Menadione sodium bisulfite inhibits the toxic aggregation of amyloid-β(1–42)

Identification of novel phenolic inhibitors from traditional Chinese medicine against toxic α-synuclein aggregation via regulating phase separation

Parkinson's disease (PD), a neurodegenerative disorder without cure, is characterized by the pathological aggregation of α-synuclein (α-Syn) in Lewy bodies. Classic deposition pathway and condensation pathway contribute to α-Syn aggregation, and liquid-liquid phase separation is the driving force for condensate formation, which subsequently undergo liquid-solid phase separation to form toxic fibrils. Traditional Chinese Medicine (TCM) has a long history in treating neurodegenerative disease; herein, we identified chemicals from herbs that inhibit α-Syn aggregation. We screened commonly prescribed TCMs for PD from the CNKI database and registered patents, 13 chemicals were identified in the TCMSP databases as candidate inhibitors, among which three phenols, forsythoside B (FTSB), echinacoside (ECH), and 4-hydroxyindole (C4-OH) efficiently inhibit α-Syn aggregation. Moreover, FTSB and ECH increase α-Syn fluidity within condensates, inhibit α-Syn transition into amyloid fibrils and reduce fibril-induced toxicity in SH-SY5Y cells. Importantly, they disaggregated preformed α-Syn amyloid fibrils. Notably, in an α-Syn overexpressing NL5901 C. elegans PD model, either FTSB or ECH treatment significantly extended the lifespan and improved the PD-like movement disorders, both in the preventive and therapeutic treatment approaches, by reducing toxic α-Syn inclusion formation and improving the fluidity of α-Syn. Together, we offer new therapeutic candidates targeting phase separation-associated aggregation for PD.

27-Hydroxymangiferolic Acid Extends Lifespan and Improves Neurodegeneration in Caenorhabditis elegans by Activating Nuclear Receptors

27-Hydroxymangiferolic acid (27-HMA) is a naturally occurring compound in mango fruits that exhibits diverse biological functions. Here, we show that 27-HMA activates the transcriptional activity of farnesoid X receptor (FXR), a nuclear receptor transcription factor, extending the lifespan and healthspan in Caenorhabditis elegans (C. elegans). Meanwhile, the longevity-promoting effect of 27-HMA was attenuated in the mutants of nhr-8 and daf-12, the FXR homologs, indicating that the longevity effects of 27-HMA in C. elegans may depend on nuclear hormone receptors (NHRs). Further analysis revealed potential associations between the longevity effects of 27-HMA and the insulin/insulin-like growth factor-1 signaling (IIS)/TORC1 pathway. Moreover, 27-HMA increased the toxin resistance of nematodes and activated the expression of detoxification genes, which rely on NHRs. Finally, 27-HMA improved the age-related neurodegeneration in Alzheimer's disease (AD) and Parkinson's disease (PD) C. elegans models. Taken together, our findings suggest that 27-HMA is a novel FXR agonist and may prolong lifespan and healthspan via activating NHRs.

A Ru3+-functionalized-NMOF nanozyme as an inhibitor and disaggregator of β-amyloid aggregates

Alzheimer's disease (AD) heavily impacts human lives and is becoming serious as societies age. Inhibiting and disaggregating β-amyloid aggregates is a possible solution for AD therapy. In this study, a novel type of nanozyme based on Ru3+-chelated nanoscale metal organic frameworks (Ru3+-NMOFs), displaying strong peroxidase-like activity, was proposed as an inhibitor and disaggregator of β-amyloid aggregates. As a high concentration of hydrogen peroxide is present at the sites of β-amyloid aggregates, Ru3+-NMOFs could catalyze the conversion of hydrogen peroxide to hydroxyl radicals. Thus, these hydroxyl radicals would attack the β-amyloid chain, oxidizing it to enhance its hydrophilicity, which results in a decreased hydrophobic interaction and reduced degree of aggregation. Ru3+-NMOFs could effectively inhibit as well as disaggregate β-amyloid fibrils both in vitro and in vivo. Additionally, the reduction of the β-amyloid aggregates and the attenuation of reactive oxygen species transfer led to lower levels of inflammatory factors, which could be beneficial in alleviating AD symptoms. In a typical treatment, Ru3+-NMOFs could mitigate the paralysis of C. elegans CL2120 and elevate survival rates. This study opens a new avenue for MOF-based nanozymes as potential treatment agents for AD therapy.

