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

N-acetyl-L-cysteine alleviated the oxidative stress-induced inflammation and necroptosis caused by excessive NiCl2 in primary spleen lymphocytes

Introduction

Nickel (Ni) is widely used in industrial manufacturing and daily life due to its excellent physical and chemical properties. However, Ni has the potential to harm animals' immune system, and spleen is a typical immune organ. Therefore, it is crucial to understand the mechanism of NiCl2 damage to the spleen. The purpose of this study is to investigate the effects of different concentrations of NiCl2 exposure and intervening with strong antioxidants on spleen lymphocytes to better understand the damage mechanism of Ni on spleen lymphocytes.

Methods

In this experiment, mice spleen lymphocytes were used as the research object. We first measured the degree of oxidative stress, inflammation, and necroptosis caused by different NiCl2 concentrations. Subsequently, we added the powerful antioxidant N-acetyl-L-cysteine (NAC) and used hydrogen peroxide (H2O2) as the positive control in subsequent experiments.

Results

Our findings demonstrated that NiCl2 could cause spleen lymphocytes to produce a large number of reactive oxygen species (ROS), which reduced the mRNA level of antioxidant enzyme-related genes, the changes in GSH-PX, SOD, T-AOC, and MDA, the same to the mitochondrial membrane potential. ROS caused the body to produce an inflammatory response, which was manifested by tumor necrosis factor (TNF-α) in an immunofluorescence experiment, and the mRNA level of related inflammatory genes significantly increased. In the case of caspase 8 inhibition, TNF-α could cause the occurrence of necroptosis mediated by RIP1, RIP3, and MLKL. AO/EB revealed that spleen lymphocytes exposed to NiCl2 had significant necroptosis, and the mRNA and protein levels of RIP1, RIP3, and MLKL increased significantly. Moreover, the findings demonstrated that NAC acted as an antioxidant to reduce oxidative stress, inflammation, and necroptosis caused by NiCl2 exposure.

Discussion

Our findings showed that NiCl2 could cause oxidative stress, inflammation, and necroptosis in mice spleen lymphocytes, which could be mitigated in part by NAC. The study provides a point of reference for understanding the toxicological effect of NiCl2. The study suggests that NAC may be useful in reducing the toxicological effect of NiCl2 on the immune system. The research may contribute to the development of effective measures to prevent and mitigate the toxicological effects of NiCl2 on the immune system.

Neuroprotective effects of methyl jasmonate in male Wistar rats exposed to delayed acetic acid-induced ulcerative colitis: involvement of antioxidant status, GFAP, and IBA-1 immunoreactivities

Neurobehavioral deficits have been severally reported as a comorbid outcome in inflammatory bowel diseases (IBDs). This study evaluated neurological changes in the experimental model of IBDs, as well potential protective effects of methyl jasmonate (MJ). The study used the acetic acid model of colitis and thereafter delayed the healing process by the administration of indomethacin (Indo) (2 mg/kg, SC). Thirty male Wistar rats (120-160 g) were divided into 5 groups (n = 6). Control, Colitis, Colitis + Indo, MJ (50 mg/kg, IP) + Colitis and MJ + Colitis + Indo. Colitis was induced by intrarectal administration of 2 mL, 4% acetic acid. Neurobehavioral studies were carried out to assess memory function, depression, and anxiety on day 7 of post-colitis induction. Animals were thereafter sacrificed to collect the brain tissues for routine histology, immunoreactivity of GFAP and IBA-1, and biochemical assays. Neurobehavioral tests showed anxiety, depression, and memory deficits, especially in the Colitis + Indo group which were accompanied by increased IBA-1 and GFAP count. MJ reversed these effects and reduced GFAP count in the hippocampus and amygdala as well as IBA-1 count in the hippocampus, amygdala, and cortex. Histological observations of these areas showed no significant histopathological changes across all groups. GPx and CAT levels were significantly reduced, while MPO was significantly increased in colitis and Colitis+indo groups when compared with control, which was attenuated in groups administered with MJ. These findings tuggest that MJ possesses neuroprotective, anti-oxidant, and neuron-regeneration properties. Therefore, it could be considered as a potential treatment for behavioral deficits associated with ulcerative colitis.

