New natural cholinesterase inhibiting and calcium channel blocking quinoline alkaloids

The Influence of Prenatal Exposure to Methamphetamine on the Development of Dopaminergic Neurons in the Ventral Midbrain

Methamphetamine, a highly addictive central nervous system (CNS) stimulant, is used worldwide as an anorexiant and attention enhancer. Methamphetamine use during pregnancy, even at therapeutic doses, may harm fetal development. Here, we examined whether exposure to methamphetamine affects the morphogenesis and diversity of ventral midbrain dopaminergic neurons (VMDNs). The effects of methamphetamine on morphogenesis, viability, the release of mediator chemicals (such as ATP), and the expression of genes involved in neurogenesis were evaluated using VMDNs isolated from the embryos of timed-mated mice on embryonic day 12.5. We demonstrated that methamphetamine (10 µM; equivalent to its therapeutic dose) did not affect the viability and morphogenesis of VMDNs, but it reduced the ATP release negligibly. It significantly downregulated Lmx1a, En1, Pitx3, Th, Chl1, Dat, and Drd1 but did not affect Nurr1 or Bdnf expression. Our results illustrate that methamphetamine could impair VMDN differentiation by altering the expression of important neurogenesis-related genes. Overall, this study suggests that methamphetamine use may impair VMDNs in the fetus if taken during pregnancy. Therefore, it is essential to exercise strict caution for its use in expectant mothers.

Natural coumarins from Murraya paniculata as mixed-type inhibitors of cholinesterases: In vitro and in silico investigations

Currently, acetylcholinesterase (AChE) inhibiting drugs in clinical use, such as tacrine, donepezil, rivastigmine, and galanthamine, are associated with serious side effects and short half-lives. In recent years, numerous phytochemicals have been identified as inhibitors of cholinesterases with potential applications in the management of Alzheimer’s disease (AD). In this study three natural coumarins, 2′-O-ethylmurrangatin (1), murranganone (2), and paniculatin (3) isolated previously by our group from the leaves of Murraya paniculata, were tested against the two cholinesterases (ChE) enzymes, AChE and butyrylcholinesterase (BChE) using in vitro assay. Molecular docking was performed to highlight the structural properties that contribute to the molecular recognition pattern in the inhibition of ChE and the structural differences resulting in the selectivity of these compounds toward AChE. Classical enzyme inhibition kinetics data suggested that compounds 2 and 3 were potent inhibitors of AChE and BChE, while 1 was found inactive against both enzymes. The findings from molecular docking studies revealed the competitive and non-competitive inhibition mechanisms of compounds 2 and 3 against both enzymes. Molecular docking and simulations have revealed that hydrogen bonding, mediated by ketone and hydroxyl functionalities in various positions, significantly contributes to the binding of the inhibitor to the receptor. According to MD simulation studies, the stability of the ligand-AChE complex for the most active compound (3) is found to be comparable to that of the widely used drug Tacrine. In addition, to evaluate the drug-likeness of compounds, in silico ADME evaluation was performed, and the compounds presented good ADME profiles. Data suggested that the coumarin nucleus having diverse side chains at the C-8 position can serve as a potential inhibitor of cholinesterases and can act as a lead to develop a new semisynthetic drug for the treatment of AD.

Identifying Possible AChE Inhibitors from Drug-like Molecules via Machine Learning and Experimental Studies

Acetylcholinesterase (AChE) is one of the most important drug targets for Alzheimer's disease (AD) treatment. In this work, a machine learning model was trained to rapidly and accurately screen large chemical databases for the potential inhibitors of AChE. The obtained results were then validated via in vitro enzyme assay. Moreover, atomistic simulations including molecular docking and molecular dynamics simulations were then used to understand molecular insights into the binding process of ligands to AChE. In particular, two compounds including benzyl trifluoromethyl ketone and trifluoromethylstyryl ketone were indicated as highly potent inhibitors of AChE because they established IC₅₀ values of 0.51 and 0.33 μM, respectively. The obtained IC₅₀ of two compounds is significantly lower than that of galantamine (2.10 μM). The predicted log(BB) suggests that the compounds may be able to traverse the blood-brain barrier. A good agreement between computational and experimental studies was observed, indicating that the hybrid approach can enhance AD therapy.

