This article throws light upon the top five activities by triterpenoid saponins. The activities are: 1. Immunological Activity by Triterpenoid Saponins 2. Cytotoxicity and Antitumor Activity by Triterpenoid Saponins 3. Anti-Inflammatory Activity 4. Antiviral Activity 5. Other Activities.
Activity # 1. Immunological Activity by Triterpenoid Saponins:
Botanicals alter immune functions in mode of modulating cytokine secretion, immunoglobulin secretion, cellular co-receptor expressions, lymphocyte expressions and phagocytosis, to exhibit immunomodulatory activity (Patwardhan and Gautam, 2005; Plaeger, 2003). Many saponins from natural sources have been included in this list of botanical immunomodulators (Kensil, 1996).
Triterpenoid saponins from Quillaja saponaria Molina and Panax ginseng C.A. Meyer, lead this list for its profound action on immune systems. In vitro study reported the increase of immune cell proliferation by Quillaja and other saponins either as crude extract or as pure compound (Chavali et al., 1987; Plohmann et al., 1997; Lacaille- Dubois et al., 1999).
In another study Quillaja saponins QH-A and QH-C in various formulations showed an in vitro and in vivo induction of IL-6 (Behboudi et al., 1997).
The purified saponins QS- 7, QS-1 7, QS-18, and QS-21 from quillaja bark increase the antibody levels by 100 fold or more in Ag BSA and beef liver cytochrome b5 immunized mouse. The same study also confirmed the toxicity of QS-18 unlike QS-7 and QS-21 (Kensil et al., 1991).
The action of Qui I A (quillaja saponins) on Th1/ Th2 immune response and the production of cytotoxic T-lymphocytes (CTLs) have promoted it as vaccine adjuvant (Sjolander et al., 1997; So et al., 1997; Coulter et al., 1998).
Further this, saponin led to form immune-stimulating complex (ISCOM), in combination with cholesterol, phospholipid, amphiphatic proteins. The adjuvant activity of ISCOM or quillaja saponins alone have been in interest for vaccine based research, since early 80’s.
The in vivo study on ICR mice reported significant increase of lgG1 level along with adjuvant effect on antigen specific lgG2a, lgG2b and lgG3 of QS-21 in combination with three type O-side-chain polysaccharide containing vaccine, compare to immunogenicity of vaccines alone (Coughlin et al., 1995).
In another study ISCOMs induced antibody response and/or protective immunity were evaluated in many experimental mammalian animals (Mowat et al., 1999). Pham et al. (Pham et al., 2006) reported the isolation of QS-7, QS-17, QS-18, and QS-21 by fractionation of Quil A and out of which only QS-7 was able to form prominent structures and a minor amount of ISCOMs in combination with lipid.
The immunomodulatory activity of ginsenoside Rg1 from Panax ginseng was evaluated by stimulating humoral immune responses of sheep red blood cells immunized mice.
Ginsenoside Rgl also increased the number of T-helper cells and production of IL-1 by macrophages (Kenarova et al., 1990). Further study reported the Th2 specific immune response of Ginsenoside Rg1 by enhancing CD4 (+) T cells and Th2 cytokine IL-4 (Lee et al., 2004).
A crude ginseng extract (GS) and the purified ginsenoside R(b1) (R(b1)) were evaluated for their adjuvant effects in dairy cattle at immunization with ovalbumin (OVA) and/or a Staphylococcus aureus bacterin.
Both GS and R (b1) were safe adjuvants, and R(b1) had the strongest adjuvant effects, when used for immunization against S. aureus in dairy cattle (Hu et al., 2003).
Ginseng-fraction Rb1 containing Porcine parvovirus (PPV) vaccines induced IL-4 and IL-10 in pre-boost animals and IFN-gamma, IL-2, IL-4, IL-10 and TNF-alpha in post-boost mice along with similar antibody titres in pre and post-boost mice, concluded the balanced Th1 and Th2 immune response of Rbl fraction as vaccine adjuvant (Rivera et al., 2005).
