Mn Overexposure Research Articles

Manganese Overexposure Alters Neurogranin Expression and Causes Behavioral Deficits in Larval Zebrafish.

Manganese (Mn), a cofactor for various enzyme classes, is an essential trace metal for all organisms. However, overexposure to Mn causes neurotoxicity. Here, we evaluated the effects of exposure to Mn chloride (MnCl2) on viability, morphology, synapse function (based on neurogranin expression) and behavior of zebrafish larvae. MnCl2 exposure from 2.5 h post fertilization led to reduced survival (60%) at 5 days post fertilization. Phenotypical changes affected body length, eye and olfactory organ size, and visual background adaptation. This was accompanied by a decrease in both the fluorescence intensity of neurogranin immunostaining and expression levels of the neurogranin-encoding genes nrgna and nrgnb, suggesting the presence of synaptic alterations. Furthermore, overexposure to MnCl2 resulted in larvae exhibiting postural defects, reduction in motor activity and impaired preference for light environments. Following the removal of MnCl2 from the fish water, zebrafish larvae recovered their pigmentation pattern and normalized their locomotor behavior, indicating that some aspects of Mn neurotoxicity are reversible. In summary, our results demonstrate that Mn overexposure leads to pronounced morphological alterations, changes in neurogranin expression and behavioral impairments in zebrafish larvae.

Melatonin modulates the differentiation of neural stem cells exposed to manganese via SIRT1/β-catenin signaling

Excessive exposure of children to manganese (Mn) in the environment has a bearing on developmental neurotoxicity. Although melatonin (Mel) can play a neuroprotective role by modulating the differentiation of neural stem cells (NSCs) in the developing brain, its specific mechanism under Mn overexposure remains to be explored. Here, we cultured primary NSCs as an available model to investigate the relevant molecular mechanism of Mel mitigation on Mn-induced disorder of NSCs differentiation through sirtuin 1 (SIRT1)/β-catenin pathway. It was found that Mel could facilitate the differentiation of Mn-treated NSCs into neurons. Further, our results uncovered that the pro-differentiation mechanism of Mel depended upon ascending the activity of SIRT1, thereby weakening β-catenin acetylation and increasing phosphorylation of β-catenin ser675 in the cytoplasm, which facilitates the nuclear translocation of β-catenin. Furthermore, the role of SIRT1 in Mel-mediated signal transduction was investigated through the pretreatment of NSCs using a highly specific SIRT1 inhibitor, EX527. After EX527 pretreatment, Mel could not maintain its protective effect. Overall, our results revealed that Mel could alleviate Mn-induced disorder of NSCs differentiation through the activation of the SIRT1/β-catenin pathway.

Manganese overexposure induces Parkinson-like symptoms, altered lipid signature and oxidative stress in C57BL/6 J mouse

Although adequate intake of manganese (Mn) is essential to humans, Mn in excess is neurotoxic. Exposure to extremely high doses of Mn results in “manganism”, a condition that exhibits Parkinson-like symptoms. However, the mechanisms underlying its neurotoxic effects in Mn-induced parkinsonism pathogenesis are unclear. In this study, 8-week-old male C57BL/6 J mice were injected intraperitoneally with saline and 50 mg/kg MnCl2 respectively once daily for 14 days to produce an acute Mn neurotoxicity model. Accumulation of Mn in the midbrain, motor dysfunction and loss of dopaminergic neurons in the substantia nigra evidenced Mn neurotoxicity. Untargeted lipidomic analysis demonstrated that Mn overexposure altered lipidome profiles. A significant modulation of 12 lipid subclasses belonging to 5 different categories were found in the midbrain and among the most abundant lipids were sphingolipids, glycerophospholipids, and glycerides. The levels of sphingomyelin (SM) were significantly decreased after Mn treatment. The expression of SM biosynthesis genes was decreased dramatically while sphingomyelinase was up-regulated. In addition, we observed oxidative stress in both the midbrain of mice and MN9D cells, indicated by the increase of MDA level, the decrease of reduced GSH level and the inhibition of SOD and GPx enzyme activities. There was a correlation between these changes and motor dysfunctions. Overall, our study is the first to use lipidomics techniques to explore the pathogenesis of Mn-induced parkinsonism in C57BL/6 J mice. Mn induced molecular events in the midbrain, such as lipid metabolism disorders, oxidative stress and dopaminergic neurons injury, may mechanistically play important roles in the pathogenesis of Parkinson-like symptoms. Moreover, these findings emphasize the necessity for reducing the health risk of environmental neurotoxic pollutants in relation to parkinsonism.

