Analysis of Ethylated Thymidine Adducts in Human Leukocyte DNA by Stable Isotope Dilution Nanoflow Liquid Chromatography鈥揘anospray Ionization Tandem Mass Spectrometry
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- 作者：Hauh-Jyun Candy Chen ; Yi-Ching Wang ; Wen-Peng Lin
- 刊名：Analytical Chemistry
- 出版年：2012
- 出版时间：March 6, 2012
- 年：2012
- 卷：84
- 期：5
- 页码：2521-2527
- 全文大小：349K
- 年卷期：v.84,no.5(March 6, 2012)
- ISSN：1520-6882
文摘
Studies showed that levels of ethylated DNA adducts in certain tissues and urine are higher in smokers than in nonsmokers. Because cigarette smoking is a major risk factor of various cancers, DNA ethylation might play an important role in cigarette smoke-induced cancer formation. Among the ethylated DNA adducts, O2-ethylthymidine (O2-edT) and O4-ethylthymidine (O4-edT) are poorly repaired and are accumulated in the body. In addition, O4-edT possesses promutagenic properties. In this study, we have developed a highly sensitive, accurate, and quantitative assay for simultaneous detection and quantification of O2-edT, N3-edT (N3-ethylthymidine), and O4-edT adducts by isotope dilution nanoflow liquid chromatography鈥搉anospray ionization tandem mass spectrometry (nanoLC鈥揘SI/MS/MS). Under the highly selected reaction monitoring (H-SRM) mode, the detection limit of O2-edT, N3-edT, and O4-edT injected on-column was 5.0, 10, and 10 fg, respectively. The quantification limit for the entire assay was 50, 100, and 100 fg of O2-edT, N3-edT, and O4-edT, respectively, corresponding to 1.1, 2.3, and 2.3 adducts in 109 normal nucleotides, respectively, starting with 50 渭g of DNA (from 1.5鈥?.0 mL of blood). Levels of O2-edT, N3-edT, and O4-edT in 20 smokers鈥?leukocyte DNA were 44.8 卤 52.0, 41.1 卤 43.8, 48.3 卤 53.9 in 108 normal nucleotides, while those in 20 nonsmokers were 0.19 卤 0.87, 4.1 卤 13.3, and 1.0 卤 2.9, respectively. Levels of O2-edT, N3-edT, and O4-edT in human leukocyte DNA are all significantly higher in smokers than in nonsmokers, with pvalues of 0.0004, 0.0009, and 0.0004, respectively. Furthermore, levels of O2-edT show a statistically significant association (纬 = 0.4789, p = 0.0327) with the smoking index in smokers. In the 40 leukocyte DNA samples, the extremely significant statistical correlations (p < 0.0001) are observed between levels of O2-edT and O4-edT (纬 = 0.9896), between levels of O2-edT and N3-edT (纬 = 0.9840), and between levels of N3-edT and O4-edT (纬 = 0.9901). To our knowledge, this is the first mass spectrometry-based assay for ethylated thymidine adducts. Using this assay, the three ethylated thymidine adducts were detected and quantified for the first time. Therefore, this highly sensitive, specific, and accurate assay should be clinically feasible for simultaneous quantification of the three ethylated thymidine adducts as potential biomarkers for exposure to ethylating agents and for cancer risk assessment.