Alzheimer's Disease Drug Discovery Research Articles

Dextran-assisted ultrasonic exfoliation of two-dimensional metal-organic frameworks to evaluate acetylcholinesterase activity and inhibitor screening

Acetylcholinesterase (AChE) is regarded as a biomarker of Alzheimer's disease (AD), and its inhibitors show great potential in AD therapy as AChE can increase the neurotoxicity of the amyloid component that induces AD. Because of this, it is crucial and significant to develop a simple and highly sensitive strategy to monitor AChE levels and screen highly efficient AChE inhibitors. Herein, we synthesize an ultrathin two-dimensional (2D) metal-organic framework (MOF) based on copper-catecholate (Cu-CAT) via dextran assisted ultrasound exfoliation, followed by construction of a sensitive sensor for the monitoring AChE and screening of its inhibitors. By adding AChE, the acetylthiocholine (ATCh) substrate is hydrolyzed to be thiocholine (TCh), which decreases the peroxidase-like activity of Cu-CAT nanosheets (Cu-CAT NSs), impairing the signal reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) to oxidized-TMB (ox-TMB). In the presence of an AChE inhibitor, the signal can be gradually restored. The newly developed sensor shows high sensitivity and selectivity for AChE and huperzine A (HA, an effective drug for AD, an acetylcholine receptor antagonist), as well as for AD drug discovery from traditional Chinese herbs. The limit of detection of the sensor for AChE is 0.01 mU mL−1 and the average IC50 value of HA is 30.81 nM under the optimal of catalysis conditions. Compared with the 3D bulk Cu-CAT, the current 2D Cu-CAT NSs exhibit higher peroxidase activity due to more catalytic active site exposure. This study provides a strategy to prepare an ultrathin 2D MOF with high catalytic activity and new insights for the construction of a biosensor to monitor AChE and new AD drugs.

Visualization of synaptic vesicle protein 2A in a rodent model of familial Alzheimer’s disease with a metabolically stable PET probe

AbstractBackgroundSynaptic loss is one of the hallmarks of Alzheimer’s disease (AD) and region‐specific changes in synaptic density is associated with a variety of neuropsychiatric diseases. Here, we investigated the expression levels of synaptic vesicle glycoprotein 2A (SV2A) in APP/PS1 and age‐matched wild‐type (WT) mice using [18F]SDM16, a novel, metabolically stable SV2A PET imaging probe.MethodsThe SV2A tracer [18F]SDM‐16 was synthesized according to previously published procedure [1]. PET scans with [18F]SDM‐16 were performed on a Focus‐220 scanner in APP/PS1 transgenic mice and WT controls. Regions of interest (ROIs) were extracted from the Ma‐Benveniste‐Mirrione mouse brain atlas and regional time‐activity curves (TACs) were obtained by applying template ROIs to the averaged PET images from 0‐90 min post‐injection (p.i.). Distribution volume ratio (DVR) values were generated using the simplified reference tissue model (SRTM), with brain stem as the reference region. Averaged SUV ratios (SUVRs) from 60‐90 min were calculated by using brain stem as reference region. Spatially normalized SUVR(BS) were assessed on a voxel‐by‐voxel basis in Matlab R2018 with Statistical Parametric Mapping.ResultsThe mouse brain PET images showed ubiquitous uptake of [18F]SDM‐16. Regional TACs showed high brain uptake in the selected brain regions of mice (SUV up to 2.38), with a steady increase after tracer injection, before plateauing at 60‐90 min p.i. (Fig. 1a). DVR results correlated well with SUVR(BS) from 60‐90 min (R2 = 0.94, p < 0.0001). Compared with age‐matched WT controls, the averaged SUVR(BS) in the whole brain and hippocampus of APP/PS1 mice showed statistically significant lower values by 5.4% (p = 0.01) and 11% (p = 0.001), respectively (Fig. 1b). These results are consistent with those from previous reports using [11C]UCB‐J (4.0% decrease in hippocampus) and [18F]SynVesT‐1 (7.5% decrease in hippocampus) [2, 3]. Voxel‐based parametric analysis also showed a global decrease in tracer uptake in the APP/PS1 mice, with the most significant decrease in the hippocampus, which is consistent with the results from ROI‐based analysis.ConclusionsWe demonstrated that the radioligand [18F]SDM‐16 had high uptake in mouse brain, and APP/PS1 mice showed lower tracer uptake than WT mice, supporting the use of [18F]SDM‐16 in preclinical AD drug discovery and development.

