α-Glucosidase Inhibitory and Cytotoxic Taxane Diterpenoids from the Stem Bark of Taxus wallichiana

Mass spectrometry imaging and single-cell transcriptional profiling reveal the tissue-specific regulation of bioactive ingredient biosynthesis in Taxus leaves

Taxus leaves provide the raw industrial materials for taxol, a natural antineoplastic drug widely used in the treatment of various cancers. However, the precise distribution, biosynthesis, and transcriptional regulation of taxoids and other active components in Taxus leaves remain unknown. Matrix-assisted laser desorption/ionization-mass spectrometry imaging analysis was used to visualize various secondary metabolites in leaf sections of Taxus mairei, confirming the tissue-specific accumulation of different active metabolites. Single-cell sequencing was used to produce expression profiles of 8846 cells, with a median of 2352 genes per cell. Based on a series of cluster-specific markers, cells were grouped into 15 clusters, suggesting a high degree of cell heterogeneity in T. mairei leaves. Our data were used to create the first Taxus leaf metabolic single-cell atlas and to reveal spatial and temporal expression patterns of several secondary metabolic pathways. According to the cell-type annotation, most taxol biosynthesis genes are expressed mainly in leaf mesophyll cells; phenolic acid and flavonoid biosynthesis genes are highly expressed in leaf epidermal cells (including the stomatal complex and guard cells); and terpenoid and steroid biosynthesis genes are expressed specifically in leaf mesophyll cells. A number of novel and cell-specific transcription factors involved in secondary metabolite biosynthesis were identified, including MYB17, WRKY12, WRKY31, ERF13, GT_2, and bHLH46. Our research establishes the transcriptional landscape of major cell types in T. mairei leaves at a single-cell resolution and provides valuable resources for studying the basic principles of cell-type-specific regulation of secondary metabolism.

Profiling of Taxoid Compounds in Plant Cell Cultures of Different Species of Yew (Taxus spp.)

Plant cell cultures of various yew species are a profitable source of taxoids (taxane diterpenoids) with antitumor activity. So far, despite intensive studies, the principles of the formation of different groups of taxoids in cultured in vitro plant cells have not been fully revealed. In this study, the qualitative composition of taxoids of different structural groups was assessed in callus and suspension cell cultures of three yew species (Taxus baccata, T. canadensis, and T. wallichiana) and two T. × media hybrids. For the first time, 14-hydroxylated taxoids were isolated from the biomass of the suspension culture of T. baccata cells, and their structures were identified by high-resolution mass spectrometry and NMR spectroscopy as 7β-hydroxy-taxuyunnanin C, sinenxane C, taxuyunnanine C, 2α,5α,9α,10β,14β-pentaacetoxy-4(20), 11-taxadiene, and yunnanxane. UPLC-ESI-MS screening of taxoids was performed in more than 20 callus and suspension cell lines originating from different explants and grown in over 20 formulations of nutrient media. Regardless of the species, cell line origin, and conditions, most of the investigated cell cultures retained the ability to form taxane diterpenoids. Nonpolar 14-hydroxylated taxoids (in the form of polyesters) were predominant under in vitro culture conditions in all cell lines. These results, together with the literature data, suggest that dedifferentiated cell cultures of various yew species retain the ability to synthesize taxoids, but predominantly of the 14-OH taxoid group compared to the 13-OH taxoids found in plants.

Taxoids-rich extract from Taxus wallichiana alleviates high-fat diet-induced insulin resistance in C57BL/6 mice through inhibition of low-grade inflammation

