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

Role of antioxidants in the neurobiology of drug addiction: An update

Relationships between protective enzymatic and non-enzymatic pro-antioxidant mechanisms and addictive substances use disorders (SUDs) are analyzed here, based on the results of previous research, as well as on the basis of our current own studies. This review introduces new aspects of comparative analysis of associations of pro-antixidant and neurobiological effects in patients taking psychoactive substances and complements very limited knowledge about relationships with SUDs from different regions, mainly Europe. In view of the few studies on relations between antioxidants and neurobiological processes acting in patients taking psychoactive substances, this review is important from the point of view of showing the state of knowledge, directions of diagnosis and treatment, and further research needed explanation. We found significant correlations between chemical elements, pro-antioxidative mechanisms, and lipoperoxidation in the development of disorders associated with use of addictive substances, therefore elements that show most relations (Pr, Na, Mn, Y, Sc, La, Cr, Al, Ca, Sb, Cd, Pb, As, Hg, Ni) may be significant factors shaping SUDs. The action of pro-antioxidant defense and lipid peroxidation depends on the pro-antioxidative activity of ions. We explain the strongest correlations between Mg and Sb, and lipoperoxidation in addicts, which proves their stimulating effect on lipoperoxidation and on the induction of oxidative stress. We discussed which mechanisms and neurobiological processes change susceptibility to SUDs. The innovation of this review is to show that addicted people have lower activity of dismutases and peroxidases than healthy ones, which indicates disorders of antioxidant system and depletion of enzymes after long-term tolerance of stressors. We explain higher level of catalases, reductases, ceruloplasmin, bilirubin, retinol, α-tocopherol and uric acid of addicts. In view of poorly understood factors affecting addiction, analysis of interactions allows for more effective understanding of pathogenetic mechanisms leading to formation of addiction and development the initiation of directed, more effective treatment (pharmacological, hormonal) and may be helpful in the diagnosis of psychoactive changes.

Melatonin is a Neuroprotective and Antioxidant Agent against Neurotoxicity Induced by an Intrahippocampal Injection of Nickel in Rats

The investigation into the hippocampal function and its response to heavy metal exposure is crucial for understanding the mechanisms underlying neurotoxicity, this can potentially inform strategies for mitigating the adverse effects associated with heavy metal exposure. Melatonin is an essential neuromodulator known for its efficacy as an antioxidant. In this study, we aimed to determine whether melatonin could protect against Nickel (Ni) neurotoxicity. To achieve this, we performed an intracerebral injection of Ni (300 µM NiCl2) into the right hippocampus of male Wistar rats, followed by melatonin treatment. Based on neurobehavioral and neurobiochemical assessments, our results demonstrate that melatonin efficiently enhances Ni-induced behavioral dysfunction and cognitive impairment. Specifically, melatonin treatment positively influences anxious behavior, significantly reduces immobility time in the forced swim test (FST), and improves learning and spatial memory abilities. Moreover, neurobiochemical assays revealed that melatonin treatment modulates the Ni-induced alterations in oxidative stress balance by increasing antioxidant enzyme activities, such as superoxide dismutase (SOD) and catalase (CAT). Additionally, we observed that melatonin significantly attenuated the increased levels of lipid peroxidation (LPO) and nitric oxide (NO). In conclusion, the data from this study suggests that melatonin attenuates oxidative stress, which is the primary mechanism responsible for Ni-induced neurotoxicity. Considering that the hippocampus is the main structure involved in the pathology associated with heavy metal intoxication, such as Ni, these findings underscore the potential therapeutic efficacy of melatonin in mitigating heavy metal-induced brain damage.

Subchronic Exposure to Mixture of Cadmium, Copper, and Nickel Induces Neurobehavioral Deficits and Hippocampal Oxidative Stress of Wistar Rats

