Establishing toxicologically relevant primary alveolar macrophage models to enable a realistic assessment of nanomaterials safety

Alveolar macrophages (AMs) are vital lung defenders, constantly monitoring and eliminating inhaled particles through sustained surveillance and phagocytosis. Investigating particle-cell interactions, crucial for evaluating the respiratory safety or toxicity of particles, remains constrained by the absence of appropriate in vitro AM models that replicate crucial resident AM characteristics.

This study compared six murine AM models, such as short-term cultured primary AMs, GM-CSF and TGF-beta maintained primary AMs, bone marrow-derived AM-like cells, an immortalized AM cell line, and a fetal liver-derived AM-like cell line, against in vivo AMs based on surface phenotype, transcriptomic identity, and responses to three carbon-based nanomaterials (CBNs).

Initial findings indicated limited AM identity in most cell lines, characterized by reduced CD11c and SiglecF but elevated CD11b surface expression. Conversely, GM-CSF and TGF-beta maintained primary AMs, and bone marrow-derived AM-like cells more accurately preserved resident AM-like surface marker profiles. Transcriptomic alterations, primarily within metabolism-related pathways like oxidative phosphorylation, exhibited features most akin to in vivo AMs in primary AM models.

Functional and toxicological evaluations using soot-like carbon nanoparticles, double-walled carbon nanotubes, and multi-walled carbon nanotubes unveiled distinct model-dependent responses. Notably, AMs GTR and bone marrow-derived AM-like cells displayed the strongest in vitro responses, encompassing cytotoxicity and inflammatory cytokine release, mirroring MWCNT-induced reductions in AM numbers observed in vivo.

In contrast, MH-S cells exhibited heightened cytotoxic sensitivity, positioning them as suitable candidates for high-throughput cytotoxicity tests. In summary, these results underscore the potential of AMs GTR and BM-AMs as the most suitable models for dissecting AM biology and AM-intrinsic responses to poorly soluble nanoparticles like CBNs, with BM-AMs potentially offering a scalable platform for mechanistic and high-throughput nanotoxicology studies.