Amyloid-β and tau aggregation dual-inhibitors: A synthetic and structure-activity relationship focused review

Biomarkers and Target-Specific Small-Molecule Drugs in Alzheimer's Diagnostic and Therapeutic Research: From Amyloidosis to Tauopathy

Alzheimer's disease (AD) is the most common type of human dementia and is responsible for over 60% of diagnosed dementia cases worldwide. Abnormal deposition of β-amyloid and the accumulation of neurofibrillary tangles have been recognised as the two pathological hallmarks targeted by AD diagnostic imaging as well as therapeutics. With the progression of pathological studies, the two hallmarks and their related pathways have remained the focus of researchers who seek for AD diagnostic and therapeutic strategies in the past decades. In this work, we reviewed the development of the AD biomarkers and their corresponding target-specific small molecule drugs for both diagnostic and therapeutic applications, underlining their success, failure, and future possibilities.

An NMR Toolkit to Probe Amyloid Oligomer Inhibition in Neurodegenerative Diseases: From Ligand Screening to Dissecting Binding Topology and Mechanisms of Action

The aggregation of amyloid peptides and proteins into toxic oligomers is a hallmark of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Machado-Joseph's disease, and transmissible spongiform encephalopathies. Inhibition of amyloid oligomers formation and interactions with biological counterparts, as well as the triggering of non-toxic amorphous aggregates, are strategies towards preventive interventions against these pathologies. NMR spectroscopy addresses the need for structural characterization of amyloid proteins and their aggregates, their binding to inhibitors, and rapid screening of compound libraries for ligand identification. Here we briefly discuss the solution experiments constituting the NMR spectroscopist's toolkit and provide examples of their application.

Evaluation of binding mechanism of dietary phytochemical, capsaicin, with human transferrin: targeting neurodegenerative diseases therapeutics

Human transferrin (htf) plays a crucial role in regulating the balance of iron within brain cells; any disruption directly contributes to the development of Neurodegenerative Diseases (NDs) and other related pathologies, especially Alzheimer's Disease (AD). In recent times, a transition towards natural compounds is evident to treat diseases and this shift is mainly attributed to their broad therapeutic potential along with minimal side effects. Capsaicin, a natural compound abundantly found in red and chili peppers, possess neuroprotective potential. The current work targets to decipher the interaction mechanism of capsaicin with htf using experimental and computational approaches. Molecular docking analysis revealed that capsaicin occupies the iron binding pocket of htf, with good binding affinity. Further, the binding mechanism was investigated atomistically using Molecular dynamic (MD) simulation approach. The results revealed no significant alterations in the structure of htf implying the stability of the complex. In silico observations were validated by fluorescence binding assay. Capsaicin binds to htf with a binding constant (K) of 3.99 × 106 M-1, implying the stability of the htf-capsaicin complex. This study lays a platform for potential applications of capsaicin in treatment of NDs in terms of iron homeostasis.

Carbamate as a potential anti-Alzheimer's pharmacophore: A review

Alzheimer's disease (AD) is a progressive age-related neurodegenerative brain disorder, which leads to loss of memory and other cognitive dysfunction. The underlying mechanisms of AD pathogenesis are very complex and still not fully explored. Cholinergic neuronal loss, accumulation of amyloid plaque, metal ions dyshomeostasis, tau hyperphosphorylation, oxidative stress, neuroinflammation, and mitochondrial dysfunction are major hallmarks of AD. The current treatment options for AD are acetylcholinesterase inhibitors (donepezil, rivastigmine, and galantamine) and NMDA receptor antagonists (memantine). These FDA-approved drugs mainly provide symptomatic relief without addressing the pathological aspects of disease progression. So, there is an urgent need for novel drug development that not only addresses the basic mechanisms of the disease but also shows the neuroprotective property. Various research groups across the globe are working on the development of multifunctional agents for AD amelioration using different core scaffolds for their design, and carbamate is among them. Rivastigmine was the first carbamate drug investigated for AD management. The carbamate fragment, a core scaffold of rivastigmine, act as a potential inhibitor of acetylcholinesterase. In this review, we summarize the last 10 years of research conducted on the modification of carbamate with different substituents which primarily target ChE inhibition, reduce oxidative stress, and modulate Aβ aggregation.

