Air pollution exposure tied to increased Parkinson’s disease risk

Reuters Health - 17/05/2021 - People exposed to high levels of nitrogen dioxide in the air may be significantly more likely to develop Parkinson's disease, a Korean study suggests.

Researchers examined data on incident Parkinson's disease and exposure to air pollutants including particulate matters (PM 2.5 and PM 10), nitrogen dioxide, ozone, sulfur dioxide, and carbon monoxide among a cohort of 78,830 adults living in Seoul. Over a median follow-up period of 8.6 years, a total of 388 people were newly diagnosed with Parkinson's disease.

For most of the pollutants examined, researchers found no association between exposure levels and incident Parkinson's disease.

However, individuals with the highest quartile of exposure to nitrogen dioxide were significantly more likely to develop Parkinson's disease (hazard ratio 1.41) than those in the lowest quartile of exposure, researchers report in JAMA Neurology.

While the study wasn't designed to establish a causal relationship between nitrogen dioxide exposure and Parkinson's disease, there are several possible pathogenic mechanisms that might explain the relationship, said senior study author Dr. Sun Ju Chung, a professor of neurology at Asan Medical and the University of Ulsan College of Medicine in Seoul.

"If you inhale nitrogen dioxide, nitrogen may have a poisonous effect on olfactory nerve, given the olfactory nerve's anatomic exposure to airborne pollutants," Dr. Chung said by email. "Interestingly, alpha-synuclein pathology of Parkinson's disease starts from olfactory bulb as well as in dorsal motor nucleus of vagus, so nitrogen dioxide may have a direct effect on the brain beginning from the olfactory nerve."

In addition, "nitrogen dioxide inhalation may increase systemic proinflammatory cytokines, such as interleukin-1beta, IL-6, IL-8, and TNF-alpha," Dr. Chung said.

"These proinflammatory cytokines may be related to neuroinflammation in (the) brain that is very important pathogenic mechanism of Parkinson's disease and other neurological diseases."

Study participants had a mean age of 54.4 years at baseline and no history of Parkinson's disease. Individuals who developed Parkinson's were significantly older than the overall study population, with a mean age of 66.5 years.

Researchers identified an association between Parkinson's disease and nitrogen dioxide exposure when levels in the air during the five years preceding the index date were higher than 0.038 parts per million.

Nitrogen dioxide, which comes primarily from fossil fuel burning by vehicles or for power generation, has remained at fairly stable levels in South Korea since the 1980s while other pollutants have declined, the authors note. The median level of nitrogen dioxide exposure during the study period was 0.033 (range 0.026-0.045) ppm.

One limitation of the study is that researchers only examined outdoor air quality, and it's possible that indoor concentrations of pollutants might have differed from outdoor exposure and influenced Parkinson's disease risk, the study team notes. Exposure was also measured for residential districts, and may not reflect the exact exposure levels at home, at work, or at other locations where participants spent the majority of their time.

Even so, the results add to a growing body of evidence linking air pollution to Parkinson's disease, said Dr. Ray Dorsey, a professor of neurology at the University of Rochester in New York who coauthored an editorial accompanying the study.

"The offending agent or agents within air pollution are not certain and could be nitrogen dioxide, particulate matter, heavy metals, or other constituents," Dr. Dorsey said by email. "The mechanism of injury is not clear either but may involve inflammation or stress on the energy-producing parts of cells that we know are damaged in Parkinson's disease."

SOURCE: https://bit.ly/3tQ6seN and https://bit.ly/3huVxoj JAMA Neurology, online May 17, 2021.

By Lisa Rapaport



Posted on 17 May, 202124 May, 2021