Local rh-VEGF administration enhances skin flap survival more than other types of rh-VEGF administration: a clinical, morphological and immunohistochemical study

The secretome of stressed peripheral blood mononuclear cells increases tissue survival in a rodent epigastric flap model

Reconstructive surgery transfers viable tissue to cover defects and to restore aesthetic and functional properties. Failure rates after free flap surgery range from 3 to 7%. Co-morbidities such as diabetes mellitus or peripheral vascular disease increase the risk of flap failure up to 4.5-fold. Experimental therapeutic concepts commonly use a monocausal approach by applying single growth factors. The secretome of γ-irradiated, stressed peripheral blood mononuclear cells (PBMCsec) resembles the physiological environment necessary for tissue regeneration. Its application led to improved wound healing rates and a two-fold increase in blood vessel counts in previous animal models. We hypothesized that PBMCsec has beneficial effects on the survival of compromised flap tissue by reducing the necrosis rate and increasing angiogenesis. Surgery was performed on 39 male Sprague-Dawley rats (control, N = 13; fibrin sealant, N = 14; PBMCsec, N = 12). PBMCsec was produced according to good manufacturing practices (GMP) guidelines and 2 ml were administered intraoperatively at a concentration of 2.5 × 107 cells/ml using fibrin sealant as carrier substance. Flap perfusion and necrosis (as percentage of the total flap area) were analyzed using Laser Doppler Imaging and digital image planimetry on postoperative days 3 and 7. Immunohistochemical stainings for von Willebrand factor (vWF) and Vascular Endothelial Growth Factor-receptor-3 (Flt-4) were performed on postoperative day 7 to evaluate formation of blood vessels and lymphatic vessels. Seroma formation was quantified using a syringe and flap adhesion and tissue edema were evaluated clinically through a cranial incision by a blinded observer according to previously described criteria on postoperative day 7. We found a significantly reduced tissue necrosis rate (control: 27.8% ± 8.6; fibrin: 22.0% ± 6.2; 20.9% reduction, p = .053 vs. control; PBMCsec: 19.1% ± 7.2; 31.1% reduction, p = .012 vs. control; 12.9% reduction, 0.293 vs. fibrin) together with increased vWF+ vessel counts (control: 70.3 ± 16.3 vessels/4 fields at 200× magnification; fibrin: 67.8 ± 12.1; 3.6% reduction, p = .651, vs. control; PBMCsec: 85.9 ± 20.4; 22.2% increase, p = .045 vs. control; 26.7% increase, p = .010 vs. fibrin) on postoperative day 7 after treatment with PBMCsec. Seroma formation was decreased after treatment with fibrin sealant with or without the addition of PBMCsec. (control: 11.9 ± 9.7 ml; fibrin: 1.7 ± 5.3, 86.0% reduction, 0.004 vs. control; PBMCsec: 0.6 ± 2.0; 94.8% reduction, p = .001 vs. control; 62.8% reduction, p = .523 vs. fibrin). We describe the beneficial effects of a secretome derived from γ-irradiated PBMCs on tissue survival, angiogenesis, and clinical parameters after flap surgery in a rodent epigastric flap model.

Inhibition of autophagy after perforator flap surgery increases flap survival and angiogenesis

BACKGROUND

The survival ratio of multiterritory perforator flap is variable. Therefore, surviving mechanisms are increasingly explored to identify novel therapeutics. The condition of the choke zone is essential for perforator flap survival. In this study, we investigated autophagy in the choke zone after flap surgery.

MATERIALS AND METHODS

The flap model involved a perforator flap with three territories that was located on the right dorsal side of a rat. A total of 36 rats were divided into six groups, including the control, 0 d postoperative (PO), 1, 3, 5, and 7 d PO groups. In addition, 72 rats were divided into three groups, including a control group, a 3-methyladenine (3-MA) group, and a rapamycin group. Skin tissue of rats was used for measuring autophagy proteins, vascular endothelial growth factor (VEGF) expression, and histological examination. On day 7 after surgery, the survival ratio of each flap was determined.

