Activation of early signaling transcription factor, NF-kappaB following low-level manganese exposure

Sodium P-aminosalicylic Acid Attenuates Manganese-Induced Neuroinflammation in BV2 Microglia by Modulating NF-κB Pathway

Exposure to high levels of manganese (Mn) leads to brain Mn accumulation, and a disease referred to as manganism. Activation of microglia plays an important role in Mn-induced neuroinflammation. Sodium p-aminosalicylic acid (PAS-Na) is a non-steroidal anti-inflammatory drug that inhibits Mn-induced neuroinflammation. The aim of the current study was to explore the role of NF-κB in the protective mechanism of PAS-Na on Mn-induced neuroinflammation in BV2 microglial experimental model. We treated BV2 microglia with 200 μM Mn for 24 h followed by 48 h treatment with graded concentrations of PAS-Na, using an NF-kB inhibitor, JSH-23, as a positive control. MTT results established that 200 and 400 μM PAS-Na treatment increased the Mn-induced cell viability reduction. NF-κB (P65) mRNA expression and the phosphorylation of p65 were increased in Mn-treated BV2 cell, and suppressed by PAS-Na, analogous to the effect of JSH-23 pretreatment. Furthermore, PAS-Na significantly reduced the contents of the inflammatory cytokine TNF-α and IL-1β, both of which were increased by Mn treatment. The current results show that PAS-Na attenuated Mn-induced inflammation by abrogating the activation of the NF-κB signaling pathways and reduced the release of pro-inflammatory cytokines.

Manganese-induced reactive oxygen species activate IκB kinase to upregulate YY1 and impair glutamate transporter EAAT2 function in human astrocytes in vitro

Dysregulation of the astrocytic glutamate transporter excitatory amino acid transporter 2 (EAAT2) is associated with several neurological disorders, including Parkinson's disease, Alzheimer's disease, and manganism, the latter induced by chronic exposure to high levels of manganese (Mn). Mechanisms of Mn-induced neurotoxicity include impairment of EAAT2 function secondary to the activation of the transcription factor Yin Yang 1 (YY1) by nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). However, the upstream mechanisms by which Mn-induced NF-κB activates YY1 remain to be elucidated. In the present study, we used the H4 human astrocyte cell line to test if Mn activates YY1 through the canonical NF-κB signaling pathway, leading to EAAT2 repression. The results demonstrate that Mn exposure induced phosphorylation of the upstream kinase IκB kinase (IKK-β), leading to NF-κB p65 translocation, increased YY1 promoter activity, mRNA/protein levels, and consequently repressed EAAT2. Results also demonstrated that Mn-induced oxidative stress and subsequent TNF-α production were upstream of IKK-β activation, as antioxidants attenuated Mn-induced TNF-α production and IKK-β activation. Moreover, TNF-α inhibition attenuated the Mn-induced activation of IKK-β and YY1. Taken together, Mn-induced oxidative stress and TNF-α mediates activation of NF-κB signaling and YY1 upregulation, leading to repression of EAAT2. Thus, targeting reactive oxygen species (ROS), TNF-α and IKK-β may attenuate Mn-induced YY1 activation and consequent EAAT2 repression.

Sodium para-aminosalicylic acid inhibits manganese-induced NLRP3 inflammasome-dependent pyroptosis by inhibiting NF-κB pathway activation and oxidative stress

Background

The activation of NOD-like receptor protein 3 (NLRP3) inflammasome-dependent pyroptosis has been shown to play a vital role in the pathology of manganese (Mn)-induced neurotoxicity. Sodium para-aminosalicylic acid (PAS-Na) has a positive effect on the treatment of manganism. However, the mechanism is still unclear. We hypothesized that PAS-Na might act through NLRP3.

Methods

The microglial cell line BV2 and male Sprague-Dawley rats were used to investigate the impacts of PAS-Na on Mn-induced NLRP3 inflammasome-dependent pyroptosis. The related protein of the NF-κB pathway and NLRP3-inflammasome-dependent pyroptosis was detected by western blot. The reactive oxygen species and mitochondrial membrane potential were detected by immunofluorescence staining and flow cytometry. The activation of microglia and the gasdermin D (GSDMD) were detected by immunofluorescence staining.

