Assessment of extracts from mistletoe (Viscum album) for herb-drug interaction by inhibition and induction of cytochrome P450 activities.

Three commercially available extracts from mistletoe (Viscum album L.) grown on ash tree (abnobaVISCUM(®) Fraxini 20 mg), on fir (abnobaVISCUM(®) Abietis 20 mg), and on pine (abnobaVISCUM(®) Pini 20 mg) were tested in vitro for their potential to interfere with the major drug metabolizing cytochromes P450 by hepatocyte viability, by inhibition of cytochromes P450 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 and 3A4, and by the induction of cytochromes P450 1A2, 2B6, 2C9, 2E1 and 3A4. As the three extracts are produced from mistletoe plants belonging to three different subspecies of Viscum album L. they have explicit differences in the content and spectrum of various active ingredients, e.g. mistletoe specific lectins. Cytotoxic effects on liver cells were observed for abnobaVISCUM(®) Fraxini with a high lectin content with an EC(50) value of 2.56 µg/mL, for abnobaVISCUM(®) Abietis with a moderate lectin content with an EC(50) value of 5.79 µg/mL and for abnobaVISCUM(®) Pini with a low lectin content with an EC(50) value of 30.86 µg/mL. The induction of cytochromes P450 was tested on human liver cells from three donors. Inhibition of cytochromes P450 was carried out on human liver microsomes. No or minor induction and inhibition was observed for all three extracts. The data indicate no or minor potential for herb-drug interactions by interference with cytochromes P450 by any of the three mistletoe extracts.