Metal binding modes of Alzheimer's amyloid beta-peptide in insoluble aggregates and soluble complexes

Time-course remodeling and pathology intervention of α-synuclein amyloid fibril by heparin and heparin-like oligosaccharides

Amyloid fibrils represent a pathological state of protein polymer that is closely associated with various neurodegenerative diseases. Polysaccharides have a prominent role in recognizing amyloid fibrils and mediating their pathogenicity. However, the mechanism underlying the amyloid-polysaccharide interaction remains elusive. We also do not know its impact on the structure and pathology of formed fibrils. Here, we used cryo-electron microscopy to analyze the atomic structures of mature α-synuclein (α-syn) fibrils upon binding with polymeric heparin and heparin-like oligosaccharides. The fibril structure, including the helical twist and conformation of α-syn, changed over time upon the binding of heparin but not oligosaccharides. The sulfation pattern and numbers of saccharide units are important for the binding. Similarly, negatively charged biopolymers typically interact with amyloid fibrils, including tau and various α-syn polymorphs, leading to alterations in their conformation. Moreover, we show that heparin-like oligosaccharides can not only block neuronal uptake and propagation of formed α-syn fibrils but also inhibit α-syn fibrillation. This work demonstrates a distinctive activity of heparin and biopolymers in remodeling amyloid fibrils and suggests the pharmaceutical potential of heparin-like oligosaccharides.

Inflammatory signaling pathways in Alzheimer's disease: Mechanistic insights and possible therapeutic interventions

The complex pathophysiology of Alzheimer's disease (AD) poses challenges for the development of therapies. Recently, neuroinflammation has been identified as a key pathogenic mechanism underlying AD, while inflammation has emerged as a possible target for the management and prevention of AD. Several prior studies have demonstrated that medications modulating neuroinflammation might lessen AD symptoms, mostly by controlling neuroinflammatory signaling pathways such as the NF-κB, MAPK, NLRP3, etc, and their respective signaling cascade. Moreover, targeting these inflammatory modalities with inhibitors, natural products, and metabolites has been the subject of intensive research because of their anti-inflammatory characteristics, with many studies demonstrating noteworthy pharmacological capabilities and potential clinical applications. Therefore, targeting inflammation is considered a promising strategy for treating AD. This review comprehensively elucidates the neuroinflammatory mechanisms underlying AD progression and the beneficial effects of inhibitors, natural products, and metabolites in AD treatment.

Recent Advances in Targeting Transition Metals (Copper, Iron, and Zinc) in Alzheimer's Disease

Changes in the transition metal homeostasis in the brain are closely linked with Alzheimer's disease (AD), including intraneuronal iron accumulation and extracellular copper and zinc pooling in the amyloid plague. The brain copper, zinc, and iron surplus are commonly acknowledged characteristics of AD, despite disagreements among some. This has led to the theory that oxidative stress resulting from abnormal homeostasis of these transition metals may be a causative explanation behind AD. In the nervous system, the interaction of metals with proteins appears to be an essential variable in the development or suppression of neurodegeneration. Chelation treatment may be an option for treating neurodegeneration induced by transition metal ion dyshomeostasis. Some clinicians even recommend using chelating agents as an adjunct therapy for AD. The current review also looks at the therapeutic strategies that have been attempted, primarily with metal-chelating drugs. Metal buildup in the nervous system, as reported in the AD, could be the result of compensatory mechanisms designed to improve metal availability for physiological functions.

NMR studies of amyloid interactions

Amyloid fibrils are insoluble, fibrous nanostructures that accumulate extracellularly in biological tissue during the progression of several human disorders, including Alzheimer's disease (AD) and type 2 diabetes. Fibrils are assembled from protein monomers via the transient formation of soluble, cytotoxic oligomers, and have a common molecular architecture consisting of a spinal core of hydrogen-bonded protein β-strands. For the past 25 years, NMR spectroscopy has been at the forefront of research into the structure and assembly mechanisms of amyloid aggregates. Until the recent boom in fibril structure analysis by cryo-electron microscopy, solid-state NMR was unrivalled in its ability to provide atomic-level models of amyloid fibril architecture. Solution-state NMR has also provided complementary information on the early stages in the amyloid assembly mechanism. Now, both NMR modalities are proving to be valuable in unravelling the complex interactions between amyloid species and a diverse range of physiological metal ions, molecules and surfaces that influence the assembly pathway, kinetics, morphology and clearance in vivo. Here, an overview is presented of the main applications of solid-state and solution-state NMR for studying the interactions between amyloid proteins and biomembranes, glycosaminoglycan polysaccharides, metal ions, polyphenols, synthetic therapeutics and diagnostics. Key NMR methodology is reviewed along with examples of how to overcome the challenges of detecting interactions with aggregating proteins. The review heralds this new role for NMR in providing a comprehensive and pathologically-relevant view of the interactions between protein and non-protein components of amyloid. Coverage of both solid- and solution-state NMR methods and applications herein will be informative and valuable to the broad communities that are interested in amyloid proteins.

Unlocking the brain's zinc code: implications for cognitive function and disease

Zn2+ transport across neuronal membranes relies on two classes of transition metal transporters: the ZnT (SLC30) and ZIP (SLC39) families. These proteins function to decrease and increase cytosolic Zn2+ levels, respectively. Dysfunction of ZnT and ZIP transporters can alter intracellular Zn2+ levels resulting in deleterious effects. In neurons, imbalances in Zn2+ levels have been implicated as risk factors in conditions such as Alzheimer's disease and neurodegeneration, highlighting the pivotal role of Zn2+ homeostasis in neuropathologies. In addition, Zn2+ modulates the function of plasma membrane proteins, including ion channels and receptors. Changes in Zn2+ levels, on both sides of the plasma membrane, profoundly impact signaling pathways governing cell development, differentiation, and survival. This review is focused on recent developments of neuronal Zn2+ homeostasis, including the impact of Zn2+ dyshomeostasis in neurological disorders, therapeutic approaches, and the increasingly recognized role of Zn2+ as a neurotransmitter in the brain.

Cu(II) binding to the λ6aJL2-R24G antibody light chain protein associated with light chain amyloidosis disease: The role of histidines

Light chain amyloidosis is a conformational disease caused by the abnormal proliferation and deposition of antibody light chains as amyloid fibers in organs and tissues. The effect of Cu(II) binding to the model recombinant protein 6aJL2-R24G was previously characterized in our group, and we found an acceleration of the aggregation kinetics of the protein. In this study, in order to confirm the Cu(II) binding sites, histidine variants of 6aJL2-R24G were prepared and the effects of their interaction with Cu(II) were analyzed by circular dichroism, fluorescence spectroscopy, isothermal calorimetry titrations, and molecular dynamics simulations. Confirming our earlier work, we found that His8 and His99 are the highest affinity Cu(II) binding sites, and that Cu(II) binding to both sites is a cooperative event.

