Selective recruitment of endothelial progenitor cells to ischemic tissues with increased neovascularization

Quantity, distribution and phenotype of newly generated cells in the intact spinal cord of adult macaque monkeys

The existence of proliferating cells in the intact spinal cord, their distribution and phenotype, are well studied in rodents. A limited number of studies also address the proliferation after spinal cord injury, in non-human primates. However, a detailed description of the quantity, distribution and phenotype of proliferating cells at different anatomical levels of the intact adult non-human primate spinal cord is lacking at present. In the present study, we analyzed normal spinal cord tissues from adult macaque monkeys (Macaca fuscata), infused with Bromo-2'-deoxyuridine (BrdU), and euthanized at 2h, 2 weeks, 5 weeks and 10 weeks after BrdU. We found a significantly higher density of BrdU + cells in the gray matter of cervical segments as compared to thoracic or lumbar segments, and a significantly higher density of proliferating cells in the posterior as compared to the anterior horn of the gray matter. BrdU + cells exhibited phenotype of microglia or endothelial cells (∼50%) or astroglial and oligodendroglial cells (∼40%), including glial progenitor phenotypes marked by the transcription factors Sox9 and Sox10. BrdU + cells also co-expressed other transcription factors known for their involvement in embryonic development, including Emx2, Sox1, Sox2, Ngn1, Olig1, Olig2, Olig3. In the central canal, BrdU + cells were located along the dorso-ventral axis and co-labeled for the markers Vimentin and Nestin. These results reveal the extent of cellular plasticity in the spinal cord of non-human primates under normal conditions.

Myeloid lineage contributes to pathological choroidal neovascularization formation via SOCS3

Background

Pathological neovascularization in neovascular age-related macular degeneration (nAMD) is the leading cause of vision loss in the elderly. Increasing evidence shows that cells of myeloid lineage play important roles in controlling pathological endothelium formation. Suppressor of cytokine signaling 3 (SOCS3) pathway has been linked to neovascularization.

Methods

We utilised a laser-induced choroidal neovascularization (CNV) mouse model to investigate the neovascular aspect of human AMD. In several cell lineage reporter mice, bone marrow chimeric mice and Socs3 loss-of-function (knockout) and gain-of-function (overexpression) mice, immunohistochemistry, confocal, and choroidal explant co-culture with bone marrow-derived macrophage medium were used to study the mechanisms underlying pathological CNV formation via myeloid SOCS3.

Findings

SOCS3 was significantly induced in myeloid lineage cells, which were recruited into the CNV lesion area. Myeloid Socs3 overexpression inhibited laser-induced CNV, reduced myeloid lineage-derived macrophage/microglia recruitment onsite, and attenuated pro-inflammatory factor expression. Moreover, SOCS3 in myeloid regulated vascular sprouting ex vivo in choroid explants and SOCS3 agonist reduced in vivo CNV.

Interpretation

These findings suggest that myeloid lineage cells contributed to pathological CNV formation regulated by SOCS3.

Funding

This project was funded by NIH/NEI (R01EY030140, R01EY029238), BrightFocus Foundation, American Health Assistance Foundation (AHAF), and Boston Children's Hospital Ophthalmology Foundation for YS and the National Institutes of Health/National Heart, Lung and Blood Institute (U01HL098166) for PZ.

Effects of microneedle length and duration of preconditioning on random pattern skin flaps in rats

To date, the surgical delay of skin flaps is the most common and reliable method that increases skin flap survival. In this study, we aimed to increase skin flap viability using preconditioning by microneedling. Seventy-two Sprague Dawley rats were randomly divided into control, surgical flap delay (SFD), and four microneedling groups (7 or 14 days of preconditioning with 0.5 mm or 1 mm needles). Modified McFarlane flaps were raised on the back of rats. In Group I, a caudal pedicled skin flap was raised and the flap survival rate was assessed on postoperative day 14. In the SFD group, a bipedicled flap was created and after 14 days of surgical delay, all skin flaps were raised. In the microneedling groups, 0.5 mm or 1 mm needles were used for 7 or 14 days. The flap survival rates of all microneedling and SFD groups were significantly higher than the control group. The plasma levels of vascular endothelial growth factor (VEGF) did not significantly differ between groups, but the VEGF level of skin samples in the SFD group was higher than the control group. The vessel counts of all microneedling and SFD groups were statistically higher than the control group in all skin samples taken before raising the flaps, but skin samples taken 14 days after raising the skin flap did not show any difference between groups. We showed that preconditioning by microneedling can be used to improve the viability of critical ischemic skin flaps at a level similar to surgical delay.

Recipient-Site Preconditioning with Deferoxamine Increases Fat Graft Survival by Inducing VEGF and Neovascularization in a Rat Model

BACKGROUND

The authors hypothesize that ischemic preconditioning of the recipient site with deferoxamine will increase fat graft survival by enhancing angiogenesis in a rat model.

METHODS

Cell viability, tube formation, and mRNA expression were measured in human umbilical vein endothelial cells treated with deferoxamine. A total of 36 rats were then used for an in vivo study. A dose of 100 mg/kg of deferoxamine was injected subcutaneously into the rat scalp every other day for five treatments. On the day after the final injection, the scalp skin was harvested from half the animals to evaluate the effects of deferoxamine on the recipient site. In the remaining animals, inguinal fat tissue was transplanted to the scalp. Eight weeks after transplantation, the grafts were harvested to evaluate the effects of deferoxamine preconditioning on fat graft survival.

RESULTS

In human umbilical vein endothelial cells, treatment with a deferoxamine concentration higher than 400 μM decreased cell viability compared with the control (p = 0.002). Treatment with 100 and 200 μM deferoxamine increased endothelial tube formation (p = 0.001) and mRNA levels of angiogenesis-related factors (p = 0.02). Rat scalps treated with deferoxamine exhibited increased capillary neoformation (p = 0.001) and vascular endothelial growth factor protein expression (p = 0.024) compared with controls. Fat graft volume retention, capillary density (p < 0.001), and adipocyte viability (p < 0.001) in the grafted fat increased when the recipient site was preconditioned with deferoxamine.

