AdVEGF165gene transfer increases survival in overdimensioned skin flaps

Biologic Brachytherapy: Genetically Modified Surgical Flap as a Therapeutic Tool-A Systematic Review of Animal Studies

Surgical flaps are rudimentary tools in reconstructive surgery, especially following extensive solid tumour resections. They cover skin and soft tissue defects but are prone to ischaemia and necrosis. Since their primary aim is reconstruction, they rarely exhibit a therapeutic activity against the treated disease. Attempts have been made to develop a new therapeutic strategy-biologic brachytherapy, which uses genetically engineered surgical flaps as a drug delivery vehicle, allowing the flap tissue to act as a "biologic pump". This systematic review summarizes the preclinical evidence on using genetically modified surgical flaps. A literature search was conducted in PubMed, EMBASE, Scopus and Web of Science. The initial literature search yielded 714 papers, and, eventually, seventy-seven studies were included in qualitative analysis. The results show that genetic enhancement of flaps has been used as a local or systemic therapy for numerous disease models. Frequently, it has been used to increase flap survival and limit ischaemia or promote flap survival in a non-ischemic context, with some studies focusing on optimizing the technique of such gene therapy. The results show that genetically modified flaps can be successfully used in a variety of contexts, but we need more studies to implement this research into specific clinical scenarios.

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.

Endothelial Phospholipase Cγ2 Improves Outcomes of Diabetic Ischemic Limb Rescue Following VEGF Therapy

Therapeutic vascular endothelial growth factor (VEGF) replenishment has met with limited success for the management of critical limb-threatening ischemia. To improve outcomes of VEGF therapy, we applied single-cell RNA sequencing (scRNA-seq) technology to study the endothelial cells of the human diabetic skin. Single-cell suspensions were generated from the human skin followed by cDNA preparation using the Chromium Next GEM Single-cell 3' Kit v3.1. Using appropriate quality control measures, 36,487 cells were chosen for downstream analysis. scRNA-seq studies identified that although VEGF signaling was not significantly altered in diabetic versus nondiabetic skin, phospholipase Cγ2 (PLCγ2) was downregulated. The significance of PLCγ2 in VEGF-mediated increase in endothelial cell metabolism and function was assessed in cultured human microvascular endothelial cells. In these cells, VEGF enhanced mitochondrial function, as indicated by elevation in oxygen consumption rate and extracellular acidification rate. The VEGF-dependent increase in cell metabolism was blunted in response to PLCγ2 inhibition. Follow-up rescue studies therefore focused on understanding the significance of VEGF therapy in presence or absence of endothelial PLCγ2 in type 1 (streptozotocin-injected) and type 2 (db/db) diabetic ischemic tissue. Nonviral topical tissue nanotransfection technology (TNT) delivery of CDH5 promoter-driven PLCγ2 open reading frame promoted the rescue of hindlimb ischemia in diabetic mice. Improvement of blood flow was also associated with higher abundance of VWF+/CD31+ and VWF+/SMA+ immunohistochemical staining. TNT-based gene delivery was not associated with tissue edema, a commonly noted complication associated with proangiogenic gene therapies. Taken together, our study demonstrates that TNT-mediated delivery of endothelial PLCγ2, as part of combination gene therapy, is effective in diabetic ischemic limb rescue.

Nonviral Locally Injected Magnetic Vectors for In Vivo Gene Delivery: A Review of Studies on Magnetofection

Magnetic nanoparticles have been widely used in nanobiomedicine for diagnostics and the treatment of diseases, and as carriers for various drugs. The unique magnetic properties of "magnetic" drugs allow their delivery in a targeted tumor or tissue upon application of a magnetic field. The approach of combining magnetic drug targeting and gene delivery is called magnetofection, and it is very promising. This method is simple and efficient for the delivery of genetic material to cells using magnetic nanoparticles controlled by an external magnetic field. However, magnetofection in vivo has been studied insufficiently both for local and systemic routes of magnetic vector injection, and the relevant data available in the literature are often merely descriptive and contradictory. In this review, we collected and systematized the data on the efficiency of the local injections of magnetic nanoparticles that carry genetic information upon application of external magnetic fields. We also investigated the efficiency of magnetofection in vivo, depending on the structure and coverage of magnetic vectors. The perspectives of the development of the method were also considered.