The present study was aimed at evaluating the influence of the subchronic exposure of cadmium (Cd), copper (Cu), and nickel (Ni) mixtures on affective behaviors, memory impairment, and oxidative stress (OS) in the hippocampus. Thirty male Wistar rats were divided into 5 equal groups. Group 1 (control) received a saline solution (NaCl 0.9%). Groups 2, 3, and 4 received Cd (0.25 mg/kg), Cu (0.5 mg/kg), and Ni (0.25 mg/kg), respectively, while group 5 received a Cd, Cu, and Ni mixture through intraperitoneal injections for 2 months. After the exposure period, all rats were submitted to behavioral tests. Subsequently, OS markers and histological changes in the rats' hippocampi were assessed. Results showed that a 2-month exposure to the mixtures of metals (MM) has led to higher anxiety-like and depression-like behaviors and cognitive deficits in rats when compared to the control group and the individual metals. Furthermore, the MM induced heightened OS, evidenced by the rise in lipid peroxidation and nitric oxide levels. These effects were accompanied by a decrease in superoxide dismutase and catalase activities in the hippocampus. The histopathological analysis also supported that MM caused a neuronal loss in the CA3 sub-region. Overall, this study underscores that subchronic exposure to the Cd, Cu, and Ni mixture induces an OS status and histological changes in the hippocampus, with important affective and cognitive behavior variations in rats.

Types of memory, dementia, Alzheimer's disease, and their various pathological cascades as targets for potential pharmacological drugs

Alzheimer's disease (AD) is the most common type of dementia accounting for 90% of cases; however, frontotemporal dementia, vascular dementia, etc. prevails only in a minority of populations. The term dementia is defined as loss of memory which further takes several other categories of memories like working memory, spatial memory, fear memory, and long-term, and short-term memory into consideration. In this review, these memories have critically been elaborated based on context, duration, events, appearance, intensity, etc. The most important part and purpose of the review is the various pathological cascades as well as molecular levels of targets of AD, which have extracellular amyloid plaques and intracellular hyperphosphorylated tau protein as major disease hallmarks. There is another phenomenon that either leads to or arises from the above-mentioned hallmarks, such as oxidative stress, mitochondrial dysfunction, neuroinflammation, cholinergic dysfunction, and insulin resistance. Several potential drugs like antioxidants, anti-inflammatory drugs, acetylcholinesterase inhibitors, insulin mimetics or sensitizers, etc. studied in various previous preclinical or clinical reports were put as having the capacity to act on these pathological targets. Additionally, agents directly or indirectly targeting amyloid and tau were also discussed. This could be further investigated in future research.

An Industry-Relevant Metal Mixture, Iron Status, and Reported Attention-Related Behaviors in Italian Adolescents

BACKGROUND

Exposure to environmental metals has been consistently associated with attention and behavioral deficits in children, and these associations may be modified by coexposure to other metals or iron (Fe) status. However, few studies have investigated Fe status as a modifier of a metal mixture, particularly with respect to attention-related behaviors.

METHODS

We used cross-sectional data from the Public Health Impact of Metals Exposure study, which included 707 adolescents (10-14 years of age) from Brescia, Italy. Manganese, chromium, and copper were quantified in hair samples, and lead was quantified in whole blood, using inductively coupled plasma mass spectrometry. Concentrations of Fe status markers (ferritin, hemoglobin, transferrin) were measured using immunoassays or luminescence assays. Attention-related behaviors were assessed using the Conners Rating Scales Self-Report Scale-Long Form, Parent Rating Scales Revised-Short Form, and Teacher Rating Scales Revised-Short Form. We employed Bayesian kernel machine regression to examine associations of the metal mixture with these outcomes and evaluate Fe status as a modifier.

RESULTS

Higher concentrations of the metals and ferritin were jointly associated with worse self-reported attention-related behaviors: metals and ferritin set to their 90th percentiles were associated with 3.0% [β = 0.03 ; 95% credible interval (CrI): - 0.01 , 0.06], 4.1% (β = 0.04 ; 95% CrI: 0.00, 0.08), and 4.1% (β = 0.04 ; 95% CrI: 0.00, 0.08) higher T -scores for self-reported attention deficit/hyperactivity disorder (ADHD) index, inattention, and hyperactivity, respectively, compared with when metals and ferritin were set to their 50th percentiles. These associations were driven by hair manganese, which exhibited nonlinear associations with all self-reported scales. There was no evidence that Fe status modified the neurotoxicity of the metal mixture. The metal mixture was not materially associated with any parent-reported or teacher-reported scale.

CONCLUSIONS

The overall metal mixture, driven by manganese, was adversely associated with self-reported attention-related behavior. These findings suggest that exposure to multiple environmental metals impacts adolescent neurodevelopment, which has significant public health implications. https://doi.org/10.1289/EHP12988.

