Evaluation of antihypertensive polyphenols of barley (Hordeum vulgare L.) seedlings via their effects on angiotensin-converting enzyme (ACE) inhibition

Angiotensin-converting enzyme (ACE) is an important therapeutic target in the regulation of high blood pressure. This study was conducted to investigate the alterations in blood pressure associated with ACE inhibition activity of the polyphenols (1–10), including 3-O-feruloylquinic acid (1), lutonarin (2), saponarin (3), isoorientin (4), orientin (5), isovitexin (6), isoorientin-7-O-[6-sinapoyl]-glucoside (7), isoorientin-7-O-[6-feruloyl]-glucoside (8), isovitexin-7-O-[6-sinapoyl]-glucoside (9), and isovitexin-7-O-[6-feruloyl]-glucoside (10), isolated from barley seedlings (BS). All the isolated polyphenols exhibited comparable IC50 values of ACE inhibition activity (7.3–43.8 µM) with quercetin (25.2 ± 0.2 µM) as a positive control, and their inhibition kinetic models were identified as noncompetitive inhibition. Especially, compound 4 was revealed to be an outstanding ACE inhibitor (IC50 = 7.3 ± 0.1 µM, Ki = 6.6 ± 0.1 µM). Based on the compound structure–activity relationships, the free hydroxyl groups of flavone-moieties and glucose connections at the A ring of the flavone moieties were important factors for inhibition of ACE. The alcohol extract of BS also demonstrated potent ACE inhibition activity (66.5% ± 2.2% at 5000 µg mL−1). The polyphenols from BS had strong inhibitory activity on ACE and this study results suggest that BS can be used as an effective blood pressure regulator through ACE inhibition.