Viscotoxin 1-PS

Background: Extracts from Viscum album L. are widely used as an adjuvant in complementary cancer therapy. While the mechanisms of mistletoe lectin (ML) cytotoxicity are well described, the viscotoxin (VT) effects are unclear at present. Thus, we treated human lymphocytes with VT and measured cell death-associated changes by flow cytometry. Results: Treatment of lymphocytes with VT for 2 hours resulted in the binding of Annexin-V, permeabilisation of cell membranes, and generation of ROI. Apart from interindividual differences in response to VT, the number of intracellulary Bcl-2 proteins increased only marginally. The VT A1, A2, A3 and 1-PS were similar in their ROI-inducing potencies, while other cationic and/or amphipathic substances such protamine sulfate, VT B, purothionin or wasp venom peptides mastoparan I and II were less effective. However, the cytotoxic properties of VT-rich whole plant extracts from mistletoe grown on different host trees (Iscador), correlated with the content of ML rather than VT. Conclusions: Permeabilisation of lymphocytes cell membranes by VT was associated with generation of ROI within 2 hours indicating accidental cell death. VT cannot be ignored any longer as they posses both immunomodulating and cytotoxic properties, which both might be of clinical relevance.

The purpose of the following study was to evaluate the presence of the most frequently investigated pharmacologically active mistletoe compounds, viscotoxins (VT) and mistletoe lectins (ML), in European mistletoe Viscum album L. and in the pharmaceutical mistletoe preparations Iscador. Quantitative analysis of the VT isoforms A1, A2, A3, B, 1-PS, and U-PS in fresh mistletoe plant material from the three European subspecies of V. album, during fermentative extraction of mistletoe and in Iscador showed that the pharmaceutical proceeding specific for the preparation of Iscador warrants a high yield of VT. No degradation or transformation of VT during the production process became apparent. The VT compositions of the three host specific European subspecies of V. album, ssp. album, ssp. abietis, and ssp. austriacum, showed characteristic differences. They ensured the identification of the subspecies specific types of Iscador. ML contents of mistletoe extracts were reduced during fermentative extraction. The quantified contents of total ML were 261 +/- 9.3 ng/ml in Iscador M 5 mg spec. and 391 +/- 18.3 ng/ml in Iscador Qu 5 mg spec. Binding of ML to the glycoprotein asialofetuin (type 1) was found to be temperature dependent. Binding activity was increased to 250 % (ML I) and 410 % (ML II and ML III) respectively by decreasing temperature from 30 degrees C to 4 degrees C. 95% of ML could be eliminated from Iscador by affinity chromatography with immobilised glycoproteins at 0 degrees C. Quantitative extraction of ML from the crude extract and their analysis by SDS-PAGE revealed the presence of about 30 % ML I, 20% ML II, and 50% ML III in Iscador M 5 mg spec. and Iscador Qu 5 mg spec. The annual course of concentrations of ML and VT in the leaves of V. album showed maximal ML contents in December and culminaton of VT in June. Seasonal fluctuations of the composition of mistletoe imply the importance of fixed harvesting seasons.