Inhibition of Amyloid Fibril Formation and Cytotoxicity by Hydroxyindole Derivatives

Inhibition of cytotoxic self-assembly of HEWL through promoting fibrillation by new synthesized α-hydroxycarbamoylphosphinic acids

The main objective of the present study is to investigate the potency of new synthesized hydroxycarbamoyl phosphinic acid derivatives in modulating cytotoxic fibrillogenesis of hen egg white lysozyme (HEWL), as a common model in protein aggregation studies. Hydroxycarbamoyl phosphinic acid derivatives were prepared by the reaction of α-hydroxyalkylphosphinic acids with isocyanates (or isothiocyanates) in the presence of trimethylsilyl chloride (TMSCl). The designed process involves the condensation reaction leading to formation of new C sp2-P bond formation. The synthesis and purity of novel designed compounds were confirmed by NMR, LC-MS, and HPLC techniques. A range of experiments, including thioflavin T (ThT) and 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence assays, Congo red binding measurement, atomic force microscopy imaging, MTT-based cell viability and hemolysis assays were employed to investigate anti-amyloidogenic effects of tested compounds. The obtained results demonstrate that these compounds are able to significantly modulate the self-assembly process of HEWL via shortening of nucleation phase leading to the acceleration of fibrillation and appearance of very large and thick fibrils with decreased surface hydrophobicity and cytotoxicity. Based on ANS binding data, we suggest that increased exposure of hydrophobic patches of oligomeric species is the possible mechanism by which tested compounds promote self-assembly process of HEWL. Fluorescence anisotropy and molecular docking studies indicate the interaction of both synthesized compounds with HEWL, and more specifically with residues that are situated in the highly aggregation-prone β-domain region of protein. This study unveils the potential of hydroxyalkylphosphinic acids as modulators of amyloid fibrillation highlighting these compounds as a promising approach for targeting protein aggregates associated with neurodegenerative diseases.

Targeting phenylalanine assemblies as a prospective disease-modifying therapy for phenylketonuria

Phenylketonuria is characterized by the accumulation of phenylalanine, resulting in severe cognitive and neurological disorders if not treated by a remarkably strict diet. There are two approved drugs today, yet both provide only a partial solution. We have previously demonstrated the formation of amyloid-like toxic assemblies by aggregation of phenylalanine, suggesting a new therapeutic target to be further pursued. Moreover, we showed that compounds that halt the formation of these assemblies also prevent their resulting toxicity. Here, we performed high-throughput screening, searching for compounds with inhibitory effects on phenylalanine aggregation. Morin hydrate, one of the most promising hits revealed during the screen, was chosen to be tested in vivo using a phenylketonuria mouse model. Morin hydrate significantly improved cognitive and motor function with a reduction in the number of phenylalanine brain deposits. Moreover, while phenylalanine levels remained high, we observed a recovery in dopaminergic, adrenergic, and neuronal markers. To conclude, the ability of Morin hydrate to halt phenylalanine aggregation without reducing phenylalanine levels implies the toxic role of the phenylalanine assemblies in phenylketonuria and opens new avenues for disease-modifying treatment.

Current understanding and future directions of cruciferous vegetables and their phytochemicals to combat neurological diseases

Neurological disorders incidences are increasing drastically due to complex pathophysiology, and the nonavailability of disease-modifying agents. Several attempts have been made to identify new potential chemicals to combat these neurological abnormalities. At present, complete abolishment of neurological diseases is not attainable except for symptomatic relief. However, dietary recommendations to help brain development or improvement have increased over the years. In recent times, cruciferous vegetables and their phytochemicals have been identified from preclinical and clinical investigations as potential neuroprotective agents. The present review highlights the beneficial effects and molecular mechanisms of phytochemicals such as indole-3-carbinol, diindolylmethane, sulforaphane, kaempferol, selenium, lutein, zeaxanthin, and vitamins of cruciferous vegetables against neurological diseases including Parkinson's disease, Alzheimer's disease, stroke, Huntington's disease, autism spectra disorders, anxiety, depression, and pain. Most of these cruciferous phytochemicals protect the brain by eliciting antioxidant, anti-inflammatory, and antiapoptotic properties. Regular dietary intake of cruciferous vegetables may benefit the prevention and treatment of neurological diseases. The present review suggests that there is a lacuna in identifying the clinical efficacy of these phytochemicals. Therefore, high-quality future studies should firmly establish the efficacy of the above-mentioned cruciferous phytochemicals in clinical settings.

Dietary glucosinolates derived isothiocyanates: chemical properties, metabolism and their potential in prevention of Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia affecting millions of people worldwide. It is a progressive, irreversible, and incurable neurodegenerative disorder that disrupts the synaptic communication between millions of neurons, resulting in neuronal death and functional loss due to the abnormal accumulation of two naturally occurring proteins, amyloid β (Aβ) and tau. According to the 2018 World Alzheimer's Report, there is no single case of an Alzheimer's survivor; even 1 in 3 people die from Alzheimer's disease, and it is a growing epidemic across the globe fruits and vegetables rich in glucosinolates (GLCs), the precursors of isothiocyanates (ITCs), have long been known for their pharmacological properties and recently attracted increased interest for the possible prevention and treatment of neurodegenerative diseases. Epidemiological evidence from systematic research findings and clinical trials suggests that nutritional and functional dietary isothiocyanates interfere with the molecular cascades of Alzheimer's disease pathogenesis and prevent neurons from functional loss. The aim of this review is to explore the role of glucosinolates derived isothiocyanates in various molecular mechanisms involved in the progression of Alzheimer's disease and their potential in the prevention and treatment of Alzheimer's disease. It also covers the chemical diversity of isothiocyanates and their detailed mechanisms of action as reported by various in vitro and in vivo studies. Further clinical studies are necessary to evaluate their pharmacokinetic parameters and effectiveness in humans.

