Generation of reactive oxygen intermediates (ROI) by the thionins from Viscum album L.

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 a t present. Thus, we treated human lymphocytes with VT and measured cell dea th-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 differ ences in response to VT, the number of intracellulary Bcl-2 proteins increa sed only marginally. The VT A1, A2, A3 and I-PS were similar in their ROI-i nducing potencies, while other cationic and/or amphipathic substances such protamine sulfate, VT B, purothionin or wasp venom peptides mastoparan I an d II were less effective. However, the cytotoxic properties of VT-rich whol e plant extracts from mistletoe grown on different host trees (Iscador), co rrelated with the content of ML rather than VT. Conclusions: Permeabilisati on of lymphocytes cell membranes by VT was associated with generation of RO I within 2 hours indicating accidental cell death. VT cannot be ignored any longer as they posses both immunomodulating and cytotoxic properties, whic h both might be of clincal relevance.