Anti-neurodegenerative benefits of acetylcholinesterase inhibitors in Alzheimer’s disease: Nexus of cholinergic and nerve growth factor dysfunction

: Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is increasingly viewed as a complex multi-dimensional disease without effective treatments. Recent randomized, placebo-controlled studies have shown volume losses of ~0.7% and ~3.5% per year, respectively, in the basal cholinergic forebrain (CBF) and hippocampus in untreated suspected prodromal AD. One year of donepezil treatment reduced these annualized rates of atrophy to about half of untreated rates. Similar positive although variable results have also been found in volumetric measurements of the cortex and whole brain in patients with mild cognitive impairment as well as more advanced AD stages after treatments with all three currently available acetylcholinesterase (AChE) inhibitors (donepezil, rivastigmine, and galantamine). Here we review the anti-neurodegenerative benefits of AChE inhibitors and the expected parallel disease-accelerating impairments caused by anticholinergics, within a framework of the cholinergic hypothesis of AD and AD-associated loss of nerve growth factor (NGF). Consistent with the “loss of trophic factor hypothesis of AD,” we propose that AChE inhibitors enhance acetylcholine-dependent release and uptake of NGF, thereby sustaining cholinergic neuronal viability and thus lowing AD-associated degeneration of the CBF, to delay dementia progression ultimately. We propose that improved cholinergic therapies for AD started early in asymptomatic persons, especially those with risk factors, will delay the onset, progression, or emergence of dementia. The currently available competitive pseudo-irreversible AChE inhibitors are not CNS-selective and thus induce gastrointestinal toxicity that limits cortical AChE inhibition to ~30% (ranges from 19% to 41%) as measured by in vivo PET studies in patients undergoing therapy. These levels of inhibition are marginal about what is required for effective symptomatic treatment of dementia or slowing AD-associated neurodegeneration. In contrast, because of the inherently slow de novo synthesis of AChE in the CNS (about one-tenth the rate of synthesis in peripheral tissues), irreversible AChE inhibitors produce significantly higher levels of inhibition in the CNS than in peripheral tissues. Such an irreversible inhibitor produces ~68% CNS AChE inhibition in patients undergoing therapy and ~80% inhibition in cortical biopsies of non-human primates. The full therapeutic benefits of AChE inhibitors, whether for symptomatic treatment of dementia or disease-slowing, thus would benefit by producing high levels of CNS inhibition. One way to obtain such higher levels of CNS AChE inhibition would be by using irreversible inhibitors.

Novel Coumarin-Thiadiazole Hybrids and Their Cu(II) and Zn(II) Complexes as Potential Antimicrobial Agents and Acetylcholinesterase Inhibitors

A series of coumarin-thiadiazole hybrids and their corresponding Cu(II) and Zn(II) complexes were synthesized and characterized with the use of spectroscopic techniques. The results obtained indicate that all the coumarin-thiadiazole hybrids act as bidentate chelators of Cu(II) and Zn(II) ions. The complexes isolated differ in their ligand:metal ratio depending on the central metal. In most cases, the Zn(II) complexes are characteristic of a 1:1 ligand:metal ratio, while in the Cu(II) complexes the ligand:metal ratio is 2:1. All compounds were tested as potential antibacterial agents against Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacterial strains demonstrating activities notably lower than commercially available antibiotics. The more promising results were obtained from the assessment of antineurodegenerative potency as all compounds showed moderate acetylcholinesterase (AChE) inhibition activity

"In-vitro Effects of Chlorpyrifos and Monocrotophos on the Activity of Acetylcholinesterase (AChE) in Different Tissues of Apple Snail Pila globosa (Swainson, 1822)"

