Catastrophic inflammatory death of monocytes and macrophages by overtaking of a critical dose of endocytosed synthetic amorphous silica nanoparticles/serum protein complexes

Aims: We tested whether phagocytic monocytes/macrophages are more susceptible than nonphagocytes to nanoparticle (NP) toxicity. Materials & methods: We compared in vitro cell death and proinflammatory cytokine production in human monocytes, macrophages, lymphocytes and HeLa cells due to synthetic amorphous silica (SiO2)-NPs in different serum concentrations and correlated them with cellular uptake and distribution. Results: Phagocytes were approximately ten-times more sensitive than nonphagocytes to SiO2-NPs and more effectively endocytosed SiO2-NP–serum protein nanoagglomerates, so determining their accumulation in acidic endocytic compartments well beyond a critical/cytotoxic threshold. Monocyte/macrophage death was paralleled by cytokine secretion. Conclusion: The physiological specialization of monocytes/macrophages to effectively capture NPs may expose them to the risk of catastrophic inflammatory death upon saturation of their maximal storage capacity.