Current biomarkers and treatment strategies in Alzheimer disease: An overview and future perspectives

Alzheimer's disease (AD), a progressive degenerative disorder first identified by Alois Alzheimer in 1907, poses a significant public health challenge. Despite its prevalence and impact, there is currently no definitive ante mortem diagnosis for AD pathogenesis. By 2050, the United States may face a staggering 13.8 million AD patients. This review provides a concise summary of current AD biomarkers, available treatments, and potential future therapeutic approaches. The review begins by outlining existing drug targets and mechanisms in AD, along with a discussion of current treatment options. We explore various approaches targeting Amyloid β (Aβ), Tau Protein aggregation, Tau Kinases, Glycogen Synthase kinase-3β, CDK-5 inhibitors, Heat Shock Proteins (HSP), oxidative stress, inflammation, metals, Apolipoprotein E (ApoE) modulators, and Notch signaling. Additionally, we examine the historical use of Estradiol (E2) as an AD therapy, as well as the outcomes of Randomized Controlled Trials (RCTs) that evaluated antioxidants (e.g., vitamin E) and omega-3 polyunsaturated fatty acids as alternative treatment options. Notably, positive effects of docosahexaenoic acid nutriment in older adults with cognitive impairment or AD are highlighted. Furthermore, this review offers insights into ongoing clinical trials and potential therapies, shedding light on the dynamic research landscape in AD treatment.

Characterizing fibril morphological changes by spirooxindoles for neurodegenerative disease application

Fibrillation of proteins and polypeptides, which leads to the deposition of plaques in cells and tissues has been widely associated with many neuropathological diseases. Inhibition of protein misfolding and aggregation is crucial for the prevention and treatment of these conditions. The growing interest in identifying inhibitor molecules to prevent the formation of fibrils in vivo has led to the results highlighted in this study. Due to their hydrophobic structure and potential to readily cross the blood brain barrier, a library of spirooxindole compounds were synthesized with those labelled Hd-63, Hd-66 and Hd-74 proving to be the most potent against fibril formation. Our spectroscopic analysis provides detailed insight, that the introduction of these spirooxindole compounds leads to morphological changes in the mechanism of fibril formation which prevent the formation of highly ordered fibrils, instead results in the formation of disordered aggregates which are not fibrillar in nature.

Silver nanoparticle-based SERS sensors for sensitive detection of amyloid-β aggregates in biological fluids

One of the hallmarks of Alzheimer's disease (AD) pathogenesis is the production, aggregation, and deposition of amyloid-β (Aβ) peptide. Surface-enhanced Raman spectroscopy (SERS) is a promising analytical technique capable of providing valuable information on chemical composition and molecule conformations in biological samples. However, one of the main challenges for introducing the SERS technique into the practice is preparation of scalable and at the same time stable nanostructured sensors with uniform spatial distribution of nanoparticles. Herein, we propose SERS platforms for reproducible, sensitive, label-free quantification of amyloid-β aggregates for short-wavelength - 532 and 633 nm - lasers. A SERS sensor - based on silver nanoparticles immobilized into a chitosan film (AgNP/CS) - provided a uniform distribution of AgNPs from a colloidal suspension across the SERS sensor, resulting in nanomolar limits of detection (LODs) for Aβ42 aggregates with a portable 532 nm laser. The laser-induced deposition was used to obtain denser periodic plasmonic sensors (AgNP/LID) with a uniform nanoparticle distribution. The AgNP/LID SERS sensor allowed for 15 pM LOD for Aβ42 aggregates with 633 nm laser. Notably, both nanostructured substrates allowed to distinguish amyloid aggregates from monomers. Therefore, our approach demonstrated applicability of SERS for detection of macromolecular volumetric objects as amyloid-β aggregates for fundamental biological studies as well as for "point-of-care" diagnostics and screening for early stages of neurodegenerative diseases.

Alzheimer's disease and clinical trials

Alzheimer's disease (AD) is spreading its root disproportionately among the worldwide population. Many genes have been identified as the hallmarks of AD. Based upon the knowledge, many clinical trials have been designed and conducted. Attempts have been made to alleviate the pathology associated with AD by targeting the molecular products of these genes. Irrespective of the understanding on the genetic component of AD, many clinical trials have failed and imposed greater challenges on the path of drug discovery. Therefore, this review aims to identify research and review articles to pinpoint the limitations of drug candidates (thiethylperazine, CT1812, crenezumab, CNP520, and lecanemab), which are under or withdrawn from clinical trials. Thorough analysis of the cross-talk pathways led to the identification of many confounding factors, which could interfere with the success of clinical trials with drug candidates such as thiethylperazine, CT1812, crenezumab, and CNP520. Though these drug candidates were enrolled in clinical trials, yet literature review shows many limitations. These limitations raise many questions on the rationale behind the enrollments of these drug candidates in clinical trials. A meticulous prior assessment of the outcome of clinical studies may stop risky clinical trials at their inceptions. This may save time, money, and resources.

Switching On/Off Amyloid Plaque Formation in Transgenic Animal Models of Alzheimer's Disease

A hallmark of Alzheimer's disease (AD) are the proteinaceous aggregates formed by the amyloid-beta peptide (Aβ) that is deposited inside the brain as amyloid plaques. The accumulation of aggregated Aβ may initiate or enhance pathologic processes in AD. According to the amyloid hypothesis, any agent that has the capability to inhibit Aβ aggregation and/or destroy amyloid plaques represents a potential disease-modifying drug. In 2023, a humanized IgG1 monoclonal antibody (lecanemab) against the Aβ-soluble protofibrils was approved by the US FDA for AD therapy, thus providing compelling support to the amyloid hypothesis. To acquire a deeper insight on the in vivo Aβ aggregation, various animal models, including aged herbivores and carnivores, non-human primates, transgenic rodents, fish and worms were widely exploited. This review is based on the recent data obtained using transgenic animal AD models and presents experimental verification of the critical role in Aβ aggregation seeding of the interactions between zinc ions, Aβ with the isomerized Asp7 (isoD7-Aβ) and the α4β2 nicotinic acetylcholine receptor.

Association between pseudoexfoliation and Alzheimer's disease-related brain atrophy

BACKGROUND/AIMS

Pseudoexfoliation (PEX) syndrome is an age-related disorder characterized by the accumulation of extracellular material in the anterior eye segment. PEX pathogenesis is not fully understood, but amyloid which accumulates in the brain of patients with Alzheimer's disease (AD) is a PEX component. PEX deposition shares features with amyloid aggregation in AD, and brain atrophy is a common AD feature, with β-amyloid accumulation among contributing factors. This study investigated whether PEX syndrome is associated with AD-related brain atrophy.

