In vitro and in silico analysis of novel astaxanthin-s-allyl cysteine as an inhibitor of butyrylcholinesterase and various globular forms of acetylcholinesterases

Paradigms and Success Stories of Natural Products in Drug Discovery Against Neurodegenerative Disorders (NDDs)

Neurodegenerative disorders (NDDs) are multifaceted complex disorders that have put a great health and economic burden around the globe nowadays. The multi-factorial nature of NDDs has presented a great challenge in drug discovery and continuous efforts are in progress in search of suitable therapeutic candidates. Nature has a great wealth of active principles in its lap that has cured the human population since ancient times. Natural products have revealed several benefits over conventional synthetic medications and scientists have shifted their vision towards exploring the therapeutic potentials of natural products in the past few years. The structural mimicking of natural compounds to endogenous ligands has presented them as a potential therapeutic candidate to prevent the development of NDDs. In the presented review, authors have summarized demographical facts about various NDDs including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and various types of sclerosis in the brain. The significant findings of new active principles of natural origin along with their therapeutic potentials on NDDs have been included. Also, a description of clinical trials and patents on natural products has been enlisted in this compilation. Although natural products have shown promising success in drug discovery against NDDs, still their use is associated with several ethical issues which need to be solved in the upcoming time.

In vitro and in silico analysis of Solanum torvum fruit and methyl caffeate interaction with cholinesterases

Oxidative stress along with dysfunction in cholinergic neurotransmission primarily underlies cognitive impairment. A significant approach to mitigate cognitive dysfunction involves the inhibition of cholinesterases, namely acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Exploring the potential antioxidant and anticholinesterase effects of edible plants holds promise for their utilization as botanicals to enhance cognition. Solanum torvum fruit with vast biological properties are used as food. In the present study, butanolic extract of S. torvum fruits (BESTF) was prepared. Additionally, the study investigated into the properties of methyl caffeate (MC), a compound present in S. torvum, obtained in its pure form. In vitro antioxidant and anticholinesterases activity of BESTF and MC were determined. BESTF and MC showed potent antioxidant property. BESTF and MC dose-dependently inhibited AChE (IC50 values: 166.6 µg/ml and 680.6 µM, respectively) and BChE (IC50 values: 161.55 µg/ml and 413 µM, respectively). BESTF and MC inhibited AChE and BChE in competitive mode. Active site gorge of AChE/BChE was occupied by MC which formed interaction with amino acids present in catalytic site and PAS in in silico. Further, molecular dynamics simulations followed by free energy calculation, principal component analysis and dynamic cross-correlation matrix provided the compelling evidence that that MC maintained stable interactions during MD simulation with AChE and BChE. Collectively, the results from the present study underlines the cognitive-enhancing effect of BESTF and MC.

Probing the intermolecular interactions, binding affinity, charge density distribution and dynamics of silibinin in dual targets AChE and BACE1: QTAIM and molecular dynamics perspective

Alzheimer's disease (AD) is the grievous neurodegenerative disorder. Reportedly, many enzymes are responsible for this disease, in which notably, acetylcholinesterase (AChE) and β-secretase (BACE1) are largely involved for AD. An experimental study reports that silibinin molecule inhibits both AChE and BACE1 enzymes. Present study aims to understand the dual binding mechanism of silibinin in the active site of AChE and BACE1 from the intermolecular interactions, conformational flexibility, charge density distribution, binding energy and the stability of molecule. To obtain the above information, the molecular docking, molecular dynamics (MD) and QTAIM (quantum theory of atoms in molecules) calculations have been performed. The molecular docking reveals that silibinin molecule is forming strong and weak intermolecular interactions with the catalytic site of both enzymes. The QTAIM analysis for the binding pockets of both complexes shows the charge density distribution of intermolecular interactions. The electrostatic potential map displays the electronegative/positive regions at the interaction zone of silibinin with AChE and BACE1 complexes. The MD simulation confirms that the silibinin molecule is stable in the active site of AChE and BACE1 enzymes. The binding free energies of silibinin with both enzymes are more favorable to have the interactions.Communicated by Ramaswamy H. Sarma.

Aaptamine - a dual acetyl - and butyrylcholinesterase inhibitor as potential anti-Alzheimer's disease agent

CONTEXT

Alzheimer's disease (AD) is a neurodegenerative disorder that affects millions of people worldwide. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) are promising therapeutic targets for AD.

