Spatial distribution of trace metals and associated transport proteins during bacterial infection

Innate immune systems alter the concentrations of trace elements in host niches in response to invading pathogens during infection. This work reports the interplay between d-block metal ions and their associated biomolecules using hyphenated elemental techniques to spatially quantify both elemental distributions and the abundance of specific transport proteins. Here, lung tissues were collected for analyses from naïve and Streptococcus pneumoniae-infected mice fed on a zinc-restricted or zinc-supplemented diet. Spatiotemporal distributions of manganese (55Mn), iron (56Fe), copper (63Cu), and zinc (66Zn) were determined by quantitative laser ablation-inductively coupled plasma-mass spectrometry. The murine transport proteins ZIP8 and ZIP14, which are associated with zinc transport, were also imaged by incorporation of immunohistochemistry techniques into the analytical workflow. Collectively, this work demonstrates the potential of a single instrumental platform suitable for multiplex analyses of tissues and labelled antibodies to investigate complex elemental interactions at the host-pathogen interface. Further, these methods have the potential for broad application to investigations of biological pathways where concomitant measurement of elements and biomolecules is crucial to understand the basis of disease and aid in development of new therapeutic approaches.

Immunolabelling perturbs the endogenous and antibody-conjugated elemental concentrations during immuno-mass spectrometry imaging

Immuno-mass spectrometry imaging uses lanthanide-conjugated antibodies to spatially quantify biomolecules via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The multi-element capabilities allow for highly multiplexed analyses that may include both conjugated antibodies and endogenous metals to reveal relationships between disease and chemical composition. Sample handling is known to perturb the composition of the endogenous elements, but there has been little investigation into the effects of immunolabelling and coverslipping. Here, we used cryofixed muscle sections to examine the impact of immunolabelling steps on the concentrations of a Gd-conjugated anti-dystrophin primary antibody, and the endogenous metals Cu and Zn. Primary antibody incubation resulted in a decrease in Zn, and an increase in Cu. Zn was removed from the cytoplasm where it was hypothesised to be more labile, whereas concentrated locations of Zn remained in the cell membrane in all samples that underwent the immunostaining process. Cu increased in concentration and was found mostly in the cell membrane. The concentration of the Gd-conjugated antibody when compared to the standard air-dried sample was not significantly different when coverslipped using an organic mounting medium, whereas use of an aqueous mounting medium significantly reduced the concentration of Gd. These results build on the knowledge of how certain sample handling techniques change elemental concentrations and distributions in tissue sections. Immunolabelling steps impact the concentration of endogenous elements, and separate histological sections are required for the quantitative analysis of endogenous elements and biomolecules. Additionally, coverslipping tissue sections for complementary immunohistochemical/immunofluorescent imaging may compromise the integrity of the elemental label, and organic mounting media are recommended over aqueous mounting media.

Increased iron in the substantia nigra pars compacta identifies patients with early Parkinson'sdisease: A 3T and 7T MRI study

Degeneration in the substantia nigra (SN) pars compacta (SNc) underlies motor symptoms in Parkinson's disease (PD). Currently, there are no neuroimaging biomarkers that are sufficiently sensitive, specific, reproducible, and accessible for routine diagnosis or staging of PD. Although iron is essential for cellular processes, it also mediates neurodegeneration. MRI can localize and quantify brain iron using magnetic susceptibility, which could potentially provide biomarkers of PD. We measured iron in the SNc, SN pars reticulata (SNr), total SN, and ventral tegmental area (VTA), using quantitative susceptibility mapping (QSM) and R2* relaxometry, in PD patients and age-matched healthy controls (HCs). PD patients, diagnosed within five years of participation and HCs were scanned at 3T (22 PD and 23 HCs) and 7T (17 PD and 21 HCs) MRI. Midbrain nuclei were segmented using a probabilistic subcortical atlas. QSM and R2* values were measured in midbrain subregions. For each measure, groups were contrasted, with Age and Sex as covariates, and receiver operating characteristic (ROC) curve analyses were performed with repeated k-fold cross-validation to test the potential of our measures to classify PD patients and HCs. Statistical differences of area under the curves (AUCs) were compared using the Hanley-MacNeil method (QSM versus R2*; 3T versus 7T MRI). PD patients had higher QSM values in the SNc at both 3T (padj = 0.001) and 7T (padj = 0.01), but not in SNr, total SN, or VTA, at either field strength. No significant group differences were revealed using R2* in any midbrain region at 3T, though increased R2* values in SNc at 7T MRI were marginally significant in PDs compared to HCs (padj = 0.052). ROC curve analyses showed that SNc iron measured with QSM, distinguished early PD patients from HCs at the single-subject level with good diagnostic accuracy, using 3T (mean AUC = 0.83, 95 % CI = 0.82-0.84) and 7T (mean AUC = 0.80, 95 % CI = 0.79-0.81) MRI. Mean AUCs reported here are from averages of tests in the hold-out fold of cross-validated samples. The Hanley-MacNeil method demonstrated that QSM outperforms R2* in discriminating PD patients from HCs at 3T, but not 7T. There were no significant differences between 3T and 7T in diagnostic accuracy of QSM values in SNc. This study highlights the importance of segmenting midbrain subregions, performed here using a standardized atlas, and demonstrates high accuracy of SNc iron measured with QSM at 3T MRI in identifying early PD patients. QSM measures of SNc show potential for inclusion in neuroimaging diagnostic biomarkers of early PD. An MRI diagnostic biomarker of PD would represent a significant clinical advance.

Iron overload suppresses hippocampal neurogenesis in adult mice: Implication for iron dysregulation-linked neurological diseases

AIMS

Adult hippocampal neurogenesis is an important player in brain homeostasis and its impairment participates in neurological diseases. Iron overload has emerged as an irreversible factor of brain aging, and is also closely related to degenerative disorders, including cognitive dysfunction. However, whether brain iron overload alters hippocampal neurogenesis has not been reported. We investigated the effect of elevated iron content on adult hippocampal neurogenesis and explored the underlying mechanism.

METHODS

Mouse models with hippocampal iron overload were generated. Neurogenesis in hippocampus and expression levels of related molecules were assessed.

RESULTS

Iron accumulation in hippocampus remarkably impaired the differentiation of neural stem cells, resulting in a significant decrease in newborn neurons. The damage was possibly attributed to iron-induced downregulation of proprotein convertase furin and subsequently decreased maturation of brain-derived neurotrophic factor (BDNF), thus contributing to memory decline and anxiety-like behavior of mice. Supportively, knockdown of furin indeed suppressed hippocampal neurogenesis, while furin overexpression restored the impairment.

CONCLUSION

These findings demonstrated that iron overload damaged hippocampal neurogenesis likely via iron-furin-BDNF pathway. This study provides new insights into potential mechanisms on iron-induced neurotoxicity and the causes of neurogenesis injury and renders modulating iron homeostasis and furin expression as novel therapeutic strategies for treatment of neurological diseases.

