Active Site Of Acetylcholinesterase Research Articles

Effect on Acetylcholinesterase and Anti-oxidant Activity of Synthetic Chalcones having a Good Predicted Pharmacokinetic Profile.

Acetylcholinesterase (AChE) is an important target in the development of drug to treat Alzheimer's disease (AD). In this work, we investigated the effect of twenty-two synthesized chalcones on AChE activity. This work is aimed to synthesize and evaluate the effect of chalcones on the AChE activity, as well as anti-oxidant activity and predict their pharmacokinetic profile. Chalcones were synthesized through a Claisen-Schmidt condensation and their inhibitory effect on the AChE was evaluated by the Elmann's colorimetric method. To determine the anti-oxidant activity the DPPH radical scavenging method was chosen. We found that all chalcones inhibit this activity, with IC50 values ranging from 0.008 to 4.8 µM. We selected the most active compound 19 with an IC50 value of 0.008 µM for a kinetic study demonstrating a competitive inhibition mode. Molecular docking simulations showed a good interaction between 19 and the active site of AChE. Considering the prediction of pharmacokinetic parameters being a useful tool for selecting potential drug candidates, our study results suggest that the majority of chalcones, including the most active one, have a promising pharmacokinetic profile and blood-brain barrier permeability. The involvement of reactive oxygen species (ROS) in AD-related events has encouraged us to evaluate these chalcones as radical scavengers. We have found that compound 19 is a potent AChE inhibitor, and based on kinetic studies, it acts as a competitive inhibitor.

Correlation of cholinergic drug induced quenching of acetylcholinesterase bound thioflavin-T fluorescence with their inhibition activity

The development of new acetylcholinesterase inhibitors (AChEIs) and subsequent assay of their inhibition efficiency is considered to be a key step for AD treatment. The fluorescence intensity of thioflavin-T (ThT) bound in the active site of acetylcholinesterase (AChE) quenches substantially in presence of standard AChEI drugs due to the dynamic replacement of the fluorophore from the AChE active site as confirmed from steady state emission as well as time-resolved fluorescence anisotropy measurement and molecular dynamics simulation in conjunction with docking calculation. The parametrized % quenching data for individual system shows excellent correlation with enzyme inhibition activity measured independently by standard Ellman AChE assay method in a high throughput plate reader system. The results are encouraging towards design of a fluorescence intensity based AChE inhibition assay method and may provide a better toolset to rapidly evaluate as well as develop newer AChE-inhibitors for AD treatment.

The Length Dependent Activity of Oximes on Reactivation of Tabun Inhibited Acetylcholinesterase; A Theoretical Study

In this work, the effect of ligand's length on interaction energy of six oximes, A [2-(hydroxyimino)-N-((1-(2-(2-((hydroxyimino)methyl)-1H-imidazol-1-yl)ethyl)-1H-1,2,3-triazol-4-yl)methyl)acetamide], B [2-(hydroxyimino)-N-((1-(3-(2-((hydroxyimino)methyl)-1H-imidazol-1-yl)propyl)-1H-1,2,3-triazol-4-yl)methyl)acetamide], C [2-(hydroxyimino)-N-((1-(4-(2-((hydroxyimino)methyl)-1H-imidazol-1-yl)butyl)-1H-1,2,3-triazol-4-yl)methyl)acetamide], D [2-(hydroxyimino)-N-((1-(5-(2-((hydroxyimino)methyl)-1H-imidazol-1-yl)pentyl)-1H-1,2,3-triazol-4-yl)methyl)acetamide], E [2-(hydroxyimino)-N-((1-(6-(2-((hydroxyimino)methyl)-1H-imidazol-1-yl)hexyl)-1H-1,2,3-triazol-4-yl)methyl)acetamide] and F [2-(hydroxyimino)-N-((1-(7-(2-((hydroxyimino)methyl)-1H-imidazol-1-yl)heptyl)-1H-1,2,3-triazol-4-yl)methyl)acetamide] with tabun inhibited acetylcholinesterase (t-AChE) is investigated by using docking methods. The results show that the size of ligands' length, due to changing the position of interactive groups of oximes in active site of enzyme can regulate oxime-enzyme interaction energy for better reactivation of inhibited cholinesterases by oximes. Indeed, increment of oxime-enzyme interaction energy has paradoxical effects both increasing of oxime affinity to t-AChE, and decreasing of the rate of the oxime access to phosphorus atom within tabun binding to the acetylcholinesterase active site. The obtained results show that to design an oxime as a drug, the length of oxime should be chosen in a size that the interaction of oxime and enzyme is neither too weak to couple, nor too strong to limit oxime mobility in reactivation t-AChE after coupling.

