DNA damage by the sulfate radical anion: hydrogen abstraction from the sugar moiety versus one-electron oxidation of guanine

ABSTRACT

The products of oxidative damage to double-stranded (ds) DNA initiated by photolytically generated sulfate radical anions SO₄^•− were analyzed using reverse-phase (RP) high-performance liquid chromatography (HPLC). Relative efficiencies of two major pathways were compared: production of 8-oxoguanine (8oxoG) and hydrogen abstraction from the DNA 2-deoxyribose moiety (dR) at C1,′ C4,′ and C5′ positions. The formation of 8oxoG was found to account for 87% of all quantified lesions at low illumination doses. The concentration of 8oxoG quickly reaches a steady state at about one 8oxoG per 100 base pairs due to further oxidation of its products. It was found that another guanine oxidation product identified as 2-amino-5-(2′-alkylamino)-4H-imidazol-4-one (X) was released in significant quantities from its tentative precursor 2-amino-5-[(2′-deoxy-β-d-erythro-pentofuranosyl)amino]-4H-imidazol-4-one (dIz) upon treatment with primary amines in neutral solutions. The linear dose dependence of X release points to the formation of dIz directly from guanine and not through oxidation of 8oxoG. The damage to dR was found to account for about 13% of the total damage, with majority of lesions (33%) originating from the C4′ oxidation. The contribution of C1′ oxidation also turned out to be significant (17% of all dR damages) despite of the steric problems associated with the abstraction of the C1′-hydrogen. However, no evidence of base-to-sugar free valence transfer as a possible alternative to direct hydrogen abstraction at C1′ was found.

KEYWORDS:

• DNA
• imidazolone
• oxidative damage
• 8-oxoguanine
• sulfate radicals

Acknowledgements

We thank Dr. David M. Close for the assistance with X-ray equipment.

Disclosure statement

The authors report no conflicts of interests. The authors alone are responsible for the contents and writing of the manuscript.

Funding information

This work was supported by startup research funding from East Tennessee State University.