Discovery of multifunctional anti-Alzheimer's agents with a unique mechanism of action including inhibition of the enzyme butyrylcholinesterase and γ-aminobutyric acid transporters

Looking for an effective anti-Alzheimer's agent is very challenging; however, a multifunctional ligand strategy may be a promising solution for the treatment of this complex disease. We herein present the design, synthesis and biological evaluation of novel hydroxyethylamine derivatives displaying unique, multiple properties that have not been previously reported. The original mechanism of action combines inhibitory activity against disease-modifying targets: β-secretase enzyme (BACE1) and amyloid β (Aβ) aggregation, along with an effect on targets associated with symptom relief - inhibition of butyrylcholinesterase (BuChE) and γ-aminobutyric acid transporters (GATs). Among the obtained molecules, compound 36 exhibited the most balanced and broad activity profile (eeAChE IC₅₀ = 2.86 μM; eqBuChE IC₅₀ = 60 nM; hBuChE IC₅₀ = 20 nM; hBACE1 IC₅₀ = 5.9 μM; inhibition of Aβ aggregation = 57.9% at 10 μM; mGAT1 IC₅₀ = 10.96 μM; and mGAT2 IC₅₀ = 19.05 μM). Moreover, we also identified 31 as the most potent mGAT4 and hGAT3 inhibitor (IC₅₀ = 5.01 μM and IC₅₀ = 2.95 μM, respectively), with high selectivity over other subtypes. Compounds 36 and 31 represent new anti-Alzheimer agents that can ameliorate cognitive decline and modify the progress of disease.

Novel Donepezil-Arylsulfonamide Hybrids as Multitarget-Directed Ligands for Potential Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is one of the most devastating neurodegenerative disorders, characterized by multiple pathological features. Therefore, multi-target drug discovery has been one of the most active fields searching for new effective anti-AD therapies. Herein, a series of hybrid compounds are reported which were designed and developed by combining an aryl-sulfonamide function with a benzyl-piperidine moiety, the pharmacophore of donepezil (a current anti-AD acetylcholinesterase AChE inhibitor drug) or its benzyl-piperazine analogue. The in vitro results indicate that some of these hybrids achieve optimized activity towards two main AD targets, by displaying excellent AChE inhibitory potencies, as well as the capability to prevent amyloid-β (Aβ) aggregation. Some of these hybrids also prevented Aβ-induced cell toxicity. Significantly, drug-like properties were predicted, including for blood-brain permeability. Compound 9 emerged as a promising multi-target lead compound (AChE inhibition (IC₅₀ 1.6 μM); Aβ aggregation inhibition 60.7%). Overall, this family of hybrids is worthy of further exploration, due to the wide biological activity of sulfonamides.

Recent Multi-Target Approaches on the Development of Anti-Alzheimer`s Agents Integrating Metal Chelation Activity

Alzheimer´s disease (AD) is the most common and severe age-dependent neurodegenerative disorder, worldwide. Notwithstanding the large amount of research dedicated to both the elucidation of this pathology and the development of an effective drug, the multifaceted nature and complexity of the disease are certainly a rationale for the absence of cure so far. Current available drugs are used, mainly, to compensate the decline of the neurotransmitter acetylcholine by acetylcholinesterase (AChE) inhibition, though they only provide temporary symptomatic benefits and cannot stop AD progression. Although the multiple factors that contribute to trigger AD onset and progression are not yet fully understood, several pathological features and underneath pathways have been recognized to contribute to its pathology, such as metal dyshomeostasis, protein misfolding, oxidative stress and neurotransmitter deficiencies, some of them being interconnected. Thus, there is a widespread recent interest in the development of multitarget-directed ligands (MTDLs) for simultaneous interaction with several pathological targets of AD. In this review, a selection of the most recent reports (2016-up to present) on metal chelators of MTDLs with multifunctionalities is presented. These compounds enable the hitting of several AD targets or pathways, such as modulation of specific biometal ions (e.g. Cu, Fe, Zn) and of protein misfolding (β-amyloid and tau protein), anti-oxidant activity and AChE inhibition. The properties found for these hybrids are discussed in comparison with the original reference compounds, some MTDLs being outlined as leading compounds for pursuing future studies in view of efficient potential applications in AD therapy.

