations for synergism/antagonism, dose ratio and dose level dependency, were applied to survival and feeding rate data. Nickel single exposure showed an LC(50) value for 48 h of 7.36 mg l(-1) and an EC(50) value for feeding impairment at 2.41 mg l(-1). In the acute exposures to high and low temperatures, 50% of mortality was observed, respectively, at 30.7 degrees C and 4.2 degrees C whereas 50% reduction on the feeding activity was recorded at 22.6 degrees C and 16.0 degrees C. Relatively to low DO levels, a LC(50) value for 48 h of 0.5 mg l(-1) was obtained; feeding activity EC(50) value was 2 mg l(-1). On acute combined experiments, antagonism was observed for the combination of nickel and extreme temperatures, whereas a synergistic behaviour was observed in the combined exposure of nickel and low DO levels. At sublethal levels, nickel showed to be the main inducer of toxicity at high and low temperatures but not at low levels of dissolved oxygen. Toxicokinetics and toxicodynamics modelling studies should be made in the future to understand the toxicological pathways involved on complex combinations of stressors and to validate any conclusions.

Mannitol prevents acute lung injury after pancreas ischemia-reperfusion: a dose-response, ex vivo study

Oxidants and their generator, xanthine oxidase (XO), play a major role in the damaging of the structural and functional integrity of the lung. Such damage has been recently demonstrated in the presence of pancreas ischemia-reperfusion (IR). We investigated whether mannitol, a clinically used agent and antioxidant, prevented lung damage after pancreas IR. Rats (n = 48) were anesthetized, after which each pancreas was isolated and perfused (controls), or made ischemic (IR) for 40 min, or made ischemic and treated upon reperfusion with four different doses of mannitol administered in the perfusate (8 replicates/group). Ischemia was followed by in-series 15-min pancreas plus normal isolated lung reperfusion. Isolated lungs were subsequently perfused for 45 min with the 15-min accumulated effluents. Pancreas injury occurred in all IR organs as demonstrated by abnormal reperfusion pressure, the wet-to-dry ratio, amylase and lipase leakage into the circulation, and XO activity and reduced glutathione (GSH) pool in the tissues. Pulmonary plateau pressure increased by 80%, and final PO(2)/FiO(2) decreased by 28% in the IR-untreated paired lungs. Bronchoalveolar lavage volume increased by 50% and 2- to 8-fold increase in their contained XO and GSH were recorded as well. The above indices of injury in lungs perfused with 0.77 mM mannitol were the least detected, compared with negligible efficacy of other (0.55 < 0.22 < 1.1 mM) dosages. Amylase and lipase did not contribute to lung injury. Ex vivo acute pancreatitis induces acute lung injury via oxidants/antioxidants imbalance, which is preventable by mannitol.

Plasma lipid peroxidation and erythrocyte antioxidants status in workers exposed to nickel

The objectives were to investigate the plasma lipid peroxidation and erythrocyte antioxidants status in workers exposed to nickel. The study groups comprised 69 nickel plating workers and 50 office workers residing in the same city, but away from the place of work of the study group subjects, considered as control group. Urinary nickel concentration was determined by graphite furnace atomic absorption spectrophotometry. The plasma lipid peroxidation and erythrocyte antioxidants were measured by spectrophotmetric methods. The plasma lipid peroxidation level was significantly increased in nickel-platers and their helpers as compared with controls. Erythrocyte antioxidants were significantly decreased in the nickel-platers compared with the controls. The level of plasma lipid peroxidation was positively and erythrocyte antioxidants were negatively and significantly correlated with the urine nickel levels. Multiple regression analysis assessed the oxidative stress associated with nickel and other potential confounding factors such as body mass index, the consumption of green vegetables, coffee, tea, smoking and alcohol consumption. Analysis showed that the lifestyle confounding factors: the consumption of green vegetables, smoking and alcohol, were not significantly associated with oxidative stress. The exposure to nickel, body mass index and coffee consumption were significantly associated with oxidative stress. The results show that the increased plasma lipid peroxidation and decreased erythrocyte antioxidants levels observed in nickel-exposed workers could be used as biomarkers of oxidative stress.

