Catechol metabolites of endogenous estrogens induce redox cycling and generate reactive oxygen species in breast epithelial cells

Abstract

Estrogens are major risk factors for the development of breast cancer; they can be metabolized to catechols, which are further oxidized to DNA-reactive quinones and semiquinones (SQs). These metabolites are mutagenic and may contribute to the carcinogenic activity of estrogens. Redox cycling of the SQs and subsequent generation of reactive oxygen species (ROS) is also an important mechanism leading to DNA damage. The SQs of exogenous estrogens have been shown to redox cycle, however, redox cycling and the generation of ROS by endogenous estrogens has never been characterized. In the present studies, we determined whether the catechol metabolites of endogenous estrogens, including 2-hydroxyestradiol, 4-hydroxyestradiol, 4-hydroxyestrone and 2-hydroxyestriol, can redox cycle in breast epithelial cells. These catechol estrogens, but not estradiol, estrone, estriol or 2-methoxyestradiol, were found to redox cycle and generate hydrogen peroxide (H(2)O(2)) and hydroxyl radicals in lysates of three different breast epithelial cell lines: MCF-7, MDA-MB-231 and MCF-10A. The generation of ROS required reduced nicotinamide adenine dinucleotide phosphate as a reducing equivalent and was inhibited by diphenyleneiodonium, a flavoenzyme inhibitor, indicating that redox cycling is mediated by flavin-containing oxidoreductases. Using extracellular microsensors, catechol estrogen metabolites stimulated the release of H(2)O(2) by adherent cells, indicating that redox cycling occurs in viable intact cells. Taken together, these data demonstrate that catechol metabolites of endogenous estrogens undergo redox cycling in breast epithelial cells, resulting in ROS production. Depending on the localized concentrations of catechol estrogens and enzymes that mediate redox cycling, this may be an important mechanism contributing to the development of breast cancer.

BRCA1 interacts with Nrf2 to regulate antioxidant signaling and cell survival

“…E2 has been shown to elicit pleiotropic effects, including cell cycle regulation (Foster et al, 2001) and ROS generation, through oxidative metabolism or by acting on mitochondrial uncoupling proteins (Fussell et al, 2011). To evaluate whether NRF2 accumulation was caused by E2-induced ROS increase, we measured ROS levels in MCF7 at 4 h after treatment with 10 nM E2, but we did not detect any changes in ROS levels between E2-treated cells and control cells (Fig.…”

SERMs Attenuate Estrogen-Induced Malignant Transformation of Human Mammary Epithelial Cells by Upregulating Detoxification of Oxidative Metabolites

“…Exposure of breast epithelial cells to catechol estrogen metabolites is associated with ROS formation (12, 50). In the present study, we observed that exposure to E 2 for 6 days significantly increased ROS in MCF-10A cells (Figure 3A).…”

“…Further oxidation of estrogen catechols to quinones causes genotoxicity through electrophilic and oxidative DNA damage, including formation of 8-oxo-7,8-dehydro-2’-deoxyguanosine (8-oxo-dG) (8-10). Formation of reactive oxygen species (ROS) from quinone redox cycling can amplify DNA damage (11, 12). Several lines of evidence strongly suggest that the estrogen catechols are the proximal carcinogens in chemical carcinogenesis (13-17).…”

Iron, Oxidative Stress, and Cancer

“…Breast tumor tissues exhibit elevated DNA damage possibly due to the formation of redox active estrogen metabolites. 47 Endogenous estradiol generates 2-hydroxy estradiol and 4-hydroxy estradiol (4-OHE) by the action of cytochrome 1A1 and 1B1, and these metabolites are shown to form hydrogen peroxide in normal or malignant breast epithelial cells. 47 In our previous study, the expression of DNA repair protein was suppressed by 4-OHE in MCF-10A breast epithelial cells.…”

“…47 Endogenous estradiol generates 2-hydroxy estradiol and 4-hydroxy estradiol (4-OHE) by the action of cytochrome 1A1 and 1B1, and these metabolites are shown to form hydrogen peroxide in normal or malignant breast epithelial cells. 47 In our previous study, the expression of DNA repair protein was suppressed by 4-OHE in MCF-10A breast epithelial cells. 48 Excess iron may replace zinc in zinc finger of estrogen receptor producing more free radicals.…”