Results

Our results showed that Mn treatment induced oxidative stress and activated the NF-κB pathway by increasing the phosphorylation of p65 and IkB-α in BV2 cells and in the basal ganglia of rats. PAS-Na could alleviate Mn-induced oxidative stress damage by inhibiting ROS generation, increasing mitochondrial membrane potential and ATP levels, thereby reducing the phosphorylation of p65 and IkB-α. Besides, Mn treatment could activate the NLRP3 pathway and promote the secretion of IL-18 and IL-1β, mediating pyroptosis in BV2 cells and in the basal ganglia and hippocampus of rats. But an inhibitor of NF-κb (JSH-23) treatment could significantly reduce LDH release, the expression of NLRP3 and Cleaved CASP1 protein and IL-1β and IL-18 mRNA level in BV2 cells. Interestingly, the effect of PAS-Na treatment in Mn-treated BV2 cells is similar to those of JSH-23. Besides, immunofluorescence results showed that PAS-Na reduced the increase number of activated microglia, which stained positively for GSDMD.

Conclusion

PAS-Na antagonized Mn-induced NLRP3 inflammasome dependent pyroptosis through inhibiting NF-κB pathway activation and oxidative stress.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-020-02018-6.

The Inflammatory Potential of Dietary Manganese in a Cohort of Elderly Men

Manganese is an essential nutrient that may play a role in the production of inflammatory biomarkers. We examined associations between estimated dietary manganese intake from food/beverages and supplements with circulating biomarkers of inflammation. We further explored whether estimated dietary manganese intake affects DNA methylation of selected genes involved in the production of these biomarkers. We analyzed 1023 repeated measures of estimated dietary manganese intakes and circulating blood inflammatory biomarkers from 633 participants in the Normative Aging Study. Using mixed-effect linear regression models adjusted for covariates, we observed positive linear trends between estimated dietary manganese intakes and three circulating interleukin proteins. Relative to the lowest quartile of estimated intake, concentrations of IL-1β were 46% greater (95% CI - 5, 126), IL-6 52% greater (95% CI - 9, 156). and IL-8 32% greater (95% CI 2, 71) in the highest quartiles of estimated intake. Estimated dietary manganese intake was additionally associated with changes in DNA methylation of inflammatory biomarker-producing genes. Higher estimated intake was associated with higher methylation of NF-κβ member activator NKAP (Q4 vs Q1: β = 3.32, 95% CI - 0.6, 7.3). When stratified by regulatory function, higher manganese intake was associated with higher gene body methylation of NF-κβ member activators NKAP (Q4 vs Q1: β = 10.10, 95% CI - 0.8, 21) and NKAPP1 (Q4 vs Q1: β = 8.14, 95% CI 1.1, 15). While needed at trace amounts for various physiologic functions, our results suggest estimated dietary intakes of manganese at levels slightly above nutritional adequacy contribute to inflammatory biomarker production.

Manganese elevates manganese superoxide dismutase protein level through protein kinase C and protein tyrosine kinase

Three experiments were conducted to investigate the effects of inorganic and organic Mn sources on MnSOD mRNA, protein and enzymatic activity and the possible signal pathways. The primary broiler myocardial cells were treated with MnCl2 (I) or one of organic chelates of Mn and amino acids with weak, moderate (M) or strong (S) chelation strength for 12 and 48 h. Cells were preincubated with superoxide radical anions scavenger N-acetylcysteine (NAC) or specific inhibitors for MAPKs and protein tyrosine kinase (PTK) or protein kinase C (PKC) for 30 min before treatments of I and M. The MnSOD mRNA, protein and enzymatic activity, phosphorylated MAPKs or protein kinases activations were examined. The results showed that additions of Mn increased (P < 0.05) MnSOD mRNA levels and M was more effective than I. Additions of Mn elevated (P < 0.05) MnSOD protein levels and enzymatic activities, and no differences were found among I and M. Addition of NAC did not decrease (P > 0.05) Mn-induced MnSOD mRNA and protein levels. None of the three MAPKs was phosphorylated (P > 0.05) by Mn. Additions of Mn decreased (P < 0.05) the PTK activities and increased (P < 0.05) the membrane PKC contents. Inhibitors for PTK or PKC decreased (P < 0.05) Mn-induced MnSOD protein levels. The results suggested that Mn-induced MnSOD mRNA and protein expressions be not related with NAC, and MAPK pathways might not involve in Mn-induced MnSOD mRNA expression. PKC and PTK mediated the Mn-induced MnSOD protein expression.

