On miCroplAstic Penetration in vivo and The mammalian innate immUne REsponse: the CAPTURE study

Introduction: We ingest and inhale microplastics on a daily basis, yet the consequences are not known. In order to make a reliable risk assessment it is important to study whether these microplastics penetrate the mucosal barriers and enter the interior of our bodies. Although some studies with reference particles have been performed it is by no means clear whether these data can be extended to particles of different sizes, shapes, weathering conditions and plasma coronas. If particles are able to penetrate the epithelial barriers, innate immune cells are the likely first cells to encounter with these foreign invaders. These cells can phagocytose the microplastics, but cannot degrade them. The effect of microplastic engulfment on phagocyte survival and function is unknown. Key hypothesis tested: We hypothesize microplastics cross epithelial barriers where they will be engulfed by phagocytes leading to impaired immune function. Aims of the study: 1. To identify conditions allowing microplastics to cross epithelial barriers 2. To elucidate mechanisms underlying recognition and engagement of microplastics by immune cells 3. To study effects of phagocytosed microplastics on immune cell function Objectives: 1. Identify whether human phagocytes engulf microplastics in vitro and whether this is size, shape, surface and/or material dependent 2. Test whether engulfed microplastics negatively impact human phagocyte survival, their pro-inflammatory phenotype and their bacterial killing function in vitro 3. Determine whether reference microplastics cross epithelial barriers after oral or intranasal application in vivo and establish whether these microplastics can be found back in phagocytes Microplastics used: We initiated research on microparticles as part of the TA-COAST “IMPACT” consortium. With our former consortium collaborators we chose three different sizes (80nm, 900 nm and 10-20µm) of standardized polystyrene spheres, polymeric particles with fibrillar shapes and irregular forms of the same sizes. Virgin particles, particles with a serum/plasma corona and particles weathered in surface water and exposure to sunlight will be used. Microplastics obtained from actual environmental sources will be studied if time allows. Methods: We will use our previously developed high-throughput assays to study human neutrophil survival, activation and bacterial killing function in the presence of the above-mentioned microplastics of different sizes, shapes, wearing conditions and coronas. Dependent on the results, particles will be chosen to study the penetration and in vivo effects in our mouse models. First proof-of-principle experiments will be performed to study the penetration of the microplastics over the epithelium into the interior of the mouse upon oral administration. Next, we will study the microplastic penetration and capture by phagocytes in vivo using two-photon intravital microscopy. Deliverables: Our studies will provide proof-of-principle in vivo data on the mechanisms of microplastic translocation over the gut epithelium. Our high-throughput in vitro assays will establish the role of size, shape, corona and weathering of microplastics on their immunotoxic effects on human neutrophils. This project will pave the way for future clinical studies as it will provide proof-of-principle for the mechanisms underlying the potential deleterious interaction between microplastics and the host.