Genipin and pyrogallol: Two natural small molecules targeting the modulation of disordered proteins in Alzheimer's disease

Alzheimer's disease (AD) is characterized by the aggregation of disordered proteins, such as amyloid beta (Aβ) and tau, leading to neurotoxicity and disease progression. Despite numerous efforts, effective inhibitors of Aβ and tau aggregates have not been developed. Thus, we aimed to screen natural small molecules from crude extracts that target various pathologies and are prescribed for patients with neurological diseases. In this study, we screened 162 natural small molecules prescribed for neurological diseases and identified genipin and pyrogallol as hit compounds capable of simultaneously regulating the aggregation of Aβ and tau K18. Moreover, we confirmed the dual modulatory effects of these compounds on the reduction of amyloid-mediated neurotoxicity in vitro and the disassembly of preformed Aβ42 and tau K18 fibrils. Furthermore, we observed the alleviatory effects of genipin and pyrogallol against AD-related pathologies in triple transgenic AD mice. Molecular dynamics and docking simulations revealed the molecular interaction dynamics of genipin and pyrogallol with Aβ42 and tau K18, providing insights into their suppression of aggregation. Our findings suggest the therapeutic potential of genipin and pyrogallol as dual modulators for the treatment of AD by inhibiting aggregation or promoting dissociation of Aβ and tau.

Drug Discovery Based on Oxygen and Nitrogen (Non-)Heterocyclic Compounds Developed @LAQV-REQUIMTE/Aveiro

Artur Silva's research group has a long history in the field of medicinal chemistry. The development of new synthetic methods for oxygen (mostly polyphenols, e.g., 2- and 3-styrylchromones, xanthones, flavones) and nitrogen (e.g., pyrazoles, triazoles, acridones, 4-quinolones) heterocyclic compounds in order to be assessed as antioxidant, anti-inflammatory, antidiabetic, and anticancer agents has been the main core work of our research interests. Additionally, the synthesis of steroid-type compounds as anti-Alzheimer drugs as well as of several chromophores as important dyes for cellular imaging broadened our research scope. In this review article, we intend to provide an enlightened appraisal of all the bioactive compounds and their biological properties that were synthesized and studied by our research group in the last two decades.

Design, Synthesis, and Proof of Concept of Balanced Dual Inhibitors of Butyrylcholinesterase (BChE) and Histone Deacetylase 6 (HDAC6) for the Treatment of Alzheimer's Disease

Concomitant inhibition of butyrylcholinesterase (BChE) and histone deacetylase 6 (HDAC6) is supposed to be effective in the treatment of Alzheimer's disease (AD). Inspired by our previous efforts in designing BChE inhibitors, herein, selective BChE and HDAC6 dual inhibitors were successfully identified through the fusion of the core pharmacophoric moiety of BChE and HDAC6 inhibitors. After the structure-activity relationship (SAR) studies, two compounds (24g and 29a) were confirmed to have superior inhibitory activity against BChE (the IC50 against hBChE are 4.0 and 1.8 nM, respectively) and HDAC6 (the IC50 against HDAC6 are 8.9 and 71.0 nM, respectively). These two compounds showed prominently neuroprotective effects in vitro, potent reactive oxygen species (ROS) scavenging effects, and effective metal ion (Fe2+ and Cu2+) chelation. In addition, they exhibited pronounced inhibition of phosphorylated tau and a moderate immunomodulatory effect, with a lack of neurotoxicity at the cellular level. In vivo studies showed that both 24g and 29a ameliorated the cognitive impairment in an Aβ1-42-induced mouse model at a low dosage (2.5 mg/kg). Our data demonstrated that BChE/HDAC6 dual inhibitors could establish the basis for a potential new symptomatic and disease-modifying strategy to treat AD.

Mechanisms of action of coffee bioactive compounds - a key to unveil the coffee paradox

The knowledge of the relationship between the chemical structure of food components with their mechanisms of action is crucial for the understanding of diet health benefits. This review relates the chemical variability present in coffee beverages with the mechanisms involved in key physiological events, supporting coffee as a polyvalent functional food. Coffee intake has been related with several health-promoting properties such as neuroprotective (caffeine, chlorogenic acids and melanoidins), anti-inflammatory (caffeine, chlorogenic acids, melanoidins, diterpenes), microbiota modulation (polysaccharides, melanoidins, chlorogenic acids), immunostimulatory (polysaccharides), antidiabetic (trigonelline, chlorogenic acids), antihypertensive (chlorogenic acids) and hypocholesterolemic (polysaccharides, chlorogenic acids, lipids). Nevertheless, caffeine and diterpenes are coffee components with ambivalent effects on health. Additionally, a large range of potentially harmful compounds, including acrylamide, hydroxymethylfurfural, furan, and advanced glycation end products, are formed during the roasting of coffee and are present in the beverages. However, coffee beverages are part of the daily human dietary healthy habits, configuring a coffee paradox.

