Multitarget Therapeutic Leads for Alzheimer's Disease: Quinolizidinyl Derivatives of Bi- and Tricyclic Systems as Dual Inhibitors of Cholinesterases and β-Amyloid (Aβ) Aggregation

New insights into butyrylcholinesterase: Pharmaceutical applications, selective inhibitors and multitarget-directed ligands

Butyrylcholinesterase (BChE), also known as pseudocholinesterase and serum cholinesterase, is an isoenzyme of acetylcholinesterase (AChE). It mediates the degradation of acetylcholine, especially under pathological conditions. Proverbial pharmacological applications of BChE, its mutants and modulators consist of combating Alzheimer's disease (AD), influencing multiple sclerosis (MS), addressing cocaine addiction, detoxifying organophosphorus poisoning and reflecting the progression or prognosis of some diseases. Of interest, recent reports have shed light on the relationship between BChE and lipid metabolism. It has also been proved that BChE is going to increase abnormally as a compensator for AChE in the middle and late stages of AD, and BChE inhibitors can alleviate cognitive disorders and positively influence some pathological features in AD model animals, foreboding favorable prospects and potential applications. Herein, the selective BChE inhibitors and BChE-related multitarget-directed ligands published in the last three years were briefly summarized, along with the currently known pharmacological applications of BChE, aiming to grasp the latest research directions. Thereinto, some emerging strategies for designing BChE inhibitors are intriguing, and the modulators based on target combination of histone deacetylase and BChE against AD is unprecedented. Furthermore, the involvement of BChE in the hydrolysis of ghrelin, the inhibition of low-density lipoprotein (LDL) uptake, and the down-regulation of LDL receptor (LDLR) expression suggests its potential to influence lipid metabolism disorders. This compelling prospect likely stimulates further exploration in this promising research direction.

Quinones as Neuroprotective Agents

Quinones can in principle be viewed as a double-edged sword in the treatment of neurodegenerative diseases, since they are often cytoprotective but can also be cytotoxic due to covalent and redox modification of biomolecules. Nevertheless, low doses of moderately electrophilic quinones are generally cytoprotective, mainly due to their ability to activate the Keap1/Nrf2 pathway and thus induce the expression of detoxifying enzymes. Some natural quinones have relevant roles in important physiological processes. One of them is coenzyme Q₁₀, which takes part in the oxidative phosphorylation processes involved in cell energy production, as a proton and electron carrier in the mitochondrial respiratory chain, and shows neuroprotective effects relevant to Alzheimer's and Parkinson's diseases. Additional neuroprotective quinones that can be regarded as coenzyme Q₁₀ analogues are idobenone, mitoquinone and plastoquinone. Other endogenous quinones with neuroprotective activities include tocopherol-derived quinones, most notably vatiquinone, and vitamin K. A final group of non-endogenous quinones with neuroprotective activity is discussed, comprising embelin, APX-3330, cannabinoid-derived quinones, asterriquinones and other indolylquinones, pyrroloquinolinequinone and its analogues, geldanamycin and its analogues, rifampicin quinone, memoquin and a number of hybrid structures combining quinones with amino acids, cholinesterase inhibitors and non-steroidal anti-inflammatory drugs.

