Effects of several quinones on insulin 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.

Rational Design of Hybrid Peptides: A Novel Drug Design Approach

Peptides play crucial roles in various physiological and pathological processes. Consequently, the investigation of peptide-based drugs is a highlight in the research and development of new drugs. However, natural peptides are not always ideal choices for clinical application due to their limited number and sometimes cytotoxicity to normal cells. Aiming to gain stronger or specific or novel biological effects and overcome the disadvantages of natural peptides, artificial hybrid peptides have been designed by combining the sequence of two or more different peptides with varied biological functions. Compared to natural peptides, hybrid peptides have shown better therapeutic potentials against bacteria, tumors, and metabolic diseases. In this review, design strategies, structure features and recent development of hybrid peptides are summarized; future directions for the research and development of hybrid peptide drugs are also discussed.

Salvation of the fallen angel: Reactivating mutant p53

The transcription factor p53 is known as the guardian of the genome for its powerful anti-tumour capacity. However, mutations of p53 that undermine their protein structure, resulting in loss of tumour suppressor function and gain of oncogenic function, have been implicated in more than half of human cancers. The crucial role of mutant forms of p53 in cancer makes it an attractive therapeutic target. A large number of candidates, including low MW compounds, peptides, and nucleic acids, have been identified or designed to rescue p53 mutants and reactivate their anti-tumour capacity through a variety of mechanisms. In this review, we summarize the progress made in the reactivation of mutant forms of p53, focusing on the pharmacological mechanisms of the reactivators of p53 mutants.

Multifunctional carbon dots as a therapeutic nanoagent for modulating Cu(ii)-mediated β-amyloid aggregation

The abnormal self-assembly of cerebral β-amyloid (Aβ) peptides into toxic aggregates is a hallmark of Alzheimer's disease (AD). Here, we report on multifunctional carbon dots that can chelate Cu(ii) ions, suppress Aβ aggregation, and photooxygenate Aβ peptides. Copper ions have high relevance to AD pathogenesis, causing Cu(ii)-mediated Aβ aggregation and oxidative damage to neuronal cells. For effective conjugation with Cu(ii)-bound Aβ complexes, we have designed carbon dots that possess nitrogen (N)-containing polyaromatic functionalities on their surface by employing o-phenylenediamine (OPD) as a polymerization precursor. We demonstrate that the polymerized OPD (pOPD)-derived carbon dots exhibit multiple capabilities against Cu(ii)-mediated Aβ aggregation. Furthermore, the pOPD-derived carbon dots exhibited dramatically enhanced absorption and fluorescence upon coordination with Cu(ii) ions and effectively photooxygenated Aβ peptides. The photodynamically modulated Aβ residues lost the propensity to coordinate with Cu(ii) and to assemble into toxic aggregates. This work demonstrates the potential of carbon dots as a multifunctional β-sheet breaker and provides a promising anti-amyloidogenic strategy for future Aβ-targeted AD treatments.

Glycated Insulin Exacerbates the Cytotoxicity of Human Islet Amyloid Polypeptides: a Vicious Cycle in Type 2 Diabetes

The aggregation of human islet amyloid polypeptide (hIAPP) is one of the triggering factors of type 2 diabetes mellitus (T2DM). hIAPP is cosynthesized, costored, and cosecreted with insulin in pancreatic β-cells, and insulin inhibits hIAPP aggregation. In T2DM patients, long-term hyperglycemia causes glycation of near 10% of total insulin. The glycation not only modifies insulin but also cross-links insulin into oligomers. However, the effect of glycated human insulin on hIAPP aggregation is unknown. In this study, four physiologically relevant monosaccharides, methylglyoxal, glucose, fructose, and ribose were used to glycate human insulin and two C-terminus truncated insulin analogues. Glycated insulin monomers or low molecular weight oligomers such as dimers significantly exacerbated the cytotoxicity of hIAPP. Notably, glycation-induced cross-linking of insulin inhibited the aggregation, membrane disruption, and cytotoxicity of hIAPP, which was corroborated by a control study using EGS-induced cross-linking of insulin or lysozyme. Removal of B29^Lys on the C terminus of the insulin B chain not only abolished glycation-induced cross-linking but also attenuated the aggravation effect of glycated insulin on hIAPP cytotoxicity. Taken together, this study reveals a vicious cycle in T2DM, that hyperglycemia-driven insulin glycation exacerbates the cytotoxicity of hIAPP, which accelerates β-cells death and further deteriorates T2DM.