Limiting angiogenesis to modulate scar formation

Angiogenesis, the process of new blood vessel formation from existing blood vessels, is a key aspect of virtually every repair process. During wound healing an extensive, but immature and leaky vascular plexus forms which is subsequently reduced by regression of non-functional vessels. More recent studies indicate that uncontrolled vessel growth or impaired vessel regression as a consequence of an excessive inflammatory response can impair wound healing, resulting in scarring and dysfunction. However, in order to elucidate targetable factors to promote functional tissue regeneration we need to understand the molecular and cellular underpinnings of physiological angiogenesis, ranging from induction to resolution of blood vessels. Especially for avascular tissues (e.g. cornea, tendon, ligament, cartilage, etc.), limiting rather than boosting vessel growth during wound repair potentially is beneficial to restore full tissue function and may result in favourable long-term healing outcomes.

Salvianolic Acid B Promotes the Survival of Random-Pattern Skin Flaps in Rats by Inducing Autophagy

Random-pattern skin flap transplantation is frequently applied in plastic and reconstructive surgery. However, the distal part of the flap often suffers necrosis due to ischemia. In this study, the effects of salvianolic acid B (Sal B) on flap survival were evaluated, and the underlying mechanisms were investigated. Sal B improved the survival area, reduced tissue edema, and increased the number of microvessels in skin flaps after 7 days, whereas an autophagy inhibitor (3-methyladenine) reversed the Sal B-induced increase in flap viability. In addition, Sal B stimulated angiogenesis, inhibited apoptosis, reduced oxidative stress, and upregulated autophagy in areas of ischemia. Moreover, the effects of Sal B on angiogenesis, apoptosis, and oxidative stress were reversed by autophagy inhibition. Overall, our findings suggest that Sal B has pro-angiogenesis, anti-apoptosis, and anti-oxidative stress effects by stimulating autophagy, which enhances the survival of random-pattern skin flaps.

Nanomedicines and gene therapy for the delivery of growth factors to improve perfusion and oxygenation in wound healing

Oxygen plays a key role in wound healing, and hypoxia is a major cause of wound healing impairment; therefore, treatments to improve hemodynamics and increase wound oxygenation are of particular interest for the treatment of chronic wounds. This article describes the roles of oxygen and angiogenesis in wound healing as well as the tools used to evaluate tissue oxygenation and perfusion and then presents a review of nanomedicines and gene therapies designed to improve perfusion and oxygenation and accelerate wound healing.

Vascular architecture in free flaps: Analysis of vessel morphology and morphometry in murine free flaps

The aim of this study was to analyze the development of vascular architecture as well as vascular morphometry and morphology of anastomosed microvascular free flaps. Free pectoral skin flaps were raised in 25 rats and anastomosed to the femoral vessels in the groin region. CD31 immunohistology was performed after 3, 7 and 12 d (each 5 animals each) to analyze microvessel density (MVD), microvessel area (MVA) and microvessel size (MVS). Microvascular corrosion casting was performed after 7 and 12 d (5 animals each) to analyze vessel diameter (VD), intervascular distance (IVD), interbranching distance (IBD), and branching angle (BA). Further on, sprout and pillar density as hallmarks of sprouting and intussusceptive angiogenesis were analyzed. Pectoral skin isles from the contralateral side served as controls. A significantly increased MVD was found after 7 and 12 d (p each <0.001). MVA was significantly increased after 3, 7 and 12 d (p each <0.001) and a significantly increased MVS was analyzed after 3 and 7 d (p each <0.001). VD and IVD were significantly increased after 7 and 12 d (p each <0.001). For IBD, a significantly increase was measured after 7 d (p < 0.001). For IBA, sprout and pillar density, no significant differences were found (p each ≥0.05). Significant changes in the vascular architecture of free flaps after successful microvascular anastomosis were seen. Since there was no evidence for sprout and pillar formation within the free flaps, the increased MVD and flap revascularization might be induced by the receiving site.