HMGB1 induces hepcidin upregulation in astrocytes and causes an acute iron surge and subsequent ferroptosis in the postischemic brain

Dysregulation of brain iron levels causes functional disturbances and damages neurons. Hepcidin (a peptide hormone) plays a principal role in regulating intracellular iron levels by modulating ferroportin (FPN, the only known iron exporter) through triggering its internalization and lysosomal degradation. We observed a significant and rapid iron surge in the cortices of ischemic hemispheres at 3 h after cerebral ischemia (middle cerebral artery occlusion, MCAO) that was maintained until 4 d post-MCAO. We showed upregulation of hepcidin expression in the brain as early as 3 h post-MCAO, mainly in astrocytes, and significant hepcidin accumulation in serum from 6 h post-MCAO, and these inductions were maintained for 1 day and 7 days, respectively. High mobility group box 1 (HMGB1), a prototypic danger-associated molecular pattern, accumulates markedly after transient MCAO and plays critical roles in damage aggravation via its proinflammatory effects. Here, we demonstrated that treatment with recombinant HMGB1 stimulated astrocytes to induce hepcidin expression in a TLR4- and CXCR4-dependent manner. Furthermore, hepcidin-mediated intracellular iron accumulation in neurons was confirmed by an experiment using N-methyl-D-aspartate (NMDA)-conditioned medium-treated primary astrocytes and fresh primary cortical neurons treated with hepcidin-containing astrocyte-conditioned medium. Moreover, HMGB1-mediated local hepcidin upregulation and subsequent local iron surge were found to cause ferroptosis in the postischemic brain, which was suppressed by the functional blocking of HMGB1 using intranasally administered HMGB1 A box or anti-HMGB1 antibody. These findings show that HMGB1 serves as a ferroptosis inducer by upregulating hepcidin in astrocytes and thus aggravates acute damage in the postischemic brain.

Iron accumulation in the ventral tegmental area in Parkinson's disease

Introduction

The ventral tegmental area (VTA) is less affected compared to substantia nigra pars compacta (SNc) in Parkinson's disease (PD). This study aimed to quantitatively evaluate iron content in the VTA across different stages of PD in order to help explain the selective loss of dopamine neurons in PD.

Methods

Quantitative susceptibility mapping (QSM) data were obtained from 101 PD patients, 35 idiopathic rapid eye movement sleep behavior disorder (RBD) patients, and 62 healthy controls (HCs). The mean QSM values in the VTA and SNc were calculated and compared among the groups.

Results

Both RBD and PD patients had increased iron values in the bilateral SNc compared with HCs. RBD and PD patients in the Hoehn-Yahr (H & Y) stage 1 did not show elevated iron values in the VTA, while PD patients with more than 1.5 H & Y staging had increased iron values in bilateral VTA compared to HCs.

Discussion

This study shows that there is no increased iron accumulation in the VTA during the prodromal and early clinical stages of PD, but iron deposition increases significantly as the disease becomes more severe.

Multiparametric Tissue Characterization Utilizing the Cellular Metallome and Immuno-Mass Spectrometry Imaging

In this study, we present a workflow that enables spatial single-cell metallomics in tissue decoding the cellular heterogeneity. Low-dispersion laser ablation in combination with inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) provides mapping of endogenous elements with cellular resolution at unprecedented speed. Capturing the heterogeneity of the cellular population by metals only is of limited use as the cell type, functionality, and cell state remain elusive. Therefore, we expanded the toolbox of single-cell metallomics by integrating the concepts of imaging mass cytometry (IMC). This multiparametric assay successfully utilizes metal-labeled antibodies for cellular tissue profiling. One important challenge is the need to preserve the original metallome in the sample upon immunostaining. Therefore, we studied the impact of extensive labeling on the obtained endogenous cellular ionome data by quantifying elemental levels in consecutive tissue sections (with and without immunostaining) and correlating elements with structural markers and histological features. Our experiments showed that the elemental tissue distribution remained intact for selected elements such as sodium, phosphorus, and iron, while absolute quantification was precluded. We hypothesize that this integrated assay not only advances single-cell metallomics (enabling to link metal accumulation to multi-dimensional characterization of cells/cell populations), but in turn also enhances selectivity in IMC, as in selected cases, labeling strategies can be validated by elemental data. We showcase the power of this integrated single-cell toolbox using an in vivo tumor model in mice and provide mapping of the sodium and iron homeostasis as linked to different cell types and function in mouse organs (such as spleen, kidney, and liver). Phosphorus distribution maps added structural information, paralleled by the DNA intercalator visualizing the cellular nuclei. Overall, iron imaging was the most relevant addition to IMC. In tumor samples, for example, iron-rich regions correlated with high proliferation and/or located blood vessels, which are key for potential drug delivery.

ATH434 Rescues Pre-motor Hyposmia in a Mouse Model of Parkinsonism

Hyposmia is a prevalent prodromal feature of Parkinson's disease (PD), though the neuropathology that underlies this symptom is poorly understood. Unlike the substantia nigra, the status of metal homeostasis in the olfactory bulbs has not been characterized in PD. Given the increasing interest in metal modulation as a therapeutic avenue in PD, we sought to investigate bulbar metals and the effect of AT434 (formerly PBT434) an orally bioavailable, small molecule modulator of metal homeostasis on hyposmia in a mouse model of parkinsonism (the tau knockout (tau-/-) mouse). 5.5 (pre-hyposmia) and 13.5-month-old (pre-motor) mice were dosed with ATH434 (30 mg/kg/day, oral gavage) for 6 weeks. Animals then underwent behavioral analysis for olfactory and motor phenotypes. The olfactory bulbs and the substantia nigra were then collected and analyzed for metal content, synaptic markers, and dopaminergic cell number. ATH434 was able to prevent the development of hyposmia in young tau-/- mice, which coincided with a reduction in bulbar iron and copper levels, an increase in synaptophysin, and a reduction in soluble α-synuclein. ATH434 was able to prevent the development of motor impairment in aged tau-/- mice, which coincided with a reduction in iron levels and reduced neurodegeneration in the substantia nigra. These data implicate metal dyshomeostasis in parkinsonian olfactory deficits, and champion a potential clinical benefit of ATH434 in both prodromal and clinical stages of PD.

Facets of ICP-MS and their potential in the medical sciences—Part 2: nanomedicine, immunochemistry, mass cytometry, and bioassays

Inductively coupled–plasma mass spectrometry (ICP-MS) has transformed our knowledge on the role of trace and major elements in biology and has emerged as the most versatile technique in elemental mass spectrometry. The scope of ICP-MS has dramatically changed since its inception, and nowadays, it is a mature platform technology that is compatible with chromatographic and laser ablation (LA) systems. Over the last decades, it kept pace with various technological advances and was inspired by interdisciplinary approaches which endorsed new areas of applications. While the first part of this review was dedicated to fundamentals in ICP-MS, its hyphenated techniques and the application in biomonitoring, isotope ratio analysis, elemental speciation analysis, and elemental bioimaging, this second part will introduce relatively current directions in ICP-MS and their potential to provide novel perspectives in the medical sciences. In this context, current directions for the characterisation of novel nanomaterials which are considered for biomedical applications like drug delivery and imaging platforms will be discussed while considering different facets of ICP-MS including single event analysis and dedicated hyphenated techniques. Subsequently, immunochemistry techniques will be reviewed in their capability to expand the scope of ICP-MS enabling analysis of a large range of biomolecules alongside elements. These methods inspired mass cytometry and imaging mass cytometry and have the potential to transform diagnostics and treatment by offering new paradigms for personalised medicine. Finally, the interlacing of immunochemistry methods, single event analysis, and functional nanomaterials has opened new horizons to design novel bioassays which promise potential as assets for clinical applications and larger screening programs and will be discussed in their capabilities to detect low-level proteins and nucleic acids.