CONCLUSION

This study demonstrated that recipient site preconditioning with deferoxamine increases fat graft survival by inducing vascular endothelial growth factor and neovascularization.

Intra-arterial injection of human adipose-derived stem cells improves viability of the random component of axial skin flaps in nude mice

BACKGROUND

Skin flap necrosis is a common postoperative complication in reconstructive surgery. Recent evidence suggests that subcutaneously injected adipose-derived stem cells (ASCs) increase the viability of random skin flaps. Here, we examined whether intra-arterial human ASC administration could improve random component survival of axial skin flaps in nude mice.

METHODS

Human ASCs isolated from a healthy volunteer by liposuction were injected into nude mice through the right femoral artery at a low (1 × 10³ cells), medium (1 × 10⁴ cells), or high (1 × 10⁵ cells) dose. After ASC infusion, right superficial inferior epigastric vessels were ligated to create unipedicled superficial inferior epigastric artery (SIEA) flap with random extension.

RESULTS

Flap survival was higher in mice from all three ASC-treated groups, and particularly the medium-dose group was 30% better, than in the control group. Histological examination demonstrated a significantly higher vascular density in the axial skin flap in nude mice treated with the medium ASC dose than in control mice. PKH26-labeled ASCs were identified in skin flaps of ASC-treated mice; some endothelial cells exhibited positive staining for human HLA-A. Compared to the control group, mice in ASC-treated groups had higher vascular endothelial growth factor levels and lower tumor necrosis factor α, interferon γ, and interleukin-6 levels.

CONCLUSIONS

Intra-arterial human ASC administration increased the survival of axial skin flaps by attenuating inflammatory reactions and enhancing neovascularization. Intra-arterial ASC administration might yield a higher rate of these cells and of engraftment in the skin flaps. This approach may have a therapeutic role in increasing flap survival.

Efficacy of Cellular Therapy for Diabetic Foot Ulcer: A Meta-Analysis of Randomized Controlled Clinical Trials

Diabetes mellitus is a widely spread chronic disease with growing incidence worldwide, and diabetic foot ulcer is one of the most serious complications of diabetes. Cellular therapy has shown promise in the management of diabetic foot ulcer in many preclinical experiments and clinical researches. Here, we performed a meta-analysis to evaluate the efficacy and safety of cellular therapy in the management of diabetic foot ulcer. We systematically searched PubMed, MEDLINE, EMBASE, and Cochrane Library databases from inception to May 2017 for randomized controlled trials assessing the efficacy of cellular therapy in diabetic foot ulcer, and a meta-analysis was conducted. A total of 6 randomized controlled clinical trials involving 241 individuals were included in this meta-analysis. The results suggested that cellular therapy could help accelerating the healing of diabetic foot ulcer, presented as higher ankle-brachial index (mean difference = 0.17, 95% confidence interval [CI] = 0.11 to 0.23), higher transcutaneous oxygen pressure (standardized mean difference [SMD] = 1.43; 95% CI, 1.09– to 1.78), higher ulcer healing rate (relative risk [RR] = 1.78; 95% CI, 1.41 to 2.25), higher amputation-free survival (RR = 1.25; 95% CI, 1.11 to 1.40), and lower scale of pain (SMD = −1.69; 95% CI, −2.05 to −1.33). Furthermore, cellular therapy seemed to be safe, with no serious complications and low risk of short-term slight complications. Cellular therapy could accelerate the rate of diabetic foot ulcer healing and may be more efficient than standard therapy for diabetic foot treatment.

Microvascular Fragment Transplantation Improves Rat Dorsal Skin Flap Survival

BACKGROUND

The development of flap necrosis distally remains a concern during microsurgical flap transfers because, at least in part, of decreased perfusion. Microvascular fragments (MVFs) are microvessels isolated from adipose tissue that are capable of improving tissue perfusion in a variety of tissue defects. The aim of this study was to determine whether the transplantation of MVFs in a dorsal rat skin flap model can improve flap survival.

METHODS

A 10 × 3 cm flap was raised in a cranial to caudal fashion on the dorsal side of 16 Lewis rats, with the caudal side remaining intact. The rats were equally divided into a treatment group (MVFs) and a control group (sterile saline). At the time of surgery, sterile saline with or without MVFs was injected directly into the flap. Microvessel density was determined after harvesting flap tissue by counting vessels that positively stained for Griffonia simplicifolia lectin I-isolectin B4. Laser Doppler was used to measure blood flow before and after surgery and 7 and 14 days later. Flap survival was evaluated 7 and 14 days after surgery by evaluating the percentage of viable tissue of the flap with photodigital planimetry.

RESULTS

Despite the lack of a significant difference in microvessel density and tissue perfusion, flap survival increased 6.4% (P < 0.05) in MVF-treated animals compared with controls.

CONCLUSIONS

The use of MVFs may be a means to improve flap survival. Future studies are required to delineate mechanisms whereby this occurs and to further optimize their application.

Macrophage Recruitment and Polarization During Collateral Vessel Remodeling in Murine Adipose Tissue

OBJECTIVE

During autologous flap transplantation for reconstructive surgeries, plastic surgeons use a surgical pre-treatment strategy called "flap delay," which entails ligating a feeding artery into an adipose tissue flap 10-14 days prior to transfer. It is believed that this blood flow alteration leads to vascular remodeling in the flap, resulting in better flap survival following transfer; however, the structural changes in the microvascular network are poorly understood. Here, we evaluate microvascular adaptations within adipose tissue in a murine model of flap delay.

METHODS AND RESULTS

We used a murine flap delay model in which we ligated an artery supplying the inguinal fat pad. Although the extent of angiogenesis appeared minimal, significant diameter expansion of pre-existing collateral arterioles was observed. There was a 5-fold increase in recruitment of CX3CR1(+) monocytes to ligated tissue, a threefold increase in CD68(+) /CD206(+) macrophages in ligated tissue, a 40% increase in collateral vessel diameters supplying ligated tissue, and a 6-fold increase in the number of proliferating cells in ligated tissue.

