Efficient reversal of Alzheimer's disease fibril formation and elimination of neurotoxicity by a small molecule

Understanding the structural dynamics of human islet amyloid polypeptide: Advancements in and applications of ion-mobility mass spectrometry

Human islet amyloid polypeptide (hIAPP) forms amyloid deposits that contribute to β-cell death in pancreatic islets and are considered a hallmark of Type II diabetes Mellitus (T2DM). Evidence suggests that the early oligomers of hIAPP formed during the aggregation process are the primary pathological agent in islet amyloid induced β-cell death. The self-assembly mechanism of hIAPP, however, remains elusive, largely due to limitations in conventional biophysical techniques for probing the distribution or capturing detailed structures of the early, structurally dynamic oligomers. The advent of Ion-mobility Mass Spectrometry (IM-MS) has enabled the characterisation of hIAPP early oligomers in the gas phase, paving the way towards a deeper understanding of the oligomerisation mechanism and the correlation of structural information with the cytotoxicity of the oligomers. The sensitivity and the rapid structural characterisation provided by IM-MS also show promise in screening hIAPP inhibitors, categorising their modes of inhibition through "spectral fingerprints". This review delves into the application of IM-MS to the dissection of the complex steps of hIAPP oligomerisation, examining the inhibitory influence of metal ions, and exploring the characterisation of hetero-oligomerisation with different hIAPP variants. We highlight the potential of IM-MS as a tool for the high-throughput screening of hIAPP inhibitors, and for providing insights into their modes of action. Finally, we discuss advances afforded by recent advancements in tandem IM-MS and the combination of gas phase spectroscopy with IM-MS, which promise to deliver a more sensitive and higher-resolution structural portrait of hIAPP oligomers. Such information may help facilitate a new era of targeted therapeutic strategies for islet amyloidosis in T2DM.

Artificial intelligence to guide precision anticancer therapy with multitargeted kinase inhibitors

BACKGROUND

Vast amounts of rapidly accumulating biological data related to cancer and a remarkable progress in the field of artificial intelligence (AI) have paved the way for precision oncology. Our recent contribution to this area of research is CancerOmicsNet, an AI-based system to predict the therapeutic effects of multitargeted kinase inhibitors across various cancers. This approach was previously demonstrated to outperform other deep learning methods, graph kernel models, molecular docking, and drug binding pocket matching.

METHODS

CancerOmicsNet integrates multiple heterogeneous data by utilizing a deep graph learning model with sophisticated attention propagation mechanisms to extract highly predictive features from cancer-specific networks. The AI-based system was devised to provide more accurate and robust predictions than data-driven therapeutic discovery using gene signature reversion.

RESULTS

Selected CancerOmicsNet predictions obtained for "unseen" data are positively validated against the biomedical literature and by live-cell time course inhibition assays performed against breast, pancreatic, and prostate cancer cell lines. Encouragingly, six molecules exhibited dose-dependent antiproliferative activities, with pan-CDK inhibitor JNJ-7706621 and Src inhibitor PP1 being the most potent against the pancreatic cancer cell line Panc 04.03.

CONCLUSIONS

CancerOmicsNet is a promising AI-based platform to help guide the development of new approaches in precision oncology involving a variety of tumor types and therapeutics.

Moxifloxacin Disrupts and Attenuates Aβ42 Fibril and Oligomer Formation: Plausibly Repositioning an Antibiotic as Therapeutic against Alzheimer's Disease

The aggregation of Aβ42 is established as a key factor in the development of Alzheimer's disease (AD). Consequently, molecules that inhibit aggregation of peptide may lead to therapies to prevent or control AD. Several studies suggest that oligomeric intermediates present during aggregation may be more cytotoxic than fibrils themselves. In this work, we examine the inhibitory activity of an antibiotic MXF on aggregation (fibrils and oligomers) and disaggregation of Aβ42 using various biophysical and microscopic studies. Computational analysis was done to offer mechanistic insight. The amyloid formation of Aβ42 is suppressed by MXF, as demonstrated by the decrease in both the corresponding ThT fluorescence intensity and other biophysical techniques. The lag phase of amyloid formation doubled from 4.53 to 9.66 h in the presence of MXF. The addition of MXF at the completion of the fibrillation reaction, as monitored by ThT, led to a rapid, concentration dependent, exponential decrease in fluorescence signal that was consistent with loss of fibrils. We used TEM to directly demonstrate that MXF caused fibrils to disassemble. Our docking results show that MXF binds to both monomeric and fibrillar forms of Aβ42 with significant affinities. We also observed breaking of fibrils in the presence of MXF through molecular dynamics simulation. These findings suggest that antibiotic MXF could be a promising lead compound with dual role as fibril/oligomer inhibitor and disaggregase for further development as potential repurposed therapeutic against AD.

Amyloids: The History of Toxicity and Functionality

Proteins can perform their specific function due to their molecular structure. Partial or complete unfolding of the polypeptide chain may lead to the misfolding and aggregation of proteins in turn, resulting in the formation of different structures such as amyloid aggregates. Amyloids are rigid protein aggregates with the cross-β structure, resistant to most solvents and proteases. Because of their resistance to proteolysis, amyloid aggregates formed in the organism accumulate in tissues, promoting the development of various diseases called amyloidosis, for instance Alzheimer's diseases (AD). According to the main hypothesis, it is considered that the cause of AD is the formation and accumulation of amyloid plaques of Aβ. That is why Aβ-amyloid is the most studied representative of amyloids. Therefore, in this review, special attention is paid to the history of Aβ-amyloid toxicity. We note the main problems with anti-amyloid therapy and write about new views on amyloids that can play positive roles in the different organisms including humans.

