Energy metabolism in astrocytes and neurons treated with manganese: relation among cell-specific energy failure, glucose metabolism, and intercellular trafficking using multinuclear NMR-spectroscopic analysis

Disulfiram Inhibits Opsonin-Independent Phagocytosis and Migration of Human Long-Lived In Vitro Cultured Phagocytes from Multiple Inflammatory Diseases

Disulfiram (DSF), an anti-alcoholism medicine, exerts treatment effects in patients suffering from persistent Borreliosis and also exhibits anti-cancer effects through its copper chelating derivatives and induction of oxidative stress in mitochondria. Since chronic/persistent borreliosis is characterized by increased amounts of pro-inflammatory macrophages, this study investigated opsonin-independent phagocytosis, migration, and surface marker expression of in vivo activated and in vitro cultured human monocyte-derived phagocytes (macrophages and dendritic cells) with and without DSF treatment. Phagocytosis of non-opsonized Dynabeads® M-450 and migration of macrophages and dendritic cells were monitored using live cell analyzer Juli™ Br for 24 h, imaging every 3.5 min. To simultaneously monitor phagocyte function, results were analyzed by a newly developed software based on the differential phase contrast images of cells before and after ingestion of Dynabeads. DSF decreased the phagocytic capacities exhibited by in vitro enriched and long-lived phagocytes. Although no chemotactic gradient was applied to the test system, vigorous spontaneous migration was observed. We therefore set up an algorithm to monitor and quantify both phagocytosis and migration simultaneously. DSF not only reduced phagocytosis in a majority of these long-lived phagocytes but also impaired their migration. Despite these selective effects by DSF, we found that DSF reduced the expression densities of surface antigens CD45 and CD14 in all of our long-lived phagocytes. In cells with a high metabolic activity and high mitochondrial contents, DSF led to cell death corresponding to mitochondrial oxidative stress, whereas metabolically inactive phagocytes survived our DSF treatment protocol. In conclusion, DSF affects the viability of metabolically active phagocytes by inducing mitochondrial stress and secondly attenuates phagocytosis and migration in some long-lived phagocytes.

An immobilization of 2-(Aminomethyl) thiazole on multi-walled carbon nanotubes used for rapid extraction of manganese ions in hepatic patients

A new method based on the immobilization of 2-(Aminomethyl) thiazole on the multi-walled carbon nanotubes (AMTZ@MWCNTs) was used to extract manganese (Mn) in the human blood, serum, and urine samples. First, 20 mg of AMTZ@MWCNTs, 0.2 mL of acetone, and 0.1 g of ionic liquid (IL) were completely mixed and injected into 2.0 mL human samples by a microscale syringe at pH 5.5. After shaking and centrifuging, the Mn ions were extracted and separated through the ultrasound-assisted- ionic liquid-dispersive micro solid-phase extraction (UAS-IL-D-μ-SPE) before being determined by the graphite furnace atomic absorption spectrometry (GF-AAS). According to the results, manganese in the blood of hepatic patients had higher concentrations than healthy people (Aged 25-60, 50 N). The Mn adsorption capacities for the AMTZ@MWCNTs and MWCNTs adsorbents were achieved at 192.5 mg/g and 26.3 mg/g, respectively. In the high enrichment factor (HEF), the limit of detection (LOD), linear range (LR), and mean relative standard division (RSD%) were calculated at 15 ng/L, 0.05-3.8 μg/L, and 2.34, respectively (n = 10). The methodology was validated using certified reference material (CRM) and spiking standard solutions to human samples.

The Link between Trace Metal Elements and Glucose Metabolism: Evidence from Zinc, Copper, Iron, and Manganese-Mediated Metabolic Regulation

Trace metal elements are of vital importance for fundamental biological processes. They function in various metabolic pathways after the long evolution of living organisms. Glucose is considered to be one of the main sources of biological energy that supports biological activities, and its metabolism is tightly regulated by trace metal elements such as iron, zinc, copper, and manganese. However, there is still a lack of understanding of the regulation of glucose metabolism by trace metal elements. In particular, the underlying mechanism of action remains to be elucidated. In this review, we summarize the current concepts and progress linking trace metal elements and glucose metabolism, particularly for the trace metal elements zinc, copper, manganese, and iron.

The interaction of ammonia and manganese in abnormal metabolism of minimal hepatic encephalopathy: A comparison metabolomics study

This study was to investigate the effects of ammonia and manganese in the metabolism of minimal hepatic encephalopathy (MHE). A total of 32 Sprague-Dawley rats were divided into four subgroups: chronic hyperammonemia (CHA), chronic hypermanganese (CHM), MHE and control group (CON). 1H-NMR-based metabolomics was used to detect the metabolic changes. Sparse projection to latent structures discriminant analysis was used for identifying and comparing the key metabolites. Significant elevated blood ammonia were shown in the CHA, CHM, and MHE rats. Significant elevated brain manganese (Mn) were shown in the CHM, and MHE rats, but not in the CHA rats. The concentrations of γ-amino butyric acid (GABA), lactate, alanine, glutamate, glutamine, threonine, and phosphocholine were significantly increased, and that of myo-inositol, taurine, leucine, isoleucine, arginine, and citrulline were significantly decreased in the MHE rats. Of all these 13 key metabolites, 10 of them were affected by ammonia (including lactate, alanine, glutamate, glutamine, myo-inositol, taurine, leucine, isoleucine, arginine, and citrulline) and 5 of them were affected by manganese (including GABA, lactate, myo-inositol, taurine, and leucine). Enrichment analysis indicated that abnormal metabolism of glutamine and TCA circle in MHE might be affected by the ammonia, and abnormal metabolism of GABA might be affected by the Mn, and abnormal metabolism of glycolysis and branched chain amino acids metabolism might be affected by both ammonia and Mn. Both ammonia and Mn play roles in the abnormal metabolism of MHE. Chronic hypermanganese could lead to elevated blood ammonia. However, chronic hyperammonemia could not lead to brain Mn deposition.

Ferrous sulfate reverses cerebral metabolic abnormality induced by minimal hepatic encephalopathy

Orally administered ferrous iron was previously reported to significantly improve the cognition and locomotion of patients with minimal hepatic encephalopathy (MHE). However, the metabolic mechanisms of the therapeutic effect of ferrous iron are unknown. In this study, MHE was induced in rats by partial portal vein ligation (PPVL), and was treated with ferrous sulfate. The Morris water maze was used to evaluate the cognitive condition of the rats. The metabolites observed by NMR and validated by liquid chromatography-mass spectrometry were defined as the key affected metabolites. The enzyme activities and trace element contents in the rat brains were also investigated. The Mn content was found to be increased but the ferrous iron content decreased in the cortex and striatum in MHE. Decreased oxoglutarate dehydrogenase activity and increased glutamine synthetase (GS) and pyruvate carboxylase (PC) activity were observed in the cortex of MHE rats. Decreased pyruvate dehydrogenase activity and increased GS and PC activity were observed in the striatum of MHE rats. The levels of BCAAs and taurine were significantly decreased, and the contents of GABA, lactate, arginine, aspartate, carnosine, citrulline, cysteine, glutamate, glutamine, glycine, methionine, ornithine, proline, threonine and tyrosine were significantly increased. These metabolic abnormalities described above were restored after treatment with ferrous sulfate. Pathway enrichment analysis suggested that urea cycle, aspartate metabolism, arginine and proline metabolism, glycine and serine metabolism, and glutamate metabolism were the major metabolic abnormalities in MHE rats, but these processes could be restored and cognitive impairment could be improved by ferrous sulfate administration.

