The global use of plastic has steadily increased over the past century, leading to the production of various types of plastic. A significant amount of this plastic ends up in oceans or landfills, resulting in substantial plastic accumulation in the environment. Plastic waste slowly degrades into microplastics (MP), which can be inhaled or ingested by both animals and humans. A growing body of evidence suggests that microplastics can cross the intestinal barrier and enter the lymphatic and systemic circulation, accumulating in tissues such as the lungs, liver, kidneys, and brain. However, the impacts of mixed MP exposure on tissue function and metabolism remain largely unexplored.
This study aims to investigate the effects of polymeric microspheres on tissue metabolism in mice by assessing the ability of the microspheres to cross the intestinal barrier and enter systemic circulation. Specifically, the goal was to examine microsphere accumulation in various organ systems, identify concentration-dependent metabolic changes, and evaluate the health effects of mixed microsphere exposure.
To investigate the impact of ingested microspheres on targeted metabolic pathways, mice were exposed to polystyrene (µ) microspheres or a mixture of polymeric microspheres composed of polystyrene (µ), polyethylene (µ), and the biodegradable and biocompatible plastic poly-(lactic-co-glycolic acid) (µ). Exposures occurred twice a week for four weeks at concentrations of 0, 2, or by oral gavage. Tissues were collected to examine microsphere entry and changes in metabolites.
In mice that ingested microspheres, polystyrene microspheres were detected in distant tissues, including the brain, liver, and kidneys. Additionally, metabolic differences were reported in the colon, liver, and brain, showing differential responses depending on the concentration and type of microsphere exposure.
This study uses a mouse model to provide critical insights into the potential health implications of the widespread issue of plastic pollution. These findings demonstrate that orally consumed polystyrene or mixed polymer microspheres can accumulate in tissues such as the brain, liver, and kidneys. Furthermore, the study highlights concentration-dependent and polymer-type-specific metabolic changes in the colon, liver, and brain following exposure to plastic microspheres. These results underscore the mobility of MPs within and between biological tissues after exposure, emphasizing the importance of understanding their metabolic impact.
Image: Visualization of the systemic translocation of polystyrene microspheres. Visualization of polystyrene microspheres resuspended from a sediment isolated in 100% EtOH. The black arrow indicates polystyrene microspheres. Credit: Environmental Health Perspectives (2024). DOI: 10.1289/EHP13435
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Microplastics are entering our bodies every day through water, food, and even the air we breathe. But what happens once these particles are inside? How do they affect our digestive system?
A recent article published in Environmental Health Perspectives reveals that microplastics can have significant impacts on digestive pathways, migrating from the gut to tissues like the kidneys, liver, and brain.
Dr. Eliseo Castillo, an associate professor in the Division of Gastroenterology and Hepatology at the University of New Mexico (UNM) and an expert in mucosal immunology, leads microplastics research at UNM.
"Over the past few decades, microplastics have been found in the ocean, animals, plants, tap water, and bottled water," Castillo explains. "They seem to be everywhere."
Scientists estimate that people ingest about 5 grams of microplastic particles each week, equivalent to the weight of a credit card.
While other researchers work to identify and quantify ingested microplastics, Castillo and his team focus on what these particles do inside the body, particularly in the gastrointestinal (GI) tract and immune system.
Over four weeks, Castillo, postdoctoral fellow Marcus García, PharmD, and other UNM researchers exposed mice to microplastics in their drinking water, equivalent to the amount humans are believed to consume weekly.
The team found that microplastics migrated from the gut to tissues in the liver, kidneys, and even the brain. The study also showed that microplastics altered metabolic pathways in the affected tissues.
"We detected microplastics in certain tissues after exposure," says Castillo. "This tells us that they can cross the intestinal barrier and infiltrate other tissues."
Castillo is concerned about the accumulation of plastic particles in the human body. "These mice were exposed for just four weeks," he says. "Now think about how that compares to humans, who are exposed from birth to old age."
Laboratory animals in this study showed changes after brief microplastic exposure. Castillo asks, "Now imagine if someone has an underlying condition. Could microplastic exposure worsen that condition?"
Castillo´s earlier work also showed that microplastics affect macrophages—immune cells that protect the body from foreign particles. In a 2021 study published in Cell Biology & Toxicology, Castillo and colleagues found that when macrophages encountered and ingested microplastics, their function was altered, and they released inflammatory molecules.
"It changes the metabolism of the cells, which can disrupt inflammatory responses," says Castillo. "In cases of intestinal inflammation, such as chronic diseases like ulcerative colitis and Crohn’s disease, these macrophages become more inflammatory and are more abundant in the gut."
The next phase of Castillo’s research, led by postdoctoral fellow Dr. Sumira Phatak, will explore how diet influences microplastic absorption.
"Everyone’s diet is different," Castillo says. "So, we’ll be giving these lab animals either a high-cholesterol, high-fat diet or a fiber-rich diet, with or without microplastic exposure. The goal is to understand whether diet affects microplastic absorption in the body."
Castillo hopes his research will uncover the potential health impacts of microplastics and help drive changes in how society produces and filters plastics.
"Ultimately, our research aims to understand how this affects gut health," he says. “Gut health is critical because it impacts the brain, liver, and many other tissues. If microplastics are doing something in the gut, chronic exposure could lead to systemic effects.”
