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

Targeting m6A mRNA demethylase FTO alleviates manganese-induced cognitive memory deficits in mice

Manganese (Mn) induced learning and memory deficits through mechanisms that are not fully understood. In this study, we discovered that the demethylase FTO was significantly downregulated in hippocampal neurons in an experimental a mouse model of Mn exposure. This decreased expression of FTO was associated with Mn-induced learning and memory impairments, as well as the dysfunction in synaptic plasticity and damage to regional neurons. The overexpression of FTO, or its positive modulation with agonists, provides protection against neurological damage and cognitive impairments. Mechanistically, FTO interacts synergistically with the reader YTHDF3 to facilitate the degradation of GRIN1 and GRIN3B through the m6A modification pathway. Additionally, Mn decreases the phosphorylation of SOX2, which specifically impairs the transcriptional regulation of FTO activity. Additionally, we found that the natural compounds artemisinin and apigenin that can bind molecularly with SOX2 and reduce Mn-induced cognitive dysfunction in mice. Our findings suggest that the SOX2-FTO-Grins axis represents a viable target for addressing Mn-induced neurotoxicity and cognitive impairments.

Biocompatible antibiotic-coupled nickel-titanium nanoparticles as a potential coating material for biomedical devices

The challenges facing metallic implants for reconstructive surgery include the leaching of toxic metal ions, a mismatch in elastic modulus between the implant and the treated tissue, and the risk of infection. These problems can be addressed by passivating the metal surface with an organic substrate and incorporating antibiotic molecules. Nitinol (NiTi), a nickel-titanium alloy, is used in devices for biomedical applications due to its shape memory and superelasticity. However, unmodified NiTi carries a risk of localized nickel toxicity and inadequately supports angiogenesis or neuroregeneration due to limited cell adhesion, poor biomineralization, and little antibacterial activity. To address these challenges, NiTi nanoparticles were modified using self-assembled phosphonic acid monolayers and functionalized with the antibiotics ceftriaxone and vancomycin via the formation of an amide. Surface modifications were monitored to confirm that phosphonic acid modifications were present on NiTi nanoparticles and 100% of the samples formed ordered films. Modifications were stable for more than a year. Elemental composition showed the presence of nickel, titanium, and phosphorus (1.9% for each sample) after surface modifications. Dynamic light scattering analysis suggested some agglomeration in solution. However, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy confirmed a particle size distribution of <100 nm, the even distribution of nanoparticles on coverslips, and elemental composition before and after cell culture. B35 neuroblastoma cells exhibited no inhibition of survival and extended neurites of approximately 100 μm in total length when cultured on coverslips coated with only poly-l-lysine or with phosphonic acid-modified NiTi, indicating high biocompatibility. The ability to support neural cell growth and differentiation makes modified NiTi nanoparticles a promising coating for surfaces in metallic bone and nerve implants. NiTi nanoparticles functionalized with ceftriaxone inhibited Escherichia coli and Serratia marcescens (SM6) at doses of 375 and 750 μg whereas the growth of Bacillus subtilis was inhibited by a dose of only 37.5 μg. NiTi-vancomycin was effective against B. subtilis at all doses even after mammalian cell culture. These are common bacteria associated with infected implants, further supporting the potential use of functionalized NiTi in coating reconstructive implants.

Manganese in autism spectrum disorder and attention deficit hyperactivity disorder: The state of the art

The objective of the present narrative review was to synthesize existing clinical and epidemiological findings linking manganese (Mn) exposure biomarkers to autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD), and to discuss key pathophysiological mechanisms of neurodevelopmental disorders that may be affected by this metal. Existing epidemiological data demonstrated both direct and inverse association between Mn body burden and ASD, or lack of any relationship. In contrast, the majority of studies revealed significantly higher Mn levels in subjects with ADHD, as well as direct relationship between Mn body burden with hyperactivity and inattention scores in children, although several studies reported contradictory results. Existing laboratory studies demonstrated that impaired attention and hyperactivity in animals following Mn exposure was associated with dopaminergic dysfunction and neuroinflammation. Despite lack of direct evidence on Mn-induced neurobiological alterations in patients with ASD and ADHD, a plethora of studies demonstrated that neurotoxic effects of Mn overexposure may interfere with key mechanisms of pathogenesis inherent to these neurodevelopmental disorders. Specifically, Mn overload was shown to impair not only dopaminergic neurotransmission, but also affect metabolism of glutamine/glutamate, GABA, serotonin, noradrenaline, thus affecting neuronal signaling. In turn, neurotoxic effects of Mn may be associated with its ability to induce oxidative stress, apoptosis, and neuroinflammation, and/or impair neurogenesis. Nonetheless, additional detailed studies are required to evaluate the association between environmental Mn exposure and/or Mn body burden and neurodevelopmental disorders at a wide range of concentrations to estimate the potential dose-dependent effects, as well as environmental and genetic factors affecting this association.

