Amyloid aggregation of lysozyme: the synergy study of red wine polyphenols

Molecular insights into the phase transition of lysozyme into amyloid nanostructures: Implications of therapeutic strategies in diverse pathological conditions

Lysozyme, a well-known bacteriolytic enzyme, exhibits a fascinating yet complex behavior when it comes to protein aggregation. Under certain conditions, this enzyme undergoes flexible transformation, transitioning from partially unfolded intermediate units of native conformers into complex cross-β-rich nano fibrillar amyloid architectures. Formation of such lysozyme amyloids has been implicated in a multitude of pathological and medical severities, like hepatic dysfunction, hepatomegaly, splenic rupture as well as spleen dysfunction, nephropathy, sicca syndrome, renal dysfunction, renal amyloidosis, and systemic amyloidosis. In this comprehensive review, we have attempted to provide in-depth insights into the aggregating behavior of lysozyme across a spectrum of variables, including concentrations, temperatures, pH levels, and mutations. Our objective is to elucidate the underlying mechanisms that govern lysozyme's aggregation process and to unravel the complex interplay between its structural attributes. Moreover, this work has critically examined the latest advancements in the field, focusing specifically on novel strategies and systems, that have been implemented to delay or inhibit the lysozyme amyloidogenesis. Apart from this, we have tried to explore and advance our fundamental understanding of the complex processes involved in lysozyme aggregation. This will help the research community to lay a robust foundation for screening, designing, and formulating targeted anti-amyloid therapeutics offering improved treatment modalities and interventions not only for lysozyme-linked amyloidopathy but for a wide range of amyloid-related disorders.

Recent Advances in the Inhibition of Membrane Lipid Peroxidation by Food-Borne Plant Polyphenols via the Nrf2/GPx4 Pathway

Lipid peroxidation (LP) leads to changes in the fluidity and permeability of cell membranes, affecting normal cellular function and potentially triggering apoptosis or necrosis. This process is closely correlated with the onset of many diseases. Evidence suggests that the phenolic hydroxyl groups in food-borne plant polyphenols (FPPs) make them effective antioxidants capable of preventing diseases triggered by cell membrane LP. Proper dietary intake of FPPs can attenuate cellular oxidative stress, especially damage to cell membrane phospholipids, by activating the Nrf2/GPx4 pathway. Nuclear factor E2-related factor 2 (Nrf2) is an oxidative stress antagonist. The signaling pathway regulated by Nrf2 is a defense transduction pathway of the organism against external stimuli such as reactive oxygen species and exogenous chemicals. Glutathione peroxidase 4 (GPx4), under the regulation of Nrf2, is the only enzyme that reduces cell membrane lipid peroxides with specificity, thus playing a pivotal role in regulating cellular ferroptosis and counteracting oxidative stress. This study explored the Nrf2/GPx4 pathway mechanism, antioxidant activity of FPPs, and mechanism of LP. It also highlighted the bioprotective properties of FPPs against LP and its associated mechanisms, including (i) activation of the Nrf2/GPx4 pathway, with GPx4 potentially serving as a central target protein, (ii) regulation of antioxidant enzyme activities, leading to a reduction in the production of ROS and other peroxides, and (iii) antioxidant effects on LP and downstream phospholipid structure. In conclusion, FPPs play a crucial role as natural antioxidants in preventing LP. However, further in-depth analysis of FPPs coregulation of multiple signaling pathways is required, and the combined effects of these mechanisms need further evaluation in experimental models. Human trials could provide valuable insights into new directions for research and application.

Efficient inhibition of amyloid fibrillation and cytotoxicity of α-synuclein and human insulin using biosynthesized silver nanoparticles decorated by green tea polyphenols

Green tea polyphenols (GTPs), particularly epigallocatechin-3-gallate, stand out among natural small molecules screened for their ability to target protein aggregates due to their potent anti-amyloidogenic and neuroprotective activities against various disease-related peptides and proteins. However, the clinical applications of GTPs in amyloid-related diseases have been greatly limited by drawbacks such as poor chemical stability and low bioavailability. To address these limitations, this study utilized an Iranian green tea polyphenolic extract as a reducing agent to neutralize silver ions and facilitate the formation of silver nanoparticle capped by GTPs (GTPs-capped AgNPs). The results obtained from this study demonstrate that GTPs-capped AgNPs are more effective than free GTPs at inhibiting amyloid fibrillation and reducing cytotoxicity induced by amyloid fibrils of human insulin and α-synuclein (α-syn). This improved efficacy is attributed to the increased surface/volume ratio of GTPs-capped AgNPs, which can enhance their binding affinity to amyloidogenic species and boosts their antioxidant activity. The mechanism by which GTPs-capped AgNPs inhibit amyloid fibrillation appears to vary depending on the target protein. For structured protein human insulin, GTPs-capped AgNPs hinder fibrillation by constraining the protein in its native-like state. In contrast, GTPs-capped AgNPs modulate fibrillation of intrinsically disordered proteins like α-syn by redirecting the aggregation pathway towards the formation of non-toxic off-pathway oligomers or amorphous aggregates. These findings highlight polyphenol-functionalized nanoparticles as a promising strategy for targeting protein aggregates associated with neurodegenerative diseases.

