Copper, iron, and zinc imbalances in severely degenerated brain regions in Alzheimer's disease: possible relation to oxidative stress

Altered copper transport in oxidative stress-dependent brain endothelial barrier dysfunction associated with Alzheimer's disease

Oxidative stress and blood-brain barrier (BBB) disruption due to brain endothelial barrier dysfunction contribute to Alzheimer's Disease (AD), which is characterized by beta-amyloid (Aβ) accumulation in senile plaques. Copper (Cu) is implicated in AD pathology and its levels are tightly controlled by several Cu transport proteins. However, their expression and role in AD, particularly in relation to brain endothelial barrier function remains unclear. In this study, we examined the expression of Cu transport proteins in the brains of AD mouse models as well as their involvement in Aβ42-induced brain endothelial barrier dysfunction. We found that the Cu uptake transporter CTR1 was upregulated, while the Cu exporter ATP7A was downregulated in the hippocampus of AD mouse models and in Aβ42-treated human brain microvascular endothelial cells (hBMECs). In the 5xFAD AD mouse model, Cu levels (assessed by ICP-MS) were elevated in the hippocampus. Moreover, in cultured hBMECs, Aβ42-induced reactive oxygen species (ROS) production, ROS-dependent loss in barrier function (measured by transendothelial electrical resistance), and tyrosine phosphorylation of CDH5 were all inhibited by either a membrane permeable Cu chelator or by knocking down CTR1 expression. These findings suggest that dysregulated expression of Cu transport proteins may lead to intracellular Cu accumulation in the AD brain, and that Aβ42 promotes ROS-dependent brain endothelial barrier dysfunction and CDH5 phosphorylation in a CTR1-Cu-dependent manner. Our study uncovers the critical role of Cu transport proteins in oxidative stress-related loss of BBB integrity in AD.

Impaired cellular copper regulation in the presence of ApoE4

The strongest genetic risk factor for late-onset Alzheimer's disease (AD) is allelic variation of the APOE gene, with the following risk structure: ε4 > ε3 > ε2. The biochemical basis for this risk profile is unclear. Here, we reveal a new role for the APOE gene product, apolipoprotein E (ApoE) in regulating cellular copper homeostasis, which is perturbed in the AD brain. Exposure of ApoE target replacement (TR) astrocytes (immortalised astrocytes from APOE knock-in mice) to elevated copper concentrations resulted in exacerbated copper accumulation in ApoE4- compared to ApoE2- and ApoE3-TR astrocytes. This effect was also observed in SH-SY5Y neuroblastoma cells treated with conditioned medium from ApoE4-TR astrocytes. Increased intracellular copper levels in the presence of ApoE4 may be explained by reduced levels and delayed trafficking of the copper transport protein, copper-transporting ATPase 1 (ATP7A/Atp7a), potentially leading to impaired cellular copper export. This new role for ApoE in copper regulation lends further biochemical insight into how APOE genotype confers risk for AD and reveals a potential contribution of ApoE4 to the copper dysregulation that is a characteristic pathological feature of the AD brain.

Altered Copper Transport in Oxidative Stress-Dependent Brain Endothelial Barrier Dysfunction Associated with Alzheimer's Disease

Oxidative stress and blood-brain barrier (BBB) disruption due to brain endothelial barrier dysfunction contribute to Alzheimer's Disease (AD), which is characterized by beta-amyloid (Aβ) accumulation in senile plaques. Copper (Cu) is implicated in AD pathology and its levels are tightly controlled by several Cu transport proteins. However, their expression and role in AD, particularly in relation to brain endothelial barrier function remains unclear. In this study, we examined the expression of Cu transport proteins in the brains of AD mouse models as well as their involvement in Aβ42-induced brain endothelial barrier dysfunction. We found that the Cu uptake transporter CTR1 was upregulated, while the Cu exporter ATP7A and/or ATP7B were downregulated in the hippocampus of AD mouse models, and in Aβ42-treated human brain microvascular endothelial cells (hBMECs). In the 5xFAD AD mouse model, Cu levels (assessed by ICP-MS) were elevated in the hippocampus. Moreover, Aβ42-induced reactive oxygen species (ROS) production, ROS-dependent loss in barrier function in hBMEC (measured by transendothelial electrical resistance), and tyrosine phosphorylation of VE-cadherin were all inhibited by either a membrane permeable Cu chelator or by knocking down CTR1 expression. These findings suggest that dysregulated expression of Cu transport proteins may lead to intracellular Cu accumulation in the AD brain, and that Aβ42 promotes ROS-dependent brain endothelial barrier dysfunction and VE-Cadherin phosphorylation in a CTR1-Cu-dependent manner. Our study uncovers the critical role of Cu transport proteins in oxidative stress-related loss of BBB integrity in AD.

Highlights

Upregulation of the Cu importer CTR1 and downregulation of the Cu exporter ATP7A in the hippocampus of AD mouse modelsAβ42 increases CTR1 expression while reduces ATP7A and ATP7B levels in human brain microvascular ECs.Aβ42 triggers increased reactive oxygen species (ROS) production in human brain microvascular ECs through a CTR1- and Cu-dependent manner.Aβ42 induces endothelial barrier dysfunction in human brain microvascular ECs through a CTR1-Cu-ROS-pendent manner.

Near-Infrared Ratiometric Fluorescent Probe for Detecting Endogenous Cu2+ in the Brain

Copper participates in a range of critical functions in the nervous system and human brain. Disturbances in brain copper content is strongly associated with neurological diseases. For example, changes in the level and distribution of copper are reported in neuroblastoma, Alzheimer's disease, and Lewy body disorders, such as Parkinson disease and dementia with Lewy bodies (DLB). There is a need for more sensitive techniques to measure intracellular copper levels to have a better understanding of the role of copper homeostasis in neuronal disorders. Here, we report a reaction-based near-infrared (NIR) ratiometric fluorescent probe CyCu1 for imaging Cu2+ in biological samples. High stability and selectivity of CyCu1 enabled the probe to be deployed as a sensor in a range of systems, including SH-SY5Y cells and neuroblastoma tumors. Furthermore, it can be used in plant cells, reporting on copper added to Arabidopsis roots. We also used CyCu1 to explore Cu2+ levels and distribution in post-mortem brain tissues from patients with DLB. We found significant decreases in Cu2+ content in the cytoplasm, neurons, and extraneuronal space in the degenerating substantia nigra in DLB compared with healthy age-matched control tissues. These findings enhance our understanding of Cu2+ dysregulation in Lewy body disorders. Our probe also shows promise as a photoacoustic imaging agent, with potential for applications in bimodal imaging.

Metallomic analysis of brain tissues distinguishes between cases of dementia with Lewy bodies, Alzheimer's disease, and Parkinson's disease dementia

Background

Dementia with Lewy bodies (DLB) can be difficult to distinguish from Alzheimer's disease (AD) and Parkinson's disease dementia (PDD) at different stages of its progression due to some overlaps in the clinical and neuropathological presentation of these conditions compared with DLB. Metallomic changes have already been observed in the AD and PDD brain-including widespread decreases in Cu levels and more localised alterations in Na, K, Mn, Fe, Zn, and Se. This study aimed to determine whether these metallomic changes appear in the DLB brain, and how the metallomic profile of the DLB brain appears in comparison to the AD and PDD brain.

Methods

Brain tissues from ten regions of 20 DLB cases and 19 controls were obtained. The concentrations of Na, Mg, K, Ca, Zn, Fe, Mn, Cu, and Se were determined using inductively coupled plasma-mass spectrometry (ICP-MS). Case-control differences were evaluated using Mann-Whitney U tests. Results were compared with those previously obtained from AD and PDD brain tissue, and principal component analysis (PCA) plots were created to determine whether cerebral metallomic profiles could distinguish DLB from AD or PDD metallomic profiles.

