Therapeutic strategies for cell-based neovascularization in critical limb ischemia

DLK1 promoted ischemic angiogenesis through notch1 signaling in endothelial progenitor cells

Delta like non-canonical Notch ligand 1 (DLK1), as a member of epidermal growth factor-like family, plays a critical role in somatic growth, tissue development and possibly tissue renewal. Though previous studies had indicated that DLK1 contributed to adipogenesis and myogenesis, it's still controversial whether DLK1 affects angiogenesis and how it interacts with Notch signaling with numerous conflicting reports from different models. Based on our preliminary finding that DLK1 expression was up-regulated in mice ischemic gastrocnemius and in the border zone of infarcted myocardium, we administered either recombinant DLK1 (rDLK1) or PBS in C57BL/6 mice after establishment of hindlimb ischemia (HLI) and myocardial infarction (MI), respectively. Exogenous rDLK1 administration significantly improved both blood perfusion of mice ischemic hindlimbs and muscle motor function on the 3rd, 7th day after HLI, by promoting neovascularization. Similar effect on neovascularization was verified in mice on the 28th day after MI as well as improvement of cardiac failure. Correspondingly, the number of CD34+KDR+ cells, indicated as endothelial progenitor cells (EPCs), was significantly in mice ischemic gastrocnemius by rDLK1 administration, which was abrogated by DAPT as the specific inhibitor of Notch intracellular domain (NICD). Furthermore, bone marrow mononuclear cells were obtained from C57BL/6 mice and differentiated to EPCs ex vivo. Incubation with rDLK1 triggered Notch1 mRNA and NICD protein expressions in EPCs as exposed to hypoxia and serum deprivation, promoting EPCs proliferation, migration, anti-apoptosis and tube formation. Otherwise, rDLK1 incubation significantly decreased intracellular and mitochondrial reactive oxygen species, increased ATP content and mitochondrial membrane potential, downregulated short isoform of OPA-1 expression whereas upregulated mitofusin (-1, -2) expression in EPCs by Notch1 signaling, which were all abrogated by DAPT. In summary, the present study unveils the pro-angiogenesis and its mechanism of rDLK1 through activation of Notch1 signaling in endothelial progenitor cells.

Immortalized mammosphere-derived epithelial cells retain a bioactive secretome with antimicrobial, regenerative, and immunomodulatory properties

BACKGROUND

The secretome of primary bovine mammosphere-derived epithelial cells (MDECs) has been shown to exert antimicrobial, regenerative, and immunomodulatory properties in vitro, which warrants its study as a potential biologic treatment with the potential to be translated to human medicine. Currently, the use of the MDEC secretome as a therapy is constrained by the limited life span of primary cell cultures and the decrease of secretome potency over cell passages.

METHODS

To address these limitations, early-passage bovine MDECs were immortalized using hTERT, a human telomerase reverse transcriptase. The primary and immortal MDECs were compared morphologically, transcriptomically, and phenotypically. The functional properties and proteomic profiles of the secretome of both cell lines were evaluated and compared. All experiments were performed with both low and high passage cell cultures.

RESULTS

We confirmed through in vitro experiments that the secretome of immortalized MDECs, unlike that of primary cells, maintained antimicrobial and pro-migratory properties over passages, while pro-angiogenic effects of the secretome from both primary and immortalized MDECs were lost when the cells reached high passage. The secretome from primary and immortalized MDECs, at low and high passages exerted immunomodulatory effects on neutrophils in vitro.

CONCLUSIONS

High passage immortalized MDECs retain a bioactive secretome with antimicrobial, regenerative, and immunomodulatory properties, suggesting they may serve as a consistent cell source for therapeutic use.

Loss of c-Kit in Endothelial Cells Protects against Hindlimb Ischemia

BACKGROUND

Critical limb ischemia (CLI) is the end stage of peripheral artery disease (PAD), and around 30% of CLI patients are ineligible for current treatments. The angiogenic benefits of c-Kit have been reported in the ischemia scenario; however, the present study demonstrates the effects of specific endothelial c-Kit signaling in arteriogenesis during hindlimb ischemia.

METHODS

We created conditional knockout mouse models that decrease c-Kit (c-Kit VE-Cadherin CreERT2-c-Kit) or its ligand (SCF VE-Cadherin CreERT2-SCF) specifically in endothelial cells (ECs) after tamoxifen treatment. These mice and a control group (wild-type VE-Cadherin CreERT2-WT) were subjected to hindlimb ischemia or aortic crush to evaluate perfusion/arteriogenesis and endothelial barrier permeability, respectively.

RESULTS

Our data confirmed the lower gene expression of c-Kit and SCF in the ECs of c-Kit and SCF mice, respectively. In addition, we confirmed the lower percentage of ECs positive for c-Kit in c-Kit mice. Further, we found that c-Kit and SCF mice had better limb perfusion and arteriogenesis compared to WT mice. We also demonstrated that c-Kit and SCF mice had a preserved endothelial barrier after aortic crush compared to WT.

CONCLUSIONS

Our data demonstrate the deleterious effects of endothelial SCF/c-Kit signaling on arteriogenesis and endothelial barrier integrity.

miR-709 exerts an angiogenic effect through a FGF2 upregulation induced by a GSK3B downregulation

The aim of this study was to identify angiogenic microRNAs (miRNAs) that could be used in the treatment of hindlimb ischemic tissues. miRNAs contained in extracellular vesicles (EVs) deriving from the plasma were analyzed in C57BL/6 mice, which have ischemia tolerance, and in BALB/c mice without ischemia tolerance as part of a hindlimb ischemia model; as a result 43 angiogenic miRNA candidates were identified. An aortic ring assay was employed by using femoral arteries isolated from BALC/c mice and EVs containing miRNA; as a result, the angiogenic miRNA candidates were limited to 14. The blood flow recovery was assessed after injecting EVs containing miRNA into BALB/c mice with hindlimb ischemia, and miR-709 was identified as a promising angiogenic miRNA. miR-709-encapsulating EVs were found to increase the expression levels of the fibroblast growth factor 2 (FGF2) mRNA in the thigh tissues of hindlimb ischemia model BALB/c mice. miR-709 was also found to bind to the 3'UTR of glycogen synthase kinase 3 beta (GSK3B) in three places. GSK3B-knockdown human artery-derived endothelial cells were found to express high levels of FGF2, and were characterized by increased cell proliferation. These findings indicate that miR-709 induces an upregulation of FGF2 through the downregulation of GSK3B.