Caenorhabditis elegans as a Model to Study Manganese-Induced Neurotoxicity.

Caenorhabditis elegans (C. elegans) is a nematode present worldwide. The worm shows homology to mammalian systems and expresses approximately 40% of human disease-related genes. Since Dr. Sydney Brenner first proposed C. elegans as an advantageous experimental worm-model system for genetic approaches, increasing numbers of studies using C. elegans as a tool to investigate topics in several fields of biochemistry, neuroscience, pharmacology, and toxicology have been performed. In this regard, C. elegans has been used to characterize the molecular mechanisms and affected pathways caused by metals that lead to neurotoxicity, as well as the pathophysiological interrelationship between metal exposure and ongoing neurodegenerative disorders. Several toxic metals, such as lead, cadmium, and mercury, are recognized as important environmental contaminants, and their exposure is associated with toxic effects on the human body. Essential elements that are required to maintain cellular homeostasis and normal physiological functions may also be toxic when accumulated at higher concentrations. For instance, manganese (Mn) is a trace essential element that participates in numerous biological processes, such as enzymatic activities, energy metabolism, and maintenance of cell functions. However, Mn overexposure is associated with behavioral changes in C. elegans, which are consistent with the dopaminergic system being the primary target of Mn neurotoxicity. Caenorhabditis elegans has been shown to be an important tool that allows for studies on neuron morphology using fluorescent transgenic worms. Moreover, behavioral tests may be conducted using worms, and neurotransmitter determination and related gene expression are likely to change after Mn exposure. Likewise, mutant worms may be used to study molecular mechanisms in Mn toxicity, as well as the expression of proteins responsible for the biosynthesis, transport, storage, and uptake of dopamine. Furthermore, this review highlights some advantages and limitations of using the experimental model of C. elegans and provides guidance for potential future applications of this model in studies directed toward assessing for Mn neurotoxicity and related mechanisms.

Manganese-Induced Toxicity in C. elegans: What Can We Learn from the Transcriptome?

Manganese (Mn) is an essential ubiquitous transition metal and, when occupationally or environmentally overexposed, a well-known risk factor for several neurological pathologies. However, the molecular mechanisms underlying Mn-induced neurotoxicity are largely unknown. In this study, addressing RNA-Seq analysis, bioavailability and survival assays, key pathways of transcriptional responses to Mn overexposure were investigated in the model organism Caenorhabditis elegans (C. elegans), providing insights into the Mn-induced cellular stress and damage response. Comparative transcriptome analyses identified a large number of differentially expressed genes (DEGs) in nematodes exposed to MnCl2, and functional annotation suggested oxidative nucleotide damage, unfolded protein response and innate immunity as major damage response pathways. Additionally, a time-dependent increase in the transcriptional response after MnCl2 exposure was identified by means of increased numbers of DEGs, indicating a time-dependent response and activation of the stress responses in Mn neurotoxicity. The data provided here represent a powerful transcriptomic resource in the field of Mn toxicity, and therefore, this study provides a useful basis for further planning of targeted mechanistic studies of Mn-induced neurotoxicity that are urgently needed in the face of increasing industrially caused environmental pollution with Mn.

Gray matter microstructural alterations in manganese-exposed welders: a preliminary neuroimaging study.

