Selective Acetylcholinesterase Inhibitor Research Articles

Safety and efficacy of donepezil hydrochloride in patients with mild to moderate Alzheimer′s disease: Findings of an observational study

Background:Alzheimer's disease (AD), a progressive brain disorder, is the most common cause of dementia among the elderly. Donepezil hydrochloride is a potent, reversible, and highly selective inhibitor of acetylcholinesterase (AChE). It is chemically distinct from other cholinesterase (ChE) inhibitors which are effective in the treatment of AD.Objectives:To evaluate the safety and efficacy of donepezil hydrochloride therapy over a 12 weeks period in patients with mild to moderate AD in Indian population.Materials and Methods:In this post-marketing study, patients with mild to moderate AD received oral donepezil hydrochloride 5 mg/day for 4 weeks followed by 10 mg/day for 8 weeks. Patients were assessed 4 times weekly for cognition on ‘Mini Mental Status Examination (MMSE) scale’, and function on ‘Activities of Daily Living (ADL) index’. Clinicians and caregivers assessment of safety and efficacy was assessed on a 5-point rating scale.Results:One hundred and seventy two of one hundred and eighty two patients completed 12 weeks of study period. MMSE score significantly improved (P<0.0001) from 16.72 at baseline to 19.77 after 12 weeks, and there was significant improvement (P<0.05) in ADL index in 13 of 17 domains after 12 weeks. Caregivers and clinicians rated the therapy as very good to good in >80% and >90% patients, respectively. Adverse events were consistent with the known pharmacological and safety profile of donepezil.Conclusions:Donepezil is well tolerated in Indian patients with mild to moderate AD with significant improvement in cognition and function.

Synthesis and docking studies of alkylene-linked dimers of (-)-huperzine A.

(-)-Huperzine A (5, HupA), an alkaloid isolated from the herb Huperzia serrata, is a potent, selective and reversible acetylcholinesterase (AchE) inhibitor. Based on the hypothesis with respect to two binding sites in the active gorge of AChE and the good example of bis-tacrine, it was predicted from the docking studies of alkylene-linked dimers of HupA that dimers 6 (n = 5, 7, 9) might have good AChE inhibitory activity. Therefore, six dimers with 7-12 methylene units as tethers were thus prepared. It was found that these dimers were less potent than HupA in inhibition of AChE. The difference of the inhibitory potency between these dimers is coincident with the results of the docking studies.

Broader Considerations of Higher Doses of Donepezil in the Treatment of Mild, Moderate, and Severe Alzheimer's Disease

Donepezil, a highly selective acetylcholinesterase inhibitor (AChEI), is approved as a symptomatic treatment mild, moderate, and severe Alzheimer's disease (AD). Donepezil exerts its treatment effect through multiple mechanisms of action including nicotinic receptor stimulation, mitigation of excitotoxicity, and influencing APP processing. The use of donepezil at higher doses is justified given the worsening cholinergic deficit as the disease advances. Donepezil has been investigated in several clinical trials of subjects with moderate-to-severe AD. While the side effects are class specific (cholinergically driven), demonstrable benefit has been shown at the 10 mg dose and the 23 mg doses. Here, we review the clinical justification, efficacy, safety, and tolerability of use of donepezil in the treatment of moderate-to-severe AD.

Synthesis, biological assessment and molecular modeling of 14-aryl-10,11,12,14-tetrahydro-9H-benzo[5,6]chromeno[2,3-b]quinolin-13-amines

The synthesis and pharmacological evaluation of racemic 14-aryl-10,11,12,14-tetrahydro-9H-benzo[5,6]chromeno[2,3-b]quinolin-13-amines (19-28), prepared by Friedländer reaction of 3-amino-1-aryl-1H-benzo[f]chromene-2-carbonitriles (10-18) with suitable cycloalkanones is described. These molecules are potent, in the nanomolar range [IC(50) (EeAChE)=7-101 nM], and selective inhibitors of acetylcholinesterase (AChE). The most potent inhibitor, 4-(13-amino-10,11,12,14-tetrahydro-9H-benzo[5,6]chromeno[2,3-b]quinolin-14-yl)phenol (20) [IC(50) (EeAChE)=7±2 nM] is four-fold more active than tacrine. Kinetic studies on compound 20 showed that this is a mixed-type inhibitor of EeAChE with a K(i) of 5.00 nM. However, racemic 20 was unable to displace propidium iodide, suggesting that the inhibitor does not strongly bind to the peripheral anionic site (PAS) of AChE. Docking, molecular dynamics stimulations, and MM-GBSA calculations agree well with this behavior.

