Micro- and nanoplastics (MNPs) are present in a variety of environmental media and human tissues (FPF reported, here and here) and are commonly taken up via diet (FPF reported). Despite their ubiquity, their health impacts are still under investigation, for example within the AURORA project.
A new study by Miao Peng and co-authors from Ghent University explores the long-term impacts of MNPs on the energy metabolism of gut epithelial cells. The study was published in Environmental Science and Technology on May 30th, 2024. The authors simulated repeated and single exposure of human intestinal epithelial cells (Caco-2 cell lines) to realistic amounts of polystyrene (PS) nanoplastics (size: 85 nm, concentration: up to 5 billion particles/mL, respectively 1.5 mg/L). They observed impacts on cytotoxicity, oxidative stress, bioenergetics, and cell differentiation over 12 days. Epithelial cells in the intestine are in close contact with ingested micro- and nanoplastics and were thus chosen as suitable cell lines for investigating chronic health impacts. Particularly small particles towards the nanoscale, such as those used in this study, may be preferentially taken up by cells (FPF reported).
Peng and co-authors found that a single exposure to PS nanoplastics led to temporary changes in the energy metabolism of Caco-2 cells. Oxidative stress and glycolysis (a backup mechanism for cells’ energy supply when mitochondria cannot function normally) were increased right after exposure and at the end of the 12-day observation period due to secondary effects. Overall, the cells could recover from single exposures without negatively affecting cell differentiation and mitochondrial mass long-term.
Repeated exposure led to more permanent damage to the mitochondria. Oxidative stress was increased throughout the entire observation period and eventually resulted in significant damage to mitochondrial functions and the cell differentiation process. Glycolysis was also permanently increased during repeated exposure to PS nanoplastics, implicating the need to compensate for the damage to the mitochondria.
The authors state that the changes observed from long-term PS nanoplastics exposure may be relevant for “the potential pathogenesis of various human metabolic disorders such as diabetes and obesity, as well as conditions including cancer, cardiovascular disease, and neurodegeneration.”
Three additional recent studies also investigated the potential health effects of PS MNPs. Maike Adler and colleagues found that PS MNPs (size: 0.5-3 μm, concentration: 37-1 500 mg/L) were taken up by human macrophages in vitro and impacted their function. Macrophages play an important role in the immune system as generalist responders to invading pathogens. PS MNPs were found to increase oxidative stress and cell death, which may impair immune response. Particularly small MNPs had a large impact on macrophage health. Ruiying Zhang and co-authors investigated the health impacts of ingesting PS MNPs (size: 1 μm, concentration: 10 mg/L) in pregnant mice. The researchers found several systemic effects, including placental malfunction, fetal growth retardation, inflammation of the liver, and increased oxidative stress. Huai Lin and co-authors investigated the effects of PS MNPs of different sizes (200 nm, 100 μm) on mice and their gut microbiome at a dose of 50 mg/kg. Both types of MNPs induced changes in the gut microbiome, low-grade inflammation, colon damage, and liver toxicity. Small MNPs additionally significantly altered the proteins produced by colon cells, disrupting intestinal metabolism and immune function.
All studies conclude that their findings may have implications for human health, but more research is needed to confirm the results from cell or animal models.
References
Peng, M., et al. (2024). ‘Probing Long-Term Impacts: Low-Dose Polystyrene Nanoplastics Exacerbate Mitochondrial Health and Evoke Secondary Glycolysis via Repeated and Single Dosing.’ Environmental Science and Technology. DOI: 10.1021/acs.est.3c10868 58
Adler, M. Y., et al. (2024). ‘Effect of micro- and nanoplastic particles on human macrophages.’ Journal of Hazardous Materials. DOI: 10.1016/j.jhazmat.2024.134253
Zhang, R., et al. (2024). ‘Polystyrene microplastics disturb maternal glucose homeostasis and induce adverse pregnancy outcomes.’ Ecotoxicology and Environmental Safety. DOI: 10.1016/j.ecoenv.2024.116492
Lin, H., et al. (2024). ‘The role of gut microbiota in mediating increased toxicity of nano-sized polystyrene compared to micro-sized polystyrene in mice.’ Chemosphere. DOI: 10.1016/j.chemosphere.2024.142275
