Triterpenoid saponins from a cytotoxic root extract of Sideroxylon foetidissimum subsp. gaumeri

Evaluation of the cytotoxicity of an ethanolic root extract of Sideroxylonfoetidissimum subsp. gaumeri (Sapotaceae) revealed activity against the murine macrophage-like cell line RAW 264.7. Systematic bioassay-guided fractionation of this extract gave an active saponin-containing fraction from which four saponins were isolated. Use of 1D ((1)H, (13)C, DEPT135) and 2D (COSY, TOCSY, HSQC, and HMBC) NMR, mass spectrometry and sugar analysis gave their structures as 3-O-(beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl)-28-O-(alpha-L-rhamnopyranosyl-(1-->3)[beta-D-xylopyranosyl-(1-->4)]-beta-D-xylopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl)-16alpha-hydroxyprotobassic acid, 3-O-beta-D-glucopyranosyl-28-O-(alpha-L-rhamnopyranosyl-(1-->3)[beta-D-xylopyranosyl-(1-->4)]-beta-D-xylopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl)-16alpha-hydroxyprotobassic acid, 3-O-(beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl)-28-O-(alpha-L-rhamnopyranosyl-(1-->3)-beta-D-xylopyranosyl-(1-->4)[beta-D-apiofuranosyl-(1-->3)]-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl)-16alpha-hydroxyprotobassic acid, and the known compound, 3-O-beta-D-glucopyranosyl-28-O-(alpha-L-rhamnopyranosyl-(1-->3)[beta-D-xylopyranosyl-(1-->4)]-beta-D-xylopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl)-protobassic acid. Two further saponins were obtained from the same fraction, but as a 5:4 mixture comprising 3-O-(beta-D-glucopyranosyl)-28-O-(alpha-L-rhamnopyranosyl-(1-->3)-beta-D-xylopyranosyl-(1-->4)[beta-D-apiofuranosyl-(1-->3)]-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl)-16alpha-hydroxyprotobassic acid and 3-O-(beta-D-apiofuranosyl-(1-->3)-beta-D-glucopyranosyl)-28-O-(alpha-L-rhamnopyranosyl-(1-->3)[beta-D-xylopyranosyl-(1-->4)]-beta-D-xylopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl)-16alpha-hydroxyprotobassic acid, respectively. This showed greater cytotoxicity (IC(50)=11.9+/-1.5 microg/ml) towards RAW 264.7 cells than the original extract (IC(50)=39.5+/-4.1 microg/ml), and the saponin-containing fraction derived from it (IC(50)=33.7+/-6.2 microg/ml).

Differential cytotoxic and prooxidnant activity of knipholone and knipholone anthrone

Knipholone (KP) and knipholone anthrone (KA) are natural 4-phenylanthraquinone structural analogues with established differential biological effects including in vitro antioxidant [1] and antimicrobial properties [2]. The present study was designed to investigate the comparative in vitro cytotoxic activity and the possible mechanism of action of these two compounds. We demonstrated that KA is by order of magnitude more cytotoxic to mammalian cells than KP. In parallel with the demonstrated cytotoxic effect, KA but not KP induces prooxidative DNA damage in the presence of copper ions. In order to establish the possible involvement of reactive oxygen species in the KA-mediated prooxidative effect, we investigated the protective effect of several metal chelators and reactive oxygen species scavengers. Our data suggest that reactive oxygen species such as hydrogen peroxide are involved and a good correlation between prooxidative action, antioxidant effect and cytotoxicity is established for these two structural analogues. The chemistry, pharmacology and potential medicinal/toxicological potential of these compounds are discussed.

Comparative antioxidant, prooxidant and cytotoxic activity of sigmoidin A and eriodictyol

Sigmoidin A (SGN) is a prenylated flavanone derivative of eriodictyol (ERD) with reported moderate antioxidant, antimicrobial and anti-inflammatory activity. Since ERD and other structurally similar antioxidant phenolic compounds have been shown to induce prooxidative macromolecular damage and cytotoxicity in cancer cells, the comparative in vitro effects of these structural analogues on cancer cell viability and Cu(II)-dependent DNA damage were studied. In the presence of Cu(II) ions, both SGN and ERD (7.4-236 µM) caused comparable concentration-dependent pBR322 plasmid DNA strand scission. The DNA damage induced by SGN and ERD could be abolished by ROS scavengers, glutathione (GSH) and catalase as well as EDTA and a specific Cu(I) chelator neocuproine. Both ERD and SGN readily reduce Cu(II) to Cu(I) suggesting a prooxidative mechanism of DNA damage. In a cell free system, ERD and SGN did also show comparable radical scavenging activity. SGN was, however, by an order of magnitude more cytotoxic to cancer cells than ERD and this effect was significantly attenuated by GSH suggesting a prooxidative mechanism of cell death. A depletion of intracellular GSH level by SGN in cancer cells is also demonstrated.

Triterpenoid saponins from the cytotoxic root extract of Sideroxylon foetidissimum, an endemic Yucatecan medicinal plant

The flora of the Yucatan peninsula (Mexico) includes approximately 3000 plant species. Sideroxylon foetidissimum Jacq. subsp. gaumeri (Sapotaceae) is an endemic plant to the Yucatan peninsula; its fruit is edible and local people use the plant for medicinal purposes, although no details on its preparation or application are available [1,2]. A preliminary cytotoxic evaluation of the ethanolic root extract of S. foetidissimum revealed a potent activity against murine macrophage like cell line RAW 264.7 (IC50=39.54±4.11µg/mL). The systematic bioassay-guided fractionation of the extract resulted in the identification of the active saponin-containing fraction (IC50=33.69±6.19µg/mL). Four new triterpenoid saponins and a 1:1 mixture of two saponins were isolated from the active saponin- containing fraction. The evaluation of their cytotoxic activity revealed no activity for the tested pure saponins; however, the 1:1 mixture of saponins showed a potent activity (IC50=11.91±1.49µg/mL). The isolation of the saponins was carried out using semi-preparative HPLC. The structural assignments of the pure saponins were based on 1D (1H and 13C and DEPT-135) and 2D (COSY, HMBC, HSQC and TOCSY) NMR and mass spectrometry analyses. In this presentation, the isolation, identification and cytotoxic activity of the isolated compounds is discussed in more detail.