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Quantitation of pyridyloxobutyl DNA adducts of tobacco-specific nitrosamines in rat tissue DNA by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry.

ABSTRACT: The tobacco-specific nitrosamines N'-nitrosonornicotine (NNN, 1) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK, 2) are potent carcinogens in rodents. Bioactivation of NNN and NNK by cytochrome P450 enzymes generates a pyridyloxobutylating agent 6, which alkylates DNA to produce pyridyloxobutyl (POB)-DNA adducts. POB-DNA adduct formation plays a critical role in NNN and NNK carcinogenicity in rodents. To further investigate the significance of this pathway, we developed a high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) method for quantitative analysis of four POB-DNA adducts with known structures. The corresponding deuterated analogues were synthesized and used as internal standards. DNA samples, spiked with internal standards, were subjected to neutral thermal hydrolysis followed by enzymatic hydrolysis. The hydrolysates were partially purified by solid phase extraction prior to HPLC-ESI-MS/MS analysis. The method was accurate and precise. Excellent sensitivity was achieved, especially for O2-[4-(3-pyridyl)-4-oxobut-1-yl]thymidine (O2-POB-dThd, 11) with a detection limit of 100 amol per mg DNA. DNA samples treated with different concentrations of 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (NNKOAc, 3) were subjected to HPLC-ESI-MS/MS analysis. 7-[4-(3-Pyridyl)-4-oxobut-1-yl]guanine (7-POB-Gua, 12) was the most abundant adduct, followed by O6-[4-(3-pyridyl)-4-oxobut-1-yl]-2'-deoxyguanosine (O6-POB-dGuo, 8), O2-POB-dThd, and O2-[4-(3-pyridyl)-4-oxobut-1-yl]cytosine (O2-POB-Cyt, 13). Lung and liver DNA isolated from NNK-treated rats were analyzed. Consistent with the in vitro data, 7-POB-Gua was the major POB-DNA adduct formed in vivo. However, levels of O6-POB-dGuo were the lowest of the four adducts analyzed, suggesting efficient repair of this adduct in vivo. In contrast to the other three adducts, O6-POB-dGuo was more abundant in lung than in liver. O2-POB-dThd appeared to be poorly repaired in vivo, and its levels were comparable to those of 7-POB-Gua. The results of this study provide a sensitive HPLC-ESI-MS/MS method for comprehensive quantitation of four POB-DNA adducts, support an important role of O6-POB-dGuo in NNK lung tumorigenicity in rats, and suggest that O2-POB-dThd may be a useful tobacco-specific DNA biomarker for future tobacco carcinogenesis studies.

SUBMITTER: Lao Y

PROVIDER: S-EPMC2518839 | biostudies-literature | 2006 May

REPOSITORIES: biostudies-literature

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Quantitation of pyridyloxobutyl DNA adducts of tobacco-specific nitrosamines in rat tissue DNA by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry.

Lao Yanbin Y Villalta Peter W PW Sturla Shana J SJ Wang Mingyao M Hecht Stephen S SS

Chemical research in toxicology 20060501 5

The tobacco-specific nitrosamines N'-nitrosonornicotine (NNN, 1) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK, 2) are potent carcinogens in rodents. Bioactivation of NNN and NNK by cytochrome P450 enzymes generates a pyridyloxobutylating agent 6, which alkylates DNA to produce pyridyloxobutyl (POB)-DNA adducts. POB-DNA adduct formation plays a critical role in NNN and NNK carcinogenicity in rodents. To further investigate the significance of this pathway, we developed a high-performan ...[more]

