Manganese inhibits NMDA receptor channel function: implications to psychiatric and cognitive effects

Signal Transduction Associated with Mn-induced Neurological Dysfunction

Manganese (Mn) is a heavy metal that occurs widely in nature and has a vital physiological role in growth and development. However, excessive exposure to Mn can cause neurological damage, especially cognitive dysfunction, such as learning disability and memory loss. Numerous studies on the mechanisms of Mn-induced nervous system damage found that this metal targets a variety of metabolic pathways, for example, endoplasmic reticulum stress, apoptosis, neuroinflammation, cellular signaling pathway changes, and neurotransmitter metabolism interference. This article reviews the latest research progress on multiple signaling pathways related to Mn-induced neurological dysfunction.

Associations of an industry-relevant metal mixture with verbal learning and memory in Italian adolescents: The modifying role of iron status

BACKGROUND

Biomarker concentrations of metals are associated with neurodevelopment, and these associations may be modified by nutritional status (e.g., iron deficiency). No prior study on associations of metal mixtures with neurodevelopment has assessed effect modification by iron status.

OBJECTIVES

We aimed to quantify associations of an industry-relevant metal mixture with verbal learning and memory among adolescents, and to investigate the modifying role of iron status on those associations.

METHODS

We used cross-sectional data from 383 Italian adolescents (10-14 years) living in proximity to ferroalloy industry. Verbal learning and memory was assessed using the California Verbal Learning Test for Children (CVLT-C), and metals were quantified in hair (manganese, copper, chromium) or blood (lead) using inductively coupled plasma mass spectrometry. Serum ferritin, a proxy for iron status, was measured using immunoassays. Covariate-adjusted associations of the metal mixture with CVLT subtests were estimated using Bayesian Kernel Machine Regression, and modification of the mixture associations by ferritin was examined.

RESULTS

Compared to the 50th percentile of the metal mixture, the 90th percentile was associated with a 0.12 standard deviation [SD] (95% CI = -0.27, 0.50), 0.16 SD (95% CI = -0.11, 0.44), and 0.11 SD (95% CI = -0.20, 0.43) increase in the number of words recalled for trial 5, long delay free, and long delay cued recall, respectively. For an increase from its 25th to 75th percentiles, copper was beneficially associated the recall trials when other metals were fixed at their 50th percentiles (for example, trial 5 recall: β = 0.31, 95% CI = 0.14, 0.48). The association between copper and trial 5 recall was stronger at the 75th percentile of ferritin, compared to the 25th or 50th percentiles.

CONCLUSIONS

In this metal mixture, copper was beneficially associated with neurodevelopment, which was more apparent at higher ferritin concentrations. These findings suggest that metal associations with neurodevelopment may depend on iron status, which has important public health implications.

Relationship between blood manganese and bone mineral density and bone mineral content in adults: A population-based cross-sectional study

PURPOSE

It has been reported that bone is the primary organ for manganese (Mn) accumulation, but the association between manganese and bone loss remains debatable. Therefore, this study aimed to evaluate the relationship between blood manganese and bone mineral density/bone mineral content (BMD/BMC) by using a representative sample from the National Health and Nutrition Examination Survey (NHANES).

METHODS

A total of 9732 subjects over the age of 18 with available data were enrolled in this study. The relationship between blood manganese and BMD/BMC of the total body, spine and femoral regions was evaluated using multivariate linear regression models. Subgroup analyses were also performed.

RESULTS

We observed a negative association between blood manganese and BMD/BMC in the femoral neck and total body in the fully adjusted model, especially femoral neck BMD in women aged 50-70 years.

CONCLUSION

In brief, people exposed to manganese should be aware of the increased risk of osteopenia or osteoporosis. Besides, due to the lack of available data, there are no definite values for the tolerable upper intake level (UL), average requirement (AR) and population reference intake (PRI) of manganese. The results of our study may provide some references for the establishment of AR, PRI and UL of Mn.

Methylcyclopentadienyl Manganese Tricarbonyl Alter Behavior and Cause Ultrastructural Changes in the Substantia Nigra of Rats: Comparison with Inorganic Manganese Chloride

The antiknock additive methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic manganese(Mn) compound. Mn neurotoxicity caused by occupational Mn exposure (mostly inorganic MnCl₂) is associated with motor and cognitive disturbances, referred to as Manganism. However, the impact of environmentally relevant Mn exposure on MMT-induced Manganism is poorly understood. In this investigation, we studied the effects of MMT on motor function and brain structure, and compared its effects with those of inorganic MnCl₂. After adaptive feeding for 7 days, male and female Sprague-Dawley (SD) rats in the MMT-treated groups and positive control group were treated for 8 weeks with MMT (1, 2 and 4 mg/kg/i.g.) or MnCl₂·4H₂O (200 mg/kg/i.g.). Mn content in blood, liver, spleen and distinct brain regions was determined by inductively coupled plasma-mass spectrometer (ICP-MS). We found that MMT and MnCl₂ exposure led to slower body-weight-gain in female rats, impaired motor and balance function and spatial learning and memory both in male and female rats. HE staining showed that MMT and MnCl₂ led to altered structure of the substantia nigra pars compacta (SNpc), and Nissl staining corroborated MMT's propensity to damage the SNpc both in male and female rat. In addition, Immunostaining of the SNpc showed decreased TH-positive neurons in MMT- and MnCl₂-treated rats, concomitant with Iba1 activation in microglia. Moreover, no statistically significant difference was noted between the rats in the H-MMT and MnCl₂ groups. In summary, these findings suggest that MMT and MnCl₂ exposure cause ultrastructural changes in the SNpc neurons culminating in altered motor behavior and cognition, suggesting that altered SNpc structure and function may underline the motor and cognitive deficits inherent to Manganism, and accounting for MMT and MnCl₂'s manifestations of atypical parkinsonism.

Are Essential Trace Elements Effective in Modulation of Mental Disorders? Update and Perspectives

The emergence of mental disorders is associated with several risk factors including genetic and environmental susceptibility. A group of nutrients serves an especially important role in a number of essential neurodevelopmental processes through brain areas promoting the high degree of brain metabolism during early life, although almost all nutrients are needed. These include macronutrients and micronutrients (e.g., iron, magnesium, zinc, copper, selenium). Numerous nutritional psychiatry trials have been performed to examine the correlation of many individual nutrients with mental health, such as essential trace elements. The increased accumulation or lack of such components will facilitate an alternative metabolic pathway that can lead to many diseases and conditions of neurodevelopment. Mental functions have biochemical bases, so the impairment of such neurochemical mechanisms due to lack of trace elements can have mental effects. In psychological conditions such as depression, anxiety, schizophrenia, and autism, scientific studies demonstrate the putative role of trace element deficiency. Therefore, given the critical roles played by essential trace elements in the neurodevelopment and mental health, the effect of these elements' intake on the modulation of psychological functioning is reviewed.

Manganese in potable water of nine districts, Bangladesh: human health risk

Safe drinking water is directly linked to good human health. An excessive amount of manganese (Mn) in drinking water supplies causes people show symptoms of neurotoxicity. In this study, the level of Mn in potable water sourced from tube wells located in 9 (nine) districts of Bangladesh was monitored. In total, 170 (one hundred and seventy) water samples were collected and Mn was quantified by atomic absorption spectroscopy (AAS). The levels of Mn found in the tube well water samples of Sirajganj, Meherpur, Chuadanga, Jhenaidah, Magura, Faridpur, Jashore, Satkhira, and Khulna were 0.37-1.86, 0.10-4.11, 0.30-0.76, 0.26-0.94, 0.01-0.18, 0.21-1.78, 0.08-1.23, 0.05-0.27, and 0.01-2.11 mg/L, respectively. Results revealed that Mn level was beyond the highest contaminated levels of 0.1 mg/L and 0.4 mg/L, which are recommended by Bangladesh Drinking Standard (BDS) and World Health Organization (WHO), respectively. The maximum Mn contaminated level reached up to 4.11 mg/L (mean, 0.53 mg/L). The Mn level in tube well water exceeded 51.1% and 75.9% set by the recommended value of WHO and BDS, respectively. Furthermore, the calculated hazard quotient (HQ) value for Mn was observed to be greater than unity, indicating both children and adults risked potential non-carcinogenic health issues. The water supply authorities should take steps to provide Mn-free drinking water for communities.

