Insights into Insulin Fibril Assembly at Physiological and Acidic pH and Related Amyloid Intrinsic Fluorescence

Insulin fibrillation under physicochemical parameters of bioprocessing and intervention by peptides and surface-active agents

Even after the centenary celebration of insulin discovery, there prevail challenges concerning insulin aggregation, not only after repeated administration but also during industrial production, storage, transport, and delivery, significantly impacting protein quality, efficacy, and effectiveness. The aggregation reduces insulin bioavailability, increasing the risk of heightened immunogenicity, posing a threat to patient health, and creating a dent in the golden success story of insulin therapy. Insulin experiences various physicochemical and mechanical stresses due to modulations in pH, temperature, ionic strength, agitation, shear, and surface chemistry, during the upstream and downstream bioprocessing, resulting in insulin unfolding and subsequent fibrillation. This has fueled research in the pharmaceutical industry and academia to unveil the mechanistic insights of insulin aggregation in an attempt to devise rational strategies to regulate this unwanted phenomenon. The present review briefly describes the impacts of environmental factors of bioprocessing on the stability of insulin and correlates with various intermolecular interactions, particularly hydrophobic and electrostatic forces. The aggregation-prone regions of insulin are identified and interrelated with biophysical changes during stress conditions. The quest for novel additives, surface-active agents, and bioderived peptides in decelerating insulin aggregation, which results in overall structural stability, is described. We hope this review will help tackle the real-world challenges of insulin aggregation encountered during bioprocessing, ensuring safer, stable, and globally accessible insulin for efficient management of diabetes.

Insulin resistance as the molecular link between diabetes and Alzheimer's disease

Diabetes mellitus (DM) and Alzheimer's disease (AD) are two major health concerns that have seen a rising prevalence worldwide. Recent studies have indicated a possible link between DM and an increased risk of developing AD. Insulin, while primarily known for its role in regulating blood sugar, also plays a vital role in protecting brain functions. Insulin resistance (IR), especially prevalent in type 2 diabetes, is believed to play a significant role in AD's development. When insulin signalling becomes dysfunctional, it can negatively affect various brain functions, making individuals more susceptible to AD's defining features, such as the buildup of beta-amyloid plaques and tau protein tangles. Emerging research suggests that addressing insulin-related issues might help reduce or even reverse the brain changes linked to AD. This review aims to explore the rela-tionship between DM and AD, with a focus on the role of IR. It also explores the molecular mechanisms by which IR might lead to brain changes and assesses current treatments that target IR. Understanding IR's role in the connection between DM and AD offers new possibilities for treatments and highlights the importance of continued research in this interdisciplinary field.

The Characterization of Multifaceted PREP1 Peptides Provides Insights into Correlations between Spectroscopic and Structural Properties of Amyloid-like Assemblies

The widespread ability of proteins and peptides to self-assemble by forming cross-β structure is one of the most significant discoveries in structural biology. Intriguingly, the cross-β association of proteins/peptides may generate intricate supramolecular architectures with uncommon spectroscopic properties. We have recently characterized self-assembled peptides extracted from the PREP1 protein that are endowed with interesting structural/spectroscopic properties. We here demonstrate that the green fluorescence emission of the peptide PREP1[117-132] (λem ~520 nm), can be induced by excitation with UV radiation. The associated unusually large Stokes shift (Δλ ~150 nm) represents, to the best of our knowledge, the first evidence of an internal resonance energy transfer in amyloid-like structures, where the blue emission of some assemblies becomes the excitation radiation for others. Moreover, the characterization of PREP1[117-132] variants provides insights into the sequence/structure and structure/spectroscopic properties relationships. Our data suggests that the green fluorescence is plausibly associated with antiparallel β-sheet states of the peptide whereas parallel β-sheet assemblies are only endowed with blue fluorescence. Notably, the different PREP1[117-132] variants also form assemblies characterized by distinct morphologies. Indeed, the parent peptide and single mutants form compact but structured aggregates whereas most of the double mutants exhibit elongated and highly extended fibers.

In-depth investigation of the effect of pH on the autofluorescence properties of DPF3b and DPF3a amyloid fibrils

Double PHD fingers 3 (DPF3) protein exists as two splicing variants, DPF3b and DPF3a, the involvement of which in human cancer and neurodegeneration is beginning to be increasingly recognised. Both isoforms have recently been identified as intrinsically disordered proteins able to undergo amyloid fibrillation. Upon their aggregation, DPF3 proteins exhibit an intrinsic fluorescence in the visible range, referred to as deep-blue autofluorescence (dbAF). Comprehension of such phenomenon remaining elusive, we investigated in the present study the influence of pH on the optical properties of DPF3b and DPF3a fibrils. By varying the excitation wavelength and the pH condition, the two isoforms were revealed to display several autofluorescence modes that were defined as violet, deep-blue, and blue-green according to their emission range. Complementarily, analysis of excitation spectra and red edge shift plots allowed to better decipher their photoselection mechanism and to highlight isoform-specific excitation-emission features. Furthermore, the observed violation to Kasha-Vavilov's rule was attributed to red edge excitation shift effects, which were impacted by pH-mediated H-bond disruption, leading to changes in intramolecular charge and proton transfer, or π-electrons delocalisation. Finally, emergence of different autofluorescence emitters was likely related to structurally distinct fibrillar assemblies between isoforms, as well as to discrepancies in the amino acid composition of their aggregation prone regions.

