The Organisation for Economic Co-operation and Development (OECD) has initiated the adverse outcome pathway (AOP) Development Program in which the concept of AOP is applied to evaluate the safety of molecules such as chemicals. This program aims to assist regulatory needs and construct a knowledge base by accumulating AOP case studies. AOP consists of a molecular initiating event (MIE) as the initiating event of the pathway; key events (KEs) as the events themselves, such as cellular-molecular interactions; and adverse outcome (AO), such as signaling transduction-induced toxicity, as adverse events. KEs are extracted as important events at various levels, such as the molecular, cellular, tissue, organ, individual, and species levels; measurement of KEs and key event relationships (KERs), including mechanisms, plausibility, species differences, and empirical support information, are gathered. The development status of the AOP relating to histone deacetylase inhibition-induced testicular toxicity, currently being reviewed by the OECD, has been introduced. The AOP describing malignancies by Wnt ligand stimulation and Wnt signaling activation using gene expression network analysis-based mechanisms in molecular pathway elucidation has been suggested.
Keywords: Organisation for Economic Co-operation and Development (OECD); adverse effect; adverse outcome pathway (AOP); gene molecular network pathway.