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Environmental exposure to hormonally active chemicals has coincided with an increase in the incidence in breast cancer (Davis et al. 1993), testicular cancer (Skakkebaek et al. 1998), and other endocrine-related diseases (Sharpe and Skakkebaek 1993). These outcomes are thought to result from extemporaneous exposure to synthetic estrogens during fetal development (Sharpe and Skakkebaek 1993) and have motivated the worldwide formation of government-sponsored committees to evaluate evidence for this hypothesis. For instance, in the United States, the U.S. Environmental Protection Agency (EPA) developed a screening program to test chemicals that may contaminate water and food to assess potential endocrine disruptor activity (Endocrine Disruptor Screening and Testing Advisory Committee 1998). At the request of the U.S. EPA, the National Toxicology Program (NTP) convened a meeting to consider whether environmentally relevant doses of endocrine disruptors caused biological effects. In 2001, the NTP Low-Dose Peer Review Panel published a final report (NTP 2001), which stated that there was “credible evidence for low-dose effects” and suggested that different experimental animal strains may account for reports of both positive and negative effects for the same parameters. In this regard, Spearow et al. (1999) observed that rodent strains selected for high fecundity and rapid growth rates, such as CD-1 mice, are more estrogen resistant than the less fecund C57Bl6. An additional controversy identified by the NTP was the shape of the dose–response curve, which was reported as nonmonotonic for some effects of prenatal xenoestrogen exposure. For example, prenatal methoxychlor exposure altered the response of the adult uterus to 17β-estradiol (E2); low doses increased uterine weight, and higher doses reduced it (Alworth et al. 2002). This type of nonmonotonic response was also observed for other end points with other estrogenic chemicals (Rubin et al. 2001; Vandenberg et al. 2006; vom Saal et al. 1997), arguing that low-dose effects cannot be deduced from effects observed at high doses. Our research focuses on the effects of perinatal exposure to environmentally relevant levels of the xenoestrogen bisphenol A (BPA). In the the present study we examined strain sensitivity and the shape of the estrogen dose–response curve in the context of our ongoing work in the mouse mammary gland. In addition, we explored the effects of perinatal BPA exposure on subsequent estrogen sensitivity at puberty. BPA, a compound used in the manufacture of polycarbonate plastics and epoxy resins, leaches from food and beverage containers (Biles et al. 1997; Brotons et al. 1994) and dental sealants and composites (Olea et al. 1996) under normal conditions of use (Markey et al. 2001b, 2003b). BPA levels have been measured in human urine (Calafat et al. 2005), serum (Takeuchi and Tsutsumi 2002), and maternal and fetal plasma, amniotic fluid, and placental tissue at birth (Ikezuki et al. 2002; Schonfelder et al. 2002). We chose to administer perinatally 0 or 250 ng BPA/kg body weight (bw)/day to mice. Based on data reported by Arakawa et al. (2004), we estimated that this level of BPA should fall within the range of reported human exposures. In the mammary gland, perinatal exposure to BPA alters ductal invasion of the stroma at puberty and increases lateral branching and the number of terminal ends during adulthood (Markey et al. 2001a; Munoz de Toro et al. 2005). Although the mechanisms by which BPA induces developmental abnormalities in the mammary gland are unknown, it is plausible that estrogen receptors (ER), which are expressed in the fetal mammary gland, may mediate BPA-induced effects. In the present study, we compared the response of the mammary glands to E2 in outbred CD-1 mice (the strain we have used previously) with inbred C57Bl6 mice, which have been used in numerous studies involving development of the mammary gland. Different levels of biological complexity within the mammary gland (i.e., tissue organization and gene expression) were examined. We also examined the effects of perinatal BPA exposure on the response to E2 at puberty in both strains.

Polychlorinated biphenyls (PCBs) have been proposed to have a weak estrogenic activity and therefore pose a risk as potential environmental endocrine disruptors to the perinatal development of the female reproductive tract. Perinatal exposure to high concentrations of the potent synthetic estrogen diethylstilbestrol (DES) induces abnormal development of the female reproductive tract via a mechanism that acts through the down-regulation of Wnt7a (wingless-type MMTV integration site family, member 7A). To test the hypothesis that PCBs act as weak estrogens, we injected neonatal mice with a commercial PCB mixture (Aroclor 1254) or with low levels of DES and measured effects of exposure on Wnt7a expression and uterine morphology. We report here that neonatal PCB or low-level DES exposure resulted in the down-regulation of Wnt7a expression. In addition, both PCB and low-level DES exposure induced changes in the uterine myometrium and gland formation. These data reveal that weak estrogens such as the PCBs act through a Wnt7a-dependent pathway and suggest that Wnt7a regulation is a sensitive biomarker for testing weak estrogenic candidate compounds. The morphologic changes that were elicited by PCBs and DES were different immediately after exposure, suggesting that Wnt7a-independent pathways are also activated by one or both of these compounds. Although Wnt7a down-regulation is transient after estrogenic exposure, subsequent morphologic changes became more pronounced during postnatal and adult life, suggesting that the female reproductive tract is permanently reprogrammed after exposure even to weak estrogenic compounds. In addition, Wnt7a heterozygous mice were more sensitive to PCB exposure, revealing an important genetic predisposition to risks of environmental endocrine disruptors.

