Amaryllidaceae Alkaloids Research Articles

Characterization of norbelladine synthase and noroxomaritidine/norcraugsodine reductase reveals a novel catalytic route for the biosynthesis of Amaryllidaceae alkaloids including the Alzheimer's drug galanthamine.

Amaryllidaceae alkaloids (AAs) are a large group of plant specialized metabolites with diverse pharmacological properties. Norbelladine is the entry compound in AAs biosynthesis and is produced from the condensation of tyramine and 3,4-dihydroxybenzaldehyde (3,4-DHBA). There are two reported enzymes capable of catalyzing this reaction in-vitro, both with low yield. The first one, norbelladine synthase (NBS), was shown to condense tyramine and 3,4-DHBA, while noroxomaritidine/norcraugsodine reductase (NR), catalyzes a reduction reaction to produce norbelladine. To clarify the mechanisms involved in this controversial step, both NBS and NR homologs were identified from the transcriptome of Narcissus papyraceus and Leucojum aestivum, cloned and expressed in Escherichia coli. Enzymatic assays performed with tyramine and 3,4-DHBA with each enzyme separately or combined, suggested that NBS and NR function together for the condensation of tyramine and 3,4-DHBA into norcraugsodine and further reduction into norbelladine. Using molecular homology modeling and docking studies, we predicted models for the binding of tyramine and 3,4-DHBA to NBS, and of the intermediate norcraugsodine to NR. Moreover, we show that NBS and NR physically interact in yeast and in-planta, that both localize to the cytoplasm and nucleus and are expressed at high levels in bulbs, confirming their colocalization and co-expression thus their ability to work together in the same catalytic route. Finally, their co-expression in yeast led to the production of norbelladine. In all, our study establishes that both NBS and NR participate in the biosynthesis of norbelladine by catalyzing the first key steps associated in the biosynthesis of the Alzheimer's drug galanthamine.

Narciclasine, a novel topoisomerase I inhibitor, exhibited potent anti-cancer activity against cancer cells

DNA topoisomerases are essential nuclear enzymes in correcting topological DNA errors and maintaining DNA integrity. Topoisomerase inhibitors are a significant class of cancer chemotherapeutics with a definite curative effect. Natural products are a rich source of lead compounds for drug discovery, including anti-tumor drugs. In this study, we found that narciclasine (NCS), an amaryllidaceae alkaloid, is a novel inhibitor of topoisomerase I (topo I). Our data demonstrated that NCS inhibited topo I activity and reversed its unwinding effect on p-HOT DNA substrate. However, it had no obvious effect on topo II activity. The molecular mechanism of NCS inhibited topo I showed that NCS did not stabilize topo-DNA covalent complexes in cells, indicating that NCS is not a topo I poison. A blind docking result showed that NCS could bind to topo I, suggesting that NCS might be a topo I suppressor. Additionally, NCS exhibited a potent anti-proliferation effect in various cancer cells. NCS arrested the cell cycle at G2/M phase and induced cell apoptosis. Our study reveals the antitumor mechanisms of NCS and provides a good foundation for the development of anti-cancer drugs based on topo I inhibition.Graphical abstract

Acetylcholinesterase Inhibition Activity of Hippeastrum papilio (Ravenna) Van Scheepen (Amaryllidaceae) Using Zebrafish Brain Homogenates.