CONCLUSIONS

Our study describes microvascular adaptations in adipose in response to altered blood flow and underscores the importance of macrophages. Our data supports the development of therapies that target macrophages in order to enhance vascular remodeling in flaps.

The role of endothelial progenitor cells in transient ischemic attack patients for future cerebrovascular events

Background:

The role of endothelial progenitor cells (EPCs) in the maintenance of vascularization following ischemic brain after experimental stroke has been established. Accordingly, in this study, we evaluated the role of circulating EPCs in transient ischemic attack (TIA) patients for future cerebrovascular (CV) events.

Materials and Methods:

The level of circulating EPCs (staining markers: CD34, CD309) were determined using flow cytometry at 24 h after TIA in thirty consecutive patients. The EPCs level was also evaluated once in thirty healthy volunteers. Over a period of 12 months, all patients were evaluated by an experienced neurologist for recurrent TIA, stroke or death induced by CV disorders.

Results:

Circulating EPCs increased in patients group following the first attack of TIA when compared with controls. By analysis of covariance, cardiovascular event history, hyperlipidemia, and statin therapy remained significant independent predictors of EPCs. The mean (standard deviation) duration of follow-up was 10.5 (3.1) months (range, 2–12 months). During follow-up, a total of three patients died due to CV accident and four patients experienced again recurrent TIA. By analyzing data with Cox regression, EPC did not predict the future CV events in TIA patients.

Conclusion:

Increased incidence of future CV events did not occur in those patients with elevated EPCs in the first attack of TIA. The significant predicting factors of EPCs were cardiovascular event history, hyperlipidemia, and statin therapy.

Low dose cranial irradiation-induced cerebrovascular damage is reversible in mice

Background

High-dose radiation-induced blood-brain barrier breakdown contributes to acute radiation toxicity syndrome and delayed brain injury, but there are few data on the effects of low dose cranial irradiation. Our goal was to measure blood-brain barrier changes after low (0.1 Gy), moderate (2 Gy) and high (10 Gy) dose irradiation under in vivo and in vitro conditions.

Methodology

Cranial irradiation was performed on 10-day-old and 10-week-old mice. Blood-brain barrier permeability for Evans blue, body weight and number of peripheral mononuclear and circulating endothelial progenitor cells were evaluated 1, 4 and 26 weeks postirradiation. Barrier properties of primary mouse brain endothelial cells co-cultured with glial cells were determined by measurement of resistance and permeability for marker molecules and staining for interendothelial junctions. Endothelial senescence was determined by senescence associated β-galactosidase staining.

Principle Findings

Extravasation of Evans blue increased in cerebrum and cerebellum in adult mice 1 week and in infant mice 4 weeks postirradiation at all treatment doses. Head irradiation with 10 Gy decreased body weight. The number of circulating endothelial progenitor cells in blood was decreased 1 day after irradiation with 0.1 and 2 Gy. Increase in the permeability of cultured brain endothelial monolayers for fluorescein and albumin was time- and radiation dose dependent and accompanied by changes in junctional immunostaining for claudin-5, ZO-1 and β-catenin. The number of cultured brain endothelial and glial cells decreased from third day of postirradiation and senescence in endothelial cells increased at 2 and 10 Gy.

Conclusion

Not only high but low and moderate doses of cranial irradiation increase permeability of cerebral vessels in mice, but this effect is reversible by 6 months. In-vitro experiments suggest that irradiation changes junctional morphology, decreases cell number and causes senescence in brain endothelial cells.

Effect of endogenous bone marrow derived stem cells induced by AMD-3100 on expanded ischemic flap

The purpose of this study was to devise an expanded ischemic flap model and to investigate the role of AMD-3100 (Plerixafor, chemokine receptor 4 inhibitor) in this model by confirming its effect on mobilization of stem cells from the bone marrow. Male Sprague-Dawley rats were used as an animal research model. The mobilization of stem cells from the bone marrow was confirmed in the AMD-3100-treated group. The fractions of endothelial progenitor cells (EPC) and the vascular endothelial growth factor receptor (VEGFR) 2+ cells in the peripheral blood were increased in groups treated with AMD-3100. The expression of vascular endothelial growth factor (VEGF) was increased in response to expansion or AMD injection. The expression of stromal cell derived factor (SDF)-1 and VEGFR2 were increased only in unexpanded flap treated with AMD-3100. Treatment with AMD-3100 increased both the number and area of blood vessels. However, there were no statistically significant differences in the survival area or physiologic microcirculation in rats from the other groups. This endogenous neovascularization induced by AMD-3100 may be a result of the increase in both the area and number of vessels, as well as paracrine augmentation of the expression of VEGF and EPCs. However, the presence of a tissue expander under the flap could block the neovascularization between the flap and the recipient regardless of AMD-3100 treatment and expansion.

R2* and R2 mapping for quantifying recruitment of superparamagnetic iron oxide-tagged endothelial progenitor cells to injured liver: tracking in vitro and in vivo

OBJECTIVE

To evaluate clinical 3.0T magnetic resonance for tracking and quantifying superparamagnetic iron oxide (SPIO)-labeled endothelial progenitor cells (EPCs) in vitro and homing to liver with acute injury in vivo.

METHODS

The bone marrow-derived EPCs were isolated and cultured for 4 days and examined in vitro for lineage markers. Then the cultured cells were labeled with a ferumoxides-protamine sulfate complex. Iron uptake was analyzed with an electron microscope and Prussian blue staining. Agarose gel phantoms containing different amounts of EPCs (0-2.5 × 10(6) cells per milliliter of 1.0% agarose gel) were analyzed with 3.0T R2 and R2* relaxometry. For in vivo tracking, liver injury was induced in healthy C57 mice (female, 6 weeks old, weight 19-20 g) by administration of carbon tetrachloride by single intraperitoneal injection. The R2* and R2 mapping of injured and normal livers of C57 mice were conducted by using 3.0T magnetic resonance on Days 0, 1, 4, and 8 after intravenous SPIO-tagged cells transplantation.