Thioxanthenone-based derivatives as multitarget therapeutic leads for Alzheimer's disease

A set of twenty-five thioxanthene-9-one and xanthene-9-one derivatives, that were previously shown to inhibit cholinesterases (ChEs) and amyloid β (Aβ₄₀) aggregation, were evaluated for the inhibition of tau protein aggregation. All compounds exhibited a good activity, and eight of them (5-8, 10, 14, 15 and 20) shared comparable low micromolar inhibitory potency versus Aβ₄₀ aggregation and human acetylcholinesterase (AChE), while inhibiting human butyrylcholinesterase (BChE) even at submicromolar concentration. Compound 20 showed outstanding biological data, inhibiting tau protein and Aβ₄₀ aggregation with IC₅₀ = 1.8 and 1.3 μM, respectively. Moreover, at 0.1-10 μM it also exhibited neuroprotective activity against tau toxicity induced by okadoic acid in human neuroblastoma SH-SY5Y cells, that was comparable to that of estradiol and PD38. In preliminary toxicity studies, these interesting results for compound 20 are somewhat conflicting with a narrow safety window. However, compound 10, although endowed with a little lower potency for tau and Aβ aggregation inhibition additionally demonstrated good inhibition of ChEs and rather low cytotoxicity. Compound 4 is also worth of note for its high potency as hBChE inhibitor (IC₅₀ = 7 nM) and for the three order of magnitude selectivity versus hAChE. Molecular modelling studies were performed to explain the different behavior of compounds 4 and 20 towards hBChE. The observed balance of the inhibitory potencies versus the relevant targets indicates the thioxanthene-9-one derivatives as potential MTDLs for AD therapy, provided that the safety window will be improved by further structural variations, currently under investigation.

Synthesis and properties of the kojic acid dimer and its potential for the treatment of Alzheimer's disease

The kojic acid dimer (KAD) is a metabolite derived from developing cottonseed when contaminated with aflatoxin. The KAD has been shown to exhibit bright greenish-yellow fluorescence, but little else is known about its biological activity. In this study, using kojic acid as a raw material, we developed a four-step synthetic route that achieved the gram-scale preparation of the KAD in approximately 25% total yield. The structure of the KAD was verified by single-crystal X-ray diffraction. The KAD showed good safety in a variety of cells and had a good protective effect in SH-SY5Y cells. At concentrations lower than 50 μM, the KAD was superior to vitamin C in ABTS⁺ free radical scavenging assay; the KAD resisted the production of reactive oxygen species induced by H₂O₂ as confirmed by fluorescence microscopy observation and flow cytometry analysis. Notably, the KAD could enhance the superoxide dismutase activity, which might be the mechanism of its antioxidant activity. The KAD also moderately inhibited the deposition of amyloid-β (Aβ) and selectively chelated Cu²⁺, Zn²⁺, Fe²⁺, Fe³⁺, and Al³⁺, which are related to the progress of Alzheimer's disease. Based on its good effects in terms of oxidative stress, neuroprotection, inhibition of Aβ deposition, and metal accumulation, the KAD shows potential for the multi-target treatment of Alzheimer's disease.

Ameliorative effects of bromelain on aluminum-induced Alzheimer's disease in rats through modulation of TXNIP pathway

Alzheimer's disease (AD) is known as "type 3 diabetes". As thioredoxin binding protein (TXNIP) has been shown to be involved in brain insulin resistance, the present study evaluated the roles of TXNIP, phospho-insulin receptor substrate 1 (P-IRS-1), and phosphatidyl inositol-3 kinase (PI3K) in the pathogenesis of AD. The potential ameliorative effect of bromelain compared to donepezil was evaluated in an aluminum chloride (AlCl3)-induced AD in rats. Behavioral tests demonstrated similar improvements in exploratory activity, cognitive and spatial memory functions, anxiety, and depression levels between rats treated with bromelain and donepezil. Donepezil was superior to bromelain in improving locomotor activity. Histopathological examinations demonstrated neuronal degeneration in the AlCl3 group that was almost normalized by bromelain and donepezil. Moreover, there was deposition of amyloid plaques in the AlCl3 group that was improved by bromelain and donepezil. Acetylcholine esterase levels were significantly increased in rats treated with AlCl3 group and significantly decreased in rats treated with bromelain and donepezil. Furthermore, AlCl3 group showed a significantly increased TXNIP and P-IRS1 and a significantly reduced PI3K levels. These effects were ameliorated by bromelain and donepezil treatment. The present study demonstrates a previously unreported modulatory effect of bromelain on the TXNIP/P-IRS-1/PI3K axis in AD model.

