A combination of omental flap and growth factor therapy induces arteriogenesis and increases myocardial perfusion in chronic myocardial ischemia: Evolving concept of biologic coronary artery bypass grafting

Rapid and chronological expression of angiogenetic genes is a major mechanism involved in cell sheet transplantation in a rat gastric ulcer model

Introduction

Cell sheet technology has been applied in the treatment of patients with severe cardiac failure. Although the paracrine effect of cell sheets accelerating angiogenesis is thought to be the intrinsic mechanism for improvement of cardiac function, little is known about how a cell sheet would function in the abdomen.

Methods

We used acetic acid-induced gastric ulcer rat model to elucidate the mechanisms of myoblast sheet transplantation in the abdomen. Myoblast sheet was implanted onto the serosal side of the gastric ulcer and the effect of sheet transplantation was analyzed. The maximal diameter of the ulcer and the changes in the gene expression of various growth factors in transplanted site was analyzed. The progenitor marker CD34 was also examined by immunohistochemistry.

Results

Cell sheet transplantation accelerated the ulcer healing. qPCR showed that angiogenic growth factors were significantly upregulated around the ulcer in the transplantation group. In addition, at first, HIF-1a and SDF-1 continued to increase from 3 h after transplantation to 72 h, then VEGF increased significantly after 24 h with a slight delay. An immunohistochemical analysis showed a statistically significant increase in CD34 positivity in the tissue around the ulcer in the transplantation group.

Conclusion

Myoblast sheet secreted various growth factors and cytokines immediately after transplantation onto the serosal side of artificial ulcer in the abdomen. Autonomous secretion, resulting in the time-dependent and well-orchestrated gene expression of various growth factors, plays a crucial role in the cell sheet function. Cell sheet transplantation is expected to be useful to support angiogenesis of the ischemic area in the abdominal cavity.

Bioactive Scaffolds in Stem Cell-Based Therapies for Myocardial Infarction: a Systematic Review and Meta-Analysis of Preclinical Trials

The use of bioactive scaffolds in conjunction with stem cell therapies for cardiac repair after a myocardial infarction shows significant promise for clinical translation. We performed a systematic review and meta-analysis of preclinical trials that investigated the use of bioactive scaffolds to support stem cell-aided cardiac regeneration, in comparison to stem cell treatment alone. Cochrane Library, Medline, Embase, PubMed, Scopus, Web of Science, and grey literature were searched through April 23, 2020 and 60 articles were included in the final analysis. The overall effect size observed in scaffold and stem cell-treated small animals compared to stem cell-treated controls for ejection fraction (EF) was 7.98 [95% confidence interval (CI): 6.36, 9.59] and for fractional shortening (FS) was 5.50 [95% CI: 4.35, 6.65] in small animal models. The largest improvements in EF and FS were observed when hydrogels were used (MD = 8.45 [95% CI: 6.46, 10.45] and MD = 5.76 [95% CI: 4.46, 7.05], respectively). Subgroup analysis revealed that cardiac progenitor cells had the largest effect size for FS, and was significant from pluripotent, mesenchymal and endothelial stem cell types. In large animal studies, the overall improvement of EF favoured the use of stem cell-embedded scaffolds compared to direct injection of cells (MD = 10.49 [95% CI: 6.30, 14.67]). Significant publication bias was present in the small animal trials for EF and FS. This study supports the use of bioactive scaffolds to aid in stem cell-based cardiac regeneration. Hydrogels should be further investigated in larger animal models for clinical translation.

Omentum support for cardiac regeneration in ischaemic cardiomyopathy models: a systematic scoping review

OBJECTIVES

Preclinical in vivo studies using omental tissue as a biomaterial for myocardial regeneration are promising and have not previously been collated. We aimed to evaluate the effects of the omentum as a support for bioengineered tissue therapy for cardiac regeneration in vivo. 

METHODS

A systematic scoping review was performed. Only English-language studies that used bioengineered cardio-regenerative tissue, omentum and ischaemic cardiomyopathy in vivo models were included.

