Quercetin inhibits amyloid fibrillation of bovine insulin and destabilizes preformed fibrils

Doxorubicin as a Drug Repurposing for Disruption of α-Chymotrypsinogen-A Aggregates

Protein conformation is affected by interaction of several small molecules resulting either stabilization or disruption depending on the nature of the molecules. In our earlier communication, Hg2+ was known to disrupt the native structure of α-Cgn A leading to aggregation (Ansari, N.K., Rais, A. & Naeem, A. Methotrexate for Drug Repurposing as an Anti-Aggregatory Agent to Mercuric Treated α-Chymotrypsinogen-A. Protein J (2024). https://doi.org/10.1007/s10930-024-10187-z ). Accumulation of β-rich aggregates in the living system is found to be linked with copious number of disorders. Here, we have investigated the effect of varying concentration of doxorubicin (DOX) i.e. 0-100 µM on the preformed aggregates of α-Cgn A upon incubation with 120 µM Hg2+. The decrease in the intrinsic fluorescence and enzyme activity with respect to increase in the Hg2+ concentration substantiate the formation of aggregates. The DOX showed the dose dependent decrease in the ThT fluorescence, turbidity and RLS measurements endorsing the dissolution of aggregates which were consistent with red shift in ANS, confirming the breakdown of aggregates. The α-Cgn A has 30% α-helical content which decreases to 3% in presence of Hg2+. DOX increased the α-helicity to 28% confirming its anti-aggregatory potential. The SEM validates the formation of aggregates with Hg2+ and their dissolution upon incubation with the DOX. Hemolysis assay checked the cytotoxicity of α-Cgn A aggregates. Docking revealed that the DOX interacted Lys203, Cys201, Cys136, Ser159, Leu10, Trp207, Val137 and Thr134 of α-Cgn A through hydrophobic interactions and Gly133, Thr135 and Lys202 forms hydrogen bonds.

Transient control of lytic activity via a non-equilibrium chemical reaction system

The development of artificial non-equilibrium chemical reaction systems has recently attracted considerable attention as a new type of biomimetic. However, due to the lack of bioorthogonality, such reaction systems could not be linked to the regulation of any biological phenomena. Here, we have newly designed a non-equilibrium reaction system based on olefin metathesis to produce the Triton X-mimetic non-ionic amphiphile as a kinetic product. Using phospholipid vesicles encapsulating fluorescent dyes and red blood cells as cell models, we demonstrate that the developed chemical reaction system is applicable for transient control of the resulting lytic activity.

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.

Experimental and hypothetical appraisal on inhibition of glucose-induced glycation of bovine serum albumin by quercetin

BACKGROUND

The specificity of protein functions depends on its folding ability into a functional structure. Protein folding is an essential systemic phenomenon that prevents incorrect folding which could result in harmful aggregation. This harmful aggregation of proteins causes neurodegenerative diseases and systemic amyloidosis. Experimental and theoretical approaches were used in this study to explicate the probable mechanisms of action of quercetin in inhibition of glucose-induced glycation through estimations of percentage glycated protein, inhibited induced protein aggregation, and unoxidized bovine serum albumin thiol groups and assessments of molecular interactions of quercetin with the structures of bovine serum albumin, amyloid beta-peptide (1-42) and 3D amyloid-beta (1-42) fibrils retrieved from the protein databank ( http://www.rcsb.org ).

RESULTS

The results showed quercetin inhibited the formation of glycated protein, protein aggregation, and thiol oxidation in a concentration-dependent manner where 200 μg/ml showed the highest inhibition while 50 μg/ml depicted the least inhibition in all the studied assessments. From the docking analysis, it was observed that quercetin had a significantly higher binding affinities - 8.67 ± 0.09 kcal/mol, - 5.37 ± 0.05 kcal/mol and - 5.93 ± 0.13 kcal/mol for the bovine serum albumin, amyloid beta-peptide (1-42) and 3D amyloid-beta (1-42) fibrils respectively compared to the glucose, the inducer. Quercetin and glucose interacted with amino acid residues at the BSA subdomain IIA thus providing a clue that quercetin may impose its inhibition through the binding domain. Also, it is important to mention that the phytochemicals shared a similar interaction profile as that of glucose with the amyloid-beta.

CONCLUSIONS

These findings established the beneficial effects of quercetin as a potential agent that could alleviate hyperglycaemic-initiated disorders associated with elevated serum glucose levels.

Polymeric curcumin nanospheres for lysozyme aggregation inhibition, antibacterial, and wound healing applications

The present study reports highly stable polymeric nanoparticles comprising curcumin and polyvinylpyrrolidone, and then conjugated with gold nanoparticles, resulting in C-PVP and C-PVP-Au, respectively. The synthesized conjugates C-PVP and C-PVP-Au were investigated for amyloid aggregation inhibition activity, antimicrobial activity, and wound healing applications. The anti-amyloidogenic capacity of nanoconjugates were studied for model protein, hen egg-white lysozyme (HEWL). The ThT binding assay, fibril size measurement, and electron microscopy results revealed that conjugates suppress fibrillogenesis in HEWL. The highest amyloid inhibition activity obtained against C-PVP and C-PVP-Au was 31 μg.mL-1 and 30 μg.mL-1, respectively. The dissociation activity for amyloid aggregation was observed against Q-PVP and Q-PVP-Au at 29 μg.mL-1 and 27 μg.mL-1, respectively. The antibacterial studies show significant efficacy against Escherichia coli (E. coli) in the presence of C-PVP and C-PVP-Au. The substantial antibacterial potential of C-PVP@PVA and C-PVP-Au@PVA membranes shows promising wound healing applications. The PVA membranes with nanoparticles promote the antibacterial activity and wound healing activity in the Drosophila model. C-PVP-Au@PVA membrane healed the wound faster than the C-PVP@PVA, and it can be used for better results in wound healing. Thus, C-PVP-Au and C-PVP have higher bioavailability and stability and can act as multifunctional therapeutic agents for amyloid-related diseases and as wound healing agents. Graphical abstract C-PVP, and C-PVP-Au conjugates for inhibition of HEWL aggregation, antibacterial and wound healing activity.

