Effects of endothelial cell growth factor on vascular compromised skin flaps

Improvement of the skin flap survival with the bone marrow-derived mononuclear cells transplantation in a rat model

Partial necrosis of skin flaps remains a significant problem in plastic and reconstructive surgery. In this study we attempted to evaluate the effect of bone marrow-derived mononuclear cells (BM-MNCs) transplantation on improvement of skin flap survival in a rat random pattern skin flap model. Thirty Wistar rats were divided into three groups with each consisting of 10 rats. BM-MNCs and the adipose-derived stem cells (ADSCs) were transplanted into the subcutaneous tissue in the area where the flap would be dissected. The flaps were then raised two days after cells transplantation. The animals receiving the preoperative Dulbecco's Modified Eagle Medium (DMEM) treatment were used as the controls. On the 7th postoperative day, the survival areas of flaps were measured and tissues were collected for examinations. The results showed that the mean survival areas were 46.33 +/- 13.46% in the ADSCs group and 50.06 +/- 13.82% in the BM-MNCs group as the percentages of the total skin flaps, which were significantly higher than that in the control group (26.33 +/- 7.14%) (P < 0.05). Histological analysis showed increased neovascularization in the flap treated with BM-MNCs when compared with ADSCs transplantation. Survival BM-MNCs and ADSCs were detected in the flap tissues. Higher levels of the basic fibroblast growth factor (bFGF) and vascular endothelium growth factor (VEGF) were found in the BM-MNCs transplantation group (P < 0.05). The findings from this study demonstrated that preoperative treatment with BM-MNCs transplantation could promote neovascularization and improve flap survival. These effects of BM-MNCs on flap survival were comparable with ADSCs transplantation, but without necessity of in vitro cells expansion.

Fibrin-embedded administration of VEGF plasmid enhances skin flap survival

The aim of the present study was to experimentally evaluate whether topical fibrin-mediated administration of a vascular endothelial growth factor (VEGF)-A plasmid to the wound bed can protect skin flaps from necrosis. A plasmid expression vector containing the VEGF-A cDNA was constructed. The plasmid was then administered to the wound bed of rat abdominal skin flaps in a fibrin sealant. The percentage of viable, ischemic and necrotic tissue was assessed postoperatively as a baseline and after 3 and 7 days using digital surface area morphometry. Laser Doppler imaging of the flaps and VEGF-A Western blot analysis of flap tissue were performed to assess angiogenesis and VEGF-A tissue levels. Flaps treated with VEGF plasmids in the presence of uptake enhancing Lipofectamine transfection reagent increased flap survival 7 days postoperatively significantly associated with markedly elevated tissue perfusion and enhanced tissue VEGF-A protein expression. Our results indicate that topical fibrin-mediated administration of a VEGF-A plasmid may serve as an alternative to previous strategies in treating ischemic skin flaps. The suggested therapeutic approach is easily applicable and inexpensive in preparation. Thus, this protocol may also enhance wound healing in posttrauma skin lacerations or in skin grafts.

Rat epigastric flap survival and VEGF expression after local copper application

BACKGROUND

Copper has been used in wound healing since ancient times, and copper insufficiency seems to impair wound healing. Much less is known about the local effects of copper application on wound healing.

METHODS

The authors studied 30 male Sprague-Dawley rats weighing between 250 and 350 g for 5 days. Full-thickness random skin flaps, measuring 1.5 x 7.5 cm, were elevated on the epigastric region. The rats were randomized into two groups according to the local treatment that was used. In group 1 (20 animals), 1 ml of copper ointment was applied on the flap bed after flap suturing. In group 2 (10 animals), 1 ml of placebo ointment (petroleum jelly) was used. Intraperitoneal injection of 30 mg/kg body weight of Hypoxyprobe-1 was performed in each rat on the fourth postoperative day and all animals were killed 3 hours later. Histologic examination of the distal end of the flaps was used for detection of hypoxic tissue changes. Expression, density, and extent of vascular endothelial growth factor activity was detected with the aid of immunocytochemistry.

