Study of the localization of iron, ferritin, and hemosiderin in Alzheimer’s disease hippocampus by analytical microscopy at the subcellular level

Visceral adiposity is associated with iron deposition and myelin loss in the brains of aged mice

Iron deposition and myelin loss are observed in the brain with aging, and iron accumulation is suggested to be involved in myelin damage. However, the exact mechanism of iron deposition with aging remains unclear. This study was aimed to determine whether expanded visceral adipose tissue contributes to iron deposition and myelin loss by inducing hepcidin in the brains of aged male mice. Compared with young adult mice, levels of hepcidin in the brain, epididymal adipose tissue, and circulation were increased in aged mice, which had expanded visceral adipose tissue with inflammation. An increase in expressions of ferritin, an indicator of intracellular iron status, was accompanied by decreased levels of proteins related to myelin sheath in the brains of aged mice. These age-related changes in the brain were improved by visceral fat removal. In addition, IL-6 level, activation of microglia/macrophages, and nuclear translocation of phosphorylated Smad1/5 (pSmad1/5) inducing hepcidin expression were reduced in the brains of aged mice after visceral fat removal, accompanied by decreases of pSmad1/5- and ferritin-positive microglia/macrophages and mature oligodendrocytes. These findings indicate that visceral adiposity contributes to hepcidin-mediated iron deposition and myelin loss with inflammation in the aged brain. Our results support the importance of preventing visceral adiposity for maintaining brain health in older individuals.

Ferritin at different iron loading: From biological to nanotechnological applications

The characterization of the structure of ferritin in solution and the arrangement of iron stored in its cavity are intriguing subjects for both cell biology and applied science, since the protein structure, stability, and easiness of production make it an ideal tool for biomedical applications. We characterized the ferritin structure over a wide range of iron loadings by visible light, X-ray, and neutron scattering techniques. We found that the arrangement of iron ions inside the protein cage resulted in a more disposable arrangement at lower loading factors and then in a crystalline structure. At very high iron content the inner core is composed of magnetite more than ferrihydrite, and the shell of the protein is elastically deformed by the iron crystal growth in an ellipsoidal arrangement. The application of an external radiofrequency (RF) magnetic field affected ferritins at low iron loading factors. Notably the RF modified the iron disposition towards a more dispersed arrangement. The structural characterization of the ferritin at different LFs and in presence of magnetic fields provides useful insights into their physiological behaviour and can help in the design and fine-tuning of ferritin-based nanosystems for biotechnological applications.

Nanoscale synchrotron x-ray analysis of intranuclear iron in melanised neurons of Parkinson's substantia nigra

Neuromelanin-pigmented neurons of the substantia nigra are selectively lost during the progression of Parkinson's disease. These neurons accumulate iron in the disease state, and iron-mediated neuron damage is implicated in cell death. Animal models of Parkinson's have evidenced iron loading inside the nucleoli of nigral neurons, however the nature of intranuclear iron deposition in the melanised neurons of the human substantia nigra is not understood. Here, scanning transmission x-ray microscopy (STXM) is used to probe iron foci in relation to the surrounding ultrastructure in melanised neurons of human substantia nigra from a confirmed Parkinson's case. In addition to the expected neuromelanin-bound iron, iron deposits are also associated with the edge of the cell nucleolus. Speciation analysis confirms these deposits to be ferric (Fe3+) iron. The function of intranuclear iron in these cells remains unresolved, although both damaging and protective mechanisms are considered. This finding shows that STXM is a powerful label-free tool for the in situ, nanoscale chemical characterisation of both organic and inorganic intracellular components. Future applications are likely to shed new light on incompletely understood biochemical mechanisms, such as metal dysregulation and morphological changes to cell nucleoli, that are important in understanding the pathogenesis of Parkinson's.

Cellular iron deposition patterns predict clinical subtypes of multiple system atrophy

BACKGROUND

Multiple system atrophy (MSA) is a primary oligodendroglial synucleinopathy, characterized by elevated iron burden in early-affected subcortical nuclei. Although neurotoxic effects of brain iron deposition and its relationship with α-synuclein pathology have been demonstrated, the exact role of iron dysregulation in MSA pathogenesis is unknown. Therefore, advancing the understanding of iron dysregulation at the cellular level is critical, especially in relation to α-synuclein cytopathology.

METHODS

Iron burden in subcortical and brainstem regions were histologically mapped in human post-mortem brains of 4 MSA-parkinsonian (MSA-P), 4 MSA-cerebellar (MSA-C), and 1 MSA case with both parkinsonian and cerebellar features. We then performed the first cell type-specific evaluation of pathological iron deposition in α-synuclein-affected and -unaffected cells of the globus pallidus, putamen, and the substantia nigra, regions of highest iron concentration, using a combination of iron staining with immunolabelling. Selective regional and cellular vulnerability patterns of iron deposition were compared between disease subtypes. In 7 MSA cases, expression of key iron- and closely related oxygen-homeostatic genes were examined.

RESULTS

MSA-P and MSA-C showed different patterns of regional iron burden across the pathology-related systems. We identified subcortical microglia to predominantly accumulate iron, which was more distinct in MSA-P. MSA-C showed relatively heterogenous iron accumulation, with greater or similar deposition in astroglia. Iron deposition was also found outside cellular bodies. Cellular iron burden associated with oligodendrocytic, and not neuronal, α-synuclein cytopathology. Gene expression analysis revealed dysregulation of oxygen homeostatic genes, rather than of cellular iron. Importantly, hierarchal cluster analysis revealed the pattern of cellular vulnerability to iron accumulation, distinctly to α-synuclein pathology load in the subtype-related systems, to distinguish MSA subtypes.

CONCLUSIONS

Our comprehensive evaluation of iron deposition in MSA brains identified distinct regional, and for the first time, cellular distribution of iron deposition in MSA-P and MSA-C and revealed cellular vulnerability patterns to iron deposition as a novel neuropathological characteristic that predicts MSA clinical subtypes. Our findings suggest distinct iron-related pathomechanisms in MSA clinical subtypes that are therefore not a consequence of a uniform down-stream pathway to α-synuclein pathology, and inform current efforts in iron chelation therapies at the disease and cellular-specific levels.

Iron associated lipid peroxidation in Alzheimers disease is increased in lipid rafts with decreased ferroptosis suppressors, tested by chelation in mice

Iron-mediated cell death (ferroptosis) is a proposed mechanism of Alzheimers disease (AD) pathology. While iron is essential for basic biological functions, its reactivity generates oxidants which contribute to cell damage and death. To further resolve mechanisms of iron-mediated toxicity in AD, we analyzed postmortem human brain and ApoEFAD mice. AD brains had decreased antioxidant enzymes, including those mediated by glutathione (GSH). Subcellular analyses of AD brains showed greater oxidative damage and lower antioxidant enzymes in lipid rafts, the site of amyloid processing, than in the non-raft membrane fraction. ApoE4 carriers had lower lipid raft yield with greater membrane oxidation. The hypothesized role of iron to AD pathology was tested in ApoEFAD mice by iron chelation with deferoxamine, which decreased fibrillar amyloid and lipid peroxidation, together with increased GSH-mediated antioxidants. These novel molecular pathways in iron mediated damage during AD.

The Irony of Iron: The Element with Diverse Influence on Neurodegenerative Diseases

Iron accumulation in the brain is a common feature of many neurodegenerative diseases. Its involvement spans across the main proteinopathies involving tau, amyloid-beta, alpha-synuclein, and TDP-43. Accumulating evidence supports the contribution of iron in disease pathologies, but the delineation of its pathogenic role is yet challenged by the complex involvement of iron in multiple neurotoxicity mechanisms and evidence supporting a reciprocal influence between accumulation of iron and protein pathology. Here, we review the major proteinopathy-specific observations supporting four distinct hypotheses: (1) iron deposition is a consequence of protein pathology; (2) iron promotes protein pathology; (3) iron protects from or hinders protein pathology; and (4) deposition of iron and protein pathology contribute parallelly to pathogenesis. Iron is an essential element for physiological brain function, requiring a fine balance of its levels. Understanding of disease-related iron accumulation at a more intricate and systemic level is critical for advancements in iron chelation therapies.

