Transepithelial Transport and Metabolism of New Lipophilic Ether Derivatives of Hydroxytyrosol by Enterocyte-like Caco-2/TC7 Cells

Intestinal transport and metabolism of a series of ether derivatives of the natural antioxidant hydroxytyrosol with differing alkyl chain lengths (methyl, ethyl, propyl, and butyl) were evaluated at 1, 2, and 4 h using a two-compartment transwell system containing human enterocyte (differentiated Caco-21TC7) monolayers, which simulates the small intestinal barrier. All four ether derivatives were transferred across the enterocyte monolayers with Papp(apical-basolateral) values between 32.6 and 43.5 cm/s x 10(-6). One hour after apical loading, the predominant forms of the compounds on the basolateral side were unmodified molecules. Glucuronides and methylated metabolites were also present in both the apical and basolateral compartments, with conjugated metabolites preferentially transported to the basolateral side. The rate of metabolism increased according to the lipohilicity of the ether derivative (butyl > propyl > ethyl > methyl). In conclusion, hydroxytyrosyl ethers are rapidly absorbed across, and partially metabolized by, Caco-2/TC7 cell monolayers, in keeping with their lipophilic nature.