Effects of several quinones on insulin aggregation

Synthesis of a highly thermostable insulin by phenylalanine conjugation at B29 Lysine

Globally, millions of diabetic patients require daily life-saving insulin injections. Insulin heat-lability and fibrillation pose significant challenges, especially in parts of the world without ready access to uninterrupted refrigeration. Here, we have synthesized four human insulin analogs by conjugating ε-amine of B29 lysine of insulin with acetic acid, phenylacetic acid, alanine, and phenylalanine residues. Of these, phenylalanine-conjugated insulin, termed FHI, was the most stable under high temperature (65 °C), elevated salt stress (25 mM NaCl), and varying pH levels (ranging from highly acidic pH 1.6 to physiological pH 7.4). It resists fibrillation for a significantly longer duration with sustained biological activity in in vitro, ex vivo, and in vivo and displays prolonged stability over its native counterpart. We further unravel the critical interactions, such as additional aromatic π-π interactions and hydrogen bonding in FHI, that are notably absent in native insulin. These interactions confer enhanced structural stability of FHI and offer a promising solution to the challenges associated with insulin heat sensitivity.

Therapeutic Effects of Natural Products on Liver Cancer and Their Potential Mechanisms

Liver cancer ranks third globally among causes of cancer-related deaths, posing a significant public health challenge. However, current treatments are inadequate, prompting a growing demand for novel, safe, and effective therapies. Natural products (NPs) have emerged as promising candidates in drug development due to their diverse biological activities, low toxicity, and minimal side effects. This paper begins by reviewing existing treatment methods and drugs for liver cancer. It then summarizes the therapeutic effects of NPs sourced from various origins on liver cancer. Finally, we analyze the potential mechanisms of NPs in treating liver cancer, including inhibition of angiogenesis, migration, and invasion; regulation of the cell cycle; induction of apoptosis, autophagy, pyroptosis, and ferroptosis; influence on tumor metabolism; immune regulation; regulation of intestinal function; and regulation of key signaling pathways. This systematic review aims to provide a comprehensive overview of NPs research in liver cancer treatment, offering a foundation for further development and application in pharmaceuticals and functional foods.

Clues to the Design of Aggregation-Resistant Insulin from Proline Scanning of Highly Amyloidogenic Peptides Derived from the N-Terminal Segment of the A-Chain

Insulin aggregation poses a significant problem in pharmacology and medicine as it occurs during prolonged storage of the hormone and in vivo at insulin injection sites. We have recently shown that dominant forces driving the self-assembly of insulin fibrils are likely to arise from intermolecular interactions involving the N-terminal segment of the A-chain (ACC1-13). Here, we study how proline substitutions within the pilot GIVEQ sequence of this fragment affect its propensity to aggregate in both neutral and acidic environments. In a reasonable agreement with in silico prediction based on the Cordax algorithm, proline substitutions at positions 3, 4, and 5 turn out to be very effective in preventing aggregation according to thioflavin T-fluorescence-based kinetic assay, infrared spectroscopy, and atomic force microscopy (AFM). Since the valine and glutamate side chains within this segment are strongly involved in the interactions with the insulin receptor, we have focused on the possible implications of the Q → P substitution for insulin's stability and interactions with the receptor. To this end, comparative molecular dynamics (MD) simulations of the Q5P mutant and wild-type insulin were carried out for both free and receptor-bound (site 1) monomers. The results point to a mild destabilization of the mutant vis à vis the wild-type monomer, as well as partial preservation of key contacts in the complex between Q5P insulin and the receptor. We discuss the implications of these findings in the context of the design of aggregation-resistant insulin analogues retaining hormonal activity.

Phytochemical characterization, isolation, antioxidant and cytogenotoxic activity of leaves of Heliotropium elongatum (Lehm) I.M. Johnst

Heliotropium elongatum is used to treat inflammation, cough, and flu. This study aimed to characterize the phytochemical profile and determine the total phenolic content (TPC), antioxidant and cytogenotoxic activity of the ethanolic extract (EE), and fractions of H. elongatum leaves. In the phytochemical profile analysis, organic acids, reducing sugars, flavonoids, saponins, anthraquinones, steroids/triterpenes, and depsides/depsidones were detected in the EE and/or fractions (hexanic/FH, chloroformic/FC, ethyl acetate/FAE, and hydromethanolic/FHM). The highest TPC and highest antioxidant activity (DPPH and ABTS) was detected in FHM. In FH, 16 compounds were identified by GC-MS, and ursolic acid was isolated by 1H NMR and 13C NMR. HPLC-DAD from EE, FAE, and FHM demonstrated characteristic wavelengths for flavonoids, flavonols, flavones, and anthraquinones. ESI-IT/MSn analysis of EE, FC, FAE, and FHM revealed alkaloids, steroids, terpenoids, flavonoids, and phenolic acids. In Allium cepa assay there was no significant cytotoxic effect initiated by EE (62.5 to 1,000 µg/ml), FHM (1,000 µg/ml), and FAE (62.5 µg/ml). Genotoxicity was evidenced only with EE at 500 and 1,000 µg/ml, and FHM (62.5 to 1,000 µg/ml) as evidenced by presence of micronuclei (MN) and nuclear buds (NB). Our results identified compounds of medicinal interest with antioxidant activity; however observed cytogenotoxic changes indicated the need for caution when using these compounds for therapeutic purposes.

