Novel Mannitol-Based Small Molecules for Inhibiting Aggregation of α-Synuclein Amyloids in Parkinson's Disease

Synthesis, structural study and antitumor activity of novel alditol-based imidazophenanthrolines (aldo-IPs)

A series of 1H-imidazo [4,5-f][1,10] phenanthroline derivatives functionalized at 2-position with chiral, and conformationally flexible polyhydroxy alkyl chains derived from carbohydrates (alditol-based imidazophenanthrolines, aldo-IPs) is presented herein. These novel glycomimetics showed relevant and differential cytotoxic activity against several cultured tumor cell lines (PC3, HeLa and HT-29), dependent on the nature and stereochemistry of the polyhydroxy alkyl chain. The mannose-based aldo-IP demonstrated the higher cytotoxicity in the series, substantially better than cisplatin metallo-drug in all cell lines tested, and better than G-quadruplex ligand 360A in HeLa and HT29 cells. Cell cycle experiments and Annexin V-PI assays revealed that aldo-IPs induce apoptosis in HeLa cells. Initial study of DNA interactions by DNA FRET melting assays proved that the aldo-IPs produce only a slight thermal stabilization of DNA secondary structures, more pronounced in the case of quadruplex DNA. Viscosity titrations with CT dsDNA suggest that the compounds behave as DNA groove binders, whereas equilibrium dialysis assays showed that the compounds bind CT with Ka values in the range 104-105 M-1. The aldo-IP derivatives were obtained with synthetically useful yields through a feasible one-pot multistep process, by aerobic oxidative cyclization of 1,10-phenanthroline-5,6-diamine with a selection of unprotected aldoses using (NH4)2SO4 as promoter.

Protection Activity of 1,4-Naphthoquinones in Rotenone-Induced Models of Neurotoxicity

The MTS cell viability test was used to screen a mini library of natural and synthetic 1,4-naphthoquinone derivatives (1,4-NQs) from marine sources. This screening identified two highly effective compounds, U-443 and U-573, which showed potential in protecting Neuro-2a neuroblastoma cells from the toxic effects of rotenone in an in vitro model of neurotoxicity. The selected 1,4-NQs demonstrated the capability to reduce oxidative stress by decreasing the levels of reactive oxygen species (ROS) and nitric oxide (NO) in Neuro-2a neuroblastoma cells and RAW 264.7 macrophage cells and displayed significant antioxidant properties in mouse brain homogenate. Normal mitochondrial function was restored and the mitochondrial membrane potential was also regained by 1,4-NQs after exposure to neurotoxins. Furthermore, at low concentrations, these compounds were found to significantly reduce levels of proinflammatory cytokines TNF and IL-1β and notably inhibit the activity of cyclooxygenase-2 (COX-2) in RAW 264.7 macrophages. The results of docking studies showed that the 1,4-NQs were bound to the active site of COX-2, analogically to a known inhibitor of this enzyme, SC-558. Both substances significantly improved the behavioral changes in female CD1 mice with rotenone-induced early stage of Parkinson's disease (PD) in vivo. It is proposed that the 1,4-NQs, U-443 and U-573, can protect neurons and microglia through their potent anti-ROS and anti-inflammatory activities.

Naphthoquinones as a Promising Class of Compounds for Facing the Challenge of Parkinson's Disease

Parkinson's disease (PD) is a degenerative disease that affects approximately 6.1 million people and is primarily caused by the loss of dopaminergic neurons. Naphthoquinones have several biological activities explored in the literature, including neuroprotective effects. Therefore, this review shows an overview of naphthoquinones with neuroprotective effects, such as shikonin, plumbagin and vitamin K, that prevented oxidative stress, in addition to multiple mechanisms. Synthetic naphthoquinones with inhibitory activity on the P2X7 receptor were also found, leading to a neuroprotective effect on Neuro-2a cells. It was found that naphthazarin can act as inhibitors of the MAO-B enzyme. Vitamin K and synthetic naphthoquinones hybrids with tryptophan or dopamine showed inhibition of the aggregation of α-synuclein. Synthetic derivatives of juglone and naphthazarin were able to protect Neuro-2a cells against neurodegenerative effects of neurotoxins. In addition, routes for producing synthetic derivatives were also discussed. With the data presented, 1,4-naphthoquinones can be considered as a promising class in the treatment of PD and this review aims to assist the scientific community in the application of these compounds. The derivatives presented can also support further research that explores their structures as synthetic platforms, in addition to helping to understand the interaction of naphthoquinones with biological targets related to PD.