Inhibitory mechanism of an antifungal drug, caspofungin against amyloid β peptide aggregation: Repurposing via neuroinformatics and an experimental approach

The multifactorial neurological condition called Alzheimer's disease (AD) primarily affects elderly individuals. Despite the calamitous consequences of AD, curative strategies for a regimen to apply remain inadequate as several factors contribute to AD etiology. Drug repurposing is an advance strategy prior to drug discovery as various effective drugs perform through alteration of multiple targets, and the present "poly-pharmacology" can be a curative approach to complex disorders. AD's multifactorial behavior actively encourages the hypothesis for a drug design approach focused on drug repurposing. In this study, we discovered that an antifungal drug, Caspofungin (CAS) is a potent Aβ aggregation inhibitor that displays significantly reduced toxicity associated with AD. Drug reprofiling and REMD simulations demonstrated that CAS interacts with the β-sheet section, known as Aβ amyloid fibrils hotspot. CAS leads to destabilization of β-sheet and, conclusively, in its devaluation. Later, in vitro experiments were acquired in which the fibrillar volume was reduced for CAS-treated Aβ peptide. For the first time ever, this study has determined an antifungal agent as the Aβ amyloid aggregation's potent inhibitor. Several efficient sequence-reliant potent inhibitors can be developed in future against the amyloid aggregation for different amyloid peptide by the processing and conformational optimization of CAS.

Somatostatin Ameliorates β-Amyloid-Induced Cytotoxicity via the Regulation of CRMP2 Phosphorylation and Calcium Homeostasis in SH-SY5Y Cells

Somatostatin is involved in the regulation of multiple signaling pathways and affords neuroprotection in response to neurotoxins. In the present study, we investigated the role of Somatostatin-14 (SST) in cell viability and the regulation of phosphorylation of Collapsin Response Mediator Protein 2 (CRMP2) (Ser522) via the blockade of Ca²⁺ accumulation, along with the inhibition of cyclin-dependent kinase 5 (CDK5) and Calpain activation in differentiated SH-SY5Y cells. Cell Viability and Caspase 3/7 assays suggest that the presence of SST ameliorates mitochondrial stability and cell survival pathways while augmenting pro-apoptotic pathways activated by Aβ. SST inhibits the phosphorylation of CRMP2 at Ser522 site, which is primarily activated by CDK5. Furthermore, SST effectively regulates Ca²⁺ influx in the presence of Aβ, directly affecting the activity of calpain in differentiated SH-SY5Y cells. We also demonstrated that SSTR2 mediates the protective effects of SST. In conclusion, our results highlight the regulatory role of SST in intracellular Ca²⁺ homeostasis. The neuroprotective role of SST via axonal regeneration and synaptic integrity is corroborated by regulating changes in CRMP2; however, SST-mediated changes in the blockade of Ca²⁺ influx, calpain expression, and toxicity did not correlate with CDK5 expression and p35/25 accumulation. To summarize, our findings suggest two independent mechanisms by which SST mediates neuroprotection and confirms the therapeutic implications of SST in AD as well as in other neurodegenerative diseases where the effective regulation of calcium homeostasis is required for a better prognosis.

Xestospongin C, a Reversible IP3 Receptor Antagonist, Alleviates the Cognitive and Pathological Impairments in APP/PS1 Mice of Alzheimer's Disease

Exaggerated Ca2+ signaling might be one of primary causes of neural dysfunction in Alzheimer's disease (AD). And the intracellular Ca2+ overload has been closely associated with amyloid-β (Aβ)-induced endoplasmic reticulum (ER) stress and memory impairments in AD. Here we showed for the first time the neuroprotective effects of Xestospongin C (XeC), a reversible IP3 receptor antagonist, on the cognitive behaviors and pathology of APP/PS1 AD mice. Male APP/PS1-AD mice (n = 20) were injected intracerebroventricularly with XeC (3μmol) via Alzet osmotic pumps for four weeks, followed by cognition tests, Aβ plaque examination, and ER stress-related protein measurement. The results showed that XeC pretreatment significantly improved the cognitive behavior of APP/PS1-AD mice, raising the spontaneous alteration accuracy in Y maze, decreasing the escape latency and increasing the target quadrant swimming time in Morris water maze; XeC pretreatment also reduced the number of Aβ plaques and the overexpression of ER stress proteins 78 kDa glucose-regulated protein (GRP-78), caspase-12, and CAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) in the hippocampus of APP/PS1 mice. In addition, in vitro experiments showed that XeC effectively ameliorated Aβ1 - 42-induced early neuronal apoptosis and intracellular Ca2+ overload in the primary hippocampal neurons. Taken together, IP3R-mediated Ca2+ disorder plays a key role in the cognitive deficits and pathological damages in AD mice. By targeting the IP3 R, XeC might be considered as a novel therapeutic strategy in AD.

Myricetin protects pancreatic β-cells from human islet amyloid polypeptide (hIAPP) induced cytotoxicity and restores islet function

The aberrant misfolding and self-assembly of human islet amyloid polypeptide (hIAPP)-a hormone that is co-secreted with insulin from pancreatic β-cells-into toxic oligomers, protofibrils and fibrils has been observed in type 2 diabetes mellitus (T2DM). The formation of these insoluble aggregates has been linked with the death and dysfunction of β-cells. Therefore, hIAPP aggregation has been identified as a therapeutic target for T2DM management. Several natural products are now being investigated for their potential to inhibit hIAPP aggregation and/or disaggregate preformed aggregates. In this study, we attempt to identify the anti-amyloidogenic potential of Myricetin (MYR)- a polyphenolic flavanoid, commonly found in fruits (like Syzygium cumini). Our results from biophysical studies indicated that MYR supplementation inhibits hIAPP aggregation and disaggregates preformed fibrils into non-toxic species. This protection was accompanied by inhibition of oxidative stress, reduction in lipid peroxidation and the associated membrane damage and restoration of mitochondrial membrane potential in INS-1E cells. MYR supplementation also reversed the loss of functionality in hIAPP exposed pancreatic islets via restoration of glucose-stimulated insulin secretion. Molecular dynamics simulation studies suggested that MYR molecules interact with the hIAPP pentameric fibril model at the amyloidogenic core region and thus prevents aggregation and distort the fibrils.