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

Alzheimer's disease (AD) is one of the most common types of dementia, especially in elderly, with an increasing number of people suffering from this disease worldwide. There are no available disease-modifying therapies and only four drugs are approved for the relief of symptoms. Currently, the therapeutic approach used for AD treatment is based on single target drugs, which are not capable to stop its progression. To address this issue, multi-target compounds, combining two or more pharmacophores in a single molecular entity, have gained increasing interest to deal with the multiple factors related to AD. The exact cause of AD is not yet completely disclosed, and several hallmarks have been associated to this neurodegenerative disease. Even though, the accumulation of both amyloid-β plaques (Aβ) and neurofibrillary tangles (NFTs) are fully accepted as the main AD hallmarks, being object of lots of research for early-stage diagnosis and pharmacological therapy. In this context, this review summarizes the state-of-the-art in the field of dual-target inhibitors of both Aβ and tau aggregation simultaneously, including the design and synthetic strategy of the dual-target compounds, as well as a brief structure-activity relationships (SAR) analysis.

Natural Products as Potential Anti-Alzheimer Agents

Medicinal plants have curative properties due to the presence of various complex chemical substances of different composition, which are found as secondary metabolites in one or more parts of the plant. The diverse secondary metabolites play an important role in the prevention and cure of various diseases including neurodegenerative diseases like Alzheimer's disease. Naturally occurring compounds such as flavonoids, polyphenols, alkaloids, and glycosides found in various parts of the plant and/or marine sources may potentially protect neurodegeneration as well as improve memory and cognitive function. Many natural compounds show anti-Alzheimer activity through specific pharmacological mechanisms like targeting β-amyloid, Beta-secretase 1 and Acetylcholinesterase. In this review, we have compiled more than 130 natural products with a broad diversity in the class of compounds, which were isolated from different sources showing anti- Alzheimer properties.

Structural and mechanistic insights into the inhibition of amyloid-β aggregation by Aβ39-42 fragment derived synthetic peptides

The inhibition of amyloid-β (Aβ) aggregation is a promising approach towards therapeutic intervention for Alzheimer's disease (AD). Thirty eight tetrapeptides based upon Aβ_39-42C-terminus fragment of the parent Aβ peptide were synthesized. The sequential replacement/modification employing unnatural amino acids imparted scaffold diversity, augmented activity, enhanced blood brain barrier permeability and offered proteolytic stability to the synthetic peptides. Several peptides exhibited promising protection against Aβ aggregation-mediated-neurotoxicity in PC-12 cells at doses ranged between 10 μM and 0.1 μM, further confirmed by the thioflavin-T fluorescence assay. CD study illustrate that these peptides restrict the β-sheet formation, and the non-appearance of Aβ₄₂ fibrillar structures in the electron microscopy confirm the inhibition of Aβ₄₂ aggregation. HRMS and ANS fluorescence spectroscopic analysis provided additional mechanistic insights. Two selected lead peptides 5 and 16 depicted enhanced blood-brain penetration and stability against serum and proteolytic enzyme. Structural insights into ligand-Aβ interactions on the monomeric and proto-fibrillar units of Aβ were computationally studied. Promising inhibitory potential and short sequence of the lead peptides offers new avenues for the advancement of peptide-derived therapeutics for AD.

Further Studies on Triazinoindoles as Potential Novel Multitarget-Directed Anti-Alzheimer's Agents