RESULTS

All rats survived throughout the study period. This experimental study showed that local application of copper at the random flap bed may promote wound-related angiogenesis by inducing vascular endothelial growth factor expression. The authors demonstrated statistically significant flap survival after local copper application at the flap bed.

CONCLUSION

The marked benefits of copper application in flap survival in this experimental model may guarantee its clinical application in flaps with questionable viability.

Vascular endothelial growth factor gene therapy with intramuscular injections of plasmid DNA enhances the survival of random pattern flaps in a rat model

The objective of this study was to determine the effects of the naked plasmid DNA encoding vascular endothelial growth factor (VEGF) on the survival of random flaps on rats. Thirty Sprague-Dawley rats whose random flaps were elevated on the back were randomised into three groups of 10 animals each. In the experimental group, the naked plasmid DNA encoding VEGF was injected directly into the panniculus carnosus of the flap. In the two control groups, either control plasmid DNA or physiologic saline was injected. After 7 days, the flaps were evaluated with the following devices: RT-PCR for the expression of VEGF gene, immunohistochemistry for the expression of VEGF protein, histology for vascular density, single photon emission computerised tomography for RBC in the flap, and image analysis for flap survival area. Notably increased expressions of VEGF mRNA and VEGF protein were found in the treatment group. Vascular density was markedly more increased in the treatment group than those in the two control groups (P < 0.01). Compared with the two control groups, the flap treated with VEGF plasmid DNA showed a more significantly enhanced tissue viability: 87 +/- 5 versus 47 +/- 6% for the control plasmid DNA group and 46 +/- 5% for the saline group (P < 0.01). Our results indicated that the VEGF gene therapy was able to enhance the survival of random pattern flaps by inducing angiogenesis.

Extracorporal shock wave may enhance skin flap survival in an animal model

Several methods have been used in an attempt to increase blood supply and tissue perfusion in ischemic tissues. The authors investigated the effect of extracorporal shock wave (ESW) treatment on compromised skin flaps. For this purpose, the epigastric skin flap model in rats, based solely on the right inferior epigastric vessels was used. Twenty male Sprague-Dawley rats were divided into two groups (ESW-group, Control group) of 10 rats each. The ESW-group was administered 2500 impulses at 0.15 mJ/mm(2) immediately after surgery, whereas, the control group received no treatment. Flap viability was evaluated on day 7 after the operation. Standardised digital pictures of the flaps were taken and transferred to the computer, and necrotic zones relative to total flap surface area were measured and expressed as percentages. Overall, there was a significant reduction in the surface area of the necrotic zones of the flaps in the ESW group compared to the control group (ESW group: 2.2+/-1.9% versus control: 17.4+/-4.4% (p < 0.01). In this study, the authors demonstrated that treatment with ESW enhanced epigastric skin flap survival, as confirmed by the significant reduction of necrotic flap zones. ESW treatment seems to represent a feasible and cost effective method to improve blood supply in ischemic tissue.

Growth factors and flap survival

Growth factors are members of a large functional group of polypeptide regulatory molecules that influence the biological activities of responsive cells. In the last decade, the use of a variety of growth factors as therapeutic agents to improve wound healing and the viability of ischemic skin flaps has aroused considerable interest. Here, we review the literature concerning the regulation of growth factors in a flap, the role of angiogenesis in flap survival, the effect of growth factors on the metabolism of a flap, and angiogenesis in flap prefabrication and maturation. The potential application of growth factors in gene therapies is also reviewed.

The effect of single administration of vascular endothelial growth factor or L-arginine on necrosis and vasculature of the epigastric flap in the rat model

OBJECTIVES

Vascular endothelial growth factor (VEGF) and nitric oxide (NO) produce vasodilation, induce angiogenesis, and improve survival of surgical flaps. We used the rat epigastric skin flap to study the effect of a single intra-arterial dose of VEGF or L-arginine, a substrate for NO production, on flap regional necrosis and pedicle dependence of flap perfusion.