RESULTS

Electron microscope and Perls Prussian blue stain revealed the efficiency of SPIO particles uptake was more than 95% and no structural changes of labeled cells were found compared with control group. R2 and R2* values were linearly correlated with the number of iron-loaded cells in the agarose gel phantoms, and R2* values were significantly greater than R2 (P<0.01). R2* values in all groups were obviously greater than R2 (P<0.01). The R2* values of the injured livers were greater than normal on Days 1 and 4 (P<0.01). No significant difference of R2 values could be found among the three groups.

CONCLUSION

Quantitative R2* mapping provides a useful method for quantifying intravascular administered SPIO-tagged EPCs homing to injured livers.

Coverage of skin defects without skin grafts using adipose-derived stem cells

A satisfying result is difficult to achieve in the repair of a full-thickness skin defect in the facial area, including the subunits of the nose. A full-thickness skin graft, nasolabial flap, or forehead flap as a major treatment still is used despite its relative potential for secondary contracture, unmatched skin color, hypertrophic scars, and donor-site morbidity. Another option, with good wound-healing power and soft tissue regeneration without skin grafts would be helpful for initiating treatment. Adult stem cells are a useful material in tissue engineering. Adipose-derived stem cells (ADSCs), an abundant population of pluripotent cells found in the stroma of adipose tissues, have been shown to differentiate in vitro into various cell lineages. As a robust source of bioactive growth factors, ADSCs contribute to recovery from ischemic damage, and they can promote the wound-healing process as well as soft tissue regeneration. The authors have experienced several cases of facial skin defect repair using ADSCs without skin grafts. In these cases, they observed rapid coverage of the wound with the patient's own regenerated tissue. During the treatment period, ADSC treatment showed an excellent wound-healing process in terms of quantity and quality.

Quality-control culture system restores diabetic endothelial progenitor cell vasculogenesis and accelerates wound closure

Delayed diabetic wound healing is, in part, the result of inadequate endothelial progenitor cell (EPC) proliferation, mobilization, and trafficking. Recently, we developed a serum-free functional culture system called the quality and quantity culture (QQc) system that enhances the number and vasculogenic potential of EPCs. We hypothesize that QQc restoration of diabetic EPC function will improve wound closure. To test this hypothesis, we measured diabetic c-kit(+)Sca-1(+)lin(-) (KSL) cell activity in vitro as well as the effect of KSL cell-adoptive transfer on the rate of euglycemic wound closure before and after QQc. KSL cells were magnetically sorted from control and streptozotocin-induced type I diabetic C57BL6J bone marrow. Freshly isolated control and diabetic KSL cells were cultured in QQc for 7 days and pre-QQc and post-QQc KSL function testing. The number of KSL cells significantly increased after QQc for both diabetic subjects and controls, and diabetic KSL increased vasculogenic potential above the fresh control KSL level. Similarly, fresh diabetic cells form fewer tubules, but QQc increases diabetic tubule formation to levels greater than that of fresh control cells (P < 0.05). Adoptive transfer of post-QQc diabetic KSL cells significantly enhances wound closure compared with fresh diabetic KSL cells and equaled wound closure of post-QQc control KSL cells. Post-QQc diabetic KSL enhancement of wound closure is mediated, in part, via a vasculogenic mechanism. This study demonstrates that QQc can reverse diabetic EPC dysfunction and achieve control levels of EPC function. Finally, post-QQc diabetic EPC therapy effectively improved euglycemic wound closure and may improve diabetic wound healing.

Improved wound healing of postischemic cutaneous flaps with the use of bone marrow-derived stem cells

OBJECTIVES/HYPOTHESIS

To determine if the intravascular delivery of mesenchymal stem cells improves wound healing and blood perfusion to postischemic cutaneous flap tissues.

STUDY DESIGN

Randomized controlled study.

METHODS

A murine model of a cutaneous flap was created based on the inferior epigastric vessels. Mice (n = 14) underwent 3.5 hours of ischemia followed by reperfusion. Bone marrow stromal cells (BMSCs) 1 × 10(6) were injected intravenously. Wound healing was then assessed measuring percent flap necrosis, flap perfusion, and tensile strength of the flap after a period of 14 days. Localization of BMSCs was determined with radiolabeled and fluorescent labeled BMSCs.

RESULTS

Postischemic cutaneous flap tissues treated with BMSCs demonstrated significantly less necrosis than control flaps (P <0.01). Beginning on postoperative day 5, BMSC-treated flaps demonstrated greater blood perfusion than untreated flaps (P <0.01). Tensile strength of BMSC-treated cutaneous flaps was significantly higher (P <0.01), with a mean strength of 283.4 ± 28.4 N/m than control flaps with a mean of 122.4 ± 23.5 N/m. Radiolabeled BMSCs localized to postischemic flaps compared to untreated tissues (P = 0.001). Fluorescent microscopy revealed incorporation of BMSCs into endothelial and epithelial tissues of postischemic flaps.

CONCLUSIONS

This study demonstrates that the intravascular delivery of BMSCs increases wound healing and promotes flap survival following ischemia-reperfusion injury of cutaneous tissue flaps.

Stem cell therapy for lower extremity diabetic ulcers: where do we stand?

The impairment of wound healing in diabetic patients is an important clinical problem affecting millions of patients worldwide. Various clinical and basic science studies show that stem cell therapy, as a regenerative medical therapy, can be a good solution. In this paper, we begin with an introduction of the cellular mechanism of the diabetic ulcer. We will then discuss the advantages and limitations of various stem cell therapies that have been under extensive recent study.

