Choosing the Appropriate Solvent for Solid Materials Tested in the Bovine Corneal Opacity and Permeability (BCOP) In Vitro Assay
In compliance with OECD Test Guideline 437 for eye irritation (BCOP assay), non-surfactant solid materials are typically tested as 20% dilutions prepared in 0.9% sodium chloride solution, distilled water, or other solvent that has been demonstrated to have no adverse effects on the test system. However, the limited solubility of some chemicals adds technical challenges in finding a vehicle that would ensure the material’s availability to the excised corneas and that itself would not affect the test system. In this study, we evaluated five solvents frequently used in the BCOP assay: distilled water, mineral oil, corn oil, polyethylene glycol (PEG)-400, and methocel solution (0.5%). Based on the available classification systems, our preliminary data showed that water, methocel, mineral oil and corn oil were predicted as non-irritants, while PEG-400 was predicted as a mild irritant. To demonstrate the influence of the type of solvent on the outcome/prediction of the BCOP assay for solid materials, we tested a 20% suspension of benzoic acid (BA) prepared in these solvents. BA has a non-polar benzoic ring that would preferably dissolve in non-polar solvents and a polar acidic group with affinity for polar solvents, thus making it a good model for testing its effect on corneas when dissolved in various solvents. Previous animal tests reported moderate to severe eye irritation induced by BA. Our results demonstrated that when mixed in water, mineral oil, corn oil, or methocel, BA was predicted to be a corrosive/severe irritant, while it was predicted to be a moderate irritant when mixed in PEG-400. These results support the need for further investigation of the solvent’s influence in the BCOP assay to allow the correct prediction of the irritation potential of solid materials.