Unlocking novel therapies: cyclic peptide design for amyloidogenic targets through synergies of experiments, simulations, and machine learning

Existing therapies for neurodegenerative diseases like Parkinson's and Alzheimer's address only their symptoms and do not prevent disease onset. Common therapeutic agents, such as small molecules and antibodies struggle with insufficient selectivity, stability and bioavailability, leading to poor performance in clinical trials. Peptide-based therapeutics are emerging as promising candidates, with successful applications for cardiovascular diseases and cancers due to their high bioavailability, good efficacy and specificity. In particular, cyclic peptides have a long in vivo stability, while maintaining a robust antibody-like binding affinity. However, the de novo design of cyclic peptides is challenging due to the lack of long-lived druggable pockets of the target polypeptide, absence of exhaustive conformational distributions of the target and/or the binder, unknown binding site, methodological limitations, associated constraints (failed trials, time, money) and the vast combinatorial sequence space. Hence, efficient alignment and cooperation between disciplines, and synergies between experiments and simulations complemented by popular techniques like machine-learning can significantly speed up the therapeutic cyclic-peptide development for neurodegenerative diseases. We review the latest advancements in cyclic peptide design against amyloidogenic targets from a computational perspective in light of recent advancements and potential of machine learning to optimize the design process. We discuss the difficulties encountered when designing novel peptide-based inhibitors and we propose new strategies incorporating experiments, simulations and machine learning to design cyclic peptides to inhibit the toxic propagation of amyloidogenic polypeptides. Importantly, these strategies extend beyond the mere design of cyclic peptides and serve as template for the de novo generation of (bio)materials with programmable properties.

Green tea leaf constituents inhibit the formation of lysozyme amyloid aggregates: An effect of mutual interactions

Amyloidoses represent a group of pathological conditions characterized by amyloid fibrils accumulating in the form of deposits in intra- or extracellular space, leading to tissue damage. The lysozyme from hen egg-white (HEWL) is often used as a universal model protein to study the anti-amyloid effects of small molecules. The in vitro anti-amyloid activity and mutual interactions of green tea leaf constituents: (-)-epigallocatechin gallate (EGCG), (-)-epicatechin (EC), gallic acid (GA), caffeine (CF) and their equimolar mixtures were studied. The inhibition of HEWL amyloid aggregation was monitored by a Thioflavin T fluorescence assay and atomic force microscopy (AFM). The interactions of the analyzed molecules with HEWL were interpreted by ATR-FTIR and protein-small ligand docking studies. EGCG was the only substance efficiently inhibiting amyloid formation (IC₅₀ ~ 193 μM), slowing the aggregation process, reducing the number of fibrils and partially stabilizing the secondary structure of HEWL. Compared to EGCG alone, EGCG-containing mixtures displayed lower overall anti-amyloid efficacy. The decrease in efficiency results from (a) the spatial interference of GA, CF and EC with EGCG while binding to HEWL, (b) the propensity of CF to form a less active adduct with EGCG, which participates in interactions with HEWL in parallel with pure EGCG. This study confirms the importance of interaction studies, revealing the possible antagonistic behavior of molecules when combined.

Insights into the remarkable attenuation of hen egg white lysozyme amyloid fibril formation mediated by biogenic gold nanoparticles stabilized by quercetin-functionalized tara gum