Single-cell transcriptomics analysis of zebrafish brain reveals adverse effects of manganese on neurogenesis

Manganese (Mn) is considered as an important environmental risk factor for Parkinson's disease. Excessive exposure to Mn can damage various neural cells and affect the neurogenesis, resulting in neurological dysfunction. However, the specific mechanisms of Mn exposure affecting neurogenesis have not been well understood, including compositional changes and heterogeneity of various neural cells. Zebrafish have been successfully used as a neurotoxicity model due to its homology with mammals in several key regions of the brain, as well as its advantages such as small size. We performed single-cell RNA sequencing of zebrafish brains from normal and Mn-exposed groups. Our results suggested that low levels of Mn exposure activated neurogenesis in the zebrafish brain, including promoting the proliferation of neural progenitor cells and differentiation to newborn neurons and oligodendrocytes, while high levels of Mn exposure inhibited neurogenesis and neural function. Mn could affect neurogenesis through specific molecular pathways. In addition, Mn regulated intercellular communication and affected cellular communication in neural cells through specific signaling pathways. Taken together, our study elucidates the cellular composition of the zebrafish brain and adds to the understanding of the mechanisms involved in Mn-induced neurogenesis damage.

In vitro evaluation of the cytotoxic and genotoxic effects of Al and Mn in ambient concentrations detected in groundwater intended for human consumption

Environmental exposure to metals can induce cytotoxic and genotoxic effects in cells and affect the health of the exposed population. To investigate the effects of aluminum (Al) and manganese (Mn), we evaluated their cytogenotoxicity using peripheral blood mononuclear cells (PBMCs) exposed to these metals at previously quantified concentrations in groundwater intended for human consumption. The cell viability, membrane integrity, nuclear division index (NDI), oxidative stress, cell death, cell cycle, and DNA damage were analyzed in PBMCs exposed to Al (0.2, 0.6, and 0.8 mg/L) and Mn (0.1, 0.3, 1.0, and 1.5 for 48 h. We found that Al induced late apoptosis; decreased cell viability, NDI, membrane integrity; and increased DNA damage. However, no significant alterations in the early apoptosis, cell cycle, and reactive oxygen species levels were observed. In contrast, exposure to Mn altered all evaluated parameters related to cytogenotoxicity. Our data show that even concentrations allowed by the Brazilian legislation for Al and Mn in groundwater intended for human consumption cause cytotoxic and genotoxic effects in PBMCs. Therefore, in view of the results found, a comprehensive approach through in vivo investigations is needed to give robustness and validity to the results obtained, thus broadening the understanding of the impacts of metals on the health of environmentally exposed people.

The binary combined toxicity of lithium, lead, and manganese on the proliferation of murine neural stem cells using two different models

As persistent environmental pollutants, more than thirty metals impose a potential global threat to the environment and humans, which has raised scientific concerns. Although the toxic effects of metals had been extensively studied, there is a paucity of information on their mixture toxicity. In this study, we examined the individual and binary combined toxicity of three common metals such as lithium (Li), lead (Pb), and manganese (Mn) on the proliferation of murine neural stem cells (mNSCs), respectively. Li, Pb, and Mn reduced cell proliferation at the concentration of 5.00 mM, 2.50 μM, and 5.00 μM, respectively (all p < 0.050), in a dose-dependent manner of each metal solely on mNSCs with the cytotoxicity rank as Pb > Mn > Li. Furthermore, the interactions of metal mixtures on mNSCs were determined by using response-additivity and dose-additivity models. Pb + Mn mixtures showed a more than additive effect (synergistic) of toxicity in both two methods. In the dose-additivity method, Pb + Li and Li + Mn mixtures exhibited synergistic effects in the compound with a high ratio of Li (25.0% Pb/75.0% Li, 75.0% Li/25.0% Mn), whereas they are antagonistic in the lower or equal ratio of Li (such as 75.0% Pb/25.0% Li, 25.0% Li/75.0% Mn). Besides, the interactions of Li + Mn mixtures showed some discrepancies between different endpoints. In conclusion, our study highlights the complexity of the mixtures' interaction patterns and the possible neuroprotective effect of Li under certain conditions. In the future, more research on different levels of metal mixtures, especially Li metal, is necessary to evaluate their underlying interactions and contribute to establishing risk assessment systems.

