Oenothein B's contribution to the anti-inflammatory and antioxidant activity of Epilobium sp.

Willow herb tea or preparation are available and relatively popular in the European market, and claimed to be effective inter alia because of their anti-inflammatory activity. The present study is therefore aimed at comparing the anti-inflammatory and antioxidant activity of extracts of the three most popular Epilobium species (E. angustifolium, E. hirsutum and E. parviflorum) and at juxtaposing this activity against the dominating compounds from the following extracts: oenothein B (OeB), quercetin-3-O-glucuronide and myricetin-3-O-rhamnoside. The phytochemical analysis of the extracts has shown that OeB quantities vary between 20% and 35%, while flavonoids content does not exceed 2%. All extracts have inhibited the activity of hyaluronidase and lipoxygenase with IC₅₀ around 5 μg/ml and 25 μg/ml. The inhibition of hyaluronidase is related with the presence of OeB, a strong inhibitor of this enzyme (IC₅₀) 1.1 μM). Additionally, the extracts inhibited myeloperoxidase (MPO) release from stimulated neutrophils. OeB inhibited MPO release similarly to the anti-inflammatory drug indomethacin with IC₅₀ 7.7 μM and 15.4 μM, respectively. Tested extracts significantly reduced the production of reactive oxygen species (ROS) from f-MLP and PMA induced neutrophils with IC₅₀ 5 μg/ml and 25 μg/ml, respectively. The flavonoids content seems to exert little influence on extracts' activity, contrary to OeB, whose high concentration explains the activity of extract obtained from Epilobium. Tested currently marketed Epilobium preparations are often wrongly assigned, but we should stress that the level of OeB in all tested herbs was high and always exceeded 2% in raw material.