Redox Cycling of Catechol Estrogens Generating Apurinic/Apyrimidinic Sites and 8-oxo-Deoxyguanosine via Reactive Oxygen Species Differentiates Equine and Human Estrogens

Abstract

Metabolic activation of estrogens to catechols and further oxidation to highly reactive o-quinones generates DNA damage including apurinic/apyrimidinic (AP) sites. 4-Hydroxyequilenin (4-OHEN) is the major catechol metabolite of equine estrogens present in estrogen replacement formulations, known to cause DNA strand breaks, oxidized bases, and stable and depurinating adducts. However, the direct formation of AP sites by 4-OHEN has not been characterized. In the present study, the induction of AP sites in vitro by 4-OHEN and the endogenous catechol estrogen metabolite, 4-hydroxyestrone (4-OHE) was examined by an aldehyde reactive probe assay. Both 4-OHEN and 4-OHE can significantly enhance the levels of AP sites in calf thymus DNA in the presence of the redox cycling agents, copper ion and NADPH. The B-ring unsaturated catechol 4-OHEN induced AP sites without added copper, whereas 4-OHE required copper. AP sites were also generated much more rapidly by 4-OHEN. For both catechol estrogens, the levels of AP sites correlated linearly with 8-oxo-dG levels, implying that depuriniation resulted from reactive oxygen species (ROS) rather than depurination of estrogen-DNA adducts. ROS modulators such as catalase which scavenges hydrogen peroxide and a Cu(I) chelator blocked the formation of AP sites. In MCF-7 breast cancer cells, 4-OHEN significantly enhanced the formation of AP sites with added NADH. In contrast, no significant induction of AP sites was detected in 4-OHE-treated cells. The greater redox activity of the equine catechol estrogen produces rapid oxidative DNA damage via ROS, which is enhanced by redox cycling agents and interestingly by NADPHdependent quinone oxidoreductase (NQO1).

High-intensity interval training beneficial effects on body mass, blood pressure, and oxidative stress in diet-induced obesity in ovariectomized mice

“…These effects include breaks in the genetic material, the formation of DNA adducts, and the oxidation of bases. 36 Additionally, there is an increase in serum concentrations of inflammatory cytokines and prooxidant factors due to menopause, suggesting the onset of OS. 37,38 HIIT improved the OS condition that developed due to OVX and the HF diet.…”

Association between 8-oxo-7,8-dihydro-2′-deoxyguanosine Excretion and Risk of Postmenopausal Breast Cancer: Nested Case–Control Study

“…7 and 8). Experimental studies indicate that estrogens, especially equine and synthetic estrogens, can induce 8-oxodG in cell types expressing ER (2,9,10). Moreover, elevated levels of 8-oxodG or oxidized purines have been found in breast cancer tissue (11)(12)(13)(14).…”

MECHANISMS IN ENDOCRINOLOGY: Nutrition as a mediator of oxidative stress in metabolic and reproductive disorders in women

“…Similarly, as shown by a mouse model by Lim et al, significant age-related increases in oxidatively damaged lipids, proteins and DNA are observed in different ovarian compartments, including granulosa cells and ovarian interstitial tissue, along with alterations of antioxidant enzyme expression (166). Finally, hormonal alterations that accompany ovarian aging, such as the marked reduction in estrogen, have been shown to increase levels of oxidative stress in the body (167).…”