International Business Department           Liu Bojia           October 04, 2023

  Plastics are already present in a wide variety of products in our lives, and many of them even come into contact with food, such as takeaway boxes, food bags and drinks bottles. When these plastic products are discarded, they are broken down with the environment into micro plastic particles that are invisible to the naked eye. There are also some studies that show that some plastic tea bags are strong enough to release large amounts of microplastics when they come into contact with hot water. (Read more: The Tea Bag You Drink Contains the DNA of Hundreds of Insects and Tens of Billions of Microplastics)

  Last year, a paper in Environment International showed that detectable microplastics already exist in the human circulation, with a quarter of blood samples having levels of polystyrene microplastics ranging from 1 to 4 μg/ml. these microplastics in the circulatory system can build up over time as they move into various organs.

  Some of these in vitro models have shown that microplastic particles are able to accumulate and permeate brain tissue, but whether these microplastics are taken up by neurons once they enter the brain, and what physiological processes are affected remains unknown.

  In a recent study, a team of researchers from Duke University confirmed that microplastics not only enter the brain, but also interact with α-synuclein (α-syn) in neurons, promoting the formation and replication of α-syn protofibrils. This physiological change is closely linked to the development of Parkinson's disease, and many Parkinson's patients experience abnormal folding and aggregation of α-syn in their brains.

  In the experiment, the authors cultured microplastic particles of polystyrene mixed with human α-syn. Originally, this type of α-syn did not appear to aggregate on its own for four days when cultured alone. However, in the environment of mixed culture with microplastics, some aggregated α-syn protofibrils appeared on individual microplastic particles after about 3 days.

  At room temperature, individual microplastic particles can form a stable complex with more than 100 α-syn monomers. However, only microplastic particles with anions can produce this binding ability; neutral or cationic microplastics do not have this effect. This is because the binding process of microplastics to α-syn is facilitated by the interaction of anions with positively charged lysine-rich residues.

  In addition, the authors designed a group of Parkinson's disease mouse models in which they would inject the brains of the mice with some α-syn. as time progresses, this α-syn gradually accumulates in the cerebral cortex and thalamus, as well as in dopaminergic neurons in the amygdala and substantia nigra. If some anionic microplastic particles are co-added along with the α-syn injection, even though these microplastic particles do not diffuse on their own, the final area of α-syn distribution will be wider and the volume of α-syn protofibrillar clusters will be larger.

  Inside neurons, most of the binding of microplastic particles to α-syn occurs in lysosomes, an organelle that is supposed to be responsible for disposing of cellular waste but ends up being the place where products that jeopardise neuronal function are born.

  The authors note that these results suggest that microplastic particles can have an effect on proteins in the body and interact with them. "Many studies will focus on the relationship between microplastic particles and cancer and autoimmune diseases, but we confirm that microplastic particles are likely to increase an individual's risk of developing Parkinson's disease."