Interaction of metal ions with tau protein. The case for a metal-mediated tau aggregation

Inhibition of toxic metal-alpha synuclein interactions by human serum albumin

Human serum albumin (HSA), the most abundant protein in plasma and cerebrospinal fluid, not only serves as a crucial carrier of various exogenous and endogenous ligands but also modulates the aggregation of amyloidogenic proteins, including alpha synuclein (αSyn), which is associated with Parkinson's disease and other α-synucleinopathies. HSA decreases αSyn toxicity through the direct binding to monomeric and oligomeric αSyn species. However, it is possible that HSA also sequesters metal ions that otherwise promote aggregation. Cu(ii) ions, for example, enhance αSyn fibrillization in vitro, while also leading to neurotoxicity by generating reactive oxygen species (ROS). However, it is currently unclear if and how HSA affects Cu(ii)-binding to αSyn. Using an integrated set of NMR experiments, we show that HSA is able to chelate Cu(ii) ions from αSyn more efficiently than standard chelators such as EDTA, revealing an unexpected cooperativity between the HSA metal-binding sites. Notably, fatty acid binding to HSA perturbs this cooperativity, thus interfering with the sequestration of Cu(ii) ions from αSyn. We also observed that glycation of HSA diminished Cu(ii)-binding affinity, while largely preserving the degree of cooperativity between the HSA metal-binding sites. Additionally, our results show that Cu(ii)-binding to HSA stabilizes the interactions of HSA with αSyn primarily at two different regions, i.e. the N-terminus, Tyr 39 and the majority of the C-terminus. Our study not only unveils the effect of fatty acid binding and age-related posttranslational modifications, such as glycation, on the neuroprotective mechanisms of HSA, but also highlights the potential of αSyn as a viable NMR-based sensor to investigate HSA-metal interactions.

DpdtpA, A Multi-metal Ion Chelator, Attenuates Tau Phosphorylation and Microglial Inflammatory Response via Regulating the PI3K/AKT/GSK-3β Signal Pathways

Tau protein hyperphosphorylation and formation of intracellular neurofibrillary tangles (NFTs) are one of the histopathological hallmarks of Alzheimer's disease (AD) and positively correlated with the severity of AD symptoms. NFTs contain a large number of metal ions that play an important role in regulating tau protein phosphorylation and AD progression. Extracellular tau induces primary phagocytosis of stressed neurons and neuronal loss by activating microglia. Here, we studied the effects of a multi-metal ion chelator, DpdtpA, on tau-induced microglial activation and inflammatory responses and the underlying mechanisms. Treatment with DpdtpA attenuated the increase in the expression of NF-κB and production of inflammatory cytokines, IL-1β, IL-6 and IL-10, in rat microglial cells induced by expression of human tau40 proteins. Treatment with DpdtpA also suppressed tau protein expression and phosphorylation. Moreover, treatment with DpdtpA prevented tau-induced activation of glycogen synthase kinase-3β (GSK-3β) and inhibition of phosphatidylinositol-3-hydroxy kinase (PI3K)/AKT. Collectively, these results show that DpdtpA can attenuate tau phosphorylation and inflammatory responses of microglia by regulating the PI3K/AKT/GSK-3β signal pathways, providing a new option to alleviate neuroinflammation for the treatment of AD.

Bioinorganic Chemistry of Micronutrients Related to Alzheimer's and Parkinson's Diseases

Metal ions are fundamental to guarantee the regular physiological activity of the human organism. Similarly, vitamins play a key role in many biological functions of the metabolism, among which are coenzymes, redox mediators, and antioxidants. Due to their importance in the human organism, both metals and vitamins have been extensively studied for their involvement in neurodegenerative diseases (NDs). However, the full potential of the interaction between vitamins and metal ions has not been fully explored by researchers yet, and further investigation on this topic is needed. The aim of this review is to provide an overview of the scientific literature on the implications of vitamins and selected metal ions in two of the most common neurodegenerative diseases, Alzheimer's and Parkinson's disease. Furthermore, vitamin-metal ion interactions are discussed in detail focusing on their bioinorganic chemistry, with the perspective of arousing more interest in this fascinating bioinorganic field.

Natural antioxidants that act against Alzheimer's disease through modulation of the NRF2 pathway: a focus on their molecular mechanisms of action

Characterized by a complex pathophysiology that includes the intraneuronal formation of neurofibrillary tangles and the extracellular deposition of β-amyloid plaques, Alzheimer's disease (AD) is a terminal neurodegenerative disease that causes dementia in older adults. Oxidative stress in the brain is considered as one of the contributing factors to the pathogenesis of AD, and thus, antioxidants have attracted much interest as potential therapeutic agents against the disorder. Natural antioxidants are typically characterized by low acute and chronic toxicity, which facilitates their potential therapeutic application. One important molecular target for the beneficial effects of natural antioxidants is the nuclear factor erythroid-derived 2-related factor 2 (NFE2L2/NRF2). NRF2 is a key transcription factor that orchestrates the cellular antioxidant response through regulating the expression of oxidative stress-related genes harboring the antioxidant response element (ARE) in their promoters. Indeed, in the case of excessive oxidative damage, NRF2 migrates to the nucleus and binds to ARE, activating the transcription of antioxidant protector genes. There is increasing evidence that NRF2 is implicated in AD pathology through dysfunction and altered localization, which renders it as a potential therapeutic target for AD. Thus, this review summarizes the most recent (2018-2023) advances on the NRF2-modulating activity of natural antioxidants observed in vitro and in AD animal models. This information will help elucidate the molecular mechanisms governing the antioxidant activity of such phytochemicals to highlight their therapeutic potential against common neurodegenerative diseases, such as AD.