RESULTS

The expression of autophagy and VEGF in the second choke zone (choke II) was increased after flap surgery. Among the three groups, the survival ratio of flaps in the 3-MA group was the highest. Furthermore, the angiogenesis level in the 3-MA group in choke II was the highest among the three groups.

CONCLUSIONS

Autophagy was initiated by surgery in choke II, and VEGF expression in choke II was increased after flap surgery. Inhibiting autophagy after perforator flap surgery is beneficial for flap survival and for promoting angiogenesis in choke II.

Chlorogenic Acid Enhances Abdominal Skin Flap Survival Based on Epigastric Artery in Nondiabetic and Diabetic Rats

Previous studies showed that chlorogenic acid (CGA) accelerates wound healing via its antioxidant activity. We aimed to investigate the effect of CGA in an experimental epigastric abdominal skin flap model in nondiabetic and diabetic rats. Rats were firstly divided into 2 groups: nondiabetic and diabetic. Diabetes was induced by streptozotocin. Then, 4 subgroups were created for each group: vehicle as well as 0.2 mg/0.5 mL, 1 mg/0.5 mL, and 5 mg/0.5 mL CGA treatments. Right epigastric artery-based abdominal skin flaps were elevated and sutured back into their original position. Chlorogenic acid or vehicle was injected once into the femoral arteries by leaving the epigastric artery as the single artery feeding the flaps during the injection. On postoperative day 7, flap survivals were evaluated, and the rats were killed. Distal flap tissues were collected for histopathological and biochemical assays. Chlorogenic acid showed greater flap survival in both nondiabetic and diabetic rats. Capillary density was increased, and necrosis was reduced in the CGA-treated rats. Chlorogenic acid decreased malondialdehyde levels as well as increased reduced glutathione and superoxide dismutase levels in the flap tissues. This study showed that CGA significantly improved flap survival by its antioxidant activities with intra-arterial local injections.

Improvement of Flap Necrosis in a Rat Random Skin Flap Model by In Vivo Electroporation-Mediated HGF Gene Transfer

BACKGROUND

Despite great understanding of underlying mechanisms for flap necrosis and advances in surgical techniques, flap necrosis remains a critical issue. In the present study, the authors investigated the efficacy of electroporation-mediated hepatocyte growth factor (HGF) gene delivery to random dorsal skin flaps (McFarlane) to accelerate wound healing and reduce flap necrosis.

METHODS

Fifteen male Wistar rats (290 to 320 g) were divided randomly into three groups. Group a, the control group (n = 5), underwent surgery and received no gene transfer. Group b received electroporation-mediated HGF gene delivery 24 hours after surgery as a treatment. Group c received electroporation-mediated HGF gene delivery 24 hours before surgery as prophylaxis (n = 5). Planimetry, laser Doppler imaging, and immunohistochemistry were used to assess the efficacy of HGF gene therapy among the groups.

RESULTS

Electroporation-mediated HGF gene delivery significantly decreased flap necrosis percentage compared with the control group in prophylactic and treatment groups (p = 0.0317 and p = 0.0079, respectively) and significantly increased cutaneous perfusion compared with the control group (p = 0.0317 and p = 0.0159, respectively). Moreover, Spearman rank correlation showed a significant negative correlation between flap necrosis percentage and laser index (p = 0.0213 and r = -0.5964, respectively). Furthermore, significantly higher mean CD31 vessel density was detected in treatment and prophylactic groups (p = 0.0079 and p = 0.0159, respectively). In addition, quantitative image analysis revealed significantly higher HGF protein expression in groups b and c (p = 0.0079 and p = 0.0079, respectively).

CONCLUSION

These findings suggested in vivo electroporation-mediated HGF gene delivery enhanced viability and vascularity of the ischemic skin flap.