OBJECTIVE

To evaluate the inhibitory effects of aaptamine on two cholinesterases and investigate the in vivo therapeutic effect on AD in a zebrafish model.

MATERIALS AND METHODS

Aaptamine was isolated from the sponge Aaptos suberitoides Brøndsted (Suberitidae). Enzyme inhibition, kinetic analysis, surface plasmon resonance (SPR) and molecular docking assays were used to determine its inhibitory effect on AChE and BuChE in vitro. Zebrafish were divided into six groups: control, model, 8 μM donepezil, 5 , 10  and 20 μM aaptamine. After three days of drug treatment, the behaviour assay was performed.

RESULTS

The IC₅₀ values of aaptamine towards AChE and BuChE were 16.0 and 4.6 μM. And aaptamine directly inhibited the two cholinesterases in the mixed inhibition type, with K_i values of 6.96 ± 0.04 and 6.35 ± 0.02 μM, with K_d values of 87.6 and 10.7 μM. Besides, aaptamine interacts with the crucial anionic sites of AChE and BuChE. In vivo studies indicated that the dyskinesia recovery rates of 5 , 10  and 20 μM aaptamine group were 34.8, 58.8 and 60.0%, respectively, and that of donepezil was 63.7%.

DISCUSSION AND CONCLUSIONS

Aaptamine showed great potential to exert its anti-AD effects by directly inhibiting the activities of AChE and BuChE. Therefore, this study identified a novel medicinal application of aaptamine and provided a new structural scaffold for the development of anti-AD drugs.

Translocation of Specific DNA Nanocarrier through an Ultrasmall Nanopipette: Toward Single-Protein-Molecule Detection with Superior Signal-to-Noise Ratio

The use of functional DNA nanostructures as carriers to ship proteins through solid-state nanopores has recently seen substantial growth in single-protein-molecule detection (SPMD), driven by the potential of this methodology and implementations that it may enable. Ultrasmall nanopores have exhibited obvious advantages in spatiotemporal biological detection due to the appropriate nanoconfined spaces and unique properties. Herein, a 6.8 nm DNA tetrahedron (TDN) with a target-specific DNA aptamer (TDN-apt) was engineered to carry the representative target of acetylcholinesterase (AChE) through an ultrasmall nanopipet with a 30 nm orifice, underpinning the advanced SPMD of AChE with good performance in terms of high selectivity, low detection limit (0.1 fM), and especially superior signal-to-noise ratio (SNR). The kinetic interaction between TDN-apt and AChE was studied and the practical applicability of the as-developed SPMD toward real samples was validated using serum samples from patients with Alzheimer's disease. This work not only presented a feasible SPMD solution toward low-abundance proteins in complex samples and but also was envisioned to inspire more interest in the design and implementation of synergized DNA nanostructure-ultrasmall nanopore systems for future SPMD development.

Synthesis of 4-substituted benzyl-2-triazole-linked-tryptamine-paeonol derivatives and evaluation of their selective inhibitions against butyrylcholinesterase and monoamine oxidase-B

Cholinesterase (ChE) and monoamine oxidase (MAO) inhibitors are being used and developed to treat Alzheimer's disease (AD), a major type of dementia patients. Fifteen 4-substituted benzyl-2-triazole-linked-tryptamine-paeonol derivatives were synthesized and evaluated for their inhibitory activities against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), monoamine oxidase-A (MAO-A), and B (MAO-B). Compound 896 was the most potent BChE inhibitor (IC₅₀ = 0.13 μM) with the selectivity index (SI) value of >769.23 for BChE over AChE. Compound 897 was the most potent selective MAO-B inhibitor (IC₅₀ = 0.73 μM; SI = 20.45 for MAO-B over MAO-A). The meta-CF₃ substituent of 896 increased BChE inhibitory activity and the para-CF₃ substituent of 897 increased MAO-B inhibitory activity. Compound 896 was a reversible noncompetitive BChE inhibitor (K_i = 0.171 μM) and 897 was a reversible competitive MAO-B inhibitor (K_i = 0.237 μM). Compound 896 had a lower binding energy (-13.75 kcal/mol) to BChE than 897 (-11.29 kcal/mol), and 897 had a lower binding energy to MAO-B (-11.31 kcal/mol) than that to MAO-A (-6.72 kcal/mol). Little cytotoxicity was observed for 896 and 897 to normal cells (MDCK) and human neuroblastoma cells (SH-SY5Y). This study suggested that 896 and 897 are therapeutic candidates for various neurodegenerative disorders such as AD.

