Potencies and selectivities of inhibitors of acetylcholinesterase and its molecular forms in normal and Alzheimer's disease brain

Eight inhibitors of acetylcholinesterase (AChE), tacrine, bis-tacrine, donepezil, rivastigmine, galantamine, heptyl-physostigmine, TAK-147 and metrifonate, were compared with regard to their effects on AChE and butyrylcholinesterase (BuChE) in normal human brain cortex. Additionally, the IC50 values of different molecular forms of AChE (monomeric, G1, and tetrameric, G4) were determined in the cerebral cortex in both normal and Alzheimer's human brains. The most selective AChE inhibitors, in decreasing sequence, were in order: TAK-147, donepezil and galantamine. For BuChE, the most specific was rivastigmine. However, none of these inhibitors was absolutely specific for AChE or BuChE. Among these inhibitors, tacrine, bis-tacrine, TAK-147, metrifonate and galantamine inhibited both the G1 and G4 AChE forms equally well. Interestingly, the AChE molecular forms in Alzheimer samples were more sensitive to some of the inhibitors as compared with the normal samples. Only one inhibitor, rivastigmine, displayed preferential inhibition for the G1 form of AChE. We conclude that a molecular form-specific inhibitor may have therapeutic applications in inhibiting the G1 form, which is relatively unchanged in Alzheimer's brain.     

Analogues of 2′-hydroxychalcone with modified C4-substituents as the inhibitors against human acetylcholinesterase

A series of C4-substituted tertiary nitrogen-bearing 2′-hydroxychalcones were designed and synthesised based on a previous mixed type acetylcholinesterase inhibitor. Majority of the 2′-hydroxychalcone analogues displayed a better inhibition against acetylcholinesterase (AChE) than butyrylcholinesterase (BuChE). Among them, compound 4c was identified as the most potent AChE inhibitor (IC₅₀: 3.3 µM) and showed the highest selectivity for AChE over BuChE (ratio >30:1). Molecular docking studies suggested that compound 4c interacts with both the peripheral anionic site (PAS) and catalytic anionic site (CAS) regions of AChE. ADMET analysis confirmed the therapeutic potential of compound 4c based on its blood–brain barrier penetrating. Overall, the results suggest that this 2′-hydroxychalcone deserves further investigation into the therapeutic lead for Alzheimer’s disease (AD).     

Cholinesterase inhibitory activity of tinosporide and 8-hydroxytinosporide isolated from Tinospora cordifolia: In vitro and in silico studies targeting management of Alzheimer’s disease

Tinosporide and 8-hydroxytinosporide isolated from Tinospora cordifolia were evaluated for acetylcholinesterase (AChE) and butylcholinesterase (BuChE) inhibitory activities. The structure of the compound was confirmed by spectroscopic analysis, whereas cholinesterase inhibition was investigated by Ellman method using donepezil as standard drug and the data were presented as IC₅₀ (μg/ml ± SEM). Furthermore, donepezil, tinosporide and 8-hydroxytinosporide were executed for docking analysis. The results from the isolated compounds TC-16R confirmed as tinosporide promisingly inhibited AChE with IC₅₀ value of 13.45 ± 0.144, whereas TC-19R confirmed as 8-hydroxytinosporide moderately inhibited AChE with IC₅₀ value of 46.71 ± 0.511. In case of BuChE inhibition, the IC₅₀ values were found to be 408.50 ± 17.197 and 317.26 ± 6.918 for tinosporide and 8-hydroxytinosporide, respectively. The in silico studies revealed that the ligand tinosporide fit with the binding sites and inhibited AChE. Overall, the study findings suggested that tinosporide would be a complementary noble molecule of donepezil which is correlated with its pharmacological activity through in vitro studies, while 8-hydroxytinosporide modestly inhibited BuChE and the results are very close to the standard donepezil.     