METHODS

We reviewed the medical records of patients diagnosed with PEX at the Veterans Health Service Medical Center between January 2015 and August 2021. This retrospective cohort study included 48 patients with PEX and 48 healthy age- and sex-matched controls. Patients with PEX were divided into two groups: with and without glaucoma. The main outcome measure was brain atrophy, using a visual rating scale, and AD incidence. Brain atrophy was measured using the Scheltens scale for medial temporal atrophy, the posterior cortical atrophy scale for parietal atrophy, and the Pasquier scale for global cortical atrophy.

RESULTS

The percentage of participants with medial temporal atrophy was 56.3% in the PEX group and 35.4% in the control group. The global cortical atrophy and parietal atrophy scores were significantly higher in the PEX group (P<0.05), whereas the PEX and PEX glaucoma groups showed no difference. Among the 96 participants, 16 and 5 participants in the PEX and control groups, respectively, were diagnosed with dementia. Patients with PEX glaucoma tended to have lower Mini-Mental State Examination scores, indicating impaired cognitive function, than those without glaucoma.

CONCLUSION

PEX is associated with brain atrophy, reflecting the risk of developing AD. Patients with PEX glaucoma may present with advanced AD stages. Our results suggest that PEX may be a predictor of AD.

A Review on Integrated ZnO-Based SERS Biosensors and Their Potential in Detecting Biomarkers of Neurodegenerative Diseases

Surface-enhanced Raman spectroscopy (SERS) applications in clinical diagnosis and spectral pathology are increasing due to the potential of the technique to bio-barcode incipient and differential diseases via real-time monitoring of biomarkers in fluids and in real-time via biomolecular fingerprinting. Additionally, the rapid advancements in micro/nanotechnology have a visible influence in all aspects of science and life. The miniaturization and enhanced properties of materials at the micro/nanoscale transcended the confines of the laboratory and are revolutionizing domains such as electronics, optics, medicine, and environmental science. The societal and technological impact of SERS biosensing by using semiconductor-based nanostructured smart substrates will be huge once minor technical pitfalls are solved. Herein, challenges in clinical routine testing are addressed in order to understand the context of how SERS can perform in real, in vivo sampling and bioassays for early neurodegenerative disease (ND) diagnosis. The main interest in translating SERS into clinical practice is reinforced by the practical advantages: portability of the designed setups, versatility in using nanomaterials of various matter and costs, readiness, and reliability. As we will present in this review, in the frame of technology readiness levels (TRL), the current maturity reached by semiconductor-based SERS biosensors, in particular that of zinc oxide (ZnO)-based hybrid SERS substrates, is situated at the development level TRL 6 (out of 9 levels). Three-dimensional, multilayered SERS substrates that provide additional plasmonic hot spots in the z-axis are of key importance in designing highly performant SERS biosensors for the detection of ND biomarkers.

Current understanding of metal-dependent amyloid-β aggregation and toxicity

The discovery of effective therapeutics targeting amyloid-β (Aβ) aggregates for Alzheimer's disease (AD) has been very challenging, which suggests its complicated etiology associated with multiple pathogenic elements. In AD-affected brains, highly concentrated metals, such as copper and zinc, are found in senile plaques mainly composed of Aβ aggregates. These metal ions are coordinated to Aβ and affect its aggregation and toxicity profiles. In this review, we illustrate the current view on molecular insights into the assembly of Aβ peptides in the absence and presence of metal ions as well as the effect of metal ions on their toxicity.

Proteomic alterations in the cerebellum and hippocampus in an Alzheimer's disease mouse model: Alleviating effect of palmatine

Alzheimer's disease (AD) is one of the most prevalent diseases that lead to memory deficiencies, severe behavioral abnormalities, and ultimately death. The need for more appropriate treatment of AD continues, and remains a sought-after goal. Previous studies showed palmatine (PAL), an isoquinoline alkaloid, might have the potential for combating AD because of its in vitro and in vivo activities. In this study, we aimed to assess PAL's therapeutic potential and gain insights into the working mechanism on protein level in the AD mouse model brain, for the first time. To this end, PAL was administered to 12-month-old 5xFAD mice at two doses after its successful isolation from the Siberian barberry shrub. PAL (10 mg/kg) showed statistically significant improvement in the memory and learning phase on the Morris water maze test. The PAL's ability to pass through the blood-brain barrier was verified via Multiple Reaction Monitoring (MRM). Label-free proteomics analysis revealed PAL administration led to changes most prominently in the cerebellum, followed by the hippocampus, but none in the cortex. Most of the differentially expressed proteins in PAL compared to the 5xFAD control group (ALZ) were the opposite of those in ALZ in comparison to healthy Alzheimer's littermates (ALM) group. HS105, HS12A, and RL12 were detected as hub proteins in the cerebellum. Collectively, here we present PAL as a potential therapeutic candidate owing to its alleviating effect in 5xFAD mice on not only cognitive impairment but also proteomes in the cerebellum and hippocampus.

Metal-organic frameworks: A promising option for the diagnosis and treatment of Alzheimer's disease

Beta-amyloid (Aβ) peptide is one of the main characteristic biomarkers of Alzheimer's disease (AD). Previous clinical investigations have proposed that unusual concentrations of this biomarker in cerebrospinal fluid, blood, and brain tissue are closely associated with the AD progression. Therefore, the critical point of early diagnosis, prevention, and treatment of AD is to monitor the levels of Aβ. In view of the potential of metal-organic frameworks (MOFs) for diagnosing and treating the AD, much attention has been focused in recent years. This review discusses the latest advances in the applications of MOFs for the early diagnosis of AD via fluorescence and electrochemiluminescence (ECL) detection of AD biomarkers, fluorescence detection of the main metal ions in the brain (Zn2+, Cu2+, Mn2+, Fe3+, and Al3+) in addition to magnetic resonance imaging (MRI) of the Aβ plaques. The current challenges and future strategies for translating the in vitro applications of MOFs into in vivo diagnosis of the AD are discussed.