Magnetic resonance spectroscopy and liquid chromatography-mass spectrometry metabolomics study may differentiate pre-eclampsia from gestational hypertension

OBJECTIVE

To investigate the findings of magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and serum metabolomics for differentiating pre-eclampsia (PE) from gestational hypertension (GH).

METHODS

This prospective study enrolled 176 subjects including a primary cohort with healthy non-pregnant women (HN, n = 35), healthy pregnant women (HP, n = 20), GH (n = 27), and PE (n = 39) and a validation cohort with HP (n = 22), GH (n = 22), and PE (n = 11). T1 signal intensity index (T1SI), apparent diffusion coefficient (ADC) value, and the metabolites on MRS were compared. The differentiating performances of single and combined MRI and MRS parameters for PE were evaluated. Serum liquid chromatography-mass spectrometry (LC-MS) metabolomics was investigated by sparse projection to latent structures discriminant analysis.

RESULTS

Increased T1SI, lactate/creatine (Lac/Cr), and glutamine and glutamate (Glx)/Cr and decreased ADC value and myo-inositol (mI)/Cr in basal ganglia were found in PE patients. T1SI, ADC, Lac/Cr, Glx/Cr, and mI/Cr yielded an area under the curves (AUC) of 0.90, 0.80, 0.94, 0.96, and 0.94 in the primary cohort, and of 0.87, 0.81, 0.91, 0.84, and 0.83 in the validation cohort, respectively. A combination of Lac/Cr, Glx/Cr, and mI/Cr yielded the highest AUC of 0.98 in the primary cohort and 0.97 in the validation cohort. Serum metabolomics analysis showed 12 differential metabolites, which are involved in pyruvate metabolism, alanine metabolism, glycolysis, gluconeogenesis, and glutamate metabolism.

CONCLUSIONS

MRS is expected to be a noninvasive and effective tool for monitoring GH patients to avoid the development of PE.

KEY POINTS

• Increased T1SI and decreased ADC value in the basal ganglia were found in PE patients than in GH patients. • Increased Lac/Cr and Glx/Cr, and decreased mI/Cr in the basal ganglia were found in PE patients than in GH patients. • LC-MS metabolomics showed that the major differential metabolic pathways between PE and GH were pyruvate metabolism, alanine metabolism, glycolysis, gluconeogenesis, and glutamate metabolism.

Mitochondrial Toxicant-Induced Neuronal Apoptosis in Parkinson's Disease: What We Know so Far

Parkinson's disease (PD) is one of the most common progressive neurodegenerative diseases caused by the loss of dopamine-producing neuronal cells in the region of substantia nigra pars compacta of the brain. During biological aging, neuronal cells slowly undergo degeneration, but the rate of cell death increases tremendously under some pathological conditions, leading to irreversible neurodegenerative diseases. By the time symptoms of PD usually appear, more than 50 to 60% of neuronal cells have already been destroyed. PD symptoms often start with tremors, followed by slow movement, stiffness, and postural imbalance. The etiology of PD is still unknown; however, besides genetics, several factors contribute to neurodegenerative disease, including exposure to pesticides, environmental chemicals, solvents, and heavy metals. Postmortem brain tissues of patients with PD show mitochondrial abnormalities, including dysfunction of the electron transport chain. Most chemicals present in our environment have been shown to target the mitochondria; remarkably, patients with PD show a mild deficiency in NADH dehydrogenase activity, signifying a possible link between PD and mitochondrial dysfunction. Inhibition of electron transport complexes generates free radicals that further attack the macromolecules leading to neuropathological conditions. Apart from that, oxidative stress also causes neuroinflammation-mediated neurodegeneration due to the activation of microglial cells. However, the mechanism that causes mitochondrial dysfunction, especially the electron transport chain, in the pathogenesis of PD remains unclear. This review discusses the recent updates and explains the possible mechanisms of mitochondrial toxicant-induced neuroinflammation and neurodegeneration in PD.

An Insight into the Molecular Mechanism of Mitochondrial Toxicant-induced Neuronal Apoptosis in Parkinson's Disease

Parkinson's disease (PD) is one of the most common progressive neurodegenerative disorders affecting approximately 1% of the world's population at the age of 50 and above. Majority of PD cases are sporadic and show symptoms after the age of 60 and above. At that time, most of the dopaminergic neurons in the region of substantia nigra pars compacta have been degenerated. Although in past decades, discoveries of genetic mutations linked to PD have significantly impacted our current understanding of the pathogenesis of this devastating disorder, it is likely that the environment also plays a critical role in the etiology of sporadic PD. Recent epidemiological and experimental studies indicate that exposure to environmental agents, including a number of agricultural and industrial chemicals, may contribute to the pathogenesis of several neurodegenerative disorders, including PD. Furthermore, there is a strong correlation between mitochondrial dysfunction and several forms of neurodegenerative disorders, including Alzheimer's disease (AD), Huntington's disease (HD), Amyotrophic lateral sclerosis (ALS) and PD. Interestingly, substantia nigra of patients with PD has been shown to have a mild deficiency in mitochondrial respiratory electron transport chain NADH dehydrogenase (Complex I) activity. This review discusses the role of mitochondrial toxicants in the selective degeneration of dopaminergic neurons targeting the electron transport system that leads to Parkinsonism.

Taurine and Astrocytes: A Homeostatic and Neuroprotective Relationship

Taurine is considered the most abundant free amino acid in the brain. Even though there are endogenous mechanisms for taurine production in neural cells, an exogenous supply of taurine is required to meet physiological needs. Taurine is required for optimal postnatal brain development; however, its brain concentration decreases with age. Synthesis of taurine in the central nervous system (CNS) occurs predominantly in astrocytes. A metabolic coupling between astrocytes and neurons has been reported, in which astrocytes provide neurons with hypotaurine as a substrate for taurine production. Taurine has antioxidative, osmoregulatory, and anti-inflammatory functions, among other cytoprotective properties. Astrocytes release taurine as a gliotransmitter, promoting both extracellular and intracellular effects in neurons. The extracellular effects include binding to neuronal GABAA and glycine receptors, with subsequent cellular hyperpolarization, and attenuation of N-methyl-D-aspartic acid (NMDA)-mediated glutamate excitotoxicity. Taurine intracellular effects are directed toward calcium homeostatic pathway, reducing calcium overload and thus preventing excitotoxicity, mitochondrial stress, and apoptosis. However, several physiological aspects of taurine remain unclear, such as the existence or not of a specific taurine receptor. Therefore, further research is needed not only in astrocytes and neurons, but also in other glial cells in order to fully comprehend taurine metabolism and function in the brain. Nonetheless, astrocyte’s role in taurine-induced neuroprotective functions should be considered as a promising therapeutic target of several neuroinflammatory, neurodegenerative and psychiatric diseases in the near future. This review provides an overview of the significant relationship between taurine and astrocytes, as well as its homeostatic and neuroprotective role in the nervous system.

Increased Dietary Manganese Impairs Neutrophil Extracellular Trap Formation Rendering Neutrophils Ineffective at Combating Staphylococcus aureus

Dietary metals can modify the risk to infection. Previously, we demonstrated that heightened dietary manganese (Mn) during systemic Staphylococcus aureus infection increases S. aureus virulence. However, immune cells also operate in these same environments and the effect of dietary Mn on neutrophil function in vivo has not been assessed. This study reveals that increased concentrations of Mn impairs mitochondrial respiration and superoxide production in neutrophils responding to S. aureus. As a result, high Mn accelerates primary degranulation, while impairing suicidal neutrophil extracellular trap (NET) formation, which decreases bactericidal activity. In vivo, elevated dietary Mn accumulated extracellularly in the heart, indicating that excess Mn may be more bioavailable in the heart. Coinciding with this phenotype, neutrophil function in the heart was most impacted by a high Mn diet, as neutrophils produced lower levels of mitochondrial superoxide and underwent less suicidal NET formation. Consistent with an ineffective neutrophil response when mice are on a high Mn diet, S. aureus burdens were increased in the heart and mice were more susceptible to systemic infection. Therefore, elevated dietary Mn not only affects S. aureus but also renders neutrophils less capable of restricting staphylococcal infection.

