Introduction: The Caco-2 adenocarcinoma cell line has been used extensively for the past couple of decades in nutrient and drug transport studies as an adequate in vitro model of the intestinal mucosa. However, due to the over-expression of tight junction protein complexes, Caco-2 monolayers fail to provide a reliable estimation in terms of in vivo paracellular permeability of small hydrophilic compounds. To address this issue, we co-cultured Caco-2 and HT29-MTX (mucus-secreting cell-line) to ensure a tunable model and emulate the intestinal transport of two classes of nanoparticles.
Methods: We exposed Caco-2/HT29-MTX of different seeding ratios, cultured on Transwell® systems, to non-cytotoxic concentration levels (20 μg/mL) of Si/SiO2 quantum dots and iron oxide (α-Fe2O3) nanoparticles. Transepithelial electric resistance was measured before and after exposure, and monolayer permeability (Peff) was assessed via the paracellular marker Lucifer Yellow. At regular intervals during the 3-hour transport study, samples were collected from the basolateral compartments for nanoparticle detection and quantitative testing. Cell morphology characterization was done by phalloidin-FITC/DAPI labelling, and Alcian Blue/eosin staining was performed on insert cross-sections in order to compare the intestinal models and evaluate the production of mucins.
Results: Morphological alterations of the Caco-2/HT29-MTX (7:3 ratio) co-cultures were observed at the end of the transport study compared to the controls. The nanoparticle suspensions tested did not diffuse across the intestinal model and were not detected in the receiving compartments, due to their tendency to precipitate at the monolayer surface level and form visible aggregates. Our preliminary results indicated the need for further nanoparticle functionalization in order to appropriately assess intestinal absorption in vitro. The intestinal models used in this study have been shown to adequately screen for prospective candidate carrier-type materials and gauge the transport dynamics of nanoparticles.
Acknowledgements: This work was supported by the project no. 77/2018 NANO-BIO-INT.