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Article Last Updated: 06/01/2006 02:55:47 AM PDT
Scientists find new link between plastic, cancer
Exposure in the womb may trigger disease later
By Douglas Fischer, STAFF WRITER
Exposure to a common plastic additive before birth permanently changes DNA signaling in laboratory animals, scientists have found, predisposing infant male rats to prostate cancer later in life and offering tantalizing clues to how cancer gains a foothold in our bodies.
The groundbreaking results, published today in the journal Cancer Research, do not mean baby boys exposed to this additive — known as bisphenol-a and found in the plastic used to make shatter-proof bottles and line tin cans — will develop prostate cancer as old men.
But for laboratory rats exposed to amounts of bisphenol-a that reportedly contaminate the blood and amniotic fluid of pregnant U.S. women, the results were clear: Prostate glands healthy at birth became predisposed to cancer much, much later.
The finding, by scientists at the University of Cincinnati and the University of Illinois at Chicago, offers some of the strongest evidence to date on a new line of thinking that chemicals we use daily affect how genes turn on and off, with unknown consequences.
"There's reasonable evidence ... that precancerous lesions can result from these brief, low-dose exposures," said Gail Prins, professor of urology at the University of Illinois at Chicago and a coauthor of the study.
"The message here is we should proceed cautiously with our exposures. This puts (us) on notice, if you would, that there can be negative impacts with regards to prostate cancer."
The results should not scare consumers away from plastics containing bisphenol-a, cautioned Steve Hentges, executive director of the polycarbonate plastics unit of the American Plastics Council. Nearly 6 billion pounds of bisphenol-a is added to plastics annually, ending up in the plastics that line food cans, shape Nalgene sports bottles and make shatter-proof plastic baby bottles.
Hentges said the study used higher doses than those typically found in humans, based on Centers for Disease Control and Prevention data. And most exposure comes orally, whereas researchers injected bisphenol-a directly into the animals' blood, bypassing protective defenses in the stomach and kidneys. Prins disputed both points.
"It's too far away to draw any major conclusions about human health," Hentges said. "There's no black-and-white standard, certainly. But for me, it certainly hasn't reached a standard where I'll change any of my consumption patterns.
"But I'm very interested in seeing more research. That is for sure."
Other researchers called the results striking, particularly because they show for the first time how a genetically clean organ can become cancerous.
"It's the first real evidence that early exposure to an agent like bisphenol-a can predispose you to cancer," said Karen Knudsen, an associate professor of cell and cancer biology at the University of Cincinnati who works with tumor cells but was not involved in the study.
"It's priming the prostate for tumor growth," she added. "It's essentially saying you're changing the DNA.
That in itself is very remarkable."
The research is part of a relatively new field known as "epigenetics." Researchers increasingly suspect endocrine disrupters such as bisphenol-a and many common pesticides act not by mutating genes but by jamming the signal: A gene programmed to fight cancer, for instance, might never turn on because it was permanently locked in the "off" position before birth.
The effect is subtler than a gene mutation, scientists say, but has the same devastating result.
"This paradigm" — that gene mutations trigger disease — "doesn't fit," said Michael Skinner, director of the Center for Reproductive Biology at Washington State University.
"Epigenetics may be a major factor in disease development, which we haven't appreciated."
To grasp genetics, Skinner visualizes a city map. Buildings and homes are the individual genes, or genome, while the DNA is the network of streets and highways. A gene mutation is akin to a fire at a particular building, altering traffic, though traffic and DNA alike generally have ways to get around it and move on.
The epigenome — hormones and other chemicals that tell portions of the DNA to replicate or not — are the traffic signals and signs and in some ways can create more chaos when tweaked. Hold a signal at a key intersection red for 30 minutes and, as any Bay Area commuter can testify, traffic gets bollixed for miles.
Except in this case, the effect lasts a lifetime. Or longer.
"If you expose an individual during the developmental phase of an organ — in this case it's the prostate — you've reprogrammed the epigenome," Skinner said. "And that, later on in adulthood, will cause disease."
Skinner's group at Washington State has seen this ripple through generations: Pregnant female rats exposed to common pesticides gave birth to males with low fertility rates. Males able to reproduce spawned offspring with the same disease — and so on for four generations.
Skinner now is finding that those animals, as they live longer, develop a host of diseases, from prostate and kidney disease to breast cancer and immune dysfunction.
"There's a whole series of new genes that become permanently changed."
This newspaper's special investigation on environmental chemicals, "A body's burden: Our chemical legacy," is available on the Web at http://www.insidebayarea.com/bodyburden.
http://www.insidebayarea.com/oaklandtribune/ci_3887148
Contact reporter Douglas Fischer at
dfischer@....
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