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

Protective effect of cholecalciferol against cobalt-induced neurotoxicity in rats: ZO-1/iFABP, ChAT/AchE and antioxidant pathways as potential therapeutic targets

Cobalt (Co) toxicity has been reported to produce central nervous system and gastrointestinal abnormalities. This study assessed the therapeutic effect of cholecalciferol (Cho) supplementation against damages caused by sub-acute (14-day) cobalt chloride (CoCl2) exposure in the brain and intestines. Thirty-five male Wistar rats were divided equally into five groups: Group I (control) received no treatment; Group II received oral CoCl2 (100 mg/kg) only; Groups III, IV, and V received 1000, 3000 and 6000 IU/kg of cholecalciferol, respectively by oral gavage, and concurrently with CoCl2. Cobalt-treated rats showed neuronal vacuolation and presence of pyknotic nuclei in the cerebral cortex and hippocampus, depletion of Purkinje cells in the cerebellum, as well as inflammation and congestion in the intestinal mucosa. Cobalt also increased brain and intestinal hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations, while simultaneously reducing glutathione (GSH) content, superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities. Further, CoCl2 induced increases in brain acetylcholinesterase (AchE) activity and serum zonulin (ZO-1) levels. Conversely, Cho administration suppressed CoCl2-induced damages in the brain and intestines by reducing lipid peroxidation and increasing the activities of antioxidant enzymes. Remarkably, Cho produced stimulation of brain choline acetyltransferase (ChAT) and suppression of AchE activity, along with dose-dependent reduction in serum levels of ZO-1, intestinal fatty acid-binding protein (iFABP) and nitric oxide. In conclusion, the protective role of cholecalciferol against cobalt-induced toxicity occurred via modulation of cholinergic, intestinal permeability and antioxidant pathways. The results may prove significant in the context of the role of gut-brain connections in neuroprotection.

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.

Intrahippocampal Effects of Nickel Injection on the Affective and Cognitive Response in Wistar Rat: Potential Role of Oxidative Stress

The present study focused on affective and cognitive behaviors in male Wistar rats, following direct and unique exposure to nickel chloride (NiCl₂), as well as the possible involvement of oxidative stress. The rats were exposed to NiCl₂ (300 μM), by intracerebral administration of 2 μL of this metal at the right hippocampus, using the stereotaxic approach. Five days after the surgery, a battery of behavioral tests was performed, including the open-field test (OFT) and elevated plus maze test (EPM) to assess the state of anxiety-like behavior and forced swimming test (FST) for depressive-like behavior. Y-maze and Morris Water Maze (MWM) were used to evaluate working memory and spatial learning. Thereafter, oxidative stress markers of the hippocampus were evaluated. The results confirm that NiCl₂ exerts anxiogenic effects in both anxiety tests and depressogenic effects in the FST. In addition, MWM and Y-maze data show that NiCl₂ causes memory and spatial learning disorders. The biochemical assay results showed that intrahippocampal injection of NiCl₂ increased the levels of nitric oxide and lipid peroxidation (p < 0.001), while the activities of catalase and superoxide dismutase were significantly decreased in the hippocampus (p < 0.01). Overall, these results suggest that NiCl₂ causes affective and cognitive disorders and oxidative stress in rats.

Exposure to variable doses of nickel oxide nanoparticles disturbs serum biochemical parameters and oxidative stress biomarkers from vital organs of albino mice in a sex-specific manner

INTRODUCTION

This study was designed to report the biological effect of nickel oxide nanoparticles (NiO NPs) in albino mice.

MATERIAL AND METHODS

Five weeks old albino mice of both sex were intraperitoneally injected either with 20 mg (low dose) or 50 mg/mL saline/kg body weight (high dose) of NiO NPs for 14 days. Saline-treated controls were maintained in parallel. Complete blood count, selected serum biochemical parameters and oxidative stress biomarkers from vital organs were determined in all subjects.

RESULTS

Male mice treated with NiO NPS had increased blood urea nitrogen, elevated superoxide dismutase (SOD) in liver elevated MDA in liver, kidney and heart and reduced catalase activity in heart and kidney. Female mice treated with NiO NPs had significantly reduced serum albumin and total proteins, SOD in lungs and elevated MDA in liver.

DISCUSSION

We are reporting that intraperitoneal injections of NiO NPs for 14 days drastically affect blood serum parameters and oxidative stress biomarkers from vital organs of albino mice.