Mechanism of the interaction of toxic SOD1 fibrils with two potent polyphenols: curcumin and quercetin

Amyotrophic lateral sclerosis (ALS) is a debilitating neurodegenerative disease commonly caused due to the aggregation of superoxide dismutase 1 (SOD1) protein. Finding inhibitors of SOD1 aggregation is of prime concern, but understanding the mechanistic action of inhibitors is equally important. Recent experiments found that two polyphenols, curcumin, and quercetin, have the ability to inhibit SOD1 aggregation. Quercetin was experimentally proven to break pre-formed fibrils into shorter segments, while curcumin did not significantly affect the pre-formed species. Here, we delve deeper into understanding the mechanism of action of quercetin and curcumin on pre-formed octameric fibrils of SOD1 (28PVKVWGSIKGL38: chains A-H) with the help of molecular dynamics (MD) simulations of a fibril docked polyphenol complex. Our results suggest that quercetin shows π-π stacking interaction with one of the key residues for toxic amyloid formation, Trp 32 of chains D, E, and F, and breaks the peptide chains G, and H from the rest of the fibril. On the other hand, curcumin binds to the hydrophobic amino acids of almost all the chains B-H and stabilizes the fibril rather than destabilizing it. Binding free energy calculations using MM/PBSA showed that curcumin binds more strongly to the SOD1 fibril due to greater van der Waals interactions compared to quercetin. These findings provide insights for the development of potential ALS treatments.

Antioxidant Polymers with Enhanced Neuroprotection Against Insulin Fibrillation

Lipoic acid (LA) and dihydrolipoic acid (DHLA) are well established antioxidants to scavenge reactive oxygen species (ROS). However, they are carboxylates with ≈4.7 pKa making them negatively charged at physiological pH (7.4) reducing their passive diffusion through cell membranes. LA is known to be capable of reducing protein fibrillation. Incorporation of LA and especially DHLA in polymer side chains are scarce. Herein, the first examples of the anti-amyloidogenic effect of LA and DHLA incorporated into the side-chain of a block copolymer with a water-soluble poly(polyethylene glycol methyl ether methacrylate) (PPEGMA) segment are presented. The resultant polymers show improved ROS scavenging activity and improved ability to reduce insulin fibrillation compared to free LA and DHLA. Furthermore, the resultant polymers are also capable of disintegrating preformed insulin firbrils. Interestingly, polymers with dihydro-lipoate moieties showed 93% free radical scavenging activity with 91% anti-fibrillating efficacies for insulin protein confirmed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and Thioflavin T (ThT) dye binding study, respectively. Further, the antioxidant polymers increase the cell viability against fibrillar insulin aggregates that may be involved in the etiology of several diseases. Overall, this work reveals that antioxidant polymer-based therapeutic agents can serve as a powerful modulation strategy for developing novel drugs in future against amyloid-related disorders.

Tuning the aggregation behavior of human insulin in the presence of luteolin: An in vitro and in silico approach

Protein misfolding and related formation of amyloid fibrils are associated with several conformational diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), prion diseases, and Diabetes mellitus, Type 2 (DM-II). Several molecules including antibiotics, polyphenols, flavonoids, anthraquinones, and other small molecules are implicated to modulate amyloid assembly. The stabilization of the native forms of the polypeptides and prevention of their misfolding and aggregation are of clinical and biotechnological importance. Among the natural flavonoids, luteolin is of great importance because of its therapeutic role against neuroinflammation. Herein, we have explored the inhibitory effect of luteolin (LUT) on aggregation of a model protein, human insulin (HI). To understand the molecular mechanism of the inhibition of aggregation of HI by LUT, we employed molecular simulation, UV-Vis, fluorescence, and circular dichroism (CD) spectroscopies along with the dynamic light scattering (DLS). The analysis of the tuning of the HI aggregation process by luteolin revealed that interaction of HI with LUT resulted in the decrease in binding of the various fluorescent dyes, such as thioflavin T (ThT) and 8-anilinonaphthalene-1-sulfonic acid (ANS) to this protein. Retention of the native-like CD spectra and resistance to the aggregation in the presence of LUT has confirmed the aggregation inhibitory potential of LUT. The maximum inhibitory effect was found at the protein-to-drug ratio of 1:12, and no significant change was observed beyond this concentration.

A computational strategy for therapeutic development against superoxide dismutase (SOD1) amyloid formation: effect of polyphenols on the various events in the aggregation pathway

Pathology of superoxide dismutase 1 (SOD1) aggregation is linked to a neurodegenerative disease known as amyotrophic lateral sclerosis (ALS). Without suitable post-translational modifications (PTMs), the protein structure tends to become aggregation-prone. Understanding the role of PTMs and targeting the aggregation-prone SOD1 with small molecules can be used to design a strategy to inhibit its aggregation. Microsecond long molecular dynamics (MD) simulations followed by free energy surface (FES) analyses show that the loss of structure in the apo monomer happens locally and stepwise. Removing the disulfide bond from apoprotein leads to further instability in the zinc-binding loop, giving rise to non-native protein conformations. Further, it was found that these non-native conformations have a higher propensity to form a non-native dimer. We chose three structurally similar polyphenols based on their binding energies and investigated their impact on SOD1 aggregation kinetics. MD simulations of apo-SOD1^SH/corkscrew fibril-polyphenol complexes were also carried out. The effect of polyphenols was seen on fibril elongation as well. Based on the experiments and MD simulation results, it can be inferred that the choice of inhibitors is influenced not only by the binding energy but also by dimer interface stabilization, the proclivity to form non-native dimers, the propensity to break fibrils, and the propensity to decrease the rate of elongation. The polyphenols with 3' and 4' hydroxyl groups are better inhibitors of SOD1 aggregation.

The Strategies of Development of New Non-Toxic Inhibitors of Amyloid Formation

In recent years, due to the aging of the population and the development of diagnostic medicine, the number of identified diseases associated with the accumulation of amyloid proteins has increased. Some of these proteins are known to cause a number of degenerative diseases in humans, such as amyloid-beta (Aβ) in Alzheimer's disease (AD), α-synuclein in Parkinson's disease (PD), and insulin and its analogues in insulin-derived amyloidosis. In this regard, it is important to develop strategies for the search and development of effective inhibitors of amyloid formation. Many studies have been carried out aimed at elucidating the mechanisms of amyloid aggregation of proteins and peptides. This review focuses on three amyloidogenic peptides and proteins-Aβ, α-synuclein, and insulin-for which we will consider amyloid fibril formation mechanisms and analyze existing and prospective strategies for the development of effective and non-toxic inhibitors of amyloid formation. The development of non-toxic inhibitors of amyloid will allow them to be used more effectively for the treatment of diseases associated with amyloid.