PMID: 16696570

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Project description:The tobacco-specific carcinogens N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) require metabolic activation to exert their carcinogenicity. NNN and NNK are metabolized to the same reactive diazonium ions, which alkylate DNA forming pyridyloxobutyl (POB) DNA base and phosphate adducts. We have characterized the formation of both POB DNA base and phosphate adducts in NNK-treated rats and the formation of POB DNA base adducts in NNN-treated rats. However, POB DNA phosphate adducts in NNN-treated rats are still uncharacterized. In this study, we quantified the levels of POB DNA phosphate adducts in tissues of rats chronically treated with ( S)-NNN or ( R)-NNN for 10, 30, 50, and 70 weeks during a carcinogenicity study. The highest amounts of POB DNA phosphate adducts were observed in the esophagus of the ( S)-NNN-treated rats, with a maximum level of 5400 ± 317 fmol/mg DNA at 50 weeks. The abundance of POB DNA phosphate adducts in the esophagus was consistent with the results of the carcinogenicity study showing that the esophagus was the primary site of tumor formation from treatment with ( S)-NNN. Compared to the ( R)-NNN group, the levels of POB DNA phosphate adducts were higher in the oral mucosa, esophagus, and liver, while lower in the nasal mucosa of the ( S)-NNN-treated rats. Among 10 combinations of all isomers of POB DNA phosphate adducts, Ap(POB)C and combinations with thymidine predominated across all the rat tissues examined. In the primary target tissue, esophageal mucosa, Ap(POB)C accounted for ?20% of total phosphate adducts in the ( S)-NNN treatment group throughout the 70 weeks, with levels ranging from 780 ± 194 to 1010 ± 700 fmol/mg DNA. The results of this study showed that POB DNA phosphate adducts were present in high levels and persisted in target tissues of rats chronically treated with ( S)- or ( R)-NNN. These results improve our understanding of DNA damage during NNN-induced carcinogenesis. The predominant POB DNA phosphate isomers observed, such as Ap(POB)C, may serve as biomarkers for monitoring chronic exposure of tobacco-specific nitrosamines in humans.

Project description:Castration resistant prostate cancer (CRPC), the fatal form of prostate cancer, remains androgen dependent despite castrate levels of circulating testosterone (T) and 5?-dihydrotestosterone (DHT). To investigate mechanisms by which the tumor can synthesize its own androgens and develop resistance to abiraterone acetate and enzalutamide, methods to measure a complete androgen profile are imperative. Here, we report the development and validation of a stable isotope dilution liquid chromatography electrospray ionization tandem mass spectrometric (SID-LC-ESI-MS/MS) method to quantify nine human hydroxy-androgens as picolinates, simultaneously with requisite specificity and sensitivity. In the established method, the fragmentation patterns of all nine hydroxy-androgen picolinates were identified, and [13C3]-5?-androstane-3?, 17?-diol and [13C3]-5?-androstane-3?, 17?-diol used as internal standards were synthesized enzymatically. Intra-day and inter-day precision and accuracy corresponds to the U.S. Food and Drug Administration Criteria for Bioanalytical Method Validation. The lower limit of quantitation (LLOQ) of nine hydroxy-androgens is 1.0pg to 2.5pg on column. Diols which have been infrequently measured: 5-androstene-3?, 17?-diol and 5?-androstane-3?, 17?-diol can be determined in serum at values as low as 1.0pg on column. The method also permits the quantitation of conjugated hydroxy-androgens following enzymatic digestion. While direct detection of steroid conjugates by electrospray-ionization tandem mass spectrometry has advantages the detection of unconjugated and conjugated steroids would require separate methods for each set of analytes. Our method was applied to pooled serum from male and female donors to provide reference values for both unconjugated and conjugated hydroxy-androgens. This method will allow us to interrogate the involvement of the conversion of 5-androstene-3?, 17?-diol to T, the backdoor pathway involving the conversion of 5?-androstane-3?, 17?-diol to DHT and the inactivation of DHT to 5?-androstane-3?, 17?-diol in advanced prostate cancer.

Dataset Information

Quantitation of pyridyloxobutyl DNA adducts of tobacco-specific nitrosamines in rat tissue DNA by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry.

Publications

Quantitation of pyridyloxobutyl DNA adducts of tobacco-specific nitrosamines in rat tissue DNA by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry.

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