Page 43 - Cellular Imaging in Regenerative Medicine, Cancer and Osteoarthritis

incubation time may result in more cells containing enough iron for detection after multiple cell divisions. For both MPIO and SPIO, no major effect on cell function in terms of tube forming capacity was observed, even at doses that did result in changes in morphological features and some cell death (< 20%).
For tracking of single cells by MR, labeling with MPIO appears to be most suitable. Only one iron particle is sufficient for detection (26). MPIO particles have higher relaxivity than SPIOs, based on equivalent iron content. The labeling protocol is easier for MPIO than for SPIO. No transfection agent is needed, medium with serum can be used and the labeling time is much shorter (4 h compared with 24 h for SPIO). MPIOs also contain a fluorescent tag, so they can be readily used in multi-modality imaging approaches combining MRI with optical imaging. However, MPIOs as used in this and other studies are not intended for clinical use but for experimental use only. SPIOs, however, exist in clinically approved formulations and have been used in clinical settings already (33–35). SPIOs are therefore better suited to clinical applications.
Using optimal labeling conditions as found for HUVEC for both SPIOs and MPIOs on other cell lines, we observed that different cell types react differently to identical labeling conditions. The mouse myoblast cell line C2C12 shows no change in cell size after administrating MPIO as opposed to HUVEC. Also, the high labeling efficiency found for MPIO in HUVEC was much less in C2C12 cells and labeling was absolutely absent in chondrocytes at an incubation time of 4 h. Even at doses of 50–100 mg and incubation times of 24 h, chondrocytes showed limited uptake. In contrast, a 100% labeling efficiency could be obtained with SPIO in these cells (36). In studies by Arbab et al. (19,37), significant differences in cell apoptosis and label incorporation were also found between different cell types when identical labeling protocols were used.
4. Conclusion
HUVECs can be labeled efficiently both with SPIO and MPIO but dose and duration of exposure of cells to these particles strongly influence label incorporation, label distribution and label retention. Optimal label incorporation requires different protocols for SPIO and MPIO. Applying
Influence of SPIO cell labeling protocol
41
2