Role of Interaction between Zinc and Amyloid Beta in Pathogenesis of Alzheimer’s Disease

Progression of Alzheimer's disease is accompanied by the appearance of extracellular deposits in the brain tissues of patients with characteristic supramolecular morphology (amyloid plaques) the main components of which are β-amyloid isoforms (Aβ) and biometal ions (zinc, copper, iron). For nearly 40 years and up to the present time, the vast majority of experimental data indicate critical role of formation and accumulation of amyloid plaques (cerebral amyloidogenesis) in pathogenesis of Alzheimer's disease, however, nature of the molecular agents that initiate cerebral amyloidogenesis, as well as causes of aggregation of the native Aβ molecules in vivo remained unknown for a long time. This review discusses the current level of fundamental knowledge about the molecular mechanisms of interactions of zinc ions with a number of Aβ isoforms present in amyloid plaques of the patients with Alzheimer's disease, and also shows how this knowledge made it possible to identify driving forces of the cerebral amyloidogenesis in Alzheimer's disease and made it possible to determine fundamentally new biomarkers and drug targets as part of development of innovative strategy for diagnosis and treatment of Alzheimer's disease.

Electrochemical Analysis in Studying β-Amyloid Aggregation

β-amyloid (Aβ) is comprised of a group of peptides formed as a result of cleavage of the amyloid precursor protein by secretases. Aβ aggregation is considered as a central event in pathogenesis of Alzheimer's disease, the most common human neurodegenerative disorder. Molecular mechanisms of Aβ aggregation have intensively being investigated using synthetic Aβ peptides by methods based on monitoring of aggregates, including determination of their size and structure. In this review, an orthogonal approach to the study of Aβ aggregation is considered, which relies on electrochemical registration of the loss of peptide monomers. Electrochemical analysis of Aβ (by voltammetry and amperometric flow injection analysis) is based on registration of the oxidation signal of electroactive amino acid residues of the peptide on an electrode surface. The Aβ oxidation signal disappears, when the peptide is included in the aggregate. The advantages and disadvantages of electrochemical analysis for the study of spontaneous and metal-induced aggregation of Aβ, comparative analysis of various peptide isoforms, and study of the process of complexation of metal ions with the metal-binding domain of Aβ are discussed. It is concluded that the combined use of the electrochemical method and the methods based on detection of Aβ aggregates makes it possible to obtain more complete information about the mechanisms of peptide aggregation.

Amyloid-beta aggregation implicates multiple pathways in Alzheimer's disease: Understanding the mechanisms

Alzheimer's disease (AD) is a progressive neurodegenerative condition characterized by tau pathology and accumulations of neurofibrillary tangles (NFTs) along with amyloid-beta (Aβ). It has been associated with neuronal damage, synaptic dysfunction, and cognitive deficits. The current review explained the molecular mechanisms behind the implications of Aβ aggregation in AD via multiple events. Beta (β) and gamma (γ) secretases hydrolyzed amyloid precursor protein (APP) to produce Aβ, which then clumps together to form Aβ fibrils. The fibrils increase oxidative stress, inflammatory cascade, and caspase activation to cause hyperphosphorylation of tau protein into neurofibrillary tangles (NFTs), which ultimately lead to neuronal damage. Acetylcholine (Ach) degradation is accelerated by upstream regulation of the acetylcholinesterase (AChE) enzyme, which leads to a deficiency in neurotransmitters and cognitive impairment. There are presently no efficient or disease-modifying medications for AD. It is necessary to advance AD research to suggest novel compounds for treatment and prevention. Prospectively, it might be reasonable to conduct clinical trials with unclean medicines that have a range of effects, including anti-amyloid and anti-tau, neurotransmitter modulation, anti-neuroinflammatory, neuroprotective, and cognitive enhancement.

Raman Spectroscopy on Brain Disorders: Transition from Fundamental Research to Clinical Applications

Brain disorders such as brain tumors and neurodegenerative diseases (NDs) are accompanied by chemical alterations in the tissues. Early diagnosis of these diseases will provide key benefits for patients and opportunities for preventive treatments. To detect these sophisticated diseases, various imaging modalities have been developed such as computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET). However, they provide inadequate molecule-specific information. In comparison, Raman spectroscopy (RS) is an analytical tool that provides rich information about molecular fingerprints. It is also inexpensive and rapid compared to CT, MRI, and PET. While intrinsic RS suffers from low yield, in recent years, through the adoption of Raman enhancement technologies and advanced data analysis approaches, RS has undergone significant advancements in its ability to probe biological tissues, including the brain. This review discusses recent clinical and biomedical applications of RS and related techniques applicable to brain tumors and NDs.

Applications of Single-Molecule Vibrational Spectroscopic Techniques for the Structural Investigation of Amyloid Oligomers

Amyloid oligomeric species, formed during misfolding processes, are believed to play a major role in neurodegenerative and metabolic diseases. Deepening the knowledge about the structure of amyloid intermediates and their aggregation pathways is essential in understanding the underlying mechanisms of misfolding and cytotoxicity. However, structural investigations are challenging due to the low abundance and heterogeneity of those metastable intermediate species. Single-molecule techniques have the potential to overcome these difficulties. This review aims to report some of the recent advances and applications of vibrational spectroscopic techniques for the structural analysis of amyloid oligomers, with special focus on single-molecule studies.

Alzheimer's Drug PBT2 Interacts with the Amyloid β 1-42 Peptide Differently than Other 8-Hydroxyquinoline Chelating Drugs

Although Alzheimer's disease (AD) was first described over a century ago, it remains the leading cause of age-related dementia. Innumerable changes have been linked to the pathology of AD; however, there remains much discord regarding which might be the initial cause of the disease. The "amyloid cascade hypothesis" proposes that the amyloid β (Aβ) peptide is central to disease pathology, which is supported by elevated Aβ levels in the brain before the development of symptoms and correlations of amyloid burden with cognitive impairment. The "metals hypothesis" proposes a role for metal ions such as iron, copper, and zinc in the pathology of AD, which is supported by the accumulation of these metals within amyloid plaques in the brain. Metals have been shown to induce aggregation of Aβ, and metal ion chelators have been shown to reverse this reaction in vitro. 8-Hydroxyquinoline-based chelators showed early promise as anti-Alzheimer's drugs. Both 5-chloro-7-iodo-8-hydroxyquinoline (CQ) and 5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline (PBT2) underwent unsuccessful clinical trials for the treatment of AD. To gain insight into the mechanism of action of 8HQs, we have investigated the potential interaction of CQ, PBT2, and 5,7-dibromo-8-hydroxyquinoline (B2Q) with Cu(II)-bound Aβ(1-42) using X-ray absorption spectroscopy (XAS), high energy resolution fluorescence detected (HERFD) XAS, and electron paramagnetic resonance (EPR). By XAS, we found CQ and B2Q sequestered ∼83% of the Cu(II) from Aβ(1-42), whereas PBT2 sequestered only ∼59% of the Cu(II) from Aβ(1-42), suggesting that CQ and B2Q have a higher relative Cu(II) affinity than PBT2. From our EPR, it became clear that PBT2 sequestered Cu(II) from a heterogeneous mixture of Cu(II)Aβ(1-42) species in solution, leaving a single Cu(II)Aβ(1-42) species. It follows that the Cu(II) site in this Cu(II)Aβ(1-42) species is inaccessible to PBT2 and may be less solvent-exposed than in other Cu(II)Aβ(1-42) species. We found no evidence to suggest that these 8HQs form ternary complexes with Cu(II)Aβ(1-42).