Results

Na was increased and Cu decreased in four and five DLB brain regions, respectively. More localised alterations in Mn, Ca, Fe, and Se were also identified. Despite similarities in Cu changes between all three diseases, PCA plots showed that DLB cases could be readily distinguished from AD cases using data from the middle temporal gyrus, primary visual cortex, and cingulate gyrus, whereas DLB and PDD cases could be clearly separated using data from the primary visual cortex alone.

Conclusion

Despite shared alterations in Cu levels, the post-mortem DLB brain shows very few other similarities with the metallomic profile of the AD or PDD brain. These findings suggest that while Cu deficiencies appear common to all three conditions, metal alterations otherwise differ between DLB and PDD/AD. These findings can contribute to our understanding of the underlying pathogenesis of these three diseases; if these changes can be observed in the living human brain, they may also contribute to the differential diagnosis of DLB from AD and/or PDD.

An N-terminal acidic β-sheet domain is responsible for the metal-accumulation properties of amyloid-β protofibrils: a molecular dynamics study

The influence of metal ions on the structure of amyloid- β (Aβ) protofibril models was studied through molecular dynamics to explore the molecular mechanisms underlying metal-induced Aβ aggregation relevant in Alzheimer's disease (AD). The models included 36-, 48-, and 188-mers of the Aβ42 sequence and two disease-modifying variants. Primary structural effects were observed at the N-terminal domain, as it became susceptible to the presence of cations. Specially when β-sheets predominate, this motif orients N-terminal acidic residues toward one single face of the β-sheet, resulting in the formation of an acidic region that attracts cations from the media and promotes the folding of the N-terminal region, with implications in amyloid aggregation. The molecular phenotype of the protofibril models based on Aβ variants shows that the AD-causative D7N mutation promotes the formation of N-terminal β-sheets and accumulates more Zn2+, in contrast to the non-amyloidogenic rodent sequence that hinders the β-sheets and is more selective for Na+ over Zn2+ cations. It is proposed that forming an acidic β-sheet domain and accumulating cations is a plausible molecular mechanism connecting the elevated affinity and concentration of metals in Aβ fibrils to their high content of β-sheet structure at the N-terminal sequence.

Impact of aging on copper isotopic composition in the murine brain

Aging is the main risk factor for Alzheimer's disease (AD). AD is linked to alterations in metal homeostasis and changes in stable metal isotopic composition can occur, possibly allowing the latter to serve as relevant biomarkers for potential AD diagnosis. Copper stable isotopes are used to investigate changes in Cu homeostasis associated with various diseases. Prior work has shown that in AD mouse models, the accumulation of 63Cu in the brain is associated with the disease's progression. However, our understanding of how the normal aging process influences the brain's isotopic composition of copper remains limited. In order to determine the utility and predictive power of Cu isotopes in AD diagnostics, we aim-in this study-to develop a baseline trajectory of Cu isotopic composition in the normally aging mouse brain. We determined the copper concentration and isotopic composition in brains of 30 healthy mice (WT) ranging in age from 6 to 12 mo, and further incorporate prior data obtained for 3-mo-old healthy mice; this range approximately equates to 20-50 yr in human equivalency. A significant 65Cu enrichment has been observed in the 12-mo-old mice compared to the youngest group, concomitant with an increase in Cu concentration with age. Meanwhile, literature data for brains of AD mice display an enrichment in 63Cu isotope compared to WT. It is acutely important that this baseline enrichment in 65Cu is fully constrained and normalized against if any coherent diagnostic observations regarding 63Cu enrichment as a biomarker for AD are to be developed.

Zinc utilization by microglia in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia defined by two key pathological characteristics in the brain, amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Microglia, the primary innate immune cells of the central nervous system (CNS), provide neuroprotection through Aβ and tau clearance but may also be neurotoxic by promoting neuroinflammation to exacerbate Aβ and tau pathogenesis in AD. Recent studies have demonstrated the importance of microglial utilization of nutrients and trace metals in controlling their activation and effector functions. Trace metals, such as zinc, have essential roles in brain health and immunity, and zinc dyshomeostasis has been implicated in AD pathogenesis. As a result of these advances, the mechanisms by which zinc homeostasis influences microglial-mediated neuroinflammation in AD is a topic of continuing interest since new strategies to treat AD are needed. Here, we review the roles of zinc in AD, including zinc activation of microglia, the associated neuroinflammatory response, and the application of these findings in new therapeutic strategies.

Are high copper levels related to Alzheimer's and Parkinson's diseases? A systematic review and meta-analysis of articles published between 2011 and 2022

Copper performs an important role in the brain, but in high levels it can be neurotoxic. Further, some authors have described that copper dyshomeostasis could be related with neurodegenerative diseases. Thus, this review was performed to observe whether high copper levels are related to Alzheimer's and Parkinson's diseases (AD and PD), using the literature published recently. Articles that measured copper levels in AD or PD patients was included, as well as they that measured copper levels in models used to mimic these diseases. Also, results about high copper levels effects and its relationship with AD and PD observed in laboratory animals are considered. In summary, 38 and 24 articles with AD and PD patients were included, respectively. Despite of the heterogeneity between the studies in humans, meta-analysis has demonstrated that there is an increase in free and total copper levels in the blood of AD patients compared to controls, and a decrease in copper levels in PD patients. A decrease in the metal content in postmortem brain tissue was observed in AD and PD. In manuscripts using animal models that mimic AD and PD, it was included seven and three articles, respectively. Two of them have reported an increase in copper concentrations in AD model, and one in PD model. Finally, studies with laboratory animals have concluded that high copper levels are related to oxidative stress, neuroinflammation, mitochondrial dysfunction, changes in neurotransmitter levels, cell death, and reduced both cognitive and locomotor activity, which are also described in AD or PD.

Insights Into the Role of Copper in Neurodegenerative Diseases and the Therapeutic Potential of Natural Compounds

Neurodegenerative diseases encompass a collection of neurological disorders originating from the progressive degeneration of neurons, resulting in the dysfunction of neurons. Unfortunately, effective therapeutic interventions for these diseases are presently lacking. Copper (Cu), a crucial trace element within the human body, assumes a pivotal role in various biological metabolic processes, including energy metabolism, antioxidant defense, and neurotransmission. These processes are vital for the sustenance, growth, and development of organisms. Mounting evidence suggests that disrupted copper homeostasis contributes to numerous age-related neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), Wilson's disease (WD), Menkes disease (MD), prion diseases, and multiple sclerosis (MS). This comprehensive review investigates the connection between the imbalance of copper homeostasis and neurodegenerative diseases, summarizing pertinent drugs and therapies that ameliorate neuropathological changes, motor deficits, and cognitive impairments in these conditions through the modulation of copper metabolism. These interventions include Metal-Protein Attenuating Compounds (MPACs), copper chelators, copper supplements, and zinc salts. Moreover, this review highlights the potential of active compounds derived from natural plant medicines to enhance neurodegenerative disease outcomes by regulating copper homeostasis. Among these compounds, polyphenols are particularly abundant. Consequently, this review holds significant implications for the future development of innovative drugs targeting the treatment of neurodegenerative diseases.

Atomistic molecular simulations of Aβ-Zn conformational ensembles

The amyloid-forming Aβ peptide is able to interact with metal cations to form very stable complexes that influence fibril formation and contribute to the onset of Alzheimer's disease. Multiple structures of peptides derived from Aβ in complex with different metals have been resolved experimentally to provide an atomic-level description of the metal-protein interactions. However, Aβ is intrinsically disordered, and hence more amenable to an ensemble description. Molecular dynamics simulations can now reach the timescales needed to generate ensembles for these type of complexes. However, this requires accurate force fields both for the protein and the protein-metal interactions. Here we use state-of-the-art methods to generate force field parameters for the Zn(II) cations in a set of complexes formed by different Aβ variants and combine them with the Amber99SB*-ILDN optimized force field. Upon comparison of NMR experiments with the simulation results, further optimized with a Bayesian/Maximum entropy approach, we provide an accurate description of the molecular ensembles for most Aβ-metal complexes. We find that the resulting conformational ensembles are more heterogeneous than the NMR models deposited in the Protein Data Bank.

