A Comprehensive Review of Cholinesterase Modeling and Simulation

Nanodisc-associated acetylcholinesterase as a novel model system of physiological relevant membrane-bound cholinesterases. Inhibition by phenolic compounds

Acetylcholinesterase (AChE) plays a pivotal role in the cholinergic system, and its inhibition is sought after in a wide range of applications, from insect control to Alzheimer's disease treatment. While the primary physiological isoforms of AChE are membrane-bound proteins, most assays for discovering new, safer, and potent inhibitors are conducted using commercially available soluble isoforms, such as the electric eel AChE (eeAChE). In this study, we conducted a comparative analysis of the activity and selectivity to phenolic inhibitors of recombinant human AChE, eeAChE and a mutant variant of human AChE known as dAChE4. Despite numerous mutations, dAChE4 closely resembles its parental protein and serves as a suitable model for monomeric human AChE. We also established an in vitro system of membrane-bound AChE to create a model that closely mimics the physiological isoforms. This system ensures the proper work of the enzyme and allowed us to control the exact concentration of enzyme and lipids per assay.

Enzyme Dynamics Determine the Potency and Selectivity of Inhibitors Targeting Disease-Transmitting Mosquitoes

Vector control of mosquitoes with insecticides is an important tool for preventing the spread of mosquito-borne diseases including malaria, dengue, chikungunya, and Zika. Development of active ingredients for insecticides are urgently needed because existing agents exhibit off-target toxicity and are subject to increasing resistance. We therefore seek to develop noncovalent inhibitors of the validated insecticidal target acetylcholinesterase 1 (AChE1) from mosquitoes. Here we use molecular dynamics simulations to identify structural properties essential for the potency of reversible inhibitors targeting AChE1 from Anopheles gambiae (AgAChE1), the malaria-transmitting mosquito, and for selectivity relative to the vertebrate Mus musculus AChE (mAChE). We show that the collective motions of apo AgAChE1 and mAChE differ, with AgAChE1 exhibiting less dynamic movement. Opening and closing of the gorge, which regulates access to the catalytic triad, is enabled by different mechanisms in the two species, which could be linked to their differing amino acid sequences. Inhibitor binding reduced the overall magnitude of dynamics of AChE. In particular, more potent inhibitors reduced the flexibility of the Ω loop at the entrance of the gorge. The selectivity of inhibitors for AgAChE1 over mAChE derives from the positioning of the α-helix lining the binding gorge. Our findings emphasize the need to consider dynamics when developing inhibitors targeting this enzyme and highlight factors needed to create potent and selective AgAChE1 inhibitors that could serve as active ingredients to combat disease-transmitting mosquitoes.

Advances in Cholinesterase Inhibitor Research-An Overview of Preclinical Studies of Selected Organoruthenium(II) Complexes

Cholinesterase (ChE) inhibitors are crucial therapeutic agents for the symptomatic treatment of certain chronic neurodegenerative diseases linked to functional disorders of the cholinergic system. Significant research efforts have been made to develop novel derivatives of classical ChE inhibitors and ChE inhibitors with novel scaffolds. Over the past decade, ruthenium complexes have emerged as promising novel therapeutic alternatives for the treatment of neurodegenerative diseases. Our research group has investigated a number of newly synthesized organoruthenium(II) complexes for their inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Three complexes (C1a, C1-C, and C1) inhibit ChE in a pharmacologically relevant range. C1a reversibly inhibits AChE and BChE without undesirable peripheral effects, making it a promising candidate for the treatment of Alzheimer's disease. C1-Cl complex reversibly and competitively inhibits ChEs, particularly AChE. It inhibits nerve-evoked skeletal muscle twitch and tetanic contraction in a concentration-dependent manner with no effect on directly elicited twitch and tetanic contraction and is promising for further preclinical studies as a competitive neuromuscular blocking agent. C1 is a selective, competitive, and reversible inhibitor of BChE that inhibits horse serum BChE (hsBChE) without significant effect on the peripheral neuromuscular system and is a highly species-specific inhibitor of hsBChE that could serve as a species-specific drug target. This research contributes to the expanding knowledge of ChE inhibitors based on ruthenium complexes and highlights their potential as promising therapeutic candidates for chronic neurodegenerative diseases.

Dynamic interchange between two protonation states is characteristic of active sites of cholinesterases

Cholinesterases are well-known and widely studied enzymes crucial to human health and involved in neurology, Alzheimer's, and lipid metabolism. The protonation pattern of active sites of cholinesterases influences all the chemical processes within, including reaction, covalent inhibition by nerve agents, and reactivation. Despite its significance, our comprehension of the fine structure of cholinesterases remains limited. In this study, we employed enhanced-sampling quantum-mechanical/molecular-mechanical calculations to show that cholinesterases predominantly operate as dynamic mixtures of two protonation states. The proton transfer between two non-catalytic glutamate residues follows the Grotthuss mechanism facilitated by a mediator water molecule. We show that this uncovered complexity of active sites presents a challenge for classical molecular dynamics simulations and calls for special treatment. The calculated proton transfer barrier of 1.65 kcal/mol initiates a discussion on the potential existence of two coupled low-barrier hydrogen bonds in the inhibited form of butyrylcholinesterase. These findings expand our understanding of structural features expressed by highly evolved enzymes and guide future advances in cholinesterase-related protein and drug design studies.

Bitter yet beneficial: The dual role of dietary alkaloids in managing diabetes and enhancing cognitive function

With the rising prevalence of diabetes and its association with cognitive impairment, interest in the use of dietary alkaloids and other natural products has grown significantly. Understanding how these compounds manage diabetic cognitive dysfunction (DCD) is crucial. This comprehensive review explores the etiology of DCD and the effects of alkaloids in foods and dietary supplements that have been investigated as DCD therapies. Data on how dietary alkaloids like berberine, trigonelline, caffeine, capsaicin, 1-deoxynojirimycin, nuciferine, neferine, aegeline, tetramethylpyrazine, piperine, and others regulate cognition in diabetic disorders were collected from PubMed, Research Gate, Web of Science, Science Direct, and other relevant databases. Dietary alkaloids could improve memory in behavioral models and modulate the mechanisms underlying the cognitive benefits of these compounds, including their effects on glucose metabolism, gut microbiota, vasculopathy, neuroinflammation, and oxidative stress. Evidence suggests that dietary alkaloids hold promise for improving cognition in diabetic patients and could open exciting avenues for future research in diabetes management.

