(Beyond Pesticides,
February 1, 2018) Scientists at the European Institutefor the Biology of Aging
are finding new information about how Parkinson’s disease manifests itself
after exposure to the herbicide paraquat, in hopes of finding ways to prevent
the progression of the disease. Despite a well-established
body of scientific literature linking the paraquat to Parkinson’s, and a ban on the use
of the chemical in the European Union that dates back to 2007,
its use is still permitted in the U.S. Many health groups, including Beyond
Pesticides and organizations like the Michael J Fox
Foundation are calling on the U.S. Environmental Protection
Agency stop the use of paraquat by denying its upcoming reregistration.
Published in the
journal Cell Reports,
this new research on Parkinson’s investigates the impact of “senescent” cells
in the body. Senescent cells are those which, despite being able to divide,
stop doing so in response to stress. This is an anti-cancer mechanism, as
stress would otherwise cause the cells to multiply unchecked and create
malignancies. Researchers suspected that despite the benefit of stopping
cancer, senescent cells may be causing other problems in the body. Rather than
dying, these cells can cause inflammation in the area around where the cell
became senescent. Scientists focused in on one particular type of
senescent cell, the astrocyte, which are essentially cells that send and
receive neurons in the brain. It was hypothesized that senescent astrocytes
could be causing localized inflammation that harms the neurons associated
Parkinson’s disease. Parkinson’s is characterized by the death of neurons
associated with dopamine production. While paraquat has long been associated
with the direct death of these neurons, this new research shows that additional
neurological impacts may be at play.
Scientists carried out
different investigations to test the impact of senescent astrocytes on the
development of Parkinson’s. First, they compared human brain tissue between
Parkinson’s patients and those without the disease. Compared to those that
never contracted Parkinson’s, individuals with the disease showed biomarkers
associated with higher levels of senesced astrocytes. Researchers then looked
at whether paraquat could cause senescence in a lab-cultured human astrocyte.
Not only did paraquat stop astrocyte cell proliferation, it did better at inducing
senescence than hydrogen peroxide and other traditional medical methods of
inducing astrocyte senescence. Scientists found that, in line with
epidemiological data that shows greater risk for Parkinson’s from chronic, low
dose exposure than acute, one-time exposure, exposing the cultured astrocytes
to paraquat for a longer time at a lower dose resulted in a greater number of
senesced cells.
A final test was
conducted on laboratory mice. After exposing mice to levels of paraquat
indicated in the literature to result in Parkinson’s disease symptoms, results
traced a very similar response to the human astrocyte cell culture. Senescent
astrocytes increased after paraquat exposure, and mice displayed increased
difficulties in movement and motor function. However, when researchers used a
drug to flush senescent cells from the substantia nigra, the area of the brain
where domapine-producing cells are located, the Parkinson’s-like symptoms of
paraquat exposure subsided. “They are almost indistinguishable from the healthy
mice,” said Marco Demaria, PhD, to The Guardian.
“As far as we know,
this is the first time it’s been demonstrated in any neurodegeneration model
that ablating [removing] senescent cells actually has an effect on disease
progression,” said study co-author Julie Anderson, PhD to The Scientist.
However, Dr. Anderson also noted to TheScientist that, “right now, we don’t
know specifically what it is about paraquat that is inducing the senescence within
the astrocytes.”
This complex study
provides a route to potentially treat not only Parkinson’s but other diseases
where senescent cells may play a role, such as ALS and Alzheimer’s. Future
research will need to uncover how to flush out specific senescent cells while
leaving others, which may be valuable in other areas, such as healing wounds,
alone. “We know the cells we want to target, but at the moment we don’t have
the therapeutics to do that,” said Dr. Demaria to The Guardian. “We cannot yet
only target the bad cells.”
While the treatment
developed by researchers in this study is promising, a better approach to
reducing and eliminating the spread of pesticide-related
diseases is to simply take the chemical off the market. Any
products linked to devastating diseases such as ALS, Alzheimer’s,
and Parkinson’s have no place in our environment. While paraquat’s use is
restricted to certified applicators in the U.S., it can still be applied to
agricultural land. Despite a ban on the chemical in Europe and a planned phase-out of use
in China, over seven million lbs of paraquat were applied to 15 million acres
of American farmland in 2015.
Support efforts to ban the
continued use of paraquat. The U.S. Environmental Protection
Agency is currently reviewing safety concerns about the chemical, but without
public involvement, the agency’s decision could be similar to its continued
allowance of another
neurotoxic pesticide – chlorpyrifos. Keep up to date with Beyond
Pesticides’ action alerts for updates, and for more information
on the link between pesticides and Parkinson’s, see the Pesticide-Induced
Diseases Database section on Parkinson’s disease.
All unattributed
positions and opinions in this piece are those of Beyond Pesticides.
Source: The Guardian,
The Scientist,
Cell Reports
https://beyondpesticides.org/dailynewsblog/2018/02/herbicide-paraquat-linked-parkinsons-symptoms-brain/
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