INTRODUCTION

Cellular therapy has been utilized in the repair of fibrotic areas caused by myocardial infarction (MI) and different types of cells have been tested [1]. Cellular cardiomyoplasty has been studied in respect to organ function recovery through two lines of research: cells for myogenesis and cells for cardiac angiogenesis [2-4].

For the first, smooth muscle cells, adult bone marrow stem cells, skeletal myoblasts and neonatal and fetal cardiomyocytes cells have been used. For cardiac angiogenesis, endothelial cells, which are removed from the intimal layer of arteries or veins, bone marrow stem cells and progenitor blood cells have been employed [5].

These cells were injected either individually or in combination in different types of experimental animals [6-9] and in clinical series [10,11] with ischemic [12] or dilated myocardiopathy [13].

A new option for the cellular treatment of cardiomyoplasty in experimental animals with left ventricle ejection fractions of less than 40% caused by ischemic myocardiopathy is proposed in this study.

Mesenchymal bone marrow stem cells (MSC) and skeletal myoblastic cells (SM) that were separately cultivated or in co-cultures and transplanted individually or co-transplanted were used in this work. The functional response was evaluated using bidimensional echocardiography, which is used to measure the left ventricle ejection fractions (LVEF) at two points in the follow-up. Also in vitro immunocytochemical studies and after euthanasia one month after cardiomyoplasty histopathologic specimens of the heart were analyzed.

METHOD

All experiments were performed according to the principles of experimental animal care laid down in the Brazilian law nº 6638 that regulates the norms of scientific-educative practices of animal vivisection [14].

The model utilized to cause ischemic myocardiopathy was ligature of the coronary artery and consequent myocardium infarction.

Male Wistar rats weighing between 250 and 300 grams were employed as the experimental animals. Myocardial infarction was caused under general anesthesia with the animals intubated and ventilated by respiratory apparatus (Harvard Apparatus, USA), by left lateral thoracotomy. After heart exposure, the anterior interventricular coronary artery was ligated, between the left atrium and the right ventricle outflow tract using a 7-0 polypropylene thread (Ethicon, USA).

Cell transplantation or an injection of the culture medium was achieved by median sternotomy seven days after myocardial infarction, with a single injection under the same anesthetic and ventilatory conditions.

Echocardiographic valuation

The animals were analyzed using a Sonos 5500 bidimensional echocardiographic apparatus (Hewlet Packard, USA), with S12 (5-12 mHz) sector transducers and 15L6 (7-15mHz) entrance. The left ventricle ejection fraction was measured in the longitudinal para-sternal position according to Simpson's method, with the animals under general anesthesia.

Cell culture method

Harvesting of cells was achieved by two different methods depending on the cell type.

1) Myoblastic skeletal cells.

Muscle cell maceration and cleaning

Anterior tibial muscle is removed from the animals using a laminar flow cell culture hood and is placed on a slide with culture medium and 1-% antibiotics (penicillin 100 U/mL and streptomycin 100 µg/mL). After, the blood vessels and the conjunctive tissues, the aponeurosis and fatty tissues, are removed using a magnifying glass and the fragments are placed on another slide and subsequently macerated.

Enzymatic digestion

The tissue cell specimen is digested in type IA Collagenase (Sigma, USA) and placed for 1 hour in a 5% CO2 incubator at 37° C and agitated at 10-minute intervals.

The cells are centrifuged and the cell pellet is recovered in trypsin _ 0.25% EDTA (Gibco, USA) in an incubator. Enzymatic digestion is interrupted using bovine fetal serum (Gibco, USA).

Filtration and seeding

The material is filtrated and centrifuged, the cell pellet is recovered and diluted in Dulbecco's Modified Eagle's Medium (DMEN) supplemented with 15% bovine fetal serum, 1% antibiotics and 10% IGF-I (insulin type I growth factor) and 10-7 M dexametazon. Cell counting is performed using a Neubauer camera.

The cells are cultivated in a culture medium for, on average, 14 days and kept in a 5% CO2 incubator at 37 ºC. The medium is changed two or three times per week and sub-cultures are obtained according to cellular confluence.

2) Mononuclear bone marrow cells

The cell harvesting is achieved by the puncture and aspiration technique.

Cell Collection

The animal, under general anesthesia, is placed in the lateral decubitus position with the posterior limb in flexion. Puncture of iliac crest is performed with a 5-mL syringe containing heparin (liquemine 5000 U/mL) with a 25x8 - 21G1 needle for aspiration. The collected material is processed using a density gradient, Ficoll-Hipaque (d=1.077) according to the method described by BOYUM in 1968 [15]. After 48 hours the hematopoietic line and debris floating of the culture are suctioned leaving the MSC. Counting of the mononuclear bone marrow cells is made using a Neubauer camera. The culture method is similar for all cells [16].

Co-Culture

After cellular isolation according to the previously described techniques, SM and mononuclear cells are distributed in a proportion of 2:1 and morphologic observations were made, in respect to the survival, adhesion to the substrate and confluence. After 48 hours the hematopoietic line and debris floating on the culture are suctioned from the flasks leaving only the SM, the MSC and fibroblasts. The cells are cultivated according to the previously described method [17].

Experimental Group

A total of 72 rats were included in this study and were divided into four groups according to the culture medium or the injected cells. The 22 rats of the control group were injected with the culture medium alone. The MSC group consisted of 17 rats, in which 2.5 x 106 cells were injected, the SM cell group had 16 rats, in which 5 x 106 cells were injected and the co-culture cell group of 17 rats were injected with 7.5x 106 cells.

