Correlative 3D studies of the cellular uptake of citrate-coated iron oxide nanoparticles for the detection of inflammatory diseases

The Collaborative-Research-Centre (CRC) 1340 aims to use inflammation as a pathological case to investigate how extracellular matrix (ECM) components can be used for in vivo imaging. The main goal is to identify initial ECM changes to improve early detection of potentially life-threatening inflammatory diseases. Our CRC’s ECM research focuses on inflammatory diseases, including atherosclerosis and neuroinflammation. One major focus lies in investigating new imaging approaches using citrate-coated magnetic iron oxide nanoparticles (MNPs) for magnetic resonance imaging. These MNPs aid tumor visualization due to greater uptake by tumor cells compared to healthy cells. The same principle applies to endothelial cells in unstable vs. stable atherosclerotic plaques. Non-targeted MNPs are also efficiently internalized by immune cells, allowing passive targeting for visualizing immune cells in inflammation. It is not fully understood which cellular structures mediate the passive targeting of MNPs and intracellular processing of MNPs, particular their transport and sorting in lysosomes. Potential candidates are the cell membrane or the cell surrounding extracellular structure, the glycocalyx. Our recent TEM studies show that MNPs cluster on the surface of THP-1 cells and citrate-coated-MNP clusters undergo endocytosis. The lack of 3D information, small sample size and field of view of TEM leave unanswered questions about the role of the size of these clusters, their distribution on cell surfaces and if there is a direct link between clusters and endocytic pits. Cryo soft X-ray tomography (SXT) offers a simpler, less invasive sample preparation method and its water-window radiation allows cells to be imaged in their native state with a larger field of view and better penetration depth. We are convinced that synchrotron 3D transmission water-window X-ray microscopy will decisively help us to understand the interaction of MNPs with cellular structures and will be even more powerful when combined with fluorescence microscopy to provide correlated functional information.