Effects of prepubertal exposure to xenoestrogen on development of estrogen target organs in female CD-1 mice

Background: There have been no previous reports comparing the effects of prepubertal xenoestrogen exposure on development of the reproductive tract and mammary glands in female mice. The effects of genistein (GEN), resveratrol (RES), zearalenone (ZEA), zeranol (ZER), bisphenol A (BPA) and diethylstilbestrol (DES) were examined. Materials and Methods: Beginning at 15 days of age, female CD-1 mice were administered 4 daily subcutaneous injections of 10 mg/kg/day of GEN, RES, ZEA, ZER or BPA, or 10 Ig/kg/day of DES dissolved in dimethylsulfoxide (DMSO), or DMSO vehicle. Vaginal opening was checked; estrous cyclicity was monitored from 5, 9 or 21 weeks of age for 21 consecutive days; 6 animals per group were autopsied at 4, 8 and 24 weeks of age. Results: Prepubertal exposure to GEN, ZEA, ZER and DES (but not RES or BPA) accelerated puberty onset (vaginal opening). Vaginal smears indicated that all xenoestrogen- treated mice were cycling, but ZEA-, ZER- and DES-treated mice spent more time in estrus. At 4 weeks of age, absence of corpora lutea (anovulatory ovary) was observed in the untreated controls (33%, 2/6) and the GEN (50%, 3/6), RES (50%, 3/6), ZEA (100%, 6/6), ZER (100%, 6/6), BPA (83%, 5/6) and DES groups (100%, 6/6). At 8 weeks of age, absence of corpora lutea was observed in the ZEA (33%, 2/6) group. Corpora lutea were present in all mice sacrificed at 24 weeks of age. Groups that received prepubertal xenoestrogen injections exhibited no morphological abnormalities of the uterus and vagina, and exhibited mammary gland growth similar to that of the untreated controls at all time-points. Conclusion: GEN, ZEA, ZER and DES (but not RES or BPA) caused early vaginal opening; mice exposed to ZEA, ZER or DES spent more time in the estrus phase; ZEA-treated mice had a longer period of anovulatory ovary than other xenoestrogen-treated mice; however, none of the xenoestrogens tested altered the uterine or vaginal morphology or mammary gland growth. Xenoestrogens (chemicals with estrogenic activity) are endocrine-disrupting chemicals that include naturally occurring substances produced by plants (phytoestrogens), molds (mycoestrogens) and man-made chemicals released into the environment (1). They may be ingested directly in plant material, in the tissues of animals that ingest xenoestrogen-producing plants or plants infected by xenoestrogen-producing molds, or in foodstuffs contaminated by release of xenoestrogens from polycarbonate plastic plates. Exposure to xenoestrogens during critical stages of growth can interfere with the development and differentiation of estrogen target organs (2). These effects can be severe, particularly in prepubertal children, whose endogenous estrogen concentration is low (3). There is evidence that exposure of humans to the xenoestrogen diethylstilbestrol (DES; (E)-3,4-bis (4-hydroxyphenyl)-3-hexene) alters the development of estrogen target organs. In utero exposure to DES as an anti-abortive has been found to induce clear cell adenocarcinoma of the vagina in daughters after puberty (4). Although the DES-exposed daughters in that study had low risk of development of clear cell adenocarcinoma (<1%), DES was associated with increased frequency of benign reproductive tract dysfunction and structural abnormality. Many experiments using rodent models have shown strikingly similar abnormalities after exposure to DES in early life (5); mouse models have proven to be effective for the examination of abnormalities in estrogen target organs. Naturally occurring and man-made chemicals that exhibit estrogenic biological activity are widely distributed in the environment (1). Among the chemicals that exhibit such activity are genistein (GEN), resveratrol (RES), zearalenone (ZEA), zeranol (·-zearalanol; ZER) and bisphenol A (BPA). GEN (4', 5, 7-trihydroxy isoflavone) is a major component of soy-based foods. It is estimated that infants