Label-Free Nanoimaging of Neuromelanin in the Brain by Soft X-ray Spectromicroscopy.

A hallmark of Parkinson's disease is the death of neuromelanin-pigmented neurons, but the role of neuromelanin is unclear. The in situ characterization of neuromelanin remains dependent on detectable pigmentation, rather than direct quantification of neuromelanin. We show that direct, label-free nanoscale visualization of neuromelanin and associated metal ions in human brain tissue can be achieved using synchrotron scanning transmission x-ray microscopy (STXM), through a characteristic feature in the neuromelanin x-ray absorption spectrum at 287.4 eV that is also present in iron-free and iron-laden synthetic neuromelanin. This is confirmed in consecutive brain sections by correlating STXM neuromelanin imaging with silver nitrate-stained neuromelanin. Analysis suggests that the 1s-σ* (C-S) transition in benzothiazine groups accounts for this feature. This method illustrates the wider potential of STXM as a label-free spectromicroscopy technique applicable to both organic and inorganic materials.

Gene co-expression networks shed light into diseases of brain iron accumulation.

Aberrant brain iron deposition is observed in both common and rare neurodegenerative disorders, including those categorized as Neurodegeneration with Brain Iron Accumulation (NBIA), which are characterized by focal iron accumulation in the basal ganglia. Two NBIA genes are directly involved in iron metabolism, but whether other NBIA-related genes also regulate iron homeostasis in the human brain, and whether aberrant iron deposition contributes to neurodegenerative processes remains largely unknown. This study aims to expand our understanding of these iron overload diseases and identify relationships between known NBIA genes and their main interacting partners by using a systems biology approach. We used whole-transcriptome gene expression data from human brain samples originating from 101 neuropathologically normal individuals (10 brain regions) to generate weighted gene co-expression networks and cluster the 10 known NBIA genes in an unsupervised manner. We investigated NBIA-enriched networks for relevant cell types and pathways, and whether they are disrupted by iron loading in NBIA diseased tissue and in an in vivo mouse model. We identified two basal ganglia gene co-expression modules significantly enriched for NBIA genes, which resemble neuronal and oligodendrocytic signatures. These NBIA gene networks are enriched for iron-related genes, and implicate synapse and lipid metabolism related pathways. Our data also indicates that these networks are disrupted by excessive brain iron loading. We identified multiple cell types in the origin of NBIA disorders. We also found unforeseen links between NBIA networks and iron-related processes, and demonstrate convergent pathways connecting NBIAs and phenotypically overlapping diseases. Our results are of further relevance for these diseases by providing candidates for new causative genes and possible points for therapeutic intervention.

Evidence of redox-active iron formation following aggregation of ferrihydrite and the Alzheimer's disease peptide ß-amyloid.

Recent work has demonstrated increased levels of redox-active iron biominerals in Alzheimer's disease (AD) tissue. However, the origin, nature, and role of iron in AD pathology remains unclear. Using X-ray absorption, X-ray microspectroscopy, and electron microscopy techniques, we examined interactions between the AD peptide ß-amyloid (Aß) and ferrihydrite, which is the ferric form taken when iron is stored in humans. We report that Aß is capable of reducing ferrihydrite to a pure iron(II) mineral where antiferromagnetically ordered Fe(2+) cations occupy two nonequivalent crystal symmetry sites. Examination of these iron(II) phases following air exposure revealed a material consistent with the iron(II)-rich mineral magnetite. These results demonstrate the capability of Aß to induce the redox-active biominerals reported in AD tissue from natural iron precursors. Such interactions between Aß and ferrihydrite shed light upon the processes of AD pathogenesis, while providing potential targets for future therapies.

Label-Free In Situ Chemical Characterization of Amyloid Plaques in Human Brain Tissues.