Phytochemical Screening of Rosmarinus officinalis L. as a Potential Anticholinesterase and Antioxidant-Medicinal Plant for Cognitive Decline Disorders

The inhibition of acetylcholinesterase (AChE) by cholinergic agents has been promoted as a potent strategy for treating and managing cognitive decline disorders. A wide range of natural products has long been used as potential sources or formulations of cholinergic inhibitors. Therefore, this study aimed to evaluate different Rosmarinus officinalis L. (R. officinalis) extracts for their AChE inhibitory activity using galanthamine as a standard AChE inhibitor. In this study, the ethyl-acetate extract (at a concentration of 250 µg/mL) exhibited the greatest inhibitory effect against AChE with significant inhibition of 75%, comparable to the inhibitor galanthamine with an inhibition of 88%. Kinetic analysis revealed that the extracts could induce a mixed type of inhibition, as observed in the case of galanthamine, with the highest increased Km and decreased Vmax values in the ethyl acetate extract. The antioxidant potential of the three extracts tested was found to be in the order of ethyl-acetate > ethanol > aqueous, with IC₅₀ values of 272 µg/mL, 387 µg/mL, and 534 µg/mL, respectively. Ethyl-acetate was found to have the highest total phenolic content in all extracts. Further, in silico study showed structural binding characterization of rosmarinic acid and carnosic acid with human AChE enzyme. Rosmarinic acid showed strong binding and formed two hydrogen-bonding interactions with Ser-293 and Arg-296. In light of this, the ethyl-acetate extract of the plant may provide some novel potential pharmacological leads for treating and managing cognitive disorders such as Alzheimer's.

Use of connectivity index and simple topological parameters for estimating the inhibition potency of acetylcholinesterase

Acetylcholinesterase (AChE) has proven to be an effective drug target in the treatment of neurodegenerative diseases such as Alzheimer’s, Parkinson’s and dementia. We developed a novel QSAR regression model for estimating potency to inhibit AChE, pK_i, on a set of 75 structurally different compounds including oximes, N-hydroxyiminoacetamides, 4-aminoquinolines and flavonoids. Although the model included only three simple descriptors, the valence molecular connectivity index of the zero-order, ⁰χ^v, the number of 10-membered rings (nR10) and the number of hydroxyl groups (nOH), it yielded excellent statistics (r = 0.937, S.E. = 0.51). The stability of the model was evaluated when an initial set of 75 compounds was broadened to 165 compounds in total, with the increase of the range of pK_i (exp) from 6.0 to 10.2, yielding r = 0.882 and S.E. = 0.89. The predictive power of the model was evaluated by calculating pK_i values for 55 randomly chosen compounds (S.E._test = 0.90) from the calibration model created on other 110 compounds (S.E. = 0.89), all taken from the pool of 165 compounds.

Development of a simple QSAR model for reliable evaluation of acetylcholinesterase inhibitor potency

With the aging of the western population, more and more people are affected by the neurodegenerative Alzheimer's and Parkinson's disease. Inhibitors of acetylcholinesterase (AChE) have proven to be effective in the treatment of disease symptoms. We report the QSAR regression model for the estimation of potency of a set of 94 structurally diverse compounds (oximes, N-hydroxyiminoacetamides, 4-aminoquinolines and flavonoids) to inhibit AChE, pK_i (AChE). The model is based on three simple descriptors: the valence molecular connectivity index of the zero-order, ⁰χ^v, combined with the number of 10-membered rings (nR10) and number of hydroxyl groups in a molecule (nOH). QSAR model yielded r = 0.947, S.E. = 0.51 and S.E._cv= 0.53; the range of pK_i (exp) = 6.03. It showed its stability when the set of 94 compounds was enlarged, comprising 184 compounds in total (r = 0.886, S.E. = 0.85 and S.E._cv = 0.88; the range of pK_i (exp) = 10.21), resulting in regression parameters which were similar, although only for ⁰χ^v coefficients within the limits of S.E. (0.167(13) and 0.172(16) for the set with 94 and 184 compounds, respectively. The predictive power of the model was shown by the prediction of pK_i values for 61 randomly chosen compounds (S.E._test = 0.86) from the calibration model made on the other 123 compounds (S.E. = 0.85), all taken from the pool of 184 compounds. QSAR descriptors ⁰χ^v, nR10 and nOH were well chosen for describing the interactions of the AChE active site (amino acid interaction) with ligands through the estimation of the inhibitory potency.

