Structurally distinct external solvent-exposed domains drive replication of major human prions.

There is a limited understanding of structural attributes that encode the iatrogenic transmissibility and various phenotypes of prions causing the most common human prion disease, sporadic Creutzfeldt-Jakob disease (sCJD). Here we report the detailed structural differences between major sCJD MM1, MM2, and VV2 prions determined with two complementary synchrotron hydroxyl radical footprinting techniques-mass spectrometry (MS) and conformation dependent immunoassay (CDI) with a panel of Europium-labeled antibodies. Both approaches clearly demonstrate that the phenotypically distant prions differ in a major way with regard to their structural organization, and synchrotron-generated hydroxyl radicals progressively inhibit their seeding potency in a strain and structure-specific manner. Moreover, the seeding rate of sCJD prions is primarily determined by strain-specific structural organization of solvent-exposed external domains of human prion particles that control the seeding activity. Structural characteristics of human prion strains suggest that subtle changes in the organization of surface domains play a critical role as a determinant of human prion infectivity, propagation rate, and targeting of specific brain structures.

Amyloid Oligomers, Protofibrils and Fibrils.

Amyloid diseases are of major concern all over the world due to a number of factors including: (i) aging population, (ii) increasing life span and (iii) lack of effective pharmacotherapy options. The past decade has seen intense research in discovering disease-modifying multi-targeting small molecules as therapeutic options. In recent years, targeting the amyloid cascade has emerged as an attractive strategy to discover novel neurotherapeutics. Formation of amyloid species, with different degrees of solubility and neurotoxicity is associated with the gradual decline in cognition leading to dementia/cell dysfunction. Here, in this chapter, we have described the recent scenario of amyloid diseases with a great deal of information about the structural features of oligomers, protofibrils and fibrils. Also, comprehensive details have been provided to differentiate the degree of toxicity associated with prefibrillar aggregates. Moreover, a review of the technologies that aid characterisation of oligomer, protofibrils and fibrils as well as various inhibition strategies to overcome protein fibrillation are also discussed.

Stabilizing proteins to prevent conformational changes required for amyloid fibril formation.

Amyloid fibrillation is associated with several human maladies, such as Alzheimer's, Parkinson's, Huntington's diseases, prions, amyotrophic lateral sclerosis, and type 2 diabetes diseases. Gaining insights into the mechanism of amyloid fibril formation and exploring novel approaches to fibrillation inhibition are crucial for preventing amyloid diseases. Here, we hypothesized that ligands capable of stabilizing the native state of query proteins might prevent protein unfolding, which, in turn, may reduce the propensity of proteins to form amyloid fibrils. We demonstrated the efficient inhibition of amyloid formation of the human serum albumin (HSA) (up to 85%) and human insulin (up to 80%) by a nonsteroidal anti-inflammatory drug, ibuprofen (IBFN). IBFN significantly increases the conformational stability of both HSA and insulin, as confirmed by differential scanning calorimetry (DSC). Moreover, increasing concentration of IBFN boosts its amyloid inhibitory propensity in a linear fashion by influencing the nucleation phase as assayed by thioflavin T fluorescence, transmission electron microscopy, and dynamic light scattering. Furthermore, circular dichroism analysis supported the DSC results, showing that IBFN binds to the native state of proteins and almost completely prevents their tendency to lose secondary and tertiary structures. Cell toxicity assay confirms that species formed in the presence of IBFN are less toxic to neuronal cells (SH-SY5Y). These results demonstrate the feasibility of using a small molecule to stabilize the native state of proteins, thereby preventing the amyloidogenic conformational changes, which appear to be the common link in several human amyloid diseases.

Explication of bovine serum albumin binding with naphthyl hydroxamic acids using a multispectroscopic and molecular docking approach along with its antioxidant activity.

In the present investigation, the protein-binding properties of naphthyl-based hydroxamic acids (HAs), N-1-naphthyllaurohydroxamic acid (1) and N-1-naphthyl-p-methylbenzohydroxamic acid (2) were studied using bovine serum albumin (BSA) and UV-visible spectroscopy, fluorescence spectroscopy, diffuse reflectance spectroscopy-Fourier transform infrared (DRS-FTIR), circular dichroism (CD), and cyclic voltammetry along with computational approaches, i.e. molecular docking. Alteration in the antioxidant activities of compound 1 and compound 2 during interaction with BSA was also studied. From the fluorescence studies, thermodynamic parameters such as Gibb's free energy (ΔG), entropy change (ΔS) and enthalpy change (ΔH) were calculated at five different temperatures (viz., 298, 303, 308, 313 or 318 K) for the HAs-BSA interaction. The results suggested that the binding process was enthalpy driven with dominating hydrogen bonds and van der Waals' interactions for both compounds. Warfarin (WF) and ibuprofen (IB) were used for competitive site-specific marker binding interaction and revealed that compound 1 and compound 2 were located in subdomain IIA (Sudlow's site I) on the BSA molecule. Conclusions based on above-applied techniques signify that various non-covalent forces were involved during the HAs-BSA interaction. Therefore the resulted HAs-BSA interaction manifested its effect in transportation, distribution and metabolism for the drug in the blood circulation system, therefore establishing HAs as a drug-like molecule.