Functional amyloid fibrils of biofilm-forming marine bacterium Pseudomonas aeruginosa PFL-P1 interact spontaneously with pyrene and augment the biodegradation

Bacteria thrive in biofilms embedding in the three-dimensional extracellular polymeric substances (EPS). Functional Amyloid in Pseudomonas (Fap), a protein in EPS, efficiently sequesters polycyclic aromatic hydrocarbons (PAHs). Present study reports the characterization of Fap fibrils from Pseudomonas aeruginosa PFL-P1 and describes the interaction with pyrene to assess the impact on pyrene degradation. Overexpression of fap in E. coli BL21(DE3) cells significantly enhances biofilm formation (p < 0.0001) and amyloid production (p = 0.0002), particularly with pyrene. Defibrillated Fap analysis reveals FapC monomers and increased fibrillation with pyrene. Circular Dichroism (CD), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD) unveil characteristic amyloid peaks and structural changes in Fap fibrils upon pyrene exposure. 3D-EEM analysis identifies a protein-like fluorophore in Fap fibrils, exhibiting pyrene-induced fluorescence quenching. Binding constants range from 5.23 to 7.78 M-1, with ΔG of -5.10 kJ mol-1 at 298 K, indicating spontaneous and exothermic interaction driven by hydrophobic forces. Exogenous Fap fibrils substantially increased the biofilm growth and pyrene degradation by P. aeruginosa PFL-P1 from 46 % to 64 % within 7 days (p = 0.0236). GC-MS identifies diverse metabolites, implying phthalic acid pathway in pyrene degradation. This study deepens insights into structural dynamics of Fap fibrils when exposed to pyrene, offering potential application in environmental bioremediation.

Biotechnological applications of amyloid fibrils

Protein aggregates and amyloid fibrils have special qualities and are used in a variety of biotechnological applications. They are extensively employed in bioremediation, biomaterials, and biocatalysis. Because of their capacity to encapsulate and release pharmaceuticals and their sensitivity to certain molecules, respectively, they are also used in drug delivery and biosensor applications. They have also demonstrated potential in the domains of food and bioremediation. Additionally, amyloid peptides have drawn interest in biological applications, especially in the investigation of illnesses like Parkinson's and Alzheimer's. The unique characteristics of amyloid fibrils, namely their mechanical strength and β-sheet structure, make them adaptable to a wide range of biotechnological uses. Even with their promise, one important factor to keep in mind before widely using modified amyloid materials is their potential toxicity. Thus, current research aims to overcome safety concerns while maximizing their potential.

Differences in clinicopathological characteristics between lipohypertrophy and localized insulin-derived amyloidosis: A scoping review

Insulin is used as a therapeutic agent in patients with diabetes, and cutaneous lipohypertrophy (LH) and localized insulin-derived amyloidosis (LIDA) are well-known adverse effects associated with insulin injections. The clinical implications, management, assessment methods, and pathological differentiation of LH and LIDA have been recently updated. This review was to update our knowledge of the pathological differentiation, effects of insulin absorption, hypoglycemic events, and recent assessment methods for LH and LIDA. A scoping review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta Analyses extension for Scoping Reviews guidelines. Original studies and case reports in English were also included. PubMed and Scopus databases were searched for keywords to identify papers published up to January 2022. A total of 113 studies were identified through a database search, and 31 were eligible for inclusion in this scoping review. In the 31 studies included in this review, patients with type 2 diabetes had high frequencies of LH and LIDA. LH outcome parameters were assessed using pathological findings and imaging. LIDA is mainly determined by pathological methods, such as hematoxylin and eosin and Congo red staining. Several in vitro and in vivo LIDA models of LIDA have been developed. These results suggest that pathological analysis is required to identify LH and LIDA. It is important to consider LIDA, as it likely influences insulin adsorption and glycemic control. Although several studies have evaluated the LIDA process, little is known about the mechanisms underlying the development of adverse effects associated with insulin injections.

Single-Particle Photoluminescence Measures a Heterogeneous Distribution of Differential Circular Absorbance of Gold Nanoparticle Aggregates near Constricted Thioflavin T Molecules

The chirality of biomacromolecules is critical for their function, but the optical signal of this chirality is small in the visible range. Plasmonic nanoparticles are antennas that can couple to this chiral signal. Here, we examine the molecular-scale mechanism behind the induced circular dichroism of gold nanorods (AuNRs) in solution with insulin fibrils and the fibril-intercalating dye thioflavin T (ThT) with polarization-resolved single-molecule fluorescence and single-particle photoluminescence (PL) imaging. We compared the PL upon excitation by left- and right-handed circularly polarized light to calculate the differential absorbance of AuNRs near insulin fibrils with and without ThT. Overall, our results indicate that AuNRs do not act as chiral absorbers near constricted ThT molecules. Instead, we hypothesize that fibrils promote AuNR aggregation, and this templating is mediated by subtle changes in the solution conditions; under the right conditions, only a few chiral aggregates with significantly higher circular dichroism signal contribute to a large net circular dichroism.

Revealing the interaction between peptide drugs and permeation enhancers in the presence of intestinal bile salts

Permeability enhancer-based formulations offer a promising approach to enhance the oral bioavailability of peptides. We used all-atom molecular dynamics simulations to investigate the interaction between two permeability enhancers (sodium caprate, and SNAC), and four different peptides (octreotide, hexarelin, degarelix, and insulin), in the presence of taurocholate, an intestinal bile salt. The permeability enhancers exhibited distinct effects on peptide release based on their properties, promoting hydrophobic peptide release while inhibiting water-soluble peptide release. Lowering peptide concentrations in the simulations reduced peptide-peptide interactions but increased their interactions with the enhancers and taurocholates. Introducing peptides randomly with enhancer and taurocholate molecules yielded dynamic molecular aggregation, and reduced peptide-peptide interactions and hydrogen bond formation compared to peptide-only systems. The simulations provided insights into molecular-level interactions, highlighting the specific contacts between peptide residues responsible for aggregation, and the interactions between peptide residues and permeability enhancers/taurocholates that are crucial within the mixed colloids. Therefore, our results can provide insights into how modifications of these critical contacts can be made to alter drug release profiles from peptide-only or mixed peptide-PE-taurocholate aggregates. To further probe the molecular nature of permeability enhancers and peptide interactions, we also analyzed insulin secondary structures using Fourier transform infrared spectroscopy. The presence of SNAC led to an increase in β-sheet formation in insulin. In contrast, both in the absence and presence of caprate, α-helices, and random structures dominated. These molecular-level insights can guide the design of improved permeability enhancer-based dosage forms, allowing for precise control of peptide release profiles near the intended absorption site.

pH-dependent self-assembly mechanism of a single repetitive domain from a spider silk protein

Spider silk is self-assembled from full-length silk proteins, and some silk protein fragments can also form silk-like fibers in vitro. However, the mechanism underlying the silk fiber formation is not understood well. In this study, we investigated the fiber formation of a single repetitive domain (RP) from a minor ampullate silk protein (MiSp). Our findings revealed that pH and salt concentration affect not only the stability of MiSp-RP but also its self-assembly into fibers and aggregates. Using nuclear magnetic resonance (NMR) spectroscopy, we solved the three-dimensional (3D) structure of MiSp RP in aqueous solution. On the basis of the structure and mutagenesis, we revealed that charge-dipole interactions are responsible for the pH- and salt-dependent properties of MiSp-RP. Our results indicate that fiber formation is regulated by a delicate balance between intermolecular and intramolecular interactions, rather than by the protein stability alone. These findings have implications for the design of silk proteins for mass production of spider silk.