Dynamics of early stem cell recruitment in skin flaps subjected to ischemia reperfusion injury

OBJECTIVE

Bone marrow-derived stromal cell (BMSCs) therapy improves survival of skin flaps subject to ischemia/reperfusion (I/R) injury. However, very little is known about the trafficking and distribution of BMSCs in post-ischemic skin tissue following intravenous administration. The aim of this study was to assess the behavior of BMSCs in post-ischemic skin flaps and to compare the magnitude and kinetics of accumulation of BMSCs and leukocytes following I/R.

METHODS

Cutaneous flaps perfused by the inferior epigastric vessels were created in C57Bl6 mice. The flaps were subjected to 3.5h of ischemia followed by reperfusion. Wound healing and vascular perfusion were assessed in 3 groups of mice (sham, I/R, and I/R+BMSCs treatment) on days 3, 5, 7 and 14 post-reperfusion. The kinetics and magnitude of BMSCs and leukocyte recruitment were quantified in additional 2 groups (Sham and I/R) after I/R using intravital fluorescence microscopy at 2 and 4h after the intravenous injection of fluorescently labeled BMSCs.

RESULTS

Wound healing after I/R was significantly enhanced in skin flaps of mice treated with BMSCs, compared to controls. The rolling velocity of BMSCs was higher compared to leukocytes both in control mice (32.4±3.7μm/s vs 24.0±2.2μm/s, p<0.05) and in I/R mice (34.6±3.8μm/s vs 20.2±2.3μm/s, p<0.005). However, the rolling velocity of both cell populations was not altered by I/R. The firm adhesion and transendothelial migration of BMSCs did not differ from the values detected for leukocytes for both control and I/R mice.

CONCLUSIONS

The magnitude and kinetics of BMSCs recruitment in skin flaps subjected to I/R are not significantly different from the responses noted for leukocytes, suggesting that similar mechanisms may be involved in the recruitment of both cell populations following I/R.

Effects of calcitriol on random skin flap survival in rats

Calcitriol, a metabolite of vitamin D, is often used in osteoporosis clinics. However, the material has other bioactivities; for example, it accelerates angiogenesis, has anti-inflammatory properties, and inhibits oxidative stress. We investigated the effects of calcitriol in a random skin flap rat model. “McFarlane flap” models were established in 84 male Sprague Dawley rats, divided into two groups. One group received intraperitoneal injections of calcitriol (2 μg/kg/day) whereas control rats received intraperitoneal injections of saline. The percentage flap survival area and tissue water content were measured 7 days later, which showed that calcitriol improved flap survival area and reduced tissue edema. It also increased the mean vessel density and upregulated levels of VEGF mRNA/protein, both of which promote flap angiogenesis. Moreover, it decreased leukocyte and macrophage infiltration, reduced the inflammatory proteins IL1β and IL6, increased SOD activity, decreased MDA content, and upregulated the level of autophagy. Overall, our results suggest that calcitriol promotes skin flap survival by accelerating angiogenesis, having anti-inflammatory effects, reducing oxidative stress, and promoting autophagy.

Gene therapy using hepatocyte growth factor expressing adenovirus improves skin flap survival in a rat model

Hepatocyte growth factor (HGF) is a potent angiogenic factor that can stimulate the production of blood vessels in ischemic tissue. We investigated whether gene therapy using HGF-expressing adenovirus could enhance skin flap survival. Sprague-Dawley rats were randomly divided into three groups. Rats were subdermally injected with HGF-expressing adenovirus (HGF virus group), recombinant HGF (rhHGF group), or phosphate buffered saline (PBS group) 2 days before and immediately after 3 × 9 cm caudal flap elevation. The survival area of the skin flap, the ratio of blood flow, CD31-positive vessels and, VEGF expression were examined. Skin flap viability was significantly increased in the HGF virus group compared to the rhHGF and PBS groups (71.4% ± 5.9%, 63.8%± 6.4%, and 39.2% ± 13.0%, respectively) (P = 0.025). Furthermore, the blood flow ratio was significantly increased in the HGF virus group. In the HGF virus group, the number of CD31-positive vessels and vascular endothelial growth factor (VEGF) expression were significantly increased. Gene therapy using HGF-expressing adenovirus increase VEGF expression, the number of viable capillaries, and blood flow to the flap, thereby improving skin flap survival.