The Amaryllidaceae family constitutes an interesting source of exclusive alkaloids with a broad spectrum of biological activity. Galanthamine, the most relevant one, has been commercialized for the palliative treatment of Alzheimer's disease symptoms since 2001 due to its potential as an acetylcholinesterase (AChE) inhibitor. In vitro screenings against AChE by applying different Amaryllidaceae species and alkaloids have been reported in the literature; however, they are usually carried out using purified market enzymes. The main goal of this work is to evaluate the AChE inhibitory potential of Hippeastrum papilio (Amaryllidaceae) extracts using zebrafish brain homogenates. The biological assays show that the H. papilio bulb extracts present an interesting AChE inhibitory activity in comparison with the positive reference control galanthamine (IC50 values of 1.20 ± 0.10 and 0.79 ± 0.15 μg/mL, respectively). The chemical profile of H. papilio shows that this species has a high amount of galanthamine, which may contribute to the inhibitory effect on AChE activity of zebrafish brains. Computational experiments were used to build the model for zebrafish AChE and to evaluate the interactions between galanthamine and the enzymic active site. This work suggests that zebrafish could represent an important model in the search for bioactive molecules from the Amaryllidaceae family for the treatment of Alzheimer's disease.

Methyl Jasmonate Elicitation for In Vitro Lycorine Accumulation in Three Zephyranthes Species and Comparative Analysis of Tissue-Cultured and Field Grown Plants

Lycorine is an important Amaryllidaceae alkaloid showing anti-cancerous activity on numerous cell lines; and it also demonstrates antiviral activity against several viruses including SARS-CoV-2 responsible for COVID-19. The in vitro cultivation of plant parts is a good alternative for elicitor mediated secondary metabolite synthesis, mass propagation, and cloning of elite genotypes. In this study, the quantification of lycorine from Zephyranthes candida, Zephyranthes grandiflora, and Zephyranthes citrina was evaluated, and the influence of methyl jasmonate (MJ) treatments on accumulation of lycorine yield was observed in the in vitro cultivated tissues. The influence of methyl jasmonate (MJ) on accumulation of lycorine was investigated for the first time in in vitro regenerated bulb, leaf, and root tissues of Zephyranthues. The efficient in vitro shoot regeneration was achieved in Z. candida (73.9%), Z. grandiflora (85.5%), and Z. citrina (76.5%) on Murashige and Skoog (MS) medium amended with 2.0 mg·L−1 Naphthalene acetic acid + 0.5 mg·L−1 Benzylaminopurine. The regenerants had the highest i.e., 7.46 mean numbers of bulblets per shoot. The best root induction (80.66%) was achieved on 2.0 mg/L Indole butyric acid (IBA). The lycorine content was quantified through High performance thin layer chromatography (HPTLC) in three field grown Zephyranthes species, was highest in Z. candida (1.93 µg g−1 dry wt.), followed by Z. grandiflora (1.87 µg g−1 dry wt.) and Z. citrina (1.62 µg g−1 dry wt.). The yield of lycorine was observed in this order i.e., bulb > leaf > root. The regenerated plants were supplemented with MJ and maximum lycorine yield was noted at 100 µM in bulb tissues of Z. candida (2.74 µg g−1 dry wt.) with an increase in percentage of 39.08. The enhancement could be due to MJ-induced stress as the biochemical attributes and anti-oxidant enzyme activity were high with elevated level of MJ. This enrichment may auger commercial manufacturing and utilization of lycorine in future.

Investigation of bio-active Amaryllidaceae alkaloidal small molecules as putative SARS-CoV-2 main protease and host TMPRSS2 inhibitors: interpretation by in-silico simulation study

The novel coronavirus disease 2019 (Covid-19) outburst is still threatening global health. This highly contagious viral disease is caused by the infection of SARS-CoV-2 virus. Covid-19 and post-Covid-19 complications induce noteworthy mortality. Potential chemical hits and leads against SARS-CoV-2 for combating Covid-19 are urgently required. In the present study, a virtual-screening protocol was executed on potential Amaryllidaceae alkaloids from a pool of natural compound library against SARS-CoV-2 main protease (Mpro) and transmembrane serine protease (TMPRSS2). For the collected 1016 alkaloids from the curated library, initially, molecular docking using AutoDock Vina (ADV), and thereafter 100 ns molecular-dynamic (MD) simulation has been executed for the best top-ranked binding affinity compounds for both the viral and host proteins. Comprehensive intermolecular-binding interactions profile of Amaryllidaceae alkaloids suggested that phyto-compounds Galantamine, Lycorenine, and Neronine as potent modulators of SARS-CoV-2 Mpro and host TMPRSS2 protein. All atomistic long range 100 ns MD simulation studies of each top ranked complex in triplicates also illustrated strong binding affinity of three compounds towards Mpro and TMPRSS2. Identified compounds might be recommended as prospective anti-viral agents for future drug development selectively targeting the SARS-CoV-2 Mpro or blocking host TMPRSS2 receptor, subjected to pre-clinical and clinical assessment for a better understanding of in-vitro molecular interaction and in-vivo validation. Communicated by Ramaswamy H. Sarma

