The uptake of manganese in brain endothelial cultures

Bioflocs attenuate Mn-induced bioaccumulation, immunotoxic and oxidative stress via inhibiting GR-NF-κB signalling pathway in Channa asiatica

Manganese (Mn) is a relatively common element in aquatic ecosystems and can be bio-concentration, but the mechanism of manganese poisoning on fish health is unclear. Here, this study's objective was to evaluate the potential mechanisms of bioflocs in ameliorating Mn-induced toxicity in Channa asiatica. Three hundred sixty juveniles were randomly divided into 12 tanks. Four C:N ratios in triplicate tanks were tried: C/N = 7.6:1 with a commercial diet (control), C/N 10:1, C/N 15:1 and C/N 20:1, and the bio-accumulation, immunotoxic, oxidative stress, GR-NF-κB related genes expression and intestinal histomorphology were assessed in three different periods after Mn exposure (0 h, 48 h and 96 h). The results showed that bioflocs had a significant protective effect on Mn poisoning by preventing alterations in bio-accumulation levels, LSZ, AKP, C3, C4 and IgM, of which the C/N 15:1 group had the best relief effect. Furthermore, bioflocs also assisted in the recovery of liver T-SOD, CAT, GPX and T-AOC levels while decreasing the content of MDA. Moreover, C/N 15:1 group significantly down-regulated the expression level of NF-κB, TNF-α, IL-1β and IL-8 and up-regulated significantly IκBα, GR, HSP70 and HSP90 expression levels considerably (P < 0.05). From the intestinal section, the C/N 15:1 group resistance was the best one, and there was no difference between C/N 20:1 group and control group. These results revealed that administration of bioflocs (C/N 15:1) has the potential to combat Mn toxicity in C. asiatica, and the specific pathway may be GR-NF-κB.

The role of zinc, copper, manganese and iron in neurodegenerative diseases

Metals are involved in different pathophysiological mechanisms associated with neurodegenerative diseases (NDDs), including Alzheimer's disease (AD), Parkinson's disease (PD) and multiple sclerosis (MS). The aim of this study was to review the effects of the essential metals zinc (Zn), copper (Cu), manganese (Mn) and iron (Fe) on the central nervous system (CNS), as well as the mechanisms involved in their neurotoxicity. Low levels of Zn as well as high levels of Cu, Mn, and Fe participate in the activation of signaling pathways of the inflammatory, oxidative and nitrosative stress (IO&NS) response, including nuclear factor kappa B and activator protein-1. The imbalance of these metals impairs the structural, regulatory, and catalytic functions of different enzymes, proteins, receptors, and transporters. Neurodegeneration occurs via association of metals with proteins and subsequent induction of aggregate formation creating a vicious cycle by disrupting mitochondrial function, which depletes adenosine triphosphate and induces IO&NS, cell death by apoptotic and/or necrotic mechanisms. In AD, at low levels, Zn suppresses β-amyloid-induced neurotoxicity by selectively precipitating aggregation intermediates; however, at high levels, the binding of Zn to β-amyloid may enhance formation of fibrillar β-amyloid aggregation, leading to neurodegeneration. High levels of Cu, Mn and Fe participate in the formation α-synuclein aggregates in intracellular inclusions, called Lewy Body, that result in synaptic dysfunction and interruption of axonal transport. In PD, there is focal accumulation of Fe in the substantia nigra, while in AD a diffuse accumulation of Fe occurs in various regions, such as cortex and hippocampus, with Fe marginally increased in the senile plaques. Zn deficiency induces an imbalance between T helper (Th)1 and Th2 cell functions and a failure of Th17 down-regulation, contributing to the pathogenesis of MS. In MS, elevated levels of Fe occur in certain brain regions, such as thalamus and striatum, which may be due to inflammatory processes disrupting the blood-brain barrier and attracting Fe-rich macrophages. Delineating the specific mechanisms by which metals alter redox homeostasis is essential to understand the pathophysiology of AD, PD, and MS and may provide possible new targets for their prevention and treatment of the patients affected by these NDDs.

