Could Microplastics Trigger Inflammation in the Brain?

Increasing evidence hints at the capability of microplastics within our bloodstream to breach the brain-blood barrier in mammals. Recent initial studies uncover the potential consequences of their presence, indicating that aged microplastics pose a greater threat to human brain cells compared to newer counterparts.

According to biologist Sung-Kyun Choi from the Daegu Gyeongbuk Institute of Science and Technology (DGIST), the implications of microplastics’ harmful effects are particularly concerning. Secondary microplastics exposed in natural settings appear to trigger a more intense inflammatory reaction within the brain.

Human society is encompassed by plastics in myriad ways. They envelop us, facilitate communication, serve as containers for our food and drinks, provide shelter, and accompany us during travel, contributing to a staggering production of 390 million tons of plastic in 2021 alone. Throughout their lifecycle, these abundant sources shed minuscule fragments known as microplastics, not just after disposal but during their usage.

Exposed to various environmental elements such as rain, wind, and sunlight, these tiny particles undergo changes in their form and composition before re-entering living organisms. Even before birth, we start absorbing a fine dust of weathered plastic fragments.

While previous studies have focused on the impact of newly manufactured plastics on our brain cells, biologist Hee-Yeon Kim from DGIST, along with colleagues, conducted an experiment with weathered particles instead. They closely observed the response of our brain’s immune cells, known as microglia, to weathered polystyrene-derived microplastics compared to similar-sized ‘untouched’ ones.

When mice were fed weathered microplastics for seven days, their blood showed heightened levels of inflammatory particles, and their brain cells experienced increased cell death. Consequently, the researchers examined weathered polystyrene particles in human microglia cultivated in a laboratory setting.

Microglia, constituting 10 to 15 percent of brain cells, act as vigilant guardians within our central nervous system, identifying and addressing foreign objects. Earlier research conducted by the team discovered the accumulation of microparticles in the microglia of mice, further highlighting their significance in this context.

Kim and the research team uncovered that weathered microplastics impacted proteins responsible for breaking down sugars into energy, elevating their presence in the microglial cells by 10 to 15 times compared to control groups. Furthermore, these microplastics increased the levels of proteins associated with brain cell demise by a factor of 5.

The team suspects that these changes are linked to the alterations microplastics undergo upon exposure to sunlight. When subjected to UV waves, polystyrene absorbs this energy, making the plastic more fragile and susceptible to breaking into smaller pieces. Kim’s team discovered that weathered polystyrene exhibited increased surface area and modified chemical bonds, two characteristics affecting their responsiveness.

All these findings contribute to a heightened inflammatory reaction within brain cells, surpassing the response provoked by new, untouched microplastics given at equivalent doses.

“We have, for the first time, pinpointed that plastics leaked into the environment undergo an expedited weathering process, transforming into secondary microplastics capable of acting as neurotoxic substances. This leads to escalated inflammation and cell demise in the brain.”

Sung-Kyun Cho

While these outcomes have, until now, been observed solely in live mice and human tissue samples within laboratory settings, the significant impact these pollutants exert on brain tissue strongly suggests their influence on our brain health.

Although the experiments were conducted using small sample sizes and high concentrations of microplastics to simulate long-term accumulation, the researchers are now planning more extensive, extended studies. These studies will involve larger sample sizes and doses reflecting real-world environmental conditions over time to validate their discoveries.

The urgency of their results becomes apparent considering the surge in plastic production driven by fossil fuel companies, despite potential reductions in fuel usage due to climate change.

As mounting evidence suggests a threat to our health, the production, usage, and disposal of plastics demand heightened attention.

Abstract

The growing use of plastic materials has resulted in a constant increase in the risk associated with microplastics (MPs). Ultra-violet (UV) light and wind break down modify MPs in the environment into smaller particles known as weathered MPs (WMPs) and these processes increase the risk of MP toxicity. The neurotoxicity of weathered polystyrene-MPs remains unclear. Therefore, it is important to understand the risks posed by WMPs. We evaluated the chemical changes of WMPs generated under laboratory-synchronized environmentally mimetic conditions and compared them with virgin MPs (VMPs). We found that WMP had a rough surface, slight yellow color, reduced molecular weight, and structural alteration compared with those of VMP. Next, 2 μg of ∼100 μm in size of WMP and VMP were orally administered once a day for one week to C57BL/6 male mice. Proteomic analysis revealed that the WMP group had significantly increased activation of immune and neurodegeneration-related pathways compared with that of the VMP group. Consistently, in in vitro experiments, the human brain-derived microglial cell line (HMC-3) also exhibited a more severe inflammatory response to WMP than to VMP. These results show that WMP is a more profound inflammatory factor than VMP. In summary, our findings demonstrate the toxicity of WMPs and provide theoretical insights into their potential risks to biological systems and even humans in the ecosystem.

https://www.sciencedirect.com/science/article/abs/pii/S001393512301215X?via%3Dihub