Probing the interactions between amyloidogenic proteins and bio-membranes

Protein misfolding diseases (PMDs) in humans are characterized by the deposition of protein aggregates in tissues, including Alzheimer's disease, Parkinson's disease, type 2 diabetes, and amyotrophic lateral sclerosis. Misfolding and aggregation of amyloidogenic proteins play a central role in the onset and progression of PMDs, and these processes are regulated by multiple factors, especially the interaction between proteins and bio-membranes. Bio-membranes induce conformational changes in amyloidogenic proteins and affect their aggregation; on the other hand, the aggregates of amyloidogenic proteins may cause membrane damage or dysfunction leading to cytotoxicity. In this review, we summarize the factors that affect the binding of amyloidogenic proteins and membranes, the effects of bio-membranes on the aggregation of amyloidogenic proteins, mechanisms of membrane disruption by amyloidogenic aggregates, technical approaches for detecting these interactions, and finally therapeutic strategies targeting membrane damage caused by amyloidogenic proteins.

Treatment Effects of Natural Products on Inflammatory Bowel Disease In Vivo and Their Mechanisms: Based on Animal Experiments

Inflammatory bowel disease (IBD) is a chronic, non-specific inflammatory disease of the intestine that can be classified as ulcerative colitis (UC) and Crohn's disease (CD). Currently, the incidence of IBD is still increasing in developing countries. However, current treatments for IBD have limitations and do not fully meet the needs of patients. There is a growing demand for new, safe, and highly effective alternative drugs for IBD patients. Natural products (NPs) are used in drug development and disease treatment because of their broad biological activity, low toxicity, and low side effects. Numerous studies have shown that some NPs have strong therapeutic effects on IBD. In this paper, we first reviewed the pathogenesis of IBD as well as current therapeutic approaches and drugs. Further, we summarized the therapeutic effects of 170 different sources of NPs on IBD and generalized their modes of action and therapeutic effects. Finally, we analyzed the potential mechanisms of NPs for the treatment of IBD. The aim of our review is to provide a systematic and credible summary, thus supporting the research on NPs for the treatment of IBD and providing a theoretical basis for the development and application of NPs in drugs and functional foods.

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.

Amyloid Disassembly: What Can We Learn from Chaperones?

Protein aggregation and subsequent accumulation of insoluble amyloid fibrils with cross-β structure is an intrinsic characteristic of amyloid diseases, i.e., amyloidoses. Amyloid formation involves a series of on-pathway and off-pathway protein aggregation events, leading to mature insoluble fibrils that eventually accumulate in multiple tissues. In this cascade of events, soluble oligomeric species are formed, which are among the most cytotoxic molecular entities along the amyloid cascade. The direct or indirect action of these amyloid soluble oligomers and amyloid protofibrils and fibrils in several tissues and organs lead to cell death in some cases and organ disfunction in general. There are dozens of different proteins and peptides causing multiple amyloid pathologies, chief among them Alzheimer's, Parkinson's, Huntington's, and several other neurodegenerative diseases. Amyloid fibril disassembly is among the disease-modifying therapeutic strategies being pursued to overcome amyloid pathologies. The clearance of preformed amyloids and consequently the arresting of the progression of organ deterioration may increase patient survival and quality of life. In this review, we compiled from the literature many examples of chemical and biochemical agents able to disaggregate preformed amyloids, which have been classified as molecular chaperones, chemical chaperones, and pharmacological chaperones. We focused on their mode of action, chemical structure, interactions with the fibrillar structures, morphology and toxicity of the disaggregation products, and the potential use of disaggregation agents as a treatment option in amyloidosis.

Modelling Parkinson's Disease in C. elegans: Strengths and Limitations

Parkinson's disease (PD) is a common neurodegenerative disease that affects the motor system and progressively worsens with age. Current treatment options for PD mainly target symptoms, due to our limited understanding of the etiology and pathophysiology of PD. A variety of preclinical models have been developed to study different aspects of the disease. The models have been used to elucidate the pathogenesis and for testing new treatments. These models include cell models, non-mammalian models, rodent models, and non-human primate models. Over the past few decades, Caenorhabditis elegans (C. elegans) has been widely adopted as a model system due to its small size, transparent body, short generation time and life cycle, fully sequenced genome, the tractability of genetic manipulation and suitability for large scale screening for disease modifiers. Here, we review studies using C. elegans as a model for PD and highlight the strengths and limitations of the C. elegans model. Various C. elegans PD models, including neurotoxin-induced models and genetic models, are described in detail. Moreover, met.

Catechol-containing compounds are a broad class of protein aggregation inhibitors: Redox state is a key determinant of the inhibitory activities

A range of neurodegenerative and related aging diseases, such as Alzheimer's disease and type 2 diabetes, are linked to toxic protein aggregation. Yet the mechanisms of protein aggregation inhibition by small molecule inhibitors remain poorly understood, in part because most protein targets of aggregation assembly are partially unfolded or intrinsically disordered, which hinders detailed structural characterization of protein-inhibitor complexes and structural-based inhibitor design. Herein we employed a parallel small molecule library-screening approach to identify inhibitors against three prototype amyloidogenic proteins in neurodegeneration and related proteinopathies: amylin, Aβ and tau. One remarkable class of inhibitors identified from these screens against different amyloidogenic proteins was catechol-containing compounds and redox-related quinones/anthraquinones. Secondary assays validated most of the identified inhibitors. In vivo efficacy evaluation of a selected catechol-containing compound, rosmarinic acid, demonstrated its strong mitigating effects of amylin amyloid deposition and related diabetic pathology in transgenic HIP rats. Further systematic investigation of selected class of inhibitors under aerobic and anaerobic conditions revealed that the redox state of the broad class of catechol-containing compounds is a key determinant of the amyloid inhibitor activities. The molecular insights we gained not only explain why a large number of catechol-containing polyphenolic natural compounds, often enriched in healthy diet, have anti-neurodegeneration and anti-aging activities, but also could guide the rational design of therapeutic or nutraceutical strategies to target a broad range of neurodegenerative and related aging diseases.