Capreomycin inhibits the initiation of amyloid fibrillation and suppresses amyloid induced cell toxicity.

Protein aggregation and amyloid fibrillation are responsible for several serious pathological conditions (like type II diabetes, Alzheimer's and Parkinson's diseases etc.) and protein drugs ineffectiveness. Therefore, a molecule that can inhibit the amyloid fibrillation and potentially clear amyloid fibrils is of great therapeutic value. In this manuscript, we investigated the antiamyloidogenic, fibril disaggregating, as well as cell protective effect of an anti-tuberculosis drug, Capreomycin (CN). Aggregation kinetics data, as monitored by ThT fluorescence, inferred that CN retards the insulin amyloid fibrillation by primarily targeting the fibril elongation step with little effect on lag time. Increasing the dose of CN boosted its inhibitory potency. Strikingly, CN arrested the growth of fibrils when added during the elongation phase, and disaggregated mature insulin fibrils. Our Circular Dichroism (CD) results showed that, although CN is not able to maintain the alpha helical structure of protein during fibrillation, reduces the formation of beta sheet rich structure. Furthermore, Dynamic Light Scattering (DLS) and Transmission Electronic Microscopy (TEM) analysis confirmed that CN treated samples exhibited different size distribution and morphology, respectively. In addition, molecular docking results revealed that CN interacts with insulin through hydrophobic interactions as well as hydrogen bonding, and the Hemolytic assay confirmed the non-hemolytic activity of CN on human RBCs. For future research, this study may assist in the rational designing of molecules against amyloid formation.

Ascorbic acid inhibits human insulin aggregation and protects against amyloid induced cytotoxicity.

Protein aggregation into oligomers and fibrils are associated with many human pathophysiologies. Compounds that modulate protein aggregation and interact with preformed fibrils and convert them to less toxic species, expect to serve as promising drug candidates and aid to the drug development efforts against aggregation diseases. In present study, the kinetics of amyloid fibril formation by human insulin (HI) and the anti-amyloidogenic activity of ascorbic acid (AA) were investigated by employing various spectroscopic, imaging and computational approaches. We demonstrate that ascorbic acid significantly inhibits the fibrillation of HI in a dose-dependent manner. Interestingly ascorbic acid destabilise the preformed amyloid fibrils and protects human neuroblastoma cell line (SH- SY5Y) against amyloid induced cytotoxicity. The present data signifies the role of ascorbic acid that can serve as potential molecule in preventing human insulin aggregation and associated pathophysiologies.

Repositioning nordihydroguaiaretic acid as a potent inhibitor of systemic amyloidosis and associated cellular toxicity.

Although the cure of amyloid related neurodegenerative diseases, non-neuropathic amyloidogenic diseases and non-neuropathic systemic amyloidosis are appealing energetic research attempts, beneficial medication is still to be discovered. There is a need to explore intensely stable therapeutic compounds, potent enough to restrict, disrupt or wipe out such toxic aggregates. We had performed a comprehensive biophysical, computational and cell based assay, that shows Nordihydroguaiaretic acid (NA) not only significantly inhibits heat induced hen egg white lysozyme (HEWL) fibrillation but also disaggregates preformed HEWL fibrils and reduces the cytoxicity of amyloid fibrils as well as disaggregated fibrillar species. The inhibitory potency of NA was determined by an IC50 of 26.3 µM. NA was also found to effectively inhibit human lysozyme (HL) fibrillation. NA interferes in the amyloid fibrillogenesis process by interacting hydrophobically with the amino acid residues found in highly prone amyloid fibril forming region of HEWL as explicated by molecular docking results. The results recommend NA as a probable neuroprotective and promising inhibitor for the therapeutic advancement prospective against amyloid related diseases.

Inhibition of primary and secondary nucleation alongwith disruption of amyloid fibrils and alleviation of associated cytotoxicity: A biophysical insight of a novel property of Chlorpropamide (an anti-diabetic drug).

