Anti-cholinesterase hybrids as multi-target-directed ligands against Alzheimer’s disease (1998–2018)

Alzheimer’s disease (AD) is a genetically complex, progressive and irreversible neurodegenerative disorder of the brain which involves multiple associated etiological targets. The complex pathogenesis of AD gave rise to multi-target-directed ligands (MTDLs) principle to combat this dreaded disease. Within this approach, the design and synthesis of hybrids prevailed greatly because of their capability to simultaneously target the intertwined pathogenesis components of the disease. The hybrids include pharmacophoric hybridization of two or more established chemical scaffolds endowed with the desired pharmacological properties into a single moiety. In AD, the primary foundation of medication therapy and drug design strategies includes the inhibition of cholinesterase (ChE) enzymes. Hence the development of ChE inhibition based hybrids is the central choice of AD medicinal chemistry research. To illustrate the progress of ChE inhibition based hybrids and novel targets, we reviewed the medicinal chemistry and pharmacological properties of the multi-target molecules published since 1998-December 2018. We hope that this article will allow the readers to easily follow the evolution of this prominent medicinal chemistry approach to develop a more efficient inhibitor.     

New classes of carbazoles as potential multi-functional anti-Alzheimer’s agents

Multi-Target approach is particularly promising way to drug discovery against Alzheimer's disease. In the present study, we synthesized a series of compounds comprising the carbazole backbone linked to the benzyl piperazine, benzyl piperidine, pyridine, quinoline, or isoquinoline moiety through an aliphatic linker and evaluated as cholinesterase inhibitors. The synthesized compounds showed IC₅₀ values of 0.11–36.5 µM and 0.02–98.6 µM against acetyl- and butyrylcholinesterase (AChE and BuChE), respectively. The ligand-protein docking simulations and kinetic studies revealed that compound 3s could bind effectively to the peripheral anionic binding site (PAS) and anionic site of the enzyme with mixed-type inhibition. Compound 3s was the most potent compound against AChE and BuChE and showed acceptable inhibition potency for self- and AChE-induced Aβ_1-42 aggregation. Moreover, compound 3s could significantly protect PC12 cells against H₂O₂-induced toxicity. The results suggested that the compounds 3s could be considered as a promising multi-functional agent for further drug discovery development against Alzheimer's disease.     

无脊椎动物乙酰胆碱酯酶研究进展

乙酰胆碱酯酶(AChE)是生物体中一种十分重要的神经递质水解酶,也是有机磷和氨基甲酸酯类杀虫剂的作用靶标。AChE在不同生物中的性质显著不同,如编码基因个数、序列保守性、表达分布及生理功能等。作为杀虫剂的主要作用靶标之一,AChE不但可以通过单个点突变引起昆虫抗药性,还能够通过多个点突变联合作用、靶标表达量变化及基因复制等方式引起抗药性并且改变昆虫的适合度代价。本文主要从AChE的基因类型、分子进化、蛋白结构、生理功能、与昆虫的抗药性关系、同一物种中不同AChE的性质等6个方面对昆虫纲、蛛形纲和线虫等无脊椎动物AChE的研究进展作一综述。     

Antioxidant and anticholinesterase investigations of Rumex hastatus D. Don: potential effectiveness in oxidative stress and neurological disorders

Background

Rumex species are traditionally used for the treatment of neurological disorders including headache, migraine, depression, paralysis etc. Several species have been scientifically validated for antioxidant and anticholinestrase potentials. This study aims to investigate Rumex hastatus D. Don crude methanolic extract, subsequent fractions, saponins and flavonoids for acetylcholinestrase, butyrylcholinestrase inhibition and diverse antioxidant activities to validate its folkloric uses in neurological disorders. Rumex hastatus crude methanolic extract (Rh. Cr), subsequent fractions; n-hexane (Rh. Hex), chloroform (Rh. Chf), ethyl acetate (Rh. EtAc), aqueous fraction (Rh. Aq), crude saponins (Rh. Sp) and flavonoids (Rh. Fl) were investigated against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) at various concentrations (125, 250, 500, 1000 μg/mL) using Ellman’s spectrophotometric analysis. Antioxidant potentials of Rh. Sp and Rh. Fl were evaluated using DPPH, H₂O₂ and ABTS free radical scavenging assays at 62.5, 125, 250, 500, 1000 μg/mL.