Impact of micronutrients and nutraceuticals on cognitive function and performance in Alzheimer's disease

Alzheimer's disease (AD) is a major global health problem today and is the most common form of dementia. AD is characterized by the formation of β-amyloid (Aβ) plaques and neurofibrillary clusters, leading to decreased brain acetylcholine levels in the brain. Another mechanism underlying the pathogenesis of AD is the abnormal phosphorylation of tau protein that accumulates at the level of neurofibrillary aggregates, and the areas most affected by this pathological process are usually the cholinergic neurons in cortical, subcortical, and hippocampal areas. These effects result in decreased cognitive function, brain atrophy, and neuronal death. Malnutrition and weight loss are the most frequent manifestations of AD, and these are also associated with greater cognitive decline. Several studies have confirmed that a balanced low-calorie diet and proper nutritional intake may be considered important factors in counteracting or slowing the progression of AD, whereas a high-fat or hypercholesterolemic diet predisposes to an increased risk of developing AD. Especially, fruits, vegetables, antioxidants, vitamins, polyunsaturated fatty acids, and micronutrients supplementation exert positive effects on aging-related changes in the brain due to their antioxidant, anti-inflammatory, and radical scavenging properties. The purpose of this review is to summarize some possible nutritional factors that may contribute to the progression or prevention of AD, understand the role that nutrition plays in the formation of Aβ plaques typical of this neurodegenerative disease, to identify some potential therapeutic strategies that may involve some natural compounds, in delaying the progression of the disease.

Levels of iron and iron-related proteins in Alzheimer's disease: A systematic review and meta-analysis

BACKGROUND AND PURPOSE

Iron homeostasis disturbance has been suggested to play a role in the pathology of Alzheimer's disease (AD). Systemic iron levels are regulated by iron-related proteins, such as ferritin and transferrin. This meta-analysis was established to evaluate iron and iron-related proteins (ferritin, transferrin, lactoferrin, haptoglobin, hepcidin) in cerebrospinal fluid (CSF) and blood samples of AD patients compared with those in healthy controls (HCs).

METHODS

Iron and iron-related proteins in Alzheimer's disease was systematically searched within five databases (PubMed, EMBASE, Web of Science, Cochrane, Scopus) up to October 23, 2022. Fifty-four studies (with data for 5105 participants: 2174 AD patients and 2931 HCs) were included in this meta-analysis. This study was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA), applying Stata 14.0 software.

RESULTS

Decreased iron in blood and increased ferritin in CSF were found in AD patients compared with the levels in HCs. AD patients also exhibited lower lactoferrin in serum. Other variables (iron in CSF, ferritin in blood, transferrin in CSF/blood, haptoglobin in CSF/blood, and hepcidin in blood) did not differ between the groups.

CONCLUSION

This meta-analysis indicated that iron and iron-related proteins were associated with the risk of AD, suggesting the value of further exploration of iron imbalance in AD using biofluids.

Single-cell transcriptomic and neuropathologic analysis reveals dysregulation of the integrated stress response in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a sporadic neurodegenerative tauopathy variably affecting brainstem and cortical structures and characterized by tau inclusions in neurons and glia. The precise mechanism whereby these protein aggregates lead to cell death remains unclear. To investigate the contribution of these different cellular abnormalities to PSP pathogenesis, we performed single-nucleus RNA sequencing and analyzed 45,559 high quality nuclei targeting the subthalamic nucleus and adjacent structures from human post-mortem PSP brains with varying degrees of pathology compared to controls. Cell-type specific differential expression and pathway analysis identified both common and discrete changes in numerous pathways previously implicated in PSP and other neurodegenerative disorders. This included EIF2 signaling, an adaptive pathway activated in response to diverse stressors, which was the top activated pathway in vulnerable cell types. Using immunohistochemistry, we found that activated eIF2α was positively correlated with tau pathology burden in vulnerable brain regions. Multiplex immunofluorescence localized activated eIF2α positivity to hyperphosphorylated tau (p-tau) positive neurons and ALDH1L1-positive astrocytes, supporting the increased transcriptomic EIF2 activation observed in these vulnerable cell types. In conclusion, these data provide insights into cell-type-specific pathological changes in PSP and support the hypothesis that failure of adaptive stress pathways play a mechanistic role in the pathogenesis and progression of PSP.

In-depth magnetometry and EPR analysis of the spin structure of human-liver ferritin: from DC to 9 GHz

Ferritin, the major iron storage protein in organisms, stores iron in the form of iron oxyhydroxide most likely involving phosphorous as a constituent, the mineral form of which is not well understood. Therefore, the question of how the ca. 2000 iron atoms in the ferritin core are magnetically coupled is still largely open. The ferritin core, with a diameter of 5-8 nm, is encapsulated in a protein shell that also catalyzes the uptake of iron and protects the core from outside interactions. Neurodegenerative disease is associated with iron imbalance, generating specific interest in the magnetic properties of ferritin. Here we present 9 GHz continuous wave EPR and a comprehensive set of magnetometry techniques including isothermal remanent magnetization (IRM) and AC susceptibility to elucidate the magnetic properties of the core of human liver ferritin. For the analysis of the magnetometry data, a new microscopic model of the ferritin-core spin structure is derived, showing that magnetic moment is generated by surface-spin canting, rather than defects. The analysis explicitly includes the distribution of magnetic parameters, such as the distribution of the magnetic moment. This microscopic model explains some of the inconsistencies resulting from previous analysis approaches. The main findings are a mean magnetic moment of 337μB with a standard deviation of 0.947μB. In contrast to previous reports, only a relatively small contribution of paramagnetic and ferrimagnetic phases is found, in the order of maximally 3%. For EPR, the over 30 mT wide signal of the ferritin core is analyzed using the model of the giant spin system [Fittipaldi et al., Phys. Chem. Chem. Phys., 2016, 18, 3591-3597]. Two components are needed minimally, and the broadening of these components suggests a broad distribution of the magnetic resonance parameters, the zero-field splitting, D, and the spin quantum number, S. We compare parameters from EPR and magnetometry and find that EPR is particularly sensitive to the surface spins of the core, revealing the potential to use EPR as a diagnostic for surface-spin disorder.

The mechanism of ferroptosis and its related diseases

Ferroptosis, a regulated form of cellular death characterized by the iron-mediated accumulation of lipid peroxides, provides a novel avenue for delving into the intersection of cellular metabolism, oxidative stress, and disease pathology. We have witnessed a mounting fascination with ferroptosis, attributed to its pivotal roles across diverse physiological and pathological conditions including developmental processes, metabolic dynamics, oncogenic pathways, neurodegenerative cascades, and traumatic tissue injuries. By unraveling the intricate underpinnings of the molecular machinery, pivotal contributors, intricate signaling conduits, and regulatory networks governing ferroptosis, researchers aim to bridge the gap between the intricacies of this unique mode of cellular death and its multifaceted implications for health and disease. In light of the rapidly advancing landscape of ferroptosis research, we present a comprehensive review aiming at the extensive implications of ferroptosis in the origins and progress of human diseases. This review concludes with a careful analysis of potential treatment approaches carefully designed to either inhibit or promote ferroptosis. Additionally, we have succinctly summarized the potential therapeutic targets and compounds that hold promise in targeting ferroptosis within various diseases. This pivotal facet underscores the burgeoning possibilities for manipulating ferroptosis as a therapeutic strategy. In summary, this review enriched the insights of both investigators and practitioners, while fostering an elevated comprehension of ferroptosis and its latent translational utilities. By revealing the basic processes and investigating treatment possibilities, this review provides a crucial resource for scientists and medical practitioners, aiding in a deep understanding of ferroptosis and its effects in various disease situations.

