Transplanted Endothelial Progenitor Cells Augment the Survival Areas of Rat Dorsal Flaps

Tissue Engineering of the Microvasculature

The ability to generate new microvessels in desired numbers and at desired locations has been a long-sought goal in vascular medicine, engineering, and biology. Historically, the need to revascularize ischemic tissues nonsurgically (so-called therapeutic vascularization) served as the main driving force for the development of new methods of vascular growth. More recently, vascularization of engineered tissues and the generation of vascularized microphysiological systems have provided additional targets for these methods, and have required adaptation of therapeutic vascularization to biomaterial scaffolds and to microscale devices. Three complementary strategies have been investigated to engineer microvasculature: angiogenesis (the sprouting of existing vessels), vasculogenesis (the coalescence of adult or progenitor cells into vessels), and microfluidics (the vascularization of scaffolds that possess the open geometry of microvascular networks). Over the past several decades, vascularization techniques have grown tremendously in sophistication, from the crude implantation of arteries into myocardial tunnels by Vineberg in the 1940s, to the current use of micropatterning techniques to control the exact shape and placement of vessels within a scaffold. This review provides a broad historical view of methods to engineer the microvasculature, and offers a common framework for organizing and analyzing the numerous studies in this area of tissue engineering and regenerative medicine. © 2019 American Physiological Society. Compr Physiol 9:1155-1212, 2019.

Allogeneic Adipose-Derived Stem Cells Protect Fat Grafts at the Early Stage and Improve Long-Term Retention in Immunocompetent Rats

BACKGROUND

Syngeneic adipose-derived stem cells (ASCs) promote the survival of fat grafts. But it is unclear whether allogeneic ASCs have a similar protective effect. In this study, we investigated the protective effect of allogeneic ASCs in a fat graft model of immunocompetent rats.

METHODS

Syngeneic and allogeneic ASCs were derived from Lewis (LEW) and Norway-Brown rats, respectively. Fifty-four LEW rats were divided into three groups. Each LEW rat was injected subcutaneously at two paravertebral spots with adipose granules premixed with DMEM (AFT group), syngeneic ASCs (SYNG group), or allogeneic ASCs (ALLG group). Fat grafts were harvested at 7 and 14 days to examine apoptosis rates and immunochemistry staining was performed for Perilipin A and CD34. At 3 months, fat graft volume retentions were measured. The proportion of regulatory T (Treg) cells and the ratio of CD4/CD8 cells in blood were analyzed at 7 days.

RESULTS

Expression of Perilipin A and CD34 was higher in the ALLG group than the AFT group at 14 days (P < 0.05). The apoptosis rate in the ALLG group decreased in comparison with the AFT group at 7 and 14 days (P < 0.05). At 3 months, allogeneic ASCs increased fat graft volume retentions (P < 0.05). No difference was found in the proportion of Treg cells and CD4/CD8 cells ratio between groups. There were no statistically significant difference between ALLG and SYNG groups at all time points (P > 0.05).

CONCLUSIONS

Allogeneic ASCs protected fat grafts at the early stage and improved long-term volume retention in the fat graft model of immunocompetent rats with no or little obvious immune rejection.

Pretreatment of endothelial progenitor cells with osteopontin enhances cell therapy for peripheral vascular disease

