Consequences of Disturbing Manganese Homeostasis

Targeted nanoprobe for magnetic resonance imaging-guided enhanced antitumor via synergetic photothermal/immunotherapy

Synergistic photothermal/immunotherapy has garnered significant attention for its potential to enhance tumor therapeutic outcomes. However, the fabrication of an intelligent system with a simple composition that simultaneously exerts photothermal/immunotherapy effect and imaging guidance function still remains a challenge. Herein, a glutathione (GSH)-responsive theranostic nanoprobe, named HA-MnO2/ICG, was elaborately constructed by loading photothermal agent (PTA) indocyanine green (ICG) onto the surface of hyaluronic acid (HA)-modified manganese dioxide nanosheets (HA-MnO2) for magnetic resonance (MR) imaging-guided synergetic photothermal/immuno-enhanced therapy. In this strategy, HA-MnO2 nanosheets were triggered by the endogenous GSH in tumor microenvironment to generate Mn2+ for MR imaging, where the longitudinal relaxation rate of HA-MnO2/ICG was up to 14.97 mM-1s-1 (∼24 times than that found in a natural environment), demonstrating excellent intratumoral MR imaging. Moreover, the HA-MnO2/ICG nanoprobe demonstrates remarkable photothermal therapy (PTT) efficacy, generating sufficient heat to induce immunogenic cell death (ICD) within tumor cells. Meanwhile the released Mn2+ ions from the nanosheets function as potent immune adjuvants, amplifying the immune response against cancer. In vivo experiments validated that HA-MnO2/ICG-mediated PTT was highly effective in eradicating primary tumors, while simultaneously enhancing immunogenicity to prevent the growth of distal metastasis. This hybrid HA-MnO2/ICG nanoprobe opened new avenues in the design of MR imaging-monitored PTT/immuno-enhanced synergistic therapy for advanced cancer.

Melatonin prevents bone loss in osteoporotic rats with valproic acid treatment by anti-inflammatory and anti-oxidative stress

Melatonin (MEL) has shown positive effects in anti-inflammatory and anti-oxidative stress research. This study investigates whether MEL can positively impact bone loss induced by valproic acid (VPA) in rats. The study examines changes in MC3T3-E1 cell viability and osteogenic potential, along with osteoclast differentiation in RAW264.7 cells in the presence of VPA using CCK-8, ALP staining, AR staining, and TRAP staining. In vitro experiments reveal that VPA-induced inhibition of osteogenic differentiation and promotion of osteoclastic differentiation are linked to increased inflammation and oxidative stress. Furthermore, MEL has demonstrated the ability to reduce oxidative stress and inflammation, boost osteogenic differentiation, and inhibit osteoclast differentiation. Animal experiments confirm that MEL significantly increases SOD2 expression and decreases TNF-α expression, leading to the restoration of impaired bone metabolism, enhanced bone strength, and higher bone mineral density. The combined experimental results strongly suggest that MEL can enhance osteogenic activity in the presence of VPA by reducing inflammation and oxidative stress, impeding osteoclast differentiation, and alleviating bone loss in VPA-treated rat models.

Assessment of manganese accumulation in dryland wheat grains via plastic film mulching: Implications for human health risk in multi-site studies

Crop manganese (Mn) accumulation and the associated human health risks stemming from excessive intake of high Mn crop foods have attracted attention. However, there is limited information available concerning the impact of plastic film mulching (PFM) on Mn concentration in cereal grains and the health risks associated with Mn intake by the human body. Field experiments were conducted from 2014 to 2016 at seven sites in the drylands of a typical wheat-growing region in China to assess the effect of PFM on grain Mn concentration, Mn accumulation and distribution in winter wheat plants, and the potential risk of Mn intake and optimal grain intake for human health. The multi-site study results revealed that grain Mn concentration and bioavailability were significantly higher under PFM compared to no mulching. Similarly, PFM was found to enhance aboveground Mn accumulation at the anthesis stage by 17.5 %, Mn harvest index by 3.9 %, grain Mn accumulation by 28.9 %, and available Mn concentration in the soil by 10.9 %. The increased uptake and accumulation of Mn in wheat plants, leading to elevated grain Mn concentration, were primarily attributed to the improved availability of Mn and moisture in the soil under PFM treatment. Furthermore, a health risk assessment indicated that long-term consumption of whole wheat grains from PFM treatment could potentially pose a non-carcinogenic risk of Mn for children and adolescents residing in rural areas. Therefore, this study established upper limits for daily consumption of whole wheat grains based on the specific needs of local residents. The findings of this research underscore the potential health risks associated with consuming grain crops grown in PFM crop production systems.

