Evaluation of angiogenesis in delayed skin flaps using a monoclonal antibody for the vascular endothelium

Effect of Endogenous Vascular Endothelial Growth Factor on Flap Surgical Delay in a Rat Flap Model

BACKGROUND

Experimental evidence suggests that endogenous vascular endothelial growth factor (VEGF) may play a major role in the surgical delay phenomenon. The purpose of this study was to investigate the effect of endogenous VEGF on flap surgical delay.

METHODS

A total of 82 adult male Sprague-Dawley rats with an average weight of 330 g were used for these experiments. These experiments were then conducted in two parts. In part 1, 32 rats were used to assess the effectiveness of VEGF inhibitor through Western blot assay and enzyme-linked immunosorbent assay. In part 2, 50 rats were used to investigate the effect of VEGF on flap surgical delay by means of arteriography, histologic analysis, and flap viability.

RESULTS

The VEGF protein inhibition ratio reached the maximum (approximately 91.6 percent) in 5 to 7 days. The number of transverse arteries and the number of vessels greater than 0.1 mm in diameter on the 3-day delay duration and the 6-day delay duration were significantly greater than those of the normal group. The number of transverse arteries and the number of vessels greater than 0.1 mm in diameter on the 6-day inhibition duration were not significantly changed compared with the normal group. Microvascular density on the 6-day delay duration obviously increased, whereas the 6-day inhibition duration was not significantly changed in comparison to the normal group.

CONCLUSION

Endogenous VEGF is an initiating factor of the surgical delay effect by controlling choke vessel dilation and neovascularization within the choke zones.

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.

Effect of topical angiotensin II on prelaminated flaps in rats and evaluation of angiogenesis with an immunohistochemical marker

The effects of a single topical dose of angiotensin II (AII) on prelamination of flaps were investigated in rats using an immunohistochemical marker. Ninety rats were randomly divided into three groups (n = 30 in each). The control group were given nothing; the vehicle group were given only carboxymethyl cellulose, and the treatment group were given topical AII with carboxymethyl cellulose between the flap and the skin graft. According to the day of evaluation of vascularisation, each group was randomly divided into three sub-groups on days 4, 7, and 14 (n = 10 in each). Paraffin sections of the tissues were cut at the flap-graft interface and stained immunohistochemically with factor VIII-related antigen (FVIIIRAg). Capillaries and venules that stained were counted. The number of vessels in the groups on day 4 were similar, but by day 7 the number of vessels was significantly greater in the treatment group than the other two. The number of vessels in the treatment group on day 14 was greater than in the other two groups, but not significantly so. We conclude that a single topical dose of AII increases the vascularisation at the flap and skin graft interface by angiogenesis.

Time course of necrosis/apoptosis and neovascularization during experimental gastric conditioning

Apoptosis, necrosis and neovascularization are three processes that occur during ischemic preconditioning in a range of organs. In the stomach, the effect of this preconditioning (the delay phenomenon) has helped to improve gastric vascularization prior to esophagogastric anastomosis after esophagectomy. Here we present a sequential study of the histological recovery of the gastric fundus and the phenomena of apoptosis, necrosis and neovascularization in an experimental model of partial gastric ischemia. Partial gastric devascularization was performed by ligature of the left gastric vessels in Sprague-Dawley rats. Rats were assigned to groups in accordance with their evaluation period: control, 1, 3, 6, 10, 15 and 21 days. Histological analysis, caspase-3 activity, DNA fragmentation and vascular endothelial cell proliferation (Ki-67) were measured in tissue samples after sacrifice. After 24 h of partial gastric ischemia, rates of apoptosis and necrosis were higher in the experimental groups than in controls. Tissue injury was higher 3 and 6 days post-ischemia. From day 10 after partial gastric ischemia, apoptosis and necrosis started to decrease, and on days 15 and 21 showed no differences in relation to controls. Neovascularization began between days 1 and 3, reaching its peak at 15 days after ischemia and coinciding with complete histological recovery. Both necrosis and apoptosis play a role in tissue injury during the first days after partial gastric ischemia. After 15 days, the evolution of both the histology and the neovascularization suggested that this is the optimal time for performing gastric transposition.

