Spectral Characterization of Catechol Estrogen Quinone (CEQ)-Derived DNA Adducts and Their Identification in Human Breast Tissue Extract

Abstract

Estrogens, including the natural hormones estrone (E₁) and estradiol (E₂), are thought to be involved in tumor induction. Catechol estrogen quinones (CEQ) derived from 4-hydroxyestrone (4-OHE₁) and 4-hydroxyestradiol (4-OHE₂) react with DNA and form depurinating N7Gua and N3Ade adducts that might be responsible for tumor initiation (Cavalieri, E. L., et al. (2000) J. Natl. Cancer Inst. Monogr. 27, 75). Current detection limits for the CEQ-derived DNA adducts by high-performance liquid chromatography with multichannel electrochemical detection are in the picomole range. To improve the limit of detection (LOD) for CEQ-derived DNA adducts, spectrophotometric monitoring was investigated. Spectroscopic studies of 4-OHE₁-1-N3Ade, 4-OHE₁-1-N7Gua, 4-OHE₂-1-N3Ade, and 4-OHE₂-1-N7Gua adduct standards were performed at 77 and 300 K. Upon laser excitation at 257 nm, the 4-OHE₁- and 4-OHE₂-derived N7Gua and N3Ade adducts are strongly phosphorescent at T = 77 K. No phosphorescence was observed at 300 K. Both N3Ade and N7Gua adduct types have weak phosphorescence origin bands near 383 and 385 nm, respectively. The corresponding phosphorescence lifetimes are 1.11 ± 0.05 and 0.37 ± 0.05 s. The LOD, based on phosphorescence measurements, is in the low femtomole range. The concentration LOD is approximately 10^-9 M, i.e., similar to that recently obtained for CEQ-derived N-acetylcysteine conjugates (Jankowiak, R., et al. (2003) Chem. Res. Toxicol. 16, 304). The LOD in capillary electrophoresis (CE) with field-amplified sample stacking and absorbance detection is about 3 × 10^-8 M. To verify whether CEQ-derived DNA adducts are formed in humans or not, tissue extracts from two breast cancer patients were analyzed by CE interfaced with room temperature absorption and low temperature (laser-excited) phosphorescence spectroscopies. For the first time, formation of CEQ-derived DNA adducts is shown in humans. For example, the level of 4-OHE₁-1-N3Ade in the breast tissue extract from a patient with breast carcinoma (8.40 ± 0.05 pmol/g of tissue) is larger by a factor of about 30 than that in the breast tissue sample from a woman without breast cancer (0.25 ± 0.05 pmol/g of tissue). In contrast, similar amounts of 4-OHE₂-1-N3Ade were observed in both types of tissue. Although more breast tissue samples from women with and without breast cancer need to be studied, these results suggest that the N3Ade adducts could serve as biomarkers to predict the risk of breast cancer.