Light, Water, and Melatonin: The Synergistic Regulation of Phase Separation in Dementia

The swift rise in acceptance of molecular principles defining phase separation by a broad array of scientific disciplines is shadowed by increasing discoveries linking phase separation to pathological aggregations associated with numerous neurodegenerative disorders, including Alzheimer’s disease, that contribute to dementia. Phase separation is powered by multivalent macromolecular interactions. Importantly, the release of water molecules from protein hydration shells into bulk creates entropic gains that promote phase separation and the subsequent generation of insoluble cytotoxic aggregates that drive healthy brain cells into diseased states. Higher viscosity in interfacial waters and limited hydration in interiors of biomolecular condensates facilitate phase separation. Light, water, and melatonin constitute an ancient synergy that ensures adequate protein hydration to prevent aberrant phase separation. The 670 nm visible red wavelength found in sunlight and employed in photobiomodulation reduces interfacial and mitochondrial matrix viscosity to enhance ATP production via increasing ATP synthase motor efficiency. Melatonin is a potent antioxidant that lowers viscosity to increase ATP by scavenging excess reactive oxygen species and free radicals. Reduced viscosity by light and melatonin elevates the availability of free water molecules that allow melatonin to adopt favorable conformations that enhance intrinsic features, including binding interactions with adenosine that reinforces the adenosine moiety effect of ATP responsible for preventing water removal that causes hydrophobic collapse and aggregation in phase separation. Precise recalibration of interspecies melatonin dosages that account for differences in metabolic rates and bioavailability will ensure the efficacious reinstatement of the once-powerful ancient synergy between light, water, and melatonin in a modern world.

Influence of Urea and Dimethyl Sulfoxide on K-Peptide Fibrillation

Protein fibrillation leads to formation of amyloids-linear aggregates that are hallmarks of many serious diseases, including Alzheimer's and Parkinson's diseases. In this work, we investigate the fibrillation of a short peptide (K-peptide) from the amyloidogenic core of hen egg white lysozyme in the presence of dimethyl sulfoxide or urea. During the studies, a variety of spectroscopic methods were used: fluorescence spectroscopy and the Thioflavin T assay, circular dichroism, Fourier-transform infrared spectroscopy, optical density measurements, dynamic light scattering and intrinsic fluorescence. Additionally, the presence of amyloids was confirmed by atomic force microscopy. The obtained results show that the K-peptide is highly prone to form fibrillar aggregates. The measurements also confirm the weak impact of dimethyl sulfoxide on peptide fibrillation and distinct influence of urea. We believe that the K-peptide has higher amyloidogenic propensity than the whole protein, i.e., hen egg white lysozyme, most likely due to the lack of the first step of amyloidogenesis-partial unfolding of the native structure. Urea influences the second step of K-peptide amyloidogenesis, i.e., folding into amyloids.

DMSO and TMAO-Differences in Interactions in Aqueous Solutions of the K-Peptide

Interactions between a solvent and their co-solute molecules in solutions of peptides are crucial for their stability and structure. The K-peptide is a synthetic fragment of a larger hen egg white lysozyme protein that is believed to be able to aggregate into amyloid structures. In this study, a complex experimental and theoretical approach is applied to study systems comprising the peptide, water, and two co-solutes: trimethylamide N-oxide (TMAO) or dimethyl sulfoxide (DMSO). Information about their interactions in solutions and on the stability of the K-peptide was obtained by FTIR spectroscopy and differential scanning microcalorimetry. The IR spectra of various osmolyte-water-model-peptide complexes were simulated with the DFT method (B3LYP/6-311++G(d,p)). The FTIR results indicate that both solutes are neutral for the K-peptide in solution. Both co-solutes affect the peptide to different degrees, as seen in the shape of its amide I band, and have different influences on its thermal stability. DFT calculations helped simplify the experimental data for easier interpretation.

Beneficial Health Effects of Glucosinolates-Derived Isothiocyanates on Cardiovascular and Neurodegenerative Diseases

Neurodegenerative diseases (NDDs) and cardiovascular diseases (CVDs) are illnesses that affect the nervous system and heart, all of which are vital to the human body. To maintain health of the human body, vegetable diets serve as a preventive approach and particularly Brassica vegetables have been associated with lower risks of chronic diseases, especially NDDs and CVDs. Interestingly, glucosinolates (GLs) and isothiocyanates (ITCs) are phytochemicals that are mostly found in the Cruciferae family and they have been largely documented as antioxidants contributing to both cardio- and neuroprotective effects. The hydrolytic breakdown of GLs into ITCs such as sulforaphane (SFN), phenylethyl ITC (PEITC), moringin (MG), erucin (ER), and allyl ITC (AITC) has been recognized to exert significant effects with regards to cardio- and neuroprotection. From past in vivo and/or in vitro studies, those phytochemicals have displayed the ability to mitigate the adverse effects of reactive oxidation species (ROS), inflammation, and apoptosis, which are the primary causes of CVDs and NDDs. This review focuses on the protective effects of those GL-derived ITCs, featuring their beneficial effects and the mechanisms behind those effects in CVDs and NDDs.

Inhibition of the formation of lysozyme fibrillar assemblies by the isoquinoline alkaloid coralyne

The isoquinoline alkaloid coralyne can efficiently attenuate fibrillogenesis in lysozyme.

Zinc oxide nanoparticle interface moderation with tyrosine and tryptophan reverses the pro-amyloidogenic property of the particle

Zinc oxide nanoparticle with negative surface potential (ZnONP) enhances bovine insulin fibrillation. Here, we are exploring ZnONP with positive surface potential (ZnONP_Unc) and surface functionalized with tyrosine and tryptophan amino acids to observe the effects of surface potential and surface functional groups on the fibrillation. ZnONP_Unc, despite of inversed surface potential, enhances the insulin fibrillation with increase in the interface concentration at physiological pH. Whereas, the interface moderation with the amino acids mitigates the surface-mediated insulin fibrillation propensity. Additionally, the study indicates that the change in interfacial functional groups at ZnONP_Unc significantly reverses the interface-mediated destabilization of insulin conformation. The functional groups from the amino acids, like CO, N-H and aromatic functional groups, are anticipated to further stabilize the insulin conformation by forming hydrogen bond and van der Waals interactions with the key amyloidogenic sequences of insulin, A13-A20 from A-chain and B9-B20 from B-chain. Hence, the altered interaction profile, with change in interfacial functional groups, mitigates the interface-mediated insulin fibrillation and the ZnONP_Unc-/fibril-mediated cytotoxicity.

Tryptophan-cardanol fluorescent nanoparticles inhibit α-synuclein aggregation and disrupt amyloid fibrils

Protein misfolding and aggregation play a vital role in several human diseases such as Parkinson's, Alzheimer's, and prion diseases. The development of nanoparticles that modulate aggregation could be potential drug candidates for these neurodegenerative disorders. Parkinson's disease pathogenesis is closely associated with the accumulation of α-synuclein oligomers and fibrils in the substantia nigra of the brain. This report discusses the interactions of novel tryptophan-cardanol nanoparticles with α-synuclein protein monomers and fibrils. These nanoparticles could effectively disrupt α-synuclein fibrils and inhibit fibril formation at low concentrations such as 5 μM. The tryptophan-cardanol nanoparticles inhibit fibril formation from unstructured protein resulting in spherical nanostructures. These nanoparticles could also disassemble amyloid fibrils; the complete disappearance of fibrils was evident after 48 h of incubation with tryptophan-cardanol. The transmission electron microscopy (TEM) micrographs after the incubation did not show any remnants of the peptide aggregates or oligomers. The thioflavin T fluorescence after the disassembly was diminished compared with that of fibrils also supports the inhibitory effect of the nanoparticles. Also, these nanoparticles did not reduce the viability of the SH-SY5Y cells. These findings suggest that the tryptophan-cardanol nanoparticles showed sufficiently high inhibitory activity and may have therapeutic potential for synucleinopathies.