Inhibition of Acetylcholinesterase by Novel Lupinine Derivatives

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive memory loss and cognitive impairment due in part to a severe loss of cholinergic neurons in specific brain areas. AD is the most common type of dementia in the aging population. Although several acetylcholinesterase (AChE) inhibitors are currently available, their performance sometimes yields unexpected results. Thus, research is ongoing to find potentially therapeutic AChE inhibitory agents, both from natural and synthetic sources. Here, we synthesized 13 new lupinine triazole derivatives and evaluated them, along with 50 commercial lupinine-based esters of different carboxylic acids, for AChE inhibitory activity. The triazole derivative 15 [1S,9aR)-1-((4-(4-(benzyloxy)-3-methoxyphenyl)-1H-1,2,3-triazol-1-yl)methyl)octahydro-2H-quinolizine)] exhibited the most potent AChE inhibitory activity among all 63 lupinine derivatives, and kinetic analysis demonstrated that compound 15 was a mixed-type AChE inhibitor. Molecular docking studies were performed to visualize interaction between this triazole derivative and AChE. In addition, a structure-activity relationship (SAR) model developed using linear discriminant analysis (LDA) of 11 SwissADME descriptors from the 50 lupinine esters revealed 5 key physicochemical features that allowed us to distinguish active versus non-active compounds. Thus, this SAR model could be applied for design of more potent lupinine ester-based AChE inhibitors.

Thioxanthenone-based derivatives as multitarget therapeutic leads for Alzheimer's disease

A set of twenty-five thioxanthene-9-one and xanthene-9-one derivatives, that were previously shown to inhibit cholinesterases (ChEs) and amyloid β (Aβ₄₀) aggregation, were evaluated for the inhibition of tau protein aggregation. All compounds exhibited a good activity, and eight of them (5-8, 10, 14, 15 and 20) shared comparable low micromolar inhibitory potency versus Aβ₄₀ aggregation and human acetylcholinesterase (AChE), while inhibiting human butyrylcholinesterase (BChE) even at submicromolar concentration. Compound 20 showed outstanding biological data, inhibiting tau protein and Aβ₄₀ aggregation with IC₅₀ = 1.8 and 1.3 μM, respectively. Moreover, at 0.1-10 μM it also exhibited neuroprotective activity against tau toxicity induced by okadoic acid in human neuroblastoma SH-SY5Y cells, that was comparable to that of estradiol and PD38. In preliminary toxicity studies, these interesting results for compound 20 are somewhat conflicting with a narrow safety window. However, compound 10, although endowed with a little lower potency for tau and Aβ aggregation inhibition additionally demonstrated good inhibition of ChEs and rather low cytotoxicity. Compound 4 is also worth of note for its high potency as hBChE inhibitor (IC₅₀ = 7 nM) and for the three order of magnitude selectivity versus hAChE. Molecular modelling studies were performed to explain the different behavior of compounds 4 and 20 towards hBChE. The observed balance of the inhibitory potencies versus the relevant targets indicates the thioxanthene-9-one derivatives as potential MTDLs for AD therapy, provided that the safety window will be improved by further structural variations, currently under investigation.

Synthesis and activities of acetylcholinesterase inhibitors

Cholinesterase (ChE) inhibitors can be divided into two categories: acetylcholinesterase (AChE) inhibitors and butylcholinesterase (BuChE) inhibitors. Therefore, the development of selective inhibition of AChE and BuChE activities is the central content of ChE pharmacochemistry research. In order to clarify the progress of AChE inhibitor-based design, synthesis, and activity studies, we reviewed the pharmacochemical and pharmacological properties of selective AChE inhibitors over the past decade. We hope that this review will make it easier for readers to understand the development of new drug chemistry methods for AChE inhibitors in order to develop more effective and selective AChE inhibitors.

Recent Progress in the Drug Development for the Treatment of Alzheimer's Disease Especially on Inhibition of Amyloid-peptide Aggregation

As the world 's population is aging, Alzheimer's disease (AD) has become a big concern since AD has started affecting younger people and the population of AD patients is increasing worldwide. It has been revealed that the neuropathological hallmarks of AD are typically characterized by the presence of neurotoxic extracellular amyloid plaques in the brain, which are surrounded by tangles of neuronal fibers. However, the causes of AD have not been completely understood yet. Currently, there is no drug to effectively prevent AD or to completely reserve the symptoms in the patients. This article reviews the pathological features associated with AD, the recent progress in research on the drug development to treat AD, especially on the discovery of natural product derivatives to inhibit Aβ peptide aggregation as well as the design and synthesis of Aβ peptide aggregation inhibitors to treat AD.

