A Comparison of Three Fluorophores for the Detection of Amyloid Fibers and Prefibrillar Oligomeric Assemblies. ThT (Thioflavin T); ANS (1-Anilinonaphthalene-8-sulfonic Acid); and bisANS (4,4′-Dianilino-1,1′-binaphthyl-5,5′-disulfonic Acid)

Nano-Collision Electrochemistry for Real-Time Monitoring of Amyloid-β Oligomerization and Rapid Screening of Degrading Drugs

Toxic oligomers of amyloid-β (Aβ) are important in the pathology of Alzheimer's disease (AD), and degradation of Aβ oligomers (AβO) in the brain is considered a promising strategy for drug development. However, conventional drug screening techniques face challenges in the rapid and real-time assessment of AβO. Here, we report a simple and reliable nanocollision electrochemical method based on silver nanoparticles (AgNPs) "tagging" that can in situ monitor Aβ oligomerization and screen potential AβO-degrading drugs. The differences in collision signals between AgNPs-Aβ complexes and AgNPs were compared to achieve rapid identification of Aβ complexes with different aggregation degrees. The degradation effect following the addition of AβO-degrading drugs can be quickly evaluated by the recovery of collision frequency (f, number of peaks per unit time), which is effective if f > 0.15. Degradation efficiency was further quantified using current lifetimes (τ, the time required for the current to decay to 1/e of the original), based on the percentage of τ ≤ 10 ms. The practicability of the method was tested using Aβ-degrading protease and several small molecules, confirming the rapid screening of AβO-degrading drugs and offering a novel strategy to accelerate the development of drugs for AD treatment.

Newer Therapeutic Approaches in Treating Alzheimer's Disease: A Comprehensive Review

Alzheimer's disease (AD) is an aging-related irreversible neurodegenerative disease affecting mostly the elderly population. The main pathological features of AD are the extracellular Aβ plaques generated by APP cleavage through the amyloidogenic pathway, the intracellular neurofibrillary tangles (NFT) resulting from the hyperphosphorylated tau proteins, and cholinergic neurodegeneration. However, the actual causes of AD are unknown, but several studies suggest hereditary mutations in PSEN1 and -2, APOE4, APP, and the TAU genes are the major perpetrators. In order to understand the etiology and pathogenesis of AD, various hypotheses are proposed. These include the following hypotheses: amyloid accumulation, tauopathy, inflammation, oxidative stress, mitochondrial dysfunction, glutamate/excitotoxicity, cholinergic deficiency, and gut dysbiosis. Currently approved therapeutic interventions are donepezil, galantamine, and rivastigmine, which are cholinesterase inhibitors (ChEIs), and memantine, which is an N-methyl-d-aspartate (NMDA) antagonist. These treatment strategies focus on only symptomatic management of AD by attenuating symptoms but not regeneration of neurons or clearance of Aβ plaques and hyperphosphorylated Tau. This review focuses on the pathophysiology, novel therapeutic targets, and disease-altering treatments such as α-secretase modulators, active immunotherapy, passive immunotherapy, natural antioxidant products, nanomaterials, antiamyloid therapy, tau aggregation inhibitors, transplantation of fecal microbiota or stem cells, and microtubule stabilizers that are in clinical trials or still under investigation.

Investigating the binding of fluorescent probes to a trypanosomal-tRNA synthetase: A fluorescence spectroscopic and molecular dynamics study

Given the high prevalence of Chagas disease in the Americas, we targeted the unique arginyl-tRNA synthetase of its causative agent Trypanosoma cruzi. Among their many possible uses, naphthalene-derived fluorescent ligands, such as ANS and bis-ANS, may be employed in pharmacokinetic research. Although ANS and bis-ANS have become prominent fluorescent probes for protein characterization, the structural and spectroscopic characteristics of protein-ANS/bis-ANS complexes remain largely unknown. Both fluorescent dyes bind to either the folded or partially folded hydrophobic regions of proteins. Additionally, they serve to identify molten globule-like intermediates. These probes have been used to study the folding problems of protein structures and the mechanisms of protein-protein interactions. ANS and bis-ANS exhibited significant enhancement and blue shift in their emission spectra upon binding to TcArgRS, the primary enzyme responsible for attaching l-arginine to its corresponding tRNA. Through fluorescence spectroscopy and computational studies, we concluded that bis-ANS binds more tightly to TcArgRS and that ATP affects bis-ANS fluorescence signal. Thus, these probes are useful resources for studying the intricate intermolecular relationships between proteins in terms of their structure, function, and mechanism. Our study provides a framework for identifying the hydrophobic regions present in TcArgRS. The utilization of hydrophobic patches on proteins for drug targeting is noteworthy because they can assist in identifying regions on the surface of proteins that are likely to interact with ligands. These patches help identify hotspot residues that play a vital role in determining binding affinity. Drugs are mainly small and hydrophobic in nature, and they target protein surfaces which have complementary properties. In this study, we elucidated the potential of TcArgRS as a target for combating trypanosomal diseases and extending life expectancy.

Recent advances in the synthesis and application of biomolecular condensates

Biomolecular condensates (BMCs) represent a group of organized and programmed systems that participate in gene transcription, chromosome organization, cell division, tumorigenesis, and aging. However, the understanding of BMCs in terms of internal organizations and external regulations remains at an early stage. Recently, novel approaches such as synthetic biology have been used for de novo synthesis of BMCs. These synthesized BMCs (SBMCs) driven by phase separation adeptly resemble the self-assembly and dynamics of natural BMCs, offering vast potentials in basic and applied research. This review introduces recent progresses in phase separation-induced SBMCs, attempting to elaborate on the intrinsic principles and regulatory methodologies used to construct SBMCs. Furthermore, the scientific applications of SBMCs are illustrated, as indicated by the studies of chromosome structure, pathogenesis, biomanufacturing, artificial cell design, and drug delivery. The controllable SBMCs offer a powerful tool for understanding metabolic regulations, cellular organizations, and disease-associated protein aggregations, raising both opportunities and challenges in the future of biomaterial, biotechnology, and biomedicine.

Targeted drug delivery in neurodegenerative diseases: the role of nanotechnology

Neurodegenerative diseases, characterized by progressive neuronal loss and cognitive impairments, pose a significant global health challenge. This study explores the potential of nanotherapeutics as a promising approach to enhance drug delivery across physiological barriers, particularly the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (B-CSFB). By employing nanoparticles, this research aims to address critical challenges in the diagnosis and treatment of conditions such as Alzheimer's, Parkinson's, and Huntington's diseases. The multifactorial nature of these disorders necessitates innovative solutions that leverage nanomedicine to improve drug solubility, circulation time, and targeted delivery while minimizing off-target effects. The findings underscore the importance of advancing nanomedicine applications to develop effective therapeutic strategies that can alleviate the burden of neurodegenerative diseases on individuals and healthcare systems.