Andrographis paniculata protects against brain hippocampus and cerebellum from mercury chloride induced damage by attenuating oxidative stress

Mercury chloride (HgCl2) is a neurotoxicant that remains a health hazard despite numerous efforts to reduce its levels in the environment. The use of medicinal plants in treating various diseases and other toxic agents has grown popular owing to their effectiveness and affordable rates. Andrographis paniculata (A. paniculata) is a plant with astringent and detoxifying characteristics and is widely used worldwide for its medicinal and antioxidant benefits. This study aimed to investigate the possible protective effects of A. paniculata aqueous extract against HgCl2-induced memory impairment, oxidative stress, and brain damage. Twenty-five adult Wistar rats were randomly divided into five groups: control, HgCl2 0.5 mg/kg, HgCl2+AP 250 mg/kg, HgCl2+AP 500 mg/kg, or HgCl2+Ascorbic acid 200 mg/kg. For 28 days, administrations were given through oral gavage once a day. HgCl2 injection resulted in memory impairment, increased glutamate concentrations in the brain, and the production of oxidative stress. Memory impairment was prevented in A. paniculata-treated groups by balancing the levels of AChE and dopamine activities, which then lowered glutamate concentration, avoided oxidative stress, and improved histopathological alterations in the brain. A. paniculata alleviated HgCl2-induced memory impairment in Wistar rats by increasing the memory index, regulating neurotransmitter levels, and reducing oxidative stress.

Sex-dependent metal accumulation and immunoexpression of Hsp70 and Nrf2 in rats' brain following manganese exposure

Manganese (Mn), although important for multiple cellular processes, has posed environmental health concerns due to its neurotoxic effects. In recent years, there have been extensive studies on the mechanism of Mn-induced neuropathology, as well as the sex-dependent vulnerability to its neurotoxic effects. Nonetheless, cellular mechanisms influenced by sex differences in susceptibility to Mn have yet to be adequately characterized. Since oxidative stress is a key mechanism of Mn neurotoxicity, here, we have probed Hsp70 and Nrf2 proteins to investigate the sex-dependent changes following exposure to Mn. Male and female rats were administered intraperitoneal injections of MnCl2 (10 mg/kg and 25 mg/kg) 48 hourly for a total of eight injections (15 days). We evaluated changes in body weight, as well as Mn accumulation, Nrf2 and Hsp70 expression across four brain regions; striatum, cortex, hippocampus and cerebellum in both sexes. Our results showed sex-specific changes in body-weight, specifically in males but not in females. Additionally, we noted sex-dependent accumulation of Mn in the brain, as well as in expression levels of Nrf2 and Hsp70 proteins. These findings revealed sex-dependent susceptibility to Mn-induced neurotoxicity corresponding to differential Mn accumulation, and expression of Hsp70 and Nrf2 across several brain regions.

Influence of heavy metals in Parkinson's disease: an overview

Parkinson's disease (PD) is an ageing disorder with deterioration of dopamine neurons which leads to motor complications like tremor, stiffness, slow movement and postural disturbances. In PD, both genetics as well as environmental factors both play a major role in causing the pathogenesis. Though there are surfeit of risk factors involved in PD occurrence, till now there is lack of an exact causative agent as a risk for PD with confirmative findings. The role of heavy metals reported to be a significant factor in PD pathogenesis. Heavy metal functions in cell maintenance but growing pieces of evidences reported to cause dyshomeostasis with increased PD rate. Metals disturb the molecular processes and results in oxidative stress, DNA damage, mitochondrial dysfunction, and apoptosis. The present review elucidates the role of cobalt, nickel, mercury, chromium, thallium metals in α-synuclein aggregation and its involvement in blood brain barrier flux. Also, the review explains the plausible role of aforementioned metals with a mechanistic approach and therapeutic recommendations in PD.