Immunocytochemical and histopathologic studies

During the in vitro culture the cells are marked with anti-vimentin to confirm the presence of MSC cells and with anti-desmin for muscle cells and in the specimens the cells are identified with the previously mentioned markers and increased with fast anti-myosin which is a specific marker for SM.

In the histopathologic studies after euthanasia of the animals (one month after the procedure) the specimens are stained using Gomori's trichrome and the results are interpreted by optic microscopy.

Statistical analysis

The four groups were compared both together and individually, in respect to the LVEF one week after MI and one month after the cell injection. The ANOVA test, student t-test for paired values and Fisher exact test were utilized and statistical differences were considered significant when p<0.05.

RESULTS

Ventricular function analysis

Left ventricle ejection fraction

When comparing the mean LVEF of the groups in the control echocardiograms, no statistical differences were evidenced (p=0.276).

In echocardiographic evaluations one month after the cell injections, significant statistical differences were confirmed between the mean ejection fractions of different groups (p=0.001). These differences were seen between the Control Group and the SM Group (p=0.037), between the Control Group and in the Co-culture Group (p<0.001) and between the MSC Group and the Co-culture Group (p=0.025). The differences between the Control Group and the MSC Group (p=0.372), between the SM Group and the MSC Group (p=0.263) and the SM Group and the Co-culture Group (p=0.267) were not considered statistically significant.

When the measurements between the first and second echocardiograms were compared within each group, significant differences were verified in the Control (p=0.005) and co-culture Groups (p=0.006). Significant differences were not found in the MSC (0.65) and SM (0.09) Groups.

The results obtained in respect to the ejection fractions are showed in the Tables 1, 2 and Figure 1.



Immunocytochemical Study

In the in vitro immunocytochemical study the MSC were identified by staining using anti-vimentin and the muscle cells using anti-desmin stain.

In the evaluation of specimens one month after transplantation, muscle cells were identified with anti-desmin stain and SM with fast anti-myosin stain.

Histopathologic Study

In the interpretation of the sections stained with Gomori trichrome, muscle tissue was identified in the group in which these cells were injected. In the group in which MSC were injected, only angiogenesis was identified in the region of MI. In the co-culture group both angiogenesis and myogenesis were verified in the fibrotic area of the left ventricle (Fig. 2).



DISCUSSION

Cardiac insufficiency is determined, among other causes, by ischemic myocardiopathy [18]. The therapeutic use of percutaneous angioplasty or of coronary artery bypass grafting surgery employing vascular grafts has been adopted to relieve symptoms or to improve the offer of nutrients to the ischemic area but this does not, however, definitively regenerating the injured cardiomyocytes which are responsible for the affected heart contractile function [19].

Heart transplantation has been, until now, the only surgical treatment that treats the cause and not the effect of the injury to the cardiac cells, as the organ is replaced. However, this is restricted by the small number of donors and the difficult postoperative follow-up [20].

With the knowledge of molecular and cellular biology, cell therapy has been used in different diseases that, until now, were incurable and intractable [21]. The development of cell therapy for heart disease started in the 1990s with the experimental utilization of fetal cardiomyocytes evolving to the use of SM and MSC [22,23].

Recovery of the supply of nutrients and metabolic substances through angiogenesis and of muscle mass through myogenesis has been tried. At the beginning of 2000 its utilization in clinical series was started and in 2001 MENASCHÉ et al. [10] described the utilization of SM as an option for heart contractile function recovery.

A study developed in PUCPR was based on the idea of trying to promote synergism among cells during culture and to offer two different cells in the regeneration of myocardial infarction scaring with the aim of developing new vessels for perfusion and also muscle mass. With this, the study aimed at reducing the high mortality of cells injected in an area with low nutrients, as has been described in the literature [1].

Thus, MSC and SM are utilized for angiogenesis and myogenesis respectively.

The in vitro immunocytochemical findings and results from tests in heart specimens obtained one month after transplantation, confirmed the presence of both isolated and co-culture cells cultivated in a laboratory.

In the histopathologic studies also performed in this period, new vessels were found in the group in which MSC had been injected, muscle cells were found in the SM group and angiogenesis and myogenesis were evidenced in the group in which the two co-cultivated cells were transplanted.

In the evaluation of the LVEF, statistical differences were not observed when comparing control echocardiograms between the four different groups.

Statistical differences were identified among the groups in the evaluation one month after transplantation: between the Control and SM Groups, between the Control and the Co-culture Groups and between the MSC and Co-culture Groups which suggests that in the group transplanted with isolated muscle cells and in the Co-culture Group improvement in the cardiac function occurs.

The comparison between the two evaluations gave significantly worse performance in the Control Group and significantly better performance in the Co-culture Group. In the MSC and SM Groups no significant difference was identified, although the ejection fraction increased in the latter group.

CONCLUSION

The histopathologic, immunocytochemical and echocardiographic findings demonstrated that:

The left ventricle ejection fraction improved only in the group in which isolated muscle cells were implanted or in the Co-culture Group and this latter group showed the most significant recovery compared to the other groups which were utilized in this study.

During co-cultivation, two cells, TMC and SM, were present, that the different types of cells were found separately or together according to the injected cells and that in the MSC Group only new vessels were found, in the SM Group only muscle cells were identified and but in the Co-culture Group both angiogenesis and myogenesis were verified.

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