Chrysamine-G, a lipophilic analogue of Congo red, inhibits A beta-induced toxicity in PC12 cells

The detection methods currently available for protein aggregation in neurological diseases

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

Small-molecule theranostics in Alzheimer's disease

Alzheimer's Disease (AD) remains one of the most challenging health-related issues for our society. It is becoming increasingly prevalent, especially in developed countries, due to the rising life expectancy and, moreover, represents a considerable economic burden worldwide. All efforts at the discovery of new diagnostic and therapeutic tools in the last decades have invariably met with failure, making AD an incurable illness and underscoring the need for new approaches. In recent years, theranostic agents have emerged as an interesting strategy. They are molecules able to simultaneously provide diagnostic information and deliver therapeutic activity, allowing for the assessment of the molecule activity, the organism response and the pharmacokinetics. This makes these compounds promising for streamlining research on AD drugs and for their application in personalized medicine. We review here the field of small-molecule theranostic agents as promising tools for the development of novel diagnostic and therapeutic resources against AD, highlighting the positive and significant impact that theranostics can be expected to have in the near future in clinical practice.

Near-Infrared Fluorescent Probes as Imaging and Theranostic Modalities for Amyloid-Beta and Tau Aggregates in Alzheimer's Disease

A person suspected of having Alzheimer's disease (AD) is clinically diagnosed for the presence of principal biomarkers, especially misfolded amyloid-beta (Aβ) and tau proteins in the brain regions. Existing radiotracer diagnostic tools, such as PET imaging, are expensive and have limited availability for primary patient screening and pre-clinical animal studies. To change the status quo, small-molecular near-infrared (NIR) probes have been rapidly developed, which may serve as an inexpensive, handy imaging tool to comprehend the dynamics of pathogenic progression in AD and assess therapeutic efficacy in vivo. This Perspective summarizes the biochemistry of Aβ and tau proteins and then focuses on structurally diverse NIR probes with coverages of their spectroscopic properties, binding affinity toward Aβ and tau species, and theranostic effectiveness. With the summarized information and perspective discussions, we hope that this paper may serve as a guiding tool for designing novel in vivo imaging fluoroprobes with theranostic capabilities in the future.

Exploring the influence of brilliant blue G on amyloid fibril formation of lysozyme

Evidence suggests that amyloid fibril mitigation/inhibition is considered a promising approach toward treating amyloid diseases. In this work, we first examined how amyloid fibrillogenesis of lysozyme was affected by BBG, a safe triphenylmethane compound with nice blood-brain-barrier-permeability, and found that shorter fibrillar species were formed in the lysozyme samples treated with BBG. Next, alterations in the features including the secondary as well as tertiary structure, extent of aggregation, and molecular distribution of lysozyme triggered by the addition of BBG were examined by various spectroscopic techniques, right-angle light scattering, dynamic light scattering, and SDS-PAGE. In addition, we have investigated how BBG affected the lysozyme fibril-induced cytotoxicity in SH-SY5Y cells. We found that a large quantity of shorter fibrillar species and more lysozyme monomers were present in the samples treated with BBG. Also, the addition of BBG rescued SH-SY5Y cells from cell death induced by amyloid fibrils of lysozyme. Finally, information about the binding sites and interacting forces involved in the BBG-lysozyme interaction was further explored using synchronous fluorescence and molecular docking approaches. Molecular docking results revealed that, apart from the hydrophobic interaction(s), hydrogen bonding, electrostatic interactions, and van der Waal forces may also be involved in the binding interaction.

Exploring Anti-Prion Glyco-Based and Aromatic Scaffolds: A Chemical Strategy for the Quality of Life

Prion diseases are fatal neurodegenerative disorders caused by protein misfolding and aggregation, affecting the brain progressively and consequently the quality of life. Alzheimer’s is also a protein misfolding disease, causing dementia in over 40 million people worldwide. There are no therapeutics able to cure these diseases. Cellular prion protein is a high-affinity binding partner of amyloid β (Aβ) oligomers, the most toxic species in Alzheimer’s pathology. These findings motivate the development of new chemicals for a better understanding of the events involved. Disease control is far from being reached by the presently known therapeutics. In this review we describe the synthesis and mode of action of molecular entities with intervention in prion diseases’ biological processes and, if known, their role in Alzheimer’s. A diversity of structures is covered, based on glycans, steroids and terpenes, heterocycles, polyphenols, most of them embodying aromatics and a structural complexity. These molecules may be regarded as chemical tools to foster the understanding of the complex mechanisms involved, and to encourage the scientific community towards further developments for the cure of these devastating diseases.

Examining the inhibitory potency of food additive fast green FCF against amyloid fibrillogenesis under acidic conditions

Amyloid fibril formation of hen lysozyme (HEWL) can be attenuated by fast green FCF.

Interactions between misfolded protein oligomers and membranes: A central topic in neurodegenerative diseases?

