Figure 1

Figure 1

Magnéli phase phagocytosis results in increased cell death in bone marrow-derived macrophages. (A–C) Characterization of Magnéli phases used in this study. (A) Schematic illustrating Magnéli phase generation. (B,C) TEM images of Magnéli phases formed by annealing P25 TiO₂ nanoparticles with coal in a pure N₂ atmosphere for 2 h at 900°C. Electron diffraction patterns were characteristic of Magnéli phases and confirmed these as predominately Ti₆O₁₁ particles. Particles were between 10 and 200nm in size. (D) Un-treated bone marrow-derived macrophages (1 × 10⁶ cells/well) and (E) macrophages treated with Ti₆O₁₁ (1, 10, 100, or 1,000 ppm) were visualized using TEM (Scale bar: 5 μm). Magnéli phases appear as punctate dark dots in the macrophages and are concentrated in phagolysosomes. (F) Macrophages containing Magnéli phases demonstrate morphological features consistent with apoptosis, including cell shrinking and membrane blebbing (red arrows) (Scale bar: 1μm). (G,H) Cytotoxicity was evaluated using trypan blue exclusion (G) across the Ti₆O₁₁ dose range and (H) at 100 ppm over a 24 h time course. (I,J) Inflammation was evaluated by assessing the production of pro-inflammatory cytokines, such as (I) IL-1β, (J) IL-6, and (K) TNF in the cell free supernatant following exposure to different doses of Magnéli phases. (L) Macrophage function was evaluated by assessing the ability of macrophages to phagocytose fluorescent Escherichia coli 24 h post-exposure to 100 ppm Magnéli phases. Data are expressed as mean ± SEM (n = 3 independent experiments). **p < 0.01.