Mesalazine Inhibits Amyloid Formation and Destabilizes Pre-formed Amyloid Fibrils in the Human Insulin

Amyloid formation due to protein aggregation is associated with several amyloid diseases (amyloidosis). The use of small organic ligands as inhibitors of protein aggregation is an attractive strategy for the treatment of these diseases. In the present study, we evaluated the in vitro inhibitory and destabilizing effects of Mesalazine on human insulin fibrillation. To induce fibrillation, human insulin was incubated in 50 mM glycine buffer (pH 2.0) at 50 °C. The effect of Mesalazine on insulin amyloid aggregation was studied using spectroscopic, imaging, and computational approaches. Based on the results, the Mesalazine in a concentration-dependent manner (different ratios (1:0.1, 1:0.5, 1:1, and 1:5) of the insulin to Mesalazine) prevented the formation of amyloid fibrils and destabilized pre-formed fibrils. In addition, our molecular docking study confirmed the binding of Mesalazine to insulin through hydrogen bonds and hydrophobic interactions. Our findings suggest that Mesalazine may have therapeutic potential in the prevention of insulin amyloidosis and localized amyloidosis.

Dietary anthocyanins inhibit insulin fibril formation and cytotoxicity in 3T3-L1 preadipocytes

Insulin fibril formation decreases the effectiveness of insulin therapy and causes amyloidosis in diabetes. Studies suggest that phytochemicals are capable of inhibiting fibril formation. Herein, we investigated the inhibitory effects of anthocyanins, including cyanidin, cyanidin-3-glucoside (C3G), cyanidin-3-rutinoside (C3R), malvidin, and malvidin-3-glucoside (M3G) on fibril formation. Our results revealed that anthocyanins (50-200 μM) significantly reduced the formation of insulin fibrils by increasing lag times and decreasing ThT fluorescence at the plateau phase. These findings were confirmed by TEM images, which showed reduced fibril length and number. Furthermore, FTIR analysis indicated that anthocyanins reduced the secondary structure transition of insulin from α-helix to β-sheet. Anthocyanins interacted with monomeric insulin (residues B8-B30) via H-bonds, van der Waals, and hydrophobic interactions, covering the fibril-prone segments of insulin (residues B12-B17). Based on the structure-activity analysis, the presence of glycosides and hydroxyl groups on phenyl rings increased intermolecular interaction, mediating the inhibitory effect of anthocyanins on fibril formation in the order of malvidin < cyanidin < M3G < C3G < C3R. Moreover, anthocyanins formed H-bonds with preformed insulin fibrils, except for malvidin. In preadipocytes, C3R, C3G, and cyanidin attenuated insulin fibril-induced cytotoxicity. In conclusion, anthocyanins are effective inhibitors of insulin fibril formation and cytotoxicity.

Tuning the surface charge of phospholipid bilayers inhibits insulin fibrilization

The interactions between proteins and materials, in particular lipid bilayers, have been studied extensively for their relevance in diseases and for the formulation of protein-based therapeutics and vaccines. However, the precise rules by which material properties induce favorable or unfavorable structural states in biomolecules are incompletely understood, and as a result, the rational design of materials remains challenging. Here, we investigated the influence of lipid bilayers (in the form of small unilamellar vesicles) on the formation of insulin amyloid fibrils using a fibril-specific assay (thioflavin T), polyacrylamide gel electrophoresis, and circular dichroism spectroscopy. Lipid bilayers composed of equal mixtures of cationic and anionic lipids effectively inhibited fibril formation and stabilized insulin in its native conformation. However, other lipid bilayer compositions failed to inhibit fibril formation or even destabilized insulin, exacerbating fibrilization and/or non-amyloid aggregation. Our findings suggest that electrostatic interactions with lipid bilayers can play a critical role in stabilizing or destabilizing insulin, and preventing the conversion of insulin to its amyloidogenic, disease-associated state.

Amyloid Fibrillation of Insulin: Amelioration Strategies and Implications for Translation

Insulin is a therapeutically relevant molecule with use in treating diabetes patients. Unfortunately, it undergoes a range of untoward and often unpredictable physical transformations due to alterations in its biochemical environment, including pH, ionic strength, temperature, agitation, and exposure to hydrophobic surfaces. The transformations are prevalent in its physiologically active monomeric form, while the zinc cation-coordinated hexamer, although physiologically inactive, is stable and less susceptible to fibrillation. The resultant molecular reconfiguration, including unfolding, misfolding, and hydrophobic interactions, often results in agglomeration, amyloid fibrillogenesis, and precipitation. As a result, a part of the dose is lost, causing a compromised therapeutic efficacy. Besides, the amyloid fibrils form insoluble deposits, trigger immunologic reactions, and harbor cytotoxic potential. The physical transformations also hold back a successful translation of non-parenteral insulin formulations, in addition to challenges related to encapsulation, chemical modification, purification, storage, and dosing. This review revisits the mechanisms and challenges that drive such physical transformations in insulin, with an emphasis on the observed amyloid fibrillation, and presents a critique of the current amelioration strategies before prioritizing some future research objectives.

Impact of the Flavonoid Quercetin on β-Amyloid Aggregation Revealed by Intrinsic Fluorescence

We report the effects of quercetin, a flavonoid present in the human diet, on early stage beta-amyloid (Aβ) aggregation, a seminal event in Alzheimer's disease. Molecular level changes in Aβ arrangements are monitored by time-resolved emission spectral (TRES) measurements of the fluorescence of Aβ's single tyrosine intrinsic fluorophore (Tyr). The results suggest that quercetin binds β-amyloid oligomers at early stages of their aggregation, which leads to the formation of modified oligomers and hinders the creation of β-sheet structures, potentially preventing the onset of Alzheimer's disease.