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.

Investigation of the Captopril-Insulin Interaction by Mass Spectrometry and Computational Approaches Reveals that Captopril Induces Structural Changes in Insulin

Post-translational modifications remarkably regulate proteins' biological function. Small molecules such as reactive thiols, metabolites, and drugs may covalently modify the proteins and cause structural changes. This study reports the covalent modification and noncovalent interaction of insulin and captopril, an FDA-approved antihypertensive drug, through mass spectrometric and computation-based approaches. Mass spectrometric analysis shows that captopril modifies intact insulin, reduces it into its "A" and "B" chains, and covalently modifies them by forming adducts. Since captopril has a reactive thiol group, it might reduce the insulin dimer or modify it by reacting with cysteine residues. This was proven with dithiothreitol treatment, which reduced the abundance of captopril adducts of insulin A and B chains and intact Insulin. Liquid chromatography tandem mass spectrometric analysis identified the modification of a total of four cysteine residues, two in each of the A and B chains of insulin. These modifications were identified to be Cys6 and Cys7 of the A chain and Cys7 and Cys19 of the B chain. Mass spectrometric analysis indicated that captopril may simultaneously modify the cysteine residues of intact insulin or its subunits A and B chains. Biophysical studies involving light scattering and thioflavin T assay suggested that the binding of captopril to the protein leads to the formation of aggregates. Docking and molecular dynamics studies provided insights into the noncovalent interactions and associated structural changes in insulin. This work is a maiden attempt to understand the detailed molecular interactions between captopril and insulin. These findings suggest that further investigations are required to understand the long-term effect of drugs like captopril.

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.

The inhibitory effect of Sunset Yellow on thermally induced Human Serum Albumin aggregates: Possible role in naturopathy

Intensive research in the field of protein aggregation confirmed that the deposition of amyloid fibrils of proteins are the major cause for the development of various neurotoxic and neurodegenerative diseases, which could be controlled by ensuring the efficient inhibition of aggregation using anti aggregation strategies. Herein, we elaborated the anti amyloidogenic potential of Sunset Yellow (SY) dye against Human Serum Albumin (HSA) fibrillogenesis utilising different biophysical, computational and microscopic techniques. The inhibitory effect of sunset yellow was confirmed by Rayleigh Light Scattering (RLS) measurements along with different dye binding assays (ANS, ThT and CR) by showing concentration dependent reduction in scattering intensity and fluorescence intensity respectively. Further, destabilization and anti fibrillation activity of HSA aggregates were characterized through spectroscopic techniques like Circular Dichroism (CD) and other microscopic techniques like Transmission Electron Microscopy (TEM) for elucidating the structural properties. The SDS-PAGE was also carried out that render the disaggregation effect of the dye on the protein. Moreover, Molecular Docking studies revealed the binding parameters justifying the stable protein-dye complex. Simulation studies were also performed accordingly. Thus, this dye which is used as food additive can serve as a potential aggregation inhibiting agent that can aid in the prevention of amyloidogenic diseases.

Antioxidants in Alzheimer's Disease: Current Therapeutic Significance and Future Prospects

Alzheimer's disease (AD) rate is accelerating with the increasing aging of the world's population. The World Health Organization (WHO) stated AD as a global health priority. According to the WHO report, around 82 million people in 2030 and 152 million in 2050 will develop dementia (AD contributes 60% to 70% of cases), considering the current scenario. AD is the most common neurodegenerative disease, intensifying impairments in cognition, behavior, and memory. Histopathological AD variations include extracellular senile plaques' formation, tangling of intracellular neurofibrils, and synaptic and neuronal loss in the brain. Multiple evidence directly indicates that oxidative stress participates in an early phase of AD before cytopathology. Moreover, oxidative stress is induced by almost all misfolded protein lumps like α-synuclein, amyloid-β, and others. Oxidative stress plays a crucial role in activating and causing various cell signaling pathways that result in lesion formations of toxic substances, which foster the development of the disease. Antioxidants are widely preferred to combat oxidative stress, and those derived from natural sources, which are often incorporated into dietary habits, can play an important role in delaying the onset as well as reducing the progression of AD. However, this approach has not been extensively explored yet. Moreover, there has been growing evidence that a combination of antioxidants in conjugation with a nutrient-rich diet might be more effective in tackling AD pathogenesis. Thus, considering the above-stated fact, this comprehensive review aims to elaborate the basics of AD and antioxidants, including the vitality of antioxidants in AD. Moreover, this review may help researchers to develop effectively and potentially improved antioxidant therapeutic strategies for this disease as it also deals with the clinical trials in the stated field.

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.

Targeting disorders in unstructured and structured proteins in various diseases

Intrinsically disordered proteins (IDPs) and intrinsically disordered protein regions (IDPRs) are proteins and protein segments that usually do not acquire well-defined folded structures even under physiological conditions. They are abundantly present and challenge the "one sequence-one structure-one function" theory due to a lack of stable secondary and/or tertiary structure. Due to conformational flexibility, IDPs/IDPRs can bind with multiple interacting partners with high-specificity and low-affinity and perform essential biological functions associated with signalling, recognition and regulation. Mis-functioning and mis-regulation of IDPs and IDPRs causes disorder in disordered proteins and disordered protein segments which results in numerous human diseases, such as cancer, Parkinson's disease (PD), Alzheimer's disease (AD), diabetes, metabolic disorders, systemic disorders and so on. Due to the strong connection of IDPs/IDPRs with human diseases they are considered potentential targets for drug therapy. Since they disobey the "one sequence-one structure-one function" concept, IDPs/IDPRs are complex systems for drug targeting. This review summarises various protein disorder diseases and different methods for therapeutic targeting of disordered proteins/segments. Targeting IDPs/IDPRs for diseases will open up a new era of rational drug design and drug discovery.

