Inhibition of acetylcholinesterase by a pseudozoanthoxanthin-like compound isolated from the zoanthid Parazoanthus axinellae (O. Schmidt)

Parazoanthus axinellae Extract Incorporated Hybrid Nanostructure and Its Potential Antimicrobial Activity

This study, it was aimed to examine the change in the antimicrobial effect of sea anemone Parazoanthus axinellae extract by forming its nanoflowers. A scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) were expended to observe the morphologies of the Cu NFs that had been produced. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were expended to analyze the managing assemblies in P. axinellae extract, which perform an effective part in the synthesis routine, as well as the crystal assembly of NFs. P. axinellae extract mediated the HNFs (Hybrid nanoflowers) are at high, pure crystalline nature, flower shape with a crystallographic system at the nanoscale with mean crystallite size 21.9 nm using XRD, and average particle size ~10 nm by SEM. The broad absorption band at 2981-2915 cm-1 in the FT-IR spectra of anemone extract and Cu-anemone NFs represents the unique peak of hydroxy groups. In addition, Cu NFs were tested for their antibacterial properties. Cu NFs have been discovered to exhibit antibacterial properties. It is suggested that P. axinellae extract and various inorganic components be used to synthesize a variety of NFs and assess their suitability for usage in biomedical fields.

Natural Alkaloids as Multi-Target Compounds towards Factors Implicated in Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia in elderly people; currently, there is no efficient treatment. Considering the increase in life expectancy worldwide AD rates are predicted to increase enormously, and thus the search for new AD drugs is urgently needed. A great amount of experimental and clinical evidence indicated that AD is a complex disorder characterized by widespread neurodegeneration of the CNS, with major involvement of the cholinergic system, causing progressive cognitive decline and dementia. The current treatment, based on the cholinergic hypothesis, is only symptomatic and mainly involves the restoration of acetylcholine (ACh) levels through the inhibition of acetylcholinesterase (AChE). Since the introduction of the Amaryllidaceae alkaloid galanthamine as an antidementia drug in 2001, alkaloids have been one of the most attractive groups for searching for new AD drugs. The present review aims to comprehensively summarize alkaloids of various origins as multi-target compounds for AD. From this point of view, the most promising compounds seem to be the β-carboline alkaloid harmine and several isoquinoline alkaloids since they can simultaneously inhibit several key enzymes of AD's pathophysiology. However, this topic remains open for further research on detailed mechanisms of action and the synthesis of potentially better semi-synthetic analogues.

Marine Organisms as Alkaloid Biosynthesizers of Potential Anti-Alzheimer Agents

The incidence of neurodegenerative diseases, such as Alzheimer's disease (AD), increases continuously demanding the urgent development of anti-Alzheimer's agents. Marine organisms (MO) have to create their own defenses due to the adverse environment where they live and so synthesize several classes of compounds, such as akaloids, to defend themselves. Therefore, the identification of marine natural products with neuroprotective effects is a necessity. Being that AD is not only a genetic but also an environmental complex disease, a treatment for AD remains to discover. As the major clinical indications (CI) of AD are extracellular plaques formed by β-amyloid (Aβ) protein, intracellular neurofibrillary tangles (NFTs) formed by hyper phosphorylated τ-protein, uncommon inflammatory response and neuron apoptosis and death caused by oxidative stress, alkaloids that may decrease CI, might be used against AD. Most of the alkalolids with those properties are derivatives of the amino acid tryptophan mainly with a planar indole scaffold. Certainly, alkaloids targeting more than one CI, multitarget-directed ligands (MTDL), have the potential to become a lead in AD treatment. Alkaloids to have a maximum of activity against CI, should be planar and contain halogens and amine quaternization.