Effect of Lipidation on the Structure, Oligomerization, and Aggregation of Glucagon-like Peptide 1

Lipidated analogues of glucagon-like peptide 1 (GLP-1) have gained enormous attention as long-acting peptide therapeutics for type 2 diabetes and also antiobesity treatment. Commercially available therapeutic lipidated GLP-1 analogues, semaglutide and liraglutide, have the great advantage of prolonged half-lives in vivo of hours and days instead of minutes as is the case for native GLP-1. A crucial factor in the development of novel lipidated therapeutic peptides is their physical stability, which greatly influences manufacturing and drug product development. This work provides a systematic study of the solubility, structure, oligomerization, and long-term stability of five different lipidated analogues of GLP-1, varying in the position of the lipidation site and the nature of lipid attachment. The lipidation was found to negatively impact the peptide solubility, in all cases, limiting it to a specific pH range. An increase in the α-helical secondary structure was observed upon lipidation, and the lipidated analogues were found to form larger and more stable oligomeric species compared to nonlipidated GLP-1. Importantly, the distributions and populations of oligomeric species formed were regulated by both the position and the nature of the lipidation. During the 6 days of sample aging, several lipidated analogues formed aggregates with variable morphologies ranging from elongated mature fibrils to amorphous structures. The kinetics of aggregation often showed multiple steps and did not follow a standard nucleation-propagation mechanism. A wide range of behaviors was observed, and while our observations indicate that the formation of a single stable oligomer results in the greatest physical stability, positioning the lipid group toward the N-terminus of the peptide results in extremely rapid amyloid formation. We believe that our study provides important findings for the development of long-acting lipidated analogues of peptide therapeutics.

Flavones Suppress Aggregation and Amyloid Fibril Formation of Human Lysozyme under Macromolecular Crowding Conditions

The crowded milieu of a biological cell significantly impacts protein aggregation and interactions. Understanding the effects of macromolecular crowding on the aggregation and fibrillation of amyloidogenic proteins is crucial for the treatment of many amyloid-related disorders. Most in vitro studies of protein amyloid formation and its inhibition by small molecules are conducted in dilute buffers, which do not mimic the complexity of the cellular environment. In this study, we used PEGs to simulate macromolecular crowding and examined the inhibitory effects of flavones DHF, baicalein, and luteolin on human lysozyme (HuL) aggregation at pH 2. Naturally occurring flavones have been effective inhibitors of amyloid formation in some proteins. Our findings indicate that while flavones inhibit HuL aggregation and fibrillation in dilute buffer solutions, complete inhibition is observed with a combination of flavones and PEGs, as shown by ThT fluorescence, light scattering, TEM, and AFM studies. The species formed in the presence of PEG 8000 and flavones were less hydrophobic, less toxic, and α-helix-rich compared to control samples, which were hydrophobic and β-sheet-rich, as demonstrated by ANS hydrophobicity, MTT assay, and CD spectroscopy. Fluorescence titration studies of flavones with HuL showed a significant increase in binding constant values under crowding conditions. These findings highlight the importance of macromolecular crowding in modulating protein aggregation and amyloid inhibition. Further studies using disease-causing mutants of HuL and other amyloidogenic proteins are needed to explore the role of macromolecular crowding in small-molecule-mediated modulation and inhibition of protein aggregation and amyloid formation.

Principles and Biomedical Applications of Self-Assembled Peptides: Potential Treatment of Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is the most prevalent metabolic disorder worldwide. There have been tremendous efforts to find a safe and prolonged effective therapy for its treatment. Peptide hormones, from certain organisms in the human body, as the pharmaceutical agents, have shown outstanding profiles of efficacy and safety in plasma glucose regulation. Their therapeutic promises have undergone intensive investigations via examining their physicochemical and pharmacokinetic properties. Their major drawback is their short half-life in vivo. To address this challenge, researchers have recently started to apply the state-of-the-art molecular self-assembly on peptide hormones to form nanofibrillar structures, as a smart nanotherapeutic drug delivery technique, to tremendously enhance their prolonged bioactivity in vivo. This revolutionary therapeutic approach would significantly improve patient compliance. First, this review provides a comprehensive summary on the pathophysiology of T2DM, various efforts to treat this chronic disorder, and the limitations and drawbacks of these treatment approaches. Next, this review lays out detailed insights on various aspects of peptide self-assembly: adverse effects, potential applications in nanobiotechnology, thermodynamics and kinetics of the process, as well as the molecular structures of the self-assembled configurations. Furthermore, this review elucidates the recent efforts on applying reversible human-derived peptide self-assembly to generate highly organized smart nanostructured drug formulations known as nanofibrils to regulate and prolong the bioactivity of the human gut hormone peptides in vivo to treat T2DM. Finally, this review highlights the future research directions to advance the knowledge on the state-of-the-art peptide self-assembly process to apply the revolutionary smart nanotherapeutics for treatment of chronic disorders such as T2DM with highly improved patient compliance.

A Matter of Charge: Electrostatically Tuned Coassembly of Amphiphilic Peptides

Coassembly of peptide biomaterials offers a compelling avenue to broaden the spectrum of hierarchically ordered supramolecular nanoscale structures that may be relevant for biomedical and biotechnological applications. In this work coassemblies of amphiphilic and oppositely charged, anionic and cationic, β-sheet peptides are studied, which may give rise to a diverse range of coassembled forms. Mixtures of the peptides show significantly lower critical coassembly concentration (CCC) values compared to those of the individual pure peptides. Intriguingly, the highest formation of coassembled fibrils is found to require excess of the cationic peptide whereas equimolar mixtures of the peptides exhibited the maximum folding into β-sheet structures. Mixtures of the peptides coassembled sequentially from solutions at concentrations surpassing each peptide's intrinsic critical assembly concentration (CAC), are also found to require a higher portion of the cationic peptide to stabilize hydrogels. This study illuminates a systematic investigation of oppositely charged β-sheet peptides over a range of concentrations, in solutions and in hydrogels. The results may be relevant to the fundamental understanding of such intricate charge-driven assembly systems and to the formulation of peptide-based nanostructures with diverse functionalities.

De novo designed YK peptides forming reversible amyloid for synthetic protein condensates in mammalian cells

In mammalian cells, protein condensates underlie diverse cell functions. Intensive synthetic biological research has been devoted to fabricating liquid droplets using de novo peptides/proteins designed from scratch in test tubes or bacterial cells. However, the development of de novo sequences for synthetic droplets forming in eukaryotes is challenging. Here, we report YK peptides, comprising 9-15 residues of alternating repeats of tyrosine and lysine, which form reversible amyloid-like fibrils accompanied by binding with poly-anion species such as ATP. By genetically tagging the YK peptide, superfolder GFPs assemble into artificial liquid-like droplets in living cells. Rational design of the YK system allows fine-tuning of the fluidity and construction of multi-component droplets. The YK system not only facilitates intracellular reconstitution of simplified models for natural protein condensates, but it also provides a toolbox for the systematic creation of droplets with different dynamics and composition for in situ evaluation.

A Spectroscopic Study on the Amyloid-β Interaction with Clicked Peptide-Porphyrin Conjugates: a Vision Toward the Detection of Aβ Peptides in Aqueous Solution

Alzheimer's disease (AD) is a multifactorial form of dementia mainly affecting people in the elderly, but no effective cure is available. According to the amyloid hypothesis the aggregation of Amyloid-β (Aβ) into oligomeric toxic species is believed to concur with the onset and progression of the disease heavily. By using a click chemistry approach, we conjugated a suitable designed peptide sequence to a metalloporphyrin moiety to obtain three hybrid peptide systems to be studied for their interaction with Amyloid-β peptides. The aim is to get new tools for the diagnosis and therapy in AD. The results described in this study, which were obtained through spectroscopic techniques (UV-Vis, CD, bis-Ans and intrinsic porphyrin Fluorescence), Microfluidics (GCI) and cell biology (MTT, Live cell imaging and flow cytometry), reveal interesting features about the structure-activity relationships connecting these conjugates with the interaction with Aβ, as well as on their potential use as sensing systems. In our opinion the data reported in this paper make the porphyrin-peptide conjugates highly compelling for further exploration as spectroscopic probes to detect Aβ biomarkers in biological fluids.

