Monitoring of MRP-like Activity in Human Erythrocytes: Inhibitory Effect of Isoflavones

A method to fluorometrically monitor efflux of 2′,7′-bis-(carboxypropyl)-5(6)-carboxyfluorescein (BCPCF) from human erythrocytes was developed. Genistein, daidzein, sophoraisoflavone A, and licoisoflavone A induced 50% inhibition (IC50) of BCPCF efflux at 15–70 μM. The IC50 value of the most efficient isoflavone, licoisoflavone A (15–25 μM), was comparable to that of indomethacin ( 10 μM) and markedly lower than for probenecid (100–200 μM), both known MRP1 inhibitors. Our results indicate that the human erythrocyte is a useful cell model in screening potential MRP inhibitors, that BCPCF is a good substrate for MRP, and that some isoflavones at low concentrations inhibit MRP-mediated efflux.