The pernicious impact of toxic chemicals in the body, from suspected roles in autism to human response to everyday stress, can manifest themselves in future generations, according to a new study from researchers at the University of Texas (UT) and Washington State University (WSU).
Published in the journal Proceedings of the National Academy of Sciences, the animal study found DNA changes wrought by a common fungicide are passed down from parents to offspring, according to a May 22, 2012, UT news release. The researchers studied how the animals respond to stress.
“The ancestral exposure of your great-grandmother alters your brain development to then respond to stress differently,” said WSU professor Michael Skinner. Along with UT's David Crews, Skinner and colleagues exposed gestating female rats to the popular fruit and vegetable fungicide vinclozolin and monitored for “epigenetic changes,” which can be passed on to subsequent generations.
Crews and Skinner subjected the exposed rats’ third generation of offspring to a variety of behavioral tests and found them to be more anxious and sensitive to stress. They also had greater activity in stress-related regions of the brain than descendants of unexposed rats.
“We are now in the third human generation since the start of the chemical revolution, since humans have been exposed to these kinds of chemicals,” Crews said in the release. “This is the animal model of that.”
Crews, whose contributions to the paper focused on the neuroscience, behavior and stress aspects, said increases in disorders like autism and bipolar disorder may be connected to the kind of “two-hit” exposure that the experiment is modeling.
“It’s more than just a change in diagnostics," he said of the documented increases in mental disorders in recent decades. "The question is: Why? Is it because we are living in a more frantic world, or because we are living in a more frantic world and are responding to that in a different way because we, or our ancestors, have been exposed to environmental contaminants. I favor the latter.”
The stress study is the second that Crews has co-authored on vinclozolin in five years. In 2007 he and UT colleague Andrea Gore found exposure to the toxin can affect mate choice in later generations. "The ancestral exposure of your great-grandmother alters your brain development to then respond to stress differently." - Professor Michael Skinner, Washington State University
Also published in the Proceedings of the National Academy of Sciences journal, the study found that female rats avoid males whose great-grandmothers were exposed to the fungicide and preferred males whose ancestors were uncontaminated, according to a March 27, 2007, UT news release.
“Even across generations, your attractiveness as a mate is decreased if your great-grandmother has been exposed to environmental chemicals,” said Gore. “That will have an impact on your ability to reproduce and could take you out of the gene pool.”
Vinclozolin is also linked early onset of cancer and kidney disease in males, they said.
Crews and Gore studied the early onset of disease in rats caused by initial exposure to vinclozolin and found it was passed down generation to generation through the males.
“The female is able to detect which male is likely to get early onset disease and which male is not before they show any manifestation of disease,” Crews said.
Gore added, “The female rats can sense something is wrong, although they can’t see it.”
Males exhibited no preference for female type and generally move on to other populations to mate, the release said. So the effect of vinclozolin exposure in the natural setting would not only span generations but could also reach other populations of animals through male migrations.
“Males disperse, and if they were to mate, it would be at times that they aren’t manifesting signs of disease,” said Crews. “They are literally time bombs.”
Crews and Gore write blogs on the Huffington Post and on March 19, 2012, penned a joint column titled "Our Contaminated World" that focused on the Food & Drug Administration's (FDA) pending decision to allow the toxic chemical bisphenol-A (BPA) in food packaging like coated metal cans and plastic wraps. "There is a long scientific history showing a link between exposure to endocrine disruptors and reproductive disorders such as infertility and early puberty." - Professors David Crews and Lauren Gore, University of Texas
"Epidemiological evidence in humans shows associations between BPA and cardiovascular disease, metabolic disorders and reproductive impairments," they wrote. "Beyond BPA, endocrine disruptors are linked to cancer, obesity, reproductive disorders and mood disorders like anxiety and depression."
Endocrine disruptors, according to the National Institute of Environmental Health Sciences (NIEHS), are chemicals that interfere with the endocrine or hormone system and can produce "adverse developmental, reproductive, neurological, and immune effects in both humans and wildlife."
In denying a complaint from the Natural Resources Defense Council, the FDA decided to continue allowing BPA in food packaging, Huffington Post blogger Lynne Peeples reported on March 20, 2012.
Chemicals like vinclozolin and BPA are undeniably useful, protecting grapes from fungus, leafy greens from pests and children from fire ants and flammable pajamas, Crews and Gore wrote the day before the FDA decision on BPA.
"They're also in us, and transforming our bodies and minds," they said. "There is a long scientific history showing a link between exposure to endocrine disruptors and reproductive disorders such as infertility and early puberty. Furthermore, the evidence is growing that the damage is much more widespread."
Chemicals have been shown to increase the risk of various cancers, to contribute to obesity and to influence the activity of neurotransmitters in the brain, they continued.
"In fact, there are even hints that exposure to the chemicals may have something to do with the dramatic rise in autism and mental disorders over the past few decades," they said.
With geneticists beginning to appreciate the fundamental role of the environment in shaping who humans are, the question is no longer simply "nature or nurture?"
"We know that nature (the environment) has been changed by contamination, and this leads to changes in how organisms are nurtured," Crews and Gore wrote.
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