Bifunctional Inhibitor Lentinan Inhibits Fibrillogenesis of Amyloid-β Protein and α-Synuclein and Alleviates Their Cytotoxicity: In Vitro and In Vivo Studies

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative diseases in the world. Misfolding of β-amyloid (Aβ) and α-synuclein (α-syn) and subsequent fibril formation are closely associated with the pathogenesis of AD and PD, respectively. Lentinan is a natural product commonly used in medicine and dietary supplements. It has potential antitumor, anti-inflammatory, and antiviral effects, but the underlying mechanism of its action on AD and PD remains unclear. In this study, lentinan inhibited the formation of Aβ and α-syn fibers in a dose-dependent manner and disrupted their mature fibers. Lentinan inhibited the conversion of Aβ and α-syn conformations to β-sheet-rich conformations. Additionally, lentinan protected Caenorhabditis elegans against damage caused by the accumulation of Aβ and α-syn aggregation and prolonged their lifespan. Notably, the beneficial effects of lentinan in AD and PD mice were also demonstrated, including ameliorating the cognitive and memory impairments in AD mice and behavioral deficits in PD mice. Finally, molecular interactions between lentinan and Aβ/α-syn pentamers were also explored using molecular docking.

Unraveling the Structure and Dynamics of Ac-PHF6-NH2 Tau Segment Oligomers

The aggregation of the proteins tau and amyloid-β is a salient feature of Alzheimer's disease, the most common form of neurodegenerative disorders. Upon aggregation, proteins transition from their soluble, monomeric, and functional state into insoluble, fibrillar deposits through a complex process involving a variety of intermediate species of different morphologies, including monomers, toxic oligomers, and insoluble fibrils. To control and direct peptide aggregation, a complete characterization of all species present and an understanding of the molecular processes along the aggregation pathway are essential. However, this is extremely challenging due to the transient nature of oligomers and the complexity of the reaction networks. Therefore, we have employed a combined approach that allows us to probe the structure and kinetics of oligomeric species, following them over time as they form fibrillar structures. Targeting the tau protein peptide segment Ac-PHF6-NH2, which is crucial for the aggregation of the full protein, soft nano-electrospray ionization combined with ion mobility mass spectrometry has been employed to study the kinetics of heparin-induced intact oligomer formation. The oligomers are identified and characterized using high-resolution ion mobility mass spectrometry, demonstrating that the addition of heparin does not alter the structure of the oligomeric species. The kinetics of fibril formation is monitored through a Thioflavin T fluorescence assay. Global fitting of the kinetic data indicates that secondary nucleation plays a key role in the aggregation of the Ac-PHF6-NH2 tau segment, while the primary nucleation rate is greatly accelerated by heparin.

In Situ Heparan Sulfate-Induced Peptide Self-Assembly to Overcome the Cell Surface Glycocalyx Barrier for Cancer Treatment

Heparan sulfate (HS) is a major component of cell surface glycocalyx with extensive negative charges and plays a protective role by preventing toxins, including small molecule drugs and anticancer cationic lytic peptides (ACLPs), from cells. However, this effect may compromise the treatment efficiency of anticancer drugs. To overcome the impedance of cancer cell glycocalyx, an HS-targeting ACLP PTP-7z was designed by fusion of an ACLP and a Zn2+-binding HS-targeting peptide. Upon Zn2+ ion binding, PTP-7z could self-assemble into uniform nanoparticles and show improved serum stability and reduced hemolysis, which enable it to self-deliver to tumor sites. The peptide PTP-7z showed a pH- and Zn2+ ion-dependent HS-binding ability, which triggers the HS-induced in situ self-assembling on the cancer cell surface in the acidic tumor microenvironment (TME). The self-assembled PTP-7z can overcome the impedance of cell glycocalyx by either disrupting cell membranes or translocating into cells through endocytosis and inducing cell apoptosis. Moreover, PTP-7z can also inhibit cancer cell migration. These results proved that HS-responsive in situ self-assembling is a practical strategy to overcome the cancer cell glycocalyx barrier for ACLPs and could be extended to the design of other peptide drugs to promote their in vivo application.

Biophysical Studies of Amyloid-Binding Fluorophores to Tau AD Core Fibrils Formed without Cofactors

Tau is an intrinsically disordered protein involved in several neurodegenerative diseases where a common hallmark is the appearance of tau aggregates in the brain. One common approach to elucidate the mechanisms behind the aggregation of tau has been to recapitulate in vitro the self-assembly process in a fast and reproducible manner. While the seeding of tau aggregation is prompted by negatively charged cofactors, the obtained fibrils are morphologically distinct from those found in vivo. The Tau AD core fragment (TADC, tau 306-378) has emerged as a new model and potential solution for the cofactor-free in vitro aggregation of tau. Here, we use TADC to further study this process combining multiple amyloid-detecting fluorophores and fibril bioimaging. We confirmed by transmission electron microscopy that this fragment forms fibrils after quiescent incubation at 37 °C. We then employed a panel of eight amyloid-binding fluorophores to query the formed species by acquiring their emission spectra. The results obtained showed that nearly all dyes detect TADC self-assembled species. However, the successful monitoring of TADC aggregation kinetics was limited to three fluorophores (X-34, Bis-ANS, and pFTAA) which yielded sigmoidal curves but different aggregation half-times, hinting to different species being detected. Altogether, this study highlights the potential of using multiple extrinsic fluorescent probes, alone or in combination, as tools to further clarify mechanisms behind the aggregation of amyloidogenic proteins.

Methods for high throughput discovery of fluoroprobes that recognize tau fibril polymorphs

Aggregation of microtubule-associated protein tau (MAPT/tau) into conformationally distinct fibrils underpins neurodegenerative tauopathies. Fluorescent probes (fluoroprobes), such as thioflavin T (ThT), have been essential tools for studying tau aggregation; however, most of them do not discriminate between amyloid fibril conformations (polymorphs). This gap is due, in part, to a lack of high-throughput methods for screening large, diverse chemical collections. Here, we leverage advances in protein adaptive differential scanning fluorimetry (paDSF) to screen the Aurora collection of 300+ fluorescent dyes against multiple synthetic tau fibril polymorphs. This screen, coupled with orthogonal secondary assays, revealed pan-fibril binding chemotypes, as well as fluoroprobes selective for subsets of fibrils. One fluoroprobe recognized tau pathology in ex vivo brain slices from Alzheimer's disease patients. We propose that these scaffolds represent entry points for development of selective fibril ligands and, more broadly, that high throughput, fluorescence-based dye screening is a platform for their discovery.

Analysis of Amyloid Fibrillation of Two Family 1 Glycoside Hydrolases

The formation and analysis of amyloid fibers by two β-glucosidases, BglA and BglB, belonging to the GH1 enzyme family, are reported. Both proteins have the (β/α)8 TIM-barrel fold, which is characteristic of this family and is also the most common protein structure. BglA is an octamer, whereas BglB is a monomer. Amyloid fibrillation using pH and temperature as perturbing agents was investigated using fluorescence spectroscopy as a preliminary approach and corroborated using wide-field optical microscopy, confocal microscopy, and field-emission scanning electron microscopy. These analyses showed that both enzymes fibrillate at a wide range of acidic and alkaline conditions and at several temperature conditions, particularly at acidic pH (3-4) and at temperatures between 45 and 65 °C. Circular dichroism spectroscopy corroborated the transition from an α-helix to a β-sheet secondary structure of both proteins in conditions where fibrillation was observed. Overall, our results suggest that fibrillation is a rather common phenomenon caused by protein misfolding, driven by a transition from an α-helix to a β-sheet secondary structure, that many proteins can undergo if subjected to conditions that disturb their native conformation.