Lung cell toxicity of co-exposure to airborne particulate matter and extremely low-frequency magnetic field

Although the toxic effects of urban airborne particulate matter (PM) have been known on lung cells, there is less attention to co-exposure to PM and extremely low frequency magnetic (ELF-MF) in occupational settings. The present study investigated the influences of PM and ELF-MF co-exposure on toxicity in human lung cells (A549).In this case, total PM (TPM) was evaluated according to NIOSH-0500. The TPM SiO₂ and metal contents were determined based on NIOSH-7602 and 7302, respectively. Besides, 900 mG ELF-MF exposure was simulated based on field measurements. The toxicity mechanisms were assessed by examining malondialdehyde, glutathione ratio, gene expression, and DNA strand breaks. Also, the toxicity indicators of the TPM samples were MDA generation, glutathione depletion, and DNA damage, and their impacts were analysed at doses below the LD₅₀ (4 µg).In addition, gene expression of OGG1 and MTH1 was upregulated after TPM exposure at the lowest dose (2 µg). But ITPA was upregulated in the presence of ELF-MF. The co-exposure to TPM and ELF-MF decreased oxidative stress and DNA damage levels compared to a single exposure to TPM.Although the ELF-MF reduced toxicity in response to TPM, this reduction was not lower than the unexposed cells.

Molecular Mechanisms of Environmental Metal Neurotoxicity: A Focus on the Interactions of Metals with Synapse Structure and Function

Environmental exposure to neurotoxic metals and metalloids such as arsenic, cadmium, lead, mercury, or manganese is a global health concern affecting millions of people worldwide. Depending on the period of exposure over a lifetime, environmental metals can alter neurodevelopment, neurobehavior, and cognition and cause neurodegeneration. There is increasing evidence linking environmental exposure to metal contaminants to the etiology of neurological diseases in early life (e.g., autism spectrum disorder) or late life (e.g., Alzheimer’s disease). The known main molecular mechanisms of metal-induced toxicity in cells are the generation of reactive oxygen species, the interaction with sulfhydryl chemical groups in proteins (e.g., cysteine), and the competition of toxic metals with binding sites of essential metals (e.g., Fe, Cu, Zn). In neurons, these molecular interactions can alter the functions of neurotransmitter receptors, the cytoskeleton and scaffolding synaptic proteins, thereby disrupting synaptic structure and function. Loss of synaptic connectivity may precede more drastic alterations such as neurodegeneration. In this article, we will review the molecular mechanisms of metal-induced synaptic neurotoxicity.

Heavy metals and adult neurogenesis

With extensive use in industrial and agriculture applications, overexposure to heavy metals has become a global public health concern. The nervous system is vulnerable to many heavy metals, including cadmium, lead, and mercury. However, the knowledge about the underlying mechanisms of these metals' neurotoxicity is still very limited. Adult neurogenesis is a process of generating functional neurons from adult neural progenitor/stem cells (aNPCs), which plays an important role in cognitive function and olfaction. The studies of adult neurogenesis provide new insights into mechanisms of heavy metal neurotoxicity. This review summarizes the current research about the effects of heavy metals on adult neurogenesis and discusses their importance in understanding the mechanisms of heavy metals neurotoxicity, as well as challenges and future directions.

Molecular Targets of Manganese-Induced Neurotoxicity: A Five-Year Update

Understanding of the immediate mechanisms of Mn-induced neurotoxicity is rapidly evolving. We seek to provide a summary of recent findings in the field, with an emphasis to clarify existing gaps and future research directions. We provide, here, a brief review of pertinent discoveries related to Mn-induced neurotoxicity research from the last five years. Significant progress was achieved in understanding the role of Mn transporters, such as SLC39A14, SLC39A8, and SLC30A10, in the regulation of systemic and brain manganese handling. Genetic analysis identified multiple metabolic pathways that could be considered as Mn neurotoxicity targets, including oxidative stress, endoplasmic reticulum stress, apoptosis, neuroinflammation, cell signaling pathways, and interference with neurotransmitter metabolism, to name a few. Recent findings have also demonstrated the impact of Mn exposure on transcriptional regulation of these pathways. There is a significant role of autophagy as a protective mechanism against cytotoxic Mn neurotoxicity, yet also a role for Mn to induce autophagic flux itself and autophagic dysfunction under conditions of decreased Mn bioavailability. This ambivalent role may be at the crossroad of mitochondrial dysfunction, endoplasmic reticulum stress, and apoptosis. Yet very recent evidence suggests Mn can have toxic impacts below the no observed adverse effect of Mn-induced mitochondrial dysfunction. The impact of Mn exposure on supramolecular complexes SNARE and NLRP3 inflammasome greatly contributes to Mn-induced synaptic dysfunction and neuroinflammation, respectively. The aforementioned effects might be at least partially mediated by the impact of Mn on α-synuclein accumulation. In addition to Mn-induced synaptic dysfunction, impaired neurotransmission is shown to be mediated by the effects of Mn on neurotransmitter systems and their complex interplay. Although multiple novel mechanisms have been highlighted, additional studies are required to identify the critical targets of Mn-induced neurotoxicity.