The accumulation of amyloid plaques and increased brain redox burdens are neuropathological hallmarks of Alzheimer's disease. Altered metabolism of essential biometals is another feature of Alzheimer's, with amyloid plaques representing sites of disturbed metal homeostasis. Despite these observations, metal-targeting disease treatments have not been therapeutically effective to date. A better understanding of amyloid plaque composition and the role of the metals associated with them is critical. To establish this knowledge, the ability to resolve chemical variations at nanometer length scales relevant to biology is essential. Here, we present a methodology for the label-free, nanoscale chemical characterization of amyloid plaques within human Alzheimer's disease tissue using synchrotron X-ray spectromicroscopy. Our approach exploits a C-H carbon absorption feature, consistent with the presence of lipids, to visualize amyloid plaques selectively against the tissue background, allowing chemical analysis to be performed without the addition of amyloid dyes that alter the native sample chemistry. Using this approach, we show that amyloid plaques contain elevated levels of calcium, carbonates, and iron compared to the surrounding brain tissue. Chemical analysis of iron within plaques revealed the presence of chemically reduced, low-oxidation-state phases, including ferromagnetic metallic iron. The zero-oxidation state of ferromagnetic iron determines its high chemical reactivity and so may contribute to the redox burden in the Alzheimer's brain and thus drive neurodegeneration. Ferromagnetic metallic iron has no established physiological function in the brain and may represent a target for therapies designed to lower redox burdens in Alzheimer's disease. Additionally, ferromagnetic metallic iron has magnetic properties that are distinct from the iron oxide forms predominant in tissue, which might be exploitable for the in vivo detection of amyloid pathologies using magnetically sensitive imaging. We anticipate that this label-free X-ray imaging approach will provide further insights into the chemical composition of amyloid plaques, facilitating better understanding of how plaques influence the course of Alzheimer's disease.

High field magnetic resonance microscopy of the human hippocampus in Alzheimer's disease: quantitative imaging and correlation with iron.

We report R(2) and R(2) in human hippocampus from five unfixed post-mortem Alzheimer's disease (AD) and three age-matched control cases. Formalin-fixed tissues from opposing hemispheres in a matched AD and control were included for comparison. Imaging was performed in a 600MHz (14T) vertical bore magnet at MR microscopy resolution to obtain R(2) and R(2) (62 µm×62 µm in-plane, 80 µm slice thickness), and R(1) at 250 µm isotropic resolution. R(1), R(2) and R(2) maps were computed for individual slices in each case, and used to compare subfields between AD and controls. The magnitudes of R(2) and R(2) changed very little between AD and control, but their variances in the Cornu Ammonis and dentate gyrus were significantly higher in AD compared for controls (p<0.001). To investigate the relationship between tissue iron and MRI parameters, each tissue block was cryosectioned at 30 µm in the imaging plane, and iron distribution was mapped using synchrotron microfocus X-ray fluorescence spectroscopy. A positive correlation of R(2) and R(2)* with iron was demonstrated. While studies with fixed tissues are more straightforward to conduct, fixation can alter iron status in tissues, making measurement of unfixed tissue relevant. To our knowledge, these data represent an advance in quantitative imaging of hippocampal subfields in unfixed tissue, and the methods facilitate direct analysis of the relationship between MRI parameters and iron. The significantly increased variance in AD compared for controls warrants investigation at lower fields and in-vivo, to determine if this parameter is clinically relevant.

Effective R2 relaxation rate, derived from dual-contrast fast-spin-echo MRI, enables detection of hemisphere differences in iron level and dopamine function in Parkinson's disease and healthy individuals.