Discovery of a tetracyclic indole alkaloid that postpones fibrillation of hen egg white lysozyme protein

Protein aggregation, such as amyloid fibril formation, is molecular hallmark of many neurodegenerative disorders including Alzheimer's, Parkinson's, and Prion disease. Indole alkaloids are well-known as the compounds having the ability to inhibit protein fibrillation. In this study, we experimentally and computationally have investigated the anti-amyloid property of a derivative of a synthesized tetracyclic indole alkaloid (TCIA), possessing capable functional groups. The fibrillation reaction of Hen White Egg Lysozyme (HEWL) was performed in absence and presence of the indole alkaloid. For quantitative analysis, we used Thioflovin T binding assay which showed ~50% reduction in fibril formation in the presence of 20 μM TCIA. Using TEM imaging, we observed a significant morphological change in our model protein in the presence of TCIA. In addition, we exploited FT-IR assay by which Amide I peak's shifting toward lower wavenumber was clearly observed. Using Molecular Docking, the interaction of the inhibitor (TCIA) with the protein's amyloidogenic region was modeled. Also, different biophysical parameters were calculated by Molecular Dynamics (MD) simulation. Various biochemical assays, conformational change, and hydrophobicity exposure of the protein during amyloid formation indicated that the compound assists HEWL to keep its native structure via destabilizing β-sheet structure.

Procyanidine resists the fibril formation of human islet amyloid polypeptide

Human islet amyloid polypeptide (hIAPP) is widely studied due to its close correlation with the pathogenic mechanism of type II diabetes mellitus (T2DM). Bioflavonoids have been used in the neurodegeneration and diabetes studies. However, the structure-activity relationship remains unclear in many of these compounds. In this work, we performed diverse biophysical and biochemical methods to explore the inhibition of procyanidine on hIAPP and compared with that on amyloid-β (Aβ) protein which is linked to Alzheimer's disease (AD). The procyanidine effectively inhibited the aggregation of hIAPP and Aβ through hydrophobic and hydrogen bonding interactions, it dissolved the aged fibrils into nanoscale particles. The compound also ameliorated the cytotoxicity and the membrane leakage by reducing the peptide oligomerization. The procyanidine showed better binding affinity and inhibitory effects on peptide aggregation and upregulated the cell viability to hIAPP than to Aβ, which could be a prospective inhibitor against hIAPP. This work also offered a possible strategy for T2DM and AD treatments.

Effect of formulation and peptide folding on the fibrillar aggregation, gelation, and oxidation of a therapeutic peptide

The physical and chemical stability of therapeutic peptides presents challenges in developing robust formulations. The stability of the formulation affects product safety, efficacy and quality. Therefore, an understanding of the effects of formulation variables on the peptide's conformational structure and on its possible physical and chemical degradation is vital. To this end, computational and experimental analysis were employed to investigate the impact of formulation, peptide folding and product handling on oxidation, fibrillar aggregation and gelation of teriparatide. Teriparatide was used as a model drug due to the correlation of its conformation in solution with its pharmacological activity. Fibrillar aggregation and gelation were monitored using four orthogonal techniques. An innovative, automated platform coupled with ion mobility mass spectrometry was used for profiling chemical degradants. Increases in teriparatide concentration, pH, and ionic strength were found to increase the rate of fibrillar aggregation and gelation. Conversely, an increase in peptide folding and stabilization of the folded structures was found to decrease the rate of fibrillar aggregation and gelation. Moreover, the rate of oxidation was found to be inversely related to its solution concentration and extent of peptide folding. The present study provides an insight into formulation strategies designed to reduce the potential risk of physical and chemical degradation of peptides with a defined conformation.

Pseudopeptide Amyloid Aggregation Inhibitors: In Silico, Single Molecule and Cell Viability Studies

Neurodegeneration in Alzheimer's disease (AD) is defined by pathology featuring amyloid-β (Aβ) deposition in the brain. Aβ monomers themselves are generally considered to be nontoxic, but misfold into β-sheets and aggregate to form neurotoxic oligomers. One suggested strategy to treat AD is to prevent the formation of toxic oligomers. The SG inhibitors are a class of pseudopeptides designed and optimized using molecular dynamics (MD) simulations for affinity to Aβ and experimentally validated for their ability to inhibit amyloid-amyloid binding using single molecule force spectroscopy (SMFS). In this work, we provide a review of our previous MD and SMFS studies of these inhibitors and present new cell viability studies that demonstrate their neuroprotective effects against Aβ(1-42) oligomers using mouse hippocampal-derived HT22 cells. Two of the tested SG inhibitors, predicted to bind Aβ in anti-parallel orientation, demonstrated neuroprotection against Aβ(1-42). A third inhibitor, predicted to bind parallel to Aβ, was not neuroprotective. Myristoylation of SG inhibitors, intended to enhance delivery across the blood-brain barrier (BBB), resulted in cytotoxicity. This is the first use of HT22 cells for the study of peptide aggregation inhibitors. Overall, this work will inform the future development of peptide aggregation inhibitors against Aβ toxicity.

Review on Alzheimer's disease: Inhibition of amyloid beta and tau tangle formation

It is reported that approximately 40 million people are suffering from dementia, globally. Dementia is a group of symptoms that affect neurons and cause some mental disorders, such as losing memory. Alzheimer's disease (AD) which is known as the most common cause of dementia, is one of the top medical care concerns across the world. Although the exact sources of the disease are not understood, is it believed that aggregation of amyloid-beta (Aβ) outside of neuron cells and tau aggregation or neurofibrillary tangles (NFTs) formation inside the cell may play crucial roles. In this paper, we are going to review studies that targeted inhibition of amyloid plaque and tau protein tangle formation, to suppress or postpone AD.

