Identifying possible neurodevelopmental effects of per- and polyfluoroalkyl substances (PFAS) through an adverse outcome pathway (AOP) network for human developmental neurotoxicology

Human studies have reported inconsistent associations between early-life exposure to per- and polyfluoroalkyl substances (PFAS), particularly during critical windows of brain development, and neurodevelopmental outcomes. To address the lack of clarity regarding how PFAS affect neurodevelopment, this study developed the first unified adverse outcome pathway (AOP) network to explore the mechanisms involved in developmental neurotoxicity (DNT). Of 343 AOPs retrieved from AOP-Wiki, 19 linear AOPs associated with DNT satisfied the inclusion criteria. To pinpoint critical nodes and relationships, the constructed DNT-AOP network was examined using topological metrics. Through a combination of qualitative weight of evidence (WoE) assessment and network topology analysis, two critical paths were identified: one based on thyroid hormone disruption and the other on the intracellular calcium (Ca²⁺) overload, highlighting their crucial roles in influencing downstream neurodevelopmental endpoints. In line with these findings, we identified gaps in developing DNT in vitro testing batteries, highlighting potential assays, including the levels of brain-derived neurotrophic factor (BDNF), intracellular Ca²⁺, and thyroxine in neuronal cells, as well as glial-mediated inflammation. To mechanistically clarify how PFAS exposure contributes to DNT, we mapped relevant evidence onto the critical paths. Toxicological evidence suggests that PFAS interferes with thyroid hormone metabolism and Ca²⁺ homeostasis, leading to reduced thyroxine levels and elevated intracellular Ca²⁺ concentrations in neural cells. These disruptions culminate in diminished synaptogenesis and neuroplasticity, weakened neuronal connectivity, and ultimately deficits in memory, learning, and cognitive performance. By establishing mechanistic links between PFAS and key neurodevelopmental events, our findings provide a foundation for assessing associated risks.