Silencing T-type voltage-gated calcium channel gene reduces the sensitivity of Tetranychus cinnabarinus (Boisduval) to scopoletin

Tetranychus cinnabarinus (Boisduval) is a major pest that harms crops and vegetables worldwide. Scopoletin is a promising acaricidal compound. Our previous study demonstrated that the acaricidal mechanism of scopoletin may be via disrupting intracellular Ca²⁺ homeostasis and calcium signaling pathway. However, the mechanism underlying the specific target location of scopoletin against T. cinnabarinus remains unclear. In this study, the full-length cDNA of the calcium channel (TcT-VDCC) gene from T. cinnabarinus was cloned and characterized. The TcT-VDCC gene is expressed at all developmental stages of T. cinnabarinus but is highly expressed in the larval and nymphal stages. The TcT-VDCC gene was significantly upregulated after treatment with scopoletin, and the RNAi method was used to feed the dsRNA in T. cinnabarinus to silence the TcT-VDCC gene and reduce its sensitivity to scopoletin. The results showed that the acaricidal mechanism of scopoletin on T. cinnabarinus may be related to TcT-VDCC.

Structure-based virtual screening leading to discovery of highly selective butyrylcholinesterase inhibitors with solanaceous alkaloid scaffolds

According to recent research advance, it is interesting to identify new, potent and selective inhibitors of human butyrylcholinesterase (BChE) for therapeutic treatment of both the Alzheimer's disease (AD) and heroin abuse. In this study, we carried out a structure-based virtual screening followed by in vitro activity assays, with the goal to identify new inhibitors that are selective for BChE over acetylcholinesterase (AChE). As a result, a set of new, selective inhibitors of human BChE were identified from natural products with solanaceous alkaloid scaffolds. The most active one of the natural products (compound 1) identified has an IC50 of 16.8 nM against BChE. It has been demonstrated that the desirable selectivity of these inhibitors for BChE over AChE is mainly controlled by three key residues in the active site cavity, i.e. residues Q119, A277, and A328 in BChE versus the respective residues Y124, W286, and Y337 in AChE. Based on this structural insight, future rational design of new, potent and selective BChE inhibitors may focus on these key structural differences in the active site cavity.

New Anti-inflammatory Triterpene Esters and Glycosides from Alstonia scholaris

BACKGROUND

Phytochemical studies on the ethanolic extract of aerial parts of Alstonia scholaris lead to the isolation of two new triterpenoid of the lanostanetype, lanosta 5ene,24-ethyl-3-O-β-D-glucopyranoside (1), lanosta,5ene,24-ethyl-3-O-β-D-glucopyranosideester (2) and new ursane type triterpenoidmethylester, 12-ursene-2,3,18,19-tetrol,28 acetate (nighascholarene) (3), together with seven known triterpenes, betuline, triterpene of the lupane type, alstoprenyol (4), 3β-hydroxy-28-β-acetoxy-5-olea triterpene (5),α-amyrin acetate (6), α-amyrin (7), lupeol acetate (8), 3β-hydroxy-24-nor-urs-4,12,28-triene triterpene (9) and ursolic acid (l0).

