Involvement of nitric oxide in survival of random pattern skin flap

Extrinsic Vascular Pathway Preservation Improves Survival in a Rat Three-Territory Flap Model Based on the Deep Circumflex Iliac Artery

BACKGROUND

Extended flaps are commonly applied for large defects. However, a postoperative flap necrosis incidence of 11% to 44% remains a major complication. Previous clinical studies have shown that maintaining the extrinsic vascular pathway (EVP) can increase the survival area of extended flaps. The authors hypothesized that preserving the EVP would improve flap survival by reducing blood resistance within the vascular territory.

METHODS

Twenty-four adult male Sprague-Dawley rats were used. Tissue samples were obtained from eight untreated rats as a baseline control. Three-territory flaps were elevated in the remaining 16 rats. The EVP was preserved or ligated. Flap perfusion was assessed immediately using indocyanine green angiography. Rats were euthanized on day 7. The flap survival area was measured using Adobe Photoshop. Hematoxylin and eosin staining, CD31 immunostaining, and Western blot analysis of vascular endothelial growth factor protein expression were used to quantitatively assess vasodilation and angiogenesis in choke zones.

RESULTS

Indocyanine green angiography revealed that blood could flow through the preserved EVP and perfuse the third vascular territory of the flap. EVP preservation significantly increased flap survival area (86.3%, 19.3% difference; P < 0.001), promoted vasodilation (5.0/choke zone, 3.0/choke zone difference; P = 0.013) and angiogenesis (29.3/mm 2 , 14.3/mm 2 difference; P = 0.002), and increased vascular endothelial growth factor expression (0.6, 0.2 difference; P = 0.067) in the second choke zone.

CONCLUSIONS

EVP preservation improves flap survival in this rat three-territory flap model. Further investigation in large-animal models is required for clinical translation.

CLINICAL RELEVANCE STATEMENT

Although further validation in large animal models and prospective clinical trials are necessary to verify the efficacy of the authors' hypothesis, their findings suggest that the EVP preservation procedure could provide an alternative for surgeons to create an extended flap in defect reconstruction.

Protective Effect of Ebselen on Ischemia-reperfusion Injury in Epigastric Skin Flaps in Rats

The purpose of this study was to determine the role of oxidized diacylglycerol (DAG) and the molecular mechanism underlying ischemia-reperfusion (I/R) injury in rat skin flaps. The protective effect of ebselen on the viability of rat skin flaps with I/R injury was investigated. Flaps were designed and raised in the left inguinal region. Then, a microvascular clamp was applied to the vascular pedicle and reperfused after 6 hr. After 7 days of I/R (I/R group), the skin flap survival area ratio was significantly reduced compared to the normal skin. The administration of ebselen significantly improved the ratio compared to the I/R group. The flap survival area ratio of the I/R + ebselen group was significantly improved compared to the I/R + vehicle group. In the I/R + ebselen group, the oxidized DAG content and intensity of phosphorylated PKCα and PKCδ were significantly lower compared to the I/R + vehicle group. Furthermore, the inflammatory response was suppressed in the I/R + ebselen group compared to the I/R + vehicle group. These results indicate that ebselen is useful as a preventive and therapeutic agent for skin flap necrosis caused by I/R, because of reduction and elimination of oxidized DAG.

Apelin/APJ-Manipulated CaMKK/AMPK/GSK3β Signaling Works as an Endogenous Counterinjury Mechanism in Promoting the Vitality of Random-Pattern Skin Flaps

A random-pattern skin flap plays an important role in the field of wound repair; the mechanisms that influence the survival of random-pattern skin flaps have been extensively studied but little attention has been paid to endogenous counterinjury substances and mechanism. Previous reports reveal that the apelin-APJ axis is an endogenous counterinjury mechanism that has considerable function in protecting against infection, inflammation, oxidative stress, necrosis, and apoptosis in various organs. As an in vivo study, our study proved that the apelin/APJ axis protected the skin flap by alleviating vascular oxidative stress and the apelin/APJ axis works as an antioxidant stress factor dependent on CaMKK/AMPK/GSK3β signaling. In addition, the apelin/APJ-manipulated CaMKK/AMPK/GSK3β-dependent mechanism improves HUVECs' resistance to oxygen and glucose deprivation/reperfusion (OGD/R), reduces ROS production and accumulation, maintained the normal mitochondrial membrane potential, and suppresses oxidative stress in vitro. Besides, activation of the apelin/APJ axis promotes vascular migration and angiogenesis under relative hypoxia condition through CaMKK/AMPK/GSK3β signaling. In a word, we provide new evidence that the apelin/APJ axis is an effective antioxidant and can significantly improve the vitality of random flaps, so it has potential be a promising clinical treatment.

Comparison of ischemic preconditioning and BotulinumA Toxin injection for the prevention of ischemia-reperfusion injury in musculocutaneous flaps

Background/aim

The aim of the study was to evaluate the protective effect of Botulinum A toxin injection against ischemia-reperfusion injury.

Materials and methods

Thirty-two Sprague-Dawley rats were divided into: control, ischemia-reperfusion, ischemic preconditioning, and botulinum groups. In all groups the musculocutaneous pedicle flap was occluded for 4 h, and then reperfused to induce ischemia-reperfusion injury. Serum and tissue myeloperoxidase (MPO) and nitric oxide (NO) levels were measured at 24 h and at 10 days.

Results

Tissue MPO levels did not differ significantly between the ischemic preconditioning and botulinum groups at 24 h but was significantly lower in the botulinum group at 10 days. Tissue NO levels were significantly higher in the ischemic preconditioning group compared to the botulinum group at 24 h and at 10 days. Serum MPO showed no significant difference between these two groups at 24 h but was significantly lower in the ischemic preconditioning group compared to the botulinum group at 10 days. Serum NO levels were not significantly different at 24 h but significantly higher in the botulinum group at 10 days.

Conclusion

Findings show that botulinum has a protective effect against the ischemia-reperfusion injury via increased NO and decreased MPO levels in tissue. Based on tissue NO levels, ischemic preconditioning was significantly higher than botulinum.

Modulation of Nitric Oxide Bioavailability Attenuates Ischemia-Reperfusion Injury in Type II Diabetes

BACKGROUND

Diabetes mellitus increases the susceptibility of free tissue transplantations to ischemia-reperfusion injury. The aim of this study was to enhance nitric oxide (NO) bioavailability through exogenous NO synthase and the substrate L-arginine to attenuate ischemia reperfusion-induced alterations in a type 2 diabetes rodent model.

MATERIAL AND METHODS

Sixty-four Wistar rats were divided into 8 experimental groups. Type 2 diabetes was established over 3 months with a combination of a high-fat diet and streptozotocin. A vascular pedicle isolated rat skin flap model that underwent 3 h of ischemia was used. At 30 min before ischemia, normal saline, endothelial NOSs (eNOSs), inducible NOSs, neuronal NOSs (1 and 2 IU), and L-arginine (50 mg/kg body weight) were administered by intravenous infusion alone or in combination. Ischemia-reperfusion-induced alterations were measured 5 days after the operation.