Helicobacter hepaticus, a bacterium discovered in 1994 and widespread in many experimental mouse populations, is associated with a high incidence of liver tumors in aging mice. A new mouse study shows that perinatal exposure to this pathogen, rather than development of hepatitis itself, may be the single most important factor in the development of liver tumors caused by H. hepaticus [EHP 116:1352–1356; Diwan et al.]. The results support evidence from other studies that progressive hepatitis and liver tumors in older mice may stem from early-life exposure. The researchers isolated a strain of H. hepaticus from infected A/J mice. Female mice received injections with a single dose of the bacteria. Females testing positive for the bacteria were bred with uninfected males. The researchers assessed liver histopathologic findings and tumor growth in male offspring aged 2 weeks to 2 years. Uninfected weanling males from another lab were injected at 3–4 weeks. The results showed a significant incidence of liver tumors in the offspring after intraperitoneal maternal exposure to the bacteria: 33% developed liver tumors, usually multiple tumors, and 18% developed hepatocellular carcinoma. None of the mice injected with the bacteria as young adults developed any tumors. Another striking result was that tumor outcome was not closely linked to severity of hepatitis; mice that contracted hepatitis did not necessarily develop hepatic tumors. Rather, it appeared that early exposure to the bacteria, not the hepatitis itself, was key to fostering tumor growth. The type of additional perinatal event required to induce tumor development is unknown but could involve DNA damage at that vulnerable early stage, followed by subacute inflammation of the liver in response to H. hepaticus infection. The authors note that similar scenarios could apply to human infection with Helicobacter pylori and other pathogens linked with cancer. The results point to the need for further study of changes in perinatal tissues in response to such infections.

A lack of regulation means that herbal remedies can be ineffective or, conversely, far more potent than users may suspect. Researchers in Taiwan have found a new reason for consumers to be wary of certain herbal remedies: some herbs used in traditional Chinese medicine contain lead, which mothers can pass to their infants through breast milk. The study, published in the 1 February 2006 issue of Science of the Total Environment, adds to the growing evidence that infants can be exposed to potentially dangerous lead levels in utero and through breast milk. Bans on leaded paint and gasoline have caused lead exposure during childhood to plummet. Now scientists are focusing more attention on perinatal exposure to lead via maternal circulating blood levels and breast milk. The neurotoxicant is associated with behavioral problems and diminished intelligence. Although lead has declined in the environment in a number of countries, it may still persist in soil, dust, and water in many parts of the world. Maternal bone lead accumulated during earlier exposure is released during pregnancy and lactation as the body redistributes its calcium stores. Principal investigator Bor-Cheng Han and colleagues originally recruited 72 pregnant women, but only 16 completed the study. The women were interviewed during pregnancy and lactation to collect information on residential and occupational lead exposures, socio-demographic characteristics, and consumption of nutritional supplements, traditional Chinese herbs, alcohol, and tobacco. The women provided breast milk samples weekly from 1 to 60 days postpartum. Nine of the women took traditional herbs, while seven did not. The researchers purchased samples of herbs that the mothers reported taking regularly—Angelicae sinensis radix, Lycii fructus, Zizyphi fructus, and a preparation known as Shy-Wuh-Tang. Then they tested the samples for lead content. All the samples contained lead; Shy-Wuh-Tang, used to treat menstrual and circulatory problems, had the highest levels, at 322.31 micrograms per kilogram (μg/kg). The nine herb users had a mean lead concentration of 9.94 μg per liter (L) in colostrum, the form of milk produced just after delivery. Lead levels in their breast milk dropped with most weekly samplings, to a mean concentration at the final sampling of 2.34 μg/L. Lead levels also declined in the seven mothers not using herbs, from 8.11 μg/L in colostrum (likely reflecting occupational or pollution exposures) to 2.36 μg/L in mature milk. The finding that Chinese herbs were contaminated with lead comes as no surprise to research scientist Richard Ko of the California Department of Health Services. In the 17 September 1998 issue of the New England Journal of Medicine, Ko reported high lead levels in 24 of 260 Chinese patent medicines sold in California. Tainted products slip easily into the hands of consumers because the FDA does not have enough resources to inspect all imported herbs, nor does it regulate herbs, which it considers dietary supplements rather than drugs. The Taiwanese researchers speculate that the herbs their subjects took were grown in contaminated soil. In spite of the risks, the worldwide market for herbal treatments is estimated to be more than $60 billion and growing fast, according to the UN Conference on Trade and Development. Some 30–50% of all medicines consumed in China are traditional herbs. It is unclear how much risk the lead-contaminated herbs posed to the babies in the Taiwan study. Jenny Pronczuk de Garbino, a physician with the WHO Department of Public Health and the Environment, says that “only if the doses were extremely high would they outweigh the benefits of breastfeeding,” but that “prevention of exposure is paramount.” The FAO/WHO Joint Expert Committee on Food Additives and Contaminants, an independent scientific expert body regularly convened by the FAO and the WHO, last assessed the risk of lead exposure to human health in 1999, and established a provisional tolerable weekly intake of 25 μg/kg body weight as a value that would not lead to any appreciable health risk. The WHO maintains in its 2003 document Global Strategy for Infant and Young Child Feeding that “[b]reastfeeding is an unequalled way of providing ideal food for the healthy growth and development of infants.” Han admits his study of just 16 mothers is too small to draw conclusions from. But it adds to the growing information about how mothers’ exposure may influence their infants’ lead levels. The Lead and Pregnancy Work Group organized by the CDC is reviewing such studies in an effort to develop national guidelines on assessing and managing risk of lead exposure during pregnancy and lactation. “We need a better understanding of neonatal exposure from breastfeeding,” says Adrienne Ettinger, a Harvard School of Public Health researcher and member of the CDC work group. “We don’t have all the scientific data yet.”