Experimental revascularization of the entire heart. Evaluation of epicardiectomy, omental graft, and/or implantation of the internal mammary artery in preventing myocardial necrosis and death of the animal

Renal revascularization by a pedicled intestinal segment wrapping the kidney: a new method for kidney revascularization

BACKGROUND

Renal artery stenosis is caused by a heterogeneous group of diseases, including atherosclerosis and fibromuscular dysplasia, which can be treated medically, via endovascular techniques, or by open revascularization; however, satisfactory and effective results are not always obtained. We aimed to assess the possibility of renal revascularization by a pedicled intestinal segment wrapping the kidney.

METHODS

Five dogs were operated on at three steps. At the first step, laparotomy was performed, and the right kidney was released. Subsequently, an 8-10 cm segment of jejunum was separated longitudinally, and mucosectomy was done. This intestinal patch wrapped up the kidney. After eight weeks, the kidney and the intestinal patch were analyzed, and the renal artery was ligated. After four weeks, the kidney and the intestinal patch were sent for pathological evaluation.

RESULTS

At the 12th week of evaluation, no evidence of abscess formation or collection was seen. All kidneys had a normal color, consistency, and size. All renal cells were alive, and neither atrophy nor necrosis was seen. Glomerulus and tubules were intact, and no inflammatory change was visible. Furthermore, thick wall vasculature was inspected in a fibromuscular tissue, rising from the intestinal flap toward the kidney. One of the dogs expired due to peritonitis and sepsis in the fifth week.

CONCLUSION

In our study, indirect perfusion of the kidney by an intestinal patch was achieved successfully. This represents new hope in patients suffering from chronic renal failure who underwent former medical and surgical interventions with undesirable results.

LC-QTOF-MS and 1H NMR Metabolomics Verifies Potential Use of Greater Omentum for Klebsiella pneumoniae Biofilm Eradication in Rats

Bacterial wound infections are a common problem associated with surgical interventions. In particular, biofilm-forming bacteria are hard to eradicate, and alternative methods of treatment based on covering wounds with vascularized flaps of tissue are being developed. The greater omentum is a complex organ covering the intestines in the abdomen, which support wound recovery following surgical procedures and exhibit natural antimicrobial activity that could improve biofilm eradication. We investigated changes in rats’ metabolome following Klebsiella pneumoniae infections, as well as the greater omentum’s ability for Klebsiella pneumoniae biofilm eradication. Rats received either sterile implants or implants covered with Klebsiella pneumoniae biofilm (placed in the peritoneum or greater omentum). Metabolic profiles were monitored at days 0, 2, and 5 after surgery using combined proton nuclear magnetic resonance (¹H NMR) and high performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry (LC–QTOF-MS) measurements of urine samples followed by chemometric analysis. Obtained results indicated that grafting of the sterile implant to the greater omentum did not cause major disturbances in rats’ metabolism, whereas the sterile implant located in the peritoneum triggered metabolic perturbations related to tricarboxylic acid (TCA) cycle, as well as choline, tryptophan, and hippurate metabolism. Presence of implants colonized with Klebsiella pneumoniae biofilm resulted in similar levels of metabolic perturbations in both locations. Our findings confirmed that surgical procedures utilizing the greater omentum may have a practical use in wound healing and tissue regeneration in the future.

Perspectives On: Local and Sustained Delivery of Angiogenic Growth Factors

This review emphasizes the role of angiogenesis in tissue engineering, introduces various angiogenic growth factors, and highlights current status of delivery systems for angiogenic growth factors using natural and synthetic biomaterials. A short overview of angiogenic growth factors is presented, followed by the introduction of emerging strategies for designing smart delivery carriers.

