Microplastics found to pass the blood brain barrier, even though ingested in drinking water

Professor Jaime Ross, with graduate students Lauren Gaspar and Sydney Bartman, is investigating the potentially serious neurological impacts of microplastics on mammals.

A news study conducted by University of Rhode Island Professor Jaime Ross investigating the infiltration of microplastics in mammals has revealed that this is far more widespread than initially thought. In fact, the plastic particles were found to bioaccumulate in every organ, including, startlingly enough, the brain.

Microplastics are among the most pervasive pollutants on the planet. They have been discovered in the air, in water systems and food chains around the world. While their negative impacts on marine organisms have been established, few studies have examined the potential health impacts on mammals.

“Research on the health effects of microplastics, especially in mammals, is still very limited,” said Ross, an assistant professor of biomedical and pharmaceutical sciences at the Ryan Institute for Neuroscience and the College of Pharmacy.

The study noted that humans are exposed to microplastics through the consumption of ‘water, seafood, consumer products (clothes, toothpaste, salt, sugar, honey, beer, anything stored in plastic bottles, plastic wrap, or cans/cartons lined with plastic), and via inhalation from textiles, synthetic rubber tires, and plastic covers’. They have been detected, among others, in blood and even breast milk - findings that warrant more investigation into the health outcomes of such exposure in mammals. Currently, there are limited studies that address the potential adverse effects of exposure to MPs on brain health in mammals and even fewer studies that consider age as an additional factor that may impact the outcome of exposure to microplastics - the reason Ross and her team chose to focus on neurobehavioral effects and inflammatory response to exposure to microplastics, as well as the accumulation of microplastics in tissues. Together with graduate students Lauren Gaspar and Sydney Bartman, she examined the biological and cognitive consequences of exposure to microplastics in mice.

The drinking water of a diverse group of older and younger mice was spiked with microplastics over a period of three weeks - with ‘striking’ results, said Ross. The researchers found that exposure to microplastics - in this case, fluorescent polystyrene particles - induced both behavioural changes and alterations in immune markers in liver and brain tissues. The mice in the study began to move peculiarly, and to exhibit behaviours reminiscent of dementia in humans. The results were even more profound in older animals.

“These were not high doses of microplastics, but in only a short period of time, we saw these changes,” Ross said. “Nobody really understands the life cycle of these microplastics in the body, so part of what we want to address is the question of what happens as you get older. Are you more susceptible to systemic inflammation from these microplastics as you age? Can your body get rid of them as easily? Do your cells respond differently to these toxins?”

After three weeks, dissection of the mice revealed that the ingested PS micro-particles had infiltrated every every tissue sample - liver, kidney, gastrointestinal tract, lung, spleen, heart, and brain tissues from both young and old exposed mice - tested. The particles were also observed in the mice’s bodily wastes.

“The detection of MPs in tissues such as the heart and lungs … suggests that the PS-MPs (polystyrene microplastics) are going beyond the digestive system and likely undergoing systemic circulation,” the authors write. An observation they note that is further supported by the detection of microplastics in urine and the brain, indicating they can pass the blood–brain barrier.

That brain infiltration also may cause a decrease in glial fibrillary acidic protein, called “GFAP”, a protein that supports many cell processes in the brain, results have shown. Previous studies have suggested that GFAP expression might decrease in early stages of some neurodegenerative diseases, such as Alzheimer’s disease, or in younger patients with depression disorders.

What is especially concerning is the fact that these changes were seen after just three weeks of exposure to microplastics. As human exposure today is inevitable it is therefore essential to better understand their toxicity to limit their impact on human health. The present study, showed that in just three weeks, polystyrene particles measuring 0.1 and 2 μm can reduce cell viability, translocate throughout the body, accumulate in tissues including brain tissue, markedly modify behaviour in mice, and significantly alter immune markers in both the liver and the brain. Additionally, the effects of exposure seem to be age-dependent.

Future work is needed to examine these factors in order to understand the mechanisms behind these effects and the changes seen with age, said Ross.

“We want to understand how plastics may change the ability for the brain to maintain its homeostasis or how exposure may lead to neurological disorders and diseases, such as Alzheimer’s disease,” she said.

The study was published in the International Journal of Molecular Science. It was supported by the Rhode Island Medical Research Foundation, Roddy Foundation, Plastics Initiative, URI College of Pharmacy, George and Anne Ryan Institute for Neuroscience, and the Rhode Island Institutional Development Award (IDeA) Network of Biomedical Research Excellence from the National Institute of General Medical Sciences of the National Institutes of Health.

Int. J. Mol. Sci. 2023, 24(15), 12308; https://doi.org/10.3390/ijms241512308

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