Tissue necrosis resulting from critical limb ischemia (CLI) leads to amputation in a significant number of patients. Autologous cell therapy using angiogenic cells such as endothelial progenitor cells (EPCs) holds promise as a treatment for CLI but a limitation of this treatment is that the underlying disease etiology that resulted in CLI may also contribute to dysfunction of the therapeutic EPCs. This study aimed to elucidate the mechanism of EPC dysfunction using diabetes mellitus as a model and to determine whether correction of this defect in dysfunctional EPCs ex vivo would improve the outcome after cell transplantation in the murine hind limb ischemia model. EPC dysfunction was confirmed in a homogenous population of patients with type 1 diabetes mellitus and a microarray study was preformed to identify dysregulated genes. Notably, the secreted proangiogenic protein osteopontin (OPN) was significantly downregulated in diabetic EPCs. Furthermore, OPN-deficient mice showed impaired recovery following hind limb ischemia, suggesting a critical role for OPN in postnatal neovascularization. EPCs isolated from OPN KO mice showed decreased ability to adhere to endothelial cells as well as impaired angiogenic potential. However, this dysfunction was reversed upon exposure to recombinant OPN, suggesting that OPN may act in an autocrine manner on EPCs. Indeed, exposure of OPN knockout (KO) EPCs to OPN was sufficient to induce the secretion of angiogenic proteins (IL-6, TGF-α, and FGF-α). We also demonstrated that vascular regeneration following hind limb ischemia in OPN KO mice was significantly improved upon injection of EPCs preexposed to OPN. We concluded that OPN acts in an autocrine manner on EPCs to induce the secretion of angiogenic proteins, thereby playing a critical role in EPC-mediated neovascularization. Modification of cells by exposure to OPN may improve the efficacy of autologous EPC transplantation via the enhanced secretion of angiogenic proteins.

Endothelial progenitor cells and their potential clinical implication in cardiovascular disorders

Risk factors associated with cardiovascular diseases reduce the availability of endothelial progenitor cells (EPC) by affecting their mobilization and integration into injured vascular sites. The existence of a bone marrow reservoir of EPC has attracted interest, especially as target for therapeutic intervention in different pathological settings. Among the cardiovascular risk factors, hypertension has been shown to be a strongest predictor of EPC migratory impairment. However, at present, data concerning EPC biology are still limited. In this article we provide an overview of data relevant to their potential clinical implications in cardiovascular disorders. In addition, the recent advances in understanding the role of EPC in the pathophysiology of hypertension are discussed.

Endothelial progenitor cells for the treatment of diabetic vasculopathy: panacea or Pandora's box?

The discovery of endothelial progenitor cell (EPC) a decade ago has refuted the previous belief that vasculogenesis only occurs during embryogenesis. The reduced circulating concentration of EPCs is a surrogate marker of endothelial function and has been implicated in the pathogenesis of many vascular diseases. To date, the therapeutic benefit of neovascularization in ischaemic conditions in a non-diabetic setting has been demonstrated. This article aims to review the biology of EPCs in the diabetic setting with special emphasis on the effects of cardiovascular risk factor modification on EPC phenotype and methods to reverse or augment EPC dysfunction. The potential of the use of EPCs in the treatment of the diabetic vascular dysfunction will also be discussed.

Acute myocardial infarction in swine rapidly and selectively releases highly proliferative endothelial colony forming cells (ECFCs) into circulation

We have recently identified endothelial colony forming cells (ECFCs) in human blood and blood vessels, and ECFC are elevated in patients with coronary artery disease. Because pigs are a favored model for studying myocardial ischemia, we questioned whether ECFCs also exist in swine and whether myocardial ischemia would alter the number of ECFC in circulation. ECFCs were present in circulating blood and aortic endothelium of healthy pigs. In pigs with an acute myocardial infarction (AMI) (n = 9), the number of circulating ECFC was markedly increased compared to sham control pigs (15 +/- 6 vs. 1 +/- 1 colonies/100 cc blood, p < 0.05). Moreover, the percentage of circulating high proliferative potential ECFCs (HPP-ECFCs) was significantly increased following AMI induction compared to sham control (38.4 +/- 5.8% vs. 0.4 +/- 0.4%, p < 0.05) and to baseline (38.4 +/- 5.8% vs. 2.4 +/- 2.4%, p < 0.05) blood samples. This is the first study to report that ECFCs are present in blood and aorta in healthy pigs and that the number and distribution of circulating ECFCs is altered following AMI. Because circulating ECFC are also altered in human subjects with severe coronary artery disease, the pig model of AMI may be an excellent preclinical model to test the role of ECFC in the pathophysiology of AMI.