The effect of platelet rich plasma on angiogenesis in ischemic flaps in VEGFR2-luc mice

To improve skin flap healing, one promising strategy in reconstructive surgery might be to optimize platelet rich plasma (PRP) bioactivity and the ischemia-altered expression of genes. We studied both the effect of PRP on ischemic flaps, and whether in vivo bioluminescence imaging (BLI) is a suitable method for the longitudinal monitoring of angiogenesis in surgical wounds. Axial murine skin flaps were created in four experimental groups. In vivo measurements of VEGFR2 expression levels were made every other day until the 14th day. The local VEGF level and microvessel density were quantified on the 14th day via ELISA and immunohistochemistry, and flap survival rates were measured. We demonstrated that PRP and induced ischemia have a beneficial influence on angiogenesis and flap healing. Combining the two resulted in a significantly robust increase in angiogenesis and flap survival rate that was corroborated by bioluminescence imaging of VEGFR2 activity. This study shows that angiogenic effects of PRP may be potentialized by the stimulus of induced ischemia during free flap harvesting, and thus the two procedures appear to have a synergistic effect on flap healing. This study further demonstrates that BLI of modulated genes in reconstructive surgery is a valuable model for longitudinal in vivo evaluation of angiogenesis.

Identification of the Fra-1 transcription factor in healing skin flaps transplants: a potential role as a negative regulator of VEGF release from keratinocytes

The molecular mechanisms underlying successful myocutaneous skin flap integration, as well as the ischemic loss of transplanted tissue on surgery, remain largely unknown. In this study we used a mouse model of caudally based skin flaps to determine molecular patterns of acute transplant re-integration. Gene chip-based transcriptional analysis revealed an up-regulation of the transcription factor Fra-1 in murine skin flap tissue. Epidermal keratinocytes at the wound margins represented a dominant cellular source of Fra-1 in mice. Moreover, Fra-1 protein showed a clear nuclear localization. In addition, Fra-1 protein was also present in nuclei of wound margin keratinocytes located near the suture line in human skin flaps. In vitro studies using the human keratinocyte cell line HaCaT showed that epidermal growth factor (EGF) was a potent inducer of Fra-1 expression in keratinocytes. Ablation of Fral-1 protein using a specific Fra-1 small interfering (si)RNA markedly increased the EGF-induced vascular endothelial growth factor (VEGF) expression from keratinocytes. These data suggest the involvement of an injury-induced Fra-1 transcription factor as a regulator of keratinocyte gene expression, which might act as an antagonistic player to restrict epithelial-driven angiogenic responses during normal skin flap integration.

Microencapsulated myoblasts transduced by the vascular endothelial growth factor (VEGF) gene for the ischemic skin flap

BACKGROUND

This experimental study aimed to explore the influence of locally administered microencapsulated vascular endothelial growth factor (VEGF)-secreting myoblasts on the survival of the ischemic skin flap in rats and to elucidate the underlying molecular mechanism.

METHODS

The pcDNA6/His A-VEGF165 plasmid was constructed, amplified, and transfected into myoblasts. Cells then were encapsulated in a sodium alginate-barium chloride microcapsule. The study investigated 64 Wistar rats (males and females). Two symmetric 2 × 10-cm, full-thickness dorsal ischemic skin flaps were elevated on each rat. One flap was used as the experiment area, and the other was used as a control. The microencapsulated VEGF-secreting myoblasts were injected into the right flap of the rat on preoperative days 0, 2, 4, and 7. The left flap in each animal was injected with the encapsulated untransfected cells. The 64 rats were randomly divided into four groups of 16 rats each.

RESULTS

The effect of the experimental group was significantly better than that of the control group. The experimental group had a certain time-dependent effect.

