Diets rich in fruits and vegetables are associated with a lower risk of tumor induction in the intestine and other sites. We investigated whether apple juice produced predominantly from old apple varieties with especially high amounts of antioxidative flavonoids/ polyphenols might be able to protect the intestine and colon against oxidative cell damage. Modulation of oxidative cell damage was determined in human colon cancer cells (Caco-2, HT29). A two-step incubation protocol was used, consisting of 24h treatment with phenolic antioxidants followed by moderate induction of oxidative stress by menadione (1h) or tert-butylhydroperoxide (40 min) to simulate moderate pathological situations. Three phenolic apple juice extracts of different origin (AE01 from Boskoop apple juice; AE02 from juice of different table and cider fruit varieties, APE03 from pomace of table apples) were tested in comparison to major constituents (rutin, phloridzin, epicatechin, caffeic acid, chlorogenic acid) and their reconstituted mixtures (rAEs). Parameters studied were (oxidative) DNA damage (Comet assay with FPG), cellular redox status (dichlorofluorescein assay) and Trolox equivalent antioxidant capacity (TEAC). AEs exhibited a distinct antioxidative capacity (3.6-4.2 mM Trolox), APE03 being more effective than the juice extracts AE02 and AE01. The higher TEAC of the respective rAEs (4.7-7.3 mM Trolox) points to the pivotal role of these constituents in admixture for antioxidant capacity. Cellular ROS level was clearly diminished (down to 60-80% of TBH control) by all extracts (1-100 μg/mL) and rAEs (0.5-50 μg/mL) in both cell lines. Oxidative DNA damage in Caco-2 cells was clearly decreased by extracts (50-100 μg/mL) and more effectively by reconstituted mixtures (1 μg/mL) of AE01 and APE03. Among the individual constituents, caffeic acid and rutin exhibited highest activity to reduce oxidative DNA damage; cellular ROS level was most effectively reduced by caffeic acid and chlorogenic acid. In conclusion, phenolic apple juice extracts, originating from old cider and table apple varieties, are effective antioxidants which reduce oxidative cell damage in human colon cells. The major phenolics, tested as mixtures and individual constituents, were found to account substantially for the preventive effects of the juice extracts. (Supported by BMBF grant no. 01EA 0101)

[Proc Amer Assoc Cancer Res, Volume 47, 2006]