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.

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.

Marine derivatives prevent wMUS81 in silico studies

The winged-helix domain of the methyl methanesulfonate and ultraviolet-sensitive 81 (wMUS81) is a potential cancer drug target. In this context, marine fungi compounds were indicated to be able to prevent wMUS81 structure via atomistic simulations. Eight compounds such as D197 (Tryptoquivaline U), D220 (Epiremisporine B), D67 (Aspergiolide A), D153 (Preussomerin G), D547 (12,13-dihydroxyfumitremorgin C), D152 (Preussomerin K), D20 (Marinopyrrole B) and D559 (Fumuquinazoline K) were indicated that they are able to prevent the conformation of wMUS81 via forming a strong binding affinity to the enzyme via perturbation approach. The electrostatic interaction is the dominant factor in the binding process of ligands to wMUS81. The residues Trp55, Arg59, Leu62, His63 and Arg69 were found to frequently form non-bonded contacts and hydrogen bonds to inhibitors. Moreover, the influence of the ligand D197, which formed the lowest binding free energy to wMUS81, on the structural change of enzyme was investigated using replica exchange molecular dynamics simulations. The obtained results indicated that D197, which forms a strong binding affinity, can modify the structure of wMUS81. Overall, the marine compounds probably inhibit wMUS81 due to forming a strong binding affinity to the enzyme as well as altering the enzymic conformation.

Inhibitory activities of anthraquinone and xanthone derivatives against transthyretin amyloidogenesis

Transthyretin is a tetrameric protein which functions as a transporter of thyroxine and retinol-binding protein. Misfolding and amyloid aggregation of transthyretin are known to cause wild-type and hereditary transthyretin amyloidosis. Stabilization of the transthyretin tetramer by low molecular weight compounds is an efficacious strategy to inhibit the aggregation pathway in the amyloidosis. Here, we investigated the inhibitory activities of anthraquinone and xanthone derivatives against amyloid aggregation, and found that xanthone-2-carboxylic acid with one chlorine or methyl group has strong inhibitory activity comparable with that of diflunisal, which is one of the best known stabilizers of transthyretin. X-ray crystallographic structures of transthyretin in complex with the compounds revealed that the introduction of chlorine, which is buried in a hydrophobic region, is important for the strong inhibitory effect of the stabilizer against amyloidogenesis. An in vitro absorption, distribution, metabolism and elimination (ADME) study and in vivo pharmacokinetic study demonstrated that the compounds have drug-like features, suggesting that they have potential as therapeutic agents to stabilize transthyretin.

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.

Alizarin and Purpurin from Rubia tinctorum L. Suppress Insulin Fibrillation and Reduce the Amyloid-Induced Cytotoxicity

Alizarin (1,2-dihydroxyanthraquinone) and purpurin (1,2,4-trihydroxyanthraquinone), natural anthraquinone compounds from Rubia tinctorum L., are reported to have diverse biological effects including antibacterial, antitumor, antioxidation, and so on, but the inhibition activity against amyloid aggregation has been rarely reported. In this study, we used insulin as a model protein to explore the anti-amyloid effects of the two compounds. The results showed that alizarin and purpurin inhibited the formation of insulin fibrils in a dose-dependent manner and reduced insulin-induced cytotoxicity. Meanwhile, purpurin had a more significant inhibitory effect on insulin amyloid fibrils compared with alizarin. In addition, computer simulations indicated that the two compounds interacted mainly with the hydrophobic residues of insulin chain B and interfered with the binding of phenylalanine residues. The research indicated that natural anthraquinone compounds had potential effects in preventing protein misfolding diseases and could be further used to design effective antiamyloidosis compounds.

Neuroprotective Natural Products for Alzheimer's Disease

Alzheimer’s disease (AD) is the number one neurovegetative disease, but its treatment options are relatively few and ineffective. In efforts to discover new strategies for AD therapy, natural products have aroused interest in the research community and in the pharmaceutical industry for their neuroprotective activity, targeting different pathological mechanisms associated with AD. A wide variety of natural products from different origins have been evaluated preclinically and clinically for their neuroprotective mechanisms in preventing and attenuating the multifactorial pathologies of AD. This review mainly focuses on the possible neuroprotective mechanisms from natural products that may be beneficial in AD treatment and the natural product mixtures or extracts from different sources that have demonstrated neuroprotective activity in preclinical and/or clinical studies. It is believed that natural product mixtures or extracts containing multiple bioactive compounds that can work additively or synergistically to exhibit multiple neuroprotective mechanisms might be an effective approach in AD drug discovery.

