Sclerotiorin Stabilizes the Assembly of Nonfibrillar Abeta42 Oligomers with Low Toxicity, Seeding Activity, and Beta-sheet Content

Natural products targeting amyloid-β oligomer neurotoxicity in Alzheimer's disease

Alzheimer's disease (AD) constitutes a major global health issue, characterized by progressive neurodegeneration and cognitive impairment, for which no curative treatment is currently available. Current therapeutic approaches are focused on symptom management, highlighting the critical need for disease-modifying therapy. The hallmark pathology of AD involves the aggregation and accumulation of amyloid-β (Aβ) peptides in the brain. Consequently, drug discovery efforts in recent decades have centered on the Aβ aggregation cascade, which includes the transition of monomeric Aβ peptides into toxic oligomers and, ultimately, mature fibrils. Historically, anti-Aβ strategies focused on the clearance of amyloid fibrils using monoclonal antibodies. However, substantial evidence has highlighted the critical role of Aβ oligomers (AβOs) in AD pathogenesis. Soluble AβOs are now recognized as more toxic than fibrils, directly contributing to synaptic impairment, neuronal damage, and the onset of AD. Targeting AβOs has emerged as a promising therapeutic approach to mitigate cognitive decline in AD. Natural products (NPs) have demonstrated promise against AβO neurotoxicity through various mechanisms, including preventing AβO formation, enhancing clearance mechanisms, or converting AβOs into non-toxic species. Understanding the mechanisms by which anti-AβO NPs operate is useful for developing disease-modifying treatments for AD. In this review, we explore the role of NPs in mitigating AβO neurotoxicity for AD drug discovery, summarizing key evidence from biophysical methods, cellular assays, and animal models. By discussing how NPs modulate AβO neurotoxicity across various experimental systems, we aim to provide valuable insights into novel therapeutic strategies targeting AβOs in AD.

Using mass spectrometry-based methods to understand amyloid formation and inhibition of alpha-synuclein and amyloid beta

Amyloid fibrils, insoluble β-sheets structures that arise from protein misfolding, are associated with several neurodegenerative disorders. Many small molecules have been investigated to prevent amyloid fibrils from forming; however, there are currently no therapeutics to combat these diseases. Mass spectrometry (MS) is proving to be effective for studying the high order structure (HOS) of aggregating proteins and for determining structural changes accompanying protein-inhibitor interactions. When combined with native MS (nMS), gas-phase ion mobility, protein footprinting, and chemical cross-linking, MS can afford regional and sometimes amino acid spatial resolution of the aggregating protein. The spatial resolution is greater than typical low-resolution spectroscopic, calorimetric, and the traditional ThT fluorescence methods used in amyloid research today. High-resolution approaches can struggle when investigating protein aggregation, as the proteins exist as complex oligomeric mixtures of many sizes and several conformations or polymorphs. Thus, MS is positioned to complement both high- and low-resolution approaches to studying amyloid fibril formation and protein-inhibitor interactions. This review covers basics in MS paired with ion mobility, continuous hydrogen-deuterium exchange (continuous HDX), pulsed hydrogen-deuterium exchange (pulsed HDX), fast photochemical oxidation of proteins (FPOP) and other irreversible labeling methods, and chemical cross-linking. We then review the applications of these approaches to studying amyloid-prone proteins with a focus on amyloid beta and alpha-synuclein. Another focus is the determination of protein-inhibitor interactions. The expectation is that MS will bring new insights to amyloid formation and thereby play an important role to prevent their formation.

