Selective dual cholinesterase inhibitors from Aconitum laeve

Assessing the Potential of Aconitum Laeve Extract for Biogenic Silver and Gold Nanoparticle Synthesis and Their Biological and Catalytic Applications

The adoption of green chemistry protocols in nanoparticle (NP) synthesis has exhibited substantial potential and is presently a central focus in research for generating versatile NPs applicable across a broad spectrum of applications. In this scientific contribution, we, for the first time, examined the ability of Aconitum Laeve (A. Laeve) crude extract to synthesize silver and gold nanoparticles (AgNPs@AL; AuNP@AL) and explored their potential applications in biological activities and the catalytic degradation of environmental pollutants. The synthesized NPs exhibited a distinctive surface plasmon resonance pattern, a spherical morphology with approximate sizes of 5-10 nm (TEM imaging), a crystalline architecture (XRD analysis), and potential functional groups identified by FTIR spectroscopy. The antibacterial activity was demonstrated by inhibition zones that measured 16 and 14 mm for the AgNPs@AL and AuNP@AL at a concentration of 80 µg/mL against Staphylococcus aureus and 14 and 12 mm against Escherichia coli, respectively. The antioxidant potential of the synthesized NPs was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2-Phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-Oxide (PTIO), and 3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assays. Our findings suggest that the AuNP@AL effectively countered the tested radicals considerably, displaying IC50 values of 115.9, 103.54, and 180.85 µg/mL against DPPH, PTIO, and ABTS, respectively. In contrast, the AgNPs@AL showed IC50 values of 144.9, 116.36, and 95.39 µg/mL against the respective radicals. In addition, both the NPs presented significant effectiveness in the photocatalytic degradation of methylene blue and rhodamine B. The overall observations indicate that A. Laeve possesses a robust capability to synthesize spherical nanoparticles, exhibiting excellent dispersion and showcasing potential applications in both biological activities and environmental remediation.

New amide and diterpene alkaloids with anticholinesterase activity from Delphinium cyphoplectrum roots

BACKGROUND

The cholinergic hypothesis posits a robust correlation between the onset of Alzheimer's disease and a pronounced deficit in acetylcholine, a pivotal neurotransmitter crucial for the central cholinergic nervous system's function, pivotal for memory and learning. Diterpene alkaloids exhibit intricate and distinctive chemical structures that facilitate their passage through the blood-brain barrier. Moreover, their potent pharmacological attributes render them promising candidates for addressing central nervous system disorders.

OBJECTIVES

This investigation aims to scrutinize the alkaloidal composition of Delphinium cyphoplectrum (Ranunculaceae) roots, further exploring their anticholinesterase inhibitory activity and mode of inhibition.

METHOD

Innovative chromatography techniques were repetitively employed to purify the alkaloids. Acetylcholinesterase (AChE) inhibition assays were conducted using Ellman's tests. The mode of inhibition was meticulously characterized through Michaelis-Menten, and Lineweaver-Burk plots. Conducting molecular docking studies, we employed the AUTO DOCK 4.2 software package.

RESULTS

Eight alkaloids were identified including five C19-diterpene alkaloids (6,14,16,18-tetramethoxy-1,7,8-trihydroxy-4-methylaconitane (1), 6,16,18-trimethoxy-1,7,8,14-tetrahydroxy-4-methylaconitane (2), 6,8,16,18-tetramethoxy-1,7,14-trihydroxy-4-methylaconitane (3), 6,14,16-trimethoxy-1,7,8,18-tetrahydroxy-4-methylaconitane (4), and 14-O-acetyl-8,16-dimethoxy-1,6,7,18-tetrahydroxy-4-methylaconitane (5)), an epoxy C18-diterpene alkaloid (6,8,16-trimethoxy-1,7,14-trihydroxy-3,4-epoxyaconitane (6)), a known (pyrrolidin-2-one (7) and an undescribed amide alkaloid (1-(2'-hydroxylethylamine)-3,5,5,-trimethyl-1,5-dihydro-2H-pyrrol-2-one (8). All diterpene alkaloids underwent assessment for acetylcholinesterase (AChE) inhibition assay and displayed noteworthy AChE activity, surpassing that of the reference drug (with IC50 values of 13.7, 21.8, 23.4, 28.2, 40.4, and 23.9 for compounds 1-6, respectively, in comparison to 98.4 for Rivastigmine). Analysis of Michaelis-Menten and Lineweaver-Burk plots represents an uncompetitive mode of inhibition for compound 1 on AChE. Notably, computational docking simulations indicated that all diterpene alkaloids were accommodated within the same enzymatic cleft as the reference ligand, and displaying superior free binding energy values (from - 10.32 to -8.59 Kcal.mol-1) in contrast to Rivastigmine (-6.31 Kcal.mol-1).