Designed inhibitors to reduce amyloid virulence and cytotoxicity and combat neurodegenerative and infectious diseases

The review highlights the role of amyloids in various diseases and the challenges associated with targeting human amyloids in therapeutic development. However, due to the better understanding of microbial amyloids' role as virulence factors, there is a growing interest in repurposing and designing anti-amyloid compounds for antivirulence therapy. The identification of amyloid inhibitors has not only significant clinical implications but also provides valuable insights into the structure and function of amyloids. The review showcases small molecules and peptides that specifically target amyloids in both humans and microbes, reducing cytotoxicity and biofilm formation, respectively. The review emphasizes the importance of further research on amyloid structures, mechanisms, and interactions across all life forms to yield new drug targets and improve the design of selective treatments. Overall, the review highlights the potential for amyloid inhibitors in therapeutic development for both human diseases and microbial infections.

14-3-3ζ Participates in the Phase Separation of Phosphorylated and Glycated Tau and Modulates the Physiological and Pathological Functions of Tau

Tau plays a major role in Alzheimer's disease (AD) and several other neurodegenerative diseases. Tau undergoing liquid-liquid phase separation (LLPS) performs specific physiological functions, induces pathological processes, and contributes to neurodegeneration. Regulating Tau phase separation helps maintain physiological functions of Tau and inhibits pathological aggregation. Here, we show that the 14-3-3 zeta isoform (14-3-3ζ) participates in Tau LLPS. 14-3-3ζ can undergo co-phase separation with WT Tau, participate in and stabilize Tau droplets, and inhibit Tau droplet-driven tubulin assembly. On the other hand, 14-3-3ζ disrupts the LLPS of phosphorylated and glycated Tau, thereby inhibiting the amyloid aggregation initiated by LLPS.

Mechanistic Insight into the Amyloid Fibrillation Inhibition of Hen Egg White Lysozyme by Three Different Bile Acids

Amyloid aggregation of protein is linked to many neurodegenerative diseases. Identification of small molecules capable of targeting amyloidogenic proteins has gained significant importance. Introduction of hydrophobic and hydrogen bonding interactions through site-specific binding of small molecular ligand to protein can effectively modulate the protein aggregation pathway. Here, we investigate the possible roles of three different bile acids, cholic acid (CA), taurocholic acid (TCA), and lithocholic acid (LCA) with varying hydrophobic and hydrogen bonding properties in inhibiting protein fibrillation. Bile acids are an important class of steroid compounds that are synthesized in the liver from cholesterol. Increasing evidence suggests that altered taurine transport, cholesterol metabolism, and bile acid synthesis have strong implications in Alzheimer's disease. We find that the hydrophilic bile acids, CA and TCA (taurine conjugated form of CA), are substantially more efficient inhibitors of lysozyme fibrillation than the most hydrophobic secondary bile acid LCA. Although LCA binds more strongly with the protein and masks the Trp residues more prominently through hydrophobic interactions, the lesser extent of hydrogen bonding interactions at the active site has made LCA a relatively weaker inhibitor of HEWL aggregation than CA and TCA. The introduction of a greater number of hydrogen bonding channels by CA and TCA with several key amino acid residues which are prone to form oligomers and fibrils has weakened the protein's internal hydrogen bonding capabilities for undergoing amyloid aggregation.

Functional and Pathological Effects of α-Synuclein on Synaptic SNARE Complexes

α-Synuclein is an abundant protein at the neuronal synapse that has been implicated in Parkinson's disease for over 25 years and characterizes the hallmark pathology of a group of neurodegenerative diseases now known as the synucleinopathies. Physiologically, α-synuclein exists in an equilibrium between a synaptic vesicle membrane-bound α-helical multimer and a cytosolic largely unstructured monomer. Through its membrane-bound state, α-synuclein functions in neurotransmitter release by modulating several steps in the synaptic vesicle cycle, including synaptic vesicle clustering and docking, SNARE complex assembly, and homeostasis of synaptic vesicle pools. These functions have been ascribed to α-synuclein's interactions with the synaptic vesicle SNARE protein VAMP2/synaptobrevin-2, the synaptic vesicle-attached synapsins, and the synaptic vesicle membrane itself. How α-synuclein affects these processes, and whether disease is due to loss-of-function or gain-of-toxic-function of α-synuclein remains unclear. In this review, we provide an in-depth summary of the existing literature, discuss possible reasons for the discrepancies in the field, and propose a working model that reconciles the findings in the literature.

Amyloid Disassembly: What Can We Learn from Chaperones?