Chemical and Biological Aspects of Different Species of the Genus Clinanthus Herb. (Amaryllidaceae) from South America.

The genus Clinanthus Herb. is found in the Andes Region (South America), mainly in Peru, Ecuador, and Bolivia. These plants belong to the Amaryllidaceae family, specifically the Amaryllidoideae subfamily, which presents an exclusive group of alkaloids known as Amaryllidaceae alkaloids that show important structural diversity and pharmacological properties. It is possible to find some publications in the literature regarding the botanical aspects of Clinanthus species, although there is little information available about their chemical and biological activities. The aim of this work was to obtain the alkaloid profile and the anti-cholinesterase activity of four different samples of Clinanthus collected in South America: Clinanthus sp., Clinanthus incarnatus, and Clinanthus variegatus. The alkaloid extract of each sample was analyzed by gas chromatography coupled with mass spectrometry (GC-MS), and their potential against the enzymes acetyl- and butyrylcholinesterase were evaluated. Thirteen alkaloids have been identified among these species, while six unidentified structures have also been detected in these plants. The alkaloid extract of the C. variegatus samples showed the highest structural diversity as well as the best activity against AChE, which was likely due to the presence of the alkaloid sanguinine. The results suggest this genus as a possible interesting new source of Amaryllidaceae alkaloids, which could contribute to the development of new medicines.

Regioselective SmI2-Mediated Radical ipso-Substitution Cyclization for the Construction of Pyrrolophenanthridinone Skeletons: The Synthesis of Amaryllidaceae Alkaloids.

Here, we report a regioselective, samarium(II) diiodide mediated intramolecular radical ipso-substitution cyclization. Through the use of a methoxy group as a leaving group, it was possible to regulate the regioselectivity of the reaction by changing the temperature and additives. We applied the developed reaction to the synthesis of four Amaryllidaceae alkaloids and have shown that the present reaction successfully overcomes regioselectivity issues encountered with other cyclization methods.

Design of semisynthetic derivatives of the Amaryllidaceae alkaloid ambelline and exploration of their in vitro cytotoxic activities

Ambelline, an alkaloid from the Amaryllidaceae family with a crinane-type skeleton, has not yet demonstrated any outstanding biological activity. However, its analogues prepared by derivatization of the C-11 hydroxyl group show different interesting effects. Continuing our earlier work, twelve novel aromatic esters were developed (10, 14, 16, 17, 22–25, 30–33) and studied, together with previously synthesized derivatives (2–9, 11–13, 15, 18–21, 26–29) in terms of their cytotoxic activity. The cytotoxic potential was determined on a panel of nine human cancer cell lines and one noncancerous cell line to characterize their biological activity spectrum. To describe and foresee the structure–activity relationship for further research, substances synthesized and described in our previous work were also included in this cytotoxicity study. The most significant activity was associated with analogues havingmethyl (10), methoxy (14–17), or ethoxy (18) substitution on the phenyl condensed to ambelline. However, the 4-chloro-3-nitrobenzoyl derivative (32) showed the most promising IC50 values, ranging from 0.6 ± 0.1 µM to 9.9 ± 0.2 µM. In vitro cytotoxicity studies indicated the most potent antiproliferative activity of 32 in a dose-dependent and time-dependent manner. Besides, 32 was found to be effective in decreasing viability and triggering apoptosis of MOLT-4 T-lymphoblastic leukemia cells.