In Silico Drug Design and Analysis of Dual Amyloid-Beta and Tau Protein-Aggregation Inhibitors for Alzheimer's Disease Treatment

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder that gradually leads to the state of dementia. The main features of AD include the deposition of amyloid-beta peptides (Aβ), forming senile plaques, and the development of neurofibrillary tangles due to the accumulation of hyperphosphorylated Tau protein (p-tau) within the brain cells. In this report, seven dual-inhibitor molecules (L_1-7) that can prevent the aggregation of both Aβ and p-tau are suggested. The drug-like features and identification of the target proteins are analyzed by the in silico method. L_1-7 show positive results in both Blood-Brain Barrier (BBB) crossing and gastrointestinal absorption, rendering to the results of the permeation method. The molecular docking test performed for L_1-7 shows binding energies in the range of -4.9 to -6.0 kcal/mol towards Aβ, and -4.6 to -5.6 kcal/mol for p-tau. The drug's effectiveness under physiological conditions is assessed by the use of solvation models on the investigated systems. Further, the photophysical properties of L_1-3 are predicted using TD-DFT studies.

Discovery of Dual Aβ/Tau Inhibitors and Evaluation of Their Therapeutic Effect on a Drosophila Model of Alzheimer's Disease

Alzheimer's disease (AD), the most common type of dementia, currently represents an extremely challenging and unmet medical need worldwide. Amyloid-β (Aβ) and Tau proteins are prototypical AD hallmarks, as well as validated drug targets. Accumulating evidence now suggests that they synergistically contribute to disease pathogenesis. This could not only help explain negative results from anti-Aβ clinical trials but also indicate that therapies solely directed at one of them may have to be reconsidered. Based on this, herein, we describe the development of a focused library of 2,4-thiazolidinedione (TZD)-based bivalent derivatives as dual Aβ and Tau aggregation inhibitors. The aggregating activity of the 24 synthesized derivatives was tested in intact Escherichia coli cells overexpressing Aβ₄₂ and Tau proteins. We then evaluated their neuronal toxicity and ability to cross the blood-brain barrier (BBB), together with the in vitro interaction with the two isolated proteins. Finally, the most promising (most active, nontoxic, and BBB-permeable) compounds 22 and 23 were tested in vivo, in a Drosophila melanogaster model of AD. The carbazole derivative 22 (20 μM) showed extremely encouraging results, being able to improve both the lifespan and the climbing abilities of Aβ₄₂ expressing flies and generating a better outcome than doxycycline (50 μM). Moreover, 22 proved to be able to decrease Aβ₄₂ aggregates in the brains of the flies. We conclude that bivalent small molecules based on 22 deserve further attention as hits for dual Aβ/Tau aggregation inhibition in AD.

Linking the Amyloid, Tau, and Mitochondrial Hypotheses of Alzheimer's Disease and Identifying Promising Drug Targets

Damage or loss of brain cells and impaired neurochemistry, neurogenesis, and synaptic and nonsynaptic plasticity of the brain lead to dementia in neurodegenerative diseases, such as Alzheimer's disease (AD). Injury to synapses and neurons and accumulation of extracellular amyloid plaques and intracellular neurofibrillary tangles are considered the main morphological and neuropathological features of AD. Age, genetic and epigenetic factors, environmental stressors, and lifestyle contribute to the risk of AD onset and progression. These risk factors are associated with structural and functional changes in the brain, leading to cognitive decline. Biomarkers of AD reflect or cause specific changes in brain function, especially changes in pathways associated with neurotransmission, neuroinflammation, bioenergetics, apoptosis, and oxidative and nitrosative stress. Even in the initial stages, AD is associated with Aβ neurotoxicity, mitochondrial dysfunction, and tau neurotoxicity. The integrative amyloid-tau-mitochondrial hypothesis assumes that the primary cause of AD is the neurotoxicity of Aβ oligomers and tau oligomers, mitochondrial dysfunction, and their mutual synergy. For the development of new efficient AD drugs, targeting the elimination of neurotoxicity, mutual potentiation of effects, and unwanted protein interactions of risk factors and biomarkers (mainly Aβ oligomers, tau oligomers, and mitochondrial dysfunction) in the early stage of the disease seems promising.

Aβ and Tau Interact with Metal Ions, Lipid Membranes and Peptide-Based Amyloid Inhibitors: Are These Common Features Relevant in Alzheimer’s Disease?