Protein aggregation and subsequent accumulation of insoluble amyloid fibrils with cross-β structure is an intrinsic characteristic of amyloid diseases, i.e., amyloidoses. Amyloid formation involves a series of on-pathway and off-pathway protein aggregation events, leading to mature insoluble fibrils that eventually accumulate in multiple tissues. In this cascade of events, soluble oligomeric species are formed, which are among the most cytotoxic molecular entities along the amyloid cascade. The direct or indirect action of these amyloid soluble oligomers and amyloid protofibrils and fibrils in several tissues and organs lead to cell death in some cases and organ disfunction in general. There are dozens of different proteins and peptides causing multiple amyloid pathologies, chief among them Alzheimer's, Parkinson's, Huntington's, and several other neurodegenerative diseases. Amyloid fibril disassembly is among the disease-modifying therapeutic strategies being pursued to overcome amyloid pathologies. The clearance of preformed amyloids and consequently the arresting of the progression of organ deterioration may increase patient survival and quality of life. In this review, we compiled from the literature many examples of chemical and biochemical agents able to disaggregate preformed amyloids, which have been classified as molecular chaperones, chemical chaperones, and pharmacological chaperones. We focused on their mode of action, chemical structure, interactions with the fibrillar structures, morphology and toxicity of the disaggregation products, and the potential use of disaggregation agents as a treatment option in amyloidosis.

Advances of functional nanomaterials for magnetic resonance imaging and biomedical engineering applications

Functional nanomaterials have been widely used in biomedical fields due to their good biocompatibility, excellent physicochemical properties, easy surface modification, and easy regulation of size and morphology. Functional nanomaterials for magnetic resonance imaging (MRI) can target specific sites in vivo and more easily detect disease-related specific biomarkers at the molecular and cellular levels than traditional contrast agents, achieving a broad application prospect in MRI. This review focuses on the basic principles of MRI, the classification, synthesis and surface modification methods of contrast agents, and their clinical applications to provide guidance for designing novel contrast agents and optimizing the contrast effect. Furthermore, the latest biomedical advances of functional nanomaterials in medical diagnosis and disease detection, disease treatment, the combination of diagnosis and treatment (theranostics), multi-model imaging and nanozyme are also summarized and discussed. Finally, the bright application prospects of functional nanomaterials in biomedicine are emphasized and the urgent need to achieve significant breakthroughs in the industrial transformation and the clinical translation is proposed. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Propagation of tau and α-synuclein in the brain: therapeutic potential of the glymphatic system

Many neurodegenerative diseases, including Alzheimer’s disease and Parkinson’s disease, are characterised by the accumulation of misfolded protein deposits in the brain, leading to a progressive destabilisation of the neuronal network and neuronal death. Among the proteins that can abnormally accumulate are tau and α-synuclein, which can propagate in a prion-like manner and which upon aggregation, represent the most common intracellular proteinaceous lesions associated with neurodegeneration. For years it was thought that these intracellular proteins and their accumulation had no immediate relationship with extracellular homeostasis pathways such as the glymphatic clearance system; however, mounting evidence has now suggested that this is not the case. The involvement of the glymphatic system in neurodegenerative disease is yet to be fully defined; however, it is becoming increasingly clear that this pathway contributes to parenchymal solute clearance. Importantly, recent data show that proteins prone to intracellular accumulation are subject to glymphatic clearance, suggesting that this system plays a key role in many neurological disorders. In this review, we provide a background on the biology of tau and α-synuclein and discuss the latest findings on the cell-to-cell propagation mechanisms of these proteins. Importantly, we discuss recent data demonstrating that manipulation of the glymphatic system may have the potential to alleviate and reduce pathogenic accumulation of propagation-prone intracellular cytotoxic proteins. Furthermore, we will allude to the latest potential therapeutic opportunities targeting the glymphatic system that might have an impact as disease modifiers in neurodegenerative diseases.

Tryptophan-cardanol fluorescent nanoparticles inhibit α-synuclein aggregation and disrupt amyloid fibrils

Protein misfolding and aggregation play a vital role in several human diseases such as Parkinson's, Alzheimer's, and prion diseases. The development of nanoparticles that modulate aggregation could be potential drug candidates for these neurodegenerative disorders. Parkinson's disease pathogenesis is closely associated with the accumulation of α-synuclein oligomers and fibrils in the substantia nigra of the brain. This report discusses the interactions of novel tryptophan-cardanol nanoparticles with α-synuclein protein monomers and fibrils. These nanoparticles could effectively disrupt α-synuclein fibrils and inhibit fibril formation at low concentrations such as 5 μM. The tryptophan-cardanol nanoparticles inhibit fibril formation from unstructured protein resulting in spherical nanostructures. These nanoparticles could also disassemble amyloid fibrils; the complete disappearance of fibrils was evident after 48 h of incubation with tryptophan-cardanol. The transmission electron microscopy (TEM) micrographs after the incubation did not show any remnants of the peptide aggregates or oligomers. The thioflavin T fluorescence after the disassembly was diminished compared with that of fibrils also supports the inhibitory effect of the nanoparticles. Also, these nanoparticles did not reduce the viability of the SH-SY5Y cells. These findings suggest that the tryptophan-cardanol nanoparticles showed sufficiently high inhibitory activity and may have therapeutic potential for synucleinopathies.