RESULTS

We initially screened 1926 studies of which 17 were included in the final qualitative analysis. Among these, 11 were methodologically comparable and 6 were non-comparable. The use of the omentum improved the engraftment of bioengineered tissue by improving cell retention and reducing infarct size. Vascularization was also improved by the induction of angiogenesis in the transplanted tissue. Omentum-supported bioengineered grafts were associated with enhanced host reverse remodelling and improved haemodynamic measurements.

CONCLUSIONS

The omentum is a promising support for myocardial regenerative bioengineering in vivo. Future studies would benefit from more homogenous methodologies and reporting of outcomes to allow for direct comparison.

Effect of sustained release of basic fibroblast growth factor using biodegradable gelatin hydrogels on frozen-thawed human ovarian tissue in a xenograft model

AIM

Ovarian tissue cryopreservation before cancer treatment is the only option to preserve fertility under some circumstances. However, tissue ischemia after transplantation while awaiting angiogenesis induces dysfunctional folliculogenesis and reduces ovarian reserve and is one of the disadvantages of frozen-thawed ovarian tissue transplantation. Basic fibroblast growth factor (bFGF) is a major regulator of angiogenesis. However, bFGF rapidly loses biological activity when its free form is injected in vivo. This study investigated whether administration of active bFGF helps establish a nurturing environment for follicular survival.

METHODS

A sheet form of a sustained release drug delivery system for bFGF was developed using biodegradable acidic gelatin hydrogel (bFGF sheet). The bFGF sheets or phosphate-buffered saline sheets, as a negative control, were transplanted with frozen-thawed human ovarian tissues subcutaneously into the backs of severe combined immunodeficient mice. Neovascularization, cell proliferation, fibrosis and follicular survival of ovarian grafts were analyzed at 6 weeks after xenografting.

RESULTS

The bFGF sheets were optimized to release bFGF for at least 10 days. The transplantation of bFGF sheets with frozen-thawed ovarian tissues significantly increased human and mouse CD31-positive areas and stromal and endothelial cell proliferations. The administration of bFGF also significantly decreased the percentage of the fibrotic area in the graft, resulting in a significant increase in primordial and primary follicular density.

CONCLUSION

Local administration of a sustained release of biologically active bFGF induced neovascularization in frozen-thawed ovarian tissue grafts, which could establish the nurturing environment required for follicular survival in heterotopic xenografts.

Cell-sheet therapy with omentopexy promotes arteriogenesis and improves coronary circulation physiology in failing heart

Cell-sheet transplantation induces angiogenesis for chronic myocardial infarction (MI), though insufficient capillary maturation and paucity of arteriogenesis may limit its therapeutic effects. Omentum has been used clinically to promote revascularization and healing of ischemic tissues. We hypothesized that cell-sheet transplantation covered with an omentum-flap would effectively establish mature blood vessels and improve coronary microcirculation physiology, enhancing the therapeutic effects of cell-sheet therapy. Rats were divided into four groups after coronary ligation; skeletal myoblast cell-sheet plus omentum-flap (combined), cell-sheet only, omentum-flap only, and sham operation. At 4 weeks after the treatment, the combined group showed attenuated cardiac hypertrophy and fibrosis, and a greater amount of functionally (CD31(+)/lectin(+)) and structurally (CD31(+)/α-SMA(+)) mature blood vessels, along with myocardial upregulation of relevant genes. Synchrotron-based microangiography revealed that the combined procedure increased vascularization in resistance arterial vessels with better dilatory responses to endothelium-dependent agents. Serial (13)N-ammonia PET showed better global coronary flow reserve in the combined group, mainly attributed to improvement in the basal left ventricle. Consequently, the combined group had sustained improvements in cardiac function parameters and better functional capacity. Cell-sheet transplantation with an omentum-flap better promoted arteriogenesis and improved coronary microcirculation physiology in ischemic myocardium, leading to potent functional recovery in the failing heart.

Scaffold biomaterials for nano-pathophysiology

This review is intended to provide an overview of tissue engineering strategies using scaffold biomaterials to develop a vascularized tissue engineered construct for nano-pathophysiology. Two primary topics are discussed. The first is the biological or synthetic microenvironments that regulate cell behaviors in pathological conditions and tissue regeneration. Second is the use of scaffold biomaterials with angiogenic factors and/or cells to realize vascularized tissue engineered constructs for nano-pathophysiology. These topics are significantly overlapped in terms of three-dimensional (3-D) geometry of cells and blood vessels. Therefore, this review focuses on neovascularization of 3-D scaffold biomaterials induced by angiogenic factors and/or cells. The novel strategy of this approach in nano-pathophysiology is to utilize the vascularized tissue engineered construct as a tissue model to predict the distribution and subsequent therapeutic efficacy of a drug delivery system with different physicochemical and biological properties.