Selective Percutaneous Desiccation of the Perforators with Radiofrequency for Strategic Transfer of Angiosomes in a Sequential Four-Territory Cutaneous Island Flap Model

BACKGROUND

Research in prevention of partial flap necrosis has recently concentrated on extending the safe length of a flap by ligating vessels of known territories. To advance this approach one step further, the authors decided to reveal the least invasive surgical strategy for transfer of angiosomes.

METHODS

The study was arranged into three experiments. In the first experiment (n = 17 rabbits), a cutaneous island flap model spanning four adjacent vascular territories was developed. In the second experiment (n = 15 rabbits), the flap model was used to test the possibility of desiccating those vessels supplying the angiosomes to be captured percutaneously with radiofrequency. The delay procedures were performed by means of minimal skin incisions, and the flaps were elevated after a 2-week delay period. In the third experiment, the effectiveness of selective interference of these pedicles was compared to minimize the number of target vessels for successful transfer of angiosomes.

RESULTS

The mean surviving area of the new flap model was 63 +/- 2 percent. The mean surviving flap area was 97 +/- 3 percent for the endoscopy equivalent technique and 94 +/- 4 percent for radiofrequency delay. The results were statistically insignificant between these two groups. In experiment 3, comparison of the results yielded a statistically insignificant difference for flap survival area among all four of the groups.

CONCLUSIONS

An alternative flap model is introduced for future investigation of the vascular delay process. Percutaneous desiccation of the perforators with radiofrequency was found to be a reliable method, and selective desiccation of the perforator(s) was as efficient as destruction of all vascular sources other than the pedicle.

Vascular Delay Revisited

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

Utilization of the delay phenomenon improves blood flow and reduces collagen deposition in esophagogastric anastomoses

OBJECTIVE

Complications of anastomotic healing are a common source of morbidity and mortality after esophagogastrostomy. The delay phenomenon is seen when a skin flap is partially devascularized in a staged procedure prior to its definitive placement, resulting in increased blood flow at the time of grafting. This effect may be applied to esophagogastrectomy, potentially reducing anastomotic complications.

SUMMARY BACKGROUND DATA

The purpose of this investigation was to apply the delay principle to the gastrointestinal tract, investigate mechanisms by which it occurs and examine the effects of delay on anastomotic healing.

METHODS

Thirty-seven opossums were assigned to Sham (n = 5), Immediate (n = 14), and Delay (n = 18) groups. Each underwent laparotomy and measurement of baseline gastric fundus blood flow. The Delay and Immediate animals underwent ligation of the left, right, and short gastric vessels and subsequent measurement of gastric fundus blood flow. The Delay group underwent repeat measurement of blood flow, esophagogastrectomy, gastric tubularization, and esophagogastrostomy 28 days after vessel ligation. The Immediate group completed the procedure immediately after vessel ligation. The anastomoses in both groups were harvested 32 days after esophagogastrostomy. The Sham group underwent blood flow measurement on initial laparotomy, followed by harvesting of esophagogastric junction 60 days later. Sections taken through the anastomoses were examined with trichrome-staining and immunohistochemistry (IHC) for actin. Collagen content of the gastric submucosa 5 mm below the anastomosis was quantified, and preservation of the muscularis propria and muscularis mucosa was determined histologically. Capillary content of the esophagogastric junction was quantified using IHC for vascular endothelium in the Delay and Sham groups.

RESULTS

Blood flow decreased by 73% following vessel ligation in Delay and Immediate groups. The Delay group had over 3 times the gastric blood flow of the Immediate group at the time of anastomosis at 16 (interquartile range [IQR] 11-17) versus 5, (IQR 5-6) mL/min/100 g (P = 0.000003). Two Immediate animals developed anastomotic leak and died; the Delay group had no complications. Submucosal collagen content in Sham, Delay, and Immediate groups were 57% (IQR 52-62), 65% (IQR 57-72), and 71% (IQR 60-82), respectively (P = 0.0004). The median distance of full-thickness atrophy of the muscularis propria was 0.10 mm (IQR 0-0.60 mm) in the Delay group and 0.53 mm (IQR 0.03-0.80 mm) in the Immediate group (P = 0.346). Five percent of the Delay group had atrophy of the muscularis mucosa, whereas 19% of Immediate animals had atrophy of this layer (P = 0.023). Compared with the Sham group, all Delay animals developed dilation of the right gastroepiploic artery and vein. A median of 27 (IQR 23-33) capillaries per 20x field was observed in the Sham fundus and 38 (IQR 31-46) in the Delay fundus (P = 0.037).

