How do they get there? What do they do?
By
Nicole San Roman
It’s happening every day. From our water, our food and even the air we breathe, tiny plastic particles are finding their way into many parts of our body.
But
what happens once those particles are inside? What do they do to our digestive
system?
In
a recent paper published in the journal Environmental
Health Perspectives, University of New Mexico researchers found
that those tiny particles – microplastics – are having a significant impact on
our digestive pathways, making their way from the gut and into the tissues of
the kidney, liver and brain.
Research
continues to show the importance of gut health. If you don't have a healthy
gut, it affects the brain, it affects the liver and so many other tissues. So
even imagining that the microplastics are doing something in the in the gut,
that chronic exposure could lead to systemic effects.
Eliseo Castillo, PhD, an associate professor in the Division of Gastroenterology & Hepatology in the UNM School of Medicine’s Department of Internal Medicine and an expert in mucosal immunology, is leading the charge at UNM on microplastic research.
“Over
the past few decades, microplastics have been found in the ocean, in animals
and plants, in tap water and bottled water,” Castillo, says. “They appear to be
everywhere.”
Scientists
estimate that people ingest 5 grams of microplastic particles each week on
average – equivalent to the weight of a credit card.
While
other researchers are helping to identify and quantify ingested microplastics,
Castillo and his team focus on what the microplastics are doing inside the
body, specifically to the gastrointestinal (GI) tract and to the gut immune
system.
Over
a four-week period, Castillo, postdoctoral fellow Marcus Garcia, PharmD, and
other UNM researchers exposed mice to microplastics in their drinking water.
The amount was equivalent to the quantity of microplastics humans are believed
to ingest each week.
Microplastics
had migrated out of the gut into the tissues of the liver, kidney and even the
brain, the team found. The study also showed the microplastics changed
metabolic pathways in the affected tissues.
“We
could detect microplastics in certain tissues after the exposure,” Castillo
says. “That tells us it can cross the intestinal barrier and infiltrate into
other tissues.”
Castillo
says he’s also concerned about the accumulation of the plastic particles in the
human body. “These mice were exposed for four weeks,” he says. “Now, think
about how that equates to humans, if we're exposed from birth to old age.”
The
healthy laboratory animals used in this study showed changes after brief
microplastic exposure, Castillo says. “Now imagine if someone has an underlying
condition, and these changes occur, could microplastic exposure exacerbate an
underlying condition?”
He
has previously found that microplastics are also impacting macrophages – the
immune cells that work to protect the body from foreign particles.
In
a paper published in the journal Cell Biology
& Toxicology in 2021, Castillo and other UNM
researchers found that when macrophages encountered and ingested microplastics,
their function was altered and they released inflammatory molecules.
“It
is changing the metabolism of the cells, which can alter inflammatory
responses,” Castillo says. “During intestinal inflammation – states of chronic
illness such as ulcerative colitis and Crohn’s disease, which are both forms of
inflammatory bowel disease – these macrophages become more inflammatory and
they’re more abundant in the gut.”
The
next phase of Castillo’s research, which is being led by postdoctoral fellow
Sumira Phatak, PhD, will explore how diet is involved in microplastic
uptake.
“Everyone’s
diet is different,” he says. “So, what we're going to do is give these
laboratory animals a high-cholesterol/high-fat diet, or high-fiber diet, and
they will be either exposed or not exposed to microplastics. The goal is to try
to understand if diet affects the uptake of microplastics into our body.”
Castillo
says one of his PhD students, Aaron Romero, is also working to understand why
there is a change in the gut microbiota. “Multiple groups have shown
microplastics change the microbiota, but how it changes the microbiota hasn’t
been addressed.”
Castillo
hopes that his research will help uncover the potential impacts microplastics
are having to human health and that it will help spur changes to how society
produces and filtrates plastics.
“At
the end of the day, the research we are trying to do aims to find out how this
is impacting gut health,” he says. “Research continues to show the importance
of gut health. If you don't have a healthy gut, it affects the brain, it
affects the liver and so many other tissues. So even imagining that the
microplastics are doing something in the in the gut, that chronic exposure
could lead to systemic effects.”