Synthesis and reactivity of the catechol metabolites from the equine estrogen, 8,9-dehydroestrone

Citation
Fg. Zhang et al., Synthesis and reactivity of the catechol metabolites from the equine estrogen, 8,9-dehydroestrone, CHEM RES T, 14(6), 2001, pp. 754-763
Citations number
62
Categorie Soggetti
Pharmacology & Toxicology
Journal title
CHEMICAL RESEARCH IN TOXICOLOGY
ISSN journal
0893228X → ACNP
Volume
14
Issue
6
Year of publication
2001
Pages
754 - 763
Database
ISI
SICI code
0893-228X(200106)14:6<754:SAROTC>2.0.ZU;2-7
Abstract
The risk factors for women developing breast and endometrial cancers are al l associated with a lifetime of estrogen exposure. Estrogen replacement the rapy in particular has been correlated with an increased cancer risk. Previ ously, we showed that the equine estrogens equilin and equilenin, which are major components of the widely prescribed estrogen replacement formulation Premarin, are metabolized to highly cytotoxic quinoids which caused oxidat ive stress and alkylation of DNA in vitro [Bolton, J. L., Pisha, E., Zhang, F., and Qiu, S. Chem. Res. Toxicol. 1998, 11, 1113-1127]. In this study, w e have synthesized 8,9-dehydroestrone (a third equine estrogen component of Premarin) and its potential catechol metabolites, 4-hydroxy-8,9-dehydroest rone and 2-hydroxy-8,9-dehydroestrone. Both 2-hydroxy-8,9-dehydroestrone an d 4-hydroxy-8,9-dehydroestrone were oxidized by tyrosinase or rat liver mic rosomes to o-quinones which reacted with GSH to give one mono-GSH conjugate and two di-GSH conjugates. Like endogenous estrogens, 8,9-dehydroestrone w as primarily converted by rat liver microsomes to the 2-hydroxylated rather than the 4-hydroxylated o-quinone GSH conjugates; the ratio of 2-hydroxy-8 ,9-dehydroestrone versus 4-hydroxy-8,9-dehydroestrone was 6:1. Also in cont rast to experiments with equilin, 4-hydroxyequilenin was not observed in mi crosomal incubations with 8,9-dehydroestrone or its catechols. The behavior of 2-hydroxy-8,9-dehydroestrone was found to be more complex than 4-hydrox y-8,9-dehydroestrone as GSH conjugates resulting from 2-hydroxy-8,9-dehydro estrone were detected even without oxidative enzyme catalysis. Under physio logical conditions, 2-hydroxy-8,9-dehydroestrone isomerized to 8-hydroxyequ ilenin to form the very stable 2-hydroxyequilenin catechol; however, 4-hydr oxy-8,9-dehydroestrone was found to be stable under similar conditions. Fin ally, preliminary studies conducted with the human breast tumor S-30 cell l ines demonstrated that the catechol metabolites of 8,9-dehydroestrone were much less toxic than 4-hydroxyequilenin (20-40-fold). These results suggest that the catechol metabolites of 8,9-dehydroestrone may have the ability t o cause cytotoxicity in vivo primarily through formation of o-quinones; how ever, most of the adverse effects of Premarin estrogens are likely due to f ormation of 4-hydroxyequilenin o-quinone from equilin and equilenin.