The inadequate clinical efficacy of the present anti-Alzheimer's disease (AD) drugs and their low impact on the progression of Alzheimer's disease in patients have revised the research focus from single targets to multitarget-directed ligands. A novel series of substituted triazinoindole derivatives were obtained by introducing various substituents on the indole ring for the development of multitarget-directed ligands as anti-AD agents. The experimental data indicated that some of these compounds exhibited significant anti-AD properties. Among them, 8-(piperidin-1-yl)-N-(6-(pyrrolidin-1-yl)hexyl)-5H-[1,2,4]triazino[5,6-b]indol-3-amine (60), the most potent cholinesterase inhibitor (AChE, IC₅₀ value of 0.32 μM; BuChE, IC₅₀ value of 0.21 μM), was also found to possess significant self-mediated Aβ_1-42 aggregation inhibitory activity (54% at 25 μM concentration). Additionally, compound 60 showed strong antioxidant activity. In the PAMPA assay, compound 60 exhibited blood-brain barrier penetrating ability. An acute toxicity study in rats demonstrated no sign of toxicity at doses up to 2000 mg/kg. Furthermore, compound 60 significantly restored the cognitive deficits in the scopolamine-induced mice model and Aβ_1-42-induced rat model. In the in silico ADMET prediction studies, the compound satisfied all the parameters of CNS acting drugs. These results highlighted the potential of compound 60 to be a promising multitarget-directed ligand for the development of potential anti-AD drugs.

Design and synthesis of multi-target directed 1,2,3-triazole-dimethylaminoacryloyl-chromenone derivatives with potential use in Alzheimer's disease

To discover multifunctional agents for the treatment of Alzheimer's disease (AD), a new series of 1,2,3-triazole-chromenone derivatives were designed and synthesized based on the multi target-directed ligands approach. The in vitro biological activities included acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibition as well as anti-Aβ aggregation, neuroprotective effects, and metal-chelating properties. The results indicated a highly selective BuChE inhibitory activity with an IC₅₀ value of 21.71 μM for compound 10h as the most potent compound. Besides, compound 10h could inhibit self-induced Aβ_1–42 aggregation and AChE-induced Aβ aggregation with 32.6% and 29.4% inhibition values, respectively. The Lineweaver–Burk plot and molecular modeling study showed that compound 10h targeted both the catalytic active site (CAS) and peripheral anionic site (PAS) of BuChE. It should be noted that compound 10h was able to chelate biometals. Thus, the designed scaffold could be considered as multifunctional agents in AD drug discovery developments.

The Role of Apolipoprotein E Isoforms in Alzheimer's Disease

Alzheimer's disease (AD), the most common type of dementia worldwide, is characterized by high levels of amyloid-β (Aβ) peptide and hyperphosphorylated tau protein. Genetically, the ɛ4 allele of apolipoprotein E (ApoE) has been established as the major risk factor for developing late-onset AD (LOAD), the most common form of the disease. Although the role ApoE plays in AD is still not completely understood, a differential role of its isoforms has long been known. The current review compiles the involvement of ApoE isoforms in amyloid-β protein precursor transcription, Aβ aggregation and clearance, synaptic plasticity, neuroinflammation, lipid metabolism, mitochondrial function, and tau hyperphosphorylation. Due to the complexity of LOAD, an accurate description of the interdependence among all the related molecular mechanisms involved in the disease is needed for developing successful therapies.

Novel carbazole-stilbene hybrids as multifunctional anti-Alzheimer agents

Molecules capable of engaging with multiple targets associated with pathological condition of Alzheimer's disease have proved to be potential anti-Alzheimer's agents. In our goal to develop multitarget-directed ligands for the treatment of Alzheimer's disease, a novel series of carbazole-based stilbene derivatives were designed by the fusion of carbazole ring with stilbene scaffold. The designed compounds were synthesized and evaluated for their anti-AD activities including cholinesterase inhibition, Aβ aggregation inhibition, antioxidant and metal chelation properties. Amongst them, (E)-1-(4-(2-(9-ethyl-9H-carbazol-3-yl)vinyl)phenyl)-3-(2-(pyrrolidin-1-yl)ethyl)thiourea (50) appeared to be the best candidate with good inhibitory activities against AChE (IC₅₀ value of 2.64 μM) and BuChE (IC₅₀ value of 1.29 μM), and significant inhibition of self-mediated Aβ_1-42 aggregation (51.29% at 25 μM concentration). The metal chelation study showed that compound (50) possessed specific copper ion chelating property. Additionally, compound (50) exhibited moderate antioxidant activity. To understand the binding mode of 50, molecular docking studies were performed, and the results indicated strong non-covalent interactions of 50 with the enzymes in the active sites of AChE, BuChE as well as of the Aβ_1-42 peptide. Additionally, it showed promising in silico ADMET properties. Putting together, these findings evidently showed compound (50) as a potential multitarget-directed ligand in the course of developing novel anti-AD drugs.