Molecular Mechanisms of Environmental Metal Neurotoxicity: A Focus on the Interactions of Metals with Synapse Structure and Function

Environmental exposure to neurotoxic metals and metalloids such as arsenic, cadmium, lead, mercury, or manganese is a global health concern affecting millions of people worldwide. Depending on the period of exposure over a lifetime, environmental metals can alter neurodevelopment, neurobehavior, and cognition and cause neurodegeneration. There is increasing evidence linking environmental exposure to metal contaminants to the etiology of neurological diseases in early life (e.g., autism spectrum disorder) or late life (e.g., Alzheimer’s disease). The known main molecular mechanisms of metal-induced toxicity in cells are the generation of reactive oxygen species, the interaction with sulfhydryl chemical groups in proteins (e.g., cysteine), and the competition of toxic metals with binding sites of essential metals (e.g., Fe, Cu, Zn). In neurons, these molecular interactions can alter the functions of neurotransmitter receptors, the cytoskeleton and scaffolding synaptic proteins, thereby disrupting synaptic structure and function. Loss of synaptic connectivity may precede more drastic alterations such as neurodegeneration. In this article, we will review the molecular mechanisms of metal-induced synaptic neurotoxicity.

Astrocyte-specific deletion of the transcription factor Yin Yang 1 in murine substantia nigra mitigates manganese-induced dopaminergic neurotoxicity

Manganese (Mn)-induced neurotoxicity resembles Parkinson's disease (PD), but the mechanisms underpinning its effects remain unknown. Mn dysregulates astrocytic glutamate transporters, GLT-1 and GLAST, and dopaminergic function, including tyrosine hydroxylase (TH). Our previous in vitro studies have shown that Mn repressed GLAST and GLT-1 via activation of transcription factor Yin Yang 1 (YY1). Here, we investigated if in vivo astrocytic YY1 deletion mitigates Mn-induced dopaminergic neurotoxicity, attenuating Mn-induced reduction in GLAST/GLT-1 expression in murine substantia nigra (SN). AAV5-GFAP-Cre-GFP particles were infused into the SN of 8-week-old YY1 ^flox/flox mice to generate a region-specific astrocytic YY1 conditional knockout (cKO) mouse model. 3 weeks after adeno-associated viral (AAV) infusion, mice were exposed to 330 μg of Mn (MnCl₂ 30 mg/kg, intranasal instillation, daily) for 3 weeks. After Mn exposure, motor functions were determined in open-field and rotarod tests, followed by Western blotting, quantitative PCR, and immunohistochemistry to assess YY1, TH, GLAST, and GLT-1 levels. Infusion of AAV5-GFAP-Cre-GFP vectors into the SN resulted in region-specific astrocytic YY1 deletion and attenuation of Mn-induced impairment of motor functions, reduction of TH-expressing cells in SN, and TH mRNA/protein levels in midbrain/striatum. Astrocytic YY1 deletion also attenuated the Mn-induced decrease in GLAST/GLT-1 mRNA/protein levels in midbrain. Moreover, YY1 deletion abrogated its interaction with histone deacetylases in astrocytes. These results indicate that astrocytic YY1 plays a critical role in Mn-induced neurotoxicity in vivo, at least in part, by reducing astrocytic GLAST/GLT-1. Thus, YY1 might be a potential target for treatment of Mn toxicity and other neurological disorders associated with dysregulation of GLAST/GLT-1.

Associations of a Metal Mixture Measured in Multiple Biomarkers with IQ: Evidence from Italian Adolescents Living near Ferroalloy Industry

BACKGROUND

Research on the health effects of chemical mixtures has focused mainly on early life rather than adolescence, a potentially important developmental life stage.

OBJECTIVES

We examined associations of a metal mixture with general cognition in a cross-sectional study of adolescents residing near ferromanganese industry, a source of airborne metals emissions.

METHODS

We measured manganese (Mn), lead (Pb), copper (Cu), and chromium (Cr) in hair, blood, urine, nails, and saliva from 635 Italian adolescents 10-14 years of age. Full-scale, verbal, and performance intelligence quotient (FSIQ, VIQ, PIQ) scores were assessed using the Wechsler Intelligence Scale for Children-III. Multivariable linear regression and Bayesian kernel machine regression (BKMR) were used to estimate associations of the metal mixture with IQ. In secondary analyses, we used BKMR's hierarchical variable selection option to inform biomarker selection for Mn, Cu, and Cr.

RESULTS

Median metal concentrations were as follows: hair Mn, 0.08 μ g / g ; hair Cu, 9.6 μ g / g ; hair Cr, 0.05 μ g / g ; and blood Pb, 1.3 μ g / dL . Adjusted models revealed an inverted U-shaped association between hair Cu and VIQ, consistent with Cu as an essential nutrient that is neurotoxic in excess. At low levels of hair Cu (10th percentile, 5.4 μ g / g ), higher concentrations (90th percentiles) of the mixture of Mn, Pb, and Cr (0.3 μ g / g , 2.6 μ g / dL , and 0.1 μ g / g , respectively) were associated with a 2.9 (95% CI: - 5.2 , - 0.5 )-point decrease in VIQ score, compared with median concentrations of the mixture. There was suggestive evidence of interaction between Mn and Cu. In secondary analyses, saliva Mn, hair Cu, and saliva Cr were selected as the biomarkers most strongly associated with VIQ score.

DISCUSSION

Higher adolescent levels of Mn, Pb, and Cr were associated with lower IQ scores, especially at low Cu levels. Findings also support further investigation into Cu as both beneficial and toxic for neurobehavioral outcomes. https://doi.org/10.1289/EHP6803.

Association between Serum Essential Metal Elements and the Risk of Schizophrenia in China

Numerous essential metal elements (EMEs) are necessary to maintain the proper function of human body. In this case-control study, we investigated the associations of 11 EMEs [Calcium (Ca), potassium (K), magnesium (Mg), sodium (Na), manganese (Mn), selenium (Se), cobalt (Co), Molybdenum (Mo), copper (Cu), zinc (Zn), and iron (Fe)] in serum with the risk of schizophrenia. We recruited first-episode and drug-naïve schizophrenic patients (cases = 99) and age-sex-matched normal subjects (controls = 99) from Tangshan, Hebei Province, China. The 11 EMEs in serum from cases and controls were quantified by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. We observed that a higher level of Mn (OR = 2.390; 95%CI: 1.504–3.796) and lower levels of Ca (OR = 0.939; 95%CI: 0.890–0.990), Mg (OR = 0.806; 95%CI: 0.669–0.972), Na (OR = 0.995; 95%CI: 0.993–0.998), and Se (OR = 0.954; 95%CI: 0.937–0.972) were associated with an elevated risk of schizophrenia. Dose–response relationships between serum EME concentrations and the risk of schizophrenia were observed in most of the schizophrenia-associated EMEs. Moreover, the serum concentrations of these schizophrenia-associated EMEs in patients were correlated with the severity of their clinical symptoms. Significant correlations were found between EMEs and biomarkers associated with schizophrenia related to metabolic and oxidative stress. This study suggested that the concentration and profile of EMEs were different between schizophrenic patients and normal controls and revealed potential metabolisms associated with EMEs and schizophrenia, suggesting EMEs might act as biomarkers of schizophrenia to improve the current situation of diagnosis and treatment.

Verbal Memory and Learning in Schoolchildren Exposed to Manganese in Mexico

Manganese (Mn) is an essential nutrient for cellular function, but in high concentrations, it is neurotoxic. Environmental exposure to Mn has been associated with cognitive effects in children. This study aimed to assess the effect of environmental exposure to Mn on verbal memory and learning in schoolchildren residents from two municipalities in the state of Hidalgo, Mexico. Cross-sectional studies were conducted in 2006 and 2013 with a total of 265 schoolchildren of 7 to 11 years old. Children's Auditory Verbal Learning Test-2 (CAVLT-2) was used to assess verbal memory and learning. Mn exposure tertiles were defined according to hair manganese (MnH) levels determined by atomic absorption spectrophotometry. Linear regression models were used to estimate the association between MnH levels and CAVLT-2 scores. The models were adjusted by potential confounders. The lowest and highest exposure tertiles were defined below and above MnH levels of ≤ 0.72 and ≥ 3.96 μg/g, respectively. Mn exposure was significantly associated with an average of 5- to 9-point decrease in learning curves and summary CAVLT-2 scores in the highest tertile. This study adds to the evidence of decreased verbal memory and learning in schoolchildren environmentally exposed to manganese.