Manganese neurotoxicity: behavioral disorders associated with dysfunctions in the basal ganglia and neurochemical transmission

Manganese (Mn) is an essential element required for many physiological functions. While it is essential at physiological levels, excessive accumulation of Mn in the brain causes severe dysfunctions in the central nervous system known as manganism. Manganism is an extrapyramidal disorder characterized by motor disturbances associated with neuropsychiatric and cognitive disabilities similar to Parkinsonism. As the primary brain regions targeted by Mn are the basal ganglia, known to be involved in the pathophysiology of extrapyramidal disorders, this review will examine the impact of Mn exposure on the basal ganglia circuitry and neurotransmitters in relation to motor and non-motor disorders. The collected data from recent available studies in humans and experimental animal models provide new information about the mechanisms by which Mn affects behavior, neurotransmitters, and basal ganglia function observed in manganism. The effects of the alterations of metals on basal ganglia and neurochemical functioning are critical to develop effective modalities not only for the treatment of vulnerable populations (e.g., Mn-exposed workers) but also for understanding the etiology of neurodegenerative diseases where brain metal imbalances are involved, such as Parkinson's disease. We examine the impact of manganese (Mn) exposure on the basal ganglia circuitry and neurotransmitters in relation with motor and non-motor disorders. The collected data from available studies show that when accumulated in the globus pallidus, Mn influences the subthalamic (STN) and substantia nigra (SN) neurons, which are at the origin of changes in the thalamus and the cortex.

Manganese rescues adverse effects on lifespan and development in Podospora anserina challenged by excess hydrogen peroxide

For biological systems, balancing cellular levels of reactive oxygen species (ROS) is of great importance because ROS are both, essential for cellular signaling and dangerous in causing molecular damage. Cellular ROS abundance is controlled by a delicate network of molecular pathways. Within this network, superoxide dismutases (SODs) are active in disproportion of the superoxide anion leading to the formation of hydrogen peroxide. The fungal aging model Podospora anserina encodes at least three SODs. One of these is the mitochondrial PaSOD3 isoform containing manganese as a cofactor. Previous work resulted in the selection of strains in which PaSod3 is strongly overexpressed. These strains display impairments in growth and lifespan. A computational model suggests a series of events to occur in Sod3 overexpressing strains leading to adverse effects due to elevated hydrogen peroxide levels. In an attempt to validate this model and to obtain more detailed information about the cellular responses involved in ROS balancing, we further investigated the PaSod3 overexpressing strains. Here we show that hydrogen peroxide levels are indeed strongly increased in the mutant strain. Surprisingly, this phenotype can be rescued by the addition of manganese to the growth medium. Strikingly, while we obtained no evidence for an antioxidant effect of manganese, we found that the metal is required for induction of components of the ROS scavenging network and lowers the hydrogen peroxide level of the mutant. A similar effect of manganese on lifespan reversion was obtained in wild-type strains challenged with exogenous hydrogen peroxide. It appears that manganese is limited under high hydrogen peroxide and suggests that a manganese-dependent activity leads to the induction of ROS scavenging components.

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.

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.