CONCLUSION

The phytochemical analysis conducted on the roots of Delphinium cyphoplectrum yielded the identification of eight alkaloidal compounds including one C18-diterpene, five C19-diterpene, one pyrrolidine and one amide alkaloids. AChE inhibition assay and molecular simulations unveiled remarkable significant potency attributed to the C19-diterpene alkaloids by the order of 1 > 2 > 3,6 > 4 > 5. Presence of hydroxyl group on C-1, C-7, C-8, C-14, and C-18 increased the effect. The best in vitro activity was recorded for compound 1 able to bind to Asp72 in the narrow region of PAS, while interacting by pi-sigma with Phe330 at the hydrophobic region of the gorge involving the acyl and choline binding site. This observation underscores the substantial promise of this category of natural products in the realm of drug discovery for Alzheimer's Disease, offering a compelling avenue for further research and therapeutic development.

The known, unknown, and the intriguing about members of a critically endangered traditional medicinal plant genus Aconitum

Humanity will always be indebted to plants. In the ongoing scientific era, the 'Herbal Revolution' has helped discover several valuable medicinal plants and associated novel secondary metabolites from the diverse unexplored ecosystems, treating several diseases via phytotherapy. The Aconitum genus comprises several economically-important poisonous mountainous medicinal plant species whose unique biodiversity is on the verge of extinction due to illegal human intervention triggered habitat loss, over-harvesting, and unrestricted trading. Owing to its vast diversity of diterpene alkaloids, most species are extensively used to treat several ailments in rural parts of the world. Irrespective of this, many unexplored and intriguing prospects exist to understand and utilize this critical plant for human benefit. This systematic review tries to fill this gap by compiling information from the sporadically available literature known for ~300 Aconitum spp. regarding its nomenclature and classification, endangerment, plant morphology, ploidy, secondary metabolites, drug pharmacokinetics, conservation, and omics-based computational studies. We also depicted the disparity in the studied model organisms for this diverse genus. The absence of genomic/metagenomic data is becoming a limiting factor in understanding its plant physiology, metabolic pathways, and plant-microbes interactions, and therefore must be promoted. Additionally, government support and public participation are crucial in establishing conservation protocols to save this plant from endangerment.

Neuropharmacological Potential of Diterpenoid Alkaloids

This study provides a narrative review of diterpenoid alkaloids (DAs), a family of extremely important natural products found predominantly in some species of Aconitum and Delphinium (Ranunculaceae). DAs have long been a focus of research attention due to their numerous intricate structures and diverse biological activities, especially in the central nervous system (CNS). These alkaloids originate through the amination reaction of tetra or pentacyclic diterpenoids, which are classified into three categories and 46 types based on the number of carbon atoms in the backbone structure and structural differences. The main chemical characteristics of DAs are their heterocyclic systems containing β-aminoethanol, methylamine, or ethylamine functionality. Although the role of tertiary nitrogen in ring A and the polycyclic complex structure are of great importance in drug-receptor affinity, in silico studies have emphasized the role of certain sidechains in C13, C14, and C8. DAs showed antiepileptic effects in preclinical studies mostly through Na⁺ channels. Aconitine (1) and 3-acetyl aconitine (2) can desensitize Na⁺ channels after persistent activation. Lappaconitine (3), N-deacetyllapaconitine (4), 6-benzoylheteratisine (5), and 1-benzoylnapelline (6) deactivate these channels. Methyllycaconitine (16), mainly found in Delphinium species, possesses an extreme affinity for the binding sites of α7 nicotinic acetylcholine receptors (nAChR) and contributes to a wide range of neurologic functions and the release of neurotransmitters. Several DAs such as bulleyaconitine A (17), (3), and mesaconitine (8) from Aconitum species have a drastic analgesic effect. Among them, compound 17 has been used in China for decades. Their effect is explained by increasing the release of dynorphin A, activating the inhibitory noradrenergic neurons in the β-adrenergic system, and preventing the transmission of pain messages by inactivating the Na⁺ channels that have been stressed. Acetylcholinesterase inhibitory, neuroprotective, antidepressant, and anxiolytic activities are other CNS effects that have been investigated for certain DAs. However, despite various CNS effects, recent advances in developing new drugs from DAs were insignificant due to their neurotoxicity.

