Abstract: In this study, we employed Caco-2 cells to establish an absorption model of exogenous nucleic acids. Using this
model, we also explored the mechanism of intestinal absorption of plasmid DNA. After culturing Caco-2 cells for 21 days
on Transwell membranes, cell morphology, transepithelial electrical resistance (TEER) and apparent permeability coefficient
(Papp) of fluorescent yellow were measured and used to evaluate whether the model was established successfully. Cytotoxicity
experiments were used to explore the effect of plasmid DNA on cell growth. The mechanism of intestinal DNA absorption
was explored by two-way transfer experiments. To further validate vesicle-mediated DNA transport, transport experiments
were performed on ice or in the presence of the specific inhibitor. The results showed that the morphology of differentiated
cells was good and both TEER and Papp of fluorescent yellow reached the requirements; therefore the model could be applied
in transport experiments. The plasmid DNA showed no significant inhibitory effect on the growth of Caco-2 cells. As time
passed, the transport of plasmid DNA gradually tended to saturate in both directions. Papp (AP→BL) was much greater than
Papp (BL→AP), indicating that the transport was related to some carrier-mediated protein, and the transmembrane transport
mode may be involved. These results further demonstrated that the transport of exogenous plasmid DNA was evidently
inhibited by low temperature and the specific inhibitor and therefore a transcellular active transport process.

Key words: Caco-2 cells model, exogenous nucleic acids, absorption mechanism, plasmid DNA