Nanomedical Relevance of the Intermolecular Interaction Dynamics-Examples from Lysozymes and Insulins

Insulin and lysozyme share the common features of being prone to aggregate and having biomedical importance. Encapsulating lysozyme and insulin in micellar nanoparticles probably would prevent aggregation and facilitate oral drug delivery. Despite the vivid structural knowledge of lysozyme and insulin, the environment-dependent oligomerization (dimer, trimer, and multimer) and associated structural dynamics remain elusive. The knowledge of the intra- and intermolecular interaction profiles has cardinal importance for the design of encapsulation protocols. We have employed various biophysical methods such as NMR spectroscopy, X-ray crystallography, Thioflavin T fluorescence, and atomic force microscopy in conjugation with molecular modeling to improve the understanding of interaction dynamics during homo-oligomerization of lysozyme (human and hen egg) and insulin (porcine, human, and glargine). The results obtained depict the atomistic intra- and intermolecular interaction details of the homo-oligomerization and confirm the propensity to form fibrils. Taken together, the data accumulated and knowledge gained will further facilitate nanoparticle design and production with insulin or lysozyme-related protein encapsulation.

Phytochemicals and inflammatory bowel disease: a review

Gastrointestinal tract is the second largest organ in the body that mainly functions in nutrients and minerals intake through the intestinal barrier. Intestinal permeability maintains the circulation of minerals and nutrients from digested foods. Life and all the metabolic processes depend either directly or indirectly on proper functioning of GI tract. Compromised intestinal permeability and related disorders are common among all the patients with inflammatory bowel disease (IBD), which is a collective term of inflammatory diseases including Crohn's disease and ulcerative colitis. Many synthetic drugs are currently in use to treat IBD such as 5-aminosalicylic acid corticosteroids. However, they all have some drawbacks as long-term use result in many complications. These problems encourage us to look out for alternative medicine. Numerous in vitro and in vivo experiments showed that the plant-derived secondary metabolites including phenolic compounds, glucosinolates, alkaloids, terpenoids, oligosaccharides, and quinones could reduce permeability, ameliorate-related dysfunctions with promising results. In addition, many of them could modulate enzymatic activity, suppress the inflammatory transcriptional factors, ease oxidative stress, and reduce pro-inflammatory cytokines secretion. In this review, we summarized the phytochemicals, which were proven potent in treating increased intestinal permeability and related complication along with their mechanism of action.

Molecular insight into the therapeutic potential of phytoconstituents targeting protein conformation and their expression

BACKGROUND

Native protein conformation is essential for the functional activity of the proteins and enzymes. Defects in conformation or alterations in expression of the proteins have been reported in various diseases.

PURPOSE

The aim of this study is to review the molecular insight into the therapeutic potential of phytoconstituents targeting protein conformations or expressions.

METHODS

Published literatures were searched in PubMed, Scopus, Web of Science; Article published till Dec 2017 were extracted. The literature was assessed from the Central University of Rajasthan, India. Present study evaluate article based on the role of active plant constituents on the conformation and expression of the different proteins.

RESULTS

Plant components play their role either at the molecular level or cellular level and exhibit antibacterial, antiviral, anti-neurodegenerative and other activities. Plant active compounds isolated from different plants may either stabilize or destabilize the conformation of proteins or alter expression level of the protein involved in these diseases, therefore, can play a significant role in preventing diseases caused by the alteration in these proteins.

CONCLUSION

In the present article, we have reviewed the molecular mechanism of plant active compounds, their target proteins, methods of extraction and identification, and their biological significances. Therefore, a proper understanding of the effect of these herbal molecules on the concerned proteins may help to develop new herbal-based therapeutics for various diseases.

