Stereoselective Conjugation, Transport and Bioactivity ofS- andR-Hesperetin Enantiomers in Vitro
立体选择性
柚皮素
圆二色性
作者
Walter Brand,Jia Shao,E.F. Hoek–van den Hil,Kathelijn N. van Elk,Bert Spenkelink,L.H.J. de Haan,Maarit J. Rein,Fabiola Dionisi,Gary Williamson,P.J. van Bladeren,Ivonne M.C.M. Rietjens
The flavanone hesperetin ((+/-)-4'-methoxy-3',5,7-trihydroxyflavanone) is the aglycone of hesperidin, which is the major flavonoid present in sweet oranges. Hesperetin contains a chiral C-atom and so can exist as an S- and R-enantiomer, however, in nature 2S-hesperidin and its S-hesperetin aglycone are predominant. The present study reports a chiral HPLC method to separate S- and R-hesperetin on an analytical and semipreparative scale. This allowed characterization of the stereoselective differences in metabolism and transport in the intestine and activity in a selected bioassay of the separated hesperetin enantiomers in in vitro model systems: (1) with human small intestinal fractions containing UDP-glucuronosyl transferases (UGTs) or sulfotransferases (SULTs); (2) with Caco-2 cell monolayers as a model for the intestinal transport barrier; (3) with mouse Hepa-1c1c7 cells transfected with human EpRE-controlled luciferase to test induction of EpRE-mediated gene expression. The results obtained indicate some significant differences in the metabolism and transport characteristics and bioactivity between S- and R-hesperetin, however, these differences are relatively small. This indicates that for these end points, including intestinal metabolism and transport and EpRE-mediated gene induction, experiments performed with racemic hesperetin may adequately reflect what can be expected for the naturally occurring S-enantiomer. This is an important finding since at present hesperetin is only commercially available as a racemic mixture, while it exists in nature mainly as an S-enantiomer.