Effects of chronic manganese exposure on working memory in non-human primates

Associations of a toenail metal mixture with attention and memory in the Gulf long-term follow-up (GuLF) study

BACKGROUND

Research on metal-associated neurodegeneration has largely focused on single metals. Since metal exposures typically co-occur as combinations of both toxic and essential elements, a mixtures framework is important for identifying risk and protective factors. This study examined associations between toenail levels of an eight-metal mixture and attention and memory in men living in US Gulf states.

METHODS

We measured toenail concentrations of toxic (arsenic, chromium, lead, and mercury) and essential (copper, manganese, selenium, and zinc) metals in 413 non-smoking men (23-69 years, 46 % Black) from the Gulf Long-Term Follow-Up (GuLF) Study. Sustained attention and working memory were assessed at the time of toenail sample collection using the continuous performance test (CPT) and digit span test (DST), respectively. Associations between toenail metal concentrations and performance on neurobehavioral tests were characterized using co-pollutant adjusted general linear models and Bayesian Kernel Machine Regression.

RESULTS

Adjusting for other metals, one interquartile range (IQR) increase in toenail chromium was associated with a 0.19 (95 % CI: -0.31, -0.07) point reduction in CPT D Prime score (poorer ability to discriminate test signals from noise). One IQR increase in toenail manganese was associated with a 0.20 (95 % CI, -0.41, 0.01) point reduction on the DST Reverse Count (fewer numbers recalled). Attention deficits were greater among Black participants compared to White participants for the same increase in toenail chromium concentrations. No evidence of synergistic interaction between metals or adverse effect of the overall metal mixture was observed for either outcome.

CONCLUSIONS

Our findings support existing studies of manganese-related memory deficits and are some of the first to show chromium related attention deficits in adults. Longitudinal study of cognitive decline is needed to verify chromium findings. Research into social and chemical co-exposures is also needed to explain racial differences in metal-associated neurobehavioral deficits observed in this study.

The Role of Oxidative Stress in Manganese Neurotoxicity: A Literature Review Focused on Contributions Made by Professor Michael Aschner

This literature review focuses on the evidence implicating oxidative stress in the pathogenesis of manganese neurotoxicity. This review is not intended to be a systematic review of the relevant toxicologic literature. Instead, in keeping with the spirit of this special journal issue, this review highlights contributions made by Professor Michael Aschner's laboratory in this field of study. Over the past two decades, his laboratory has made significant contributions to our scientific understanding of cellular responses that occur both in vitro and in vivo following manganese exposure. These studies have identified molecular targets of manganese toxicity and their respective roles in mitochondrial dysfunction, inflammation, and cytotoxicity. Other studies have focused on the critical role astrocytes play in manganese neurotoxicity. Recent studies from his laboratory have used C. elegans to discover new facets of manganese-induced neurotoxicity. Collectively, his body of work has dramatically advanced the field and presents broader implications beyond metal toxicology.

Executive functions in school-aged children exposed to airborne manganese: A multilevel analysis

Neuropsychological alterations have been identified in populations heavily exposed to metals with neurotoxic potential, such as manganese (Mn). This study examined the associations between Mn environmental exposure in school-aged children and executive functions, using structural equation modeling. Children, aged between 7 and 12 years (N = 181), were recruited from four elementary schools located in a region that is under the influence of atmospheric emissions from a ferro-manganese alloy plant in the municipality of Simões Filho, Bahia, Brazil. The following cognitive functions were evaluated: Intelligence, Inhibitory Control, Cognitive Flexibility, Verbal and Design Fluency, Verbal and Visual Working Memory and Attention. We performed structural equation modeling to identify the following executive functions latent variables: working memory, inhibitory control and cognitive flexibility. We further analyzed the relations between executive functions and Mn measured in hair (MnH) and toenails (MnTn) with linear mixed models, after controlling for co-variables. A positive effect at the individual level on working memory, inhibition control and cognitive flexibility was observed with MnTn after controlling for co-variables, but no association was found with MnH levels. However, children attending school most environmentally exposed to Mn emissions, which had the highest rate of Mn dust deposition, had the poorest scores on working memory. These findings suggest both benefits and risk of Mn on children's cognitive development.

Chronic exposure to heavy metals from informal e-waste recycling plants and children's attention, executive function and academic performance

E-waste contains valuable metals that require appropriate waste management plans. However, rudimentary e-waste processing methods are a source of heavy metals environmental pollution. This study has characterised concentrations of heavy metals in soil (n = 10), water (n = 10) and hair (n = 44) of children in areas surrounding Jakarta (Indonesia), where e-waste is being or has been conducted in the past, and in a reference unexposed site. Chronic exposure to Mn, Pb, Hg, As and Cd and its associations with attention and executive function, characterised with the Trail Making Test (TMT), along with academic performance scores was conducted using multivariate regression analysis. Models were adjusted for age, gender, parental education, environmental tobacco smoke and residential traffic. Lead (3653 ± 3355 mg/kg), cadmium (3.4 ± 0.9 mg/kg) and mercury (15.2 ± 28.5 mg/kg) concentrations from soil and manganese concentrations in water (1.43 ± 0.64 mg/L) in the exposed sites were higher than current regulations. Heavy metal concentrations in hair of children living near e-waste facilities was higher than for children living in non-exposed areas (Pb: 0.155 ± 0.187 vs 0.0729 ± 0.08 mg/g; Mn: 0.130 ± 0.212 vs 0.018 ± 0.045 mg/g; Hg: 0.008 ± 0.0042 vs 0.002 ± 0.0011 mg/g) suggesting chronic exposure to heavy metals. Manganese exposure was associated with worse cognitive performance in the domains of attention (TMT-A score: 66 s, 95% CI 0.09, 132), executive function (TMT-B score: 105 s, 95% CI 11.5, 198) and social sciences (-29%, 95% CI -54, -4.7) (per unit of Mn in hair mg/g). These results suggest that informal e-waste activities contribute to local heavy metal soil contamination, and could be an important source of metal exposure to children living in the vicinity of these facilities with putative impacts on their cognitive performance. E-waste management regulation and remediation programmes should be implemented to reduce environmental pollution and associated health effects.

PET imaging of dopamine release in the frontal cortex of manganese-exposed non-human primates

Humans and non-human primates exposed to excess levels of manganese (Mn) exhibit deficits in working memory and attention. Frontal cortex and fronto-striatal networks are implicated in working memory and these circuits rely on dopamine for optimal performance. Here, we aimed to determine if chronic Mn exposure alters in vivo dopamine release (DAR) in the frontal cortex of non-human primates. We used [¹¹ C]-FLB457 positron emission tomography with amphetamine challenge to measure DAR in Cynomolgus macaques. Animals received [¹¹ C]-FLB457 positron emission tomography scans with and without amphetamine challenge prior to Mn exposure (baseline), at different time points during the Mn exposure period, and after 10 months of Mn exposure cessation. Four of six Mn-exposed animals expressed significant impairment of frontal cortex in vivo DAR relative to baseline. One Mn animal had no change in DAR and another Mn animal expressed increased DAR relative to baseline. In the reversal studies, one Mn-exposed animal exhibited complete recovery of DAR while the second animal had partial recovery. In both animals, frontal cortex Mn concentrations normalized after 10 months of exposure cessation based on T1-weighted magnetic resonance imaging. D1-dopamine receptor (D1R) autoradiography in frontal cortex tissue indicates that Mn animals that experienced cessation of Mn exposure expressed D1R levels that were approximately 50% lower than Mn animals that did not experience cessation of Mn exposure or control animals. The present study provides evidence of Mn-induced alterations in frontal cortex DAR and D1R that may be associated with working memory and attention deficits observed in Mn-exposed subjects.

