Upregulation of P-glycoprotein expression by ophthalmic drugs in different corneal in-vitro models

Objectives The purpose of this study was to analyse P‐glycoprotein (P‐gp) expression in different human in‐vitro cornea models (HCE‐T epithelial model and Hemicornea construct) after stimulation with P‐gp substrates (rhodamine 123, levofloxacin and acebutolol). Methods The influence of P‐gp substrates on mRNA expression was analysed using reverse transcriptase polymerase chain reaction (PCR) and real‐time PCR. The effect of stimulation on the transporter functionality was estimated with a digoxin efflux assay. The Caco‐2 cell line was used as positive control. Key findings The reverse transcriptase PCR results showed an increase in band intensity compared with the control medium for all substrates. The real‐time PCR for the Caco‐2 and HCE‐T epithelial model yielded a similar outcome, in which all tested substrates upregulated P‐gp. In contrast, the Hemicornea construct showed no significant increase in the mRNA expression after stimulation. Both in‐vitro models possessed similar drug transport profiles after stimulation. A significantly increased efflux of digoxin was measured after 24 and 72 h of stimulation with levofloxacin and acebutolol. Conclusions The expression and functionality of the P‐gp in corneal tissue can be influenced through time exposure with specific substrates. However, the exact mechanism still requires further elucidation.