The Role of Trace Metals in the Development and Progression of Prostate Cancer

Over the years, prostate cancer (PCa) research has been of great interest, and trace metals have attracted a lot of attention due to their association with prostate cancer development and progression. PCa has a complex etiology, with genetic, environmental, and lifestyle factors being implicated. Trace metals such as zinc (Zn), mercury (Hg), selenium (Se), lead (Pb), cadmium (Cd), manganese (Mn), arsenic (As), and nickel (Ni) have garnered much attention in recent years, suspected of having direct links to the modulation of cancer risk and progression through their impacts on prostate cancer omics (genomics, epigenetics, proteomics, and transcriptomics). This has led to them being the subject of extensive research in this regard. In this review, we explored the influence of trace metals and offered a comprehensive analysis of the current knowledge on how trace metals affect the biology of prostate cancer at a molecular level by integrating findings from the recent literature to help suggest possible directions for future research.

Neuroprotective effects of punicalagin and/or micronized zeolite clinoptilolite on manganese-induced Parkinson's disease in a rat model: Involvement of multiple pathways

BACKGROUND

Manganism, a central nervous system dysfunction correlated with neurological deficits such as Parkinsonism, is caused by the substantial collection of manganese chloride (MnCl2) in the brain.

OBJECTIVES

To explore the neuroprotective effects of natural compounds, namely, micronized zeolite clinoptilolite (ZC) and punicalagin (PUN), either individually or in combination, against MnCl2-induced Parkinson's disease (PD).

METHODS

Fifty male albino rats were divided into 5 groups (Gps). Gp I was used as the control group, and the remaining animals received MnCl2 (Gp II-Gp V). Rats in Gps III and IV were treated with ZC and PUN, respectively. Gp V received both ZC and PUN as previously reported for the solo-treated plants.

RESULTS

ZC and/or PUN reversed the depletion of monoamines in the brain and decreased acetyl choline esterase activity, which primarily adjusted the animals' behavior and motor coordination. ZC and PUN restored the balance between glutamate/γ-amino butyric acid content and markedly improved the brain levels of brain-derived neurotrophic factor and nuclear factor erythroid 2-related factor 2/heme oxygenase-1 and decreased glycogen synthase kinase-3 beta activity. ZC and PUN also inhibited inflammatory and oxidative markers, including nuclear factor kappa-light-chain-enhancer of activated B cells, Toll-like receptor 4, nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 and caspase-1. Bcl-2-associated X-protein and B-cell leukemia/lymphoma 2 protein (Bcl-2) can significantly modify caspase-3 expression. ZC and/or PUN ameliorated PD in rats by decreasing the levels of endoplasmic reticulum (ER) stress markers (p-protein kinase-like ER kinase (PERK), glucose-regulated protein 78, and C/EBP homologous protein (CHOP)) and enhancing the levels of an autophagy marker (Beclin-1).

DISCUSSION AND CONCLUSION

ZC and/or PUN mitigated the progression of PD through their potential neurotrophic, neurogenic, anti-inflammatory, antioxidant, and anti-apoptotic activities and by controlling ER stress through modulation of the PERK/CHOP/Bcl-2 pathway.