Exploring the Effects of Human Bone Marrow-Derived Mononuclear Cells on Angiogenesis In Vitro

Cell therapies involving the administration of bone marrow-derived mononuclear cells (BM-MNCs) for patients with chronic limb-threatening ischemia (CLTI) have shown promise; however, their overall effectiveness lacks evidence, and the exact mechanism of action remains unclear. In this study, we examined the angiogenic effects of well-controlled human bone marrow cell isolates on endothelial cells. The responses of endothelial cell proliferation, migration, tube formation, and aortic ring sprouting were analyzed in vitro, considering both the direct and paracrine effects of BM cell isolates. Furthermore, we conducted these investigations under both normoxic and hypoxic conditions to simulate the ischemic environment. Interestingly, no significant effect on the angiogenic response of human umbilical vein endothelial cells (HUVECs) following treatment with BM-MNCs was observed. This study fails to provide significant evidence for angiogenic effects from human bone marrow cell isolates on human endothelial cells. These in vitro experiments suggest that the potential benefits of BM-MNC therapy for CLTI patients may not involve endothelial cell angiogenesis.

Novel Metal Nanomaterials to Promote Angiogenesis in Tissue Regeneration

Angiogenesis-the formation of new blood vessels from existing blood vessels-has drawn significant attention in medical research. New techniques have been developed to control proangiogenic factors to obtain desired effects. Two important research areas are 1) understanding cellular mechanisms and signaling pathways involved in angiogenesis and 2) discovering new biomaterials and nanomaterials with proangiogenic effects. This paper reviews recent developments in controlling angiogenesis in the context of regenerative medicine and wound healing. We focus on novel proangiogenic materials that will advance the field of regenerative medicine. Specifically, we mainly focus on metal nanomaterials. We also discuss novel technologies developed to carry these proangiogenic inorganic molecules efficiently to target sites. We offer a comprehensive overview by combining existing knowledge regarding metal nanomaterials with novel developments that are still being refined to identify new nanomaterials.

Bovine milk-derived cells express transcriptome markers of pluripotency and secrete bioactive factors with regenerative and antimicrobial activity

The bovine mammary stem/progenitor cell secretome stimulates regeneration in vitro and contains proteins associated with antimicrobial defense. This has led to the exploration of the secretome as a biologic treatment for mastitis, a costly inflammation of the udder commonly caused by bacteria. This study reports on a population of bovine mammary stem/progenitor cells isolated non-invasively from milk (MiDCs). MiDCs were characterized by immunophenotyping, mammosphere formation assays, and single cell RNA sequencing. They displayed epithelial morphology, exhibited markers of mammary stem/progenitor cells, and formed mammospheres, like mammary gland tissue-isolated stem/progenitor cells. Single cell RNA sequencing revealed two sub-populations of MiDCs: epithelial cells and macrophages. Functionally, the MiDC secretome increased fibroblast migration, promoted angiogenesis of endothelial cells, and inhibited the growth of mastitis-associated bacteria, including antibiotic-resistant strains, in vitro. These qualities of MiDCs render them a source of stem cells and stem cell products that may be used to treat diseases affecting the dairy industry, including mastitis.

Hybrid spheroids containing mesenchymal stem cells promote therapeutic angiogenesis by increasing engraftment of co-transplanted endothelial colony-forming cells in vivo

BACKGROUND

Peripheral artery disease is an ischemic vascular disease caused by the blockage of blood vessels supplying blood to the lower extremities. Mesenchymal stem cells (MSCs) and endothelial colony-forming cells (ECFCs) have been reported to alleviate peripheral artery disease by forming new blood vessels. However, the clinical application of MSCs and ECFCs has been impeded by their poor in vivo engraftment after cell transplantation. To augment in vivo engraftment of transplanted MSCs and ECFCs, we investigated the effects of hybrid cell spheroids, which mimic a tissue-like environment, on the therapeutic efficacy and survival of transplanted cells.

METHODS

The in vivo survival and angiogenic activities of the spheroids or cell suspension composed of MSCs and ECFCs were measured in a murine hindlimb ischemia model and Matrigel plug assay. In the hindlimb ischemia model, the hybrid spheroids showed enhanced therapeutic effects compared with the control groups, such as adherent cultured cells or spheroids containing either MSCs or ECFCs.

RESULTS

Spheroids from MSCs, but not from ECFCs, exhibited prolonged in vivo survival compared with adherent cultured cells, whereas hybrid spheroids composed of MSCs and ECFCs substantially increased the survival of ECFCs. Moreover, single spheroids of either MSCs or ECFCs secreted greater levels of pro-angiogenic factors than adherent cultured cells, and the hybrid spheroids of MSCs and ECFCs promoted the secretion of several pro-angiogenic factors, such as angiopoietin-2 and platelet-derived growth factor.

CONCLUSION

These results suggest that hybrid spheroids containing MSCs can serve as carriers for cell transplantation of ECFCs which have poor in vivo engraftment efficiency.

Efficacy and safety of tibial cortex transverse transport for diabetic foot: A protocol for systematic review and meta-analysis

Introduction

Diabetic foot (DF) is one of the most serious chronic complications of diabetes. In recent years, the use of the tibial cortex transverse transport (TTT) technique has enabled great progress in microcirculation reconstruction and achievement of good outcomes in DF treatment. The objective of this systematic review protocol is to evaluate the efficacy and safety of TTT for DF.

Methods

Literature search was conducted using the Cochrane Library, Embase, PubMed, Web of Science, China Science Technology Journal Database (VIP), Wanfang Data, China National Knowledge Infrastructure (CNKI), Chinese Biomedical Literature Service System (SinoMed), and Chinese Biomedical Literature Service System (CBM) from inception until March, 1st 2022. In addition, our reviewers will retrieve dissertations, grey literature, systematic reviews, and reference lists of the relevant studies. Randomized controlled trials (RCTs) which compared the TTT for DF with conventional treatment will be included. Our reviewers will perform subgroup analysis, sensitivity analysis, and publication bias analysis to evaluate the heterogeneity and robustness. RevMan 5.3 software and Stata V.16.0 software will be used to analyze the available data.

Ethics and dissemination

Ethical approval was not required because this protocol neither collected private information, nor involved animal experiments. The research was disseminated by academic journals or related meetings.

PROSPERO registration number

CRD42021279717.