The needle powder of Taxus wallichiana is in use for the management of diabetes and inflammation-related complications in the Indian and Chinese Systems of Traditional Medicine but the lack of proper pharmacological intervention has prompted us to investigate the pharmacological mechanism against inflammation-induced insulin resistance in high-fat diet-fed C57BL/6 mice. Hexane (Tw-H), chloroform (Tw-C), and ethyl acetate (Tw-EA) extracts were prepared from a needle of T. wallichiana and its effect on glucose uptake against TNF-α-induced insulin resistance in skeletal muscle cells was studied. Among all, Tw-EA extract has shown promising glucose uptake potential. Tw-EA treatment is also able to decrease the lipid accumulation in adipocytes. Chemical signature of Tw-EA using HPLC showed the presence of taxoids. Efficacy of taxoids-rich extract from T. wallichiana (Tw-EA) was further validated in in vivo system against high-fat diet (HFD)-induced insulin resistance in C57BL/6 mice. Oral treatment of Tw-EA showed significant reduction in blood glucose, pro-inflammatory cytokine production and body weight gain when compared with vehicle-treated HFD-induced insulin resistance in C57BL/6 mice. Histopathology and immunohistochemistry study in skeletal muscle and adipose tissue revealed that oral treatment of Tw-EA is able to reduce the infiltration of inflammatory cells in skeletal muscles, ameliorate the hypertrophy in adipose tissue and upregulate the GLUT4 protein expression. Treatment with Tw-EA significantly up-regulated mRNA expression of insulin signaling pathway (IRS-1, PI3K, AKT, GLUT 4). This study suggested the beneficial effect of taxoids-rich extract from Taxus wallichiana against the inflammation-associated insulin resistance condition.

Alkaloids and Styryl lactones from Goniothalamus ridleyi King and Their α-Glucosidase Inhibitory Activity

Gonioridleylactam (1), a new compound, is a unique dimeric aristolactam isolated from the EtOAc extract of the twigs of Goniothalamus ridleyi King. The structure of gonioridleylactam (1) consists of two different aristolactams linked together with two methylenedioxy bridges at C-3/C-3' and C-4/C-4', generating a ten-membered ring of [1,3,6,8]tetraoxecine. A new natural product, gonioridleyindole (3-hydroxymethyl-1-methyl-1H-benz[f]indole-4,9-dione, 2), together with eight known compounds (3-10) were also isolated from this plant. Their structures were extensively characterized by spectroscopic methods and comparisons were made with the literature. Compounds 1-4, 7, and 9 were evaluated for their α-glucosidase inhibitory activity. Of these, 3,5-demethoxypiperolide (7) displayed the highest α-glucosidase inhibitory activity, with an IC₅₀ value of 1.25 µM.

A New abeo-Icetexane-Type Diterpenoid from the Stem Barks of Taxus wallichiana

From a CH2 Cl2 -soluble fraction of the stem barks of Taxus wallichiana, one new abeo-icetexane-type diterpenoid, taxamairin I (1), was isolated. Its absolute configuration was elucidated based on spectroscopic interpretation and time-dependent density functional theory (TD-DFT) calculation of optical rotation. In addition, the plausible biosynthesis pathway for the formation of the new abeo-icetexane-type diterpenoid was proposed. Taxamairin I (1), at a concentration of 100 μM, did not show cytotoxicity against Hep3B human liver cancer cell lines.

New Diterpenes with Potential Antitumoral Activity Isolated from Plants in the Years 2017-2022

Diterpenes represent a wider class of isoprenoids, with more than 18,000 isolated compounds, and are present in plants, fungi, bacteria, and animals in both terrestrial and marine environments. Here, we report on the fully characterised structures of 251 new diterpenes, isolated from higher plants and published from 2017, which are shown to have antitumoral activity. An overview on the most active compounds, showing IC50 < 20 μM, is provided for diterpenes of different classes. The most active compounds were extracted from 29 different plant families; particularly, Euphorbiaceae (69 compounds) and Lamiaceae (54 compounds) were the richest sources of active compounds. A better activity than the positive control was obtained with 33 compounds against the A549 cell line, 28 compounds against the MCF-7 cell line, 9 compounds against the HepG2 cell line, 8 compounds against the Hep3B cell line, 19 compounds against the SMMC-7721 cell line, 9 compounds against the HL-60 cell line, 24 compounds against the SW480 cell line, and 19 compounds against HeLa.

A review of alpha-glucosidase inhibitors from plants as potential candidates for the treatment of type-2 diabetes

Diabetes mellitus is a multifactorial global health disorder that is rising at an alarming rate. Cardiovascular diseases, kidney damage and neuropathy are the main cause of high mortality rates among individuals with diabetes. One effective therapeutic approach for controlling hyperglycemia associated with type-2 diabetes is to target alpha-amylase and alpha-glucosidase, enzymes that catalyzes starch hydrolysis in the intestine. At present, approved inhibitors for these enzymes are restricted to acarbose, miglitol and voglibose. Although these inhibitors retard glucose absorption, undesirable gastrointestinal side effects impede their application. Therefore, research efforts continue to seek novel inhibitors with improved efficacy and minimal side effects. Natural products of plant origin have been a valuable source of therapeutic agents with lesser toxicity and side effects. The anti-diabetic potential through alpha-glucosidase inhibition of plant-derived molecules are summarized in this review. Eight molecules (Taxumariene F, Akebonoic acid, Morusin, Rhaponticin, Procyanidin A2, Alaternin, Mulberrofuran K and Psoralidin) were selected as promising drug candidates and their pharmacokinetic properties and toxicity were discussed where available.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11101-021-09773-1.

