The effect of L-Arginine therapy on achilles tendon healing: A histological and biomechanical investigation in an animal model.

PURPOSE: Several clinical and experimental studies have revealed that L-Arginine, which has antioxidant properties, accelerates tissue healing. This study examined the in vivo effects of oral L - Arginine supplementation on tendon regeneration in Wistar rats. METHOD: For each weighting of an average of 250-300 g, 24 Wistar rats were separated into three equal groups. Each rat's right hind leg Achilles tendons were tenotomized and then repaired. The first group (Control) was followed up with a regimen of standard food and water. In the second group (L-Arg Low Dose), 300 mg/kg, and in the third group (L-Arg High Dose), 600 mg/kg L-Arginine was administered in water daily with a regimen of standard food and water ad libitum. After eight weeks, the rats were sacrificed, and the tendons were histologically and biomechanically analyzed. RESULTS: Tendon peak strength values of the L-Arg Low Dose and L-Arg High Dose groups were similar but significantly higher than the control group. A statistically significant difference was observed between the groups in terms of ground substance, fiber arrangement, cellularity, hyalinization, and GAG properties ( p = 0.05, p = 0.002, p = 0.016, p = 0.027, p = 0.05). There was no statistically significant difference between the groups according to the histological examination of collagen properties, fiber structure, tenocyte properties, rounding of the nuclei, and collagen stainability. (p = 0.999, p = 0.061, p = 0.195, p = 0.195, p = 0.130). No mortality, wound complications, or re-ruptures were observed. CONCLUSION: Compared with the control group, histologically and biomechanically distinct therapeutic effects of L-Arginine supplementation on tendon healing were determined. LEVEL OF CLINICAL EVIDENCE: 5.

Clinical, Histopathological and Immunohistochemical Aspects of Digital Papillary Adenocarcinoma: A Case Report and Literature Review.

Digital papillary adenocarcinoma (DPA) is a rare malignant eccrine tumor. A 62-year-old female presented with a subcutaneous nodular 1.5cm-mass in the thumb. Macroscopically, a poorly circumscribed mass containing cystic and solid components was observed. Microscopically, epithelial neoplasm consisting of tubular-cystic structures with back-to-back arrangements was observed. The lining epithelium was composed of cuboidal/columnar cells with mild atypia, with micropapillary extensions. Immunohistochemistry revealed double-layered neoplastic epithelium containing two different types of cells: basaloid/myoepithelial and luminal. We recommend two out of vimentin, HMWCK, and D2-40 for myoepithelial/basaloid cells, also CK7 and EMA for luminal/columnar cells. As the tumor had infiltrated the surgical margins, the patient underwent axillary sentinel lymph node (SLN) dissection and re-excision with Mohs micrographic surgery (MMS). Two additional MMS stages were required due to suspicious surgical margin positivity in the frozen sections. The operation was continued despite the risk of loss of function. Upon examination of the permanent sections, we observed no tumors in the suspected positive foci. Additionally, no tumor was found in the surgical margins. No metastasis was detected in the sentinel lymph node. We have reached 300 reported cases of DPA in the literature. We discussed the histopathological and intraoperative diagnostic pitfalls of DPA with a literature review and our experience.

A unique case of isolated thoracic spinal Rosai-Dorfman disease related to IgG4.

Rosai-Dorfman disease (RDD) is a rare benign histiocytosis usually characterized by massive cervical lymphadenopathy and systemic manifestations. Extranodal, especially spinal involvement, is extremely rare. Our case was deemed worthy of presentation because it was the first reported isolated case of spinal RDD related to IgG4 and mimicked meningioma clinically and radiologically. A case with an intradural extramedullary mass causing neurological compression findings in the thoracic spinal region and radiologically mimicking meningioma is presented. In the histomorphological examination of the resection material, polymorphonuclear leukocytes in the dura, histiocytes showing emperipolesis, an increase in collagenized fibrous connective tissue, and intense lymphoplasmacytic cell infiltration accompanied by obliterative phlebitis were observed. Immunohistochemically, the histiocytic cells were found to be S-100 protein, CD68, and CD163 positive and CD1a and langerin negative, and more than half of the plasma cells were immunoglobulin-G4 (IgG4) positive. Although rare, RDD or IgG4-related meningeal disease should be considered in the differential diagnosis of dural-based spinal masses that radiologically suggest meningioma. The pathologist should be aware that these two histopathological entities may coexist. To our knowledge, this is the first case of "isolated spinal RDD related to IgG4" reported in the literature.