Benzophenone-based derivatives: A novel series of potent and selective dual inhibitors of acetylcholinesterase and acetylcholinesterase-induced beta-amyloid aggregation

The leading mechanistic theory of Alzheimer’s disease (AD) is the “amyloid hypothesis” which states that the accumulation of the amyloid β protein (Aβ), and its subsequent aggregation into plaques, is responsible for the initiation of a cascade of events resulting in neurodegeneration and dementia. The anti-amyloid disease-modifying approach, based on the decrease in the production of Aβ, gained thus a paramount importance. The aim of this study was the design and synthesis of a new series of acetylcholinesterase inhibitors (AChEIs) endowed with anti-Aβ aggregating capability. These dual binding inhibitors, being able to interact both with the peripheral anionic site (PAS) of AChE and the catalytic subsite, proved to be able to inhibit the AChE-induced Aβ aggregation. Thus, starting from the lead compound 1, an AChEI composed by a benzophenone scaffold and a N, N′-methylbenzylamino group, a substantial modification aimed at targeting the PAS was performed. To this aim, different amino-terminal side chains were incorporated into this main framework, in order to mimic the diethylmethylammonium alkyl moiety of the pure PAS ligand propidium. The synthesized compounds proved to effectively and selectively inhibit AChE. Moreover, compounds 16a– c and 18a, b, with a propoxy and a hexyloxy tether respectively, showed a good activity against the AChE-induced Aβ aggregation. In particular, molecular modeling studies confirmed that compounds carrying the diethylaminopropoxy and the diethylaminohexyloxy side chains (compounds 16a and 19a, respectively) could suitably contact the PAS pocket of the enzyme.

Huperzine A Activates Wnt/β-Catenin Signaling and Enhances the Nonamyloidogenic Pathway in an Alzheimer Transgenic Mouse Model

Huperzine A (HupA) is a reversible and selective inhibitor of acetylcholinesterase (AChE), and it has multiple targets when used for Alzheimer's disease (AD) therapy. In this study, we searched for new mechanisms by which HupA could activate Wnt signaling and reduce amyloidosis in AD brain. A nasal gel containing HupA was prepared. No obvious toxicity of intranasal administration of HupA was found in mice. HupA was administered intranasally to β-amyloid (Aβ) precursor protein and presenilin-1 double-transgenic mice for 4 months. We observed an increase in ADAM10 and a decrease in BACE1 and APP695 protein levels and, subsequently, a reduction in Aβ levels and Aβ burden were present in HupA-treated mouse brain, suggesting that HupA enhances the nonamyloidogenic APP cleavage pathway. Importantly, our results further showed that HupA inhibited GSK3α/β activity, and enhanced the β-catenin level in the transgenic mouse brain and in SH-SY5Y cells overexpressing Swedish mutation APP, suggesting that the neuroprotective effect of HupA is not related simply to its AChE inhibition and antioxidation, but also involves other mechanisms, including targeting of the Wnt/β-catenin signaling pathway in AD brain.

Sublethal genotoxicity and cell alterations by organophosphorus pesticides in MCF‐7 cells: Implications for environmentally relevant concentrations

