2-APB br Acknowledgement This research was supported by Basi

Acknowledgement This research was supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (NRF-2016R1A2B4012818).
Oral 2-APB is the most popular administration route due to good patients’ compliance, safety and convenience. However, a large amount of drugs are difficult to exert optimal effect by oral delivery due to poor solubility or permeability [,]. Nowadays, nanoparticle is considered as an effective carrier to improve the oral bioavailability of most drug molecules [,]. Firstly, nanoparticles are able to protect drug molecules from degradation by numerous enzymes in gastrointestinal (GI) tract []. In addition, nanoparticles disperse throughout the intestine with gastric emptying after oral administration, which produces tremendous absorption areas []. Most of biodegradable nanoparticles are degraded by enzymes in GI lumens, such as liposomes and lipid nanoparticles [,]. The components resulting from degradation would reconstitute to be mixed micelles together with endogenous bile salts and phospholipids, which is capable of enhanced absorption []. However, some nanoparticles are relatively stable in GI tract, such as polystyrene or inorganic nanoparticles [,]. Many papers consider the non-biodegradable nanoparticles could improve the cellular uptake and transport [, , ]. After cellular uptake, nanoparticles could be decomposed in lysosome and release drugs into the cell or excreted out of cell from basolateral side [], which contributes to enhanced absorption. However, there is lack of attentions on exocytosis towards apical side. Nanoparticles internalizing into epithelia would undergo different traffic processes. Some nanoparticles are degraded in cells and release drug molecules which subsequently are transported across basolateral membrane into circulation [], while rare intact nanoparticles could penetrate through basolateral membrane []. However, many researches have demonstrated that nanoparticles were taken up easily but hard to be transported across cell monolayer []. There is rare evidence to prove that a large amount of nanoparticles are able to transport across intestinal epithelia integrally []. Therefore, other two possible pathways are also important for nanoparticles after cellular uptake, including staying inside cells or exocytosis towards apical side. It is possible to show cytotoxicity if nanoparticles stay inside cells for a long period with no degradation []. Moreover, exocytosis towards apical side is a disadvantage for improving absorption or treatment of intestinal diseases. Therefore, it is necessary to elucidate the possible fate of nanoparticles after cellular uptake. The exocytosis of nanoparticles in endothelial cells has been elucidated in many papers, which illustrates that the exocytosis is highly dependent on size [, , ]. However, the intestinal epithelia are completely different from endothelial cells []. The epithelia include apical and basolateral sides which are highly different in biological characteristics. Therefore, it is extraordinary important for understanding the influence of nanoparticles characteristics on oral absorption by elucidating the bidirectional exocytosis in epithelia. Our previous study illustrated that the uptake of polystyrene nanoparticles in Caco-2 cell was shape-dependent []. More nanorods were internalized into Caco-2 cells compared to their spherical or discal counterparts. But the influence of shape on intracellular fate of nanoparticles has not been well understood. In this paper, we attempt to clarify the behaviors of different shaped nanoparticles after cellular uptake, including exocytosis towards apical or basolateral sides, and retention in cells, which will further provide fundamental knowledge for oral application of different shaped nanoparticles. Nanorods were produced by stretching nanospheres which were obtained from market according to previous reports [,]. The labeled size of nanospheres is 200 nm and size determined by dynamic light scattering (DLS) is about 180 nm as shown in A. The aspect ratio of nanorods was fixed at 2:1 in stretching. Hence, the size of nanorods is significantly different in length and width.