A novel multi-target strategy to attenuate the progression of Parkinson's disease by diamine hybrid AGE/ALE inhibitor

Instead of a conventional 'one-drug-one-target approach', this article presents a novel multi-target approach with a concept of trapping simultaneously as many detrimental factors as possible involved in the progression of Parkinson's disease. These factors include reactive carbonyl species, reactive oxygen species, Fe^3+/Cu²⁺ and ortho-quinones (o-quinone), in particular. Different from the known multi-target strategies for Parkinson's disease, it is a sort of 'vacuum cleaning' strategy. The new agent consists of reactive carbonyl species scavenging moiety and reactive oxygen species scavenging and metal chelating moiety linked by a spacer. Provided that the capacity of scavenging o-quinones is demonstrated, this type of agent can further broaden its potential therapeutic profile. In order to support this new hypothetical approach, a number of simple in vitro experiments are proposed.

Dual concentration-dependent effect of ascorbic acid on PAP(248-286) amyloid formation and SEVI-mediated HIV infection

Human semen contains various amyloidogenic peptides derived from Prostatic Acid Phosphatase (PAP) and Semenogelin proteins that are capable of enhancing HIV-1 infection when assembled into fibrils. The best characterized among them is a 39 amino acid peptide PAP(248–286), which forms amyloid fibrils termed SEVI (semen-derived enhancer of viral infection) that increase the infectivity of HIV-1 by orders of magnitude. Inhibiting amyloid formation by PAP(248–286) may mitigate the sexual transmission of HIV-1. Several vitamins have been shown to reduce the aggregation of amyloids such as Aβ, α-Synuclein, and Tau, which are associated with neurodegenerative diseases. Since ascorbic acid (AA, vitamin C) is the most abundant vitamin in semen with average concentrations of 0.4 mM, we here examined how AA affects PAP(248–286) aggregation in vitro. Using ThT binding assays, transmission electron microscopy, and circular dichroism spectroscopy, a dual and concentration-dependent behavior of AA in modulating PAP(248–286) fibril formation was observed. We found that low molar ratios of AA:PAP(248–286) promoted whereas high molar ratios inhibited PAP(248–286) fibril formation. Accordingly, PAP(248–286) aggregated in the presence of low amounts of AA enhanced HIV-1 infection, whereas excess amounts of AA during aggregation reduced the infectivity enhancing effect in cell culture. Collectively, this work provides a biophysical insight into the effect of AA, an important seminal component, on SEVI fibrillation which might impact amyloid formation kinetics, thereby modulating the biological activity of semen amyloids.

Human semen contains various amyloidogenic peptides derived from Prostatic Acid Phosphatase (PAP) and Semenogelin proteins that are capable of enhancing HIV-1 infection when assembled into fibrils.

Permeation Challenges of Drugs for Treatment of Neurological Tuberculosis and HIV and the Application of Magneto-Electric Nanoparticle Drug Delivery Systems

The anatomical structure of the brain at the blood-brain barrier (BBB) creates a limitation for the movement of drugs into the central nervous system (CNS). Drug delivery facilitated by magneto-electric nanoparticles (MENs) is a relatively new non-invasive approach for the delivery of drugs into the CNS. These nanoparticles (NPs) can create localized transient changes in the permeability of the cells of the BBB by inducing electroporation. MENs can be applied to deliver antiretrovirals and antibiotics towards the treatment of human immunodeficiency virus (HIV) and tuberculosis (TB) infections in the CNS. This review focuses on the drug permeation challenges and reviews the application of MENs for drug delivery for these diseases. We conclude that MENs are promising systems for effective CNS drug delivery and treatment for these diseases, however, further pre-clinical and clinical studies are required to achieve translation of this approach to the clinic.

