Overexpression of MRP3 in HeLa-UGT1A9 Cells Enhances Glucuronidation Capability of the Cells.

Abstract

The interplay between phase II enzymes and efflux transporters leads to extensive metabolism and low systemic bioavailability of flavonoids. In this study, the dynamic interplay between multiple UGTs and multiple efflux transporters that occur inside the cells was fully investigated. A new HeLa-UGT1A9-MRP3 cell was established to overexpress two dominant efflux transporters MRP3 and BCRP, and two UGT isoforms UGT1A9 and UGT1A3. The metabolism and glucuronides excretion for a model flavonoid genistein were determined in HeLa-UGT1A9-MRP3 cells and HeLa-UGT1A9-Con cells that overexpressed one UGT (1A9) and one efflux transporter (BCRP). The excretion rate grew nearly 6-fold, cellular clearance of glucuronides increased about 3-fold, and fraction of genistein metabolized (fmet) increased (14%, p<0.01) in the new cells. Small interfering (siRNA)-mediated MRP3 functional knockdown resulted in marked decreases in the excretion rates (26%-78%), intracellular amounts (56%-93%), and cellular clearance (54%-96%) in both cells, but the magnitude of the differences in HeLa- UGT1A9-Con cells was relatively small. Reductions in fmet values were similarly moderate (11%-14%). In contrast, UGT1A9 knockdown with siRNA caused large decreases in the excretion rates (46%-88%), intracellular amounts (80%-97%), cellular clearance (80%-98%) as well as fmet value (33%-43%, p<0.01) in both UGT1A9 cells. Comparisons of the kinetic parameters and profiles of genistein glucuronidation as well as UGT mRNA expression suggest that HeLa-UGT1A9-MRP3 has increased expression of both MRP3 and UGT1A3. The newly engineered HeLa-UGT1A9-MRP3 cells is an appropriate model to study the kinetic interplay between multiple UGTs and efflux transporters, and a promising biosynthetic tool to obtain flavonoid glucuronides of high purity.