Microbial Transformation of Lycorine by Talaromyces pinophilus Isolated from the Rhizosphere of Leucojum aestivum L.

In the present study we report on the isolation of 12 strains of filamentous fungi from the rhizosphere of Leucojum aestivum L. (Amaryllidaceae). They were screened for ability to transform the Amaryllidaceae alkaloid lycorine. Gas chromatography-mass spectrometry was applied to analyze the samples. The Talaromyces pinophilus S120 strain was found to transform 19% of lycorine into its 2-oxo-derivative. To the best of our knowledge, this is the first report on transformation of lycorine by a filamentous fungus.

GC-MS of some Amaryllidaceae alkaloids of homolycorine type.

Gas chromatography-mass spectrometry (GC-MS) is the most frequently applied technique for analysis of Amaryllidaceae alkaloids in plant extracts. These compounds, known for their potent bioactivities, are a distinctive chemotaxonomic feature of the Amaryllidoideae subfamily (Amaryllidaceae). The Amaryllidaceae alkaloids of homolycorine type with a C3-C4 double bond generally show molecular and diagnostic ions at the high mass region with low intensity in EIMS mode leading to problematic identification in complex plant extracts. Eleven standard homolycorine-type alkaloids (isolated and identified by 1D and 2D nuclear magnetic resonance) were subjected to separation with gas chromatography and studied with electron impact mass spectrometry including single quadropole (GC-EIMS), tandem (GC-EIMS/MS), and high resolution (GC-HR-EIMS) detectors, as well as with chemical ionisation mass spectrometry (GC-CIMS). Alkaloid fractions from two Hippeastrum species and Clivia miniata were subjected to GC-EIMS and GC-CIMS for alkaloid identification. GC-EIMS in combination with GC-CIMS provided significant structural information for homolycorine-type alkaloids with C3-C4 double bond facilitating their unambiguous identification. Based on the obtained typical fragmentation, other eleven homolycorine-type compounds were identified in extracts from two Hippeastrum species by parallel GC-EIMS, GC-CIMS and LC-ESI/ToF/MS and in extracts from Clivia miniata by GC-EIMS. GC-MS can be successfully applied for identification of new and known homolycorine-type alkaloids, as well as for chemotaxonomical and chemoecological studies, among others within the Amaryllidoideae subfamily.

Anti-SARS-CoV-2 Activity and Cytotoxicity of Amaryllidaceae Alkaloids from Hymenocallis littoralis.

The Amaryllidaceae species are well-known as a rich source of bioactive compounds in nature. Although Hymenocallis littoralis has been studied for decades, its polar components were rarely explored. The current phytochemical investigation of Amaryllidaceae alkaloids from H. littoralis led to the identification of three previously undescribed compounds: O-demethyl-norlycoramine (1), (-)-2-epi-pseudolycorine (2) and (+)-2-epi-pseudolycorine (3), together with eight known compounds: 6α-hydroxyhippeastidine (4), 6β-hydroxyhippeastidine (5), lycorine (6), 2-epi-lycorine (7), zephyranthine (8), ungeremine (9), pancratistatin (10) and 9-O-demethyl-7-O-methyllycorenine (11). Among the eight previously reported compounds, five were isolated from H. littoralis for the first time (compounds 4, 5, 7, 8, and 9). Compounds 1, 4, 5, 7, 8, and 11 exhibited weak anti-SARS-CoV-2 activity (EC50 = 40-77 µM) at non-cytotoxic concentrations. Assessment of cytotoxicity on the Vero-E6 cell line revealed lycorine and pancratistatin as cytotoxic substances with CC50 values of 1.2 µM and 0.13 µM, respectively. The preliminary structure-activity relationship for the lycorine-type alkaloids in this study was further investigated, and as a result ring C appears to play a crucial role in their anti-SARS-CoV-2 activity.