Antecedent thermal injury worsens split-thickness skin graft quality: A clinically relevant porcine model of full-thickness burn, excision and grafting

Current standard of care for full-thickness burn is excision followed by autologous split-thickness skin graft placement. Skin grafts are also frequently used to cover surgical wounds not amenable to linear closure. While all grafts have potential to contract, clinical observation suggests that antecedent thermal injury worsens contraction and impairs functional and aesthetic outcomes. This study evaluates the impact of antecedent full-thickness burn on split-thickness skin graft scar outcomes and the potential mediating factors. Full-thickness contact burns (100°C, 30s) were created on the backs of anesthetized female Yorkshire Pigs. After seven days, burn eschar was tangentially excised and covered with 12/1000th inch (300μm) split-thickness skin graft. For comparison, unburned wounds were created by sharp excision to fat before graft application. From 7 to 120days post-grafting, planimetric measurements, digital imaging and biopsies for histology, immunohistochemistry and gene expression were obtained. At 120days post-grafting, the Observer Scar Assessment Scale, colorimetry, contour analysis and optical graft height assessments were performed. Twenty-nine porcine wounds were analyzed. All measured metrics of clinical skin quality were significantly worse (p<0.05) in burn injured wounds. Histological analysis supported objective clinical findings with marked scar-like collagen proliferation within the dermis, increased vascular density, and prolonged and increased cellular infiltration. Observed differences in contracture also correlated with earlier and more prominent myofibroblast differentiation as demonstrated by α-SMA staining. Antecedent thermal injury worsens split-thickness skin graft quality, likely by multiple mechanisms including burn-related inflammation, microscopically inadequate excision, and dysregulation of tissue remodeling. A valid, reliable, clinically relevant model of full-thickness burn, excision and skin replacement therapy has been demonstrated. Future research to enhance quality of skin replacement therapies should be directed toward modulation of inflammation and assessments for complete excision.

Vascular Endothelial Growth Factor and Angiogenesis in the Regulation of Cutaneous Wound Repair

Significance: Angiogenesis, the growth of new blood vessels from existing vessels, is an important aspect of the repair process. Restoration of blood flow to damaged tissues provides oxygen and nutrients required to support the growth and function of reparative cells. Vascular endothelial growth factor (VEGF) is one of the most potent proangiogenic growth factors in the skin, and the amount of VEGF present in a wound can significantly impact healing. Recent Advances: The activity of VEGF was once considered to be specific for endothelial cells lining the inside of blood vessels, partly because VEGF receptor (VEGFR) expression was believed to be restricted to endothelial cells. It is now known, however, that VEGFRs can be expressed by a variety of other cell types involved in wound repair. For example, keratinocytes and macrophages, which both carry out important functions during wound healing, express VEGFRs and are capable of responding directly to VEGF. Critical Issues: The mechanisms by which VEGF promotes angiogenesis are well established. Recent studies, however, indicate that VEGF can directly affect the activity of several nonendothelial cell types present in the skin. The implications of these extra-angiogenic effects of VEGF on wound repair are not yet known, but they suggest that this growth factor may play a more complex role during wound healing than previously believed. Future Directions: Despite the large number of studies focusing on VEGF and wound healing, it is clear that the current knowledge of how VEGF contributes to the repair of skin wounds is incomplete. Further research is needed to obtain a more comprehensive understanding of VEGF activities during the wound healing process.