Enhanced survival of transplanted human induced pluripotent stem cell-derived cardiomyocytes by the combination of cell sheets with the pedicled omental flap technique in a porcine heart

BACKGROUND

Transplantation of cardiomyocytes that are derived from human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) shows promise in generating new functional myocardium in situ, whereas the survival and functionality of the transplanted cells are critical in considering this therapeutic impact. Cell-sheet method has been used to transplant many functional cells; however, potential ischemia might limit cell survival. The omentum, which is known to have rich vasculature, is expected to be a source of blood supply. We hypothesized that transplantation of hiPS-CM cell sheets combined with an omentum flap may deliver a large number of functional hiPS-CMs with enhanced blood supply.

METHODS AND RESULTS

Retrovirally established human iPS cells were treated with Wnt signaling molecules to induce cardiomyogenic differentiation, followed by superparamagnetic iron oxide labeling. Cell sheets were created from the magnetically labeled hiPS-CMs using temperature-responsive dishes and transplanted to porcine hearts with or without the omentum flap (n=8 each). Two months after transplantation, the survival of superparamagnetic iron oxide-labeled hiPS-CMs, assessed by MRI, was significantly greater in mini-pigs with the omentum than in those without it; histologically, vascular density in the transplanted area was significantly greater in mini-pigs with the omentum than in those without it. The transplanted tissues contained abundant cardiac troponin T-positive cells surrounded by vascular-rich structures.

CONCLUSIONS

The omentum flap enhanced the survival of hiPS-CMs after transplantation via increased angiogenesis, suggesting that this strategy is useful in clinical settings. The combination of hiPS-CMs and the omentum flap may be a promising technique for the development of tissue-engineered vascular-rich new myocardium in vivo.

Myocardial cell sheet therapy and cardiac function

Heart failure (HF) is the leading cause of death in developed countries. Regenerative medicine has the potential to drastically improve treatment for advanced HF. Stem cell-based medicine has received attention as a promising candidate therapy over the past decade; however, it has not yet realized this potential in terms of reliability. The cell sheet is an innovative technology for constructing aligned graft cells, and several cell sources have been investigated for making a feasible cell sheet. The most representative thus far is skeletal myoblast, although such cells raise the issue of arrhythmogenicity. Regenerative cardiomyocytes (CMs) derived from pluripotent stem cells (PSCs), such as embryonic stem cells or induced PSCs, are the most promising, because a myocardial cell sheet (MCS) constructed with regenerative CMs can potentially enable contraction recovery and electromechanical coupling with host CMs. The functional outcomes of experimental MCS are reduction of ventricular wall stress and paracrine effects rather than contraction recovery. Several technical obstacles still hamper the clinical application of MCSs, with graft survival the most pivotal issue. Ischemia, apoptosis, inflammation, and immune response can all cause graft cell death, and a stable blood supply to the MCS is critical for successful engraftment. Ventricular tachycardia must also be considered in any myocardial cell therapy, and multiple layering of MCS (>3 layers) is necessary to reconstruct human myocardium. Innervation is also a potential issue. The future application of myocardial cell therapy with MCS for advanced HF depends on resolving these difficulties.

Identification of a novel developmental mechanism in the generation of mesothelia

Mesothelium is the surface layer of all coelomic organs and is crucial for the generation of their vasculature. Still, our understanding of the genesis of this essential cell type is restricted to the heart where a localized exogenous population of cells, the proepicardium, migrates to and envelops the myocardium supplying mesothelial, vascular and stromal cell lineages. Currently it is not known whether this pattern of development is specific to the heart or applies broadly to other coelomic organs. Using two independent long-term lineage-tracing studies, we demonstrate that mesothelial progenitors of the intestine are intrinsic to the gut tube anlage. Furthermore, a novel chick-quail chimera model of gut morphogenesis reveals these mesothelial progenitors are broadly distributed throughout the gut primordium and are not derived from a localized and exogenous proepicardium-like source of cells. These data demonstrate an intrinsic origin of mesothelial cells to a coelomic organ and provide a novel mechanism for the generation of mesothelial cells.