Elucidating the Inhibitory Potential of Designed Peptides Against Amyloid Fibrillation and Amyloid Associated Cytotoxicity

Inhibition of fibrillation process and disaggregation of mature fibrils using small peptide are the promising remedial strategies to combat neurodegenerative diseases. However, designing peptide-based drugs to target β-sheet-rich amyloid has been a major challenge. The current work describes, for the first time, the amyloid inhibitory potential of the two short peptides (selected on the basis of predisposition of their amino acid residues toward β-sheet formation) using combination of biophysical, imaging methods, and docking approaches. Results showed that peptides employed different mechanisms to inhibit the amyloid fibrillation. Furthermore, they were also effective in blocking the amyloid fibrillation pathway. In contrary to the insulin fibrillar mesh, significantly less fibrillar species appeared in the presence of peptides, as confirmed by transmission electron microscopy. Circular dichroism analysis indicated that although peptides did not stabilize the native state of insulin, they inhibited amyloid aggregation by reducing the formation of β-sheet rich structures. Hemolytic assay revealed the non-hemolytic nature of the species formed when insulin was co-incubated with the peptides. Therefore, despite the inherent potential to form β-sheet structure, these peptides inhibited the amyloid formation and potentially can be used as therapeutics for the treatment of amyloid-related diseases.

Mechanistic Studies of the Inhibition of Insulin Fibril Formation by Rosmarinic Acid

The self-assembly of insulin to form amyloid fibrils has been widely studied because it is a significant problem in the medical management of diabetes and is an important model system for the investigation of amyloid formation and its inhibition. A few inhibitors of insulin fibrillation have been identified with potencies that could be higher. Knowledge of how these work at the molecular level is not known but important for the development of more potent inhibitors. Here we show that rosmarinic acid completely inhibits amyloid formation by dimeric insulin at pH 2 and 60 °C. In contrast to other polyphenols, rosmarinic acid is soluble in water and does not degrade at elevated temperatures, and thus we were able to decipher the mechanism of inhibition by a combination of solution-state 1H NMR spectroscopy and molecular docking. On the basis of 1H chemical shift perturbations, intermolecular nuclear Overhauser effect enhancements between rosmarinic acid and specific residues of insulin, and slowed dynamics of rosmarinic acid in the presence of insulin, we show that rosmarinic acid binds to a pocket found on the surface of each insulin monomer. This results in the formation of a mixed tetramolecular aromatic network on the surface of insulin dimer, resulting in increased resistance of the amyloidogenic protein to thermal unfolding. This finding opens new avenues for the design of potent inhibitors of amyloid formation and provides strong experimental evidence for the role of surface aromatic clusters in increasing the thermal stability of proteins.

Cyanidin-3-rutinoside reduces insulin fibrillation and attenuates insulin fibrils-induced oxidative hemolysis of human erythrocytes

Insulin is able to form amyloid-like fibrils, a misfolding process by which insulin molecules interact with each other to form aggregates and pathological amyloid deposition. Inhibition of amyloid aggregation using natural products is proposed as a new strategy to prohibit the development of amyloid diseases. Herein, we demonstrated the inhibitory effect of cyanidin-3-rutinoside (C3R), a natural anthocyanin with multiple biological activities, against insulin amyloid fibrillation. The results showed that increased insulin concentration resulted in faster growth and higher amounts of insulin fibrils. C3R (10.6-170μM) concentration dependently decreased insulin fibril growth and increased the duration of lag time of insulin fibril formation. Moreover, C3R directly decreased the secondary structure transition from α-helix to β-sheet structure. C3R (0.31-5μM) attenuated insulin fibrils-induced oxidative hemolysis of human erythrocytes in a concentration-dependent manner. Moreover, C3R reduced insulin fibrils-induced erythrocyte membrane disruption through the inhibition of reactive oxygen species (ROS) generation. The findings also suggest that C3R reduced fibrils-induced membrane lipid peroxidation by maintaining the catalase activity and oxidized/reduced glutathione content (GSH/GSSH) in erythrocytes. These findings suggest that C3R may serve as a potential inhibitory agent against amyloid fibril formation and insulin fibrils-induced oxidative hemolysis.

