Human corneal equivalent as cell culture model for in vitro drug permeation studies

Aims: For the study of transcorneal in vitro permeation of ophthalmic drugs, excised animal cornea or corneal epithelial cell culture are frequently used as a replacement for the human cornea. The main purposes of this study were to reconstruct a complete human organotypic cornea equivalent, consisting of all three different cell types ( epithelial, stromal, and endothelial); to test the barrier function of this bioengineered human cornea using three different model drugs ( pilocarpine hydrochloride (PHCl), befunolol hydrochloride (BHCl), and hydrocortisone ( HC)); and to determine its usefulness as an in vitro model for prediction of ocular drug absorption into the human eye. Methods: A multilayer tissue construct was created step by step in Transwell cell culture insert using SV-40 immortalised human endothelial and epithelial cells and native stromal cells ( fibroblasts). Morphology was characterised by light microscopy using routine H&E staining. Scanning electron microscopy was used to evaluate ultrastructural features. Ocular permeation of drugs across the human cornea construct was tested using modified Franz cells and compared with data obtained from excised porcine cornea and previously described porcine cornea constructs. Results and conclusion: The cornea construct exhibited typical corneal structures such as a monolayer of hexagonally shaped endothelial cells and a multilayered epithelium consisting of seven to nine cell layers with flat superficial cells. The formation of microplicae and microvilli was also confirmed. The human cornea construct showed similar permeation behaviour for all substances compared with excised porcine cornea. However, permeability ( permeation coefficients K-p) of the human cornea equivalent ( PHCl 13.4 . 10(-6) (SD 3.01 . 10(-6)); BHCl 9.88 . 10(-6) (SD 1.79 . 10(-6)); HC 5.41 . 10(-6) (SD 0.40 . 10(-6)) cm/s) was about 1.6 - 1.8 fold higher than excised porcine cornea. Compared with data from the porcine cornea construct the cultivated human equivalent showed a decreased permeability. The reconstructed human cornea could be appropriate to predict drug absorption into the human eye.