Abstract 4697: Liquid chromatography-electrospray ionization tandem mass spectrometry analysis of 7-ethylguanine in human urine

Abstract

Abstract Considerable evidence in the literature demonstrates the exposure of humans to an unknown ethylating agent. Previous studies have demonstrated the presence of 3-ethyl-Ade in urine, 7-ethylguanine (7-ethyl-Gua) in urine and human liver DNA, 7-ethyldGuo and O4-ethyl-dThd in human lung DNA, and ethylvaline in hemoglobin. Some studies also report higher levels of ethyl adducts in smokers compared to nonsmokers, and there is convincing evidence for an uncharacterized ethylating agent in cigarette smoke. To further investigate this question and evaluate the potential role of ethylating agents in smoking-induced cancer we have developed a liquid chromatography-electrospray ionization tandem mass spectrometry-selected reaction monitoring (LC-ESI-MS/MS-SRM) method for analysis of 7-ethyl-Gua in human urine. A two-dimensional chromatography approach was used with [15N5]7-ethyl-Gua as the internal standard. Human urine was diluted with 15 mM ammonium acetate and partially purified by a solid-phase extraction cartridge (Strata-X 33 µm, 30 mg/1 mL, Phenomenex) and a mixed mode cation exchange reversed-phase extraction cartridge (Oasis MCX, 30 mg/cartridge, Waters). The fraction from this last purification step containing the analyte (30% MeOH, 5% NH4OH) was dried and redissolved in 80% acetonitrile, 0.1% formic acid and purified by HPLC on a YMC Polyamino II column (150 × 1.0 mm I.D. 5 μm). The fraction containing 7-ethyl-Gua was collected, dried, dissolved in H2O and analysed by LC-ESI-MS/MS-SRM using a Thermo Hypersil Gold PFP column (150 × 0.5 mm I.D. 3 μm). The analysis was carried out using the transition m/z 180 [M + H]+ → m/z 152 [Gua+ H]+ for 7-ethyl-Gua and m/z 185 → m/z 157 for the internal standard. Recovery was about 50%. The detection limit was approximately 10 fmol on column. The peaks attributed to 7-ethyl-Gua and the labeled internal standard had identical retention time and were observed in most of the human urine samples analyzed. The identity of the peak was confirmed by re-injecting the samples after spiking with a standard solution of 7-ethyl-Gua. Twenty-one human urine samples (1 mL) from 11 smokers and 10 nonsmokers were analyzed. 7-Ethyl-Gua was clearly detected in 8 out of 11 samples from smokers and 5 out of 10 samples from nonsmokers. These results strongly indicate that 7-ethyl-Gua is present in human urine and demonstrate that it can be detected and quantified. Further investigation is required to clarify its relationship to cigarette smoking. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4697.