Oxidative damage to DNA constituents by iron-mediated Fenton reactions: the deoxyadenosine family

Abstract

The effect of exposing 2′-deoxyadenosine (dA), 5′-dAMP, 3′-dAMP, dApA, dA(pdA)_19, and poly(dA): oligo(dT) to iron/H₂O₂ in the presence and absence of ethanol or NADH has been studied. HPLC retention times, enzyme treatments, radio-labeled substrates, UV absorption spectra, and fast atom bombardment mass spectrometry (FABMS) have been used to distinguish 20 products arising from the reaction, of which 16 have been identified and four anomers proposed by comparison with earlier gamma radiation studies. The radical responsible for the reactions seems to be analogous to radiation-derived , has many products in common, but has some novel ones probably specific for Fenton-induced damage. Two new dimeric adducts arising from the generation of hydroxylamine at N7 and its subsequent condensation with two known sugar damage products, dR-adenine-N1-oxide, and two isomers of dR-FAPy arising from radical attacks at C4 and C5, may be considered novel in the present study. Unlike radiation-derived , the radical under study is difficult to eliminate due to its generation in the proximity of the substrate molecules. It is proposed that the iron binds to the phosphate group and generates the radical in its vicinity. Strand breaks in dA(pdA)₁₁ resulting from the Fenton reaction are of two types, spontaneous and alkali-labile. Duplex DNA is less sensitive to attack by this radical, as its various degradation products are a subset of those obtained with monomer substrates and only dR-FAPy production is relatively enhanced for poly (dA): oligo (dT) as compared to those from other substrates.

Keywords:

• DNA damage
• deoxyadenosine
• Fenton reaction

Acknowledgments

We thank Prof. Stuart Linn for advice regarding the experiments performed during 1988–1990, related discussions, and recommendations later. We thank Mrs Sherry Ogden of the UC Berkeley mass spectrometric facility for analyzing our samples. Ernst S. Henle and Yongzhang Luo are thanked for relevant discussions and for raising questions. RC remembers with gratitude his first wife Moushumi (1959–2006) for all support during their stay in California and the paper is dedicated to her memory. This work was supported by NIH Grant R29GM19020 to SM Linn and Department of Atomic Energy Grant, Government of India, No. 4/5/95-R&D-II/703 to RC.