Cross-linking enhances deposition of human endothelial progenitor cells in the rat heart after intracoronary transplantation.

Transplantation of human endothelial progenitor cells (hEPCs) may improve vascularization and left ventricular function after myocardial infarction. The scope of this study was to explore, whether cross-linking of EPCs may enhance the deposition of cells in the rat heart after clinical-like, intracoronary transplantation. To this end, (111)In-oxinate-labeled hEPCs were infused by a minimally invasive technique into the coronary arteries of immunosuppressed Wistar rats under control conditions and after ischemia/reperfusion. In a second set of experiments hEPCs were treated with phytohemagglutinin to create small cell clusters prior to transplantation. Continous three-dimensional HiSPECT images for 1 h and after 48 h revealed that cell deposition was significantly higher when hEPCs were cross-linked. Therefore, cross-linking of hEPCs may provide a promising approach to enhance the number of trapped cells also in a clinical setting.

Dynamic observation of the three-dimensional distribution of labeled liposomes using the novel high-resolution single-photon emission computed tomography.

The aim of this study was to show that the multipinhole technique (high-resolution single-photon emission computed tomography [HiSPECT]) is suitable for dynamic imaging of both biodistribution and temporal uptake behavior of radiolabeled cationic liposomes in Balb/c-mice. HiSPECT uses multipinhole collimators adapted to a clinical SPECT scanner, together with a dedicated iterative reconstruction program. This technique provides both high spatial resolution and an improvement in sensitivity. Six male Balb/c mice received 9.8 +/- 4.0 MBq of the In 111-labeled liposomes. The measurements started directly after the injection and tomographic data were acquired in steps of 5 minutes. The regional evaluation displayed a high initial uptake of liposomes in the lungs (45.4%), which decreased to 25.1% after 30 minutes and to below 2% after 48 hours. In contrast, liver uptake increased in the first 30 minutes from 13.1 to 21.2% and remained relatively stable at 24.4% (24 hours) and 18.8% (48 hours). The data are interpreted as a slow shift of liposomes from the lungs into the liver and later to other organs such as the spleen and bladder. This study shows that the HiSPECT technique is capable of dynamically visualizing the uptake behavior of radioactively labeled liposomes in vivo with high temporal and spatial resolution.

Horizontal gene transfer from human endothelial cells to rat cardiomyocytes after intracoronary transplantation.

AIMS: Recent studies suggested that human umbilical vein endothelial cells (HUVECs) transdifferentiate into cardiomyocytes and smooth muscle cells in vitro. To test the functional relevance of this observation, we examined the transdifferentiation potential of HUVECs in vivo after intracoronary cell application in Wistar rats. METHODS AND RESULTS: SPECT measurements (single photon emission computed tomography) revealed that 18% of (111)In-labelled HUVECs infused by intracoronary delivery stably transplanted to the rat heart. For long-term tracking, HUVECs-expressing enhanced green fluorescent protein (EGFP) were infused. Two days following transplantation, HUVECs were positive for caspase-3. Within 3 days, EGFP was associated with individual cardiomyocytes. No labelling of endothelial and smooth muscle cells was observed. The total number of EGFP-labelled cardiomyocytes accounted for 58% of all initially trapped cells. These EGFP positive cells stained negatively for human mitochondrial proteins, but were positive for rat monocarboxylate transporter-1 protein (MCT-1). Furthermore, EGFP-mRNA was detected in these cells by single-cell RT-PCR (reverse transcription followed by polymerase chain reaction). After 21 days, EGFP positive cells were no longer observed. To investigate the underlying mechanism, we generated in vitro apoptotic bodies from EGFP-labelled HUVECs and found them to contain the genetic information for EGFP. Co-incubation of apoptotic bodies with neonatal rat cardiomyocytes caused cardiomyocytes to express EGFP. CONCLUSION: When transplanted into the rat heart by efficient intracoronary delivery, EGFP-expressing HUVECs cause the exclusive but transient labelling of cardiomyocytes. Our in vivo findings suggest that it is not cell fusion and/or transdifferentiation that occurs under these conditions but rather a horizontal gene transfer of the EGFP marker via apoptotic bodies from endothelial cells to cardiomyocytes.