CONCLUSIONS

The delay effect is associated with both vasodilation and angiogenesis and results in increased blood flow to the gastric fundus prior to esophagogastric anastomosis. Animals undergoing delayed operations have less anastomotic collagen deposition and ischemic injury than those undergoing immediate resection. Clinical application of the delay effect in patients undergoing esophagogastrectomy may lead to a decreased incidence of leak and stricture formation.

Evolution of a “falx lunatica” in demarcation of critically ischemic myocutaneous tissue

Using intravital microscopy in a chronic in vivo mouse model, we studied the demarcation of myocutaneous flaps and evaluated microvascular determinants for tissue survival and necrosis. Chronic ischemia resulted in a transition zone, characterized by a red fringe and a distally adjacent white falx, which defined the demarcation by dividing the proximally normal from the distally necrotic tissue. Tissue survival in the red zone was determined by hyperemia, as indicated by recovery of the transiently reduced functional capillary density, and capillary remodeling, including dilation, hyperperfusion, and increased tortuosity. Angiogenesis and neovascularization were not observed over the 10-day observation period. The white rim distal to the red zone, appearing as “falx lunatica,” showed a progressive decrease of functional capillary density similar to that of the necrotic distal area but without desiccation, and thus transparency, of the tissue. Development of the distinct zones of the critically ischemic tissue could be predicted by partial tissue oxygen tension (Pt[Formula: see text]) analysis by the time of flap elevation. The falx lunatica evolved at a Pt[Formula: see text] between 6.2 ± 1.3 and 3.8 ± 0.7 mmHg, whereas tissue necrosis developed at <3.8 ± 0.7 mmHg. Histological analysis within the falx lunatica revealed interstitial edema formation and muscle fiber nuclear rarefaction but an absence of necrosis. We have thus demonstrated that ischemia-induced necrosis does not demarcate sharply from normal tissue but develops beside a fringe of tissue with capillary remodeling an adjacent falx lunatica that survives despite nutritive capillary perfusion failure, probably by direct oxygen diffusion.

Vascular endothelium growth factor, surgical delay, and skin flap survival

OBJECTIVE

Cytokines may be a mechanism by which surgical delay can increase flap survival. We previously found that preoperative vascular endothelium growth factor (VEGF) administration in the rat transverse rectus abdominis myocutaneous (TRAM) flap could improve skin paddle survival. In this study, we used partial elevation of the rat TRAM flap as a surgical delay to assess endogenous cytokine expression and tissue survival comparable to undelayed TRAM flaps.

METHODS

In Part I, TRAM flaps underwent surgical delay procedures; 7 days later, the flaps were completely elevated and reinset. At the same time, other flaps were raised and reinset without delay. Skin paddle survival in both groups was evaluated at 7 days. In Part II, skin biopsies from TRAM zones I to IV were taken at the time of delay and at intervals of 12, 24, 48, and 72 hours. Specimens were assessed for selected cytokine gene expression by reverse transcription-polymerase chain reaction analysis (TR-PCR).

RESULTS

Surgical delay significantly (P < 0.001) increased skin paddle survival in the delayed TRAM flaps (16.14 +/- 1.53 cm, 81.9%) compared with undelayed flaps (7.68 +/- 3.16 cm, 40.9%). TGF-beta and PDGF expressions were not changed by surgical delay, but basic fibroblast growth factor (bFGF) and VEGF expressions increased significantly (P < 0.05 and P < 0.01) after delay.

CONCLUSIONS

In the rat TRAM model, surgical delay resulted in increased VEGF expression and increased skin paddle survival. These results correlate with previous studies showing the preoperative injection of VEGF increases skin paddle survival. VEGF may be an important element in the delay phenomenon and may be an agent for pharmacological delay.