The deposition of amyloid material has been associated with many different diseases. Although these diseases are very diverse the amyloid material share many common features such as cross-β-sheet structure of the backbone of the proteins deposited. Another common feature of the aggregation process for a wide variety of proteins is the presence of prefibrillar oligomers. These oligomers are linked to the cytotoxicity occurring during the aggregation of proteins. These prefibrillar oligomers interact extensively with lipid membranes and in some cases leads to destabilization of lipid membranes. This interaction is however highly dependent on the nature of both the oligomer and the lipids. Anionic lipids are often required for interaction with the lipid membrane while increased exposure of hydrophobic patches from highly dynamic protein oligomers are structural determinants of cytotoxicity of the oligomers. To explore the oligomer lipid interaction in detail the interaction between oligomers of α-synuclein and the 4th fasciclin-1 domain of TGFBIp with lipid membranes will be examined here. For both proteins the dynamic species are the ones causing membrane destabilization and the membrane interaction is primarily seen when the lipid membranes contain anionic lipids. Hence the dynamic nature of oligomers with exposed hydrophobic patches alongside the presence of anionic lipids could be essential for the cytotoxicity observed for prefibrillar oligomers in general. This article is part of a Special Issue entitled: Lipid-protein interactions.

Carnosine's effect on amyloid fibril formation and induced cytotoxicity of lysozyme

Carnosine, a common dipeptide in mammals, has previously been shown to dissemble alpha-crystallin amyloid fibrils. To date, the dipeptide's anti-fibrillogensis effect has not been thoroughly characterized in other proteins. For a more complete understanding of carnosine's mechanism of action in amyloid fibril inhibition, we have investigated the effect of the dipeptide on lysozyme fibril formation and induced cytotoxicity in human neuroblastoma SH-SY5Y cells. Our study demonstrates a positive correlation between the concentration and inhibitory effect of carnosine against lysozyme fibril formation. Molecular docking results show carnosine's mechanism of fibrillogenesis inhibition may be initiated by binding with the aggregation-prone region of the protein. The dipeptide attenuates the amyloid fibril-induced cytotoxicity of human neuronal cells by reducing both apoptotic and necrotic cell deaths. Our study provides solid support for carnosine's amyloid fibril inhibitory property and its effect against fibril-induced cytotoxicity in SH-SY5Y cells. The additional insights gained herein may pave way to the discovery of other small molecules that may exert similar effects against amyloid fibril formation and its associated neurodegenerative diseases.

Small-molecule theranostic probes: a promising future in neurodegenerative diseases

Prion diseases are fatal neurodegenerative illnesses, which include Creutzfeldt-Jakob disease in humans and scrapie, chronic wasting disease, and bovine spongiform encephalopathy in animals. They are caused by unconventional infectious agents consisting primarily of misfolded, aggregated, β -sheet-rich isoforms, denoted prions, of the physiological cellular prion protein (PrP(C)). Many lines of evidence suggest that prions (PrP(Sc)) act both as a template for this conversion and as a neurotoxic agent causing neuronal dysfunction and cell death. As such, PrP(Sc) may be considered as both a neuropathological hallmark of the disease and a therapeutic target. Several diagnostic imaging probes have been developed to monitor cerebral amyloid lesions in patients with neurodegenerative disorders (such as Alzheimer's disease, Parkinson's disease, and prion disease). Examples of these probes are Congo red, thioflavin T, and their derivatives. We synthesized a series of styryl derivatives, denoted theranostics, and studied their therapeutic and/or diagnostic potentials. Here we review the salient traits of these small molecules that are able to detect and modulate aggregated forms of several proteins involved in protein misfolding diseases. We then highlight the importance of further studies for their practical implications in therapy and diagnostics.

Development of positron emission tomography β-amyloid plaque imaging agents

For 100 years, β-amyloid (Aβ) plaques and neurofibrillary tangles (NFTs) have been recognized as the neuropathological hallmarks of Alzheimer's disease (AD), and their presence or absence could only be assessed postmortem using stains and dyes that identified these microscopic structures. Approximately 10 years ago, the first successful Aβ plaque-specific positron emission tomography (PET) imaging study was conducted in a living human subject clinically diagnosed with probable AD using the (11)C-labeled radiopharmaceutical Pittsburgh Compound B (PiB). Laboratory studies and preclinical evaluations to design PiB began a decade earlier than the first human PiB PET study and involved chemical modifications of different well-known dyes that bound specifically to the extended β-pleated sheets that comprise the fibrils of amyloid proteins such as Aβ plaques, NFTs, α-synuclein deposits, and prions. These preclinical studies were conducted in our laboratories at the University of Pittsburgh, starting with Congo red derivatives, followed by Chrysamine G derivatives, followed by X-series compounds, and finally with neutral derivatives of thioflavin-T. The in vitro and in vivo evaluations of the different derivatives as candidate PET radioligands for imaging Aβ plaques and neurofibrillary tangles in human brain are described in this review, along with the specific evaluation criteria by which the candidate radioligands were judged. Out of these studies came PiB, a PET radioligand that binds selectively and with high affinity to only fibrillar forms of Aβ. PiB has been used in many different human research protocols throughout the world and has demonstrated the usefulness of assessing the Aβ plaque status of subjects many years before the clinical diagnosis of probable AD. Recently, longer-lived (18)F-radiolabeled Aβ-selective radiopharmaceuticals have been developed. It is likely that the full clinical impact of these imaging agents will be realized by identifying presymptomatic subjects who would benefit from early drug treatments with future disease-modifying AD therapeutics.

