|Biochemistry. 2009 Apr 21;48(15):3477-82. |
|Alpha-hederin, but not hederacoside C and hederagenin from Hedera helix, affects the binding behavior, dynamics, and regulation of beta 2-adrenergic receptors.[Pubmed: 19278262 ]|
|Hederacoside C, alpha-hederin, and Hederagenin are saponins of dry extracts obtained from the leaves of ivy (Hedera helix L.).
METHODS AND RESULTS:
Internalization of beta(2)-adrenergic receptor-GFP fusion proteins after stimulation with 1 microM terbutaline was inhibited by preincubation of stably transfected HEK293 cells with 1 microM alpha-hederin for 24 h, whereas neither hederacoside C nor Hederagenin (1 microM each) influenced this receptor regulation. After incubation of A549 cells with 5 nM Alexa532-NA, two different diffusion time constants were found for beta(2)AR-Alexa532-NA complexes by fluorescence correlation spectroscopy. Evaluation of the autocorrelation curve revealed diffusion time constants: tau(bound1) = 1.4 +/- 1.1 ms (n = 6) found for receptor-ligand complexes with unrestricted lateral mobility, and tau(bound2) = 34.7 +/- 14.1 ms (n = 6) for receptor-ligand complexes with hindered mobility. The distribution of diffusion time constants was 24.3 +/- 2.5% for tau(bound1) and 8.7 +/- 4.3% for tau(bound2) (n = 6). A549 cells pretreated with 1 microM alpha-hederin for 24 h showed dose-dependent alterations in this distribution with 37.1 +/- 5.5% for tau(bound1) and 4.1 +/- 1.1% for tau(bound2). Simultaneously, the level of Alexa532-NA binding was significantly increased from 33.0 +/- 6.8 to 41.2 +/- 4.6%. In saturation experiments, alpha-hederin did not influence the beta(2)-adrenergic receptor density (B(max)), whereas the K(D) value for Alexa532-NA binding decreased from 36.1 +/- 9.2 to 24.3 +/- 11.1 nM. Pretreatment of HASM cells with alpha-hederin (1 microM, 24 h) revealed an increased intracellular cAMP level of 13.5 +/- 7.0% under stimulating conditions. Remarkably, structure-related saponins like hederacoside C and Hederagenin did not influence either the binding behavior of beta(2)AR or the intracellular cAMP level.
|Planta Med. 2000 May;66(4):329-32. |
|Essential moiety for antimutagenic and cytotoxic activity of hederagenin monodesmosides and bisdesmosides isolated from the stem bark of Kalopanax pictus.[Pubmed: 10865448 ]|
METHODS AND RESULTS:
For the elucidation of the antimutagenic and cytotoxic principles from the stem bark of Kalopanax pictus, seven isolated components of this crude drug were tested in the Ames test and the MTT test. Hederagenin and its monodesmosides, kalopanaxsaponin A and I in addition to its bisdesmosides, kalopanaxsaponin B and H, showed potent antimutagenic activities against aflatoxin B1 (AFB1). However, they had no inhibitory effects on mutagenicity induced by the direct mutagen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). This suggested that Hederagenin glycosides might effectively prevent the metabolic activation of AFB1 or scavenge the electrophilic intermediate capable of inducing mutation. Hederagenin was found to be an essential moiety for the exhibition of antimutagenicity. Moreover, Hederagenin and its 3-O-glycosides were found to be cytotoxic on various tumor cell lines, P-388, L-1210, U-937, HL-60, SNU-5 and HepG2, while 3,28-di-O-glycosides of Hederagenin were not cytotoxic.
Hence, Hederagenin and its 3-O-glycosides could be suitable for cancer treatment chemopreventive drugs.
|Langmuir. 2014 Apr 29;30(16):4556-69. |
|Domain formation and permeabilization induced by the saponin α-hederin and its aglycone hederagenin in a cholesterol-containing bilayer.[Pubmed: 24690040]|
|Saponins and triterpenic acids have been shown to be able to interact with lipid membranes and domains enriched with cholesterol (rafts). How saponins are able to modulate lipid phase separation in membranes and the role of the sugar chains for this activity is unknown.
METHODS AND RESULTS:
We demonstrate in a binary membrane model composed of DMPC/Chol (3:1 mol/mol) that the saponin α-hederin and its aglycone presenting no sugar chain, the triterpenic acid Hederagenin, are able to induce the formation of lipid domains. We show on multilamellar vesicles (MLV), giant unilamellar vesicles (GUV), and supported planar bilayers (SPB) that the presence of sugar units on the sapogenin accelerates domain formation and increases the proportion of sterols within these domains. The domain shape is also influenced by the presence of sugars because α-hederin and Hederagenin induce the formation of tubular and spherical domains, respectively. These highly curved structures should result from the induction of membrane curvature by both compounds. In addition to the formation of domains, α-hederin and Hederagenin permeabilize GUV. The formation of membrane holes by α-hederin comes along with the accumulation of lipids into nonbilayer structures in SPB. This process might be responsible for the permeabilizing activity of both compounds. In LUV, permeabilization by α-hederin was sterol-dependent.
The biological implications of our results and the mechanisms involved are discussed in relation to the activity of saponins and triterpenic acids on membrane rafts, cancer cells, and hemolysis.