Amaryllidaceae alkaloids in skin cancer management: Photoprotective effect on human keratinocytes and anti-proliferative activity in melanoma cells.

Skin cancer has high rates of mortality and therapeutic failure. In this study, to develop a multi-agent strategy for skin cancer management, the selective cytotoxicity of several alkaloid fractions and pure alkaloids isolated from Amaryllidaceae species was evaluated in melanoma cells. In addition, UVB-stimulated keratinocytes (HaCaT) were exposed to seven alkaloid fractions characterized by GC-MS, and the production of intracellular reactive oxygen species (ROS) and IL-6, were measured to evaluate their photoprotection effects. The Eucharis caucana (bulb) alkaloid fraction (20 μg/ml) had a clear effect on the viability of melanoma cells, reducing it by 45.7% without affecting healthy keratinocytes. This alkaloid fraction and tazettine (both at 2.5 μg/ml) suppressed UVB-induced ROS production by 31.6% and 29.4%, respectively. The highest anti-inflammatory potential was shown by the Zephyranthes carinata (bulb) alkaloid fraction (10 μg/ml), which reduced IL-6 production by 90.8%. According to the chemometric analysis, lycoramine and tazettine had a photoprotective effect on the UVB-exposed HaCaT cells, attenuating the production of ROS and IL-6. These results suggest that Amaryllidaceae alkaloids have photoprotective and therapeutic potential in skin cancer management, especially at low concentrations.

Highly selective butyrylcholinesterase inhibitors related to Amaryllidaceae alkaloids - Design, synthesis, and biological evaluation

Butyrylcholinesterase (BChE) is one of the most frequently implicated enzymes in the advanced stage of Alzheimer's disease (AD). As part of our endeavors to develop new drug candidates for AD, we have focused on natural template structures, namely the Amaryllidaceae alkaloids carltonine A and B endowed with high BChE selectivity. Herein, we report the design, synthesis, and in vitro evaluation of 57 novel highly selective human BChE (hBChE) inhibitors. Most synthesized compounds showed hBChE inhibition potency ranging from micromolar to low nanomolar scale. Compounds that revealed BChE inhibition below 100 nM were selected for detailed biological investigation. The CNS-targeted profile of the presented compounds was confirmed theoretically by calculating the BBB score algorithm, these data were corroborated by determining the permeability in vitro using PAMPA-assay for the most active derivatives. The study highlighted compounds 87 (hBChE IC50 = 3.8 ± 0.2 nM) and 88 (hBChE IC50 = 5.7 ± 1.5 nM) as the top-ranked BChE inhibitors. Compounds revealed negligible cytotoxicity for the human neuroblastoma (SH-SY5Y) and hepatocellular carcinoma (HepG2) cell lines compared to BChE inhibitory potential. A crystallographic study was performed to inspect the binding mode of compound 87, revealing essential interactions between 87 and hBChE active site. In addition, multidimensional QSAR analyses were applied to determine the relationship between chemical structures and biological activity in a dataset of designed agents. Compound 87 is a promising lead compound with potential implications for treating the late stages of AD.

Derivatives of Amaryllidaceae Alkaloid Ambelline as Selective Inhibitors of Hepatic Stage of Plasmodium berghei Infection In Vitro.

The incidence rate of malaria and the ensuing mortality prompts the development of novel antimalarial drugs. In this work, the activity of twenty-eight Amaryllidaceae alkaloids (1-28) belonging to seven different structural types was assessed, as well as twenty semisynthetic derivatives of the β-crinane alkaloid ambelline (28a-28t) and eleven derivatives of the α-crinane alkaloid haemanthamine (29a-29k) against the hepatic stage of Plasmodium infection. Six of these derivatives (28h, 28m, 28n and 28r-28t) were newly synthesized and structurally identified. The most active compounds, 11-O-(3,5-dimethoxybenzoyl)ambelline (28m) and 11-O-(3,4,5-trimethoxybenzoyl)ambelline (28n), displayed IC50 values in the nanomolar range of 48 and 47 nM, respectively. Strikingly, the derivatives of haemanthamine (29) with analogous substituents did not display any significant activity, even though their structures are quite similar. Interestingly, all active derivatives were strictly selective against the hepatic stage of infection, as they did not demonstrate any activity against the blood stage of Plasmodium infection. As the hepatic stage is a bottleneck of the plasmodial infection, liver-selective compounds can be considered crucial for further development of the malaria prophylactics.

