In vitro intestinal models show how microplastics affect the gastrointestinal tract

In vitro intestinal models show how microplastics affect the gastrointestinal tract

Plastics were discovered in 1950 and have since become one of the most commonly used materials worldwide. The increased demand for plastics has led to the accumulation of these materials in landfills and the oceans, making plastic pollution a significant environmental threat that impacts all ecosystems.

Study: Microplastics: What happens in the human digestive tract? First findings in adults using in vitro intestinal models. Photo credit: Lucio Pepe / Shutterstock.com

background

Plastics undergo natural weathering in the environment, converting them into small particles.

Microplastics (MPs) are small polymer matrices with a diameter ranging from one micrometer (μm) to five millimeters (mm). MPs are regular or irregularly shaped, insoluble substances that are sometimes produced voluntarily or released through plastic weathering and fragmentation.

MPs enter the food chain due to their presence in many foods and drinking water. Several studies have confirmed the presence of MPs in human blood, stool and colon tissue. However, despite these observations, very few studies have investigated the fate of MPs in the human gastrointestinal tract.

After ingestion, MPs encounter the gastrointestinal barrier, which consists of intestinal epithelium and mucus. Furthermore, MPs interact with the gut microbiota, which forms a complex and diverse community of microbes, including bacteria, fungi, archaea, protozoa, and viruses. A viscoelastic gel of the mucus layer is the first chemical, physical and biological line of defense that protects the intestinal epithelium.

The gut microbiota also plays an essential role in regulating host immunity and metabolism of toxins, drugs and xenobiotics. In addition, these microorganisms are also associated with the breakdown of undigested foods and the production of secondary metabolites such as short-chain fatty acids (SCFAs), aryl hydrocarbon receptor ligands (AhR), volatile organic compounds (VOCs), and gas.

AhR ligands and SCFAs are responsible for maintaining the integrity of intercellular tight junctions in the intestinal epithelium. A close relationship has been found between intestinal microbial activity and the effective maintenance of intestinal barrier function.

Several in vivo models have highlighted different effects of MPs depending on their size, shape, type of polymer matrix, duration of exposure, surface charge, and route of administration. These effects include, but are not limited to, changes in mucus secretion patterns and microbial dysbiosis.

About the study

In a current one Hazardous Materials Journal In this study, researchers hypothesize that exposure to polyethylene (PE) MPs under realistic conditions could affect the human gastrointestinal system in adults in vitro. The researchers were particularly interested in determining the interactions that arise between the gut microbiome and PE-MPs.

The effects of exposure to PE MPs on human metabolic activity and gut microbiota composition were analyzed after participants were exposed to a daily dose of 21 mg/day for two weeks.

A total of four healthy adult volunteers took part in the current study. The in vitro model of mucosal artificial colon (M-ARCOL) was also used.

The M-ARCOL model is a single-stage fermentation system that simulates the average microbial and physicochemical parameters of the human colon. This model includes both luminal and mucosal microbiota through an external mucin-alginate bead compartment.

Both human intestinal Caco-2 and mucus-secreting HT29-MTX cells were incubated with M-ARCOL luminal supernatants collected after 2 weeks of exposure.

Overall, the current analysis provided a deeper understanding of the effects of MPs, such as permeability, cytotoxicity and inflammation, on the intestinal epithelium and mucus.

Study results

The initial fecal microbiota used for M-ARCOL inoculation showed significant interindividual variability. Furthermore, these variabilities were maintained throughout the course of the in vitro experiment.

All participants exposed to PE MPs observed a significant change in microbial diversity. An increasing trend associated with α-diversity of the luminal microbiota was noted. In addition to interindividual variability, similar effects related to the lumen and mucus-associated microbiota have been reported.

After exposure to PE-MPs, increased concentrations of Desulfovibrionaceae, Dethiosulfovibrionaceae, and Enterobacteriaceae and decreased concentrations of Christensenellaceae and Akkermansiaceae were observed. The latter two groups are associated with an individual's health status.

Some of the variations in microbial structures corresponded to microbial diversity in individuals suffering from irritable bowel syndrome (IBS) or inflammatory diseases of the gastrointestinal tract. Exposure of MPs to polyethylene terephthalate (PET) also reduced Bacteroidota in the colon of three donors. An increase in Desulfobacterota was observed in one participant.

The effect of PE MPs on the production of gas, SCFAs and VOCs showed no significant difference between the control group and the treated group. However, an increase in indole, 3-methyl and skatole levels after exposure to PE-MPs suggested the possibility of microbiota-mediated gastrointestinal dysregulation, which requires further investigation.

Reduced AhR activity was observed in association with PE-MP exposed gut microbiota. Similar results have also been reported in people with IBD and celiac disease. The present study highlights that intestinal cells exposed to two sizes of PE did not significantly reduce cell viability; However, they caused oxidative stress.

Conclusions

The current study examined the effects of daily exposure to PE-MPs on the gastrointestinal system of adult humans. To this end, the effect of PE-MPs on intestinal mucosal microbiota and intestinal mucosa was found to depend on individual characteristics.

Further studies are required in the future to characterize the specific “intestinal plasticsphere” in terms of composition and metabolism.

Reference:

• Fournier, E., Leveque, M., Ruiz, P., et al. (2022). Mikroplastik: Was passiert im menschlichen Verdauungstrakt? Erste Erkenntnisse bei Erwachsenen anhand von In-vitro-Darmmodellen. Zeitschrift für gefährliche Materialien. doi:10.1016/j.jhazmat.2022.130010