Iron metabolism mediates microglia susceptibility in ferroptosis

Ferroptosis is implicated in a range of brain disorders, but it is unknown whether neurons or glia in the brain are particularly effected. Here, we report that primary cortical astrocytes (PA), microglia (PM), and neurons (PN) varied in their sensitivities to ferroptosis. Specifically, PM were the most sensitive to ferroptosis, while PN were relatively insensitive. In contrast, PN and PM were equally susceptible to apoptosis, with PA being less affected, whereas all three cell types were similarly susceptible to autophagic cell death. In the tri-culture system containing PA, PM, and PN, the cells were more resistant to ferroptosis than that in the monoculture. These results demonstrated that brain cells exhibit different sensitivities under ferroptosis stress and the difference may be explained by the differentially regulated iron metabolism and the ability to handle iron. Continued elucidation of the cell death patterns of neurons and glia will provide a theoretical basis for related strategies to inhibit the death of brain cells.

Facets of ICP-MS and their potential in the medical sciences-Part 1: fundamentals, stand-alone and hyphenated techniques

Since its inception in the early 80s, inductively coupled plasma–mass spectrometry has developed to the method of choice for the analysis of elements in complex biological systems. High sensitivity paired with isotopic selectivity and a vast dynamic range endorsed ICP-MS for the inquiry of metals in the context of biomedical questions. In a stand-alone configuration, it has optimal qualities for the biomonitoring of major, trace and toxicologically relevant elements and may further be employed for the characterisation of disrupted metabolic pathways in the context of diverse pathologies. The on-line coupling to laser ablation (LA) and chromatography expanded the scope and application range of ICP-MS and set benchmarks for accurate and quantitative speciation analysis and element bioimaging. Furthermore, isotopic analysis provided new avenues to reveal an altered metabolism, for the application of tracers and for calibration approaches. In the last two decades, the scope of ICP-MS was further expanded and inspired by the introduction of new instrumentation and methodologies including novel and improved hardware as well as immunochemical methods. These additions caused a paradigm shift for the biomedical application of ICP-MS and its impact in the medical sciences and enabled the analysis of individual cells, their microenvironment, nanomaterials considered for medical applications, analysis of biomolecules and the design of novel bioassays. These new facets are gradually recognised in the medical communities and several clinical trials are underway. Altogether, ICP-MS emerged as an extremely versatile technique with a vast potential to provide novel insights and complementary perspectives and to push the limits in the medical disciplines. This review will introduce the different facets of ICP-MS and will be divided into two parts. The first part will cover instrumental basics, technological advances, and fundamental considerations as well as traditional and current applications of ICP-MS and its hyphenated techniques in the context of biomonitoring, bioimaging and elemental speciation. The second part will build on this fundament and describe more recent directions with an emphasis on nanomedicine, immunochemistry, mass cytometry and novel bioassays.

Deciphering Dual Modes of Parkinsonian Biomolecules Derived Fluorescent Nanoparticles: Protein Specificity and White Light Generation

Dopamine (DA) and 3,4-dihydroxy-l-phenylalanine (L-Dopa or DPA), a marker and medicine for the neurological disorder Parkinson's disease (PD), lead to the formation of polymeric fluorescent nanoparticles (F-Poly NPs or F-NPs or simply, NPs). The interaction study between proteins and NPs shows prominent interaction with strong specificity toward albumin type proteins for DPA derived and mixed NPs. Furthermore, encapsulation of the anticancer drug doxorubicin hydrochloride (Dox) inside the NP-protein conjugates results in excellent white light emission with pronounced specificity toward albumin proteins for F-PDPA and F-Mix NPs. Finally, the use of BSA protein fibril resulting in strong binding with NPs along with Dox assisted white light emission has also been studied.

Brain regions susceptible to alpha-synuclein spreading

The spreading of misfolded alpha-synuclein (α-syn) protein has been observed in animal models of Parkinson's disease (PD) and other α-synucleinopathies that mimic human PD pathologies. In animal models, the spreading of α-syn has been associated with motor dysfunction and neuronal death. However, variability in both susceptible brain regions and cellular populations limits our understanding of the consequences of α-syn spreading and the development of associated therapies. Here, we have reviewed the physiological and pathological functions of α-syn and summarized the susceptible brain regions and cell types identified from human postmortem studies and exogenous α-syn injection-based animal models. We have reviewed the methods for inducing α-syn aggregation, the specific hosts, the inoculation sites, the routes of propagation, and other experimental settings that may affect the spreading pattern of α-syn, as reported in current studies. Understanding the spread of α-syn to produce a consistent PD animal model is vital for future drug discovery.

Essential Metals in the Brain and the Application of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry for their Detection

Metals are natural component of the ecosystem present throughout the layers of atmosphere; their abundant expression in the brain indicates their importance in the central nervous system (CNS). Within the brain tissue, their distribution is highly compartmentalized, the pattern of which is determined by their primary roles. Bio-imaging of the brain to reveal spatial distribution of metals within specific regions has provided a unique understanding of brain biochemistry and architecture, linking both the structures and the functions through several metal mediated activities. Bioavailability of essential trace metal is needed for normal brain function. However, disrupted metal homeostasis can influence several biochemical pathways in different fields of metabolism and cause characteristic neurological disorders with a typical disease process usually linked with aberrant metal accumulations. In this review we give a brief overview of roles of key essential metals (Iron, Copper and Zinc) including their molecular mechanisms and bio-distribution in the brain as well as their possible involvement in the pathogenesis of related neurodegenerative diseases. In addition, we also reviewed recent applications of Laser Ablation Inductively Couple Plasma Mass Spectrophotometry (LA-ICP-MS) in the detection of both toxic and essential metal dyshomeostasis in neuroscience research and other related brain diseases.

Parkinson's Disease and the Metal-Microbiome-Gut-Brain Axis: A Systems Toxicology Approach

Parkinson's Disease (PD) is a neurodegenerative disease, leading to motor and non-motor complications. Autonomic alterations, including gastrointestinal symptoms, precede motor defects and act as early warning signs. Chronic exposure to dietary, environmental heavy metals impacts the gastrointestinal system and host-associated microbiome, eventually affecting the central nervous system. The correlation between dysbiosis and PD suggests a functional and bidirectional communication between the gut and the brain. The bioaccumulation of metals promotes stress mechanisms by increasing reactive oxygen species, likely altering the bidirectional gut-brain link. To better understand the differing molecular mechanisms underlying PD, integrative modeling approaches are necessary to connect multifactorial perturbations in this heterogeneous disorder. By exploring the effects of gut microbiota modulation on dietary heavy metal exposure in relation to PD onset, the modification of the host-associated microbiome to mitigate neurological stress may be a future treatment option against neurodegeneration through bioremediation. The progressive movement towards a systems toxicology framework for precision medicine can uncover molecular mechanisms underlying PD onset such as metal regulation and microbial community interactions by developing predictive models to better understand PD etiology to identify options for novel treatments and beyond. Several methodologies recently addressed the complexity of this interaction from different perspectives; however, to date, a comprehensive review of these approaches is still lacking. Therefore, our main aim through this manuscript is to fill this gap in the scientific literature by reviewing recently published papers to address the surrounding questions regarding the underlying molecular mechanisms between metals, microbiota, and the gut-brain-axis, as well as the regulation of this system to prevent neurodegeneration.

Research progress on the mechanism of ferroptosis and its clinical application

Ferroptosis is a mode of cell death dependent on iron ions, which is mainly induced by the decrease of the biological activity of glutathione peroxidase or the accumulation of lipid peroxidation and reactive oxygen species (ROS). It is significantly different from autophagy and other forms of cell death in terms of cell morphology and biochemistry. The exact mechanisms of ferroptosis are not clear. More and more studies have shown that various tumor diseases and nervous system diseases are closely related to ferroptosis. The occurrence and development of related diseases can be tolerated by stimulating or inhibiting the occurrence of ferroptosis. Therefore, ferroptosis has occupied a very important position in recent years. This article reviews the discovery process, characteristics, mechanisms, inducers, inhibitors of ferroptosis and its related clinical applications to lay a foundation for follow-up researchers to study ferroptosis and provide some reference value.