δ-Tocopherol derivatives from the leaves of Muntingia calabura L

From an ethyl acetate-soluble fraction of the leaves of Muntingia calabura, one new trimeric δ-tocopherol derivative named as tocomuntin A (1), together with three known δ-tocopherol derivatives (2-4) were isolated. Their structures were elucidated based on the interpretation of NMR and MS spectroscopic data. In this work, δ-tocopherol (3) was found to have α-glucosidase inhibitory activity for the first time (IC₅₀, 47.3 μM).

Pipercyclobutanamide D, a new member of the cyclobutanamide-type alkaloid, from the roots of Piper nigrum

From the EtOH-soluble extract of the roots of Piper nigrum, one new dimeric alkamide, pipercyclobutanamide D (1) was isolated. Its structure was elucidated on the basis of NMR spectroscopic interpretation. The relative configuration of 1 was determined based on the NOESY analysis. Compound 1 showed α-glucosidase inhibitory activity with an IC₅₀ value of 158.5 µM. In addition, compound 1 exhibited cytotoxicity against the MCF-7 and HepG2 cell lines with the IC₅₀ values of 45.6 and 63.9 µM, respectively. Plausible biosynthetic pathway for the formation of 1 was proposed based on regioselective [2 + 2] cycloaddition reaction.

A new 8,3'-neolignan from Solanum procumbens Lour

The phytochemical investigation of the EtOAc-soluble fraction of the aerial parts of Solanum procumbens Lour. has been carried out to obtain seven compounds, including a new 8,3'-neolignan named solacanin A (1). Their chemical structures were elucidated based on the spectroscopic data interpretation. All isolated compounds were tested for their α-glucosidase inhibitory activity. Compounds 1 and 3-6 showed inhibitory activity with IC₅₀ values of 221.5, 18.9, 6.0, 104.1, and 219.7 µM, respectively.

New calogenin pregnane glycoside derivative from Huernia saudi- arabica and its Lipase and α-Glucosidase Inhibitory Activities

As ongoing investigation of Huernia saudi-arabica D.V.Field (Asclepiadaceae), a new steroidal pregnane glycoside (Huernioside A) was isolated from dichloromethane fraction (DCM); it was identified as 3β, 11, 14β, 20(R)-tetrahydroxy-pregna-5,9(11)-diene-3-O-β-D-thevetopyranosyl-(1-4)-β-D-cymaropyranoside(HCP) through analysis of 1D, 2D NMR besides ESI-MS data. The alcoholic extract of the aerial part (ALE), DCM and HCP showed inhibitory potential against pancreatic lipase compared to orilstat. Among the tested samples, the ALE and HCP exhibited a promising pancreatic lipase inhibitory commotion through IC₅₀ values of 0.61 ± 0.15, 1.23 ± 0.07 mg/ml (equivalent to 88.8 μM), respectively. HCP was prevailed to have a mixed mode of inhibition as exposed by enzyme kinetic studies. Hydrophobic interactions were the major forces involved in ligand enzyme interactions. In contrast, moderate α-glucosidase inhibitory activities were evidenced for ALE and HCP (% inhibition: 24.8 ± 1.8 and 26.6 ± 2.5, respectively) compared to acarbose. This investigation is the first to report on the possible in vitro anti-obesity and anti-diabetic impact of H. saudi-arabica.