The detection methods currently available for protein aggregation in neurological diseases

Protein aggregation is a pathological feature in various neurodegenerative diseases and is thought to play a crucial role in the onset and progression of neurological disorders. This pathological phenomenon has attracted increasing attention from researchers, but the underlying mechanism has not been fully elucidated yet. Researchers are increasingly interested in identifying chemicals or methods that can effectively detect protein aggregation or maintain protein stability to prevent aggregation formation. To date, several methods are available for detecting protein aggregates, including fluorescence correlation spectroscopy, electron microscopy, and molecular detection methods. Unfortunately, there is still a lack of methods to observe protein aggregation in situ under a microscope. This article reviews the two main aspects of protein aggregation: the mechanisms and detection methods of protein aggregation. The aim is to provide clues for the development of new methods to study this pathological phenomenon.

Crystal Violet Selectively Detects Aβ Oligomers but Not Fibrils In Vitro and in Alzheimer's Disease Brain Tissue

Deposition of extracellular Amyloid Beta (Aβ) and intracellular tau fibrils in post-mortem brains remains the only way to conclusively confirm cases of Alzheimer's Disease (AD). Substantial evidence, though, implicates small globular oligomers instead of fibrils as relevant biomarkers of, and critical contributors to, the clinical symptoms of AD. Efforts to verify and utilize amyloid oligomers as AD biomarkers in vivo have been limited by the near-exclusive dependence on conformation-selective antibodies for oligomer detection. While antibodies have yielded critical evidence for the role of both Aβ and tau oligomers in AD, they are not suitable for imaging amyloid oligomers in vivo. Therefore, it would be desirable to identify a set of oligomer-selective small molecules for subsequent development into Positron Emission Tomography (PET) probes. Using a kinetics-based screening assay, we confirm that the triarylmethane dye Crystal Violet (CV) is oligomer-selective for Aβ42 oligomers (AβOs) grown under near-physiological solution conditions in vitro. In postmortem brains of an AD mouse model and human AD patients, we demonstrate that A11 antibody-positive oligomers but not Thioflavin S (ThioS)-positive fibrils colocalize with CV staining, confirming in vitro results. Therefore, our kinetic screen represents a robust approach for identifying new classes of small molecules as candidates for oligomer-selective dyes (OSDs). Such OSDs, in turn, provide promising starting points for the development of PET probes for pre-mortem imaging of oligomer deposits in humans.

Cyclic-NDGA Effectively Inhibits Human γ-Synuclein Fibrillation, Forms Nontoxic Off-Pathway Species, and Disintegrates Preformed Mature Fibrils

Parkinson's disease arises from protein misfolding, aggregation, and fibrillation and is characterized by LB (Lewy body) deposits, which contain the protein α-synuclein (α-syn) as their major component. Another synuclein, γ-synuclein (γ-syn), coexists with α-syn in Lewy bodies and is also implicated in various types of cancers, especially breast cancer. It is known to seed α-syn fibrillation after its oxidation at methionine residue, thereby contributing in synucleinopathy. Despite its involvement in synucleinopathy, the search for small molecule inhibitors and modulators of γ-syn fibrillation remains largely unexplored. This work reveals the modulatory properties of cyclic-nordihydroguaiaretic acid (cNDGA), a natural polyphenol, on the structural and aggregational properties of human γ-syn employing various biophysical and structural tools, namely, thioflavin T (ThT) fluorescence, Rayleigh light scattering, 8-anilinonaphthalene-1-sulfonic acid binding, far-UV circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR) spectroscopy, atomic force microscopy, ITC, molecular docking, and MTT-toxicity assay. cNDGA was observed to modulate the fibrillation of γ-syn to form off-pathway amorphous species that are nontoxic in nature at as low as 75 μM concentration. The modulation is dependent on oxidizing conditions, with cNDGA weakly interacting (Kd ∼10-5 M) with the residues at the N-terminal of γ-syn protein as investigated by isothermal titration calorimetry and molecular docking, respectively. Increasing cNDGA concentration results in an increased recovery of monomeric γ-syn as shown by sodium dodecyl sulfate and native-polyacrylamide gel electrophoresis. The retention of native structural properties of γ-syn in the presence of cNDGA was further confirmed by far-UV CD and FTIR. In addition, cNDGA is most effective in suppression of fibrillation when added at the beginning of the fibrillation kinetics and is also capable of disintegrating the preformed mature fibrils. These findings could, therefore, pave the ways for further exploring cNDGA as a potential therapeutic against γ-synucleinopathies.

Fusion of amyloid beta with ferritin yields an isolated oligomeric beta-sheet-rich aggregate inside the ferritin cage

Alzheimer's disease is a severe brain condition caused by the formation of amyloid plaques composed of amyloid beta (Aβ) peptides. These peptides form oligomers, protofibrils, and fibrils before deposition into amyloid plaques. Among these intermediates, Aβ oligomers (AβOs) were found to be the most toxic and therefore an appealing target for drug development and understanding their role in the disease. However, precise isolation and characterization of AβOs have proven challenging because AβOs tend to aggregate and form heterogeneous mixtures in solution. As a solution, we genetically fused the Aβ peptide with a ferritin monomer. Such fusion allowed the encapsulation of precisely 24 Aβ peptides inside the 24-mer ferritin cage. Using high-speed atomic force microscopy (HS-AFM), we disassembled ferritin and directly visualized the Aβ core enclosed within the cage. The thioflavin-T assay (ThT) and attenuated total reflection infrared spectroscopy (ATR-IR) revealed the presence of a β-sheet structure in the encapsulated oligomeric aggregate. Gallic acid, an amyloid inhibitor, can inhibit the fluorescence of ThT bound AβOs. Our approach represents a significant advancement in the isolation and characterization of β-sheet rich AβOs and is expected to be useful for future studies of other disordered peptides such as α-synuclein and tau.

Reductive amination of ω-conotoxin MVIIA: synthesis, determination of modification sites, and self-assembly

Peptide drugs have disadvantages such as low stability, short half-life and side effects, which limit their widespread use in clinical practice. Therefore, peptide drugs can be modified to improve these disadvantages. Numerous studies have shown that alkyl-modified peptide drugs can self-assemble to prolong the duration of efficacy and/or reduce side effects. However, the commonly used solid-phase synthesis method for alkyl-modified peptides is time-consuming. To overcome this, a simple reductive amination reaction was employed, which can directly graft the alkyl chain to the peptide sequence and effectively avoid stepwise synthesis from C- to N-terminal with amino acids. In this study, ω-conotoxin MVIIA was used as the peptide drug, while myristic aldehyde was used as the alkylating agent. To obtain the maximum productivity of modified peptides, the molar ratio of peptide MVIIA to myristic aldehyde in the reductive amination reaction was optimized. Furthermore, the peptide modification sites in this reaction were confirmed by secondary mass spectrometry analysis. Besides, alkyl-modified peptide MVIIA was able to form micelles by self-assembly and improved stability in serum, which was related to our previous work where myristoylated peptide MVIIA micelles can improve the drug stability. Finally, this study was intended to provide a methodological basis for modifying the alkyl chain of peptide drugs.

Impact of Membrane Phospholipids and Exosomes on the Kinetics of Amyloid-β Fibril Assembly

Alzheimer's disease (AD) is linked with the self-association of the amyloid-β peptide (Aβ) into oligomers and fibrils. The brain is a lipid rich environment for Aβ to assemble, while the brain membrane composition varies in an age dependent manner, we have therefore monitored the influence of lipid bilayer composition on the kinetics of Aβ40 fibril assembly. Using global-fitting models of fibril formation kinetics, we show that the microscopic rate constant for primary nucleation is influenced by variations in phospholipid composition. Anionic phospholipids and particularly those with smaller headgroups shorten fibril formation lag-times, while zwitterionic phospholipids tend to extend them. Using a physiological vesicle model, we show cellular derived exosomes accelerate Aβ40 and Aβ42 fibril formation. Two distinct effects are observed, the presence of even small amounts of any phospholipid will impact the slope of the fibril growth curve. While subsequent additions of phospholipids only affect primary nucleation with the associated change in lag-times. Heightened anionic phospholipids and cholesterol levels are associated with aging and AD respectively, both these membrane components strongly accelerate primary nucleation during Aβ assembly, making a link between disrupted lipid metabolism and Alzheimer's disease.