RESULTS

The three isoforms of NOS significantly increased the flap vitality rate (VR) between 20% and 28% as compared to the control group (3%). Sole L-arginine administration increased the VR to 33%. The combination of L-arginine with NOS resulted in a further increase in flap VRs (39%-50%). Best results were achieved with the combination of eNOS and L-arginine (50%). An increase in enzyme dosage led to decreased VRs in all NOS isoforms alone and even in combination with L-arginine.

CONCLUSION

Modulation of NO bioavailability through the exogenous application of NOSs and L-arginine significantly attenuated ischemia-reperfusion-induced alterations in a type 2 diabetic skin flap rat model. The combination of enzyme and substrate result in the highest VRs. Higher enzyme dosage seems to be less effective. This pharmacological preconditioning could be an easy and effective interventional strategy to support the conversion of L-arginine to NO in ischemic and in type 2 diabetic conditions.

A new approach at diabetic foot treatment: Phosphodiesterase 5 inhibitors

Diabetic foot (DF), is one of the most serious and prevalent complications of diabetes mellitus (DM). Disruption in tissue oxygenation due to atherosclerosis in peripheral veins has an important place in DF development. In recent years, phosphodiesterase type 5 (PDE5) inhibitor drugs like sildenafil, which cause peripheral vasodilation, are used commonly in cases of erectile dysfunction, pulmonary hypertension and cardiac insufficiency. In that sense, PDE5 inhibitors, which cause vasodilation in peripheral veins, can increase blood build up in tissues of patients with DF and its stand-alone usage or its usage with already used treatments can increase tissue healing speed and quality.

Pharmaceutical Preconditioning With Nitric Oxide Synthase and L-Arginine in Ischemic Tissues

BACKGROUND

Nitric oxide (NO) is a multifunctional signaling molecule involved in regulating vascular tone and tissue oxygenation. It is also an important cytoprotective agent against ischemia-reperfusion injury (IRI). Enhancing NO bioavailability via exogenous NO synthases (NOSs) and L-arginine promotes conversation to NO, circumventing the problem of nonfunctioning NOSs under hypoxic and acidic conditions. In this study, the authors evaluated the therapeutic efficacy of neuronal, inducible, and endothelial NOS and L-arginine on reperfusion-induced skin flap alterations.

METHODS

The vascular pedicle isolated rat skin flap model was used and underwent 3 hours of ischemia. At 30 minutes before ischemia, normal saline, endothelial-, inducible-, and neuronal NOSs (1/2 IU) and L-arginine (100 mg/kg body weight) were administered by means of intravenous infusion. The IRI-induced alterations were measured 5 days after the operation.

RESULTS

The 3 isoforms of NOS increased the flap vitality rate (VR) from 10% to 23% compared with the control group. L-Arginine treatment also increased the VR by approximately 15%. The combination of L-arginine with NOS resulted in even higher flap VRs. The best results could be achieved with the combination of endothelial NOS (2 IU) and L-arginine.

CONCLUSIONS

Modulation of NO bioavailability via exogenous application of NOSs and L-arginine significantly improved VRs in a skin flap rat model. This pharmacologic preconditioning has the potential to attenuate IRI-induced alterations in skin flaps.

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.

Prevention of unfavourable effects of cigarette smoke on flap viability using botulinum toxin in random pattern flaps: An experimental study

BACKGROUND

There are numerous clinical and experimental studies reporting unfavourable effects of cigarette smoke on skin flaps.

OBJECTIVE

To investigate whether unfavourable effects of cigarette smoke on flap survival could be reduced by botulinum toxin type A.

METHODS

Twenty-eight male Wistar albino rats (15 months of age, mean weight 210 g [range 180 g to 230 g]) were included. They were divided into four groups of seven animals each. The control group underwent the surgical procedure alone. Surgical procedure was performed after administration of botulinum toxin type A in the botulinum toxin (BTX) group, after exposure to cigarette smoke in the cigarette smoke (CS) group, and after BTX type A administration and exposure to CS in the CS+BTX (CS+BTX) group. Random pattern cutaneous flaps (3 cm × 9 cm) were elevated from the dorsum of all rats. Necrosis area was calculated in percentages (%) using Image J computer software. Tissue samples were examined histopathologically.

RESULTS

The mean necrotic area in the control group (26%) and in the BTX group (21%) were similar (P=0.497), whereas administration of BTX type A significantly decreased flap necrosis area in the rats exposed to CS (the mean necrosis areas were 41.5% in the CS group, and 26% in the CS+BTX group; P<0.001). Histopathological examination findings corroborated the unfavourable effects of CS and preventive effects of BTX type A.

CONCLUSION

Preoperative administration of BTX significantly enhanced flap viability in the rats exposed to CS. Further human studies are warranted to verify whether BTX type A could be used as an agent to reduce the risk of flap necrosis in patients who smoke.

Prevention of unfavourable effects of cigarette smoke on flap viability using botulinum toxin in random pattern flaps: An experimental study

Background

There are numerous clinical and experimental studies reporting unfavourable effects of cigarette smoke on skin flaps.

Objective

To investigate whether unfavourable effects of cigarette smoke on flap survival could be reduced by botulinum toxin type A.

Methods

Twenty-eight male Wistar albino rats (15 months of age, mean weight 210 g [range 180 g to 230 g]) were included. They were divided into four groups of seven animals each. The control group underwent the surgical procedure alone. Surgical procedure was performed after administration of botulinum toxin type A in the botulinum toxin (BTX) group, after exposure to cigarette smoke in the cigarette smoke (CS) group, and after BTX type A administration and exposure to CS in the CS+BTX (CS+BTX) group. Random pattern cutaneous flaps (3 cm × 9 cm) were elevated from the dorsum of all rats. Necrosis area was calculated in percentages (%) using Image J computer software. Tissue samples were examined histopathologically.

Results

The mean necrotic area in the control group (26%) and in the BTX group (21%) were similar (P=0.497), whereas administration of BTX type A significantly decreased flap necrosis area in the rats exposed to CS (the mean necrosis areas were 41.5% in the CS group, and 26% in the CS+BTX group; P<0.001). Histopathological examination findings corroborated the unfavourable effects of CS and preventive effects of BTX type A.

Conclusion

Preoperative administration of BTX significantly enhanced flap viability in the rats exposed to CS. Further human studies are warranted to verify whether BTX type A could be used as an agent to reduce the risk of flap necrosis in patients who smoke.

Effect of Natural Hirudin on Random Pattern Skin Flap Survival in a Porcine Model

Objective:

The effect of local administration of hirudin on random pattern skin flap survival was investigated in a porcine model.

Methods:

Three random pattern skin flaps (4 × 14 cm) were created on each flank of five Chinese minipigs. The experimental group (10 flaps) received 20 antithrombin units of hirudin, injected subdermally into the distal half immediately after surgery and on days 1 and 2; a control group (10 flaps) was injected with saline and a sham group (10 flaps) was not injected. All flaps were followed for 10 days postoperatively.

Results:

Macroscopically, the congested/necrotic length in the experimental group was significantly decreased compared with the other two groups by day 3. Histopathological evaluation revealed venous congestion and inflammation in the control and sham groups from day 1, but minimal changes in the experimental group. By day 10, the mean ± SD surviving area was significantly greater in the experimental group (67.6 ± 2.1%) than in the control (45.2 ± 1.4%) or sham (48.3 ± 1.1%) groups.

