Adenovirus-mediated transforming growth factor-β ameliorates ischemic necrosis of epigastric skin flaps in a rat model1, 2

VEGF and Other Gene Therapies Improve Flap Survival-A Systematic Review and Meta-Analysis of Preclinical Studies

Surgical flaps are basic tools in reconstructive surgery. Their use may be limited by ischemia and necrosis. Few therapies address or prevent them. Genetic therapy could improve flap outcomes, but primary studies in this field present conflicting results. This systematic review and meta-analysis aimed to appraise the efficacy of external gene delivery to the flap for its survival in preclinical models. This review was registered with PROSPERO (CRD42022359982). PubMed, Embase, Web of Science, and Scopus were searched to identify studies using animal models reporting flap survival outcomes following any genetic modifications. Random-effects meta-analysis was used to calculate mean differences in flap survival with accompanying 95% CI. The risk of bias was assessed using the SYRCLE tool. Subgroup and sensitivity analyses were performed to ascertain the robustness of primary analyses, and the evidence was assessed using the GRADE approach. The initial search yielded 690 articles; 51 were eventually included, 36 of which with 1576 rats were meta-analyzed. VEGF gene delivery to different flap types significantly improved flap survival area by 15.66% (95% CI 11.80-19.52). Other interventions had smaller or less precise effects: PDGF-13.44% (95% CI 3.53-23.35); VEGF + FGF-8.64% (95% CI 6.94-10.34); HGF-5.61% (95% CI 0.43-10.78); FGF 3.84% (95% CI 1.13-6.55). Despite considerable heterogeneity, moderate risk of bias, and low quality of evidence, the efficacy of VEGF gene therapy remained significant in all sensitivity analyses. Preclinical data indicate that gene therapy is effective for increasing flap survival, but further animal studies are required for successful clinical translation.

miR-31, miR-155, and miR-221 expression profiles and their association with graft skin tolerance in a syngeneic vs. allogeneic murine skin transplantation model

Grafting is the gold standard for the treatment of severe skin burns. Frequently, allogeneic tissue is the only transient option for wound coverage, but their use risks damage to surrounding tissues. MicroRNAs have been associated with acute rejection of different tissues/organs. In this study, we analyzed the expression of miR-31, miR-155, and miR-221 and associate it with graft tolerance or rejection using a murine full-thickness skin transplantation model. Recipient animals for the syngeneic and allogeneic groups were BALB/c and C57BL/6 mice, respectively; donor tissues were obtained from BALB/c mice. After 7 days post-transplantation (DPT), the recipient skin and grafts in the syngeneic group maintained most of their structural characteristics and transforming growth factor (TGF)β1 and TGFβ3 expression. Allografts were rejected early (Banff grades II and IV at 3 and 7 DPT, respectively), showing damage to the skin architecture and alteration of TGFβ3 distribution. miRNAs skin expression changed in both mouse strains; miR-31 expression increased in the recipient skin of syngeneic grafts relative to that of allogeneic grafts at 3 and 7 DPT (p < 0.05 and p < 0.01, respectively); miR-221 expression increased in the same grafts at 7 DPT (p < 0.05). The only significant difference between donor tissues was observed for miR-155 expression at 7 DPT which was associated with necrotic tissue. Only miR-31 and miR-221 levels were increased in the blood of BALB/c mice that received syngeneic grafts after 7 DPT. Our data suggest that local and systemic miR-31 and miR-221 overexpression are associated with graft tolerance.

Extracorporeal Shock Wave Stimulates Angiogenesis and Collagen Production in Facial Soft Tissue

BACKGROUND

This study investigated the efficacy of extracorporeal shock wave (ESW) application in stimulating dermal thickness, vascularity, and collagen synthesis of facial skin in a large animal model.

MATERIALS AND METHODS

The facial skin of the maxillary and mandibular areas of goats (n = 6 per group) was treated with ESWs of different intensities (0.15 and 0.45 mJ/mm²; 1000 pulses). After 4 d, histology and immunohistochemistry were used to evaluate the following: dermal thickness, total number and abundance of microvessels, amount of type 1 collagen, and α-smooth muscle actin expression.

RESULTS

Dermal thickness, number and abundance of microvessels, and collagen synthesis increased after ESW application at both intensities (each P < 0.05). When comparing ESW groups, the highest collagen abundance was seen after 0.15 mJ/mm² (P = 0.034), whereas the highest number of microvessels was detected after treatment with 0.45 mJ/mm² (P = 0.002).

