Manganese neurotoxicity and the role of reactive oxygen species

PI3K/Akt signaling pathway and Hsp70 activate in hippocampus of rats with chronic manganese sulfate exposure

Manganese (Mn) has come to the forefront of environmental concerns due to its neurotoxicity. However, the toxic effect of Mn is not fully understood. The purpose of this study is to investigate the impacts of chronic manganese sulfate (MnSO₄) exposure in regulating the phosphatidylinositol 3 kinase/protein kinase B (PI3K/Akt) signaling pathway in rats. In this study, rats were treated with 0, 5.0, 10.0, and 20.0 mg/kg MnSO₄•H₂O five days a week for 24 weeks via intraperitoneal injection. At the end of the exposure period, the levels of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), malondialdehyde (MDA), and heat shock protein (Hsp70) in rats' plasma were quantified; the mRNA expression levels of caspase-3, B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), serine-threonine protein kinase (Akt-1), and forkhead box O3a (FoxO3a) were measured through real-time quantitative PCR (RT-PCR); and the levels of protein Hsp70 and Akt were assessed by western blot. With an increasing dose of MnSO₄, the organ coefficients of all tested organs were significantly increased, except the testis. Compared with the control group, the activities of plasma SOD, GSH-Px, and CAT in MnSO₄-exposed groups were significantly decreased, while the concentrations of plasma MDA and Hsp70 were significantly increased. Moreover, the hippocampal mRNA levels of Bcl-2, caspase-3, Akt-1, and FoxO3a in MnSO₄-exposed groups were downregulated, but the level of Bax was upregulated. Meanwhile, the level of phosphorylation of Akt (p-Akt) and Hsp70 proteins tends to be upregulated by increasing MnSO₄ exposure (P < 0.05). The plasma Hsp70 level was negatively associated with SOD, CAT, and GSH-Px activities (P < 0.05), and positively associated with blood MDA concentration and hippocampal Hsp70 levels (P < 0.05). Chronic MnSO₄ exposure can result in apoptosis of central nerve cells, activate the PI3K/Akt signaling pathway in rats' hippocampus, and upregulate Hsp70 transcription and translation.

Gene sequence screening for manganese poisoning-susceptible genes and analysis of gene interaction effects

Manganese poisoning is a common occupational disease, studies have found that the susceptibility to manganese poisoning differs in individuals. We adopted genome-wide sequencing methods to screen for susceptibility genes involved in gene-mediated metabolic pathways from the perspective of manganese poisoning. We identified 18,439 genes in this study, including 14,272 known genes and 4398 new genes. We then selected 17 differential genes using p values, of which 7 genes were down-regulated and 10 genes were up-regulated. Possible interaction genes for each differential gene were selected according to the String database. Sgk1, HCRTr1, HspB1, Rem2, Oprd1, ATF5, and TRHr identified in this study may be involved in oxidative stress mechanisms, dopamine (DA) synthesis, and neuronal survival during apoptosis and may affect susceptibility to manganese poisoning.

Regulated Necrosis Orchestrates Microglial Cell Death in Manganese-Induced Toxicity

Microglia, the brain resident immune cells, play prominent roles in immune surveillance, tissue repair and neural regeneration. Despite these pro-survival actions, the relevance of these cells in the progression of several neuropathologies has been established. In the context of manganese (Mn) overexposure, it has been proposed that microglial activation contributes to enhance the neurotoxicity. However, the occurrence of a direct cytotoxic effect of Mn on microglial cells remains controversial. In the present work, we investigated the potential vulnerability of immortalized mouse microglial cells (BV-2) toward Mn²⁺, focusing on the signaling pathways involved in cell death. Evidence obtained showed that Mn²⁺ induces a decrease in cell viability which is associated with reactive oxygen species (ROS) generation. In this report we demonstrated, for the first time, that Mn²⁺ triggers regulated necrosis (RN) in BV-2 cells involving two central mechanisms: parthanatos and lysosomal disruption. The occurrence of parthanatos is supported by several cellular and molecular events: (i) DNA damage; (ii) AIF translocation from mitochondria to the nucleus; (iii) mitochondrial membrane permeabilization; and (iv) PARP1-dependent cell death. On the other hand, Mn²⁺ induces lysosomal membrane permeabilization (LMP) and cathepsin D (CatD) release into the cytosol supporting the lysosomal disruption. Pre-incubation with CatB and D inhibitors partially prevented the Mn²⁺-induced cell viability decrease. Altogether these events point to lysosomes as players in the execution of RN. In summary, our results suggest that microglial cells could be direct targets of Mn²⁺ damage. In this scenario, Mn²⁺ triggers cell death involving RN pathways.

Neurotoxicity Linked to Dysfunctional Metal Ion Homeostasis and Xenobiotic Metal Exposure: Redox Signaling and Oxidative Stress

SIGNIFICANCE

Essential metals such as copper, iron, manganese, and zinc play a role as cofactors in the activity of a wide range of processes involved in cellular homeostasis and survival, as well as during organ and tissue development. Throughout our life span, humans are also exposed to xenobiotic metals from natural and anthropogenic sources, including aluminum, arsenic, cadmium, lead, and mercury. It is well recognized that alterations in the homeostasis of essential metals and an increased environmental/occupational exposure to xenobiotic metals are linked to several neurological disorders, including neurodegeneration and neurodevelopmental alterations. Recent Advances: The redox activity of essential metals is key for neuronal homeostasis and brain function. Alterations in redox homeostasis and signaling are central to the pathological consequences of dysfunctional metal ion homeostasis and increased exposure to xenobiotic metals. Both redox-active and redox-inactive metals trigger oxidative stress and damage in the central nervous system, and the exact mechanisms involved are starting to become delineated.

CRITICAL ISSUES

In this review, we aim to appraise the role of essential metals in determining the redox balance in the brain and the mechanisms by which alterations in the homeostasis of essential metals and exposure to xenobiotic metals disturb the cellular redox balance and signaling. We focus on recent literature regarding their transport, metabolism, and mechanisms of toxicity in neural systems.

FUTURE DIRECTIONS

Delineating the specific mechanisms by which metals alter redox homeostasis is key to understand the pathological processes that convey chronic neuronal dysfunction in neurodegenerative and neurodevelopmental disorders. Antioxid. Redox Signal. 28, 1669-1703.

