Lead optimization based design, synthesis, and pharmacological evaluation of quinazoline derivatives as multi-targeting agents for Alzheimer's disease treatment.

The complexity and multifaceted nature of Alzheimer's disease (AD) have driven us to further explore quinazoline scaffolds as multi-targeting agents for AD treatment. The lead optimization strategy was utilized in designing of new series of derivatives (AK-1 to AK-14) followed by synthesis, characterization, and pharmacological evaluation against human cholinesterase's (hChE) and ß-secretase (hBACE-1) enzymes. Amongst them, compounds AK-1, AK-2, and AK-3 showed good and significant inhibitory activity against both hAChE and hBACE-1 enzymes with favorable permeation across the blood-brain barrier. The most active compound AK-2 revealed significant propidium iodide (PI) displacement from the AChE-PAS region and was non-neurotoxic against SH-SY5Y cell lines. The lead molecule (AK-2) also showed Aß aggregation inhibition in a self- and AChE-induced Aß aggregation, Thioflavin-T assay. Further, compound AK-2 significantly ameliorated Aß-induced cognitive deficits in the Aß-induced Morris water maze rat model and demonstrated a significant rescue in eye phenotype in the Aꞵ-phenotypic drosophila model of AD. Ex-vivo immunohistochemistry (IHC) analysis on hippocampal rat brains showed reduced Aß and BACE-1 protein levels. Compound AK-2 suggested good oral absorption via pharmacokinetic studies and displayed a good and stable ligand-protein interaction in in-silico molecular modeling analysis. Thus, the compound AK-2 can be regarded as a lead molecule and should be investigated further for the treatment of AD.

Protection of Si Nanowires against Aß Toxicity by the Inhibition of Aß Aggregation.

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by the accumulation of amyloid beta (Aß) plaques in the brain. Aß1-42 is the main component of Aß plaque, which is toxic to neuronal cells. Si nanowires (Si NWs) have the advantages of small particle size, high specific surface area, and good biocompatibility, and have potential application prospects in suppressing Aß aggregation. In this study, we employed the vapor-liquid-solid (VLS) growth mechanism to grow Si NWs using Au nanoparticles as catalysts in a plasma-enhanced chemical vapor deposition (PECVD) system. Subsequently, these Si NWs were transferred to a phosphoric acid buffer solution (PBS). We found that Si NWs significantly reduced cell death in PC12 cells (rat adrenal pheochromocytoma cells) induced by Aß1-42 oligomers via double staining with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and fluorescein diacetate/propyl iodide (FDA/PI). Most importantly, pre-incubated Si NWs largely prevented Aß1-42 oligomer-induced PC12 cell death, suggesting that Si NWs exerts an anti-Aß neuroprotective effect by inhibiting Aß aggregation. The analysis of Fourier Transform Infrared (FTIR) results demonstrates that Si NWs reduce the toxicity of fibrils and oligomers by intervening in the formation of ß-sheet structures, thereby protecting the viability of nerve cells. Our findings suggest that Si NWs may be a potential therapeutic agent for AD by protecting neuronal cells from the toxicity of Aß1-42.

Quercetin-derived red emission carbon dots: A multifunctional theranostic nano-agent against Alzheimer's ß-amyloid fibrillogenesis.

Multifunctional agents with therapeutic and diagnostic capabilities are imperative to the prevention of Alzheimer's disease (AD), which is considered due to abnormal aggregation and deposition of ß-amyloid protein (Aß) as well as oxidative stress. Herein, quercetin (Que)- and p-phenylenediamine (p-PD)-derived red emission carbon dots (CDs) synthesized via a one-step hydrothermal method were designed as a novel theranostic nano-agent for the multi-target treatment of AD. R-CD-75 with an optimized composition exhibited significant inhibition of Aß aggregation and rapid depolymerization of mature Aß fibrils (<4 h) at micromolar concentrations (2 and 5 µg/mL, respectively). Moreover, R-CD-75 potently scavenged reactive oxygen species and showed turned-on red fluorescence imaging of Aß plaques both in vitro and in vivo. In vitro assays proved that R-CD-75 significantly mitigated the Aß-induced cytotoxicity and enhanced the cultured cell viability from 74.9 % to 98.0 %, while in vivo studies demonstrated that R-CD-75 prolonged the lifespan of AD nematodes by over 50 % (from 13 to 20 d). Compared to the precursors Que and p-PD, R-CD-75 inherited some of their structures and functional groups, such as aromatic structures, phenolic hydroxyl and amino groups, which were considered to interact with Aß species through hydrogen bonding, electrostatic interactions, hydrophobic interactions, and π-π stacking, thus contributing to its effectiveness in its theranostic functions. This research has opened a new avenue to the development of potent theranostic agents by designing novel carbon dots.

