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Chemical May Increase Prostate-Cancer Risk

Posted on: Thursday, 1 June 2006, 18:00 CDT

By CHRISTINE DELL'AMORE

A male fetus mildly exposed to estrogen-like compounds in the environment may become predisposed to developing prostate cancer later in life, researchers report for the first time.

In an animal model, rats that were given injections of bisphenol A -- a man-made compound commonly used in the manufacture of consumer plastics -- had a significantly higher incidence of precancerous lesions in the prostate than rats who did not receive the chemical injection.

What's tremendously exciting on the scientific realm is we found what is called epigenetic changes in the prostate gland, said Dr. Gail Prins, leader of the research team and a professor of physiology at the University of Illinois, Chicago.

The research was published June 1 in Cancer Research. Dr. Shuk-Mei Ho of the University of Cincinnati was the lead author.

Epigenetic changes occur when the DNA reprograms itself but does not mutate. Scientists know epigenetic changes are widespread in cancer development, possibly even more so than genetic mutations.

In scientific studies, a newborn rat is comparable to a human in utero. With this in mind, the researchers injected a dose of bisphenol A into rats at days one, three and five of life, when the prostate gland develops. At seven months, when rats are considered an aging animal, Prins looked at their prostate glands. The rats given bisphenol A did not appear abnormal.

However, when the older rats who had received bisphenol A injections as babies were given estradiol, a natural estrogen present in older men, these rats had increased susceptibility to prostate cancer.

The researchers concluded the bisphenol A sensitized the prostate to develop cancerous lesions after exposure to estradiol.

In recent years a controversy has arisen over the potential health effects of low-dose exposure to bisphenol A, which is used in the production of polycarbonate plastic items such as sunglasses, water bottles, CDs and baby bottles. The synthetic chemical tricks the body's estrogen receptors to bring about similar physiological effects as true estrogen, which is a known carcinogen.

The plastics industry has claimed the chemical is safe at typical levels of human exposure, yet dozens of independent studies have indicated there are health risks, particularly to fetuses. Scientists believe every American carries the compound in his or her body.

Pregnant mothers also possess five to ten times more of the chemical in their placenta and amniotic fluid than an average adult, Prins said. Since fetuses are more sensitive to outside agents during development, exposure to bisphenol A could be detrimental to their future health.

Past research has shown estrogens or estrogen-like chemicals can bring about changes in the prostate, according to Karen Knudsen, a cell biologist and associate professor at the University of Cincinnati.

But the most remarkable part of Prins and colleagues' study is the discovery that estrogen-like chemicals can alter DNA's gene expression.

That is a huge change in our understanding, said Knudsen. You have to take it for what it's worth -- it's in an (animal) system -- but it is interesting nonetheless, and potentially important because (people) are exposed to these compounds, she said.

It's unknown whether these findings could be extended to human biology, yet it's a relevant question for future study, Prins said. Because men get prostate cancer through many causes, to be able to pinpoint it to an exposure to a chemical 50 years prior, during fetal life, is going to be extremely difficult to do, Prins said.

Prins plans to create what she calls an epigenetic fingerprint, which can identify not just one gene affected by exposure to bisphenol A but an entire set of genes.

There's a lot of work to be done. It's not the final study, but it's provocative, she said.

Source: United Press International

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