Interactions of polystyrene nanoplastics with in vitro models of the human intestinal barrier

The universal presence of micro-nanoplastics (MNPLs) and its relative unknown effects on human health is a concern demanding reliable data to evaluate their safety. As ingestion is one of the main exposure routes for humans, we have assessed their hazard using two in vitro models that simulate the human intestinal barrier and its associated lymphoid system. Two different coculture models (differentiated Caco-2/HT29 intestinal cells and Caco-2/HT29 + Raji-B cells) were exposed to polystyrene nanoparticles (PSNPs) for 24 h. Endpoints such as viability, membrane integrity, NPS localization and translocation, ROS induction, and genotoxic damage were evaluated to have a comprehensive view of their potentially harmful effects. No significant cytotoxic effects were observed in any of the analyzed systems. In addition, no adverse effects were detected in the integrity or in the permeability of the barrier model. Nevertheless, confocal microscopy analysis showed that MNPLs were highly uptaken by both of the barrier model systems, and that translocation across the membrane occurred. Thus, MNPLs were detected into Raji-B cells, placed in the basolateral compartment of the insert. The internalization followed a dose-dependent pattern, as assessed by flow cytometry. Nonetheless, no genotoxic or oxidative DNA damage induction was detected in either case. Finally, no variations in the transcription of oxidative and stress genes could be detected in any of the in vitro barrier models. Our results show that MNPLs can enter and cross the epithelial barrier of the digestive system, as demonstrated when Raji-B cells were included in the model, but without exerting apparent hazardous effects.