Modulation of the inflammatory response by increasing fetal wound size or interleukin-10 overexpression determines wound phenotype and scar formation

Wound size impacts the threshold between scarless regeneration and reparative healing in the fetus with increased inflammation showed in fetal scar formation. We hypothesized that increased fetal wound size increases pro-inflammatory and fibrotic genes with resultant inflammation and fibroplasia and that transition to scar formation could be reversed by overexpression of interleukin-10 (IL-10). To test this hypothesis, 2-mm and 8-mm dermal wounds were created in mid-gestation fetal sheep. A subset of 8-mm wounds were injected with a lentiviral vector containing the IL-10 transgene (n = 4) or vehicle (n = 4). Wounds were harvested at 3 or 30 days for histology, immunohistochemistry, analysis of gene expression by microarray, and validation with real-time polymerase chain reaction. In contrast to the scarless 2-mm wounds, 8-mm wounds showed scar formation with a differential gene expression profile, increased inflammatory cytokines, decreased CD45+ cells, and subsequent inflammation. Lentiviral-mediated overexpression of the IL-10 gene resulted in conversion to a regenerative phenotype with decreased inflammatory cytokines and regeneration of dermal architecture. In conclusion, increased fetal wounds size leads to a unique gene expression profile that promotes inflammation and leads to scar formation and furthermore, these results show the significance of attenuated inflammation and IL-10 in the transition from fibroplasia to fetal regenerative healing.

Mammalian cardiac regeneration after fetal myocardial infarction requires cardiac progenitor cell recruitment

BACKGROUND

In contrast to the adult, fetal sheep consistently regenerate functional myocardium after myocardial infarction. We hypothesize that this regeneration is due to the recruitment of cardiac progenitor cells to the infarct by stromal-derived factor-1α (SDF-1α) and that its competitive inhibition will block the regenerative fetal response.

METHODS

A 20% apical infarct was created in adult and fetal sheep by selective permanent coronary artery ligation. Lentiviral overexpression of mutant SDF-1α competitively inhibited SDF-1α in fetal infarcts. Echocardiography was performed to assess left ventricular function and infarct size. Cardiac progenitor cell recruitment and proliferation was assessed in fetal infarcts at 1 month by immunohistochemistry for nkx2.5 and 5-bromo-2-deoxyuridine.

RESULTS

Competitive inhibition of SDF-1α converted the regenerative fetal response into a reparative response, similar to the adult. SDF-inhibited fetal infarcts demonstrated significant infarct expansion by echocardiography (p < 0.001) and a significant decrease in the number of nkx2.5+ cells repopulating the infarct (p < 0.001).

CONCLUSIONS

The fetal regenerative response to myocardial infarction requires the recruitment of cardiac progenitor cells and is dependent on SDF1α. This novel model of mammalian cardiac regeneration after myocardial infarction provides a powerful tool to better understand cardiac progenitor cell biology and to develop strategies to cardiac regeneration in the adult.

Sex differences in the pressor response to angiotensin II when the endogenous renin-angiotensin system is blocked

The present study determined whether there are sex differences in the pressor response to angiotensin II (Ang II) when the endogenous renin-angiotensin system (RAS) is blocked by enalapril (ACEI), and whether this pressor response is changed in the presence of high salt (HS). Telemetry BP was measured in rats treated with ACEI (250 mg/L drinking water) (n=6 to 7/grp), or with ACEI and Ang II (150 ng/kg/min, sc; n=5 to 6/grp), for 3 wk. For the last 2 wk of the study, rats received HS (4% NaCl). MAP was lower in females during baseline (100.8+/-1.1 versus 105.2+/-1.3; P<0.05), and with ACEI the last 3 days on normal salt diet (78.8+/-1.2 versus 88.5+/-0.9; P<0.05), but increased to higher levels than in males on day 6 of Ang II (129.0+/-2.2 versus 117.3+/-2.9; P<0.05). One week of Ang II increased albuminuria in males, but not females, and urinary 8-iso-PGF2alpha (F2-isoP) was not increased in either males or females. MAP was salt-sensitive in both sexes receiving ACEI, but was only salt-sensitive in males with Ang II (129.3+/-3.7 versus 145.1+/-5.7; P<0.05). Albuminuria continued to increase with HS and Ang II in males, but not in females. F2-isoP excretion increased with MAP during the last week of HS and Ang II in males but was independent of MAP in females. With ACEI, MAP in females on normal salt is more responsive to Ang II but is independent of oxidative stress or renal injury. MAP in males is salt-sensitive with Ang II, which may be mediated by oxidative stress and renal injury.

