The role of dietary
antioxidants in human health remains controversial. Fruits and vegetables in the diet are associated with lower rates of
chronic disease, and this is often attributed to their content of
antioxidants, and a resulting protection against oxidative stress. However, large-scale human trials with
antioxidant supplements have shown, if anything, an increase in mortality. We have investigated the
biological properties of
beta-cryptoxanthin, a common
carotenoid, in cell culture model systems, using the comet assay to measure DNA damage. At low concentrations, close to those found in plasma,
beta-cryptoxanthin does not itself cause damage, but protects transformed human cells (HeLa and Caco-2) from damage induced by H(2)O(2) or by visible light in the presence of a
photosensitizer. In addition, it has a striking effect on DNA repair, measured in different ways. Incubation of H(2)O(2)-treated cells with
beta-cryptoxanthin led to a doubling of the rate of rejoining of strand breaks and had a similar effect on the rate of removal of oxidized
purines by base excision repair. The latter effect was confirmed with an in vitro assay: cells were incubated with or without
beta-cryptoxanthin before preparing an extract, which was then incubated with substrate
DNA containing 8-oxo-7,8-dihydroguanine; incision was more rapid with the extract prepared from
carotenoid-preincubated cells. No significant increases were seen in
protein content of human
8-oxoguanine DNA glycosylase 1 or
apurinic endonuclease 1. The apparent
cancer-preventive effects of dietary
carotenoids may depend on the enhancement of DNA repair as well as
antioxidant protection against damage.