Purpose: Tea flavonoids, including (-)-epicatechin (EC), have been suggested to have chemopreventive properties in cancer. However, there is limited knowledge of the oral bioavailability of these dietary compounds. The purpose of this study was to gain a better understanding of the absorption of EC.
Methods: The intestinal epithelial membrane transport of EC was examined using the monolayer of the human Caco-2 cell line grown in Transwells, a common model of intestinal absorption. EC and its metabolites were measured by high performance liquid chromatography with diode array detection.
Results: EC showed no apical to basolateral absorption at concentrations ranging from 5 to 50 microM. In contrast, EC demonstrated basolateral to apical efflux with a Papp value of 0.67 +/- 0.05 x l0(-6) cm/sec, i.e., slightly higher than for mannitol, 0.50 +/- 0.30 x 10(-6) cm/ sec, a paracellular transport marker. There was a 50% reduction in the efflux of EC in the presence of 50 microM MK-571, a competitive inhibitor of the MRP2 transporter expressed in the apical membrane of Caco-2 cells. Most important. the presence of 50 microM MK-571 resulted in clearly measurable apical to basolateral absorption of EC with a Papp of 0.31 +/- 0.06 x 10(-6) cm/sec. Two polar metabolites, M1 and M2, were formed from EC, both of which appeared exclusively on the apical side. MK-571 (50 microM) dramatically inhibited the transport for both of these metabolites. Incubations with inorganic 35SO4(2-) and hydrolysis by aryl sulfatase strongly suggested that these metabolites were sulfate conjugates.
Conclusions: These results suggest an important role for the multispecific organic anion transporter MRP2 in the bioavailability of EC and possibly other tea flavonoids.