Mechanisms of ingested polystyrene micro-nanoplastics (MNPs) uptake and translocation in an in vitro tri-culture small intestinal epithelium
Glen M. DeLoid, Zhenning Yang, Lila Bazina, Davood Kharaghani, Faranguisse Sadrieh, Philip Demokritou
Abstract
Micro and nanoplastics (MNPs) are now ubiquitous contaminants of food and water. Many cellular and animal studies have shown that ingested MNPs can breach the intestinal barrier to reach the circulation. To date however, the cellular mechanisms involved in intestinal absorption of MNPs have not been investigated with physiologically relevant models, and thus remain unknown. We employed in vitro simulated digestion, a tri-culture small intestinal epithelium model, and a panel of inhibitors to assess the contributions of the possible mechanisms to absorption of 26 nm carboxylated polystyrene (PS26C) MNPs. Inhibition of ATP synthesis reduced translocation by only 35%, suggesting uptake by both active endocytic pathways and passive diffusion. Translocation was also decreased by inhibition of dynamin and clathrin, suggesting involvement of clathrin mediated endocytosis (CME) and fast endophilin-mediated endocytosis (FEME). Inhibition of actin polymerization also significantly reduced translocation, suggesting involvement of macropinocytosis or phagocytosis. However, inhibition of the Na+-H+ exchanger had no effect on translocation, thus ruling out macropinocytosis. Together these results suggest uptake by passive diffusion as well as by active phagocytosis, CME, and FEME pathways. Further studies are needed to assess uptake mechanisms for other environmentally relevant MNPs as a function of polymer, surface chemistry, and size. Micro-nano plastics (MNPs) have become ubiquitous contaminants of the environment, and have been found in every type of food tested to date. Numerous studies have shown that ingested MNPs are readily absorbed by the intestine to reach the circulation, and significant quantities of MNPs have been detected in human blood and every human organ examined to date. Our understanding of human health impact of ingested MNPs is in its infancy. In this study we sought to identify the mechanisms by which a model MNP are absorbed by the GI tract, which is a critical first step in understanding the fate and potential effects of ingested MNPs.