Combined Presence of Ferrous Ions and Hydrogen Peroxide in Normal Saline and In Vitro Models Induces Enhanced Aggregation of Therapeutic IgG due to Hydroxyl Radicals

Therapeutic monoclonal antibodies (mAb) are known to form aggregates and fragments upon exposure to hydrogen peroxide (H₂O₂) and ferrous ions (Fe²⁺). H₂O₂ and Fe²⁺ react to form hydroxyl radicals that are detrimental to protein structures. In this study, aggregation of mAb in the combined presence of Fe²⁺ and H₂O₂ was investigated in saline and physiologically relevant in vitro models. In the first case study, forced degradation of mAb in saline (a fluid used for administration of mAb) was carried out at 55 °C in the combined presence of 0.2 mM Fe²⁺ and 0.1% H₂O₂. The control and stressed samples were analyzed using an array of techniques including visual observation, size-exclusion chromatography (SEC), dynamic light scattering (DLS), microscopy, UV-vis, fluorescence, Fourier transform infrared spectroscopy, and cell-based toxicity assays. At the end of 1 h, samples having the combined presence of both Fe²⁺ and H₂O₂ exhibited more than 20% HMW (high molecular weight species), whereas samples having only Fe²⁺, H₂O₂, or neither resulted in less than 3% HMW. Aggregate-rich samples also exhibited altered protein structures and hydrophobicity. Aggregation increased upon increasing the time, temperature, and concentration of Fe²⁺ and H₂O₂. Samples having both Fe²⁺ and H₂O₂ also showed higher cytotoxicity in red blood cells. Samples of mAb with chlorides of copper and cobalt with H₂O₂ also resulted in multifold degradation. The first case study showed enhanced aggregation of mAb in the combined presence of Fe²⁺ and H₂O₂ in saline. In the second case study, aggregation of mAb was investigated in artificially prepared extracellular saline and in vitro models such as macromolecule free fraction of serum and serum. In the presence of both Fe²⁺ and H₂O₂, %HMW was higher in extracellular saline compared to macromolecule free fraction of serum. Further, in vitro models having the combined presence of Fe²⁺ and H₂O₂ resulted in enhanced aggregation of mAb compared to models that had neither.

Systemic Metabolism and Mitochondria in the Mechanism of Alzheimer's Disease: Finding Potential Therapeutic Targets

Elderly people over the age of 65 are those most likely to experience Alzheimer's disease (AD), and aging and AD are associated with apparent metabolic alterations. Currently, there is no curative medication against AD and only several drugs have been approved by the FDA, but these drugs can only improve the symptoms of AD. Many preclinical and clinical trials have explored the impact of adjusting the whole-body and intracellular metabolism on the pathogenesis of AD. The most recent evidence suggests that mitochondria initiate an integrated stress response to environmental stress, which is beneficial for healthy aging and neuroprotection. There is also an increasing awareness of the differential risk and potential targeting strategies related to the metabolic level and microbiome. As the main participants in intracellular metabolism, mitochondrial bioenergetics, mitochondrial quality-control mechanisms, and mitochondria-linked inflammatory responses have been regarded as potential therapeutic targets for AD. This review summarizes and highlights these advances.

Cannabidiol: Bridge between Antioxidant Effect, Cellular Protection, and Cognitive and Physical Performance

The literature provides scientific evidence for the beneficial effects of cannabidiol (CBD), and these effects extend beyond epilepsy treatment (e.g., Lennox-Gastaut and Dravet syndromes), notably the influence on oxidative status, neurodegeneration, cellular protection, cognitive function, and physical performance. However, products containing CBD are not allowed to be marketed everywhere in the world, which may ultimately have a negative effect on health as a result of the uncontrolled CBD market. After the isolation of CBD follows the discovery of CB1 and CB2 receptors and the main enzymatic components (diacylglycerol lipase (DAG lipase), monoacyl glycerol lipase (MAGL), fatty acid amino hydrolase (FAAH)). At the same time, the antioxidant potential of CBD is due not only to the molecular structure but also to the fact that this compound increases the expression of the main endogenous antioxidant systems, superoxide dismutase (SOD), and glutathione peroxidase (GPx), through the nuclear complex erythroid 2-related factor (Nrf2)/Keep1. Regarding the role in the control of inflammation, this function is exercised by inhibiting (nuclear factor kappa B) NF-κB, and also the genes that encode the expression of molecules with a pro-inflammatory role (cytokines and metalloproteinases). The other effects of CBD on cognitive function and physical performance should not be excluded. In conclusion, the CBD market needs to be regulated more thoroughly, given the previously listed properties, with the mention that the safety profile is a very good one.

