Selective inhibition of Alzheimer disease-like tau aggregation by phenothiazines

Hyperphosphorylated tau-based Alzheimer's Disease drug discovery: Identification of inhibitors of tau aggregation and cytotoxicity

Alzheimer's disease (AD) is a neurodegenerative disorder that affects more than 30 million people worldwide. Underlying the progressive decline of cognitive functions are the neurofibrillary tangles (NFTs) in neurons of the brain. The spatiotemporal distribution of NFTs predicts the progression of cognitive symptoms. In contrast, the senile plaques of amyloid-β aggregates, another major biomarker for AD, do not correlate with the clinical symptom development, consistent with the negligible benefits to cognitive functions in patients receiving anti-Aβ immunotherapies. A new drug discovery avenue targeting tau pathologies is therefore urgently needed. Using a recombinant hyperphosphorylated tau (p-tau) that presents characters key to the disease, e.g., formation of neurotoxic aggregates, we conducted a fluorescence p-tau aggregation assay and completed a 100K-compound high-throughput screen (HTS) and identified inhibitors of p-tau aggregation and cytotoxicity. This dual functional screen resulted in several potent compounds that effectively curbed both p-tau aggregation and cytotoxicity. Results presented in this work are the first HTS for small-molecule compounds that target the cellular toxicity of hyperphosphorylated tau. Top hits found in this screen and their analogues to be developed in the near future may lead to breakthroughs in the therapeutic development for Alzheimer's disease and other neurodegenerative tauopathies.

Hydromethylthionine sustains truncated tau-dependent inflammation-lowering effects in mouse brain

Tauopathies are a heterogeneous mixture of neurodegenerative disorders, including Alzheimer's disease and frontotemporal dementia (FTD), characterised by the accumulation of tau filaments in brain tissue. Tau protein aggregation is inhibited by hydromethylthionine (HMT), an effect that appeared to be prevented in clinical trials for subjects already receiving acetylcholinesterase inhibitors or memantine. Since neuroinflammatory responses are associated with tauopathies, we investigated the effect of HMT on the brain immune response and inflammatory status in line 66 (L66) mice, an FTD-like model overexpressing human tau, in the presence of memantine. We determined whether HMT (5 and 15 mg·kg-1), either singly or combined with memantine (20 mg·kg-1), would have a sustained impact on neuroinflammation following the cessation of drug administration. The levels of core tau fragments in L66+/- mice (P301S/G335D-hTau) were decreased in a dose-dependent manner 12 weeks after the last administration of HMT, an effect that was not affected by memantine. HMT lowered the levels of tumour necrosis factor alpha (TNF-α), thus favouring an environment conducive to neuronal protection and repair. HMT sustained increased microglial reactivity after its discontinuation, which may assist in the removal of tau aggregates, but co-administration with memantine prevented the HMT-sustained activation of microglia. These findings indicate that HMT has a beneficial effect in reducing neuroinflammation that accompanies a decrease in the accumulation of truncated tau species and that these benefits are not susceptible to interference by memantine. In turn, the nature of drug interference between HMT and memantine seems to be independent of tau and related to microglia reactivity.

Targeting Tau Protein with Proximity Inducing Modulators: A New Frontier to Combat Tauopathies

Dysregulation of correct protein tau homeostasis represents the seed for the development of several devastating central nervous system disorders, known as tauopathies, that affect millions of people worldwide. Despite massive public and private support to research funding, these diseases still represent unmet medical needs. In fact, the tau-targeting tools developed to date have failed to translate into the clinic. Recently, taking advantage of the modes that nature uses to mediate the flow of information in cells, researchers have developed a new class of molecules, called proximity-inducing modulators, which exploit spatial proximity to modulate protein function(s) and redirect cellular processes. In this perspective, after a brief discussion about tau protein and the classic tau-targeting approaches, we will discuss the different classes of proximity-inducing modulators developed so far and highlight the applications to modulate tau protein's function and tau-induced toxicity.

Targeting tau in Alzheimer's and beyond: Insights into pathology and therapeutic strategies

Tauopathies encompass a group of approximately 20 neurodegenerative diseases characterized by the accumulation of the microtubule-associated protein tau in brain neurons. The pathogenesis of intracellular neurofibrillary tangles, a hallmark of tauopathies, is initiated by hyperphosphorylated tau protein isoforms that cause neuronal death and lead to diseases like Alzheimer's, Parkinson's disease, frontotemporal dementia, and other complex neurodegenerative diseases. Current applications of tau biomarkers, including imaging, cerebrospinal fluid, and blood-based assays, assist in the evaluation and diagnosis of tauopathies. Emerging research is providing various potential strategies to prevent cellular toxicity caused by tau aggregation such as: 1) suppressing toxic tau aggregation, 2) preventing post-translational modifications of tau, 3) stabilizing microtubules and 4) designing tau-directed immunogens. This review aims to discuss the role of tau in tauopathies along with neuropathological features of the different tauopathies and the new developments in treating tau aggregation with the therapeutics for treating and possibly preventing tauopathies.

Natural products against tau hyperphosphorylation-induced aggregates: Potential therapies for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline and memory impairments and is considered the most prevalent form of dementia. Among the contributing factors to AD lies the hyperphosphorylation of the microtubule-associated protein tau. Phosphorylated tau reduces its affinity for microtubules and triggers other posttranslational modifications that result in its aggregation and assembly into filaments. These structures progressively accumulate within neurons leading to neurodegeneration. While current AD medications often involve undesirable side effects, the exploration of natural products as a potential therapeutic alternative has gained considerable attention. Numerous compounds have shown potential capacity for reducing tau pathology through different mechanisms, such as inhibiting kinases to reduce tau hyperphosphorylation, enhancing phosphatase activity, and blocking fibril formation. Since tau hyperphosphorylation-induced aggregation is pivotal in AD onset, this review aims to elucidate the potential of natural products in modulating this crucial molecular mechanism.

Post-Translational Modifications Control Phase Transitions of Tau

The self-assembly of Tau into filaments, which mirror the structures observed in Alzheimer's disease (AD) brains, raises questions about the role of AD-specific post-translational modifications (PTMs) in the formation of paired helical filaments (PHFs). To investigate this, we developed a synthetic approach to produce Tau(291-391) featuring N-acetyllysine, phosphoserine, phosphotyrosine, and N-glycosylation at positions commonly modified in post-mortem AD brains. Using various electron and optical microscopy techniques, we discovered that these modifications generally hinder the in vitro assembly of Tau into PHFs. Interestingly, while acetylation's effect on Tau assembly displayed variability, either promoting or inhibiting phase transitions in cofactor-free aggregation, heparin-induced aggregation, and RNA-mediated liquid-liquid phase separation (LLPS), phosphorylation uniformly mitigated these processes. Our observations suggest that PTMs, particularly those situated outside the rigid core, are pivotal in the nucleation of PHFs. Moreover, with heparin-induced aggregation leading to the formation of heterogeneous aggregates, most AD-specific PTMs appeared to decelerate aggregation. The impact of acetylation on RNA-induced LLPS was notably site-dependent, whereas phosphorylation consistently reduced LLPS across all proteoforms examined. These insights underscore the complex interplay between site-specific PTMs and environmental factors in modulating Tau aggregation kinetics, highlighting the role of PTMs located outside the ordered filament core in driving the self-assembly.

