Genistein: A Dual Inhibitor of Both Amyloid β and Human Islet Amylin Peptides

Daurichromenic Acid from the Chinese Traditional Medicinal Plant Rhododendron dauricum Inhibits Sphingomyelin Synthase and Aβ Aggregation

Species of the genus Rhododendron have been used in traditional Chinese medicine, with the medicinal herb "Manshanfong" used as an expectorant and for the treatment of acute bronchitis. Daurichromenic acid (DCA), a constituent of Rhododendron dauricum, is a meroterpenoid with antibacterial, anti-HIV, and anti-inflammatory activities. However, the mechanisms underlying these pharmacologic activities are poorly understood. To develop new drugs based on DCA, more information is required regarding its interactions with biomolecules. The present study showed that DCA inhibits the activity of the enzyme sphingomyelin synthase, with an IC₅₀ of 4 µM. The structure-activity relationships between DCA and sphingomyelin synthase were evaluated using derivatives and cyclized hongoquercin A. In addition, DCA was found to inhibit amyloid β aggregation. These results may help in the design of effective drugs based on DCA.

Role of lysine residue of islet amyloid polypeptide in fibril formation, membrane binding, and inhibitor binding

The aggregation of islet amyloid polypeptide (IAPP) is implicated in the pathogenesis of type 2 diabetes (T2D). In T2D, this peptide aggregates to form amyloid fibrils; the mechanism responsible for islet amyloid formation is unclear. However, it is known that the aggregation propensity of IAPP is highly related to its primary sequence. Several residues have been suggested to be critical in modulating IAPP amyloid formation, but role of the sole lysine residue at position 1 (Lys-1) in IAPP has not been discussed. In our previous study, we found that glycated IAPP can form amyloid faster than normal IAPP and induce normal IAPP to expedite the aggregation process. To gain more insight into the contribution of Lys-1 in the kinetics of fibril formation, we synthesized another two IAPP variants, K1E-IAPP and K1Nle-IAPP, in which the Lys residue was mutated to glutamate and norleucine, respectively. Interestingly, we observed that the negative or neutral charged side chain at this position was preferred for amyloid formation. The findings suggested this residue may take part in the inter- or intra-molecular interaction during IAPP aggregation, even though it was proposed not to be in part of fibril core structure. Our data also revealed that the inhibitory mechanism of some inhibitors for IAPP aggregation require reaction with Lys-1. Modifications of Lys-1, such as protein glycation, may affect the effectiveness of the inhibitory action of some potential drugs in the treatment of amyloidosis.

Protective Effects of a Neurohypophyseal Hormone Analogue on Prion Aggregation, Cellular Internalization, and Toxicity

Herein, we report novel neuroprotective activity of the neurohypophyseal hormone analogue desmopressin (DDAVP) against toxic conformations of human prion protein. Systematic analysis using biophysical techniques in conjunction with surface plasmon resonance, high-end microscopy, conformational antibodies, and cell-based assays demonstrated DDAVP's specific binding and potent antiaggregating effects on prion protein (rPrP^res). In addition to subjugating conformational conversion of rPrP^res into oligomeric forms, DDAVP also exhibits potent fibril modulatory effects. It eventually ameliorated neuronal toxicity of rPrP^res oligomers by significantly reducing their cellular internalization. Molecular dynamics simulations showed that DDAVP prevents β-sheet transitions in the N-terminal amyloidogenic region of prion and induces antagonistic mobilities in its α2-α3 and β2-α2 loop regions. Collectively, our data proposes DDAVP as a new structural motif for rational drug discovery against prion diseases.

