MEDIATION OF OXIDATIVE DNA-DAMAGE BY NICKEL(II) AND COPPER(II) COMPLEXES WITH THE N-TERMINAL SEQUENCE OF HUMAN PROTAMINE HP2

The potential of Ni(II) and Cu(II) complexes with -Gln-Ser-His-Tyr-Arg -Arg-Arg-His-Cys-Ser-Arg-amide (Hp2(1-15)), a peptide modeling the N-t erminal amino acid sequence of human protamine HP2, to mediate oxidati ve DNA damage was studied by measurements of 8-oxo-7,8-dihydro-2'-deox yguanosine (8-oxo-dG) generation from 2'-deoxyguanosine (dG) and calf thymus DNA and by formation of double-strand breaks in calf thymus DNA . The concentrations of reagents were 0.1 mM dG and the metal-HP2(1-15 ) complex, 1 mM H2O2, 1.5 mM DNA (per phosphate group), 100 mM phospha te buffer, pH 7.4, ambient O-2. Samples were incubated at 37 degrees C for 16-24 h. The Cu(II)-HP2(1-15) complex was found to be an effectiv e promoter of the formation of 8-oxo-dG from both dG and DNA with ambi ent Oz (approximately 13- and 3-fold increase versus the oxidant alone , respectively) and H2O2 (approximately 25-fold increase in either cas e). The Ni(II)-HP2(1-15) complex was ineffective with Oz versus 8-oxo- dG production from both substrates but markedly enhanced the attack of H2O2 on dG and DNA (approximately Ei-fold increase of 8-oxo-dG produc tion in either case). Both Cu(II)- and Ni(II)-HP2(1-15) equally promot ed double-strand scission by H2O2 in calf thymus DNA. The promotion by the complexes of dG and DNA oxidation with H2O2 was accompanied by ox idative damage to the complexes themselves, consisting of decreasing c ontents of their His (to approximately 50% of control in either comple x) and especially Tyr (down to 48% of control in Cu(II)- and 19% in Ni (IT)-HP2(1-15)) residues, as well as appearance of aspartic acid, the known oxidation product of His residues in peptides (up to 22% vs Gly for Cu(II)- and 10% for Ni(II)-HP2(1-15)). The above results provide a novel chemical mechanism of Cu(II) and Ni(II) toxicity and may have w ide implications for reproductive and transgenerational effects of met al exposure.