Parkinson Disease: Translating Insights from Molecular Mechanisms to Neuroprotection

Parkinson disease (PD) used to be considered a nongenetic condition. However, the identification of several autosomal dominant and recessive mutations linked to monogenic PD has changed this view. Clinically manifest PD is then thought to occur through a complex interplay between genetic mutations, many of which have incomplete penetrance, and environmental factors, both neuroprotective and increasing susceptibility, which variably interact to reach a threshold over which PD becomes clinically manifested. Functional studies of PD gene products have identified many cellular and molecular pathways, providing crucial insights into the nature and causes of PD. PD originates from multiple causes and a range of pathogenic processes at play, ultimately culminating in nigral dopaminergic loss and motor dysfunction. An in-depth understanding of these complex and possibly convergent pathways will pave the way for therapeutic approaches to alleviate the disease symptoms and neuroprotective strategies to prevent disease manifestations. This review is aimed at providing a comprehensive understanding of advances made in PD research based on leveraging genetic insights into the pathogenesis of PD. It further discusses novel perspectives to facilitate identification of critical molecular pathways that are central to neurodegeneration that hold the potential to develop neuroprotective and/or neurorestorative therapeutic strategies for PD. SIGNIFICANCE STATEMENT: A comprehensive review of PD pathophysiology is provided on the complex interplay of genetic and environmental factors and biologic processes that contribute to PD pathogenesis. This knowledge identifies new targets that could be leveraged into disease-modifying therapies to prevent or slow neurodegeneration in PD.

Therapeutic potential of iron modulating drugs in a mouse model of multiple system atrophy

Multiple System Atrophy (MSA) is a rare neurodegenerative synucleinopathy which leads to severe disability followed by death within 6-9 years of symptom onset. There is compelling evidence suggesting that biological trace metals like iron and copper play an important role in synucleinopathies like Parkinson's disease and removing excess brain iron using chelators could slow down the disease progression. In human MSA, there is evidence of increased iron in affected brain regions, but role of iron and therapeutic efficacy of iron-lowering drugs in pre-clinical models of MSA have not been studied. We studied age-related changes in iron metabolism in different brain regions of the PLP-αsyn mice and tested whether iron-lowering drugs could alleviate disease phenotype in aged PLP-αsyn mice. Iron content, iron-ferritin association, ferritin protein levels and copper-ceruloplasmin association were measured in prefrontal cortex, putamen, substantia nigra and cerebellum of 3, 8, and 20-month-old PLP-αsyn and age-matched non-transgenic mice. Moreover, 12-month-old PLP-αsyn mice were administered deferiprone or ceruloplasmin or vehicle for 2 months. At the end of treatment period, motor testing and stereological analyses were performed. We found iron accumulation and perturbed iron-ferritin interaction in substantia nigra, putamen and cerebellum of aged PLP-αsyn mice. Furthermore, we found significant reduction in ceruloplasmin-bound copper in substantia nigra and cerebellum of the PLP-αsyn mice. Both deferiprone and ceruloplasmin prevented decline in motor performance in aged PLP-αsyn mice and were associated with higher neuronal survival and reduced density of α-synuclein aggregates in substantia nigra. This is the first study to report brain iron accumulation in a mouse model of MSA. Our results indicate that elevated iron in MSA mice may result from ceruloplasmin dysfunction and provide evidence that targeting iron in MSA could be a viable therapeutic option.

Multiparametric MRI for Characterization of the Basal Ganglia and the Midbrain

Objectives To characterize subcortical nuclei by multi-parametric quantitative magnetic resonance imaging.

Materials and Methods: The following quantitative multiparametric MR data of five healthy volunteers were acquired on a 7T MRI system: 3D gradient echo (GRE) data for the calculation of quantitative susceptibility maps (QSM), GRE sequences with and without off-resonant magnetic transfer pulse for magnetization transfer ratio (MTR) calculation, a magnetization−prepared 2 rapid acquisition gradient echo sequence for T₁ mapping, and (after a coil change) a density-adapted 3D radial pulse sequence for ²³Na imaging. First, all data were co-registered to the GRE data, volumes of interest (VOIs) for 21 subcortical structures were drawn manually for each volunteer, and a combined voxel-wise analysis of the four MR contrasts (QSM, MTR, T₁, ²³Na) in each structure was conducted to assess the quantitative, MR value-based differentiability of structures. Second, a machine learning algorithm based on random forests was trained to automatically classify the groups of multi-parametric voxel values from each VOI according to their association to one of the 21 subcortical structures.

Results The analysis of the integrated multimodal visualization of quantitative MR values in each structure yielded a successful classification among nuclei of the ascending reticular activation system (ARAS), the limbic system and the extrapyramidal system, while classification among (epi-)thalamic nuclei was less successful. The machine learning-based approach facilitated quantitative MR value-based structure classification especially in the group of extrapyramidal nuclei and reached an overall accuracy of 85% regarding all selected nuclei.

Conclusion Multimodal quantitative MR enabled excellent differentiation of a wide spectrum of subcortical nuclei with reasonable accuracy and may thus enable sensitive detection of disease and nucleus-specific MR-based contrast alterations in the future.

Ferroptosis: A potential therapeutic target for neurodegenerative diseases

Ferroptosis is a newly identified regulated form of cell death, which is thought to play a major role in neurodegenerative diseases. In this review, we discuss recent studies elucidating the molecular mechanisms involved in the regulation and execution of ferroptotic cell death and also its role in the brain. Ferroptosis is regulated mainly via iron homeostasis, glutathione metabolism, and lipid peroxidation. Ferroptotic cell death and pro-ferroptotic factors are correlated with the etiopathogenesis of Parkinson's disease (PD) and Alzheimer's disease (AD). Ferroptosis and etiological factors act synergistically in PD and AD pathogenesis. Furthermore, several preclinical and clinical studies targeting ferroptosis in PD and AD have also shown positive results. Evidence of ferroptosis in the brain thus gives new insights into understanding neurodegenerative diseases. Ferroptosis studies in the brain are still in their infancy, but the existing pieces of evidence suggest a strong correlation between ferroptotic cell death and neurodegenerative diseases. Thus, ferroptosis might be a promising target for treating neurodegenerative diseases.

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry Imaging in Biology

Elemental imaging gives insight into the fundamental chemical makeup of living organisms. Every cell on Earth is comprised of a complex and dynamic mixture of the chemical elements that define structure and function. Many disease states feature a disturbance in elemental homeostasis, and understanding how, and most importantly where, has driven the development of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) as the principal elemental imaging technique for biologists. This review provides an outline of ICP-MS technology, laser ablation cell designs, imaging workflows, and methods of quantification. Detailed examples of imaging applications including analyses of cancers, elemental uptake and accumulation, plant bioimaging, nanomaterials in the environment, and exposure science and neuroscience are presented and discussed. Recent incorporation of immunohistochemical workflows for imaging biomolecules, complementary and multimodal imaging techniques, and image processing methods is also reviewed.

