The effects of nitroxide radicals on oxidative DNA damage

The indolinonic and quinolinic aromatic nitroxides synthesized by us are a novel class of biological antioxidants, which afford a good degree of prote ction against free radical-induced oxidation in different lipid and protein systems. To further our understanding of their antioxidant behavior, we th ought it essential to have more information on their effects on DNA exposed to free radicals. Here, we report on the results obtained after exposure o f plasmid DNA and calf thymus DNA to peroxyl radicals generated by the wate r-soluble radical initiator, 2,2'-azobis(2-amidinopropane)dihydrochloride ( AAPH), and the protective effects of the aromatic nitroxides and their hydr oxylamines, using a simple in vitro assay for DNA damage. In addition, we a lso tested for the potential of these nitroxides to inhibit hydroxyl radica l-mediated DNA damage inflicted by Fenton-type reactions using copper and i ron ions. The commercial aliphatic nitroxides 2,2,6,6-tetramethylpiperidine -1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), a nd bis(2,2,6,6-tetramethyl-1-oxyl-piperidin-4-yl)sebacate (TINUVIN 770) wer e included for comparison. The results show that the majority of compounds tested protect: (i) both plasmid DNA and calf thymus DNA against AAPH-media ted oxidative damage in a concentration-dependent fashion (1-0.1 mM), (ii) both Fe(II) and Cu(I) induced DNA oxidative damage. However, all compounds failed to protect DNA against damage inflicted by the presence of the trans ition metals in combination with H2O2. The differences in protection betwee n the compounds are discussed in relation to their molecular structure and chemical reactivity. (C) 2000 Elsevier Science Inc.