Tau Protein and Tauopathies: Exploring Tau Protein-Protein and Microtubule Interactions, Cross-Interactions and Therapeutic Strategies

Tau, a microtubule-associated protein (MAP), is essential to maintaining neuronal stability and function in the healthy brain. However, aberrant modifications and pathological aggregations of Tau are implicated in various neurodegenerative disorders, collectively known as tauopathies. The most common Tauopathy is Alzheimer's Disease (AD) counting nowadays more than 60 million patients worldwide. This comprehensive review delves into the multifaceted realm of Tau protein, puzzling out its intricate involvement in both physiological and pathological roles. Emphasis is put on Tau Protein-Protein Interactions (PPIs), depicting its interaction with tubulin, microtubules and its cross-interaction with other proteins such as Aβ1-42, α-synuclein, and the chaperone machinery. In the realm of therapeutic strategies, an overview of diverse possibilities is presented with their relative clinical progresses. The focus is mostly addressed to Tau protein aggregation inhibitors including recent small molecules, short peptides and peptidomimetics with specific focus on compounds that showed a double anti aggregative activity on both Tau protein and Aβ amyloid peptide. This review amalgamates current knowledge on Tau protein and evolving therapeutic strategies, providing a comprehensive resource for researchers seeking to deepen their understanding of the Tau protein and for scientists involved in the development of new peptide-based anti-aggregative Tau compounds.

A framework for translating tauopathy therapeutics: Drug discovery to clinical trials

The tauopathies are defined by pathological tau protein aggregates within a spectrum of clinically heterogeneous neurodegenerative diseases. The primary tauopathies meet the definition of rare diseases in the United States. There is no approved treatment for primary tauopathies. In this context, designing the most efficient development programs to translate promising targets and treatments from preclinical studies to early-phase clinical trials is vital. In September 2022, the Rainwater Charitable Foundation convened an international expert workshop focused on the translation of tauopathy therapeutics through early-phase trials. Our report on the workshop recommends a framework for principled drug development and a companion lexicon to facilitate communication focusing on reproducibility and achieving common elements. Topics include the selection of targets, drugs, biomarkers, participants, and study designs. The maturation of pharmacodynamic biomarkers to demonstrate target engagement and surrogate disease biomarkers is a crucial unmet need. HIGHLIGHTS: Experts provided a framework to translate therapeutics (discovery to clinical trials). Experts focused on the "5 Rights" (target, drug, biomarker, participants, trial). Current research on frontotemporal degeneration, progressive supranuclear palsy, and corticobasal syndrome therapeutics includes 32 trials (37% on biologics) Tau therapeutics are being tested in Alzheimer's disease; primary tauopathies have a large unmet need.

A novel peptide-based tau aggregation inhibitor as a potential therapeutic for Alzheimer's disease and other tauopathies

INTRODUCTION

As aggregation underpins Tau toxicity, aggregation inhibitor peptides may have disease-modifying potential. They are therefore currently being designed and target either the 306VQIVYK311 aggregation-promoting hotspot found in all Tau isoforms or the 275VQIINK280 aggregation-promoting hotspot found in 4R isoforms. However, for any Tau aggregation inhibitor to potentially be clinically relevant for other tauopathies, it should target both hotspots to suppress aggregation of Tau isoforms, be stable, cross the blood-brain barrier, and rescue aggregation-dependent Tau phenotypes in vivo.

METHODS

We developed a retro-inverso, stable D-amino peptide, RI-AG03 [Ac-rrrrrrrrGpkyk(ac)iqvGr-NH2], based on the 306VQIVYK311 hotspots which exhibit these disease-relevant attributes.

RESULTS

Unlike other aggregation inhibitors, RI-AG03 effectively suppresses aggregation of multiple Tau species containing both hotspots in vitro and in vivo, is non-toxic, and suppresses aggregation-dependent neurodegenerative and behavioral phenotypes.

DISCUSSION

RI-AG03 therefore meets many clinically relevant requirements for an anti-aggregation Tau therapeutic and should be explored further for its disease-modifying potential for Tauopathies.

HIGHLIGHTS

Our manuscript describes the development of a novel peptide inhibitor of Tau aggregation, a retro-inverso, stable D-amino peptide called RI-AG03 that displays many clinically relevant attributes. We show its efficacy in preventing Tau aggregation in both in vitro and in vivo experimental models while being non-toxic to cells. RI-AG03 also rescues a biosensor cell line that stably expresses Tau repeat domains with the P301S mutation fused to Cer/Clo and rescues aggregation-dependent phenotypes in vivo, suppressing neurodegeneration and extending lifespan. Collectively our data describe several properties and attributes of RI-AG03 that make it a promising disease-modifying candidate to explore for reducing pathogenic Tau aggregation in Tauopathies such as Alzheimer's disease. Given the real interest in reducing Tau aggregation and the potential clinical benefit of using such agents in clinical practice, RI-AG03 should be investigated further for the treatment of Tauopathies after validation in mammalian models. Tau aggregation inhibitors are the obvious first choice as Tau-based therapies as much of Tau-mediated toxicity is aggregation dependent. Indeed, there are many research efforts focusing on this therapeutic strategy with aggregation inhibitors being designed against one of the two aggregation-promoting hotspots of the Tau protein. To our knowledge, RI-AG03 is the only peptide aggregation inhibitor that inhibits aggregation of Tau by targeting both aggregation-promoting hotspot motifs simultaneously. As such, we believe that our study will have a significant impact on drug discovery efforts in this arena.

The Antiproteinopathy, Antioxidant, and Antiapoptotic Effects of Methylene Blue and 4-Phenylbutyric Acid Alone, and in Combination on Familial Alzheimer's Disease PSEN1 I416T Cholinergic-Like Neurons

Familial Alzheimer's disease (FAD) is a chronic neurological condition that progresses over time. Currently, lacking a viable treatment, the use of multitarget medication combinations has generated interest as a potential FAD therapy approach. In this study, we examined the effects of 4-phenylbutyric acid (4-PBA) and methylene blue (MB) either separately or in combination on PSEN1 I416T cholinergic-like neuron cells (ChLNs), which serve as a model for FAD. We found that MB was significantly efficient at reducing the accumulation of intracellular Aβ, phosphorylation of TAU Ser202/Thr205, and increasing Δψm, whereas 4-PBA was significantly efficient at diminishing oxidation of DJ-1Cys106-SH, expression of TP53, and increasing ACh-induced Ca2+ influx. Both agents were equally effective at blunting phosphorylated c-JUN at Ser63/Ser73 and activating caspase 3 (CASP3) into cleaved caspase 3 (CC3) on mutant cells. Combination of MB and 4-PBA at middle (0.1, 1) concentration significantly reduced iAβ, p-TAU, and oxDJ-1 and augmented the ACh-induced Ca2+ influx compared to combined agents at low (0.05, 0.5) or high (0.5, 5) concentration. However, combined MB and 4-PBA were efficient only at dropping DJ-1Cys106-SO3 and increasing ACh-induced Ca2+ inward in mutant ChLNs. Our data show that the reagents MB and 4-PBA alone possess more than one action (e.g., antiamyloid, antioxidant, anti-TAU, antiapoptotic, and ACh-induced Ca2+ influx enhancers), that in combination might cancel or diminish each other. Together, these results strongly argue that MB and 4-PBA might protect PSEN1 I416T ChLNs from Aβ-induced toxicity by working intracellularly as anti-Aβ and anti-Tau agents, improving Δψm and cell survival, and extracellularly, by increasing ACh-induced Ca2+ ion influx. MB and 4-PBA are promising drugs with potential for repurposing in familial AD.

Tau in neurodegenerative diseases: molecular mechanisms, biomarkers, and therapeutic strategies

The deposition of abnormal tau protein is characteristic of Alzheimer's disease (AD) and a class of neurodegenerative diseases called tauopathies. Physiologically, tau maintains an intrinsically disordered structure and plays diverse roles in neurons. Pathologically, tau undergoes abnormal post-translational modifications and forms oligomers or fibrous aggregates in tauopathies. In this review, we briefly introduce several tauopathies and discuss the mechanisms mediating tau aggregation and propagation. We also describe the toxicity of tau pathology. Finally, we explore the early diagnostic biomarkers and treatments targeting tau. Although some encouraging results have been achieved in animal experiments and preclinical studies, there is still no cure for tauopathies. More in-depth basic and clinical research on the pathogenesis of tauopathies is necessary.