Discovery and structure activity relationship of small molecule inhibitors of toxic β-amyloid-42 fibril formation

Increasing evidence implicates Aβ peptides self-assembly and fibril formation as crucial events in the pathogenesis of Alzheimer disease. Thus, inhibiting Aβ aggregation, among others, has emerged as a potential therapeutic intervention for this disorder. Herein, we employed 3-aminopyrazole as a key fragment in our design of non-dye compounds capable of interacting with Aβ42 via a donor-acceptor-donor hydrogen bond pattern complementary to that of the β-sheet conformation of Aβ42. The initial design of the compounds was based on connecting two 3-aminopyrazole moieties via a linker to identify suitable scaffold molecules. Additional aryl substitutions on the two 3-aminopyrazole moieties were also explored to enhance π-π stacking/hydrophobic interactions with amino acids of Aβ42. The efficacy of these compounds on inhibiting Aβ fibril formation and toxicity in vitro was assessed using a combination of biophysical techniques and viability assays. Using structure activity relationship data from the in vitro assays, we identified compounds capable of preventing pathological self-assembly of Aβ42 leading to decreased cell toxicity.

Investigating the effects of sodium dodecyl sulfate on the aggregative behavior of hen egg-white lysozyme at acidic pH

The research presented here is aimed at examining the effects of sodium dodecyl sulfate on the aggregative behavior of hen egg-white lysozyme at pH 2.0. Through various spectroscopic techniques, dynamic light scattering, and electron microscopy, we first demonstrated that SDS exhibited a biphasic effect on lysozyme fibrillation. The presence of SDS at higher concentrations (e.g., 0.25, 5.00, or 20.00 mM SDS) was found to suppress fibril formation of lysozyme whereas fibrillogenic lysozyme-SDS ensemble containing beta-sheet-rich conformation was observed upon the addition of lower concentrations of SDS (e.g., 0.00, 0.06, or 0.1mM SDS). Next, our equilibrium urea-unfolding data revealed that lysozyme samples with higher SDS concentrations showed superior thermodynamic stabilities over the ones with no or lower levels of SDS. Finally, the correlation between SDS concentration and lysozyme aggregative/fibrillogenic propensity and the underlying interacting mechanism were further explored using surface tensiometry and isothermal titration calorimetry. We believe the outcome from this work may not only help decipher the molecular mechanism of amyloid fibrillation, but also shed light on a rational design of potential therapeutic strategies for amyloid pathology.

Substoichiometric inhibition of Abeta(1-40) aggregation by a tandem Abeta(40-1-Gly8-1-40) peptide

Abeta peptides aggregate to form insoluble and neurotoxic fibrils associated with Alzheimer's disease. Inhibition of the aggregation has been the subject of numerous studies. Here we describe a novel, substoichiometric inhibitor of Abeta(1-40) fibrillization as a tandem dimeric construct consisting of Abeta(40-1) (reverse sequence) linked to Abeta(1-40) via an eight residue glycine linker. At molar ratios of the tandem peptide to Abeta(1-40) of 1:10 to 1:25 inhibition of fibrillization, as measured by ThioflavinT, was observed. We postulate that the tandem construct binds to a fibrillar intermediate but the reverse sequence delays or prevents further monomer association.

Amyloid fibrillation and cytotoxicity of insulin are inhibited by the amphiphilic surfactants

Amyloid fibrils have been associated with at least 25 different degenerative diseases. The 51-residue polypeptide hormone insulin, which is associated with type II diabetes, has been shown to self-assemble to form amyloid fibrils in vitro. With bovine insulin as a model, the research presented here explores the effects of two amphiphilic surfactants (1,2-dihexanoyl-sn-glycero-3-phosphocholine (di-C7-PC) and 1,2-diheptanoyl-sn-glycero-3-phosphocholine (di-C7-PC)) on the in vitro fibrillation process of bovine insulin at pH 2.0 and 55 degrees C. We demonstrated that insulin fibrillation may be inhibited by both surfactants in a dose-dependent fashion. The best inhibition of fibril formation is observed when insulin is incubated with 4mM di-C7-PC. Moreover, the addition of either surfactant at the concentrations studied attenuated insulin fibril-induced cytotoxicity in both PC12 and SH-SY5Y cell lines. The results from this work may contribute to the understanding of the molecular factors affecting amyloid fibrillation and the molecular mechanism(s) of the interactions between the membrane and amyloid proteins.