NICOTIANAMINE SYNTHASE activity affects nucleolar iron accumulation and impacts rDNA silencing and RNA methylation in Arabidopsis

In plant cells, a large pool of iron (Fe) is contained in the nucleolus, as well as in chloroplasts and mitochondria. A central determinant for intracellular distribution of Fe is nicotianamine (NA) generated by NICOTIANAMINE SYNTHASE (NAS). Here, we used Arabidopsis thaliana plants with disrupted NAS genes to study the accumulation of nucleolar iron and understand its role in nucleolar functions and more specifically in rRNA gene expression. We found that nas124 triple mutant plants, which contained lower quantities of the iron ligand NA, also contained less iron in the nucleolus. This was concurrent with the expression of normally silenced rRNA genes from nucleolar organizer regions 2 (NOR2). Notably, in nas234 triple mutant plants, which also contained lower quantities of NA, nucleolar iron and rDNA expression were not affected. In contrast, in both nas124 and nas234, specific RNA modifications were differentially regulated in a genotype dependent manner. Taken together, our results highlight the impact of specific NAS activities in RNA gene expression. We discuss the interplay between NA and nucleolar iron with rDNA functional organization and RNA methylation.

Induction Mechanism of Ferroptosis, Necroptosis, and Pyroptosis: A Novel Therapeutic Target in Nervous System Diseases

In recent years, three emerging cell deaths, ferroptosis, necroptosis and pyroptosis, have gradually attracted everyone's attention, and they also play an important role in the occurrence and development of various diseases. Ferroptosis is an idiographic iron-dependent form regulated cell death with the hallmark of accumulation of the intracellular reactive oxygen species (ROS). Necroptosis is a form of regulated necrotic cell death mediated by the receptor-interacting protein kinase 1(RIPK1) and receptor-interacting protein kinase 3RIPK3. Pyroptosis, also known as cell inflammatory necrosis, is a programmed cell necrosis mediated by Gasdermin D (GSDMD). It is manifested by the continuous swelling of the cells until the cell membrane ruptures, resulting in the release of the cell contents and the activation of a strong inflammatory response. Neurological disorders remain a clinical challenge and patients do not respond well to conventional treatments. Nerve cell death can aggravate the occurrence and development of neurological diseases. This article reviews the specific mechanisms of these three types of cell death and their relationship with neurological diseases and the evidence for the role of the three types of cell death in neurological diseases; understanding these pathways and their mechanisms is helpful for the treatment of neurological diseases.

Autolysis Affects the Iron Cargo of Ferritins in Neurons and Glial Cells at Different Rates in the Human Brain

Iron is known to accumulate in neurological disorders, so a careful balance of the iron concentration is essential for healthy brain functioning. An imbalance in iron homeostasis could arise due to the dysfunction of proteins involved in iron homeostasis. Here, we focus on ferritin-the primary iron storage protein of the brain. In this study, we aimed to improve a method to measure ferritin-bound iron in the human post-mortem brain, and to discern its distribution in particular cell types and brain regions. Though it is known that glial cells and neurons differ in their ferritin concentration, the change in the number and distribution of iron-filled ferritin cores between different cell types during autolysis has not been revealed yet. Here, we show the cellular and region-wide distribution of ferritin in the human brain using state-of-the-art analytical electron microscopy. We validated the concentration of iron-filled ferritin cores to the absolute iron concentration measured by quantitative MRI and inductively coupled plasma mass spectrometry. We show that ferritins lose iron from their cores with the progression of autolysis whereas the overall iron concentrations were unaffected. Although the highest concentration of ferritin was found in glial cells, as the total ferritin concentration increased in a patient, ferritin accumulated more in neurons than in glial cells. Summed up, our findings point out the unique behaviour of neurons in storing iron during autolysis and explain the differences between the absolute iron concentrations and iron-filled ferritin in a cell-type-dependent manner in the human brain. The rate of loss of the iron-filled ferritin cores during autolysis is higher in neurons than in glial cells.

Cell-Specific Dysregulation of Iron and Oxygen Homeostasis as a Novel Pathophysiology in PSP

OBJECTIVE

Progressive supranuclear palsy (PSP) is a 4R-tauopathy showing heterogeneous tau cytopathology commencing in the globus pallidus (GP) and the substantia nigra (SN), regions also associated with age-related iron accumulation. Abnormal iron levels have been extensively associated with tau pathology in neurodegenerative brains, however, its role in PSP pathogenesis remains yet unknown. We perform the first cell type-specific evaluation of PSP iron homeostasis and the closely related oxygen homeostasis, in relation to tau pathology in human postmortem PSP brains.

METHODS

In brain regions vulnerable to PSP pathology (GP, SN, and putamen), we visualized iron deposition in tau-affected and unaffected neurons, astroglia, oligodendrocytes, and microglia, using a combination of iron staining with immunolabelling. To further explore molecular pathways underlying our observations, we examined the expression of key iron and oxygen homeostasis mRNA transcripts and proteins.

RESULTS

We found astrocytes as the major cell type accumulating iron in the early affected regions of PSP, highly associated with cellular tau pathology. The same regions are affected by dysregulated expression of alpha and beta hemoglobin and neuroglobin showing contrasting patterns. We discovered changes in iron and oxygen homeostasis-related gene expression associated with aging of the brain, and identified dysregulated expression of rare neurodegeneration with brain iron accumulation (NBIA) genes associated with tau pathology to distinguish PSP from the healthy aging brain.

INTERPRETATION

We present novel aspects of PSP pathophysiology highlighting an overlap with NBIA pathways. Our findings reveal potential novel targets for therapy development and have implications beyond PSP for other iron-associated neurodegenerative diseases. ANN NEUROL 2023;93:431-445.

Exposure of metal toxicity in Alzheimer’s disease: An extensive review

Metals serve important roles in the human body, including the maintenance of cell structure and the regulation of gene expression, the antioxidant response, and neurotransmission. High metal uptake in the nervous system is harmful because it can cause oxidative stress, disrupt mitochondrial function, and impair the activity of various enzymes. Metal accumulation can cause lifelong deterioration, including severe neurological problems. There is a strong association between accidental metal exposure and various neurodegenerative disorders, including Alzheimer’s disease (AD), the most common form of dementia that causes degeneration in the aged. Chronic exposure to various metals is a well-known environmental risk factor that has become more widespread due to the rapid pace at which human activities are releasing large amounts of metals into the environment. Consequently, humans are exposed to both biometals and heavy metals, affecting metal homeostasis at molecular and biological levels. This review highlights how these metals affect brain physiology and immunity and their roles in creating harmful proteins such as β-amyloid and tau in AD. In addition, we address findings that confirm the disruption of immune-related pathways as a significant toxicity mechanism through which metals may contribute to AD.

Iron and Alzheimer's Disease: From Pathology to Imaging

Alzheimer's disease (AD) is a debilitating brain disorder that afflicts millions worldwide with no effective treatment. Currently, AD progression has primarily been characterized by abnormal accumulations of β-amyloid within plaques and phosphorylated tau within neurofibrillary tangles, giving rise to neurodegeneration due to synaptic and neuronal loss. While β-amyloid and tau deposition are required for clinical diagnosis of AD, presence of such abnormalities does not tell the complete story, and the actual mechanisms behind neurodegeneration in AD progression are still not well understood. Support for abnormal iron accumulation playing a role in AD pathogenesis includes its presence in the early stages of the disease, its interactions with β-amyloid and tau, and the important role it plays in AD related inflammation. In this review, we present the existing evidence of pathological iron accumulation in the human AD brain, as well as discuss the imaging tools and peripheral measures available to characterize iron accumulation and dysregulation in AD, which may help in developing iron-based biomarkers or therapeutic targets for the disease.

