Oral treatment with the d-enantiomeric peptide D3 improves the pathology and behavior of Alzheimer's Disease transgenic mice

Tau- and α-synuclein-targeted gold nanoparticles: applications, opportunities, and future outlooks in the diagnosis and therapy of neurodegenerative diseases

The use of nanomaterials in medicine offers multiple opportunities to address neurodegenerative disorders such as Alzheimer's and Parkinson's disease. These diseases are a significant burden for society and the health system, affecting millions of people worldwide without sensitive and selective diagnostic methodologies or effective treatments to stop their progression. In this sense, the use of gold nanoparticles is a promising tool due to their unique properties at the nanometric level. They can be functionalized with specific molecules to selectively target pathological proteins such as Tau and α-synuclein for Alzheimer's and Parkinson's disease, respectively. Additionally, these proteins are used as diagnostic biomarkers, wherein gold nanoparticles play a key role in enhancing their signal, even at the low concentrations present in biological samples such as blood or cerebrospinal fluid, thus enabling an early and accurate diagnosis. On the other hand, gold nanoparticles act as drug delivery platforms, bringing therapeutic agents directly into the brain, improving treatment efficiency and precision, and reducing side effects in healthy tissues. However, despite the exciting potential of gold nanoparticles, it is crucial to address the challenges and issues associated with their use in the medical field before they can be widely applied in clinical settings. It is critical to ensure the safety and biocompatibility of these nanomaterials in the context of the central nervous system. Therefore, rigorous preclinical and clinical studies are needed to assess the efficacy and feasibility of these strategies in patients. Since there is scarce and sometimes contradictory literature about their use in this context, the main aim of this review is to discuss and analyze the current state-of-the-art of gold nanoparticles in relation to delivery, diagnosis, and therapy for Alzheimer's and Parkinson's disease, as well as recent research about their use in preclinical, clinical, and emerging research areas.

Exploring Peptido-Nanocomposites in the Context of Amyloid Diseases

Therapeutic peptides are a major class of pharmaceutical drugs owing to their target-binding specificity as well as their versatility in inhibiting aberrant protein-protein interactions associated with human pathologies. Within the realm of amyloid diseases, the use of peptides and peptidomimetics tailor-designed to overcome amyloidogenesis has been an active research endeavor since the late 90s. In more recent years, incorporating nanoparticles for enhancing the biocirculation and delivery of peptide drugs has emerged as a frontier in nanomedicine, and nanoparticles have further demonstrated a potency against amyloid aggregation and cellular inflammation to rival strategies employing small molecules, peptides, and antibodies. Despite these efforts, however, a fundamental understanding of the chemistry, characteristics and function of peptido-nanocomposites is lacking, and a systematic analysis of such strategy for combating a range of amyloid pathogeneses is missing. Here we review the history, principles and evolving chemistry of constructing peptido-nanocomposites from bottom up and discuss their future application against amyloid diseases that debilitate a significant portion of the global population.

Mirror-Image Phage Display for the Selection of D-Amino Acid Peptide Ligands as Potential Therapeutics

In neurodegenerative diseases like Alzheimer's disease (AD), endogenous proteins or peptides aggregate with themselves. These proteins may lose their function or aggregates and/or oligomers can obtain toxicity, causing injury or death to cells. Aggregation of two major proteins characterizes AD. Amyloid-β peptide (Aβ) is deposited in amyloid plaques within the extracellular space of the brain and Tau in so-called neurofibrillary tangles in neurons. Finding peptide ligands to halt protein aggregation is a promising therapeutical approach. Using mirror-image phage display with a commercially available, randomized 12-mer peptide library, we have selected D-amino acid peptides, which bind to the Tau protein and modulate its aggregation in vitro. Peptides can bind specifically and selectively to a target molecule, but natural L-amino acid peptides may have crucial disadvantages for in vivo applications, as they are sensitive to protease degradation and may elicit immune responses. One strategy to circumvent these disadvantages is the use of non-naturally occurring D-amino acid peptides as they exhibit increased protease resistance and generally do not activate the immune system. To perform mirror-image phage display, the target protein needs to be synthesized as D-amino acid version. If the target protein sequence is too long to be synthesized properly, smaller peptides derived from the full length protein can be used for the selection process. This also offers the possibility to influence the binding region of the selected D-peptides in the full-length target protein. Here we provide the protocols for mirror-image phage display selection on the PHF6* peptide of Tau, based on the commercially available Ph.D.™-12 Phage Display Peptide Library Kit, leading to D-peptides that also bind the full length Tau protein (Tau441), next to PHF6*. In addition, we provide protocols and data for the first characterization of those D-peptides that inhibit Tau aggregation in vitro. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Mirror image phage display selection against D-PHF6* fibrils Support Protocol 1: Single phage ELISA Basic Protocol 2: Sequencing and D-peptide generation Basic Protocol 3: Thioflavin-T (ThT) test to control inhibition of Tau aggregation Support Protocol 2: Purification of full-length Tau protein Basic Protocol 4: ELISA to demonstrate the binding of the generated D-peptides to PHF6* and full-length Tau fibrils.

Advances in Alzheimer's Disease-Associated Aβ Therapy Based on Peptide

Alzheimer's disease (AD) urgently needs innovative treatments due to the increasing aging population and lack of effective drugs and therapies. The amyloid fibrosis of AD-associated β-amyloid (Aβ) that could induce a series of cascades, such as oxidative stress and inflammation, is a critical factor in the progression of AD. Recently, peptide-based therapies for AD are expected to be great potential strategies for the high specificity to the targets, low toxicity, fast blood clearance, rapid cell and tissue permeability, and superior biochemical characteristics. Specifically, various chiral amino acids or peptide-modified interfaces draw much attention as effective manners to inhibit Aβ fibrillation. On the other hand, peptide-based inhibitors could be obtained through affinity screening such as phage display or by rational design based on the core sequence of Aβ fibrosis or by computer aided drug design based on the structure of Aβ. These peptide-based therapies can inhibit Aβ fibrillation and reduce cytotoxicity induced by Aβ aggregation and some have been shown to relieve cognition in AD model mice and reduce Aβ plaques in mice brains. This review summarizes the design method and characteristics of peptide inhibitors and their effect on the amyloid fibrosis of Aβ. We further describe some analysis methods for evaluating the inhibitory effect and point out the challenges in these areas, and possible directions for the design of AD drugs based on peptides, which lay the foundation for the development of new effective drugs in the future.

Synthesis and applications of mirror-image proteins

The homochirality of biomolecules in nature, such as DNA, RNA, peptides and proteins, has played a critical role in establishing and sustaining life on Earth. This chiral bias has also given synthetic chemists the opportunity to generate molecules with inverted chirality, unlocking valuable new properties and applications. Advances in the field of chemical protein synthesis have underpinned the generation of numerous 'mirror-image' proteins (those comprised entirely of D-amino acids instead of canonical L-amino acids), which cannot be accessed using recombinant expression technologies. This Review seeks to highlight recent work on synthetic mirror-image proteins, with a focus on modern synthetic strategies that have been leveraged to access these complex biomolecules as well as their applications in protein crystallography, drug discovery and the creation of mirror-image life.