CONCLUSIONS

A single-session application of focused low-energy ESWs to facial skin can increase dermal thickness by stimulating collagen production and local microcirculation. These findings commend the technique for future investigation for pretreatment of local or microvascular skin flaps to enhance tissue healing.

The Effect of Ozonated Olive Oil on Neovascularizatıon in an Experimental Skin Flap Model

OBJECTIVE

Angiogenesis is an important factor for flap viability. It has been reported that ozonated oil contributed to improved neovascularization in an acute cutaneous wound healing model. This study was undertaken to evaluate the effect of ozonated olive oil on vascular endothelial growth factor (VEGF)-mediated neovascularization of skin flaps in rats.

STUDY DESIGN

A skin flap model was established in 21 rats and evaluated within 3 groups. No treatment was given to the rats in group 1. Olive oil and ozonated olive oil were topically applied (twice daily) to the flap surface for 7 days in groups 2 and 3, respectively. Immunohistochemical staining was performed to analyze the expressions of VEGF and CD34.

RESULTS

The mean numbers of VEGF- and CD34-positive staining microvascular structures were 8.86 (SD, 1.35) and 10.29 (SD, 1.80) in group 1, 15.00 (SD, 1.41) and 15.57 (SD, 1.72) in group 2, and 25.14 (SD, 2.41) and 25.00 (SD, 2.16) in group 3. The VEGF and CD34 expressions in group 3 were significantly higher than those in group 2 (P < .001). Their expressions in group 2 were significantly higher than those in group 1 (P < .001).

CONCLUSIONS

Both ozonated olive oil and olive oil improved neovascularization when they were topically applied on skin flaps. The effect of ozone was more prominent.

The rat groin flap model redesigned for evaluating treatment effects on ischemia-reperfusion injury

BACKGROUND

Although there is a wide application of the rat extended groin flap (epigastric skin flap) in studying different clinical issues, inconsistency arises between studies because many parameters of the extended groin flap have not been well defined.

MATERIALS AND METHODS

The flap is based on the superficial inferior epigastric vessels, which give into a lateral and a medial branch distally. Herein, three steps were taken to redesign this model: First, the ventral vascular anatomy was visualized through an imaging study to determine the flap borders. Second, different ischemic durations were induced on five groups of Lewis rats (n = 5 in each group) by clamping the femoral artery; group 1 (sham group) received no ischemic insult after elevation and was immediately repositioned, and groups 2, 3, 4, and 5 received 12-, 14-, 16-, and 18-hour ischemia, respectively. Percentage of necrosis area was measured after 5 days. Third, the redesigned groin flap model was tested with the ischemic postconditioning for validation.

RESULTS

The flap borders were determined such that both branches of the superficial inferior epigastric vessels were always included to ensure blood supply consistency. As the 14-hour ischemia induced the least variation in necrotic area on rats, it was chosen for further studies. In addition, ischemic postconditioning after 14-hr ischemia resulted in significant reduction of necrosis in this model.

CONCLUSIONS

We have redesigned the extended groin flap model with better-defined borders and consistent vascular anatomy. The ischemia duration was calibrated with predictable necrosis pattern and the practicality was demonstrated. With this model, precise assessment of treatment efficacies on ischemia-reperfusion injury could be achieved in future studies.

Effect of preoperative subcutaneous platelet-rich plasma and fibrin glue application on skin flap survival

BACKGROUND

The aim of this study was to compare the effects of preoperative subcutaneous platelet-rich plasma and fibrin glue administration on skin flap survival.

METHODS

One week before surgery; saline, platelet-rich plasma, fibrin glue, and thrombin solutions were applied under rat skin flap areas in Groups I, II, III, and IV, respectively. Unipedicled epigastric flaps were elevated in the first three groups but could not be elevated in Group IV because of preoperative abdominal skin necrosis. Necrotic area measurements, microangiography, and histological and immunohistochemical evaluations were performed.

RESULTS

Platelet-rich plasma reduced the percentage of necrotic area when compared to other groups. Histologically and microangiographically an increased number of arterioles were observed in the platelet-rich plasma group. Thrombin (when used alone) caused abdominal skin necrosis. Increased expression of VEGF and PDGF was found in all platelet-rich plasma-treated flaps. There was no significant difference between groups with respect to TGF-β3 staining intensity.

CONCLUSION

In this study preoperative administration of platelet-rich plasma mimicked the pharmacological delay effect and enhanced flap survival. Individual use of thrombin was found to be unsuitable in flap surgery.