D-Ribose-LCysteine attenuates manganese-induced cognitive and motor deficit, oxidative damage, and reactive microglia activation

Due to overexposure, manganese (Mn) accumulation in the brain can trigger the inhibition of glutathione synthesis and lead to increased generation of reactive oxygen species (ROS) and oxidative stress. D-Ribose-L-Cysteine (RibCys) has been demonstrated to effectively support glutathione synthesis to scavenge ROS and protect cells from oxidative damage. In the present study, we examined the effects of RibCys on weight changes, cognitive and motor associated activities, oxidative stress markers, striatal and cortical histology, and microglia activation following Mn exposure. Rats were exposed to either saline, Mn or/and RibCys for two weeks. The Mn exposed rats received RibCys either as pre-, co-, or post-treatments. Mn caused a significant decrease in weight, memory and motor activities, increased lactate dehydrogenase level, overexpression of IBA1 reflecting microglia activation, and distortion of the neuronal cytoarchitecture of the striatum and motor cortex, respectively. Interventions with RibCys mitigated Mn-induced neurotoxic events. Our novel study demonstrates that RibCys effectively ameliorates the neurotoxicity following Mn treatment and maybe a therapeutic strategy against the neurological consequences of Mn overexposurec.

Melatonin ameliorates nickel induced autophagy in mouse brain: diminution of oxidative stress

Nickel（Ni) is a neurotoxic environmental pollutant. Oxidative stress is thought to be the main mechanism behind the development of Ni neurotoxicity. Melatonin (Mt) has significant efficacy as an antioxidant. In this paper, we investigated the damage that Ni causes to the autophagy of the nervous system. Furthermore, Mt has can intervene upon the damage caused by Ni, which can protect the nervous system. Herein, we randomly divided 80 8-week-old male wild-type C57BL/6N mice into four groups, including the C group, Ni group, Mt group, and Mt+Ni group. Ni was gavaged at a concentration of 10mg/kg, while was Mt was administered at a concentration of 2mg/kg for 21 days at 0.1ml/10g body weight of the mice. Histopathological and ultrastructural observations demonstrated altered states, such as neuronal atrophy, as well as typical autophagic features in the Ni group. Mt was able to intervene effectively in Ni-induced neurotoxicity. The antioxidant capacity assay also demonstrated that Ni can lead to a large amount of reactive oxygen species (ROS) production within the mouse brain. Furthermore, the same Mt was effective at reducing ROS production. In order to further illustrate this point, we added the broad-spectrum phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 to NS20Y cells. The presence of inhibitors effectively demonstrates that, within the PI3K/AKT/mTOR pathway, autophagy occurs. In conclusion, these data suggest that Ni causes oxidative stress damage and induces autophagy within the mouse brain by inhibiting the PI3K/AKT/mTOR pathway, and that Mt can effectively alleviate the oxidative stress caused by Ni, and reducing Ni induces autophagy in the mouse brain through the PI3K/AKT/mTOR pathway.

Protective Effects of Selenium and Zinc Against Nickel Chloride-Induced Hormonal Changes and Oxidative Damage in Thyroid of Pregnant Rats

