Two New Oleanane Saponins from Anemone flaccida

New triterpenoid saponins from the whole plants of Clematis heracleifolia

Three new triterpenoid saponins, heracleifolianosides A-C (1-3), together with seven known compounds (4-10), were isolated from the whole plants of Clematis heracleifolia. Moreover, three new secondary saponins (1a, 2a and 3a), two known secondary metabolites (5a and 7a) were obtained by alkaline hydrolysis. Their structures were elucidated by extensive spectroscopic analysis and chemical evidences. The cytotoxicity of eight native saponins and five prosapogenins against human breast tumor MDA-MB-231 and gastric carcinoma SGC-7901 cell lines were evaluated by MTT method. Remarkably, the prosapogenin monodesmosidic saponin 7a showed significant cytotoxicity against MDA-MB-231 or SGC-7901 cell lines with IC₅₀ values in the range of 6.05-6.32 μmol/L. It is suggested that it might be a feasible way to change the inactive bisdesmosic triterpenoid saponins to active monodesmosic saponins by a simple procedure of alkaline hydrolysis.

Chemical Synthesis of Saponins

Saponins are a large family of amphiphilic glycosides of steroids and triterpenes found in plants and some marine organisms. By expressing a large diversity of structures on both sugar chains and aglycones, saponins exhibit a wide range of biological and pharmacological properties and serve as major active principles in folk medicines, especially in traditional Chinese medicines. Isolation of saponins from natural sources is usually a formidable task due to the microheterogeneity of saponins in Nature. Chemical synthesis can provide access to large amounts of natural saponins as well as congeners for understanding their structure-activity relationships and mechanisms of action. This article presents a comprehensive account on chemical synthesis of saponins. First highlighted are general considerations on saponin synthesis, including preparation of aglycones and carbohydrate building blocks, assembly strategies, and protecting-group strategies. Next described is the state of the art in the synthesis of each type of saponins, with an emphasis on those representative saponins having sophisticated structures and potent biological activities.

Flaccidoside II ameliorates collagen-induced arthritis in mice

Flaccidoside II (FLA II), the primary active constituent from Anemone flaccida rhizome, was proven to exert therapeutic effect against collagen-induced arthritis (CIA). In this study, a research based on the CIA mouse model was carried out in order to elucidate its therapeutic mechanisms preliminarily. The mice were immunized with porcine type-II collagen to induce CIA and administrated intragastrically with FLA II daily from day 7-42 of the first collagen immunization. The arthritis scores as reflected by the severity of paw swelling and erythema were significantly reduced in FLA II (32 mg/kg) from day 33 onwards. On day 42, the joints of FLA II-treated mice exhibited obvious reductions of inflammatory cells infiltration, synovial hyperplasia and bone destruction. When the concentration of FLA II was no less than 40 nmol/ml, the treatment notably inhibited T and B lymphocyte proliferative responses. As compared to the model group, in FLA II groups, the serum levels of pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α) were significantly decreased while those of Th2 type cytokines (IL-4 and IL-10) were clearly enhanced. In addition, FLA II treatment showed little regulatory effect on the levels of Th1 type cytokines (IFN-γ and IL-2). The severity of mice CIA was improved by FLA II, further confirming its potential value for the safe treatment of rheumatoid arthritis. The main mechanisms likely involve the inhibition of lymphocyte proliferation and pro-inflammatory cytokine secretion, and the modulation of Th1/Th2-related cytokine balance in CIA.

Triterpenoid saponin flaccidoside II from Anemone flaccida triggers apoptosis of NF1-associated malignant peripheral nerve sheath tumors via the MAPK-HO-1 pathway

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive soft tissue neoplasms that are extremely rare and are frequently associated with neurofibromatosis type 1 patients. MPNSTs are typically fatal, and there is no effective treatment so far. In our previous study, we showed that flaccidoside II, one of the triterpenoid saponins isolated from Anemone flaccida Fr. Schmidt, has antitumor potential by inducing apoptosis. In the present study, we found that flaccidoside II inhibits proliferation and facilitates apoptosis in MPNST cell lines ST88-14 and S462. Furthermore, this study provides a mechanism by which the downregulation of heme oxygenase-1 via extracellular signal-regulated kinase-1/2 and p38 mitogen-activated protein kinase pathways is involved in the apoptotic role of flaccidoside II. This study suggested the potential of flaccidoside II as a novel pharmacotherapeutic approach for MPNSTs.

