ISOLATION OF AN ANGIOTENSIN-CONVERTING ENZYME (ACE) INHIBITOR FROM OLEA-EUROPAEA AND OLEA-LANCEA

The aqueous extract of the leaves of Olea europaea and Olea lancea bot h inhibited Angiotensin Converting Enzyme (ACE) in vitro. A bioassay-d irected fractionation resulted in the isolation of a strong ACE-inhibi tor namely the secoiridoid 2-(3,4-dihydroxyphenyl)ethyl 4-formyl-3-(2- oxoethyl)-4E -hexenoate (oleacein) (IC50 = 26 mu M). Five secoiridoid glycosides (oleuropein, ligstroside, excelcioside, oleoside 11-methyl ester, oleoside) isolated from Oleaceous plants showed no significant ACE-inhibition whereas, after enzymatic hydrolysis, the ACE-inhibition at 0.33 mg/ml was between 64% to 95%. Secoiridoids have not been desc ribed previously in the literature as inhibitors of ACE. Oleacein show ed a low toxicity in the brine shrimp (Artemia salina)lethality test ( LC(50) (24 h) = 969 ppm).