New-onset cutaneous nodule arising from hypertrichotic brownish patch in a 6-year-old girl.

A 6-year-old girl presented with an enlarging asymptomatic nodule within a hyperpigmented hypertrichotic patch on her left thigh. Histopathological examination revealed tumour cells with round to fusiform nuclei in a fine fibrillary collagenous stroma, along with increased cellularity. Most of the tumour cells were positive for S-100 and negative for HMB-45 and Melan-A.

The Effect of Adipose Derived Stromal Vascular Fraction on Flap Viability in Experimental Diabetes Mellitus and Chronic Renal Disease.

BACKGROUND: The presence of chronic renal disease(CRD) concurrently with diabetes mellitus(DM) increases the flap failure. Adipose derived stromal vascular fraction (SVF) is known to enhance skin flap viability in both healthy and diabetic individuals. The aim of this experimental study was to investigate the effect of SVF on skin flap viability in rats with DM and CRD. METHODS: 48 Sprague-Dawley rats were separated into four groups as follows: group I (control), group II (diabetes mellitus), group III (chronic renal disease), and group IV (diabetes with chronic renal disease).Two dorsal flaps were elevated. Flaps on left side of all groups received 0.5 cc of SVF, while same amount of plasma-buffered saline (PBS) was injected into right side. On postoperative day 7, flaps were harvested for macroscopic, histopathologic and biochemical assessments. Areas of flap survival were measured macroscopically. Blood level of vascular endothelial growth factor (VEGF) was measured after injection of SVF. RESULTS: Macroscopically, SVF has significantly improved flap viability (p < 0.05). Flap viability percentage was lower in DM and CRD groups when compared with healthy control group. In respect of new capillary formation, there was a statistically significant difference between SVF injected flaps and PBS injected sides (p < 0.05). Similarly, VEGF levels were higher in all study groups and there was a significant difference in comparison to control group (p < 0.05). CONCLUSIONS: The study showed that injection of SVF increased flap viability via endothelial differentiation and neovascularization. In vivo function of stem cells might be impaired due to uremia and diabetes-related microenviromental changes.

Aneurysmal Bone Cyst in a Renal Transplant Patient.

Aneurysmal bone cysts constitute 1% to 2% of all primary bone tumors.They are rapidly growing benign bone tumors. Nearly 80% of aneurysmal bone cysts occur in the first 20 years of life, and most are primary tumors. Aneurysmal bone cysts are mostly benign, locally aggressive, and highly vascularized tumors. Generally, the period required for postoperative recovery and new bone formation is long. The relapse rate can be up to 50%. Although computed tomography and magnetic resonance imaging scans are the preferred diagnostic methods, biopsy is the most necessary prerequisite to confirm diagnosis, as aspects of these cysts can show similarity to many other bone lesions. Correct histopathologic diagnosis is important since malignancies may be seen in transplant recipients.

The promising effects of BMP2 transfected mesenchymal stem cells on human osteosarcoma.

