Effects of Orally Ingested Microplastics on the Structure and Function of the Kidneys

Background: Plastics are chemically inert and durable materials with long-term deposition in the environment. Little is known about the functional consequences of oral microplastic (MP) ingestion. Most MP particles in the environment consist of fibers and irregular fragments. The size, shape, and composition of the MP particles presumably determine the degree of MP toxicity. Thus, fibers are generally more critical than aspherical fragments, and fragments are more problematic than spherical particles. In the present study we assessed the distribution of MP particles in the organism and the consequences of MP deposition in the kidney. We hypothesized that sharp and aspheric particles, mimicking the real-world situation of MP in the environment, are more deleterious compared with spherical particles. Methods: Aspheric and spheric MP of different polymers were synthetized, and fluorescence labeled (polystyrene, polypropylene, polyethylene terephthalate, 1-50 µm). The deposition of the labeled particles was determined in mice after oral gavage (2.5 mg/d, 5 or 10 consecutive days, 30 mice (n=6 each)). 3-D histological assessment was performed by fluorescence confocal microscopy of thick tissue sections. In addition, the quantitative organ distribution was determined in vivo using MP with embedded upconverting nanoparticles (NaYF4:Yb,Tm). Results: We found a considerable enrichment of MP particles in the kidney. Furthermore, MP particles were present in renal blood vessels including glomerular capillaries. Large MP particles (> 5 µm) were also found in the lumen of some tubules of the renal cortex and were accompanied by an influx of immune cells, suggesting a pro-inflammatory effect of MP particles. Experiments using the isolated perfused kidney model showed the increased tubular uptake of labeled albumin in nephrons in which particles were located, suggesting a loss of the integrity of the filtration barrier with subsequent passage of particles from glomerular capillaries into the tubular system. Conclusion: In summary, ingested MP particles with properties similar to those found in the environment, compromise the structural and functional integrity of the kidney and may trigger local inflammatory responses leading to kidney injury. Funding: Government Support – Non-U.S.