Iron Chelators and Alzheimer's Disease Clinical Trials

Alzheimer's disease (AD) is a major neurodegenerative disorder impacting millions of people with cognitive impairment and affecting activities of daily living. The deposition of neurofibrillary tangles of hyperphosphorylated tau proteins and accumulation of amyloid-β (Aβ) are the main pathological characteristics of AD. However, the actual causal process of AD is not yet identified. Oxidative stress occurs prior to amyloid Aβ plaque formation and tau phosphorylation in AD. The role of master antioxidant, glutathione, and metal ions (e.g., iron) in AD are the frontline area of AD research. Iron overload in specific brain regions in AD is associated with the rate of cognitive decline. We have presented the outcome from various interventional trials involving iron chelators intended to minimize the iron overload in AD. To date, however, no significant positive outcomes have been reported using iron chelators in AD and warrant further research.

Copper binding and protein aggregation: a journey from the brain to the human lens

Metal ions have been implicated in several proteinopathies associated to degenerative and neurodegenerative diseases. While the molecular mechanisms for protein aggregation are still under investigation, recent findings from Cryo-EM point out to polymorphisms in aggregates obtained from patients, as compared to those formed in vitro, suggesting that several factors may impact aggregation in vivo. One of these factors could be the direct binding of metal ions to the proteins engaged in aggregate formation. In this opinion article, three case studies are discussed to address the question of how metal ion binding to a peptide or protein may impact its conformation, folding, and aggregation, and how this may be relevant in understanding the polymorphic nature of the aggregates related to disease. Specifically, the impact of Cu2+ ions in the amyloid aggregation of amyloid-β and amylin (or IAPP- islet amyloid polypeptide) are discussed and then contrasted to the case of Cu2+-induced non-amyloid aggregation of human lens γ-crystallin proteins. For the intrinsically disordered peptides amyloid-β and IAPP, the impact of Cu2+ ion binding is highly dependent on the relative location of the metal binding site and the hydrophobic regions involved in β-sheet folding and amyloid formation. Further structural studies of how Cu2+ binding impacts amyloid aggregation pathways and the molecular structure of the final amyloid fibril, both, in vitro and in vivo, will certainly shed light into the molecular origins of the polymorphisms observed in diseased tissue. Finally, contrasting these cases to that of Cu2+-induced non-amyloid aggregation of γ-crystallins, it is evident that, although the impact in aggregation - and the nature of the aggregate - may differ in each system, at the molecular level there is a competition between metal ion coordination and the stability of β-sheet structures. Considering the importance of the β-sheet fold in biology, it is fundamental to understand the energetics and molecular details behind such competition. This opinion article aims to highlight future research directions in the field that can help tackle the important question of how metal ion binding may impact protein folding and aggregation and how this relates to disease.

Rules governing metal coordination in Aβ-Zn(II) complex models from quantum mechanical calculations

Transition metals directly contribute to the neurotoxicity of the aggregates of the amyloid-forming Aβ peptide. The understanding and rationalization of the coordination modes of metals to Aβ amyloid is, therefore, of paramount importance to understand the capacity of a given metal to promote peptide aggregation. Experimentally, multiple Aβ-metal structures have been resolved, which exhibit different modes of coordination in both the monomeric and oligomeric forms of Aβ. Although Zn(II) metalloproteins are very abundant and often involve cysteine residues in the first coordination shell, in the case of Aβ-Zn(II), though, Zn(II) is coordinated by glutamic/aspartic acid and/or histidine residues exclusively, making for an interesting case study. Here we present a systematic analysis of the underlying chemistry on Aβ-Zn(II) coordination, where relative stabilities of different coordination arrangements indicate that a mixture of Glu/Asp and His residues is favored. A detailed comparison between different coordination shell geometries shows that tetrahedral coordination is generally favored in the aqueous phase. Our calculations show an interplay between dative covalent interactions and electrostatics which explains the observed trends. Multiple structures deposited in the Protein Data Bank support our findings, suggesting that the trends found in our work may be transferable to other Zn(II) metalloproteins with this type of coordination.

Oxidative Stress Occurs Prior to Amyloid Aβ Plaque Formation and Tau Phosphorylation in Alzheimer's Disease: Role of Glutathione and Metal Ions

Alzheimer's disease (AD) is an insidious and progressive neurodegenerative disorder that affects millions of people worldwide. Although the pathogenesis remains obscure, there are two dominant causal hypotheses. Since last three decades, amyloid beta (Aβ) deposition was the most prominent hypothesis, and the other is the tau hyperphosphorylation hypothesis. The confirmed diagnostic criterion for AD is the presence of neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau and the deposition of toxic oligomeric Aβ in the autopsied brain. Consistent with these hypotheses, oxidative stress (OS) is garnering major attention in AD research. OS results from an imbalance of pro-oxidants and antioxidants. There is a considerable debate in the scientific community on which process occurs first, OS or plaque deposition/tau hyperphosphorylation. Based on recent scientific observations of various laboratories including ours along with critical analysis of those information, we believe that OS is the early event that leads to oligomeric Aβ deposition as well as dimerization of tau protein and its subsequent hyperphosphorylation. This OS hypothesis immediately suggests the consideration of novel therapeutic approaches to include antioxidants involving glutathione enrichment in the brain by supplementation with or without an iron chelator.

Zn2+ decoration of microtubules arrests axonal transport and displaces tau, doublecortin, and MAP2C

Intracellular Zn2+ concentrations increase via depolarization-mediated influx or intracellular release, but the immediate effects of Zn2+ signals on neuron function are not fully understood. By simultaneous recording of cytosolic Zn2+ and organelle motility, we find that elevated Zn2+ (IC50 ≈ 5-10 nM) reduces both lysosomal and mitochondrial motility in primary rat hippocampal neurons and HeLa cells. Using live-cell confocal microscopy and in vitro single-molecule TIRF imaging, we reveal that Zn2+ inhibits activity of motor proteins (kinesin and dynein) without disrupting their microtubule binding. Instead, Zn2+ directly binds to microtubules and selectively promotes detachment of tau, DCX, and MAP2C, but not MAP1B, MAP4, MAP7, MAP9, or p150glued. Bioinformatic predictions and structural modeling show that the Zn2+ binding sites on microtubules partially overlap with the microtubule binding sites of tau, DCX, dynein, and kinesin. Our results reveal that intraneuronal Zn2+ regulates axonal transport and microtubule-based processes by interacting with microtubules.

Multimodal comparisons of QSM and PET in neurodegeneration and aging

Quantitative susceptibility mapping (QSM) has been used to study susceptibility changes that may occur based on tissue composition and mineral deposition. Iron is a primary contributor to changes in magnetic susceptibility and of particular interest in applications of QSM to neurodegeneration and aging. Iron can contribute to neurodegeneration through inflammatory processes and via interaction with aggregation of disease-related proteins. To better understand the local susceptibility changes observed on QSM, its signal has been studied in association with other imaging metrics such as positron emission tomography (PET). The associations of QSM and PET may provide insight into the pathophysiology of disease processes, such as the role of iron in aging and neurodegeneration, and help to determine the diagnostic utility of QSM as an indirect indicator of disease processes typically evaluated with PET. In this review we discuss the proposed mechanisms and summarize prior studies of the associations of QSM and amyloid PET, tau PET, TSPO PET, FDG-PET, 15O-PET, and F-DOPA PET in evaluation of neurologic diseases with a focus on aging and neurodegeneration.