Evaluation of the 18F-labeled analog of the therapeutic all-D-enantiomeric peptide RD2 for amyloid β imaging

Positron emission tomography (PET) imaging with radiotracers that bind to fibrillary amyloid β (Aβ) deposits is an important tool for the diagnosis of Alzheimer's disease (AD) and for the recruitment of patients into clinical trials. However, it has been suggested that rather than the fibrillary Aβ deposits, it is smaller, soluble Aβ aggregates that exert a neurotoxic effect and trigger AD pathogenesis. The aim of the current study is to develop a PET probe that is capable of detecting small aggregates and soluble Aβ oligomers for improved diagnosis and therapy monitoring. An ¹⁸F-labeled radioligand was prepared based on the Aβ-binding d-enantiomeric peptide RD2, which is currently being evaluated in clinical trials as a therapeutic agent to dissolve Aβ oligomers. ¹⁸F-labeling was carried out using palladium-catalyzed S-arylation of RD2 with 2-[¹⁸F]fluoro-5-iodopyridine ([¹⁸F]FIPy). Specific binding of [¹⁸F]RD2-cFPy to brain material from transgenic AD (APP/PS1) mice and AD patients was demonstrated with in vitro autoradiography. In vivo uptake and biodistribution of [¹⁸F]RD2-cFPy were evaluated using PET analyses in wild-type and transgenic APP/PS1 mice. Although brain penetration and brain wash-out kinetics of the radioligand were low, this study provides proof of principle for a PET probe based on a d-enantiomeric peptide binding to soluble Aβ species.

Tau Aggregation Inhibiting Peptides as Potential Therapeutics for Alzheimer Disease

Alzheimer disease (AD) is the most common progressive neurodegenerative disorder. AD causes enormous personal and economic burden to society as currently only limited palliative therapeutic options are available. The pathological hallmarks of the disease are extracellular plaques, composed of fibrillar amyloid-β (Aβ), and neurofibrillary tangles inside neurons, composed of Tau protein. Until recently, the search for AD therapeutics was focussed more on the Aβ peptide and its pathology, but the results were unsatisfying. As an alternative, Tau might be a promising therapeutic target as its pathology is closely correlated to clinical symptoms. In addition, pathological Tau aggregation occurs in a large group of diseases, called Tauopathies, and in most of them Aβ aggregation does not play a role in disease pathogenesis. The formation of Tau aggregates is triggered by two hexapeptide motifs within Tau; PHF6* and PHF6. Both fragments are interesting targets for the development of Tau aggregation inhibitors (TAI). Peptides represent a unique class of pharmaceutical compounds and are reasonable alternatives to chemical substances or antibodies. They are attributed with high biological activity, valuable specificity and low toxicity, and often are developed as drug candidates to interrupt protein-protein interactions. The preparation of peptides is simple, controllable and the peptides can be easily modified. However, their application may also have disadvantages. Currently, a few peptide compounds acting as TAI are described in the literature, most of them developed by structure-based design or phage display. Here, we review the current state of research in this promising field of AD therapy development.

Aβ-oligomers: A potential therapeutic target for Alzheimer's disease

The cascade of amyloid formation relates to multiple complex events at the molecular level. Previous research has established amyloid plaque deposition as the leading cause of Alzheimer's disease (AD) pathogenesis, detected mainly in aged population. The primary components of the plaques are two alloforms of amyloid-beta (Aβ), Aβ_1-42 and Aβ_1-40 peptides. Recent studies have provided considerable evidence contrary to the previous claim indicating that amyloid-beta oligomers (AβOs) as the main culprit responsible for AD-associated neurotoxicity and pathogenesis. In this review, we have discussed the primary features of AβOs, such as assembly formation, the kinetics of oligomer formation, interactions with various membranes/membrane receptors, the origin of toxicity, and oligomer-specific detection methods. Recently, the discovery of rationally designed antibodies has opened a gateway for using synthesized peptides as a grafting component in the complementarity determining region (CDR) of antibodies. Thus, the Aβ sequence motif or the complementary peptide sequence in the opposite strand of the β-sheet (extracted from the Protein Data Bank: PDB) helps design oligomer-specific inhibitors. The microscopic event responsible for oligomer formation can be targeted, and thus prevention of the overall macroscopic behaviour of the aggregation or the associated toxicity can be achieved. We have carefully reviewed the oligomer formation kinetics and associated parameters. Besides, we have depicted a thorough understanding of how the synthesized peptide inhibitors can impede the early aggregates (oligomers), mature fibrils, monomers, or a mixture of the species. The oligomer-specific inhibitors (peptides or peptide fragments) lack in-depth chemical kinetics and optimization control-based screening. In the present review, we have proposed a hypothesis for effectively screening oligomer-specific inhibitors using the chemical kinetics (determining the kinetic parameters) and optimization control strategy (cost-dependent analysis). Further, it may be possible to implement the structure-kinetic-activity-relationship (SKAR) strategy instead of structure-activity-relationship (SAR) to improve the inhibitor's activity. The controlled optimization of the kinetic parameters and dose usage will be beneficial for narrowing the search window for the inhibitors.

From Small Peptides to Large Proteins against Alzheimer’sDisease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder in the elderly. The two cardinal neuropathological hallmarks of AD are the senile plaques, which are extracellular deposits mainly constituted by beta-amyloids, and neurofibrillary tangles formed by abnormally phosphorylated Tau (p-Tau) located in the cytoplasm of neurons. Although the research has made relevant progress in the management of the disease, the treatment is still lacking. Only symptomatic medications exist for the disease, and, in the meantime, laboratories worldwide are investigating disease-modifying treatments for AD. In the present review, results centered on the use of peptides of different sizes involved in AD are presented.

Why the Ala-His-His Peptide Is an Appropriate Scaffold to Remove and Redox Silence Copper Ions from the Alzheimer’s-Related Aβ Peptide

The progressive, neurodegenerative Alzheimer’s disease (AD) is the most widespread dementia. Due to the ageing of the population and the current lack of molecules able to prevent or stop the disease, AD will be even more impactful for society in the future. AD is a multifactorial disease, and, among other factors, metal ions have been regarded as potential therapeutic targets. This is the case for the redox-competent Cu ions involved in the production of reactive oxygen species (ROS) when bound to the Alzheimer-related Aβ peptide, a process that contributes to the overall oxidative stress and inflammation observed in AD. Here, we made use of peptide ligands to stop the Cu(Aβ)-induced ROS production and we showed why the AHH sequence is fully appropriate, while the two parents, AH and AAH, are not. The AHH peptide keeps its beneficial ability against Cu(Aβ)-induced ROS, even in the presence of Zn^II-competing ions and other biologically relevant ions. The detailed kinetic mechanism by which AHH could exert its action against Cu(Aβ)-induced ROS is also proposed.

Signature Effects of Vector-Guided Systemic Nano Bioconjugate Delivery Across Blood-Brain Barrier of Normal, Alzheimer's, and Tumor Mouse Models

The ability to cross the blood-brain barrier (BBB) is critical for targeted therapy of the central nerve system (CNS). Six peptide vectors were covalently attached to a 50 kDa poly(β-l-malic acid)-trileucine polymer forming P/LLL(40%)/vector conjugates. The vectors were Angiopep-2 (AP2), B6, Miniap-4 (M4), and d-configurated peptides D1, D3, and ACI-89, with specificity for transcytosis receptors low-density lipoprotein receptor-related protein-1 (LRP-1), transferrin receptor (TfR), bee venom-derived ion channel, and Aβ/LRP-1 related transcytosis complex, respectively. The BBB-permeation efficacies were substantially increased ("boosted") in vector conjugates of P/LLL(40%). We have found that the copolymer group binds at the endothelial membrane and, by an allosterically membrane rearrangement, exposes the sites for vector-receptor complex formation. The specificity of vectors is indicated by competition experiments with nonconjugated vectors. P/LLL(40%) does not function as an inhibitor, suggesting that the copolymer binding site is eliminated after binding of the vector-nanoconjugate. The two-step mechanism, binding to endothelial membrane and allosteric exposure of transcytosis receptors, is supposed to be an integral feature of nanoconjugate-transcytosis pathways. In vivo brain delivery signatures of the nanoconjugates were recapitulated in mouse brains of normal, tumor (glioblastoma), and Alzheimer's disease (AD) models. BBB permeation of the tumor was most efficient, followed by normal and then AD-like brain. In tumor-bearing and normal brains, AP2 was the top performing vector; however, in AD models, D3 and D1 peptides were superior ones. The TfR vector B6 was equally efficient in normal and AD-model brains. Cross-permeation efficacies are manifested through modulated vector coligation and dosage escalation such as supra-linear dose dependence and crossover transcytosis activities.