Genistein and Galantamine Combinations Decrease β-Amyloid Peptide (1-42)-Induced Genotoxicity and Cell Death in SH-SY5Y Cell Line: an In Vitro and In Silico Approach for Mimic of Alzheimer's Disease

Alzheimer's disease (AD) is the primary dementia-causing disease worldwide, involving a multifactorial combination of environmental, genetic, and epigenetic factors, with essential participation of age and sex. Biochemically, AD is characterized by the presence of abnormal deposition of beta amyloid peptide (Aβ_(1-42)), which in the brain is strongly correlated with oxidative stress, inflammation, DNA damage, and cholinergic impairment. The multiple mechanisms involved in its etiology create significant difficulty in producing an effective treatment. Neuroprotective properties of genistein and galantamine have been widely demonstrated through different mechanisms; however, it is unknown a possible synergistic neuroprotective effect against Aβ_(1-42). In order to understand how genistein and galantamine combinations regulate the mechanisms of neuroprotection, we conducted a set of bioassays in vitro to evaluate cell viability, clonogenic survival, cell death, and anti-genotoxicity. Through molecular docking and therapeutic viability assays, we analyzed the inhibitory activity exerted by genistein on three major protein targets (AChE, BChE, and NMDA) involved in AD. The results showed that genistein and galantamine afforded significant protection at higher concentrations; however, combinations of sub-effective concentrations of both compounds provided marked neuroprotection when they were combined. In silico approaches showed that genistein has higher scores than the positive controls and low toxicity levels; nevertheless, the therapeutic viability indicated that unlike galantamine, genistein cannot undergo the action by P glycoprotein (PGP) and probably may be unable to cross the blood-brain barrier. In conclusion, our results show that genistein and galantamine exert neuroprotective by decreasing genotoxicity and cell death. In silico analysis, suggest that genistein modulates positively the expression of AChE, BChE, and NMDA. In this context, a combination of two or more drugs could inspire an attractive therapeutic strategy.

Cichoric acid from witloof inhibit misfolding aggregation and fibrillation of hIAPP

The misfolding, aggregation and fibrillation of human islet amyloid polypeptide (hIAPP) has been acknowledged as a hallmark event in type-II diabetes. Hence, inhibiting the misfolding, aggregation and fibrillation of hIAPP have been accepted as a vital factor to treat the disease. Here cichoric acid was extracted from witloof to explore its inhibition effects on misfolding, aggregation and fibrillation of hIAPP. Thioflavin-T (ThT) fluorescence assay, dynamic light scattering (DLS) and atomic force microscopy (AFM) images showed that cichoric acid inhibited the aggregation and fibrillation of hIAPP in a dosage-dependent manner. Circular dichroism (CD) spectra showed that cichoric acid inhibited the misfolding of hIAPP from unfolded to β-sheet. Molecular docking and further experiments revealed interactions between hIAPP and cichoric acid. Cichoric acid could bind to K1 and R11 of hIAPP via electrostatic interaction. In addition, cichoric acid could form π-π stacking with hIAPP residues F15 and F23. These interactions inhibited the misfolding, aggregation and fibrillation of hIAPP. These results, together with cichoric acid's good cytocompatibility and significant protective effects in hIAPP lesioned cell models, not only showed that cichoric acid could be used to fight against amyloidosis, but also brought a new perspective for Chinese herbal medicine as natural compound's medical potential.

Islet Amyloid Polypeptide: A Partner in Crime With Aβ in the Pathology of Alzheimer's Disease

Diabetes affects hundreds of millions of patients worldwide. Despite the advances in understanding the disease and therapeutic options, it remains a leading cause of death and of comorbidities globally. Islet amyloid polypeptide (IAPP), or amylin, is a hormone produced by pancreatic β-cells. It contributes to the maintenance of glucose physiological levels namely by inhibiting insulin and glucagon secretion as well as controlling adiposity and satiation. IAPP is a highly amyloidogenic polypeptide forming intracellular aggregates and amyloid structures that are associated with β-cell death. Data also suggest the relevance of unprocessed IAPP forms as seeding for amyloid buildup. Besides the known consequences of hyperamylinemia in the pancreas, evidence has also pointed out that IAPP has a pathological role in cognitive function. More specifically, IAPP was shown to impair the blood–brain barrier; it was also seen to interact and co-deposit with amyloid beta peptide (Aß), and possibly with Tau, within the brain of Alzheimer's disease (AD) patients, thereby contributing to diabetes-associated dementia. In fact, it has been suggested that AD results from a metabolic dysfunction in the brain, leading to its proposed designation as type 3 diabetes. Here, we have first provided a brief perspective on the IAPP amyloidogenic process and its role in diabetes and AD. We have then discussed the potential interventions for modulating IAPP proteotoxicity that can be explored for therapeutics. Finally, we have proposed the concept of a “diabetes brain phenotype” hypothesis in AD, which may help design future IAPP-centered drug developmentstrategies against AD.