Activated omentum slows progression of CKD

Stem cells show promise in the treatment of AKI but do not survive long term after injection. However, organ repair has been achieved by extending and attaching the omentum, a fatty tissue lying above the stomach containing stem cells, to various organs. To examine whether fusing the omentum to a subtotally nephrectomized kidney could slow the progression of CKD, we used two groups of rats: an experimental group undergoing 5/6 nephrectomy only and a control group undergoing 5/6 nephrectomy and complete omentectomy. Polydextran gel particles were administered intraperitoneally before suture only in the experimental group to facilitate the fusion of the omentum to the injured kidney. After 12 weeks, experimental rats exhibited omentum fused to the remnant kidney and had lower plasma creatinine and urea nitrogen levels; less glomerulosclerosis, tubulointerstitial injury, and extracellular matrix; and reduced thickening of basement membranes compared with controls. A fusion zone formed between the injured kidney and the omentum contained abundant stem cells expressing stem cell antigen-1, Wilms' tumor 1 (WT-1), and CD34, suggesting active, healing tissue. Furthermore, kidney extracts from experimental rats showed increases in expression levels of growth factors involved in renal repair, the number of proliferating cells, especially at the injured edge, the number of WT-1-positive cells in the glomeruli, and WT-1 gene expression. These results suggest that contact between the omentum and injured kidney slows the progression of CKD in the remnant organ, and this effect appears to be mediated by the presence of omental stem cells and their secretory products.

Cellular basis of tissue regeneration by omentum

The omentum is a sheet-like tissue attached to the greater curvature of the stomach and contains secondary lymphoid organs called milky spots. The omentum has been used for its healing potential for over 100 years by transposing the omental pedicle to injured organs (omental transposition), but the mechanism by which omentum helps the healing process of damaged tissues is not well understood. Omental transposition promotes expansion of pancreatic islets, hepatocytes, embryonic kidney, and neurons. Omental cells (OCs) can be activated by foreign bodies in vivo. Once activated, they become a rich source for growth factors and express pluripotent stem cell markers. Moreover, OCs become engrafted in injured tissues suggesting that they might function as stem cells.

Omentum consists of a variety of phenotypically and functionally distinctive cells. To understand the mechanism of tissue repair support by the omentum in more detail, we analyzed the cell subsets derived from the omentum on immune and inflammatory responses. Our data demonstrate that the omentum contains at least two groups of cells that support tissue repair, immunomodulatory myeloid derived suppressor cells and omnipotent stem cells that are indistinguishable from mesenchymal stem cells. Based on these data, we propose that the omentum is a designated organ for tissue repair and healing in response to foreign invasion and tissue damage.

Omentum facilitates liver regeneration

AIM: To investigate the mechanism of liver regeneration induced by fusing the omentum to a small traumatic injury created in the liver. We studied three groups of rats. In one group the rats were omentectomized; in another group the omentum was left in situ and was not activated, and in the third group the omentum was activated by polydextran particles.

METHODS: We pre-activated the omentum by injecting polydextran particles and then made a small wedge wound in the rat liver to allow the omentum to fuse to the wound. We monitored the regeneration of the liver by determining the ratio of liver weight/body weight, by histological evaluation (including immune staining for cytokeratin-19, an oval cell marker), and by testing for developmental gene activation using reverse transcription polymerase chain reaction (RT-PCR).

RESULTS: There was no liver regeneration in the omentectomized rats, nor was there significant regeneration when the omentum was not activated, even though in this instance the omentum had fused with the liver. In contrast, the liver in the rats with the activated omentum expanded to a size 50% greater than the original, and there was histologically an interlying tissue between the wounded liver and the activated omentum in which bile ducts, containing cytokeratin-19 positive oval cells, extended from the wound edge. In this interlying tissue, oval cells were abundant and appeared to proliferate to form new liver tissue. In rats pre-treated with drugs that inhibited hepatocyte growth, liver proliferation was ongoing, indicating that regeneration of the liver was the result of oval cell expansion.

CONCLUSION: Activated omentum facilitates liver regeneration following injury by a mechanism that depends largely on oval cell proliferation.

Activated omentum becomes rich in factors that promote healing and tissue regeneration

In order to study the mechanism by which an omental pedicle promotes healing when applied to an injured site, we injected a foreign body into the abdominal cavity to activate the omentum. One week after the injection, we isolated the omentum and measured blood vessel density, blood content, growth and angiogenesis factors (VEGF and others), chemotactic factors (SDF-1 alpha), and progenitor cells (CXCR-4, WT-1). We found that the native omentum, which consisted mostly of adipose tissue, expanded the mass of its non-adipose part (milky spots) 15- to 20-fold. VEGF and other growth factors increased by two- to four-fold, blood vessel density by three-fold, and blood content by two-fold. The activated omentum also showed increases in SDF-1 alpha, CXCR-4, and WT-1 cells (factors and cells positively associated with tissue regeneration). Thus, we propose that an omentum activated by a foreign body (or by injury) greatly expands its milky-spot tissue and becomes rich in growth factors and progenitor cells that facilitate the healing and regeneration of injured tissue.