Putrescine as indicator of manganese neurotoxicity: Dose-response study in human SH-SY5Y cells

Disrupted polyamine metabolism with elevated putrescine is associated with neuronal dysfunction. Manganese (Mn) is an essential nutrient that causes neurotoxicity in excess, but methods to evaluate biochemical responses to high Mn are limited. No information is available on dose-response effects of Mn on putrescine abundance and related polyamine metabolism. The present research was to test the hypothesis that Mn causes putrescine accumulation over a physiologically adequate to toxic concentration range in a neuronal cell line. We used human SH-SY5Y neuroblastoma cells treated with MnCl2 under conditions that resulted in cell death or no cell death after 48 h. Putrescine and other metabolites were analyzed by liquid chromatography-ultra high-resolution mass spectrometry. Putrescine-related pathway changes were identified with metabolome-wide association study (MWAS). Results show that Mn caused a dose-dependent increase in putrescine over a non-toxic to toxic concentration range. MWAS of putrescine showed positive correlations with the polyamine metabolite N8-acetylspermidine, methionine-related precursors, and arginine-associated urea cycle metabolites, while putrescine was negatively correlated with γ-aminobutyric acid (GABA)-related and succinate-related metabolites (P < 0.001, FDR < 0.01). These data suggest that measurement of putrescine and correlated metabolites may be useful to study effects of Mn intake in the high adequate to UL range.

Role of autophagy in environmental neurotoxicity

Human exposure to neurotoxic pollutants (e.g. metals, pesticides and other chemicals) is recognized as a key risk factor in the pathogenesis of neurodegenerative disorders. Emerging evidence indicates that an alteration in autophagic pathways may be correlated with the onset of the neurotoxicity resulting from chronic exposure to these pollutants. In fact, autophagy is a natural process that permits to preserving cell homeostasis, through the seizure and degradation of the cytosolic damaged elements. However, when an excessive level of intracellular damage is reached, the autophagic process may also induce cell death. A correct modulation of specific stages of autophagy is important to maintain the correct balance in the organism. In this review, we highlight the critical role that autophagy plays in neurotoxicity induced by the most common classes of environmental contaminants. The understanding of this mechanism may be helpful to discover a potential therapeutic strategy to reduce side effects induced by these compounds.

Neuroprotective activity of macamides on manganese-induced mitochondrial disruption in U-87 MG glioblastoma cells

Macamides are a distinct class of secondary metabolites, benzylamides of long chain fatty acids, which were isolated from the Peruvian plant Lepidium meyenii (Maca). As structural analogues of the endocannabinoid anandamide (AEA), they have demonstrated neuroprotective effects in vitro and in vivo. The purpose of this study was to demonstrate the neuroprotective activity of the macamides: N-(3-methoxybenzyl)oleamide (MAC 18:1), N-(3-methoxybenzyl)linoleamide (MAC 18:2) and N-(3-methoxybenzyl)linolenamide (MAC 18:3) in a neurotoxic environment caused by exposure of U-87 MG glioblastoma cells to manganese chloride (MnCl₂). The neuroprotective effects of these macamides were reversed by the CB₁ antagonist AM251. The mechanism by which manganese (Mn) induces cell damage was investigated by studying its effects on mitochondria. Reactive oxygen species (ROS) increase intracellular calcium and enhance the opening of mitochondrial permeability transition pores (MPTP), which leads to decreased mitochondrial membrane potential (MMP), to disruption of mitochondria and to neuron death in neurodegenerative disorders. In this study, MnCl₂ at 50μM was responsible for mitochondrial disruption, which was attenuated by all three of the macamides tested. Human peroxisome proliferator-activated receptor gamma (PPARγ) has been proposed to be a cannabinoid target, and PPARγ has also been demonstrated to mediate some of the longer-term vascular effects of the plant cannabinoid, ∆9-tetrahydrocannabinol. PPARγ activation was observed in response to exposures of cells to MAC 18:2 and MAC 18:3. These findings suggest that macamides achieve their neuroprotective effects by binding to CB₁ receptors to protect against Mn-induced toxicity in U-87 MG glioblastoma cells. Additionally these macamides, in a manner similar to the analogous endocannabinoid AEA, interact with other targets such as PPARγ to regulate metabolism and energy homeostasis, cell differentiation and inflammation.

17β-estradiol and tamoxifen protect mice from manganese-induced dopaminergic neurotoxicity

Chronic exposure to manganese (Mn) causes neurotoxicity, referred to as manganism, with common clinical features of parkinsonism. 17β-estradiol (E2) and tamoxifen (TX), a selective estrogen receptor modulator (SERM), afford neuroprotection in several neurological disorders, including Parkinson's disease (PD). In the present study, we tested if E2 and TX attenuate Mn-induced neurotoxicity in mice, assessing motor deficit and dopaminergic neurodegeneration. We implanted E2 and TX pellets in the back of the neck of ovariectomized C57BL/6 mice two weeks prior to a single injection of Mn into the striatum. One week later, we assessed locomotor activity and molecular mechanisms by immunohistochemistry, real-time quantitative PCR, western blot and enzymatic biochemical analyses. The results showed that both E2 and TX attenuated Mn-induced motor deficits and reversed the Mn-induced loss of dopaminergic neurons in the substantia nigra. At the molecular level, E2 and TX reversed the Mn-induced decrease of (1) glutamate aspartate transporter (GLAST) and glutamate transporter 1 (GLT-1) mRNA and protein levels; (2) transforming growth factor-α (TGF-α) and estrogen receptor-α (ER-α) protein levels; and (3) catalase (CAT) activity and glutathione (GSH) levels, and Mn-increased (1) malondialdehyde (MDA) levels and (2) the Bax/Bcl-2 ratio. These results indicate that E2 and TX afford protection against Mn-induced neurotoxicity by reversing Mn-reduced GLT1/GLAST as well as Mn-induced oxidative stress. Our findings may offer estrogenic agents as potential candidates for the development of therapeutics to treat Mn-induced neurotoxicity.

