Nonlinear Magnetic Response Measurements in Study of Magnetic Nanoparticles Uptake by Mesenchymal Stem Cells

Abstract

Stem cells therapies offer a promising approach in translational oncology, as well as in regenerative medicine due to the tropism of these cells to the damage site. To track the distribution of stem cells, the latter could be labeled by MRI-sensitive superparamagnetic (SPM) iron oxide nanoparticles. In the current study, magnetic properties of the magnetic nanoparticles (MNPs) incorporated into the bone marrow-derived fetal mesenchymal stem cells (FetMSCs) were evaluated employing nonlinear magnetic response measurements. Synthesized dextran-coated iron oxide nanoparticles were additionally characterized by X-ray diffraction, transmission electron microscopy, and dynamic light scattering. The MNP uptake by the FetMSCs 24 h following coincubation was studied by longitudinal nonlinear response to weak alternating magnetic field with registration of the second harmonic of magnetization. Subsequent data processing using a formalism based on the numerical solution of the Fokker-Planck kinetic equation allowed us to determine magnetic and dynamic parameters and the state of MNPs in the cells, as well as in the culture medium. It was found that MNPs formed aggregates in the culture medium; they were absorbed by the cells during coincubation. The aggregates exhibited SPM regime in the medium, and the parameters of the MNP aggregates remained virtually unchanged in the cells, indicating the preservation of the aggregation state of MNPs inside the cells. This implies also the preservation of the organic shell of the nanoparticles inside FetMSCs. The accumulation of MNPs by mesenchymal stem cells gradually increased with the concentration of MNPs. Thus, the study confirmed that the labeling of MSCs with MNPs is an effective method for subsequent cell tracking as incorporated nanoparticles retain their magnetic properties.

Keywords: longitudinal response to weak alternating (ac) magnetic field; magnetic nanoparticles; mesenchymal stem cells.

Figure 1

X-ray diffraction intensity from MNPs vs. diffraction angle (a) and TEM image of nanoparticles (b).

Figure 2

Distribution of hydrodynamic radii of MNPs’ aggregates in colloidal aqueous solution (histogram).

Figure 3

Real and imaginary parts of M₂ response as functions of dc magnetic field from suspensions of MNPs in medium before coincubation with MSCs (a,b), and from MSCs washed with phosphate buffer after coincubation (c,d), at iron concentrations of 50 and 100 μg/mL. The signals were registered at H-scan frequencies 8 Hz (a,c) and 0.25 Hz (b,d), respectively. Filled and open symbols present direct and reverse H scans, accordingly, and solid curves display simultaneous best fit of both phase components for each concentration. Every 60th point is shown in (a) and (b), and every 40th point in (c) and (d) panels, respectively.

Figure 4

Average numbers of magnetic centers (aggregates) (a) and MNPs per aggregate (b) in medium before coincubation of MSCs with MNPs and in the samples with the cells washed with the phosphate buffer after coincubation at different concentrations of MNPs.

Figure 5

The average number of MNPs per MSC after 24 h of coincubation at different Fe concentrations.