Comparison between 5-aminosalicylic acid (5-ASA) and para-aminosalicylic acid (4-PAS) as potential protectors against Mn-induced neurotoxicity

Manganese (Mn) is an essential metal for biological systems; however, occupational or clinical exposure to high levels of Mn can produce a neurological disorder called manganism. Oxidative stress and neuroinflammation play major roles in the Mn-induced neurodegeneration leading to dysfunction of the basal ganglia. We investigated the toxic effects of MnCl2 in an immortalized rat brain endothelial cell line (RBE4) and the protective effects of the radical scavenging aminosalicylic acids, 5-aminosalicylic acid (5-ASA) and 4-aminosalicylic acid (4-PAS). Mn cytotoxicity was determined with 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) activity. A significant decrease in MTT reduction concomitant with increased LDH release was noted in RBE4 cells exposed for 24 h to MnCl2 (600 and 800 μM; p < 0.0001). Our results establish that compared to 4-PAS, 5-ASA has greater efficacy in protecting RBE4 cells from Mn-induced neurotoxicity after preexposure to MnCl2 800 μM (p < 0.0001).

Role of glial cells in manganese neurotoxicity

The objectives of this focused review are to (i) provide a systematic overview of recent advances pertaining to the role of glia, namely microglia and astrocytes, in the neuropathology associated with excessive exposure to manganese (Mn), (ii) highlight possible mechanisms and factors involved in Mn-modulated, glia-derived neuroinflammation, and (iii) discuss the implications of excessive neuroinflammation on neuronal injury within the context of Mn overexposure. As this is not meant to be a comprehensive review on the topic of Mn neurotoxicity, the reader may wish to refer to several broader and more comprehensive reviews. After a brief introduction to Mn neurotoxicity, we first discuss the role of glial cells in neurodegeneration. Next, we review existing in vitro and in vivo studies that implicate Mn as a modulator of glial activation and ensuing neuroinflammation. This is followed by an examination of recognized and potential mechanisms that are involved in the modulation of glial inflammatory output by Mn; here the common pathways activated by Mn in glial and neuronal cells, including outcomes of such activation, are also addressed. We finish with a discussion of the implications of Mn-modulated glial activation for neuronal survival and with a list of data gaps in the topic that need to be filled in the future.

Characterization of the expression, promoter activity and molecular architecture of fibin

Background

Fibin was initially discovered as a secreted signal molecule essential for pectoral fin bud initiation in zebrafish. Currently, there is little information about the molecular architecture and biological relevance of fibin in humans and other mammals.

Results

Fibin is expressed in cerebellum, skeletal muscle and many other embryonic and adult mouse tissues suggesting not only a role during embryonic development but also in adult functions. A 2.5-kbp genomic sequence fragment upstream of the coding sequence is sufficient to drive and regulate fibin expression through stimulation by glucocorticoids, activators of the protein kinase C signalling pathways and manganese ions. Fibin is an evolutionarily conserved protein, carries a cleavable signal peptide (amino acids 1-18) and is glycosylated at Asn³⁰. The two conserved cysteines participate in intermolecular disulfide bond and multimer formation. Although fibin displays all features of a secretory protein, it is mostly retained in the endoplasmic reticulum when heterologously expressed.

Conclusion

Fibin is functionally relevant during embryogenesis and adult life. Its expression is regulated by a number of cellular signalling pathways and the protein is routed via the secretory pathway. However, proper secretion presumably requires an unknown covalently-linked or associated co-factor.

Multiwalled carbon nanotubes activate NF-κB and AP-1 signaling pathways to induce apoptosis in rat lung epithelial cells

Our previous report on multiwall carbon nanotubes (MWCNT) has demonstrated the generation of reactive radicals and depletion of intracellular antioxidants which in turn cause cell death through activation of caspases. The molecular mechanism of cellular death due to MWCNT is not clear yet. In this study, we investigated the signaling pathways implicated in MWCNT-induced apoptosis in rat lung epithelial cells. First, we assessed the DNA damage in response to MWCNT treatment and showed the significant DNA damage as compared to control. The collapse of the mitochondrial membrane integrity, release of cytochrome c into the cytosol, reduction in cellular ATP content, increased levels of mitochondrial apoptogenic factor and activation and nuclear translocation of NF-κB were observed in MWCNT treated cells. In addition, a time-dependent induction of phosphorylated IκBα and its degradation were detected in cells exposed to MWCNT. Furthermore, MWCNT activated several death related proteins including apoptosis inducing factor, p53, p21 and bax. Together, our results suggest that signaling pathways such as NF-κB and AP-1 are activated upon MWCNT treatment for cellular cytotoxicity.