CONCLUSIONS

Microencapsulated VEGF-secreting-myoblasts may be a promising therapy for ischemic flaps in rats.

Role of wound macrophages in skin flap loss or survival in an experimental diabetes model

BACKGROUND

Tightly controlled wound inflammation is a central determinant of skin flap survival in healthy mice. This study investigated inflammatory response patterns in caudally pedicled skin flaps in diabetic mice during severely impaired conditions of necrotic skin flap tissue loss.

METHODS

Skin flap biopsies were analysed by RNase protection assay, quantitative real-time polymerase chain reaction, immunohistochemistry, enzyme-linked immunosorbent assay and immunoblotting.

RESULTS

Skin flaps were characterized by the necrotic loss of tissue starting from distal areas of the flaps in diabetic mice. Decay of epidermal and dermal structures within skin flap tissue was paralleled by an immune cell-mediated expression of chemokines (macrophage inflammatory protein 2, macrophage chemoattractant protein 1), cyclo-oxygenase (COX) 2 and inducible nitric oxide synthase (iNOS). Distal regions of necrotic skin flap tissue were infiltrated by excess numbers of neutrophils and macrophages, and the latter were polarized towards a proinflammatory state as they expressed COX-2 and iNOS. Experimental depletion of inflammatory macrophages inhibited necrotic destruction of the distal skin flap tissue in diabetic mice despite the persistence of neutrophil infiltration and inflammation.

CONCLUSION

Wound macrophages play a pivotal role in determining the survival or loss of skin flap tissue under disturbed wound healing conditions in obese diabetic mice.

Cartilage oligometric matrix protein-angiopoietin-1 promotes revascularization through increased survivin expression in dermal endothelial cells of skin grafts in mice

The present study examined the effects of cartilage oligometric matrix protein angiopoietin-1 (COMP-Ang1) on the revascularization of mice skin grafts. Full-thickness skin grafts were autotransferred into BALB/c mice. The donor grafts were soaked in COMP-Ang1 protein (50 mug/ml, n = 10) or in bovine serum albumin (BSA) (50 mug/ml, n = 10) dissolved in 1 ml of sterile, phosphate-buffered saline for 5 minutes before transfer. Revascularization of the grafts was monitored using an intravital microscope on postoperative days 3, 4, and 5. Morphological and immunohistochemical analyses were performed to evaluate platelet-endothelial cell adhesion molecule-1 and survivin expression and apoptotic signal in the transplanted grafts. Grafts soaked in COMP-Ang1 (COMP-Ang1 group) showed significantly increased revascularization compared with grafts soaked in BSA (BSA group) on intravital microscopy and platelet-endothelial cell adhesion molecule-1 staining. The COMP-Ang1 group showed a significant increase of survivin expression in the endothelial cells and a reduction of apoptotic signal in comparison to the BSA group. Therefore, we believe that COMP-Ang1 provides the therapeutic benefit of enhancing the survival of vascular endothelial cells during transplantation of skin graft.

The effect of chitosan hydrogel containing DMEM/F12 medium on full-thickness skin defects after deep dermal burn

Burn wound excision is considered necessary to prepare skin for grafting, and the success of graft "take" is thought to be dependent on the vascular supply to the wound. We previously showed that photocrosslinkable chitosan hydrogel containing DMEM/F12 medium (medium-Az-CH-LA) is a biocompatible and biodegradable biomaterial that promotes re-epithelialization and neovascularization. The current study was designed to determine the effect of medium-Az-CH-LA on deep dermal burn. Sixteen male Wistar rats were randomly divided into two groups that were treated with medium-Az-CH-LA (n=5) or a collagen sponge (n=5). Under anesthesia, the dorsal fur was shaved and the skin was exposed to water at 95 degrees C for 10s. After 2h, damaged tissue was removed from the fascia and dressed with medium-Az-CH-LA or a collagen sponge. Specimens were obtained after 2, 4, 6, 8, 12, 16 and 32 days for histological analysis. There was no significant difference in the time required for wound closure between the two groups, but the thickness of the granulation tissue in the medium-Az-CH-LA-treated group was greater than that in the collagen sponge-treated group. Moreover, degradation and neovascularization occurred earlier in the group treated with medium-Az-CH-LA compared with the collagen sponge-treated group. These findings suggest that early degradative and angiogenic activities of medium-Az-CH-LA may be beneficial for granulation tissue formation in deep dermal burn wounds.