Pro-topanaxadiol saponins (Rg3, Rd, Rc, Rb1 and Rb2) and protopanaxatriol saponins (Rg1, Re and Rg2) from the root of Panax ginseng were evaluated for their adjuvant effects in ovalbumin (OVA) immunized mice by increasing antibody responses and cytokine production.
The study showed Rg1, Re, Rg2, Rg3 and Rbl have more potent adjuvant properties than the others, indicating that they are the major constituents contributing to the adjuvant activities of total ginseng saponins (Sun et al., 2007).
Saponins extracted from ginseng stems and leaves (GSLS) and GSLS with oil emulsion showed potent adjuvant effects by modulating cellular and humoral immune responses and by promoting both Th1 and Th2 immune responses of mice to vaccination against foot-and-mouth disease virus (FMDV) serotype
Asia 1 (Song et al., 2009). Triterpenoid saponins from Clycyrrhiza uralensis showed humoral and cellular immune response similar to Quil A in Oval albumin immunized ICR mice by stimulating splenocyte proliferation and enhancing OVA- specific IgG, lgG1, and lgG2b antibody responses (Sun and Pan, 2006).
Platycodin D2 (PD2), triterpenoid saponin from Platycodon grandiflorum showed potent immunomodulatory activity in Ovalalbumin immunized ICR mice by stimulating splenocyte proliferation and enhancing OVA- specific IgG, lgG1, and lgG2b antibody responses, which concluded the balanced Th1 and Th2 directing immune response by the saponins (Xie et al., 2008; Xie et al., 2008).
A novel triterpenoidal saponin, called pulcherrimasaponin (CP05) from the leaves of Calliandra pulcherrima Benth showed vaccine adjuvant activity similar to QS21 saponin (Quillaja saponaria Molina) with fucose- mannose ligand (FML) antigen of Leishmania donovani by enhancing FML specific antibody responses and delayed type hypersensitivity against leishmanial antigen (Silva et al., 2005).
Another study specified the vaccine adjuvant activity by monoterpene deprived fraction of CP05 in comparison with QS21 saponin with same FML vaccines. Where intact saponins CP05, which lacks the C4 aldehyde group was unable to augment anti-FML antibody, CD4 (+) and CD8 (+) Leishmania specific lymphocytes and IFN-gamma splenocyte secretion (Nico et al., 2005).
Eight pure triterpenoid saponins from Polygala senega L. have been reported for potent immunomodulatory activity against OVA immunized mice and enhancement of IL-2 levels in in vitro study of spleen cell culture from immunized mice (Katselis et al., 2007).
Triterpenoid saponins from Acacia victoriae, have been reported for its modification of NF- êâ molecule to prevent stimulation of genes involved in immune and inflammatory pathways in response to stress signal (Haridas et al., 2001).
Activity # 2. Cytotoxicity and Antitumor Activity by Triterpenoid Saponins:
Triterpenoid saponins from plant species reported for antitumor activity for allogeneic sarcoma 180 and syngeneic DBA/2-MC.SC-1 fibro sarcoma tumor models, which presumed to be driven by immunomodulation effect by augmentation of TNF-alpha release (Plohmann et al., 1997).
Aster-lingulatoside C and D, triterpenoid saponins from Aster lingulatus, showed good inhibitory activity against NA synthesis in human leukemia HL-60 cells with IC50 values of 8.8 and 6.1 microM, respectively (Shao et al., 1997).
Novel triterpenoid saponins, capilliposide A-C from Lysimachia capillipes evaluated for cytotoxic activity, where only capilliposide B showed significant cytotoxicity against human A-2780 cells (Tian et al., 2006).