UHPLC-Q-TOF/MS based plasma metabolomics reveals the metabolic perturbations by manganese exposure in rat models

Although manganese (Mn) is an essential metal ion biological cofactor, high concentrations could potentially induce an accumulation in the brain and lead to manganism. However, there is no "gold standard" for manganism assessment due to a lack of objective biomarkers. We hypothesized that Mn-induced alterations are associated with metabolic responses to manganism. Here we use an untargeted metabolomics approach by performing ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) on control and Mn-treated rat plasma, to identify metabolic disruptions under high Mn exposure conditions. Sprague-Dawley rats had access to deionized drinking water that was either Mn-free or contained 200 mg Mn per L for 5 weeks. Mn-exposure significantly increased liver Mn concentration in comparison with the control, and also resulted in extensive necrosis and dissolved nuclei, which suggested liver damage from hepatic histopathology. Principal component analysis readily distinguished the metabolomes between the control group and the Mn-treated group. Using multivariate and univariate analysis, Mn significantly altered the concentrations of 36 metabolites (12 metabolites showed a remarkable increase in number and 24 metabolites reduced significantly in concentration) in the plasma of the Mn-treated group. Major alterations were observed for purine metabolism, amino acid metabolism and fatty acid metabolism. These data provide metabolic evidence and putative biomarkers for the Mn-induced alterations in plasma metabolism. The targets of these metabolites have the potential to improve our understanding of cell-level Mn trafficking and homeostatic mechanisms.

Mitochondria: A Common Target for Genetic Mutations and Environmental Toxicants in Parkinson's Disease

Parkinson's disease (PD) is a devastating neurological movement disorder. Since its first discovery 200 years ago, genetic and environmental factors have been identified to play a role in PD development and progression. Although genetic studies have been the predominant driving force in PD research over the last few decades, currently only a small fraction of PD cases can be directly linked to monogenic mutations. The remaining cases have been attributed to other risk associated genes, environmental exposures and gene-environment interactions, making PD a multifactorial disorder with a complex etiology. However, enormous efforts from global research have yielded significant insights into pathogenic mechanisms and potential therapeutic targets for PD. This review will highlight mitochondrial dysfunction as a common pathway involved in both genetic mutations and environmental toxicants linked to PD.

Biometal Dyshomeostasis and Toxic Metal Accumulations in the Development of Alzheimer's Disease

Biometal dyshomeostasis and toxic metal accumulation are common features in many neurodegenerative disorders, including Alzheimer’s disease (AD), Parkinson’s disease, and Huntington’s disease. The neurotoxic effects of metal imbalance are generally associated with reduced enzymatic activities, elevated protein aggregation and oxidative stress in the central nervous system, in which a cascade of events lead to cell death and neurodegeneration. Although the links between biometal imbalance and neurodegenerative disorders remain elusive, a major class of endogenous proteins involved in metal transport has been receiving increasing attention over recent decades. The abnormal expression of these proteins has been linked to biometal imbalance and to the pathogenesis of AD. Here, we present a brief overview of the physiological roles of biometals including iron, zinc, copper, manganese, magnesium and calcium, and provide a detailed description of their transporters and their synergistic involvement in the development of AD. In addition, we also review the published data relating to neurotoxic metals in AD, including aluminum, lead, cadmium, and mercury.

Assessment of gender and age effects on serum and hair trace element levels in children with autism spectrum disorder

The primary objective of the present study was to investigate the levels of essential trace elements in hair and serum in children with autism spectrum disorder (ASD) and investigate the age and gender effects. Children with ASD were characterized by significantly higher levels of copper (Cu) (+8%), iron (Fe) (+5%), and selenium (Se) (+13%) levels in hair and only 8% higher serum Cu levels. After stratification for gender, ASD boys were characterized by significantly increased hair Cu (+ 25%), Fe (+ 25%), and Se (+ 9%) levels, whereas in girls only Se content was elevated (+ 15%). Boys and girls suffering from ASD were characterized by significantly higher serum manganese (Mn) (+20%) and Cu (+18%) as compared to the control values, respectively. In the group of younger children (2-5 years), no significant group difference in hair trace element levels was detected, whereas serum Cu levels were significantly higher (+7%). In turn, the serum concentration of Se in ASD children was 11% lower than that in neurotypical children. In the group of older children with ASD (6-10 years), hair Fe and Se levels were 21% and 16% higher, whereas in serum only Cu levels were increased (+12%) as compared to the controls. Correlation analysis also revealed a different relationship between serum and hair trace element levels with respect to gender and age. Therefore, it is highly recommended to assess several bioindicative matrices for critical evaluation of trace element status in patients with ASD in order to develop adequate personalized nutritional correction.

The overlaying oil type influences in vitro embryo production: differences in composition and compound transfer into incubation medium between oils

The oil overlay micro-drop system is widely used for cultures of mammalian gametes and embryos. We evaluated hereby the effects of two unaltered commercial oils- Sigma mineral oil (S-MO) and Nidoil paraffin oil (N-PO)-on in vitro embryo production (IVP) outcomes using a pig model. The results showed that while either oil apparently did not affect oocyte maturation and fertilization rates, S-MO negatively affected embryo cleavage rates, blastocyst formation rates, and, consequently, total blastocyst efficiency of the system. No differences in the oxidation state were found between the oils or culture media incubated under S-MO or N-PO. Although both oils slightly differed in elemental composition, there were no differences in the concentrations of elements between fresh media and media incubated under oils. By contrast, we demonstrated clear oil-type differences in both the composition of volatile organic compounds (VOC) and the transfer of some of these VOC´s (straight-chain alkanes and pentanal and 1,3-diethyl benzene) to the culture medium, which could have influenced embryonic development.

Nanoparticles as contrast agents for brain nuclear magnetic resonance imaging in Alzheimer's disease diagnosis

Nuclear Magnetic Resonance Imaging (MRI) of amyloid plaques is a powerful non-invasive approach for the early and accurate diagnosis of Alzheimer's disease (AD) along with clinical observations of behavioral changes and cognitive impairment. The present article aims at giving a critical and comprehensive review of recent advances in the development of nanoparticle-based contrast agents for brain MRI. Nanoparticles considered for the MRI of AD must comply with a highly stringent set of requirements including low toxicity and the ability to cross the blood-brain-barrier. In addition, to reach an optimal signal-to-noise ratio, they must exhibit a specific ability to target amyloid plaques, which can be achieved by grafting antibodies, peptides or small molecules. Finally, we propose to consider new directions for the future of MRI in the context of Alzheimer's disease, in particular by enhancing the performances of contrast agents and by including therapeutic functionalities following a theranostic strategy.