Anti-amyloid potential of some phytochemicals against Aβ-peptide and α-synuclein, tau, prion, and Huntingtin protein

Some molecules self-assemble to create complex structures through molecular self-assembly. Hydrogel preparation, tissue repair, and therapeutic drug delivery are a few applications of molecular self-assembly. However, the self-assembly of amino acids, peptides, and proteins forms amyloid fibrils, resulting in various disorders, most notably neurodegenerative ailments. Examples include the self-assembly of phenylalanine, which causes phenylketonuria; Aβ, which causes Alzheimer's disease; the tau protein, which causes both Alzheimer's and Parkinson's diseases; and α-synuclein, which causes Parkinson's illness. This review provides information related to phytochemicals of great significance that can prevent the formation of, or destabilize, amino acid, peptide, and protein self-assemblies.

Silicon-Carbon Dots-Loaded Mesoporous Silica Nanocomposites (mSiO2@SiCDs): An Efficient Dual Inhibitor of Cu2+-Mediated Oxidative Stress and Aβ Aggregation for Alzheimer's Disease

The redox-active metal ions, especially Cu2+, are highly correlated to Alzheimer's disease (AD) by causing metal ion-mediated oxidative stress and toxic metal-bound β-amyloid (Aβ) aggregates. Numerous pieces of evidence have revealed that the regulation of metal homeostasis could be an effective therapeutic strategy for AD. Herein, in virtue of the interaction of both amino-containing silane and ethylenediaminetetraacetic acid disodium salt for Cu2+, the silicon-carbon dots (SiCDs) are deliberately prepared using these two raw materials as the cocarbon source; meanwhile, to realize the local enrichment of SiCDs and further maximize the chelating ability to Cu2+, the SiCDs are feasibly loaded to the biocompatible mesoporous silica nanoparticles (mSiO2) with the interaction between residual silane groups on SiCDs and silanol groups of mSiO2. Thus-obtained nanocomposites (i.e., mSiO2@SiCDs) could serve as an efficient Cu2+ chelator with satisfactory metal selectivity and further modulate the enzymic activity of free Cu2+ and the Aβ42-Cu2+ complex to alleviate the pathological oxidative stress with an anti-inflammatory effect. Besides, mSiO2@SiCDs show an inspiring inhibitory effect on Cu2+-mediated Aβ aggregation and further protect the neural cells against the toxic Aβ42-Cu2+ complex. Moreover, the transgenic Caenorhabditis elegans CL2120 assay demonstrates the protective efficacy of mSiO2@SiCDs on Cu2+-mediated Aβ toxicity in vivo, indicating its potential for AD treatment.

Congo Red-Derived Carbon Dots: Simultaneously as Fluorescence Probe for Protein Aggregates, Inhibitor for Protein Aggregation, and Scavenger of Free Radicals

The pathological aggregation of some proteins is claimed to be highly related to several human diseases, such as β-amyloid 1-42 (Aβ₄₂ ) to Alzheimer's disease (AD), islet amyloid polypeptide, and insulin to type 2 diabetes mellitus. Therefore, it is in desperate need to develop effective methods for detection of protein aggregates and inhibition of abnormal aggregation. Herein, to construct all-in-one probe with both diagnosis and treatment potentials for protein aggregation diseases, Congo red (CR), a classical staining reagent with red fluorescence signal output for protein aggregates, is deliberately adopted to react with three different reductive carbon sources and ammonium persulfate to generate three CR-derived carbon dots (CDs). The obtained CDs exhibit the capabilities of turn-on red fluorescence imaging of protein aggregates, and/or inhibition of protein aggregation as well as scavenging of free radicals. Among them, CA-CDs, using citric acid as the reductive carbon source, demonstrate the superiority to the other two studied CDs in integrating all of these functions, and particularly exert excellent cytoprotection effect against toxic Aβ₄₂ species, possessing tremendous potential in diagnosis and treatment of AD for future study. The present study paves a new way to develop all-in-one CDs for the protein disease research.