Anti-β-amyloid aggregation activity of enantiomeric furolactone-type lignans from Archidendron clypearia (Jack) I.C.N

The phytochemical investigation on the twigs and leaves of Archidendron clypearia (Jack) I.C.N. led to the isolation of three pairs of furolactone-type lignans enantiomers, including a pair of new compounds (1R,5S,6S)-Kachiranol (1a) and (1S,5R,6R)-Kachiranol (1b) and four known compounds (2a/2b and 3a/3b). Separation of the furolactone-type lignans enantiomeric mixtures was achieved using chiral HPLC for the first time. Their structures were determined by spectroscopic analysis and comparison between the experimental and calculated electronic circular dichroism (ECD) spectra. All optical pure compounds were evaluated for their inhibitory effects on β-amyloid aggregation by ThT assay. Among them, the inhibitory activity of the compound 1b (71.1%) was higher than the positive control (61.0%) and other compounds. In addition, molecular dynamics and molecular docking were employed to explore the binding relationship between the ligand and the receptor.

Osmolytes: A Possible Therapeutic Molecule for Ameliorating the Neurodegeneration Caused by Protein Misfolding and Aggregation

Most of the neurological disorders in the brain are caused by the abnormal buildup of misfolded or aggregated proteins. Osmolytes are low molecular weight organic molecules usually built up in tissues at a quite high amount during stress or any pathological condition. These molecules help in providing stability to the aggregated proteins and protect these proteins from misfolding. Alzheimer’s disease (AD) is the uttermost universal neurological disorder that can be described by the deposition of neurofibrillary tangles, aggregated/misfolded protein produced by the amyloid β-protein (Aβ). Osmolytes provide stability to the folded, functional form of a protein and alter the folding balance away from aggregation and/or degradation of the protein. Moreover, they are identified as chemical chaperones. Brain osmolytes enhance the pace of Aβ aggregation, combine with the nearby water molecules more promptly, and avert the aggregation/misfolding of proteins by providing stability to them. Therefore, osmolytes can be employed as therapeutic targets and may assist in potential drug design for many neurodegenerative and other diseases.

Dengzhan Shengmai capsules and their active component scutellarin prevent cognitive decline in APP/PS1 mice by accelerating Aβ aggregation and reducing oligomers formation

There is currently no effective treatment to prevent the progress of Alzheimer's disease (AD). The traditional Chinese herbs Dengzhan Shengmai (DZSM) capsules and their active component scutellarin possess multiple effects and are clinically used for the treatment of cerebrovascular diseases. Scutellarin has been reported to affect Aβ aggregation. However, the effects of DZSM capsules on AD remain unknown. Through in vivo experiments, our study proved that the alleviating effects of DZSM capsules on cognitive deficits of AD mice were due to the role of scutellarin, which up-regulated low toxic amyloid plaques and down-regulated highly toxic soluble Aβ42 and Aβ40 levels in cortex. In vitro, we confirmed scutellarin's role in accelerating transforming Aβ42 monomers into high-molecular-mass aggregates by biochemical assays, which supported the results observed in drug-treated APP/PS1 mice. In detail, the 1:10 ratio of scutellarin/Aβ42 mixtures promoted production of large β-sheet-rich fibrils whereas the 1:1 ratio promoted production of protofibrils. In addition, the binding between scutellarin and Aβ monomers was quantified by microscale thermophoresis test and the apparent dissociation constant (Kd) was 1284.4 ± 238.8 μM. What's more, binding regions between scutellarin and Aβ fibrils were predicted by computational docking models and scutellarin might bind parallel to the long axis of Aβ42 fibrils targeting hydrophobic grooves at residues 35-36 or 39. In conclusion, DZSM capsules protected against cognitive defects of AD through scutellarin-mediated acceleration of Aβ aggregation into fibrils or protofibrils and reduction of soluble Aβ oligomers, thus suggesting potential clinical applications of DZSM capsules and scutellarin in the treatment of AD.