METHODS

In 30 Sprague-Dawley rats an 8 x 8 cm2 skin flap, consisting of four vertical zones marked A through D (right to left), based on the proximal right inferior epigastric vessels was raised. Subsequently, 1 ml of either saline (control, n =10), 5 microg VEGF (VEGF, n = 10), or 50 mg of L-arginine (L-arginine, n = 10) was injected into the arterial pedicle by cannulating the right saphenous artery, and the flap was resutured in place. After 8 days, the animals were perfused systemically with 15 microm coloured fluorescent microspheres before (blue) and after (yellow-green) ligation of the right inferior epigastric vascular pedicle. After sacrifice, the area of flap necrosis was measured in each zone by templates and weight-to-surface ratio, and the flap zones were harvested and processed for determination of fluorescence and blood flow.

RESULTS

Administration of VEGF or L-arginine resulted in decreased total and regional (zone D) flap necrosis (ANOVA <0.001). The total and regional flap shrinkage was greater in the experimental groups (ANOVA <0.02). While VEGF and L-arginine decreased the percentage of necrosis in the zone most distal to the pedicle (ANOVA <0.01) only L-arginine diminished percentage of total flap necrosis (p = 0.04). In the VEGF group, total and regional flap perfusion did not change after pedicle ligation, but perfusion decreased significantly in zones B through D in the L-arginine treated rats.

CONCLUSION

Single intra-pedicle administration of VEGF or L-arginine decreased necrosis of the epigastric skin flap at 8 days postoperatively, but flap shrinkage also increased in the zone with the greatest degree of necrosis. Perfusion data suggest that beneficial effects of VEGF and L-arginine on flap survival may be based on different mechanisms.

Gene therapy in flap survival

Growth factors are members of a large functional group of polypeptide regulatory molecules that exert a powerful influence on all phases of wound healing and repair through interactions with specific cell surface receptors. The use of growth factors to improve wound healing and the viability of ischemic skin flaps has been well-documented throughout the last decade. In this article, we review the literature concerning the use gene therapy in flap survival, including the various methods employed to transplant plasmids or viruses capable of coding and producing growth factors in ischemic tissue.

Vascular endothelial growth factor (VEGF) expression and the effect of exogenous VEGF on survival of a random flap in the rat

The induction of endogenous vascular endothelial growth factor (VEGF) production in the skin flap with ischemic injury and the effect of exogenous VEGF on survival of the ischemic skin flap were studied in rats. A dorsal flap model (3x10 cm(2)) was used in this study. In Part I, biopsies were taken from the flap at 2.5, 5.5, and 8.5 cm distances from the distal edge at 0, 6, 12, and 24 h after the flaps were sutured. Malonyldialdehyde (MDA) and VEGF(165) protein level were measured. In Part II, exogenous VEGF (1 microg/ml) was injected subdermally into the flaps in 14 rats before the flaps were replaced. Flaps that received a saline injection were used as the controls. The skin paddle survival was measured on postoperative day five. The results showed that the MDA level in the distal part of the flap significantly increased at 24 h postoperatively when compared to MDA in other parts of the flap. However, VEGF levels in the distal part of the flap significantly decreased when compared to the middle part of the flap. Subdermal injection of exogenous VEGF to the distal area of the flap could significantly improve survival of the distal flap (89% of total skin paddle) when compared to the control, which had a 64% mean percent survival. We conclude that production of endogenous VEGF protein is significantly increased in the skin flap with mild ischemia, but decreased in the flap with severe ischemia. Administration of exogenous VEGF could significantly enhance survival of ischemic flaps.

