The selective permeability of mucin hydrogels is modulated by nanoplastic contaminations

The mucosa lining all wet epithelial tissues in our body is mainly established by mucin glycoproteins and constitutes the first line of defense that controls the selective uptake of substances into sub-mucosal tissues. However, this biological barrier faces a broad range of environmental pollutants. Micro- and nanoplastics are ubiquitous contaminants that occur in our food and beverages, and they are still used as additives in cosmetics and healthcare products. Whereas there are clear indications that an exposure to microplastics can create health issues for humans, little is known about the microscopic mechanisms that are responsible for this. In this study, we investigate the selective permeability properties of mucus reconstituted from different mucin sub-types, i.e., model systems of the mucosal barriers in the lungs, the intestine, and the stomach, and evaluate alterations in this permeability as brought about by nanoplastic contaminations. Particularly, we elucidate how nanoplastic particles remodulate the molecular mechanisms governing the selective filtration capabilities of mucin networks. We find that nanoplastic can adsorb to the mucosal interface, and this effect is particularly pronounced for cationic particles. As a consequence, the surface potential of the mucosal interface is changed and the barrier properties of the mucosal hydrogel towards small molecules are altered by introducing new, hydrophobic binding sites. Together, those effects can be expected to influence the translocation of physiologically important molecules across mucus which may affect, for instance, nutrient uptake. Furthermore, nanoplastic-induced alternations of the mucosa's protective function should be considered for drug delivery applications, where the mucosal barrier needs to be navigated by therapeutic agents.