Conclusions:

Local administration of hirudin can significantly increase the surviving area in overdimensioned random pattern skin flaps, in a porcine model.

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.

Hypothyroidism improves random-pattern skin flap survival in rats

BACKGROUND

The protective effect of hypothyroidism against ischemic or toxic conditions has been shown in various tissues. We investigated the effect of propylthiouracil (PTU)/methimazole (MMI)-induced hypothyroidism and acute local effect of MMI on the outcome of lethal ischemia in random-pattern skin flaps.

MATERIALS AND METHODS

Dorsal flaps with caudal pedicles were elevated at midline and flap survival was measured at the seventh day after surgery. The first group, as control, received 1 mL of 0.9% saline solution in the flap before flap elevation. In groups 2 and 3, hypothyroidism was induced by administration of either PTU 0.05% or MMI 0.04% in drinking water. The next four groups received local injections of MMI (10, 20, 50, or 100 μg/flap) before flap elevation. Local PTU injection was ignored due to insolubility of the agent.

RESULTS

Hypothyroidism was induced in chronic PTU- and MMI-treated groups, and animals in these groups showed significant increase in their flap survival, compared to control euthyroid rats (79.47% ± 10.49% and 75.48% ± 12.93% versus 52.26% ± 5.75%, respectively, P < 0.01). Acute local treatment of skin flaps with MMI failed to significantly affect the flap survival.

CONCLUSION

This study demonstrates for the first time that hypothyroidism improves survival of random-pattern skin flaps in rats.

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.

Intradermal delivery of plasmid VEGF(165) by electroporation promotes wound healing

Skin flaps are extensively used in reconstructive surgeries to repair large defects and deep wounds, but severe ischemia and necrosis often results in loss of the transplanted tissue. Thus, skin flap models are often used to study the biology of healing and necrosis of acute ischemic wounds. Delivery of exogenous vascular endothelial growth factor (VEGF) to areas of ischemia has shown promise for promoting therapeutic angiogenesis, but its expression must be tightly regulated to avoid adverse effects. In this study, plasmid DNA encoding VEGF(165) (pVEGF) was delivered to the ischemic skin of a rat skin flap model by intradermal injection followed by electroporation (EP) (pVEGFE+). Treatment with pVEGFE+ significantly increased VEGF expression for 5 days after delivery compared to injection of pVEGF without EP (pVEGFE-). The short-term increase in VEGF was sufficient to mediate an upregulation of endothelial nitric oxide synthase, an angiogenic factor that increases vascular permeability. pVEGFE+ significantly increased skin flap perfusion at both days 10 and 14 postoperatively. The observed increase in perfusion with pVEGFE+ correlated with an increase in skin flap healing and survival. Our results demonstrate that pVEGFE+ is a potential nonviral noninvasive therapy to increase perfusion and healing of skin flaps and ischemic wounds.

Evaluation of the effect of sildenafil and vascular endothelium growth factor combination treatment on skin flap survival in rats

BACKGROUND

Distal ischemic necrosis of surgical flaps remains a challenging problem for the reconstructive surgeon. Recent studies have shown that either sildenafil or vascular endothelium growth factor (VEGF) treatment significantly improves ischemic skin flap viability. In this study, the effect of the combination of sildenafil and VEGF165 was evaluated on a rat skin flap model using orthogonal polarization spectral imaging and histologic analysis.

METHODS

Rats were assigned to either a sham (n = 31), vehicle (n = 24), sildenafil (n = 24), VEGF (n = 23), or sildenafil and VEGF combination treatment (n = 21) groups. Distances from the distal end of the flap to avascular, stasis, and normal capillary blood flow zones were determined using orthogonal polarization spectral imaging on a skin flap model. Vessel density assessment was done at 7 days post surgery.

RESULTS

Imaging analysis showed significant reduction in avascular and stasis areas in sildenafil and VEGF combination-treated groups at 7 days post surgery (p < 0.05). The combination-treated group, however, was not significantly different when compared to the group treated with sildenafil only. The sildenafil-treated group showed a significant (p < 0.05) reduction in both areas at day 7 compared to the VEGF and control groups. Histologic analysis showed no significant differences in vessel density between the groups.

CONCLUSION

The combination of sildenafil and VEGF decreases the extent of avascular and stasis zones in skin flaps. The skin flap improvement seen with the combination treatment was similar to the sildenafil treatment alone suggesting that enhanced flap survival was due solely to the effect of sildenafil.

Nitric oxide in flow-through venous flaps and effects of L-arginine and nitro-L-arginine methyl ester (L-NAME) on nitric oxide and flap survival in rabbits

OBJECT

Venous flaps are relatively recent practices in plastic surgery, and their life mechanisms are not known exactly. Partial necroses frequently occur in these flaps; therefore, their survival should be enhanced. Nitric oxide (NO) is an endogenous compound which has recently been dwelt upon frequently in flap pathophysiology, and its effect on viability in conventional flaps has been demonstrated. However, its role in venous flaps is unknown. The purpose of this study is to determine possible changes in the NO level in venous flaps and to investigate the possible effects of NO synthesis precursor and inhibitor on the venous flap NO level and flap survival.

MATERIAL AND METHODS

Thirty white male rabbits of New Zealand type, aged 6 months, were divided into 3 groups as control (n = 10), L-arginine (n = 10), and nitro-L-arginine methyl ester (L-NAME) (n = 10). Blood and tissue samples were taken from one ear of 10 rabbits in the control group for the determination of NO basal levels 2 weeks before flap practice. The 3-x-5-cm flow-through venous flaps, which are sitting on the anterior branch of the central vein, were elevated on each ear of 10 rabbits in all groups. After flaps were sutured to their beds, 2 mL/d saline, 1 g/kg/d L-arginine (NO synthesis precursor), and 50 mg/kg/d L-NAME (NO synthesis inhibitor) were administered intraperitoneally in control, L-arginine, and L-NAME groups, respectively, for 3 days. At the 24th postoperative hour, blood and tissue samples were taken from all animals for biochemical analyses. At day 7, flap survivals were assessed.

RESULTS

Mean NO levels in the blood following the flap elevation (129 +/- 76 micromol/mg protein) increased in comparison with basal levels (59 +/- 44 micromol/mg protein) (P < 0.06); however, the tissue level remained unchanged. NO levels in the blood in the L-arginine and L-NAME groups were alike compared with the control group. The tissue NO level in L-NAME group (0.08 +/- 0.03 micromol/mg protein) decreased significantly compared to the control group (0.46 +/- 0.36 micromol/mg protein) (P < 0.001). Mean flap survival in the L-arginine group (95% +/- 6) increased according to the control group (61% +/- 14) (P < 0.001), whereas it did not change in the L-NAME group (55% +/- 13).

CONCLUSION

In our model of venous flap, NO level in the blood increased, while it did not change in the tissue; L-arginine significantly enhanced flap viability without affecting NO level. Additionally, L-NAME decreased NO level, but it did not affect flap survival. In light of these findings, NO increases in venous flaps; the change in its level does not affect flap survival, though. However, L-arginine enhances venous flap survival if not by virtue of NO.