Discorhabdin alkaloids from Antarctic Latrunculia spp. sponges as a new class of cholinesterase inhibitors

The brominated pyrroloiminoquinone alkaloids discorhabdins B, L and G and 3-dihydro-7,8- dehydrodiscorhabdin C, isolated from methanol extracts of two specimens of Latrunculia sp. sponges collected near the Antarctic Peninsula, are here demonstrated for the first time to be reversible competitive inhibitors of cholinesterases. They showed Ki for electric eel acetylcholinesterase of 1.6–15.0 μM, for recombinant human acetylcholinesterase of 22.8–98.0 μM, and for horse serum butyrylcholinesterase of 5.0–76.0 μM. These values are promising when compared to the current cholinesterase inhibitors used for treatment of patients with Alzheimer's disease, to counteract the acetylcholine deficiency in the brain. Good correlation was obtained between IC50 data and results by molecular docking calculation on the binding interactions within the acetylcholinesterase active site, which also indicated the moieties in discorhabdin structures involved. To avoid unwanted peripheral side effects that can appear in patients using some acetylcholinesterase inhibitors, electrophysiological experiments were carried out on one of the most active of these compounds, discorhabdin G, which confirmed that it had no detectable undesirable effects on neuromuscular transmission and skeletal muscle function. These findings are promising for development of cholinesterase inhibitors based on the scaffold of discorhabdins, as potential new agents for treatment of patients with Alzheimer's disease.

Construction of an Acetylcholinesterase Sensor Based on Synthesized Paramagnetic Nanoparticles, a Simple Tool for Neurotoxic Compounds Assay.

Magnetic particles (MPs) have been widely used in biological applications in recent years as a carrier for various molecules. Their big advantage is in repeated use of immobilized molecules including enzymes. Acetylcholinesterase (AChE) is an enzyme playing crucial role in neurotransmission and the enzyme is targeted by various molecules like Alzheimer’s drugs, pesticides and warfare agents. In this work, an electrochemical biosensor having AChE immobilized onto MPs and stabilized through glutaraldehyde (GA) molecule was proposed for assay of the neurotoxic compounds. The prepared nanoparticles were modified by pure AChE and they were used for the measurement anti-Alzheimer’s drug galantamine and carbamate pesticide carbofuran with limit of detection 1.5 µM and 20 nM, respectively. All measurements were carried out using screen-printed sensor with carbon working, silver reference, and carbon auxiliary electrode. Standard Ellman’s assay was used for validation measurement of both inhibitors. Part of this work was the elimination of reversible inhibitors represented by galantamine from the active site of AChE. For this purpose, we used a lower pH to get the original activity of AChE after inhibition by galantamine. We also observed decarbamylation of the AChE-carbofuran adduct. Influence of organic solvents to AChE as well as repeatability of measurement with MPs with AChE was also established.

Acetylcholinesterase-capped Mesoporous Silica Nanoparticles Controlled by the Presence of Inhibitors.

Two different acetylcholinesterase (AChE)-capped mesoporous silica nanoparticles (MSNs), S1-AChE and S2-AChE, were prepared and characterized. MSNs were loaded with rhodamine B and the external surface was functionalized with either pyridostigmine derivative P1 (to yield solid S1) or neostigmine derivative P2 (to obtain S2). The final capped materials were obtained by coordinating grafted P1 or P2 with AChE's active sites (to give S1-AChE and S2-AChE, respectively). Both materials were able to release rhodamine B in the presence of diisopropylfluorophosphate (DFP) or neostigmine in a concentration-dependent manner via the competitive displacement of AChE through DFP and neostigmine coordination with the AChE's active sites. The responses of S1-AChE and S2-AChE were also tested with other enzyme inhibitors and substrates. These studies suggest that S1-AChE nanoparticles can be used for the selective detection of nerve agent simulant DFP and paraoxon.

DL0410 Ameliorates Memory and Cognitive Impairments Induced by Scopolamine via Increasing Cholinergic Neurotransmission in Mice.