From Small Molecules to Synthesized Polymers: Potential Role in Combating Amyloidogenic Disorders

The concept of developing novel anti-amyloid inhibitors in the scientific community has engrossed remarkable research interests and embraced significant potential to resolve numerous pathological conditions including neurological as well as non-neuropathic disorders associated with amyloid protein aggregation. These pathological conditions have harmful effects on cellular activities which include malfunctioning of organs and tissue, cellular impairment, etc. To date, different types of small molecular probes like polyphenolic compounds, nanomaterials, surfactants, etc. have been developed to address these issues. Recently synthetic polymeric materials are extensively investigated to explore their role in the protein aggregation pathway. On the basis of these perspectives, in this review article, we have comprehensively summarized the current perspectives on protein misfolding and aggregation and importance of therapeutic approaches in designing novel effective inhibitors. The main purpose of this review article is to provide a detailed perspective of the current landscape as well as trailblazing voyage of various inhibitors ranging from small molecular probes to polymeric scaffolds in the field of protein misfolding and aggregation. A particular emphasis is given on the structural role and molecular mechanistic pathway involved in modulating the aggregation pathway to further inspire the researchers and shed light in this bright research field.

A Systematic Screening of Traditional Chinese Medicine Identifies Two Novel Inhibitors Against the Cytotoxic Aggregation of Amyloid Beta

The toxic aggregates of amyloid beta (Aβ) disrupt the cell membrane, induce oxidative stress and mitochondrial dysfunction, and eventually lead to Alzheimer’s disease (AD). Intervening with this cytotoxic aggregation process has been suggested as a potential therapeutic approach for AD and other protein misfolding diseases. Traditional Chinese Medicine (TCM) has been used to treat AD and related cognitive impairment for centuries with obvious efficacy. Extracts or active ingredients of TCMs have been reported to inhibit the aggregation and cytotoxicity of Aβ. However, there is a lack of systematic research on the anti-Aβ aggregation effects of TCM components. In this study, we performed a systematic screening to identify the active ingredients of TCM against the cytotoxic aggregation of Aβ42. Through a literature and database survey, we selected 19 TCM herbals frequently used in the treatment of AD, from which 76 major active chemicals without known anti-amyloid effects were further screened. This took place through two rounds of MTT-based screening detection of the cytotoxicity of these chemicals and their effects on Aβ42-induced cytotoxicity, respectively. Tetrahydroxystilbene-2-O-β-D-glucoside (TSG) and sinapic acid (SA) were found to be less toxic, and they inhibited the cytotoxicity of Aβ42. Further studies demonstrated that TSG and SA concentration-dependently attenuated the amyloidosis and membrane disruption ability of Aβ42. Thus, we identified two novel chemicals (TSG and SA) against the cytotoxic aggregation of Aβ42. Nonetheless, further exploration of their therapeutic potential is warranted.

N-Methylated Analogs of hIAPP Fragments 18-22, 23-27, 33-37 Inhibit Aggregation of the Amyloidogenic Core of the Hormone

Amylin (hIAPP) aggregation leads to the formation of insoluble deposits and is one of the factors in the development of type II diabetes. The aim of this research was to find N-methylated analogs of the aggregating amylin fragments 18-22, 23-27, and 33-37, which would not themselves be susceptible to aggregation and would inhibit the aggregation of the amyloidogenic cores of the hormone. None of the analogs of fragment 18-22 containing one or two N-methylated amino acid residues showed any tendency to aggregate. Only the peptide H-F(N-Me)GA(N-Me) IL-OH (6) derived from the 23-27 hIAPP hot spot did not form fibrous structures. All analogs of the 33-37 amylin fragment were characterized by the ability to form aggregates, despite the presence of N-methylated amino acids in their structures. N-Methylated peptides 1-5 demonstrated inhibitory properties against the aggregation of fragment 18-22. Aggregation of the amyloidogenic core of 23-27 was significantly inhibited by N-methylated peptides 1-3 derived from the (18-22) H-HSSNN-OH fragment and by the H-F(N-Me)GA(N-Me)IL-OH (6) fragment derived from the 23-27 amylin hot spot. Fragment (33-37) H-GSNTY-NH₂ was found to be inhibited in the presence of N-methylated peptides 1-3 derived from the 18-22 fragment and by the double methylated peptide H-F(N-Me)GA(N-Me)IL-OH (6). Research on the possibility of using N-methylated analogs of amyloidogenic amylin cores as inhibitors of hormone aggregation is ongoing, with a focus on finding the minimum concentration of N-methylated peptides capable of inhibiting the aggregation of hIAPP hot spots.

Inhibition of amyloid fibrillation of γD-crystallin model peptide by the cochineal Carmine

γD-crystallin is among the most abundant γ-crystallins in the human eye lens which are essential for preserving its transparency. Aging, and environmental changes, cause crystallins to lose their native soluble structure and aggregate, resulting in the formation of cataract. Current treatment of cataract is surgical removal which is costly. Pharmaceutical therapeutics of cataract is an unmet need. We report a screen for small molecules capable of inhibiting aggregation of human γD-crystallin. Using a highly amyloidogenic hexapeptide model ⁴¹GCWMLY⁴⁶ derived from the full-length protein, we screened a library of 68 anthraquinone molecules using ThT fluorescence assay. A leading hit, the cochineal Carmine, effectively reduced aggregation of the model GDC6 peptide in dose dependent manner. Similar effect was observed toward aggregation of the full-length γD-crystallin. Transmission electron microscopy, intrinsic Tryptophan fluorescence and ANS fluorescence assays corroborated these results. Insights obtained from molecular docking suggested that Carmine interaction with monomeric GDC6 involved hydrogen bonding with Ace group, Cys, Met residues and hydrophobic contact with Trp residue. Carmine was non-toxic toward retinal cells in culture. It also reduced ex vivo the turbidity of human extracted cataract material. Collectively, our results indicate that Carmine could be used for developing new therapeutics to treat cataract.