A turn for the worse: Aß ß-hairpins in Alzheimer's disease.

Amyloid-ß (Aß) oligomers are a cause of neurodegeneration in Alzheimer's disease (AD). These soluble aggregates of the Aß peptide have proven difficult to study due to their inherent metastability and heterogeneity. Strategies to isolate and stabilize homogenous Aß oligomer populations have emerged such as mutations, covalent cross-linking, and protein fusions. These strategies along with molecular dynamics simulations have provided a variety of proposed structures of Aß oligomers, many of which consist of molecules of Aß in ß-hairpin conformations. ß-Hairpins are intramolecular antiparallel ß-sheets composed of two ß-strands connected by a loop or turn. Three decades of research suggests that Aß peptides form several different ß-hairpin conformations, some of which are building blocks of toxic Aß oligomers. The insights from these studies are currently being used to design anti-Aß antibodies and vaccines to treat AD. Research suggests that antibody therapies designed to target oligomeric Aß may be more successful at treating AD than antibodies designed to target linear epitopes of Aß or fibrillar Aß. Aß ß-hairpins are good epitopes to use in antibody development to selectively target oligomeric Aß. This review summarizes the research on ß-hairpins in Aß peptides and discusses the relevance of this conformation in AD pathogenesis and drug development.

Chemical constituents from stipes of Lentinus edodes and their protective effects against Aß25-35-induced N9 microglia cells injury.

Nine undescribed compounds, along with eight known compounds, were isolated from the stipes of Lentinus edodes. Their structures were established by extensive spectroscopic and circular dichroism analyses. The protective effects against Aß25-35-induced N9 microglia cells injury of these compounds were tested by MTT method, and the levels of apoptosis and ROS were detected by flow cytometry. In addition, the binding sites and interactions of compound with amyloid precursor protein were revealed using molecular docking simulations. These findings further establish the structural diversity and bioactivity of stipes of L. edodes, and provide an experimental basis for targeting Alzheimer's disease as a potential strategy.

Design, synthesis, and biological evaluation of some 2-(3-oxo-5,6-diphenyl-1,2,4-triazin-2(3H)-yl)-N-phenylacetamide hybrids as MTDLs for Alzheimer's disease therapy.

Inspite of established symptomatic relief drug targets, a multi targeting approach is highly in demand to cure Alzheimer's disease (AD). Simultaneous inhibition of cholinesterase (ChE), ß secretase-1 (BACE-1) and Dyrk1A could be promising in complete cure of AD. A series of 18 diaryl triazine based molecular hybrids were successfully designed, synthesized, and tested for their hChE, hBACE-1, Dyrk1A and Aß aggregation inhibitory potentials. Compounds S-11 and S-12 were the representative molecules amongst the series with multi-targeted inhibitory effects. Compound S-12 showed hAChE inhibition (IC50 value = 0.486 ± 0.047 µM), BACE-1 inhibition (IC50 value = 0.542 ± 0.099 µM) along with good anti-Aß aggregation effects in thioflavin-T assay. Only compound S-02 of the series has shown Dyrk1A inhibition (IC50 value = 2.000 ± 0.360 µM). Compound S-12 has also demonstrated no neurotoxic liabilities against SH-SY5Y as compared to donepezil. The in vivo behavioral studies of the compound S-12 in the scopolamine- and Aß-induced animal models also demonstrated attanuation of learning and memory functions in rats models having AD-like characteristics. The ex vivo studies, on the rat hippocampal brain demonstrated reduction in certain biochemical markers of the AD brain with a significant increase in ACh level. The Western blot and Immunohistochemistry further revealed lower tau, APP and BACE-1 molecular levels. The drosophilla AD model also revealed improved eyephenotype after treatment with compound S-12. The molecular docking studies of the compounds suggested that compound S-12 was interacting with the ChE-PAS & CAS residues and catalytic dyad residues of the BACE-1 enzymes. The 100 ns molecular dynamics simulation studies of the ligand-protein complexed with hAChE and hBACE-1 also suggested stable ligand-protein confirmation throughout the simulation run.