Manganese transporter Slc39a14 deficiency revealed its key role in maintaining manganese homeostasis in mice

SLC39A14 (also known as ZIP14), a member of the SLC39A transmembrane metal transporter family, has been reported to mediate the cellular uptake of iron and zinc. Recently, however, mutations in the SLC39A14 gene have been linked to manganese (Mn) accumulation in the brain and childhood-onset parkinsonism dystonia. It has therefore been suggested that SLC39A14 deficiency impairs hepatic Mn uptake and biliary excretion, resulting in the accumulation of Mn in the circulation and brain. To test this hypothesis, we generated and characterized global Slc39a14-knockout (Slc39a14-/- ) mice and hepatocyte-specific Slc39a14-knockout (Slc39a14fl/fl;Alb-Cre+ ) mice. Slc39a14-/- mice develop markedly increased Mn concentrations in the brain and several extrahepatic tissues, as well as motor deficits that can be rescued by treatment with the metal chelator Na2CaEDTA. In contrast, Slc39a14fl/fl;Alb-Cre+ mice do not accumulate Mn in the brain or other extrahepatic tissues and do not develop motor deficits, indicating that the loss of Slc39a14 expression selectively in hepatocytes is not sufficient to cause Mn accumulation. Interestingly, Slc39a14fl/fl;Alb-Cre+ mice fed a high Mn diet have increased Mn levels in the serum, brain and pancreas, but not in the liver. Taken together, our results indicate that Slc39a14-/- mice develop brain Mn accumulation and motor deficits that cannot be explained by a loss of Slc39a14 expression in hepatocytes. These findings provide insight into the physiological role that SLC39A14 has in maintaining Mn homeostasis. Our tissue-specific Slc39a14-knockout mouse model can serve as a valuable tool for further dissecting the organ-specific role of SLC39A14 in regulating the body's susceptibility to Mn toxicity.

Inhibition of Calpains Protects Mn-Induced Neurotransmitter release disorders in Synaptosomes from Mice: Involvement of SNARE Complex and Synaptic Vesicle Fusion

Overexposure to manganese (Mn) could disrupt neurotransmitter release via influencing the formation of SNARE complex, but the underlying mechanisms are still unclear. A previous study demonstrated that SNAP-25 is one of substrate of calpains. The current study investigated whether calpains were involved in Mn-induced disorder of SNARE complex. After mice were treated with Mn for 24 days, Mn deposition increased significantly in basal nuclei in Mn-treated and calpeptin pre-treated groups. Behaviorally, less time spent in the center of the area and decreased average velocity significantly in an open field test after 24 days of Mn exposure. With the increase in MnCl₂ dosage, intracellular Ca²⁺ increased significantly, but pretreatment with calpeptin caused a dose-dependent decrease in calpains activity. There were fragments of N-terminal of SNAP-25 protein appearance in Mn-treated groups, but it is decreased with pretreatment of calpeptin. FM1-43-labeled synaptic vesicles also provided evidence that the treatment with Mn resulted in increasing first and then decreasing, which was consistent with Glu release and the 80 kDa protein levels of SNARE complexes. In summary, Mn induced the disorder of neurotransmitter release through influencing the formation of SNARE complex via cleaving SNAP-25 by overactivation of calpains in vivo.

Manganese exposure induces neuroinflammation by impairing mitochondrial dynamics in astrocytes

Chronic manganese (Mn) exposure induces neurotoxicity, which is characterized by Parkinsonian symptoms resulting from impairment in the extrapyramidal motor system of the basal ganglia. Mitochondrial dysfunction and oxidative stress are considered key pathophysiological features of Mn neurotoxicity. Recent evidence suggests astrocytes as a major target of Mn neurotoxicity since Mn accumulates predominantly in astrocytes. However, the primary mechanisms underlying Mn-induced astroglial dysfunction and its role in metal neurotoxicity are not completely understood. In this study, we examined the interrelationship between mitochondrial dysfunction and astrocytic inflammation in Mn neurotoxicity. We first evaluated whether Mn exposure alters mitochondrial bioenergetics in cultured astrocytes. Metabolic activity assessed by MTS assay revealed an IC₅₀ of 92.68μM Mn at 24h in primary mouse astrocytes (PMAs) and 50.46μM in the human astrocytic U373 cell line. Mn treatment reduced mitochondrial mass, indicative of impaired mitochondrial function and biogenesis, which was substantiated by the significant reduction in mRNA of mitofusin-2, a protein that serves as a ubiquitination target for mitophagy. Furthermore, Mn increased mitochondrial circularity indicating augmented mitochondrial fission. Seahorse analysis of bioenergetics status in Mn-treated astrocytes revealed that Mn significantly impaired the basal mitochondrial oxygen consumption rate as well as the ATP-linked respiration rate. The effect of Mn on mitochondrial energy deficits was further supported by a reduction in ATP production. Mn-exposed primary astrocytes also exhibited a severely quiescent energy phenotype, which was substantiated by the inability of oligomycin to increase the extracellular acidification rate. Since astrocytes regulate immune functions in the CNS, we also evaluated whether Mn modulates astrocytic inflammation. Mn exposure in astrocytes not only stimulated the release of proinflammatory cytokines, but also exacerbated the inflammatory response induced by aggregated α-synuclein. The novel mitochondria-targeted antioxidant, mito-apocynin, significantly attenuated Mn-induced inflammatory gene expression, further supporting the role of mitochondria dysfunction and oxidative stress in mediating astrogliosis. Lastly, intranasal delivery of Mn in vivo elevated GFAP and depressed TH levels in the olfactory bulbs, clearly supporting the involvement of astrocytes in Mn-induced dopaminergic neurotoxicity. Collectively, our study demonstrates that Mn drives proinflammatory events in astrocytes by impairing mitochondrial bioenergetics.

Quercetin Improves Neurobehavioral Performance Through Restoration of Brain Antioxidant Status and Acetylcholinesterase Activity in Manganese-Treated Rats

The present study investigated the neuroprotective mechanism of quercetin by assessing the biochemical and behavioral characteristics in rats sub-chronically treated with manganese alone at 15 mg/kg body weight or orally co-treated with quercetin at 10 and 20 mg/kg body weight for 45 consecutive days. Locomotor behavior was monitored using video-tracking software during a 10-min trial in a novel environment whereas the brain regions namely the hypothalamus, cerebrum and cerebellum of the rats were processed for biochemical analyses. Results indicated that co-treatment with quercetin significantly (p < 0.05) prevented manganese-induced locomotor and motor deficits specifically the decrease in total distance travelled, total body rotation, maximum speed, absolute turn angle as well as the increase in time of immobility and grooming. The improvement in the neurobehavioral performance of manganese-treated rats following quercetin co-treatment was confirmed by track and occupancy plot analyses. Moreover, quercetin assuaged manganese-induced decrease in antioxidant enzymes activities and the increase in acetylcholinesterase activity, hydrogen peroxide generation and lipid peroxidation levels in the hypothalamus, cerebrum and cerebellum of the rats. Taken together, quercetin mechanisms of ameliorating manganese-induced neurotoxicity is associated with restoration of acetylcholinesterase activity, augmentation of redox status and inhibition of lipid peroxidation in brain of rats.