Bioactive Agent Discovery from the Natural Compounds for the Treatment of Type 2 Diabetes Rat Model

Diabetes mellitus is a well-known chronic metabolic disease that poses a long-term threat to human health and is characterized by a relative or absolute lack of insulin, resulting in hyperglycemia. Type 2 diabetes mellitus (T2DM) typically affects many metabolic pathways, resulting in β-cell dysfunction, insulin resistance, abnormal blood glucose levels, inflammatory processes, excessive oxidative reactions, and impaired lipid metabolism. It also leads to diabetes-related complications in many organ systems. Antidiabetic drugs have been approved for the treatment of hyperglycemia in T2DM; these are beneficial for glucose metabolism and promote weight loss, but have the risk of side effects, such as nausea or an upset stomach. A wide range of active components, derived from medicinal plants, such as alkaloids, flavonoids, polyphenol, quinones, and terpenoids may act as alternative sources of antidiabetic agents. They are usually attributed to improvements in pancreatic function by increasing insulin secretions or by reducing the intestinal absorption of glucose. Ease of availability, low cost, least undesirable side effects, and powerful pharmacological actions make plant-based preparations the key player of all available treatments. Based on the study of therapeutic reagents in the pathogenesis of humans, we use the appropriate animal models of T2DM to evaluate medicinal plant treatments. Many of the rat models have characteristics similar to those in humans and have the advantages of ease of genetic manipulation, a short breeding span, and access to physiological and invasive testing. In this review, we summarize the pathophysiological status of T2DM rat models and focus on several bioactive compounds from herbal medicine with different functional groups that exhibit therapeutic potential in the T2DM rat models, in turn, may guide future approach in treating diabetes with natural drugs.

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.

Gallic acid oxidation products alter the formation pathway of insulin amyloid fibrils

Amyloidogenic protein assembly into insoluble fibrillar aggregates is linked with several neurodegenerative disorders, such as Alzheimer’s or Parkinson’s disease, affecting millions of people worldwide. The search for a potential anti-amyloid drug has led to the discovery of hundreds of compounds, none of which have passed all clinical trials. Gallic acid has been shown to both modulate factors leading to the onset of neurodegenerative disorders, as well as directly inhibit amyloid formation. However, the conditions under which this effect is seen could lead to oxidation of this polyphenol, likely changing its properties. Here we examine the effect of gallic acid and its oxidised form on the aggregation of a model amyloidogenic protein–insulin at low pH conditions. We show a vastly higher inhibitory potential of the oxidised form, as well as an alteration in the aggregation pathway, leading to the formation of a specific fibril conformation.

Nanostructures Formed by Custom-Made Peptides Based on Amyloid Peptide Sequences and Their Inhibition by 2-Hydroxynaphthoquinone

Extensive research on amyloid fibril formations shows that certain core sequences within Aβ peptide play an important role in their formation. It is impossible to track these events in vivo. Many proteins and peptides with such core sequences form amyloid fibrils and such Aβ sheet mimics have become excellent tools to study amyloid fibril formation and develop therapeutic strategies. A group of peptides based on amyloid peptide sequences obtained from PDB searches, where glycine residues are substituted with alanine and isoleucine, are tested for aggregation by SEM and ThT binding assay. SEM of different peptide sequences showed morphologically different structures such as nanorods, crystalline needles and nanofibrils. The peptides were co-incubated with HNQ (a quinone) to study its effect on the process of aggregation and/or fibrillation. In conclusion, this group of peptides seem to be Aβ sheet mimics and can be very useful in understanding the different morphologies of amyloid fibrils arising from different peptide sequences and the effective strategies to inhibit or anneal them.

Small-Molecule Inhibitor Prevents Insulin Fibrillogenesis and Preserves Activity

Amyloidosis is a well-known but poorly understood phenomenon caused by the aggregation of proteins, often leading to pathological conditions. For example, the aggregation of insulin poses significant challenges during the preparation of pharmaceutical insulin formulations commonly used to treat diabetic patients. Therefore, it is essential to develop inhibitors of insulin aggregation for potential biomedical applications and for important mechanistic insights into amyloidogenic pathways. Here, we have identified a small molecule M1, which causes a dose-dependent reduction in insulin fibril formation. Biophysical analyses and docking results suggest that M1 likely binds to partially unfolded insulin intermediates. Further, M1-treated insulin had lower cytotoxicity and remained functionally active in regulating cell proliferation in cultured Drosophila wing epithelium. Thus, M1 is of great interest as a novel agent for inhibiting insulin aggregation during biopharmaceutical manufacturing.

Resveratrol as a nontoxic excipient stabilizes insulin in a bioactive hexameric form

Insulin aggregation is the leading cause of considerable reduction in the amount of active drug molecules in liquid formulations manufactured for diabetes management. Phenolic compounds, such as phenol and m-cresol, are routinely used to stabilize insulin in a hexameric form during its commercial preparation. However, long term usage of commercial insulin results in various adverse secondary responses, for which toxicity of the phenolic excipients is primarily responsible. In this study we aimed to find out a nontoxic insulin stabilizer. To that end, we have selected resveratrol, a natural polyphenol, as a prospective nontoxic insulin stabilizer because of its structural similarity with commercially used phenolic compounds. Atomic force microscopy visualization of resveratrol-treated human insulin revealed that resveratrol has a unique ability to arrest hINS in a soluble oligomeric form having discrete spherical morphology. Most importantly, resveratrol-treated insulin is nontoxic for HepG2 cells and it effectively maintains low blood glucose in a mouse model. Cryo-electron microscopy revealed 3D morphology of resveratrol-stabilized insulin that strikingly resembles crystal structures of insulin hexamer formulated with m-cresol. Significantly, we found that, in a condition inductive to amyloid fibrillation at physiological pH, resveratrol is capable of stabilizing insulin more efficiently than m-cresol. Thus, this study describes resveratrol as an effective nontoxic natural molecule that can be used for stabilizing insulin in a bioactive oligomeric form during its commercial formulation.