Marine-Derived Compounds with Anti-Alzheimer's Disease Activities

Alzheimer's disease (AD) is an irreversible and progressive brain disorder that slowly destroys memory and thinking skills, and, eventually, the ability to perform simple tasks. As the aging population continues to increase exponentially, AD has become a big concern for society. Therefore, neuroprotective compounds are in the spotlight, as a means to tackle this problem. On the other hand, since it is believed-in many cultures-that marine organisms in an individual diet cannot only improve brain functioning, but also slow down its dysfunction, many researchers have focused on identifying neuroprotective compounds from marine resources. The fact that the marine environment is a rich source of structurally unique and biologically and pharmacologically active compounds, with unprecedented mechanisms of action, marine macroorganisms, such as tunicates, corals, sponges, algae, as well as microorganisms, such as marine-derived bacteria, actinomycetes, and fungi, have been the target sources of these compounds. Therefore, this literature review summarizes and categorizes various classes of marine-derived compounds that are able to inhibit key enzymes involved in AD, including acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), β-secretase (BACE-1), and different kinases, together with the related pathways involved in the pathogenesis of AD. The compounds discussed herein are emerging as promising anti-AD activities for further in-depth in vitro and in vivo investigations, to gain more insight of their mechanisms of action and for the development of potential anti-AD drug leads.

Monophosphoramide derivatives: synthesis and crystal structure, theoretical and experimental studies of their biological effects

Synthesizing new chemical compounds and studying their biological applications have been important issues in scientific research. In this investigation, we synthesized and characterized ten new N-acetyl phosphoramidate compounds and explored the crystal structure of three others. Furthermore, not only were some kinetic inhibition parameters measured, like IC₅₀, K_i, k_p, K_D for 7 compounds on human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), but also their hydrophobic parameter was determined by shake-flask technique. All compounds (number 1-10) were investigated for anti-bacterial activity against three Gram-positive and three Gram-negative bacteria, while chloramphenicol was used as a standard antibiotic. In order to find new insecticide, toxicities of 13 acephate (Ace)-derived compounds (number 20-32) were bioassayed on third larval instar of elm leaf beetle and Xanthogaleruca luteola. Additionally, screening in vivo tests revealed that two compounds had had the greatest insecticidal potential in comparison with others. It means these ones inhibited AChE (with mixed mechanisms) and general esterase more than the rest. According to ChE-QSAR models, the inhibitory potency for enzyme and bacteria is directly influenced by the electronic parameters versus structural descriptors. AChE-QSPR model of fluorescence assay indicated that the inhibitory power of AChE is primarily influenced by a set of electronic factors with the priority of: E_HB > PL > δ(³¹P) versus structural descriptor (SA and Mv). Synthesizing new chemical compounds and studying their biological applications have been important issues in scientific research. Toxicities of 13 acephate (Ace)-derived compounds (number 20-32) were bioassayed on third larval instar of elm leaf beetle and Xanthogaleruca luteola. Insect-QSAR equations of these compounds, based on MLR and PCA, showed that non-descriptor net charge nitrogen atom (which was affected by the polarization of N-H group) had the greatest effect on insecticidal potential.

Marine natural products from zoantharians: bioactivity, biosynthesis, systematics, and ecological roles

The dazzling marine zoantharians represent a reservoir of chemical diversity that remains to be unveiled. These fragile animals have so far been found to harbour the highly bioactive palytoxins or zoanthamines but also the harmless ecdysteroids or zoanthozanthins.

Natural cholinesterase inhibitors from marine organisms

Covering: Published between 1974 up to 2018Inhibition of cholinesterases is a common approach for the management of several disease states. Most notably, cholinesterase inhibitors are used to alleviate the symptoms of neurological disorders like dementia and Alzheimer's disease and treat myasthenia gravis and glaucoma. Historically, most drugs of natural origin have been isolated from terrestrial sources and inhibitors of cholinesterases are no exception. However, the last 50 years have seen a rise in the quantity of marine natural products with close to 25 000 reported in the scientific literature. A number of marine natural products with potent cholinesterase inhibitory properties have also been reported; isolated from a variety of marine sources from algae to ascidians. Representing a diverse range of structural classes, these compounds provide inspirational leads that could aid the development of therapeutics. The current paper aims to, for the first time, comprehensively summarize the literature pertaining to cholinesterase inhibitors derived from marine sources, including the first papers published in 1974 up to 2018. The review does not report bioactive extracts, only isolated compounds, and a specific focus lies on compounds with reported dose-response data. In vivo and mechanistic data is included for compounds where this is reported. In total 185 marine cholinesterase inhibitors and selected analogs have been identified and reported and some of the compounds display inhibitory activities comparable or superior to cholinesterase inhibitors in clinical use.