Unveiling the fungal color palette: pigment analysis of Fusarium solani species complex and Curvularia verruculosa clinical isolates

Fungal species in the Nectriaceae, such as Fusarium spp. (Hypocreales: Nectriaceae), are etiologic agents of hyalohyphomycosis capable of producing violaceous or yellowish pigments under certain conditions, while Curvularia spp. (Pleosporales: Pleosporaceae) are agents of phaeohyphomycosis and typically produce melanin in their cell walls. In nectriaceous and pleosporaceous fungi, these pigments are mainly constituted by polyketides (e.g., azaphilones, naphthoquinones, and hydroxyanthraquinones). Considering the importance of pigments synthesized by these genera, this work focused on the selective extraction of pigments produced by eight Fusarium solani species complex and one Curvularia verruculosa isolate recovered from dermatomycosis specimens, their separation, purification, and posterior chemical analysis. The pigments were characterized through spectral and acid-base analysis, and their maximum production time was determined. Moreover, spectral identification of isolates was carried out to approach the taxonomic specificity of pigment production. Herein we describe the isolation and characterization of three acidic pigments, yellowish and pinkish azaphilones (i.e., coaherin A and sclerotiorin), and a purplish xanthone, reported for the first time in the Nectriaceae and Pleosporaceae, which appear to be synthesized in a species-independent manner, in the case of fusaria.

Natural Compounds as Inhibitors of Aβ Peptide and Tau Aggregation

Neurodegenerative conditions like Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) encompass disorders characterized by the degeneration of neurons in specific circumstances. The quest for novel agents to influence these diseases, particularly AD, has unearthed various natural compounds displaying multifaceted activities and diverse pharmacological mechanisms. Given the ongoing extensive study of pathways associated with the accumulation of neurofibrillary aggregates and amyloid plaques, this paper aims to comprehensively review around 130 studies exploring natural products. These studies focus on inhibiting the formation of amyloid plaques and tau protein tangles, with the objective of potentially alleviating or delaying AD.

Small Molecules N-Phenylbenzofuran-2-carboxamide and N-Phenylbenzo[b]thiophene-2-carboxamide Promote Beta-Amyloid (Aβ42) Aggregation and Mitigate Neurotoxicity

This study reports the unusual ability of small molecules N-phenylbenzofuran-2-carboxamide (7a) and N-phenylbenzo[b]thiophene-2-carboxamide (7b) to promote and accelerate Aβ42 aggregation. In the in vitro aggregation kinetic assays, 7a was able to demonstrate rapid increases in Aβ42 fibrillogenesis ranging from 1.5- to 4.7-fold when tested at 1, 5, 10, and 25 μM compared to Aβ42-alone control. Similarly, compound 7b also exhibited 2.9- to 4.3-fold increases in Aβ42 fibrillogenesis at the concentration range tested. Electron microscopy studies at 1, 5, 10, and 25 μM also demonstrate the ability of compounds 7a and 7b to promote and accelerate Aβ42 aggregation with the formation of long, elongated fibril structures. Both 7a and 7b were not toxic to HT22 hippocampal neuronal cells and strikingly were able to prevent Aβ42-induced cytotoxicity in HT22 hippocampal neuronal cells (cell viability ∼74%) compared to the Aβ42-treated group (cell viability ∼20%). Fluorescence imaging studies using BioTracker 490 green, Hoeschst 33342, and the amyloid binding dye ProteoStat further demonstrate the ability of 7a and 7b to promote Aβ42 fibrillogenesis and prevent Aβ42-induced cytotoxicity to HT22 hippocampal neuronal cells. Computational modeling studies suggest that both 7a and 7b can interact with the Aβ42 oligomer and pentamers and have the potential to modulate the self-assembly pathways. The 8-anilino-1-naphthalenesulfonic acid (ANS) dye binding assay also demonstrates the ability of 7a and 7b to expose the hydrophobic surface of Aβ42 to the solvent surface that promotes self-assembly and rapid fibrillogenesis. These studies demonstrate the unique ability of small molecules 7a and 7b to alter the self-assembly and misfolding pathways of Aβ42 by promoting the formation of nontoxic aggregates. These findings have direct implications in the discovery and development of novel small-molecule-based chemical and pharmacological tools to study the Aβ42 aggregation mechanisms, and in the design of novel antiamyloid therapies to treat Alzheimer's disease.