Selective targeting of transfected mesenchymal stem cells (MSCs) carrying specific antioncogenes to the tumor was suggested as a treatment option. Bone morphogenetic protein-2 (BMP2) was shown to inhibit the proliferation and aggressiveness of osteosarcoma (OS) cells. Here, we aimed to assess the homing efficiency of intraperitoneally administered hMSCs transfected with BMP2 to the tumoral site and their effects on OS using an orthotopic xenograft murine model. Orthotopic xenograft murine model of OS in six-week-old female NOD/SCID mice using 143B cells was established. hMSCs transfected with BMP2 (BMP2+hMSC) were used. In vivo experiments performed on four groups of mice that received no treatment, or intraperitoneally administered BMP2, hMSCs, and BMP2+hMSCs. Histopathological and immunohistochemical studies were used to evaluate the pathological identification and to assess the dimensions and necrotic foci of the tumor, the features of lung metastases, and immunostaining against p27, Ki-67, and caspase-3 antibodies. The osteogenic differentiation markers BMP2, BMP4, COL1A1, OPN, OCN and PF4 evaluated using RT-PCR. The tumor dimensions in the hMSCs group were significantly higher than those of the remaining groups (p < 0.01). The number of metastatic foci in the BMP2+hMSCs group was significantly lower than those of the other groups (p < 0.01). The current results showed that the intraperitoneal route could be efficiently used for targeting hMSCs to the tumoral tissues for effective BMP2 delivery. In this study, the effects of BMP2 transfected hMSCs on human OS and metastasis were promising for achieving osteogenic differentiation and reduced metastatic process.

The Effects of Adipose Derived Stromal Vascular Fraction and Platelet-Rich Plasma on Bone Healing of a Rat Model With Chronic Kidney Disease.

BACKGROUND: Chronic kidney disease (CKD) impairs osteoblast/osteoclast balance and damages bone structure with diminished mineralization and results in bone restoration disorders. In this study, we investigate the effects of adipose-derived stromal vascular fraction and platelet-rich plasma (PRP) on bone healing model in rats with CKD. METHODS: Sprague-Dawley rats were separated into 4 groups. All groups except group I (healthy control) had CKD surgery using 5/6 nephrectomy model. All groups had intramedullary pin fixation after receiving bone fracture using drilling tools. Group II rats were used as control group for CKD. Group III rats received PRP treatment on fracture site. Group IV rats received PRP and stromal vascular fraction treatment on fracture site.Weight loss and blood samples were followed at the time of kidney surgery, third, sixth, and 12th weeks. Bone healing and callus formations were compared, biomechanically, radiologically, histopathologically, and immunohistochemically. Osteoblastic transformation of stem cells was assessed with DiI staining. RESULTS: Negative effects of CKD on bone healing were reduced by increasing mechanical, histological, radiological, and biochemical properties of the bone with stromal vascular fraction and PRP treatments. Although thickness of callus tissue delayed bone healing process, it also enhanced biomechanical features and bone tissue organization. CONCLUSIONS: Platelet-rich plasma and adipose-derived stromal vascular fraction treatments were effective for bone healing in animal model, which can be promising for clinical trials.

Platelet-rich plasma decreases fibroblastic activity and woven bone formation with no significant immunohistochemical effect on long-bone healing: An experimental animal study with radiological outcomes.

PURPOSE: This study aimed to analyze the immunohistochemical effect of platelet-rich plasma (PRP) on healing of long-bone fractures in terms of bone morphogenetic protein-2 (BMP-2), vascular endothelial growth factor (VEGF), the Ki-67 proliferation index, and radiological and histological analyses. METHODS: Sixteen adult rabbits, whose right femoral diaphysis was fractured and fixed with Kirschner wires, were randomly divided into two groups, control and PRP (groups A and B, respectively). PRP was given to group B at 1 week postoperatively, and all animals were euthanized after 12 weeks. Radiographic evaluations were performed periodically. Cortical callus formation, chondroid and woven bone area percentages, osteoblastic and fibroblastic activities, and mature bone formation were examined. The depths of BMP-2 and VEGF staining were measured. The Ki-67 proliferation index was also calculated. RESULTS: The mean radiological union score of group B was significantly higher than that of group A. There were also statistically significant differences between groups A and B in terms of cortical callus formation, woven bone area percentage, fibroblast proliferation, and mature bone formation. Group B had significantly more cortical callus and mature bone formation with less woven bone and fibroblast proliferation. Immunohistochemical analysis revealed no statistically significant difference between the groups in terms of BMP-2 and VEGF staining and the Ki-67 index. CONCLUSIONS: PRP had no effect on BMP-2 or VEGF levels with no increase in the Ki-67 proliferation index, although its application had a positive effect on bone healing by increasing callus and mature bone formation with decreased woven bone and fibroblast proliferation.

