ROCHESTER, 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
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 properties.
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 unknown.
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.