Transepithelial absorption and intracellular antioxidant activity of hydroxytyrosol in rat intestine

Hydroxytyrosol is the olive natural polyphenol with the highest free radical scavenger activity ever reported for any natural compound. The aim of this work was: 1) to investigate the mechanisms involved in hydroxytyrosol intestinal transport, using Ussing chamber mounted rat jejunum; 2) to investigate hydroxytyrosol intracellular antioxidant activity in intestinal cells, by confocal microscopy on native tissue charged with the fluorescent probe CM-H2- DCFDA. A mucosa-serosa flux of hydroxytyrosol was demonstrated in rat jejunum. It showed a saturating kinetic with a Km apparent of 4.34 µM and a Vmax of 13.47 nmol/min/cm2. No significant effect was observed on transepithelial potential, short circuit current, and transepithelial resistance. The intracellular antioxidant activity was determined on rat colon segments incubated with different hydroxytyrosol concentrations, charged with the fluorescent probe, then exposed to H2O2 as oxidant agent and observed by confocal microscopy. Hydroxytyrosol was able to significantly inhibit ROS production in surface colonocytes either in basal or under oxidative stress condition in a dose-dependent manner. In conclusion, a specific transepithelial hydroxytyrosol transport was demonstrated in rat jejunum. In intestinal cells hydroxytyrosol was demonstrated to exert a significant antioxidant intracellular activity suggesting a possible protecting effect on intestinal mucosa from pathological conditions related to oxidative stress.