Effects of dietary antioxidants on human DNA ex vivo

Free Radic Res. 2002 Jan;36(1):113-8. doi: 10.1080/10715760210161.


The protective effect of fruits and vegetables against cancer is well established. It is believed that this effect is mediated by antioxidants and decreased oxidative damage to DNA. However, the identity of the antioxidant(s) responsible is not clear. Moreover, a potentially damaging pro-oxidant effect of some antioxidants has been reported. In this study the ex vivo effects of several dietary antioxidants, including quercetin, various catechins, ascorbic acid and alpha-tocopherol, were investigated, at concentrations up to 200 microM, using the single cell gel electrophoresis (comet) assay for DNA damage. Lymphocytes from three healthy subjects were pre-incubated with these antioxidants, and the comet assay was performed on treated, untreated, challenged and unchallenged cells in parallel, oxidant challenge being induced by 5 min exposure to hydrogen peroxide (final concentrations H2O2: 30, 45, or 60 microM). Results using this ex vivo cellular assay showed protection by some antioxidants (quercetin, caffeic acid), no effect by some (catechin, epicatechin, catechin gallate, epicatechin gallate) and an apparently damaging effect by others (epigallocatechin, epigallocatechin gallate). Damage may have been caused by production of H2O2 from these polyphenolics. Neither ascorbic acid nor alpha-tocopherol protected or damaged DNA. Further study of the role of quercetin and caffeic acid in DNA protection is needed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antioxidants / pharmacology*
  • Ascorbic Acid / pharmacology
  • Caffeic Acids / pharmacology
  • Catechin / analogs & derivatives
  • Catechin / pharmacology
  • Cells, Cultured
  • Comet Assay
  • DNA / drug effects*
  • DNA Damage
  • Dose-Response Relationship, Drug
  • Female
  • Free Radical Scavengers / pharmacology
  • Humans
  • Hydrogen Peroxide / pharmacology
  • Lymphocytes / drug effects
  • Male
  • Oxidative Stress
  • Quercetin / pharmacology
  • Time Factors
  • alpha-Tocopherol / pharmacology


  • Antioxidants
  • Caffeic Acids
  • Free Radical Scavengers
  • Catechin
  • DNA
  • Quercetin
  • Hydrogen Peroxide
  • epigallocatechin gallate
  • alpha-Tocopherol
  • Ascorbic Acid
  • caffeic acid