Inhibitory Activity of Insulin on Aβ Aggregation Is Restricted Due to Binding Selectivity and Specificity to Polymorphic Aβ States

Clinical trials of intranasal insulin treatment for Alzheimer’s patients have shown cognitive and memory improvement, but the effect of insulin has shown a limitation. It was suggested that insulin molecule binds to Aβ aggregates and impedes Aβ aggregation. Yet, the specific interactions between insulin molecule and Aβ aggregates at atomic resolution are still elusive. Three main conclusions are observed in this work. First, insulin can interact across the fibril only to “U-shape” Aβ fibrils and not to “S-shape” Aβ fibrils. Therefore, insulin is not expected to influence the “S-shape” Aβ fibrils. Second, insulin disrupts β-strands along Aβ fibril-like oligomers via interaction with chain A, which is not a part of the recognition motif. It is suggested that insulin affects as an inhibitor of Aβ fibrillation, but it is limited due to the specificity of the polymorphic Aβ fibril-like oligomer. Third, the current work proposes that insulin promotes Aβ aggregation, when interacting along the fibril axis of Aβ fibril-like oligomer. The coaggregation could be initiated via the recognition motif. The lack of the interactions of insulin in the recognition motif impede the coaggregation of insulin and Aβ. The current work reports the specific binding domains between insulin molecule and polymorphic Aβ fibril-like oligomers. This research provides insights into the molecular mechanisms of the functional activity of insulin on Aβ aggregation that strongly depends on the particular polymorphic Aβ aggregates.

Interactions between Curcumin Derivatives and Amyloid-β Fibrils: Insights from Molecular Dynamics Simulations

The aggregation of amyloid-β (Aβ) peptides into senile plaques is a hallmark of Alzheimer's disease (AD) and is hypothesized to be the primary cause of AD related neurodegeneration. Previous studies have shown the ability of curcumin to both inhibit the aggregation of Aβ peptides into oligomers or fibrils and reduce amyloids in vivo. Despite the promise of curcumin and its derivatives to serve as diagnostic, preventative, and potentially therapeutic AD molecules, the mechanism by which curcumin and its derivatives bind to and inhibit Aβ fibrils' formation remains elusive. Here, we investigated curcumin and a set of curcumin derivatives in complex with a hexamer peptide model of the Aβ1-42 fibril using nearly exhaustive docking, followed by multi-ns molecular dynamics simulations, to provide atomistic-detail insights into the molecules' binding and inhibitory properties. In the vast majority of the simulations, curcumin and its derivatives remain firmly bound in complex with the fibril through primarily three different principle binding modes, in which the molecules interact with residue domain 17LVFFA21, in line with previous experiments. In a small subset of these simulations, the molecules partly dissociate the outermost peptide of the Aβ1-42 fibril by disrupting β-sheets within the residue domain 12VHHQKLVFF20. A comparison between binding modes leading or not leading to partial dissociation of the outermost peptide suggests that the latter is attributed to a few subtle key structural and energetic interaction-based differences. Interestingly, partial dissociation appears to be either an outcome of high affinity interactions or a cause leading to high affinity interactions between the molecules and the fibril, which could partly serve as a compensation for the energy loss in the fibril due to partial dissociation. In conjunction with this, we suggest a potential inhibition mechanism of Αβ1-42 aggregation by the molecules, where the partially dissociated 16KLVFF20 domain of the outermost peptide could either remain unstructured or wrap around to form intramolecular interactions with the same peptide's 29GAIIG33 domain, while the molecules could additionally act as a patch against the external edge of the second outermost peptide's 16KLVFF20 domain. Thereby, individually or concurrently, these could prohibit fibril elongation.