Manganese increases Aβ and Tau protein levels through proteasome 20S and heat shock proteins 90 and 70 alteration, leading to SN56 cholinergic cell death following single and repeated treatment

Manganese (Mn) produces cholinergic neuronal loss in basal forebrain (BF) region that was related to cognitive dysfunction induced after single and repeated Mn treatment. All processes that generate cholinergic neuronal loss in BF remain to be understood. Mn exposure may produce the reduction of BF cholinergic neurons by increasing amyloid beta (Aβ) and phosphorylated Tau (pTau) protein levels, altering heat shock proteins' (HSPs) expression, disrupting proteasome P20S activity and generating oxidative stress. These mechanisms, described to be altered by Mn in regions different than BF, could lead to the memory and learning process alteration produced after Mn exposure. The research performed shows that single and repeated Mn treatment of SN56 cholinergic neurons from BF induces P20S inhibition, increases Aβ and pTau protein levels, produces HSP90 and HSP70 proteins expression alteration, and oxidative stress generation, being the last two effects mediated by NRF2 pathway alteration. The increment of Aβ and pTau protein levels was mediated by HSPs and proteasome dysfunction. All these mechanisms mediated the cell decline observed after Mn treatment. Our results are relevant because they may assist to reveal the processes leading to the neurotoxicity and cognitive alterations observed after Mn exposure.

Brain manganese and the balance between essential roles and neurotoxicity

Manganese (Mn) is an essential micronutrient required for the normal development of many organs, including the brain. Although its roles as a cofactor in several enzymes and in maintaining optimal physiology are well-known, the overall biological functions of Mn are rather poorly understood. Alterations in body Mn status are associated with altered neuronal physiology and cognition in humans, and either overexposure or (more rarely) insufficiency can cause neurological dysfunction. The resultant balancing act can be viewed as a hormetic U-shaped relationship for biological Mn status and optimal brain health, with changes in the brain leading to physiological effects throughout the body and vice versa. This review discusses Mn homeostasis, biomarkers, molecular mechanisms of cellular transport, and neuropathological changes associated with disruptions of Mn homeostasis, especially in its excess, and identifies gaps in our understanding of the molecular and biochemical mechanisms underlying Mn homeostasis and neurotoxicity.

Taurine Treatment Provides Neuroprotection in a Mouse Model of Manganism

Manganese (Mn) is a trace element involved in many physiological processes. However, excessive Mn exposure leads to neurological complications. Although no precise mechanism(s) has been found for Mn-induced neurotoxicity, oxidative stress and mitochondrial injury seem to play a relevant role in this complication. On the other hand, there is no protective strategy against Mn neurotoxicity so far. Taurine is an amino acid with significant neuroprotective properties. The current study was designed to evaluate the effect of taurine supplementation and its potential mechanism(s) of action in a mouse model of manganism. Animals were treated with Mn (100 mg/kg, s.c) alone and/or in combination with taurine (50, 100, and 500 mg/kg, i.p, for eight consecutive days). Severe locomotor dysfunction along with a significant elevation in brain tissue biomarkers of oxidative stress was evident in Mn-exposed mice. On the other hand, it was revealed that mitochondrial indices of functionality were hampered in Mn-treated animals. Taurine supplementation (50, 100, and 500 mg/kg, i.p) alleviated Mn-induced locomotor deficit. Moreover, this amino acid mitigated oxidative stress biomarkers and preserved brain tissue mitochondrial indices of functionality. These data introduce taurine as a potential neuroprotective agent against Mn neurotoxicity. Antioxidative and mitochondria protecting effects of taurine might play a fundamental role in its neuroprotective properties against Mn toxicity.

Carnosine Mitigates Manganese Mitotoxicity in an In Vitro Model of Isolated Brain Mitochondria

Purpose: Manganese (Mn) is a neurotoxic chemical which induces a wide range of complications in the brain tissue. Impaired locomotor activity and cognitive dysfunction are associated with high brain Mn content. At the cellular level, mitochondria are potential targets for Mn toxicity. Carnosine is a dipeptide abundantly found in human brain. Several pharmacological properties including mitochondrial protecting and antioxidative effects have been attributed to carnosine. The current study aimed to evaluate the effect of carnosine treatment on Mn-induced mitochondrial dysfunction in isolated brain mitochondria.

Methods: Mice brain mitochondria were isolated based on the differential centrifugation method and exposed to increasing concentrations of Mn (10 µM-10 mM). Carnosine (1 mM) was added as the protective agent. Mitochondrial indices including mitochondrial depolarization, reactive oxygen species (ROS) formation, mitochondrial dehydrogenases activity, ATP content, and mitochondrial swelling and permeabilization were assessed.

Results: Significant deterioration in mitochondrial indices were evident in Mn-exposed brain mitochondria. On the other hand, it was found that carnosine (1 mM) treatment efficiently prevented Mn-induced mitochondrial impairment.

Conclusion: These data propose mitochondrial protection as a fundamental mechanism for the effects of carnosine against Mn toxicity. Hence, this peptide might be applicable against Mn neurotoxicity with different etiologies (e.g., in cirrhotic patients).

Prenatal manganese and cord blood mitochondrial DNA copy number: Effect modification by maternal anemic status

INTRODUCTION

Manganese (Mn) is an essential nutrient but also a toxicant at high exposures, when it can induce oxidative stress (OS). Mn uptake is inversely correlated with iron status, therefore anemic individuals may be more susceptible to Mn overload induced-OS, which can manifest as changes in mitochondrial DNA copy number (mtDNA CN). Our objectives were to: 1) determine stage-specific associations of prenatal Mn exposure with cord blood MtDNA CN; and 2) investigate effect modification by maternal anemia, ferritin, and mean corpuscular volume (MCV).

MATERIALS AND METHODS

We measured whole blood Mn, hemoglobin, serum ferritin, and MCV in the 2nd and 3rd trimester, in maternal blood at birth, and in cord blood from a prospective birth cohort in Mexico City, Mexico (n = 485). We then extracted DNA from cord blood leukocytes to determine mtDNA CN. We used robust regression to measure associations between Mn and mtDNA CN at each trimester and at birth. Anemia (hemoglobin ≤11 g/dL), iron deficiency (ferritin ≤15 ng/mL) and MCV (stratified at median), were examined as effect modifiers.

RESULTS

Mn levels increased throughout pregnancy, and Mn was inversely correlated with ferritin. We observed a positive association between Mn in the 3rd trimester and Mn in cord blood and mtDNA CN (β = 0.04-0.05; 95% CI = 0.01, 0.08). Anemia significantly modified the association between mtDNA CN and Mn in the 2nd trimester. We found a positive association between 2nd trimester Mn and mtDNA CN in mothers with normal hemoglobin, and a negative association in those with low hemoglobin. (βhigh = 0.06; 95% CI = 0.01, 0.11; p = 0.01 and βlow = -0.06; 95% CI = 0.03, -0.13; p = 0.06). No associations were detected between anemia, iron deficiency and MCV and mtDNA CN.