Chronic occupational manganese (Mn) exposure is characterized by motor and cognitive dysfunction. This study aimed to investigate structural abnormalities in Mn-exposed welders compared to healthy controls (HCs). Thirty-five HCs and forty Mn-exposed welders underwent magnetic resonance imaging (MRI) scans in this study. Based on T1-weighted MRI, the voxel-based morphometry (VBM), structural covariance, and receiver operating characteristic (ROC) curve were applied to examine whole-brain structural changes in Mn-exposed welders. Compared to HCs, Mn-exposed welders had altered gray matter volume (GMV) mainly in the medial prefrontal cortex, lentiform nucleus, hippocampus, and parahippocampus. ROC analysis indicated the potential highest classification power of the hippocampus/parahippocampus. Moreover, distinct structural covariance patterns in the two groups were associated with regions, mainly including the thalamus, insula, amygdala, sensorimotor area, and middle temporal gyrus. No significant relationships were found between the findings and clinical characteristics. Our findings showed Mn-exposed welders had changed GMV and structural covariance patterns in some regions, which implicated in motivative response, cognitive control, and emotional regulation. These results might provide preliminary evidence for understanding the pathophysiology of Mn overexposure. • Chronic Mn exposure might be related to abnormal brain structural neural mechanisms. • Mn-exposed welders had morphological changes in brain regions implicated in emotional modulation, cognitive control, and motor-related response. • Altered gray matter volume in the hippocampus/parahippocampus and putamen might serve as potential biomarkers for Mn overexposure.

The association of bone and blood manganese with motor function in Chinese workers

Manganese (Mn) is an essential element. However, Mn overexposure is associated with motor dysfunction. This cross-sectional study assessed the association between bone Mn (BnMn) and whole blood Mn (BMn) with motor function in 59 Chinese workers. BnMn and BMn were measured using a transportable in vivo neutron activation analysis system and inductively coupled plasma mass spectrometry, respectively. Motor function (manual coordination, postural sway, postural hand tremor, and fine motor function) was assessed using the Coordination Ability Test System (CATSYS) and the Purdue Pegboard. Relationships between Mn biomarkers and motor test scores were analyzed with linear regression models adjusted for age, education, current employment, and current alcohol consumption. BMn was significantly inversely associated with hand tremor intensity (dominant hand (β=-0.04, 95 % confidence interval (CI):-0.07, -0.01; non-dominant hand β=-0.05, 95 % CI:-0.08, -0.01) hand tremor center frequency (non-dominant hand β=-1.61, 95 % CI:-3.03, -0.19) and positively associated with the Purdue Pegboard Assembly Score (β = 4.58, 95 % CI:1.08, 8.07). BnMn was significantly inversely associated with finger-tapping performance (non-dominant hand β=-0.02, 95 % CI:-0.04,-0.004), mean sway (eyes closed and foam β=-0.68, 95 % CI:-1.31,-0.04), and positively associated with hand tremor center frequency (dominant hand, β = 0.40, 95 % CI:0.002, 0.80). These results suggest BMn is related to better postural hand tremor and fine motor control and BnMn is related to worse motor coordination and postural hand tremor but better (i.e., less) postural sway. The unexpected positive results might be explained by choice of biomarker or confounding by work-related motor activities. Larger, longitudinal studies in this area are recommended.

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

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

Gut Microbiota as a Potential Player in Mn-Induced Neurotoxicity.

Manganese (Mn) is an essential metal, which at high exposures causes neurotoxic effects and neurodegeneration. The neurotoxic effects of Mn are mediated by neuroinflammation, oxidative and endoplasmic reticulum stress, mitochondrial dysfunction, and other mechanisms. Recent findings have demonstrated the potential impact of Mn overexposure on gut microbiota dysbiosis, which is known to contribute to neurodegeneration via secretion of neuroactive and proinflammatory metabolites. Therefore, in this review, we discuss the existing data on the impact of Mn exposure on gut microbiota biodiversity, bacterial metabolite production, and gut wall permeability regulating systemic levels. Recent data have demonstrated that Mn exposure may affect gut microbiota biodiversity by altering the abundance of Shiegella, Ruminococcus, Dorea, Fusicatenibacter, Roseburia, Parabacteroides, Bacteroidetes, Firmicutes, Ruminococcaceae, Streptococcaceae, and other bacterial phyla. A Mn-induced increase in Bacteroidetes abundance and a reduced Firmicutes/Bacteroidetes ratio may increase lipopolysaccharide levels. Moreover, in addition to increased systemic lipopolysaccharide (LPS) levels, Mn is capable of potentiating LPS neurotoxicity. Due to the high metabolic activity of intestinal microflora, Mn-induced perturbations in gut microbiota result in a significant alteration in the gut metabolome that has the potential to at least partially mediate the biological effects of Mn overexposure. At the same time, a recent study demonstrated that healthy microbiome transplantation alleviates Mn-induced neurotoxicity, which is indicative of the significant role of gut microflora in the cascade of Mn-mediated neurotoxicity. High doses of Mn may cause enterocyte toxicity and affect gut wall integrity through disruption of tight junctions. The resulting increase in gut wall permeability further promotes increased translocation of LPS and neuroactive bacterial metabolites to the systemic blood flow, ultimately gaining access to the brain and leading to neuroinflammation and neurotransmitter imbalance. Therefore, the existing data lead us to hypothesize that gut microbiota should be considered as a potential target of Mn toxicity, although more detailed studies are required to characterize the interplay between Mn exposure and the gut, as well as its role in the pathogenesis of neurodegeneration and other diseases.