Insights into the Role of Erythrina corallodendron L. in Alzheimer's Disease: in Vitro and in Silico Approach

Alzheimer's disease (AD) is a major health problem. Cholinergic transmission is greatly affected in AD. Phytochemical investigation of the alkaloid rich fraction (AF) of Erythrina corallodendron L leaves resulted in isolation of five known alkaloids: erysodine, erythrinine, 8-oxoerythrinine, erysovine N-oxide and erythrinine N-oxide. In this study, eysovine N-oxide was reported for the second time in nature. AF was assayed for cholinesterase inhibition at the concentration of 100 μg mL⁻¹. AF showed a higher percent inhibition for butyrylcholinesterase enzyme (BuChE) (83.28 %) compared to acetylcholinesterase enzyme (AChE) (64.64 %). The isolated alkaloids were also assayed for their anti-BuChE effect. In-silico docking study was done for the isolated compounds at the binding sites of AChE and BuChE to determine their binding pattern and interactions, also molecular dynamics were estimated for the compound displaying the best fit for AChE and BuChE. In addition, ADME parameters and toxicity were predicted for the isolated alkaloids compared to donepezil.     

Kinetic analysis of the inhibition of human butyrylcholinesterase with cymserine

Accompanying the gradual rise in the average age of the population of most industrialized countries is a regrettable progressive rise in the number of individuals afflicted with age-related neurodegenerative disorders, epitomized by Alzheimer's disease (AD) but, additionally, including Parkinson's disease (PD) and stroke. The primary therapeutic strategy, to date, involves the use of cholinesterases inhibitors (ChEIs) to amplify residual cholinergic activity. The enzyme, acetylcholinesterase (AChE), along with other elements of the cholinergic system is depleted in the AD brain. In contrast, however, its sister enzyme, butyrylcholinesterase (BuChE), that likewise cleaves acetylcholine (ACh), is elevated and both AChE and BuChE co-localize in high amounts with the classical pathological hallmarks of AD. The mismatch between increased brain BuChE and depleted levels of both ACh and AChE, particularly late in the disease, has supported the design and development of new ChEIs with a preference for BuChE; exemplified by the novel agent, cymserine, whose binding kinetics are characterized for the first time. Specifically, as assessed by the Ellman method, cymserine demonstrated potent concentration-dependent binding with human BuChE. The IC50 was determined as 63 to 100 nM at the substrate concentration range of 25 to 800 microM BuSCh. In addition, the following new binding constants were investigated for human BuChE inhibition by cymserine: T(FPnubeta), K(nubeta), K(Bs), K(MIBA), M(IC50), D(Sc), R(f), (O)K(m), OIC100, K(sl), theta(max) and R(i). These new kinetic constants may open new avenues for the kinetic study of the inhibition of a broad array of other enzymes by a wide variety of inhibitors. In synopsis, cymserine proved to be a potent inhibitor of human BuChE in comparison to its structural analogue, phenserine.     

Cerebrospinal Fluid (CSF) 25-Hydroxyvitamin D Concentration and CSF Acetylcholinesterase Activity Are Reduced in Patients with Alzheimer's Disease

Background

Little is known of vitamin D concentration in cerebrospinal fluid (CSF) in Alzheimer´s disease (AD) and its relation with CSF acetylcholinesterase (AChE) activity, a marker of cholinergic function.

Methods

A cross-sectional study of 52 consecutive patients under primary evaluation of cognitive impairment and 17 healthy controls. The patients had AD dementia or mild cognitive impairment (MCI) diagnosed with AD dementia upon follow-up (n = 28), other dementias (n = 12), and stable MCI (SMCI, n = 12). We determined serum and CSF concentrations of calcium, parathyroid hormone (PTH), 25-hydroxyvitamin D (25OHD), and CSF activities of AChE and butyrylcholinesterase (BuChE).

