Antioxidant and antihypertensive activities of acteoside and its analogs

Acteoside (Act), a phenylethanoid glycoside, is an active compound in several plants and traditional herbal medicines. Act along with its structural isomer, isoacteoside (Isoact), and an analog, 6-O-acetylacteoside (6-O-acetylact), were used in the study to investigate the antioxidant, anti-angiotensin-converting enzyme (ACE), and hemolysis inhibitory activities in vitro and antihypertensive activity against spontaneously hypertensive rats (SHR) in vivo. We showed that Act, Isoact, and 6-O-acetylact effectively scavenged 1,1-diphenyl- 2-picryl-hydrazyl radicals (with IC₅₀ at 11.4, 9.48, and 9.55 μM, respectively) and superoxide radicals (with IC₅₀ at 66.0, 38.5, and 39.1 μM, respectively). As Isoact and 6-O-acetylact had similar radical-scavenging activities, only Act and Isoact were used for following studies. Both Act and Isoact inhibited xanthine oxidase activity with IC₅₀ at 53.3 and 62.2 μM, respectively. Both Act and Isoact also significantly inhibited ACE activity and the hemolysis induced by 2,2'-azo-bis(2-amidinopropane)dihydrochloride, but the effects of Act were stronger than Isoact. We then orally administered a single dose of Act or Isoact (10 mg/Kg body weight) to SHR and measured the changes of systolic blood pressure (SBP) and diastolic blood pressure (DBP) over 24 h. Act, but not Isoact, showed antihypertensive activity in lowering SBP and DBP. The results suggest the potential usefulness of Act as a health food product for antioxidant protection and blood pressure regulation.