Amyloid-beta fibrillogenesis: structural insight and therapeutic intervention

Structural insight into the conformational changes associated with aggregation and assembly of fibrils has provided a number of targets for therapeutic intervention. Solid-state NMR, hydrogen/deuterium exchange and mutagenesis strategies have been used to probe the secondary and tertiary structure of amyloid fibrils and key intermediates. Rational design of peptide inhibitors directed against key residues important for aggregation and stabilization of fibrils has demonstrated effectiveness at inhibiting fibrillogenesis. Studies on the interaction between Abeta and cell membranes led to the discovery that inositol, the head group of phosphatidylinositol, inhibits fibrillogenesis. As a result, scyllo-inositol is currently in clinical trials for the treatment of AD. Additional small-molecule inhibitors, including polyphenolic compounds such as curcumin, (-)-epigallocatechin gallate (EGCG), and grape seed extract have been shown to attenuate Abeta aggregation through distinct mechanisms, and have shown effectiveness at reducing amyloid levels when administered to transgenic mouse models of AD. Although the results of ongoing clinical trials remain to be seen, these compounds represent the first generation of amyloid-based therapeutics, with the potential to alter the progression of AD and, when used prophylactically, alleviate the deposition of Abeta.

Effect of curcumin on the amyloid fibrillogenesis of hen egg-white lysozyme

At least twenty human proteins can fold abnormally to form pathological deposits that are associated with several degenerative diseases. Despite extensive investigation on amyloid fibrillogenesis, its detailed molecular mechanisms remain unknown. This study is aimed at exploring the inhibitory activity of curcumin against the fibrillation of hen lysozyme. We found that the formation of amyloid fibrils at pH 2.0 in vitro was inhibited by curcumin in a dose-dependent manner. Moreover, quenching analysis confirmed the existence of an interaction between curcumin and lysozyme, and Van't Hoff analysis indicated that the curcumin-lysozyme interaction is predominantly governed by Van Der Waals force or hydrogen bonding. Curcumin was also found to acquire disaggregating ability on preformed lysozyme fibrils. Finally, we observed that curcumin pre-incubated at 25 degrees C for at least 7 days inhibited lysozyme fibrillogenesis better than untreated curcumin and the enhanced inhibition against HEWL fibrillation might be attributed to the presence of dimeric species.

Synthesis and characterization of fluorinated magnetic core-shell nanoparticles for inhibition of insulin amyloid fibril formation

Maghemite (gamma-Fe2O3) magnetic nanoparticles of 15.0 +/- 2.1 nm are formed by nucleation followed by controlled growth of maghemite thin films on gelatin-iron oxide nuclei. Uniform magnetic gamma-Fe2O3/poly (2,2,3,3,4,4,4-heptafluorobutyl acrylate) (gamma-Fe2O3/PHFBA) core-shell nanoparticles are prepared by emulsion polymerization of the fluorinated monomer 2,2,3,3,4,4,4-heptafluorobutyl acrylate (HFBA) in the presence of the maghemite nanoparticles. The kinetics of the insulin fibrillation process in the absence and in the presence of the gamma-Fe2O3/PHFBA core-shell nanoparticles are elucidated. A significant direct slow transition from alpha-helix to beta-sheets during insulin fibril formation is observed in the presence of the gamma-Fe2O3/PHFBA nanoparticles. This is in contradiction to our previous manuscript, which illustrated that the gamma-Fe2O3 core nanoparticles do not affect the kinetics of the formation of the insulin fibrils, and to other previous publications that describe acceleration of the fibrillation process by using various types of nanoparticles. These core-shell nanoparticles may therefore be also useful for the inhibition of conformational changes of other amyloidogenic proteins that lead to neurodegenerative diseases such as Alzheimer's, Parkinson's, Huntington's, mad cow and prion diseases.

Molecular mechanism of thioflavin-T binding to the surface of beta-rich peptide self-assemblies

A number of small organic molecules have been developed that bind to amyloid fibrils, a subset of which also inhibit fibrillization. Among these, the benzothiol dye Thioflavin-T (ThT) has been used for decades in the diagnosis of protein-misfolding diseases and in kinetic studies of self-assembly (fibrillization). Despite its importance, efforts to characterize the ThT-binding mechanism at the atomic level have been hampered by the inherent insolubility and heterogeneity of peptide self-assemblies. To overcome these challenges, we have developed a minimalist approach to designing a ThT-binding site in a "peptide self-assembly mimic" (PSAM) scaffold. PSAMs are engineered water-soluble proteins that mimic a segment of beta-rich peptide self-assembly, and they are amenable to standard biophysical techniques and systematic mutagenesis. The PSAM beta-sheet contains rows of repetitive amino acid patterns running perpendicular to the strands (cross-strand ladders) that represent a ubiquitous structural feature of fibril-like surfaces. We successfully designed a ThT-binding site that recapitulates the hallmarks of ThT-fibril interactions by constructing a cross-strand ladder consisting of contiguous tyrosines. The X-ray crystal structures suggest that ThT interacts with the beta-sheet by docking onto surfaces formed by a single tyrosine ladder, rather than in the space between adjacent ladders. Systematic mutagenesis further demonstrated that tyrosine surfaces across four or more beta-strands formed the minimal binding site for ThT. Our work thus provides structural insights into how this widely used dye recognizes a prominent subset of peptide self-assemblies, and proposes a strategy to elucidate the mechanisms of fibril-ligand interactions.