Nickel chloride (NiCl₂) is a heavy metal that may affect the function of the thyroid. Selenium (Se) and zinc (Zn) are essential trace elements involved in thyroid hormone metabolism. However, little is reported about thyrotoxicity during gestation. The current study aimed to investigate the protective effects of selenium and zinc against NiCl₂-induced thyrotoxicity in pregnant Wistar rats. Female rats were treated subcutaneously (s.c.) on the 3rd day of pregnancy, with NaCl 0.9% and served as control, NiCl₂ (100 mg/kg body weight (BW)) alone, or in association with Se (0.3 mg/kg, s.c.), ZnCl₂ (20 mg/kg, s.c.), or both of them simultaneously. Oxidative stress parameters, thyroid biomarkers, and histopathological examination were evaluated. Results showed that NiCl₂ exposure caused a significant decrease in maternal body weight and an increase in absolute and relative thyroid weight compared to the controls. NiCl₂ administration also led to decreased plasma triiodothyronine (T3) and thyroxine (T4) with a concomitant significant increase in thyroid-stimulating hormone (TSH) levels when compared to that of control. In addition, an overall pro-oxidant effect was associated with a decrease in the reduced glutathione (GSH) and nonprotein thiol (NPSH) contents and the enzymatic activity of glutathione peroxidase (GPx) and superoxide dismutase (SOD), and an increase in malondialdehyde (MDA). These biochemical disturbances were confirmed by histological changes. However, the co-treatment of Se and/or ZnCl₂ attenuates NiCl₂-induced changes. Our findings suggested that Se and ZnCl₂ ameliorated NiCl₂-induced thyrotoxicity in pregnant Wistar rats by exhibiting antioxidant effects.

D-Ribose-L-Cysteine Improves Glutathione Levels, Neuronal and Mitochondrial Ultrastructural Damage, Caspase-3 and GFAP Expressions Following Manganese-Induced Neurotoxicity

Repeated manganese (Mn) exposure may cause increased production of reactive oxygen species (ROS), with a consequent imbalance in the glutathione (GSH) antioxidant defence system, resulting in cellular dysfunctions, and eventually cell death, particularly in the brain. D-ribose-L-cysteine (RibCys) has been demonstrated to effectively promote the synthesis of glutathione, a potent neutralizer of ROS. In the present study, we examined the effects of RibCys on glutathione levels, apoptotic and astrocytic responses, neuronal ultrastructural integrity, following Mn exposure. Wild-type rats were exposed to either saline, Mn, or/and RibCys for 2 weeks. The Mn-exposed rats received RibCys either as pre-, co-, or post-treatments. Mn caused a marked decrease in GSH levels, overexpression of GFAP and caspase-3, reflecting astrocytosis and apoptosis, and altered ultrastructural integrities of the neuronal nuclei, mitochondria, and myelin sheath of the striatum and motor cortex respectively, while all interventions with RibCys minimized and prevented the neurotoxic events. Our study demonstrates that RibCys effectively attenuates the neurotoxic effects of Mn and may be useful as a therapeutic strategy against neurological consequences of Mn overexposure.

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.

Nω-nitro-L-arginine, a nitric oxide synthase inhibitor, attenuates nickel-induced neurotoxicity

The various mediums of exposure to nickel (Ni) compounds have raised enormous public health concerns, as it has been illustrated to exert toxic effects in biological organs, including the brain. We have previously implicated the involvement of elevated nitric oxide (NO) in Ni-induced oxidative stress in the brain. Hence, the present study investigated the ameliorative potential of N^ω-nitro-L-arginine (L-NA), a NO synthase inhibitor, following Ni-induced neurotoxicity. Adult male rats were divided into four groups; control (normal saline), 10 mg/kg Ni chloride (NiCl₂) only, 1 mg/kg L-NA, or 2 mg/kg L-NA co-administered with NiCl₂. The administration was via daily intraperitoneal injections for three weeks. Neurobehavioural assessments performed thereafter ascertained short-term spatial memory and anxiety. Furthermore, histological evaluations of the cortex, hippocampus, and striatum were carried out using routine hematoxylin and eosin technique, while the phosphotungstic acid hematoxylin method was used to express the degree of astrogliosis. Biochemical analysis of NO levels was examined along with other oxidative stress markers (superoxide dismutase, catalase, glutathione, glutathione S transferase, glutathione peroxidase, myeloperoxidase, and lipid peroxidation). The results illustrated altered behavioral responses, a higher population of degenerating neurons, and astrocytes in the NiCl₂ group. There was also an elevation in the NO level and a corresponding reduction in antioxidant activities. However, these debilitating changes were ameliorated in the L-NA treated groups. These results demonstrate an association between alterations in NO synthesis pathway and Ni neurotoxicity, which may render neuronal cells susceptible to damage by oxidative stress. This may yet be another mechanism and useful therapeutic marker in deciphering Ni-induced neurotoxicity.