Evaluation of the mechanism of vascular endothelial growth factor improvement of ischemic flap survival in rats

This study evaluated the effects of exogenous vascular endothelial growth factor (VEGF) on the regulation of cytokines in a rat dorsal ischemic skin flap model. Exogenous VEGF (1 microg/ml) was injected subdermally into the flaps of 12 rats before the flaps were sutured back in place. Another 12 rats with flaps received saline injections, as a control group. Biopsy specimens were obtained from the flaps treated with VEGF or saline solution, at positions 2.5, 5.5, and 8.5 cm from the distal edge of the flaps, at 12 hours (n = 6 for each group) and 24 hours (n = 6 for each group) after suturing of the flaps. Expression of cytokine, growth factor, and inducible nitric oxide synthase was measured. The results demonstrated that expression of tumor necrosis factor-alpha and nitric oxide synthase in the distal part of the VEGF-treated flaps was significantly decreased, compared with the control values, at 12 and 24 hours postoperatively. It was concluded that administration of exogenous VEGF could protect flaps from ischemia-reperfusion injury through the regulation of proinflammatory cytokines and the inhibition of cytotoxic nitric oxide production.

Barium sulphate and soft-tissue radiology: allying the old and the new for the investigation of animal cutaneous microcirculation

The study of microcirculation using angiography is essential to the advancement of flap and angiogenesis research in plastic surgery. Until the mid-1980s, barium sulphate was the most commonly used contrast material, although it did not provide optimal visualisation of the vascular tree. In 1986, a new technique using lead oxide was proposed, which permitted very high-quality imaging and rapidly became the technique of choice, despite its high toxicity. We reconsider the former technique of barium-sulphate injection and combine it with soft-tissue radiology using mammographic film to achieve a radiological definition similar to that obtained with lead oxide, and discuss the advantages and disadvantages of the two methods. We conclude that barium sulphate and the use of mammographic film is an accurate, simple and non-toxic method of analysing the cutaneous circulation in small animals.

Improvement of skin paddle survival by application of vascular endothelial growth factor in a rat TRAM flap model

The effect of vascular endothelial growth factor (VEGF) on skin flap survival and its ability to induce a pharmacological delay by promoting angiogenesis in a flap was studied in a rat transverse rectus abdominis musculocutaneous flap, using a 3 x 8-cm skin paddle with the inferior epigastric vessels as its main vascular supply. Forty-three Sprague-Dawley rats were divided into four groups. In group 1, VEGF was injected into the femoral vein after the flap was elevated. In group 2, VEGF was injected intra-arterially into the flap through the superior epigastric artery after the flap was elevated. In group 3, VEGF was injected into the subcutaneous fascial layer in the area where the flap would be dissected, and the flap was then raised 7 days after injection. In group 4, the flap was dissected and replaced, using saline injection as the control. On postoperative day 5, the survival area of each skin paddle was measured and the flap was harvested for histological analysis. The results showed that the mean survival area +/- standard deviation for the skin paddle was 6.82 +/- 4.89 cm2 (28.4 +/- 20.4% of the whole skin paddle) in the control group, and 4.2 +/- 3.0 cm2 (17.5 +/- 12.5%) and 6.02 +/- 5.97 cm2 (25.1 +/- 24.9%) in the groups with VEGF systemic and intra-arterial administration respectively. The skin survival area in the group with preoperative subcutaneous administration of VEGF was 17.85 +/- 2.88 cm2 (74.4 +/- 12%), which was significantly higher than the other three groups (p < 0.01). Histological semiquantitative analysis showed increased neovascularization in the flap treated with VEGF preoperatively. The data demonstrate that preoperative treatment with VEGF can induce angiogenesis and enhance skin paddle survival in a musculocutaneous flap.

Vascular and epidermal effects of fibroblast growth factor on irradiated and nonirradiated skin flaps

Head and neck cancer surgeons are often faced with the challenge of managing previously irradiated soft tissue that has poor vascularity and slower epithelialization. This study investigates the effect of supplemental basic fibroblast growth factor (bFGF) on flap vascularity, tissue oxygenation, and epidermal regeneration in nonirradiated (n = 40) and irradiated porcine skin flaps (n = 40). Supplemental bFGF increased vascularity in nonirradiated flaps by 80% (p = .005), with a trend to a higher tissue oxygen level by day 14. The irradiated bFGF-treated flaps did not show increased vascularity or higher tissue oxygen levels 2 weeks after surgery. However, in both irradiated and nonirradiated groups, epidermal regeneration increased by greater than 70% with supplemental bFGF (p < .002). The results of this study suggest that supplemental bFGF can increase tissue vascularity in nonirradiated tissues and epidermal regeneration in both nonirradiated and irradiated conditions.

