Antiproliferative activity of the ellagic acid-derived gut microbiota isourolithin A and comparison with its urolithin A isomer: the role of cell metabolism
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Urolithins, metabolites produced by the gut microbiota from ellagic acid, have been acknowledged with cancer chemopreventive activity. Although urolithin A (Uro-A) has been reported to be the most active one, 10–50 % of humans can also produce the isomer isourolithin A (IsoUro-A). However, no biological activity for IsoUro-A has been reported so far. Herein, we describe for the first time the antiproliferative effect of IsoUro-A, compared to Uro-A, against both human colon cancer (Caco-2) and normal (CCD18-Co) cell lines.
Cell proliferation was evaluated by MTT and Trypan blue exclusion assays. Cell cycle was analyzed by flow cytometry and apoptosis measured by the Annexin V/PI method. Finally, urolithins metabolism was analyzed by HPLC–DAD-MS/MS.
IsoUro-A inhibited the proliferation of Caco-2 cells in a time- and dose-dependent manner, though it was significantly lower than Uro-A (IC50 = 69.7 ± 4.5 and 49.2 ± 3.8 μM at 48 h, respectively). Both urolithins arrested Caco-2 cell cycle at S and G2/M phases and induced apoptosis at concentrations previously found in human colon tissues. Notably, Caco-2 cells glucuronidated more efficiently IsoUro-A than Uro-A (~50 vs. ~20 % of conversion after 48 h, respectively). Both Uro-A and IsoUro-A glucuronides did not exert antiproliferative effects. In addition, cell growth inhibition was higher in Caco-2 than in normal cells.
IsoUro-A exerts strong antiproliferative activity, which is reduced by the extensive glucuronidation at 9-position in cancer cells. Further studies are needed to elucidate whether the in vitro structure–activity relationship found for Uro-A and IsoUro-A plays any role in humans.
KeywordsUrolithins Isourolithin A Ellagic acid Cell cycle Apoptosis Colon cancer
American type culture collection
Fetal bovine serum
High-performance liquid chromatography
Half-maximal inhibitory concentration
Minimal essential medium
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