Upgrading Monocytes Therapy for Critical Limb Ischemia Patient Treatment: Pre-Clinical and GMP-Validation Aspects

Advanced cell therapy medicinal products (ATMP) are at the forefront of a new range of biopharmaceuticals. The use of ATMP has evolved and increased in the last decades, representing a new approach to treating diseases that are not effectively managed with conventional treatments. The standard worldwide recognized for drug production is the Good Manufacturing Practices (GMP), widely used in the pharma production of synthesized drugs but applying also to ATMP. GMP guidelines are worldwide recognized standards to manufacture medicinal products to guarantee high quality, safety, and efficacy. In this report, we describe the pre-clinical and the GMP upgrade of peripheral blood mononuclear cell (PBMC) preparation, starting from peripheral blood and ending up with a GMP-grade clinical product ready to be used in patients with critical limb ischemia (CLI). We also evaluated production in hypoxic conditions to increase PBMC functional activity and angiogenic potential. Furthermore, we extensively analyzed the storage and transport conditions of the final product as required by the regulatory body for ATMPs. Altogether, results suggest that the whole manufacturing process can be performed for clinical application. Peripheral blood collected by a physician should be transported at room temperature, and PBMCs should be isolated in a clean room within 8 h of venipuncture. Frozen cells can be stored in nitrogen vapors and thawed for up to 12 months. PBMCs resuspended in 5% human albumin solution should be stored and transported at 4 °C before injection in patients within 24 h to thawing. Hypoxic conditioning of PBMCs should be implemented for clinical application, as it showed a significant enhancement of PBMC functional activity, in particular with increased adhesion, migration, and oxidative stress resistance. We demonstrated the feasibility and the quality of a GMP-enriched suspension of monocytes as an ATMP, tested in a clean room facility for all aspects related to production in respect of all the GMP criteria that allow its use as an ATMP. We think that these results could ease the way to the clinical application of ATMPs.

Transformed extracellular vesicles with high angiogenic ability as therapeutics of distal ischemic tissues

Introduction: The therapeutic effects of endothelial progenitor cells (EPC) in neovascularization have been suggested; however, to date, few studies have been conducted on the ability of EPC-derived extracellular vesicles (EV) to rescue the ischemic tissues. In order to examine the functional sources of EV for cell-free therapy of ischemic diseases, we compared the functions of EPC-EV and those of Wharton’s Jelly-derived mesenchymal stem cell (WJ-EV) in the flap mouse model.

Results and conclusion: Our results demonstrated that in the intravenous injection, EPC-EV, but not WJ-EV, were uptaken by the ischemic tissues. However, EPC-EV showed poor abilities to induce neovascularization and the recovery of ischemic tissues. In addition, compared to EPC-EV, WJ-EV showed a higher ability to rescue the ischemic injury when being locally injected into the mice. In order to induce the secretion of high-functional EPC-EV, EPC were internalized with hypoxic pre-treated WJ-EV, which resulted in a transformed hwEPC. In comparison to EPC, hwEPC showed induced proliferation and upregulation of angiogenic genes and miRNAs and promoted angiogenic ability. Interestingly, hwEPC produced a modified EV (hwEPC-EV) that highly expressed miRNAs related to angiogenesis, such as miR-155, miR-183, and miR-296. Moreover, hwEPC-EV significantly induced the neovascularization of the ischemic tissues which were involved in promoting the proliferation, the expression of VEGF and miR-183, and the angiogenic functions of endothelial cells. Of note, hwEPC-EV were highly uptaken by the ischemic tissues and showed a greater effect with regard to inducing recovery from ischemic injury in the intravenous administration, compared to EPC-EV. Therefore, hwEPC-EV can be considered a functional candidate for cell-free therapy to treat the distal ischemic tissues.

PFKFB3-mediated glycometabolism reprogramming modulates endothelial differentiation and angiogenic capacity of placenta-derived mesenchymal stem cells

BACKGROUND

Mesenchymal stem cells (MSCs) have a great potential ability for endothelial differentiation, contributing to an effective means of therapeutic angiogenesis. Placenta-derived mesenchymal stem cells (PMSCs) have gradually attracted attention, while the endothelial differentiation has not been fully evaluated in PMSCs. Metabolism homeostasis plays an important role in stem cell differentiation, but less is known about the glycometabolic reprogramming during the PMSCs endothelial differentiation. Hence, it is critical to investigate the potential role of glycometabolism reprogramming in mediating PMSCs endothelial differentiation.

METHODS

Dil-Ac-LDL uptake assay, flow cytometry, and immunofluorescence were all to verify the endothelial differentiation in PMSCs. Seahorse XF Extracellular Flux Analyzers, Mito-tracker red staining, Mitochondrial membrane potential (MMP), lactate secretion assay, and transcriptome approach were to assess the variation of mitochondrial respiration and glycolysis during the PMSCs endothelial differentiation. Glycolysis enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) was considered a potential modulator for endothelial differentiation in PMSCs by small interfering RNA. Furthermore, transwell, in vitro Matrigel tube formation, and in vivo Matrigel plug assays were performed to evaluate the effect of PFKFB3-induced glycolysis on angiogenic capacities in this process.

RESULTS

PMSCs possessed the superior potential of endothelial differentiation, in which the glycometabolic preference for glycolysis was confirmed. Moreover, PFKFB3-induced glycometabolism reprogramming could modulate the endothelial differentiation and angiogenic abilities of PMSCs.

CONCLUSIONS

Our results revealed that PFKFB3-mediated glycolysis is important for endothelial differentiation and angiogenesis in PMSCs. Our understanding of cellular glycometabolism and its regulatory effects on endothelial differentiation may propose and improve PMSCs as a putative strategy for clinical therapeutic angiogenesis.

Cryopreserved allogenic fibroblast sheets: development of a promising treatment for refractory skin ulcers

The purpose of this study was to investigate the therapeutic effect of cryopreserved allogenic fibroblast cell sheets in a mouse model of skin ulcers. It is necessary to reduce the cost of regenerative medicine for it to be widely used. We consider that cell sheets could be applied to various diseases if cryopreservation of allogenic cell sheets was possible. In this study, fibroblasts were frozen using a three-dimensional freezer. Freeze-thawed fibroblasts had ~80% cell viability, secreted ≥ 50% vascular endothelial growth factor, hepatocyte growth factor, and stromal derived factor-1α compared with non-frozen fibroblast sheets, and secreted approximately the same amount of transforming growth factor-β1. There was no difference in wound-healing rates in the skin ulcer model between non-frozen and freeze-thawed fibroblast sheets regardless of autologous and allogenic cells. The degree of angiogenesis was comparable between autologous and allogenic cells. The number of CD3-positive cells in healed tissues was larger for allogenic fibroblast sheets compared with autologous fibroblast sheets. However, histopathological images showed that the fibrosis, microvascular density, and healing phase of the wound in allogenic freeze-thawed fibroblast sheets were more similar to autologous freeze-thawed fibroblast sheets than to allogenic non-frozen fibroblast sheets. These results suggest that allogenic freeze-thawed fibroblast sheets may be a promising therapeutic option for refractory skin ulcers.