Diosmetin derivatives as multifunctional anti-AD ligands: Design, synthesis, and biological evaluation.

With the increasing aging population, rational design of drugs for Alzheimer's disease (AD) treatment has become an important research area. Based on the multifunctional design strategy, four diosmetin derivatives (1-4) were designed, synthesized, and characterized by 1H NMR, 13C NMR, and MS. Docking study was firstly applied to substantiate the design strategies and then the biological activities including cholinesterase inhibition, metal chelation, antioxidation and ß-amyloid (Aß) aggregation inhibition in vitro were evaluated. The results showed that 1-4 had good acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibition, metal chelation (selective chelation of Cu2+ ions), antioxidation, self-induced, Cu2+-induced, and AChE-induced Aß aggregation inhibition activities, and suitable blood-brain barrier (BBB) permeability. Especially, compound 3 had the strongest inhibitory effect on AChE (10-8 M magnitude) and BuChE (10-7 M magnitude) and showed the best inhibition on AChE-induced Aß aggregation with 66.14% inhibition ratio. Furthermore, compound 3 could also reduce intracellular reactive oxygen species (ROS) levels in Caenorhabditis elegans and had lower cytotoxicity. In summary, 3 might be considered as a potential multifunctional anti-AD ligand.

Design, synthesis, and evaluation of dual-target inhibitors for the treatment of Alzheimer's disease.

Aß1-42 and acetylcholinesterase (AChE) are two key therapeutic targets for Alzheimer's disease (AD). The purpose of this study is to develop a dual-target inhibitor that inhibits both of these targets by fusing the chemical structure of baicalein and donepezil. Among them, we modified the structure of baicalein to arylcoumarin, synthesized three kinds of structural compounds, and evaluated their biological activities. The results showed that compound 3b had the strongest inhibitory effect on AChE (IC50 = 0.05 ± 0.02 µM), which was better than those of donepezil and baicalein. In addition, compound 3b has a strong ability to inhibit the aggregation of Aß1-42 and protect nerve cells, and it can also penetrate the blood-brain barrier well. Using a zebrafish behavioral analyzer test, it was found that compound 3b can alleviate the behavioral effects of AlCl3-induced zebrafish larval movement retardation, which has a certain guiding significance for simulating the movement disorders of AD patients. In summary, compound 3b is expected to become a multifunctional agent for treating and alleviating the symptoms of AD patients.

Design, synthesis, and activity evaluation of novel multitargeted l-tryptophan derivatives with powerful antioxidant activity against Alzheimer's disease.

Alzheimer's disease (AD) is a multifactorial neurological disease, and the multitarget directed ligand (MTDL) strategy may be an effective approach to delay its progression. Based on this strategy, 27 derivatives of l-tryptophan, 3a-1-3d-1, were designed, synthesized, and evaluated for their biological activity. Among them, IC50 (inhibitor concentration resulting in 50% inhibitory activity) values of compounds 3a-18 and 3b-1 were 0.58 and 0.44 µM for human serum butyrylcholinesterase (hBuChE), respectively, and both of them exhibited more than 30-fold selectivity for human serum acetylcholinesterase. Enzyme kinetics studies showed that these two compounds were mixed inhibitors of hBuChE. In addition, these two derivatives possessed extraordinary antioxidant activity in OH radical scavenging and oxygen radical absorption capacity fluorescein assays. Meanwhile, these compounds could also prevent ß-amyloid (Aß) self-aggregation and possessed low toxicity on PC12 and AML12 cells. Molecular modeling studies revealed that these two compounds could interact with the choline binding site, acetyl binding site, and peripheral anionic site to exert submicromolar BuChE inhibitory activity. In the vitro blood-brain barrier permeation assay, compounds 3a-18 and 3b-1 showed enough blood-brain barrier permeability. In drug-likeness prediction, compounds 3a-18 and 3b-1 showed good gastrointestinal absorption and a low risk of human ether-a-go-go-related gene toxicity. Therefore, compounds 3a-18 and 3b-1 are potential multitarget anti-AD lead compounds, which could work as powerful antioxidants with submicromolar selective inhibitory activity for hBuChE as well as prevent Aß self-aggregation.