Findings

CSF 25OHD level was reduced in AD patients (P < 0.05), and CSF AChE activity was decreased both in patients with AD (P < 0.05) and other dementias (P < 0.01) compared to healthy controls. None of the measured variables differed between BuChE K-variant genotypes whereas the participants that were homozygous in terms of the apolipoprotein E (APOE) ε4 allele had decreased CSF AChE activity compared to subjects lacking the APOE ε4 allele (P = 0.01). In AD patients (n=28), CSF AChE activity correlated positively with CSF levels of total tau (T-tau) (r = 0.44, P < 0.05) and phosphorylated tau protein (P-tau) (r = 0.50, P < 0.01), but CSF activities of AChE or BuChE did not correlate with serum or CSF levels of 25OHD.

Conclusions

In this pilot study, both CSF 25OHD level and CSF AChE activity were reduced in AD patients. However, the lack of correlations between 25OHD levels and CSF activities of AChE or BuChE might suggest different mechanisms of action, which could have implications for treatment trials.     

Measuring Affinities of Fission Yeast Spindle Pole Body Proteins in Live Cells across the Cell Cycle

Characterizing protein-protein interactions is essential for understanding molecular mechanisms, although reproducing cellular conditions in vitro is challenging and some proteins are difficult to purify. We developed a method to measure binding to cellular structures using fission yeast cells as reaction vessels. We varied the concentrations of Sid2p and Mob1p (proteins of the septation initiation network) and measured their binding to spindle pole bodies (SPBs), the centrosome equivalent of yeast. From our measurements we infer that Sid2p and Mob1p both exist as monomeric, heterodimeric, and homodimeric species throughout the cell cycle. During interphase these species have widely different affinities for their common receptor Cdc11p on the SPB. The data support a model with a subset of Cdc11p binding the heterodimeric species with a K_d < 0.1 μM when Sid2p binds Mob1p-Cdc11p and K_d in the micromolar range when Mob1p binds Sid2p-Cdc11p. During mitosis an additional species presumed to be the phosphorylated Sid2p−Mob1p heterodimer binds SPBs with a lower affinity. Homodimers of Sid2p or Mob1p bind to the rest of Cdc11p at SPBs with lower affinity: K_ds > 10 μM during interphase and somewhat stronger during mitosis. These measurements allowed us to account for the fluctuations in Sid2p binding to SPBs throughout the cell cycle.     

Structure–activity relationship,in vitro and in vivo evaluation of novel dienyl sulphonyl fluorides as selective BuChE inhibitors for the treatment of Alzheimer's disease

To discover novel scaffolds as leads against dementia, a series of δ-aryl-1,3-dienesulfonyl fluorides with α-halo, α-aryl and α-alkynyl were assayed for ChE inhibitory activity, in which compound A10 was identified as a selective BuChE inhibitor (IC₅₀ = 0.021 μM for eqBChE, 3.62 μM for hBuChE). SAR of BuChE inhibition showed: (i) o- > m- > p-; –OCH₃ > –CH₃ > –Cl (–Br) for δ-aryl; (ii) α-Br > α-Cl, α-I. Compound A10 exhibited neuroprotective, BBB penetration, mixed competitive inhibitory effect on BuChE (K_i = 29 nM), and benign neural and hepatic safety. Treatment with A10 could almost entirely recover the Aβ_1-42-induced cognitive dysfunction to the normal level, and the assessment of total amount of Aβ_1-42 confirmed its anti-amyloidogenic profile. Therefore, the potential BuChE inhibitor A10 is a promising effective lead for the treatment of AD.     

Highly potent and selective aryl-1,2,3-triazolyl benzylpiperidine inhibitors toward butyrylcholinesterase in Alzheimer's disease

Acetylcholinesterase (AChE) is the key enzyme targeted in Alzheimer's disease (AD) therapy, nevertheless butyrylcholinesterase (BuChE) has been drawing attention due to its role in the disease progression. Thus, we aimed to synthesize novel cholinesterases inhibitors considering structural differences in their peripheral site, exploiting a moiety replacement approach based on the potent and selective hAChE drug donepezil. Hence, two small series of N-benzylpiperidine based compounds have successfully been synthesized as novel potent and selective hBuChE inhibitors. The most promising compounds (9 and 11) were not cytotoxic and their kinetic study accounted for dual binding site mode of interaction, which is in agreement with further docking and molecular dynamics studies. Therefore, this study demonstrates how our strategy enabled the discovery of novel promising and privileged structures. Remarkably, compound 11 proved to be one of the most potent (0.17?nM) and selective (>58,000-fold) hBuChE inhibitor ever reported.     