Influence of plant growth regulators on in vitro biomass production and biosynthesis of cytotoxic Amaryllidaceae alkaloids in Caliphuria tenera Baker

Plants of the Amaryllidoideae subfamily are characterized by the presence of isoquinoline alkaloids called Amaryllidaceae alkaloids. These compounds have exhibited a broad spectrum of pharmacological effects, including anti-Alzheimer and anti-cancer. In this study, Caliphruria tenera Baker, Amaryllidaceae, an endangered and endemic species, was selected to evaluate the effect of growth regulators on plant micropropagation, biomass increase, and production of cytotoxic alkaloids. Different growth regulators were used individually and mixed, and the Amaryllidaceae alkaloids were identified and quantified by GC-MS. The maximum number of in vitro shoots (4.8) was recorded with 6-benzylaminopurine (BAP) (1 mg/L) + Kinetin (KIN) (1 mg/L) + Naphthaleneacetic acid (NAA) (0.2 mg/L). In addition, nineteen alkaloids were identified as crinine, galantamine, lycorine, narciclasine, and tazzetine-type alkaloids in cultivated and micropropagated plants. In general, the biomass was maximized with the growth hormone combination BAP + KIN + NAA, but the biosynthesis of alkaloids was minimized. However, the combination BAP + NAA showed the greatest productivity of trisphaeridine (632.01 μg/g). The growth regulators showed also a positive effect on the production of lycorine-type alkaloids with a content of 396.33 μg/g for KIN, 142.38 μg/g for BAP, and 41.67 μg/g for NAA. All alkaloid fractions were evaluated for their antiproliferative effects against human lung carcinoma (A549) and human keratinocytes (HaCat) cells. The alkaloids produced in the BAP + NAA treatment present a potent and selective cytotoxic against the A549 cell line at 30 μg/mL. This study shows that micropropagation is a promising approach for the production of cytotoxic Amaryllidaceae alkaloids in C. tenera without affecting natural populations.

Cytotoxic Activity of Amaryllidaceae Plants against Cancer Cells: Biotechnological, In Vitro, and In Silico Approaches.

Cancer is a major cause of death and an impediment to increasing life expectancy worldwide. With the aim of finding new molecules for chemotherapeutic treatment of epidemiological relevance, ten alkaloid fractions from Amaryllidaceae species were tested against six cancer cell lines (AGS, BT-549, HEC-1B, MCF-7, MDA-MB 231, and PC3) with HaCat as a control cell line. Some species determined as critically endangered with minimal availability were propagated using in vitro plant tissue culture techniques. Molecular docking studies were carried out to illustrate binding orientations of the 30 Amaryllidaceae alkaloids identified in the active site of some molecular targets involved with anti-cancer activity for potential anti-cancer drugs. In gastric cancer cell line AGS, the best results (lower cell viability percentages) were obtained for Crinum jagus (48.06 ± 3.35%) and Eucharis bonplandii (45.79 ± 3.05%) at 30 µg/mL. The research focused on evaluating the identified alkaloids on the Bcl-2 protein family (Mcl-1 and Bcl-xL) and HK2, where the in vitro, in silico and statistical results suggest that powelline and buphanidrine alkaloids could present cytotoxic activity. Finally, combining experimental and theoretical assays allowed us to identify and characterize potentially useful alkaloids for cancer treatment.