Neuroprotective Effect of 1,4-Naphthoquinones in an In Vitro Model of Paraquat and 6-OHDA-Induced Neurotoxicity

Targeted screening using the MTT cell viability test with a mini-library of natural and synthetic 1,4-naphthoquinones and their derivatives was performed in order to increase the survival of Neuro-2a neuroblastoma cells in in vitro paraquat and 6-hydroxydopamine models of Parkinson’s disease. As a result, 10 compounds were selected that could protect neuronal cells from the cytotoxic effects of both paraquat and 6-hydroxydopamine. The five most active compounds at low concentrations were found to significantly protect the activity of nonspecific esterase from the inhibitory effects of neurotoxins, defend cell biomembranes from lytic destruction in the presence of paraquat and 6-hydroxydopamine, and normalize the cell cycle. The protective effects of these compounds are associated with the suppression of oxidative stress, decreased expression of reactive oxygen species and nitric oxide formation in cells and normalization of mitochondrial function, and restoration of the mitochondrial membrane potential altered by neurotoxins. It was suggested that the neuroprotective activity of the studied 1,4-NQs is attributable to their pronounced antioxidant and free radical scavenging activity and their ability to reduce the amount of reactive oxygen species formed by paraquat and 6-hydroxydopamine action on neuronal cells. The significant correlation between the neuroprotective properties of 1,4-naphthoquinones and Quantitative Structure–Activity Relationship descriptors describing the physicochemical properties of these compounds means that the hydrophobicity, polarity, charge, and shape of the molecules can be of decisive importance in determining the biological activity of studied substances.

α-Synuclein: An All-Inclusive Trip Around its Structure, Influencing Factors and Applied Techniques

Alpha-synuclein (αSyn) is a highly expressed and conserved protein, typically found in the presynaptic terminals of neurons. The misfolding and aggregation of αSyn into amyloid fibrils is a pathogenic hallmark of several neurodegenerative diseases called synucleinopathies, such as Parkinson’s disease. Since αSyn is an Intrinsically Disordered Protein, the characterization of its structure remains very challenging. Moreover, the mechanisms by which the structural conversion of monomeric αSyn into oligomers and finally into fibrils takes place is still far to be completely understood. Over the years, various studies have provided insights into the possible pathways that αSyn could follow to misfold and acquire oligomeric and fibrillar forms. In addition, it has been observed that αSyn structure can be influenced by different parameters, such as mutations in its sequence, the biological environment (e.g., lipids, endogenous small molecules and proteins), the interaction with exogenous compounds (e.g., drugs, diet components, heavy metals). Herein, we review the structural features of αSyn (wild-type and disease-mutated) that have been elucidated up to present by both experimental and computational techniques in different environmental and biological conditions. We believe that this gathering of current knowledge will further facilitate studies on αSyn, helping the planning of future experiments on the interactions of this protein with targeting molecules especially taking into consideration the environmental conditions.

Sequential and cellular detection of copper and lactic acid by disaggregation and reaggregation of the fluorescent panchromatic fibres of an acylthiourea based sensor

We report, for the first time, the self-assembly of an acyl-thiourea based sensor, N-{(6-methoxy-pyridine-2-yl) carbamothioyl}benzamide (NG1), with panchromatic fluorescent fibres and its dual-sensing properties for the sequential detection of Cu2+ ions and lactic acid. The panchromatic fibres formed by NG1 were disrupted in the presence of Cu2+ ions and this was accompanied by a visible colour change in the solution from colourless to yellow. The addition of lactic acid to the NG1 + Cu2+ solution, on the other hand, induced re-aggregation to fibrillar structures and the colour of the solution again changed to colourless. Hence, it may be surmised that the disaggregation and re-aggregation impart unique dual-sensing properties to NG1 for the sequential detection of Cu2+ ions and lactic acid. The application of NG1 as a selective sensor for Cu2+ ions and lactic acid has been assessed in detail by UV-visible and fluorescence spectroscopy. Furthermore, two structural variants of NG1, namely, NG2 and NG3, were synthesized, which suggest the crucial role of pyridine in imparting panchromatic emission properties and of both pyridine and acyl-thiourea side chain in the binding of Cu2+ ions. The O-methoxy group plays an important part in making NG1 the most sensitive probe of its structural analogs. Finally, the utility of NG1 for the sequential and cellular detection of Cu2+ ions and lactic acid was studied in human RPE cells. The experimental results of the interaction of NG1 with Cu2+ ions and lactic acid have also been validated theoretically by using quantum chemical calculations based on density functional theory (DFT). To the best of our knowledge, this is the first report wherein a dual sensor for Cu2+ ions and lactate ions is synthesized. More importantly, the aggregation properties of the sensor have been studied extensively and an interesting correlation of the photophysical properties of the probe with its self-assembling behavior has been elucidated.