Thrombospondin-1: a physiological regulator of nitric oxide signaling

Thrombospondin-1 is a secreted protein that modulates vascular cell behavior via several cell surface receptors. In vitro, nanomolar concentrations of thrombospondin-1 are required to alter endothelial and vascular smooth muscle cell adhesion, proliferation, motility, and survival. Yet, much lower levels of thrombospondin-1 are clearly functional in vivo. This discrepancy was explained with the discovery that the potency of thrombospondin-1 increases more than 100-fold in the presence of physiological levels of nitric oxide (NO). Thrombospondin-1 binding to CD47 inhibits NO signaling by preventing cGMP synthesis and activation of its target cGMP-dependent protein kinase. This potent antagonism of NO signaling allows thrombospondin-1 to acutely constrict blood vessels, accelerate platelet aggregation, and if sustained, inhibit angiogenic responses. Acute antagonism of NO signaling by thrombospondin-1 is important for hemostasis but becomes detrimental for tissue survival of ischemic injuries. New therapeutic approaches targeting thrombospondin-1 or CD47 can improve recovery from ischemic injuries and overcome a deficit in NO-responsiveness in aging. (Part of a Multi-author Review).

The influence of local and systemic preconditioning on oxygenation, metabolism and survival in critically ischaemic skin flaps in pigs

Stress proteins represent a group of highly conserved intracellular proteins that provide adaptation against cellular stress. The present study aims to elucidate the stress protein-mediated effects of local hyperthermia and systemic administration of monophosphoryl lipid A (MPL) on oxygenation, metabolism and survival in bilateral porcine random pattern buttock flaps. Preconditioning was achieved 24h prior to surgery by applying a heating blanket on the operative site (n = 5), by intravenous administration of MPL at a dosage of 35 microg/kg body weight (n = 5) or by combining the two (n = 5). The flaps were monitored with laser Doppler flowmetry, polarographic microprobes and microdialysis until 5h postoperatively. Semiquantitative immunohistochemistry was performed for heat shock protein 70 (HSP70), heat shock protein 32 (also termed haem oxygenase-1, HO-1), and inducible nitrc oxide synthase (iNOS). The administration of MPL increased the impaired microcirculatory blood flow in the proximal part of the flap and partial oxygen tension in the the distal part by approximately 100% each (both P<0.05), whereas both variables remained virtually unaffected by local heat preconditioning. Lactate/pyruvate (L/P) ratio and glycerol concentration (representing cell membrane disintegration) in the distal part of the flap gradually increased to values of approximately 500 mmol/l and approximately 350 micromol/l, respectively (both P<0.01), which was substantially attenuated by heat application (P<0.01 for L/P ratio and P<0.05 for glycerol) and combined preconditioning (P<0.01 for both variables), whereas the effect of MPL was less marked (not significant). Flap survival was increased from 56% (untreated animals) to 65% after MPL (not significant), 71% after heat application (P<0.05) and 78% after both methods of preconditioning (P<0.01). iNOS and HO-1 were upregulated after each method of preconditioning (P<0.05), whereas augmented HSP70 staining was only observed after heat application (P<0.05). We conclude that local hyperthermia is more effective in preventing flap necrosis than systemic MPL administration because of enhancing the cellular tolerance to hypoxic stress, which is possibly mediated by HSP70, whereas some benefit may be obtained with MPL due to iNOS and HO-1-mediated improvement in tissue oxygenation.

Hyperbaric oxygen therapy mediates increased nitric oxide production associated with wound healing: a preliminary study

OBJECTIVE

The objective of this preliminary study was to document general somatic and wound nitric oxide (NO) levels during and after hyperbaric oxygen therapy (HBOT).

DESIGN

The study evaluated 6 chronic wound patients that responded favorably to HBOT treatment (20 treatments; 2.0 atmosphere absolute [ATA] x 90 minutes). Successful HBOT was associated with increased wound granulation tissue formation and significantly improved wound closure. Wound fluid and fasting plasma samples were obtained for measurement of nitrate and nitrite (NOx), the stable oxidation products of NO; plasma L-arginine (L-Arg); and asymmetric dimethylarginine (ADMA). NOx measurements were obtained before treatment (baseline), after 10 and 20 treatments, and at 1 and 4 weeks after therapy.

RESULTS

Wound fluid NOx levels tended to increase during treatments, were significantly elevated at 1 and 4 weeks after therapy, and correlated with reductions in wound area. Plasma L-Arg and ADMA were unchanged during and after HBOT.

CONCLUSION

This preliminary study documents a significant increase in local wound NO levels (by NOx measurements) after successful HBOT and suggests that this mechanism may be an important factor in promoting enhanced wound healing and wound closure associated with this therapy.

Pharmacologic Preconditioning of Random-Pattern Skin Flap in Rats Using Local Cyclosporine and FK-506

It has been suggested that immunophilin ligands such as cyclosporine and FK-506 (tacrolimus) affect the survival of ischemic tissues. Our objective was to show an acute effect of local cyclosporin-A (CsA) and FK-506 on ischemic protection in a random-pattern skin-flap model in rats and investigate the effect of nitric oxide (NO) pathways as a modulator of protection of these agents. Ninety male Sprague-Dawley rats were randomly assigned to treatment groups. Bipedicled dorsal flaps (2 x 8 cm) were elevated at midline. Prior to cutting the cranial pedicle to induce permanent ischemia, pharmacologic preconditioning groups received local injection of CsA (0.3, 1, or 3 nmol/flap) or FK-506 (0.01, 0.03, or 0.1 pmol/flap), and the ischemic preconditioning (IPC) group underwent temporary clamping of the cranial pedicle. At the seventh day postoperatively, the survival of the flaps was measured. In other groups, nitric oxide synthase inhibitor N omega-nitro-l-arginine methyl ester hydrochloride (L-NAME) was administered with effective CsA and FK-506, and ischemic preconditioning. Nitric oxide precursor L-arginine doses were also studied, and a systemic subeffective dose (100 mg/kg) was coadministered with subeffective CsA and FK-506. Significant increase in flap survival was obtained with CsA (1 nmol/flap), FK-506 (0.1 pmol/flap), and IPC. These protections were abolished by systemic administration of L-NAME (10 mg/kg). Coadministration of subeffective doses of CsA (0.3 nmol/flap) and FK-506 (0.03 pmol/flap), with subeffective systemic l-arginine, significantly improved flap survival.Pharmacologic preconditioning with local, single, low doses of CsA or FK-506 is shown to be even more effective than IPC. Administration of the NOS substrate l-arginine potentiates these effects.

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.

Effects of nitric oxide synthase inhibition on blood flow and survival in experimental skin flaps

The aim of the present study was to examine the effect of the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME) on skin and flap blood flow, NOS activity and flap survival in an ischaemic dorsal flap model in the rat. Fifty-four rats were used in the study. l-NAME or the inactive enantiomere d-NAME was given intravenously either pre-, per- and postoperatively or only postoperatively. Controls received saline treatment. Blood pressure and skin and flap blood flow were monitored. NOS activity was measured in intact skin before and after l-NAME and d-NAME infusion and in flap tissue 48h postoperatively. Forty-eight hours postoperatively flap survival was determined in all rats. l-NAME treatment caused: (1) a marked attenuation of constitutive Ca(2+) dependent NOS activity in intact skin (p<0.001), (2) an increase in blood pressure (p<0.05), (3) a decrease in blood flow in intact skin and in skin flaps (p<0.05), and (4) a decrease in flap survival (p<0.05). In saline and d-NAME treated animals no change in blood pressure, blood flow or NOS activity in intact skin was noted. In conclusion this study shows that l-NAME attenuates constitutive Ca(2+) dependent NOS activity in intact skin, decreases skin and flap blood flow and decreases the survival of skin flaps. These results indicate that constitutive nitric oxide synthase is important for basal blood flow in skin and flap tissue and for the survival of skin flaps.

