To comply with the EU Cosmetic Directive, accurate sensitive and predictive alternative methods are required in order to evaluate eye damage potential of chemicals. Linked to the complexity of both the eye irritation mechanism and the diversity of the intrinsic molecular behavior of chemicals, assessment of the potential eye irritation of ingredients is a complicated issue.
The role of corneal epithelium is crucial because it represents the first line of defense against many types of injury. Thus we have used the standardized SkinEthic reconstructed human corneal epithelial (HCE) model to evaluate in vitro eye irritancy (Cotovio et al, 2010).
We have determined the chemical reactivity parameter by measuring the depletion of synthetic peptide containing Cysteine or Lysine residues in contact with chemicals. The reactivity peptide binding assay (RPBA-HCE) defining the reactivity status of chemicals was optimized from the DPRA assay (skin sensitization evaluation) for assessing the eye irritancy using the SkinEthic HCE test method.
The Prediction Model (PM), applied for a set of more than 180 chemicals, is based on a 5.95 % depletion cut off, with 2 categorizations (reactive and non reactive).
In parallel, SkinEthic HCE protocol (10 min and 1 hr + 16 hrs post-exposure incubation) used with the same set of chemicals confirmed that the PM based on a 50 % viability cut-off allowed the drawing up of irritants and non irritants classes. Results (~1/3 reactive versus ~2/3 non reactive chemicals) showed that the measure of molecular reactivity of these chemicals used to orientate the tested chemicals towards the suitable time exposure allowed to discriminate irritants from non irritants. Consequently, the resulting performances of the testing battery combining SkinEthic HCE assays and chemical reactivity measurement greatly enhanced the applicability domain of the SkinEthic HCE assay.