Noninvasive quantification and optimization of acute cell retention by in vivo positron emission tomography after intramyocardial cardiac-derived stem cell delivery

Abstract

Objectives: The aim of this study was to quantify acute myocardial retention of cardiac-derived stem cells (CDCs) and evaluate different delivery methods with positron emission tomography (PET).

Background: Success of stem cell transplantation for cardiac regeneration is partially limited by low retention/engraftment of the delivered cells. A clinically applicable method for accurate quantification of cell retention would enable optimization of cell delivery.

Methods: The CDCs were derived from syngeneic, male Wistar Kyoto (WK) rats labeled with [(18)F]-fluoro-deoxy-glucose ((18)FDG) and injected intramyocardially into the ischemic region of female WK rats after permanent left coronary artery ligation. The effects of fibrin glue (FG), bradycardia (adenosine), and cardiac arrest were examined. Imaging with (18)FDG PET was performed for quantification of cell retention. Quantitative polymerase chain reaction (PCR) for the male-specific SRY gene was performed to validate the PET results.

Results: Myocardial retention of cells suspended in phosphate-buffered saline 1 h after delivery was 17.6 +/- 11.5% by PCR and 17.8 +/- 7.3% by PET. When CDCs were injected immediately after induction of cardiac arrest, retention was increased to 75.6 +/- 18.6%. Adenosine slowed the ventricular rate and doubled CDC retention (35.4 +/- 5.3%). A similar increase in CDC retention was observed after epicardial application of FG at the injection site (37.5 +/- 8.2%). The PCR revealed a significant increase in 3-week cell engraftment in the FG animals (22.1 +/- 18.6% and 5.3 +/- 3.1%, for FG and phosphate-buffered saline, respectively).

Conclusions: In vivo PET permits accurate measurement of CDC retention early after intramyocardial delivery. Sealing injection sites with FG or lowering ventricular rate by adenosine might be clinically translatable methods for improving stem cell engraftment in a beating heart.

Figure 1. Detection of ¹⁸FDG labeled cells injected in the myocardium by micro-PET

A: transverse, B:coronal, C: sagittal image orientation. In a different experiment, fusion of CT and micro-PET images provides more detailed anatomical information. D: transverse, E:coronal, F: sagittal image orientation

Figure 2. Retention of intramyocardially injected cells at 60 min after cell injection, in the different experimental groups

P values correspond to comparisons between the cells in PBS and the intervention groups. Values are reported as mean±SD.

Figure 3. Retention of intramyocardially injected cells 60 min after cell injection measured by in vivo PET and Real Time quantitative PCR

Cells in PBS group-values are reported as mean±SD.

Figure 4. Comparison of engraftment at 3 weeks between the cells in PBS and FG groups

Assessment by Real Time quantitative PCR-values are reported as mean±SD.

Figure 5. Immunocytochemistry of frozen cardiac sections at 3 weeks after cell injection

The presence of eGFP+ cells (green) at the infarct border zone (red: Troponin I), in an animal of the FG group, was revealed.

Figure 6. % change in Fractional Area Change (FAC) between day 2 and 21 post-MI, in animals treated with cells in PBS, cells and FG, PBS only and FG only

One-way ANOVA, P=0.002. P values on the figure correspond to post-hoc comparisons between the PBS only and the intervention groups. Values are reported as mean±SEM.