Interaction between amyloidogenic proteins and biomembranes in protein misfolding diseases: Mechanisms, contributors, and therapy

The toxic deposition of misfolded amyloidogenic proteins is associated with more than fifty protein misfolding diseases (PMDs), including Alzheimer's disease, Parkinson's disease and type 2 diabetes mellitus. Protein deposition is a multi-step process modulated by a variety of factors, in particular by membrane-protein interaction. The interaction results in permeabilization of biomembranes contributing to the cytotoxicity that leads to PMDs. Different biological and physiochemical factors, such as protein sequence, lipid composition, and chaperones, are known to affect the membrane-protein interaction. Here, we provide a comprehensive review of the mechanisms and contributing factors of the interaction between biomembranes and amyloidogenic proteins, and a summary of the therapeutic approaches to PMDs that target this interaction. This article is part of a Special Issue entitled: Protein Aggregation and Misfolding at the Cell Membrane Interface edited by Ayyalusamy Ramamoorthy.

Misfolded proinsulin in the endoplasmic reticulum during development of beta cell failure in diabetes

The endoplasmic reticulum (ER) is broadly distributed throughout the cytoplasm of pancreatic beta cells, and this is where all proinsulin is initially made. Healthy beta cells can synthesize 6000 proinsulin molecules per second. Ordinarily, nascent proinsulin entering the ER rapidly folds via the formation of three evolutionarily conserved disulfide bonds (B7-A7, B19-A20, and A6-A11). A modest amount of proinsulin misfolding, including both intramolecular disulfide mispairing and intermolecular disulfide-linked protein complexes, is a natural by-product of proinsulin biosynthesis, as is the case for many proteins. The steady-state level of misfolded proinsulin-a potential ER stressor-is linked to (1) production rate, (2) ER environment, (3) presence or absence of naturally occurring (mutational) defects in proinsulin, and (4) clearance of misfolded proinsulin molecules. Accumulation of misfolded proinsulin beyond a certain threshold begins to interfere with the normal intracellular transport of bystander proinsulin, leading to diminished insulin production and hyperglycemia, as well as exacerbating ER stress. This is most obvious in mutant INS gene-induced Diabetes of Youth (MIDY; an autosomal dominant disease) but also likely to occur in type 2 diabetes owing to dysregulation in proinsulin synthesis, ER folding environment, or clearance.

Destabilization of Human Insulin Fibrils by Peptides of Fruit Bromelain Derived From Ananas comosus (Pineapple)

Deposition of insulin aggregates in human body leads to dysfunctioning of several organs. Effectiveness of fruit bromelain from pineapple in prevention of insulin aggregate was investigated. Proteolyses of bromelain was done as par human digestive system and the pool of small peptides was separated from larger peptides and proteins. Under conditions of growth of insulin aggregates from its monomers, this pool of peptides restricted the reaction upto formation of oligomers of limited size. These peptides also destabilized preformed insulin aggregates to oligomers. These processes were followed fluorimetrically using Thioflavin T and 1-ANS, size-exclusion HPLC, dynamic light scattering, atomic force microscopy, and transmission electron microscopy. Sequences of insulin (A and B chains) and bromelain were aligned using Clustal W software to predict most probable sites of interactions. Synthetic tripeptides corresponding to the hydrophobic interactive sites of bromelain showed disaggregation of insulin suggesting specificity of interactions. The peptides GG and AAA serving as negative controls showed no potency in destabilization of aggregates. Disaggregation potency of the peptides was also observed when insulin was deposited on HepG2 liver cells where no formation of toxic oligomers occurred. Amyloidogenic des-octapeptide (B23-B30 of insulin) incapable of cell signaling showed cytotoxicity similar to insulin. This toxicity could be neutralized by bromelain derived peptides. FT-IR and far-UV circular dichroism analysis indicated that disaggregated insulin had structure distinctly different from that of its hexameric (native) or monomeric states. Based on the stoichiometry of interaction and irreversibility of disaggregation, the mechanism/s of the peptides and insulin interactions has been proposed. J. Cell. Biochem. 118: 4881-4896, 2017. © 2017 Wiley Periodicals, Inc.