Orange G is a potential inhibitor of human insulin amyloid fibrillation and can be used as a probe to study mechanism of amyloid fibrillation and its inhibition

The extracellular insoluble deposits of highly ordered cross-β-structure-containing amyloid fibrils form the pathological basis for protein misfolding diseases. As amyloid fibrils are cytotoxic, inhibition of the process is a therapeutic strategy. Several small molecules have been identified and used as fibrillation inhibitors in the recent past. In this work, we investigate the effect of Orange G on insulin amyloid formation using fluorescence-based assays and negative-stain electron microscopy (EM). We show that Orange G effectively attenuates nucleation, thereby inhibiting amyloid fibrillation in a dose-dependent manner. Fluorescence quenching titrations of Orange G showed a reasonably strong binding affinity to native insulin. Binding isotherm measurements revealed the binding of Orange G to pre-formed insulin fibrils too, indicating that Orange G likely binds and stabilizes the mature fibrils and prevents the release of toxic oligomers which could be potential nuclei or templates for further fibrillation. Molecular docking of Orange G with native insulin and amyloid-like peptide structures were also carried out to analyse the contributing interactions and binding free energy. The findings of our study emphasize the use of Orange G as a molecular probe to identify and design inhibitors of amyloid fibrillation and to investigate the structural and toxic mechanisms underlying amyloid formation.

Mechanistic insight into inhibition of amyloid fibrillation of human serum albumin by Vildagliptin

Protein aggregation leads to several human pathologies such as Alzheimer's disease (AD), type 2 diabetes (T2D), Parkinson's disease (PD), etc. Due to the overlap in the mechanisms of type 2 diabetes and brain disorders, common effective pharmacological interventions to treat both T2D and AD is under extensive research. Therefore, major aim of research is to repurpose already established treatment of diabetes to cure AD as well. This study evaluates mechanistic insight into anti-amyloidogenic potential of anti-diabetic drug Vildagliptin (VLD) on human serum albumin fibrillation (HSA) by using biophysical, calorimetric, imaging techniques along with hemolytic assay. Dynamic light scattering (DLS) and Rayleigh light scattering (RLS) results showed presence of few small-sized aggregates in the presence of VLD which are formed by deaccelerating the amyloidogenesis as shown by thioflavin T (ThT) fluorescence and Congo red (CR) binding assay. Further, Isothermal titration calorimetry (ITC), steady state fluorescence quenching, molecular docking results revealed that VLD form complex with amyloid facilitating state of HSA and consequently mask the hydrophobic residues involved in amyloidogenesis as evident from decrease in ANS fluorescence. Differential scanning calorimetry (DSC) results confirm that VLD stabilizes the amyloid facilitating state of HSA. In addition, SEM images demonstrated that VLD alleviates the hemolytic effect induced by fibrils of HSA. This study reports VLD as a potential inhibitor of amyloid fibrillation and provides promising results to repurpose VLD as a drug candidate for the cure of Alzheimer's diseases along with diabetes.

Quercetin binding accelerates prion fibrillation into proteinase sensitive and loosely structured amyloids

Amyloidoses are caused by the deposition of amyloid fibrils ascribed to protein misfolding. In this study, we examined the antiamyloidogenic and antioxidative activities of quercetin, a plant flavonol from the flavonoid group of polyphenols, on mouse prion protein (moPrP) with biophysical approaches. As the results show, quercetin binds to the C-terminal region of moPrP, and quercetin binding does not affect the structure of moPrP. However, quercetin binding accelerates moPrP fibrillation and changes the structure of moPrP fibrils. Unlike typical prion fibrils, quercetin-bound fibrils are sensitive to proteinase K and are loosely structured. Moreover, due to high antioxidant activity of flavonoid, quercetin-bound fibrils lack imbalance of free radicals and, therefore, they are nontoxic towards neuroblastoma cells. The quercetin shows its uniqueness from typical antiamyloidogenic drugs which either suppress the development of amyloid or eliminate formed amyloids. Quercetin binding converts moPrP into protease-sensitive and non-cytotoxic fibrils. This work provides a powerful resolution in the advancement of antiamyloidogenic treatment.

Experimental and theoretical studies on the anti-amyloidogenic and destabilizing effects of pyrogallol against human insulin protein

One of the major problems caused by repeated subcutaneous insulin injections in patients with diabetes is insulin amyloidosis. Understanding the molecular mechanism of amyloid fibril formation of insulin and finding effective compounds to inhibit or eliminate them is very important, and extensive research has been done on it. In this study, the anti-amyloidogenic and destabilizing effects of the pyrogallol, as a phenolic compound, on human insulin protein were investigated by CR absorbance, ThT and ANS fluorescence, FTIR spectroscopy, and atomic force microscopy. According to the obtained results, the formation of amyloid fibrils at pH 2.0 and 50°C was confirmed by CR, ThT, ANS, and FTIR assays. Microscopic images also showed the twisted and long structures of amyloid fibrils. Simultaneous incubation of the protein with pyrogallol at different concentrations reduced the intensities of CR, ThT, and ANS in a dose-dependent manner, and no trace of fibrillar structures was observed in the microscopic images. FTIR spectroscopy also showed that the position of the amide I band in the spectrum of samples containing pyrogallol was shifted. Based on the findings of this study, it can be concluded that pyrogallol can be effective in preventing and suppressing human insulin amyloid fibrils. PRACTICAL APPLICATIONS: In recent years, finding a strategy for the treatment of amyloid diseases has been considered by many researchers. Targeting protein aggregates by small organic molecules such as polyphenols is one of the most desirable and effective strategies to prevent and improve amyloid disease, which has received much attention in recent years. 1,2,3-Trihydroxybenzene, commonly known as pyrogallol (Py), is a phenolic compound like other natural polyphenols that are present in human food sources, including fruits and vegetables, and a variety of edible and medicinal plants. So far, many beneficial activities for pyrogallol such as anti-cancer, antioxidant, antibacterial, antiviral, and antifungal have been reported in various studies. Since various studies have shown that natural polyphenols have special properties to prevent amyloid disease, the present study could be useful in advancing the design purposes of new anti-amyloid drugs in the future.

