Identification of a deoxyguanosine‐malondialdehyde adduct in rat and human urine

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Abstract
In an ongoing study, rat and human urine have been examined for the presence of malondialdehyde (MDA) derivatives as indicators of the nature of lipid peroxidative damage caused by this compoundin vivo. MDA in urine was found to be present mainly in the form of two lysine adducts, one acetylated and the other unacetylated, reflectingin vivo reactions with tissue proteins. Two minor metabolites were identified as adducts with the phospholipid bases serine and ethanolamine and a third one as an adduct with the nucleic acid base guanine. The identification of an MDA adduct with deoxyguanosine (dG‐MDA) among the products of hydrolysis of rat liver DNA suggested the possible occurrence of this compound in urine. In the present study dG‐MDA was identified in rat and in human urine, and a high‐performance liquid chromatographic method utilizing fluorescence detection was developed for its estimation. The method is sensitive to 1 pmol of dG‐MDA and requires a minimum of 1 mL of rat urine or 5 mL of human urine. Its rate of excretion by five‐week‐old rats (28.54±2.28 nmol/kg/24 h) (mean±SEM) was higher than that for nine‐week‐old rats (6.29±1.02) and much higher than that for adult humans (0.40±0.05). The results indicate that, as reported for 8‐hydroxy‐deoxyguanosine, dG‐MDA excretion is related to metabolic rate. Excretion of dG‐MDA by the rat, like the excretion of total MDA, declines during growth on a body weight basis at a rate similar to the decrease in resting energy metabolism. In contrast to other MDA derivatives excreted in rat urine, vitamin E deficiency had no effect on the excretion of dG‐MDA. Together with evidence that the dG‐MDA content of rat liver DNA likewise is unaffected by vitamin E depletion or by administration of catalysts ofin vivo lipid peroxidation, these findings indicate that DNA is protected from lipid peroxidative damage, possibly through conservation of the vitamin E associated with the lipids of the nuclear membrane.