Interpretable deep learning translation of GWAS and multi-omics findings to identify pathobiology and drug repurposing in Alzheimer's disease.

Translating human genetic findings (genome-wide association studies [GWAS]) to pathobiology and therapeutic discovery remains a major challenge for Alzheimer's disease (AD). We present a network topology-based deep learning framework to identify disease-associated genes (NETTAG). We leverage non-coding GWAS loci effects on quantitative trait loci, enhancers and CpG islands, promoter regions, open chromatin, and promoter flanking regions under the protein-protein interactome. Via NETTAG, we identified 156 AD-risk genes enriched in druggable targets. Combining network-based prediction and retrospective case-control observations with 10 million individuals, we identified that usage of four drugs (ibuprofen, gemfibrozil, cholecalciferol, and ceftriaxone) is associated with reduced likelihood of AD incidence. Gemfibrozil (an approved lipid regulator) is significantly associated with 43% reduced risk of AD compared with simvastatin using an active-comparator design (95% confidence interval 0.51-0.63, p<0.0001). In summary, NETTAG offers a deep learning methodology that utilizes GWAS and multi-genomic findings to identify pathobiology and drug repurposing in AD.

Building in vitro models of the brain to understand the role of APOE in Alzheimer's disease.

Alzheimer's disease (AD) is a devastating, complex, and incurable disease that represents an increasingly problematic global health issue. The etiology of sporadic AD that accounts for a vast majority of cases remains poorly understood, with no effective therapeutic interventions. Genetic studies have identified AD risk genes including the most prominent, APOE, of which the ɛ4 allele increases risk in a dose-dependent manner. A breakthrough discovery enabled the creation of human induced pluripotent stem cells (hiPSCs) that can be differentiated into various brain cell types, facilitating AD research in genetically human models. Herein, we provide a brief background on AD in the context of APOE susceptibility and feature work employing hiPSC-derived brain cell and tissue models to interrogate the contribution of APOE in driving AD pathology. Such models have delivered crucial insights into cellular mechanisms and cell type-specific roles underlying the perturbed biological functions that trigger pathogenic cascades and propagate neurodegeneration. Collectively, hiPSC-based models are envisioned to be an impactful platform for uncovering fundamental AD understanding, with high translational value toward AD drug discovery and testing.

Covalent fragment inhibits intramembrane proteolysis.

Alzheimer’s disease (AD) is a serious public health crisis with only one current modifying treatment. The reduction of amyloid load by targeting γ-secretase (GS) has been a leading approach in AD drug discovery and development. Despite the focus on GS inhibition, multiple GS inhibitors (GSIs) have failed in clinical trials as a result of side effects including exacerbated cognitive decline. These side effects are largely attributable to inhibition of normal GS function. Standard enzyme inhibitors target catalytic or allosteric sites of the enzyme, including the active site presenilin, as previous GSIs did. To avoid issues observed from broad-spectrum GSIs we discovered that fragment 6H8 that covalently binds to the substrate of GS, the transmembrane domain of amyloid precursor protein (APPTM). Nuclear Magnetic Resonance (NMR) Spectroscopy combined with MALDI-TOF-MS established 6H8 covalently binds to APPTM. 6H8 acts as a Michael acceptor and covalently links to the side chain amines of lysine residues, specifically targeting a cluster of C-terminal lysines K53–K55. Through this modification, 6H8 can inhibit intramembrane proteolysis of an archaeal homolog of presenilin (the active subunit of GS) via substrate binding with a 2–4 μM IC50, determined by a gel-based cleavage assay. 6H8, while too small to be an effective drug candidate, can be combined with a specific non-covalent partner and function as an effective covalent warhead of a targeted covalent inhibitor (TCI). The future development of the 6H8 fragment into the covalent warhead of a TCI is, to our knowledge, a novel approach to AD drug discovery.

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.