Age-dependent changes in essential elements and oxidative stress biomarkers in blood of red deer and vulnerability to nutritional deficiencies

Changes in the concentration of circulating essential elements in animals over life may be indicative of periods of vulnerability to deficiencies and associated diseases. Here we studied age-related variations in essential elements (Se, Cu, Zn and Mn) and some selected oxidative stress biomarkers (GPx, SOD, vitamin A and vitamin E) in blood of an Iberian red deer (Cervus elaphus hispanicus) population living in semicaptive conditions. Animals during their first year of life showed to be especially vulnerable to suffer Se- and Cu-related diseases and disorders. Older female deer had lower blood levels of Zn and Mn, which was accompanied by a lower blood SOD activity. On the contrary, GPx blood activity was elevated in older deer, which may help to compensate the reduction of other antioxidants with during aging. Age-related changes in GPx and SOD and their positive relationships with the essential elements suggest that the observed nutritional deficiencies at certain age stages may have a detrimental effect on the antioxidant system, increasing the risk of oxidative stress. Thus, the biomarkers used in the present study may be important tools for the subclinical diagnosis of nutritional disorders and diseases related to the generation of oxidative stress in both domestic and wild ungulates.

Manganese(II) Chloride Alters Nucleotide and Nucleoside Catabolism in Zebrafish (Danio rerio) Adult Brain

ATP and adenosine, the main signaling molecules of purinergic system, are involved in toxicological effects induced by metals. The manganese (Mn) exposure induces several cellular changes, which could interfere with signaling pathways, such as the purinergic system. In this study, we evaluated the effects of exposure to manganese(II) chloride (MnCl₂) during 96 h on nucleoside triphosphate diphosphohydrolase (NTPDase), ecto-5'-nucleotidase, and adenosine deaminase (ADA) activities, followed by analyzing the gene expression patterns of NTPDases (entpd1, entpd2a.1, entpd2a.2, entpd2-like, entpd3) and ADA (ADA ₁ , ADA _2.1 , ADA _2.2 , ADAasi, ADAL) families in zebrafish brain. In addition, the brain metabolism of nucleotides and nucleosides was evaluated after MnCl₂ exposure. The results showed that MnCl₂ exposure during 96 h inhibited the NTPDase (1.0 and 1.5 mM) and ecto-ADA (0.5, 1.0, and 1.5 mM) activities, further decreasing ADA2.1 expression at all MnCl₂ concentrations analyzed. Purine metabolism was also altered by the action of MnCl₂. An increased amount of ADP appeared at all MnCl₂ concentrations analyzed; however, AMP and adenosine levels are decreased at the concentrations of 1.0 and 1.5 mM MnCl₂, whereas decreased inosine (INO) levels were observed at all concentrations tested. The findings of this study demonstrated that MnCl₂ may inhibit NTPDase and ecto-ADA activities, consequently modulating nucleotide and nucleoside levels, which may contribute for the toxicological effects induced by this metal.

Manganese(II) chloride alters behavioral and neurochemical parameters in larvae and adult zebrafish

Manganese (Mn) is an essential metal for organisms, but high levels can cause serious neurological damage. The aim of this study was to evaluate the effects of MnCl₂ exposure on cognition and exploratory behavior in adult and larval zebrafish and correlate these findings with brain accumulation of Mn, overall brain tyrosine hydroxylase (TH) levels, dopamine (DA) levels, 3,4-dihydroxyphenylacetic acid (DOPAC) levels and cell death markers in the nervous system. Adults exposed to MnCl₂ for 4days (0.5, 1.0 and 1.5mM) and larvae exposed for 5days (0.1, 0.25 and 0.5mM) displayed decreased exploratory behaviors, such as distance traveled and absolute body turn angle, in addition to reduced movement time and an increased number of immobile episodes in larvae. Adults exposed to MnCl₂ for 4days showed impaired aversive long-term memory in the inhibitory avoidance task. The overall brain TH levels were elevated in adults and larvae evaluated at 5 and 7 days post-fertilization (dpf). Interestingly, the protein level of this enzyme was decreased in larval animals at 10dpf. Furthermore, DOPAC levels were increased in adult animals exposed to MnCl₂. Protein analysis showed increased apoptotic markers in both the larvae and adult nervous system. The results demonstrated that prolonged exposure to MnCl₂ leads to locomotor deficits that may be associated with damage caused by this metal in the CNS, particularly in the dopaminergic system.