Brain region- and metal-specific effects of embedded metals in a shrapnel wound model in the rat

The health effects of prolonged exposure to embedded metal fragments, such as those found in shrapnel wounds sustained by an increasing number of military personnel, are not well known. As part of a large collaborative effort to expand this knowledge, we use an animal model of shrapnel wounds originally developed to investigate effects of embedded depleted uranium to investigate effects of military-relevant metals tungsten, nickel, cobalt, iron, copper, aluminum, lead, and depleted uranium compared to an inert control, tantalum. Rats are surgically implanted with pellets of one of the metals of interest in the gastrocnemius (leg) muscle and tracked until 1 month, 3 months, 6 months, or 12 months from the time of implant, at which point they are euthanized and multiple organs and tissue samples are collected for inspection. Here we focus on four regions of the brain: frontal cortex, hippocampus, amygdala, and cerebellum. We examined changes in accumulated metal concentration in each region as well as changes in expression of proteins related to blood brain barrier tight junction formation, occludin and ZO-1, and synapse function, PSD95, spinophilin, and synaptotagmin. We report few changes in metal accumulation or blood brain barrier protein expression, but a large number of synapse proteins have reduced expression levels, particularly within the first 6 months of exposure, but there are regional and metal-specific differences in effects.

Neuroprotective effect of melatonin on nickel-induced affective and cognitive disorders and oxidative damage in rats

The present work is carried out to explore the neuroprotective potential of Melatonin(Mel), on Ni-induced neurobehavioral, biochemical and histological alterations in male and female rats. The rats were intraperitoneally administered by nickel chloride (NiCl2, 1 mg/kg) and Mel (4 mg/kg) for 60 days. A neurobehavioral assessment was performed. Biochemical determinations of oxidative stress (OS) levels, and histological analysis of hippocampal tissues were also performed. Results showed that Nickel (Ni) treatment increased anxiety-like and depression-like behavior in rats. Besides, cognitive behavior on the Morris water maze was compromised following Ni treatment. Alongside this, Ni elevated hippocampal OS markers like lipid peroxidation and nitric oxide formation with a decrease in superoxide dismutase and catalase activities. Histological observations confirmed these results. Significantly, Mel administration alleviated neurobehavioral changes in Ni-treated rats of both genders. Also, Mel attenuated Ni-induced OS and increased the activities of antioxidant enzymes. The histopathological studies in the hippocampus supported that Mel markedly reduced the Ni-induced neuronal loss. In conclusion, this study suggests that Mel has a neuroprotective effect against Ni-induced neurobehavioral alterations, which may be related to lowering OS in the hippocampus.

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.

Epigenetic influence of environmentally neurotoxic metals

Continuous globalization and industrialization have ensured metals are an increasing aspect of daily life. Their usefulness in manufacturing has made them vital to national commerce, security and global economy. However, excess exposure to metals, particularly as a result of environmental contamination or occupational exposures, has been detrimental to overall health. Excess exposure to several metals is considered environmental risk in the aetiology of several neurological and neurodegenerative diseases. Metal-induced neurotoxicity has been a major health concern globally with intensive research to unravel the mechanisms associated with it. Recently, greater focus has been directed at epigenetics to better characterize the underlying mechanisms of metal-induced neurotoxicity. Epigenetic changes are those modifications on the DNA that can turn genes on or off without altering the DNA sequence. This review discusses how epigenetic changes such as DNA methylation, post translational histone modification and noncoding RNA-mediated gene silencing mediate the neurotoxic effects of several metals, focusing on manganese, arsenic, nickel, cadmium, lead, and mercury.

