Reduction of Alzheimer's disease amyloid plaque load in transgenic mice by D3, A D-enantiomeric peptide identified by mirror image phage display

Applications of the phage display technology in molecular biology, biotechnology and medicine

The phage display technology is based on the presentation of peptide sequences on the surface of virions of bacteriophages. Its development led to creation of sophisticated systems based on the possibility of the presentation of a huge variability of peptides, attached to one of proteins of bacteriophage capsids. The use of such systems allowed for achieving enormous advantages in the processes of selection of bioactive molecules. In fact, the phage display technology has been employed in numerous fields of biotechnology, as diverse as immunological and biomedical applications (in both diagnostics and therapy), the formation of novel materials, and many others. In this paper, contrary to many other review articles which were focussed on either specific display systems or the use of phage display in selected fields, we present a comprehensive overview of various possibilities of applications of this technology. We discuss an usefulness of the phage display technology in various fields of science, medicine and the broad sense of biotechnology. This overview indicates the spread and importance of applications of microbial systems (exemplified by the phage display technology), pointing to the possibility of developing such sophisticated tools when advanced molecular methods are used in microbiological studies, accompanied with understanding of details of structures and functions of microbial entities (bacteriophages in this case).

Secretomic changes of amyloid beta peptides on Alzheimer's disease related proteins in differentiated human SH-SY5Y neuroblastoma cells

Alzheimer's disease (AD) is a neurodegenerative disease that causes physical damage to neuronal connections, leading to brain atrophy. This disruption of synaptic connections results in mild to severe cognitive impairments. Unfortunately, no effective treatment is currently known to prevent or reverse the symptoms of AD. The aim of this study was to investigate the effects of three synthetic peptides, i.e., KLVFF, RGKLVFFGR and RIIGL, on an AD in vitro model represented by differentiated SH-SY5Y neuroblastoma cells exposed to retinoic acid (RA) and brain-derived neurotrophic factor (BDNF). The results demonstrated that RIIGL peptide had the least significant cytotoxic activity to normal SH-SY5Y while exerting high cytotoxicity against the differentiated cells. The mechanism of RIIGL peptide in the differentiated SH-SY5Y was investigated based on changes in secretory proteins compared to another two peptides. A total of 380 proteins were identified, and five of them were significantly detected after treatment with RIIGL peptide. These secretory proteins were found to be related to microtubule-associated protein tau (MAPT) and amyloid-beta precursor protein (APP). RIIGL peptide acts on differentiated SH-SY5Y by regulating amyloid-beta formation, neuron apoptotic process, ceramide catabolic process, and oxidative phosphorylation and thus has the potentials to treat AD.

Phage Display Technology in Biomarker Identification with Emphasis on Non-Cancerous Diseases

In recent years, phage display technology has become vital in clinical research. It helps create antibodies that can specifically bind to complex antigens, which is crucial for identifying biomarkers and improving diagnostics and treatments. However, existing reviews often overlook its importance in areas outside cancer research. This review aims to fill that gap by explaining the basics of phage display and its applications in detecting and treating various non-cancerous diseases. We focus especially on its role in degenerative diseases, inflammatory and autoimmune diseases, and chronic non-communicable diseases, showing how it is changing the way we diagnose and treat illnesses. By highlighting important discoveries and future possibilities, we hope to emphasize the significance of phage display in modern healthcare.

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.

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.

Designed inhibitors to reduce amyloid virulence and cytotoxicity and combat neurodegenerative and infectious diseases

The review highlights the role of amyloids in various diseases and the challenges associated with targeting human amyloids in therapeutic development. However, due to the better understanding of microbial amyloids' role as virulence factors, there is a growing interest in repurposing and designing anti-amyloid compounds for antivirulence therapy. The identification of amyloid inhibitors has not only significant clinical implications but also provides valuable insights into the structure and function of amyloids. The review showcases small molecules and peptides that specifically target amyloids in both humans and microbes, reducing cytotoxicity and biofilm formation, respectively. The review emphasizes the importance of further research on amyloid structures, mechanisms, and interactions across all life forms to yield new drug targets and improve the design of selective treatments. Overall, the review highlights the potential for amyloid inhibitors in therapeutic development for both human diseases and microbial infections.

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.