Short- and Long-Term Effects of Sildenafil on Skin Flap Survival in Rats

OBJECTIVE

Distal ischemic necrosis of the flap remains an unsolved, challenging problem. Phosphodiesterase (PDE) inhibitors, which include the drug sildenafil, are a relatively new class of U.S. Food and Drug Administration-approved medications whose effect on tissue viability has not been widely explored. The vasodilatory effects of these drugs have the potential to enhance blood flow to flaps and increase their survivability. The purpose of this study was to examine the short- and long-term effects of sildenafil, administered intraperitoneally at a dose of 9 mg/kg per day, on the survival of surgical skin flaps in rats.

METHODS

A McFarlane-type random pattern skin (3 x 10-cm) flap model was used to evaluate the effect of sildenafil on necrosis at multiple time points. Rats were assigned to sildenafil-treated (9 mg/kg per day intraperitoneally; n = 34), vehicle control (n = 35), or sham (no injection; n = 40) groups. In each group, caudally based, dorsal, rectangular (3 x 10-cm) flaps were created. Flap necrosis was determined using orthogonal polarization spectral imaging and digital photography analysis on days 1, 3, 5, and 7 postsurgery.

RESULTS

Orthogonal polarization spectral imaging results showed a significant decrease in necrosis and stasis in rats treated with sildenafil on days 1 and 3. Although reductions observed at days 5 and 7 were not as dramatic as days 1 and 3, digital photography analysis confirmed a decrease in the area of necrosis at all time points evaluated.

CONCLUSIONS

These results suggest that PDE 5 inhibitors may play a more important role in early postoperative skin flap viability rather than at later time points and may be beneficial for skin flap viability as shown in the rat model. PDE 5 inhibitors may reduce the extent of necrosis after reconstructive surgeries.

Preconditioning with Monophosphoryl Lipid A Improves Survival of Critically Ischemic Tissue

In this study we sought to assess the effects of preconditioning with monophosphoryl lipid A on critically ischemic wound margins and on systemic and local hemodynamics and oxygenation during prolonged anesthesia with volatile anesthetics and narcotics. Twenty large white pigs were randomly assigned to receive either monophosphoryl lipid A 35 mug/kg IV or saline 24 h before dissection of a buttock flap. The animals were anesthetized with isoflurane (end-tidal concentration approximately 1.25%) for surgery and subsequent monitoring of hemodynamics and oxygenation both systemically and in the flap tissue for 6 h. Preconditioning resulted in increased cardiac index and oxygen delivery (both P < 0.05) and in decreased central venous pressure and systemic vascular resistance (both P < 0.01). In the preconditioned flap tissue, microcirculatory blood flow (laser Doppler flowmetry) and partial tissue oxygen tension (polarographic microprobes) were up to 2.5-fold higher compared with control (both P < 0.05) and flap necrosis was reduced by 20% on postoperative day 14 (P < 0.05). Our results suggest that preconditioning with a single dose of monophosphoryl lipid A may attenuate ischemia-related wound healing complications, which may be related to an improvement in perfusion and oxygenation of this tissue. Furthermore, preconditioning exerted a systemic cardiovascular stabilization effect during prolonged isoflurane anesthesia.

Ischemia/reperfusion injury: a review in relation to free tissue transfers

Events during ischemia/reperfusion (I/R) injury include: neutrophil-mediated endothelial cytotoxicity and activation, generation of free radicals, triggering of cytokines and chemokines, and activation of adhesion molecules and complement system. This article briefly reviews events occurring during tissue ischemia and reperfusion in relation to free tissue transfers. The consequences of tissue damage at the microcirculatory level are presented. Preventive measures of I/R injury are outlined.

Regulation of inducible nitric oxide synthase in ischemic preconditioning of muscle flap in a rat model

PURPOSE

Ischemic preconditioning has been shown to influence flap tolerance to prolonged ischemia. Nitric oxide (NO) synthesis is one of the proposed mechanisms involved in ischemic preconditioning. In this study, the molecular marker of NO is examined in correlation with ischemic preconditioning on improving muscle flap survival.

METHODS

Fifty male Sprague-Dawley rats were randomized into experimental and control groups. The gracilis muscle flap with femoral vascular pedicle was used as a flap model. Ischemic preconditioning consisted of 3 sequences of clamping the pedicle for 10 minutes followed by 10 minutes of reperfusion for a total of 1 hour. In part I, the experimental group (n = 10) underwent ischemic preconditioning for 1 hour. In the control group (n = 10), the flaps were dissected without clamping of the pedicle. Both groups were then subjected to 4 hours of global ischemia by continuous pedicle clamping, after which the flaps were sutured to their beds. On postoperative day 3, flap survival was determined by gross and histologic examinations. The evaluators were blinded to the treatment. In part II, the experimental group (n = 12) underwent ischemic preconditioning, while the control group (n = 12) did not. The flaps from each group were harvested for inducible nitric oxide synthase (iNOS) gene expression using reverse transcriptase-polymerase chain reaction at the end of 1 hour after reperfusion and at 4 hours of global ischemia.

RESULTS

The results indicated a significantly higher survival rate in the experimental group than in the control group (90 versus 50%, P < 0.05). iNOS gene expression was significantly higher in the experimental group than in the control group at 1 hour after ischemic preconditioning (0.73+/-0.18 versus 0.26+/-0.11, P < 0.01). However, after 4 hours of global ischemia, iNOS expression in the control group was statistically higher than in the experimental group (0.83+/-0.16 versus 0.26+/-0.07, P < 0.01).

CONCLUSIONS

We conclude that ischemic preconditioning can enhance flap tolerance to ischemia-reperfusion injury and improve flap viability rate. This study provides evidence that the regulation of NOS may play a role in ischemic preconditioning phenomenon and warrants further investigation.

The effect of short- versus long-term administration of alpha tocopherol on the survival of random flaps in experimental diabetes mellitus

The effects of short- versus long-term alpha tocopherol administration on oxidative stress and survival of dorsal random flaps were studied in diabetic rats. Seven groups, with 20 rats in each, were constructed: (1) control, (2) noncontrolled diabetes, (3) noncontrolled diabetes+short-term alpha tocopherol, (4) noncontrolled diabetes+long-term alpha tocopherol, (5) insulin treatment, (6) insulin+short-term alpha tocopherol, and (7) insulin+long-term alpha tocopherol. After 3 months of diabetes, dorsal McFarlane flaps were raised. Flap viability and free-radical measurements with histopathological examination were investigated. Mean flap survival in Groups I to VII were 84.0+/-2.2%, 55.0+/-2.4%, 57.0+/-2.5%, 57.8+/-3.7%, 64.1+/-4.1%, 70.0+/-4.9%, and 77.0+/-6.6%, respectively. Free-radical concentration, as assessed with luminol- and lucigenin-enhanced chemiluminiscence, was inversely correlated with flap survival. The results for viability and free-radical concentrations were significant between Groups 1, 2, 5, 6, and 7. Random flaps in diabetic animals showed significantly greater necrosis compared with controls. Among the diabetic animals, group receiving combination of insulin and long-term alpha tocopherol treatment had the greatest flap viability and least tissue free-radical concentration. Histopathological studies showed a hyalinization of arterioles in diabetics with long-term alpha tocopherol treatment protecting the vessel wall. In conclusion, random flaps in experimental diabetes mellitus show greater tissue oxidative stress and necrosis, which is only partially corrected with insulin treatment. Long-term antioxidant supplementation as an adjunct to insulin further lowers the oxidative stress, protects vessel structure and function, and therefore increases flap survival.