The impact of manganese on vascular endothelium

Manganese (Mn) is an essential trace element involved in various physiological processes, but excessive exposure may lead to toxicity. The vascular endothelium, a monolayer of endothelial cells within blood vessels, is a primary target of Mn toxicity. This review provides a comprehensive overview of the impact of Mn on vascular endothelium, focusing on both peripheral and brain endothelial cells. In vitro studies have demonstrated that high concentrations of Mn can induce endothelial cell cytotoxicity, increase permeability, and disrupt cell-cell junctions through mechanisms involving oxidative stress, mitochondrial damage, and activation of signaling pathways, such as Smad2/3-Snail. Conversely, low concentrations of Mn may protect endothelial cells from the deleterious effects of high glucose and advanced glycation end-products. In the central nervous system, Mn can cross the blood-brain barrier (BBB) and accumulate in the brain parenchyma, leading to neurotoxicity. Several transport mechanisms, including ZIP8, ZIP14, and SPCA1, have been identified for Mn uptake by brain endothelial cells. Mn exposure can impair BBB integrity by disrupting tight junctions and increasing permeability. In vivo studies have corroborated these findings, highlighting the importance of endothelial barriers in mediating Mn toxicity in the brain and kidneys. Maintaining optimal Mn homeostasis is crucial for preserving endothelial function, and further research is needed to develop targeted therapeutic strategies to prevent or mitigate the adverse effects of Mn overexposure.

Graphical Abstract

Bioaccumulation dynamics, noncarcinogenic and carcinogenic risks of heavy metals in commercially valuable shellfish and finfish species from the world largest floating slum, Makoko, Nigeria

This study examined ten heavy metals in five species: Macrobrachium vollenhovenii, Penaeus monodon, P. notialis, Chloroscombrus chrysurus, and Pseudotolithus typus, from Makoko floating slum, Lagos Lagoon to discern their bioaccumulation potentials, sources of origin, and health implications. The concentrations were in this order: Fe (4.172-10.176) > Zn (1.310-5.754) > Mn (0.475-2.330) > Cu (0.238-1.735) > Pb (0.121-0.391) > Cd (0.055-0.283) > Co (0.056-0.144) > Ni (0.039-0.121) > Cr (0.022-0.095) > As (0.003-0.031) mg/kg. The MPDI denotes "low toxicity," and the BAF/BSAF revealed that benthic species had higher bioconcentration potentials. Multivariate analyses revealed that heavy metals exhibited mutual relationships during chemical transport, and their sources were both geogenic and human-induced. The HI values were below 1, and the TCR values were below the threshold of 1 × 10-4. This suggests that the probabilities of noncancer and carcinogenic risks in human populations due to long-term consumption of the evaluated species are unlikely.

Manganese inhibits HBV transcription and promotes HBsAg degradation at non-toxic levels

Chronic hepatitis B virus (HBV) infection continues to pose a significant global health challenge. However, therapeutic measures for a cure are lacking in clinical practice. Manganese, an essential trace element, has garnered attention due to its potential to activate innate immune pathways and its significant role in antiviral and antitumor immunity. Yet, the specific impact of manganese on chronic hepatitis B has been largely unexplored. Our research reveals that manganese substantially inhibits HBV replication in hepatocellular carcinoma cells at non-toxic levels. This suppression occurs independently of well-known anti-HBV innate immune pathways, such as the cGAS-STING pathway. Mechanistically, manganese decreases HBV transcription by diminishing the levels of liver-specific transcription factors. Furthermore, it activates the mTOR pathway, enhancing HBsAg ubiquitination through the upregulation of the ubiquitin ligase β-TrCP and increasing proteasome activity via the augmentation of its subunits, leading to a ubiquitin-dependent degradation of HBsAg. Significantly, our study also uncovers a notable clinical correlation between manganese levels and chronic hepatitis B infection. These findings position manganese as a critical element in diminishing HBV replication, offering a new direction in the management of chronic hepatitis B.