Aggregation of physiologically synthesized soluble proteins to insoluble, cytotoxic fibrils is a pre-requisite for pathogenesis of amyloid associated disorders including Alzheimer's disease, non-systemic amyloidosis, Parkinson's disease, etc. Considerable advancement has been made to understand the mechanism behind aggregation process but till date we have no efficient cure and preventive therapy for associated diseases. Strategies to prevent protein aggregation are nevertheless many which have been proved promisingly successful in vitro. One of those is repurposing already approved drugs that saves time and money too and has been employed in this study. Here, for the first time we are reporting the effectiveness of an anti-diabetic drug chlorpropamide (CHL) under dosage conditions, a novel property to inhibit aggregation in human lysozyme (HL) in vitro. Spectroscopic (Turbidity, RLS, ThT, DLS, ANS) and microscopic (CLSM) results demonstrates that CHL has the potency to suppress aggregation in HL up to 70 %. CHL is shown to affect the elongation of fibrils with IC50 value of 88.5 µM as clear from the kinetics results, may be by interacting near/with aggregation prone regions of HL. Hemolytic assay also revealed the reduced cytotoxicity in the presence of CHL. Disruption of amyloid fibrils and inhibition of secondary nucleation in the presence of CHL was also evidenced by ThT, CD and CLSM results with reduced cytotoxicity as confirmed by hemolytic assay. We also performed preliminary studies on α-synuclein fibrillation inhibition and surprisingly found that CHL is not just inhibiting the fibrillation but also stabilizing the protein in its native state. These findings insinuate that CHL (anti-diabetic) possess multiple roles and can be a promising drug for developing therapeutic against non-systemic amyloidosis, Parkinson's disease and other amyloid associated disorders.

Biophysical insight into the anti-fibrillation potential of Glyburide for its possible implication in therapeutic intervention of amyloid associated diseases.

Protein aggregation is an underlying cause of many neurodegenerative diseases. Also, the overlapping pathological disturbances between neurodegenerative diseases and type-2 diabetes mellitus have urged the scientific community to explore potential of already available anti-diabetic medications in impeding amyloid formation too. Recent study brief out promising potential of an anti-diabetic drug Glyburide(GLY) as an inhibitor of amyloid fibrillation utilizing several biophysical techniques, computational methods and imaging tools. The mechanism of interaction was elucidated and the structural alterations in human serum albumin(HSA) as well as the microenvironment changes of its fluorophores(tryptophan, tyrosine) upon interacting with GLY were studied by spectroscopic techniques like Circular dichroism and synchronous fluorescence. Binding studies detailing about the GLY-HSA complex distance and the energy transfer efficiency was obtained by Fluorescence resonance energy transfer. For aggregation inhibition studies, the existence and size of aggregates formed in HSA and their inhibition by GLY was determined by Turbidity assay, Dynamic light scattering and Rayleigh light scattering along with dye binding assays. The ThT kinetics measurements analysis suggested that GLY deaccelerates fibrillation by decrement of apparent rate(Kapp) constant. The inhibitory effect of GLY might be attributed to native structure stabilization of HSA by obstruction into ß-sheet conversion as confirmed by CD spectroscopy results. Amyloid inhibition and suppression of amyloid-induced hemolysis by GLY was further delineated by TEM and SEM analysis respectively. All these findings for the first time report the new facet of the anti-amyloidogenic potential of GLY, making it a promising candidate to treat neurodegenerative diseases too in the near future.

Populations of Tau Conformers Drive Prion-like Strain Effects in Alzheimer's Disease and Related Dementias.

Recent findings of diverse populations of prion-like conformers of misfolded tau protein expand the prion concept to Alzheimer's disease (AD) and monogenic frontotemporal lobar degeneration (FTLD)-MAPT P301L, and suggest that distinct strains of misfolded proteins drive the phenotypes and progression rates in many neurodegenerative diseases. Notable progress in the previous decades has generated many lines of proof arguing that yeast, fungal, and mammalian prions determine heritable as well as infectious traits. The extraordinary phenotypic diversity of human prion diseases arises from structurally distinct prion strains that target, at different progression speeds, variable brain structures and cells. Although human prion research presents beneficial lessons and methods to study the mechanism of strain diversity of protein-only pathogens, the fundamental molecular mechanism by which tau conformers are formed and replicate in diverse tauopathies is still poorly understood. In this review, we summarize up to date advances in identification of diverse tau conformers through biophysical and cellular experimental paradigms, and the impact of heterogeneity of pathological tau strains on personalized structure- and strain-specific therapeutic approaches in major tauopathies.

Cholic acid inhibits amyloid fibrillation: Interplay of protonation and deprotonation.

