Plastic particles found in mouse brains just two hours after eating: ScienceAlert

Thanks to their flexibility, durability and affordability, plastics have infiltrated almost every aspect of our lives.

When these elements eventually break down, the resulting micro- and nanoplastics (MNPs) can harm wildlife, the environment, and ourselves. MNPs have been found in the blood, lungs, and placenta, and we know they can enter our bodies through the foods and liquids we consume.

A new study by a team of researchers from Austria, the United States, Hungary and the Netherlands has found that MNPs can reach the brain within hours of being consumed, possibly thanks to the way d other chemicals stick to their surface.

Not only is the speed alarming, but the very possibility of tiny polymers slipping through our nervous system sets off serious alarm bells.

“In the brain, plastic particles could increase the risk of inflammation, neurological disorders or even neurodegenerative diseases such as Alzheimer’s or Parkinson’s disease”, explains the co-lead author of the study, the pathologist Lukas Kenner from the Medical University of Vienna in Austria.

In the study, tiny fragments of MNP given orally to mice were detectable in their brains in as little as two hours. But how do MNPs cross the blood-brain barrier, which is supposed to protect the brain?

As a tightly packed system of blood vessels and surface tissues, the blood-brain barrier helps protect our brain from potential threats by blocking the passage of toxins and other unwanted ones, while allowing more useful substances to pass through. It stands to reason that plastic particles would be considered a material to be kept well and truly out of sensitive brain tissue.

“With the help of computer models, we discovered that a certain surface structure (biomolecular crown) was crucial for allowing plastic particles to pass through the brain,” explains co-lead author Oldamur Hollóczki, a biochemical chemist. nanoplastics at the University of Debrecen in Hungary. .

Representative immunofluorescence images of male mouse brains, with tissue sections in blue and nanoplastic particles in green.
Immunofluorescence images of mouse brains, control (Ctr) and 2 or 4 hours after polystyrene ingestion. Tissue sections are stained blue and arrows show green fluorescent nanoplastic particles. (Kopatz et al., Nanomaterials2023)

To verify that the particles can actually enter the brain, MNPs made of polystyrene (a plastic commonly used in food packaging) of three sizes (9.5, 1.14 and 0.293 micrometers) were marked with fluorescent markers and pretreated in a mixture similar to digestive fluid before being fed to mice.

“To our surprise, we found specific nano-sized green fluorescent signals in the brain tissue of mice exposed to MNP after only two hours,” the researchers write in their published paper.

“Only particles of the size of 0.293 micrometers could be taken from the gastrointestinal tract and penetrate the blood-brain barrier”.

How these tiny coated plastics cross cellular barriers in the body is complicated and depends on factors such as particle size, charge and cell type.

Smaller plastic particles have a higher surface-to-volume ratio, which makes them more reactive and potentially more dangerous than larger microplastics. This reactivity is supposed to allow small pieces of plastic gather other molecules around themsqueezing them tightly with molecular forces to form a durable coat called the corona.

The researchers created a computer model of a blood-brain barrier from a double lipid membrane composed of a phospholipid present in the human body, to investigate how particles might cross the all-important neurological barrier.

Simulations of plastic particles in dark gray and cholesterol molecules in light gray passing through a bilayer blood-brain barrier model of orange and green molecules.
Simulations showing the entry of a dark gray polystyrene plastic particle with a crown of light gray cholesterol molecules into a model blood-brain barrier of orange hydrophobic molecules and green hydrophilic molecules. (Kopatz et al., Nanomaterials2023)

Four different plastic models were used to investigate the role of the plastic particle corona. Simulations showed that particles with a protein crown could not penetrate the barrier. However, those with a cholesterol crown could cross over, even if they couldn’t progress deeper into the brain tissue.

The findings raise the possibility that plastic could be transported across the membrane and into brain tissue using the right molecular cocktail. Knowing the basic mechanisms is an important first step in managing their adverse effects.

It’s important to note that the results are based on mice and computer simulations, so it’s unclear if the same behavior occurs in humans. It’s also unclear how many plastic particles are needed to cause damage. Yet knowing that it’s possible for coated plastic particles to cross the blood-brain barrier in such a short time advances research in this area, according to the authors.

“To minimize the potential harm of micro- and nanoplastic particles to humans and the environment, it is crucial to limit exposure and restrict their use while further research is conducted into the effects of MNPs,” says Kenner.

The research was published in the journal Nanomaterials.

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