Flavones in pomelo peel resist fibril formation of human islet amyloid polypeptide

Objective

Exploring the formation and aggregation of human islet amyloid polypeptide (hIAPP) (amylin) fibers is significant for promoting the prevention and treatment of type II diabetes mellitus (T2DM). Flavones in pomelo peel have visible biological activity in the anti-diabetes aspect. The present study aimed to investigate the effects of five flavones [naringin (NRG), narirutin (NRR), nobiletin (NOB), sinensetin (SIN), and neohesperidin (NHP)] in pomelo peel on peptide aggregation and explore its possible mechanisms. The cell viability of flavones against peptide aggregation was also evaluated.

Methods

The thioflavin T (ThT) assay and transmission electron microscopy (TEM) were used for evaluating the inhibition and disaggregation of flavones on peptide aggregation. The interaction mechanism was analyzed by endogenous fluorescence, molecular dynamics (MD) simulations, ultraviolet spectroscopy (UV) and isothermal titration calorimetry (ITC) experiments. The 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and immune assays were performed to characterize the cell viability of flavones against peptide aggregation.

Results

The five flavones showed a decrease in fluorescence intensity, fiber number and size under incubation with different molar ratios of hIAPP. The compounds can bind to the aromatic tyrosine (Tyr) residueTyr 37, resulting in the intrinsic fluorescence quenching of the peptides. Five flavones can form hydrogen bonds with hIAPP, which is likely to be based on their phenolic hydroxyl structure. They showed strong binding affinity with peptides. The reaction system of NRG and NRR observed an exothermic reaction, and the others were endothermic reactions. The absorption peaks of the compounds with hIAPP changed and showed hypochromic effects, indicating that there may be π-π stacking interaction. Flavones noticeably increased the cell viability in the presence of amyloid peptides and reduced the absorption intensity induced by peptide oligomers.

Conclusion

A total of five flavones in pomelo peel have inhibitory and depolymerization effects on amyloid fibrils, and can significantly protect cells from the toxic effect of hIAPP and reduce the production of toxic oligomers.

Luteoloside inhibits Aβ1-42 fibrillogenesis, disintegrates preformed fibrils, and alleviates amyloid-induced cytotoxicity

Abnormal aggregation and fibrillogenesis of amyloid-β protein (Aβ) can cause Alzheimer's disease (AD). Thus, the discovery of effective drugs that inhibit Aβ fibrillogenesis in the brain is crucial for the treatment of AD. Luteoloside, as one of the polyphenolic compounds, is found to have a certain therapeutic effect on nervous system diseases. However, it remains unknown whether luteoloside is a potential drug for treating AD by modulating Aβ aggregation pathway. In this study, we performed diverse biophysical and biochemical methods to explore the inhibition of luteoloside on Aβ1-42 which is linked to AD. The results demonstrated that luteoloside efficiently prevented amyloid oligomerization and cross-β-sheet formation, reduced the rate of amyloid growth and the length of amyloid fibrils in a dose-dependent manner. Moreover, luteoloside was able to influence aggregation and conformation of Aβ1-42 during different fiber-forming phases, and it could disintegrate already preformed fibrils of Aβ1-42 and convert them into nontoxic aggregates. Furthermore, luteoloside protected cells from amyloid-induced cytotoxicity and hemolysis, and attenuated the level of reactive oxygen species (ROS). The molecular docking study showed that luteoloside interacted with Aβ1-42 mainly via Conventional Hydrogen Bond, Carbon Hydrogen Bond, Pi-Pi T-shaped, Pi-Alkyl and Pi-Anion, thereby possibly preventing it from forming the aggregates. These observations indicate that luteoloside, a natural anti-oxidant molecule, may be applicable as an effective inhibitor of Aβ, and promote further exploration of the therapeutic strategy against AD.