LEVEL OF EVIDENCE I

This journal requires that authors assign a level of evidence to each article.

Topical application of 17β-estradiol (E2) improves skin flap survival through activation of endothelial nitric oxide synthase in rats

This study investigates the influence of 17β-estradiol (E2) on nitric oxide (NO) production in endothelial cell cultures and the effect of topical E2 on the survival of skin flap transplants in a rat model. Human umbilical vein endothelial cells were treated with three different E2 concentrations and nitrite (NO2) concentrations, as well as endothelial nitric oxide synthase (eNOS) protein expressions were analyzed. In vivo, random-pattern skin flaps were raised in female Wistar rats 14 days following ovariectomy and treated with placebo ointment (group 1), E2 as gel (group 2), and E2 via plaster (group 3). Flap perfusion, survival, and NO2 levels were measured on postoperative day 7. In vitro, E2 treatment increased NO2 concentration in cell supernatant and eNOS expression in cell lysates (p < 0.05). In vivo, E2 treated (gel and plaster groups) demonstrated significantly increased skin flap survival compared to the placebo group (p < 0.05). E2 plaster-treated animals exhibited higher NO2 blood levels than placebo (p < 0.05) paralleling the in vitro observations. E2 increases NO production in endothelial cells via eNOS activation. Topical E2 application can significantly increase survival of ischemically challenged skin flaps in a rat model and may augment wound healing in other ischemic situations via activation of NO production.

The role of androgens on hypoxia-inducible factor (HIF)-1α-induced angiogenesis and on the survival of ischemically challenged skin flaps in a rat model

BACKGROUND

Effects of androgens on angiogenesis are controversial. Hypoxia-inducible factor (HIF)-1α promotes expression of vascular endothelial growth factor (VEGF) that stimulates angiogenesis.

PURPOSE

This study investigates whether androgens stabilize HIF-1α in endothelial cells, and androgen depletion decreases VEGF concentrations and skin flap survival.

MATERIALS AND METHODS

Male human umbilical vein endothelial cells (HUVECs) were exposed to dihydrotestosterone (DHT) and HIF-1α expression was measured. In male Wistar rats, standardized proximally based random pattern dorsal skin flaps (3 × 9 cm) were raised 4 weeks after orchiectomy and sham operation, respectively (n = 10, each). Flap VEGF concentrations (immunohistochemistry), perfusion (Laser Doppler), and viability (digital planimetry) were measured.

RESULTS

DHT induced HIF-1α expression in HUVECs. Androgen depletion induced decreased VEGF expression (P = 0.003), flap perfusion (P < 0.05), and survival (44.4% ± 5.2%) compared to controls (35.5% ± 4.5%; P = 0.003).

CONCLUSION

In vitro, androgens may stimulate HIF-1α under normoxic conditions. In rats, androgen depletion decrease VEGF expression and flap survival.

Dimethyloxalylglycine stabilizes HIF-1α in cultured human endothelial cells and increases random-pattern skin flap survival in vivo

BACKGROUND

The goal of this study was to evaluate in vitro and in vivo the effects of up-regulation of the proangiogenic hypoxia inducible factor (HIF)-1α induced by dimethyloxalylglycine on endothelial cell cultures and on skin flap survival.

METHODS

Human umbilical vein endothelial cell cultures were exposed to hypoxic conditions, to dimethyloxalylglycine, and to cobalt chloride for up to 24 hours. Expression of HIF-1α and vascular endothelial growth factor (VEGF) in cell culture media was analyzed. In vivo, 20 male Wistar rats were assigned randomly to either the treatment group (dimethyloxalylglycine intraperitoneal injection, n = 10) or the control group (saline intraperitoneal injection, n = 10). A dorsal skin flap was raised in all animals and sutured back into place. Flap survival was evaluated on postoperative day 7 by laser Doppler and digital planimetry.

RESULTS

In vitro treatment of human umbilical vein endothelial cells during a 24-hour period showed a significant elevation of VEGF expression with dimethyloxalylglycine exposure (92 ± 35 pg/mg total cellular protein) or hypoxia exposure (88 ± 21 pg/mg total cellular protein) compared with controls (23 ± 10 pg/mg total cellular protein) (p < 0.05 for both). In vivo experiments showed a significant decrease of flap necrosis in the treatment group animals versus controls (35.95 ± 5.03 percent versus 44.42 ± 5.18 percent, p < 0.05). The laser Doppler evaluation revealed significantly increased blood flow in the proximal two-thirds of the flap in the treatment group compared with the control group (p < 0.05).

