• Posted May 19, 2023

At Least 10 Pesticides Could Have Links to Parkinson's

Scientists say they've identified 10 pesticides that kill neurons involved in Parkinson's disease, marking a leap forward in their understanding of the movement disorder.

Pesticide exposure has long been associated with Parkinson's, but investigators hadn't been able to pinpoint specific culprits.

A team from the University of California, Los Angeles and Harvard University paired epidemiology and toxicity screening to isolate which among the many thousands of pesticide products could be involved.

"We were able to implicate individual agents more than any other study has before," Kimberly Paul said in a UCLA news release. Paul is a lead author of the study and an assistant professor of neurology at UCLA.

The 10 pesticides her team identified included insecticides, fungicides and herbicides. They were directly toxic to dopaminergic neurons, which are involved in voluntary movement. Death of these neurons is a hallmark of Parkinson's, the study noted.

Researchers also found that exposure to combinations of pesticides used in cotton farming was more toxic than any single pesticide in that group.

The study team first looked at exposure history over decades for 288 pesticides in patients with Parkinson's disease who had participated in previous studies. These patients were from California's Central Valley.

After determining long-term exposure for each person, the team used a pesticide-wide association analysis, testing each pesticide individually for its association with Parkinson's.

They were able to identify 53 pesticides that appeared to be implicated in Parkinson's. Most of these had not been previously studied for a potential link and are still in use.

The UCLA team shared the results for lab analysis with a team led by Dr. Richard Krolewski, an instructor of neurology at Harvard.

Krolewski tested the toxicity for most of those pesticides in dopaminergic neurons derived from Parkinson's patients using pluripotent stem cells. They're a type of "blank slate"cell that can be reprogrammed into neurons that closely resemble those lost in Parkinson's disease.

Researchers found 10 pesticides directly toxic to these neurons:

• Four are insecticides: dicofol, endosulfan, naled, propargite.
• Three are herbicides: diquat, endothall, trifluralin.
• Three are fungicides, both basic and pentahydrate copper sulfate and folpet.

These pesticides are structurally distinct and do not share a prior toxicity classification. Most are used in the United States today, according to the study.

When the team tested the toxicity of multiple pesticides commonly applied in cotton fields around the same time, they found that combinations involving trifluralin were most toxic. This is one of the most commonly used herbicides in California, the researchers noted.

A previous study had also implicated this pesticide in Parkinson's disease.

Study results were published May 16 in Nature Communications.

More information

The U.S. National Library of Medicine has more on Parkinson's disease.

SOURCE: University of California, Los Angeles, news release, May 16, 2023