BACKGROUND: Clinical estimates of brain iron concentration are achievable with quantitative transverse relaxation rate R2, via time-consuming multiple spin-echo (SE) sequences. The objective of this study was to investigate whether quantitative iron-sensitive information may be derived from 3.0 T dual-contrast fast-spin-echo (FSE) sequences (typically employed in anatomical non-quantitative evaluations), as a routinely-collected alternative to evaluate iron levels in healthy (HC) and Parkinson's disease (PD) brains. NEW METHOD: MRI 3.0 T FSE data from the Parkinson's Progression Markers Initiative (PPMI) (12 PD, 12 age- and gender-matched HC subjects) were cross-sectionally and longitudinally evaluated. A new measure, 'effective R2', was calculated for bilateral subcortical grey matter (caudate nucleus, putamen, globus pallidus, red nucleus, substantia nigra). Linear regression analysis was performed to correlate 'effective R2' with models of age-dependent brain iron concentration and striatal dopamine transporter (DaT) receptor binding ratio. RESULTS: Effective R2 was strongly correlated with estimated brain iron concentration. In PD, putaminal effective R2 difference was observed between the hemispheres contra-/ipsi-lateral to the predominantly symptomatic side at onset. This hemispheric difference was correlated with the putaminal DaT binding ratios in PD. COMPARISON WITH EXISTING METHOD(S): Effective R2, derived from rapid dual-contrast FSE sequences, showed viability as an alternative to R2 from SE sequences. Linear correlation of effective R2 with estimated iron concentration was comparable to documented iron-dependent R2. The effective R2 correlation coefficient was consistent with theoretical R2 iron-dependence at 3.0 T. CONCLUSIONS: Effective R2 has clinical potential as a fast quantitative method, as an alternative to R2, to aid evaluation of brain iron levels and DaT function.

A Systematic Review and Meta-Analysis of Cerebrospinal Fluid Amyloid and Tau Levels Identifies Mild Cognitive Impairment Patients Progressing to Alzheimer's Disease.

Reported levels of amyloid-beta and tau in human cerebrospinal fluid (CSF) were evaluated to discover if these biochemical markers can predict the transition from Mild Cognitive Impairment (MCI) to Alzheimer's disease (AD). A systematic review of the literature in PubMed and Web of Science (April 2021) was performed by a single researcher to identify studies reporting immunologically-based (xMAP or ELISA) measures of CSF analytes Aß(1-42) and/or P-tau and/or T-tau in clinical studies with at least two timepoints and a statement of diagnostic criteria. Of 1137 screened publications, 22 met the inclusion criteria for CSF Aß(1-42) measures, 20 studies included T-tau, and 17 included P-tau. Six meta-analyses were conducted to compare the analytes for healthy controls (HC) versus progressive MCI (MCI_AD) and for non-progressive MCI (Stable_MCI) versus MCI_AD; effect sizes were determined using random effects models. The heterogeneity of effect sizes across studies was confirmed with very high significance (p < 0.0001) for all meta-analyses except HC versus MCI_AD T-tau (p < 0.05) and P-tau (non-significant). Standard mean difference (SMD) was highly significant (p < 0.0001) for all comparisons (Stable_MCI versus MCI_AD: SMD [95%-CI] Aß(1-42) = 1.19 [0.96,1.42]; T-tau = −1.03 [−1.24,−0.82]; P-tau = −1.03 [−1.47,−0.59]; HC versus MCI_AD: SMD Aß(1-42) = 1.73 [1.39,2.07]; T-tau = −1.13 [−1.33,−0.93]; P-tau = −1.10 [−1.23,−0.96]). The follow-up interval in longitudinal evaluations was a critical factor in clinical study design, and the Aß(1−42)/P-tau ratio most robustly differentiated progressive from non-progressive MCI. The value of amyloid-beta and tau as markers of patient outcome are supported by these findings.

Cu(III)-bis-thiolato complex forms an unusual mono-thiolato Cu(III)-peroxido adduct.

The stable complex [bis(toluene-3,4-dithiolato)copper(iii)][NEt3H] has been synthesised and characterised as a square-planar Cu(iii) complex by X-ray photoelectron spectroscopy, cyclic voltammetry and DFT calculations. Intriguingly, when fragmented in FTICR-MS, an unusual [(toluene-3,4-dithiolate)Cu(iii)(peroxide)]- complex is formed by reaction with oxygen. Natural 1,2-dithiolenes known to bind molybdenum might stabilise Cu(iii) in vivo.

Biogenic metallic elements in the human brain?

