Scientists have been debating the origin of the harmful proteins that cause Parkinson’s disease for the last 20 years. Heiko Braak, MD, a German pathologist, was the first to suggest that the illness starts outside of the brain in 2003. More recently, Per Borghammer, MD, of Aarhus University Hospital in Denmark, and his associates contend that the illness is the outcome of processes that originate in the body’s digestive tract (body-first) or the brain’s smell centre (brain-first).
On World Parkinson’s Day, a new hypothesis study published in the Journal of Parkinson’s Condition combines the body-first and brain-first theories with environmental toxicants that may be consumed or breathed as potential origins of the condition. Borghammer and the other authors of the current study contend that breathing in common dry cleaning chemicals, insecticides, and air pollution predisposes one to a brain-first model of the illness. The body-first model of the illness is caused by additional toxicants that are consumed, such as contaminated food and drinking water.
In both the brain-first and body-first scenarios the pathology arises in structures in the body closely connected to the outside world.
Here we propose that Parkinson’s is a systemic disease and that its initial roots likely begin in the nose and in the gut and are tied to environmental factors increasingly recognized as major contributors, if not causes, of the disease. This further reinforces the idea that Parkinson’s, the world’s fastest growing brain disease, may be fueled by toxicants and is therefore largely preventable.
Ray Dorsey, MD, a professor of Neurology at the University of Rochester Medical Center
For the past 25 years, researchers have focused on alpha-synuclein, a misfolded protein, as one of the potential causes of Parkinson’s disease. The protein causes gradual malfunction and death of many different types of nerve cells, including those in the dopamine-producing areas of the brain that govern motor function, over time as it builds up in the brain in clumps known as Lewy bodies. When the theory was initially put up, Braak believed that the illness may be caused by an unknown infection, like a virus.
The current article makes the case that air pollution, weed killer paraquat, dry cleaning and degreasing chemicals trichloroethylene (TCE) and perchloroethylene (PCE), and other environmental toxins may be frequent contributors to the production of hazardous alpha-synuclein. Thousands of former industrial, commercial, and military sites including the Marine Corps base Camp Lejeune are contaminated by TCE and PCE, and paraquat is one of the most commonly used herbicides in the US even though it is prohibited for safety reasons in over 30 countries, including China and the European Union. James Parkinson, whose birthday is today, originally identified the disease when air pollution reached lethal levels in nineteenth-century London.
There are established connections between the nose and the stomach, which are both lined with soft, porous tissue, and the brain. According to the brain-first concept, the chemicals are breathed and may go through the nerve that senses scent to reach the brain. Alpha-synuclein originates in the smell centre of the brain and diffuses to other areas mostly on one side of the brain, including areas where dopamine-producing neurons are concentrated. One of the hallmarks of Parkinson’s disease is the loss of these cells. Asymmetric tremor, slowness of movement, delayed onset of the disease’s development following diagnosis, and only much later substantial cognitive impairment or dementia are possible side effects.
The substances are absorbed through the gastrointestinal tract’s lining. The alpha-synuclein disorder may have its origins in the neurological system of the stomach, from which it can extend to the brain and spinal cord on both sides. This body-first pathway is frequently linked to Lewy body dementia, a Parkinson’s disease family disease that begins with constipation and disrupts sleep before progressing through both hemispheres of the brain to cause earlier dementia and more symmetric slowing of movement.
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These environmental toxicants are widespread and not everyone has Parkinson’s disease.
The timing, dose, and duration of exposure and interactions with genetic and other environmental factors are probably key to determining who ultimately develops Parkinson’s. In most instances, these exposures likely occurred years or decades before symptoms develop.
Ray Dorsey
Citing an increasing amount of studies that relate environmental exposure to Parkinson’s disease, the authors think the new models might help researchers correlate certain exposures to particular disease types. Growing public knowledge of the harmful health impacts of several substances in our environment will support this endeavour. “May explain many of the riddles of Parkinson’s disease and open the door towards the ultimate goal–prevention,” the scientists write in their conclusion.
Source: University of Rochester Medical Centre Newsroom
Journal Reference: Dorsey, E. Ray et al. ‘The Body, the Brain, the Environment, and Parkinson’s Disease’. 1 Jan. 2024 : 1 – 19. https://doi.org/10.3233/JPD-240019
