Evidence of Anti-amyloid Characteristics of Plumbagin via Inhibition of Protein Aggregation and Disassembly of Protein Fibrils.

The biological consequences associated with the conversion of soluble proteins into insoluble toxic amyloids are not only limited to the onset of neurodegenerative diseases but also to the potential health risks associated with supplements of protein therapeutic agents as well. Hence, finding inhibitors against amyloid formation is important, and natural product-based anti-amyloid compounds have gained much interest because of their higher efficacy and biocompatibility. Plumbagin has been identified as a potential natural product with multiple medical benefits; however, it remains largely unclear whether plumbagin can act against amyloid formation of proteins. Here, we show that plumbagin can effectively inhibit the temperature-induced amyloid aggregation of important proteins (insulin and serum albumin). Both experimental and computational data revealed that the presence of plumbagin in protein solutions, under aggregating conditions, promotes a direct protein-plumbagin interaction, which is predominantly stabilized by stronger H-bonds and hydrophobic interactions. Plumbagin-mediated retention of the native structures of proteins appears to play a crucial role in preventing their conversion into insoluble ß-sheet-rich amyloid aggregates. More importantly, the addition of plumbagin into a suspension of protein fibrils triggered their spontaneous disassembly, promoting the release of soluble proteins. The results highlight that a possible synergistic effect via both the stabilization of protein structures and the restriction of the monomer recruitment at the fibril growth sites could be important for the mechanism of plumbagin's anti-aggregation effect. These findings may inspire the development of plumbagin-based formulations to benefit both the prevention and treatment of amyloid-related health complications.

Osmoprotectant Coated Thermostable Gold Nanoparticles Efficiently Restrict Temperature-Induced Amyloid Aggregation of Insulin.

Naturally occurring osmoprotectants are known to prevent aggregation of proteins under various stress factors including extreme pH and elevated temperature conditions. Here, we synthesized gold nanoparticles coated with selected osmolytes (proline, hydroxyproline, and glycine) and examined their effect on temperature-induced amyloid-formation of insulin hormone. These uniform, thermostable, and hemocompatible gold nanoparticles were capable of inhibiting both spontaneous and seed-induced amyloid aggregation of insulin. Both quenching and docking experiments suggest a direct interaction between the osmoprotectant-coated nanoparticles and aggregation-prone hydrophobic stretches of insulin. Circular-dichroism results confirmed the retention of insulin's native structure in the presence of these nanoparticles. Unlike the indirect solvent-mediated effect of free osmolytes, the inhibition effect of osmolyte-coated gold nanoparticles was observed to be mediated through their direct interaction with insulin. The results signify the protection of the exposed aggregation-prone domains of insulin from temperature-induced self-assembly through osmoprotectant-coated nanoparticles, and such effect may inspire the development of osmolyte-based antiamyloid nanoformulations.

Piperine-Coated Gold Nanoparticles Alleviate Paraquat-Induced Neurotoxicity in Drosophila melanogaster.

Parkinson's disease (PD) is the most common progressive neurodegenerative disease known to impart bradykinesia leading to diverse metabolic complications. Currently, scarcity of effective drug candidates against this long-term devastating disorder poses a big therapeutic challenge. Here, we have synthesized biocompatible, polycrystalline, and uniform piperine-coated gold nanoparticles (AuNPspiperine) to specifically target paraquat-induced metabolic complications both in Drosophila melanogaster and SH-SY5Y cells. Our experimental evidence clearly revealed that AuNPspiperine can effectively reverse paraquat-induced lethal effects in both in vitro and in vivo model systems of PD. AuNPspiperine were found to suppress oxidative stress and mitochondrial dysfunction, leading to inhibition of apoptotic cell death in paraquat-treated flies. AuNPspiperine were also found to protect SH-SY5Y cells against paraquat-induced toxicity at the cellular level preferably by maintaining mitochondrial membrane potential. Both experimental and computational data point to the possible influence of AuNPspiperine in regulating the homeostasis of parkin and p53 which may turn out to be the key factors in reducing PD symptoms. The findings of this work may facilitate the development of piperine-based nanoformulations against PD.