Non-polyphenolic natural inhibitors of amyloid aggregation

Protein misfolding diseases (PMDs) are chronic and progressive, with no effective therapy so far. Aggregation and misfolding of amyloidogenic proteins are closely associated with the onset and progression of PMDs, such as amyloid-β (Aβ) in Alzheimer's disease, α-Synuclein (α-Syn) in Parkinson's disease and human islet amyloid polypeptide (hIAPP) in type 2 diabetes. Inhibiting toxic aggregation of amyloidogenic proteins is regarded as a promising therapeutic approach in PMDs. The past decade has witnessed the rapid progresses of this field, dozens of inhibitors have been screened and verified in vitro and in vivo, demonstrating inhibitory effects against the aggregation and misfolding of amyloidogenic proteins, together with beneficial effects. Natural products are major sources of small molecule amyloid inhibitors, a number of natural derived compounds have been identified with great bioactivities and translational prospects. Here, we review the non-polyphenolic natural inhibitors that potentially applicable for PMDs treatment, along with their working mechanisms. Future directions are proposed for the development and clinical applications of these inhibitors.

Human Molecular Chaperone Hsp60 and Its Apical Domain Suppress Amyloid Fibril Formation of α-Synuclein

Heat shock proteins play roles in assisting other proteins to fold correctly and in preventing the aggregation and accumulation of proteins in misfolded conformations. However, the process of aging significantly degrades this ability to maintain protein homeostasis. Consequently, proteins with incorrect conformations are prone to aggregate and accumulate in cells, and this aberrant aggregation of misfolded proteins may trigger various neurodegenerative diseases, such as Parkinson's disease. Here, we investigated the possibilities of suppressing α-synuclein aggregation by using a mutant form of human chaperonin Hsp60, and a derivative of the isolated apical domain of Hsp60 (Hsp60 AD(Cys)). In vitro measurements were used to detect the effects of chaperonin on amyloid fibril formation, and interactions between Hsp60 proteins and α-synuclein were probed by quartz crystal microbalance analysis. The ability of Hsp60 AD(Cys) to suppress α-synuclein intracellular aggregation and cytotoxicity was also demonstrated. We show that Hsp60 mutant and Hsp60 AD(Cys) both effectively suppress α-synuclein amyloid fibril formation, and also demonstrate for the first time the ability of Hsp60 AD(Cys) to function as a mini-chaperone inside cells. These results highlight the possibility of using Hsp60 AD as a method of prevention and treatment of neurodegenerative diseases.

Therapeutic Effects of Natural Drugs on Alzheimer's Disease

Alzheimer disease (AD) is characterized as a chronic neurodegenerative disease associated with aging. The clinical manifestations of AD include latent episodes of memory and cognitive impairment, psychiatric symptoms and behavioral disorders, as well as limited activities in daily life. In developed countries, AD is now acknowledged as the third leading cause of death, following cardiovascular disease and cancer. The pathogenesis and mechanism of AD remain unclear, although some theories have been proposed to explain AD, such as the theory of β-amyloid, the theory of the abnormal metabolism of tau protein, the theory of free radical damage, the theory of the inflammatory response, the theory of cholinergic damage, etc. Effective methods to predict, prevent or reverse AD are unavailable, and thus the development of new, efficient therapeutic drugs has become a current research hot spot worldwide. The isolation and extraction of active components from natural drugs have great potential in treating AD. These drugs possess the advantages of multiple targets in multiple pathways, fewer side effects and a long duration of curative effects. This article summaries the latest research progress regarding the mechanisms of natural drugs in the treatment of AD, providing a review of the literature and a theoretical basis for improving the clinical treatment of AD.

Both beta sheet breaker and alpha helix forming pentapeptide inhibits protein fibrillation: Implication for the treatment of amyloid disorders

For the first time, the effect of two novel designed pentapeptides on amyloid growth of human insulin using combined biophysical, microscopic, cell viability and computational approaches. Collective experimental data from ThT, ANS, and TEM demonstrate that in spite of having contrasting features, both peptides can effectively inhibit amyloid formation by prolonging lag phase, slowing down aggregation rate, and reducing final fibril formation (up to 84.26% and 85.24% by P1 and P7 respectively). Although pure amyloid caused profound cellular toxicity in SH-SY5Y neuronal cells, amyloid formed in the presence of peptides showed much reduced cellular toxicity. Such an inhibitory effect can be attributed to interference with the structural transition of insulin toward β-sheet structure by peptides. Furthermore, molecular dynamic simulations confirm that peptide preferentially binds to nearby region which is more prone to form aggregates that consequently disrupts self-assembly into amyloid fibrils (P1 and P7 possess inhibition constant value of 0.000183 and 0.000216 nm, respectively), supporting our experimental observations. This study underscores the information about the sequence based inhibition mechanism of peptides that might dictate their inhibition or modulation capacity, which might be helpful in designing anti-amyloid therapeutics.