Non-destructive real-time monitoring and investigation of the self-assembly process using fluorescent probes

Self-assembly has been considered as a strategy to construct superstructures with specific functions, which has been widely used in many different fields, such as bionics, catalysis, and pharmacology. A detailed and in-depth analysis of the self-assembly mechanism is beneficial for directionally and accurately regulating the self-assembly process of substances. Fluorescent probes exhibit unique advantages of sensitivity, non-destructiveness, and real-time self-assembly tracking, compared with traditional methods. In this work, the design principle of fluorescent probes with different functions and their applications for the detection of thermodynamic and kinetic parameters during the self-assembly process were systematically reviewed. Their efficiency, limitations and advantages are also discussed. Furthermore, the promising perspectives of fluorescent probes for investigating the self-assembly process are also discussed and suggested.

Catalytic physiological amyloids

Amyloid fibrils have been identified in many protein systems, mostly linked to progression and cytotoxicity in neurodegenerative diseases and other pathologies, but have also been observed in normal physiological systems. A growing body of work has shown that amyloid fibrils can catalyze chemical reactions. Most studies have focused on catalysis by de-novo synthetic amyloid-like peptides; however, recent studies reveal that physiological, native amyloids are catalytic as well. Here, we discuss methodologies and major experimental aspects pertaining to physiological catalytic amyloids. We highlight analyzes of kinetic parameters related to the catalytic activities of amyloid fibrils, structure-function considerations, characterization of the catalytic active sites, and deciphering of catalytic mechanisms.

Copper(II) Can Kinetically Trap Arctic and Italian Amyloid-β40 as Toxic Oligomers, Mimicking Cu(II) Binding to Wild-Type Amyloid-β42: Implications for Familial Alzheimer's Disease

The self-association of amyloid-β (Aβ) peptide into neurotoxic oligomers is believed to be central to Alzheimer's disease (AD). Copper is known to impact Aβ assembly, while disrupted copper homeostasis impacts phenotype in Alzheimer's models. Here we show the presence of substoichiometric Cu(II) has very different impacts on the assembly of Aβ40 and Aβ42 isoforms. Globally fitting microscopic rate constants for fibril assembly indicates copper will accelerate fibril formation of Aβ40 by increasing primary nucleation, while seeding experiments confirm that elongation and secondary nucleation rates are unaffected by Cu(II). In marked contrast, Cu(II) traps Aβ42 as prefibrillar oligomers and curvilinear protofibrils. Remarkably, the Cu(II) addition to preformed Aβ42 fibrils causes the disassembly of fibrils back to protofibrils and oligomers. The very different behaviors of the two Aβ isoforms are centered around differences in their fibril structures, as highlighted by studies of C-terminally amidated Aβ42. Arctic and Italian familiar mutations also support a key role for fibril structure in the interplay of Cu(II) with Aβ40/42 isoforms. The Cu(II) dependent switch in behavior between nonpathogenic Aβ40 wild-type and Aβ40 Arctic or Italian mutants suggests heightened neurotoxicity may be linked to the impact of physiological Cu(II), which traps these familial mutants as oligomers and curvilinear protofibrils, which cause membrane permeability and Ca(II) cellular influx.

Advances in targeted tracking and detection of soluble amyloid-β aggregates as a biomarker of Alzheimer's disease

Misfolding and aggregation of amyloid-β (Aβ) peptides are key hallmarks of Alzheimer's disease (AD). With accumulating evidence suggesting that different Aβ species have varied neurotoxicity and implications in AD development, the discovery of affinity ligands and analytical approaches to selective distinguish, detect, and monitor Aβ becomes an active research area. Remarkable advances have been achieved, which not only promote our understanding of the biophysical chemistry of the protein aggregation during neurodegeneration, but also provide promising tools for early detection of the disease. In view of this, we summarize the recent progress in selective and sensitive approaches for tracking and detection of Aβ species. Specific attentions are given to soluble Aβ oligomers, due to their crucial roles in AD development and occurrence at early stages. The design principle, performance of targeting units, and their cooperative effects with signal reporters for Aβ analysis are discussed. The applications of the novel targeting probes and sensing systems for dynamic monitoring oligomerization, measuring Aβ in biosamples and in vivo imaging in brain are summarized. Finally, the perspective and challenges are discussed regarding the future development of Aβ-targeting analytical tools to explore the unknown field to contribute to the early diagnosis and treatment of AD.

Curli Amyloid Fibers in Escherichia coli Biofilms: The Influence of Water Availability on their Structure and Functional Properties

Escherichia coli biofilms consist of bacteria embedded in a self-produced matrix mainly made of protein fibers and polysaccharides. The curli amyloid fibers found in the biofilm matrix are promising versatile building blocks to design sustainable bio-sourced materials. To exploit this potential, it is crucial to understand i) how environmental cues during biofilm growth influence the molecular structure of these amyloid fibers, and ii) how this translates at higher length scales. To explore these questions, the effect of water availability during biofilm growth on the conformation and functions of curli is studied. Microscopy and spectroscopy are used to characterize the amyloid fibers purified from biofilms grown on nutritive substrates with different water contents, and micro-indentation to measure the rigidity of the respective biofilms. The purified curli amyloid fibers present differences in the yield, structure, and functional properties upon biofilm growth conditions. Fiber packing and β-sheets content correlate with their hydrophobicity and chemical stability, and with the rigidity of the biofilms. This study highlights how E. coli biofilm growth conditions impact curli structure and functions contributing to macroscopic materials properties. These fundamental findings infer an alternative strategy to tune curli structure, which will ultimately benefit engineering hierarchical and functional curli-based materials.

Secondary Modification of S100B Influences Anti Amyloid-β Aggregation Activity and Alzheimer's Disease Pathology

Proteinaceous aggregates accumulate in neurodegenerative diseases such as Alzheimer's Disease (AD), inducing cellular defense mechanisms and altering the redox status. S100 pro-inflammatory cytokines, particularly S100B, are activated during AD, but recent findings reveal an unconventional molecular chaperone role for S100B in hindering Aβ aggregation and toxicity. This suggests a potential protective role for S100B at the onset of Aβ proteotoxicity, occurring in a complex biochemical environment prone to oxidative damage. Herein, we report an investigation in which extracellular oxidative conditions are mimicked to test if the susceptibility of S100B to oxidation influences its protective activities. Resorting to mild oxidation of S100B, we observed methionine oxidation as inferred from mass spectrometry, but no cysteine-mediated crosslinking. Structural analysis showed that the folding, structure, and stability of oxidized S100B were not affected, and nor was its quaternary structure. However, studies on Aβ aggregation kinetics indicated that oxidized S100B was more effective in preventing aggregation, potentially linked to the oxidation of Met residues within the S100:Aβ binding cleft that favors interactions. Using a cell culture model to analyze the S100B functions in a highly oxidative milieu, as in AD, we observed that Aβ toxicity is rescued by the co-administration of oxidized S100B to a greater extent than by S100B. Additionally, results suggest a disrupted positive feedback loop involving S100B which is caused by its oxidation, leading to the downstream regulation of IL-17 and IFN-α2 expression as mediated by S100B.

