Parkinson's disease, which is one of the most common neurodegenerative diseases, has been associated abnormalities of mitochondria, which are the "power plants" that provide all cells with energy. Rotenone and many other pesticides are known to damage the mitochondria by inhibiting a mitochondrial enzyme called complex I. In earlier experiments, Dr. Greenamyre and his colleagues found that chronic treatment with low levels of rotenone caused gradual degeneration of the dopamine neurons in rats, and reproduced many of the features of Parkinsonism.
In the new study, the Emory scientists exposed human neuroblastoma cells to the pesticides rotenone, pyridaben, fenazaquin, and fenpyroximate, all of which inhibit complex I. Pyridaben was by far the most potent toxic compound, followed by rotenone and fenpyroximate, with fenazaquin being the least toxic. Pyridaben was also more potent than rotenone in producing "free radicals" and oxidative damage to the cells, both of which are thought to be important in causing Parkinson's disease.
"These results show that commonly used pesticides are toxic to cells, and may cause the kinds of cellular damage that lead to diseases such as Parkinson's," Dr. Sherer says. "Although our study does not prove that any particular pesticide causes Parkinson's, it does lead to more questions about the safety of chronic exposure to these environmental agents and certainly warrants additional research." Last year Emory created a new Emory Collaborative Center for Parkinson's Disease Environmental Research through a grant of more than $6.5 million from the National Institute of Environmental Health Sciences.
"For quite a while scientists have believed that environmental factors, including pesticides, may be important in causing Parkinson's disease," Dr. Greenamyre says. "We are continuing our research to determine exactly how these exposures cause nerve cell damage and death."
Other Emory scientists involved in the research study were Gary W. Miller, PhD, associate professor in Emory's Rollins School of Public Health, and neurologists Alexander Panov, PhD and Jason Richardson, PhD.