Apoptosis-inducing properties of Viscum album L. extracts from different host trees, correlate with their content of toxic mistletoe lectins.
BACKGROUND: Extracts from Viscum album L. (VAL), which are one of the most widely used alternative cancer therapies in Europe, have been recognised to induce apoptosis. A clinically relevant direct anti-tumour effect might be induced only by their intratumoural or intrapleural injection, and thus effectiveness is highly dependent on the apoptosis-inducing potencies of the extracts used. MATERIALS AND METHODS: To characterise these properties, human lymphocytes were incubated for 72 hours with VAL extracts from different host trees and harvest times. Cell death-associated changes such as an apoptotic sub-G1 peak, binding of Annexin-V, generation of reactive oxygen intermediates (ROI), expression of mitochondrial Apo2.7 molecules, and uptake of the DNA-intercalating dye propidium iodide were measured by flow cytometry. RESULTS AND CONCLUSIONS: Biologically active VAL compounds, and thus cytotoxicity, are dependent on the manufacturing process, host tree, and time of harvest. Although the mistletoe lectin (ML) content of VAL extracts strongly correlated with their apoptosis-inducing properties, the presence of these proteins will not guarantee its biological activity, indicating the involvement of other components which may modulate ML cytotoxicity.