Identification of the cis-thymine glycol moiety in chemically oxidized and gamma-irradiated deoxyribonucleic acid by high-pressure liquid chromatography analysis.

Abstract

5,6-Dihydroxy-5,6-dihydrothymine (thymine glycol) is formed in DNA by chemical oxidants and ionizing radiation. We describe the separation of thymine glycol, 5,6-dihydroxy-5,6-dihydrothymidine (thymidine glycol), thymine, and thymidine by high-pressure liquid chromatography (HPLC). Enzymatic hydrolysates of chemically oxidized or gamma-irradiated single-stranded DNA were cochromatographed with 14C-containing marker compounds. In chemically oxidized DNA, thymidine glycol was the major derivative formed. In addition, there were four rapidly eluting thymine-derived components. In irradiated DNA, thymidine glycol constituted about 5% of the modified thymines, and the rapidly eluting fractions were proportionately increased. DNA isolated from gamma-irradiated and nonirradiated HeLa cells grown in the presence of [3H]thymidine was subjected to enzymatic hydrolysis and HPLC analysis. In control DNA, 0.3% of the thymines were modified. Thirty-six kilorads of gamma radiation caused a 30% increase in thymine damage. Thus, most of the base damage was due to internal beta radiation from incorporated [3H]thymidine. The chromatographic patterns of irradiated and nonirradiated samples were qualitatively the same, but the yields of some products increased 2-fold, while others remained unchanged. A comparison of the HPLC profiles of hydrolysates of in vitro oxidized and irradiated DNA with those of the cellular DNA revealed one fast eluting peak to be absent in cellular DNA, suggesting that it was formed only in single-stranded DNA. In cellular DNA, the major modified thymine was a more hydrophobic derivative not formed by in vitro radiation nor chemical oxidation. As in in vitro irradiated DNA, thymidine glycol constituted 5% of the modified thymines. The presence of cis-thymidine glycol in hydrolysates was confirmed by chromatography on Sephadex LH-20 using water and borate as eluants.