In Vivo Micro-CT Imaging of Human Mesenchymal Stem Cells Labeled with Gold-Poly-l-Lysine Nanocomplexes

Abstract

Developing in vivo cell tracking is an important prerequisite for further development of cell-based therapy. So far, few computed tomography (CT) cell tracking studies have been described due to its notoriously low sensitivity and lack of efficient labeling protocols. We present a simple method to render human mesenchymal stem cells (hMSCs) sufficiently radiopaque by complexing 40 nm citrate-stabilized gold nanoparticles (AuNPs) with poly-L-lysine (PLL) and rhodamine B isothiocyanate (RITC). AuNP-PLL-RITC labeling did not affect cellular viability, proliferation, or downstream cell differentiation into adipocytes and osteocytes. Labeled hMSCs could be clearly visualized in vitro and in vivo with a micro-CT scanner, with a detection limit of approximately 2×104 cells/μl in vivo. Calculated HU values were 2.27 /pg of intracellular Au as measured with inductively coupled plasma mass spectrophotometry (ICP-MS), and were linear over a wide range of cell concentrations. This linear CT attenuation was observed for both naked AuNPs and those that were taken up by hMSCs, indicating that the number of labeled cells can be quantified similar to the use of radioactive or fluorine tracers. This approach for CT cell tracking may find applications in CT image-guided interventions and fluoroscopic procedures commonly used for the injection of cellular therapeutics.

CT/Bioluminescence Dual‐Modal Imaging Tracking of Mesenchymal Stem Cells in Pulmonary Fibrosis

“…Gold nanoparticles (AuNPs), due to their significant X‐ray attenuation coefficient, excellent biocompatibility, as well as facile and controllable preparation and surface modification, have been explored extensively as CT tracers for MSCs tracking . However, the effective dose of the CT nanotracer in tracking of stem cells is very high (in the millimolar range), compared to that of the MRI nanotracer (in micromolar range), therefore a large amount of CT nanotracer in the cells is needed to gain sufficient cellular CT contrast .…”

“…However, the effective dose of the CT nanotracer in tracking of stem cells is very high (in the millimolar range), compared to that of the MRI nanotracer (in micromolar range), therefore a large amount of CT nanotracer in the cells is needed to gain sufficient cellular CT contrast . By coating of an overlayer of poly‐l‐lysine onto the surface of AuNPs, Kim et al improved the internalization of AuNPs into MSCs. In another approach, Oh et al covalently conjugated cell penetrating peptides on the AuNPs surface.…”

Cell tracking using gold nanoparticles and computed tomography imaging

“…Top: Intracellular uptake of AuNP complexed with poly‐l‐lysine and rhodamine B isothiocyanate (RITC) in human mesenchymal stem cells (MSCs). Shown are (a) bright field, (b) fluorescence (blue = DAPI, red = RITC), and (c) TEM images . Center: (a) SEM image of a labeled C6 cancer cell, and b) zoom in of a cluster of AuNPs inside the cell .…”

“…MRI of nanoparticle‐labeled cells has been broadly studied over the past decade . More recently, the concept of CT imaging of nanoparticle‐labeled cells has been introduced, and is being increasingly used in research …”

“…The novel concept of labeling cells with AuNPs, followed by in vivo injection and CT imaging, enables noninvasive tracking and visualizing of the therapeutic cells as they migrate and accumulate at sites of injury or malignancy (Figure ). This concept was first introduced by Astolfo et al several years ago, and recently several other groups have applied this concept for tracking cells using different particle coatings, labeling techniques and in vivo cell tracking applications …”