Parkinson's disease: Alterations in iron and redox biology as a key to unlock therapeutic strategies

A plethora of studies indicate that iron metabolism is dysregulated in Parkinson's disease (PD). The literature reveals well-documented alterations consistent with established dogma, but also intriguing paradoxical observations requiring mechanistic dissection. An important fact is the iron loading in dopaminergic neurons of the substantia nigra pars compacta (SNpc), which are the cells primarily affected in PD. Assessment of these changes reveal increased expression of proteins critical for iron uptake, namely transferrin receptor 1 and the divalent metal transporter 1 (DMT1), and decreased expression of the iron exporter, ferroportin-1 (FPN1). Consistent with this is the activation of iron regulator protein (IRP) RNA-binding activity, which is an important regulator of iron homeostasis, with its activation indicating cytosolic iron deficiency. In fact, IRPs bind to iron-responsive elements (IREs) in the 3ꞌ untranslated region (UTR) of certain mRNAs to stabilize their half-life, while binding to the 5ꞌ UTR prevents translation. Iron loading of dopaminergic neurons in PD may occur through these mechanisms, leading to increased neuronal iron and iron-mediated reactive oxygen species (ROS) generation. The "gold standard" histological marker of PD, Lewy bodies, are mainly composed of α-synuclein, the expression of which is markedly increased in PD. Of note, an atypical IRE exists in the α-synuclein 5ꞌ UTR that may explain its up-regulation by increased iron. This dysregulation could be impacted by the unique autonomous pacemaking of dopaminergic neurons of the SNpc that engages L-type Ca+2 channels, which imparts a bioenergetic energy deficit and mitochondrial redox stress. This dysfunction could then drive alterations in iron trafficking that attempt to rescue energy deficits such as the increased iron uptake to provide iron for key electron transport proteins. Considering the increased iron-loading in PD brains, therapies utilizing limited iron chelation have shown success. Greater therapeutic advancements should be possible once the exact molecular pathways of iron processing are dissected.

Deferiprone Treatment in Aged Transgenic Tau Mice Improves Y-Maze Performance and Alters Tau Pathology

The accumulation of neurofibrillary tangles (NFTs), which is composed of abnormally hyperphosphorylated tau aggregates, is the classic neuropathology associated with cognitive dysfunction in tauopathies such as Alzheimer's disease (AD). However, there is an emerging theory suggesting that dysregulation in cerebral iron may contribute to NFT formation. Iron is speculated to bind to tau and induce conformational changes of the protein, potentially leading to subsequent aggregation and cognitive decline. Deferiprone (DFP) is a clinically available iron chelator, which has demonstrated potential therapeutic advantages of chelating iron in neurodegenerative disorders, and is currently in clinical trials for AD. However, its effect on tau pathology remains unclear. Here, we report the effects of short-term DFP treatment (4 weeks, 100 mg/kg/daily, via oral gavage) in a mixed-gender cohort of the rTg(tauP301L)4510 mouse model of tauopathy. Our results revealed that DFP improved Y-maze and open field performance, accompanied by a 28% decrease in brain iron levels, measured by inductively coupled plasma mass spectrometry (ICP-MS) and reduced AT8-labeled p-tau within the hippocampus in transgenic tau mice. This data supports the notion that iron may play a neurotoxic role in tauopathies and may be a potential therapeutic target for this class of disorders that can be modulated by the clinically available metal chelator DFP.

Quantitative immuno-mass spectrometry imaging of skeletal muscle dystrophin

Emerging and promising therapeutic interventions for Duchenne muscular dystrophy (DMD) are confounded by the challenges of quantifying dystrophin. Current approaches have poor precision, require large amounts of tissue, and are difficult to standardize. This paper presents an immuno-mass spectrometry imaging method using gadolinium (Gd)-labeled anti-dystrophin antibodies and laser ablation-inductively coupled plasma-mass spectrometry to simultaneously quantify and localize dystrophin in muscle sections. Gd is quantified as a proxy for the relative expression of dystrophin and was validated in murine and human skeletal muscle sections following k-means clustering segmentation, before application to DMD patients with different gene mutations where dystrophin expression was measured up to 100 µg kg-1 Gd. These results demonstrate that immuno-mass spectrometry imaging is a viable approach for pre-clinical to clinical research in DMD. It rapidly quantified relative dystrophin in single tissue sections, efficiently used valuable patient resources, and may provide information on drug efficacy for clinical translation.

Mini-Review: Is iron-mediated cell death (ferroptosis) an identical factor contributing to the pathogenesis of some neurodegenerative diseases?

The review article briefly discusses a hypothesis based on the potential participation of iron dyshomeostasis and iron-mediated cell death (ferroptosis) in the pathogenesis of some neurodegenerative diseases. Iron dyshomeostasis (especially cellular iron overload) is considered to be a critical condition of neurodegeneration. The etiopathogenesis of many neurodegenerative diseases including Alzheimer's and Parkinson's diseases, Multiple sclerosis, and others, is different. However, there are several identical cellular processes, such as iron dyshomeostasis (an excessive iron deposition), iron-induced oxidative stress, the accumulation of lipid-generated reactive oxygen species, and ferroptosis that accompany these diseases. Based on the existing theoretical and experimental evidence, the article provides current insight into iron dyshomeostasis and ferroptosis as a contributing factor to the pathogenesis of neurodegeneration. In addition, special attention is addressed to the possible relationship between cellular iron overload and key pathological features of selected neurodegenerative diseases, such as β-amyloid and tau proteins, α-synuclein, and demyelination. The mechanism by which ferroptosis may be involved in the pathogenesis of various neurodegenerative diseases is not fully elucidated. Further experimental and clinical studies are needed to clarify the hypothesis on the potential role of ferroptosis in the pathogenesis of neurodegenerative diseases.

The essential elements of Alzheimer's disease

Treatments for Alzheimer’s disease (AD) directed against the prominent amyloid plaque neuropathology are yet to be proved effective despite many phase 3 clinical trials. There are several other neurochemical abnormalities that occur in the AD brain that warrant renewed emphasis as potential therapeutic targets for this disease. Among those are the elementomic signatures of iron, copper, zinc, and selenium. Here, we review these essential elements of AD for their broad potential to contribute to Alzheimer’s pathophysiology, and we also highlight more recent attempts to translate these findings into therapeutics. A reinspection of large bodies of discovery in the AD field, such as this, may inspire new thinking about pathogenesis and therapeutic targets.

Characterising the spatial and temporal brain metal profile in a mouse model of tauopathy

A dysregulation in the homeostasis of metals such as copper, iron and zinc is speculated to be involved in the pathogenesis of tauopathies, which includes Alzheimer's disease (AD). In particular, there is a growing body of evidence to support a role for iron in facilitating the hyperphosphorylation and aggregation of the tau protein into neurofibrillary tangles (NFTs) - a primary neuropathological hallmark of tauopathies. Therefore, the aim of this study was to characterize the spatial and temporal brain metallomic profile in a mouse model of tauopathy (rTg(tauP301L)4510), so as to provide some insight into the potential interaction between tau pathology and iron. Using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), our results revealed an age-dependent increase in brain iron levels in both WT and rTg(tauP301L)4510 mice. In addition, size exclusion chromatography-ICP-MS (SEC-ICP-MS) revealed significant age-related changes in iron bound to metalloproteins such as ferritin. The outcomes from this study may provide valuable insight into the inter-relationship between iron and tau in ageing and neurodegeneration.