Deriving A Drinking Water Guideline for A Non-Carcinogenic Contaminant: The Case of Manganese

Manganese is a natural contaminant of water sources. It is an essential oligo-element, which may exert toxicity at high doses, particularly via inhalation. Its toxicity by the oral route is less known, but epidemiological and experimental studies tend to support its neurodevelopmental toxicity in infants and children. This paper describes the method used by a middle-size public health institution to derive a Drinking Water Guideline (DWG) for manganese. After reviewing the work done by major public health institutions, authors confirmed the use of experimental data to derive a point-of-departure (POD) of 25 mg of manganese/kg/day, based on neurodevelopmental effects on pup rats. Then, a total uncertainty factor of 450 was applied to calculate a Toxicological Reference Value (TRV) of 55 µg/kg/day. The final DWG proposed for manganese is 60 µg/L and is based on a relative source contribution (RSC) of water of 20% and an infant drinking scenario of 182 mL/kg of body weight (BW) of water (95th percentile of the ingestion rate distribution for 0⁻6 months). Despite its limitations, e.g., starting with the work done by other agencies, such an approach demonstrates in a transparent way the rationale and challenging choices made by regulators when deriving a DWG.

Environmental manganese exposure and associations with memory, executive functions, and hyperactivity in Brazilian children

Manganese (Mn) is an essential element, however high levels of Mn have been associated with lower neuropsychological performance and behavioral problems in children. We investigated the associations between hair Mn concentrations and neuropsychological and behavioral performances among children with long-term exposure to airborne Mn aged between 7 and 12 years. Neuropsychological performance included tests of: verbal memory, inhibitory control, cognitive flexibility, verbal fluency, and motor function. We used the Conners Abbreviated Rating Scale for teachers to assess students' behaviors of hyperactivity. Hair manganese (MnH) concentrations in children and exposure to airborne manganese from a ferro-manganese alloy plant were analyzed and correlated with tests scores. Multivariable linear models adjusting for potential confounders showed that elevated levels of MnH were associated with lower performance in verbal memory, as measured by the free recall after interference (β = - 1.8; 95% CI: - 3.4, - 0.2), which indicates susceptibility to interference, and Delayed Effect (β = -2.0; 95% CI: -3.7, - 0.2), representing a loss of information over time. Additionally, we found patterns of effect modification by sex in three subtests measuring verbal memory: the free recall after interference score, Interference Effect, and Delayed Effect (all at p < 0.10). Overall, the results suggest that long-term airborne Mn exposure may be associated with lower performance in verbal memory, and hyperactivity behaviors.

Manganese in teeth and neurobehavior: Sex-specific windows of susceptibility

BACKGROUND

Manganese (Mn) is an essential element required for growth and development, but higher body burdens have been associated with neurobehavioral decrements in children.

OBJECTIVES

We examined whether prenatal or postnatal Mn measured in deciduous teeth was associated with scores on a test of visuospatial learning and memory.

METHODS

Deciduous teeth were collected from 142 participants (ages 10-14years) residing near varied ferro‑manganese industry in Italy. Mn concentrations were measured in prenatal and postnatal tooth regions by laser ablation inductively coupled plasma mass spectrometry (ICP-MS). The Virtual Radial Arm Maze (VRAM), an animal-human analogue task, was used to assess visuospatial learning and memory. We used generalized additive, linear and zero-inflated Poisson mixed regression models to estimate associations between prenatal or postnatal Mn concentrations and repeated measures of all four VRAM outcomes: time, distance, working and reference memory errors. Effect measure modification by sex was examined in stratified models.

RESULTS

U-shaped associations between prenatal Mn and VRAM outcomes were observed among girls only (pGAMM=0.001 to 0.02 in stratified models). Compared to the mid-tertile of prenatal Mn, girls in the highest tertile took 7.7s [95% CI: -6.1, 21.5] longer to complete the task, traveled 2.3 maze units [0.1, 4.4] farther, and committed more working and reference memory errors (β for count ratio=1.33 [1.01, 1.83]; 1.10 [0.98, 1.24], respectively). This association was not observed among boys. In contrast, for postnatal Mn, no significant associations were found, and patterns were similar for boys and girls.

CONCLUSIONS

The prenatal period may be a critical window for the impact of environmental Mn on visuospatial ability and executive function, especially for females.

Sodium p-Aminosalicylic Acid Reverses Sub-Chronic Manganese-Induced Impairments of Spatial Learning and Memory Abilities in Rats, but Fails to Restore γ-Aminobutyric Acid Levels

Excessive manganese (Mn) exposure is not only a health risk for occupational workers, but also for the general population. Sodium para-aminosalicylic acid (PAS-Na) has been successfully used in the treatment of manganism, but the involved molecular mechanisms have yet to be determined. The present study aimed to investigate the effects of PAS-Na on sub-chronic Mn exposure-induced impairments of spatial learning and memory, and determine the possible involvements of γ-aminobutyric acid (GABA) metabolism in vivo. Sprague-Dawley male rats received daily intraperitoneal injections MnCl₂ (as 6.55 mg/kg Mn body weight, five days per week for 12 weeks), followed by daily subcutaneous injections of 100, 200, or 300 mg/kg PAS-Na for an additional six weeks. Mn exposure significantly impaired spatial learning and memory ability, as noted in the Morris water maze test, and the following PAS-Na treatment successfully restored these adverse effects to levels indistinguishable from controls. Unexpectedly, PAS-Na failed to recover the Mn-induced decrease in the overall GABA levels, although PAS-Na treatment reversed Mn-induced alterations in the enzyme activities directly responsible for the synthesis and degradation of GABA (glutamate decarboxylase and GABA-transaminase, respectively). Moreover, Mn exposure caused an increase of GABA transporter 1 (GAT-1) and decrease of GABA A receptor (GABA_A) in transcriptional levels, which could be reverted by the highest dose of 300 mg/kg PAS-Na treatment. In conclusion, the GABA metabolism was interrupted by sub-chronic Mn exposure. However, the PAS-Na treatment mediated protection from sub-chronic Mn exposure-induced neurotoxicity, which may not be dependent on the GABA metabolism.

"Manganese-induced neurotoxicity: a review of its behavioral consequences and neuroprotective strategies"

Manganese (Mn) is an essential heavy metal. However, Mn’s nutritional aspects are paralleled by its role as a neurotoxicant upon excessive exposure. In this review, we covered recent advances in identifying mechanisms of Mn uptake and its molecular actions in the brain as well as promising neuroprotective strategies. The authors focused on reporting findings regarding Mn transport mechanisms, Mn effects on cholinergic system, behavioral alterations induced by Mn exposure and studies of neuroprotective strategies against Mn intoxication. We report that exposure to Mn may arise from environmental sources, occupational settings, food, total parenteral nutrition (TPN), methcathinone drug abuse or even genetic factors, such as mutation in the transporter SLC30A10. Accumulation of Mn occurs mainly in the basal ganglia and leads to a syndrome called manganism, whose symptoms of cognitive dysfunction and motor impairment resemble Parkinson’s disease (PD). Various neurotransmitter systems may be impaired due to Mn, especially dopaminergic, but also cholinergic and GABAergic. Several proteins have been identified to transport Mn, including divalent metal tranporter-1 (DMT-1), SLC30A10, transferrin and ferroportin and allow its accumulation in the central nervous system. Parallel to identification of Mn neurotoxic properties, neuroprotective strategies have been reported, and these include endogenous antioxidants (for instance, vitamin E), plant extracts (complex mixtures containing polyphenols and non-characterized components), iron chelating agents, precursors of glutathione (GSH), and synthetic compounds that can experimentally afford protection against Mn-induced neurotoxicity.

