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.

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.

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.

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.

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.

Elucidating the inhibitory potential of Vitamin A against fibrillation and amyloid associated cytotoxicity.

Protein aggregation and amyloid fibrillation are associated with many serious human pathophysiologies like Alzheimer's, Parkinson's diseases, type II diabetes etc. A powerful strategy for controlling and understanding amyloid protein aggregation is the modulation of protein self-assembly. In this study, anti-fibrillation activity of vitamin A (VA) and its effect on the kinetics of amyloid formation of Aß-42 peptide was investigated by employing various spectroscopic, imaging and computational approaches. The present data of Thioflavin T (ThT) fluorescence assay, circular dichroism (CD), dynamic light scattering assay, transmission electron microscopy and cell cytotoxicity assay demonstrated that vitamin A significantly inhibits fibril formation. Our experimental studies inferred that Vitamin A protects human neuroblastoma cell line (SH-SY5Y) and the neuroprotective effect against amyloid induced cytotoxicity is through modification of the amyloid formation towards formation of nontoxic aggregates. Molecular docking demonstrated that vitamin A interacts with Aß-42 through hydrophobic interactions as well as hydrogen bonding. Therefore, the study signifies the role of vitamin A as a potential molecule in preventing Aß-42 aggregation and associated pathophysiology. Hence, Vitamin A and related compounds can thus act as effective inhibitors in the therapeutic development to combat systemic amyloidosis.

An In Vitro elucidation of the antiaggregatory potential of Diosminover thermally induced unfolding of hen egg white lysozyme; A preventive quest for lysozyme amyloidosis.

Protein misfolding diseases are associated with human pathologies. These neurodegenerative diseases remain challenging task for researchers because of their adverse effect on vital organs system. Lysozyme amyloidosis is also associated with multi-organ dysfunction. Hence elucidation of its folding pathway is of great importance, for which hen egg white lysozyme (HEWL) being homological to its human counterpart was taken into consideration. Here in this study we have investigated the effect of diosmin (DSN), a flavonoid over thermally aggregated HEWL. Decrease in ANS, ThT and Rayleigh scattering fluorescence intensity suggests the transition between ß to α conformations. Further decrease in absorbance at 360 nm and of congo red with slight blue shift also indicated the disappearance of ß sheeted structure under the under the influence of increasing concentration of DSN. These results were also supported by circular dichroism in which gradual appearance α helical structure was observed. Finally visualization under transmission electron microscopy (TEM) authenticated the maximum structural alteration in the previously formed aggregates of HEWL at 250 µM DSN. Molecular docking followed by 100 ns MD simulations help to understand the interaction mechanism of HEWL with DSN. Results suggest DSN could be a useful in the treatment of amyloid related disorders.

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.

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.

Exploring the intermolecular interactions and contrasting binding of flufenamic acid with hemoglobin and lysozyme: A biophysical and docking insight.

The intermolecular interaction of flufenamic acid (Hfluf) with two model proteins i.e., hemoglobin and lysozyme was explored using fluorescence, UV-vis, circular dichroism, DLS, and molecular docking techniques. The corroborative spectroscopic techniques suggested efficient binding of Hfluf to both the proteins. The S-V plot in Hb-Hfluf system showed positive deviation highlighting the presence of both static and dynamic quenching. Hence, ground state complex model and sphere of action quenching model were used for the study. In Lyz-Hfluf system, a linear S-V plot was obtained indicating the presence of a single quenching mechanism. FRET study suggested a high probability of energy transfer from Hb/Lyz to Hfluf. Our thermodynamic results revealed that binding reaction in both the systems was exothermic and spontaneous. The UV-vis spectroscopy demonstrated that the binding of Hfluf affected the globin, Soret and oxy-bands of Hb along with globin band and polypeptide backbone of Lyz. CD spectra revealed the enhancement of ɑ-helicity in Lyz and decrease in case of Hb whereas the Rh values of proteins from DLS experiment corroborated the CD findings. 3-D fluorescence spectra highlighted the conformational changes upon binding whereas docking studies predicted the active binding site of both the proteins as the binding site of Hfluf.

Biophysical insight into the interaction mechanism of plant derived polyphenolic compound tannic acid with homologous mammalian serum albumins.