Aloe emodin, an anthroquinone from Aloe vera acts as an anti aggregatory agent to the thermally aggregated hemoglobin

Aggregation of proteins is a physiological process which contributes to the pathophysiology of several maladies including diabetes mellitus, Huntington's and Alzheimer's disease. In this study we have reported that aloe emodin (AE), an anthroquinone, which is one of the active components of the Aloe vera plant, acts as an inhibitor of hemoglobin (Hb) aggregation. Hb was thermally aggregated at 60°C for four days as evident by increased thioflavin T and ANS fluorescence, shifted congo red absorbance, appearance of β sheet structure, increase in turbidity and presence of oligomeric aggregates. Increasing concentration of AE partially reverses the aggregation of the model heme protein (hemoglobin). The maximum effect of AE was observed at 100μM followed by saturation at 125μM. The results were confirmed by UV-visible spectrometry, intrinsic fluorescence, ThT, ANS, congo red assay as well as transmission electron microscopy (TEM). These results were also supported by fourier transform infrared spectroscopy (FTIR) and circular dichroism (CD) which shows the disappearance of β sheet structure and appearance of α helices. This study will serve as baseline for translatory research and the development of AE based therapeutics for diseases attributed to protein aggregation.

Inhibition of amyloid oligomerization into different supramolecular architectures by small molecules: mechanistic insights and design rules

Protein misfolding and aggregation have been associated with several human disorders, including Alzheimer’s, Parkinson’s and Huntington’s diseases, as well as senile systemic amyloidosis and Type II diabetes. However, there is no current disease-modifying therapy available for the treatment of these disorders. In spite of extensive academic, pharmaceutical, medicinal and clinical research, a complete mechanistic model for this family of diseases is still lacking. In this review, we primarily discuss the different types of small molecular entities which have been used for the inhibition of the aggregation process of different amyloidogenic proteins under diseased conditions. These include small peptides, polyphenols, inositols, quinones and their derivatives, and metal chelator molecules. In recent years, these groups of molecules have been extensively studied using in vitro, in vivo and computational models to understand their mechanism of action and common structural features underlying the process of inhibition. A salient feature found to be instrumental in the process of inhibition is the balance between the aromatic unit that functions as the amyloid recognition unit and the hydrophilic amyloid breaker unit. The establishment of structure–function relationship for amyloid-modifying therapies by the various functional entities should serve as an important step toward the development of efficient therapeutics.

Inhibition of protein aggregation by zwitterionic polymer-based core-shell nanogels

Protein aggregation is a process by which misfolded proteins polymerizes into aggregates and forms fibrous structures with a β-sheet conformation, known as amyloids. It is an undesired outcome, as it not only causes numerous neurodegenerative diseases, but is also a major deterrent in the development of protein biopharmaceuticals. Here, we report a rational design for the synthesis of novel zwitterionic polymer-based core-shell nanogels via controlled radical polymerization. Nanogels with different sizes and functionalities in the core and shell were prepared. The nanogels exhibit remarkable efficiency in the protection of lysozyme against aggregation. Addition of nanogels suppresses the formation of toxic fibrils and also enables lysozyme to retain its enzymatic activity. Increasing the molecular weight and degree of hydrophobicity markedly increases its overall efficiency. Investigation of higher order structures revealed that lysozyme when heated without any additive loses its secondary structure and transforms into a random coil conformation. In contrast, presence of nanogels facilitates the retention of higher order structures by acting as molecular chaperones, thereby reducing molecular collisions. The present study is the first to show that it is possible to design zwitterionic nanogels using appropriate polymerization techniques that will protect proteins under conditions of extreme stress and inhibit aggregation.