Evaluation of Toxicological Effects of an Aqueous Extract of Shells from the Pecan Nut Carya illinoinensis (Wangenh.) K. Koch and the Possible Association with Its Inorganic Constituents and Major Phenolic Compounds

Background. Industrial processing of the pecan nut Carya illinoinensis K. Koch generated a large amount of shells, which have been used to prepare nutritional supplements and medicinal products; however, the safe use of shells requires assessment. This study evaluated the toxic, genotoxic, and mutagenic effects of pecan shell aqueous extract (PSAE) and the possible contribution of phenolic compounds, ellagic and gallic acids, and inorganic elements present in PSAE to induce toxicity. Results. Levels of inorganic elements like K, P, Cl, and Rb quantified using the Particle-Induced X-Ray Emission method were higher in PSAE than in pecan shells, while Mg and Mn levels were higher in shells. Mice showed neurobehavioral toxicity when given high PSAE doses (200-2,000 mg kg(-1)). The LD50 was 1,166.3 mg kg(-1). However, PSAE (50-200 mg·kg(-1)) and the phenolic compounds (10-100 mg·kg(-1)) did not induce DNA damage or mutagenicity evaluated using the comet assay and micronucleus test. Treatment with ellagic acid (10-100 mg·kg(-1)) decreased triglyceride and glucose levels, while treatments with PSAE and gallic acid had no effect. Conclusion. Pecan shell toxicity might be associated with high concentrations of inorganic elements such as Mn, Al, Cu, and Fe acting on the central nervous system, besides phytochemical components, suggesting that the definition of the safe dose should take into account the consumption of micronutrients.

Manganese accumulation in hair and teeth as a biomarker of manganese exposure and neurotoxicity in rats

Manganese (Mn) is an essential trace element to humans. However, excessive Mn causes cognitive impairment resulting from injury to the central nervous system within the hippocampus. No ideal biomarker is currently available for evaluating Mn exposure and associated neurotoxicity in the body. Hence, this study used Mn levels in the serum (MnS), teeth (MnT), and hair (MnH) as biomarkers for evaluating the association between Mn exposure and cognitive impairment in Mn-treated rats. A total of 32 male Sprague-Dawley rats were randomly divided into four groups, received 0, 5, 10, and 20 mg/(kg day) of MnCl2·4H2O for 5 days a week for 18 weeks, respectively. Lifetime Mn cumulative dose (LMCD) was used to evaluate external Mn exposure. Hippocampus, serum, teeth, and hair specimens were collected from the rats for Mn determination by graphite furnace atomic absorption spectrometry. Learning and memory functions were assessed using the Morris water maze test. Results showed that chronic Mn exposure increased the hippocampus (MnHip), MnS, MnT, and MnH levels, as well as impaired learning and memory function in rats. MnHip, MnT, and MnH levels were positively correlated with LMCD (r = 0.759, r = 0.925, and r = 0.908, respectively; p < 0.05), escape latency (r = 0.862, r = 0.716, and r = 0.814, respectively; p < 0.05), and the number of platform crossings (r = -0.734, r = -0.514, and r = -0.566, respectively; p < 0.05). No association was observed between MnS levels and the number of platform crossings (r = -0.286, p > 0.05). Thus, MnT and MnH detected long-term low-dose Mn exposure. These parameters can be reliable biomarkers for Mn exposure and associated neurotoxicity in Mn-treated rats.

Associations among environmental exposure to manganese, neuropsychological performance, oxidative damage and kidney biomarkers in children

Environmental exposure to manganese (Mn) results in several toxic effects, mainly neurotoxicity. This study investigated associations among Mn exposure, neuropsychological performance, biomarkers of oxidative damage and early kidney dysfunction in children aged 6-12 years old. Sixty-three children were enrolled in this study, being 43 from a rural area and 20 from an urban area. Manganese was quantified in blood (B-Mn), hair (H-Mn) and drinking water using inductively coupled plasma mass spectrometry (ICP-MS). The neuropsychological functions assessed were attention, perception, working memory, phonological awareness and executive functions - inhibition. The Intelligence quotient (IQ) was also evaluated. The biomarkers malondialdehyde (MDA), protein carbonyls (PCO), δ-aminolevulinate dehydratase (ALA-D), reactivation indexes with dithiothreitol (ALA-RE/DTT) and ZnCl2 (ALA-RE/ZnCl2), non-protein thiol groups, as well as microalbuminuria (mALB) level and N-acetyl-β-D-glucosaminidase (NAG) activity were assessed. The results demonstrated that Mn levels in blood, hair and drinking water were higher in rural children than in urban children (p<0.01). Adjusted for potential confounding factors, IQ, age, gender and parents' education, significant associations were observed mainly between B-Mn and visual attention (β=0.649; p<0.001). Moreover, B-Mn was negatively associated with visual perception and phonological awareness. H-Mn was inversely associated with working memory, and Mn levels from drinking water with written language and executive functions - inhibition. Rural children showed a significant increase in oxidative damage to proteins and lipids, as well as alteration in kidney function biomarkers (p<0.05). Moreover, significant associations were found between B-Mn, H-Mn and Mn levels in drinking water and biomarkers of oxidative damage and kidney function, besides between some oxidative stress biomarkers and neuropsychological tasks (p<0.05). The findings of this study suggest an important association between environmental exposure to Mn and toxic effects on neuropsychological function, oxidative damage and kidney function in children.

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.

Effects of chronic manganese exposure on attention and working memory in non-human primates

Manganese (Mn) is essential for a variety of physiological processes, but at elevated levels, can be neurotoxic. While cognitive dysfunction has been recently appreciated to occur as a result of chronic Mn exposures, it is still unclear as to which cognitive domains are most susceptible to disruption by Mn exposure. We previously described early appearing Mn-induced changes in performance on a paired associate learning task in monkeys chronically exposed to Mn and suggested that performance of this task might be a sensitive tool for detecting cognitive dysfunction resulting from Mn exposure. As chronic Mn exposure has been suggested to be associated with attention, working memory and executive function deficits, the present study was conducted to assess the extent to which detrimental effects of chronic Mn exposure could be detected using tasks specifically designed to preferentially assess attention, working memory, and executive function. Six cynomolgus monkeys received Mn exposure over an approximate 12 month period and three served as control animals. All animals were trained to perform a self-ordered spatial search (SOSS) task and a five choice serial reaction time (5-CSRT) task. Deficits in performance of the SOSS task began to appear by the fourth month of Mn exposure but only became consistently significantly impaired beginning at the ninth month of Mn exposure. Performance on the 5-CSRT became significantly affected by the third month of Mn exposure. These data suggest that in addition to the paired associate learning task, cognitive processing speed (as measured by the 5-CSRT) may be a sensitive measure of Mn toxicity and that brain circuits involved in performance of the SOSS task may be somewhat less sensitive to disruption by chronic Mn exposure.

Extrapyramidal system neurotoxicity: animal models

The central nervous system's extrapyramidal system provides involuntary motor control to the muscles of the head, neck, and limbs. Toxicants that affect the extrapyramidal system are generally clinically characterized by impaired motor control, which is usually the result of basal ganglionic dysfunction. A variety of extrapyramidal syndromes are recognized in humans and include Parkinson's disease, secondary parkinsonism, other degenerative diseases of the basal ganglia, and clinical syndromes that result in dystonia, dyskinesia, essential tremor, and other forms of tremor and chorea. This chapter briefly reviews the anatomy of the extrapyramidal system and discusses several naturally occurring and experimental models that target the mammalian (nonhuman) extrapyramidal system. Topics discussed include extrapyramidal syndromes associated with antipsychotic drugs, carbon monoxide, reserpine, cyanide, rotenone, paraquat, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and manganese. In most cases, animals are used as experimental models to improve our understanding of the toxicity and pathogenesis of these agents. Another agent discussed in this chapter, yellowstar thistle poisoning in horses, however, represents an important spontaneous cause of parkinsonism that naturally occurs in animals. The central focus of the chapter is on animal models, especially the concordance between clinical signs, neurochemical changes, and neuropathology between animals and people.