The effect of the source and dose of manganese on the performance, digestibility and distribution of selected minerals, redox, and immune status of turkeys

The aim of this study was to determine the effect of various levels of manganese added to the diet of growing turkeys in the conventional form of MnO or in the form of NP-Mn2O3 nanoparticles on growth performance, absorption, and accumulation of Mn, Zn, and Cu, and antioxidant and immune status. The experiment was conducted on 1080 one-day-old Hybrid Converter turkeys randomly assigned to 6 groups with 10 replications, in a two-factor design with three dosages of manganese - 100, 50, and 10 mg/kg, and two sources-manganese oxide (MnO) and manganese nanoparticles (NP-Mn2O3). Neither reducing the addition of Mn from 100 to 50 or even 10 mg/kg of the diet nor replacing MnO with NP-Mn2O3 had a negative effect on the growth performance of the turkeys. Replacing MnO with NP-Mn2O3 in the turkey diet improved ileal digestibility of Mn and decreased accumulation of Cu in the liver and breast muscle. The study showed that irrespective of the form used, reducing the level of Mn supplementation of the diet from the 100 mg/kg recommended by British United Turkey to 50 or 10 mg/kg decreased its ileal digestibility and increased its accumulation in the liver, breast muscle, and skin. Reducing the addition of Mn to the turkey diet increased intestinal absorption of Zn and reduced accumulation of Zn and Cu in the liver, breast muscle, and skin. It did not increase oxidation processes in the liver or breast muscle of the turkeys. Reducing the addition of Mn to the turkey diet stimulated the immune system, which was manifested by stimulation of B cells to produce immunoglobulin M and by the release of the cytokine IL-6, but did not intensify apoptosis. The results of the study indicate that the recommended manganese supplement in turkey diets can be reduced. The use of manganese nanoparticles in turkey feeding requires further study.

Noise-Induced Cochlear Synaptopathy and Ribbon Synapse Regeneration: Repair Process and Therapeutic Target

The synapse between the inner hair cells (IHCs) and the spiral ganglion neurons (SGNs) in mammalian cochleae is characterized as having presynaptic ribbons and therefore is called ribbon synapse. The special molecular organization is reviewed in this chapter in association with the functional feature of this synapse in signal processing. This is followed by the review on noise-induced damage to this synapse with a focus on recent reports in animal models in which the effect of brief noise exposures is observed without causing significant permanent threshold shift (PTS). In this regard, the potential mechanism of the synaptic damage by noise and the impact of this damage on hearing are summarized to clarify the concept of noise-induced hidden hearing loss, which is defined as the functional deficits in hearing without threshold elevation. A controversial issue is addressed in this review as whether the disrupted synapses can be regenerated. Moreover, the review summarizes the work of therapeutic research to protect the synapses or to promote the regeneration of the synapse after initial disruption. Lastly, several unresolved issues are raised for investigation in the future.

Copper in depressive disorder: A systematic review and meta-analysis of observational studies

Copper (Cu) has been associated with mental disorders such as autism and epilepsy. So far, publications evaluating copper levels in patients with depressive disorder showed conflicted results. To derive a comprehensive estimation of the relationship between body burden of copper and depressive disorder and explore the possible role of copper in mental health, we performed a systematic review and meta-analysis. Relevant published data were obtained by searching PubMed, Web of Science, Chinese National Knowledge Infrastructure (CNKI) and Chinese Biomedical Database (CBM) before October 10, 2017. Weighted mean difference (WMD) with a 95% confidence interval (95%CI) was calculated using STATA 12.0. A total of 21 studies with 1487 patients and 943 controls were collected in this meta-analysis. Pooled analysis found that patients with depression had higher blood levels of copper than the controls without depression, while there was no difference of copper content in hair between the two groups. Subgroup analysis suggested that age had influence on the relationship between copper and depression. No evidence of publication bias was observed. This meta-analysis suggests that increased levels of blood copper might be associated with depressive disorder and therefore the possible role of copper as a biomarker of depression.

Neurotoxic Agent-Induced Injury in Neurodegenerative Disease Model: Focus on Involvement of Glutamate Receptors

Glutamate receptors play a crucial role in the central nervous system and are implicated in different brain disorders. They play a significant role in the pathogenesis of neurodegenerative diseases (NDDs) such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Although many studies on NDDs have been conducted, their exact pathophysiological characteristics are still not fully understood. In in vivo and in vitro models of neurotoxic-induced NDDs, neurotoxic agents are used to induce several neuronal injuries for the purpose of correlating them with the pathological characteristics of NDDs. Moreover, therapeutic drugs might be discovered based on the studies employing these models. In NDD models, different neurotoxic agents, namely, kainic acid, domoic acid, glutamate, β-N-Methylamino-L-alanine, amyloid beta, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1-methyl-4-phenylpyridinium, rotenone, 3-Nitropropionic acid and methamphetamine can potently impair both ionotropic and metabotropic glutamate receptors, leading to the progression of toxicity. Many other neurotoxic agents mainly affect the functions of ionotropic glutamate receptors. We discuss particular neurotoxic agents that can act upon glutamate receptors so as to effectively mimic NDDs. The correlation of neurotoxic agent-induced disease characteristics with glutamate receptors would aid the discovery and development of therapeutic drugs for NDDs.

Thalamic GABA levels and occupational manganese neurotoxicity: Association with exposure levels and brain MRI

Excessive occupational exposure to Manganese (Mn) has been associated with clinical symptoms resembling idiopathic Parkinson's disease (IPD), impairing cognitive and motor functions. Several studies point towards an involvement of the brain neurotransmitter system in Mn intoxication, which is hypothesized to be disturbed prior to onset of symptoms. Edited Magnetic Resonance Spectroscopy (MRS) offers the unique possibility to measure γ-amminobutyric acid (GABA) and other neurometabolites in vivo non-invasively in workers exposed to Mn. In addition, the property of Mn as Magnetic Resonance Imaging (MRI) contrast agent may be used to study Mn deposition in the human brain. In this study, using MRI, MRS, personal air sampling at the working place, work history questionnaires, and neurological assessment (UPDRS-III), the effects of chronic Mn exposure on the thalamic GABAergic system was studied in a group of welders (N=39) with exposure to Mn fumes in a typical occupational setting. Two subgroups of welders with different exposure levels (Low: N=26; mean air Mn=0.13±0.1mg/m3; High: N=13; mean air Mn=0.23±0.18mg/m3), as well as unexposed control workers (N=22, mean air Mn=0.002±0.001mg/m3) were recruited. The group of welders with higher exposure showed a significant increase of thalamic GABA levels by 45% (p<0.01, F(1,33)=9.55), as well as significantly worse performance in general motor function (p<0.01, F(1,33)=11.35). However, welders with lower exposure did not differ from the controls in GABA levels or motor performance. Further, in welders the thalamic GABA levels were best predicted by past-12-months exposure levels and were influenced by the Mn deposition in the substantia nigra and globus pallidus. Importantly, both thalamic GABA levels and motor function displayed a non-linear pattern of response to Mn exposure, suggesting a threshold effect.

The effect of postnatal manganese exposure on the NMDA receptor signaling pathway in rat hippocampus

Overexposure to manganese (Mn) is associated with neurological disorders in children. Evidence indicated that N-methyl-d-aspartate (NMDA) receptor signaling pathway was critical for neurobehavioral function. However, whether NMDA receptor signaling pathway contributes to Mn-induced neurotoxicity remains unknown. In this study, newborn Sprague-Dawley rats were randomly assigned to four groups exposed to 0, 10, 20, and 30 mg/kg of Mn²⁺ by intraperitoneal injection (n = 10/group: five males and five females). After 3 weeks of Mn exposure, messenger RNA (mRNA) and protein expression of NMDA receptor subunits (NR1, NR2A, and NR2B), cAMP-response element binding protein (CREB), and brain-derived neurotrophic factor (BDNF) in hippocampus were measured by real-time quantitative RT-PCR and Western blot. In Mn-exposed rats, decreased mRNA and protein expression of NR1, NR2A, and NR2B, CREB, and BDNF was observed. The results imply that downregulated NMDA receptor signaling pathway may be of vital importance in the neuropathological process of Mn-induced neurotoxicity.