Regional iron distribution and soluble ferroprotein profiles in the healthy human brain

Iron is essential for brain development and health where its redox properties are used for a number of neurological processes. However, iron is also a major driver of oxidative stress if not properly controlled. Brain iron distribution is highly compartmentalised and regulated by a number of proteins and small biomolecules. Here, we examine heterogeneity in regional iron levels in 10 anatomical structures from seven post-mortem human brains with no apparent neuropathology. Putamen contained the highest levels, and most case-to-case variability, of iron compared with the other regions examined. Partitioning of iron between cytosolic and membrane-bound iron was generally consistent in each region, with a slightly higher proportion (55 %) in the 'insoluble' phase. We expand on this using the Allen Human Brain Atlas to examine patterns between iron levels and transcriptomic expression of iron regulatory proteins and using quantitative size exclusion chromatography-inductively coupled plasma-mass spectrometry to assess regional differences in the molecular masses to which cytosolic iron predominantly binds. Approximately 60 % was associated with ferritin, equating to approximately 25 % of total tissue iron essentially in storage. This study is the first of its kind in human brain tissue, providing a valuable resource and new insight for iron biologists and neuroscientists, alike.

Super-Resolution Reconstruction for Two- and Three-Dimensional LA-ICP-MS Bioimaging

The resolution of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) elemental bioimaging is usually constrained by the diameter of the laser spot size and is often not adequate to explore in situ subcellular distributions of elements and proteins in biological tissue sections. Super-resolution reconstruction is a method typically used for many imaging modalities and combines multiple lower resolution images to create a higher resolution image. Here, we present a super-resolution reconstruction method for LA-ICP-MS imaging by ablating consecutive layers of a biological specimen with offset orthogonal scans, resulting in a 10× improvement in resolution for quantitative measurement of dystrophin in murine muscle fibers. Layer-by-layer image reconstruction was also extended to the third dimension without the requirement of image registration across multiple thin section specimens. Quantitative super-resolution reconstruction, combined with Gaussian filtering and application of the Richardson-Lucy total variation algorithm, provided superior image clarity and fidelity in two- and three-dimensions.

Mapping Chemical Elements and Iron Oxidation States in the Substantia Nigra of 6-Hydroxydopamine Lesioned Rats Using Correlative Immunohistochemistry With Proton and Synchrotron Micro-Analysis

Brain metal homeostasis is altered in neurodegenerative diseases and the concentration, the localization and/or the chemical speciation of the elements can be modified compared to healthy individuals. These changes are often specific to the brain region affected by the neurodegenerative process. For example, iron concentration is increased in the substantia nigra (SN) of Parkinson's disease patients and iron redox reactions might be involved in the pathogenesis. The identification of the molecular basis behind metal dyshomeostasis in specific brain regions is the subject of intensive research and chemical element imaging methods are particularly useful to address this issue. Among the imaging modalities available, Synchrotron X-ray fluorescence (SXRF) and particle induced X-ray emission (PIXE) using focused micro-beams can inform about the quantitative distribution of metals in specific brain regions. Micro-X-ray absorption near edge spectroscopy (XANES) can in addition identify the chemical species of the elements, in particular their oxidation state. However, in order to bring accurate information about metal changes in specific brain areas, these chemical imaging methods must be correlated to brain tissue histology. We present a methodology to perform chemical element quantitative mapping and speciation on well-identified brain regions using correlative immunohistochemistry. We applied this methodology to the study of an animal model of Parkinson's disease, the 6-hydroxydopamine (6-OHDA) lesioned rat. Tyrosine hydroxylase immunohistochemical staining enabled to identify the SN pars compacta (SNpc) and pars reticulata (SNpr) as well as the ventral tegmental area (VTA). Using PIXE we found that iron content was higher respectively in the SNpr > SNpc > VTA, but was not statistically significantly modified by 6-OHDA treatment. In addition, micro-SXRF revealed the higher manganese content in the SNpc compared to the SNpr. Using micro-XANES we identified Fe oxidation states in the SNpr and SNpc showing a spectral similarity comparable to ferritin for all brain regions and exposure conditions. This study illustrates the capability to correlate immunohistochemistry and chemical element imaging at the brain region level and this protocol can now be widely applied to other studies of metal dyshomeostasis in neurology.

Mobility Deficits Assessed With Mobile Technology: What Can We Learn From Brain Iron-Altered Animal Models?

Background: Recent developments in mobile technology have enabled the investigation of human movements and mobility under natural conditions, i.e., in the home environment. Iron accumulation in the basal ganglia is deleterious in Parkinson's disease (i.e., iron accumulation with lower striatal level of dopamine). The effect of iron chelation (i.e., re-deployment of iron) in Parkinson's disease patients is currently tested in a large investigator-initiated multicenter study. Conversely, restless legs syndrome (RLS) is associated with iron depletion and higher striatal level of dopamine. To determine from animal models which movement and mobility parameters might be associated with iron content modulation and the potential effect of therapeutic chelation inhuman.

Methods: We recapitulated pathophysiological aspects of the association between iron, dopamine, and neuronal dysfunction and deterioration in the basal ganglia, and systematically searched PubMed to identify original articles reporting about quantitatively assessed mobility deficits in animal models of brain iron dyshomeostasis.

Results: We found six original studies using murine and fly models fulfilling the inclusion criteria. Especially postural and trunk stability were altered in animal models with iron overload. Animal models with lowered basal ganglia iron suffered from alterations in physical activity, mobility, and sleep fragmentation.

Conclusion: From preclinical investigations in the animal model, we can deduce that possibly also in humans with iron accumulation in the basal ganglia undergoing therapeutic chelation may primarily show changes in physical activity (such as daily “motor activity”), postural and trunk stability and sleep fragmentation. These changes can readily be monitored with currently available mobile technology.

Iron concentrations in neurons and glial cells with estimates on ferritin concentrations

Background

Brain iron is an essential as well as a toxic redox active element. Physiological levels are not uniform among the different cell types. Besides the availability of quantitative methods, the knowledge about the brain iron lags behind. Thereby, disclosing the mechanisms of brain iron homeostasis helps to understand pathological iron-accumulations in diseased and aged brains. With our study we want to contribute closing the gap by providing quantitative data on the concentration and distribution of iron in neurons and glial cells in situ. Using a nuclear microprobe and scanning proton induced X-ray emission spectrometry we performed quantitative elemental imaging on rat brain sections to analyze the iron concentrations of neurons and glial cells.

Results

Neurons were analyzed in the neocortex, subiculum, substantia nigra and deep cerebellar nuclei revealing an iron level between \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(0.53\pm 2)$$\end{document}(0.53±2) and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(0.68\pm 2)\,\upmu \hbox {M}$$\end{document}(0.68±2)μM. The iron concentration of neocortical oligodendrocytes is fivefold higher, of microglia threefold higher and of astrocytes twofold higher compared to neurons. We also analyzed the distribution of subcellular iron concentrations in the cytoplasm, nucleus and nucleolus of neurons. The cytoplasm contains on average 73% of the total iron, the nucleolus—although a hot spot for iron—due to its small volume only 6% of total iron. Additionally, the iron level in subcellular fractions were measured revealing that the microsome fraction, which usually contains holo-ferritin, has the highest iron content. We also present an estimate of the cellular ferritin concentration calculating \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$133\pm 25$$\end{document}133±25 ferritin molecules per \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu \hbox {m}$$\end{document}μm in rat neurons.

Conclusion

Glial cells are the most iron-rich cells in the brain. Imbalances in iron homeostasis that lead to neurodegeneration may not only be originate from neurons but also from glial cells. It is feasible to estimate the ferritin concentration based on measured iron concentrations and a reasonable assumptions on iron load in the brain.