Environmental influence on neurodevelopmental disorders: Potential association of heavy metal exposure and autism

Environmental factors have been severally established to play major roles in the pathogenesis of neurodevelopmental disorders including autism spectrum disorder (ASD). ASD is a neurodevelopmental disorder that is associated with symptoms that reduce the quality of life of affected individuals such as social interaction deficit, cognitive impairment, intellectual disabilities, restricted and repetitive behavioural patterns. ASD pathogenesis has been associated with environmental and genetic factors that alter physiologic processes during development. Here, we review literatures highlighting the environmental impact on neurodevelopmental disorders, and mechanisms by which environmental toxins may influence neurodevelopment. Furthermore, this review discusses reports highlighting neurotoxic metals (specifically, lead, mercury, cadmium, nickel and manganese) as environmental risk factors in the aetiology of ASD. This work, thus suggests that improving the environment could be vital in the management of ASD.

The aging brain: impact of heavy metal neurotoxicity

The aging process is accompanied by critical changes in cellular and molecular functions, which upset the homeostatic balance in the central nervous system. Accumulation of metals renders the brain susceptible to neurotoxic insults by mechanisms such as mitochondrial dysfunction, neuronal calcium-ion dyshomeostasis, buildup of damaged molecules, compromised DNA repair, reduction in neurogenesis, and impaired energy metabolism. These hallmarks have been identified to be responsible for neuronal injuries, resulting in several neurological disorders. Various studies have shown solid associations between metal accumulation, abnormal protein expressions, and pathogenesis of neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and Amyotrophic lateral sclerosis. This review highlights metals (such as manganese, zinc, iron, copper, and nickel) for their accumulation, and consequences in the development of neurological disorders, in relation to the aging brain.

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.

The sustaining effects of e-waste-related metal exposure on hypothalamus-pituitary-adrenal axis reactivity and oxidative stress

Taizhou is one of the three largest electronic waste (e-waste) recycling locations in China. At present, to prevent the environmental problems stem from e-waste dismantling, the local government shut down all the industries in 2015. However, little is known to the sustaining effects of e-waste exposure on human health after the e-waste recycling factories were closed. In this study, we collected blood samples in the residents living near e-waste dismantling factories (exposed group) and a chosen reference area (reference group) for comparison in Taizhou in December 2017.17 metals were quantitatively determined in all blood samples. Among them, the concentrations of altogether 9 metals, including chromium (Cr), arsenic (As), cobalt (Co), nickel (Ni), silver (Ag), stannum (Sn), mercury (Hg), lanthanum (La) and cerium (Ce) were significant higher in the individuals in exposed group than in reference group. Hypothalamus-pituitary-adrenal axis (HPA axis) is critical endocrine system in regulating many physical functions. We found that the concentrations of hormones in HPA axis, including corticotropin releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and cortisol, were higher in exposed group than in reference group. Moreover, we also observed significantly higher concentrations of biomarkers of oxidative stress (OS), including malondialdehyde (MDA) and 8-isoprostane (8-I), in exposed group compared with reference group even though the e-waste industries have been shut down for over 2 years. Meanwhile, the hormones in the HPA axis and the biomarkers of OS showed sinificantly positive correlation. The results of Pearson correlation and multiple linear regression showed that blood Cr and Ni positively correlated with the 3 hormones and 2 biomarkers of OS. Considering the relationship between Ni and Cr, HPA axis, OS, we speculated that high concentrations of Cr and Ni exposure could induce oxidative damage in e-waste exposure persons, and the regulations of HPA axis could play the important role during the process.