Mesenchymal stem cells transduced by vascular endothelial growth factor gene for ischemic random skin flaps

BACKGROUND

Vascular endothelial growth factor (VEGF) plays an important role in inducing angiogenesis. Mesenchymal stem cells may have the potential for differentiation into several types of cells, including vascular endothelial cells. In this study, the authors explored the feasibility of applying mesenchymal stem cells transduced by the VEGF gene to the treatment of ischemic random skin flaps.

METHODS

Mesenchymal stem cells were isolated from Sprague-Dawley rat bone marrow and cultured in vitro. Plasmid pcDNA3.1(-)/VEGF165 containing the VEGF gene was transduced into the mesenchymal stem cells by liposome. The mesenchymal stem cells were stained with chloromethyl-1-1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanineperchlorate before the transplantation. Thirty rats were randomized into three groups. Groups A, B, and C were injected with mesenchymal stem cells transduced with pcDNA3.1(-)/VEGF165 plasmid, mesenchymal stem cells, and medium only, respectively. On the fourth day after injection, random dorsal skin flaps measuring 9 x 2 cm were elevated. The survival, neovascularization, and blood flow recovery of the flaps were detected.

RESULTS

VEGF-transduced mesenchymal stem cells expressed VEGF highly in vitro and in vivo. Transplanted mesenchymal stem cells survived and incorporated into the capillary networks in the ischemic rat flaps. The viability measurements showed an increased percentage flap survival in group A (83.1 +/- 2.6 percent) as compared with either group B (66.4 +/- 6.1 percent) or group C (51.5 +/- 7.5 percent) (p < 0.01). The capillary density and the blood perfusion of the flaps in the experimental group were significantly higher than those in the other two groups (p < 0.01).

CONCLUSION

VEGF-transduced mesenchymal stem cells can increase ischemic flap neovascularization and augment the surviving areas.

Influence of vascularized transplant bed on fat grafting

Recent advances in regenerative medicine have opened up the option of materials used for transplantation. However, only a few studies have examined the take of transplanted tissues. We attempted to establish a functional bed for transplanted tissues using growth factors. A cylinder-type silicone substrate (spacer) was coated with a photoreactive gelatin containing basic fibroblast growth factor. This spacer was transplanted into the dorsal subdermal layer in a rabbit. After 2 and 4 weeks, the capsule formed around the spacer was histologically assessed for use as a transplant bed. In addition, after 2-4 weeks of spacer grafting, autologous fat was transplanted into the capsule. After 4 more weeks, the grafted fat was assessed immunohistochemically to evaluate the capsule as a functional bed for transplantation. In the groups pretreated with growth factors, proliferation of blood vessels was observed in the capsules. After fat grafting, a pattern of overall necrosis was observed in controls. However, good proliferation of blood vessels and favorable fat take were observed in the groups pretreated with growth factors. Necrosis, however, was found at the center of the grafted fat. We conclude that a vascularized transplant bed was useful for promoting take of the grafted fat.

Endothelial progenitor cells: diagnostic and therapeutic considerations

Endothelial progenitor cells (EPCs) may be defined as adherent cells derived from peripheral blood- or bone marrow-derived mononuclear cells demonstrating acLDL uptake and isolectin-binding capacity. The number of circulating EPCs inversely correlates with the number of cardiovascular risk factors and is reduced in cardiovascular disease. This measurement may therefore serves as a surrogate marker for cardiovascular disease risk. EPC numbers can be modified by various means. However, the effectiveness of risk-factor modification on EPC number and function is currently unknown. Furthermore, EPCs may be used as a potential therapy for a variety of vascular disease states including ischaemia, restenosis and pulmonary hypertension. This review provides an update on multiple factors that affect EPC number as well as highlighting the potential use of EPCs as a novel marker of vascular dysfunction. Furthermore, potential gene- and/or EPC-based approaches to a number of vascular disease states are explored.

Transplantation of endothelial progenitor cells transferred by vascular endothelial growth factor gene for vascular regeneration of ischemic flaps

BACKGROUND

Neovascularization occurs through two mechanisms: angiogenesis and vasculogenesis. Therefore, there are two strategies to promote neovascularization: therapeutic angiogenesis and therapeutic vasculogenesis (endothelial progenitor cells therapy).