CONCLUSIONS

Maternal blood Mn in the 3rd trimester and in cord blood was positively associated with mtDNA CN, suggesting that higher late pregnancy prenatal Mn exposures can impact newborn mitochondria by promoting OS. Furthermore, 2nd trimester Mn was positively associated with mtDNA in non-anemic mother-child pairs but inversely associated in anemic individuals, indicating potential interactions between Mn and chronic anemia.

Environmental neurotoxicant-induced dopaminergic neurodegeneration: a potential link to impaired neuroinflammatory mechanisms

With the increased incidence of neurodegenerative diseases worldwide, Parkinson's disease (PD) represents the second-most common neurodegenerative disease. PD is a progressive multisystem neurodegenerative disorder characterized by a marked loss of nigrostriatal dopaminergic neurons and the formation of Lewy pathology in diverse brain regions. Although the mechanisms underlying dopaminergic neurodegeneration remain poorly characterized, data from animal models and postmortem studies have revealed that heightened inflammatory responses mediated via microglial and astroglial activation and the resultant release of proinflammatory factors may act as silent drivers of neurodegeneration. In recent years, numerous studies have demonstrated a positive association between the exposure to environmental neurotoxicants and the etiology of PD. Although it is unclear whether neuroinflammation drives pesticide-induced neurodegeneration, emerging evidence suggests that the failure to dampen neuroinflammatory mechanisms may account for the increased vulnerability to pesticide neurotoxicity. Furthermore, recent studies provide additional evidence that shifts the focus from a neuron-centric view to glial-associated neurodegeneration following pesticide exposure. In this review, we propose to summarize briefly the possible factors that regulate neuroinflammatory processes during environmental neurotoxicant exposure with a focus on the potential roles of mitochondria-driven redox mechanisms. In this context, a critical discussion of the data obtained from experimental research and possible epidemiological studies is included. Finally, we hope to provide insights on the pivotal role of exosome-mediated intercellular transmission of aggregated proteins in microglial activation response and the resultant dopaminergic neurodegeneration after exposure to pesticides. Collectively, an improved understanding of glia-mediated neuroinflammatory signaling might provide novel insights into the mechanisms that contribute to neurodegeneration induced by environmental neurotoxicant exposure.

The neuroprotective properties of carnosine in a mouse model of manganism is mediated via mitochondria regulating and antioxidative mechanisms

Objective(s): Manganese (Mn) is an essential trace element physiologically incorporated in the structure of several vital enzymes. Despite its essentiality, excessive Mn exposure is toxic with brain tissue as the primary target organ. There is no specific and clinically available therapeutic/preventive option against Mn neurotoxicity. Carnosine is a neuropeptide with several physiological roles. The neuroprotective properties of this peptide have been evaluated in different experimental models. The current study was designed to investigate the effect of carnosine supplementation and its potential mechanisms of action in an animal model of Mn-induced neurotoxicity. Materials and Methods: Male C57BL/6 mice received Mn (100 mg/kg, s.c) alone and/or in combination with carnosine (10, 50, and 100 mg/kg, i.p). Several locomotor activity indices were monitored. Moreover, biomarkers of oxidative stress and mitochondrial function were assessed in the brain tissue of Mn-exposed animals. Results: Significant locomotor dysfunction was revealed in Mn-exposed animals. Furthermore, brain tissue biomarkers of oxidative stress were significantly increased, and mitochondrial indices of functionality were impaired in Mn-treated animals. It was found that carnosine supplementation (10, 50, and 100 mg/kg, i.p) alleviated the Mn-induced locomotor deficit. Moreover, this peptide mitigated oxidative stress biomarkers and preserved brain tissue mitochondrial functionality in the animal model of manganism. Conclusion: These data indicate that carnosine is a potential neuroprotective agent against Mn neurotoxicity. Antioxidative and mitochondria protecting effects of carnosine might play a fundamental role in its neuroprotective properties against Mn toxicity.

Affected energy metabolism under manganese stress governs cellular toxicity

Excessive manganese exposure is toxic, but a comprehensive biochemical picture of this assault is poorly understood. Whether oxidative stress or reduced energy metabolism under manganese exposure causes toxicity is still a debate. To address this, we chose ΔmntPEscherichia coli, a highly manganese-sensitive strain, in this study. Combining microarray, proteomics, and biochemical analyses, we show that the chronic manganese exposure rewires diverse regulatory and metabolic pathways. Manganese stress affects protein and other macromolecular stability, and envelope biogenesis. Most importantly, manganese exposure disrupts both iron-sulfur cluster and heme-enzyme biogenesis by depleting cellular iron level. Therefore, the compromised function of the iron-dependent enzymes in the tricarboxylic acid cycle, and electron transport chain impede ATP synthesis, leading to severe energy deficiency. Manganese stress also evokes reactive oxygen species, inducing oxidative stress. However, suppressing oxidative stress does not improve oxidative phosphorylation and cell growth. On the contrary, iron supplementation resumed cell growth stimulating oxidative phosphorylation. Therefore, we hypothesize that affected energy metabolism is the primal cause of manganese toxicity.

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

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

Magnetic Resonance Spectroscopy for Evaluating Portal-Systemic Encephalopathy in Patients with Chronic Hepatic Schistosomiasis Japonicum

Portal-systemic encephalopathy (PSE) is classified as type B hepatic encephalopathy. Portal-systemic shunting rather than liver dysfunction is the main cause of PSE in chronic hepatic schistosomiasis japonicum (HSJ) patients. Owing to lack of detectable evidence of intrinsic liver disease, chronic HSJ patients with PSE are frequently clinically undetected or misdiagnosed, especially chronic HSJ patients with covert PSE (subclinical encephalopathy). In this study, we investigated whether magnetic resonance spectroscopy (MRS) could be a useful tool for diagnosing PSE in chronic HSJ patients. Magnetic resonance (MR) T1-weighted imaging, diffusion-weighted imaging, and MRS were performed in 41 chronic HSJ patients with suspected PSE and in 21 age-matched controls. The T1 signal intensity index (T1SI) and apparent diffusion coefficient (ADC) value were obtained in the Globus pallidus. Liver function was also investigated via serum ammonia and liver function tests. Higher T1SI and ADC values, increased lactate and glutamine levels, and decreased myo-inositol were found in the bilateral Globus pallidus in chronic HSJ patients with PSE. No significantly abnormal serum ammonia or liver function tests were observed in chronic HSJ patients with PSE. On the basis of these findings, we propose a diagnostic procedure for PSE in chronic HSJ patients. This study reveals that MRS can be useful for diagnosing PSE in chronic HSJ patients.

Portal-systemic encephalopathy (PSE) is classified as type B hepatic encephalopathy. Portal-systemic shunting rather than liver dysfunction is the main cause of PSE in chronic hepatic schistosomiasis japonicum (HSJ) patients. Chronic HSJ patients with PSE are frequently misdiagnosed as suffering from dementia, depression, and other psychiatric disorders. However, there are few studies of this type of encephalopathy. In this study, magnetic resonance spectroscopy (MRS) was used as a noninvasive tool to detect abnormalities in brain metabolism in chronic HSJ patient with PSE. The results demonstrate that MRS would be useful for the diagnosis of PSE in chronic HSJ patients. Based on the results, a diagnostic procedure for PSE has also been proposed.

