Purpose: The objectives were (i) to test in vivo functional activity of MRP2 on rabbit corneal epithelium and (ii) to evaluate modulation of P-gp and MRP2 mediated efflux of erythromycin when co-administered with corticosteroids.
Methods: Cultured rabbit primary corneal epithelial cells (rPCECs) was employed as an in vitro model for rabbit cornea. Cellular accumulation and bi-directional transport studies were conducted across Madin-Darby Canine Kidney (MDCK) cells overexpressing MDR1 and MRP2 proteins to delineate transporter specific interaction of steroids. Ocular pharmacokinetic studies were conducted in rabbits following a single-dose infusion of erythromycin in the presence of specific inhibitors and steroids.
Results: Bi-directional transport of erythromycin across MDCK-MDR1 and MDCK-MRP2 cells showed significant difference between BL-AP and AP-BL permeability, suggesting that erythromycin is a substrate for P-gp and MRP2. Cellular accumulation of erythromycin in rPCEC was inhibited by steroids in a dose dependent manner. MK571, a specific MRP inhibitor, modulated the aqueous humor concentration of erythromycin in vivo. Even, steroids inhibited P-gp and MRP2 mediated efflux with maximum increase in k(a), AUC(0-infinity), C(max) and C(last) values of erythromycin, observed with 6alpha-methyl prednisolone.
Conclusion: MRP2 is functionally active along with P-gp in effluxing drug molecules out of corneal epithelium. Steroids were able to significantly inhibit both P-gp and MRP2 mediated efflux of erythromycin.