Environmental Factor, June 2011, National Institute of Environmental Health Sciences
Williams discusses the effects of neonatal phytoestrogen exposure
By Eddy Ball
Williams said adult vegetarians consume about one milligram per kilogram daily. “Babies who only drink soy formula as their source of nutrition take in five- to ten-fold that amount,” she said. (Photo courtesy of Steve McCaw)
Miller selects a principal investigator to speak at each Council meeting, highlighting the leading-edge research happening in the Institute's intramural program. (Photo courtesy of Steve McCaw)
Members of the National Advisory Environmental Health Sciences Council (http://www.niehs.nih.gov/about/boards/naehsc/index.cfm)enjoyed a scientific talk by NIEHS Principal Investigator Carmen Williams, M.D., Ph.D., during their spring meeting May 19 at NIEHS.
Williams, who heads the Reproductive Medicine Group, outlined results of her group's most recent investigations using a mouse model. Her presentation was titled “Permanent Reprogramming of Gene Expression in Response to Neonatal Phytoestrogen Exposure: Implications for Female Reproductive Tract Function and Pathology.” The work, as Williams explained, addresses important public health issues - unexplained infertility and difficulty of conception, reproductive tract abnormalities, and premature birth - linked to widespread environmental exposures that could be mitigated by primary preventive measures.
In his introduction of Williams, NIEHS Acting Scientific Director David Miller, Ph.D., praised her accomplishments as a physician-scientist capable of integrating basic, clinical, and translational research. “She adds quite a bit to our Laboratory of Reproductive and Developmental Toxicology,” he said.
From bedside to bench
Following her M.D. and advanced clinical training in reproductive endocrinology and infertility, Williams completed her Ph.D. in cell and molecular biology and then served as an attending physician in the University of Pennsylvania Health System. As she said at the beginning of her talk, her interest in endocrine disrupting compounds in the environment actually began in the hospital, where one of her first gynecological cancer patients was an 18 year old who died from vaginal cancer triggered by prenatal exposure to diethylstilbestrol (DES), a synthetic form of estrogen.
Her current work in gene expression reprogramming initiated by exposure to phytoestrogens, she said, involved taking, to the next stage, a dormant project that was actually initiated here at NIEHS more than ten years ago to study the effect of estrogens on female reproductive tract development. Williams has advanced the original project, which studied DES exposure in a rodent model, to focus on neonatal exposure to plant-based phytoestrogens at levels comparable to those in formula-fed infants, specifically genistein, the most abundant isoflavone in these formulas.
Elegantly designed experiments
In previous work on the project by NIEHS investigators Retha Newbold and Wendy Jefferson, Ph.D., neonatally exposed animals were mated at two months, four months, and six months of age. Animals receiving the higher dose of genistein, 50 milligrams per kilogram daily, were unable to carry their embryos to term. There was evidence to suggest that they did conceive at lower rates, but with smaller implantation sites than controls and loss of embryos soon afterwards. Animals exposed to a lower dose could conceive but tended to have a smaller average number of pups. Testing determined that hormone levels in exposed animals were normal.
After Williams picked up the project, further testing in vitro and in nonexposed foster dams indicated that there was also no problem with egg quality, suggesting that something in the oviduct or uterus was the cause of infertility. After flushing embryos from the oviducts of exposed animals, Williams was able to determine that the loss of embryos was taking place somewhere between day two and day three.
Although there was evidence of problems in both oviduct and uterus, which failed to support the embryos, Williams decided to focus her follow-up experiments on the oviduct on day two of pregnancy. At that point, the group removed the oviducts from controls and treated animals to look at morphology and gene expression.
Pinpointing gene expression
Through histology and microarray analysis of the adult oviducts of neonatally exposed and control animals, Williams' group determined that genistein-exposed mice showed abnormal oviduct morphology attributable to changes in expression of genes that modulate neonatal oviduct morphogenesis, including Hoxa, Wnt, and hedgehog signaling genes. There was also permanent upregulation of homeobox genes normally expressed only in the cervix and vagina, including Six1, Pitx1, and Nkx3-1.
According to Williams, numerous immune response genes were significantly altered in the adult oviduct before and during early pregnancy, suggesting that the abnormal oviduct responded inappropriately to hormone-mediated modulation of mucosal immunity that is required for survival of the embryos.