Inhibition potential evaluation of two synthetic bis-indole compounds on amyloid fibrillation: a molecular simulation study

Protein aggregation is known as the main mechanism of amyloid fibrillation in amyloidosis diseases. Recent studies confirmed that compounds with one or two indole rings have inhibitory potential against amyloid fibrillation. Herein, the interaction of two similar compounds 'bis(indolyl)-2-methyl-phenyl-methene' and 'bis(indolyl)-2-chloro-phenyl-methene' with an amyloid core model was investigated. To this aim, molecular docking and all-atom molecular dynamics (MD) simulations were used. Docking results between aggregation-prone region (APR) of hen egg-white lysozyme (HEWL) and either of ligands showed that they interact with different residues of the APR (amyloid fibril nucleus). According to MD results, bis(indolyl)-2-methyl-phenyl-methene made a distance between the two cores, which was 1.5 times greater than that bis(indolyl)-2-chloro-phenyl-methene made. Analysis of RMSD/RMSF values revealed that bis(indolyl)-2-methyl-phenyl-methene stabilized strands of A and B, while destabilized strands C and D. The hydrophobic 'methyl' functional group in bis(indolyl)-2-methyl-phenyl-methene facilitate its deep penetration between core nuclei, via destabilizing outer strands of C and D. Considering this fact that results of this study are in agreement with experimental findings, details of the discovered mechanism of interaction between ligands and HEWL's APR would be inspiring for further anti-fibrillation drug designs.Communicated by Ramaswamy H. Sarma.

Novel Isatin Thiosemicarbazone Derivatives as Potent Inhibitors of β-Amyloid Peptide Aggregation and Toxicity

Inhibition of β-amyloid peptide (Αβ) aggregation in Alzheimer's disease (AD) is among the therapeutic approaches against AD which still attracts scientific research interest. In the search for compounds that interact with Aβ and disrupt its typical aggregation course toward oligomeric or polymeric toxic assemblies, small organic molecules of natural origin, combining low molecular weight (necessary blood-brain barrier penetration) and low toxicity (necessary for pharmacological application), are greatly sought after. Isatin (1H-indoline-2,3-dione), a natural endogenous indole, and many of its derivatives exhibit a wide spectrum of neuropharmacological and chemotherapeutic properties. The synthesis and biological evaluation of four new isatins as inhibitors of Aβ aggregation is presented herein. In these derivatives, the N-phenyl thiosemicarbazide moiety is joined at the 3-oxo position of isatin through Schiff base formation, and substitutions are present at the indole nitrogen and position 5 of the isatin core. Biophysical studies employing circular dichroism, thioflavin T fluorescence assay, and transmission electron microscopy reveal the potential of the isatin thiosemicarbazones (ITSCs) to alter the course of Αβ aggregation, with two of the derivatives exhibiting outstanding inhibition of the aggregation process, preventing completely the formation of amyloid fibrils. Furthermore, in in vitro studies in primary neuronal cell cultures, the ITSCs were found to inhibit the Aβ-induced neurotoxicity and reactive oxygen species production at concentrations as low as 1 μM. Taken all together, the novel ITSCs can be considered as privileged structures for further development as potential AD therapeutics.

Resveratrol-mediated cleavage of amyloid β1-42 peptide: potential relevance to Alzheimer's disease

Aggregation of amyloid β_1-42 (Aβ_1-42) peptide within the brain is considered one of the main causes of the neuropathological changes associated with Alzheimer's disease. Resveratrol is a well-known antioxidant but has also been reported to bind to Aβ_1-42 peptide, thereby reducing aggregation. However, little is known of the precise mechanism by which resveratrol reduces Aβ_1-42 peptide aggregation. Using the thioflavin-T assay, the ability of resveratrol to reduce the extent of Aβ_1-42 peptide aggregation was investigated. The findings of the present study demonstrate that interaction of resveratrol with Aβ_1-42 peptide resulted in the cleavage of Aβ_1-42 peptide into smaller fragments, as detected by matrix assisted laser desorption ionization-time of flight mass spectrometry. Atomic force microscopy analyses revealed Aβ_1-42 peptide, under control conditions, aggregated into oligomers, protofibrils, and fibrils, whereas there was a distinct lack of these structures when Aβ_1-42 peptide was incubated with resveratrol. Following 10 days incubation of Aβ_1-42 peptide with resveratrol, particles with a mean z-height of 1.940 nm (range 0.675-3.275 nm) were observed, which are characteristic of shorter peptide species. In cell-based studies, resveratrol significantly reduced the cytotoxicity of Aβ_1-42 peptide toward SH-SY5Y human neuroblastoma cells, suggesting a protective effect of the polyphenol. We therefore propose a novel mechanism by which resveratrol disrupts Aβ_1-42 aggregation by mediating fragmentation of Aβ_1-42 into smaller peptides, which have no propensity to aggregate further.

Indole Compound NC009-1 Augments APOE and TRKA in Alzheimer's Disease Cell and Mouse Models for Neuroprotection and Cognitive Improvement

Alzheimer's disease (AD), associated with abnormal accumulation of amyloid-β (Aβ), is the most common cause of dementia among older people. A few studies have identified substantial AD biomarkers in blood but their results were inconsistent. Here we screened gene expression alterations on Aβ-GFP SH-SY5Y neuronal model for AD, and evaluated the findings on peripheral leukocytes from 78 patients with AD and 56 healthy controls. The therapeutic responses of identified biomarker candidates were further examined in Aβ-GFP SH-SY5Y neuronal and APP/PS1/Tau triple transgenic (3×Tg-AD) mouse models. Downregulation of apolipoprotein E (APOE) and tropomyosin receptor kinase A (TRKA) were detected in Aβ-GFP SH-SY5Y cells and validated by peripheral leukocytes from AD patients. Treatment with an in-house indole compound NC009-1 upregulated the expression of APOE and TRKA accompanied with improvement of neurite outgrowth in Aβ-GFP SH-SY5Y cells. NC009-1 further rescued the downregulated APOE and TRKA and reduced Aβ and tau levels in hippocampus and cortex, and ameliorated cognitive deficits in streptozocin-induced hyperglycemic 3×Tg-AD mice. These results suggest the role of APOE and TRKA as potential peripheral biomarkers in AD, and offer a new drug development target of AD treatment. Further studies of a large series of AD patients will be warranted to verify the findings and confirm the correlation between these markers and therapeutic efficacy.