Myricetin inhibits amyloid fibril formation of globular proteins by stabilizing the native structures.

Myricetin has been identified as a naturally occurring flavonoid class of polyphenolic compound which shows multiple medical benefits including antidiabetic, anticancerous and antioxidant properties. Here, we report the protective effect of myricetin against in vitro amyloid fibril formation of selected globular proteins. The results reveal that myricetin is capable of inhibiting amyloid fibril formation of both insulin and serum albumin. Seed-induced aggregation of both proteins was also substantially suppressed in the presence of myricetin. Fluorescence quenching data indicated binding of myricetin with protein monomers as well as fibrils. The molecular docking studies revealed strong affinity of myricetin for both the native and partially unfolded conformation of proteins mediated by H-bonds and hydrophobic interactions. Myricetin was also observed to promote disassembly of mature amyloid fibrils. The results reveal that myricetin molecule has the potential for suppressing amyloid formation and such an inherent property may help in developing myricetin-based antiamyloid drugs.

Amyloid cross-seeding raises new dimensions to understanding of amyloidogenesis mechanism.

Hallmarks of most of the amyloid pathologies are surprisingly found to be heterocomponent entities such as inclusions and plaques which contain diverse essential proteins and metabolites. Experimental studies have already revealed the occurrence of coaggregation and cross-seeding during amyloid formation of several proteins and peptides, yielding multicomponent assemblies of amyloid nature. Further, research reports on the co-occurrence of more than one type of amyloid-linked pathologies in the same individual suggest the possible cross-talk among the disease related amyloidogenic protein species during their amyloid growth. In this review paper, we have tried to gain more insight into the process of coaggregation and cross-seeding during amyloid aggregation of proteins, particularly focusing on their relevance to the pathogenesis of the protein misfolding diseases. Revelation of amyloid cross-seeding and coaggregation seems to open new dimensions in our mechanistic understanding of amyloidogenesis and such knowledge may possibly inspire better designing of anti-amyloid therapeutics.

Tyrosine-Generated Nanostructures Initiate Amyloid Cross-Seeding in Proteins Leading to a Lethal Aggregation Trap.

Here, we show that aromatic amino acid tyrosine, under a physiologically mimicking condition, readily forms amyloid-like entities that can effectively drive aggregation of different globular proteins and aromatic residues. Tyrosine self-assembly resulted in the formation of cross-ß rich regular fibrils as well as spheroidal oligomers. Computational data suggest intermolecular interaction between specifically oriented tyrosine molecules mediated through π-π stacking and H-bonding interactions, mimicking a cross-ß-like architecture. Both individual protein samples and mixed protein samples underwent aggregation in the presence of tyrosine fibrils, confirming the occurrence of amyloid cross-seeding. The surface of the tyrosine's amyloid like entities was predicted to trap native protein structures, preferably through hydrophobic and electrostatic interactions initiating an aggregation event. Because tyrosine is a precursor to vital neuromodulators, the inherent cross-seeding potential of the tyrosine fibrils may have direct relevance to amyloid-linked pathologies.

Aß1-40 mediated aggregation of proteins and metabolites unveils the relevance of amyloid cross-seeding in amyloidogenesis.

The multicomponent nature of neuronal plaques in Alzheimer's disease signifies the possible recruitment of non-Aß candidates during the amyloid growth of Aß peptides. Here, we show that amyloid fibrils of Aß1-40 peptide can effectively initiate amyloid formation in different globular proteins and metabolites, converting native structures into ß-sheet rich assemblies. Structural and biophysical properties of the resultant protein fibrils display amyloid like characteristic features. Viable contacts between Aß peptide's cross-ß architecture and the native structure of proteins, mediated through H-bonds and hydrophobic interactions seem crucial for the onset of amyloid cross-seeding. Results reveal the inherent cross-seeding potential of Aß amyloids to initiate amyloid formation process in proteins and metabolites and revelation of such a property may further our mechanistic understanding of amyloid pathologies.