CONCLUSION

Dimethyloxalylglycine treatment significantly increases VEGF and HIF-1α expression in endothelial cell cultures and enhances skin flap survival in vivo in a rat model.

Exercise enhances myocardial ischemic tolerance via an opioid receptor-dependent mechanism

Exercise increases serum opioid levels and improves cardiovascular health. Here we tested the hypothesis that opioids contribute to the acute cardioprotective effects of exercise using a rat model of exercise-induced cardioprotection. For the standard protocol, rats were randomized to 4 days of treadmill training and 1 day of vigorous exercise ( day 5), or to a sham exercise control group. On day 6, animals were killed, and global myocardial ischemic tolerance was assessed on a modified Langendorff apparatus. Twenty minutes of ischemia followed by 3 h of reperfusion resulted in a mean infarct size of 42 ± 4% in hearts from sham exercise controls and 21 ± 3% ( P < 0.001) in the exercised group. The cardioprotective effects of exercise were gone by 5 days after the final exercise period. To determine the role of opioid receptors in exercise-induced cardioprotection, rats were exercised according to the standard protocol; however, just before exercise on days 4 and 5, rats were injected subcutaneously with 10 mg/kg of the opioid receptor antagonist naltrexone. Similar injections were performed in the sham exercise control group. Naltrexone had no significant effect on baseline myocardial ischemic tolerance in controls (infarct size 43 ± 4%). In contrast, naltrexone treatment completely blocked the cardioprotective effect of exercise (infarct size 40 ± 5%). Exercise was also associated with an early increase in myocardial mRNA levels for several opioid system genes and with sustained changes in a number of genes that regulate inflammation and apoptosis. These findings demonstrate that the acute cardioprotective effects of exercise are mediated, at least in part, through opioid receptor-dependent mechanisms that may include changes in gene expression.

Enhanced angiogenesis in grafted skins by laser-induced stress wave-assisted gene transfer of hepatocyte growth factor

Treatment to increase secretion of growth factors related to angiogenesis by gene transfection is a promising therapeutic solution for improving the outcome of tissue transplantation. We attempted to deliver a therapeutic vector construct carrying the human hepatocyte growth factor (hHGF) gene to skin grafts of rats using laser-induced stress waves (LISWs), with the objective of enhancing their adhesion. First we delivered the hHGF gene to rat native skin in vivo to determine the optimum gene transfer conditions. We then transferred the hHGF gene to excised rat skins, with which autografting was performed. We found that the density and uniformity of neovascularities were significantly enhanced in the grafted skins that were transfected using LISWs. These results suggest the efficacy of this method to improve the outcome of skin grafting. To our knowledge, this is the first experimental demonstration of a therapeutic efficacy based on LISW-mediated gene transfection. Since the present method can be applied not only to various types of tissues but also to bioengineered tissues, this technique has the potential to contribute to progress in transplantation medicine and future regenerative medicine.

Improvement of survival of skin flaps by combined gene transfer of hepatocyte growth factor and prostacyclin synthase

BACKGROUND

Increasing the local blood flow is a critical factor for long-term survival of skin flaps. Thus, a molecular therapy to increase the blood flow by means of an angiogenic factor is considered to be a useful strategy to improve skin flap survival. We focused on a combined strategy to stimulate not only angiogenesis, but also vasodilation of local microvessels, using co-transfection of the hepatocyte growth factor (HGF) and prostacyclin synthase (PGIS) genes to enhance the survival of random-pattern skin flaps.

METHODS AND RESULTS

A 2 x 8 cm full thickness cranial pedicled random-pattern flap was made on the back of each 12-week-old male rat. At 3 days before operation, 400 microg of human HGF and PGIS naked plasmid DNA or control plasmid was transfected into the flaps by needle-less injection using a Shima Jet, resulting in successful expression of human HGF and PGIS in the skin flaps. Transfection of both genes into the distal half of skin flaps at 3 days prior to operation significantly increased the survival rate of skin flaps, while transfection all over the flaps did not. In addition, transfection prior to operation was more effective than simultaneous treatment. Moreover, co-transfection of these genes improved the survival area of skin flaps, accompanied by an increase in blood flow of skin flaps, even in a diabetic model.

CONCLUSIONS

Overall, these results indicate that combination treatment with HGF and PGIS genes by Shima Jet could be an effective strategy to improve skin flap survival.