Role of transcription factor yin yang 1 in manganese-induced reduction of astrocytic glutamate transporters: Putative mechanism for manganese-induced neurotoxicity

Astrocytes are the most abundant non-neuronal glial cells in the brain. Once relegated to a mere supportive role for neurons, contemporary dogmas ascribe multiple active roles for these cells in central nervous system (CNS) function, including maintenance of optimal glutamate levels in synapses. Regulation of glutamate levels in the synaptic cleft is crucial for preventing excitotoxic neuronal injury. Glutamate levels are regulated predominantly by two astrocytic glutamate transporters, glutamate transporter 1 (GLT-1) and glutamate aspartate transporter (GLAST). Indeed, the dysregulation of these transporters has been linked to several neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD) and Parkinson's disease (PD), as well as manganism, which is caused by overexposure to the trace metal, manganese (Mn). Although Mn is an essential trace element, its excessive accumulation in the brain as a result of chronic occupational or environmental exposures induces a neurological disorder referred to as manganism, which shares common pathological features with Parkinsonism. Mn decreases the expression and function of both GLAST and GLT-1. Astrocytes are commonly targeted by Mn, and thus reduction in astrocytic glutamate transporter function represents a critical mechanism of Mn-induced neurotoxicity. In this review, we will discuss the role of astrocytic glutamate transporters in neurodegenerative diseases and Mn-induced neurotoxicity.

Manganese neurotoxicity: a focus on glutamate transporters

Manganese (Mn) is an essential element that is required in trace amount for normal growth, development as well maintenance of proper function and regulation of numerous cellular and biochemical reactions. Yet, excessive Mn brain accumulation upon chronic exposure to occupational or environmental sources of this metal may lead to a neurodegenerative disorder known as manganism, which shares similar symptoms with idiopathic Parkinson's disease (PD). In recent years, Mn exposure has gained public health interest for two primary reasons: continuous increased usage of Mn in various industries, and experimental findings on its toxicity, linking it to a number of neurological disorders. Since the first report on manganism nearly two centuries ago, there have been substantial advances in the understanding of mechanisms associated with Mn-induced neurotoxicity. This review will briefly highlight various aspects of Mn neurotoxicity with a focus on the role of astrocytic glutamate transporters in triggering its pathophysiology.

Manganese efflux in Parkinsonism: insights from newly characterized SLC30A10 mutations

Although manganese (Mn) is required for normal cellular function, overexposure to this metal may cause an extrapyramidal syndrome resembling Parkinson's disease (PD). Notably, high whole-blood Mn levels have been reported in patients with idiopathic PD. Because Mn is both essential at low dose and toxic at higher dose; its transport and homeostasis are tightly regulated. Previously, the only protein known to be operant in cellular Mn export was the iron-regulating transporter, ferroportin (Fpn). The causal role for Mn in PD has yet to be fully understood, but evidence of a familial predisposition to PD associated with Mn toxicity is mounting. A recently discovered mutation in SLC30A10 identified its gene product as putatively involved in Mn efflux. Patients with the SLC30A10 mutation display Parkinsonian-like gate disturbances and hypermanganesemia. This review will address Mn transport proteins, the newly discovered SLC30A10 mutations and their implications to Parkinsonism and Mn regulation.

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.

Rat brain endothelial cells are a target of manganese toxicity

Manganese (Mn) is an essential trace metal; however, exposure to high Mn levels can result in neurodegenerative changes resembling Parkinson's disease (PD). Information on Mn's effects on endothelial cells of the blood-brain barrier (BBB) is lacking. Accordingly, we tested the hypothesis that BBB endothelial cells are a primary target for Mn-induced neurotoxicity. The studies were conducted in an in vitro BBB model of immortalized rat brain endothelial (RBE4) cells. ROS production was determined by F(2)-isoprostane (F(2)-IsoPs) measurement. The relationship between Mn toxicity and redox status was investigated upon intracellular glutathione (GSH) depletion with diethylmaleate (DEM) or L-buthionine sulfoximine (BSO). Mn exposure (200 or 800 microM MnCl(2) or MnSO(4)) for 4 or 24h led to significant decrease in cell viability vs. controls. DEM or BSO pre-treatment led to further enhancement in cytotoxicity vs. exposure to Mn alone, with more pronounced cell death after 24-h DEM pre-treatment. F(2)-IsoPs levels in cells exposed to MnCl(2) (200 or 800 microM) were significantly increased after 4h and remained elevated 24h after exposure compared with controls. Consistent with the effects on cell viability and F(2)-IsoPs, treatment with MnCl(2) (200 or 800 microM) was also associated with a significant decrease in membrane potential. This effect was more pronounced in cells exposed to DEM plus MnCl(2) vs. cells exposed to Mn alone. We conclude that Mn induces direct injury to mitochondria in RBE4 cells. The ensuing impairment in energy metabolism and redox status may modify the restrictive properties of the BBB compromising its function.

