The colon epithelium as a target for the intracellular antioxidant activity of hydroxytyrosol: a study on rat colon explants

Oxidative stress is involved in the genesis and progress of many disorders of the gastrointestinal (GI) tract. In particular, the colon epithelium is one of the GI tract segments more exposed to pro-oxidant conditions. We aimed to study the intracellular antioxidant activity of hydroxytyrosol (HT), one of the most potent natural antioxidant phenolic compounds typically present in olive oil, directly on the colon epithelium, under basal physiological and pro-oxidant conditions. Our approach was based on the application of in situ confocal microscopy on rat colon explants loaded with the fluorescent probe 5-(and-6)-chloromethyl-2’,7’-dichlorodihydrofluoresceindiacetate, which is sensitive to intracellular oxidative stress. In the intact mucosa, HT exerted a dose-dependent decrease of the basal intracellular reactive oxygen species (ROS) production of superficial colonocytes. Also, it induced a direct dose-dependent antioxidant action on the colon mucosa exposed to a pro-oxidant condition such as the H2O2 challenge. The effect of 100 µM HT was comparable to that of 10 µM Trolox, which is widely used as a standard in in vitro assays for the determination of antioxidant activity. The intracellular antioxidant activity of HT on the intact mucosa was also tested against tert-butyl peroxide, another pro-oxidant. The results show that HT can directly contribute to the redox balance of colonic epithelium by reducing ROS in both basal and pro-oxidant conditions, and support the potential of HT as a functional food ingredient with applications in protecting the intestinal mucosa against oxidative stress