Untersuchungen zu SPIO-Partikeln: SPIO-Markierung in vitro, Differenzierungspotential humaner mesenchymaler Stammzellen und Relaxivitätsmessungen.

Magnetic nanoparticles are widely used in biomedical sciences as biosensors and as contrast agents in imaging applications. They are also used if the targeted release of a drug is required. In addition, molecular MRI plays an important part in tumor diagnostics. Due to the rapid development of nanotechnology, the increasing number of different nanomaterials which are used because of their special physical properties, and the good biocompatibility of metal and anorganic nanoparticles, a growing number of new nanostructures come into contact with man and environment. Iron oxide based MRI contrast agents include SPIO particles. They are used clinically in liver imaging and absorbed by the mononuclear phagocyte system. Moreover, cells can be labeled with SPIO particles and used as in vivo contrast markers for MR-Imaging. The cell labeling technique should optimize various parameters, such as size, coating and particle dose as well as incubation time. For this reason, the current focus of many studies is on modified and differently coated SPIO particles. For the present thesis, two different SPIO formulations were tested and the uptake of SPIO particles into various cell types – murine macrophages, human leucaemic monocytes and human mesenchymal stem cells – has been studied. Many researchers try to achieve a specific labeling by modified SPIO particles. In this respect, however, there are strong doubts concerning the biosafety of these particles. In this thesis, SPIO formulations that achieved good results without modifications and at a relatively low concentration were used. Phagocytic cells were incubated with 2.79 µg Fe/ml and 27.92 µg Fe/ml. After 12 h, the iron concentration per J774A.1 cell was 13.77 ± 0.5 pg. With THP-1 cells, a lower uptake could be observed; the intracellular iron was 9.84 ± 1.6 pg Fe per cell 24 h after labeling. Due to their outstanding properties, stem cells have great potential in regenerative medicine. Nevertheless, the mechanisms on which the transplantation of stem cells into a target organ is based are not yet understood. After labeling the cells with SPIO particles, cell migration can be observed by means of MRI after transplantation. For this study, human mesenchymal stem cells were labeled with SPIO, but without the aid of a transfection agent. Labeling the stem cells was started with a higher concentration of SPIO particles (25 µg Fe/ml) compared to the labeling of phagocytic cells. Labeling of hMSC was efficient. One of the most important properties of stem cells is their ability to differentiate, which was investigated in this thesis as well. The labeling with SPIO particles did not affect the differentiation potential of hMSC to osteoblasts and adipocytes. To determine if SPIO particles have a T2-intensifying effect, the T1 and T2 values of various contrast agent solution at 7 T were measured and the r2/r1 ratio calculated. Both 1/T1 and 1/T2 increased linearly with the SPIO concentration. For the iron oxide containing contrast agent under analysis, an r2 value of 178 mM-1s-1 in water was determined. The r2/r1 ratio was 66 (measured in water). With an increase of the viscosity, r2 also increased so that an r2 value of 184.6 mM-1s-1 in mouse plasma was determined. The tested SPIO particles showed an r2/r1 ratio of 108.6 at 7 T (in mouse plasma, measured at RT). The higher r2 values expected at 7 T, compared to published reference contrast agent Ferucarbotran values when measure at 4.7 T, were not observed. This may have been due to the different temperatures and a possible field inhomogeneity during the measurements.