Saponins are amphiphilic substances consisting of a hydrophobic backbone with one or two hydrophilic sugar units. Recently it was shown that saponinum album (SA) from Gypsophila paniculata L. enhanced cytotoxicity of a saporin-based chimeric toxin (up to 385,000-fold) as well as the toxicity of saporin (up to 100,000-fold) with N-glycosidase activity. Previously we have shown that toxicity of other N-glycosidases such as ricin A-chain, nigrin b, and toxins such as diphtheria toxin or microcystin-LR was not enhanced by SA. This points to a specific SA-dependent mechanism of toxicity enhancement on saporin and saporin-based toxins. Although the cytotoxicity enhancing effect was observed in up to 10 different cell lines, nothing is known about the kinetic of SA under cell culture conditions. Therefore SA was titrated, and the uptake respective liberation profile of SA was investigated in ECV-304 cells. Treatment of cells with [3H]-SA leads to an immediate uptake of saponin molecules. After cells were saturated with [3H]-SA, a first equilibrium (first eq.) was reached. The first eq. was disturbed by washing until a second equilibrium was reached between the activity observed within cells and that seen in the supernatant. After a further extensive washing, a small portion of saponin molecules remained durable associated with the cell. This portion was sufficient to induce a drastic toxicity enhancement on saporin indicating a long-lasting sensitization of cells against the toxin.
The RNA N-glycosidase activity of ricin A-chain. The characteristics of the enzymatic activity of ricin A-chain with ribosomes and with rRNA.
