Bioinorganic chemistry of Alzheimer's disease

Metal-organic frameworks-based moisture responsive essential oil hydrogel beads for fresh-cut pineapple preservation

The preservation of fresh-cut fruits and vegetables has attracted attention to the shelf-life reduction caused by high humidity. Herein, alginate/copper ions cross-linking, in-situ growth and self-assembly techniques of metal-organic frameworks (MOFs) were utilized to prepare a moisture responsive hydrogel bead (HKUST-1@ALG). As the multistage porous structure formation, tea tree essential oil (TTO) load capacity in hydrogel bead (TTO-HKUST-1@ALG) was increased from 6.1% to 21.6%. TTO-HKUST-1@ALG had excellent moisture response performance, and the release rates of TTO increased from 33.89% to 70.98% with moisture increasing from 45% to 95%. Besides, TTO-HKUST-1@ALG exhibited excellent antimicrobial, antioxidant capacity, and biocompatibility. During storage, TTO-HKUST-1@ALG effectively improved the cell membrane integrity by maintaining the balance of reactive oxygen species metabolism. The degradation of cell wall structure and tissue softening were delayed by inhibiting the cell wall-degrading enzymes activity. Briefly, TTO-HKUST-1@ALG improved the storage quality and extended shelf-life of fresh-cut pineapple, which was a promising preservative.

Profiling of the Proteins Interacting with Amyloid Beta Peptides in Clinical Samples by PACTS-TPP

The accumulation of amyloid beta (Aβ1-42) results in neurotoxicity and is strongly related to neurodegenerative disorders, especially Alzheimer's disease (AD), but the underlying molecular mechanism is still poorly understood. Therefore, there is an urgent need for researchers to discover the proteins that interact with Aβ1-42 to determine the molecular basis. Previously, we developed peptide-ligand-induced changes in the abundance of proTeinS (PACTS)-assisted thermal proteome profiling (TPP) to identify proteins that interact with peptide ligands. In the present study, we applied this technique to analyze clinical samples to identify Aβ1-42-interacting proteins. We detected 115 proteins that interact with Aβ1-42 in human frontal lobe tissue. Pathway enrichment analysis revealed that the differentially expressed proteins were involved mainly in neurodegenerative diseases. Further orthogonal validation revealed that Aβ1-42 interacted with the AD-associated protein mitogen-activated protein kinase 3 (MAPK3), and knockdown of the Aβ1-42 amyloid precursor protein (APP) inhibited the MAPK signaling pathway, suggesting potential functional roles for Aβ1-42 in interacting with MAPK3. Overall, this study demonstrated the application of the PACTS-TPP in clinical samples and provided a valuable data source for research on neurodegenerative diseases.

Therapeutic implications of glycogen synthase kinase-3β in Alzheimer's disease: a novel therapeutic target

Alzheimer's disease (AD) is an extremely popular neurodegenerative condition associated with dementia, responsible for around 70% of the cases. There are presently 50 million people living with dementia in the world, but this number is anticipated to increase to 152 million by 2050, posing a substantial socioeconomic encumbrance. Despite extensive research, the precise mechanisms that cause AD remain unidentified, and currently, no therapy is available. Numerous signalling paths related to AD neuropathology, including glycogen synthase kinase 3-β (GSK-3β), have been investigated as potential targets for the treatment of AD in current years.GSK-3β is a proline-directed serine/threonine kinase that is linked to a variety of biological activities, comprising glycogen metabolism to gene transcription. GSK-3β is also involved in the pathophysiology of sporadic as well as familial types of AD, which has led to the development of the GSK3 theory of AD. GSK-3β is a critical performer in the pathology of AD because dysregulation of this kinase affects all the main symbols of the disease such as amyloid formation, tau phosphorylation, neurogenesis and synaptic and memory function. The current review highlights present-day knowledge of GSK-3β-related neurobiology, focusing on its role in AD pathogenesis signalling pathways. It also explores the possibility of targeting GSK-3β for the management of AD and offers an overview of the present research work in preclinical and clinical studies to produce GSK-3β inhibitors.

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

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

Unveiling new thiazole-clubbed piperazine derivatives as multitarget anti-AD: Design, synthesis, and in silico studies

New thiazole-clubbed piperazine derivatives were designed, synthesized, evaluated for their inhibitory capabilities against human acetylcholinesterase and butyrylcholinesterase (hAChE and/or hBuChE) and β-amyloid (Aβ) aggregation, and investigated for their metal chelating potential as multitarget agents for the treatment of Alzheimer's disease. Compounds 10, 19-21, and 24 showed the highest hAChE inhibitory activity at submicromolar concentrations, of which compound 10 was the most potent with a half-maximal inhibitory concentration (IC50) value of 0.151 μM. Compounds 10 and 20 showed the best hBuChE inhibitory activities (IC50 values of 0.135 and 0.103 μM, respectively), in addition to remarkable Aβ1-42 aggregation inhibitory activities and metal chelating capabilities. Both compounds were further evaluated against human neuroblastoma SH-SY5Y and PC12 neuronal cells, where they proved noncytotoxic at their active concentrations against hAChE or hBuChE. They also offered a significant neuroprotective effect against Aβ25-35-induced cytotoxicity in human neuroblastoma SH-SY5Y cells. Compound 10 displayed acceptable physicochemical properties and could pass the blood-brain barrier. The molecular docking study revealed the good binding interactions of compound 10 with the key amino acids of both the catalytic active site and the peripheral anionic site of hAChE, explaining its significant potency.

Catalytic Nanoparticles in Biomedical Applications: Exploiting Advanced Nanozymes for Therapeutics and Diagnostics

Catalytic nanoparticles (CNPs) as heterogeneous catalyst reveals superior activity due to their physio-chemical features, such as high surface-to-volume ratio and unique optical, electric, and magnetic properties. The CNPs, based on their physio-chemical nature, can either increase the reactive oxygen species (ROS) level for tumor and antibacterial therapy or eliminate the ROS for cytoprotection, anti-inflammation, and anti-aging. In addition, the catalytic activity of nanozymes can specifically trigger a specific reaction accompanied by the optical feature change, presenting the feasibility of biosensor and bioimaging applications. Undoubtedly, CNPs play a pivotal role in pushing the evolution of technologies in medical and clinical fields, and advanced strategies and nanomaterials rely on the input of chemical experts to develop. Herein, a systematic and comprehensive review of the challenges and recent development of CNPs for biomedical applications is presented from the viewpoint of advanced nanomaterial with unique catalytic activity and additional functions. Furthermore, the biosafety issue of applying biodegradable and non-biodegradable nanozymes and future perspectives are critically discussed to guide a promising direction in developing span-new nanozymes and more intelligent strategies for overcoming the current clinical limitations.