Reversal of genetic brain iron accumulation by N,N'-bis(2-mercaptoethyl)isophthalamide, a lipophilic metal chelator, in mice

N,N'-bis(2-mercaptoethyl)isophthalamide (NBMI) is a novel lipophilic metal chelator and antioxidant used in mercury poisoning. Recent studies have suggested that NBMI may also bind to other metals such as lead and iron. Since NBMI can enter the brain, we evaluated if NBMI removes excess iron from the iron-loaded brain and ameliorates iron-induced oxidative stress. First, NBMI exhibited preferential binding to ferrous (Fe²⁺) iron with a negligible binding affinity to ferric (Fe³⁺) iron, indicating a selective chelation of labile iron. Second, NBMI protected SH-SY5Y human neuroblastoma cells from the cytotoxic effects of high iron. NBMI also decreased cellular labile iron and lessened the production of iron-induced reactive oxygen species in these cells. Deferiprone (DFP), a commonly used oral iron chelator, failed to prevent iron-induced cytotoxicity or labile iron accumulation. Next, we validated the efficacy of NBMI in Hfe H67D mutant mice, a mouse model of brain iron accumulation (BIA). Oral gavage of NBMI for 6 weeks decreased iron accumulation in the brain as well as liver, whereas DFP showed iron chelation only in the liver, but not in the brain. Notably, depletion of brain copper and anemia were observed in BIA mice treated with DFP, but not with NBMI, suggesting a superior safety profile of NBMI over DFP for long-term use. Collectively, our study demonstrates that NBMI provides a neuroprotective effect against BIA and has therapeutic potential for neurodegenerative diseases associated with BIA.

Microglial Inflammatory-Metabolic Pathways and Their Potential Therapeutic Implication in Major Depressive Disorder

Increasing evidence supports the notion that neuroinflammation plays a critical role in the etiology of major depressive disorder (MDD), at least in a subset of patients. By virtue of their capacity to transform into reactive states in response to inflammatory insults, microglia, the brain's resident immune cells, play a pivotal role in the induction of neuroinflammation. Experimental studies have demonstrated the ability of microglia to recognize pathogens or damaged cells, leading to the activation of a cytotoxic response that exacerbates damage to brain cells. However, microglia display a wide range of responses to injury and may also promote resolution stages of inflammation and tissue regeneration. MDD has been associated with chronic priming of microglia. Recent studies suggest that altered microglial morphology and function, caused either by intense inflammatory activation or by senescence, may contribute to depression and associated impairments in neuroplasticity. In this context, modifying microglia phenotype by tuning inflammatory pathways might have important translational relevance to harness neuroinflammation in MDD. Interestingly, it was recently shown that different microglial phenotypes are associated with distinct metabolic pathways and analysis of the underlying molecular mechanisms points to an instrumental role for energy metabolism in shaping microglial functions. Here, we review various canonical pro-inflammatory, anti-inflammatory and metabolic pathways in microglia that may provide new therapeutic opportunities to control neuroinflammation in brain disorders, with a strong focus on MDD.

Ferritin-Based Single-Electron Devices

We report on the fabrication of single-electron devices based on horse-spleen ferritin particles. At low temperatures the current vs. voltage characteristics are stable, enabling the acquisition of reproducible data that establishes the Coulomb blockade as the main transport mechanism through them. Excellent agreement between the experimental data and the Coulomb blockade theory is demonstrated. Single-electron charge transport in ferritin, thus, establishes a route for further characterization of their, e.g., magnetic, properties down to the single-particle level, with prospects for electronic and medical applications.

In vivo brain iron concentration in healthy individuals at 3.0 T magnetic resonance imaging: a prospective cross-sectional study

OBJECTIVE

To quantify iron deposits in the basal ganglia and to evaluate its relation to age, sex, body mass index and brain laterality.

METHODS

Prospective observational study. Data were collected from the patients' electronic medical records. The concentration of iron deposits in the brain was assessed using whole-brain MRI at 3.0 Tesla.

RESULTS

138 participants were selected, 69.6% were female and the mean age was 47 ± 19 years. The κ coefficient was very strong (k = 0.92, p < 0.001). Age showed a moderate correlation between iron deposits in the caudate and putamen nuclei, on both right and left sides. In overall and right-handed individuals, a significantly higher iron concentration was observed on the left side for the caudate nucleus, putamen, thalamus, globus pallidus, and centrum semiovale, and for left-handed individuals, it was also observed in the left side-for the putamen and centrum semiovale. A weak correlation was shown between body mass index and left and right substantia nigra, left caudate nuclei, left putamen and right globus pallidus.

CONCLUSION

Our results showed a significantly higher iron deposit on the left side in most brain regions. In addition, the body mass index may also be related to iron overload, especially in the caudate nucleus.

ADVANCES IN KNOWLEDGE

Brain iron deposits may be normal, owing to aging, or be pathological, such as neurodegeneration. Thus, it is important to know how much is expected of iron deposition in the brain of healthy populations.

Ferroptosis and Its Potential Role in the Nervous System Diseases

Ferroptosis is a novel regulated cell death characterized by metabolic disorders and iron-dependent oxidative destruction of the lipid bilayer. It is primarily caused by the imbalance of oxidation and anti-oxidation in the body and is precisely regulated by numerous factors and pathways inside and outside the cell. Recent studies have indicated that ferroptosis plays a vital role in the pathophysiological process of multiple systems of the body including the nervous system. Ferroptosis may be closely linked to the occurrence and development of neurodegenerative diseases, strokes, and brain tumors. It may also be involved in the development, maturation, and aging of the nervous system. Therefore, this study aims to investigate ferroptosis’s occurrence and regulatory mechanism and summarize its research progress in the pathogenesis and treatment of neurological diseases. This would allow for novel ideas for basic and clinical research of neurological diseases.

The effect of beta-amyloid and tau protein aggregations on magnetic susceptibility of anterior hippocampal laminae in Alzheimer's diseases

Previous studies have reported the changes of magnetic susceptibility induced by iron deposition in hippocampus of Alzheimer's disease (AD) brains. It is well-known that hippocampus is divided into well-defined laminar architecture, which, however, is difficult to be resolved with in-vivo MRI due to the limited imaging resolution. The present study aims to investigate layer-specific magnetic susceptibility in the hippocampus of AD patients using high-resolution ex-vivo MRI, and elucidate its relationship with beta amyloid (Aβ) and tau protein histology. We performed quantitative susceptibility mapping (QSM) and T2* mapping on postmortem anterior hippocampus samples from four AD, four Primary Age-Related Tauopathy (PART), and three control brains. We manually segmented each sample into seven layers, including four layers in the cornu ammonis1 (CA1) and three layers in the dentate gyrus (DG), and then evaluated AD-related alterations of susceptibility and T2* values and their correlations with Aβ and tau in each hippocampal layer. Specifically, we found (1) layer-specific variations of susceptibility and T2* measurements in all samples; (2) the heterogeneity of susceptibility were higher in all layers of AD patients compared with the age- and gender-matched PART cases while the heterogeneity of T2* values were lower in four layers of CA1; and (3) voxel-wise MRI-histological correlation revealed both susceptibility and T2* values in the stratum molecular (SM) and stratum lacunosum (SL) layers were correlated with the Aβ content in AD, while the T2* values in the stratum radiatum (SR) layer were correlated with the tau content in the PART but not AD. These findings suggest a selective effect of the Aβ- and tau-pathology on the susceptibility and T2* values in the different layers of anterior hippocampus. Particularly, the alterations of magnetic susceptibility in the SM and SL layers may be associated with Aβ aggregation, while those in the SR layermay reflect the age-related tau protein aggregation.

Insight into the Double-Edged Role of Ferroptosis in Disease

Ferroptosis, a newly described type of iron-dependent programmed cell death that is distinct from apoptosis, necroptosis, and other types of cell death, is involved in lipid peroxidation (LP), reactive oxygen species (ROS) production, and mitochondrial dysfunction. Accumulating evidence has highlighted vital roles for ferroptosis in multiple diseases, including acute kidney injury, cancer, hepatic fibrosis, Parkinson's disease, and Alzheimer's disease. Therefore, ferroptosis has become one of the research hotspots for disease treatment and attracted extensive attention in recent years. This review mainly summarizes the relationship between ferroptosis and various diseases classified by the system, including the urinary system, digestive system, respiratory system, nervous system. In addition, the role and molecular mechanism of multiple inhibitors and inducers for ferroptosis are further elucidated. A deeper understanding of the relationship between ferroptosis and multiple diseases may provide new strategies for researching diseases and drug development based on ferroptosis.