Inhibition of tau amyloid formation and disruption of its preformed fibrils by Naphthoquinone-Dopamine hybrid

Misfolding and aggregation of tau protein, into pathological amyloids, are hallmarks of a group of neurodegenerative diseases collectively termed tauopathies and their modulation may be therapeutically valuable. Herein, we describe the synthesis and characterization of a dopamine-based hybrid molecule, naphthoquinone-dopamine (NQDA). Using thioflavin S assay, CD, transmission electron microscopy, dynamic light scattering, Congo Red birefringence, and large unilamellar vesicle leakage assays, we demonstrated its efficacy in inhibiting the in vitro aggregation of key tau-derived amyloidogenic fragments, PHF6 (VQIVYK) and PHF6* (VQIINK), prime drivers of aggregation of full-length tau in disease pathology. Isothermal titration calorimetry analysis revealed that the interaction between NQDA and PHF6 is spontaneous and has significant binding efficiency driven by both entropic and enthalpic processes. Furthermore, NQDA efficiently disassembled preformed fibrils of PHF6 and PHF6* into nontoxic species. Molecular dynamic simulations supported the in vitro results and provided a plausible mode of binding of NQDA with PHF6 fibril. NQDA was also capable of inhibiting the aggregation of full-length tau protein and disrupting its preformed fibrils in vitro in a dose-dependent manner. In a comparative study, the IC₅₀ value (50% inhibition of fibril formation) of NQDA in inhibiting the aggregation of PHF6 (25 µm) was ~ 17 µm, which is lower than for other bona fide amyloid inhibitors, naphthoquinone-tryptophan, rosmarinic acid, epigallocatechin gallate, ~ 21, ~ 77, or ~ 19 µm, respectively. Comparable superiority of NQDA was observed for inhibition of PHF6*. These findings suggest that NQDA can be a useful scaffold for designing new therapeutics for Alzheimer's disease and other tauopathies.

Effect of ionic liquids on the fluorescence properties and aggregation of superfolder green fluorescence protein

Proteins generally tend to aggregate with less desirable properties in numerous solvents, which is one of the major challenges in the development of solvents for functional proteins. This work aims to utilize fluorescence spectroscopy and small angle X-ray scattering (SAXS) to understand the effects of ionic liquids (ILs) on the fluorescence and aggregation behavior of superfolder green fluorescent protein (sfGFP). The studied ILs consisted of four different anions coupled with primary, tertiary and quaternary ammonium cations. The results show that the chromophore fluorescence was generally maintained in 1 mol% IL-water mixtures, then decreased with increasing IL concentration. We primarily employed the pseudo-radius of gyration (pseudo-R_g) to evaluate sfGFP aggregation. The sfGFP was less aggregated with nitrate-based ILs compared to in buffer, and more aggregated in the mesylate-based ILs. Further, we show that the polyol additives of glycerol and glucose in IL-water mixtures slightly decreased the sfGFP propensity to aggregate. Size-exclusion chromatography (SEC)-SAXS was used to characterize the monomeric sfGFP in ethylammonium nitrate (EAN) and triethylammonium mesylate (TEAMs)-water mixtures. The presence of 1 mol% TEAMs maintained the sfGFP fluorescence, promoted the compact structure, but slightly increased the amount of large aggregates, which contrasted with that of EAN.

Inhibition of tau aggregation and associated cytotoxicity on neuron-like cells by calycosin

In this study, the in vitro assembly of tau and anti-amyloidogenic properties of one naturally occurring phytoestrogen, calycosin, was investigated by spectroscopic techniques including ThT and ANS fluorescence, CD, Congo red absorbance as well as TEM analysis. Afterwards the cytotoxicity of different amyloid species against SH-SY5Y cells was evaluated by MTT assay. Fluorescence spectroscopic studies revealed that calycosin exerts its anti-amyloidogenic effects through increasing the lag time and reducing the apparent growth rate constant (k_app), the amount of fibrillation, and the exposure of hydrophobic regions. Congo red absorbance and CD studies indicated that calycosin prevented the formation of tau aggregate species and β-sheets structures, respectively. TEM analysis also determined the capacity of calycosin to inhibit tau fibrillogenesis through formation of large amorphous aggregates. Furthermore, cellular assays disclosed that calycosin mitigated the cell mortality, LDH release, ROS level, and expression of Bax, Bcl-2, and Caspase-3 in both mRNA and protein levels induced by tau amyloid fibrils. In conclusion, this data may suggest that calycosin can prevent tau amyloid fibrillation and the associated cytotoxicity, mainly due to its effects on formation of lower content of oligomeric and fibrillar aggregates with lower solvent-exposed hydrophobic patches compared to those produced in the absence of calycosin.