Chimeric cerebral organoids reveal the essentials of neuronal and astrocytic APOE4 for Alzheimer’s tau pathology

The apolipoprotein E4 (APOE4) genotype is one of the strongest genetic risk factors for Alzheimer’s disease (AD), and is generally believed to cause widespread pathological alterations in various types of brain cells. Here, we developed a novel engineering method of creating the chimeric human cerebral organoids (chCOs) to assess the differential roles of APOE4 in neurons and astrocytes. First, the astrogenic factors NFIB and SOX9 were introduced into induced pluripotent stem cells (iPSCs) to accelerate the induction of astrocytes. Then the above induced iPSCs were mixed and cocultured with noninfected iPSCs under the standard culturing condition of cerebral organoids. As anticipated, the functional astrocytes were detected as early as 45 days, and it helped more neurons matured in chCOs in comparation of the control human cerebral organoids (hCOs). More interestingly, this method enabled us to generate chCOs containing neurons and astrocytes with different genotypes, namely APOE3 or APOE4. Then, it was found in chCOs that astrocytic APOE4 already significantly promoted lipid droplet formation and cholesterol accumulation in neurons while both astrocytic and neuronal APOE4 contributed to the maximum effect. Most notably, we observed that the co-occurrence of astrocytic and neuronal APOE4 were required to elevate neuronal phosphorylated tau levels in chCOs while Aβ levels were increased in chCOs with neuronal APOE4. Altogether, our results not only revealed the essence of both neuronal and astrocytic APOE4 for tau pathology, but also suggested chCOs as a valuable pathological model for AD research and drug discovery.

A Phenotypic‐based Drug Discovery Approach to Inhibit the Misfolding of Hyperphosphorylated Tau Isoform 1N4R

The vast majority of Alzheimer’s disease (AD) drug development efforts have failed because of significant gap in the understanding of the pathophysiological processes and insufficient effort in identifying, optimizing, and validating small molecules inhibitors of aggregation. AD involves the misfolding of amyloid‐beta which forms Aβ plaques and, subsequently, activates different types of microglial cells leading to a pro‐inflammatory state. Microglia when activated have been known to increase tau phosphorylation and drive the trans‐synaptic spread of aggregated hyperphosphorylated tau (p‐tau). Most importantly, the spatiotemporal distribution of neurofibrillary tangles predicts cognitive impairment. Instead of the unmodified tau that shows minimal effects on cell viability, our research focuses on the control of p‐tau that possesses disease‐relevant molecular features, including hyperphosphorylation and cytotoxicity. Our drug discovery project is centered on the isoform 1N4R due to its prevalence (1N) and long‐distance trans‐synaptic propagation (4R). We identified compounds that inhibit the aggregation and cytotoxicity of p‐tau, which represent a novel approach for AD drug discovery and development. Due to lack of binding pocket(s) and fast‐switching conformation of p‐tau, we opted for a phenotypic‐based drug screening approach to identify and optimize hit candidates. In our current project, the anti‐aggregation activity and cellular protection of newly synthesized small molecules were evaluated with biophysical methods (thioflavin S fluorescence assays, photo‐induced cross‐linking of unmodified proteins, dynamic light scattering) and survival assays with human neuroblastoma SH‐SY5Y cells. We prepared and tested 3 different series of small molecules and challenged these molecules with our first‐tier screening assay, i.e. thioflavin S fluorescence assays. Ureas and sulfonylureas series failed to inhibit the aggregation of p‐tau 1N4R. The best prototypical representative of the sulfonamide series, compound JF‐19‐73, effectively antagonized the cytotoxicity of p‐tau in vitro at low micromolar concentrations, suggesting the potential for neuroprotection in vivo. Other representatives of the sulfonamide series exhibited an intermediate effect to antagonize the aggregation and cytotoxicity of p‐tau isoform 1N4R. This project opens doors in targeting undruggable prone‐to‐aggregate proteins such as p‐tau and provides a molecular scaffold for further optimization and pre‐clinical studies focused on AD drug development.