Implantation of Hypoxia-Induced Mesenchymal Stem Cell Advances Therapeutic Angiogenesis

Hypoxia preconditioning enhances the paracrine abilities of mesenchymal stem cells (MSCs) for vascular regeneration and tissue healing. Implantation of hypoxia-induced mesenchymal stem cells (hi-MSCs) may further improve limb perfusion in a murine model of hindlimb ischemia. This study is aimed at determining whether implantation of hi-MSCs is an effective modality for improving outcomes of treatment of ischemic artery diseases. We evaluated the effects of human bone marrow-derived MSC implantation on limb blood flow in an ischemic hindlimb model. hi-MSCs were prepared by cell culture under 1% oxygen for 24 hours prior to implantation. A total of 1 × 10⁵ MSCs and hi-MSCs and phosphate-buffered saline (PBS) were intramuscularly implanted into ischemic muscles at 36 hours after surgery. Restoration of blood flow and muscle perfusion was evaluated by laser Doppler perfusion imaging. Blood perfusion recovery, enhanced vessel densities, and improvement of function of the ischemia limb were significantly greater in the hi-MSC group than in the MSC or PBS group. Immunochemistry revealed that hi-MSCs had higher expression levels of hypoxia-inducible factor-1 alpha and vascular endothelial growth factor A than those in MSCs. In addition, an endothelial cell-inducing medium showed high expression levels of vascular endothelial growth factor, platelet endothelial cell adhesion molecule-1, and von Willebrand factor in hi-MSCs compared to those in MSCs. These findings suggest that pretreatment of MSCs with a hypoxia condition and implantation of hi-MSCs advances neovascularization capability with enhanced therapeutic angiogenic effects in a murine hindlimb ischemia model.

Collateral Arteriogenesis Involves a Sympathetic Denervation That Is Associated With Abnormal α-Adrenergic Signaling and a Transient Loss of Vascular Tone

Stimulating collateral arteriogenesis is an attractive therapeutic target for peripheral artery disease (PAD). However, the potency of arteriogenesis-stimulation in animal models has not been matched with efficacy in clinical trials. This may be because the presence of enlarged collaterals is not sufficient to relieve symptoms of PAD, suggesting that collateral function is also important. Specifically, collaterals are the primary site of vascular resistance following arterial occlusion, and impaired collateral vasodilation could impact downstream tissue perfusion and limb function. Therefore, we evaluated the effects of arteriogenesis on collateral vascular reactivity. Following femoral artery ligation in the mouse hindlimb, collateral functional vasodilation was impaired at day 7 (17 ± 3 vs. 60 ± 8%) but restored by day 28. This impairment was due to a high resting diameter (73 ± 4 μm at rest vs. 84 ± 3 μm dilated), which does not appear to be a beneficial effect of arteriogenesis because increasing tissue metabolic demand through voluntary exercise decreased resting diameter and restored vascular reactivity at day 7. The high diameter in sedentary animals was not due to sustained NO-dependent vasodilation or defective myogenic constriction, as there were no differences between the enlarged and native collaterals in response to eNOS inhibition with L-NAME or L-type calcium channel inhibition with nifedipine, respectively. Surprisingly, in the context of reduced vascular tone, vasoconstriction in response to the α-adrenergic agonist norepinephrine was enhanced in the enlarged collateral (−62 ± 2 vs. −37 ± 2%) while vasodilation in response to the α-adrenergic antagonist prazosin was reduced (6 ± 4% vs. 22 ± 16%), indicating a lack of α-adrenergic receptor activation by endogenous norepinephrine and suggesting a denervation of the neuroeffector junction. Staining for tyrosine hydroxylase demonstrated sympathetic denervation, with neurons occupying less area and located further from the enlarged collateral at day 7. Inversely, MMP2 presence surrounding the enlarged collateral was greater at day 7, suggesting that denervation may be related to extracellular matrix degradation during arteriogenesis. Further investigation on vascular wall maturation and the functionality of enlarged collaterals holds promise for identifying novel therapeutic targets to enhance arteriogenesis in patients with PAD.

Pro-angiogenic approach for skeletal muscle regeneration

The angiogenesis process is a phenomenon in which numerous molecules participate in the stimulation of the new vessels' formation from pre-existing vessels. Angiogenesis is a crucial step in tissue regeneration and recovery of organ and tissue function. Muscle diseases affect millions of people worldwide overcome the ability of skeletal muscle to self-repair. Pro-angiogenic therapies are key in skeletal muscle regeneration where both myogenesis and angiogenesis occur. These therapies have been based on mesenchymal stem cells (MSCs), exosomes, microRNAs (miRs) and delivery of biological factors. The use of different calls of biomaterials is another approach, including ceramics, composites, and polymers. Natural polymers are use due its bioactivity and biocompatibility in addition to its use as scaffolds and in drug delivery systems. One of these polymers is the natural rubber latex (NRL) which is biocompatible, bioactive, versatile, low-costing, and capable of promoting tissue regeneration and angiogenesis. In this review, the advances in the field of pro-angiogenic therapies are discussed.

Stem Cell-Based Therapies: What Interventional Radiologists Need to Know

As the basic units of biological organization, stem cells and their progenitors are essential for developing and regenerating organs and tissue systems using their unique self-renewal capability and differentiation potential into multiple cell lineages. Stem cells are consistently present throughout the entire human development, from the zygote to adulthood. Over the past decades, significant efforts have been made in biology, genetics, and biotechnology to develop stem cell-based therapies using embryonic and adult autologous or allogeneic stem cells for diseases without therapies or difficult to treat. Stem cell-based therapies require optimum administration of stem cells into damaged organs to promote structural regeneration and improve function. Maximum clinical efficacy is highly dependent on the successful delivery of stem cells to the target tissue. Direct image-guided locoregional injections into target tissues offer an option to increase therapeutic outcomes. Interventional radiologists have the opportunity to perform a key role in delivering stem cells more efficiently using minimally invasive techniques. This review discusses the types and sources of stem cells and the current clinical applications of stem cell-based therapies. In addition, the regulatory considerations, logistics, and potential roles of interventional Radiology are also discussed with the review of the literature.