New amide and diterpene alkaloids with anticholinesterase activity from Delphinium cyphoplectrum roots

BACKGROUND

The cholinergic hypothesis posits a robust correlation between the onset of Alzheimer's disease and a pronounced deficit in acetylcholine, a pivotal neurotransmitter crucial for the central cholinergic nervous system's function, pivotal for memory and learning. Diterpene alkaloids exhibit intricate and distinctive chemical structures that facilitate their passage through the blood-brain barrier. Moreover, their potent pharmacological attributes render them promising candidates for addressing central nervous system disorders.

OBJECTIVES

This investigation aims to scrutinize the alkaloidal composition of Delphinium cyphoplectrum (Ranunculaceae) roots, further exploring their anticholinesterase inhibitory activity and mode of inhibition.

METHOD

Innovative chromatography techniques were repetitively employed to purify the alkaloids. Acetylcholinesterase (AChE) inhibition assays were conducted using Ellman's tests. The mode of inhibition was meticulously characterized through Michaelis-Menten, and Lineweaver-Burk plots. Conducting molecular docking studies, we employed the AUTO DOCK 4.2 software package.

RESULTS

Eight alkaloids were identified including five C19-diterpene alkaloids (6,14,16,18-tetramethoxy-1,7,8-trihydroxy-4-methylaconitane (1), 6,16,18-trimethoxy-1,7,8,14-tetrahydroxy-4-methylaconitane (2), 6,8,16,18-tetramethoxy-1,7,14-trihydroxy-4-methylaconitane (3), 6,14,16-trimethoxy-1,7,8,18-tetrahydroxy-4-methylaconitane (4), and 14-O-acetyl-8,16-dimethoxy-1,6,7,18-tetrahydroxy-4-methylaconitane (5)), an epoxy C18-diterpene alkaloid (6,8,16-trimethoxy-1,7,14-trihydroxy-3,4-epoxyaconitane (6)), a known (pyrrolidin-2-one (7) and an undescribed amide alkaloid (1-(2'-hydroxylethylamine)-3,5,5,-trimethyl-1,5-dihydro-2H-pyrrol-2-one (8). All diterpene alkaloids underwent assessment for acetylcholinesterase (AChE) inhibition assay and displayed noteworthy AChE activity, surpassing that of the reference drug (with IC50 values of 13.7, 21.8, 23.4, 28.2, 40.4, and 23.9 for compounds 1-6, respectively, in comparison to 98.4 for Rivastigmine). Analysis of Michaelis-Menten and Lineweaver-Burk plots represents an uncompetitive mode of inhibition for compound 1 on AChE. Notably, computational docking simulations indicated that all diterpene alkaloids were accommodated within the same enzymatic cleft as the reference ligand, and displaying superior free binding energy values (from - 10.32 to -8.59 Kcal.mol-1) in contrast to Rivastigmine (-6.31 Kcal.mol-1).

CONCLUSION

The phytochemical analysis conducted on the roots of Delphinium cyphoplectrum yielded the identification of eight alkaloidal compounds including one C18-diterpene, five C19-diterpene, one pyrrolidine and one amide alkaloids. AChE inhibition assay and molecular simulations unveiled remarkable significant potency attributed to the C19-diterpene alkaloids by the order of 1 > 2 > 3,6 > 4 > 5. Presence of hydroxyl group on C-1, C-7, C-8, C-14, and C-18 increased the effect. The best in vitro activity was recorded for compound 1 able to bind to Asp72 in the narrow region of PAS, while interacting by pi-sigma with Phe330 at the hydrophobic region of the gorge involving the acyl and choline binding site. This observation underscores the substantial promise of this category of natural products in the realm of drug discovery for Alzheimer's Disease, offering a compelling avenue for further research and therapeutic development.

Centella asiatica improves memory and executive function in middle-aged rats by controlling oxidative stress and cholinergic transmission

ETHNOPHARMACOLOGICAL RELEVANCE

Centella asiatica (L.) Urban, is a medicinal herb with rich history of traditional use in Indian subcontinent. This herb has been valued for its diverse range of medicinal properties including memory booster, and also as a folk treatment for skin diseases, wound healing and mild diuretic.

AIM OF STUDY

Aging is a gradual and continuous process of natural decay in the biological systems, including the brain. This work aims to evaluate the effectiveness of ethanolic extract of Centella asiatica (CAE) on age-associated cognitive impairments in rats, as well as the underlying mechanism.

MATERIAL AND METHODS

Rats were allocated into five distinct groups of 5 animals each: Young rats (3 months old rats), middle-aged (m-aged) rats (13-14 months old), and the remaining three groups were comprised of m-aged rats treated with different concentrations of CAE, viz., 150, 300, and 450 mg/kg b. w., orally for 42 days. Y-maze, open field, novel object recognition, and elevated plus maze tests were used to assess animal behavior. The malondialdehyde (MDA), superoxide dismutase (SOD), and acetylcholinesterase (AChE) assays; and H&E staining were done in the rat brain to assess the biochemical and structural changes. CAE was also subjected to HPLC analysis, in vitro antioxidant and anti-cholinergic activity. The active compounds of CAE were docked with AChE and BuChE in molecular docking study.

RESULTS

The results showed that CAE treatment improves behavioral performance; attenuates the age-associated increase in MDA content, SOD, and AChE activity; and reduces neuronal loss. In vitro study showed that CAE has concentration-dependent antioxidant and anti-AChE activity. Furthermore, the presence of Asiatic acid and Madecassic acid in CAE and their good binding with cholinergic enzymes (in silico) also suggest the anticholinergic effect of CAE.

CONCLUSION

The findings of the current study show that the anticholinergic and antioxidant effects of CAE are attributable to the presence of Asiatic acid and Madecassic acid, which not only provide neuroprotection against age-associated cognitive decline but also reverse it.

The Potential Risk of Reduced Serum Cholinesterase Activity in COVID-19 Patients Suffering From Cytokine Storm