Novel multifunctional tacrine-donepezil hybrids against Alzheimer's disease: Design synthesis and bioactivity studies

A series of tacrine-donepezil hybrids were synthesized as potential multifunctional anti-Alzheimer's disease (AD) compounds. For this purpose, tacrine and the benzylpiperidine moiety of donepezil were fused with a hydrazone group to achieve a small library of tacrine-donepezil hybrids. In agreement with the design, all compounds showed inhibitory activity toward both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with IC50 values in the low micromolar range. Kinetic studies on the most potent cholinesterase (ChE) inhibitors within the series showed a mixed-type inhibition mechanism on both enzymes. Also, the docking studies indicated that the compounds inhibit ChEs by dual binding site (DBS) interactions. Notably, tacrine-donepezil hybrids also exhibited significant neuroprotection against H2O2-induced cell death in a differentiated human neuroblastoma (SH-SY5Y) cell line at concentrations close to their IC50 values on ChEs and showed high to medium blood-brain barrier (BBB) permeability on human cerebral microvascular endothelial cells (HBEC-5i). Besides, the compounds do not cause remarkable toxicity in a human hepatocellular carcinoma cell line (HepG2) and SH-SY5Y cells. Additionally, the compounds were predicted to also have good bioavailability. Among the tested compounds, H4, H16, H17, and H24 stand out with their biological profile. Taken together, the proposed novel tacrine-donepezil scaffold represents a promising starting point for the development of novel anti-ChE multifunctional agents against AD.

Neuromodulation by nanozymes and ultrasound during Alzheimer's disease management

Alzheimer's disease (AD) is a neurodegenerative disorder with complex pathogenesis and effective clinical treatment strategies for this disease remain elusive. Interestingly, nanomedicines are under extensive investigation for AD management. Currently, existing redox molecules show highly bioactive property but suffer from instability and high production costs, limiting clinical application for neurological diseases. Compared with natural enzymes, artificial enzymes show high stability, long-lasting catalytic activity, and versatile enzyme-like properties. Further, the selectivity and performance of artificial enzymes can be modulated for neuroinflammation treatments through external stimuli. In this review, we focus on the latest developments of metal, metal oxide, carbon-based and polymer based nanozymes and their catalytic mechanisms. Recent developments in nanozymes for diagnosing and treating AD are emphasized, especially focusing on their potential to regulate pathogenic factors and target sites. Various applications of nanozymes with different stimuli-responsive features were discussed, particularly focusing on nanozymes for treating oxidative stress-related neurological diseases. Noninvasiveness and focused application to deep body regions makes ultrasound (US) an attractive trigger mechanism for nanomedicine. Since a complete cure for AD remains distant, this review outlines the potential of US responsive nanozymes to develop future therapeutic approaches for this chronic neurodegenerative disease and its emergence in AD management.

Insight into the activation mechanism of carbonic anhydrase(II) through 2-(2-aminoethyl)-pyridine: a promising pathway for enhanced enzymatic activity

Activation of human carbonic anhydrase II (hCA II) holds great promise for treating memory loss symptoms associated with Alzheimer's disease. Despite its importance, the activation mechanism of hCA II has been largely overlooked in favor of the well-studied inhibition mechanism. To address this unexplored realm, we use first-principles calculations to tease out the activation mechanism of hCA II using 2-(2-aminoethyl)-pyridine (2-2AEPy), a promising in vitro activator. We explored both stepwise and concerted mechanisms via both available nitrogen sites of 2-2AEPy: (i) aminoethyl group (Nα) and (ii) pyridine ring (Nβ). Our results show that a concerted mechanism via Nα holds the key to hCA II activation. The activation process of the concerted mechanism exhibits the characteristics of an exergonic reaction, wherein the transition state resembles the reactant with a notably low imaginary frequency of 452.4i cm-1 and barrier height of 5.2 kcal mol-1. Such meager transition barriers propel the activation of hCA II at in vivo temperatures. These findings initiate future research into hCA II activation mechanisms and the development of efficient activators, which may lead to promising therapeutic interventions for Alzheimer's disease.

Near-infrared II theranostic agents for the diagnosis and treatment of Alzheimer's disease

BACKGROUND

Near-infrared II theranostic agents have gained great momentum in the research field of AD owing to the appealing advantages. Recently, an array of activatable NIR-II fluorescence probes has been developed to specifically monitor pathological targets of AD. Furthermore, various NIR-II-mediated nanomaterials with desirable photothermal and photodynamic properties have demonstrated favorable outcomes in the management of AD.

METHODS

We summerized amounts of references and focused on small-molecule probes, nanomaterials, photothermal therapy, and photodynamic therapy based on NIR-II fluorescent imaging for the diagnosis and treatment in AD. In addition, design strategies for NIR-II-triggered theranostics targeting AD are presented, and some prospects are also addressed.

RESULTS

NIR-II theranostic agents including small molecular probes and nanoparticles have received the increasing attention for biomedical applications. Meanwhile, most of the theranostic agents exhibited the promising results in animal studies. To our surprise, the multifunctional nanoplatforms also show a great potential in the diagnosis and treatment of AD.

CONCLUSIONS

Although NIR-II theranostic agents showed the great potential in diagnosis and treatment of AD, there are still many challenges: 1) Faborable NIR-II fluorohpores are still lacking; 2) Biocompatibility, bioseurity and dosage of NIR-II theranostic agents should be further revealed; 3) New equipment and software associated with NIR-II imaging system should be explored.

First-in-Class Selenium-Containing Potent Serotonin Receptor 5-HT6 Agents with a Beneficial Neuroprotective Profile against Alzheimer's Disease

Alzheimer's disease (AD) has a complex and not-fully-understood etiology. Recently, the serotonin receptor 5-HT6 emerged as a promising target for AD treatment; thus, here a new series of 5-HT6R ligands with a 1,3,5-triazine core and selenoether linkers was explored. Among them, the 2-naphthyl derivatives exhibited strong 5-HT6R affinity and selectivity over 5-HT1AR (13-15), 5-HT7R (14 and 15), and 5-HT2AR (13). Compound 15 displayed high selectivity for 5-HT6R over other central nervous system receptors and exhibited low risk of cardio-, hepato-, and nephrotoxicity and no mutagenicity, indicating its "drug-like" potential. Compound 15 also demonstrated neuroprotection against rotenone-induced neurotoxicity as well as antioxidant and glutathione peroxidase (GPx)-like activity and regulated antioxidant and pro-inflammatory genes and NRF2 nuclear translocation. In rats, 15 showed satisfying pharmacokinetics, penetrated the blood-brain barrier, reversed MK-801-induced memory impairment, and exhibited anxiolytic-like properties. 15's neuroprotective and procognitive-like effects, stronger than those of the approved drug donepezil, may pave the way for the use of selenotriazines to inhibit both causes and symptoms in AD therapy.

Peptide-antifouling interface for monitoring β-amyloid based on electrochemiluminescence resonance energy transfer

In this study, a novel antifouling electrochemiluminescence (ECL) analytical platform has been developed for the highly sensitive quantification of β-amyloid (Aβ) peptides based on the ECL resonance energy transfer (ECL-RET) mechanism. Specifically, glassy carbon electrodes (GCE) were initially coated with graphite-phase carbon nitride (g-C3N4) nanosheets, followed by the electropolymerization of polyaniline (PANI) onto the electrode surface. Subsequently, a promising peptide motif candidate (COOH-CPPPPDKDKDKDKKLVFF) was immobilized onto the PANI-modified electrode, functioning as a critical component for both antifouling and specific recognition of full-length Aβ peptides. Furthermore, this peptide motif demonstrated inhibitory effects on Aβ aggregation and dissociation. Upon immobilization of the peptide motif, Aβ aptamer-CdS QDs were bound to the electrode surface through peptide-specific interactions with Aβ, thereby facilitating the highly sensitive ECL detection of Aβ. Under the optimal conditions, the proposed biosensor exhibited an Aβ detection range from 0.1 pM to 100 nM with a detection limit of 16.1 fM. As such, this innovative platform offers a straightforward approach to antifouling, quantification, and monitoring of Aβ concentrations in the blood samples.

