Omentum: Power to Heal and Regenerate

General Morphological Characteristics of the Results of Experimental Modeling of Aseptic Peritonitis

BACKGROUND

Aseptic peritonitis is a reaction of the local immune system aimed at rejection of a foreign body, which, having antigenic properties, does not (unlike a pathogen) counteract the immune system. The suture materials, namely catgut thread, used in intracavitary surgical operations possess xenogenic properties and can be used for antigenic stimulation of the immune system of the peritoneal cavity. Consequently, we decided to use a catgut suture for antigenic stimulation of the immune system of the peritoneal cavity and to study the morphological features of the results of experimental modeling of aseptic peritonitis in albino rats.

METHOD

The study involved 15 Wistar albino male rats, weighing 286,13 ± 6,26 g. To study the dynamics of destructive changes made by the catgut implant in the peritoneal cavity of the experimental animals, the animals were assigned into three groups in accordance with the time interval of their euthanasia at 3, 7, and 14 days of the experiment.

RESULTS

After modeling an aseptic peritonitis, the investigation the abdominal cavity showed that in four out of five animals of the first group, that is, on day 3 of the experiment, the catgut implant had adhered to the greater omentum. The search for the fifth implant led to an unexpected discovery: we found it conjoined with the second derivative of the visceral peritoneum, similar in structure to the greater omentum, but related to the testes. On day 7, the implant embedded into the peritoneal cavity of the animals, had adhered to the serous formations of the testes in all five cases (100%, three of them - to the left epididymal omentum, and another two - to the right one). On day 14 (n = 5) it was found that in three cases it had adhered to the serous formations of the testes (60%, one of them to the left epididymal omentum, another two - to the right one) and in two cases it had adhered to the greater omentum (40%).

CONCLUSION

During the experiment on implantation of a xenogenic substrate in the form of flat bundles made from the catgut thread into the peritoneal cavity of sexually mature male rats, it was found for the first time that their acceptors were not only the greater omentum, but also two derivatives of the peritoneum, homeomorphic to it and associated with the epididymides, which we reasonably called epididymal omenta and described in details.

Application of pedicled greater omentum flap tamponade combined with laparoscopic fenestration in diaphragmatic hepatic cyst

Objective

To investigate the efficacy and clinical application advantage of omental tamponade with vascular pedicle combined with Laparoscopic fenestration for the treatment of diaphragmatic hepatic cyst.

Methods

A total of 56 patients with diaphragmatic hepatic cysts underwent laparoscopic surgery in a single tertiary academic medical center from January 2010 to October 2020, including 21 patients (non-omental group) underwent laparoscopic fenestration of liver cysts, and 36 patients underwent laparoscopic liver cyst fenestration combined with vascular pedicle omentum tamponade (omental group). The general conditions and follow-up results of the two groups were compared and annalyzed.

Results

The operation time of the omental group was longer than that of the non-omental group (P = 1.358E-4). There was no significant difference in postoperative complications, postoperative laboratory values and hospital costs (P>0.05). The length of hospital stay in omental group was shorter than that in non-omental group (P = 0.034). In the omental group, recurrence occurred in 1 of 35 patients (4.65%) who were followeded up 12 months after surgery. In the non-omental group, of the 21 patients followed, 3 patients (14.28%) recurred 6 months after surgery, and 8 patients (38.10%) recurred 12 months after surgery.

Conclusion

It is an effective method to prevent the recurrence of diaphragmatic hepatic cyst after laparoscopic fenestration by packing the cyst with vascularized omentum.

Heterogeneity of Adipose Stromal Vascular Fraction Cells from the Different Harvesting Sites in Rats