Role of the Cysteine in R3 Tau Peptide in Copper Binding and Reactivity

Tau is a widespread neuroprotein that regulates the cytoskeleton assembly. In some neurological disorders, known as tauopathies, tau is dissociated from the microtubule and forms insoluble neurofibrillary tangles. Tau comprises four pseudorepeats (R1-R4), containing one (R1, R2, R4) or two (R3) histidines, that potentially act as metal binding sites. Moreover, Cys291 and Cys322 in R2 and R3, respectively, might have an important role in protein aggregation, through possible disulfide bond formation, and/or affecting the binding and reactivity of redox-active metal ions, as copper. We, therefore, compare the interaction of copper with octadeca-R3-peptide (R3C) and with the mutant containing an alanine residue (R3A) to assess the role of thiol group. Spectrophotometric titrations allow to calculate the formation constant of the copper(I) complexes, showing a remarkable stronger interaction in the case of R3C (l log Kf = 13.4 and 10.5 for copper(I)-R3C and copper(I)-R3A, respectively). We also evaluate the oxidative reactivity associated to these copper complexes in the presence of dopamine and ascorbate. Both R3A and R3C peptides increase the capability of copper to oxidize catechols, but copper-R3C displays a peculiar mechanism due to the presence of cysteine. HPLC-MS analysis shows that cysteine can form disulfide bonds and dopamine-Cys covalent adducts, with potential implication in tau aggregation process.

Aβ and Tau Interact with Metal Ions, Lipid Membranes and Peptide-Based Amyloid Inhibitors: Are These Common Features Relevant in Alzheimer’s Disease?

In the last two decades, the amyloid hypothesis, i.e., the abnormal accumulation of toxic Aβ assemblies in the brain, has been considered the mainstream concept sustaining research in Alzheimer’s Disease (AD). However, the course of cognitive decline and AD development better correlates with tau accumulation rather than amyloid peptide deposition. Moreover, all clinical trials of amyloid-targeting drug candidates have been unsuccessful, implicitly suggesting that the amyloid hypothesis needs significant amendments. Accumulating evidence supports the existence of a series of potentially dangerous relationships between Aβ oligomeric species and tau protein in AD. However, the molecular determinants underlying pathogenic Aβ/tau cross interactions are not fully understood. Here, we discuss the common features of Aβ and tau molecules, with special emphasis on: (i) the critical role played by metal dyshomeostasis in promoting both Aβ and tau aggregation and oxidative stress, in AD; (ii) the effects of lipid membranes on Aβ and tau (co)-aggregation at the membrane interface; (iii) the potential of small peptide-based inhibitors of Aβ and tau misfolding as therapeutic tools in AD. Although the molecular mechanism underlying the direct Aβ/tau interaction remains largely unknown, the arguments discussed in this review may help reinforcing the current view of a synergistic Aβ/tau molecular crosstalk in AD and stimulate further research to mechanism elucidation and next-generation AD therapeutics.

Cerebral Iron Deposition in Neurodegeneration

Disruption of cerebral iron regulation appears to have a role in aging and in the pathogenesis of various neurodegenerative disorders. Possible unfavorable impacts of iron accumulation include reactive oxygen species generation, induction of ferroptosis, and acceleration of inflammatory changes. Whole-brain iron-sensitive magnetic resonance imaging (MRI) techniques allow the examination of macroscopic patterns of brain iron deposits in vivo, while modern analytical methods ex vivo enable the determination of metal-specific content inside individual cell-types, sometimes also within specific cellular compartments. The present review summarizes the whole brain, cellular, and subcellular patterns of iron accumulation in neurodegenerative diseases of genetic and sporadic origin. We also provide an update on mechanisms, biomarkers, and effects of brain iron accumulation in these disorders, focusing on recent publications. In Parkinson’s disease, Friedreich’s disease, and several disorders within the neurodegeneration with brain iron accumulation group, there is a focal siderosis, typically in regions with the most pronounced neuropathological changes. The second group of disorders including multiple sclerosis, Alzheimer’s disease, and amyotrophic lateral sclerosis shows iron accumulation in the globus pallidus, caudate, and putamen, and in specific cortical regions. Yet, other disorders such as aceruloplasminemia, neuroferritinopathy, or Wilson disease manifest with diffuse iron accumulation in the deep gray matter in a pattern comparable to or even more extensive than that observed during normal aging. On the microscopic level, brain iron deposits are present mostly in dystrophic microglia variably accompanied by iron-laden macrophages and in astrocytes, implicating a role of inflammatory changes and blood–brain barrier disturbance in iron accumulation. Options and potential benefits of iron reducing strategies in neurodegeneration are discussed. Future research investigating whether genetic predispositions play a role in brain Fe accumulation is necessary. If confirmed, the prevention of further brain Fe uptake in individuals at risk may be key for preventing neurodegenerative disorders.