Deficiency of the cholinergic system is thought to play a vital role in cognitive impairment of dementia. DL0410 was discovered as a dual inhibitor of acetylcholinesterase (AChE) and butyrylcholinestease (BuChE), with potent efficiency in in-vitro experiments, but its in vivo effect on the cholinergic model has not been evaluated, and its action mechanism has also not been illustrated. In the present study, the capability of DL0410 in ameliorating the amnesia induced by scopolamine was investigated, and its effect on the cholinergic system in the hippocampus and its binding mode in the active site of AChE was also explored. Mice were administrated DL0410 (3 mg/kg, 10 mg/kg, and 30 mg/kg), and mice treated with donepezil were used as a positive control. The Morris water maze, escape learning task, and passive avoidance task were used as behavioral tests. The test results indicated that DL0410 could significantly improve the learning and memory impairments induced by scopolamine, with 10 mg/kg performing best. Further, DL0410 inhibited the AChE activity and increased acetylcholine (ACh) levels in a dose-dependent manner, and interacted with the active site of AChE in a similar manner as donepezil. However, no difference in the activity of BuChE was found in this study. All of the evidence indicated that its AChE inhibition is an important mechanism in the anti-amnesia effect. In conclusion, DL0410 could be an effective therapeutic drug for the treatment of dementia, especially Alzheimer’s disease.

Targeting Alzheimer's disease by investigating previously unexplored chemical space surrounding the cholinesterase inhibitor donepezil

A series of twenty seven acetylcholinesterase inhibitors, as potential agents for the treatment of Alzheimer's disease, were designed and synthesised based upon previously unexplored chemical space surrounding the molecular skeleton of the drug donepezil, which is currently used for the management of mild to severe Alzheimer's disease. Two series of analogues were prepared, the first looking at the replacement of the piperidine ring in donepezil with different sized saturated N-containing ring systems and the second looking at the introduction of different linkers between the indanone and piperidine rings in donepezil. The most active analogue 5,6-dimethoxy-1-oxo-2,3-dihydro-1H-inden-2-yl 1-benzylpiperidine-4-carboxylate (67) afforded an in vitro IC50 value of 0.03 ± 0.07 μM against acetylcholinesterase with no cytotoxicity observed (IC50 of >100 μM, SH-SY5Y cell line). In comparison donepezil had an IC50 of 0.05 ± 0.06 μM and an observed cytotoxicity IC50 of 15.54 ± 1.12 μM. Molecular modelling showed a strong correlation between activity and in silico binding in the active site of acetylcholinesterase.

Halogen-directed drug design for Alzheimer's disease: a combined density functional and molecular docking study.

A series of halogen-directed donepezil drugs has been designed to inhibit acetyl cholinesterase (AChE). Density Functional theory (DFT) has been employed to optimize the chair as well as boat conformers of the parent drug and modified ligands at B3LYP/MidiX and B3LYP/6-311G + (d,p) level of theories. Charge distribution, dipole moment, enthalpy, free energy and molecular orbitals of these ligands are also investigated to understand how the halogen-directed modifications impact the ligand structure and govern the non-bonding interactions with the receptors. Molecular docking calculation has been performed to understand the similarities and differences between the binding modes of unmodified and halogenated chair-formed ligands. Molecular docking indicated donepezil and modified ligands had non-covalent interactions with hydrophobic gorges and anionic subsites of AChE. The –CF3-directed ligand possessed the most negative binding affinity. Non-covalent interactions within the ligand–receptor systems were found to be mostly hydrophobic and π- stacking type. F, Cl and –CF3 containing ligands emerge as effective and selective AChE inhibitors, which can strongly interact with the two active sites of AChE. In addition, we have also investigated selected pharmacokinetic parameters of the parent and modified ligands.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-2996-5) contains supplementary material, which is available to authorized users.

Biological evaluation and docking studies of some benzoxazole derivatives as inhibitors of acetylcholinesterase and butyrylcholinesterase.

A series of 2,5-disubstituted-benzoxazole derivatives (1-13) were evaluated as possible inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The results demonstrated that the compounds exhibited a broad spectrum of AChE and BChE inhibitory activity ranging between 6.80% and 90.21% except one compound which showed no activity against AChE at the specified molar concentration. Another derivative displayed a similar activity to that of reference drug (galanthamine) for inhibition of AChE and BChE. In addition, molecular docking of the compounds into active site of AChE was performed using recombinant human AChE (PDB ID: 4ey6) in order to understand ligand-protein interactions.

Novel N-allyl/propargyl tetrahydroquinolines: Synthesis via Three-component Cationic Imino Diels-Alder Reaction, Binding Prediction, and Evaluation as Cholinesterase Inhibitors.