Zinc homeostasis and zinc signaling in white matter development and injury

Zinc is an essential dietary micronutrient that is abundant in the brain with diverse roles in development, injury, and neurological diseases. With new imaging tools and chelators selectively targeting zinc, the field of zinc biology is rapidly expanding. The importance of zinc homeostasis is now well recognized in neurodegeneration, but there is emerging data that zinc may be equally important in white matter disorders. This review provides an overview of zinc biology, including a discussion of clinical disorders of zinc deficiency, different zinc pools, zinc biomarkers, and methods for measuring zinc. It emphasizes our limited understanding of how zinc is regulated in oligodendrocytes and white matter. Gaps in knowledge about zinc transporters and zinc signaling are discussed. Zinc-induced oligodendrocyte injury pathways relevant to white matter stroke, multiple sclerosis, and white matter injury of prematurity are reviewed and examples of zinc-dependent proteins relevant to myelination highlighted. Finally, a novel ratiometric zinc sensor is reviewed, revealing new information about mobile zinc during oligodendrocyte differentiation. With a better understanding of zinc biology in oligodendrocytes, new therapeutic targets for white matter disorders may be possible and the necessary tools to appropriately study zinc are finally available.

Striking while the iron is hot: Iron metabolism and ferroptosis in neurodegeneration

Perturbations in iron homeostasis and iron accumulation feature in several neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). Proteins such as α-synuclein, tau and amyloid precursor protein that are pathologically associated with neurodegeneration are involved in molecular crosstalk with iron homeostatic proteins. Quantitative susceptibility mapping, an MRI based non-invasive technique, offers proximal evaluations of iron load in regions of the brain and powerfully predicts cognitive decline. Further, small molecules that target elevated iron have shown promise against PD and AD in preclinical studies and clinical trials. Despite these strong links between altered iron homeostasis and neurodegeneration the molecular biology to describe the association between enhanced iron levels and neuron death, synaptic impairment and cognitive decline is ill defined. In this review we discuss the current understanding of brain iron homeostasis and how it may be perturbed under pathological conditions. Further, we explore the ramifications of a novel cell death pathway called ferroptosis that has provided a fresh impetus to the "metal hypothesis" of neurodegeneration. While lipid peroxidation plays a central role in the execution of this cell death modality the removal of iron through chelation or genetic modifications appears to extinguish the ferroptotic pathway. Conversely, tissues that harbour elevated iron may be predisposed to ferroptotic damage. These emerging findings are of relevance to neurodegeneration where ferroptotic signalling may offer new targets to mitigate cell death and dysfunction.

Laser ablation ICP-MS for simultaneous quantitative imaging of iron and ferroportin in hippocampus of human brain tissues with Alzheimer's disease

Laser ablation inductively coupled plasma - mass spectrometry (LA-ICP-MS) is proposed for a better understanding of metals and proteins distribution in micrometre structures of human brain tissues. Simultaneous absolute quantitative imaging of Fe and ferroportin (FPN), in 5 µm thick tissue sections of the stratum pyramidale of hippocampus CA1 region, was carried out for Alzheimer disease (AD) patients and healthy controls (HC). For the imaging of FPN by LA-ICP-MS, antibodies were labelled via carbodiimide crosslinking with fluorescent gold nanoclusters (AuNCs) of 2.2 nm diameter, enabling a high amplification (314 gold atoms per NC). Laboratory made gelatin standards containing Fe and Au were used for LA-ICP-MS calibration. Results showed that iron presents an increased concentration in AD donors compared with HC donors, whereas similar concentrations of FPN in AD donors with respect to HC donors were obtained. The average absolute FPN concentrations in selected areas obtained with the proposed AuNCs method were compared with the levels obtained by densitometric analysis with a traditional IHC approach, observing a similar trend in all cases.

Kinetic Modeling of pH-Dependent Oxidation of Dopamine by Iron and Its Relevance to Parkinson's Disease

Parkinson's disease is the second most common neurodegenerative disease. While age is the most significant risk factor, the exact cause of this disease and the most effective approaches to mitigation remain unclear. It has long been proposed that dopamine may play a role in the pathology of Parkinson's disease in view of its ability to generate both protein-modifying quinones such as aminochrome and reactive oxygen species, especially in the presence of pathological iron accumulation in the primary site of neuron loss. Given the clinically measured acidosis of post-mortem Parkinson's disease brain tissue, the interaction between dopamine and iron was investigated over a pH range of 7.4 to 6.5 with emphasis on the accumulation of toxic quinones and generation of reactive oxygen species. Our results show that the presence of iron accelerates the formation of aminochrome with ferrous iron (Fe[II]) being more efficient in this regard than ferric iron (Fe[III]). Our results further suggest that a reduced aminochrome rearrangement rate coupled with an enhanced turnover rate of Fe[II] as a result of brain tissue acidosis could result in aminochrome accumulation within cells. Additionally, under these conditions, the enhanced redox cycling of iron in the presence of dopamine aggravates oxidative stress as a result of the production of damaging reactive species, including hydroxyl radicals.

Quantitative mapping of specific proteins in biological tissues by laser ablation-ICP-MS using exogenous labels: aspects to be considered

Laser ablation (LA) coupled with inductively coupled plasma mass spectrometry (ICP-MS) is a versatile tool for direct trace elemental and isotopic analysis of solids. The development of new strategies for quantitative elemental mapping of biological tissues is one of the growing research areas in LA-ICP-MS. On the other hand, the latest advances are related to obtaining not only the elemental distribution of heteroatoms but also molecular information. In this vein, mapping of specific proteins in biological tissues can be done with LA-ICP-MS by use of metal-labelled immunoprobes. However, although LA-ICP-MS is, in principle, a quantitative technique, critical requirements should be met for absolute quantification of protein distribution. In this review, progress based on the use of metal-labelled antibodies for LA-ICP-MS mapping of specific proteins is reported. Critical requirements to obtain absolute quantitative mapping of specific proteins by LA-ICP-MS are highlighted. Additionally, illustrative examples of the advances made so far with LA-ICP-MS are provided. Graphical abstract In the proposed critical review, last advances based on the use of metal-labelled antibodies and critical requirements for LA-ICP-MS quantitative mapping of specific proteins are tackled.

No effects without causes: the Iron Dysregulation and Dormant Microbes hypothesis for chronic, inflammatory diseases

Since the successful conquest of many acute, communicable (infectious) diseases through the use of vaccines and antibiotics, the currently most prevalent diseases are chronic and progressive in nature, and are all accompanied by inflammation. These diseases include neurodegenerative (e.g. Alzheimer's, Parkinson's), vascular (e.g. atherosclerosis, pre-eclampsia, type 2 diabetes) and autoimmune (e.g. rheumatoid arthritis and multiple sclerosis) diseases that may appear to have little in common. In fact they all share significant features, in particular chronic inflammation and its attendant inflammatory cytokines. Such effects do not happen without underlying and initially 'external' causes, and it is of interest to seek these causes. Taking a systems approach, we argue that these causes include (i) stress-induced iron dysregulation, and (ii) its ability to awaken dormant, non-replicating microbes with which the host has become infected. Other external causes may be dietary. Such microbes are capable of shedding small, but functionally significant amounts of highly inflammagenic molecules such as lipopolysaccharide and lipoteichoic acid. Sequelae include significant coagulopathies, not least the recently discovered amyloidogenic clotting of blood, leading to cell death and the release of further inflammagens. The extensive evidence discussed here implies, as was found with ulcers, that almost all chronic, infectious diseases do in fact harbour a microbial component. What differs is simply the microbes and the anatomical location from and at which they exert damage. This analysis offers novel avenues for diagnosis and treatment.