Background and objective Several blood biochemical parameters are used to biomonitor coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Reduced serum cholinesterase (ChE) has been suggested to be a predictive indicator of the severity and outcome of COVID-19 infection. This study aimed to examine serum ChE activity in hospitalized and terminally ill COVID-19 patients with cytokine storm and evaluate the enzyme for the in vitro ChE-inhibitory activity of the organophosphate dichlorvos. Methods We determined the serum ChE activity, electrometrically, among hospitalized COVID-19-cytokine storm patients and their non-cytokine storm counterparts. Aliquots of serum samples from healthy volunteers, COVID-19-cytokine storm patients, and non-cytokine storm COVID-19 patients were pooled separately. They were incubated in vitro for 10 minutes with dichlorvos at 0.25 or 0.5 μM. Serum samples from the three groups were subjected to ChE inhibition temporally (5-60 minutes) by 0.25 μM dichlorvos to evaluate the kinetics of enzyme inhibition using steady-state kinetics. Results Of the 165 hospitalized patients with COVID-19, 33 (20%) suffered from the cytokine storm. Serum ChE activity of female COVID-19 patients with cytokine storm was significantly lower than that of the non-cytokine storm counterparts. Risk analysis of reduced serum ChE activity (≥20%) among the 33 COVID-19 patients with cytokine storm compared to 111 non-cytokine storm COVID-19 patients revealed that the former were significantly at risk of reduced enzyme activity. In vitro, dichlorvos at 0.25 μM and 0.5 μM significantly inhibited serum ChE activity in all the groups. The COVID-19-cytokine storm group was the least affected. Dichlorvos at 0.25 μM progressively (5-60 minutes) inhibited serum ChE activity. The inhibition kinetic parameters in COVID-19-cytokine storm patients showed a decrease in the half-life of inhibition (14.54%), inhibition rate (51.46%), and total inhibition time (14.55%). Conclusions Reduced serum ChE in COVID-19 patients with cytokine storm could be adopted as a potential additional laboratory examination tool for bedside risk assessment. The in vitro inhibition profile of serum ChE activity by dichlorvos in COVID-19-cytokine storm patients suggests reduced susceptibility of the enzyme to inhibition. The response of COVID-19 patients to ChE-inhibiting medications should be cautiously evaluated with prior in vitro tests.

Dual-target inhibitors of cholinesterase and GSK-3β to modulate Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease that affects over 55 million patients worldwide. Most of the approved small-molecule drugs for AD have been designed to tackle a single pathological hallmark, such as cholinergic dysfunction or amyloid toxicity, and thus may not fully address the multifactorial nature of the disease. Inhibition of both cholinesterase and glycogen synthase kinase-3β (GSK-3β) has emerged as a promising strategy to modulate AD. However, the dual inhibition of these two targets posts challenges in molecular design: issues related to target engagements and biopharmaceutical properties in particular must be overcome. In this review, we discuss the physiopathological roles and structures of cholinesterase and GSK-3β as well as recently reported dual-target inhibitors. We critically evaluate the current status of the discovery of dual-target inhibitors of cholinesterase and GSK-3β, and highlight further perspectives.

Inhibitory effect of galantamine and donepezil combination against cholinesterase: An in silico and in vitro study

This study aimed to evaluate the in silico and in vitro inhibitory effect of the combined use of galantamine (GAL) and donepezil (DON) against acetylcholinesterase and butyrylcholinesterase (BuChE) enzymes. In silico and in vitro cholinesterase analysis were carried out for GAL and DON alone and combined. Molecular modeling studies were carried out (docking analysis, molecular dynamics simulation, and quantum theory of atoms in molecules). Cholinesterase's inhibitory activities by modified Ellman's method and the drug combination effect using the Chou-Talalay method were assayed. GAL/DON combination showed the co-occupancy of the ligands in both enzymes through in silico studies. Regarding in vitro BuChE inhibition analyses, three of five combinations showed an interaction between GAL and DON at the threshold of additive affect (0.9 < CI < 1.1), with a tendency toward a synergistic effect for higher concentrations. This is the first report showing the efficacy of the GAL/DON combinations inhibiting BuChE, showing the importance of analyzing the behavior of different ligands when co-occupancy into the active site is possible. These combinations might be a possible therapy to improved efficacy, reduced doses, minor side effects, and high levels of the neurotransmitter in the synaptic space for Alzheimer's disease.

Emerging significance of butyrylcholinesterase

Butyrylcholinesterase (BChE; EC 3.1.1.8), an enzyme structurally related to acetylcholinesterase, is widely distributed in the human body. It plays a role in the detoxification of chemicals such as succinylcholine, a muscle relaxant used in anesthetic practice. BChE is well-known due to variant forms of the enzyme with little or no hydrolytic activity which exist in some endogamous communities and result in prolonged apnea following the administration of succinylcholine. Its other functions include the ability to hydrolyze acetylcholine, the cholinergic neurotransmitter in the brain, when its primary hydrolytic enzyme, acetylcholinesterase, is absent. To assess its potential roles, BChE was studied in relation to insulin resistance, type 2 diabetes mellitus, cognition, hepatic disorders, cardiovascular and cerebrovascular diseases, and inflammatory conditions. Individuals who lack the enzyme activity of BChE are otherwise healthy, until they are given drugs hydrolyzed by this enzyme. Therefore, BChE is a candidate for the study of loss-of-function mutations in humans. Studying individuals with variant forms of BChE can provide insights into whether they are protected against metabolic diseases. The potential utility of the enzyme as a biomarker for Alzheimer's disease and the response to its drug treatment can also be assessed.

Human blood markers of cholinergic neurotoxicity and neuropathy: A useful guide for laboratory applications

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are useful markers to assess the effects of exposure to anticholinesterase insecticides (Anti-AChE). In addition, lymphocyte neuropathy target esterase (LNTE) has been used as biomarker of neuropathic organophosphate compounds (OPs). Thus, this study evaluates the main types of circulating biomarkers related to the cholinergic system and to the neuropathy induced by OPs in standardized human samples. To achieve this objective, total protein of human plasma, erythrocytes and lymphocytes were first standardized, and then AChE, BChE and LNTE activities in human blood were evaluated in the presence of inhibitors. The acceptance criteria of the regulatory agency were respected with coefficients of regression of curves of 0.9972 for cholinesterase and 0.9956 for LNTE analyses. The wavelength established to perform cholinesterase assay was 450 nm and the time of incubation of the enzymes with inhibitors was 30 min. Differences were observed among the IC50 values regarding the in vitro inhibition of AChE, BChE and LNTE in the presence of OPs. In conclusion, the procedures demonstrated by the present work were simple, fast, inexpensive, sensitive, easy to be replicated and suitable to make conclusions about the neurotoxicity induced by Anti-AChE and neuropathic OPs.