New Research Strategy for Measuring Pre- and Postnatal Metal Dysregulation in Psychotic Disorders

While previous studies have found evidence for detrimental effects of metals on neurodevelopment, the long-term effects on mental health remain unclear. The objective was to explore the effect of early metal exposure on risk of psychotic disorder and on symptom severity following illness onset. Through the use of validated tooth-biomarkers, we estimated pre- and postnatal exposure levels of essential elements (copper, magnesium, manganese, and zinc) and elements associated with neurotoxicity (lead, arsenic, lithium, and tin). We found consistently higher levels of lithium in patients compared to controls. Higher levels of magnesium and lower levels of zinc were associated with more severe psychopathology over 20 years after metal exposure. The results show promise for the use of teeth biomarkers in examining early environmental risk for psychosis and underscore the relevance of studying metal exposure during critical neurodevelopmental periods.

Endogenous Two-Photon Excited Fluorescence Imaging Characterizes Neuron and Astrocyte Metabolic Responses to Manganese Toxicity

As neurodegenerative conditions are increasingly linked to mitochondrial dysfunction, methods for studying brain cell metabolism at high spatial resolution are needed to elucidate neurodegeneration mechanisms. Two-photon excited fluorescence (TPEF) imaging is a non-destructive, high-resolution technique for studying cell metabolism via endogenous fluorescence of reduced nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and flavin adenine dinucleotide (FAD). We employed TPEF to study the metabolism of primary rat astrocyte and neuronal cultures under normal growth conditions and in response to manganese (Mn) treatment. Histograms of pixel-wise optical redox ratio, defined as FAD/(FAD + NAD(P)H), revealed three distinct redox distributions and significant differences in their relative weights between astrocytes and neurons. When treated with Mn, both cell types exhibited redox ratio shifts consistent with increased oxidative stress. However, the manner in which the redox distributions was affected was distinct for the two cell types. Furthermore, NAD(P)H fluorescence lifetime imaging revealed an increase in bound NAD(P)H fraction upon Mn treatment for neurons, consistent with enhanced apoptosis. Astrocytes showed a decrease in bound fraction, possibly due to a shift towards glycolytic metabolism in response to impaired respiration. These results exhibit TPEF’s utility for characterizing detailed metabolic changes of different brain cell types in response to neurotoxins.

Estrogenic Endocrine Disrupting Chemicals Influencing NRF1 Regulated Gene Networks in the Development of Complex Human Brain Diseases

During the development of an individual from a single cell to prenatal stages to adolescence to adulthood and through the complete life span, humans are exposed to countless environmental and stochastic factors, including estrogenic endocrine disrupting chemicals. Brain cells and neural circuits are likely to be influenced by estrogenic endocrine disruptors (EEDs) because they strongly dependent on estrogens. In this review, we discuss both environmental, epidemiological, and experimental evidence on brain health with exposure to oral contraceptives, hormonal therapy, and EEDs such as bisphenol-A (BPA), polychlorinated biphenyls (PCBs), phthalates, and metalloestrogens, such as, arsenic, cadmium, and manganese. Also we discuss the brain health effects associated from exposure to EEDs including the promotion of neurodegeneration, protection against neurodegeneration, and involvement in various neurological deficits; changes in rearing behavior, locomotion, anxiety, learning difficulties, memory issues, and neuronal abnormalities. The effects of EEDs on the brain are varied during the entire life span and far-reaching with many different mechanisms. To understand endocrine disrupting chemicals mechanisms, we use bioinformatics, molecular, and epidemiologic approaches. Through those approaches, we learn how the effects of EEDs on the brain go beyond known mechanism to disrupt the circulatory and neural estrogen function and estrogen-mediated signaling. Effects on EEDs-modified estrogen and nuclear respiratory factor 1 (NRF1) signaling genes with exposure to natural estrogen, pharmacological estrogen-ethinyl estradiol, PCBs, phthalates, BPA, and metalloestrogens are presented here. Bioinformatics analysis of gene-EEDs interactions and brain disease associations identified hundreds of genes that were altered by exposure to estrogen, phthalate, PCBs, BPA or metalloestrogens. Many genes modified by EEDs are common targets of both 17 β-estradiol (E2) and NRF1. Some of these genes are involved with brain diseases, such as Alzheimer's Disease (AD), Parkinson's Disease, Huntington's Disease, Amyotrophic Lateral Sclerosis, Autism Spectrum Disorder, and Brain Neoplasms. For example, the search of enriched pathways showed that top ten E2 interacting genes in AD-APOE, APP, ATP5A1, CALM1, CASP3, GSK3B, IL1B, MAPT, PSEN2 and TNF-underlie the enrichment of the Kyoto Encyclopedia of Genes and Genomes (KEGG) AD pathway. With AD, the six E2-responsive genes are NRF1 target genes: APBB2, DPYSL2, EIF2S1, ENO1, MAPT, and PAXIP1. These genes are also responsive to the following EEDs: ethinyl estradiol (APBB2, DPYSL2, EIF2S1, ENO1, MAPT, and PAXIP1), BPA (APBB2, EIF2S1, ENO1, MAPT, and PAXIP1), dibutyl phthalate (DPYSL2, EIF2S1, and ENO1), diethylhexyl phthalate (DPYSL2 and MAPT). To validate findings from Comparative Toxicogenomics Database (CTD) curated data, we used Bayesian network (BN) analysis on microarray data of AD patients. We observed that both gender and NRF1 were associated with AD. The female NRF1 gene network is completely different from male human AD patients. AD-associated NRF1 target genes-APLP1, APP, GRIN1, GRIN2B, MAPT, PSEN2, PEN2, and IDE-are also regulated by E2. NRF1 regulates targets genes with diverse functions, including cell growth, apoptosis/autophagy, mitochondrial biogenesis, genomic instability, neurogenesis, neuroplasticity, synaptogenesis, and senescence. By activating or repressing the genes involved in cell proliferation, growth suppression, DNA damage/repair, apoptosis/autophagy, angiogenesis, estrogen signaling, neurogenesis, synaptogenesis, and senescence, and inducing a wide range of DNA damage, genomic instability and DNA methylation and transcriptional repression, NRF1 may act as a major regulator of EEDs-induced brain health deficits. In summary, estrogenic endocrine disrupting chemicals-modified genes in brain health deficits are part of both estrogen and NRF1 signaling pathways. Our findings suggest that in addition to estrogen signaling, EEDs influencing NRF1 regulated communities of genes across genomic and epigenomic multiple networks may contribute in the development of complex chronic human brain health disorders.

Preclinical Magnetic Resonance Imaging and Spectroscopy Studies of Memory, Aging, and Cognitive Decline

Neuroimaging provides for non-invasive evaluation of brain structure and activity and has been employed to suggest possible mechanisms for cognitive aging in humans. However, these imaging procedures have limits in terms of defining cellular and molecular mechanisms. In contrast, investigations of cognitive aging in animal models have mostly utilized techniques that have offered insight on synaptic, cellular, genetic, and epigenetic mechanisms affecting memory. Studies employing magnetic resonance imaging and spectroscopy (MRI and MRS, respectively) in animal models have emerged as an integrative set of techniques bridging localized cellular/molecular phenomenon and broader in vivo neural network alterations. MRI methods are remarkably suited to longitudinal tracking of cognitive function over extended periods permitting examination of the trajectory of structural or activity related changes. Combined with molecular and electrophysiological tools to selectively drive activity within specific brain regions, recent studies have begun to unlock the meaning of fMRI signals in terms of the role of neural plasticity and types of neural activity that generate the signals. The techniques provide a unique opportunity to causally determine how memory-relevant synaptic activity is processed and how memories may be distributed or reconsolidated over time. The present review summarizes research employing animal MRI and MRS in the study of brain function, structure, and biochemistry, with a particular focus on age-related cognitive decline.

Early-life metal exposure and schizophrenia: A proof-of-concept study using novel tooth-matrix biomarkers

BACKGROUND

Despite evidence for the effects of metals on neurodevelopment, the long-term effects on mental health remain unclear due to methodological limitations. Our objective was to determine the feasibility of studying metal exposure during critical neurodevelopmental periods and to explore the association between early-life metal exposure and adult schizophrenia.

METHODS

We analyzed childhood-shed teeth from nine individuals with schizophrenia and five healthy controls. We investigated the association between exposure to lead (Pb(2+)), manganese (Mn(2+)), cadmium (Cd(2+)), copper (Cu(2+)), magnesium (Mg(2+)), and zinc (Zn(2+)), and schizophrenia, psychotic experiences, and intelligence quotient (IQ). We reconstructed the dose and timing of early-life metal exposures using laser ablation inductively coupled plasma mass spectrometry.

RESULTS

We found higher early-life Pb(2+) exposure among patients with schizophrenia than controls. The differences in log Mn(2+) and log Cu(2+) changed relatively linearly over time to postnatal negative values. There was a positive correlation between early-life Pb(2+) levels and psychotic experiences in adulthood. Moreover, we found a negative correlation between Pb(2+) levels and adult IQ.

