IDENTIFICATION OF A DEOXYGUANOSINE-MALONDIALDEHYDE ADDUCT IN RAT AND HUMAN URINE

In an ongoing study, rat and human urine have been examined for the pr esence of malondialdehyde (MDA) derivatives as indicators of the natur e of lipid peroxidative damage caused by this compound in vivo. MDA in urine was found to be present mainly in the form of two lysine adduct s, one acetylated and the other unacetylated, reflecting in vivo react ions with tissue proteins. Two minor metabolites were identified as ad ducts with the phospholipid bases serine and ethanolamine and a third one as an adduct with the nucleic acid base guanine. The identificatio n 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 a nd in human urine, and a high-performance liquid chromatographic metho d utilizing fluorescence detection was developed for its estimation. T he method is sensitive to 1 pmol of dG-MDA and requires a minimum of 1 mt of rat urine or 5 mt of human urine. Its rate of excretion by five -week-old rats (28.54 +/- 2.8 nmol/kg/24 h) (mean + SEM) was higher th an that for nine-week-old rats (6.29 +/- 1.02) and much higher than th at for adult humans (0.40 +/- 10.05). The results indicate that, as re ported for 8-hydroxy-deoxyguanosine, dG-MDA excretion is related to me tabolic rate. Excretion of dG-MDA by the rat, Like the excretion of to tal MDA, declines during growth on a body weight basis at a rate simil ar to the decrease in resting energy metabolism. In contrast to other MDA derivatives excreted in rat urine, vitamin E deficiency had no eff ect on the excretion of dG-MDA. Together with evidence that the dG-MDA content of rat liver DNA likewise is unaffected by vitamin E depletio n or by administration of catalysts of in vivo lipid peroxidation, the se findings indicate that DNA is protected from lipid peroxidative dam age, possibly through conservation of the vitamin E associated with th e lipids of the nuclear membrane.