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Estrogen carcinogenesis: specific identification of estrogen-modified nucleobase in breast tissue from women.

ABSTRACT: Prolonged exposure to estrogens correlates with an increased risk for breast cancer. One explanation is that estrogen metabolites cause mutations by reacting with DNA, leading to depurination. We describe an extraction procedure and a liquid chromatographic tandem mass spectrometric (LC/MS/MS) assay to detect estrone-metabolite-modified adenine (Ade) in 100-200 mg samples of human breast tissue. To ensure reliable analyses, we used a synthetic estrone-metabolite-modified, U-(15)N-labeled Ade as an internal standard (IS). Appropriate high-pressure liquid chromatography gives sharp (approximately 5 s at half-height) and identical retention times for the analyte and the IS. In breast tissue from women with and without cancer, we found a coeluting material with similar MS/MS fragmentation as the IS, providing high specificity in the identification of the modified Ade; the recovery was approximately 50%. For women with and without breast cancer, the levels of the modified Ade are in the range of 20-70 fmol/g of breast tissue from five women and not detectable in tissue from another woman. The sample size and detection limits are not yet sufficient to permit distinctions between cancer and noncancer patients.

SUBMITTER: Zhang Q

PROVIDER: S-EPMC2742319 | biostudies-literature | 2008 Aug

REPOSITORIES: biostudies-literature

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Estrogen carcinogenesis: specific identification of estrogen-modified nucleobase in breast tissue from women.

Zhang Qiang Q Aft Rebecca L RL Gross Michael L ML

Chemical research in toxicology 20080802 8

Prolonged exposure to estrogens correlates with an increased risk for breast cancer. One explanation is that estrogen metabolites cause mutations by reacting with DNA, leading to depurination. We describe an extraction procedure and a liquid chromatographic tandem mass spectrometric (LC/MS/MS) assay to detect estrone-metabolite-modified adenine (Ade) in 100-200 mg samples of human breast tissue. To ensure reliable analyses, we used a synthetic estrone-metabolite-modified, U-(15)N-labeled Ade as ...[more]

PMID: 18672910

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Project description:Estrogen receptors play critical roles in both the normal physiological, and disease states of numerous tissues, including breast and uterus. Estrogen receptor alpha (ER) can activate or repress the expression of target genes upon estrogen stimulation. In order to better understand the transcriptional network of ER in breast and uterus, we generated genome wide maps ofM-BM- ER binding sites (ERBS) and gene expression profiles in breast cancer cells (MCF7 and T47D) and uterine cancer cells (ECC1 and Ishikawa) through ChIP-Seq and microarray techniques. Surprisingly, we identified large scale differences in the numbers of ERBS between these cell lines when treated with E2 (17-M-NM-2 estradiol). Besides identification of common and unique ERBS between breast and uterine cancer cell types., our data also suggest that both cell types could recruit a large set of common co-operating transcription factors (Co-TFs) and a few unique Co-TFs as well. Besides the genes that are commonly regulatedM-BM- between the different cell lines, there are a number of genes that are differentially regulated in different cell types. Gene pathway analyses of E2 target genes suggest that ER regulates many biological pathways and processes in both tissue-type dependent and independent manners. Our results showed that cell lines derived from same tissue display a greater similarity for both profiles of ERBS and gene expression, and that the differential profiles of ER and preferential recruitment of some Co-TFs are the main determinants for the differential regulation of E2 signaling in breast and uterine cancer cells. In order to explore common and distinctive features of ERM-NM-1 (estrogen receptor alpha) binding profiles between breast and uterus, we generated eight ChIP-Seq libraries for the four cell lines (MCF7, T47D, ECC1 and Ishikawa) under two different treatments (E2, ethanol). In addition, we generated four control libraries for the four cell lines. For all treatment libraries, we generated about 7-12 million unique tags each. ER antibody catalog number is (Santa Cruz,sc-543).

Project description:BackgroundEstrogens are recognized causal factors in breast cancer. Interindividual variation in estrogen metabolism may also influence the risk of breast cancer and could provide clues to mechanisms of breast carcinogenesis. Long-standing hypotheses about how estrogen metabolism might influence breast cancer have not been adequately evaluated in epidemiological studies because of the lack of accurate, reproducible, and high-throughput assays for estrogen metabolites.MethodsWe conducted a prospective case-control study nested within the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO). Participants included 277 women who developed invasive breast cancer (case subjects) and 423 matched control subjects; at PLCO baseline, all subjects were aged 55-74 years, postmenopausal and not using hormone therapy, and provided a blood sample. Liquid chromatography-tandem mass spectrometry was used to measure serum concentrations of 15 estrogens and estrogen metabolites, in unconjugated and conjugated forms, including the parent estrogens, estrone and estradiol, and estrogen metabolites in pathways defined by irreversible hydroxylation at the C-2, C-4, or C-16 positions of the steroid ring. We calculated hazard ratios (HRs) approximating risk in highest vs lowest deciles of individual estrogens and estrogen metabolites, estrogens and estrogen metabolites grouped by metabolic pathways, and metabolic pathway ratios using multivariable Cox proportional hazards models. All statistical tests were two-sided.ResultsNearly all estrogens, estrogen metabolites, and metabolic pathway groups were associated with an increased risk of breast cancer; the serum concentration of unconjugated estradiol was strongly associated with the risk of breast cancer (HR = 2.07, 95% confidence interval [CI] = 1.19 to 3.62). No estrogen, estrogen metabolite, or metabolic pathway group remained statistically significantly associated with the risk of breast cancer after adjusting for unconjugated estradiol. The ratio of the 2-hydroxylation pathway to parent estrogens (HR = 0.66, 95% CI = 0.51 to 0.87) and the ratio of 4-hydroxylation pathway catechols to 4-hydroxylation pathway methylated catechols (HR = 1.34, 95% CI = 1.04 to 1.72) were statistically significantly associated with the risk of breast cancer and remained so after adjustment for unconjugated estradiol.ConclusionsMore extensive 2-hydroxylation of parent estrogens is associated with lower risk, and less extensive methylation of potentially genotoxic 4-hydroxylation pathway catechols is associated with higher risk of postmenopausal breast cancer.

Dataset Information

Estrogen carcinogenesis: specific identification of estrogen-modified nucleobase in breast tissue from women.

Publications

Estrogen carcinogenesis: specific identification of estrogen-modified nucleobase in breast tissue from women.

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