Results

All the test samples showed concentration dependent cholinesterase inhibition and radicals scavenging activity. The AChE inhibition potential of Rh. Sp and Rh. Fl were most prominent i.e., 81.67 ± 0.88 and 91.62 ± 1.67 at highest concentration with IC₅₀ 135 and 20 μg/mL respectively. All the subsequent fractions exhibited moderate to high AChE inhibition i.e., Rh. Cr, Rh. Hex, Rh. Chf, Rh. EtAc and Rh. Aq showed IC₅₀ 218, 1420, 75, 115 and 1210 μg/mL respectively. Similarly, against BChE various plant extracts i.e., Rh. Sp, Rh. Fl, Rh. Cr, Rh. Hex, Rh. Chf, Rh. EtAc and Rh. Aq resulted IC₅₀ 165, 175, 265, 890, 92, 115 and 220 μg/mL respectively. In DPPH free radical scavenging assay, Rh. Sp and Rh. Fl showed comparable results with the positive control i.e., 63.34 ± 0.98 and 76.93 ± 1.13% scavenging at 1 mg/mL concentration (IC₅₀ 312 and 104 μg/mL) respectively. The percent ABTS radical scavenging potential exhibited by Rh. Sp and Rh. Fl (1000 μg/mL) were 82.58 ± 0.52 and 88.25 ± 0.67 with IC₅₀ 18 and 9 μg/mL respectively. Similarly in H₂O₂ scavenging assay, the Rh. Sp and Rh. Fl exhibited IC₅₀ 175 and 275 μg/mL respectively.

Conclusion

The strong anticholinesterase and antioxidant activities of Rh. Sp, Rh. Fl and various fractions of R. hastatus support the purported ethnomedicinal uses and recommend R. hastatus as a possible remedy for the treatment of AD and neurodegenerative disorders.     

Swimming impairment and acetylcholinesterase inhibition in zebrafish exposed to copper or chlorpyrifos separately,or as mixtures

Pesticides such as chlorpyrifos (CPF) and metals such as copper can impair swimming behavior in fish. However, the impact to swimming behavior from exposure to mixtures of neurotoxicants has received little attention. In the current study, we analyzed spontaneous swimming rates of adult zebrafish (Danio rerio) to investigate in vivo mixture interactions involving two chemical classes. Zebrafish were exposed to the neurotoxicants copper chloride (CuCl, 0.1 μM, 0.25 μM, 0.6 μM, or 6.3, 16, 40 ppb), chlorpyrifos (CPF, 0.1 μM, 0.25 μM, 0.6 μM, or 35, 88, 220 ppb) and binary mixtures for 24 h to better understand the effects of Cu on CPF neurotoxicity. Exposure to CPF increased the number of animals undergoing freeze responses (an anti-predator behavior) and, at the highest CPF dose (0.6 μM), elicited a decrease in zebrafish swimming rates. Interestingly, the addition of Cu caused a reduction in the number of zebrafish in the CPF exposure groups undergoing freeze responses. There was no evidence of additive or synergistic toxicity between Cu and CPF. Although muscle AChE activity was significantly reduced by CPF, there was a relatively poor relationship among muscle AChE concentrations and swimming behavior, suggesting non-muscle AChE mechanisms in the loss of swimming behavior. In summary, we have observed a modulating effect of Cu on CPF swimming impairment that appears to involve both AChE and non-AChE mechanisms. Our study supports the utility of zebrafish in understanding chemical mixture interactions and neurobehavioral injury.     