CONCLUSION

Toxic effects of NiO NPs were dose and sex dependent and they were more pronounced at higher dose and in male mice.

Ethanol extract of Nigella sativa has antioxidant and ameliorative effect against nickel chloride-induced hepato-renal injury in rats

Background

Nickel exposure causes hepato-renal toxicity via oxidative stress. Medicinal plants with antioxidants properties are being explored as treatment options. In this study, the effect of ethanol extract of Nigella sativa (ENS) on nickel chloride (NiCl2)-induced hepato-renal damage was evaluated by monitoring biochemical and oxidative stress markers. Additionally, the antioxidant capacity and phytochemical constituents of ENS were quantified using HPLC and GC-MS.

Result

NiCl2 significantly increased (p < 0.05) aspartate aminotransferase, creatinine, sodium ion, chloride ion and malondialdehyde levels, while antioxidant enzymes were decreased in the organs except for kidney glutathione-S-transferase when compared to the control. However, ENS exerted inhibitory effect against NiCl2 toxicity in both organs by reversing the biomarkers towards control levels. ENS has a high antioxidant capacity and is rich in antioxidants including gallic acid, quercetin, eucalyptol and levomenthol that may have accounted for the improvement of hepato-renal health in co-exposed rats.

Conclusion

Our result suggests that amelioration of nickel chloride-induced hepato-renal pathology by ethanol extract of Nigella sativa was related to its antioxidant properties. Therefore, Nigella sativa could be valuable in the management of nickel-induced toxicity.

Nickel reduces calcium dependent dimerization in neural cadherin

Cadherins are the transmembrane component in adherens junctions, structures that link the actin cytoskeletons in adjacent cells within solid tissues including neurological synapses, epithelium and endothelium. Cell-cell adhesion by cadherins requires the binding of calcium ions to specific sites in the extracellular region. Given the complexity of the cell adhesion microenvironment, we are investigating whether other divalent cations might affect calcium-dependent dimerization of neural (N) cadherin. The studies reported herein characterize the impact of binding physiological magnesium(ii) or neurotoxic nickel(ii) on calcium-dependent N-cadherin function. Physiological levels of magnesium have only a small effect on the calcium-binding affinity and calcium-induced dimerization of N-cadherin. However, a tenfold lower concentration of nickel decreases the apparent calcium-binding affinity and calcium-induced dimerization of N-cadherin. Competitive binding studies indicate that the apparent dissociation constants for nickel and magnesium are 0.2 mM and 2.5 mM, respectively. These Kd values are consistent with concentrations observed for a range of divalent cations in the extracellular space. Results from these studies indicate that calcium-induced dimerization by N-cadherin is attenuated by natural and non-physiological divalent cations in the extracellular microenvironment.

Neurotransmitters and Behavioral Alterations Induced by Nickel Exposure

BACKGROUND

Nickel ions (Ni2+) are a heavy metal with wide industrial uses. Environmental and occupational exposures to Ni are potential risk factors for brain dysfunction and behavioral and neurological symptoms in humans.

METHODS

We reviewed the current evidence about neurochemical and behavioral alterations associated with Ni exposure in laboratory animals and humans.

RESULTS

Ni2+ exposure can alter (both inhibition and stimulation) dopamine release and inhibit glutamate NMDA receptors. Few reports claim an effect of Ni2+ at the level of GBA and serotonin neurotransmission. At behavioral levels, exposure to Ni2+ in rodents alters motor activity, learning and memory as well as anxiety and depressive-like symptoms. However, no analysis of the dose-dependent relationship has been carried out regarding these effects and the levels of the Ni2+ in the brain, in blood or urine.

CONCLUSION

Further research is needed to correlate the concentration of Ni2+ in biological fluids with specific symptoms/deficits. Future studies addressing the impact of Ni2+ under environmental or occupational exposure should consider the administration protocols to find Ni2+ levels similar in the general population or occupationally exposed workers.