Neurobehavioral function in school-age children exposed to manganese in drinking water

BACKGROUND

Manganese neurotoxicity is well documented in individuals occupationally exposed to airborne particulates, but few data are available on risks from drinking-water exposure.

OBJECTIVE

We examined associations of exposure from concentrations of manganese in water and hair with memory, attention, motor function, and parent- and teacher-reported hyperactive behaviors.

METHODS

We recruited 375 children and measured manganese in home tap water (MnW) and hair (MnH). We estimated manganese intake from water ingestion. Using structural equation modeling, we estimated associations between neurobehavioral functions and MnH, MnW, and manganese intake from water. We evaluated exposure-response relationships using generalized additive models.

RESULTS

After adjusting for potential confounders, a 1-SD increase in log10 MnH was associated with a significant difference of -24% (95% CI: -36, -12%) SD in memory and -25% (95% CI: -41, -9%) SD in attention. The relations between log10 MnH and poorer memory and attention were linear. A 1-SD increase in log10 MnW was associated with a significant difference of -14% (95% CI: -24, -4%) SD in memory, and this relation was nonlinear, with a steeper decline in performance at MnW > 100 μg/L. A 1-SD increase in log10 manganese intake from water was associated with a significant difference of -11% (95% CI: -21, -0.4%) SD in motor function. The relation between log10 manganese intake and poorer motor function was linear. There was no significant association between manganese exposure and hyperactivity.

CONCLUSION

Exposure to manganese in water was associated with poorer neurobehavioral performances in children, even at low levels commonly encountered in North America.

A hypothesis regarding the molecular mechanism underlying dietary soy-induced effects on seizure propensity

Numerous neurological disorders including fragile X syndrome, Down syndrome, autism, and Alzheimer’s disease are co-morbid with epilepsy. We have observed elevated seizure propensity in mouse models of these disorders dependent on diet. Specifically, soy-based diets exacerbate audiogenic-induced seizures in juvenile mice. We have also found potential associations between the consumption of soy-based infant formula and seizure incidence, epilepsy comorbidity, and autism diagnostic scores in autistic children by retrospective analyses of medical record data. In total, these data suggest that consumption of high levels of soy protein during postnatal development may affect neuronal excitability. Herein, we present our theory regarding the molecular mechanism underlying soy-induced effects on seizure propensity. We hypothesize that soy phytoestrogens interfere with metabotropic glutamate receptor signaling through an estrogen receptor-dependent mechanism, which results in elevated production of key synaptic proteins and decreased seizure threshold.

BDNF and Huntingtin protein modifications by manganese: implications for striatal medium spiny neuron pathology in manganese neurotoxicity

High levels of manganese (Mn) exposure decrease striatal medium spiny neuron (MSN) dendritic length and spine density, but the mechanism(s) are not known. The Huntingtin (HTT) gene has been functionally linked to cortical brain-derived neurotrophic factor (BDNF) support of striatal MSNs via phosphorylation at serine 421. In Huntington's disease, pathogenic CAG repeat expansions of HTT decrease synthesis and disrupt transport of cortical-striatal BDNF, which may contribute to disease, and Mn is a putative environmental modifier of Huntington's disease pathology. Thus, we tested the hypothesis that changes in MSN dendritic morphology Mn due to exposure are associated with decreased BDNF levels and alterations in Htt protein. We report that BDNF levels are decreased in the striatum of Mn-exposed non-human primates and in the cerebral cortex and striatum of mice exposed to Mn. Furthermore, proBDNF and mature BDNF concentrations in primary cortical and hippocampal neuron cultures were decreased by exposure to Mn confirming the in vivo findings. Mn exposure decreased serine 421 phosphorylation of Htt in cortical and hippocampal neurons and increased total Htt levels. These data strongly support the hypothesis that Mn-exposure-related MSN pathology is associated with decreased BDNF trophic support via alterations in Htt.

Subacute manganese exposure in rats is a neurochemical model of early manganese toxicity

Manganese (Mn) is an essential trace element, but excess exposure leads to accumulation in biological tissues, including the brain. Chronically high Mn levels in the brain are neurotoxic and can result in a progressive, irreversible neurological disorder known as manganism. Manganism has signs and symptoms similar to, but distinguishable from idiopathic Parkinson's disease, which include both psychological and motor disturbances. Evidence suggests that Mn exposure impacts neurotransmitter levels in the brain. However, it remains unclear if subacute, low-level Mn exposure resulted in alterations in neurotransmitter systems with concomitant behavioral deficits. The current study used high performance liquid chromatography to quantify neurotransmitter levels in rat striatum (STR), substantia nigra (SN), and hippocampus (HP). Subacute Mn exposure via i.p. injection of 15mg Mn/kg as MnCl2 caused significantly increased dopamine (DA) levels in the STR. The enhancement was accompanied by significantly elevated levels of the DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the STR. In addition, levels of HVA were significantly increased in the SN and HP. These data indicate that subacute, low-level Mn exposure disrupts multiple neurotransmitter systems in the rat brain which may be responsible, in part, for observed locomotor deficits.

Noninvasive biomarkers of manganese exposure and neuropsychological effects in environmentally exposed adults in Brazil

Manganese (Mn), an essential element to humans, in excess can cause neurotoxic damage. So far, Mn exposure assessment has no ideal biomarker. This study aims to investigate the association between Mn exposure, using noninvasive biomarkers, and neuropsychological effects in environmentally exposed adults. The residents of two communities near to a ferromanganese refinery in Bahia, Brazil were evaluated. Volunteers aged 15-55 of both sexes provided scalp hair, axillary hair, fingernail and saliva specimens for Mn determination by electrothermal absorption spectrometry. Several neuropsychological tests were used to evaluate cognitive, attention, memory, motor and executive functions. Significant correlations were observed between Mn in hair (MnH, median 8.95 μg/g), axillary hair (MnAxH,18.49 μg/g) and fingernail (MnFN, 6.91 μg/g) with the performances in several neuropsychological tests. No association was observed between manganese levels in saliva (MnSal, 4.2 μg/L) and any neuropsychological function. Multiple regression analysis detected an inverse association between Log MnH and IQ (β=-4.76 [CI 95% -9.17 to -0.36]) and between Log MnFN and visual working memory (β=-3.33 [CI 95% -6.15 to -0.52]). Direct association was observed between Log MnFN and time of completion in the cognitive flexibility task (β=56.29 [CI 95% 2.41-110.18]). The Mn biomonitoring using noninvasive biomarkers was able to detect high exposure levels, which were associated with detrimental neuropsychological effects in adults exposed to industrial emissions.

Monkeys rely on recency of stimulus repetition when solving short-term memory tasks

Seven monkeys performed variants of two short-term memory tasks that others have used to differentiate between selective and nonselective memory mechanisms. The first task was to view a list of sequentially presented images and identify whether a test matched any image from the list, but not a distractor from a preceding list. Performance was best when the test matched the most recently presented image. Response rates depended linearly on recency of repetition whether the test matched a sample from the current list or a distractor from a preceding list, suggesting nonselective memorization of all images viewed instead of just the sample images. The second task was to remember just the first image in a list selectively and ignore subsequent distractors. False alarms occurred frequently when the test matched a distractor presented near the beginning of the sequence. In a pilot experiment, response rates depended linearly on recency of repetition irrespective of whether the test matched the first image or a distractor, again suggesting nonselective memorization of all images instead of just the first image. Modification of the second task improved recognition of the first image, but did not abolish use of recency. Monkeys appear to perform nonspatial visual short-term memory tasks often (or exclusively) using a single, nonselective, memory mechanism that conveys the recency of stimulus repetition.