Propofol Improves Skin Flap Survival in a Rat Model

Accumulation of neutrophils in a random pattern skin flap has been demonstrated to contribute to the necrosis of distal flap tissue. This study proposes that administration of propofol anesthesia can effectively reduce neutrophil activity and enhance skin flap survival. The study was a randomized controlled trial using male Sprague-Dawley rats as subjects. For flap survival studies, a 3- by 12-cm, dorsal, cranial-based, random pattern skin flap was elevated and reapproximated. Flaps were examined for viability 10 days postsurgery. To assess neutrophil activity, flap biopsies were taken 12, 24, or 48 hours postsurgery from distal, middle, and proximal flap regions, and myeloperoxidase enzyme content was analyzed. Animals were randomly assigned to 1 of 4 groups: group 1, ketamine anesthesia (controls); group 2, propofol anesthesia; group 3, ketamine anesthesia plus 10% lipid emulsion (propofol vehicle); group 4, ketamine anesthesia without flap elevation (nonoperated controls for myeloperoxidase study). Flap survival was significantly improved in the propofol group compared with both the ketamine and vehicle control groups (P <0.01). Increased flap viability was correlated with a reduction in myeloperoxidase content in the propofol group compared with control operated animals, with minor variations observed in the different flap regions and time points tested. This study indicates that the use of propofol can potentially improve skin flap survival. The beneficial effects may be attributed to a reduction in neutrophil activity within the flap.

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.

Oral Administration of L-Arginine Decreases Necrosis of the Epigastric Skin Flap in the Rat

BACKGROUND

We investigated the effect of prolonged oral arginine administration on tissue necrosis and perfusion in the rat skin flap.

METHODS

Twenty-five Sprague-Dawley rats had an 8 x 8 - cm epigastric skin flap elevated and were divided in 2 groups, l-Arginine and Control, which respectively received oral 6% l-arginine solution or water for 8 days postoperatively. On postoperative day 8, area of flap necrosis was measured, and the animals were perfused systemically with 15-microm colored fluorescent microspheres before (blue) and after (yellow-green) ligation of the flap pedicle.

RESULTS

l-Arginine reduced total flap necrosis (6.53 +/- 3.76 cm versus 11.91 +/- 4.12 cm; P < 0.01). After pedicle ligation, total flap perfusion remained unchanged in Control but diminished in the l-Arginine group (Control: 0.47 +/- 0.23 and 0.42 +/- 0.06; P = nonsignificant versus l-Arginine: 0.58 +/- 0.29 and 0.27 +/- 0.19; P < 0.01). Serum levels of l-arginine were higher in the l-arginine-treated animals (504 +/- 154 versus 152 +/- 34 micromol/l; P < 0.0001).

CONCLUSIONS

Postoperative oral administration of l-arginine decreased flap necrosis in the rat epigastric skin flap. Flap perfusion following oral l-arginine was more dependent on the main vascular pedicle.

Nitrosoglutathione modulation of platelet activation and nitric oxide synthase expression in promotion of flap survival after ischemia/reperfusion injury1

BACKGROUND

Recent studies have shown that platelets play an important role in the pathogenesis of reperfusion injury. Using an inferior epigastric artery skin flap as a flap ischemia/reperfusion (I/R) injury model, we investigated whether the administration of a nitric oxide (NO) donor, nitrosoglutathione (GSNO), could decrease platelet activation and modulate the NO synthase (NOS) activity of platelets and promote flap survival.

METHODS

Thirty minutes before flap reperfusion, normal saline (1 mL), nitrosoglutathione (GSNO 0.2, 0.6, 3 mg/kg), or N(G)-nitro-L-arginine-methyl ester (450 mg/kg) was injected intravenously in 10 rats, respectively. The p-selectin (CD62P) expression of platelet activation was detected by a flow cytometry. Immunohistochemical staining was performed to investigate the CD62P deposition on the microvasculature of the flap vessels. NOS isoform expression in the platelets was evaluated by Western blot. Tissue perfusion was monitored by using laser-Doppler flowmetry. Survival areas were assessed at 7 days postoperatively

RESULTS

An optimal dose of GSNO (0.6 mg/kg), significantly decreased in CD62P expression on platelets (P < 0.001) and its deposition on the flap vessels, selectively suppressed iNOS induction of platelet, and significantly improved blood perfusion and the flap survival rate (59.8 +/- 4.9% versus 22.1 +/- 6.1%, P < 0.001). In contrast, the NO synthase inhibitor, N(G)-nitro-l-arginine methyl ester, although inhibiting iNOS expression of platelets, compromised platelet activation, tissue perfusion, and flap survival.

CONCLUSION

This study suggests that GSNO can appropriately donate NO to suppress platelet activation and platelet iNOS induction, resulting in less platelet activation, better blood perfusion, and flap survival after I/R injury.

Full-thickness skin necrosis after arginine extravasation--a case report and review of literature

The arginine test is highly useful in the evaluation of short-stature children and adolescents. Extravasation of arginine can cause full-thickness skin necrosis that requires serious surgical intervention with aesthetic and functional sequellea. The authors describe a case of distal forearm skin necrosis caused by arginine extravasation that was treated by wide debridement and a combination of groin flap and later with split-thickness skin graft. The authors emphasize the need for early and active management of arginine extravasation injuries.

Nitrosoglutathione improves blood perfusion and flap survival by suppressing iNOS but protecting eNOS expression in the flap vessels after ischemia/reperfusion injury

BACKGROUND

The effects of nitric oxide (NO) on the microcirculation and free tissue survival remain controversial. With the use of a rat inferior epigastric artery flap as an ischemia/reperfusion injury (I/R) model, we investigated whether exogenous NO donation regulates endogenous NO synthase (NOS) expression in the flap vessels and promotes flap survival.

METHODS

Thirty minutes before flap reperfusion, normal saline (1 ml), nitrosoglutathione (GSNO 0.2, 0.6, 3 mg/kg), or N(G)-nitro-L-arginine-methyl ester (L-NAME, 450 mg/kg), was injected intravenously into 20 rats. Total plasma NOx (NO(2)-/NO(3)-) was measured to reflect NO production. Immunohistochemical staining was investigated for the endothelin-1 (ET-1) and NOS isoforms expression on the flap vessels. NOS isoforms expression was evaluated by Western blot. Laser-Doppler flowmetry monitored flap perfusion. Survival areas were assessed by gross examination at 7 days postoperatively.