Furofuranoid-Type Lignans and Related Phenolics from Anisacanthus virgularis (Salisb.) Nees with Promising Anticholinesterase and Anti-Ageing Properties: A Study Supported by Molecular Modelling

Lignan phytomolecules demonstrate promising anti-Alzheimer activity by alleviating dementia and preserving nerve cells. The purpose of this work is to characterize the lignans of Anisacanthus virgularis and explore their potential anti-acetylcholinesterase and anti-ageing effects. Phytochemical investigation of A. virgularis aerial parts afforded a new furofuranoid-type lignan (1), four known structural analogues, namely pinoresinol (2), epipinoresinol (3), phillyrin (4), and pinoresinol 4-O-β-d-glucoside (5), in addition to p-methoxy-trans-methyl cinnamate (6) and 1H-indole-3-carboxaldehyde (7). The structures were established from thorough spectroscopic analyses and comparisons with the literature. Assessment of the anticholinesterase activity of the lignans 1-5 displayed noticeable enzyme inhibition of 1 (IC50 = 85.03 ± 4.26 nM) and 5 (64.47 ± 2.75 nM) but lower activity of compounds 2-4 as compared to the reference drug donepezil. These findings were further emphasized by molecular docking of 1 and 5 with acetylcholinesterase (AChE). Rapid overlay chemical similarity (ROCS) and structure-activity relationships (SAR) analysis highlighted and rationalized the anti-AD capability of these compounds. Telomerase activation testing of the same isolates revealed 1.64-, 1.66-, and 1.72-fold activations in cells treated with compounds 1, 5, and 4, respectively, compared to untreated cells. Our findings may pave the way for further investigations into the development of anti-Alzheimer and/or anti-ageing drugs from furofuranoid-type lignans.

Enzyme ChE, cholinergic therapy and molecular docking: Significant considerations and future perspectives

Enzyme Che plays an essential role in cholinergic and non-cholinergic functions. It is present in the fertilized/unfertilized eggs and sperm of different species. Inclusion criteria for data collection from electronic databases NCBI and Google Scholar are enzyme AChE/BChE, cholinergic therapy, genomic organization and gene transcription, enzyme structure, biogenesis, transport, processing and localization, molecular signaling and biological function, polymorphism and influencing factors. Enzyme Che acts as a signaling receptor during hematopoiesis, protein adhesion, amyloid fiber formation, neurite outgrowth, bone development, and maturation, explaining the activity out of synaptic neurotransmission. Polymorphism in the Che genes correlates to various diseases and diverse drug responses. In particular, change accompanies cancer, neurodegenerative, and cardiovascular disease. Literature knowledge indicates the importance of Che inhibitors that influence biochemical and molecular pathways in disease treatment, genomic organization, gene transcription, structure, biogenesis, transport, processing, and localization of Che enzyme. Enzyme Che polymorphism changes indicate the possibility of efficient and new inhibitor drug target mechanisms in diverse research areas.

13C NMR-based dereplication using MixONat software to decipher potent anti-cholinesterase compounds in Mesua lepidota bark

A bio-assay guided fractionation strategy based on cholinesterase assay combined with 13C NMR-based dereplication was used to identify active metabolites from the bark of Mesua lepidota. Eight compounds were identified with the aid of the 13C NMR-based dereplication software, MixONat, i.e., sitosterol (1), stigmasterol (2), α-amyrin (3), friedelin (6), 3β-friedelinol (7), betulinic acid (9), lepidotol A (10) and lepidotol B (11). Further bio-assay guided isolation of active compounds afforded one xanthone, pyranojacareubin (12) and six coumarins; lepidotol A (10), lepidotol B (11), lepidotol E (13), lepidotin A (14), and lepidotin B (15), including a new Mammea coumarin, lepidotin C (16). All the metabolites showed strong to moderate butyrylcholinesterase (BChE) inhibition. Lepidotin B (15) exhibited the most potent inhibition towards BChE with a mix-mode inhibition profile and a Ki value of 1.03 µM. Molecular docking and molecular dynamics simulations have revealed that lepidotin B (15) forms stable interactions with key residues within five critical regions of BChE. These regions encompass residues Asp70 and Tyr332, the acyl hydrophobic pocket marked by Leu286, the catalytic triad represented by Ser198 and His438, the oxyanion hole (OH) constituted by Gly116 and Gly117, and the choline binding site featuring Trp82. To gauge the binding strength of lepidotin B (15) and to pinpoint pivotal residues at the binding interface, free energy calculations were conducted using the Molecular Mechanics Generalized Born Surface Area (MM-GBSA) approach. This analysis not only predicted a favourable binding affinity for lepidotin B (15) but also facilitated the identification of significant residues crucial for the binding interaction.

Association of Reduced Maternal Plasma Cholinesterase Activity With Preeclampsia: A Meta-Analysis

Blood butyrylcholinesterase (BChE) activity has been found to decrease during pregnancy and reportedly decrease even more in preeclampsia (PE). The purpose of the present meta-analysis was to answer a specific question of whether BChE activity (in the plasma, serum, or whole blood) is reduced in pregnant women suffering from PE compared to those with normal pregnancy. The meta-analysis included 15 studies with 20 records of BChE activity in 608 women compared to 569 healthy pregnant (control) ones. The studies were subjected to quality assessment using the Newcastle-Ottawa Scale (NOS). Using the Meta-Essentials software program 1.5, the one-group random effects model and forest plot revealed that the percentage of BChE activity in pregnant women with PE was 84.84% of the control value, with a standard error of 4.09 and 95% C.I. of 76.28, 93.41, indicating a significant 15.16% reduction in BChE activity in comparison to healthy pregnancy. No significant heterogeneity was seen in the analyzed data and the funnel plot did show publication bias. Subgroup (mild, severe, and unclassified PE) forest plot analysis revealed that the % BChE activities in PE compared to respective healthy pregnancies were 96.28%, 97.08%, and 76.62%, respectively with no heterogeneity. The median NOS score of the 15 studies included in the meta-analysis was 7, ranging from 5 to 8 (medium to high quality), and the forest plot showed an effect size of 0.735. This meta-analysis shows that BChE activity is reduced in PE compared with normal pregnancy and its value as a biomarker warrants further clinical studies.

Synthesis and evaluation of Fmoc-amino esters and amides bearing a substrate like quaternary ammonium group as selective butyrylcholinesterase inhibitors

The depletion of the neurotransmitter acetylcholine has been suggested to contribute to the reduced cognitive function observed in individuals suffering from neurodegenerative diseases such as Alzheimer's Disease (AD). For the two major cholinesterases, butyrylcholinesterase (BChE) and acetylcholinesterase (AChE), increased BChE activity observed in individuals with AD has been suggested to deplete acetylcholine levels. To reduce acetylcholine degradation and help restore the pool of the neurotransmitter, specific and potent BChE inhibitors are sought. Our previous findings have identified 9-fluorenylmethoxycarbonyl (Fmoc) amino acid-based inhibitors as effective BChE inhibitors. The amino acid-based compounds offered the opportunity to survey a range of structural features to enhance interactions with the enzyme active site. As enzymes interact with features of their substrates, incorporation of substrate-like features was predicted to lead to better inhibitors. Specifically, incorporation of a trimethylammonium moiety to mimic the cationic group of acetylcholine may lead to increased potency and selectivity. To test this model, a series of inhibitors bearing a cationic trimethylammonium group were synthesized, purified, and characterized. While the Fmoc-ester derivatives inhibited the enzyme, additional experiments showed the compounds acted as substrates and were enzymatically hydrolyzed. Inhibition studies with the Fmoc-amide derivatives showed that the compounds do not act as substrates and selectively inhibit BChE with IC50 values in the 0.06-10.0 µM range. Computational docking studies suggest that the inhibitors can interact with cholinyl binding site and peripheral site. Overall, the results suggest that introducing substrate-like characteristics within the Fmoc-amino acid-based background increases their potency. The versatile and ready access to amino acid-based compounds offers an attractive system to further our understanding of the relative importance of protein-small molecule interactions while guiding the development of better inhibitors.