Multitarget Biological Profiling of New Naphthoquinone and Anthraquinone-Based Derivatives for the Treatment of Alzheimer's Disease

Two series of naphthoquinone and anthraquinone derivatives decorated with an aromatic/heteroaromatic chain have been synthesized and evaluated as potential promiscuous agents capable of targeting different factors playing a key role in Alzheimer’s disease (AD) pathogenesis. On the basis of the in vitro biological profiling, most of them exhibited a significant ability to inhibit amyloid aggregation, PHF6 tau sequence aggregation, acetylcholinesterase (AChE), and monoamine oxidase (MAO) B. In particular, naphthoquinone 2 resulted as one of the best performing multitarget-directed ligand (MTDL) experiencing a high potency profile in inhibiting β-amyloid (Aβ₄₀) aggregation (IC₅₀ = 3.2 μM), PHF6 tau fragment (91% at 10 μM), AChE enzyme (IC₅₀ = 9.2 μM) jointly with a remarkable inhibitory activity against MAO B (IC₅₀ = 7.7 nM). Molecular modeling studies explained the structure–activity relationship (SAR) around the binding modes of representative compound 2 in complex with hMAO B and hAChE enzymes, revealing inhibitor/protein key contacts and the likely molecular rationale for enzyme selectivity. Compound 2 was also demonstrated to be a strong inhibitor of Aβ₄₂ aggregation, with potency comparable to quercetin. Accordingly, atomic force microscopy (AFM) revealed that the most promising naphthoquinones 2 and 5 and anthraquinones 11 and 12 were able to impair Aβ₄₂ fibrillation, deconstructing the morphologies of its fibrillar aggregates. Moreover, the same compounds exerted a moderate neuroprotective effect against Aβ₄₂ toxicity in primary cultures of cerebellar granule cells. Therefore, our findings demonstrate that these molecules may represent valuable chemotypes toward the development of promising candidates for AD therapy.

Journey on Naphthoquinone and Anthraquinone Derivatives: New Insights in Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disease that is characterized by memory loss, cognitive impairment, and functional decline leading to dementia and death. AD imposes neuronal death by the intricate interplay of different neurochemical factors, which continue to inspire the medicinal chemist as molecular targets for the development of new agents for the treatment of AD with diverse mechanisms of action, but also depict a more complex AD scenario. Within the wide variety of reported molecules, this review summarizes and offers a global overview of recent advancements on naphthoquinone (NQ) and anthraquinone (AQ) derivatives whose more relevant chemical features and structure-activity relationship studies will be discussed with a view to providing the perspective for the design of viable drugs for the treatment of AD. In particular, cholinesterases (ChEs), β-amyloid (Aβ) and tau proteins have been identified as key targets of these classes of compounds, where the NQ or AQ scaffold may contribute to the biological effect against AD as main unit or significant substructure. The multitarget directed ligand (MTDL) strategy will be described, as a chance for these molecules to exhibit significant potential on the road to therapeutics for AD.

Pharmacophore Modeling and 3D-QSAR Study of Indole and Isatin Derivatives as Antiamyloidogenic Agents Targeting Alzheimer's Disease

Thirty-six novel indole-containing compounds, mainly 3-(2-phenylhydrazono) isatins and structurally related 1H-indole-3-carbaldehyde derivatives, were synthesized and assayed as inhibitors of beta amyloid (Aβ) aggregation, a hallmark of pathophysiology of Alzheimer’s disease. The newly synthesized molecules spanned their IC₅₀ values from sub- to two-digit micromolar range, bearing further information into structure-activity relationships. Some of the new compounds showed interesting multitarget activity, by inhibiting monoamine oxidases A and B. A cell-based assay in tau overexpressing bacterial cells disclosed a promising additional activity of some derivatives against tau aggregation. The accumulated data of either about ninety published and thirty-six newly synthesized molecules were used to generate a pharmacophore hypothesis of antiamyloidogenic activity exerted in a wide range of potencies, satisfactorily discriminating the ‘active’ compounds from the ‘inactive’ (poorly active) ones. An atom-based 3D-QSAR model was also derived for about 80% of ‘active’ compounds, i.e., those achieving finite IC₅₀ values lower than 100 μM. The 3D-QSAR model (encompassing 4 PLS factors), featuring acceptable predictive statistics either in the training set (n = 45, q² = 0.596) and in the external test set (n = 14, r²_ext = 0.695), usefully complemented the pharmacophore model by identifying the physicochemical features mainly correlated with the Aβ anti-aggregating potency of the indole and isatin derivatives studied herein.