Pharmacotherapies for the Treatment of Progressive Supranuclear Palsy: A Narrative Review

Progressive supranuclear palsy (PSP) is a neurodegenerative disorder resulting from the deposition of misfolded and neurotoxic forms of tau protein in specific areas of the midbrain, basal ganglia, and cortex. It is one of the most representative forms of tauopathy. PSP presents in several different phenotypic variations and is often accompanied by the development of concurrent neurodegenerative disorders. PSP is universally fatal, and effective disease-modifying therapies for PSP have not yet been identified. Several tau-targeting treatment modalities, including vaccines, monoclonal antibodies, and microtubule-stabilizing agents, have been investigated and have had no efficacy. The need to treat PSP and other tauopathies is critical, and many clinical trials investigating tau-targeted treatments are underway. In this review, the PubMed database was queried to collect information about preclinical and clinical research on PSP treatment. Additionally, the US National Library of Medicine's ClinicalTrials.gov website was queried to identify past and ongoing clinical trials relevant to PSP treatment. This narrative review summarizes our findings regarding these reports, which include potential disease-modifying drug trials, modifiable risk factor management, and symptom treatments.

Methylene blue and its potential in the treatment of traumatic brain injury, brain ischemia, and Alzheimer's disease

Traumatic brain injury (TBI) and brain ischemia/reperfusion cause neurodegenerative processes that can continue after the acute stage with the development of severe brain atrophy with dementia. In this case, the long-term neurodegeneration of the brain is similar to the neurodegeneration characteristic of Alzheimer's disease (AD) and is associated with the accumulation of beta amyloid and tau protein. In the pathogenesis of AD as well as in the pathogenesis of cerebral ischemia and TBI oxidative stress, progressive inflammation, glial activation, blood-brain barrier dysfunction, and excessive activation of autophagy are involved, which implies the presence of many targets that can be affected by neuroprotectors. That is, multivariate cascades of nerve tissue damage represent many potential targets for therapeutic interventions. One of such substances that can be used in multi-purpose therapeutic strategies is methylene blue (MB). This drug can have an antiapoptotic and anti-inflammatory effect, activate autophagy, inhibit the aggregation of proteins with an irregular shape, inhibit NO synthase, and bypass impaired electron transfer in the respiratory chain of mitochondria. MB is a well-described treatment for methemoglobinemia, malaria, and encephalopathy caused by ifosfamide. In recent years, this drug has attracted great interest as a potential treatment for a number of neurodegenerative disorders, including the effects of TBI, ischemia, and AD.

PKM2 aggregation drives metabolism reprograming during aging process

While protein aggregation's association with aging and age-related diseases is well-established, the specific proteins involved and whether dissolving them could alleviate aging remain unclear. Our research addresses this gap by uncovering the role of PKM2 aggregates in aging. We find that PKM2 forms aggregates in senescent cells and organs from aged mice, impairing its enzymatic activity and glycolytic flux, thereby driving cells into senescence. Through a rigorous two-step small molecule library screening, we identify two compounds, K35 and its analog K27, capable of dissolving PKM2 aggregates and alleviating senescence. Further experiments show that treatment with K35 and K27 not only alleviate aging-associated signatures but also extend the lifespan of naturally and prematurely aged mice. These findings provide compelling evidence for the involvement of PKM2 aggregates in inducing cellular senescence and aging phenotypes, and suggest that targeting these aggregates could be a promising strategy for anti-aging drug discovery.

Molecular Dynamics Simulation Study of the Self-Assembly of Tau-Derived PHF6 and Its Inhibition by Oleuropein Aglycone from Extra Virgin Olive Oil

Alzheimer's disease (AD) and other taupathies are neurodegenerative disorders associated with the amyloid deposition of the Tau protein in the brain. This amyloid formation may be inhibited by small molecules, which is recognized as one of the best therapeutic strategies to stop the progression of the disease. This work focuses on the small nucleating segment, hexapeptide-paired helical filament 6 (PHF6), responsible for Tau aggregation. Using computational modeling and classical molecular dynamics simulations, we show that PHF6 monomers collapse in water to form β-sheet rich structures, and the main olive oil polyphenol oleuropein aglycone (OleA) prevents peptide aggregation significantly. We gradually increase the ratio of the PHF6-OleA from 1:1 to 1:3 and find that for the 1:1 ratio, the peptide monomers are prone to form aggregated structures, while for the 1:2 ratio, the formation of the extended β-sheet structure is significantly less. For a 1:3 ratio of protein/OleA, the peptide residues are sufficiently crowded by OleA molecules through hydrogen bonding, hydrophobic interactions, and π-π stacking; hence, the peptide chains prefer to exist in a monomeric random coil conformation.

Hyperphosphorylated Tau Inflicts Intracellular Stress Responses that Are Mitigated by Apomorphine

Abnormal phosphorylation of the microtubule-binding protein tau in the brain is a key pathological marker for Alzheimer's disease and additional neurodegenerative tauopathies. However, how hyperphosphorylated tau causes cellular dysfunction or death that underlies neurodegeneration remains an unsolved question critical for the understanding of disease mechanism and the design of efficacious drugs. Using a recombinant hyperphosphorylated tau protein (p-tau) synthesized by the PIMAX approach, we examined how cells responded to the cytotoxic tau and explored means to enhance cellular resistance to tau attack. Upon p-tau uptake, the intracellular calcium levels rose promptly. Gene expression analyses revealed that p-tau potently triggered endoplasmic reticulum (ER) stress, unfolded protein response (UPR), ER stress-associated apoptosis, and pro-inflammation in cells. Proteomics studies showed that p-tau diminished heme oxygenase-1 (HO-1), an ER stress-associated anti-inflammation and anti-oxidative stress regulator, while stimulated the accumulation of MIOS and other proteins. p-Tau-induced ER stress-associated apoptosis and pro-inflammation are ameliorated by apomorphine, a brain-permeable prescription drug widely used to treat Parkinson's disease symptoms, and by overexpression of HO-1. Our results reveal probable cellular functions targeted by hyperphosphorylated tau. Some of these dysfunctions and stress responses have been linked to neurodegeneration in Alzheimer's disease. The observations that the ill effects of p-tau can be mitigated by a small compound and by overexpressing HO-1 that is otherwise diminished in the treated cells inform new directions of Alzheimer's disease drug discovery.

Molecular Deformation Is a Key Factor in Screening Aggregation Inhibitor for Intrinsically Disordered Protein Tau

Direct inhibitor of tau aggregation has been extensively studied as potential therapeutic agents for Alzheimer's disease. However, the natively unfolded structure of tau complicates the structure-based ligand design, and the relatively large surface areas that mediate tau-tau interactions in aggregation limit the potential for identifying high-affinity ligand binding sites. Herein, a group of isatin-pyrrolidinylpyridine derivative isomers (IPP1-IPP4) were designed and synthesized. They are like different forms of molecular "transformers". These isatin isomers exhibit different inhibitory effects on tau self-aggregation or even possess a depolymerizing effect. Our results revealed for the first time that the direct inhibitor of tau protein aggregation is not only determined by the previously reported conjugated structure, substituent, hydrogen bond donor, etc. but also depends more importantly on the molecular shape. In combination with molecular docking and molecular dynamics simulations, a new inhibition mechanism was proposed: like a "molecular clip", IPP1 could noncovalently bind and fix a tau polypeptide chain at a multipoint to prevent the transition from the "natively unfolded conformation" to the "aggregation competent conformation" before nucleation. At the cellular and animal levels, the effectiveness of the inhibitor of the IPP1 has been confirmed, providing an innovative design strategy as well as a lead compound for Alzheimer's disease drug development.