Recent progress in the development of fluorescent probes for imaging pathological oxidative stress

Oxidative stress is closely related to the physiopathology of numerous diseases. Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) are direct participants and important biomarkers of oxidative stress. A comprehensive understanding of their changes can help us evaluate disease pathogenesis and progression and facilitate early diagnosis and drug development. In recent years, fluorescent probes have been developed for real-time monitoring of ROS, RNS and RSS levels in vitro and in vivo. In this review, conventional design strategies of fluorescent probes for ROS, RNS, and RSS detection are discussed from three aspects: fluorophores, linkers, and recognition groups. We introduce representative fluorescent probes for ROS, RNS, and RSS detection in cells, physiological/pathological processes (e.g., Inflammation, Drug Induced Organ Injury and Ischemia/Reperfusion Injury etc.), and specific diseases (e.g., neurodegenerative diseases, epilepsy, depression, diabetes and cancer, etc.). We then highlight the achievements, current challenges, and prospects for fluorescent probes in the pathophysiology of oxidative stress-related diseases.

Role of TPEN in Amyloid-β25-35-Induced Neuronal Damage Correlating with Recovery of Intracellular Zn2+ and Intracellular Ca2+ Overloading

The overproduction of neurotoxic amyloid-β (Aβ) peptides in the brain is a hallmark of Alzheimer's disease (AD). To determine the role of intracellular zinc ion (_iZn²⁺) dysregulation in mediating Aβ-related neurotoxicity, this study aimed to investigate whether N, N, N', N'‑tetrakis (2‑pyridylmethyl) ethylenediamine (TPEN), a Zn²⁺‑specific chelator, could attenuate Aβ_25-35‑induced neurotoxicity and the underlying mechanism. We used the 3-(4, 5-dimethyl-thiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay to measure the viability of primary hippocampal neurons. We also determined intracellular Zn²⁺ and Ca²⁺ concentrations, mitochondrial and lysosomal functions, and intracellular reactive oxygen species (ROS) content in hippocampal neurons using live-cell confocal imaging. We detected L-type voltage-gated calcium channel currents (L-I_Ca) in hippocampal neurons using the whole‑cell patch‑clamp technique. Furthermore, we measured the mRNA expression levels of proteins related to the _iZn²⁺ buffer system (ZnT-3, MT-3) and voltage-gated calcium channels (Cav1.2, Cav1.3) in hippocampal neurons using RT-PCR. The results showed that TPEN attenuated Aβ_25-35‑induced neuronal death, relieved the Aβ_25-35‑induced increase in intracellular Zn²⁺ and Ca²⁺ concentrations; reversed the Aβ_25-35‑induced increase in ROS content, the Aβ_25-35‑induced increase in the L-I_Ca peak amplitude at different membrane potentials, the Aβ_25-35‑induced the dysfunction of the mitochondria and lysosomes, and the Aβ_25-35‑induced decrease in ZnT-3 and MT-3 mRNA expressions; and increased the Cav1.2 mRNA expression in the hippocampal neurons. These results suggest that TPEN, the Zn²⁺-specific chelator, attenuated Aβ_25-35‑induced neuronal damage, correlating with the recovery of intracellular Zn²⁺ and modulation of abnormal Ca²⁺-related signaling pathways.

Revisiting the Role of Vitamins and Minerals in Alzheimer's Disease

Alzheimer's disease (AD) is the most common type of dementia that affects millions of individuals worldwide. It is an irreversible neurodegenerative disorder that is characterized by memory loss, impaired learning and thinking, and difficulty in performing regular daily activities. Despite nearly two decades of collective efforts to develop novel medications that can prevent or halt the disease progression, we remain faced with only a few options with limited effectiveness. There has been a recent growth of interest in the role of nutrition in brain health as we begin to gain a better understanding of what and how nutrients affect hormonal and neural actions that not only can lead to typical cardiovascular or metabolic diseases but also an array of neurological and psychiatric disorders. Vitamins and minerals, also known as micronutrients, are elements that are indispensable for functions including nutrient metabolism, immune surveillance, cell development, neurotransmission, and antioxidant and anti-inflammatory properties. In this review, we provide an overview on some of the most common vitamins and minerals and discuss what current studies have revealed on the link between these essential micronutrients and cognitive performance or AD.

Bio-Metal Dyshomeostasis-Associated Acceleration of Aging and Cognitive Decline in Down Syndrome

Down syndrome (DS), which is caused by triplication of human chromosome 21 (Hsa21), exhibits some physical signs of accelerated aging, such as graying hair, wrinkles and menopause at an unusually young age. Development of early-onset Alzheimer's disease, which is frequently observed in adults with DS, is also suggested to occur due to accelerated aging of the brain. Several Hsa21 genes are suggested to be responsible for the accelerated aging in DS. In this review, we summarize these candidate genes and possible molecular mechanisms, and discuss the related key factors. In particular, we focus on copper, an essential trace element, as a key factor in the accelerated aging in DS. In addition, the physiological significance of brain copper accumulation in cognitive impairment is discussed. We herein provide our hypothesis on the copper dyshomeostasis-based pathophysiology of DS.

Exploring the K isotope composition of Göttingen minipig brain regions, and implications for Alzheimer's disease

Natural stable metal isotopes have shown utility in differentiation between healthy and diseased brain states (e.g. Alzheimer's disease, AD). While the AD brain accumulates some metals, it purges others, namely K (accompanied by increased serum K, suggesting brain-blood transferal). Here, K isotope compositions of Göttingen minipig brain regions for two AD models at midlife are reported. Results indicate heavy K isotope enrichment where amyloid beta (Aβ) accumulation is observed, and this enrichment correlates with relative K depletion. These results suggest preferential efflux of isotopically light K+ from the brain, a linkage between brain K concentrations and isotope compositions, and linkage to Aβ (previously shown to purge cellular brain K+). Brain K isotope compositions differ from that for serum and brain K is much more abundant than in serum, suggesting that changes in brain K may transfer a measurable K isotope excursion to serum, thereby generating an early AD biomarker.

Clinical relevance of biomarkers, new therapeutic approaches, and role of post-translational modifications in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that causes progressive loss of cognitive functions like thinking, memory, reasoning, behavioral abilities, and social skills thus affecting the ability of a person to perform normal daily functions independently. There is no definitive cure for this disease, and treatment options available for the management of the disease are not very effective as well. Based on histopathology, AD is characterized by the accumulation of insoluble deposits of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs). Although several molecular events contribute to the formation of these insoluble deposits, the aberrant post-translational modifications (PTMs) of AD-related proteins (like APP, Aβ, tau, and BACE1) are also known to be involved in the onset and progression of this disease. However, early diagnosis of the disease as well as the development of effective therapeutic approaches is impeded by lack of proper clinical biomarkers. In this review, we summarized the current status and clinical relevance of biomarkers from cerebrospinal fluid (CSF), blood and extracellular vesicles involved in onset and progression of AD. Moreover, we highlight the effects of several PTMs on the AD-related proteins, and provide an insight how these modifications impact the structure and function of proteins leading to AD pathology. Finally, for disease-modifying therapeutics, novel approaches, and targets are discussed for the successful treatment and management of AD.

Hippocampal glutathione depletion with enhanced iron level in patients with mild cognitive impairment and Alzheimer’s disease compared with healthy elderly participants

Oxidative stress has been implicated in Alzheimer’s disease, and it is potentially driven by the depletion of primary antioxidant, glutathione, as well as elevation of the pro-oxidant, iron. Present study evaluates glutathione level by magnetic resonance spectroscopy, iron deposition by quantitative susceptibility mapping in left hippocampus, as well as the neuropsychological scores of healthy old participants (N = 25), mild cognitive impairment (N = 16) and Alzheimer’s disease patients (N = 31). Glutathione was found to be significantly depleted in mild cognitive impaired (P < 0.05) and Alzheimer’s disease patients (P < 0.001) as compared with healthy old participants. A significant higher level of iron was observed in left hippocampus region for Alzheimer’s disease patients as compared with healthy old (P < 0.05) and mild cognitive impairment (P < 0.05). Multivariate receiver-operating curve analysis for combined glutathione and iron in left hippocampus region provided diagnostic accuracy of 82.1%, with 81.8% sensitivity and 82.4% specificity for diagnosing Alzheimer’s disease patients from healthy old participants. We conclude that tandem glutathione and iron provides novel avenue to investigate further research in Alzheimer’s disease.