A Comprehensive Analysis of the Intrinsic Visible Fluorescence Emitted by Peptide/Protein Amyloid-like Assemblies

Amyloid aggregation is a widespread process that involves proteins and peptides with different molecular complexity and amino acid composition. The structural motif (cross-β) underlying this supramolecular organization generates aggregates endowed with special mechanical and spectroscopic properties with huge implications in biomedical and technological fields, including emerging precision medicine. The puzzling ability of these assemblies to emit intrinsic and label-free fluorescence in regions of the electromagnetic spectrum, such as visible and even infrared, usually considered to be forbidden in the polypeptide chain, has attracted interest for its many implications in both basic and applied science. Despite the interest in this phenomenon, the physical basis of its origin is still poorly understood. To gain a global view of the available information on this phenomenon, we here provide an exhaustive survey of the current literature in which original data on this fluorescence have been reported. The emitting systems have been classified in terms of their molecular complexity, amino acid composition, and physical state. Information about the wavelength of the radiation used for the excitation as well as the emission range/peak has also been retrieved. The data collected here provide a picture of the complexity of this multifaceted phenomenon that could be helpful for future studies aimed at defining its structural and electronic basis and/or stimulating new applications.

Influence of Ionizing Radiation on Spontaneously Formed Aggregates in Proteins or Enzymes Solutions

We have shown that many proteins and enzymes (ovalbumin, β-lactoglobulin, lysozyme, insulin, histone, papain) undergo concentration-dependent reversible aggregation as a result of the interaction of the studied biomolecules. Moreover, irradiation of those protein or enzyme solutions under oxidative stress conditions results in the formation of stable soluble protein aggregates. We assume that protein dimers are mainly formed. A pulse radiolysis study has been made to investigate the early stages of protein oxidation by N3• or ^•OH radicals. Reactions of the N3• radical with the studied proteins lead to the generation of aggregates stabilized by covalent bonds between tyrosine residues. The high reactivity of the ^•OH with amino acids contained within proteins is responsible for the formation of various covalent bonds (including C-C or C-O-C) between adjacent protein molecules. In the analysis of the formation of protein aggregates, intramolecular electron transfer from the tyrosine moiety to Trp^• radical should be taken into account. Steady-state spectroscopic measurements with a detection of emission and absorbance, together with measurements of the dynamic scattering of laser light, made it possible to characterize the obtained aggregates. The identification of protein nanostructures generated by ionizing radiation using spectroscopic methods is difficult due to the spontaneous formation of protein aggregates before irradiation. The commonly used fluorescence detection of dityrosyl cross-linking (DT) as a marker of protein modification under the influence of ionizing radiation requires modification in the case of the tested objects. A precise photochemical lifetime measurement of the excited states of radiation-generated aggregates is useful in characterizing their structure. Resonance light scattering (RLS) has proven to be an extremely sensitive and useful technique to detect protein aggregates.

Fluorescence by self-assembly: autofluorescent peptide vesicles and fibers

A series of oxidized cysteinyl peptides ([P-Cys-X-OMe]₂; P = Boc or H; X = Trp or Glu) showed vesicular and fibrillar assemblies. The anatomy of the self-assembled vesicles from the water-soluble cystine peptide [Cys-Trp-OMe]₂ (1a) has been investigated by using various fluorescent probes such as ammonium 8-anilinonaphthalene-1-sulfonate, Nile Red and pyrene. The morphological characterization was carried out by fluorescence lifetime imaging microscopy (FLIM) and super resolution-structured illumination microscopy (SR-SIM) utilizing the autofluorescence of the vesicles stemming from the self-assembly. The self-assembled structures are also observed in solution as evident from the quantitative phase images obtained using a dual-mode digital holographic microscope (DHM) system. Present investigations show that the self-assembly is enthalpy- and entropy-driven in the aqueous medium. Based on the CD spectral studies, we proposed that 1a organizes into vesicles through the sequestration of indole units. We observed that the solutions of dipeptides 1a-b exhibit autofluorescence in the blue region upon excitation at a wavelength >350 nm. Detailed spectroscopic studies on the peptides lacking tryptophan 2a-b unequivocally showed that the autofluorescence stems exclusively from peptide aggregation. Our experimental results with appropriate controls revealed that the clustering of carbonyl chromophores is central to autofluorescence. Autofluorescence was also used to probe the vesicle formation without using any external fluorescent probe. To the best of our knowledge, this is the first report on autofluorescent vesicles formed by the spontaneous association of dipeptides. We also found that the vesicles formed by 1a can act as a host for guests like C₆₀. The biocompatibility and biodegradability of these peptides along with the autofluorescent nature and guest binding ability of peptide-based vesicles offer numerous applications in the biomedical area.

Peptide Inhibitors of Insulin Fibrillation: Current and Future Challenges

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

Profiling of insulin and resveratrol interaction using multi-spectroscopy and molecular docking study

Background

Resveratrol, a phenolic compound, has various medicinal properties, including anticancer, anti-diabetic, antioxidant, anti-inflammatory, etc. Diabetes is a killing disease, especially for people who cannot maintain a healthy lifestyle. People with diabetes need additional information about a supplement that can prevent and treat diabetes. The present study aims to investigate the interaction of insulin with resveratrol using fluorescence spectroscopy, UV–Vis spectroscopy, CD spectropolarimeter, and molecular docking methods. As an outcome of this study, we expect to understand the contribution of resveratrol in insulin resistance.