Amyloidopathies are the consequence of misfolding with subsequent aggregation affecting people worldwide. Irrespective of speedy advancement in the field of therapeutics no agent for treating amyloidopathies has been discovered and thus targeting amyloid fibrillation process via repositioning of small molecules can be fruitful. According to previous reports potential amyloid inhibitors possess unique features like, hydrophobicity, aromaticity, charge etc. Herein, we have explored the effect of Cholic acid (CA) on amyloid fibrillation irrespective of the charge (determined by Zetasizer) using four proteins Human Serum Albumin, Bovine Serum Albumin, Human Insulin and Beta-lactoglobulin (HSA, BSA, HI and BLG) employing biophysical, imaging and computational techniques. ThT results revealed that CA in both protonated and deprotonated form is potent to curb HSA, BSA, BLG aggregation ~50% and HI aggregation ~96% in a dose dependent manner (in accord with CD, ANS and Congo red assay). Interestingly, CA treated samples displayed reduced cytotoxicity (Hemolytic assay) with altered morphology (TEM) and mechanism behind inhibition may be the interaction of CA with proteins via hydrophobic interactions and hydrogen bonding (supported by molecular docking results). This study proved CA (irrespective of the pH) a potential inhibitor of amyloidosis thus can be helpful in generalizing and repurposing the related drugs/compounds for their anti-aggregation behavior as an implication towards treating amyloidopathies.

On the binding reaction of loratadine with human serum acute phase protein alpha 1-acid glycoprotein.

Loratadine is an important anti-allergic drug. It is a second generation antihistamine drug used to treat allergic rhinitis, hay fever and urticaria. Human serum alpha 1-acid glycoprotein (AG) is an important acute phase protein and its serum concentration is found to increase in inflammation and acute response.The binding interaction between loratadine and AG is studied using spectroscopy and molecular docking techniques. The results obtained from fluorescence quenching experiments demonstrated that the fluorescence intensity of AG is quenched by loratadine. Loratadine was found to bind AG with the binding constant of ≈104 at 298 K. The Gibb's free energy change was found to be negative for the interaction of loratadine with AG indicating the binding process is spontaneous. Binding of loratadine with AG induced ordered structures in the protein. Hydrogen bonding and hydrophobic interactions were the main bonding forces between AG-loratadine as revealed by molecular docking results. This study suggests the importance of binding of anti-allergic drug to AG spatially in the diseases where the plasma concentration of AG increases many folds and interaction with this protein becomes significant. This study will help in design of drug dosage and adjustment accordingly to achieve optimal treatment outcome. Communicated by Ramaswamy H. Sarma.

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

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

Chickpea Peptide: A Nutraceutical Molecule Corroborating Neurodegenerative and ACE-I Inhibition.

Chickpea seeds are the source of proteins in human nutrition and attribute some nutraceutical properties. Herein, we report the effects of chickpea seed bioactive peptide on albumin, insulin, lactoglobulin and lysozyme amyloid fibril formation. Employing thioflavin T (ThT) assays and circular dichroism (CD), amyloid structural binding transition was experimented to analyze the inhibition of amyloid fibril formation. The purified active peptide with a molecular mass of 934.53 Da was evaluated in vitro for its ACE-I inhibitory, antibacterial, antifungal and antidiabetic activities. Further, in vivo animal studies were carried out in wistar rats for blood pressure lowering action. In hypertensive rats, chickpea peptide decreased 131 ± 3.57 mm of Hg for systolic blood pressure and 86 ± 1.5 mm of Hg for diastolic blood pressure after 8 h intraperitoneal administration. Additionally, the peptide suppressed the fibrillation of amyloid and destabilized the preformed mature fibrils. Data emphasize efficacy of chickpea peptide vis-a-vis ACE-Inhibitory, antibacterial, antifungal, antidiabetic and anti-amyloidogenic activities, allowing us to propose this novel peptide as a suitable candidate for nutraceutical-based drugs and seems the first kind of its nature.

Biophysical insight into the interaction of levocabastine with human serum albumin: spectroscopy and molecular docking approach.

Interaction of levocabastine with human serum albumin (HSA) is investigated by applying fluorescence spectroscopy, circular dichroism spectroscopy and molecular docking methods. Levocabastine is an important drug in treatment of allergy and currently a target drug for drug repurposing to treat other diseases like vernal keratoconjuctivitis. Fluorescence quenching data revealed that levocabastine bind weakly to protein with binding constant in the order of 103 M-1. Förster resonance energy transfer results indicated the binding distance of 2.28 nm for levocabastine. Synchronous fluorescence result suggest slight blue shift for tryptophan upon levocabastine binding, binding of levocabastine impelled rise in α-helical structure in protein, while there are minimal changes in tertiary structure in protein. Moreover, docking results indicate levocabastine binds to pocket near to the drug site-I in HSA via hydrogen bonding and hydrophobic interactions. Understanding the interaction of levocabastine with HSA is significant for the advancement of therapeutic and diagnostic strategies for optimal treatment results.Communicated by Ramaswamy H. Sarma.