Efficacy of caffeic acid in preventing nickel induced oxidative damage in liver of rats

Nickel (Ni), a major environmental pollutant, is known for its wide toxic manifestations. In the present study caffeic acid (CA), one of the most commonly occurring phenolic acids in fruits, grains and dietary supplements, was evaluated for its protective effect against the Ni induced oxidative damage in liver. In this investigation, Ni (20 mg/kg body weight) was administered intraperitoneally for 20 days to induce toxicity. CA was administered orally (15, 30 and 60 mg/kg body weight) for 20 days with intraperitoneal administration of Ni. Ni induced liver damage was clearly shown by the increased activities of serum hepatic enzymes namely aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), gamma glutamyl transferase (GGT) and lactate dehydrogenase (LDH) along with increased elevation of lipid peroxidation indices (thiobarbituric reactive acid substances (TBARS) and lipid hydroperoxides). The toxic effect of Ni was also indicated by significantly decreased levels of enzymatic (superoxide dismutase (SOD), catalase (CAT) glutathione peroxidase (GPx) and glutathione S-transferase (GST)) and non-enzymatic antioxidants (glutathione (GSH), vitamin C and vitamin E). CA administered at a dose of 60 mg/kg body weight significantly reversed the activities of hepatic marker enzymes to their near normal levels when compared with other two doses. In addition, CA significantly reduced lipid peroxidation and restored the levels of antioxidant defense in the liver. All these changes were supported by histological observations. The results indicate that CA may be beneficial in ameliorating the Ni induced oxidative damage in the liver of rats.

Effects of nickel on human and fish red blood cells

The objective of this study was to assess the effects of nickel chloride on human and rainbow trout erythrocytes in vitro. The cells were incubated with 0, 0.5 and 1 mM nickel chloride for 1 h at pH 7.40 and 25 degrees C, then K(+) efflux, SO (4) (2-) uptake and GSH and GSSG concentrations were measured. In both kind of cells, "high concentration" nickel treatment increased KCl efflux with respect to the control. The SO (4) (2-) uptake was not significantly different at "low nickel concentration" but was lower in erythrocytes treated with 1 mM nickel chloride; the rate constant of SO (4) (2-) uptake decreased by 35% in human erythrocytes and by 44% in fish erythrocytes. Nickel chloride also acts on cellular metabolism and in particular on erythrocyte glutathione peroxidase with consequent increase in oxidative stress; the data show a significant decrease in intracellular GSH in both human (25%) and fish erythrocytes (18%) after treatment with nickel chloride, with concomitantly high GSSG concentrations and lower GSH/GSSG ratios.

Role of oxidative stress, mitochondrial membrane potential, and calcium homeostasis in nickel subsulfide-induced human lymphocyte death in vitro

When isolated human lymphocytes were treated in vitro either with various concentrations (0-2 mM) of soluble form of nickel subsulfide (Ni3S2) at 37 degrees C for 4 h or at various times (0-240 min), both concentration- and time-dependent effects of Ni3S2 on lymphocyte death were observed. Increased generation of hydrogen peroxide (H2O2), and superoxide anion (O2-), lipid peroxidation and depletion of both nonprotein (NP-) and protein (P-) sulfhydryl (SH) contents were induced by 1 mM Ni3S2. Ni3S2-induced lymphocyte death was significantly prevented by pre-treatment with either catalase (a H2O2 scavenger), or superoxide dismutase (scavenger of O2- radical), or dimethylthiourea/mannitol (hydroxyl radical scavengers), or deferoxamine (iron-chelator), or glutathione/N-acetylcysteine. Co-treatment with cyclosporin A (a mitochondrial membrane potential' inhibitor) inhibited Ni3S2-induced disturbances in mitochondrial membrane potential, and significantly prevented Ni3S2-induced lymphocyte death. Ni3S2-induced lymphocyte death was also significantly prevented by modulating intracellular calcium fluxes using both Ca2+ channel blockers and intracellular Ca2+ antagonists. Thus, the mechanism of soluble Ni3S2-induced activation of lymphocyte death signalling pathways involves increasing generation of different types of oxidative stress, disturbances in mitochondrial membrane potential and cellular calcium homeostasis' destabilization.