ZOMEC via the p-Akt/Nrf2 Pathway Restored PTZ-Induced Oxidative Stress-Mediated Memory Dysfunction in Mouse Model

A new mechanistic approach to overcome the neurodegenerative disorders caused by oxidative stress in Alzheimer's disease (AD) is highly stressed in this article. Thus, a newly formulated drug (zinc ortho-methyl carbonodithioate (ZOMEC)) was investigated for five weeks on seven-week-old BALB/c male mice. ZOMEC 30 mg/kg was postadministered intraperitoneally during the third week of pentylenetetrazole (PTZ) injection. The brain homogenates of the mice were evaluated for their antioxidant potential for ZOMEC. The results including catalase (CAT), glutathione S transferase (GST), and lipid peroxidation (LPO) demonstrated that ZOMEC significantly reverted the oxidative stress stimulated by PTZ in the mouse brain. ZOMEC upregulated p-Akt/Nrf-2 pathways (also supported by molecular docking methods) to revoke PTZ-induced apoptotic protein markers. ZOMEC reversed PTZ-induced neuronal synapse deficits, improved oxidative stress-aided memory impairment, and inhibited the amyloidogenic pathway in mouse brains. The results suggested the potential of ZOMEC as a new, safe, and neurotherapeutic agent to cure neurodegenerative disorders by decreasing AD-like neuropathology in the animal PTZ model.

Azo-Stilbene and Pyridine-Amine Hybrid Multifunctional Molecules to Target Metal-Mediated Neurotoxicity and Amyloid-β Aggregation in Alzheimer's Disease

Neurodegenerative diseases such as Alzheimer's disease (AD) are associated with progressive neuronal cell death, and they are commonly correlated with aberrant protein misfolding and aggregation of Aβ peptides. Transition metal ions (Cu, Fe, and Zn) have been shown to promote aggregation and oxidative stress through formation of Aβ-metal complexes. In this context, integrating molecular scaffolds rationally is used here to generate multifunctional molecules as modulators for metal-induced abnormalities. This work encompasses two azo-stilbene (AS)-derived compounds (AS-HL1 and AS-HL2), the rationale behind the design, their synthesis, characterization, and metal chelation ability [Cu(II) and Zn(II)]. The molecular frameworks of the designed compounds consist of stilbene as an Aβ-interacting moiety, whereas N,N,O and N,N,N,O donor atoms are linked to generate the metal chelation moiety. Furthermore, we went on exploring their multifunctionality with respect to (w.r.t.) (i) their metal chelating capacities and (ii) their utility to modulate the aggregation pathways of both metal-free and metal-bound amyloid-β, (iii) scavenge free radicals, and (iv) inhibit the activity of acetylcholinesterase and (v) cytotoxicity. Moreover, the compounds were able to sequester Cu²⁺ from the Aβ-Cu complex as studied by the UV-visible spectroscopic assay. Molecular docking studies were also performed with Aβ and acetylcholinesterase enzyme. Overall, the studies presented here qualify these molecules as promising candidates for further investigation in the quest for finding a treatment for Alzheimer's disease.

Neglected N-Truncated Amyloid-β Peptide and Its Mixed Cu-Zn Complexes

Amyloid-β (Aβ) peptides are involved in Alzheimer's disease (AD) development. The interactions of these peptides with copper and zinc ions also seem to be crucial for this pathology. Although Cu(II) and Zn(II) ions binding by Aβ peptides has been scrupulously investigated, surprisingly, this phenomenon has not been so thoroughly elucidated for N-truncated Aβ_4-x-probably the most common version of this biomolecule. This negligence also applies to mixed Cu-Zn complexes. From the structural in silico analysis presented in this work, it appears that there are two possible mixed Cu-Zn(Aβ_4-x) complexes with different stoichiometries and, consequently, distinct properties. The Cu-Zn(Aβ_4-x) complex with 1:1:1 stoichiometry may have a neuroprotective superoxide dismutase-like activity. On the other hand, another mixed 2:1:2 Cu-Zn(Aβ_4-x) complex is perhaps a seed for toxic oligomers. Hence, this work proposes a novel research direction for our better understanding of AD development.

Second Sphere Interactions in Amyloidogenic Diseases

Amyloids are protein aggregates bearing a highly ordered cross β structural motif, which may be functional but are mostly pathogenic. Their formation, deposition in tissues and consequent organ dysfunction is the central event in amyloidogenic diseases. Such protein aggregation may be brought about by conformational changes, and much attention has been directed toward factors like metal binding, post-translational modifications, mutations of protein etc., which eventually affect the reactivity and cytotoxicity of the associated proteins. Over the past decade, a global effort from different groups working on these misfolded/unfolded proteins/peptides has revealed that the amino acid residues in the second coordination sphere of the active sites of amyloidogenic proteins/peptides cause changes in H-bonding pattern or protein-protein interactions, which dramatically alter the structure and reactivity of these proteins/peptides. These second sphere effects not only determine the binding of transition metals and cofactors, which define the pathology of some of these diseases, but also change the mechanism of redox reactions catalyzed by these proteins/peptides and form the basis of oxidative damage associated with these amyloidogenic diseases. The present review seeks to discuss such second sphere modifications and their ramifications in the etiopathology of some representative amyloidogenic diseases like Alzheimer's disease (AD), type 2 diabetes mellitus (T2Dm), Parkinson's disease (PD), Huntington's disease (HD), and prion diseases.

Aggregates Sealed by Ions

The chapter draws a line connecting some recent results where the role of ions is found essential in sealing more or less pre-organized assemblies of macromolecules. We draw some dots along the line that starts from the effect of the ionic atmosphere and ends with the chemical bonds formed by multivalent ions acting as bridges between macromolecules. Many of these dots involve structurally disordered peptides and disordered regions of proteins. A broad perspective of the role of multivalent ions in assisting the assembly process, shifting population in polymorphic states, and sealing protein aggregates, is suggested.