Inhibition of Amyloid Fibrillation by Small Molecules and Nanomaterials: Strategic Development of Pharmaceuticals Against Amyloidosis

Amyloid fibrils are a special class of self-assembled protein molecules, which exhibit various toxic effects in cells. Different physiological disorders such as Alzheimer's, Parkinson's, Huntington's diseases, etc. happen due to amyloid formation and lack of proper cellular mechanism for the removal of fibrils. Therefore, inhibition of amyloid fibrillation will find immense applications to combat the diseases associated with amyloidosis. The development of therapeutics against amyloidosis is definitely challenging and numerous strategies have been followed to find out anti-amyloidogenic molecules. Inhibition of amyloid aggregation of proteins can be achieved either by stabilizing the native conformation or by decreasing the chances of assembly formation by the unfolded/misfolded structures. Various small molecules such as naturally occurring polyphenols, flavonoids, small organic molecules, surfactants, dyes, chaperones, etc. have demonstrated their capability to interrupt the amyloid fibrillation of proteins. In addition to that, in last few years, different nanomaterials were evolved as effective therapeutic inhibitors against amyloidosis. Aromatic and hydrophobic interactions between the partially unfolded protein molecules and the inhibitors had been pointed as a general mechanism for inhibition. In this review article, we are presenting an overview on the inhibition of amyloidosis by using different small molecules (both natural and synthetic origin) as well as nanomaterials for development of pharmaceutical strategies against amyloid diseases.

Rapid Dissolution of Amyloid β Fibrils by Silver Nanoplates

Plaques of amyloid beta (Aβ) protein are associated with neurodegenerative diseases, and preventing their formation and dissolution of plaques are essential to the development of therapeutics. In this study, silver triangular nanoplates (AgTNPs) are shown to dissolve mature Aβ fibrils because of their plasmonic photothermal property. Mature Aβ fibrils treated with AgTNPs under near-infrared (NIR)-illuminated conditions are dissolved in less than 1 h, while an equal concentration of silver spherical nanoparticles took about 70 h. The concentration of the fibrils decreased from 10 to 0.3 μM upon treating the amyloid fibrils with AgTNPs under NIR. AgTNPs are also shown to prevent the formation of Aβ fibrils by selective binding to the positively charged amyloidogenic sequence of the Aβ monomer. The kinetics of inhibition by AgTNPs follows the predictions of the detailed kinetic model (Ramesh et al., Langmuir 2018, 34, 4004-4012). The kinetics of dissolution and inhibition are characterized by Congo red/ThT assay, transmission electronic microscopy, atomic force microscopy, and attenuated total reflectance Fourier transform-infrared spectroscopy. Cell viability studies on SH-SY5Y and BE-(2)-C cells using 3-[4,5-dimethy-lthi-azol-2-yl]-2,5-diphenyl-tetrazdium bromide and lactate dehydrogenase assay show that the viability of the cells increased from 33 to 70% on treating the cells with AgTNP-incubated Aβ fibrils compared to the mature Aβ fibrils. The study provides new insights to design plasmonic nanoparticle-based therapeutics to cure neurodegenerative diseases.

Insights into Structure-Activity Relationships of 3-Arylhydrazonoindolin-2-One Derivatives for Their Multitarget Activity on β-Amyloid Aggregation and Neurotoxicity

Despite the controversial outcomes of clinical trials executed so far, the prevention of β-amyloid (Aβ) deposition and neurotoxicity by small molecule inhibitors of Aβ aggregation remains a target intensively pursued in the search of effective drugs for treating Alzheimer’s disease (AD) and related neurodegeneration syndromes. As a continuation of previous studies, a series of new 3-(2-arylhydrazono)indolin-2-one derivatives was synthesized and assayed, investigating the effects of substitutions on both the indole core and arylhydrazone moiety. Compared with the reference compound 1, we disclosed equipotent derivatives bearing alkyl substituents at the indole nitrogen, and fairly tolerated bioisosteric replacements at the arylhydrazone moiety. For most of the investigated compounds, the inhibition of Aβ₄₀ aggregation (expressed as pIC₅₀) was found to be correlated with lipophilicity, as assessed by a reversed-phase HPLC method, through a bilinear relationship. The N¹-cyclopropyl derivative 28 was tested in cell-based assays of Aβ₄₂ oligomer toxicity and oxidative stress induced by hydrogen peroxide, showing significant cytoprotective effects. This study confirmed the versatility of isatin in preparing multitarget small molecules affecting different biochemical pathways involved in AD.

Rosmarinic Acid Restores Complete Transparency of Sonicated Human Cataract Ex Vivo and Delays Cataract Formation In Vivo

Cataract, the leading cause of vision impairment worldwide, arises from abnormal aggregation of crystallin lens proteins. Presently, surgical removal is the only therapeutic approach. Recent findings have triggered renewed interest in development of non-surgical treatment alternatives. However, emerging treatments are yet to achieve full and consistent lens clearance. Here, the first ex vivo assay to screen for drug candidates that reduce human lenticular protein aggregation was developed. This assay allowed the identification of two leading compounds as facilitating the restoration of nearly-complete transparency of phacoemulsified cataractous preparation ex vivo. Mechanistic studies demonstrated that both compounds reduce cataract microparticle size and modify their amyloid-like features. In vivo studies confirmed that the lead compound, rosmarinic acid, delays cataract formation and reduces the severity of lens opacification in model rats. Thus, the ex vivo assay may provide an initial platform for broad screening of potential novel therapeutic agents towards pharmacological treatment of cataract.

Indole-3-carbinol: a plant hormone combatting cancer

A diet rich in cruciferous vegetables such as cauliflower, broccoli, and cabbage has long been considered healthy, and various epidemiological studies suggest that the consumption of cruciferous vegetables contributes to a cancer-protecting diet. While these vegetables contain a vast array of phytochemicals, the mechanism by which these vegetables counteract cancer is still largely unresolved. Numerous in situ studies have implicated indole-3-carbinol, a breakdown product of the glucosinolate indole-3-ylmethylglucosinolate, as one of the phytochemicals with anti-cancer properties. Indole-3-carbinol influences a range of cellular processes, but the mechanisms by which it acts on cancer cells are slowly being revealed. Recent studies on the role of indole-3-carbinol in Arabidopsis opens the door for cross-kingdom comparisons that can help in understanding the roles of this important phytohormone in both plant biology and combatting cancer.