Three-repeat and four-repeat tau isoforms form different oligomers

Different tauopathies are characterized by the isoform-specific composition of the aggregates found in the brain and by structurally distinct tau strains. Although tau oligomers have been implicated as important neurotoxic species, little is known about how the primary structures of the six human tau isoforms affect tau oligomerization because the oligomers are metastable and difficult to analyze. To address this knowledge gap, here, we analyzed the initial oligomers formed by the six tau isoforms in the absence of posttranslational modifications or other manipulations using dot blots probed by an oligomer-specific antibody, native-PAGE/western blots, photo-induced cross-linking of unmodified proteins, mass-spectrometry, and ion-mobility spectroscopy. We found that under these conditions, three-repeat (3R) isoforms are more prone than four-repeat (4R) isoforms to form oligomers. We also tested whether known inhibitors of tau aggregation affect its oligomerization using three small molecules representing different classes of tau aggregation inhibitors, Methylene Blue (MB), the molecular tweezer CLR01, and the all-D peptide TLKIVW, for their ability to inhibit or modulate the oligomerization of the six tau isoforms. Unlike their reported inhibitory effect on tau fibrillation, the inhibitors had little or no effect on the initial oligomerization. Our study provides novel insight into the primary-quaternary structure relationship of human tau and suggests that 3R-tau oligomers may be an important target for future development of compounds targeting pathological tau assemblies.

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.

Mass Spectrometry-Based Structural Proteomics for Metal Ion/Protein Binding Studies

Metal ions are critical for the biological and physiological functions of many proteins. Mass spectrometry (MS)-based structural proteomics is an ever-growing field that has been adopted to study protein and metal ion interactions. Native MS offers information on metal binding and its stoichiometry. Footprinting approaches coupled with MS, including hydrogen/deuterium exchange (HDX), "fast photochemical oxidation of proteins" (FPOP) and targeted amino-acid labeling, identify binding sites and regions undergoing conformational changes. MS-based titration methods, including "protein-ligand interactions by mass spectrometry, titration and HD exchange" (PLIMSTEX) and "ligand titration, fast photochemical oxidation of proteins and mass spectrometry" (LITPOMS), afford binding stoichiometry, binding affinity, and binding order. These MS-based structural proteomics approaches, their applications to answer questions regarding metal ion protein interactions, their limitations, and recent and potential improvements are discussed here. This review serves as a demonstration of the capabilities of these tools and as an introduction to wider applications to solve other questions.

Probing the Role of Cu(II) Ions on Protein Aggregation Using Two Model Proteins

Copper is an essential trace element for human biology where its metal dyshomeostasis accounts for an increased level of serum copper, which accelerates protein aggregation. Protein aggregation is a notable feature for many neurodegenerative disorders. Herein, we report an experimental study using two model proteins, bovine serum albumin (BSA) and human serum albumin (HSA), to elucidate the mechanistic pathway by which serum albumins get converted from a fully folded globular protein to a fibril and an amorphous aggregate upon interaction with copper. Steady-state fluorescence, time-resolved fluorescence studies, and Raman spectroscopy were used to monitor the unfolding of serum albumin with increasing copper concentrations. Steady-state fluorescence studies have revealed that the fluorescence quenching of BSA/HSA by Cu(II) has occurred through a static quenching mechanism, and we have evaluated both the quenching constants individually. The binding constants of BSA-Cu(II) and HSA-Cu(II) were found to be 2.42 × 104 and 0.05 × 104 M-1, respectively. Further nanoscale morphological changes of BSA mediated by oligomers to fibril and HSA to amorphous aggregate formation were studied using atomic force microscopy. This aggregation process correlates with the Stern-Volmer plots in the absence of discernible lag phase. Raman spectroscopy results obtained are in good agreement with the increase in antiparallel β-sheet structures formed during the aggregation of BSA in the presence of Cu(II) ions. However, an increase in α-helical fractions is observed for the amorphous aggregate formed from HSA.

A New Insight into an Alternative Therapeutic Approach to Restore Redox Homeostasis and Functional Mitochondria in Neurodegenerative Diseases

Neurodegenerative diseases are accompanied by oxidative stress and mitochondrial dysfunction, leading to a progressive loss of neuronal cells, formation of protein aggregates, and a decrease in cognitive or motor functions. Mitochondrial dysfunction occurs at the early stage of neurodegenerative diseases. Protein aggregates containing oxidatively damaged biomolecules and other misfolded proteins and neuroinflammation have been identified in animal models and patients with neurodegenerative diseases. A variety of neurodegenerative diseases commonly exhibits decreased activity of antioxidant enzymes, lower amounts of antioxidants, and altered cellular signalling. Although several molecules have been approved clinically, there is no known cure for neurodegenerative diseases, though some drugs are focused on improving mitochondrial function. Mitochondrial dysfunction is caused by oxidative damage and impaired cellular signalling, including that of peroxisome proliferator-activated receptor gamma coactivator 1α. Mitochondrial function can also be modulated by mitochondrial biogenesis and the mitochondrial fusion/fission cycle. Mitochondrial biogenesis is regulated mainly by sirtuin 1, NAD⁺, AMP-activated protein kinase, mammalian target of rapamycin, and peroxisome proliferator-activated receptor γ. Altered mitochondrial dynamics, such as increased fission proteins and decreased fusion products, are shown in neurodegenerative diseases. Due to the restrictions of a target-based approach, a phenotype-based approach has been performed to find novel proteins or pathways. Alternatively, plasma membrane redox enzymes improve mitochondrial function without the further production of reactive oxygen species. In addition, inducers of antioxidant response elements can be useful to induce a series of detoxifying enzymes. Thus, redox homeostasis and metabolic regulation can be important therapeutic targets for delaying the progression of neurodegenerative diseases.

