Reduction in free-radical-induced DNA strand breaks and base damage through fast chemical repair by flavonoids

This paper provides evidence that dietary flavonoids can repair a range of oxidative radical damages on DNA, and thus give protection against radical- induced strand breaks and base alterations. We have irradiated dilute aqueo us solutions of plasmid DNA in the absence and presence of flavonoids (F) i n a "constant (OH)-O-. radical scavenging environment", k of 1.5 x 10(7) s( -1) by decreasing the concentration of TRIS buffer in relation to the conce ntration of added flavonoids. We have shown that the flavonoids can reduce the incidence of single-strand breaks in double-stranded DNA as well as res idual base damage (assayed as additional single-strand breaks upon post-irr adiation incubation with endonucleases) with dose modification factors of u p to 2.0 +/- 0.2 at [F] < 100 mu M by a mechanism other than through direct scavenging of (OH)-O-. radicals. Pulse radiolysis measurements support the mechanism of electron transfer or H-. atom transfer from the flavonoids to free radical sites on DNA which result in the fast chemical repair of some of the oxidative damage on DNA resulting from (OH)-O-. radical attack. The se in vitro assays point to a possible additional role fur antioxidants in reducing DNA damage.