Targeting Amyloids with Coated Nanoparticles: A Review on Potential Combinations of Nanoparticles and Bio-Compatible Coatings

Amyloidosis is the major cause of many neurodegenerative diseases, such as, Alzheimer's and Parkinson's where the misfolding and deposition of a previously functional protein make it inept for carrying out its function. The genesis of amyloid fibril formation and the strategies to inhibit it have been studied extensively, although some parts of this puzzle still remain unfathomable to date. Many classes of molecules have been explored as potential drugs in vitro, but their inability to work in vivo by crossing the blood-brain-barrier has made them an inadequate treatment option. In this regard, nanoparticles (NPs) have turned out to be an exciting alternative because they could overcome many drawbacks of previously studied molecules and provide advantages, such as, greater bioavailability of molecules and target-specific delivery of drugs. In this paper, we present an overview on several coated NPs which have shown promising efficiency in inhibiting fibril formation. A hundred and thirty papers published in the past two decades have been comprehensively reviewed, which majorly encompass NPs comprising different materials like gold, silver, iron-oxide, poly(lactic-co-glycolic acid), polymeric NP, etc., which are coated with various molecules of predominantly natural origin, such as different types of amino acids, peptides, curcumin, drugs, catechin, etc. We hope that this review will shed light on the advancement of symbiotic amalgamation of NPs with molecules from natural sources and will inspire further research on the tremendous therapeutic potential of these combinations for many amyloid-related diseases.

Multi-targeted anti-Alzheimer's agents: Synthesis, biological evaluation, and molecular modeling study of some pyrazolopyridine hybrids

A new series of compounds bearing a pyrazolopyridine scaffold was synthesized as integrated anti-Alzheimer's disease (AD) multi-targeted ligands. Compounds 49 and 51 showed remarkable activity as hAChE inhibitors with IC50 values of 0.17 and 0.16 μM, respectively; and proved to be active hBuChE inhibitors with IC50 values 0.17 and 0.69 μM, eight and two-fold more active than the reference compound rivastigmine, respectively. Compounds 49 and 51 showed potent GSK3β inhibition with IC50 values of 0.21 and 0.26 μM, respectively compared to L807mts. Also, 49 and 51 showed 66.0 and 60.0% as tau protein aggregation inhibitors; and Aβ1-42 self-aggregation inhibitors with 79.0 and 75.0% respectively. Furthermore, 49 and 51 could bind virtually with the PAS affecting Aβ aggregation, thus preventing Aβ-dependent neurotoxicity. They proved to have the ability to chelate bio-metals such as Fe2+, Cu2+, and Zn2+ preventing their oxidative damage in the brain of AD patients, in addition to their safety upon WI-38 cell line. Both compounds could virtually penetrate BBB and obeyed Lipinski's rule of five. Compounds 49 and 51 could be considered as MTDLs for AD patients and the obtained model and pattern of substitution could be used for further development of new multi-targeted anti-Alzheimer's agents.

Target-Specific Bioorthogonal Reactions for Precise Biomedical Applications

Bioorthogonal chemistry is a promising toolbox for dissecting biological processes in the native environment. Recently, bioorthogonal reactions have attracted considerable attention in the medical field for treating diseases, since this approach may lead to improved drug efficacy and reduced side effects via in situ drug synthesis. For precise biomedical applications, it is a prerequisite that the reactions should occur in the right locations and on the appropriate therapeutic targets. In this minireview, we highlight the design and development of targeted bioorthogonal reactions for precise medical treatment. First, we compile recent strategies for achieving target-specific bioorthogonal reactions. Further, we emphasize their application for the precise treatment of different therapeutic targets. Finally, a perspective is provided on the challenges and future directions of this emerging field for safe, efficient, and translatable disease treatment.

Chromone-based monoamine oxidase B inhibitor with potential iron-chelating activity for the treatment of Alzheimer's disease

Based on the multitarget-directed ligands (MTDLs) strategy, a series of chromone-hydroxypyridinone hybrids were designed, synthesised, and evaluated as potential multimodal anti-AD ligands. Prospective iron-chelating effects and favourable monoamine oxidase B (MAO-B) inhibitory activities were observed for most of the compounds. Pharmacological assays led to the identification of compound 17d, which exhibited favourable iron-chelating potential (pFe³⁺ = 18.52) and selective hMAO-B inhibitory activity (IC₅₀ = 67.02 ± 4.3 nM, SI = 11). Docking simulation showed that 17d occupied both the substrate and the entrance cavity of MAO-B, and established several key interactions with the pocket residues. Moreover, 17d was determined to cross the blood-brain barrier (BBB), and can significantly ameliorate scopolamine-induced cognitive impairment in AD mice. Despite its undesired pharmacokinetic property, 17d remains a promising multifaceted agent that is worth further investigation.

Butyrylcholinesterase signal sequence self-aggregates and enhances amyloid fibril formation in vitro

Alzheimer's disease (AD) pathogenesis has been attributed to extracellular aggregates of amyloid β (Aβ) plaques and neurofibrillary tangles in the human brain. It has been reported that butyrylcholinesterase (BChE) also accumulates in the brain Aβ plaques in AD. We have previously found that the BChE substitution in 5'UTR caused an in-frame N-terminal extension of 41 amino acids of the BChE signal peptide. The resultant variant with a 69 amino acid signal peptide, designated N-BChE, could play a role in AD development. Here, we report that the signal sequence of the BChE, if produced in an extended 69 aa version, can self-aggregate and could form seeds that enhance amyloid fibril formation in vitro in a dose-dependent manner and create larger co-aggregates. Similar phenomena could have been observed in the human brain if such an extended form of the signal sequence had been, in some circumstances, translated.

Recent progress of small-molecule-based theranostic agents in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of neurodegenerative dementia. As a multifactorial disease, AD involves several etiopathogenic mechanisms, in which multiple pathological factors are interconnected with each other. This complicated and unclear pathogenesis makes AD lack effective diagnosis and treatment. Theranostics, exerting the synergistic effect of diagnostic and therapeutic functions, would provide a promising strategy for exploring AD pathogenesis and developing drugs for combating AD. With the efforts in small drug-like molecules for both diagnosis and treatment of AD, small-molecule-based theranostic agents have attracted significant attention owing to their facile synthesis, high biocompatibility and reproducibility, and easy clearance from the body through the excretion systems. In this review, the small-molecule-based theranostic agents reported in the literature for anti-AD are classified into four groups according to their diagnostic modalities. Their design rationales, chemical structures, and working mechanisms for theranostics are summarized. Finally, the opportunities for small-molecule-based theranostic agents in AD are also proposed.

A Fenton Approach to Aromatic Radical Cations and Diarylmethane Synthesis

Manipulating carbon-centered radicals to add to electron-deficient systems is a well-precedented process. By coupling the Fe(II)-mediated Fenton reaction with the Fe(III)-mediated single-electron oxidation of anisolic compounds, we demonstrate how electron-rich carbon-centered radicals can react with electron-rich arenes through a radical-polar cascade pathway. This bioinspired approach produces diarylmethane derivatives from simple unfunctionalized precursors.

