Bioavailability of flavonoids: The role of cell membrane transporters

Dietary flavonoids play an important role in the prevention of diseases related to oxidative stress in living systems. Although much attention has been focused on studying the protective functions of flavonoids, so far only limited biochemical research has been done to tackle the fundamental issues of how flavonoids enter cells. Flavonoids have limited bioavailability, and consequently low plasma concentrations. Thus, in order to enter the intracellular compartment of cells in target tissues, flavonoids must exploit specific cell membrane transporter systems. This interaction between flavonoids and the proteins that mediate their transmembrane transport is of critical importance since it affects both the pharmacokinetic and pharmacodynamic properties of flavonoids. Extensive knowledge on cell membrane transporters is, therefore, essential to fully understand the mechanisms of flavonoid-mediated protective activity in the cardiovascular, renal, hepatic and central nervous systems, and also to elucidate flavonoid-drug interactions.