Exploring possibility of promiscuity of amyloid inhibitor: Studies on effect of selected compounds on folding and amyloid formation of proteins

An approach to characterize mechanisms of action of anti-amyloidogenic compounds in vitro and in situ

Amyloid aggregation is associated with neurodegenerative disease and its modulation is a focus of drug development. We developed a chemical proteomics pipeline to probe the mechanism of action of anti-amyloidogenic compounds. Our approach identifies putative interaction sites with high resolution, can probe compound interactions with specific target conformations and directly in cell and brain extracts, and identifies off-targets. We analysed interactions of six anti-amyloidogenic compounds and the amyloid binder Thioflavin T with different conformations of the Parkinson's disease protein α-Synuclein and tested specific compounds in cell or brain lysates. AC Immune compound 2 interacted with α-Synuclein in vitro, in intact neurons and in neuronal lysates, reduced neuronal α-Synuclein levels in a seeded model, and had protective effects. EGCG, Baicalein, ThT and doxycycline interacted with α-Synuclein in vitro but not substantially in cell lysates, with many additional putative targets, underscoring the importance of testing compounds in situ. Our pipeline will enable screening of compounds against any amyloidogenic proteins in cell and patient brain extracts and mechanistic studies of compound action.

Extending the investigation of 4-thiazolidinone derivatives as potential multi-target ligands of enzymes involved in diabetes mellitus and its long-term complications: A study with pancreatic α-amylase

Diabetes mellitus is a multifactorial disease, which is frequently complicated by the development of hyperglycaemia-induced chronic complications. The therapy of diabetes mellitus often requires combinations of two or more drugs in order both to control glycaemic levels and to prevent hyperglycaemia-induced dangerous affairs. The application of multi-target agents, which are able to control simultaneously several pathogenic mechanisms, represents a useful alternative and, in fact, their discovery is a pursued aim of the research. Some (5-arylidene-4-oxo-2-thioxothiazolidin-3-yl)acetic acids, which we had previously reported as inhibitors of selected enzymes critically implicated in diabetes mellitus, were tested against pancreatic α-amylase and intestinal α-glucosidase. These enzymes catalyse the hydrolysis of dietary oligo- and polysaccharides into monosaccharides and, consequently, are responsible for postprandial hyperglycaemia; therefore, their inhibition is one of the possible strategies to control glycaemic levels in diabetes mellitus. In addition, we investigated the aggregation tendency of the tested compounds, through direct and indirect methods, in order to evaluate the mechanism of their multiple action and discover if aggregation may contribute to the inhibition of the target enzymes. Overall, compounds 1, 3 and 4 exhibited the most favourable profile since they were shown to act as multi-target inhibitors of enzymes involved in pathways related to diabetes mellitus, without producing aggregates even at high micromolar concentrations and, therefore, can be promising agents for further developments.

Conditions Governing Food Protein Amyloid Fibril Formation-Part I: Egg and Cereal Proteins

Conditions including heating mode, time, temperature, pH, moisture and protein concentration, shear, and the presence of alcohols, chaotropic/reducing agents, enzymes, and/or salt influence amyloid fibril (AF) formation as they can affect the accessibility of amino acid sequences prone to aggregate. As some conditions applied on model protein resemble conditions in food processing unit operations, we here hypothesize that food processing can lead to formation of protein AFs with a compact cross β-sheet structure. This paper reviews conditions and food constituents that affect amyloid fibrillation of egg and cereal proteins. While egg and cereal proteins often coexist in food products, their impact on each other's fibrillation remains unknown. Hen egg ovalbumin and lysozyme form AFs when subjected to moderate heating at acidic pH separately. AFs can also be formed at higher pH, especially in the presence of alcohols or chaotropic/reducing agents. Tryptic wheat gluten digests can form fibrillar structures at neutral pH and maize and rice proteins do so in aqueous ethanol or at acidic pH, respectively.

Functionalisation of Polyvinylpyrrolidone on Gold Nanoparticles Enhances Its Anti-Amyloidogenic Propensity towards Hen Egg White Lysozyme

Protein amyloids are characterized by aggregates that usually consist of fibres containing misfolded proteins and having a cross β-sheet conformation. These aggregates can eventually lead to several degenerative diseases like Alzheimer’s disease, amyotrophic lateral sclerosis (ALS), Huntington’s disease and Parkinson’s disease. The present study describes the effect of chemically synthesized polyvinylpyrrolidone (PVP)-conjugated gold nanoparticles (PVP-AuNps) on hen egg white lysozyme (HEWL) amyloids. The synthesized nanoparticles have been characterized using various biophysical techniques like Ultraviolet-Visible (UV-Vis) Spectroscopy, Transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, dynamic light scattering (DLS), zeta-potential measurement and Fourier transform infrared spectroscopy (FTIR). The aggregation studies showed that PVP acts as a partial inhibitor of HEWL amyloidogenesis. However, when conjugated to gold nanoparticle surface, it leads to complete inhibition of amyloid formation. Apart from inhibition, PVP-conjugated gold nanoparticles also exhibited a significant disaggregation effect on mature amyloids and hence can be exploited as an effective therapeutic agent against hereditary systemic amyloidosis.