Target-modulated mineralization of wood channels as enzyme-free electrochemical sensors for detecting amyloid-β species

Alzheimer's disease (AD) is an irreversible brain disorder, which has been found to be associated with neurotoxic amyloid-β oligomers (AβO). The early diagnosis of AD is still a great challenge. Herein, inspired by the hierarchical channel structure of natural wood, we design and demonstrate a low-cost and sensitive wood channel-based fluidic membrane for electrochemical sensing of AβO1-42. In this design, Zn/Cu-2-methylimidazole (Zn/Cu-Hmim) with artificial peroxidase (POD)-like activity was asymmetrically fabricated at one side of the wood channels by biomimetic mineralization and a subsequent ion exchange reaction. The strong affinity between Cu(II) and AβO1-42 enables Cu(II) species in Zn/Cu-Hmim to be extracted by AβO1-42, thus suppressing the POD-like performance via Zn/Cu-Hmim disassembly. Using Zn/Cu-Hmim to catalyze the oxidation reaction of 2,2'-diazo-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) by H2O2, the current-voltage (I-V) properties of wood channels are influenced by the generated oxidation product (ABTS•+), thus providing information useful for the quantitative analysis of AβO1-42. Importantly, the three aggregation states of Aβ1-42 (AβM1-42, AβO1-42, and AβF1-42) can also be identified, owing to the affinity difference and available reaction sites. The proposed wood membrane provides a novel, assessable, and scalable channel device to develop sensitive electrochemical sensors; moreover, the sustainable wood materials represent alternative candidates for developing channel-structured sensing platforms.

Influence of metal binding on the conformational landscape of neurofilament peptides

In order to understand the preferred modes of chelation in metal-binding peptides, quantum mechanical calculations can be used to compute energies, resulting in a hierarchy of binding affinities. These calculations often produce increasing stabilization energies the higher the coordination of the complex. However, as the coordination of a metal increases, the conformational freedom of the polypeptide chain is inevitably reduced, resulting in an entropic penalty. Estimating the magnitude of this penalty from the many different degrees of freedom of biomolecular systems is very challenging, and as a result this contribution to the free energy is often ignored. Here we explore this problem focusing on a family of phosphorylated neuropeptides that bind to aluminum. We find that there is a general negative correlation between both stabilization energy and entropy. Our results suggest that a subtle interplay between enthalpic and entropic forces will determine the population of the most favourable species. Additionally, we discuss the requirements for a possible "Metal Ion Hypothesis" based on our findings.

The amyloid cascade hypothesis: an updated critical review

Results from recent clinical trials of antibodies that target amyloid-β (Aβ) for Alzheimer's disease have created excitement and have been heralded as corroboration of the amyloid cascade hypothesis. However, while Aβ may contribute to disease, genetic, clinical, imaging and biochemical data suggest a more complex aetiology. Here we review the history and weaknesses of the amyloid cascade hypothesis in view of the new evidence obtained from clinical trials of anti-amyloid antibodies. These trials indicate that the treatments have either no or uncertain clinical effect on cognition. Despite the importance of amyloid in the definition of Alzheimer's disease, we argue that the data point to Aβ playing a minor aetiological role. We also discuss data suggesting that the concerted activity of many pathogenic factors contribute to Alzheimer's disease and propose that evolving multi-factor disease models will better underpin the search for more effective strategies to treat the disease.

Metal Binding of Alzheimer's Amyloid-β and Its Effect on Peptide Self-Assembly

Metal ions have been identified as key factors modulating the aggregation of amyloid-β peptide (Aβ) implicated in Alzheimer's disease (AD). The presence of elevated levels of metal ions in the amyloid plaques in AD patients supports the notion that the dysfunction of metal homeostasis is connected to the development of AD pathology. Here, recent findings from high- and low-resolution biophysical techniques are put into perspective, providing detailed insights into the molecular structures and dynamics of metal-bound Aβ complexes and the effect of metal ions on the Aβ aggregation process. In particular, the development of theoretical kinetic models deducing different microscopic nucleation events from the macroscopic aggregation behavior has enabled deciphering of the effect of metal ions on specific nucleation processes. In addition to these macroscopic measurements of bulk aggregation to quantify microscopic rates, recent NMR studies have revealed details about the structures and dynamics of metal-Aβ complexes, thereby linking structural events to bulk aggregation. Interestingly, transition-metal ions, such as copper, zinc, and silver ions, form a compact complex with the N-terminal part of monomeric Aβ, respectively, where the metal-bound "folded" state is in dynamic equilibrium with an "unfolded" state. The rates and thermodynamic features of these exchange dynamics have been determined by using NMR relaxation dispersion experiments. Additionally, the application of specifically tailored paramagnetic NMR experiments on the Cu(II)-Aβ complex has been fruitful in obtaining structural constraints within the blind sphere of conventional NMR experiments. This enables the determination of molecular structures of the "folded" Cu(II)-coordinated N-terminal region of Aβ. Furthermore, the discussed transition-metal ions modulate Aβ self-assembly in a concentration-dependent manner, where low metal ion concentrations inhibit Aβ fibril formation, while at high metal ion concentrations other processes occur, resulting in amorphous aggregate formation. Remarkably, the metal-Aβ interaction predominately reduces one specific nucleation step, the fibril-end elongation, whereas primary and surface-catalyzed secondary nucleation mechanisms are less affected. Specific inhibition of fibril-end elongation theoretically predicts an enhanced generation of Aβ oligomers, which is an interesting contribution to understanding metal-Aβ-associated neurotoxic effects. Taken together, the metal binding process creates a metal-bound Aβ complex, which is seemingly inert to aggregation. This process hence efficiently reduces the aggregation-prone peptide pool, which on the macroscopic level is reflected as slower aggregation kinetics. Thus, the specific binding of metals to the Aβ monomer can be linked to the macroscopic inhibitory effect on Aβ bulk aggregation, providing a molecular understanding of the Aβ aggregation mechanism in the presence of metal ions, where the metal ion can be seen as a minimalist agent against Aβ self-assembly. These insights can help to target Aβ aggregation in vivo, where metal ions are key factors modulating the Aβ self-assembly and Aβ-associated neurotoxicity.

Metal ion mediated aggregation of Alzheimer's disease peptides and proteins in solutions and at surfaces

Although the pathogenesis of Alzheimer's disease (AD) is still unclear, abnormally high concentrations of metal ions, like copper, iron and zinc, were found in senile plaques of AD brain, which inspires extensive studies on the fundamental molecular interactions of metal ions with the pathogenic hallmarks, amyloid-β (Aβ) peptides and tau proteins, respectively forming senile plaques and neurofibrillary tangles (NFTs) in AD brains. Early works concern the concentration effect of the metal ions on Aβ and tau aggregation. Yet, it is obvious that the surrounding environment of the metal ions must also be considered, not just the metal ions as free accessible forms in the solution phase. The most important surrounding environment in vivo is a very large surface area from cell membranes and other macromolecular surfaces. These bio-interfaces make the kinetic pathways of metal ion mediated Aβ and tau aggregation radically different from those in the solution phase. To better understand the role of metal ions in AD peptide and protein aggregation, we summarize and discuss the recent achievements in the research of metal ion mediated Aβ and tau aggregation, particularly the corresponding mechanism differences between the solution phase and the surface environment. The metal ion chelation therapy for AD is also discussed from the point of the surface pool of metal ions.