Platelet Activating Factor Receptor Exaggerates Microglia-Mediated Microenvironment by IL10-STAT3 Signaling: A Novel Potential Biomarker and Target for Diagnosis and Treatment of Alzheimer’s Disease

BackgroundEarly diagnosis and effective intervention are the keys to delaying the progression of Alzheimer’s Disease (AD). Therefore, we aimed to identify new biomarkers for the early diagnosis of AD through bioinformatic analysis and elucidate the possible underlying mechanisms.Methods and ResultsGSE1297, GSE63063, and GSE110226 datasets from the GEO database were used to screen the highly differentially expressed genes. We identified a potential biomarker, Platelet activating factor receptor (PTAFR), significantly upregulated in the brain tissue, peripheral blood, and cerebrospinal fluid of AD patients. Furthermore, PTAFR levels in the plasma and brain tissues of APP/PS1 mice were significantly elevated. Simultaneously, PTAFR could mediate the inflammatory responses to exaggerate the microenvironment, particularly mediated by the microglia through the IL10-STAT3 pathway. In addition, PTAFR was a putative target of anti-AD compounds, including EGCG, donepezil, curcumin, memantine, and Huperzine A.ConclusionPTAFR was a potential biomarker for early AD diagnosis and treatment which correlated with the microglia-mediated microenvironment. It is an important putative target for the development of a novel strategy for clinical treatment and drug discovery for AD.

Drug delivery of memantine with carbon dots for Alzheimer’s disease: blood–brain barrier penetration and inhibition of tau aggregation

Neurofibrillary tangle, composed of aggregated tau protein, is a pathological hallmark of Alzheimer’s disease (AD). The inhibition of tau aggregation is therefore an important direction for AD drug discovery. In this work, we explored the efficacy of two types of carbon dots in targeting tau aggregation, as versatile nano-carriers for the development of carbon dots (CDs)-based AD therapy. We carried out synthesis, biophysical and biochemical characterizations of two types of CDs, namely, carbon nitride dots (CNDs) and black carbon dots (B-CDs). CDs, which are biocompatible and non-toxic, were successfully conjugated with memantine hydrochloride (MH) through EDC/NHS mediated amidation reactions followed by systematic characterizations using various biophysical techniques including UV–vis spectroscopy (UV–vis), photoluminescence (PL), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), mass spectrometry (MS), Transmission electron microscopy (TEM) and atomic force microscopy (AFM). The surface diversity along with small particle sizes of CDs allowed facile delivery of MH across the blood–brain barrier (BBB), as demonstrated using a zebrafish in vivo model. The tau aggregation inhibition experiments were conducted using the thioflavin-T (ThT) assay to identify the most effective inhibitor. The kinetics and magnitude of tau aggregation were measured in the presence of CDs, which demonstrates that both B-CDs-MH and B-CDs alone are the most effective inhibitors of tau aggregation with IC50 values of 1.5 ± 0.3 and 1.6 ± 1.5 μg/mL, respectively. Taken together, our findings hold therapeutic significance to enhance the efficient delivery of MH to target AD pathology in the brain for improved efficacy.

Cognitive enhancement and neuroprotective effects of OABL, a sesquiterpene lactone in 5xFAD Alzheimer's disease mice model

Alzheimer's disease (AD) is a neurodegenerative disease in which oxidative stress and neuroinflammation were demonstrated to be associated with neuronal loss and cognitive deficits. However, there are still no specific treatments that can prevent the progression of AD. In this study, a screening of anti-inflammatory hits from 4207 natural compounds of two different molecular libraries indicated 1,6-O,O-diacetylbritannilactone (OABL), a 1,10-seco-eudesmane sesquiterpene lactone isolated from the herb Inula britannica L., exhibited strong anti-inflammatory activity in vitro as well as favorable BBB penetration property. OABL reduced LPS-induced neuroinflammation in BV-2 microglial cells as assessed by effects on the levels of inflammatory mediators including NO, PGE2, TNF-α, iNOS, and COX-2, as well as the translocation of NF-κB. Besides, OABL also exhibited pronounced neuroprotective effects against oxytosis and ferroptosis in the rat pheochromocytoma PC12 cell line. For in vivo research, OABL (20 mg/kg B.W., i.p.) for 21 d attenuated the impairments in cognitive function observed in 6-month-old 5xFAD mice, as assessed with the Morris water maze test. OABL restored neuronal damage and postsynaptic density protein 95 (PSD95) expression in the hippocampus. OABL also significantly reduced the accumulation of amyloid plaques, the Aβ expression, the phosphorylation of Tau protein, and the expression of BACE1 in AD mice brain. In addition, OABL attenuated the overactivation of microglia and astrocytes by suppressing the expressions of inflammatory cytokines, and increased glutathione (GSH) and reduced malondialdehyde (MDA) and super oxide dismutase (SOD) levels in the 5xFAD mice brain. In conclusion, these results highlight the beneficial effects of the natural product OABL as a novel treatment with potential application for drug discovery in AD due to its pharmacological profile.

