Surfactant Responses in the Bovine Corneal Opacity and Permeability Assay: Points to Consider for In Vitro Eye Irritation Testing
The Bovine Corneal Opacity and Permeability (BCOP) assay is an ex vivo test used to evaluate the ocular irritation of a broad range of chemicals. In the regulatory classification and labeling arena, BCOP can be used to identify severe and corrosive eye irritants according to the OECD Test Guideline (TG) 437. However, BCOP has historically under-predicted certain anionic surfactants, when tested according to the standard liquid protocol. TG 437 specifies that liquid surfactants may be tested as 10% aqueous dilutions for 10 minutes (although alternate dilutions and exposure times may be conducted with scientific rationale), and the relevant guidance document (GD) No. 160 suggests that solid and concentrated liquid surfactants may be diluted to 10% for testing. However, GD No. 160 further directs that surfactant-based formulations are usually tested neat, but could be diluted with justification, imparting some confusion in identifying the most appropriate test methods. Since neither the basis for selecting the appropriate surfactant test methods, nor the justification for modifications are clearly presented in TG 437 or GD No. 160, we present on the testing of sodium lauryl sulfate (SLS) in the BCOP assay, using standard and modified dilutions and exposures, to elucidate the impact of these variables on eye irritation prediction. For example, in vitro scores of 20.7, 28.4, and 28.3 were obtained when testing SLS at concentrations of 50, 20, and 10% for 10 minutes, showing that irritation responses were not fully concentrationdependent, but demonstrated optimally at intermediate doses. When tested using modified exposure times, SLS showed time-related responses, with improvements in irritation predictions at the 20 and 30 minute exposures. Histopathology was performed to assess the surfactant-induced corneal changes. Based upon these results, a framework for testing surfactants, and surfactant-based formulations is proposed.