Assessing the mediating role of iron status on associations between an industry-relevant metal mixture and verbal learning and memory in Italian adolescents

BACKGROUND

Metals, including lead (Pb), manganese (Mn), chromium (Cr) and copper (Cu), have been associated with neurodevelopment; iron (Fe) plays a role in the metabolism and neurotoxicity of metals, suggesting Fe may mediate metal-neurodevelopment associations. However, no study to date has examined Fe as a mediator of the association between metal mixtures and neurodevelopment.

OBJECTIVE

We assessed Fe status as a mediator of a mixture of Pb, Mn, Cr and Cu in relation to verbal learning and memory in a cohort of Italian adolescents.

METHODS

We used cross-sectional data from 383 adolescents (10-14 years) in the Public Health Impact of Metals Exposure Study. Metals were quantified in blood (Pb) or hair (Mn, Cr, Cu) using ICP-MS, and three markers of Fe status (blood hemoglobin, serum ferritin and transferrin) were quantified using luminescence assays or immunoassays. Verbal learning and memory were assessed using the California Verbal Learning Test for Children (CVLT-C). We used Bayesian Kernel Machine Regression Causal Mediation Analysis to estimate four mediation effects: the natural direct effect (NDE), natural indirect effect (NIE), controlled direct effect (CDE) and total effect (TE). Beta (β) coefficients and 95 % credible intervals (CIs) were estimated for all effects.

RESULTS

The metal mixture was jointly associated with a greater number of words recalled on the CVLT-C, but these associations were not mediated by Fe status. For example, when ferritin was considered as the mediator, the NIE for long delay free recall was null (β = 0.00; 95 % CI = -0.22, 0.23). Conversely, the NDE (β = 0.23; 95 % CI = 0.01, 0.44) indicated a beneficial association of the mixture with recall that operated independently of Fe status.

CONCLUSION

An industry-relevant metal mixture was associated with learning and memory, but there was no evidence of mediation by Fe status. Further studies in populations with Fe deficiency and greater variation in metal exposure are warranted.

Ni and Al mixture amplifies cerebellar oxido-inflammatory responses, down regulates AChE and BDNF/NGF levels in motor impairment in male albino rats

BACKGROUND

Aluminum and nickel are potent neurotoxicants to which humans are constantly exposed. Previous studies have demonstrated that these two metals can affect the motor system, but their effects on the cerebellum, a central nervous system region with the highest number of neurons, have remained largely unexplored. Therefore, we conducted a study to investigate the adverse effects of Al, Ni, and Al+Ni in vivo.

METHODS

In our study, seven male Sprague Dawley rats per group were orally exposed to deionized water, 0.2 mg/kg of Ni, 1 mg/kg of Al, and 0.2 mg/kg of Ni + 1 mg/kg of Al (as a binary heavy metals mixture; HMM), respectively.

RESULTS

Ni, Al, and HMM exposed rats accumulated higher levels of Al and Ni compared to controls, and HMM treated animals had higher levels of Ca and Fe in the cerebellum (p < 0.05). Malondialdehyde (MDA) levels were significantly (p < 0.05) higher in the HMM, Ni, and Al treated groups compared to the control group that received deionized water. Superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and glutathione peroxidase (GPx) activities were significantly (p < 0.05) reduced in the HMM, Ni, and Al treated groups compared to the control group that received deionized water. Ni, Al, and HMM significantly (p < 0.05) shortened the length of time of the grip in comparison to the control. Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) levels were significantly decreased in the nickel, Al, and heavy metal mixture groups compared with the control group. Moreover, there was a significant decrease in the activity of acetylcholinesterase (AChE) and a increase in cyclooxygenase-2 (COX-2) activity in the Ni, Al, and HMM treated groups compared to the control group.

CONCLUSION

HMM exposed animals had significantly poorer performance in the Rotarod test (p < 0.05) than controls. Al and Ni induced impairment of cerebellar function at various levels.

Antioxidant theranostic copolymer-mediated reduction in oxidative stress following traumatic brain injury improves outcome in a mouse model

Following a traumatic brain injury (TBI), excess reactive oxygen species (ROS) and lipid peroxidation products (LPOx) are generated and lead to secondary injury beyond the primary insult. A major limitation of current treatments is poor target engagement, which has prevented success in clinical trials. Thus, nanoparticle-based treatments have received recent attention because of their ability to increase accumulation and retention in damaged brain. Theranostic neuroprotective copolymers (NPC3) containing thiol functional groups can neutralize ROS and LPOx. Immediate administration of NPC3 following injury in a controlled cortical impact (CCI) mouse model provides a therapeutic window in reducing ROS levels at 2.08-20.83 mg/kg in males and 5.52-27.62 mg/kg in females. This NPC3-mediated reduction in oxidative stress improves spatial learning and memory in males, while females show minimal improvement. Notably, NPC3-mediated reduction in oxidative stress prevents the bilateral spread of necrosis in male mice, which was not observed in female mice and likely accounts for the sex-based spatial learning and memory differences. Overall, these findings suggest sex-based differences to oxidative stress scavenger nanoparticle treatments, and a possible upper threshold of antioxidant activity that provides therapeutic benefit in injured brain since female mice benefit from NPC3 treatment to a lesser extent than male mice.