In both veterinary and human health, regenerative medicine offers a promising cure for various disorders. One of the rate-limiting challenges in regenerative medicine is the considerable time and technique required to expand and grow cells in culture. Therefore, the stromal vascular fraction (SVF) shows a significant promise for various cell therapy approaches. The present study aimed to define and investigate the optimal harvest site of freshly isolated SVF cells from various adipose tissue (AT) depot sites in the female Sprague-Dawley (S.D.) rat. First, Hematoxylin and eosin (H&E) were used to analyze the morphological variations in AT samples from peri-ovarian, peri-renal, mesenteric, and omental sites. The presence of putative stromal cells positive CD34 was detected using immunohistochemistry. Then, the isolated SVF cells were examined for cell viability and cellular yield differences. Finally, the expression of mesenchymal stem cells and hematopoietic markers in the SVF cells subpopulation was studied using flow cytometry. The pluripotent gene expression profile was also evaluated. CD34 staining of the omental AT was substantially higher than those of other anatomical sites. Despite having the least quantity of fat, omental AT has the highest SVF cell fraction and viable cells. Along with CD90 and CD44 higher expression, Oct4, Sox2, and Rex-1 genes levels were higher in SVF cells isolated from the omental AT. To conclude, omental fat is the best candidate for SVF cell isolation in female S.D. rats with the highest SVF cell fraction with higher MSCs phenotypes and pluripotency gene expression.

Autologous omentum transposition for regeneration of a renal injury model in rats

BACKGROUND

After renal trauma, surgical treatment is vital, but sometimes there may be loss of function due to fibrosis. This study aimed to evaluate the effect of autologous omentum flaps on injured renal tissues in a rat model.

METHODS

A total of 30 Wistar albino rats were included and randomly divided equally into a control group and four intervention groups. Iatrogenic renal injuries were repaired using a surgical technique (primary repair 1 group and primary repair 2 group) or transposition of the autologous omentum (omentum repair 1 group and omentum repair 2 group). Blood samples were taken preoperatively and on the 1st and 7th postoperative days in all groups and on the 18th postoperative day in the control and two intervention groups. All rats were sacrificed on the 7th or 18th day postoperatively, and their right kidneys were taken for histopathological evaluation.

RESULTS

The mean urea level significantly decreased from day 1 to day 7 and from day 1 to day 18 in the omentum repair 2 group (P = 0.005 and P = 0.004, respectively). There were no other significant changes in urea or creatinine levels within the intervention groups (P > 0.05). There was no significant correlation between the urea and creatinine levels and the histological scores (P > 0.05). The primary repair 1 and 2 groups had significantly higher median granulation and inflammation scores in the kidney specimen than the control and omentum repair groups (P < 0.05). The omentum repair 2 group had significantly lower median granulation and inflammation scores in the surrounding tissues than the primary repair 2 group (P < 0.05). The completion score for the healing process in the kidney specimen was significantly higher in the omentum repair groups than in the primary repair groups (P < 0.05). The omentum repair 2 group had significantly lower median granulation and inflammation scores in the surrounding tissues than the primary repair 2 group (P < 0.05). Granulation degree in the kidney specimen was strongly and positively correlated with the inflammation degree (r = 0.824, P < 0.001) and foreign body reaction in the kidney specimen (r = 0.872, P < 0.001) and a strong and negative correlation with the healing process completion score in the kidney (r = - 0.627, P = 0.001). Inflammation degree in the kidney specimen was strongly and positively correlated with the foreign body reaction in the kidney specimen (r = 0.731, P = 0.001) and strongly and negatively correlated with the healing process completion score in the kidney specimen (r = - 0.608, P = 0.002).

CONCLUSION

Autologous omentum tissue for kidney injury repair attenuated inflammation and granulation. Additionally, the use of omental tissue to facilitate healing of kidney injury may theoretically lead to a more effective healing process and reduced fibrosis and tissue and function loss.

The omentum harbors unique conditions in the peritoneal cavity to promote healing and regeneration for diaphragm muscle repair in mdx mice

Although the primary cause of Duchenne muscular dystrophy (DMD) is a genetic mutation, the inflammatory response contributes directly to severity and exacerbation of the diaphragm muscle pathology. The omentum is a lymphoid organ with unique structural and immune functions serving as a sanctuary of hematopoietic and mesenchymal progenitors that coordinate immune responses in the peritoneal cavity. Upon activation, these progenitors expand and the organ produces large amounts of growth factors orchestrating tissue regeneration. The omentum of mdx mouse, a DMD murine model, is rich in milky spots and produces growth factors that promote diaphragm muscle regeneration. The present review summarizes the current knowledge of the omentum as an important immunologic structure and highlights its contribution to resolution of dystrophic muscle injury by providing an adequate environment for muscle regeneration, thus being a potential site for therapeutic interventions in DMD.