ATP modulates self-perpetuating conformational conversion generating structurally distinct yeast prion amyloids that limit autocatalytic amplification

Prion-like self-perpetuating conformational conversion of proteins into amyloid aggregates is associated with both transmissible neurodegenerative diseases and non-Mendelian inheritance. The cellular energy currency ATP is known to indirectly regulate the formation, dissolution, or transmission of amyloid-like aggregates by providing energy to the molecular chaperones that maintain protein homeostasis. In this work, we demonstrate that ATP molecules, independent of any chaperones, modulate the formation and dissolution of amyloids from a yeast prion domain (NM domain of Saccharomyces cerevisiae Sup35) and restricts autocatalytic amplification by controlling the amount of fragmentable and seeding-competent aggregates. ATP, at (high) physiological concentrations in the presence of Mg²⁺, kinetically accelerates NM aggregation. Interestingly, ATP also promotes phase-separation-mediated aggregation of a human protein harboring a yeast prion-like domain. We also show that ATP disaggregates preformed NM fibrils in a dose-independent manner. Our results indicate that ATP-mediated disaggregation, unlike the disaggregation by the disaggregase Hsp104, yields no oligomers that are considered one of the critical species for amyloid transmission. Furthermore, high concentrations of ATP delimited the number of seeds by giving rise to compact, ATP-bound NM fibrils that exhibited nominal fragmentation by either free ATP or Hsp104 disaggregase to generate lower molecular weight amyloids. Additionally, (low) pathologically relevant ATP concentrations restricted autocatalytic amplification by forming structurally distinct amyloids which are found seeding-inefficient due to their reduced β-content. Our results provide key mechanistic underpinnings of concentration-dependent chemical chaperoning by ATP against prion-like transmissions of amyloids.

Discovery of dual PKS involved in sclerotiorin biosynthesis in Penicillium meliponae using genome mining and gene knockout

Fungi of the genus Penicillium section Sclerotiora have as their main characteristic the presence of orange-pigmented mycelium, which is associated with sclerotiorin, a chlorinated secondary metabolite of the azaphilone subclass of polyketides. Sclerotiorin presents anti-diabetes, antioxidant, anti-inflammatory, anti-Alzheimer, antiviral, and antimicrobial activities, which has always attracted the attention of researchers worldwide. During our ongoing search for azaphilone-producing Amazonian fungi, the strain of Penicillium MMSRG-058 was isolated as an endophyte from the roots of Duguetia stelechantha and showed great capacity for producing sclerotiorin-like metabolites. Using multilocus phylogeny, this strain was identified as Penicillium meliponae. Moreover, based on the genome mining of this strain through the reverse approach, a cluster of putative biosynthetic genes (BGC) responsible for the biosynthesis of sclerotiorin-like metabolites (scl cluster) was identified. The knockout of the sclA (highly reducing PKS) and sclI (non-reducing PKS) genes resulted in mutants with loss of mycelial pigmentation and terminated the biosynthesis of sclerotiorin-like metabolites: geumsanol B, chlorogeumsanol B, 7-deacetylisochromophilone VI, isochromophilone VI, ochrephilone, isorotiorin, and sclerotiorin. Based on these results, a biosynthetic pathway was proposed considering the homology of BGC scl genes with the azaphilone BGCs that have already been functionally characterized.

The screening for marine fungal strains with high potential in alkaloids production by in situ colony assay and LC-MS/MS based secondary metabolic profiling

Background

Alkaloids are the second primary class of secondary metabolites (SMs) from marine organisms, most of which have antioxidant, antitumor, antibacterial, anti-inflammatory, and other activities. However, the SMs obtained by traditional isolation strategies have drawbacks such as highly reduplication and weak bioactivity. Therefore, it is significantly important to establish an efficient strategy for screening strains and mining novel compounds.

