Symposium Proceedings: Replacing the Draize Eye Irritation Test: Scientific Background and Research NeedsTechnical Committee on Alternatives to Animal Testing

Estimation of the chemical-induced eye injury using a weight-of-evidence (WoE) battery of 21 artificial neural network (ANN) c-QSAR models (QSAR-21): part I: irritation potential

Evaluation of potential chemical-induced eye injury through irritation and corrosion is required to ensure occupational and consumer safety for industrial, household and cosmetic ingredient chemicals. The historical method for evaluating eye irritant and corrosion potential of chemicals is the rabbit Draize test. However, the Draize test is controversial and its use is diminishing - the EU 7th Amendment to the Cosmetic Directive (76/768/EEC) and recast Regulation now bans marketing of new cosmetics having animal testing of their ingredients and requires non-animal alternative tests for safety assessments. Thus, in silico and/or in vitro tests are advocated. QSAR models for eye irritation have been reported for several small (congeneric) data sets; however, large global models have not been described. This report describes FDA/CFSAN's development of 21 ANN c-QSAR models (QSAR-21) to predict eye irritation using the ADMET Predictor program and a diverse training data set of 2928 chemicals. The 21 models had external (20% test set) and internal validation and average training/verification/test set statistics were: 88/88/85(%) sensitivity and 82/82/82(%) specificity, respectively. The new method utilized multiple artificial neural network (ANN) molecular descriptor selection functionalities to maximize the applicability domain of the battery. The eye irritation models will be used to provide information to fill the critical data gaps for the safety assessment of cosmetic ingredient chemicals.

A Comparison of Three Cytotoxicity Endpoints in the Corneal HCE-T Model

The prediction of ocular irritation potential from in vitro assays still presents a problem, despite a number of validation trials. A study with coded cosmetic formulations, for which historic in vivo data were available, has been conducted with a human corneal multi-layered model system. This corneal model, the HCE-T model, was developed by using HCE-T cells, a transfected human corneal epithelial cell line. The relative effectiveness of three endpoints that provide a measure of cytotoxicity in the HCE-T model was evaluated. Cell viability immediately after exposure to the test materials was determined by using the MTT and Alamar Blue™ (AB) assays, and, 24 hours later, by using the MTT, AB and lactate assays. Viability measurements with the MTT, AB and lactate assays gave similar dose-response curves at the 24-hour endpoint. One formulation (an anti-dandruff shampoo) caused a less severe drop in viability in assays conducted immediately after the exposure than at the 24-hour time-point. There was little deterioration in viability with the other test materials. The ranking of the test formulations on the basis of relative loss of viability and release of lactate resulted in the same order as for the Modified Maximum Average Draize Test Score. Comparison of the HCE-T model cytotoxicity assay results with historic in vitro data from two different cytotoxicity assays, conducted by using fibroblast monolayer cultures and the same materials, indicated that the multi-layered corneal model had a greater predictive ability. The results of a blind trial with the lactate assay in two laboratories indicated that the techniques required were transferable between laboratories. The lactate results were reproducible between laboratories, even when cultures derived from different passage human corneal cells were tested, provided that the passage number was below 20.

Proposed new classification scheme for chemical injury to the human eye

PURPOSE

Various ocular alkali burn classification schemes have been published and used to grade human chemical eye injuries for the purpose of identifying treatments and forecasting outcomes. The ILSI chemical eye injury classification scheme was developed for the additional purpose of collecting detailed human eye injury data to provide information on the mechanisms associated with chemical eye injuries. This information will have clinical application, as well as use in the development and validation of new methods to assess ocular toxicity.

METHODS

A panel of ophthalmic researchers proposed the new classification scheme based upon current knowledge of the mechanisms of eye injury, and their collective clinical and research experience. Additional ophthalmologists and researchers were surveyed to critique the scheme. The draft scheme was revised, and the proposed scheme represents the best consensus from at least 23 physicians and scientists.

RESULTS

The new scheme classifies chemical eye injury into five categories based on clinical signs, symptoms, and expected outcomes. Diagnostic classification is based primarily on two clinical endpoints: (1) the extent (area) of injury at the limbus, and (2) the degree of injury (area and depth) to the cornea.

CONCLUSIONS

The new classification scheme provides a uniform system for scoring eye injury across chemical classes, and provides enough detail for the clinician to collect data that will be relevant to identifying the mechanisms of ocular injury.