Antifungal Activities of Fluorinated Pyrazole Aldehydes on Phytopathogenic Fungi, and Their Effect on Entomopathogenic Nematodes, and Soil-Beneficial Bacteria

Fluoro-substituted pyrazoles have a wide range of biological activities, such as antibacterial, antiviral, and antifungal activities. The aim of this study was to evaluate the antifungal activities of fluorinated 4,5-dihydro-1H-pyrazole derivatives on four phytopathogenic fungi: Sclerotinia sclerotiorum, Macrophomina phaseolina, Fusarium oxysporum f. sp. lycopersici, and F. culmorum. Moreover, they were tested on two soil beneficial bacteria-Bacillus mycoides and Bradyrhizobium japonicum-as well as two entomopathogenic nematodes (EPNs)-Heterorhabditis bacteriophora and Steinernema feltiae. The molecular docking was performed on the three enzymes responsible for fungal growth, the three plant cell wall-degrading enzymes, and acetylcholinesterase (AChE). The most active compounds against fungi S. sclerotiorum were 2-chlorophenyl derivative (H9) (43.07% of inhibition) and 2,5-dimethoxyphenyl derivative (H7) (42.23% of inhibition), as well as H9 against F. culmorum (46.75% of inhibition). Compounds were shown to be safe for beneficial soil bacteria and nematodes, except for compound H9 on EPN H. bacteriophora (18.75% mortality), which also showed the strongest inhibition against AChE (79.50% of inhibition). The molecular docking study revealed that antifungal activity is possible through the inhibition of proteinase K, and nematicidal activity is possible through the inhibition of AChE. The fluorinated pyrazole aldehydes are promising components of future plant protection products that could be environmentally and toxicologically acceptable.

Novel thienocycloalkylpyridazinones as useful scaffolds for acetylcholinesterase inhibition and serotonin 5-HT6 receptor interaction

A library of eighteen thienocycloalkylpyridazinones was synthesized for human acetylcholinesterase (hAChE) and butyrylcholinesterase (hBChE) inhibition and serotonin 5-HT₆ receptor subtype interaction by following a multitarget-directed ligand approach (MTDL), as a suitable strategy for treatment of Alzheimer's disease (AD). The novel compounds featured a tricyclic scaffold, namely thieno[3,2-h]cinnolinone, thienocyclopentapyridazinone and thienocycloheptapyridazinone, connected through alkyl chains of variable length to proper amine moieties, most often represented by N-benzylpiperazine or 1-(phenylsulfonyl)-4-(piperazin-1-ylmethyl)-1H-indole as structural elements addressing AChE and 5-HT₆ interaction, respectively. Our study highlighted the versatility of thienocycloalkylpyridazinones as useful architectures for AChE interaction, with several N-benzylpiperazine-based analogues emerging as potent and selective hAChE inhibitors with IC₅₀ in the 0.17-1.23 μM range, exhibiting low to poor activity for hBChE (IC₅₀ = 4.13-9.70 μM). The introduction of 5-HT₆ structural moiety phenylsulfonylindole in place of N-benzylpiperazine, in tandem with a pentamethylene linker, gave potent 5-HT₆ thieno[3,2-h]cinnolinone and thienocyclopentapyridazinone-based ligands both displaying hAChE inhibition in the low micromolar range and unappreciable activity towards hBChE. While docking studies provided a rational structural explanation for AChE/BChE enzyme and 5-HT₆ receptor interaction, in silico prediction of ADME properties of tested compounds suggested further optimization for development of such compounds in the field of MTDL for AD.

The kinetic and molecular docking analysis of interactions between three V-type nerve agents and four human cholinesterases

G and V-type nerve agents represent the most toxic chemical warfare agents. Their primary toxicity was the consequence of the covalent inhibition of the pivotal acetylcholinesterase (AChE), which induces overstimulation of cholinergic receptors and overaccumulation of cholines, eventually leading to death by respiratory arrest. The inhibitory and reactivation kinetics of cholinesterase (ChE) are essential for the toxicology and countermeasures of nerve agents. Medical defensive research on V-type nerve agents (V agents) has been mainly reported on VX and VR. Here we demonstrated the first systematical kinetic analysis between the type of ChE [native or recombinant human AChE and butyrylcholinesterase (BChE)] and three V agents, including VX, VR, and Vs, another isomer of VX, and highlighted the effects of native and recombinant ChE differences. The spontaneous reactivation and aging kinetics data of Vs-inhibited BChEs were firstly reported here. The results showed that AChE was more easily inhibited by three V agent compared to BChE, regardless of whether it is native or recombinant. The increased inhibitory potency order on AChE was VX, Vs, then VR, and on BChE was VX, then Vs and VR. The difference between native and recombinant ChE could influence the inhibition, aging, and spontaneous reactivation kinetics of three V agents, whether AChE or BChE, which was systematically revealed for the first time. For inhibition kinetics, the k_i of three V agents for recombinant AChE was significantly higher than native AChE, and the stronger the inhibitory potency of V agents, the more pronounced difference in k_i. In terms of aging and spontaneous reactivation kinetics, recombinant ChE was found to be more prone to spontaneous reactivation, but more resistant to aging compared to native ChE, particularly for AChE. The performed covalent molecular docking results partially explained the effects of differences between native and recombinant ChE on enzyme kinetics from the perspective of binding energy and conformation.

An Overview of 1,2,3-triazole-Containing Hybrids and Their Potential Anticholinesterase Activities

Acetylcholine (ACh) neurotransmitter of the cholinergic system in the brain is involved in learning, memory, stress responses, and cognitive functioning. It is hydrolyzed into choline and acetic acid by two key cholinesterase enzymes, viz., acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). A loss or degeneration of cholinergic neurons that leads to a reduction in ACh levels is considered a significant contributing factor in the development of neurodegenerative diseases (NDs) such as Alzheimer's disease (AD). Numerous studies have shown that cholinesterase inhibitors can raise the level of ACh and, therefore, enhance people's quality of life, and, at the very least, it can temporarily lessen the symptoms of NDs. 1,2,3-triazole, a five-membered heterocyclic ring, is a privileged moiety, that is, a central scaffold, and is capable of interacting with a variety of receptors and enzymes to exhibit a broad range of important biological activities. Recently, it has been clubbed with other pharmacophoric fragments/molecules in hope of obtaining potent and selective AChE and/or BuChE inhibitors. The present updated review succinctly summarizes the different synthetic strategies used to synthesize the 1,2,3-triazole moiety. It also highlights the anticholinesterase potential of various 1,2,3-triazole di/trihybrids reported in the past seven years (2015-2022), including a rationale for hybridization and with an emphasis on their structural features for the development and optimization of cholinesterase inhibitors to treat NDs.

