Assessment of three techniques for delivering stem cells to the heart using PET and MR imaging

Abstract

Background: Stem cell therapy has a promising potential for the curing of various degenerative diseases, including congestive heart failure (CHF). In this study, we determined the efficacy of different delivery methods for stem cell administration to the heart for the treatment of CHF. Both positron emission tomography (PET) and magnetic resonance imaging (MRI) were utilized to assess the distribution of delivered stem cells.

Methods: Adipose-derived stem cells of male rats were labeled with super-paramagnetic iron oxide (SPIO) and 18 F-fluorodeoxyglucose (FDG). The left anterior descending coronary artery (LAD) of the female rats was occluded to induce acute ischemic myocardial injury. Immediately after the LAD occlusion, the double-labeled stem cells were injected into the ischemic myocardium (n = 5), left ventricle (n = 5), or tail vein (n = 4). In another group of animals (n = 3), the stem cells were injected directly into the infarct rim 1 week after the LAD occlusion. Whole-body PET images and MR images were acquired to determine biodistribution of the stem cells. After the imaging, the animals were euthanized and retention of the stem cells in the vital organs was determined by measuring the cDNA specific to the Y chromosome.

Results: PET images showed that retention of the stem cells in the ischemic myocardium was dependent on the cell delivery method. The tail vein injection resulted in the least cell retention in the heart (1.2% ± 0.6% of total injected cells). Left ventricle injection led to 3.5% ± 0.9% cell retention and direct myocardial injection resulted in the highest rate of cell retention (14% ± 4%) in the heart. In the animals treated 1 week after the LAD occlusion, rate of cell retention in the heart was only 4.5% ±1.1%, suggesting that tissue injury has a negative impact on cell homing. In addition, there was a good agreement between the results obtained through PET-MR imaging and histochemical measurements.

Conclusion: PET-MR imaging is a reliable technique for noninvasive tracking of implanted stem cells in vivo. Direct injection of stem cells into the myocardium is the most effective way for cell transplantation to the heart in heart failure models.

Figure 1

Percentage of injected dose of FDG-labeled ASCs in various organs for different methods of injection as determined from PET data. Percentage of injected dose values are presented as the mean value, with + SD error bars. Myo (1 Wk), direct myocardial injection after 1 week of induced infarction; Myo, direct myocardial injection; LV, left ventricle injection; Tail, tail vein injection. Refer to the text for information on the numbers of samples in each group.

Figure 2

Example of PET and MR coregistered images. MR image (a), PET image (b), and registered PET-MR image (c) of the heart of a rat injected with FDG- and SPIO-labeled stem cells directly in the myocardium, showing the high concentration of stem cells in the myocardium. The dark regions (indicated by arrows) in the MRI image are the SPIO-labeled stem cells, whereas the bright regions (indicated by arrows) in the PET image are FDG-labeled stem cells. Images were registered using MIPAV software using landmark registration algorithm. The PET-MR registered image was used to accurately define the region of interest for quantifying the ID% of the stem cell retention.

Figure 3

Biodistribution of labeled ASCs in a rat injected via tail vein. Maximum intensity projection of whole-body PET image (a) of a rat injected with double-labeled ASCs via tail vein (25 μg/ml SPIO and 2.3 MBq FDG). The image is reconstructed with MAP algorithm and attenuation corrected. The panel on the right (b) represents the image with the heart at the center of field of view. The arrow heads point out to the lungs (solid) and the heart (dashed). It is evident that the majority of the cells are retained in the lungs and the heart is not visible.

Figure 4

Biodistribution of labeled ASCs in a rat injected via left ventricle. Maximum intensity projection of whole-body PET image (a) from a rat injected with double-labeled ASCs via left ventricle (25 μg/ml SPIO and 1.34 MBq FDG). The image is reconstructed with MAP algorithm and attenuation corrected. The arrow heads point out to the lungs (solid) and the heart (dashed). The panel on the right (b) represents the image with the heart at the center of field of view. It is evident that a portion of the cells are retained in the myocardium, with some in the lungs.

Figure 5

Biodistribution of labeled ASCs in a rat injected via myocardium. Maximum intensity projection of whole-body PET image (a) from a rat injected with double-labeled ASCs via myocardium (25 μg/ml SPIO and 0.44 MBq FDG). The image is reconstructed with MAP algorithm and attenuation corrected. The arrow heads point out to the lungs (solid) and the heart (dashed). The panel on the right (b) represents the image with the heart at the center of field of view. It is evident that the majority of the cells are retained in the myocardium, with some in the lungs.

Figure 6

Histochemical and PCR results for tail vein injection. Microscopic pictures of histochemical assays (a); arrows indicate Prussian blue-stained SPIO in the cells. Average number of ASCs per microgram of DNA in different tissue types of female animals injected with male ASCs via the tail vein (b); each bar represents the average for n = 3 subjects and the error bars are + SD (*p < 0.01, n = 3).

Figure 7

Histochemical and PCR results for left ventricle injection. Microscopic pictures of histochemical assays (a); arrows indicate Prussian blue-stained SPIO in the cells. Average number of ASCs per microgram of DNA in different tissue types of female animals injected with male ASCs into the left ventricle (b); each bar represents the average for n = 3 subjects and the error bars are + SD (*p < 0.01, n = 3).

Figure 8

Histochemical and PCR results for myocardial injection. Microscopic pictures of histochemical assays (a); arrows indicate Prussian blue-stained SPIO in the cells; Average number of ASCs per microgram of DNA in different tissue types of female animals injected with male ASCs into the myocardium (b); each bar represents the average for n = 3 subjects and the error bars are + SD, kidney tissue (n = 1) (*p < 0.01, n = 3).