Post-Translational Modifications Control Phase Transitions of Tau

The self-assembly of Tau(297-391) into filaments, which mirror the structures observed in Alzheimer's disease (AD) brains, raises questions about the role of AD-specific post-translational modifications (PTMs) in the formation of paired helical filaments (PHFs). To investigate this, we developed a synthetic approach to produce Tau(291-391) featuring N-acetyllysine, phosphoserine, phosphotyrosine, and N-glycosylation at positions commonly modified in post-mortem AD brains, thus facilitating the study of their roles in Tau pathology. Using transmission electron microscopy (TEM), cryo-electron microscopy (cryo-EM), and a range of optical microscopy techniques, we discovered that these modifications generally hinder the in vitro assembly of Tau into PHFs. Interestingly, while acetylation's effect on Tau assembly displayed variability, either promoting or inhibiting phase transitions in the context of cofactor free aggregation, heparin-induced aggregation, and RNA-mediated liquid-liquid phase separation (LLPS), phosphorylation uniformly mitigated these processes. Our observations suggest that PTMs, particularly those situated outside the fibril's rigid core are pivotal in the nucleation of PHFs. Moreover, in scenarios involving heparin-induced aggregation leading to the formation of heterogeneous aggregates, most AD-specific PTMs, except for K311, appeared to decelerate the aggregation process. The impact of acetylation on RNA-induced LLPS was notably site-dependent, exhibiting both facilitative and inhibitory effects, whereas phosphorylation consistently reduced LLPS across all proteoforms examined. These insights underscore the complex interplay between site-specific PTMs and environmental factors in modulating Tau aggregation kinetics, enhancing our understanding of the molecular underpinnings of Tau pathology in AD and highlighting the critical role of PTMs located outside the ordered filament core in driving the self-assembly of Tau into PHF structures.

Phenothiazines: Nrf2 activation and antioxidant effects

Phenothiazines (PTZs) are an emerging group of molecules showing effectiveness toward redox signaling and reduction of oxidative injury to cells, via the activation on Kelch-like ECH-associated protein 1/nuclear factor erythroid 2-related factor 2 (Nrf2). Although several electrophilic and indirect Nrf2 activators have been reported, the risk of "off-target" effect due to the complexity of their molecular mechanisms of action, has aroused research interest toward non-electrophilic and direct modulators of Nrf2 pathway, such as PTZs. This review represents the first overview on the roles of PTZs as non-electrophilic Nrf2 activator and free radical scavengers, as well as on their potential therapeutic effects in oxidative stress-mediated diseases. Here, we provide a collective and comprehensive information on the PTZs ability to scavenge free radicals and activate the Nrf2 signaling pathway, with the aim to broaden the knowledge of their therapeutic potentials and to stimulate innovative research ideas.

Assays for the Screening and Characterization of Tau Aggregation Inhibitors

Aggregation of tau protein is a pathological hallmark of Alzheimer's disease and other neurodegenerative tauopathies. Inhibition of tau aggregation may provide a method for treatment of these disorders. Methods to identify tau aggregation inhibitors (TAIs) in vitro are useful and here we describe assays for TAIs using purified recombinant tau protein fragments in a cell-free immunoassay format and in a stably transfected cell model to create a more physiological environment.

In Silico Prediction of Quercetin Analogs for Targeting Death-Associated Protein Kinase 1 (DAPK1) Against Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder that greatly affects the health and life quality of the elderly population. Existing drugs mainly alleviate symptoms but fail to halt disease progression, underscoring the urgent need for the development of novel drugs. Based on the neuroprotective effects of flavonoid quercetin in AD, this study was designed to identify potential AD-related targets for quercetin and perform in silico prediction of promising analogs for the treatment of AD. Database mining suggested death-associated protein kinase 1 (DAPK1) as the most promising AD-related target for quercetin among seven protein candidates. To achieve better biological effects for the treatment of AD, we devised a series of quercetin analogs as ligands for DAPK1, and molecular docking analyses, absorption, distribution, metabolism, and excretion (ADME) predictions, as well as molecular dynamics (MD) simulations, were performed. The energy for drug-protein interaction was predicted and ranked. As a result, quercetin-A1a and quercetin-A1a1 out of 19 quercetin analogs exhibited the lowest interaction energy for binding to DAPK1 than quercetin, and they had similar dynamics performance with quercetin. In addition, quercetin-A1a and quercetin-A1a1 were predicted to have better water solubility. Thus, quercetin-A1a and quercetin-A1a1 could be promising agents for the treatment of AD. Our findings paved the way for further experimental studies and the development of novel drugs.

Recent advancement in therapeutic strategies for Alzheimer's disease: Insights from clinical trials

Alzheimer's disease (AD) is the most prevalent form of dementia, characterized by the presence of plaques of amyloid beta and Tau proteins. There is currently no permanent cure for AD; the only medications approved by the FDA for mild to moderate AD are cholinesterase inhibitors, NMDA receptor antagonists, and immunotherapies against core pathophysiology, that provide temporary relief only. Researchers worldwide have made significant attempts to find new targets and develop innovative therapeutic molecules to treat AD. The FDA-approved drugs are palliative and couldn't restore the damaged neuron cells of AD. Stem cells have self-differentiation properties, making them prospective therapeutics to treat AD. The promising results in pre-clinical studies of stem cell therapy for AD seek attention worldwide. Various stem cells, mainly mesenchymal stem cells, are currently in different phases of clinical trials and need more advancements to take this therapy to the translational level. Here, we review research from the past decade that has identified several hypotheses related to AD pathology. Moreover, this article also focuses on the recent advancement in therapeutic strategies for AD treatment including immunotherapy and stem cell therapy detailing the clinical trials that are currently undergoing development.

Therapies for Tau-associated neurodegenerative disorders: targeting molecules, synapses, and cells

Advances in experimental and computational technologies continue to grow rapidly to provide novel avenues for the treatment of neurodegenerative disorders. Despite this, there remain only a handful of drugs that have shown success in late-stage clinical trials for Tau-associated neurodegenerative disorders. The most commonly prescribed treatments are symptomatic treatments such as cholinesterase inhibitors and N-methyl-D-aspartate receptor blockers that were approved for use in Alzheimer's disease. As diagnostic screening can detect disorders at earlier time points, the field needs pre-symptomatic treatments that can prevent, or significantly delay the progression of these disorders (Koychev et al., 2019). These approaches may be different from late-stage treatments that may help to ameliorate symptoms and slow progression once symptoms have become more advanced should early diagnostic screening fail. This mini-review will highlight five key avenues of academic and industrial research for identifying therapeutic strategies to treat Tau-associated neurodegenerative disorders. These avenues include investigating (1) the broad class of chemicals termed "small molecules"; (2) adaptive immunity through both passive and active antibody treatments; (3) innate immunity with an emphasis on microglial modulation; (4) synaptic compartments with the view that Tau-associated neurodegenerative disorders are synaptopathies. Although this mini-review will focus on Alzheimer's disease due to its prevalence, it will also argue the need to target other tauopathies, as through understanding Alzheimer's disease as a Tau-associated neurodegenerative disorder, we may be able to generalize treatment options. For this reason, added detail linking back specifically to Tau protein as a direct therapeutic target will be added to each topic.