Result

The fluorescence spectroscopy results showed that the peak intensity of insulin emission decreased with resveratrol. The interaction of insulin with resveratrol involved a combination of static and dynamic quenching effects. Temperature changes caused the binding constant (K) and the binding site (n) unstable. The interaction occurred through hydrogen bonding, van der Waal, and was hydrophobic. The results of UV–Vis spectroscopy showed that the addition of resveratrol caused a peak in a blueshift, and the absorbance was hyperchromic. Also, there was a reduction in electron transition and the extinction coefficient. The CD spectropolarimeter results showed that the addition of resveratrol affected the secondary structure of insulin. The amount of α-helix and β-sheet slightly change and increase in the secondary structure’s length. The molecular docking study showed that resveratrol interacts via hydrogen bonding with glycine and asparagine. van der Waal interactions occurred in asparagine, phenylalanine, and cysteine. The interaction of electrons occurred through the π orbitals of resveratrol with tyrosine A and B. The binding energy of molecules interaction happened spontaneously on a hydrophobic surface.

Conclusion

Profiling the interaction of insulin and resveratrol shows that resveratrol can stabilize insulin structure and prevent insulin resistance in diabetes.

Polyisobutylene-based glycopolymers as potent inhibitors for in vitro insulin aggregation

A family of amphiphilic diblock copolymers containing a hydrophobic polyisobutylene (PIB, M_n = 1000 g mol^-1) segment and a hydrophilic block with sugar pendants has been synthesized by combining living cationic and reversible addition-fragmentation chain transfer (RAFT) polymerization techniques; to explore their potential in insulin fibrillation inhibition. The glucose content in the hydrophilic segment has been tailor-made from 20 to 57 units to prepare block copolymers. The removal of the acetates from the pendent glucose units resulted in amphiphilic block copolymers that generated micellar aggregates in aqueous media. The treatment of insulin with these block copolymers affected the fibril formation process which was demonstrated using an array of biophysical techniques, namely, thioflavin T (ThT) fluorescence, tyrosine (Tyr) fluorescence, Nile red (NR) fluorescence, isothermal titration calorimetry (ITC), etc. The Tyr fluorescence assay and NR fluorescence study revealed the crucial role of hydrophobic interaction in the inhibition process, whereas ITC measurements confirmed the importance of polar interaction. Thus, the block copolymers exhibit potent inhibition of insulin fibrillation owing to hydrophobic (from PIB segment) and glycosidic cluster effect (from sugar pendant block).

Morphological integrity of insulin amyloid-like aggregates depends on preparation methods and post-production treatments

Protein aggregates are often varying extensively in their morphological characteristics, which may lead to various biological outcomes, such as increased immunogenicity risk. However, isolation of aggregates with a specific morphology within an ensemble is often challenging. To gain vital knowledge on the effects of aggregate characteristics, samples containing a single morphology must be produced by direct control of the aggregation process. Moreover, the formed aggregates need to be in an aqueous solution suitable for biological assays, while keeping their morphology intact. Here we evaluated the dependence of morphology and integrity of amyloid-like fibrils and spherulites on preparation conditions and post-treatment methods. Samples containing either amyloid-like fibrils or spherulites produced from human insulin in acetic acid solutions are dependent on the presence of salt (NaCl). Moreover, mechanical shaking (600 rpm) inhibits spherulite formation, while only affecting the length of the formed fibrils compared to quiescent conditions. Besides shaking, the initial protein concentration in the formulation was found to control fibril length. Surprisingly, exchanging the solution used for aggregate formation to a physiologically relevant buffer, had a striking effect on the morphological integrity of the fibril and spherulite samples. Especially the secondary structure of one of our spherulite samples presented dramatic changes of the aggregated β-sheet content after exchanging the solution, emphasizing the importance of the aggregate stability. These results and considerations have profound implications on the data interpretation and should be implemented in the workflow for both fundamental characterization of aggregates as well as assays for evaluation of their corresponding biological effects.

Poly(trehalose methacrylate) as an Excipient for Insulin Stabilization: Mechanism and Safety

Insulin, the oldest U.S. Food and Drug Administration (FDA)-approved recombinant protein and a World Health Organization (WHO) essential medicine for treating diabetes globally, faces challenges due to its storage instability. One approach to stabilize insulin is the addition of poly(trehalose methacrylate) (pTrMA) as an excipient. The polymer increases the stability of the peptide to heat and mechanical agitation and has a low viscosity suitable for injection and pumps. However, the safety and stabilizing mechanism of pTrMA is not yet known and is required to understand the potential suitability of pTrMA as an insulin excipient. Herein is reported the immune response, biodistribution, and insulin plasma lifetime in mice, as well as investigation into insulin stabilization. pTrMA alone or formulated with ovalbumin did not elicit an antibody response over 3 weeks in mice, and there was no observable cytokine production in response to pTrMA. Micropositron emission tomography/microcomputer tomography of ⁶⁴Cu-labeled pTrMA showed excretion of 78-79% ID/cc within 24 h and minimal liver accumulation at 6-8% ID/cc when studied out to 120 h. Further, the plasma lifetime of insulin in mice was not altered by added pTrMA. Formulating insulin with 2 mol equiv of pTrMA improved the stability of insulin to standard storage conditions: 46 weeks at 4 °C yielded 87.0% intact insulin with pTrMA present as compared to 7.8% intact insulin without the polymer. The mechanism by which pTrMA-stabilized insulin was revealed to be a combination of inhibiting deamidation of amino acid residues and preventing fibrillation, followed by aggregation of inactive and immunogenic amyloids all without complexing insulin into its hexameric state, which could delay the onset of insulin activity. Based on the data reported here, we suggest that pTrMA stabilizes insulin as an excipient without adverse effects in vivo and is promising to investigate further for the safe formulation of insulin.

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.

Spidroin N-terminal domain forms amyloid-like fibril based hydrogels and provides a protein immobilization platform

Recombinant spider silk proteins (spidroins) have multiple potential applications in development of novel biomaterials, but their multimodal and aggregation-prone nature have complicated production and straightforward applications. Here, we report that recombinant miniature spidroins, and importantly also the N-terminal domain (NT) on its own, rapidly form self-supporting and transparent hydrogels at 37 °C. The gelation is caused by NT α-helix to β-sheet conversion and formation of amyloid-like fibrils, and fusion proteins composed of NT and green fluorescent protein or purine nucleoside phosphorylase form hydrogels with intact functions of the fusion moieties. Our findings demonstrate that recombinant NT and fusion proteins give high expression yields and bestow attractive properties to hydrogels, e.g., transparency, cross-linker free gelation and straightforward immobilization of active proteins at high density.