Design,synthesis, cholinesterase inhibition and molecular modelling study of novel tacrine hybrids with carbohydrate derivatives

A series of hybrids containing tacrine linked to carbohydrate-based moieties, such as d-xylose, d-ribose, and d-galactose derivatives, were synthesized by the nucleophilic substitution between 9-aminoalkylamino-1,2,3,4-tetrahydroacridines and the corresponding sugar-based tosylates. All compounds were found to be potent inhibitors of both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the nanomolar IC₅₀ scale. Most of the d-xylose derivatives (6a-e) were selective for AChE and the compound 6e (IC₅₀?=?2.2?nM for AChE and 4.93?nM for BuChE) was the most active compound for both enzymes. The d-galactose derivative 8a was the most selective for AChE exhibiting an IC₅₀ ratio of 7.6 for AChE over BuChE. Only two compounds showed a preference for BuChE, namely 7a (d-ribose derivative) and 6b (d-xylose derivative). Molecular docking studies indicated that the inhibitors are capable of interacting with the entire binding cavity and the main contribution of the linker is to enable the most favorable positioning of the two moieties with CAS, PAS, and hydrophobic pocket to provide optimal interactions with the binding cavity. This finding is reinforced by the fact that there is no linear correlation between the linker size and the observed binding affinities. The majority of the new hybrids synthesized in this work do not violate the Lipinski's rule-of-five according to FAF-Drugs4, and do not demonstrated predicted hepatotoxicity according ProTox-II.     

New cholinesterase inhibitors for Alzheimer’s disease: Structure Activity Studies (SARs) and molecular docking of isoquinolone and azepanone derivatives

A library of isoquinolinone and azepanone derivatives were screened for both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activity. The strategy adopted included (a) in vitro biological assays, against eel AChE (EeAChE) and equine serum BuChE (EqBuChE) in order to determine the compounds IC₅₀ and their dose-response activity, consolidated by (b) molecular docking studies to evaluate the docking poses and interatomic interactions in the case of the hit compounds, validated by STD-NMR studies. Compound (1f) was identified as one of these hits with an IC₅₀ of 89.5 μM for EeAChE and 153.8 μM for EqBuChE, (2a) was identified as a second hit with an IC₅₀ of 108.4 μM (EeAChE) and 277.8 μM (EqBuChE). In order to gain insights into the binding mode and principle active site interactions of these molecules, (R)-(1f) along with 3 other analogues (also as the R-enantiomer) were docked into both RhAChE and hBuChE models. Galantamine was used as the benchmark. The docking study was validated by performing an STD-NMR study of (1f) with EeAChE using galantamine as the benchmark.     

Molecular Structure-Affinity Relationship of Bufadienolides and Human Serum Albumin In Vitro and Molecular Docking Analysis

