Synthesis, Formulation, and Adjuvanticity of Monodesmosidic Saponins with Olenanolic Acid, Hederagenin and Gypsogenin Aglycones, and some C-28 Ester Derivatives

Adjuvant activity of tubeimosides by mediating the local immune microenvironment

Rhizoma Bolbostemmatis, the dry tuber of Bolbostemma paniculatum, has being used for the treatment of acute mastitis and tumors in traditional Chinese medicine. In this study, tubeimoside (TBM) I, II, and III from this drug were investigated for the adjuvant activities, structure-activity relationships (SAR), and mechanisms of action. Three TBMs significantly boosted the antigen-specific humoral and cellular immune responses and elicited both Th1/Th2 and Tc1/Tc2 responses towards ovalbumin (OVA) in mice. TBM I also remarkably facilitated mRNA and protein expression of various chemokines and cytokines in the local muscle tissues. Flow cytometry revealed that TBM I promoted the recruitment and antigen uptake of immune cells in the injected muscles, and augmented the migration and antigen transport of immune cells to the draining lymph nodes. Gene expression microarray analysis manifested that TBM I modulated immune, chemotaxis, and inflammation-related genes. The integrated analysis of network pharmacology, transcriptomics, and molecular docking predicted that TBM I exerted adjuvant activity by interaction with SYK and LYN. Further investigation verified that SYK-STAT3 signaling axis was involved in the TBM I-induced inflammatory response in the C2C12 cells. Our results for the first time demonstrated that TBMs might be promising vaccine adjuvant candidates and exert the adjuvant activity through mediating the local immune microenvironment. SAR information contributes to developing the semisynthetic saponin derivatives with adjuvant activities.

An investigation of the antileishmanial properties of semi-synthetic saponins

Leishmaniasis is a neglected tropical disease caused by insect-vector borne protozoan parasites of the, Leishmania species. Whilst infection threatens and affects millions of the global poor, vaccines are absent and drug therapy limited. Extensive efforts have recently been made to discover new leads from small molecule synthetic compound libraries held by industry; however, the number of new chemical entities identified and entering development as anti-leishmanials has been very low. This has led to increased interest in the possibility of discovering naturally derived compounds with potent antileishmanial activity which may be developed towards clinical applications. Plant-derived triterpenoid and steroidal saponins have long been considered as anti-microbials and here we describe an investigation of a library of 137 natural (9) and semi-synthetic saponins (128) for activity against Leishmania mexicana, a causative agent of cutaneous leishmaniasis. The triterpenoid sapogenin, hederagenin, readily obtained in large quantities from Hedera helix (common ivy), was converted into a range of 128 derivatives. These semi-synthetic compounds, as well as saponins isolated from ivy, were examined with a phenotypic screening approach to identify potent and selective anti-leishmanial hits. This led to the identification of 12 compounds, including the natural saponin gypsogenin, demonstrating high potency (ED50 < 10.5 μM) against axenic L. mexicana amastigotes, the mammalian pathogenic form. One of these, hederagenin disuccinate, was sufficiently non-toxic to the macrophage host cell to facilitate further analyses, selectivity index (SI) > 10. Whilst this was not active in an infected cell model, the anti-leishmanial properties of hederagenin-derivatives have been demonstrated, and the possibility of improving the selectivity of natural hederagenin through chemical modification has been established.

What is the aquatic toxicity of saponin-rich plant extracts used as biopesticides?

Saponin-rich extracts from Quillaja saponaria and Chenopodium quinoa have been registered by US EPA as active ingredients in biopesticides, and extract from tea seed powder, Camellia oleifera has been proposed for biocidal use. If saponin-rich biopesticides are efficient against pests, they are most likely also bioactive in the aquatic environment against non-target organisms. The aim of this study was to conduct an effect assessment of saponin-rich plant extracts by using species sensitivity distributions based on acute toxicity tests. The maximal concentrations protecting 95% of the aquatic species (HC₅) of saponins extracted from quillaja bark, tea seed coat and quinoa seed coat were 2.91 ± 1.00, 0.22 ± 0.11 and 22.9 ± 5.84 mg/L, respectively. The 100-fold difference in toxicity between the saponin-rich extracts from different plant species, indicate that saponin toxicity depends on the species it origins from, making "read-across" between saponins a dubious exercise. In addition, the predicted environmental concentrations of different saponins are close to or higher than their water quality standard, which means that the extracts might pose a risk to the aquatic environment if not used cautiously.

