Labeling human embryonic stem-cell-derived cardiomyocytes for tracking with MR imaging.

BACKGROUND: Human embryonic stem cells (hESC) can generate cardiomyocytes (CM), which offer promising treatments for cardiomyopathies in children. However, challenges for clinical translation result from loss of transplanted cell from target sites and high cell death. An imaging technique that noninvasively and repetitively monitors transplanted hESC-CM could guide improvements in transplantation techniques and advance therapies. OBJECTIVE: To develop a clinically applicable labeling technique for hESC-CM with FDA-approved superparamagnetic iron oxide nanoparticles (SPIO) by examining labeling before and after CM differentiation. MATERIALS AND METHODS: Triplicates of hESC were labeled by simple incubation with 50 µg/ml of ferumoxides before or after differentiation into CM, then imaged on a 7T MR scanner using a T2-weighted multi-echo spin-echo sequence. Viability, iron uptake and T2-relaxation times were compared between groups using t-tests. RESULTS: hESC-CM labeled before differentiation demonstrated significant MR effects, iron uptake and preserved function. hESC-CM labeled after differentiation showed no significant iron uptake or change in MR signal (P < 0.05). Morphology, differentiation and viability were consistent between experimental groups. CONCLUSION: hESC-CM should be labeled prior to CM differentiation to achieve a significant MR signal. This technique permits monitoring delivery and engraftment of hESC-CM for potential advancements of stem cell-based therapies in the reconstitution of damaged myocardium.

MR signal characteristics of viable and apoptotic human mesenchymal stem cells in matrix-associated stem cell implants for treatment of osteoarthritis.

OBJECTIVE: To compare magnetic resonance (MR) signal characteristics of contrast agent-labeled apoptotic and viable human mesenchymal stem cells (hMSCs) in matrix-associated stem cell implants. METHODS: hMSCs were labeled with Food and Drug Administration-approved ferumoxides nanoparticles. One group (A) remained untreated whereas a second group (B) underwent mitomycin C-induced apoptosis induction. Viability of group A and apoptosis of group B was confirmed by caspase-assays and terminal dUTP nick-end labeling (TUNEL) stains. Labeled viable hMSCs, unlabeled viable hMSCs, labeled apoptotic hMSCs, and unlabeled apoptotic hMSCs (n = 7 samples each) in an agarose scaffold were implanted into cartilage defects of porcine patellae specimens and underwent MR imaging at 7 T, using T1-weighted spin-echo sequences, T2-weighted spin-echo sequences, and T2*-weighted gradient-echo sequences. Signal-to-noise ratios (SNR) of the implants were calculated and compared between different experimental groups using linear mixed regression models. RESULTS: Ferumoxides-labeled hMSCs provided a strong negative T2 and T2*-enhancement. Corresponding SNR data of labeled hMSCs were significantly lower compared with unlabeled controls (P < 0.05). Apoptosis induction resulted in a significant signal decline of ferumoxides-labeled hMSC transplants on short echo time T2-weighted spinecho sequences. SNR data of labeled apoptotic hMSCs were significantly lower compared with labeled viable hMSCs (P < 0.05). CONCLUSION: Apoptosis of transplanted ferumoxides-labeled stem cells in cartilage defects can be visualized noninvasively by a significant signal decline on T2-weighted MR images. The described MR signal characteristics may serve as a noninvasive outcome measure for the assessment of matrix-associated stem cell implants in clinical practice. Additional studies are needed to further enhance the observed differences between viable and apoptotic cells, for example, by further optimizing the applied MR pulse sequence parameters or intracellular contrast agent concentration.

A head holder for magnetic resonance imaging that allows the stereotaxic alignment of spontaneously occurring intracranial mouse tumors.

The use of stereotaxic neurosurgery in rodent models of human disease requires the alignment of central nervous system (CNS) structures that can be identified and surgically approached with great accuracy. Current technologies make possible development of mouse lines with enhanced predispositions for the development of various diseases including tumors. When such tumors arise in the brain their location is unpredictable. Obtaining a biopsy or stereotaxically delivering local therapy requires that the site of such tumors be known with great precision. We devised a method to correlate images of mouse brain tumors acquired by magnetic resonance imaging (MRI) with stereotaxic coordinates that can be used for obtaining biopsies or administering local therapy. We constructed a head holder containing a pair of tubes filled with a substance that could be imaged by MR and which were separated by varying distances. This allowed the precise localization of the tumor in all three dimensions. The strategy we employed is adaptable to other imaging modalities and to other body sites.