Hybrid surgical angiogenesis: omentopexy can enhance myocardial angiogenesis induced by cell therapy

BACKGROUND

The conditions at the injection site are important in cell transplantation for severe ischemic heart disease. The omentum is both a well-vascularized tissue and a source of angiogenic factors. We examined the effectiveness of autologous bone marrow-derived mononuclear cells (BM-MNCs) with or without omentopexy in a large animal model.

METHODS

Myocardial infarction was generated in the lateral wall by ligation of coronary artery branches in miniswine. Animals received BM-MNC injection with or without omentopexy. Controls received saline only. Three weeks after surgery, regional myocardial blood flow and contractility were measured, and density of arterioles was evaluated immunohistologically. Angiography and postmortem examinations were performed to determine collateral communication.

RESULTS

Regional myocardial contractility was significantly improved by BM-MNC transplantation both with and without omentopexy (0.29 +/- 0.02 vs 0.11 +/- 0.03, p < 0.01, 0.30 +/- 0.02 vs 0.12 +/- 0.01, p < 0.01, respectively). Relative regional myocardial blood flow in the combined omentopexy group was significantly higher than the controls both at rest (1.05 +/- 0.11 vs 0.57 +/- 0.07, p < 0.01) and under stress (1.09 +/- 0.08 vs 0.40 +/- 0.10, p < 0.01). The number of arterioles (< 50 microm) in both groups were higher than the controls (88.1 +/- 5.00 vs 38.1 +/- 8.99, p < 0.01 and 109.2 +/- 9.91 vs 38.1 +/- 8.99, p < 0.01, respectively). The number of large arterioles (> 50 microm) in the combined omentopexy group was significantly higher than in both BM-MNC alone (26.9 +/- 2.4 vs 17.6 +/- 1.8, p = 0.011) and controls (26.9 +/- 2.4 vs 10.0 +/- 1.3, p < 0.01). Collateral communication between the omentum and myocardium was demonstrated by angiography and postmortem injection.

CONCLUSIONS

The BM-MNC transplantation may attenuate cardiac contractile dysfunction, and omentopexy may enhance angiogenesis induced by BM-MNC transplantation.

Development of biologic coronary artery bypass grafting in a rabbit model: revival of a classic concept with modern biotechnology

OBJECTIVE

We have developed a technique for biologic coronary artery bypass grafting, which is a revival of a classic concept with modern biotechnology.

METHODS

Acute myocardial infarction was created by ligating the major branch of the circumflex artery in rabbits. Animals were divided into four groups: a nontreated group (group N), a group in which omentum was used to wrap the infarcted area (group G), a group in which a gelatin hydrogel sheet incorporating 100 microg basic fibroblast growth factor was placed over the infarcted area (group F), and a group in which the infarcted area was similarly treated with basic fibroblast growth factor followed by omental wrapping (group FG). Cardiac function was subsequently assessed by echocardiography. Postmortem angiography through the gastroepiploic artery was done in groups G and FG. Infarct size and arteriolar density were evaluated.

RESULTS

Group FG showed a better fractional area change than did the other groups (group N P <.001, group G P =.002, group F P <.001). Angiography revealed that communication from the gastroepiploic artery to the coronary artery was created through a rich bed of neovascularization in all 7 animals of group FG, whereas poor collaterals were recognized in only 2 of 7 animals in group G. Infarct size was reduced to a greater extent in group FG than in groups F, G, and N (10% +/- 3%, 16% +/- 5%, 19% +/- 7%, 23% +/- 2%, respectively, group F P =.04, groups G and N P <.01). The number of arterioles 20 to 100 microm in diameter was increased to a greater extent in group FG than in groups F, G, and N (23 +/- 5 arterioles/mm(2), 14 +/- 3 arterioles/mm(2), 10 +/- 1 arterioles/mm(2), 4 +/- 2 arterioles/mm(2), respectively), with the differences being significant.

CONCLUSIONS

These results show that bypass from the gastroepiploic artery to coronary arteries can be achieved without surgical anastomosis through slow release of basic fibroblast growth factor in this rabbit acute myocardial infarction model. This new revascularization concept, biologic coronary artery bypass grafting, could be applicable for revascularizing many tiny coronary vessels in patients who are difficult to treat with conventional surgery or catheter intervention.