In the last two decades, the amyloid hypothesis, i.e., the abnormal accumulation of toxic Aβ assemblies in the brain, has been considered the mainstream concept sustaining research in Alzheimer’s Disease (AD). However, the course of cognitive decline and AD development better correlates with tau accumulation rather than amyloid peptide deposition. Moreover, all clinical trials of amyloid-targeting drug candidates have been unsuccessful, implicitly suggesting that the amyloid hypothesis needs significant amendments. Accumulating evidence supports the existence of a series of potentially dangerous relationships between Aβ oligomeric species and tau protein in AD. However, the molecular determinants underlying pathogenic Aβ/tau cross interactions are not fully understood. Here, we discuss the common features of Aβ and tau molecules, with special emphasis on: (i) the critical role played by metal dyshomeostasis in promoting both Aβ and tau aggregation and oxidative stress, in AD; (ii) the effects of lipid membranes on Aβ and tau (co)-aggregation at the membrane interface; (iii) the potential of small peptide-based inhibitors of Aβ and tau misfolding as therapeutic tools in AD. Although the molecular mechanism underlying the direct Aβ/tau interaction remains largely unknown, the arguments discussed in this review may help reinforcing the current view of a synergistic Aβ/tau molecular crosstalk in AD and stimulate further research to mechanism elucidation and next-generation AD therapeutics.

The Prophylactic and Multimodal Activity of Two Isatin Thiosemicarbazones against Alzheimer's Disease In Vitro

Alzheimer’s disease (AD) is a multifactorial disorder strongly involving the formation of amyloid-β (Aβ) oligomers, which subsequently aggregate into the disease characteristic insoluble amyloid plaques, in addition to oxidative stress, inflammation and increased acetylcholinesterase activity. Moreover, Aβ oligomers interfere with the expression and activity of Glycogen synthase kinase-3 (GSK3) and Protein kinase B (PKB), also known as AKT. In the present study, the potential multimodal effect of two synthetic isatin thiosemicarbazones (ITSCs), which have been previously shown to prevent Aβ aggregation was evaluated. Both compounds resulted in fully reversing the Aβ-mediated toxicity in SK-NS-H cells treated with exogenous Aβ peptides at various pre-incubation time points and at 1 μM. Cell survival was not recovered when compounds were applied after Aβ cell treatment. The ITSCs were non-toxic against wild type and 5xFAD primary hippocampal cells. They reversed the inhibition of Akt and GSK-3β phosphorylation in 5xFAD cells. Finally, they exhibited good antioxidant potential and moderate lipoxygenase and acetylcholinesterase inhibition activity. Overall, these results suggest that isatin thiosemicarbazone is a suitable scaffold for the development of multimodal anti-AD agents.

Butyrylcholinesterase inhibitors as potential anti-Alzheimer's agents: an updated patent review (2018-present)

INTRODUCTION

Alzheimer's disease (AD) constitutes one of the most complex and devastating diseases, with an extraordinarily high increase expected for the next few years. Despite the numerous efforts accomplished so far there is still no cure but just palliative treatments.

AREAS COVERED

The main topic covered herein has been the development of butyrylcholinesterase (BuChE) inhibitors with the aim of increasing the levels of the neurotransmitter acetylcholine (ACh). Two main groups of compounds have been considered: multitarget and non-multitarget ligands, depending if the structural design is focused or not on other key targets and pathogenic factors of the disease. Seventeen patents regarding multitarget-directed ligands (MTDLs), twelve for not multitarget derivatives, and three for miscellaneous uses have been covered in the period 2018‒2021.

EXPERT OPINION

BuChE is an attractive target in the treatment of AD for many reasons. It is the most prevalent cholinesterase within more advanced stages of the disease, so drugs inhibiting it would be suitable for the treatment of mid- to severe Alzheimer's patients. Moreover, BuChE has been proved to be connected with some other key hallmarks of the disease, like amyloidogenesis; hybridization of a BuChE-targeting pharmacophore with other scaffolds designed for other therapeutic targets is quite a promising design for potential anti-Alzheimer's drugs.

