Cytotoxicity of β-aescin/agrostin mixtures in different cell lines depends on their growth characteristics

Agrostin (Mr: 27kDa), a ribosome-inactivating- protein (RIPs) from Agrostemma githago L., cleaves an essential adenin residue from the rRNA, leading to inhibition of protein syntheses [1]. In previous studies it was shown, that only the combination of specific triterpenoid saponins such as Saponinum album L. with a formyl function attached to position C₄ together with agrostin was cytotoxic in ECV-304 cells [2]. This enhancement in cytotoxicity by Saponinum album L is due to an enhanced penetration of agrostin through the cell membrane, indicating the induction of endocytosis, because the treatment with latranculin A und bafilomycin A ₁ inhibited the cytotoxicity in ECV-304 cells [3]. β-Aescin is also a triterpenoid saponin and the major compound of aescin, a mixture of glycosids synthesized by Aesculus hippocastanum L.. In this study we investigated the cytotoxic effect of β-aescin (10–2.5µg/mL) /agrostin (150 ng/mL) mixtures in ECV-304, Hep-G2, SK-N-SH, U-937 and H-2171 cells. In contrast to the non-adherent U-937 and H 2171 cells the proliferation of adherent growing cell lines like ECV-304, Hep-G2 and SK-N-SH was significantly reduced by the mixture of β-aescin and agrostin. It is therefore concluded that the stimulation of endocytosis of the cytotoxic agrostin by β-aescin depends on specific membrane structures present on the cell surface of adherent growing cells. Especially the difference in the caveolin-1 expression between adherent growing (high) and in suspension growing cells (low) was demonstrated [4]. Caveolin-1 is an integral membrane protein and correlates with the number of caveolae in the cell membrane. The caveolae, flask shaped invaginations in the cell membrane, are necessary for internalization of endocytotic markers and by that strongly involved in endocytosis.

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