Organophosphorus pesticide (OPP) toxicity is believed to be mediated through inhibition of acetylcholinesterase (AChE). Given their widespread distribution in aquatic systems and their ability to undergo chemical transformation, their environmental impacts at sublethal concentrations in nontarget organisms have become an important question. We conducted a number of mammalian-cell genotoxic and gene expression assays and examined cellular biochemical changes that followed low-dose exposure of MCF-7 cells to fenitrothion, diazinon, and the aqueous degradate of diazinon, 2-isopropyl-6-methyl-4-pyrimidinol (IMP). After exposure to the OPPs at low concentrations (10(-12) M to 10(-8) M), greater than twofold elevations in micronucleus formation were noted in MCF-7 cell cultures that went on to exhibit greater than 75% clonogenic survival; these levels of chromosomal damage were comparable to those induced by 10(-6) M benzo[a]pyrene, a known genotoxic agent. At this low concentration range, a fenitrothion-induced twofold elevation in B-cell leukemia/lymphoma-2 (BCL-2) and cytochrome P450 isoenzyme (CYP1A1) gene expressions was observed. Principal component analysis-linear discriminant analysis (PCA-LDA) of derived infrared (IR) spectra of vehicle control (nonexposed) and OPP-exposed cells highlighted that both fenitrothion and diazinon induced marked biochemical alterations in the lipid, protein, and DNA/RNA absorbance regions. Our findings demonstrate that the two OPP parent chemicals and IMP degradate can mediate a number of toxic effects or cellular alterations at very low concentrations. These are independent of just selective inhibition of AChE, with potential consequences for nontarget organisms exposed at environmentally relevant concentrations. Further assays on relevant aquatic organism cell lines are now recommended to understand the mechanistic low-dose toxicity of these chemicals present in aquatic systems.

Selective Acetylcholinesterase Inhibitor Activated by Acetylcholinesterase Releases an Active Chelator with Neurorescuing and Anti-Amyloid Activities

The finding that acetylcholinesterase (AChE) colocalizes with β-amyloid (Aβ) and promotes and accelerates Aβ aggregation has renewed an intense interest in developing new multifunctional AChE inhibitors as potential disease-modifying drugs for Alzheimer's therapy. To this end, we have developed a new class of selective AChE inhibitors with site-activated chelating activity. The identified lead, HLA20A, exhibits little affinity for metal (Fe, Cu, and Zn) ions but can be activated following inhibition of AChE to liberate an active chelator, HLA20. HLA20 has been shown to possess neuroprotective and neurorescuing activities in vitro and in vivo with the ability to lower amyloid precursor holoprotein (APP) expression and Aβ generation and inhibit Aβ aggregation induced by metal (Fe, Cu, and Zn) ion. HLA20A inhibited AChE in a time and concentration dependent manner with an HLA20A-AChE complex constant (K(i)) of 9.66 × 10(-6) M, a carbamylation rate (k(+2)) of 0.14 min(-1), and a second-order rate (k(i)) of 1.45 × 10 (4) M(-1) min(-1), comparable to those of rivastigmine. HLA20A showed little iron-binding capacity and activity against iron-induced lipid peroxidation (LPO) at concentrations of 1-50 μM, while HLA20 exhibited high potency in iron-binding and in inhibiting iron-induced LPO. At a concentration of 10 μM, HLA20A showed some activity against monoamine oxidase (MAO)-A and -B when tested in rat brain homogenates. Defined restrictively by Lipinski's rules, both HLA20A and HLA20 satisfied drug-like criteria and possible oral and brain permeability, but HLA20A was more lipophilic and considerably less toxic in human SHSY5Y neuroblastoma cells at high concentrations (25 or 50 μM). Together our data suggest that HLA20A may represent a promising lead for further development for Alzheimer's disease therapy.

Enhanced dendritic spine number of neurons of the prefrontal cortex, hippocampus, and nucleus accumbens in old rats after chronic donepezil administration.

In Alzheimer's disease brains, morphological changes in the dendrites of pyramidal neurons of the prefrontal cortex (PFC) and hippocampus have been observed. These changes are particularly reflected in the decrement of both the dendritic tree and spine number. Donepezil is a potent and selective acetylcholinesterase inhibitor used in the treatment of Alzheimer's disease. We have studied the effect of oral administration of this drug on the morphology of neuronal cells from the brain of aged rats. We examined dendrites of pyramidal neurons of the PFC, dorsal or ventral hippocampus (VH), and medium spiny neurons of the nucleus accumbens (NAcc). Donepezil (1 mg/kg, vo) was administrated every day for 60 days to rats aged 10 and 18 months. Dendritic morphology was studied by the Golgi-Cox stain procedure followed by Sholl analysis at 12 and 20 months ages, respectively. In all Donepezil-treated rats, a significant increment of the dendritic spines number in pyramidal neurons of the PFC and dorsal hippocampus was observed. However, pyramidal neurons of the VH and medium spiny cells of the NAcc only showed an increase in the number of their spines in 12-month-old rats. Our results suggest that Donepezil prevents the alterations of the neuronal dendrite morphology caused by aging.