四种杀虫剂对两种书虱羧酸酯酶和乙酰胆碱酯酶的抑制作用

选用有机磷类杀虫剂(敌敌畏、毒死蜱、对氧磷)和氨基甲酸酯类杀虫剂(丁硫克百威),通过生物测定(药膜法)和生化测定(比色法)比较了嗜卷书虱和嗜虫书虱对所选药剂的敏感差异性。根据LC50可知嗜虫书虱对所选药剂比嗜卷书虱敏感。离体酶活性分析结果显示嗜卷书虱和嗜虫书虱的羧酸酯酶只对敌敌畏敏感,且嗜卷书虱比嗜虫书虱更敏感;4种药剂对乙酰胆碱酯酶均有强烈的抑制作用,同样是嗜卷书虱比嗜虫书虱敏感。乙酰胆碱酯酶的动力学研究结果和离体酶活性测定相一致。聚丙烯酰胺凝胶电泳分析显示,4种杀虫剂离体条件下对2种书虱的酯酶同工酶的抑制能力有明显差异,其中敌敌畏的抑制力最强;但对不同同功酶的抑制趋势(对大分子的抑制似乎较强)是一致的。酶的敏感性分析结果与生测结果比较表明,2种书虱的耐药力差异与其乙酰胆碱酯酶和酯酶对药剂的敏感性无关。如要弄清耐药力机制,需做进一步研究。     

Design,synthesis and biological evaluation of 1,3-dihydroxyxanthone derivatives: Effective agents against acetylcholinesterase

The present work concerns the rational design and development of new inhibitors of acetylcholinesterase (AChE) based on the privileged xanthone scaffold. In order to understand and rationalize the mode of action of these target structures a theoretical study was initially conducted. From the results of rational design, a new variety of amphiphilic xanthone derivatives were synthesized, structurally characterized and evaluated as potential anti-Alzheimer agents. The results showed that most of the synthesized compounds exhibited high AChE inhibitory activity at the micromolar range (IC₅₀, 0.46–12.09 μM). The synthetic xanthone 11 showed the best inhibitory effect on AChE and a molecular modeling study revealed that 11 targeted both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. Therefore, this compound could be considered as a potential lead compound towards new drugs for the treatment of Alzheimer’s disease.     

Synthesis and biological evaluation of aminomethyl and alkoxymethyl derivatives as carbonic anhydrase,acetylcholinesterase and butyrylcholinesterase inhibitors

Compounds containing nitrogen and sulfur atoms can be widely used in various fields such as industry, medicine, biotechnology and chemical technology. Therefore, the reactions of aminomethylation and alkoxymethylation of mercaptobenzothiazole, mercaptobenzoxazole and 2-aminothiazole were developed. Additionally, the alkoxymethyl derivatives of mercaptobenzoxazole and 2-aminothiazole were synthesized by a reaction with hemiformals, which are prepared by the reaction of alcohols and formaldehyde. In this study, the inhibitory effects of these molecules were investigated against acetylcholinesterase (AChE), butyrylcholinesterase (BChE) enzymes and carbonic anhydrase I, and II isoenzymes (hCA I and II). Both hCA isoenzymes were significantly inhibited by the recently synthesized molecules, with K_i values in the range of 58–157?nM for hCA I, and 81–215?nM for hCA II. Additionally, the K_i parameters of these molecules for BChE and AChE were calculated in the ranges 23–88 and 18–78?nM, respectively.     

Acetylcholinesterase activity in Clytia hemisphaerica (Cnidaria)

Cholinesterase activity is known in representatives of all living organisms phyla but the origin of the cholinergic system as known in bilaterian animals is still undeciphered. In particular the implication of cholinesterases in the nervous system of non-bilaterian Metazoa is not well known. We thus chose to investigate this activity in the Clytia hemisphaerica (Cnidaria) medusa. In toto histochemical staining revealed an acetylcholinesterase activity in the tentacle bulbs but not in the nervous system. Sequences homologous to acetylcholinesterase were searched within Clytia ESTs and compared to other sequences found in public databases.