Methods

In this study, we utilized in situ colony assay combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify the strain with high potential in alkaloids production. The strain was identified by genetic marker genes and morphological analysis. The secondary metabolites from the strain were isolated by the combine use of vacuum liquid chromatography (VLC), ODS column chromatography, and Sephadex LH-20. Their structures were elucidated by 1D/2D NMR, HR-ESI-MS, and other spectroscopic technologies. Finally, these compounds bioactivity were assay, including anti-inflammatory and anti-β aggregation.

Results

Eighteen marine fungi were preliminarily screened for alkaloids production by in situ colony assay using Dragendorff reagent as dye, and nine of them turned orange, which indicated abundant alkaloids. By thin-layer chromatography (TLC), LC-MS/MS, and multiple approaches assisted Feature-Based Molecular Networking (FBMN) analysis of fermentation extracts, a strain ACD-5 (Penicillium mallochii with GenBank accession number OM368350) from sea cucumber gut was selected for its diverse alkaloids profiles especially azaphilones. In bioassays, the crude extracts of ACD-5 in Czapek-dox broth and brown rice medium showed moderate antioxidant, acetylcholinesterase inhibitory, anti-neuroinflammatory, and anti-β aggregation activities. Three chlorinated azaphilone alkaloids, compounds 1-3 (sclerotioramine, isochromophilone VI, and isochromophilone IX, respectively), were isolated from the fermentation products of ACD-5 in brown rice medium guided by bioactivities and mass spectrometry analysis. Compound 1 had shown remarkable anti-neuroinflammatory activity in liposaccharide induced BV-2 cells.

Conclusion

In summary, in situ colony screening together with LC-MS/MS, multi-approach assisted FBMN can act as an efficient screening method for strains with potential in alkaloids production.

Amyloid β structural polymorphism, associated toxicity and therapeutic strategies

A review of the multidisciplinary scientific literature reveals a large variety of amyloid-β (Aβ) oligomeric species, differing in molecular weight, conformation and morphology. These species, which may assemble via either on- or off-aggregation pathways, exhibit differences in stability, function and neurotoxicity, according to different experimental settings. The conformations of the different Aβ species are stabilized by intra- and inter-molecular hydrogen bonds and by electrostatic and hydrophobic interactions, all depending on the chemical and physical environment (e.g., solvent, ions, pH) and interactions with other molecules, such as lipids and proteins. This complexity and the lack of a complete understanding of the relationship between the different Aβ species and their toxicity is currently dictating the nature of the inhibitor (or inducer)-based approaches that are under development for interfering with (or inducing) the formation of specific species and Aβ oligomerization, and for interfering with the associated downstream neurotoxic effects. Here, we review the principles that underlie the involvement of different Aβ oligomeric species in neurodegeneration, both in vitro and in preclinical studies. In addition, we provide an overview of the existing inhibitors (or inducers) of Aβ oligomerization that serve as potential therapeutics for neurodegenerative diseases. The review, which covers the exciting studies that have been published in the past few years, comprises three main parts: 1) on- and off-fibrillar assembly mechanisms and Aβ structural polymorphism; 2) interactions of Aβ with other molecules and cell components that dictate the Aβ aggregation pathway; and 3) targeting the on-fibrillar Aβ assembly pathway as a therapeutic approach.

Spontaneous Formation of β-sheet Nano-barrels during the Early Aggregation of Alzheimer's Amyloid Beta

Soluble low-molecular-weight oligomers formed during the early aggregation of amyloid peptides have been hypothesized as a major toxic species of amyloidogenesis. Herein, we performed the first synergic in silico, in vitro and in vivo validations of the structure, dynamics and toxicity of Aβ42 oligomers. Aβ peptides readily assembled into β-rich oligomers comprised of extended β-hairpins and β-strands. Nanosized β-barrels were observed with certainty with simulations, transmission electron microscopy and Fourier transform infrared spectroscopy, corroborated by immunohistochemistry, cell viability, apoptosis, inflammation, autophagy and animal behavior assays. Secondary and tertiary structural proprieties of these oligomers, such as the sequence regions with high β-sheet propensities and inter-residue contact frequency patterns, were similar to the properties known for Aβ fibrils. The unambiguous spontaneous formation of β-barrels in the early aggregation of Aβ42 supports their roles as the common toxic intermediates in Alzheimer's pathobiology and a target for Alzheimer's therapeutics.

