Journal Article

Quantitative determination of urinary N7-ethylguanine in smokers and non-smokers using an isotope dilution liquid chromatography/tandem mass spectrometry with on-line analyte enrichment

Mu-Rong Chao, Chien-Jen Wang, Louis W. Chang and Chiung-Wen Hu

in Carcinogenesis

Volume 27, issue 1, pages 146-151
Published in print January 2005 | ISSN: 0143-3334
Published online July 2005 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgi177
Quantitative determination of urinary N7-ethylguanine in smokers and non-smokers using an isotope dilution liquid chromatography/tandem mass spectrometry with on-line analyte enrichment

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Previous studies demonstrated the presence of unknown direct-acting ethylating agents arising from cigarette smoke. We hypothesized that such agents would also lead to ethylation of guanine in DNA followed by depurination/repair and excretion of N7-ethylguanine (N7-EtG) in urine. In this study, a highly specific and sensitive liquid chromatographic/tandem mass spectrometric (LC/MS/MS) method was firstly developed for measuring urinary N7-EtG. With the use of an isotope internal standard (15N5-N7-EtG) and on-line enrichment techniques, the detection limit of this method was estimated as 0.59 pg/ml (0.33 pmol) on-column. This method was then applied to measure urinary samples obtained from 35 non-smokers and 32 smokers with dietary control. The results showed that the mean urinary levels of N7-EtG were 85.5 ± 105 and 28.1 ± 19.4 pg/mg creatinine for smokers and non-smokers, respectively. Smokers had about three times higher level of N7-EtG than non-smokers (P < 0.005). It was further noted that the urinary level of N7-EtG was significantly associated with cotinine for smokers (r = 0.49, P < 0.005). Taken together, this is the first study that demonstrated the presence of N7-EtG in urine, and that cigarette smoke was highly responsible for the increased urinary excretion of N7-EtG. This non-invasive measurement of urinary N7-EtG would be useful for the surveillance of ethylating agent exposure and its associated cancer risk in the future.

Keywords: ACN, acetonitrile; BMI, body mass index; FA, formic acid; HPLC, high performance liquid chromatography; LC/MS/MS, liquid chromatography with tandem mass spectrometry; LOD, limit of detection; N3-EtA, N3-ethyladenine; N7-EtG, N7-ethylguanine; O4-EtT, O4-ethylthyminine; TSNA, tobacco-specific nitrosamine

Journal Article.  4911 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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