Role of oxidative stress, mitochondrial membrane potential, and calcium homeostasis in human lymphocyte death induced by nickel carbonate hydroxide in vitro

When isolated human lymphocytes were treated in vitro with various concentrations of soluble form of nickel carbonate hydroxide (NiCH) (0-1 mM), at 37 degrees C for 4 h, both concentration- and time-dependent effects of NiCH on lymphocyte death were observed. Increased generation of hydrogen peroxide (H(2)O(2)), superoxide anion (O(2)(-) ), depletion of both no protein (NP-) and protein (P-) sulfhydryl (SH) contents and lipid peroxidation (LPO) were induced by NiCH. Pretreatment of lymphocytes with either catalase (H(2)O(2) scavenger), or deferoxamine (DFO) (iron chelator), or excess glutathione (GSH) (an antioxidant) not only significantly reduced the NiCH-induced generation of H(2)O(2) and LPO, but also increased the NP-SH and P-SH contents initially reduced by NiCH. NiCH-induced generation of excess O(2)(-) but not excess LPO was significantly reduced by pretreatment with superoxide dismutase (SOD). NiCH-induced lymphocyte death was significantly prevented by pre-treatment with either catalase, or dimethylthiourea/mannitol (hydroxyl radical scavengers), or DFO, or excess GSH/N-acetylcysteine. NiCH-induced lymphocyte death was also significantly prevented by pretreatment with excess SOD. Thus, various types of oxidative stresses play an important role in NiCH-induced lymphocyte death. Cotreatment with cyclosporin A (a specific inhibitor of alteration in mitochondrial membrane potential (DeltaPsi(m)) not only inhibited NiCH-induced alteration in DeltaPsi(m), but also significantly prevented Ni-compound-induced lymphocyte death. Furthermore, NiCH-induced destabilization of cellular calcium homeostasis. As such, NiCH-induced lymphocyte death was significantly prevented by modulating intracellular calcium fluxes such as Ca(2+) channel blockers and intracellular Ca(2+) antagonist. Thus, the mechanism of NiCH (soluble form)-induced activation of lymphocyte death signalling pathways involves not only the excess generation of different types of oxidative stress, but also the induction of alteration in DeltaPsi(m) and destabilization of cellular calcium homeostasis as well.

Responses to Nickel in the Proteome of the Hyperaccumulator Plant Alyssum lesbiacum

A proteomic analysis of the Ni hyperaccumulator plant Alyssum lesbiacum was carried out to identify proteins that may play a role in the exceptional degree of Ni tolerance and accumulation characteristic of this metallophyte. Of the 816 polypeptides detected in root tissue by 2D SDS-PAGE, eleven increased and one decreased in abundance relative to total protein after 6-week-old plants were transferred from a standard nutrient solution containing trace concentrations of Ni to a moderately high Ni treatment (0.3 mM NiSO4) for 48 h. These polypeptides were identified by tandem mass spectrometry and the majority were found to be involved in sulphur metabolism (consistent with a re-allocation of sulphur towards cysteine and glutathione), protection against reactive oxygen species, or heat-shock response. In contrast, very few polypeptides were found to change in abundance in root or shoot tissue after plants were exposed for 28 days to 0.03 mM NiSO4, a concentration representing the optimum for growth of this species but sufficient to lead to hyperaccumulation of Ni in the shoot. Under these conditions, constitutively expressed genes in this highly Ni-tolerant species may be sufficient to allow for effective chelation and sequestration of Ni without the need for additional protein synthesis.

Role of oxidative stress, mitochondrial membrane potential, and calcium homeostasis in nickel sulfate-induced human lymphocyte death in vitro

When isolated human lymphocytes were treated in vitro with various concentrations of nickel sulfate (NiSO4) (0-4 mM) at 37 degrees C for 4 h, both concentration- and time-dependent effects of NiSO4 on lymphocyte death were observed. Increased generation of hydrogen peroxide, depletion of both nonprotein and protein sulfhydryl contents, and lipid peroxidation were induced by NiSO4. NiSO4-induced lymphocyte death was significantly prevented by pre-treatment with either catalase, or dimethylthiourea/mannitol, or deferoxamine, or excess glutathione/N-acetylcysteine. Cotreatment with cyclosporin A (a specific inhibitor of mitochondrial membrane potential) not only inhibited NiSO4-induced mitochondrial membrane potential, but also significantly prevented Ni compound-induced lymphocyte death. NiSO4-induced lymphocyte death was also significantly prevented by modulating intracellular calcium fluxes using both Ca2+ channel blockers and intracellular Ca2+ antagonist. Thus, the mechanism of NiSO4-induced activation of lymphocyte death signalling pathways involves not only the excess generation of different types of oxidative stress but also NiSO4-induced loss of mitochondrial membrane potential and destabilization of cellular calcium homeostasis as well.