The Aging of Iron Man

Brain iron is tightly regulated by a multitude of proteins to ensure homeostasis. Iron dyshomeostasis has become a molecular signature associated with aging which is accompanied by progressive decline in cognitive processes. A common theme in neurodegenerative diseases where age is the major risk factor, iron dyshomeostasis coincides with neuroinflammation, abnormal protein aggregation, neurodegeneration, and neurobehavioral deficits. There is a great need to determine the mechanisms governing perturbations in iron metabolism, in particular to distinguish between physiological and pathological aging to generate fruitful therapeutic targets for neurodegenerative diseases. The aim of the present review is to focus on the age-related alterations in brain iron metabolism from a cellular and molecular biology perspective, alongside genetics, and neuroimaging aspects in man and rodent models, with respect to normal aging and neurodegeneration. In particular, the relationship between iron dyshomeostasis and neuroinflammation will be evaluated, as well as the effects of systemic iron overload on the brain. Based on the evidence discussed here, we suggest a synergistic use of iron-chelators and anti-inflammatories as putative anti-brain aging therapies to counteract pathological aging in neurodegenerative diseases.

Advances in the Chemical Biology of Desferrioxamine B

Desferrioxamine B (DFOB) was discovered in the late 1950s as a hydroxamic acid metabolite of the soil bacterium Streptomyces pilosus. The exquisite affinity of DFOB for Fe(III) identified its potential for removing excess iron from patients with transfusion-dependent hemoglobin disorders. Many studies have used semisynthetic chemistry to produce DFOB adducts with new properties and broad-ranging functions. More recent approaches in chemical biology have revealed some nuances of DFOB biosynthesis and discovered new DFOB-derived drugs and radiometal imaging agents. The current and potential applications of DFOB continue to inspire a rich body of chemical biology research focused on this bacterial metabolite.

The Relevance of Iron in the Pathogenesis of Multiple System Atrophy: A Viewpoint

Iron is essential for cellular development and maintenance of multiple physiological processes in the central nervous system. The disturbance of its homeostasis leads to abnormal iron deposition in the brain and causes neurotoxicity via generation of free radicals and oxidative stress. Iron toxicity has been established in the pathogenesis of Parkinson's disease; however, its contribution to multiple system atrophy (MSA) remains elusive. MSA is characterized by cytoplasmic inclusions of misfolded α-synuclein (α-SYN) in oligodendrocytes referred to as glial cytoplasmic inclusions (GCIs). Remarkably, the oligodendrocytes possess high amounts of iron, which together with GCI pathology make a contribution toward MSA pathogenesis likely. Consistent with this observation, the GCI density is associated with neurodegeneration in central autonomic networks as well as olivopontocerebellar and striatonigral pathways. Iron converts native α-SYN into a β-sheet conformation and promotes its aggregation either directly or via increasing levels of oxidative stress. Interestingly, α-SYN possesses ferrireductase activity and α-SYN expression underlies iron mediated translational control via RNA stem loop structures. Despite a correlation between progressive putaminal atrophy and iron accumulation as well as clinical decline, it remains unclear whether pathologic iron accumulation in MSA is a secondary event in the cascade of neuronal degeneration rather than a primary cause. This review summarizes the current knowledge of iron in MSA and gives evidence for perturbed iron homeostasis as a potential pathogenic factor in MSA-associated neurodegeneration.

Oxidative stress and cellular pathologies in Parkinson's disease

Parkinson’s disease (PD) is a chronic and progressive neurodegeneration of dopamine neurons in the substantia nigra. The reason for the death of these neurons is unclear; however, studies have demonstrated the potential involvement of mitochondria, endoplasmic reticulum, α-synuclein or dopamine levels in contributing to cellular oxidative stress as well as PD symptoms. Even though those papers had separately described the individual roles of each element leading to neurodegeneration, recent publications suggest that neurodegeneration is the product of various cellular interactions. This review discusses the role of oxidative stress in mediating separate pathological events that together, ultimately result in cell death in PD. Understanding the multi-faceted relationships between these events, with oxidative stress as a common denominator underlying these processes, is needed for developing better therapeutic strategies.

Promises and Pitfalls of Metal Imaging in Biology

A picture may speak a thousand words, but if those words fail to form a coherent sentence there is little to be learned. As cutting-edge imaging technology now provides us the tools to decipher the multitude of roles played by metals and metalloids in molecular, cellular, and developmental biology, as well as health and disease, it is time to reflect on the advances made in imaging, the limitations discovered, and the future of a burgeoning field. In this Perspective, the current state of the art is discussed from a self-imposed contrarian position, as we not only highlight the major advances made over the years but use them as teachable moments to zoom in on challenges that remain to be overcome. We also describe the steps being taken toward being able to paint a completely undisturbed picture of cellular metal metabolism, which is, metaphorically speaking, the Holy Grail of the discipline.

Subcellular compartmentalisation of copper, iron, manganese, and zinc in the Parkinson's disease brain

Elevated iron and decreased copper levels are cardinal features of the degenerating substantia nigra pars compacta in the Parkinson's disease brain. Both of these redox-active metals, and fellow transition metals manganese and zinc, are found at high concentrations within the midbrain and participate in a range of unique biological reactions. We examined the total metal content and cellular compartmentalisation of manganese, iron, copper and zinc in the degenerating substantia nigra, disease-affected but non-degenerating fusiform gyrus, and unaffected occipital cortex in the post mortem Parkinson's disease brain compared with age-matched controls. An expected increase in iron and a decrease in copper concentration was isolated to the soluble cellular fraction, encompassing both interstitial and cytosolic metals and metal-binding proteins, rather than the membrane-associated or insoluble fractions. Manganese and zinc levels did not differ between experimental groups. Altered Fe and Cu levels were unrelated to Braak pathological staging in our cases of late-stage (Braak stage V and VI) disease. The data supports our hypothesis that regional alterations in Fe and Cu, and in proteins that utilise these metals, contribute to the regional selectively of neuronal vulnerability in this disorder.

Interactions of iron, dopamine and neuromelanin pathways in brain aging and Parkinson's disease

There are several interrelated mechanisms involving iron, dopamine, and neuromelanin in neurons. Neuromelanin accumulates during aging and is the catecholamine-derived pigment of the dopamine neurons of the substantia nigra and norepinephrine neurons of the locus coeruleus, the two neuronal populations most targeted in Parkinson's disease. Many cellular redox reactions rely on iron, however an altered distribution of reactive iron is cytotoxic. In fact, increased levels of iron in the brain of Parkinson's disease patients are present. Dopamine accumulation can induce neuronal death; however, excess dopamine can be removed by converting it into a stable compound like neuromelanin, and this process rescues the cell. Interestingly, the main iron compound in dopamine and norepinephrine neurons is the neuromelanin-iron complex, since neuromelanin is an effective metal chelator. Neuromelanin serves to trap iron and provide neuronal protection from oxidative stress. This equilibrium between iron, dopamine, and neuromelanin is crucial for cell homeostasis and in some cellular circumstances can be disrupted. Indeed, when neuromelanin-containing organelles accumulate high load of toxins and iron during aging a neurodegenerative process can be triggered. In addition, neuromelanin released by degenerating neurons activates microglia and the latter cause neurons death with further release of neuromelanin, then starting a self-propelling mechanism of neuroinflammation and neurodegeneration. Considering the above issues, age-related accumulation of neuromelanin in dopamine neurons shows an interesting link between aging and neurodegeneration.