Roles of Apigenin and Nepetin in the Assembly Behavior and Cytotoxicity of Prion Neuropeptide PrP106-126

Development of potential inhibitors to prevent prion protein (PrP) fibrillation is a therapeutic strategy for prion diseases. The prion neuropeptide PrP106-126, a research model of abnormal PrP (PrPSc), presents similar physicochemical and biochemical characters to PrPSc, which is also a target of potential inhibitors against prion deposition. Many flavones have antioxidant, anti-inflammatory, and antibacterial properties, and they are applied in treating prion disorder and other amyloidosis as well. However, the inhibition mechanism of flavones on PrP106-126 fibrillation is still unclear. In the current work, apigenin and nepetin were used to suppress the aggregation of PrP106-126 and to alleviate the peptide-induced cytotoxicity. The results showed that apigenin and nepetin impeded the fibril formation of PrP106-126 and depolymerized the preformed fibrils. They were bound to PrP106-126 predominantly by hydrophobic and hydrogen bonding interactions. In addition, both flavones upregulated cell viability and decreased membrane leakage through reducing peptide oligomerization. The differences in inhibition and cell protection between the two small molecules were presumably attributed to the substitution of hydroxyl and methoxy groups in nepetin, which demonstrated the significant structure-function relationship of flavones with prion neuropeptide and the prospect of flavonoids as drug candidates against prion diseases.

An Innate Host Defense Protein β2-Microglobulin Keeps a Check on α-Synuclein amyloid Assembly: Implications in Parkinson's Disease

Amyloid formation due to protein misfolding has gained significant attention due to its association with neurodegenerative diseases. α-Synuclein (α-syn) is one such protein that undergoes a profound conformational switch to form higher order cross-β-sheet structures, resulting in amyloid formation, which is linked to the pathophysiology of Parkinson's disease (PD). The present status of research on α-syn aggregation and PD reveals that the disease progression may be linked with many other diseases, such as kidney-related disorders. Unraveling the link between PD and non-neurological diseases may help in early detection and a better understanding of PD progression. Herein, we investigated the modulation of α-syn in the presence of β2-microglobulin (β2m), a structural protein associated with dialysis-related amyloidosis. We took a multi-disciplinary approach to establish that β2m mitigates amyloid formation by α-syn. Our fluorescence, microscopy and toxicity data demonstrated that sub-stoichiometric ratio of β2m drives α-syn into off-pathway non-toxic aggregates incompetent of transforming into amyloids. Using AlphaFold2 and all-atom MD simulation, we showed that the β-strand segments (β1 and β2) of α-synuclein, which frequently engage in interactions within amyloid fibrils, interact with the last β-strand at the C-terminal of β2m. The outcome of this study will unravel the yet unknown potential linkage of PD with kidney-related disorders. Insights from the cross-talk between two amyloidogenic proteins will lead to early diagnosis and new therapeutic approaches for treating Parkinson's disease. Finally, disruption of the nucleation process of α-syn amyloids by targeting the β1-β2 region will constitute a potential therapeutic approach for inhibiting amyloid formation.

An AIE-Active NIR Fluorescent Probe with Good Water Solubility for the Detection of Aβ1-42 Aggregates in Alzheimer's Disease

Alzheimer's disease (AD), an amyloid-related disease, seriously endangers the health of elderly individuals. According to current research, its main pathogenic factor is the amyloid protein, which is a kind of fibrillar aggregate formed by noncovalent self-assembly of proteins. Based on the characteristics of aggregation-induced emission (AIE), a bislactosyl-decorated tetraphenylethylene (TPE) molecule TMNL (TPE + malononitrile + lactose), bearing two malononitrile substituents, was designed and synthesized in this work. The amphiphilic TMNL could self-assemble into fluorescent organic nanoparticles (FONs) with near-infrared (NIR) fluorescence emission in physiological PBS (phosphate buffered saline), achieving excellent fluorescent enhancement (47-fold) upon its combination with Aβ_1-42 fibrils. TMNL was successfully applied to image Aβ_1-42 plaques in the brain tissue of AD transgenic mice, and due to the AIE properties of TMNL, no additional rinsing process was necessary. It is believed that the probe reported in this work should be useful for the sensitive detection and accurate localization mapping of Aβ_1-42 aggregates related to Alzheimer's disease.