Characterization of adipose-derived mesenchymal stem cell combinations for vascularized bone engineering

Since bone repair and regeneration depend on vasculogenesis and osteogenesis, both of these processes are essential for successful vascularized bone engineering. Using adipose-derived stem cells (ASCs), we investigated temporal gene expression profiles, as well as bone nodule and endothelial tubule formation capacities, during osteogenic and vasculogenic ASC lineage commitment. Osteoprogenitor-enriched cell populations were found to express RUNX2, MSX2, SP7 (osterix), BGLAP (osteocalcin), SPARC (osteonectin), and SPP1 (osteopontin) in a temporally specific sequence. Irreversible commitment of ASCs to the osteogenic lineage occurred between days 6 and 9 of differentiation. Endothelioprogenitor-enriched cell populations expressed CD34, PECAM1 (CD31), ENG (CD105), FLT1 (Vascular endothelial growth factor [VEGFR1]), and KDR (VEGFR2). Capacity for microtubule formation was evident in as early as 3 days. Functional capacity was assessed in eight coculture combinations for both bone nodule and endothelial tubule formation, and the greatest expression of these end-differentiation phenotypes was observed in the combination of well-differentiated endothelial cells with less-differentiated osteoblastic cells. Taken together, our results demonstrate vascularized bone engineering utilizing ASCs is a promising enterprise, and that coculture strategies should focus on developing a more mature vascular network in combination with a less mature osteoblastic stromal cell.

Hypoxia preconditioning enhances the viability of ADSCs to increase the survival rate of ischemic skin flaps in rats

Use of a skin flap has been a common technique in reconstructive surgery for more than five decades. However, partial necrosis of its distal end is still a serious postoperative complication. Many theories about this problem have been proposed, including deficient blood supply, which is the most accepted theory. In this study we demonstrated that hypoxic preconditioning enhanced the viability of adipose-derived stem cells (ADSCs) in vivo and improved their ability to increase the survival rate of ischemic skin flaps in rats. Seven days after flap elevation, the flap survival rate in the hypoxic preconditioned ADSC group was higher than that in the control group. Moreover, histological examination showed that more ADSCs survived in flaps treated by hypoxic preconditioning. Vascular density in the hypoxic preconditioned ADSC group was 30-90 % greater than that in the control group. In addition, the expressions of vascular endothelial growth factor and hypoxia inducible factor-1α (HIF-1α) were higher in the hypoxic preconditioned ADSC group than in the control group (p < 0.05). This enhancive phenomenon reached its highest level at the precondition times of 3 and 7 days in the hypoxic preconditioned ADSC group. We conclude that hypoxia preconditioning effectively enhances the viability of ADSCs to increase the survival rate of ischemic skin flaps. Furthermore, 3 days is the optimal preconditioning time point.

LEVEL OF EVIDENCE II

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Pathogenesis of infantile hemangiomas

1.Review the key features of the life cycle of infantile hemangiomas.2.Highlight cellular and molecular pathways involved in hemangioma-genesis.3.Discuss theories that may account for hemangioma-genesis.In the past, it was believed that a mother's visual impressions or behavior during pregnancy caused the growth of infantile hemangioma in her unborn child. She might have had an excessive craving for strawberries, witnessed the slaughter of an animal, directly contacted human or animal blood, or mocked a child with a similar birthmark.1 This folklore began to slowly fade once hemangiomas were examined through the light microscope. In 1863, Virchow2 suggested that hemangiomas are composed of proliferating new blood vessels resulting from progressive irritation of tissue. In 1933, Laidlow and Murray3 proposed a phylogenetic origin for hemangiomas and hypothesized that hemangiomas are remnants of vascular tufts functioning as accessory lungs for primitive amphibia. Pack and Miller4 (1950) hypothesized that hemangiomas develop from embryonic islands of angioblastic cells that were isolated from the systemic vasculature during fetal development.

Tissue engineering for the management of chronic wounds: current concepts and future perspectives

Chronic wounds constitute a significant and growing biomedical burden. With the increasing growth of populations prone to dysfunctional wound healing, there is an urgent and unmet need for novel strategies to both prevent and treat these complications. Tissue engineering offers the potential to create functional skin, and the synergistic efforts of biomedical engineers, material scientists, and molecular and cell biologists have yielded promising therapies for non-healing wounds. However, traditional paradigms for wound healing focus largely on the role of inflammatory cells and fail to incorporate more recent research highlighting the importance of stem cells and matrix dynamics in skin repair. Approaches to chronic wound healing centred on inflammation alone are inadequate to guide the development of regenerative medicine-based technologies. As the molecular pathways and biologic defects underlying non-healing wounds are further elucidated, multifaceted bioengineering systems must advance in parallel to exploit this knowledge. In this viewpoint essay, we highlight the current concepts in tissue engineering for chronic wounds and speculate on areas for future research in this increasingly interdisciplinary field.

Endothelial progenitor cells are integrated in newly formed capillaries and alter adjacent fibrovascular tissue after subcutaneous implantation in a fibrin matrix

Vascularization of bioartificial matrices is crucial for successful tissue engineering. Endothelial progenitor cells (EPC) have shown vascularization potential in ischemic conditions and may also support blood vessel formation in tissue-engineered matrices. The aim of our study was to investigate the impact of a well-characterized murine embryonal EPC line (T17b-EPC) on vascularization and fibrovascular granulation tissue formation after suspension in a fibrine matrix followed by subcutaneous implantation in a separation chamber in rats. EPC were fluorescently labelled in vitro prior to implantation. After 3, 7 or 14 days, animals were killed followed by explantation and histological analysis of the constructs. Before the end of the experiment, Bandeirea Simplicifolia lectin was intravenously injected to mark the vascular ingrowth into the implanted constructs. The transplanted cells were histologically detected at all time-points and located almost exclusively within the fibrin matrix at day 3 but the number of cells in the clot continuously decreased over day 7 to day 14. Conversely, cells were detected within the newly formed granulation tissue in increasing numbers from day 3 over day 7 to day 14. Transplanted cells were also found in the intermuscular septa. Cell viability was confirmed by use of an EPC clone expressing β-galactosidase. Fluorescence microscopy demonstrated integration of the transplanted cells in newly formed blood vessels within the fibrovascular granulation tissue adjacent to the fibrin clot. Presence of cells in the fibrin clot lead to thicker granulation tissue and an increased blood vessel diameter compared to cell-free controls. Organ standard controls showed presence of the transplanted cells in spleens at day 14 after transplantation. In summary, EPC exhibited biological activity after subcutaneous implantation in a fibrin matrix by migration from the fibrin clot into the granulation tissue and along intermuscular septae, undergoing differentiation into mature endothelial cells and integration into newly formed blood vessels and altering fibrovascular granulation tissue development. EPC may hold promise to modulate blood vessel formation in bioartificial matrices.