Unravelling the inhibitory and cytoprotective potential of diuretics towards amyloid fibrillation.

Protein misfolding and deposition of aggregated proteins inside as well as outside of the cells have been associated with several neurotoxic and neurodegenerative disorders like Alzheimer's, Parkinson's and familial amyloid polyneuropathy etc. that could be controlled by anti-aggregation methodologies employing either inhibition or disaggregation of toxic aggregates. Also, the Alzheimer's disease develops in later life is somehow related to the high mid-life blood pressure. Therefore the present work targets the amyloid inhibiting potential of diuretics (a class of antihypertensive drugs) - Indapamide (INDP) and Hydrochlorothiazide (HCTZ) against human serum albumin (HSA) and human lysozyme (HL) fibrillogenesis. The effect of both INDP and HCTZ on the kinetics of amyloid formation of HSA and HL was illustrated and various biophysical techniques like Thioflavin T (ThT) and 8-Anilinonaphthalene-1-sulfonic acid (ANS) fluorescence measurement, Congo red measurements and circular dichroism (CD) measurements depicted the inhibitory action of both INDP and HCTZ in a dose dependent manner. Transmission Electronic Microscopy (TEM) confirmed the absence of fibrillar structures when HSA and HL were co-incubated with INDP and HCTZ. In addition, molecular docking results revealed that both the drugs interacts with HSA and HL through hydrophobic interactions as well as hydrogen bonding, and also showed non-hemolytic activity on human RBCs demonstrated by the Hemolytic assay. Thus, both INDP and HCTZ could be propitious as a therapeutic agent and aid in the cure of amyloid related diseases.

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 ß-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.

Molecular docking of Aß1-40 peptide and its Iowa D23N mutant using small molecule inhibitors: Possible mechanisms of Aß-peptide inhibition.

Alzheimer's disease (AD) is the most common form of neurodegenerative diseases, characterized by the deposition of Aß (amyloid beta) peptide. In this study, we have unravelled the interactions as well as anti amyloidogenic behaviour of 40 small molecule inhibitors with Aß1-40 peptide and Iowa mutant D23N-Aß115-42 peptide at atomic level and their modes of binding by docking approaches. The binding mode between wild type peptide and drug is distinctly different from the Iowa-mutant-peptide and drug. Here we proposed possible mechanisms of amyloid beta peptide inhibition by small molecule and prevent monomer-monomer interactions via at least three different mechanisms. In the first mechanism, four catechins efficiently interacted with the C-terminal region of peptides through hydrogen bonds and inhibited the peptides. This may lead to blockage of access of second molecule of Aß-peptide. Secondly, in the case Iowa mutant D23N-Aß15-42 peptide, same catechin form hydrogen bond with the important mutated Asn23 residue which acts as hydrogen bond donor and acceptor leading to tight binding of inhibitor with the peptide and may prevent monomer-monomer interactions. The third mechanism relies on the ability of drug molecules to mask hydrophobic residues of the peptide, thereby possibly inhibiting hydrophobic interactions between the two beta peptides.

Cytotoxic species in amyloid-associated diseases: Oligomers or mature fibrils.

Amyloid diseases especially, Alzheimer's disease (AD), is characterized by an imbalance between the production and clearance of amyloid-ß (Aß) species. Amyloidogenic proteins or peptides can transform structurally from monomers into ß-stranded fibrils via multiple oligomeric states. Among various amyloid species, structured oligomers are proposed to be more toxic than fibrils; however, the identification of amyloid oligomers has been challenging due to their heterogeneous and metastable nature. Multiple techniques have recently helped in better understanding of oligomer's assembly details and structural properties. Moreover, some progress on elucidating the mechanisms of oligomer-triggered toxicity has been made. Based on the collection of current findings, there is growing consensus that control of toxic amyloid oligomers could be a valid approach to regulate amyloid-associated toxicity, which could advance development of new diagnostics and therapeutics for amyloid-related diseases. In this review, we have described the recent scenario of amyloid diseases with a great deal of information about the recent understanding of oligomers' assembly, structural properties, and toxicity. Also comprehensive details have been provided to differentiate the degree of toxicity associated with prefibrillar aggregates.

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 Aß-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 Aß-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 ß 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.