Involvement of multidrug resistance-associated proteins in regulating cellular levels of (-)-epigallocatechin-3-gallate and its methyl metabolites.

(-)-Epigallocatechin-3-gallate (EGCG), a major polyphenol of green tea, has many interesting biological activities. The uptake of EGCG and involvement of specific efflux pumps were studied in MDCKII cells transfected with hPgp, hMRP1, and hMRP2 genes. Total cell associated [3H]EGCG increased 7-fold in the presence of the MRP inhibitors, indomethacin and probenecid, in MDCKII/MRP1 cells, compared to a 2-fold increase in wild-type cells. Intracellular levels of EGCG, 4(")-O-methyl EGCG, and 4('),4(")-di-O-methyl EGCG were increased by 13-, 11-, and 3-fold, respectively, by indomethacin in MDCKII/MRP1 cells. Accumulation of EGCG and its methyl metabolites was also increased approximately 10-fold in the presence of MK-571 in MDCKII/MRP2 cells. Co-treatment with isoflavones, curcumin and tetrahydrocurcumin, increased [3H]EGCG accumulation significantly in MDCKII/MRP1 and HT-29 cells. The results indicate that EGCG and its methyl metabolites are substrates for MRP1 and MRP2, but not for Pgp. MRP type efflux pumps may limit the bioavailability of EGCG.