RESULTS

Flap ischemia at 12 hours followed by reperfusion resulted in endothelial cell damage, as demonstrated by induction of iNOS and ET-1 expression in the flap vessels. An optimal dose of nitrosoglutathione (0.6 mg GSNO/kg) significantly increased plasma NOx levels (P=.027) and improved flap perfusion by laser Doppler measurement (P=.014), and increased the flap viability area (P<.001). Additionally, it selectively suppressed iNOS induction, but enhanced eNOS expression and decreased ET-1 deposition in the flap vessels. In contrast, an NOS inhibitor, N(G)-nitro-L-arginine methyl ester, inhibited both iNOS and eNOS expression in the flap vessels, decreased endogenous NOx production, and compromised flap viability.

CONCLUSION

This study indicates that intravenous administration of exogenous GSNO can appropriately donate NO to suppress iNOS induction and enhance eNOS expression in pedicle vessels, resulting in better blood perfusion and a higher flap survival after I/R injury.

Local administration of nitric oxide donor significantly impacts microvascular thrombosis

OBJECTIVES/HYPOTHESIS

Clinical pharmacotherapy has demonstrated a role in preventing microvascular thrombosis in both experimental and clinical settings. Previous studies in the rabbit model have noted an increased rate of thrombosis with intravenous infusion of nitric oxide antagonists. The study assessed the effects of local application of nitric oxide agonists and antagonists on microvascular anastomotic patency rates.

STUDY DESIGN

A randomized, prospective analysis.

METHODS

An arterial inversion graft microvascular thrombosis model was used in New Zealand white rabbits. The rabbits were randomly assigned to nitric oxide agonist, antagonist, and control groups. In each rabbit, the common femoral artery was surgically exposed and a 2-mm arterial inversion graft was harvested. The anastomosis of the graft to the common femoral artery was performed in solutions of either 100 micromol/L spermine NONOate (nitric oxide donor), 100 micromol/L nitro-L-arginine-methyl ester (L-NAME) (nitric oxide synthase inhibitor), or 0.9% sodium chloride (control) solution. The contralateral common femoral artery also underwent arterial inversion graft testing with the use of the same solution. Arterial patency was assessed 1 hour after anastomosis.

RESULTS

Sixteen of 22 arterial inversion grafts performed in the spermine NONOate solution remained patent, and 6 of 22 clotted. Eleven of 21 arterial inversion grafts performed in the control solution remained patent, and 10 clotted. Seven of 21 arterial inversion grafts performed in the L-NAME solution remained patent, and 14 clotted. These results were found to be statistically significant using the chi test with a value of less than.05.

CONCLUSIONS

In the rabbit model, local application of nitric oxide agonists and antagonists can significantly impact anastomotic patency rates. Further studies may demonstrate a role for the clinical use of nitric oxide in microvascular surgery.

Special issues in plastic and reconstructive surgery

Intensivists frequently collaborate with plastic and reconstructive surgeons in treating patients with major wounds, following significant reconstructive procedures, and following free-tissue transfers. Pressure ulcers are a significant source of morbidity and mortality in the intensive care unit; prevention, early recognition, and multidisciplinary treatment are critical components for successful management. Necrotizing fasciitis is an aggressive, soft-tissue infection that requires rapid diagnosis, early surgical intervention frequent operative debridements, and soft-tissue reconstruction Catastrophic abdominal injuries and infections can be treated with an open abdominal approach and require the expertise of a plastic surgeon to reconstruct the abdominal wall. The success of free-tissue transfers and complex reconstructive procedures requires a thorough understanding of the factors that improve flap survival.

Protective effect of a novel NO-donor on ischemia/reperfusion injury in a rat epigastric flap model

An altered metabolism of endothelial cell-derived nitric oxide has been implicated in the microvascular dysfunction associated with ischemia/reperfusion. The objective of this study was to examine whether S-nitroso human serum albumin, a novel nitric oxide-donor, improves flap viability and whether it influences edema formation after prolonged ischemia when administered prior to and in the initial phase of reperfusion. Denervated epigastric island skin flaps were elevated in 30 male Sprague Dawley rats, rendered ischemic for 8 hours, subsequently reperfused and further observed for either 3 hours (acute) or 7 days (chronic). In the sham rats (n = 6), skin flaps were elevated only. Starting 1 hour prior to reperfusion, S-nitroso human serum albumin (n = 12) or human serum albumin (n = 12) as placebo was infused systemically for 2 hours. In the chronic model, flap necrosis as well as viable flap size was evaluated after 7 days of reperfusion in six rats per group, comparing to sham rats. In the acute model, edema formation was evaluated after 3 hours of reperfusion in six rats per group. Administration of S-nitroso human serum albumin significantly decreased flap necrosis from 18.1 +/- 15.6% in the human serum albumin group to 2.1 +/- 1.5% in the S-nitroso human serum albumin group, which was similar to the sham group (2.5 +/- 4.2%). Viable flap size (sham 13.4 +/- 1.6 cm2) was also significantly improved in the S-nitroso human serum albumin group (10.1 +/- 1 cm2) versus the human serum albumin group (7.0 +/- 2.2 cm2). There was no significant difference between the groups regarding postischemic edema formation. These results show that administration of S-nitroso human serum albumin prior to and in the initial phase of reperfusion significantly improves flap viability after 7 days but does not influence early observable edema formation. These findings support the role of nitric oxide as an important mediator in the protection against skin flap ischemia/reperfusion injury.

Inhibitors of nitric oxide promote microvascular thrombosis

BACKGROUND

Microvascular free tissue transfer is a widely utilized method of head and neck reconstruction. Despite advances in the field, reports of experienced microvascular surgeons on large series of free flap procedures reveal that the incidence of free flap failure varies between 5% and 9%. Most cases of free flap failure are initiated by platelet-mediated events that result in thrombosis at the microvascular anastomoses. Recent evidence indicates that nitric oxide (NO) plays a critical role in preventing thrombosis by inhibiting platelet adhesion and aggregation. The role of NO in microvascular anastomotic thrombosis has not been studied.

OBJECTIVE

To determine the role of NO in microvascular thrombosis using an in vivo rabbit model.

METHODS

An arterial inversion graft (AIG)-induced microvascular thrombosis model was utilized in New Zealand white rabbits. The femoral arteries were used bilaterally to create 3-mm AIGs. Intravenous NO donor, NO inhibitor, or isotonic sodium chloride solution (control) was administered for 1 hour following the completion of the AIG, and vessel patency was then checked using a direct "milking test." Sixteen rabbits (32 AIGs) were used as controls. A potent NO inhibitor, N(w)-nitro-L-arginine methylester (L-NAME), was administered to 13 rabbits (26 AIGs) and L-arginine, a NO precursor/donor, was given to 10 rabbits (20 AIGs).

RESULTS

The control animals had a thrombosis rate of 46.9%. The rate of thrombosis in animals exposed to an NO inhibitor (L-NAME) was significantly higher, at 76.9% (P<.05, chi( 2) = 4.23). The L-arginine group did not show a statistical difference with the control in the rate of thrombosis (50.0%).

CONCLUSIONS

Nitric oxide plays a role in microvascular anastamotic thrombosis. Intravenous NO inhibitors appear to increase the short-term rate of microvascular thrombosis. L-arginine, an NO precursor, does not appear to produce the opposite effect. Further studies using local NO donors and antagonists as well as more potent NO precursors are needed to further evaluate NO's role in microvascular thrombosis. The results of this study may have applications to human microvascular surgery.