AD Informer Set: Chemical tools to facilitate Alzheimer's disease drug discovery.

IntroductionThe portfolio of novel targets to treat Alzheimer's disease (AD) has been enriched by the Accelerating Medicines Partnership Program for Alzheimer's Disease (AMP AD) program.MethodsPublicly available resources, such as literature and databases, enabled a data‐driven effort to identify existing small molecule modulators for many protein products expressed by the genes nominated by AMP AD and suitable positive control compounds to be included in the set. Compounds contained within the set were manually selected and annotated with associated published, predicted, and/or experimental data.ResultsWe built an annotated set of 171 small molecule modulators targeting 98 unique proteins that have been nominated by AMP AD consortium members as novel targets for the treatment of AD. The majority of compounds included in the set are inhibitors. These small molecules vary in their quality and should be considered chemical tools that can be used in efforts to validate therapeutic hypotheses, but which will require further optimization. A physical copy of the AD Informer Set can be requested on the Target Enablement to Accelerate Therapy Development for Alzheimer's Disease (TREAT‐AD) website.DiscussionSmall molecules that enable target validation are important tools for the translation of novel hypotheses into viable therapeutic strategies for AD.

Multimodal single-cell/nucleus RNA-sequencing data analysis uncovers molecular networks between disease-associated microglia and astrocytes with implications for drug repurposing in Alzheimer's disease.

Systematic identification of molecular networks in disease relevant immune cells of the nervous system is critical for elucidating the underlying pathophysiology of Alzheimer's disease (AD). Two key immune cell types, disease-associated microglia (DAM) and disease-associated astrocytes (DAA), are biologically involved in AD pathobiology. Therefore, uncovering molecular determinants of DAM and DAA will enhance our understanding of AD biology, potentially identifying novel therapeutic targets for AD treatment. We systematically investigate molecular networks between DAM and DAA in order to uncover novel therapeutic targets for AD. Specifically, we develop a network-based methodology that leverages single-cell/nucleus RNA-sequencing data from both transgenic mouse models and AD patient brains, as well as drug-target network, metabolite-enzyme associations, the human protein-protein interactome, and large-scale longitudinal patient data. We prioritize repurposed drugs for potential treatment of AD by identifying those that specifically reverse dysregulated gene expression of microglia and astrocytes. Finally, top drug candidates are selected to be validated further using the state-of-the-art pharmacoepidemiologic observations of a longitudinal patient database with 7.2 million subjects. Through this approach, we find both common and unique gene network regulators between DAM (i.e., PAK1, MAPK14, and CSF1R) and DAA (i.e., NFKB1, FOS, and JUN) that are significantly enriched by neuro-inflammatory pathways and well-known genetic variants (i.e., BIN1). We identify shared immune pathways between DAM and DAA, including Th17 cell differentiation and chemokine signaling. Lastly, integrative metabolite-enzyme network analyses suggest that fatty acids and amino acids may trigger molecular alterations in DAM and DAA. Combining network-based prediction and retrospective case-control observations with 7.2 million subjects, we identify that usage of fluticasone (an approved glucocorticoid receptor agonist) is significantly associated with a reduced incidence of AD (hazard ratio (HR) = 0.86, 95% confidence interval (CI) 0.83-0.89, p<1.0x10-8 ). Propensity score-matching cohort studies reveal that usage of mometasone (a stronger glucocorticoid receptor agonist) is significantly associated with a decreased risk of AD (HR=0.74, 95% CI 0.68-0.81, p<1.0x10-8 ) compared to fluticasone after adjusting age, gender, and disease comorbidities. In summary, we present a network-based, multimodal methodology for single-cell/nucleus genomics-informed drug discovery in AD that has identified fluticasone and mometasone as potential treatments.