Nickel and aluminium mixture elicit memory impairment by activation of oxidative stress, COX-2, and diminution of AChE, BDNF and NGF levels in cerebral cortex and hippocampus of male albino rats

This study evaluated nickel and aluminium-induced neurotoxicity, as a binary metal mixture. Twenty-eight male Sprague Dawley albino rats were weight-matched and divided into four groups. Group 1 (control) received deionized water. Group 2 and 3 received Aluminium (1 mg/kg) and Nickel (0.2 mg/kg) respectively, while Group 4 received Ni and Al mixture HMM three times a week orally for 90 days. Barnes maze tests was performed. Rats were sacrificed under pentobarbital anaesthesia, cerebral cortex and hippocampus were separated, and metal levels were measured using Atomic Absorption Spectroscopy (AAS). Malondialdehyde (MDA), catalase (CAT), glutathione content (GSH), superoxide dismutase (SOD), glutathione peroxidase (GPx), Brain Derived Neurotrophic Factor (BDNF), Nerve growth factor NGF, cyclo-oxygenase COX-2 and Acetylcholinesterase (AChE) were assayed using ELISA kits. Ni/Al binary mixture exposed rats showed a shorter latency period (though not significant) of 3.21 ± 1.40 s in comparison to 3.77 ± 1.11 (Ni only) and 3.99 ± 1.16(Al only). Ni/Al mixture gp had the lowest levels of Mg in both the hippocampus and frontal cortex when compared with the individual metals. In the hippocampus Al only exposed rats significantly showed p < 0.05 higher iron and Ca levels in comparison to Ni/Al mixture. Al alone significantly showed p < 0.05 lower levels of Fe but higher Ca than the Ni/Al mixture group. Exposure to Al only showed lower levels of BDNF in comparison to Ni/Al combination, whereas Ni/Al mixture gp had lower levels of NGF in comparison to the individual metals in the hippocampus. In the frontal cortex Ni only, group showed significantly lower BDNF in comparison to Ni/Al mixture whereas the mixture showed significantly lower NGF when compared with Al only group. There were higher levels of COX-2 in the Ni/Al mixture than individual metal treated rats in both hippocampus and frontal cortex. AChE levels in the Ni/Al mixture group was higher than Ni or Al only gps in the hippocampus whereas in the frontal cortex, Ni/Al exposed rats showed significantly lower AChE levels in comparison to Al only group. Ni, Al and Ni/Al mixture exhibited memory impairment by activation of oxidative stress, COX-2, and diminution of AChE, BDNF and NGF levels in cerebral cortex and hippocampus. The BDNF-COX-2 AChE signalling pathway may be involved in the neurotoxicity of Ni and Al.

Potential Role of Oxidative Stress in the Effects of Chronic Administration of Iron on Affective and Cognitive Behavior on Male Wistar Rat

In this work, we studied the impact of chronic iron exposure, in the form of iron sulfate (FeSo4), on affective and cognitive disorders and oxidative stress in the male Wistar rat. The treatment was carried out for 8 weeks, the rats received an intraperitoneal injection of iron at different doses: 0.25, 0.5, and 1 mg/kg. Affective and cognitive disorders are assessed in open field test (OFT), elevated plus maze (EPM), forced swimming test (FST), Morris water maze (MWM), and Y-maze. The hippocampus and prefrontal cortex of each animal were taken for biochemical examination. Our results show that iron exerts anxiogenic and depressogenic effects, which were observed first at the dose of 0.5 mg/kg and continued in a dose-dependent manner up to the maximum tested dose of 1 mg/kg. According to results from the MWM and Y-maze tests, continuous exposure to iron induces cognitive disorders that are defined by the disturbance of working memory and influences spatial learning performance causing a deficit of spatial memory retention. We noted that chronic exposure to iron can be associated with the appearance of a state of oxidative stress in the hippocampus and the prefrontal cortex demonstrated by an increase in lipid peroxidation, an increase in nitric oxide, and also by disturbances in the antioxidant defense systems following a determination of the concentrations of catalase. In conclusion, we can deduce from this work that chronic iron exposure can be related to the induction of cognitive and affective disorders and oxidative stress.