ChemInform Abstract: Total Synthesis of Biologically Active Natural Products Possessing Unique Structural Features

This review describes the total synthesis of natural products involving kopsine, popolophuanone E, hydantocidin, and huperzine A, all of which possess not only unique structural features but also prominent biologically properties. The first total synthesis of the heptacyclic indole alkaloid kopsine was accomplished by employing intramolecular Diels-Alder reactions and Pummerer-type cyclization as the key steps. In the synthetic studies of popolophuanone E, a topoisomerase- II inhibitor from a marine sponge, popolophuanone E trimethyl ether was successfully synthesized by a method featuring the biogenetic-type annulation. The synthetic pathway to hydantocidin, a novel herbicide from Streptomyces sp., has been developed based on the plausible biosynthetic pathway. Total syntheses of both enantiomers of huperzine A, a powerful selective inhibitor of acetylcholinesterase, were accomplished by employing two types of methods which involves the tandem Cinchona alkaloids-promoted asymmetric Michael addition/aldol reaction and the palladium-catalyzed asymmetric bicycloannulation. Furthermore, the novel fluorinated huperzine A analogues were synthesized in order to explore the structure-activity relationships.

ChemInform Abstract: A Facile Synthesis of Bis-tacrine Isosteres.

Abstract An efficient synthesis of highly potent and selective acetylcholinesterase (AChE) inhibitors, bis-tacrines and their isosteres 2–4, has been accomplished by bis-amination of 9-chloro-tetrahydroacridine (9a) and its analogs. The critical intermediates were concisely prepared in situ by heating the corresponding ortho-amino aromatic acids and cycloketones in the presence of phosphorus oxychloride.

3D-pharmacophore model based virtual screening to identify dual-binding site and selective acetylcholinesterase inhibitors

The formation of β-amyloid plaques in the brain is a key neurodegenerative event in Alzheimer’s disease (AD). Interestingly, research on acetylcholinesterase (AChE) enzyme has increased due to findings supporting this enzyme involvement in the β-amyloid peptide fibril formation during AD pathogenesis. In this investigation, chemical features based 3D pharmacophore models were developed from structurally diverse xanthostigmine derivatives, known inhibitors of AChE enzyme, using 3D-QSAR pharmacophore generation module in Discovery Studio2.5 (DS2.5). The constructed pharmacophore models for AChE inhibitors was further cross-validated using test set and Cat-Scramble methodology. The best quantitative pharmacophore model Hypo1, was used for screening the chemical databases of small compounds including Specs, NCI, and IBScreen, to identify the new compounds that are presumably able to act as dual-binding site AChE inhibitors. The screened virtual hits were then subjected to the Lipinski’s rule of five, blood–brain barrier (BBB), PSA, LogS, percent human oral absorption, and toxicity analysis. Finally, 32 compounds were identified as potential leads against AChE enzyme, showing good estimated activities and promising ADMET properties. Molecular docking of these compounds using FlexX software showed catalytic and peripheral anionic binding site interactions, so called dual binding of the AChE enzyme. Docking study was also performed on butyrylcholinesterase in order to understand the compound selectivity. This study may assist in the discovery and design of novel dual binding site and selective AChE inhibitors with potent inhibitory activity.

Clinical trial: dose-dependent therapeutic efficacy of acotiamide hydrochloride (Z-338) in patients with functional dyspepsia - 100 mg t.i.d. is an optimal dosage

Acotiamide is a selective acetylcholinesterase inhibitor and enhances the actions of cholinergic neurons localized in the stomach. The present two studies were conducted to examine the optimal dosage of acotiamide hydrochloride (Z-338) in patients with functional dyspepsia (FD) in Japan. The improvement rate of 'subjects global assessment of overall treatment efficacy (OTE)' at the final evaluation was approximately 10% higher in the acotiamide 100 mg group than that in the placebo group with good reproducibility though there was no significant differences at primary endpoint. The elimination rate of postprandial fullness in the acotiamide 100 mg group was significantly higher compared to placebo group. In addition, the post hoc analysis showed that in patients whose main complaints are meal-related symptoms such as postprandial fullness, upper abdominal bloating and/or early satiety, the improvement rate of 'OTE' at final evaluation in acotiamide 100 mg group was significantly superior to that in the placebo group. These results suggest that acotiamide possesses efficacy on FD and more specifically its meal-related symptoms of FD.