Protein Nanotubes as Advanced Material Platforms and Delivery Systems

Protein nanotubes (PNTs) as state-of-the-art nanocarriers are promising for various potential applications both in the food and pharmaceutical industries. Derived from edible starting sources like α-lactalbumin, lysozyme, and ovalbumin, PNTs bear properties of biocompatibility and biodegradability. Their large specific surface area and hydrophobic core facilitate chemical modification and loading of bioactive substances, respectively. Moreover, their enhanced permeability and penetration ability across biological barriers such as intestinal mucus, extracellular matrix, and thrombus clot, make it promising platforms for health-related applications. Most importantly, their simple preparation processes enable large-scale production, supporting applications in the biomedical and nanotechnological fields. Understanding the self-assembly principles is crucial for controlling their morphology, size, and shape, and thus provides the ground to a multitude of applications. Here, the current state-of-the-art of PNTs including their building materials, physicochemical properties, and self-assembly mechanisms are comprehensively reviewed. The advantages and limitations, as well as challenges and prospects for their successful applications in biomaterial and pharmaceutical sectors are then discussed and highlighted. Potential cytotoxicity of PNTs and the need of regulations as critical factors for enabling in vivo applications are also highlighted. In the end, a brief summary and future prospects for PNTs as advanced platforms and delivery systems are included.

Selective recognition and discrimination of single isomeric changes in peptide strands with a host : guest sensing array

An indirect competitive binding mechanism can be exploited to allow a combination of cationic fluorophores and water-soluble synthetic receptors to selectively recognize and discriminate peptide strands containing a single isomeric residue in the backbone. Peptide isomerization occurs in long-lived proteins and has been linked with diseases such as Alzheimer's, cataracts and cancer, so isomers are valuable yet underexplored targets for selective recognition. Planar cationic fluorophores can selectively bind hydrophobic, Trp-containing peptide strands in solution, and when paired with receptors that provide a competitive host for the fluorophore, can form a differential sensing array that enables selective discrimination of peptide isomers. Residue variations such as D- and L-Asp, D- and L-isoAsp, D-Ser and D-Glu can all be recognized, simply by their effects on the folded structure of the flexible peptide. Molecular dynamics simulations were applied to determine the most favorable conformation of the peptide : fluorophore conjugate, indicating that favorable π-stacking with internal tryptophan residues in a folded binding pocket enables micromolar binding affinity.

Physiology and pharmacological targeting of phase separation

Liquid-liquid phase separation (LLPS) in biology describes a process by which proteins form membraneless condensates within a cellular compartment when conditions are met, including the concentration and posttranslational modifications of the protein components, the condition of the aqueous solution (pH, ionic strength, pressure, and temperature), and the existence of assisting factors (such as RNAs or other proteins). In these supramolecular liquid droplet-like inclusion bodies, molecules are held together through weak intermolecular and/or intramolecular interactions. With the aid of LLPS, cells can assemble functional sub-units within a given cellular compartment by enriching or excluding specific factors, modulating cellular function, and rapidly responding to environmental or physiological cues. Hence, LLPS is emerging as an important means to regulate biology and physiology. Yet, excessive inclusion body formation by, for instance, higher-than-normal concentrations or mutant forms of the protein components could result in the conversion from dynamic liquid condensates into more rigid gel- or solid-like aggregates, leading to the disruption of the organelle's function followed by the development of human disorders like neurodegenerative diseases. In summary, well-controlled formation and de-formation of LLPS is critical for normal biology and physiology from single cells to individual organisms, whereas abnormal LLPS is involved in the pathophysiology of human diseases. In turn, targeting these aggregates or their formation represents a promising approach in treating diseases driven by abnormal LLPS including those neurodegenerative diseases that lack effective therapies.

Endotoxin accelerates insulin amyloid formation and inactivates insulin signal transduction

AIMS AND OBJECTIVES

The aim of this study is to discuss the influence of endotoxin on insulin amyloid formation, to provide guidance for therapeutic insulin preparation and storage.

MATERIALS AND METHODS

The ThT and ANS binding assays were applied to characterize the dynamics curve of insulin amyloid formation with the presence or absence of endotoxin. The morphological structures of intermediate and mature insulin fibrils were observed with SEM and TEM. Secondary structural changes of insulin during fibriliation were examined with CD, FTIR and Raman spectral analysis. The cytotoxic effects of oligomeric and amyloidogenic insulin aggregates were detected using a cck-8 cell viability assay kit. The influence of endotoxin on insulin efficacy was analyzed by monitoring the activation of insulin signal transduction.

KEY FINDINGS

ThT analysis showed that endotoxin, regardless of species, accelerated insulin fibrils formation in a dose-dependent manner, as observed with a shorter lag phase. ANS binding assay demonstrated endotoxin provoked the exposure of insulin hydrophobic patches. The results of SEM and TEM data displayed that endotoxin drove insulin to cluster into dense and viscous form, with thicker and stronger filaments. Based on CD, FTIR and Raman spectra, endotoxin promoted the transition of α-helix to random coil and β-strand secondary structures during insulin aggregation. Insulins in both oligomeric and amyloidogenic forms were cytotoxic to HepG2 cells, with the former being more severe. Finally, the efficacy of endotoxin treated insulin obviously decreased.

SIGNIFICANCE

Our studies revealed that endotoxin disrupts the structural integrity of insulin and promotes its amyloidosis. These findings offered theoretical guidance for insulin storage and safe utilization, as well as pointing up a new direction for insulin resistance research.

Targeting the binding pocket of the fluorophore 8-anilinonaphthalene-1-sulfonic acid in the bacterial enzyme MurA

8-Anilinonaphthalene-1-sulfonic acid (ANS) has been extensively used as a fluorescent probe to detect conformational changes of proteins. It has been cocrystallized with several of the proteins it is used to monitor, including the bacterial cell wall synthesis enzyme MurA. MurA catalyzes the first committed step of peptidoglycan biosynthesis, converting UDP-N-acetylglucosamine (UDP-GlcNAc) into enolpyruvyl UDP-GlcNAc. It has been reported before that ANS binds to MurA from Enterobacter cloacae without inhibiting the enzyme's activity up to a concentration of 1 mM ANS. In this study, we present evidence that ANS inhibits the activity of several isoforms of MurA with IC50 values of 18, 22, and 31 µM against wild-type Escherichia coli, C115D E. coli, and E. cloacae MurA, respectively. This prompted us to test a larger series of structural analogs of ANS for the inhibition of these MurA enzymes, which led to the discovery of compound 26. This ANS analog showed enhanced inhibition of MurA (WT and C115D MurA from E. coli, and E. cloacae MurA) with IC50 values of 2.7, 10, and 14 µM, respectively. Based on our results, the ANS binding pocket was identified as a novel target site for the development of potential antibiotics.

Imaging Amyloid-β Membrane Interactions: Ion-Channel Pores and Lipid-Bilayer Permeability in Alzheimer's Disease

The accumulation of the amyloid-β peptides (Aβ) is central to the development of Alzheimer's disease. The mechanism by which Aβ triggers a cascade of events that leads to dementia is a topic of intense investigation. Aβ self-associates into a series of complex assemblies with different structural and biophysical properties. It is the interaction of these oligomeric, protofibril and fibrillar assemblies with lipid membranes, or with membrane receptors, that results in membrane permeability and loss of cellular homeostasis, a key event in Alzheimer's disease pathology. Aβ can have an array of impacts on lipid membranes, reports have included: a carpeting effect; a detergent effect; and Aβ ion-channel pore formation. Recent advances imaging these interactions are providing a clearer picture of Aβ induced membrane disruption. Understanding the relationship between different Aβ structures and membrane permeability will inform therapeutics targeting Aβ cytotoxicity.