Rhanteriol, a New Rhanterium suaveolens Desf. Lignan with Pharmacological Potential as an Inhibitor of Enzymes Involved in Neurodegeneration and Type 2 Diabetes

Several specialized plant metabolites are reported to be enzyme inhibitors. In this investigation, the phytochemical composition and the biological activity of Rhanterium suaveolens Desf. were studied. One new lignan (rhanteriol 1) and seven known secondary metabolites were isolated from the aerial parts of R. suaveolens by using different chromatographic procedures. The biological properties of the R. suaveolens extracts and the new compound were evaluated by measuring their ability to inhibit the cholinesterase and carbohydrate-hydrolyzing enzymes, using cell-free in vitro methods. The new lignan, rhanteriol, was shown to inhibit α-amylase and α-glucosidase (IC₅₀ = 46.42 ± 3.25 μM and 26.76 ± 3.29 μM, respectively), as well as butyrylcholinesterase (IC₅₀ = 10.41 ± 0.03 μM), with an effect comparable to that of the respective standards, acarbose and galantamine. Furthermore, docking studies were performed suggesting the interaction mode of rhanteriol with the active sites of the investigated enzymes. The obtained data demonstrated that the aerial part of R. suaveolens could represent a source of active molecules, such as rhanteriol, usable in the development of treatments for preventing or treating type 2 diabetes mellitus and neurodegeneration.

Potential revival of cholinesterase inhibitors as drugs in veterinary medicine

The cholinergic system is involved in the regulation of all organ systems and has acetylcholine (ACh) as almost its only neurotransmitter. Any substance is called cholinergic if it can alter the action of acetylcholine. Cholinesterases (ChEs) are enzymes that enable the hydrolysis of acetylcholine and in this way ensure homeostasis in cholinergic synapses. Cholinesterase inhibitors (ChEi) are a group of indirect-acting cholinergic agonists that influence the activity of the cholinergic system. Several compounds that can inhibit cholinesterases are of importance to veterinary medicine from pharmacological and toxicological perspective. The frequency of their use in veterinary medicine has fluctuated over the years and is now reduced to a minimum. They are mainly used in agriculture as pesticides, and some are rarely used as parasiticides for companion animals and livestock. In recent years, interest in the use of new cholinesterase inhibitors has increased since canine cognitive dysfunction (CCD) became a recognized and extensively studied disease. Similar to Alzheimer's disease (AD) in humans, CCD can be treated with cholinesterase inhibitors that cross the blood-brain barrier. In this review, the mammalian cholinergic system and the drugs that interact with cholinesterases are introduced. Cholinesterase inhibitors that can be used for the treatment of CCD are described in detail.

Levetiracetam Ameliorates Doxorubicin-Induced Chemobrain by Enhancing Cholinergic Transmission and Reducing Neuroinflammation Using an Experimental Rat Model and Molecular Docking Study

Cancer chemotherapy-induced cognitive impairment (chemobrain) is a major complication that affects the prognosis of therapy. Our study evaluates the nootropic-like activity of levetiracetam (LEVE) against doxorubicin (DOX)-induced memory defects using in vivo and molecular modelling. Rats were treated with LEVE (100 and 200 mg/kg, 30 days) and chemobrain was induced by four doses of DOX (2 mg/kg, i.p.). Spatial memory parameters were evaluated using an elevated plus maze (EPM) and Y-maze. Additionally, acetylcholinesterase (AChE) and the neuroinflammatory biomarkers cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2), nuclear factor-κB (NF-κB), and tumor necrosis factor-alpha (TNF-α) were analyzed using brain homogenate. PharmMapper was used for inverse docking and AutoDock Vina was used for molecular docking. LEVE treatment significantly diminished the DOX-induced memory impairment parameters in both the EPM and Y-maze. In addition, the drug treatment significantly reduced AChE, COX-2, PGE2, NF-κB, and TNF-α levels compared to DOX-treated animals. The inverse docking procedures resulted in the identification of AChE as the potential target. Further molecular modelling studies displayed interactions with residues Gly118, Gly119, and Ser200, critical for the hydrolysis of ACh. Analysis of the results suggested that administration of LEVE improved memory-related parameters in DOX-induced animals. The ‘nootropic-like’ activity could be related to diminished AChE and neuroinflammatory mediator levels.

Synthesis, anticholinesterase activity, molecular docking, and molecular dynamic simulation studies of 1,3,4-oxadiazole derivatives

Two new series of 1,3,4-oxadiazoles bearing pyridine and thiazole heterocycles (4a-h and 5a-h) were synthesized (2,5-disubstituted-1,3,4-oxadiazoles). The structures of these newly synthesized compounds were confirmed by ¹ H nuclear magnetic resonance (NMR), ¹³ C NMR, high-resolution mass spectrometric and Fourier transform infrared spectroscopic methods. All these compounds were evaluated for their enzyme inhibitory activities against two cholinesterase enzymes, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). From the studies, we identified compounds 4a, 4h, 5a, 5d, and 5e as selective AChE inhibitors, with IC₅₀ values ranging from 0.023 to 0.037 μM. Furthermore, docking studies of these compounds were performed at the active sites of their target enzymes. The molecular docking study showed that 5e possessed an ideal docking pose with interactions inside AChE.