Versatile Fluorescent Carbon Dots from Citric Acid and Cysteine with Antimicrobial, Anti-biofilm, Antioxidant, and AChE Enzyme Inhibition Capabilities

Nanostructured fluorescent particles derived from natural molecules were prepared by a green synthesis technique employing a microwave method. The precursors citric acid (CA) and cysteine (Cys) were used in the preparation of S- and N-doped Cys carbon dots (Cys CDs). Synthesis was completed in 3 min. The graphitic structure revealed by XRD analysis of Cys CDs dots had good water dispersity, with diameters in the range of 2-20 nm determined by TEM analysis. The isoelectric point of the S, N-doped CDs was pH value for 5.2. The prepared Cys CDs displayed excellent fluorescence intensity with a high quantum yield of 75.6 ± 2.1%. Strong antimicrobial capability of Cys CDs was observed with 12.5 mg/mL minimum bactericidal concentration (MBC) against gram-positive and gram-negative bacteria with the highest antimicrobial activity obtained against Staphylococcus aureus. Furthermore, Cys CDs provided total biofilm eradication and inhibition abilities against Pseudomonas aeruginosa at 25 mg/mL concentration. Cys CDs are promising antioxidant materials with 1.3 ± 0.1 μmol Trolox equivalent/g antioxidant capacity. Finally, Cys CDs were also shown to inhibit the acetylcholinesterase (AChE) enzyme, which is used in the treatment of Alzheimer's disease, even at the low concentration of 100 μg/mL.

Astaxanthin-s-allyl cysteine diester against high glucose-induced neuronal toxicity in vitro and diabetes-associated cognitive decline in vivo: Effect on p53, oxidative stress and mitochondrial function

Neuroprotective effect of astaxanthin-s-allyl cysteine diester (AST-SAC) against high glucose (HG)-induced oxidative stress in in vitro and cognitive decline under diabetes conditions in in vivo has been explored. Pretreatment of AST-SAC (5, 10 and 15 μM) dose-dependently preserved the neuronal cells (SH-SY5Y) viability against HG toxicity through i) decreasing oxidative stress (decreasing reactive oxygen species generation and increasing endogenous antioxidants level); ii) protecting mitochondrial function [oxidative phosphorylation (OXPHOS) complexes activity and mitochondrial membrane potential (MMP)]; and iii) decreasing p53 level thereby subsequently decreasing the level of apoptotic marker proteins. Male Spraque-Dawley rats were orally administered AST-SAC (1 mg/kg/day) for 45 days in streptozotocin-induced diabetes mellitus (DM) rats. AST-SAC administration prevented the loss of spatial memory in DM rats as determined using the novel object location test. AST-SAC administration alleviated the DM-induced injury in brain such as increased cholinesterases activity, elevated oxidative stress and mitochondrial dysfunction. Altogether, the results from the present study demonstrated that AST-SAC averted the neuronal apoptosis and preserved the cognitive function against HG toxicity under DM conditions.

Acetylcholinesterase and monoamine oxidase-B inhibitory activities by ellagic acid derivatives isolated from Castanopsis cuspidata var. sieboldii

Among 276 herbal extracts, a methanol extract of Castanopsis cuspidata var. sieboldii stems was selected as an experimental source for novel acetylcholinesterase (AChE) inhibitors. Five compounds were isolated from the extract by activity-guided screening, and their inhibitory activities against butyrylcholinesterase (BChE), monoamine oxidases (MAOs), and β-site amyloid precursor protein cleaving enzyme 1 (BACE-1) were also evaluated. Of these compounds, 4'-O-(α-L-rhamnopyranosyl)-3,3',4-tri-O-methylellagic acid (3) and 3,3',4-tri-O-methylellagic acid (4) effectively inhibited AChE with IC₅₀ values of 10.1 and 10.7 µM, respectively. Ellagic acid (5) inhibited AChE (IC₅₀ = 41.7 µM) less than 3 and 4. In addition, 3 effectively inhibited MAO-B (IC₅₀ = 7.27 µM) followed by 5 (IC₅₀ = 9.21 µM). All five compounds weakly inhibited BChE and BACE-1. Compounds 3, 4, and 5 reversibly and competitively inhibited AChE, and were slightly or non-toxic to MDCK cells. The binding energies of 3 and 4 (- 8.5 and - 9.2 kcal/mol, respectively) for AChE were greater than that of 5 (- 8.3 kcal/mol), and 3 and 4 formed a hydrogen bond with Tyr124 in AChE. These results suggest 3 is a dual-targeting inhibitor of AChE and MAO-B, and that these compounds should be viewed as potential therapeutics for the treatment of Alzheimer's disease.