Recombinant spider silks are of interest but the multimodal and aggregation-prone nature of them is a limitation. Here, the authors report on a miniature spidroin based on the N-terminal domain which forms a hydrogel at 37 °C which allows for ease of production and fusion protein modification to generate functional biomaterials.

The Possible Role of the Type I Chaperonins in Human Insulin Self-Association

Insulin is a hormone that attends to energy metabolism by regulating glucose levels in the bloodstream. It is synthesised within pancreas beta-cells where, before being released into the serum, it is stored in granules as hexamers coordinated by Zn²⁺ and further packaged in microcrystalline structures. The group I chaperonin cpn60, known for its assembly-assisting function, is present, together with its cochaperonin cpn10, at each step of the insulin secretory pathway. However, the exact function of the heat shock protein in insulin biosynthesis and processing is still far from being understood. Here we explore the possibility that the molecular machine cpn60/cpn10 could have a role in insulin hexameric assembly and its further crystallization. Moreover, we also evaluate their potential protective effect in pathological insulin aggregation. The experiments performed with the cpn60 bacterial homologue, GroEL, in complex with its cochaperonin GroES, by using spectroscopic methods, microscopy and hydrodynamic techniques, reveal that the chaperonins in vitro favour insulin hexameric organisation and inhibit its aberrant aggregation. These results provide new details in the field of insulin assembly and its related disorders.

Arabidopsis thaliana Plant Natriuretic Peptide Active Domain Forms Amyloid-like Fibrils in a pH-Dependent Manner

Plant natriuretic peptides (PNPs) are hormones that have been extracted from many different species, with the Arabidopsis thaliana PNP (AtPNP-A) being the most studied among them. AtPNP-A is a signaling molecule that consists of 130 residues and is secreted into the apoplast, under conditions of biotic or abiotic stress. AtPNP-A has distant sequence homology with human ANP, a protein that forms amyloid fibrils in vivo. In this work, we investigated the amyloidogenic properties of a 34-residue-long peptide, located within the AtPNP-A sequence, in three different pH conditions, using transmission electron microscopy, X-ray fiber diffraction, ATR FT-IR spectroscopy, Congo red and Thioflavin T staining assays. We also utilize bioinformatics tools to study its association with known plant amyloidogenic proteins and other A. thaliana proteins. Our results reveal a new case of a pH-dependent amyloid forming peptide in A. thaliana, with a potential functional role.

Intrinsic fluorescence-based label-free detection of bovine amyloid A amyloidosis

Amyloidosis is diagnosed by the histologic detection of amyloid deposits; however, this method has limitations such as a prolonged diagnosis time and the need for histologic proficiency. We aimed to develop a rapid and simple method for diagnosing amyloidosis by targeting amyloid-specific endogenous fluorescence, which has not been reported previously, to our knowledge. Fluorescence fingerprint analysis of amyloid extracts and tissue homogenates derived from amyloid A (AA) amyloidosis-affected cattle exhibited a specific intrinsic fluorescence pattern. Furthermore, principal component analysis using analytical data revealed that AA could be identified by peaks near λ_ex 350 nm and λ_em 430 nm. Fluorescence spectrometry analysis using tissue homogenates, which does not require special histochemical staining, enables the rapid detection of bovine AA.

Exploring the Propensities of Fluorescent Carbazole Analogs toward the Inhibition of Amyloid Aggregation in Type 2 Diabetes: An Experimental and Theoretical Endeavor

Amyloid aggregation is a pathological trait observed in many incurable and fatal neurodegenerative and metabolic diseases associated with misfolding and self-assembly of various proteins. Noncovalent interactions between these structural motifs and small molecules can, however, prevent this aggregation. Herein, five structurally different synthetic (Cz1-Cz4) and naturally occurring (Cz5, mahanimbine) fluorescent carbazole analogs are explored for their comparative amyloid aggregation inhibitory activities. Cz3 inhibited the amyloid deposition on the pancreatic β-cells of diabetic mice. Moreover, Cz3 and Cz5 also showed efficacy as the fluorescent cell (MIN6) imaging agents. Further structural modifications of these carbazoles may lead to development of low-cost and non-toxic therapeutic agents for Type 2 diabetes and other amyloidosis-related diseases.

Aggregation Condition-Structure Relationship of Mouse Prion Protein Fibrils

Prion diseases are associated with conformational conversion of cellular prion protein into a misfolded pathogenic form, which resembles many properties of amyloid fibrils. The same prion protein sequence can misfold into different conformations, which are responsible for variations in prion disease phenotypes (prion strains). In this work, we use atomic force microscopy, FTIR spectroscopy and magic-angle spinning NMR to devise structural models of mouse prion protein fibrils prepared in three different denaturing conditions. We find that the fibril core region as well as the structure of its N- and C-terminal parts is almost identical between the three fibrils. In contrast, the central part differs in length of β-strands and the arrangement of charged residues. We propose that the denaturant ionic strength plays a major role in determining the structure of fibrils obtained in a particular condition by stabilizing fibril core interior-facing glutamic acid residues.

Effective inhibition of insulin amyloid fibril aggregation by nickel(II) complexes containing heterocyclic thiosemicarbazones

The sensitivity of protein molecular structures makes them susceptible to aggregation in conditions unfavorable for the maintenance of their native folds. The aggregation of proteins leads to many disorders, but the inhibition of amyloid fibril formation using metal-containing small molecules is gaining popularity. Herein we report the effect of nickel(II) complexes (N1, N2, N3, and N4) bearing thiosemicarbazones on the inhibition of amyloid fibril formation by insulin. The interactions of the complexes with amyloid fibrils were investigated using various biophysical techniques, including light scattering, intrinsic fluorescence assay, thioflavin T (ThT) assay, and Fourier transform-infrared spectroscopy. The results revealed that the phenyl-substituted N3 was an efficient inhibitor of amyloid fibril formation and maintained the insulin in its native structure despite conditions promoting fibrillation. Nickel(II) complexes containing indole based thiosemicarbazones were efficient in inhibiting the amyloid fibril formation and maintaining the insulin in its native structure in unfavorable conditions.