Natural Inhibitors of Cholinesterases: Chemistry, Structure-Activity and Methods of Their Analysis

This article aims to provide an updated description and comparison of the data currently available in the literature (from the last 15 years) on the studied natural inhibitors of cholinesterases (IChEs), namely, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). These data also apply to the likely impact of the structures of the compounds on the therapeutic effects of available and potential cholinesterase inhibitors. IChEs are hitherto known compounds with various structures, activities and origins. Additionally, multiple different methods of analysis are used to determine the cholinesterase inhibitor potency. This summary indicates that natural sources are still suitable for the discovery of new compounds with prominent pharmacological activity. It also emphasizes that further studies are needed regarding the mechanisms of action or the structure-activity correlation to discuss the issue of cholinesterase inhibitors and their medical application.

Poisonous Piperidine Plants and the Biodiversity of Norditerpenoid Alkaloids for Leads in Drug Discovery: Experimental Aspects

There are famous examples of simple (e.g., hemlock, Conium maculatum L.) and complex (e.g., opium poppy, Papaver somniferum L., Papaveraceae) piperidine-alkaloid-containing plants. Many of these are highly poisonous, whilst pepper is well-known gastronomically, and several substituted piperidine alkaloids are therapeutically beneficial as a function of dose and mode of action. This review covers the taxonomy of the genera Aconitum, Delphinium, and the controversial Consolida. As part of studying the biodiversity of norditerpenoid alkaloids (NDAS), the majority of which possess an N-ethyl group, we also quantified the fragment occurrence count in the SciFinder database for NDA skeletons. The wide range of NDA biodiversity is also captured in a review of over 100 recently reported isolated alkaloids. Ring A substitution at position 1 is important to determine the NDA skeleton conformation. In this overview of naturally occurring highly oxygenated NDAs from traditional Aconitum and Delphinium plants, consideration is given to functional effect and to real functional evidence. Their high potential biological activity makes them useful candidate molecules for further investigation as lead compounds in the development of selective drugs.

In Vitro and In Silico Investigation of Diterpenoid Alkaloids Isolated from Delphinium chitralense

This study reports the isolation of three new C₂₀ diterpenoid alkaloids, Chitralinine A–C (1–3) from the aerial parts of Delphinium chitralense. Their structures were established on the basis of latest spectral techniques and single crystal X-rays crystallographic studies of chitralinine A described basic skeleton of these compounds. All the isolated Compounds (1–3) showed strong, competitive type inhibition against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in comparison to standard allanzanthane and galanthamine however, chitralinine-C remained the most potent with IC₅₀ value of 11.64 ± 0.08 μM against AChE, and 24.31 ± 0.33 μM against BChE, respectively. The molecular docking reflected a binding free energy of −16.400 K Cal-mol⁻¹ for chitralinine-C, having strong interactions with active site residues, TYR334, ASP72, SER122, and SER200. The overall findings suggest that these new diterpenoid alkaloids could serve as lead drugs against dementia-related diseases including Alzheimer’s disease.

Isoquinoline Alkaloid Contents in Macleaya cordata Extracts and Their Acetylcholinesterase and Butyrylcholinesterase Inhibition