The impact of two organophosphorus insecticides [Chlorpyrifos (CPF) and Monocrotophos (MCP)] on non-target wild natural gastropod, Pila globosa (apple snail) from the paddy fields was studied. The activity of acetylcholinesterase (AChE) was monitored on foot-muscle and hepatopancreas tissues of control and exposed snails. In the foot- muscle AChE inhibition progressed and reached 54.19% and 63.13% of the control, whereas, the AChE inhibition in the hepatopancreas reached 46.96% and 53.67% over control after 48 hours of exposure to 1.5 mL.L-1 and 2.5 mL.L-1 CPF respectively. After 48 hours of MCP exposure at 1.5 mL.L-1 and 2.5 mL.L-1 separately, the AChE inhibition of foot muscle was 49.07% and 57.59% respectively while in hepatopancreas it was 44.65% and 48.84% respectively. Our results show more inhibition of AChE activities on the foot-muscle than hepatopancreas in a concentration and time-dependent manner with greater severity by CPF in comparison to MCP. AChE inhibition increased with the increasing exposure time.

Revealing the molecular interplay of curcumin as Culex pipiens Acetylcholine esterase 1 (AChE1) inhibitor

Emergence of vector borne diseases has continued to take toll on millions of lives since its inception. The use of insecticides began as vector control strategy in the early 1900’s but the menace of insects is still prevalent. Additionally, the inadequate use of organophosphates and carbamates which target acetylcholine esterase (AChE), are known to develop resistance amongst vectors of transmission and are toxic to humans. In this study, extensive computational screening was performed using homology modelling, molecular docking, molecular dynamics (MD) simulation and free energy change calculation, which highlighted curcumin as a lead molecule out of ~ 1700 phytochemicals against Culex pipiens AChE. In vivo larvicidal activity was carried out along with in vivo and in vitro AChE inhibition assay to determine the biochemical efficacy of curcumin. Our study reveals that curcumin induces mortality in Cx. pipiens at an early stage of its life cycle by AChE inhibition. This also underlines the use of curcumin as a coming-age natural product insecticide.

Multi-Target Actions of Acridones from Atalantia monophylla towards Alzheimer’s Pathogenesis and Their Pharmacokinetic Properties

Ten acridones isolated from Atalantia monophylla were evaluated for effects on Alzheimer’s disease pathogenesis including antioxidant effects, acetylcholinesterase (AChE) inhibition, prevention of beta-amyloid (Aβ) aggregation and neuroprotection. To understand the mechanism, the type of AChE inhibition was investigated in vitro and binding interactions between acridones and AChE or Aβ were explored in silico. Drug-likeness and ADMET parameters were predicted in silico using SwissADME and pKCSM programs, respectively. All acridones showed favorable drug-likeness and possessed multifunctional activities targeting AChE function, Aβ aggregation and oxidation. All acridones inhibited AChE in a mixed-type manner and bound AChE at both catalytic anionic and peripheral anionic sites. In silico analysis showed that acridones interfered with Aβ aggregation by interacting at the central hydrophobic core, C-terminal hydrophobic region, and the key residues 41 and 42. Citrusinine II showed potent multifunctional action with the best ADMET profile and could alleviate neuronal cell damage induced by hydrogen peroxide and Aβ1-42 toxicity.

In-vitro Acetylcholinesterase and antioxidant activity of Ficus dalhousie and Melissa parviflora Benth

Ficus dalhousie and Melissa parviflora Benth both plants have been used as Tranquiliser, Relaxants, Nervine tonic and Calming aids throughout the world. The present study was aimed to identify the antioxidant potential of the Ethyl acetate and Hydro alcoholic extract of these plants by in vitro methods. Anti-Alzheimer activity of the plant extract were screened by Acetylcholinesterase (AChE) inhibition and antioxidant by DPPH and Hydrogen oxide. The results of the assays were calculated by the percentage inhibition of these free radicals. In Acetylcholinesterase (AChE) assay inhibitory potentials of Ficus dalhousie exhibited 73.34 ± 1.12%, whereas in Melissa arviflora it was 86.88± 2.12%. In DPPH radical scavenging assay the percentage inhibition was 77.87 ± 2.02% in Ficus dalhousie and 76.92± 1.32% in Melissa arviflora. Hydrogen peroxide scavenging assay the percentage inhibition was 86.56 ± 1.05% in Ficus dalhousie and 80.75± 1.92% was in Melissa arviflora. In all the research assays, the extract showed a concentration dependent increase in free radical scavenging activity. The results revealed that the antioxidant effects of the plant extract might be due to the presence of phenol and flavonoid compounds.