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

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

Iron and Alzheimer's Disease: From Pathology to Imaging

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

Zinc in Regulating Protein Kinases and Phosphatases in Neurodegenerative Diseases

Zinc is essential for human growth and development. As a trace nutrient, zinc plays important roles in numerous signal transduction pathways involved in distinct physiologic or pathologic processes. Protein phosphorylation is a posttranslational modification which regulates protein activity, degradation, and interaction with other molecules. Protein kinases (PKs) and phosphatases (PPs), with their effects of adding phosphate to or removing phosphate from certain substrates, are master regulators in controlling the phosphorylation of proteins. In this review, we summarize the disturbance of zinc homeostasis and role of zinc disturbance in regulating protein kinases and protein phosphatases in neurodegenerative diseases, with the focus of that in Alzheimer’s disease, providing a new perspective for understanding the mechanisms of these neurologic diseases.

Estropause, Sex Hormones and Metal Homeostasis in the Mouse Brain

Alterations in brain metal ion homeostasis have been reported with aging and are implicated in the pathogenesis of neurodegenerative diseases. To assess whether age-related changes in hypothalamic-pituitary-gonadal (HPG) hormones might be involved in modulating brain metal ion homeostasis, we treated 7.5-month intact, sham-ovariecomized and ovariectomized C57B6SJL mice with vehicle or leuprolide acetate (for 9-months) to differentiate between whether sex steroids or gonadotropins might modulate brain metal ion concentrations. Unlike other aging mammals, there was no increase in plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) concentrations following estropause in mice, suggesting there was sufficient residual production by the follicle depleted ovary, of sex steroids like estrogens and protein hormones like the inhibins, in order to suppress pituitary LH/FSH production. Castration on the other hand induced significant increases in circulating LH and FSH. Modulation of plasma sex steroid and gonadotropin levels did not significantly alter the concentrations of brain metals tested (Fe, Zn, Cu, Mn, Co, Ni, Al, Li), although there was a tendency for a decrease in all brain metals following ovariectomy (low estrogens and progesterone, high gonadotropins), a response that was reversed with leuprolide acetate treatment (low sex steroids, low gonadotropins). Brain Cu concentration was the only metal correlated with plasma LH (−0.37, n = 30, p < 0.05) and FSH (−0.42, n = 29, p < 0.01). This study demonstrates that sex hormones do not markedly alter brain metal ion homeostasis, unlike previously reported studies of circulating metal ion homeostasis. The role of gonadotropins in regulating metal ion homeostasis does however warrant further study.

Post-translational Modifications of the p53 Protein and the Impact in Alzheimer's Disease: A Review of the Literature

Our understanding of Alzheimer's disease (AD) pathogenesis has developed with several hypotheses over the last 40 years, including the Amyloid and Tau hypotheses. More recently, the p53 protein, well-known as a genome guardian, has gained attention for its potential role in the early evolution of AD. This is due to the central involvement of p53's in the control of oxidative stress and potential involvement in the Amyloid and Tau pathways. p53 is commonly regulated by post-translational modifications (PTMs), which affect its conformation, increasing its capacity to adopt multiple structural and functional states, including those that can affect brain processes, thus contributing to AD development. The following review will explore the impact of p53 PTMs on its function and consequential involvement in AD pathogenesis. The greater understanding of the role of p53 in the pathogenesis of AD could result in more targeted therapies benefiting the many patients of this debilitating disease.

Do glutathione and copper interact to modify Alzheimer's disease pathogenesis?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder first described in 1906 that is currently estimated to impact ∼40 million people worldwide. Extensive research activities have led to a wealth of information on the pathogenesis, hallmarks, and risk factors of AD; however, therapeutic options remain extremely limited. The large number of pathogenic factors that have been reported to potentially contribute to AD include copper dyshomeostasis as well as increased oxidative stress, which is related to alterations to molecular antioxidants like glutathione (GSH). While the individual roles of GSH and copper in AD have been studied by many research groups, their interactions have received relatively little attention, although they appear to interact and affect each other's regulation. Existing knowledge on how GSH-copper interactions may affect AD is sparse and lacks focus. This review first highlights the most relevant individual roles that GSH and copper play in physiology and AD, and then collects and assesses research concerning their interactions, in an effort to provide a more accessible and understandable picture of the role of GSH, copper, and their interactions in AD.

Rapamycin Attenuated Zinc-Induced Tau Phosphorylation and Oxidative Stress in Rats: Involvement of Dual mTOR/p70S6K and Nrf2/HO-1 Pathways

Alzheimer's disease is pathologically characterized by abnormal accumulation of amyloid-beta plaques, neurofibrillary tangles, oxidative stress, neuroinflammation, and neurodegeneration. Metal dysregulation, including excessive zinc released by presynaptic neurons, plays an important role in tau pathology and oxidase activation. The activities of mammalian target of rapamycin (mTOR)/ribosomal S6 protein kinase (p70S6K) are elevated in the brains of patients with Alzheimer's disease. Zinc induces tau hyperphosphorylation via mTOR/P70S6K activation in vitro. However, the involvement of the mTOR/P70S6K pathway in zinc-induced oxidative stress, tau degeneration, and synaptic and cognitive impairment has not been fully elucidated in vivo. Here, we assessed the effect of pathological zinc concentrations in SH-SY5Y cells by using biochemical assays and immunofluorescence staining. Rats (n = 18, male) were laterally ventricularly injected with zinc, treated with rapamycin (intraperitoneal injection) for 1 week, and assessed using the Morris water maze. Evaluation of oxidative stress, tau phosphorylation, and synaptic impairment was performed using the hippocampal tissue of the rats by biochemical assays and immunofluorescence staining. The results from the Morris water maze showed that the capacity of spatial memory was impaired in zinc-treated rats. Zinc sulfate significantly increased the levels of P-mTOR Ser2448, P-p70S6K Thr389, and P-tau Ser356 and decreased the levels of nuclear factor erythroid 2-related factor-2 (Nrf2) and heme oxygenase-1 (HO-1) in SH-SY5Y cells and in zinc-treated rats compared with the control groups. Increased expression of reactive oxygen species was observed in zinc sulfate-induced SH-SY5Y cells and in the hippocampus of zinc-injected rats. Rapamycin, an inhibitor of mTOR, rescued zinc-induced increases in mTOR/p70S6K activation, tau phosphorylation, and oxidative stress, and Nrf2/HO-1 inactivation, cognitive impairment, and synaptic impairment reduced the expression of synapse-related proteins in zinc-injected rats. In conclusion, our findings imply that rapamycin prevents zinc-induced cognitive impairment and protects neurons from tau pathology, oxidative stress, and synaptic impairment by decreasing mTOR/p70S6K hyperactivity and increasing Nrf2/HO-1 activity.

