Acetylcholinesterase inhibition of Alzheimer's disease: identification of potential phytochemicals and designing more effective derivatives to manage disease condition

Alzheimer's disease (AD) is a brain disease characterized by gradual memory loss and cognitive impairments. Acetylcholinesterase (AChE) inhibitors-such as donepezil, memantine, and tacrine-are FDA-approved medications for AD treatment. Due to the lack of their efficacy and higher side effects, many researchers have been searching for effective and safer alternatives. In this study, experimentally proved phytochemicals against brain diseases were screened based on their binding energies to the target site of AChE, pharmacokinetic properties, and drug-likeness. Although some phytochemicals showed higher binding affinities than the control drug (donepezil), they did not show permeability across the blood-brain barrier (BBB). However, berberine, anthocyanin, and diterpene alkaloid can cross the BBB and showed good binding affinities of -10.3, -10.1, and -10.2 kcal/mol, respectively. MD simulation and PCA of the simulation data of the protein and protein-ligand complexes proved that the complexes are stable in the biological environment. A total of 16 derivatives of berberine and 3 derivatives of anthocyanin also showed higher binding energies compared to the binding affinity (-11.5 kcal/mol) of the donepezil. The derivatives were designed by substituting -F, -CF3, -CN, and -NH2, and provided higher docking scores due to increasing of nonbonding interactions. MM/GBSA calculations show that the binding free energies of the best predicted derivatives of diterpene alkaloid, anthocyanin, and berberine (DA22, AC11, and BB40) are -100.4 ± 8.4, -79.3 ± 8.7, and -78.3 ± 10.7 kcal/mol, respectively, with the protein. Overall, this study was successful in finding new, highly effective, and possibly safer inhibitors of AChE.Communicated by Ramaswamy H. Sarma.

A Novel Donepezil–Caffeic Acid Hybrid: Synthesis, Biological Evaluation, and Molecular Docking Studies

A novel donepezil-caffeic acid (DP-CA) hybrid molecule was designed, synthesis, and investigated by molecular modeling. Its biological activity and protective effect were investigated by the IR spectroscopy, ¹H and ¹³C NMR spectroscopy, and mass spectrometry. DP-CA was highly active against acetylcholine esterase and inhibited it at the micromolar concentrations. Fluorescence and UV-Vis spectroscopy studies showed strong binding of DP-CA to DNA. Moreover, DP-CA exhibited protective effects against H2O2-induced toxicity in U-118 MG glioblastoma cells. Finally, molecular docking showed a high affinity of DP-CA in all concentrations, and the active 4EY7 site exhibited essential residues with polar and apolar contacts. Taken together, these findings indicate that DP-CA could be a prospective multifunctional agent for the treatment of neurodegenerative diseases.

Discovery of new acetylcholinesterase inhibitors for Alzheimer's disease: virtual screening and in vitro characterisation

For more than two decades, the development of potent acetylcholinesterase (AChE) inhibitors has been an ongoing task to treat dementia associated with Alzheimer's disease and improve the pharmacokinetic properties of existing drugs. In the present study, we used three docking-based virtual screening approaches to screen both ZINC15 and MolPort databases for synthetic analogs of physostigmine and donepezil, two highly potent AChE inhibitors. We characterised the in vitro inhibitory concentration of 11 compounds, ranging from 14 to 985 μM. The most potent of these compounds, S-I 26, showed a fivefold improved inhibitory concentration in comparison to rivastigmine. Moderate inhibitors carrying novel scaffolds were identified and could be improved for the development of new classes of AChE inhibitors.