Architecture of the Two Metal Binding Sites in Prolactin

Metal binding by members of the growth hormone (GH) family of hematopoietic cytokines has been a subject of considerable interest. However, beyond appreciation of its role in reversible packing of GH proteins in secretory granules, the molecular mechanisms of metal binding and granule formation remain poorly understood. Here, we investigate metal binding by a GH family member prolactin (PRL) using paramagnetic metal titration and chelation experiments. Cu²⁺-mediated paramagnetic relaxation enhancement measurements identified two partial metal-binding sites on the opposite faces of PRL composed of residues H30/H180 and E93/H97, respectively. Coordination of metal ions by these two sites causes formation of inter-molecular bridges between the PRL protomers and enables formation of reversible higher aggregates. These findings in vitro suggest a model for reversible packaging of PRL in secretory granules. The proposed mechanism of metal-promoted PRL aggregation lends insight and support to the previously suggested role of metal coordination in secretory granule formation by GH proteins.

A computational protocol for the calculation of the standard reduction potential of iron complexes: application to Fe2+/3+-Aβ model systems relevant to Alzheimer's disease

Iron complexes play a key role in several biological processes, and they are also related to the development of neurological disorders, such as Alzheimer's and Parkinson's diseases. One of the main properties involved in these processes is the standard reduction potential (SRP) of iron complexes. However, the calculation of this property is challenging, mainly due to problems in the electronic structure description, solvent effects and the thermodynamic cycles used for its calculation. In this work, we proposed a computational protocol for the calculation of SRPs of iron complexes by evaluating a wide range of density functionals for the electronic structure description, two implicit solvent models with varying radii and two thermodynamic cycles. Results show that the M06L density functional in combination with the SMD solvation model and the isodesmic method provides good results compared with SRP experimental values for a set of iron complexes. Finally, this protocol was applied to three Fe^2+/3+-Aβ model systems involved in the development of Alzheimer's disease and the obtained SRP values are in good agreement with those reported previously by means of MP2 calculations.

Iron complexes play a key role in the development of neurological disorders, such as Alzheimer's disease. We provide a computational protocol based on DFT for the calculation of standard reduction potentials of iron complexes relevant to Alzheimer's disease.

Time-Evolved SERS Signatures of DEP-Trapped Aβ and Zn2+Aβ Peptides Revealed by a Sub-10 nm Electrode Nanogap

Alzheimer's disease (AD) has become highly relevant in aging societies, yet the fundamental molecular basis for AD is still poorly understood. New tools to study the undergoing structural conformation changes of amyloid beta (Aβ) peptides, the pathogenic hallmark of AD, could play a crucial role in the understanding of the underlying mechanisms of misfolding and cytotoxicity of this peptide. It has been recently reported that Zn²⁺ interacts with Aβ and changes its aggregation pathway away from less harmful fibrillar forms to more toxic species. Here, we present a versatile platform based on a set of sub-10 nm nanogap electrodes for the manipulation and sensing of biomolecules in the physiological condition at a low copy number, where molecules are trapped via dielectrophoresis (DEP) across the nanogap, which also serves as a surface-enhanced Raman spectroscopy hotspot. In this study, we demonstrate that our electrode nanogap platform can be used to study the structural difference between Aβ40 and ZnAβ40 peptides at different aggregation stages in the physiologically relevant concentration and in solution phase. The Raman spectroscopic signatures of the DEP-captured neuropeptides prove the device to be attractive as a label-free bioanalytical tool.

Investigation of bovine serum albumin aggregation upon exposure to silver(i) and copper(ii) metal ions using Zetasizer

Depending upon the metal coordination capacity and the binding sites of proteins, interaction between metal and proteins leads to a number of changes in the protein molecule which may include the change in conformation, unfolding, overall charge, and aggregation in some cases. In this study, Cu(ii) and Ag(i) metal ions were selected to investigate aggregation of bovine serum albumin (BSA) molecule upon interaction by measuring the size and charge of the aggregates using nano-Zetasizer instrument. Two concentrations of metal ions were made to interact with a specific concentration of BSA and the size and zeta potential of BSA aggregates were measured from 0 min upto 18 h. The Cu(ii) and Ag(i) metal ions showed almost similar behavior in inducing the BSA aggregation and the intensity of peak corresponding to the normal-sized protein decreased with time, whereas the peak corresponding to the protein aggregate increased. However, the effect on zeta potential of the aggregates was observed to be different with both metal ions. The aggregation of protein due to interaction of different metal ions is important to study as it gives insight to the pathogenesis of many neurological disorders and would result in developing effective ways to limit their exposure.

Copper Imbalance in Alzheimer's Disease and Its Link with the Amyloid Hypothesis: Towards a Combined Clinical, Chemical, and Genetic Etiology

The cause of Alzheimer's disease (AD) is incompletely defined. To date, no mono-causal treatment has so far reached its primary clinical endpoints, probably due to the complexity and diverse neuropathology contributing to the neurodegenerative process. In the present paper, we describe the plausible etiological role of copper (Cu) imbalance in the disease. Cu imbalance is strongly associated with neurodegeneration in dementia, but a complete biochemical etiology consistent with the clinical, chemical, and genetic data is required to support a causative association, rather than just correlation with disease. We hypothesize that a Cu imbalance in the aging human brain evolves as a gradual shift from bound metal ion pools, associated with both loss of energy production and antioxidant function, to pools of loosely bound metal ions, involved in gain-of-function oxidative stress, a shift that may be aggravated by chemical aging. We explain how this may cause mitochondrial deficits, energy depletion of high-energy demanding neurons, and aggravated protein misfolding/oligomerization to produce different clinical consequences shaped by the severity of risk factors, additional comorbidities, and combinations with other types of pathology. Cu imbalance should be viewed and integrated with concomitant genetic risk factors, aging, metabolic abnormalities, energetic deficits, neuroinflammation, and the relation to tau, prion proteins, α-synuclein, TAR DNA binding protein-43 (TDP-43) as well as systemic comorbidity. Specifically, the Amyloid Hypothesis is strongly intertwined with Cu imbalance because amyloid-β protein precursor (AβPP)/Aβ are probable Cu/Zn binding proteins with a potential role as natural Cu/Zn buffering proteins (loss of function), and via the plausible pathogenic role of Cu-Aβ.

The Progress of Label-Free Optical Imaging in Alzheimer's Disease Screening and Diagnosis

As the major neurodegenerative disease of dementia, Alzheimer's disease (AD) has caused an enormous social and economic burden on society. Currently, AD has neither clear pathogenesis nor effective treatments. Positron emission tomography (PET) and magnetic resonance imaging (MRI) have been verified as potential tools for diagnosing and monitoring Alzheimer's disease. However, the high costs, low spatial resolution, and long acquisition time limit their broad clinical utilization. The gold standard of AD diagnosis routinely used in research is imaging AD biomarkers with dyes or other reagents, which are unsuitable for in vivo studies owing to their potential toxicity and prolonged and costly process of the U.S. Food and Drug Administration (FDA) approval for human use. Furthermore, these exogenous reagents might bring unwarranted interference to mechanistic studies, causing unreliable results. Several label-free optical imaging techniques, such as infrared spectroscopic imaging (IRSI), Raman spectroscopic imaging (RSI), optical coherence tomography (OCT), autofluorescence imaging (AFI), optical harmonic generation imaging (OHGI), etc., have been developed to circumvent this issue and made it possible to offer an accurate and detailed analysis of AD biomarkers. In this review, we present the emerging label-free optical imaging techniques and their applications in AD, along with their potential and challenges in AD diagnosis.