Optimal timing of extracorporeal shock wave treatment to protect ischemic tissue

Enhancement of flap survival through extracorporeal shock wave treatment (ESWT) is a promising new technique; however, no attempt has been made to define the optimal time point and frequency of ESWT to optimize treatment with ESWT for ischemic indications. Twenty-eight male Wistar rats were randomized into 4 groups and an oversized, random-pattern flap was raised and reattached in place in each animal. ESWT was applied 7 days before (group E7) or immediately after the surgical intervention (group E0). The third group was treated with ESWT 7 days before and additionally immediately after the operation (group E7/0). The fourth group served as a control group and did not receive any ESWT (group C). Seven days after flap harvest the results of flap survival, perfusion, microvessel density, and vascular endothelial growth factor concentrations were assessed. Flap survival was significantly increased in all ESWT groups as compared with the control group. The groups (E7 and E0) that received ESWT pre- or postoperatively showed a significant increase in flap perfusion and microvessel density. Combined pre- and postoperative ESWT application (group E0/E7) did not demonstrate a cumulative effect in any evaluation. In this study, we were be able to prove the effectiveness of ESWT in the protection of ischemic tissue flaps. This study suggests that single postoperative application is the most efficacious protocol for clinical applications of ESWT in the treatment of ischemic tissue.

Preoperative shock wave treatment enhances ischemic tissue survival, blood flow and angiogenesis in a rat skin flap model

INTRODUCTION

Extracorporeal shock wave treatment (ESWT) has recently been shown to enhance skin flap survival. However, the bio-mechanisms operating during preoperative ESWT remain unclear. The aim of our study was to investigate whether preoperative ESWT can improve blood flow in ischemic skin flaps and to elucidate its possible mechanisms.

METHODS

14 male-rats were randomized into two groups and an oversized ventral random-pattern flap was raised. Experimental group received extracorporeal shock-wave treatment (ESWT) with an energy of 500 mJ/mm(2) seven days prior to total flap elevation, while control group received no treatment prior to total flap elevation. Seven days postoperatively, surviving flap area, perfused flap area, microvessel density and VEGF concentration were measured.

RESULTS

Surviving flap area (59.43 ± 14.72 % to 42.71 ± 10.75 %, p = 0.026), perfused flap area (62.00 ± 8.58 % to 45.14 ± 10.50 %, p = 0.007), microvessel density (18.13 ± 5.11 to 11.09 ± 1.12, p = 0.016) and VEGF to total protein ratio (0.2107 ± 0.0935 to 0.0123 ± 0.0069, p = 0.008) were significantly elevated in the ESWT group.

CONCLUSION

Preoperative ESWT can improve skin flap survival through enhanced topical blood perfusion and neovascularization via elevation of angio-active factors.

Iontophoretic delivery of nitric oxide donor improves local skin flap viability

The dimensions of local flaps are often limited by the vascular supply to the distal aspect of the flap. Distal flap necrosis occurs if the vascular supply is inadequate. The purpose of this study was to investigate the use of iontophoretic delivery of nitric oxide (NO) donors to a local skin flap model to improve the survival area of the flap. Thirty-two male Sprague-Dawley rats (300 g) were divided into seven experimental groups to determine the effect of iontophoretic delivery of NO on surface perfusion and flap survival area. A caudally based 3 x 11 cm dorsal skin flap was used to measure the effect of iontophoretic delivery of NO donors to a local skin flap to improve survival area of the flap. Iontophoretic delivery of the NO donors sodium nitroprusside (SNP) and diethylenetriamine NONOate (DETA-NO) resulted in a significant increase in survival area and surface perfusion when compared with sham controls. Iontophoretic delivery of saline was associated with a 13% improvement in flap survival when compared with nontreated controls. Iontophoretic delivery and subcutaneous injection of NO donors (SNP and DETA-NO) increased skin flap viability by demonstrating improved flap survival areas. The results of this study suggest that NO may serve as a postoperative treatment of skin flaps to encourage skin flap survival and prevent distal necrosis.

[Ischemic preconditioning in a rat adipocutaneous flap model]

INTRODUCTION

Flap necrosis in ear, nose, and throat surgery, especially in high-risk groups, is not rare, but not all of the individual pathophysiological processes are known. The objective of this study was to establish an animal model to determine whether acute ischemic preconditioning, which has been reported to be successful in organ transplantation, will result in enhanced flap survival.

