Triterpene saponins from Silphium radula

Characteristics of Selected Silphium Species as Alternative Plants for Cultivation and Industry with Particular Emphasis on Research Conducted in Poland: A Review

This article reviews the available research results of selected species of the genus Silphium L. (Asteraceae) as alternative plants for crops and industry. Silphium species have valuable qualities across a wide range of uses, which is very important in considering plant resources as a green alternative to a sustainable future. Species of the genus Silphium are tall perennials found in fields, prairies, open forests, and groves in the central and eastern parts of the United States and Canada. Various tribes of Native North American used Silphium for medicinal purposes. The cup plant Silphium perfoliatum L. is the most popular species of the genus Silphium due to its attractive ornamental, honey−giving, healing, and forage qualities. As the literature review shows, species of the genus Silphium are characterized by a high production potential in terms of yields and contain significant amounts of nutrients, i.e., carbohydrates, proteins, and L-ascorbic acid, as well as minerals and biologically active substances, e.g., terpenoids and essential oils, flavonoids, phenolic acids, and oleanosides. In addition, the research confirmed the possibility of using Silphium for fodder, as honeybee forage, phytoremediation plants, for reclamation of degraded land, as plants for energy purposes (biomass, biogas), and as plants that provide components with antimicrobial activity. This review largely takes into account many years of research experience conducted in Poland.

Saponin toxicity as key player in plant defense against pathogens

Microbial pathogens attack every plant tissue, including leaves, roots, shoots, and flowers during all growth stages. Thus, they cause several diseases resulting in a plant's failure or loss of the whole crop in severe cases. To combat the pathogens attack, plants produce some biologically active toxic compounds known as saponins. The saponins are secondary metabolic compounds produced in healthy plants with potential anti-pathogenic activity and serve as potential chemical barriers against pathogens. Saponins are classified into two major groups the steroidal and terpenoid saponins. Here, we reported the significance of saponin toxins in the war against insect pests, fungal, and bacterial pathogens. Saponins are present in both cultivated (chilies, spinach, soybean, quinoa, onion, oat, tea, etc.) and wild plant species. As they are natural toxic constituents of plant defense, breeders and plant researchers aiming to boost plant imm unity should focus on transferring these compounds in cash crops.

Suppression of Nrf2 Activity by Chestnut Leaf Extract Increases Chemosensitivity of Breast Cancer Stem Cells to Paclitaxel

Due to metastatic potential and drug resistance, cancer stem cells (CSCs) have become a critical target for the development of chemotherapeutic agents. Recent studies showed that CSCs highly express NF-E2-related factor 2 (Nrf2)-mediated antioxidant enzymes and thereby retain relatively low levels of reactive oxygen species (ROS). Since anticancer agents usually utilize ROS as an arsenal for killing cancer cells, we hypothesized that inhibition of Nrf2 activity could increase the sensitivity of CSCs to anticancer drugs, and thus enhancing their therapeutic efficacy. We found that MCF-7-derived CSCs with a CD44^high/CD24^low phenotype formed mammospheres and highly expressed Nrf2 compared to the adherent parental MCF-7 cells. In a separate experiment, we screened 89 different edible plant extracts for inhibitory activity against the Nrf2 signaling pathway by using an antioxidant response element (ARE)-luciferase assay system. Among those extracts, Castanea crenata (chestnut) leaf extract significantly decreased the nuclear translocation of Nrf2 and protein expression of antioxidant enzymes in MCF-7-derived CSCs. The combined treatment of the CSCs with chestnut leaf extract and paclitaxel resulted in more effective cell death than the treatment with paclitaxel alone. These findings suggest that the chestnut leaf extract or its constituents could increase the susceptibility of breast CSCs to an anticancer drug, paclitaxel, through inhibition of the Nrf2 signaling pathway, and could be utilized as an adjuvant for chemotherapy.

Novel microspheres based on triterpene saponins from the roots of Physospermum verticillatum (Waldst & Kit) (Apiaceae) for the improvement of gemcitabine release

Objectives

This study concerns the preparation and characterization of microspheres based on a mixture of triterpene saponins, from Physospermum verticillatum (Waldst & Kit), as a carrier for the specific release of gemcitabine.

Methods

Triterpene saponins were derivatized with acrylic acid. The obtained polymerizable product was characterized by Fourier transform infrared to confirm the ester linkage. Then, spherical microparticles were prepared by suspension radical copolymerization and impregnated with gemcitabine.

Key findings

Microspheres exhibited a mean diameter of 2.7 μ. The swelling studies showed that particles swell most at pH 6.2, typical of the tumour pathology, than at pH 7.4, miming physiological conditions. The microspheres were loaded with gemcitabine (LE 72.2%). Their release profile showed an initial dot of around 24% and a further release for 24 h.

Conclusions

This carrier could be potentially release the drug in the lung, as a function of different pHs between tumour cells and healthy, reducing the systemic drug toxicity, allowing the reduction of the doses number, increasing the drug half-life and eliminating the problems related to the fast clearance of gemcitabine administration.

Saponins with highly hydroxylated oleanane-type aglycones from Silphium asteriscus L

Silphium asteriscus L., commonly known as starry rosinweed, is a plant found in prairies, glades, woodlands and savannas of the southeastern United States. The phytochemical investigation of the methanolic extract of S. asteriscus leaves led to the isolation of eighteen saponins with highly hydroxylated oleanane-type aglycones never reported before. Their structures were elucidated by extensive spectroscopic methods including 1D- ((1)H and (13)C) and 2D-NMR (DQF-COSY, HSQC, HMBC, TOCSY and ROESY) experiments as well as ESIMS analysis. The antiproliferative activity of the isolated compounds was evaluated against three cancer cell lines including Hela (human epitheloid cervix carcinoma), Jurkat cells (leukaemic T-cell line) and DLD-1 (colorectal adenocarcinoma). Compounds 1, 5 and 17 displayed weak activity with IC50 values ranging from 50 to 75 μM.