Manganese transport in eukaryotes: the role of DMT1

Manganese (Mn) is a transition metal that is essential for normal cell growth and development, but is toxic at high concentrations. While Mn deficiency is uncommon in humans, Mn toxicity is known to be readily prevalent due to occupational overexposure in miners, smelters and possibly welders. Excessive exposure to Mn can cause Parkinson's disease-like syndrome; patients typically exhibit extrapyramidal symptoms that include tremor, rigidity and hypokinesia [Calne DB, Chu NS, Huang CC, Lu CS, Olanow W. Manganism and idiopathic parkinsonism: similarities and differences. Neurology 1994;44(9):1583-6; Dobson AW, Erikson KM, Aschner M. Manganese neurotoxicity. Ann NY Acad Sci 2004;1012:115-28]. Mn-induced motor neuron diseases have been the subjects of numerous studies; however, this review is not intended to discuss its neurotoxic potential or its role in the etiology of motor neuron disorders. Rather, it will focus on Mn uptake and transport via the orthologues of the divalent metal transporter (DMT1) and its possible implications to Mn toxicity in various categories of eukaryotic systems, such as in vitro cell lines, in vivo rodents, the fruitfly, Drosophila melanogaster, the honeybee, Apis mellifera L., the nematode, Caenorhabditis elegans and the baker's yeast, Saccharomyces cerevisiae.

Manganese accumulates primarily in nuclei of cultured brain cells

Manganese (Mn) is known to pass across the blood-brain barrier and interact with dopaminergic neurons. However, the knowledge on the subcellular distribution of Mn in these cell types upon exposure to Mn remained incomplete. This study was designed to investigate the subcellular distribution of Mn in blood-brain barrier endothelial RBE4 cells, blood-cerebrospinal fluid barrier choroidal epithelial Z310 cells, mesencephalic dopaminergic neuronal N27 cells, and pheochromocytoma dopaminergic PC12 cells. The cells were incubated with 100 microM MnCl(2) with radioactive tracer (54)Mn in the culture media for 24h. The subcellular organelles, i.e., nuclei, mitochondria, microsomes, and cytoplasm, were isolated by centrifugation and verified for their authenticity by determining the markers specific to cellular organelles. Data indicated that maximum Mn accumulation was observed in PC12 cells, which was 2.8, 5.2- and 5.9-fold higher than that in N27, Z310 and RBE4 cells, respectively. Within cells, about 92%, 72%, and 52% of intracellular (54)Mn were found to be present in nuclei of RBE4, Z310, and N27 cells, respectively. The recovery of (54)Mn in nuclei and cytoplasm of PC12 cells were 27% and 69%, respectively. Surprisingly, less than 0.5% and 2.5% of cellular (54)Mn was found in mitochondrial and microsomal fractions, respectively. This study suggests that the nuclei may serve as the primary pool for intracellular Mn; mitochondria and microsomes may play an insignificant role in Mn subcellular distribution.

Putative proteins involved in manganese transport across the blood-brain barrier

Manganese (Mn) is an essential nutrient required for proper growth and maintenance of numerous biological systems. At high levels it is known to be neurotoxic. While focused research concerning the transport of Mn across the blood-brain barrier (BBB) is on-going, the exact identity of the transporter(s) responsible is still debated. The transferrin receptor (TfR) and the divalent metal transporter-1 (DMT-1) have long been thought to play a role in brain Mn deposition. However, evidence suggests that Mn may also be transported by other proteins. One model system of the BBB, rat brain endothelial (RBE4) cells, are known to express many proteins suspected to be involved in metal transport. This review will discuss the biological importance of Mn, and then briefly describe several proteins that may be involved in transport of this metal across the BBB. The latter section will examine the potential usefulness of RBE4 cells in characterizing various aspects of Mn transport, and basic culture techniques involved in working with these cells. It is hoped that ideas put forth in this article will stimulate further investigations into the complex nature of Mn transport, and address the importance as well as the limitation of in vitro models in answering these questions.

