Interactions of Carboxylated Nanodiamonds With Mouse Macrophages Cell Line and Primary Cells

Nanodiamonds (ND) have attracted significant interest for their use in several biomedical applications. These applications can be very useful if the safety and compatibility of ND are proven. We assessed the effects of ND (100 nm, Carboxylated) on primary macrophages and a macrophage-like cell line and found that these particles are not toxic to these cells at lower concentrations but may interfere with cell functions and differentiation. Internalization of ND by these cells in a time- and dose-dependent manner was mostly via phagocytosis and clathrin-dependent endocytosis and localized to the cytoplasm but not into the nucleus. No significant induction of inflammatory cytokines or reduction in the ability of these cells to respond to lipopolysaccharides (LPS) was noted. However, the endocytic activity of these cells is significantly reduced. In addition, ND exposure reduced the ability of differentiating bone marrow cells to express macrophage surface markers. Measurement of the fluorescence and absorbance of ND-treated cells clearly showed the ability of these particles to produce a signal at different wavelengths. Therefore, it is important to consider interference of ND in different colorimetric and fluorometric assays when testing interactions or effects of ND on cells. Our findings suggest that ND are not cytotoxic to macrophages at the tested concentrations, but it can interfere with macrophage functions and differentiation and may interfere with assays’ result through the production of a signal at different wavelengths.