Identification of a new angiotensin-converting enzyme (ACE) inhibitor from Thai edible plants

Eight Thai edible plants were tested for their inhibitory activity against an angiotensin-converting enzyme (ACE) using an in vitro assay. The methanol extract of Apium graveolens exhibited significant ACE inhibitory activity with an IC50 value of 1.7 mg/ml, and was then subjected to an isolation procedure that resulted in identification of a pure active constituent, junipediol A 8-O-β-d-glucoside (1-β-d-glucosyloxy-2-(3-methoxy-4-hydroxyphenyl)-propane-1,3-diol) (1), which had good ACE inhibitory activity with an IC50 value of 76 μg/ml. Another eight known compounds, isofraxidin-β-d-glucoside (2), roseoside (3), apigenin-7-O-β-d-glucoside (4), luteolin-7-O-β-d-glucoside (5), icariside D2 (6), apiin (7), chrysoeriol-7-O-β-d-apiosylglucoside (8), and 11,21-dioxo-3 β,15α,24-trihydroxyurs-12-ene-24-O-β-d-glucopyranoside (9) were also identified. Although each of these five constituents (2-6) isolated from the same fraction as 1 showed no activity at concentrations of 500 μM, together, when each was present at 300 μg/ml, they enhanced the inhibitory activity of 500 μM of 1 from 64% to 81%.