Blood-Brain Barrier Permeable and NO-Releasing Multifunctional Nanoparticles for Alzheimer's Disease Treatment: Targeting NO/cGMP/CREB Signaling Pathways

The development of novel therapeutic strategies for combating Alzheimer's disease (AD) is challenging but imperative. Multifunctional nanoparticles are promising tools for regulating complex pathological dysfunctions for AD treatment. Herein, we constructed multifunctional nanoparticles consisting of regadenoson (Reg), nitric oxide (NO) donor, and YC-1 in a single molecular entity that can spontaneously self-assemble into nanoparticles and load donepezil to yield Reg-nanoparticles (Reg-NPs). The Reg moiety enabled the Reg-NPs to effectively regulate tight junction-associated proteins in the blood-brain barrier, thus facilitating the permeation of donepezil through the barrier and its accumulation in the brain. Moreover, the released NO and YC-1 activated the NO/cGMP/CREB signaling pathway by stimulating soluble guanylyl cyclase and inhibiting phosphodiesterase activity, which finally reduced cytotoxicity induced by aggregated Aβ in the neurons and was beneficial for synaptic plasticity and memory formation.

Polypseudorotaxane and polydopamine linkage-based hyaluronic acid hydrogel network with a single syringe injection for sustained drug delivery

Polypseudorotaxane structure and polydopamine bond-based crosslinked hyaluronic acid (HA) hydrogels including donepezil-loaded microspheres were developed for subcutaneous injection. Both dopamine and polyethylene glycol (PEG) were covalently bonded to the HA polymer for catechol polymerization and inclusion complexation with alpha-cyclodextrin (α-CD), respectively. A PEG chain of HA-dopamine-PEG (HD-PEG) conjugate was threaded with α-CD to make a polypseudorotaxane structure and its pH was adjusted to 8.5 for dopamine polymerization. Poly(lactic-co-glycolic acid) (PLGA)/donepezil microsphere (PDM) was embedded into the HD-PEG network for its sustained release. The HD-PEG/α-CD/PDM 8.5 hydrogel system exhibited an immediate gelation pattern, injectability through single syringe, self-healing ability, and shear-thinning behavior. Donepezil was released from the HD-PEG/α-CD/PDM 8.5 hydrogel in a sustained pattern. Following subcutaneous injection, the weight of excised HD-PEG/α-CD/PDM 8.5 hydrogel was higher than the other groups on day 14. These findings support the clinical feasibility of the HD-PEG/α-CD/PDM 8.5 hydrogel for subcutaneous injection.

The Impact of Dextran Sodium Sulfate-Induced Gastrointestinal Injury on the Pharmacokinetic Parameters of Donepezil and Its Active Metabolite 6-O-desmethyldonepezil, and Gastric Myoelectric Activity in Experimental Pigs

Gastrointestinal side effects of donepezil, including dyspepsia, nausea, vomiting or diarrhea, occur in 20–30% of patients. The pathogenesis of these dysmotility associated disorders has not been fully clarified yet. Pharmacokinetic parameters of donepezil and its active metabolite 6-O-desmethyldonepezil were investigated in experimental pigs with and without small intestinal injury induced by dextran sodium sulfate (DSS). Morphological features of this injury were evaluated by a video capsule endoscopy. The effect of a single and repeated doses of donepezil on gastric myoelectric activity was assessed. Both DSS-induced small intestinal injury and prolonged small intestinal transit time caused higher plasma concentrations of donepezil in experimental pigs. This has an important implication for clinical practice in humans, with a need to reduce doses of the drug if an underlying gastrointestinal disease is present. Donepezil had an undesirable impact on porcine myoelectric activity. This effect was further aggravated by DSS-induced small intestinal injury. These findings can explain donepezil-associated dyspepsia in humans.

Claulansine F-Donepezil Hybrids as Anti-Alzheimer's Disease Agents with Cholinergic, Free-Radical Scavenging, and Neuroprotective Activities

The multifactorial nature of Alzheimer's disease (AD) calls for the development of multitarget agents addressing key pathogenic processes. A total of 26 Claulansine F-donepezil hybrids were designed and synthesized as multitarget drugs. Among these compounds, six compounds exhibited excellent acetylcholinesterase (AChE) inhibitory activity (half maximal inhibitory concentration (IC50) 1.63-4.62 μM). Moreover, (E)-3-(8-(tert-Butyl)-3,3-dimethyl-3,11-dihydropyrano[3,2-a]carbazol-5-yl)-N-((1-(2-chlorobenzyl)piperidin-4-yl)methyl)acrylamide (6bd) exhibited better neuroprotective effects against OGD/R (oxygen-glucose deprivation/reoxygenation) than lead compound Claulansine F. Furthermore, 6bd could cross the blood-brain barrier in vitro. More importantly, compared to edaravone, 6bd had stronger free-radical scavenging activity. Molecular docking studies revealed that 6bd could interact with the catalytic active site of AChE. All of these outstanding in vitro results indicate 6bd as a leading structure worthy of further investigation.