Intracerebral Transplantation of Neural Stem Cells Restores Manganese-Induced Cognitive Deficits in Mice

Manganese (Mn) is a potent neurotoxin known to cause long-lasting structural damage and progressive cognitive deficits in the brain. However, new therapeutic approaches are urgently needed since current treatments only target symptoms of Mn exposure. Recent studies have suggested a potential role for multipotent neural stem cells (NSCs) in the etiology of Mn-induced cognitive deficits. In this study, we evaluated the effect of direct intracerebral transplantation of NSCs on cognitive function of mice chronically exposed to MnCl₂, and further explored the distribution of transplanted NSCs in brain tissues. NSCs were isolated and bilaterally injected into the hippocampal regions or lateral ventricles of Mn-exposed mice. The results showed that many transplanted cells migrated far away from the injection sites and survived in vivo in the Mn-exposed mouse brain, implying enhanced neurogenesis in the host brain. We found that NSCs transplanted into either the hippocampal regions or the lateral ventricles significantly improved spatial learning and memory function of the Mn-exposed mice in the Morris water maze. Immunofluorescence analyses indicated that some surviving NSCs differentiated into neurons or glial cells, which may have become functionally integrated into the impaired local circuits, providing a possible cellular basis for the improvement of cognitive function in NSC-transplanted mice. Taken together, our findings confirm the Mn-induced impairment of neurogenesis in the brain and underscore the potential of treating Mn exposure by NSC transplantation, providing a practical therapeutic strategy against this type of neurotoxicity.

Intracellular nickel accumulation induces apoptosis and cell cycle arrest in human astrocytic cells

Nickel, a heavy metal found in electronic wastes and fume from electronic cigarettes, induces neuronal cell death and is associated with neurocognitive impairment. Astrocytes are the first line of defense against nickel after entering the brain; however, the effects of nickel on astrocytes remain unknown. Herein, we investigated the effect of nickel exposure on cell survival and proliferation and the underlying mechanisms in U-87 MG human astrocytoma cells and primary human astrocytes. Intracellular nickel levels were elevated in U-87 MG cells in a dose- and time-dependent manner after exposure to nickel chloride. The median toxic concentrations of nickel in astrocytoma cells and primary human astrocytes were 600.60 and >1000 µM at 48 h post-exposure, respectively. Nickel exposure triggered apoptosis in concomitant with the decreased expression of anti-apoptotic B-cell lymphoma protein (Bcl-2) and increased caspase-3/7 activity. Nickel induced reactive oxygen species formation. Additionally, nickel suppressed astrocyte proliferation in a dose- and time-dependent manner by delaying G2 to M phase transition through the upregulation of cyclin B1 and p27 protein expression. These results indicate that nickel-induced cytotoxicity of astrocytes is mediated by the activation of apoptotic pathway and disruption of cell cycle regulation.

A global life cycle assessment of manganese mining processes based on EcoInvent database

This paper presents the life cycle assessment (LCA) carried out on the manganese beneficiation and refining process. This cradle-to-gate analysis is carried out using SimaPro software version 8.5. The considered case is the manganese beneficiation and refining process, and the final product is 1 kg of refined manganese. The global average dataset is collected from the EcoInvent and AusLCI database, which are originated from literature source. The analysis methodologies considered in this study are the International Life Cycle Reference Data System (ILCD) method and Cumulative Energy Demand (CED) method. A comparative analysis is also presented which compared among ILCD, Australian Indicator, and Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI) methods to identify the best practice method for global analysis of mining processes. A detailed sensitivity analysis has been carried out considering different scenarios, to suggest possible solutions to reduce the environmental impacts associated with manganese beneficiation and refining processes. The analysis results reveal that particulate matter, climate change, categories of eutrophication, human toxicity (cancer and non-cancer effects), and acidification are some of the noteworthy impact categories. The analysis results also showed that coal consumption is significantly higher than other types of renewables and non-renewable energy consumption in manganese beneficiation and refining processes. The analysis results further reveal that using the chromium steel in manganese beneficiation process and ferromanganese consumption in the refining process has a significant effect over other materials involved in manganese beneficiation and refining operations. The obvious reason behind this result is ferromanganese utilization as an energy-intensive process, which in turn increases the environmental emissions. The analysis results also showed that, between the beneficiation and refining process, manganese refining has a much greater impact on the environment rather than the beneficiation process due to the fossil fuel and electricity consumption in refining operations.