Synthesis and evaluation of novel rutaecarpine derivatives and related alkaloids derivatives as selective acetylcholinesterase inhibitors

A series of novel rutaecarpine derivatives and related alkaloid derivatives 3-aminoalkanamido-substituted rutaecarpine 4a– f and 7,8-dehydrorutaecarpine 5a– c, and 6-aminoalkanamido-substituted 3-[2-(3-Indolyl)ethyl]-4( 3a)-quinazolinones 8a– c, were synthesized and subjected to pharmacological evaluation as acetylcholinesterase (AChE) inhibitors. The synthetic compounds exhibited strong inhibitory activity for AChE and high selectivity for AChE over BuChE. The structure–activity relationships were discussed and their binding conformation and simultaneous interactions mode were further clarified by kinetic characterization and the molecular docking studies.

Facile synthesis of novel tacrine analogues

The synthesis of highly potent and selective acetylcholinesterase inhibitors, tacrine analogues with the structure of fused 4-aminoquinolines and 4-aminopyridines, has been accomplished by direct cyclocondensation of 1-aryl-4-cyano-5-aminopyrazoles with cyclic ketones using tin(IV) chloride as catalyst.

Distribution of Huperzine A in Malaysia Lycopodiaceae

Alzheimer's disease is a neurodegenerative disorder affecting the elderly population throughout the world. Huperzine A found in the genera of Lycopodiaceae is a potent, reversible and selective acetylcholinesterase inhibitor and is a promising drug for treatment of symptoms of Alzheimer's disease. The content of Huperzine A in the Lycopodium species collected from the subtropics in Malaysia was evaluated. The dried Lycopodium species were dried, pulverized and macerated in 70% aqueous methanol. After five cycles of extraction, the pooled methanol extract was dried under reduced pressure with a rotary evaporator. The dried methanol extract was dissolved in methanol before subjecting for further analysis. A high performance liquid chromatography system with a diode array detector connected to a reverse phase column was developed to evaluate the content of huperzine A in the Lycopodium species. The separation was achieved with a gradient mobile phase system with an increasing amount (20–70%) of methanol in 0.01% trifluoroacetic acid for 30 minutes monitored from 200 to 500nm. The peak area was linear (r2=0.998) from 5 to 100µg/mL and has a repeatability between 0.4 to 1.4% relative standard deviation within five replicate chromatograms. The evaluated Lycopodium species collected in Malaysia contained Huperzine A ranging from 0.00 to 0.04% of the crude plant.

Tacrine–Melatonin Hybrids as Multifunctional Agents for Alzheimer's Disease, with Cholinergic, Antioxidant, and Neuroprotective Properties

Tacrine-melatonin hybrids were designed and synthesized as new multifunctional drug candidates for Alzheimer's disease. These compounds may simultaneously palliate intellectual deficits and protect the brain against both beta-amyloid (A beta) peptide and oxidative stress. They show improved cholinergic and antioxidant properties, and are more potent and selective inhibitors of human acetylcholinesterase (hAChE) than tacrine. They also capture free radicals better than melatonin. Molecular modeling studies show that these hybrids target both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. At sub-micromolar concentrations they efficiently displace the binding of propidium iodide from the PAS and could thus inhibit A beta peptide aggregation promoted by AChE. Moreover, they also inhibit A beta self-aggregation and display neuroprotective properties in a human neuroblastoma line against cell death induced by various toxic insults, such as A beta(25-35), H(2)O(2), and rotenone. Finally, they exhibit low toxicity and may be able to penetrate the central nervous system according to an in vitro parallel artificial membrane permeability assay for the blood-brain barrier (PAMPA-BBB).