Luminescent imaging of insulin amyloid aggregation using a sensitive ruthenium-based probe in the red region

A sensitive and selective strategy to identify insulin fibrils remains a challenge for researchers in amyloid protein research. Thus, it is critical to detect, in vitro, the species generated during amyloid aggregation, particularly the fibrillar species. Here we demonstrate that the luminescent complex cis-[Ru(phen)₂(3,4Apy)₂]²⁺ (RuApy; phen = 1,10-phenanthroline; 3,4Apy = 3,4-diaminopyridine) is a rapid, low-cost alternative to in vitro detection of fibrillar insulin, using conventional optical techniques. The RuApy complex displays emission intensity enhancement at 655 nm when associated with insulin, which enables imaging of the conformational changes of the protein's self-aggregation. The complex shows high sensitivity to fibrillar insulin with a limit of detection of 0.85 μM and binding affinity of 12.40 ± 1.84 μM which is comparable to those of Thioflavin T and Congo red, with the advantage of minimizing background fluorescence, absorption of light by biomolecules, and light scattering from physiologic salts in the medium.

Interaction between phloretin and insulin: a spectroscopic study

Diabetes is among the top ten deadly diseases in the world. It occurs either when the pancreas does not produce enough insulin (INS) or when the body cannot effectively use the insulin it produces. Phloretin (PHL) has a biological effect that can treat diabetes. A spectroscopic study was carried out to explore the interaction between phloretin and insulin. UV/Vis spectroscopy, fluorescence spectroscopy, and circular dichroism spectropolarimeter were used in the study. UV/Vis spectra showed that the interaction between PHL and INS produced strong absorption at a wavelength of 282 nm. The fluorescence analysis results showed that the excitation and emission occurred at 280-nm and 305-nm wavelengths, respectively. Temperature changes did not affect INS emissions. However, the interaction of PHL–INS caused a redshift at 305 to 317 nm. Temperature affected the binding constant (Ka) and the binding site (n). Ka decreased with increasing temperature and increased the binding site. The thermodynamic parameters such as enthalpy (ΔH0) and entropy (ΔS0) each had a value of − 16,514 kJ/mol and 22.65 J/mol·K. PHL and INS interaction formed hydrogen bonds and hydrophobic interaction. The free energy (ΔG0) recorded was negative. PHL and INS interactions took place spontaneously. The quenching effect was dynamic and static. KD values were greater than KS. The higher the temperature, the less was KD and KS. The appearance of two negative signals on circular dichroism (CD) spectropolarimeter implies that phloretin could induce regional configuration changes in insulin. The addition of PHL has revealed that the proportion of α-helix in the insulin stabilizes its structure. Phloretin’s stabilization and enhancement of the α-helix structural configuration in insulin indicate that phloretin can improve insulin resistance.

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

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

Hydroxytyrosol Selectively Affects Non-Enzymatic Glycation in Human Insulin and Protects by AGEs Cytotoxicity

Hydroxytyrosol (HT), the major phenolic compound in olive oil, is attracting increasing interest for its beneficial properties including a notable antioxidant and anti-inflammatory power. In this study, using a combination of biophysical and cell biology techniques, we have tested the role of HT in the formation of advanced glycation end-products (AGEs). AGEs have a key role in clinical sciences as they have been associated to diabetes, neurodegenerative and cardiovascular diseases. In addition, as the incidence of Alzheimer’s disease (AD) is strongly increased in diabetic patients, AGE formation is supposed to be involved in the development of the pathological hallmarks of AD. Our data show that HT selectively inhibits protein glycation reaction in human insulin, and it is able to counteract the AGE-induced cytotoxicity in human neurotypical cells by acting on SIRT1 level and oxidative stress, as well as on inflammatory response. This study identifies new beneficial properties for HT and suggests it might be a promising molecule in protecting against the AGE-induced toxicity, a key mechanism underlying the development and progression of neurodegenerative disorders.

Insulin Fibril Formation Caused by Mechanical Shock and Cavitation

Cavitation can occur when liquids are exposed to pressure waves of sufficient amplitude, producing rapidly expanding and collapsing gas bubbles that generate localized regions of high energy dissipation. When vials containing insulin were subjected to mechanical shock or when ultrasound was applied to the vials, the resulting cavitation events induced formation of insulin amyloid fibril nuclei that were detected by transmission electron microscopy and quantified by fluorescence spectroscopy following staining with the amyloid-sensitive dye thioflavin-T. Dropping insulin solutions in glass vials produced only minute amounts of insulin fibril nuclei, which could be detected by allowing the nuclei to grow. Cavitation-induced formation of amyloid aggregates may be relevant for iatrogenic insulin deposition disease, where insulin fibrils formed in vitro prior to administration to patients could serve as nuclei for growing fibril deposits in vivo.

Understanding the Role of Protein Glycation in the Amyloid Aggregation Process

Protein function and flexibility is directly related to the native distribution of its structural elements and any alteration in protein architecture leads to several abnormalities and accumulation of misfolded proteins. This phenomenon is associated with a range of increasingly common human disorders, including Alzheimer and Parkinson diseases, type II diabetes, and a number of systemic amyloidosis characterized by the accumulation of amyloid aggregates both in the extracellular space of tissues and as intracellular deposits. Post-translational modifications are known to have an active role in the in vivo amyloid aggregation as able to affect protein structure and dynamics. Among them, a key role seems to be played by non-enzymatic glycation, the most unwanted irreversible modification of the protein structure, which strongly affects long-living proteins throughout the body. This study provided an overview of the molecular effects induced by glycation on the amyloid aggregation process of several protein models associated with misfolding diseases. In particular, we analyzed the role of glycation on protein folding, kinetics of amyloid formation, and amyloid cytotoxicity in order to shed light on the role of this post-translational modification in the in vivo amyloid aggregation process.