Comparison of the effectiveness of gene therapy with transforming growth factor-beta or extracorporal shock wave therapy to reduce ischemic necrosis in an epigastric skin flap model in rats

The induction of neoangiogenesis by exogenous growth factors in failing skin flaps has recently yielded promising results. Gene transfer with virus vectors has been introduced as a highly capable route of administration for growth factors, such as vascular endothelial growth factor or fibroblast growth factor. Extracorporal shock waves (ESW) deliver energy by means of high amplitudes of sound to the target tissue and have been shown to induce angiogenesis. We compared the effectiveness of gene therapy with adenovirus-mediated transforming growth factor-beta (TGF-beta) and ESW therapy to treat ischemically challenged epigastric skin flaps in a rat model. Thirty male Sprague-Dawley rats were divided into three groups of 10 each with an 8 x 8 cm epigastric skin flap. Rats received either subdermal injections of adenovirus (Ad) encoding TGF-beta (10(8) pfu) or ESW treatment with 750 impulses at 0.15 mJ/mm2. The third group received no treatment and served as a control group. Flap viability was evaluated after 7 days and digital images of the epigastric flaps were taken and areas of necrotic zones relative to total flap surface area calculated. Histologic evaluation and increased angiogenesis were confirmed by CD31 immunohistochemistry. Overall, there was a significant increase in mean percent surviving area in the Ad-TGF-beta group and the ESW group compared to the control group (ESW group: 97.7 +/- 1.8% vs. Ad-TGF-beta: 90.3 +/- 4.0% and control group: 82.6 +/- 4.3%; p < 0.05). Furthermore, in the ESW group mean percent surviving areas were significantly larger than in the Ad-TGF-beta group (ESW group: 97.7 +/- 1.8% vs. Ad-TGF-beta: 90.3 +/- 4.0%; p < 0.05). Flap vascularization was increased by Ad-TGF-beta and ESW with numerous vessels, however, there was no significant difference between the two treatment groups. We conclude that treatment with ESW enhances epigastric skin flap survival significantly more than Ad-TGF-beta treatment and thus represents a modality that is feasible, cost-effective, and less invasive compared to gene therapy with growth factors to improve blood supply to ischemic tissue.

Gene therapy with adenovirus-mediated VEGF enhances skin flap prefabrication

We investigated the feasibility in rats of enhancing skin-flap prefabrication with subdermal injections of adenovirus-encoding vascular endothelial growth factor (Ad-VEGF). The left saphenous vascular pedicle was used as a source for vascular induction. A peninsular abdominal flap (8 x 8 cm) was elevated as distally based, keeping the epigastric vessels intact on both sides. After the vascular pedicle was tacked underneath the abdominal flap, 34 rats were randomly divided into three groups according to treatment protocol. The implantation site around the pedicle was injected with Ad-VEGF in group I (n = 10), with adenovirus-encoding green fluorescent protein (Ad-GFP) in control group I (n = 14), and with saline in control group II (n = 10). All injections were given subdermally at four points around the implanted vessel by an individual blinded to the treatment protocol. The peninsular flap was sutured in its place, and 4 weeks later, an abdominal island flap based solely on the implanted vessels was elevated. The prefabricated island flap was sutured back, and flap viability was evaluated on day 7. Skin specimens were stained with hematoxylin and eosin for histological evaluation. In two rats from each group, microangiography was performed to visualize the vascularity of the prefabricated flaps. There was a significant increase in survival of prefabricated flaps in the Ad-VEGF group compared to the control groups: Ad-VEGF, 88.9 +/- 6.1% vs. Ad-GFP, 65.6 +/- 9.4% (P < 0.05) and saline, 56.0 +/- 3.4% (P < 0.05). Sections from four prefabricated flaps treated with Ad-GFP revealed multiple sites of shiny deposits of green fluorescent protein around the area of local administration 1 day and 3 weeks after gene therapy. Histological examination done under high-power magnification (x400) with a light microscope revealed increased vascularity and mild inflammation surrounding the implanted vessel in all groups. However, we were unable to demonstrate any significant quantitative difference with respect to vascularity and inflammatory infiltrates in prefabricated flaps treated with Ad-VEGF compared with controls. Microangiographic studies showed increased vascularity around the implanted pedicle, which was similar in all groups. However, vascularization was distributed in a larger area in the prefabricated flaps treated with Ad-VEGF. In this study, the authors demonstrated that adenovirus-mediated VEGF gene therapy increased the survival of prefabricated flaps, suggesting that it may allow prefabrication of larger flaps and have the potential to reduce the time required for flap maturation.