Quinolizidine-Derived Lucanthone and Amitriptyline Analogues Endowed with Potent Antileishmanial Activity

Leishmaniases are neglected diseases that are endemic in many tropical and sub-tropical Countries. Therapy is based on different classes of drugs which are burdened by severe side effects, occurrence of resistance and high costs, thereby creating the need for more efficacious, safer and inexpensive drugs. Herein, sixteen 9-thioxanthenone derivatives (lucanthone analogues) and four compounds embodying the diarylethene substructure of amitriptyline (amitriptyline analogues) were tested in vitro for activity against Leishmania tropica and L. infantum promastigotes. All compounds were characterized by the presence of a bulky quinolizidinylalkyl moiety. All compounds displayed activity against both species of Leishmania with IC₅₀ values in the low micromolar range, resulting in several fold more potency than miltefosine, comparable to that of lucanthone, and endowed with substantially lower cytotoxicity to Vero-76 cells, for the best of them. Thus, 4-amino-1-(quinolizidinylethyl)aminothioxanthen-9-one (14) and 9-(quinolizidinylmethylidene)fluorene (17), with selectivity index (SI) in the range 16-24, represent promising leads for the development of improved antileishmanial agents. These two compounds also exhibited comparable activity against intramacrophagic amastigotes of L. infantum. Docking studies have suggested that the inhibition of trypanothione reductase (TryR) may be at the basis (eventually besides other mechanisms) of the observed antileishmanial activity. Therefore, these investigated derivatives may deserve further structural improvements and more in-depth biological studies of their mechanisms of action in order to develop more efficient antiparasitic agents.

Unexpected species diversity in electric eels with a description of the strongest living bioelectricity generator

Is there only one electric eel species? For two and a half centuries since its description by Linnaeus, Electrophorus electricus has captivated humankind by its capacity to generate strong electric discharges. Despite the importance of Electrophorus in multiple fields of science, the possibility of additional species-level diversity in the genus, which could also reveal a hidden variety of substances and bioelectrogenic functions, has hitherto not been explored. Here, based on overwhelming patterns of genetic, morphological, and ecological data, we reject the hypothesis of a single species broadly distributed throughout Greater Amazonia. Our analyses readily identify three major lineages that diverged during the Miocene and Pliocene-two of which warrant recognition as new species. For one of the new species, we recorded a discharge of 860 V, well above 650 V previously cited for Electrophorus, making it the strongest living bioelectricity generator.

Advancement of multi-target drug discoveries and promising applications in the field of Alzheimer's disease

Complex diseases (e.g., Alzheimer's disease) or infectious diseases are usually caused by complicated and varied factors, including environmental and genetic factors. Multi-target (polypharmacology) drugs have been suggested and have emerged as powerful and promising alternative paradigms in modern medicinal chemistry for the development of versatile chemotherapeutic agents to solve these medical challenges. The multifunctional agents capable of modulating multiple biological targets simultaneously display great advantages of higher efficacy, improved safety profile, and simpler administration compared to single-targeted agents. Therefore, multifunctional agents would certainly open novel avenues to rationally design the next generation of more effective but less toxic therapeutic agents. Herein, the authors review the recent progress made in the discovery and design processes of selective multi-targeted agents, especially the successful application of multi-target drugs for the treatment of Alzheimer's disease.

