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We studied the influence of structurally different saponins on the cholesterol content of cellular membranes. Therefore a cell culture model using ECV-304 urinary bladder carcinoma cells was developed. To measure the cholesterol content we used radiolabeled (3)H-cholesterol which is chemically and physiologically identical to natural cholesterol. The cells were pre-incubated with (3)H-cholesterol and after a medium change, they were treated with saponins to assess a saponin-induced cholesterol liberation from the cell membrane. In another experiment the cells were pre-incubated with saponins and after a medium change, they were treated with (3)H-cholesterol to assess a saponin-induced inhibition of cholesterol uptake into the cell membrane. Furthermore, the membrane toxicity of all applied saponins was analyzed using extracellular LDH quantification and the general cytotoxicity was analyzed using a colorimetric MTT-assay and DNA quantification. Our results revealed a correlation between membrane toxicity and general cytotoxicity. We also compared the results from the experiments on the saponin-induced cholesterol liberation as well as the saponin-induced inhibition of cholesterol uptake with the membrane toxicity. A significant reduction in the cell membrane cholesterol content was noted for those saponins who showed membrane toxicity (IC50 <60 μM). These potent membrane toxic saponins either liberated (3)H-cholesterol from intact cell membranes or blocked the integration of supplemented (3)H-cholesterol into the cell membrane. Saponins with little influence on the cell membrane (IC50 >100 μM) insignificantly altered the cell membrane cholesterol content. The results suggested that the general cytotoxicity of saponins is mainly dependent on their membrane toxicity and that the membrane toxicity might be caused by the loss of cholesterol from the cell membrane. We also analyzed the influence of a significantly membrane toxic saponin on the cholesterol content of intracellular membranes such as those of endosomes and lysosomes. In these experiments ECV-304 cells were either incubated with (3)H-cholesterol or with (3)H-cholesterol and 5 μM saponin. After isolation of the endosomes/lysosomes their (3)H-cholesterol content was measured. A significant influence of the saponins on the cholesterol content of endosomal/lysosomal membranes was not detected., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

A bioassay-guided phytochemical analysis of the triterpene saponins from under ground parts of Gypsophila arrostii var. nebulosa allowed the isolation of two triterpene saponins; nebuloside A, B based on gypsogenin and quillaic acid aglycone. Two new oleanane type triterpenoid saponins (nebuloside A, B) and three known saponins (1-3) were isolated from the root bark of Gypsophila arrostii var. nebulosa. The structures of the two new compounds were elucidated as 3-O-β-D-galactopyranosyl-(1→2)-[β-D-xylopyranosyl-(1→3)]-β-D-glucuronopyranosyl quillaic acid 28-O-β-D-glucopyranosyl-(1→3)-[β-D-xylopyranosyl-(1→3)-β-D-xylopyranosyl-(1→4)]-α-L-rhamnopyranosyl-(1→2)-β-D-fucopyranosyl ester (nebuloside A) and 3-O-β-D-xylopyranosyl-(1→3)-[β-D-galactopyranosyl(1→3)-β-D-galactopyranosyl-(1→2)]-β-D-glucuronopyranosyl gypsogenin 28-O-β-D-glucopyranosyl-(1→3)-[β-D-xylopyranosyl-(1→3)-β-D-xylopyranosyl-(1→4)]-α-L-rhamnopyranosyl-(1→2)-β-D-fucopyranosyl ester (nebuloside B), on the basis of extensive spectral analysis and chemical evidence. Nebuloside A and B showed toxicity enhancing properties on saporin a type-I RIP without causing toxicity by themselves at 15 μg/mL., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Twelve C-ring modified spirostanyl glycosides were synthesized and evaluated for their cytotoxicity against the human myeloid leukemia cell line (HL-60). With the aim of assessing the influence of the hydrophobic character, the conformational flexibility and the stereochemistry of the C-ring functionalities on the cytotoxic activity, a variety of spirostanic aglycones incorporating methylene, methoxyl, α,β-unsaturated ketone and lactone groups were subjected to a linear glycosylation strategy leading to glycosides derived from the 3,6-dipivaloylated β-D-glucoside and the β-chacotrioside moieties. The 3,6-dipivaloylated spirostanyl β-D-glucosides showed moderate to good cytotoxic activity against HL-60, but no significant cytotoxicity against benign blood cells. However, the cytotoxicity of spirostanyl β-chacotriosides was highly dependent on the nature of the C-ring functional groups of the steroidal aglycones. Actually, the chacotrioside-based saponins either with no functionality or bearing a hydrophobic methylene group at C-12 were the most cytotoxic ones against both HL-60 and benign blood cells. On the other hand, the incorporation of very polar functionalities and the opening of the ring C with the consequent loss of rigidity led to a significant drop in the cytotoxicity against HL-60. These results confirm that spirostanyl β-chacotriosides including very lipophilic aglycones are the most cytotoxic ones among their congeners., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

