Common Plastics Cause Gene Changes In MiceMar 31, 2003 | UPI
A compound found in common plastic containers could cause abnormal pregnancies in mice, research released Monday reveals.
Low-level exposure to Bisphenol A, used in food and beverage containers and baby bottles, interfered with cell division in female mouse eggs, researchers discovered. The interference resulted in the chromosomal abnormality known as aneuploidy, which can lead to mental retardation and birth defects in humans.
Patricia Hunt, genetics professor at Case Western Reserve University, said she was "happily" studying the effects of age on chromosome abnormalities in female mouse eggs when something unexpected happened.
"One day our control values went completely crazy," Hunt told United Press International. The rates of chromosome abnormalities increased dramatically.
Some sleuthing revealed a temporary worker had picked up the floor detergent to clean the mouse cages. A harsh cleanser, the detergent started to degrade the rodents' plastic enclosures. "Once the damage is done, the plastic degrades and continues to degrade," Hunt said. After a while, the almost transparent cages went white then bubbly, she said.
Knowing from previous research that Bisphenol A, a compound in the plastic cages, mimics estrogen and could contribute to early onset of girls' puberty, Hunt figured the damage to the cages might have contaminated the mice's water with BPA.
To confirm this suspicion, Hunt worked with collaborator Terry Hassold and a team of researchers to get to the bottom of the mystery. The evidence pointed to BPA, which in increasing doses raised the number of chromosomal abnormalities in the eggs of female mice.
"The chromosomes should line up and divide into two equal groups," Hunt said. "They weren't lining up right."
Although the results cannot be extended to humans, there has been research on human levels of BPA. Hunt said a German study had determined blood levels of the compound in pregnant women, their fetuses and placenta.
"The levels they reported are not far from the range we were at," Hunt noted, although the source of the BPA in the German research was not determined. Other studies, however, suggest resin coatings used to line food and beverage containers can leach the compound, she added.
The reason for the cell division interference is unclear. Hunt said BPA is not structurally similar to estrogen but can bind to the hormone's receptors. Because the attraction is weak, some scientists think BPA should not affect humans adversely, Hunt said. However, she added, the compound might act in an unsuspected way not related to its timid affinity to estrogen receptors.
Hunt said she would not suggest doing away with all plastics, which would be impossible, but noted some are more stable than others. Instead, she suggested that less stable polycarbonate plastics which are composed of BPA be switched with glass or other alternatives.
The new data are consistent with historical research on environmental estrogens and are a big deal, said John McLachlan, director of the Center for Bioenvironmental Research at Tulane and Xavier Universities, New Orleans.
"It's big because it gives a plausible explanation for why there is this high percentage of chromosomal abnormalities in human embryos," McLachlan told UPI. Although environmental estrogens might not explain for all of the cases, the possibility "adds another kind of biology to our thinking," he continued.
The implications of the results should mobilize manufacturers and regulators to act, said Frederick vom Saal, professor of reproductive biology at the University of Missouri in Columbia.
"The use of these products in Japan has already decreased dramatically," said vom Saal. A number of studies have shown BPA can affect behavior, decrease sperm count and cause changes in the urinary tract, he said.
Hunt's is the first to show BPA can have chromosomal effects. Vom Saal said the consequences of this phenomenon are dire. The new findings show the compound can damage fetuses and it can kill them, he said, and regulatory agencies will no longer be able to ignore the harmful effects.
"This is something that has to be of significant concern," vom Saal said. "These animals get (BPA) from drinking out of the equivalent of old baby bottles."
Although the study was done in mice, vom Saal said the process of oocyte, or egg, formation in mice is the same as that in humans.
"This is simply not a product that should be used to put food in," vom Saal told UPI. "Or people should be told to use it a few times then throw it away."