Metformin and its sulphonamide derivative simultaneously potentiateanti-cholinesterase activity of donepezil and inhibit beta-amyloid aggregation

The aim of this study was to assess in vitro the effects of sulphenamide and sulphonamide derivatives of metformin on the activity of human acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), establish the type of inhibition, and assess the potential synergism between biguanides and donepezil towards both cholinesterases (ChEs) and the effects on the β-amyloid aggregation. Sulphonamide 5 with para-trifluoromethyl- and ortho-nitro substituents in aromatic ring inhibited AChE in a mixed-type manner at micromolar concentrations (IC50 = 212.5 ± 48.3 µmol/L). The binary mixtures of donepezil and biguanides produce an anti-AChE effect, which was greater than either compound had alone. A combination of donepezil and sulphonamide 5 improved the IC50 value by 170 times. Compound 5 at 200 µmol/L inhibited Aβ aggregation by ∼20%. In conclusion, para-trifluoromethyl-ortho-nitro-benzenesulphonamide presents highly beneficial anti-AChE and anti-Aβ aggregation properties which could serve as a promising starting point for the design and development of novel biguanide-based candidates for AD treatment.

Design, synthesis and biological evaluation of tricyclic pyrazolo[1,5-c][1,3]benzoxazin-5(5H)-one scaffolds as selective BuChE inhibitors

Based on the structural analysis of tricyclic scaffolds as butyrylcholinesterase (BuChE) inhibitors, a series of pyrazolo[1,5-c][1,3]benzoxazin-5(5H)-one derivatives were designed, synthesized and evaluated for their acetylcholinesterase (AChE) and BuChE inhibitory activity. Compounds with 5-carbonyl and 7- or/and 9-halogen substitutions showed potential BuChE inhibitory activity, among which compounds 6a, 6c and 6g showed the best BuChE inhibition (IC₅₀ = 1.06, 1.63 and 1.63 µM, respectively). The structure–activity relationship showed that the 5-carbonyl and halogen substituents significantly influenced BuChE activity. Compounds 6a and 6g were found nontoxic, lipophilic and exhibited remarkable neuroprotective activity and mixed-type inhibition against BuChE (K_i = 7.46 and 3.09 µM, respectively). Docking studies revealed that compound 6a can be accommodated into BuChE via five hydrogen bonds, one Pi–Sigma interaction and three Pi–Alkyl interactions.

New amyloid beta-disaggregating agents: synthesis, pharmacological evaluation, crystal structure and molecular docking of N-(4-((7-chloroquinolin-4-yl)oxy)-3-ethoxybenzyl)amines

In the journey towards the development of potent multi-targeted ligands for the treatment of Alzheimer's disease, a series of Aβ aggregation inhibitors having quinoline scaffold were designed utilizing computational biology tools, synthesized and characterized by various spectral techniques including single-crystal X-ray crystallography. Organic syntheses relying upon convergent synthetic routes were employed. Investigations via ThT fluorescence assay, electron microscopy and transmission electron microscopy revealed the synthesized derivatives to exhibit Aβ self-aggregation inhibition. Molecules 5g and 5a showed the highest inhibitory potential, 53.73% and 53.63% at 50 μM respectively; higher than the standard Aβ disaggregating agent, curcumin. Molecules 5g and 5a disaggregated AChE-induced (58.26%, 47.36%) Aβ aggregation more than two fold more than the standard drug-donepezil (23.66%) and inhibited Cu²⁺-induced Aβ aggregation. A docking study significantly showed their interaction with key residues of Aβ and the results were in accordance with the study. Besides, these compounds also exhibited potential antioxidant activity (5a, 2.7240 Trolox equivalent by ORAC assay) and metal chelating property. Furthermore, the stoichiometric ratio of Cu (ii)-5a and Cu(ii)-5g complexes were found by Job's method (0.5 : 1 for 5a and 0.8 : 1 for 5g). In silico ADMET profiling showed these derivatives to have drug like properties with very low toxicity effects in the pharmacokinetic study. Overall, these results displayed a multi-activity profile with promising Aβ aggregation inhibition and antioxidation and metal chelation activity that could be helpful for developing new multifunctional agents against Alzheimer's disease.