Neurotoxicity Assessment of Four Different Pesticides Using In Vitro Enzymatic Inhibition Assays

Pesticides affect different organs and tissues according to their bioavailability, chemical properties and further molecular interactions. In animal models exposed to several classes of pesticides, neurotoxic effects have been described, including the reduction of acetylcholinesterase activity in tissue homogenates. However, in homogenates, the reduction in enzymatic activity may also result from lower enzymatic expression and not only from enzymatic inhibition. Thus, in this work, we aimed to investigate the neurotoxic potential of four distinct pesticides: glyphosate (herbicide), imazalil (fungicide), imidacloprid (neonicotinoid insecticide) and lambda-cyhalothrin (pyrethroid insecticide), by assessing their inhibitory effect on the activity of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and tyrosinase, by using direct in vitro enzymatic inhibition methods. All pesticides dose-dependently inhibited AChE activity, with an inhibition of 11 ± 2% for glyphosate, 48 ± 2% for imidacloprid, 49 ± 3% for imazalil and 50 ± 3% for lambda-cyhalothrin, at 1 mM. Only imazalil inhibited BChE. Imazalil induced dose-dependent inhibition of BChE with identical pattern as that observed for AChE; however, for lower concentrations (up to 500 μM), imazalil showed higher specificity for AChE, and for higher concentrations, the same specificity was found. Imazalil, at 1 mM, inhibited the activity of BChE by 49 ± 1%. None of the pesticides, up to 1 mM, inhibited tyrosinase activity. In conclusion, the herbicide glyphosate shows specificity for AChE but low inhibitory capacity, the insecticides imidacloprid and λ-cyhalothrin present selective AChE inhibition, while the fungicide IMZ is a broad-spectrum cholinesterase inhibitor capable of inhibiting AChE and BChE in an equal manner. Among these pesticides, the insecticides and the fungicide are the ones with higher neurotoxic potential.

New naphtho/thienobenzo-triazoles with interconnected anti-inflammatory and cholinesterase inhibitory activity

New 1,2,3-triazolo(thieno)stilbenes were synthesized by Wittig reaction and photochemically transformed to corresponding substituted thienobenzo/naphtho-triazoles in high isolated yields. They were prepared to study the acetyl- and butyrylcholinesterase inhibition associated with the inhibition of TNFα cytokine production and anti-inflammatory activity. The best experimental results were achieved with the allyl-thienobenzotriazole and isopropyl, p-methoxybenzyl, and hydroxybutyl substituted naphthotriazoles bearing additional chloro or methoxy groups. The allyl-thienobenzotriazole photoproduct is twice as potent an inhibitor of eqBChE compared to the standard galantamine. At the same time, this compound strongly inhibited TNFα production in PBMCs in response to the LPS stimulus. The complexes between selected compounds with the active site of BChE and AChE are assessed by docking, providing insight into the stabilizing interactions between the potential inhibitor and the active site.

A Cobalt-Containing Compound as a Stronger Inhibitor than Galantamine to Inhibit Acetylcholinesterase Activity: A New Drug Candidate for Alzheimer’s Disease Treatment

Background: Acetylcholinesterase (AChE) regulates the transmission of neural messages by hydrolyzing acetylcholine in synaptic spaces. Objective: The effects of many AChE inhibitors have been evaluated in the treatment of Alzheimer’s disease, but the present study examined a synthetic complex containing cobalt (SC) for the first time in the field of enzyme activity to evaluate enzyme inhibitory function. Methods: Ellman’s test was applied. AChE function was assessed in the presence of SC through docking and molecular dynamics analyses. The second structure of AChE was studied through circular dichroism (CD) spectroscopy. Results: Several enzymatic methods were utilized for the kinetics of AChE, which indicated the non-Michaelis and positive homotropic behavior of AChE in the absence of inhibitors (Hill coefficient = 1.33). However, the existence of inhibitors did not eliminate this homotropic state, and even AChE had a more sigmoidal shape than the galantamine at the presence of SC. Based on the CD spectroscopy results, AChE structure changed in the existence of inhibitors and substrates. Bioinformatics analysis revealed SC bonding to the channel of active site AChE. The number of hydrogen bonds was such that the flexibility of the enzyme protein structure due to inhibitor binding reduced AChE function. Conclusion: The results reflected that AChE exhibited a non-Michaelis and positive homotropic behavior, leading to a more inhibitory effect on the SC than the galantamine. The positive homotropic behavior of AChE was intensified due to the alteration in AChE protein structure by binding SC to hydrophobic region in the active site pathway and impressing Trp84.

In Silico Screening of Cinnamon (Cinnamomum burmannii) Bioactive Compounds as Acetylcholinesterase Inhibitors

Alzheimer’s is a progressive and neurodegenerative disease that mainly affects people aged 65 years and older. The pathophysiology of Alzheimer’s is possibly related to the depletion of the neurotransmitter acetylcholine (ACh) due to beta-amyloid plaques and neurofibrillary tangles. Secondary metabolites found in cinnamon bark (Cinnamomum burmannii) have the potential as anticholinesterases to treat Alzheimer’s symptoms. This study aimed to identify the potency of bioactive compounds from cinnamon bark as AChE inhibitors in silico through analysis of binding energy, inhibition constants, and types of interactions. The research was conducted by screening virtually 60 test ligands using the PyRx program and molecular docking using the Autodock Tools program. The results of the ligand-receptor interaction analysis showed that 12 of the 15 tested ligands had potential as AChE inhibitors. Epicatechin and medioresinol are the ligands with the best potential for AChE inhibition with affinity close to the natural ligand or donepezil. Epicatechin has a binding energy of −10.0 kcal/mol and inhibition constant of 0.0459 M, with four hydrogen bonds and seven hydrophobic bonds. Meanwhile, medioresinol has −9.9 kcal/mol binding energy and inhibition constant of 0.0543 M, with one hydrogen bond and thirteen hydrophobic bonds.

Spatial Distribution and Stability of Cholinesterase Inhibitory Protoberberine Alkaloids from Papaver setiferum

During a research program to identify new cholinesterase inhibitors of natural origin, two new 7,8-didehydroprotoberberine alkaloids (1 and 2) and nine known compounds (3-11) were isolated from the capsules of the common ornamental poppy, Papaver setiferum (previously P. pseudo-orientale). Despite their reported instability, the 7,8-didehydroprotoberberines isolated herein appeared relatively stable, particularly as their trifluoroacetic acid salts. The spatial distributions of the isolated alkaloids were also analyzed using desorption electrospray ionization imaging mass spectrometry. The alkaloids were localized predominantly within the walls and vascular bundles of the capsules, with the highest relative abundances occurring in the lower half of the capsules toward the peduncle. The relative abundances of the alkaloids were also compared across plant development stages. Although most alkaloids did not show clear patterns in their concentration across development stages, the concentration of suspected oxidation products clearly spiked upon plant death. Finally, all isolated natural products were screened for inhibitory activities against a panel of cholinesterases, from both human and animal sources. These studies identified several competitive inhibitors of cholinesterases with potency in the low micromolar range (1-4, 6, 7), offering new lead compounds for the development of cholinesterase inhibitory drugs.

