Effect of flavonoids on 2′-deoxyguanosine and DNA oxidation caused by singlet molecular oxygen

Antioxidant potential is generally investigated by assaying the ability of a compound to protect biological systems from free radicals. However, non-radical reactive oxygen species can also be harmful. Singlet molecular oxygen (1O21O2) is generated by energy transfer to molecular oxygen. The resulting 1O21O2 is able to oxidize the nucleoside 2′-deoxyguanosine (dGuo), which leads to the formation of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo) and spiroiminodihydantoin 2′-deoxyribonucleoside diastereomers (dSp) in an aqueous solution. The main objective of the present study was to verify whether the presence of flavonoids (flavone, apigenin, quercetin, morin and catechin) at different concentrations could protect dGuo from 1O21O2 damage. Of the tested flavonoids, flavone possessed antioxidant activity, as determined by a decrease in the formation of both products. Apigenin, morin, quercetin and catechin all increased the formation of 8-oxodGuo at a concentration of 100 μM. The quantification of plasmid strand breaks after treatment with formamidopyrimidine–DNA glycosylase showed that flavone protected and quercetin and catechin enhanced DNA oxidation. Our results show that compounds, such as flavonoids, may affect the product distribution of 1O21O2-mediated oxidation of dGuo, and, in particular, high concentrations of flavonoids with hydroxyl groups in their structure lead to an increase in the formation of the mutagenic lesion 8-oxodGuo.