1,2,4-trihydroxynaphthalene-2-O-β-D-glucopyranoside delays amyloid-β42 aggregation and reduces amyloid cytotoxicity

Presently, misfolding and aggregation of amyloid-β₄₂ (Aβ₄₂ ) are considered early events in Alzheimer's disease (AD) pathogenesis. The use of natural products to inhibit the aggregation process and to protect cells from cytotoxicity of early aggregate grown at the onset of the aggregation path is one of the promising strategies against AD. Recently, we have purified a new powerful antioxidant and inhibitor of Aβ₄₂ aggregation from the leaves of Lawsonia inermis. The new compound was identified as a new Lawsoniaside; 1,2,4-trihydroxynaphthalene-2-O-β-D-glucopyranoside (THNG). Herein, we show that THNG interferes with Aβ₄₂ aggregation, inhibits its conformational change to a β-sheet-rich structure, decreases its polymerization into large fibrillar species, reduces oxidative stress, and aggregate cytotoxicity. These results indicate that THNG has great potential as a neuroprotective and therapeutic agent against AD. © 2018 BioFactors, 44(3):272-280, 2018.

Synergistic Inhibitory Effect of Peptide-Organic Coassemblies on Amyloid Aggregation

Inhibition of amyloid aggregation is important for developing potential therapeutic strategies of amyloid-related diseases. Herein, we report that the inhibition effect of a pristine peptide motif (KLVFF) can be significantly improved by introducing a terminal regulatory moiety (terpyridine). The molecular-level observations by using scanning tunneling microscopy reveal stoichiometry-dependent polymorphism of the coassembly structures, which originates from the terminal interactions of peptide with organic modulator moieties and can be attributed to the secondary structures of peptides and conformations of the organic molecules. Furthermore, the polymorphism of the peptide-organic coassemblies is shown to be correlated to distinctively different inhibition effects on amyloid-β 42 (Aβ42) aggregations and cytotoxicity.

Key Points Concerning Amyloid Infectivity and Prion-Like Neuronal Invasion

Amyloid aggregation has been related to an increasing number of human illnesses, from Alzheimer’s and Parkinson’s diseases (AD/PD) to Creutzfeldt-Jakob disease. Commonly, only prions have been considered as infectious agents with a high capacity of propagation. However, recent publications have shown that many amyloid proteins, including amyloid β-peptide, α-synuclein (α-syn) and tau protein, also propagate in a “prion-like” manner. Meanwhile, no link between propagation of pathological proteins and neurotoxicity has been demonstrated. The extremely low infectivity under natural conditions of most non-prion amyloids is far below the capacity to spread exhibited by prions. Nonetheless, it is important to elucidate the key factors that cause non-prion amyloids to become infectious agents. In recent years, important advances in our understanding of the amyloid processes of amyloid-like proteins and unrelated prions (i.e., yeast and fungal prions) have yielded essential information that can shed light on the prion phenomenon in mammals and humans. As shown in this review, recent evidence suggests that there are key factors that could dramatically modulate the prion capacity of proteins in the amyloid conformation. The concentration of nuclei, the presence of oligomers, and the toxicity, resistance and localization of these aggregates could all be key factors affecting their spread. In short, those factors that favor the high concentration of extracellular nuclei or oligomers, characterized by small size, with a low toxicity could dramatically increase prion propensity; whereas low concentrations of highly toxic intracellular amyloids, with a large size, would effectively prevent infectivity.

Molecular insights into cell toxicity of a novel familial amyloidogenic variant of β2-microglobulin

The first genetic variant of β₂‐microglobulin (b2M) associated with a familial form of systemic amyloidosis has been recently described. The mutated protein, carrying a substitution of Asp at position 76 with an Asn (D76N b2M), exhibits a strongly enhanced amyloidogenic tendency to aggregate with respect to the wild‐type protein. In this study, we characterized the D76N b2M aggregation path and performed an unprecedented analysis of the biochemical mechanisms underlying aggregate cytotoxicity. We showed that, contrarily to what expected from other amyloid studies, early aggregates of the mutant are not the most toxic species, despite their higher surface hydrophobicity. By modulating ganglioside GM1 content in cell membrane or synthetic lipid bilayers, we confirmed the pivotal role of this lipid as aggregate recruiter favouring their cytotoxicity. We finally observed that the aggregates bind to the cell membrane inducing an alteration of its elasticity (with possible functional unbalance and cytotoxicity) in GM1‐enriched domains only, thus establishing a link between aggregate‐membrane contact and cell damage.

De novo design of self-assembled hexapeptides as β-amyloid (Aβ) peptide inhibitors

The ability of peptides to construct specific secondary structures provides a useful function for biomaterial design that cannot be achieved with traditional organic molecules and polymers. Inhibition of amyloid formation is a promising therapeutic approach for the treatment of neurodegenerative diseases. Existing peptide-based inhibitors are mainly derived from original amyloid sequences, which have very limited sequence diversity and activity. It is highly desirable to explore other peptide-based inhibitors that are not directly derived from amyloid sequences. Here, we develop a hybrid high-throughput computational method to efficiently screen and design hexapeptide inhibitors against amyloid-β (Aβ) aggregation and toxicity from the first principle. Computationally screened/designed inhibitors are then validated for their inhibition activity using biophysical experiments. We propose and demonstrate a proof-of-concept of the "like-interacts-like" design principle that the self-assembling peptides are able to interact strongly with conformationally similar motifs of Aβ peptides and to competitively reduce Aβ-Aβ interactions, thus preventing Aβ aggregation and Aβ-induced toxicity. Such a de novo design can also be generally applicable to design new peptide inhibitors against other amyloid diseases, beyond traditional peptide inhibitors with homologous sequences to parent amyloid peptides.

When amyloids become prions

The conformational diseases, linked to protein aggregation into amyloid conformations, range from non-infectious neurodegenerative disorders, such as Alzheimer disease (AD), to highly infectious ones, such as human transmissible spongiform encephalopathies (TSEs). They are commonly known as prion diseases. However, since all amyloids could be considered prions (from those involved in cell-to-cell transmission to those responsible for real neuronal invasion), it is necessary to find an underlying cause of the different capacity to infect that each of the proteins prone to form amyloids has. As proposed here, both the intrinsic cytotoxicity and the number of nuclei of aggregation per cell could be key factors in this transmission capacity of each amyloid.

Protein folding and misfolding on surfaces

Protein folding, misfolding and aggregation, as well as the way misfolded and aggregated proteins affects cell viability are emerging as key themes in molecular and structural biology and in molecular medicine. Recent advances in the knowledge of the biophysical basis of protein folding have led to propose the energy landscape theory which provides a consistent framework to better understand how a protein folds rapidly and efficiently to the compact, biologically active structure. The increased knowledge on protein folding has highlighted its strict relation to protein misfolding and aggregation, either process being in close competition with the other, both relying on the same physicochemical basis. The theory has also provided information to better understand the structural and environmental factors affecting protein folding resulting in protein misfolding and aggregation into ordered or disordered polymeric assemblies. Among these, particular importance is given to the effects of surfaces. The latter, in some cases make possible rapid and efficient protein folding but most often recruit proteins/peptides increasing their local concentration thus favouring misfolding and accelerating the rate of nucleation. It is also emerging that surfaces can modify the path of protein misfolding and aggregation generating oligomers and polymers structurally different from those arising in the bulk solution and endowed with different physical properties and cytotoxicities.