Preweaning Mn exposure leads to prolonged astrocyte activation and lasting effects on the dopaminergic system in adult male rats

Little is known about the effects of manganese (Mn) exposure over neurodevelopment and whether these early insults result in effects lasting into adulthood. To determine if early Mn exposure produces lasting neurobehavioral and neurochemical effects, we treated neonate rats with oral Mn (0, 25, or 50 mg Mn/kg/d over PND 1-21) and evaluated (1) behavioral performance in the open arena in the absence (PND 97) and presence (PND 98) of a d-amphetamine challenge, (2) brain dopamine D1 and D2-like receptors and dopamine transporter densities in the prefrontal cortex, striatum, and nucleus accumbens (PND 107), and (3) astrocyte marker glial fibrillary acidic protein (GFAP) levels in these same brain regions (PND 24 and 107). We found that preweaning Mn exposure did not alter locomotor activity or behavior disinhibition in adult rats, though Mn-exposed animals did exhibit an enhanced locomotor response to d-amphetamine challenge. Preweaning Mn exposure led to increased D1 and D2 receptor levels in the nucleus accumbens and prefrontal cortex, respectively, compared with controls. We also found increased GFAP expression in the prefrontal cortex in Mn-exposed PND 24 weanlings, and increased GFAP levels in prefrontal cortex, medial striatum and nucleus accumbens of adult (PND 107) rats exposed to preweaning Mn, indicating an effect of Mn exposure on astrogliosis that persisted and/or progressed to other brain regions in adult animals. These data show that preweaning Mn exposure leads to lasting molecular and functional impacts in multiple brain regions of adult animals, long after brain Mn levels returned to normal.

Involvement of the chemokine-like receptor GPR33 in innate immunity

Chemokine receptors control leukocyte chemotaxis and cell-cell communication but have also been associated with pathogen entry. GPR33, an orphan member of the chemokine-like receptor family, is a pseudogene in most humans. After the appearance of GPR33 in first mammalian genomes, this receptor underwent independent pseudogenization in humans, other hominoids and some rodent species. It was speculated that a likely cause of GPR33 inactivation was its interplay with a rodent-hominoid-specific pathogen. Simultaneous pseudogenization in several unrelated species within the last 1 million years (myr) caused by neutral drift appears to be very unlikely suggesting selection on the GPR33 null-allele. Although there are no signatures of recent selection on human GPR33 we found a significant increase in the pseudogene allele frequency in European populations when compared with African and Asian populations. Because its role in the immune system was still hypothetical expression analysis revealed that GPR33 is highly expressed in dendritic cells (DC). Murine GPR33 expression is regulated by the activity of toll-like receptors (TLR) and AP-1/NF-kappaB signaling pathways in cell culture and in vivo. Our data indicate an important role of GPR33 function in innate immunity which became dispensable during human evolution most likely due to past or balancing selection.

Cellular stress response pathway system as a sentinel ensemble in toxicological screening

High costs, long test times, and societal concerns related to animal use have required the development of in vitro assays for the rapid and cost-effective toxicological evaluation and characterization of compounds in both the pharmaceutical and environmental arenas. Although the pharmaceutical industry has developed very effective, high-throughput in vitro assays for determining the therapeutic potential of compounds, the application of this approach to toxicological screening has been limited. A primary reason for this is that while drug candidate screens are directed to a specific target/mechanism, xenobiotics can cause toxicity through any of a myriad of undefined interactions with cellular components and processes. Given that it is not practical to design assays that can interrogate each potential toxicological target, an integrative approach is required if there is to be a rapid and low-cost toxicological evaluation of chemicals. Cellular stress response pathways offer a viable solution to the creation of a set of integrative assays as there is a limited and hence manageable set (a small ensemble of 10 or less) of major cellular stress response pathways through which cells mount a homoeostatic response to toxicants and which also participate in cell fate/death decisions. Further, over the past decades, these pathways have been well characterized at a molecular level thereby enabling the development of high-throughput cell-based assays using the components of the pathways. Utilization of the set of cellular stress response pathway-based assays as indicators of toxic interactions of chemicals with basic cellular machinery will potentially permit the clustering of chemicals based on biological response profiles of common mode of action (MOA) and also the inference of the specific MOA of a toxicant. This article reviews the biochemical characteristics of the stress response pathways, their common architecture that enables rapid activation during stress, their participation in cell fate decisions, the essential nature of these pathways to the organism, and the biochemical basis of their cross-talk that permits an assay ensemble screening approach. Subsequent sections describe how the stress pathway ensemble assay approach could be applied to screening potentially toxic compounds and discuss how this approach may be used to derive toxicant MOA from the biological activity profiles that the ensemble strategy provides. The article concludes with a review of the application of the stress assay concept to noninvasive in vivo assessments of chemical toxicants.