MATERIALS AND METHODS

In this study, we examined whether or not endothelial progenitor cells combined with vascular endothelial growth factor (VEGF) gene therapy is useful for ischemia surgical flaps in vivo. At the same time, we quantitatively compared the neovascularization ability of transplanted endothelial progenitor cells (EPCs) transducted with VEGF165 gene and EPCs alone. EPCs were isolated from cord blood of healthy human volunteers, cultured in vitro for 7 days and identified by immunofluorescence. After transduced with VEGF165 gene in vitro, proliferative activity of EPCs was assessed using MTT assay. CM-DiI was used to trace EPCs in vivo 4 days after injection of 5 x 10(5) VEGF-transduced EPCs(VEGF-transduced EPCs group, n = 10), 5 x 10(5) EPCs (non-transduced EPCs group, n = 10) in 500 microL EBM-2 media, or 500 microL EBM-2 media (EBM-2 media group, n = 10) local, a cranially based flap was elevated on the back of nude mice. The percent flap survival, neovasculariztion and blood flow recovery of flaps was detected.

RESULTS

EPCs expressed cell markers CD34, KDR, and CD133. A statistically significant increase in percent flap survival was observed in mice of VEGF-transduced EPCs group as compared with that of non-transduced EPCs group: 67.99 +/- 6.64% versus 59.43 +/- 4.69% (P < 0.01), and 41.24 +/- 2.44% in EBM-2 media group (P < 0.01). The capillary density and blood flow recovery of flaps in VEGF-transduced EPCs group were both improved. CM-DiI-labeled VEGF-transduced EPCs were observed in vivo and the numbers of cells increased.

CONCLUSION

EPCs from human cord blood can increased neovascularization of ischemic flaps and augmented the survival areas, and VEGF-transduced EPCs have more powerful ability of promoting neovascularization in animal model of ischemic flaps.

Improved Survival of Ischemic Random Skin Flaps Through the Use of Bone Marrow Nonhematopoietic Stem Cells and Angiogenic Growth Factors

Surgical skin flaps are frequently used in plastic and reconstructive surgery to repair acquired or congenital defects. Necrosis is a common complication associated with these flaps postoperatively as a result of inadequate blood supply. Stem cells are precursor cells with the potential to differentiate into more specialized cells. Angiogenic factors act to direct cellular differentiation and organization to form new vascular elements. Our theory was that the combination of angiogenic growth factors with stem cells derived from the subject preoperatively would augment neovascularization, thereby increasing blood supply to the flap, which may ultimately improve flap survival. In phase I, 40 Lewis rats were randomized into 4 groups of 10. Random dorsal skin flaps were elevated and treated at the same time. The first group was injected with only medium, the second with stem cells, the third with stem cells and angiogenic factors, and the fourth with angiogenic growth factors. Millimetric measurements of flap viability at 7 and 14 days did not show any statistically significant differences between the studied groups. In phase II, 24 rats were also randomized into 4 groups of 6, but this time were treated 1 week before flap elevation. The viability measurements showed an increased rate of viability in the group in which stem cells and the angiogenic factors were administered simultaneously (84.5% +/- 3.2%) as compared with the unmodified control group (62.6% +/- 7.3%) or to the groups in which only precursor cells (60.4% +/- 7.9%) or angiogenic factors (62.3%+/- 10.1%). Increased blood supply brought by these manipulations is believed translated to increased tissue flap survival. Punch biopsies showed that "green fluorescent protein"-labeled precursor cells was noted to form luminal structures in the treated flaps. The vascular cast of all flaps was filled with Mercox plastic resin. After euthanasia, the soft tissues of the harvested flaps were dissolved and the remaining vascular cast was weighted. The weight-based ratio of the vascular composition was determined. The flaps injected with both stem cells and angiogenic factors showed higher values. We conclude that the administration of bone marrow stem cells with angiogenic factors 1 week before flap creation improves the survival of ischemic random skin flaps.