Elucidating the Mechanisms of Action of Saponin-Derived Adjuvants

Numerous triterpenoid saponins are adjuvants that modify the activities of T cells and antigen-presenting cells, like dendritic cells (DCs). Saponins can induce either proinflammatory Th1/Th2 or sole anti-inflammatory Th2 immunities. Structure-activity relationships (SARs) have shown that imine-forming carbonyl groups are needed for T cell activation leading to induction of Th1/Th2 immunities. While saponins having different triterpenoid aglycons and oligosaccharide chains can activate DCs to induce Th1/Th2 immunoresponses, fucopyranosyl residues from their oligosaccharides by binding to the DC-SIGN receptor can bias DCs toward a sole Th2 immunity. Here we discuss the mechanisms of action of these saponins in view of new information, which may serve as a basis to design improved adjuvants and related drugs.

Preparation and antitumor evaluation of self-assembling oleanolic acid-loaded Pluronic P105/d-α-tocopheryl polyethylene glycol succinate mixed micelles for non-small-cell lung cancer treatment

Oleanolic acid (OA) is a triterpenoid found in various fruits and vegetables and used in traditional Chinese medicine. OA plays a crucial role in the treatment of several cancers, but poor water solubility, low permeability, and significant efflux have limited its widespread clinical use. Vitamin E-d-α-tocopheryl polyethylene glycol succinate (vitamin E-TPGS) and Pluronic P105 were used to improve the solubility and permeability and to decrease the efflux of OA. OA-loaded mixed micelles were prepared by ethanol thin-film hydration. The physicochemical properties of the micelles, including zeta potential, morphology, particle size, solubility, drug loading, and drug entrapment efficiency were characterized. OA release from micelles was slower than that from the free drug system. OA uptake by A549 non-small-cell lung cancer (NSCLC) cells was enhanced by the micelles. A tumor model was established by injecting A549 cells into nude mice. In vivo imaging showed that OA-micelles could accumulate in the tumors of nude mice. Additionally, smaller tumor size and increased expression of pro-apoptotic proteins were observed in OA-micelle-treated mice, indicating that OA-micelles are more effective than free OA in treating cancer. In vitro experiments were performed using two NSCLC cell lines (A549 and PC-9). Cytotoxicity evaluations showed that the half-maximal inhibitory concentrations of free OA and OA-micelles were 36.8±4.8 and 20.9±3.7 μM, respectively, in A549 cells and 82.7±7.8 and 56.7±4.7 μM, respectively, in PC-9 cells. Apoptosis assays revealed that the apoptotic rate of OA-micelle-treated A549 and PC-9 cells was higher than that of cells treated with the same concentration of free OA. Wound healing and transwell assays showed that migration and invasion were significantly suppressed in OA-micelle-treated cells. Immunofluorescence and Western blot analyses confirmed that the epithelial–mesenchymal transition was reversed in OA-micelle-treated cells. Mixed micelles are a promising nano-drug delivery system for lung cancer treatment.

Synthesis, Formulation, and Adjuvanticity of Monodesmosidic Saponins with Olenanolic Acid, Hederagenin and Gypsogenin Aglycones, and some C-28 Ester Derivatives

In an attempt to discover a new synthetic vaccine adjuvant, the glycosylation of hederagenin, gypsogenin, and oleanolic acid acceptors with di- and trisaccharide donors to generate a range of mimics of natural product QS-21 was carried out. The saponins were formulated with phosphatidylcholine and cholesterol, and the structures analyzed by transmission electron microscopy. 3-O-(Manp(1→3)Glcp)hederagenin was found to produce numerous ring-like micelles when formulated, while C-28 choline ester derivatives preferred self-assembly and did not interact with the liposomes. When alone and in the presence of cholesterol and phospholipid, the choline ester derivatives produced nanocrystalline rods or helical micelles. The effects of modifying sugar stereochemistry and the aglycone on the immunostimulatory effects of the saponins was then evaluated using the activation markers MHC class II and CD86 in murine bone marrow dendritic cells. The most active saponin, 3-O-(Manp(1→3)Glcp)hederagenin, was stimulatory at high concentrations in cell culture, but this did not translate to strong responses in vivo.