Aberrant protein misfolding and/or aggregation and fibrillation has been linked to the pathogenesis of several debilitating chronic diseases including Alzheimer's and Parkinson's disease. Inhibiting protein amyloidogenesis has been proposed as a viable strategy to prevent or ameliorate associated disorders. Herein, we investigated the anti-amyloidogenic properties of biogenic gold nanoparticles (QTG-GNP) prepared via a simple green chemistry route and stabilized by quercetin-functionalized tara gum (QTG). The synthesized QTG-GNP was extensively characterized for its physicochemical attributes via UV-visible spectroscopy, TEM, FESEM, EDX, DLS/Zeta potential, FTIR, RAMAN, XRD, XPS, and TGA analyses, as well as for its biological properties. The results revealed that small-sized (5.01 ± 1.17 nm), well-dispersed, highly stable and round-shaped biogenic gold nanoparticles were successfully synthesized at room temperature with QTG as the sole reductant /stabilizer. Importantly, QTG-GNP demonstrated potent anti-aggregation and fibrillation inhibitory effects against amyloidogenic hen egg white lysozyme (HEWL). Also, QTG-GNP was able to dissociate pre-formed HEWL amyloid fibrils. Furthermore, the constructed nanoparticles exhibited potent anti-radical activities against DPPH and ABTS⁺ and were cytocompatible with mouse L929 fibroblast cells. On the basis of these findings, it was established that QTG-GNP holds strong prospects for further development as an agent for countering protein aggregation and associated disease conditions.

An investigation into the potential action of polyphenols against human Islet Amyloid Polypeptide aggregation in type 2 diabetes

Type 2 diabetes (T2D), a chronic metabolic disease characterized by hyperglycemia, results in significant disease burden and financial costs globally. Whilst the majority of T2D cases seem to have a genetic basis, non-genetic modifiable and non-modifiable risk factors for T2D include obesity, diet, physical activity and lifestyle, smoking, age, ethnicity, and mental stress. In healthy individuals, insulin secretion from pancreatic islet β-cells is responsible for keeping blood glucose levels within normal ranges. T2D patients suffer from multifactorial onset of β-cell dysfunction and/or loss of β-cell mass owing to reactive oxygen species (ROS) production, mitochondrial dysfunction, autophagy, and endoplasmic reticulum (ER) stress. Most predominantly however, and the focus of this review, it is the aggregation and misfolding of human Islet Amyloid Polypeptide (hIAPP, also known as amylin), which is detrimental to β-cell function and health. Whilst hIAPP is found in healthy individuals, its misfolded version is cytotoxic and able to induce β-cell dysfunction and/or death through various mechanisms including membrane changes in β-cell causing influx of calcium ions, arresting complete granule membrane recovery and ER stress. There are several existing therapeutics for T2D. However, there is a need for alternative or adjunct therapies for T2D with milder adverse effects and greater availability. Foremost among the potential natural therapeutics are polyphenols. Extensive data from studies evaluating the potential of polyphenols to inhibit hIAPP aggregation and disassemble aggregated hIAPP are promising. Moreover, in-vivo, and in-silico studies also highlight the potential effects of polyphenols against hIAPP aggregation and mitigation of larger pathological effects of T2D. Whilst there have been some promising clinical studies on the therapeutic potential of polyphenols, extensive further clinical studies and in-vitro studies evaluating the mechanisms of action and ideal doses for many of these compounds are required. The need for these studies is made more important by the postulated link between Alzheimer's disease (AD) and T2D pathophysiology given the similar aggregation process of their respective amyloid proteins, which evokes thoughts of cross-reactive polyphenols which can be effective for both AD and T2D patients.

UV Resonance Raman explores protein structural modification upon fibrillation and ligand interaction

Amyloids are proteinaceous deposits considered an underlying pathological hallmark of several degenerative diseases. The mechanism of amyloid formation and its inhibition still represent challenging issues, especially when protein structure cannot be investigated by classical biophysical techniques as for the intrinsically disordered proteins (IDPs). In this view, the need to find an alternative way for providing molecular and structural information regarding IDPs prompted us to set a novel, to our knowledge, approach focused on UV Resonance Raman (UVRR) spectroscopy. To test its applicability, we study the fibrillation of hen-egg white lysozyme (HEWL) and insulin as well as their interaction with resveratrol, employing also intrinsic fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The increasing of the β-sheet structure content at the end of protein fibrillation probed by FTIR occurs simultaneously with a major solvent exposure of tryptophan (Trp) and tyrosine (Tyr) residues of HEWL and insulin, respectively, as revealed by UVRR and intrinsic fluorescence spectroscopy. However, because the latter technique is successfully used when proteins naturally contain Trp residues, it shows poor performances in the case of insulin, and the information regarding its tertiary structure is exclusively provided by UVRR spectroscopy. The presence of an increased concentration of resveratrol induces mild changes in the secondary structure of both protein fibrils while remodeling HEWL fibril length and promoting the formation of amorphous aggregates in the case of insulin. Although the intrinsic fluorescence spectra of proteins are hidden by resveratrol signal, UVRR Trp and Tyr bands are resonantly enhanced, showing a good sensitivity to the presence of resveratrol and marking a modification in the noncovalent interactions in which they are involved. Our findings demonstrate that UVRR is successfully employed in the study of aggregation-prone proteins and of their interaction with ligands, especially in the case of Trp-lacking proteins.