Numerous phenolic compounds have been reported in the last decade that have a good antioxidant property and interaction affinity towards mammalian serum albumins. In the present study, we have utilized mammalian serum albumins as a model protein to examine their comparative interaction property with polyphenolic compound tannic acid (TA) by using various spectroscopic and calorimetric methods We have also monitored the esterase and antioxidant activity of mammalian serum albumins in the absence and presence of TA. The obtain results recommended that the TA have a good binding affinity (∼104 to 106M-1) towards mammalian serum albumins and shows double sequential binding sites, which depends on the concentration of TA that induced the conformational alteration which responsible for the thermal stability of proteins. Binding affinity, structural transition and thermodynamic parameters were calculated from spectroscopic and calorimetric method reveals that non-covalent interaction causes partial conformational alteration in the secondary structure of protein ie.; increase in α-helical content with decrease in ß-sheet, random coil and other structure. Meanwhile, we have found that esterase activities of serum albumins were also stabilized against hydrolysis and shows higher antioxidant activity in the presence of TA because albumins its self have an immense antioxidant activity beside TA.

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.

Anti-Parkinsonian L-Dopa can also act as anti-systemic amyloidosis-A mechanistic exploration.

In spite of the fact that amyloid related neurodegenerative illnesses and non-neuropathic systemic amyloidosis have allured the research endeavors, as no cure has been announced yet apart from symptomatic treatment. Therapeutic agents which can reduce or disaggregate those toxic oligomers and fibrillar species have been studied with more compounds are on their way. The current research work describes comprehensive biophysical, computational and microscopic studies which reveal that L-3, 4-dihydroxyphenylalanine (L-Dopa) have indisputable efficacy to hinder the heat induced amyloid fibrillation of the human lysozyme (HL) and also preserve the fibril disaggregating potential. The IC50 value of L-Dopa is calculated to be 63.0±0.09µM. L-Dopa intervenes in the process of amyloid fibrillogenesis through hydrophobic interaction and hydrogen bond formation with the amino acid residues found in the amyloid fibril forming prone region of HL as clarified by molecular simulation data. L-Dopa also disaggregates the mature amyloid fibrils into some unorganized species and the DC50 value was estimated to be 19.95±0.063µM. Hence, L-Dopa and related compounds can act as effective inhibitors in the therapeutic development to combat systemic amyloidosis.

Vitamin B12 offers neuronal cell protection by inhibiting Aß-42 amyloid fibrillation.

Protein misfolding and aggregation has been implicated as the cause of more than 20 diseases in humans such as Alzheimer's and Parkinson's and systemic amyloidosis. Retardation of Aß- 42 aggregation is considered as a promising and challenging strategy for developing effective therapeutics against Alzheimer's disease. Herein, we demonstrated the effect of vitamin B12 (VB) on inhibiting amyloid formation by employing ThT fluorescence assay, circular dichroism, ANS fluorescence assay, dynamic light scattering measurements and transmission electron microscopy and cell viability assay. Our results demonstrate that vitamin B12 (VB), inhibits Aß- 42 aggregation in a concentration dependent manner. Further VB also provide protection against amyloid induced cytotoxicity in human neuronal cell line. This study points towards a promising strategy to combat Aß- 42 aggregation and may have broader implication for targeting other neurological disorders whose distinct hallmark is also amyloid formation.

Biophysical insights into the interaction of hen egg white lysozyme with therapeutic dye clofazimine: modulation of activity and SDS induced aggregation of model protein.

The present study details the binding process of clofazimine to hen egg white lysozyme (HEWL) using spectroscopy, dynamic light scattering, transmission electron microscopy (TEM), and molecular docking techniques. Clofazimine binds to the protein with binding constant (Kb) in the order of 1.57 × 104 at 298 K. Binding process is spontaneous and exothermic. Molecular docking results suggested the involvement of hydrogen bonding and hydrophobic interactions in the binding process. Bacterial cell lytic activity in the presence of clofazimine increased to more than 40% of the value obtained with HEWL only. Interaction of the drug with HEWL induced ordered secondary structure in the protein and molecular compaction. Clofazimine also effectively inhibited the sodium dodecyl sulfate (SDS) induced amyloid formation in HEWL and caused disaggregation of preformed fibrils, reinforcing the notion that there is involvement of hydrophobic interactions and hydrogen bonding in the binding process of clofazimine with HEWL and clofazimine destabilizes the mature fibrils. Further, TEM images confirmed that fibrillar species were absent in the samples where amyloid induction was performed in the presence of clofazimine. As clofazimine is a drug less explored for the inhibition of fibril formation of the proteins, this study reports the inhibition of SDS-induced amyloid formation of HEWL by clofazimine, which will help in the development of clofazimine-related molecules for the treatment of amyloidosis.