Cumulative risk assessment of the dietary heavy metal and aluminum exposure of Finnish adults

While directly comparable toxicological data are unavailable, this pilot study used published toxicological endpoints for neurological damage to weigh the relative importance of cadmium, lead, arsenic, mercury, nickel, and aluminum in the mixture Finnish adults receive from their daily diet. In addition, the effects of a selection of these chemicals on cognition, kidney tubular damage, and fertility were assessed using the toxicological endpoints available in the Chemical Mixture Calculator developed by the Technical University of Denmark. Consumption data from the FinDiet 2012 national survey of 25 to 74-year-olds and occurrence data mainly obtained in national monitoring were used to estimate the cumulative dietary exposure, which was found to be so high that the possibility of neurological damage or kidney effects cannot be ruled out for most of the population, particularly fertile age women. For Finns below the age of 65 years, the main sources of cumulative exposure were bread and other cereals, non-alcoholic drinks, and vegetables. When mean exposure was statistically compared between age groups and genders, women aged 25 to 45 years had a statistically significantly higher exposure than men of the same age (P < 0.05) and women aged 46 to 64 years (P < 0.001).

Disease-associated metabolic pathways affected by heavy metals and metalloid

Increased exposure to environmental heavy metals and metalloids and their associated toxicities has become a major threat to human health. Hence, the association of these metals and metalloids with chronic, age-related metabolic disorders has gained much interest. The underlying molecular mechanisms that mediate these effects are often complex and incompletely understood. In this review, we summarize the currently known disease-associated metabolic and signaling pathways that are altered following different heavy metals and metalloids exposure, alongside a brief summary of the mechanisms of their impacts. The main focus of this study is to explore how these affected pathways are associated with chronic multifactorial diseases including diabetes, cardiovascular diseases, cancer, neurodegeneration, inflammation, and allergic responses upon exposure to arsenic (As), cadmium (Cd), chromium (Cr), iron (Fe), mercury (Hg), nickel (Ni), and vanadium (V). Although there is considerable overlap among the different heavy metals and metalloids-affected cellular pathways, these affect distinct metabolic pathways as well. The common pathways may be explored further to find common targets for treatment of the associated pathologic conditions.

Among Gerontogens, Heavy Metals Are a Class of Their Own: A Review of the Evidence for Cellular Senescence

Advancements in modern medicine have improved the quality of life across the globe and increased the average lifespan of our population by multiple decades. Current estimates predict by 2030, 12% of the global population will reach a geriatric age and live another 3-4 decades. This swelling geriatric population will place critical stress on healthcare infrastructures due to accompanying increases in age-related diseases and comorbidities. While much research focused on long-lived individuals seeks to answer questions regarding how to age healthier, there is a deficit in research investigating what aspects of our lives accelerate or exacerbate aging. In particular, heavy metals are recognized as a significant threat to human health with links to a plethora of age-related diseases, and have widespread human exposures from occupational, medical, or environmental settings. We believe heavy metals ought to be classified as a class of gerontogens (i.e., chemicals that accelerate biological aging in cells and tissues). Gerontogens may be best studied through their effects on the "Hallmarks of Aging", nine physiological hallmarks demonstrated to occur in aged cells, tissues, and bodies. Evidence suggests that cellular senescence-a permanent growth arrest in cells-is one of the most pertinent hallmarks of aging and is a useful indicator of aging in tissues. Here, we discuss the roles of heavy metals in brain aging. We briefly discuss brain aging in general, then expand upon observations for heavy metals contributing to age-related neurodegenerative disorders. We particularly emphasize the roles and observations of cellular senescence in neurodegenerative diseases. Finally, we discuss the observations for heavy metals inducing cellular senescence. The glaring lack of knowledge about gerontogens and gerontogenic mechanisms necessitates greater research in the field, especially in the context of the global aging crisis.

