An overview of DNA and RNA bindings to antioxidant flavonoids.

In this report we are examining how the antioxidant flavonoids can prevent DNA damage and what mechanism of action is involved in the process. Flavonoids are strong antioxidants that prevent DNA damage. The anticancer and antiviral activities of these natural products are implicated in their mechanism of actions. We study the interactions of quercetin (que), kaempferol (kae), and delphinidin (del) with DNA and transfer RNA in aqueous solution at physiological conditions, using constant DNA or RNA concentration 6.25 mmol (phosphate) and various pigment/polynucleotide(phosphate) ratios of 1/65 to 1 (DNA) and 1/48 to 1/8 (tRNA). The structural analysis showed quercetin, kaempferol, and delphinidin intercalate DNA and RNA duplexes with minor external binding to the major or minor groove and the backbone phosphate group with overall binding constants for DNA adducts K(que) = 7.25 (+/-0.65) x 10(4) M(-1), K(kae) = 3.60 (+/-0.33) x 10(4) M(-1), and K(del) = 1.66 (+/-0.25) x 104 (-1) and for tRNA adducts K(que) = 4.80 (+/-0.50) x 10(4) M(-1), K(kae) = 4.65 (+/-0.45) x 10(4) M(-1), and K(del) = 9.47 (+/-0.70) x 10(4) M(-1). The stability of adduct formation is in the order of del>que>kae for tRNA and que>kae>del for DNA. Low flavonoid concentration induces helical stabilization, whereas high pigment content causes helix opening. A partial B to A-DNA transition occurs at high drug concentration, while tRNA remains in A-family structure. The antioxidant activity of flavonoids changes in order delphinidin>quercetin>kaempferol. The results show intercalated flavonoids can make them strong antioxidants to protect DNA from harmful free radical reactions.