Manganese exposure during early larval stages of C. elegans causes learning disability in the adult stage

Manganese (Mn), even though an essential trace element, causes neurotoxicity in excess. In adults, over-exposure to Mn causes clinical manifestations, including dystonia, progressive bradykinesia, disturbance of gait, slurring, and stuttering of speech. These symptoms are mainly because of Mn-associated oxidative stress and degeneration of dopamine neurons in the central nervous system. Children with excessive Mn exposure often show learning disabilities but rarely show symptoms associated with dopaminergic neuron dysfunction. It is unclear why Mn exposure shows distinctive clinical outcomes in developing brains versus adult brains. Studies on nematode C. elegans have demonstrated that it is an excellent model to elucidate Mn-associated toxicity in the nervous system. In this study, we chronically exposed Mn to L1 larval stage of the worms to understand the effects on dopamine neurons and cognitive development. The worms showed modified behavior to exogenous dopamine compared to the control. The dopamine neurons showed resistance to neurodegeneration on repeated Mn exposure during the adult stage. As observed in mammalian systems, these worms showed significantly low olfactory adaptive learning and memory. This study shows that C. elegans alters adaptive developmental plasticity during Mn overexposure, modifying its sensitivity towards the metal ion and leads to remodeling in its innate learning behavior.

Manganese and Movement Disorders: A Review.

Scientific and technological advances achieved with industrial expansion have led to an ever-increasing demand for heavy metals. This demand has, in turn, led to increased contamination of soil, water and air with these metals. Chronic exposure to metals may be detrimental not only to occupational workers but also to the nonoccupational population exposed to these metals. Manganese (Mn), a commonly used heavy metal, is an essential cofactor for many enzymatic processes that drive biological functions. However, it is also a potential source of neurotoxicity, particularly in the field of movement disorders. The typical manifestation of Mn overexposure is parkinsonism, which may be difficult to differentiate from the more common idiopathic Parkinson’s disease. In addition to environmental exposure to Mn, other potential etiologies causing hypermanganesemia include systemic health conditions, total parenteral nutrition and genetic mutations causing Mn dyshomeostasis. In this review, we critically analyze Mn and discuss its sources of exposure, pathophysiology and clinical manifestations. We have highlighted the global public health impact of Mn and emphasize that movement disorder specialists should record a detailed social and occupational history to ensure that a toxic etiology is not misdiagnosed as a neurodegenerative disease. In the absence of a definite therapeutic option, early diagnosis and timely institution of preventive measures are the keys to managing its toxic effects.

Manganese exposure induces permeability in renal glomerular endothelial cells via the Smad2/3-Snail-VE-cadherin axis.

Manganese (Mn) is an essential micronutrient. However, it is well established that Mn overexposure causes nervous system diseases. In contrast, there are few reports on the effects of Mn exposure on glomerular endothelium. In the present study, the potential effects of Mn exposure on glomerular endothelium were evaluated. Sprague Dawley rats were used as a model of Mn overexposure by intraperitoneal injection of MnCl2·H2O at 25mg/kg body weight. Mn exposure decreased expression of vascular endothelial-cadherin, a key component of adherens junctions, and increased exudate from glomeruli in Sprague Dawley rats. Human renal glomerular endothelial cells were cultured with different concentration of Mn. Exposure to 0.2 mM Mn increased permeability of human renal glomerular endothelial cell monolayers and decreased vascular endothelial-cadherin expression without inducing cytotoxicity. In addition, Mn exposure increased phosphorylation of mothers against decapentaplegic homolog 2/3 and upregulated expression of zinc finger protein SNAI1, a negative transcriptional regulator of vascular endothelial-cadherin. Our data suggest Mn exposure may contribute to development of glomerular diseases by inducing permeability of glomerular endothelium.