Efficacy and mechanism of adenovirus-mediated VEGF-165 gene therapy for augmentation of skin flap viability

Skin ischemic necrosis due to vasospasm and/or insufficient vascularity is the most common complication in the distal portion of the skin flap in reconstructive surgery. This project was designed to test our hypothesis that preoperative subdermal injection of adenoviral vectors encoding genes for vascular endothelial growth factor-165 (Ad.VEGF-165) or endothelial nitric oxide (NO) synthase (Ad.eNOS) effectively augments skin viability in skin flap surgery and that the mechanism of Ad.VEGF-165 gene therapy involves an increase in synthesis/release of the angiogenic and vasodilator factor NO. PBS (0.5 ml) or PBS containing Ad.VEGF-165, Ad.eNOS, or adenovirus (Ad.Null) was injected subdermally into the distal half of a mapped rat dorsal skin flap (4 × 10 cm) 7 days preoperatively, and skin flap viability was assessed 7 days postoperatively. Local subdermal gene therapy with 2 × 107–2 × 1010 plaque-forming units of VEGF-165 increased skin flap viability compared with PBS- or Ad.Null-injected control ( P < 0.05). Subdermal Ad.VEGF-165 and Ad.eNOS gene therapies were equally effective in increasing skin flap viability at 5 × 108 plaque-forming units. Subdermal Ad.VEGF-165 therapy was associated with upregulation of eNOS protein expression, Ca2+-dependent NOS activity, synthesis/release of NO, and increase in capillary density and blood flow in the distal portion of the skin flap. Injection of the NOS inhibitor Nω-nitro-l-arginine (15 mg/kg im), but not the cyclooxygenase inhibitor indomethacin (5 mg/kg im), 45 min preoperatively completely abolished the increase in skin flap blood flow and viability induced by Ad.VEGF-165 injected subdermally into the mapped skin flap 7 days preoperatively. We have demonstrated for the first time that 1) Ad.VEGF-165 and Ad.eNOS mapped skin flap injected subdermally into the mapped skin flap 7 days preoperatively are equally effective in augmenting viability in the rat dorsal skin flap compared with control, 2) the mechanism of subdermal Ad.VEGF-165 gene therapy in augmenting skin flap viability involves an increase in NO synthesis/release downstream of upregulation of eNOS protein expression and Ca2+-dependent NOS activity, and 3) the vasodilating effect of NO may predominantly mediate subdermal Ad.VEGF gene therapy in augmenting skin flap blood flow and viability.

Vascular endothelial growth factor 121 is the predominant isoform in psoriatic scales

Vascular endothelial growth factor (VEGF) is a powerful agent that causes hyperpermeability of blood vessels as well as endothelial cell proliferation. Recent investigations have revealed that production of VEGF increases in epidermis of psoriatic lesions, and the overproduced VEGF plays an important role in the pathogenesis of psoriasis. In this study, we used immunohistochemical staining as well as extraction of stratum corneum with physiological saline to further analyse VEGF produced in psoriatic lesions. Biological activity of VEGF in the psoriatic scales was assayed by cultured human umbilical vein endothelial cells in vitro. The immunohistochemical examination confirmed an increased production of VEGF in the keratinocytes of psoriatic lesions. In addition, we found that the content of VEGF contained in the psoriatic scales was approximately 50 times greater than that in normal stratum corneum. We also found that VEGF 121 isoform, which has an exclusive ability to cause hyperpermeability of blood vessels, was predominantly detected in psoriatic scales, suggesting a major role of VEGF 121 isoform on the altered structure of microvessels in psoriatic lesions.