New N‐allyl/propargyl 4‐substituted 1,2,3,4‐tetrahydroquinolines derivatives were efficiently synthesized using acid‐catalyzed three components cationic imino Diels–Alder reaction (70–95%). All compounds were tested in vitro as dual acetylcholinesterase and butyryl‐cholinesterase inhibitors and their potential binding modes, and affinity, were predicted by molecular docking and binding free energy calculations (∆G) respectively. The compound 4af (IC 50 = 72 μ m) presented the most effective inhibition against acetylcholinesterase despite its poor selectivity (SI = 2), while the best inhibitory activity on butyryl‐cholinesterase was exhibited by compound 4ae (IC 50 = 25.58 μ m) with considerable selectivity (SI = 0.15). Molecular docking studies indicated that the most active compounds fit in the reported acetylcholinesterase and butyryl‐cholinesterase active sites. Moreover, our computational data indicated a high correlation between the calculated ∆G and the experimental activity values in both targets.

Structure and mode of action of organophosphate pesticides: A computational study

Six organophosphate pesticides of high to moderate toxicity (dichlorvos (DCV), dicrotophos (DTP), ethoprophos (EPP), methamidophos (MAP), mevinphos (MVP) and omethoate (OMT)) are computationally studied to determine their structure and up to 12 different mechanisms of reaction with methanol. Methanol is chosen as a surrogate molecule to represent the serine residue and imidazole to represent histidine in the active site of acetylcholinesterase, the target enzyme in the central nervous system of organisms. Transition states (first order saddle points) and intermediates along several plausible reaction pathways are computed, along with activation enthalpies, entropies, and free energies. Pathways for different leaving groups are also analyzed. All geometry optimizations of products, reactants, intermediate complexes, and saddle points were performed using hybrid density functional theory method mPW1B95-44 in conjunction with the 6-31+G(d,p) basis set, with and without a polarized continuum model of implicit solvation. Composite rate constants were calculated using a steady-state analysis for mechanisms with more than one activation barrier. Mechanisms explored fall into two main categories, direct and indirect, all involving proton transfer from the methanol hydroxyl group to the oxygen or sulfur of the leaving group. The indirect proton-transfer mechanism is a Wright-type mechanism (Wright and White, 1998) which relays the proton through the phosphinyl oxygen, and the leaving group is positioned on the opposite side to the incoming hydroxyl nucleophile in a distorted trigonal bipyramidal transition state. We explored mechanisms in which one or two water molecules and/or an imidazole molecule assisted in the proton transfer. Generally speaking, whether direct or indirect, the lowest activation energies were obtained for mechanisms in which the phosphinyl oxygen plays a role in transfer, and additionally water assistance (ubiquitous in the enzyme active site) lowers activation barriers.

Erratum for: Sesquiterpene Lactones from Cynara cornigera: Acetyl Cholinesterase Inhibition and In Silico Ligand Docking.

Wild artichoke (Cynara cornigera), a thistle-like perennial belonging to the Asteraceae family, is native to the Mediterranean region, northwestern Africa, and the Canary Islands. While the pleasant, albeit bitter, taste of the leaves and flowers is attributed to the sesquiterpene lactones cynaropicrin and cynarin, a comprehensive phytochemical investigation still needs to be reported. In this study seven sesquiterpene lactones were isolated from an aqueous methanol plant extract, including a new halogenated metabolite (1), the naturally isolated compound sibthorpine (2), and five metabolites isolated for the first time from C. cornigera. Structures were established by spectroscopic methods, including HREIMS, (1 )H, (13 )C, DEPT, (1 )H-(1 )H COSY, HMQC, and HMBC-NMR experiments as well as by X-ray analysis. The isolated bioactive nutrients were analyzed for their antioxidant and metal chelating activity. Compound 1 exhibited a potent metal chelating activity as well as a high antioxidant capacity. Moreover, select compounds were effective as acetyl cholinesterase inhibitors presenting the possibility for such compounds to be examined for anti-neurodegenerative activity. A computational pharmacophore elucidation and docking study was performed to estimate the pharmacophoric features and binding conformation of isolated compounds in the acetyl cholinesterase active site.

Sesquiterpene Lactones from Cynara cornigera: Acetyl Cholinesterase Inhibition and In Silico Ligand Docking.