Lanosterol Suppresses the Aggregation and Cytotoxicity of Misfolded Proteins Linked with Neurodegenerative Diseases

Accumulation of misfolded or aberrant proteins in neuronal cells is linked with neurodegeneration and other pathologies. Which molecular mechanisms fail and cause inappropriate folding of proteins and what is their relationship to cellular toxicity is not well known. How does it happen and what are the probable therapeutic or molecular approaches to counter them are also not clear. Here, we demonstrate that treatment of lanosterol diminishes aberrant proteotoxic aggregation and mitigates their cytotoxicity via induced expression of co-chaperone CHIP and elevated autophagy. The addition of lanosterol not only reduces aggregation of mutant bonafide misfolded proteins but also effectively prevents accumulation of various mutant disease-prone proteotoxic proteins. Finally, we observed that lanosterol mitigates cytotoxicity in cells, mediated by different stress-inducing agents. Taken together, our present results suggest that upregulation of cellular molecular chaperones, primarily using small molecules, can probably offer an efficient therapeutic approach in the future against misfolding of different disease-causing proteins and neurodegenerative disorders. Graphical Abstract ᅟ.

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 (K_b) 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.

Copper(II) directs formation of toxic amorphous aggregates resulting in inhibition of hen egg white lysozyme fibrillation under alkaline salt-mediated conditions

Hen egg white lysozyme (HEWL) adopts a molten globule-like state at high pH (~12.75) and is found to form amyloid fibrils at alkaline pH. Here, we report that Cu(II) inhibits self-association of HEWL at pH 12.75 both at 37 and 65 °C. A significant reduction in Thioflavin T fluorescence intensity, attenuation in β-sheet content and reduction in hydrophobic exposure were observed with increasing Cu(II) stoichiometry. Electron paramagnetic resonance spectroscopy suggests a 4N type of coordination pattern around Cu(II) during fibrillation. Cu(II) is also capable of altering the cytotoxicity of the proteinaceous aggregates. Fibrillar species of diverse morphology were found in the absence of Cu(II) with the generation of amorphous aggregates in the presence of Cu(II), which are more toxic compared to the fibrils alone.

Rottlerin and curcumin: a comparative analysis

Rottlerin and curcumin are natural plant polyphenols with a long tradition in folk medicine. Over the past two decades, curcumin has been extensively investigated, while rottlerin has received much less attention, in part, as a consequence of its reputation as a selective PKCδ inhibitor. A comparative analysis of genomic, proteomic, and cell signaling studies revealed that rottlerin and curcumin share a number of targets and have overlapping effects on many biological processes. Both molecules, indeed, modulate the activity and/or expression of several enzymes (PKCδ, heme oxygenase, DNA methyltransferase, cyclooxygenase, lipoxygenase) and transcription factors (NF-κB, STAT), and prevent aggregation of different amyloid precursors (α-synuclein, amyloid Aβ, prion proteins, lysozyme), thereby exhibiting convergent antioxidant, anti-inflammatory, and antiamyloid actions. Like curcumin, rottlerin could be a promising candidate in the fight against a variety of human diseases.

Rottlerin dissolves pre-formed protein amyloid: a study on hen egg white lysozyme

BACKGROUND

Deposition of protein fibrillar aggregates called amyloids in the tissue, is the principal cause of several degenerative diseases. Here, we have shown the disaggregation potential of rottlerin towards hen egg white lysozyme (HEWL) fibrils formed under alkaline conditions (pH-12.2).

METHODS

Several biophysical methods like Atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) and fluorescence emission spectra were used for the study.

RESULTS AND CONCLUSION

Rottlerin exhibited instantaneous disaggregation effect on HEWL fibrils as monitored by Thioflavin T assay, anisotropy study and AFM imaging. Further we have monitored the conformational changes induced by rottlerin on the fibril in terms of surface hydrophobicity and secondary structure through 8-anilino-1-naphthalene sulfonic acid (ANS) fluorescence and FTIR study respectively. We have also attempted to elucidate the type of interaction between HEWL and rottlerin at pH-12.2 employing techniques like quenching study and FTIR.

GENERAL SIGNIFICANCE

Rottlerin seems to have potential application as anti-amyloid compound.