Exploring the Role of Monoamine Oxidase Activity in Aging and Alzheimer's Disease

Monoamine oxidases (MAOs) are a family of flavin adenine dinucleotide-dependent enzymes that exert a crucial role in the metabolism of neurotransmitters of the central nervous system. The impaired function of MAOs is associated with copious brain diseases. The alteration of monoamine metabolism is a characteristics feature of aging. MAO plays a crucial role in the pathogenesis of Alzheimer's disease (AD) - a progressive neurodegenerative disorder associated with an excessive accumulation of amyloid-beta (Aβ) peptide and neurofibrillary tangles (NFTs). Activated MAO has played a critical role in the development of amyloid plaques from Aβ, as well as the formation of the NFTs. In the brain, MAO mediated metabolism of monoamines is the foremost source of reactive oxygen species formation. The elevated level of MAO-B expression in astroglia has been reported in the AD brains adjacent to amyloid plaques. Increased MAO-B activity in the cortical and hippocampal regions is associated with AD. This review describes the pathogenic mechanism of MAOs in aging as well as the development and propagation of Alzheimer's pathology.

Measurement of Interpeptidic CuII Exchange Rate Constants of CuII-Amyloid-β Complexes to Small Peptide Motifs by Tryptophan Fluorescence Quenching

The interpeptidic Cu^II exchange rate constants were measured for two Cu amyloid-β complexes, Cu(Aβ_1-16) and Cu(Aβ_1-28), to fluorescent peptides GHW and DAHW using a quantitative tryptophan fluorescence quenching methodology. The second-order rate constants were determined at three pH values (6.8, 7.4, and 8.7) important to the two Cu(Aβ) coordination complexes, components Cu(Aβ)_I and Cu(Aβ)_II. The interpeptidic Cu^II exchange rate constant is approximately 10⁴ M^-1 s^-1 but varies in magnitude depending on many variables. These include pH, length of the Aβ peptide, location of the anchoring histidine ligand in the fluorescent peptide, number of amide deprotonations required in the tryptophan peptide to coordinate Cu^II, and interconversion between Cu(Aβ)_I and Cu(Aβ)_II. We also present EPR data probing the Cu^II exchange between peptides and the formation of ternary species between Cu(Aβ) and GHW. As the nonfluorescent GHK and DAHK peptides are important motifs found in the blood and serum, their ability to sequester Cu^II ions from Cu(Aβ) complexes may be relevant for the metal homeostasis and its implication in Alzheimer's disease. Thus, their kinetic Cu^II interpeptidic exchange rate constants are important chemical rate constants that can help elucidate the complex Cu^II trafficking puzzle in the synaptic cleft.

Defining the Neuropathological Aggresome across in Silico, in Vitro, and ex Vivo Experiments

The loss of proteostasis over the life course is associated with a wide range of debilitating degenerative diseases and is a central hallmark of human aging. When left unchecked, proteins that are intrinsically disordered can pathologically aggregate into highly ordered fibrils, plaques, and tangles (termed amyloids), which are associated with countless disorders such as Alzheimer's disease, Parkinson's disease, type II diabetes, cancer, and even certain viral infections. However, despite significant advances in protein folding and solution biophysics techniques, determining the molecular cause of these conditions in humans has remained elusive. This has been due, in part, to recent discoveries showing that soluble protein oligomers, not insoluble fibrils or plaques, drive the majority of pathological processes. This has subsequently led researchers to focus instead on heterogeneous and often promiscuous protein oligomers. Unfortunately, significant gaps remain in how to prepare, model, experimentally corroborate, and extract amyloid oligomers relevant to human disease in a systematic manner. This Review will report on each of these techniques and their successes and shortcomings in an attempt to standardize comparisons between protein oligomers across disciplines, especially in the context of neurodegeneration. By standardizing multiple techniques and identifying their common overlap, a clearer picture of the soluble neuropathological aggresome can be constructed and used as a baseline for studying human disease and aging.

Hierarchical chemical determination of amyloid polymorphs in neurodegenerative disease

Amyloid aggregation, which disrupts protein homeostasis, is a common pathological event occurring in human neurodegenerative diseases (NDs). Numerous evidences have shown that the structural diversity, so-called polymorphism, is decisive to the amyloid pathology and is closely associated with the onset, progression, and phenotype of ND. But how could one protein form so many stable structures? Recently, atomic structural evidence has been rapidly mounting to depict the involvement of chemical modifications in the amyloid fibril formation. In this Perspective, we aim to present a hierarchical regulation of chemical modifications including covalent post-translational modifications (PTMs) and noncovalent cofactor binding in governing the polymorphic amyloid formation, based mainly on the latest α-synuclein and Tau fibril structures. We hope to emphasize the determinant role of chemical modifications in amyloid assembly and pathology and to evoke chemical biological approaches to lead the fundamental and therapeutic research on protein amyloid state and the associated NDs.

The Influence of Ca2+ and Zn2+ on the Amyloid Fibril Formation by β-Casein

BACKGROUND

The amyloid fibril formation in different tissues or organs is related to amyloidosis. The Ca2+, Zn2+ and heparan sulfate (HS) are important elements and compositions in human body, which play a key role in regulating various physiological activities. Recently, there are increasing evidence suggest that they are closely linked to the amyloid fibril formation.

OBJECTIVE

The effect of Ca2+ and Zn2+ on the amyloid fibril formation by β-casein was investigated in the absence and presence of HS, which was significantly to explore the relationship between the concentration changes of Ca2+ and Zn2+ and amyloid fibril formation.

METHODS

In this work, the influence of Ca2+ and Zn2+ on the β-casein fibril formation in the absence and presence of HS was investigated by various methods of Thioflavin T fluorescence assay, transmission electron microscopy and intrinsic fluorescence measure.

RESULTS

The results demonstrated that Ca2+ and Zn2+ promoted the β-casein fibril formation. The effect of Ca2+ was greater than that of Zn2+. Meanwhile, the both metal ions had stronger effects when β-casein was incubated with HS together. In addition, it was also observed that the microenvironment of β-casein was changed because the intrinsic fluorescence peaks were red-shifted on the influence of Ca2+ and Zn2+.

