AOP report: Adverse Outcome Pathway Network for Developmental Androgen Signalling-Inhibition Leading to Hypospadias.

Abstract

This report summarizes an adverse outcome pathway network (AOPN) describing how reduced androgen signaling during fetal life may lead to hypospadias in male offspring. Hypospadias is a penile malformation caused by disrupted masculinization of the genital tubercle. Under normal physiological conditions, androgen action promotes differentiation of the genital tubercle to a penis in male fetuses. Suboptimal androgen receptor (AR) signaling can impair genital tubercle development, causing hypospadias in humans and other mammals. In rodent toxicity studies, including Organisation for Economic Co-operation and Development (OECD) Test Guideline studies for reproductive toxicity, hypospadias is assessed as an adverse outcome (AO). This report presents three adverse outcome pathways (AOPs) (AOP-wiki IDs 477, 570, 571), each with distinct upstream events representing anti-androgenic mechanisms. Downstream, the pathways converge at the nodal key event (KE)-1614 'decrease, AR activation' and share AO-2082 'hypospadias'. This report provides assessments of all three AOPs (477, 570, and 571), including one new KE (2082), and three new key event relationships (KERs 2828, 3350, and 3488) not previously reported. The three KERs, connecting upstream events non-adjacently with the AO, were developed using a systematic weight-of-evidence approach. Overall, empirical evidence for the AOPs is strong, with few exceptions or uncertainties. The AOPN is considered applicable to male mammals, but supporting data comes primarily from rodent and human studies, hence the applicability domain is currently restricted to these species. While quantitative understanding remains limited, the AOPN establishes robust mechanistic links between anti-androgenic activity and hypospadias, providing a foundation for future efforts to quantify KERs and develop predictive methods based on upstream events, often measured in vitro.