A phytochemical analysis of Aesculus pavia has led to the isolation of eight novel triterpenoid saponins, based on oleane type skeleton and named paviosides A-H (1a, 1b-4a, 4b). On the basis of chemical, and 2D NMR and mass spectrometry data, the structures of the new compounds were elucidated as 3-O-[β-D-xylopyranosyl (1 → 2)] [-β-d-glucopyranosyl (1 → 4)]-β-D-glucopyranosiduronic acid 21-tigloyl-22-acetyl barringtogenol C (1a), 3-O-[β-D-xylopyranosyl (1 → 2)] [-β-D-glucopyranosyl (1 → 4)]-β-D-glucopyranosiduronic acid 21-angeloyl-22-acetyl barringtogenol C (1b), 3-O-[β-D-xylopyranosyl (1 → 2)] [-β-D-galactopyranosyl (1 → 4)]-β-D-glucopyranosiduronic acid 21-tigloyl-22-acetyl barringtogenol C (2a), 3-O-[β-D-xylopyranosyl (1 → 2)] [-β-D-galactopyranosyl (1 → 4)]-β-D-glucopyranosiduronic acid 21-angeloyl-22-acetyl barringtogenol C (2b), 3-O-[β-D-xylopyranosyl (1 → 2)] [-β-D-xylopyranosyl (1 → 4)]-β-D-glucopyranosiduronic acid 21-tigloyl-22-acetyl barringtogenol C (3a), 3-O-[β-D-xylopyranosyl (1 → 2)] [-β-D-xylopyranosyl (1 → 4)]-β-d-glucopyranosiduronic acid 21-angeloyl-22-acetyl barringtogenol C (3b), 3-O-[β-D-xylopyranosyl (1 → 2)] [-β-D-xylopyranosyl (1 → 4)]-β-D-glucopyranosiduronic acid 21-tigloyl-22-acetyl protoaescigenin (4a), and 3-O-[β-D-xylopyranosyl (1 → 2)] [-β-D-xylopyranosyl (1 → 4)]-β-D-glucopyranosiduronic acid 21-angeloyl-22-acetyl protoaescigenin (4b). The compounds showed cytotoxic activity on J-774, murine monocyte/macrophage, and WEHI-164, murine fibrosarcoma, cell lines. Among them, paviosides E-H (3a, 3b and 4a, 4b) showed higher activity with values ranging from 2.1 to 3.6 μg/mL. Structure-activity relationship studies indicated the positive effect on the activity of xylose unit in the place of glucose, while a little detrimental effect is observed when glucose is substituted by galactose. The aglycone structure and the presence of a tigloyl or an angeloyl group at C-21 do not affect significantly the inhibitory activity on both tested cell lines., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Saponins are secondary plant compounds. They have a triterpenoid or steroidal backbone. Sugars are attached to one or more points of this structure, forming chains that can be branched. This appearance leads to amphiphilic properties giving saponins the ability to interact with both lipophilic and hydrophilic structures. The surfactant behavior lets them lower the surface tension in aqueous solutions and form micelles when reaching the critical micelle concentration (cmc). It also lets them interact with biologic membrane layers that usually consist of phospholipids and cholesterol. This action may perturb the membrane and its function leading to membrane perforation or complete lysis. Thus saponins are also known for their cytotoxicity and membranolytic, respectively hemolytic features. In our studies we wanted to answer the question if there is a correlation between the unspecific detergent behavior when lowering the surface tension and the ability to perforate cell membranes and to act cytotoxic. Do saponins showing a considerable reduction in the surface tension also reveal an evident cytotoxicity or/and a marked cell membrane perforation? We tested a variety of saponins with distinct structures. The reduction in the surface tension and the cmc were analyzed on a tensiometer using the Wilhelmy plate method. The general cytotoxicity was determined in a cell model by DNA quantification. The cell membrane toxicity or membrane perforation was explored in a cell model by quantification of the leakage of the intracellular enzyme lactate dehydrogenase (LDH). The experiments revealed a correlation between the membrane toxicity and the reduction in surface tension., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Bioactivity-guided fractionation of the extract from a Fijian red alga Peyssonnelia sp. led to the isolation of two novel sterol glycosides 19-O-β-d-glucopyranosyl-19-hydroxy-cholest-4-en-3-one (1) and 19-O-β-d-N-acetyl-2-aminoglucopyranosyl-19-hydroxy-cholest-4-en-3-one (2), and two known alkaloids indole-3-carboxaldehyde (3) and 3-(hydroxyacetyl)indole (4). Their structures were characterized by 1D and 2D NMR and mass spectral analysis. The sterol glycosides inhibited cancer cell growth with mean IC₅₀ values (for 11 human cancer cell lines) of 1.63 and 1.41μM for 1 and 2, respectively. The most sensitive cancer cell lines were MDA-MB-468 (breast) and A549 (lung), with IC₅₀'s in of 0.71-0.97μM for 1 and 2. Modification of the sterol glycoside structures revealed that the α,β-unsaturated ketone at C-3 and oxygenation at C-19 of 1 and 2 are crucial for anticancer activity, whereas the glucosidic group was not essential but contributed to enhanced activity against the most sensitive cell lines., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

The haemolysis of red blood cells inducing toxicity in most animals including humans is a major drawback for the clinical development of saponins as antitumour agents. In this study, the haemolytic and cytotoxic activities as well as the membrane cell permeabilization property of a library of 31 semi-synthetic and natural lupane- and oleanane-type saponins were evaluated and the structure-activity relationships were established. It was shown that lupane-type saponins do not exhibit any haemolytic activity and membrane cell permeabilization property at the maximum concentration tested (100 microM) independently of the nature of the sugar moieties. While oleanane-type saponins such as beta-hederin (25) and hederacolchiside A(1) (27) cause the death of cancer cell lines by permeabilizing the cellular membranes, lupane-type saponins seem to proceed via another mechanism, which could be related to the induction of apoptosis. Altogether, the results indicate that the cytotoxic lupane-type glycosides 10 and 22 bearing an alpha-l-rhamnopyranose moiety at the C-3 position represent promising antitumour agents for further studies on tumour-bearing mice since they are devoid of toxicity associated with the haemolysis of red blood cells.

This paper reports on the cytotoxic effect induced by a new natural steroidal saponin, icogenin, on the myeloid leukemia cell line HL-60. Icogenin was found to be a cytotoxic compound IC(50) 2.6+/-0.9microM at 72h, with growth inhibition caused by the induction of apoptosis, as determined by microscopy of nuclear changes and the fragmentation of poly(ADP-ribose) polymerase-1.