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. Low temperature radiolysis requires ca. 100 times higher radiation dose for the creation of comparable strand breaks due to the suppression of Fenton-type reactions. Room temperature radiolysis produces a relatively large number of multi-single strand breaks (ssb) and, on absorption of 100 Gy, less double-strand breaks (dsb), ca. 4%, while under cryogenic conditions at a dose 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 damage to DNA even without irradiation, in comparison to the strong effect of Fe(II)/EDTA. Under our experimental conditions hydrogen peroxide does not influence 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 reserved.