Redox dynamics of manganese as a mitochondrial life-death switch

Sten Orrenius, M.D., Ph.D., pioneered many areas of cellular and molecular toxicology and made seminal contributions to our knowledge of oxidative stress and glutathione (GSH) metabolism, organellar functions and Ca+2-dependent mechanisms of cell death, and mechanisms of apoptosis. On the occasion of his 80th birthday, we summarize current knowledge on redox biology of manganese (Mn) and its role in mechanisms of cell death. Mn is found in all organisms and has critical roles in cell survival and death mechanisms by regulating Mn-containing enzymes such as manganese superoxide dismutase (SOD2) or affecting expression and activity of caspases. Occupational exposures to Mn cause "manganism", a Parkinson's disease-like condition of neurotoxicity, and experimental studies show that Mn exposure leads to accumulation of Mn in the brain, especially in mitochondria, and neuronal cell death occurs with features of an apoptotic mechanism. Interesting questions are why a ubiquitous metal that is essential for mitochondrial function would accumulate to excessive levels, cause increased H2O2 production and lead to cell death. Is this due to the interactions of Mn with other essential metals, such as iron, or with toxic metals, such as cadmium? Why is the Mn loading in the human brain so variable, and why is there such a narrow window between dietary adequacy and toxicity? Are non-neuronal tissues similarly vulnerable to insufficiency and excess, yet not characterized? We conclude that Mn is an important component of the redox interface between an organism and its environment and warrants detailed studies to understand the role of Mn as a mitochondrial life-death switch.

Role of neurotoxicants and traumatic brain injury in α-synuclein protein misfolding and aggregation

Protein misfolding and aggregation are key pathological features of many neurodegenerative diseases including Parkinson's disease (PD) and other forms of human Parkinsonism. PD is a complex and multifaceted disorder whose etiology is not fully understood. However, several lines of evidence support the multiple hit hypothesis that genetic vulnerability and environmental toxicants converge to trigger PD pathology. Alpha-synuclein (α-Syn) aggregation in the brain is an important pathophysiological characteristic of synucleinopathies including PD. Epidemiological and experimental studies have shown that metals and pesticides play a crucial role in α-Syn aggregation leading to the onset of various neurodegenerative diseases including PD. In this review, we will emphasize key findings of several epidemiological as well as experimental studies of metal- and pesticide-induced α-Syn aggregation and neurodegeneration. We will also discuss other factors such as traumatic brain injury and oxidative insult in the context of α-Syn-related neurodegenerative processes.

Manganese neurotoxicity and protective effects of resveratrol and quercetin in preclinical research

BACKGROUND

Exposure to Mn results in a neurological syndrome known as manganism.

METHODS

We examined how 4-week Mn exposure (20mg/kg MnCl₂po, 5days/week) induces neurotoxic effects in rats. Oxidized-to-reduced glutathione ratio (GSSG/GSH), malondialdehyde (MDA), superoxide dismutase (SOD) activity, catalase (CAT) activity, vitamin E content and caspase-3 activity were measured in several rat brain structures. Further, we examined protective effects of the polyphenols: resveratrol (R) or quercetin (QCT) against Mn-induced neurotoxicity.

RESULTS

After exposure to Mn, we found a rise in GSSG/GSH ratio and a reduction in SOD activity in the rat striatum (STR), while in the nucleus accumbens (NAC) decreases in alpha-tocopherol content and in SOD activity were noted. In the frontal cortex (FCX), an enhancement in GSSG/GSH ratio and a reduction in SOD and CAT activities were observed. In the cerebellum (CER), a significant increase in the caspase-3 activity paralleled a rise in the GSSG/GSH ratio and a diminution of SOD activity. In the rat hippocampus (HIP), Mn evoked an enhancement in GSSG/GSH ratio. There were no changes in the MDA levels. Pretreatment with R and QCT protected against the Mn-induced (i) enhancement in GSSG/GSH ratio in the STR, (ii) decreases in the NAC alpha-tocopherol content and (iii) reduction in SOD activity in FCX, NAC and CER.

CONCLUSION

Repeated Mn administration induces toxic effects in several rat brain structures and treatment with R and QCT may be a potential therapeutic strategy to attenuate the metal neurotoxicity.

Effects of Divalent Cations on Outward Potassium Currents in Leech Retzius Nerve Cells

The present study examines the effects of divalent metals, cadmium (Cd2+) and manganese (Mn2+), on the outward potassium currents of Retzius cells in the hirudinid leeches Haemopis sanguisuga using conventional two-microelectrode voltageclamp techniques. The outward potassium current is activated by depolarization and plays an important role in determining both the neuronal excitability and action potential duration. A strong inhibition of the fast current and a clear reduction in the late currents of the outward current with 1 mM Cd2+were obtained, which indicated that both components are sensitive to this metal. Complete blockage of the fast and partial reduction of the slow outward currents was observed after adding 1 mM Mn2+to the extracellular fluid. These data show that the outward K+current in leech Retzius nerve cells comprises at least two components: a voltage-dependent K+current and a Ca2+- activated K+current. These observations also indicate that Cd2+is more eff ective than Mn2+in blocking ion fl ow through these channels and that suppressing Ca2+-activated K+outward currents can prolong the action potential in nerve cells.

Manganese ions enhance mitochondrial H2O2 emission from Krebs cycle oxidoreductases by inducing permeability transition

Manganese-induced toxicity has been linked to mitochondrial dysfunction and an increased generation of reactive oxygen species (ROS). We could recently show in mechanistic studies that Mn²⁺ ions induce hydrogen peroxide (H₂O₂) production from the ubiquinone binding site of mitochondrial complex II (II_Q) and generally enhance H₂O₂ formation by accelerating the rate of superoxide dismutation. The present study with intact mitochondria reveals that manganese additionally enhances H₂O₂ emission by inducing mitochondrial permeability transition (mPT). In mitochondria fed by NADH-generating substrates, the combination of Mn²⁺ and different respiratory chain inhibitors led to a dynamically increasing H₂O₂emission which was sensitive to the mPT inhibitor cyclosporine A (CsA) as well as Ru-360, an inhibitor of the mitochondrial calcium uniporter (MCU). Under these conditions, flavin-containing enzymes of the mitochondrial matrix, e.g. the mitochondrial 2-oxoglutaratedehydrogenase (OGDH), were major sources of ROS. With succinate as substrate, Mn²⁺ stimulated ROS production mainly at complex II, whereby the applied succinate concentration had a marked effect on the tendency for mPT. Also Ca²⁺ increased the rate of H₂O₂ emission by mPT, while no direct effect on ROS-production of complex II was observed. The present study reveals a complex scenario through which manganese affects mitochondrial H₂O₂ emission: stimulating its production from distinct sites (e.g. site II_Q), accelerating superoxide dismutation and enhancing the emission via mPT which also leads to the loss of soluble components of the mitochondrial antioxidant systems and favors the ROS production from flavin-containing oxidoreductases of the Krebs cycle.