Recent advances in the modulation of amyloid protein aggregation using the supramolecular host-guest approaches

Misfolding of proteins is associated with many incurable diseases in human beings. Understanding the process of aggregation from monomers to fibrils, the characterization of all intermediate species, and the origin of toxicity is very challenging. Extensive research including computational and experimental shed some light on these tricky phenomena. Non-covalent interactions between amyloidogenic domains of proteins play a major role in their self-assembly which can be disrupted by designed chemical tools. This will lead to the development of inhibitors of detrimental amyloid formations. In supramolecular host-guest chemistry approaches, different macrocycles function as hosts for encapsulating hydrophobic guests, i.e. phenylalanine residues of proteins, in their hydrophobic cavities via non-covalent interactions. In this way, they can disrupt the interactions between adjacent amyloidogenic proteins and prevent their self-aggregation. This supramolecular approach has also emerged as a prospective tool to modify the aggregation of several amyloidogenic proteins. In this review, we discussed recent supramolecular host-guest chemistry-based strategies for the inhibition of amyloid protein aggregation.

Nanoparticle Scanners for the Identification of Key Sequences Involved in the Assembly and Disassembly of β-Amyloid Peptides

The aggregation of β-amyloid peptides (Aβ), implied in the development and progression of Alzheimer's disease, is driven by a complex set of intramolecular and intermolecular interactions involving both hydrophobic and polar residues. The key residues responsible for the forward assembling process may be different from those that should be targeted to disassemble already formed aggregates. Molecularly imprinted nanoparticle (MINP) receptors are reported in this work to strongly and selectively bind specific segments of Aβ₄₀. Combined fluorescence spectroscopy, atomic force microscopy (AFM) imaging, and circular dichroism (CD) spectroscopy indicate that binding residues 21-30 near the loop region is most effective at inhibiting the aggregation of monomeric Aβ₄₀, but residues 11-20 that include the internal β strand closer to the N-terminal represent the best target for disaggregating already formed aggregates in the polymerization phase. Once the aggregation proceeds to the saturation phase, binding residues 1-10 has the largest effect on the disaggregation, likely because of the accessibility of these amino acids relative to others to the MINP receptors.

Peptide Inhibitors of Insulin Fibrillation: Current and Future Challenges

Amyloidoses include a large variety of local and systemic diseases that share the common feature of protein unfolding or refolding into amyloid fibrils. The most studied amyloids are those directly involved in neurodegenerative diseases, while others, such as those formed by insulin, are surprisingly far less studied. Insulin is a very important polypeptide that plays a variety of biological roles and, first and foremost, is at the basis of the therapy of diabetic patients. It is well-known that it can form fibrils at the site of injection, leading to inflammation and immune response, in addition to other side effects. In this concise review, we analyze the current knowledge on insulin fibrillation, with a focus on the development of peptide-based inhibitors, which are promising candidates for their biocompatibility but still pose challenges to their effective use in therapy.

Macrocyclic Cavitand β-Cyclodextrin Inhibits the Alcohol-induced Trypsin Aggregation

Trypsin, the most abundant pancreatic protein, aids in protein digestion by hydrolysis and exhibits aggregation propensity in presence of alcohol which can further lead to pancreatitis and eventually pancreatic cancer. Herein, by several experimental and theoretical approaches, we unearth the inhibition of alcohol-induced aggregation of Trypsin by macrocyclic cavitand, β-cyclodextrin (β-CD). β-CD interacts with the native protein and shows inhibitory effect in a dose dependent manner. Moreover, the secondary structures and morphologies of Trypsin in presence of β-CD also clearly emphasize the inhibition of fibril formation. From Fluorescence Correlation Spectroscopy, we observed an enhancement in diffusion time of Nile Red with ~ 2.5 times increase in hydrodynamic radius, substantiating the presence of fibrillar structure. Trypsin also shows reduction in its functional activity due to alcohol-induced aggregation. Our simulation data reports the probable residues responsible for fibril formation which was validated by molecular docking studies.

KLVFF oligopeptide-decorated amphiphilic cyclodextrin nanomagnets for selective amyloid beta recognition and fishing

