Applicability of in vitro mouse lung epithelial cell responses for potency grouping and hazard identification of metal oxide nanoparticles: impact of form, size, surface area, and solubility on toxicity

Human health risk assessment of engineered nanomaterials (ENM; materials with any dimension or structure between 1 and 100 nm) is challenged by the large number of compounds requiring assessment and the intricate association between physicochemical properties and toxicity. Previously, a number of high-content and high-throughput Novel Approach Methodologies (NAMs) were applied to investigate the impact of dissolution on toxicity induced by metal oxide (MOs) nanoparticles (NPs) in lung epithelial cells. This study evaluated the applicability of the data, including information from cell viability, transcriptomics, and genotoxicity endpoints, to conduct potency grouping and hazard identification for 7 individual MOs and their forms-NPs, dissolved equivalents, and bulk microparticle (MPs) analogues (18 total compounds). Benchmark concentration modeling was performed across a range of benchmark responses (BMRs), followed by hierarchical clustering to facilitate potency grouping and hazard identification. Correlation was assessed between endpoints used for potency grouping, and between endpoints and primary particle size, specific surface area, and solubility in cell culture medium across all BMRs. Instantaneously dissolving zinc oxide (ZnO) NPs presented similar potency to dissolved zinc and ZnO MPs, while aluminum oxide, iron oxide, and titanium dioxide NPs showed low potency. Thus, these particles were considered low priority for further testing. Copper oxide, nickel oxide and manganese dioxide NPs exhibited distinct potency and hazards compared to their dissolved or MPs forms, implying these particles warrant further assessment. Material solubility and the form of MOs were associated with endpoint potency. These results demonstrate the applicability of in vitro NAMs-based potency screening for first-tier assessment of MONP-induced acute toxicity.