In vivo evaluation of heme and non-heme iron content and neuronal density in human basal ganglia

Non-heme iron is an important element supporting the structure and functioning of biological tissues. Imbalance in non-heme iron can lead to different neurological disorders. Several MRI approaches have been developed for iron quantification relying either on the relaxation properties of MRI signal or measuring tissue magnetic susceptibility. Specific quantification of the non-heme iron can, however, be constrained by the presence of the heme iron in the deoxygenated blood and contribution of cellular composition. The goal of this paper is to introduce theoretical background and experimental MRI method allowing disentangling contributions of heme and non-heme irons simultaneously with evaluation of tissue neuronal density in the iron-rich basal ganglia. Our approach is based on the quantitative Gradient Recalled Echo (qGRE) MRI technique that allows separation of the total R2* metric characterizing decay of GRE signal into tissue-specific (R2t*) and the baseline blood oxygen level-dependent (BOLD) contributions. A combination with the QSM data (also available from the qGRE signal phase) allowed further separation of the tissue-specific R2t* metric in a cell-specific and non-heme-iron-specific contributions. It is shown that the non-heme iron contribution to R2t* relaxation can be described with the previously developed Gaussian Phase Approximation (GPA) approach. qGRE data were obtained from 22 healthy control participants (ages 26-63 years). Results suggest that the ferritin complexes are aggregated in clusters with an average radius about 100nm comprising approximately 2600 individual ferritin units. It is also demonstrated that the concentrations of heme and non-heme iron tend to increase with age. The strongest age effect was seen in the pallidum region, where the highest age-related non-heme iron accumulation was observed.

Chemistry and biology of ferritin

Iron is an essential element required by cells and has been described as a key player in ferroptosis. Ferritin operates as a fundamental iron storage protein in cells forming multimeric assemblies with crystalline iron cores. We discuss the latest findings on ferritin structure and activity and its link to cell metabolism and ferroptosis. The chemistry of iron, including its oxidation states, is important for its biological functions, its reactivity, and the biology of ferritin. Ferritin can be localized in different cellular compartments and secreted by cells with a variety of functions depending on its spatial context. Here, we discuss how cellular ferritin localization is tightly linked to its function in a tissue-specific manner, and how impairment of iron homeostasis is implicated in diseases, including cancer and coronavirus disease 2019. Ferritin is a potential biomarker and we discuss latest research where it has been employed for imaging purposes and drug delivery.

Prolific shedding of magnetite nanoparticles from banknote surfaces

Here, we use magnetic methods first to quantify the content of strongly magnetic particles of banknotes (US dollars, USD, and British pounds sterling, GBP), and then examine the possibility of their release from handled banknote surfaces. The content of magnetic particles, from magnetic remanence measurements, for the USD and paper GBP banknotes is high; greater, for example, than that in vehicle engine-exhaust emissions, and similar to that for airborne roadside particulate matter (PM). Our magnetic analyses of USD and GBP banknotes, and of the ink pigment widely used in their printing, reveal not only that the banknotes are highly magnetic, but also that strongly magnetic, nano-sized particles are readily and prolifically shed from their surfaces (especially from the USD banknotes). A common practice, prior to increased automation, was for bank tellers to count banknotes by licking a finger to adhere to each successive counted note, and thus speed up the manual counting process. Given the rate of particle shedding reported here, this traditional manual counting procedure must have resulted in prolific transfer of iron-rich nanoparticles both to the fingers and thence to the tongue. We hypothesise that, pre-automation, magnetite and other metal-bearing nanoparticles were repetitively and frequently ingested by bank tellers, and subsequently entered the brain directly via the taste nerve pathway, and/or indirectly via the systemic circulation and the neuroenteric system. This hypothesis may plausibly account for the reported and currently unexplained association between elevated neurodegeneration-related mortality odds ratios and this specific occupation.

Exploring valence states of abnormal mineral deposits in biological tissues using correlative microscopy and spectroscopy techniques: A case study on ferritin and iron deposits from Alzheimer's disease patients

Abnormal accumulation of inorganic trace elements in a human brain, such as iron, zinc and aluminum, oftentimes manifested as deposits and accompanied by a chemical valence change, is pathologically relevant to various neurodegenerative diseases. In particular, Fe²⁺ has been hypothesized to produce free radicals that induce oxidative damage and eventually cause Alzheimer's disease (AD). However, traditional biomedical techniques, e.g. histology staining, are limited in studying the chemical composition and valence states of these inorganic deposits. We apply commonly used physical (phys-) science methods such as X-ray energy dispersive spectroscopy (EDS), focused-ion beam (FIB) and electron energy loss spectroscopy (EELS) in transmission electron microscopy in conjunction with magnetic resonance imaging (MRI), histology and optical microscopy (OM) to study the valence states of iron deposits in AD patients. Ferrous ions are found in all deposits in brain tissues from three AD patients, constituting 0.22-0.50 of the whole iron content in each specimen. Such phys-techniques are rarely used in medical science and have great potential to provide unique insight into biomedical problems.

Source apportionment of magnetite particles in roadside airborne particulate matter

Exposure to airborne particulate matter (PM) is associated with pulmonary, cardiovascular and neurological problems. Magnetite, a mixed Fe²⁺/Fe³⁺ oxide, is ubiquitous and abundant in PM in urban environments, and might play a specific role in both neurodegeneration and cardiovascular disease. We collected samples of vehicle exhaust emissions, and of heavily-trafficked roadside and urban background dusts from Lancaster and Birmingham, U.K. Then, we measured their saturation magnetic remanence and used magnetic component analysis to separate the magnetite signal from other contributing magnetic components. Lastly, we estimated the contributions made by specific traffic-related sources of magnetite to the total airborne magnetite in the roadside environment. The concentration of magnetite in exhaust emissions is much lower (3-14 x lower) than that in heavily- trafficked roadside PM. The magnetite concentration in petrol-engine exhaust emissions is between ~0.06 and 0.12 wt%; in diesel-engine exhaust emissions ~0.08-0.18 wt%; in background dust ~0.05-0.20 wt% and in roadside dust ~0.18-0.95 wt%. Here, we show that vehicle brake wear is responsible for between ~68 and 85% of the total airborne magnetite at the two U.K. roadside sites. In comparison, diesel-engine exhaust emissions account for ~7% - 12%, petrol-engine exhaust emissions for ~2% - 4%, and background dust for 6% - 10%. Thus, vehicle brake wear is by far the most dominant source of airborne magnetite in the roadside environment at the two sites examined. Given the potential risk posed, post-inhalation, by ultrafine magnetite and co-associated transition metal-rich particles to human cardiovascular and neurological health, the high magnetite content of vehicle brake wear might need to be reduced in order to mitigate such risk, especially for vulnerable population groups.

Indoor particulate air pollution from open fires and the cognitive function of older people

Exposure to indoor air pollution is known to affect respiratory and cardiovascular health, but little is known about its effects on cognitive function. We measured the concentrations and magnetite content of airborne particulate matter (PM) in the indoor environment arising from burning peat, wood or coal in residential open fires. Highest indoor PM_2.5 concentrations (60 μg/m³ i.e. 2.4 times the WHO-recommended 24-h mean) occurred when peat was burned, followed by burning of coal (30 μg/m³) and wood (17 μg/m³). Conversely, highest concentrations of coarser PM (PM_10-2.5) were associated with coal burning (20 μg/m³), with lower concentrations emitted during burning of wood (10 μg/m³) and peat (8 μg/m³). The magnetic content of the emitted PM, greatest (for both PM size fractions) when coal was burned, is similar to that of roadside airborne PM. Exposure to PM, and to strongly magnetic airborne PM, can be greater for individuals spending ~5 h/day indoors with a coal-burning open fire for 6 months/year compared to those commuting via heavily-trafficked roads for 1 h/day for 12 months/year. Given these high indoor PM and magnetite concentrations, and the reported associations between (outdoor) PM and impaired neurological health, we used individual-level data from The Irish Longitudinal Study on Ageing (TILDA) to examine the association between the usage of open fires and the cognitive function of older people. Using a sample of nearly seven thousand older people, we estimated multi-variate models of the association between cognitive function and open fire usage, in order to account for relevant confounders such as socio-economic status. We found a negative association between open fire usage and cognitive function as measured by widely-used cognitive tests such as word recall and verbal fluency tests. The negative association was largest and statistically strongest among women, a finding explained by the greater exposure of women to open fires in the home because they spent more time at home than men. Our findings were also robust to stratifying the sample between old and young, rich and poor, and urban and rural.