Design of aggregation-induced emission-active fluorogen-based nanoparticles for imaging and scavenging Alzheimer's β-amyloid by photo-oxygenation

Photo-oxygenation has emerged as an effective modality for scavenging Alzheimer's amyloid-β (Aβ) plaques. However, limitations of the current photo-oxidants, such as low Aβ-targeting and single functionality, hinder the scavenging of Aβ plaques via photo-oxygenation. Herein, based on an aggregation-induced emission (AIE)-active fluorogen (named TPMD), we designed AIE photo-oxidant nanoparticles (T-LD NPs) for Aβ imaging, inhibition, and disaggregation. The T-LD NPs were prepared by the assembly of hydrophobic TPMD with an Aβ-targeting peptide (LPPFD, L) conjugated amphiphilic polymer (DSPE-PEG). Such T-LD NPs could specifically label Aβ plaques for image-guided therapy. Under laser irradiation, T-LD NPs generated a plethora of reactive oxygen species (ROS), including 1O2, ˙OH, and O2˙-, to oxygenate Aβ species, leading to the potent inhibition of Aβ fibrillization, and significant alleviation of Aβ-mediated neurotoxicity (36% to 10% at 20 μg mL-1). Notably, T-LD NPs could rapidly disaggregate mature Aβ fibrils into fractured β-sheet rich aggregates via photo-oxygenation, resulting in alleviated cytotoxicity. In vivo studies revealed that the photo-activated T-LD NPs scavenged amyloid plaques in the transgenic C. elegans strain CL2006 and extended the lifespan by 4 days. Taken together, this multifunctional T-LD NP integrated Aβ-targeting, near-infrared fluorescence imaging, and photo-oxygenation, provides a new strategy for the development of multifunctional AIE photo-oxidants for the treatment of Alzheimer's disease.

Designing multi-target-directed flavonoids: a strategic approach to Alzheimer's disease

The underlying causes of Alzheimer's disease (AD) remain a mystery, with multiple pathological components, including oxidative stress, acetylcholinesterase, amyloid-β, and metal ions, all playing a role. Here we report a strategic approach to designing flavonoids that can effectively tackle multiple pathological elements involved in AD. Our systematic investigations revealed key structural features for flavonoids to simultaneously target and regulate pathogenic targets. Our findings led to the development of a highly promising flavonoid that exhibits a range of functions, based on a complete structure-activity relationship analysis. Furthermore, our mechanistic studies confirmed that this flavonoid's versatile reactivities are driven by its redox potential and direct interactions with pathogenic factors. This work highlights the potential of multi-target-directed flavonoids as a novel solution in the fight against AD.

Isotope dilution LA-ICP-MS for quantitative imaging of trace elements in mouse brain sections

Isotope dilution (ID) analysis is considered one of the most accurate quantitative methods. However, it has not been widely applied to the quantitative imaging of trace elements in biological samples using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), mainly because of difficulties in homogeneously mixing enriched isotopes (the spike) with the sample (e.g., a tissue section). In this study, we present a novel method for the quantitative imaging of trace elements (copper and zinc) in mouse brain sections using ID-LA-ICP-MS. We used an electrospray-based coating device (ECD) to evenly distribute a known amount of the spike (⁶⁵Cu and ⁶⁷Zn) on the sections. The optimal conditions for this process involved evenly distributing the enriched isotopes on mouse brain sections mounted on indium tin oxide (ITO) glass slides using the ECD with the 10 mg g^-1 ɑ-cyano-4-hydroxycinnamic acid (CHCA) in methanol at 80 °C. The mass of the spiked isotopes and the tissue sections on the ITO slides was calculated by weighing them on an analytical balance. Quantitative images of Cu and Zn in Alzheimer's disease (AD) mouse brain sections were obtained using ID-LA-ICP-MS. These imaging results showed that Cu and Zn concentrations in various brain regions typically ranged from 10 to 25 μg g^-1 and 30-80 μg g^-1, respectively. But it is worth noting that the hippocampus contained up to 50 μg g^-1 of Zn, while the cerebral cortex and hippocampus had Cu contents as high as 150 μg g^-1. These results were validated by acid digestion and solution analysis with ICP-MS. The novel ID-LA-ICP-MS method provides an accurate and reliable means for quantitative imaging of biological tissue sections.

Design, synthesis and biological evaluation of new multi-target scutellarein hybrids for treatment of Alzheimer's disease

Scutellarein hybrids were designed, synthesized and evaluated as multifunctional therapeutic agents for the treatment of Alzheimer's disease (AD). Compounds 11a-i, containing a 2-hydroxymethyl-3,5,6-trimethylpyrazine fragment at the 7-position of scutellarein, were found to have balanced and effective multi-target potencies against AD. Among them, compound 11e exhibited the most potent inhibition of electric eel and human acetylcholinesterase enzymes with IC50 values of 6.72 ± 0.09 and 8.91 ± 0.08 μM, respectively. In addition, compound 11e displayed not only excellent inhibition of self- and Cu2+-induced Aβ1-42 aggregation (91.85% and 85.62%, respectively) but also induced disassembly of self- and Cu2+-induced Aβ fibrils (84.54% and 83.49% disaggregation, respectively). Moreover, 11e significantly reduced tau protein hyperphosphorylation induced by Aβ25-35, and also exhibited good inhibition of platelet aggregation. A neuroprotective assay demonstrated that pre-treatment of PC12 cells with 11e significantly decreased lactate dehydrogenase levels, increased cell viability, enhanced expression of relevant apoptotic proteins (Bcl-2, Bax and caspase-3) and inhibited RSL3-induced PC12 cell ferroptosis. Furthermore, hCMEC/D3 and hPepT1-MDCK cell line permeability assays indicated that 11e would have optimal blood-brain barrier and intestinal absorption characteristics. In addition, in vivo studies revealed that compound 11e significantly attenuated learning and memory impairment in an AD mice model. Toxicity experiments with the compound did not reveal any safety concerns. Notably, 11e significantly reduced β-amyloid precursor protein (APP) and β-site APP cleaving enzyme-1 (BACE-1) protein expression in brain tissue of scopolamine-treated mice. Taken together, these outstanding properties qualified compound 11e as a promising multi-target candidate for AD therapy, worthy of further studies.

Stretching the chains: the destabilizing impact of Cu2+ and Zn2+ ions on K48-linked diubiquitin

Ubiquitin signalling and metal homeostasis play key roles in controlling several physiological cellular activities, including protein trafficking and degradation. While some relationships between these two biochemical pathways have started to surface, our knowledge of their interplay remains limited. Here, we employ a variety of techniques, such as circular dichroism, differential scanning calorimetry, pressure perturbation calorimetry, fluorescence emission, SDS-PAGE, and small-angle X-ray scattering (SAXS) to evaluate the impact of Cu2+ and Zn2+ ions on the structure and stability of K48 linked diubiquitin (K48-Ub2), a simple model for polyubiquitin chains. The SAXS analysis results show that the structure of the metal-free protein is similar to that observed when the protein is bound to the E2 conjugating enzyme, lending support to the idea that the structure of unanchored K48-linked ubiquitin chains is sufficient for identification by conjugating enzymes without the need for an induced fit mechanism. Our results indicate that K48-Ub2 can coordinate up to four metal ions with both copper and zinc ions inducing slight changes to the secondary structure of the protein. However, we noted significant distinctions in their impacts on protein stability and overall architecture. Specifically, Cu2+ ions resulted in a destabilization of the protein structure, which facilitated the formation of dimer aggregates. Next, we observed a shift in the conformational dynamics of K48-Ub2 toward less compact and more flexible states upon metal ion binding, with Zn2+ inducing a more significant effect than Cu2+ ions. Our structural modelling study demonstrates that both metal ions induced perturbations in the K48-Ub2 structure, leading to the separation of the two monomers thus inhibiting interactions with E2 enzymes. In conclusion, the findings from this study enhance our comprehension of the mechanisms underlying Ub chains recognition. Moreover, they strengthen the notion that drug discovery initiatives aimed at targeting metal-mediated disruptions in Ub signaling hold great potential for treating a wide range of diseases that stem from abnormal protein accumulation.