Trace concentrations, heavy implications: Influences of biometals on major brain pathologies of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative condition that involves accumulation of toxic protein species, notably amyloid-β (Aβ)plaques and neurofibrillary tau tangles that are associated with cognitive decline. These proteins can bind metal ions, ultimately affecting their structure and function. In this review, we discuss key biometals such as zinc, copper, and iron that interact with protein species involved in AD, mainly Aβ, tau, and the late-onset AD risk factor Apolipoprotein E (APOE). These metals interact with Aβ and tau proteins, affecting their aggregation and toxicity. The allele variants of APOE also have different interactions with these metals, affecting APOE protein expression and aggregation of AD protein species.

Thermodynamics and structural characterization of the nickel(II) and zinc(II) complexes of various peptide fragments of tau protein

Nickel(II) and zinc(II) complexes of various peptide fragments of tau protein have been investigated by potentiometric, UV-Vis, CD and ESI-MS techniques. The peptides include the native fragment tau(9-16) (Ac-EVMEDHAG-NH₂), and the Gln/Lys and Tyr/Ala mutated peptides (Ac-KGGYTMHK-NH₂ and Ac-KGGATMHK-NH₂) of tau(26-33). Similar to copper(II) the complexes of a chimeric peptide containing both His14 and His32 residues in one molecule (Ac-EDHAGTMHQD-NH₂) were also studied. The metal binding ability of the R3 domain was studied by using the native fragment tau(326-333) (Ac-GNIHHKPG-NH₂), and its two mutants (Ac-GNIHHKAG-NH₂) and (Ac-GNGHHKPG-NH₂) and the corresponding 1-histidine mutants (Ac-GNGAHKPG-NH₂ and Ac-GNGHAKPG-NH₂). The results of this study reveal that the histidyl residues of the N-terminal and R3 regions of tau protein can effectively bind nickel(II) and zinc(II) ions. In the case of nickel(II) and zinc(II) the M-N_im coordinated complexes are the major species in the physiological pH range and their stability is significantly enhanced by the presence of Glu and Asp residues in the neighbourhood of the His14 site. For all studied peptides, nickel(II) ions are able to promote the deprotonation and coordination of amide groups preceding histidine resulting in the exclusive formation of square planar (N_im,3N^-) complexes in alkaline solutions. The native fragment of the R3 region and its mutants containing two adjacent histidine moieties also bind only one nickel(II) ion with the His330 residue being the primary metal binding site. Exclusive binding of the independent imidazole side chains (His14 and His32 sites) cannot prevent the hydrolysis of zinc(II) in a slightly basic solution but the adjacent histidines of the R3 domain can promote the formation of amide coordinated zinc(II) complexes.

Copper, Iron, Selenium and Lipo-Glycemic Dysmetabolism in Alzheimer's Disease

The aim of the present review is to discuss traditional hypotheses on the etiopathogenesis of Alzheimer's disease (AD), as well as the role of metabolic-syndrome-related mechanisms in AD development with a special focus on advanced glycation end-products (AGEs) and their role in metal-induced neurodegeneration in AD. Persistent hyperglycemia along with oxidative stress results in increased protein glycation and formation of AGEs. The latter were shown to possess a wide spectrum of neurotoxic effects including increased Aβ generation and aggregation. In addition, AGE binding to receptor for AGE (RAGE) induces a variety of pathways contributing to neuroinflammation. The existing data also demonstrate that AGE toxicity seems to mediate the involvement of copper (Cu) and potentially other metals in AD pathogenesis. Specifically, Cu promotes AGE formation, AGE-Aβ cross-linking and up-regulation of RAGE expression. Moreover, Aβ glycation was shown to increase prooxidant effects of Cu through Fenton chemistry. Given the role of AGE and RAGE, as well as metal toxicity in AD pathogenesis, it is proposed that metal chelation and/or incretins may slow down oxidative damage. In addition, selenium (Se) compounds seem to attenuate the intracellular toxicity of the deranged tau and Aβ, as well as inhibiting AGE accumulation and metal-induced neurotoxicity.