Sodium Para-aminosalicylic Acid Protected Primary Cultured Basal Ganglia Neurons of Rat from Manganese-Induced Oxidative Impairment and Changes of Amino Acid Neurotransmitters

Manganese (Mn), an essential trace metal for protein synthesis and particularly neurotransmitter metabolism, preferentially accumulates in basal ganglia. However, excessive Mn accumulation may cause neurotoxicity referred to as manganism. Sodium para-aminosalicylic acid (PAS-Na) has been used to treat manganism with unclear molecular mechanisms. Thus, we aim to explore whether PAS-Na can inhibit Mn-induced neuronal injury in basal ganglia in vitro. We exposed basal ganglia neurons with 50 μM manganese chloride (MnCl2) for 24 h and then replaced with 50, 150, and 450 μM PAS-Na treatment for another 24 h. MnCl2 significantly decreased cell viability but increased leakage rate of lactate dehydrogenase and DNA damage (as shown by increasing percentage of DNA tail and Olive tail moment). Mechanically, Mn reduced glutathione peroxidase and catalase activity and interrupted amino acid neurotransmitter balance. However, PAS-Na treatment reversed the aforementioned Mn-induced toxic effects. Taken together, these results showed that PAS-Na could protect basal ganglia neurons from Mn-induced neurotoxicity.

The autophagic- lysosomal pathway determines the fate of glial cells under manganese- induced oxidative stress conditions

Manganese (Mn) overexposure is frequently associated with the development of a neurodegenerative disorder known as Manganism. The Mn-mediated generation of reactive oxygen species (ROS) promotes cellular damage, finally leading to apoptotic cell death in rat astrocytoma C6 cells. In this scenario, the autophagic pathway could play an important role in preventing cytotoxicity. In the present study, we found that Mn induced an increase in the amount and total volume of acidic vesicular organelles (AVOs), a process usually related to the activation of the autophagic pathway. Particularly, the generation of enlarged AVOs was a ROS- dependent event. In this report we demonstrated for the first time that Mn induces autophagy in glial cells. This conclusion emerged from the results obtained employing a battery of autophagy markers: a) the increase in LC3-II expression levels, b) the formation of autophagic vesicles labeled with monodansylcadaverine (MDC) or LC3 and, c) the increase in Beclin 1/ Bcl-2 and Beclin 1/ Bcl-X(L) ratio. Autophagy inhibition employing 3-MA and mAtg5(K130R) resulted in decreased cell viability indicating that this event plays a protective role in Mn- induced cell death. In addition, mitophagy was demonstrated by an increase in LC3 and TOM-20 colocalization. On the other hand, we proposed the occurrence of lysosomal membrane permeabilization (LMP) based in the fact that cathepsins B and D activities are essential for cell death. Both cathepsin B inhibitor (Ca-074 Me) or cathepsin D inhibitor (Pepstatin A) completely prevented Mn- induced cytotoxicity. In addition, low dose of Bafilomycin A1 showed a similar effect, a finding that adds evidence about the lysosomal role in Mn cytotoxicity. Finally, in vivo experiments demonstrated that Mn induces injury and alters LC3 expression levels in rat striatal astrocytes. In summary, our results demonstrated that autophagy is activated to counteract the harmful effect caused by Mn. These data is valuable to be considered in future research concerning Manganism therapies.

Changes in Brain Metallome/Metabolome Pattern due to a Single i.v. Injection of Manganese in Rats

Exposure to high concentrations of Manganese (Mn) is known to potentially induce an accumulation in the brain, leading to a Parkinson related disease, called manganism. Versatile mechanisms of Mn-induced brain injury are discussed, with inactivation of mitochondrial defense against oxidative stress being a major one. So far, studies indicate that the main Mn-species entering the brain are low molecular mass (LMM) compounds such as Mn-citrate. Applying a single low dose MnCl₂ injection in rats, we observed alterations in Mn-species pattern within the brain by analysis of aqueous brain extracts by size-exclusion chromatography—inductively coupled plasma mass spectrometry (SEC-ICP-MS). Additionally, electrospray ionization—ion cyclotron resonance-Fourier transform-mass spectrometry (ESI-ICR/FT-MS) measurement of methanolic brain extracts revealed a comprehensive analysis of changes in brain metabolisms after the single MnCl₂ injection. Major alterations were observed for amino acid, fatty acid, glutathione, glucose and purine/pyrimidine metabolism. The power of this metabolomic approach is the broad and detailed overview of affected brain metabolisms. We also correlated results from the metallomic investigations (Mn concentrations and Mn-species in brain) with the findings from metabolomics. This strategy might help to unravel the role of different Mn-species during Mn-induced alterations in brain metabolism.

Mitochondrial Redox Dysfunction and Environmental Exposures

SIGNIFICANCE

Mitochondria are structurally and biochemically diverse, even within a single type of cell. Protein complexes localized to the inner mitochondrial membrane synthesize ATP by coupling electron transport and oxidative phosphorylation. The organelles produce reactive oxygen species (ROS) from mitochondrial oxygen and ROS can, in turn, alter the function and expression of proteins used for aerobic respiration by post-translational and transcriptional regulation.

RECENT ADVANCES

New interest is emerging not only into the roles of mitochondria in disease development and progression but also as a target for environmental toxicants.

CRITICAL ISSUES

Dysregulation of respiration has been linked to cell death and is a major contributor to acute neuronal trauma, peripheral diseases, as well as chronic neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease.

FUTURE DIRECTIONS

Here, we discuss the mechanisms underlying the sensitivity of the mitochondrial respiratory complexes to redox modulation, as well as examine the effects of environmental contaminants that have well-characterized mitochondrial toxicity. The contaminants discussed in this review are some of the most prevalent and potent environmental contaminants that have been linked to neurological dysfunction, altered cellular respiration, and oxidation.

Manganese-Induced Parkinsonism and Parkinson's Disease: Shared and Distinguishable Features

Manganese (Mn) is an essential trace element necessary for physiological processes that support development, growth and neuronal function. Secondary to elevated exposure or decreased excretion, Mn accumulates in the basal ganglia region of the brain and may cause a parkinsonian-like syndrome, referred to as manganism. The present review discusses the advances made in understanding the essentiality and neurotoxicity of Mn. We review occupational Mn-induced parkinsonism and the dynamic modes of Mn transport in biological systems, as well as the detection and pharmacokinetic modeling of Mn trafficking. In addition, we review some of the shared similarities, pathologic and clinical distinctions between Mn-induced parkinsonism and Parkinson’s disease. Where possible, we review the influence of Mn toxicity on dopamine, gamma aminobutyric acid (GABA), and glutamate neurotransmitter levels and function. We conclude with a survey of the preventive and treatment strategies for manganism and idiopathic Parkinson’s disease (PD).

Enhanced analgesic effects of tramadol and common trace element coadministration in mice

Chronic pain is managed mostly by the daily administration of analgesics. Tramadol is one of the most commonly used drugs, marketed in combination with coanalgesics for enhanced effect. Trace elements are frequent ingredients in dietary supplements and may enhance tramadol's analgesic effect either through synergic mechanisms or through analgesic effects of their own. Swiss Weber male mice were divided into nine groups and were treated with a combination of the trace elements Mg, Mn, and Zn in three different doses and a fixed dose of tramadol. Two groups served as positive (tramadol alone) and negative (saline) controls. Nociceptive assessment by tail-flick (TF) and hot-plate (HP) tests was performed at baseline and at 15, 30, 45, and 60 min after intraperitoneal administration. Response latencies were recorded and compared with the aid of ANOVA testing. All three trace elements enhanced tramadol's analgesic effect, as assessed by TF and HP test latencies. Coadministration of these trace elements led to an increase of approximately 30% in the average pain inhibition compared with the tramadol-alone group. The most effective doses were 0.6 mg/kg b.w. for Zn, 75 mg/kg b.w. for Mg, and 7.2 mg/kg b.w. for Mn. Associating trace elements such as Zn, Mg, and Mn with the standard administration of tramadol increases the drug's analgesic effect, most likely a consequence of their synergic action. These findings impact current analgesic treatment because the addition of these trace elements may reduce the tramadol dose required to obtain analgesia.