Genetic control of RNA editing in neurodegenerative disease

A-to-I RNA editing diversifies human transcriptome to confer its functional effects on the downstream genes or regulations, potentially involving in neurodegenerative pathogenesis. Its variabilities are attributed to multiple regulators, including the key factor of genetic variants. To comprehensively investigate the potentials of neurodegenerative disease-susceptibility variants from the view of A-to-I RNA editing, we analyzed matched genetic and transcriptomic data of 1596 samples across nine brain tissues and whole blood from two large consortiums, Accelerating Medicines Partnership-Alzheimer's Disease and Parkinson's Progression Markers Initiative. The large-scale and genome-wide identification of 95 198 RNA editing quantitative trait loci revealed the preferred genetic effects on adjacent editing events. Furthermore, to explore the underlying mechanisms of the genetic controls of A-to-I RNA editing, several top RNA-binding proteins were pointed out, such as EIF4A3, U2AF2, NOP58, FBL, NOP56 and DHX9, since their regulations on multiple RNA-editing events were probably interfered by these genetic variants. Moreover, these variants may also contribute to the variability of other molecular phenotypes associated with RNA editing, including the functions of 3 proteins, expressions of 277 genes and splicing of 449 events. All the analyses results shown in NeuroEdQTL (https://relab.xidian.edu.cn/NeuroEdQTL/) constituted a unique resource for the understanding of neurodegenerative pathogenesis from genotypes to phenotypes related to A-to-I RNA editing.

Revisiting the Role of Vitamins and Minerals in Alzheimer's Disease

Alzheimer's disease (AD) is the most common type of dementia that affects millions of individuals worldwide. It is an irreversible neurodegenerative disorder that is characterized by memory loss, impaired learning and thinking, and difficulty in performing regular daily activities. Despite nearly two decades of collective efforts to develop novel medications that can prevent or halt the disease progression, we remain faced with only a few options with limited effectiveness. There has been a recent growth of interest in the role of nutrition in brain health as we begin to gain a better understanding of what and how nutrients affect hormonal and neural actions that not only can lead to typical cardiovascular or metabolic diseases but also an array of neurological and psychiatric disorders. Vitamins and minerals, also known as micronutrients, are elements that are indispensable for functions including nutrient metabolism, immune surveillance, cell development, neurotransmission, and antioxidant and anti-inflammatory properties. In this review, we provide an overview on some of the most common vitamins and minerals and discuss what current studies have revealed on the link between these essential micronutrients and cognitive performance or AD.

Role of Intracellular Amyloid β as Pathway Modulator, Biomarker, and Therapy Target

The β- and γ-secretase-driven cleavage of the amyloid precursor protein (APP) gives rise to the amyloid β peptide, which is believed to be the main driver of neurodegeneration in Alzheimer’s disease (AD). As it is prominently detectable in extracellular plaques in post-mortem AD brain samples, research in recent decades focused on the pathological role of extracellular amyloid β aggregation, widely neglecting the potential meaning of very early generation of amyloid β inside the cell. In the last few years, the importance of intracellular amyloid β (iAβ) as a strong player in neurodegeneration has been indicated by a rising number of studies. In this review, iAβ is highlighted as a crucial APP cleavage fragment, able to manipulate intracellular pathways and foster neurodegeneration. We demonstrate its relevance as a pathological marker and shed light on initial studies aiming to modulate iAβ through pharmacological treatment, which has been shown to have beneficial effects on cognitive properties in animal models. Finally, we display the relevance of viral infections on iAβ generation and point out future directions urgently needed to manifest the potential relevance of iAβ in Alzheimer’s disease.

