Transport of the Fluorescent Substrate ASP⁺by Organic Cation Transporter-3 in Human Cornea Epithelial Cells

Abstract ID 101093 Poster Board 332 The organic cation transporter-3 (OCT3) is expressed abundantly throughout the body, but little is known about the presence of these transporters within the eye and, more specifically, the cornea epithelium. An extensive library of compounds interacts with OCT3, including the fluorescent molecule ASP⁺ and metformin. Metformin is an OCT3 substrate and antidiabetic medication that can lower the risk of eye-related diseases like keratopathy and retinopathy linked to hyperglycemia. Utilizing high throughput microplate assays in a human cornea epithelial cell line (HCE-S), this project evaluated the time-dependent saturation of ASP+ uptake and the competition of ASP⁺ uptake by metformin and corticosterone, a known selective inhibitor of OCT3. Our saturation (Bmax and Kd) and competition (IC₅₀) data help to establish the expression and function of OCT3 in HCE-S cells as a model to understand better the transporter's function in the human cornea epithelial cells. Our experiment findings suggest OCT3 is robustly expressed in HCE-S cells and can function to transport ASP⁺. Our results also imply other non-OCT3 transporters are present in this endogenous cell model that are capable of ASP⁺ uptake, as evidenced by our non-specific binding measurements using a non-selective inhibitor, decynium-22. Ongoing competition experiments with metformin will confirm that OCT3 is active in the HCE-S cell line. In addition, we are testing whether hyperglycemic cell culture growth conditions alter the expression and function of OCT3 in the HCE-S cell line. This work has future implications for establishing cornea cells as a new model to study OCT3 activity, test the pharmacological characteristics of ligands, and develop alternate administration routes for metformin (e.g., as eye drops). This project was funded through an internal Feik School of Pharmacy Research grant (RFS) and funding support from the MS in Applied Pharmaceutical Sciences Program (JL).