The Potential of Ferroptosis-Targeting Therapies for Alzheimer's Disease: From Mechanism to Transcriptomic Analysis

Alzheimer’s disease (AD), the most common form of dementia, currently affects 40–50 million people worldwide. Despite the extensive research into amyloid β (Aβ) deposition and tau protein hyperphosphorylation (p-tau), an effective treatment to stop or slow down the progression of neurodegeneration is missing. Emerging evidence suggests that ferroptosis, an iron-dependent and lipid peroxidation-driven type of programmed cell death, contributes to neurodegeneration in AD. Therefore, how to intervene against ferroptosis in the context of AD has become one of the questions addressed by studies aiming to develop novel therapeutic strategies. However, the underlying molecular mechanism of ferroptosis in AD, when ferroptosis occurs in the disease course, and which ferroptosis-related genes are differentially expressed in AD remains to be established. In this review, we summarize the current knowledge on cell mechanisms involved in ferroptosis, we discuss how these processes relate to AD, and we analyze which ferroptosis-related genes are differentially expressed in AD brain dependant on cell type, disease progression and gender. In addition, we point out the existing targets for therapeutic options to prevent ferroptosis in AD. Future studies should focus on developing new tools able to demonstrate where and when cells undergo ferroptosis in AD brain and build more translatable AD models for identifying anti-ferroptotic agents able to slow down neurodegeneration.

Probable Reasons for Neuron Copper Deficiency in the Brain of Patients with Alzheimer’s Disease: The Complex Role of Amyloid

Alzheimer’s disease is a progressive neurodegenerative disorder that eventually leads the affected patients to die. The appearance of senile plaques in the brains of Alzheimer’s patients is known as a main symptom of this disease. The plaques consist of different components, and according to numerous reports, their main components include beta-amyloid peptide and transition metals such as copper. In this disease, metal dyshomeostasis leads the number of copper ions to simultaneously increase in the plaques and decrease in neurons. Copper ions are essential for proper brain functioning, and one of the possible mechanisms of neuronal death in Alzheimer’s disease is the copper depletion of neurons. However, the reason for the copper depletion is as yet unknown. Based on the available evidence, we suggest two possible reasons: the first is copper released from neurons (along with beta-amyloid peptides), which is deposited outside the neurons, and the second is the uptake of copper ions by activated microglia.

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.

Contrasting Effects of Ferric and Ferrous Ions on Oligomerization and Droplet Formation of Tau: Implications in Tauopathies and Neurodegeneration

The dysregulation of metal homeostasis is reported to enhance the aggregation of tau, a key neuronal microtubule-associated protein. Herein, we found that ferric (Fe³⁺) ions enhanced tau aggregation. Fe³⁺ and Al³⁺ induced tau aggregation while several trivalent metal ions such as Cr³⁺, La³⁺, and V³⁺ had no discernable effect on tau aggregation. Fe³⁺ reduced the critical concentration of tau required for the liquid-liquid phase separation (LLPS); however, Cr³⁺, La³⁺, and V³⁺ did not affect tau droplet formation. Dynamic light scattering, atomic force microscopic, and transmission electron microscopic analysis suggested that Fe³⁺ significantly increased the formation of tau oligomers and fibrils. In contrast, Fe²⁺ neither enhanced tau droplet formation nor increased the heparin-induced aggregation of tau. Using a tryptophan mutant (Y310W-tau) of tau, Fe³⁺ was found to bind to tau with four times higher affinity than Fe²⁺. Acrylamide quenching of the tryptophan fluorescence of Y310W-tau, 1-anilino-8-naphthalene sulfonate (ANS) fluorescence experiment, and far-UV circular dichroism analysis indicated that Fe³⁺ decreased the solvent exposure of the tryptophan residue, perturbed the hydrophobic surface arrangement, and disrupted the secondary structure of tau, respectively. The increase in the β-sheet content and a subsequent decrease in the disordered content of tau due to the binding of Fe³⁺ may favor tau aggregation. Fe³⁺ may enhance and stabilize the non-covalent interactions between disordered domains of tau molecules leading to tau aggregation. The data highlighted the relationship between the dysregulation of ferric ions and neurodegenerative disorders.

Crossroads between membrane trafficking machinery and copper homeostasis in the nerve system

Imbalanced copper homeostasis and perturbation of membrane trafficking are two common symptoms that have been associated with the pathogenesis of neurodegenerative and neurodevelopmental diseases. Accumulating evidence from biophysical, cellular and in vivo studies suggest that membrane trafficking orchestrates both copper homeostasis and neural functions-however, a systematic review of how copper homeostasis and membrane trafficking interplays in neurons remains lacking. Here, we summarize current knowledge of the general trafficking itineraries for copper transporters and highlight several critical membrane trafficking regulators in maintaining copper homeostasis. We discuss how membrane trafficking regulators may alter copper transporter distribution in different membrane compartments to regulate intracellular copper homeostasis. Using Parkinson's disease and MEDNIK as examples, we further elaborate how misregulated trafficking regulators may interplay parallelly or synergistically with copper dyshomeostasis in devastating pathogenesis in neurodegenerative diseases. Finally, we explore multiple unsolved questions and highlight the existing challenges to understand how copper homeostasis is modulated through membrane trafficking.

Genetic differences in ethanol consumption: effects on iron, copper, and zinc regulation in mouse hippocampus

One common characteristic of neurodegenerative diseases is dysregulation of iron, usually with observed increases in its concentration in various regions. Heavy alcohol consumption is believed to contribute to such iron dysregulation in the brain with accompanying dementia. To examine this effect and related genetic-based individual differences in an animal model, we subjected female mice from 12 BXD recombinant inbred strains to 16 weeks of alcohol consumption using the drinking in the dark (DID) method. Daily consumption was recorded and at the end of 16 weeks hippocampus tissues harvested. Concentrations of iron, copper and zinc were measured using X-ray fluorescence technology. The results showed that, DID increased iron overall across all strains, ranging from 3 to 68%. Copper and Zinc both decreased, ranging from 0.4-42 and 5-35% respectively. Analysis of variance revealed significant strain by treatment interactions for all three metals. Additionally, in the DID group, we observed strain differences in reduction of hippocampus mass. These findings are particularly interesting to us because high alcohol consumption in humans has been associated with neurodegeneration and dementia related to disruption of iron regulation. The findings of alcohol consumption associated decreases in copper and zinc are novel. The role of copper regulation and neurological function related to alcohol consumption is as yet largely unexplored. The role of zinc is better known as a neuromodulator in the hippocampus and appears to be protective against neurological damage. It would seem then, that the alcohol-related decrease in zinc in the hippocampus would be of concern and warrants further study.

Novel Biomarkers of Alzheimer's Disease: Based Upon N-methyl-D-aspartate Receptor Hypoactivation and Oxidative Stress

Early detection and prevention of Alzheimer’s disease (AD) is important. The current treatment for early AD is acetylcholine esterase inhibitors (AChEIs); however, the efficacy is poor. Besides, AChEI did not show efficacy in mild cognitive impairment (MCI). Beta-amyloid (Aβ) deposits have been regarded to be highly related to the pathogenesis of AD. However, many clinical trials aiming at the clearance of Aβ deposits failed to improve the cognitive decline of AD, even at its early phase. There should be other important mechanisms unproven in the course of AD and MCI. Feasible biomarkers for the diagnosis and treatment response of AD are lacking to date. The N-methyl-D-aspartate receptor (NMDAR) activation plays an important role in learning and memory. On the other hand, oxidative stress has been regarded to contribute to aging with the assumption that free radicals damage cell constituents and connective tissues. Our recent study found that an NMDAR enhancer, sodium benzoate (the pivotal inhibitor of D-amino acid oxidase [DAAO]), improved the cognitive and global function of patients with early-phase AD. Further, we found that peripheral DAAO levels were higher in patients with MCI and AD than healthy controls. We also found that sodium benzoate was able to change the activity of antioxidant. These pieces of evidence suggest that the NMDAR function is associated with anti-oxidation, and have potential to be biomarkers for the diagnosis and treatment response of AD.