Mechanistic insights into the cure of prion disease by novel antiprion compounds

Prion diseases are fatal neurodegenerative disorders. Identification of possible therapeutic tools is important in the search for a potential treatment for these diseases. Congo red is an azo dye that has been used for many years to detect abnormal prion protein in the brains of diseased patients or animals. Congo red has little therapeutic potential for the treatment of these diseases due to toxicity and poor permeation of the blood-brain barrier. We have prepared two Congo red derivatives, designed without these liabilities, with potent activity in cellular models of prion disease. One of these compounds cured cells of the transmissible agent. The mechanism of action of these compounds is possibly multifactorial. The high affinity of Congo red derivatives, including compounds that are ineffective and are effective at the cure of prion disease, for abnormally folded prion protein suggests that the amyloidophylic property of these derivatives is not as critical to the mechanism of action as other effects. Congo red derivatives that are effective at the cure of prion disease increased the degradation of abnormal PrP by the proteasome. Therefore, the principal mechanism of action of the Congo red analogues was to prevent inhibition of proteasomal activity by PrPSc.

Styryl-Based Compounds as Potential in vivo Imaging Agents for β-Amyloid Plaques

A group of styryl-based neutral compounds has been synthesized in this study for potential use as in vivo imaging agents for beta-amyloid plaques. Of 56 candidates, 14 compounds were found to label beta-amyloid plaques well on Alzheimer's disease (AD) human brain sections in vitro. The binding affinity to beta-amyloid fibrils was then determined by measuring the change in fluorescence intensity. Interestingly, we found that a class of quinaldine-styryl scaffold compounds displays specific binding to beta-amyloid fibrils. A representative compound, STB-8, was used in ex vivo and in vivo imaging experiments on an AD transgenic mouse model and demonstrated excellent blood-brain barrier (BBB) permeability and specific staining of the AD beta-amyloid plaques.

Cyanine dye–protein interactions: Looking for fluorescent probes for amyloid structures

We ascertained the ability to detect fibrillar beta-lactoglobulin (BLG) of a series of mono-, tri-, penta-, and heptamethinecyanines based on benzothiazole and benzimidazole heterocycles, and of benzothiazole squaraine. Fluorescence properties of these cyanine dyes were measured in the unbound state and in the presence of monomeric and fibrillar BLG and compared with those for the commercially available benzothiazole dye Thioflavin T. The correlation between the chemical nature of the dye molecules and the ability of dyes to bind aggregated proteins was established. We found that meso-substituted cyanines with amino substituents in heterocycle in contrast to the corresponding unsubstituted dyes have a binding preference to fibrillar BLG and a noticeable fluorescence response in the presence of the aggregated protein. For the squaraines and benzimidazole penthamethinecyanines studied, fluorescence emission increased both in the presence of native and fibrillar protein. The trimethinecyanines T-49 and SH-516 exhibit specifically increased fluorescence in the presence of fibrillar BLG. These dyes demonstrated the same or higher emission intensity and selectivity to aggregated BLG as Thioflavin T, and are proposed for application in selective fluorescent detection of aggregated proteins.

Congo red and protein aggregation in neurodegenerative diseases

Congo red is a commonly used histological dye for amyloid detection. The specificity of this staining results from Congo red's affinity for binding to fibril proteins enriched in beta-sheet conformation. Unexpectedly, recent investigations indicate that the dye also possesses the capacity to interfere with processes of protein misfolding and aggregation, stabilizing native protein monomers or partially folded intermediates, while reducing concentration of more toxic protein oligomers. Inhibitory effects of Congo red upon amyloid toxicity may also range from blockade of channel formation and interference with glycosaminoglycans binding or immune functions, to the modulation of gene expression. Particularly, Congo red exhibits ameliorative effect in models of neurodegenerative disorders, such as Alzheimer's, Parkinson's, Huntington's and prion diseases. Another interesting application of Congo red analogues is the development of imaging probes. Based on their small molecular size and penetrability through blood-brain barrier, Congo red congeners can be used for both antemortem and in vivo visualization and quantification of brain amyloids. Therefore, understanding mechanisms involved in dye-amyloidal fibril binding and inhibition of aggregation will provide instructive guides for the design of future compounds, potentially useful for monitoring and treating neurodegenerative diseases.

