Parameters influencing intestinal epithelial permeability and microparticle uptake in vitro.

The hypothesis that, in vivo in situ, villous uptake of 2 microm latex microparticles involves changes at enterocyte tight junctions (TJs) was tested using Caco-2 cells on porous membranes. Epithelial permeability was measured by transepithelial resistance (TER) and particle numbers in surface, intraepithelial and sub-epithelial compartments by microscopy. Apical particle or medium addition initially closed TJs, but this was subsequently reversed in particle-treated groups. Peristaltic onward movement of a bolus was simulated by removing apical particles after an exposure period and leaving the remaining particles to interact with the epithelium: this produced marked TJ loosening during the interaction period. For particle exposure groups, the early similarity with particle numbers in vivo taken up in young adult rats became less marked with time, although bolus removal counteracted this tendency. The TJ response to vasoactive intestinal polypeptide (VIP) was time-dependent. Adsorbed and intraepithelial particle numbers increased with particle exposure time; epithelial-associated microparticle aggregation varied with treatment and submembranous particles were seen in all groups. Correlation between TER changes and particle numbers suggests TJ loosening may be important in microparticle uptake. This Caco-2 model gives epithelial particle numbers that approximate well to published figures for microparticle uptake in vivo and allows effective microenvironmental manipulation.