PROTECTION OF PLASMID PBR322 DNA BY FLAVONOIDS AGAINST SINGLE-STRAND BREAKS INDUCED BY SINGLET MOLECULAR-OXYGEN

Flavonoids, the dominant colouring pigments of plants, as well as the related polyphenol tannic acid significantly inhibit single-strand bre aks in plasmid pBR322 DNA induced by singlet molecular oxygen (O-1(2)) . This reactive species of oxygen was generated in an aqueous buffer s ystem by the thermal dissociation of the endoperoxide of 3,3'-(1,4-nap hthylene)dipropionate. Among the antioxidants examined, myricetin show ed the highest protective ability, followed by tannic acid, (+)catechi n, rutin, fisetin, luteolin and apigenin, when the inhibitory abilitie s were compared at 90 min after incubation. The protective abilities o f these compounds were both time and concentration dependent. At equim olar concentrations (100 mu M) the antioxidant effect of myricetin was better than that of other known antioxidants such as lipoate, alpha-t ocopherol and beta-carotene. Data, when analysed in relation to the st ructures of various compounds, showed a rough correlation with protect ive abilities. Owing to the abundance of these compounds in our normal diet, they may play significant roles in preventing oxidative damage resulting from potentially deleterious O-1(2).