Plastic nanoparticle toxicity is accentuated in the immune-competent inflamed intestinal tri-culture cell model

Introduction: Important cell-based models of intestinal inflammation have been advanced in hopes of predicting the impact of nanoparticles on disease. We sought to determine whether a high level and extended exposure of nanoplastic might result in the added intestinal inflammation caused by nanoplastic reported in a mouse model of irritable bowel disease. Methods: The cell models consist of a Transwell©-type insert with a filter membrane upon which lies a biculture monolayer of Caco-2 and HT29-MTX-E12 made up the barrier cells (apical compartment). This monolayer was exposed to digested 40 nm diameter polymethacrylate (PMA) with surface-functionalized COOH (PMA-) or NH₂ (PMA+) at a 'low level' (143 µg/cm² monolayer surface area) or 'high level' (571 µg/cm²) for 24 or 48 h. Beyond the apical compartment in the well of the tissue culture plate, was a monolayer of macrophages, previously differentiated from THP-1 cells (basolateral compartment). Thus, the immune competent tri-cultures were examined as two models: healthy and inflamed. The inflamed model, the barrier cell monolayer having been previously activated with IFN-γ and the macrophages having been previously activated with IFN-γ and LPS expressed a greater secretion of pro-inflammation cytokines. Results: Sedimentation, Diffusion and Dosimetry model (ISDD) simulated that 8%-12% of the PMA was deposited onto the barrier cell monolayer in 24-48-h. The structure of the barrier cells in the inflamed model was disorganized for both PMA, high level, 48-h experiments. While neither the amount of PMA nor the exposure duration influenced the lactate dehydrogenase (LDH) secretion in the healthy model, only the high levels of both PMA- and PMA+ in 48-h exposure experiments resulted in a significantly increased LDH secreted by the barrier cells in the inflamed model, compared to inflamed control. This study is the first to show an additive inflammation of nanoplastic in an inflamed intestinal model of the intestine.