Quantification of Urinary Excretion of 1,N6-Ethenoadenine, a Potential Biomarker of Lipid Peroxidation, in Humans by Stable Isotope Dilution Liquid Chromatography−Electrospray Ionization−Tandem Mass Spectrometry: Comparison with Gas Chromatography−Mass Spectrometry

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Abstract
Etheno DNA adducts are promutagenic DNA lesions derived from exogenous as well as endogenous sources. The levels of etheno adducts in tissue DNA are elevated in cancer prone tissues, and the urinary excretion of etheno adducts is associated with oxidative stress. In this report, a new assay based on isotope dilution liquid chromatography−electrospray ionization−tandem mass spectrometry (LC-ESI-MS/MS) is developed for the quantification of 1,N6-ethenoadenine (εAde) in human urine samples without the need for derivatization. Sample purification before analysis by MS only requires a reversed phase solid phase extraction column. Two multiple reaction monitoring transitions with two product ion fragments generated from a common parent ion were used to quantify urinary εAde. The detection limit of εAde using LC-ESI-MS/MS is 2 pg injected standard εAde on-column, and the assay allows accurate quantification of urinary εAde at concentrations higher than 10 pg/mL. The presence of εAde in human urine is confirmed by the collision-induced daughter ion spectrum. Using this assay, the levels of εAde in the 24 h urine samples from 18 healthy individuals are determined, and the results are in very good agreement with those obtained using isotope dilution gas chromatography−negative ion chemical ionization−mass spectrometry. The high specificity and simple sample pretreatment of this LC-ESI-MS/MS method render it a valuable tool in measuring εAde in the complex mixture of human urine as a promising noninvasive biomarker for DNA damage associated with oxidative stress and for cancer chemoprevention studies.

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