Hippeastrum reticulatum (Amaryllidaceae): Alkaloid Profiling, Biological Activities and Molecular Docking

Characterization of cinnamate 4-hydroxylase (CYP73A) and p-coumaroyl 3'-hydroxylase (CYP98A) from Leucojum aestivum, a source of Amaryllidaceae alkaloids

Biosynthesis of Amaryllidaceae alkaloids (AA) starts with the condensation of tyramine with 3,4-dihydroxybenzaldehyde. The latter derives from the phenylpropanoid pathway that involves modifications of trans-cinnamic acid, p-coumaric acid, caffeic acid, and possibly 4-hydroxybenzaldehyde, all potentially catalyzed by hydroxylase enzymes. Leveraging bioinformatics, molecular biology techniques, and cell biology tools, this research identifies and characterizes key enzymes from the phenylpropanoid pathway in Leucojum aestivum. Notably, we focused our work on trans-cinnamate 4-hydroxylase (LaeC4H) and p-coumaroyl shikimate/quinate 3'-hydroxylase (LaeC3'H), two key cytochrome P450 enzymes, and on the ascorbate peroxidase/4-coumarate 3-hydroxylase (LaeAPX/C3H). Although LaeAPX/C3H consumed p-coumaric acid, it did not result in the production of caffeic acid. Yeasts expressing LaeC4H converted trans-cinnamate to p-coumaric acid, whereas LaeC3'H catalyzed specifically the 3-hydroxylation of p-coumaroyl shikimate, rather than of free p-coumaric acid or 4-hydroxybenzaldehyde. In vivo assays conducted in planta in this study provided further evidence for the contribution of these enzymes to the phenylpropanoid pathway. Both enzymes demonstrated typical endoplasmic reticulum membrane localization in Nicotiana benthamiana adding spatial context to their functions. Tissue-specific gene expression analysis revealed roots as hotspots for phenylpropanoid-related transcripts and bulbs as hubs for AA biosynthetic genes, aligning with the highest AAs concentration. This investigation adds valuable insights into the phenylpropanoid pathway within Amaryllidaceae, laying the foundation for the development of sustainable production platforms for AAs and other bioactive compounds with diverse applications.

Auxin and light-mediated regulation of growth, morphogenesis, and alkaloid biosynthesis in Crinum x powellii 'Album' callus

Crinum x powellii 'Album' belongs to the Amaryllidaceae medicinal plant family that produces a range of structurally diverse alkaloids with potential therapeutic properties. The optimal conditions for in vitro tissue growth, morphogenesis, and alkaloid biosynthesis remain unclear. Auxin and light play critical roles in regulating plant growth, development, and alkaloid biosynthesis in several Amaryllidaceae plants. Here, we have succeeded in showing, for the first time, that the combination of auxin and light significantly influence C. x powellii "Album" in vitro tissue growth, survival, and morphogenesis compared to individual treatments. Furthermore, this combination also upregulates the expression of alkaloid biosynthetic genes and led to an increase in the content of certain alkaloids, suggesting a positive impact on the defense and therapeutic potential of the calli. Our findings provide insights into the regulation of genes involved in alkaloid biosynthesis in C. x powellii "Album" callus and underline the potential of auxin and light as tools for enhancing their production in plants. This study provides a foundation for further exploration of C. x powellii "Album" calli as a sustainable source of bioactive alkaloids for pharmaceutical and agricultural applications. Furthermore, this study paves the way to the discovery of the biosynthetic pathway of specialized metabolites from C. x powellii "Album", such as cherylline and lycorine.

