Application of the KeratinoSens Assay for Prediction of Dermal Sensitization Hazard for Botanical Cosmetic Ingredients
An essential step in the safety review of cosmetic/personal care ingredients is hazard assessment for a series of endpoints, including dermal sensitization potential. In vitro methods have been developed to identify allergic (haptenic) potential for individual chemicals based on electrophilic interaction with marker peptides or cellular target systems. These assays generally use a specific molar ratio of the test chemical to the test system. Botanical extracts are used increasingly in formulas and, as mixtures, specific molar ratios cannot be determined for these assays. Often, the botanical extract portion is a relatively small portion of the complete ingredient. To assess these mixtures, the KeratinoSens assay was selected because it operates over a wide dose range and sets cytotoxicity limits on doses used to measure marker gene expression (Emter et al, 2010 ). In the KeratinoSens assay, the induction of a luciferase gene, under the control of the antioxidant response element (ARE) derived from the human gene AKR1C2 gene, is measured. In parallel, cytotoxicity is assessed by both Neutral Red Uptake (NRU) and MTT assays. Test concentrations ranged up to 1000 μg/mL (of complete ingredient) and a test concentration was considered positive if the relative viability was ≥ 70% and the fold induction of luciferase was 1.5x relative to the solvent controls. The goal of the study was to measure the activity of 3 known sensitizers (gluteraldehyde (GA) [strong], dimethyl maleate (DM) [moderate] and cinnamic aldehyde (CA) [moderate] spiked into four different botanical ingredients (each with a different excipient solvent systems). The “spiked” botanical ingredients were used as the test article as no sensitizing botanical ingredient was available. Activity of the spiked sample was measured relative to the EC1.5 of the neat sensitizer as a function of sensitizer concentration and extract composition. Three independent trials were performed on each test material. No appreciable cytotoxicity was observed with any of the samples. The recovery of the GA spike required at least a ~3 fold increase in concentration relative to the chemical alone and botanical ingredient #3 reduced the activity below detection. The DM and CA showed activity at about the same effective concentrations as the neat chemical although the DM showed reduced activity in botanical ingredient #3 as well. These data suggest that the KeratinoSens assay has the potential to identify electrophile allergens within a botanical ingredient matrix.