Recognition and capture of amyloid beta (Aβ) is a challenging task for the early diagnosis of neurodegenerative disorders, such as Alzheimer's disease. Here, we report a novel KLVFF-modified nanomagnet based on magnetic nanoparticles (MNP) covered with a non-ionic amphiphilic β-cyclodextrin (SC16OH) and decorated with KLVFF oligopeptide for the self-recognition of the homologous amino-acids sequence of Aβ to collect Aβ (1-42) peptide from aqueous samples. MNP@SC16OH and MNP@SC16OH/Ada-Pep nanoassemblies were fully characterized by complementary techniques both as solid powders and in aqueous dispersions. Single domain MNP@SC16OH/Ada-Pep nanomagnets of 20-40 nm were observed by TEM analysis. DLS and ζ-potential measurements revealed that MNP@SC16OH nanoassemblies owned in aqueous dispersion a hydrodynamic radius of about 150 nm, which was unaffected by Ada-Pep decoration, while the negative ζ-potential of MNP@SC16OH (-40 mV) became less negative (-30 mV) in MNP@SC16OH/Ada-Pep, confirming the exposition of positively charged KLVFF on nanomagnets surface. The ability of MNP@SC16OH/Ada-Pep to recruit Aβ (1-42) in aqueous solution was evaluated by MALDI-TOF and compared with the ineffectiveness of undecorated MNP@SC16OH and VFLKF scrambled peptide-decorated nanoassemblies (MNP@SC16OH/Ada-scPep), pointing out the selectivity of KLVFF-decorated nanohybrid towards Aβ (1-42). Finally, the property of nanomagnets to extract Aβ in conditioned medium of cells over-producing Aβ peptides was investigated as proof of concept of effectiveness of these nanomaterials as potential diagnostic tools.

Two-photon excited lasing for detection of amyloids in brain tissue

Two-photon excitation of emissive markers with near-infrared (NIR) light is of a particular interest for imaging in biology and medicine because NIR light is relatively weakly absorbed and scattered by tissues. At the same time the mechanism of two-photon absorption allows excitation of molecules located deep inside a scattering medium. In this work we demonstrate that the two-photon excitation combined with the effect of light amplification in the stimulated emission process provides a sensitive method for detecting amyloids of different forms. We investigate the two-photon excited amplified spontaneous emission (ASE) of a fluorescent dye, coumarin 307, in the brain tissue infiltrated with various amyloid phantoms i.e. oligomers, protofibrils and mature fibrils. All these forms of amyloids can be detected by observation of ASE and determination of thresholds for light amplification. On this basis we suggest that a relatively simple extension of currently used emission-based optical spectroscopy techniques can provide key information on pathogenic amyloid structures in tissue.

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

The isoquinoline alkaloid coralyne can efficiently attenuate fibrillogenesis in lysozyme.

Controllable signal molecule release from Au NP-gated MSNs for photocathodic detection of ultralow level AβO

By integrating a target-responsive MSN-based controlled release system with a sensitization-SPR co-enhanced thionine/MoS₂ QDs/Cu NWs photocathode, a highly sensitive split-type PEC aptasensing platform for AβO detection in blood is constructed. Ultralow detection limit (2.1 fM) and high selectivity show great potential in early AD diagnosis.

Fibril-induced neurodegenerative disorders in an Aβ-mutant Drosophila model: therapeutic targeting using ammonium molybdate

The ability of polyanionic molybdate to inhibit and degrade protein fibrils both in vitro (insulin protein) and in vivo (Drosophila fly model) has been demonstrated. We establish the disappearance of fibrillar structures and recovery from neurodegenerative disorders in molybdate-treated Aβ42-mutant Drosophila flies as compared to the untreated ones, corroborating the therapeutic ability of ammonium molybdate towards the treatment of Alzheimer's disease.

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.

Using amyloid autofluorescence as a biomarker for lysozyme aggregation inhibition

The assembly of proteins into amyloidogenic aggregates underlies the onset and symptoms of several pathologies, including Alzheimer's disease, Parkinson's disease and type II diabetes. Among the efforts for fighting these diseases, there is a great demand for developing novel, fast and reliable methods for in vitro screening of new drugs that may suppress or reverse amyloidogenesis. Recent studies unravelled a progressive increase in a blue autofluorescence upon amyloid formation originated from many different proteins, including the peptide amyloid-β, lysozyme or insulin. Herein, we propose a drug screening method using this property, avoiding the use of external probe dyes. We demonstrate that the inhibition of lysozyme amyloid formation by means of two known inhibitors, tartrazine and amaranth, can be monitored based on the autofluorescence of lysozyme amyloid aggregates. Our results show that amyloid luminescence is an intrinsic property that can be potentially applied in a screening assay, allowing the ranking of drug efficiency. The assays demonstrated here are fast to perform and suitable for scaling using microplate assays, configuring a new sensitive and economically feasible method.