Molecular Aspects of Insulin Aggregation and Various Therapeutic Interventions

Protein aggregation leading to the formation of amyloid fibrils has various adverse effects on human health ranging from fatigue and numbness to organ failure and death in extreme cases. Insulin, a peptide hormone commonly used to treat diabetes, undergoes aggregation at the site of repeated injections in diabetic patients as well as during its industrial production and transport. The reduced bioavailability of insulin due to aggregation hinders the proper control of glucose levels in diabetic patients. Thus, it is necessary to develop rational approaches for inhibiting insulin aggregation, which in turn requires a detailed understanding of the mechanism of fibrillation. Given the relative simplicity of insulin and ease of access, insulin has also served as a model system for studying amyloids. Approaches to inhibit insulin aggregation have included the use of natural molecules, synthetic peptides or small molecules, and bacterial chaperone machinery. This review focuses on insulin aggregation with an emphasis on its mechanism, the structural features of insulin fibrils, and the reported inhibitors that act at different stages in the aggregation pathway. We discuss molecules that can serve as leads for improved inhibitors for use in commercial insulin formulations. We also discuss the aggregation propensity of fast- and slow-acting insulin biosimilars, commonly administered to diabetic patients. The development of better insulin aggregation inhibitors and insights into their mechanism of action will not only aid diabetic therapies, but also enhance our knowledge of protein amyloidosis.

Strategies for interference of insulin fibrillogenesis: challenges and advances

The discovery of insulin came up with very high hopes for diabetic patients. In the year 2021, the world celebrated the 100 th anniversary of the discovery of this vital hormone. However, external use of insulin is highly affected by its aggregating tendency that occurs during its manufacturing, transportation, and improper handling which ultimately leads its pharmaceutically and biologically ineffective form. In this review, we aim to discuss the various approaches used for decelerating insulin aggregation which results in the enhancement of its overall structural stability and usage. The approaches that are discussed are broadly classified as either a measure through excipient additions or by intrinsic modifications in the insulin native structure.

Inhibition of Islet Amyloid Polypeptide Fibrillation by Structurally Diverse Phenolic Compounds and Fibril Disaggregation Potential of Rutin and Quercetin

The influence of 12 food-derived phenolic compounds on islet amyloid polypeptide (IAPP) fibrillation was investigated. Results from thioflavin T assay demonstrated that gallic acid, caffeic acid, and rutin and its aglycone, quercetin, inhibited IAPP fibrillation at 1:0.5, 1:1, and 1:2 IAPP-phenolic molar ratios. Circular dichroism and dynamic light scattering at the 1:1 IAPP-phenolic ratio confirmed the inhibition of fibril formation. Rutin and quercetin increased the lag time by 90 and 6%, and the relative α-helix content by 63 and 48%, respectively. Gallic acid decreased the elongation rate by 30%, whereas caffeic acid decreased the maximum fluorescence intensity by 65%. Furthermore, fluorescence microscopy and transmission electron microscopy (TEM) showed IAPP fibril morphologies indicative of fibrillation reduction by the compounds. Molecular docking and TEM showed that rutin and quercetin disaggregated preformed IAPP fibrils potentially through fibrillar-monomeric equilibrium shifts. These findings demonstrate important structural features of phenolic compounds for disaggregating IAPP fibrils or inhibiting their formation.

Anti-amyloidogenic property of gold nanoparticle decorated quercetin polymer nanorods in pH and temperature induced aggregation of lysozyme

Quercetin is an abundant plant polyphenol effective against several diseases due to its antioxidant and anti-inflammatory activity. Herein, we report novel polymeric quercetin nanorods and the former decorated with gold nanoparticles for the first time. The prepared conjugates quercetin-polyvinylpyrrolidone (Q-PVP) and quercetin-polyvinylpyrrolidone-gold nanoparticles (Q-PVP-Au) were characterized by UV-visible spectroscopy, Fourier transform infrared, dynamic light scattering, and zeta potential measurements. The surface morphology of conjugates was analyzed by field emission scanning electron microscopy. These conjugates exhibit harmonized rod-like morphology with a narrow size distribution. Furthermore, the quercetin conjugates with nanorod morphology exhibited enhanced and prolonged drug release over a long period. The synthesized conjugates were investigated for lysozyme aggregation kinetics. ThT binding assay, fibril size measurement, and electron microscopy results revealed that conjugates could suppress fibrillogenesis in lysozyme. The highest amyloid aggregation inhibition activity (IC₅₀) was obtained against Q-PVP and Q-PVP-Au at 32 μg mL⁻¹ and 30 μg mL⁻¹ respectively. The amyloid aggregate disintegration activity (DC₅₀) obtained against Q-PVP and Q-PVP-Au was 27 μg mL⁻¹ and 29 μg mL⁻¹ respectively. The present quercetin conjugates exhibit enhanced bioavailability and stability. They were potent inhibitors of lysozyme aggregation that may find applications as a therapeutic agent in neurological diseases like Alzheimer's and Parkinson's.

Q-PVP, and Q-PVP-Au conjugates for inhibition of HEWL aggregation.

Fatty Acid-Based Polymeric Micelles to Ameliorate Amyloidogenic Disorders

To develop anti-amyloidogenic inhibitors for ameliorating the treatment of diabetes, herein, we have synthesized amphiphilic block copolymers with side-chain fatty acid (FA) moieties via reversible addition fragmentation chain-transfer (RAFT) polymerization....

Modulating Insulin Aggregation with Charge Variable Cholic Acid-Derived Polymers

To understand the effect of cholic acid (CA)-based charge variable polymeric architectures on modulating the insulin aggregation process, herein, we have designed side-chain cholate-containing charge variable polymers. Three different types of copolymers from 2-(methacryloyloxy)ethyl cholate with anionic or cationic or neutral units have been synthesized by reversible addition-fragmentation chain transfer polymerization. The effects of these copolymers on the insulin fibrillation process was studied by multiple biophysical approaches including different types of spectroscopic and microscopic analyses. Interestingly, the CA-based cationic polymer (CP-10) was observed to inhibit the insulin fibrillation process in a dose-dependent manner and to act as an effective anti-amyloidogenic agent. Corresponding anionic (AP-10) and neutral (NP-10) copolymers with cholate pendants remained insignificant in controlling the aggregation process. Tyrosine fluorescence assays and Nile red fluorescence measurements demonstrate the role of hydrophobic interaction to explain the inhibitory potencies of CP-10. Furthermore, circular dichroism spectroscopic measurements were carried out to explore the secondary structural changes of insulin fibrils in the presence of cationic polymers with and without cholate moieties. Isothermal titration calorimetry measurements revealed the involvement of electrostatic polar interaction between the CA-based cationic polymer and insulin at different stages of fibrillation. Overall, this work demonstrates the efficacy of the CA-based cationic polymer in controlling the insulin aggregation process and provides a novel dimension to the studies on protein aggregation.

