Effects of nanoparticles on murine macrophages

Metallic nanoparticles are more and more widely used in an increasing number of applications. Consequently, they are more and more present in the environment, and the risk that they may represent for human health must be evaluated. This requires to increase our knowledge of the cellular responses to nanoparticles. In this context, macrophages appear as an attractive system. They play a major role in eliminating foreign matter, e.g. pathogens or infectious agents, by phagocytosis and inflammatory responses, and are thus highly likely to react to nanoparticles. We have decided to study their responses to nanoparticles by a combination of classical and wide-scope approaches such as proteomics. The long term goal of this study is the better understanding of the responses of macrophages to nanoparticles, and thus to help to assess their possible impact on human health. We chose as a model system bone marrow-derived macrophages and studied the effect of commonly used nanoparticles such as TiO2 and Cu. Classical responses of macrophage were characterized and proteomic approaches based on 2D gels of whole cell extracts were used. Preliminary proteomic data resulting from whole cell extracts showed different effects for TiO2-NPs and Cu-NPs. Modifications of the expression of several proteins involved in different pathways such as, for example, signal transduction, endosome-lysosome pathway, Krebs cycle, oxidative stress response have been underscored. These first results validate our proteomics approach and open a new wide field of investigation for NPs impact on macrophages

💡 Research Summary

This study addresses the growing concern that metallic nanoparticles (NPs), which are increasingly incorporated into consumer products, medical devices, and industrial processes, may pose health risks through their interactions with immune cells. The authors selected bone‑marrow‑derived murine macrophages as a physiologically relevant model because these cells are professional phagocytes that encounter and internalize particulate matter in vivo. Two widely used NPs were examined: titanium dioxide (TiO₂), a chemically inert oxide commonly found in sunscreens and paints, and copper (Cu) nanoparticles, which possess redox activity and antibacterial properties.

Experimental design
Primary macrophages were generated from C57BL/6 mice, cultured for seven days in the presence of L929‑conditioned medium, and verified by flow cytometry for CD11b⁺/CD14⁺ expression and functional responsiveness to lipopolysaccharide (LPS). Nanoparticles were sterilized in ethanol, coated with 0.2 % polyvinylpyrrolidone (PVP40) to mimic protein‑corona formation, and sonicated. Dynamic light scattering showed that, after 24 h in culture medium, TiO₂ formed aggregates with an average hydrodynamic diameter of ~320 nm, while Cu formed larger aggregates (~430 nm). Cells were exposed for 24 h to 100 µg mL⁻¹ TiO₂ or 10 µg mL⁻¹ Cu, concentrations previously determined to cause ≤20 % loss of viability (LD₂₀).

Proteomic workflow
Cellular proteins were extracted in a urea/thiourea/spermine buffer, clarified by ultracentrifugation, and quantified. One hundred fifty micrograms of total protein per sample were separated by two‑dimensional electrophoresis (IEF on 4–8 pH strips followed by SDS‑PAGE). Gels were silver‑stained, digitized, and analyzed with Delta2D software. Spots showing at least a 1.5‑fold change relative to untreated controls were excised, digested in‑gel with trypsin, and identified by nano‑LC‑MS/MS on an Agilent 1100 nanoLC coupled to a Bruker HCT‑Plus ion trap. Mascot searches against a target‑decoy SwissProt mammalian database required a minimum of two peptides and a Mascot score >10 for confident identification.

Key findings – TiO₂ exposure
Nine protein spots were up‑regulated and one down‑regulated. Up‑regulated proteins included metabolic enzymes (malate dehydrogenase, aldehyde dehydrogenase, glucosidase), the mitochondrial outer‑membrane channel VDAC, peroxiredoxin‑4 (Prx4) in its reduced form, proteasome α6 subunit, the G‑protein β subunit (Gnb1), ferritin light chain, and an O₂‑regulated protein associated with hypoxia signaling. The only down‑regulated spot corresponded to the c1 subunit of the vacuolar H⁺‑ATPase. The pattern suggests a modest “light stress” that stimulates overall metabolism, activates a hypoxia‑like response, and engages canonical stress‑related proteins.

Key findings – Cu exposure
Six spots were up‑regulated and one down‑regulated. Up‑regulated proteins comprised ATPase subunit d, prohibitin, heat‑shock protein 70 (HSP70), heme oxygenase‑1 (HO‑1), and the oxidized form of peroxiredoxin‑1 (Prx1). The oxidized Prx1 spot increased almost four‑fold, a well‑established marker of severe oxidative injury. HO‑1 induction reflects a cellular attempt to mitigate free heme and ROS. Additionally, the multivesicular body protein 4b (MVB‑prot4b) decreased, while the d1 subunit of the vacuolar H⁺‑ATPase increased, indicating remodeling of the endosome‑lysosome trafficking pathway.

Comparative interpretation
No protein was common between the TiO₂ and Cu lists, underscoring distinct mechanistic signatures. TiO₂ primarily modulated metabolic fluxes and induced a hypoxia‑like state, whereas Cu provoked a robust oxidative stress response, as evidenced by the strong up‑regulation of oxidized Prx1 and HO‑1. Both treatments altered proteins involved in the endosomal‑lysosomal system, consistent with the known route of NP internalization. The data collectively demonstrate that 2‑D proteomics can capture both expected stress markers and novel candidates (e.g., G‑protein β, ferritin, MVB‑prot4b) that may serve as biomarkers for NP exposure.

Strengths, limitations, and future directions
The study’s strength lies in its unbiased, systems‑level approach, which goes beyond conventional assays (viability, ROS, cytokine release) to reveal network‑wide alterations. However, 2‑D gels have limited resolution for low‑abundance, highly hydrophobic, or extreme‑pI proteins, and quantitative accuracy is constrained by gel‑based intensity measurements. Future work should incorporate label‑based quantitative LC‑MS/MS (SILAC, TMT) for deeper coverage, time‑course experiments to map dynamic responses, and validation in human monocyte‑derived macrophages to improve translational relevance. Moreover, exploring a broader panel of NP physicochemical properties (size, shape, surface chemistry) will help delineate structure‑activity relationships that underpin toxicity.

Conclusion
The authors successfully applied a classical 2‑D gel‑based proteomic workflow to characterize the cellular response of primary murine macrophages to two representative metallic nanoparticles. TiO₂ induced metabolic and hypoxia‑related changes, while Cu triggered a pronounced oxidative stress signature. These findings highlight that nanoparticle composition dictates distinct intracellular pathways and that proteomics offers a powerful platform for uncovering novel biomarkers and mechanistic insights essential for risk assessment of nanomaterials.