A review on flavonoid-based scaffolds as multi-target-directed ligands (MTDLs) for Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is a multifactorial neurodegenerative disease. The target enzymes inhibition including cholinesterase, beta-secretase, monoamine oxidase and inhibition of amyloid-β aggregation as well as oxidative stress and metal chelation play an important role in the pathogenesis of AD. Chroman-4-one scaffold with benzo-γ-pyrone network is a privileged structure in organic synthesis and drug design. A large number of research has been carried out on modified naturally occurring chromanone scaffolds and/or synthesized new analogues, to obtain effective drugs for AD management. The present review summarizes aspects related to the multi-target-directed ligands (MTDLs) strategy in enzyme targets modulation performed with natural and synthesized chroman-4-one-based structures to look at their potential in the management of multifactorial Alzheimer's disease.

Effect of the Cycle Size and Spacer Structure in Tacrine and its Cyclopentyl Homologue Conjugates with 5-(4-trifluoromethyl-phenylamino)-1,2,4-thiadiazole on the Spectrum of their Biological Activity

The conjugates of tacrine and its cyclopentyl analogue with 5-(4-trifluoromethyl-phenylamino)-1,2,4-thiadiazole, combined with two different spacers, pentylaminopropane and pentylaminopropene, were synthesized. Their esterase profile, the ability to displace propidium from the peripheral anionic site (PAS) of acetylcholinesterase (AChE) and antioxidant activity in the ABTS test were investigated. The compounds obtained effectively inhibit cholinesterases with a predominant effect on butyrylcholinesterase, displace propidium from the PAS of Electrophorus electricus AChE (EeAChE) and exhibit a high radical-scavenging capacity. It is shown that, depending on the spacer structure, particulary, the presence of a propenamine or propanamine fragment, the spectrum of biological activity of the conjugates changes.

Dual/multitargeted xanthone derivatives for Alzheimer's disease: where do we stand?

To date, the current therapy for Alzheimer's disease (AD) based on acetylcholinesterase inhibitors is only symptomatic, being its efficacy limited. Hence, the recent research has been focused in the development of different pharmacological approaches. Here we discuss the potential of xanthone derivatives as new anti-Alzheimer agents. The interference of xanthone derivatives with acetylcholinesterase and other molecular targets and cellular mechanisms associated with AD have been recently systematically reported. Therefore, we report xanthones with anticholinesterase, monoamine oxidase and amyloid β aggregation inhibitory activities as well as antioxidant properties, emphasizing xanthone derivatives with dual/multitarget activity as potential agents to treat AD. We also propose the structural features for these activities that may guide the design of new, more effective xanthone derivatives. [Formula: see text].

Mannich base approach to 5-methoxyisatin 3-(4-isopropylphenyl)hydrazone: A water-soluble prodrug for a multitarget inhibition of cholinesterases, beta-amyloid fibrillization and oligomer-induced cytotoxicity

Targeting protein aggregation for the therapy of neurodegenerative diseases remains elusive for medicinal chemists, despite a number of small molecules known to interfere in amyloidogenesis, particularly of amyloid beta (Aβ) protein. Starting from previous findings in the antiaggregating activity of a class of indolin-2-ones inhibiting Aβ fibrillization, 5-methoxyisatin 3-(4-isopropylphenyl)hydrazone 1 was identified as a multitarget inhibitor of Aβ aggregation and cholinesterases with IC₅₀s in the low μM range. With the aim of increasing aqueous solubility, a Mannich-base functionalization led to the synthesis of N-methylpiperazine derivative 2. At acidic pH, an outstanding solubility increase of 2 over the parent compound 1 was proved through a turbidimetric method. HPLC analysis revealed an improved stability of the Mannich base 2 at pH2 along with a rapid release of 1 in human serum as well as an outstanding hydrolytic stability of the parent hydrazone. Coincubation of Aβ_1-42 with 2 resulted in the accumulation of low MW oligomers, as detected with PICUP assay. Cell assays on SH-SY5Y cells revealed that 2 exerts strong cytoprotective effects in both cell viability and radical quenching assays, mainly related to its active metabolite 1. These findings show that 2 drives the formation of non-toxic, off-pathway Aβ oligomers unable to trigger the amyloid cascade and toxicity.