Imaging Amyloid-β Membrane Interactions: Ion-Channel Pores and Lipid-Bilayer Permeability in Alzheimer's Disease

The accumulation of the amyloid-β peptides (Aβ) is central to the development of Alzheimer's disease. The mechanism by which Aβ triggers a cascade of events that leads to dementia is a topic of intense investigation. Aβ self-associates into a series of complex assemblies with different structural and biophysical properties. It is the interaction of these oligomeric, protofibril and fibrillar assemblies with lipid membranes, or with membrane receptors, that results in membrane permeability and loss of cellular homeostasis, a key event in Alzheimer's disease pathology. Aβ can have an array of impacts on lipid membranes, reports have included: a carpeting effect; a detergent effect; and Aβ ion-channel pore formation. Recent advances imaging these interactions are providing a clearer picture of Aβ induced membrane disruption. Understanding the relationship between different Aβ structures and membrane permeability will inform therapeutics targeting Aβ cytotoxicity.

Dual functional antifouling and bactericidal proteinaceous coating

Coatings with both anti-fouling and bactericidal functions are used in many fields. In this work, lysozyme (Lyso) and poly (2-Methylallyloxyethyl phosphorylcholine) (PMPC) conjugate (Lyso-PMPC) is successfully designed and synthesized for the first time. A new nanofilm (PTL-PMPC) is then obtained by phase transition of lysozyme via the reduction of disulfide bonds in Lyso-PMPC. Benefit from lysozyme amyloid-like aggregates as surface anchors, the nanofilm shows excellent stability, it remains unchanged after treatment under extreme conditions such as ultrasonic and 3 M tape peeling. Due to the presence of zwitterionic polymer (PMPC) brush, the PTL-PMPC film has excellent antifouling properties against cell, bacterium, fungi, proteins, biofluids, phosphatide, polyose, esters, and carbohydrates. Meanwhile, the PTL-PMPC film is colourless and transparent. Further, a new coating (PTL-PMPC/PHMB) is fabricated by hybridizing PTL-PMPC with poly (hexamethylene biguanide) (PHMB). This coating had excellent antibacterial properties, and the antibacterial rate against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) is more than 99.99%. In addition, the coating exhibit good hemocompatibility and low cytotoxicity.

Hyperphosphorylated tau (p-tau) and drug discovery in the context of Alzheimer's disease and related tauopathies

Alzheimer's disease (AD) is the most common form of dementia, characterized by intracellular neurofibrillary tangles (NFTs) and extracellular β-amyloid (βA) plaques. No disease-modifying therapy is currently available to prevent the progression of, or cure, the disease. Misfolded hyperphosphorylated tau (p-tau) is considered a pivotal point in the pathogenesis of AD and other tauopathies. Compelling evidence suggests that it is a key driver of the accumulation of NFTs and can be directly correlated with the extent of dementia in patients with AD. Therefore, inhibiting tau hyperphosphorylation-induced aggregation could be a viable strategy to discover and develop therapeutics for patients with AD.

A guide to studying protein aggregation

Disrupted protein folding or decreased protein stability can lead to the accumulation of (partially) un- or misfolded proteins, which ultimately cause the formation of protein aggregates. Much of the interest in protein aggregation is associated with its involvement in a wide range of human diseases and the challenges it poses for large-scale biopharmaceutical manufacturing and formulation of therapeutic proteins and peptides. On the other hand, protein aggregates can also be functional, as observed in nature, which triggered its use in the development of biomaterials or therapeutics as well as for the improvement of food characteristics. Thus, unmasking the various steps involved in protein aggregation is critical to obtain a better understanding of the underlying mechanism of amyloid formation. This knowledge will allow a more tailored development of diagnostic methods and treatments for amyloid-associated diseases, as well as applications in the fields of new (bio)materials, food technology and therapeutics. However, the complex and dynamic nature of the aggregation process makes the study of protein aggregation challenging. To provide guidance on how to analyse protein aggregation, in this review we summarize the most commonly investigated aspects of protein aggregation with some popular corresponding methods.

Potential Alzheimer's disease therapeutic nano-platform: Discovery of amyloid-beta plaque disaggregating agent and brain-targeted delivery system using porous silicon nanoparticles

There has been a lot of basic and clinical research on Alzheimer's disease (AD) over the last 100 years, but its mechanisms and treatments have not been fully clarified. Despite some controversies, the amyloid-beta hypothesis is one of the most widely accepted causes of AD. In this study, we disclose a new amyloid-beta plaque disaggregating agent and an AD brain-targeted delivery system using porous silicon nanoparticles (pSiNPs) as a therapeutic nano-platform to overcome AD. We hypothesized that the negatively charged sulfonic acid functional group could disaggregate plaques and construct a chemical library. As a result of the in vitro assay of amyloid plaques and library screening, we confirmed that 6-amino-2-naphthalenesulfonic acid (ANA) showed the highest efficacy for plaque disaggregation as a hit compound. To confirm the targeted delivery of ANA to the AD brain, a nano-platform was created using porous silicon nanoparticles (pSiNPs) with ANA loaded into the pore of pSiNPs and biotin-polyethylene glycol (PEG) surface functionalization. The resulting nano-formulation, named Biotin-CaCl2-ANA-pSiNPs (BCAP), delivered a large amount of ANA to the AD brain and ameliorated memory impairment of the AD mouse model through the disaggregation of amyloid plaques in the brain. This study presents a new bioactive small molecule for amyloid plaque disaggregation and its promising therapeutic nano-platform for AD brain-targeted delivery.

pH Dependence of Amyloid-β Fibril Assembly Kinetics: Unravelling the Microscopic Molecular Processes

Central to Alzheimer's disease (AD) is the assembly of the amyloid-beta peptide (Aβ) into fibrils. A reduction in pH accompanying inflammation or subcellular compartments, may accelerate fibril formation as the pH approaches Aβ's isoelectric point (pI). Using global fitting of fibril formation kinetics over a range of pHs, we identify the impact net charge has on individual fibril assembly microscopic rate constants. We show that the primary nucleation has a strong pH dependence. The titration behaviour exhibits a mid-point or pKa of 7.0, close to the pKa of Aβ histidine imidazoles. Surprisingly, both the secondary nucleation and elongation rate constants are pH independent. This indicates the charge of Aβ, in particular histidine protonation, has little impact on this stage of Aβ assembly. These fundamental processes are key to understanding the forces that drive the assembly of Aβ into toxic oligomers and fibrils.

pH Dependence of Amyloid-β Fibril Assembly Kinetics: Unravelling the Microscopic Molecular Processes

Central to Alzheimer's disease (AD) is the assembly of the amyloid-beta peptide (Aβ) into fibrils. A reduction in pH accompanying inflammation or subcellular compartments, may accelerate fibril formation as the pH approaches Aβ's isoelectric point (pI). Using global fitting of fibril formation kinetics over a range of pHs, we identify the impact net charge has on individual fibril assembly microscopic rate constants. We show that the primary nucleation has a strong pH dependence. The titration behaviour exhibits a mid-point or pK a of 7.0, close to the pK a of Aβ histidine imidazoles. Surprisingly, both the secondary nucleation and elongation rate constants are pH independent. This indicates the charge of Aβ, in particular histidine protonation, has little impact on this stage of Aβ assembly. These fundamental processes are key to understanding the forces that drive the assembly of Aβ into toxic oligomers and fibrils.