In Silico and Ex Vivo Analyses of the Inhibitory Action of the Alzheimer Drug Posiphen and Primary Metabolites with Human Acetyl- and Butyrylcholinesterase Enzymes

Alzheimer’s disease (AD) is the most common neurodegenerative disorder worldwide. Ongoing research to develop AD treatments has characterized multiple drug targets including the cholinergic system, amyloid-β peptide, phosphorylated tau, and neuroinflammation. These systems have the potential to interact to either drive or slow AD progression. Promising agents that simultaneously impact many of these drug targets are the AD experimental drug Posiphen and its enantiomer phenserine that, currently, are separately being evaluated in clinical trials. To define the cholinergic component of these agents, the anticholinesterase activities of a ligand dataset comprising Posiphen and primary metabolites ((+)-N1-norPosiphen, (+)-N8-norPosiphen, and (+)-N1,N8-bisnorPosiphen) were characterized and compared to those of the enantiomer phenserine. The “target” dataset involved the human cholinesterase enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Binding interactions between the ligands and targets were analyzed using Autodock 4.2. The computationally determined inhibitory action of these ligands was then compared to ex vivo laboratory-measured values versus human AChE and BChE. While Posiphen lacked AChE inhibitory action, its major and minor metabolites (+)-N1-norPosiphen and (+)-N1,N8-bisnorPosiphen, respectively, possessed modest AChE inhibitory activity, and Posiphen and all metabolites lacked BChE action. Phenserine, as a positive control, demonstrated AChE-selective inhibitory action. In light of AChE inhibitory action deriving from a major and minor Posiphen metabolite, current Posiphen clinical trials in AD and related disorders should additionally evaluate AChE inhibition; particularly if Posiphen should be combined with a known anticholinesterase, since this drug class is clinically approved and the standard of care for AD subjects, and excessive AChE inhibition may impact drug tolerability.

FDA-Approved Oximes and Their Significance in Medicinal Chemistry

Despite the scientific advancements, organophosphate (OP) poisoning continues to be a major threat to humans, accounting for nearly one million poisoning cases every year leading to at least 20,000 deaths worldwide. Oximes represent the most important class in medicinal chemistry, renowned for their widespread applications as OP antidotes, drugs and intermediates for the synthesis of several pharmacological derivatives. Common oxime based reactivators or nerve antidotes include pralidoxime, obidoxime, HI-6, trimedoxime and methoxime, among which pralidoxime is the only FDA-approved drug. Cephalosporins are β-lactam based antibiotics and serve as widely acclaimed tools in fighting bacterial infections. Oxime based cephalosporins have emerged as an important class of drugs with improved efficacy and a broad spectrum of anti-microbial activity against Gram-positive and Gram-negative pathogens. Among the several oxime based derivatives, cefuroxime, ceftizoxime, cefpodoxime and cefmenoxime are the FDA approved oxime-based antibiotics. Given the pharmacological significance of oximes, in the present paper, we put together all the FDA-approved oximes and discuss their mechanism of action, pharmacokinetics and synthesis.

Steady-state kinetic analysis of human cholinesterases over wide concentration ranges of competing substrates

Substrate competition for human acetylcholinesterase (AChE) and human butyrylcholinesterase (BChE) was studies under steady-state conditions using wide range of substrate concentrations. Competing couples of substates were acetyl-(thio)esters. Phenyl acetate (PhA) was the reporter substrate and competitor were either acetylcholine (ACh) or acetylthiocholine (ATC). The common point between investigated substrates is that the acyl moiety is acetate, i.e. same deacylation rate constant for reporter and competitor substrate. Steady-state kinetics of cholinesterase-catalyzed hydrolysis of PhA in the presence of ACh or ATC revealed 3 phases of inhibition as concentration of competitor increased: a) competitive inhibition, b) partially mixed inhibition, c) partially uncompetitive inhibition for AChE and partially uncompetitive activation for BChE. This sequence reflects binding of competitor in the active centrer at low concentration and on the peripheral anionic site (PAS) at high concentration. In particular, it showed that binding of a competing ligand on PAS may affect the catalytic behavior of AChE and BChE in an opposite way, i.e. inhibition of AChE and activation of BChE, regardless the nature of the reporter substrate. For both enzymes, progress curves for hydrolysis of PhA at very low concentration (≪K_m) in the presence of increasing concentration of ATC showed that: a) the competing substrate and the reporter substrate are hydrolyzed at the same time, b) complete hydrolysis of PhA cannot be reached above 1 mM competing substrate. This likely results from accumulation of hydrolysis products (P) of competing substrate and/or accumulation of acetylated enzyme·P complex that inhibit hydrolysis of the reporter substrate.

Novel tacrine-based acetylcholinesterase inhibitors as potential agents for the treatment of Alzheimer's disease: Quinolotacrine hybrids

A new series of quinolotacrine hybrids including cyclopenta- and cyclohexa-quinolotacrine derivatives were designed, synthesized, and assessed as anti-cholinesterase (ChE) agents. The designed derivatives indicated higher inhibitory effect on the acetylcholinesterase (AChE) with IC₅₀ values of 0.285-100 µM compared to butyrylcholinesterase (BChE) with IC₅₀ values of > 100 µM. Of these compounds, cyclohexa-quinolotacrine hybrids displayed a little better anti-AChE activity than cyclopenta-quinolotacrine hybrids. Compound 8-amino-7-(3-hydroxyphenyl)-5,7,9,10,11,12-hexahydro-6H-pyrano[2,3-b:5,6-c'] diquinolin-6-one (6m) including 3-hydroxyphenyl and cyclohexane ring moieties exhibited the best AChE inhibitory activity with IC₅₀ value of 0.285 µM. The kinetic and molecular docking studies indicated that compound 6m occupied both the catalytic anionic site (CAS) and peripheral anionic site (PAS) of AChE as a mixed inhibitor. Using neuroprotective assay against H₂O₂-induced cell death in PC12 cells, the compound 6h illustrated significant protection among the assessed compounds. In silico ADME studies estimated good drug-likeness for the designed compounds. As a result, these quinolotacrine hybrids can be very encouraging AChE inhibitors to treat Alzheimer's disease. A novel series of quinolotacrine hybrids were designed, synthesized, and evaluated against AChE and BChE enzymes as potential agents for the treatment of AD. The hybrids showed good to significant inhibitory activity against AChE (0.285-100 μM) compared to butyrylcholinesterase (BChE) with IC₅₀ values of > 100 μM. Among them, compound 8-amino-7-(3-hydroxyphenyl)-5,7,9,10,11,12-hexahydro-6H-pyrano[2,3-b:5,6-c'] diquinolin-6-one (6 m) bearing 3-hydroxyphenyl moiety and cyclohexane ring exhibited the highest anti-AChE activity with IC₅₀ value of 0.285 μM. The kinetic and molecular docking studies illustrated that compound 6 m is a mixed inhibitor and binds to both the catalytic anionic site (CAS) and peripheral anionic site (PAS) of AChE.