The Role of Traditional Chinese Medicine Natural Products in β-Amyloid Deposition and Tau Protein Hyperphosphorylation in Alzheimer's Disease

Alzheimer's disease is a prevalent form of dementia among elderly individuals and is characterized by irreversible neurodegeneration. Despite extensive research, the exact causes of this complex disease remain unclear. Currently available drugs for Alzheimer's disease treatment are limited in their effectiveness, often targeting a single aspect of the disease and causing significant adverse effects. Moreover, these medications are expensive, placing a heavy burden on patients' families and society as a whole. Natural compounds and extracts offer several advantages, including the ability to target multiple pathways and exhibit high efficiency with minimal toxicity. These attributes make them promising candidates for the prevention and treatment of Alzheimer's disease. In this paper, we provide a summary of the common natural products used in Chinese medicine for different pathogeneses of AD. Our aim is to offer new insights and ideas for the further development of natural products in Chinese medicine and the treatment of AD.

Wherefore Art Tau? Functional importance of site-specific tau phosphorylation in diverse subcellular domains

Tau has canonically been considered as an axonal protein, but studies have observed tau localization in other subcellular domains of neurons. This relocated tau has been identified in both physiological and pathological conditions, and it is often labeled mislocalized. Furthermore, these forms of tau are referred to as "hyperphosphorylated" without specifying the phosphosites involved. On the contrary, we speculate that tau may have multiple physiological functions in various locations regulated via specific phosphorylation sites, although this picture is obscured by a lack of comprehensive phosphosite analysis. Here, we examine findings in the literature on the subcellular location of tau and potential roles tau has in those regions. We intentionally focus on the site-specific phosphorylated patterns involved in governing these properties, which are not well elucidated. To facilitate understanding of these events, we have begun establishing a comprehensive map of tau phosphorylation signatures. Such efforts may clarify tau's diverse physiological functions beyond the axon as well as promote development of novel therapeutic strategies directed against distinct tau subpopulations.

Hematoxylin modulates tau-RD protein fibrillization and ameliorates Alzheimer's disease-like symptoms in a yeast model

Alzheimer's disease (AD) is one of the most serious neurodegenerative diseases with no effective treatment options available. The formation of insoluble amyloid fibrils of the hyperphosphorylated tau protein is intimately associated with AD, hence the tau protein has been a key target for AD drug development. In this work, hematoxylin was discovered as a dual functional compound, that is, acting in the inhibition of repeat domain of tau (tau-RD) protein fibrillogenesis and remodeling of pre-formed tau-RD fibrils in vitro. Meanwhile, hematoxylin was able to reduce the accumulation of tau-RD aggregates in Saccharomyces cerevisiae. Experimental and computational studies indicated that hematoxylin directly interacts with tau-RD protein through hydrophobic forces, hydrogen bonds, π-cation interactions, and π-π stackings. In addition, cellular viability assays showed that hematoxylin greatly reduced cytotoxicity induced by tau-RD aggregates. In summary, hematoxylin might be a promising candidate for further development as a potential therapeutic drug for AD patients.

Methylene blue accelerates liquid-to-gel transition of tau condensates impacting tau function and pathology

Preventing tau aggregation is a potential therapeutic strategy in Alzheimer's disease and other tauopathies. Recently, liquid-liquid phase separation has been found to facilitate the formation of pathogenic tau conformations and fibrillar aggregates, although many aspects of the conformational transitions of tau during the phase transition process remain unknown. Here, we demonstrate that the tau aggregation inhibitor methylene blue promotes tau liquid-liquid phase separation and accelerates the liquid-to-gel transition of tau droplets independent of the redox activity of methylene blue. We further show that methylene blue inhibits the conversion of tau droplets into fibrils and reduces the cytotoxicity of tau aggregates. Although gelation slows down the mobility of tau and tubulin, it does not impair microtubule assembly within tau droplets. These findings suggest that methylene blue inhibits tau amyloid fibrillization and accelerates tau droplet gelation via distinct mechanisms, thus providing insights into the activity of tau aggregation inhibitors in the context of phase transition.

Fully co-factor-free ClearTau platform produces seeding-competent Tau fibrils for reconstructing pathological Tau aggregates

Tau protein fibrillization is implicated in the pathogenesis of several neurodegenerative diseases collectively known as Tauopathies. For decades, investigating Tau fibrillization in vitro has required the addition of polyanions or other co-factors to induce its misfolding and aggregation, with heparin being the most commonly used. However, heparin-induced Tau fibrils exhibit high morphological heterogeneity and a striking structural divergence from Tau fibrils isolated from Tauopathies patients' brains at ultra- and macro-structural levels. To address these limitations, we developed a quick, cheap, and effective method for producing completely co-factor-free fibrils from all full-length Tau isoforms and mixtures thereof. We show that Tau fibrils generated using this ClearTau method - ClearTau fibrils - exhibit amyloid-like features, possess seeding activity in biosensor cells and hiPSC-derived neurons, retain RNA-binding capacity, and have morphological properties and structures more reminiscent of the properties of the brain-derived Tau fibrils. We present the proof-of-concept implementation of the ClearTau platform for screening Tau aggregation-modifying compounds. We demonstrate that these advances open opportunities to investigate the pathophysiology of disease-relevant Tau aggregates and will facilitate the development of Tau pathology-targeting and modifying therapies and PET tracers that can distinguish between different Tauopathies.

Mitochondrial Effects of Hydromethylthionine, Rivastigmine and Memantine in Tau-Transgenic Mice

Tau protein aggregations are important contributors to the etiology of Alzheimer's disease (AD). Hydromethylthionine (HMT) is a potent inhibitor of tau aggregation in vitro and in vivo and is being developed as a possible anti-dementia medication. HMT was also shown to affect the cholinergic system and to interact with mitochondria. Here, we used tau-transgenic (L1 and L66) and wild-type NMRI mice that were treated with HMT, rivastigmine and memantine and with combinations thereof, for 2-4 weeks. We measured HMT concentrations in both brain homogenates and isolated mitochondria and concentrations of glucose, lactate and pyruvate in brain by microdialysis. In isolated brain mitochondria, we recorded oxygen consumption of mitochondrial complexes by respirometry. While rivastigmine and memantine lowered mitochondrial respiration, HMT did not affect respiration in wild-type animals and increased respiration in tau-transgenic L1 mice. Glucose and lactate levels were not affected by HMT administration. The presence of HMT in isolated mitochondria was established. In summary, traditional anti-dementia drugs impair mitochondrial function while HMT has no adverse effects on mitochondrial respiration in tau-transgenic mice. These results support the further development of HMT as an anti-dementia drug.

Hyperphosphorylated tau Inflicts Intracellular Stress Responses That Are Mitigated by Apomorphine

Background

Abnormal phosphorylation of the microtubule-binding protein tau in the brain is a key pathological marker for Alzheimer's disease and additional neurodegenerative tauopathies. However, how hyperphosphorylated tau causes cellular dysfunction or death that underlie neurodegeneration remains an unsolved question critical for the understanding of disease mechanism and the design of efficacious drugs.

Methods

Using a recombinant hyperphosphorylated tau protein (p-tau) synthesized by the PIMAX approach, we examined how cells responded to the cytotoxic tau and explored means to enhance cellular resistance to tau attack.

Results

Upon p-tau uptake, the intracellular calcium levels rose promptly. Gene expression analyses revealed that p-tau potently triggered endoplasmic reticulum (ER) stress, Unfolded Protein Response (UPR), ER stress-associated apoptosis, and pro-inflammation in cells. Proteomics studies showed that p-tau diminished heme oxygenase-1 (HO-1), an ER stress associated anti-inflammation and anti-oxidative stress regulator, while stimulated the accumulation of MIOS and other proteins. P-tau-induced ER stress-associated apoptosis and pro-inflammation are ameliorated by apomorphine, a brain-permeable prescription drug widely used to treat Parkinson's disease symptoms, and by overexpression of HO-1.

Conclusion

Our results reveal probable cellular functions targeted by hyperphosphorylated tau. Some of these dysfunctions and stress responses have been linked to neurodegeneration in Alzheimer's disease. The observations that the ill effects of p-tau can be mitigated by a small compound and by overexpressing HO-1 that is otherwise diminished in the treated cells inform new directions of Alzheimer's disease drug discovery.