Differential interaction of hGDH1 and hGDH2 with manganese: Implications for metabolism and toxicity

Manganese (Mn) is an essential trace element that serves as co-factor for many important mammalian enzymes. In humans, the importance of this cation is highlighted by the fact that low levels of Mn cause developmental and metabolic abnormalities and, on the other hand, chronic exposure to excessive amounts of Mn is characterized by neurotoxicity, possibly mediated by perturbation of astrocytic mitochondrial energy metabolism. Here we sought to study the effect of Mn on the two human glutamate dehydrogenases (hGDH1 and hGDH2, respectively), key mitochondrial enzymes involved in numerous cellular processes, including mitochondrial metabolism, glutamate homeostasis and neurotransmission, and cell signaling. Our studies showed that, compared to magnesium (Mg) and calcium (Ca), Mn exerted a significant inhibitory effect on both human isoenzymes with hGDH2 being more sensitive than hGDH1, especially under conditions of low ADP levels. Specifically, in the presence of 0.25 mM ADP, the Mn IC50 was 1.14 ± 0.02 mM and 1.54 ± 0.08 mM for hGDH2 and for hGDH1, respectively (p = 0.0001). Increasing Mn levels potentiated this differential effect, with 3 mM Mn inhibiting hGDH2 by 96.5% and hGDH1 by 70.2%. At 1 mM ADP, the Mn IC50 was 1.84 ± 0.02 mM and 2.04 ± 0.07 mM (p = 0.01) for hGDH2 and hGDH1, respectively, with 3 mM Mn inhibiting hGDH2 by 93.6% and hGDH1 by 70.9%. These results were due to the sigmoidal inhibitory curve of Mn that was more pronounced for hGDH2 than for hGDH1. Indeed, at 0.25 mM, the Hill coefficient value was higher for hGDH2 (3.42 ± 0.20) than for hGDH1 (1.94 ± 0.25; p = 0.0002) indicating that interaction of Mn with hGDH2 was substantially more co-operative than for hGDH1. These findings, showing an enhanced sensitivity of the hGDH2 isoenzyme to Mn, especially at low ADP levels, might be of pathophysiological relevance under conditions of Mn neurotoxicity.

Impact of manganese on the hippocampus metabolism in the context of MEMRI: a proton HRMAS MRS study

The HRMAS spectrum revealed an important impact of Mn 500 nmol on the hippocampal metabolism, not observed with Mn 8 nmol.

Manganese-enhanced magnetic resonance imaging reveals increased DOI-induced brain activity in a mouse model of schizophrenia

Maternal infection during pregnancy increases the risk for schizophrenia in offspring. In rodent models, maternal immune activation (MIA) yields offspring with schizophrenia-like behaviors. None of these behaviors are, however, specific to schizophrenia. The presence of hallucinations is a key diagnostic symptom of schizophrenia. In mice, this symptom can be defined as brain activation in the absence of external stimuli, which can be mimicked by administration of hallucinogens. We find that, compared with controls, adult MIA offspring display an increased stereotypical behavioral response to the hallucinogen 2,5-dimethoxy-4-iodoamphetamine (DOI), an agonist for serotonin receptor 2A (5-HT2AR). This may be explained by increased levels of 5-HT2AR and downstream signaling molecules in unstimulated MIA prefrontal cortex (PFC). Using manganese-enhanced magnetic resonance imaging to identify neuronal activation elicited by DOI administration, we find that, compared with controls, MIA offspring exhibit a greater manganese (Mn(2+)) accumulation in several brain areas, including the PFC, thalamus, and striatum. The parafascicular thalamic nucleus, which plays the role in the pathogenesis of hallucinations, is activated by DOI in MIA offspring only. Additionally, compared with controls, MIA offspring demonstrate higher DOI-induced expression of early growth response protein 1, cyclooxygenase-2, and brain-derived neurotrophic factor in the PFC. Chronic treatment with the 5-HT2AR antagonist ketanserin reduces DOI-induced head twitching in MIA offspring. Thus, the MIA mouse model can be successfully used to investigate activity induced by DOI in awake, behaving mice. Moreover, manganese-enhanced magnetic resonance imaging is a useful, noninvasive method for accurately measuring this type of activity.

Activation of MAPK and FoxO by manganese (Mn) in rat neonatal primary astrocyte cultures

Environmental exposure to manganese (Mn) leads to a neurodegenerative disease that has shared clinical characteristics with Parkinson's disease (PD). Mn-induced neurotoxicity is time- and dose-dependent, due in part to oxidative stress. We ascertained the molecular targets involved in Mn-induced neurodegeneration using astrocyte culture as: (1) Astrocytes are vital for information processing within the brain, (2) their redox potential is essential in mitigating reactive oxygen species (ROS) levels, and (3) they are targeted early in the course of Mn toxicity. We first tested protein levels of Mn superoxide dismutase -2 (SOD-2) and glutathione peroxidase (GPx-1) as surrogates of astrocytic oxidative stress response. We assessed levels of the forkhead winged-helix transcription factor O (FoxO) in response to Mn exposure. FoxO is highly regulated by the insulin-signaling pathway. FoxO mediates cellular responses to toxic stress and modulates adaptive responses. We hypothesized that FoxO is fundamental in mediating oxidative stress response upon Mn treatment, and may be a biomarker of Mn-induced neurodegeneration. Our results indicate that 100 or 500 µM of MnCl₂ led to increased levels of FoxO (dephosphorylated and phosphorylated) compared with control cells (P<0.01). p-FoxO disappeared from the cytosol upon Mn exposure. Pre-treatment of cultured cells with (R)-(−)-2-oxothiazolidine-4-carboxylic acid (OTC), a cysteine analog rescued the cytosolic FoxO. At these concentrations, MAPK phosphorylation, in particular p38 and ERK, and PPAR gamma coactivator-1 (PGC-1) levels were increased, while AKT phosphorylation remained unchanged. FoxO phosphorylation level was markedly reduced with the use of SB203580 (a p38 MAPK inhibitor) and PD98059 (an ERK inhibitor). We conclude that FoxO phosphorylation after Mn exposure occurs in parallel with, and independent of the insulin-signaling pathway. FoxO levels and its translocation into the nucleus are part of early events compensating for Mn-induced neurotoxicity and may serve as valuable targets for neuroprotection in the setting of Mn-induced neurodegeneration.

Protective role of sodium para-amino salicylic acid against manganese-induced hippocampal neurons damage

Manganese (Mn) is an essential trace element of human. However, excessive Mn can cause manganism. Mn selectively accumulated in Mn-exposed workers' hippocampus which is crucial for higher brain functions such as learning, memory, and motivation during our postnatal life. Studies suggested sodium para-aminosalicylic acid (PAS) appeared to be therapeutic for manganism. We aimed to explore whether PAS could block Mn-induced neuronal injury in hippocampus in vitro. Hippocampal neurons were exposed to 50 μM manganese chloride (MnCl(2)) for 24 h, following by 50, 500, or 5000 μM PAS treatment for 24 h. Cell viability, apoptosis rate, mean fluorescence intensity of mitochondrial and DNA damage were respectively performed. MnCl(2) significantly decreased neurons' viability and fluorescence intensity of comet head of DNA, while increasing the apoptosis rate, mean fluorescence intensity of mitochondrial, percentage of tail DNA, and Olive tail moment of DNA. PAS reduced the percentage of tail DNA and Olive tail moment of Mn-exposed neurons. These data suggested that Mn caused hippocampal neurons' injury, and 50-5000 μM PAS could inhibit Mn-induced DNA damage.

