Grantee Research Project Results

2006 Progress Report: Low Dose Effects of In Utero Exposure to Cadmium on Puberty

EPA Grant Number: R832136
Title: Low Dose Effects of In Utero Exposure to Cadmium on Puberty
Investigators: Martin, Mary Beth , Hilakivi-Clarke, Leena , Lumpkin, Michael
Institution: Georgetown University
EPA Project Officer: Hahn, Intaek
Project Period: December 1, 2004 through November 30, 2007 (Extended to November 30, 2009)
Project Period Covered by this Report: December 1, 2005 through November 30,2006
Project Amount: $738,798
RFA: Development and Characterization of Biological Systems for Studying Low Dose Effects of Endocrine Disrupting Chemicals (2004) RFA Text | Recipients Lists
Research Category: Endocrine Disruptors , Environmental Justice , Safer Chemicals

Objective:

During the last century, the onset of puberty and menarche in girls has occurred at significantly younger ages. Studies from our laboratory show that the heavy metal cadmium has potent estrogen-like activity in vitro and in vivo, and that in utero exposure to environmentally relevant amounts of cadmium advances the onset of puberty, increases weight gain, and alters the development of the mammary gland in female rat offspring. This project is designed to test the hypothesis that in utero exposure to low doses of cadmium alters the hypothalamic-pituitary-gonadal axis and consequently alters the onset of puberty, predisposes to obesity, and accelerates the development of the mammary gland.

This project has four objectives. Objective 1 will determine the dose-response effects of in utero exposure to cadmium on the onset of puberty, weight gain, and mammary gland development. Objective 2 is designed to determine the mechanism by which in utero exposure to cadmium alters the onset of puberty. Two hypotheses have been proposed for the regulation of the onset of puberty and will be tested. Objective 3 will determine the mechanism by which in utero exposure to cadmium alters weight gain. Objective 4 will determine the mechanism by which in utero exposure to cadmium accelerates the development of the mammary gland.

Approach:

To achieve these goals: Objective 1 will determine whether there is a linear relationship between the in utero exposure to low doses of cadmium (0.05, 0.5, 5, 50 and 500 ng/kgbw) and the estrogen like effects on puberty onset, body weight, and mammary gland development in female offspring. Two hypotheses have been proposed for the regulation of the onset of puberty. The gonadostat hypothesis proposes that the onset of puberty is due to a decreased sensitivity of the hypothalamus to the negative feedback of gonadol steroids, whereas the intrinsic restraint hypothesis proposes that the onset of puberty is regulated by the production of stimulatory signals [glutamate, neuropeptide Y (NPY), and transforming growth factor-alpha (TGFa)] that override the inhibitory signal [gamma-aminobutyric acid (GABA)] in the hypothalamus. Objective 2 is designed to determine whether in utero exposure to cadmium alters either or both of these pathways. Energy homeostasis is also controlled by the hypothalamus. Objective 3 will determine whether in utero exposure to cadmium alters the development and/or the responsiveness of the hypothalamus to endocrine [gherlin, PYY3-36, insulin, and leptin] and neuronal [NPY and agouti-related peptide (AgRP)] signals. Objective 4 will then determine whether cadmium alters the development of the mammary gland in utero or whether the metal alters the onset of puberty and consequently the development of the gland.

Progress Summary:

During the second year of funding, the dose-response and mechanism studies were initiated. Three doses of cadmium (0.5, 5, and 50 μg/kg bw) were examined in Sprague-Dawley rats. In these studies, pregnant animals were treated with cadmium on day 12 and day 17 of gestation, and the female offspring were monitored for vaginal opening. The results of this study suggest that the animals were more sensitive to the lower doses of the metal. Exposure to 50 μg/kg bw had no effect on vaginal opening, while exposure to the lower doses, 0.5 and 5 μg/kg bw, resulted in a significantly earlier onset of puberty. To determine the critical time of exposure to the metal, animals were exposed in utero and cross-fostered on control dams. Compared to control animals, animals exposed in utero or exposed during neonatal development had a significantly earlier onset of vaginal opening, suggesting that exposure to cadmium during both stages of development alters puberty onset. To understand the mechanism by which in utero exposure to the metal alters the onset of puberty, the animals were ovariectomized at 45 days of age and allowed to rest for 2 weeks. The animals were then divided into 3 groups, including control, treated with estradiol, or treated with an antiestrogen, and the effects on the expression of estrogen-regulated genes in the uterus and liver were measured. In the uterus, in utero exposure to cadmium appeared to increase the basal level of expression of the estrogen-regulated genes, progesterone receptor and c-fos, suggesting that the metal may have epigenetic effects on gene expression. In the liver, in utero exposure to cadmium appeared to decrease basal expression and did not alter the sensitivity of the liver to estradiol. To determine the precise mechanism by which in utero exposure to cadmium alters puberty onset, weight gain, and mammary gland development, the effects of the metal on gene expression in the hypothalamus, pituitary, ovary, mammary gland, uterus, and liver will be determined as a function of time after birth. We are now collecting target tissue at 0, 5, 10, 15, 20, 25, 30, and 35 days of age from animals exposed to cadmium in utero.

Expected Results:

Endocrine related diseases have reached or are reaching epidemic levels in Western populations such as the United States; however, the underlying causes of these diseases are not fully understood. We have recently identified metals as potent endocrine disruptors with estrogen-like activity. Our understanding of the potential significance of this finding to human populations is still in its infancy. In this application, we propose to study the estrogen like effects of cadmium, as a prototype of bivalent metals, at doses that are environmentally relevant.

Future Activities:

We are currently asking whether in utero exposure to cadmium alters the expression of key developmental genes in the hypothalamus, pituitary, ovary, mammary gland, uterus, and liver. These studies are designed to define the mechanism by which in utero exposure to the metal alters development.

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Publications Views
Other project views:	All 2 publications	2 publications in selected types	All 2 journal articles

Publications
Type	Citation	Project	Document Sources
Journal Article	Martin MB, Reiter R, Johnson M, Shah MS, Iann MC, Singh B, Richards JK, Wang A, Stoica A. Effects of tobacco smoke condensate on estrogen receptor-alpha gene expression and activity. Endocrinology 2007;148:4676-4686	R832136 (2006)	not available
Journal Article	Veselik DJ, Divekar S, Dakshanamurthy S, Storchan GB, Turner JM, Graham KL, Huang L, Stoica A, Martin MB. Activation of estrogen receptor-alpha by the anion nitrite. Cancer Research 2008;68(10):3950-3958	R832136 (2006)	not available

Supplemental Keywords:

endocrine disruptors, puberty, obesity, mammary gland development,, Health, RFA, Scientific Discipline, PHYSICAL ASPECTS, Health Risk Assessment, Physical Processes, Risk Assessments, Biology, Environmental Chemistry, Endocrine Disruptors - Human Health, endocrine disruptors, Biochemistry, Endocrine Disruptors - Environmental Exposure & Risk, Toxicology, Genetics, altered gene expression, altered sexual development, EDCs, in utero exposure, developmental biology, cadmium, endocrine disrupting chemicals, exposure, biological effects, HPG axis, human health risk, animal models, gene expression

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.