Scientists in the US and Canada studying the effects of bisphenol-A (BPA), an ingredient of polycarbonate plastic used to make common everyday items for storing food and medicines, found it caused loss of connections between brain cells in primates and may lead to disruption in memory and learning as well as depression. Based on their findings the scientists suggest the US Environmental Protection Agency lower the current safe limit for human daily exposure to BPA.

The study was the work of researchers from the Yale University School of Medicine, New Haven, Connecticut, and Ontario Veterinary College, Guelph, Canada and was published online on 3rd September in the Proceedings of the National Academy of Sciences (PNAS).

Previous studies have looked at the effect of BPA on rodents, but this is the first to look at what happens to primates, and it is also the first to use lower levels of the chemical, in fact the daily dose used in the study corresponded to the US EPA's reference safe daily limit.

As co-author Dr Csaba Leranth, professor in the Department of Obstetrics, Gynecology & Reproductive Sciences and in Neurobiology at Yale, explained:

"Our goal was to more closely mimic the slow and continuous conditions under which humans would normally be exposed to BPA."

"As a result, this study is more indicative than past research of how BPA may actually affect humans," he said.

For the study, Leranth and colleagues gave each primate a daily dose of 50 micrograms per kg of body weight of BPA for 28 days. They also gave them estradiol, a human estrogen hormone that is involved in the control of synaptic connections between brain cells. Previous research has shown this hormone is not only produced in the ovaries but also in the brain, where it contributes to the development and working of the hippocampus and prefrontal cortex, two parts of the brain that regulate mood and help form memories.

Using an electron microscope to count synaptic connections, Leranth and colleagues found that BPA stopped them forming in the hippocampus and prefrontal cortex. They wrote:

"Our data indicate that even at this relatively low exposure level, BPA completely abolishes the synaptogenic response to estradiol."

The authors said that remodelling of spine synapses is crucial to cognitive and mood function, and if, as shown, BPA interferes with building synapse connections, it could have "profound implications". They concluded that:

"This study is the first to demonstrate an adverse effect of BPA on the brain in a nonhuman primate model and further amplifies concerns about the widespread use of BPA in medical equipment, and in food preparation and storage."

Co-author Dr Tibor Hajszan, an associate research scientist who works with Leranth at Yale, said:

"Our primate model indicates that BPA could negatively affect brain function in humans."

"Based on these new findings, we think the EPA may wish to consider lowering its 'safe daily limit' for human BPA consumption," said Hajszan.

While the average person is unlikely to reach the daily exposure limit set by the EPA, the authors were concerned about cumulative exposure to BPA and also that the negative effects could be worse in people with lower than normal estradiol levels, such as babies and the elderly.

"Bisphenol A prevents the synaptogenic response to estradiol in hippocampus and prefrontal cortex of ovariectomized nonhuman primates."
Csaba Leranth, Tibor Hajszan, Klara Szigeti-Buck, Jeremy Bober, and Neil J. MacLusky.
PNAS published September 3, 2008.
DOI:10.1073/pnas.0806139105

Click here for Abstract.

Sources: Journal article, Yale University.

Written by: Catharine Paddock, PhD