Microplastics in the bloodstream may pose hidden risks to brain health

In a recent study published in the journal Science Advances, researchers investigated the impact of microplastics on blood flow and neurobehavioral functions in mice. Using advanced imaging techniques, they observed that microplastics obstruct cerebral blood vessels by causing individual immune cells to become trapped in capillaries. The findings revealed a novel mechanism through which microplastics indirectly disrupt vascular and neurological functions without crossing the blood-brain barrier.

Microplastics and human health

Microplastics originate from plastic degradation and are being recognized as environmental pollutants with potential health risks to humans and ecosystems. These particles can enter the human body through ingestion, inhalation, or medical devices. Research shows that microplastics can cross biological barriers, such as the blood-brain barrier, and interact with various physiological systems, including the immune and cardiovascular systems.

While nanoscale plastics have been linked to neurological disorders (e.g., exacerbating α-synuclein pathology associated with Parkinson’s disease) and inflammation, the impact of micron-sized microplastics remains unclear. Previous studies have demonstrated that microplastics can induce immune responses, alter cellular functions, and affect blood perfusion, potentially leading to organ dysfunction. However, the specific mechanisms of microplastic-induced vascular or neurological disruptions, particularly in vivo, are poorly understood.

About the study

The present study employed various in vivo and ex vivo methods to investigate how microplastics affect blood flow and neurobehavioral functions in mice. Eight-week-old male mice were housed under controlled conditions and used as the study model. The researchers intravenously injected fluorescently labeled polystyrene microplastics of three sizes — 5 µm (micron-sized), 2 µm, and 80 nm (nanoscale) — into mice at concentrations designed to mimic human exposure levels.

The study used advanced imaging techniques, including laser speckle contrast imaging and miniature two-photon microscopy, to visualize the microplastics within cerebral blood vessels. These methods provided high-resolution, real-time tracking of microplastic movements and vascular interactions.

Blood samples were also collected for flow cytometry analysis to identify the immune cells responsible for microplastic uptake and obstruction. Specifically, the cells labeled with fluorescent microplastics were sorted and characterized to understand the role of immune cells, such as neutrophils and macrophages, in the phagocytosis of microplastics. Phagocytosis altered immune cell morphology, increasing their size (forward scatter) and reducing granularity (side scatter), which contributed to vascular blockages.

Additionally, behavioral experiments, including open-field, Y-maze, rotarod, and rod-hanging tests, were conducted to evaluate the neurobehavioral effects of microplastics in mice. These tests assessed exploratory behavior, memory, motor coordination, and endurance after microplastic exposure.

Laser speckle imaging was also performed to measure cerebral blood perfusion at various time points post-injection to determine how microplastics affected vascular flow. The combination of imaging, behavioral, and cellular analyses provided a comprehensive understanding of how microplastics interact with the vascular and neurological systems.

Key findings

The study found that microplastics disrupt vascular and neurobehavioral functions by causing immune cells that ingested them to become mechanically trapped in narrow cerebral vessels. The researchers observed individual immune cells (termed MPL-Cells) laden with microplastics obstructing blood flow, particularly in capillaries.

These obstructions reduced cerebral blood perfusion within 30 minutes, with the most significant effects in smaller vessels. Unlike classical blood clots, these blockages stemmed from physical cell entrapment rather than platelet activation or clotting cascades.

The behavioral experiments demonstrated that mice exposed to microplastics exhibited decreased locomotion, impaired memory, and reduced motor coordination. Open-field and Y-maze tests showed significant reductions in movement speed and spatial memory, while rotarod and rod-hanging tests indicated decreased motor skills and endurance. Although neurobehavioral impairments resolved within four weeks, some vascular obstructions persisted at lower densities.

Further analysis indicated that larger microplastics (5 µm) caused prolonged obstructions, while smaller particles (2 µm and 80 nm) were cleared faster. The results from flow cytometry revealed that phagocytosis of microplastics altered immune cells’ morphology and adhesive properties, contributing to vascular blockages. These findings suggested that microplastics’ size, concentration, and interactions with immune cells are critical factors in their impact on vascular and neurological health.

The study emphasized the potential health risks of microplastics, particularly their ability to obstruct blood vessels and disrupt brain function. However, the authors cautioned that translating these findings to humans requires further research due to differences in vascular size and physiology between mice and humans.

Conclusions

To summarize, the findings revealed the mechanisms through which microplastics obstruct blood flow and impair neurobehavioral functions via immune cell entrapment in cerebral vessels. Factors such as particle size were also found to influence these effects, with smaller microplastics causing less obstruction.

While the neurobehavioral impairments due to microplastics in mice were largely reversible, residual vascular obstructions persisted even after behavioral recovery. The findings emphasized the need for further research on the long-term health risks posed by microplastics, particularly in individuals with pre-existing cardiovascular conditions or narrowed blood vessels.