Ellagitannins, ellagic acid and their derived metabolites: A review about source, metabolism, functions and health

Ellagitannins (ETs) and ellagic acid (EA) are polyphenols present in some fruits, nuts and seeds, such as pomegranates, black raspberries, raspberries, strawberries, walnuts and almonds. ETs are hydrolyzed to EA under physiological conditions in vivo and EA is then gradually metabolized by the intestinal microbiota to produce different types of urolithins. Epidemiological evidence indicates that intake of ET and EA-rich foods may be protective against certain chronic diseases, although in vitro results often do not coincide with the findings of in vivo studies. This could be explained by the low bioavailability of ETs and EA antioxidant and the fact that urolithins are not as potent antioxidants as ellagitannins. On the other hand, urolithins could display estrogenic and/or anti-estrogenic activity and tissue disposition studies reveal that urolithins are enriched in prostate, intestinal, and colon tissues in mouse, which could explain why urolithins inhibit prostate and colon cancer cell growth. Moreover, antiproliferative and apoptosis-inducing activities of EA and urolithins have been demonstrated by the inhibition of cancer cell growth. The present work reviews the source, dietary intake, metabolism, functions and effects of ETs, EA and their derivate metabolites. Moreover, prebiotic, antioxidant and anti-inflammatory effects are also discussed.