1-Benzylpyrrolidine-3-amine-based BuChE inhibitors with anti-aggregating, antioxidant and metal-chelating properties as multifunctional agents against Alzheimer's disease

Complex pathomechanism of Alzheimer's disease (AD) prompts researchers to develop multifunctional molecules in order to find effective therapy against AD. We designed and synthesized novel multifunctional ligands for which we assessed their activities towards butyrylcholinesterase, beta secretase, amyloid beta (Aβ) and tau protein aggregation as well as antioxidant and metal-chelating properties. All compounds showed dual anti-aggregating properties towards Aβ and tau protein in the in cellulo assay in Escherichia coli. Of particular interest are compounds 24b and 25b, which efficiently inhibit aggregation of Aβ and tau protein at 10 μM (24b: 45% for Aβ, 53% for tau; 25b: 49% for Aβ, 54% for tau). They display free radical scavenging capacity and antioxidant activity in ABTS and FRAP assays, respectively, and selectively chelate copper ions. Compounds 24b and 25b are also the most potent inhibitors of BuChE with IC₅₀ of 2.39 μM and 1.94 μM, respectively. Promising in vitro activities of the presented multifunctional ligands as well as their original scaffold are a very interesting starting point for further research towards effective anti-AD treatment.

Triterpenes from Archidendron clypearia (Jack) I.C.N. with anti-β-amyloid aggregation activity

A new triterpene as well as five known compounds were isolated from the twigs and leaves of Archidendron clypearia (Jack) I.C.N. Their structures were established by comprehensive spectroscopic analyses including 1D, 2D NMR and HRESIMS data. The ability of all isolated compounds to inhibit β-amyloid aggregation was investigated by a ThT-based fluorometric assay. Among them, compounds 3 (67.8%) and 6 (77.7%) exhibited higher inhibitory activity than the positive (48.0%). In addition, molecular dynamics and molecular docking have been utilized to predict the detailed binding interaction between ligands and Aβ_1-42.

Ginkgo biloba attenuates aluminum lactate-induced neurotoxicity in reproductive senescent female rats: behavioral, biochemical, and histopathological study

Extensive use of aluminum (Al) in industry, cooking utensils, and wrapping or freezing the food items, due to its cheapness and abundance in the environment, has become a major concern. Growing evidence supports that environmental pollutant Al promotes the aggregation of amyloid beta (Aβ) in the brain, which is the main pathological marker of Alzheimer's disease (AD). Further, AD- and Al-induced neurotoxic effects are more common among women following reproductive senescence due to decline in estrogen. Though clinically Ginkgo biloba extract (GBE) has been exploited as a memory enhancer, its role in Al-induced neurotoxicity in reproductive senescent female rats needs to be evaluated. Animals were exposed to intraperitoneal dose (10 mg/kg b.wt) of Al and oral dose (100 mg/kg b.wt.) of GBE daily for 6 weeks. A significant decline in the Al-induced Aβ aggregates was observed in hippocampal and cortical regions of the brain with GBE supplementation, as confirmed by thioflavin (ThT) and Congo red staining. GBE administration significantly decreased the reactive oxygen species, lipid peroxidation, nitric oxide, and citrulline levels in comparison to Al-treated rats. On the contrary, a significant increase in the reduced glutathione, GSH/GSSG ratio as well as in the activities of antioxidant enzymes was observed with GBE administration. Based on the above results, GBE prevented the neuronal loss in the hippocampus and cortex, hence caused significant improvement in the learning and memory of the animals in terms of AChE activity, serotonin levels, Morris water maze, and active and passive avoidance tests. In conclusion, GBE has alleviated the behavioral, biochemical, and histopathological alterations due to Al toxicity in rats. However, molecular studies are going on to better understand the mechanism of GBE protection against the environmental toxicant Al exposure. Graphical abstract .