Studies on the Nonalkaloidal Secondary Metabolites of Hippeastrum vittatum (L'Her.) Herb. Bulbs

Sixteen chemically varied metabolites were isolated from the bulbs of Hippeastrum vittatum (L'Her.) Herb., including eight flavonoids [3'-methyl isoliquiritigenin (2), 7-hydroxyflavan (8), 7-hydroxyflavanone (9), 7-hydroxyflavan-3-ol (10), 7-methoxy-3',4'-methylenedioxyflavan-3-ol (11), 7-hydroxy-3',4'-methylenedioxy flavan (12), 2',4'-dihydroxy-3'-methyl-3,4-methylenedioxychalcone (13), and isoliquiritigenin (14)], four acetophenones [2,6-dimethoxy-4-hydroxyacetophenone (3), 2,4-dihydroxyacetophenone (4), 2,4-dihydroxy-6-methoxy-3-methylacetophenone (6), and 2,4,6-trimethoxyacetophenone (7)], two alkaloids [lycorine (1) and narciprimine (15)], one phenol derivative [p-nitrophenol (5)], and one steroid [β-sitosterol 3-O-β-glucopyranoside (16)]. Their structures were elucidated by combining one- and two-dimensional NMR and ESI-MS techniques and by comparison with the reported literature data and some authentic samples. Except for lycorine (1), the isolated metabolites were obtained herein for the first time from Hippeastrum plants, among which compound 13 was identified as a new chalcone derivative. Additionally, the total phenolic and flavonoid contents of the total ethanol extract and different fractions of the bulbs were determined by the Folin-Ciocalteu and aluminum chloride colorimetric methods, respectively, whereas their antioxidant potential was compared using the phosphomolybdenum and 2,2'-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assays. Finally, the binding affinities of compounds 1-16 to some key target proteins of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), namely, main protease (Mpro), papain-like protease (PLpro), and RNA-dependent RNA polymerase (RdRp), were screened and compared using molecular docking analysis. The possible chemotaxonomic significance of the identified metabolites was also discussed.

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.

Antiparasitic Activity of Hippeastrum Species and Synergistic Interaction between Montanine and Benznidazole against Trypanosoma cruzi

BACKGROUND

Hippeastrum species have a wide range of biological properties. In Argentina, this genus comprises ten widely distributed species.

PURPOSE

To evaluate the antiparasitic and anticholinesterase activities and chemical profiles of seven Argentinean Hippeastrum species and determine the synergism between the major isolated alkaloid-montanine-and benznidazole in anti-Trypanosoma cruzi activity.

METHODS

The antiparasitic activity was evaluated through antiproliferative and viability assays against T. cruzi epimastigotes. Synergism assays were performed using the Chou-Talalay method. AChE and BuChE inhibitory activities were also assessed. The alkaloid composition was obtained using GC-MS analysis.

RESULTS

All extracts showed strong growth inhibition of T. cruzi epimastigote proliferation. The extracts from H. aglaiae, H. aulicum, and H. hybrid stand out for their potent and total growth inhibition, which was comparable to benznidazole. The H. reticulatum extract showed strong Acetylcholinesterase (AChE) inhibitory activities, while five species showed moderate Butyrylcholinesterase (BuChE) inhibition. Fifteen alkaloids were identified by means of GC-MS. Regarding the synergism assessment, the highest synergistic effect was obtained from the combination of montanine and benznidazole.

CONCLUSION

Hippeastrum species bulb extracts from Argentina were shown to be a good source of antiparasitic alkaloids and cholinesterase inhibitors. The synergism between montanine and benznidazole emerges as a potential combination for future studies to treat Chagas disease.

Hippeastrum stapfianum (Kraenzl.) R.S.Oliveira & Dutilh (Amaryllidaceae) Ethanol Extract Activity on Acetylcholinesterase and PPAR-α/γ Receptors