Albizia adianthifolia (Mimosaceae) triterpenoid saponins reported for induction of apoptosis on human leukemia cells. The result showed cytotoxic and/or lymph proliferative effect of adianthifoliosides A, B, and D (AdA, AdB, and AdD) and prosapogenins (Prol and Pro2) on human leukemia T-cells (Jurkat cells), where only lymphoproliferative effect found on splenocytes.
The study suggested the apoptosis as an alternative mechanism for cytotoxic activity other than membrane permeabilization formation (Haddad et al., 2004).
Study on triterpenoid saponins form Chinese horse chestnut seeds showed vacuolization, apoptotic nuclei fragmentation and apoptotic body formation in human leukaemia cells as signs of apoptosis, which could be established the mechanism of action for cytotoxic effect. Whereas, anti-proliferative activity of saponins on the same cell lines were caused by cell cycle arrest at G1 -S phase (Niu et al., 2008).
Ginsenoside Rg3 exhibited the anti-proliferative activity by seems to be same mechanism. The apoptosis induction in human cancer and other cell lines by saponins irrespective of triterpenoid or steroid can be caused by stimulating cytochrome c—caspase 9—caspase 3 pathway (Lee et al., 2000; Liu et al., 2000; Haridas et al., 2001; Cai et al., 2002).
The property was followed for cytotoxic activity showed by triterpenoid saponins from Securidaca inappendiculata (Yui et al., 2001).
Symplocososides G-K, triterpenoid saponins from root of Symplocos chinensis, showed significant cytotoxicity against cancer cell lines KB, HCT-8, Bel-7402, BGC-823 and A549 with IC (50) values ranging from 0.82 muM to 5.09 muM, except for symplo- cososide I against cancer cell lines KB, BGC-823, A549 and symplocososide K against cancer cell line BGC-823 with IC (50) values >10.00 muM (Fu etal., 2005).
However, the diverse groups of saponins from variety of plant species have shown cytotoxic activity in different manner.
As in recent work, apoptosis based mechanism for cytotoxicity of triterpenoid saponins was challenged by avicin D. This triterpenoid saponins were able to cause the death for apoptosis inhibitor (benzyloxycarbonyl- valyl-alanyl-aspartic acid (O-methyl)-fluoro-meth- ylketone) treated and apoptosis-resistant cells.
This non-apoptotic cell death claimed to be mediated by different mechanism, autophagy, which can be regulated by set of events like, decreasing cellular ATP levels, stimulating the activation of AMP- activated protein kinase (AMPK), and inhibiting mammalian target of rapamycin (mTOR) and S6 kinase activity.
The autophagy cell death was found to be decreased by inhibiting the events from AMPK to mTOR, which put a further support to hold autophagy as a mechanism for cell death (Xu et al., 2007). Soyasaponins from soya bean also showed the cytotoxicity for human colon cancer cells by induction of macro autophagy (Ellington et al., 2005).
The triterpenoid saponins-initiated tumor-specific cytotoxicity seems to be structure related and sugar moieties were found to be responsible for this action (Hosny and Rosazza, 2002).
The finding further supported by a work on enzymatic hydrolysis of virgaureasaponin 1 (triterpenoid saponins), where sugar moieties showed the cytotoxic activity (Bader et al., 1998). The study on cytotoxic activity of hederagenin also supported the structural activity relationship (Chwalek et al., 2006).
Activity # 3. Anti-Inflammatory Activity by Triterpenoid Saponins:
Six triterpenoid saponins from the roots of Codonopsis lariceolata, were investigated for anti-inflammatory activity.
The isolated new compound named codonolaside III, showed promising inhibitory effect for xylene-induced mouse ear edema compare to other triterpenoid saponins (Xu et al., 2008). A new triterpenoid saponin from Carthamus tinctorius linn., showed anti-inflammatory activity in experimental model (Yadava and Chakravarti, 2008).
A comparative study of anti-inflammatory activity in mice model between isolated triterpenoid saponins and total saponins extract of Aesculus chinensis, showed a potent activity by isolated compound than total extract (Wei et al., 2004).