Untangling the Manganese-α-Synuclein Web

Neurodegenerative diseases affect a significant portion of the aging population. Several lines of evidence suggest a positive association between environmental exposures, which are common and cumulative in a lifetime, and development of neurodegenerative diseases. Environmental or occupational exposure to manganese (Mn) has been implicated in neurodegeneration due to its ability to induce mitochondrial dysfunction, oxidative stress, and α-synuclein (α-Syn) aggregation. The role of the α-Syn protein vis-a-vis Mn is controversial, as it seemingly plays a duplicitous role in neuroprotection and neurodegeneration. α-Syn has low affinity for Mn, however an indirect interaction cannot be ruled out. In this review we will examine the current knowledge surrounding the interaction of α-Syn and Mn in neurodegenerative process.

Shawn, the Drosophila Homolog of SLC25A39/40, Is a Mitochondrial Carrier That Promotes Neuronal Survival

Mitochondria play an important role in the regulation of neurotransmission, and mitochondrial impairment is a key event in neurodegeneration. Cells rely on mitochondrial carrier proteins of the SLC25 family to shuttle ions, cofactors, and metabolites necessary for enzymatic reactions. Mutations in these carriers often result in rare but severe pathologies in the brain, and some of the genes, including SLC25A39 and SLC25A40, reside in susceptibility loci of severe forms of epilepsy. However, the role of most of these carriers has not been investigated in neurons in vivo. We identified shawn, the Drosophila homolog of SLC25A39 and SLC25A40, in a genetic screen to identify genes involved in neuronal function. Shawn localizes to mitochondria, and missense mutations result in an accumulation of reactive oxygen species, mitochondrial dysfunction, and neurodegeneration. Shawn regulates metal homeostasis, and we found in shawn mutants increased levels of manganese, calcium, and mitochondrial free iron. Mitochondrial mutants often cannot maintain synaptic transmission under demanding conditions, but shawn mutants do, and they also do not display endocytic defects. In contrast, shawn mutants harbor a significant increase in neurotransmitter release. Our work provides the first functional annotation of these essential mitochondrial carriers in the nervous system, and the results suggest that metal imbalances and mitochondrial dysfunction may contribute to defects in synaptic transmission and neuronal survival.

SIGNIFICANCE STATEMENT

We describe for the first time the role of the mitochondrial carrier Shawn/SLC25A39/SLC25A40 in the nervous system. In humans, these genes reside in susceptibility loci for epilepsy, and, in flies, we observe neuronal defects related to mitochondrial dysfunction and metal homeostasis defects. Interestingly, shawn mutants also harbor increased neurotransmitter release and neurodegeneration. Our data suggest a connection between maintaining a correct metal balance and mitochondrial function to regulate neuronal survival and neurotransmitter release.

Manganese and aging

Manganese (Mn) is an essential metal that is required as a cofactor for many enzymes and is necessary for optimal biological function. Mn is abundant in the earth's crust and is present in soil and well water. Mn is also found in industrial settings, including mining, welding, and battery manufacture. Mn is also present in infant formula, parenteral nutrition, as well as pesticides and gasoline additives. A sufficient amount of Mn is obtained from most diets, and Mn deficiency is exceedingly rare. Excessive exposure to Mn in high doses can result in a condition known as manganism that results in psychological and emotional disturbances and motor symptoms that are reminiscent of Parkinson's disease, including gait disturbance, tremor, rigidity, and bradykinesia. Treatment for manganism is to remove the patient from Mn exposure, though symptoms are generally irreversible. The effects of exposure to Mn at lower doses are less clear. Little work has been done to evaluate the effects of chronic exposure to subclinical levels of Mn, especially in regard to lifelong exposures and the effects on the aging process. Mn is known to have effects on some of the same mechanistic processes that are altered in aging. This review will describe the general effects of Mn exposure and will focus on how Mn may be related to some of the mechanism of aging: neurogenesis, oxidative stress, and microglial activation and inflammation.

Gender influence on manganese induced depression-like behavior and Mn and Fe deposition in different regions of CNS and excretory organs in intraperitoneally exposed rats

Manganese (Mn) is an essential metal for mammals. It can modulate the action of endogenous substances, as neurotransmitters, but in excess also can trigger known neurotoxic effects. Many studies have been conducted assessing Mn neurotoxicity. However, Mn bioaccumulation in different brain tissues and behavior effects involving gender-specific studies are conflicted in the literature. Therefore, the aim of this work was to compare Mn effects, after 30days of intraperitoneal treatment, in male and female rats, submitted to forced swim and open field tests. After that, were evaluated Mn and Fe tissue levels in CNS, liver, and kidneys. Wistar rats were divided into saline, Mn 1mg/kg, Mn 5mg/kg, and imipramine (as forced swim control). Then, animals were euthanized by anesthesia overdose followed by decapitation and the collected tissue were striatum, hippocampus, brainstem, cortex, cerebellum, hepatic tissue, and renal tissue. Mn and Fe were determined by ICP-MS. There was a dose-dependent effect on accumulation of Mn in the cerebellum and brainstem to the dosage of 5mg/kg. In hippocampus there were bioaccumulation differences between gender and dose, and an increase of Fe in the groups exposed to Mn. Excess metals in the brain dissected has a strong influence on memory and learning processes and suggests pro-depressive effects, possibly triggered by the reduction of monoamines due to excessive metal bioaccumulation. It was concluded that, under this experimental design, Mn exposure cause metal deposition on dissected CNS, liver and kidney. There an effect at lower doses that was gender-dependent and males had more pronounced behavioral damage compared to females, although with increasing dose, females had an indication of motor damage.

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.

Brain biometals and Alzheimer's disease - boon or bane?