Paracrine effects of mesenchymal stem cells enhance vascular regeneration in ischemic murine skin

New theories on the regeneration of ischemic vasculature have emerged indicating a pivotal role of adult stem cells. The aim of this study was to investigate homing and hemodynamic effects of circulating bone marrow-derived mesenchymal stem cells (MSCs) in a critically ischemic murine skin flap model. Bone marrow-derived mesenchymal stem cells (Lin(-)CD105(+)) were harvested from GFP(+)-donor mice and transferred to wildtype C57BL/6 mice. Animals receiving GFP(+)-fibroblasts served as a control group. Laser scanning confocal microscopy and intravital fluorescence microscopy were used for morphological analysis, monitoring and quantitative assessment of the stem cell homing and microhemodynamics over two weeks. Immunohistochemical staining was performed for GFP, eNOS, iNOS, VEGF. Tissue viability was analyzed by TUNEL-assay. We were able to visualize perivascular homing of MSCs in vivo. After 4 days, MSCs aligned along the vascular wall without undergoing endothelial or smooth muscle cell differentiation during the observation period. The gradual increase in arterial vascular resistance observed in the control group was abolished after MSC administration (P<0.01). At capillary level, a strong angiogenic response was found from day 7 onwards. Functional capillary density was raised in the MSC group to 197% compared to 132% in the control group (P<0.01). Paracrine expression of VEGF and iNOS, but not eNOS could be shown in the MSC group but not in the controls. In conclusion, we demonstrated that circulating bone marrow-derived MSCs home to perivascular sites in critically ischemic tissue, exhibits paracrine function and augment microhemodynamics. These effects were mediated through arteriogenesis and angiogenesis, which contributed to vascular regeneration.

Increased endothelial progenitor cells and vasculogenic factors in higher-staged arteriovenous malformations

ACKGROUND:: Arteriovenous malformations cause significant morbidity, primarily because they expand over time and recur after treatment. The authors hypothesized that neovascularization might contribute to arteriovenous malformation progression.

METHODS

Arteriovenous malformation tissue was collected prospectively from 12 patients after resection. Schobinger stage was determined by clinical history. Neovascularization in stage II lesions (n=7) was compared with stage III arteriovenous malformations (n=5) that had progressed. Specimens were analyzed using immunohistochemistry for CD31, Ki67, and CD34/CD133. Quantitative real-time reverse-transcriptase polymerase chain reaction was used to determine mRNA expression of factors that recruit endothelial progenitor cells: vascular endothelial growth factor (VEGF), stromal cell-derived factor-1α (SDF-1α), and hypoxia-inducible factor-1α (HIF-1α). VEGF receptors (VEGFR1, VEGFR2, neuropilin 1, and neuropilin 2) also were quantified using quantitative real-time reverse-transcriptase polymerase chain reaction.

RESULTS

Stage III arteriovenous malformations showed greater microvessel density (5.8 percent) than stage II lesions (1.3 percent) (p=0.004); no difference in proliferating endothelial cells was noted (p=0.67). CD133CD34 endothelial progenitor cells were elevated in stage III (0.53 percent) compared with stage II arteriovenous malformations (0.25 percent) (p=0.03). HIF-1α and SDF-1α were increased 7.6- and 7.9-fold in stage III compared with stage II lesions (1.7-fold and 3.3-fold), respectively (p=0.02). Neuropilin 1 and neuropilin 2 expression was greater in stage III (5.8-fold and 4.6-fold) than stage II arteriovenous malformations (3.0-fold and 2.4-fold) (p=0.03).

CONCLUSIONS

Higher-staged arteriovenous malformations exhibit increased expression of endothelial progenitor cells and factors that stimulate their recruitment. Neovascularization by vasculogenesis may be involved in progression of arteriovenous malformation.

Effect of mesenchymal stem cells on skin graft to flap prefabrication: an experimental study

Angiogenetic potential has been reported for bone marrow-derived stem cells (BSCs) and adipose-derived stem cells (ASCs). The superficial femoral artery, vein, and fascia were used as a vascular crane for prefabrication model of skin graft to flap. BSCs or ASCs were injected before the adaptation of the graft to the vascular crane depending on the group. The prefabricated grafts were then transferred to inguinal region in every 7 days to observe the viability. In experiment part I (n = 18), the critical time for the prefabrication was found to be 1 week. In experiment part II (n = 12), the control and experiment assays were performed on the same animal to support the data of the experiment part I. The viability of flaps was evaluated. The vascular density was higher in BSC, and ASC groups. The Vascular Endothelial Growth Factor immunohistochemical staining was quantified. Furthermore, mesenchymal stem cells could be helpful in any prefabrication procedure in which neovascularization is indispensable.

Effect of stem cells and fibrin concentration on the vascularization of the Medpor orbital implant

BACKGROUND

To determine the effect of adipose-derived adult stem cells (ADASCs) and optimal concentration of fibrin on fibrovascular ingrowth into porous polyethylene orbital implants (Medpor).

METHODS

Medpor sheet treated with O.25% fibrin only and ADASCs in mixtures containing fibrin (0.25%, 0.5% or 1.25%) were applied to a Medpor sheet and implanted in the back of each of 20 athymic nude mice. After 10 days, implants were removed and observed for fibrovascularization and stability. Haemoglobin, collagen and cellular DNA content were determined in quantitative assays.

RESULTS

Haemoglobin, collagen and cellular DNA levels were significantly higher in ADASC group than in the cell-free implant (0.25% fibrin only) group (P < 0.01). The level of haemoglobin and collagen content was significantly higher in the ADASC + 0.5% fibrin group among the ADASC and fibrin mixtures (P < 0.01).

CONCLUSION

ADASCs significantly improved fibrovascularization on Medpor compared with implants alone. Fibrin, used together with ADASCs to potentiate fibrovascularization, was most effective at concentrations of 0.5%.