METHODOLOGY

The triterpenoid structures of these colorless compounds were deduced from the 1H and 13C-NMR data, and in particular from the application of two-dimensional 1H, 13C correlation experiments as well as by comparison with reported literature data.

CONCLUSION

This study deals with isolation and structural elucidation of natural new triterpenoidesters and glycosides with anti-inflammatory activity.

Profiling and Pharmacokinetic Studies of Alkaloids in Rats After Oral Administration of Zanthoxylum nitidum Decoction by UPLC-Q-TOF-MS/MS and HPLC-MS/MS

Zanthoxylum nitidum (Roxb.) DC (Rutaceae), called as “liangmianzhen” in China, is well known for its anti-inflammation and analgesic effect. Alkaloids are its main active constituents. However, little has been known about the absorption of main alkaloids in vivo. In this study, an ultra-performance liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry was employed for identification of absorbed alkaloids in rats after oral administration of Z. nitidum decoction. By analyzing the fragmentation patterns, a total of nineteen alkaloids were exactly or tentatively identified in rat plasma after treatment, of which magnoflorine, α-allocryptopine, and skimmianine are dominant. Moreover, a high performance liquid chromatography coupled mass spectrometry method was developed for simultaneous quantification of magnoflorine, α-allocryptopine, and skimmianine, and successfully applied to pharmacokinetic study in rats after oral administration of Z. nitidum decoction. The research would contribute to comprehensive understanding of the material basis and function mechanism of Z. nitidum decoction.

Antioxidant and Cholinesterase Inhibitory Activities of Ethyl Acetate Extract of Terminalia chebula: Cell-free In vitro and In silico Studies

Background

Alzheimer's disease (AD) is a progressive neurodegenerative disorder clinically characterized by memory loss and impaired cognitive function. Cholinergic enzyme deficiency and oxidative stress are the two major factors implicated in the pathogenesis of AD. The symptomatic treatment, as of now, is the use of cholinesterase inhibitors toward cholinergic "downturn." Therefore, there is a search for compounds that will be useful in focused therapies. There has been suggestion that Terminalia chebula fruit would be a potential source.

Objective

To assess the anticholinesterase and antioxidant activities of T. chebula fruit which is widely practiced in the Ayurvedic medicines for memory enhancement.

Materials and Methods

Ethyl acetate extract of T. chebula fruit (TCEA) was subjected to phytochemical investigation of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitory activities and cell-free antioxidant activity. TCEA was further subjected to gas chromatography-mass spectrum (GC-MS) analysis. The bioactive compounds were analyzed for molecular docking with AChE and BuChE proteins.

Results

TCEA exhibited potent AChE and BuChE inhibitory activities comparable to the standard drug donepezil. In vitro cell-free antioxidant assays demonstrated that TCEA possesses excellent free radical scavenging activity, reducing power, and potent metal-chelating activity. Total polyphenolic content of TCEA was 596.75 ± 0.35 µg gallic acid equivalents/mg of extract, which correlates with the antioxidant activity of TCEA. Molecular docking of compounds expounded in GC-MS analysis for AChE and BuChE enzyme activities revealed that methyl N-(N-benzyloxycarbonyl-beta-l-aspartyl)-beta-d-glucosaminide as the most potent compound with good predicted activities.

Conclusion

Overall, the results revealed that the bioactive molecule methyl N-(N-benzyloxycarbonyl-beta-l-aspartyl)-beta-d-glucosaminide present in TCEA is a potential depressant for the treatment of AD and related neurodegenerative disorders.