Correlative Microscopy to Localize and Characterize Iron Deposition in Alzheimer's Disease

Background:

Recent evidence suggests that the accumulation of iron, specifically ferrous Fe²⁺, may play a role in the development and progression of neurodegeneration in Alzheimer’s disease (AD) through the production of oxidative stress.

Objective:

To localize and characterize iron deposition and oxidation state in AD, we analyzed human hippocampal autopsy samples from four subjects with advanced AD that have been previously characterized with correlative MRI-histology.

Methods:

We perform scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron energy loss spectroscopy (EELS) in the higher resolution transmission electron microscope on the surface and cross-sections of specific iron-rich regions of interest.

Results:

Specific previously analyzed regions were visualized using SEM and confirmed to be iron-rich deposits using EDS. Subsequent analysis using focused ion beam cross-sectioning and SEM characterized the iron deposition throughout the 3-D volumes, confirming the presence of iron throughout the deposits, and in two out of four specimens demonstrating colocalization with zinc. Analysis of traditional histology slides showed the analyzed deposits overlapped both with amyloid and tau deposition. Following higher resolution analysis of a single iron deposit using scanning transmission electron microscope (STEM), we demonstrated the potential of monochromated STEM-EELS to discern the relative oxidation state of iron within a deposit.

Conclusion:

These findings suggest that iron is present in the AD hippocampus and can be visualized and characterized using combined MRI and EM techniques. An altered relative oxidation state may suggest a direct link between iron and oxidative stress in AD. These methods thus could potentially measure an altered relative oxidation state that could suggest a direct link between iron and oxidative stress in AD. Furthermore, we have demonstrated the ability to analyze metal deposition alongside commonly used histological markers of AD pathology, paving the way for future insights into the molecular interactions between Aβ, tau, iron, and other putative metals, such as zinc.

Quadruple abnormal protein aggregates in brainstem pathology and exogenous metal-rich magnetic nanoparticles (and engineered Ti-rich nanorods). The substantia nigrae is a very early target in young urbanites and the gastrointestinal tract a key brainstem portal

Fine particulate air pollution (PM_2.5) exposures are linked with Alzheimer's and Parkinson's diseases (AD,PD). AD and PD neuropathological hallmarks are documented in children and young adults exposed lifelong to Metropolitan Mexico City air pollution; together with high frontal metal concentrations (especially iron)-rich nanoparticles (NP), matching air pollution combustion- and friction-derived particles. Here, we identify aberrant hyperphosphorylated tau, ɑ synuclein and TDP-43 in the brainstem of 186 Mexico City 27.29 ± 11.8y old residents. Critically, substantia nigrae (SN) pathology seen in mitochondria, endoplasmic reticulum and neuromelanin (NM) is co-associated with the abundant presence of exogenous, Fe-, Al- and Ti-rich NPs.The SN exhibits early and progressive neurovascular unit damage and mitochondria and NM are associated with metal-rich NPs including exogenous engineered Ti-rich nanorods, also identified in neuroenteric neurons. Such reactive, cytotoxic and magnetic NPs may act as catalysts for reactive oxygen species formation, altered cell signaling, and protein misfolding, aggregation and fibril formation. Hence, pervasive, airborne and environmental, metal-rich and magnetic nanoparticles may be a common denominator for quadruple misfolded protein neurodegenerative pathologies affecting urbanites from earliest childhood. The substantia nigrae is a very early target and the gastrointestinal tract (and the neuroenteric system) key brainstem portals. The ultimate neural damage and neuropathology (Alzheimer's, Parkinson's and TDP-43 pathology included) could depend on NP characteristics and the differential access and targets achieved via their portals of entry. Thus where you live, what air pollutants you are exposed to, what you are inhaling and swallowing from the air you breathe,what you eat, how you travel, and your occupational longlife history are key. Control of NP sources becomes critical.

Leukocyte telomere length is associated with iron overload in male adults with hereditary hemochromatosis

Background: Hereditary hemochromatosis (HH) is a primary iron overload (IO) condition. Absolute telomere length (ATL) is a marker of cellular aging and DNA damage associated with chronic diseases and mortality.

Aim: To evaluate the relationship between ATL and IO in patients with HH.

Methods: Cross-sectional study including 25 patients with HH: 8 with IO and 17 without IO (ferritin < 300 ng/ml) and 25 healthy controls. Inclusion criteria were: age > 18 years, male sex and HH diagnosis. Patients with diabetes or other endocrine and autoimmune diseases were excluded. ATL was measured by real-time PCR.

Results: HH patients with IO were older (P<0.001) and showed higher ferritin concentration (P<0.001). Patients with HH, disregarding the iron status, showed higher glucose and body mass index (BMI) than controls (both P<0.01). ATL was shorter in patients with IO than controls [with IO: 8 (6–14), without IO: 13 (9–20), and controls: 19 (15–25) kilobase pairs, P<0.01]; with a linear trend within groups (P for trend <0.01). Differences in ATL remained statistically significant after adjusting by age, BMI and glucose (P<0.05).

Discussion: Patients with IO featured shorter ATL while patients without IO showed only mild alterations vs. controls. Screening for IO is encouraged to prevent iron-associated cellular damage and early telomere attrition.

Superficial white matter imaging: Contrast mechanisms and whole-brain in vivo mapping

Superficial white matter (SWM) contains the most cortico-cortical white matter connections in the human brain encompassing the short U-shaped association fibers. Despite its importance for brain connectivity, very little is known about SWM in humans, mainly due to the lack of noninvasive imaging methods. Here, we lay the groundwork for systematic in vivo SWM mapping using ultrahigh resolution 7 T magnetic resonance imaging. Using biophysical modeling informed by quantitative ion beam microscopy on postmortem brain tissue, we demonstrate that MR contrast in SWM is driven by iron and can be linked to the microscopic iron distribution. Higher SWM iron concentrations were observed in U-fiber-rich frontal, temporal, and parietal areas, potentially reflecting high fiber density or late myelination in these areas. Our SWM mapping approach provides the foundation for systematic studies of interindividual differences, plasticity, and pathologies of this crucial structure for cortico-cortical connectivity in humans.

The Association Between Anemia of Chronic Inflammation and Alzheimer's Disease and Related Dementias

Background

Dementia is a spectrum of neurological diseases characterized by memory impairment and cognitive decline with the pathogenesis and effective management remaining elusive. Several studies have identified a correlation between anemia and Alzheimer's disease and related dementias (ADRD); however, anemia subtypes and association with ADRD have yet to be studied conclusively.

Objective

To study an association between ADRD and anemia of chronic inflammation.

Methods

We conducted a retrospective case-control study of the patients, diagnosed with ADRD at Brookdale Hospital. Pair-wise comparisons between means of controls and cases in terms of iron studies and laboratory results were performed using a Mann-Whitney U test. Pair-wise comparisons between anemia subgroups (moderate and severe) were performed using a Two Sample proportion Z-Test, where for each couple of normally distributed population.

Results

There was a total of 4,517 (1,274 ADRD group; 3,243 Control group) patients. There was significant difference in hemoglobin 10.15 versus 11.04 [p-value <0.001]. Iron studies showed a significant difference in ferritin 395±488.18 versus 263±1023.4 [p < 0.001], total iron binding capacity 225±84.08 versus 266±82.30 [p < 0.001] and serum iron level 64±39.34 versus 53±41.83 [p < 0.001]. Folic acid and vitamin B12 levels were normal in both groups. Severe and moderate anemia in the ADRD group were respectively 6.2% [95% CI: 4.2-8.4] and 13% [95% CI: 9.8-16.2] higher. Overall, incidence of moderate-to-severe anemia was found to be 19% higher in ADRD group [95% CI: 15.8-22.1].