The development of bufadienolides as anti-tumor agents is limited due to poor pharmacokinetic properties regarding drug half-lives and toxicity in vivo. These serious factors might be improved by increasing the drug/albumin-binding ratio. This study therefore investigated the relationship between the structural properties of nine bufadienolides and their affinities for human serum albumin (HSA) by a fluorescence spectroscopy-based analysis and molecular docking. Fluorescence quenching data showed that the interaction of each bufadienolide with HSA formed a non-fluorescent complex, while thermodynamic parameters revealed negative ΔS and ΔH values, corresponding to changes in enthalpy and entropy, respectively. The structural differences between the various bufadienolides markedly influenced their binding affinity for HSA. With the exception of a C = O bond at the C12 position that decreased the binding affinity for HSA, other polar groups tended to increase the affinity, especially a hydroxyl (OH) group at assorted bufadienolide sites. The rank order of binding affinities for drugs with tri-hydroxyl groups was as follows: 11-OH > 5-OH > 16-OH; in addition, 16-acetoxy (OAc), 10-aldehyde and 14-epoxy constituents notably enhanced the binding affinity. Among these groups, 11-OH and 16-acetyl were especially important for a seamless interaction between the bufadienolides and HSA. Furthermore, molecular docking analysis revealed that either an 11-OH or a 16-OAc group spatially close to a five-membered lactone ring significantly facilitated the anchoring of these compounds within site I of the HSA pocket via hydrogen bonding (H-bonding) with Tyr150 or Lys199, respectively. In summary, bufadienolide structure strongly affects binding with HSA, and 11-OH or 16-OAc groups improve the drug association with key amino acid residues. This information is valuable for the prospective development of bufadienolides with improved pharmacological profiles as novel anti-tumor drugs.     

The Acetylcholinesterase Inhibitors Competitively Inhibited an Acetyl l-Carnitine Transport Through the Blood–Brain Barrier

We investigated the interaction of acetylcholinesterase (AChE) inhibitors with acetyl-L-carnitine (ALCAR) transporter at the blood-brain barrier (BBB). ALCAR uptake by conditionally immortalized rat brain capillary endothelial cell lines (TR-BBB cells), as an in vitro model of BBB, were characterized by cellular uptake study using [(3)H]ALCAR. In vivo brain uptake of [(3)H]ALCAR was determined by brain uptake index after carotid artery injection in rats. In results, the transport properties for [(3)H]ALCAR by TR-BBB cell were consistent with those of ALCAR transport by the organic cation/carnitine transporter 2 (OCTN2). Also, OCTN2 was confirmed to be expressed in the cells. The uptake of [(3)H]ALCAR by TR-BBB cells was inhibited by AChE inhibitors such as donepezil, tacrine, galantamine and rivastigmine, which IC(50) values are 45.3, 74.0, 459 and 800 μM, respectively. Especially, donepezil and galantamine inhibited the uptake of [(3)H]ALCAR competitively, but tacrine and rivastigmine inhibited noncompetitively. Furthermore, [(3)H]ALCAR uptake by the rat brain was found to be significantly decreased by quinidine, donepezil and galantamine. Our results suggest that transport of AChE inhibitors such as donepezil and galantamine through the BBB is at least partly mediated by OCTN2 which is involved in transport of ALCAR.     

Synthesis and evaluation of multi-target-directed ligands for the treatment of Alzheimer’s disease based on the fusion of donepezil and melatonin

A novel series of compounds obtained by fusing the acetylcholinesterase (AChE) inhibitor donepezil and the antioxidant melatonin were designed as multi-target-directed ligands for the treatment of Alzheimer’s disease (AD). In vitro assay indicated that most of the target compounds exhibited a significant ability to inhibit acetylcholinesterase (eeAChE and hAChE), butyrylcholinesterase (eqBuChE and hBuChE), and β-amyloid (Aβ) aggregation, and to act as potential antioxidants and biometal chelators. Especially, 4u displayed a good inhibition of AChE (IC₅₀ value of 193 nM for eeAChE and 273 nM for hAChE), strong inhibition of BuChE (IC₅₀ value of 73 nM for eqBuChE and 56 nM for hBuChE), moderate inhibition of Aβ aggregation (56.3% at 20 μM) and good antioxidant activity (3.28 trolox equivalent by ORAC assay). Molecular modeling studies in combination with kinetic analysis revealed that 4u was a mixed-type inhibitor, binding simultaneously to catalytic anionic site (CAS) and the peripheral anionic site (PAS) of AChE. In addition, 4u could chelate metal ions, reduce PC12 cells death induced by oxidative stress and penetrate the blood–brain barrier (BBB). Taken together, these results strongly indicated the hybridization approach is an efficient strategy to identify novel scaffolds with desired bioactivities, and further optimization of 4u may be helpful to develop more potent lead compound for AD treatment.     

