Biological activity of extracts from defatted seeds of Oenothera paradoxa

Oenothera sp. (Oenotheraceae) is native to Central and South America and has been used for different medicinal purposes. The oil from seeds of Oenothera paradoxa, one species of evening primroses, has been shown to have several pharmacological effects such as anti-hypertension, anti-atherosclerosis, antidiabetic, anti-inflammatory, anti-premenstrual and anti-tumor effects. In the last years interest of this plant has been growing because of its content of polyphenols (flavonoids, phenolic acids and hydrolysable tannins). The aim of our study was to determine the antioxidant activity of an aqueous extract, isopropanolic extract and condensed fraction of polyphenols (CFP) of the defatted seeds of Oenothera paradoxa. Antioxidant capacity was assessed according to slightly modified version of the DPPH photometric assay and modified xanthine oxidase assay [1]. We also determined biological effects of mentioned above extracts against activity of enzymes: angiotensin-converting enzyme (ACE), aminopeptidase N (APN) and neutral endopeptidase (NEP) according to Bormann and Melzig [2]. All samples (50–1.65ug/ml) showed dose dependent free radical scavenging effect and dose dependent inhibitory effect on xanthine oxidase. The strongest inhibition of xanthine oxidase activity was demonstrated by CFP (IC₅₀=3.3µg/ml) while the highest radical scavenging activity was obtained with isopropanolic extract (IC₅₀=7.1µg/ml). Each extract contained gallic acid as main compound. Pure gallic acid demonstrated the strongest antioxidant activity (IC₅₀=1.1µg/ml in DPPH trial and IC₅₀=6.4µg/ml in xanthine oxidase assay). All investigated extracts significantly inhibited peptidases activity. The strongest effect on ACE activity was exhibited by the CFP with IC₅₀=26µg/ml. The highest APN and NEP inhibitions were demonstrated by aqueous extract (IC₅₀=2.8µg/ml and IC₅₀=4.7µg/ml, respectively) while gallic acid showed a weaker activity against peptidases (IC₅₀>100µg/ml). The results of our study demonstrate a high biological activity of the extracts of defatted seeds of Oenothera paradoxa.

References: [1] Choi C. W. et al. (2002) Plant Science 163, 1161–68, [2] Bormann H., Melzig M.F. (2000) Pharmazie 55: 129–32