Studies on the effect of a Fupenzi glycoprotein on the fibrillation of bovine serum albumin and its antioxidant activity

In this study, the effect of a glycoprotein obtained from Fupenzi (FPZ) (Rubus chingii Hu.) on the fibrillation of bovine serum album (BSA) was investigated by multi-spectroscopic methods and transmission electron microscopy. Moreover, the cytotoxicity of the glycoprotein and the effect of it on H₂O₂-induced cell viability were investigated by cell counting kit and β-galactosidase kit, respectively. The experimental results indicated that the glycoprotein showed very low toxicity to NRK-52E cells and could obviously delay cell senescence and improve cell viability. Moreover, the glycoprotein could effectively inhibit the formation of BSA fibrils and destroy the stability of preformed BSA fibrils in a concentration-dependent manner. Generally, antioxidant capacities are thought to be related to the anti-amyloidogenic activity of inhibitors; therefore, to reveal the inhibitory mechanism, the anti-oxidative property of the glycoprotein was examined by DPPH and ABTS assays. The results demonstrated that FPZ glycoprotein had a remarkable antioxidant activity and the IC₅₀ values of DPPH and ABTS were 0.249 mg mL^-1 and 0.092 mg mL^-1, respectively. This work suggested that the FPZ glycoprotein had the potential to be designed a new therapeutic agent for attenuating aging and preventing the age-related diseases.

Amyloid Aggregation of Insulin: An Interaction Study of Green Tea Constituents

Exogenous insulin, used as a therapeutic agent for diabetes, forms insoluble deposits containing amyloid fibrillar structures near the administration site. We have analyzed the in vitro anti-amyloid activity of four green tea constituents: (-)-epigallocatechin gallate (EGCG), (-)-epicatechin (EC), gallic acid (GA), caffeine (CF), and their equimolar mixtures. Regarding individually tested compounds, only EGCG inhibited the fibrillization process. The individual EC, GA, and CF molecules were ineffective. The presence of EGCG in equimolar combinations with GA, EC, or CF was required for the inhibitory activity of most mixtures. Molecular docking revealed that EGCG interacts with an essential amyloidogenic region of insulin chain B. Individually inactive GA had a potentiating effect on the activity of EGCG. In contrast, EC and CF had a negative impact on the activity of the mixtures. We have observed diverse morphology and the amount of insulin amyloid aggregates formed in the presence of studied compounds. The distinct types of amyloid aggregates created in vitro in the presence of EGCG and other green tea constituents were characterized. Results indicate that the biological activity of individual molecules is not directly applicable to the pooled samples effects prediction.

Probing the fibrillation of lysozyme by nanoscale-infrared spectroscopy

Amyloid fibrillation is the root cause of several neuro as well as non-neurological disorders. Understanding the molecular basis of amyloid aggregate formation is crucial for deciphering various neurodegenerative diseases. In our study, we have examined the lysozyme fibrillation process using nano-infrared spectroscopy (nanoIR). NanoIR enabled us to investigate both structural and chemical characteristics of lysozyme fibrillar species concurrently. The spectroscopic results indicate that lysozyme transformed into a fibrillar structure having mainly parallel β-sheets, with almost no antiparallel β-sheets. Features such as protein stiffness have a good correlation with obtained secondary structural information showing the state of the protein within the fibrillation state. The structural and chemical details were compared with transmission electron microscopy (TEM) and circular dichroism (CD). We have utilized nanoIR and measured infrared spectra to characterize lysozyme amyloid fibril structures in terms of morphology, molecular structure, secondary structure content, stability, and size of the cross-β core. We have shown that the use of nanoIR can complement other biophysical studies to analyze the aggregation process and is particularly useful for studying proteins involved in aggregation to help in designing molecules against amyloid aggregation. Specifically, the nanoIR spectra afford higher resolution information and a characteristic fingerprint for determining states of aggregation.Communicated by Ramaswamy H. Sarma.