Structural Proteomics Methods to Interrogate the Conformations and Dynamics of Intrinsically Disordered Proteins

Intrinsically disordered proteins (IDPs) and regions of intrinsic disorder (IDRs) are abundant in proteomes and are essential for many biological processes. Thus, they are often implicated in disease mechanisms, including neurodegeneration and cancer. The flexible nature of IDPs and IDRs provides many advantages, including (but not limited to) overcoming steric restrictions in binding, facilitating posttranslational modifications, and achieving high binding specificity with low affinity. IDPs adopt a heterogeneous structural ensemble, in contrast to typical folded proteins, making it challenging to interrogate their structure using conventional tools. Structural mass spectrometry (MS) methods are playing an increasingly important role in characterizing the structure and function of IDPs and IDRs, enabled by advances in the design of instrumentation and the development of new workflows, including in native MS, ion mobility MS, top-down MS, hydrogen-deuterium exchange MS, crosslinking MS, and covalent labeling. Here, we describe the advantages of these methods that make them ideal to study IDPs and highlight recent applications where these tools have underpinned new insights into IDP structure and function that would be difficult to elucidate using other methods.

Zinc determines dynamical properties and aggregation kinetics of human insulin

Protein aggregation is a widespread process leading to deleterious consequences in the organism, with amyloid aggregates being important not only in biology but also for drug design and biomaterial production. Insulin is a protein largely used in diabetes treatment, and its amyloid aggregation is at the basis of the so-called insulin-derived amyloidosis. Here, we uncover the major role of zinc in both insulin dynamics and aggregation kinetics at low pH, in which the formation of different amyloid superstructures (fibrils and spherulites) can be thermally induced. Amyloid aggregation is accompanied by zinc release and the suppression of water-sustained insulin dynamics, as shown by particle-induced x-ray emission and x-ray absorption spectroscopy and by neutron spectroscopy, respectively. Our study shows that zinc binding stabilizes the native form of insulin by facilitating hydration of this hydrophobic protein and suggests that introducing new binding sites for zinc can improve insulin stability and tune its aggregation propensity.

Copper (II) binding properties of an octapeptide fragment from the R3 region of tau protein: A combined potentiometric, spectroscopic and mass spectrometric study

The copper(II) complexes of a peptide fragment of the R3 domain of tau protein (tau(326-333) Ac-GNIHHKPG-NH₂) and its mutants (Ac-GNGHHKPG-NH₂, Ac-GNIHHKAG-NH₂, Ac-GNGAHKPG-NH₂ and Ac-GNGHAKPG-NH₂) have been studied by potentiometric and spectroscopic (UV-Vis, CD) methods. ESR spectroscopy and mass spectrometry were also used to prove the coordination mode of the mononuclear complexes and the formation of dinuclear species, respectively. It has been demonstrated that the (326-333) fragment of tau protein is a versatile and effective ligand for copper(II) coordination. The versatility of copper(II) binding is related to the presence of two adjacent histidyl residues in the sequence, which results in the coexistence of mononuclear, bis(ligand) and dinuclear complexes at different metal to ligand ratios. The 1:1 mononuclear complexes are, however, the dominant species with all peptides and the imidazole-N and one to three deprotonated amide nitrogen atoms towards the N-terminal side of the histidyl residue have been suggested as metal binding sites. This binding mode allows the formation of coordination isomers because any of the two histidine moieties can be the primary anchoring site. It is evident from the CD spectroscopic measurements that the isomers are present in almost equal concentration. The copper(II) binding affinity of the native fragment of tau protein is comparable to that of a similar 2-histidine fragment of amyloid-β mutant, Ac-SGAEGHHQK-NH₂ but the comparison with an independent histidyl residue (H32) from the N-terminal region of the protein reveals the predominance of H32 over the histidines in the R3 domain.

Cu, Fe, and Zn isotope ratios in murine Alzheimer's disease models suggest specific signatures of amyloidogenesis and tauopathy

Alzheimer’s disease (AD) is characterized by accumulation of tau and amyloid-beta in the brain, and recent evidence suggests a correlation between associated protein aggregates and trace elements, such as copper, iron, and zinc. In AD, a distorted brain redox homeostasis and complexation by amyloid-beta and hyperphosphorylated tau may alter the isotopic composition of essential mineral elements. Therefore, high-precision isotopic analysis may reveal changes in the homeostasis of these elements. We used inductively coupled plasma–mass spectrometry (ICP-MS)-based techniques to determine the total Cu, Fe, and Zn contents in the brain, as well as their isotopic compositions in both mouse brain and serum. Results for male transgenic tau (Line 66, L66) and amyloid/presenilin (5xFAD) mice were compared with those for the corresponding age- and sex-matched wild-type control mice (WT). Our data show that L66 brains showed significantly higher Fe levels than did those from the corresponding WT. Significantly less Cu, but more Zn was found in 5xFAD brains. We observed significantly lighter isotopic compositions of Fe (enrichment in the lighter isotopes) in the brain and serum of L66 mice compared with WT. For 5xFAD mice, Zn exhibited a trend toward a lighter isotopic composition in the brain and a heavier isotopic composition in serum compared with WT. Neither mouse model yielded differences in the isotopic composition of Cu. Our findings indicate significant pathology-specific alterations of Fe and Zn brain homeostasis in mouse models of AD. The associated changes in isotopic composition may serve as a marker for proteinopathies underlying AD and other types of dementia.

