Comparative effects of dietary flavanols on antioxidant defences and their response to oxidant-induced stress on Caco2 cells

Abstract

Flavanols are an important fraction of our diet both for their antioxidant capacity and because they are constituents of greatly accepted foodstuffs such as tea, wine and cocoa. In addition to their antioxidant activity by directly scavenging intracellular reactive oxygen species (ROS), flavanols have been recently shown to enhance protective enzymes. The objective was to evaluate the antioxidant response of colon-derived Caco2 cells to dietary flavanols. Four representative flavanols were selected: epicatechin (EC), epicatechin-3-gallate (ECG), epigallocatechin-3-gallate (EGCG) and procyanidin B2 (PB2). Cell viability, concentration of ROS and reduced glutathione (GSH), and activity of antioxidant/detoxification enzymes and caspase 3 were determined. Treatment of Caco2 cells with flavanols decreased ROS production but did not affect GSH content. ECG induced glutathione peroxidase (GPx), whereas PB2 evoked a dose-dependent increase in GPx, glutathione reductase and glutathione-S-transferase. Enhancement of the antioxidant defences implies an improved cell response to an oxidative challenge. Hence, Caco2 cells treated 20 h with the flavanols, especially PB2, and then submitted to an oxidative stress induced by a pro-oxidant, tert-butyl-hydroperoxide, showed a reduced ROS production, restricted activation of caspase 3 and higher viability than cells plainly submitted to the stressor. Flavanols protect Caco2 cells against an induced oxidative stress and subsequent cellular death by reducing ROS production and preventing caspase-3 activation. In particular, PB2 increases the activity of antioxidant/detoxification enzymes and thus protects Caco2 cells by directly counteracting free radicals and also by activating the antioxidant defence system.