Pharmacological Modulators of Tau Aggregation and Spreading

Tauopathies are neurodegenerative disorders characterized by the deposition of aggregates composed of abnormal tau protein in the brain. Additionally, misfolded forms of tau can propagate from cell to cell and throughout the brain. This process is thought to lead to the templated misfolding of the native forms of tau, and thereby, to the formation of newer toxic aggregates, thereby propagating the disease. Therefore, modulation of the processes that lead to tau aggregation and spreading is of utmost importance in the fight against tauopathies. In recent years, several molecules have been developed for the modulation of tau aggregation and spreading. In this review, we discuss the processes of tau aggregation and spreading and highlight selected chemicals developed for the modulation of these processes, their usefulness, and putative mechanisms of action. Ultimately, a stronger understanding of the molecular mechanisms involved, and the properties of the substances developed to modulate them, will lead to the development of safer and better strategies for the treatment of tauopathies.

Polyampholyte-Based Synthetic Chaperone Modulate Amyloid Aggregation and Lithium Delivery

Protein misfolding and aggregation is the pathological hallmark of Alzheimer's disease (AD). The etiopathogenesis of AD involves the accumulation of amyloid-β (Aβ) plaques in the brain, which disrupt the neuronal network and communication, causing neuronal death and severe cognitive impairment. Modulation of Aβ aggregation by exogenous therapeutic agents is considered an effective strategy to treat AD. Frequent failure of drug candidates in various phases of clinical trials reiterates the need for alternative therapeutic strategies for AD treatment. Polyampholytes with cationic and anionic segments are considered as artificial protein mimics capable of modulating the protein misfolding and aggregation. We report a diblock copolymer of tryptophan-functionalized methacrylic acid (PTMA) polyampholyte synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization. Investigation revealed that PTMA acts as a synthetic chaperone to protect the native structure of the lysozyme under heat-induced aggregation conditions. PTMA effectively modulates Aβ aggregation and rescues neuronal cells. Lithium has been shown to exhibit therapeutic efficacy in chronic neurological diseases including AD. PTMA sequesters and releases lithium ions in response to neuropathological pH stimuli, making it a promising candidate for lithium transport and delivery. The detailed studies demonstrate PTMA as aggregation modulator and lithium carrier with implications for combinational therapy to treat AD.

Tryptophan-galactosylamine conjugates inhibit and disaggregate amyloid fibrils of Aβ42 and hIAPP peptides while reducing their toxicity

Self-assembly of proteins into amyloid fibrils is a hallmark of various diseases, including Alzheimer's disease (AD) and Type-2 diabetes Mellitus (T2DM). Aggregation of specific peptides, like Aβ42 in AD and hIAPP in T2DM, causes cellular dysfunction resulting in the respective pathology. While these amyloidogenic proteins lack sequence homology, they all contain aromatic amino acids in their hydrophobic core that play a major role in their self-assembly. Targeting these aromatic residues by small molecules may be an attractive approach for inhibiting amyloid aggregation. Here, various biochemical and biophysical techniques revealed that a panel of tryptophan-galactosylamine conjugates significantly inhibit fibril formation of Aβ42 and hIAPP, and disassemble their pre-formed fibrils in a dose-dependent manner. They are also not toxic to mammalian cells and can reduce the cytotoxicity induced by Aβ42 and hIAPP aggregates. These tryptophan-galactosylamine conjugates can therefore serve as a scaffold for the development of therapeutics towards AD and T2DM.

A luminescence-based assay for monitoring changes in alpha-synuclein aggregation in living cells

Parkinson's disease is characterized by the accumulation of protein aggregates in the brain, termed Lewy bodies. Lewy bodies are predominantly composed of α-synuclein and mutations that increase the aggregation potential of α-synuclein have been associated with early on-set disease. Assays capable of reporting on the solubility of α-synuclein in living cells could provide a means to interrogate the influence of mutations on aggregation as well as identify small molecules capable of modulating the aggregation of α-synuclein. Herein, we repurpose our previously reported self-assembling NanoLuc luciferase fragments to engineer a platform for detecting α-synuclein solubility in living cells. This new assay is capable of reporting on changes in α-synuclein solubility caused by disease-relevant mutations as well as inhibitors of aggregation. In the long term, this new assay platform provides a means to investigate the influence of mutations on α-synuclein solubility as well as identify potential tool compounds capable of modulating α-synuclein aggregation.

Novel approaches to counter protein aggregation pathology in Parkinson's disease

The primary neuropathological characteristics of the Parkinsonian brain are the loss of nigral dopamine neurons and the aggregation of alpha synuclein protein. Efforts to development potentially disease-modifying treatments have largely focused on correcting these aspects of the condition. In the last decade treatments targeting protein aggregation have entered the clinical pipeline. In this chapter we provide an overview of ongoing clinical trial programs for different therapies attempting to reduce protein aggregation pathology in Parkinson's disease. We will also briefly consider various novel approaches being proposed-and being developed preclinically-to inhibit/reduce aggregated protein pathology in Parkinson's.

