A pragmatic upstream network for disrupted steroidogenesis through reduced enzyme activity and steroid hormone...

The Adverse Outcome Pathway (AOP) framework offers a structured approach to organize mechanistic knowledge of toxicological pathways. By describing biological events linking molecular initiating events (MIEs) to an adverse outcome (AO) at the organismal level, it aims to aid regulatory decision-making through predictive toxicology approaches. To serve this purpose, however, it is recognized that AOP networks are required to adequately capture complex biology. Another central feature of the AOP concept is that upstream molecular networks will be shared between numerous downstream AOs. This report focuses on steroidogenesis, a common target of endocrine disrupting chemicals, and the development of an upstream network for reduced steroidogenesis focusing on hormones and enzymes that are particularly relevant to mammalian reproduction. The AOP-Wiki was mapped for existing content related to steroidogenesis and the resulting network expanded by incorporating additional key events (KEs) and KE Relationships (KERs) not yet inventoried. All existing KEs and KERs were evaluated for completeness. Using a pragmatic approach, we developed the identified KEs and KERs by integrating evidence from recent review articles. The focus was particularly on the impact of disrupted cholesterol transport, altered enzyme activities and hormone levels. The resulting upstream AOP network serves as a foundation for developing complete AOPs linking disrupted steroidogenesis with downstream AOs. This upstream network will also contribute to identifying relevant test assays for development and understanding the predictive capabilities of existing in vitro assays, such as the OECD-validated H295R steroidogenesis assay.