Functional Gene Module-Based Identification of Phillyrin as an Anticardiac Fibrosis Agent

Cardiac fibrosis (CF) greatly influences the therapeutic effects of heart diseases and remains an urgent challenge in clinical therapy. Till now, only a few methods are used to find potential anti-CF drugs effectively. This study aimed to construct a gene functional module to represent the core pathological process of CF and screen antifibrotic agents capable of decreasing the expression of the gene functional module. First, three CF marker genes Postn, Ddr2, and Pdgfra were selected to identify the corresponding highest coexpressed genes in the genome-based transcriptional profiles of human hearts. Both the marker genes and the coexpressed genes formed the CF-related gene functional module. Second, the correlation of the module with the CF process was measured in a collection of gene expression profiles of heart diseases to evaluate the participation of the functional module in heart diseases. Third, the anti-CF effects of phillyrin were predicted by the enrichment analysis of the module in the phillyrin-induced transcriptional profile. Finally, the myocardial infarction animal model was used to validate the cardioprotective and anti-CF effects of phillyrin experimentally. The results showed that phillyrin was a novel antifibrotic agent in heart diseases.

Polymer-Peptide Conjugates Convert Amyloid into Protein Nanobundles through Fragmentation and Lateral Association

The assembly of proteins into amyloid fibrils has become linked not only with the progression of myriad human diseases, but also important biological functions. Understanding and controlling the formation, structure, and stability of amyloid fibrils is therefore a major scientific goal. Here we utilize electron microscopy-based approaches combined with quantitative statistical analysis to show how recently developed kind of amyloid modulators-multivalent polymer-peptide conjugates (mPPCs)-can be applied to control the structure and stability of amyloid fibrils. In doing so, we demonstrate that mPPCs are able to convert 40-residue amyloid beta fibrils into ordered nanostructures through a combination of fragmentation and bundling. Fragmentation is shown to be consistent with a model where the rate constant of fibril breakage is independent of the fibril length, suggesting a local and specific interaction between fibrils and mPPCs. Subsequent bundling, which was previously not observed, leads to the formation of sheet-like nanostructures which are surprisingly much more uniform than the starting fibrils. These nanostructures have dimensions independent of the molecular weight of the mPPC and retain the molecular-level ordering of the starting amyloid fibrils. Collectively, we reveal quantitative and nanoscopic understanding of how mPPCs can be applied to control amyloid structure and stability, and demonstrate approaches to elucidate nanoscale amyloid phase behavior in the presence of functional macromolecules and other modulators.

Oleuropein aglycone and hydroxytyrosol interfere differently with toxic Aβ1-42 aggregation

Oleuropein aglycone (OleA), the most abundant polyphenol in extra virgin olive oil (EVOO), and Hydroxythyrosol (HT), the OleA main metabolite, have attracted our interest due to their multitarget effects, including the interference with amyloid aggregation path. However, the mechanistic details of their anti-amyloid effect are not known yet. We report here a broad biophysical approach and cell biology techniques that enabled us to characterize the different molecular mechanisms by which OleA and HT modulate the Aβ_1-42 fibrillation, a main histopathological feature of Alzheimer's disease (AD). In particular, OleA prevents the growth of toxic Aβ_1-42 oligomers and blocks their successive growth into mature fibrils following its interaction with the peptide N-terminus, while HT speeds up harmless fibril formation. Our data demonstrate that, by stabilizing oligomers and fibrils, both polyphenols reduce their seeding activity and aggregate/membrane interaction on human neuroblastoma SH-SY5Y cells. These findings highlight the great potential of EVOO polyphenols and offer the possibility to validate and to optimize their use for possible AD prevention and therapy.

An AIE-active theranostic probe for light-up detection of Aβ aggregates and protection of neuronal cells

An AIE-active probe of Cur-N-BF₂ is developed for light-up detection of Aβ fibrils and plaques, inhibition of Aβ fibrillation, disassembly of preformed Aβ fibrils, and protection of neuronal cells.

Gallic acid influence on bovine serum albumin thermal stability

A thermoanalytical approach reveals the dual action of GA on BSA thermal stability.

Peptide Self-Assembly and Its Modulation: Imaging on the Nanoscale

This chapter intends to review the progress in obtaining site-specific structural information for peptide assemblies using scanning tunneling microscopy. The effects on assembly propensity due to mutations and modifications in peptide sequences, small organic molecules and conformational transitions of peptides are identified. The obtained structural insights into the sequence-dependent assembly propensity could inspire rational design of peptide architectures at the molecular level.

Aminopyrimidine Class Aggregation Inhibitor Effectively Blocks Aβ-Fibrinogen Interaction and Aβ-Induced Contact System Activation

Accumulating evidence suggests that fibrinogen, a key protein in the coagulation cascade, plays an important role in circulatory dysfunction in Alzheimer's disease (AD). Previous work has shown that the interaction between fibrinogen and β-amyloid (Aβ), a hallmark pathological protein in AD, induces plasmin-resistant abnormal blood clots, delays fibrinolysis, increases inflammation, and aggravates cognitive function in mouse models of AD. Since Aβ oligomers have a much stronger affinity for fibrinogen than Aβ monomers, we tested whether amyloid aggregation inhibitors could block the Aβ-fibrinogen interaction and found that some Aβ aggregation inhibitors showed moderate inhibitory efficacy against this interaction. We then modified a hit compound so that it not only showed a strong inhibitory efficacy toward the Aβ-fibrinogen interaction but also retained its potency toward the Aβ42 aggregation inhibition process. Furthermore, our best hit compound, TDI-2760, modulated Aβ42-induced contact system activation, a pathological condition observed in some AD patients, in addition to inhibiting the Aβ-fibrinogen interaction and Aβ aggregation. Thus, TDI-2760 has the potential to lessen vascular abnormalities as well as Aβ aggregation-driven pathology in AD.

