| Cortex Albizzia, i.e. the dried stem bark of the leguminous plant Albizzia julibrissin Durazz, was specified in Chinese Pharmacopoeia (2000 edit.) as a traditional Chinese medicine to be used to relieve melancholia and uneasiness of body and mind, to invigorate the circulation of blood and to reduce a swelling. Although a lot of studies on chemistry and pharmacology of Albizzia were reported, there are not any research on the anti-tumor activity mechanisms of this medicine. In order to exploit the plant resource and find new antitumor compounds, the following studies were carried out.1. The bioactive parts of the sedative and cytotoxicity were determined by the pharmacological tests. The bioactive part of the cytotoxicity from the stem barks of Albizia julibrissin was subjected to a series of solvent and chromatographic separations, including the alternative HPLC methods, giving 18 pentacyclic triterpenoid saponins. Based on chemical methods and spectroscopic evidences, the structures of all the saponins were identified (Figure 1). The saponins were trisdesmosidic saponins, which were composed of a pentacyclic triterpenoid aglycone, 8-10 sugar moieties, 1-2 monoterpenoid moieties, and exhibited their molecular ion peaks at m/z 2000 or so. Their carbon-13 signals and most of proton signals were assigned bassed on extensive 1D and 2D NMR and TOF-MS experiments. Five lignanoids were separated from the bioactive part of the sedative.2. The compounds isolated from Albizia julibrissin together with six analogues or related compounds were tested for their cyotoxicities against six tumor cell lines by MTT and SRB methods. Some structure-activity relationships in cytotoxicity test were identified. The evaluation of cytotoxicity test revealed that some important structural features are required for activity. The lignans, triterpenoid aglycones and monoterpene glycosides showed no cytotoxic activity against the HeLa, Bel-7402 and MDA-MB-435 cancer lines, the triterpenoid saponins showed significant inhibition action against Hela, Bel-7402 ,Hella and MDA-MB-435 cancer cell lines in vitro.The monoterpene units at C-28 oligosaccharide chain of aglycone and 2-deoxy-amidoglucose at 3 position of aglycone were crucial for the activity.3. In this present paper the antitumor activity of pentacyclic triterpenoid saponins from Albizzia julibrissin was investigated. The saponins showed significant cyotoxicity against Bel-7402, HeLa and MCF-7 cell lines. In HeLa cells, Albizzia triterpenoid saponins initiated classic apoptotic pathway. Giemsa staining showed apoptotic bodies, and DMA electrophoresis appeared DMA ladder, which were believed to be the hallmark of classic apoptosis. In Western blot experiment, Bcl-2 expression was down-regulated and Bax expression was up-regulated by Albizzia triterpenoid saponins. Moreover, Albizzia triterpenoid saponins induced cell cycle arrest at G2/M phase. In MCF-7 cells, although apoptotic bodies were not observed in DMA fragmentation, a hallmark of apoptosis was not detected, it apparent that MCF-7cells incubated with saponins for 24 hours were controlled. In summary, we first demonstrated that the saponins induced cell death through distinct mechanisms in HeLa, and MCF-7cells respectively. |