Linking Oxidative Stress and Proteinopathy in Alzheimer's Disease

Proteinopathy and excessive production of reactive oxygen species (ROS), which are the principal features observed in the Alzheimer’s disease (AD) brain, contribute to neuronal toxicity. β-amyloid and tau are the primary proteins responsible for the proteinopathy (amyloidopathy and tauopathy, respectively) in AD, which depends on ROS production; these aggregates can also generate ROS. These mechanisms work in concert and reinforce each other to drive the pathology observed in the aging brain, which primarily involves oxidative stress (OS). This, in turn, triggers neurodegeneration due to the subsequent loss of synapses and neurons. Understanding these interactions may thus aid in the identification of potential neuroprotective therapies that could be clinically useful. Here, we review the role of β-amyloid and tau in the activation of ROS production. We then further discuss how free radicals can influence structural changes in key toxic intermediates and describe the putative mechanisms by which OS and oligomers cause neuronal death.

Modulation of amyloid-β aggregation by metal complexes with a dual binding mode and their delivery across the blood-brain barrier using focused ultrasound

One of the key hallmarks of Alzheimer's disease is the aggregation of the amyloid-β peptide to form fibrils. Consequently, there has been great interest in studying molecules that can disrupt amyloid-β aggregation. While a handful of molecules have been shown to inhibit amyloid-β aggregation in vitro, there remains a lack of in vivo data reported due to their inability to cross the blood-brain barrier. Here, we investigate a series of new metal complexes for their ability to inhibit amyloid-β aggregation in vitro. We demonstrate that octahedral cobalt complexes with polyaromatic ligands have high inhibitory activity thanks to their dual binding mode involving π-π stacking and metal coordination to amyloid-β (confirmed via a range of spectroscopic and biophysical techniques). In addition to their high activity, these complexes are not cytotoxic to human neuroblastoma cells. Finally, we report for the first time that these metal complexes can be safely delivered across the blood-brain barrier to specific locations in the brains of mice using focused ultrasound.

Reference values for trace element levels in the human brain: A systematic review of the literature

Some trace elements (TE) are eminently toxic for humans (e.g., Al, Pb, Hg, Cd) and its presence in the central nervous system has been linked to the etiology of neurodegenerative diseases (ND). More recently, the focus has shifted to the potential role of the imbalances on essential TE levels (e.g., Fe, Cu, Zn, Se) within the brain tissue, and they have also been identified as potentially responsible for the cognitive decline associated with normal ageing and the development of some ND, although their definite role remains unclear. Accurately, well-defined reference values for TE levels in human body fluids and tissues are indispensable to identify possible disturbances in individual cases. Moreover, since the brain is a highly heterogeneous organ, with anatomically and physiologically very different areas, a detailed mapping of TE distribution across the brain tissue of normal individuals, with an in-depth analysis of TE levels in the different brain regions, is a mandatory prior work so that the results obtained from patients suffering from ND and other brain diseases can be interpreted. This review aims to compile and summarize the available data regarding TE levels in the different human brain regions of "normal" (non-diseased) individuals in order to contribute to the establishment of robust reference values. Fifty-four studies, published since 1960, were considered. The results showed a great variability between different studies. The potential sources of this variability are discussed. The need for increased harmonization of experimental strategies is highlighted in order to improve the comparability of the data obtained.

Copper Imbalance in Alzheimer's Disease: Meta-Analysis of Serum, Plasma, and Brain Specimens, and Replication Study Evaluating ATP7B Gene Variants

Evidence indicates that patients with Alzheimer's dementia (AD) show signs of copper (Cu) dyshomeostasis. This study aimed at evaluating the potential of Cu dysregulation as an AD susceptibility factor. We performed a meta-analysis of 56 studies investigating Cu biomarkers in brain specimens (pooled total of 182 AD and 166 healthy controls, HC) and in serum/plasma (pooled total of 2929 AD and 3547 HC). We also completed a replication study of serum Cu biomarkers in 97 AD patients and 70 HC screened for rs732774 and rs1061472 ATP7B, the gene encoding for the Cu transporter ATPase7B. Our meta-analysis showed decreased Cu in AD brain specimens, increased Cu and nonbound ceruloplasmin (Non-Cp) Cu in serum/plasma samples, and unchanged ceruloplasmin. Serum/plasma Cu excess was associated with a three to fourfold increase in the risk of having AD. Our replication study confirmed meta-analysis results and showed that carriers of the ATP7B AG haplotype were significantly more frequent in the AD group. Overall, our study shows that AD patients fail to maintain a Cu metabolic balance and reveals the presence of a percentage of AD patients carrying ATP7B AG haplotype and presenting Non-Cp Cu excess, which suggest that a subset of AD subjects is prone to Cu imbalance. This AD subtype can be the target of precision medicine-based strategies tackling Cu dysregulation.

Amyloid β Perturbs Cu(II) Binding to the Prion Protein in a Site-Specific Manner: Insights into Its Potential Neurotoxic Mechanisms

Amyloid β (Aβ) is a Cu-binding peptide that plays a key role in the pathology of Alzheimer's disease. A recent report demonstrated that Aβ disrupts the Cu-dependent interaction between cellular prion protein (PrP^C) and N-methyl-d-aspartate receptor (NMDAR), inducing overactivation of NMDAR and neurotoxicity. In this context, it has been proposed that Aβ competes for Cu with PrP^C; however, there is no spectroscopic evidence to support this hypothesis. Prion protein (PrP) can bind up to six Cu(II) ions: from one to four at the octarepeat (OR) region, producing low- and high-occupancy modes, and two at the His96 and His111 sites. Additionally, PrP^C is cleaved by α-secretases at Lys110/His111, yielding a new Cu(II)-binding site at the α-cleaved His111. In this study, the competition for Cu(II) between Aβ(1-16) and peptide models for each Cu-binding site of PrP was evaluated using circular dichroism and electron paramagnetic resonance. Our results show that the impact of Aβ(1-16) on Cu(II) coordination to PrP is highly site-specific: Aβ(1-16) cannot effectively compete with the low-occupancy mode at the OR region, whereas it partially removes the metal ion from the high-occupancy modes and forms a ternary OR-Cu(II)-Aβ(1-16) complex. In contrast, Aβ(1-16) removes all Cu(II) ions from the His96 and His111 sites without formation of ternary species. Finally, at the α-cleaved His111 site, Aβ(1-16) yields at least two different ternary complexes depending on the ratio of PrP/Cu(II)/Aβ. Altogether, our spectroscopic results indicate that only the low-occupancy mode at the OR region resists the effect of Aβ, while Cu(II) coordination to the high-occupancy modes and all other tested sites of PrP is perturbed, by either removal of the metal ion or formation of ternary complexes. These results provide important insights into the intricate effect of Aβ on Cu(II) binding to PrP and the potential neurotoxic mechanisms through which Aβ might affect Cu-dependent functions of PrP^C, such as NMDAR modulation.

Biofabricated zinc oxide nanoparticles impair cognitive function via modulating oxidative stress and acetylcholinesterase level in mice

Current work was designed to explore the effect of ZnO nanoparticles (ZnONP) biofabricated by using Trianthema portulacastrum (TP) leaves extract on mice brain hippocampus. ZnO nanoparticles of TP leaves (ZnOTP) were synthesized by co-precipitation method and further characterized by using various techniques such as UV-Vis spectrophotometer, Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared (FTIR), and Energy Dispersive X-ray (EDX). ZnOTP were evaluated for in vitro antioxidant activity, in vivo behavior models (for assessment of cognitive ability), acetylcholinesterase (AChE) activity along with other neurotransmitters content determination, estimation of various oxidative stress parameters and analysis of zinc content in the brain as well as plasma. Histopathological evaluation of the brain hippocampus of each group was performed to corroborate the statistical results. Spherical ZnOTP of 10 to 20 nm size embedded with different phytoconstituents of TP was confirmed. Results of our study revealed a significant memory deficit in mice treated with ZnOTP. Neuronal degeneration was also observed via a significant increase in AChE activity and oxidative stress levels in the brain of mice administered with ZnOTP. Exposure of ZnOTP was also found responsible for modulation of neurotransmission in hippocampus area. Further, ZnOTP disturbed the zinc homeostasis in hippocampus via elevation of zinc content in brain as well as plasma. Histopathology of hippocampus supported the damaging impact of ZnOTP by an increase in vacuolated cytoplasm and focal gliosis in groups treated with ZnOTP. Results demonstrated the neurotoxic effect of ZnOTP on brain hippocampus via cognitive impairment by alteration of neurotransmitter level, zinc content and oxidative stress.

