A review on the structure-activity relationship of dietary flavonoids for protecting vascular endothelial function: Current understanding and future issues

Nowadays dietary flavonoids attract considerable attention in the prevention of cardiovascular diseases, even though the definitive structure–activity relationships (SARs) of flavonoids are not completely understood. This review exclusively aims to summarize recent evidence for the correlation between structural features of dietary flavonoids and effects on vascular endothelial function (EF). In human studies, the diets rich in one of six flavonoid subclasses namely, flavonol, flavone, flavanol, flavanone, anthocyanin, and isoflavone were reported to have positive effects on EF. However, the clinical evidence supporting SAR establishment was limited and often inconclusive. In in vitro models, the evidence for the activities of metabolized and unmetabolized flavonoids in three protective pathways of EF: nitric oxide bioavailability, induction of antioxidant enzymes, and anti-inflammation are highlighted. The specific structural characteristics favorable in modulation of each pathway are summarized. Nevertheless, the roles of the substituent property of flavonoid metabolites on endothelial cells function remain to be investigated. Practical applications Due to the potential benefits for cardiovascular health, dietary flavonoids have come into the focus of utilization as a nutraceutical ingredient in food and pharmaceutical industries. Since there are many hundreds of flavonoids in human diets, thus it is very necessary to known if specific structural motifs could confer some flavonoids with higher cardiovascular bioactivity than others. The discussion on SARs for protecting vascular endothelial function will give us important information on utilization of flavonoids in human precise nutrition.