Synthesis of biphenyltrienes as probes for beta-amyloid plaques

We report a series of p-hydroxy-, p-amino-, p-monomethylamino-, and p-monofluoroethylamino-substituted biphenyltrienes that displayed high binding affinities to beta-amyloid plaques. In an in vitro binding assay using postmortem brain homogenates of Alzheimer's patients and [(125)I]9, the triene compounds showed excellent binding affinities. When labeled with suitable radionuclides, they are useful as in vivo imaging agents for detecting Abeta plaques in the brains of Alzheimer's patients.

The development of anti-amyloid therapy for Alzheimer's disease : from secretase modulators to polymerisation inhibitors

The leading hypothesis of the pathophysiology of Alzheimer's disease holds that the pivotal event is cleavage of the amyloid precursor protein to release intact the 42-amino-acid amyloid-beta peptide (Abeta); this hypothesis best explains the known genetic causes of Alzheimer's disease. If this theory is correct, optimal strategies for altering the disease process should be directed toward modifying the generation, clearance and/or toxicity of Abeta. Abeta is highly aggregable, spontaneously assuming a beta-sheet conformation and polymerising into oligomers, protofibrils, fibrils and plaques. The relative contribution of the various forms of Abeta to neuronal dysfunction in Alzheimer's disease remains uncertain; however, recent evidence implicates diffusible oligomeric species. This article reviews the range of strategies that have been investigated to target Abeta to slow the progression of Alzheimer's disease, from secretase modulators to anti-polymerisation agents. One amyloid-binding drug, tramiprosate (3-amino-1-propanesulfonic acid; Alzhemed), which is effective in reducing polymerisation in vitro and plaque deposition in animals, has now reached phase III clinical trials. Thus, it is plausible that an effective anti-amyloid strategy will become available for the treatment of Alzheimer's disease within the next few years.

Liver transplantation and new therapeutic approaches for familial amyloidotic polyneuropathy (FAP)

Liver transplantation has been considered as a promising therapy to halt the progression of clinical symptoms in familial amyloidotic polyneuropathy (FAP) because most transthyretin (TTR) is produced by the liver. In addition, domino liver transplantation using an FAP patient's liver has been performed because of a shortage of donor livers. However, because the use of liver transplantation as therapy for FAP has given rise to several problems, an alternative treatment is needed. We have tried several other approaches. Recent studies suggested that certain metal ions affect amyloidogenesis. Among metal ions tested in an in vitro amyloid formation study, Cr3+ increased stability of both normal and mutant TTR tetramers and suppressed TTR amyloidogenesis induced by low pH. Our findings indicate that Cr3+ acts to suppress TTR amyloidogenesis. BSB, a Congo red derivative that binds to amyloid fibrils in FAP as well as to those in senile plaques in Alzheimer's disease, effectively suppressed TTR amyloid formation in vitro. BSB may thus be useful for preventing amyloid formation. Free radical scavenger therapy was also tried in FAP patients but yielded no conclusive results. Immunization for transgenic mice having the ATTR V30M gene using ATTR Y78P resulted in suppression of amyloid deposits. Finally, an RNA/DNA chimera and single-stranded oligonucleotides (SSOs) were tested in vitro and in vivo in an attempt to repair the amyloidogenic TTR gene in the liver and retina. On the basis of results achieved so far, SSO is a promising tool for gene therapy.

Identification of combinatorial drug regimens for treatment of Huntington's disease using Drosophila

We explore the hypothesis that pathology of Huntington's disease involves multiple cellular mechanisms whose contributions to disease are incrementally additive or synergistic. We provide evidence that the photoreceptor neuron degeneration seen in flies expressing mutant human huntingtin correlates with widespread degenerative events in the Drosophila CNS. We use a Drosophila Huntington's disease model to establish dose regimens and protocols to assess the effectiveness of drug combinations used at low threshold concentrations. These proof of principle studies identify at least two potential combinatorial treatment options and illustrate a rapid and cost-effective paradigm for testing and optimizing combinatorial drug therapies while reducing side effects for patients with neurodegenerative disease. The potential for using prescreening in Drosophila to inform combinatorial therapies that are most likely to be effective for testing in mammals is discussed.

Mechanism of accelerated assembly of beta-amyloid filaments into fibrils by KLVFFK(6)

Extracellular senile plaques are a central pathological feature of Alzheimer's disease. At the core of these plaques are fibrillar deposits of beta-amyloid peptide (Abeta). In vitro, Abeta spontaneously assembles into amyloid fibrils of cross-beta sheet structure. Although it was once believed that the fibrils themselves were toxic, more recent data supports the hypothesis that aggregation intermediates, rather than fully formed fibrils, are the most damaging to neuronal tissue. In previously published work, we identified several small peptides that interact with Abeta and increase its aggregation rate while decreasing its toxicity. In this work, we examined in detail the interaction between Abeta and one of these peptides. Using a mathematical model of Abeta aggregation kinetics, we show that the dominant effect of the peptide is to accelerate lateral association of Abeta filaments into fibrils.

