The Impact of Glucose Exposure on Organic Cation Transporters (OCT) Function in a Corneal Epithelial Cell Line

Author

• David A. Garza, University of the Incarnate WordFollow

Date of Degree

5-2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Program

Pharmaceutical Sciences

Advisor

frasersp@uiwtx.edu

Advisor

gouldg@uthscsa.edu

Advisor

shiqbal@uiwtx.edu

Abstract

Organic cation transporters (OCT) facilitate the movement of neurochemicals and medications, contribute to the removal of cellular waste, and facilitate neuronal communication. Three subtypes of these high-capacity, low-affinity transporters (OCT1, OCT2, and OCT3) are differently expressed in peripheral tissues such as the liver, kidneys, as well as the central nervous system. OCTs are also expressed in ocular tissues. Chronic hyperglycemia is a complication commonly associated with diabetes that can lead to ocular diseases such as diabetic keratopathy, which affects the cornea. In this project, we expose immortalized human corneal epithelial cells (HCE-S) to various glucose concentrations to study their impact on endogenous OCT activity. Literature shows that elevated glucose levels may alter transporter function and enhance ligand interaction. We hypothesize that cells grown in a hyperglycemic environment will enhance the binding characteristics of compounds with OCT in the HCE-S cell line model. To mimic a range of glucose environments, HCE-S cells were cultured in normal, complete growth media containing 25 mM glucose or glucose-free media supplemented with 0.25, 1.0, 28, or 32 mM glucose. Importantly, the 0.25- and 1.0-mM glucose concentrations mimic measurements reported in the tear fluid of diabetic patients. Concentrations greater than 10 mM align with postprandial glucose levels in type 2 diabetic patients. Saturation assays were conducted using a microplate reader to detect the relative fluorescence units (RFU) of ASP⁺, a known fluorescent substrate for OCT. The uptake capacity (B_max) and affinity (K_d) were determined in the absence (total) and presence (non-specific) of known OCT inhibitors – corticosterone (CORT) or decynium-22 (D22) – to calculate specific ASP⁺ uptake. The results from saturation assays were 2335 RFU (B_max) and 22666 µM (K_d) for nonspecific uptake with CORT; and 448.4 RFU (B_max) 3324 µM (K_d) for nonspecific uptake with D22. However, due to wide error margins, these parameters were not statistically different. MTT assays were also performed to assess HCE-S cell viability after exposing cells to varied glucose concentrations for 24, 72, or 120 hours. The MTT results showed cell viability was generally stable at all time periods from 0.25 - 25 mM glucose but decreased at the 28 and 32 mM glucose concentrations. Future directions will consider detecting the subtypes of OCTs expressed in corneal epithelial cells, the expression of OCTs in corneal cell mitochondria, and the effect of glucose on the transport of metformin, an important antidiabetic medication, in corneal cell lines. These experiments will clarify how OCT uptake function within corneal epithelial cells are affected by hyperglycemic environments, which can potentially impact neurochemical transport in the eye or the delivery of eye drop medications.

Recommended Citation

Garza, David A., "The Impact of Glucose Exposure on Organic Cation Transporters (OCT) Function in a Corneal Epithelial Cell Line" (2026). Theses & Dissertations. 483.
https://athenaeum.uiw.edu/uiw_etds/483