Derivatives of Tenuazonic Acid as Potential New Multi-Target Anti-Alzheimer's Disease Agents

Alzheimer's disease (AD) is generally recognized as a multifactorial neurodegenerative pathology with an increasing impact on society. Tenuazonic acid (TA) is a natural compound that was recently identified as a potential multitarget ligand with anti-cholinesterase, anti-amyloidogenic and antioxidant activities. Using its structure as a chemical scaffold, we synthesized and evaluated new derivatives (1-5), including tenuazonic-donepezil (TA-DNP) hybrids (4 and 5) due to the clinical importance of the anti-AD drug donepezil. These novel compounds all achieved activity in the micromolar range towards all selected targets and demonstrated to be potentially orally absorbed. Moreover, a selected compound (1) was further investigated as a chelating agent towards copper (II), zinc (II) and iron (III) and showed good chelating ability (pFe = 16.6, pCu = 11.6, pZn = 6.0 at pH 7.4). Therefore, the TA motif can be considered an interesting building block in the search for innovative multi-functional anti-neurodegenerative drugs, as exemplified by hybrid 5, a promising non-cytotoxic lead compound adequate for the early stages of AD, and capable of ameliorating the oxidative status of SH-SY5Y human neuroblastoma cells.

Design, Synthesis, and In Vitro Evaluation of Hydroxybenzimidazole-Donepezil Analogues as Multitarget-Directed Ligands for the Treatment of Alzheimer's Disease

A series of multi-target-directed ligands (MTDLs), obtained by attachment of a hydroxyphenylbenzimidazole (BIM) unit to donepezil (DNP) active mimetic moiety (benzyl-piperidine/-piperazine) was designed, synthesized, and evaluated as potential anti-Alzheimer's disease (AD) drugs in terms of biological activity (inhibition of acetylcholinesterase (AChE) and β-amyloid (Aβ) aggregation), metal chelation, and neuroprotection capacity. Among the DNP-BIM hybrids studied herein, the structural isomerization did not significantly improve the biological properties, while some substitutions, namely fluorine atom in each moiety or the methoxy group in the benzyl ring, evidenced higher cholinergic AChE activity. All the compounds are able to chelate Cu and Zn metal ions through their bidentate BIM moieties, but compound 5, containing a three-dentate chelating unit, is the strongest Cu(II) chelator. Concerning the viability on neuroblastoma cells, compounds 9 and 10 displayed the highest reduction of Aβ-induced cell toxicity. In silico calculations of some pharmacokinetic descriptors indicate that all the compounds but the nitro derivatives have good potential oral-bioavailability. Overall, it can be concluded that most of the studied DNP-BIM conjugates showed quite good anti-AD properties, therefore deserving to be considered in further studies with the aim of understanding and treating AD.

Combining Chalcones with Donepezil to Inhibit Both Cholinesterases and Aβ Fibril Assembly

The fact that the number of people with Alzheimer's disease is increasing, combined with the limited availability of drugs for its treatment, emphasize the need for the development of novel effective therapeutics for treating this brain disorder. Herein, we focus on generating 12 chalcone-donepezil hybrids, with the goal of simultaneously targeting amyloid-β (Aβ) peptides as well as cholinesterases (i.e., acetylcholinesterase (AChE) and butyrylcholinesterase (BChE)). We present the design, synthesis, and biochemical evaluation of these two series of novel 1,3-chalcone-donepezil (15a-15f) or 1,4-chalcone-donepezil (16a-16f) hybrids. We evaluate the relationship between their structures and their ability to inhibit AChE/BChE activity as well as their ability to bind Aβ peptides. We show that several of these novel chalcone-donepezil hybrids can successfully inhibit AChE/BChE as well as the assembly of N-biotinylated Aβ(1-42) oligomers. We also demonstrate that the Aβ binding site of these hybrids differs from that of Pittsburgh Compound B (PIB).