In Silico Identification and Experimental Validation of Novel Anti-Alzheimer's Multitargeted Ligands from a Marine Source Featuring a "2-Aminoimidazole plus Aromatic Group" Scaffold

Multitargeting or polypharmacological approaches, looking for single chemical entities retaining the ability to bind two or more molecular targets, are a potentially powerful strategy to fight complex, multifactorial pathologies. Unfortunately, the search for multiligand agents is challenging because only a small subset of molecules contained in molecular databases are bioactive and even fewer are active on a preselected set of multiple targets. However, collections of natural compounds feature a significantly higher fraction of bioactive molecules than synthetic ones. In this view, we searched our library of 1175 natural compounds from marine sources for molecules including a 2-aminoimidazole+aromatic group motif, found in known compounds active on single relevant targets for Alzheimer's disease (AD). This identified two molecules, a pseudozoanthoxanthin (1) and a bromo-pyrrole alkaloid (2), which were predicted by a computational approach to possess interesting multitarget profiles on AD target proteins. Biochemical assays experimentally confirmed their biological activities. The two compounds inhibit acetylcholinesterase, butyrylcholinesterase, and β-secretase enzymes in high- to sub-micromolar range. They are also able to prevent and revert β-amyloid (Aβ) aggregation of both Aβ_1-40 and Aβ_1-42 peptides, with 1 being more active than 2. Preliminary in vivo studies suggest that compound 1 is able to restore cholinergic cortico-hippocampal functional connectivity.

Marine Sponges and Bacteria as Challenging Sources of Enzyme Inhibitors for Pharmacological Applications

Enzymes play key roles in different cellular processes, for example, in signal transduction, cell differentiation and proliferation, metabolic processes, DNA damage repair, apoptosis, and response to stress. A deregulation of enzymes has been considered one of the first causes of several diseases, including cancers. In the last several years, enzyme inhibitors, being good candidates as drugs in the pathogenic processes, have received an increasing amount of attention for their potential application in pharmacology. The marine environment is considered a challenging source of enzyme inhibitors for pharmacological applications. In this review, we report on secondary metabolites with enzyme inhibitory activity, focusing our attention on marine sponges and bacteria as promising sources. In the case of sponges, we only reported the kinase inhibitors, because this class was the most representative isolated so far from these marine organisms.

Fluorescent natural products as probes and tracers in biology

Fluorescence is a remarkable property of many natural products in addition to their medicinal and biological value. Herein, we provide a review of these peculiar secondary metabolites to stimulate prospecting of them as original fluorescent tracers, endowed with unique photophysical properties and with applications in most fields of biology.

Insights and ideas garnered from marine metabolites for development of dual-function acetylcholinesterase and amyloid-β aggregation inhibitors

Due to the diversity of biological activities that can be found in aquatic ecosystems, marine metabolites have been an active area of drug discovery for the last 30 years. Marine metabolites have been found to inhibit a number of enzymes important in the treatment of human disease. Here, we focus on marine metabolites that inhibit the enzyme acetylcholinesterase, which is the cellular target for treatment of early-stage Alzheimer’s disease. Currently, development of anticholinesterase drugs with improved potency, and drugs that act as dual acetylcholinesterase and amyloid-β aggregation inhibitors, are being sought to treat Alzheimer’s disease. Seven classes of marine metabolites are reported to possess anti-cholinesterase activity. We compared these metabolites to clinically-used acetylcholinesterase inhibitors having known mechanisms of inhibition. We performed a docking simulation and compared them to published experimental data for each metabolite to determine the most likely mechanism of inhibition for each class of marine inhibitor. Our results indicate that several marine metabolites bind to regions of the acetylcholinesterase active site that are not bound by the clinically-used drugs rivastigmine, galanthamine, donepezil, or tacrine. We use the novel poses adopted for computational drug design of tighter binding anticholinesterase drugs likely to act as inhibitors of both acetylcholinesterase activity and amyloid-β aggregation inhibition.