The chemistry of copper and iron plays a critical role in normal brain function. A variety of enzymes and proteins containing positively charged Cu+, Cu2+, Fe2+, and Fe3+ control key processes, catalyzing oxidative metabolism and neurotransmitter and neuropeptide production. Here, we report the discovery of elemental (zero-oxidation state) metallic Cu0 accompanying ferromagnetic elemental Fe0 in the human brain. These nanoscale biometal deposits were identified within amyloid plaque cores isolated from Alzheimer's disease subjects, using synchrotron x-ray spectromicroscopy. The surfaces of nanodeposits of metallic copper and iron are highly reactive, with distinctly different chemical and magnetic properties from their predominant oxide counterparts. The discovery of metals in their elemental form in the brain raises new questions regarding their generation and their role in neurochemistry, neurobiology, and the etiology of neurodegenerative disease.

Regional segmentation strategy for DTI analysis of human corpus callosum indicates motor function deficit in mild cognitive impairment.

BACKGROUND: The corpus callosum is the largest white matter tract in the human brain, involved in inter-hemispheric transfer and integration of lateralised visual, sensory-motor, language, and cognitive information. Microstructural alterations are implicated in ageing as well as various neurological conditions. NEW METHOD: Cross-sectional diffusion-weighted images of 107 healthy adults were used to create a linear regression model of the ageing corpus callosum and its sub-regions to evaluate the impact of analysis by sub-region, and to test for deviations from healthy ageing parameters in 28 subjects with mild cognitive impairment (MCI). Alterations in diffusion properties including fractional anisotropy, mean, radial and axial diffusivities were investigated as a function of age. RESULTS: Changes in DTI parameters showed age-dependent regional differences, likely arising from axonal diameter variation across cross-sectional regions of interest in the corpus callosum. Patterns suggestive of degeneration with healthy ageing were observed in all regions. Diffusion parameters in sub-regions projecting to pre-motor, primary, and supplementary motor areas of the brain differed for MCI versus healthy controls, and MCI subjects were more likely than healthy controls to experience a reduction in motor skills. COMPARISON WITH EXISTING METHODS: Statistical analyses of the corpus callosum by five manually-defined sub-regions, instead of a single manually-defined region of interest, revealed region-specific changes in microstructure in healthy ageing and MCI, and accounted for clinically-evaluated differences in motor skills between cohorts. CONCLUSION: This method will support future studies of corpus callosum, enabling identification and measurement of white matter changes that are undetectable with the single ROI approach.

Iron stored in ferritin is chemically reduced in the presence of aggregating Aß(1-42).

Atypical low-oxidation-state iron phases in Alzheimer's disease (AD) pathology are implicated in disease pathogenesis, as they may promote elevated redox activity and convey toxicity. However, the origin of low-oxidation-state iron and the pathways responsible for its formation and evolution remain unresolved. Here we investigate the interaction of the AD peptide ß-amyloid (Aß) with the iron storage protein ferritin, to establish whether interactions between these two species are a potential source of low-oxidation-state iron in AD. Using X-ray spectromicroscopy and electron microscopy we found that the co-aggregation of Aß and ferritin resulted in the conversion of ferritin's inert ferric core into more reactive low-oxidation-states. Such findings strongly implicate Aß in the altered iron handling and increased oxidative stress observed in AD pathogenesis. These amyloid-associated iron phases have biomarker potential to assist with disease diagnosis and staging, and may act as targets for therapies designed to lower oxidative stress in AD tissue.

Analysis of neuronal iron deposits in Parkinson's disease brain tissue by synchrotron x-ray spectromicroscopy.