Doliroside A from Dolichos falcata Klein suppressing amyloid β-protein 42 fibrillogenesis: An insight at molecular level

A bioactive chemical constituent, doliroside A, from Chinese traditional herbal medicine Dolichos falcata Klein was isolated, purified and identified by 60% ethanol extraction, thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy. Molecular interaction mechanism between doliroside and amyloid β42 protein was evaluated by thioflavin T fluorescence (ThT), circular dichroism (CD), atomic force microscope (AFM), and differential scanning calorimeter (DSC) from the aspects of kinetics, secondary structure, morphology, and thermodynamics, respectively. Results show that the purity of doliroside A is 99.9% by HPLC, and its chemical structure is identified by ¹H- and ¹³C-NMR. Doliroside A is observed to be concentration-dependent inhibiting the fibrillation of Aβ42 with the IC50 value of 26.57 ± 1.6 μM. CD and DSC results imply that doliroside A can bind to the nuclei and oligomers of Aβ42 to form a stable complex and suppress Aβ42 fibrillation. AFM images show that doliroside A, after bound to the nuclei and oligomers, redirect Aβ42 into off-pathway, amorphous oligomers. These findings not only provide a full insight into the molecular interaction mechanisms between Aβ42 and doliroside A, but also facilitate the development of new native anti-AD drug of doliroside A compound.

Hematite-Based Photoelectrode Materials for Photoelectrocatalytic Inhibition of Alzheimer's β-Amyloid Self-Assembly

A visible light-active, hematite-based photoelectrode platform for suppressing β-amyloid (Aβ) self-assembly in vitro is reported. Upon illumination of a light-emitting diode with an anodic bias, the hematite photoanode generates reactive radical species, such as superoxide ions and hydroxyl radicals, via photoelectrocatalytic process. According to our analyses, the hematite photoanode exhibited a strong inhibitory effect on Aβ aggregation under visible light illumination and anodic bias. We found that hole-derived radicals played a significant role of oxidizing Aβ peptides, which effectively blocked further aggregation. The efficacy of photoelectrocatalytic inhibition on Aβ aggregation was enhanced by introducing cobalt phosphate (Co-Pi) as a co-catalyst on the hematite photoanode, which facilitated the separation of electron-hole pairs. We verified that both bare and Co-Pi@hematite photoanodes are biocompatible and effective in reducing Aβ aggregation-induced cytotoxicity.

Influence of a curcumin derivative on hIAPP aggregation in the absence and presence of lipid membranes

The deposition of aggregates of human islet amyloid polypeptide (hIAPP) has been correlated with the death of β-cells in type II diabetes mellitus. The actual molecular mechanism of cell death remains largely unknown; however, it has been postulated that the process of aggregation from monomeric hIAPP is closely involved. A possible cause of cellular toxicity may be through the disruption of structural integrity of the cell membrane by IAPP. Herein, a water-soluble curcumin derivative, CurDAc, is used to investigate the mitigation of hIAPP aggregation in the absence and presence of lipid membrane.

Yeast as a model for the identification of novel survival-promoting compounds applicable to treat degenerative diseases

Programmed cell death (PCD) plays an important role in development and normal metabolic functioning of organisms. Excessive cell death is the cause of many degenerative diseases, like neurodegenerative disorders and Wilson's disease, for which current therapies remain insufficient. Current therapies are mainly focused on decreasing the disease symptoms following cell death, rather than blocking the cell death process itself. The latter can be obtained by either decreasing the presence of the toxic trigger (like protein aggregation in case of many commonly known neurodegenerative diseases) or by blocking death-inducing signaling cascade(s). Given the high conservation in PCD processes between yeast and mammalian cells, in this review, we will focus on yeast as a model organism to study PCD-related diseases as well as on its use for drug discovery purposes. More specifically, we will provide a comprehensive overview of new compounds, which were identified in yeast-based drug screens, that either decrease the amount of toxic trigger or inhibit PCD signaling cascades under PCD-inducing conditions.

Effect of Ca(2+) on Aß40 fibrillation is characteristically different

Alzheimer's disease (AD) is the only one among top ten diseases in USA that cannot be cured, prevented or slowed down. At molecular level the mechanism of onset has been closely associated with mis-folding of Aβ40 and Aβ42 and is well supported by the genetic data for AD. Extensive research efforts have led to identification of factors and metal ions that could manipulate Aβ equilibrium, especially Ca(2+). Previously, we reported selectively acceleration of Aβ42 fibril formation by Ca(2+)in vitro within physiological concentrations (BBA (2009) 1794:1536). Aβ40 on the other hand did not appear to be significantly affected by Ca(2+) addition. In an effort to understand the distinctive behavior of Aβ40, we monitored changes of Aβ40 aggregation by intrinsic tyrosine fluorescence and CD and took different approaches for data processing. Our analysis of CD data indicates a complex effect induced by the addition of 2mM Ca(2+) resulting in an increase in the rate of transformation from monomer to β-sheet rich fibrilar or intermediate species formation in Aβ40. Surprisingly, the kinetics observed by intrinsic fluorescence studies in this article and ThT, SEC or EM studies in our previous report were not able to unravel the existence of this effect in Aβ40.

Inhibition of IAPP Aggregation and Toxicity by Natural Products and Derivatives

Fibrillar aggregates of human islet amyloid polypeptide, hIAPP, a pathological feature seen in some diabetes patients, are a likely causative agent for pancreatic beta-cell toxicity, leading to a transition from a state of insulin resistance to type II diabetes through the loss of insulin producing beta-cells by hIAPP induced toxicity. Because of the probable link between hIAPP and the development of type II diabetes, there has been strong interest in developing reagents to study the aggregation of hIAPP and possible therapeutics to block its toxic effects. Natural products are a class of compounds with interesting pharmacological properties against amyloids which have made them interesting targets to study hIAPP. Specifically, the ability of polyphenolic natural products, EGCG, curcumin, and resveratrol, to modulate the aggregation of hIAPP is discussed. Furthermore, we have outlined possible mechanistic discoveries of the interaction of these small molecules with the peptide and how they may mitigate toxicity associated with peptide aggregation. These abundantly found agents have been long used to combat diseases for many years and may serve as useful templates toward developing therapeutics against hIAPP aggregation and toxicity.