Transition metal ions and neurotransmitters: coordination chemistry and implications for neurodegeneration

Neurodegeneration is characterized by a disturbance in neurotransmitter-mediated signaling pathways. Recent studies have highlighted the significant role of transition metal ions, including Cu(i/ii), Zn(ii), and Fe(ii/iii), in neurotransmission, thereby making the coordination chemistry of neurotransmitters a growing field of interest in understanding signal dysfunction. This review outlines the physiological functions of transition metal ions and neurotransmitters, with the metal-binding properties of small molecule-based neurotransmitters and neuropeptides. Additionally, we discuss the structural and conformational changes of neurotransmitters induced by redox-active metal ions, such as Cu(i/ii) and Fe(ii/iii), and briefly describe the outcomes arising from their oxidation, polymerization, and aggregation. These observations have important implications for neurodegeneration and emphasize the need for further research to develop potential therapeutic strategies.

Interaction studies of oxindole-derivatives with β-amyloid peptides inhibiting its aggregation induced by metal ions

Some hydrazones and Schiff bases derived from isatin, an endogenous oxindole formed in the metabolism of tryptophan, were obtained to investigate their effects on in vitro aggregation of β-amyloid peptides (Aβ), macromolecules implicated in Alzheimer's disease. Some hydrazone ligands, prepared by condensation reactions of isatin with hydrazine derivatives, showed a large affinity binding to the synthetic peptides Aβ, particularly to Aβ1-16. Measurements by NMR spectroscopy indicated that those interactions occur mainly at the metal binding site of the peptide, involving His6, His13, and His14 residues, and that hydrazone E-diastereoisomer interacts preferentially with the amyloid peptides. Experimental results were consistent with simulations using a docking approach, where it is demonstrated that the amino acid residues Glu3, His6, His13, and His14 are those that mostly interact with the ligands. Further, these oxindole-derived ligands can efficiently chelate copper(II) and zinc(II) ions, forming moderate stable [ML] 1:1 species. The corresponding formation constants were determined by UV/Vis spectroscopy, by titrations of the ligands with increasing amounts of metal salts, and the obtained log K values were in the range 2.74 to 5.11. Both properties, good affinity for amyloid peptides, and reasonably good capacity of chelating biometal ions, like copper and zinc, can explain the efficient inhibition of Aβ fragments aggregation, as shown by experiments carried out with the oxindole derivatives in the presence of metal ions.

Modified Tacrine Derivatives as Multitarget-Directed Ligands for the Treatment of Alzheimer's Disease: Synthesis, Biological Evaluation, and Molecular Modeling Study

To develop multitarget-directed ligands (MTDLs) as potential treatments for Alzheimer's disease (AD) and to shed light on the effect of the chromene group in designing these ligands, 35 new tacrine-chromene derivatives were designed, synthesized, and biologically evaluated. Compounds 5c and 5d exhibited the most desirable multiple functions for AD; they were strong hAChE inhibitors with IC₅₀ values of 0.44 and 0.25 μM, respectively. Besides, their potent BuChE inhibitory activity was 10- and 5-fold more active than rivastigmine with IC₅₀ = 0.08 and 0.14 μM, respectively. Moreover, they could bind to the peripheral anionic site (PAS), influencing Aβ aggregation and decreasing Aβ-related neurodegeneration, especially compound 5d, which was 8 times more effective than curcumin with IC₅₀ = 0.74 μM and 76% inhibition at 10 μM. Compounds 5c and 5d showed strong BACE-1 inhibition at the submicromolar level with IC₅₀ = 0.38 and 0.44 μM, respectively, which almost doubled the activity of curcumin. They also showed single-digit micromolar inhibitory activity against MAO-B with IC₅₀ = 5.15 and 2.42 μM, respectively. They also had antioxidant activities and showed satisfactory metal-chelating properties toward Fe⁺², Zn⁺², and Cu⁺², inhibiting oxidative stress in AD brains. Furthermore, compounds 5c and 5d showed acceptable relative safety upon normal cells SH-SY5Y and HepG2. It was shown that 5c and 5d were blood-brain barrier (BBB) penetrants by online prediction. Taken together, these multifunctional properties highlight that compounds 5c and 5d can serve as promising candidates for the further development of multifunctional drugs against AD.

An AIE-Active NIR Fluorescent Probe with Good Water Solubility for the Detection of Aβ1-42 Aggregates in Alzheimer's Disease

Alzheimer's disease (AD), an amyloid-related disease, seriously endangers the health of elderly individuals. According to current research, its main pathogenic factor is the amyloid protein, which is a kind of fibrillar aggregate formed by noncovalent self-assembly of proteins. Based on the characteristics of aggregation-induced emission (AIE), a bislactosyl-decorated tetraphenylethylene (TPE) molecule TMNL (TPE + malononitrile + lactose), bearing two malononitrile substituents, was designed and synthesized in this work. The amphiphilic TMNL could self-assemble into fluorescent organic nanoparticles (FONs) with near-infrared (NIR) fluorescence emission in physiological PBS (phosphate buffered saline), achieving excellent fluorescent enhancement (47-fold) upon its combination with Aβ_1-42 fibrils. TMNL was successfully applied to image Aβ_1-42 plaques in the brain tissue of AD transgenic mice, and due to the AIE properties of TMNL, no additional rinsing process was necessary. It is believed that the probe reported in this work should be useful for the sensitive detection and accurate localization mapping of Aβ_1-42 aggregates related to Alzheimer's disease.

Biological Oxidations and Nitrations Promoted by the Hemin-Aβ16 Complex

Both β-amyloid (Aβ) peptides and oxidative stress conditions play key roles in Alzheimer's disease. Hemin contributes to the development of the disease as it possesses redox properties and its level increases in pathological conditions or traumatic brain injuries. The aim of this work was to deepen the investigation of the reactivity of the hemin-Aβ₁₆ complex, considering its ability to catalyze oxidation and nitration reactions. We performed kinetic studies in the presence of hydrogen peroxide and nitrite with phenolic and catechol substrates, as well as mass spectrometry studies to investigate the modifications occurring on the peptide itself. The kinetic constants were similar for oxidation and nitration reactions, and their values suggest that the hemin-Aβ₁₆ complex binds negatively charged substrates with higher affinity. Mass spectrometry studies showed that tyrosine residue is the endogenous target of nitration. Hemin degradation analysis showed that hemin bleaching is only partly prevented by the coordinated peptide. In conclusion, hemin has rich reactivity, both in oxidation and nitration reactions on aromatic substrates, that could contribute to redox equilibrium in neurons. This reactivity is modulated by the coordination of the Aβ₁₆ peptide and is only partly quenched when oxidative and nitrative conditions lead to hemin degradation.

