Irregularly Shaped Microplastic Particles Compromise the Integrity of the Glomerular Filtration Barrier of the Kidney

BACKGROUND: Environmental pollution with microplastics (MPs) is continuously increasing. Humans are inevitably exposed to MPs. Although the shape of MPs influences their biological effects, for practical reasons, most studies use spherical particles instead of more realistic irregular MP fragments. Consequently, we compared spherical and irregular particles to determine the distribution of MPs in the body and to determine the effects of MP on kidney function. METHODS: Labeled spherical and irregular MP fragments were fed to mice via oral gavage, as a single dose or daily dose over seven days. The distribution of MP particles was assessed in various organs, and the effects of MPs on the kidney was determined by histochemistry and intravital multiphoton microscopy. Addition functional experiments were performed using the isolated perfused mouse kidney model. RESULTS: Overall, the intestinal absorption of MP particles was limited, with >99% of the MP being excreted via feces. Irregular MP fragments persisted in the circulation for several days and accumulated in all organs following oral uptake. Irregular MP particles were also observed in the urine, suggesting that MPs can pass through the glomerular filtration barrier (GFB). In the kidney, irregular MP particles were found in blood vessels, glomeruli, and tubules, where they attracted phagocytotic cells. Functional studies using mouse isolated perfused kidneys and intravital microscopy revealed that irregular MPs caused capillary flow disturbances, lesions to blood vessels and the tubular system. Furthermore, MPs induced glomerular albumin hyperfiltration and increased proximal tubular albumin uptake, suggesting lesions of the GFB. No such effects were observed after ingestion of spherical MP particles. CONCLUSIONS: Our data suggest that (i) the morphology of MP particles is critical in terms of tissue distribution and the formation of local lesions, and that (ii) irregular MP particles, such as those observed in the environment, cause long-term damage to the kidney.