Novel hexapeptide interacts with tubulin and microtubules, inhibits Aβ fibrillation, and shows significant neuroprotection

Herein, we report a novel hexapeptide, derived from activity dependent neuroprotective protein (ADNP), that spontaneously self-assembles to form antiparallel β-sheet structure and produces nanovesicles under physiological conditions. This peptide not only strongly binds with β-tubulin in the taxol binding site but also binds with the microtubule lattice in vitro as well as in intracellular microtubule networks. Interestingly, it shows inhibition of amyloid fibril formation upon co-incubation with Aβ peptide following an interesting mechanistic pathway and excellent neuroprotection in PC12 cells treated with anti-nerve growth factor (NGF). The potential of this hexapeptide opens up a new paradigm in design and development of novel therapeutics for AD.

Phytomedicines as potential inhibitors of β amyloid aggregation: significance to Alzheimer's disease

Throughout the history of drug development, plants have been an important source for the discovery of novel therapeutically active compounds for many diseases. The ethnopharmacological approach has provided several leads to identify potential new drugs from plant sources, including those for memory disorders. For the treatment of Alzheimer's disease the drug discovery focus shifted from cholinesterase inhibitors, to other targets primarily based on two key neuropathological hallmarks, namely the hyperphosphorylation of the tau protein resulting in the formation of neurofibrillary tangles (NFTs), and the increased formation and aggregation of amyloid-beta peptide (Aβ) derived from amyloid precursor protein (APP). The present article aims to provide a comprehensive literature survey of plants and their constituents that have been tested for Aβ aggregation, thus possibly relieving several features of Alzheimer's disease (AD).

Anti-amyloidogenic properties of some phenolic compounds

A family of 21 polyphenolic compounds consisting of those found naturally in danshen and their analogues were synthesized and subsequently screened for their anti-amyloidogenic activity against the amyloid beta peptide (Aβ₄₂) of Alzheimer’s disease. After 24 h incubation with Aβ₄₂, five compounds reduced thioflavin T (ThT) fluorescence, indicative of their anti-amyloidogenic propensity (p < 0.001). TEM and immunoblotting analysis also showed that selected compounds were capable of hindering fibril formation even after prolonged incubations. These compounds were also capable of rescuing the yeast cells from toxic changes induced by the chemically synthesized Aβ₄₂. In a second assay, a Saccharomyces cerevisiae AHP1 deletant strain transformed with GFP fused to Aβ₄₂ was treated with these compounds and analyzed by flow cytometry. There was a significant reduction in the green fluorescence intensity associated with 14 compounds. We interpret this result to mean that the compounds had an anti-amyloid-aggregation propensity in the yeast and GFP-Aβ₄₂ was removed by proteolysis. The position and not the number of hydroxyl groups on the aromatic ring was found to be the most important determinant for the anti-amyloidogenic properties.

WIN 55,212-2, agonist of cannabinoid receptors, prevents amyloid β1-42 effects on astrocytes in primary culture

Alzheimer´s disease (AD), a neurodegenerative illness involving synaptic dysfunction with extracellular accumulation of Aβ_1-42 toxic peptide, glial activation, inflammatory response and oxidative stress, can lead to neuronal death. Endogenous cannabinoid system is implicated in physiological and physiopathological events in central nervous system (CNS), and changes in this system are related to many human diseases, including AD. However, studies on the effects of cannabinoids on astrocytes functions are scarce. In primary cultured astrocytes we studied cellular viability using MTT assay. Inflammatory and oxidative stress mediators were determined by ELISA and Western-blot techniques both in the presence and absence of Aβ_1-42 peptide. Effects of WIN 55,212-2 (a synthetic cannabinoid) on cell viability, inflammatory mediators and oxidative stress were also determined. Aβ_1-42 diminished astrocytes viability, increased TNF-α and IL-1β levels and p-65, COX-2 and iNOS protein expression while decreased PPAR-γ and antioxidant enzyme Cu/Zn SOD. WIN 55,212-2 pretreatment prevents all effects elicited by Aβ_1-42. Furthermore, cannabinoid WIN 55,212-2 also increased cell viability and PPAR-γ expression in control astrocytes. In conclusion cannabinoid WIN 55,212-2 increases cell viability and anti-inflammatory response in cultured astrocytes. Moreover, WIN 55,212-2 increases expression of anti-oxidant Cu/Zn SOD and is able to prevent inflammation induced by Aβ_1-42 in cultured astrocytes. Further studies would be needed to assess the possible beneficial effects of cannabinoids in Alzheimer's disease patients.

Specific aromatic foldamers potently inhibit spontaneous and seeded Aβ42 and Aβ43 fibril assembly

Amyloid fibrils are self-propagating entities that spread pathology in several devastating disorders including Alzheimer's disease (AD). In AD, amyloid-β (Aβ) peptides form extracellular plaques that contribute to cognitive decline. One potential therapeutic strategy is to develop inhibitors that prevent Aβ misfolding into proteotoxic conformers. Here, we design specific aromatic foldamers, synthetic polymers with an aromatic salicylamide (Sal) or 3-amino benzoic acid (Benz) backbone, short length (four repetitive units), basic arginine (Arg), lysine (Lys) or citrulline (Cit) side chains, and various N- and C-terminal groups that prevent spontaneous and seeded Aβ fibrillization. Ac-Sal-(Lys-Sal)3-CONH2 and Sal-(Lys-Sal)3-CONH2 selectively inhibited Aβ42 fibrillization, but were ineffective against Aβ43, an overlooked species that is highly neurotoxic and frequently deposited in AD brains. By contrast, (Arg-Benz)4-CONH2 and (Arg-Sal)3-(Cit-Sal)-CONH2 prevented spontaneous and seeded Aβ42 and Aβ43 fibrillization. Importantly, (Arg-Sal)3-(Cit-Sal)-CONH2 inhibited formation of toxic Aβ42 and Aβ43 oligomers and proteotoxicity. None of these foldamers inhibited Sup35 prionogenesis, but Sal-(Lys-Sal)3-CONH2 delayed aggregation of fused in sarcoma (FUS), an RNA-binding protein with a prion-like domain connected with amyotrophic lateral sclerosis and frontotemporal dementia. We establish that inhibitors of Aβ42 fibrillization do not necessarily inhibit Aβ43 fibrillization. Moreover, (Arg-Sal)3-(Cit-Sal)-CONH2 inhibits formation of toxic Aβ conformers and seeding activity, properties that could have therapeutic utility.

