Dietary flavonoids protect human colonocyte DNA from oxidative attack in vitro.
OBJECTIVE
Epidemiological studies suggest that antioxidant polyphenols in the human diet may protect against diseases such as cancer. In this study we investigated the cytoprotective potential of the flavonoids, quercetin, myricetin, kaempferol and rutin against oxidative DNA damage in human colonocytes in vitro.


METHODS
Caco-2 cells, which display specialised enterocyte/colonocyte cell functions, were used as an in vitro model for human colonocytes. Hydrogen peroxide was employed as the oxidant. DNA damage (strand breakage, oxidised purines and oxidised pyrimidines) was determined using the alkaline single cell gel electrophoresis or comet assay. Cell growth and viability were measured.


RESULTS
Hydrogen peroxide caused a dose-dependent increase in DNA strand breakage in human colonocytes, presumably via oxygen free radical generation. Quercetin and myricetin protected Caco-2 cells against oxidative attack. In addition, quercetin decreased hydrogen peroxide-mediated inhibition of growth. Neither rutin nor kaempferol was effective. However, quercetin, while inhibiting DNA strand breakage, did not alter the levels of oxidised bases following peroxide treatment. The antifungal agent ketoconazole, prevented quercetin cytoprotection in Caco-2 cells, indicating that P450-mediated metabolism may alter the efficacy of the flavonoids against oxidative DNA damage.


CONCLUSIONS
Flavonoids, particularly quercetin, the most abundant flavonoid in the human diet, are likely to be important in defending human colonocytes from oxidative attack.
Duthie
S J
SJ
Rowett Research Institute, Bucksburn, Aberdeen, United Kingdom.
Dobson
V L
VL
D002470:Cell Survival / Q000187:drug effects*; D002478:Cells, Cultured; D003110:Colonic Neoplasms; D004249:DNA Damage; D004032:Diet; D005419:Flavonoids / Q000494:pharmacology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000037:antagonists & inhibitors / Q000633:toxicity; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D044949:Kaempferols; D007700:Kinetics; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects* / Q000473:pathology; D018384:Oxidative Stress / Q000187:drug effects* / Q000502:physiology; D011794:Quercetin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D012431:Rutin / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured
D005419:Flavonoids; D044949:Kaempferols; D012431:Rutin; C006552:kaempferol; C040015:myricetin; D011794:Quercetin; D006861:Hydrogen Peroxide