7-Methoxytacrine and 2-Aminobenzothiazole Heterodimers: Structure-Mechanism Relationship of Amyloid Inhibitors Based on Rational Design

The formation and accumulation of amyloid aggregates are the phenomena that accompany amyloidoses, which are currently untreatable and include Alzheimer's and Parkinson's diseases, diabetes mellitus, non-neuropathic lysozyme systemic amyloidosis, and others. One of the very promising therapeutic approaches seems to be an inhibition of amyloid formation and/or clearance of amyloid aggregates. Small molecules have a great potential to interfere with amyloid fibrillation of peptides and polypeptides, which can be improved by connection of cyclic structures into single multicyclic molecules and their dimerization. In our study, we focused on heterodimers consisting of 7-methoxytacrine (7-MEOTA) and 2-aminobenzothiazole (BTZ) parent molecules connected by an aliphatic linker. Using in vitro and in silico methods, we investigated the ability of studied compounds to inhibit the amyloid aggregation of hen egg white lysozyme. Heterodimerization led to significant improvement of inhibitory activity compared to that of the parent molecules. The efficiency of the heterodimers varied; the most effective inhibitor contained the longest linker, eight carbons long. We suggest that binding of a heterodimer to a lysozyme blocks the interaction between the β-domain and C-helix region essential for the formation of amyloid cross-β structure. Elongation of the linker ultimately enhances the compound's ability to prevent this interaction by allowing the BTZ part of the heterodimer to bind more effectively, increasing the compound's binding affinity, and also by greater steric obstruction. This study represents an important contribution to the recent rational design of potential lead small molecules with anti-amyloid properties, and the heterodimers studied are prospective candidates for the treatment of systemic lysozyme amyloidosis and other amyloid-related diseases.

Recent Advances on the Anti-Inflammatory and Antioxidant Properties of Red Grape Polyphenols: In Vitro and In Vivo Studies

In this review, special emphasis will be placed on red grape polyphenols for their antioxidant and anti-inflammatory activities. Therefore, their capacity to inhibit major pathways responsible for activation of oxidative systems and expression and release of proinflammatory cytokines and chemokines will be discussed. Furthermore, regulation of immune cells by polyphenols will be illustrated with special reference to the activation of T regulatory cells which support a tolerogenic pathway at intestinal level. Additionally, the effects of red grape polyphenols will be analyzed in obesity, as a low-grade systemic inflammation. Also, possible modifications of inflammatory bowel disease biomarkers and clinical course have been studied upon polyphenol administration, either in animal models or in clinical trials. Moreover, the ability of polyphenols to cross the blood-brain barrier has been exploited to investigate their neuroprotective properties. In cancer, polyphenols seem to exert several beneficial effects, even if conflicting data are reported about their influence on T regulatory cells. Finally, the effects of polyphenols have been evaluated in experimental models of allergy and autoimmune diseases. Conclusively, red grape polyphenols are endowed with a great antioxidant and anti-inflammatory potential but some issues, such as polyphenol bioavailability, activity of metabolites, and interaction with microbiota, deserve deeper studies.

Dengzhan Shengmai capsules and their active component scutellarin prevent cognitive decline in APP/PS1 mice by accelerating Aβ aggregation and reducing oligomers formation

There is currently no effective treatment to prevent the progress of Alzheimer's disease (AD). The traditional Chinese herbs Dengzhan Shengmai (DZSM) capsules and their active component scutellarin possess multiple effects and are clinically used for the treatment of cerebrovascular diseases. Scutellarin has been reported to affect Aβ aggregation. However, the effects of DZSM capsules on AD remain unknown. Through in vivo experiments, our study proved that the alleviating effects of DZSM capsules on cognitive deficits of AD mice were due to the role of scutellarin, which up-regulated low toxic amyloid plaques and down-regulated highly toxic soluble Aβ42 and Aβ40 levels in cortex. In vitro, we confirmed scutellarin's role in accelerating transforming Aβ42 monomers into high-molecular-mass aggregates by biochemical assays, which supported the results observed in drug-treated APP/PS1 mice. In detail, the 1:10 ratio of scutellarin/Aβ42 mixtures promoted production of large β-sheet-rich fibrils whereas the 1:1 ratio promoted production of protofibrils. In addition, the binding between scutellarin and Aβ monomers was quantified by microscale thermophoresis test and the apparent dissociation constant (Kd) was 1284.4 ± 238.8 μM. What's more, binding regions between scutellarin and Aβ fibrils were predicted by computational docking models and scutellarin might bind parallel to the long axis of Aβ42 fibrils targeting hydrophobic grooves at residues 35-36 or 39. In conclusion, DZSM capsules protected against cognitive defects of AD through scutellarin-mediated acceleration of Aβ aggregation into fibrils or protofibrils and reduction of soluble Aβ oligomers, thus suggesting potential clinical applications of DZSM capsules and scutellarin in the treatment of AD.