Sulfated polysaccharide ascophyllan prevents amyloid fibril formation of human insulin and inhibits amyloid-induced hemolysis and cytotoxicity in PC12 cells

We found that ascophyllan significantly inhibited the fibrillation of human insulin and was the most effective among the sulfated polysaccharides tested. Gel-filtration analysis suggested that ascophyllan was capable of forming a complex with insulin through a weak interaction. Secondary structure transition from native α-helix to β-sheet predominant structure of insulin under the fibrillation conditions was suppressed in the presence of ascophyllan. Interestingly, ascophyllan attenuated insulin fibril-induced hemolysis of human erythrocytes. Moreover, ascophyllan attenuated insulin amyloid-induced cytotoxicity on rat pheochromocytoma PC12 cells and reduced the level of intracellular reactive oxygen species. This is the first report indicating that a sulfated polysaccharide, ascophyllan, can suppress the insulin amyloid fibril formation and inhibit the fibril-induced detrimental bioactivities.

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.

Fruit juices are effective anti-amyloidogenic agents

Amyloid fibril formation has been associated with a great variety of human diseases. Fruits contain different important bioactive molecules without causing various undesirable side effects, which are necessary for disease prevention and treatment. Here we report that various fruit juices inhibited the amyloid formation by α-chymotrypsin in aqueous ethanol at pH 7.0. Turbidity measurements, total phenolic content determination, as well as Congo red binding assay were used to analyse the inhibition of amyloid fibril formation. We showed that the black currant juice possessed the strongest inhibitory potential against protein aggregation because it contains the most polyphenolic compounds too and its effect was concentration dependent. Interestingly, white grapes, figs and bananas are relatively effective although they are not high in polyphenols. These fruits are typically sweet. The sugars in them also contribute to their effectiveness. Eating black currant can reduce the likelihood of formation of amyloid fibrils.

Prion-derived tetrapeptide stabilizes thermolabile insulin via conformational trapping

Unfolding followed by fibrillation of insulin even in the presence of various excipients grappled with restricted clinical application. Thus, there is an unmet need for better thermostable, nontoxic molecules to preserve bioactive insulin under varying physiochemical perturbations. In search of cross-amyloid inhibitors, prion-derived tetrapeptide library screening reveals a consensus V(X)YR motif for potential inhibition of insulin fibrillation. A tetrapeptide VYYR, isosequential to the β2-strand of prion, effectively suppresses heat- and storage-induced insulin fibrillation and maintains insulin in a thermostable bioactive form conferring adequate glycemic control in mouse models of diabetes and impedes insulin amyloidoma formation. Besides elucidating the critical insulin-IS1 interaction (R4 of IS1 to the N24 insulin B-chain) by nuclear magnetic resonance spectroscopy, we further demonstrated non-canonical dimer-mediated conformational trapping mechanism for insulin stabilization. In this study, structural characterization and preclinical validation introduce a class of tetrapeptide toward developing thermostable therapeutically relevant insulin formulations.

Synthesis and Evaluation of Arylamides with Hydrophobic Side Chains for Insulin Aggregation Inhibition

Insulin, a peptide hormone, forms fibrils under aberrant physiological conditions leading to a reduction in its biological activity. To ameliorate insulin aggregation, we have synthesized a small library of oligopyridylamide foldamers decorated with different combination of hydrophobic side chains. Screening of these compounds for insulin aggregation inhibition using a Thioflavin-T assay resulted in the identification of a few hit molecules. The best hit molecule, BPAD2 inhibited insulin aggregation with an IC₅₀ value of 0.9 μM. Mechanistic analyses suggested that BPAD2 inhibited secondary nucleation and elongation processes during aggregation. The hit molecules worked in a mechanistically distinct manner, thereby underlining the importance of structure-activity relationship studies in obtaining a molecular understanding of protein aggregation.

Valorization of Apple Peels through the Study of the Effects on the Amyloid Aggregation Process of κ-Casein

Waste valorization represents one of the main social challenges when promoting a circular economy and environmental sustainability. Here, we evaluated the effect of the polyphenols extracted from apple peels, normally disposed of as waste, on the amyloid aggregation process of κ-casein from bovine milk, a well-used amyloidogenic model system. The effect of the apple peel extract on protein aggregation was examined using a thioflavin T fluorescence assay, Congo red binding assay, circular dichroism, light scattering, and atomic force microscopy. We found that the phenolic extract from the peel of apples of the cultivar “Fuji”, cultivated in Sicily (Caltavuturo, Italy), inhibited κ-casein fibril formation in a dose-dependent way. In particular, we found that the extract significantly reduced the protein aggregation rate and inhibited the secondary structure reorganization that accompanies κ-casein amyloid formation. Protein-aggregated species resulting from the incubation of κ-casein in the presence of polyphenols under amyloid aggregation conditions were reduced in number and different in morphology.

Identifying Insulin Fibril Conformational Differences by Thioflavin-T Binding Characteristics

Amyloidogenic protein aggregation into highly structured fibrils is linked to more than 30 amyloidoses, including several neurodegenerative disorders. Despite significant progress in trying to understand the process of amyloid formation, there is still no cure or effective treatment available. A number of studies involving potential anti-amyloid compounds rely on the use of a fluorescent probe—thioflavin-T—to track the appearance, growth, or disassembly of these cytotoxic aggregates. Despite the wide application of this dye molecule, its interaction with amyloid fibrils is still poorly understood. Recent reports have shown it may possess distinct binding modes and fluorescence intensities based on the conformation of the examined fibrils. In this work, we generate insulin fibrils under four different conditions and attempt to identify distinct conformations using both classic methods, such as atomic force microscopy and Fourier-transform infrared spectroscopy, as well as their ThT binding ability and fluorescence quantum yield. We show that there is a significant variance of ThT fluorescence quantum yields, excitation/emission maxima positions, and binding modes between distinct insulin fibril conformations.

