Replacement of the Draize rabbit eye test for ocular irritancy testing remains an elusive goal. Many believe a corneal full thickness (CFT) model is necessary to completely model the interaction of exogenous chemicals with human cornea. During Phase 1, human corneal epithelial, stromal, and endothelial cells were isolated from native tissue, expanded in monolayer culture, and cryopreserved. Culture conditions were identified to produce highly differentiated 2-layer (corneal epithelium and keratocyte-containing stroma) and 3- layer (epithelium, stroma, and endothelium) CFT tissues. The CFT tissues exhibited improvements over epithelial tissues in terms of barrier and differentiated phenotype. An assay and prediction model (PM) was developed which allowed the CFT tissue to distinguish between irritants and non-irritants with 100% accuracy. Other functional studies showed that the CFT tissue appears suitable to evaluate time to recovery (TTR) and depth of injury (DOI) following chemical injury. Finally, an analysis of CFT tissue production showed that the economics of CFT are favorable. Phase II will expand upon the Phase 1 result to further develop the CFT tissue model. Initial goals will focus on preparing the CFT tissue model for commercial production - cell stocks will be expanded to insure a stable cell supply and quality control parameters will be developed. The database of materials tested using the CFT will be expanded, the PM for irritant/non-irritant classification will be finalized, and inter-laboratory transferability of the assay will be demonstrated. Finally, the CFT tissues will be used for TTR and DOI measurements and an assay and prediction model for replacement of the Draize test will be developed. Due to these enhanced capabilities, the CFT will provide toxicologists and scientists with a tool that will dramatically decrease, if not entirely eliminate, the need for animal testing to determine ocular irritancy.
Safety assessment of all new chemicals and products requires evaluation of potential ocular irritancy in case of intentional or unintentional exposure to the eye. Current animal-based test methods are suboptimal because of animal welfare concerns and in vitro methods lack the complexity required to completely model in vivo responses. We will develop a corneal full thickness tissue and in vitro test methods that will dramatically reduce or eliminate the need to use animals to assess ocular irritancy of chemicals and products.