Considerations for the Use of Polyphenols as Therapies in Neurodegenerative Diseases

Over the last two decades, the increase in the incidence of neurodegenerative diseases due to the increasingly ageing population has resulted in a major social and economic burden. At present, a large body of literature supports the potential use of functional nutrients, which exhibit potential neuroprotective properties to mitigate these diseases. Among the most studied dietary molecules, polyphenols stand out because of their multiple and often overlapping reported modes of action. However, ambiguity still exists as to the significance of their influence on human health. This review discusses the characteristics and functions of polyphenols that shape their potential therapeutic actions in neurodegenerative diseases while the less-explored gaps in knowledge of these nutrients will also be highlighted.

Nanomedical Relevance of the Intermolecular Interaction Dynamics-Examples from Lysozymes and Insulins

Insulin and lysozyme share the common features of being prone to aggregate and having biomedical importance. Encapsulating lysozyme and insulin in micellar nanoparticles probably would prevent aggregation and facilitate oral drug delivery. Despite the vivid structural knowledge of lysozyme and insulin, the environment-dependent oligomerization (dimer, trimer, and multimer) and associated structural dynamics remain elusive. The knowledge of the intra- and intermolecular interaction profiles has cardinal importance for the design of encapsulation protocols. We have employed various biophysical methods such as NMR spectroscopy, X-ray crystallography, Thioflavin T fluorescence, and atomic force microscopy in conjugation with molecular modeling to improve the understanding of interaction dynamics during homo-oligomerization of lysozyme (human and hen egg) and insulin (porcine, human, and glargine). The results obtained depict the atomistic intra- and intermolecular interaction details of the homo-oligomerization and confirm the propensity to form fibrils. Taken together, the data accumulated and knowledge gained will further facilitate nanoparticle design and production with insulin or lysozyme-related protein encapsulation.

Eduscho Coffee Extract Effectively Inhibits the Formation of Amyloid-like Fibrils by Trypsin in Aqueous Ethanol

In this work we used an in vitro trypsin aggregation model to show that certain commercial coffee extracts can inhibit protein aggregation. Aggregation experiments were performed using several spectroscopic methods and a dye binding assay, such as turbidity, Congo red (CR) and electronic circular dichroism (ECD), that was further supported by transmission electron microscopy (TEM). A correlation was found between the anti-aggregation properties and the total phenolic content of the coffee extracts. The results revealed that the greatest effect was exerted by the Eduscho coffee extract. It was found that the inhibitory effect of this extract was concentration dependent. Using size exclusion chromatography, we demonstrated that the inhibitory effect of the Eduscho coffee extract on the formation of amyloid-like fibrils was due to its capacity to stabilize the oligomeric form of the protein.

Chaperone-like effect of ceftriaxone on HEWL aggregation: A spectroscopic and computational study

BACKGROUND

Lysozyme is a widely distributed enzyme present in a variety of tissue and body fluids. Human and hen egg white lysozyme are used as validated model to study protein folding and stability and to understand protein misfolding and aggregation. We recently found that ceftriaxone, a β-lactam antibiotic able to overcome the blood-brain barrier, successfully eliminated the cellular toxic effects of misfolded proteins as Glial Fibrillary Acidic Protein (GFAP) and α-synuclein. To further understand the anti-amyloidogenic properties of ceftriaxone, we studied its activity towards lysozyme aggregation with the aim to investigate a possible chaperone-like activity of this molecule.

METHODS

Here we present the results obtained from fluorescence and synchrotron radiation circular dichroism spectroscopies and from molecular docking and molecular dynamics about the lysozyme-ceftriaxone interaction at neutral and acidic pH values.

RESULTS

We found that ceftriaxone exhibits comparable affinity constants to lysozyme in both experimental pH conditions and that its addition enhanced lysozyme stability reducing its aggregation propensity in acidic conditions. Computational methods allowed the identification of the putative binding site of ceftriaxone, thus rationalizing the spectroscopic results.

CONCLUSIONS

Spectroscopy data and molecular dynamics indicated a protective effect of ceftriaxone on pathological aggregation phenomena suggesting a chaperone-like effect of this molecule on protein folding. General significance These results, in addition to our previous studies on α-synuclein and GFAP, confirm the property of ceftriaxone to inhibit the pathological protein aggregation of lysozyme also by a chaperone-like mechanism, extending the potential therapeutic application of this molecule to some forms of human hereditary systemic amyloidosis.