Freezing of cell sheets using a 3D freezer produces high cell viability after thawing

In cell therapy, transplanting an appropriate number of cells to the target site is crucial. One way to achieve this is to transplant cell sheets. Transplantation of cell sheets has already been utilized for various diseases in clinical practice. However, reducing the cost of cell sheet utilization is essential so as to facilitate the spread of regenerative medicine. Several ways to reduce costs are available, one of which is the use of allogenic cells. Another alternative is the use of cell sheets, which necessitates the development of methods for freezing cell sheets. This is the first study to report the use of a 3D Freezer for freezing cells. 3D Freezers have been used in the field of food processing and technology for a long time. The 3D Freezer freezes objects using cold air at a uniform temperature from all directions. In this study, we analyzed the cooling speed of human fibroblast sheets in 11 cell preservation solutions using a 3D Freezer and a Program Freezer. The cooling speed was −2 °C per min in the 3D Freezer. Supercooling in 10 cell preservation solutions was lower in the 3D Freezer than in the Program Freezer. Cell viability after freeze–thaw of the cell sheets using 3D Freezer was more than 70% in five cell preservation solutions. The levels of hepatocyte growth factor and transforming growth factor-β1 were the same not only in the fibroblast sheets frozen using the five cell preservation solutions but also in the non-frozen fibroblast sheets. These results suggest that the 3D Freezer can freeze implantable cell sheets immediately after thawing.

•

3D Freezer operates using cold air with uniform temperature directed at an object from all directions.

•

3D Freezer was trialed for freezing 3D cell sheets for the first time.

•

3D Freezer can generate high cell viability after freezing and thawing for cell therapy.

Chronic intermittent hypobaric hypoxia attenuates ischemic limb injury by promoting angiogenesis in mice

This study aimed to evaluate the protective effect of chronic intermittent hypobaric hypoxia (CIHH) against limb ischemic injury. C57BL/6 mice were randomly divided into three groups: limb ischemic injury group (Ischemia, induced by ligation and excision of the left femoral artery), limb ischemia following CIHH pretreatment group (CIHH+Ischemia, simulated a 5000 m altitude hypoxia, 6 h per day for 28 days, before induction of hind-limb ischemia), and sham group (Sham). The blood flow in the mouse models of hind-limb ischemia was examined using laser doppler imaging. The functional and morphological performance of ischemic muscle was evaluated using contraction force and hematoxylin-eosin and Masson's trichrome staining. Angiogenesis was determined by immunohistochemistry staining of the endothelial markers CD31 and CD34. The protein expressions of angiogenesis-related genes were detected using Western blot assay. Chronic ischemia resulted in reduced blood perfusion, decreased contraction tension, and morphological destruction in gastrocnemius muscle. CIHH pretreatment increased the contractile force and muscle fiber diameter and decreased necrosis and fibrosis of the ischemic muscle. Also, CIHH significantly increased the density of CD31+ and CD34+ cells and promoted the expression of angiogenesis-related molecules in ischemic muscle. These data demonstrate that CIHH has a protective effect against chronic limb ischemia by promoting angiogenesis.

Plicosepalus acacia Extract and Its Major Constituents, Methyl Gallate and Quercetin, Potentiate Therapeutic Angiogenesis in Diabetic Hind Limb Ischemia: HPTLC Quantification and LC-MS/MS Metabolic Profiling

Plicosepalus acacia (Fam. Loranthaceae) has been reported to possess hypoglycemic, antioxidant, antimicrobial, and anti-inflammatory effects. Liquid chromatography combined with tandem mass spectrometry (LC-MS/MS) analysis revealed the presence of a high content of polyphenolic compounds that are attributed to the therapeutic effects of the crude extract. In addition, methyl gallate and quercetin were detected as major phytomedicinal agents at concentrations of 1.7% and 0.062 g%, respectively, using high-performance thin layer chromatography (HPTLC). The present study investigated the effect of the P. acacia extract and its isolated compounds, methyl gallate and quercetin, on hind limb ischemia induced in type 1 diabetic rats. Histopathological examination revealed that treatment with P. acacia extract, methyl gallate, and quercetin decreased degenerative changes and inflammation in the ischemic muscle. Further biochemical assessment of the hind limb tissue showed decreased oxidative stress, increased levels of nitric oxide and endothelial nitric oxide synthase (eNOS), and enhancement of the levels of heme oxygenase-1 (HO-1) and vascular endothelial growth factor (VEGF) in the groups treated with methyl gallate and quercetin. Expression levels of hypoxia inducible factor-1 alpha (HIF-1α), VEGF, fibroblast growth factor-2 (FGF-2), and miR-146a were upregulated in the muscle tissue of methyl gallate- and quercetin-treated groups along with downregulation of nuclear factor kappa B (NF-κB). In conclusion, P. acacia extract and its isolated compounds, methyl gallate and quercetin, mediated therapeutic angiogenesis in diabetic hind limb ischemia.

Zinc-containing Mohs' paste affects blood flow and angiogenesis suppression

PURPOSE

Mohs' paste, which is composed of zinc chloride and zinc oxide starch, is used for hemostasis of superficial malignancy in the clinical setting. We investigated the concentration of intramuscular zinc in mice after Mohs' paste application and evaluated its relationship with angiogenesis from the perspective of blood flow levels within 24 h.

METHODS

Male C57BL/6JJmsSlc mice were administered single dose of Mohs' paste at 25%, 50%, and 75% after unilateral hind limb surgery, and glycerin, a viscosity modifier, was administered to the control group (0%). Hind limb blood flow levels were measured with a laser Doppler perfusion imaging system (n = 6). The amounts of intramuscular zinc and vascular endothelial growth factor-A (VEGF-A) expression were analyzed using inductively coupled plasma mass spectrometry (ICP-MS) and western blotting, respectively (n = 5 or 3).

RESULTS

Blood flow levels were significantly decreased in the 50% group after 8 h, and significantly decreased in the 25% and 50% groups after 24 h. Intramuscular zinc was significantly increased in the 50% and 75% groups after 8 h. Western blotting showed that VEGF-A levels were significantly increased in the 25% and 50% groups after 8 h. Based on analytical experiments and biological investigation, we predicated the pharmacological effect of Mohs' paste and found over 50% of it is critical in the blood flow and angiogenesis suppression after more than 8 h of its application.

CONCLUSIONS

The results suggest that the mechanism of blood flow suppression is independent of VEGF-A levels and might suppress future angiogenesis. Our findings support that of previous studies, in which Mohs' paste was expected to induce hemostasis and suppress angiogenesis. It is an excellent ointment that facilitates hemostasis by suppressing blood flow regardless of angiogenesis, and may be apt for situations where hemostasis is required in the clinical setting.

A pilot study using cell-mixed sheets of autologous fibroblast cells and peripheral blood mononuclear cells to treat refractory cutaneous ulcers

BACKGROUND/AIMS

We invented a cell-mixed sheet consisting of autologous fibroblast cells and peripheral blood mononuclear cells (PBMNCs) to treat refractory cutaneous ulcers. These sheets secrete the growth factors needed throughout the wound healing process in animal models.