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.

Topical purified omental lipid formulations in the prevention of skin ulcers: a narrative review

The omentum is a large peritoneal fold. Its main function is to protect abdominal organs, exerting a defensive action against infective agents. The tissue promotes repair after several types of injury. An extensive vascularisation is the key characteristic of this tissue and the omentum has the highest level of production and content of vascular endothelial growth factor (VEGF). A component of omentum is the lipid compound, which carries out important activities for the organism. Omentum is rich in neutral glycerides, phospholipids, glycolipids and gangliosides. Dermatological products containing purified omental lipids are commercially available and topical omental extracts have been useful in the softening, moisturising and smoothing of skin. Animal-derived omental lipids could be use in topical products with different textures (creams, fluids, emulsions and cleansers) and at different concentrations (10-25%) for the treatment of fragile skin or skin conditions causing risk of ulcer formation. This review summarises the pharmacological rationale of purified omental lipids in topical formulations for use in fragile skin conditions, the clinical efficacy data available in the scientific literature and the potential future perspectives. Efficacy of topical purified omental lipids have been demonstrated in numerous clinical controlled trials involving a total of 320 subjects. These studies demonstrated that this product helps prevent the formation of pressure ulcers (PU) in hospitalised high-risk subjects, improves wound healing process, normalises skin hydration in diabetic subjects with moderate-severe skin xerosis and improve the clinical evolution of diabetic foot. Therefore, purified omental lipid could be an effective tool for the management of fragile skin and the skin at high risk of PU formation.

Omentum a powerful biological source in regenerative surgery

The Omentum is a large flat adipose tissue layer nestling on the surface of the intra-peritoneal organs. Besides fat storage, omentum has key biological functions in immune-regulation and tissue regeneration.

Omentum biological properties include neovascularization, haemostasis, tissue healing and regeneration and as an in vivo incubator for cells and tissue cultivation. Some of these properties have long been noted in surgical practice and used empirically in several procedures.

In this review article, the author tries to highlight the omentum biological properties and their application in regenerative surgery procedures. Further, he has started a process of standardisation of basic biological principles to pave the way for future surgical practice.

Effects of omentectomy in addition to sleeve gastrectomy on the metabolic and inflammatory profiles of obese rats

BACKGROUND

Visceral obesity has been considered a risk factor for metabolic and cardiovascular complications. In an attempt to reduce the visceral adipose tissue, omentectomy has been proposed to be performed along with bariatric surgery.

OBJECTIVE

The goal of this study was to evaluate whether omentectomy associated with sleeve gastrectomy (SG) is beneficial to the inflammatory and metabolic profile of rats fed a standard diet (STD) or high-fat diet (HFD).

SETTING

University hospital, Brazil.

METHODS

For this experiment, male Wistar rats were randomly divided into 6 groups as follows: sham surgery (STD+L or HFD+L), SG alone (STD+SG or HFD+SG), or SG with omentectomy (STD+SGO or HFD+SGO). Anthropometric data and metabolic profiles were evaluated, and the tissue expression of inflammatory markers in the visceral adipose tissue was measured.

RESULTS

In rats with diet-induced obesity treated with SG with or without omentectomy, there was a reduction in weight (HFD+SG: P<.01 and HFD+SGO: P<.05), adiposity (HFD+SG: P<.001 and HFD+SGO: P<.05), plasma levels of glucose (HFD+SG: P<.01 and HFD+SGO: P<.01), plasma levels of C-peptide (HFD+SG: P<.01 and HFD+SGO: P<.001), plasma levels of insulin (HFD+SG: P<.05 and HFD+SGO: P<.001), plasma levels of total cholesterol (HFD+SG: P<.01 and HFD+SGO: P<.01), and tissue expression of TNF-α (HFD+SG: P<.001 and HFD+SGO: P<.01), but there was no statistically significant difference between the groups in which omentectomy was performed or was not.

CONCLUSION

In this study, we did not observe additional beneficial effects due to omentectomy associated with SG in the metabolic profile and tissue expression of inflammatory markers.

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.