Conclusion

We demonstrated an association between ADRD and anemia of chronic inflammation independent of age, renal function, and HgbA1C levels.

Ferroptosis Is Regulated by Mitochondria in Neurodegenerative Diseases

BACKGROUND

Neurodegenerative diseases are characterized by a gradual decline in motor and/or cognitive function caused by the selective degeneration and loss of neurons in the central nervous system, but their pathological mechanism is still unclear. Previous research has revealed that many forms of cell death, such as apoptosis and necrosis, occur in neurodegenerative diseases. Research in recent years has noticed that there is a new type of cell death in neurodegenerative diseases: ferroptosis. An increasing body of literature provides evidence for an involvement of ferroptosis in neurodegenerative diseases.

SUMMARY

In this article, we review a new form of cell death in neurodegenerative diseases: ferroptosis. Ferroptosis is defined as an iron-dependent form of regulated cell death, which occurs through the lethal accumulation of lipid-based reactive oxygen species when glutathione-dependent lipid peroxide repair systems are compromised. Several salient and established features of neurodegenerative diseases (including lipid peroxidation and iron dyshomeostasis) are consistent with ferroptosis, which means that ferroptosis may be involved in the progression of neurodegenerative diseases. In addition, as the center of energy metabolism in cells, mitochondria are also closely related to the regulation of iron homeostasis in the nervous system. At the same time, neurodegenerative diseases are often accompanied by degeneration of mitochondrial activity. Mitochondrial damage has been found to be involved in lipid peroxidation and iron dyshomeostasis in neurodegenerative diseases. Key Messages: Based on the summary of the related mechanisms of ferroptosis, we conclude that mitochondrial damage may affect neurodegenerative diseases by regulating many aspects of ferroptosis, including cell metabolism, iron dyshomeostasis, and lipid peroxidation.

The influence of iron oxidation state on quantitative MRI parameters in post mortem human brain

A variety of Magnetic Resonance Imaging (MRI) techniques are known to be sensitive to brain iron content. In principle, iron sensitive MRI techniques are based on local magnetic field variations caused by iron particles in tissue. The purpose of this study was to investigate the sensitivity of MR relaxation and magnetization transfer parameters to changes in iron oxidation state compared to changes in iron concentration. Therefore, quantitative MRI parameters including R₁, R₂, R₂∗, quantitative susceptibility maps (QSM) and magnetization transfer ratio (MTR) of post mortem human brain tissue were acquired prior and after chemical iron reduction to change the iron oxidation state and chemical iron extraction to decrease the total iron concentration. All assessed parameters were shown to be sensitive to changes in iron concentration whereas only R₂, R₂∗ and QSM were also sensitive to changes in iron oxidation state. Mass spectrometry confirmed that iron accumulated in the extraction solution but not in the reduction solution. R₂∗ and QSM are often used as markers for iron content. Changes in these parameters do not necessarily reflect variations in iron content but may also be a result of changes in the iron's oxygenation state from ferric towards more ferrous iron or vice versa.

In Situ Visualization of Ferritin Biomineralization via Graphene Liquid Cell-Transmission Electron Microscopy

Ferritin biomineralization is essential to regulate the toxic Fe²⁺ iron ions in the human body. Unravelling the mechanism of biomineralization in ferritin facilitates our understanding of the causes underlying many iron disorder-related diseases. Until now, no report of in situ visualization of ferritin biomineralization events at nanoscale exists due to the requirement for high-resolution imaging of nanometer-sized ferritin proteins in their hydrated states. Herein, for the first time, we show that the biomineralization processes within individual ferritin proteins can be visualized by means of graphene liquid cell-transmission electron microscopy (GLC-TEM). The increase in the ratio of Fe³⁺/Fe²⁺ ions over time monitored via electron energy loss spectroscopy (EELS) reveals the change in oxidation state of iron oxide phases with time. This study lays a foundation for future investigations on iron regulation mechanisms in healthy and dysfunctional ferritins.

Peroxidase activity of heme bound amyloid β peptides associated with Alzheimer's disease

The amyloid cascade hypothesis attributes the neurodegeneration observed in Alzheimer's disease (AD) to the deposition of the amyloid β (Aβ) peptide into plaques and fibrils in the AD brain. The metal ion hypothesis which implicates several metal ions, viz. Zn²⁺, Cu²⁺ and Fe³⁺, in the AD pathology on account of their abnormal accumulation in the Aβ plaques along with an overall dyshomeostasis of these metals in the AD brain was proposed a while back. Metal ion chelators and ionophores, put forward as possible drug candidates for AD, are yet to succeed in clinical trials. Heme, which is widely distributed in the mammalian body as the prosthetic group of several important proteins and enzymes, has been thought to be associated with AD by virtue of its colocalization in the Aβ plaques along with the similarity of several heme deficiency symptoms with those of AD and most importantly, due to its ability to bind Aβ. This feature article illustrates the active site environment of heme-Aβ which resembles those of peroxidases. It also discusses the peroxidase activity of heme-Aβ, its ability to effect oxidative degradation of neurotransmitters like serotonin and also the identification of the highly reactive high-valent intermediate, compound I. The effect of second sphere residues on the formation and peroxidase activity of heme-Aβ along with the generation and decay of compound I is highlighted throughout the article. The reactivities of heme bound Aβ peptides give an alternative theory to understand the possible cause of this disease.

Across the spectrum: integrating multidimensional metal analytics for in situ metallomic imaging

To know how much of a metal species is in a particular location within a biological context at any given time is essential for understanding the intricate roles of metals in biology and is the fundamental question upon which the field of metallomics was born. Simply put, seeing is powerful. With the combination of spectroscopy and microscopy, we can now see metals within complex biological matrices complemented by information about associated molecules and their structures. With the addition of mass spectrometry and particle beam based techniques, the field of view grows to cover greater sensitivities and spatial resolutions, addressing structural, functional and quantitative metallomic questions from the atomic level to whole body processes. In this perspective, I present a paradigm shift in the way we relate to and integrate current and developing metallomic analytics, highlighting both familiar and perhaps less well-known state of the art techniques for in situ metallomic imaging, specific biological applications, and their use in correlative studies. There is a genuine need to abandon scientific silos and, through the establishment of a metallomic scientific platform for further development of multidimensional analytics for in situ metallomic imaging, we have an incredible opportunity to enhance the field of metallomics and demonstrate how discovery research can be done more effectively.

Iron dyshomeostasis, lipid peroxidation and perturbed expression of cystine/glutamate antiporter in Alzheimer's disease: Evidence of ferroptosis

Iron dyshomeostasis is implicated in Alzheimer’s disease (AD) alongside β-amyloid and tau pathologies. Despite the recent discovery of ferroptosis, an iron-dependent form cell death, hitherto, in vivo evidence of ferroptosis in AD is lacking. The present study uniquely adopts an integrated multi-disciplinary approach, combining protein (Western blot) and elemental analysis (total reflection X-ray fluorescence) with metabolomics (¹H nuclear magnetic resonance spectroscopy) to identify iron dyshomeostasis and ferroptosis, and possible novel interactions with metabolic dysfunction in age-matched male cognitively normal (CN) and AD post-mortem brain tissue (n = 7/group). Statistical analysis was used to compute differences between CN and AD, and to examine associations between proteins, elements and/or metabolites. Iron dyshomeostasis with elevated levels of ferritin, in the absence of increased elemental iron, was observed in AD. Moreover, AD was characterised by enhanced expression of the light-chain subunit of the cystine/glutamate transporter (xCT) and lipid peroxidation, reminiscent of ferroptosis, alongside an augmented excitatory glutamate to inhibitory GABA ratio. Protein, element and metabolite associations also greatly differed between CN and AD suggesting widespread metabolic dysregulation in AD. We demonstrate iron dyshomeostasis, upregulated xCT (impaired glutathione metabolism) and lipid peroxidation in AD, suggesting anti-ferroptotic therapies may be efficacious in AD.