METHODS

We performed this study as a pilot phase I clinical trial (UMIN-CTR: UMIN000031645). Fibroblast cells were isolated and cultured from the oral tissue, and PBMNCs were collected by apheresis. A cell-mixed sheet was prepared by co-culturing these collected cells for 3 days. The primary observation index was safety, including all adverse events. Additional observation indices were wound healing over 1, 3, and 6 months; wound healing rate at 7 days and 1, 3, and 6 months.

RESULTS

Six patients with venous leg ulcers (VLUs) were enrolled in the study, including three patients who were treated with the cell-mixed sheet transplantation. One patient was excluded because no fibroblast cells grew from the oral tissue culture, and other two were excluded because the growth factor secreted from mixed-cell sheets did not reach the reference value. The VLUs of two patients who received the cell-mixed sheet transplantation healed, and the VLU in one patient decreased in size.

CONCLUSIONS

This pilot study demonstrated that cell-mixed sheets might be a new topical intervention to treat VLUs. However, it was also suggested that this treatment might be limited when using autologous cells collected from patients with VLUs. Therefore, it may be necessary to use high-quality allogeneic cells instead of autologous cells to improve the feasibility of this treatment.

Therapeutic Biomaterial Approaches to Alleviate Chronic Limb Threatening Ischemia

Chronic limb threatening ischemia (CLTI) is a severe condition defined by the blockage of arteries in the lower extremities that leads to the degeneration of blood vessels and is characterized by the formation of non-healing ulcers and necrosis. The gold standard therapies such as bypass and endovascular surgery aim at the removal of the blockage. These therapies are not suitable for the so-called "no option patients" which present multiple artery occlusions with a likelihood of significant limb amputation. Therefore, CLTI represents a significant clinical challenge, and the efforts of developing new treatments have been focused on stimulating angiogenesis in the ischemic muscle. The delivery of pro-angiogenic nucleic acid, protein, and stem cell-based interventions have limited efficacy due to their short survival. Engineered biomaterials have emerged as a promising method to improve the effectiveness of these latter strategies. Several synthetic and natural biomaterials are tested in different formulations aiming to incorporate nucleic acid, proteins, stem cells, macrophages, or endothelial cells in supportive matrices. In this review, an overview of the biomaterials used alone and in combination with growth factors, nucleic acid, and cells in preclinical models is provided and their potential to induce revascularization and regeneration for CLTI applications is discussed.

A novel model of chronic limb ischemia to therapeutically evaluate the angiogenic effects of drug candidates

Critical limb ischemia (CLI) is a severe state of peripheral artery disease with high unmet clinical needs. Further, there are no effective treatment options for patients with CLI. Based on preclinical study results, predicting the clinical efficacy of CLI treatments is typically difficult because conventional hindlimb ischemia (HLI) rodent models display spontaneous recovery from ischemia, which is not observed in patients with CLI. Therefore, we aimed to develop a novel chronic and severe HLI model to properly evaluate the therapeutic effects of drug candidates for CLI. Severe HLI mice (Type-N) were generated by increasing the excised area of blood vessels in a hindlimb of NOG mice. Immunohistochemistry and gene expression analysis at 9 wk after the Type-N operation revealed that the ischemic limb was in a steady state with impaired angiogenesis, like that observed in patients with CLI. We did selection of chronic Type-N mice based on the number of necrotic nails and blood flow rate at 2 wk after surgery because some Type-N mice showed mild symptoms. Therapeutic treatment with cilostazol, which is used for intermittent claudication, did not restore blood flow in chronic Type-N mice. In contrast, therapeutic transplantation of pericytes and vascular endothelial cells, which can form new blood vessels in vivo, significantly improved blood flow in a subset of Type-N mice. These findings suggest that this novel chronic and severe HLI model may be a valuable standard animal model for therapeutic evaluation of the angiogenic effects of CLI drug candidates.NEW & NOTEWORTHY We developed a chronic and severe hindlimb ischemia (HLI) mouse model for preclinical research on critical limb ischemia (CLI). This model partially reflects human CLI pathology in that it does not show spontaneous restoration of blood flow or expression of angiogenic genes in the ischemic limb. This novel model may be valuable for therapeutic evaluation of the angiogenic effects of CLI drug candidates.

Notch signaling-modified mesenchymal stem cells improve tissue perfusion by induction of arteriogenesis in a rat hindlimb ischemia model

Notch signaling-modified human mesenchymal stem cell, SB623 cell, is a promising cell therapy product for ischemic stroke. With the aim to expand indications for their use for critical limb-threatening ischemia (CLTI), we hypothesized that SB623 cells improved tissue perfusion by inducing angiogenesis or arteriogenesis in a hindlimb ischemia model rat. In Sprague–Dawley rats, hindlimb ischemia was generated by femoral artery removal, then seven days after ischemic induction 1 × 10⁵ SB623 cells or PBS was injected into the ischemic adductor muscle. As compared with the PBS group, tissue perfusion was significantly increased in the SB623 group. While capillary density did not vary between the groups, αSMA- and vWF-positive arterioles with a diameter  > 15 μm were significantly increased in the SB623 group. Whole transcriptome analysis of endothelial cells co-cultured with SB623 cells showed upregulation of the Notch signaling pathway as well as several other pathways potentially leading to arteriogenesis. Furthermore, rat muscle treated with SB623 cells showed a trend for higher ephrin-B2 and significantly higher EphB4 expression, which are known as arteriogenic markers. In the hindlimb ischemia model, SB623 cells improved tissue perfusion by inducing arteriogenesis, suggesting a promising cell source for treatment of CLTI.

Development of Arabinoxylan-Reinforced Apple Pectin/Graphene Oxide/Nano-Hydroxyapatite Based Nanocomposite Scaffolds with Controlled Release of Drug for Bone Tissue Engineering: In-Vitro Evaluation of Biocompatibility and Cytotoxicity against MC3T3-E1

Fabrication of reinforced scaffolds to repair and regenerate defected bone is still a major challenge. Bone tissue engineering is an advanced medical strategy to restore or regenerate damaged bone. The excellent biocompatibility and osteogenesis behavior of porous scaffolds play a critical role in bone regeneration. In current studies, we synthesized polymeric nanocomposite material through free-radical polymerization to fabricate porous nanocomposite scaffolds by freeze drying. Functional group, surface morphology, porosity, pore size, and mechanical strength were examined through Fourier Transform Infrared Spectroscopy (FTIR), Single-Electron Microscopy (SEM), Brunauer-Emmet-Teller (BET), and Universal Testing Machine (UTM), respectively. These nanocomposites exhibit enhanced compressive strength (from 4.1 to 16.90 MPa), Young’s modulus (from 13.27 to 29.65 MPa) with well appropriate porosity and pore size (from 63.72 ± 1.9 to 45.75 ± 6.7 µm), and a foam-like morphology. The increasing amount of graphene oxide (GO) regulates the porosity and mechanical behavior of the nanocomposite scaffolds. The loading and sustained release of silver-sulfadiazine was observed to be 90.6% after 260 min. The in-vitro analysis was performed using mouse pre-osteoblast (MC3T3-E1) cell lines. The developed nanocomposite scaffolds exhibited excellent biocompatibility. Based on the results, we propose these novel nanocomposites can serve as potential future biomaterials to repair defected bone with the load-bearing application, and in bone tissue engineering.