Alzheimer's disease (AD) is the most common form of dementia. Several hypotheses have been put forward to explain the basis of disease onset and progression. A complicated array of molecular events has been implicated in the pathogenesis of AD. It is attributed to a variety of pathological conditions that share similar critical processes, such as oxidative stress, proteinaceous aggregations, mitochondrial dysfunctions and energy failure. There is increasing evidence suggesting that metal homeostasis is dysregulated in the pathology of AD. Biometals play an important role in the normal body functioning but AD may be mediated or triggered by disproportion of metal ions leading to changes in critical biological systems and initiating a cascade of events finally leading to neurodegeneration and cell death. The link is multifactorial, and although the source of the shift in oxidative homeostasis is still unclear, current evidence points to changes in the balance of redox transition metals, especially iron, copper (Cu) and other trace metals. Their levels in the brain are found to be elevated in AD. In other neurodegenerative disorders, Cu, zinc, aluminum and manganese are involved. This paper is a review of recent advances of the role of metals in the pathogenesis and pathophysiology of AD and related neurodegenerative diseases.

Blood levels of trace metals and amyotrophic lateral sclerosis

Some trace metals may increase risk of amyotrophic lateral sclerosis (ALS), whereas others may be beneficial. Our goal was to examine associations of ALS with blood levels of selenium (Se), zinc (Zn), copper (Cu), and manganese (Mn). We conducted a case-control study of 163 neurologist confirmed patients from the National Registry of Veterans with ALS and 229 frequency-matched veteran controls. We measured metal levels in blood using inductively coupled plasma mass spectrometry and estimated odds ratios (ORs) and 95% confidence intervals (CIs) for associations between ALS and a doubling of metal levels using unconditional logistic regression, adjusting for age, gender, and race/ethnicity. ALS was inversely associated with both Se (OR=0.4, 95% CI: 0.2-0.8) and Zn (OR=0.4, 95% CI: 0.2-0.8). Inverse associations with Se were stronger in patients with bulbar compared to spinal onset, worse function, longer diagnostic delay, and longer collection delay; inverse associations with Zn were stronger for those with worse function and longer collection delay. In contrast, ALS was positively associated with Cu (OR=3.4, 95% CI: 1.5-7.9). For Mn, no linear trend was evident (OR=0.9, 95% CI: 0.6-1.3, Ptrend=0.51). Associations of Se, Zn, Cu, and Mn with ALS were independent of one another. Adjustment for lead levels attenuated the positive association of ALS with Cu but did not change associations with Se, Zn, or Mn. In conclusion, Se and Zn were inversely associated with ALS, particularly among those with worse function, suggesting that supplementation with these metals may benefit such patients, while Cu was positively associated with ALS. Deficiencies of Se and Zn and excess Cu may have a role in ALS etiology.

Metals and Neurodegeneration

Metals play important roles in the human body, maintaining cell structure and regulating gene expression, neurotransmission, and antioxidant response, to name a few. However, excessive metal accumulation in the nervous system may be toxic, inducing oxidative stress, disrupting mitochondrial function, and impairing the activity of numerous enzymes. Damage caused by metal accumulation may result in permanent injuries, including severe neurological disorders. Epidemiological and clinical studies have shown a strong correlation between aberrant metal exposure and a number of neurological diseases, including Alzheimer’s disease, amyotrophic lateral sclerosis, autism spectrum disorders, Guillain–Barré disease, Gulf War syndrome, Huntington’s disease, multiple sclerosis, Parkinson’s disease, and Wilson’s disease. Here, we briefly survey the literature relating to the role of metals in neurodegeneration.

Chemical and toxicological effects of medicinal Baccharis trimera extract from coal burning area

The entire process of power generation, extraction, processing and use of coal strongly impact water resources, soil, air quality and biota leads to changes in the fauna and flora. Pollutants generated by coal burning have been contaminating plants that grow in area impacted by airborne pollution with high metal contents. Baccharis trimera is popularly consumed as tea, and is widely developed in Candiota (Brazil), one of the most important coal burning regions of the Brazil. This study aims to investigate the phytochemical profile, in vivo genotoxic and mutagenic potential of extracts of B. trimera collected from an exposed region to pollutants generated by coal burning (Candiota City) and other unexposed region (Bagé City), using the Comet assay and micronucleus test in mice and the Salmonella/microsome short-term assay. The HPLC analyses indicated higher levels of flavonoids and phenolic acids for B. trimera aqueous extract from Bagé and absence of polycyclic aromatic hydrocarbons for both extracts. The presence of toxic elements such as cobalt, nickel and manganese was statistically superior in the extract from Candiota. For the Comet assay and micronucleus test, the mice were treated with Candiota and Bagé B. trimera aqueous extracts (500-2000 mg/kg). Significant genotoxicity was observed at higher doses treated with B. trimera aqueous extract from Candiota in liver and peripheral blood cells. Micronuclei were not observed but the results of the Salmonella/microsome short-term assay showed a significant increase in TA98 revertants for B. trimera aqueous extract from Candiota. The extract of B. trimera from Candiota bioacumulated higher levels of trace elements which were associated with the genotoxic effects detected in liver and peripheral blood cells.

Autophagy in Neurodegenerative Diseases and Metal Neurotoxicity

Autophagy generally refers to cell catabolic and recycling process in which cytoplasmic components are delivered to lysosomes for degradation. During the last two decades, autophagy research has experienced a recent boom because of a newfound connection between this process and many human diseases. Autophagy plays a significant role in maintaining cellular homeostasis and protects cells from varying insults, including misfolded and aggregated proteins and damaged organelles, which is particularly crucial in neuronal survival. Mounting evidence has implicated autophagic dysfunction in the pathogenesis of several major neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease and Huntington's disease, where deficient elimination of abnormal and toxic protein aggregates promotes cellular stress, failure and death. In addition, autophagy has also been found to affect neurotoxicity induced by exposure to essential metals, such as manganese, copper, and iron, and other heavy metals, such as cadmium, lead, and methylmercury. This review examines current literature on the role of autophagy in the mechanisms of disease pathogenesis amongst common neurodegenerative disorders and of metal-induced neurotoxicity.