Supplementation with Curcuma longa Reverses Neurotoxic and Behavioral Damage in Models of Alzheimer's Disease: A Systematic Review

Background:

The formation of senile plaques and neurofibrillary tangles of the tau protein are the main pathological mechanism of Alzheimer’s disease (AD). Current therapies for AD offer discrete benefits to the clinical symptoms and do not prevent the continuing degeneration of neuronal cells. Therefore, novel therapeutic strategies have long been investigated, where curcumin (Curcuma longa) has shown some properties that can prevent the deleterious processes involved in neurodegenerative diseases.

Objective:

The aim of the present work is to review studies that addressed the effects of curcumin in experimental models (in vivo and in vitro) for AD.

Method:

This study is a systematic review conducted between January and June 2017, in which a consultation of scientific articles from indexed periodicals was carried out in Science Direct, United States National Library of Medicine (PubMed), Cochrane Library and Scielo databases, using the following descriptors: “Curcuma longa”, “Curcumin” and “Alzheimer’s disease”.

Results:

A total of 32 studies were analyzed, which indicated that curcumin supplementation reverses neurotoxic and behavioral damages in both in vivo and in vitro models of AD.

Conclusion:

The administration of curcumin in experimental models seems to be a promising approach in AD, even though it is suggested that additional studies must be conducted using distinct doses and through other routes of administration.

Drugs for Targeted Therapies of Alzheimer's Disease

Alzheimer's disease (AD) is one type of neurodegenerative diseases, which is prevalent in the elderly. Beta-amyloid (Aβ) plaques and phosphorylated tau-induced neurofibrillary tangles are two pathological hallmarks of this disease and the corresponding pathological pathways of these hallmarks are considered as the therapeutic targets. There are many drugs scheduled for pre-clinical and clinical trial that target to inhibit the initiators of pathological Aβ and tau aggregates as well as critical Aβ secretases and kinases in tau hyperphosphorylation. In addition, studies in disease gene variations, and detection of key prognostic effectors in early development are also important for AD control. The discovery of potential drug targets contributed to targeted therapy in a stage-dependent manner, However, there are still some issues that cause concern such as the low bioavailability and low efficacy of candidate drugs from clinical trial reports. Therefore, modification of drug candidates and development of delivery agents are essential and critical. With other medical advancements like cell replacement therapy, there is hope for the cure of Alzheimer's disease in the foreseeable future.

Discovery of Neuroregenerative Peptoid from Amphibian Neuropeptide That Inhibits Amyloid-β Toxicity and Crosses Blood-Brain Barrier

Development of potential therapeutics for Alzheimer's disease (AD) requires a multifaceted strategy considering the high levels of complexity of the human brain and its mode of function. Here, we adopted an advanced strategy targeting two key pathological hallmarks of AD: senile plaques and neurofibrillary tangles. We derived a lead short tetrapeptide, Ser-Leu-Lys-Pro (SLKP), from a dodeca-neuropeptide of amphibian (frog) brain. Results suggested that the SLKP peptide had a superior effect compared to the dodecapeptide in neuroprotection. This result encouraged us to adopt peptidomimetic approach to synthesize an SLKP peptoid. Remarkably, we found that the SLKP peptoid is more potent than its peptide analogue, which significantly inhibits Aβ fibrillization, moderately binds with tubulin, and promotes tubulin polymerization as well as stabilization of microtubule networks. Further, we found that SLKP peptoid is stable in serum, shows significant neuroprotection against Aβ mediated toxicity, promotes significant neurite outgrowth, maintains healthy morphology of rat primary cortical neurons and crosses the blood-brain barrier (BBB). To the best of our knowledge, our SLKP peptoid is the first and shortest peptoid to show significant neuroprotection and neuroregeneration against Aβ toxicity, as well as to cross the BBB offering a potential lead for AD therapeutics.