Antiviral Effects of the Plant Family Amaryllidaceae

Background In spite of the significant progress in modern medicine, viruses continue to be a formidable challenge to human health. The use of plants for the remediation of viral-borne diseases stretches back to the very dawn of mankind. Among bulbous plants, the Amaryllidaceae is one of the most popular families exploited in the traditional remediation of infectious diseases. Methods This account details the findings from a literature search carried out on the antiviral properties of the Amaryllidaceae. The keyword engaged in the search was “antiviral” in combination with the words “Amaryllidaceae,” “Amaryllidaceae specie,” and “Amaryllidaceae alkaloid.” Results Thirty-six taxa from 13 countries, notably in Africa and parts of Asia, have been cited as traditional remedies for viral diseases. Alcoholic bulb extracts of 18 species were evaluated against 23 different pathogens from 13 viral families. A wide range of activities was observed, with the whole-plant methanol extract of Zephyranthes candida seen to be the most striking (IC50 0.0019 µg/mL against poliovirus). The active principles in the main were isoquinoline alkaloids, of which lycorine impressed against the Avian influenza virus (strain H5N1). The mechanisms underlying the antiviral effects were seen to be related to the inhibition of DNA, RNA, and protein synthesis as well as inhibitory effects toward reverse transcriptase and protease enzymes. Conclusion Amaryllidaceae provides a richly diverse platform for antiviral drug research. Such endeavors have been fortified by the significant amounts of information emerging from indigenous knowledge systems. Ongoing studies will continue to target the active entities, particularly from taxa with verifiable ethnomedicinal backgrounds.

Bioinspired Formal Synthesis of Pancracine via Selective Hydro­genation of an Indole Derivative

AbstractA bioinspired formal synthesis of the montanine-type Amaryllidaceae alkaloid pancracine through selective hydrogenation of a 3-arylindole derivative is disclosed. The key features of this synthesis include a hexahydroindole synthesis by a chemoselective hydrogenation of an aryl-substituted indole and a diastereoselective silyl hydride reduction of an iminium intermediate generated from an enaminone through Tf2O activation. The eight-step assembly of the 5,11-methanomorphanthridine framework represents a novel and efficient strategy that permits one of the shortest syntheses of pancracine reported so far.

SWATH-MS-Based Proteomics Reveals the Regulatory Metabolism of Amaryllidaceae Alkaloids in Three Lycoris Species.

Alkaloids are a class of nitrogen-containing alkaline organic compounds found in nature, with significant biological activity, and are also important active ingredients in Chinese herbal medicine. Amaryllidaceae plants are rich in alkaloids, among which galanthamine, lycorine, and lycoramine are representative. Since the difficulty and high cost of synthesizing alkaloids have been the major obstacles in industrial production, particularly the molecular mechanism underlying alkaloid biosynthesis is largely unknown. Here, we determined the alkaloid content in Lycoris longituba, Lycoris incarnata, and Lycoris sprengeri, and performed a SWATH-MS (sequential window acquisition of all theoretical mass spectra)-based quantitative approach to detect proteome changes in the three Lycoris. A total of 2193 proteins were quantified, of which 720 proteins showed a difference in abundance between Ll and Ls, and 463 proteins showed a difference in abundance between Li and Ls. KEGG enrichment analysis revealed that differentially expressed proteins are distributed in specific biological processes including amino acid metabolism, starch, and sucrose metabolism, implicating a supportive role for Amaryllidaceae alkaloids metabolism in Lycoris. Furthermore, several key genes collectively known as OMT and NMT were identified, which are probably responsible for galanthamine biosynthesis. Interestingly, RNA processing-related proteins were also abundantly detected in alkaloid-rich Ll, suggesting that posttranscriptional regulation such as alternative splicing may contribute to the biosynthesis of Amaryllidaceae alkaloids. Taken together, our SWATH-MS-based proteomic investigation may reveal the differences in alkaloid contents at the protein levels, providing a comprehensive proteome reference for the regulatory metabolism of Amaryllidaceae alkaloids.

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.