Design,synthesis and evaluation of novel heterodimers of donepezil and huperzine fragments as acetylcholinesterase inhibitors

Four series of novel heterodimers comprised of donepezil and huperzine A (HupA) fragments were designed, synthesized, and evaluated in search of potent acetylcholinesterase (AChE) inhibitors as potential therapeutic treatment for Alzheimer’s disease. Heterodimers comprised of dimethoxyindanone (from donepezil), hupyridone (from HupA), and connected with a multimethylene linker, were identified as potent and selective inhibitors of AChE. Diastereomeric heterodimers (RS,S)-17b (with a tetramethylene linker) exhibited the highest potency of inhibition towards AChE with an IC₅₀ value of 9 nM and no detectable inhibitory effect on butyrylcholinesterase at 1 mM.     

Molecular Determinants of Epidermal Growth Factor Binding: A Molecular Dynamics Study

The epidermal growth factor receptor (EGFR) is a member of the receptor tyrosine kinase family that plays a role in multiple cellular processes. Activation of EGFR requires binding of a ligand on the extracellular domain to promote conformational changes leading to dimerization and transphosphorylation of intracellular kinase domains. Seven ligands are known to bind EGFR with affinities ranging from sub-nanomolar to near micromolar dissociation constants. In the case of EGFR, distinct conformational states assumed upon binding a ligand is thought to be a determining factor in activation of a downstream signaling network. Previous biochemical studies suggest the existence of both low affinity and high affinity EGFR ligands. While these studies have identified functional effects of ligand binding, high-resolution structural data are lacking. To gain a better understanding of the molecular basis of EGFR binding affinities, we docked each EGFR ligand to the putative active state extracellular domain dimer and 25.0 ns molecular dynamics simulations were performed. MM-PBSA/GBSA are efficient computational approaches to approximate free energies of protein-protein interactions and decompose the free energy at the amino acid level. We applied these methods to the last 6.0 ns of each ligand-receptor simulation. MM-PBSA calculations were able to successfully rank all seven of the EGFR ligands based on the two affinity classes: EGF>HB-EGF>TGF-α>BTC>EPR>EPG>AR. Results from energy decomposition identified several interactions that are common among binding ligands. These findings reveal that while several residues are conserved among the EGFR ligand family, no single set of residues determines the affinity class. Instead we found heterogeneous sets of interactions that were driven primarily by electrostatic and Van der Waals forces. These results not only illustrate the complexity of EGFR dynamics but also pave the way for structure-based design of therapeutics targeting EGF ligands or the receptor itself.     

CHRNA7 Polymorphisms and Response to Cholinesterase Inhibitors in Alzheimer's Disease

Background

CHRNA7 encodes the α7 nicotinic acetylcholine receptor subunit, which is important to Alzheimer''s disease (AD) pathogenesis and cholinergic neurotransmission. Previously, CHRNA7 polymorphisms have not been related to cholinesterase inhibitors (ChEI) response.

Methods

Mild to moderate AD patients received ChEIs were recruited from the neurology clinics of three teaching hospitals from 2007 to 2010 (n = 204). Nine haplotype-tagging single nucleotide polymorphisms of CHRNA7 were genotyped. Cognitive responders were those showing improvement in the Mini-Mental State Examination score ≧2 between baseline and 6 months after ChEI treatment.

Results

AD women carrying rs8024987 variants [GG+GC vs. CC: adjusted odds ratio (AOR) = 3.62, 95% confidence interval (CI) = 1.47–8.89] and GG haplotype in block1 (AOR = 3.34, 95% CI = 1.38–8.06) had significantly better response to ChEIs (false discovery rate <0.05). These variant carriers using galantamine were 11 times more likely to be responders than female non-carriers using donepezil or rivastigmine.

Conclusion

For the first time, this study found a significant association between CHRNA7 polymorphisms and better ChEI response. If confirmed by further studies, CHRNA7 polymorphisms may aid in predicting ChEI response and refining treatment choice.     