Evaluation of fructose 1,6 diphosphate for salvage of ischemic gracilis flaps in rats

Fructose 1, 6 diphosphate (FDP), a metabolic intermediate, provides an alternative mechanism to circumvent the rate-limiting step in the Kreb's cycle. This agent has been observed to prevent the effects of ischemia on heart tissue and kidney function and the effects of endotoxic shock. It has been shown conclusively to minimize the adverse effects of ischemia-reperfusion injury in experimental pedicled skin flaps in animals. The present study was done to evaluate the effect of intra-arterial administration of FDP on salvage of ischemic microvascular transfer of gracilis muscle flaps in rats, with the premise that it might prolong the ischemia time of muscle flaps at room temperature, thus increasing chances of flap survival. Irrigation with FDP did not change the quantitative survival of the flaps, but there was qualitative improvement on histologic evaluation and DNA analysis. Decreased inflammatory damage and DNA fragmentation were seen at the 2.5-hr period. Histologic staining for mitochondrial oxygenation in gracilis muscle also showed increased uptake in the FDP-treated group vs. control at the 2.5-hr ischemia period. Further experiments with different modes of FDP administration should be carried out to identify more effective means of amelioration of flap ischemia.

Effect of vascular endothelial growth factor on rat Achilles tendon healing

This study evaluated the effect of exogenous vascular endothelial growth factor (VEGF) on tendon healing and regulation of other growth factors in a rat Achilles tendon model. Fifty Sprague-Dawley rats were used. In the experimental group, the left Achilles tendon was transected and repaired with the modified Kessler suture technique, and the right Achilles tendon was transected and repaired with resection of plantaris tendon. VEGF, 100 mul (50 mug/ml), was injected into each tendon at the repair site. The same surgical procedures were performed in the control group, with the same volume of saline injected into the repair sites. At intervals of 1, 2, and 4 weeks, the animals were killed and the tendons were harvested and evaluated for tensile strength (1, 2, and 4 weeks) and gene expression (postoperative day 4). At 1 week postoperatively, when plantaris tendon was preserved, the tensile strength of the repaired tendons with VEGF treatment (3.63 +/- 0.62 MPa) was significantly higher than the tensile strength of the repaired tendons with saline treatment (2.20 +/- 0.36 MPa). There was no difference in tensile strength between the two groups without the plantaris tendon support. At 2 weeks postoperatively, the tensile strength was 11.34 +/- 3.89 MPa in the group with VEGF treatment and plantaris tendon preservation, which was significantly higher than the tensile strength in the other groups. There was no significant difference in tensile strength among the groups at 4 weeks postoperatively. The gene expression showed that transforming growth factor-beta in the VEGF-treated tendon was up-regulated in the early stage of tendon healing, whereas expression of platelet-derived growth factor, basic fibroblast growth factor, and insulin-like growth factor-1 was not significantly different among the groups. In conclusion, administration of exogenous VEGF can significantly improve tensile strength early in the course of the rat Achilles tendon healing and was associated with increased expression of transforming growth factor-beta.

Effect of Sodium Diphenylhydantoin on Skin Wound Healing in Rats

This study evaluated the effect of phenytoin (sodium diphenylhydantoin) on skin wound healing in a rat model. The study was divided into two parts. In part I, 20 mul of phenytoin (10 mg/ml) was subcutaneously injected into the 3-cm dorsal full-thickness incisional wounds of 14 rats on postoperative days 0, 3, and 6. Twelve rats that received saline injections were used as the controls. The skin samples were harvested and tested for tensile strength and histology. An additional 12 rats with the same incisional wounds were tested for chemokine gene expressions. In part II, 20 mul of phenytoin (10 mg/ml) was applied topically once a day on a 4 x 4 cm area of the open dorsal wounds of 10 rats. Saline was applied to the wounds of the 10 control group rats. The wounds were measured weekly. The results showed that the average tensile strength of the phenytoin-treated wound was 0.49 +/- 0.08 MPa compared with the control group at 0.02 +/- 0.01 MPa (p < 0.05). The density ratio of chemokine monocyte chemotactic protein (MCP-1) to beta-actin in the phenytoin-treated group was also significantly higher than in the control group (p < 0.05). Histologic analysis of the phenytoin group showed a large amount of fibroblast proliferation, collagen synthesis, and neovascularization. Phenytoin-treated wounds were also smaller at 1 to 6 weeks postoperatively than the control group wounds. The authors conclude that the administration of phenytoin can promote wound healing and significantly increase MCP-1 expression. Phenytoin-treated wounds showed significant increase in collagen deposition and neovascularization, which resulted in an increased wound tensile strength and accelerated healing of both open and closed wounds.