Quantitative Iron Neuroimaging Can Be Used to Assess the Effects of Minocycline in an Intracerebral Hemorrhage Minipig Model

Iron-mediated toxicity is a key factor causing brain injury after intracerebral hemorrhage (ICH). This study was performed to investigate the noninvasive neuroimaging method for quantifying brain iron content using a minipig ICH model and assess the effects of minocycline treatment on ICH-induced iron overload and brain injury. The minipig ICH model was established by injecting 2 ml of autologous blood into the right basal ganglia, which were then subjected to the treatments of minocycline and vehicle. Furthermore, the quantitative susceptibility mapping (QSM) was used to quantify iron content, and diffusion tensor imaging (DTI) was performed to evaluate white matter tract. Additionally, we also performed immunohistochemistry, Western blot, iron assay, Perl's staining, brain water content, and neurological score to evaluate the iron overload and brain injury. Interestingly, we found that the ICH-induced iron overload could be accurately quantified by the QSM. Moreover, the minocycline was quite beneficial for protecting brain injury by reducing the lesion volume and brain edema, preventing brain iron accumulation, downsizing ventricle enlargement, and alleviating white matter injury and neurological deficits. In summary, we suggest that the QSM be an accurate and noninvasive method for quantifying brain iron level, and the minocycline may be a promising therapeutic agent for patients with ICH.

Redox active metals in neurodegenerative diseases

Copper (Cu) and iron (Fe) are redox active metals essential for the regulation of cellular pathways that are fundamental for brain function, including neurotransmitter synthesis and release, neurotransmission, and protein turnover. Cu and Fe are tightly regulated by sophisticated homeostatic systems that tune the levels and localization of these redox active metals. The regulation of Cu and Fe necessitates their coordination to small organic molecules and metal chaperone proteins that restrict their reactions to specific protein centres, where Cu and Fe cycle between reduced (Fe²⁺, Cu⁺) and oxidised states (Fe³⁺, Cu²⁺). Perturbation of this regulation is evident in the brain affected by neurodegeneration. Here we review the evidence that links Cu and Fe dyshomeostasis to neurodegeneration as well as the promising preclinical and clinical studies reporting pharmacological intervention to remedy Cu and Fe abnormalities in the treatment of Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS).

On the structure and chemistry of iron oxide cores in human heart and human spleen ferritins using graphene liquid cell electron microscopy

Ferritin is a protein that regulates the iron ions in humans by storing them in the form of iron oxides. Despite extensive efforts to understand the ferritin iron oxide structures, it is still not clear how ferritin proteins with a distinct light (L) and heavy (H) chain subunit ratio impact the biomineralization process. In situ graphene liquid cell-transmission electron microscopy (GLC-TEM) provides an indispensable platform to study the atomic structure of ferritin mineral cores in their native liquid environment. In this study, we report differences in the iron oxide formation in human spleen ferritins (HSFs) and human heart ferritins (HHFs) using in situ GLC-TEM. Scanning transmission electron microscopy (STEM) along with selected area electron diffraction (SAED) of the mineral core and electron energy loss spectroscopy (EELS) analyses enabled the visualization of morphologies, crystal structures and the chemistry of iron oxide cores in HSFs and HHFs. Our study revealed the presence of metastable ferrihydrite (5Fe2O3·9H2O) as a dominant phase in hydrated HSFs and HHFs, while a stable hematite (α-Fe2O3) phase predominated in non-hydrated HSFs and HHFs. In addition, a higher Fe3+/Fe2+ ratio was found in HHFs in comparison with HSFs. This study provides new understanding on iron-oxide phases that exist in hydrated ferritin proteins from different human organs. Such new insights are needed to map ferritin biomineralization pathways and possible correlations with various iron-related disorders in humans.

Biometals as Potential Predictors of the Neurodegenerative Decline in Alzheimer's Disease

Alzheimer’s Disease (AD) is a debilitating neurodegenerative disease that is diagnosed by gradual memory loss and certain cognitive impairments involving attention, reasoning, and language. Most of the research on Alzheimer’s disease focuses on the correlation of its neuropathological changes in the neurofibrillary tangles caused by hyper-phosphorylated tau protein and β-amyloid plaques with respect to cognitive impairment. Its pathology, however, remains incompletely understood. Currently, research has demonstrated that environmental factors such as biometals play a crucial role in exacerbating AD progression. The present review examines the role of metals in AD progression and how metal dyshomeostasis attributes to AD pathogenesis. 

It was found that certain metals possess both beneficial and harmful properties in terms of AD progression. Depending upon the concentration of the metal of interest, copper, zinc, iron, and selenium have general beneficial properties. However, when present in excess, they can lead to oxidative stress and hyperphosphorylation of tau protein, amongst other harmful effects, while calcium and magnesium were seen to have beneficial effects by regulating biometal uptake. 

In this review, we have provided evidential studies that focus on the involvement of certain metals in antioxidant pathways leading to the formation of reactive species indicative of neurodegeneration.

Airborne, Vehicle-Derived Fe-Bearing Nanoparticles in the Urban Environment: A Review

Airborne particulate matter poses a serious threat to human health. Exposure to nanosized (<0.1 μm), vehicle-derived particulates may be hazardous due to their bioreactivity, their ability to penetrate every organ, including the brain, and their abundance in the urban atmosphere. Fe-bearing nanoparticles (<0.1 μm) in urban environments may be especially important because of their pathogenicity and possible association with neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. This review examines current knowledge regarding the sources of vehicle-derived Fe-bearing nanoparticles, their chemical and mineralogical compositions, grain size distribution and potential hazard to human health. We focus on data reported for the following sources of Fe-bearing nanoparticles: exhaust emissions (both diesel and gasoline), brake wear, tire and road surface wear, resuspension of roadside dust, underground, train and tram emissions, and aircraft and shipping emissions. We identify limitations and gaps in existing knowledge as well as future challenges and perspectives for studies of airborne Fe-bearing nanoparticles.

Colocalization of Aluminum and Iron in Nuclei of Nerve Cells in Brains of Patients with Alzheimer's Disease

Increasing evidence indicates that metal-induced oxidative stress plays a pivotal role in the pathogenesis of Alzheimer's disease (AD). Recently, the presence of 8-hydroxydeoxyguanosine, a biomarker of oxidative DNA damage, was demonstrated in nuclear DNA (nDNA) in the AD brain. Iron (Fe) is a pro-oxidant metal capable of generating hydroxyl radicals that can oxidize DNA, and aluminum (Al) has been reported to facilitate Fe-mediated oxidation. In the present study, we examined the elements contained in the nuclei of nerve cells in AD brains using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Our results demonstrated that Al and Fe were colocalized in the nuclei of nerve cells in the AD brain. Within the nuclei, the highest levels of both Al and Fe were measured in the nucleolus. The SEM-EDS analysis also revealed the colocalization of Al and Fe in the heterochromatin and euchromatin in neuronal nuclei in the AD brain. Notably, the levels of Al and Fe in the nucleus of nerve cells in the AD brain were markedly higher than those in age-matched control brains. We hypothesize that the colocalization of Al and Fe in the nucleus of nerve cells might induce oxidative damage to nDNA and concurrently inhibit the repair of oxidatively damaged nDNA. An imbalance caused by the increase in DNA damage and the decrease in DNA repair activities might lead to the accumulation of unrepaired damaged DNA, eventually causing neurodegeneration and the development of AD.

Possible magneto-mechanical and magneto-thermal mechanisms of ion channel activation in magnetogenetics

The palette of tools for perturbation of neural activity is continually expanding. On the forefront of this expansion is magnetogenetics, where ion channels are genetically engineered to be closely coupled to the iron-storage protein ferritin. Initial reports on magnetogenetics have sparked a vigorous debate on the plausibility of physical mechanisms of ion channel activation by means of external magnetic fields. The criticism leveled against magnetogenetics as being physically implausible is based on the specific assumptions about the magnetic spin configurations of iron in ferritin. I consider here a wider range of possible spin configurations of iron in ferritin and the consequences these might have in magnetogenetics. I propose several new magneto-mechanical and magneto-thermal mechanisms of ion channel activation that may clarify some of the mysteries that presently challenge our understanding of the reported biological experiments. Finally, I present some additional puzzles that will require further theoretical and experimental investigation.