SUMMARY

The present study was carried out to assess the neuroprotective effect of Terminalia chebula fruit and its phytoconstituent. Phytochemical analysis of fruit ethyl acetate extract of T. chebula (TCEA) showed the presence of alkaloid, cardiac glycoside, and tannin. TCEA showed potent acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitory activities when compared to standard drug donepezil. Results of in vitro antioxidant assays revealed excellent free radical scavenging activity, reducing power, and potent metal-chelating activity. Gas chromatography-mass spectrum analysis illustrated the presence of 22 active compounds, among which methyl N-(N-benzyloxycarbonyl-beta-l-aspartyl)-beta-d-glucosaminide exhibited potent AChE and BuChE inhibition analyzed through in silico studies. Abbreviations used: AD: Alzheimer's disease; TCEA: Ethyl acetate extract of Terminalia chebula; GC-MS: Gas chromatography-mass spectrum; ROS: Reactive oxygen species; RNS: Reactive nitrogen species; AChE: Acetylcholinesterase; BuChE: Butyrylcholinesterase; NFT: Neurofibrillary tangles; Aμ: μ-amyloid; NSAIDS: Nonsteroidal anti-inflammatory drugs; FDA: Food and Drug Administration; RT: Room temperature; HCl: Hydrochloric acid; ATCI: Acetylthiocholine iodide; BTCI: Butyrylthiocholine iodide; BHT: Butylated hydroxytoluene; DPPH: 2,2-diphenyl-1-picrylhydrazyl; TCA: Trichloroacetic acid; GAE: Gallic acid equivalent; NICT: National Institute of Information and Communications Technology; 3D: Three-dimensional; PDB: Protein data bank; OPLS: Optimized potentials for liquid simulations; XP: Extra precision; SD: Standard deviation; ANOVA: Analysis of variance; EDTA: Ethylenediaminetetraacetic acid.

Phytochemistry of the genus Skimmia (Rutaceae)

The genus Skimmia is a rich source of interesting secondary metabolites, including 20 alkaloids derived from anthranilic acid, 45 coumarins, 21 limonoids, four cholestane derivatives, six pentacyclic triterpenes, six flavonoids, and two unusual fatty acid derivatives. Skimmia is employed in folk medicine e.g. against fever, inflammations, and rheumatism. Skimmia extracts, Skimmia essential oils and pure compounds isolated from Skimmia extracts have been experimentally shown to have various bioactivities such as antioxidant, anti-inflammatory, antimicrobial, and insecticidal. In this review we discuss the exact structures of compounds isolated from members of the genus Skimmia, bioactivities of Skimmia extracts and pure compounds derived from them, and systematic implications of the patterns of occurrence of these compounds. Moreover, research gaps and interesting avenues for future research are discussed briefly.

Chemical composition and biological activities of the essential oil of Skimmia laureola leaves

The composition of the essential oil from leaves of Skimmia laureola was determined by GC and GC-MS. Twenty-eight components were identified, accounting for 93.9% of the total oil. The oil is mainly composed of monoterpenes (93.5%), of which monoterpene hydrocarbons and oxygenated monoterpenes represent 11.0% and 82.5%, respectively. Sesquiterpenes constitute only 0.3% of the total oil. Linalyl acetate is the main component (50.5%), with linalool (13.1%), geranyl acetate (8.5%) and cis-p-menth-2-en-1-ol (6.2%) as other principal constituents. The essential oil showed a significant antispasmodic activity, in a dose range of 0.03–10 mg/mL. The essential oil also possesses antibacterial and antifungal activities against some pathogenic strains. The phytotoxic and cytotoxic activities were also assessed.

Natural AChE Inhibitors from Plants and their Contribution to Alzheimer's Disease Therapy

As acetylcholinesterase (AChE) inhibitors are an important therapeutic strategy in Alzheimer's disease, efforts are being made in search of new molecules with anti-AChE activity. The fact that naturally-occurring compounds from plants are considered to be a potential source of new inhibitors has led to the discovery of an important number of secondary metabolites and plant extracts with the ability of inhibiting the enzyme AChE, which, according to the cholinergic hypothesis, increases the levels of the neurotransmitter acetylcholine in the brain, thus improving cholinergic functions in patients with Alzheimer's disease and alleviating the symptoms of this neurological disorder. This review summarizes a total of 128 studies which correspond to the most relevant research work published during 2006-2012 (1st semester) on plant-derived compounds, plant extracts and essential oils found to elicit AChE inhibition.