Temperature-Dependent Structural Variability of Prion Protein Amyloid Fibrils

Prion protein aggregation into amyloid fibrils is associated with the onset and progression of prion diseases—a group of neurodegenerative amyloidoses. The process of such aggregate formation is still not fully understood, especially regarding their polymorphism, an event where the same type of protein forms multiple, conformationally and morphologically distinct structures. Considering that such structural variations can greatly complicate the search for potential antiamyloid compounds, either by having specific propagation properties or stability, it is important to better understand this aggregation event. We have recently reported the ability of prion protein fibrils to obtain at least two distinct conformations under identical conditions, which raised the question if this occurrence is tied to only certain environmental conditions. In this work, we examined a large sample size of prion protein aggregation reactions under a range of temperatures and analyzed the resulting fibril dye-binding, secondary structure and morphological properties. We show that all temperature conditions lead to the formation of more than one fibril type and that this variability may depend on the state of the initial prion protein molecules.

Phenolic Preservative Removal from Commercial Insulin Formulations Reduces Tissue Inflammation while Maintaining Euglycemia

Background: Exogenous insulin therapy requires stabilization of the insulin molecule, which is achieved through the use of excipients (e.g., phenolic preservatives (PP)) that provide protein stability, sterility and prolong insulin shelf life. However, our laboratory recently reported that PP, (e.g., m-creosol and phenol) are also cytotoxic, inducing inflammation and fibrosis. Optimizing PP levels through filtration would balance the need for insulin preservation with PP-induced inflammation. Method: Zeolite Y (Z-Y), a size-exclusion-based resin, was employed to remove PP from commercial insulin formulations (Humalog) before infusion. Results: PP removal significantly decreased cell toxicity in vitro and inflammation in vivo. Infusion site histological analysis after a 3 day study demonstrated that leukocyte accumulation increased with nonfiltered preparations but decreased after filtration. Additional studies demonstrated that a Z-Y fabricated filter effectively removed excess PP such that the filtered insulin solution achieved equivalent glycemic control in diabetic mice when compared to nonfiltered insulin. Conclusion: This approach represents the proof of concept that using Z-Y for in-line PP removal assists in lowering inflammation at the site of insulin infusion and thus could lead to extending the functional lifespan of insulin infusion sets in vivo.

Amyloid-like Prep1 peptides exhibit reversible blue-green-red fluorescence in vitro and in living cells

PREP1-based peptides form amyloid-like aggregates endowed with an intrinsic blue-green-red fluorescence with an unusual sharp maximum at 520 nm upon excitation with visible light under physiological conditions. The peptide PREP1[117-132], whose sequence does not contain aromatic residues, presents a pH-dependent and reversible fluorescence, in line with its structural transition from β-sheet rich aggregates to α-helix structures. These findings further demonstrate that the non-canonical fluorescence exhibited by amyloids is an articulated phenomenon.

Characterization of Insulin Mucoadhesive Buccal Films: Spectroscopic Analysis and In Vivo Evaluation

Insulin mucoadhesive buccal films (MBF) are a noninvasive insulin delivery system that offers an advantageous alternative route of administration to subcutaneous injection. One major concern in the formulation of insulin MBF is the preservation of an insulin secondary structure in the presence of the other film components. Buccal films were formulated using chitosan, glycerin, and L-arginine. The MBF-forming solutions (MBF-FS) and the films (MBF) were examined for their chemical and structural stability and for their in vivo activity. Enzyme-Linked Immunosorbent Assay (ELISA) of the insulin-loaded MBF showed that each individualized unit dose was at least loaded with 80% of the insulin theoretical dose. Results of Synchrotron Radiation Circular Dichroism (SRCD) measurements revealed that MBF-FS retained the α-helices and β–sheets conformations of insulin. Fourier transform infrared (FTIR)-microspectroscopy (FTIR-MS) examination of insulin MBF revealed the protective action of L-arginine on insulin structure by interacting with chitosan and minimizing the formation of an unordered structure and β-strand. A blood glucose-lowering effect of insulin MBF was observed in comparison with subcutaneous (S.C) injection using a rat model. As a result; chitosan-based MBFs were formulated and characterized using SRCD and FTIR-MS techniques. Furthermore, the results of in vivo testing suggested the MBFs as a promising delivery system for insulin.

Defects in Protein Folding and/or Quality Control Cause Protein Aggregation in the Endoplasmic Reticulum

Protein aggregation is now a common hallmark of numerous human diseases, most of which involve cytosolic aggregates including Aβ (AD) and ⍺-synuclein (PD) in Alzheimer's disease and Parkinson's disease. However, it is also evident that protein aggregation can also occur in the lumen of the endoplasmic reticulum (ER) that leads to specific diseases due to loss of protein function or detrimental effects on the host cell, the former is inherited in a recessive manner where the latter are dominantly inherited. However, the mechanisms of protein aggregation, disaggregation and degradation in the ER are not well understood. Here we provide an overview of factors that cause protein aggregation in the ER and how the ER handles aggregated proteins. Protein aggregation in the ER can result from intrinsic properties of the protein (hydrophobic residues in the ER), oxidative stress or nutrient depletion. The ER has quality control mechanisms [chaperone functions, ER-associated protein degradation (ERAD) and autophagy] to ensure only correctly folded proteins exit the ER and enter the cis-Golgi compartment. Perturbation of protein folding in the ER activates the unfolded protein response (UPR) that evolved to increase ER protein folding capacity and efficiency and degrade misfolded proteins. Accumulation of misfolded proteins in the ER to a level that exceeds the ER-chaperone folding capacity is a major factor that exacerbates protein aggregation. The most significant ER resident protein that prevents protein aggregation in the ER is the heat shock protein 70 (HSP70) homologue, BiP/GRP78, which is a peptide-dependent ATPase that binds unfolded/misfolded proteins and releases them upon ATP binding. Since exogenous factors can also reduce protein misfolding and aggregation in the ER, such as chemical chaperones and antioxidants, these treatments have potential therapeutic benefit for ER protein aggregation-associated diseases.