Drug repositioning approaches for the discovery of new therapeutics for Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia and represents one of the highest unmet needs in medicine today. Drug development efforts for AD have been encumbered by largely unsuccessful clinical trials in the last decade. Drug repositioning, a process of discovering a new therapeutic use for existing drugs or drug candidates, is an attractive and timely drug development strategy especially for AD. Compared with traditional de novo drug development, time and cost are reduced as the safety and pharmacokinetic properties of most repositioning candidates have already been determined. A majority of drug repositioning efforts for AD have been based on positive clinical or epidemiological observations or in vivo efficacy found in mouse models of AD. More systematic, multidisciplinary approaches will further facilitate drug repositioning for AD. Some experimental approaches include unbiased phenotypic screening using the library of available drug collections in physiologically relevant model systems (e.g. stem cell-derived neurons or glial cells), computational prediction and selection approaches that leverage the accumulating data resulting from RNA expression profiles, and genome-wide association studies. This review will summarize several notable strategies and representative examples of drug repositioning for AD.

Effect of Cinnamomum Verum Extract on the Amyloid Formation of Hen Egg-white Lysozyme and Study of its Possible Role in Alzheimer's Disease

INTRODUCTION

Diagnosing and treating diseases associated with amyloid fibers remain a great challenge despite of intensive research carried out. One important approach in the development of therapeutics is the use of herbal extracts which are rich in aromatic small molecules. Cinnamomum verum extract (CE) contains proanthocyanidin and cinnamaldehyde, which have been suggested to be capable of directly inhibiting amyloid fibril formation in vitro. This study is aimed at characterizing the inhibitory activity of CE against the fibrillation of hen egg white lysozyme (HEWL).

METHODS

Acidic pH and high temperatures were used to drive the protein towards amyloid formation. Lysozyme was dissolved at 2 mg/mL in 50mM glycine buffer (pH 2.5), and then incubated at 57 °C for the specified durations while stirred gently by Teflon magnetic bars. Various techniques including thioflavin T, fluorescence, Congo red absorbance assay and AFM micrography were used to characterize the HEWL fibrillation processes.

RESULTS

In the absence of CE typical amyloid fibrils (like amyloids formed in Alzheimer disease) became evident after 48 h of incubation. Upon incubation with various extract concentrations in the range of 0.1-1 mg/ml, formation of fibrillar assemblies were significantly inhibited (P<0.05). AFM analysis and MTT assay also confirmed the role of the extract in amyloid inhibition. Our studies showed that the presence of CE did not have any effect on protein stabilization and thus directly interact with amyloid structure and inhibit formation of these structures. Furthermore, a docking experiment showed that a pi-pi interaction may occur between the aromatic component of cinnamaldehyde and W62. Interestingly, W62 is one of the principal aromatic residues that interact with glycine amide, which is an aggregation suppressor of HEWL.

DISCUSSION

These observations suggest that aromatic small molecules of CE may directly insert into amyloidogenic core of early aggregates and inhibit amyloid fibril formation by disrupting the pi-pi interactions.

On the Environmental Factors Affecting the Structural and Cytotoxic Properties of IAPP Peptides

Pancreatic islets in type 2 diabetes mellitus (T2DM) patients are characterized by reduced β-cells mass and diffuse extracellular amyloidosis. Amyloid deposition involves the islet amyloid polypeptide (IAPP), a neuropancreatic hormone cosecreted with insulin by β-cells. IAPP is physiologically involved in glucose homeostasis, but it may turn toxic to β-cells owing to its tendency to misfold giving rise to oligomers and fibrils. The process by which the unfolded IAPP starts to self-assemble and the overall factors promoting this conversion are poorly understood. Other open questions are related to the nature of the IAPP toxic species and how exactly β-cells die. Over the last decades, there has been growing consensus about the notion that early molecular assemblies, notably small hIAPP oligomers, are the culprit of β-cells decline. Numerous environmental factors might affect the conformational, aggregation, and cytotoxic properties of IAPP. Herein we review recent progress in the field, focusing on the influences that membranes, pH, and metal ions may have on the conformational conversion and cytotoxicity of full-length IAPP as well as peptide fragments thereof. Current theories proposed for the mechanisms of toxicity will be also summarized together with an outline of the underlying molecular links between IAPP and amyloid beta (Aβ) misfolding.

Medication development for agitation and aggression in Alzheimer disease: review and discussion of recent randomized clinical trial design

ABSTRACT Background: The management of disruptive neuropsychiatric symptom (NPS) such as agitation and aggression (A/A) is a major priority in caring for people with Alzheimer's disease (AD). Few effective pharmacological or non-pharmacological options are available. Results of randomized clinical trials (RCTs) of drugs for A/A have been disappointing. This may result from the absence of biological efficacy for medications tested in treating A/A. It may also be related to methodological issues such as the choice of outcomes. The aim of this review was to highlight key methodological issues pertaining to RCTs of current and emerging medications for the treatment of A/A in AD. Methods: We searched PubMed/Medline, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov for RCTs comparing medications with either placebo or other drugs in the treatment of A/A in AD, between January 2008 and December 2013. Results: We identified a total of 18 RCTs; of these, 11 were completed and 7 ongoing. Of the ongoing RCTs, only one is in Phase III. Seven of 10 completed RCTs with reported results did not report greater benefit from drug than placebo. Each of the completed RCTs used a different definition of "clinically significant A/A." There was considerable heterogeneity in study design. The primary endpoints were largely proxy-based but a variety of scales were used. The definition of caregiver and scales used to assess caregiver outcomes were similarly heterogeneous. Placebo response was notable in all trials. Conclusions: This review highlights a great heterogeneity in RCTs design of drugs for A/A in AD and some key methodological issues such as definition of A/A, choice of outcome measures and caregiver participation that could be addressed by an expert consensus to optimize future trials design.