Dual functional liposomes carrying antioxidants against tau hyperphosphorylation and apoptosis of neurons

Quercetin (QU) and rosmarinic acid (RA) were loaded in phosphatidic acid-liposomes (QU/RA-PA-liposomes) with surface apolipoprotein E (ApoE) using a process of thin-film hydration, followed by covalent crosslinking to activate biological pathways for penetrating the blood-brain barrier (BBB) and redeeming the neuronal apoptosis from attack of β-amyloid 1-42 (Aβ1-42) and neurofibrillary tangles. The conjugation of liposomes with PA improved the activity of QU and RA against neurotoxicity of Aβ1-42. The fluorescent images of brain capillaries revealed that surface modification with ApoE improved the permeation ability of QU/RA-PA-ApoE-liposomes across the BBB. In addition, the highest therapeutic efficacy was obtained in the case of QU/RA-PA-ApoE-liposomes, compared to other QU/RA formulations studied using in vivo Aβ1-42-insulted rats mimicking Alzheimer's disease (AD). The cellular and molecular evidence from AD rats included the decrease in Aβ1-42 plaque formation and interleukin-6 secretion, increase in the neuronal count in Nissl staining, and reduction in the expression of phosphorylated extracellular signal-regulated kinase 1/2, c-Jun N-terminal kinase, p38 kinase and tau protein at serine 202 as well as caspase-3. The use of PA-ApoE-liposomes as a dual targeting formulation enhances the QU and RA ability to infiltrate the BBB, docks Aβ1-42 plaques and can be a potent approach to rescue degenerated neurons from AD.

Flavonoids with Vicinal Hydroxyl Groups Inhibit Human Calcitonin Amyloid Formation

Human calcitonin (hCT) is a 32-residue peptide hormone that can aggregate into amyloid fibrils and cause cellular toxicity. In this study, we investigated the inhibition effects of a group of polyphenolic molecules on hCT amyloid formation. Our results suggest that the gallate moiety in epigallocatechin-3-gallate (EGCG), a well-recognized amyloid inhibitor, is not critical for its inhibition function in the hCT amyloid formation. Our results demonstrate that flavonoid compounds, such as myricetin, quercetin, and baicalein, that contain vicinal hydroxyl groups on the phenyl ring effectively prevent hCT fibrillization. This structural feature may also be applied to non-flavonoid polyphenolic inhibitors. Moreover, our results indicate a plausible mechanistic role of these vicinal hydroxyl groups which might include the oxidation to form a quinone and the subsequent covalent linkage with amino acid residues such as lysine or histidine in hCT. This may further disrupt the crucial electrostatic and aromatic interactions involved in the process of hCT amyloid fibril formation. The inhibition activity of the polyphenolic compounds against hCT fibril formation may likely be attributed to a combination of factors such as covalent linkage formation, aromatic stacking, and hydrogen bonding interactions.

Potential Role of Natural Polyphenols against Protein Aggregation Toxicity: In Vitro, In Vivo, and Clinical Studies

One of the main features of neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease is the amyloidogenic behavior of disease-specific proteins including amyloid β, tau, α-synuclein, and mutant Huntingtin which participate in the formation, accumulation, and deposition of toxic misfolded aggregates. Consequently, these proteins not only associated with the progress of their respective neurodegenerative pathologies but also qualify as disease-specific biomarkers. The aim of using natural polyphenols is to target amyloid-dependent proteopathies by decreasing free radical damage and inhibiting and dissolving amyloid fibrils. We explore the effectiveness of the polyphenols epigallocatechin-3-gallate, oleuropein aglycone, and quercetin on their ability to inhibit aggregation of amyloid β, tau, and α-synuclein and mitigate other pathological features for Alzheimer's disease and Parkinson's disease. The analysis was carried from in vitro and cell line studies to animal models and clinical trials. This Review describes the use of phytochemical compounds as prophylactic agents for Alzheimer's disease, Parkinson's disease, and other proteopathies.

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.

Anti-aggregation effect of Ascorbic Acid and Quercetin on aggregated Bovine Serum Albumin Induced by Dithiothreitol: Comparison of Turbidity and Soluble Protein Fraction Methods

Studies on the anti-aggregation of dithiothreitol (DTT) induced - protein is generally determined by the fraction soluble (non-aggregated) protein. While the turbidity method is commonly used in studies of anti-aggregation, in which protein is induced by heat, in this study, both methods are compared in observing the anti-aggregation activity of ascorbic acid and quercetin toward bovine serum albumin induced by DTT. The DTT is a reducing agent for protein disulfide bonds and capable of inducing protein aggregation at physiological pH and temperature. The work was performed by the formation of Bovine Serum Albumin (BSA) aggregates induced by DTT under physiological conditions, which are pH 7.4 and 37°C. The aggregated protein profile was observed using the turbidity method at the end of incubation and measuring the difference of concentration between the fraction of soluble protein before and after incubation. The measurement was carried out using a spectrophotometer UV-Vis. The results indicate that both methods show similar inhibition profiles. The potential inhibition of ascorbic acid (AA) toward BSA protein aggregation induced by DTT increased along with incubation time. While quercetin shows the highest inhibition at 12 hours but decreased at 18 hours, this study reveals that both methods can observe the anti-aggregation activity of ascorbic acid and quercetin.

Quercetin and Baicalein Act as Potent Antiamyloidogenic and Fibril Destabilizing Agents for SOD1 Fibrils

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that has been associated with the deposition of aggregates of superoxide dismutase 1 (SOD1). Effective therapeutics against SOD1 fibrillation is still an area of active research. Herein, we demonstrate the potential of two naturally occurring flavonoids (quercetin and baicalein) to inhibit fibrillation of wild-type SOD1 with the aid of a series of biophysical techniques. Our seeding experiments reveal that both of these flavonoids significantly affect the fibril elongation. Interestingly, our ThT binding assay, TEM, and SDS-PAGE experiments suggest that these flavonoids also disintegrate the fibrils into shorter fragments but do not completely depolymerize them into monomers. Binding parameters obtained from the analysis of UV-vis spectra suggest that these flavonoids bind moderately to native SOD1 dimer and have different binding sites. Docking of these flavonoids with a non-native monomer, non-native trimer, and oligomer derived from the 11-residue segment of SOD1 indicates that both quercetin and baicalein can bind to these species and thus can arrest the elongation of fibrils by blocking the fibrillar core regions on the intermediate species formed during aggregation of SOD1. MTT assay data revealed that both the flavonoids reduced the cytotoxicity of SOD1 fibrils. Experimental data also show the antiamyloidogenic potential of both flavonoids against A4V SOD1 mutant fibrillation. Thus, our findings may provide a direction for designing effective therapeutic agents against ALS which can act as promising antiamyloidogenic and fibril destabilizing agents.