Redox ticklers and beyond: Naphthoquinone repository in the spotlight against inflammation and associated maladies

Cellular redox status has been considered as a focal point for the pathogenesis of multiple disorders. High and persistent levels of free radicals kick off inflammation and associated disorders. Though oxidative stress at high levels is harmful but at low levels it has been shown to exert cytoprotective effects. Therefore, cytoprotection by perturbation in cellular redox balance is a leading strategy for therapeutic interventions. Prooxidants are potent redox modifiers that generate mild oxidative stress leading to a spectrum of bioactivities. Naphthoquinones are a group of highly reactive organic chemical species that interact with biological systems owing to their prooxidants nature. Owing to the ability of naphthoquinones and its derivatives to perturb redox balance in a cell and modulate redox signaling, they have been in epicenter of drug development for plausible utilization in multiple clinical settings. The present review highlights the potential of 1,4-naphthoquinone and its natural derivatives (plumbagin, juglone, lawsone, menadione, lapachol and β-lapachone) as redox modifiers with anti-inflammatory, anti-cancer, anti-diabetic and anti-microbial activities for implication in therapeutic settings.

Scaffold Searching of FDA and EMA-Approved Drugs Identifies Lead Candidates for Drug Repurposing in Alzheimer's Disease

Clinical trials of novel therapeutics for Alzheimer's Disease (AD) have consumed a significant amount of time and resources with largely negative results. Repurposing drugs already approved by the Food and Drug Administration (FDA), European Medicines Agency (EMA), or Worldwide for another indication is a more rapid and less expensive option. Therefore, we apply the scaffold searching approach based on known amyloid-beta (Aβ) inhibitor tramiprosate to screen the DrugCentral database (n = 4,642) of clinically tested drugs. As a result, menadione bisulfite and camphotamide substances with protrombogenic and neurostimulation/cardioprotection effects were identified as promising Aβ inhibitors with an improved binding affinity (ΔGbind) and blood-brain barrier permeation (logBB). Finally, the data was also confirmed by molecular dynamics simulations using implicit solvation, in particular as Molecular Mechanics Generalized Born Surface Area (MM-GBSA) model. Overall, the proposed in silico pipeline can be implemented through the early stage rational drug design to nominate some lead candidates for AD, which will be further validated in vitro and in vivo, and, finally, in a clinical trial.

A Systematic Screening of Traditional Chinese Medicine Identifies Two Novel Inhibitors Against the Cytotoxic Aggregation of Amyloid Beta

The toxic aggregates of amyloid beta (Aβ) disrupt the cell membrane, induce oxidative stress and mitochondrial dysfunction, and eventually lead to Alzheimer’s disease (AD). Intervening with this cytotoxic aggregation process has been suggested as a potential therapeutic approach for AD and other protein misfolding diseases. Traditional Chinese Medicine (TCM) has been used to treat AD and related cognitive impairment for centuries with obvious efficacy. Extracts or active ingredients of TCMs have been reported to inhibit the aggregation and cytotoxicity of Aβ. However, there is a lack of systematic research on the anti-Aβ aggregation effects of TCM components. In this study, we performed a systematic screening to identify the active ingredients of TCM against the cytotoxic aggregation of Aβ42. Through a literature and database survey, we selected 19 TCM herbals frequently used in the treatment of AD, from which 76 major active chemicals without known anti-amyloid effects were further screened. This took place through two rounds of MTT-based screening detection of the cytotoxicity of these chemicals and their effects on Aβ42-induced cytotoxicity, respectively. Tetrahydroxystilbene-2-O-β-D-glucoside (TSG) and sinapic acid (SA) were found to be less toxic, and they inhibited the cytotoxicity of Aβ42. Further studies demonstrated that TSG and SA concentration-dependently attenuated the amyloidosis and membrane disruption ability of Aβ42. Thus, we identified two novel chemicals (TSG and SA) against the cytotoxic aggregation of Aβ42. Nonetheless, further exploration of their therapeutic potential is warranted.