Focusing on oligomeric tau as a therapeutic target in Alzheimer's disease and other tauopathies

INTRODUCTION

Tau has commanded much attention as a potential therapeutic target in neurodegenerative diseases. Tau pathology is a hallmark of primary tauopathies, such as progressive supranuclear palsy (PSP), corticobasal syndrome (CBS), and subtypes of frontotemporal dementia (FTD), as well as secondary tauopathies, such as Alzheimer's disease (AD). The development of tau therapeutics must reconcile with the structural complexity of the tau proteome, as well as an incomplete understanding of the role of tau in both physiology and disease.

AREAS COVERED

This review offers a current perspective on tau biology, discusses key barriers to the development of effective tau-based therapeutics, and promotes the idea that pathogenic (as opposed to merely pathological) tau should be at the center of drug development efforts.

EXPERT OPINION

An efficacious tau therapeutic will exhibit several primary features: 1) selectivity for pathogenic tau versus other tau species; 2) blood-brain barrier and cell membrane permeability, enabling access to intracellular tau in disease-relevant brain regions; and 3) minimal toxicity. Oligomeric tau is proposed as a major pathogenic form of tau and a compelling drug target in tauopathies.

Human Tau Aggregates Are Permissive to Protein Synthesis-Dependent Memory in Drosophila Tauopathy Models

Tauopathies including Alzheimer's disease, are characterized by progressive cognitive decline, neurodegeneration, and intraneuronal aggregates comprised largely of the axonal protein Tau. It has been unclear whether cognitive deficits are a consequence of aggregate accumulation thought to compromise neuronal health and eventually lead to neurodegeneration. We use the Drosophila tauopathy model and mixed-sex populations to reveal an adult onset pan-neuronal Tau accumulation-dependent decline in learning efficacy and a specific defect in protein synthesis-dependent memory (PSD-M), but not in its protein synthesis-independent variant. We demonstrate that these neuroplasticity defects are reversible on suppression of new transgenic human Tau expression and surprisingly correlate with an increase in Tau aggregates. Inhibition of aggregate formation via acute oral administration of methylene blue results in re-emergence of deficient memory in animals with suppressed human Tau (hTau)0N4R expression. Significantly, aggregate inhibition results in PSD-M deficits in hTau0N3R-expressing animals, which present elevated aggregates and normal memory if untreated with methylene blue. Moreover, methylene blue-dependent hTau0N4R aggregate suppression within adult mushroom body neurons also resulted in emergence of memory deficits. Therefore, deficient PSD-M on human Tau expression in the Drosophila CNS is not a consequence of toxicity and neuronal loss because it is reversible. Furthermore, PSD-M deficits do not result from aggregate accumulation, which appears permissive, if not protective of processes underlying this memory variant.SIGNIFICANCE STATEMENT Intraneuronal Tau aggregate accumulation has been proposed to underlie the cognitive decline and eventual neurotoxicity that characterizes the neurodegenerative dementias known as tauopathies. However, we show in three experimental settings that Tau aggregates in the Drosophila CNS do not impair but rather appear to facilitate processes underlying protein synthesis-dependent memory within affected neurons.

Hypochlorous Acid-Activated UCNPs-LMB/VQIVYK Multifunctional Nanosystem for Alzheimer's Disease Treatment

The development of nanosystems, which can photooxygenate amyloid-β (Aβ), detect the Tau protein, and inhibit effectively the Tau aggregation, is increasingly important in the diagnosis and therapy of Alzheimer's disease (AD). Herein, UCNPs-LMB/VQIVYK (UCNPs: upconversion nanoparticles, LMB: Leucomethylene blue, and VQIVYK: Biocompatible peptide) is designed as a HOCl-controlled released nanosystem for AD synergistic treatment. Under exposure to high levels of HOCl, the released MB from UCNPs-LMB/VQIVYK will produce singlet oxygen (¹O₂) under red light to depolymerize Aβ aggregation and reduce cytotoxicity. Meanwhile, UCNPs-LMB/VQIVYK can act as an inhibitor to decrease Tau-induced neurotoxicity. Besides, UCNPs-LMB/VQIVYK can be used for upconversion luminescence (UCL) due to its unexceptionable luminescence properties. This HOCl-responsive nanosystem offers a new therapy for AD treatment.

JNK Activation in Alzheimer's Disease Is Driven by Amyloid β and Is Associated with Tau Pathology

c-Jun N-terminal kinase 3 (JNK3) is suggested to play a key role in neurodegenerative disorders, especially in Alzheimer's disease (AD). However, it remains unclear whether JNK or amyloid β (Aβ) appears first in the disease onset. Postmortem brain tissues from four dementia subtypes of patients (frontotemporal dementia, Lewy body dementia, vascular dementia, and AD) were used to measure activated JNK (pJNK) and Aβ levels. pJNK expression is significantly increased in AD; however, similar pJNK expression was found in other dementias. Furthermore, there was a significant correlation, co-localization, and direct interaction between pJNK expression and Aβ levels in AD. Significant increased levels of pJNK were also found in Tg2576 mice, a model of AD. In this line, Aβ₄₂ intracerebroventricular injection in wild-type mice was able to induce a significant elevation of pJNK levels. JNK3 overexpression, achieved by intrahippocampal injection of an adeno-associated viral vector expressing this protein, was enough to induce cognitive deficiencies and precipitate Tau aberrant misfolding in Tg2576 mice without accelerating amyloid pathology. JNK3 overexpression may therefore be triggered by increased Aβ. The latter, together with subsequent involvement of Tau pathology, may be underlying cognitive alterations in early stages of AD.

Crystal structure of three chloridocuprate(I, II) complexes with methylene blue (MB) counterions

Three chloridocuprate complexes with methylene blue counterions of the chemical compositions [MB]+ 2[CuCl4]2− · H2O (1), [MB]+ 2[CuCl4]2− (2) and [(MB)+(CuCl2)−]3 (3) (where [MB]+ – methylthioninium cation; methylene blue cation) have been prepared by solvent-assisted mechanochemical synthesis. The reactions were carried out by mixing the copper(II) chloride dihydrate, CuCl2⋅2H2O, and methylene blue pentahydrate, [MB]+Cl− · 5H2O by grinding in an agate mortar with the addition of DMF as a solvent. The crystal structures of the compounds have been determined by single-crystal X-ray diffraction. The content of an asymmetric unit of the crystals consists of: (1) a tetrahedral [CuCl4]2− anion, two [MB]+ cations and one water molecule of crystallization; (2) a tetrahedral [CuCl4]2− anion and two [MB]+ cations; (3) trimeric [(MB)+(CuCl2)−]3 molecules with the Cu atoms coordinated by a nitrogen atom of the phenothiazine ring and two chlorine ions in a trigonal planar geometry with the copper atom in the oxidation state of +1.

Development of Small Molecules Targeting α-Synuclein Aggregation: A Promising Strategy to Treat Parkinson's Disease

Parkinson's disease, the second most common neurodegenerative disorder worldwide, is characterized by the accumulation of protein deposits in the dopaminergic neurons. These deposits are primarily composed of aggregated forms of α-Synuclein (α-Syn). Despite the extensive research on this disease, only symptomatic treatments are currently available. However, in recent years, several compounds, mainly of an aromatic character, targeting α-Syn self-assembly and amyloid formation have been identified. These compounds, discovered by different approaches, are chemically diverse and exhibit a plethora of mechanisms of action. This work aims to provide a historical overview of the physiopathology and molecular aspects associated with Parkinson's disease and the current trends in small compound development to target α-Syn aggregation. Although these molecules are still under development, they constitute an important step toward discovering effective anti-aggregational therapies for Parkinson's disease.