Vertebral Body Lipoma: An Unusual Pathology Treated With Kyphoplasty.

STUDY DESIGN: Case report. OBJECTIVE: This case report is unique since this is the first vertebral lipom case that was treated by kyphoplasty alone. SUMMARY OF BACKGROUND DATA: Vertebral lipoma is extremely rare and our search of the English literature has revealed 20 patients in 16 reports. METHODS: A 32-year-old female patient was admitted to our neurosurgery department with the chief complaint of low back pain that had lasted nearly 1 year. A lumbar MR suggested a hemangioma and the patient was operated on. RESULTS: On microscopic examination, the lesion was seen to have a widely infiltrating appearance of mature fat tissue between bone trabeculae diagnosis was intraosseous lipoma. CONCLUSION: We believe that the management should be surgical total removal of the lesion even in incidentally found cases in order to obtain histologic diagnosis and pain relief. LEVEL OF EVIDENCE: 5.

Recurrence of Primary Vascular Leiomyosarcoma Five Years after Initial Diagnosis in the Lower Extremity.

Primary leiomyosarcomas of vascular origin are rare tumors. They frequently arise within the inferior vena cava; however, the peripheral vein was also affected. To date, only a few hundred cases have been reported in the world literature. Although it is an extremely aggressive tumor, the symptoms may be unspecific, especially in the lower extremities. In this report, we present a case of primary vascular leiomyosarcoma, arising from the short saphenous vein, with symptoms mimicking thrombus in the initial diagnosis. The diagnosis of leiomyosarcomas was confirmed by standard H&E staining and immunohistochemical staining. Recurrence of the tumor has been observed five years after surgical treatment. Due to its rarity, experience in the management of this type of tumor is limited. The mainstay of treatment for these tumors is complete surgical resection. The purpose of the presented case is to discuss the clinicopathological features and management options of this tumor, under the light of the most recent literatures.

Traumatic Neuroma Causing Biliary Stricture After Orthotopic Liver Transplant, Treated With Hepaticojejunostomy: A Case Report.

Traumatic neuromas of the biliary tract have occasionally been reported to cause strictures at the cystic duct stump as a late complication of cholecystectomy with common bile duct exploration. The incidence of symptomatic traumatic biliary neuroma appears to be low after orthotopic liver transplant, as only 25 patients have been described previously in the English-language literature. Traumatic (amputation) neuroma is a reactive proliferation of pericholangial nerve fibers induced by injury, but it is not a true neoplasm. The diagnosis of traumatic neuroma is possible only by histopathologic examination; the diagnostic finding is a mass of hyperplastic nerve bundles. We report a patient with a traumatic neuroma causing an early biliary stricture with intrahepatic extension after an orthotopic liver transplant. The lesion failed to respond to repeated endoscopic stenting and eventually required hepaticojejunostomy. A biopsy of the liver graft, performed in the 13th month after transplant, showed chronic ductopenic rejection.

Metastatic Embryonal Conjunctival Rhabdomyosarcoma in a 4-Year-Old Boy.

The authors report the case of a 4-year-old boy who presented with unilateral ptosis and a mass lesion of palpebral conjunctiva of the left upper eyelid, that had been present for 2 weeks, and had rapidly enlarged. The lesion was salmon colored and was easily distinguished from the conjunctiva. There was no obvious orbital extension in the MRI studies. Excisional biopsy was performed through a conjunctival approach. The histopathology was consistent with embryonal rhabdomyosarcoma. Thoracoabdominal CT scans revealed nodules in both lungs, indicating stage 4 disease. The patient received chemotheraphy and intensity-modulated radiation therapy. Rhabdomyosarcoma confined to the conjunctiva and distant metastasis without orbital involvement is rare. It should be included in the differential diagnosis of any atypical conjunctival mass lesions in children, and histopathology is necessary to establish proper treatment. As the case indicates, detailed systemic evaluation and careful systemic follow up of these patients are mandatory.