Attenuation of amyloid fibrillation in presence of Warfarin: A biophysical investigation.

Protein misfolding and aggregation are associated with more than twenty diseases, such as neurodegenerative diseases. The amyloid oligomers and fibrils may induce cell membrane disruption and lead to cell apoptosis. A great number of studies have focused on discovery of amyloid inhibitors which may prevent or treat amyloidosis. In this study, we used human serum albumin (HSA) as an amyloid model to test the anti-amyloid effects of warfarin (WFN), a very well-known drug for treatment of thrombosis and also used by biophysicists to characterize the specific binding site on HSA (site I of subdomain IIA). We have used a combination of different biophysical, spectroscopic and imaging techniques to prove the anti-amyloidogenic behavior of WFN. Our results demonstrated that WFN is capable enough to inhibit the HSA fibrillation. Exposed HSA surface hydrophobicity was decreased by 50% as judged by ANS analysis. Moreover, anti-amyloidegenic behavior of WFN was found to be concentration dependent as supported by decreased ThT fluorescence by 22.4% and 46% at WFN concentrations of 500 and 1000µM, respectively. Circular dichroism technique showed the change in secondary structure of native HSA as well as in presence of WFN. These results suggests that WFN is capable of inhibiting amyloid aggregation, hence, WFN related compounds may thus be further explored for designing effective anti-amyloidosis compounds.

Mechanisms of protein aggregation and inhibition.

Protein and peptide aggregation raises keen interest due to their involvement in number of pathological conditions ranging from neurodegenerative disorders to systemic amyloidosis. Here, we have reviewed recent advances in mechanisms of aggregation, emerging technologies towards exploration, characterization of aggregate structures, detection at molecular level and the strategies to combat the phenomenon of aggregation both in cellular and in vitro conditions. In consistence, we have illustrated almost all factors that influence the protein aggregation both in vitro and in vivo environments. In addition, we have discussed a detailed journey of protein aggregation phenomenon that starts with very first events of protein aggregation. We had also described advancement in current scenarios, present aspects of fibril association to several life threatening disorders and current experimental strategies that are employed to oppose or reverse the amyloid formation.

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.

Correction: A Comprehensive Spectroscopic and Computational Investigation to Probe the Interaction of Antineoplastic Drug Nordihydroguaiaretic Acid with Serum Albumins.

[This corrects the article DOI: 10.1371/journal.pone.0158833.].

A Comprehensive Spectroscopic and Computational Investigation to Probe the Interaction of Antineoplastic Drug Nordihydroguaiaretic Acid with Serum Albumins.

Exogenous drugs that are used as antidote against chemotheray, inflammation or viral infection, gets absorbed and interacts reversibly to the major serum transport protein i.e. albumins, upon entering the circulatory system. To have a structural guideline in the rational drug designing and in the synthesis of drugs with greater efficacy, the binding mechanism of an antineoplastic and anti-inflammatory drug Nordihydroguaiaretic acid (NDGA) with human and bovine serum albumins (HSA & BSA) were examined by spectroscopic and computational methods. NDGA binds to site II of HSA with binding constant (Kb) ~105 M-1 and free energy (ΔG) ~ -7.5 kcal.mol-1. It also binds at site II of BSA but with lesser binding affinity (Kb) ~105 M-1 and ΔG ~ -6.5 kcal.mol-1. The negative value of ΔG, ΔH and ΔS for both the albumins at three different temperatures confirmed that the complex formation process between albumins and NDGA is spontaneous and exothermic. Furthermore, hydrogen bonds and hydrophobic interactions are the main forces involved in complex formation of NDGA with both the albumins as evaluated from fluorescence and molecular docking results. Binding of NDGA to both the albumins alter the conformation and causes minor change in the secondary structure of proteins as indicated by the CD spectra.