Cell Therapy
Cardiac accumulation of bone marrow mononuclear progenitor cells after intracoronary or intravenous injection in pigs subjected to acute myocardial infarction with subsequent reperfusion

https://doi.org/10.1016/j.carrev.2006.09.001Get rights and content

Abstract

Objective

The purpose of the present study was to compare the efficacy of intracoronary and intravenous injection of autologous progenitor cells for homing to the acutely infarcted but reperfused myocardium in pigs.

Methods

Myocardial infarction was induced in 11 anesthetized pigs by 60-min balloon inflation in the mid LAD. After balloon deflation, reperfusion was verified and autologous CD31+ progenitor cells, or bone marrow mononuclear cells, labeled with PKH67, were injected either intracoronarily (n=6) or intravenously (n=3). By autopsy, 4–5 days after induction of infarction, tissue from the heart and other organs was obtained for fluorescence microscopy.

Results

In the heart, PKH+ cells were detected throughout the reperfused infarcted myocardium, and the number of PKH+ cells was significantly higher after intracoronary than after intravenous injection (3.2±0.55 vs. 0.33±0.17 cells/high-power field/106 cells injected, P=.01). Few PKH+ cells were detected in the spleen, lung, mesenteric lymph node, and bone marrow. In an additional animal with a coil placed in the mid LAD, progenitor cells were not detected in the infarcted myocardium or in the normal myocardium.

Conclusion

Autologous mononuclear and CD31+ cells from bone marrow accumulated in the infarcted myocardium when injected intracoronarily or intravenously after established reperfusion, and the accumulation of cells was significantly greater after intracoronary injection than after intravenous injection. Accumulation of PKH+ cells did not appear in the normal myocardium or in the nonreperfused infarcted myocardium. PKH+ cells were detected in spleen, lung, and bone marrow but to a lesser degree than in the infarcted myocardium.

Introduction

Stem cells have the capability to proliferate and differentiate into various cell types [1], [2]. Furthermore, adult stem cells from the bone marrow may act as precursors for specialized tissue development and take part in myocardial regeneration [3], [4], [5], [6], [7]. These regenerative properties of stem cells have been found advantageous in the attempt to restore myocardial function in patients with acute myocardial infarction (AMI), and results from clinical trials have already been published [8], [9], [10], [11]. Intracoronary autologous administration of bone marrow mononuclear cells (BMMNC), endothelial progenitor cells (EPC), and mesenchymal stem cells (MSC) has been well tolerated [4], [9], [11]. Some trials have revealed improved global left ventricular function [8], [9], [11], [12], whereas two studies failed to demonstrate a similar improvement in function [13], [14]. However, it appears proven that administration of adult stem cells in the acute phase of myocardial infarction is feasible and safe, although the optimal cell type and the best way to deliver cells to the infarcted myocardium are not established. To our best knowledge, homing of progenitor cells to the infarcted myocardium after intravenous injection has only been compared in two studies [15], [16]. In one of these studies, MSC were used and their homing to the infarcted myocardium seemed to be limited by lung entrapment after intravenous injection, probably due to the large size of MSC [15]. In the other study [16], the homing efficacy to the infarcted myocardium might have been limited by subsiding homing signals from the infarcted tissue since the cells were administered 6 days after AMI.

Only when the infarcted myocardium is reperfused do circulating progenitor cells have direct access to the infarcted tissue. Furthermore, circulating cells may be more heavily exposed to chemotactic signaling substances released from the infarcted myocardium when reperfused. In a person with AMI, early revascularization procedure with percutaneous coronary intervention (PCI) is the preferred treatment to salvage the myocardium, and in the present study, we used pigs because revascularization of the infarcted myocardial tissue is possible and verifiable in this species.

Opposite to the situation in mice and man, purification of porcine bone-marrow-derived progenitor cells proved to be difficult due to lack of appropriate cell surface markers. However, the pig CD31+ cell population from the bone marrow has prominent colony-forming ability, indicating progenitor cell properties [17], [18]. Thus, either mononuclear progenitor cells or CD31+ cells were isolated from the bone marrow and used in the present study.

Section snippets

Methods

Animals used in the present study were maintained and housed in accordance with the conditions set by the Norwegian Council of Animal Research. The investigation conformed to the Guide for the Care and Use of Laboratory Animals published by the U.S. National Institutes of Health (NIH Publication No. 85-23, revised 1996). Fourteen domestic pigs of either sex, weighing 21–38 kg, entered the study. Three animals were excluded from the study: two due to technical problems and one due to intractable

Results

Fig. 1 shows the significantly higher number of colonies formed along the hematopoietic lineages from the CD31+ population compared with the colonies formed by BMMNC. This finding is an indication of enrichment of progenitors within the CD31+ fraction, with significantly greater proliferation capacity than the total BMMNC. In fact, the CD31+ cells and the BMMNC from the present study formed colonies in methylcellulose with the same characteristics as the colonies derived from nonrefined human

Discussion

In the present study, we demonstrate that CD31+ and BMMNC “home” to the infarcted myocardium in the pig heart when the vascular supply to the infarcted region is intact. No cells were detected in the normal neighboring tissue and were accordingly unavailable for potential migration into infarcted tissue, as also verified in an additional experiment in which reperfusion was not established. These results point at the necessity of revascularization of infarcted tissue to facilitate “homing” of

Acknowledgments

We thank Marianne Nesheim, Lise Tollefsen, and Tove Noren for their skilled technical assistance.

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    This work was supported by Anders Jahre's Fund for the promotion of science and Rakel and Otto Kr. Bruun's legacy.

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