VARIATION IN THE MODULATION OF SUPEROXIDE-INDUCED SINGLE-STRAND BREAKS IN PLASMID PBR322 DNA BY BIOLOGICAL ANTIOXIDANTS

Superoxide radical (O-2(-)), generated by the xanthine-xanthine oxidas e system, induces significant amount (20%) of single-strand breaks in plasmid pBR322 DNA. This is almost completely inhibited by its specifi c scavenger, superoxide dismutase. The biological antioxidants, at nea r physiological concentrations show great variation in their modulatio n of DNA damage induced by O-2(-). The thiols glutathione, cysteine an d dithiothreitol do not protect DNA instead they greatly enhance the s trand-breaking activity of this free radical. However, the lipid solub le antioxidants tannic acid, butein, canthaxanthin, beta-carotene and lipoate offered significant protection to plasmid DNA against O-2(-). Since O-2(-) is the most abundant reactive oxygen species generated, t he above mentioned modulating abilities of biological antioxidants may have significant biological implications.