Managing Magnetic Nanoparticle Aggregation and Cellular Uptake: a Precondition for Efficient Stem‐Cell Differentiation and MRI Tracking

Abstract

The labeling of stem cells with iron oxide nanoparticles is increasingly used to enable MRI cell tracking and magnetic cell manipulation, stimulating the fields of tissue engineering and cell therapy. However, the impact of magnetic labeling on stem-cell differentiation is still controversial. One compromising factor for successful differentiation may arise from early interactions of nanoparticles with cells during the labeling procedure. It is hypothesized that the lack of control over nanoparticle colloidal stability in biological media may lead to undesirable nanoparticle localization, overestimation of cellular uptake, misleading MRI cell tracking, and further impairment of differentiation. Herein a method is described for labeling mesenchymal stem cells (MSC), in which the physical state of citrate-coated nanoparticles (dispersed versus aggregated) can be kinetically tuned through electrostatic and magnetic triggers, as monitored by diffusion light scattering in the extracellular medium and by optical and electronic microscopy in cells. A set of statistical cell-by-cell measurements (flow cytometry, single-cell magnetophoresis, and high-resolution MRI cellular detection) is used to independently quantify the nanoparticle cell uptake and the effects of nanoparticle aggregation. Such aggregation confounds MRI cell detection as well as global iron quantification and has adverse effects on chondrogenetic differentiation. Magnetic labeling conditions with perfectly stable nanoparticles-suitable for obtaining differentiation-capable magnetic stem cells for use in cell therapy-are subsequently identified.

Impact of Photosensitizers Activation on Intracellular Trafficking and Viscosity

“…The cells were then incubated with Roswell Park Memorial Institute medium (RPMI) containing citrate coated magnetic nanoparticles (maghemite, negatively charged, 8 nm in diameter, iron concentration 2mM)[31,49] and the photosensitizers (m-THPC or TPCS2a) at a concentration of 5µM. After incubation for 2 hours, the cells were rinsed three times and placed in complete DMEM.…”

Variability in contrast agent uptake by different but similar stem cell types

“…53 The 'rod-like' structures have not been reported before, except for labeling experiments where cells were exposed to external magnetic fields. 54 Those aggregates can potentially be beneficial in applications where pre-labeled cells are transplanted for longitudinal studies. If stable over time, such aggregates will not be further diluted with proliferation, hereby enabling longer detectability in vivo.…”

Cell labeling with magnetic nanoparticles: Opportunity for magnetic cell imaging and cell manipulation

“…We use serum-free culture medium to avoid adsorption of proteins on the nanoparticles that could affect both their stability and their affinity for the cell membrane. Moreover the stability of citrate-coated particles (measured through their hydrodynamic size) can be modulated by controlling the concentration of free citrate ions: the nanoparticles remain isolated in culture medium supplemented with 5 mM free citrate, while they aggregate in citrate-free medium and eventually form chains when submitted to a magnetic field [8] (Figure 4). Thus, to avoid MNP aggregation, cell labeling should be performed in the serum-free medium supplemented with citrate.…”

“…The expression of specific genes of interest can also be quantified to assess subtle phenotypical alterations following SPIO labeling [14,15]. An example is given in Figure 6[8]. …”

“…the capacity to differentiate in cells of cartilage) was partially inhibited in one study [19], but not in others [14,20-22], whereas adipogenesis and osteogenesis were not impaired. On the contrary, while labeling cells with citrate-coated MNP, we could modulate the amount and the physical state of nanoparticles interacting with cells and could conclude that only high dose of MNPs or an aggregated state, could have adverse effects on cell differentiation (chondrogenesis) [8] (Figure 6). Labeling conditions with perfectly stable MNP is thus recommended for use in cell therapy assays.…”