METHODS AND MATERIALS

Forty-two Wistar rats were divided into three experimental groups. An epigastric adipocutaneous flap, based on both superficial epigastric arteries and veins, was raised. The flap was either raised (control), clamped for 2 h (ischemic), or subjected to ischemia of 30 min, followed by 30 min of reperfusion and another 2 h of induced ischemia (IP). The mean flap necrosis area was assessed in all groups on the 5th postoperative day.

RESULTS

All animals were doing well on the final day. The average necrosis in the ischemic group was significantly greater than in the control group. No significant superiority in the IP group was demonstrated.

CONCLUSION

The data show that the experimental animal model is practicable and that additional approaches to ischemic preconditioning should be verified.

Non-viral VEGF(165) gene therapy--magnetofection of acoustically active magnetic lipospheres ('magnetobubbles') increases tissue survival in an oversized skin flap model

Adenoviral transduction of the VEGF gene in an oversized skin flap increases flap survival and perfusion. In this study, we investigated the potential of magnetofection of magnetic lipospheres containing VEGF₁₆₅-cDNA on survival and perfusion of ischemic skin flaps and evaluated the method with respect to the significance of applied magnetic field and ultrasound. We prepared perfluoropropane-filled magnetic lipospheres (‘magnetobubbles’) from Tween60-coated magnetic nanoparticles, Metafectene, soybean-oil and cDNA and studied the effect in an oversized random-pattern-flap model in the rats (n= 46). VEGF-cDNA-magnetobubbles were administered under a magnetic field with simultaneously applied ultrasound, under magnetic field alone and with applied ultrasound alone. Therapy was conducted 7 days pre-operative. Flap survival and necrosis were measured 7 days post-operatively. Flap perfusion, VEGF-protein concentration in target and surrounding tissue, formation and appearance of new vessels were analysed additionally. Magnetofection with VEGF-cDNA-magnetobubbles presented an increased flap survival of 50% and increased flap perfusion (P < 0.05). Without ultrasound and without magnetic field, the effect is weakened. VEGF concentration in target tissue was elevated (P < 0.05), while underlying muscle was not affected. Our results demonstrate the successful VEGF gene therapy by means of magnetobubble magnetofection. Here, the method of magnetofection of magnetic lipospheres is equally efficient as adenoviral transduction, but has a presumable superior safety profile.

[Pathogenesis of chronic wounds]

Chronic, nonhealing wounds and their therapy are not only a medical problem but a severe economic one as well. Such wounds have a great effect on quality of life. Basic research has enhanced our understanding of the stimulation and inhibition of wound healing and provides the basis for introducing new and innovative treatment methods. This paper reviews the most relevant in- and extrinsic factors that disturb physiologic wound healing to result in chronic nonhealing wounds. In addition, molecular intervention modalities targeting various aspects of wound repair are demonstrated.

Regulation of scar formation by vascular endothelial growth factor

Vascular endothelial growth factor (VEGF-A) is known for its effects on endothelial cells and as a positive mediator of angiogenesis. VEGF is thought to promote repair of cutaneous wounds due to its proangiogenic properties, but its ability to regulate other aspects of wound repair, such as the generation of scar tissue, has not been studied well. We examined the role of VEGF in scar tissue production using models of scarless and fibrotic repair. Scarless fetal wounds had lower levels of VEGF and were less vascular than fibrotic fetal wounds, and the scarless phenotype could be converted to a scar-forming phenotype by adding exogenous VEGF. Similarly, neutralization of VEGF reduced vascularity and decreased scar formation in adult wounds. These results show that VEGF levels have a strong influence on scar tissue formation. Our data suggest that VEGF may not simply function as a mediator of wound angiogenesis, but instead may play a more diverse role in the wound repair process.