Bone marrow mesenchymal stem cell-derived endothelial cells increase capillary density and accelerate angiogenesis in mouse hindlimb ischemia model

Background

Mesenchymal stem cells (MSCs) can improve limb perfusion and increase vessel density in a murine model of hindlimb ischemia. But low engraftment rate of those cells limited their therapeutic effect. Endothelial cells (ECs) play an important role in neovascularization. And MSCs can differentiate into ECs in vitro. The aim of this study is to investigate if EC differentiation of MSCs in vitro before transplantation is effective in improving therapeutic outcomes in the treatment of ischemic disease in a murine ischemia animal model.

Methods

MSCs were isolated from the bone marrow of EGFP-transgenic mice by density gradient centrifugation. The identity of the MSCs was determined by their cluster of differentiation (CD) marker profile by flow cytometry. Inducing medium containing a few cytokines was applied to induce the MSCs to differentiate into ECs. Endothelial differentiation was quantitatively evaluated using flow cytometry, quantitative real-time PCR (qRT-PCR), immunofluorescence, Matrigel tube formation assay, and Dil-labeled acetylated low-density lipoprotein uptake assay. Mouse hindlimb ischemia model was made by excision of the femoral artery. Uninduced EGFP+ MSCs, induced EGFP+ MSCs, and PBS were intramuscularly injected into the gastrocnemius following ischemia no later than 24 h after operation. Restoration of blood flow and muscle function was evaluated by laser Doppler perfusion imaging. Immunofluorescence was conducted to evaluate the engraftment of transplanted MSCs. Histological analysis was performed to evaluate blood vessel formation.

Results

Induced EGFP+ MSCs expressed endothelial markers and exhibited tube formation capacity. Mice in the induced EGFP+ MSCs group had a better blood perfusion recovery, enhanced vessel densities, higher engraftment, and improved function of the ischemic limb than those in the uninduced EGFP+ MSCs or PBS groups.

Conclusions

This study reveals that after short-term pre-treatment in the EC-inducing medium, induced MSCs acquire stronger vessel formation capability and enhanced angiogenic therapeutic effect in the murine hindlimb ischemia model.

An injectable, self-assembled multicellular microsphere with the incorporation of fibroblast-derived extracellular matrix for therapeutic angiogenesis

Decellularized human lung fibroblast-derived matrix (hFDM) has demonstrated its excellent proangiogenic capability. In this study, we propose a self-assembled, injectable multicellular microspheres containing human umbilical vein endothelial cells (HUVECs) and mesenchymal stem cell (MSCs), collagen hydrogel (Col), and hFDM toward therapeutic angiogenesis. Those multicellular microspheres are spontaneously formed by the mixtures of cell and hydrogel after being dropped on the parafilm for several hours. The size of microspheres can be manipulated via adjusting the initial volume of droplets and the culture period. The cells in the microspheres are highly viable. Multicellular microspheres show good capability of cell migration on 2D culture plate and also exhibit active cell sprouting in 3D environment (Col) forming capillary-like structures. We also find that multiple angiogenic-related factors are significantly upregulated with the multicellular microspheres prepared via Col and hFDM (Col/hFDM) than those prepared using Col alone or single cells (harvested from cocultured HUVECs/MSCs in monolayer). For therapeutic efficacy evaluation, three different groups of single cells, Col and Col/hFDM microspheres are injected to a hindlimb ischemic model, respectively, along with PBS injection as a control group. It is notable that Col/hFDM microspheres significantly improve the blood reperfusion and greatly attenuate the fibrosis level of the ischemic regions. In addition, Col/hFDM microspheres show higher cell engraftment level than that of the other groups. The incorporation of transplanted cells with host vasculature is detectable only with the treatment of Col/hFDM. Current results suggest that hFDM plays an important role in the multicellular microspheres for angiogenic cellular functions in vitro as well as in vivo. Taken together, our injectable multicellular microspheres (Col/hFDM) offer a very promising platform for cell delivery and tissue regenerative applications.

Review of the Long-term Effects of Autologous Bone-Marrow Mononuclear Cell Implantation on Clinical Outcomes in Patients with Critical Limb Ischemia

Critical limb ischemia (CLI) is associated with a high risk of limb amputation. It has been shown that cell therapy is safe and has beneficial effects on ischemic clinical symptoms in patients with CLI. The aim of this study was to further investigate the outcomes of intramuscular injection of autologous bone-marrow mononuclear cells (BM-MNCs) in a long-term follow-up period in atherosclerotic peripheral arterial disease (PAD) patients who have no optional therapy. This study was a retrospective and observational study that was carried out to evaluate long-term clinical outcomes in 42 lower limbs of 30 patients with atherosclerotic PAD who underwent BM-MNC implantation. The median follow-up period was 9.25 (range, 6–16) years. The overall amputation-free rates were 73.0% at 5 years after BM-MNC implantation and 70.4% at 10 years in patients with atherosclerotic PAD. The overall amputation-free rates at 5 years and at 10 years after implantation of BM-MNCs were significantly higher in atherosclerotic PAD patients than in internal controls and historical controls. There were no significant differences in amputation rates between the internal control group and historical control group. The rate of overall survival was not significantly different between the BM-MNC implantation group and the historical control group. Implantation of autologous BM-MNCs is feasible for a long-term follow-up period in patients with CLI who have no optional therapy.

Possibility of Injecting Adipose-Derived Stromal Vascular Fraction Cells to Accelerate Microcirculation in Ischemic Diabetic Feet: A Pilot Study

Background and Objectives

Beneficial effects of human adipose-derived stromal vascular fraction (SVF) cell injection on microcirculation have been recently reported in in vitro and in vivo studies. However, no clinical studies have reported its effect in diabetic patients who commonly experience compromised tissue perfusion, regardless of the status of intravascular blood flow. The present piloting study was designed to clinically examine the possibility of SVF cell injection to accelerate microcirculation, particularly in ischemic diabetic feet.

Methods

Ten diabetic feet were included to receive subcutaneous injection of SVF cells around wounds. Transcutaneous partial oxygen pressure (TcPO₂) and cutaneous microvascular blood flow were measured before and every four weeks after cell injection until the 12^th week visit.

