Archives for the day of: July 2, 2011

From Slate:

The last quarter of a century has taught science some newfangled things about breasts. For one thing, they appear to be showing up earlier in young girls, with possible consequences for breast cancer later on. For another, the way they grow and develop varies from woman to woman, and—if lab animals are any indication—normal exposures to commercial chemicals can alter that process. The growing human breast is also more vulnerable than we thought. Data from atomic-bomb survivors in Japan show that it was adolescents—not grown women—near the explosions who were most likely to develop breast cancer in later years. Since then, there’s been similar data for girls who were exposed to medical X-rays or radiation therapy, as well as research showing that the pesticide DDT, now banned but pervasive in the 1950s and 1960s, is associated with a higher risk of breast cancer in women exposed as girls.

So it may come as a surprise that the federal agencies responsible for public health don’t routinely take childhood exposures into account when testing whether commercial chemicals cause mammary tumors. In fact, in many lab-animal tests, they don’t bother to look at the mammary gland at all. Breast cancer may be the No. 1 killer of middle-aged women in the United States, but as a new set of reports makes clear, the breast is a major blind spot in federal chemical-safety policy. “They just throw the mammary glands in the trash can,” says Ruthann Rudel, research director with the nonprofit Silent Spring Institute and lead author of one of the papers, a review of the latest science on mammary gland development and toxic exposures.

The reports, published last week in the journal Environmental Health Perspectives, grew out of a 2009 workshop on mammary gland risk assessment, which involved scientists from federal and international agencies as well as independent groups. Breast cancer is just one of the areas federal agencies neglect, the reports show, along with health issues surrounding lactation and the timing of breast development in puberty. “Few chemicals coming into the marketplace are evaluated for these effects,” state Rudel and her co-authors.

But blowing off these tests is a big mistake. The mammary gland—the breast’s intricate milk-making structure—is uniquely sensitive to toxic chemicals, says Suzanne Fenton, a reproductive endocrinologist with the National Toxicology Program of the National Institutes of Health, and a co-author of the science review. In both rodents and humans, it starts to develop in the fetus, undergoes a colossal growth spurt at puberty, and doesn’t fully develop until late pregnancy. During these times, its cells appear particularly vulnerable to carcinogens and other organ-altering substances. While lab rats and mice aren’t perfect proxies for humans, their mammary glands undergo similar development patterns under similar hormonal influences, says Fenton.


From PBS NewsHour:

A chemical used to produce baby bottles, cups and plastic packaging may cause male mice to act like females, a new study finds.

Published Monday in the Proceedings of the National Academy of Sciences, the study shows that male deer mice exposed to the organic compound Bisphenol A – or BPA – appeared more anxious and lost their ability to quickly navigate a maze. Both traits are highly uncommon for male deer mice but typical in females, the scientists say.

The male mice also appeared to lose their ability to attract females. At a rate of 2-to-1, test females rejected BPA-exposed males as potential breeding partners, leading the study’s authors to conclude that BPA exposure for males “could impact behavioral cues, pheromone signaling, or both.”

The study is just the latest strike against BPA, which many scientists call an endocrine-disrupting agent that mimics the body’s hormones and causes a slate of health defects in humans. Previous animal studies have found that BPA may accelerate puberty and could lead to cancer, heart disease and diabetes.

Even so, it continues to be widely used in the manufacturing of polycarbonate plastics – especially plastic bottles – as well as in the lining of canned food containers, dental sealants and some medical devices.

In 2008, the Food and Drug Administration said products in the American marketplace did not contain enough of the substance to be dangerous. But that same year, the Department of Health and Human Services’ National Toxicology Program issued a report expressing “some concern for neural and behavioral effects in fetuses, infants, and children at current human exposures.”

Just last week, the American Medical Association adopted a policy at its annual meeting officially “recognizing BPA as an endocrine-disrupting agent and urging that BPA-containing products with the potential for human exposure be clearly identified.” The organization also urged industry leaders to stop producing baby bottles and infant feeding cups with BPA.

Nine states – Connecticut, Maine, Maryland, Massachusetts, Minnesota, New York, Vermont, Washington, and Wisconsin – have BPA bans in place. Legislation is currently in the works to ban the chemical in baby food containers in California and Delaware.

Dr. Retha Newbold, a retired developmental biologist from the National Institute of Environmental Health Sciences, has studied BPA extensively and called the deer mice study “another marker of our sick environment.” But she stopped short of drawing any connections to humans.

“I think we have to be careful when we extrapolate any of these behavior studies in animals to humans,” she said. “But it gives us markers where we can start looking at some of these sexual behavior and cognitive learning processes in humans.”

We spoke with the lead author of the PNAS study, Dr. Cheryl Rosenfeld, associate professor of biomedical sciences at the University of Missouri.

What were you hoping to find in this latest BPA study?

Our guess was that if males are exposed to BPA in utero, when testosterone begins programming the brain, later behaviors would be affected. And we thought that the primary differences might be in sexually selective traits, or behaviors that are differently expressed between males and females. In many species, these are essential to produce offspring but they’re dependent on the development and physical condition of the animal as it’s in the womb and during the postnatal period. So we presumed these traits might be susceptible to BPA exposure.

Did your study mimic the way humans are exposed to BPA?

Yes, we only exposed the mice to BPA through the mother’s diet en utero and while they were nursing. That replicates what’s happening in the real world. Most health organizations agree that our primary exposure to BPA is through diet. A fetus has less ability to metabolize BPA, and it can get from the mother to fetus easily. When we measured the blood BPA concentrations in the females, we found the range of exposure is within the limits of what’s been detecting in humans.

And how does the maze relate to BPA exposure?

When these mice are sexually mature, their brains undergo significant remodeling that allows them to exhibit certain behaviors – like increased spatial-navigational skills in males. In humans, too, men tend to have a better ability than girls to locate in their environment – to know where they are in their environment, to remember where things are and where to find them. So when the males got to adulthood, we started them on behavioral testing in a maze that is well-recognized to test this ability. There are several holes and only one leads to the home cage. Non-BPA exposed males can almost immediately get to the correct hole. The BPA exposed male took quite a bit longer. They didn’t use the most efficient strategy and just wandered around randomly, aimlessly. When we tested the females, both the non-exposed and BPA-exposed females had similar responses. They were acting behaviorally like females.


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