Selective Recognition of Amino Acids and Peptides by Small Supramolecular Receptors

To this day, the recognition and high affinity binding of biomolecules in water by synthetic receptors remains challenging, while the necessity for systems for their sensing, transport and modulation persists. This problematic is prevalent for the recognition of peptides, which not only have key roles in many biochemical pathways, as well as having pharmacological and biotechnological applications, but also frequently serve as models for the study of proteins. Taking inspiration in nature and on the interactions that occur between several receptors and peptide sequences, many researchers have developed and applied a variety of different synthetic receptors, as is the case of macrocyclic compounds, molecular imprinted polymers, organometallic cages, among others, to bind amino acids, small peptides and proteins. In this critical review, we present and discuss selected examples of synthetic receptors for amino acids and peptides, with a greater focus on supramolecular receptors, which show great promise for the selective recognition of these biomolecules in physiological conditions. We decided to focus preferentially on small synthetic receptors (leaving out of this review high molecular weight polymeric systems) for which more detailed and accurate molecular level information regarding the main structural and thermodynamic features of the receptor biomolecule assemblies is available.

Resistance of nepetin and its analogs on the fibril formation of human islet amyloid polypeptide

The self-aggregation of human islet amyloid polypeptide (hIAPP) into toxic oligomers and fibrils is closely linked to the pathogenesis of type II diabetes mellitus. Inhibitors can resist hIAPP misfolding, and the resistance can be considered an alternative therapeutic strategy for this disease. Flavones have been applied in the field of diabetes research, however, the inhibition mechanism of many compounds on the fibril formation of related pathogenic peptides remains unclear. In this work, four flavones, namely, nepetin (1), genkwanin (2), luteolin (3), and apigenin (4), were used to impede the peptide aggregation of hIAPP and compared with that on Aβ protein, which is correlated with Alzheimer's disease. Results indicated that the four flavones effectively inhibited the aggregation of the two peptides and mostly dispersed the mature fibrils to monomers. The interactions of flavones with the two peptides demonstrated a spontaneous and exothermic reaction through predominant hydrophobic and hydrogen bonding interactions. The binding affinities of 1 and 3 were stronger than those of 2 and 4 possibly because of the difference in the substituent groups of these molecules. These flavones could also decrease membrane leakage and upregulate cell viability by reducing the formation of toxic oligomers. Moreover, the performance of these flavones in terms of binding affinity, cellular viability, and decreased oligomerization was better on hIAPP than on Aβ. This work offered valuable data about these flavones as prospective therapeutic agents against relevant diseases.

Fluorescence Lifetime and Intensity of Thioflavin T as Reporters of Different Fibrillation Stages: Insights Obtained from Fluorescence Up-Conversion and Particle Size Distribution Measurements

Thioflavin T (ThT) assay is extensively used for studying fibrillation kinetics in vitro. However, the differences in the time course of ThT fluorescence intensity and lifetime and other physical parameters of the system, such as particle size distribution, raise questions about the correct interpretation of the aggregation kinetics. In this work, we focused on the investigation of the mechanisms, which underlay the difference in sensitivity of ThT fluorescence intensity and lifetime to the formation of protein aggregates during fibrillation by the example of insulin and during binding to globular proteins. The assessment of aggregate sizes and heterogeneity was performed using dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA). Using the sub-nanosecond resolution measurements, it was shown that the ThT lifetime is sensitive to the appearance of as much as a few percent of ThT bound to the high-affinity sites that occur simultaneously with an abrupt increase of the average particle size, particles concentration, and size heterogeneity. The discrepancy between ThT fluorescence intensity and a lifetime can be explained as the consequence of a ThT molecule fraction with ultrafast decay and weak fluorescence. These ThT molecules can only be detected using time-resolved fluorescence measurements in the sub-picosecond time domain. The presence of a bound ThT subpopulation with similar photophysical properties was also demonstrated for globular proteins that were attributed to non-specifically bound ThT molecules with a non-rigid microenvironment.