Widespread Decreases in Cerebral Copper Are Common to Parkinson's Disease Dementia and Alzheimer's Disease Dementia

Several studies of Parkinson's disease (PD) have reported dysregulation of cerebral metals, particularly decreases in copper and increases in iron in substantia nigra (SN). However, few studies have investigated regions outside the SN, fewer have measured levels of multiple metals across different regions within the same brains, and there are no currently-available reports of metal levels in Parkinson's disease dementia (PDD). This study aimed to compare concentrations of nine essential metals across nine different brain regions in cases of PDD and controls. Investigated were: primary motor cortex (MCX); cingulate gyrus (CG); primary visual cortex (PVC); hippocampus (HP); cerebellar cortex (CB); SN; locus coeruleus (LC); medulla oblongata (MED); and middle temporal gyrus (MTG), thus covering regions with severe, moderate, or low levels of neuronal loss in PDD. Levels of eight essential metals and selenium were determined using an analytical methodology involving the use of inductively-coupled plasma mass spectrometry (ICP-MS), and compared between cases and controls, to better understand the extent and severity of metal perturbations. Findings were also compared with those from our previous study of sporadic Alzheimer's disease dementia (ADD), which employed equivalent methods, to identify differences and similarities between these conditions. Widespread copper decreases occurred in PDD in seven of nine regions (exceptions being LC and CB). Four PDD-affected regions showed similar decreases in ADD: CG, HP, MTG, and MCX. Decreases in potassium and manganese were present in HP, MTG and MCX; decreased manganese was also found in SN and MED. Decreased selenium and magnesium were present in MCX, and decreased zinc in HP. There was no evidence for increased iron in SN or any other region. These results identify alterations in levels of several metals across multiple regions of PDD brain, the commonest being widespread decreases in copper that closely resemble those in ADD, pointing to similar disease mechanisms in both dementias.

Structural alterations in the catalytic core of hSIRT2 enzyme predict therapeutic benefits of Garcinia mangostana derivatives in Alzheimer's disease: molecular dynamics simulation study

Recent studies have shown that inhibition of the hSIRT2 enzyme provides favorable effects in neurodegenerative diseases such as Alzheimer's disease. Prenylated xanthone phytochemicals including α-mangostin, β-mangostin and γ-mangostin obtained from Garcinia mangostana, a well-established tropical plant, have been shown experimentally to inhibit sirtuin enzymatic activity. However, the molecular mechanism of this sirtuin inhibition has not been reported. Using comprehensive integrated computational techniques, we provide molecular and timewise dynamical insights into the structural alterations capable of facilitating therapeutically beneficial effects of these phytochemicals at the catalytic core of the hSIRT2 enzyme. Findings revealed the enhanced conformational stability and compactness of the hSIRT2 catalytic core upon binding of γ-mangostin relative to the apoenzyme and better than α-mangostin and β-mangostin. Although thermodynamic calculations revealed favorable binding of all the phytochemicals to the hSIRT2 enzyme, the presence of only hydroxy functional groups on γ-mangostin facilitated the occurrence of additional hydrogen bonds involving Pro115, Phe119, Asn168 and His187 which are absent in α-mangostin- and β-mangostin-bound systems. Per-residue energy contributions showed that van der Waals and more importantly electrostatic interactions are involved in catalytic core stability with Phe96, Tyr104 and Phe235 notably contributing π-π stacking, π-π T shaped and π-sigma interactions. Cumulatively, our study revealed the structural alterations leading to inhibition of hSIRT2 catalysis and findings from this study could be significantly important for the future design and development of sirtuin inhibitors in the management of Alzheimer's disease.

Trace element alterations in Alzheimer's disease: A review

Dyshomeostasis of trace elements have been implicated in the progression of Alzheimer's disease (AD), which is characterized by amyloid-β (Aβ) plaques. Trace elements are particularly associated with the Aβ plaques. Metal-protein attenuating compounds have been developed to inhibit metals from binding to Aβ proteins, which result in Aβ termination, in the hope of improving cognitive functioning. However, there are still some contradicting reports. This review aims to first establish which trace elements are increased or decreased in the brains of Alzheimer's patients, and secondly, to review the effectiveness of clinical trials with metal-protein attenuating compounds for AD. Studies have consistently reported unchanged or increased iron, contradicting reports for zinc, decreased copper, unchanged or decreased manganese, inconsistent results for calcium, and magnesium seems to be unaffected. However, varied results have been reported for all trace elements. Clinical trials using metal-protein attenuating compounds to treat AD have also reported varied results. Copper chelators have repeatedly been used in clinical trials, even though few studies report increased brain copper levels in AD patients. Homeostasis of copper levels is important since copper has a vital role in several enzymes, such as cytochrome c, Cu/Zn superoxide dismutase and ceruloplasmin. Dyshomeostasis of copper levels can lead to increased oxidative stress and neuronal loss. Future studies should assess a variety of trace element levels in moderately and severely affected AD patients since there are contradicting reports. This review thus provides some insight into trace element alterations in the brains of individuals with AD.

Multi-element Analysis of Brain Regions from South African Cadavers

Trace elements are vital for a variety of functions in the brain. However, an imbalance can result in oxidative stress. It is important to ascertain the normal levels in different brain regions, as such information is still lacking. Therefore, this study aimed to provide baseline trace element concentrations from a South African population, as well as determine trace element differences between sex and brain regions. Samples from the caudate nucleus, putamen, globus pallidus and hippocampus were analysed using inductively coupled plasma mass spectrometry. Aluminium, antimony, arsenic, barium, boron, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, mercury, molybdenum, nickel, phosphorus, potassium, selenium, silicon, sodium, strontium, vanadium and zinc were assessed. A multiple median regression model was used to determine differences between sex and regions. Twenty-nine male and 13 female cadavers from a Western Cape, South African population were included (mean age 35 years, range 19 to 45). Trace element levels were comparable to those of other populations, although magnesium was considerably lower. While there were no sex differences, significant anatomical regional differences existed; the caudate nucleus and hippocampus were the most similar, and the globus pallidus and hippocampus the most different. In conclusion, this is the first article to report the trace element concentrations of brain regions from a South African population. Low magnesium levels in the brain may be linked to a dietary deficiency, and migraines, depression and epilepsy have been linked to low magnesium levels. Future research should be directed to increase the dietary intake of magnesium.

Modifiable, Non-Modifiable, and Clinical Factors Associated with Progression of Alzheimer's Disease

There is an extensive literature relating to factors associated with the development of Alzheimer's disease (AD), but less is known about factors which may contribute to its progression. This review examined the literature with regard to 15 factors which were suggested by PubMed search to be positively associated with the cognitive and/or neuropathological progression of AD. The factors were grouped as potentially modifiable (vascular risk factors, comorbidities, malnutrition, educational level, inflammation, and oxidative stress), non-modifiable (age at clinical onset, family history of dementia, gender, Apolipoprotein E ɛ4, genetic variants, and altered gene regulation), and clinical (baseline cognitive level, neuropsychiatric symptoms, and extrapyramidal signs). Although conflicting results were found for the majority of factors, a positive association was found in nearly all studies which investigated the relationship of six factors to AD progression: malnutrition, genetic variants, altered gene regulation, baseline cognitive level, neuropsychiatric symptoms, and extrapyramidal signs. Whether these or other factors which have been suggested to be associated with AD progression actually influence the rate of decline of AD patients is unclear. Therapeutic approaches which include addressing of modifiable factors associated with AD progression should be considered.