Probing the Nongeneralized Amyloid Inhibitory Mechanism of Hydrophobic Chaperone

Increasing prevalence of protein misfolding disorders urges the search for effective therapies. Although several antiaggregation molecules have been identified, their molecular process of aggregation and clinical trials are underway. The present study is focused on the mechanism through which phenyl butyrate (PB), a chemical chaperone, triggers inhibition of human serum albumin (HSA) fibrillation. Turbidity and Rayleigh light scattering (RLS) measurements reveal the marked presence of aggregates in HSA that were confirmed as amyloid fibrils by thioflavin T (ThT) and Congo red (CR) and were subsequently inhibited by PB in a dose dependent manner. ThT fluorescence kinetics reveals a decrease in the apparent rate constant, K_app, in the presence of PB without triggering a lag phase in HSA suggesting PB's interference with the elongation phase. Dynamic light scattering (DLS) results display a reduction in the aggregate size in the presence of PB. Isothermal titration calorimetry (ITC) data reveals strong binding of PB at site II both at 25 °C (K_b ≈ 1.94 × 10⁵ M^-1) and 65 °C (K_b ≈ 2.90 × 10⁴ M^-1), mediated by hydrogen bonding. Overall, our finding establishes that PB stabilizes partially unfolded HSA molecules through hydrogen bonding, thereby preventing establishment of hydrogen bonds between them and hindering their progression into amyloid fibrils. This is in contrast to its chaperone effect manifested with other proteins.

Inhibitory effect of coumarin and its analogs on insulin fibrillation /cytotoxicity is depend on oligomerization states of the protein

Looking through a historical lens, attention to the stabilization of pharmaceutical proteins/peptides has been dramatically increased. Human insulin is the most challenging and the most widely used pharmaceutical protein in the world. In this study, the protein and coumarin as a plant-derived phenolic compound and two coumarin analogs with different moieties were investigated to evaluate the protein fibrillation and cytotoxicity. The obtained data showed that with a change in environmental pH, the behavior of the compounds on the process of insulin fibrillation will be changed completely. Coumarin (C1) and its hydrophobic analog, 7-methyl coumarin (C2), in an acidic environment, inhibit insulin fibrillation, change the oligomerization state of insulin and produce fibrils with notable lateral interactions with low cytotoxicity. However, negatively-charged 3-trifluoromethyl coumarin (C3) without significant changes in insulin structure and by altering the oligomerization state of the protein, slightly accelerates hormone fibrillation. Also, the compounds showed a disulfide protecting role during protein aggregation. Regarding the toxicity of the fibrils, it was observed that in addition to the secondary structures of proteinous fibrils, the ability to destroy the cell membrane is also related to the length of the fibrils and their degree of lateral interactions. By and large, this work can be useful in finding a better formulation for bio-pharmaceutical macro-molecules.

The effect of the applied compounds on insulin fibrillation at two pHs. By and large, the compounds through changing the oligomerization states and altering structure integrity of insulin can govern the fibrillation process.

Insulin fibrillation: toward strategies for attenuating the process

The environmental factors affecting the rate of insulin fibrillation. The factors are representative.

Amyloidophilic Molecule Interactions on the Surface of Insulin Fibrils: Cooperative Binding and Fluorescence Quenching

Protein aggregation into insoluble fibrillar aggregates is linked to several neurodegenerative disorders, such as Alzheimer’s or Parkinson’s disease. Commonly used methods to study aggregation inhibition or fibril destabilization by potential drugs include spectroscopic measurements of amyloidophilic dye molecule fluorescence or absorbance changes. In this work we show the cross-interactions of five different dye molecules on the surface of insulin amyloid fibrils, resulting in cooperative binding and fluorescence quenching.

Catanionic nanocarriers as a potential vehicle for insulin delivery

Diabetes is a disease that affects millions of people in the World, constituting a global problem. Patients are administered insulin subcutaneous injections, resulting in high costs and frequent infections in the injection site. A possible solution to this problem may be the use of nanotechnology. Nanotransporters can act as specific release systems able to overcome the current limitations to drug delivery. Liposomes and vesicles can deliver drugs directly and efficiently to the site of action, decreasing toxicity and adverse effects. In previous studies, we demonstrated the biocompatibility and safety of catanionic benzyl n-hexadecyldimethylammonium 1,4 -bis-2-ethylhexylsulfosuccinate (BHD-AOT) vesicles using both in vitro and in vivo tests. Thus, the aims of this work were to evaluate the ability of the BHD-AOT vesicles to encapsulate insulin; to analyze the structural properties and stability of the system, vesicle-Insulin (VIn), at different pH conditions; and to study the ability of VIn to decrease the glycemia in miceby different administration routes. Our results showed that 2 and 5 mg mL^-1 of vesicles were able to encapsulate about 55 % and 73 % of insulin, respectively. The system VIn showed a significant increase in size from 120 to 350 nm, changes in the surface zeta potential value, and high stability to different pH conditions. A significant decrease of the glycemia after VIn administration was demonstrated in in vivo assays, including the oral route. Our results reveal that BHD-AOT vesicles may be an appropriate system to encapsulate and protect insulin, and may be a potential system to be administrated in different ways as an alternative strategy to conventional therapy.

A computational approach to get insights into multiple faces of additives in modulation of protein aggregation pathways

An enormous population worldwide is presently confronted with debilitating neurodegenerative diseases. The etiology of the disease is connected to protein aggregation and the events involved therein. Thus, a complete understanding of an inhibitor at different stages in the process is imperative for the formulation of a drug molecule. This review presents a detailed summary of the current status of different cosolvents. It further develops how the complex aggregation pathway can be simplified into three steps common to all proteins and the way computer simulations can be exploited to gain insights into the ways by which known inhibitors can affect all these stages. Computation of theoretical parameters in this regard and their correlation with experimental techniques is accentuated. In addition to providing an outline of the scope of different additives, this review showcases the way by which the problem of analyzing an effect of an additive can be addressed effectively via MD simulations.

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

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