Three new ursane-type triterpenoids from the stems of Saprosma merrillii

Three new ursane-type triterpenoids, 3α,6α,30-trihydroxy-ursan-28-oic acid (1), 3α,30-dihydroxy-6-oxo-ursan-28-oic acid (2) and 3α,6α,7α,30-tetrahydroxy-ursan-28-oic acid (3), together with one known triterpenoid, betulinic acid (4), one known anthraquinone, 1,7-dihydroxy-2-methylanthraquinone (5), four known phenols, 1,3,5-trimethoxybenzene (6), p-hydroxybenzoic acid (7), syringic acid (8), isovanillin (9), two steroids, sitosterol (10) and daucosterol (11), were isolated from the ethanol extract of the stems of S. merrillii. Their structures were elucidated on the basis of physical and spectral techniques, besides comparison with literature data. Compounds 1-3 showed inhibitory activities against the A549, HEPG2, and B16F10 cell lines.

Saponins as cytotoxic agents: a review

Saponins are natural glycosides which possess a wide range of pharmacological properties including cytotoxic activity. In this review, the recent studies (2005-2009) concerning the cytotoxic activity of saponins have been summarized. The correlations between the structure and the cytotoxicity of both steroid and triterpenoid saponins have been described as well as the most common mechanisms of action.

Chemical study and medical application of saponins as anti-cancer agents

Saponins are a group of naturally occurring plant glycosides, characterized by their strong foam-forming properties in aqueous solution. The presence of saponins has been reported in more than 100 families of plants out of which at least 150 kinds of natural saponins have been found to possess significant anti-cancer properties. There are more than 11 distinguished classes of saponins including dammaranes, tirucallanes, lupanes, hopanes, oleananes, taraxasteranes, ursanes, cycloartanes, lanostanes, cucurbitanes and steroids. Due to the great variability of their structures, saponins always display anti-tumorigenic effects through varieties of antitumor pathways. In addition, there are a large amount of saponins that still either remain to be trapped or studied in details by the medicinal chemists. This article reviews many such structures and their related chemistry along with the recent advances in understanding mechanism of action and structure-function relationships of saponins at the molecular and cellular levels. These aglycones have been described and their classification and distribution have been listed in the review. Some special saponins with strong antitumor effects have also been exhibited. Ginsenosides, belonging to dammaranes, have been found beneficial targeted on inhibition of tumor angiogenesis by suppressing its inducer in the endothelial cells of blood vessels, and then on prevention of adhering, invasion, and metastasis of tumor cells. Dioscin, one of the steroidal saponins, and its aglycone diosgenin also have been extensively studied on its antitumor effect by cell cycle arrest and apoptosis. Other important molecules discussed include oleanane saponins such as avicins, platycodons, saikosaponins, and soysaponins along with tubeimosides.

Triterpenoids

This review covers the isolation and structure determination of triterpenoids including squalene derivatives, protostanes, lanostanes, holostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, lupanes, oleananes, friedelanes, ursanes, hopanes, isomalabaricanes and saponins; 574 references are cited.

Cytotoxic activity and inhibitory effect on nitric oxide production of triterpene saponins from the roots of Physospermum verticillatum (Waldst & Kit) (Apiaceae)

Three triterpene saponins isolated from the roots of Physospermum verticillatum and identified as saikosaponin a (1), buddlejasaponin IV (2), and songarosaponin D (3) were investigated in vitro for their cytotoxic activity against a panel of seven different cancer cell lines including ACHN, C32, Caco-2, COR-L23, A375, A549, and Huh-7D12 cell lines. The hydrolysis of sugar unit was performed on saikosaponin a (1) to obtain saikosapogenin a (4). All isolated saponins exhibited strong cytotoxic activity against COR-L23 cell line with IC(50) values ranged from 0.4 to 0.6 microM. A similar activity was recorded for saikogenin a (4). None of the tested compounds affected the proliferation of skin fibroblasts 142BR suggesting a selective action against cancer cells. Moreover, buddlejasaponin IV (2) and songarosaponin D (3) exerted significant inhibition of NO production in LPS induced RAW 264.7 macrophages with IC(50) of 4.2 and 10.4 microM, respectively.

The Flavonoids and Phenolic Acids of the Genus Silphium and Their Chemosystematic Value

The current review outlines the distribution of flavonoids and phenolic acids in eleven species of Silphium (Asteraceae). The chemosystematic significance of these findings is discussed and compared with DNA and morphological-based assignments for eleven species. Special attention is given to the five flavonol triglycosides that were previously isolated and characterized from Silphium species: isorhamnetin 3- O-α-L-rhamnosyl (1″′→6″)- O-β-D-galactopyranoside 7- O-β-L-apiofuranoside (1), quercetin 3- O-α-L-rhamnosyl (1″′→6″)- O-β-D-galactopyranoside 7- O-β-L-apiofuranoside (2), quercetin 3- O-β-L-galactosyl (1″′→6″)- O-β-D-rhamnopyranoside 7- O-α-L-apiofuranoside (3), kaempferol 3- O-β-D-apiofuranoside 7- O-αL-rhamnosyl (1″″→6″′)- O-β-D-galactopyranoside (4) and kaempferol 3- O-β-D-apiofuranoside 7- O-α-L-rhamnosyl (1″″→6″′)- O-βD (2″′- O- E-caffeoylgalactopyranoside) (5). In addition, several other known mono and diglycosidic flavonoids, along with 18 phenolic acids, were also identified and the structures of all of the compounds were established by LC/MS and NMR spectral investigations.