Inhibition of carrageenan induced rat paw oedema was showed by triterpenoid saponins from Polygala japonica. The saponins were found to inhibit the production of inflammatory mediators-nitric oxide (NO) in LPS-stimulated RAW264.7 macrophages, advocated the anti-inflammatory activity by compounds (Wang et al., 2008).
Anti-rheumatic effect of triterpenoid glycoside nigaichigoside F1 (NIF1) and its aglycone 23-hydroxytormentic acid (23-HTA) from Rubus coreanus (Rosaceae) were investigated in Freund’s complete adjuvant-induced rheumatism in rats.
The saponins were significantly decreasing rheumatoid arthritis (RA) factor and C-reactive protein (CRP) factor, which was found to be reason for anti-rheumatic effect of compounds (Nam et al., 2006). The triterpenoid saponins (Avicin) showed anti-inflammatory activity by suppressing pro-inflammatory components of the innate immune system in human cells by redox regulation (Haridas et al., 2004).
Triterpenoid saponins, clematichinenosides AR and AR (2) from Clematis chinensis Osbeck, also showed anti-inflammatory activity by the same mechanism (Liu et al., 2009). In structure-activity relationship study for anti-inflammatory activity of tubeimosides showed the key role of C-16 hydroxyl group for the effect.
In the study Tubeimosides I, II, and III form Bolbostemmapaniculatum (Maxim) Franquet (Cucurbitaceae) were investigated for anti-inflammatory activity, where C-16 hydroxyl group containing tubeimosides II only showed potent effect (Yu et al., 2001).
Activity # 4. Antiviral Activity by Triterpenoid Saponins:
Diverse group of triterpenoid saponins have been reported for antiviral activity against various viruses and their mechanism of action also found to be erratic.
Tubeimoside-1 (Tub), the triterpenoid saponin from Bolbostemma paniculatum (Maxim) Franquet, showed anti-HIV activity by mechanism of inhibiting HIV core protein p24 production and HIV mediated cytopathogenesis HTLV-IIIB and also by neutralizing the infection of 2 other isolates, HTLV-IIIRF and HTLV-IIIMN (Yu et al., 1994).
Triterpenoid saponins (zingibroside R1) were also reported for anti-HIV activity mediated by cytotoxicity (Hasegawa et al., 1994). Cleditsia saponin C and gymnocladus saponin C from Gleditsia japonica and Cymnocladus chinensis, respectively, were shown anti-HIV activity by following the same principles (Konoshima et al., 1995).
Ardisia japonica triterpenoid saponins showed anti-HIV activity in in vitro experiment (Piacente et al., 1996). Whereas, triterpenoid saponins from natural sources showed antiviral activity against herpes simplex virus type 1 either by inhibiting viral DNA synthesis (by oleanolic group) or by inhibiting viral capsid protein synthesis (by ursane group) but never shown any cytotoxic activity (Simoes et al., 1999).
Antiviral activity of Quillaja extracts against six viruses: vaccinia virus, herpes simplex virus type 1, varicella zoster virus, human immunodeficiency viruses 1 and 2 (HIV-1, HIV-2) and reovirus were also supported the mechanism based upon direct virucidal activity other than cell cytotoxicity (Roner et al., 2007).
Oleanolic acid glycosides from Calendula armsis were reported for antiviral effects by inhibition of vesicular stomatitis virus (VSV) and rhinovirus (HRV) infection in cell cultures (De Tommasi et al., 1991).
The study on synthetic triterpenoid saponins revealed the responsibility of sugar linkage for antiviral activity (Takechi et al., 2003). In other study acylated triterpenoid saponins from Maesa lanceolata showed antiviral activity which was related to the di-acylation of compounds (Apers et al., 2001).