Spindle cell carcinoma of the conjunctiva: A rare entity.

An 85-year-old male presented with painless bulging lesion over the cornea. Clinical history, diagnostic imaging studies, and histopathologic sections were evaluated. The patient clinically displayed an vascularized conjunctival lesion located at the superior bulbar conjunctiva with extension onto cornea covering 2/3 of his pupillary aperture superiorly. His visual acuity was counting fingers at 4 m. The patient underwent a total excision of the lesion including conjunctival and corneal parts. Histopathologic evaluation revealed spindle cell carcinoma which involves the whole conjunctival squamous epithelium with significant polarity loss, nuclear enlargement with hyperchromasia and pleomorphism, and mitotic activity. Diagnosis of spindle cell carcinoma is challenging because of overlapping histopathological features with other spindle cell tumors. The detailed pathologic examination is very important for the decision of proper treatment.

The effect of adipose stromal vascular fraction on transverse rectus abdominis musculocutaneous flap: an experimental study.

BACKGROUND: Transverse rectus abdominis musculocutaneous (TRAM) flap is one of the options in reconstruction after breast cancer surgery for breast reconstruction. Tissue necrosis often occurs in the third and fourth perfusion zones of the flap. A study was planned to find out the effects of adipose stromal vascular fraction (SVF) cells on viability of TRAM flap and the experimental model was designed to be applicable in clinical practice. METHODS: Right inferior epigastric artery pedicled, 5 × 2.5 cm sized TRAM flap was used as a flap model in 30 rats in three groups (group 1: sham; group 2: phosphate-buffered saline (PBS); group 3: SVF cell injected). The viability of the flaps were assessed on the postoperative 7th day with photographs and software for the calculations. RESULTS: The mean viable flap percentage to total flap area was recorded as 51.8% ± 11.19, 49.5% ± 10.30, 82.3% ± 9.56, in group 1, group 2, and group 3, respectively (p < 0.05). The mean capillary density was noted as 5.15 ± 0.56, 4.37 ± 0.58, and 12.40 ± 1.17 in groups 1, 2, and 3, respectively (p < 0.05). The fibrosis gradient indicated no difference between the groups (p > 0.05). The in-vivo differentiation of SVF cells to endothelial cells was noted. The blood VEGF levels showed a marked increase in the experimental group (p < 0.05). CONCLUSION: The adipose SVF cells were found out to improve the TRAM flap viability and decrease necrosis, especially in zone 3 and 4.

Brown Tumor of the Thoracic Spine: First Manifestation of Primary Hyperparathyroidism.

Brown tumors also called as osteoclastomas, are rare nonneoplastic lesions that arise in the setting of primary or secondary hyperparathyroidism. Parathyroid adenomas or hyperplasia constitute the major Brown tumor source in primary hyperparathyroidism while chronic renal failure is the leading cause in secondary hyperparathyroidism. Most of the patients with the diagnosis of primary hyperparathyroidism present with kidney stones or isolated hypercalcemia. However, nearly one third of patients are asymptomatic and hypercalcemia is found incidentally. Skeletal involvement such as generalized osteopenia, bone resorption, bone cysts and Brown tumors are seen on the late phase of hyperparathyroidism. The symptoms include axial pain, radiculopathy, myelopathy and myeloradiculopathy according to their locations. Plasmocytoma, lymphoma, giant cell tumors and metastates should be ruled out in the differential diagnosis of Brown tumors. Treatment of Brown tumors involve both the management of hyperparathyroidism and neural decompression. The authors report a very rare spinal Brown tumor case, arisen as the initial manifestation of primary hyperparathyroidism that leads to acute paraparesis.