Laser Flap Delay: Comparison of Erbium: YAG and CO2Lasers

The delay phenomenon has long been recognized as a powerful tool in reconstructive surgery. This phenomenon involves creating alterations in skin flap blood supply or microcirculation to increase the size of the surviving flap. In the past many reconstructive surgeons depended on surgical delay as an integral part of their surgical planning. Today surgical delay remains a reliable method for maximizing flap survival. Although surgical delay remains the gold standard many have searched for methods to create the same effect with less morbidity and reduced cost. The purpose of this study was to determine whether near-scarless delay can be performed with either the Erbium:YAG or CO2 laser using a standard McFarlane skin flap model. Four groups were identified. Surgical delay, Erbium laser delay, and CO2 laser delay groups were each compared with a nondelayed control. Each group consisted of ten Sprague-Dawley rats. On Day 0 all delay procedures were performed on the lateral periphery of the outlined dorsal skin flaps. Interruption of this lateral blood supply was accomplished by two parallel 10-cm incisions in the surgical delay group. Likewise blood supply and microcirculatory alterations were accomplished in the laser delay groups by two parallel 10-cm laser treatments. On Day 7 a 10 x 4-cm cranially based dorsal skin flap was elevated. On Day 14 flap survival was analyzed by calculating percentage flap survival. The Erbium:YAG laser delay of the McFarlane flaps resulted in an average of 32 per cent less flap loss compared with controls ( P = 0.0001). The CO2 laser resulted in an average of 36 per cent less flap loss compared with controls ( P = 0.0002), whereas the surgical delay group had a 23 per cent smaller flap loss ( P = 0.009). There was no significant difference between any of the delay groups. These results indicated that CO2 and Erbium:YAG lasers are as effective as surgery for delay of skin flaps in the rat model. They may provide an effective and inexpensive method for near-scarless skin flap delay in humans.

Platelet-derived growth factor-AA-mediated functional angiogenesis in the rat epigastric island flap after genetic modification of fibroblasts is ischemia dependent

BACKGROUND

The aim of this study was to induce therapeutic angiogenesis in ischemically challenged flap tissue by means of gene transfer.

METHODS

Isogenic rat fibroblasts were retrovirally transfected to produce platelet-derived growth factor (PDGF)-AA. Stable gene expression was monitored by PDGF-AA enzyme-linked immunosorbent assay. Eighty animals were divided into 2 groups (1 and 2), each with 4 subgroups. The angiogenic target was a 7 x 7-cm epigastric island flap used as a necrosis model. Group 1 received flap treatment 1 week before flap elevation: 10(7) genetically modified fibroblasts, expressing PDGF-AA (genetically modified fibroblasts) plus 1 mL of Dulbecco's modified Eagle's medium (DMEM) (1A), 10(7) nonmodified fibroblasts (NMFB) plus 1 mL of DMEM (1B), 1 mL of DMEM (1C), and 1 mL of sodium chloride 0.9% (1D). All substances were injected at evenly distributed spots into the panniculus carnosus of the entire flap. Group 2 had the same flap treatment at the day of flap elevation. All flaps were sutured back. Seven days later, the flaps were harvested and examined both clinically, histologically, and immunohistochemically.

RESULTS

In vitro, the GMFB produced up to 117.9 +/- 57.2 ng of PDGF-AA/mL medium during a 4-day period, compared with 0.7 +/- 0.6 ng of PDGF-AA/mL medium produced by NMFB in the same time period. In vivo production of PDGF-AA in flaps amounted to 1.3 +/- 0.7 ng of PDGF-AA/1 microL flap tissue for group 1A and 1.7 +/- 1.1 ng of PDGF-AA/1 microL flap tissue for group 2A seven days after cell transplantation. Fibroblasts persisted in all flaps from groups 1A, 1B, 2A, and 2B without major inflammatory reaction. Clinically, group 2A developed significantly less flap necrosis compared with all other groups, including group 1A. Accordingly, only group 2A gave significant histologic and immunohistochemical evidence for enhanced angiogenesis within the flap tissue.

CONCLUSIONS

After retroviral gene transfer, isogenic rat fibroblasts produce high amounts of PDGF-AA in vitro. In vivo, PDGF-AA can be detected in flaps receiving genetically modified fibroblasts, which suggests survival of the implanted fibroblasts in this model. PDGF-AA produced by GMFB can induce flap angiogenesis only under ischemic conditions in this model. Transplantation of PDGF-AA-overexpressing fibroblasts results in higher flap survival in this model.