Effects of Rivastigmine and Donepezil on Brain Acetylcholine Levels in Acetylcholinesterase-Deficient Mice

Alzheimer s disease is characterized by a dysfunction of central cholinergic systems and is treated by inhibitors of acetylcholinesterase (AChE). This study tests the effect of two AChE inhibitors in therapeutic use, rivastigmine and donepezil, in mice that are devoid of AChE (AChE-/- mice). Rivastigmine is an inhibitor of both AChE and butyrylcholinesterase (BChE) whereas donepezil is a selective inhibitor of AChE. We have used in vivo microdialysis to investigate the effects of the two drugs on the extracellular concentration of acetylcholine (ACh) in the hippocampus of AChE-/- mice. Extracellular ACh levels in the hippocampus were 30-fold elevated in AChE-/- mice compared to wild-type (AChE+/+) animals. Infusion of rivastigmine (1 and 10 microM) caused a further doubling of ACh levels in AChE-/- mice within 90-120 min. In contrast, infusion of donepezil (1 microM) did not affect hippocampal ACh levels in AChE-/- mice although it increased ACh levels more than twofold in wild-type mice. In the absence of AChE, rivastigmine enhances the levels of extracellular ACh by inhibiting BChE. This finding may be of therapeutic relevance because BChE activity is preserved, but AChE activity is strongly decreased, in late-stage Alzheimer s disease.

Donepezil Improves Cognitive Function in Mice by Increasing the Production of Insulin-Like Growth Factor-I in the Hippocampus

Insulin-like growth factor-I (IGF-I) exerts beneficial effects on cognitive function. The selective acetylcholinesterase inhibitor donepezil increases serum IGF-I levels in elderly subjects. Because stimulation of sensory neurons induces IGF-I production by releasing calcitonin gene-related peptide (CGRP) in the mouse brain, we hypothesized that donepezil increases IGF-I production by sensory neuron stimulation to improve the cognitive function in mice. Donepezil, but not tacrine, increased the CGRP release from dorsal root ganglion neurons isolated from wild-type (WT) mice. Pretreatment with the protein kinase A inhibitor KT5720 [(9S,10S,12R)-2,3,9,10,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg: 3',2',1'-kl]pyrrolo[3,4-i][1,6]-benzo-diazocine-10-carboxylic acid hexyl ester] reversed the effects induced by donepezil. Increase in tissue levels of CGRP, IGF-I, and IGF-I mRNA in the hippocampus was observed at 4 weeks after oral administration of donepezil in WT mice. In these animals, c-fos expression in spinal dorsal horns, parabrachial nuclei, the solitary tract nucleus, and the hippocampus was increased. Enhancement in angiogenesis and neurogenesis was observed in the dentate gyrus of the hippocampus of WT mice after donepezil administration. Improvement of spatial learning was observed in WT mice after donepezil administration. Oral administration of tacrine for 4 weeks produced none of the aforementioned effects induced by donepezil in WT mice. However, none of the effects observed in WT mice was seen after donepezil administration in CGRP-knockout mice and WT mice subjected to functional denervation. These observations suggest that donepezil may improve cognitive function in mice by increasing the hippocampal production of IGF-I through sensory neuron stimulation. These effects of donepezil may not be dependent on its acetylcholinesterase inhibitory activity.

Acetylcholinesterase inhibitors in MG: To be or not to be?

Myasthenia gravis (MG) is an autoimmune disorder usually caused by antibodies against either the acetylcholine receptor (AChR) or muscle-specific tyrosine kinase (MuSK) at the neuromuscular junction. Neuromuscular transmission failure results in muscle fatigue and weakness that can be treated symptomatically with acetylcholinesterase inhibitors (AChEIs). Long-term treatment with nonselective AChEIs may have considerable drawbacks; thus, this medication is ideally tapered when strength improves. Patients with AChR antibodies respond beneficially to treatment, whereas patients with MuSK antibodies generally do not. Recently, the selective AChEI EN101, which specifically targets the isoform of "read-through" AChE (AChE-R), has been developed and may be of importance for symptomatic relief in AChR-antibody seropositive MG. This article is a review of the mechanisms, therapeutic effects, and drawbacks, with both old and new AChEIs in MG.