Manganese neurotoxicity: lessons learned from longitudinal studies in nonhuman primates

BACKGROUND

Exposure to excess levels of the essential trace element manganese produces cognitive, psychiatric, and motor abnormalities. The understanding of Mn neurotoxicology is heavily governed by pathologic and neurochemical observations derived from rodent studies that often employ acute Mn exposures. The comparatively sparse studies incorporating in vivo neuroimaging in nonhuman primates provide invaluable insights on the effects of Mn on brain chemistry.

OBJECTIVES

The purpose of this review is to discuss important aspects of Mn neurotoxicology and to synthesize recent findings from one of the largest cohorts of nonhuman primates used to study the neurologic effects of chronic Mn exposure.

DISCUSSION

We reviewed our recent in vivo and ex vivo studies that have significantly advanced the understanding of Mn-induced neurotoxicity. In those studies, we administered weekly doses of 3.3-5.0 (n=4), 5.0-6.7 (n=5), or 8.3-10.0 mg Mn/kg (n=3) for 7-59 weeks to cynomolgus macaque monkeys. Animals expressed subtle deficits in cognition and motor function and decreases in the N-acetylaspartate-to-creatine ratio in the parietal cortex measured by magnetic resonance spectroscopy reflective of neuronal dysfunction. Impaired striatal dopamine release measured by positron emission tomography was observed in the absence of changes in markers of dopamine neuron degeneration. Neuropathology indicated decreased glutamine synthetase expression in the globus pallidus with otherwise normal markers of glutamatergic and GABAergic neurotransmission. Increased amyloid beta (A4) precursor-like protein 1 gene expression with multiple markers of neurodegeneration and glial cell activation was observed in the frontal cortex.

CONCLUSIONS

These findings provide new information on mechanisms by which Mn affects behavior, neurotransmitter function, and neuropathology in nonhuman primates.

The addition of high manganese to a copper-deficient diet further depresses copper status and growth of cattle

A study was conducted evaluating the effect of long-term Cu deficiency, with or without high Mn, on growth, gene expression and Cu status of beef cattle. Twenty-one Angus calves were born to cows receiving one of the following treatments: (1) 10 mg supplemental Cu/kg DM (+Cu); (2) no supplemental Cu and 2 mg Mo/kg DM ( - Cu); (3) - Cu diet plus 500 mg supplemental Mn/kg DM ( - Cu+Mn). Calves were weaned at approximately 183 d of age and individually fed throughout the growing and finishing phases. Plasma Cu was lower (P < 0.01) in - Cu calves compared with +Cu calves while high dietary Mn further depressed (P < 0.01) plasma Cu in - Cu+Mn calves v. - Cu calves. Liver Cu concentrations in +Cu calves were greater (P < 0.01) than in - Cu calves, with no differences between - Cu and - Cu+Mn calves. The daily body-weight gain of +Cu calves was greater (P < 0.01) than - Cu calves during the period from birth to weaning, but did not differ during the growing phase. - Cu+Mn calves gained less (P < 0.05) than - Cu calves during the growing phase. DM intake was lower (P < 0.01) in - Cu+Mn calves v. - Cu calves, and did not differ among +Cu and - Cu calves. The relative gene expression of cytochrome c oxidase in the liver was lower (P < 0.05) in - Cu calves compared with +Cu or - Cu+Mn calves. In conclusion, feeding a Cu - deficient diet in combination with high Mn negatively affected the growth and Cu status of beef cattle.

