Toxicity and absorption of polystyrene micro-nanoplastics in healthy and Crohn's disease human duodenum-chip models

Micro and nanoplastics (MNPs) are widespread contaminants of our environment and food web that can be absorbed by the intestine and distributed to most or all organs, and may cause significant toxicity and dysfunction. In our recent study, we investigated the toxicity and mechanisms underlying uptake and translocation of 26 nm carboxylated polystyrene MNPs (PS26C) using a combination of simulated digestion and a static, immortalized cell-based, three cell type (triculture) small intestinal epithelial model. Results revealed that PS26 caused minimal toxicity, and inhibitor studies revealed that uptake mechanisms included passive diffusion, phagocytosis, clathrin-mediated endocytosis (CME), and fast endophilin-mediated endocytosis (FEME). However, the triculture model is somewhat lacking in physiological relevance, and studies in a more relevant and accurate model are required to validate and expand upon those results. In the current study, we therefore employed a microfluidic intestine-on-a-chip model developed using primary human intestinal epithelial organoids from both healthy and Crohn’s disease donors, and primary human microvascular endothelial cells to evaluate the toxicological impacts and mechanisms effectuating uptake and translocation of 25 nm polystyrene shell-gold core tracer (quantifiable by ICP-MS) MNPs (AuPS25). As in our previous study, AuPS25 caused minimal toxicity after 24 h exposure in either the healthy or Crohn’s IOC model. RNAseq analysis of epithelial cell lysates identified only 9 dysregulated genes, which notably included downregulation of IFI6 (interferon alpha-induced protein 6), which has antiviral and negative innate immune regulatory functions in the intestine. Inhibitor studies revealed that AuPS25 uptake occurred by both passive and active mechanisms, including phagocytosis and/or macropinocytosis, and CME and/or FEME. Interestingly, uptake and translocation of AuPS25 was greater in healthy than in unstimulated Crohn’s disease epithelium.