Effects of Oenothera paradoxa defatted seed extracts on metallopeptidase activity

Oenothera sp. (Oenotheraceae) are native to Central and South America. Today, these species are also cultivated in Europe for the production of seeds. Oil from seeds of Oenothera biennis L., as well as Oenothera paradoxa Hudziok, are the main source of γ-linolenic acid (GLA). In traditional medicine, the whole plant is reputed for its sedative, analgesic, astringent and wound healing properties.

Companies manufacturing evening primrose oil may produce 50 tones of defatted seeds each year, on average, and therefore there is a growing need for utilization of this material. Angiotensin-converting enzyme (ACE), neutral endopeptidase (NEP) and aminopeptidase N are zinc metallopeptidases which play an important role in the metabolism of a number of regulatory peptides of the human nervous, cardiovascular, inflammatory and immune system.

With this in mind, we chose the in vitro metallopeptidases as a model for the purpose of identification of a potential novel activity of defatted seed extracts, and for defining the active compounds present in them. Prepared extracts of different polarity (aqueous, 60%ethanolic, isopropanolic and 30% isopropanolic) at concentrations of 1.5–100µg/ml exhibited a significant and dose dependent inhibition of the three tested enzymes. The 50% inhibition of enzyme activity showed that APN was the enzyme affected to the greatest extent with an IC₅₀ of 2.8µg/ml and 2.9µg/ml for aqueous and 30% isopropanolic extracts, respectively. The activity of NEP was quite strongly inhibited by the extracts as well. The HPLC-DAD analysis and bioguided fractionation led to the identification of four active compounds: (-)-epicatechin gallate, proanthocyanidin B3, oenothein B and penta-O-galloyl-β-D-glucose (PGG). PGG and procyanidins, as the dominant compounds in O. paradoxa seeds, seemed to play a role in the crude extracts activity.