An important strategy for treating neurodegenerative disorders is to maintain the levels of acetylcholine in the synaptic cleft by blocking the cholinesterases. Searching for new effective compounds with inhibited acetylcholinesterase and butyrylcholinesterase activity is one of the most significant challenges of the modern scientific research. The aim of this study was the optimization of the condition for cholinesterase activity determination by high-performance liquid chromatography coupled with diode array detector (HPLC-DAD) in terms of concentrations of enzymatic reaction mixture components, temperature of incubation, and incubation time. In vitro investigation of acetylcholinesterase and butyrylcholinesterase activity inhibition by some isoquinoline alkaloids and extracts obtained from the aerial part and roots of Macleaya cordata collected in May, July, and September. Acetylcholinesterase and butyrylcholinesterase activity inhibition of the extracts obtained from the plant had not been tested previously. The application of the HPLC method allowed eliminating absorption of interfering components, for example, alkaloids such as sanguinarine and berberine. The HPLC method was successfully applied for the evaluation of the acetylcholinesterase inhibitory activity in samples such as plant extracts, especially those containing colored components adsorbing at the same wavelength as the adsorption wavelength of 5-thio-2-nitro-benzoic acid, which is the product of the reaction between thiocholine (product of the hydrolysis of acetyl/butyrylthiocholine reaction) with Ellman’s reagent. Moreover, liquid chromatography coupled with a triple quadrupole mass spectrometer (LC–QqQ–ESI–MS/MS) analysis allowed evaluating the identification of relevant bioactive compounds in the obtained plant extracts. The investigated alkaloids, especially sanguinarine and chelerythrine, and all the Macleaya cordata extracts, especially the extract obtained from the aerial part collected in May, exhibited very high cholinesterase activity inhibition. HPLC-DAD was also applied for the kinetics study of the most active alkaloids sanguinarine and chelerythrine. Our investigations demonstrated that these plant extracts can be recommended for further in vivo experiments to confirm their cholinesterase inhibition activity.

Green synthesis of gold nanaoparticles using Delphinium Chitralense tuber extracts, their characterization and enzyme inhibitory potential

Green synthesis has been introduced as an alternative to chemical synthesis due to the serious consequences. Metal nanoparticles synthesized through green approach have different pharmaceutical, medical and agricultural applications. The present study followed a green and simple route for the preparation of potentially bioactive gold nanoparticles (Au NPs). Au NPs were prepared via green synthesis approach using crude basic alkaloidal portion of the tuber of Delphinium chitralense. The green synthesized Au NPs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) fourier transform infrared (FTIR), and UV-Visible spectrophotometer. Morphological analysis shows that Au NPs have cubic geometry with different sizes. UV-Vis spectroscopic analysis confirmed the synthesis of Au NPs while XRD proved their pure crystalline phase. The Au NPs showed promising dose dependent inhibition of both AChE and BChE as compared to the crude as well as standard drug.

The diterpenoid alkaloids

The diterpenoid alkaloids are a family of extremely important natural products that have long been a research hotspot due to their myriad of intricate structures and diverse biological properties. This chapter systematically summarizes the past 11 years (2009-2019) of studies on the diterpenoid alkaloids, including the "so-called" atypical ones, covering the classification and biogenetic relationships, phytochemistry together with 444 new alkaloids covering 32 novel skeletons and the corrected structures, chemical reactions including conversion toward toxoids, synthetic studies, as well as biological activities. It should be noted that the synthetic studies, especially the total syntheses of various diterpenoid alkaloids, are for the first time reviewed in this treatise. This chapter, in combination with our four previous reviews in volumes 42, 59, 67, and 69, will present to the readers a more completed and updated profile of the diterpenoid alkaloids.

A Recent Look into Natural Products that have Potential to Inhibit Cholinesterases and Monoamine Oxidase B: Update for 2010-2019

With respect to the unknowns of pathophysiology of Alzheimer's Disease (AD)-, and Parkinson's Disease (PD)-like neurodegenerative disorders, natural product research is still one of the valid tools in order to provide alternative and/or better treatment options. At one hand, various extracts of herbals provide a combination of actions targeting multiple receptors, on the other hand, the discovery of active natural products (i.e., secondary metabolites) generally offers alternative chemical structures either ready to be employed in clinical studies or available to be utilized as important scaffolds for the design of novel agents. Regarding the importance of certain enzymes (e.g. cholinesterase and monoamine oxidase B), for the treatment of AD and PD, we have surveyed the natural product research within this area in the last decade. Particularly novel natural agents discovered within this period, concomitant to novel biological activities displayed for known natural products, are harmonized within the present study.