Analgesic and antibutyrylcholinestrasic activities of the venom prepared from the Mediterranean jellyfish Pelagia noctiluca (Forsskal, 1775)

Background

Toxins derived from jellyfishes have been exploited as a model for the development of new drug promising applications to treat neurodegenerative diseases. The present work is aimed to evaluate the acute toxicity of crude venom of Pelagia noctiluca and then to screen the analgesic and antibutyrylcholinestrasic (anti-BuChE) activities of the crude venom and its fractions.

Methods

Sephadex G75 gel was used to separate crude venom of Pelagia noctiluca, which led to some fractions. In addition, in vivo analgesic and in vitro plasma antibutyrylcholinestrasic activities were carried out with Pelagia crude venom and its fractions respectively.

Results

The crude venom and its fractions displayed analgesic and anti-BuChE activities at different doses without inducing acute toxicity. Fraction 2 possesses the highest analgesic and antibutyrylcholinestrasic properties. The crude venom and fraction 1 had shown to possess less significant inhibitory activity against analgesic and antibutyrylcholinestrasic models.

Conclusions

Based on this study, the crude venom of Pelagia noctiluca is found to be a useful tool for probing pharmacological activity. The purification and the determination of chemical structures of compounds of active fractions of the venom are under investigation.

Low molecular weight compounds from Zoanthus sociatus impair insulin secretion via Ca(+2) influx blockade and cause glucose intolerance in vivo

Cnidarians comprise a taxon with a high biodiversity of cytolitic, neurotoxic and cardiotoxic compounds, which have not been studied on insulin release. We tested the effect of a crude extract of Zoanthus sociatus (Ellis, 1767) and the low molecular weight fraction of this extract on insulin secretion in isolated rat β-cells and also in a glucose tolerance test in vivo. We observed that the extract inhibited insulin release by reducing the amount secreted by individual β-cells and also by silencing a fraction of the secreting population. This effect coincided with a diminished rise of intracellular Ca(+2) in response to high glucose and high K+ -induced depolarization. Moreover intraperitoneal administration of the low molecular weight fraction produced glucose intolerance in adult rats. The active fraction exhibited molecular weights similar to the neurotoxins described in the phylum. Our results broaden the toxic effects of cnidarian venoms and show evidence of potential modulators of voltage-gated Ca(+2) channels in this group.

Parazoanthoxanthin A blocks Torpedo nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors are implicated in different nervous system-related disorders, and their modulation could improve existing therapy of these diseases. Parazoanthoxanthin A (ParaA) is a fluorescent pigment of the group of zoanthoxanthins. Since it is a potent acetylcholinesterase inhibitor, it may also bind to nicotinic acetylcholine receptors (nAChRs). For this reason its effect on Torpedo nAChR (alpha1(2)betagammadelta) transplanted to Xenopus laevis oocytes was evaluated, using the voltage-clamp technique. ParaA dose-dependently reduced the acetylcholine-induced currents. This effect was fully reversible only at lower concentrations. ParaA also reduced the Hill coefficient and the time to peak current, indicating a channel blocking mode of action. On the other hand, the combined effect of ParaA and d-tubocurarine (d-TC) on acetylcholine-induced currents exhibited only partial additivity, assuming a competitive mode of action of ParaA on nAChR. These results indicate a dual mode of action of ParaA on the Torpedo AChR.