T17b murine embryonal endothelial progenitor cells can be induced towards both proliferation and differentiation in a fibrin matrix

Endothelial progenitor cells (EPC) may enhance blood vessel formation in a variety of clinical settings such as ischaemia and tumour angiogenesis as well as in tissue-engineered matrices. In the present study, we cultured a murine endothelial progenitor cell line, T17b, in vitro in cell culture as well as in an FDA-approved fibrin matrix and investigated cell proliferation, differentiation and secretion patterns of the angiogenic growth factor VEGF under hypoxia and differentiation. We show that T17b EPC remain viable for at least 8 days in the fibrin matrix where they proliferate and form clusters including lumen-like structures. Proliferation in fibrin clots overlayed with basal medium (BM) was confirmed morphologically and immunohistochemically by positive Ki67 staining, indicating mitotic activity. Significant cell proliferation and Ki-67 expression were absent when cells were incubated with dibutyryl-cAMP and retinoic acid (RA). Incubation with dibutyryl-cAMP and RA stimulated the expression of the EPC differentiation markers von Willebrand Factor (vWF) and VEGF receptor 2 (VEGFR-2), indicating successful differentiation in the fibrin clot. EPC differentiation induced by dibutyryl-cAMP and RA was confirmed in 2-D chamber slide cultures by positive vWF immunostaining, which was absent in BM controls. EPC chamber slides also displayed positive vWF staining when exposed to hypoxia under BM conditions, indicating EPC activation and differentiation could also be induced by hypoxia. Taken together, T17b EPC secrete increased levels of VEGF when submitted to either hypoxia or differentiation and can be differentiated into mature endothelial cells not only in cell and matrigel cultures but also in a fibrin matrix that is FDA approved for clinical application.

The effect of adipose-derived stem cells on ischemia-reperfusion injury: immunohistochemical and ultrastructural evaluation

BACKGROUND

Advances in the treatment of reperfusion injury have created an opportunity for plastic surgeons to apply these treatments to flaps and implanted tissues. The authors examined the direct and indirect effects of adipose-derived stem cells on ischemia-reperfusion injury on a skin flap model to determine the in vivo differentiation of adipose-derived stem cells to endothelial cells; the levels of vascular endothelial growth factor (VEGF), transforming growth factor-beta, and fibroblast growth factor; and the ultrastructural changes apparent with scanning electron microscopy to clarify the initial events and the following cascades.

METHODS

Two identical cranial based random flaps with a dimension of 1 x 5 cm were elevated on the dorsums of 20 ICR mice. The left flap was designated as the control and the right flap was injected with adipose-derived stem cells. The flaps were then subjected to 6 hours of ischemia by clamping the pedicle, and then reperfusion.

RESULTS

The mean viable flap length in the control and experimental groups was 15.2 +/- 3.4 mm and 24.4 +/- 2.9 mm, respectively. The mean viable flap area in the control and experimental groups was 12.9 +/- 4.1 mm and 21.8 +/- 3.7 mm, respectively. The in vivo differentiation of adipose-derived stem cells to endothelial cells was observed. The immunohistochemical stainings, VEGF, transforming growth factor-beta, and fibroblast growth factor revealed increased levels in the experimental groups. Scanning electron microscopy indicated mild injury in the experimental group.

CONCLUSIONS

The adipose-derived stem cells could prevent ischemia-reperfusion injury, mainly by regulating the growth factors. Although VEGF was the foremost inhibitor of injury, the overall cascade was enhanced by adipose-derived stem cells, with the help of the other growth factors.

Improved viability of random pattern skin flaps through the use of adipose-derived stem cells

BACKGROUND

Flap necrosis caused by inadequate blood supply is a common postoperative complication in reconstructive surgery. Because a putative stem cell population within the adipose tissue has been found to possess angiogenic potential, the authors sought to determine whether these cells might selectively induce neovascularization and increase the viability of random pattern skin flaps.

METHODS

Adipose-derived stem cells were isolated from the inguinal fat pads of ICR mice and expanded ex vivo for three passages. After the elevation of cranially based random pattern skin flaps (3 cm long and 1 cm wide), 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (DiI)-labeled adipose-derived stem cells were then injected into the pedicle base (group A) or 1.5 cm distal to the pedicle (group B). Medium containing no adipose-derived stem cells, mature adipocytes, or basic fibroblast growth factor were injected in three other control groups separately (n = 10 for each group). Millimetric measurements were taken at postoperative day 7 for evaluation of flap viability. Specimens were harvested for histologic analyses.

RESULTS

Adipose-derived stem cells led to a statistically significant increase in flap viability in both group A and group B compared with the control and the adipocyte groups. Histologic examination also demonstrated a statistically significant increase in capillary density in both group A and group B. Moreover, some of the endothelial cells were stained positively for DiI.

CONCLUSIONS

These findings suggest that adipose-derived stem cells have a potential for enhancing the blood supply of random pattern skin flaps. This mechanism might be both the direct differentiation of adipose-derived stem cells into endothelial cells and the indirect effect of angiogenic growth factor released from adipose-derived stem cells.

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.

Hypoxia-induced mediators of stem/progenitor cell trafficking are increased in children with hemangioma

OBJECTIVE

The mechanism of neovascularization during the proliferative phase of infantile hemangioma is poorly understood. It is known that circulating bone marrow-derived endothelial progenitor cells (EPCs) form new blood vessels in ischemic tissues using mediators regulated by the transcription factor, HIF-1alpha. Mobilization of EPCs is enhanced by VEGF-A, matrix metalloproteinase (MMP)-9, and estrogen, whereas homing is secondary to localized expression of stromal cell-derived factor-1alpha (SDF-1alpha). We examined whether these mediators of EPC trafficking are upregulated during the proliferation of infantile hemangioma.

METHODS AND RESULTS

Surgical specimens and blood samples were obtained from children with proliferating hemangioma and age-matched controls (n=10, each group). VEGF-A and MMP-9 levels were measured in blood, and tissue sections were analyzed for SDF-1alpha, MMP-9, VEGF-A, and HIF-1alpha. The role of estrogen as a modulator of hemangioma endothelial cell growth was also investigated. We found that all these mediators of EPC trafficking are elevated in blood and specimens from children with proliferating infantile hemangioma. In vitro, the combination of hypoxia and estrogen demonstrated a synergistic effect on hemangioma endothelial cell proliferation.