Biometals in Alzheimer disease: emerging therapeutic and diagnostic potential of molybdenum and iodine

The current ageing trend of the world population has, in part, accounted for Alzheimer disease (AD) being a public health issue in recent times. Although some progress has been made in clarifying AD-related pathophysiological mechanisms, effective intervention is still elusive. Biometals are indispensable to normal physiological functions of the human body-for example, neurogenesis and metabolism. However, their association with AD remains highly controversial. Copper (Cu) and zinc (Zn) are biometals that have been investigated at great length in relation to neurodegeneration, whereas less attention has been afforded to other trace biometals, such as molybdenum (Mo), and iodine. Given the above context, we reviewed the limited number of studies that have evidenced various effects following the usage of these two biometals in different investigative models of AD. Revisiting these biometals via thorough investigations, along with their biological mechanisms may present a solid foundation for not only the development of effective interventions, but also as diagnostic agents for AD.

Unveiling the impact of oxidation-driven endogenous protein interactions on the dynamics of amyloid-β aggregation and toxicity

Cytochrome c (Cyt c), a multifunctional protein with a crucial role in controlling cell fate, has been implicated in the amyloid pathology associated with Alzheimer's disease (AD); however, the interaction between Cyt c and amyloid-β (Aβ) with the consequent impact on the aggregation and toxicity of Aβ is not known. Here we report that Cyt c can directly bind to Aβ and alter the aggregation and toxicity profiles of Aβ in a manner that is dependent on the presence of a peroxide. When combined with hydrogen peroxide (H₂O₂), Cyt c redirects Aβ peptides into less toxic, off-pathway amorphous aggregates, whereas without H₂O₂, it promotes Aβ fibrillization. The mechanisms behind these effects may involve a combination of the complexation between Cyt c and Aβ, the oxidation of Aβ by Cyt c and H₂O₂, and the modification of Cyt c by H₂O₂. Our findings demonstrate a new function of Cyt c as a modulator against Aβ amyloidogenesis.

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

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

Construction of a microcavity-based microfluidic chip with simultaneous SERS quantification of dual biomarkers for early diagnosis of Alzheimer's disease

Since there is no effective Alzheimer's disease (AD)-modifying therapy available currently, early analysis of AD core biomarkers has become one of great significance and common concern in clinical diagnosis. Herein, we designed an Au-plasmonic shell attached polystyrene (PS) microsphere in a microfluidic chip for simultaneous detection of Aβ1-42 and p-Tau181 protein. The corresponding Raman reporters were identified in femto gram level by ultrasensitive surface enhanced Raman spectroscopy (SERS). Both of Raman experimental data and finite-difference time-domain modeling demonstrates the synergetic coupling between PS microcavity with the optical confinement property and the localized surface plasmon resonance (LSPR) of AuNPs, so leading to highly amplified electromagnetic fields at the 'hot spot'. Moreover, the microfluidic system is designed with multiplex testing and control channels in which the AD-related dual proteins were detected quantitatively with a lower limit of 100 fg mL^-1. Thus, the proposed microcavity-based SERS strategy initiates a new way for accurately prediction of AD in human blood samples and provides the potential application for synchronous determination of multiple analytes in general disease assays.

Dual-Mode Ratiometric Electrochemical and Turn-On Fluorescent Detection of Butyrylcholinesterase Utilizing a Single Probe for the Diagnosis of Alzheimer's Disease

Biomarkers detection in blood with high accuracy is crucial for the diagnosis and treatment of many diseases. In this study, the proof-of-concept fabrication of a dual-mode sensor based on a single probe (Re-BChE) using a dual-signaling electrochemical ratiometric strategy and a "turn-on" fluorescent method is presented. The probe Re-BChE was synthesized in a single step and demonstrated dual mode response toward butyrylcholinesterase (BChE), a promising biomarker of Alzheimer's disease (AD). Due to the specific hydrolysis reaction, the probe Re-BChE demonstrated a turn-on current response for BChE at -0.28 V, followed by a turn-off current response at -0.18 V, while the fluorescence spectrum demonstrated a turn-on response with an emission wavelength of 600 nm. The developed ratiometric electrochemical sensor and fluorescence detection demonstrated high sensitivity with BChE concentrations with a low detection limit of 0.08 μg mL^-1 and 0.05 μg mL^-1, respectively. Importantly, the dual-mode sensor presents the following advantages: (1) dual-mode readout can correct the impact of systematic or background error, thereby achieving more accurate results; (2) the responses of dual-mode readout originate from two distinct mechanisms and relatively independent signal transduction, in which there is no interference between two signaling routes. Additionally, compared with the reported single-signal electrochemical assays for BChE, both redox potential signals were detected in the absence of biological interference within a negative potential window. Furthermore, it was discovered that the outcomes of direct dual-mode electrochemical and fluorescence quantifications of the level of BChE in serum were in agreement with those obtained from the use of commercially available assay kits for BChE sensing. This method has the potential to serve as a useful point-of-care tool for the early detection of AD.

Exploring the Multitarget Activity of Wedelolactone against Alzheimer's Disease: Insights from In Silico Study

In this study, Wedelolactone's multitarget activity against Alzheimer's disease was examined using density functional theory and molecular docking techniques. At physiological pH, the pK _a and molar fractions have been estimated. The most likely relative rate constants of two radical scavenger mechanisms are formal hydrogen transfer in a lipid environment and single-electron transfer in a water solvent. Compared to Trolox (k _overall = 8.96 × 10⁴ M^-1 s^-1), Wedelolactone (k _overall = 4.26 × 10⁹ M^-1 s^-1) is more efficient in scavenging the HOO^• radical in an aqueous environment. The chelation capacity of metals was investigated by examining the complexation of the Cu(II) ion at various coordination positions and calculating the complexation kinetic constants. Furthermore, molecular docking simulations showed that the known forms of Wedelolactone at physiological pH effectively inhibited the AChE and BChE enzymes by comparing their activity to that of tacrine (control). Wedelolactone is a promising drug candidate for Alzheimer's disease therapy in light of these findings.

Discovery of novel 5-(2-hydroxyphenyl)-2-phthalide-3(3H)-pyrazolones as balanced multifunctional agents against Alzheimer's disease

Based on previous work, a series of novel 5-(2-hydroxyphenyl)-2-phthalide-3(3H)-pyrazolones derivatives were identified as potential multifunctional therapeutic agents for Alzheimer's disease. Biological evaluation exhibited that these derivatives had great performance against MAO-B, Aβ_1-42 aggregation, oxidative stress and metal ion dyshomeostasis. Among them, 10x was selected as the optimal agent for its excellent MAO-B inhibitory activity (IC₅₀ = 0.41 μM, SI > 24.4), good antioxidant activity (1.16 Trolox equivalent) and anti-Aβ aggregation activity (56.03% and 57.51% for inhibition of self- and Cu²⁺-induced Aβ_1-42 aggregation; 81.91% and 82.40% for disaggregation of self- and Cu²⁺-induced Aβ_1-42 fibrils at 25.0 μM). Besides, 10x also exhibited obvious metal-ion chelating ability, anti-neuroinflammation (NO, TNF-α), neuroprotective activity and BBB permeability. More importantly, in vivo behavioral assessment demonstrated 10x could remarkably improve the memory and cognitive impairment in Aβ_1-42 induced AD mice model. Overall, these test results indicated 10x could serve as a balanced multifunctional anti-AD agent and deserved further research.