Rational and Translational Implications of D-Amino Acids for Treatment-Resistant Schizophrenia: From Neurobiology to the Clinics

Schizophrenia has been conceptualized as a neurodevelopmental disorder with synaptic alterations and aberrant cortical–subcortical connections. Antipsychotics are the mainstay of schizophrenia treatment and nearly all share the common feature of dopamine D2 receptor occupancy, whereas glutamatergic abnormalities are not targeted by the presently available therapies. D-amino acids, acting as N-methyl-D-aspartate receptor (NMDAR) modulators, have emerged in the last few years as a potential augmentation strategy in those cases of schizophrenia that do not respond well to antipsychotics, a condition defined as treatment-resistant schizophrenia (TRS), affecting almost 30–40% of patients, and characterized by serious cognitive deficits and functional impairment. In the present systematic review, we address with a direct and reverse translational perspective the efficacy of D-amino acids, including D-serine, D-aspartate, and D-alanine, in poor responders. The impact of these molecules on the synaptic architecture is also considered in the light of dendritic spine changes reported in schizophrenia and antipsychotics’ effect on postsynaptic density proteins. Moreover, we describe compounds targeting D-amino acid oxidase and D-aspartate oxidase enzymes. Finally, other drugs acting at NMDAR and proxy of D-amino acids function, such as D-cycloserine, sarcosine, and glycine, are considered in the light of the clinical burden of TRS, together with other emerging molecules.

Interaction of Therapeutic d-Peptides with Aβ42 Monomers, Thermodynamics, and Binding Analysis

The aggregation of the amyloid-β (Aβ) peptide is a major hallmark of Alzheimer's disease. This peptide can aggregate into oligomers, proto-fibrils, and mature fibrils, which eventually assemble into amyloid plaques. The peptide monomers are the smallest assembly units and play an important role in most of the individual processes involved in amyloid fibril formation, such as primary and secondary nucleation and elongation. Several d-peptides have been confirmed as promising candidates to inhibit the aggregation of Aβ into toxic oligomers and fibrils by specifically interacting with monomeric species. In this work, we elucidate the structural interaction and thermodynamics of binding between three d-peptides (D3, ANK6, and RD2) and Aβ42 monomers by means of enhanced molecular dynamics simulations. Our study derives thermodynamic energies in good agreement with experimental values and suggests that there is an enhanced binding for D3 and ANK6, which leads to more stable complexes than for RD2. The binding of D3 to Aβ42 is shown to be weakly exothermic and mainly entropically driven, whereas the complex formation between the ANK6 and RD2 with the Aβ42 free monomer is weakly endothermic. In addition, the changes in the solvent-accessible surface area and the radius of gyration support that the binding between Aβ42 and d-peptides is mainly driven by electrostatic and hydrophobic interactions and leads to more compact conformations.

Aβ oligomer concentration in mouse and human brain and its drug-induced reduction ex vivo

The elimination of amyloid beta (Aβ) oligomers is a promising strategy for therapeutic drug development of Alzheimer's disease (AD). AD mouse models that develop Aβ pathology have been used to demonstrate in vivo efficacy of compounds that later failed in clinical development. Here, we analyze the concentration and size distribution of Aβ oligomers in different transgenic mouse models of AD and in human brain samples by surface-based fluorescence intensity distribution analysis (sFIDA), a highly sensitive method for detecting and quantitating protein aggregates. We demonstrate dose- and time-dependent oligomer elimination by the compound RD2 in mouse and human AD brain homogenates as sources of native Aβ oligomers. Such ex vivo target engagement analyses with mouse- and human-brain-derived oligomers have the potential to enhance the translational value from pre-clinical proof-of-concept studies to clinical trials.

A novel D-amino acid peptide with therapeutic potential (ISAD1) inhibits aggregation of neurotoxic disease-relevant mutant Tau and prevents Tau toxicity in vitro

Background

Alzheimer’s disease (AD), the most common form of dementia, is a progressive neurodegenerative disorder that mainly affects older adults. One of the pathological hallmarks of AD is abnormally aggregated Tau protein that forms fibrillar deposits in the brain. In AD, Tau pathology correlates strongly with clinical symptoms, cognitive dysfunction, and neuronal death.

Methods

We aimed to develop novel therapeutic D-amino acid peptides as Tau fibrillization inhibitors. It has been previously demonstrated that D-amino acid peptides are protease stable and less immunogenic than L-peptides, and these characteristics may render them suitable for in vivo applications. Using a phage display procedure against wild type full-length Tau (Tau^FL), we selected a novel Tau binding L-peptide and synthesized its D-amino acid version ISAD1 and its retro inversed form, ISAD1rev, respectively.

Results

While ISAD1rev inhibited Tau aggregation only moderately, ISAD1 bound to Tau in the aggregation-prone PHF6 region and inhibited fibrillization of Tau^FL, disease-associated mutant full-length Tau (Tau^FLΔK, Tau^FL-A152T, Tau^FL-P301L), and pro-aggregant repeat domain Tau mutant (Tau^RDΔK). ISAD1 and ISAD1rev induced the formation of large high molecular weight Tau^FL and Tau^RDΔK oligomers that lack proper Thioflavin-positive β-sheet conformation even at lower concentrations. In silico modeling of ISAD1 Tau interaction at the PHF6 site revealed a binding mode similar to those known for other PHF6 binding peptides. Cell culture experiments demonstrated that ISAD1 and its inverse form are taken up by N2a-Tau^RDΔK cells efficiently and prevent cytotoxicity of externally added Tau fibrils as well as of internally expressed Tau^RDΔK.

Conclusions

ISAD1 and related peptides may be suitable for therapy development of AD by promoting off-pathway assembly of Tau, thus preventing its toxicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-00959-z.

finDr: A web server for in silico D-peptide ligand identification

In the rapidly expanding field of peptide therapeutics, the short in vivo half-life of peptides represents a considerable limitation for drug action. D-peptides, consisting entirely of the dextrorotatory enantiomers of naturally occurring levorotatory amino acids (AAs), do not suffer from these shortcomings as they are intrinsically resistant to proteolytic degradation, resulting in a favourable pharmacokinetic profile. To experimentally identify D-peptide binders to interesting therapeutic targets, so-called mirror-image phage display is typically performed, whereby the target is synthesized in D-form and L-peptide binders are screened as in conventional phage display. This technique is extremely powerful, but it requires the synthesis of the target in D-form, which is challenging for large proteins. Here we present finDr, a novel web server for the computational identification and optimization of D-peptide ligands to any protein structure (https://findr.biologie.uni-freiburg.de/). finDr performs molecular docking to virtually screen a library of helical 12-mer peptides extracted from the RCSB Protein Data Bank (PDB) for their ability to bind to the target. In a separate, heuristic approach to search the chemical space of 12-mer peptides, finDr executes a customizable evolutionary algorithm (EA) for the de novo identification or optimization of D-peptide ligands. As a proof of principle, we demonstrate the validity of our approach to predict optimal binders to the pharmacologically relevant target phenol soluble modulin alpha 3 (PSMα3), a toxin of methicillin-resistant Staphylococcus aureus (MRSA). We validate the predictions using in vitro binding assays, supporting the success of this approach. Compared to conventional methods, finDr provides a low cost and easy-to-use alternative for the identification of D-peptide ligands against protein targets of choice without size limitation. We believe finDr will facilitate D-peptide discovery with implications in biotechnology and biomedicine.