Some triterpenoid saponins were also found to be effective against type A influenza virus by their structure modification (Flekhter et al., 2007). Six triterpenoid saponins (oblonganoside A-F) from Ilex oblonga were reported for their activity against Tobacco mosaic virus (TMV) by inhibiting TMV replication (Wu et al., 2007).
In a recent study, astragaloside IV, a triterpenoid saponin from Chinese herb radix Astragali (huangqi) showed potent anti-hepatitis B virus (HBV) activity in duck hepatitis B virus (DHBV)-infected ducklings (Wang et al., 2009), which also supported the previous anti-HBV activity showed by whole extract of same plant.
Activity # 5. Other Activities of Triterpenoid Saponins:
Saponins are found to have hemolytic activity, irrespective of their aglycone structure. The triterpenoid saponins form Symplocos glomerata King showed 50% haemolysis of a 10% suspension of sheep erythrocytes (Waffo-Teguo et al., 2004). Acylated triterpenoid saponins from Harpullia austrocaledonica also caused 100% haemolysis of a 10% suspension of sheep erythrocytes (Voutquenne et al., 2005).
In another study, Mae- sasaponin mixture B from Maesa lanceolata hemo- lyzed 50% of human erythrocytes (1 % suspension) at concentration of 1.6 microg/mL (Sindambiwe et al., 1998). However the mechanism for hemolytic activity is not fully understood.
In that context Lin and Wang reported that triterpenoid saponins (dioscin) possibly caused the destabilization of membrane by penetrating the membrane lipid bi-layer and consequent membrane curvature, which may eventually result in the hemolysis of red cells (Lin and Wang, 2009).
SoyasaponinsI and III, and de-hydro-soya-saponin I caused membrane hyperpolarization by opening large Ca-dependent K conductance channels, which relaxed smooth muscle (McManus et al., 1993).
Glycosides Rb1, Rg1, 20 (S) pro-topanaxadiol also showed the effect on lipid bilayer (DPPC) for phase transition (Akoev et al., 1997). The ability of acylated triterpenoid saponins from ginseng to integrate transiently into membrane and to form pore like structure, were suggested that the hemolytic activity directly dependent on the numbers of polar groups in aglycone moiety (Namba et al., 1973).
It was also observed that triterpenoid saponins with a single sugar chain (monodesmosides) showed more hemolytic potential than those with a two sugar chains (bidesmosides) (Fukuda et al., 1985; Woldemichael and Wink, 2001).
Besides, cell membrane permeabilization and hemolytic activity triterpenoid saponins like hederagenin or oleanolic acid also showed antifungal activity on Yeast as well as Dermatophyte species and Candida glabrata (Favel et al., 1994).
Triterpenoid saponins from Pithecellobium race-mosum (M.) were found to have moderate antifungal activity against T. mentogrophytes, C. albicans and S. cerevisiae with MIC values of 6.25, 12.5 and 12.5 micrograms/ml respectively (Khan et al., 1997).
Glycosides of polygalacic acid were evaluated for antifungal activity in micro-dilution assay by using various funguses: Candida albicans, C. glabrata, C. krusei and C. tropicalis (Bader et al., 2000). The molluscicidal activity was also found in glycosides of oleanolic acid of Dialium guineense (Houghton et al., 1997).
Platycodin A, from Platycodi radix exhibited significant neuroprotective activities against giutamate-induced toxicity, exhibiting cell viability of about 50%, at concentrations ranging from 0.1 microM to 10 microM (Son et al., 2007).
Sixteen triterpenoid saponins from Polygala tenuifolia Willd., showed protective action on neurotoxicity induced by glutamate and serum deficiency in PCI 2 cells at the concentration of 10 (-5) mol/L (Li et al., 2008).
Sapinmusaponins Q and R of Sapindus mukorossi demonstrated potent anti-platelet aggregation activity than aspirin (Huang et al., 2007). The triterpenoid saponins were also showed anti-sweetening activity (Yoshikawa et al., 1997; Yoshikawa et al., 2000).