Hippeastrum stapfianum (Kraenzl.) R.S.Oliveira & Dutilh (Amaryllidaceae) is an endemic plant species from the Brazilian savannah with biological and pharmacological potential. This study evaluated the effects of ethanol extract from H. stapfianum leaves on acetylcholinesterase enzyme activity and the action on nuclear receptors PPAR-α and PPAR-γ. A gene reporter assay was performed to assess the PPAR agonist or antagonist activity with a non-toxic dose of H. stapfianum ethanol extract. The antioxidant capacity was investigated using DPPH^• scavenging and fosfomolybdenium reduction assays. The identification of H. stapfianum's chemical composition was performed by gas chromatography-mass spectrometry (GC-MS) and HPLC. The ethanol extract of H. stapfianum activated PPAR-α and PPAR-γ selectively, inhibited the acetylcholinesterase enzyme, and presented antioxidant activity in an in vitro assay. The major compounds identified were lycorine, 7-demethoxy-9-O-methylhostasine, and rutin. Therefore, H. stapfianum is a potential source of drugs for Alzheimer's disease due to its ability to activate PPAR receptors, acetylcholinesterase inhibition activity, and antioxidant attributes.

Structural Diversity and Biological Potential of Alkaloids from the Genus Hippeastrum, Amaryllidaceae: an Update

The subfamily Amaryllidoideae, Amaryllidaceae, presents an exclusive group of structures known as Amaryllidaceae alkaloids, which have a broad spectrum of biological activities. These plants are classified into 59 genera, including Hippeastrum Herb., which comprises approximately 60 species distributed mainly in South America, being widely used as ornamental plants due to the beauty of its flowers. This review presents an update about the alkaloid profiling of Hippeastrum extracts published between 2012 and 2021, as well as an approach to the biological potential of these compounds.

GRAPHICAL ABSTRACT

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s43450-021-00211-z.

Amaryllidaceae plants: a potential natural resource for the treatment of Chagas disease

Background

Chagas disease is a neglected zoonosis caused by the parasite Trypanosoma cruzi. It affects over six million people, mostly in Latin America. Drugs available to treat T. cruzi infection have associated toxicity and questionable efficacy at the chronic stage. Hence, the discovery of more effective and safer drugs is an unmet medical need. For this, natural products represent a pool of unique chemical diversity that can serve as excellent templates for the synthesis of active molecules.

Methods

A collection of 79 extracts of Amaryllidaceae plants were screened against T. cruzi. Active extracts against the parasite were progressed through two cell toxicity assays based on Vero and HepG2 cells to determine their selectivity profile and discard those toxic to host cells. Anti-T. cruzi-specific extracts were further qualified by an anti-amastigote stage assay.

Results

Two extracts, respectively from Crinum erubescens and Rhodophiala andicola, were identified as highly active and specific against T. cruzi and its mammalian replicative form.

Conclusions

The results retrieved in this study encourage further exploration of the chemical content of these extracts in search of new anti-T. cruzi drug development starting points.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04837-9.

Untargeted GC/MS-based approach for identification of anti-inflammatory alkaloids from Hippeastrum elegans (Amaryllidaceae) using a human neutrophil model

Hippeastrum elegans is an Amaryllidaceae species producing alkaloids with pharmaceutical potential including lycorine and galanthamine. Herein, we developed a non-targeted metabolomic study associated to chemometrics and biological evaluations to identify the H. elegans constituents that were able to reduce the human neutrophils proinflammatory mechanisms. The alkaloid fractions were extracted from bulbs cultivated for 15 months (m) and harvested in six harvest periods (5, 7, 9, 11, 13, and 15 m). The GC-MS analysis allowed the detection of 41 alkaloids being 31 identified. All alkaloid components varied over the cultivation and most of them were lycorine-type skeletons. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) distinguished three groups according to the chemical profile (group I: 5, 7, and 9 m; group II: 11 m and group III: 13 and 15 m). Therefore, the biological assays were only performed with one of the representative samples of each group: 7 m, 11 m and 15 m. None of them was toxic to human neutrophils by LDH activity and MTT test. The 7 m and 15 m-alkaloid fractions showed anti-inflammatory effects by reducing human neutrophil degranulation. However, the former one was more effective in inhibiting the cell activation based on the reduction of myeloperoxidase (MPO) release and reactive oxygen species (ROS) production. Afterwards, Partial Least Squares analysis (PLS) indicated lycorine and 11,12-dehydro-2-methoxy-assoanine as the compounds responsible for the anti-inflammatory activity of the bioactive fraction. Thus, the 7 m-alkaloid fraction of H. elegans seems to be a promising anti-inflammatory drug that deserves additional research.