Benzylphenylpyrrolizinones with Anti-amyloid and Radical Scavenging Effects, Potentially Useful in Alzheimer's Disease Treatment

Herein we describe the drug design steps developed to increase the radical scavenging and β-amyloid aggregation inhibitory activities of a previously described series of benzylidenephenylpyrrolizinones. Among the newly synthesized derivatives, some benzylphenylpyrrolizinones exhibited interesting results in regard to those activities. Initial druggability parameters were measured, and suggest these compounds as a suitable starting point for potential alternatives in treating Alzheimer's disease.

Assessment of in-vitro cholinesterase inhibitory and thrombolytic potential of bark and seed extracts of Tamarindus indica (L.) relevant to the treatment of Alzheimer's disease and clotting disorders

BACKGROUND

Low level of acetylcholine (ACh) is an important hallmark of Alzheimer's disease (AD), a common type of progressive neurodegenerative disorder. Effective treatment strategies rely mostly on either enhancing the cholinergic function of the brain by improving the level of ACh from being a breakdown by cholinesterase enzymes. Again atherothrombosis is major life-threatening cerebral diseases. Traditionally Tamarindus indica (L.) has widely known for its medicinal values. Our aim is to investigate the cholinesterase inhibitory activities as well as thrombolytic activities of the bark and seeds crude methanolic extracts (CMEs) in the treatment of AD and clotting disorder.

MATERIALS AND METHODS

The crude methanol extract was prepared by cold extraction method and was assessed for acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitory activities by the Ellman's method. For thrombolytic activity clot lysis method was applied.

RESULTS

To compare both the fractions, extracts from the bark got more AChE inhibitory activity than the seed with the inhibitory concentration 50% IC50 values of 268.09 and 287.15 µg/ml, respectively. The inhibitory activity of BuChE was quiet similar to that of AChE as IC50 values of both the fractions were 201.25 and 254.71 µg/ml. Again in-vitro thrombolytic activity of bark was 30.17% and of seed it was 22.53%.

CONCLUSION

The results revealed that the CME of bark and seed both have moderate cholinesterases inhibitory activities as well as thrombolytic activities, worth of further investigations to identify the promising molecule(s) potentially useful in the treatment of AD as well as in clotting disorders.

Monoaminergic and Histaminergic Strategies and Treatments in Brain Diseases

The monoaminergic systems are the target of several drugs for the treatment of mood, motor and cognitive disorders as well as neurological conditions. In most cases, advances have occurred through serendipity, except for Parkinson's disease where the pathophysiology led almost immediately to the introduction of dopamine restoring agents. Extensive neuropharmacological studies first showed that the primary target of antipsychotics, antidepressants, and anxiolytic drugs were specific components of the monoaminergic systems. Later, some dramatic side effects associated with older medicines were shown to disappear with new chemical compounds targeting the origin of the therapeutic benefit more specifically. The increased knowledge regarding the function and interaction of the monoaminergic systems in the brain resulting from in vivo neurochemical and neurophysiological studies indicated new monoaminergic targets that could achieve the efficacy of the older medicines with fewer side-effects. Yet, this accumulated knowledge regarding monoamines did not produce valuable strategies for diseases where no monoaminergic drug has been shown to be effective. Here, we emphasize the new therapeutic and monoaminergic-based strategies for the treatment of psychiatric diseases. We will consider three main groups of diseases, based on the evidence of monoamines involvement (schizophrenia, depression, obesity), the identification of monoamines in the diseases processes (Parkinson's disease, addiction) and the prospect of the involvement of monoaminergic mechanisms (epilepsy, Alzheimer's disease, stroke). In most cases, the clinically available monoaminergic drugs induce widespread modifications of amine tone or excitability through neurobiological networks and exemplify the overlap between therapeutic approaches to psychiatric and neurological conditions. More recent developments that have resulted in improved drug specificity and responses will be discussed in this review.

