Transepithelial transport of rosmarinic acid in intestinal Caco-2 cell monolayers

The absorption characteristics of rosmarinic acid (RA) were examined by measuring permeation across Caco-2 cell monolayers using an HPLC-electrochemical detector (ECD) fitted with a coulometric detection system. RA exhibited nonsaturable transport even at 30 mM, and the permeation at 5 mM in the apical-to-basolateral direction, J(ap-->bl), was 0.13 nmol/min/mg of protein. This permeation rate is nearly the same as that of 5 mM chlorogenic acid (CLA) and gallic acid, which are paracellularly transported compounds. Almost all of the apically loaded RA was retained on the apical side, and J(ap-->bl) was inversely correlated with paracellular permeability. These results indicate that RA transport was mainly via paracelluar diffusion, and the intestinal absorption efficiency of RA was low. Furthermore, RA appeared to be unsusceptible to hydrolysis by mucosa esterase in Caco-2 cells. These results, together with our previous work (J. Agric. Food Chem., 52, 2518-2526 (2004), J. Agric. Food Chem., 52, 6418-6424 (2004)) suggest that the majority of RA is further metabolized and degraded into m-coumaric and hydroxylated phenylpropionic acids by gut microflora, which are then efficiently absorbed and distributed by the monocarboxylic acid transporter (MCT) within the body. The potential of orally administered RA in vivo will be further investigated.