Concentration Effect, Structural Properties, and Driving Force on Aβ28 Dimerization with and without Zn2+ Cooperation: Learning from Replica Exchange Sampling

Zn²⁺ is a very important factor in promoting the formation of amyloid beta (Aβ) aggregates and amyloid plaques. The Zn²⁺ -bound Aβ species generate amorphous or low molecular-weight oligomers. However, it is a lack of studies to approach the starting structural features (dimerization) in Aβ nucleation processes with and without Zn²⁺ , which is the key point in understanding Zn²⁺ -induced nucleation mechanisms. To better understand the effect of concentration, structural properties, and the driving force, 14 independent replica exchange molecular dynamics simulations were performed in Aβ₂₈ dimerization with and without Zn²⁺ (zAβ₂₈ ) cooperation. Our scanning results show that the aggregation propensity is easier in Aβ₂₈ -Aβ₂₈ and Aβ₂₈ -zAβ₂₈ systems than zAβ₂₈ -zAβ₂₈ system. In binding property, the Aβ₂₈ -Aβ₂₈ model (-61.5 kcal mol^-1 ) is stronger than zAβ₂₈ -zAβ₂₈ (-26.6 kcal mol^-1 ) and Aβ₂₈ -zAβ₂₈ (-7.24 kcal mol^-1 ) models. Further analysis confirmed that H13 and H14 residues play specific roles in the three systems. The key point is the orientation of N atom of the imidazole ring in histidine residues. Furthermore, we discovered different driving forces for each system. Our current study contributes to the understanding of how the Aβ₂₈ dimer interacts with Zn²⁺ , which could lead to new insights into Zn²⁺ -induced nucleation mechanisms.

Synthesis and Photophysical Study of Tetraphenyl Substituted BODIPY Based Phenyl-Monoselenide Probe for Selective Detection of Superoxide

Selenium containing tetraphenyl substituted BODIPY probe was successfully synthesized from respective selenium aldehyde and tetraphenyl pyrrole using Knoevenagel-type condensation. The product was characterized using various spectroscopic techniques (¹ H, ¹³ C, ⁷⁷Se, ¹¹B, and ¹⁹ F) and mass spectrometry. The probe was found to be selective and sensitive towards detection of superoxide over other ROS with a "turn-off" (quenched) fluorescence response. The detection limit of the probe was found to be 4.87 µM. The probe reacted with superoxide in less than a sec with a stoke shift of 35 nm.

A Nanoenzyme Constructed from Manganese and Strandberg-Type Phosphomolybdate with Versatility in Antioxidant and Modulating Conformation of Aβ Protein Misfolding Aggregates In Vitro

Amyloid β-peptide (Aβ) misfolding aggregates with β-sheet structures and surplus reactive oxygen species (ROS) are both considered to be the culprit of neuronal toxicity in Alzheimer's disease (AD). Therefore, modulating the misfolding mode of Aβ and inhibiting ROS simultaneous has become an important method for anti-AD. Herein, a nanoscale manganese-substituted polyphosphomolybdate (H₂en)₃[Mn(H₂O)₄][Mn(H₂O)₃]₂[P₂Mo₅O₂₃]₂·14.5H₂O (abbreviated as MnPM) (en = ethanediamine) was designed and synthesized by single crystal to single crystal transformation method. MnPM can modulate the β-sheet rich conformation of Aβ aggregates, and thus reduce the formation of toxic species. Moreover, MnPM also possesses the ability to eliminate the free radicals produced by Cu²⁺-Aβ aggregates. It can inhibit the cytotoxicity of β-sheet-rich species and protect synapses of PC12 cells. MnPM combines the conformation modulating ability of Aβ and anti-oxidation ability, which makes a promising multi-funcational molecular with a composite mechanism for the new conceptual designing in treatment of such protein-misfolding diseases.

Anthracene scaffold as highly selective chemosensor for Al3+ and its AIEE activity

Fluorescent chemosensor, 3-(Anthracen-2-yliminomethyl)-benzene-1,2-diol (ANB) has been synthesized by one-step condensation of 2-aminoanthracene and 2,3-dihydroxybenzaldehyde and characterized using ¹H-NMR, FT-IR and Mass spectroscopic techniques. The probe ANB was found to be an efficient 'turn-on' fluorescence chemosensor for the selective detection of Al³⁺ ion over other metal ions in an aqueous solution. The chemosensor exhibits ~ 27-fold enhancement of emission intensity in presence of Al³⁺ ion. Fluorescence quantum values for ANB and (Al³⁺-ANB)-complex are 0.004 and 0.097, respectively. In addition, the binding constant and the limit of detection were found to be 1.22 × 10⁴ M^-1 and 0.391 µM, respectively. The chemosensor ANB binds to Al³⁺ ions in 2:1 stoichiometric ratio which was supported by Job's plot, ¹H-NMR titration and florescence titration. Fluorescence reversibility of the sensor complex was well established by adding EDTA in the same condition and a molecular INHIBIT logic gate was fabricated using this reversible nature of the sensor complex. Additionally, the chemosensor ANB shows a novel aggregation-induced enhanced emission phenomenon, where the aggregate hydrosol of ANB shows enhance emission intensity.

How Can Static and Oscillating Electric Fields Serve in Decomposing Alzheimer's and Other Senile Plaques?

Alzheimer's disease is one of the most common neurodegenerative conditions, which are ascribed to extracellular accumulation of β-amyloid peptides into plaques. This phenomenon seems to typify other related neurodegenerative diseases. The present study uses classical molecular-dynamics simulations to decipher the aggregation-disintegration behavior of β-amyloid peptide plaques in the presence of static and oscillating oriented external electric fields (OEEFs). A long-term disintegration of such plaques is highly desirable since this may improve the prospects of therapeutic treatments of Alzheimer's disease and of other neurodegenerative diseases typified by senile plaques. Our study illustrates the spontaneous aggregation of the β-amyloid, its prevention and breakdown when OEEF is applied, and the fate of the broken aggregate when the OEEF is removed. Notably, we demonstrate that the usage of an oscillating OEEF on β-amyloid aggregates appears to lead to an irreversible disintegration. Insight is provided into the root causes of the various modes of aggregation, as well as into the different fates of OEEF-induced disintegration in oscillating vs static fields. Finally, our simulation results are compared to the well-established TTFields and the Deep Brain Stimulation (DBS) therapies, which are currently used options for treatments of Alzheimer's disease and other related neurodegenerative diseases.

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.

Role of Metal Cations of Copper, Iron, and Aluminum and Multifunctional Ligands in Alzheimer's Disease: Experimental and Computational Insights

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of people around the world. Even though the causes of AD are not completely understood due to its multifactorial nature, some neuropathological hallmarks of its development have been related to the high concentration of some metal cations. These roles include the participation of these metal cations in the production of reactive oxygen species, which have been involved in neuronal damage. In order to avoid the increment in the oxidative stress, multifunctional ligands used to coordinate these metal cations have been proposed as a possible treatment to AD. In this review, we present the recent advances in experimental and computational works aiming to understand the role of two redox active and essential transition-metal cations (Cu and Fe) and one nonbiological metal (Al) and the recent proposals on the development of multifunctional ligands to stop or revert the damaging effects promoted by these metal cations.