Vulnerability of welders to manganese exposure--a neuroimaging study

Increased manganese (Mn) exposure is known to cause cognitive, psychiatric and motor deficits. Mn exposure occurs in different occupational settings, where the airborne Mn level and the size of respirable particulates may vary considerably. Recently the importance of the role of the cerebral cortex in Mn toxicity has been highlighted, especially in Mn-induced neuropsychological effects. In this study we used magnetic resonance imaging (MRI) to evaluate brain Mn accumulation using T1 signal intensity indices and to examine changes in brain iron content using T2* contrast, as well as magnetic resonance spectroscopy (MRS) to measure exposure-induced metabolite changes non-invasively in cortical and deep brain regions in Mn-exposed welders, Mn-exposed smelter workers and control factory workers with no measurable exposure to Mn. MRS data as well as T1 signal intensity indices and T2* values were acquired from the frontal cortex, posterior cingulate cortex, hippocampus, and thalamus. Smelters were exposed to higher air Mn levels and had a longer duration of exposure, which was reflected in higher Mn levels in erythrocytes and urine than in welders. Nonetheless, welders had more significant metabolic differences compared to controls than did the smelter workers, especially in the frontal cortex. T1 hyperintensities in the globus pallidus were observed in both Mn-exposed groups, but only welders showed significantly higher thalamic and hippocampal T1 hyperintensities, as well as significantly reduced T2* values in the frontal cortex. Our results indicate that (1) the cerebral cortex, in particular the frontal cortex, is clearly involved in Mn neurotoxic effects and (2) in spite of the lower air Mn levels and shorter duration of exposure, welders exhibit more extensive neuroimaging changes compared to controls than smelters, including measurable deposition of Mn in more brain areas. These results indicate that the type of exposure (particulate sizes, dust versus fume) and route of exposure play an important role in the extent of Mn-induced toxic effects on the brain.

Manganese neurotoxicity and the role of reactive oxygen species

Manganese (Mn) is an essential dietary nutrient, but an excess or accumulation can be toxic. Disease states, such as manganism, are associated with overexposure or accumulation of Mn and are due to the production of reactive oxygen species, free radicals, and toxic metabolites; alteration of mitochondrial function and ATP production; and depletion of cellular antioxidant defense mechanisms. This review focuses on all of the preceding mechanisms and the scientific studies that support them as well as providing an overview of the absorption, distribution, and excretion of Mn and the stability and transport of Mn compounds in the body.

Hypothalamic metabolic compartmentation during appetite regulation as revealed by magnetic resonance imaging and spectroscopy methods

We review the role of neuroglial compartmentation and transcellular neurotransmitter cycling during hypothalamic appetite regulation as detected by Magnetic Resonance Imaging (MRI) and Spectroscopy (MRS) methods. We address first the neurochemical basis of neuroendocrine regulation in the hypothalamus and the orexigenic and anorexigenic feed-back loops that control appetite. Then we examine the main MRI and MRS strategies that have been used to investigate appetite regulation. Manganese-enhanced magnetic resonance imaging (MEMRI), Blood oxygenation level-dependent contrast (BOLD), and Diffusion-weighted magnetic resonance imaging (DWI) have revealed Mn²⁺ accumulations, augmented oxygen consumptions, and astrocytic swelling in the hypothalamus under fasting conditions, respectively. High field ¹H magnetic resonance in vivo, showed increased hypothalamic myo-inositol concentrations as compared to other cerebral structures. ¹H and ¹³C high resolution magic angle spinning (HRMAS) revealed increased neuroglial oxidative and glycolytic metabolism, as well as increased hypothalamic glutamatergic and GABAergic neurotransmissions under orexigenic stimulation. We propose here an integrative interpretation of all these findings suggesting that the neuroendocrine regulation of appetite is supported by important ionic and metabolic transcellular fluxes which begin at the tripartite orexigenic clefts and become extended spatially in the hypothalamus through astrocytic networks becoming eventually MRI and MRS detectable.

Role of astrocytes in manganese mediated neurotoxicity

Astrocytes are responsible for numerous aspects of metabolic support, nutrition, control of the ion and neurotransmitter environment in central nervous system (CNS). Failure by astrocytes to support essential neuronal metabolic requirements plays a fundamental role in the pathogenesis of brain injury and the ensuing neuronal death. Astrocyte-neuron interactions play a central role in brain homeostasis, in particular via neurotransmitter recycling functions. Disruption of the glutamine (Gln)/glutamate (Glu) -γ-aminobutyric acid (GABA) cycle (GGC) between astrocytes and neurons contributes to changes in Glu-ergic and/or GABA-ergic transmission, and is associated with several neuropathological conditions, including manganese (Mn) toxicity. In this review, we discuss recent advances in support of the important roles for astrocytes in normal as well as neuropathological conditions primarily those caused by exposure to Mn.

Complex II of the mitochondrial respiratory chain is the key mediator of divalent manganese-induced hydrogen peroxide production in microglia

Exposure to excessive levels of manganese (Mn) is associated with the development of movement disorders, with symptoms overlapping with Parkinson's disease. Oxidative damage has been implicated as a key contributor to Mn-induced neurotoxicity. We have recently reported that divalent Mn (Mn(2+)) stimulates brain microglia to produce and release hydrogen peroxide (H2O2), and microglial-free radical generation facilitates Mn(2+)-induced dopaminergic neurotoxicity. The goal of this study was to elucidate the underlying mechanism of the Mn(2+)-induced H2O2 production in microglia. Exposure to low micromolar concentrations of Mn(2+), but not divalent copper, cadmium, nickel, cobalt, zinc, and iron, induced a significant production of H2O2 from rat microglial but not astroglial cells. Subcellular fractionation studies revealed that Mn(2+) was capable of inducing significant H2O2 production in the mitochondrial but not the cytosolic or nuclear fraction prepared from microglia. Analysis of the relative contribution of mitochondrial respiratory chain complexes indicated that Mn(2+)-induced mitochondrial H2O2 production required the presence of complex II substrate succinate. In contrast, complex I substrates malate and glutamate failed to support H2O2 production in the presence of Mn(2+). Furthermore, the succinate-supported Mn(2+)-induced mitochondrial H2O2 production was abolished by pharmacological inhibition of complex II but not that of complexes I and III, suggesting that mitochondrial complex II is a key mediator in Mn(2+)-induced H2O2 production. These findings advance our knowledge on the mechanisms by which Mn induces oxidative stress and the potential contribution to Mn neurotoxicity.

Manganese in health and disease

Manganese is an important metal for human health, being absolutely necessary for development, metabolism, and the antioxidant system. Nevertheless, excessive exposure or intake may lead to a condition known as manganism, a neurodegenerative disorder that causes dopaminergic neuronal death and parkinsonian-like symptoms. Hence, Mn has a paradoxal effect in animals, a Janus-faced metal. Extensive work has been carried out to understand Mn-induced neurotoxicity and to find an effective treatment. This review focuses on the requirement for Mn in human health as well as the diseases associated with excessive exposure to this metal.