The Amyloid-β1-42-oligomer interacting peptide D-AIP possesses favorable biostability, pharmacokinetics, and brain region distribution

We have previously developed a unique 8-amino acid Aβ42 oligomer-Interacting Peptide (AIP) as a novel anti-amyloid strategy for the treatment of Alzheimer’s disease. Our lead candidate has successfully progressed from test tubes (i.e., in vitro characterization of protease-resistant D-AIP) to transgenic flies (i.e., in vivo rescue of human Aβ42-mediated toxicity via D-AIP-supplemented food). In the present study, we examined D-AIP in terms of its stability in multiple biological matrices (i.e., ex-vivo mouse plasma, whole blood, and liver S9 fractions) using MALDI mass spectrometry, pharmacokinetics using a rapid and sensitive LC-MS method, and blood brain barrier (BBB) penetrance in WT C57LB/6 mice. D-AIP was found to be relatively stable over 3 h at 37 °C in all matrices tested. Finally, label-free MALDI imaging showed that orally administered D-AIP can readily penetrate the intact BBB in both male and female WT mice. Based upon the favorable stability, pharmacokinetics, and BBB penetration outcomes for orally administered D-AIP in WT mice, we then examined the effect of D-AIP on amyloid “seeding” in vitro (i.e., freshly monomerized versus preaggregated Aβ42). Complementary biophysical assays (ThT, TEM, and MALDI-TOF MS) showed that D-AIP can directly interact with synthetic Aβ42 aggregates to disrupt primary and/or secondary seeding events. Taken together, the unique mechanistic and desired therapeutic potential of our lead D-AIP candidate warrants further investigation, that is, testing of D-AIP efficacy on the altered amyloid/tau pathology in transgenic mouse models of Alzheimer’s disease.

All-d-Enantiomeric Peptide D3 Designed for Alzheimer's Disease Treatment Dynamically Interacts with Membrane-Bound Amyloid-β Precursors

Alzheimer's disease (AD) is a severe neurodegenerative pathology with no effective treatment known. Toxic amyloid-β peptide (Aβ) oligomers play a crucial role in AD pathogenesis. All-d-Enantiomeric peptide D3 and its derivatives were developed to disassemble and destroy cytotoxic Aβ aggregates. One of the D3-like compounds is approaching phase II clinical trials; however, high-resolution details of its disease-preventing or pharmacological actions are not completely clear. We demonstrate that peptide D3 stabilizing Aβ monomer dynamically interacts with the extracellular juxtamembrane region of a membrane-bound fragment of an amyloid precursor protein containing the Aβ sequence. MD simulations based on NMR measurement results suggest that D3 targets the amyloidogenic region, not compromising its α-helicity and preventing intermolecular hydrogen bonding, thus creating prerequisites for inhibition of early steps of Aβ conversion into β-conformation and its toxic oligomerization. An enhanced understanding of the D3 action molecular mechanism facilitates development of effective AD treatment and prevention strategies.

Potent Tau Aggregation Inhibitor D-Peptides Selected against Tau-Repeat 2 Using Mirror Image Phage Display

Alzheimer's disease and other Tauopathies are associated with neurofibrillary tangles composed of Tau protein, as well as toxic Tau oligomers. Therefore, inhibitors of pathological Tau aggregation are potentially useful candidates for future therapies targeting Tauopathies. Two hexapeptides within Tau, designated PHF6* (275-VQIINK-280) and PHF6 (306-VQIVYK-311), are known to promote Tau aggregation. Recently, the PHF6* segment has been described as the more potent driver of Tau aggregation. We therefore employed mirror-image phage display with a large peptide library to identify PHF6* fibril binding peptides consisting of D-enantiomeric amino acids. The suitability of D-enantiomeric peptides for in vivo applications, which are protease stable and less immunogenic than L-peptides, has already been demonstrated. The identified D-enantiomeric peptide MMD3 and its retro-inverso form, designated MMD3rev, inhibited in vitro fibrillization of the PHF6* peptide, the repeat domain of Tau as well as full-length Tau. Dynamic light scattering, pelleting assays and atomic force microscopy demonstrated that MMD3 prevents the formation of tau β-sheet-rich fibrils by diverting Tau into large amorphous aggregates. NMR data suggest that the D-enantiomeric peptides bound to Tau monomers with rather low affinity, but ELISA (enzyme-linked immunosorbent assay) data demonstrated binding to PHF6* and full length Tau fibrils. In addition, molecular insight into the binding mode of MMD3 to PHF6* fibrils were gained by in silico modelling. The identified PHF6*-targeting peptides were able to penetrate cells. The study establishes PHF6* fibril binding peptides consisting of D-enantiomeric amino acids as potential molecules for therapeutic and diagnostic applications in AD research.

Breaker peptides against amyloid-β aggregation: a potential therapeutic strategy for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, for which blocking the early steps of extracellular misfolded amyloid-β (Aβ) aggregation is a promising therapeutic approach. However, the pathological features of AD progression include the accumulation of intracellular tau protein, membrane-catalyzed cell death and the abnormal deposition of Aβ. Here, we focus on anti-amyloid breaker peptides derived from the Aβ sequence and non-Aβ-based peptides containing both natural and modified amino acids. Critical aspects of the breaker peptides include N-methylation, conformational restriction through cyclization, incorporation of unnatural amino acid, fluorinated molecules, polymeric nanoparticles and PEGylation. This review confers a general idea of such breaker peptides with in vitro and in vivo studies, which may advance our understanding of AD pathology and develop an effective treatment strategy against AD.

Gene therapy using Aβ variants for amyloid reduction

Numerous aggregation inhibitors have been developed with the goal of blocking or reversing toxic amyloid formation in vivo. Previous studies have used short peptide inhibitors targeting different amyloid β (Aβ) amyloidogenic regions to prevent aggregation. Despite the specificity that can be achieved by peptide inhibitors, translation of these strategies has been thwarted by two key obstacles: rapid proteolytic degradation in the bloodstream and poor transfer across the blood-brain barrier. To circumvent these problems, we have created a minigene to express full-length Aβ variants in the mouse brain. We identify two variants, F20P and F19D/L34P, that display four key properties required for therapeutic use: neither peptide aggregates on its own, both inhibit aggregation of wild-type Aβ in vitro, promote disassembly of pre-formed fibrils, and diminish toxicity of Aβ oligomers. We used intraventricular injection of adeno-associated virus (AAV) to express each variant in APP/PS1 transgenic mice. Lifelong expression of F20P, but not F19D/L34P, diminished Aβ levels, plaque burden, and plaque-associated neuroinflammation. Our findings suggest that AAV delivery of Aβ variants may offer a novel therapeutic strategy for Alzheimer's disease. More broadly our work offers a framework for identifying and delivering peptide inhibitors tailored to other protein-misfolding diseases.

Potent intracellular antibacterial activity of a marine peptide-N6NH2 and its D-enantiomer against multidrug-resistant Aeromonas veronii

Aeromonas veronii can cause a variety of diseases such as sepsis in humans and animals. However, there has been no effective way to eradicate A. veronii. In this study, the intracellular antibacterial activities of the C-terminal aminated marine peptide N6 (N6NH₂) and its D-enantiomer (DN6NH₂) against A. veronii were investigated in macrophages and in mice, respectively. The result showed that DN6NH₂ with the minimum inhibitory concentration (MIC) of 1.62 μM is more resistant to cathepsin B than N6NH₂ (3.23 μM). The penetration percentages of the cells treated with 4-200 μg/mL fluorescein isothiocyanate (FITC)-DN6NH₂ were 52.5-99.6%, higher than those of FITC-N6NH₂ (27.0-99.1%). Both N6NH₂ and DN6NH₂ entered macrophages by macropinocytosis and an energy-dependent manner. DN6NH₂ reduced intracellular A. veronii by 34.57%, superior to N6NH₂ (19.52%). After treatment with 100 μg/mL DN6NH₂, the levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β were reduced by 53.45%, 58.54%, and 44.62%, respectively, lower than those of N6NH₂ (15.65%, 12.88%, and 14.10%, respectively); DN6NH₂ increased the IL-10 level (42.94%), higher than N6NH₂ (7.67%). In the mice peritonitis model, 5 μmol/kg DN6NH₂ reduced intracellular A. veronii colonization by 73.22%, which was superior to N6NH₂ (32.45%) or ciprofloxacin (45.67%). This suggests that DN6NH₂ may be used as the candidate for treating intracellular multidrug-resistant (MDR) A. veronii. KEY POINTS: • DN6NH₂ improved intracellular antibacterial activity against MDR A. veronii. • DN6NH₂ entered macrophages by micropinocytosis and enhanced the internalization rates. • DN6NH₂ effectively protected the mice from infection with A. veronii.

