Intracellular antioxidant activity of hydroxytyrosol in rat colon epithelium

Hydroxytyrosol (HT) is a phenolic compound occurring in olive leaves and pulp, known for its antioxidant activity. It is significantly present in olive oil, which is the most diffused fat source in Mediterranean countries. The work is aimed to improve the knowledge about the direct biological effects of HT on the intestinal mucosa, which is the district of the body exposed to the highest HT concentrations through the diet intake. In particular, the work is addressed to explore the antioxidant activity of intracellularly absorbed HT on colon epithelium, which is one of the gastrointestinal tract segments more exposed to pro-oxidant conditions. The study was carried out by in situ confocal microscopy on rat colon explants, loaded with the ROS sensitive fluorescent probe CM-H2DCFDA, under basal physiological and pro-oxidant conditions. HT was able to dose-dependently decrease the intracellular reactive oxygen species (ROS) production under basal physiological conditions in superficial colonocytes. Moreover, it produced a direct dose-dependent antioxidant protective effect on the colon epithelium exposed to a pro-oxidant condition such as H2O2 exposure. Moreover, the antioxidant effect of HT was significantly expressed also against the oxidative stress induced by another pro-oxidant agent, ter-butyl-peroxyde. The results demonstrated that HT can positively contribute to the redox balance of colon epithelium by decreasing intracellular ROS either in basal or pro-oxidant conditions, suggesting the potential use of HT as a functional food ingredient useful for the protection of the intestinal mucosa against oxidative stress.