(NaturalNews) Pesticide exposure may not just increase the risk of Parkinson's disease, but may actually start a cascade of events that directly cause the disease, according to a study conducted by researchers from the University of California-Los Angeles (UCLA), UC-Berkeley and the University of Southern California, and published in the Proceedings of the National Academy of Sciences.
Parkinson's disease is an incurable, degenerative neurological disease characterized by symptoms such as tremor, rigidity and a dramatic slowing of speech and movement. It is believed to be caused by the destruction of neurons in the brain, particularly in the substantia nigra region of the mid-brain. One of this region's functions is the production of dopamine, which plays an important role in communication between cells. By the time Parkinson's disease is detected, it is not uncommon for more than 50 percent of the brain's dopamine-producing neurons to have already been destroyed.
Although a small percentage of Parkinson's cases appear to be due to inherited, genetic causes, the vast majority of cases seem unlinked to genetics.
"As a result, environmental factors almost certainly play an important role in this disorder," co-author Arthur G. Fitzmaurice said. "Understanding the relevant mechanisms - particularly what causes the selective loss of dopaminergic neurons - may provide important clues to explain how the disease develops."
Investigating the pesticide link
Over the past several years, UCLA researchers have successively established a link between exposure to various pesticides and Parkinson's disease, including the common agricultural chemicals maneb, paraquat and ziram. This link is seen among both farm workers and those living or working near agricultural fields.
In the new study, the researchers sought to determine whether there might be a link between Parkinson's and benomyl, a pesticide that was banned in the United States in 2001 after 30 years of use, after it was linked to cancer, brain defects, liver tumors and reproductive damage.
The researchers confirmed in a laboratory study that dopaminergic neurons were damaged or destroyed upon exposure to benomyl. They then exposed zebrafish to the chemical, confirming that it led to significant death among dopaminergic neurons, but not among any other nerve cells. This destruction occurred because benomyl blocked the action of an enzyme known as ALDH, which normally interferes with the action of a naturally occurring brain toxin called DOPAL. Without ALDH, DOPAL builds up and destroys the dopaminergic cells.
The ultimate cause of Parkinson's?
The findings surprised the researchers, because ALDH had never before been linked to Parkinson's disease, which was believed instead to be caused by a protein called a-synuclein. If the study's findings are correct, ALDH disruption may turn out to be a cause of the disease even in people who have not been exposed to pesticides.
"We've known that in animal models and cell cultures, agricultural pesticides trigger a neurodegenerative process that leads to Parkinson's," senior author Jeff Bronstein said.
"Our work reinforces the hypothesis that pesticides may be partially responsible, and the discovery of this new pathway may be a new avenue for developing therapeutic drugs."