CONCLUSION

Ca2+ and Zn2+ were capable of promoting the β-casein fibril formation in the both absence and presence of HS. This work set up the foundation for further researching of the amyloidosis pathogenesis and provided new insight for us to understand relationship between the inflammation and amyloidosis.

Colorimetric determination of amyloid-β peptide using MOF-derived nanozyme based on porous ZnO-Co3O4 nanocages

A sensitive and rapid colorimetric biosensor has been developed for determination of amyloid-β peptide (Aβ) and study of amyloidogenesis based on the high peroxidase-like activity of porous bimetallic ZnO-Co₃O₄ nanocages (NCs). Due to the high binding ability of Aβ monomer to ZnO-Co₃O₄ NCs, the catalytic activity of ZnO-Co₃O₄ NCs can be significantly suppressed by Aβ monomer. This finding forms the basis for a colorimetric assay for Aβ monomer detection. The detection limit for Aβ monomer is 3.5 nM with a linear range of 5 to 150 nM (R² = 0.997). The system was successfully applied to the determination of Aβ monomer in rat cerebrospinal fluid. Critically, the different inhibition effects of monomeric and aggregated Aβ species on the catalytic activity of ZnO-Co₃O₄ NCs enabled the sensor to be used for tracking the dynamic progress of Aβ aggregation and screening Aβ inhibitors. Compared with the commonly used thioflavin T fluorescence assay, this method provided higher sensitivity to the formation of Aβ oligomer at the very early assembly stage. Our assay shows potential application in early diagnosis and therapy of Alzheimer's disease (AD).

"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.

Ordered Nanofibers Fabricated from Hierarchical Self-Assembling Processes of Designed α-Helical Peptides

Peptide self-assembly is fast evolving into a powerful method for the development of bio-inspired nanomaterials with great potential for many applications, but it remains challenging to control the self-assembling processes and nanostrucutres because of the intricate interplay of various non-covalent interactions. A group of 28-residue α-helical peptides is designed including NN, NK, and HH that display distinct hierarchical events. The key of the design lies in the incorporation of two asparagine (Asn) or histidine (His) residues at the a positions of the second and fourth heptads, which allow one sequence to pack into homodimers with sticky ends through specific interhelical Asn-Asn or metal complexation interactions, followed by their longitudinal association into ordered nanofibers. This is in contrast to classical self-assembling helical peptide systems consisting of two complementary peptides. The collaborative roles played by the four main non-covalent interactions, including hydrogen-bonding, hydrophobic interactions, electrostatic interactions, and metal ion coordination, are well demonstrated during the hierarchical self-assembling processes of these peptides. Different nanostructures, for example, long and short nanofibers, thin and thick fibers, uniform metal ion-entrapped nanofibers, and polydisperse globular stacks, can be prepared by harnessing these interactions at different levels of hierarchy.

Longitudinal biometal accumulation and Ca isotope composition of the Göttingen minipig brain

Biometals play a critical role in both the healthy and diseased brain's functioning. They accumulate in the normal aging brain, and are inherent to neurodegenerative disorders and their associated pathologies. A prominent example of this is the brain accumulation of metals such as Ca, Fe and Cu (and more ambiguously, Zn) associated with Alzheimer's disease (AD). The natural stable isotope compositions of such metals have also shown utility in constraining biological mechanisms, and in differentiating between healthy and diseased states, sometimes prior to conventional methods. Here we have detailed the distribution of the biologically relevant elements Mg, P, K, Ca, Fe, Cu and Zn in brain regions of Göttingen minipigs ranging in age from three months to nearly six years, including control animals and both a single- and double-transgenic model of AD (PS1, APP/PS1). Moreover, we have characterized the Ca isotope composition of the brain for the first time. Concentration data track rises in brain biometals with age, namely for Fe and Cu, as observed in the normal ageing brain and in AD, and biometal data point to increased soluble amyloid beta (Aβ) load prior to AD plaque identification via brain imaging. Calcium isotope results define the brain as the isotopically lightest permanent reservoir in the body, indicating that brain Ca dyshomeostasis may induce measurable isotopic disturbances in accessible downstream reservoirs such as biofluids.

Cobalt(III) Schiff base complexes stabilize non-fibrillar amyloid-β aggregates with reduced toxicity

The aggregation of amyloid-β (Aβ) is believed to be foundational to the pathogenesis of Alzheimer's disease (AD). In vitro aggregation kinetics have been shown to correlate with rates of disease progression in both AD patients and animal models, thus proving to be a useful metric for testing Aβ-targeted therapeutics. Here we present evidence of cobalt(III) Schiff base complex ([Co(acetylacetonate)(NH₃)₂]Cl; Co(III)-sb) modulation of Aβ aggregation kinetics by a variety of complementary techniques. These include Thioflavin T (ThT) fluorescence, circular dichroism (CD) spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM). Our data was fitted to kinetic rate laws using a mathematical model developed by Knowles et al. in order to extract mechanistic information about the effect of Co(III)-sb on aggregation kinetics. Our analysis revealed that Co(III)-sb alters Aβ aggregation by decreasing the polymerization rate and increasing the nucleation rate, suggesting that Co(III)-sb causes Aβ to rapidly stabilize oligomeric species with reduced elongation into mature fibrils. This result was corroborated by TEM and AFM of Aβ aggregates in vitro. We also demonstrate that Aβ aggregate mixtures produced in the presence of Co(III)-sb exhibit decreased cytotoxicity compared to untreated samples.

The aroylhydrazone INHHQ prevents memory impairment induced by Alzheimer's-linked amyloid-β oligomers in mice

Converging evidence indicates that neurotoxicity and memory impairment in Alzheimer's disease is induced by brain accumulation of soluble amyloid-β oligomers (AβOs). Physiological metals are poorly distributed and concentrated in the senile plaques typical of Alzheimer's disease, where they may be coordinated to the amyloid-β peptide (Aβ). Indeed, zinc and copper increase Aβ oligomerization and toxicity. Metal-protein attenuating compounds represent a class of agents proposed for Alzheimer's disease treatment, as they reduce abnormal interactions of metal ions with Aβ, inhibit Aβ oligomerization and prevent deleterious redox reactions in the brain. The present work investigates the protective action of an isoniazid-derived aroylhydrazone, INHHQ, on AβO-induced memory impairment. Systemic administration of a single dose of INHHQ (1 mg/kg) prevented both short-term and long-term memory impairment caused by AβOs in mice. In-vitro studies showed that INHHQ prevents Cu(Aβ)-catalyzed production of reactive oxygen species. Although the mechanism of protection by INHHQ is not yet fully understood at a molecular level, the results reported herein certainly point to the value of aroylhydrazones as promising neuroprotective agents in Alzheimer's disease and related disorders.