Synthesis and biological evaluation of novel 8- substituted sampangine derivatives as potent inhibitor of Zn2+-Aβ complex mediated toxicity, oxidative stress and inflammation

A series of 8-substituted sampangine derivatives have been designed, synthesized and tested for their ability to inhibit cholinesterase and penetrate the blood-brain barrier. Their chelating ability toward Zn²⁺ and other biologically relevant metal ions was also demonstrated by isothermal titration calorimetry. The new derivatives exhibited high acetylcholinesterase inhibitory activity, high blood-brain barrier penetration ability and high chelating selectivity for Zn²⁺. Moreover, compound 10 with the strongest binding affinity to Zn²⁺ was selected for further research. Western blotting analysis, transmission electron microscopy, DCFH-DA assay and paralysis experiment indicated that compound 10 suppressed the formation of Zn²⁺-Aβ complexes, alleviated the Zn²⁺ induced neurotoxicity and inhibited the production of ROS catalyzed by Zn²⁺ in Aβ42 transgenic C. elegans. Furthermore, compound 10 also inhibited the expressions of pro-inflammatory cytokines, such as NO, TNF-α, IL-6 and IL-1β, induced by Zn²⁺ + Aβ_1-42 in BV2 microglial cells. In general, this work provided new insights into the design and development of potent metal-chelating agents for Alzheimer's disease treatment.

Novel sampangine derivatives as potent inhibitors of Cu2+-mediated amyloid-β protein aggregation, oxidative stress and inflammation

A series of 11-substituted sampangine derivatives have been designed, synthesized, and tested for their ability to inhibit cholinesterase. Their chelating ability and selectivity for Cu²⁺ over other biologically relevant metal ions were demonstrated by isothermal titration calorimetry. Their blood-brain barrier permeability was also tested by parallel artificial membrane permeation assay. Among the synthesized derivatives, compound 11 with the strong anti-acetylcholinesterase activity, high blood-brain barrier penetration ability and high binding affinity to Cu²⁺ was selected for further research. Western blotting analysis, transmission electron microscopy, DCFH-DA assay and paralysis experiment indicated that compound 11 suppressed the formation of Cu²⁺-Aβ complexes, alleviated the Cu²⁺ induced neurotoxicity and inhibited the production of ROS catalyzed by Cu²⁺ in Aβ42 transgenic C. elegans. Moreover, compound 11 also inhibited the expressions of proinflammatory cytokines, such as NO, TNF-α, IL-6 and IL-1β, induced by Cu²⁺ + Aβ_1-42 in BV2 microglial cells. In general, this work provided new insights into the design and development of potent metal-chelating agents for AD treatment.

Copper and iron ions accelerate the prion-like propagation of α-synuclein: A vicious cycle in Parkinson's disease

Protein fibrils drive the onset and progression of many diseases in a prion-like manner, i.e. they transcellular propagate through the extracellular space to health cells to initiate toxic aggregation as seeds. The conversion of native α-synuclein into filamentous aggregates in Lewy bodies is a hallmark of Parkinson's disease (PD). Copper and iron ions accumulate in PD brains, however, whether they influence the prion-like propagation of α-synuclein remain unclear. Here, we reported that copper/iron ions accelerate prion-like propagation of α-synuclein fibrils by promoting cellular internalization of α-synuclein fibrils, intracellular α-synuclein aggregation and the subsequent release of mature fibrils to the extracellular space to induce further propagation. Mechanistically, copper/iron ions enhanced α-synuclein fibrils internalization was mediated by negatively charged membrane heparan sulfate proteoglycans (HSPGs). α-Synuclein fibrils formed in the presence of copper/iron ions were more cytotoxic, causing increased ROS production, cell apoptosis, and shortened the lifespan of a C. elegans PD model overexpressing human α-synuclein. Notably, these deleterious effects were ameliorated by two clinically used chelators, triethylenetetramine and deferiprone. Together, our results suggest a new role for heavy metal ions, e.g. copper and iron, in the pathogenesis of PD through accelerating prion-like propagation of α-synuclein fibrils.