CONCLUSIONS

These findings demonstrate that proliferating hemangiomas express known mediators of vasculogenesis and suggest that this process may play a role in the initiation or progression of this disease.

The role of the donor in the repair of the marrow vascular niche following hematopoietic stem cell transplant

Bone marrow sinusoids maintain homeostasis between developing hematopoietic cells and the circulation, and they provide niches for hematopoietic progenitors. Sinusoids are damaged by chemotherapy and radiation. Hematopoietic stem cells (HSCs) have been shown to produce endothelial progenitor cells that contribute to the repair of damaged blood vessels. Because HSCs home to the marrow during bone marrow transplant, these cells may play a role in repair of marrow sinusoids. Here, we explore the role of donor HSCs in the repair of damaged sinusoids following hematopoietic stem cell transplant. We used three methods to test this role: (a) expression of platelet endothelial cell adhesion molecule to identify endothelial progenitors and the presence of the Y chromosome to identify male donor cells in female recipients; (b) presence of the Y chromosome to identify male donor cells in female recipients, and expression of the panendothelial marker mouse endothelial cell antigen-32 to identify sinusoidal endothelium; and (c) use of Tie-2/green fluorescent protein mice as donors or recipients and presence of Dil-Ac-LDL to identify sinusoids. We found that sinusoids were predominantly host-derived posttransplant. Donor cells spread along the marrow vasculature early post-transplant in a pattern that matched stromal-derived factor-1 expression. Furthermore, these engrafting progenitors were positioned to provide physical support, as well as growth and survival signals in the form of vascular-endothelial growth factor-A. Occasionally, donor cells provide cellular "patches" in the damaged sinusoids, although this occurred at a low level compared with hematopoietic engraftment. Donor support for the repair of the marrow vascular niche may be a critical first step of hematopoietic engraftment.

Peripheral infusion of rat bone marrow derived endothelial progenitor cells leads to homing in acute lung injury

BACKGROUND

Bone marrow-derived progenitors for both epithelial and endothelial cells have been observed in the lung. Besides mature endothelial cells (EC) that compose the adult vasculature, endothelial progenitor cells (EPC) are supposed to be released from the bone marrow into the peripheral blood after stimulation by distinct inflammatory injuries. Homing of ex vivo generated bone marrow-derived EPC into the injured lung has not been investigated so far. We therefore tested the hypothesis whether homing of EPC in damaged lung tissue occurs after intravenous administration.

METHODS

Ex vivo generated, characterized and cultivated rat bone marrow-derived EPC were investigated for proliferation and vasculogenic properties in vitro. EPC were tested for their homing in a left-sided rat lung transplant model mimicking a severe acute lung injury. EPC were transplanted into the host animal by peripheral administration into the femoral vein (10(6) cells). Rats were sacrificed 1, 4 or 9 days after lung transplantation and homing of EPC was evaluated by fluorescence microscopy. EPC were tested further for their involvement in vasculogenesis processes occurring in subcutaneously applied Matrigel in transplanted animals.

RESULTS

We demonstrate the integration of intravenously injected EPC into the tissue of the transplanted left lung suffering from acute lung injury. EPC were localized in vessel walls as well as in destructed lung tissue. Virtually no cells were found in the right lung or in other organs. However, few EPC were found in subcutaneous Matrigel in transplanted rats.

CONCLUSION

Transplanted EPC may play an important role in reestablishing the endothelial integrity in vessels after severe injury or at inflammatory sites and might further contribute to vascular repair or wound healing processes in severely damaged tissue. Therapeutic applications of EPC transplantation may ensue.

Involvement of marrow-derived endothelial cells in vascularization

Until recently, the adult neovasculature was thought to arise only through angiogenesis, the mechanism by which new blood vessels form from preexisting vessels through endothelial cell migration and proliferation. However, recent studies have provided evidence that postnatal neovasculature can also arise though vasculogenesis, a process by which endothelial progenitor cells are recruited and differentiate into mature endothelial cells to form new blood vessels. Evidence for the existence of endothelial progenitors has come from studies demonstrating the ability of bone marrow-derived cells to incorporate into adult vasculature. However, the exact nature of endothelial progenitor cells remains controversial. Because of the lack of definitive markers of endothelial progenitors, the in vivo contribution of progenitor cells to physiological and pathological neovascularization remains unclear. Early studies reported that endothelial progenitor cells actively integrate into the adult vasculature and are critical in the development of many types of vascular-dependent disorders such as neoplastic progression. Moreover, it has been suggested that endothelial progenitor cells can be used as a therapeutic strategy aimed at promoting vascular growth in a variety of ischemic diseases. However, increasing numbers of studies have reported no clear contribution of endothelial progenitors in physiological or pathological angiogenesis. In this chapter, we discuss the origin of the endothelial progenitor cell in the embryo and adult, and we discuss the cell's link to the primitive hematopoietic stem cell. We also review the potential significance of endothelial progenitor cells in the formation of a postnatal vascular network and discuss the factors that may account for the current lack of consensus of the scientific community on this important issue.

Vascular Delay Revisited

The technique of vascular delay has been used by plastic surgeons for nearly 500 years and has proven useful for reliably transferring tissue and allowing for a greater volume of tissue to be reliably harvested. Delay procedures are an essential plastic surgical tool for a variety of aesthetic and reconstructive procedures. Despite the widespread use of vascular delay procedures, the mechanism by which this phenomenon occurs remains unclear. A number of groups have exhaustively examined microvascular changes that occur during vascular delay. Theories have been proposed ranging from the dilation of choke vessels to changes in metabolism and new blood vessel formation. Inherent in these theories is the concept that ischemia is able to act as the primary stimulus for vascular changes. The purpose of this review is to revisit the theories proposed to underlie the delay phenomenon in light of recent advances in vascular biology. In particular, the participation of bone marrow-derived endothelial progenitor cells in the delay phenomenon is explored. Greater understanding of the role these cells play in new blood vessel formation will be of considerable clinical benefit to high-risk patients in future applications of delay procedures.