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Environmental Factor

August 2011

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Study finds BPA-exposed male deer mice less attractive to females

By Thaddeus Schug
August 2011

Cheryl Rosenfeld, Ph.D., D.V.M.

According to Rosenfeld, BPA exposure through the diet has been underestimated by previous lab tests. “We believe that these mouse model studies are a more accurate representation of what happens to BPA as the human body attempts to process this toxic substance.” (Photo courtesy of Cheryl Rosenfeld)

mouse looking up

According to the study, a mouse's luck finding a soul mate may depend on the mother's dietary exposure to BPA. (Photo courtesy of Cheryl Rosenfeld)

In a new study, published June 27, NIEHS-funded investigators add to the ongoing debate surrounding the safety of products made with the chemical bisphenol A (BPA). With BPA studies having varying results and interpretations, experts are still uncertain about what these results mean to human health. 

NIEHS grantee Cheryl Rosenfeld, Ph.D., D.V.M. ( Exit NIEHS, and her group at the University of Missouri-Columbia (UM), who report that male deer mice whose mothers were fed a diet containing BPA while pregnant are subtly, yet significantly, different from males with no BPA exposure. The BPA-exposed mice exhibit traits indicating decreased masculinity and learning ability, differences that could impair their mating behaviors and their likelihood of producing offspring.

In the study ( Exit NIEHS, BPA-exposed male deer mice were unable to navigate their way out of a maze, even though their untainted male peers quickly mastered the same maze. By a two-to-one margin, female deer mice showed less sexual interest in BPA-affected males compared to unexposed males.

"The BPA-exposed deer mice in our study look normal; there is nothing obviously wrong with them. Yet, they are clearly different," said Cheryl Rosenfeld, associate professor of biomedical sciences in the College of Veterinary Medicine and investigator in the Bond Life Sciences Center. "Females do not want to mate with BPA-exposed male deer mice, and BPA-exposed males perform worse on spatial navigation tasks that assess their ability to find female partners in the wild.”

BPA is one of the most widely produced chemicals in the world, resulting in widespread exposure of humans to this chemical. BPA is used in the manufacturing of polycarbonate plastics, epoxy resins, and flame retardants. Exposure to BPA occurs through many sources, including reusable water bottles, baby bottles, metallic food cans, thermal paper, carbonless copy paper, and consumer electronics, including computers, cell phones, and video game consoles.

Addressing the controversy surrounding BPA

In 2008, the NTP announced that it had “some concern” about the potential negative effects BPA may have on developing children, based on a thorough review of academic and regulatory studies.  The current acceptable limit of BPA exposure set by FDA is 50 micrograms per kilogram of weight per day for humans, but animal studies show that chronic exposure to lower levels has effects on biological processes in first- and second-generation offspring, which has prompted a reevaluation of this acceptable limit.

In response to the many inconsistencies in studies involving BPA and growing public concern over its potential to act as a hormone mimic, NIEHS has invested heavily in research related to BPA and other endocrine disrupting chemicals. In 2009, NIEHS awarded 11 BPA Grand Opportunities and Challenge grants, and currently funds a total of 35 projects studying the health effects and risks associated with BPA exposure. The overall goal of these efforts is to sponsor scientifically sound studies on a wide range of BPA-related health concerns, in both animal and human models, that can be used to enhance regulatory decision-making.

According to Jerry Heindel, Ph.D., program administrator and branch chief in the NIEHS Division of Extramural Research and Training (DERT), who oversees much of the Institute's grants portfolio on BPA, work by Rosenfeld, along with the many other current BPA-related studies sponsored by NIEHS, may put to rest many of the controversies surrounding BPA and other endocrine disrupting chemicals. “Cheryl's work adds to the list of over 20 studies showing adverse effects of BPA on some aspect of brain function and significantly expands the data demonstrating changes in one sex more than the other.  Thus, we are getting consistent results across labs. I expect to see clarity over the next year from the work of the scientists in the NIEHS-funded BPA consortium,” said Heindel.

In the days ahead, researchers will be trying to refine animal and epidemiological studies for more insight into whether the compound is a harmless chemical, as some studies have found, or a potential threat to human health.

The lead author of the paper, which was published in the June issue of the Proceedings of the National Academy of Sciences, was Eldin Jasarevic, a graduate student in the MU Interdisciplinary Neurosciences Program.

Citation: Jasarevic E, Sieli PT, Twellman EE, Welsh TH Jr, Schachtman TR, Roberts RM, Geary DC, Rosenfeld CS. Exit NIEHS 2011. Disruption of adult expression of sexually selected traits by developmental exposure to bisphenol A. Proc Natl Acad Sci U S A. 108(28):11715-20.

(Thaddeus Schug, Ph.D., is a postdoctoral research fellow in the NIEHS Laboratory of Signal Transduction and a regular contributor to the Environmental Factor. He is currently on detail as a program analyst in the NIEHS Division of Extramural Research and Training.)

model diagram explaining how exposure relates to cognition

Model explaining how daily exposure to BPA prevents the normal estradiol-induced increase in synapses in the hippocampus and prefrontal cortex of nonhuman primates, which could in turn impair cognition. (Graphic courtesy of Cheryl Rosenfeldd)

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