Molecular mechanism of manganese exposure-induced dopaminergic toxicity

Manganese (Mn) is an essential mineral that is found in varying amounts in aerosols or dust. Exposure to atmospheric Mn at high concentration is a risk factor in humans that can manifest as neuronal degeneration resembling Parkinson's disease (PD). Since the underlying mechanism of Mn and dopamine (DA) interaction-induced cell death remains unclear, here, we showed that Mn exposure alone to mesencephalic cells for 24h induced minimal apoptotic cell death. However, cells pre-exposed to DA for 2h accelerated Mn-induced apoptosis. The vulnerability of Mn-induced apoptotic cell death to DA was determined by measuring lactate dehydrogenase (LDH) and Apoptag TUNEL staining (terminaldeoxynucleotidyl transferase DNA labeling). This was further confirmed by the cell viability assay to support our hypothesis that DA at the cellular level interacts with Mn and causes cells to be more susceptible. Pretreatment with nitric oxide blocker (7-nitroindazole, 7-NI), vitamin E or NF-kappaB inhibitor (SN50) significantly protected the cells from Mn and DA interaction-induced reactive oxygen species (ROS) and apoptosis. Western blot analysis showed that Mn in the presence of DA markedly induced induction of NOS (iNOS) expression. Pretreatment with 7-NI, SN50 or vitamin E significantly attenuated increased iNOS expression indicating that iNOS expression is regulated by ROS and the transcription factor NF-kappaB. Further, the generation of ROS as an early event in Mn and DA interaction is not controlled by NF-kappaB as SN50 pretreatment did not prevent ROS. These findings suggest that NF-kappaB induction and the activation of nitric oxide synthase through ROS represent a proximate mechanism for Mn-induced neurotoxicity.

Manganese modulates pro-inflammatory gene expression in activated glia

Redox-active metals are of paramount importance for biological functions. Their impact and cellular activities participate in the physiological and pathophysiological processes of the central nervous system (CNS), including inflammatory responses. Manganese is an essential trace element and it is required for normal biological activities and ubiquitous enzymatic reactions. However, excessive chronic exposure to manganese results in neurobehavioral deficits. Recent evidence suggests that manganese neurotoxicity involves activation of microglia or astrocytes, representative CNS immune cells. In this study, we assessed the molecular basis of the effects of manganese on the modulation of pro-inflammatory cytokines and nitric oxide (NO) production in primary rat cortical glial cells. Cultured glial cells consisted of 85% of astrocytes and 15% of microglia. Within the assayed concentrations, manganese was unable to induce tumor necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) expression, whereas it potentiated iNOS and TNF-alpha gene expression by lipopolysaccharide/interferon-gamma-activated glial cells. The enhancement was accompanied by elevation of free manganese, generation of oxidative stress, activation of mitogen-activated protein kinases, and increased NF-kappaB and AP-1 binding activities. The potentiated degradation of inhibitory molecule IkappaB-alpha was one of underlying mechanisms for the increased activation of NF-kappaB by manganese. However, manganese decreased iNOS enzymatic activity possibly through the depletion of cofactor since exogenous tetrahydrobiopterin reversed manganese's action. These data indicate that manganese could modulate glial inflammation through variable strategies.

Effects of select PM-associated metals on alveolar macrophage phosphorylated ERK1 and -2 and iNOS expression during ongoing alteration in iron homeostasis

