Nanomaterial grouping: Unraveling the relationship of induced mechanisms and potency at a temporal scale

Grouping is a fundamental step to generalize engineered nanomaterials (ENM) hazard. However, most strategies lack comprehensiveness in ENM and experimental settings. Toxicogenomics allows the characterization of the direct molecular mechanisms of action (MOA) associated to ENM hazard. In this study, we implemented an adverse outcome pathway (AOP)-based framework for ENM grouping. We hypothesized that AOP-direct MOA along with ENM potency, i.e., the dose required to activate a molecular response, could be used to robustly group distinct ENM exposures by considering a mechanistic and multiscale level of response. Our results highlighted a critical role of the exposure duration and ENM potency respectively on the specificity and progression of the response. Moreover, we investigated the complexity and time scale of the biological events triggered by ENM. In particular, genotoxicity-related AOPs were found triggered at longer exposures. Higher ENM potency was linked to shorter exposure and basic and starting events. While lower potency was linked to prolonged exposures and advanced stages of biological processes. Our results also highlighted shared molecular responses in groups of ENM both at shorter (5 clusters) and longer (3 clusters) exposure periods. Based on computed features for cluster predictions, grouping could have likely resulted from the influence of chemical composition, size-dependent properties of ENM, and biological descriptors. Finally, features were interdependent and differed in quantity and connectivity, indicating differences in the response dynamics. Notably, our study does not include every ENM currently available. Hereby, our findings pave the way for the construction of quantitative AOPs and hold significant implications for ENM hazard assessment and regulatory decision-making.