CONCLUSIONS

In our proof-of-concept study, using tooth-matrix biomarker that provides direct measurement of exposure in the fetus and newborn, we provide support for the role of metal exposure during critical neurodevelopmental periods in psychosis.

Lysosomal iron modulates NMDA receptor-mediated excitation via small GTPase, Dexras1

Background

Activation of NMDA receptors can induce iron movement into neurons by the small GTPase Dexras1 via the divalent metal transporter 1 (DMT1). This pathway under pathological conditions such as NMDA excitotoxicity contributes to metal-catalyzed reactive oxygen species (ROS) generation and neuronal cell death, and yet its physiological role is not well understood.

Results

We found that genetic and pharmacological ablation of this neuronal iron pathway in the mice increased glutamatergic transmission. Voltage sensitive dye imaging of hippocampal slices and whole-cell patch clamping of synaptic currents, indicated that the increase in excitability was due to synaptic modification of NMDA receptor activity via modulation of the PKC/Src/NR2A pathway. Moreover, we identified that lysosomal iron serves as a main source for intracellular iron signaling modulating glutamatergic excitability.

Conclusions

Our data indicates that intracellular iron is dynamically regulated in the neurons and robustly modulate synaptic excitability under physiological condition. Since NMDA receptors play a central role in synaptic neurophysiology, plasticity, neuronal homeostasis, neurodevelopment as well as in the neurobiology of many diseases, endogenous iron is therefore likely to have functional relevance to each of these areas.

Environmental exposure to metals, neurodevelopment, and psychosis

PURPOSE OF REVIEW

This article presents a new hypothesis about the possible relation between early life exposure to metals and psychosis. We review limitations of available research, and discuss novel approaches to overcome previous methodological barriers.

RECENT FINDINGS

Mechanistic studies suggest a possible association between excess lead, manganese, cadmium, arsenic, or copper, and zinc deficiency, and several biochemical disturbances related to psychosis, such as altered neurotransmitters levels, excitotoxicity, and inflammation. Furthermore, studies suggest that some metals (lead, manganese, cadmium excess, and zinc deficiency) are associated with schizophrenia or psychosis-related phenotype. However, previous studies had multiple methodological limitations. Importantly, metal exposure was often measured after disease development and seldom determined during critical developmental periods. Most studies fell short of depicting the exact timing of exposure and the change in exposure over time. Here, we propose several methods to overcome these methodological limitations.

SUMMARY

There is a plausible role of early life exposure to metals in the cause of psychosis. Owing to methodological limitations in exposure measurement, this has not been well characterized. Considering the wide exposure to metals and the high cost of psychosis to society, this hypothesis should be rigorously examined.

Effect of Hfe Deficiency on Memory Capacity and Motor Coordination after Manganese Exposure by Drinking Water in Mice

Excess manganese (Mn) is neurotoxic. Increased manganese stores in the brain are associated with a number of behavioral problems, including motor dysfunction, memory loss and psychiatric disorders. We previously showed that the transport and neurotoxicity of manganese after intranasal instillation of the metal are altered in Hfe-deficient mice, a mouse model of the iron overload disorder hereditary hemochromatosis (HH). However, it is not fully understood whether loss of Hfe function modifies Mn neurotoxicity after ingestion. To investigate the role of Hfe in oral Mn toxicity, we exposed Hfe-knockout (Hfe (-/-)) and their control wild-type (Hfe (+/+)) mice to MnCl2 in drinking water (5 mg/mL) for 5 weeks. Motor coordination and spatial memory capacity were determined by the rotarod test and the Barnes maze test, respectively. Brain and liver metal levels were analyzed by inductively coupled plasma mass spectrometry. Compared with the water-drinking group, mice drinking Mn significantly increased Mn concentrations in the liver and brain of both genotypes. Mn exposure decreased iron levels in the liver, but not in the brain. Neither Mn nor Hfe deficiency altered tissue concentrations of copper or zinc. The rotarod test showed that Mn exposure decreased motor skills in Hfe (+/+) mice, but not in Hfe (-/-) mice (p = 0.023). In the Barns maze test, latency to find the target hole was not altered in Mn-exposed Hfe (+/+) compared with water-drinking Hfe (+/+) mice. However, Mn-exposed Hfe (-/-) mice spent more time to find the target hole than Mn-drinking Hfe (+/+) mice (p = 0.028). These data indicate that loss of Hfe function impairs spatial memory upon Mn exposure in drinking water. Our results suggest that individuals with hemochromatosis could be more vulnerable to memory deficits induced by Mn ingestion from our environment. The pathophysiological role of HFE in manganese neurotoxicity should be carefully examined in patients with HFE-associated hemochromatosis and other iron overload disorders.

Manganese-Disrupted Interaction of Dopamine D1 and NMDAR in the Striatum to Injury Learning and Memory Ability of Mice

Manganese (Mn) is widely regarded as a neurotoxic heavy metal that causes learning and memory deficits. Recently, it has been proved that the striatum is related to memory and learning ability. However, no previous study focused on the effect of Mn-induced learning and memory deficits on the striatum. This study aims to investigate the probable interaction of dopamine D1 receptor (DR1) and N-methyl-D-aspartate receptor (NMDAR), two cognition-related receptors in the striatum during Mn exposure. Mice are randomly divided into four groups, including control group, 12.5 mg/kg MnCl₂ group, 25 mg/kg MnCl₂ group, and 50 mg/kg MnCl₂ group. The mice receive intraperitoneal injections of 0, 12.5, 25, and 50 mg/kg MnCl₂ once daily for 2 weeks. Then, learning and memory ability, pathological changes, expression, and interaction of DR1 and NMDAR are determined. It has been found that Mn disrupted spatial learning and memory ability of mice by Morris water maze test and the passive avoidance test. Pathological and ultrastructure were injured. Mn decreased the immunohistochemical activities, protein levels, and messenger RNA (mRNA) expression of DR1, NR1, and NR2A. Mn exposure inhibited interaction between DR1 and NMDAR in striatum by double immunofluorescent staining and co-immunoprecipitation. In conclusion, our study illustrated that Mn caused learning and memory dysfunction via injury of striatum and inhibition of interaction between DR1 and NMDAR in striatum.

The effects of preweaning manganese exposure on spatial learning ability and p-CaMKIIα level in the hippocampus

BACKGROUND

The effects and mechanisms of preweaning Manganese (Mn) exposure on cognitive dysfunction remain unclear.

OBJECTIVE

This study evaluated the effects of preweaning Mn exposure on spatial learning and memory as well as the protein expression of CaMKIIα and p-CaMKIIα.

METHODS

We treated neonate rats with Mn(2+) doses of 0 (control group), 10, 20 and 30mg of Mn(2+) per kg body weight (Mn-exposed groups) over postnatal day (PND) 1-21 by intraperitoneal injection. The ability of spatial learning and memory was tested on PND 22 using the Morris water maze (MWM), while the protein expressions of CaMKIIα and p-CaMKIIα in the hippocampus were evaluated by Western blotting. The levels of Mn in the blood and hippocampus were measured by inductively coupled plasma-mass spectrometry (ICP-MS).

RESULTS

The rats in Mn-exposed groups showed a significant delay in spatial learning ability on the third day of the MWM without dose-dependent differences, but there was no effect on the spatial memory ability. p-CaMKIIα, but not CaMKIIα protein expression significantly reduced in the Mn-exposed group.

CONCLUSION

These findings suggested that the inhibition of p-CaMKIIα could be one of the mechanisms involved in the occurrence of Mn-induced cognitive impairments.