Naphthoquinone Tryptophan Hybrids: A Promising Small Molecule Scaffold for Mitigating Aggregation of Amyloidogenic Proteins and Peptides

A current challenge faced by researchers is the lack of disease-modifying therapeutics for amyloid formation that is associated with several human diseases. Although the monomeric proteins or peptides involved in various amyloidogenic diseases do not have amino acid sequence homology, there appears to be a structural correlation among the amyloid assemblies, which are responsible for distinct pathological conditions. Here, we review our work on Naphthoquinone Tryptophan (NQTrp) hybrids, a small molecule scaffold that can generically modulate neuronal and non-neuronal amyloid aggregation both in vitro and in vivo. NQTrp reduces the net amyloid load by inhibiting the process of amyloid formation and disassembling the pre-formed fibrils, both in a dose-dependent manner. As a plausible mechanism of action, NQTrp effectively forms hydrogen bonding and hydrophobic interactions, such as π-π stacking, with the vital residues responsible for the initial nucleation of protein/peptide aggregation. This review highlights the effectiveness of the NQTrp hybrid scaffold for developing novel small molecule modulators of amyloid aggregation.

Antibiotic-induced microbiome depletion protects against MPTP-induced dopaminergic neurotoxicity in the brain

Although the brain-gut axis appears to play a role in the pathogenesis of Parkinson's disease, the precise mechanisms underlying the actions of gut microbiota in this disease are unknown. This study was undertaken to investigate whether antibiotic-induced microbiome depletion affects dopaminergic neurotoxicity in the mouse brain after administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP significantly decreased dopamine transporter (DAT) immunoreactivity in the striatum and tyrosine hydroxylase (TH) immunoreactivity in the substantia nigra of water-treated mice. However, MPTP did not decrease DAT or TH immunoreactivity in the brains of mice treated with an antibiotic cocktail. Furthermore, antibiotic treatment significantly decreased the diversity and altered the composition of the host gut microbiota at the genus and species levels. Interestingly, MPTP also altered microbiome composition in antibiotic-treated mice. These findings suggest that antibiotic-induced microbiome depletion might protect against MPTP-induced dopaminergic neurotoxicity in the brain via the brain-gut axis.

Amphiphilic surface chemistry of fullerenols is necessary for inhibiting the amyloid aggregation of alpha-synuclein NACore

Featuring small sizes, caged structures, low cytotoxicity and the capability to cross biological barriers, fullerene hydroxy derivatives named fullerenols have been explored as nanomedicinal candidates for amyloid inhibition. Understanding the surface chemistry effect of hydroxylation extents and the corresponding amyloid inhibition mechanisms is necessary for enabling applications of fullerenols and also future designs of nanomedicines in mitigating amyloid aggregation. Here, we investigated effects of C60(OH)n with n = 0-40 on the aggregation of NACore (the amyloidogenic core region of the non-amyloid-β component in α-synuclein), the amyloidogenic core of α-synuclein, by computational simulations, transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thioflavin-T (ThT) fluorescence kinetics and viability assays. Computationally, NACore assembled into cross-β aggregates via intermediates including β-barrels, which are postulated as toxic oligomers of amyloid aggregation. Hydrophobic C60 preferred to self-assemble, and NACore bound to the surface of C60 nano-clusters formed β-sheet rich aggregates - i.e., having little inhibition effect. Amphiphilic C60(OH)n with n = 4-20 displayed significant inhibition effects on NACore aggregation, where hydrogen bonding between hydroxyls and peptide backbones interrupted the formation of β-sheets between peptides adsorbed onto the surfaces of fullerenols or fullerenol nano-assemblies due to hydrophobic interactions. Thus, both cross-β aggregates and β-barrel intermediates were significantly suppressed. With hydroxyls increased to 40, fullerenols became highly hydrophilic with reduced peptide binding and thus an inhibition effect on amyloid aggregation. ThT, FTIR and TEM characterization of C60(OH)n with n = 0, 24, & 40 confirmed the computational predictions. Our results and others underscore the importance of amphiphilic surface chemistry and the capability of polar groups in forming hydrogen bonds with peptide backbones to render amyloid inhibition, offering a new insight for de-novo design of anti-amyloid inhibitors.

Tryptophan–glucosamine conjugates modulate tau-derived PHF6 aggregation at low concentrations

Tryptophan–glucosamine conjugates efficiently inhibit tau-derived PHF6-peptide fibrillization and disrupt its preformed fibrils at very low concentrations.