Synthesis of Analogues of Congo Red and Evaluation of Their Anti-Prion Activity

No cure as of yet exists for any of the transmissible spongiform encephalopathies. In this paper, we describe the synthesis of analogues of Congo red and evaluation against a cellular model of infection, the SMB (scrapie mouse brain) persistently infected cell line, for their ability to inhibit the infectivity of the abnormal form of prion protein (PrP-res). The compounds have also been tested for their ability to inhibit the polymerization of PrPC by PrP-res. A number of analogues showed inhibition of PrP-res infectivity at nanomolar concentrations. Several analogues show promise; the most active compound, 2a, inhibits the formation of PrP-res in SMB cells with an EC50 of 25-50 nM.

Abeta aggregation inhibitors. Part 1: Synthesis and biological activity of phenylazo benzenesulfonamides

Phenylazo benzenesulfonamides were designed and synthesized as beta-amyloid (Abeta40) fibril assembly inhibitors, and evaluated for inhibition of Abeta40 aggregation and neurotoxicity using rat cortical neurons. Compound 2 (LB-152) was the most potent compound in this study, and the para-NMe(2) group on the end of the phenylazo moiety may play an important role in preventing Abeta40 fibril formation. LB-152 provides a new lead for further development of potential beta-amyloid aggregation inhibitors to treat AD.

In vivo labeling of amyloid with BF-108

Detection of aggregated amyloid-beta (Abeta) with a non-invasive imaging modality such as positron emission tomography (PET) was suggested to be ideal for the diagnosis of Alzheimer's disease (AD) prior to the onset of clinical symptoms. We have been searching for imaging probe candidates with a high affinity for aggregated Abeta in vitro and in vivo and high lipophilicity, a characteristic that allows for the permeation of the blood-brain barrier (BBB). As analyzed by Thioflavin T (ThT) assay and octanol/water partition coefficient test (PC), 3-diethylamino-6-(2-fluoroethyl)ethylaminoacridine (BF-108) were found to have high affinity for Abeta aggregates in vitro and high lipophilicity. Intravenously administrated BF-108 labeled Abeta aggregates injected into the amygdala as observed under a fluorescence microscope, showing this compound's permeability of BBB and an ability to label Abeta in vivo. BF-108 also labeled neuritic senile plaques (SPs), neurofibrillary tangles, and amyloid-laden vessels in temporal and hippocampal sections from AD patients. Following intravenous administration of BF-108 to an APP23 transgenic (TG) mouse, in vivo labeling of endogenous plaques was seen in brain sections by fluorescence microscopy. These properties suggest the potential utility of BF-108 for in vivo imaging of AD pathology.

A novel tool for detecting amyloid deposits in systemic amyloidosis in vitro and in vivo

We synthesized (trans,trans)-1-bromo-2,5-bis-(3-hydroxycarbonyl-4-hydroxy)styrylbenzene (BSB) and used this compound to detect amyloid fibrils in autopsy and biopsy samples from patients with localized amyloidosis, such as familial prion disease, and systemic amyloidosis, such as familial amyloidotic polyneuropathy, amyloid A (AA) amyloidosis, light chain (AL) amyloidosis, and dialysis-related amyloidosis. BSB showed reactions in all Congo red-positive and immunoreactive regions of the samples examined in the study, and some amyloid fibrils in the tissues could be detected more precisely with BSB than with the other methods. In the mouse model of AA amyloidosis, injected BSB reacted with amyloid in all regions in the serial sections in which Congo red staining was positive. A highly sensitive 27-MHz quartz crystal microbalance analysis revealed that BSB showed a significant affinity for amyloid fibrils purified from familial amyloidotic polyneuropathy and dialysis-related amyloidosis samples and suppressed formation of transthyretin amyloid in vitro. These results suggest that BSB may become a valuable tool for detection of amyloid deposits in amyloidosis and of the mechanism of amyloid formation.

Targeted control of kinetics of beta-amyloid self-association by surface tension-modifying peptides

Brain tissue from Alzheimer's patients contains extracellular senile plaques composed primarily of deposits of fibrillar aggregates of beta-amyloid peptide. beta-Amyloid aggregation is postulated to be a major factor in the onset of this neurodegenerative disease. Recently proposed is the hypothesis that oligomeric intermediates, rather than fully formed insoluble fibrils, are cytotoxic. Previously, we reported the discovery of peptides that accelerate beta-amyloid aggregation yet inhibit toxicity in vitro, in support of this hypothesis. These peptides contain two domains: a recognition element designed to bind to beta-amyloid and a disrupting element that alters beta-amyloid aggregation kinetics. Here we show that the aggregation rate-enhancing activity of the disrupting element correlates strongly with its ability to increase surface tension of aqueous solutions. Using the Hofmeister series as a guide, we designed a novel peptide with terminal side-chain trimethylammonium groups in the disrupting domain. The derivatized peptide greatly increased solvent surface tension and accelerated beta-amyloid aggregation kinetics by severalfold. Equivalent increases in surface tension in the absence of a recognition domain had no effect on beta-amyloid aggregation. These results suggest a novel strategy for targeting localized changes in interfacial energy to specific proteins, as a way to selectively alter protein folding, stability, and aggregation.

