Exposure to dieldrin and DDT--chlorinated insecticides--may increase the risk of developing Parkinson's disease, according to research presented at the annual meeting of the American Chemical Society. The findings support epidemiological studies from the last two decades linking pesticide exposure to Parkinson's disease.
Parkinson's disease, which affects as many as one million Americans, results from the deterioration of parts of the brain that produce and distribute the chemical neurotransmitter dopamine. A deficiency of dopamine leaves Parkinson's patients unable to control movement normally.
Researchers from Emory University School of Medicine, the Georgia Institute of Technology and Emory's Rollins School of Public Health analyzed post-mortem brain tissue of Parkinson's patients and found concentrations of dieldrin and DDE, the main metabolite of DDT, were more than three times higher in the tissue of Parkinson's patients than the levels measured in age-matched controls.
Follow-up studies in mice revealed that dieldrin increased levels of biomarkers of oxidative stress in the brain regions affected in Parkinson's disease. Although scientists are not certain about the exact mechanisms of Parkinson's disease, research has shown that oxidative stress in the brain may be a contributing factor. The substantia nigra, one of the key regions damaged in Parkinson's disease, may be particularly vulnerable to oxidative damage because it contains low levels of anti-oxidant molecules. The study found that mice treated with dieldrin had increased markers of oxidative stress, as well as reduced levels of the antioxidant glutathione. The investigators also observed evidence of altered function of the dopamine neurons. While dieldrin was not shown to kill dopamine neurons, the evidence of oxidative damage suggests that dieldrin may increase the vulnerability of these neurons.
The study was led by Kurt D. Pennell, PhD, PE, of Emory's Center for Neurodegenerative Disease and the Georgia Tech School of Civil and Environmental Engineering and Gary W. Miller, PhD, of Emory's Center for Neurodegenerative Disease and associate professor of environmental and occupational health in the Rollins School of Public Health.
"Our findings illustrate how dieldrin exposure may disrupt dopamine function and increase oxidative stress, and they support the link between dieldrin exposure and increased risk of Parkinson's disease," said Dr. Pennell.
Other authors included Emory scientists Jaime M. Hatcher, W. Michael Caudle, Allan I. Levey, Marla Gearing, Dean P. Jones and Jason R. Richardson.
The research was supported by the Georgia Tech Foundation, the Woodruff Health Science Center Fund, the Collaborative Centers for Parkinson's Disease Environmental Research, and the National Institute of Environmental Health Sciences.