The inhibition of acetylcholinesterase by quaternary ammonium ions

Side effects based network construction and drug repositioning of ropinirole as a potential molecule for Alzheimer's disease: an in-silico, in-vitro, and in-vivo study

Alzheimer's disease (AD) is the leading cause of dementia in older adults. Drug repositioning is a process of finding new therapeutic applications for existing drugs. One of the methods in drug repositioning is to use the side-effect profile of a drug to identify a new therapeutic indication. The drugs with similar side-effects may act on similar biological targets and could affect the same biochemical process. In this study, we explored the Food and Drug Administration-approved drugs using PROMISCUOUS database to find those that have adverse effects profile comparable with the ligands being studied or used to treat AD. Here, we found that the ropinirole, a dopamine receptor agonist, shared a maximum number of side-effects with the drugs proven beneficial for treating AD. Furthermore, molecular modelling demonstrated that ropinirole exhibited strong binding affinity (-9.313 kcal/mol) and best ligand efficiency (0.49) with sigma-1 receptor. Here, we observed that the quaternary amino group of ropinirole is essential for binding with sigma-1 receptor. Molecular dynamic simulation indicated that the movement of the carboxy-terminal helices (α4/α5) could play a major role in the receptor's physiological functions. The neurotoxicity induced by Aβ25-35 in SH-SY5Y cells was reduced by ropinirole at concentrations 10, 30, and 50 µM. The effect on spatial learning and memory was examined in mice with Aβ25-35 induced memory deficit using the radial arm maze. Ropinirole (10 and 20 mg/kg) significantly improved the short and long-term memories in the radial arm maze test. Our results suggest that ropinirole has the potential to be repositioned for AD treatment.Communicated by Ramaswamy H. Sarma.

Donepezil-Inspired Multitargeting Indanone Derivatives as Effective Anti-Alzheimer's Agents

In continuous efforts to develop anti-Alzheimer's agents, we rationally designed and synthesized a series of multitargeting molecules by incorporating the essential molecular features of the standard drug donepezil. Among the series, compound 4b showed multitargeting properties to act as an anti-Alzheimer's agent, which is better tolerable in vivo than donepezil. Acetylcholinesterase (AChE) inhibition data showed that compound 4b inhibits the enzyme with a half-maximal inhibitory concentration (IC₅₀) value of 0.78 μM and also showed DNA protection, which was confirmed through the DNA nicking assay, suggesting the protective effect of 4b against oxidative DNA damage. Compound 4b also showed 53.04% inhibition against Aβ_1-42 aggregations, which was found comparable to that of the standard compound curcumin. Molecular dynamics simulations were performed to check the stability of compound 4b with the enzyme AChE, which showed that the enzyme-ligand complex is stable enough to block the hydrolysis of acetylcholine in the brain. Its higher LD₅₀ cutoff value (50 mg/kg) in comparison to donepezil (LD₅₀: 25 mg/kg) made it safer, suggesting that it can be used in further clinical experiments. To evaluate its anti-Alzheimer property, a mice model with melamine-induced cognitive dysfunction was used, and Morris water maze and Rotarod tests were performed. A significant improvement in memory was observed after the treatment with compound 4b and donepezil. The study postulated that the introduction of important structural features of donepezil (dimethoxyindanone moiety as ring-A) embarked with terminal aromatic ether (ring-B and ring-C) made 4b a multitargeting molecule that offers a way for developing alternative therapeutics in the future against Alzheimer's disease (AD).

ACETYLCHOLINESTERASE

The general characteristics of acetylcholinesterase are described. The mechanism of action of the enzyme is considered primarily in relation to the two steps in the hydrolysis of acetylcholine, the acetylation and deacetylation reactions. Competitive and non-competitive inhibition, and inhibitions by hydrogen ion and by substrate, are explained in terms of this two-step process. On the basis of the available evidence, a suggestion is made regarding the configuration of groups in the active center.