Small intestinal submucosa in abdominal wall repair after TRAM flap harvesting in a rat model

The strength of porcine small intestinal submucosa in abdominal wall repair after transverse rectus abdominis myocutaneous flap harvesting was examined in a rat model. Changes in the levels of selected molecular markers of inflammation after small intestinal submucosa implantation were also studied. Eighty-three rats were divided into three groups. In experimental group I, an abdominal wall defect created by removal of the rectus abdominis muscle was repaired with placement of a 1.5 x 5-cm2 patch of small intestinal submucosa. In experimental group II, the muscle defect was repaired with a combination of small intestinal submucosa patch placement and fascial closure. In the control group, the defect was repaired with direct fascial closure. At postoperative times of 3 days, 2 weeks, 1 month, and 2 months, the muscle tissues adjacent to the abdominal wall repair site were subjected to biopsies for assessment of inflammation markers. Full-thickness sections of the abdominal wall from the repair site in each animal were removed for tensile strength testing and histological examinations. The results demonstrated that interleukin-6 and interferon-gamma levels were increased in the two experimental, small intestinal submucosa-treated groups at 3 days and 2 weeks postoperatively. The results of mechanical testing demonstrated that the average tensile strength of the repaired abdominal wall in the repair model with combined small intestinal submucosa placement and fascial repair was significantly greater than the values for repairs with fascial closure or small intestinal submucosa placement alone. The use of small intestinal submucosa placement in combination with fascial repair can significantly improve the strength of the repaired abdominal wall after transverse rectus abdominis myocutaneous flap harvesting.

Role of free radicals in necrosis of skin graft compromised with hematoma

It has been observed previously that a hematoma affects skin flap survival adversely through free radical action. The current study was undertaken to determine whether similar mechanisms are operative in skin grafts. The experiment was divided into two parts. During part I, 2 x 2 cm2 split-thickness skin grafts (STSGs) were harvested from 18 Fischer rats and were divided randomly into three groups (each consisted of six grafts), and incubated with plasma, blood, and blood plus 70 mg deferoxamine for 48 hours respectively. Tissue samples were assayed for lipoperoxidation (malondialdehyde [MDA]), superoxide dismutase (SOD), and nitric oxide synthase (NOS). During part II, 36 STSGs were harvested and were divided randomly into three groups. The grafts were incubated as in part I for 48 hours. The STSGs were then affixed to the same dimension recipient beds created on the back of 36 inbred rats. Survival was evaluated 7 days postoperatively. The results showed that there was no significant difference in MDA and NOS levels between each incubated graft group in part I. Only the SOD level in both grafts incubated with plasma and blood plus deferoxamine were significantly higher than the grafts over blood alone (p < 0.05). During part II, there was no significant difference of the average STSG survival percentage between the groups incubated with blood and blood plus deferoxamine (35.8 +/- 6.5% and 52.0 +/- 9.5%). The survival percentage of the group incubated with plasma was 81.8 +/- 7.3%, which was significantly higher than the other two groups (p < 0.01). The authors concluded that unlike a distal flap model, the pathological importance of free radicals in survival of the STSG over a hematoma is insignificant. A more likely hypothesis, as suggested by others, is that a hematoma serves as a barrier preventing angiogenesis.