Enhanced angiogenesis by multiple release of platelet-rich plasma contents and basic fibroblast growth factor from gelatin hydrogels

The objective of this study is to evaluate the angiogenic effects induced by biodegradable gelatin hydrogel granules incorporating mixed platelet-rich plasma (PRP) growth factor mixture (PGFM) and bioactive basic fibroblast growth factor (bFGF). The PRP was prepared by a double-spinning technique for isolating animal bloods, followed by treatment with different concentrations of calcium chloride (CaCl(2)) solution. The CaCl(2) solution treatment activated the platelets of PRP, allowing the release of various growth factors, such as platelet-derived growth factor (PDGF)-BB, vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-β(1), and epithelial growth factor (EGF). In the PRP treated with different CaCl(2) solutions, high amounts of representative platelet growth factor, PDGF-BB, VEGF, EGF, and TGF-β(1) were detected in the CaCl(2) concentrations of 1, 2, and 4 wt.% compared with higher or lower ones. The PRP treated was impregnated into gelatin hydrogel granules freeze-dried at 37°C for 1h, and then the percentage of PGFM desorbed from the gelatin hydrogel granules was evaluated. The percentages of PDGF-BB, VEGF, EGF, and TGF-β(1) desorbed tended to decrease with decreasing CaCl(2) concentration. Taken together, the CaCl(2) concentration to activate PRP for PGFM release was fixed at 2 wt.%. In vitro release tests demonstrated that the PGFM was released from the gelatin hydrogel granules with time. For the gelatin hydrogels incorporating PGFM and bFGF, the time profile of PDGF-BB or bFGF release was in good correspondence with that of gelatin hydrogel degradation. The gelatin hydrogel granules incorporating mixed PGFM and bFGF were prepared and intramuscularly injected to a mouse leg ischemia model to evaluate the angiogenic effects in terms of histological and laser Doppler perfusion imaging examinations. As controls, hydrogel granules incorporating bFGF, PGFM, and platelet-poor plasma were used for the angiogenic evaluation. The number of blood vessels newly formed and the percentage of anti-α-smooth muscle actin antibody-positive cells increased around ischemic sites injected with the gelatin hydrogel granules incorporating mixed PGFM and bFGF, in marked contrast to other control groups. The blood reperfusion level of ischemic tissues was enhanced by the hydrogel granules incorporating mixed PGFM and bFGF, whereas no enhancement was observed for other groups. It is concluded that the dual-release system of PGFM and bFGF from gelatin hydrogel granules shows promise as a method to enhance angiogenic effects.

A novel vascularized patch enhances cell survival and modifies ventricular remodeling in a rat myocardial infarction model

OBJECTIVE

Although stem cells hold a great therapeutic potential for injured tissues, limited survival of transplanted stem cells has hindered the clinical application of this technology. We hypothesized that an omentum-based stem cell-supporting patch could provide adequate nutrients and microenvironment to prolong cell survival. We examined this hypothesis in rats with experimental myocardial infarction.

METHODS

The omentum-based supporting patch was constructed by stitching polylactic acid-co-glycolic acid polymer seeded with mesenchymal stem cells from male Sprague-Dawley rats. Eight weeks after the experimental myocardial infarction, which was created by ligating the left coronary artery of female Sprague-Dawley rats, mesenchymal stem cells were transplanted with (n = 16) or without (n = 14) the supporting patch. After 4 weeks, transplanted mesenchymal stem cell survival, ventricular remodeling, and cardiac performance were examined.

RESULTS

Significantly more cells survived after 4 weeks in rats transplanted with mesenchymal stem cells on the supporting patch assessed by means of polymerase chain reaction detection of the Sry gene than seen in those without the supporting patch (2.61 ± 0.40 vs 1.19 ± 0.12, P < .05). Rats with myocardial infarction that received mesenchymal stem cells with the patch also had significantly improved ventricular remodeling and cardiac function than those without the patch. Wrapping infarcted myocardium with omentum alone did not change the myocardial function.