A Multichannel Fluorescent Tongue for Amyloid-β Aggregates Detection

Attention has been paid to the early diagnosis of Alzheimer's disease, due to the maximum benefit acquired from the early-stage intervention and treatment. However, the sensing techniques primarily depended upon for neuroimaging and immunological assays for the detection of AD biomarkers are expensive, time-consuming and instrument dependent. Here, we developed a multichannel fluorescent tongue consisting of four fluorescent dyes and GO through electrostatic and π-π interaction. The array distinguished multiple aggregation states of 1 µM Aβ40/Aβ42 with 100% prediction accuracy via 10-channel signal outputs, illustrating the rationality of the array design. Screening vital sensor elements for the simplified sensor array and the optimization of sensing system was achieved by machine learning algorithms. Moreover, our sensing tongue was able to detect the aggregation states of Aβ40/Aβ42 in serum, demonstrating the great potential of multichannel array in diagnosing the Alzheimer's diseases.

Comparative Study of the Solid-Liquid Interfacial Adsorption of Proteins in Their Native and Amyloid Forms

The adhesive properties of amyloid fibers are thought to play a crucial role in various negative and positive aggregation processes, the study of which might help in their understanding and control. Amyloids have been prepared from two proteins, lysozyme and β-lactoglobulin, as well as an Exendin-4 derivative miniprotein (E5). Thermal treatment was applied to form amyloids and their structure was verified by thioflavin T (ThT), 8-Anilino-1-naphthalenesulfonic acid (ANS) dye tests and electronic circular dichroism spectroscopy (ECD). Adsorption properties of the native and amyloid forms of the three proteins were investigated and compared using the mass-sensitive quartz crystal microbalance (QCM) technique. Due to the possible electrostatic and hydrophobic interactions, similar adsorbed amounts were found for the native or amyloid forms, while the structures of the adsorbed layers differed significantly. Native proteins formed smooth and dense adsorption layers. On the contrary, a viscoelastic, highly loose layer was formed in the presence of the amyloid forms, shown by increased motional resistance values determined by the QCM technique and also indicated by atomic force microscopy (AFM) and wettability measurements. The elongated structure and increased hydrophobicity of amyloids might contribute to this kind of aggregation.

Impact of the Flavonoid Quercetin on β-Amyloid Aggregation Revealed by Intrinsic Fluorescence

We report the effects of quercetin, a flavonoid present in the human diet, on early stage beta-amyloid (Aβ) aggregation, a seminal event in Alzheimer's disease. Molecular level changes in Aβ arrangements are monitored by time-resolved emission spectral (TRES) measurements of the fluorescence of Aβ's single tyrosine intrinsic fluorophore (Tyr). The results suggest that quercetin binds β-amyloid oligomers at early stages of their aggregation, which leads to the formation of modified oligomers and hinders the creation of β-sheet structures, potentially preventing the onset of Alzheimer's disease.

Dihydrocaffeic Acid-Decorated Iron Oxide Nanomaterials Effectively Inhibit Human Calcitonin Aggregation

To date, more than 30 human peptides or proteins have been found to form amyloid fibrils, most of which are associated with human diseases. However, currently, no cure for amyloidosis exists. Therefore, development of therapeutic strategies to inhibit amyloid formation is urgently required. Although the role of some amyloidogenic proteins has not been identified in certain diseases, their self-assembling behavior largely affects their bioactivity. Human calcitonin (hCT) is a hormone peptide containing 32 amino acids and is secreted by the parafollicular cells of the thyroid gland in the human body. It can regulate the concentration of calcium ions in the blood and block the activity of osteoclasts. Therefore, calcitonin has also been considered a therapeutic peptide. However, the aggregation of hCT hinders this process, and hCT has been replaced by salmon calcitonin in drug formulations. Recently, iron oxide nanomaterials have been developed as potential materials for various applications owing to their high biocompatibility, low toxicity, and ease of functionalization. In this study, nanoparticles (NPs) were prepared using a simple chemical coprecipitation method. We first demonstrated that dopamine-conjugated Fe₃O₄ inhibited hCT aggregation, similar to what we found when carbon dots were used as core materials in the previous study. Later, we continued to simplify the preparation process, that is, the mixing of dihydrocaffeic acid (DCA) and iron oxide NPs, to maintain their stability and inhibitory effect against hCT aggregation. Furthermore, DCA-decorated Fe₃O₄ can dissociate preformed hCT amyloid fibrils. This appears to be one of the most promising ways to stabilize hCT in solution and may be helpful for amyloidosis treatment.

Tetramerization of the S100B Chaperone Spawns a Ca2+ Independent Regulatory Surface that Enhances Anti-aggregation Activity and Client Specificity

Alzheimer's disease (AD) hallmarks include the aggregation of amyloid-β (Aβ), tau and neuroinflammation promoted by several alarmins. Among these is S100B, a small astrocytic homodimeric protein, upregulated in AD, whose multiple biological activities depend on localization, concentration, and assembly state. S100B was reported to inhibit the aggregation and toxicity of Aβ42 and tau similarly to a holdase-type chaperone. This activity is dependent of Ca²⁺-binding, which triggers the exposure of a regulatory binding cleft at the S100B dimer interface with which amyloidogenic clients dynamically interact. Although the dimer prevails, a significant portion of secreted S100B in the human brain occurs as higher order multimers, whose protective functions remain uncharacterized and which we here investigate. Resorting to ThT-monitored aggregation kinetics, we determined that unlike the dimer, tetrameric S100B inhibits Aβ42 aggregation at sub/equimolar ratios, an effect that persists in the absence of Ca²⁺ binding. Structural analysis revealed that S100B tetramerization spawns a novel extended cleft accommodating an aggregation-prone surface that mediates interactions with monomeric Aβ client via hydrophobic interactions, as corroborated by Bis-ANS fluorescence and docking analysis. Correspondingly, at high ionic strength that reduces solvation and favours hydrophobic contacts, the inhibition of Aβ42 aggregation by tetrameric S100B is 3-fold increased. Interestingly, this extended Ca²⁺-independent surface favours Aβ42 as substrate, as tau K18 aggregation is not inhibited by the apo tetramer. Overall, results illustrate a mechanism through which oligomerization of the S100B chaperone fine-tunes anti-aggregation activity and client specificity, highlighting the potential functional relevance of S100B multimers in the regulation of AD proteotoxicity.

Mechanistic insight into inhibition of amyloid fibrillation of human serum albumin by Vildagliptin

Protein aggregation leads to several human pathologies such as Alzheimer's disease (AD), type 2 diabetes (T2D), Parkinson's disease (PD), etc. Due to the overlap in the mechanisms of type 2 diabetes and brain disorders, common effective pharmacological interventions to treat both T2D and AD is under extensive research. Therefore, major aim of research is to repurpose already established treatment of diabetes to cure AD as well. This study evaluates mechanistic insight into anti-amyloidogenic potential of anti-diabetic drug Vildagliptin (VLD) on human serum albumin fibrillation (HSA) by using biophysical, calorimetric, imaging techniques along with hemolytic assay. Dynamic light scattering (DLS) and Rayleigh light scattering (RLS) results showed presence of few small-sized aggregates in the presence of VLD which are formed by deaccelerating the amyloidogenesis as shown by thioflavin T (ThT) fluorescence and Congo red (CR) binding assay. Further, Isothermal titration calorimetry (ITC), steady state fluorescence quenching, molecular docking results revealed that VLD form complex with amyloid facilitating state of HSA and consequently mask the hydrophobic residues involved in amyloidogenesis as evident from decrease in ANS fluorescence. Differential scanning calorimetry (DSC) results confirm that VLD stabilizes the amyloid facilitating state of HSA. In addition, SEM images demonstrated that VLD alleviates the hemolytic effect induced by fibrils of HSA. This study reports VLD as a potential inhibitor of amyloid fibrillation and provides promising results to repurpose VLD as a drug candidate for the cure of Alzheimer's diseases along with diabetes.