Protein nitration in cutaneous inflammation in the rat: essential role of inducible nitric oxide synthase and polymorphonuclear leukocytes

1: We have examined the relationship between neutrophil accumulation, NO(*) production and nitrated protein levels in zymosan-mediated inflammation in rat skin in vivo. 2: Rats were anaesthetized and cutaneous inflammation was induced by zymosan (injected intradermally, i.d.). Experiments were carried out up to 48 h, in recovery procedures as appropriate. Assays for neutrophil accumulation (measurement of myeloperoxidase), nitric oxide (assessment of NO(2)(-)/NO(3)(-)) and nitrated proteins (detected by ELISA and Western blot) were performed in skin extracts. 3: The results demonstrate a close temporal relationship between these parameters. Samples were assayed at 1, 4, 8, 24 and 48 h after i.d. injection of zymosan. The highest levels measured of each parameter (P<0.001 compared with vehicle) were found at 4-8 h, with a reduction towards basal levels by 24 h. 4: Selective depletion of circulating neutrophils with anti-neutrophil antibody abolished neutrophil accumulation and protein nitration. In addition substantially decreased NO levels were found. 5: A selective inducible nitric oxide synthase (iNOS) inhibitor, N-3-aminomethyl-benzyl-acetamidine-dihydrochloride (1400W) also significantly reduced neutrophil levels and NO production and substantially inhibited protein nitration. 6: We conclude that the neutrophil leukocyte plays an essential role in the formation of iNOS-derived NO and nitrated proteins in inflammation, in a time-dependent and reversible manner. The NO-derived iNOS also has a role in stimulating further neutrophil accumulation into skin. This suggests a close mechanistic coupling between neutrophils, NO production and protein nitration.

Presence and activity of nitric oxide synthase isoforms in ischemia-reperfusion-injured flaps

Nitric oxide is produced from the amino acid L-arginine by nitric oxide synthase, which has three known isoforms: (1) endothelial nitric oxide synthase and (2) brain nitric oxide synthase, both of which are constitutive nitric oxide synthase; and (3) inducible nitric oxide synthase. The authors' hypothesis is that after reperfusion injury, endothelial cell dysfunction leads to disruption of nitric oxide synthase-mediated nitric oxide production and that this may in part explain the deleterious effects of ischemia-reperfusion injury on tissue survival and blood reflow in flaps. An experiment was designed to study the effects of ischemia-reperfusion injury on the bioactivity of all three isoforms of nitric oxide synthase. Buttock skin flaps and latissimus dorsi myocutaneous flaps were elevated in eight pigs. Flaps on one side of the animal were randomized to receive 6 hours of arterial ischemia, whereas flaps on the other side served as controls. At 6 hours of ischemia and at 1, 4, and 18 hours after reflow, tissue biopsy specimens were obtained and were processed for both constitutive nitric oxide synthase and inducible nitric oxide synthase enzyme activity on the basis of the L-citrulline assay. In addition, specimens were processed for Western blot analysis of the three isoforms. The authors' results revealed three key findings: first, there was a statistically significant (p < 0.001) decrease in constitutive nitric oxide synthase activity of ischemia-reperfusion-injured flaps as compared with controls in both skin and muscle for all time intervals measured. Second, Western blot analyses of endothelial nitric oxide synthase and brain nitric oxide synthase showed a significant decrease in the signal intensity in ischemic and reperfused tissue as compared with controls. Third, the inducible nitric oxide synthase isoform's activity and protein remained undetectable in both tissue types for all time points measured. The authors' data demonstrated that following ischemia-reperfusion injury in the pig flap model there was a disruption of constitutive nitric oxide synthase expression and activity, which may lead to decreased nitric oxide production. The significant decrease in nitric oxide synthase activity found in the current study may partly explain the mechanism of tissue damage in flaps subjected to ischemia-reperfusion injury. Knowledge of the kinetics of nitric oxide synthase activity under conditions of ischemia-reperfusion injury has important implications for the choice and timing of delivery of therapeutic agents whose goal is to increase the bioavailability of nitric oxide in reperfused tissue.

Tyrosine nitration: localisation, quantification, consequences for protein function and signal transduction

The nitration of free tyrosine or protein tyrosine residues generates 3-nitrotyrosine the detection of which has been utilised as a footprint for the in vivo formation of peroxynitrite and other reactive nitrogen species. The detection of 3-nitrotyrosine by analytical and immunological techniques has established that tyrosine nitration occurs under physiological conditions and levels increase in most disease states. This review provides an updated, comprehensive and detailed summary of the tissue, cellular and specific protein localisation of 3-nitrotyrosine and its quantification. The potential consequences of nitration to protein function and the pathogenesis of disease are also examined together with the possible effects of protein nitration on signal transduction pathways and on the metabolism of proteins.

Local heat-shock priming-induced improvement in microvascular perfusion in osteomyocutaneous flaps is mediated by heat-shock protein 32

BACKGROUND

Stress conditioning is thought to improve microvascular free flap survival but the mechanisms of protection are not clear. The aim of this study was to determine whether local induction of heat-shock protein (HSP) 32 improves microvascular perfusion in transferred osteomyocutaneous flaps.

METHODS

The hindlimb harvest region of osteomyocutaneous flaps in Wistar rats was subjected to stress conditioning by local heating (30 min, 42.5 degrees C) 24 h before microvascular flap transfer. In a second group of animals, after heat-shock priming, the action of HSP-32 was inhibited by tin protoporphyrin IX. Animals with unconditioned flaps served as controls. After transfer, the microcirculation of the muscle, cutaneous, subcutaneous and periosteal tissue of the flap was analysed quantitatively for 6 h using intravital fluorescence microscopy.

RESULTS

Immunohistochemistry revealed that HSP-32 was detectable only after priming and not in unconditioned flaps. Priming did not alter functional capillary density or capillary red blood cell velocity compared with that in unconditioned flaps. However, heat-shock priming induced significant capillary dilatation (P < 0.05) and thus a substantial increase in capillary blood flow volume (P < 0.05) in all tissues of the transferred flaps. Inhibition of HSP-32 by tin protoporphyrin IX completely abolished the priming-induced improvement in capillary perfusion, as indicated by the lack of increased capillary diameters and volumetric blood flow.

CONCLUSION

The present study demonstrated that stress conditioning by local heat-shock priming improves nutritive perfusion in osteomyocutaneous flaps by capillary dilatation, probably mediated through the vasoactive action of HSP-32.

Nitric oxide: a review for veterinary surgeons

Nitric oxide (NO) is an endogenous gas that serves as a biologic messenger in many physiologic processes including neurotransmission, blood-pressure control, the immune system's ability to kill tumor cells, and wound healing. NO is produced after oxidation of L-arginine by a family of nitric oxide synthase (NOS) enzymes. Two of the NOS enzymes are present continuously and are thereby termed constitutive NOS. One of the enzymes, inducible NOS, is not typically expressed in resting cells and is induced by various substances including endotoxin, some cytokines, and microbial products. Thus, NO often has paradoxical activities. When NO is over- or underproduced, it can result in potentiation of disease states with disastrous results. This review discusses the biochemistry of NO, its functions in normal and disease states, and therapy for modulating NO production in disease states.