Unraveling Plant Natural Chemical Diversity for Drug Discovery Purposes

The screening and testing of extracts against a variety of pharmacological targets in order to benefit from the immense natural chemical diversity is a concern in many laboratories worldwide. And several successes have been recorded in finding new actives in natural products, some of which have become new drugs or new sources of inspiration for drugs. But in view of the vast amount of research on the subject, it is surprising that not more drug candidates were found. In our view, it is fundamental to reflect upon the approaches of such drug discovery programs and the technical processes that are used, along with their inherent difficulties and biases. Based on an extensive survey of recent publications, we discuss the origin and the variety of natural chemical diversity as well as the strategies to having the potential to embrace this diversity. It seemed to us that some of the difficulties of the area could be related with the technical approaches that are used, so the present review begins with synthetizing some of the more used discovery strategies, exemplifying some key points, in order to address some of their limitations. It appears that one of the challenges of natural product-based drug discovery programs should be an easier access to renewable sources of plant-derived products. Maximizing the use of the data together with the exploration of chemical diversity while working on reasonable supply of natural product-based entities could be a way to answer this challenge. We suggested alternative ways to access and explore part of this chemical diversity with in vitro cultures. We also reinforced how important it was organizing and making available this worldwide knowledge in an "inventory" of natural products and their sources. And finally, we focused on strategies based on synthetic biology and syntheses that allow reaching industrial scale supply. Approaches based on the opportunities lying in untapped natural plant chemical diversity are also considered.

A new phenolic acid from the wood of Mangifera gedebe

From the methanol extract of the wood of Mangifera gedebe (Anacardiaceae), we had isolated a new secondary metabolite named gedebic acid (1) and six known compounds (2-7). Their chemical structures were determined by spectroscopic methods as well as comparing with data in the literature. All compounds were tested for α-glucosidase inhibitory activity. Compounds 4-7 showed more potent inhibitory activity, with IC₅₀ values ranging from 45.3 to 142.6 μM, than that of a positive control acarbose (IC₅₀, 214.5 μM).

Nimbandiolactone-21 and nimbandioloxyfuran, two new 28-norlimonoids from the leaves of Azadirachta indica (Meliaceae)

From an EtOAc-soluble fraction of the leaves of Azadirachta indica, two new 28-norlimonoids named nimbandiolactone-21 (1) and nimbandioloxyfuran (2), together with nimbandiolactone-23 (3), were isolated. Their relative structures were elucidated based on NMR spectroscopic interpretation and biosynthetic consideration. Nimbandioloxyfuran (2) and nimbandiolactone-23 (3) showed potent α-glucosidase inhibitory activity, with the IC₅₀ values of 46.2 and 38.7 μM, respectively.

Cytotoxic Tigliane Diterpenoids from Croton damayeshu

Chemical investigation of an EtOH extract of the twigs and leaves of Croton damayeshu afforded 10 new tigliane diterpenoids, crodamoids A-J (1-10), along with five known compounds. Their structures were elucidated by physical data analysis. Compounds 8, 9, and 15 displayed cytotoxic effects against two human tumor cell lines, A549 and HL-60 (IC₅₀: 0.9-2.4 μM).

Bioassay-Guided Isolation of Triterpenoids as α-Glucosidase Inhibitors from Cirsium setosum

Cirsium setosum (C. setosum) has a potential antihyperglycemic effect, but it is unclear what bioactive components play a key role. According to the α-glucosidase inhibition activity, three new taraxastane-type triterpenoids of 3β-hydroxy-30-hydroperoxy-20-taraxastene (1), 3β-hydroxy-22α-methoxy-20-taraxastene (2), and 30-nor-3β,22α-dihydroxy-20-taraxastene (3), as well as five known taraxastane triterpenoids of 3β,22-dihydroxy-20-taraxastene (4), 20-taraxastene-3,22-dione (5), 3β-acetoxy-20-taraxasten-22-one (6), 3β-hydroxy-20-taraxasten-22-one (7), and 30-nor-3β-hydroxy-20-taraxastene (8) were obtained from the petroleum ether-soluble portion of the ethanol extract from C. setosum. All chemical structures of the compounds were elucidated by spectroscopic data analysis and compared with literature data. Compounds 4-8 were identified for the first time from this plant, and compounds 1, 2, 4, and 7 exhibited more potent α-glucosidase inhibitory activity-with IC50 values of 18.34 ± 1.27, 26.98 ± 0.89, 17.49 ± 1.42, and 22.67 ± 0.25 μM, respectively-than acarbose did (positive control, IC50 42.52 ± 0.32 μM).

Diterpenoids of terrestrial origin

This review covers the isolation and chemistry of diterpenoids from terrestrial sources from 2017.

