Role of iron ions in damage to DNA: influence of ionising radiation, UV light and H2O2

Addition of Fe(III) increases the number of strand breaks of plasmid DNA in aqueous solution under gamma-radiolysis at room temperature and at 77 K. L ow temperature radiolysis requires ca. 100 times higher radiation dose for the creation of comparable strand breaks due to the suppression of Fenton-t ype reactions. Room temperature radiolysis produces a relatively large numb er of multi-single strand breaks (ssb) and, on absorption of 100 Gy, less d ouble-strand breaks (dsb), ca. 4%, while under cryogenic conditions at a do se of 10 kGy, are produced ca. 10% dsb for a similar total number of strand breaks. Fe(Ill) in its complex with EDTA exhibits small, but distinct dama ge to DNA even without irradiation, in comparison to the strong effect of F e(II)/EDTA. Under our experimental conditions hydrogen peroxide does not in fluence the damage in a noticeable way in the presence of Fe(II) and Fe(III ), although UV light exhibits a very strong effect on the addition of both Fe(III) and H2O2. In our system, iron forms complexes with EDTA and also is bound by other components. A molar excess of iron in relation to EDTA has no striking effect. The chelators seem to be responsible for creation of a reactive form of iron, able to produce reactive oxygen species in solutions containing dissolved air. (C) 2001 Elsevier Science B.V. All rights reserv ed.