γ-AApeptides-based Small Molecule Ligands That Disaggregate Human Islet Amyloid Polypeptide

The abnormal folding and aggregation of functional proteins into amyloid is a typical feature of many age-related diseases, including Type II diabetes. Growing evidence has revealed that the prevention of aggregate formation in culprit proteins could retard the progression of amyloid diseases. Human Amylin, also known as human islet amyloid polypeptide (hIAPP), is the major factor for categorizing Type II diabetes as an amyloid disease. Specifically, hIAPP has a great aggregation potential, which always results in a lethal situation for the pancreas. Many peptide inhibitors have been constructed from the various segments of the full-length hIAPP peptide; however, only a few have their origin from the screening of combinatorial peptidomimetic library. In this study, based on HW-155, which was previously discovered from a one-bead-one compound (OBOC) library to inhibit Aβ40 aggregation, we investigated eight (8) analogues and evaluated their amyloid-prevention capabilities for inhibiting fibrillization of hIAPP. Characterization studies revealed that all analogues of HW-155, as well as HW-155, were effective inhibitors of the fibril formation by hIAPP.

Revealing the Mechanism of EGCG, Genistein, Rutin, Quercetin, and Silibinin Against hIAPP Aggregation via Computational Simulations

To inhibit hIAPP aggregation and reduce toxicity of its oligomers are one of the potential strategies for the treatment of Type 2 diabetes (T2D). It has been reported that there is an effective inhibitory effect on hIAPP aggregation by five natural flavonoids, including Genistein, Rutin, Quercetin, Epigallocatechin gallate (EGCG), and Silibinin, which are widely found in our daily food. However, the detailed mechanisms to inhibit hIAPP aggregation remain unclear. Here, we explore the mechanisms of the five flavonoids against hIAPP aggregation by molecular docking and molecular dynamics simulations. We show that these flavonoids can disaggregate Chain A and Chain B of hIAPP to reduce the extended conformation by binding with two regions of hIAPP, Leu₁₂-Ala₁₃-Asn₁₄ and Asn₃₁-Val₃₂-Gly₃₃-Ser₃₄-Asn₃₅, with the inhibitory ability of Genistein > Rutin > Quercetin > EGCG > Silibinin. These five compounds exhibit a common mechanism for disaggregation of the hIAPP pentamer; that is, they loosen the two nearest peptide chains to potentially destroy the hIAPP oligomer. Mutations of eight key residues remarkably affected by the flavonoids indicate that the secondary structures of the hIAPP pentamer change from β-sheet to be random coil, thereby to destroy its structural stability; moreover, the 28th (Ser), 12th (Leu) and 32nd (Val) amino acids exhibit significant effects on structural stability of the hIAPP pentamer, providing an important hint that these amino acids can be considered as potential targets for design of new candidate inhibitors against hIAPP oligomers. This work is beneficial to understanding of mechanism of these inhibits against hIAPP aggregation and will facilitate screening, modification, and design of new inhibitors.

Design principles and fundamental understanding of biosensors for amyloid-β detection

Aβ as biomarker in Alzheimer’s disease (AD) drives the significant research efforts for developing different biosensors with different sensing strategies, materials, and mechanisms for Aβ detection.

Bleomycin modulates amyloid aggregation in β-amyloid and hIAPP

Aberrant misfolding and amyloid aggregation, which result in amyloid fibrils, are frequent and critical pathological incidents in various neurodegenerative disorders. Multiple drugs or inhibitors have been investigated to avert amyloid aggregation in individual peptides, exhibiting sequence-dependent inhibition mechanisms. Establishing or inventing inhibitors capable of preventing amyloid aggregation in a wide variety of amyloid peptides is quite a daunting task. Bleomycin (BLM), a complex glycopeptide, has been widely used as an antibiotic and antitumor drug due to its ability to inhibit DNA metabolism, and as an antineoplastic, especially for solid tumors. In this study, we investigated the dual inhibitory effects of BLM on Aβ aggregation, associated with Alzheimer's disease and hIAPP, which is linked to type 2 diabetes, using both computational and experimental techniques. Combined results from drug repurposing and replica exchange molecular dynamics simulations demonstrate that BLM binds to the β-sheet region considered a hotspot for amyloid fibrils of Aβ and hIAPP. BLM was also found to be involved in β-sheet destabilization and, ultimately, in its reduction. Further, experimental validation through in vitro amyloid aggregation assays was obtained wherein the fibrillar load was decreased for the BLM-treated Aβ and hIAPP peptides in comparison to controls. For the first time, this study shows that BLM is a dual inhibitor of Aβ and hIAPP amyloid aggregation. In the future, the conformational optimization and processing of BLM may help develop various efficient sequence-dependent inhibitors against amyloid aggregation in various amyloid peptides.