Design and development of novel N-(pyrimidin-2-yl)-1,3,4-oxadiazole hybrids to treat cognitive dysfunctions

Novel hybrids bearing a 2-aminopyrimidine (2-AP) moiety linked to substituted 1,3,4-oxadiazoles were designed, synthesized and biologically evaluated. Among the developed compounds, 28 noncompetitively inhibited human acetylcholinesterase (hAChE; pIC₅₀ = 6.52; Ki = 0.17 µM) and showed potential in vitro antioxidant activity (60.0%) when evaluated using the Ellman's and DPPH assays, respectively. Compound 28 competitively displaced propidium iodide (PI) from the peripheral anionic site (PAS) of hAChE (17.6%) and showed high blood-brain barrier (BBB) permeability, as observed in the PAMPA-BBB assay. Additionally, compound 28 inhibited hAChE-induced Aβ aggregation in a concentration-dependent manner according to the thioflavin T assay and was devoid of neurotoxic liability towards SH-SY5Y cell lines, as demonstrated by the MTT assay. The behavioral studies of compound 28 in mice showed a significant reversal of scopolamine-induced amnesia, as observed in Y-maze and passive avoidance tests. Furthermore, compound 28 exhibited significant AChE inhibition in the brain in ex vivo studies. An evaluation of oxidative stress biomarkers revealed the antioxidant potential of 28. Moreover, in silico molecular docking and dynamics simulation studies were used as a computational tool to evaluate the interactions of compound 28 with the active site residues of hAChE.

New Multitarget Hybrids Bearing Tacrine and Phenylbenzothiazole Motifs as Potential Drug Candidates for Alzheimer's Disease

Research on neurodegenerative brain disorders, namely the age-dependent Alzheimer's disease (AD), has been intensified in the last decade due to the absence of a cure and the recognized increasing of life expectancy for populations. To address the multifactorial nature and complexity of AD, a multi-target-directed ligand approach was herein employed, by designing a set of six selected hybrids (14⁻19) that combine in the same entity two pharmacophores: tacrine (TAC) and 2-phenylbenzothiazole (PhBTA). The compounds contain a methoxy substituent at the PhBTA moiety and have a variable length linker between that and the TAC moiety. The docking studies showed that all the compounds assure a dual-binding mode of acetylcholinesterase (AChE) inhibition, establishing π-stacking and H-bond interactions with aminoacid residues at both active binding sites of the enzyme (CAS and PAS). The bioassays revealed that the designed compounds display excellent AChE inhibitory activity in the sub-micromolar range (0.06⁻0.27 μM) and moderate inhibition values for amyloid-β (Aβ) self-aggregation (27⁻44.6%), compounds 14 and 15 being the lead compounds. Regarding neuroprotective effects in neuroblastoma cells, compounds 15, 16 and 19 revealed the capacity to prevent Aβ-induced toxicity, but compound 16 showed the highest neuroprotective effect. Overall these hybrid compounds, in particular 15 and 16, with promising multitarget anti-AD ability, encourage further pursuing studies on this type of TAC-PhBTA derivatives for potential AD therapy.

Genesis of Neuroprotective Peptoid from Aβ30-34 Inhibits Aβ Aggregation and AChE Activity

Aβ peptide and hyper-phosphorylated microtubule associated protein (Tau) aggregation causes severe damage to both the neuron membrane and key signal processing microfilament (microtubule) in Alzheimer's disease (AD) brains. To date, the key challenge is to develop nontoxic, proteolytically stable amyloid inhibitors, which can simultaneously target multiple pathways involved in AD. Various attempts have been made in this direction; however, clinical outcomes of those attempts have been reported to be poor. Thus, we choose development of peptoid (N-substituted glycine oligomers)-based leads as potential AD therapeutics, which are easy to synthesize, found to be proteolytically stable, and exhibit excellent bioavailability. In this paper, we have designed and synthesized a new short peptoid for amyloid inhibition from 30-34 hydrophobic pocket of amyloid beta (Aβ) peptide. The peptoid selectively binds with 17-21 hydrophobic region of Aβ and inhibits Aβ fibril formation. Various in vitro assays suggested that our AI peptoid binds with tubulin/microtubule and promotes its polymerization and stability. This peptoid also inhibits AChE-induced Aβ fibril formation and provides significant neuroprotection against toxicity generated by nerve growth factor (NGF) deprived neurons derived from rat adrenal pheochromocytoma (PC12) cell line. Moreover, this peptoid shows serum stability and is noncytotoxic to primary rat cortical neurons.