Loss of hfe function reverses impaired recognition memory caused by olfactory manganese exposure in mice

Excessive manganese (Mn) in the brain promotes a variety of abnormal behaviors, including memory deficits, decreased motor skills and psychotic behavior resembling Parkinson’s disease. Hereditary hemochromatosis (HH) is a prevalent genetic iron overload disorder worldwide. Dysfunction in HFE gene is the major cause of HH. Our previous study has demonstrated that olfactory Mn uptake is altered by HFE deficiency, suggesting that loss of HFE function could alter manganese-associated neurotoxicity. To test this hypothesis, Hfe-knockout (Hfe^−/−) and wild-type (Hfe^+/+) mice mice were intranasally-instilled with manganese chloride (MnCl₂ 5 mg/kg) or water daily for 3 weeks and examined for memory function. Olfactory Mn diminished both short-term recognition and spatial memory in Hfe^+/+ mice, as examined by novel object recognition task and Barnes maze test, respectively. Interestingly, Hfe^−/− mice did not show impaired recognition memory caused by Mn exposure, suggesting a potential protective effect of Hfe deficiency against Mn-induced memory deficits. Since many of the neurotoxic effects of manganese are thought to result from increased oxidative stress, we quantified activities of anti-oxidant enzymes in the prefrontal cortex (PFC). Mn instillation decreased superoxide dismutase 1 (SOD1) activity in Hfe^+/+ mice, but not in Hfe^−/− mice. In addition, Hfe deficiency up-regulated SOD1 and glutathione peroxidase activities. These results suggest a beneficial role of Hfe deficiency in attenuating Mn-induced oxidative stress in the PFC. Furthermore, Mn exposure reduced nicotinic acetylcholine receptor levels in the PFC, indicating that blunted acetylcholine signaling could contribute to impaired memory associated with intranasal manganese. Together, our model suggests that disrupted cholinergic system in the brain is involved in airborne Mn-induced memory deficits and loss of HFE function could in part prevent memory loss via a potential up-regulation of anti-oxidant enzymes in the PFC.

Expression and Transport of α-Synuclein at the Blood-Cerebrospinal Fluid Barrier and Effects of Manganese Exposure

The choroid plexus maintains the homeostasis of critical molecules in the brain by regulating their transport between the blood and cerebrospinal fluid (CSF). The current study was designed to investigate the potential role of the blood-CSF barrier (BCSFB) in α-synuclein (a-Syn) transport in the brain as affected by exposure to manganese (Mn), the toxic metal implicated in Parkinsonian disorders. Immunohistochemistry was used to identify intracellular a-Syn expression at the BCSFB. Quantitative real-time PCR was used to quantify the change in a-Syn mRNA expression following Mn treatments at the BCSFB in vitro. ELISA was used to quantify a-Syn levels following in vivo and in vitro treatments of Mn, copper (Cu), and/or external a-Syn. Thioflavin-T assay was used to investigate a-Syn aggregation after incubating with Mn and/or Cu in vitro. A two-chamber Transwell system was used to study a-Syn transport by BCSFB monolayer. Data revealed the expression of endogenous a-Syn in rat choroid plexus tissue and immortalized choroidal epithelial Z310 cells. The cultured primary choroidal epithelia from rats showed the ability to take up a-Syn from extracellular medium and transport a-Syn across the cellular monolayer from the donor to receiver chamber. Exposure of cells with Mn induced intracellular a-Syn accumulation without causing any significant changes in a-Syn mRNA expression. A significant increase in a-Syn aggregation in a cell-free system was observed with the presence of Mn. Moreover, Mn exposure resulted in a significant uptake of a-Syn by primary cells. These data indicate that the BCSFB expresses a-Syn endogenously and is capable of transporting a-Syn across the BCSFB monolayer; Mn exposure apparently increases a-Syn accumulation in the BCSFB by facilitating its uptake and intracellular aggregation.

The critical fetal stage for maternal manganese exposure

Prenatal exposure and the health effects of that exposure have been intensively studied for a variety of environmental pollutants and trace elements. However, few studies have compared susceptibilities among the three trimesters of gestation. Manganese (Mn) is a naturally occurring and abundant trace element in the environment. Although the effects of Mn on animals are well documented, knowledge of the effects of Mn exposure on pregnant women and fetuses remains limited. A longitudinal study was conducted by collecting blood samples during all three trimesters, and Mn exposure was completely characterized during gestation. The aims of this study were to examine the effects of maternal Mn exposure on neonatal birth outcomes and to explore the critical stage of these effects. In total, 38, 76 and 76 samples were obtained from singleton pregnant women in their first, second and third trimesters, respectively. The cohort of pregnant women was selected at a medical center in northern Taiwan. Erythrocyte samples were collected during the first, second and third trimesters of gestation. Erythrocyte Mn concentrations were measured by inductively coupled plasma mass spectrometry. Neonatal birth outcomes were evaluated immediately after delivery. A multivariate regression model was used to determine the associations between maternal Mn levels in erythrocytes in each trimester and neonatal birth outcomes. The geometric mean concentrations of Mn were 2.93 μg/dL, 3.96 μg/dL and 4.41 μg/dL in the first, second and third trimesters, respectively. After adjusting for potential confounders, a consistently negative association was found between maternal Mn levels throughout the three trimesters and birth outcomes. Log-transformed Mn levels in maternal erythrocytes in the second trimester were significantly associated with neonatal birth weight, head and chest circumferences, respectively (β=-556.98 g, p=0.038; β=-1.87 cm, p=0.045; β=-2.74 cm, p=0.024). Despite the limited sample size in the first trimester, negative effects of maternal Mn levels on birth weight (β=-1108.95 g, p<0.01) and chest circumference (β=-4.40 cm, p=0.019) were also observed.

Effects of developmental exposure to manganese and/or low iron diet: Changes to metal transporters, sucrose preference, elevated zero-maze, open-field, and locomotion in response to fenfluramine, amphetamine, and MK-801

Manganese overexposure (MnOE) can be neurotoxic. In humans this can occur through occupational exposure, air or water contamination, well water, soy milk, and some baby formulas. In children MnOE has been associated with cognitive and behavioral deficits. The effects of MnOE may be modified by factors such as iron status. We hypothesized that developmental MnOE would be exacerbated by iron deficiency. A diet with a 90% decrease in iron (FeD) was given to gravid female rats starting on embryonic day 15 and continued through postnatal day (P)28. Mn (100 mg/kg) or vehicle (VEH) was administered by gavage every other day from P4-28. Metal transporters and receptors (divalent metal transporter-1 (DMT1), transferrin (Tf), transferrin receptor (TfR), and zip8 (zrt8)) were quantified in brain at P28. These markers were increased but the changes were specific: MnOE increased TfR and decreased Tf in hippocampus, whereas FeD increased TfR in neostriatum and increased TfR and DMT1 in the hippocampus, and the combination increased TfR in neostriatum (zip8 was unaffected). Identically treated animals were tested behaviorally at P29 or P60. The combination of FeD+MnOE increased head dips in an elevated zero-maze, reversed deficits in sucrose preference induced by MnOE alone, and increased spontaneous locomotion in an open-field. Rats were also evaluated for changes in locomotor activity after challenge with (±)-fenfluramine (FEN, a 5-HT agonist: 5 mg/kg), MK-801 (MK801, an NMDA antagonist: 0.2 mg/kg), or (+)amphetamine (AMPH, a dopamine agonist: 1 mg/kg). Compared with VEH animals, MnOE animals were more hyperactive after fenfluramine, amphetamine, or MK-801, regardless of FeD exposure. The results indicate persistent effects of developmental MnOE on brain and behavior but few interactions with dietary iron deficiency.

Regulation of copper transport crossing brain barrier systems by Cu-ATPases: effect of manganese exposure

Regulation of cellular copper (Cu) homeostasis involves Cu-transporting ATPases (Cu-ATPases), i.e., ATP7A and ATP7B. The question as to how these Cu-ATPases in brain barrier systems transport Cu, i.e., toward brain parenchyma, cerebrospinal fluid (CSF), or blood, remained unanswered. This study was designed to characterize roles of Cu-ATPases in regulating Cu transport at the blood-brain barrier (BBB) and blood-CSF barrier (BCB) and to investigate how exposure to toxic manganese (Mn) altered the function of Cu-ATPases, thereby contributing to the etiology of Mn-induced parkinsonian disorder. Studies by quantitative real-time RT-PCR (qPCR), Western blot, and immunocytochemistry revealed that both Cu-ATPases expressed abundantly in BBB and BCB. Transport kinetic studies by in situ brain infusion and ventriculo-cisternal (VC) perfusion in Sprague Dawley rat suggested that the BBB was a major site for Cu entry into brain, whereas the BCB was a predominant route for Cu efflux from the CSF to blood. Confocal evidence showed that the presence of excess Cu or Mn in the choroid plexus cells led to ATP7A relocating toward the apical microvilli facing the CSF, but ATP7B toward the basolateral membrane facing blood. Mn exposure inhibited the production of both Cu-ATPases. Collectively, these data suggest that Cu is transported by the BBB from the blood to brain, which is mediated by ATP7A in brain capillary. By diffusion, Cu ions move from the interstitial fluid into the CSF, where they are taken up by the BCB. Within the choroidal epithelial cells, Cu ions are transported by ATP7B back to the blood. Mn exposure alters these processes, leading to Cu dyshomeostasis-associated neuronal injury.