Biophysical Elucidation of Amyloid Fibrillation Inhibition and Prevention of Secondary Nucleation by Cholic Acid: An Unexplored Function of Cholic Acid

Protein misfolding and its deviant self-assembly to converge into amyloid fibrils is associated with the perturbation of cellular functions and thus with debilitating neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, etc. A great deal of research has already been carried out to discover a potential amyloid inhibitor that can slow down, prevent, or remodel toxic amyloids. In the present study with the help of a combination of biophysical, imaging, and computational techniques, we investigated the mechanism of interaction of cholic acid (CA), a primary bile acid, with human insulin and Aβ-42 and found CA to be effective in inhibiting amyloid formation. From ThT data, we inferred that CA encumbers amyloid fibrillation up to 90% chiefly by targeting elongation of fibrils with an insignificant effect on lag time, while in the case of Aβ-42, CA stabilizes the peptide in its native state preventing its fibrillation. Strikingly upon adding initially at the secondary nucleation stage, CA also detained the progression/growth of insulin fibrils. CA is unable to prevent the conformational changes completely during fibrillation but tends to resist and maintain an α helical structure up to a significant extent at a primary nucleation stage while reducing the β sheet rich content at the secondary nucleation stage. Moreover, CA treated samples exhibited reduced cytotoxicity and different morphology. Furthermore, the results obtained after molecular docking indicated that CA is interacting with insulin via hydrogen bonds. For future research, this study can be considered as preliminary research for the development of CA, a metabolite of our body, as a potential therapeutic agent against Alzheimer's disease without even stimulating the immunological responses.

The Potential of Serratiopetidase and Lumbrokinase for the Degradation of Prion Peptide 106-126 - an In Vitro and In Silico Perspective

BACKGROUND

PrPC is a host-encoded prion protein, which gets post translationally modified into a transmissible, β-sheet rich disease associated protein called PrPSc, responsible for the Prion disease including mad cow disease in cattle and CJD in humans. The PrP 106-126 region in PrPSc peptide initiates the conformational change in that protein leading to fibrillation. Any agent that can destabilize or disintegrate such proteins can be served as a potential drug candidate for Prion diseases.

METHODS

In the present study, an enzyme Lumbrokinase (LK) was isolated from earthworm and its activity was exploited towards PrP 106-126 amyloids in vitro along with another enzyme Serratiopeptidase (SP) taking Nattokinase (NK) as a standard.

RESULTS

The results showed that PrP 106-126 amyloid formation was inhibited by both LK and SP, as evidenced from Thioflavin T fluorescence assay. Further, the size of fibrils as estimated by dynamic light scattering, was also found to be lower at different time intervals after incubation of the prion amyloids with LK and SP. Additionally, the molecular dynamics simulation revealed the thermodynamically favorable interaction of PrP 106-126 with LK as well as with SP with high affinity.

CONCLUSION

Finally, the toxicity of the disintegrated amyloids was assessed using PC12 cell lines which showed higher cell viability in case of LK and SP treated amyloids compared to only PrP 106- 126 amyloid treatment. Altogether, the study concluded that the serine proteases like LK and SP have the potential to disintegrate PrP 106-126 amyloids with improved cell viability. The in vivo studies are needed to be executed in future.

Physical PEGylation to Prevent Insulin Fibrillation

Insulin is one of the most marketed therapeutic proteins worldwide. However, its formulation suffers from fibrillation, which affects the long-term storage limiting the development of novel devices for sustained delivery including portable infusion devices. We have investigated the effect of physical PEGylation on structural and colloidal stability of insulin by using 2 PEGylating agents terminating with polycyclic hydrophobic moieties, cholane and cholesterol: mPEG_5kDa-cholane and mPEG_5kDa-cholesterol, respectively. Microcalorimetric analyses showed that mPEG_5kDa-cholane and mPEG_5kDa-cholesterol efficiently bind insulin with binding constants (Ka) of 3.98 10⁴ and 1.14 10⁵ M^-1, respectively. At room temperature, the 2 PEGylating agents yielded comparable structural stabilization of α-helix conformation and decreased dimerization of insulin. However, melting studies showed that mPEG_5kDa-cholesterol has superior stabilizing effect of the protein conformation than mPEG_5kDa-cholane. Furthermore, the fibrillation study showed that at a 1:1 and 1:5 insulin/polymer molar ratios, mPEG_5kDa-cholesterol delays insulin fibrillation 40% and 26% more efficiently, respectively, as compared to mPEG_5kDa-cholane which was confirmed by transmission electron microscopy imaging. Insulin was released from the mPEG_5kDa-cholane and mPEG_5kDa-cholesterol assemblies with comparable kinetic profiles. The physical PEGylation has a beneficial effect on the stabilization and shielding of the insulin structure into the monomeric form, which is not prone to fibrillation and aggregation.

Naphthoquinone Tryptophan Hybrids: A Promising Small Molecule Scaffold for Mitigating Aggregation of Amyloidogenic Proteins and Peptides

A current challenge faced by researchers is the lack of disease-modifying therapeutics for amyloid formation that is associated with several human diseases. Although the monomeric proteins or peptides involved in various amyloidogenic diseases do not have amino acid sequence homology, there appears to be a structural correlation among the amyloid assemblies, which are responsible for distinct pathological conditions. Here, we review our work on Naphthoquinone Tryptophan (NQTrp) hybrids, a small molecule scaffold that can generically modulate neuronal and non-neuronal amyloid aggregation both in vitro and in vivo. NQTrp reduces the net amyloid load by inhibiting the process of amyloid formation and disassembling the pre-formed fibrils, both in a dose-dependent manner. As a plausible mechanism of action, NQTrp effectively forms hydrogen bonding and hydrophobic interactions, such as π-π stacking, with the vital residues responsible for the initial nucleation of protein/peptide aggregation. This review highlights the effectiveness of the NQTrp hybrid scaffold for developing novel small molecule modulators of amyloid aggregation.