Mitochondrial respiratory chain inhibition and Na+K+ATPase dysfunction are determinant factors modulating the toxicity of nickel in the brain of indian catfish Clarias batrachus L

Nickel is a potential neurotoxic pollutant inflicting damage in living organisms, including fish, mainly through oxidative stress. Previous studies have demonstrated the impact of nickel toxicity on mitochondrial function, but there remain lacunae on the damage inflicted at mitochondrial respiratory level. Deficient mitochondrial function usually affects the activities of important adenosinetriphosphatases responsible for the maintenance of normal neuronal function, namely Na⁺K⁺ATPase, as explored in our study. Previous reports demonstrated the dysfunction of this enzyme upon nickel exposure but the contributing factors for the inhibition of this enzyme remained unexplored. The main purpose of this study was to elucidate the impact of nickel neurotoxicity on mitochondrial respiratory complexes and Na⁺K⁺ATPase in the piscine brain and to determine the contributing factors that had an impact on the same. Adult Clarias batrachus were exposed to nickel treated water at 10% and 20% of the 96 h LC50 value (41 mg.l^–1) respectively and sampled on 20, 40 and 60 days. Exposure of fish brain to nickel led to partial inhibition of complex IV of mitochondrial respiratory chain, however, the activities of complex I, II and III remained unaltered. This partial inhibition of mitochondrial respiratory chain might have been sufficient to lower mitochondrial energy production in mitochondria that contributed to the partial dysfunction of Na⁺K⁺ATPase. Besides energy depletion other contributing factors were involved in the dysfunction of this enzyme, like loss of thiol groups for enzyme activity and lipid peroxidation-derived end products that might have induced conformational and functional changes. However, providing direct evidence for such conformational and functional changes of Na⁺K⁺ATPase was beyond the scope of the present study. In addition, immunoblotting results also showed a decrease in Na⁺K⁺ATPase protein expression highlighting the impact of nickel neurotoxicity on the expression of the enzyme itself. The implication of the inhibition of mitochondrial respiration and Na⁺K⁺ATPase dysfunction was the neuronal death as evidenced by enhanced caspase-3 and caspase-9 activities. Thus, this study established the deleterious impact of nickel neurotoxicity on mitochondrial functions in the piscine brain and identified probable contributing factors that can act concurrently in the inhibition of Na⁺K⁺ATPase. This study also provided a vital clue about the specific areas that the therapeutic agents should target to counter nickel neurotoxicity.

Effects of Nickel Supplementation on Antioxidant Status, Immune Characteristics, and Energy and Lipid Metabolism in Growing Cattle

Nickel (Ni) has not been elucidated as an essential mineral in dairy animals, though in plants and lower organisms, its role in activation of urease enzyme is well known. This study was conducted to evaluate the effect of Ni supplementation on intake, growth performance, urease activity, antioxidant and immune status, and energy and lipid metabolism in growing cattle. Eighteen growing Hariana heifers were randomly allocated into three groups on body weight (125 ± 3.0 kg) and age basis (10 ± 2.0 months). Feeding regimen was similar in all the groups except that treatment groups were supplemented with 0.0 (Ni_0.0), 1.5 (Ni_1.5), and 3.0 (Ni_3.0) mg of Ni/kg dry matter (DM) in three respective groups. DM intake (DMI), average daily gain (ADG), feed efficiency, plasma urease activity, biomarkers of antioxidant and immune status, energy and lipid metabolism, and plasma Ni levels were observed during the 90-day experimental period. There was linear increase (p < 0.05) in mean DMI and ADG without affecting feed efficiency was observed in 3.0 mg of Ni/kg DM supplemented heifers. Dietary Ni supplementation showed linear increase (p < 0.05) in mean plasma urease activity. No effects of (p > 0.05) of Ni supplementation were observed on superoxide dismutase (SOD) and catalase (CAT) activity and plasma lipid peroxide (LPO) concentration; whereas, mean plasma total antioxidant status (TAS) showed linear decrease (p < 0.001) in Ni-supplemented groups. Adding Ni up to 3.0 mg of Ni/kg DM did not exert (p > 0.05) any effect on plasma total immunoglobulin and immunoglobulin G (IgG) concentrations. Mean plasma cortisol level showed negative association with supplemental Ni levels and concentration was found lowest (p < 0.05) in 3.0 mg of Ni/kg DM-added group. Dietary Ni supplementation did not affect mean plasma concentrations of glucose, cholesterol, triglyceride, and non-esterified fatty acids (NEFA). There was a linear increase (p < 0.001) in plasma Ni concentrations as the Ni concentrations increased in the diet. The results of present study indicated that dietary supplementation of 3.0 mg of Ni/kg DM improved performance of growing cattle by increasing urease activity.