It was hypothesized that relative mass relationships among select constituent metals and iron (Fe3+) govern the pulmonary immunotoxic potential of any PM(2.5) sample, as these determine the extent to which Fe3+ binding by transferrin is affected (resulting in altered alveolar macrophage [AM] Fe status and subsequent antibacterial function). Iron response protein (IRP) binding activity is a useful indirect measurement of changes in Fe status, as reductions in cell Fe levels lead to increases in IRP binding. However, AM IRP activity can be affected by an increased presence of nitric oxide generated by inducible nitric oxide synthase (iNOS). This study sought to determine if any changes in AM IRP activity induced by PM(2.5) constituents V, Mn, or Al were independent from effects of the metals on cell NO formation. NR8383 rat AM were exposed to Fe3+ alone or combined with V, Mn, or Al at metal:Fe ratios representative of those in PM(2.5) collected in New York City, Los Angeles, and Seattle during fall 2001. Cells were then assessed for changes in IRP activity and iNOS expression. Phosphorylated extracellular signal-regulated kinase (ERK) 1 and 2 levels were also measured since activated ERKs are involved in signaling pathways that lead to increased iNOS expression. The results indicate that V and Al, and to a lesser extent Mn, altered IRP activity, though the effects were not consistently concentration dependent. Furthermore, while V and Mn treatments did not induce iNOS expression, Al did. These results confirmed our hypothesis that certain metals associated with PM(2.5) might alter the pulmonary immunocompetence of exposed hosts by affecting the Fe status of AM, a major class of deep lung defense cells.

Low levels of arsenite activates nuclear factor-kappaB and activator protein-1 in immortalized mesencephalic cells

Degeneration of dopaminergic neurons is one of the major features of Parkinson's disease. Many redox-active metals such as iron and manganese have been implicated in neuronal degeneration characterized by symptoms resembling Parkinson's disease. Even though, arsenic, which is another redox-active metal, has been shown to affect the central monoaminergic systems, but its potential in causing dopaminergic cell degeneration has not been fully known. Hence, the present study was designed to investigate arsenic signaling especially that is mediated by reactive oxygen species and its effect on early transcription factors in dopamine producing mesencephalic cell line 1RB3AN27. These mesencephalic cells were treated with low concentrations of sodium arsenite (0.1, 0.5, 1, 5, and 10 microM) and incubated for different periods of time (0-4 h). Arsenite was cytotoxic at 5 and 10 microM concentrations only after 72-h incubation period. Arsenite, in a dose-dependent manner, induced generation of reactive oxygen species (ROS) and activation of early transcription factors such as nuclear factor-kappa B (NF-kappaB) and activator protein-1 (AP-1) as shown by electro mobility shift assay. Incubation of antioxidants, either N-acetyl-L-cysteine (50 microM) or alpha-tocopherol (50 microM) with 1 microM arsenite, suppressed ROS generation. Arsenite at 1 microM concentration was sufficient for maximal activation of NF-kappaB and AP-1 activation. Time kinetics studies showed maximal activation of NF-kappaB by 1 microM concentration of arsenite was seen at 120 min and correlated with complete degradation of Ikappa Balpha at 60 min. Similarly, maximal activation of AP-1 by 1 microM concentration of arsenite occurred at 120 min. N-acetyl-L-cysteine at 50 microM concentration inhibited arsenite-induced NF-kappa B and AP-1. In addition, arsenite was shown to induce phosphorylation of extracellular signal regulated kinase (ERK) 1/2 at concentrations of 1 microM and above. These results suggest that arsenite, at low and subcytoxic concentrations, appears to induce oxidative stress leading to activation of early transcription factors whereas addition of antioxidant inhibited the activation of these factors.

Oxidative Basis of Manganese Neurotoxicity

Exposure to excessive levels of manganese, an essential trace element, can evoke severe psychiatric and extrapyramidal motor dysfunction closely resembling Parkinson's disease. The clinical manifestations of manganese toxicity arise from focal injury to the basal ganglia. This region, characterized by intense consumption of oxygen and significant dopamine content, can incur mitochondrial dysfunction, depletion of levels of peroxidase and catalase, and catecholamine biochemical imbalances following manganese exposure. The site specificity of the pathology and the nature of the cellular damage caused by manganese have been attributed to its capacity to produce cytotoxic levels of free radicals. However, support for such a pro-oxidant role for manganese has been largely limited to inferences drawn from histopathological observations. More recently, research efforts into the molecular details of manganese toxicity have provided evidence of an etiological relationship between oxidative stress and manganese-related neurodegeneration. This review focuses on studies that evaluate the redox chemistry of manganese during the neurodegenerative process and its molecular consequences.