11C-labeled stilbene derivatives as Abeta-aggregate-specific PET imaging agents for Alzheimer's disease

A series of stilbene derivatives as potential diagnostic imaging agents targeting amyloid plaques in Alzheimer's disease (AD) were synthesized and evaluated. The syntheses of the stilbenes were successfully achieved by a simple Wadsworth-Emmons reaction between diethyl (4-nitrobenzyl)phosphonate and 4-methoxybenzaldehyde. 4-N,N-dimethylamino-4'-methyoxy and the corresponding 4-N-monomethylamino-, 4'-hydroxy stilbenes showed good binding affinities towards Abeta aggregates in vitro (K(i) < 10 nM). The (11)C labeled 4-N-methylamino-4'-hydroxystilbene, [(11)C]4, was prepared by (11)C methylation of 4-amino-4'-hydroxystilbene. The [(11)C]4 displayed a moderate lipophilicity (log P = 2.36), and showed a very good brain penetration and washout from normal rat brain after an iv injection. In vitro autoradiography of transgenic AD mouse brain sections showed a high specific labeling of beta-amyloid plaques, whereas the control sections showed no binding. Taken together the data suggest that a relatively simple stilbene derivative, [(11)C]4, N-[(11)C]methylamino-4'-hydroxystilbene, may be useful as a positron emission tomography (PET) imaging agent for mapping Abeta plaques in the brain of patients with Alzheimer's disease.

Aspartic proteases involved in Alzheimer's disease

Alzheimer's disease afflicts every tenth human aged over 65. Despite the dramatic progress that has been made in understanding the disease, the exact cause of Alzheimer's disease is still unknown. Most gene mutations associated with Alzheimer's disease point at the same culprits: amyloid precursor protein and ultimately amyloid beta. The enigmatic proteases alpha-,beta-, and gamma-secretase are the three executioners of amyloid precursor protein processing, and disruption of their delicate balance is suspected to result in Alzheimer's disease. Significant progress has been made in the selective control of these proteases, regardless of the availability of structural information. Not even the absence of a robust cell-free assay for gamma-secretase could hamper the identification of nonpeptidic inhibitors of this enzyme for long. Within five years, four distinctly different structural moieties were developed and the first drug candidates are in clinical trials. Unfortunately, selective inhibition of amyloid beta formation remains a crucial issue because fundamental fragments of the gamma-secretase complex are important for other signaling events. This problem makes beta-secretase inhibition and alpha-secretase induction even more appealing.

Identification of benzothiazoles as potential polyglutamine aggregation inhibitors of Huntington's disease by using an automated filter retardation assay

Preventing the formation of insoluble polyglutamine containing protein aggregates in neurons may represent an attractive therapeutic strategy to ameliorate Huntington's disease (HD). Therefore, the ability to screen for small molecules that suppress the self-assembly of huntingtin would have potential clinical and significant research applications. We have developed an automated filter retardation assay for the rapid identification of chemical compounds that prevent HD exon 1 protein aggregation in vitro. Using this method, a total of 25 benzothiazole derivatives that inhibit huntingtin fibrillogenesis in a dose-dependent manner were discovered from a library of approximately 184,000 small molecules. The results obtained by the filter assay were confirmed by immunoblotting, electron microscopy, and mass spectrometry. Furthermore, cell culture studies revealed that 2-amino-4,7-dimethyl-benzothiazol-6-ol, a chemical compound similar to riluzole, significantly inhibits HD exon 1 aggregation in vivo. These findings may provide the basis for a new therapeutic approach to prevent the accumulation of insoluble protein aggregates in Huntington's disease and related glutamine repeat disorders.

Beta-amyloid production, aggregation, and clearance as targets for therapy in Alzheimer's disease

1. Despite major efforts aimed at elucidating the molecular basis and physiopathology of Alzheimer's disease (AD), there is still no effective treatment available for this devastating disorder. The biological mechanisms underlying the development of AD are complex, as multiple factors appear to modulate (either positively or negatively) the progression of neurodegeneration in the brains of AD patients. Not surprisingly, a number of different therapeutic approaches aimed at distinct aspects of the disease are currently being pursued. Given its central role in the neuropathology of AD, the beta-amyloid peptide (Abeta) is the focus of many such approaches. 2. In this review, we discuss recent developments along three major lines of investigation: (i) identification and characterization of inhibitors of the enzymes involved in proteolytic processing of the amyloid precursor protein and production of Abeta; (ii) identification of the pathways involved in cerebral degradation and clearance of Abeta; and (iii) characterization of small-molecule inhibitors of amyloid aggregation that prevent cerebral amyloid deposition and neurotoxicity. 3. Significant progress has been achieved in these directions, opening up new perspectives toward the development of effective approaches for the treatment or prevention of AD.