Digestion of Microplastics with Simulated Gastrointestinal Conditions Mitigates Uptake by Intestinal Epithelial Cells: Quantified by Imaging Flow Cytometry

Humans are chronically exposed to microplastics (plastic particles < 1 mm) via oral ingestion. Yet, intestinal absorption of microplastics requires robust quantification and in vitro studies have largely lacked digestive conditions in experimental design. This study aimed to quantify how simulated digestion of microplastics affected the rate of internalisation by an intestinal epithelial cell line (IEC-6). Spherical 0.56 µm polystyrene microplastics were simulatively digested using a static digestion protocol. IEC-6 cells were exposed to 1 µg/mL of pristine or digested microplastics for 24 h. Microplastic internalisation was visualised with confocal microscopy and novelly quantified by imaging flow cytometry. Confocal microscopy confirmed internalisation of pristine and digested microplastics by IEC-6 cells, where pristine microplastics were internalised by 62.2 ± 11.8 % of cells which was lessened to 24.6 ± 5.3 % for digested microplastics. Most IEC-6 cells internalised 1-2 microplastics, and internalisation of > 2 microplastics per cell was increased (p < 0.01) after exposure to pristine microplastics (34.3 ± 10.3 %) compared to digested microplastics (8.9 ± 0.74 %). This study demonstrated that simulated digestion of polystyrene microplastics reduced internalisation by IEC-6 cells, providing unprecedented insights into the gastrointestinal effect of microplastic exposure and raising important considerations for future research.