The influence of microplastics on the human intestine: an in vitro study on uptake and transport under different exposure conditions

Abstract

Nowadays, microplastics are an omnipresent environmental pollutant. They are small enough to be ingested by humans directly or via consumption of, for example, contaminated (sea)food. Consequently, microplastics enter the gastrointestinal tract and interact with the intestinal epithelium. Current data on microplastic uptake and transport is inconclusive due to variations in experimental approach and lack of fundamental understanding. This study aims to provide an overview of the effects of different exposure conditions on the uptake and transport of Polystyrene microplastics in vitro. Human epithelial Caco-2 cells, and a co-culture with HT29-MTX cells, were exposed to carboxylated Polystyrene spheres (200 nm or 2 µm). After physicochemical characterisation, uptake and transport were evaluated using FACS, confocal microscopy, and fluorescence intensity measurements. Our data show that MPs are taken up and transported by Caco-2 cells. In addition, they suggest that the presence of serum proteins in cell medium causes a reduction in uptake (up to 36%). We found increased uptake for longer exposure durations and smaller microplastic size. Lastly, further differentiation of the cells negatively affected uptake, and the presence of mucus reduced transport to less than half. These results indicate that caution should be taken when comparing and interpreting research data as varying exposure conditions significantly affect microplastic uptake and transport across a Caco-2 monolayer.