An amyloid inhibitor octapeptide forms amyloid type fibrous aggregates and affects microtubule motility

Peptide in dual action: an amyloid inhibitor octapeptide spontaneously forms amyloid like fibrillar aggregates in solution and slows down the microtubule gliding speed through strong peptide–tubulin interaction.

Alzheimer's disease-associated peptide Aβ42 mobilizes ER Ca(2+) via InsP3R-dependent and -independent mechanisms

Dysregulation of Ca²⁺ homeostasis is considered to contribute to the toxic action of the Alzheimer's disease (AD)-associated amyloid-β-peptide (Aβ). Ca²⁺ fluxes across the plasma membrane and release from intracellular stores have both been reported to underlie the Ca²⁺ fluxes induced by Aβ₄₂. Here, we investigated the contribution of Ca²⁺ release from the endoplasmic reticulum (ER) to the effects of Aβ₄₂ upon Ca²⁺ homeostasis and the mechanism by which Aβ₄₂ elicited these effects. Consistent with previous reports, application of soluble oligomeric forms of Aβ₄₂ induced an elevation in intracellular Ca²⁺. The Aβ₄₂-stimulated Ca²⁺ signals persisted in the absence of extracellular Ca²⁺ indicating a significant contribution of Ca²⁺ release from the ER Ca²⁺ store to the generation of these signals. Moreover, inositol 1,4,5-trisphosphate (InsP₃) signaling contributed to Aβ₄₂-stimulated Ca²⁺ release. The Ca²⁺ mobilizing effect of Aβ₄₂ was also observed when applied to permeabilized cells deficient in InsP₃ receptors, revealing an additional direct effect of Aβ₄₂ upon the ER, and a mechanism for induction of toxicity by intracellular Aβ₄₂.

Tanshinones inhibit amyloid aggregation by amyloid-β peptide, disaggregate amyloid fibrils, and protect cultured cells

The misfolding and aggregation of amyloid-β (Aβ) peptides into amyloid fibrils is regarded as one of the causative events in the pathogenesis of Alzheimer's disease (AD). Tanshinones extracted from Chinese herb Danshen (Salvia Miltiorrhiza Bunge) were traditionally used as anti-inflammation and cerebrovascular drugs due to their antioxidation and antiacetylcholinesterase effects. A number of studies have suggested that tanshinones could protect neuronal cells. In this work, we examine the inhibitory activity of tanshinone I (TS1) and tanshinone IIA (TS2), the two major components in the Danshen herb, on the aggregation and toxicity of Aβ1-42 using atomic force microscopy (AFM), thioflavin-T (ThT) fluorescence assay, cell viability assay, and molecular dynamics (MD) simulations. AFM and ThT results show that both TS1 and TS2 exhibit different inhibitory abilities to prevent unseeded amyloid fibril formation and to disaggregate preformed amyloid fibrils, in which TS1 shows better inhibitory potency than TS2. Live/dead assay further confirms that introduction of a very small amount of tanshinones enables protection of cultured SH-SY5Y cells against Aβ-induced cell toxicity. Comparative MD simulation results reveal a general tanshinone binding mode to prevent Aβ peptide association, showing that both TS1 and TS2 preferentially bind to a hydrophobic β-sheet groove formed by the C-terminal residues of I31-M35 and M35-V39 and several aromatic residues. Meanwhile, the differences in binding distribution, residues, sites, population, and affinity between TS1-Aβ and TS2-Aβ systems also interpret different inhibitory effects on Aβ aggregation as observed by in vitro experiments. More importantly, due to nonspecific binding mode of tanshinones, it is expected that tanshinones would have a general inhibitory efficacy of a wide range of amyloid peptides. These findings suggest that tanshinones, particularly TS1 compound, offer promising lead compounds with dual protective role in anti-inflammation and antiaggregation for further development of Aβ inhibitors to prevent and disaggregate amyloid formation.

Protein folding and aggregation into amyloid: the interference by natural phenolic compounds

Amyloid aggregation is a hallmark of several degenerative diseases affecting the brain or peripheral tissues, whose intermediates (oligomers, protofibrils) and final mature fibrils display different toxicity. Consequently, compounds counteracting amyloid aggregation have been investigated for their ability (i) to stabilize toxic amyloid precursors; (ii) to prevent the growth of toxic oligomers or speed that of fibrils; (iii) to inhibit fibril growth and deposition; (iv) to disassemble preformed fibrils; and (v) to favor amyloid clearance. Natural phenols, a wide panel of plant molecules, are one of the most actively investigated categories of potential amyloid inhibitors. They are considered responsible for the beneficial effects of several traditional diets being present in green tea, extra virgin olive oil, red wine, spices, berries and aromatic herbs. Accordingly, it has been proposed that some natural phenols could be exploited to prevent and to treat amyloid diseases, and recent studies have provided significant information on their ability to inhibit peptide/protein aggregation in various ways and to stimulate cell defenses, leading to identify shared or specific mechanisms. In the first part of this review, we will overview the significance and mechanisms of amyloid aggregation and aggregate toxicity; then, we will summarize the recent achievements on protection against amyloid diseases by many natural phenols.