Inhibition of HEWL fibril formation by taxifolin: Mechanism of action

Among therapeutic approaches for amyloid-related diseases, attention has recently turned to the use of natural products as effective anti-aggregation compounds. Although a wealth of in vitro and in vivo evidence indicates some common inhibitory activity of these compounds, they don't generally suggest the same mechanism of action. Here, we show that taxifolin, a ubiquitous bioactive constituent of foods and herbs, inhibits formation of HEWL amyloid fibrils and their related toxicity by causing formation of very large globular, chain-like aggregates. A range of amyloid-specific techniques were employed to characterize this process. We found that taxifolin exerts its effect by binding to HEWL prefibrillar species, rather than by stabilizing the molecule in its native-like state. Furthermore, it's binding results in diverting the amyloid pathway toward formation of very large globular, chain-like aggregates with low β-sheet content and reduced solvent-exposed hydrophobic patches. ThT fluorescence measurements show that the binding capacity of taxifolin is significantly reduced, upon generation of large protofibrillar aggregates at the end of growth phase. We believe these results may help design promising inhibitors of protein aggregation for amyloid-related diseases.

Interaction of nonionic detergents with the specific sites of lysozyme amyloidogenic region - inhibition of amyloid fibrillization

Two nonionic detergents, Triton X-100 (TX-100) and n-dodecyl-β-d-maltoside (DDM) were tested for their ability to affect lysozyme amyloid aggregation. We have demonstrated that fibrillization of lysozyme is completely inhibited by low sub-micellar concentrations of both of these detergents. The apparent IC₅₀ values were calculated to be 22μM and 26μM for TX-100 and DDM, respectively. The detergent/protein ratio is not the only parameter controlling inhibition. The precise timing of the detergent addition was found to be also crucial. It appears that the primary inhibitory activity of detergents resulted from inhibition of nuclei formation, in addition to inhibition of fibril polymerization at the early stage of protofibrils growth. The docking study revealed that Asn-59, Trp-63 and Ala-107, all present within the lysozyme amyloidogenic region, were involved in the interaction with both detergents. In addition, TX-100 also interacted with Gln-57 and Asp-103 within lysozyme. Moreover, based on our computational results, TX-100 bridges the Gln-57 and Ala-107 amino acids of the amyloidogenic segment of lysozyme and therefore inhibits more effectively the amyloid fibril formation. Along these lines, the knowledge gained from our study indicates that the detergents or their derivatives may be applicable as a promising strategy for the modulation of lysozyme protein aggregation.

Benzbromarone, Quercetin, and Folic Acid Inhibit Amylin Aggregation

Human Amylin, or islet amyloid polypeptide (hIAPP), is a small hormone secreted by pancreatic β-cells that forms aggregates under insulin deficiency metabolic conditions, and it constitutes a pathological hallmark of type II diabetes mellitus. In type II diabetes patients, amylin is abnormally increased, self-assembled into amyloid aggregates, and ultimately contributes to the apoptotic death of β-cells by mechanisms that are not completely understood. We have screened a library of approved drugs in order to identify inhibitors of amylin aggregation that could be used as tools to investigate the role of amylin aggregation in type II diabetes or as therapeutics in order to reduce β-cell damage. Interestingly, three of the compounds analyzed-benzbromarone, quercetin, and folic acid-are able to slow down amylin fiber formation according to Thioflavin T binding, turbidimetry, and Transmission Electron Microscopy assays. In addition to the in vitro assays, we have tested the effect of these compounds in an amyloid toxicity cell culture model and we have found that one of them, quercetin, has the ability to partly protect cultured pancreatic insulinoma cells from the cytotoxic effect of amylin. Our data suggests that quercetin can contribute to reduce oxidative damage in pancreatic insulinoma β cells by modulating the aggregation propensity of amylin.

Challenges in Analyzing the Biological Effects of Resveratrol

The suggested health effects (e.g., disease prevention) of dietary bioactive compounds such as resveratrol are challenging to prove in comparison to man-made drugs developed for therapeutic purposes. Dietary bioactive compounds have multiple cellular targets and therefore have a variety of biological effects. Extrapolating the biological effects of dietary compounds from in vitro and in vivo animal experiments to humans may lead to over- or under-estimation of the effect and role of these compounds. The present paper will discuss a few of these challenges and suggest directions for future research. Questions we address include: (1) Is the combinatorial effect of resveratrol and other compounds real? (2) What are the real and relevant doses of resveratrol after administration? and (3) Is it possible to estimate the preventive effect of resveratrol by clinical trials using standard experimental designs? The examples concerning resveratrol taken from the scientific literature are mainly from 2010 and later. The challenges pointed out in this review are similar to most naturally occurring bioactive compounds.