Stabilization of Monomeric Tau Protein by All D-Enantiomeric Peptide Ligands as Therapeutic Strategy for Alzheimer's Disease and Other Tauopathies

Alzheimer's disease and other tauopathies are the world's leading causes of dementia and memory loss. These diseases are thought to be caused by the misfolding and aggregation of the intracellular tau protein, ultimately leading to neurodegeneration. The tau protein is involved in a multitude of different neurodegenerative diseases. During the onset of tauopathies, tau undergoes structural changes and posttranslational modifications and aggregates into amyloid fibrils that are able to spread with a prion-like behavior. Up to now, there is no therapeutic agent which effectively controls or reverses the disease. Most of the therapeutics that were developed and underwent clinical trials targeted misfolded or aggregated forms of tau. In the current manuscript, we present the selection and characterization of two all D-enantiomeric peptides that bind monomeric tau protein with a low nanomolar K_D, stabilize tau in its monomeric intrinsically disordered conformation, and stop the conversion of monomers into aggregates. We show that the effect of the two all D-enantiomeric peptides is strong enough to stop ongoing tau aggregation in vitro and is able to significantly reduce tau fibril assembly in cell culture. Both compounds may serve as new lead components for the development of therapeutic agents against Alzheimer's disease and other tauopathies.

Peptides as Pharmacological Carriers to the Brain: Promises, Shortcomings and Challenges

Central nervous system (CNS) diseases are among the most difficult to treat, mainly because the vast majority of the drugs fail to cross the blood-brain barrier (BBB) or to reach the brain at concentrations adequate to exert a pharmacological activity. The obstacle posed by the BBB has led to the in-depth study of strategies allowing the brain delivery of CNS-active drugs. Among the most promising strategies is the use of peptides addressed to the BBB. Peptides are versatile molecules that can be used to decorate nanoparticles or can be conjugated to drugs, with either a stable link or as pro-drugs. They have been used to deliver to the brain both small molecules and proteins, with applications in diverse therapeutic areas such as brain cancers, neurodegenerative diseases and imaging. Peptides can be generally classified as receptor-targeted, recognizing membrane proteins expressed by the BBB microvessels (e.g., Angiopep2, CDX, and iRGD), "cell-penetrating peptides" (CPPs; e.g. TAT_47-57, SynB1/3, and Penetratin), undergoing transcytosis through unspecific mechanisms, or those exploiting a mixed approach. The advantages of peptides have been extensively pointed out, but so far few studies have focused on the potential negative aspects. Indeed, despite having a generally good safety profile, some peptide conjugates may display toxicological characteristics distinct from those of the peptide itself, causing for instance antigenicity, cardiovascular alterations or hemolysis. Other shortcomings are the often brief lifetime in vivo, caused by the presence of peptidases, the vulnerability to endosomal/lysosomal degradation, and the frequently still insufficient attainable increase of brain drug levels, which remain below the therapeutically useful concentrations. The aim of this review is to analyze not only the successful and promising aspects of the use of peptides in brain targeting but also the problems posed by this strategy for drug delivery.

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.

Surface enhanced fluorescence effect improves the in vivo detection of amyloid aggregates

The β-amyloid (Aβ) peptide is one of the key etiological agents in Alzheimer's disease (AD). The in vivo detection of Aβ species is challenging in all stages of the illness. Currently, the development of fluorescent probes allows the detection of Aβ in animal models in the near-infrared region (NIR). However, considering future applications in biomedicine, it is relevant to develop strategies to improve detection of amyloid aggregates using NIR probes. An innovative approach to increase the fluorescence signal of these fluorophores is the use of plasmonic gold nanoparticles (surface-enhanced fluorescence effect). In this work, we improved the detection of Aβ aggregates in C. elegans and mouse models of AD by co-administering functionalized gold nanorods (GNRs-PEG-D1) with the fluorescent probes CRANAD-2 or CRANAD-58, which bind selectively to different amyloid species (soluble and insoluble). This work shows that GNRs improve the detection of Aβ using NIR probes in vivo.

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.

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.