Unveiling the Multitarget Anti-Alzheimer Drug Discovery Landscape: A Bibliometric Analysis

Multitarget anti-Alzheimer agents are the focus of very intensive research. Through a comprehensive bibliometric analysis of the publications in the period 1990-2020, we have identified trends and potential gaps that might guide future directions. We found that: (i) the number of publications boomed by 2011 and continued ascending in 2020; (ii) the linked-pharmacophore strategy was preferred over design approaches based on fusing or merging pharmacophores or privileged structures; (iii) a significant number of in vivo studies, mainly using the scopolamine-induced amnesia mouse model, have been performed, especially since 2017; (iv) China, Italy and Spain are the countries with the largest total number of publications on this topic, whereas Portugal, Spain and Italy are the countries in whose scientific communities this topic has generated greatest interest; (v) acetylcholinesterase, β-amyloid aggregation, oxidative stress, butyrylcholinesterase, and biometal chelation and the binary combinations thereof have been the most commonly pursued, while combinations based on other key targets, such as tau aggregation, glycogen synthase kinase-3β, NMDA receptors, and more than 70 other targets have been only marginally considered. These results might allow us to spot new design opportunities based on innovative target combinations to expand and diversify the repertoire of multitarget drug candidates and increase the likelihood of finding effective therapies for this devastating disease.

Recent Trends and Practices Toward Assessment and Rehabilitation of Neurodegenerative Disorders: Insights From Human Gait

The study of human movement and biomechanics forms an integral part of various clinical assessments and provides valuable information toward diagnosing neurodegenerative disorders where the motor symptoms predominate. Conventional gait and postural balance analysis techniques like force platforms, motion cameras, etc., are complex, expensive equipment requiring specialist operators, thereby posing a significant challenge toward translation to the clinics. The current manuscript presents an overview and relevant literature summarizing the umbrella of factors associated with neurodegenerative disorder management: from the pathogenesis and motor symptoms of commonly occurring disorders to current alternate practices toward its quantification and mitigation. This article reviews recent advances in technologies and methodologies for managing important neurodegenerative gait and balance disorders, emphasizing assessment and rehabilitation/assistance. The review predominantly focuses on the application of inertial sensors toward various facets of gait analysis, including event detection, spatiotemporal gait parameter measurement, estimation of joint kinematics, and postural balance analysis. In addition, the use of other sensing principles such as foot-force interaction measurement, electromyography techniques, electrogoniometers, force-myography, ultrasonic, piezoelectric, and microphone sensors has also been explored. The review also examined the commercially available wearable gait analysis systems. Additionally, a summary of recent progress in therapeutic approaches, viz., wearables, virtual reality (VR), and phytochemical compounds, has also been presented, explicitly targeting the neuro-motor and functional impairments associated with these disorders. Efforts toward therapeutic and functional rehabilitation through VR, wearables, and different phytochemical compounds are presented using recent examples of research across the commonly occurring neurodegenerative conditions [viz., Parkinson's disease (PD), Alzheimer's disease (AD), multiple sclerosis, Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS)]. Studies exploring the potential role of Phyto compounds in mitigating commonly associated neurodegenerative pathologies such as mitochondrial dysfunction, α-synuclein accumulation, imbalance of free radicals, etc., are also discussed in breadth. Parameters such as joint angles, plantar pressure, and muscle force can be measured using portable and wearable sensors like accelerometers, gyroscopes, footswitches, force sensors, etc. Kinetic foot insoles and inertial measurement tools are widely explored for studying kinematic and kinetic parameters associated with gait. With advanced correlation algorithms and extensive RCTs, such measurement techniques can be an effective clinical and home-based monitoring and rehabilitation tool for neuro-impaired gait. As evident from the present literature, although the vast majority of works reported are not clinically and extensively validated to derive a firm conclusion about the effectiveness of such techniques, wearable sensors present a promising impact toward dealing with neurodegenerative motor disorders.

Steroid-Quinoline Hybrids for Disruption and Reversion of Protein Aggregation Processes

Reversing protein aggregation within cells may be an important tool to fight protein-misfolding disorders such as Alzheimer's, Parkinson's, and cardiovascular diseases. Here we report the design and synthesis of a family of steroid-quinoline hybrid compounds based on the framework combination approach. This set of hybrid compounds effectively inhibited Aβ1-42 self-aggregation in vitro by delaying the exponential growth phase and/or reducing the quantity of fibrils in the steady state. Their disaggregation efficacy was further demonstrated against preaggregated Aβ1-42 peptides in cellular assays upon their endocytosis by neuroblastoma cells, as they reverted both the number and the average area of fibrils back to basal levels. The antiaggregation effect of these hybrids was further tested and demonstrated in a cellular model of general protein aggregation expressing a protein aggregation fluorescent sensor. Together, our results show that the new cholesterol-quinoline hybrids possess wide and marked disaggregation capacities and are therefore promising templates for the development of new drugs to deal with conformational disorders.