Does Manganese Contribute to Methamphetamine-Induced Psychosis?

This review describes the increasing global problem of methamphetamine (MA) use and development of psychosis, the molecular and structural basis for this form of psychosis, and its treatment. The putative contribution of manganese (Mn), a common element found widely in nature and industry, to the development of MA-induced psychosis is discussed in relation to its shared toxicity with MA. Both MA and Mn cause damage to brain monoaminergic, glutaminergic, and GABAergic systems and to the blood brain barrier, leading to higher exposure to Mn. Iron (Fe) deficiency can also lead to Mn overexposure. Polymorphisms for genes encoding metabolic enzymes and transport proteins increase risk of toxicity and development of psychosis. Impaired hepatic Mn excretion from viral hepatitis also risks Mn toxicity. It is possible that potential synergistic and/or additive effects of Mn in concert with MA may worsen, prolong, or shorten onset of psychosis.

Manganese-Induced Nephrotoxicity Is Mediated through Oxidative Stress and Mitochondrial Impairment

Manganese (Mn) is an essential element that is incorporated in various metabolic pathways and enzyme structures. On the other hand, a range of adverse effects has been described in association with Mn overexposure. Mn is a well-known neurotoxic agent in mammals. Renal injury is another adverse effect associated with Mn intoxication. No precise mechanism for Mn nephrotoxicity has been identified so far. The current study was designed to evaluate the potential mechanisms of Mn-induced renal injury. Rats were treated with Mn (20 and 40 mg/mL, respectively, in drinking water) for 30 consecutive days. Markers of oxidative stress, as well as several mitochondrial indices, were assessed in the kidney tissue. Renal injury was evident in Mn-treated animals, as judged by a significant increase in serum BUN and creatinine. Moreover, urinalysis revealed a significant increase in urine glucose, phosphate, and protein in Mn-treated rats. Kidney histopathological alterations, including tubular atrophy, interstitial inflammation, and necrosis, were also detected in Mn-treated animals. Biomarkers of oxidative stress, including an increment in reactive oxygen species (ROS), lipid peroxidation, and oxidized glutathione (GSSG), were detected in Mn-treated groups. On the other hand, kidney glutathione (GSH) stores and total antioxidant capacity were depleted in Mn groups. Mn exposure was associated with significant mitochondrial depolarization, decreased mitochondrial dehydrogenases activity, mitochondrial permeabilization, and depletion of adenosine tri-phosphate (ATP) content. These data highlight oxidative stress and mitochondrial impairment as potential mechanisms involved in Mn-induced renal injury.

Role of Astrocytes in Manganese Neurotoxicity Revisited.

Manganese (Mn) overexposure is a public health concern due to its widespread industrial usage and the risk for environmental contamination. The clinical symptoms of Mn neurotoxicity, or manganism, share several pathological features of Parkinson's disease (PD). Biologically, Mn is an essential trace element, and Mn in the brain is preferentially localized in astrocytes. This review summarizes the role of astrocytes in Mn-induced neurotoxicity, specifically on the role of neurotransmitter recycling, neuroinflammation, and genetics. Mn overexposure can dysregulate astrocytic cycling of glutamine (Gln) and glutamate (Glu), which is the basis for Mn-induced excitotoxic neuronal injury. In addition, reactive astrocytes are important mediators of Mn-induced neuronal damage by potentiating neuroinflammation. Genetic studies, including those with Caenorhabditis elegans (C. elegans) have uncovered several genes associated with Mn neurotoxicity. Though we have yet to fully understand the role of astrocytes in the pathologic changes characteristic of manganism, significant strides have been made over the last two decades in deciphering the role of astrocytes in Mn-induced neurotoxicity and neurodegeneration.