Identification of Compounds for Butyrylcholinesterase Inhibition

Butyrylcholinesterase (BChE) is a nonspecific cholinesterase enzyme that hydrolyzes choline-based esters. BChE plays a critical role in maintaining normal cholinergic function like acetylcholinesterase (AChE) through hydrolyzing acetylcholine (ACh). Selective BChE inhibition has been regarded as a viable therapeutic approach in Alzheimer’s disease. As of now, a limited number of selective BChE inhibitors are available. To identify BChE inhibitors rapidly and efficiently, we have screened 8998 compounds from several annotated libraries against an enzyme-based BChE inhibition assay in a quantitative high-throughput screening (qHTS) format. From the primary screening, we identified a group of 125 compounds that were further confirmed to inhibit BChE activity, including previously reported BChE inhibitors (e.g., bambuterol and rivastigmine) and potential novel BChE inhibitors (e.g., pancuronium bromide and NNC 756), representing diverse structural classes. These BChE inhibitors were also tested for their selectivity by comparing their IC50 values in BChE and AChE inhibition assays. The binding modes of these compounds were further studied using molecular docking analyses to identify the differences between the interactions of these BChE inhibitors within the active sites of AChE and BChE. Our qHTS approach allowed us to establish a robust and reliable process to screen large compound collections for potential BChE inhibitors.

Catalytic activity and stereoselectivity of engineered phosphotriesterases towards structurally different nerve agents in vitro

Highly toxic organophosphorus nerve agents, especially the extremely stable and persistent V-type agents such as VX, still pose a threat to the human population and require effective medical countermeasures. Engineered mutants of the Brevundimonas diminuta phosphotriesterase (BdPTE) exhibit enhanced catalytic activities and have demonstrated detoxification in animal models, however, substrate specificity and fast plasma clearance limit their medical applicability. To allow better assessment of their substrate profiles, we have thoroughly investigated the catalytic efficacies of five BdPTE mutants with 17 different nerve agents using an AChE inhibition assay. In addition, we studied one BdPTE version that was fused with structurally disordered PAS polypeptides to enable delayed plasma clearance and one bispecific BdPTE with broadened substrate spectrum composed of two functionally distinct subunits connected by a PAS linker. Measured kcat/KM values were as high as 6.5 and 1.5 × 108 M−1 min−1 with G- and V-agents, respectively. Furthermore, the stereoselective degradation of VX enantiomers by the PASylated BdPTE-4 and the bispecific BdPTE-7 were investigated by chiral LC–MS/MS, resulting in a several fold faster hydrolysis of the more toxic P(−) VX stereoisomer compared to P(+) VX. In conclusion, the newly developed enzymes BdPTE-4 and BdPTE-7 have shown high catalytic efficacy towards structurally different nerve agents and stereoselectivity towards the toxic P(−) VX enantiomer in vitro and offer promise for use as bioscavengers in vivo.

Development of Novel 2-Acetylphenol-O-Alkylhydroxyethylamine Derivatives as Multifunctional Agents for Alzheimer’s Disease Treatment

Due to the complex pathogenesis of AD, the multi-target-directed ligands (MTDLs) strategy presented the best pharmacological option for AD treatment. Herein, a series of novel 2-acetylphenol-O-alkylhydroxyethylamine derivatives was rationally designed and synthesized. Of these derivatives, 5c was a good multifunctional agent (eeAChE IC50 =7.9 μM, MAO-B IC50 = 9.9 μM, BACE1 IC50 = 8.3 μM) in vitro and displayed a mixed-type AChE inhibition, which could bind to the CAS and PAS of AChE. Compound 5c also exhibited good antioxidant activity (ORAC = 2.5 eq) and neuroprotective effects. Furthermore, compound 5c was a selective metal ions chelator. And it could cross blood-brain barrier in vitro and complied with drug-like properties rule of 5. Therefore, compound 5c was a promising multifunctional agent for the treatment of AD.