Chemical in Plastics Linked to Prostate Cancer
CHICAGO, Illinois, June 2, 2006 (ENS) - The first evidence that exposure to low doses of environmental estrogens during development of the prostate gland in the male fetus may result in a predisposition to prostate cancer later in life is presented by a study in the June 1 issue of the journal "Cancer Research."
In this study, a research team led by Dr. Gail Prins of the University of Illinois at Chicago (UIC) and Dr. Shuk-Mei Ho of the University of Cincinnati worked with rats during the developmental period corresponding to the second and third trimester of human pregnancy.
The scientists exposed the rats to low doses of estradiol, a natural estrogen, or to a manufactured compound that mimics the hormone action of estrogens. They found that this early exposure predisposed male rats to precancerous lesions of the prostate gland in old age.
The manufactured compound, bisphenol A (BPA), is used in making plastics and epoxy resins such as the polycarbonate plastic found in baby bottles, reusable water bottles, food storage containers, toys, pacifiers and baby teethers. BPA is also used to make epoxy resins, which coat the inside of metal food cans, and dental sealants.
"Most remarkably, early BPA exposure sensitized the prostate to precancerous lesions brought on by exposure of the adult animal to elevated estradiol," said Prins, professor of urology at UIC and senior author of the study.
The doses of estradiol and BPA used in the study were similar to levels found in human serum, in the circulation of some pregnant women, and in the fetus, the researchers said.
Transfer of BPA from mother to fetus has been reported in other studies, they noted, and levels in male fetuses have been shown to be higher than those of female fetuses.
The researchers were able to demonstrate that early estrogen or BPA exposure permanently changed the methylation, or tagging, of specific stretches of DNA in the neonate's prostate cells, a phenomenon referred to as epigenetic reprogramming.
In epigenetic reprogramming, gene expression is altered without changing DNA sequences or content. Several of the epigenetically altered sites turned out to be in important genes that regulate cellular functions, they said.
The researchers conclude that exposure to environmental estrogens, such as BPA, or natural estrogens affect the pattern of gene expression in the prostate during development, and in so doing promote prostate disease with aging.
"These findings are true for an animal model, and application to human prostate disease will await future studies," the authors concluded. Ho is first author of the study and professor and chairman of environmental health at the University of Cincinnati.
Wan-Yee Tang, of the University of Cincinnati, and Jessica Belmonte de Frausto of UIC also contributed to the study, which was funded by grants from the National Institutes of Health and the Department of Defense.
The United States produces over 1.6 million pounds of BPA annually, and this chemical has been detected in the bodies of nearly all humans tested in the United States.
The University of Missouri-Columbia (MU) researcher whose original study brought the adverse health effects of BPA to light, now has the backing of more than 95 other independent scientific studies.
Frederick vom Saal, professor of biological sciences, said recent studies have shown that BPA is extremely harmful in very low doses because it acts like the female hormone estrogen and interferes with the body's natural processes.
BPA can leach from plastics when heated, according to a 1993 study at the Stanford University School of Medicine, among others. A Spanish study published in 1995 showed that once plastic has been heated, BPA can continue to leach out. For instance, when a plastic-lined can was washed out and refilled with water, that water picked up measurable quantities of BPA.
BPA has been linked to adverse effects on male and female reproduction, altered immune system function, behavioral changes, learning disabilities, brain damage and an increased chance for certain cancers.
"The science is clear and the findings are not just scary, they are horrific," vom Saal said. "When you feed a baby out of a clear, hard plastic bottle, it's like giving the baby a birth control pill."
Vom Saal makes the case for a new government safety standard concerning BPA in an article published April 13, 2005 issue of the journal "Environmental Health Perspectives."
The last U.S. Environmental Protection Agency risk assessment for BPA was conducted in the 1980s. In his paper, vom Saal says that the latest research showing adverse effects of the chemical are all conducted with an amount of BPA less than the government standard at levels normally found in the human body.
"If BPA was treated as a drug, it would have been pulled immediately," vom Saal said. "We are not saying get rid of plastics. This chemical can be replaced right now by safer materials and the public would never notice the difference."
But BPA is approved for use in food packaging by the U.S. Food and Drug Administration.
Plastics industry representatives say the trace amounts that migrate from some products pose no danger and are far below safety thresholds set by the U.S. Environmental Protection Agency and other agencies.
The American Plastics Council, which represents manufacturers of polycarbonate bottles, says that bisphenol A does not leach out of plastic bottles when treated as most people would use them even when the bottles are old and have been heated repeatedly.
The Plastics Council cites a 2005 study by the Dutch Food and Consumer Product Safety Authority that measured migration from 22 new baby bottles, representing 14 brands, and 20 old baby bottles, representing 11 brands.
The old bottles had been used for up to three years in households under typical conditions including microwave heating, boiling before use and dishwashing.
"Consistent with many other studies," says the Plastics Council, "no migration of bisphenol A was detected from the new bottles. Significantly, trace migration levels were detected in only three of the old bottles. Contrary to what is commonly claimed, these results indicate that typical use of polycarbonate bottles does not lead to extensive migration."