To evaluate the capacity of human monocytes to phagocytose various approved iron oxide based magnetic resonance (MR) contrast agents and to optimize in vitro labeling of these cells. Human monocytes were incubated with two superparamagnetic iron oxide particles (SPIO) as well as two ultrasmall SPIO (USPIO) at varying iron oxide concentrations and incubation times. Iron uptake in monocytes was proven by histology, quantified by atomic emission absorption spectrometry and depicted with T2* weighted fast field echo (FFE) MR images at 1.5 T. Additionally, induction of apoptosis in iron oxide labeled monocytes was determined by YO-PRO-1 staining. Cellular iron uptake was significantly (P<0.01) higher after incubation with SPIO compared with USPIO. For SPIO, the iron oxide uptake was significantly (P<0.01) higher after incubation with the ionic Ferucarbotran as compared with the non-ionic Ferumoxides. Efficient cell labeling was achieved after incubation with Ferucarbotran at concentrations > or = 500 microg Fe/ml and incubation times > or = 1 h, resulting in a maximal iron oxide uptake of up to 50 pg Fe/cell without impairment of cell viability. In vitro labeling of human monocytes for MR imaging is most effectively obtained with the approved SPIO Ferucarbotran. Potential subsequent in vivo cell tracking applications comprise, e.g. specific targeting of inflammatory processes.
The neutron scattering spectrum of bound H,O has been determined from the excess scattering of H,O-hydrated myoglobin relative to a sample hydrated with D,O. The resulting vibrational difference spectrum shows the well known translational and librational bands of bulk water. Significant discrepancies arise at low frequencies indicating that the diffusive motion is strongly retarded by interactions with the protein surface. By Fourier deconvolution of constant Q-spectra we obtain the intermediate scattering function and the time-resolved mean square displacement of the water protons on a 15 ps timescale. We observe a sublinear increase in the squared displacements with time suggesting anomalous diffusion. Furthermore, the fourth moment (r4(t)) exceeds the value expected for a Gaussian distribution, which indicates either strong heterogeneity or anisotropic motions. The data are discussed in relation to simulations and theoretical results on strongly coupled liquids.
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