Oxidative stress due to nickel toxicity in the liver of protein-deficient rats

This study was designed to determine the oxidative stress induced by nickel sulfate in the liver in the protein-deficient rats. Nickel sulfate in the dose of 800 mg/L in drinking water was administrated to Sprauge Dawley (SD) rats as well as protein-deficient rats for a total duration of 8 weeks. The effects of nickel treatment and protein deficiency separately and in combination were studied on rat liver antioxidant defense system enzymes like catalase, glutathione peroxidase (GPX), glutathione reductase (GR), superoxide dismutase (SOD), reduced glutathione (GSH), and glutathione-S-transferase (GST), as well as on lipid peroxidation (LPO). The investigations revealed a significant increase in the activity of enzymes, which include catalase, Gpx, GR and GST, and in the levels with LPO following nickel treatment in combination with protein deficiency. On the contrary, feeding to control rats resulted in a significant depression in the levels of SOD and GSH. However, nickel treatment to normal rats caused a significant increase in the activity of enzymes catalase and GST and in the levels of LPO, whereas the levels of GSH get significantly depressed. Further, nickel treatment to protein-deficient rats did not cause any additional alteration in the status of liver antioxidants as were observed in conditions of protein deficiency.

Protective role of zinc in nickel induced hepatotoxicity in rats

This study was planned to determine the protective role of zinc, if any, in attenuating the toxicity induced by nickel sulfate in rat liver. Female Sprague Dawley (SD) rats received either nickel alone in the dose of 800 mg/l in drinking water, zinc alone in the dose of 227 mg/l in drinking water, and nickel plus zinc or drinking water alone for a total duration of eight weeks. The effects of different treatments were studied on various parameters in rat liver which include antioxidant enzymes, levels of nickel and zinc and histoarchitecture at the light microscopic level. Further, the activities of hepatic marker enzymes AST and ALT were also studied in rat serum. Nickel treatment to the normal control animals, resulted in a significant increase in lipid peroxidation and enzyme activities of catalase and glutathione-S-transferase. On the contrary, nickel treatment to normal rats caused a significant inhibition in the levels of reduced glutathione. Superoxide dismutase activity was found to be decreased which however was not significant. Interestingly, when Zn was supplemented to nickel treated rats, the activities of catalase, and glutathione-S-transferase and the levels of GSH and lipid peroxidation came back to within normal limits. Activities of serum AST and ALT were increased significantly following nickel treatment to normal rats. Simultaneous zinc administration to nickel treated rats tended to restore the altered levels of AST and ALT. Normal control and zinc treated animals revealed normal histology of liver. On the other hand, nickel treated animals showed alterations in normal hepatic histoarchitecture which comprise of vacuolization of the hepatocytes and dilatation of sinusoids as well as increase in the number of bi-nucleated cells. Administration of zinc to nickel treated rats resulted in marked improvement in the structure of hepatocytes, thus emphasizing the protective potential of zinc in restoring the altered hepatic histoarchitecture. The nickel administration to normal rats indicated increased concentrations of nickel and decreased concentrations of zinc. However, zinc effectively brought the altered levels of nickel and zinc to within normal range. The study concludes that zinc has the potential in alleviating the toxic effects of nickel in rat liver because of its property to induce metallothionein (S-rich protein) as a free radical scavenger, or its indirect action in reducing the levels of oxygen reactive species.

Nickel induces oxidative stress and genotoxicity in human lymphocytes

In order to elucidate the oxidative effects and genotoxicity of nickel on human lymphocytes in vitro, we report the level of intracellular reactive oxygen species (ROS), lipid peroxidation, hydroxyl radical ((*)OH), and DNA damage in human lymphocytes after acute exposure to inorganic nickel. NiCl(2) appeared to increase the formation of the fluorescent oxidized compound dichlorofluorescein (DCF). Lipid peroxidation in lymphocytes significantly increased compared to control. 2,3- and 2,5-DHB increased markedly in a concentration-dependent manner. Single-strand DNA breakage induced by Ni in lymphocytes was evaluated by Comet assay. Significant increase in DNA damage score (arbitrary units) showed a dose-related elevation after treatment with NiCl(2). NiCl(2) induced lipid peroxidation at 0.5 mM but had no effect on DNA strand breakage. These results support the emerging concept that NiCl(2)-induced oxidative stress and genotoxicity may be caused by oxygen radical intermediates. NiCl(2)-induced DNA strand breakage is related to the generation of the (*)OH radical.

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

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