From pathways to people: applying the adverse outcome pathway (AOP) for skin sensitization to risk assessment.

Consumer safety risk assessment of skin sensitization requires information on both consumer exposure to the ingredient through product use and the hazardous properties of the ingredient. Significant progress has been made in determining the hazard potential of ingredients without animal testing. However, hazard identification is insufficient for risk assessment, and an understanding of the dose-response is needed. Obtaining such knowledge without animal testing is challenging and requires applying available mechanistic knowledge to both assay development and the integration of these data. The recent OECD report "The Adverse Outcome Pathway for Skin Sensitization Initiated by Covalent Binding to Proteins" presents the available mechanistic knowledge of the sensitization response within an adverse outcome pathway (AOP). We propose to use this AOP as the mechanistic basis for physiologically- and mechanistically-based toxicokinetic-toxicodynamic models of the sensitization response. The approach would be informed by non-animal data, provide predictions of the dose-response required for risk assessment, and would be evaluated against human clinical data.