The Vasodilating Effect and Angiotensin Converting Enzyme Inhibition Activity of Three Dietary Flavonols: Comparsion between Myricetin, Quercetin and Morin, in vitro

The aim of this study is to compare the vasodiating effects and angiotensin converting enzyme inhibition activity of three dietary flavonols, myricetin, quercetin and morin, in vitro. The three flavonols ranging from 0 to 200 μM show no cytotoxicity to small vessel endothelial cells (SVEC). For vasodilative assay, of the three flavonols, myricetin showed the greatest induction in the levels of nitric oxide (NO) and prostacyclin (PGI2), and the expression of cyclooxygenase (COX-2). Myricetin, quercetin and morin enhanced the expression of eNOS, but no significant differences (p > 0.05) were found between three flavonols. Myricetin, quercetin and morin showed marked inhibitory effect on reactive oxygen species (ROS) production in H2O2-induced SVEC cells. In addition, myricetin and quercetin showed relatively higher inhibitory activity on ACE activity than morin. Taken together, of the three flavonols, myricetin with the substitution by more hydroxyl groups in the flavonol structure enhanced vasodilating activity. Enzyme kinetic analysis showed myricetin is a non-competitive inhibitor of ACE. These structure-function relationships facilitate the design of new antihypertensive drugs based on flavonols