"What Doesn't Kill You Makes You Stronger": Future Applications of Amyloid Aggregates in Biomedicine

Amyloid proteins are linked to the pathogenesis of several diseases including Alzheimer's disease, but at the same time a range of functional amyloids are physiologically important in humans. Although the disease pathogenies have been associated with protein aggregation, the mechanisms and factors that lead to protein aggregation are not completely understood. Paradoxically, unique characteristics of amyloids provide new opportunities for engineering innovative materials with biomedical applications. In this review, we discuss not only outstanding advances in biomedical applications of amyloid peptides, but also the mechanism of amyloid aggregation, factors affecting the process, and core sequences driving the aggregation. We aim with this review to provide a useful manual for those who engineer amyloids for innovative medicine solutions.

Copper Modulation and Memory Impairment due to Hippocampal Tau Pathology

Background:Environmental copper has been implicated in the pathogenesis of Alzheimer’s disease based on evidence that: 1) brain copper levels increase with age, 2) copper promotes misfolding and toxicity of amyloid-β in vitro, 3) copper-modulating interventions reduce amyloid pathology in animal models. However, the effect of copper upon non-amyloid Alzheimer’s pathology is relatively under-explored.Objective:To determine if modulation of brain copper level affects brain tau pathology and/or associated cognitive impairment.Methods:We tested the hypothesis that brain copper modulates tau pathology by manipulating brain levels of copper in the PS19 transgenic mouse model of tau pathology. We treated PS19 and wild-type mice with oral zinc acetate, an established therapy for long term control of excess brain copper, and examined treatment effects upon brain copper, brain tau, NFT-like pathology, and spatial memory. We treated a second cohort of mice with exogenous dietary copper in order to evaluate whether excess environmental copper promotes brain tau pathology.Results:Copper-lowering with oral zinc attenuated spatial memory impairment in female but not male PS19 mice, without a significant effect upon tau pathology. Copper loading increased brain copper, but did not have an effect on brain tau pathology or spatial memory function.Conclusion:These findings suggest that a strategy to lower brain copper may be viable for symptomatic benefit in the setting of tau neuropathology, but unlikely to have robust effects on the underlying pathology. These findings are consistent with dietary or other exogenous copper being unlikely to promote tau pathology.

Attenuation of Oxidative Stress by Cannabinoids and Cannabis Extracts in Differentiated Neuronal Cells

In this proof-of-concept study, the antioxidant activity of phytocannabinoids, namely cannabidiol (CBD) and Δ9- tetrahydrocannabinol (THC), were investigated using an in vitro system of differentiated human neuronal SY-SH5Y cells. The oxidative stress was induced by hydrogen peroxide, as reactive oxygen species (ROS). Alzheimer's disease (AD)-like pathological conditions were mimicked in vitro by treating the differentiated neuronal cells with amyloid-β_1-42 (Aβ_1-42) in the presence of Cu(II). We showed that THC had a high potency to combat oxidative stress in both in vitro models, while CBD did not show a remarkable antioxidant activity. The cannabis extracts also exhibited a significant antioxidant activity, which depended on the ratio of the THC and CBD. However, our results did not suggest any antagonist effect of the CBD on the antioxidant activity of THC. The effect of cannabis extracts on the cell viability of differentiated human neuronal SY-SH5Y cells was also investigated, which emphasized the differences between the bioactivity of cannabis extracts due to their composition. Our preliminary results demonstrated that cannabis extracts and phytocannabinoids have a promising potential as antioxidants, which can be further investigated to develop novel pharmaceuticals targeting oxidative stress therapy.

Overdosing on iron: Elevated iron and degenerative brain disorders

IMPACT STATEMENT

Brain degenerative disorders, which include some neurodevelopmental disorders and age-associated diseases, cause debilitating neurological deficits and are generally fatal. A large body of emerging evidence indicates that iron accumulation in neurons within specific regions of the brain plays an important role in the pathogenesis of many of these disorders. Iron homeostasis is a highly complex and incompletely understood process involving a large number of regulatory molecules. Our review provides a description of what is known about how iron is obtained by the body and brain and how defects in the homeostatic processes could contribute to the development of brain diseases, focusing on Alzheimer's disease and Parkinson's disease as well as four other disorders belonging to a class of inherited conditions referred to as neurodegeneration based on iron accumulation (NBIA) disorders. A description of potential therapeutic approaches being tested for each of these different disorders is provided.

