A phenolic extract from grape by-products and its main hydroxybenzoic acids protect Caco-2 cells against pro-oxidant induced toxicity

Grape/wine industry produces large amounts of by-products, however knowledge on their health-promoting qualities is limited. This study investigated the effects of a grape phenolic extract (GPE) and its phenolic compounds, gallic acid (GA) and syringic acid (SA) on human intestinal Caco-2 cells, directly or after cytotoxicity induced by tert-butylhydroperoxide (t-BOOH). Direct treatment with 0.1-10 μg/mL GPE, or 0.1-10 μM GA and SA produced no major cytotoxic effect, either changes in antioxidant defences (glutathione content, glutathione peroxidase and reductase activities) or protein damage (carbonyl groups). However, 10 μg/mL GPE, 1 and 10 μM GA and 10 μM SA decreased reactive oxygen species (ROS) production. Pre-treatment with GPE, SA and GA at the same concentrations for 20 h showed that 10 μg/mL GPE and 10 μM GA or SA significantly counteracted ROS increase induced by t-BOOH. 10 μg/mL GPE and 1-10 μM GA or 10 μM of SA significantly reduced pro-oxidant-induced cytotoxicity. 1-10 μg/mL GPE, 1-10 μM GA and 10 μM SA significantly recovered both depleted glutathione and enhanced glutathione reductase and peroxidase activities, and reduced protein oxidative damage. Therefore, treatment with realistic concentrations of GPE and its main hydroxybenzoic acids protected Caco-2 cells against induced oxidative stress.