Effect of Ionic Strength on Thioflavin-T Affinity to Amyloid Fibrils and Its Fluorescence Intensity

The formation of amyloid fibrils is linked to multiple neurodegenerative disorders, including Alzheimer’s and Parkinson’s disease. Despite years of research and countless studies on the topic of such aggregate formation, as well as their resulting structure, the current knowledge is still fairly limited. One of the main aspects prohibiting effective aggregation tracking is the environment’s effect on amyloid-specific dyes, namely thioflavin-T (ThT). Currently, there are only a few studies hinting at ionic strength being one of the factors that modulate the dye’s binding affinity and fluorescence intensity. In this work we explore this effect under a range of ionic strength conditions, using insulin, lysozyme, mouse prion protein, and α-synuclein fibrils. We show that ionic strength is an extremely important factor affecting both the binding affinity, as well as the fluorescence intensity of ThT.

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.

"What Doesn't Kill You Makes You Stronger": Future Applications of Amyloid Aggregates in Biomedicine

Amyloid proteins are linked to the pathogenesis of several diseases including Alzheimer's disease, but at the same time a range of functional amyloids are physiologically important in humans. Although the disease pathogenies have been associated with protein aggregation, the mechanisms and factors that lead to protein aggregation are not completely understood. Paradoxically, unique characteristics of amyloids provide new opportunities for engineering innovative materials with biomedical applications. In this review, we discuss not only outstanding advances in biomedical applications of amyloid peptides, but also the mechanism of amyloid aggregation, factors affecting the process, and core sequences driving the aggregation. We aim with this review to provide a useful manual for those who engineer amyloids for innovative medicine solutions.

Williams G, Brocchini S, Awwad S. Injectables and Depots to Prolong Drug Action of Proteins and Peptides

Proteins and peptides have emerged in recent years to treat a wide range of multifaceted diseases such as cancer, diabetes and inflammation. The emergence of polypeptides has yielded advancements in the fields of biopharmaceutical production and formulation. Polypeptides often display poor pharmacokinetics, limited permeability across biological barriers, suboptimal biodistribution, and some proclivity for immunogenicity. Frequent administration of polypeptides is generally required to maintain adequate therapeutic levels, which can limit efficacy and compliance while increasing adverse reactions. Many strategies to increase the duration of action of therapeutic polypeptides have been described with many clinical products having been developed. This review describes approaches to optimise polypeptide delivery organised by the commonly used routes of administration. Future innovations in formulation may hold the key to the continued successful development of proteins and peptides with optimal clinical properties.

Amyloidogenic Propensities of Ribosomal S1 Proteins: Bioinformatics Screening and Experimental Checking

Structural S1 domains belong to the superfamily of oligosaccharide/oligonucleotide-binding fold domains, which are highly conserved from prokaryotes to higher eukaryotes and able to function in RNA binding. An important feature of this family is the presence of several copies of the structural domain, the number of which is determined in a strictly limited range from one to six. Despite the strong tendency for the aggregation of several amyloidogenic regions in the family of the ribosomal S1 proteins, their fibril formation process is still poorly understood. Here, we combined computational and experimental approaches for studying some features of the amyloidogenic regions in this protein family. The FoldAmyloid, Waltz, PASTA 2.0 and Aggrescan programs were used to assess the amyloidogenic propensities in the ribosomal S1 proteins and to identify such regions in various structural domains. The thioflavin T fluorescence assay and electron microscopy were used to check the chosen amyloidogenic peptides' ability to form fibrils. The bioinformatics tools were used to study the amyloidogenic propensities in 1331 ribosomal S1 proteins. We found that amyloidogenicity decreases with increasing sizes of proteins. Inside one domain, the amyloidogenicity is higher in the terminal parts. We selected and synthesized 11 amyloidogenic peptides from the Escherichia coli and Thermus thermophilus ribosomal S1 proteins and checked their ability to form amyloids using the thioflavin T fluorescence assay and electron microscopy. All 11 amyloidogenic peptides form amyloid-like fibrils. The described specific amyloidogenic regions are actually responsible for the fibrillogenesis process and may be potential targets for modulating the amyloid properties of bacterial ribosomal S1 proteins.

Hydroxytyrosol Inhibits Protein Oligomerization and Amyloid Aggregation in Human Insulin

Hydroxytyrosol (HT), one of the main phenolic components of olive oil, has attracted considerable interest for its biological properties, including a remarkable antioxidant and anti-inflammatory power and, recently, for its ability to interfere with the amyloid aggregation underlying several human diseases. We report here a broad biophysical approach and cell biology techniques that allowed us to characterize the molecular mechanisms by which HT affects insulin amyloid aggregation and the related cytotoxicity. Our data show that HT is able to fully inhibit insulin amyloid aggregation and this property seems to be ascribed to the stabilization of the insulin monomeric state. Moreover, HT completely reverses the toxic effect produced by amyloid insulin aggregates in neuroblastoma cell lines by fully inhibiting the production of toxic amyloid species. These findings suggest that the beneficial effects of olive oil polyphenols, including HT, may arise from multifunctional activities and suggest possible a application of this natural compound in the prevention or treatment of amyloid-associated diseases.

Interaction of ZnO Nanostructures with Proteins: In Vitro Fibrillation/Antifibrillation Studies and in Silico Molecular Docking Simulations

Protein amyloidosis is related to many neurological disorders. Nanoparticles (NPs) due to their small size can regulate both the polypeptide monomers/oligomers assembly into amyloid fibrils/plaques and the disintegration of the existent plaques. Herein, we have synthesized ZnO nanoflowers and polyol-coated ZnO NPs of relatively small size (40 nm) with cylindrical shape, through solvothermal and microwave-assisted routes, respectively. The effect of the different morphology of nanostructures on the fibrillation/antifibrillation process was monitored in bovine serum albumin (BSA) and human insulin (HI) by fluorescence Thioflavin T (ThT) measurements. Although both nanomaterials affected the amyloid formation mechanism as well as their disaggregation, ZnO nanoflowers with their sharp edges exhibited the greatest amyloid degradation rate in both model proteins (73% and 35%, respectively) and inhibited the most the insulin fibril growth, while restrained also the fibrillation process in the case of albumin solution. In silico molecular docking simulations on the crystal structure of BSA and HI were performed to analyze further the observed in vitro activity of ZnO nanostructures. The binding energy of ZnO NPs was found lower for BSA (-5.44), highlighting their ability to act as catalysts in the fibrillation process of albumin monomers.

Insulin fibrillation: toward strategies for attenuating the process

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