Repurposed anti-cancer epidermal growth factor receptor inhibitors: mechanisms of neuroprotective effects in Alzheimer's disease

Numerous molecular mechanisms are being examined in an attempt to discover disease-modifying drugs to slow down the underlying neurodegeneration in Alzheimer’s disease. Recent studies have shown the beneficial effects of epidermal growth factor receptor inhibitors on the enhancement of behavioral and pathological sequelae in Alzheimer’s disease. Despite the promising effects of epidermal growth factor receptor inhibitors in Alzheimer’s disease, there is no irrefutable neuroprotective evidence in well-established animal models using epidermal growth factor receptor inhibitors due to many un-explored downstream signaling pathways. This caused controversy about the potential involvement of epidermal growth factor receptor inhibitors in any prospective clinical trial. In this review, the mystery beyond the under-investigation of epidermal growth factor receptor in Alzheimer’s disease will be discussed. Furthermore, their molecular mechanisms in neurodegeneration will be explained. Also, we will shed light on SARS-COVID-19 induced neurological manifestations mediated by epidermal growth factor modulation. Finally, we will discuss future perspectives and under-examined epidermal growth factor receptor downstream signaling pathways that warrant more exploration. We conclude that epidermal growth factor receptor inhibitors are novel effective therapeutic approaches that require further research in attempts to be repositioned in the delay of Alzheimer’s disease progression.

Taurine Stabilizing Effect on Lysozyme

Taurine is an important organic osmolyte in mammalian cells, and it weakens inflammation and oxidative stress mediated injuries in some diseases. Recently, taurine has been demonstrated to play a therapeutic role against neurodegenerative disorders, although its parallel involvement in several biochemical mechanisms makes not clear taurine specific role in these diseases. Furthermore, the stabilizing effect of this molecule in terms of protein stability is known, but not deeply investigated. In this work we explore by Circular Dichroism the stabilizing impact of taurine in lysozyme thermal denaturation and its influence in lysozyme aggregation into amyloid fibrils. Taurine even at low concentration modifies protein-protein interactions in lysozyme native state, as revealed by Small Angle X-ray Scattering experiments, and alters the amyloid aggregation pattern without completely inhibiting it, as confirmed by UV/Vis spectroscopy with Congo Red and by Atomic Force Microscopy. Evaluation of the cytotoxicities of the amyloid fibrils grown in presence or in absence of taurine is investigated on SH-SY5Y neuroblastoma cells.

Joint Computational/Cell-Based Approach for Screening Inhibitors of Tau Oligomerization: A Proof-of-Concept Study

BACKGROUND

Tau assembly produces soluble oligomers and insoluble neurofibrillary tangles, which are neurotoxic to the brain and associated with Alzheimer's and Parkinson's diseases. Therefore, preventing tau aggregation is a promising therapy for those neurodegenerative disorders.

OBJECTIVE

The aim of this study was to develop a joint computational/cell-based oligomerization protocol for screening inhibitors of tau assembly.

METHODS

Virtual oligomerization inhibition (VOI) experiment using molecular dynamics simulation was performed to screen potential oligomerization inhibitors of PHF6 hexapeptide. Tau seeding assay, which is directly related to the outcome of therapeutic intervention, was carried out to confirm a ligand's ability in inhibiting tau assembly formation.

RESULTS

Our protocol was tested on two known compounds, EGCG and Blarcamesine. EGCG inhibited both the aggregation of PHF6 peptide in VOI and tau assembly in tau seeding assay, while Blarcamesine was not a good inhibitor at the two tasks. We also pointed out that good binding affinity to tau aggregates is needed, but not sufficient for a ligand to become a good inhibitor of tau oligomerization.

CONCLUSION

VOI goes beyond traditional computational inhibitor screening of amyloid aggregation by directly examining the inhibitory ability of a ligand to tau oligomerization. Comparing with the traditional biochemical assays, tau seeding activities in cells is a better indicator for the outcome of a therapeutic intervention. Our hybrid protocol has been successfully validated. It can effectively and efficiently identify the inhibitors of amyloid oligomerization/aggregation processes, thus, facilitate to the drug development of tau-related neurodegenerative diseases.

Multitargeting approaches involving carbonic anhydrase inhibitors: hybrid drugs against a variety of disorders

Carbonic anhydrases (CAs, EC 4.2.1.1) are enzymes involved in a multitude of diseases, and their inhibitors are in clinical use as drugs for the management of glaucoma, epilepsy, obesity, and tumours. In the last decade, multitargeting approaches have been proposed by hybridisation of CA inhibitors (CAIs) of sulphonamide, coumarin, and sulphocoumarin types with NO donors, CO donors, prostaglandin analogs, β-adrenergic blockers, non-steroidal anti-inflammatory drugs, and a variety of anticancer agents (cytotoxic drugs, kinase/telomerase inhibitors, P-gp and thioredoxin inhibitors). Many of the obtained hybrids showed enhanced efficacy compared to the parent drugs, making multitargeting an effective and innovative approach for various pharmacological applications.