Signal Transduction Associated with Mn-induced Neurological Dysfunction

Manganese (Mn) is a heavy metal that occurs widely in nature and has a vital physiological role in growth and development. However, excessive exposure to Mn can cause neurological damage, especially cognitive dysfunction, such as learning disability and memory loss. Numerous studies on the mechanisms of Mn-induced nervous system damage found that this metal targets a variety of metabolic pathways, for example, endoplasmic reticulum stress, apoptosis, neuroinflammation, cellular signaling pathway changes, and neurotransmitter metabolism interference. This article reviews the latest research progress on multiple signaling pathways related to Mn-induced neurological dysfunction.

Morphographic Changes in the Electrocardiogram of Colossoma macropomum Caused by Exposure to Manganese

Manganese (Mn2+) is an abundant chemical element in the earth's crust and is present in soil, water, and industrial environments, including mining, welding, and battery manufacturing. Manganese (Mn) is an essential metal needed as a cofactor for many enzymes to maintain proper biological functions. Excessive exposure to Mn in high doses can result in a condition known as manganism, which results in disorders of the neurological, cardiac, and pulmonary systems. The aim of this study was to assess cardiac susceptibility to manganese intoxication in Colossoma macropomum subjected to a fixed concentration of 4 mg/mL for a period of up to 96 h. This study used 45 Tambaquis (30.38 ± 3.5 g) divided into five groups of 9 animals/treatment. The treated groups were exposed to the manganese concentration for a period of 24, 48, 72, and 96 h, after which the animals' ECGs were recorded, showing heart rate, R-R interval, P-Q interval, QRS complex duration and S-T interval. The results showed that cardiac activity decreased as the contact time increased, with an increase in the P-Q and S-T intervals. This indicates that the breakdown of circulatory homeostasis in these animals was caused by contact time with manganese.

The Manganese-Bone Connection: Investigating the Role of Manganese in Bone Health

The complex relationship between trace elements and skeletal health has received increasing attention in the scientific community. Among these minerals, manganese (Mn) has emerged as a key element affecting bone metabolism and integrity. This review examines the multifaceted role of Mn in bone health, including its effects on bone regeneration, mineralization, and overall skeletal strength. This review article is based on a synthesis of experimental models, epidemiologic studies, and clinical trials of the mechanisms of the effect of Mn on bone metabolism. Current research data show that Mn is actively involved in the processes of bone remodeling by modulating the activity of osteoblasts and osteoclasts, as well as the main cells that regulate bone formation and resorption. Mn ions have a profound effect on bone mineralization and density by intricately regulating signaling pathways and enzymatic reactions in these cells. Additionally, Mn superoxide dismutase (MnSOD), located in bone mitochondria, plays a crucial role in osteoclast differentiation and function, protecting osteoclasts from oxidative damage. Understanding the nuances of Mn's interaction with bone is essential for optimizing bone strategies, potentially preventing and managing skeletal diseases. Key findings include the stimulation of osteoblast proliferation and differentiation, the inhibition of osteoclastogenesis, and the preservation of bone mass through the RANK/RANKL/OPG pathway. These results underscore the importance of Mn in maintaining bone health and highlight the need for further research into its therapeutic potential.

Manganese transporter SLC30A10 and iron transporters SLC40A1 and SLC11A2 impact dietary manganese absorption

SLC30A10 deficiency is a disease of severe manganese excess attributed to loss of SLC30A10-dependent manganese excretion via the gastrointestinal tract. Patients develop dystonia, cirrhosis, and polycythemia. They are treated with chelators but also respond to oral iron, suggesting that iron can outcompete manganese for absorption in this disease. Here we explore the latter observation. Intriguingly, manganese absorption is increased in Slc30a10-deficient mice despite manganese excess. Studies of multiple mouse models indicate that increased dietary manganese absorption reflects two processes: loss of manganese export from enterocytes into the gastrointestinal tract lumen by SLC30A10, and increased absorption of dietary manganese by iron transporters SLC11A2 (DMT1) and SLC40A1 (ferroportin). Our work demonstrates that aberrant absorption contributes prominently to SLC30A10 deficiency and expands our understanding of biological interactions between iron and manganese. Based on these results, we propose a reconsideration of the role of iron transporters in manganese homeostasis is warranted.