The effects of VEGF on survival of a random flap in the rat: examination of various routes of administration

The purpose of the present study was to determine the effects of vascular endothelial growth factor (VEGF) on survival of a full thickness random pattern, McFarlane musculocutaneous flap in the rat. In addition, this study examined a number of different methods of VEGF delivery in an attempt to determine the most effective route of administration. A 2 x 8 cm full thickness dorsal flap with the pedicle remaining attached at the anterior end was elevated in 72 male Sprague-Dawley rats. The rats were randomised into six groups and immediately received the following treatment: Group I (n = 12): systemic VEGF injection into the femoral vein (50 microg/ml); Group II (n = 10): multiple systemic VEGF injections at 0, 24 and 48 h post flap elevation (50 microg/ml); Group III (n = 12): subdermal VEGF injection into the flap (1 microg/ml); Group IV (n = 12): subfascial VEGF injections into the recipient bed (1 microg/ml); Group V (n = 10): topical VEGF onto the recipient bed (1 microg/ml); Group VI (n = 16): control group with no treatment. Following 5 days recovery, the area of flap survival was measured. Mean flap survival ranged from 91% in Group II to 78% in Group V, and was significantly greater in all experimental groups (P< 0.001 for Groups I-IV and P< 0.05 for Group V) as compared to the control group (mean survival of 66%). The only significant difference between the experimental groups was between the mean survival in Group II and Group V (P< 0. 05). Histological analysis demonstrated a qualitatively greater amount of granulation tissue and neovascularisation in the experimental groups. These results support the notion that VEGF rescues tissue at risk of hypoxic damage by inducing angiogenesis, and the use of growth factors such as VEGF holds promise as a method of increasing skin viability.

Effects of angiogenic growth factors and a penetrance enhancer on composite grafts

Skin-cartilage composite grafts are invaluable tissues used in facial reconstruction, yet their survival is unpredictable beyond a 1-cm diameter. In this study, the angiogenic growth factors basic fibroblast growth factor (bFGF) and endothelial cell growth factor (ECGF) and a penetrance enhancer (dimethyl sulfoxide [DMSO]) were applied to composite grafts to determine their effects on survival and vascularization. We applied ECGF, bFGF, and DMSO either topically or by intradermal injection to 120 auricular composite grafts (3.0 cm diameter) in New Zealand White rabbits. Dermabrasion was performed in 2 groups to attempt to increase transdermal delivery. Graft viability and vascularity were evaluated 3 weeks later by template analysis and angiography. In the results, ECGF and bFGF, when grouped together, had a 40% increase in vascular ingrowth as compared to controls (p < .001). However, neither ECGF nor bFGF increased graft survival. A coincidental finding was that DMSO with dermabrasion significantly improved graft viability (>100%) with or without an angiogenic agent (p < .02). The potential of DMSO with dermabrasion to increase composite graft viability warrants further investigation.

The effect of endothelial cell growth factor on peripheral nerve regeneration

Neural regeneration after grafting can be unpredictable. In an effort to enhance the return of function after cable grafting, we studied the effects of an angiogenic factor, endothelial cell growth factor (ECGF), on regenerating nerves. Cable grafts on the sciatic nerve were established in 18 rats and treated with ECGF or a control saline solution. At 5 weeks, nerve conduction studies were performed, and the animals were killed for histologic measurements of graft vascularity and axon counts. A significant increase in vascularity was noted in the treated group versus the control group; neither the axon counts nor the nerve conduction velocities differed significantly between the two groups, although the treated group appeared to show improved neural conduction compared with the control group.