Relationship between blood manganese levels and children's attention, cognition, behavior, and academic performance--a nationwide cross-sectional study

Manganese (Mn) is neurotoxic at high concentrations. However, Mn is an essential element that can protect against oxidative damage; thus, extremely low levels of Mn might be harmful. Our aim was to examine whether either high or low environmental Mn exposure is related to academic and attention function development among school-aged children. This cross-sectional study included 1089 children 8-11 years of age living in five representative areas in South Korea. Blood Mn, blood lead, and urine cotinine were measured. We assessed IQ with the Wechsler Abbreviated Scale of Intelligence; attention with a computerized continuous performance test called the Attention-deficit/hyperactivity disorder (ADHD) Diagnostic System (ADS), the Korean version of the Stroop Color-Word Test, the Children's Color Trails Test (CCTT), and the ADHD Rating Scale; academic functions with the Learning Disability Evaluation Scale (LDES); and emotional and behavioral problems with the Korean version of the Child Behavior Checklist (CBCL). We further assessed the presence of ADHD using a highly structured diagnostic interview, the Diagnostic Interview Schedule for Children Version IV (DISC-IV). The median blood concentration of Mn was 14.14 µg/L. We observed a nonlinear association between the CCTT2 completion time and the CPT commission error (F=3.14, p=0.03 and F=4.05, p=0.01, respectively). We divided the data into three groups: lower (<8.154 µg/L), and upper 5th percentile (>21.453 µg/L) and middle 90th percentile to determine whether a lack or overload of Mn could cause adverse effects. After adjusting for urine cotinine, blood lead, children's IQ, and other potential confounders, the high Mn group showed lower scores in thinking (B=-0.83, p=0.006), reading (B=-0.93, p=0.004), calculations (B=-0.72, p=0.005), and LQ (B=-4.06, p=0.006) in the LDES and a higher commission error in the CPT (B=8.02, p=0.048). The low Mn group showed lower color scores in the Stroop test (B=-3.24, p=0.040). We found that excess Mn in children is associated with lower scores of thinking, reading, calculation, and LQ in the LDES and higher scores of commission error in the ADS test. In contrast, lower Mn in children is associated with lower color scores in the Stroop test. The findings of this cross-sectional study suggest that excess exposure or deficiency of Mn can cause harmful effects in children.

The impact of environmental metals in young urbanites' brains

Air pollution exposures are linked to cognitive and olfaction deficits, oxidative stress, neuroinflammation and neurodegeneration including frontal hyperphosphorylated tau and diffuse amyloid plaques in Mexico City children and young adults. Mexico City residents are chronically exposed to fine particulate matter (PM(2.5)) concentrations (containing toxic combustion and industrial metals) above the annual standard (15 μg/m(3)) and to contaminated water and soil. Here, we sought to address the brain-region-specific effects of metals and key neuroinflammatory and DNA repair responses in two air pollution targets: frontal lobe and olfactory bulb from 12 controls vs. 47 Mexico City children and young adults average age 33.06±4.8 SE years. Inductively coupled plasma mass spectrometry (metal analysis) and real time PCR (for COX2, IL1β and DNA repair genes) in target tissues. Mexico City residents had higher concentrations of metals associated with PM: manganese (p=0.003), nickel and chromium (p=0.02) along with higher frontal COX2 mRNA (p=0.008) and IL1β (p=0.0002) and COX2 (p=0.005) olfactory bulb indicating neuroinflammation. Frontal metals correlated with olfactory bulb DNA repair genes and with frontal and hippocampal inflammatory genes. Frontal manganese, cobalt and selenium increased with age in exposed subjects. Together, these findings suggest PM-metal neurotoxicity causes brain damage in young urbanites, the olfactory bulb is a target of air pollution and participates in the neuroinflammatory response and since metal concentrations vary significantly in Mexico City urban sub-areas, place of residency has to be integrated with the risk for CNS detrimental effects particularly in children.

Manganese neurotoxicity: new perspectives from behavioral, neuroimaging, and neuropathological studies in humans and non-human primates

Manganese (Mn) is an essential metal and has important physiological functions for human health. However, exposure to excess levels of Mn in occupational settings or from environmental sources has been associated with a neurological syndrome comprising cognitive deficits, neuropsychological abnormalities and parkinsonism. Historically, studies on the effects of Mn in humans and experimental animals have been concerned with effects on the basal ganglia and the dopaminergic system as it relates to movement abnormalities. However, emerging studies are beginning to provide significant evidence of Mn effects on cortical structures and cognitive function at lower levels than previously recognized. This review advances new knowledge of putative mechanisms by which exposure to excess levels of Mn alters neurobiological systems and produces neurological deficits not only in the basal ganglia but also in the cerebral cortex. The emerging evidence suggests that working memory is significantly affected by chronic Mn exposure and this may be mediated by alterations in brain structures associated with the working memory network including the caudate nucleus in the striatum, frontal cortex and parietal cortex. Dysregulation of the dopaminergic system may play an important role in both the movement abnormalities as well as the neuropsychiatric and cognitive function deficits that have been described in humans and non-human primates exposed to Mn.

Chronic manganese exposure impairs visuospatial associative learning in non-human primates

Manganese (Mn) is an essential trace metal nutrient, however, excess Mn can be neurotoxic. The degree to which chronic environmental or occupational exposures to Mn in adults cause neuropsychological dysfunction is of considerable interest. Descriptions of neuropsychological dysfunction following chronic Mn exposure have been somewhat inconsistent though, likely owing to different measures of exposure in different populations, complicated by factors of mixed exposures and differences in neuropsychological tests administered. We previously described up-regulation of the mRNA expression for amyloid-beta (A-beta) precursor-like protein 1 (APLP1) and the presence of A-beta diffuse plaques in frontal cortex of Mn-exposed monkeys. The present study examined Mn-induced changes in performance on a paired associate learning (PAL) task that has been suggested as a marker for preclinical Alzheimer's disease. Aspects of performance of this task were affected early following initiation of Mn exposure. Thus, PAL performance may be a sensitive and valuable tool for the early, preclinical detection of incipient dementia and it may also be a sensitive tool for detecting cognitive dysfunction from Mn exposure. The current cognitive data, combined with our previous findings, suggest that frontal cortex may be a particularly sensitive target for the effects of Mn on cognition and that chronic Mn exposure may initiate or accelerate a process that could lead to or predispose to Alzheimer's like pathology and cognitive dysfunction.

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.

Manganese exposure induces α-synuclein aggregation in the frontal cortex of non-human primates

Aggregation of α-synuclein (α-syn) in the brain is a defining pathological feature of neurodegenerative disorders classified as synucleinopathies. They include Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). Occupational and environmental exposure to manganese (Mn) is associated with a neurological syndrome consisting of psychiatric symptoms, cognitive impairment and parkinsonism. In this study, we examined α-syn immunoreactivity in the frontal cortex of Cynomolgus macaques as part of a multidisciplinary assessment of the neurological effects produced by exposure to moderate levels of Mn. We found increased α-syn-positive cells in the gray matter of Mn-exposed animals, typically observed in pyramidal and medium-sized neurons in deep cortical layers. Some of these neurons displayed loss of Nissl staining with α-syn-positive spherical aggregates. In the white matter we also observed α-syn-positive glial cells and in some cases α-syn-positive neurites. These findings suggest that Mn exposure promotes α-syn aggregation in neuronal and glial cells that may ultimately lead to degeneration in the frontal cortex gray and white matter. To our knowledge, this is the first report of Mn-induced neuronal and glial cell α-syn accumulation and aggregation in the frontal cortex of non-human primates.