Cinnamic Acid and Its Derivatives: Mechanisms for Prevention and Management of Diabetes and Its Complications

With recent insight into the development of dietary supplements and functional foods, search of effective phytochemical compounds and their mechanisms involved in prevention and management of diabetes and its complications are now being assessed. Cinnamic acid and its derivatives occur naturally in high levels of plant-based foods. Among various biological activities, cinnamic acid and its derivatives are associated with a beneficial influence on diabetes and its complications. The aim of the review is to summarize the potential mechanisms of these compounds for prevention and management of diabetes and its complications. Based on several in vitro studies and animal models, cinnamic acid and its derivatives act on different mechanism of actions, including stimulation of insulin secretion, improvement of pancreatic β-cell functionality, inhibition of hepatic gluconeogenesis, enhanced glucose uptake, increased insulin signaling pathway, delay of carbohydrate digestion and glucose absorption, and inhibition of protein glycation and insulin fibrillation. However, due to the limited intestinal absorption being a result of low bioavailability of cinnamic acid and its derivatives, current improvement efforts with entrapping into solid and liquid particles are highlighted. Further human clinical studies are needed to clarify the effects of cinnamic acid and its derivatives in diabetic patients.

Eugenol prevents amyloid formation of proteins and inhibits amyloid-induced hemolysis

Eugenol has attracted considerable attention because of its potential for many pharmaceutical applications including anti-inflammatory, anti-tumorigenic and anti-oxidant properties. Here, we have investigated the effect of eugenol on amyloid formation of selected globular proteins. We find that both spontaneous and seed-induced aggregation processes of insulin and serum albumin (BSA) are significantly suppressed in the presence of eugenol. Isothermal titration calorimetric data predict a single binding site for eugenol-insulin complex confirming the affinity of eugenol for native soluble insulin species. We also find that eugenol suppresses amyloid-induced hemolysis. Our findings reveal the inherent ability of eugenol to stabilize native proteins and to delay the conversion of protein species of native conformation into β-sheet assembled mature fibrils, which seems to be crucial for its inhibitory effect.

Inhibition of Insulin Amyloid Fibrillation by a Novel Amphipathic Heptapeptide: MECHANISTIC DETAILS STUDIED BY SPECTROSCOPY IN COMBINATION WITH MICROSCOPY

The aggregation of insulin into amyloid fibers has been a limiting factor in the development of fast acting insulin analogues, creating a demand for excipients that limit aggregation. Despite the potential demand, inhibitors specifically targeting insulin have been few in number. Here we report a non-toxic and serum stable-designed heptapeptide, KR7 (KPWWPRR-NH2), that differs significantly from the primarily hydrophobic sequences that have been previously used to interfere with insulin amyloid fibrillation. Thioflavin T fluorescence assays, circular dichroism spectroscopy, and one-dimensional proton NMR experiments suggest KR7 primarily targets the fiber elongation step with little effect on the early oligomerization steps in the lag time period. From confocal fluorescence and atomic force microscopy experiments, the net result appears to be the arrest of aggregation in an early, non-fibrillar aggregation stage. This mechanism is noticeably different from previous peptide-based inhibitors, which have primarily shifted the lag time with little effect on later stages of aggregation. As insulin is an important model system for understanding protein aggregation, the new peptide may be an important tool for understanding peptide-based inhibition of amyloid formation.

TCM, brain function and drug space

Covering: up to 2015. Traditional Chinese medicine has played a significant role in the mainstream healthcare system in China for thousands of years. Here, we summarize 84 major compounds from 15 selected herbal medicines targeting neurodegenerative diseases. We present a perspective based on the analysis of physicochemical properties of these TCM compounds, and comparison with current drugs and candidates for the treatment of Parkinson's and Alzheimer's disease. The results demonstrate that traditional Chinese medicines contain compounds possessing physicochemical properties that have excellent overlap with developed western medicines.

Isoliquiritigenin and liquiritin from Glycyrrhiza uralensis inhibit α-synuclein amyloid formation

Bioactive isoliquiritigenin and liquiritin inhibit α-synuclein aggregation and extend the life span of theC. elegansmodel of Parkinson's disease.

Inhibition effects of tanshinone on the aggregation of α-synuclein

Bioactive tanshinone compounds inhibit the aggregation of α-synuclein and extend the life span of aC. elegansmodel of Parkinson's disease.

Bisphenol analogues differently affect human islet polypeptide amyloid formation

Bisphenols (BPs) are widely used in the production of plastic material, misfolded human islet amyloid polypeptide (hIAPP) is a causal factor in diabetes. We demonstrated BPs analogues show different effects on hIAPP amyloid formation.