Sulfonated Compounds Bind with Prostatic Acid Phosphatase (PAP248-286) to Inhibit the Formation of Amyloid Fibrils

The peptide segment of prostatic acid phosphatase (PAP248-286) aggregates to form SEVI (semen-derived enhancer of virus infection) amyloid fibrils. These are characteristic seminal amyloids that have the ability to promote the effect of HIV infection. In this paper, we explore the binding of sulfonated compounds with PAP248-286 through an in silico study. Three derivatives of suramin, NF110, NF279, and NF340, are selected. All of these sulfonated molecules bind to PAP248-286 and alter the conformation of the peptide, even though they have various structures, sizes, and configurations. The compounds bind with PAP248-286 through multiple interactions, such as hydrogen-bonding interactions, hydrophobic interactions, π-π stacking interactions, and electrostatic interactions. However, NF110, which has an X-shaped configuration, has the highest binding affinity of the three derivatives investigated. We also perform surface plasmon resonance and a Congo red assay to validate the results. The interactions between PAP248-286 and the sulfonated compounds are proposed to depend on the orientations of the sulfonate groups and the specific configurations of the compounds instead of the number of sulfonate groups. NF110 molecules occupy the exposed binding sites of PAP248-286, blocking interactions between the peptides. Therefore, these compounds are important in inhibiting the aggregation of PAP248-286. Herein, we provide useful information to develop new efficient microbicides to antagonize seminal amyloid fibrils and to block HIV transmission.

Newfound effect of N-acetylaspartate in preventing and reversing aggregation of amyloid-beta in vitro

Although N-acetylaspartate (NAA) has long been recognized as the most abundant amino acid in neurons by far, its primary role has remained a mystery. Based on its unique tertiary structure, we explored the potential of NAA to modulate aggregation of amyloid-beta (Aβ) peptide 1-42 via multiple corroborating aggregation assays along with electron microscopy. Thioflavin-T fluorescence assay demonstrated that at physiological concentrations, NAA substantially inhibited the initiation of Aβ fibril formation. In addition, NAA added after 25 min of Aβ aggregation was shown to break up preformed fibrils. Electron microscopy analysis confirmed the absence of mature fibrils following NAA treatment. Furthermore, fluorescence correlation spectroscopy and dynamic light scattering measurements confirmed significant reductions in Aβ fibril hydrodynamic radius following treatment with NAA. These results suggest that physiological levels of NAA could play an important role in controlling Aβ aggregation in vivo where they are both found in the same neuronal compartments.

Real-time monitoring of the aggregation of Alzheimer's amyloid-β via1H magic angle spinning NMR spectroscopy

Proton magic-angle-spinning NMR used for real-time analysis of amyloid aggregation reveals that mechanical rotation of Aβ_1-40 monomers increases the rate of formation of aggregates, and that the increasing lag-time with peptide concentration suggests the formation of growth-incompetent species. EGCG's ability to shift off-pathway aggregation is also demonstrated.

Dual Role of Gold Nanorods: Inhibition and Dissolution of Aβ Fibrils Induced by Near IR Laser

Extracellular plaques of amyloid beta (Aβ) fibrils and neurofibrillary tangles are known to be associated with neurological diseases such as Alzheimer's disease. Studies have shown that spherical nanoparticles inhibit the formation of Aβ fibrils by intercepting the nucleation and growth pathways of fibrillation. In this report, gold nanorods (AuNRs) are used to inhibit the formation of Aβ fibrils and the shape-dependent plasmonic properties of AuNRs are exploited to faciliate faster dissolution of mature Aβ fibrils. Negatively charged, lipid (DMPC) stabilized AuNRs inhibit the formation of fibrils due to selective binding to the positevly charged amyloidogenic sequence of Aβ protein. The kinetics of inhibition is characterized by thioflavin T (ThT) fluorescence, transmission electronic microscopy (TEM), atomic force microscopy (AFM), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). An increase in the aspect ratio of DMPC-AuNR in the range of 2.2-4.2 decreased the fibrils content proportionally. Further, the fibrils content is decreased by increasing the concentration of AuNR for all aspect ratios. As AuNR absorb near-infrared (NIR) light and creates a localized hotspot, NIR laser (800 nm) is applied for 2 min to facilitate the thermal dissolution of mature Aβ fibrils. Majority of Aβ fibrils are disintegrated into smaller fragments after exposure to NIR in the presence of AuNR. Thus, the DMPC-AuNRs exhibit a dual effect: inhibition of fibrillation and NIR laser facilitated dissolution of mature amyloid fibrils. This study essentially provides guidelines to design efficient nanoparticle-based therapeutics for neurodegenerative diseases.

The β-cell assassin: IAPP cytotoxicity

Islet amyloid polypeptide (IAPP) forms cytotoxic oligomers and amyloid fibrils in islets in type 2 diabetes (T2DM). The causal factors for amyloid formation are largely unknown. Mechanisms of molecular folding and assembly of human IAPP (hIAPP) into β-sheets, oligomers and fibrils have been assessed by detailed biophysical studies of hIAPP and non-fibrillogenic, rodent IAPP (rIAPP); cytotoxicity is associated with the early phases (oligomers/multimers) of fibrillogenesis. Interaction with synthetic membranes promotes β-sheet assembly possibly via a transient α-helical molecular conformation. Cellular hIAPP cytotoxicity can be activated from intracellular or extracellular sites. In transgenic rodents overexpressing hIAPP, intracellular pro-apoptotic signals can be generated at different points in β-cell protein synthesis. Increased cellular trafficking of proIAPP, failure of the unfolded protein response (UPR) or excess trafficking of misfolded peptide via the degradation pathways can induce apoptosis; these data indicate that defects in intracellular handling of hIAPP can induce cytotoxicity. However, there is no evidence for IAPP overexpression in T2DM. Extracellular amyloidosis is directly related to the degree of β-cell apoptosis in islets in T2DM. IAPP fragments, fibrils and multimers interact with membranes causing disruption in vivo and in vitro These findings support a role for extracellular IAPP in β-sheet conformation in cytotoxicity. Inhibitors of fibrillogenesis are useful tools to determine the aberrant mechanisms that result in hIAPP molecular refolding and islet amyloidosis. However, currently, their role as therapeutic agents remains uncertain.

Methods of probing the interactions between small molecules and disordered proteins

It is generally recognized that a large fraction of the human proteome is made up of proteins that remain disordered in their native states. Despite the fact that such proteins play key biological roles and are involved in many major human diseases, they still represent challenging targets for drug discovery. A major bottleneck for the identification of compounds capable of interacting with these proteins and modulating their disease-promoting behaviour is the development of effective techniques to probe such interactions. The difficulties in carrying out binding measurements have resulted in a poor understanding of the mechanisms underlying these interactions. In order to facilitate further methodological advances, here we review the most commonly used techniques to probe three types of interactions involving small molecules: (1) those that disrupt functional interactions between disordered proteins; (2) those that inhibit the aberrant aggregation of disordered proteins, and (3) those that lead to binding disordered proteins in their monomeric states. In discussing these techniques, we also point out directions for future developments.