Differential influence of additives on the various stages of insulin aggregation

The different species in the aggregation pathway of insulin are stabilized/destabilized to different extent in the presence of various additives.

DNA induced aggregation of stem bromelain; a mechanistic insight

Negatively charged species such as nucleic acids have commonly been found to be associated with the proteinaceous deposits in the tissues of patients with amyloid diseases.

Inhibiting amyloid β-protein assembly: Size-activity relationships among grape seed-derived polyphenols

Epidemiological evidence that red wine consumption negatively correlates with risk of Alzheimer's disease has led to experimental studies demonstrating that grape seed extracts inhibit the aggregation and oligomerization of Aβ in vitro and ameliorate neuropathology and behavioral deficits in a mouse model of Alzheimer's disease. The active agent in the extracts is a mixed population of polyphenolic compounds. To evaluate the relative potency of each of these compounds, HPLC was used to fractionate the mixture into monomers, dimers, and oligomers. Each fraction was analyzed for its effect on Aβ conformational dynamics (circular dichroism), oligomerization (zero-length photochemical cross-linking), aggregation kinetics (Thioflavin T fluorescence), and morphology (electron microscopy). The relative activities of each fraction were determined on the basis of molar concentration (mol/L) or mass concentration (g/L). When molar concentration, the number concentration of each polyphenolic compound, was considered, the oligomer fraction was the most potent inhibitor of Aβ oligomerization and aggregation. However, when mass concentration, the number concentration of phenolic groups, was considered, monomers were the most potent inhibitors. To understand these ostensibly contradictory results, a model of polyphenol:Aβ complexation was developed. This model, which was found to be consistent with published X-ray crystallographic studies, offers an explanation for the effects of functional group polyvalency on inhibitor activity. Our data emphasize the importance of an in-depth understanding of the mechanism(s) underlying 'concentration dependence' in inhibitor systems involving polyfunctional agents.

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

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

Role of the osmolyte taurine on the folding of a model protein, hen egg white lysozyme, under a crowding condition

Taurine is one of the osmolytes that maintain the structure of proteins in cells exposed to denaturing environmental stressors. Recently, cryoelectron tomographic analysis of eukaryotic cells has revealed that their cytoplasms are crowded with proteins. Such crowding conditions would be expected to hinder the efficient folding of nascent polypeptide chains. Therefore, we examined the role of taurine on the folding of denatured and reduced lysozyme, as a model protein, under a crowding condition. The results confirmed that taurine had a better effect on protein folding than did β-alanine, which has a similar chemical structure, when the protein to be folded was present at submillimolar concentration. NMR analyses further revealed that under the crowding condition, taurine had more interactions than did β-alanine with the lysozyme molecule in both the folded and denatured states. We concluded that taurine improves the folding of the reduced lysozyme at submillimolar concentration to allow it to interact more favorably with the lysozyme molecule. Thus, the role of taurine, as an osmolyte in vivo, may be to assist in the efficient folding of proteins.

Inhibition of insulin amyloid fibrillization by glyco-acridines: an in vitro and in silico study

The structure of glyco-acridines determines their impact on insulin amyloid aggregation and newly introduced geometrical descriptors allow us to distinguish different binding affinities.

Molecular mechanism of the inhibition and remodeling of human islet amyloid polypeptide (hIAPP(1-37)) oligomer by resveratrol from molecular dynamics simulation

Natural polyphenols are one of the most actively investigated categories of amyloid inhibitors, and resveratrol has recently been reported to inhibit and remodel the human islet amyloid polypeptide (hIAPP) oligomers and fibrils. However, the exact mechanism of its action is still unknown, especially for the full-length hIAPP1-37. To this end, we performed all-atom molecular dynamics simulations for hIAPP1-37 pentamer with and without resveratrol. The obtained results show that the binding of resveratrol is able to cause remarkable conformational changes of hIAPP1-37 pentamer, in terms of secondary structures, order degree, and morphology. By clustering analysis, two possible binding sites of resveratrol on the hIAPP1-37 pentamer were found, located at the grooves of the top and bottom surfaces of β-sheet layer, respectively. After the binding free energy calculation and residue energy decomposition, it can be concluded that the bottom site is the more possible one, and that the nonpolar interactions act as the driving force for the binding of hIAPP1-37 to resveratrol. In addition, Arg11 is the most important residue for the binding of resveratrol. The full understanding of inhibitory mechanism of resveratrol on the hIAPP1-37 oligomer, and the identification of its binding sites on this protein are helpful for the future design and discovery of new amyloid inhibitors.

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.