Preparation, COX-2 Inhibition and Anticancer Activity of Sclerotiorin Derivatives

The latest research has indicated that anti-tumor agents with COX-2 inhibitory activity may benefit their anti-tumor efficiency. A series of sclerotiorin derivatives have been synthesized and screened for their cytotoxic activity against human lung cancer cells A549, breast cancer cells MDA-MB-435 using the MTT method. Among them, compounds 3, 7, 12, 13, 15, 17 showed good cytotoxic activity with IC₅₀ values of 6.39, 9.20, 9.76, 7.75, 9.08, and 8.18 μM, respectively. In addition, all compounds were tested in vitro the COX-2 inhibitory activity. The results disclosed compounds 7, 13, 25 and sclerotiorin showed moderate to good COX-2 inhibition with the inhibitory ratios of 58.7%, 51.1%, 66.1% and 56.1%, respectively. Notably, compound 3 displayed a comparable inhibition ratio (70.6%) to the positive control indomethacin (78.9%). Furthermore, molecular docking was used to rationalize the potential of the sclerotiorin derivatives as COX2 inhibitory agents by predicting their binding energy, binding modes and optimal orientation at the active site of the COX-2. Additionally, the structure-activity relationships (SARS) have been addressed.

Natural Compounds as Inhibitors of Aβ Peptide Aggregation: Chemical Requirements and Molecular Mechanisms

Alzheimer’s disease (AD) is one of the most common neurodegenerative disorders, with no cure and preventive therapy. Misfolding and extracellular aggregation of Amyloid-β (Aβ) peptides are recognized as the main cause of AD progression, leading to the formation of toxic Aβ oligomers and to the deposition of β-amyloid plaques in the brain, representing the hallmarks of AD. Given the urgent need to provide alternative therapies, natural products serve as vital resources for novel drugs. In recent years, several natural compounds with different chemical structures, such as polyphenols, alkaloids, terpenes, flavonoids, tannins, saponins and vitamins from plants have received attention for their role against the neurodegenerative pathological processes. However, only for a small subset of them experimental evidences are provided on their mechanism of action. This review focuses on those natural compounds shown to interfere with Aβ aggregation by direct interaction with Aβ peptide and whose inhibitory mechanism has been investigated by means of biophysical and structural biology experimental approaches. In few cases, the combination of approaches offering a macroscopic characterization of the oligomers, such as TEM, AFM, fluorescence, together with high-resolution methods could shed light on the complex mechanism of inhibition. In particular, solution NMR spectroscopy, through peptide-based and ligand-based observation, was successfully employed to investigate the interactions of the natural compounds with both soluble NMR-visible (monomer and low molecular weight oligomers) and NMR-invisible (high molecular weight oligomers and protofibrils) species. The molecular determinants of the interaction of promising natural compounds are here compared to infer the chemical requirements of the inhibitors and the common mechanisms of inhibition. Most of the data converge to indicate that the Aβ regions relevant to perturb the aggregation cascade and regulate the toxicity of the stabilized oligomers, are the N-term and β1 region. The ability of the natural aggregation inhibitors to cross the brain blood barrier, together with the tactics to improve their low bioavailability are discussed. The analysis of the data ensemble can provide a rationale for the selection of natural compounds as molecular scaffolds for the design of new therapeutic strategies against the progression of early and late stages of AD.