Bone marrow involvement by lymphoproliferative disorders after solid-organ transplant.

OBJECTIVES: Posttransplant lymphoproliferative disorders are classified as monomorphic, polymorphic, early lesions, or Hodgkin lymphoma. Bone marrow staging examination is recommended in posttransplant lymphoproliferative disorder patients. However, information about bone marrow involvement in these disorders is scarce. We evaluated 19 transplant patients with posttransplant lymphoproliferative disorder to investigate incidence of bone marrow involvement, associated morphologic changes, and prognosis. MATERIALS AND METHODS: We retrospectively assessed bone marrow findings of 19 transplant patients with posttransplant lymphoproliferative disorder who underwent bone marrow staging at Baskent University from 1985 to 2013. Clinical and pathologic data were reviewed from the medical records. Follow-up information was obtained from medical records or communication with patients or families. Data collected including age, sex, Epstein-Barr virus status, immunosuppressive therapy, elapsed time from transplant to diagnosis of posttransplant lymphoproliferative disorder, B symptoms, number of extranodal sites, involvement of different organs, Ann Arbor clinical staging, hematologic parameters, and serum lactate dehydrogenase levels. RESULTS: There were 5 of 19 patients (26.3%) who had bone marrow involvement with posttransplant lymphoproliferative disorder, including 2 patients diagnosed with posttransplant lymphoproliferative disorder by lymph node biopsy and 1 patient each diagnosed by native liver biopsy, nasopharyngeal biopsy, or allograft liver biopsy. In 4 patients, there was monomorphic posttransplant lymphoproliferative disorder subtype and 1 patient had early lesion posttransplant lymphoproliferative disorder subtype. In 10 of 19 patients (52.6%), Epstein-Barr virus was detected with in situ hybridization, including 3 patients with bone marrow involvement who were diagnosed with Burkitt lymphoma (n = 1), diffuse large B-cell lymphoma (n = 1), or early lesion (n = 1). CONCLUSIONS: Patients with posttransplant lymphoproliferative disorder have high incidence of bone marrow involvement and high mortality rates. Therefore, bone marrow examination may be important in the diagnosis and staging evaluation of posttransplant lymphoproliferative disorder.

A single-center retrospective clinicopathologic study of endomyocardial biopsies after heart transplant at Baskent University Hospital in Ankara, 1993-2014.

OBJECTIVES: The purpose of this study was to investigate the frequency and prognostic importance of acute cellular rejection after heart transplant. MATERIALS AND METHODS: All 84 heart transplant patients at our center from January 1993 to January 2014, including all 576 endomyocardial biopsies, were evaluated with retrospective review of clinical records and endomyocardial biopsies. Routine and clinically indicated endomyocardial biopsies after heart transplant were graded for acute cellular rejection (2005 International Society for Heart and Lung Transplantation Working Formulation). Survival analysis was performed using Kaplan-Meier method. RESULTS: There were 61 male (73%) and 23 female recipients. Median age at heart transplant was 29 years (range, 1-62 y). Posttransplant early mortality rate was 17.9% (15 patients). In the other 69 patients, 23 patients died and 46 patients (66.7%) were alive at mean 69.3 ± 7.2 months after heart transplant. Mean follow-up was 35.4 ± 29.8 months (range, 0.07-117.5 mo). Mean 8.4 ± 4.2 endomyocardial biopsies (range, 1-19 biopsies) were performed per patient. Median first biopsy time was 7 days (range, 1-78 d). The frequency of posttransplant acute cellular rejection was 63.8% (44 of 69 patients) by histopathology; 86% patients experienced the first episode of acute cellular rejection within 6 months after transplant. There were 18 patients with acute cellular rejection ≥ grade 2R on ≥ 1 endomyocardial biopsy in 44 patients with acute cellular rejection. No significant difference was observed between survival rates of patients with grade 1R or ≥ grade 2R acute cellular rejection, or between survival rates of patients with or without diagnosis of any grade of acute cellular rejection. Acute cellular rejection was not related to any prognostic risk factor. CONCLUSIONS: Acute cellular rejection had no negative effect on heart recipient long-term survival, but it was a frequent complication after heart transplant, especially within the first 6 months.