Wild artichoke (Cynara cornigera), a thistle-like perennial belonging to the Asteraceae family, is native to the Mediterranean region, northwestern Africa, and the Canary Islands. While the pleasant, albeit bitter, taste of the leaves and flowers is attributed to the sesquiterpene lactones cynaropicrin and cynarin, a comprehensive phytochemical investigation still needs to be reported. In this study seven sesquiterpene lactones were isolated from an aqueous methanol plant extract, including a new halogenated metabolite (1), the naturally isolated compound sibthorpine (2), and five metabolites isolated for the first time from C. cornigera. Structures were established by spectroscopic methods, including HREIMS, (1 )H, (13 )C, DEPT, (1 )H-(1 )H COSY, HMQC, and HMBC-NMR experiments as well as by X-ray analysis. The isolated bioactive nutrients were analyzed for their antioxidant and metal chelating activity. Compound 1 exhibited a potent metal chelating activity as well as a high antioxidant capacity. Moreover, select compounds were effective as acetyl cholinesterase inhibitors presenting the possibility for such compounds to be examined for anti-neurodegenerative activity. A computational pharmacophore elucidation and docking study was performed to estimate the pharmacophoric features and binding conformation of isolated compounds in the acetyl cholinesterase active site.

Use of ligand-based pharmacophore modeling and docking approach to find novel acetylcholinesterase inhibitors for treating Alzheimer's

Alzheimer's disease is a neurological disorder in which the patient suffers from memory loss and impaired cognitive abilities. Though the main cause of the disease is not yet known, depletion of neurotransmitter at synaptic junctions, accumulation of insoluble beta amyloid plaques and neurofibrillary tangles are the main pathologies associated with it. The FDA approved drugs for alzheimer's belong to the category of acetylcholinesterase inhibitors. But most of the drugs have been observed to be associated with adverse side effects. In this study, we have developed a pharmacophore (responsible for interaction with acetylcholinesterase active site) based on the already existing drugs and drug candidates. This pharmacophore was used to search for novel AChE inhibitors with altogether different chemical scaffold using high throughput virtual screening and docking studies. Finally, we have reported two compounds, OPA and OMT, which possess high affinity for catalytic site of AChE enzyme and thus, can be considered as potential AChE inhibitors for the symptomatic treatment of Alzheimer's.

Chapter 10 - Organophosphorus and carbamate insecticide poisoning

Both organophosphorus (OP) and carbamate insecticides inhibit acetylcholinesterase (AChE), which results in accumulation of acetylcholine (ACh) at autonomic and some central synapses and at autonomic postganglionic and neuromuscular junctions. As a consequence, ACh binds to, and stimulates, muscarinic and nicotinic receptors, thereby producing characteristic features. With OP insecticides (but not carbamates), "aging" may also occur by partial dealkylation of the serine group at the active site of AChE; recovery of AChE activity requires synthesis of new enzyme in the liver. Relapse after apparent resolution of cholinergic symptoms has been reported with OP insecticides and is termed the intermediate syndrome. This involves the onset of muscle paralysis affecting particularly upper-limb muscles, neck flexors, and cranial nerves some 24-96 hours after OP exposure and is often associated with the development of respiratory failure. OP-induced delayed neuropathy results from phosphorylation and subsequent aging of at least 70% of neuropathy target esterase. Cramping muscle pain in the lower limbs, distal numbness, and paresthesiae are followed by progressive weakness, depression of deep tendon reflexes in the lower limbs and, in severe cases, in the upper limbs. The therapeutic combination of oxime, atropine, and diazepam is well established experimentally in the treatment of OP pesticide poisoning. However, there has been controversy as to whether oximes improve morbidity and mortality in human poisoning. The explanation may be that the solvents in many formulations are primarily responsible for the high morbidity and mortality; oximes would not be expected to reduce toxicity in these circumstances. even if given in appropriate dose.

Molecular modeling and in vitro reactivation study between the oxime BI-6 and acetylcholinesterase inhibited by different nerve agents

Nerve agents are organophosphates acting as potent inhibitors of acetylcholinesterase (AChE), the enzyme responsible for the hydrolysis of acetylcholine and, consequently, the termination of the transmission of nerve impulses. The inhibition of AChE by an organophosphate can be reversed by a nucleophilic agent able to dephosphorylate a serine residue in the active site of AChE. In this sense, the oximes are compounds capable of removing the nerve agent and reactivate the enzyme. Here, we have applied a methodology involving theoretical docking and Quantum Mechanics/Molecular Mechanics, using the softwares Molegro® and Spartan®, to evaluate the kinetic constants of reactivation and the interactions of the oxime BI-6 with AChE inhibited by different organophosphorus compounds in comparison to in vitro data. Results confirm that this method is suitable for the prediction of kinetic and thermodynamic parameters of oximes, which may be useful in the design and selection of new and more effective oximes.