Improved survival of rat ischemic cutaneous and musculocutaneous flaps after VEGF gene transfer

When harvesting microsurgical flaps, the main goals are to obtain as much tissue as possible based on a single vascular pedicle and a reliable vascularization of the entire flap. These aims being in contrast to each other, microsurgeons have been looking for an effective way to enhance skin and muscle perfusion in order to avoid partial flap loss in reconstructive surgery. In this study we demonstrate the efficacy of VEGF 165 delivered by an Adeno-Associated Virus (AAV) vector in two widely recognized rat flap models. In the rectus abdominis myocutaneous flap, intramuscular injection of AAV-VEGF reduced flap necrosis by 50%, while cutaneous delivery of the same amount of vector put down the epigastric flap's ischemia by >40%. Histological evidence of neoangiogenesis (enhanced presence of CD31-positive capillaries and alpha-Smooth Muscle Actin-positive arteriolae) confirmed the therapeutic effect of AAV-VEGF on flap perfusion.

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.

Adenoviral-mediated expression and local deposition of recombinant tenascin-C perturbs cell-dependent matrix contraction

BACKGROUND

To mimic the wound environment, we have developed a three-dimensional (3-D) fibrin-fibronectin (FN) matrix model that is formed in vitro from purified proteins and approximates the provisional matrix. Tenascin-C, a large extracellular matrix (ECM) glycoprotein, is expressed transiently in tissue adjacent to areas of injury and contacts the provisional matrix in vivo. We have constructed a novel recombinant adenovirus vector (Ad-70Ten) to up-regulate local expression and secretion of a recombinant form of tenascin-C.

METHODS

Ad-70Ten and a control vector were constructed and used to infect cultured mammalian cells. Post-infection monitoring of expression was accomplished by immunoblot and immunohistochemical techniques. Local protein deposition was examined by immunofluorescence. Cell contractility was assessed by ability of infected cells to contract 3-D fibrin-FN matrices. Some matrices also contained lysophosphatidic acid (LPA), an activator of Rho GTPase.

RESULTS

Adenovirus-infected cells demonstrated high recombinant tenascin-C expression and deposited protein at sites of cell-matrix contacts resulting in significantly reduced contractility with 2.5-fold lower contraction of the matrix compared with control cells. Matrix contraction could be restored by treatment with LPA.

CONCLUSION

These results show that endogenous expression of tenascin-C down-regulates cell contractility and strongly suggest that it exerts its effects via a Rho GTPase signaling pathway. Taken with previous findings, these results suggest that tenascin-C acts in both a paracrine and autocrine manner via Rho GTPase pathways. This report demonstrates that recombinant adenovirus infection is a feasible method to induce high expression of large matrix proteins in mammalian cells, allowing better approximation of in vivo circumstances for investigations of locally secreted matrix protein. While the current vector has been constructed for research purposes, it also represents a proof in principle that adenoviral vectors encoding large proteins may have potential benefit in clinical applications.

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.

Prediction of flap necrosis with laser induced indocyanine green fluorescence in a rat model

Prediction of necrosis has a clinical relevance in all fields of plastic surgery. The new application of indocyanine green (ICG) fluoroscopy in plastic surgery allows an objective quantification of skin perfusion and a high topographical resolution. The aim of the present study is to determine threshold values for flap perfusion under well-defined experimental conditions. Twenty random pattern flaps with a length to width ratio of 4:1 (8 x 2 cm(2)) were dissected on the anterior abdominal wall of 20 male Sprague-Dawley rats. ICG fluoroscopy was performed at the end of the operation. The animals were sacrificed at the seventh postoperative day with a reliable necrosis of the distal part of the flaps. Postoperative ICG fluoroscopy then was analysed both in regions that will survive and undergo necrosis. At day 7 a mean area of 5.5 cm(2) (57% of the total flap area) survived and a mean of 3.8 cm(2) (43%) became necrotic. The surviving part of the flap had a mean perfusion index of 62% compared to reference skin. The distal parts of the flap that necrotised showed an average perfusion index of only 19% postoperatively. Differences were statistically highly significant (p<0.001). Indocyanine green fluoroscopy is a useful tool to evaluate perfusion topographically and predict necrosis. From a statistical point of view a perfusion index of less than 25% of the reference skin can be considered as a sign of developing flap necrosis.