Evaluation of the toxic effects of micro- and nanoplastic particles, in co-contamination with metals, on human intestinal models, in vitro

Thanks to their attractive characteristics and affordable price, plastics have become widespread in our daily lives. The ubiquitous presence of disposable plastic items in everyday life, combined with inappropriate waste management and the persistence of conventional plastics, has led to a significant accumulation of plastic in the environment. In nature, plastic waste is exposed to physicochemical and biological stresses that lead to its gradual degradation into micro- and nanoplastics (MNPs). Due to their large specific surface area and hydrophobic nature, MNPs have the ability to carry environmental contaminants on their surface, such as persistent organic pollutants, pathogens, or metallic pollutants on their surface. Due to their ubiquitous nature, human exposure to MNPs is a daily occurrence, mainly through inhalation of polluted air and ingestion of contaminated food and beverages, such as bottled water, seafood, salt and honey. Although human exposure to plastic particles is now accepted, the consequences for the body are not yet well understood.This thesis project was conducted to evaluate the biological effects of polyethylene terephthalate (PET) particles derived from plastic water bottles and commercial particles of polylactic acid (PLA), a biosourced and biodegradable plastic, under realistic environmental conditions. These particles, with sizes ranging from 100 to 500 nm, were artificially aged in a Q-SUN climatic chamber simulating solar irradiation and the temperature of a sunny day at noon at the equator. Nickel, copper and tributyltin were chosen as models of toxic metal co-pollutants, because they are ubiquitous contaminants in the environment that pose problems in terms of food safety. The toxic effects of these plastic/metal combinations were assessed on co-cultures of Caco-2/HT2-MTX, two human intestinal epithelial cell lines. Two types of Caco-2 were used, representative either of healthy individuals, expressing wild-type NOD2 gene, or of patients with genetic susceptibility to Crohn's disease, a chronic inflammatory bowel disease, expressing the 1007fs NOD2 mutation.The effects of accelerated ageing on the physicochemical properties of the particles were characterized by various complementary methods: their size by transmission and scanning electron microscopy, dynamic light scattering, their surface charge by zeta potential characterization and the release of oligomers by HPLC-MS/MS. Adsorption/desorption interactions between MNPs and metals (copper, nickel and tributyltin) were quantified by ICP-MS. Finally, the biological effects of exposure to these pristine or aged MNPs, alone or combined with copper and tributyltin, were assessed on both models of intestinal epithelium. Their impact on cell viability, DNA integrity, the level of intracellular reactive oxygen species, the inflammatory state of the cell and the integrity of the intestinal barrier were monitored. This work, which is part of the ANR PLASTOX project (ANR-21-CE34-0028), provide essential data for assessing the risk associated with the ingestion of MNPs and associated metal pollutants.