Results

TcPO₂ values increased from 31.3±7.4 before injection to 46.4±8.2 mmHg at 12 weeks after SVF injection (1.5-fold, p<0.05). Cutaneous microvascular blood flow levels increased from 34.0±21.1 before injection to 76.1±32.5 perfusion unit at 12 weeks after SVF injection (2.2-fold, p<0.05). There were no adverse events related to SVF cell injection.

Conclusions

Results of this study demonstrate that adipose-derived SVF cell injection have the possibility to provide beneficial effects on microcirculation in ischemic diabetic feet.

Protein disulfide isomerase as a prosurvival factor in cell therapy for muscular and vascular diseases

Background

Cell therapy for degenerative diseases aims at rescuing tissue damage by delivery of precursor cells. Thus far, this strategy has been mostly unsuccessful due to massive loss of donor cells shortly after transplantation. Several strategies have been applied to increase transplanted cell survival but only with limited success. The endoplasmic reticulum (ER) is an organelle involved in protein folding, calcium homeostasis, and lipid biosynthesis. Protein disulfide isomerase (PDI) is a molecular chaperone induced and activated by ER stress. PDI is induced by hypoxia in neuronal, cardiac, and endothelial cells, supporting increased cell survival to hypoxic stress and protection from apoptosis in response to ischemia.

Methods

We achieved ex vivo PDI gene transfer into luciferase-expressing myoblasts and endothelial cells. We assessed cell engraftment upon intramuscular transplantation into a mouse model of Duchenne muscular dystrophy (mdx mouse) and into a mouse model of ischemic disease.

Results

We observed that loss of full-length dystrophin expression in mdx mice muscle leads to an increase of PDI expression, possibly in response to augmented ER protein folding load. Moreover, we determined that overexpression of PDI confers a survival advantage for muscle cells in vitro and in vivo to human myoblasts injected into murine dystrophic muscle and to endothelial cells administered upon hindlimb ischemia damage, improving the therapeutic outcome of the cell therapy treatment.

Conclusions

Collectively, these results suggest that overexpression of PDI may protect transplanted cells from hypoxia and other possibly occurring ER stresses, and consequently enhance their regenerative properties.

Future directions for therapeutic strategies in post-ischaemic vascularization: a position paper from European Society of Cardiology Working Group on Atherosclerosis and Vascular Biology

Modulation of vessel growth holds great promise for treatment of cardiovascular disease. Strategies to promote vascularization can potentially restore function in ischaemic tissues. On the other hand, plaque neovascularization has been shown to associate with vulnerable plaque phenotypes and adverse events. The current lack of clinical success in regulating vascularization illustrates the complexity of the vascularization process, which involves a delicate balance between pro- and anti-angiogenic regulators and effectors. This is compounded by limitations in the models used to study vascularization that do not reflect the eventual clinical target population. Nevertheless, there is a large body of evidence that validate the importance of angiogenesis as a therapeutic concept. The overall aim of this Position Paper of the ESC Working Group of Atherosclerosis and Vascular biology is to provide guidance for the next steps to be taken from pre-clinical studies on vascularization towards clinical application. To this end, the current state of knowledge in terms of therapeutic strategies for targeting vascularization in post-ischaemic disease is reviewed and discussed. A consensus statement is provided on how to optimize vascularization studies for the identification of suitable targets, the use of animal models of disease, and the analysis of novel delivery methods.

Stromal vascular fraction cells for the treatment of critical limb ischemia: a pilot study

BACKGROUND

Cell-based therapy is being explored as an alternative treatment option for critical limb ischemia (CLI), a disease associated with high amputation and mortality rates and poor quality of life. However, therapeutic potential of uncultured adipose-derived stromal vascular fraction (SVF) cells has not been evaluated as a possible treatment. In this pilot study, we investigated the efficacy of multiple injections of autologous uncultured adipose-derived SVF cells to treat patients with CLI.

METHODS

This study included 15 patients, from 35 to 77 years old, with rest pain and ulceration. SVF cells were injected once or twice in the ischemic limb along the arteries. Digital subtraction angiography was performed before and after cell therapy. The clinical follow up was carried out for the subsequent 12 months after the beginning of the treatment.

RESULTS

Multiple intramuscular SVF cell injections caused no complications during the follow-up period. Clinical improvement occurred in 86.7% of patients. Two patients required major amputation, and the amputation sites healed completely. The rest of patients achieved a complete ulcer healing, pain relief, improved ankle-brachial pressure index and claudication walking distance, and had ameliorated their quality of life. Digital subtraction angiography performed before and after SVF cell therapy showed formation of numerous vascular collateral networks across affected arteries.

CONCLUSION

Results of this pilot study demonstrate that the multiple intramuscular SVF cell injections stimulate regeneration of injured tissue and are effective alternative to achieve therapeutic angiogenesis in CLI patients who are not eligible for conventional treatment. Trial registration number at ISRCTN registry, ISRCTN13001382. Retrospectively registered at 26/04/2017.

Ghrelin, MicroRNAs, and Critical Limb Ischemia: Hungering for a Novel Treatment Option

Critical limb ischemia (CLI) is the most severe manifestation of peripheral artery disease. It is characterized by chronic pain at rest, skin ulcerations, and gangrene tissue loss. CLI is a highly morbid condition, resulting in a severely diminished quality of life and a significant risk of mortality. The primary goal of therapy for CLI is to restore blood flow to the affected limb, which is only possible by surgery, but is inadvisable in up to 50% of patients. This subset of patients who are not candidates for revascularisation are referred to as "no-option" patients and are the focus of investigation for novel therapeutic strategies. Angiogenesis, arteriogenesis and vasculogenesis are the processes whereby new blood vessel networks form from the pre-existing vasculature and primordial cells, respectively. In therapeutic angiogenesis, exogenous stimulants are administered to promote angiogenesis and augment limb perfusion, offering a potential treatment option for "no option" patients. However, to date, very few clinical trials of therapeutic angiogenesis in patients with CLI have reported clinically significant results, and it remains a major challenge. Ghrelin, a 28-amino acid peptide, is emerging as a potential novel therapeutic for CLI. In pre-clinical models, exogenous ghrelin has been shown to induce therapeutic angiogenesis, promote muscle regeneration, and reduce oxidative stress via the modulation of microRNAs (miRs). miRs are endogenous, small, non-coding ribonucleic acids of ~20-22 nucleotides which regulate gene expression at the post-transcriptional level by either translational inhibition or by messenger ribonucleic acid cleavage. This review focuses on the mounting evidence for the use of ghrelin as a novel therapeutic for CLI, and highlights the miRs which orchestrate these physiological events.