Sex-based differences of antioxidant enzyme nanoparticle effects following traumatic brain injury

Following traumatic brain injury (TBI), reactive oxygen species (ROS) are released in excess, causing oxidative stress, carbonyl stress, and cell death, which induce the additional release of ROS. The limited accumulation and retention of small molecule antioxidants commonly used in clinical trials likely limit the target engagement and therapeutic effect in reducing secondary injury. Small molecule drugs also need to be administered every several hours to maintain bioavailability in the brain. Therefore, there is a need for a burst and sustained release system with high accumulation and retention in the injured brain. Here, we utilized Pro-NP™ with a size of 200 nm, which was designed to have a burst and sustained release of encapsulated antioxidants, Cu/Zn superoxide dismutase (SOD1) and catalase (CAT), to scavenge ROS for >24 h post-injection. Here, we utilized a controlled cortical impact (CCI) mouse model of TBI and found the accumulation of Pro-NP™ in the brain lesion was highest when injected immediately after injury, with a reduction in the accumulation with delayed administration of 1 h or more post-injury. Pro-NP™ treatment with 9000 U/kg SOD1 and 9800 U/kg CAT gave the highest reduction in ROS in both male and female mice. We found that Pro-NP™ treatment was effective in reducing carbonyl stress and necrosis at 1 d post-injury in the contralateral hemisphere in male mice, which showed a similar trend to untreated female mice. Although we found that male and female mice similarly benefit from Pro-NP™ treatment in reducing ROS levels 4 h post-injury, Pro-NP™ treatment did not significantly affect markers of post-traumatic oxidative stress in female CCI mice as compared to male CCI mice. These findings of protection by Pro-NP™ in male mice did not extend to 7 d post-injury, which suggests subsequent treatments with Pro-NP™ may be needed to afford protection into the chronic phase of injury. Overall, these different treatment effects of Pro-NP™ between male and female mice suggest important sex-based differences in response to antioxidant nanoparticle delivery and that there may exist a maximal benefit from local antioxidant activity in injured brain.

Ferroptosis contributes to nickel-induced developmental neurotoxicity in zebrafish

Nickel (Ni) is a widely utilized heavy metal that can cause environmental pollution and health hazards. Its safety has attracted the attention of both the environmental ecology and public health fields. While the central nervous system (CNS) is one of the main targets of Ni, its neurotoxicity and the underlying mechanisms remain unclear. Here, by taking advantage of the zebrafish model for live imaging, genetic analysis and neurobehavioral studies, we reveal that the neurotoxic effects induced by exposure to environmentally relevant levels of Ni are closely related to ferroptosis, a newly-described form of iron-mediated cell death. In vivo two-photon imaging, neurobehavioral analysis and transcriptome sequencing consistently demonstrate that early neurodevelopment, neuroimmune function and vasculogenesis in zebrafish larvae are significantly affected by environmental Ni exposure. Importantly, exposure to various concentrations of Ni activates the ferroptosis pathway, as demonstrated by physiological/biochemical tests, as well as the expression of ferroptosis markers. Furthermore, pharmacological intervention of ferroptosis via deferoxamine (DFO), a classical iron chelating agent, strongly implicates iron dyshomeostasis and ferroptosis in these Ni-induced neurotoxic effects. Thus, this study elucidates the cellular and molecular mechanisms underlying Ni neurotoxicity, with implications for our understanding of the physiologically damaging effects of other environmental heavy metal pollutants.

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.

Recent Neurotherapeutic Strategies to Promote Healthy Brain Aging: Are we there yet?

Owing to the global exponential increase in population ageing, there is an urgent unmet need to develop reliable strategies to slow down and delay the ageing process. Age-related neurodegenerative diseases are among the main causes of morbidity and mortality in our contemporary society and represent a major socio-economic burden. There are several controversial factors that are thought to play a causal role in brain ageing which are continuously being examined in experimental models. Among them are oxidative stress and brain inflammation which are empirical to brain ageing. Although some candidate drugs have been developed which reduce the ageing phenotype, their clinical translation is limited. There are several strategies currently in development to improve brain ageing. These include strategies such as caloric restriction, ketogenic diet, promotion of cellular nicotinamide adenine dinucleotide (NAD+) levels, removal of senescent cells, 'young blood' transfusions, enhancement of adult neurogenesis, stem cell therapy, vascular risk reduction, and non-pharmacological lifestyle strategies. Several studies have shown that these strategies can not only improve brain ageing by attenuating age-related neurodegenerative disease mechanisms, but also maintain cognitive function in a variety of pre-clinical experimental murine models. However, clinical evidence is limited and many of these strategies are awaiting findings from large-scale clinical trials which are nascent in the current literature. Further studies are needed to determine their long-term efficacy and lack of adverse effects in various tissues and organs to gain a greater understanding of their potential beneficial effects on brain ageing and health span in 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.