Deregulation of excitatory neurotransmission underlying synapse failure in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly. Memory loss in AD is increasingly attributed to soluble oligomers of the amyloid-β peptide (AβOs), toxins that accumulate in AD brains and target particular synapses. Glutamate receptors appear to be centrally involved in synaptic targeting by AβOs. Once bound to neurons, AβOs dysregulate the activity and reduce the surface expression of both N-methyl-D-aspartate (NMDA) and 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid (AMPA) types of glutamate receptors, impairing signaling pathways involved in synaptic plasticity. In the extracellular milieu, AβOs promote accumulation of the excitatory amino acids, glutamate and D-serine. This leads to overactivation of glutamate receptors, triggering abnormal calcium signals with noxious impacts on neurons. Here, we review key findings linking AβOs to deregulated glutamate neurotransmission and implicating this as a primary mechanism of synapse failure in AD. We also discuss strategies to counteract the impact of AβOs on excitatory neurotransmission. In particular, we review evidence showing that inducing neuronal hyperpolarization via activation of inhibitory GABA(A) receptors prevents AβO-induced excitotoxicity, suggesting that this could comprise a possible therapeutic approach in AD.

Mibampator (LY451395) randomized clinical trial for agitation/aggression in Alzheimer's disease

BACKGROUND

Mibampator, an amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor potentiator, was evaluated for treatment of agitation and aggression (A/A) in Alzheimer's disease (AD).

METHODS

Outpatients (n = 132) with probable AD and A/A randomized to 12 weeks of double-blind treatment with 3-mg po mibampator or placebo were assessed using the 4-domain A/A subscale of the Neuropsychiatric Inventory (NPI-4-A/A) derived from the Neuropsychiatric Inventory. Secondary measures included the Cohen-Mansfield Agitation Inventory, Cornell Scale for Depression in Dementia, Frontal Systems Behavior Inventory (FrSBe), and Alzheimer's Disease Assessment Scale-Cognitive. Efficacy was analyzed using mixed-effects model repeated measures from baseline to endpoint. Adverse events (AEs), labs, vital signs, and electrocardiograms were monitored.

RESULTS

Baseline characteristics were comparable between groups. Both groups improved on the NPI-4-A/A, but without group differences. Among secondaries, mibampator was significantly better (p = 0.007) than placebo only on the FrSBe. AEs were similar between groups. One death occurred in the placebo group.

CONCLUSION

Possible explanations for no significant group differences include caregiver, drug target engagement, and design issues. This trial is registered on ClinicalTrials.gov; ID: NCT00843518.

A plant cell-based system that predicts aβ42 misfolding: potential as a drug discovery tool for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the accumulation of amyloid β (Aβ) peptides and the failure of mechanisms to clear toxic aggregates. The Aβ42 peptide is considered to be a causative factor that underlies the pathophysiology of AD, in part due to its propensity for misfolding and aggregation; the small oligomers that result represent toxic species. Thus agents that prevent Aβ42 misfolding/aggregation or, alternatively improve Aβ42 oligomer clearance, may have significant therapeutic value. We have developed the basis for a drug screening system based on transgenic plant cells that express Aβ42 fusion proteins to serve as the reliable indicators of the general conformational status of Aβ42. Within cells of transgenic tobacco and Nicotiana benthamiana, misfolding of Aβ42 causes the misfolding of a GFP fusion partner, and consequently there is a loss of fluorescence associated with the native GFP protein. In a similar fusion consisting of Aβ42 linked to hygromycin phosphotransferase II (Hpt II), a hygromycin-resistance marker, misfolding of Aβ42 leads to a misfolded Hpt II, and consequently the transgenic cells are unable to grow on media containing hygromycin. Importantly, substitution of the 'aggregation-prone' Aβ42 with a missense mutant of Aβ42 (F19S/L34F) that is not prone to misfolding/aggregation, 'rescues' both fusion partners. Several 'positive control' chemicals that represent inhibitors of Aβ42 aggregation, including curcumin, epigallocatechin-3-gallate (EGCG), and resveratrol show efficacy in preventing the Aβ42-fusion proteins from misfolding/aggregating in the transgenic plant cells. We discuss the potential of the two fusion protein systems to serve as the basis for an inexpensive, selective, and efficient screening system in which a plant cell can fluoresce or survive only in the presence of drug candidates that are able to prevent Aβ42 misfolding/aggregation.

Treatment strategies targeting amyloid β-protein

With the advent of the key discovery in the mid-1980s that the amyloid β-protein (Aβ) is the core constituent of the amyloid plaque pathology found in Alzheimer disease (AD), an intensive effort has been underway to attempt to mitigate its role in the hope of treating the disease. This effort fully matured when it was clarified that the Aβ is a normal product of cleavage of the amyloid precursor protein, and well-defined proteases for this process were identified. Further therapeutic options have been developed around the concept of anti-Aβ aggregation inhibitors and the surprising finding that immunization with Aβ itself leads to reduction of pathology in animal models of the disease. Here we review the progress in this field toward the goal of targeting Aβ for treatment and prevention of AD and identify some of the major challenges for the future of this area of medicine.

Aβ(1-42) assembly in the presence of scyllo-inositol derivatives: identification of an oxime linkage as important for the development of assembly inhibitors

To identify a lead skeleton structure for optimization of scyllo-inositol-based inhibitors of amyloid-beta peptide (Aβ) aggregation, we have synthesized aldoxime, hydroxamate, carbamate, and amide linked scyllo-inositol derivatives. These structures represent backbones that can be readily expanded into a wide array of derivatives. They also provide conservative modifications of the scyllo-inositol backbone, as they maintain the display of the equatorial polar atoms, preserving the stereochemical requirement necessary for maximum inhibition of Aβ(1-42) fiber formation. In addition, a reliable work plan for screening derivatives was developed in order to preferentially identify a backbone(s) structure that prevents fibrillogenesis and stabilizes nontoxic small molecular weight oligomers, as we have previously reported for scyllo-inositol. In the present studies, we have adapted a high throughput ELISA-based oligomerization assay followed by atomic force microscopy to validate the results screen compounds. The lead compounds were then tested for toxicity and ability to rescue Aβ(1-42) induced toxicity in vitro and the affinity of the compounds for Aβ(1-42) compared by mass spectrometry. The data to suggest that compounds must maintain a planar conformation to exhibit activity similar to scyllo-inositol and that the oxime derivative represents the lead backbone for future development.