Efficient suppression of amyloid-β peptide aggregation and cytotoxicity with photosensitive polymer nanodots

The deposition of amyloid plaques resulting from the aggregation of amyloid-β (Aβ) peptides is closely related to Alzheimer's disease (AD). With the development of various therapeutic methods, the oxidative modification of Aβ has emerged as a fascinating noninvasive photo-therapeutic intervention for treating AD by altering the Aβ aggregation tendency. Herein, we report the photo-triggered inhibition of Aβ aggregation and cytotoxicity by utilizing polymer nanodots (Pdots) modified with rose bengal (RB), methylene blue (MB), and riboflavin (RF). Experimental results demonstrate that these functionalized Pdots manifest a superior suppression effect on Aβ aggregation under irradiation. This can be attributed to the formation of reactive oxygen species (ROS) (i.e., singlet oxygen (¹O₂)), resulting in the oxygenation of Aβ and the change of Aβ aggregation tendency. Especially, RB-Pdots manifest better biocompatibility and higher ¹O₂ productivity. In a word, this hybridized nanostructure will provide a promising platform for the noninvasive photo-therapeutic treatment of AD in the future.

[D-enantiomeric peptides could be a new therapeutic approach in Alzheimer's disease]

Pour la quatrième année, dans le cadre du module d’enseignement « Physiopathologie de la signalisation » proposé par l’université Paris-sud, les étudiants du Master « Biologie Santé » de l’université Paris-Saclay se sont confrontés à l’écriture scientifique. Ils ont sélectionné 15 articles scientifiques récents dans le domaine de la signalisation cellulaire présentant des résultats originaux, via des approches expérimentales variées, sur des thèmes allant des relations hôte-pathogène aux innovations thérapeutiques, en passant par la signalisation hépatique et le métabolisme. Après un travail préparatoire réalisé avec l’équipe pédagogique, les étudiants, organisés en binômes, ont ensuite rédigé, guidés par des chercheurs, une Nouvelle soulignant les résultats majeurs et l’originalité de l’article étudié. Ils ont beaucoup apprécié cette initiation à l’écriture d’articles scientifiques et, comme vous pourrez le lire, se sont investis dans ce travail avec enthousiasme ! Deux de ces Nouvelles sont publiées dans ce numéro, les autres le seront dans des prochains numéros.

Toward the Mode of Action of the Clinical Stage All-d-Enantiomeric Peptide RD2 on Aβ42 Aggregation

The aggregation of amyloid-β (Aβ) into oligomers and fibrillary structures is critical for the pathogenesis of Alzheimer's disease (AD). Recently, research effort has been focused on developing novel agents that can preferentially suppress Aβ oligomer mediated toxicities, for example, by directly targeting these toxic assemblies. The compound RD2 has been developed and optimized for Aβ42 monomer binding and stabilization of the monomer in its native intrinsically disordered conformation. It has been demonstrated to improve and even reverse the cognitive and behavioral deficits in AD mouse models, while the detailed mechanism of action is not fully clarified. Here we focused on exploring the interaction between RD2 and Aβ42 monomers and its consequences for the fibrillation of Aβ42. RD2 binds to Aβ42 monomers with nanomolar affinities, according to microscale thermophoresis and surface plasmon resonance measurements. Complexes between RD2 and Aβ42 monomers are formed at 1:1 and other stoichiometries, as revealed by analytical ultracentrifugation. At substoichiometric levels, RD2 slows down the secondary structure conversion of Aβ42 and significantly delays the fibril formation. Our research provides experimental evidence in supporting that RD2 eliminates toxic Aβ assemblies by stabilizing Aβ monomers in their native intrinsically disordered conformation. The study further supports the promising application of RD2 in counteracting Aβ aggregation related pathologies.

Computational screening of nanoparticles coupling to Aβ40 peptides and fibrils

Blocking the formation, growth, and breaking of amyloid fibrils by synthetic nanosystems could provide a treatment of neurodegenerative diseases. With this in mind, here atomistic molecular dynamics simulations are used to screen for nanoparticles (NPs), covered with different mixtures of ligands, including positively and negatively charged ligands, Aβ40-cut-peptide, and synthetic inhibitor ligands, in their selective coupling to Aβ40 peptides and their fibrils. The simulations reveal that only Aβ40-cut-peptide-covered NPs have strong and selective coupling to Aβ40 monomers. On the other hand, positive, positive-neutral, Janus, and peptide NPs couple to the beta sheet surfaces of Aβ40 fibrils and only the negative-neutral NPs couple to the fibril tips.

Structural Insights into Curli CsgA Cross-β Fibril Architecture Inspire Repurposing of Anti-amyloid Compounds as Anti-biofilm Agents

Curli amyloid fibrils secreted by Enterobacteriaceae mediate host cell adhesion and contribute to biofilm formation, thereby promoting bacterial resistance to environmental stressors. Here, we present crystal structures of amyloid-forming segments from the major curli subunit, CsgA, revealing steric zipper fibrils of tightly mated β-sheets, demonstrating a structural link between curli and human pathological amyloids. D-enantiomeric peptides, originally developed to interfere with Alzheimer's disease-associated amyloid-β, inhibited CsgA fibrillation and reduced biofilm formation in Salmonella typhimurium. Moreover, as previously shown, CsgA fibrils cross-seeded fibrillation of amyloid-β, providing support for the proposed structural resemblance and potential for cross-species amyloid interactions. The presented findings provide structural insights into amyloidogenic regions important for curli formation, suggest a novel strategy for disrupting amyloid-structured biofilms, and hypothesize on the formation of self-propagating prion-like species originating from a microbial source that could influence neurodegenerative diseases.

In Vitro Potency and Preclinical Pharmacokinetic Comparison of All-D-Enantiomeric Peptides Developed for the Treatment of Alzheimer's Disease

Diffusible amyloid-β (Aβ) oligomers are currently presumed to be the most cytotoxic Aβ assembly and held responsible to trigger the pathogenesis of Alzheimer’s disease (AD). Thus, Aβ oligomers are a prominent target in AD drug development. Previously, we reported on our solely D-enantiomeric peptide D3 and its derivatives as AD drug candidates. Here, we compare one of the most promising D3 derivatives, ANK6, with its tandem version (tANK6), and its head-to-tail cyclized isoform (cANK6r). In vitro tests investigating the D-peptides’ potencies to inhibit Aβ aggregation, eliminate Aβ oligomers, and reduce Aβ-induced cytotoxicity revealed that all three D-peptides efficiently target Aβ. Subsequent preclinical pharmacokinetic studies of the three all-D-peptides in wildtype mice showed promising blood-brain barrier permeability with cANK6r yielding the highest levels in brain. The peptides’ potencies to lower Aβ toxicity and their remarkable brain/plasma ratios make them promising AD drug candidates.