New lobane and cembrane diterpenes from two comorian soft corals

Preliminary biological investigation of a collection of Comorian soft corals resulted in the selection of two specimens, one of Sarcophyton and the other of Lobophytum, on the basis of their toxicity on larvae of the brine shrimp (Artemia salina) and inhibition of acetylcholinesterase, respectively. Bioassay-guided fractionations provided a known antitumor promoter cembrane diterpenoid, (+)-sarcophytol-A (1), along with a new lobane diterpenoid, carbomethoxyfuscol (2), from Sarcophyton sp., and a new cembranoid, crassumolide E (3), from Lobophytum sp. The structures of compounds 1–3 were determined by spectroscopic analysis and by comparison of the spectral data with previously reported values. The cembranoid 3 was found to exhibit a moderate inhibitory effect on acetylcholinesterase.

In vivo effects of cnidarian toxins and venoms

Cnidarians (Coelenterates), a very old and diverse animal phylum, possess a wide variety of biologically active substances that can be considered as toxins. Anthozoan toxins can be classified into two chemically very different groups, namely polypeptide toxins isolated from sea anemones and diterpenes isolated from octocorals. Cubozoan and scyphozoan protein toxins have been the most elusive cnidarian toxins to investigate - despite a tremendous effort in the past few decades, very few of these large, relatively unstable protein toxins were isolated, but recently this has been achieved for cubozoan venoms. Hydrozoans mainly contain large proteins with physiological mechanisms of action similar to the sea anemone and jellyfish pore-forming toxins. This article will focus on the in vivo physiological effects of cnidarian toxins and venoms; their actions at the cellular level will only be considered to understand their actions at the organ and whole animal levels. An understanding of mechanisms underlying the in vivo toxic effects will facilitate the development of more effective treatments of cnidarian envenomations.

Inhibition of acetylcholinesterase by an alkylpyridinium polymer from the marine sponge, Reniera sarai

Large polymeric 3-alkylpyridinium salts have been isolated from the marine sponge Reniera sarai. They are composed of N-butyl(3-butylpyridinium) repeating subunits, polymerized head-to-tail, and exist as a mixture of two main polymers with molecular weights without counterion of about 5520 and 18900. The monomer analogue of the inhibitor, N-butyl-3-butylpyridinium iodide has been synthesized. This molecule shows mixed reversible inhibition of acetylcholinesterase. The polymers also act as acetylcholinesterase inhibitors and show an unusual inhibition pattern. We tentatively describe it as quick initial reversible binding, followed by slow binding or irreversible inhibition of the enzyme. This kinetics suggests that there are several affinity binding sites on the acetylcholinesterase molecule where the polymer can bind. The first binding favors binding to other sites which leads to an apparently irreversibly linked enzyme-inhibitor complex.

Anticholinesterase activity of the fluorescent zoanthid pigment, parazoanthoxanthin A

A synthetic linear tetrazacyclopent(f)azulene compound, parazoanthoxanthin A (m.w. 214.2), strongly fluorescent pigment occurring in zoanthids, was characterized and assayed for anticholinesterase activity. The pigment, emitting fluorescence at lambda(em) 420 nm, was found to be a pure competitive inhibitor of cholinesterases. At pH 8.0, a Ki value of 19 and 26 microM was determined with insect recombinant, and electric eel acetylcholinesterase. Horse serum butyrylcholinesterase was less sensitive with a Ki of 70 microM.

Pseudozoanthoxantin-like compound from Parazoanthus axinellae Adriaticus inhibits acetylcholinesterase

Acetylcholinesterase is an enzyme responsible for the timely termination of acetylcholine action at muscarinic and nicotinic receptors, so it is essential for the normal function of cholinergic synapses. Naturally occurring acetylcholinesterase inhibitors are relatively rare, but several synthetic acetylcholinesterase inhibitors have been developed as potent remedies, pesticides, and neurotoxins. Here we describe the inhibition of soluble and membrane-bound cholinesterases with a recently isolated and purified acetylcholinesterase inhibitor isolated from the crust coral Parazoanthus axinellae Adriaticus. This substance with a novel chemical structure might serve as a new prototype of cholinesterase inhibitors.