By Roger Meissen | Bond LSC

After a decade of work, Cheryl Rosenfeld is no stranger to bisphenol A (BPA), and her most recent study challenges the dangers posed by developmental exposure the chemical.

Her results continue to raise concerns about how BPA can potentially turn on or off genes in animals and subsequent effects on that early exposure can have on the development and brains of rats. Their research was published in the journal Epigenetics in July.

Rosenfeld and the University of Missouri joined experts from University of Cincinnati and FDA researchers as part of the Consortium Linking Academic and Regulatory Insights on BPA Toxicity, or CLARITY-BPA Consortium project. This collaboration is one of several across the United States meant to judge the chemical’s effect using standardized protocols established by the FDA to determine whether BPA exposure, especially during perinatal life, leads harmful effects.

“This is the first study published since a February 2018 BPA statement that challenges the FDA assertion that there is no concern for BPA,” Rosenfeld said. “We’ve shown using the FDA models and studies done right there at their facility that, indeed, early life exposure to BPA can result in gene expression and epigenetic changes that persist into adulthood.”

The study looked at gene expression changes in two brain regions — the hippocampus and the hypothalamus. The hippocampus is associated with long-term learning and memory and the hypothalamus plays a large role in hormone production that influence both the endocrine and nervous systems and affects diverse behaviors, including socialization, sexual behaviors, and appetite control.

Partners at the FDA/National Center for Toxicological Research fed Sprague-Dawley groups of rats — a standardized animal model in this research — diets of BPA, the synthetic estrogen present in birth control pills, ethinyl estradiol, or a chemical-free diet during a developmental period.

The brains from these animals were sent to Rosenfeld’s laboratory, who took biopsies from specific regions of the brain. They used these samples to evaluate whether a group of 10 genes, shown to be affected by BPA exposure in other studies, was affected by this exposure. They also examined the DNA methylation patterns for the promoters of three of these genes to determine whether prior BPA exposure led to persistent epigenetic changes. Epigenetic modifications do not affect the DNA sequence itself but gene and/or eventual protein expression.

Investigators determined that for several of the genes examined BPA exposure altered the expression pattern relative to animals not exposed to either chemical. Sex differences in gene expression in these two brain regions exists in normal animals, and such differences might thus contribute to masculinization or feminization of the brain manifesting as differences in various behavioral patterns, such as male or female sexual behavior. However, previous exposure to BPA abolished many of these gene expression differences between males and females, suggesting that it could disrupt male- and female-typical behaviors. For a gene, brain derived neural factor (BDNF), involved in learning and memory, BPA exposure led to increased methylation of its promoter, which could affect the expression of this key gene. Hippocampal expression of several genes was associated with prior performance in a test designed to measure learning and memory.

“It has become increasingly apparent that BPA can act as a weak estrogen, but what we’re seeing in these results is that it can elicit other effects in addition to those mirroring estrogen and likely independent of estrogen receptor pathways,” Rosenfeld said.

Initiatives like this and other CLARITY-BPA studies aim to answer questions that may later inform government regulators on how to limit or balance the health effects of manufactured chemicals that end up in the environment and may affect human and animal growth in previously unknown ways. With more than 15 billion pounds of BPA were estimated to be produced in 2013, its ubiquitous use in making plastics, lining cans and other manufacturing is of concern. Rosenfeld hopes a closer look at its epigenetic effects may lead to better regulation of the chemical.

“When people are thinking about the effects of BPA, they need to be thinking about it on a molecular scale,” she said. “These results might be subtle, but they can lead to dramatic consequences with long-standing, irreversible changes. Once BPA exposure resculpts an animal’s brain through DNA methylation and other epigenetic changes, it may be permanent.”

“Gene Expression and DNA Methylation Changes in the Hypothalamus and Hippocampus of Adult Rats Developmentally Exposed to Bisphenol A or Ethinyl Estradiol: A CLARITY-BPA Consortium Study,” was published in Epigenetics in July 2018.