Design, Synthesis, biological investigations and molecular interactions of triazole linked tacrine glycoconjugates as Acetylcholinesterase inhibitors with reduced hepatotoxicity

Tacrine is a known Acetylcholinesterase (AChE) inhibitors having hepatotoxicity as main liability associated with it. The present study aims to reduce its hepatotoxicity by synthesizing tacrine linked triazole glycoconjugates via Huisgen’s [3 + 2] cycloaddition of anomeric azides and terminal acetylenes derived from tacrine. A series of triazole based glycoconjugates containing both acetylated (A-1 to A-7) and free sugar hydroxyl groups (A-8 to A-14) at the amino position of tacrine were synthesized in good yield taking aid from molecular docking studies and evaluated for their in vitro AChE inhibition activity as well as hepatotoxicity. All the hybrids were found to be non-toxic on HePG2 cell line at 200 μM (100 % cell viability) as compared to tacrine (35 % cell viability) after 24 h of incubation period. Enzyme kinetic studies carried out for one of the potent hybrids in the series A-1 (IC50 0.4 μM) revealed its mixed inhibition approach. Thus, compound A-1 can be used as principle template to further explore the mechanism of action of different targets involved in Alzheimer’s disease (AD) which stands as an adequate chemical probe to be launched in an AD drug discovery program.

Pharmacological and Neuroprotective Natural Products in the Treatment of Alzheimer’s Disease

Alzheimer's illness (AD) is a progressive, neurodegenerative issue and has become an incredible medical condition especially among the old individuals, for the most part happens after the age of 55 years and expansion in frequency with propelling age, however its therapy alternatives are generally not many and inadequate. The reason for AD isn't actually known, yet is thought to incorporate both hereditary and natural elements (multifactorial). There is no known remedy for Alzheimer's sickness, since it is beyond the realm of imagination to expect to invert the demise of synapses however the indications can be overseen by some pharmacological specialists and Neuroprotective Natural Products. In spite of the improvement of various pharmacological methodologies throughout the years pointed toward treating Alzheimer's Disease (AD) without a doubt, not many have been supported for clinical use in patients. To date there still exists no illness adjusting treatment that could forestall or protect the intellectual debilitation, especially of memory aquisition, that is normal for AD. One of the opportunities for this situation may be that most of medication disclosure endeavors centers around result proportions of diminished neuropathological biomarkers normal for AD, without taking into acount neuronal cycles fundamental for the age and support of memory measures. In endeavors to find new methodologies for AD treatment, regular items have stirred interest in the examination local area and in the drug business for their neuroprotective movement, focusing on various obsessive instruments related with AD. A wide assortment of normal items from various beginnings have been assessed preclinically and clinically for their neuroprotective instruments in forestalling and lessening the multifactorial pathologies of AD. It is accepted that normal item blends or concentrates containing different bioactive mixtures that can work additively or synergistically to display various neuroprotective systems may be a compelling methodology in AD drug discovery. Keywords: Alzheimer’s disease (AD); neurodegenerative disease, natural products, pharmacological agents.

Neuroprotective Natural Products for Alzheimer’s Disease

Alzheimer’s disease (AD) is the number one neurovegetative disease, but its treatment options are relatively few and ineffective. In efforts to discover new strategies for AD therapy, natural products have aroused interest in the research community and in the pharmaceutical industry for their neuroprotective activity, targeting different pathological mechanisms associated with AD. A wide variety of natural products from different origins have been evaluated preclinically and clinically for their neuroprotective mechanisms in preventing and attenuating the multifactorial pathologies of AD. This review mainly focuses on the possible neuroprotective mechanisms from natural products that may be beneficial in AD treatment and the natural product mixtures or extracts from different sources that have demonstrated neuroprotective activity in preclinical and/or clinical studies. It is believed that natural product mixtures or extracts containing multiple bioactive compounds that can work additively or synergistically to exhibit multiple neuroprotective mechanisms might be an effective approach in AD drug discovery.