Intranasal exposure to manganese disrupts neurotransmitter release from glutamatergic synapses in the central nervous system in vivo

Chronic exposure to aerosolized manganese induces a neurological disorder that includes extrapyramidal motor symptoms and cognitive impairment. Inhaled manganese can bypass the blood-brain barrier and reach the central nervous system by transport down the olfactory nerve to the brain's olfactory bulb. However, the mechanism by which Mn disrupts neural function remains unclear. Here we used optical imaging techniques to visualize exocytosis in olfactory nerve terminals in vivo in the mouse olfactory bulb. Acute Mn exposure via intranasal instillation of 2-200 μg MnCl(2) solution caused a dose-dependent reduction in odorant-evoked neurotransmitter release, with significant effects at as little as 2 μg MnCl(2) and a 90% reduction compared to vehicle controls with a 200 μg exposure. This reduction was also observed in response to direct electrical stimulation of the olfactory nerve layer in the olfactory bulb, demonstrating that Mn's action is occurring centrally, not peripherally. This is the first direct evidence that Mn intoxication can disrupt neurotransmitter release, and is consistent with previous work suggesting that chronic Mn exposure limits amphetamine-induced dopamine increases in the basal ganglia despite normal levels of dopamine synthesis (Guilarte et al., J Neurochem 2008). The commonality of Mn's action between glutamatergic neurons in the olfactory bulb and dopaminergic neurons in the basal ganglia suggests that a disruption of neurotransmitter release may be a general consequence wherever Mn accumulates in the brain and could underlie its pleiotropic effects.

Effect of intranasal manganese administration on neurotransmission and spatial learning in rats

The effect of intranasal manganese chloride (MnCl(2)·4H(2)O) exposure on spatial learning, memory and motor activity was estimated in Morris water maze task in adult rats. Three-month-old male Wistar rats received for 2weeks MnCl(2)·4H(2)O at two doses the following: 0.2mg/kg b.w. (Mn0.2) or 0.8mg/kg b.w. (Mn0.8) per day. Control (Con) and manganese-exposed groups were observed for behavioral performance and learning in water maze. ANOVA for repeated measurements did not show any significant differences in acquisition in the water maze between the groups. However, the results of the probe trial on day 5, exhibited spatial memory deficits following manganese treatment. After completion of the behavioral experiment, the regional brain concentrations of neurotransmitters and their metabolites were determined via HPLC in selected brain regions, i.e. prefrontal cortex, hippocampus and striatum. ANOVA demonstrated significant differences in the content of monoamines and metabolites between the treatment groups compared to the controls. Negative correlations between platform crossings on the previous platform position in Southeast (SE) quadrant during the probe trial and neurotransmitter turnover suggest that impairment of spatial memory and cognitive performance after manganese (Mn) treatment is associated with modulation of the serotonergic, noradrenergic and dopaminergic neurotransmission in the brain. These findings show that intranasally applied Mn can impair spatial memory with significant changes in the tissue level and metabolism of monoamines in several brain regions.

Emergency Do Not Consume/Do Not Use concentrations for potassium permanganate in drinking water

Over the past decade, regulatory authorities and water purveyors have become increasingly concerned with accidental or intentional adulteration of municipal drinking water. Emergency response guidelines, such as the ‘Do Not Consume’ or use concentration limits derived herein, can be used to notify the public in such cases. Potassium permanganate (KMnO4) is used to control iron concentrations and to reduce the levels of nuisance materials that affect odor or taste of finished drinking water. Manganese (Mn) is recognized an essential nutrient, permanganate (MnO4−) and manganous (Mn+2) ions are caustic, and the acute toxicity of KMnO4 is defined by its oxidant/irritant properties and by the toxicity of Mn. Ingestion of small amounts (4–20 mg/kg) of aqueous KMnO4 solutions that are above 200 mg/L causes gastrointestinal distress, while bolus ingestion has caused respiratory arrest following coagulative necrosis and hemorrhage in the esophagus, stomach, or liver. Dilute KMnO4 solutions (1–100 mg/L) are used as a topical antiseptics and astringents, but >1:5000 (200 mg/L) dilutions can irritate or discolor sensitive mucous membranes and direct skin or ocular contact with concentrated KMnO4 can perforate tissues. Based on clinical experience with 200 mg/L KMnO4, a Do Not Consume concentration of 7 mg/L KMnO4 (equivalent to 2 mg Mn/L) is recommended. Recognizing limited empirical data from which to calculate an ocular reference value, a skin contact ‘Do Not Use’ concentration of 30 mg Mn/L is recommended based on the skin irritation in some patients after a 10-min contact with 100 mg KMnO4/L.

Impaired spatial working memory learning and performance in normal aged rhesus monkeys

Aged non-human primates may have deficits in a variety of cognitive functions. However, it is possible that at least some age-related performance deficits relate to a deficit in initial task learning. To assess this, aged rhesus monkeys were trained to perform a Self-Ordered Spatial Search (SOSS) task using the same training and testing parameters used previously with normal young animals. Aged animals failed to reach criterion at the easiest task level. In an attempt to improve learning, a group of aged animals were first trained on SOSS using a standard 5s ITI, followed by trials with low inter-trial interference (e.g., a stimulus used in a trial would not be used again for the next 2 trials) or with trials in which the spatial distance between the stimuli on the screen was maximized. Because performance improved but failed to reach criterion, this was followed by sessions with increasing ITIs (from 5 s to 10 or 15 s). Only increasing the ITI improved the performance of the aged animals enough to allow them to learn the task to criterion. Once the criterion was reached, memory was taxed by increasing the delay between stimulus presentations and increasing the number of spatial positions to be remembered. Performance declined for young animals, but even more so for aged animals. The results of the present study suggests that aged primates have difficulty initially learning a complex working memory task, and that the ITI may be an important parameter to manipulate to improve learning. However, once the task is learned, performance of aged animals is inferior to that of young animals, particularly when memory demands are increased.

Manganese and Parkinson's disease: a critical review and new findings

The goal of this review was to examine whether chronic Mn exposure produces dopamine neuron degeneration and PD or whether it has a distinct neuropathology and clinical presentation. I reviewed available clinical, neuroimaging, and neuropathological studies in humans and nonhuman primates exposed to Mn or other human conditions that result in elevated brain Mn concentrations. Human and nonhuman primate literature was examined to compare clinical, neuroimaging, and neuropathological changes associated with Mn-induced parkinsonism. Clinical, neuroimaging, and neuropathological evidence was used to examine whether Mn-induced parkinsonism involves degeneration of the nigrostriatal dopaminergic system as is the case in PD. The overwhelming evidence shows that Mn-induced parkinsonism does not involve degeneration of midbrain dopamine neurons and that l-dopa is not an effective therapy. New evidence is presented on a putative mechanism by which Mn may produce movement abnormalities. Confirmation of this hypothesis in humans is essential to make rational decisions about treatment, devise effective therapeutic strategies, and set regulatory guidelines.

Does soy-based infant formula cause ADHD? Update and public policy considerations

An earlier article hypothesized a relationship between soy-based infant formulas, manganese (Mn) neurotoxicity and symptoms of ADHD. In this update, more recent literature on ADHD, Mn and Mn neurotoxicity is reviewed, as well as the risks of Mn toxicity that may accompany ingestion of soy-based infant formula. The results of several critical studies are described, including rodent and primate models that demonstrate an association between ingestion of relatively high levels of Mn and: overactivity, disinhibition and inattention; stereotypes and disturbances of social relatedness; and alterations of dopamine D1 and D2 receptors and dopamine transporter in critical brain regions. Similar deficits have been shown in children with ADHD. In addition, ADHD-like symptoms of behavioral disinhibition were found to be correlated with Mn content in tooth enamel, apparently deposited at or before the fifth gestational month. The results are discussed in terms of their weight as a risk factor in ADHD, vis-à-vis compelling evidence of genetic, epigenetic and other environmental risk factors associated with the disorder, as well as the appropriateness of additional public policy decisions regarding the safety of soy formula.

