|ANGELINO, DONATO - University Of Illinois|
|NINFALI, PAOLINO - University Of Illinois|
|JEFFERY, ELIZABETH - University Of Illinois|
Submitted to: Food & Function
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2013
Publication Date: 9/1/2013
Citation: Angelino, D., Berhow, M.A., Ninfali, P., Jeffery, E.H. 2013. Caecal absorption of vitexin-2-O-xyloside and its aglycone apigenin, in the rat. Food and Function. 4:1339-1345.
Interpretive Summary: Nearly all plants have a group of compounds known as flavonoids which have a number of nutriceutical functions in human and animal nutrition. Generally flavonoids are absorbed from foods either as intact flavonoid-sugar complexes (flavonoid-O-glycosides) or as just as the flavonoid form with the sugar complexes removed by the action of the gut micro biota. As the absorption takes place the flavonoids are often modified again and transported around the body where it is either further metabolized or excreted in the urine. However some plant flavonoids, known as flavonoid-C-glycosides have not been extensively examined. We followed the absorption and metabolism of vitexin, a flavonoid-C-glycoside found in Swiss chard. Instead of being metabolized and converted like the flavonoid-O-glycosides, vitexin was absorbed both in a unchanged form, or a form that had the loss of the extra O-glycoside, which is different than the pathway of absorption of the regular flavonoid-O-glycosides. This finding is significant because it shows an additional form of flavonoids can be absorbed by mammals and may have a biological function such as serving as additional antioxidants.
Technical Abstract: The in vivo bioavailability of the flavone-C-glycosides has been little studied compared to their O-glycoside analogues, which are both more common in nature and considered more easily hydrolyzed than C-glycosides, by enterocytes and gut microbiota. In this study, we used vitexin-2-O-xyloside (VOX), an apigenin-8-C-glucoside-2-O-xyloside, purified from seeds of Swiss chard (Beta vulgaris cicla), to investigate VOX absorption into portal blood compared to its aglycone, apigenin. We used a rat model in which we ligated the ileo- and colo-caecal junctions, then administered apigenin or VOX directly into the caecum. Blood samples were drawn from the portal vein at timed intervals over 40 min. The kinetic profile of appearance in portal blood of the compounds and their metabolites was evaluated by the HPLC-ESI-MS. Apigenin was found in portal blood both as the aglycone and as an apigenin-glucuronide derivative. The VOX was found unchanged and as a reduced monoglycoside. By collecting the bile, we confirmed that the liver received unchanged VOX, which was returned to the gut by enterohepatic recirculation for reabsorption from the ileum. The amount of apigenin and VOX remaining in the caecum, accounted for ~15% and ~26%, respectively. These data show for the first time that the C-glycoside VOX is absorbed unchanged and undergoes enterohepatic recirculation in addition to hydrolysis to the monoglycoside, reduction and conjugation to form a bioavailable glucuronide.