BACKGROUND: Neuromelanin-pigmented neurons, which are highly susceptible to neurodegeneration in the Parkinson's disease substantia nigra, harbour elevated iron levels in the diseased state. Whilst it is widely believed that neuronal iron is stored in an inert, ferric form, perturbations to normal metal homeostasis could potentially generate more reactive forms of iron capable of stimulating toxicity and cell death. However, non-disruptive analysis of brain metals is inherently challenging, since use of stains or chemical fixatives, for example, can significantly influence metal ion distributions and/or concentrations in tissues. AIMS: The aim of this study was to apply synchrotron soft x-ray spectromicroscopy to the characterisation of iron deposits and their local environment within neuromelanin-containing neurons of Parkinson's disease substantia nigra. METHODS: Soft x-ray spectromicroscopy was applied in the form of Scanning Transmission X-ray Microscopy (STXM) to analyse resin-embedded tissue, without requirement for chemically disruptive processing or staining. Measurements were performed at the oxygen and iron K-edges in order to characterise both organic and inorganic components of anatomical tissue using a single label-free method. RESULTS: STXM revealed evidence for mixed oxidation states of neuronal iron deposits associated with neuromelanin clusters in Parkinson's disease substantia nigra. The excellent sensitivity, specificity and spatial resolution of these STXM measurements showed that the iron oxidation state varies across sub-micron length scales. CONCLUSIONS: The label-free STXM approach is highly suited to characterising the distributions of both inorganic and organic components of anatomical tissue, and provides a proof-of-concept for investigating trace metal speciation within Parkinson's disease neuromelanin-containing neurons.

Metallic iron in cornflakes.

Iron is an essential element, and cornflake-style cereals are typically fortified with iron to a level up to 14 mg iron per 100 g. Even single cornflakes exhibit magnetic behaviour. We extracted iron microparticles from samples of two own-brand supermarket cornflakes using a strong permanent magnet. Synchrotron iron K-edge X-ray absorption near-edge spectroscopic data were consistent with identification as metallic iron, and X-ray diffraction studies provided unequivocal identification of the extracted iron as body-centred cubic (BCC) α-iron. Magnetometry measurements were also consistent with ca. 14 mg per 100 g BCC iron. These findings emphasise that attention must be paid to the speciation of trace elements, in relation to their bioavailability. To mimic conditions in the stomach, we suspended the iron extract in dilute HCl (pH 1.0-2.0) at 310 K (body temperature) and found by ICP-MS that over a period of 5 hours, up to 13% of the iron dissolved. This implies that despite its metallic form in the cornflakes, the iron is potentially bioavailable for oxidation and absorption into the body.

The status of the terminal regions of α-synuclein in different forms of aggregates during fibrillization.

The α-synuclein (αSN) amyloid fibrillization process is known to be a crucial phenomenon associated with neuronal loss in various neurodegenerative diseases, most famously Parkinson's disease. The process involves different aggregated species and ultimately leads to formation of ß-sheet rich fibrillar structures. Despite the essential role of αSN aggregation in the pathoetiology of various neurological disorders, the characteristics of various assemblies are not fully understood. Here, we established a fluorescence-based model for studying the end-parts of αSN to decipher the structural aspects of aggregates during the fibrillization. Our model proved highly sensitive to the events at the early stage of the fibrillization process, which are hardly detectable with routine techniques. Combining fluorescent and PAGE analysis, we found different oligomeric aggregates in the nucleation phase of fibrillization with different sensitivity to SDS and different structures based on αSN termini. Moreover, we found that these oligomers are highly dynamic: after reaching peak levels during fibrillization, they decline and eventually disappear, suggesting their transformation into other αSN aggregated species. These findings shed light on the structural features of various αSN aggregates and their dynamics in synucleinopathies.

Impact of Autophagy and Aging on Iron Load and Ferritin in Drosophila Brain.

Biometals such as iron, copper, potassium, and zinc are essential regulatory elements of several biological processes. The homeostasis of biometals is often affected in age-related pathologies. Notably, impaired iron metabolism has been linked to several neurodegenerative disorders. Autophagy, an intracellular degradative process dependent on the lysosomes, is involved in the regulation of ferritin and iron levels. Impaired autophagy has been associated with normal pathological aging, and neurodegeneration. Non-mammalian model organisms such as Drosophila have proven to be appropriate for the investigation of age-related pathologies. Here, we show that ferritin is expressed in adult Drosophila brain and that iron and holoferritin accumulate with aging. At whole-brain level we found no direct relationship between the accumulation of holoferritin and a deficit in autophagy in aged Drosophila brain. However, synchrotron X-ray spectromicroscopy revealed an additional spectral feature in the iron-richest region of autophagy-deficient fly brains, consistent with iron-sulfur. This potentially arises from iron-sulfur clusters associated with altered mitochondrial iron homeostasis.