Interference with Amyloid-β Nucleation by Transient Ligand Interaction

Amyloid-β peptide (Aβ) is an intrinsically disordered protein (IDP) associated with Alzheimer's disease. The structural flexibility and aggregation propensity of Aβ pose major challenges for elucidating the interaction between Aβ monomers and ligands. All-D-peptides consisting solely of D-enantiomeric amino acid residues are interesting drug candidates that combine high binding specificity with high metabolic stability. Here we characterized the interaction between the 12-residue all-D-peptide D3 and Aβ42 monomers, and how the interaction influences Aβ42 aggregation. We demonstrate for the first time that D3 binds to Aβ42 monomers with submicromolar affinities. These two highly unstructured molecules are able to form complexes with 1:1 and other stoichiometries. Further, D3 at substoichiometric concentrations effectively slows down the β-sheet formation and Aβ42 fibrillation by modulating the nucleation process. The study provides new insights into the molecular mechanism of how D3 affects Aβ assemblies and contributes to our knowledge on the interaction between two IDPs.

d-Enantiomeric RTHLVFFARK-NH2: A Potent Multifunctional Decapeptide Inhibiting Cu2+-Mediated Amyloid β-Protein Aggregation and Remodeling Cu2+-Mediated Amyloid β Aggregates

Aggregation of amyloid β-protein (Aβ) into β-sheet-rich plaques is a general feature of Alzheimer's disease (AD). Homeostasis dysregulation of Cu²⁺ mediates Aβ to form high cytotoxic aggregates, which causes cell damage by generation of reactive oxygen species (ROS). To improve the inhibitory potency and explore the multifaceted functions of our previously designed decapeptide, RTHLVFFARK-NH₂ (RK10), we have herein reformulated the decapeptide into its d-enantiomer, rk10, and the effects of chirality on Aβ aggregation, Cu²⁺-mediated Aβ aggregations, and aggregate-remodeling effects were investigated. The results revealed the following: (1) The d-enantiomer presented enhanced inhibitory potency on Aβ fibrillogenesis in comparison to RK10; rk10 and RK10 increased the cell viability from 60% to 91% and 71%, respectively, at an equimolar concentration to Aβ. (2) The enantiomers were chemically equivalent to Cu²⁺ chelation, ROS suppression and oxidative damage rescue. (3) The d-enantiomer exhibited higher performance to inhibit Cu²⁺-mediated Aβ aggregation, and more significantly attenuated the cytotoxicity caused by Aβ₄₂-Cu²⁺ complex than RK10. Cell viability was rescued from 51% to 89% and 74% by coincubating with rk10 and RK10 at 50 μM, respectively. Intracellular ROS levels generated by Aβ₄₂ and Aβ₄₂-Cu²⁺ species were also remarkably decreased by treating with rk10. (4) The enantiomers could remodel mature Aβ₄₂-Cu²⁺ aggregates by Cu²⁺ chelation, and rk10 showed higher performance than RK10, as evidenced by the enhanced cell viability from 57% to 86% by RK10 and to 96% by rk10. The d-enantiomer also showed higher ability than RK10 on protecting the disrupted species from reaggregation. Taken together, D-chiral derivatization of the decapeptide resulted in a potent multifunctional agent in inhibiting Cu²⁺-mediated Aβ aggregation and remodeling mature Aβ-Cu²⁺ species. To the best of our knowledge, this is the first investigation on the chirality effect of a multifunctional peptide inhibitor on Cu²⁺-mediated Aβ aggregation and on the remodeling effect of mature Aβ-Cu²⁺ aggregates. The work provides new insights into the critical role of chirality in the multifaceted functions of peptide inhibitors against amyloid formation and its toxicity.

Role of Hydrophobicity and Charge of Amyloid-Beta Oligomer Eliminating d-Peptides in the Interaction with Amyloid-Beta Monomers

Inhibition of the self-assembly process of amyloid-beta and even more the removal of already existing toxic amyloid-beta assemblies represent promising therapeutic strategies against Alzheimer's disease. To approach this aim, we selected a d-enantiomeric peptide by phage-display based on the interaction with amyloid-beta monomers. This lead compound was successfully optimized by peptide microarrays with respect to its affinity and specificity to the target resulting in d-peptides with both increased hydrophobicity and net charge. Here, we present a detailed biophysical characterization of the interactions between these optimized d-peptides and amyloid-beta monomers in comparison to the original lead compound in order to obtain a more thorough understanding of the physicochemical determinants of the interactions. Kinetics and apparent stoichiometry of complex formation were studied using surface plasmon resonance. Potential modes of binding to amyloid-beta were identified, and the influences of ionic strength on complex stability, as well as on the inhibitory effect on amyloid-beta aggregation were investigated. The results reveal a very different mode of interaction of the optimized d-peptides based on a combination of electrostatic and hydrophobic interactions as compared to the mostly electrostatically driven interaction of the lead compound. These conclusions were supported by the thermodynamic profiles of the interaction between optimized d-peptides and Aβ monomers, which indicate an increase in binding entropy with respect to the lead compound.

Deceleration of the neurodegenerative phenotype in pyroglutamate-Aβ accumulating transgenic mice by oral treatment with the Aβ oligomer eliminating compound RD2

Alzheimer's disease, a multifactorial incurable disorder, is mainly characterised by progressive neurodegeneration, extracellular accumulation of amyloid-β protein (Aβ), and intracellular aggregation of hyperphosphorylated tau protein. During the last years, Aβ oligomers have been claimed to be the disease causing agent. Consequently, development of compounds that are able to disrupt already existing Aβ oligomers is highly desirable. We developed d-enantiomeric peptides, consisting solely of d-enantiomeric amino acid residues, for the direct and specific elimination of toxic Aβ oligomers. The drug candidate RD2 did show high oligomer elimination efficacy in vitro and the in vivo efficacy of RD2 was demonstrated in treatment studies by enhanced cognition in transgenic mouse models of amyloidosis. Here, we report on the in vitro and in vivo efficacy of the compound towards pyroglutamate-Aβ, a particular aggressive Aβ species. Using the transgenic TBA2.1 mouse model, which develops pyroglutamate-Aβ_(3-42) induced neurodegeneration, we are able to show that oral RD2 treatment resulted in a significant deceleration of the progression of the phenotype. The in vivo efficacy against this highly toxic Aβ species further validates RD2 as a drug candidate for the therapeutic use in humans.

A d-enantiomeric peptide interferes with heteroassociation of amyloid-β oligomers and prion protein

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects millions of people worldwide. One AD hallmark is the aggregation of β-amyloid (Aβ) into soluble oligomers and insoluble fibrils. Several studies have reported that oligomers rather than fibrils are the most toxic species in AD progression. Aβ oligomers bind with high affinity to membrane-associated prion protein (PrP), leading to toxic signaling across the cell membrane, which makes the Aβ-PrP interaction an attractive therapeutic target. Here, probing this interaction in more detail, we found that both full-length, soluble human (hu) PrP(23-230) and huPrP(23-144), lacking the globular C-terminal domain, bind to Aβ oligomers to form large complexes above the megadalton size range. Following purification by sucrose density-gradient ultracentrifugation, the Aβ and huPrP contents in these heteroassemblies were quantified by reversed-phase HPLC. The Aβ:PrP molar ratio in these assemblies exhibited some limited variation depending on the molar ratio of the initial mixture. Specifically, a molar ratio of about four Aβ to one huPrP in the presence of an excess of huPrP(23-230) or huPrP(23-144) suggested that four Aβ units are required to form one huPrP-binding site. Of note, an Aβ-binding all-d-enantiomeric peptide, RD2D3, competed with huPrP for Aβ oligomers and interfered with Aβ-PrP heteroassembly in a concentration-dependent manner. Our results highlight the importance of multivalent epitopes on Aβ oligomers for Aβ-PrP interactions and have yielded an all-d-peptide-based, therapeutically promising agent that competes with PrP for these interactions.

d-Amino Acid Pseudopeptides as Potential Amyloid-Beta Aggregation Inhibitors

A causative factor for neurotoxicity associated with Alzheimer's disease is the aggregation of the amyloid-β (Aβ) peptide into soluble oligomers. Two all d-amino acid pseudo-peptides, SGB1 and SGD1, were designed to stop the aggregation. Molecular dynamics (MD) simulations have been carried out to study the interaction of the pseudo-peptides with both Aβ13⁻23 (the core recognition site of Aβ) and full-length Aβ1⁻42. Umbrella sampling MD calculations have been used to estimate the free energy of binding, ∆G, of these peptides to Aβ13⁻23. The highest ∆Gbinding is found for SGB1. Each of the pseudo-peptides was also docked to Aβ1⁻42 and subjected up to seven microseconds of all atom molecular dynamics simulations. The resulting structures lend insight into how the dynamics of Aβ1⁻42 are altered by complexation with the pseudo-peptides and confirmed that SGB1 may be a better candidate for developing into a drug to prevent Alzheimer's disease.