Effect of Chronic Administration of Nickel on Affective and Cognitive Behavior in Male and Female Rats: Possible Implication of Oxidative Stress Pathway

Nickel (Ni) toxicity has been reported to produce biochemical and behavioral dysfunction. The present study was undertaken to examine whether Ni chronic administration can induce alterations of affective and cognitive behavior and oxidative stress in male and female rats. Twenty-four rats, for each gender, divided into control and three test groups (n = 6), were injected intraperitoneally with saline (0.9% NaCl) or NiCl2 (0.25 mg/kg, 0.5 mg/kg and 1 mg/kg) for 8 weeks. After treatment period, animals were tested in the open-field, elevated plus maze tests for anxiety-like behavior, and forced swimming test for depression-like behavior. The Morris Water Maze was used to evaluate the spatial learning and memory. The hippocampus of each animal was taken for biochemical examination. The results showed that Ni administration dose dependently increased anxiety-like behavior in both tests. A significant increase in depression-like symptoms was also exhibited by Ni treated rats. In the Morris Water Maze test, the spatial learning and memory were significantly impaired just in males treated with 1 mg/kg of Ni. With regard to biochemical analysis, activity of catalase (CAT) and superoxide dismutase (SOD) were significantly decreased, while the levels of nitric oxide (NO) and lipid peroxidation (LPO) in the hippocampus were significantly increased in the Ni-treated groups. Consequently, chronic Ni administration induced behavioral and biochemical dysfunctions.

Sub-acute nickel exposure impairs behavior, alters neuronal microarchitecture, and induces oxidative stress in rats' brain

Nickel (Ni) is a heavy metal with wide industrial uses. Environmental and occupational exposures to Ni are potential risk factors for neurological symptoms in humans. The present study investigated the behavior and histomorphological alterations in brain of rats sub-acutely exposed to nickel chloride (NiCl₂) and the possible involvement of oxidative stress. Rats were administered with 5, 10 or 20 mg/kg NiCl₂ via intraperitoneal injections for 21 days. Neurobehavioral assessment was performed using the Y-maze and open field test (OFT). Histomorphological analyses of brain tissues, as well as biochemical determination of oxidative stress levels were performed. Results showed that Ni treatments significantly reduced body weight and food intake. Cognitive and motor behaviors on the Y-maze and OFT, respectively, were compromised following Ni treatments. Administration of Ni affected neuronal morphology in the brain and significantly reduced percentage of intact neurons in both hippocampus and striatum. Additionally, markers of oxidative stress levels and nitric oxide (NO) levels were significantly altered following Ni treatments. These data suggest that compromised behavior and brain histomorphology following Ni exposures is associated with increase in oxidative stress.

Dermal exposure to tannery effluent causes neurobehavioral changes in C57Bl/6J and Swiss mice

Tannery effluents constitute highly polluting residues, which can cause negative impacts to people's health and the environment. However, studies that have investigated the effects of the exposure to these xenobiotics on the central nervous system of mammal experimental models are rare, the few that have been published focusing on the exposure via oral intake (ingestion of water containing tannery effluent concentrations). In this sense, and with the objective of expanding the knowledge beyond the neurotoxic effects observed when water contaminated by these xenobiotics is ingested, the neurobehavioral effects of dermal exposure of male C57Bl/6J and Swiss mice were analyzed. The animals were exposed to raw (wet blue-type) tannery effluent for two hours during five days, totalizing 15 days of exposure. Afterwards, the animals underwent the elevated plus-maze (predictive of anxiety) and the object recognition tests (identification of memory deficit). Our data show that the dermal exposure to the tannery effluent caused an anxiogenic behavior in these animals, when compared those that did not have direct contact with these xenobiotics. It was also observed that the animals exposed to the tannery effluent obtained lower novel object recognition indices, thus evidencing memory deficit and indicating a possible influence of the tannery effluent constituents in animal cognition. The present study attests the hypothesis that dermal exposure to tannery effluents containing neurotoxic substances causes behavioral disorders in C57Bl/6J and Swiss mice.

