Micrometer-sized iron oxide particle labeling of mesenchymal stem cells for magnetic resonance imaging-based monitoring of cartilage tissue engineering

PURPOSE

To examine mesenchymal stem cell (MSC) labeling with micrometer-sized iron oxide particles (MPIOs) for magnetic resonance imaging (MRI)-based tracking and its application to monitoring articular cartilage regeneration.

METHODS

Rabbit MSCs were labeled using commercial MPIOs. In vitro MRI was performed with gradient echo (GRE) and spin echo (SE) sequences at 3T and quantitatively characterized using line profile and region of interest analysis. Ex vivo MRI of hydrogel-encapsulated labeled MSCs implanted within a bovine knee was performed with spoiled GRE (SPGR) and T(1ρ) sequences. Fluorescence microscopy, labeling efficiency, and chondrogenesis of MPIO-labeled cells were also examined.

RESULTS

MPIO labeling results in efficient contrast uptake and signal loss that can be visualized and quantitatively characterized via MRI. SPGR imaging of implanted cells results in ex vivo detection within native tissue, and T(1ρ) imaging is unaffected by the presence of labeled cells immediately following implantation. MPIO labeling does not affect quantitative glycosaminoglycan production during chondrogenesis, but iron aggregation hinders extracellular matrix visualization. This aggregation may result from excess unincorporated particles following labeling and is an issue that necessitates further investigation.

CONCLUSION

This study demonstrates the promise of MPIO labeling for monitoring cartilage regeneration and highlights its potential in the development of cell-based tissue engineering strategies.

Magnetic resonance imaging of iron oxide labelled stem cells: applications to tissue engineering based regeneration of the intervertebral disc

Minimally-invasive monitoring of regeneration in diseased tissue is an important aspect of stem cell therapy. Magnetic resonance imaging (MRI) based tracking of cells labelled with ferumoxides has the potential for non-invasive in vivo detection and longitudinal assessment of implanted cells. Cells labelled with ferumoxides appear as hypointense regions on MR images and thus can be distinguished from the surroundings. Application of this methodology to intervertebral disc degeneration (IVD), and detection of labelled cells implanted into the disc for tissue regeneration was examined. Mesenchymal stem cells labelled with a ferumoxide contrast agent were imaged in vitro to quantitatively characterize the signal intensity loss using MRI relaxation parameters (T1, T2, and T2*). To determine whether labelled cells could be detected within scaffolds suitable for implantation, labelled cells were seeded within both natural and synthetic polymers and imaged using MRI. Labelled cells were loaded within poly(ethylene glycol) hydrogels and imaged in vitro using both MRI and confocal microscopy. Labelled cells were also loaded into fibrin gels, and detected ex vivo within rat IVDs using MRI. Lastly, the effect of ferumoxide labelling on cell viability was investigated. Quantitatively, labelled cells demonstrate the greatest signal intensity loss and contrast on T2*-weighted images. Labelled cells can be detected in both synthetic and natural polymers, and can be distinguished from the native tissue environment of the rat IVD. Finally, labelling does not significantly impair cell viability. Consequently, this technique shows promise as a potential method for in vivo longitudinal tracking of stem cell based regeneration of the IVD.