High concentration of blood cobalt is associated with the impairment of blood-brain barrier permeability

Excess heavy metals can lead to many kinds of adverse effects in human. The present study is designed to investigate whether the internal excess burden of heavy metals relate to the disturbance of the Blood-brain-barrier (BBB) and oxidative stress (OS) in subjects, and identify specific metallic constituents responsible for the disturbance. We collected the blood from recruited 122 subjects for our comparison study, 69 were living at an area near e-waste dismantling factories (exposed group), who have higher levels of heavy metals in the body; and others were in a chosen reference area (reference group), who were the general residents in city, in December 2017 in Taizhou, Zhejiang province. The analyses showed that the concentrations of altogether 4 metals, including nickel (Ni), cobalt (Co), mercury (Hg) and stannum (Sn), and the triggers of BBB disruption (Apolipoprotein E4 and matrix-metalloproteinase-9), indicators of BBB (Myelin basic protein, serotonin and dopamine) and biomarkers of OS (Malondialdehyde and 8-isoprostane) were statistically significant higher in exposed group than in reference group. Moreover, they are also significantly positively correlated with each other. Among all the metals, both Pearson correlation and multiple linear regression showed Co was positive correlated with almost all biomarkers. Considering the explicit correlation between Co and BBB permeability, we speculated that high burden of Co in blood may have a connection with neurodegenerative diseases, which propose a requirement for constructing the environmental criteria for Co and might provide a potential new hint for the intervention of dementia.

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.

Melatonin Ameliorates Cadmium-Induced Affective and Cognitive Impairments and Hippocampal Oxidative Stress in Rat

The present work aims to evaluate the effect of melatonin (Mel) on affective and cognitive disorders induced by chronic exposure to Cadmium (Cd). Male and female Wistar rats received either an intraperitoneal injection of saline solution NaCl (0.9%), Mel (4 mg/kg), Cd (1 mg/kg), or Cd (1 mg/kg) + Mel (4 mg/kg) for 8 weeks. Behavioral disorders were evaluated by different tests mainly the open field and elevated plus maze tests for anxiety-like behavior, forced swimming test (FST) for depression-like behavior, and the Y-maze and Morris water maze (MWM) tests for cognitive disorders. Thereafter, oxidative stress indices and histology of the hippocampus were evaluated. The results confirm that Cd administration has anxiogenic-like effects in both anxiety tests and depressive-like effects in the FST and leads to memory and learning disabilities in the Y-maze and MWM. We also report that Mel counteracts these neurobehavioral disorders. Biochemical assays showed that rats intoxicated with Cd significantly increased levels of nitric oxide (NO) and lipid peroxidation (LPO), while the activities of catalase (CAT) and superoxide dismutase (SOD) were significantly decreased in the hippocampus. In contrast, Mel administration attenuates the Cd-induced changes. The histopathological studies in the hippocampus of rats also supported that Mel markedly reduced the Cd-induced neuronal loss in CA3 sub-region. Overall, our results suggest that Mel could be used to protect against Cd-induced neurobehavioral changes via its antioxidant properties in the hippocampus. The effects of Cd and Mel are sex-dependent, knowing that Cd is more harmful in males, while Mel is more protective in females.

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.

Melatonin modulates copper-induced anxiety-like, depression-like and memory impairments by acting on hippocampal oxidative stress in rat

Copper (Cu) is a heavy metal with the ability to induce, at high levels, neurobehavioral alterations, and oxidative stress (OS). On the other hand, melatonin (Mel) is a neurohormone that protects neurons from OS and has a modulatory effect on several behavioral processes. The present experiment was aimed to examine the effect of Mel treatment on Cu-induced anxiety-like, depression-like behaviors, memory impairment, and OS in hippocampus. Herein, adult Wistar rats of both genders received daily Mel (4 mg/kg) thirty minutes before CuCl₂ (1 mg/kg), by intraperitoneal injections for 8 weeks. After the administration period, all rats were submitted to the behavioral tests. Thereafter, OS parameters and histology of the hippocampus were evaluated. The results demonstrate that Mel treatment attenuated Cu-induced anxiety-like and depression-like behaviors, and it improved memory deficits Cu-treated rats. Furthermore, Mel attenuated Cu-provoked OS by reducing lipid peroxidation (LPO) and nitric oxide (NO) levels and enhancing superoxide dismutase (SOD) and catalase (CAT) activities in the hippocampus. The histopathological analysis also supported these results. In conclusion, these findings show that Mel treatment exerted neuroprotective effects against Cu-induced neurobehavioral changes which may be related to reduction of hippocampal OS. Besides, the effects of Cu and Mel were gender dependent, being more marked in females compared to male rats.