Screening for Novel Inhibitors of Amyloid Beta Aggregation and Toxicity as Potential Drugs for Alzheimer's Disease.

AD is the most common neurodegenerative disorder characterized by progressive memory impairment and cognitive deficits. The pathology of AD is still unclear; however, several studies have shown that the aggregation of the Aß peptide in the CNS is an exclusively pathological process involved in AD. Currently, there is no proven medication to cure or prevent the disease progression. Nevertheless, various therapeutic approaches for AD show only relief of symptoms and mostly work on cognitive recovery. However, one of the promising approaches for therapeutic intervention is to use inhibitors for blocking the Aß peptide aggregation process. Recently, herbal phenolic compounds have been shown to have a therapeutic property for treatment of AD due to their multifaceted action. In this study, we investigated the effectiveness of SA, Gn Rb1, and DMyr on inhibiting the aggregation and toxicity of Aß40 and Aß42 using different biochemical and cell-based assays. Our results showed that SA and DMyr inhibit Aß40 and Aß42 fibrillation, seeded aggregation, and toxicity. Gn Rb1 did not have any effect on the aggregation or toxicity induced by Aß40 and Aß42. Moreover, SA and DMyr were able to disaggregate the preformed fibrils. Overall, these compounds may be used alone or synergistically and could be considered as a lead for designing new compounds that could be used as effective treatment of AD and related disorders.

Catalpol rescues cognitive deficits by attenuating amyloid ß plaques and neuroinflammation.

This study sought to investigate the anti-amyloid ß (Aß) and anti-neuroinflammatory effects of catalpol in an Alzheimer's disease (AD) mouse model. METHODS: The effects of catalpol on Aß formation were investigated by thioflavin T assay. The effect of catalpol on generating inflammatory cytokines from microglial cells and the cytotoxicity of microglial cells on HT22 hippocampal cells were assessed by real-time quantitative PCR, ELISA, redox reactions, and cell viability. APPswe/PS1ΔE9 mice were treated with catalpol, and their cognitive ability was investigated using the water maze and novel object recognition tests. Immunohistochemistry and immunofluorescence were used to probe for protein markers of microglia and astrocyte, Aß deposits, and NF-κB pathway activity. Aß peptides, neuroinflammation, and nitric oxide production were examined using ELISA and redox reactions. RESULTS: Catalpol potently inhibited Aß fibril and oligomer formation. In microglial cells stimulated by Aß, catalpol alleviated the expression of the proinflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and inducible nitric oxide synthase (iNOS) but promoted the expression of the anti-inflammatory cytokine IL-10. Catalpol alleviated the cytotoxic effects of Aß-exposed microglia on HT22 cells. Treatment with catalpol in APPswe/PS1ΔE9 mice downregulated neuroinflammation production, decreased Aß deposits in the brains and alleviated cognitive impairment. Catalpol treatment decreased the number of IBA-positive microglia and GFAP-positive astrocytes and their activities of the NF-κB pathway in the hippocampus of APPswe/PS1ΔE9 mice. CONCLUSION: The administration of catalpol protected neurons by preventing neuroinflammation and Aß deposits in an AD mouse model. Therefore, catalpol may be a promising strategy for treating AD.

Three new meroterpenoids from Sargassum macrocarpum and their inhibitory activity against amyloid ß aggregation.