Vascular permeability factor/vascular endothelial growth factor: a multifunctional angiogenic cytokine

VPF/VEGF is a multifunctional cytokine that contributes to angiogenesis by both direct and indirect mechanisms. On the one hand, VPF/VEGF stimulates the endothelial cells lining nearby microvessels to proliferate, to migrate and to alter their pattern of gene expression. On the other hand, VPF/VEGF renders these same microvascular endothelial cells hyperpermeable so that they spill plasma proteins into the extravascular space, leading to profound alterations in the extracellular matrix that favor angiogenesis. These same principles apply in tumors, in several examples of non-neoplastic pathology, and in physiological processes that involve angiogenesis and new stroma generation. In all of these examples, microvascular hyperpermeability and the introduction of a provisional, plasma-derived matrix precede and accompany the onset of endothelial cell division and new blood vessel formation. It would seem, therefore, that tumors have made use of fundamental pathways that developed in multicellular organisms for purposes of tissue defense, renewal and repair. VPF/VEGF, therefore, has taught us something new about angiogenesis; namely, that vascular hyperpermeability and consequent plasma protein extravasation are important--perhaps essential--elements in its generation. However, this finding raises a paradox. While VPF/VEGF induces vascular hyperpermeability, other potent angiogenic factors apparently do not, at least in sub-toxic concentrations that are more than sufficient to induce angiogenesis (Connolly et al., 1989a). Nonetheless, wherever angiogenesis has been studied, the newly generated vessels have been found to be hyperpermeable. How, therefore, do angiogenic factors other than VPF/VEGF lead to the formation of new and leaky blood vessels? We do not as yet have a complete answer to this question. One possibility is that at least some angiogenic factors mediate their effect by inducing or stimulating VPF/VEGF expression. In fact, there are already clear example of this. A number of putative angiogenic factors including small molecules (e.g. prostaglandins, adenosine) as well as many cytokines (e.g. TGF-alpha, bFGF, TGF-beta, TNF-alpha, KGF, PDGF) have all been shown to upregulate VPF/VEGF expression. Further studies that elucidate the crosstalk among various angiogenic factors are likely to contribute significantly to a better understanding of the mechanisms by which new blood vessels are formed in health and in disease.

Vascular effects of sustained-release fibroblast growth factors

Since the half-life of most angiogenic growth factors is several hours or less, sustained-release delivery would be optimal for their future clinical use. Two fibroblast growth factors, basic fibroblast growth factor (bFGF) and endothelial cell growth factor (ECGF), were delivered in two sustained-released modalities (poloxamer 407 and a gelatin sponge [Gelfoam]) to attempt to increase soft tissue vascularity. In vitro bioactivity of ECGF-poloxamer formulations was also tested on endothelial cell cultures. Among vascular-compromised skin flaps in rabbits, ECGF-poloxamer (N = 26), bFGF-poloxamer (N = 5), ECGF-poloxamer (N = 9, irradiated), and bFGF-Gelfoam flaps (N = 22) did not demonstrate significant differences in viability and vascularity compared to controls (p > .05). Irradiation had a detrimental effect on both flap vascularity and viability (p = .02). Future efforts for sustained delivery of angiogenic proteins are critical in order to make them clinically useful in wound healing.

Endothelial cell growth factor (ECGF) application to irradiated soft tissue

Delayed postoperative wound healing in previously radiated cancer patients is a common and debilitating occurrence. Prior studies have given evidence that endothelial cell growth factor (ECGF) can accelerate neovascularization in soft tissue. To explore its effects in irradiated tissue, an ECGF-heparin formulation (7200 micrograms/mL) contained in Gelfoam was applied to previously irradiated (N = 38) and nonirradiated skin flaps (N = 38) on rabbit ears. Both peripheral neovascularization and flap viability were quantitatively documented by polar planimetry and digital angiography in all flaps. The ECGF-heparin flaps had a greater than twofold increase in both vascularity and viability when compared to their controls among the irradiated and nonirradiated flaps (P < .01). Also, the additional viability and vascularization effects from ECGF-heparin did not appear statistically altered by previous radiation. These results support the promising angiogenic effect of ECGF-heparin in previously irradiated surgical wounds.