Manganese inhibits ATP-induced calcium entry through the transient receptor potential channel TRPC3 in astrocytes

Chronic exposure to elevated levels of manganese (Mn(2+)) causes neuronal injury and inflammatory activation of glia. Astrocytes selectively accumulate Mn(2+), which inhibits mitochondrial respiration and increases production of reactive oxygen species. We previously reported that sub-acute exposure to low micromolar levels of Mn(2+) in primary astrocytes inhibited ATP-induced calcium (Ca(2+)) signaling, associated with decreased levels of endoplasmic reticulum Ca(2+) and increased mitochondrial Ca(2+) loads. In the present studies, we postulated that the mechanism underlying the capacity of Mn(2+) to inhibit these purinergic signals in astrocytes could be due to competition with Ca(2+) for entry through a plasma membrane channel. These data demonstrate that acutely applied Mn(2+) rapidly inhibited ATP-induced Ca(2+) waves and transients in primary striatal astrocytes. Mn(2+) also decreased influx of extracellular Ca(2+) induced by 1-oleoyl-2-acetyl-sn-glycerol (OAG), a direct activator of the transient receptor potential channel, TRPC3. The TRPC3 inhibitor, pyrazole-3, prevented ATP- and OAG-dependent transport of Mn(2+) from extracellular stores, demonstrated by a dramatic reduction in the rate of fluorescence quenching of Fura-2. These data indicate that Mn(2+) can acutely inhibit ATP-dependent Ca(2+) signaling in astrocytes by blocking Ca(2+) entry through the receptor-operated cation channel, TRPC3. Loss of normal astrocytic responses to purinergic signals due to accumulation of Mn(2+) could therefore comprise critical homeostatic functions necessary for metabolic and trophic support of neurons.

Manganese alters rat brain amino acids levels

Manganese (Mn) is an essential element and it acts as a cofactor for a number of enzymatic reactions, including those involved in amino acid, lipid, protein, and carbohydrate metabolism. Excessive exposure to Mn can lead to poisoning, characterized by psychiatric disturbances and an extrapyramidal disorder. Mn-induced neuronal degeneration is associated with alterations in amino acids metabolism. In the present study, we analyzed whole rat brain amino acid content subsequent to four or eight intraperitoneal injections, with 25 mg MnCl₂/kg/day, at 48-h intervals. We noted a significant increase in glycine brain levels after four or eight Mn injections (p < 0.05 and p < 0.01, respectively) and arginine also after four or eight injections (p < 0.001). Significant increases were also noted in brain proline (p < 0.01), cysteine (p < 0.05), phenylalanine (p < 0.01), and tyrosine (p < 0.01) levels after eight Mn injections vs. the control group. These findings suggest that Mn-induced alterations in amino acid levels secondary to Mn affect the neurochemical milieu.

Manganese transport via the transferrin mechanism

Excessive manganese (Mn) uptake by brain cells, particularly in regions like the basal ganglia, can lead to toxicity. Mn(2+) is transported into cells via a number of mechanisms, while Mn(3+) is believed to be transported similarly to iron (Fe) via the transferrin (Tf) mechanism. Cellular Mn uptake is therefore determined by the activity of the mechanisms transporting Mn into each type of cell and by the amounts of Mn(2+), Mn(3+) and their complexes to which these cells are exposed; this complicates understanding the contributions of each transporter to Mn toxicity. While uptake of Fe(3+) via the Tf mechanism is well understood, uptake of Mn(3+) via this mechanism has not been systematically studied. The stability of the Mn(3+)Tf complex allowed us to form and purify this complex and label it with a fluorescent (Alexa green) tag. Using purified and labeled Mn(3+)Tf and biophysical tools, we have developed a novel approach to study Mn(3+)Tf transport independently of other Mn transport mechanisms. This approach was used to compare the uptake of Mn(3+)Tf into neuronal cell lines with published descriptions of Fe(3+) uptake via the Tf mechanism, and to obtain quantitative information on Mn uptake via the Tf mechanism. Results confirm that in these cell lines significant Mn(3+) is transported by the Tf mechanism similarly to Fe(3+)Tf transport; although Mn(3+)Tf transport is markedly slower than other Mn transport mechanisms. This novel approach may prove useful for studying Mn toxicity in other systems and cell types.

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

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

Glutamatergic and GABAergic metabolism in mouse brain under chronic nicotine exposure: implications for addiction

Background and Purpose

The effects of nicotine on cerebral metabolism and its influence on smoking behavior is poorly understood. An understanding of the chronic effects of nicotine on excitatory and inhibitory metabolic demand, and corresponding neurotransmission may provide clues for designing strategies for the optimal smoking cessation intervention. The objective of the current study was to investigate neuronal and astroglial metabolism in mice exposed to nicotine (0.5 and 2.0 mg/kg, sc) three times in a day for 4 weeks.

Experimental Approach/Principal Findings

Metabolic measurements were carried out by co-infusing [U-¹³C₆]glucose and [2-¹³C]acetate, and monitoring ¹³C labeling of amino acids in brain tissue extract using ¹H-[¹³C] and ¹³C-[¹H]-NMR spectroscopy. Concentration of ¹³C-labeled glutamate-C4 was increased significantly from glucose and acetate with chronic nicotine treatment indicating an increase in glucose oxidation by glutamatergic neurons in all brain regions and glutamate-glutamine neurotransmitter cycle in cortical and subcortical regions. However, chronic nicotine treatment led to increased labeling of GABA-C2 from glucose only in the cortical region. Further, increased labeling of glutamine-C4 from [2-¹³C]acetate is suggestive of increased astroglial activity in subcortical and cerebellum regions of brain with chronic nicotine treatment.

Conclusions and Significance

Chronic nicotine exposure enhanced excitatory activity in the majority of brain regions while inhibitory and astroglial functions were enhanced only in selected brain regions.

Effect of manganese chloride on the neurochemical profile of the rat hypothalamus

Manganese (Mn(2+))-enhanced magnetic resonance imaging studies of the neuronal pathways of the hypothalamus showed that information about the regulation of food intake and energy balance circulate through specific hypothalamic nuclei. The dehydration-induced anorexia (DIA) model demonstrated to be appropriate for studying the hypothalamus with Mn(2+)-enhanced magnetic resonance imaging. Manganese is involved in the normal functioning of a variety of physiological processes and is associated with enzymes contributing to neurotransmitter synthesis and metabolism. It also induces psychiatric and motor disturbances. The molecular mechanisms by which Mn(2+) produces alterations of the hypothalamic physiological processes are not well understood. (1)H-magnetic resonance spectroscopy measurements of the rodent hypothalamus are challenging due to the distant location of the hypothalamus resulting in limited measurement sensitivity. The present study proposed to investigate the effects of Mn(2+) on the neurochemical profile of the hypothalamus in normal, DIA, and overnight fasted female rats at 14.1 T. Results provide evidence that γ-aminobutyric acid has an essential role in the maintenance of energy homeostasis in the hypothalamus but is not condition specific. On the contrary, glutamine, glutamate, and taurine appear to respond more accurately to Mn(2+) exposure. An increase in glutamine levels could also be a characteristic response of the hypothalamus to DIA.

Role of manganese in neurodegenerative diseases

Manganese (Mn) is an essential ubiquitous trace element that is required for normal growth, development and cellular homeostasis. Exposure to high Mn levels causes a clinical disease characterized by extrapyramidal symptom resembling idiopathic Parkinson's disease (IPD). The present review focuses on the role of various transporters in maintaining brain Mn homeostasis along with recent methodological advances in real-time measurements of intracellular Mn levels. We also provide an overview on the role for Mn in IPD, discussing the similarities (and differences) between manganism and IPD, and the relationship between α-synuclein and Mn-related protein aggregation, as well as mitochondrial dysfunction, Mn and PD. Additional sections of the review discuss the link between Mn and Huntington's disease (HD), with emphasis on huntingtin function and the potential role for altered Mn homeostasis and toxicity in HD. We conclude with a brief survey on the potential role of Mn in the etiologies of Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS) and prion disease. Where possible, we discuss the mechanistic commonalities inherent to Mn-induced neurotoxicity and neurodegenerative disorders.