New York, February 9, 2005 (ENS): University
of Rochester scientists investigating the link between
PCBs, pesticides and Parkinson's disease have discovered
intricate reactions that occur in certain brain cells,
making them more vulnerable to injury after exposures
to these toxics.
In two papers published in the journal "NeuroToxicology"
in the December 2004 and February 2005 issues, the group
describes how polychlorinated biphenyls (PCBs) disrupt
dopamine neurons, which are the cells that degenerate
during the course of Parkinson's disease.
Researchers also show that low levels of maneb, a fungicide
commonly used in farming, can injure the antioxidant
system in those same types of cells.
Environmental contaminants might make dopamine cells
more vulnerable to damage from normal aging, infection,
or subsequent exposure to pollutants, researchers say.
The investigation is part of a nationwide effort to
better understand every aspect of Parkinson's disease,
which affects up to one million Americans.
Parkinson's is a progressive neurological disorder
that occurs when certain nerve cells die or can no longer
produce the brain chemical dopamine. A lack of dopamine
is what causes patients to experience tremors, stiffness
in the limbs and trunk, and impaired movement or balance.
In the 1990s scientists reported that the brains of
Parkinson's patients contained elevated levels of PCBs
and certain pesticides. While researchers believe that
genetics, the aging process and exposure to toxicants
all play a role in the development of Parkinson's, the
group led by Lisa Opanashuk, Ph.D., is focused on environmental
exposures. The National Institute of Environmental Health
Sciences is funding the work.
"If we can identify the mechanisms by which PCBs
or pesticides perturb dopamine neuron function, it may
lead to the development of therapies that can prevent,
slow or stop the progression of Parkinson's," says
Opanashuk, an assistant professor of environmental medicine.
PCBs trigger the body to produce free radicals, which
leads to a process known as oxidative stress - thought
to be one of the main causes of cell degeneration.
Normally, antioxidants can balance the damage done
by oxidative stress. But toxic pesticide exposure, combined
with the normal aging process, shifts the equilibrium
toward oxidative stress and neurodegeneration.
The Rochester studies demonstrate, for the first time,
the intricate oxidative stress and antioxidant responses
to PCBs in dopamine neurons.
PCBs, used as industrial coolants and lubricants, were
banned in 1977 but remain widespread in the environment
due to their improper disposal. They linger in the food
chain, particularly in wild and farmed salmon and other
fish. PCBs accumulate in the body in fat and brain cells
and other tissues.
The potential adverse health effects of PCBs are dependent
on levels of exposure, the toxicities of individual
chemicals present in any given mixture, and their interactive
Pesticides such as maneb remain in farmed soil for
20 to 75 days following application and can be found
on produce for more than three weeks, even after washing,
according to researchers. Until now, the effect of maneb
on oxidative stress responses in dopamine neurons was
Opanashuk's group shows that cells treated with low
levels of maneb also undergo changes that disturb the
balance in the antioxidant defense system. Another concern
is whether maneb causes more damage when people are
exposed in combination with other pesticides, which
occurs in rural communities.