Accelerating flap maturation by vascular endothelium growth factorin a rat tube flap model

The effect of exogenous vascular endothelium growth factor (VEGF) on the survival of the distal skin paddle with early pedicle division was studied in a rat tubed pedicle flap model. In part I, tubed pedicle skin flaps were created on the backs of 14 rats. The pedicle was divided after an interval of 3, 4, 5 or 7 days, and the survival area of each distal skin paddle was measured 5 days after the pedicle was divided. The percentages of survival were 0, 24.9%, 89.9% and 100%, respectively. In part II, tube flaps were created in 20 rats. In the experimental group, 2 ml of VEGF (50 microg ml(-1)) was injected into the recipient bed during tube flap creation in each rat. In the control group, 2 ml of saline was given. The tubed pedicle was divided 4 days after creation. The mean survival area of the distal skin paddle in the group treated with VEGF was 7.32 +/- 1.36 cm(2) (80.91%) at 5 days after pedicle division, which was of statistical significance when compared with the survival in the control group of 2.70 +/- 1.89 cm(2) (27.9%). The histology showed angiogenesis at the skin paddle-recipient bed interface following VEGF injection. These results demonstrate that the subcutaneous administration of VEGF into the recipient bed of the tube flap transfer can induce angiogenes is at the junction between the donor and the recipient bed, and improve skin paddle survival with early pedicle division.

Influence of recipient-bed isolation on survival rates of skin-flap transfer in rats

The effect of recipient-bed isolation with artificial barriers on skin-flap survival, compared to flap transfer without bed isolation, was evaluated in a modified rat epigastric skin-flap model. The pattern of blood flow in the raised flap with a proximal axial portion and distal random portion was confirmed by laser Doppler flowmetry. Forty rats were divided into four groups. Three of the groups had one of three different artificial barriers-silicone, polypropylene, or gelatin sponge. In each of these three groups, one of the artificial barriers was placed between the flap and its recipient bed after flap replacement. The flaps without bed isolation (Group 4) were used as controls. The survival area was measured 7 days postoperatively. Results demonstrated that necrosis in the groups with silicone and polypropylene barriers was significantly higher than in the controls. Histologically, neovascularization was shown in the flaps without artificial barriers. Foreign-body reactions were observed in the flaps with bed isolation and among these, severe inflammation and congestion were seen in the flaps with polypropylene isolation. In this study, the authors demonstrated that the random portion of a rat skin flap could survive partially through imbibition of plasma and the ingrowth of new vessels from the recipient bed. This neovascularization can be prevented by recipient-bed isolation with an artificial barrier. Bed isolation with a silicone sheet is suggested for use in the study of rat skin-flap survival.

Vascular grafts in the rat model: an anatomic study

Vascular grafts in animal models have been used extensively in the microsurgical laboratory, and the rat offers an excellent source of graft to meet these needs. In this study, we compiled a list of vessels that were previously identified in experimental literature for use as vascular grafts in the rat model. We then dissected and measured both arterial and venous grafts taken from these sites in 12 adult rats. The surgical procedure for approaching each vascular graft was recorded. The diameter and harvestable length, the start and end points, and the number of branches of the graft were tabulated. We believe that these data will provide valuable insight applicable to the use of the rat vascular graft in microsurgical research and training.

Reconstruction of ureteral defects with microvascular vein grafts in a rat model

This study was undertaken to test the performance of an autologous vein graft as a ureteral replacement in the rat model. Twenty-six rats were divided into three groups. In Group 1 (n = 10), the animals had a 3-mm segment of the ipsilateral ureter excised and the ureteral defect repaired, using a superficial epigastric vein graft. In Group 2 (n = 10), the same ureteral defect was created and again repaired, using a superficial epigastric vein graft, with the addition of a Silastic stent. The control, Group 3 (n = 6), had the ureter transected and repaired solely by means of primary anastomosis. Animals from each group underwent urography and were sacrificed for histology at three different postoperative intervals: 1, 4, and 12 weeks. Postoperative urography results showed normal renal function in the animals with ureteral reconstruction using vein grafting aided by a stent, as well as in those with primary ureteral anastomosis. No renal function return was seen in the animals with ureteral reconstruction by vein grafting alone, without stent support. Histologically, a progressive loss of the vascular endothelium, and replacement with the urothelium typical of the ureter, was seen in the stented vein grafts. Severe ureteral obstruction at the proximal site of the graft and hydronephrosis were seen in the vein-graft group without stenting. This study demonstrates that autologous vein grafts can be used successfully to correct a ureteral deficit, contingent on accurate microsurgical technique and immediate stenting.

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

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

Role of medical students in microsurgery research

Microsurgery is an integral element in many surgical specialties, as well as an important technique for surgical research. Student participation in microsurgery research programs can be a source for both high quality training in skills and for research contributions. In this article, the authors review their experience in developing general principles for setting up medical student microsurgery research programs, and analyze the research output and career choices made by the students who have participated.