Microwave assisted synthesis of novel hybrid tacrine-sulfonamide derivatives and investigation of their antioxidant and anticholinesterase activities

A novel series of tacrine derivatives containing sulfonamide group were synthesized and their inhibitory effects on acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) were evaluated. The result showed that all the synthesized tacrine-sulfonamides (VIIIa–o) exhibited inhibitory activity on both cholinesterases. VIIIg showed the highest inhibitory activity on AChE IC₅₀ = 0.009 μM. This value is 220-fold greater than that of galantamine (IC₅₀ = 2.054 μM) and 6-fold greater than tacrine (IC₅₀ = 0.055 μM). VIIIf displayed the strongest inhibition of BuChE (IC₅₀ = 2.250 μM), which is close to donepezil (IC₅₀ = 2.680 μM) and 8-fold greater than that of galantamine (IC₅₀ = 18.130 μM) Furthermore, all of the synthesized tacrine derivatives showed higher inhibition of BuChE than that of galantamine. In addition, the cupric reducing antioxidant capacities (CUPRAC) and ABTS cation radical scavenging abilities of the synthesized compounds were investigated for the antioxidant activity. Among them, VIIIb (IC₅₀ = 94.390 ± 2.310 μM) showed significantly better ABTS cation radical scavenging ability than all of the new synthesized compounds.     

In silico, NMR and pharmacological evaluation of an hydroxyoxindole cholinesterase inhibitor

From a screening study of various potential inhibitors for cholinesterases (ChEs), compound (rac)-1 (4-((3-hydroxy-2-oxo-3-phenylindolin-1-yl) methyl) piperidin-1-ium chloride) showed an IC₅₀ of 18?μM for butyrylcholinesterase (BuChE). Herein we present a toxicological and pharmacological evaluation of (rac)-1 to determine its potential for use as an alternative ChE inhibitor for the treatment of Alzheimer’s disease. The strategy adopted included in vivo and ex vivo studies with mouse models, Molecular Modelling and Saturation Transfer Difference (STD) NMR studies.Preliminary molecular docking studies were conducted with both (R) and (S)-1 with acetylcholinesterase (AChE) and BuChE, prior to advancing to the mouse model, and indeed favorable interactions were observed, with (R)-1 showing the best binding with AChE and (S)-1 with BuChE. STD-NMR studies were used to successfully validate these results. Toxicological studies were also conducted using the Artemia salina model, with donepezil as reference. It was found that in the in vivo mouse studies that (rac)-1 presented a slightly better inhibition of AChE (0.096?µmol.min^?1.mg^?1) than donepezil (0.112?µmol.min^?1.mg^?1) and the same level of inhibition for BuChE as donepezil (0.014?µmol.min^?1.mg^?1).     

Enantiomer effects of huperzine A on the aryl acylamidase activity of human cholinesterases

1. Acetylcholinesterase (AChE, EC 3.1.1.7) and butyrylcholinesterase (BuChE, EC 3.1.1.8) are serine hydrolase enzymes that catalyze the hydrolysis of acetylcholine.2. (–) Huperzine A is an inhibitor of AChE and is being considered for the treatment of Alzheimer's disease.3. In addition to esterase activity, AChE and BuChE have intrinsic aryl acylamidase activity.4. The function of aryl acylamidase is unknown but has been speculated to be important in Alzheimer pathology.5. Kinetic effects of (–) huperzine A and ( ±)$ huperzine A on the aryl acylamidase activity of human cholinesterases were examined.6. (–) Huperzine A inhibited the aryl acylamidase activities of both AChE and BuChE.7. (±) Huperzine A inhibited this function in AChE but stimulated BuChE aryl acylamidase suggesting that the (+) enantiomer is a powerful activator of this enzyme activity.8. The two huperzine enantiomers may prove to be useful tools to examine the function of aryl acylamidase activity, including its role in Alzheimer pathology.