Recovery of human lymphocytes from oxidative DNA damage; the apparent enhancement of DNA repair by carotenoids is probably simply an antioxidant effect

Background: Many epidemiological studies have identified a protection again st cancer associated with consumption of fruit and vegetables. One factor i n this protection may be the enhancement of cellular DNA repair activity by micronutrients, such as carotenoids, found in these foods. Aims of the study: To measure the capacity of lymphocytes isolated from vol unteers supplemented with beta-carotene, lutein or lycopene to recover from DNA damage induced in vitro by treatment with H2O2. Methods: Healthy volunteers were given supplements of lutein (15 mg/day), l ycopene (15 mg/day) and beta-carotene (15 mg/day), each for 1 week, the sup plementation periods being separated by 3-week wash-out periods. Blood samp les were taken at the beginning and end of each supplementation, and at 1 w eek and 3 weeks during the wash-out period. Carotenoid levels were measured in plasma. Lymphocytes were isolated and frozen. Subsequently, they were t reated with 100 mu M H2O2 and incubated for up to 24 h; DNA damage was meas ured with the comet assay (single cell gel electrophoresis) after 0, 2, 4, 8 and 24 h. Results: Increases of 2- to 3-fold in mean plasma lutein and beta-carotene concentrations were seen at the end of the respective supplementation perio ds; they returned virtually to basal levels after wash-out. Lycopene concen trations were less affected by supplementation, and were more variable. H2O 2-induced DNA strand breaks were apparently only slowly rejoined by the lym phocytes. The rejoining of breaks in the first few hours appeared substanti ally faster in lymphocytes following supplementation with beta-carotene, bu t no such effect was seen with lutein. In those individuals who showed incr eases in lycopene concentrations, the recovery was significantly faster. Ly mphocytes that were not treated with H2O2 showed a transient increase in DN A breakage to about double the background level in 2 h, presumably as a res ult of exposure to atmospheric oxygen; this effect, too, was relieved by su pplementation with lycopene or beta-carotene. Conclusions: While certain carotenoids appear to enhance recovery from oxid ative damage, this is probably in fact an antioxidant protective effect aga inst additional damage induced by atmospheric oxygen, rather than a stimula tion of DNA repair.