Multitarget strategies in Alzheimer's disease: benefits and challenges on the road to therapeutics

Alzheimer's disease is a multifactorial syndrome, for which effective cures are urgently needed. Seeking for enhanced therapeutic efficacy, multitarget drugs have been increasingly sought after over the last decades. They offer the attractive prospect of tackling intricate network effects, but with the benefits of a single-molecule therapy. Herein, we highlight relevant progress in the field, focusing on acetylcholinesterase inhibition and amyloid pathways as two pivotal features in multitarget design strategies. We also discuss the intertwined relationship between selected molecular targets and give a brief glimpse into the power of multitarget agents as pharmacological probes of Alzheimer's disease molecular mechanisms.

Synthesis, Molecular Modelling and Biological Evaluation of Novel Heterodimeric, Multiple Ligands Targeting Cholinesterases and Amyloid Beta

Cholinesterases and amyloid beta are one of the major biological targets in the search for a new and efficacious treatment of Alzheimer's disease. The study describes synthesis and pharmacological evaluation of new compounds designed as dual binding site acetylcholinesterase inhibitors. Among the synthesized compounds, two deserve special attention--compounds 42 and 13. The former is a saccharin derivative and the most potent and selective acetylcholinesterase inhibitor (EeAChE IC50 = 70 nM). Isoindoline-1,3-dione derivative 13 displays balanced inhibitory potency against acetyl- and butyrylcholinesterase (BuChE) (EeAChE IC50 = 0.76 μM, EqBuChE IC50 = 0.618 μM), and it inhibits amyloid beta aggregation (35.8% at 10 μM). Kinetic studies show that the developed compounds act as mixed or non-competitive acetylcholinesterase inhibitors. According to molecular modelling studies, they are able to interact with both catalytic and peripheral active sites of the acetylcholinesterase. Their ability to cross the blood-brain barrier (BBB) was confirmed in vitro in the parallel artificial membrane permeability BBB assay. These compounds can be used as a solid starting point for further development of novel multifunctional ligands as potential anti-Alzheimer's agents.

Synthesis and Antiplasmodial Activity of Novel Chloroquine Analogues with Bulky Basic Side Chains

Chloroquine is commonly used in the treatment and prevention of malaria, but Plasmodium falciparum, the main species responsible for malaria-related deaths, has developed resistance against this drug. Twenty-seven novel chloroquine (CQ) analogues characterized by a side chain terminated with a bulky basic head group, i.e., octahydro-2H-quinolizine and 1,2,3,4,5,6-hexahydro-1,5-methano-8H-pyrido[1,2-a][1,5]diazocin-8-one, were synthesized and tested for activity against D-10 (CQ-susceptible) and W-2 (CQ-resistant) strains of P. falciparum. Most compounds were found to be active against both strains with nanomolar or sub-micromolar IC50 values. Eleven compounds were found to be 2.7- to 13.4-fold more potent than CQ against the W-2 strain; among them, four cytisine derivatives appear to be of particular interest, as they combine high potency with low cytotoxicity against two human cell lines (HMEC-1 and HepG2) along with easier synthetic accessibility. Replacement of the 4-NH group with a sulfur bridge maintained antiplasmodial activity at a lower level, but produced an improvement in the resistance factor. These compounds warrant further investigation as potential drugs for use in the fight against malaria.