Beyond the Mind-Serum Trace Element Levels in Schizophrenic Patients: A Systematic Review

The alterations in serum trace element levels are common phenomena observed in patients with different psychiatric conditions such as schizophrenia, autism spectrum disorder, or major depressive disorder. The fluctuations in the trace element concentrations might act as potential diagnostic and prognostic biomarkers of many psychiatric and neurological disorders. This paper aimed to assess the alterations in serum trace element concentrations in patients with a diagnosed schizophrenia. The authors made a systematic review, extracting papers from the PubMed, Web of Science, and Scopus databases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Among 5009 articles identified through database searching, 59 of them were assessed for eligibility. Ultimately, 33 articles were included in the qualitative synthesis. This review includes the analysis of serum levels of the following trace elements: iron, nickel, molybdenum, phosphorus, lead, chromium, antimony, uranium, magnesium, aluminum, zinc, copper, selenium, calcium, and manganese. Currently, there is no consistency regarding serum trace element levels in schizophrenic patients. Thus, it cannot be considered as a reliable prognostic or diagnostic marker of schizophrenia. However, it can be assumed that altered concentrations of those elements are crucial regarding the onset and exaggeration of either psychotic or negative symptoms or cognitive dysfunctions.

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.

Chronic copper exposure leads to hippocampus oxidative stress and impaired learning and memory in male and female rats

Environmental and occupational exposures to copper (Cu) play a pivotal role in the etiology of some neurological diseases and reduced cognitive functions. However, the precise mechanisms of its effects on cognitive function have not been yet thoroughly established. In our study, we aimed to investigate the behavior and neurochemical alterations in hippocampus of male and female rats, chronically exposed to copper chloride (CuCl2) and the possible involvement of oxidative stress. Twenty-four rats, for each gender, were divided into control and three test groups (n = 6), and were injected intraperitoneally with saline (0.9% NaCl) or CuCl2 (0.25 mg/kg, 0.5 mg/kg and 1 mg/kg) for 8 weeks. After the treatment period, Y-maze test was used for the evaluation of spatial working memory and the Morris Water Maze (MWM) to test the spatial learning and memory. Biochemical determination of oxidative stress levels in hippocampus was performed. The main results of the present work are working memory impairment in spatial Y-maze which induced by higher Cu intake (1 mg/kg) in male and female rats. Also, In the MWM test, the spatial learning and memory were significantly impaired in rats treated with Cu at dose of 1 mg/kg. Additionally, markers of oxidative stress such as catalase, superoxide dismutase, lipid peroxidation products and nitric oxide levels were significantly altered following Cu treatments. These data propose that compromised behavior following Cu exposure is associated with increase in oxidative stress.

Serum metallome in pregnant women and the relationship with congenital malformations of the central nervous system: a case-control study

BACKGROUND

Congenital malformations of the central nervous system (CNS) consist of a wide range of birth defects of multifactorial origin.

METHODS

Concentrations of 44 metals were determined by Inductively Coupled Plasma Mass Spectrometry in serum of 111 mothers in the second trimester of pregnancy who carried a malformed fetus and compared them with serum concentrations of the same metals in 90 mothers with a normally developed fetus at the same week of pregnancy. Data are reported as means ± standard deviations.

RESULTS

We found a direct relationship between congenital defects of the CNS and maternal serum concentration of aluminum: it was statistically higher in women carrying a fetus with this class of malformation, compared both to mothers carrying a fetus with another class of malformation (6.45 ± 15.15 μg/L Vs 1.44 ± 4.21 μg/L, p < 0.0006) and to Controls (i.e. mothers carrying a normally-developed fetus) (6.45 ± 15.15 μg/L Vs 0.11 ± 0.51 μg/L, p < 0.0006). Moreover, Aluminum abundances were below the limit of detection in the majority of control samples.

CONCLUSION

CAluminum may play a role in the onset of central nervous system malformations, although the exact Aluminum species and related specific type of malformation needs further elucidation.

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.