Metabolic Derangement of Essential Transition Metals and Potential Antioxidant Therapies

Essential transition metals have key roles in oxygen transport, neurotransmitter synthesis, nucleic acid repair, cellular structure maintenance and stability, oxidative phosphorylation, and metabolism. The balance between metal deficiency and excess is typically ensured by several extracellular and intracellular mechanisms involved in uptake, distribution, and excretion. However, provoked by either intrinsic or extrinsic factors, excess iron, zinc, copper, or manganese can lead to cellular damage upon chronic or acute exposure, frequently attributed to oxidative stress. Intracellularly, mitochondria are the organelles that require the tightest control concerning reactive oxygen species production, which inevitably leaves them to be one of the most vulnerable targets of metal toxicity. Current therapies to counteract metal overload are focused on chelators, which often cause secondary effects decreasing patients' quality of life. New therapeutic options based on synthetic or natural antioxidants have proven positive effects against metal intoxication. In this review, we briefly address the cellular metabolism of transition metals, consequences of their overload, and current therapies, followed by their potential role in inducing oxidative stress and remedies thereof.

Algae-Boosted Chickpea Hummus: Improving Nutrition and Texture with Seaweeds and Microalgae

The global food industry faces a critical challenge in ensuring sustainable practices to meet the demands of a growing population while minimizing environmental impact. At the same time, consumer awareness and the demand for quality products drive innovation and inspire positive changes in the food supply chain. Aiming to create a more sustainable and nutrient-rich alternative, this study is summarized by characterizing the physical and chemical characteristics of algae-enriched chickpea hummus: an innovative approach to popular food products. The algae-enriched hummuses were developed with an incorporation (6% w/w) of Gelidium corneum and Fucus vesiculosus seaweeds and Chlorella vulgaris (hetero and autotrophic) microalgae to reveal their technological potential and evaluate the nutritional and rheological characteristics relative to a control hummus (without algae). From a nutritional perspective, the main results indicated that hummus enriched with microalgae showed an increase in protein content and an improved mineral profile. This was particularly notable for the seaweed F. vesiculosus and the autotrophic microalga C. vulgaris, leading to claims of being a "source of" and "rich in" various minerals. Additionally, the antioxidant activity of hummus containing F. vesiculosus and C. vulgaris increased significantly compared to the control. From a rheological perspective, incorporating algae into the humus strengthened its structure. The microalgae further enhanced the dish's elasticity and firmness, thus improving this chickpea-based dish´s overall texture and quality.

Magnetic Resonance Imaging and Manganism: A Narrative Review and Laboratory Recommendations

In recent years, a series of articles has been published concerning magnetic resonance imaging (MRI) studies in a group of patients exposed to manganism, specifically factory workers, welders, and individuals with liver diseases, as well as those abusing home-produced ephedrone. Some potential symptoms of manganese toxicity include motor disturbances, neurocognitive problems, sleep disorders, and psychosocial changes. Despite various publications on MRI research in individuals with an elevated risk of manganism, there is a noticeable absence of a comprehensive review in this field. The detection of the accumulation of manganese in the brain through MRI can confirm the diagnosis and guide appropriate treatment. Due to the high cost of determining manganese ion levels in biological material, an additional aim of the manuscript was to identify simple medical laboratory parameters that, when performed concurrently with MRI, could assist in the diagnosis of manganism. Among these types of parameters are the levels of bilirubin, magnesium, liver enzymes, creatinine, hemoglobin, and hematocrit.