A systematic review of pharmacological activities, toxicological mechanisms and pharmacokinetic studies on Aconitum alkaloids

The tubers and roots of Aconitum (Ranunculaceae) are widely used as heart medicine or analgesic agents for the treatment of coronary heart disease, chronic heart failure, rheumatoid arthritis and neuropathic pain since ancient times. As a type of natural products mainly extracted from Aconitum plants, Aconitum alkaloids have complex chemical structures and exert remarkable biological activity, which are mainly responsible for significant effects of Aconitum plants. The present review is to summarize the progress of the pharmacological, toxicological, and pharmacokinetic studies of Aconitum alkaloids, so as to provide evidence for better clinical application. Research data concerning pharmacological, toxicological and pharmacokinetic studies of Aconitum alkaloids were collected from different scientific databases (PubMed, CNKI, Google Scholar, Baidu Scholar, and Web of Science) using the phrase Aconitum alkaloids, as well as generic synonyms. Aconitum alkaloids are both bioactive compounds and toxic ingredients in Aconitum plants. They produce a wide range of pharmacological activities, including protecting the cardiovascular system, nervous system, and immune system and anti-cancer effects. Notably, Aconitum alkaloids also exert strong cardiac toxicity, neurotoxicity and liver toxicity, which are supported by clinical studies. Finally, pharmacokinetic studies indicated that cytochrome P450 proteins (CYPs) and efflux transporters (ETs) are closely related to the low bioavailability of Aconitum alkaloids and play an important role in their metabolism and detoxification in vivo.

Potential therapeutic natural products against Alzheimer's disease with Reference of Acetylcholinesterase

Alzheimer's disease (AD), is the most common type of dementia primarily affecting the later years of life. Its prevalence is likely to increase in any aging population and will be a major burden on healthcare system by the mid of the century. Despite scientific and technological breakthroughs in the last 50 years, that have expanded our understanding of the disease on a system, cellular and molecular level, therapies that could stop or slow the progression of the disease are still unavailable. The Food and Drug Administration (FDA), has approved acetylcholinesterase (AChE) inhibitors (donepezil, galantamine, tacrine and rivastigmine) and glutamate receptor antagonist (memantine) for the treatment of AD. In this review we summarize the studies reporting phytocompounds and extracts from medicinal plants that show AChE inhibitory activities and could be of potential benefit in AD. Future research directions are suggested and recommendations made to expand the use of medicinal plants and their formulations to prevent, mitigate and treat AD.

Neuroprotective Effects of Dried Tubers of Aconitum napellus

The present study was designed to explore the neuroprotective properties of Aconitum napellus (Ranunculaceae). The plant detoxification was done using either water, or cow or goat milk as per the Ayurvedic shodhana method. The evaluation of the neuroprotective role of A. napellus was performed on diabetic neuropathy induced by streptozotocin in Sprague Dawley (SD) rats. Body mass, blood sugar level, oral glucose tolerance test, hyperalgesia, cold allodynia, motor co-ordination test, and locomotor activity, oxidative biomarkers (TBARS, reduced glutathione, catalase and superoxide dismutase) and sciatic nerve histomorphology were assessed. The in vitro studies were done on human neuroblastoma cell line SHSY-5Y and used an MTT assay to assess the antiproliferative activity of different extracts. Results suggest that the goat milk treated chloroform extract has less percentage of aconitine. After administration of the detoxified chloroform extract to the diabetic animals, there was a significant improvement in the myelination and degenerative changes of the nerve fibers along with behavioral changes (p < 0.05 as compared with diabetic control group). The findings of the in vitro research show an effective neuroprotective role of A. napellus. This suggests that A. napellus should be further investigated for its effect in diabetic pathology.

Norditerpenoid alkaloids of Delphinium denudatum as cholinesterase inhibitors

Three new norditerpenoids alkaloids, 1β-hydroxy,14β-acetyl condelphine (1), jadwarine-A (2), jadwarine-B (3) along with two known alkaloids isotalatizidine hydrate (4) and dihydropentagynine (5) were isolated from medicinal plant Delphinium denudatum. The structures of natural products 1-5 were established on the basis of HR-EIMS, ¹H and ¹³C NMR (1D & 2D) spectroscopic data as well as by comparison from literature data. The structures of compound 1 and 4 were also confirmed by single crystal X-ray diffraction studies. In-vitro AChE and BChE enzyme inhibitory activities of compounds 1-5 and molecular docking studies were performed to investigate the possible molecular inhibitory mechanism of the isolated natural products. Compound 2, 4 and 5 showed competitive inhibitory effects by inhibiting AChE and BChE, respectively, while 1 and 3 showed non-competitive inhibition. This work is the first report that provides a supporting evidence about the use of constituents of Delphinium denudatum in cerebral dementia and Alzheimer diseases.