Evaluating the inhibitory potential of natural compound luteolin on human lysozyme fibrillation

Flavones Suppress Aggregation and Amyloid Fibril Formation of Human Lysozyme under Macromolecular Crowding Conditions

The crowded milieu of a biological cell significantly impacts protein aggregation and interactions. Understanding the effects of macromolecular crowding on the aggregation and fibrillation of amyloidogenic proteins is crucial for the treatment of many amyloid-related disorders. Most in vitro studies of protein amyloid formation and its inhibition by small molecules are conducted in dilute buffers, which do not mimic the complexity of the cellular environment. In this study, we used PEGs to simulate macromolecular crowding and examined the inhibitory effects of flavones DHF, baicalein, and luteolin on human lysozyme (HuL) aggregation at pH 2. Naturally occurring flavones have been effective inhibitors of amyloid formation in some proteins. Our findings indicate that while flavones inhibit HuL aggregation and fibrillation in dilute buffer solutions, complete inhibition is observed with a combination of flavones and PEGs, as shown by ThT fluorescence, light scattering, TEM, and AFM studies. The species formed in the presence of PEG 8000 and flavones were less hydrophobic, less toxic, and α-helix-rich compared to control samples, which were hydrophobic and β-sheet-rich, as demonstrated by ANS hydrophobicity, MTT assay, and CD spectroscopy. Fluorescence titration studies of flavones with HuL showed a significant increase in binding constant values under crowding conditions. These findings highlight the importance of macromolecular crowding in modulating protein aggregation and amyloid inhibition. Further studies using disease-causing mutants of HuL and other amyloidogenic proteins are needed to explore the role of macromolecular crowding in small-molecule-mediated modulation and inhibition of protein aggregation and amyloid formation.

Luteolin: A promising multifunctional natural flavonoid for human diseases

Natural products are closely associated with human health. Luteolin (LUT), a flavonoid polyphenolic compound, is widely found in fruits, vegetables, flowers, and herbs. It is noteworthy that LUT exhibits a variety of beneficial pharmacological properties and holds significant potential for clinical applications, particularly in antitumor, anti-convulsion, diabetes control, anti-inflammatory, neuroprotection, anti-oxidation, anti-cardiovascular, and other aspects. The potential mechanism of action has been partially elucidated, including the mediation of NF-κB, toll-like receptor, MAPK, Wnt/β-catenin, PI3K/Akt, AMPK/mTOR, and Nrf-2, among others. The review that aimed to comprehensively consolidate essential information on natural sources, pharmacological effects, therapeutic and preventive potential, as well as potential mechanisms of LUT. The objective is to establish a theoretical basis for the continued development and application of LUT.

Experimental and computational investigation of the effect of Hsc70 structural variants on inhibiting amylin aggregation

The misfolding and aggregation of human islet amyloid polypeptide (hIAPP), also known as amylin, have been implicated in the pathogenesis of type 2 diabetes (T2D). Heat shock proteins, specifically, heat shock cognate 70 (Hsc70), are molecular chaperones that protect against hIAPP misfolding and inhibits its aggregation. Nevertheless, there is an incomplete understanding of the mechanistic interactions between Hsc70 domains and hIAPP, thus limiting their potential therapeutic role in diabetes. This study investigates the inhibitory capacities of different Hsc70 variants, aiming to identify the structural determinants that strike a balance between efficacy and cytotoxicity. Our experimental findings demonstrate that the ATPase activity of Hsc70 is not a pivotal factor for inhibiting hIAPP misfolding. We underscore the significance of the C-terminal substrate-binding domain of Hsc70 in inhibiting hIAPP aggregation, emphasizing that the removal of the lid subdomain diminishes the inhibitory effect of Hsc70. Additionally, we employed atomistic discrete molecular dynamics simulations to gain deeper insights into the interaction between Hsc70 variants and hIAPP. Integrating both experimental and computational findings, we propose a mechanism by which Hsc70's interaction with hIAPP monomers disrupts protein-protein connections, primarily by shielding the β-sheet edges of the Hsc70-β-sandwich. The distinctive conformational dynamics of the alpha helices of Hsc70 potentially enhance hIAPP binding by obstructing the exposed edges of the β-sandwich, particularly at the β5-β8 region along the alpha helix interface. This, in turn, inhibits fibril growth, and similar results were observed following hIAPP dimerization. Overall, this study elucidates the structural intricacies of Hsc70 crucial for impeding hIAPP aggregation, improving our understanding of the potential anti-aggregative properties of molecular chaperones in diabetes treatment.

Inhibition and disaggregation effect of flavonoid-derived carbonized polymer dots on protein amyloid aggregation

In this research, four water-insoluble flavonoid compounds were utilized and reacted with arginine to prepare four carbonized polymer dots with good water-solubility in a hydrothermal reactor. Structural characterization demonstrated that the prepared carbonized polymer dots were classic core-shell structure. Effect of the prepared carbonized polymer dots on protein amyloid aggregation was further investigated using hen egg white lysozyme and human lysozyme as model protein in aqueous solution. All of the prepared carbonized polymer dots could retard the amyloid aggregation of hen egg white lysozyme and human lysozyme in a dose-depended manner. All measurements displayed that the inhibition ratio of luteolin-derived carbonized polymer dots (CPDs-1) was higher than that of the other three carbonized polymer dots under the same dosage. This result may be interpreted by the highest content of phenolic hydroxyl groups on the periphery. The inhibition ratio of CPDs-1 on hen egg white lysozyme and human lysozyme reached 88 % and 83 % at the concentration of 0.5 mg/mL, respectively. CPDs-1 also could disaggregate the formed mature amyloid fibrils into short aggregates.