The neuroprotective effects of taurine against nickel by reducing oxidative stress and maintaining mitochondrial function in cortical neurons

Previous studies have indicated that oxidative stress and mitochondrial dysfunction are involved in the toxicity of nickel. Taurine is recognized as an efficient antioxidant and is essential for mitochondrial function. To investigate whether taurine could protect against the neurotoxicity of nickel, we exposed primary cultured cortical neurons to various concentrations of nickel chloride (NiCl2; 0.5mM, 1mM and 2mM) for 24h or to 1mM NiCl2 for various periods (0 h, 12h, 24h and 48 h). Our results showed that taurine efficiently reduced lactate dehydrogenase (LDH) release induced by NiCl2. Along with this protective effect, taurine pretreatment not only significantly reversed the increase of ROS production and mitochondrial superoxide concentration, but also attenuated the decrease of superoxide dismutase (SOD) activity and glutathione (GSH) concentration in neurons exposed to NiCl2 for 24h. Moreover, nickel exposure reduced ATP production, disrupted the mitochondrial membrane potential and decreased mtDNA content. These types of oxidative damage in the mitochondria were efficiently ameliorated by taurine pretreatment. Taken together, our results indicate that the neuroprotective effects of taurine against the toxicity of nickel might largely depend on its roles in reducing oxidative stress and improving mitochondrial function. Taurine may have great pharmacological potential in treating the adverse effects of nickel in the nervous system.

Reproductive impacts and physiological adaptations of zebrafish to elevated dietary nickel

Nickel (Ni) concentrations in the environment can rise due to human industrial activities. The toxicity of waterborne Ni to aquatic animals has been examined in a number of previous studies; however, little is known about the impacts of elevated dietary Ni. In the present study, zebrafish were chronically fed diets containing two concentrations of Ni [3.7 (control) and 116 μg Ni/g diet]. Ni-exposed males, but not females, were significantly smaller (26%) compared to controls at 80 days. In addition, total egg production was decreased by 65% in the Ni treatment at 75-78 days of the experiment. Ni was ubiquitously distributed in control animals (similar to previous studies), and concentrations varied between tissues by 15-fold. Ni exposure resulted in modest but significant Ni accumulation in some tissues (increases were highest in brain, vertebrae and gut; 44%, 34% and 25%, respectively), an effect observed only at 80 days. The limited Ni accumulation may be due to (1) the lack of an acidified stomach in zebrafish and/or (2) the efficient upregulation of Ni transport and excretion mechanisms, as indicated by the 4.5-fold increase in waterborne (63)Ni uptake by Ni-exposed fish. Eggs from Ni-exposed adults had Ni concentrations that were 5.2-fold higher than controls. However, by 4 days post fertilization, larvae had similar Ni concentrations as controls, demonstrating a capacity for rapid Ni depuration. Larvae from Ni-exposed adults were also more resistant to waterborne Ni (35% increase in the 96-h LC50 over controls). In conclusion, elevated dietary Ni significantly affected zebrafish reproduction despite only modest tissue Ni accumulation. There were also indications of adaptation, including increased Ni uptake rates and increased Ni tolerance of offspring from Ni-exposed adults. Ni concentrations were particularly elevated in the brain with exposure; possible relations to growth and reproductive impacts require further study.

Disturbance of aerobic metabolism accompanies neurobehavioral changes induced by nickel in mice

The oral ingestion of soluble nickel compounds leads to neurological symptoms in humans. Deficiencies in aerobic metabolism induced by neurotoxic stimulus can cause an energy crisis in the brain that results in a variety of neurotoxic effects. In the present study, we focused on the aerobic metabolic states to investigate whether disturbance of aerobic metabolism was involved in nickel-induced neurological effects in mice. Mice were orally administered nickel chloride, and neurobehavioral performance was evaluated using the Morris water maze and open field tests at different time points. Aerobic metabolic states in the cerebral cortex were analyzed at the same time points at which neurobehavioral changes were evident. We found that nickel exposure caused deficits in both spatial memory and exploring activity in mice and that nickel was deposited in their cerebral cortex. Deficient aerobic metabolism manifested as decreased O2 consumption and ATP concentrations, lactate and NADH accumulation, and oxidative stress. Meanwhile, the activity of prototypical iron-sulfur clusters (ISCs) containing enzymes that are known to control aerobic metabolism, including complex I and aconitase, and the expression of ISC assembly scaffold protein (ISCU) were inhibited following nickel deposition. Overall, these data suggest that aerobic metabolic disturbances, which accompanied the neurobehavioral changes, may participate in nickel-induced neurologic effects. The inactivation of ISC containing metabolic enzymes may result in the disturbance of aerobic metabolism. A better understanding of how nickel impacts the energy metabolic processes may provide insight into the prevention of nickel neurotoxicity.