Stabilization of native amyloid β-protein oligomers by Copper and Hydrogen peroxide Induced Cross-linking of Unmodified Proteins (CHICUP)

Oligomeric assemblies are postulated to be proximate neurotoxic species in human diseases associated with aberrant protein aggregation. Their heterogeneous and transient nature makes their structural characterization difficult. Size distributions of oligomers of several amyloidogenic proteins, including amyloid β-protein (Aβ) relevant to Alzheimer's disease (AD), have been previously characterized in vitro by photo-induced cross-linking of unmodified proteins (PICUP) followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Due to non-physiological conditions associated with the PICUP chemistry, Aβ oligomers cross-linked by PICUP may not be representative of in vivo conditions. Here, we examine an alternative Copper and Hydrogen peroxide Induced Cross-linking of Unmodified Proteins (CHICUP), which utilizes naturally occurring divalent copper ions and hydrogen peroxide and does not require photo activation. Our results demonstrate that CHICUP and PICUP applied to the two predominant Aβ alloforms, Aβ40 and Aβ42, result in similar oligomer size distributions. Thioflavin T fluorescence data and atomic force microscopy images demonstrate that both CHICUP and PICUP stabilize Aβ oligomers and attenuate fibril formation. Relative to noncross-linked peptides, CHICUP-treated Aβ40 and Aβ42 cause prolonged disruption to biomimetic lipid vesicles. CHICUP-stabilized Aβ oligomers link the amyloid cascade, metal, and oxidative stress hypotheses of AD into a more comprehensive understanding of the molecular basis of AD pathology. Because copper and hydrogen peroxide are elevated in the AD brain, CHICUP-stabilized Aβ oligomers are biologically relevant and should be further explored as a new therapeutic target.

Inhibition of insulin fibrillation by osmolytes: Mechanistic insights

We have studied here using a number of biophysical tools the effects of osmolytes, betaine, citrulline, proline and sorbitol which differ significantly in terms of their physical characteristics such as, charge distribution, polarity, H-bonding abilities etc, on the fibrillation of insulin. Among these, betaine, citrulline, and proline are very effective in decreasing the extent of fibrillation. Proline also causes a substantial delay in the onset of fibrillation in the concentration range (50–250 mM) whereas such an effect is seen for citrulline only at 250 mM, and in case of betaine this effect is not seen at all in the whole concentration range. The enthalpies of interaction at various stages of fibrillation process have suggested that the preferential exclusion of the osmolyte and its polar interaction with the protein are important in inhibition. The results indicate that the osmolytes are most effective when added prior to the elongation stage of fibrillation. These observations have significant biological implications, since insulin fibrillation is known to cause injection amyloidosis and our data may help in designing lead drug molecules and development of potential therapeutic strategies.

Inhibitory effects of magnolol and honokiol on human calcitonin aggregation

Amyloid formation is associated with multiple amyloidosis diseases. Human calcitonin (hCT) is a typical amyloidogenic peptide, its aggregation is associated with medullary carcinoma of the thyroid (MTC), and also limits its clinical application. Magnolia officinalis is a traditional Chinese herbal medicine; its two major polyphenol components, magnolol (Mag) and honokiol (Hon), have displayed multiple functions. Polyphenols like flavonoids and their derivatives have been extensively studied as amyloid inhibitors. However, the anti-amyloidogenic property of a biphenyl backbone containing polyphenols such as Mag and Hon has not been reported. In this study, these two compounds were tested for their effects on hCT aggregation. We found that Mag and Hon both inhibited the amyloid formation of hCT, whereas Mag showed a stronger inhibitory effect; moreover, they both dose-dependently disassembled preformed hCT aggregates. Further immuno-dot blot and dynamic light scattering studies suggested Mag and Hon suppressed the aggregation of hCT both at the oligomerization and the fibrillation stages, while MTT-based and dye-leakage assays demonstrated that Mag and Hon effectively reduced cytotoxicity caused by hCT aggregates. Furthermore, isothermal titration calorimetry indicated Mag and Hon both interact with hCT. Together, our study suggested a potential anti-amyloidogenic property of these two compounds and their structure related derivatives.