Phenolic-rich juice prevents DNA single-strand breakage and cytotoxicity caused by tert-butylhydroperoxide in U937 cells: the role of iron chelation

The antioxidant potential of phenolic compounds is generally linked to their ability to scavenge free radicals. However, in addition to their radical-scavenging activity, phenolic compounds can chelate metal ions, such as iron, to prevent their participation in Fenton-type reactions, which lead to the formation of free radicals. The aim of the present study was to evaluate the ability of a phenolic-rich juice made from grapes, cherries and berries to protect human myeloid leukemia (U937) cells from oxidative stress caused by tert-butylhydroperoxide (tB-OOH). Preincubation of cells with extracts of the phenolic-rich juice at different concentrations (0-200 microM ferulic acid equivalents) for 3 h partially prevented cell death and abolished the DNA cleavage induced by tB-OOH. Moreover, when preincubating cells with the 100-microM juice extract (the dose that diminished cell death by around 50%), the partial prevention of tB-OOH-induced formation of reactive oxygen species (ROS) and mitochondrial permeability transition pore opening was observed. The radical scavenger antioxidant N,N'-diphenyl-1,4-phenylene-diamine (DPPD) and the intracellular iron chelator o-phenanthroline (o-Phe) were also tested to know whether protective effects depended on radical-scavenging or iron-chelating activities. o-Phe prevented cell death, DNA cleavage and ROS generation, whereas DPPD only prevented cell death, suggesting that phenolics in the juice afforded protection against induced oxidative stress, most probably by means of an iron-chelating mechanism.