The effects of heavy metal exposure on brain and gut microbiota: A systematic review of animal studies

The gut-brain axis is a crucial interface between the central nervous system and the gut microbiota. Recent evidence shows that exposure to environmental contaminants, such as heavy metals, can cause dysbiosis in gut microbiota, which may affect the gut-brain communication, impacting aspects of brain function and behavior. This systematic review of the literature aims to evaluate whether deleterious effects on brain function due to heavy metal exposure could be mediated by changes in the gut microbiota profile. Animal studies involving exposure to heavy metals and a comparison with a control group that evaluated neuropsychological outcomes and/or molecular outcomes along with the analysis of microbiota composition were reviewed. The authors independently assessed studies for inclusion, extracted data and assessed risk of bias using the protocol of Systematic Review Center for Laboratory Animal Experimentation (SYRCLE) for preclinical studies. A search in 3 databases yielded 16 eligible studies focused on lead (n = 10), cadmium (n = 1), mercury (n = 3), manganese (n = 1), and combined exposure of lead and manganese (n = 1). The animal species were rats (n = 7), mice (n = 4), zebrafish (n = 3), carp (n = 1) and fruit fly (n = 1). Heavy metals were found to adversely affect cognitive function, behavior, and neuronal morphology. Moreover, heavy metal exposure was associated with changes in the abundance of specific bacterial phyla, such as Firmicutes and Proteobacteria, which play crucial roles in gut health. In some studies, these alterations were correlated with learning and memory impairments and mood disorders. The interplay of heavy metals, gut microbiota, and brain suggests that heavy metals can induce direct brain alterations and indirect effects through the microbiota, contributing to neurotoxicity and the development of neuropsychological disorders. However, the small number of papers under review makes it difficult to draw definitive conclusions. Further research is warranted to unravel the underlying mechanisms and evaluate the translational implications for human health.

Tracking the Variations in Trace and Heavy Elements in Smoking Products Marketed in Oman and Egypt: Risk Assessment After Implementation of Constraining Protocols

Tobacco smoking is becoming one of the major worldwide concerns regarding environmental pollution as well as health threats. In 2005, the World Health Organization (WHO) released the Framework Convention On Tobacco Control (FCTC), which outlined protocols for controlling tobacco products. Oman was one of the leading countries to follow these protocols; however, Egypt has only followed these protocols recently in 2020. One of the main challenges in tobacco product control is the variation in their trace element's types and amounts from country to country owing to differences in agriculture techniques and used chemical additives. Smoking releases different toxic metal ions found in them into the air, and hence, analyzing trace amounts of metals in tobacco smoking products is becoming more critical. The proposed research aims to evaluate the current levels of 11 heavy metals (namely, As, Pb, Cd, Co, Cr, Be, Ba, Mn, Ni, Fe, and Hg) in 22 tobacco products available in Egypt and Oman using inductively coupled plasma optical emission spectroscopy and a direct mercury analyzer. Although some elements such as Be, Co, and Cd were absent, the positive detection of As and Pb and the levels of Ba, Cr, and Ni are still alarming, especially for heavy smokers. The obtained results were then statistically related to previously published data in 2017 to explore the effectiveness of implementing the FCTC protocols within the Egyptian market. The outcomes suggested a positive impact of FCTC protocol implementation in Egypt, besides the lower levels of elemental content for Omani products compared to the Egyptian market.

Zinc and manganese homeostasis closely interact in mammalian cells

Understanding the homeostatic interactions among essential trace metals is important for explaining their roles in cellular systems. Recent studies in vertebrates suggest that cellular Mn metabolism is related to Zn metabolism in multifarious cellular processes. However, the underlying mechanism remains unclear. In this study, we examined the changes in the expression of proteins involved in cellular Zn and/or Mn homeostatic control and measured the Mn as well as Zn contents and Zn enzyme activities to elucidate the effects of Mn and Zn homeostasis on each other. Mn treatment decreased the expression of the Zn homeostatic proteins metallothionein (MT) and ZNT1 and reduced Zn enzyme activities, which were attributed to the decreased Zn content. Moreover, loss of Mn efflux transport protein decreased MT and ZNT1 expression and Zn enzyme activity without changing extracellular Mn content. This reduction was not observed when supplementing with the same Cu concentrations and in cells lacking Cu efflux proteins. Furthermore, cellular Zn homeostasis was oppositely regulated in cells expressing Zn and Mn importer ZIP8, depending on whether Zn or Mn concentration was elevated in the extracellular milieu. Our results provide novel insights into the intricate interactions between Mn and Zn homeostasis in mammalian cells and facilitate our understanding of the physiopathology of Mn, which may lead to the development of treatment strategies for Mn-related diseases in the future.