Pallidal neuronal apolipoprotein E in pantothenate kinase-associated neurodegeneration recapitulates ischemic injury to the globus pallidus

Pantothenate kinase-associated neurodegeneration (PKAN) is a progressive movement disorder that is due to mutations in PANK2. Pathologically, it is a member of a class of diseases known as neurodegeneration with brain iron accumulation (NBIA) and features increased tissue iron and ubiquitinated proteinaceous aggregates in the globus pallidus. We have previously determined that these aggregates represent condensed residue derived from degenerated pallidal neurons. However, the protein content, other than ubiquitin, of these aggregates remains unknown. In the present study, we performed biochemical and immunohistochemical studies to characterize these aggregates and found them to be enriched in apolipoprotein E that is poorly soluble in detergent solutions. However, we did not determine a significant association between APOE genotype and the clinical phenotype of disease in our database of 81 cases. Rather, we frequently identified similar ubiquitin- and apolipoprotein E-enriched lesions in these neurons in non-PKAN patients in the penumbrae of remote infarcts that involve the globus pallidus, and occasionally in other brain sites that contain large γ-aminobutyric acid (GABA)ergic neurons. Our findings, taken together, suggest that tissue or cellular hypoxic/ischemic injury within the globus pallidus may underlie the pathogenesis of PKAN.

Mechanisms of divalent metal toxicity in affective disorders

Metals are required for proper brain development and play an important role in a number of neurobiological functions. The divalent metal transporter 1 (DMT1) is a major metal transporter involved in the absorption and metabolism of several essential metals like iron and manganese. However, non-essential divalent metals are also transported through this transporter. Therefore, altered expression of DMT1 can modify the absorption of toxic metals and metal-induced toxicity. An accumulating body of evidence has suggested that increased metal stores in the brain are associated with elevated oxidative stress promoted by the ability of metals to catalyze redox reactions, resulting in abnormal neurobehavioral function and the progression of neurodegenerative diseases. Metal overload has also been implicated in impaired emotional behavior, although the underlying mechanisms are not well understood with limited information. The current review focuses on psychiatric dysfunction associated with imbalanced metabolism of metals that are transported by DMT1. The investigations with respect to the toxic effects of metal overload on behavior and their underlying mechanisms of toxicity could provide several new therapeutic targets to treat metal-associated affective disorders.

Alpha-Synuclein Regulates Neuronal Levels of Manganese and Calcium

Manganese (Mn) may foster aggregation of alpha-synuclein (αSyn) contributing to the pathogenesis of PD. Here, we examined the influence of αSyn overexpression on distribution and oxidation states of Mn in frozen-hydrated primary midbrain neurons (PMNs) by synchrotron-based X-ray fluorescence (XRF) and X-ray absorption near edge structure spectroscopy (XANES). Overexpression of αSyn increased intracellular Mn levels, whereas levels of Ca, Zn, K, P, and S were significantly decreased. Mn oxidation states were not altered. A strong correlation between Cu-/Mn-levels as well as Fe-/Mn-levels was observed in αSyn-overexpressing cells. Subcellular resolution revealed a punctate or filament-like perinuclear and neuritic distribution of Mn, which resembled the expression of DMT1 and MnSOD. While overexpression of αSyn did not significantly alter the expression patterns of the most-expressed Mn transport proteins (DMT1, VGCC, Fpn1), it attenuated the Mn release from Mn-treated neurons. Thus, these data suggest that αSyn may act as an intracellular Mn store. In total, neurotoxicity in PD could be mediated via regulation of transition metal levels and the metal-binding capacity of αSyn, which could represent a promising therapeutic target for this neurodegenerative disorder.

Manganese Exposure and Neurocognitive Outcomes in Rural School-Age Children: The Communities Actively Researching Exposure Study (Ohio, USA)

BACKGROUND

Manganese (Mn) plays a vital role in brain growth and development, yet excessive exposure can result in neurotoxicity. Marietta, Ohio, is home to the nation's longest-operating ferromanganese refinery, and community concern about exposure led to the development of the research study.

OBJECTIVES

Our overall goal was to address the community's primary research question: "Does Mn affect cognitive development of children?" We evaluated the relationships between Mn exposure as measured by blood and hair Mn, along with other neurotoxicants including blood lead (Pb) and serum cotinine, and child cognition.

METHODS

Children 7-9 years of age were enrolled (n = 404) in the Communities Actively Researching Exposure Study (CARES) from Marietta and Cambridge, Ohio, and their surrounding communities from October 2008 through March 2013. Blood and hair were analyzed for Mn and Pb, and serum was analyzed for cotinine. We used penalized splines to assess potential nonlinear associations between biological measures and IQ subscale scores, followed by multivariable regression models with categorical variables based on quartiles of the distribution for biological measures with nonlinear associations and continuous variables for biological measures with linear associations.

RESULTS

Geometric mean blood (n = 327) and hair Mn (n = 370) concentrations were 9.67 ± 1.27 μg/L and 416.51 ± 2.44 ng/g, respectively. After adjusting for potential confounders, both low and high blood and hair Mn concentrations were associated with lower Full Scale IQ and subscale scores, with significant negative associations between the highest quartile and middle two quartiles of blood Mn (β -3.51; 95% CI: -6.64, -0.38) and hair Mn (β -3.66; 95% CI: -6.9, -0.43%) and Full Scale IQ.

CONCLUSIONS

Both low and high Mn concentrations in blood and hair were negatively associated with child IQ scores. Serum cotinine was negatively associated with child cognitive function.

Protective effect of edaravone against manganese-induced toxicity in cultured rat astrocytes

Manganese (Mn), a trace metal, is essential for maintaining the normal regulation of many biochemical and cellular processes. However, accumulation of Mn due to excessive environmental exposure leads to neurological impairment, referred to as manganism. Edaravone (EDA) is a potent free radical scavenger that has been clinically shown to reduce the neuronal injury after cerebral ischemia. In the present study, we aimed to examine the protective effects of EDA against Mn toxicity in astrocyte cultures. Astrocyte cultures were prepared from cerebral cortices of newborn Sprague-Dawley rats. The experiments were performed between 16 and 18 days of cultures. Astrocytes were treated in DMEM medium containing Mn (1-1000μM) for 24h to test Mn toxicity. In order to assess the effect of EDA, cells were pre-treated with different doses of EDA (10, 100 and 1000μM) 6h before Mn treatment. Cell viability (MTT), apoptotic cell death (Hoechst test) and lipid peroxide levels were evaluated in cultures. Our results showed that Mn significantly and dose-dependently reduced cell viability in astrocyte cultures. The apoptotic cell death and lipid peroxides were significantly higher in Mn treated cultures. Treatment of astrocytes with EDA successfully suppressed oxidative stress and cell death due to Mn exposure. The findings of the present study suggest that Mn cytotoxicity is mainly associated with ROS generation and apoptotic cell death. Besides, EDA may have beneficial effects against Mn toxicity. However, further studies are needed to elucidate the molecular mechanisms underlying protective effect of EDA.