CONCLUSIONS

The omentum-based cell-supporting patch provided a favorable microenvironment for transplanted mesenchymal stem cell survival, which resulted in favorable ventricular remodeling and restoration of cardiac function in rats with experimental myocardial infarction. Further validation of the technique in human subjects could make mesenchymal stem cell transplantation a viable therapeutic option for patients with cardiac disease.

Paracrine factors released by GATA-4 overexpressed mesenchymal stem cells increase angiogenesis and cell survival

Transplanted mesenchymal stem cells (MSC) release soluble factors that contribute to cardiac repair and vascular regeneration. We hypothesized that overexpression of GATA-4 enhances the MSC secretome, thereby increasing cell survival and promoting postinfarction cardiac angiogenesis. MSCs harvested from male rat bone marrow were transduced with GATA-4 (MSC(GATA-4)) using the murine stem cell virus retroviral expression system; control cells were either nontransduced (MSC(bas)) or transduced with empty vector (MSC(Null)). Compared with these control cells, MSC(GATA-4) were shown by immunofluorescence, real-time PCR, and Western blotting to have higher expression of GATA-4. An increased expression of angiogenic factors in MSC(GATA-4) and higher MSC resistance against hypoxia were observed. Human umbilical vein endothelial cells (HUVEC) treated with MSC(GATA-4) conditioned medium exhibited increased formation of capillary-like structures and promoted migration, compared with HUVECs treated with MSC(Null) conditioned medium. MSC(GATA-4) were injected into the peri-infarct region in an acute myocardial infarction model in Sprague-Dawley rats developed by ligation of the left anterior descending coronary artery. Survival of MSC(GATA-4), determined by Sry expression, was increased at 4 days postengraftment. MSC(GATA-4)-treated animals showed significantly improved cardiac function as assessed by echocardiography. Furthermore, fluorescent microsphere and histological studies revealed increased blood flow and blood vessel density and reduced infarction size in MSC(GATA-4)-treated animals. We conclude that GATA-4 overexpression in MSCs increased both MSC survival and angiogenic potential in ischemic myocardium and may therefore represent a novel and efficient therapeutic approach for postinfarct remodeling.

Mesothelial cells vs. skeletal myoblasts for myocardial infarction

Cell transplantation for the regeneration of ischemic myocardium is limited by poor graft viability and low cell retention. Omental flaps in association with growth factors and cell sheets have recently been used to increase the vascularization of ischemic hearts. This experimental study was undertaken to evaluate the hemodynamic evolution and histological modifications of infarcted myocardium treated with mesothelial cells, and to compare the results with those of hearts treated with skeletal myoblasts. Myocardial infarction was created by surgical ligature of 2 coronary branches in 34 sheep; 6 died immediately due to ventricular fibrillation. Mesothelial cells were isolated from greater omentum, and myoblasts from skeletal muscle. After expanding the cells for 3 weeks, infarcted areas were treated with culture medium (control group), mesothelial cells, or myoblasts. After 3 months, echocardiographic studies showed significant limitation of ventricular dilatation and improved ejection fractions in both cell-treated groups compared to the controls. In the mesothelial cell group, histological studies showed significantly more angiogenesis and arteriogenesis than in the control and skeletal myoblast groups. Mesothelial cells might be useful for biological revascularization in patients with ischemic heart disease.

Quantitative analysis of myocardial perfusion in rabbits by transthoracic real-time myocardial contrast echocardiography