Atomic-resolution map of the interactions between an amyloid inhibitor protein and amyloid β (Aβ) peptides in the monomer and protofibril states

Self-association of amyloid β (Aβ) peptides is a hallmark of Alzheimer's disease and serves as a general prototype for amyloid formation. A key endogenous inhibitor of Aβ self-association is human serum albumin (HSA), which binds ∼90% of plasma Aβ. However, the exact molecular mechanism by which HSA binds Aβ monomers and protofibrils is not fully understood. Here, using dark-state exchange saturation transfer NMR and relaxation experiments complemented by morphological characterization, we mapped the HSA-Aβ interactions at atomic resolution by examining the effects of HSA on Aβ monomers and soluble high-molecular weight oligomeric protofibrils. We found that HSA binds both monomeric and protofibrillar Aβ, but the affinity of HSA for Aβ monomers is lower than for Aβ protofibrils (K_d values are submillimolar rather than micromolar) yet physiologically relevant because of the ∼0.6-0.7 mm plasma HSA concentration. In both Aβ protofibrils and monomers, HSA targets key Aβ self-recognition sites spanning the β strands found in cross-β protofibril structures, leading to a net switch from direct to tethered contacts between the monomeric Aβ and the protofibril surface. These HSA-Aβ interactions are isoform-specific, because the HSA affinity of Aβ monomers is lower for Aβ(1-42) than for Aβ(1-40). In addition, the HSA-induced perturbations of the monomer/protofibrils pseudo-equilibrium extend to the C-terminal residues in the Aβ(1-42) isoform but not in Aβ(1-40). These results provide an unprecedented view of how albumin interacts with Aβ and illustrate the potential of dark-state exchange saturation transfer NMR in mapping the interactions between amyloid-inhibitory proteins and amyloidogenic peptides.

Interaction and inhibitory influence of the azo dye carmoisine on lysozyme amyloid fibrillogenesis

The azo dye carmoisine has a significant inhibitory effect on fibrillogenesis in lysozyme.

The Potential of Indole/Indolylquinoline Compounds in Tau Misfolding Reduction by Enhancement of HSPB1

BACKGROUND

Neurofibrillary tangles formed from tau misfolding have long been considered one of the pathological hallmarks of Alzheimer's disease (AD). The misfolding of tau in AD correlates with the clinical progression of AD and inhibition or reversal of tau misfolding may protect the affected neurons.

METHODS

We generated 293 and SH-SY5Y cells expressing DsRed-tagged pro-aggregation mutant of repeat domain of tau (ΔK280 tau_RD ) to test indole/indolylquinoline derivatives for reducing tau misfolding and neuroprotection.

RESULTS

Four of the 10 derivatives tested displayed good misfolding-inhibitory effects on Tet-On 293 cells. Among them, NC009-1 and NC009-7 enhanced heat-shock 27 kDa protein 1 (HSPB1) expression to increase ∆K280 tau_RD -DsRed solubility and promoted neurite outgrowth in Tet-On SH-SY5Y cells. Knockdown of HSPB1 resulted in decreased ∆K280 tau_RD -DsRed solubility and reduced neurite outgrowth, which were rescued by addition of NC009-1/NC009-7. Treatment with indole/indolylquinoline derivatives also improved neuronal cell viability and neurite outgrowth in mouse hippocampal primary culture under tau cytotoxicity.

CONCLUSION

Our results demonstrate how indole/indolylquinoline derivatives are likely to work in tau misfolding reduction, providing insight into the possible working mechanism of indole and indolylquinoline derivatives in AD treatment.

Study on the inter- and intra-peptide salt-bridge mechanism of Aβ23-28 oligomer interaction with small molecules: QM/MM method

Amyloid β (Aβ) peptides have long been known to be a potential candidate for the onset of Alzheimer's disease (AD). The biophysical properties of Aβ42 peptide aggregates are of significant importance for the amyloid cascade mechanism of AD. It is necessary to design an inhibitor using small molecules to reduce the aggregation process in Aβ42 peptides. Attention has been given to use the natural products as anti-aggregation compounds, directly targeting Aβ peptides. Polyphenols have been extensively studied as a class of amyloid inhibitors. 9,10-Anthraquinone (AQ) is present in abundance in medicinal plants (rhubarb), the Trp-Pro-Tyr (TPT) peptide has been found in the venom of the black mamba snake, and the morin molecule is naturally present in wine and green tea; several other polyphenol derivatives are under clinical trials to develop anti-neurodegenerative drugs. In vitro and in vivo results strongly suggest that AQ and morin molecules are potential inhibitors of Aβ aggregation; however, the detailed understanding of the inhibition mechanism remains largely unknown. The formation of Aβ fibrils and oligomers requires a conformational change from α-helix to β-sheet, which occurs due to the formation of a salt-bridge between Asp(23) and Lys(28) residues. The present study focused on investigating the salt-bridge mechanism in the monomer, dimer and oligomer of the Aβ23-28 peptide during the interaction with TPT, morin and AQ molecules. Interaction energy and natural bond orbital analyses have been carried out using the ONIOM(M05-2X/6-31++G(d,p):UFF) method. The QM/MM studies have been performed to study the mechanism of salt-bridge formation during the inhibition process of amyloid β protein aggregation. The TPT molecule, which binds with the Asp(23) and Lys(28) residues of Aβ, prevents the salt-bridge formation between Asp(23) and Lys(28) residues and consequently the probability of the formation of Aβ fibrils is reduced.

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.

Inhibition of Beta-Amyloid Fibrillation by Luminescent Iridium(III) Complex Probes

We report herein the application of kinetically inert luminescent iridium(III) complexes as dual inhibitors and probes of beta-amyloid fibrillogenesis. These iridium(III) complexes inhibited Aβ_1–40 peptide aggregation in vitro, and protected against Aβ-induced cytotoxicity in neuronal cells. Furthermore, the complexes differentiated between the aggregated and unaggregated forms of Aβ_1–40 peptide on the basis of their emission response.