Phytochemical and enzyme inhibitory studies on indigenous medicinal plant Rhazya stricta

A new triterpenoid 3alpha-hydroxy-ursane-5-ene (1) and a known steroid stigma sterol (2) have been isolated for the first time from the fruit of Rhazya stricta. The structures of these compounds were elucidated and identified by spectral studies. The crude ethanolic extract of R. stricta fruit has led to the determination of good results of antibacterial, lipoxygenase and acetylcholinesterase activities. In addition, we also reported the acetylcholinesterase activity of stigma sterol (2) isolated from this plant. Stigma sterol (2) was found to be an acetyl-cholinesterase inhibitor with IC(50) at a concentration of 644.0 +/- 11.75 microM. Eserine [(-)-physostigmine, IC(50) = 61 nM)] was used as a positive control.

Muscarinic, Ca++ antagonist and specific butyrylcholinesterase inhibitory activity of dried ginger extract might explain its use in dementia

Ginger rhizome (Zingiber officinale) has been used for centuries to treat dementia in South Asia. This study was undertaken to possibly justify its use. A 70% aqueous/methanolic extract of dried ginger (Zo.Cr) was used. Zo.Cr tested positive for the presence of terpenoids, flavonoids, secondary amines, phenols, alkaloids and saponins. When tested on isolated rat stomach fundus, Zo.Cr showed a spasmogenic effect (0.03–5.00 mg mL−1); it relaxed the tissue at concentrations ≥5 mg mL−1. The stimulant effect was resistant to blockade by hexamethonium and methysergide, but sensitive to atropine, indicating activity via muscarinic receptors. In atropinized (0.1 μM) preparations, Zo.Cr (0.3–3.0 mg mL−1) relaxed high K+ (80 mm)-induced contractions, indicating Ca++ antagonism in addition to the muscarinic effect. This possible Ca++ antagonist activity was investigated in Ca++-free conditions, with the inhibitory effect of the extract tested against contractions induced by externally administered Ca++. Zo.Cr (0.1–0.3 mg mL−1), similar to verapamil (0.03–0.10 μm), shifted the contractions induced by externally administered Ca++ to the right, thus suggesting an inhibitory interaction between Zo.Cr and voltage-operated Ca++ channels. Zo.Cr (0.1–3.0 μg mL−1) also potentiated acetylcholine peak responses in stomach fundus, similar to physostigmine, a cholinesterase inhibitor. Zo.Cr, in an in-vitro assay, showed specific inhibition of butyrylcholinesterase (BuChE) rather than acetylcholinesterase enzyme. Different pure compounds of ginger also showed spasmolytic activity in stomach fundus, with 6-gingerol being the most potent. 6-Gingerol also showed a specific anti-BuChE effect. This study shows a unique combination of muscarinic, possible Ca++ antagonist and BuChE inhibitory activities of dried ginger, indicating its benefit in dementia, including Alzheimer's disease.

Molecular interactions of cholinesterases inhibitors using in silico methods: current status and future prospects

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a low amount of acetylcholine (ACh) in hippocampus and cortex. Acetylcholinesterase (AChE) is one of the most important enzymes in many living organisms including human being and other vertebrates, insects like mosquitoes, among others. Several reports have been published where it has been clearly shown that the genesis of amyloid protein plaques associated with AD is connected to modifications of both AChE and butyrylcholinesterase (BChE), since the plaque is significantly decreased in AD patients using cholinesterase inhibitors (ChEIs). This review gives some examples of these inhibitors discovered during past couple of years that have shown very prominent interactions at the active site triad of the proteins as well as different other parts of the active site like, peripheral anionic site (PAS), oxyanionic hole, anionic subsite or acyl binding pocket (ABP). Most of the inhibition and their interactions have been visualized by X-ray crystallography, but some of the other inhibitors have been studied either by molecular docking or molecular dynamic (MD) simulations or by both the in silico methods. Some of these prominent studies have been crucially observed and reported here.