Mechanism of KAT2A regulation of H3K36ac in manganese-induced oxidative damage to mitochondria in the nervous system and intervention by curcumin

Excessive exposure to manganese in the environment or workplace is strongly linked to neurodegeneration and cognitive impairment, but the precise pathogenic mechanism and preventive measures are still not fully understood. The study aimed to investigate manganese -induced oxidative damage in the nervous system from an epigenetic perspective, focusing on the H3K36ac-dependent antioxidant pathway. Additionally, it sought to examine the potential of curcumin in preventing manganese-induced oxidative damage. Histopathology and transmission electron microscopy revealed that apoptosis and necrosis of neurons and mitochondrial ultrastructure damage were observed in the striatum of manganese-exposed rats. manganese suppressed the expression of mitochondrial antioxidant genes, leading to oxidative damage in the rats' striatum and SH-SY5Y cells. With higher doses of manganese, levels of histone acetyltransferase lysine acetyltransferase 2 A (KAT2A) expression and H3K36ac level decreased. ChIP-qPCR confirmed that H3K36ac enrichment in the promoter regions of antioxidant genes SOD2, PRDX3, and TXN2 was reduced in SH-SY5Y cells after manganese exposure, leading to decreased expression of these genes. Overexpression of KAT2A confirms that it attenuates manganese-induced mitochondrial oxidative damage by regulating H3K36ac levels, which in turn controls the expression of antioxidant genes SOD2, PRDX3, and TXN2 in the manganese-exposed cell model. Furthermore, curcumin might control H3K36ac levels by influencing KAT2A expression, boosting antioxidant genes expression, and reducing manganese-induced mitochondrial oxidative damage. In conclusion, the regulation of mitochondrial oxidative stress by histone acetylation may be an important mechanism of manganese-induced neurotoxicity. This regulation could be achieved by reducing the level of H3K36ac near the promoter region of mitochondrial-associated antioxidant genes via KAT2A. Curcumin mitigates manganese-induced oxidative damage in mitochondria and plays a crucial protective role in manganese-induced oxidative injury in the nervous system.

Signaling Pathways Involved in Manganese-Induced Neurotoxicity

Manganese (Mn) is an essential trace element, but insufficient or excessive bodily amounts can induce neurotoxicity. Mn can directly increase neuronal insulin and activate insulin-like growth factor (IGF) receptors. As an important cofactor, Mn regulates signaling pathways involved in various enzymes. The IGF signaling pathway plays a protective role in the neurotoxicity of Mn, reducing apoptosis in neurons and motor deficits by regulating its downstream protein kinase B (Akt), mitogen-activated protein kinase (MAPK), and mammalian target of rapamycin (mTOR). In recent years, some new mechanisms related to neuroinflammation have been shown to also play an important role in Mn-induced neurotoxicity. For example, DNA-sensing receptor cyclic GMP-AMP synthase (cCAS) and its downstream signal efficient interferon gene stimulator (STING), NOD-like receptor family pyrin domain containing 3(NLRP3)-pro-caspase1, cleaves to the active form capase1 (CASP1), nuclear factor κB (NF-κB), sirtuin (SIRT), and Janus kinase (JAK) and signal transducers and activators of the transcription (STAT) signaling pathway. Moreover, autophagy, as an important downstream protein degradation pathway, determines the fate of neurons and is regulated by these upstream signals. Interestingly, the role of autophagy in Mn-induced neurotoxicity is bidirectional. This review summarizes the molecular signaling pathways of Mn-induced neurotoxicity, providing insight for further understanding of the mechanisms of Mn.