Comparison of gastrotomy closure modalities for natural orifice transluminal surgery: a canine study

BACKGROUND

Reliable closure of the gastrotomy after transgastric natural orifice transluminal endoscopic surgery (NOTES) remains unresolved.

OBJECTIVE

To compare the technical aspects and clinical and histologic outcomes of NOTES gastrotomy closure techniques.

DESIGN

Experimental study.

SETTING

Animal laboratory.

PATIENTS

Thirty-four dogs, 14 for nonsurvival study and 20 for survival study.

INTERVENTIONS

The animals randomly received different gastrotomy closures after NOTES: endoclip, omentoplasty, over-the-scope-clip (OTSC), and hand-suturing.

MAIN OUTCOME MEASUREMENTS

Procedure time, closure strength, survival, postoperative adverse events, and histologic evaluation of wound healing.

RESULTS

Omentoplasty and OTSC groups needed shorter procedure times and fewer clips than the endoclip group. The endoclip and omentoplasty groups generated similar leakage pressures (34.5 ± 2.6 vs 42.2 ± 4.1 mm Hg, P > .05), both lower than OTSC and hand-suturing groups (81.5 ± 2.1 and 87.0 ± 3.0 mm Hg, respectively, P < .001). Of the 20 animals in the survival study (all 4 groups), only 2 of 6 in the endoclip group were killed prematurely due to sepsis. Necropsy revealed the OTSC group reached a 100% clip retention rate, higher than the endoclip (47.9%) and omentoplasty groups (44.4%, P < .05) rates. Complete healing, defined as intact and continuous gastric layers microscopically, was seen in 83.3% of animals (5 of 6) in the omentoplasty group, comparable with OTSC (4 of 6, 66.7%, P = .500) but higher than the endoclip group (1 of 6, 16.7%, P = .04).

LIMITATIONS

Animal study.

CONCLUSIONS

Omentoplasty is easier and safer for NOTES gastrotomy closure than endoclips and offers safety profile and efficacy similar to OTSC and hand-suturing.

Omentum in the pediatric umbilical hernia: is it a potential alarm for the appearance of complications?

Umbilical hernia is a common benign condition which resolves spontaneously during the first five years of life. However, in certain cases there are some characteristics which may be indicative of a different prognostic approach, as they increase the possibility of complications. The two cases of umbilical hernia that we describe here were treated operatively and revealed the presence of strangulated and adhered omentum, respectively. Reflecting on the adhesive properties of the omentum, we hypothesized that this may occur more often than it is believed, especially in those cases that are described as recurrent symptomatic herniations. In such cases, there should be increased alert for the possibility of complications during the period of the conservative expectance for resolution.

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.

Management of tracheobronchial ulceration induced by high-dose brachytherapy

The most severe complication of high-dose endobronchial brachytherapy is fatal hemoptysis. Intractable tracheobronchial ulceration due to high-dose endobronchial brachytherapy often develops into tracheobronchial necrosis and fatal hemoptysis. Our experience demonstrated that when bleeding from tracheobronchial ulcer, after high-dose endobronchial brachytherapy occurs, blocking the blood supply to the tracheobronchial ulcer alone is ineffective. Prophylactic tracheobronchial wrapping using the omentum should be added before the occurrence of fatal hemoptysis. This is the first report that describes an effective management for preventing fatal hemoptysis.

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.

Stromal cells cultured from omentum express pluripotent markers, produce high amounts of VEGF, and engraft to injured sites

When rat omentum becomes activated by intraperitoneal injection of inert polydextran particles, these particles are rapidly surrounded by cells that express markers of adult stem cells (SDF-1alpha, CXCR4, WT-1) and of embryonic pluripotent cells (Oct-4, Nanog, SSEA-1). We have cultured such cells, because they may offer a convenient source of adult stem cells, and have found that they retain stem cell markers and produce high levels of vascular endothelial growth factor for up to ten passages. After systemic or local injection of these cultured cells into rats with acute injury of various organs, the cells specifically engraft at the injured sites. Thus, our experiments show that omental stromal cells can be cultured from activated omentum, and that these cells exhibit stem cell properties enabling them to be used for repair and possibly for the regeneration of damaged tissues.