In vivo manganese exposure modulates Erk, Akt and Darpp-32 in the striatum of developing rats, and impairs their motor function

Manganese (Mn) is an essential metal for development and metabolism. However, exposures to high Mn levels may be toxic, especially to the central nervous system (CNS). Neurotoxicity is commonly due to occupational or environmental exposures leading to Mn accumulation in the basal ganglia and a Parkinsonian-like disorder. Younger individuals are more susceptible to Mn toxicity. Moreover, early exposure may represent a risk factor for the development of neurodegenerative diseases later in life. The present study was undertaken to investigate the developmental neurotoxicity in an in vivo model of immature rats exposed to Mn (5, 10 and 20 mg/kg; i.p.) from postnatal day 8 (PN8) to PN12. Neurochemical analysis was carried out on PN14. We focused on striatal alterations in intracellular signaling pathways, oxidative stress and cell death. Moreover, motor alterations as a result of early Mn exposure (PN8-12) were evaluated later in life at 3-, 4- and 5-weeks-of-age. Mn altered in a dose-dependent manner the activity of key cell signaling elements. Specifically, Mn increased the phosphorylation of DARPP-32-Thr-34, ERK1/2 and AKT. Additionally, Mn increased reactive oxygen species (ROS) production and caspase activity, and altered mitochondrial respiratory chain complexes I and II activities. Mn (10 and 20 mg/kg) also impaired motor coordination in the 3^rd, 4^th and 5^th week of life. Trolox™, an antioxidant, reversed several of the Mn altered parameters, including the increased ROS production and ERK1/2 phosphorylation. However, Trolox™ failed to reverse the Mn (20 mg/kg)-induced increase in AKT phosphorylation and motor deficits. Additionally, Mn (20 mg/kg) decreased the distance, speed and grooming frequency in an open field test; Trolox™ blocked only the decrease of grooming frequency. Taken together, these results establish that short-term exposure to Mn during a specific developmental window (PN8-12) induces metabolic and neurochemical alterations in the striatum that may modulate later-life behavioral changes. Furthermore, some of the molecular and behavioral events, which are perturbed by early Mn exposure are not directly related to the production of oxidative stress.

Pathophysiology of manganese-associated neurotoxicity

Manganese (Mn) is a well established neurotoxin associated with specific damage to the basal ganglia in humans. The phenotype associated with Mn neurotoxicity was first described in two workers with occupational exposure to Mn oxide (Couper, 1837). Although the description did not use modern clinical terminology, a parkinsonian illness characterized by slowness of movement (bradykinesia), masked facies, and gait impairment (postural instability) appears to have predominated. Nearly 100 years later an outbreak of an atypical parkinsonian illness in a Chilean Mn mine provided a phenotypic description of a fulminant neurologic disorder with parkinsonism, dystonia, and neuropsychiatric symptoms (Rodier, 1955). Exposures associated with this syndrome were massive and an order of magnitude greater than modern exposures (Rodier, 1955; Hobson et al., 2011). The clinical syndrome associated with Mn neurotoxicity has been called manganism. Modern exposures to Mn occur primarily through occupations in the steel industry and welding. These exposures are often chronic and varied, occurring over decades in the healthy workforce. Although the severe neurologic disorder described by Rodier and Couper are no longer seen, several reports have suggested a possible increased risk of neurotoxicity in these workers (Racette et al., 2005b; Bowler et al., 2007; Harris et al., 2011). Based upon limited prior imaging and pathologic investigations into the pathophysiology of neurotoxicity in Mn exposed workers (Huang et al., 2003), many investigators have concluded that the syndrome spares the dopamine system distinguishing manganism from Parkinson disease (PD), the most common cause of parkinsonism in the general population, and a disease with characteristic degenerative changes in the dopaminergic system (Jankovic, 2005). The purpose of this symposium was to highlight recent advances in the understanding of the pathophysiology of Mn associated neurotoxicity from Caenorhabditis elegans to humans. Dr. Aschner's presentation discussed mechanisms of dopaminergic neuronal toxicity in C. elegans and demonstrates a compelling potential role of Mn in dopaminergic degeneration. Dr. Guilarte's experimental, non-human primate model of Mn neurotoxicity suggests that Mn decreases dopamine release in the brain without loss of neuronal integrity markers, including dopamine. Dr. Racette's presentation demonstrates a unique pattern of dopaminergic dysfunction in active welders with chronic exposure to Mn containing welding fumes. Finally, Dr. Dydak presented novel magnetic resonance (MR) spectroscopy data in Mn exposed smelter workers and demonstrated abnormalities in the thalamus and frontal cortex for those workers. This symposium provided some converging evidence of the potential neurotoxic impact of Mn on the dopaminergic system and challenged existing paradigms on the pathophysiology of Mn in the central nervous system.

Manganese exposure from drinking water and children's academic achievement

Drinking water manganese (WMn) is a potential threat to children's health due to its associations with a wide range of outcomes including cognitive, behavioral and neuropsychological effects. Although adverse effects of Mn on cognitive function of the children indicate possible impact on their academic achievement little evidence on this issue is available. Moreover, little is known regarding potential interactions between exposure to Mn and other metals, especially water arsenic (WAs). In Araihazar, a rural area of Bangladesh, we conducted a cross-sectional study of 840 children to investigate associations between WMn and WAs and academic achievement in mathematics and languages among elementary school-children, aged 8-11 years. Data on As and Mn exposure were collected from the participants at the baseline of an ongoing longitudinal study of school-based educational intervention. Annual scores of the study children in languages (Bangla and English) and mathematics were obtained from the academic achievement records of the elementary schools. WMn above the WHO standard of 400μg/L was associated with 6.4% score loss (95% CI=-12.3 to -0.5) in mathematics achievement test scores, adjusted for WAs and other sociodemographic variables. We did not find any statistically significant associations between WMn and academic achievement in either language. Neither WAs nor urinary As was significantly related to any of the three academic achievement scores. Our finding suggests that a large number of children in rural Bangladesh may experience deficits in mathematics due to high concentrations of Mn exposure in drinking water.

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.

Manganese exposure from drinking water and children's classroom behavior in Bangladesh

BACKGROUND

Evidence of neurological, cognitive, and neuropsychological effects of manganese (Mn) exposure from drinking water (WMn) in children has generated widespread public health concern. At elevated exposures, Mn has been associated with increased levels of externalizing behaviors, including irritability, aggression, and impulsivity. Little is known about potential effects at lower exposures, especially in children. Moreover, little is known regarding potential interactions between exposure to Mn and other metals, especially arsenic (As).

OBJECTIVES

We conducted a cross-sectional study of 201 children to investigate associations of Mn and As in tube well water with classroom behavior among elementary school children, 8-11 years of age, in Araihazar, Bangladesh.

METHODS

Data on exposures and behavioral outcomes were collected from the participants at the baseline of an ongoing longitudinal study of child intelligence. Study children were rated by their school teachers on externalizing and internalizing items of classroom behavior using the standardized Child Behavior Checklist-Teacher's Report Form (CBCL-TRF).

RESULTS

Log-transformed WMn was positively and significantly associated with TRF internalizing [estimated β = 0.82; 95% confidence interval (CI), 0.08-1.56; p = 0.03], TRF externalizing (estimated β = 2.59; 95% CI, 0.81-4.37; p =0.004), and TRF total scores (estimated β = 3.35; 95% CI, 0.86-5.83; p = 0.008) in models that adjusted for log-transformed water arsenic (WAs) and sociodemographic covariates. We also observed a positive monotonic dose-response relationship between WMn and TRF externalizing and TRF total scores among the participants of the study. We did not find any significant associations between WAs and various scales of TRF scores.

CONCLUSION

These observations reinforce the growing concern regarding the neurotoxicologic effects of WMn in children.