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.

Solid-state NMR of paired helical filaments formed by the core tau fragment tau(297-391)

Aggregation of the tau protein into fibrillar cross-β aggregates is a hallmark of Alzheimer's diseases (AD) and many other neurodegenerative tauopathies. Recently, several core structures of patient-derived tau paired helical filaments (PHFs) have been solved revealing a structural variability that often correlates with a specific tauopathy. To further characterize the dynamics of these fibril cores, to screen for strain-specific small molecules as potential biomarkers and therapeutics, and to develop strain-specific antibodies, recombinant in-vitro models of tau filaments are needed. We recently showed that a 95-residue fragment of tau (from residue 297 to 391), termed dGAE, forms filaments in vitro in the absence of polyanionic co-factors often used for in vitro aggregation of full-length tau. Tau(297-391) was identified as the proteolytic resistant core of tau PHFs and overlaps with the structures characterized by cryo-electron microscopy in ex vivo PHFs, making it a promising model for the study of AD tau filaments in vitro. In the present study, we used solid-state NMR to characterize tau(297-391) filaments and show that such filaments assembled under non-reducing conditions are more dynamic and less ordered than those made in the presence of the reducing agent DTT. We further report the resonance assignment of tau(297-391)+DTT filaments and compare it to existing core structures of tau.

Therapeutics of Alzheimer's Disease: Recent Developments

With increasing aging, dementia is a growing public health concern globally. Patients with dementia have multiple psychological and behavioral changes, including depression, anxiety, inappropriate behavior, paranoia, agitation, and hallucinations. The major types of dementia are Alzheimer's disease (AD), vascular dementia (VCID), Lewy body dementia (LBD), frontotemporal dementia (FTD), and mixed dementia (MiAD). Among these, AD is the most common form of dementia in the elderly population. In the last three decades, tremendous progress has been made in understanding AD's biology and disease progression, particularly its molecular basis, biomarker development, and drug discovery. Multiple cellular changes have been implicated in the progression of AD, including amyloid beta, phosphorylated tau, synaptic damage, mitochondrial dysfunction, deregulated microRNAs, inflammatory changes, hormonal deregulation, and others; based on these changes, therapeutic strategies have been developed, which are currently being tested in animal models and human clinical trials. The purpose of our article is to highlight recent therapeutic strategies' developments, critically discuss current strategies' failures, and propose new strategies to combat this devasting mental illness.

Targeting Microtubule-Associated Protein Tau in Chemotherapy-Resistant Models of High-Grade Serous Ovarian Carcinoma

Relapsed, recurrent, chemotherapy-resistant high-grade serous ovarian carcinoma is the deadliest stage of this disease. Expression of microtubule-associated protein tau (tau) has been linked to resistance to paclitaxel treatment. Here, I used models of platinum-resistant and created models of platinum/paclitaxel-resistant high-grade serous ovarian carcinoma to examine the impact of reducing tau expression on cell survival and tumor burden in cell culture and xenograft and syngeneic models of the disease. Tau was overexpressed in platinum/paclitaxel-resistant models; expression of phosphoSer396 and phosphoThr181 species was also found. A treatment with leucomethylene blue reduced the levels of tau in treated cells, was cytotoxic in cell cultures, and efficiently reduced the tumor burden in xenograft models. Furthermore, a combination of leucomethylene blue and paclitaxel synergized in eliminating cancer cells in cell culture and xenograft models. These findings underscore the feasibility of targeting tau as a treatment option in terminal-stage high-grade serous ovarian cancer.

Molecular Mechanisms of the Neuroprotective Effect of Methylene Blue

Methylene blue (MB) is the first fully synthetic compound that had found its way into medicine over 120 years ago as a treatment against malaria. MB has been approved for the treatment of methemoglobinemia, but there are premises for its repurposing as a neuroprotective agent based on the efficacy of this compound demonstrated in the models of Alzheimer's, Parkinson's, and Huntington's diseases, traumatic brain injury, amyotrophic lateral sclerosis, depressive disorders, etc. However, the goal of this review was not so much to focus on the therapeutic effects of MB in the treatment of various neurodegeneration diseases, but to delve into the mechanisms of direct or indirect effect of this drug on the signaling pathways. MB can act as an alternative electron carrier in the mitochondrial respiratory chain in the case of dysfunctional electron transport chain. It also displays the anti-inflammatory and anti-apoptotic effects, inhibits monoamine oxidase (MAO) and nitric oxide synthase (NOS), activates signaling pathways involved in the mitochondrial pool renewal (mitochondrial biogenesis and autophagy), and prevents aggregation of misfolded proteins. Comprehensive understanding of all aspects of direct and indirect influence of MB, and not just some of its effects, can help in further research of this compound, including its clinical applications.

Toluidine blue O attenuates tau phosphorylation in N2a-APPSwe cells

Alzheimer's disease (AD) is characterized by extracellular amyloid plaques composed of amyloid-β peptide (Aβ), intracellular neurofibrillary tangles containing hyperphosphorylated tau protein and neuronal loss. Most of the FDA-approved AD drugs currently on the market are cholinesterase inhibitors, which are only effective in relieving the symptoms of AD. However, recent studies in AD drug discovery focus on multi-targeted strategies, including anti-amyloid and anti-tau therapy. In the current study, we have investigated the effects of toluidine blue O (TBO), a cholinesterase inhibitor, on amyloid precursor protein (APP) processing, tau phosphorylation, and tau kinases/phosphatase in N2a mouse neuroblastoma cells stably expressing the Swedish mutation of human APP695 (N2a-APPSwe). The results demonstrated that TBO reduces Aβ40/42 levels by decreasing expression levels of β-secretase 1 (BACE1), presenilin 1 (PS1) and total APP without causing cytotoxic effects in N2a-APPSwe cells. TBO also decreased the levels of both total tau and phosphorylated tau at residues Ser202/Thr205, Thr181, Ser396 and Ser 396/Ser404. Moreover, when the possible mechanisms underlying its effects on tau pathology were explored, TBO was found to decrease tau phosphorylation at those sites by reducing the expression levels of Akt, GSK-3β, Cdk5, inactive p-PP2A and increasing the expression levels of p-Akt Ser473 and inactive p-GSK-3β Ser9. Our new data support the idea that TBO may be a promising multi-target drug candidate for the treatment of AD.

Deciphering the Role of ATP on PHF6 Aggregation

The aggregation of Tau protein, which are involved in Alzheimer's disease, are associated with the self-assembly of the hexapeptide sequence, paired helical filament 6 (PHF6) from repeat 3 of Tau. In order to treat Alzheimer's disease and other such tauopathies, one of the therapeutic strategies is to inhibit aggregation of Tau and its nucleating segments. Therefore, we have studied the effect of adenosine triphosphate (ATP) on the aggregation of PHF6. ATP has, interestingly, demonstrated its ability to inhibit and dissolve protein aggregates. Using classical molecular dynamics simulations, we observed that the hydrophobic core of PHF6 segment displays extended β-sheet conformation, which stabilizes PHF6 aggregates. However, the distribution of ATP around the vicinity of the peptides enables PHF6 to remain discrete and attain random coil conformers. The interpeptide interactions are substituted by PHF6-ATP interactions through hydrogen bonding and hydrophobic interactions (including π-π stacking). Furthermore, the adenosine moiety of ATP contributes more than the triphosphate chain toward PHF6-ATP interaction. Ultimately, this work establishes the inhibitory activity of ATP against Tau aggregation; hence, the therapeutic effect of ATP should be explored further in regard to the effective treatment of Alzheimer's disease.