Arginine and Arginine-Rich Peptides as Modulators of Protein Aggregation and Cytotoxicity Associated With Alzheimer's Disease

A substantial body of evidence indicates cationic, arginine-rich peptides (CARPs) are effective therapeutic compounds for a range of neurodegenerative pathologies, with beneficial effects including the reduction of excitotoxic cell death and mitochondrial dysfunction. CARPs, therefore, represent an emergent class of promising neurotherapeutics with multimodal mechanisms of action. Arginine itself is a known chaotrope, able to prevent misfolding and aggregation of proteins. The putative role of proteopathies in chronic neurodegenerative diseases such as Alzheimer's disease (AD) warrants investigation into whether CARPs could also prevent the aggregation and cytotoxicity of amyloidogenic proteins, particularly amyloid-beta and tau. While monomeric arginine is well-established as an inhibitor of protein aggregation in solution, no studies have comprehensively discussed the anti-aggregatory properties of arginine and CARPs on proteins associated with neurodegenerative disease. Here, we review the structural, physicochemical, and self-associative properties of arginine and the guanidinium moiety, to explore the mechanisms underlying the modulation of protein aggregation by monomeric and multimeric arginine molecules. Arginine-rich peptide-based inhibitors of amyloid-beta and tau aggregation are discussed, as well as further modulatory roles which could reduce proteopathic cytotoxicity, in the context of therapeutic development for AD.

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.

In Vitro and In Vivo Efficacies of the Linear and the Cyclic Version of an All-d-Enantiomeric Peptide Developed for the Treatment of Alzheimer's Disease

Multiple sources of evidence suggest that soluble amyloid β (Aβ)-oligomers are responsible for the development and progression of Alzheimer’s disease (AD). In order to specifically eliminate these toxic Aβ-oligomers, our group has developed a variety of all-d-peptides over the past years. One of them, RD2, has been intensively studied and showed such convincing in vitro and in vivo properties that it is currently in clinical trials. In order to further optimize the compounds and to elucidate the characteristics of therapeutic d-peptides, several rational drug design approaches have been performed. Two of these d-peptides are the linear tandem (head-to-tail) d-peptide RD2D3 and its cyclized form cRD2D3. Tandemization and cyclization should result in an increased in vitro potency and increase pharmacokinetic properties, especially crossing the blood–brain-barrier. In comparison, cRD2D3 showed a superior pharmacokinetic profile to RD2D3. This fact suggests that higher efficacy can be achieved in vivo at equally administered concentrations. To prove this hypothesis, we first established the in vitro profile of both d-peptides here. Subsequently, we performed an intraperitoneal treatment study. This study failed to provide evidence that cRD2D3 is superior to RD2D3 in vivo as in some tests cRD2D3 failed to show equal or higher efficacy.

Brain Targeting and Aβ Binding Bifunctional Nanoparticles Inhibit Amyloid Protein Aggregation in APP/PS1 Transgenic Mice

Alzheimer's disease (AD) is an insidious and progressive neurodegenerative disease with few disease-modifying treatments. A variety of peptide/protein drugs have neuroprotective effects, which brings new hope for the treatment of AD. However, the application of these drugs is limited because of their low specificity and difficulty in crossing the blood-brain barrier. Herein, using the phage display technology, we identified the Aβ oligomer binding peptide (KH) and the brain targeting peptide (IS). We combined these peptides to develop a bifunctional nanoparticle (IS@NP/KH) for the delivery of Aβ_1-42 oligomer binding peptide into the brain. Intranasal administration of IS@NP/KH significantly attenuated the cognitive and behavioral deficits and reduced the Aβ deposition in the brain of an AD animal model (APPswe/PS 1d9 double-transgenic mice). Our results suggest that intranasal IS@NP/KH administration could be a novel therapeutic strategy for the treatment of AD.

A Non-immunogenic Bivalent d-Protein Potently Inhibits Retinal Vascularization and Tumor Growth

We report a general approach to engineering multivalent d-proteins with antibody-like activities in vivo. Mirror-image phage display and structure-guided design were utilized to create a d-protein that uses receptor mimicry to antagonize vascular endothelial growth factor A (VEGF-A). Selections against the d-protein form of VEGF-A using phage-displayed libraries of two different domain scaffolds yielded two proteins that bound distinct receptor interaction sites on VEGF-A. X-ray crystal structures of the d-protein/VEGF-A complexes were used to guide affinity maturation and to construct a heterodimeric d-protein VEGF-A antagonist with picomolar activity. The d-protein VEGF-A antagonist prevented vascular leakage in a rabbit eye model of wet age-related macular degeneration and slowed tumor growth in the MC38 syngeneic mouse tumor model with efficacies comparable to those of approved antibody drugs, and in contrast with antibodies, the d-protein was non-immunogenic during treatment and following subcutaneous immunizations.