Human Serum Albumin-Inspired Glycopeptide-Based Multifunctional Inhibitor of Amyloid-β Toxicity

In Alzheimer's disease (AD), insoluble Aβ42 peptide fragments self-aggregate and form oligomers and fibrils in the brain, causing neurotoxicity. Further, the presence of redox-active metal ions such as Cu2+ enhances the aggregation process through chelation with these Aβ42 aggregates as well as generation of Aβ42-mediated reactive oxygen species (ROS). Herein, we have adopted a bioinspired strategy to design and develop a multifunctional glycopeptide hybrid molecule (Glupep), which can serve as a potential AD therapeutic. This molecule consists of a natural metal-chelating tetrapeptide motif of human serum albumin (HSA), a β-sheet breaker peptide, and a sugar moiety for better bioavailability. We performed different biophysical and docking experiments, which revealed that Glupep not only associates with Aβ42 but also prevents its self-aggregation to form toxic oligomers and fibrils. Moreover, Glupep was also shown to sequester out Cu2+ from the Aβ-Cu2+ complex, reducing the ROS formation and toxicity. Besides, this study also revealed that Glupep could protect PC12-derived neurons from Aβ-Cu2+-mediated toxicity by reducing intracellular ROS generation and stabilizing the mitochondrial membrane potential. All these exciting features show Glupep to be a potent inhibitor of Aβ42-mediated multifaceted toxicity and a prospective therapeutic lead for AD.

Fluorescence Phenomena in Amyloid and Amyloidogenic Bionanostructures

Nanoscale optical labeling is an advanced bioimaging tool. It is mostly based on fluorescence (FL) phenomena and enables the visualization of single biocells, bacteria, viruses, and biological tissues, providing monitoring of functional biosystems in vitro and in vivo, and the imaging-guided transportation of drug molecules. There is a variety of FL biolabels such as organic molecular dyes, genetically encoded fluorescent proteins (green fluorescent protein and homologs), semiconductor quantum dots, carbon dots, plasmonic metal gold-based nanostructures and more. In this review, a new generation of FL biolabels based on the recently found biophotonic effects of visible FL are described. This intrinsic FL phenomenon is observed in any peptide/protein materials folded into β-sheet secondary structures, irrespective of their composition, complexity, and origin. The FL effect has been observed both in natural amyloid fibrils, associated with neurodegenerative diseases (Alzheimer’s, Parkinson’s, and more), and diverse synthetic peptide/protein structures subjected to thermally induced biological refolding helix-like→β-sheet. This approach allowed us to develop a new generation of FL peptide/protein bionanodots radiating multicolor, tunable, visible FL, covering the entire visible spectrum in the range of 400–700 nm. Newly developed biocompatible nanoscale biomarkers are considered as a promising tool for emerging precise biomedicine and advanced medical nanotechnologies (high-resolution bioimaging, light diagnostics, therapy, optogenetics, and health monitoring).

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.

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.

First synthesis of cryptands with sucrose scaffold

Cryptands with sucrose scaffold, an unknown class of such derivatives, were prepared from the readily available 2,3,3’,4,4’-penta-O-benzylsucrose and 1’,2,3,3’,4,4’-hexa-O-benzylsucrose.

Rational Design of Near-Infrared Aggregation-Induced-Emission-Active Probes: In Situ Mapping of Amyloid-β Plaques with Ultrasensitivity and High-Fidelity

High-fidelity mapping of amyloid-β (Aβ) plaques is critical for the early detection of Alzheimer's disease. However, in vivo probing of Aβ plaques by commercially available thioflavin derivatives (ThT or ThS) has proven to be extremely limited, as evident by the restriction of enrichment quenching effect, low signal-to-noise ( S/ N) ratio, and poor blood-brain barrier (BBB) penetrability. Herein, we demonstrate a rational design strategy of near-infrared (NIR) aggregation-induced emission (AIE)-active probes for Aβ plaques, through introducing a lipophilic π-conjugated thiophene-bridge for extension to NIR wavelength range with enhancement of BBB penetrability, and tuning the substituted position of the sulfonate group for guaranteeing specific hydrophilicity to maintain the fluorescence- off state before binding to Aβ deposition. Probe QM-FN-SO₃ has settled well the AIE dilemma between the lipophilic requirement for longer emission and aggregation behavior from water to protein fibrillogenesis, thus making a breakthrough in high-fidelity feedback on in vivo detection of Aβ plaques with remarkable binding affinity, and serving as an efficient alternative to the commercial probe ThT or ThS.

