Novel primary epithelial cell toxicity assay using porcine corneal explants.

Purpose: The purpose of this study was to develop a novel primary epithelial cell toxicity assay using porcine corneal explant and evaluate the assay using benzalkonium chloride (BAK).
Methods: Circular corneal explants were trephined from the peripheral cornea of porcine eyes using 2-mm biopsy punches, and placed on 6-well culture dishes with a culture medium. After incubation for 12 hours, 50 μL of BAK at 0.00001%, 0.0001%, 0.001%, or 0.01% was applied to each well for 2 minutes. After washing, explants were cultured for another 24 hours, then epithelial outgrowth was photographed and measured. Corneal immunohistochemical characteristics were evaluated by cytokeratin (CK) 3, CK12, and ZO-1. Cell toxicity was evaluated by WST-8 assay, Ki-67 staining, and TUNEL assay.
Results: Epithelial cells migrated outward concentrically from the corneal explant as time elapsed and were positive for CK3, CK12, and ZO-1. The outgrowth rate decreased significantly with 0.0001%, 0.001%, and 0.01% BAK compared with the phosphate-buffered saline (PBS) control (P < 0.01), and the decrease was BAK concentration dependent. Numbers of viable cells and Ki-67-positive cells also decreased significantly with 0.01% BAK compared with the PBS control (P < 0.05). TUNEL-positive cells were present in the epithelial outgrowth. Moreover, TUNEL-positive cell density tended to increase with 0.01% BAK compared with the PBS control (P = 0.14) and 0.00001% BAK (P = 0.081).
Conclusions: Our novel toxicity assay using porcine corneal explant is simple and reflects the effect of single and short-duration instillation of eye drops. The method is useful for evaluation of corneal toxicity at low concentrations of BAK.