Urinary excretion of 3,N4-etheno-2'-deoxycytidine in humans as a biomarker of oxidative stress: association with cigarette smoking.

Smokers are known to have elevated levels of lipid peroxidation, a form of oxidative stress. Etheno DNA adduct formation can originate from endogenous lipid peroxidation or from exogenous exposure of carcinogens. Using a modified stable isotope dilution GC/negative ion chemical ionization/MS assay originally developed for urinary 3,N(4)-ethenocytosine (epsilonCyt), the nucleoside 3,N(4)-etheno-2'-deoxycytidine (epsilondCyd) was detected for the first time in human urine. The presence of epsilondCyd in human urine was confirmed by LC/electrospray ionization/tandem MS. Concentrations of epsilondCyd in the 24 h urine samples from healthy individuals not occupationally exposed to industrial chemicals were in the range between 0 and 0.80 nM. A statistically significant correlation was established between cigarette smoking and urinary excretion of epsilondCyd after being adjusted for creatinine (p = 0.004). Furthermore, the urinary total antioxidant capacity was found to correlate inversely with the epsilondCyd levels (r = -0.50, p = 0.02). The results indicate that urinary epsilondCyd may provide a valuable noninvasive biomarker for oxidative DNA damage.