Insights and Ideas Garnered from Marine Metabolites for Development of Dual-Function Acetylcholinesterase and Amyloid-β Aggregation Inhibitors

Due to the diversity of biological activities that can be found in aquatic ecosystems, marine metabolites have been an active area of drug discovery for the last 30 years. Marine metabolites have been found to inhibit a number of enzymes important in the treatment of human disease. Here, we focus on marine metabolites that inhibit the enzyme acetylcholinesterase, which is the cellular target for treatment of early-stage Alzheimer’s disease. Currently, development of anticholinesterase drugs with improved potency, and drugs that act as dual acetylcholinesterase and amyloid-β aggregation inhibitors, are being sought to treat Alzheimer’s disease. Seven classes of marine metabolites are reported to possess anti-cholinesterase activity. We compared these metabolites to clinically-used acetylcholinesterase inhibitors having known mechanisms of inhibition. We performed a docking simulation and compared them to published experimental data for each metabolite to determine the most likely mechanism of inhibition for each class of marine inhibitor. Our results indicate that several marine metabolites bind to regions of the acetylcholinesterase active site that are not bound by the clinically-used drugs rivastigmine, galanthamine, donepezil, or tacrine. We use the novel poses adopted for computational drug design of tighter binding anticholinesterase drugs likely to act as inhibitors of both acetylcholinesterase activity and amyloid-β aggregation inhibition.

Novel structural hybrids of pyrazolobenzothiazines with benzimidazoles as cholinesterase inhibitors

Two series of novel pyrazolobenzothiazine-based hybrid compounds were efficiently synthesized starting from saccharin sodium salt. Pyrazolo[4,3-c][1,2]benzothiazine scaffolds were N-arylated by using p-fluorobenzaldehyde, followed by the incorporation of a benzimidazole or similar ring systems by treatment with arylenediamines. These phenylene-connected hybrid compounds were investigated as potential inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). Compounds 12d and 12k were the most potent AChE inhibitors with IC50 values of 11 and 13 nM, respectively, while 6j (IC50 = 17 nM) proved to be the most active inhibitor against BuChE with remarkable selectivity for BuChE over AChE. Molecular docking studies were also performed on human AChE and BuChE to suggest possible binding modes in which the inhibitor's extended structure is accommodated along the active site gorge of both enzymes.

ZnII/pyridyloxime complexes as potential reactivators of OP-inhibited acetylcholinesterase: In vitro and docking simulation studies

In order to investigate the ability of metal complexes to act as reactivators of organophosphorus compounds (OP)-inhibited acetylcholinesterase (AChE), we have synthesized and crystallographically characterized three novel mononuclear ZnII complexes formulated as [ZnCl2{(4-py)CHNOH}2] (1), [ZnBr2{(4-py)CHNOH}2] (2) and [Zn(O2CMe)2{(4-py)CHNOH}2]∙2MeCN (3∙2MeCN), where (4-py)CHNOH is 4-pyridinealdoxime. Their reactivation potency was tested in vitro with a slight modification of the Ellman's method using Electric eel acetylcholinesterase and the insecticide paraoxon (diethyl 4-nitrophenyl phosphate) as inhibitor. The activity of the already reported complex [Zn2(O2CPh)2{(4-py)CHNOH}2]·2MeCN (4·2MeCN) and of the clinically used drug obidoxime 1,1′-[oxybis(methylene)]bis{4-[(E)- (hydroxyimino)methyl]pyridinium} was also examined. The results of the in vitro experiments demonstrate moderate reactivation of the metal complexes compared to the drug obidoxime. On the other hand, it is clearly shown that the metal complex is the responsible molecular entity for the observed activity, as the reactivation efficacy of the organic ligand (4-pyridinealdoxime) is found to be inconsequential. Docking simulation studies were performed in the light of predicted complex-enzyme interactions using the paraoxon-inhibited enzyme along with the four ZnII complexes and obidoxime as a reference reactivator. The results showed that the three mononuclear metal complexes possess the required characteristics to be accommodated into the active site of AChE, while the entrance of the dinuclear ZnII compound is unsuccessful. An interesting outcome of docking simulations is the fact that the mononuclear compounds accommodate into the active site of AChE in a similar mode as obidoxime.