Blockade of nifedipine‐sensitive Ca2+ channels decreases manganese accumulation on the dopamine neurons

Manganese (Mn) is an essential trace element involved in many physiological processes. Mn is transported into the cells through a number of transporters. Overexposure to Mn leads to its accumulation in the basal ganglia where it induces circuit dysregulation and a Parkinson-like syndrome referred to as manganism. The mechanisms by which Mn regulates the intrinsic firing behaviors of dopamine neurons and how Mn overexposure dysregulates this activity are not well understood. In this study, we investigated Mn's modulation of the excitability, intrinsic firing activity, Ca2+ homeostasis, and voltage-gated Ca2 channel expression in mouse dopamine neurons. We found that Mn increases the spontaneous firing activity of dopamine neuron via a concentration-dependent mechanism (10–100mM). Analysis of action potential morphology revealed that Mn truncated the amplitude and narrowed the width of action potentials and reduced coefficients of variation of the interspike interval. Unexpectedly, we found neither removal of external Ca2+ (Ca2+-free), chelation of intracellular Ca2+, nor combined chelation of internal and external Ca2+ altered Mn-regulation of action potential in dopamine neurons. Therefore, we asked whether Mn alters Ca2+ currents via the voltage-gated Ca2+ channels in the dopamine neurons. We found that Mn suppressed the peak amplitude of Ca2+ channel-mediated currents, and blockade of Ca2+ channels prevented Mn-stimulation of firing rate, reduction of action potential amplitude in dopamine neurons, and reduced 54Mn uptake in the CaV1-2, CaV1-3 expressing cells (p< 0.05, n=8–10). Finally, in vivo magnetic resonance imaging (MEMRI) revealed nifidepine-blockade of Ca2+ channels decreased Mn accumulation in the midbrain region of C57BL mice (p<0.05, n=6–8). Our data suggest a potential mechanism by which Mn can induce defects in basal ganglia function, namely a marked increase the excitability of dopaminergic neurons. Mn increases the spontaneous firing activity of dopamine neurons. Blockade of L-type Ca2+ channels inhibited Mn-stimulation of spontaneous firing activity of dopamine neurons. Manganese enhanced magnetic resonance imaging (MEMRI) provides evidence of an in vivo calcium-dependent mechanism involved in midbrain Mn accumulation. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Sex differences in subacute manganese intoxication: Oxidative parameters and metal deposition in peripheral organs of adult Wistar rats

IntroductionManganese (Mn) is an essential element required for several biological systems. However, it is toxic in excessive accumulation. The toxic effects following Mn overexposure is well known in the CNS but other studies evaluating other target tissues remain scarce. ObjectiveThis study aimed to investigate sex-related differences in oxidative stress, metabolic parameters and Mn deposition in peripheral organs of Wistar rats exposed to subacute model of intoxication. MethodsMale and female adult Wistar rats received 6 or 15 mg/kg of MnCl2, intraperitoneally, 5 days a week, for 4 consecutive weeks to mimic subacute intoxication. Control group received sterile saline 0,9% following the same protocol. After this period, the metal accumulation, oxidative stress, mitochondrial activity and histological parameters in cardiac muscle, kidney, lungs and liver were analysed. ResultsIncreased Mn concentrations were found in all organs, especially kidneys. The cardiac muscle analysis revealed increased lipid peroxidation and decreasing of GSH levels in both doses of Mn in male and female rats. The increase of lipid peroxidation in liver was more evident in the male group, and there was a significant decrease of antioxidant capacity in males’ kidney. Nevertheless, there was an increase of mitochondrial complex I activity in kidney of females and increase of mitochondrial complex II activity in male group. Histological analysis revealed morphological changes in hepatic and pulmonary tissue. ConclusionTaken together, our results showed that subacute Mn exposure lead to significant metabolic, biochemical alterations especially in kidney and liver. Nevertheless, despite Mn deposition was virtually the same in the peripheral organs of male and female rats, it promotes different toxic effects between sexes.