Biosynthesis and Biological Activities of Newly Discovered Amaryllidaceae Alkaloids

Alkaloids are an important group of specialized nitrogen metabolites with a wide range of biochemical and pharmacological effects. Since the first publication on lycorine in 1877, more than 650 alkaloids have been extracted from Amaryllidaceae bulbous plants and clustered together as the Amaryllidaceae alkaloids (AAs) family. AAs are specifically remarkable for their diverse pharmaceutical properties, as exemplified by the success of galantamine used to treat the symptoms of Alzheimer's disease. This review addresses the isolation, biological, and structure activity of AAs discovered from January 2015 to August 2020, supporting their therapeutic interest.

Combining In Silico and In Vitro Studies to Evaluate the Acetylcholinesterase Inhibitory Profile of Different Accessions and the Biomarker Triterpenes of Centella asiatica

Alzheimer's disease (AD) is a neurodegenerative disease and the most cause of dementia in elderly adults. Acetylcholinesterase (AChE) is an important beneficial target for AD to control cholinergic signaling deficit. Centella asiatica (CA) has proven to be rich with active ingredients for memory enhancement. In the present study, the chemical profiling of three accession extracts of CA namely SECA-K017, SECA-K018, and, SECA-K019 were performed using high-performance liquid chromatography (HPLC). Four biomarker triterpene compounds were detected in all CA accessions. Quantitative analysis reveals that madecassoside was the highest triterpene in all the CA accessions. The biomarker compounds and the ethanolic extracts of three accessions were investigated for their acetylcholinesterase (AChE) inhibitory activity using Ellman's spectrophotometer method. The inhibitory activity of the triterpenes and accession extracts was compared with the standard AChE inhibitor eserine. The results from the in vitro study showed that the triterpene compounds exhibited an AChE inhibitory activity with the half-maximal inhibitory concentration (IC₅₀) values between 15.05 ± 0.05 and 59.13 ± 0.18 µg/mL. Asiatic acid was found to possess strong AChE inhibitory activity followed by madecassic acid. Among the CA accession extracts, SECA-K017 and SECA-K018 demonstrated a moderate AChE inhibitory activity with an IC₅₀ value of 481.5 ± 0.13 and 763.5 ± 0.16 µg/mL, respectively from the in silico docking studies, it is observed that asiatic acid and madecassic acid showed very good interactions with the active sites and fulfilled docking parameters against AChE. The present study suggested that asiatic acid and madecassic acid in the CA accessions could be responsible for the AChE inhibitory action and could be used as markers to guide further studies on CA as potential natural products for the treatment of AD.

Amaryllidaceae alkaloids with anti-Trypanosoma cruzi activity

Background

Chagas disease, caused by the protozoan Trypanosoma cruzi, is a neglected disease that affects ~7 million people worldwide. Development of new drugs to treat the infection remains a priority since those currently available have frequent side effects and limited efficacy at the chronic stage. Natural products provide a pool of diversity structures to lead the chemical synthesis of novel molecules for this purpose. Herein we analyzed the anti-T. cruzi activity of nine alkaloids derived from plants of the family Amaryllidaceae.

Methods

The activity of each alkaloid was assessed by means of an anti-T. cruzi phenotypic assay. We further evaluated the compounds that inhibited parasite growth on two distinct cytotoxicity assays to discard those that were toxic to host cells and assure parasite selectivity.

Results

We identified a single compound (hippeastrine) that was selectively active against the parasite yielding selectivity indexes of 12.7 and 35.2 against Vero and HepG2 cells, respectively. Moreover, it showed specific activity against the amastigote stage (IC₅₀ = 3.31 μM).

Conclusions

Results reported here suggest that natural products are an interesting source of new compounds for the development of drugs against Chagas disease.