Deep Learning Based Multimodal Progression Modeling for Alzheimer’s Disease

The progression of Alzheimer’s disease (AD) is a continuous process in cognitive and biomarker changes, with only a fraction of mild cognitive impairment (MCI) patients eventually advancing to AD. There is no definite biomarker signature to determine this eventual progress. The discovery and development of prognostic biomarker signatures for AD is essential to address the challenges of AD drug discovery and development. The deep learning (DL) technique is a recent breakthrough in data science that enables researchers to discover previously unknown features comprised by complicated patterns learnt from large datasets. It has outperformed many traditional machine learning methods in computer vision tasks. In this article, we evaluated the performance of DL algorithms in differentiating patients with diagnosis of AD, MCI, or no evidence of dementia using baseline MRI data of the brain, and integrated features extracted from the neural network with other baseline biomarkers to develop an AD prognostic signature. This signature can be used to understand the patient heterogeneity in a study cohort and provide enrichment strategies for AD clinical trial design.

Amyloid binding and beyond: a new approach for Alzheimer's disease drug discovery targeting Aβo-PrPC binding and downstream pathways.

Amyloid β oligomers (Aβo) are the main toxic species in Alzheimer's disease, which have been targeted for single drug treatment with very little success. In this work we report a new approach for identifying functional Aβo binding compounds. A tailored library of 971 fluorine containing compounds was selected by a computational method, developed to generate molecular diversity. These compounds were screened for Aβo binding by a combined 19F and STD NMR technique. Six hits were evaluated in three parallel biochemical and functional assays. Two compounds disrupted Aβo binding to its receptor PrPC in HEK293 cells. They reduced the pFyn levels triggered by Aβo treatment in neuroprogenitor cells derived from human induced pluripotent stem cells (hiPSC). Inhibitory effects on pTau production in cortical neurons derived from hiPSC were also observed. These drug-like compounds connect three of the pillars in Alzheimer's disease pathology, i.e. prion, Aβ and Tau, affecting three different pathways through specific binding to Aβo and are, indeed, promising candidates for further development.

Sowing the Seeds of Discovery: Tau-Propagation Models of Alzheimer's Disease.

The propagation of pathological proteins throughout the brain is the primary physiological hallmark of the progression of Alzheimer's Disease (AD). A growing body of evidence indicates that hyperphosphorylated Tau proteins are spread transcellularly between neurons in a prionlike fashion, inducing misfolding and aggregation into neurofibrillary tangles which accumulate along specific connectivity pathways. Earlier transgenic rodent AD models did not capture this disease-relevant spread, and therefore, seeded Tau-propagation models have been developed. Here, mutant human Tau (as isolated protein or packaged into an adeno-associated virus (AAV) viral vector) is stereotaxically injected into select brain regions and its histopathological propagation to downstream neurons quantified. These models offer a faster and more direct mechanism to evaluate genetic components and therapeutic approaches which attenuate Tau spreading in vivo. Recently, these Tau-seeding models have revealed several new targets for AD drug discovery, including nSMase2, SIRT1, p300/CBP, LRP1, and TYROBP, as well as the potential therapeutics based on melatonin and chondroitinase ABC. Importantly, these Tau-propagation rodent models more closely phenocopy the progression of AD in humans and are therefore likely to improve preclinical studies and derisk future moves into clinical trials.

Molecular imaging of Alzheimer's disease-related gamma-secretase in mice and nonhuman primates.

The pathogenesis of Alzheimer's disease (AD) is primarily driven by brain accumulation of the amyloid-β-42 (Aβ42) peptide generated from the amyloid-β precursor protein (APP) via cleavages by β- and γ-secretase. γ-Secretase is a prime drug target for AD; however, its brain regional expression and distribution remain largely unknown. Here, we are aimed at developing molecular imaging tools for visualizing γ-secretase. We used our recently developed γ-secretase modulators (GSMs) and synthesized our GSM-based imaging agent, [11C]SGSM-15606. We subsequently performed molecular imaging in rodents, including AD transgenic animals, and macaques, which revealed that our probe displayed good brain uptake and selectivity, stable metabolism, and appropriate kinetics and distribution for imaging γ-secretase in the brain. Interestingly, rodents and macaques shared certain brain areas with high γ-secretase expression, suggesting a functional conservation of γ-secretase. Collectively, we have provided the first molecular brain imaging of γ-secretase, which may not only accelerate our drug discovery for AD but also advance our understanding of AD.