Bleomycin acts as a dual inhibitor against both amyloid β and human islet amyloid polypeptide by binding to the β-sheet grooves considered as the amyloids hotspot.

Regulation of Artemisinin and Its Derivatives on the Assembly Behavior and Cytotoxicity of Amyloid Polypeptides hIAPP and Aβ

The misfolding and aggregation of human islet amyloid polypeptide (hIAPP) and amyloid-β (Aβ) protein are closely associated with type 2 diabetes mellitus (T2DM) and Alzheimer's disease, respectively. Inhibitors of amyloid peptides include short peptides, aromatic organic molecules, nanoparticles, and even metal compounds. Sesquiterpenoid artemisinins are widely used in anti-malaria treatments, and they may modulate glucose homeostasis against diabetes. However, the antidiabetic mechanism of these compounds remains unclear. In this work, four compounds, namely, artemisinin (1), dihydroartemisinin (2), artesunate (3), and artemether (4), were exploited to inhibit the assembly behavior of hIAPP and compared with that of Aβ. Although structurally distinct from other aromatic inhibitors of amyloid peptides, these sesquiterpenoids effectively altered the two peptides' fibril morphologies and disaggregated the mature fibrils mostly to the monomers. The interaction of artemisinins with the two peptides demonstrated a spontaneous, exothermic, and entropy-driven binding process predominantly through hydrophobic and hydrogen bonding interactions. Moreover, they reversed cytotoxicity and membrane leakage by reducing peptides' oligomerization. The results suggested that these compounds had better inhibition and disaggregation capability against hIAPP than against Aβ. Furthermore, the effects of these compounds' structural modification on the amyloid fibril formation of the two peptides were observed. The molecular screening offered a new perspective for artemisinins as promising inhibitors against amyloidosis related diseases.

Genistein Decreases APP/tau Phosphorylation and Ameliorates Aβ Overproduction Through Inhibiting CIP2A

Background:

Upregulation of Cancerous Inhibitor of PP2A (CIP2A) plays an important role in disease-related phosphorylation of tau/APP and tau pathology/Aβ overproduction through inhibiting PP2A in AD brain. Genistein has been shown to potently reduce CIP2A in experimental cancer treatment research. Whether Genistein can ameliorate AD pathology through targeting CIP2A needs further investigation.

Methods:

The inhibitory effects of Genistein on tau/APP phosphorylation and Aβ overproduction in AD cell models have been explored. HEK293-T cells were co-transfected with CIP2A and APP plasmids, or CIP2A and tau plasmids, with Genistein incubation at 0, 30, 60 or 120 µM for 48 h, cell viability and PP2A activities were measured. HEK293-T cells with CIP2A/APP overexpression treated with Genistein at 30 µM for 48 h were collected and lyzed for Western blotting detection of CIP2A, PP2Ac, APP-T668, total APP, PS1, BACE1, sAPPα and sAPPβ. Aβ40 and Aβ42 levels in cell supernatant, soluble fraction (RIPA) and insoluble fraction (formic acid soluble) of cell lysates were measured by ELISA. HEK293-T cells with CIP2A/tau overexpression treated with Genistein at 30 µM for 48 h were collected for Western blotting detection of CIP2A, PP2Ac, tau-S396, tau-S404 and total tau.

Conclusion:

CIP2A is a target of Genistein in AD therapy. Genistein reduces APP/tau hyperphosphorylation and Aβ production through inhibiting the effect of CIP2A on PP2A.