Emerging Approaches to Investigate the Influence of Transition Metals in the Proteinopathies.

Transition metals have essential roles in brain structure and function, and are associated with pathological processes in neurodegenerative disorders classed as proteinopathies. Synchrotron X-ray techniques, coupled with ultrahigh-resolution mass spectrometry, have been applied to study iron and copper interactions with amyloid ß (1-42) or α-synuclein. Ex vivo tissue and in vitro systems were investigated, showing the capability to identify metal oxidation states, probe local chemical environments, and localize metal-peptide binding sites. Synchrotron experiments showed that the chemical reduction of ferric (Fe3+) iron and cupric (Cu2+) copper can occur in vitro after incubating each metal in the presence of Aß for one week, and to a lesser extent for ferric iron incubated with α-syn. Nanoscale chemical speciation mapping of Aß-Fe complexes revealed a spatial heterogeneity in chemical reduction of iron within individual aggregates. Mass spectrometry allowed the determination of the highest-affinity binding region in all four metal-biomolecule complexes. Iron and copper were coordinated by the same N-terminal region of Aß, likely through histidine residues. Fe3+ bound to a C-terminal region of α-syn, rich in aspartic and glutamic acid residues, and Cu2+ to the N-terminal region of α-syn. Elucidating the biochemistry of these metal-biomolecule complexes and identifying drivers of chemical reduction processes for which there is evidence ex-vivo, are critical to the advanced understanding of disease aetiology.

Metal Ion Binding to the Amyloid ß Monomer Studied by Native Top-Down FTICR Mass Spectrometry.

Native top-down mass spectrometry is a fast, robust biophysical technique that can provide molecular-scale information on the interaction between proteins or peptides and ligands, including metal cations. Here we have analyzed complexes of the full-length amyloid ß (1-42) monomer with a range of (patho)physiologically relevant metal cations using native Fourier transform ion cyclotron resonance mass spectrometry and three different fragmentation methods-collision-induced dissociation, electron capture dissociation, and infrared multiphoton dissociation-all yielding consistent results. Amyloid ß is of particular interest as its oligomerization and aggregation are major events in the etiology of Alzheimer's disease, and it is known that interactions between the peptide and bioavailable metal cations have the potential to significantly damage neurons. Those metals which exhibited the strongest binding to the peptide (Cu2+, Co2+, Ni2+) all shared a very similar binding region containing two of the histidine residues near the N-terminus (His6, His13). Notably, Fe3+ bound to the peptide only when stabilized toward hydrolysis, aggregation, and precipitation by a chelating ligand, binding in the region between Ser8 and Gly25. We also identified two additional binding regions near the flexible, hydrophobic C-terminus, where other metals (Mg2+, Ca2+, Mn2+, Na+, and K+) bound more weakly-one centered on Leu34, and one on Gly38. Unexpectedly, collisional activation of the complex formed between the peptide and [CoIII(NH3)6]3+ induced gas-phase reduction of the metal to CoII, allowing the peptide to fragment via radical-based dissociation pathways. This work demonstrates how native mass spectrometry can provide new insights into the interactions between amyloid ß and metal cations.

Synchrotron XRF imaging of Alzheimer's disease basal ganglia reveals linear dependence of high-field magnetic resonance microscopy on tissue iron concentration.

