BIOAVAILABILITY OF FLAVONOIDS: A REVIEW OF THEIR MEMBRANE TRANSPORT AND THE FUNCTION OF BILITRANSLOCASE IN ANIMAL AND PLANT ORGANISMS

Fruits and vegetables are rich in flavonoids, and ample epidemiological data show that diets rich in fruits and vegetables con-fer protection against cardiovascular, neurodegenerative and inflammatory diseases, and cancer. However, flavonoid bioavailability is re-portedly very low in mammals and the molecular mechanisms of their action are still poorly known. This review focuses on membrane transport of flavonoids, a critical determinant of their bioavailability. Cellular influx and efflux transporters are reviewed for their in-volvement in the absorption of flavonoids from the gastro-intestinal tract and their subsequent tissue distribution. A focus on the mam-malian bilirubin transporter bilitranslocase (TCDB 2.A.65.1.1) provides further insight into flavonoid bioavailability and its relationship with plasma bilirubin (an endogenous antioxidant). The general function of bilitranslocase as a flavonoid membrane transporter is further demonstrated by the occurrence of a plant homologue in organs (petals, berries) where flavonoid biosynthesis is most active. Bilitranslo-case appears associated with sub-cellular membrane compartments and operates as a flavonoid membrane transporter.