Chemical Profiling and Cholinesterase Inhibitory Activity of Five Phaedranassa Herb. (Amaryllidaceae) Species from Ecuador

It is estimated that 50 million people in the world live with dementia, 60-70% of whom suffer from Alzheimer's disease (AD). Different factors are involved in the development of AD, including a reduction in the cholinergic neurotransmission level. The Amaryllidaceae plant family contains an exclusive, large, and still understudied alkaloid group characterized by a singular skeleton arrangement and a broad spectrum of biological activities. The chemistry and biodiversity of Ecuadorian representatives of the Phaedranassa genus (Amaryllidaceae) have not been widely studied. In this work, five Ecuadorian Phaedranassa species were examined in vitro for their activity towards the enzymes acetyl- (AChE) and butyrylcholinesterase (BuChE), and the alkaloid profile of bulb extracts was analyzed by GC-MS. The species Phaedranassa cuencana and Phaedranassa dubia showed the most AChE and BuChE inhibitory activity, respectively. To obtain insight into the potential role of the identified alkaloids in these inhibitory effects, docking experiments were carried out, and cantabricine showed in silico inhibitory activity against both cholinesterase structures. Our results show that Amaryllidaceae species from Ecuador are a potential source of new drugs for the palliative treatment of AD.

Clinanthus microstephium, an Amaryllidaceae Species with Cholinesterase Inhibitor Alkaloids: Structure-Activity Analysis of Haemanthamine Skeleton Derivatives

Plants of the Amaryllidaceae family are well-known (not only) for their ornamental value but also for the alkaloids that they produce. In this report, the first phytochemical study of Clinanthus genus was carried out. The chemical composition of alkaloid fractions from Clinanthus microstephium was analyzed by GC/MS and NMR. Seven known compounds belonging to three structural types of Amaryllidaceae alkaloids were identified. An epimeric mixture of a haemanthamine-type compound (6-hydroxymaritidine) was tested as an inhibitor against acetyl- and butyrylcholinesterase enzymes (AChE and BChE, respectively), two enzymes relevant in the treatment of Alzheimer's disease, with good results. Structure-activity relationships through molecular docking studies with this alkaloid and other structurally related compounds were discussed.

Cholinesterase Inhibition Activity, Alkaloid Profiling and Molecular Docking of Chilean Rhodophiala (Amaryllidaceae)

Amaryllidaceae plants are the commercial source of galanthamine, an alkaloid approved for the clinical treatment of Alzheimer’s disease. The chemistry and bioactivity of Chilean representatives of Rhodophiala genus from the family of Amaryllidaceae have not been widely studied so far. Ten collections of five different Chilean Rhodophiala were analyzed in vitro for activity against enzymes such as acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) as well as for their alkaloid composition by GC-MS. To obtain an insight into the potential AChE and BuChE inhibitory activity of the alkaloids identified in the most active samples, docking experiments were carried out. Although galanthamine was found neither in aerial parts nor in bulbs of R. splendens, these plant materials were the most active inhibitors of AChE (IC₅₀: 5.78 and 3.62 μg/mL, respectively) and BuChE (IC₅₀: 16.26 and 14.37 μg/mL, respectively). Some 37 known alkaloids and 40 still unidentified compounds were detected in the samples, suggesting high potential in the Chilean Amaryllidaceae plants as sources of both novel bioactive agents and new alkaloids.

N-oxide alkaloids from Crinum amabile (Amaryllidaceae)

Natural products play an important role in the development of new drugs. In this context, the Amaryllidaceae alkaloids have attracted considerable attention in view of their unique structural features and various biological activities. In this study, twenty-three alkaloids were identified from Crinum amabile by GC-MS and two new structures (augustine N-oxide and buphanisine N-oxide) were structurally elucidated by NMR. Anti-parasitic and cholinesterase (AChE and BuChE) inhibitory activities of six alkaloids isolated from this species, including the two new compounds, are described herein. None of the alkaloids isolated from C. amabile gave better results than the reference drugs, so it was possible to conclude that the N-oxide group does not increase their therapeutic potential.