Preparation of 4-Flexible Amino-2-Arylethenyl-Quinoline Derivatives as Multi-target Agents for the Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is a complex and multifactorial neurodegenerative disorder of aged people. The development of multitarget-directed ligands (MTDLs) to act as multifunctional agents to treat this disease is the mainstream of current research. As a continuation of our previous studies, a series of 4-flexible amino-2-arylethenylquinoline derivatives as multi-target agents was efficiently synthesized and evaluated for the treatment of AD. Among these synthesized derivatives, some compounds exhibited strong self-induced Aβ_1–42 aggregation inhibition and antioxidant activity. The structure-activity relationship was summarized, which confirmed that the introduction of a flexible amino group featuring a N,N-dimethylaminoalkylamino moiety at the 4-position increased the Aβ_1–42 aggregation inhibition activity, with an inhibition ratio of 95.3% at 20 μM concentration. Compound 6b₁, the optimal compound, was able to selectively chelate copper (II), and inhibit Cu²⁺-induced Aβ aggregation effectively. It also could disassemble the self-induced Aβ_1–42 aggregation fibrils with a ratio of 64.3% at 20 μM concentration. Moreover, compound 6b₁ showed low toxicity and a good neuroprotective effect against Aβ_1–42-induced toxicity in SH-SY5Y cells. Furthermore, the step-down passive avoidance test indicated compound 6b₁ significantly reversed scopolamine-induced memory deficit in mice. Taken together, these results suggested that compound 6b₁ was a promising multi-target compound worthy of further study for AD.

Synthesis and biological evaluation of new N-benzylpyridinium-based benzoheterocycles as potential anti-Alzheimer's agents

A novel series of benzylpyridinium-based benzoheterocycles (benzimidazole, benzoxazole or benzothiazole) were designed as potent acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitors. The title compounds 4a-q were conveniently synthesized via condensation reaction of 1,2-phenylenediamine, 2-aminophenol or 2-aminothiophenol with pyridin-4-carbalehyde, followed by N-benzylation using various benzyl halides. The results of in vitro biological assays revealed that most of them, especially 4c and 4g, had potent anticholinesterase activity comparable or more potent than reference drug, donepezil. The kinetic study demonstrated that the representative compound 4c inhibits AChE in competitive manner. According to the ligand-enzyme docking simulation, compound 4c occupied the active site at the vicinity of catalytic triad. The compounds 4c and 4g were found to be inhibitors of Aβ self-aggregation as well as AChE-induced Aβ aggregation. Meanwhile, these compounds could significantly protect PC12 cells against H₂O₂-induced injury and showed no toxicity against HepG2 cells. As multi-targeted structures, compounds 4c and 4g could be considered as promising candidate for further lead developments to treat Alzheimer's disease.

Amyloid-β Peptide Interactions with Amphiphilic Surfactants: Electrostatic and Hydrophobic Effects

The amphiphilic nature of the amyloid-β (Aβ) peptide associated with Alzheimer's disease facilitates various interactions with biomolecules such as lipids and proteins, with effects on both structure and toxicity of the peptide. Here, we investigate these peptide-amphiphile interactions by experimental and computational studies of Aβ(1-40) in the presence of surfactants with varying physicochemical properties. Our findings indicate that electrostatic peptide-surfactant interactions are required for coclustering and structure induction in the peptide and that the strength of the interaction depends on the surfactant net charge. Both aggregation-prone peptide-rich coclusters and stable surfactant-rich coclusters can form. Only Aβ(1-40) monomers, but not oligomers, are inserted into surfactant micelles in this surfactant-rich state. Surfactant headgroup charge is suggested to be important as electrostatic peptide-surfactant interactions on the micellar surface seems to be an initiating step toward insertion. Thus, no peptide insertion or change in peptide secondary structure is observed using a nonionic surfactant. The hydrophobic peptide-surfactant interactions instead stabilize the Aβ monomer, possibly by preventing self-interaction between the peptide core and C-terminus, thereby effectively inhibiting the peptide aggregation process. These findings give increased understanding regarding the molecular driving forces for Aβ aggregation and the peptide interaction with amphiphilic biomolecules.