C-Terminal Fragment, Aβ39-42-Based Tetrapeptides Mitigates Amyloid-β Aggregation-Induced Toxicity

Since the introduction of acetyl cholinesterase inhibitors as the first approved drugs by the US Food and Drug Administration for Alzheimer's disease (AD) in clinics, less than satisfactory success in the design of anti-AD agents has impelled the scientists to also focus toward inhibition of Aβ aggregation. Considering the specific binding of fragments for their parent peptide, herein, we synthesized more than 40 new peptides based on a C-terminus tetrapeptide fragment of Aβ_1-42. Initial screening by MTT cell viability assay and supportive results by ThT fluorescence assay led us to identify a tetrapeptide showing complete inhibition for Aβ_1-42 aggregation. Peptide 20 displayed 100% cell viability at 20 μM concentration, while at lower concentrations of 10 and 2 μM 76.6 and 70% of cells were viable. Peptide 20 was found to restrict the conformational transition of Aβ_1-42 peptide toward β-sheet structure. Inhibitory activity of tetrapeptide 20 was further evidenced by the absence of Aβ_1-42 aggregates in electron microscopy. Peptide 20 and other significantly active tetrapeptide analogues could prove imperative in the future design of anti-AD agents.

Peptides, Peptidomimetics, and Carbohydrate-Peptide Conjugates as Amyloidogenic Aggregation Inhibitors for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder accounting for 60-80% of dementia cases. For many years, AD causality was attributed to amyloid-β (Aβ) aggregated species. Recently, multiple therapies that target Aβ aggregation have failed in clinical trials, since Aβ aggregation is found in AD and healthy patients. Attention has therefore shifted toward the aggregation of the tau protein as a major driver of AD. Numerous inhibitors of tau-based pathology have recently been developed. Diagnosis of AD has shifted from measuring late stage senile plaques to early stage biomarkers, amyloid-β and tau monomers and oligomeric assemblies. Synthetic peptides and some derivative structures are being explored for use as theranostic tools as they possess the capacity both to bind the biomarkers and to inhibit their pathological self-assembly. Several studies have demonstrated that O-linked glycoside addition can significantly alter amyloid aggregation kinetics. Furthermore, natural O-glycosylation of amyloid-forming proteins, including amyloid precursor protein (APP), tau, and α-synuclein, promotes alternative nonamyloidogenic processing pathways. As such, glycopeptides and related peptidomimetics are being investigated within the AD field. Here we review advancements made in the last 5 years, as well as the arrival of sugar-based derivatives.

Structure, function and antagonism of semen amyloids

Amyloid fibrils are linear polypeptide aggregates with a cross-β structure. These fibrils are best known for their association with neurodegenerative diseases, such as Alzheimer's or Parkinson's, but they may also be used by living organisms as functional units, e.g. in the synthesis of melanin or in the formation of bacterial biofilms. About a decade ago, in a search for semen factors that modulate infection by HIV-1 (a sexually transmitted virus and the causative agent of the acquired immune deficiency syndrome (AIDS)), it was demonstrated that semen harbors amyloid fibrils capable of markedly increasing HIV infection rates. This discovery not only created novel opportunities to prevent sexual HIV-1 transmission but also stimulated research to unravel the natural role of these factors. We discuss here the identification of these intriguing structures, their molecular properties, and their effects on both sexually transmitted diseases and reproductive health. Moreover, we review strategies to antagonize semen amyloid to prevent sexual transmission of viruses.

Aβ Oligomer Elimination Restores Cognition in Transgenic Alzheimer's Mice with Full-blown Pathology

Oligomers of the amyloid-β (Aβ) protein are suspected to be responsible for the development and progression of Alzheimer’s disease. Thus, the development of compounds that are able to eliminate already formed toxic Aβ oligomers is very desirable. Here, we describe the in vivo efficacy of the compound RD2, which was developed to directly and specifically eliminate toxic Aβ oligomers. In a truly therapeutic, rather than a preventive study, oral treatment with RD2 was able to reverse cognitive deficits and significantly reduce Aβ pathology in old-aged transgenic Alzheimer’s Disease mice with full-blown pathology and behavioral deficits. For the first time, we demonstrate the in vivo target engagement of RD2 by showing a significant reduction of Aβ oligomers in the brains of RD2-treated mice compared to placebo-treated mice. The correlation of Aβ elimination in vivo and the reversal of cognitive deficits in old-aged transgenic mice support the hypothesis that Aβ oligomers are relevant not only for disease development and progression, but also offer a promising target for the causal treatment of Alzheimer’s disease.

Inhibition of amyloid Aβ aggregation by high pressures or specific d-enantiomeric peptides

Pressure can shift the polymer-monomer equilibrium of Aβ, increasing pressure first leads to a release of Aβ-monomers, surprisingly at pressures higher than 180 MPa repolymerization is induced. By high pressure NMR spectroscopy, differences of partial molar volumes ΔV0 and compressibility factors Δβ' of polymerization were determined at different temperatures. The d-enantiomeric peptides RD2 and RD2D3 bind to monomeric Aβ with affinities substantially higher than those determined for fibril formation. By reducing the Aβ concentration below the critical concentration for polymerization they inhibit the formation of toxic oligomers. Chemical shift perturbation allows the identification of the binding sites. The d-peptides are candidates for drugs preventing Alzheimer's disease. We show that RD2D3 has a positive effect on the cognitive behaviour of transgenic (APPSwDI) mice prone to Alzheimer's disease. The heterodimer complexes have a smaller Stokes radius than Aβ alone indicating the recognition of a more compact conformation of Aβ identified by high pressure NMR before.

Light-triggered dissociation of self-assembled β-amyloid aggregates into small, nontoxic fragments by ruthenium (II) complex

The self-assembly of β-amyloid (Aβ) peptides into highly stable plaques is a major hallmark of Alzheimer's disease. Here, we report visible light-driven dissociation of β-sheet-rich Aβ aggregates into small, nontoxic fragments using ruthenium (II) complex {[Ru(bpy)₃]²⁺} that functions as a highly sensitive, biocompatible, photoresponsive anti-Aβ agent. According to our multiple analyses using thioflavin T, bicinchoninic acid, dynamic light scattering, atomic force microscopy, circular dichroism, and Fourier transform infrared spectroscopy, [Ru(bpy)₃]²⁺ successfully disassembled Aβ aggregates by destabilizing the β-sheet secondary structure under illumination of white light-emitting diode light. We validated that photoexcited [Ru(bpy)₃]²⁺ causes oxidative damages of Aβ peptides, resulting in the dissociation of Aβ aggregates. The efficacy of [Ru(bpy)₃]²⁺ is attributed to reactive oxygen species, such as singlet oxygen, generated from [Ru(bpy)₃]²⁺ that absorbed photon energy in the visible range. Furthermore, photoexcited [Ru(bpy)₃]²⁺ strongly inhibited the self-assembly of Aβ monomers even at concentrations as low as 1 nM and reduced the cytotoxicity of Aβ aggregates.