BACKGROUND: Chemical imaging of the human brain has great potential for diagnostic and monitoring purposes. The heterogeneity of human brain iron distribution, and alterations to this distribution in Alzheimer's disease, indicate iron as a potential endogenous marker. The influence of iron on certain magnetic resonance imaging (MRI) parameters increases with magnetic field, but is under-explored in human brain tissues above 7 T. NEW METHOD: Magnetic resonance microscopy at 9.4 T is used to calculate parametric images of chemically-unfixed post-mortem tissue from Alzheimer's cases (n = 3) and healthy controls (n = 2). Iron-rich regions including caudate nucleus, putamen, globus pallidus and substantia nigra are analysed prior to imaging of total iron distribution with synchrotron X-ray fluorescence mapping. Iron fluorescence calibration is achieved with adjacent tissue blocks, analysed by inductively coupled plasma mass spectrometry or graphite furnace atomic absorption spectroscopy. RESULTS: Correlated MR images and fluorescence maps indicate linear dependence of R2, R2* and R2' on iron at 9.4 T, for both disease and control, as follows: [R2(s-1) = 0.072[Fe] + 20]; [R2*(s-1) = 0.34[Fe] + 37]; [R2'(s-1) = 0.26[Fe] + 16] for Fe in µg/g tissue (wet weight). COMPARISON WITH EXISTING METHODS: This method permits simultaneous non-destructive imaging of most bioavailable elements. Iron is the focus of the present study as it offers strong scope for clinical evaluation; the approach may be used more widely to evaluate the impact of chemical elements on clinical imaging parameters. CONCLUSION: The results at 9.4 T are in excellent quantitative agreement with predictions from experiments performed at lower magnetic fields.

Three-dimensional tomographic imaging and characterization of iron compounds within Alzheimer's plaque core material.

Although it has been known for over 50 years that abnormal concentrations of iron are associated with virtually all neurodegenerative diseases, including Alzheimer's disease, its origin, nature and role have remained a mystery. Here, we use high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray (EDX) spectroscopy and electron energy-loss spectroscopy (EELS), electron tomography, and electron diffraction to image and characterize iron-rich plaque core material - a hallmark of Alzheimer's disease pathology - in three dimensions. In these cores, we unequivocally identify biogenic magnetite and/or maghemite as the dominant iron compound. Our results provide an indication that abnormal iron biomineralization processes are likely occurring within the plaque or the surrounding diseased tissue and may play a role in aberrant peptide aggregation. The size distribution of the magnetite cores implies formation from a ferritin precursor, implicating a malfunction of the primary iron storage protein in the brain.

Metallome of cerebrovascular endothelial cells infected with Toxoplasma gondii using µ-XRF imaging and inductively coupled plasma mass spectrometry.

In this study, we measured the levels of elements in human brain microvascular endothelial cells (ECs) infected with T. gondii. ECs were infected with tachyzoites of the RH strain, and at 6, 24, and 48 hours post infection (hpi), the intracellular concentrations of elements were determined using a synchrotron-microfocus X-ray fluorescence microscopy (µ-XRF) system. This method enabled the quantification of the concentrations of Zn and Ca in infected and uninfected (control) ECs at sub-micron spatial resolution. T. gondii-hosting ECs contained less Zn than uninfected cells only at 48 hpi (p < 0.01). The level of Ca was not significantly different between infected and control cells (p > 0.05). Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis revealed infection-specific metallome profiles characterized by significant increases in the intracellular levels of Zn, Fe, Mn and Cu at 48 hpi (p < 0.01), and significant reductions in the extracellular concentrations of Co, Cu, Mo, V, and Ag at 24 hpi (p < 0.05) compared with control cells. Zn constituted the largest part (74%) of the total metal composition (metallome) of the parasite. Gene expression analysis showed infection-specific upregulation in the expression of five genes, MT1JP, MT1M, MT1E, MT1F, and MT1X, belonging to the metallothionein gene family. These results point to a possible correlation between T. gondii infection and increased expression of MT1 isoforms and altered intracellular levels of elements, especially Zn and Fe. Taken together, a combined µ-XRF and ICP-MS approach is promising for studies of the role of elements in mediating host-parasite interaction.