Iron deficient and manganese supplemented diets alter metals and transporters in the developing rat brain

Manganese (Mn) neurotoxicity in adults can result in psychological and neurological disturbances similar to Parkinson's disease, including extrapyramidal motor system defects and altered behaviors. Iron (Fe) deficiency is one of the most prevalent nutritional disorders in the world, affecting approximately 2 billion people, especially pregnant and lactating women, infants, toddlers, and adolescents. Fe deficiency can enhance brain Mn accumulation even in the absence of excess Mn in the environment or the diet. To assess the neurochemical interactions of dietary Fe deficiency and excess Mn during development, neonatal rats were exposed to either a control diet, a low-Fe diet (ID), or a low-Fe diet supplemented with Mn (IDMn) via maternal milk during the lactation period (postnatal days [PN] 4-21). In PN21 pups, both the ID and IDMn diets produced changes in blood parameters characteristic of Fe deficiency: decreased hemoglobin (Hb) and plasma Fe, increased plasma transferrin (Tf), and total iron binding capacity (TIBC). Treated ID and IDMn dams also had decreased Hb throughout lactation and ID dams had decreased plasma Fe and increased Tf and TIBC on PN21. Both ID and IDMn pups had decreased Fe and increased copper brain levels; in addition, IDMn pups also had increased brain levels of several other essential metals including Mn, chromium, zinc, cobalt, aluminum, molybdenum, and vanadium. Concurrent with altered concentrations of metals in the brain, transport proteins divalent metal transporter-1 and transferrin receptor were increased. No significant changes were determined for the neurotransmitters gamma aminobutyric acid and glutamate. The results of this study confirm that there is homeostatic relationship among several essential metals in the brain and not simply between Fe and Mn.

A manganese-enhanced diet alters brain metals and transporters in the developing rat

Manganese (Mn) neurotoxicity in adults can result in psychological and neurological disturbances similar to Parkinson's disease, including extrapyramidal motor system defects and altered behaviors. However, virtually nothing is known regarding excess Mn accumulation during central nervous system development. Developing rats were exposed to a diet high in Mn via maternal milk during lactation (PN4-21). The high Mn diet resulted in changes in hematological parameters similar to those seen with iron (Fe) deficiency in dams (decreased plasma Fe; increased plasma transferrin [Tf]) and pups (decreased hemoglobin [Hb] and plasma Fe; increased plasma Tf and total iron binding capacity). Mn-exposed pups showed an increase in brain Mn, chromium, and zinc concurrent with a decrease in brain Fe. In conjunction with the altered transport and distribution of essential metals within the brain, there was enhanced protein expression of the divalent metal transporter-1 (DMT-1) and transferrin receptor (TfR) overall in the brain; there was a general increase in each region analyzed (cerebellum, cortex, hippocampus, midbrain, and striatum). Neurochemical changes were observed as an increase in gamma-aminobutyric acid (GABA) and the ratio of GABA to glutamate, indicating enhanced inhibitory transmission in the brain. The results of this study demonstrate that developing rats undergo alterations in the transport and distribution of essential metals translating to neurochemical perturbations after maternal exposure to a diet supplemented with excess levels of Mn.

Iron interactions and other biological reactions mediating the physiological and toxic actions of manganese

Chronic exposure to the divalent heavy metals, such as iron, lead, manganese (Mn), and chromium, has been linked to the development of severe, often irreversible neurological disorders and increased vulnerability to developing Parkinson's disease. Although the mechanisms by which these metals elicit or facilitate neuronal cell death are not well defined, neurotoxicity is limited by the extent to which they are transported across the blood-brain barrier and their subsequent uptake within targeted neurons. Once inside the neuron, these heavy metals provoke a series of biochemical and molecular events leading to cell death induced by either apoptosis and/or necrosis. The toxicological properties of Mn have been studied extensively in recent years because of the potential health risk created by increased atmospheric levels owing to the impending use of the gas additive methylcyclopentadienyl manganese tricarbonyl. Individuals exposed to high environmental levels of Mn, which include miners, welders, and those living near ferroalloy processing plants, display a syndrome known as manganism, best characterized by debilitating symptoms resembling those of Parkinson's disease. Mn disposition in vivo is influenced by dietary iron intake and stores within the body since the two metals compete for the same binding protein in serum (transferrin) and subsequent transport systems (divalent metal transporter, DMT1). There appear to be two distinct carrier-mediated transport systems for Mn and ferrous ion: a transferrin-dependent and a transferrin-independent pathway, both of which utilize DMT1 as the transport protein. Accordingly, this commentary focuses on the biochemical and molecular processes responsible for the cytotoxic actions of Mn and the role that cellular transport plays in mediating the physiological as well as the toxicological actions of this metal.