Copper(II) Coordination Abilities of the Tau Protein's N-Terminus Peptide Fragments: A Combined Potentiometric, Spectroscopic and Mass Spectrometric Study

Copper(II) complexes of the N-terminal peptide fragments of tau protein have been studied by potentiometric and various spectroscopic techniques (UV-vis, CD, ESR and ESI-MS). The octapeptide Tau(9-16) (Ac-EVMEDHAG-NH₂ ) contains the H14 residue of the native protein, while Tau(26-33) (Ac-QGGYTMHQ-NH₂ ) and its mutants Tau(Q26K-Q33K) (Ac-KGGYTMHK-NH₂ ) and Tau(Q26K-Y29A-Q33K) (Ac-KGGATMHK-NH₂ ) include the H32 residue. To compare the binding ability of H14 and H32 in a single molecule the decapeptide Ac-EDHAGTMHQD-NH₂ (Tau(12-16)(30-34)) has also been synthesized and studied. The histidyl residue is the primary metal binding site for metal ions in all the peptide models studied. In the case of Tau(9-16) the side chain carboxylate functions enhance the stability of the M-N_im coordinated complexes compared to Tau(26-33) (logK(Cu-N_im )=5.04 and 3.78, respectively). Deprotonation and metal ion coordination of amide groups occur around the physiological pH range for copper(II). The formation of the imidazole- and amide-coordinated species changes the metal ion preference and the complexes formed with the peptides containing the H32 residue predominate over those of H14 at physiological pH values (90 %-10 %) and in alkaline samples (96 %-4 %).

Enhancing Protein Electrospray Charge States by Multivalent Metal Ions: Mechanistic Insights from MD Simulations and Mass Spectrometry Experiments

The structure and reactivity of electrosprayed protein ions is governed by their net charge. Native proteins in non-denaturing aqueous solutions produce low charge states. More highly charged ions are formed when electrospraying proteins that are unfolded and/or exposed to organic supercharging agents. Numerous studies have explored the electrospray process under these various conditions. One phenomenon that has received surprisingly little attention is the charge enhancement caused by multivalent metal ions such as La³⁺ when electrospraying proteins out of non-denaturing solutions. Here, we conducted mass spectrometry and ion mobility spectrometry experiments, in combination with molecular dynamics (MD) simulations, to uncover the mechanistic basis of this charge enhancement. MD simulations of aqueous ESI droplets reproduced the experimental observation that La³⁺ boosts protein charge states relative to monovalent metals (e.g., Na⁺). The simulations showed that gaseous proteins were released by solvent evaporation to dryness, consistent with the charged residue model. Metal ion ejection kept the shrinking droplets close to the Rayleigh limit until ∼99% of the solvent had left. For droplets charged with Na⁺, metal adduction during the final stage of solvent evaporation produced low protein charge states. Droplets containing La³⁺ showed a very different behavior. The trivalent nature of La³⁺ favored adduction to the protein at a very early stage, when most of the solvent had not evaporated yet. This irreversible binding via multidentate contacts suppressed La³⁺ ejection from the vanishing droplets, such that the resulting gaseous proteins carried significantly more charge. Our results illustrate that MD simulations are suitable for uncovering intricate aspects of electrospray mechanisms, paving the way toward an atomistic understanding of mass spectrometry based analytical workflows.

Hydroxypyridinone-Diamine Hybrids as Potential Neuroprotective Agents in the PC12 Cell-Line Model of Alzheimer's Disease

There is an urgent need to propose effective treatments for Alzheimer’s disease (AD). Although the origin of the disease is poorly understood, several therapeutic options have been proposed. The new therapeutic approaches targeting biometal-mediated neurodegenerative pathways appear to be interesting ones. As a continuation of our preceding studies, two novel series of advanced glycation endproducts (AGE)/advanced lipid peroxidation endproducts (ALE) inhibitors have been developed as multifunctional scavengers. This extended work allowed us to highlight the new hydroxypyridinone-diamine hybrid IIa-3 bearing a C4 alkyl linker between the two pharmacophores. This derivative exhibited preserved potent capacities to trap reactive carbonyl species (vicinal diamine function) as well as reactive oxygen species and transition metals (hydroxypyridinone moiety) in comparison with previously described lead compound 1. In addition, its good predicted absorption, distribution, metabolism and excretion (ADME) properties were correlated with a better efficacy to inhibit in vitro methylglyoxal-induced apoptosis in neuronal-like PC12 cells. This new promising agent revealed improved druglikeness and ability to prevent biometal-mediated oxidative and carbonyl stress amplification involved in AD pathogenesis.

Aggregation of Microtubule Binding Repeats of Tau Protein is Promoted by Cu2

Understanding the factors that give rise to tau aggregation and reactive oxygen species (ROS) is the key aspect in Alzheimer's disease pathogenesis. Microtubule (MT) binding repeats of tau protein were suggested to play a critical role in tau aggregation. Here, we show that the interaction of Cu²⁺ with full-length MT binding repeats R1-R4 leads to the aggregation, and a Cys-based redox chemistry is critically involved in tau aggregation leading to disulfide-bridge dimerization of R2 and R3 and further aggregation into a fibrillar structure. Notably, ascorbate and glutathione, the most abundant antioxidants in neurons, cannot prevent the effect of Cu²⁺ on R2 and R3 aggregation. Detailed ESI-MS and NMR experiments demonstrate the interaction of Cu²⁺ with MT binding repeats. We show that redox activity of copper increases when bound to the MT repeats leading to ROS formation, which significantly contribute to cellular damage and neuron death. Results presented here provide new insights into the molecular mechanism of tau aggregation and ROS formation and suggest a new target domain for tau aggregation inhibitors.