Donepezil + chromone + melatonin hybrids as promising agents for Alzheimer's disease therapy

We describe herein the design, multicomponent synthesis and biological studies of new donepezil + chromone + melatonin hybrids as potential agents for Alzheimer's disease (AD) therapy. We have identified compound 14n as promising multitarget small molecule showing strong BuChE inhibition (IC50 = 11.90 ± 0.05 nM), moderate hAChE (IC50 = 1.73 ± 0.34 μM), hMAO A (IC50 = 2.78 ± 0.12 μM), and MAO B (IC50 = 21.29 ± 3.85 μM) inhibition, while keeping a strong antioxidant power (3.04 TE, ORAC test). Consequently, the results reported here support the development of new multitarget Donepezil + Chromone + Melatonin hybrids, such as compound 14n, as a potential drug for AD patients cure.

Butyrylcholinesterase Protein Ends in the Pathogenesis of Alzheimer's Disease-Could BCHE Genotyping Be Helpful in Alzheimer's Therapy?

Late-onset Alzheimer’s disease (AD) is clinically characterized by a progressive decline of memory and other cognitive functions leading to the loss of the ability to perform everyday activities. Only a few drugs have been approved to treat AD dementia over the past century since the first AD patient was diagnosed. Drugs increasing the availability of neurotransmitters at synapses in the brain are used clinically in the treatment of AD dementia, and cholinesterase inhibitors (ChEIs) are the mainstay of the therapy. A detrimental effect on cognitive function has been reported in patients with pharmacological inhibition of acetylcholinesterase (AChE) by ChEIs and reduced butyrylcholinesterase (BChE) activity due to the single nucleotide polymorphisms. The BChE K-variant (rs1803274), the most common genetic variant of the BCHE gene, was thought to reduce enzyme activity reflecting the lower clinical response to rivastigmine in AD patients. During ChEIs therapy, patients carrying reduced-activity BChE do not present such improved attention like patients with the wild-type enzyme. On the other hand, alterations in the BCHE gene causing enzyme activity reduction may delay AD onset in patients at risk by preserving the level of cortical acetylcholine (ACh). Based on our previous results, we conclude that SNPs localized outside of the coding sequence, in 5’UTR (rs1126680) and/or intron 2 (rs55781031) of the BCHE gene, but not solely K-variant alteration (p.A539T) itself, are responsible for reduced enzyme activity. Therefore, we suspect that not BChE-K itself, but these coexisting SNPs (rs1126680 and rs55781031), could be associated with deleterious changes in cognitive decline in patients treated with ChEIs. Based on the results, we suggest that SNPs (rs1126680) and/or (rs55781031) genotyping should be performed to identify subjects at risk for lowered efficacy ChEIs therapy, and such patients should be treated with a lower rivastigmine dosage. Finally, our sequence analysis of the N-terminal end of N-BChE revealed evolutionarily conserved amino acid residues that can be involved in disulfide bond formation and anchoring of N-BChE in the cell membrane.

Nasal delivery of donepezil HCl-loaded hydrogels for the treatment of Alzheimer's disease