Manganese-exposed developing rats display motor deficits and striatal oxidative stress that are reversed by Trolox

While manganese (Mn) is essential for proper central nervous system (CNS) development, excessive Mn exposure may lead to neurotoxicity. Mn preferentially accumulates in the basal ganglia, and in adults it may cause Parkinson's disease-like disorder. Compared to adults, younger individuals accumulate greater Mn levels in the CNS and are more vulnerable to its toxicity. Moreover, the mechanisms mediating developmental Mn-induced neurotoxicity are not completely understood. The present study investigated the developmental neurotoxicity elicited by Mn exposure (5, 10 and 20 mg/kg; i.p.) from postnatal day 8 to PN27 in rats. Neurochemical analyses were carried out on PN29, with a particular focus on striatal alterations in intracellular signaling pathways (MAPKs, Akt and DARPP-32), oxidative stress generation and cell death. Motor alterations were evaluated later in life at 3, 4 or 5 weeks of age. Mn exposure (20 mg/kg) increased p38(MAPK) and Akt phosphorylation, but decreased DARPP-32-Thr-34 phosphorylation. Mn (10 and 20 mg/kg) increased caspase activity and F2-isoprostane production (a biological marker of lipid peroxidation). Paralleling the changes in striatal biochemical parameters, Mn (20 mg/kg) also caused motor impairment, evidenced by increased falling latency in the rotarod test, decreased distance traveled and motor speed in the open-field test. Notably, the antioxidant Trolox™ reversed the Mn (20 mg/kg)-dependent augmentation in p38(MAPK) phosphorylation and reduced the Mn (20 mg/kg)-induced caspase activity and F2-isoprostane production. Trolox™ also reversed the Mn-induced motor coordination deficits. These findings are the first to show that long-term exposure to Mn during a critical period of neurodevelopment causes motor coordination dysfunction with parallel increment in oxidative stress markers, p38(MAPK) phosphorylation and caspase activity in the striatum. Moreover, we establish Trolox™ as a potential neuroprotective agent given its efficacy in reversing the Mn-induced neurodevelopmental effects.

Effect of environmental manganese exposure on verbal learning and memory in Mexican children

Manganese (Mn) is an essential metal, but in excess it becomes neurotoxic. Children's developing nervous system may be especially vulnerable to the neurotoxic effects of overexposure to this metal. The aim of this study was to assess the effect of Mn exposure on verbal memory and learning in 7- to 11-year-old children. We tested 79 children living in the Molango Mn-mining district and 95 children from a non-exposed community in the same State of Mexico. The Children's Auditory Verbal Learning Test (CAVLT) was administered. Blood and hair samples were obtained to determine Mn concentrations using atomic absorption spectrophotometry. CAVLT performance was compared between the two groups and multilevel regression models were constructed to estimate the association between biomarkers of Mn exposure and the CAVLT scores. The exposed group presented higher hair and blood Mn (p<0.001) than the non-exposed group (median 12.6 vs. 0.6μg/g, 9.5vs. 8.0μg/L respectively), as well as lower scores (p<0.001) for all the CAVLT subscales. Hair Mn was inversely associated with most CAVLT subscales, mainly those evaluating long-term memory and learning (β=-0.47, 95% CI -0.84, -0.09). Blood Mn levels showed a negative but non-significant association with the CAVLT scores. These results suggest that Mn exposure has a negative effect on children's memory and learning abilities.

Common trace elements alleviate pain in an experimental mouse model

Trace elements represent a group of essential metals or metaloids necessary for life, present in minute amounts. Analgesic adjuvants can enhance the effect of other pain drugs or be used for pain control themselves. Previous studies on the effects of trace elements on nociception and their potential use as analgesic adjuvants have yielded conflicting results. In this study, we tested the hypothesis that three vital trace elements (Zn²⁺, Mg²⁺, Cu²⁺) have direct antinociceptive effects. Groups of eight Swiss mice were intraperitoneally (i.p) injected with incremental concentrations of Zn²⁺ sulfate (0.5, 2.0 mg/kg), Zn²⁺ citrate (0.125, 0.5 mg/kg), Mg²⁺ chloride (37.5, 75, 150 mg/kg), Cu²⁺ chloride (0.5, 1.0, 2.0 mg/kg), and Cu²⁺ sulfate (0.5, 1.0 mg/kg) or saline (control). Evaluations were made by hot plate (HP) and tail flick (TF) tests for central antinociceptive effect, writhing test (WT) for visceral antinociceptive effect, and activity cage (AC) test for spontaneous behavior. Zn²⁺ induced pain inhibition in HP/TF tests (up to 17%) and WT (up to 25%), with no significant differences among the salts used. Mg²⁺ salts induced pain inhibition for all performed tests (up to 85% in WT). Cu²⁺ salts showed antinociceptive effects for HP/TF (up to 28.6%) and WT (57.28%). Only Mg²⁺ and Cu²⁺ salts have displayed significant effects in AC (Mg²⁺ anxiolytic/depressant effect; Cu²⁺ anxiolytic effect). We interpret these data to mean that all tested trace elements induced antinociceptive effects in central and visceral pain tests. Our data indicate the potential use of these cheap adjuvants in pain therapy.

Is lead exposure in early life an environmental risk factor for Schizophrenia? Neurobiological connections and testable hypotheses

Schizophrenia is a devastating neuropsychiatric disorder of unknown etiology. There is general agreement in the scientific community that schizophrenia is a disorder of neurodevelopmental origin in which both genes and environmental factors come together to produce a schizophrenia phenotype later in life. The challenging questions have been which genes and what environmental factors? Although there is evidence that different chromosome loci and several genes impart susceptibility for schizophrenia; and epidemiological studies point to broad aspects of the environment, only recently there has been an interest in studying gene × environment interactions. Recent evidence of a potential association between prenatal lead (Pb(2+)) exposure and schizophrenia precipitated the search for plausible neurobiological connections. The most promising connection is that in schizophrenia and in developmental Pb(2+) exposure there is strong evidence for hypoactivity of the N-methyl-d-aspartate (NMDA) subtype of excitatory amino acid receptors as an underlying neurobiological mechanism in both conditions. A hypofunction of the NMDA receptor (NMDAR) complex during critical periods of development may alter neurobiological processes that are essential for brain growth and wiring, synaptic plasticity and cognitive and behavioral outcomes associated with schizophrenia. We also describe on-going proof of concept gene-environment interaction studies of early life Pb(2+) exposure in mice expressing the human mutant form of the disrupted in schizophrenia 1 (DISC-1) gene, a gene that is strongly associated with schizophrenia and allied mental disorders.

Essential Nutrients for Bone Health and a Review of their Availability in the Average North American Diet

Osteoporosis and low bone mineral density affect millions of Americans. The majority of adults in North America have insufficient intake of vitamin D and calcium along with inadequate exercise. Physicians are aware that vitamin D, calcium and exercise are essential for maintenance of bone health. Physicians are less likely to be aware that dietary insufficiencies of magnesium, silicon, Vitamin K, and boron are also widely prevalent, and each of these essential nutrients is an important contributor to bone health. In addition, specific nutritional factors may improve calcium metabolism and bone formation. It is the authors' opinion that nutritional supplements should attempt to provide ample, but not excessive, amounts of factors that are frequently insufficient in the typical American diet.In contrast to dietary insufficiencies, several nutrients that support bone health are readily available in the average American diet. These include zinc, manganese, and copper which may have adverse effects at higher levels of intake. Some multivitamins and bone support products provide additional quantities of nutrients that may be unnecessary or potentially harmful.The purpose of this paper is to identify specific nutritional components of bone health, the effects on bone, the level of availability in the average American diet, and the implications of supplementation for each nutritional component. A summary of recommended dietary supplementation is included.