Total Saponin from Anemone flaccida Fr. Schmidt Prevents Bone Destruction in Experimental Rheumatoid Arthritis via Inhibiting Osteoclastogenesis

Anemone flaccida Fr. Schmidt is used in the clinical compound prescription for the treatment of rheumatoid arthritis (RA) in China and has the traditional use of draining dampness, diminishing swelling, and relieving pain. Total saponins (TS) are the characteristic components and also the main active ingredients of A. flaccida. Previous reports indicated that TS possess anti-inflammatory and immunoregulatory properties; however, the effects of TS on bone destruction of RA have not been evaluated. In this study, our data first showed the therapeutic effects of TS on severity of arthritis and arthritis progression in collagen-induced arthritis (CIA) rats. Then, by microfocal computed tomography (CT) quantification, TS significantly increased bone mineral density, bone volume fraction, and trabecular thickness and decreased trabecular separation of inflamed joints both at peri-articular and extra-articular locations. TS also diminished the level of the bone resorption marker CTX-I and simultaneously increased the bone formation marker osteocalcin in sera of CIA rats. Interestingly, TS prevented bone destruction by reducing the number of osteoclasts in inflamed joints, reducing the expression of receptor activator of nuclear factor-κF (RANK) ligand (RANKL) and RANK, increasing the expression of osteoprotegerin (OPG), at both mRNA and protein levels, and decreasing the ratio of RANKL to OPG in inflamed joints and sera of CIA rats. This was further confirmed in the co-culture system of human fibroblast-like synovial and peripheral blood mononuclear cells. In addition, TS inhibited the levels of pro-inflammatory cytokines implicated in bone resorption, such as interleukin-1β (IL-1β), tumor necrosis factor-α (TNFα), IL-6, IL-17, and IL-23 in sera and joints. These findings offer convincing evidence that TS attenuate RA partially by preventing both focal bone destruction and systemic bone loss. This anti-erosive effect results in part from inhibiting osteoclastogenesis by regulating the RANKL/RANK/OPG signaling pathway. The suppression of systemic and local pro-osteoclastogenic cytokines by TS was also highly effective.

Chemical synthesis of saponins

Saponins are a large family of amphiphilic glycosides of steroids and triterpenes found in plants and some marine organisms. By expressing a large diversity of structures on both sugar chains and aglycones, saponins exhibit a wide range of biological and pharmacological properties and serve as major active principles in folk medicines, especially in traditional Chinese medicines. Isolation of saponins from natural sources is usually a formidable task due to the microheterogeneity of saponins in Nature. Chemical synthesis can provide access to large amounts of natural saponins as well as congeners for understanding their structure-activity relationships and mechanisms of action. This article presents a comprehensive account on chemical synthesis of saponins. First highlighted are general considerations on saponin synthesis, including preparation of aglycones and carbohydrate building blocks, assembly strategies, and protecting-group strategies. Next described is the state of the art in the synthesis of each type of saponins, with an emphasis on those representative saponins having sophisticated structures and potent biological activities.

Triterpenoid saponins from the rhizomes of Anemone flaccida and their inhibitory activities on LPS-induced NO production in macrophage RAW264.7 cells

A new ursane-type triterpenoid saponin, flaccidoside IV (1), and three new oleanane-type triterpenoid saponins, flaccidosides V-VII (2-4), along with 17 known saponins (5-21), were isolated from the rhizomes of Anemone flaccida. The structures of the new triterpenoid saponins were determined based on spectroscopic analyses and chemical methods. All the isolated saponins were tested for their inhibitory activities on lipopolysaccharide-induced nitric oxide production in RAW264.7 macrophages, and several bisdesmosidic oleanane-type triterpenoid saponins (2, 7, and 10) showed significant inhibitory activities, which indicated they had potential anti-inflammatory activities under their noncytotoxic concentrations in vitro.

Triterpenoid saponins from Anemone flaccida induce apoptosis activity in HeLa cells

Five triterpenoid saponins were isolated from Anemone flaccida Fr. Schmidt. Their structures were identified as glycoside St-I4a (1), glycoside St-J (2), anhuienoside E (3), hederasaponin B (4), and flaccidoside II (5). Compounds 1-2 were isolated from Anemone family for the first time, and compounds 3-4 were isolated from this plant for the first time. The inhibitory effects of saponins on proliferation of HeLa cells were studied by MTT assay, the apoptosis-induction activity was observed by cell-cycle analysis and caspase-3 expression assay. The antitumor activities of the saponins were ranked in the following order: 5 > 3 > 4 > 1 > 2. The data presented here indicated that naturally occurring triterpenoid saponins can be regarded as excellent structures for the potential development of new anticancer agents.

Four new oleanane saponins from Anemone anhuiensis

Four new oleanane triterpene saponins, anhuienosides C-F, together with three known saponins, were isolated from the rhizomes of Anemone anhuiensis (Ranunculaceae). The structures of anhuienosides C-F were elucidated as 3-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-xylopyranosyl oleanolic acid 28-O-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl ester, 3-O-beta-D-xylopyranosyl oleanolic acid 28-O-alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl ester, 3-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucopyranosyl oleanolic acid 28-O-alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl ester, 3-O-beta-D-glucopyranosyl-(1-->3)-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-xylopyranosyl oleanolic acid 28-O-alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl ester, respectively.