Amyloid ß (Aß) is thought to be involved in the pathogenesis of Alzheimer's disease (AD). Aß aggregation in the brain is considered the cause of AD. Therefore, inhibiting Aß aggregation and degrading existing Aß aggregates is a promising approach for the treatment and prevention of the disease. In searching for inhibitors of Aß42 aggregation, we found that meroterpenoids isolated from Sargassum macrocarpum possess potent inhibitory activities. Therefore, we searched for active compounds from this brown alga and isolated 16 meroterpenoids, which contain three new compounds. The structures of these new compounds were elucidated using two-dimensional nuclear magnetic resonance techniques. Thioflavin-T assay and transmission electron microscopy were used to reveal the inhibitory activity of these compounds against Aß42 aggregation. All the isolated meroterpenoids were found to be active, and compounds with a hydroquinone structure tended to have stronger activity than those with a quinone structure.

Aza-Residue Modulation of Cyclic d,l-α-Peptide Nanotube Assembly with Enhanced Anti-Amyloidogenic Activity.

Transient soluble oligomers of amyloid-ß (Aß) are considered among the most toxic species in Alzheimer's disease (AD). Soluble Aß oligomers accumulate early prior to insoluble plaque formation and cognitive impairment. The cyclic d,l-α-peptide CP-2 (1) self-assembles into nanotubes and demonstrates promising anti-amyloidogenic activity likely by a mechanism involving engagement of soluble oligomers. Systematic replacement of the residues in peptide 1 with aza-amino acid counterparts was performed to explore the effects of hydrogen bonding on propensity to mitigate Aß aggregation and toxicity. Certain azapeptides exhibited improved ability to engage, alter the secondary structure, and inhibit aggregation of Aß. Moreover, certain azapeptides disassembled preformed Aß fibrils and protected cells from Aß-mediated toxicity. Substitution of the l-norleucine3 and d-serine6 residues in peptide 1 with aza-norleucine and aza-homoserine provided, respectively, nontoxic [azaNle3]-1 (4) and [azaHse6]-1 (7), that significantly abated symptoms in a transgenic Caenorhabditis elegans AD model by decreasing Aß oligomer levels.

De novo designed protein inhibitors of amyloid aggregation and seeding.

Neurodegenerative diseases are characterized by the pathologic accumulation of aggregated proteins. Known as amyloid, these fibrillar aggregates include proteins such as tau and amyloid-ß (Aß) in Alzheimer's disease (AD) and alpha-synuclein (αSyn) in Parkinson's disease (PD). The development and spread of amyloid fibrils within the brain correlates with disease onset and progression, and inhibiting amyloid formation is a possible route toward therapeutic development. Recent advances have enabled the determination of amyloid fibril structures to atomic-level resolution, improving the possibility of structure-based inhibitor design. In this work, we use these amyloid structures to design inhibitors that bind to the ends of fibrils, "capping" them so as to prevent further growth. Using de novo protein design, we develop a library of miniprotein inhibitors of 35 to 48 residues that target the amyloid structures of tau, Aß, and αSyn. Biophysical characterization of top in silico designed inhibitors shows they form stable folds, have no sequence similarity to naturally occurring proteins, and specifically prevent the aggregation of their targeted amyloid-prone proteins in vitro. The inhibitors also prevent the seeded aggregation and toxicity of fibrils in cells. In vivo evaluation reveals their ability to reduce aggregation and rescue motor deficits in Caenorhabditis elegans models of PD and AD.

Decreasing pdzd8-mediated mito-ER contacts improves organismal fitness and mitigates Aß42 toxicity.

Mitochondria-ER contact sites (MERCs) orchestrate many important cellular functions including regulating mitochondrial quality control through mitophagy and mediating mitochondrial calcium uptake. Here, we identify and functionally characterize the Drosophila ortholog of the recently identified mammalian MERC protein, Pdzd8. We find that reducing pdzd8-mediated MERCs in neurons slows age-associated decline in locomotor activity and increases lifespan in Drosophila. The protective effects of pdzd8 knockdown in neurons correlate with an increase in mitophagy, suggesting that increased mitochondrial turnover may support healthy aging of neurons. In contrast, increasing MERCs by expressing a constitutive, synthetic ER-mitochondria tether disrupts mitochondrial transport and synapse formation, accelerates age-related decline in locomotion, and reduces lifespan. Although depletion of pdzd8 prolongs the survival of flies fed with mitochondrial toxins, it is also sufficient to rescue locomotor defects of a fly model of Alzheimer's disease expressing Amyloid ß42 (Aß42). Together, our results provide the first in vivo evidence that MERCs mediated by the tethering protein pdzd8 play a critical role in the regulation of mitochondrial quality control and neuronal homeostasis.