This study aims to prepare, characterize and evaluate the pharmacokinetics of liposomal donepezil HCl (LDH) dispersed into thiolated chitosan hydrogel (TCH) in rabbits. Various hydrogels including TCH were prepared, and after characterization, TCH was selected for subsequent evaluations, due to the promising results. TCH was then incorporated with LDH prepared by reverse phase evaporation method. The hydrogel was characterized using scanning electron microscope, dialysis membrane technique, and ultra-performance liquid chromatography methods. The optimized resultant was then evaluated in terms of pharmacokinetics in an in vivo environment. The mean size of LDH and drug entrapment efficiency were 438.7 ± 28.3 nm and 62.5% ± 0.6, respectively. The controlled drug release pattern results showed that the half-life of the loaded drug was approximately 3.5 h. Liposomal hydrogel and free liposomes were more stable at 4 °C compared to those in 20 °C. The pharmacokinetics study in the rabbit showed that the optimized hydrogel increased the mean peak drug concentration and area under the curve by 46% and 39%, respectively, through nasal route compared to the oral tablets of DH. Moreover, intranasal delivery of DH through liposomal hydrogel increased the mean brain content of the drug by 107% compared to the oral DH tablets. The results suggested that liposomes dispersed into TCH is a promising device for the nasal delivery of DH and can be considered for the treatment of Alzheimer's disease.

Discovery of Novel Acetylcholinesterase Inhibitors as Potential Candidates for the Treatment of Alzheimer's Disease

Acetylcholinesterase (AChE) catalyzes the hydrolysis of neurotransmitter acetylcholine to acetate and choline in a synaptic cleft. Deficits in cholinergic neurotransmitters are linked closely with the progression of Alzheimer’s disease (AD), which is a neurodegenerative disorder characterized by memory impairment, and a disordered cognitive function. Since the previously approved AChE inhibitors, donepezil (Aricept), galantamine (Reminyl), and rivastigmine (Exelon), have side effects and several studies are being carried out out to develop novel AD drugs, we have applied a three-dimensional quantitative structure−activity relationship (3D QSAR) and structure-based pharmacophore modeling methodologies to identify potential candidate inhibitors against AChE. Herein, 3D QSAR and structure-based pharmacophore models were built from known inhibitors and crystal structures of human AChE in complex with donepezil, galantamine, huperzine A, and huprine W, respectively. The generated models were used as 3D queries to screen new scaffolds from various chemical databases. The hit compounds obtained from the virtual screening were subjected to an assessment of drug-like properties, followed by molecular docking. The final hit compounds were selected based on binding modes and molecular interactions in the active site of the enzyme. Furthermore, molecular dynamics simulations for AChE in complex with the final hits were performed to evaluate that they maintained stable interactions with the active site residues. The binding free energies of the final hits were also calculated using molecular mechanics/Poisson-Boltzmann surface area method. Taken together, we proposed that these hits can be promising candidates for anti-AD drugs.

Metal based donepezil analogues designed to inhibit human acetylcholinesterase for Alzheimer's disease

Among neurodegenerative disorders, Alzheimer's disease (AD) is one of the most common disorders showing slow progressive cognitive decline. Targeting acetylcholinesterase (AChE) is one of the major strategies for AD therapeutics, as cholinergic pathways in the cerebral cortex and basal forebrain are compromised. Herein, we report the design of some copper and other metal based donepezil derivatives, employing density functional theory (DFT). All designed compounds are optimized at the B3LYP/SDD level of theory. Dipole moments, electronic energie, enthalpies, Gibbs free energies, and HOMO-LUMO gaps of these modified compounds are also investigated in the subsequent analysis. The molecules were then subjected to molecular docking analysis with AChE to study the molecular interactions broadly. Ensemble based docking and molecular dynamics (MD) simulations of the best candidates were also performed. Docking and MD simulation reveal that modified drugs are more potent than unmodified donepezil, where Trp86, Tyr337, Phe330 residues play some important roles in drug-receptor interactions. According to ensemble based docking, D9 shows greater binding affinity compared to the parent in most conformations obtained from protein data bank and MD simulation. In addition, it is observed that the π- π stacking with the residues of Trp86, Tyr337, Tyr341, Tyr124 and Trp286 may be required for strong ligand binding. Moreover, ADME/T analysis suggests that modified derivatives are less toxic and have improved pharmacokinetic properties than those of the parent drug. These results further confirm the ability of metal-directed drugs to bind simultaneously to the active sites of AChE and support them as potential candidates for the future treatment of Alzheimer's disease.