To evaluate the feasibility of real-time myocardial contrast echocardiography (RTMCE) by quantitative analysis of myocardial perfusion in rabbits, transthoracic RTMCE was performed in 10 healthy rabbits by using continuous infusion of SonoVue into the auricular vein. The short axis view at the papillary muscle level was obtained. The duration of the time that the contrast took to appear in right heart, left heart and myocardium was recorded. The regional myocardial signal intensity (SI) versus refilling time plots were fitted to an exponential function: y(t) =A(1-e(-beta(t-t0))) + C, where y is SI at any given time, A is the SI plateau that reflects myocardial blood volume, and beta is the slope of the refilling curve that reflects myocardial microbubble velocity. The A, beta and Axbeta values at different infusion rate of SonoVue were analyzed and the A, beta and Axbeta values in each segment in the short axis view at the papillary muscle level were compared. All the animal experiments were successful and high-quality images were obtained. The best intravenous infusion rate for SonoVue was 30 mL/h. The contrast appeared in right heart, left heart and myocardium at 7.5+/-2.2 s, 9.1+/-2.4 s and 12.2+/-1.6 s respectively. After 16.6+/-2.3s, myocardial opacification reached a steady state. The mean A, beta and Axbeta value in the short axis view at the papillary muscle level were 9.8+/-3.0 dB, 1.4+/-0.5 s(-1) and 13.5+/-3.6 dBxs(-1) respectively. A, beta and Axbeta values showed no significant differences among 6 segments. It was suggested that RTMCE was feasible for quantitative analysis of myocardial perfusion in rabbits. It provides a non-invasive method to evaluate the myocardial perfusion in rabbit disease models.

Impact of different topical negative pressure levels on myocardial microvascular blood flow

BACKGROUND

We have previously shown that a myocardial topical negative pressure (TNP) of -50 mmHg significantly increases microvascular blood flow in the underlying myocardium in normal, ischemic, and reperfused porcine myocardium. The present study was designed to elucidate the effect of different TNP levels between -50 and -150 mmHg on microvascular flow in normal and ischemic myocardium.

MATERIALS AND METHODS

Seven pigs underwent median sternotomy. The microvascular blood flow in the myocardium was recorded, before and after the application of TNP, using laser Doppler velocimetry. Analyses were performed before left anterior descending artery (LAD) occlusion (normal myocardium) and after 20 min of LAD occlusion (ischemic myocardium).

RESULTS

A TNP of -50 mmHg significantly increased microvascular blood flow in both normal (from 320.0+/-56.1 PU before TNP application to 435.7+/-65.5 PU after TNP application, P=.028) and ischemic myocardium (from 110.0+/-36.7 PU before TNP application to 194.3+/-56.2 PU after TNP application, P=.012). TNP between -75 and -150 mmHg showed no significant increase in microvascular blood flow in normal or ischemic myocardium.

CONCLUSIONS

Of pressures between -50 and -150 mmHg, a TNP of -50 mmHg seems to be the most effective negative pressure concerning significant increase in microvascular blood flow in both normal and ischemic myocardium.

A Novel Approach to Therapeutic Angiogenesis for Patients With Critical Limb Ischemia by Sustained Release of Basic Fibroblast Growth Factor Using Biodegradable Gelatin Hydrogel An Initial Report of the Phase I-IIa Study

BACKGROUND

Limb ischemia remains a challenge. To overcome shortcomings or limitations of gene therapy or cell transplantation, a sustained release system of basic fibroblast growth factor (bFGF) using biodegradable gelatin hydrogel has been developed.

METHODS AND RESULTS

A phase I-IIa study was performed, in which 7 patients had critical limb ischemia. They were intramuscularly injected with 200 microg of bFGF-incorporated gelatin hydrogel microspheres into the gastrocnemius of the ischemic limb. End-points were safety and feasibility of treatment after 4 and 24 weeks. One patient was excluded from the study for social reasons, but only after symptomatic improvements. In the evaluation of the other 6 patients, significant improvements were observed in the distance walked in 6 min (295+/-42 m vs 491+/-85 m for pretreatment vs after 24 weeks, p=0.023) and in transcutaneous oxygen pressure (53.5+/-5.2 mmHg vs 65.5+/-4.0 mmHg, p=0.03). The rest pain scale also improved (3.5+/-0.2 vs 1.0+/-0.6, p=0.022). The ankle-brachial pressure index improved at 4 weeks but not at 24 weeks. Among 5 patients who had a non-healing foot ulcer, the ulcer was completely healed in 3 patients, reduced in 1, and there was no change in 1 patient at 24 weeks. The blood levels of bFGF were undetected or within the normal level in all patients.

CONCLUSIONS

The sustained release of bFGF from gelatin hydrogel might be simple, safe, and effective to achieve therapeutic angiogenesis because it did not need genetic materials or collection of implanted cells, and because it did not have any general effects, which was supported by there being no elevation of the bFGF serum level.