The Notch pathway is a critical regulator of angiogenesis in a skin model of ischemia.

The Notch pathway is definitely required for normal vascular development. Although the contribution of Notch in postnatal angiogenesis is the focus of intense investigation, the implication of Notch in reparative neovascularization in the skin remains unexplored. In this study, we investigated Notch changes using a skin model of ischemia. Thirty Sprague-Dawley rats were divided into two groups. In the surgery group (n = 24), a caudally based dorsal skin flap was raised and sutured back into its initial position. In the control group, no surgical procedure was performed. Tissue biopsies were obtained at different time intervals. Tissue specimens were assessed for Delta-like ligand 4 (DLL4) and vascular endothelial growth factor (VEGF) gene expression by real-time polymerase chain reaction (PCR). Immunohistochemical staining was used for detection of DLL4 in tissue materials. Quantitative assessment of skin flap microvasculature was made. Compared with normoperfused tissue, VEGF and DLL4 expressions increased significantly (p < 0.01). Immunohistochemical analysis revealed weak and patchy expression of DLL4 in microvascular endothelial cells of normoperfused tissues. Conversely, DLL4 expression was upregulated in capillary endothelial cells after ischemia. In conclusion, in this study we have shown that the Notch ligand DLL4 is upregulated in skin tissue after ischemia. A deeper understanding of these fundamental principles will aid in the development of new avenues for the treatment of blood vessel-related skin pathologies.

Inhibition of the Notch Pathway Promotes Flap Survival by Inducing Functional Neoangiogenesis.

OBJECTIVE: The Notch pathway seems to function as an antiangiogenic factor, negatively regulating the sprouting effect of vascular endothelial growth factor (VEGF). This function is well defined in embryonic and tumor vasculature. However, little is known about its function in ischemia-induced angiogenesis. In the first part of this study, we investigated the role of Notch in reparative angiogenesis after ischemia. In the second part, we hypothesized that anti-Notch therapy will result in increased angiogenic sprouting. We analyzed the effect of Notch inhibition in the induction of angiogenic sprouting. METHODS: In the first part, we investigated the effect of ischemia on the Notch ligand delta-like ligand 4 (DLL4). Twenty rats were divided equally into 2 groups. In the surgery group, dorsal skin flap was used as model of ischemia. In the control group, no surgical procedure was performed. DLL4 and VEGF gene expressions were assessed. Immunohistochemical staining was used for detection of DLL4 in tissue materials. Plasma levels of VEGF and DLL4 were measured. In the second part, we investigated the effect of Notch inhibition using a gamma-secretase inhibitor (GSI) on inducing neoangiogenesis. Twenty rats were assigned to 2 equal groups. In all animals, dorsal skin flap was raised and sutured back into its bed. Animals in the GSI-treated group received GSI intravenously after surgery for 3 days. Saline was administered in the control group. Necrotic area measurements, microangiography, and histologic evaluations were performed to compare groups. RESULTS: In the first part, VEGF and DLL expressions increased in ischemic tissues (P < 0.01). Immunohistochemical analysis revealed that DLL4 expression was upregulated in capillary endothelial cells after ischemia. Plasma levels for VEGF and DLL4 were higher in the animals that underwent surgery (P < 0.01). In the second part, GSI treatment resulted in higher flap survival rates (P < 0.05). Microscopic analysis exhibited increase in the number of microvascular structures after GSI treatment (P < 0.05). Microangiographic evaluation showed that neovascularization increased in the GSI-applied flaps. CONCLUSIONS: We present an evidence for the importance of the Notch pathway in the regulation of ischemia-induced angiogenesis. Notch inhibition promotes flap survival by creating a neovasculature that has an increase in vascular density.