Metal bashing: iron deficiency and manganese overexposure impact on peripheral nerves

ABSTRACTIron (Fe) deficiency (FeD) and manganese (Mn) overexposure (MnOE) may result in several neurological alterations in the nervous system. Iron deficiency produces unique neurological deficits due to its elemental role in central nervous system (CNS) development and myelination, which might persist after normalization of Fe in the diet. Conversely, MnOE is associated with diverse neurocognitive deficits. Despite these well-known neurotoxic effects on the CNS, the influence of FeD and MnOE on the peripheral nervous system (PNS) remains poorly understood. The aim of the present investigation was to examine the effects of developmental FeD and MnOE or their combination on the sciatic nerve of young and adult rats. The parameters measured included divalent metal transporter 1 (DMT1), transferrin receptor (TfR), myelin basic protein (MBP) and peripheral myelin protein 22 (PMP22) expression, as well as Fe levels in the nerve. Our results showed that FeD produced a significant reduction in MBP and PMP22 content at P29, which persisted at P60 after Fe-sufficient diet replenishment regardless of Mn exposure levels. At P60 MnOE significantly increased sciatic nerve Fe content and DMT1 expression. However, the combination of FeD and MnOE produced no marked motor skill impairment. Evidence indicates that FeD appears to hinder developmental peripheral myelination, while MnOE may directly alter Fe homeostasis. Further studies are required to elucidate the interplay between these pathological conditions.

Effects of Preweaning Manganese in Combination with Adult Striatal Dopamine Lesions on Monoamines, BDNF, TrkB, and Cognitive Function in Sprague-Dawley Rats.

Manganese (Mn) is an essential nutrient especially during development, but Mn overexposure (MnOE) produces long-term cognitive deficits. Evidence of long-term changes in dopamine in the neostriatum was found in rats from developmental MnOE previously. To examine the relationship between MnOE and dopamine, we tested whether the effects of developmental MnOE would be exaggerated by dopamine reductions induced by 6-hydroxydopamine (6-OHDA) neostriatal infusion when the rats were adults. The experiment consisted of four groups of females and males: Vehicle/Sham, MnOE/Sham, Vehicle/6-OHDA, and MnOE/6-OHDA. Both MnOE/Sham and Vehicle/6-OHDA groups displayed egocentric and allocentric memory deficits, whereas MnOE+6-OHDA had additive effects on spatial memory in the Morris water maze and egocentric learning in the Cincinnati water maze. 6-OHDA reduced dopamine in the neostriatum and nucleus accumbens, reduced norepinephrine in the hippocampus, reduced TH+ cells and TrkB and TH expression in the substantia nigra pars compacta (SNpc), but increased TrkB in the neostriatum. MnOE alone had no effect on monoamines or TrkB in the neostriatum or hippocampus but reduced BDNF in the hippocampus. A number of sex differences were noted; however, only a few significant interactions were found for MnOE and/or 6-OHDA exposure. These data further implicate dopamine and BDNF in the cognitive deficits arising from developmental MnOE.

Environmentally relevant manganese overexposure alters neural cell morphology and differentiation in vitro

Manganese (Mn) is a trace metal and micronutrient that is necessary for neurological function. Because of its ability to cross the blood brain barrier, excessive amounts of Mn are neurotoxic and can lead to a neurological disorder, manganism. Environmental overexposure to Mn correlates with impaired cognitive development in children. Though symptoms of manganism and overexposure are well defined, the changes in cellular mechanisms underlying these symptoms are not fully understood. We used cultured adult neural stem cells (NSCs) from young adult rats as an accessible model to investigate the effect of Mn on cellular mechanisms underlying neural differentiation. Concentrations of Mn below current EPA limits caused a dose- and time-dependent collapse of neurites and restructuring of cellular morphology. This effect was confirmed in B35 neuroblastoma cells. These findings indicate that Mn alters cytoskeleton dynamics during differentiation. In addition, Mn overexposure caused downregulation of DCX, a neuronal migration marker, and GFAP, a neural stem cell and astrocyte marker, in NSCs. We conclude that environmentally relevant concentrations of Mn impair cytoskeletal structure and morphology, and may impair differentiation in NSCs. These effects of Mn overexposure on brain cell function could underlie manganism and neurocognitive and developmental defects associated with environmental Mn overexposure.