Results:

Genistein effectively reduced CIP2A expression, and restored PP2A activities both in CIP2A/APP, CIP2A/tau co-expressed cells. Genistein reduced APP phosphorylation at T668 site and inhibited Aβ production. Meantime, Genistein ameliorated tau hyperphosphorylation through repressing the inhibitory effect of CIP2A on PP2A.

Antagonistic Activity of Naphthoquinone-Based Hybrids toward Amyloids Associated with Alzheimer's Disease and Type-2 Diabetes

Protein misfolding and amyloid formation are associated with various human diseases including Alzheimer's disease (AD), Parkinson's disease (PD), and Type-2 Diabetes mellitus (T2DM). No disease-modifying therapeutics are available for them. Despite the lack of sequence homology between the corresponding proteins, aromatic residues are recognized as common key motifs in the formation and stabilization of amyloid structures via π-π stacking. Thus, targeting aromatic recognition interfaces could be a useful approach for inhibiting amyloid formation as well as disrupting the preformed amyloid fibrils. Combining experimental and computational approaches, we demonstrated the anti-amyloidogenic effect of naphthoquinone-tryptophan-based hybrid molecules toward PHF6 (τ-derived aggregative peptide), Amyloid β (Aβ42), and human islet amyloid polypeptide (hIAPP) implicated in AD and T2DM, respectively. These hybrid molecules significantly inhibited the aggregation and disrupted their preformed fibrillar aggregates in vitro, in a dose-dependent manner as evident from Thioflavin T/S binding assay, CD spectroscopy, and electron microscopy. Dye leakage assay from LUVs and cell-based experiments indicated that the hybrid molecules inhibit membrane disruption and cytotoxicity induced by these amyloids. Furthermore, in silico studies provided probable mechanistic insights into the interaction of these molecules with the amyloidogenic proteins in their monomeric or aggregated forms, including the role of hydrophobic interaction, hydrogen bond formation, and packing during inhibition of aggregation and fibril disassembly. Our findings may help in designing novel therapeutics toward AD, T2DM, and other proteinopathies based on the naphthoquinone derived hybrid molecules.

Inhibitory effects of oxidovanadium complexes on the aggregation of human islet amyloid polypeptide and its fragments

Human islet amyloid polypeptide (hIAPP) is synthesized by pancreatic β-cells and co-secreted with insulin. Misfolding and amyloidosis of hIAPP induce β-cell dysfunction in type II diabetes mellitus. Numerous small organic molecules and metal complexes act as inhibitors against amyloid-related diseases, justifying the need to explore the inhibitory mechanism of these compounds. In this work, three oxidovanadium complexes, namely, (NH₄)[VO(O₂)₂(bipy)]·4H₂O (1) (bipy = 2,2' bipyridine), bis(ethyl-maltolato, O,O)oxido-vanadium(IV) (2), and (bipyH₂)H₂[O{VO(O₂)(bipy)}₂]·5H₂O (3), were synthesized and used to inhibit the aggregation of hIAPP and its fragments, namely, hIAPP19-37 and hIAPP20-29. Results revealed that shortening the peptide sequence decreased the aggregation capability of hIAPP fragments, and the oxidovanadium complexes inhibited the fibrillization of hIAPP better than its fragments. Interestingly, the binding of oxidovanadium complexes to hIAPP and its fragments presented a distinct thermodynamic behavior. Oxidovanadium complexes featured the disaggregation capability against hIAPP, better than against its fragments. These complexes also decreased the cytotoxicity caused by hIAPP and its fragments by reducing the production of oligomers. 3 may be a good hIAPP inhibitor based on its inhibition, disaggregation capability, and regulatory effect on peptide-induced cytotoxicity. Oxidovanadium complexes exhibit potential as metallodrugs against amyloidosis-related diseases.