Curcumin as a Holistic Treatment for Tau Pathology

Global forecasts for prevalence of Alzheimer’s Disease (AD) estimate that 152.8 million people will have dementia in 2050, a sharp rise from 57.4 million in 2019 (GBD 2019). This rise can be attributable to increases in population growth and aging, but in the absence of disease-modifying therapies it poses a huge societal challenge that must be addressed urgently. One way to combat this challenge is to explore the utility of holistic treatments that may protect against AD, including traditional herbs, spices and other nutraceuticals that are pharmacologically safe, inexpensive and readily available. In this light, the spice turmeric, and its active ingredient curcumin, has been investigated as a potential holistic treatment for AD over the past 2 decades; however, promising results with animal studies have not translated to success in clinical trials. One issue is that most animal models examining the effects of curcumin and curcumin derivatives in AD have been done with a focus at ameliorating amyloid pathology. Due to the limited success of Amyloid-β-based drugs in recent clinical trials, tau-focused therapeutics provide a promising alternative. In this article, we aim to provide a clearer picture of what is currently known about the effectiveness of curcumin and curcumin derivatives to ameliorate tau pathology. Tau focused studies may help inform more successful clinical studies by placing greater emphasis on the development and optimised delivery of curcumin derivatives that more effectively target tau pathology.

Tauopathies: new perspectives and challenges

BACKGROUND

Tauopathies are a class of neurodegenerative disorders characterized by neuronal and/or glial tau-positive inclusions.

MAIN BODY

Clinically, tauopathies can present with a range of phenotypes that include cognitive/behavioral-disorders, movement disorders, language disorders and non-specific amnestic symptoms in advanced age. Pathologically, tauopathies can be classified based on the predominant tau isoforms that are present in the inclusion bodies (i.e., 3R, 4R or equal 3R:4R ratio). Imaging, cerebrospinal fluid (CSF) and blood-based tau biomarkers have the potential to be used as a routine diagnostic strategy and in the evaluation of patients with tauopathies. As tauopathies are strongly linked neuropathologically and genetically to tau protein abnormalities, there is a growing interest in pursuing of tau-directed therapeutics for the disorders. Here we synthesize emerging lessons on tauopathies from clinical, pathological, genetic, and experimental studies toward a unified concept of these disorders that may accelerate the therapeutics.

CONCLUSIONS

Since tauopathies are still untreatable diseases, efforts have been made to depict clinical and pathological characteristics, identify biomarkers, elucidate underlying pathogenesis to achieve early diagnosis and develop disease-modifying therapies.

HMTM-Mediated Enhancement of Brain Bioenergetics in a Mouse Tauopathy Model Is Blocked by Chronic Administration of Rivastigmine

The tau protein aggregation inhibitor hydromethylthionine mesylate (HMTM) was shown recently to have concentration-dependent pharmacological activity in delaying cognitive decline and brain atrophy in phase 3 Alzheimer’s disease (AD) clinical trials; the activity was reduced in patients receiving symptomatic therapies. The methylthionine (MT) moiety has been reported to increase the clearance of pathological tau and to enhance mitochondrial activity, which is impaired in AD patients. In line 1 (L1) mice (a model of AD), HMTM (5/15 mg/kg) was administered either as a monotherapy or as an add-on to a chronic administration with the cholinesterase inhibitor rivastigmine (0.1/0.5 mg/kg) to explore mitochondrial function and energy substrate utilization as potential targets of drug interference. Compared with wild-type NMRI mice, the L1 mice accumulated greater levels of l-lactate and of the LDH-A subunit responsible for the conversion of pyruvate into l-lactate. In contrast, the levels of LDH-B and mitochondrial ETC subunits and the activity of complexes I and IV was not altered in the L1 mice. The activity of complex I and complex IV tended to increase with the HMTM dosing, in turn decreasing l-lactate accumulation in the brains of the L1 mice, despite increasing the levels of LDH-A. The chronic pre-dosing of the L1 mice with rivastigmine partially prevented the enhancement of the activity of complexes I and IV by HMTM and the increase in the levels of LDH-A while further reducing the levels of l-lactate. Thus, HMTM in combination with rivastigmine leads to a depletion in the energy substrate l-lactate, despite bioenergetic production not being favoured. In this study, the changes in l-lactate appear to be regulated by LDH-A, since neither of the experimental conditions affected the levels of LDH-B. The data show that HMTM monotherapy facilitates the use of substrates for energy production, particularly l-lactate, which is provided by astrocytes, additionally demonstrating that a chronic pre-treatment with rivastigmine prevented most of the HMTM-associated effects.

Therapeutic strategies for tauopathies and drug repurposing as a potential approach

Tauopathies are neurodegenerative diseases characterized by the deposition of abnormal tau in the brain. To date, there are no disease-modifying therapies approved by the U.S. Food and Drug Administration (US FDA) for the treatment of tauopathies. In the past decades, extensive efforts have been provided to develop disease-modifying therapies to treat tauopathies. Specifically, exploring existing drugs with the intent of repurposing for the treatment of tauopathies affords a reasonable alternative to discover potent drugs for treating these formidable diseases. Drug repurposing will not only reduce formulation and development stage effort and cost but will also take a key advantage of the established toxicological studies, which is one of the main causes of clinical trial failure of new molecules. In this review, we provide an overview of the current treatment strategies for tauopathies and the recent progress in drug repurposing as an alternative approach to treat tauopathies.

Microtubule-modulating Agents in the Fight Against Neurodegeneration: Will it ever Work?

The microtubule skeleton plays an essential role in nerve cells as the most important structural determinant of morphology and as a highway for axonal transport processes. Many neurodegenerative diseases are characterized by changes in the structure and organization of microtubules and microtubule-regulating proteins such as the microtubule-associated protein tau, which exhibits characteristic changes in a whole class of diseases collectively referred to as tauopathies. Changes in the dynamics of microtubules appear to occur early under neurodegenerative conditions and are also likely to contribute to age-related dysfunction of neurons. Thus, modulating microtubule dynamics and correcting impaired microtubule stability can be a useful neuroprotective strategy to counteract the disruption of the microtubule system in disease and aging. In this article, we review current microtubule- directed approaches for the treatment of neurodegenerative diseases with microtubules as a drug target, tau as a drug target, and post-translational modifications as potential modifiers of the microtubule system. We discuss limitations of the approaches that can be traced back to the rather unspecific mechanism of action, which causes undesirable side effects in non-neuronal cell types or which are due to the disruption of non-microtubule-related interactions. We also develop some thoughts on how the specificity of the approaches can be improved and what further targets could be used for modulating substances.

Pleiotropic actions of phenothiazine drugs are detrimental to Gram-negative bacterial persister cells

Bacterial persister cells are temporarily tolerant to bactericidal antibiotics but are not necessarily dormant and may exhibit physiological activities leading to cell damage. Based on the link between fluoroquinolone-mediated SOS responses and persister cell recovery, we screened chemicals that target fluoroquinolone persisters. Metabolic inhibitors (e.g., phenothiazines) combined with ofloxacin (OFX) perturbed persister levels in metabolically active cell populations. When metabolically stimulated, intrinsically tolerant stationary phase cells also became OFX-sensitive in the presence of phenothiazines. The effects of phenothiazines on cell metabolism and physiology are highly pleiotropic: at sublethal concentrations, phenothiazines reduce cellular metabolic, transcriptional, and translational activities; impair cell repair and recovery mechanisms; transiently perturb membrane integrity; and disrupt proton motive force by dissipating the proton concentration gradient across the cell membrane. Screening a subset of mutant strains lacking membrane-bound proteins revealed the pleiotropic effects of phenothiazines potentially rely on their ability to inhibit a wide range of critical metabolic proteins. Altogether, our study further highlights the complex roles of metabolism in persister cell formation, survival and recovery, and suggests metabolic inhibitors such as phenothiazines can be selectively detrimental to persister cells.