A New Taxane Diterpenoid and a New Neolignan from Taxus baccata

Two new compounds, baccataxinine (1) and baccalignan (2), were isolated from the Taxus baccata, together with 16 known ones. Their structures were elucidated by comprehensive spectroscopic analyses of HR-ESI-MS, NMR and IR. Compound 1 is a taxane diterpenoid possessing a rare dioxolane ring between C-1 and C-2, while 2 is the first benzofuran neolignan from this species. Furthermore, they were also evaluated for their α-glucosidase inhibitory activity, but none of them showed considerable inhibitory effects.

A new lactam 28-norlimonoid from the leaves of Azadirachta indica A. Juss. (Meliaceae)

From an EtOAc-soluble fraction of the leaves of Azadirachta indica, one new lactam 28-norlimonoid named nimbandiolactam-21 (1), together with 2 known limonoids (2 and 3) were isolated. Their relative structures were elucidated based on NMR spectroscopic analysis. Nimbandiolactone-23 (2) showed the most potent α-glucosidase inhibitory activity, with an IC₅₀ value of 38.7 μM. Compound 1 represents the first naturally occurring example of a 28-norlimonoid having the lactam moiety. The plausible biosynthetic pathway for the formation of lactam moiety in 1 was proposed.

Mesenchymal Stromal Cells for Antineoplastic Drug Loading and Delivery

Mesenchymal stromal cells are a population of undifferentiated multipotent adult cells possessing extensive self-renewal properties and the potential to differentiate into a variety of mesenchymal lineage cells. They express broad anti-inflammatory and immunomodulatory activity on the immune system and after transplantation can interact with the surrounding microenvironment, promoting tissue healing and regeneration. For this reason, mesenchymal stromal cells have been widely used in regenerative medicine, both in preclinical and clinical settings. Another clinical application of mesenchymal stromal cells is the targeted delivery of chemotherapeutic agents to neoplastic cells, maximizing the cytotoxic activity against cancer cells and minimizing collateral damage to non-neoplastic tissues. Mesenchymal stem cells are home to the stroma of several primary and metastatic neoplasms and hence can be used as vectors for targeted delivery of antineoplastic drugs to the tumour microenvironment, thereby reducing systemic toxicity and maximizing antitumour effects. Paclitaxel and gemcitabine are the chemotherapeutic drugs best loaded by mesenchymal stromal cells and delivered to neoplastic cells, whereas other agents, like pemetrexed, are not internalized by mesenchymal stromal cells and therefore are not suitable for advanced antineoplastic therapy. This review focuses on the state of the art of advanced antineoplastic cell therapy and its future perspectives, emphasizing in vitro and in vivo preclinical results and future clinical applications.

Quinoliniumolate and 2H-1,2,3-Triazole Derivatives from the Stems of Paramignya trimera and Their α-Glucosidase Inhibitory Activities: In Vitro and in Silico Studies

From a CHCl₃-soluble extract of the stems of Paramignya trimera, two new alkaloids, (E)-2-(prop-1-enyl)-N-methylquinolinium-4-olate (1) and (R)-2-ethylhexyl 2H-1,2,3-triazole-4-carboxylate (2), were isolated. Their structures were elucidated based on the spectroscopic data interpretation. Compound 2 possesses α-glucosidase inhibitory activity, with an IC₅₀ value of 137.9 μM. Molecular docking studies of 1 and 2 with human maltase-glucoamylase (MGAM) were performed for the first time; thus, the 2,3-diH⁺-1H-1,2,3-triazolium cation (2i) showed good interactions with both MGAM-N (2QMJ) and -C (3TOP) terminal subunits.

Lignans from the Roots of Taxus wallichiana and Their α-Glucosidase Inhibitory Activities

From an EtOAc-soluble extract of the roots of Taxus wallichiana, six new (1-6) and 11 known lignans were isolated. The structures of the new compounds were elucidated based on interpretation of spectroscopic data. (+)-7'-epi-Tsugacetal (1) is a rare aryltetralin-type lignan having a cis-orientation of H-7' and H-8'. Compounds 3-6 were identified as the first naturally occurring tetrahydrofuranoid lignans having a cis-orientation of H-7 and H-8. All tested compounds were found to possess α-glucosidase inhibitory activity, with formosanol (9) showing the most potent effect with an IC₅₀ value of 35.3 μM.