In vivo synaptic activity-independent co-uptakes of amyloid β1-42 and Zn2+ into dentate granule cells in the normal brain

Neuronal amyloid β_1–42 (Aβ_1–42) accumulation is considered an upstream event in Alzheimer’s disease pathogenesis. Here we report the mechanism on synaptic activity-independent Aβ_1–42 uptake in vivo. When Aβ_1–42 uptake was compared in hippocampal slices after incubating with Aβ_1–42, In vitro Aβ_1–42 uptake was preferentially high in the dentate granule cell layer in the hippocampus. Because the rapid uptake of Aβ_1–42 with extracellular Zn²⁺ is essential for Aβ_1–42-induced cognitive decline in vivo, the uptake mechanism was tested in dentate granule cells in association with synaptic activity. In vivo rapid uptake of Aβ_1–42 was not modified in the dentate granule cell layer after co-injection of Aβ_1–42 and tetrodotoxin, a Na⁺ channel blocker, into the dentate gyrus. Both the rapid uptake of Aβ_1–42 and Zn²⁺ into the dentate granule cell layer was not modified after co-injection of CNQX, an AMPA receptor antagonist, which blocks extracellular Zn²⁺ influx, Both the rapid uptake of Aβ_1–42 and Zn²⁺ into the dentate granule cell layer was not also modified after either co-injection of chlorpromazine or genistein, an endocytic repressor. The present study suggests that Aβ_1–42 and Zn²⁺ are synaptic activity-independently co-taken up into dentate granule cells in the normal brain and the co-uptake is preferential in dentate granule cells in the hippocampus. We propose a hypothesis that Zn-Aβ_1–42 oligomers formed in the extracellular compartment are directly incorporated into neuronal plasma membranes and form Zn²⁺-permeable ion channels.

ADAM10 in Alzheimer's disease: Pharmacological modulation by natural compounds and its role as a peripheral marker

Alzheimer's disease (AD) represents a global burden in the economics of healthcare systems. Amyloid-β (Aβ) peptides are formed by amyloid-β precursor protein (AβPP) cleavage, which can be processed by two pathways. The cleavage by the α-secretase A Disintegrin And Metalloprotease 10 (ADAM10) releases the soluble portion (sAβPPα) and prevents senile plaques. This pathway remains largely unknown and ignored, mainly regarding pharmacological approaches that may act via different signaling cascades and thus stimulate non-amyloidogenic cleavage through ADAM10. This review emphasizes the effects of natural compounds on ADAM10 modulation, which eventuates in a neuroprotective mechanism. Moreover, ADAM10 as an AD biomarker is revised. New treatments and preventive interventions targeting ADAM10 regulation for AD are necessary, considering the wide variety of ADAM10 substrates.

Binding Modes of a Glycopeptidomimetic Molecule on Aβ Protofibrils: Implication for Its Inhibition Mechanism

We recently reported that a glycopeptidomimetic molecule significantly delays the fibrillization process of Aβ₄₂ peptide involved in Alzheimer's disease. However, the binding mode of this compound, named 3β, was not determined at the atomic scale, hindering our understanding of its mechanism of action and impeding structure-based design of new inhibitors. In the present study, we performed molecular docking calculations and molecular dynamics simulations to investigate the most probable structures of 3β complexed with Aβ protofibrils. Our results show that 3β preferentially binds to an area of the protofibril surface that coincides with the protofibril dimerization interface observed in the solid-state NMR structure 5KK3 from the PDB. Based on these observations, we propose a model of the inhibition mechanism of Aβ fibrillization by compound 3β.

Computational Insight into the Effect of Natural Compounds on the Destabilization of Preformed Amyloid-β(1⁻40) Fibrils

One of the principal hallmarks of Alzheimer’s disease (AD) is related to the aggregation of amyloid-β fibrils in an insoluble form in the brain, also known as amyloidosis. Therefore, a prominent therapeutic strategy against AD consists of either blocking the amyloid aggregation and/or destroying the already formed aggregates. Natural products have shown significant therapeutic potential as amyloid inhibitors from in vitro studies as well as in vivo animal tests. In this study, the interaction of five natural biophenols (curcumin, dopamine, (-)-epigallocatechin-3-gallate, quercetin, and rosmarinic acid) with amyloid-β(1–40) fibrils has been studied through computational simulations. The results allowed the identification and characterization of the different binding modalities of each compounds and their consequences on fibril dynamics and aggregation. It emerges that the lateral aggregation of the fibrils is strongly influenced by the intercalation of the ligands, which modulates the double-layered structure stability.