Non-polyphenolic natural inhibitors of amyloid aggregation

Protein misfolding diseases (PMDs) are chronic and progressive, with no effective therapy so far. Aggregation and misfolding of amyloidogenic proteins are closely associated with the onset and progression of PMDs, such as amyloid-β (Aβ) in Alzheimer's disease, α-Synuclein (α-Syn) in Parkinson's disease and human islet amyloid polypeptide (hIAPP) in type 2 diabetes. Inhibiting toxic aggregation of amyloidogenic proteins is regarded as a promising therapeutic approach in PMDs. The past decade has witnessed the rapid progresses of this field, dozens of inhibitors have been screened and verified in vitro and in vivo, demonstrating inhibitory effects against the aggregation and misfolding of amyloidogenic proteins, together with beneficial effects. Natural products are major sources of small molecule amyloid inhibitors, a number of natural derived compounds have been identified with great bioactivities and translational prospects. Here, we review the non-polyphenolic natural inhibitors that potentially applicable for PMDs treatment, along with their working mechanisms. Future directions are proposed for the development and clinical applications of these inhibitors.

Ligand accessibility to heme cytochrome b5 coordinating sphere and enzymatic activity enhancement upon tyrosine ionization

Recently, we observed that at extreme alkaline pH, cytochrome b5 (Cb5) acquires a peroxidase-like activity upon formation of a low spin hemichrome associated with a non-native state. A functional characterization of Cb5, in a wide pH range, shows that oxygenase/peroxidase activities are stimulated in alkaline media, and a correlation between tyrosine ionization and the attained enzymatic activities was noticed, associated with an altered heme spin state, when compared to acidic pH values at which the heme group is released. In these conditions, a competitive assay between imidazole binding and Cb5 endogenous heme ligands revealed the appearance of a binding site for this exogenous ligand that promotes a heme group exposure to the solvent upon ligation. Our results shed light on the mechanism behind Cb5 oxygenase/peroxidase activity stimulation in alkaline media and reveal a role of tyrosinate anion enhancing Cb5 enzymatic activities on the distorted protein before maximum protein unfolding.

Salvation of the fallen angel: Reactivating mutant p53

The transcription factor p53 is known as the guardian of the genome for its powerful anti-tumour capacity. However, mutations of p53 that undermine their protein structure, resulting in loss of tumour suppressor function and gain of oncogenic function, have been implicated in more than half of human cancers. The crucial role of mutant forms of p53 in cancer makes it an attractive therapeutic target. A large number of candidates, including low MW compounds, peptides, and nucleic acids, have been identified or designed to rescue p53 mutants and reactivate their anti-tumour capacity through a variety of mechanisms. In this review, we summarize the progress made in the reactivation of mutant forms of p53, focusing on the pharmacological mechanisms of the reactivators of p53 mutants.

Glycated Insulin Exacerbates the Cytotoxicity of Human Islet Amyloid Polypeptides: a Vicious Cycle in Type 2 Diabetes

The aggregation of human islet amyloid polypeptide (hIAPP) is one of the triggering factors of type 2 diabetes mellitus (T2DM). hIAPP is cosynthesized, costored, and cosecreted with insulin in pancreatic β-cells, and insulin inhibits hIAPP aggregation. In T2DM patients, long-term hyperglycemia causes glycation of near 10% of total insulin. The glycation not only modifies insulin but also cross-links insulin into oligomers. However, the effect of glycated human insulin on hIAPP aggregation is unknown. In this study, four physiologically relevant monosaccharides, methylglyoxal, glucose, fructose, and ribose were used to glycate human insulin and two C-terminus truncated insulin analogues. Glycated insulin monomers or low molecular weight oligomers such as dimers significantly exacerbated the cytotoxicity of hIAPP. Notably, glycation-induced cross-linking of insulin inhibited the aggregation, membrane disruption, and cytotoxicity of hIAPP, which was corroborated by a control study using EGS-induced cross-linking of insulin or lysozyme. Removal of B29^Lys on the C terminus of the insulin B chain not only abolished glycation-induced cross-linking but also attenuated the aggravation effect of glycated insulin on hIAPP cytotoxicity. Taken together, this study reveals a vicious cycle in T2DM, that hyperglycemia-driven insulin glycation exacerbates the cytotoxicity of hIAPP, which accelerates β-cells death and further deteriorates T2DM.