Relative contribution of CTR1 and DMT1 in copper transport by the blood-CSF barrier: implication in manganese-induced neurotoxicity

The homeostasis of copper (Cu) in the cerebrospinal fluid (CSF) is partially regulated by the Cu transporter-1 (CTR1) and divalent metal transporter-1 (DMT1) at the blood-CSF barrier (BCB) in the choroid plexus. Data from human and animal studies suggest an increased Cu concentration in blood, CSF, and brains following in vivo manganese (Mn) exposure. This study was designed to investigate the relative role of CTR1 and DMT1 in Cu transport under normal or Mn-exposed conditions using an immortalized choroidal Z310 cell line. Mn exposure in vitro resulted in an increased cellular 64Cu uptake and the up-regulation of both CTR1 and DMT1. Knocking down CTR1 by siRNA counteracted the Mn-induced increase of 64Cu uptake, while knocking down DMT1 siRNA resulted in an increased cellular 64Cu uptake in Mn-exposed cells. To distinguish the roles of CTR1 and DMT1 in Cu transport, the Z310 cell-based tetracycline (Tet)-inducible CTR1 and DMT1 expression cell lines were developed, namely iZCTR1 and iZDMT1 cells, respectively. In iZCTR1 cells, Tet induction led to a robust increase (25 fold) of 64Cu uptake with the time course corresponding to the increased CTR1. Induction of DMT1 by Tet in iZDMT1 cells, however, resulted in only a slight increase of 64Cu uptake in contrast to a substantial increase in DMT1 mRNA and protein expression. These data indicate that CTR1, but not DMT1, plays an essential role in transporting Cu by the BCB in the choroid plexus. Mn-induced cellular overload of Cu at the BCB is due, primarily, to Mn-induced over-expression of CTR1.

Metal toxicity at the synapse: presynaptic, postsynaptic, and long-term effects

Metal neurotoxicity is a global health concern. This paper summarizes the evidence for metal interactions with synaptic transmission and synaptic plasticity. Presynaptically metal ions modulate neurotransmitter release through their interaction with synaptic vesicles, ion channels, and the metabolism of neurotransmitters (NT). Many metals (e.g., Pb(2+), Cd(2+), and Hg(+)) also interact with intracellular signaling pathways. Postsynaptically, processes associated with the binding of NT to their receptors, activation of channels, and degradation of NT are altered by metals. Zn(2+), Pb(2+), Cu(2+), Cd(2+), Ni(2+), Co(2+), Li(3+), Hg(+), and methylmercury modulate NMDA, AMPA/kainate, and/or GABA receptors activity. Al(3+), Pb(2+), Cd(2+), and As(2)O(3) also impair synaptic plasticity by targeting molecules such as CaM, PKC, and NOS as well as the transcription machinery involved in the maintenance of synaptic plasticity. The multiple effects of metals might occur simultaneously and are based on the specific metal species, metal concentrations, and the types of neurons involved.

Toxic agents causing cerebellar ataxias

The cerebellum is particularly vulnerable to intoxication and poisoning, especially so the cerebellar cortex and Purkinje neurons. In humans, the most common cause of a toxic lesion to the cerebellar circuitry is alcohol related, but the cerebellum is also a main target of drug exposure (such as anticonvulsants, antineoplastics, lithium salts, calcineurin inhibitors), drug abuse and addiction (such as cocaine, heroin, phencyclidine), and environmental toxins (such as mercury, lead, manganese, toluene/benzene derivatives). Although data for the prevalence and incidence of cerebellar lesions related to intoxication and poisoning are still unknown in many cases, clinicians should keep in mind the list of agents that may cause cerebellar deficits, since toxin-induced cerebellar ataxias are not rare in daily practice. Moreover, the patient's status may require immediate therapies when the intoxication is life-threatening.

Blood manganese levels in patients with hepatic encephalopathy

PROJECT

Hepatic encephalopathy is an increasingly common disease. Identification of prognosis risk factors in patients with liver damage may lead to preventive actions, towards decreasing its mortality. Manganese (Mn) levels are increased in basal ganglia of patients with hepatic encephalopathy as well as in cases of cirrhotic and liver failure patients. The present is a clinical, prospective, prolective and observational study developed at the Internal Medicine Service from "Dr. Darío Fernández Fierro" General Hospital, ISSSTE, Mexico City. The objective of this work was to report whole blood Mn levels and mortality in encephalopathic patients.

PROCEDURE

Consecutive patients over 18 years of age, diagnosed with hepatic encephalopathy were recruited at the emergency room service. An informed consent, signed by their families was collected. Patients' clinical characteristics, biochemical tests of renal function, hemoglobin, glucose, bilirubins and albumin levels were obtained along with a blood sample to analyze Mn. Patients evolution was followed up for 6 months.

RESULTS

Blood Mn in patients [median, (range)] [20.5, (10.5-39.5) μg/L] were higher than blood levels from a group of healthy volunteers [7.5, (6.1-12.8) μg/L] (P<0.001). Among 9 patients studied four died, 2 women and 2 men, those patients showed higher (P=0.032) Mn levels [28, (17-39.5) μg/L] than those alive [13.5, (10.5-32) μg/L] after the follow up period.

CONCLUSIONS

In this pilot study, Mn blood levels were higher in hepatic encephalopathy that died as consequence of the disease that those that survived in a 6 month follow up period. Blood Mn could be a potential prognosis factor for death in patients with hepatic encephalopathy.

Protective effects of antioxidants and anti-inflammatory agents against manganese-induced oxidative damage and neuronal injury

Exposure to excessive manganese (Mn) levels leads to neurotoxicity, referred to as manganism, which resembles Parkinson's disease (PD). Manganism is caused by neuronal injury in both cortical and subcortical regions, particularly in the basal ganglia. The basis for the selective neurotoxicity of Mn is not yet fully understood. However, several studies suggest that oxidative damage and inflammatory processes play prominent roles in the degeneration of dopamine-containing neurons. In the present study, we assessed the effects of Mn on reactive oxygen species (ROS) formation, changes in high-energy phosphates and associated neuronal dysfunctions both in vitro and in vivo. Results from our in vitro study showed a significant (p<0.01) increase in biomarkers of oxidative damage, F(2)-isoprostanes (F(2)-IsoPs), as well as the depletion of ATP in primary rat cortical neurons following exposure to Mn (500 μM) for 2h. These effects were protected when neurons were pretreated for 30 min with 100 of an antioxidant, the hydrophilic vitamin E analog, trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), or an anti-inflammatory agent, indomethacin. Results from our in vivo study confirmed a significant increase in F(2)-IsoPs levels in conjunction with the progressive spine degeneration and dendritic damage of the striatal medium spiny neurons (MSNs) of mice exposed to Mn (100mg/kg, s.c.) 24h. Additionally, pretreatment with vitamin E (100mg/kg, i.p.) or ibuprofen (140 μg/ml in the drinking water for two weeks) attenuated the Mn-induced increase in cerebral F(2)-IsoPs? and protected the MSNs from dendritic atrophy and dendritic spine loss. Our findings suggest that the mediation of oxidative stress/mitochondrial dysfunction and the control of alterations in biomarkers of oxidative injury, neuroinflammation and synaptodendritic degeneration may provide an effective, multi-pronged therapeutic strategy for protecting dysfunctional dopaminergic transmission and slowing of the progression of Mn-induced neurodegenerative processes.

Intellectual function in Mexican children living in a mining area and environmentally exposed to manganese

BACKGROUND

Excessive exposure to manganese (Mn), an essential trace element, has been shown to be neurotoxic, especially when inhaled. Few studies have examined potential effects of Mn on cognitive functions of environmentally exposed children.

OBJECTIVE

This study was intended to estimate environmental exposure to Mn resulting from mining and processing and to explore its association with intellectual function of school-age children.

METHODS

Children between 7 and 11 years of age from the Molango mining district in central Mexico (n = 79) and communities with similar socioeconomic conditions that were outside the mining district (n = 93) participated in the cross-sectional evaluation. The revised version of the Wechsler Intelligence Scale for Children adapted for the Mexican population was applied. Concentrations of Mn in blood (MnB) and hair (MnH) were used as biomarkers of exposure.

RESULTS

Exposed children had significantly higher median values for MnH (12.6 μg/g) and MnB (9.5 μg/L) than did nonexposed children (0.6 μg/g and 8.0 μg/L, respectively). MnH was inversely associated with Verbal IQ [β = -0.29; 95% confidence interval (CI), -0.51 to -0.08], Performance IQ (β = -0.08; 95% CI, -0.32 to 0.16), and Total Scale IQ (β = -0.20; 95% CI, -0.42 to 0.02). MnB was inversely but nonsignificantly associated with Total and Verbal IQ score. Age and sex significantly modified associations of MnH, with the strongest inverse associations in young girls and little evidence of associations in boys at any age. Associations with MnB did not appear to be modified by sex but appeared to be limited to younger study participants.

CONCLUSIONS

The findings from this study suggest that airborne Mn environmental exposure is inversely associated with intellectual function in young school-age children.