STATEMENT OF SIGNIFICANCE

Alzheimer's disease is the most common progressive neurodegenerative disease, affecting more than 13% of the population over age 65. Over the last decades, researchers have focused on understanding the mechanism of amyloid formation, the hallmark of various amyloid diseases including Alzheimer's and Parkinson's. In this paper, we successfully demonstrate the dissociation of β-Amyloid (Aβ) aggregates into small, less-amyloidic fragments by photoexcited [Ru(bpy)₃]²⁺ through destabilization of β-sheet secondary structure. We validated the light-triggered dissociation of amyloid structure using multiple analytical tools. Furthermore, we confirmed that photoexcited [Ru(bpy)₃]²⁺ reduces cytotoxicity of Aβ aggregates. Our work should open a new horizon in the study of Alzheimer's amyloid aggregation by showing the potential of photoexcited dye molecules as an alternative therapeutic strategy for treating Alzheimer's disease in future.

Aβ oligomer eliminating compounds interfere successfully with pEAβ(3-42) induced motor neurodegenerative phenotype in transgenic mice

Currently, there are no causative or disease modifying treatments available for Alzheimer's disease (AD). Previously, it has been shown that D3, a small, fully d-enantiomeric peptide is able to eliminate low molecular weight Aβ oligomers in vitro, enhance cognition and reduce plaque load in AD transgenic mice. To further characterise the therapeutic potential of D3 towards N-terminally truncated and pyroglutamated Aβ (pEAβ(3-42)) we tested D3 and its head-to-tail tandem derivative D3D3 both in vitro and in vivo in the new mouse model TBA2.1. These mice produce human pEAβ(3-42) leading to a strong, early onset motor neurodegenerative phenotype. In the present study, we were able to demonstrate 1) strong binding affinity of both D3 and D3D3 to pEAβ(3-42) in comparison to Aβ(1-42) and 2) increased affinity of the tandem derivative D3D3 in comparison to D3. Subsequently we tested the therapeutic potentials of both peptides in the TBA2.1 animal model. Truly therapeutic, non-preventive treatment with D3 and D3D3 clearly slowed the progression of the neurodegenerative TBA2.1 phenotype, indicating the strong therapeutic potential of both peptides against pEAβ(3-42) induced neurodegeneration.

Peptides as Potential Therapeutics for Alzheimer's Disease

Intracellular synthesis, folding, trafficking and degradation of proteins are controlled and integrated by proteostasis. The frequency of protein misfolding disorders in the human population, e.g., in Alzheimer's disease (AD), is increasing due to the aging population. AD treatment options are limited to symptomatic interventions that at best slow-down disease progression. The key biochemical change in AD is the excessive accumulation of per-se non-toxic and soluble amyloid peptides (Aβ(1-37/44), in the intracellular and extracellular space, that alters proteostasis and triggers Aβ modification (e.g., by reactive oxygen species (ROS)) into toxic intermediate, misfolded soluble Aβ peptides, Aβ dimers and Aβ oligomers. The toxic intermediate Aβ products aggregate into progressively less toxic and less soluble protofibrils, fibrils and senile plaques. This review focuses on peptides that inhibit toxic Aβ oligomerization, Aβ aggregation into fibrils, or stabilize Aβ peptides in non-toxic oligomers, and discusses their potential for AD treatment.

Intranasal Administration of a Polyethylenimine-Conjugated Scavenger Peptide Reduces Amyloid-β Accumulation in a Mouse Model of Alzheimer's Disease

Amyloid-β (Aβ) aggregation in the brain plays a central and initiatory role in pathogenesis and/or progression of Alzheimer's disease (AD). Inhibiting Aβ aggregation is a potential strategy in the prevention of AD. A scavenger peptide, V24P(10-40), designed to decrease Aβ accumulation in the brain, was conjugated to polyethylenimine (PEI) and tested as a preventive/therapeutic strategy for AD in this study. This PEI-conjugated V24P(10-40) peptide was delivered intranasally, as nasal drops, to four-month-old APP/PS1 double transgenic mice for four or eight months. Compared with control values, peptide treatment for four months significantly reduced the amount of GdnHCl-extracted Aβ40 and Aβ42 in the mice's hippocampus and cortex. After treatment for eight months, amyloid load, as quantified by Pittsburgh compound B microPET imaging, was significantly decreased in the mice's hippocampus, cortex, amygdala, and olfactory bulb. Our data suggest that this intranasally delivered scavenger peptide is effective in decreasing Aβ accumulation in the brain of AD transgenic mice. Nasal application of peptide drops is easy to use and could be further developed to prevent and treat AD.

An intranasally delivered peptide drug ameliorates cognitive decline in Alzheimer transgenic mice

Alzheimer's disease (AD) is the most common neurodegenerative disease. Imbalance between the production and clearance of amyloid β (Aβ) peptides is considered to be the primary mechanism of AD pathogenesis. This amyloid hypothesis is supported by the recent success of the human anti‐amyloid antibody aducanumab, in clearing plaque and slowing clinical impairment in prodromal or mild patients in a phase Ib trial. Here, a peptide combining polyarginines (polyR) (for charge repulsion) and a segment derived from the core region of Aβ amyloid (for sequence recognition) was designed. The efficacy of the designed peptide, R₈‐Aβ(25–35), on amyloid reduction and the improvement of cognitive functions were evaluated using APP/PS1 double transgenic mice. Daily intranasal administration of PEI‐conjugated R₈‐Aβ(25–35) peptide significantly reduced Aβ amyloid accumulation and ameliorated the memory deficits of the transgenic mice. Intranasal administration is a feasible route for peptide delivery. The modular design combining polyR and aggregate‐forming segments produced a desirable therapeutic effect and could be easily adopted to design therapeutic peptides for other proteinaceous aggregate‐associated diseases.

Comparison of blood-brain barrier penetration efficiencies between linear and cyclic all-d-enantiomeric peptides developed for the treatment of Alzheimer's disease

Alzheimer's disease (AD), until now, is an incurable progressive neurodegenerative disease. To target toxic amyloid β oligomers in AD patients' brains and to convert them into non-toxic aggregation-incompetent species, we designed peptides consisting solely of d-enantiomeric amino acid residues. The original lead compound was named D3 and several D3 derivatives were designed to enhance beneficial properties. Here, we compare four d-peptides concerning their efficiencies to pass the blood-brain barrier (BBB). We demonstrate that the d-peptides' concentrations in murine brain directly correlate with concentrations in cerebrospinal fluid. The cyclic d-enantiomeric peptide cRD2D3 is characterized by the highest efficiency to pass the BBB. For in total three cyclic peptides we show that administration of cyclic peptides resulted in up to tenfold higher peak concentrations in brain as compared to their linear equivalents which have partially been characterized before (Jiang et al., 2015; Leithold et al., 2016a). These results suggest that cyclic peptides pass the murine BBB more efficiently than their linear equivalents. cRD2D3's proteolytic stability, oral bioavailability, long duration of action and its favorable brain/plasma ratio reveal that it may become a suitable drug for long-term AD-treatment from a pharmacokinetic point of view.

The Aβ oligomer eliminating D-enantiomeric peptide RD2 improves cognition without changing plaque pathology

While amyloid-β protein (Aβ) aggregation into insoluble plaques is one of the pathological hallmarks of Alzheimer’s disease (AD), soluble oligomeric Aβ has been hypothesized to be responsible for synapse damage, neurodegeneration, learning, and memory deficits in AD. Here, we investigate the in vitro and in vivo efficacy of the d-enantiomeric peptide RD2, a rationally designed derivative of the previously described lead compound D3, which has been developed to efficiently eliminate toxic Aβ42 oligomers as a promising treatment strategy for AD. Besides the detailed in vitro characterization of RD2, we also report the results of a treatment study of APP/PS1 mice with RD2. After 28 days of treatment we observed enhancement of cognition and learning behaviour. Analysis on brain plaque load did not reveal significant changes, but a significant reduction of insoluble Aβ42. Our findings demonstrate that RD2 was significantly more efficient in Aβ oligomer elimination in vitro compared to D3. Enhanced cognition without reduction of plaque pathology in parallel suggests that synaptic malfunction due to Aβ oligomers rather than plaque pathology is decisive for disease development and progression. Thus, Aβ oligomer elimination by RD2 treatment may be also beneficial for AD patients.