Magnetic targeting of stem cell spheroids into specific lobe of liver using nanohybrid system

Abstract

Diabetes mellitus is an autoimmune disease in which a patient’s body cannot secrete insulin. This can lead to serious complications without proper treatment. One way to stop the progress of complications is transplanting pancreatic islets to liver. However, immune cells present in the liver blood destroy a significant number of implanted islets. One way to solve this problem is implanting mesenchymal stem cells (MSCs) together with islets. MSCs enhance the survivor rate of islets by suppressing immune responses in the site of transplantation. However, implanting MSCs also has several limitations. Most of the cells including MSCs have pro-inflammatory high motility group box 1 (HMGB1) proteins inside the nuclei. When MSCs are damaged, HMGB1 proteins are released out of the cells and activate phagocytes to destroy the damaged cells. In addition, strongly rejected MSCs may reduce the functions of surrounding liver cells. Once the MSCs have spread throughout the liver, they can hardly be removed. In this study, glycyrrhizin-chitosan coated superparamagnetic iron oxide (GC-SPIO) nanoparticles were developed and internalized into MSCs. Glycyrrhizin coated on the surface of SPIO nanoparticles can inhibit HMGB1 proteins through strong binding. Iron based SPIO nanoparticles can be used to magnetically guide MSCs into a specific lobe of liver. The lobe can be partially resected in case of strong rejection. To synthesize GC-SPIO nanoparticles, the ring structures of glycyrrhizin molecules were first oxidized into aldehyde groups using sodium periodate. Then the oxidized glycyrrhizin molecules were conjugated on the amine moiety of glycol chitosan. Meanwhile, SPIO nanoparticles were synthesized by co-precipitating divalent and trivalent iron ions using ammonium hydroxide. Finally, positively charged amine groups of glycyrrhizin-chitosan (GC) conjugates were added to negatively charged SPIO nanoparticles for surface coating. The synthesis of GC-SPIO was confirmed using NMR spectroscopy and TEM images. To find the optimal condition for GC-SPIO uptake, various concentrations from 0 to 100 ug/ml GC-SPIO nanoparticles were added to MSCs. Neodymium magnet was used to improve the efficiency of GC-SPIO uptake into MSCs. Optical images of MSC spheroids and cytotoxicity test showed that GC-SPIO nanoparticles above 20 ug/ml may interfere with the metabolism of MSCs. Therefore, in vivo tests were performed with 20 ug/ml concentration. However, 20 ug/ml GC-SPIO showed blurring effects on MRI which made it difficult to monitor the amount of implanted MSC spheroids. Therefore, by taking MRI in agarose gels, it was found out that 5 ug/ml GC-SPIO nanoparticles could be clearly monitored through MRI. In addition, it was confirmed in vitro that 1 to 5 ug/ml GC-SPIO nanoparticles have HMGB1 inhibiting and magnetic guiding effects. Finally, by taking MRI in vivo, 5 ug/ml appeared to be the best candidate for clear MRI detection and effective magnetic targeting. In conclusion, 5 ug/ml GC-SPIO internalized MSC spheroids reduced inflammation, located in a specific lobe, and were clearly detected on MRI.