*3.1. Barrier Function and Transporter Activities*

EpiIntestinal microtissues as an intestinal permeability model have been tested in detail by Ayehunie et al. [11]. Our evaluation with in-house compounds and reference drugs (atenolol, fexofenadine, dabigatran, dabigatran etexilate, fenoterol, and otenzepad) showed similar data (not shown). However, the drug rosuvastatin which was used as a P-gp model drug by Ayehunie et al. [11] showed different results in our hands. Both in Caco-2 cells and in EpiIntestinal microtissues, the selective BCRP inhibitor Ko-143 (3 µM) strongly reduced the efflux of rosuvastatin, whereas the selective P-gp inhibitor zosuquidar (5 µM) only showed a minor effect on the efflux of rosuvastatin (Table 3). These data indicate BCRP as the major transporter in both in vitro models.

**Table 3.** Inhibition of transporter-mediated efflux of rosuvastatin in Caco-2 and EpiIntestinal microtissues. Data are mean values of duplicates (Caco-2) or triplicates (EpiIntestinal microtissues).