The potential of synthetic indolylquinoline derivatives for Aβ aggregation reduction by chemical chaperone activity

Alzheimer's disease (AD) is the most prevalent form of dementia associated with progressive cognitive decline and memory loss. Extracellular β-amyloid (Aβ) is a major constituent of senile plaques, one of the pathological hallmarks of AD. Aβ deposition causes neuronal death via a number of possible mechanisms such as increasing oxidative stress. Therefore therapeutic approaches to identify novel Aβ aggregate reducers could be effective for AD treatment. Using a Trx-His-Aβ biochemical assay, we screened 11 synthetic indolylquinoline compounds, and found NC009-1, -2, -6 and -7 displaying potential to reduce Aβ aggregation. Treating Tet-On Aβ-GFP 293 cells with these compounds reduced Aβ aggregation and reactive oxygen species. These compounds also promoted neurite outgrowth in Tet-On Aβ-GFP SH-SY5Y cells. Furthermore, treatment with above compounds improved neuronal cell viability, neurite outgrowth, and synaptophysin expression level in mouse hippocampal primary culture under oligomeric Aβ-induced cytotoxicity. Moreover, the tested NC009-1 significantly ameliorated Aβ-induced inhibition of hippocampal long-term potentiation in mouse hippocampal slices. Our results demonstrate how synthetic indolylquinoline compounds are likely to work as chemical chaperones in Aβ-aggregation reduction and neuroprotection, providing insight into the possible applications of indolylquinoline compounds in AD treatment.

Inhibition of amyloid fibrillation and cytotoxicity of lysozyme fibrillation products by polyphenols

An increasing number of studies conducted under in vitro and in vivo conditions, have concluded that polyphenols, compounds frequently occurring in many herbs with antioxidant properties, prevent and reverse amyloid fibril formation. However, the mechanisms by which these natural products modulate the protein aggregation process are poorly understood. Herein, a range of techniques including thioflavin T (ThT) and ANS fluorescence assays, electron microscopy and circular dichroism have been employed to determine the efficacy of rosmarinic acid (RA) and resveratrol (Res) on the inhibition/reversion of fibrillogenesis and hindering cytotoxicity induced by protofibrils and amyloid fibrils of hen egg white lysozyme (HEWL). Results demonstrated that both polyphenols effectively inhibit fibrillogenesis and destabilize preformed fibrils of HEWL in a concentration-dependent manner. Cytotoxicity protection on PC12 cells was also observed using the MTT assay, ROS production assay, and phase-contrast microscopy. It is suggested that the mechanism underlying the inhibitory effects of RA and Res is to prevent hydrophobic interactions between HEWL amyloidogenic prefibrillar species, although additional studies is needed to elucidate the detailed mechanisms involved. A combination of antioxidative and anti-amyloidogenic properties of these molecules may provide them with the described neuroprotective capacities.

Photodegradation of amyloid β and reduction of its cytotoxicity to PC12 cells using porphyrin derivatives

A purpose-designed porphyrin-peptide hybrid effectively degraded amyloid β monomer and oligomers associated with Alzheimer's disease. Degradation was achieved using light irradiation in the absence of any additives and under neutral conditions. Moreover, the hybrid effectively neutralized the cytotoxicity of amyloid β in PC12 cells upon photoirradiation.

Self-Assembly of Aβ40, Aβ42 and Aβ43 Peptides in Aqueous Mixtures of Fluorinated Alcohols

Fluorinated alcohols such as hexafluoroisopropanol (HFIP) and trifluoroethanol (TFE) have the ability to promote α-helix and β-hairpin structure in proteins and peptides. HFIP has been used extensively to dissolve various amyloidogenic proteins and peptides including Aβ, in order to ensure their monomeric status. In this paper, we have investigated the self-assembly of Aβ40, Aβ42, and Aβ43 in aqueous mixtures of fluorinated alcohols from freshly dissolved stock solutions in HFIP. We have observed that formation of fibrillar and non-fibrillar structures are dependent on the solvent composition. Peptides form fibrils with ease when reconstituted in deionized water from freshly dissolved HFIP stocks. In aqueous mixtures of fluorinated alcohols, either predominant fibrillar structures or clustered aggregates were observed. Aqueous mixtures of 20% HFIP are more favourable for Aβ fibril formation as compared to 20% TFE. When Aβ40, Aβ42, and Aβ43 stocks in HFIP are diluted in 50% aqueous mixtures in phosphate buffer or deionized water followed by slow evaporation of HFIP, Aβ peptides form fibrils in phosphate buffer and deionized water. The clustered structures could be off-pathway aggregates. Aβ40, Aβ42, and Aβ43 showed significant α-helical content in freshly dissolved HFIP stocks. The α-helical conformational intermediate in Aβ40, Aβ42, and Aβ43 could favour the formation of both fibrillar and non-fibrillar aggregates depending on solvent conditions and rate of α-helical to β-sheet transition.

Ortho-methylated 3-hydroxypyridines hinder hen egg-white lysozyme fibrillogenesis

Protein aggregation with the concomitant formation of amyloid fibrils is related to several neurodegenerative diseases, but also to non-neuropathic amyloidogenic diseases and non-neurophatic systemic amyloidosis. Lysozyme is the protein involved in the latter, and it is widely used as a model system to study the mechanisms underlying fibril formation and its inhibition. Several phenolic compounds have been reported as inhibitors of fibril formation. However, the anti-aggregating capacity of other heteroaromatic compounds has not been studied in any depth. We have screened the capacity of eleven different hydroxypyridines to affect the acid-induced fibrillization of hen lysozyme. Although most of the tested hydroxypyridines alter the fibrillation kinetics of HEWL, only 3-hydroxy-2-methylpyridine, 3-hydroxy-6-methylpyridine and 3-hydroxy-2,6-dimethylpyridine completely abolish fibril formation. Different biophysical techniques and several theoretical approaches are combined to elucidate their mechanism of action. O-methylated 3-hydroxypyridines bind non-cooperatively to two distinct but amyloidogenic regions of monomeric lysozyme. This stabilises the protein structure, as evidenced by enhanced thermal stability, and results in the inhibition of the conformational transition that precedes fibril assembly. Our results point to o-methylated 3-hydroxypyridines as a promising molecular scaffold for the future development of novel fibrillization inhibitors.

Cysteine inhibits the fibrillisation and cytotoxicity of amyloid-β 40 and 42: implications for the contribution of the thiophilic interaction

Inhibitors of amyloid fibril formation have been at the centre of intense research efforts for the prevention of amyloidosis. Here, we hypothesise that a specific non-covalent interaction, the thiophilic interaction between the side chain of an aromatic residue in a polypeptide and a sulphur atom of the compound, effectively inhibits amyloid fibril formation. Fluorescence spectroscopy and transmission electron microscopy revealed that sulphur compounds, particularly Cys, inhibit the fibrillisation of amyloid-β 1-40 (Aβ40) and 1-42 (Aβ42). Interestingly, aggregates of Aβ40 and Aβ42 induced by Cys were less cytotoxic than those induced by catechin, which is the most typical inhibitor of amyloid fibril formation. Because the essential amino acid, Cys, is an abundant molecule in the blood and cytosol, our data provide a new basis for the prevention of amyloid-related diseases and the elucidation of the mechanism of these diseases.