Rational Multitargeted Drug Design Strategy from the Perspective of a Medicinal Chemist

The development of multitarget-directed ligands (MTDLs) has become a widely focused research topic, but rational design remains as an enormous challenge. This paper reviews and discusses the design strategy of incorporating the second activity into an existing single-active ligand. If the binding sites of both targets share similar endogenous substrates, MTDLs can be designed by merging two lead compounds with similar functional groups. If the binding sites are large or adjacent to the solution, two key pharmacophores can be fused directly. If the binding regions are small and deep inside the proteins, the linked-pharmacophore strategy might be the only way. The added pharmacophores of second targets should not affect the binding mode of the original ones. Moreover, the inhibitory activities of the two targets need to be adjusted to achieve an optimal ratio.

Multitarget therapeutic approaches for Alzheimer's and Parkinson's diseases: an opportunity or an illusion?

Alzheimer's and Parkinson's disease are the most prevalent neurodegenerative diseases and the leading causes of dementia worldwide. The etiology of these multifactorial pathologies is not completely known. The available therapeutic approaches can cause temporary relief of symptoms but cannot slow down their progression or cure them. Life-changing therapeutic solutions are urgently needed, as the number of people suffering from these pathologies has been increasing quickly over the last few decades. Several targets are being studied, and innovative approaches are being pursued to find new therapeutic options. This overview is focused on the most recent information regarding the paradigm of using multitarget compounds to treat both Alzheimer's and Parkinson's disease.

Dual Inhibitors of Amyloid-β and Tau Aggregation with Amyloid-β Disaggregating Properties: Extended In Cellulo, In Silico, and Kinetic Studies of Multifunctional Anti-Alzheimer's Agents

In Alzheimer’s disease, neurons slowly degenerate due to the accumulation of misfolded amyloid β and tau proteins. In our research, we performed extended studies directed at amyloid β and tau aggregation inhibition using in cellulo (Escherichia coli model of protein aggregation), in silico, and in vitro kinetic studies. We tested our library of 1-benzylamino-2-hydroxyalkyl multifunctional anti-Alzheimer’s agents and identified very potent dual aggregation inhibitors. Among the tested derivatives, we selected compound 18, which exhibited a unique profile of biological activity. This compound was the most potent and balanced dual aggregation inhibitor (Aβ₄₂ inhibition (inh.) 80.0%, tau inh. 68.3% in 10 μM), with previously reported in vitro inhibitory activity against hBuChE, hBACE1, and Aβ (hBuChE IC₅₀ = 5.74 μM; hBACE1 IC₅₀ = 41.6 μM; Aβ aggregation (aggr.) inh. IC₅₀ = 3.09 μM). In docking studies for both proteins, we tried to explain the different structural requirements for the inhibition of Aβ vs tau. Moreover, docking and kinetic studies showed that compound 18 could inhibit the amyloid aggregation process at several steps and also displayed disaggregating properties. These results may help to design the next generations of dual or selective aggregation inhibitors.

Chromeno[3,4-b]xanthones as First-in-Class AChE and Aβ Aggregation Dual-Inhibitors

Alzheimer’s disease (AD) is a complex multifactorial disorder, mainly characterized by the progressive loss of memory and cognitive, motor, and functional capacity. The absence of effective therapies available for AD alongside the consecutive failures in the central nervous system (CNS) drug development has been motivating the search for new disease-modifying therapeutic strategies for this disease. To address this issue, the multitarget directed ligands (MTDLs) are emerging as a therapeutic alternative to target the multiple AD-related factors. Following this concept, herein we describe the design, synthesis, and biological evaluation of a family of chromeno[3,4-b]xanthones as well as their (E)-2-[2-(propargyloxy)styryl]chromone precursors, as first-in-class acetylcholinesterase (AChE) and β-amyloid (Aβ) aggregation dual-inhibitors. Compounds 4b and 10 emerged as well-balanced dual-target inhibitors, with IC₅₀ values of 3.9 and 2.9 μM for AChE and inhibitory percentages of 70 and 66% for Aβ aggregation, respectively. The molecular docking showed that most of the compounds bound to AChE through hydrogen bonds with residues of the catalytic triad and π-stacking interactions between the main scaffold and the aromatic residues present in the binding pocket. The interesting well-balanced activities of these compounds makes them interesting templates for the development of new multitarget compounds for AD.