Activation of the sigma-1 receptor attenuates blood-brain barrier disruption by inhibiting amyloid deposition in Alzheimer's disease mice.

The sigma-1 receptor is an important target for drug development in several neuropsychiatric diseases, including Alzheimer's disease (AD). Accumulating evidence has shown that the integrity and functional activity of the blood-brain barrier (BBB) in AD are impaired, which is closely related to the movement of amyloid beta (Aß) across the BBB and the formation of Aß plaques. In this study, we investigated the effects of sigma-1 receptor activation on BBB disruption and Aß levels in AD mice. We found that PRE-084, a sigma-1 receptor agonist, attenuated learning and memory deficits in Aß-injected mice, significantly increased levels of low-density lipoprotein receptor-related protein 1 (LRP-1), and lowered the Aß level synergistically in the brain. Moreover, the upregulation of vascular endothelial growth factor (VEGF) levels through the sigma-1 receptor may be involved in the reduction of the BBB permeability by PRE-084. The identification of this previously unexplored role of the sigma-1 receptor in alleviating BBB disruption via upregulating the levels of VEGF and LRP-1 in AD suggests that reversing BBB dysfunction through sigma-1 receptor activation may be a promising treatment for AD.

Development of naringenin-O-alkylamine derivatives as multifunctional agents for the treatment of Alzheimer's disease.

In this study, a series of naringenin-O-alkylamine derivatives were designed and obtained by introducing an alkylamine fragment into the naringenin skeleton. The in vitro biological activity results revealed that compounds 5f and 7k showed good antioxidant activity with ORAC values of 2.3eq and 1.2eq, respectively. Compounds 5f and 7k were reversible and excellent huAChE inhibitors with IC50 values of 0.91 µM and 0.57 µM, respectively. Moreover, compounds 5f and 7k could inhibit self-induced Aß1-42 aggregation with 62.1% and 43.8% inhibition rate, respectively, and significantly inhibited huAChE-Aß1-40 aggregation with 51.7% and 43.4% inhibition rate, respectively. In addition, compounds 5f and 7k were selective metal chelators and remarkably inhibited Cu2+-induced Aß1-42 aggregation with 73.5% and 68.7% inhibition rates, respectively. Furthermore, compounds 5f and 7k could cross the blood-brain barrier in vitro and displayed good neuroprotective effects and anti-inflammatory properties. Further investigation showed that compound 5f did not show obvious hepatotoxicity and displayed a good hepatoprotective effect by its antioxidant activity. The in vivo study displayed that compound 5f significantly improved scopolamine-induced mice memory impairment. Therefore, compound 5f was a potential multifunctional candidate for the treatment of AD.

A Dual-Pronged Approach: A Ruthenium(III) Complex That Modulates Amyloid-ß Aggregation and Disrupts Its Formed Aggregates.

Alzheimer's disease (AD) is a devastating neurological disorder for which soluble oligomers of the peptide amyloid-ß (Aß) are now recognized as the neurotoxic species. Metal-based therapeutics are uniquely suited to target Aß, with ruthenium-based (Ru) complexes emerging as propitious candidates. Recently, azole-based Ru(III) complexes were observed to modulate the aggregation of Aß in solution, where the inclusion of a primary amine proximal to the ligand coordination site improved the activity of the complexes. To advance these structure-activity relationships, a series of oxazole-based Ru complexes were prepared and evaluated for their ability to modulate Aß aggregation. From these studies, a lead candidate, Oc, emerged that had superior activity relative to its azole predecessors in modulating the aggregation of soluble Aß and diminishing its cytotoxicity. Further evaluation of Oc demonstrated its ability to disrupt formed Aß aggregates, resulting in smaller amorphous species. Because altering both sides of the aggregation equilibrium for Aß has not been previously suggested for metal-based complexes for AD, this work represents an exciting new avenue for improved therapeutic success.