Metal brain bioaccumulation and neurobehavioral effects on the wild rodent Liomys irroratus inhabiting mine tailing areas

Ecotoxicological studies are necessary in order to evaluate the effects of environmental exposure of chemicals on wild animals and their ecological consequences. Particularly, neurobehavioral effects of heavy metal elements on wild rodents have been scarcely investigated. In the present study, we analyzed the effect of metal bioaccumulation (Pb, As, Mg, Ni, and Zn) in the brain and in the liver on exploratory activity, learning, memory, and on some dopaminergic markers in the wild rodent Liomys irroratus living inside mine tailings, at Huautla, Morelos, Mexico. We found higher Pb concentration but lower Zn in striatum, nucleus accumbens, midbrain, and hippocampus in exposed animals in comparison to rodents from the reference site. Exposed rodents exhibited anxious behavior evaluated in the open field, while no alterations in learning were found. However, they displayed slight changes in the memory test in comparison to reference group. The neurochemical evaluation showed higher levels of dopamine and 5-hydroxyindolacetic acid in midbrain, while lower levels of metabolites dihydroxyphenyl acetic acid and homovanillic acid in striatum of exposed rodents. In addition, mRNA expression levels of dopaminergic D2 receptors in nucleus accumbens were lower in animals from the mining zone than in animals from the reference zone. This is the first study that shows that chronic environmental exposure to metals results in behavioral and neurochemical alterations in the wild rodent L. irroratus, a fact that may comprise the survival of the individuals resulting in long-term effects at the population level. Finally, we suggest the use of L. irroratus as a sentinel species for environmental biomonitoring of mining sites.

Associations between Trace Elements and Cognitive Decline: An Exploratory 5-Year Follow-Up Study of an Elderly Cohort

Trace elements (TE) homeostasis is crucial in normal brain functioning. Although imbalances have the potential to exacerbate events leading neurodegenerative diseases, few studies have directly addressed the eventual relationships between TE levels in the human body and future cognitive status. The present study aimed to assess how different TE body-levels relate to cognitive decline. This exploratory research included a study-group (RES) of 20 elderly individuals living in two Portuguese geographical areas of interest (Estarreja; Mértola), as well as a 20 subjects neuropsychological control-group (CTR). Participants were neuropsychologically assessed through the Mini Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA) and the RES group was biomonitored for TE through fingernail analysis. After 5 years, the cognitive assessments were repeated. Analyses of the RES neuropsychological data showed an average decrease of 6.5 and 5.27 points in MMSE and MoCA, respectively, but TE contents in fingernails were generally within the referenced values for non-exposed individuals. Higher levels of Nickel and Selenium significantly predicted lesser cognitive decline within 5 years. Such preliminary results evidence an association between higher contents of these TE and higher cognitive scores at follow-up, suggesting their contribution to the maintenance of cognitive abilities. Future expansion of the present study is needed in order to comprehensively assess the potential benefits of these TE.

Early life metal dysregulation in amyotrophic lateral sclerosis

OBJECTIVE

Deficiencies and excess of essential elements and toxic metals are implicated in amyotrophic lateral sclerosis (ALS), but the age when metal dysregulation appears remains unknown. This study aims to determine whether metal uptake is dysregulated during childhood in individuals eventually diagnosed with ALS.

METHODS

Laser ablation-inductively coupled plasma-mass spectrometry was used to obtain time series data of metal uptake using biomarkers in teeth from autopsies or dental extractions of ALS (n = 36) and control (n = 31) participants. Covariate data included sex, smoking, occupational exposures, and ALS family history. Case-control differences were identified in temporal profiles of metal uptake for individual metals using distributed lag models. Weighted quantile sum (WQS) regression was used for metals mixture analyses. Similar analyses were performed on an ALS mouse model to further verify the relevance of dysregulation of metals in ALS.

RESULTS

Metal levels were higher in cases than in controls: 1.49 times for chromium (1.11-1.82; at 15 years), 1.82 times for manganese (1.34-2.46; at birth), 1.65 times for nickel (1.22-2.01; at 8 years), 2.46 times for tin (1.65-3.30; at 2 years), and 2.46 times for zinc (1.49-3.67; at 6 years). Co-exposure to 11 elements indicated that childhood metal dysregulation was associated with ALS. The mixture contribution of metals to disease outcome was likewise apparent in tooth biomarkers of an ALS mouse model, and differences in metal distribution were evident in ALS mouse brains compared to brains from littermate controls.

