Characterization of the effect of Epilobium extracts on human cell proliferation

We have previously shown that extracts of different Epilobium species, a phytotherapeutic agent used in folk medicine as a treatment for benign prostatic hyperplasia, inhibit proliferation of human prostate cells. The selectivity of this effect was evaluated in four different human cell lines (PZ-HPV-7, normal prostate cells; LNCaP, transformed prostate cells; HMEC, mammary cells, and 1321N1, astrocytoma cells). Different extracts of Epilobium species (E. rosmarinifolium, E. spicatum, and E. tetragonum) had similar growth-inhibitory effects in all cell lines tested, indicating a lack of specificity for prostate cells. Inhibition of DNA synthesis was mostly due to the nonpolar fraction of the extracts which is expected to contain flavonoids and sterols. Polar fractions were devoid of activity with the exception of that from E. rosmarinifolium. This species is the most potent in the antiproliferative effect and contains the highest concentration of oenothein B, a hydrolyzable ellagitannin. Oenothein B inhibited DNA synthesis in all four cell lines tested. Extracts of E. angustifolium (the Linné denomination of E. spicatum) and of E. spicatum from different sources were compared for their ability to inhibit DNA synthesis and for their oenothein B content. The E. angustifolium extract contained an amount of oenothein B 40-fold higher than the other extract of the same species and was ten times more potent in inhibiting DNA synthesis in a human prostate cell line. These results indicate that Epilobium extracts inhibit proliferation of prostate cells in a nonspecific manner. Oenothein B may play a role in this effect, but other active compounds are also present. The difference observed between extracts from the same species underscores the importance of determination and standardization of active ingredients in phytotherapeutic agents.