More research needed to investigate the impact of pesticides on brain cells in Parkinson’s

Parkinson’s is associated with a loss of brain cells that produce dopamine. If we can understand why these cells are lost, we might be able to find new ways to prevent or slow down the damage to these cells.

The impact of environmental factors, such as pesticides, on the development of Parkinson’s is an area of research that has attracted much attention. In this study, the researchers wanted to understand more about the impact of some widely used pesticides on these dopamine-producing cells. They also wanted to see if a combination of pesticides could be more toxic than one on its own.

By finding out what pesticides do to cells in people with Parkinson’s, and which may have more of an effect, it may help prioritise future research and public health policy.

What did the researchers do?

Researchers analysed results from a previous study in 2017 that looked at agricultural records in California. The records showed which pesticides were used near the homes and work of 829 people with Parkinson’s and 824 people without Parkinson’s. 

The 2017 study showed those with Parkinson’s were more likely to live or work near an area where more pesticides were used. A number of pesticides were identified near their home or work. 

The researchers narrowed it down to test 39 pesticides in this new study. These were pesticides that were associated with being near the home or work of people with Parkinson’s.

In dishes in a lab, researchers used human stem cells to make dopamine-producing brain cells. Stem cells are cells that can be made into any type of cell in the body. They added high concentrations of the pesticides to the brain cells in a dish, and monitored how the cells reacted. 

What did the study show?

10 out of the 39 pesticides investigated showed a toxic effect on brain cells, including causing cell death. Some of these were previously known about, but some of these were new links. 

Of these 10, 5 of the pesticides were particularly harmful to brain cells in comparison to other types of cells, such as heart cells. This could suggest that these pesticides may be more linked to conditions in the brain such as Parkinson’s, than other conditions that affect the heart. 

One particular pesticide that is used in cotton agriculture was found to be the most toxic to dopamine-producing brain cells. This pesticide was called trifluralin, which was banned in the UK in 2008 due to its toxic effects on aquatic life. Combinations of pesticides that included trifluralin were consistently the most toxic to the brain cells. This suggests that more research into trifluralin is needed to understand its potential link to Parkinson’s.

Important things to consider when looking at the results 

It is important to make clear that the results do not show that Parkinson’s is caused by pesticides. More research is needed to understand the link between pesticides and Parkinson’s. 

This study was done in the lab, in conditions that don’t reflect what would happen in the outside world. The pesticides were tested at high concentrations, and added directly to the brain cells grown in a dish. In everyday life, humans are exposed to much lower concentrations, and have many barriers between our brain cells and the environment. Dopamine-producing brain cells wouldn’t be exposed to pesticides in the same way. 

It is also important to understand that the concentrations of the pesticides tested on the brain cells in this study are very high. They used high concentrations in this study over a short period of time. In daily life, people will not be exposed to such high concentrations, so the results are not comparable. 

Parkinson’s is a complex condition, and it is still not completely known what causes it. The evidence so far indicates it’s likely to be a combination of genetic susceptibility, environmental factors, lifestyle and ageing. It’s very difficult to know what environmental factors may have contributed to someone’s Parkinson’s, and some people may be more susceptible than others to various risk factors.

We need more detailed research, including in animal models, and also in the brains of people who had Parkinson’s in their life, to develop a further understanding of how brain cells may be affected in real life.