Role of metal ions in aggregation of intrinsically disordered proteins in neurodegenerative diseases

Neurodegenerative diseases constitute a set of pathological conditions originating from the slow, irreversible, and systematic cell loss within the various regions of the brain and/or the spinal cord. Depending on the affected region, the outcomes of the neurodegeneration are very broad and diverse, ranging from the problems with movements to dementia. Some neurodegenerative diseases are associated with protein misfolding and aggregation. Many proteins that misfold in human neurodegenerative diseases are intrinsically disordered; i.e., they lack a stable tertiary and/or secondary structure under physiological conditions in vitro. These intrinsically disordered proteins (IDPs) functionally complement ordered proteins, being typically involved in regulation and signaling. There is accumulating evidence that altered metal homeostasis may be related to the progression of neurodegenerative diseases. This review examines the effects of metal ion binding on the aggregation pathways of IDPs found in neurodegenerative diseases.

Environmental exposure to manganese and motor function of children in Mexico

OBJECTIVES

Occupational manganese (Mn) exposure has been associated with motor deficits in adult workers, but data on the potential effects of environmental exposure to Mn on the developing motor function for a children population is scarce. The aim of this study was to evaluate the association between exposure to Mn and motor function of school aged children.

METHODS

We conducted a cross-sectional study selecting 195 children (100 exposed and 95 unexposed) between 7 and 11 years old. The following tests were used to evaluate the motor function: Grooved pegboard, finger tapping, and Santa Ana test. Mn exposure was assessed by blood (MnB) and hair concentrations (MnH). We constructed linear regression models to evaluate the association between exposure to Mn and the different test scores adjusting for age, sex, maternal education, hemoglobin and blood lead.

RESULTS

The median concentration of MnH and MnB was significantly higher in exposed (12.6 μg/g and 9.5 μg/L) compared to unexposed children (0.6 μg/g and 8.0 μg/L). The exposed children on average performed the grooved pegboard test faster, but made more errors, although these results did not reach statistical significance with neither one of the Mn exposure biomarkers. MnB showed an inverse association on the execution of the finger tapping test (average in 5 trials β -0.4, p=0.02), but no association was observed with MnH.

CONCLUSIONS

A subtle negative association of Mn exposure on motor speed and coordination was shown. In adults, the main effect of environmental Mn exposure has been associated with motor skills, but these results suggest that such alterations are not the main effect on children.

Manganese and acute paranoid psychosis: a case report

Introduction

Manganese regulates many enzymes and is essential for normal development and body function. Chronic manganese intoxication has an insidious and progressive course and usually starts with complaints of headache, fatigue, sleep disturbances, irritability and emotional instability. Later, several organ systems may be affected and, due to neurotoxicity, an atypical parkinsonian syndrome may emerge. With regard to neuropsychiatry, an array of symptoms may develop up to 30 years after intoxication, of which gait and speech abnormalities, cognitive and motor slowing, mood changes and hallucinations are the most common. Psychotic phenomena are rarely reported.

Case presentation

We describe the case of a 49-year-old Caucasian man working as a welder who was referred to our facility for evaluation of acute paranoid psychotic behavior. Our patient's medical history made no mention of any somatic complaints or psychiatric symptoms, and he had been involved in a professional career as a metalworker. On magnetic resonance imaging scanning of his brain, a bilateral hyperdensity of the globus pallidus, suggestive for manganese intoxication, was found. His manganese serum level was 52 to 97 nmol/L (range: 7 to 20 nmol/L). A diagnosis of organic psychotic disorder due to manganese overexposure was made. His psychotic symptoms disappeared within two weeks of treatment with low-dose risperidone. At three months later, serum manganese was decreased to slightly elevated levels and the magnetic resonance imaging T1 signal intensity was reduced. No signs of Parkinsonism were found and a definite diagnosis of manganese-induced apathy syndrome was made.

Conclusion

Although neuropsychiatric and neurological symptoms caused by (chronic) manganese exposure have been reported frequently in the past, in the present day the disorder is rarely diagnosed. In this report we stress that manganese intoxication can still occur, in our case in a confined-space welder, and may present clinically with a paranoid psychotic state that necessitates a rapid diagnostic procedure in order to avoid the permanent structural brain damage that may occur with chronic exposure.

Manganese exposure induces microglia activation and dystrophy in the substantia nigra of non-human primates

Chronic manganese (Mn) exposure produces neurological deficits including a form of parkinsonism that is different from Parkinson's disease (PD). In chronic Mn exposure, dopamine neurons in the substantia nigra (SN) do not degenerate but they appear to be dysfunctional. Further, previous studies have suggested that the substantia nigra pars reticulata (SNr) is affected by Mn. In the present study, we investigated whether chronic Mn exposure induces microglia activation in the substantia nigra pars compacta (SNc) and SNr in Cynomolgus macaques. Animals were exposed to different weekly doses of Mn (3.3-5.0, 5.0-6.7, 8.3-10 mg Mn/kg body weight) and microglia were examined in the substantia nigra using LN3 immunohistochemistry. We observed that in control animals, LN3 labeled microglia were characterized by a resting phenotype. However, in Mn-treated animals, microglia increased in number and displayed reactive changes with increasing Mn exposure. This effect was more prominent in the SNr than in the SNc. In the SNr of animals administered the highest Mn dose, microglia activation was the most advanced and included dystrophic changes. Reactive microglia expressed increased iNOS, L-ferritin, and intracellular ferric iron which were particularly prominent in dystrophic compartments. Our observations indicate that moderate Mn exposure produces structural changes on microglia, which may have significant consequences on their function.

Lead, manganese, and methylmercury as risk factors for neurobehavioral impairment in advanced age

Contamination of the environment by metals is recognized as a threat to health. One of their targets is the brain, and the adverse functional effects they induce are reflected by neurobehavioral assessments. Lead, manganese, and methylmercury are the metal contaminants linked most comprehensively to such disorders. Because many of these adverse effects can appear later in life, clues to the role of metals as risk factors for neurodegenerative disorders should be sought in the exposure histories of aging populations. A review of the available literature offers evidence that all three metals can produce, in advanced age, manifestations of neurobehavioral dysfunction associated with neurodegenerative disease. Among the critical unresolved questions is timing; that is, during which periods of the lifespan, including early development, do environmental exposures lay the foundations for their ultimate effects?

Millimolar Mn2+ influences agonist binding to 5-HT1A receptors by inhibiting guanosine nucleotide binding to receptor-coupled G-proteins

Manganese is an essential trace element but its overexposure causes poisoning (called manganism) that shares several symptoms with Parkinson's disease, but with a mechanism that is still not well understood: in addition to involvement of the dopaminergic system, both serotonergic and peptiergic systems have been implicated. In the present report we have studied the influence of Mn(2+) on 5-HT(1A) receptor signaling complexes in rat brain and found that Mn(2+) in millimolar concentration caused an increase of high-affinity agonist binding to rat hippocampal membranes in comparison with experiments in the presence of Mg(2+), but not in rat cortical membranes and in Sf9 cell membranes expressing 5-HT(1A) receptors and G(i1) heterotrimers. Activation of G proteins with 30μM GTPγS turned all 5-HT(1A) receptors in these preparations into a low-affinity state for agonist binding in the presence of 1mM Mg(2+), but not in the presence of 1mM Mn(2+) in rat hippocampal membranes. However, if 1μM GTPγS was used for G protein activation, a substantial amount of high affinity agonist binding was detected in the presence of Mn(2+) also in cortical membranes and Sf9 cells, but not with Mg(2+) or EDTA. Comparison of the abilities of GDP and GTPγS to modulate high affinity agonist binding to 5-HT(1A) receptors indicated that both nucleotides were almost 10-fold less potent in the presence of MnCl(2) compared to MgCl(2). This means that by inhibiting guanosine nucleotide binding to G proteins in complex with 5-HT(1A) receptors, Mn(2+) acts as an enhancer for agonist binding and signal transduction. As the influence of Mn(2+) resembles the hypersensitivity of dopaminergic system in Parkinsonial models, it can be proposed that at least some symptoms of manganism are connected with a change of signal transduction complex caused by manganese-nucleotide complexes.

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.