Chemical Exposure Is Key Risk Factor for Parkinson’s, Scientists Say
Toxic pollutants can activate genes implicated in neurogenerative diseases
New scientific evidence supports a link between exposure to toxic environmental factors — pesticides, air pollutants, man-made materials, and more — to an increased risk of developing neurodegenerative diseases, including Parkinson’s.
The evidence, which has spearheaded a new research area in neuroscience, was presented at the 147th Annual Meeting of American Neurological Association that took place Oct. 23 at the Hyatt Regency Chicago. The symposium was titled “Neurologic Dark Matter: Exploring the Exposome that Drives Neurological Disorders.”
Researchers highlighted increased human exposure to pollutants and how current environmental policies fail to consider the interactions between neurotoxic chemicals and their detrimental effects following a lifetime of exposure.
“The world’s fastest-growing brain disease is largely man-made,” E. Ray Dorsey, MD, the David M. Levy professor of neurology at the University of Rochester Medical Center, and one of the symposium speakers, said in a press release. “The principal causes are toxic exposures to chemicals synthesized in the labs of chemical companies worldwide.”
Environmental and genetic risk factors likely contribute to Parkinson’s
Parkinson’s is a complex disorder and unlikely to have a single cause. While the fact that more people living into old age accounts for its rising incidence, past evidence suggests that both environmental and genetic risk factors contribute to the disease.
However, few studies had assessed the true impact of human exposure to chemicals — dubbed the exposome — and how much it can influence people’s health, including their risk of developing neurodegenerative diseases or developmental disorders.
In his talk, titled “Is the Rise in Incidence of Parkinson’s Largely Human-Made?,” Dorsey highlighted the potential triggers of Parkinson’s, such as inhaled pesticides — for instance, the herbicide paraquat, used for weed and grass control — and substances like trichloroethylene (TCE, a chemical used to make refrigerants and to degrease metal).
“Many of these likely causes of Parkinson’s disease are inhaled,” Dorsey said. “The nose may be the front door to the brain.”
Exposure to chemicals can have an effect even in rare Parkinson’s cases with a genetic component.
“For the vast majority of cases, [Parkinson’s disease] is largely a composite of genetic makeup and a lifetime of environmental exposures,” said J. Timothy Greenamyre, MD, PhD, also a speaker at the symposium, and vice-chair of neurology, and director of the Pittsburgh Institute for Neurodegenerative Diseases at the University of Pittsburgh.
Exposure to toxic pollutants can activate genes implicated in Parkinson’s
In his talk, “Convergent Mechanisms of Environmental Toxicant-Induced Parkinson’s Disease,” Greenamyre discussed the mechanisms by which these exposures lead to disease.
Research by his lab and colleagues has shown that exposure to toxic pollutants can activate genes implicated in Parkinson’s. Once active, these genes can further enhance the toxicity of the pollutants.
While blocking the activity of these genes could help dampen the impact of toxic pollutants, the main strategy to lessen the risk of Parkinson’s is to avoid exposure to these pollutants in the first place, according to Greenamyre.
Despite this evidence, the use of paraquat has doubled in the past five years, Dorsey noted in his talk. Contrary to initiatives to ban its use in several countries, including China, the U.S. recently re-approved its use in the country.
While the use of TCE has dropped, it is still found in groundwater. Moreover, it can evaporate into the air, spreading into people’s homes, schools, and workplaces undetected. According to the press release, 7,300 TCE contamination sites were found in Michigan alone.
The Netherlands, which placed measures to reduce air pollution and pesticide use in the past century, is currently the only industrialized country showing evidence of a decrease in Parkinson’s.
In the U.S., more than 40,000 industrial chemicals are currently in use, according to Deborah A. Cory-Slechta, PhD, professor of environmental medicine at the University of Rochester Medical School, and a symposium speaker. Her talk was titled “Chemical Exposures: The Ignored Environmental Risk Factor(s) for Neurodegenerative Diseases and Neurodevelopmental Disorders.”
In general, people are exposed to a multitude of chemicals, with certain jobs, such as farming, putting workers at higher exposure risk.
The world’s fastest-growing brain disease is largely man-made. The principal causes are toxic exposures to chemicals synthesized in the labs of chemical companies worldwide.
Chemicals can interact with each other and with a person’s genetic makeup
Regulatory applications to approve certain chemicals are usually supported by animal studies that investigate the effects of these chemicals in isolation. However, chemicals can interact with each other and with the genetic makeup of each person.
“Most neurological disorders arise through interactions between genes and the environment,” said Rick Woychik, PhD, director of the National Institute of Environmental Health Sciences and symposium co-moderator. “We’re studying chemicals found in industrial products, building materials, agricultural pesticides — in the air we breathe, the water we consume, the soil we use to grow our crops. It’s not just [a single exposure,] it’s all of these things, and we have to consider a person’s genetic heritage.”
The evidence calls for regulatory agencies, including the U.S. Environmental Protection Agency, to “consider the shared causes of neurodegenerative and neurodevelopmental disorders, and to address cumulative risk,” the press release noted.
Cory-Slechta posed the questions: “How much of our health are we willing to give up? Are we willing to lose one IQ point? Two IQ points?”
Dorsey and others called for a shift in current funding for biomedical research from treatment to prevention, and for further advocacy. The new policies should seek to reduce the prevalence of chemical exposure, among other goals, and mimic the efforts of smoking prevention campaigns, which have led to a steep drop in lung cancer.
“If we care, we can prevent millions of people from ever developing these debilitating and deadly diseases,” Dorsey said. “If we educate the communities we’re supposed to serve, we can have them be mobilized and change the course of all these diseases.”
It’s a daunting task, said Walter J. Koroshetz, MD, director of the National Institute of Neurological Disorders and Stroke and co-moderator of the symposium, “but I think it’s time to start now.”
He said the institute has launched an office for exposome research, which will be conducted in close collaboration with the National Institute of Environmental Health Sciences.
“These cumulative exposures are an existential threat in our modern environment, and we as neurologists and neuroscientist must focus our attention on this under-recognized and growing issue,” said Frances E. Jensen, MD, president of the American Neurological Association, and chair of the symposium.
“We need more researchers and clinicians to go into this field,” said Jensen, who’s also chair of the neurology department at the University of Pennsylvania’s Perelman School of Medicine. “Voices of expertise are needed to get this message out.”
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