Combined Structure and Ligand-Based Design of Selective Acetylcholinesterase Inhibitors

Acetylcholinesterase is a prime target for therapeutic intervention in Alzheimer's disease. Acetylcholinesterase inhibitors (AChEIs) are used to improve cognitive abilities, playing therefore an important role in disease management. Drug repurposing screening has been performed on a corporate chemical library containing 11 353 compounds using a target fishing approach comprising three-dimensional (3D) shape similarity and pharmacophore modeling against an approved drug database, Drugbank. This initial screening identified 108 hits. Among them, eight molecules showed structural similarity to the known AChEI drug, pyridostigmine. Further structure-based screening using a pharmacophore-guided rescoring method identifies one more potential hit. Experimental evaluations of the identified hits sieve out a highly selective AChEI scaffold. Further lead optimization using a substructure search approach identifies 24 new potential hits. Three of the 24 compounds (compounds 10b, 10h, and 10i) based on a 6-(2-(pyrrolidin-1-yl)pyrimidin-4-yl)-thiazolo[3,2-a]pyrimidine scaffold showed highly promising AChE inhibition ability with IC₅₀ values of 13.10 ± 0.53, 16.02 ± 0.46, and 6.22 ± 0.54 μM, respectively. Moreover, these compounds are highly selective toward AChE. Compound 10i shows AChE inhibitory activity similar to a known Food and Drug Administration (FDA)-approved drug, galantamine, but with even better selectivity. Interaction analysis reveals that hydrophobic and hydrogen-bonding interactions are the primary driving forces responsible for the observed high affinity of the compound with AChE.

Combining In Silico and In Vitro Studies to Evaluate the Acetylcholinesterase Inhibitory Profile of Different Accessions and the Biomarker Triterpenes of Centella asiatica

Alzheimer's disease (AD) is a neurodegenerative disease and the most cause of dementia in elderly adults. Acetylcholinesterase (AChE) is an important beneficial target for AD to control cholinergic signaling deficit. Centella asiatica (CA) has proven to be rich with active ingredients for memory enhancement. In the present study, the chemical profiling of three accession extracts of CA namely SECA-K017, SECA-K018, and, SECA-K019 were performed using high-performance liquid chromatography (HPLC). Four biomarker triterpene compounds were detected in all CA accessions. Quantitative analysis reveals that madecassoside was the highest triterpene in all the CA accessions. The biomarker compounds and the ethanolic extracts of three accessions were investigated for their acetylcholinesterase (AChE) inhibitory activity using Ellman's spectrophotometer method. The inhibitory activity of the triterpenes and accession extracts was compared with the standard AChE inhibitor eserine. The results from the in vitro study showed that the triterpene compounds exhibited an AChE inhibitory activity with the half-maximal inhibitory concentration (IC₅₀) values between 15.05 ± 0.05 and 59.13 ± 0.18 µg/mL. Asiatic acid was found to possess strong AChE inhibitory activity followed by madecassic acid. Among the CA accession extracts, SECA-K017 and SECA-K018 demonstrated a moderate AChE inhibitory activity with an IC₅₀ value of 481.5 ± 0.13 and 763.5 ± 0.16 µg/mL, respectively from the in silico docking studies, it is observed that asiatic acid and madecassic acid showed very good interactions with the active sites and fulfilled docking parameters against AChE. The present study suggested that asiatic acid and madecassic acid in the CA accessions could be responsible for the AChE inhibitory action and could be used as markers to guide further studies on CA as potential natural products for the treatment of AD.