INTERPRETATION

Overall, our study reveals direct evidence that altered metal uptake during specific early life time windows is associated with adult-onset ALS.

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.

Impact of Heavy Metals on Host Cells: Special Focus on Nickel-Mediated Pathologies and Novel Interventional Approaches

BACKGROUND

Heavy metals [arsenic, aluminium, cadmium, chromium, cobalt, lead, nickel (Ni), palladium and titanium] are environmental contaminants able to impact with host human cells, thus, leading to severe damage.

OBJECTIVE

In this review, the detrimental effects of several heavy metals on human organs will be discussed and special emphasis will be placed on Ni. In particular, Ni is able to interact with Toll-like receptor-4 on immune and non-immune cells, thus, triggering the cascade of pro-inflammatory cytokines. Then, inflammatory and allergic reactions mediated by Ni will be illustrated within different organs, even including the central nervous system, airways and the gastrointestinal system.

DISCUSSION

Different therapeutic strategies have been adopted to mitigate Ni-induced inflammatoryallergic reactions. In this context, the ability of polyphenols to counteract the inflammatory pathway induced by Ni on peripheral blood leukocytes from Ni-sensitized patients will be outlined. In particular, polyphenols are able to decrease serum levels of interleukin (IL)-17, while increasing levels of IL- 10. These data suggest that the equilibrium between T regulatory cells and T helper 17 cells is recovered with IL-10 acting as an anti-inflammatory cytokine. In the same context, polyphenols reduced elevated serum levels of nitric oxide, thus, expressing their anti-oxidant potential. Finally, the carcinogenic potential of heavy metals, even including Ni, will be highlighted.

CONCLUSION

Heavy metals, particularly Ni, are spread in the environment. Nutritional approaches seem to represent a novel option in the treatment of Ni-induced damage and, among them, polyphenols should be taken into consideration for their anti-oxidant and anti-inflammatory activities.

Nickel Enhances Zinc-Induced Neuronal Cell Death by Priming the Endoplasmic Reticulum Stress Response

Trace metals such as zinc (Zn), copper (Cu), and nickel (Ni) play important roles in various physiological functions such as immunity, cell division, and protein synthesis in a wide variety of species. However, excessive amounts of these trace metals cause disorders in various tissues of the central nervous system, respiratory system, and other vital organs. Our previous analysis focusing on neurotoxicity resulting from interactions between Zn and Cu revealed that Cu²⁺ markedly enhances Zn²⁺-induced neuronal cell death by activating oxidative stress and the endoplasmic reticulum (ER) stress response. However, neurotoxicity arising from interactions between zinc and metals other than copper has not been examined. Thus, in the current study, we examined the effect of Ni²⁺ on Zn²⁺-induced neurotoxicity. Initially, we found that nontoxic concentrations (0–60 μM) of Ni²⁺ enhance Zn²⁺-induced neurotoxicity in an immortalized hypothalamic neuronal cell line (GT1-7) in a dose-dependent manner. Next, we analyzed the mechanism enhancing neuronal cell death, focusing on the ER stress response. Our results revealed that Ni²⁺ treatment significantly primed the Zn²⁺-induced ER stress response, especially expression of the CCAAT-enhancer-binding protein homologous protein (CHOP). Finally, we examined the effect of carnosine (an endogenous peptide) on Ni²⁺/Zn²⁺-induced neurotoxicity and found that carnosine attenuated Ni²⁺/Zn²⁺-induced neuronal cell death and ER stress occurring before cell death. Based on our results, Ni²⁺ treatment significantly enhances Zn²⁺-induced neuronal cell death by priming the ER stress response. Thus, compounds that decrease the ER stress response, such as carnosine, may be beneficial for neurological diseases.