Aggregation-Induced Emission for Visualization in Materials Science

Fluorescent imaging techniques have attracted much attention as a powerful tool to realize the visualization of structural and morphological evolution of various materials. However, the traditional fluorescent dyes usually suffered from aggregation-caused quenching, which severely limits the visualization results. In contrast, aggregation-induced emission (AIE) molecules with high quantum yields in the condensed state showed great opportunities for imaging techniques. In this feature article, recent progresses in visualization with AIE molecules are discussed. Assembly processes including crystallization, gelation process, and dissipative assembly have been observed. To better study information obtained regarding the processes, visualization during reactions, phase transitions, and molecular motions are successfully presented. Based on these successes, AIE molecules were further applied for phase recognition, macro-dispersion evaluation, and damage detection. Finally, we also present the outlook and perspectives, in our opinion, for the development of visualization by AIE molecules.

Inhibition of amyloid fibril formation of β-lactoglobulin by natural and synthetic curcuminoids

The aggregation of proteins has been associated with several aspects of daily life, including food processing, blood coagulation and many neurodegenerative infections.

Gold nanocolloid–protein interactions and their impact on β-sheet amyloid fibril formation

The influence of the presence of small molecules and nanoparticles on the mechanism of amyloid fibril formation has attracted attention because amyloid protein fibrils are associated with degenerative diseases. Here, we studied the interaction between gold nanoparticles (AuNPs) and a model protein (lysozyme). Both the formation of amyloid fibrils in the presence of gold nanoparticles, as well as the interaction between lysozyme and the amyloid fibrils with AuNPs, were investigated to gain an understanding of the distinct behaviour of lysozyme in its fibrillar and globular form. It was observed that the presence of AuNPs delayed the unfolding of α-helixes present in the globular lysozyme and the formation of the amyloid fibrils. However, the addition of AuNPs was also associated with a larger amount of β-sheet structures in the system once equilibrium was reached. Furthermore, the results showed that the driving force of the interaction between AuNPs and lysozyme in its fibrillar and globular forms was significantly different, and that the interaction of AuNPs with the preformed lysozyme amyloid fibrils led to a structural change in the protein.

Formation of amyloid protein fibrils is associated with degenerative diseases. Here, the interaction mechanism between globular and fibrillar proteins with AuNPs were investigated in order to potentially control and reverse the fibrillation process.

pH-responsive molecular assemblies of pyridylbutadiene derivative with cucurbit[7]uril

pH-responsive emission behavior of supramolecular complexes between pyridylbutadiene with CB7 and formation of molecular assemblies is described.

A sensitive probe for amyloid fibril detection with strong fluorescence and early response

We synthesized a new probe, 4-[2-(2-naphthyl)-(E)-ethenyl]-benzyl(triphenyl)phosphonium bromide (NEB), to detect the formation of amyloid fibrils of bovine insulin. The fluorescence intensity of NEB in the presence of insulin fibrils was 30 times higher than that before fibrillation, with the fluorescence quantum yield increased from 2.5% to 78%. In comparison with the commercially available probe, thioflavin T (ThT), NEB exhibits a 10 times stronger fluorescence and a shorter identification lag phase for detecting insulin fibrillation, indicating a higher sensitivity in detection of insulin oligomers and fibrils.

We synthesized a new probe, 4-[2-(2-naphthyl)-(E)-ethenyl]-benzyl(triphenyl)phosphonium bromide (NEB), to detect the formation of amyloid fibrils of bovine insulin.

Modulation in the acidity constant of acridine dye with cucurbiturils: stimuli-responsive pKa tuning and dye relocation into live cells

Cucurbit[7/8]uril–acridine complexes result in striking modulation of the excited state properties of acridine and allowed a tunable upward pK_a shift, which is applied for controlled relocation of the dye from the host to live cells.

Metal ion-induced supramolecular pKa tuning and fluorescence regeneration of a p-sulfonatocalixarene encapsulated neutral red dye

Supramolecular pK_a shift and fluorescence quenching in a neutral red dye in the presence of p-sulfonatocalix[4/6]arenes have been demonstrated, which are relevant for the off–on switch, ion sensitive electrodes and drug delivery vehicles.

Cyclodextrin-assisted modulation of the photophysical properties and acidity constant of pyrene-armed calix[4]arene

The supramolecular pK_a shift and modulation in the monomer and excimer emission behaviour of pyrene-armed calixarene with cyclodextrins find applications in ratiometric sensing.