Cationic Arginine-Rich Peptides (CARPs): A Novel Class of Neuroprotective Agents With a Multimodal Mechanism of Action

There are virtually no clinically available neuroprotective drugs for the treatment of acute and chronic neurological disorders, hence there is an urgent need for the development of new neuroprotective molecules. Cationic arginine-rich peptides (CARPs) are an expanding and relatively novel class of compounds, which possess intrinsic neuroprotective properties. Intriguingly, CARPs possess a combination of biological properties unprecedented for a neuroprotective agent including the ability to traverse cell membranes and enter the CNS, antagonize calcium influx, target mitochondria, stabilize proteins, inhibit proteolytic enzymes, induce pro-survival signaling, scavenge toxic molecules, and reduce oxidative stress as well as, having a range of anti-inflammatory, analgesic, anti-microbial, and anti-cancer actions. CARPs have also been used as carrier molecules for the delivery of other putative neuroprotective agents across the blood-brain barrier and blood-spinal cord barrier. However, there is increasing evidence that the neuroprotective efficacy of many, if not all these other agents delivered using a cationic arginine-rich cell-penetrating peptide (CCPPs) carrier (e.g., TAT) may actually be mediated largely by the properties of the carrier molecule, with overall efficacy further enhanced according to the amino acid composition of the cargo peptide, in particular its arginine content. Therefore, in reviewing the neuroprotective mechanisms of action of CARPs we also consider studies using CCPPs fused to a putative neuroprotective peptide. We review the history of CARPs in neuroprotection and discuss in detail the intrinsic biological properties that may contribute to their cytoprotective effects and their usefulness as a broad-acting class of neuroprotective drugs.

Peptide-Based Molecular Strategies To Interfere with Protein Misfolding, Aggregation, and Cell Degeneration

Protein misfolding into amyloid fibrils is linked to more than 40 as yet incurable cell- and neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and type 2 diabetes. So far, however, only one of the numerous anti-amyloid molecules has reached patients. This Minireview gives an overview of molecular strategies and peptide chemistry "tools" to design, develop, and discover peptide-based molecules as anti-amyloid drug candidates. We focus on two major inhibitor rational design strategies: 1) the oldest and most common strategy, based on molecular recognition elements of amyloid self-assembly, and 2) a more recent approach, based on cross-amyloid interactions. We discuss why peptide-based amyloid inhibitors, in particular their advanced generations, can be promising leads or candidates for anti-amyloid drugs as well as valuable tools for deciphering amyloid-mediated cell damage and its link to disease pathogenesis.

[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.

Recent advances in the design and applications of amyloid-β peptide aggregation inhibitors for Alzheimer's disease therapy

Alzheimer's disease (AD) is an irreversible neurological disorder that progresses gradually and can cause severe cognitive and behavioral impairments. This disease is currently considered a social and economic incurable issue due to its complicated and multifactorial characteristics. Despite decades of extensive research, we still lack definitive AD diagnostic and effective therapeutic tools. Consequently, one of the most challenging subjects in modern medicine is the need for the development of new strategies for the treatment of AD. A large body of evidence indicates that amyloid-β (Aβ) peptide fibrillation plays a key role in the onset and progression of AD. Recent studies have reported that amyloid hypothesis-based treatments can be developed as a new approach to overcome the limitations and challenges associated with conventional AD therapeutics. In this review, we will provide a comprehensive view of the challenges in AD therapy and pathophysiology. We also discuss currently known compounds that can inhibit amyloid-β (Aβ) aggregation and their potential role in advancing current AD treatments. We have specifically focused on Aβ aggregation inhibitors including metal chelators, nanostructures, organic molecules, peptides (or peptide mimics), and antibodies. To date, these molecules have been the subject of numerous in vitro and in vivo assays as well as molecular dynamics simulations to explore their mechanism of action and the fundamental structural groups involved in Aβ aggregation. Ultimately, the aim of these studies (and current review) is to achieve a rational design for effective therapeutic agents for AD treatment and diagnostics.

Bacterial production and direct functional screening of expanded molecular libraries for discovering inhibitors of protein aggregation

Protein misfolding and aggregation are associated with a many human disorders, including Alzheimer's and Parkinson's diseases. Toward increasing the effectiveness of early-stage drug discovery for these conditions, we report a bacterial platform that enables the biosynthesis of molecular libraries with expanded diversities and their direct functional screening for discovering protein aggregation inhibitors. We illustrate this approach by performing, what is to our knowledge, the largest functional screen of small-size molecular entities described to date. We generated a combinatorial library of ~200 million drug-like, cyclic peptides and rapidly screened it for aggregation inhibitors against the amyloid-β peptide (Aβ42), linked to Alzheimer's disease. Through this procedure, we identified more than 400 macrocyclic compounds that efficiently reduce Aβ42 aggregation and toxicity in vitro and in vivo. Finally, we applied a combination of deep sequencing and mutagenesis analyses to demonstrate how this system can rapidly determine structure-activity relationships and define consensus motifs required for bioactivity.

