Expression of Efflux Transporters in Human Ocular Tissues

To investigate the expression profiles of efflux transporters in human ocular tissues, quantitative real-time polymerase chain reaction, Western blotting, and immunohistochemistry were used to obtain the relative mRNA and protein expressions of various efflux transporters in human ocular tissues. The cornea, conjunctiva, irisciliary body (ICB), retina and choroid, human corneal epithelial cell line (HCEC), and human retinal pigment epithelial cell line (ARPE-19) were examined for the expressions of multidrug resistance-associated proteins 1-7 (MRP1-7), multidrug resistance 1 (MDR1) P-glycoprotein, lung resistance protein (LRP), and breast cancer-resistance protein (BCRP). The expression sites and patterns of efflux transporters were significantly different in ocular tissues, HCEC, and ARPE-19, as well as the expression profiles of efflux transporters in mRNA and protein levels in ocular tissues. At the protein level, MRP1-7, MDR1, and LRP were expressed in the corneal epithelium; MRP1-7, MDR1, LRP, and BCRP were expressed in the conjunctival epithelium; MRP1-2, MRP6-7, MDR1, and LRP were expressed in the ICB; MRP1-3, MRP6-7, MDR1, and LRP were expressed in the retina; MRP1-3, MRP6-7, MDR1, and LRP were expressed in the HCEC; and MRP7, MDR1, LRP, and BCRP were expressed in the ARPE-19. This quantitative and systematic study of efflux transporters in normal ocular tissues and cell lines provides evidence of cross-ocular tissue transporter expression differences, implying that efflux transporter expression variability should be taken into consideration for better understanding of ocular pharmacokinetic and pharmacodynamic data.