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.

The effect of retro-inverse D-amino acid Aβ-peptides on Aβ-fibril formation

Peptides build from D-amino acids resist enzymatic degradation. The resulting extended time of biological activity makes them prime candidates for the development of pharmaceuticals. Of special interest are D-retro-inverso (DRI) peptides where a reversed sequence of D-amino acids leads to molecules with almost the same structure, stability, and bioactivity as the parent L-peptides but increased resistance to proteolytic degradation. Here, we study the effect of DRI-Aβ₄₀ and DRI-Aβ₄₂ peptides on fibril formation. Using molecular dynamics simulations, we compare the stability of typical amyloid fibril models with such where the L-peptides are replaced by DRI-Aβ₄₀ and DRI-Aβ₄₂ peptides. We then explore the likelihood for cross fibrilization of Aβ L- and DRI-peptides by investigating how the presence of DRI peptides alters the elongation and stability of L-Aβ-fibrils. Our data suggest that full-length DRI-peptides may enhance the fibril formation and decrease the ratio of soluble toxic Aβ oligomers, pointing out potential for D-amino-acid-based drug design targeting Alzheimer's disease.

A Hendecad Motif Is Preferred for Heterochiral Coiled-Coil Formation

The structural principles that govern interactions between l- and d-peptides are not well understood. Among natural proteins, coiled-coil assemblies formed between or among α-helices are the most regular feature of tertiary and quaternary structures. We recently reported the first high-resolution structures for heterochiral coiled-coil dimers, which represent a starting point for understanding associations of l- and d-polypeptides. These structures were an unexpected outcome from crystallization of a racemic peptide corresponding to the transmembrane domain of the influenza A M2 protein (M2-TM). The reported structures raised the possibility that heterochiral coiled-coil dimers prefer an 11-residue (hendecad) sequence repeat, in contrast to the 7-residue (heptad) sequence repeat that is dominant among natural coiled coils. To gain insight on sequence repeat preferences of heterochiral coiled-coils, we have examined three M2-TM variants containing substitutions intended to minimize steric clashes between side chains at the coiled-coil interface. In each of the three new crystal structures, we observed heterochiral coiled-coil associations that closely match a hendecad sequence motif, which strengthens the conclusion that this motif is intrinsic to the pairing of α-helices with opposite handedness. In each case, the presence of a hendecad motif was established by comparing the observed helical frequency to that of an ideal hendecad. This comparison revealed that decreasing the size of the amino acid side chain at positions that project toward the superhelical axis produces tighter packing, as determined by the size of the coiled-coil radius. These results provide a basis for future design of heterochiral coiled-coil pairings.

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.

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.

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.

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.

Peptide functionalized magneto-plasmonic nanoparticles obtained by microfluidics for inhibition of β-amyloid aggregation

Synthesis of magneto-plasmonic nanoparticles for the inhibition of β-amyloid fibril formation.

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.

Large-Scale Oral Treatment Study with the Four Most Promising D3-Derivatives for the Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that is associated with the aggregation of the amyloid β protein (Aβ). Aβ oligomers are currently thought to be the major neurotoxic agent responsible for disease development and progression. Thus, their elimination is highly desirable for therapy development. Our therapeutic approach aims at specific and direct elimination of toxic Aβ oligomers by stabilizing Aβ monomers in an aggregation-incompetent conformation. We have proven that our lead compound “D3”, an all d-enantiomeric-peptide, specifically eliminates Aβ oligomers in vitro. In vivo, D3 enhances cognition and reduces plaque load in several transgenic AD mouse models. Here, we performed a large-scale oral proof of concept efficacy study, in which we directly compared four of the most promising D3-derivatives in transgenic mice expressing human amyloid precursor protein with Swedish and London mutations (APP_SL), transgenic mice, to identify the most effective compound. RD2 and D3D3, both derived from D3 by rational design, were discovered to be the most effective derivatives in improving cognition in the Morris water maze. The performance of RD2- and D3D3-treated mice within the Morris water maze was significantly better than placebo-treated mice and, importantly, nearly as good as those of non-transgenic littermates, suggesting a complete reversal of the cognitive deficit of APP_SL mice.